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the si(100)-2@xmath01 surface is composed of silicon atom pairs dimers arranged into rows .
it represents a natural template for spontaneous growing linear structures of many materials , like group iii - v metals .
group iii metals ( al , ga , in , tl ) are known to grow in one - dimensional ( 1d ) atomic chains when deposited on the si(100 ) surface @xcite .
technique of scanning tunneling microscopy ( stm ) enabled detailed study of metal layers with atomic resolution .
an especially powerful tool for investigation of growth kinetics is the stm @xmath1-@xmath2 technique @xcite which allows direct monitoring of the layer as it grows .
1d metal chains grow perpendicularly to the underlying silicon dimer rows of the si(100)-2@xmath01 surface .
they are composed of metal dimers ( oriented parallel to the silicon dimers ) sitting in the `` trenches '' on the silicon surface @xcite .
growth of the metal chains has been explained by a surface polymerization reaction @xcite .
metal chain ends act as nucleation centers .
since the sites adjacent to a chain are energetically unfavorable for adsorption ( no adsorption has been observed there ) the chains grow only in length .
the chains are always separated by a distance of at least 2a ( a@xmath3 nm , surface unit cell spacing ) .
thus , the surface is saturated by metal adatoms at a coverage of 0.5 ml ( 1 ml@xmath4 @xmath5 ) .
some differences exist between various group iii metals .
while al and ga chains are believed to be stable at room temperature @xcite , indium atoms are known to detach from chains and re - attach to other chains @xcite and tl chains were shown to be even more unstable @xcite . though a qualitative description of diffusion and growth processes for group iii metals exists , the corresponding values of microscopic parameters are not known .
the heights of diffusion barriers on si(100 ) have not been yet determined for in and the values reported by albao @xmath6 @xcite for ga and by brocks @xmath6 @xcite for al are very different .
similar discrepancy exists for estimation of ga dimer pair - interaction energy
tokar and dreyss @xcite suggest @xmath7 0.2 ev while takeuchi s ab - initio calculation gave @xmath7 0.8 ev @xcite .
recently kocn @xmath6 reported @xcite that detachment of indium atoms from chains is length dependent , so interactions other than nearest neighbor ( nn ) might play a role .
the role of surface defects present on the si(100)-2@xmath01 surface @xcite at the metal adsorption and nucleation was reported and discussed @xcite .
experimental results showed that influence of a- and b - type defects ( one and two missing dimers , respectively ) can be neglected but c - type defects are important .
the c - type defects , which appear on stm images as a small bright protrusion next to a dark spot in filled states and as a larger bright spot in empty states , are reported to be very reactive and act as nucleation centers @xcite .
the c - defects were independently interpreted by hossain @xmath6@xcite and okano and oshiyama @xcite as dissociated h@xmath8o molecules , with the h and hydroxyl group bonded to neighboring silicon atoms of two adjacent surface dimers .
the results both of experimental and theoretical study of in nucleation at the c - defects were reported in ref . .
after adsorption of an in adatom at a c - defect ( exclusively on the unoccupied side of the two adjacent si dimers ) the chain begins to grow in one direction only ( see fig . 1 in ref . ) .
the chain termination at the defect is stable , the opposite `` free '' end is active as an adsorption site for adatoms .
albao @xmath9 @xmath10 @xcite reported growth characteristics for ga on si(100 ) at room temperature ( rt ) .
an unconventional monotonously decreasing scaled island ( chain ) size distribution function obtained for low coverage was explained by an irreversible growth model and kinetic monte carlo ( kmc ) simulations .
the simulations resulted in the monotonous size distribution only if highly anisotropic surface diffusion of ga adatoms was introduced otherwise a monomodal form of the distribution function was obtained .
the presence of c - defects included later @xcite did not change the results significantly .
similar growth characteristics at rt we reported for indium @xcite .
the chain length distributions obtained for various coverages are monotonously decreasing and obey a scaling relation .
most of in chains ( 6090 % ) in observed layers were on at least one end terminated by a c - type defect . in the @xmath1-@xmath2 experiments the percentage was higher , 90100 % ( due to low deposition rates of in during the @xmath1-@xmath2 measurements ) .
density of indium chains and average chain length depend on c - defect concentration .
another phenomenon ( observed at higher coverage ) is that indium atoms are able to migrate throughout sites adjacent to an indium chain even though no adsorption is observed ( such an effect seems to be negligible at low coverage ) . in this paper
, we use stm data and kmc simulations for detail studying indium growth on the reconstructed surface si(100)-2@xmath01 .
a growth model , which includes presence of c - defects and a process of atom detachment from indium chains , is used for studying a role of c - defects at metal chain nucleation , determination of diffusion barriers and investigation of relation between growth processes and a form of chain length distribution function .
processes and parameters included in the growth model are discussed with respect to experimental data obtained by means of stm .
performed experiments are characterized in sec .
ii , consequently experimental results are presented in sec .
a simulation model is described in sec .
iv , results of simulations are compared with the experimental data and discussed in sec .
v , formulas for calculation of deviations between experimental and simulated growth characteristics are given in the appendix . finally , sec .
vi contains our conclusions . 1 .
the bright spots at ends of some chains indicate termination by a single indium atom @xcite ; stable terminations at c - defects are marked by the arrows perpendicular to chains .
unoccupied c - defects are marked by the arrows parallel with chains the arrows are directed from the side of possible chain growing .
coverage 0.044 ml , @xmath1-@xmath11 measurements 2 hours after deposition ; image size 30@xmath1230 nm@xmath13 .
, width=302 ]
all experiments were carried out at room temperature in a non - commercial uhv stm system with base pressure @xmath14 pa .
si(100 ) samples were cut from an n - type , sb doped silicon wafer with resistivity @xmath15 0.014 @xmath16 cm . to obtain the 2@xmath01 reconstruction
, samples were flashed several times for @xmath7 20 @xmath17 to @xmath7 1200@xmath18 c. indium was deposited from tungsten wire evaporators either before or during imaging the surface by means of stm . in the latter case ( experiment _ in - vivo _ ) a miniature evaporator was in a distance of 4 cm from the sample and a beam of in atoms was determined by means of two apertures with a diameter of 1 mm .
incidental angle of the beam was 30@xmath18 .
the apex shape of a tungsten electrochemically etched tip enabled deposition `` under '' the stm tip onto the scanned area .
the thermal drift during deposition was compensated by the stm control unit .
the @xmath1-@xmath2 measurements provided continuous stm imaging of the investigated surface area before and during the deposition at a rate of 1 image / min . at standard @xmath1-@xmath11 measurements the indium layers
were observed 0.54 hours after deposition .
we used a tip voltage of + 2 v and tunneling current 0.3 na , the values at which tip influence on the detachment of indium adatoms from the chains is minimized as we proved earlier @xcite .
an example of indium chains grown on the si(100 ) surface at low coverage is shown in fig . [ stmimage ] .
length of the chains can be easily determined with atomic precision from filled states images where the `` free '' terminations of chains containing an odd number of atoms appear much brighter than in case of even number @xcite .
chain terminations at c - defects and unoccupied c - defect are marked by arrows .
concentration of the c - defects increases during deposition at @xmath1-@xmath2 experiments ( probably due to thermal desorption of residual water molecules from heated parts near the evaporation source in a relatively small distance from the sample ) .
the increase was found linear and corresponds to a deposition rate of @xmath19 ml / s .
the deposition rate of c - defects at @xmath1-@xmath11 experiments was negligible ( due to a large distance of the evaporation source and better screening of the sample ) and the initial concentration of the c - defects can be considered as unchanged .
since the atomic structure of in chains is well known @xcite we focused on statistical characteristics of the chains .
obtained data are summarized in the table [ tab : table1 ] .
the data were acquired from images of the size of 30@xmath030 nm@xmath20 or 40@xmath040 nm@xmath20 .
the image areas are large enough ( 30 nm corresponds to a @xmath21 100-atoms long chain ) and the resolution is sufficient to discern the number of atoms in the chain .
data were collected only from terraces much wider than an average chain length to exclude the influence of step edges on the chain growth .
statistical characteristics were evaluated for both types of growth experiments ( @xmath1-@xmath2 and @xmath1-@xmath11 ) . [ cols="<,<,<,<,<,<,<,<,<",options="header " , ] the diffusion barriers for indium determined from kmc simulations ( see table [ tab : table2 ] ) correspond to almost isotropic diffusion .
it is in contrast to albao s @xmath22 .
anisotropic results ( e@xmath23 ev ; e@xmath24 ev ) .
the vales obtained theoretically for al by brock and kelly @xcite are anisotropic as well ( e@xmath25 ev ; e@xmath26 ev ) but much lower . + _ scaled chain length distribution function . _
it follows from the nucleation theory @xcite that during the submonolayer growth the density ( per site ) @xmath27 of islands composed of @xmath17 atoms fulfils the scaling form : @xmath28 where @xmath29 is coverage and @xmath30 represents the mean island size density .
the function @xmath31 , @xmath32 is the scaled island size distribution function .
the relation ( [ scaledfunction ] ) was confirmed by simulations using different models of irreversible 2d aggregation and from stm experiments . in most cases
the shape of the scaled distribution function is monomodal with a peak for @xmath33 .
a monomodal function was observed both for homogeneous and heterogeneous nucleation .
the scaling for the passage from irreversible to reversible aggregation was examined theoretically in ref . .
the unconventional shape of the scaled distribution function monotonously decreasing observed for 1d growth of ga on si(100 ) by albao @xmath22 .
( and explained by means of kmc simulations using strongly anisotropic surface diffusion ) @xcite was theoretically investigated by tokar and dreyss @xcite .
they showed that for equilibrium growth and a model with atomic interactions restricted to only nearest neighbors , the scaled distribution function is exponentially decreasing .
here we obtained for 1d submonolayer growth of in similar monotonously decreasing chain length distribution functions fig .
[ expscaledfunction ] and fig .
[ scaled ] .
if we consider homogeneous nucleation with the detachment only and the c - defects are excluded from our model the simulated distribution function remains monotonously decreasing . on the other side excluding the process of detachment ( irreversible model ) results in a conventional monomodal distribution function independently on presence of the c - defects in the model .
for the irreversible model the monotonous distribution can be simulated only when strong diffusion anisotropy is introduced similarly as reported albao @xmath22.@xcite we conclude that the monotonous form of the chain length distribution function obtained for indium layers with low coverage ( @xmath34 ml ) at rt and used deposition rates can be explained by the process of atom detachment from indium chains during the growth . + _
postdeposition relaxation_. further we used our reversible growth model for exploring postdeposition relaxation indicated by experimental data obtained from stm measurements at various time after deposition ( see fig . [ expscaledfunction ] ) .
we simulated the growth using the diffusion barriers determined and deposition rate 0.002 ml / s for two different values of the detachment barrier .
the time evolution of the distribution functions obtained for various time after deposition is in fig .
[ relax]a , b. if the detachment rate is small enough with respect to deposition rate ( a high energy barrier for detachment ) the distribution function is monomodal just after the deposition and relaxes into a monotonous one fig .
[ relax]a .
if the detachment rate increases the distribution function changes from the monomodal to monotonous form even during the growth
see fig .
[ relax]b .
the simulation shows that the observed system reaches an equilibrium state after @xmath21 6 hours ( estimation for the used experimentally determined barrier @xmath35 ev ) , though the most dramatic change occurs during the first 10 minutes after the deposition .
+ _ influence of c - defects_. the time constant for the detachment of an in atom from an adsorption site at a c - defect is @xmath36 bigger than for the detachment from in chains , making the c - defects practically perfect diffusion traps @xcite . to describe a role of c - defects at heterogeneous nucleation and submonolayer growth of in quantitatively we simulated growth using the same parameters as for a real experiment , only concentration of the c - defects
was changed .
[ c - defects]a shows dependence of average chain length on coverage obtained for parameters of the @xmath37 experiment with a low deposition rate @xmath38 ml / s . the average chain length is controlled by concentration of the c - defects .
the dependence of the average chain length on the c - defect concentration is on fig .
[ c - defects]b .
it can be seen that an effect of postdeposition relaxation disappears with the increasing concentration .
+ -@xmath2 experiment .
b ) average chain length is controlled by concentration of c - defects .
note also the relaxation of average chain length during time .
@xmath39 ev and @xmath40 ev , @xmath35 ev.,width=302 ] _ growth scenario_. the simulations and analysis of results allow to suggest a scenario for the experimentally observed submonolayer growth and discuss a role of participating processes at rt .
simulations of the postdeposition relaxation show that only a population of atoms detached from chains exist on the surface after the deposition .
they nucleate as new chains or attach to other chains and the system moves towards dynamical equilibrium . during the deposition ,
if the deposition flux is small enough with respect to detachment rate and surface mobility , the growth proceeds at thermal equilibrium and a postdeposition effect consists from thermal fluctuations only the scaled chain length distribution function is monotonously decreasing . at sufficiently high deposition flux
the growth of chains due to attachment of deposited atoms dominates and the effect of the detachment is suppressed .
the growth becomes irreversible and the scaled distribution function has a monomodal form ( at almost isotropic surface diffusion ) .
+ _ comparison with an equilibrium model_. the model of tokar and dryss @xcite for equilibrium homogeneous growth can provide the only parameter , the nearest - neighbor interaction energy @xmath41 .
it can be determined from the dependence of average chain length on coverage ( using the equation ( 14 ) in ref . ) . in case of the equilibrium model growth characteristics
are independent of a kinetic path .
our data from @xmath1-@xmath2 experiments at a rather low deposition rate may reflect a situation not too far from an equilibrium state , but the considered growth is heterogeneous . the data in fig .
[ expscaledfunction]b can be approximated by an exponential scaling function .
the value @xmath42 ev obtained from our experimental data for indium is similar to the pair - interaction energy determined in ref . for gallium ( @xmath43 ev ) .
+ simulations of experimental data showed that the deposition rate is a crucial parameter for growing indium on si(100 ) surface at rt and determines a transition between irreversible and reversible character of the growth .
the measured growth characteristics depend on a process of postdeposition relaxation , which has to be included into the growth simulation .
the monotonous character of the scaled chain length distribution function can be related to a mechanism of atom detachment from the chains .
the deposition rate and substrate temperature can be used for controlling competition between _ kinetics _ and _ equilibrium_. the model formulated for simulations is too simplified to be used for explanation all experimentally observed details @xcite for example a plateau in average chain length dependence on coverage within 0.05 and 0.12 ml ( see fig .
[ expdata ] ) obtained from two various @xmath1-@xmath2 measurements but the model explains the most important features of the growth of indium on the surface si(100)-2@xmath01 at room temperature .
stm technique was used for studying growth of indium on the si(100)-2@xmath01 surface at low coverage and room temperature . direct observation during the deposition
@xmath1-@xmath2 measurements showed that the c - defects act as nucleation centers for indium adatoms . the majority of indium chain is pinned on one or both ends by a c - defect , that determines the average chain length for a given coverage .
the @xmath1-@xmath2 observations further revealed the reversible character of the growth due to atom detachment from the chains .
statistical characteristics of the in layers ( average chain length , average length of chains not terminated at c - defects , dependence of average chain length on coverage , scaled island - size distribution function ) were obtained from the experiments of two types the @xmath1-@xmath2 measurements and the standard @xmath1-@xmath11 observations after the deposition of various coverages . the atomistic model with anisotropic diffusion which includes presence of c defects on the surface as well as detachment of atoms from the chain was developed .
both @xmath1-@xmath2 and @xmath1-@xmath11 experiments were simulated using kmc method .
the simulations showed that the process of atom detachment can explain the monotonously decreasing shape of the scaled chain length distribution function .
free parameters of the model - activation energies for anisotropic surface diffusion - were determined by comparison of experimental and simulated characteristic of the indium layers .
the values obtained for the activation energies ( see table [ tab : table2 ] ) correspond to almost isotropic surface diffusion in contrary with anisotropic data reported for the same group metals ga and al earlier .
the work is a part of the research plan msm 0021620834 that is financed by ministry of education of the czech republic and was partly supported by projects gacr 202/06/0049 , avoz 10100520 of ascr , gauk 227/2006/b , gauk 225/2006/b and gauk 100907 .
the access to the metacentrum computing facilities provided under the research intent msm6383917201 is highly appreciated .
the deviations between experimental and simulated characteristics were determined as follows : + ( i ) for the average chain length @xmath44 : @xmath45 + ( ii ) for the dependence of average length on coverage : @xmath46 where @xmath47 is a weight parameter
mean square deviation of chain length at a given coverage @xmath29 obtained from simulation experiments ; + + ( iii ) for the scaled chain length distribution functions : @xmath48 where function values @xmath49 are calculated for each chain length of @xmath17 atoms contained in the data . | growth of atomic indium chains - 1d islands - on the si(100)-2@xmath01 surface was observed by scanning tunneling microscopy ( stm ) at room temperature and simulated by means of a kinetic monte carlo method .
density of indium islands and island size distribution were obtained for various deposition rates and coverage .
stm observation of growth during deposition of indium provided information on growth kinetics and relaxation of grown layers .
important role of c - type defects at adsorption of metal atoms was observed .
measured growth characteristics were simulated using a microscopic model with anisotropic surface diffusion and forbidden zones along the metal chains .
an analysis of experimental and simulation data shows that detachment of indium adatoms from the chains substantially influences a growth scenario and results in monotonously decreasing chain length distribution function at low coverage .
diffusion barriers determined from the simulations correspond to almost isotropic diffusion of indium adatoms on the surface .
the results are discussed with respect to data reported in earlier papers for other metals . |
On April 9, 2018, Roger Stone sent an email that would play a role in his future arrest. Though it wasn’t the only reason he was hauled into a Florida courtroom on Friday morning, Special Counsel Robert Mueller quoted portions of it in his indictment of the Trump ally—an indictment that shook Washington and added an absurdist edge to the Mueller probe.
The email, which The Daily Beast obtained before a grand jury indicted Stone on several charges, shows just how irate Stone was about an acquaintance, Randy Credico. The exchange began when Credico emailed a group of people on the evening of April 9, 2018, about what he called an upcoming “media tour.”
“It’s the “RANDY IS FULL OF SHIT “ tour Co- sponsored by Jack Daniels and Pablo Escobar,” Stone replied.
In another email, about an upcoming Credico appearance on MSNBC, Stone speculated that he would be able to sue Credico over comments he might make.
“Send me your address,” Stone wrote. “I bet I can get you served in a lawsuit the very next morning.”
“Remember to bathe,” he added.
Another email included more invective.
“When I wipe my ass what’s on the toilet paper is worth more than You are,” Stone wrote.
“Your threats are a violation of state and federal law,” Credico replied.
Then Stone sent the email Mueller would quote portions of.
“I know u are a dumb shit but read the Constitution,” he wrote.
I have a constitutional right to call you a lightweight pantywaist cocksucker drunk asshole piece of shit and I just did You are a rat. A stoolie. You backstab your friends-run your mouth my lawyers are dying Rip you to shreds I’m going to take that dog away from you. Not a fucking thing you can do about it either because you are a weak broke piece of shit I will prove to the world you’re a liar
“You don't have a constitutional right to threaten me and especially not threaten my dog… you crossed a red line,” Credico retorted. Stone had threatened to steal his service dog.
“Rot in hell,” Stone replied.
A month later, they had another semi-incomprehensible exchange that included accusations of drug abuse and financial problems. Stone emailed Credico, “I will piss on your grave.”
A few weeks after that later, Stone and Credico had another dramatic exchange.
“You are a pathetic loser,” Stone wrote on May 21. “Let’s see who’s around a year from now and who isn’t cocksucker”
“Another one of your threats,” Credico replied.
“Not a threat. A prediction. How you feeling champ ?” Roger replied.
The Daily Beast shared screenshots of the emails with Stone’s lawyer, Grant Smith. When asked if he had any comment, Smith replied, “No.”
After publication, Smith said Mueller was misusing the emails.
“You are presenting things that are completely out of context with a decades long relationship,” he texted. “These two people talk like that to one another for years and years, it is nothing unusual and it certainly does not rise to the level of what the special counsel’s office charged.”
Martin Stolar, a lawyer for Credico, declined to comment. “Randy will make public statements concerning the indictment if and when he’s called to testify.” he said.
Stone and Credico’s relationship—the link between a political arch-villain and a New York stand-up comic—has found its way into the investigation of the century. And it highlights one of the most amusing realities of the special counsel's into Russian meddling in the 2016 election: Mueller, a notoriously serious and straight-faced law man, has spent a huge amount of time dealing with clowns.
Stone, for his part, is basically a political performance artist. He spent his decades-long career in the public eye enmeshing himself in scandals, lobbing wild-eyed accusations at his critics, and honing the practice of wildly over-the-top political dirty tricks. He also wrote a column on men’s fashion for The Daily Caller.
He wore a top hat to Trump’s inauguration. He paraded around the 2016 Republican National Convention alongside conspiracy-monger Alex Jones while sporting a T-shirt accusing Bill Clinton of rape. He suggested Trump fans should storm the hotel rooms of RNC delegates who didn’t support Trump. He got booted from Twitter and banned from CNN.
He ran a lobbying firm with Paul Manafort. He got fired from Bob Dole’s campaign for putting out a newspaper ad for swingers. He starred in a Netflix documentary. He left the Trump campaign under contested circumstances and endeared himself to the internet conspiracy community, even questioning the scientific consensus on vaccines.
This is the man Mueller has dogged for months.
Credico, whose communications with Stone featured in his indictment, is also an ur-eccentric. As a comedian and drug-legalization activist, he drew notoriety for marching into the New York State Capitol dressed as the ancient Greek philosopher Diogenes, complete with a toga and a fake beard. Once there, he protested the state’s drug laws by lighting up a joint.
Credico is an expert at mimicking other people’s voices, impersonating Richard Nixon, Ronald Reagan or Donald Trump at the drop of a hat. A small, white long-haired dog named Bianca is his constant companion. He even took her along for questioning by Mueller’s team.
Both men drew Mueller’s interest—Credico as a witness, Stone as a target—because of their shared interest in WikiLeaks founder Julian Assange. Credico, a self-described lefty, has long been a fan of WikiLeaks for revealing government secrets. Stone, meanwhile, wanted to get to Assange during the 2016 campaign in the his site had emails Hillary Clinton hadn’t made public.
A few weeks before the election, Credico interviewed Assange on his radio show. He would later visit the Ecuadorian embassy in London. The two men exchanged emails about Wikileaks before Assange started dumping emails stolen from Clinton’s campaign chairman, John Podesta. And Stone also made a series of cryptic, apparently prescient, statements about Wikileaks, which generated noisy speculation that he was getting information from inside the embassy.
After the election, when Special Counsel Mueller started investigating potential coordination between the Kremlin and Trumpworld, he soon zeroed in on Stone. As Mueller questioned a host of Stone’s long-time associates, congressional investigators grilled Stone himself.
Credico, in turn, faced questions about his relationships with WikiLeaks, ties to Stone, and alleged work as an intermediary between Stone and Assange. Stone had hinted in the past that Credico connected him to WikiLeaks, while Credico has long denied acting as any sort of go-between.
As those probes unfolded, Stone grew increasingly agitated. He told reporters he expected to be charged, and he lambasted Mueller for running a witch hunt. A few days before his indictment, he texted The Daily Beast to say he would expose monstrous misconduct by Mueller’s team if indicted.
On Friday morning, it was clear Stone’s actions after Mueller’s probe started had created his most immediate legal problems. The indictment alleges that he lied to Congress about his communications with Credico and another associate, Jerome Corsi; that he obstructed an official proceeding; and that he tampered with an unnamed witness, known to be Credico. And it cites the email printed above as one example of a statement “intended to prevent Person 2 from cooperating with the investigations.”
That’s how a foul-mouthed exchange that reads like it's written on the wall of a dive-bar bathroom found its way into what’s arguably the most geopolitically consequential criminal investigation in decades. ||||| The tragedy in West Virginia reminds us that some careers are deadlier than others. From pilots to oilmen, The Daily Beast pores over the data to determine the toughest jobs in America.
Monday's horrific accident in the mines of West Virginia serves a grim reminder that for many Americans, going to work involves a significant amount of personal risk. The bad news for workers, particularly the one-third who perform the kind of vital blue-collar jobs that dominate this list, is that 5,071 people died from job-related injuries in 2008, the last year statistics are available, according the U.S. Bureau of Labor Statistics. The good news: That figure is the lowest since 1992. The majority of fatal injuries are caused by highway accidents and transportation incidents, but the most statistically dangerous isolated occupations range from farmers to tugboat crew members.
Click Here To See the 20 Most Dangerous Jobs in America
To compile the list of the most dangerous jobs in America, we considered two categories: fatality rates and injury and illness rates as tracked by the Bureau of Labor Statistics for 2008. Fatality rate represents the total fatalities per 100,000 full-time equivalent workers using data on total hours worked for each occupation. Injury and illness rate was based on incidents counted per 100,000 workers. The latter vastly undercounts the actual number of injuries and illnesses, since only a small fraction are reported, but the statistic is highly useful to compare jobs relative to each other. Median (in few cases average) salaries, according to BLS, are also provided for each occupation. Which job is the most deadly, and is the danger worth the pay? Click here.
Clark Merrefield and Lauren Streib reported and wrote these rankings.
For More of The Daily Beast, become a fan on Facebook and follow us on Twitter.
For inquiries, please contact The Daily Beast at [email protected]. | – Tunneling deep into the earth is dangerous business, as West Virginian miners were reminded this week. With that in mind, the Daily Beast takes a look at the most dangerous professions, broken down by deaths per 100,000, injuries per 100,000, and average annual salary: Fisherman: 129 deaths, 61 injuries, $27,950 salary Logger: 116 deaths, 7 injuries, $30,360 salary Farmer/rancher: 40 deaths. 7 injuries, $49,140 salary Structural construction worker: 46 deaths, 6 injuries, $47,170 salary Sanitation worker: 37 deaths, 5 injuries, $32,790 salary Airplane pilot: 72 deaths, 2 injuries, $111,680 salary Roofer: 34 deaths, 3 injuries, $37,430 salary Coal miner: 22 deaths, 6 injuries, $46,540 salary Merchant mariners: 23 deaths, 5 injuries, $61,960 salary Miller: 12 deaths, 9 injuries, $37,400 salary For the rest of the list, click here. |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Communities Helping Invest through
Property and Improvements Needed for Veterans Act of 2016'' or the
``CHIP IN for Vets Act of 2016''.
SEC. 2. PILOT PROGRAM ON ACCEPTANCE BY THE DEPARTMENT OF VETERANS
AFFAIRS OF DONATED FACILITIES AND RELATED IMPROVEMENTS.
(a) Pilot Program Authorized.--
(1) In general.--Notwithstanding sections 8103 and 8104 of
title 38, United States Code, the Secretary of Veterans Affairs
may carry out a pilot program under which the Secretary may
accept donations of the following property from entities
described in paragraph (2):
(A) Real property (including structures and
equipment associated therewith)--
(i) that includes a constructed facility;
or
(ii) to be used as the site of a facility
constructed by the entity.
(B) A facility to be constructed by the entity on
real property of the Department of Veterans Affairs.
(2) Entities described.--Entities described in this
paragraph are the following:
(A) A State or local authority.
(B) An organization that is described in section
501(c)(3) of the Internal Revenue Code of 1986 and is
exempt from taxation under section 501(a) of such Code.
(C) A limited liability corporation.
(D) A private entity.
(E) A donor or donor group.
(F) Any other non-Federal Government entity.
(3) Limitation.--The Secretary may accept not more than
five donations of real property and facility improvements under
the pilot program and as described in this section.
(b) Conditions for Acceptance of Property.--The Secretary may
accept the donation of a property described in subsection (a)(1) under
the pilot program only if--
(1) the property is--
(A) a property with respect to which funds have
been appropriated for a Department facility project; or
(B) a property identified as--
(i) meeting a need of the Department as
part of the long-range capital planning process
of the Department; and
(ii) the location for a Department facility
project that is included on the Strategic
Capital Investment Planning process priority
list in the most recent budget submitted to
Congress by the President pursuant to section
1105(a) of title 31, United States Code; and
(2) an entity described in subsection (a)(2) has entered
into or is willing to enter into a formal agreement with the
Secretary in accordance with subsection (c) under which the
entity agrees to independently donate the real property,
improvements, goods, or services, for the Department facility
project in an amount acceptable to the Secretary and at no
additional cost to the Federal Government.
(c) Requirement To Enter Into an Agreement.--
(1) In general.--The Secretary may accept real property and
improvements donated under the pilot program by an entity
described in subsection (a)(2) only if the entity enters into a
formal agreement with the Secretary that provides for--
(A) the donation of real property and improvements
(including structures and equipment associated
therewith) that includes a constructed facility; or
(B) the construction by the entity of a facility
on--
(i) real property and improvements of the
Department of Veterans Affairs; or
(ii) real property and improvements donated
to the Department by the entity.
(2) Content of certain agreements.--With respect to an
entity described in subsection (a)(2) that seeks to enter into
a formal agreement under paragraph (1) of this subsection that
includes the construction by the entity of a facility, the
formal agreement shall provide for the following:
(A) The entity shall conduct all necessary
environmental and historic preservation due diligence,
shall comply with all local zoning requirements (except
for studies and consultations required of the
Department under Federal law), and shall obtain all
permits required in connection with the construction of
the facility.
(B) The entity shall use construction standards
required of the Department when designing and building
the facility, except to the extent the Secretary
determines otherwise.
(C) The entity shall provide the real property,
improvements, goods, or services in a manner described
in subsection (b)(2) sufficient to complete the
construction of the facility, at no additional cost to
the Federal Government.
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not inconsistent with this section. | Communities Helping Invest through Property and Improvements Needed for Veterans Act of 2016 or the CHIP IN for Vets Act of 2016 This bill authorizes the Department of Veterans Affairs (VA) to carry out a pilot program under which it may accept up to five donations from specified non-federal entities of: (1) real property that includes a constructed facility or that is to be used as the site of a facility constructed by the entity, and (2) a facility to be constructed by the entity on real property of the VA. The VA may accept such a donation only if the property is: (1) a property for which funds have been appropriated for a VA facility project, or (2) identified both as meeting a VA need as part of its long-range capital planning process and as the location for a VA facility project that is included on the Strategic Capital Investment Planning process priority list in the most recent budget submitted by the President. Also, the entity must agree to: independently donate the real property, improvements, goods, or services for the VA facility project in an amount acceptable to the VA and at no additional cost to the federal government; conduct all necessary environmental and historic preservation due diligence; comply with all local zoning requirements (except for federally required studies and consultations); obtain all permits required in connection with the construction of the facility; use construction standards required of the VA when designing and building the facility; and provide the real property, improvements, goods, or services in a manner sufficient to complete the construction of the facility, at no additional cost to the federal government. The Government Accountability Office shall report to Congress, at least biennially, on the donation arrangements entered into under the pilot program. The VA's authority to accept donations under the program shall terminate five years after the date of this bill's enactment. |
a system of atoms interacting with a common reservoir ( the electromagnetic vacuum ) is often treated using an assumption of independent dissipation rates for the atoms .
this is a valid assumption for the case when the interatomic distances are large ( compared to an optical wavelength ) ; however , when the distances between atoms become smaller or comparable to an optical wavelength , the mode structure around one atom is changed due to the presence of other atoms located in its immediate vicinity , and the decay rates are modified .
equivalently , the radiation emitted by one atom can be scattered off the second atom , thus changing the radiative properties of the system . as a consequence
, the radiative decay of the ensemble must be viewed as a cooperative effect .
a quantitative analysis of cooperative effects was given by dicke @xcite for an ensemble of two - level systems confined to a spherical volume whose radius is much smaller than an optical wavelength .
for such a system , the collective decay rate can be increased by a factor proportional to the number of atoms in the ensemble .
further investigations extend the treatment to arbitrary interatomic distances , although the calculations become more complex .
formalisms for the treatment of cooperative spontaneous emission and resonance fluorescence from a system of many atoms have been developed @xcite , and have been applied to a system of two two - level atoms @xcite .
cooperative decay in multilevel atomic systems has yet to be treated in detail . a multilevel atom has properties not possessed by a two - level atom : for example , it can store information in superpositions of ground state magnetic sublevels .
such ensembles are extensively discussed in the literature as convenient systems for information storage or large scale entanglement generation @xcite . in particular ,
pencil - shaped media have been used for the generation of spin squeezed and schrodinger cat states , in the context of continuous measurement of a scattered field @xcite . in such schemes , the coupling to the vacuum has a two - fold function : on one hand it gives rise to the signal while , on the other hand , it leads to an irreversible leakage of information from the system to the environment . in treating the losses due to spontaneous emission , the above mentioned assumption of independent atoms
is generally used , which is a sound assumption as long as the atomic density is low . however
, optimal results ( e.g. strong entanglement ) are found in the regime of resonant optical depths greater than unity , a regime in which pencil - shaped media of two - level atoms exhibit superradiant behavior @xcite .
even if the dynamics of a collection of multilevel atoms might be substantially different from that of the two - level ensemble , the validity of the independent spontaneous emission regime is questionable .
we proceed in the present publication with an analysis of cooperative effects in a system of two , four - level atoms .
this provides the starting point for an extension to many atom systems , while it also addresses the non - trivial question of the importance of cooperative decoherence in a simple quantum information system of two qubits .
the calculations are performed for a @xmath0 transition irradiated with a monochromatic , off - resonant , @xmath1 polarized , classical laser field .
the collective decoherence of an initial equal superposition of ground sublevels ( @xmath2 polarized atomic state ) is obtained for arbitrary interatomic separations and compared with that of atoms independently coupled to the reservoir .
in addition , the transfer of population from a @xmath3 polarized atomic state with both atoms in one of the ground sublevels to another @xmath3 polarized state with both atoms in the other sublevel , is analyzed .
a polarization swap effect is also discussed , where an @xmath2 polarized atom induces @xmath2 coherence in a neighboring atom @xcite .
the paper is organized as follows : in sec .
ii the theoretical method used is described . in sec .
iii analytical solutions for the case of close atoms are obtained .
numerical solutions for arbitrary separations are discussed and plotted in sec .
iv . in sec . v the polarization swap effect for arbitrary separations is discussed , while sec .
vi contains some conclusions .
as indicated in fig . [ scheme](a ) , the two atoms ( having natural frequency @xmath4 ) are located at the origin , @xmath5 , and at @xmath6 , respectively . the traveling wave driving field propagates in the positive @xmath3 direction with wave vector @xmath7 , frequency @xmath8 ( detuned from @xmath9by @xmath10 ) , and circular polarization @xmath1 .
[ h ] fig1.eps denoting the @xmath11 states of a single atom with @xmath12 ( ground , @xmath13 eigenvalue ) , @xmath14 ( ground , @xmath15 eigenvalue ) , @xmath16 ( excited , @xmath17 eigenvalue ) and @xmath18 ( excited , @xmath19 eigenvalue ) , the classical field drives the @xmath20 @xmath18 transitions .
the hamiltonian for the system ( composed of the two atoms indexed with @xmath21 , where @xmath22 ) is a sum of the free hamiltonian ( @xmath23 ) , the classical field - atom interaction hamiltonian ( @xmath24 ) and quantized bath - atom interaction hamiltonian ( @xmath25 ) given by:@xmath26 + \underset{\mathbf{k},\lambda}{% % tcimacro{\tsum } % % beginexpansion { \textstyle\sum } % endexpansion } \hbar\omega_{k}a_{\mathbf{k},\lambda}^{\dagger}a_{\mathbf{k},\lambda~},\\ v_{c~ } & = \underset{i=1,2}{% % tcimacro{\tsum } % % beginexpansion { \textstyle\sum } % endexpansion } \hbar\chi\left [ \left\vert \alpha\right\rangle _ { i}\left\langle \downarrow\right\vert _ { i~}e^{i\mathbf{k}_{l}\mathbf{\cdot r}_{i~}}e^{-i\omega t}+\left\vert \downarrow\right\rangle _ { i}\left\langle \alpha\right\vert _ { i~}e^{-i\mathbf{k}_{l}\mathbf{\cdot r}_{i~}}e^{i\omega t}\right ] , \nonumber\\ v_{q~ } & = \underset{i=1,2}{% % tcimacro{\tsum } % % beginexpansion { \textstyle\sum } % endexpansion } \left [ \underset{j=\downarrow,\uparrow}{% % tcimacro{\tsum } % % beginexpansion { \textstyle\sum } % endexpansion } \underset{j^{\prime}=\beta,\alpha}{% % tcimacro{\tsum } % % beginexpansion { \textstyle\sum } % endexpansion } \underset{\mathbf{k},\lambda}{% % tcimacro{\tsum } % % beginexpansion { \textstyle\sum } % endexpansion } \hbar\left
[ g_{\mathbf{k},\lambda~}^{jj^{\prime}}\left\vert j\right\rangle _ { i}\left\langle j^{\prime}\right\vert _ { i~}a_{\mathbf{k},\lambda~}^{\dagger } e^{-i\mathbf{k\cdot r}_{i~}}+\left ( g_{\mathbf{k},\lambda~}^{jj^{\prime}% } \right ) ^{\ast}\left\vert j^{\prime}\right\rangle _ { i}\left\langle j\right\vert _ { i~}a_{\mathbf{k},\lambda~}e^{i\mathbf{k\cdot r}_{i~}}\right ] \right ] .\nonumber\end{aligned}\ ] ] as usual , the field is quantized in a volume @xmath27 and is described by the creation and annihilation operators @xmath28and @xmath29 , corresponding to modes with wave vector @xmath7 and polarization @xmath30 .
the atomic dipole moment @xmath31 ( the same for both atoms ) couples to both the classical and quantized fields .
the cw driving field at the position of the atoms ( @xmath32 for @xmath22 ) is expressed as @xmath33 \widehat{\mathbf{\epsilon}}_{+~}$ ] .
the classical part of the interaction contains the rabi frequency defined as:@xmath34 where @xmath35 is the matrix element @xmath36 ; the interaction with the quantum vacuum has an associated coupling strength@xmath37 proportional to the dipole matrix element in the direction of the unit polarization vector @xmath38 .
the quantities that are relevant in what follows are the collective coherence operator@xmath39 and the normalized population operator@xmath40 the derivation of the time evolution of the expectation values of these two operators is the goal of our calculations . they can expressed in terms of density matrix elements as@xmath41
@xmath42 we consider two problems : first , one with both atoms prepared initially in a superposition of ground states with maximum coherence @xmath43 ( collective coherence equal to @xmath44 ) and , second , one where the population is transferred from the state with both atoms in the @xmath45 state to the one with both atoms in the @xmath14 state .
qualitative ( and some quantitative ) details of the calculations are described in the following .
the subspace of interest in which the collective operators defined above act ( henceforth named the ground subspace ) is of dimension @xmath11 and it is spanned by state vectors containing the ground substates of the two atoms ( @xmath46,@xmath47 , @xmath48 and @xmath49 ) .
a set of @xmath50 density matrix equations completely describes the dynamics of this space .
however , the ground subspace is coupled to the ground - excited subspace of dimension @xmath51 ( containing states with one excitation as for example @xmath52 ) through the classical field .
this is , in its turn , coupled to the excited subspace of dimension @xmath11 ( containing states of two excitations like @xmath53 ) which can decay back to the ground states . in a density operator approach ,
a total of @xmath54 density matrix elements coupled to each other come into play , which makes the task at hand extremely complex .
some simplifications are possible .
first , terms occurring in the evolution of the ground state density matrix elements are separated into in - terms ( due to spontaneous emission from upper states ) and out - terms ( driving terms due to the presence of the classical field ) , and these terms are treated separately .
second , an amplitude rather than a density matrix approach is sufficient to obtain expressions for the excited - ground and excited subspace density matrix elements which enter the equations .
the procedure is described in appendix b where it is applied to the derivation of the decoherence and population transfer rate for a single 4-level atom .
the treatment is perturbative in the sense that excited state populations are assumed to be negligibly small , as in many treatments of optical pumping .
the states coupled by the fields in this approximation are denoted by @xmath55 , @xmath56 and @xmath57 where the convention used is that the prime indicates excited states ( @xmath58 or @xmath59 ) , while the unprimed symbols indicate ground states ( @xmath60 or @xmath61 ) . by eliminating the intermediate states involving the radiation field ( procedure outlined in refs .
@xcite ) , one can obtain the following coupled equations of motion for the state amplitudes containing one excitation ( @xmath62 and @xmath63 ) , in an interaction picture:@xmath64 in the equation above for @xmath65 , the first term on the right - hand side is the decay ( at a rate @xmath66 equal to half the excited state population decay rate ) of the excited state amplitude of an atom independently coupled to the quantum vacuum .
the second term contains a propagator @xmath67 which includes the effects of the radiation exchange between atoms : an atom makes a transition from state @xmath68 ( quantum number @xmath69 ) to state @xmath70 which is accompanied by a transition in the other atom ( @xmath71 to @xmath72 ) .
the real part of @xmath73 gives a contribution to the decay rate that varies from @xmath44 , for maximum cooperation between atoms when their separation is much less than @xmath30 , to @xmath74 , when no exchange of radiation between atoms is present ( infinite separation ) .
the imaginary part leads to a shift in energy ( which adds to @xmath10 in the equations above ) and varies from @xmath74 ( large separation ) to infinity when the atoms are in the same location .
if the minimum interatomic separation is small but finite , the shift can always be kept small compared to the detuning and can be neglected .
the explicit expressions for the propagators involved in this problem are given in appendix a. the geometrical information on the radiation exchange is contained in the clebsch - gordan coefficients @xmath75 .
the last two terms in the right - hand side arise from driving field induced transitions and from the off - resonant nature of the interaction .
to calculate the out - terms , we note that , as a result of the driving field , ground state amplitudes ( @xmath76 ) are coupled to excited state amplitudes via@xmath77 .
st . amp}%\ ] ] as a result one finds@xmath78 b_{mn~}^{\ast}+\label{out - terms}\\ & + b_{\mu\nu~}\left [ i\chi e^{-i\mathbf{k}_{l}\mathbf{\cdot r}_{1~}% } b_{\alpha n~}\delta_{-1/2,m_{m~}~}+e^{-i\mathbf{k}_{l}\mathbf{\cdot r}_{2~}% } b_{m\alpha~}\delta_{-1/2,m_{n~}~}\right ] .\nonumber\end{aligned}\ ] ] the system of equations ( eqs .
( [ ampeqs ] ) ) is solved for the @xmath51 amplitudes @xmath79 and @xmath80 as functions of the @xmath11 ground state amplitudes @xmath76 ; these expressions are replaced in the above equation and with the identification @xmath81 , the rate equations for @xmath82 are obtained in terms of the @xmath50 density matrix elements @xmath83(with @xmath84 ) .
next , repopulation from the upper states to the lower states is taken into account ( in - terms)@xmath85 where@xmath86 note that some coherence is returned to the ground state as a result of the `` in terms '' .
the derivation of the terms in the right - hand side of eq .
( [ in - terms ] ) is done by tracing over the field states with one - photon occupation number , a procedure which has been used in the case of single multilevel atoms [ see for example ref .
the first two terms describe repopulation and recoherence of the ground manifold from the excited state manifold in a single atom .
cross coupling between atoms is reflected in the next two terms . using again the solutions of eqs .
( [ ampeqs ] ) , the right - hand side of the in - term equations can be expressed in terms of ground state density matrix elements .
a complete system of @xmath50 linear equations is thus obtained by adding the in - term to the out - term contributions .
in this limit , owing to angular momentum conservation rules , the propagators @xmath88 vanish except for @xmath89 .
a few photon exchange processes between atoms are illustrated in fig .
[ exchange1](c ) , along with their accompanying propagators .
notice that due to momentum conservation the polarization of the emitted photon matches the polarization of the absorbed photon .
taking as an example the transfer of excitation from atom @xmath44 in state @xmath90 ( with atom @xmath91 in state @xmath45 ) to atom @xmath91 in state @xmath92 ( with atom @xmath44 in state @xmath93 ) depicted in fig .
[ exchange1 ] , from eq .
( [ in - terms ] ) , one finds that the propagator associated with the exchange is @xmath94 .
[ h ] fig2.eps as in @xcite , the two - atom system can be described by superpositions of states that are either symmetrical or antisymmetrical under particle exchange ( dicke states ) .
the indistinguishability of the particles restricts the system to the symmetric subspace .
the ground state manifold is symmetrized as follows:@xmath95 while ground - excited symmetric states are defined as:@xmath96 rewriting eqs .
( [ ampeqs ] ) in terms of the new coefficients @xmath97and @xmath98 , one finds@xmath99 with quasistatic solutions @xmath100 , \nonumber\\ s_{-1~ } & = 0.\nonumber\end{aligned}\ ] ] notice that the symmetric states containing the excited @xmath59 states have either identically zero or negligibly small amplitude , which substantially simplifies the calculation . in the following two subsections ,
these expressions for the state amplitudes are used to derive the time evolution of the collective coherence and population . in the new basis
the matrix elements are denoted by @xmath101 , with @xmath102 .
the expression for the collective coherence operator expectation value in the new basis is given by@xmath103 in the limit @xmath104,@xmath42the following rate equations are obtained for the out - terms [ from eq .
( [ out - terms])]@xmath105 while the in - terms , obtained from eq .
( [ in - terms ] ) , evolve as@xmath106 adding the out - term contribution to the in - terms , and with the notation @xmath107 ( optical pumping rate ) , the equations for the density matrix elements relevant for the coherence decay are@xmath108 substituting the solutions of the eqs .
( [ coheqs ] ) into eq .
( [ coh ] ) , one obtains@xmath109 this is to be compared with the independent atom coherence decay derived in appendix b [ eq
. b4]@xmath110 [ h ] fig3.eps the increase in the coherence decay rate for intermediate times , as shown in fig .
[ cohdecayx=0 ] , can be understood in terms of the exchange processes in the uncoupled basis illustrated in fig .
[ exchange1 ] . for an independent atom
, the state @xmath90 is reached from the @xmath93 state through the action of the classical field , and decays into @xmath93 and @xmath111with rates @xmath112 and @xmath113 respectively . in the cooperative case ,
other channels responsible for coherence generation or decay appear owing to the presence of the second atom .
an interesting behavior is observed at the initiation stage of the decoherence process , where the coupled system decoheres at a rate equal to that for independent atoms .
however , this is not a general result , but rather a consequence of the initial state prepared with equal ground substate populations .
when both atoms start in the same arbitrary state @xmath114 with @xmath115 and @xmath116 , the evolution of the coupled system coherence takes the following form@xmath117 , \label{arbitrary}%\ ] ] while the independent atom coherence evolves as:@xmath118 expanding the exponentials in eqs .
( [ arbitrary ] ) and ( [ arbitraryindep ] ) for small times @xmath119 , we find@xmath120 \text{,}%\end{aligned}\ ] ] which shows that the decoherence rate of the coupled system is modified by the term @xmath121 .
this indicates that , given a population imbalance between the up and down states , at the initiation stage , the decoherence rate of the coupled system can be either larger or smaller than the one for the independent atoms , and vanishes for the balanced case only , when @xmath122 .
[ h ] fig4.eps in the symmetric basis , the expectation value of the collective population operator is expressed as@xmath123 three density matrix elements are coupled to each other : @xmath124 , @xmath125and @xmath126 .
the evolution resulting from the classical field can be obtained [ from eq .
( [ out - terms ] ) ] as@xmath127 while the in - terms are given by [ see eq .
( [ in - terms])]@xmath128 combining the in - terms with out - terms , one finds rate equations@xmath129 that are solved to give@xmath130 this is to be compared with the independent atom population evolution@xmath131 where only one mechanism for populating state @xmath132 is present : excitation of state @xmath92 by the classical field followed by decay at a rate @xmath133 to state @xmath134 .
[ h ] fig5.eps the increase in the population transfer rate , plotted in fig .
[ opticalpumpingx=0 ] vs. the independent atoms rate , is due to photons emitted by the second atom that drive the first atom into the @xmath18 state .
a faster excitation of state @xmath135leads to a faster transfer to @xmath132 for intermediate times .
it is interesting to isolate the dynamics of a single atom with the purpose of identifying the mechanisms that lead to the modification of its radiative properties due to the presence of a second atom in its vicinity .
we analyze the rate of change of the expectation value of the one atom coherence operator @xmath136 .
this is expressed in terms of density matrix elements as @xmath137 , and it is found to satisfy the following equation of motion [ using eqs .
( [ out - terms ] ) and ( [ in - terms])]@xmath138 .
\label{oneatcoh}%\ ] ] the first term in the right - hand side in the above equation simply indicates the decay of the coherence of the independent atom at the expected rate @xmath139 .
the second term contains the modification induced by the action of the neighboring atom . at the moment when the interaction between atoms is initiated
, the density matrix of the coupled system can be factorized and this term can be written as : @xmath140 , where @xmath141 is the population difference operator for the first atom .
the significance of this term is that @xmath2 polarization ( coherence ) established in the second atom induces @xmath2 polarization in the first atom through the vacuum , given a population difference .
we proceed now to analyze the origin of this coupling term by considering two distinct situations in which atom @xmath91 is prepared in a superposition @xmath142 exhibiting coherence equal to @xmath143 , while atom @xmath44 is prepared either in the @xmath134 state or the @xmath12 state . in both cases
no initial @xmath2 atomic polarization in the atom of interest is present . when starting with the population in the @xmath134 state , using eqs .
( [ out - terms ] ) and ( [ in - terms ] ) , expressions for the density matrix elements present in the right - hand side of eq .
( [ oneatcoh ] ) can be derived , and an out - term is found to be responsible with the generation of coherence@xmath144 the process leading to this can be represented as follows@xmath145 where in the first step , the field induces an excitation in the second atom , followed by a swap of excitation between atoms through the vacuum ( collision - like effect ) and a stimulated emission from the first atom . in the second case , where the population is initially stored in the @xmath45 state , both an
in - term and an out - term are present : @xmath146 the coherence generation through the out - term is similar to the process shown above [ eq .
( [ upprocess ] ) ] , while the in - term takes the following path@xmath147 where consecutive excitations for both atoms are followed by spontaneous decay into a state with coherence in the first atom .
simple analytical results are not available in this regime . coupling through propagators other than @xmath148 takes place .
the polarization of the emitted photon does nt have to match the one of the absorbed photon , a situation which is illustrated in fig .
[ exchange2 ] , where the coupling of the two - atom state @xmath149 to other states is shown and the corresponding elements of the @xmath73 matrix ( including non - diagonal ones ) responsible for the coupling specified .
[ h ] fig6.eps the calculations are now performed in the uncoupled basis .
numerical solutions of @xmath150 coupled rate equations give the coherence decay , whereas @xmath151 rate equations are solved to obtain the population transfer rate .
the output of our numerical simulations is dependent both on time and on the spherical coordinates of the second atom @xmath152and @xmath153 .
since the system has azimuthal symmetry , the interesting cases are obtained by varying @xmath154 and @xmath155 .
two orientations of the system with respect to the field propagation are examined : @xmath156@xmath157(@xmath158 ) and @xmath159@xmath157(@xmath160 ) .
the @xmath11 density matrix elements responsible for the coherence [ eq .
( [ cohandpop ] ) ] , are coupled to @xmath51 more through nondiagonal elements of @xmath73 .
a system of @xmath150 linear differential equations has to be solved containing @xmath161 .
the expressions for all @xmath150 rate equations are not given here ; instead a single one is written to illustrate the way the coupling among different states comes into play@xmath162{c}% -5\rho_{\uparrow\downarrow;\downarrow\downarrow~}-e^{-ik_{l}r_{21}\cos\theta } \left ( \begin{array } [ c]{c}% \sqrt{2}g_{10~}(r_{21},\theta,\varphi)\rho_{\downarrow\downarrow ; \downarrow\downarrow~}+2g_{00~}(r_{21},\theta,\varphi)\rho_{\downarrow \uparrow;\downarrow\downarrow~}\\ + 2g_{11~}(r_{21},\theta,\varphi)\rho_{\uparrow\downarrow;\downarrow \downarrow~}% \end{array } \right ) \\ + e^{ik_{l}r_{21}\cos\theta}\left ( \begin{array } [ c]{c}% 2g_{11~}(r_{21},\theta,\varphi)\rho_{\uparrow\downarrow;\downarrow\downarrow ~}+\sqrt{2}g_{01~}(r_{21},\theta,\varphi)\rho_{\uparrow\downarrow ; \downarrow\uparrow~}\\ + \sqrt{2}g_{01~}(r_{21},\theta,\varphi)\rho_{\uparrow\downarrow;\uparrow
\downarrow~}% \end{array } \right ) \end{array } \right ] .\ ] ] [ h ] fig7.eps the time evolution of the collective coherence is shown in fig .
[ intermediatecohdecay ] for @xmath163 . for both @xmath164@xmath165 and @xmath166@xmath165
, the coherence decays more rapidly than for the independent atom case , and the decay for @xmath156@xmath165 is faster than that for @xmath166@xmath165 . to obtain some idea of the dependence of the decay rate on interatomic separation , we plot in fig .
[ ratevardistance ] the decoherence rate ( @xmath167 ) as a function of distance , at a fixed time @xmath168 , for both the @xmath169and @xmath170 . even though a numerical solution has been used to obtain the plot in fig .
[ ratevardistance ] , an approximate analytical treatment can provide insight into the qualitative nature of the results . in particular it can help explain why the parallel case decay rate is larger than that for closely separated atoms .
the coupled equations of motion for the coherence operators associated with each atom [ similar to eq .
( [ oneatcoh ] ) but with the difference that now the coupling coefficients are @xmath171dependent ] are solved approximately at a fixed time . it is found that the perpendicular case differs from the close atoms case only insofar as the coupling between atoms is modulated by the real part of @xmath172 . an analytical expression for a fixed time @xmath173 gives a decoherence rate of the collective coherence that varies with the separation as @xmath174 $ ] .
there is , however , a fundamental difference between the perpendicular and parallel case that is reflected in the system s response . in the perpendicular case
the spatial phase of the laser field does not enter since @xmath175 . as a result
the spin coherence associated with each atom evolves in an identical fashion . on the other hand , in the parallel case
there is a relative phase difference of @xmath176 associated with the laser field as it interacts with atoms at the two sites .
consequently , the response of the two atoms need no longer be identical , since the spatial symmetry has been broken by the field .
three coupling terms are present in the parallel case : @xmath177 , @xmath178and @xmath179 ; the importance of the laser induced spatial phase is evident in these expressions . owing to the extra couplings , the two atoms accumulate different spatial phases , and the collective coherence ( obtained as the sum of individual coherences ) shows a spatial modulation that varies as @xmath180 .
a full analytical solution for the variation of the decay rate with the distance for any fixed time is not available ; however , a perturbative treatment for small times ( @xmath119 ) indicates an increase in the decay rate @xmath181 @xmath182 .
[ h ] fig8.eps just as in the case of close atoms , we extend our simulations to analyze the decay of an arbitrary initial state @xmath183 .
the observed behavior is quite different here .
even for relatively large separation ( @xmath184 ) , a state with most population in the down state decays much faster than in the independent atom case , while an inhibition of decoherence is obtained when the initial state is prepared with more population in the up state [ as shown in fig .
[ abstatex=1and2.5 ] for @xmath156@xmath165 and @xmath166@xmath165 ] .
[ h ] fig9.eps one more density matrix element ( @xmath186 ) is coupled to the @xmath150 listed before and a system of @xmath151 rate equations is solved to obtain the collective population transfer as a function of time .
[ h ] fig10.eps an interesting behavior is obtained in both the parallel and perpendicular cases ( see fig .
[ intermediatepoptransfer ] ) : the optical pumping rate is initially larger and afterwards smaller than the one for independent atoms .
the saturation effect at large times is due to the addition of a decay channel ( the @xmath187state ) which provides a way for the transfer of population from @xmath134 back to the initial @xmath93 state .
this accounts for a slow down at large times where the repopulation from the second atom ( resulting in population in state @xmath188 ) is comparable with the population produced by the classical field .
as seen in sec .
iii b , a partial transfer of coherence from an @xmath189polarized atom to an initially unpolarized atom ( in a @xmath3 state , either up or down ) can be achieved .
the two distinct situations discussed there can be extended for variable interatomic separations .
figures [ down ] and [ up ] show the evolution of the coherence of the first atom as a function of time for @xmath190 and @xmath184 and @xmath191 , respectively , when @xmath156@xmath165 . in both cases , owing to the oscillating nature of the coupling between atoms ( as a function of separation ) the sign of the effect produced in the initially @xmath3 polarized atom
depends dramatically on the distance .
[ h ] fig11.eps the decay dynamics are still given by eqs .
( [ upeq ] ) and ( [ downeq ] ) , with the distinction that the decay parameter , which for close atoms is simply equal to @xmath192 , is now spatially modulated by @xmath193 . in the case where the first atom is initially in the up state , the coherence is driven only by the out - term , which leads to a simple time behavior , where @xmath194 changes sign only due to the spatial oscillation of the coupling term .
in contrast , in the down case , the competition between the in - term and out - term leads to a change in the sign of @xmath195 for intermediate distances .
[ h ] fig12.eps
we examined a system of two multilevel atoms coherently driven by a single - mode classical laser field and coupled to the electromagnetic vacuum .
the decoherence ( of a quantum superposition stored in the ground sublevels ) that necessarily accompanies the process of manipulation of the atomic states has been analyzed in the context of cooperative behavior .
two cases have been treated , where the atoms are either at the same position or separated by a distance comparable to the optical wavelength .
it has been found ( not surprisingly ) that , for the case of close atoms , the `` communication '' between atoms leads to an increase in both the decoherence and population transfer rates . with increasing interatomic separation , in the case of the field propagating perpendicularly to the line joining the atoms ,
the decoherence rate is less than that for close atoms .
this is an expected result since , from the point of view of the classical field the atoms are located at equivalent positions , and a simple decrease of the interatomic coupling due to the increasing separation is expected . for certain distances , however , owing to the oscillating behavior of this coupling , a small effect of decoherence inhibition is also observed .
a more interesting situation arises for the case when the atoms are aligned parallel to the field propagation direction . the equivalency of positions does not hold here anymore , and a spatial phase difference between atoms resulting from the classical field is established .
the coupling through the vacuum is modulated by this spatial phase difference , and a considerable enhancement in the decay rate is observed at separations of order @xmath196 .
these results will be generalized in a future planned publication to a large ensemble of atoms in a pencil - shaped geometry .
in such a medium , at fresnel numbers close to unity , the atoms are practically aligned along the direction of the field ; for large optical depths , the phase effect described above is expected to lead to a substantial increase in the decay of the collective atomic coherence .
this work is supported by the national science foundation under grant no .
phy-0244841 and the focus center grant .
the expressions for the propagators involve spherical harmonics and hankel functions of the first kind , @xmath197 and @xmath198 [ ref .
we explicitly derive the equations of motion for the ground state coherence and populations for a single 4-level atom interacting with a @xmath1 polarized field . in the perturbative limit where a maximum of one excitation is allowed ,
a basis set in the hilbert space of atom and radiation field is comprised of states @xmath200 , @xmath201 , @xmath202 , @xmath203 , @xmath204 and @xmath205 . the first ket denotes the state of the atom while , the second one describes a vacuum field or a one photon state with wave number @xmath7 and polarization @xmath30 .
the state amplitudes obey the following equations of motion : @xmath206 using a master equation approach one can write density matrix equations of motion for the ground state sublevels as:@xmath207 the first observation that we make here is that the terms in the right hand side of the above equations , that are due to the field ( out - terms ) and to the coupling to the vacuum ( in - terms ) can be derived separately .
in other words , the presence of dissipation can be neglected when writing equations describing the driving effect of the field and later added to the equations phenomenologically .
the derivation of rate equations can now be carried out by writing equations for the ground - excited coherences and excited state populations and coherences and adiabatically eliminating them . however
, this is an unnecessary complication ; the second observation that we make provides an easier way of doing this . only the first @xmath11 equations in eqs .
( b1 ) have to be solved and the excited amplitudes can be written in terms of ground state amplitudes .
next , the density matrix elements can be written simply as if the state of the system were a pure state ( as products of amplitudes ) and replaced in eqs .
( 2 ) to obtain rate equations .
the separation of in - terms from out - terms in these equations insures the validity of this approach .
following this recipe , it is found that ( in the limit @xmath208)@xmath209 replacing these expressions into eqs .
( b2 ) , rate equations are obtained in a final form:@xmath210 the decoherence of an initial state @xmath211 can now be calculated as described by the evolution of @xmath212(neglecting the phase associated with the ac stark shift ) @xmath213 while the population transfer from state @xmath93 to state @xmath134 is given by@xmath214 l. k. thomsen , s. mancini and h. m. wiseman , phys .
rev a * 65 * , 061801 ( 2002 ) ; s. massar and e. s. polzik , phys . rev . lett . *
91 * , 060401 ( 2003 ) ; j. k. stockton , r. van handel and h. mabuchi , phys .
a * 70 * , 022106 ( 2004 ) ; c. genes and p. r. berman , phys . rev .
a * 73 * , 013801 ( 2006 ) .
it should be noted that the qualitative results for this particular case can not be generalized to other level scheme or field polarization .
for example , a calculation on two close atoms ( not presented here ) that uses @xmath2 instead of @xmath1 polarized driving fields and the same @xmath0 transition , indicates that the collective decoherence rate is not different from the independent atom coherence decay rate . | an ensemble of multilevel atoms is a good candidate for a quantum information storage device .
the information is encrypted in the collective ground state atomic coherence , which , in the absence of external excitation , is decoupled from the vacuum and therefore decoherence free .
however , in the process of manipulation of atoms with light pulses ( writing , reading ) , one inadvertently introduces a coupling to the environment , i.e. a source of decoherence .
the dissipation process is often treated as an independent process for each atom in the ensemble , an approach which fails at large atomic optical depths where cooperative effects must be taken into account . in this paper , the cooperative behavior of spin decoherence and population transfer for a system of two , driven multilevel - atoms is studied . not surprisingly , an enhancement in the decoherence rate is found , when the atoms are separated by a distance that is small compared to an optical wavelength ; however , it is found that this rate increases even further for somewhat larger separations for atoms aligned along the direction of the driving field s propagation vector .
a treatment of the cooperative modification of optical pumping rates and an effect of polarization swapping between atoms is also discussed , lending additional insight into the origin of the collective decay . |
PROGRAM.
(a) Waiver of Existing Grazing Permit or Lease.--A permittee or
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grazing permit or lease authorizing commercial livestock grazing on
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(b) Cancellation of Waived Grazing Permit or Lease.--The Secretary
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permanently retire the associated grazing allotments from commercial
livestock grazing, notwithstanding any other provision of law.
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SEC. 5. COMPENSATION FOR WAIVED GRAZING PERMIT OR LEASE.
(a) Compensation Required.--A permittee or lessee who waives a
grazing permit or lease (other than an ephemeral grazing permit or
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animal unit month based on the average of the highest three years of
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In the case of an ephemeral grazing permit or lease, the permittee or
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SEC. 8. RETIREMENT OF GRAZING ALLOTMENTS FOR WHICH NO VALID GRAZING
PERMIT OR LEASE EXISTS.
The Secretary shall not issue grazing permits or leases for grazing
allotments for which no valid permit or lease exists as of the date of
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provision of law.
SEC. 9. EFFECT OF NONUSE OR REDUCED USE.
Notwithstanding any other provision of law, a permittee or lessee
may opt not to graze a grazing allotment or to graze the grazing
allotment at less than the minimum permitted level and still retain the
grazing permit or lease for the remainder of its term. Such nonuse
shall be considered to be in compliance with the terms of the grazing
permit or lease when it becomes due for renewal.
SEC. 10. COUNTY TRANSITION PAYMENTS.
(a) Payments Required.--For each grazing permit or lease waived
under section 4 (other than an ephemeral grazing permit or lease), the
Secretary shall pay to the county in which the associated allotment is
located $10 per animal unit month based on the average of the highest
three years of authorized animal unit months out of the last 10 years
authorized to the permittee or lessee or the predecessors of the
permittee or lessee. In the case of an ephemeral grazing permit or
lease, the Secretary shall pay to the county in which the associated
allotment is located $10 per animal unit month based on the average
over the last 10 years of the actual animal unit months of grazing use.
(b) Proportional Allocation Among Counties.--In cases where an
allotment is located in more than one county, the payment under
subsection (a) to each county in which the allotment is located shall
be proportional to the allotment's land area located in that county.
SEC. 11. AUTHORIZATION OF APPROPRIATION.
There is authorized to be appropriated to the Secretaries
$100,000,000, to remain available until expended, to provide
compensation to permittees and lessees under section 5 and to make
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appropriated pursuant to this section shall be used by any Federal
agency for administrative costs related to the purposes of this Act. | Multiple-Use Conflict Resolution Act of 2005 - Establishes a voluntary grazing permit and lease buyout program for commercial livestock operators on federal land. Sets forth land priorities if funds are insufficient to meet all buyouts.
Provides for: (1) voluntary donation of grazing permits; (2) county transitional payments; and (3) permanent retirement of grazing allotments which have no valid grazing permits or allotment leases.
States that a permittee or lessee shall maintain a lease for the remainder of its term in instances of voluntary nonuse or less than minimum use. |
starburst galaxies contain prominent populations of x - ray sources @xcite including unusually luminous ones @xcite .
the young stellar ages within starbursts suggest that the associated x - ray sources are likely to be young objects @xcite .
strong x - ray variability in many sources further suggests those sources are accreting compact objects @xcite . in starburst galaxies , a substantial fraction of young stars
are found in compact , luminous star clusters @xcite . indeed ,
tremonti et al . ( 2001 ) and harris et al . (
2001 ) find evidence that most high mass stars in starbursts could form in dense clusters which quickly dissolve to feed the surrounding field .
consistent with this , the young compact cluster r136a contains a rich population of massive stars , evidently following a standard salpeter - like upper initial mass function @xcite . however , there also are indications that some compact young massive clusters have either a flatter than normal upper mass function or a cutoff at low mass @xcite
. the current data are insufficient to distinguish between these two possibilities @xcite . in either case
, the clusters would contain relatively more massive stars , and thus potentially more massive x - ray binaries .
star clusters in starburst regions usually are centrally concentrated , with as much as @xmath0 of stars within a half light radius of a few parsecs ( e.g. ho & filippenko 1996a , b ) .
stellar encounters in such dense clusters may enhance the production of x - ray binaries @xcite .
interactions of binaries in clusters @xcite and binary recoil following supernovae leading to compact object formation @xcite can lead to ejection of x - ray binaries from their point of origin .
therefore , if the x - ray sources are x - ray binaries , then they may be expected to be spread over a larger spatial area than the star clusters . here , we study the spatial offsets between x - ray point sources and star clusters in three starburst galaxies with dense clusters and deep , high - resolution x - ray observations .
we describe our sample , the observations , and our analysis in 2 , the results in 3 , and discuss the implications in 4 .
our selected galaxies are : m82 , ngc 1569 , and ngc 5253 .
all three are relatively nearby , within 4 mpc .
hence , relatively dim x - ray sources can be detected with modest exposures .
ngc 5253 is a dwarf galaxy which has been undergoing a starburst for no more than 10 myr @xcite and the young star clusters have ages between 1 myr and 8 myr @xcite .
m82 is the prototypical starburst galaxy .
the nuclear star burst has been active for roughly 10 myr @xcite and may consist of two events with ages of 5 myr and 10 myr @xcite .
there is also a more spatially extended `` fossil '' starburst which occurred 0.61 gyr ago @xcite .
ngc 1569 is a dwarf irregular galaxy which has been in a starburst phase for 10 - 20 myr @xcite . for each galaxy
, we require the positions of the star clusters . for ngc 1569
, we used the list of star clusters compiled by hunter et al.(2000 ) based on hst observations in the optical band . because this galaxy has a relatively low gas / dust content and therefore low internal extinction
, the optical data should provide a complete cluster list .
m82 is a larger galaxy and has high obscuration near its core , where most of the star clusters are located @xcite .
comparison of optical and ir images shows that many clusters are missed in the optical due to the high obscuration .
we chose to derive a cluster list from ir observations obtained with nicmos on hst . the observations and reduction of data to images
are described in alonso - herrero et al.(2003 ) .
we used a sliding cell algorithm to detect compact sources within the images from the nic2 camera using the f160w filter with a central wavelength 1.6 @xmath1 m and covering a wavelength range of 1.4 - 1.8 @xmath1 m , and the nic3 camera using the f166n filter with a central wavelength 1.66 @xmath1 m and a 1% bandpass ( images in the f160w filter were not available with nic3 ) .
the nic2 images are higher resolution ( 75 mas pixels ) and cover the inner regions of the galaxy .
the nic3 images extend the imaged field at lower resolution ( 200 mas pixels ) .
we found clusters in each image .
clusters found in multiple images were used to align the relative positions of the various nicmos images .
we determined the absolute astrometry of the nicmos images using the positions of four clusters detected in the 2mass survey which lie well outside the crowded central region of the galaxy . after applying one global shift to the nicmos
coordinates , the positions of all four clusters agree within @xmath2 with the 2mass source positions .
a mosaic of the nicmos data is shown in fig .
[ m82ir ] . for ngc 5253
, we also used nicmos observations taken using the nic2 camera and the f160w filter .
the details of these observations , the analysis , and the cluster list will be presented elsewhere ( alonso - herrero et al .
, in preparation ) .
the nicmos field of view is @xmath3 and covers the central region of the galaxy .
the astrometry was set using the accurate position for the dominant 1.3 cm radio source @xcite which is coincident with one of the ir clusters . due to the small field of view , the roll angle uncertainty from the hst aspect solution
leads to only small uncertainties in the cluster positions .
we extracted the longest available observation of each galaxy from the chandra x - ray observatory data archive .
all observations employed the advanced ccd imaging spectrometer and the high - resolution mirror assembly .
the data for m82 @xcite and ngc 1569 @xcite have been published previously .
we reanalyzed the data to have consistent results for all three galaxies . for each galaxy , we extracted an image of x - rays in the 0.38 kev band .
we calculated an exposure map for an assumed powerlaw spectrum with interstellar absorption .
the powerlaw photon index was fixed to 1.8 in all cases , and the absorption column density set to the galactic line - of - sight value for each galaxy .
we detected sources using the routine _ wavdetect _ in ciao version 2.3 requiring a source significance of @xmath4 .
we compared the resulting source list with optical images from the poss2 to remove foreground stars and with the ned extragalactic object database to remove background agn .
we used x - ray sources with either agn or optical star counterparts ( from the usno b catalog ) to check the astrometry .
the absolute x - ray source positions should be accurate to better than @xmath5 . because spectral fitting is not feasible except for the few brightest sources , we calculated an x - ray flux using the same spectrum assumed for the exposure map and correcting only for interstellar absorption within our galaxy .
if the sources have intrinsic absorption or there is absorption within the host galaxy , the true fluxes may be higher .
we calculated a luminosity for each x - ray source assuming that it is at the distance to the corresponding galaxy which we take to be 3.6 mpc for m82 , 2.2 mpc for ngc 1569 , and 3.3 mpc for ngc 5253 @xcite .
note that we calculate luminosities assuming isotropic emission .
if the x - rays are beamed , then the luminosities would be lower .
the luminosities are calculated for the 0.38 kev band .
the weakest detected sources are @xmath6 for m82 , @xmath7 for ngc 1569 , and @xmath8 for ngc 5253 .
while some of the x - ray sources may be supernova remnants ( snrs ) or young supernovae , the fraction of such sources is likely to be small .
martin et al .
( 2002 ) identify only one chandra x - ray source in ngc 1569 as a possible snr .
griffiths et al . ( 2000 ) report three close coincidences ( within @xmath5 ) of chandra x - ray sources with radio snrs in m82 .
however , the sources have hard x - ray spectra rather the soft spectra which are found for snrs @xcite and young supernovae @xcite . .statistics of the displacement distributions . [ cols="<,^,^,^,^ " , ] the table contains for each galaxy : the galaxy name , the number of x - ray sources within 1 kpc of a star cluster , the number of star clusters , and the average and median of the displacements of x - ray sources from star clusters .
to investigate the relation between star clusters and x - ray sources , we found the nearest star cluster to each x - ray source . for x - ray sources born in clusters ,
this provides a lower bound on the displacement of the source from its parent cluster .
the uncertainty in the relative alignment of the x - ray source and star cluster positions is @xmath5 or less , corresponding to uncertainties in the displacements of about 10 pc .
displacements smaller than 10 pc have been set to 10 pc .
displacements smaller than about 20 pc should be considered as upper bounds .
we examine only sources within 1 kpc of a star cluster .
the distributions of the spatial displacements are shown in fig .
[ dhist ] and some statistics of the distributions are shown in table [ disttable ] .
our cluster lists contains all of the most luminous clusters for each galaxy , but may be incomplete at low luminosities . to determine if our results are sensitive to the completeness of the sample , we varied the detection threshold for the clusters in m82 and found the distributions of the spatial displacements of x - ray sources from the clusters for the various cluster lists .
we found no significant changes in the distribution for reasonable changes in the threshold .
this may be because the lower luminosity clusters tend to be located near brighter clusters already in the list .
thus , the displacements are decreased only slightly . to determine if the clustering of the x - ray sources near the star clusters is statistically significant , we generated random sets of uniformly distributed sources and found the spatial displacements from the star clusters following the same procedures used for the actual x - ray sources .
the displacement distributions of the x - ray sources are inconsistent with that expected for a uniform distribution of sources .
the probabilities of chance occurrence from a uniform distribution are @xmath9 for m82 , @xmath10 for ngc 1569 , and @xmath11 for ngc 5253 . for each galaxy ,
the average displacement of x - ray sources from star clusters is significantly smaller than for the random source distribution , indicating that the x - ray sources are preferentially located near the star clusters .
the distributions of the spatial displacements are similar in all three galaxies , see fig .
[ dhist ] .
we compared the various distributions using a kolmogorov - smirnov ( ks ) test and also by calculating the average source displacement .
we applied both tests to both the full data sample and also restricting the source luminosities to the range @xmath12 . in all cases , the distributions of the spatial displacements for the x - ray sources in the three galaxies are consistent with being drawn from the same distribution .
the median displacement for ngc 1569 appears somewhat smaller than for the other galaxies , but the difference is not statistically significant .
the 90% confidence level error intervals for the median overlap for all three galaxies . fig .
[ lumd ] shows the luminosity of each x - ray source plotted versus its spatial displacement from the nearest star cluster .
the striking feature of the plot is that there are no high luminosity sources at large displacements from star clusters .
furthermore , there is an apparent trend of decreasing luminosity with increasing displacement from the nearest star cluster . to evaluate
if this trend is statistically significant , we performed a ` boot - strap ' analysis .
we used the set of displacements and luminosities shown in fig .
[ lumd ] and then randomly re - arranged the pairings .
this corresponds to the null hypothesis in which luminosity and displacement are unrelated . in @xmath13 trials
, we found 1920 cases in which no sources lay in the same region of the luminosity - displacement plot which is empty in fig .
this corresponds to a chance probability of occurrence of @xmath14 . for m82
there is also an absence of dim sources at small displacements .
this is likely due to the high level of diffuse x - ray emission in the central 200 pc of m82 @xcite which precludes detection of dim sources in the central regions of m82 .
dim sources are detected very near star clusters in ngc 1569 .
we have shown that x - ray sources in these three starburst galaxies are preferentially located near star clusters . because the star clusters are very good tracers of current star formation activity in the galaxies
, this confirms that the x - ray binaries are young objects associated with current star formation .
we also found significant displacements of the x - ray sources from the clusters .
because x - ray binaries , unlike other bright x - ray sources such as young supernovae , can exhibit high velocities , this suggests that much of the x - ray source population consists of x - ray binaries .
several mechanisms can put a binary in motion . for
neutron star binaries , a ` kick ' due to an asymmetric explosion in the formation of the neutron star can lead to high velocities @xcite . even in the absence of ` kicks ' from supernova explosions , momentum conservation following a symmetric ejection of matter in the formation of the neutron star or black hole in a binary with a high mass companion can produce a runaway speed of @xmath15 ; the ejected matter continues to move with the instantaneous orbital velocity of the compact object at the moment of ejection and the binary must move in the opposite direction to conserve momentum @xcite . for
binaries in clusters , interactions with other stars and binaries in the cluster can eject the binary from the cluster @xcite . in young , dense star clusters
such interactions can occur on time scales of a few myr @xcite .
objects ejected via dynamical interactions tend to escape with close to the minimum energy needed to escape @xcite .
the runaway velocities ( at infinity ) should be of the same magnitude as the stellar velocity dispersions of the clusters , which are typically @xmath16 in these galaxies @xcite .
the displacements we observe in the starburst galaxies are likely due to motion of the x - ray sources caused by one or more of these mechanisms . furthermore , we found that there is an absence of bright x - ray sources with large displacements .
this suggests that there is some correlation between the maximum possible brightness of an x - ray source and its motion .
this correlation appears to hold only for ( isotropic equivalent ) luminosities above @xmath17 .
the excluded region appears to be bounded by a linear relation between ( isotropic equivalent ) source luminosity @xmath18 and source displacement from the nearest star cluster @xmath19 , @xmath20 . in discussing this correlation
, we first consider the case where the x - ray sources emit isotropically . in this case , the systems producing such high luminosities likely contain black holes accreting via roche lobe overflow because such high luminosities would be difficult to achieve in a wind accretor due to the low efficiency of wind capture and black holes and needed to not violate the eddington limit @xcite .
if the x - ray sources are ejected from the star clusters with speeds which are roughly independent of mass , then the inverse correlation between maximum x - ray source luminosity and displacement from the nearest star cluster would arise if the source lifetime varies inversely with luminosity .
an upper bound on the source lifetime can be obtained from the time required to fully accrete the stellar companion . for a companion mass @xmath21 and an efficiency for the conversion of mass lost by the companion to luminosity of @xmath22 ,
the source lifetime must be @xmath23 where @xmath24 is the average luminosity and @xmath25 is the speed of light . for sources traveling with a speed @xmath26 perpendicular to the line of sight , the displacement from the point of origin will then be @xmath27 .
if the companion mass is independent of the compact object mass , then this would reproduce the required dependence of source lifetime on luminosity . given a typical runaway velocity @xmath28
, we must have @xmath29 to match the line plotted in fig .
[ lumd ] which bounds the region where x - ray sources are found .
if roche lobe overflow is occurring , then accretion onto the compact object may be efficient with little mass loss giving @xmath30 . in this case , the companion mass would be @xmath31 . such intermediate mass companions could be captured via dynamical interactions in the cluster . however , the capture must be directly into a roche - lobe filling orbit or the binary must hardened into a roche - lobe filling orbit via successive interactions in order to begin accretion promptly , since the evolutionary time scale of the companion is long . a better understanding of the imf and the dynamical interactions within the clusters is needed to determine if this scenario is viable .
even with accretion via roche lobe overflow , the efficiency @xmath22 may be less than @xmath32 since outflows are often observed in x - ray binaries .
super - eddington mass transfer would also produce @xmath33 . if @xmath33 , then a higher companion mass may be compatible with the data shown in fig . [ lumd ] .
if the x - ray sources have high - mass companions and maximum speeds near @xmath15 , then the absence of high luminosity source at large displacements implies a limit on the x - ray emitting lifetime of the sources .
we find no sources at luminosities above @xmath17 at displacements larger than 200 pc . at @xmath34 ,
this would imply that the lifetimes of these luminous sources must be less than 4 myr , corresponding to very massive stars .
an alternative is that the luminosity of the sources decreases with age .
this would require an evolutionary path for binaries which produces an accretion rate which decreases with age .
the x - ray binaries may also be beamed @xcite .
if the x - ray sources are high - mass systems with high velocities , then the observed correlation would imply that beaming only occurs when the binaries are quite young .
king et al . ( 2001 ) suggest that the ulxs in starburst galaxies are high mass x - ray binaries with beamed x - ray emission in a phase of thermal - timescale mass transfer .
the delay between the formation of the black hole ( and , presumably , the start of the binary s motion away from it point of origin ) and the onset of the thermal - timescale mass transfer phase depends on the stellar evolution of the companion .
the delay could be @xmath35 20 myr for a @xmath36 companion , which would imply that very bright x - ray sources should be visible out to 1 kpc .
the data appear inconsistent with this , unless highly beamed x - ray emission occurs in the thermal - timescale mass transfer phase only for very massive companions .
large displacements of high flux sources , inconsistent with the data , also appear allowed in the relativistic beamed model of kording et al .
we thank the aspen center for physics for its hospitality during the workshop where this work was begun .
pk acknowledges partial support from nasa grant nag5 - 7405 and chandra grant go2 - 3102x .
jsg thanks the university of wisconsin - madison for support of this research . | we examine the spatial offsets between x - ray point sources and star clusters in three starburst galaxies . we find that the x - ray sources are preferentially located near the star clusters .
because the star clusters are very good tracers of the star formation activity in the galaxies , this indicates that the x - ray sources are young objects associated with current star formation .
we find significant displacements of the x - ray sources from the clusters .
these displacements are likely due to motion of the x - ray sources and indicates that they are x - ray binaries .
we find that brighter x - ray sources preferentially occur closer to clusters .
the absence of very bright sources at large displacements from clusters may help constrain models of the sources .
[ firstpage ] black hole physics galaxies : individual : m82 , ngc 1569 , ngc 5253 galaxies : starburst galaxies : stellar content
x - rays : galaxies |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Sacramento-San Joaquin Delta
National Heritage Area Establishment Act''.
SEC. 2. SACRAMENTO-SAN JOAQUIN DELTA NATIONAL HERITAGE AREA.
(a) Definitions.--In this section:
(1) Heritage area.--The term ``Heritage Area'' means the
Sacramento-San Joaquin Delta Heritage Area established by this
section.
(2) Heritage area management plan.--The term ``Heritage
Area management plan'' means the plan developed and adopted by
the management entity under this section.
(3) Management entity.--The term ``management entity''
means the management entity for the Heritage Area designated by
subsection (b)(4).
(4) Secretary.--The term ``Secretary'' means the Secretary
of the Interior.
(b) Sacramento-San Joaquin Delta Heritage Area.--
(1) Establishment.--There is established the ``Sacramento-
San Joaquin Delta Heritage Area'' in the State of California.
(2) Boundaries.--The boundaries of the Heritage Area shall
be in the counties of Contra Costa, Sacramento, San Joaquin,
Solano, and Yolo in the State of California, as generally
depicted on the map entitled ``Sacramento-San Joaquin Delta
National Heritage Area Proposed Boundary'', numbered T27/
105,030, and dated September 2010.
(3) Availability of map.--The map described in paragraph
(2) shall be on file and available for public inspection in the
appropriate offices of the National Park Service and the Delta
Protection Commission.
(4) Management entity.--The management entity for the
Heritage Area shall be the Delta Protection Commission
established by section 29735 of the California Public Resources
Code.
(5) Administration; management plan.--
(A) Administration.--For purposes of carrying out
the Heritage Area management plan, the Secretary,
acting through the management entity, may use amounts
made available under this section in accordance with
section 8001(c) of the Omnibus Public Land Management
Act of 2009 (Public Law 111-11; 123 Stat. 991).
(B) Management plan.--
(i) In general.--Subject to clause (ii),
the management entity shall submit to the
Secretary for approval a proposed management
plan for the Heritage Area in accordance with
section 8001(d) of the Omnibus Public Land
Management Act of 2009 (Public Law 111-11; 123
Stat. 991).
(ii) Restrictions.--The Heritage Area
management plan submitted under this paragraph
shall--
(I) ensure participation by
appropriate Federal, State, tribal, and
local agencies, including the Delta
Stewardship Council, special districts,
natural and historical resource
protection and agricultural
organizations, educational
institutions, businesses, recreational
organizations, community residents, and
private property owners; and
(II) not be approved until the
Secretary has received certification
from the Delta Protection Commission
that the Delta Stewardship Council has
reviewed the Heritage Area management
plan for consistency with the plan
adopted by the Delta Stewardship
Council pursuant to State law.
(6) Relationship to other federal agencies; private
property.--
(A) Relationship to other federal agencies.--The
provisions of section 8001(e) of the Omnibus Public
Land Management Act of 2009 (Public Law 111-11; 123
Stat. 991) shall apply to the Heritage Area.
(B) Private property.--
(i) In general.--Subject to clause (ii),
the provisions of section 8001(f) of the
Omnibus Public Land Management Act of 2009
(Public Law 111-11; 123 Stat. 991) shall apply
to the Heritage Area.
(ii) Opt out.--An owner of private property
within the Heritage Area may opt out of
participating in any plan, project, program, or
activity carried out within the Heritage Area
under this section, if the property owner
provides written notice to the management
entity.
(7) Evaluation; report.--The provisions of section 8001(g)
of the Omnibus Public Land Management Act of 2009 (Public Law
111-11; 123 Stat. 991) shall apply to the Heritage Area.
(8) Effect of designation.--Nothing in this section--
(A) precludes the management entity from using
Federal funds made available under other laws for the
purposes for which those funds were authorized; or
(B) affects any water rights or contracts.
(9) Authorization of appropriations.--
(A) In general.--There is authorized to be
appropriated to carry out this section $20,000,000, of
which not more than $2,000,000 may be made available
for any fiscal year.
(B) Cost-sharing requirement.--The Federal share of
the total cost of any activity under this section shall
be determined by the Secretary, but shall be not more
than 50 percent.
(C) Non-federal share.--The non-Federal share of
the total cost of any activity under this section may
be in the form of--
(i) in-kind contributions of goods or
services; or
(ii) State or local government fees, taxes,
or assessments.
(10) Termination of authority.--If a proposed management
plan has not been submitted to the Secretary by the date that
is 5 years after the date of enactment of this title, the
Heritage Area designation shall be rescinded. | Sacramento-San Joaquin Delta National Heritage Area Establishment Act - Establishes the Sacramento-San Joaquin Delta National Heritage Area in California.
Designates the Delta Protection Commission as the management entity for the Heritage Area.
Requires the Commission to submit a proposed management plan for the Heritage Area to the Secretary of the Interior for approval.
Bars approval of the management plan until the Secretary has received certification from the Commission that the Delta Stewardship Council has reviewed such plan for consistency with the plan adopted by the Council pursuant to state law. |
mbius syndrome is a heterogeneous congenital disorder that is linked to bilateral palsies of the cranial nerves vi and vii , resulting in congenital facial paralysis sometimes associated with impaired ocular abduction .
we present the case of a 44-year - old woman with mbius syndrome and inferior recurrent keratitis secondary to scleral show in both eyes .
we decided to use a cartilage graft from the ear in the inferior eyelid to avoid eyelid retraction and scleral show .
their treatment must be individualized , depending on their age , clinical examination and symptoms .
mbius syndrome is a heterogeneous congenital disorder that is linked to bilateral palsies of the cranial nerves vi and vii [ 1 , 2 ] . from an ophthalmological perspective ,
these patients present symmetrical facial diplegia with variable patterns of horizontal gaze paresis and facial paralysis [ 3 , 4 ] , which affect palpebral dynamics in adult life .
we present the case of a 44-year - old woman with mbius syndrome and congenital craniofacial cleft . during her childhood
, she had undergone multiple surgeries in the departments of traumatology , plastic surgery and maxillofacial surgery .
the patient was being monitored due to her eye problems derived from the facial paralysis .
four years ago , she had undergone a permanent partial bilateral tarsorrhaphy that improved her eyelid closure problems .
however , at the last checkups , the lower eyelids had retracted again , and she presented recurrent lower keratitis caused by a scleral exposure of 12 mm in both eyes , in spite of a good bell 's phenomenon and an intensive treatment with lubricants ( fig .
1 ) . we decided to introduce a graft for the lower eyelid in order to alleviate the retraction and reduce the scleral exposure . in view of the fact that the patient had undergone surgery of the palatal area on several occasions due to her craniofacial malformations ( fig .
we performed an incision at the end of the lower conjunctival sac , we separated the retractor muscles from the tarsal plate , and we disinserted the capsulopalpebral ligament , so that the tarsal plate was left free and completely exposed . a 6 20 mm section of auricular cartilage was extracted and its upper border was sewn into the lower edge of the lower tarsal plate with 7 - 0 vicryl .
the lower edge of the graft was sutured to the retractors , and the incision in the conjunctival sac was also sutured with 7 - 0 vicryl .
two weeks after the procedure , we observed that the lower eyelid retraction had improved notably .
the patient did not present scleral exposure , and the eyelid closure had also improved ( fig .
, the patient presented recurrent type iii keratitis despite intensive treatment with lubricants ; however , after the graft had been inserted , we only observed type i keratitis sporadically and always when she had forgotten to apply tear supplements .
mbius syndrome is a rare complex of malformations which was first described by von graefe in 1880 .
its etiology is unknown , although some components have been described , either genetic , vascular or related with the intake of some drugs like misoprostol during pregnancy .
it is characterized by bilateral congenital paralysis of the cranial nerve pairs vi and vii , and it is accompanied by symmetrical facial diplegia with variable patterns of horizontal gaze paresis . facial paralysis and lagophthalmos
have been documented in as many as 80% of cases with mbius syndrome . during childhood , the phenomena derived from facial paralysis are not very noticeable .
lagophthalmos or other alterations of the eyelid dynamics are rare before 20 years of age , but facial amimia of the patients is common in the patients , especially in expressions like crying or smiles . in patients younger than
7 years of age , a certain function of the facial muscles can be achieved with the transference of the temporal muscle or the latissimus dorsi , or the gracilis muscle , which can be reinnervated with the mandibular branch of the trigeminal nerve or with a ramification of the spinal nerve [ 6 , 7 , 8 ] .
however , patients are usually admitted as adults with no previous treatment , when the effects of facial paralysis are more evident .
the main reasons for consultation are problems caused by the appearance of exposure keratitis due to poor eyelid closure during the night . in this case , the main therapeutic measure is a medical approach with lubricants and hygienic measures in order to prevent the evaporation of tears .
when the alterations in the eyelid dynamics increase , patients suffer a retraction of the lower eyelid with scleral exposure .
this aggravates the recurrence and severity of keratitis , which in some cases causes extremely severe corneal ulcers that increase the risk of neurotrophy and can lead to corneal perforation and endophthalmitis .
it is also common to see ectropion of the lower eyelid and eyebrow ptosis . in these cases ,
surgery is required , and the approach will depend on the severity of the facial paralysis , the exploration of the dynamic and static condition of the eyelids and the symptoms of the patient .
static approaches narrow the opening of the eyelid either horizontally ( tarsorrhaphy ) or vertically ( elevation of the lower eyelid via desinsertion of the retractors , placing of spacers and/or a facial lifting ) .
dynamic approaches improve the eyelid closure , and the most common procedure is a gold weight implant . to transfer a muscle , either vascularized or nonvascularized , such as the platysma muscle , towards the free edge of the eyelid and to combine it with a gold weight implant
the authors report no conflicts of interest . the authors alone are responsible for the content and writing of the paper . | introductionmbius syndrome is a heterogeneous congenital disorder that is linked to bilateral palsies of the cranial nerves vi and vii , resulting in congenital facial paralysis sometimes associated with impaired ocular abduction.case reportwe present the case of a 44-year - old woman with mbius syndrome and inferior recurrent keratitis secondary to scleral show in both eyes .
we decided to use a cartilage graft from the ear in the inferior eyelid to avoid eyelid retraction and scleral show.discussionpatients with mbius syndrome have a severe dysfunction of their facial mimic .
their treatment must be individualized , depending on their age , clinical examination and symptoms . |
a 24-year - old male was admitted to the hospital due to systemic erythema and wheals with an itchy sensation , which he had had for 9 years .
a stinging pain , rated 7 cm on a visual analogue scale ( vas : from 0 to 10 cm ) , was one of the dermatological symptoms and was predominant when the patient ate hot or spicy foods , engaged in a vigorous workout , took a hot bath , or experienced situational nervousness or stress .
the symptoms disappeared within 30 - 90 minutes of rest or symptomatic relief . when the patient was exposed to heat
, the symptoms worsened , with an excessive hot flush sensation ; the symptoms were relieved when he rested in cool conditions .
there were no signs of autonomic dysfunction such as orthostatic hypotension , impotence , and photophobia .
the results of the blood laboratory test , liver function test , urinalysis , rheumatoid factor , coagulation test , erythrocyte sedimentation rate ( esr ) , c - reactive protein ( crp ) , and chest x - ray were either within the normal range or negative .
glycopyrrolate 2 mg / day was administered orally for 1 week for diagnostic purposes , and a symptomatic change was observed .
after the reduction in diaphoresis from the administration of glycopyrrolate , the hot flush became severe and the patient still complained of pain with a vas rating of 7 cm .
the medication was ceased under the impression of possible cholinergic urticaria with generalized hypohidrosis , and a right and left stellate ganglion block was carried out by administering mepivacaine 10 cc with a 20-minute interval . in the 1-week follow - up ,
the frequency of symptoms was similar , but there was a reduction in the degree of excessive hot flushes , and the systemic pain had a vas rating of 4 cm .
an extra stellate ganglion block was since carried out , and the vas rating was reduced to 2 cm .
cholinergic urticaria is characterized by systemic erythema and wheals with an itchy sensation and is brought by an increase in body temperature after an exercise or hot bath .
the diagnosis is generally made from the patient history , and differential diagnosis should be made with respect to exercise - induced urticaria or anaphylactic reaction to foods through a provocation test .
the pathology of cholinergic urticaria is not clearly identified but can be divided into 4 large categories according to the cause : poral occlusion , acquired generalized hypohidrosis , sweat allergy , and idiopathic . from these 4 categories , cholinergic
urticaria with generalized hypohidrosis is defined by urticaria with reduced sweat secretion even with sufficient stimulation .
the etiological factors are occlusion of the sweat glands due to keratinization , autoimmune disease or disappearance of the sweat glands as a congenital defect , and a malfunction of the autonomic nervous system .
stimulation of the sympathetic nervous system causes the secretion of acetylcholine , and sweat secretion occurs as feedback of the reaction of acetylcholine receptors in the sweat glands .
reported through skin tissue biopsies that patients with cholinergic urticaria with generalized hypohidrosis have reduced cholinergic receptor muscarinic 3 ( chrm 3 ) .
they hypothesized that the reduction of chrm 3 in sweat glands leads to insufficient sweat secretion and an increase in acetylcholine secretion through a feedback mechanism , and the increased serum acetylcholine induces the surrounding master cells to secrete histamine or stimulate sensory nerve terminals , which in turn causes cholinergic urticaria and pain .
the authors used anticholinergic drugs to differentiate sweat allergy from a hypersensitivity reaction after sweat secretion and cholinergic urticaria with generalized hypohidrosis , and a worsening of the patient 's symptoms was observed soon after administration of the medication and the reduction in sweat secretion .
therefore , the reduction of sweat is thought to be the etiological factor in this patient . in this case
, the patient did not have any significant medical history such as specific physical appearances or intellectual abnormalities to suggest the possibility of congenital diseases .
moreover , the patient did not present any abnormalities in the autonomic nervous system except for hypohidrosis .
diagnosis is thus possible , as the sweat glands disappeared due to autoimmune disease or were occluded by keratinization rather than congenital defects .
antihistamines and anticholinergic drugs are the standard treatments for cholinergic urticaria . however , most patients experience moderate relief from an antihistamine and minor relief from anticholinergic drugs .
systemic steroids can be administered when the cause of hypohidrosis is destruction or occlusion of sweat glands due to autoimmune disease .
keratolysis can be chosen as a treatment for the blockade of the opening of sweat glands due to keratinization .
the stellate ganglion block is effective at stabilizing the hypertonic sympathetic nerve system in the head , neck , and arms .
it is known to temporarily block the sympathetic nervous system , and it also disconnects the pain circle and recovers the balance of the somatic nervous system and sympathetic nervous system within the area where pain occurs .
cholinergic urticaria with generalized hypohidrosis is a symptom that arises when the sympathetic nerve system is activated due to excessive exercise or bathing and sufficient sweat secretion does not occur .
this increases the serum acetylcholine level and activation of the sympathetic nervous system through a feedback system , and the stellate ganglion block can facilitate improvement of symptoms .
however , persistent nerve therapy and follow - up observations are needed for an accurate determination of efficacy , consideringthat stellate ganglion block also causes hypohidrosis and the low frequency of the stellate ganglion block procedure . | cholinergic urticaria with acquired generalized hypohidrosis , and its pathophysiology is not well known .
autoimmunity to sweat glands or to acetylcholine receptors on sweat glands has been mentioned as one of the possible etiologies .
systemic steroid therapy , antihistamines , anticholinergics , and avoidance of the stimulatory situations are recommended for treatment .
we experienced a case of cholinergic urticaria with acquired generalized hypohidrosis in a patient who had no other associated disease , and the symptoms eased after repeated bilateral stellate ganglion block .
stellate ganglion block normalized the elevated sympathetic tone and may relieve symptoms in patients with this condition . |
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Use of this Site constitutes acceptance of our User Agreement (updated 4/30/2015) and Privacy Policy (updated 4/30/2015) Your California Privacy Rights The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Athlon Media Group. Ad Choices ||||| "I joined the Air Force. I took to it immediately when I arrived there. I did three years, eight months, and ten days in all, but it took me a year and a half to get disabused of my romantic notions about it."
Now famed for a sonorous voice and genteel manner, Morgan Freeman took a winding road to his current fame. Born on June 1, 1937, he grew up in a segregated community in Mississippi but frequently moved around. Growing up, Freeman acted in a number of school plays and competitions, often taking leading roles and winning awards. Despite his talent, passion, and success in drama, he put his acting ambitions aside after completing high school.
Freeman was always entranced by war films, particularly pieces about fighter pilots. In love with the idea of flying, he joined the U.S. Air Force in 1955 but was relegated to being a radar technician. His interest in flight was so strong that he turned down a scholarship for drama from Jackson State University to enlist. Despite his initial occupation not living up to his dream, he held on to his romantic visions for over a year.
Eventually, Freeman got the chance to train as a fighter pilot. Despite years of anticipation for that very job, as soon as he sat in the cockpit he had a "distinct feeling [he] was sitting in the nose of a bomb." "I had this very clear epiphany," he told AARP Magazine. "You are not in love with this; you are in love with the idea of this." Freeman didn’t hesitate to act on his gut instinct, and left the Air Force in 1959.
After moving to Los Angeles, Freeman struggled to get by day to day while pursuing a career in acting. He took acting lessons at the Pasadena Playhouse, and learned to dance in San Francisco. It took Freeman roughly twenty years of acting in stage productions to gain notoriety in film and television. His first strides towards national fame were made in the soap opera "Another World" and the long-running children's program "The Electric Company."
Freeman went on to act in prominent supporting roles, and later as a star in such movies as "the Shawshank Redemption," "Seven," and "Invictus." With no signs of his career slowing down, he has also produced over a dozen films. Although the military has provided numerous individuals with a foundation for success, by following his gut instinct, Morgan Freeman has become the successful entertainer that audiences know and love today. ||||| Drew Carey Comedian & Actor
Drew Carey, the famous comedian and star of The Drew Carey Show, served in the Marine Corps Reserves from 1980 - 1986. According to Carey, he adopted his trademark crew cut and horn-rimmed glasses during his time of service.
Carey, born May 23, 1958 in Cleveland, was a member of his high school marching band and later attended Kent State, where he was a member of the Delta Tau Delta fraternity. During his service in the Marine Corps, he began performing stand-up comedy that eventually led to supporting roles on television. Finally, he was given a starring role in his own sitcom playing an "everyman" who works as a manager of a department store. He also hosts the United States version of the popular British improv comedy show, Whose Line Is It Anyway?
When asked how he got his start, Carey said, "While in the Marine Reserves, I was looking for a way to make some more money, and it was suggested that I try using my jokes." Carey was paid about $10 a joke during his first stand-up. Eventually, he found his way into show business.
Carey's comedy reflects an appreciation for the trials of everyday life as well as a devilish sense of the absurd. Mr. Carey still supports the troops, and does overseas touring with the USO.
"I think if I did not have such a great break, I would still be in the military," said Carey. "I still wear my hair short and have the glasses. Also, I enjoyed the regimen and camaraderie. I knew that once I left the Reserves, I would give back to the military, so I teamed up with the USO." ||||| Chuck Norris is famous as a world-champion martial artist, and movie and television star. What many people don't know is that Norris is also very dedicated to the military community. Carlos Ray "Chuck" Norris was born on March 10, 1940 in Ryan, Oklahoma. His mother was Irish-English and his father was Cherokee. Norris joined the Air Force after high school, with the goal of training in the Security Police in preparation for a career in law enforcement. It was in the Air Force, while stationed in Korea, that Chuck was introduced to martial arts. One night on duty, Norris realized that he couldn't arrest a rowdy drunk without pulling his weapon.
He thus studied Tang Soo Do and Tae Kwan Do, both Korean martial arts, and became the first Westerner to be awarded an eighth-degree Black Belt in Tae Kwan Do. When he returned to the US, Norris served at March Air Force Base, California before being discharged in August 1962. He then worked for Northrop Aviation, but moonlighted as a karate instructor and soon was teaching full-time and running a number of martial arts schools, teaching famous celebrities such as the Osmonds, Priscilla Presley and Steve McQueen. He held the world middleweight karate champion title for six years, and was named Black Belt magazine's "Fighter of the Year" in 1969, eventually founding 32 martial arts schools. It was McQueen who encouraged Norris to go into acting. After bit roles, he captured the public's attention with his show-stopping turn as Bruce Lee's martial arts opponent in "Return of the Dragon" (1973). By the late 70s he was popular enough to headline his own movies, and starred in cult classics such as "Good Guys Wear Black," "Delta Force" and "Missing in Action." He currently stars in the popular TV series "Walker, Texas Ranger." Norris' fame grew to the point that fans began making up "Chuck Norris facts" about him (i.e., "Chuck Norris once kicked a horse in the chin. Its descendants today are known as giraffes"), and to this day new "Chuck Norris facts" are still being created, much to the good-natured Norris' amusement.
Norris has used his success to give back to the military community. He has been a spokesman on behalf of the Veteran's Administration and hospitalized veterans. In 1990 he created the "Kick Drugs out of America" Foundation, and has also been named "Veteran of the Year" at the American Veteran awards show. ||||| Born in Baltimore, Maryland, on July 3, 1956, Williams enlisted in the U.S. Marines upon graduating high school in 1974. He took basic training at Parris Island, South Carolina, where he was promoted to platoon guide. After basic training, he was sent to the Desert Warfare Training Center at Twenty-nine Palms, near Palm Springs, California.
While at Twenty-nine Palms, his superiors became impressed with his leadership skills, and he was recommended for, and accepted to, the Naval Academy Preparatory school at Newport, Rhode Island. He completed the one-year course, and was accepted to the U.S. Naval Academy at Annapolis.
When he arrived at Annapolis on July 6, 1976, he was honorably discharged as a corporal from the marines, and enlisted into the navy as a midshipman. While at Annapolis, Williams studied Mandarin Chinese and graduated with a degree in general engineering and a minor in International Security Affairs. It was at Annapolis that Williams first began to shave his head. Upon his graduation in 1980, he became the first black enlisted marine to complete and graduate both the Academy Prep School and Annapolis.
Commissioned an ensign, he spent the next one and a half years in Guam as a cryptologic officer for naval intelligence, where he served at sea and ashore. In 1982 he was transferred to Defense Language Institute in Monterey, California, where he studied the Russian language for one year. In 1983 he was transferred to Ft. Meade in Maryland, where he worked with the National Security Agency. What Williams did there is vague, due to the sensitive nature of intelligence work, but he performed various intelligence missions. He was offshore aboard ship during the invasion of Grenada.
After three years aboard submarines, Williams, now a full lieutenant, was made supervising cryptologic officer with the Naval Security Fleet Support Division at Ft. Meade. It was while counseling his crew that he discovered a gift for public speaking. In 1988, he began conducting informal counseling for the wives and families of the servicemen in his command. He was later asked to speak to a local group of kids in Kansas City, MO about the importance of leadership and how to overcome obstacles on the road to success -- thus beginning a three-year career in motivational speaking.
Williams traveled the country talking to more than three million teenagers nationwide and gave up his naval commission to pursue speaking full-time. He left the navy with the rank of lieutenant, and received the Navy Achievement Medal, the Meritorious Service Medal, and the Navy Commendation Medal. In addition, he reached out to thousands of parents, educators and business leaders, encouraging them to work together to address youth issues, trends and to inspire youngsters to reach their highest potential. These efforts to reach out to the community eventually lead to the Montel Williams Show on television. ||||| "When I had my daughter I was like, man, I'm going to go to jail, I got to do something, and I went to an enlistment office. Next thing you know, I'm in the military, four years infantry."
Now known as prominent actor and musician Ice-T, Tracy Marrow was born in Newark, New Jersey to Solomon and Alice Marrow. Ice-T's mother died of a heart attack when he was in third grade. His father raised him on his own until he also passed away a few years later. The 12 year old Ice-T moved to live with various relatives until settling with an aunt in South Los Angeles. While in high school, Ice-T abstained from drugs, cigarettes, and alcohol, but did affiliate himself with members of the Crips. He read books by Iceberg Slim, and was able to quote lines to his friends. It was in high school that he began writing rhymes.
Right out of high school, Ice-T struggled to support his girlfriend and daughter. He decided to join the Army for the financial benefits, and served four years in the 25th Infantry Division. Early in his career, he was part of a small group that stole an infantry rug and subsequently deserted. After a month, once the rug had been recovered, Ice-T returned and received a non-judicial punishment which allowed him to complete Advanced Infantry Training.
During his deployment in Hawaii, Ice-T served as a squad leader at Schofield Barracks. According to his memoir, it was here that he purchased stereo equipment including turntables, a mixer, and speakers. At one point during his career, a sergeant told Ice-T that he served in the army because he couldn't survive on his own in the civilian world. Despite the sergeant's claim, Ice-T utilized his time in the army to built financial stability, hone his skills, and launch a career in the entertainment industry.
When Ice-T returned to the civilian world, he lived in Hollywood and made inroads into the hip-hop scene. His first major deal was sealed with Sire Records, but he quickly created his own label, Rhyme Syndicate. He went on to start a metal band, win a Grammy, and produce the controversial song "Cop Killer." He later launched a successful career in film and television, most notably as detective Odafin Tutuola on "Law & Order: SVU." | – Veterans Day is coming up on Wednesday, and in a nod to it, Parade lists 13 celebrities who've served in the military. Here are 6 standouts, along with some details from Military.com about their service: Chuck Norris: Air Force, 1958-1962. The champion martial artist was first exposed to the martial arts while stationed in Korea. Clint Eastwood: Army, 1951-1953. He was drafted during the Korean War and, thanks to the GI Bill, studied drama in college after he was discharged. Drew Carey: Marine Corps Reserves, 1980-1986. The crew-cut hairstyle and horn-rimmed glasses he's known is a look that stretches back to his days of service. Ice-T: Army, 1971-1975. "When I had my daughter I was like, man, I'm going to go to jail, I got to do something, and I went to an enlistment office. Next thing you know, I'm in the military, four years infantry." Montel Williams: Marine Corps and Navy, 1974-1996. After high school he became a Marine, but he went on to attend the Naval Academy Preparatory School and the US Naval Academy at Annapolis; he was the "first black enlisted Marine" to graduate from both. Morgan Freeman: Air Force, 1955-1959. He was so enthralled with the idea of being a fighter pilot that he declined a scholarship that would have had him study drama at Jackson State University. He later realized what his true passion was. Click for the complete list—including one woman. |
there has been a great deal of attention devoted in recent years to the properties of the hot x - ray - emitting plasma ( the intracluster medium , hereafter icm ) in the central regions of massive galaxy groups and clusters . to a large extent , the focus has been on the competition between radiative cooling losses and various mechanisms that could be heating the gas and therefore ( at least partially ) offsetting the effects of cooling . prior to the launch of the _ chandra _ and _ xmm - newton _ x - ray observatories
, it was generally accepted that large quantities of the icm should be cooling down to very low energies , where it would cease to emit x - rays and eventually condense out into molecular clouds and form stars ( fabian 1994 ) .
however , the amount of cold gas and star formation actually observed in most systems is well below what was expected based on analyses of _ rosat _ , _ asca _ , and _ einstein _
x - ray data ( e.g. , voit & donahue 1995 ; edge 2001 ) . new high spatial and spectral resolution data from _ chandra _ and _ xmm - newton _ has shown that , while cooling is clearly important in many groups and clusters ( so - called ` cool core ' systems ) , relatively little gas is actually cooling out of the x - ray band to temperatures below @xmath0 k ( peterson et al . 2003 ) .
it is now widely believed that some energetic form of non - gravitational heating is compensating for the losses due to cooling .
indeed , it seems likely that such heating goes beyond a simple compensation for the radiated energy .
as well as having a profound effect on the properties of the icm , it seems that the heat input also has important consequences for the formation and evolution of the central brightest cluster galaxy ( bcg ) and therefore for the bright end of the galaxy luminosity function ( e.g. , benson et al .
2003 ; bower et al . 2006 , 2008 ) .
the thermal state of the icm therefore provides an important probe of these processes and a concerted theoretical effort has been undertaken to explore the effects of various heating sources ( e.g. , supermassive black holes , supernovae , thermal conduction , dynamical friction heating of orbiting satellites ) using analytic and semi - analytic models , in addition to idealised and full cosmological hydrodynamic simulations ( e.g. , binney & tabor 1995 ; narayan & medvedev 2001 ; ruszkowski et al . 2004 ; mccarthy et al . 2004 ; kim et al . 2005 ;
voit & donahue 2005 ; sijacki et al .
2008 ) . in most of these approaches
, it is implicitly assumed that _ gravitationally - induced _ heating ( e.g. , via hydrodynamic shocks , turbulent mixing , energy - exchange between the gas and dark matter ) that occurs during mergers / accretion is understood and treated with a sufficient level of accuracy .
for example , most current analytic and semi - analytic models of groups and clusters attempt to take the effects of gravitational heating into account by assuming distributions for the gas that are taken from ( or inspired by ) non - radiative cosmological hydrodynamic simulations the assumption being that these simulations accurately and self - consistently track gravitational processes .
however , it has been known for some time that , even in the case of identical initial setups , the results of non - radiative cosmological simulations depend on the numerical scheme adopted for tracking the gas hydrodynamics . in particular , mesh - based eulerian ( such as adaptive mesh refinement , hereafter amr ) codes appear to systematically produce higher entropy ( lower density ) gas cores within groups and clusters than do particle - based lagrangian ( such as smoothed particle hydrodynamics , hereafter sph ) codes ( see , e.g. , frenk et al .
1999 ; ascasibar et al .
2003 ; voit , kay , & bryan 2005 ; dolag et al .
2005 ; oshea et al .
this may be regarded as somewhat surprising , given the ability of these codes to accurately reproduce a variety of different analytically solvable test problems ( e.g. , sod shocks , sedov blasts , the gravitational collapse of a uniform sphere ; see , e.g. , tasker et al .
2008 ) , although clearly hierarchical structure formation is a more complex and challenging test of the codes . at present
, the origin of the cores and the discrepancy in their amplitudes between eulerian and lagrangian codes in cosmologically - simulated groups and clusters is unclear .
there have been suggestions that it could be the result of insufficient resolution in the mesh simulations , artificial entropy generation in the sph simulations , galilean non - invariance of the mesh simulations , and differences in the amount of mixing in the sph and mesh simulations ( e.g. , dolag et al . 2005 ; wadsley et al .
we explore all of these potential causes in 4 .
clearly , though , this matter is worth further investigation , as it potentially has important implications for the competition between heating and cooling in groups and clusters ( the cooling time of the icm has a steep dependence on its core entropy ) and the bright end of the galaxy luminosity function . and
it is important to consider that the total heating is not merely the sum of the gravitational and non - gravitational heating terms .
the rankine - hugoniot jump conditions tell us that the efficiency of shock heating ( either gravitational or non - gravitational in origin ) _ depends on the density of the gas at the time of heating _ ( see , e.g. , the discussion in mccarthy et al .
this implies that if gas has been heated before being shocked , the entropy generated in the shock can actually be amplified ( voit et al .
2003 ; voit & ponman 2003 ; borgani et al . 2005
; younger & bryan 2007 ) .
the point is that gravitational and non - gravitational heating will couple together in complex ways , so it is important that we are confident that gravitational heating is being handled with sufficient accuracy in the simulations .
a major difficulty in studying the origin of the cores in cosmological simulations is that the group and cluster environment can be extremely complex , with many hundreds of substructures ( depending on the numerical resolution ) orbiting about at any given time .
furthermore , such simulations can be quite computationally - expensive if one wishes to resolve in detail the innermost regions of groups and clusters ( note that , typically , the simulated cores have sizes @xmath1 ) .
an alternative approach , which we adopt in the present study , is to use idealised simulations of binary mergers to study the relevant gravitational heating processes .
the advantages of such an approach are obviously that the environment is much cleaner , therefore offering a better chance of isolating the key processes at play , and that the systems are fully resolved from the onset of the simulation .
the relatively modest computational expense of such idealised simulations also puts us in a position to be able to vary the relevant physical and numerical parameters in a systematic way and to study their effects .
idealised merger simulations have been used extensively to study a variety of phenomena , such as the disruption of cooling flows ( gmez et al .
2002 ; ritchie & thomas 2002 ; poole et al . 2008 ) , the intrinsic scatter in cluster x - ray and sunyaev - zeldovich effect scaling relations ( ricker & sarazin 2001 ; poole et al .
2007 ) , the generation of cold fronts and related phenomena ( e.g. , ascasibar & markevitch 2006 ) , and the ram pressure stripping of orbiting galaxies ( e.g. , mori & burkert 2000 ; mccarthy et al . 2008b ) .
however , to our knowledge , idealised merger simulations have not been used to elucidate the important issue raised above , nor have they even been used to demonstrate whether or not this issue even exists in non - cosmological simulations . in the present study
, we perform a detailed comparison of idealised binary mergers run with the widely - used public simulations codes ( an amr code ) and ( a sph code ) .
the paper is organised as follows . in
2 we give a brief description of the simulation codes and the relevant adopted numerical parameters .
in addition , we describe the initial conditions ( e.g. , structure of the merging systems , mass ratio , orbit ) of our idealised simulations . in 3 , we present a detailed comparison of results from the and runs and confirm that there is a significant difference in the amount of central entropy generated with the two codes . in
4 we explore several possible causes for the differences we see .
finally , in 5 , we summarise and discuss our findings .
below , we provide brief descriptions of the and hydrodynamic codes used in this study and the parameters we have adopted .
the interested reader is referred to springel , yoshida , & white ( 2001 ) and springel ( 2005b ) for in - depth descriptions of and to fryxell et al .
( 2000 ) for the code .
both codes are representative examples of their respective amr and sph hydrodynamic formulations , as has been shown in the recent code comparison of tasker et al .
( 2008 ) .
[ [ section ] ] is a publicly available amr code developed by the alliances center for astrophysical thermonuclear flashes .
originally intended for the study of x - ray bursts and supernovae , it has since been adapted for many astrophysical conditions and now includes modules for relativistic hydrodynamics , thermal conduction , radiative cooling , magnetohydrodynamics , thermonuclear burning , self - gravity and particle dynamics via a particle - mesh approach . in this study
we use version 2.5 .
solves the reimann problem using the piecewise parabolic method ( ppm ; colella & woodward 1984 ) .
the present work uses the default parameters , which have been thoroughly tested against numerous analytical tests ( see fryxell et al .
the maximum number of newton - raphson iterations permitted within the riemann solver was increased in order to allow it to deal with particularly sharp shocks and discontinuities whilst the default tolerance was maintained .
the hydrodynamic algorithm also adopted the default settings with periodic boundary conditions being applied to the gas as well as to the gravity solver .
we have modified the gravity solver in to use an fft on top of the multigrid solver ( written by t. theuns ) .
this results in a vast reduction in the time spent calculating the self - gravity of the simulation relative to the publicly available version .
we have rigorously tested the new algorithm against the default multigrid solver , more tests are presented in tasker et al .
( 2008 ) . to identify regions of rapid flow change , s refinement and de - refinement criteria
can incorporate the adapted lhner ( 1987 ) error estimator .
this calculates the modified second derivative of the desired variable , normalised by the average of its gradient over one cell . with
this applied to the density as is common place , we imposed the additional user - defined criteria whereby the density has to exceed a threshold of @xmath2 , below which the refinement is set to the minimum @xmath3 mesh .
this restricts the refinement to the interior of the clusters and , as we demonstrate below , was found to yield nearly identical results to uniform grid runs with resolution equal to the maximum resolution in the equivalent amr run .
uses an oct - tree block - structured amr grid , in which the block to be refined is replaced by 8 blocks ( in three dimensions ) , of which the cell size is one half of that of the parent block .
each block contains the same number of cells , @xmath4 cells in each dimension in our runs .
the maximum allowed level of refinement , @xmath5 , is one of the parameters of the run . at refinement level @xmath5
, a fully refined amr grid will have @xmath6 cells on a side .
all the merger runs are simulated in 20 mpc on a side periodic boxes in a non - expanding ( newtonian ) space and are run for a duration of @xmath7 gyr . by default
, our simulations are run with a maximum of @xmath8 levels of refinement ( @xmath9 cells when fully refined ) , corresponding to a minimum cell size of @xmath10 kpc , which is small in comparison to the entropy cores produced in non - radiative cosmological simulations of clusters ( but note we explicitly test the effects of resolution in 3 ) .
the simulations include non - radiative hydrodynamics and gravity .
is a publicly available treesph code designed for the simulation of cosmological structure formation . by default , the code implements the entropy conserving sph formalism proposed by springel & hernquist ( 2002 ) .
the code is massively parallel , has been highly optimised and is very memory efficient .
this has led to it being used for some of the largest cosmological simulations to date , including the first n - body simulation with more than @xmath11 dark matter particles ( the _ millennium simulation _ ; springel et al .
2005a ) .
the sph formalism is inherently lagrangian in nature and fully adaptive , with ` refinement ' based on the density .
the particles represent discrete mass elements with the fluid variables being obtained through a kernel interpolation technique ( lucy 1977 ; gingold & monaghan 1977 ; monaghan 1992 ) .
the entropy injected through shocks is captured through the use of an artificial viscosity term ( see , e.g. , monaghan 1997 ) .
we will explore the sensitivity of our merger simulation results to the artificial viscosity in [ viscosity ] . by default
, gravity is solved through the use of a combined tree particle - mesh ( treepm ) approach .
the treepm method allows for substantial speed ups over the traditional tree algorithm by calculating long range forces with the particle - mesh approach using fast fourier techniques .
higher gravitational spatial resolution is then achieved by applying the tree over small scales only , maintaining the dynamic range of the tree technique .
this allows to vastly exceed the gravitational resolving power of mesh codes which rely on the particle - mesh technique alone and are thus limited to the minimum cell spacing .
we adopt the following numerical parameters by default for our runs ( but note that most of these are systematically varied in 3 ) . the artificial bulk viscosity , @xmath12 ,
is set to 0.8 .
the number of sph smoothing neighbours , @xmath13 , is set to 32 .
each of our @xmath14 model clusters ( see 2.1 ) are comprised of @xmath15 gas and dark matter particles within @xmath16 , and the gas to total mass ratio is @xmath17 .
thus , the particle masses are @xmath18 and @xmath19 .
the gravitational softening length is set to 10 kpc , which corresponds to @xmath20 initially .
all the merger runs are simulated in 20 mpc on a side periodic boxes in a non - expanding ( newtonian ) space and are run for a duration of @xmath21 10 gyr .
the simulations include basic hydrodynamics only ( i.e. , are non - radiative ) . in our simulations ,
the galaxy clusters are initially represented by spherically - symmetric systems composed of a realistic mixture of dark matter and gas .
the dark matter is assumed to follow a nfw distribution ( navarro et al . 1996 ; 1997 ) : @xmath22 where @xmath23 and @xmath24 here , @xmath16 is the radius within which the mean density is 200 times the critical density , @xmath25 , and @xmath26 .
the dark matter distribution is fully specified once an appropriate scale radius ( @xmath27 ) is selected .
the scale radius can be expressed in terms of the halo concentration @xmath28 .
we adopt a concentration of @xmath29 for all our systems .
this value is typical of massive clusters formed in @xmath30cdm cosmological simulations ( e.g. , neto et al .
2007 ) . in order to maintain the desired nfw configuration ,
appropriate velocities must be assigned to each dark matter particle .
for this , we follow the method outlined in mccarthy et al .
briefly , the three velocity components are selected randomly from a gaussian distribution whose width is given by the local velocity dispersion [ i.e , @xmath31 . the velocity dispersion profile itself is determined by solving the jeans equation for the mass density distribution given in eqn .
( 1 ) . as in mccarthy
( 2007 ) , the dark matter haloes are run separately in isolation in for many dynamical times to ensure that they have fully relaxed . for the gaseous component
, we assume a powerlaw configuration for the entropy is the not the actual thermodynamic specific entropy ( @xmath32 ) of the gas , but is related to it via the simple relation @xmath33 .
however , for historical reasons we will refer to @xmath34 as the entropy .
] , @xmath35 , by default .
in particular , @xmath36 where the ` virial entropy ' , @xmath37 , is given by @xmath38 this distribution matches the entropy profiles of groups and clusters formed in the non - radiative cosmological simulations of voit , kay , & bryan ( 2005 ) ( vkb05 ) for @xmath39 .
it is noteworthy that vkb05 find that this distribution approximately matches the entropy profiles of both sph ( the code ) and amr ( the code ) simulations . within @xmath40 , however , the amr and sph simulations show evidence for entropy cores , but of systematically different amplitudes .
we initialise our systems without an entropy core [ i.e. , eqn .
( 3 ) is assumed to hold over all radii initially ] to see , first ,
if such cores are established during the merging process and , if so , whether the amplitudes differ between the sph and amr runs , as they do in cosmological simulations . we leave it for future work to explore the differences that result ( if any ) between sph and amr codes when large cores are already present in the initial systems ( e.g. , the merger of two ` non - cool core ' systems ) . with the mass distribution of dark matter established ( i.e. , after having run the dark matter haloes in isolation ) and an entropy distribution for the gas given by eqn .
( 3 ) , we numerically compute the radial gas pressure profile ( and therefore also the gas density and temperature profiles ) , taking into account the self - gravity of the gas , by simultaneously solving the equations of hydrostatic equilibrium and mass continuity : @xmath41 two boundary conditions are required to solve these equations .
the first condition is that @xmath42 .
the second condition is that the total mass of hot gas within @xmath16 yields a realistic baryon fraction of @xmath43 . in order to meet the second condition
, we choose a value for @xmath44 and propagate the solution outwards to @xmath16 .
we then iteratively vary the inner pressure until the desired baryon fraction is achieved . for the simulations ,
the gas particle positions are assigned by radially morphing a glass distribution until the desired gas mass profile is obtained ( see mccarthy et al .
the entropy ( or equivalently internal energy per unit mass ) of each particle is specified by interpolating with eqn . ( 3 ) . for the simulations , the gas density and entropy of each grid cell is computed by using eqn . ( 3 ) and interpolating within the radial gas density profile resulting from the solution of eqns . ( 5 ) and ( 6 ) .
thus , for both the and simulations we start with identical dark matter haloes ( using particle positions and velocities from the isolated runs with a gravitational softening length of 10kpc ) and gas haloes , which have been established by interpolating within radial profiles that have been computed numerically under the assumption that the gas is initially in hydrostatic equilibrium within the dark matter halo . note that when varying the resolution of the simulations we simply change the maximum number of refinements @xmath5 we do not vary the number of dark matter particles in this way , the initial dark matter distribution is always the same as in the low resolution run in all the simulations we have run . in both the and simulations ,
the gaseous haloes are surrounded by a low density pressure - confining gaseous medium that prevents the systems from expanding prior to the collision ( i.e. , so that in the case of an isolated halo the object would be static ) but otherwise it has a negligible dynamical effect on the system .
isolated gas+dm haloes were run in both and for 10 gyr in order to test the stability of the initial gas and dark matter haloes .
although deviations in the central entropy develop over the course of the isolated simulations , indicating the systems are not in perfect equilibrium initially , they are small in amplitude ( the central entropy increases by @xmath45 over 10 gyr ) , especially in comparison to the factor of @xmath46 jump in the central entropy that occurs as a result of shock heating during the merger . furthermore
, we note that the amplitude of the deviations in the isolated runs are significantly decreased as the resolution of these runs is increased .
our merger simulations , however , are numerically converged ( see 3 ) , indicating that the deviations have a negligible effect on merger simulation results and the conclusions we have drawn from them .
= 8.4 cm = 8.4 cm
the existence of a discrepancy between the inner properties of the gas in groups and clusters formed in amr and sph cosmological simulations was first noticed in the santa barbara code comparison of frenk et al .
it was subsequently verified in several works , including dolag et al .
( 2005 ) , oshea et al .
( 2005 ) , kravtsov , nagai & vikhlinin ( 2005 ) , and vkb05 .
the latter study in particular clearly demonstrated , using a relatively large sample of @xmath47 simulated groups and clusters , that those systems formed in the amr simulations had systematically larger entropy cores than their sph counterparts . since this effect
was observed in cosmological simulations , it was generally thought that the discrepancy was due to insufficient resolution in the mesh codes at high redshift ( we note , however , that vkb05 argued against resolution being the cause ) .
this would result in under - resolved small scale structure formation in the early universe .
this explanation is consistent with the fact that in the santa barbara comparison the entropy core amplitude tended to be larger for the lower resolution mesh code runs .
our first aim is therefore to determine whether the effect is indeed due to resolution limitations , or if it is due to a more fundamental difference between the two types of code .
we test this using identical idealised binary mergers of spherically - symmetric clusters in and , where it is possible to explore the effects of finite resolution with relatively modest computational expense ( compared to full cosmological simulations ) . as a starting point
, we investigate the generation of entropy cores in a head on merger between two identical @xmath48 clusters , each colliding with an initial speed of @xmath49 km / s [ i.e. , the initial _ relative _ velocity is @xmath50 , which is typical of merging systems in cosmological simulations ; see , e.g. , benson 2005 ] .
the system is initialised such that the two clusters are just barely touching ( i.e. , their centres are separated by @xmath51 ) .
the simulations are run for a duration of 10 gyr , by the end of which the merged system has relaxed and there is very little entropy generation ongoing .
l l l flash sim .
cells & max .
spatial res .
+ & & ( kpc ) + @xmath52 & equiv .
@xmath53 & 78 + @xmath8 ( default ) & equiv .
@xmath9 & 39 + @xmath54 & equiv .
@xmath55 & 19.5 + @xmath56 & equiv .
@xmath57 & 9.8 + @xmath9 & @xmath9 & 39 + + gadget-2 sim . &
gas particles & max .
spatial res .
+ & & ( kpc ) + low res .
& @xmath58 & @xmath59 + default & @xmath60 & @xmath61 + hi res .
& @xmath62 & @xmath63 + our idealised test gives very similar results to non - radiative cosmological simulations there is a distinct difference in the amplitude of the entropy cores in the amr and sph simulations , with the entropy in the mesh code a factor @xmath64 higher than the sph code .
it is evident that the difference between the codes is captured in a single merger event .
an immediate question is whether this is the result of the different effective resolutions of the codes .
resolution tests can be seen in the left hand panel of figure [ entropy_radius ] , where we plot the resulting radial entropy distributions . for
, we compare runs with @xmath58 , @xmath60 ( the default ) , and @xmath62 particles .
for we compare amr runs with minimum cell sizes of @xmath65 , @xmath66 ( the default ) , @xmath67 , and @xmath68 kpc and a uniform grid run with the default 39 kpc cell size .
the simulation characteristics for these head on mergers are presented in table 1 .
to make a direct comparison with the cosmological results of vkb05 ( see their fig .
5 ) , we normalise the entropy by the initial ` virial ' entropy ( @xmath37 ; see eqn . 4 ) and the radius by the initial virial radius , @xmath16 .
the plot clearly shows that the simulations converge on two distinctly different solutions within the inner ten percent of @xmath16 , whereas the entropy at large radii shows relatively good agreement between the two codes .
the simulations performed for the resolution test span a factor of 8 in spatial resolution in and approximately a factor of 5 in .
the amr runs effectively converge after reaching a peak resolution equivalent to a @xmath69 run ( i.e. , a peak spatial resolution of @xmath70 kpc or @xmath71 ) .
we have also tried a run with a uniform ( as opposed to adaptive ) @xmath9 grid and the results essentially trace the amr run with an equivalent peak resolution .
this reassures us that our amr refinement criteria is correctly capturing all regions of significance .
the lowest resolution sph run , which only has @xmath72 gas particles within @xmath16 initially , has a slightly higher final central entropy than the default and high resolution sph runs .
this may not be surprising given the tests and modelling presented in steinmetz & white ( 1997 ) .
these authors demonstrated that with such small particle numbers , two - body heating will be important if the mass of a dark matter particle is significantly above the mass of a gas particle .
the runs converge , however , when the number of gas and dark matter particles are increased by an order magnitude ( i.e. , as in our default run ) , yielding a maximum spatial resolution of @xmath61 kpc ( here we use the minimum sph smoothing length as a measure of the maximum spatial resolution ) . a comparison of the left hand panel of fig . 1 to fig .
5 of vkb05 reveals a remarkable correspondence between the results of our idealised merger simulations and those of their cosmological simulations ( which spanned system masses of @xmath73 ) .
they find that the ratio of the amr and sph core amplitudes is @xmath64 in both the idealised and cosmological simulations .
this difference is also seen in the santa barbara comparison of frenk et al .
( 1999 ) when comparisons are made between the sph simulations and the highest resolution amr simulations carried out in that study ( ie . ,
the ` bryan ' amr results ) amr run in fig . 1 ) .
this consistency presumably indicates that whatever mechanism is responsible for the differing core amplitudes in the cosmological simulations is also responsible for the differing core amplitudes in our idealised simulations .
this is encouraging , as it implies the generation of the entropy cores can be studied with idealised simulations .
as outlined in 1 , the advantage of idealised simulations over cosmological simulations is their relative simplicity .
this gives us hope that we can use idealised simulations to track down the underlying cause of the discrepancy between particle - based and mesh - based hydrodynamic codes .
the right hand panel of figure [ entropy_radius ] shows the resulting entropy distributions plotted in a slightly different fashion .
here we plot the entropy as a function of ` enclosed ' gas mass @xmath74 .
this is constructed by simply ranking the particles / cells by entropy in ascending order and then summing the masses of the particles / cells [ the inverse , @xmath75 , would therefore be the total mass of gas with entropy lower than @xmath34 ] .
convective stability ensures that , eventually when the system is fully relaxed , the lowest - entropy gas will be located at the very centre of the potential well , while the highest entropy gas will be located at the system periphery .
@xmath74 is therefore arguably a more fundamental quantity than @xmath77 and we adopt this test throughout the rest of the paper .
it is also noteworthy that in order to compute @xmath78 one does not first need to select a reference point ( e.g. , the centre of mass or the position of the particle with the lowest potential energy ) or to bin the particles / cells in any way , both of which could introduce ambiguities in the comparison between the sph and amr simulations ( albeit likely minor ones ) . in the right hand panel of figure [ entropy_radius ] , we plot the resulting @xmath74 distributions normalised to the final entropy distribution of the default run .
here we see that the lowest - entropy gas in the runs have a higher entropy , by a factor of @xmath79 , than the lowest - entropy gas in the default run .
naively , looking at the right hand panel of figure [ entropy_radius ] one might conclude that the discrepancy is fairly minor , given that @xmath80% of the gas has been heated to a similar degree in the sph and amr simulations .
but it is important to keep in mind that it is the properties of the lowest - entropy gas in particular that are most relevant to the issue of heating vs. cooling in groups and clusters ( and indeed in haloes of all masses ) , since this is the gas that has the shortest cooling time .
the agreement between our results and those from cosmological simulations ( e.g. , frenk et al .
1999 ; vkb05 ) is striking .
the convergence of the entropy distributions in our idealised simulations negates the explanation that inadequate resolution of the high redshift universe in cosmological amr simulations is the root cause of the discrepancy between the entropy cores in sph and amr simulations ( although we note that some of the lower resolution amr simulations in the study of frenk et al .
may not have been fully converged and therefore the discrepancy may have been somewhat exaggerated in that study for those simulations ) .
we therefore conclude that the higher entropy generation in amr codes relative to sph codes within the cores of groups and clusters arises out of a more fundamental difference in the adopted algorithms . below
we examine in more detail how the entropy is generated during the merging process in the simulations and we then systematically explore several possible causes for the differences in the simulations .
we have demonstrated that the entropy generation that takes place in our idealised mergers is robust to our choice of resolution , yet a difference persists in the amount of central entropy that is generated in the sph and mesh simulations .
we now examine the entropy generation as a function of time in the simulations , which may provide clues to the origin of the difference between the codes .
figure [ 8panelimage ] shows @xmath81 in a slice through the centre of the default simulation at times 0 , 1 , 2 , 3 , 4 , 5 , 7 and 10 gyr .
this may be compared to figure [ entropygastime ] , which shows the entropy distribution of the simulations as a function of time ( this figure is described in detail below ) .
briefly , as the cores approach each other , a relatively gentle shock front forms between the touching edges of the clusters , with gas being forced out perpendicular to the collision axis .
strong heating does not actually occur until approximately the time when the cores collide , roughly 1.8 gyrs into the run .
the shock generated through the core collision propagates outwards , heating material in the outer regions of the system .
this heating causes the gas to expand and actually overshoot hydrostatic equilibrium .
eventually , the gas , which remains gravitationally bound to the system , begins to fall back onto the system , producing a series of weaker secondary shocks .
gas at the outskirts of the system , which is the least bound , takes the longest to re - accrete .
this dependence of the time for gas to be re - accreted upon the distance from the centre results in a more gradual increase in entropy than seen in the initial core collision . in a _ qualitative _ sense , the heating process that takes place in the simulations is therefore very similar to that seen in the simulations ( see 3 of mccarthy et al .
2007 for an overview of the entropy evolution in idealised mergers ) .
the top left panel in figure [ entropygastime ] shows the ratio of @xmath74 in the default run relative to @xmath74 in the default run .
the various curves represent the ratio at different times during the simulations ( see figure key note that these correspond to the same outputs displayed in figure [ 8panelimage ] ) .
it can clearly be seen that the bulk of the difference in the _ final _ entropy distributions of the simulations is established around the time of core collision .
the ratio of the central entropy in the simulation to the central entropy in the simulation converges after @xmath82 gyr .
the top right panel shows the time evolution of the lowest - entropy gas only in both the and runs .
here we see there are similar trends with time , in the sense that there are two main entropy generation episodes ( core collision and re - accretion ) , but that the entropy generated in the first event is much larger in the run than in the run . far outside the core , however , the results are very similar . for completeness ,
the bottom two panels show @xmath74 at different times for the and runs separately .
the small initial drop in the central entropy at 1 gyr in the run ( see bottom left panel ) is most likely due to interpolation errors at low resolution . this drop in entropy should not physically occur without cooling processes ( which are not included in our simulations ) , but there is nothing to prevent a dip from occurring in the simulations due to numerical inaccuracies ( the second law of thermodynamics is not explicitly hardwired into the mesh code ) . at low resolutions , small violations in entropy conservation can occur due to inaccurate interpolations made by the code .
we have verified that the small drop in entropy does not occur in the higher resolution runs .
we note that while this effect is present in default run , it is small and as demonstrated in fig .
1 the default run is numerically converged .
it is interesting that the to central entropy ratio converges relatively early on in the simulations .
this is in spite of the fact that a significant fraction of the entropy that is generated in both simulations is actually generated at later times , during the re - accretion phase .
evidently , this phase occurs in a very similar fashion in both simulations . in 4 , we will return to the point that the difference between the results of the amr and sph simulations arises around the time of core collision .
= 6.0 cm = 6.0 cm = 6.0 cm = 6.0 cm it is important to verify that the conclusions we have drawn from our default setup are not unique to that specific initial configuration . using a suite of merger simulations of varying mass ratio and orbital parameters , mccarthy et al .
( 2007 ) demonstrated that the entropy generation that takes place does so in a qualitatively similar manner to that described above in all their simulations .
however , these authors examined only sph simulations .
we have therefore run several additional merger simulations in both and to check the robustness of our conclusions .
all of these mergers are carried out using the same resolution as adopted for the default and runs . in figure
[ orbit_test ] , we plot the final to @xmath74 ratio for equal mass mergers with varying orbital parameters ( see figure caption ) . in all cases , systematically produces larger entropy cores than , and by a similar factor to that seen in the default merger setup .
interestingly , the off - axis case results in a somewhat larger central entropy discrepancy between and , even though the bulk energetics of this merger are the same as for the default case .
a fundamental difference between the off - axis case and the default run is that the former takes a longer time for the cores to collide and subsequently relax ( but note by the end of the off - axis simulation there is very little ongoing entropy generation , as in the default case ) .
this may suggest that the timescale over which entropy is generated plays some role in setting the magnitude of the discrepancy between the amr and sph simulations .
for example , one possibility is that ` pre - shocking ' due to the artificial viscosity i.e. , entropy generation during the early phases of the collision when the interaction is subsonic or mildly transonic ) in the sph simulations becomes more relevant over longer timescales .
another possibility is that mixing , which is expected to be more prevalent in eulerian mesh simulations than in sph simulations , plays a larger role if the two clusters spend more time in orbit about each other before relaxing into a single merged system ( of course , one also expects enhanced mixing in the off - axis case simply because of the geometry ) .
we explore these and other possible causes of the difference in 4 .
in addition to varying the orbital parameters , we have also experimented with colliding a cluster composed of dark matter only with another cluster composed of a realistic mixture of gas and dark matter ( in this case , we simulated the head on merger of two equal mass @xmath48 clusters with an initial relative velocity of @xmath83 km / s ) .
obviously , this is not an astrophysically reasonable setup .
however , a number of studies have suggested that there is a link between the entropy core in clusters formed in non - radiative cosmological simulations and the amount of energy exchanged between the gas and the dark matter in these systems ( e.g. , lin et al . 2006 ; mccarthy et al . 2007 ) . it is therefore interesting to see whether this experiment exposes any significant differences with respect to the results of our default merger simulation . ) .
the long - dashed green and short - dashed cyan curves represent head on collisions with initial relative velocities of @xmath84 and @xmath85 ( i.e. , at rest initially ) .
the dot dashed red curve represents an off - axis collision with an initial relative radial velocity of @xmath86 and an initial relative tangential velocity of @xmath87 ( i.e. , the total energy is equivalent to that of the default setup ) .
also shown ( dotted magenta curve ) , is the entropy ratio of a run where one of the clusters is composed of dark matter only and the other of a realistic mixture of gas and dark matter ( see text ) .
all these simulations result in a comparable difference in entropy profile between the mesh code and the sph code .
, width=317 ] the dotted magenta curve in figure [ orbit_test ] represents the final to @xmath74 ratio for the case where a dark matter only cluster merges with another cluster composed of both gas and dark matter .
the results of this test are remarkably similar to that of our default merger case .
this indicates that the mechanism responsible for the difference in heating in the mesh and sph simulations in the default merger simulation is also operating in this setup .
although this does not pin down the difference between the mesh and sph simulations , it does suggest that the difference has little to do with differences in the properties of the large hydrodynamic shock that occurs at core collision , as there is no corresponding large hydrodynamic shock in the case where one cluster is composed entirely of dark matter .
however , it is clear from figure 3 that the difference between the default mesh and sph simulations is established around the time of core collision , implying that some source of heating other than the large hydrodynamic shock is operating at this time ( at least in the simulation ) .
we return to this point in 4 .
there are fundamental differences between eulerian mesh - based and lagrangian particle - based codes in terms of how they compute the hydrodynamic and gravitational forces .
ideally , in the limit of sufficiently high resolution , the two techniques would yield identical results for a given initial setup .
indeed , both techniques have been shown to match with high accuracy a variety of test problems with known analytic solutions . however , as has been demonstrated above ( and in other recent studies ; e.g. , agertz et al . 2007 ; trac et al . 2007 ; wadsley et al .
2008 ) differences that do not appear to depend on resolution present themselves in certain complex , but astrophysically - relevant , circumstances . in what follows , we explore several different possible causes for why the central heating that takes place in mesh simulations exceeds that in the sph simulations .
the possible causes we explore include : * [ gravitysolvers ] a difference in gravity solvers - most currently popular mesh codes ( including and ) use a particle - mesh ( pm ) approach to calculate the gravitational force . to accurately capture short range
forces it is therefore necessary to have a finely - sampled mesh .
by contrast , particle - based codes ( such as and ) often make use of tree algorithms or combined tree particle - mesh ( treepm ) algorithms , where the tree is used to compute the short range forces and a mesh is used to compute long range forces .
since the gravitational potential can vary rapidly during major mergers and large quantities of mass can temporarily be compressed into small volumes , it is conceivable differences in the gravity solvers and/or the adopted gravitational force resolution could give rise to different amounts of entropy generation in the simulations .
* [ galileaninv ] galilean non - invariance of mesh codes - given explicit dependencies in the riemann solver s input states , all eulerian mesh codes are inherently not galilean invariant to some degree .
this can lead to spurious entropy generation in the cores of systems as they merely translate across the simulation volume ( e.g. , tasker et al .
* [ viscosity ] ` pre - shocking ' in the sph runs - artificial viscosity is required in sph codes to capture the effects of shock heating .
however , the artificial viscosity can in principle lead to entropy production in regions where no shocks should be present ( e.g. , dolag et al .
if such pre - shocking is significant prior to core collision in our sph simulations , it could result in a reduced efficiency of the primary shock . * [ mixing ] a difference in the amount of mixing in sph and mesh codes - mixing will be suppressed in standard sph implementations where steep density gradients are present , since rayleigh - taylor and kelvin - helmholtz instabilities are artificially damped in such circumstances ( e.g. , agertz et al .
in addition , the standard implementation of artificial viscosity will damp out even _ subsonic _ motions in sph simulations , thereby inhibiting mixing ( dolag et al .
on the other hand , one expects there to be some degree of over - mixing in mesh codes , since fluids are implicitly assumed to be fully mixed on scales smaller than the minimum cell size .
+ + we now investigate each of these possible causes in turn .
we do not claim that these are the only possible causes for the differences we see in the simulations .
they do , however , represent the most commonly invoked possible solutions ( along with hydrodynamic resolution , which we explored in 3 ) to the entropy core discrepancy between sph and mesh codes . 5 , 6 , 7 , and 8 , respectively , which correspond to peak grid cell sizes of @xmath65 , @xmath66 , @xmath67 , and @xmath68 kpc ( respectively ) . the thin solid red curve represents the uniform @xmath9 run . the gravitational softening length adopted for the run is 10 kpc . for reference , @xmath88 kpc .
the vertical dashed line indicates four softening lengths .
the dark matter distribution converges to the result when the numerical resolutions become similar : the observed differences in gas entropy are not due to differences in the underlying dark matter dynamics .
, width=317 ] in the simulations , gravity is computed using a standard particle - mesh approach . with this approach ,
the gravitational force will be computed accurately only on scales larger than the finest cell size . by contrast , the simulations make use of a combined treepm approach , where the tree algorithm computes the short range gravitational forces and the particle - mesh algorithm is used only to compute long range forces . to test whether or not differences in the gravity solvers ( and/or gravitational force resolution )
are important , we compare the final mass distributions of the dark matter in our simulations .
the distribution of the dark matter should be insensitive to the properties of the diffuse baryonic component , since its contribution to the overall mass budget is small by comparison to the dark matter .
thus , the final distribution of the dark matter tells us primarily about the gravitational interaction alone between the two clusters .
figure [ dmconverge ] shows the ratio of the final dark matter mass profiles to the final dark matter mass profile . recall that in all runs the number of dark matter particles is the same .
the differences that are seen in this figure result from solving for gravitational potential on a finer mesh .
for the lowest resolution run , we see that the final dark matter mass profile deviates significantly from that of the default run for @xmath89 .
however , this should not be surprising , as the minimum cell size in the default run is @xmath90 . by increasing the maximum refinement level , @xmath5
, we see that the discrepancy between the final and dark matter mass profiles is limited to smaller and smaller radii . with @xmath91 ,
the minimum cell size is equivalent to the gravitational softening length adopted in the default run . in this case
, the final dark matter mass distribution agrees with that of the default run to within a few percent at all radii beyond a few softening lengths ( or a few cell sizes ) , which is all that should be reasonably expected .
a comparison of the various runs with one another ( compare , e.g. , the default run with the @xmath56 run , for which there is a @xmath92% discrepancy out as far as @xmath40 ) may suggest a somewhat slower rate of convergence to the default result than one might naively have expected .
given that we have tested the new fft gravity solver against both the default multigrid solver and a range of simple analytic problems and confirmed its accuracy to a much higher level than this , we speculate that the slow rate of convergence is due to the relatively small number of dark matter particles used in the mesh simulations . in the future , it would be useful to vary the number of dark matter particles in the mesh simulations to verify this hypothesis . in summary , we find that the resulting dark matter distributions agree very well in the and simulations when the effective resolutions are comparable .
the intrinsic differences between the solvers therefore appear to be minor .
more importantly for our purposes , even though the gravitational force resolution for the default run is not as high as for the default run , this has no important consequences for the comparison of the final entropy distributions of the gas .
it is important to note that , even though the final mass distribution in the simulations shows small differences between @xmath93 and 8 , figure [ entropy_radius ] shows that the entropy distribution is converged for @xmath94 and is not at all affected by the improvement in the gravitational potential .
and 45 degrees with @xmath56 , respectively .
this comparison illustrates that the effects of galilean non - invariance on the resulting entropy distribution are minor and do not account for the difference in the entropy core amplitudes of the mesh and sph simulations .
, width=317 ] due to the nature of riemann solvers ( which are a fundamental feature of amr codes ) , it is possible for the evolution of a system to be galilean non - invariant .
this arises from the fixed position of the grid relative to the fluid . the riemann shock tube initial conditions are constructed by determining the amount of material that can influence the cell boundary from either side , within a given time step based on the sound speed
the riemann problem is then solved at the boundary based on the fluid properties either side of the boundary . by applying a bulk velocity to the medium in a given direction , the nature of the solution changes .
although an ideal solver would be able to decouple the bulk velocity from the velocity discontinuity at the shock , the discrete nature of the problem means that the code may not be galilean invariant .
since one expects large bulk motions to be relevant for cosmological structure formation , and clearly is quite relevant for our merger simulations , it is important to quantify what effects ( if any ) galilean non - invariance has on our amr simulations .
we have tested the galilean non - invariance of our simulations in two ways . in the first test
, we simulate an isolated cluster moving across the mesh with an ( initial ) bulk velocity of @xmath50 ( @xmath83 km / s ) and compare it to an isolated cluster with zero bulk velocity .
this is similar to the test carried out recently by tasker et al .
( 2008 ) . in agreement with
tasker et al .
( 2008 ) , we find that there is some spurious generation of entropy in the very central regions ( @xmath95 ) of the isolated cluster that was given an initial bulk motion .
however , after @xmath96 gyr of evolution ( i.e. , the time when the clusters collide in our default merger simulation ) , the increase in the central entropy is only @xmath97% .
this is small in comparison to the @xmath98% jump that takes place at core collision in our merger simulations .
this suggests that spurious entropy generation prior to the merger is minimal and does not account for the difference we see between the sph and amr simulations .
in the second test , we consider different implementations of the default merger simulation .
in one case , instead of giving both systems equal but opposite bulk velocities ( each with magnitude @xmath99 ) , we fix one and give the other an initial velocity that is twice the default value , so that the relative velocity is unchanged .
( we also tried reducing the size of the time steps for this simulation by an order magnitude . ) in addition , we have tried mergers that take place at oblique angles relative to the grid . if the merger is well - resolved and the dynamics are galilean invariant
, all these simulations should yield the same result .
figure [ flashgalilean ] shows the resulting entropy distributions for these different runs .
the results of this test confirm what was found above ; i.e. , that there is some dependence on the reference frame adopted , but that this effect is minor in general ( the central entropy is modified by @xmath100% ) and does not account for the discrepancy we see between entropy core amplitudes in the default and simulations . ) until @xmath101 1.6 , 1.7 , 1.8 gyr , respectively , at which point the artificial viscosity is set back to its default value .
the solid magenta squares represent a run with low artificial viscosity throughout , and the open triangles represent the default simulation . reducing the value of the artificial viscosity parameter before the cores collide delays the increase in entropy ( cyan , green and solid red ) , however as soon as the original value is restored , the entropy @xmath34 increases to a level nearly independent of when @xmath102 was restored .
therefore pre - shocking has little effect on the post - shock value of @xmath34 .
, width=317 ] artificial viscosity is required in sph codes in order to handle hydrodynamic shocks .
the artificial viscosity acts as an excess pressure in the equation of motion , converting gas kinetic energy into internal energy , and therefore raising the entropy of the gas . in standard sph implementations ,
the magnitude of the artificial viscosity is fixed in both space and time for particles that are approaching one another ( it being set to zero otherwise ) .
this implies that even in cases where the mach number is less than unity , i.e. , where formally a shock should not exist , ( spurious ) entropy generation can occur .
this raises the possibility that significant ` pre - shocking ' could occur in our sph merger simulations .
this may have the effect of reducing the efficiency of the large shock that occurs at core collision and could therefore potentially explain the discrepancy between the mesh and sph simulations .
= 8.4 cm = 8.4 cm dolag et al .
( 2005 ) raised this possibility and tested it in sph cosmological simulations of massive galaxy clusters .
they implemented a new variable artificial viscosity scheme by embedding an on - the - fly shock detection algorithm in that indicates if particles are in a supersonic flow or not . if so , the artificial viscosity is set to a typical value , if not the artificial viscosity is greatly reduced .
this new implementation should significantly reduce the amount of pre - shocking that takes place during formation of the clusters .
the resulting clusters indeed had somewhat higher central entropies relative to clusters simulated with the standard artificial viscosity implementation ( although the new scheme does not appear to fully alleviate the discrepancy between mesh and sph codes ) .
however , whether the central entropy was raised because of the reduction in pre - shocking or if it was due to an increase in the amount of mixing is unclear .
our idealised mergers offer an interesting opportunity to re - examine this test .
in particular , because of the symmetrical geometry of the merger , little or no mixing is expected until the cores collide , as prior to this time there is no interpenetration of the gas particles belonging to the two clusters ( we have verified this ) .
this means that we are in a position to isolate the effects of pre - shocking from mixing early on in the simulations .
to do so , we have devised a crude method meant to mimic the variable artificial viscosity scheme of dolag et al .
in particular , we run the default merger with a low artificial viscosity ( with @xmath103 , i.e. , approximately the minimum value adopted by dolag et al . ) until the cores collide , at which point we switch the viscosity back to its default value .
we then examine the amount of entropy generated in the large shock .
figure [ viscosityswitch ] shows the evolution of the central entropy around the time of core collision .
shown are a few different runs where we switch the artificial viscosity back to its default value at different times ( since the exact time of ` core collision ' is somewhat ill - defined ) . here
we see that prior to the large shock very little entropy has been generated , which is expected given the low artificial viscosity adopted up to this point .
a comparison of these runs to the default simulation ( see inset in figure [ viscosityswitch ] ) shows that there is evidence for a small amount of pre - shocking in the default run .
however , we find that for the cases where the artificial viscosity is set to a low value , the resulting entropy jump ( after the viscosity is switched back to the default value ) is nearly the same as in the default merger simulation . in other words , pre - shocking appears to have had a minimal effect on the strength of the heating that occurs at core collision in the default sph simulation .
this argues against pre - shocking as the cause of the difference we see between the mesh and sph codes .
lastly , we have also tried varying @xmath12 over the range @xmath104 and @xmath105 ( i.e. , values typically adopted in sph studies ; springel 2005b ) for the default run .
we find that the sph results are robust to variations in @xmath12 and can not reconcile the differences between sph and amr results .
= 8.4 cm = 8.4 cm our experiments with off - axis collisions and collisions with a cluster containing only dark matter suggest that mixing plays an important role in generating the differences between the codes .
several recent studies ( e.g. , dolag et al . 2005 ; wadsley et al .
2008 ) have argued that mixing is handled poorly in standard implementations of sph , both because ( standard ) artificial viscosity acts to damp turbulent motions and because the growth of kh and rt instabilities is inhibited in regions where steep density gradients are present ( agertz et al .
2007 ) . using cosmological sph simulations that have been modified in order to enhance mixing , dolag et al .
( 2005 ) and wadsley et al .
( 2008 ) have shown that it is possible to generate higher central entropies in their galaxy clusters ( relative to clusters simulated using standard implementations of sph ) , yielding closer agreement with the results of cosmological mesh simulations .
this is certainly suggestive that mixing may be the primary cause of the discrepancy between mesh and sph codes .
however , these authors did not run mesh simulations of galaxy clusters and therefore did not perform a direct comparison of the amount of mixing in sph vs. mesh simulations of clusters .
even if one were to directly compare cosmological sph and mesh cluster simulations , the complexity of the cosmological environment and the hierarchical growth of clusters would make it difficult to clearly demonstrate that mixing is indeed the difference .
our idealised mergers offer a potentially much cleaner way to test the mixing hypothesis .
to do so , we re - run the default merger simulation but this time we include a large number of ` tracer particles ' , which are massless and follow the hydrodynamic flow of the gas during the simulation .
the tracer particles are advanced using a second order accurate predictor - corrector time advancement scheme with the particle velocities being interpolated from the grid ( further details are given in the flash manual ( version 2.5 ) at : + http://flash.uchicago.edu/ ) .
each tracer particle has a unique i d that is preserved throughout the simulation , allowing us to track the gas in a lagrangian fashion , precisely as is done in lagrangian sph simulations . to simplify the comparison further ,
we initially distribute the tracer particles within the two clusters in our simulation in exactly the same way as the particles in our initial setup . in the left hand panel of figure [ tracers ] ,
we plot the final vs. the initial entropy of particles in the default and merger simulations .
this plot clearly demonstrates that the lowest - entropy gas is preferentially heated in both simulations , however the degree of heating of that gas in the mesh simulation is much higher than in the sph simulation .
consistent with our analysis in 3 , we find that the bulk of this difference is established around the time of core collision .
it is also interesting that the scatter in the final entropy ( for a given initial entropy ) is much larger in the mesh simulation .
the larger scatter implies that convective mixing is more prevalent in the mesh simulation . at or immediately following core collision ( @xmath106 gyr ) , there is an indication that , typically , gas initially at the very centre of the two clusters ( which initially had the lowest entropy ) has been heated more strongly than gas further out [ compare , e.g. , the median @xmath107 at @xmath108 to the median at @xmath109 .
such an entropy inversion does not occur in the sph simulations and likely signals that the extra mixing in the mesh simulation has boosted entropy production .
= 8.4 cm = 8.4 cm in the right hand panel of figure [ tracers ] we plot the final vs. the initial enclosed gas mass of particles in the default and merger simulations .
the enclosed gas mass of each particle ( or tracer particle ) is calculated by summing the masses of all other particles ( or cells ) with entropies lower than the particle under consideration , by summing the masses of all particles with potentials lower than @xmath110 for the @xmath111th particle . ] .
this plot confirms our mixing expectations based on the entropy plot in the left hand panel .
in particular , only a small amount of mass mixing is seen in the sph simulation , whereas in the mesh simulation the central @xmath112 of the gas mass has been fully mixed .
the higher degree of mixing in the simulation is shown pictorially in figure [ particles ] .
the left panel shows the final spatial distribution of the initially lowest - entropy particles in simulation , while the right panel is the analogous plot for tracer particles in the simulation ( see figure caption ) . the larger degree of mixing in the mesh simulation relative to the sph simulation is clearly evident . in the simulation , particles from the two clusters
are intermingled in the final state , while distinct red and blue regions are readily apparent in the sph calculation , a difference which arises immediately following core collision . the increased mixing boosts entropy production in the simulations , but what is the origin of the increased mixing ?
we now return to the point raised in 3 , that the bulk of the difference between mesh and sph simulation is established around the time of core collision .
this is in spite of the fact that significant entropy generation proceeds in both simulations until @xmath113 gyr .
evidently , both codes treat the entropy generation in the re - accretion phase in a very similar manner .
what is different about the initial core collision phase ? as pointed out recently by agertz et al .
( 2007 ) , sph suppresses the growth of instabilities in regions where steep density gradients are present due to spurious pressure forces acting on the particles .
could this effect be responsible for the difference we see ? to test this idea , we generate 2d projected entropy maps of the sph and mesh simulations to search for signs of clear instability development .
in the case of the sph simulation , we first smooth the particle entropies ( and densities ) onto a 3d grid using the sph smoothing kernel and the smoothing lengths of each particle computed by .
we then compute a gas mass - weighted projected entropy by projecting along the @xmath114-axis . in the case of the simulation
, the cell entropies and densities are interpolated onto a 3d grid and projected in the same manner as for the simulation .
figure [ instabilities ] shows a snap shot of the two simulations at @xmath115 gyr , just after core collision .
large vortices and eddies are easily visible in the projected entropy map of the simulation but none are evident in the simulation . in order to study the duration of these eddies ,
we have generated 100 such snap shots for each simulation , separated by fixed 0.1 gyr intervals .
analysing the projected entropy maps as a movie , we find that these large vortices and eddies persist in the simulation from @xmath116 gyr .
this corresponds very well with the timescale over which the difference between the sph and mesh codes is established ( see , e.g. , the dashed black curve in the top right panel of figure [ entropygastime ] ) .
we therefore conclude that extra mixing in the mesh simulations , brought on by the growth of instabilities around the time of core collision , is largely responsible for the difference in the final entropy core amplitudes between the mesh and sph simulations .
physically , one expects the development of such instabilities , since the kh timescale , @xmath117 , is relatively short at around the time of core collision .
we therefore conclude that there is a degree of under - mixing in the sph simulations whether or not the simulations yield the correct result , however , is harder to ascertain . as fluids are _ forced _ to numerically mix on scales smaller than the minimum cell size , it is possible that there is a non - negligible degree of over - mixing in the mesh simulations .
our resolution tests ( see 3 ) show evidence for the default mesh simulation being converged , but it may be that the resolution needs to be increased by much larger factors than we have tried ( or are presently accessible with current hardware and software ) in order to see a difference .
in this paper , we set out to investigate the origin of the discrepancy in the entropy structure of clusters formed in eulerian mesh - based simulations compared to those formed in lagrangian sph simulations .
while sph simulations form clusters with almost powerlaw entropy distributions down to small radii , eulerian simulations form much larger cores with the entropy distribution being truncated at significantly higher values .
previously it has been suspected that this discrepancy arose from the limited resolution of the mesh based methods , making it impossible for such codes to accurately trace the formation of dense gas structures at high redshift . by running simulations of the merging of idealised clusters
, we have shown that this is not the origin of the discrepancy .
we used the code ( springel 2005b ) to compute the sph solution and the code ( fryxell et al .
2000 ) to compute the eulerian mesh solution . in these idealised simulations ,
the initial gas density structure is resolved from the onset of the simulations , yet the final entropy distributions are significantly different .
the magnitude of the difference generated in idealised mergers is comparable to that seen in the final clusters formed in full cosmological simulations .
a resolution study shows that the discrepancy in the idealised simulations can not be attributed to a difference in the effective resolutions of the simulations .
thus , the origin of the discrepancy must lie in the code s different treatments of gravity and/or hydrodynamics .
we considered various causes in some detail .
we found that the difference was _ not _ due to : * the use of different gravity solvers .
the two codes differ in that uses a treepm method to determine forces , while uses the pm method alone .
the different force resolutions of the codes could plausibly lead to differences in the energy transfer between gas and dark matter .
yet we find that the dark matter distributions produced by the two codes are almost identical when the mesh code is run at comparable resolution to the sph code .
* galilean non - invariance of mesh codes .
we investigate whether the results are changed if we change the rest - frame defined by the hydrodynamic mesh .
although we find that an artificial core can be generated in this way in the mesh code , its size is much smaller than the core formed once the clusters collide , and is not enough to explain the difference between and .
we show that most of this entropy difference is generated in the space of @xmath118 gyr when the cluster cores first collide . * pre - shocking in sph .
we consider the possibility that the artificial viscosity of the sph method might generate entropy in the flow prior to the core collision , thus reducing the efficiency with which entropy is generated later . by greatly reducing the artificial viscosity ahead of the core collision ,
we show that this effect is negligible . having shown that none of these numerical issues can explain the difference of the final entropy distributions , we investigated the role of fluid mixing in the two codes .
several recent studies ( e.g. , dolag et al . 2005 ; wadsley et al .
2008 ) have argued that if one increases the amount of mixing in sph simulations the result is larger cluster entropy cores that resemble the amr results . while this is certainly suggestive
, it does not clearly demonstrate that it is the enhanced mixing in mesh simulations that is indeed the main driver of the difference ( a larger entropy core in the mesh simulations need not necessarily have been established by mixing ) . by injecting tracer particles into our simulations ,
we have been able to make an explicit comparison of the amount of mixing in the sph and mesh simulations of clusters .
we find very substantial differences . in the sph computation , there is a very close relation between the initial entropy of a particle and its final entropy .
in contrast , tracer particles in the simulation only show a close connection for high initial entropies .
the lowest @xmath119% of gas ( by initial entropy ) is completely mixed in the simulation .
we conclude that mixing and fluid instabilities are the cause of the discrepancy between the simulation methods .
the origin of this mixing is closely connected to the suppression of turbulence in sph codes compared to the eulerian methods .
this can easily be seen by comparing the flow structure when the clusters collide : while the image is dominated by large scale eddies , these are absent from the sph realisation ( see figure [ instabilities ] ) .
it is now established that sph codes tend to suppress the growth of kelvin - helmholtz instabilities in shear flows , and this seems to be the origin of the differences in our simulation results ( e.g. , agertz et al .
these structures result in entropy generation through mixing , an irreversible process whose role is underestimated by the sph method .
of course , it is not clear that the turbulent structures are correctly captured in the mesh simulations ( iapichino & niemeyer 2008 ; wadsley et al .
the mesh forces fluids to be mixed on the scale of individual cells . in nature , this is achieved through turbulent cascades that mix material on progressively smaller and smaller scales : the mesh code may well overestimate the speed and effectiveness of this process . ultimately , deep x - ray observations may be able to tell us whether the mixing that occurs in the mesh simulations is too efficient .
an attempt at studying large - scale turbulence in clusters was made recently by schuecker et al .
their analysis of _ xmm - newton _ observations of the coma cluster indicated the presence of a scale - invariant pressure fluctuation spectrum on scales of 40 - 90 kpc and found that it could be well described by a projected kolmogorov / oboukhov - type turbulence spectrum . if the observed pressure fluctuations are indeed driven by scale - invariant turbulence , this would suggest that current mesh simulations have the resolution required to accurately treat the turbulent mixing process . alternatively , several authors have suggested that icm may be highly viscous ( eg . , fabian et al .
2003 ) with the result that fluid instabilities will be strongly suppressed by physical processes .
this might favour the use of sph methods which include a physical viscosity ( sijacki & springel 2006 ) .
it is a significant advance that we now understand the origin of this long standing discrepancy .
our work also has several important implications .
firstly , as outlined in 1 , there has been much discussion in the recent literature on the competition between heating and cooling in galaxy groups and clusters .
the current consensus is that heating from agn is approximately sufficient to offset cooling losses in observed cool core clusters ( e.g. , mcnamara & nulsen 2007 ) .
however , observed present - day agn power output seems energetically incapable of explaining the large number of systems that do not possess cool cores% of all massive x - ray clusters in flux - limited samples do not have cool cores ( e.g. , chen et al .
since at fixed mass cool core clusters tend to be more luminous than non - cool core clusters , the fraction of non - cool core cluster in flux - limited samples may actually be an underestimate of the true fraction . ]
( mccarthy et al .
recent high resolution x - ray observations demonstrate that these systems have higher central entropies than typical cool core clusters ( e.g. , dunn & fabian 2008 ) . one way of getting around the energetics issue is to invoke an early episode of preheating ( e.g. , kaiser 1991 ; evrard & henry 1991 ) .
energetically , it is more efficient to raise the entropy of the ( proto-)icm prior to it having fallen into the cluster potential well , as its density would have been much lower than it is today ( mccarthy et al .
preheating remains an attractive explanation for these systems .
however , as we have seen from our idealised merger simulations , the amount of central entropy generated in our mesh simulations is significant and is even comparable to the levels observed in the central regions of non - cool core clusters .
it is therefore tempting to invoke mergers and the mixing they induce as an explanation for these systems .
however , before a definitive statement to this effect can be made , much larger regions of parameter space should be explored . in particular , a much larger range of impact parameters and mass ratios is required , in addition to switching on the effects of radiative cooling ( which we have neglected in the present study ) .
this would be the mesh code analog of the sph study carried out by poole et al .
( 2006 ; see also poole et al .
we leave this for future work . alternatively , large cosmological mesh simulations , which self - consistently track the hierarchical growth of clusters , would be useful for testing the merger hypothesis
. indeed , burns et al .
( 2008 ) have recently carried out a large mesh cosmological simulation ( with the code ) and argue that mergers at high redshift play an important role in the establishment of present - day entropy cores . however , these results appear to be at odds with the cosmological mesh simulations ( run with the code ) of nagai et al .
( 2007 ) ( see also kravtsov et al .
these authors find that most of their clusters have large cooling flows at the present - day , similar to what is seen in some sph cosmological simulations ( e.g. , kay et al .
2004 ; borgani et al .
on the other hand , the sph simulations of keres et al .
( 2008 ) appear to yield clusters with large entropy cores .
this may be ascribed to the lack of effective feedback in their simulations , as radiative cooling selectively removes the lowest entropy gas ( see , e.g. , bryan 2000 ; voit et al .
2002 ) , leaving only high entropy ( long cooling time ) gas remaining in the simulated clusters .
however , all the simulations just mentioned suffer from the overcooling problem ( balogh et al .
2001 ) , so it is not clear to what extent the large entropy cores in clusters _ in either mesh or sph _ simulations are produced by shock heating , overcooling , or both .
all of these simulations implement different prescriptions for radiative cooling ( e.g. , metal - dependent or not ) , star formation , and feedback , and this may lie at the heart of the different findings
. a new generation of cosmological code comparisons will be essential in sorting out these apparently discrepant findings
. the focus should not only be on understanding the differences in the hot gas properties , but also on the distribution and amount of stellar matter , as the evolution of the cold and hot baryons are obviously intimately linked .
reasonably tight limits on the amount of baryonic mass in the form of stars now exists ( see , e.g. , balogh et al.z 2008 ) and provides a useful target for the next generation of simulations . at present , merger - induced mixing as an explanation for intrinsic scatter in the hot gas properties of groups and clusters remains an open question . secondly , we have learnt a great deal about the nature of gas accretion and the development of hot gas haloes from sph simulations of the universe . since we now see that these simulations may underestimate the degree of mixing that occurs , which of these results are robust , which need revision ?
for example , keres et al .
( 2005 ) ( among others ) have argued that cold accretion by galaxies plays a dominant role in fuelling the star formation in galaxies .
is it plausible that turbulent eddies could disrupt and mix such cold streams as they try to penetrate through the hot halo ?
we can estimate the significance of the effect by comparing the kelvin - helmholtz timescale , @xmath117 , with the free - fall time , @xmath120 .
the kh timescale is given by ( see , e.g. , nulsen 1982 ; price 2008 ) @xmath121
where @xmath122 and @xmath123 is the density of the hot halo , @xmath124 is the density of the cold stream , @xmath125 is the wave number of the instability , and @xmath126 the velocity of the stream relative to the hot halo .
if the stream and hot halo are in approximate pressure equilibrium , this implies a large density contrast ( e.g. , a @xmath127 k stream falling into a @xmath60 k hot halo of a milky way - type system would imply a density contrast of @xmath128 ) . in the limit of @xmath129 and recognising that the mode responsible for the destruction of the stream is comparable to the size of the stream ( i.e. , @xmath130 ) , eqns .
( 7 ) and ( 8) reduce to : @xmath131 adopting @xmath132 , @xmath133 kpc , and @xmath134 km / s ( perhaps typical numbers for a cold stream falling into a milky way - type system ) , we find @xmath135 gyr . the free - fall time , @xmath136 [ where @xmath137 is the virial radius of main system and @xmath138 is the circular velocity of the main system at its virial radius ] , is @xmath118 gyr for a milky way - type system with mass @xmath139 .
on this basis , it seems that the stream would be stable because of the large density contrast in the flows .
it is clear , however , that the universality of these effects need to be treated with caution , as the free - fall and kh timescales are not vastly discrepant .
high resolution mesh simulations ( cosmological or idealised ) of milky way - like systems would provide a valuable check of the sph results . finally , the sph method has great advantages in terms of computational speed , effective resolution and galilean invariance .
is it therefore possible to keep these advantages and add additional small scale transport processes to the code in order to offset the suppression of mixing ?
wadsley et al . (
2008 ) and price ( 2008 ) have presented possible approaches based on including a thermal diffusion term in the sph equations .
although the approaches differ in their mathematical details , the overall effect is the same .
however , it is not yet clear how well this approach will work in cosmological simulations that include cooling ( and feedback ) , since the thermal diffusion must be carefully controlled to avoid unphysical suppression of cooling in hydrostatic regions ( e.g. , dolag et al .
one possibility might be to incorporate such terms as a negative surface tension in regions of large entropy contrast ( hu & adams 2006 ) . an alternative approach is to combine the best features of the sph method , such as the way that it continuously adapts to the local gas density and its flow , with the advantage of a riemann based method of solving the fluid dynamic equations ( e.g. , inutsuka 2002 ) .
clearly , there is a great need to find simple problems in which to test these codes : simple shock tube experiments are not sufficient because they do not include the disordered fluid motions that are responsible for generating the entropy core .
idealised mergers represent a step forward , but the problem is still not sufficiently simple that it is possible to use self - similar scaling techniques ( e.g. , bertschinger 1985 , 1989 ) to establish the correct solution .
one possibility is to consider the generation of turbulent eddies in a fluctuating gravitational potential .
we have begun such experiments , but ( although the fluid flow patterns are clearly different ) simply passing a gravitational potential through a uniform plasma at constant velocity does not expose the differences between sph and eulerian mesh based methods that we see in the idealised merger case .
we will tackle the minimum complexity that is needed to generate these differences in a future paper .
the authors thank the referee for a careful reading of the manuscript and suggestions that improved that paper .
they also thank volker springel , mark voit , and michael balogh for very helpful discussions .
nlm and rac acknowledge support from stfc studentships .
igmcc acknowledges support from a nserc postdoctoral fellowship at the icc in durham and a kavli institute fellowship at the kavli institute for cosmology , cambridge .
these simulations were performed and analysed on cosma , the hpc facilities at the icc in durham and we gratefully acknowledge kind support from lydia heck for computing support .
the software used in this work was in part developed by the doe - supported asc / alliance center for astrophysical thermonuclear flashes at the university of chicago . | the diffuse plasma that fills galaxy groups and clusters ( the intracluster medium , hereafter icm ) is a by - product of galaxy formation . the present thermal state of this gas results from a competition between gas cooling and heating .
the heating comes from two distinct sources : gravitational heating associated with the collapse of the dark matter halo and additional thermal input from the formation of galaxies and their black holes .
a long term goal of this research is to decode the observed temperature , density and entropy profiles of clusters and to understand the relative roles of these processes .
however , a long standing problem has been that cosmological simulations based on smoothed particle hydrodynamics ( sph ) and eulerian mesh - based codes predict different results even when cooling and galaxy / black hole heating are switched off .
clusters formed in sph simulations show near powerlaw entropy profiles , while those formed in eulerian simulations develop a core and do not allow gas to reach such low entropies . since the cooling rate is closely connected to the minimum entropy of the gas distribution , the differences are of potentially key importance . in this paper , we investigate the origin of this discrepancy . by comparing simulations
run using the sph code and the adaptive eulerian mesh code , we show that the discrepancy arises during the idealised merger of two clusters , and that the differences are not the result of the lower effective resolution of eulerian cosmological simulations .
the difference is not sensitive to the minimum mesh size ( in eulerian codes ) or the number of particles used ( in sph codes ) .
we investigate whether the difference is the result of the different gravity solvers , the galilean non - invariance of the mesh code or an effect of unsuitable artificial viscosity in the sph code .
instead , we find that the difference is inherent to the treatment of vortices in the two codes .
particles in the sph simulations retain a close connection to their initial entropy , while this connection is much weaker in the mesh simulations .
the origin of this difference lies in the treatment of eddies and fluid instabilities .
these are suppressed in the sph simulations , while the cluster mergers generate strong vortices in the eulerian simulations that very efficiently mix the fluid and erase the low entropy gas .
we discuss the potentially profound implications of these results .
[ firstpage ] hydrodynamics methods : n - body simulations galaxies : clusters : general cosmology : theory |
a large class of dilute magnetic semiconductors ( dms ) is based on manganese doping of iii - v or group - iv hosts having the zincblende , wurzite , or diamond structure .
formally , mn is either a single or double acceptor , depending on whether it substitutes for a group - iii or -iv atom , respectively.@xcite aside from this difference , there are no simple guidelines for predicting how the magnetic behavior of the resulting dms depends on the choice of host semiconductor . elucidating such guidelines would be of great practical interest for efforts to control and optimize the magnetic properties of dms materials . in particular
, it would be very helpful to understand how the resulting curie temperatures depend on the choice of host semiconductor .
an important and early contribution was made by , who used a mean - field solution of the zener model to predict the curie temperatures for mn doping of a wide range of ii - vi , iii - v , and group - iv host semiconductors.@xcite mn ions with localized spin @xmath0=5/2 were assumed to substitute on the cation site , and to interact by an indirect exchange interaction mediated by holes .
curie temperatures were calculated for fixed mn content @xmath1 and hole concentration @xmath2 @xmath3 using the mean - field result @xmath4 in this equation , the most direct dependence of @xmath5 on the host semiconductor comes from the density per unit volume of cation sites @xmath6 , which varies with the host lattice constant as @xmath7 . a much weaker dependence on the host arises from the density - of - states effective mass @xmath8 and the fermi wavevector @xmath9 .
the remaining variables , i.e. the @xmath10-@xmath11 exchange integral @xmath12 and the fermi - liquid parameter @xmath13 , were assumed not to depend on the host . the full numerical evaluation of eq .
( 1 ) for different host semiconductors@xcite leads to values of @xmath5 that indeed track the prefactor @xmath7 quite closely.@xcite for example , the hosts with the largest lattice constants ( cdte , inas , ge ) lead to the smallest predicted curie temperatures ( below @xmath1475 k ) .
likewise , the hosts with the smallest lattice constants ( zno , gan , c ) lead to the largest predicted values of @xmath5 ( well above room temperature ) . diamond has the smallest lattice constant of all the semiconductors ( @xmath15 ) and , accordingly , the highest predicted curie temperature ( @xmath16 470 k ) .
these extreme values make diamond a logical choice for examining some of the assumptions underlying the predictions of high curie temperatures for hosts having small lattice constants . in this paper
, we use first - principles theoretical methods to test the assumption that mn occupies the substitutional site , with spin @xmath17 , in the diamond lattice .
we find that substitutional mn has a low - spin @xmath0=1/2 ground state in diamond .
moreover , because of diamond s small lattice constant , the substitutional site is energetically unfavorable relative to the much larger `` divacancy site , '' denoted @xmath18 , which we identify as the more likely mn impurity location .
we analyze the electronic and magnetic structure of this divacancy mn impurity in diamond , and show that it is unlikely to lead to magnetic ordering at any reasonable temperature .
most of the results reported in this article are for isolated mn impurities , which we simulate using a supercell of 64 carbon atoms in the diamond structure .
all atomic positions were relaxed using total energies and forces calculated within the generalized - gradient approximation to density - functional theory ( dft ) , as implemented in vasp.@xcite carbon and mn ultrasoft pseudopotentials were used with a cutoff energy of 286 ev . for total energies , we used 2@xmath192@xmath192 monkhorst - pack sampling of the brillouin zone , and 4@xmath194@xmath194 sampling for convergence checks . in the discussion of the electronic structure of the isolated mn impurity at a divacancy site , eigenvalues at the zone center of a 128-atom supercell
are reported in order that degeneracies are properly represented . within the supercell formalism , the formation energy of a mn impurity is given by @xmath20 = e_t[{\rm mn}^q ] - n_{\rm c } \mu_{\rm c } - \mu_{\rm mn } + q e_f,\ ] ] where @xmath21 $ ] is the total energy of a supercell containing @xmath22 carbon atoms and one mn impurity , with chemical potentials @xmath23 and @xmath24 , @xmath25 is the charge state of the mn impurity , and @xmath26 is the fermi level . since the host crystal is elemental , the chemical potentials are simply the energy per atom in the diamond phase of carbon and the ground - state @xmath27mn .
the electrical activity of a mn impurity is determined by its formation energy as a function of charge state .
electrically active defects will have more than one stable charge state within the host band gap ; the value of @xmath26 for which two such charge states have equal formation energies is referred to as a `` charge transition level . '' the charge transition level between the neutral and @xmath28 states is the donor ionization energy , while the transition level between neutral and @xmath29 states is the acceptor ionization energy . in practice
, the total energy of a charged supercell must be calculated by adding a uniform compensating background charge to the supercell .
the long - range nature of the coulomb interaction then gives rise to a spurious madelung - like contribution to the total energy , which must be subtracted from the calculated total energy .
this was done using a standard approach in which a multipole expansion of the defect charge ( up to quadrupole order ) was used to estimate the interaction energy analytically and then subtract it off.@xcite the magnetic interaction between mn impurities in nearby divacancy sites was calculated using larger supercells of 128 carbon atoms .
no relaxations were performed for these calculations ; tests for a few configurations confirmed that this approximation did not change the results significantly .
the interactions are represented by numerically mapping the dft total energies into the heisenberg form . in practice
this amounts to computing the difference in total energy between the parallel and antiparallel spin alignment of two mn impurities in a supercell .
the mn impurity enjoys a special status as a dopant in dilute magnetic semiconductors such as mn@xmath30ga@xmath31as and mn@xmath30ge@xmath31 .
it preferentially occupies the substitutional ( cation ) site , where it serves two roles : it is electrically active as an acceptor , and it contributes a localized spin @xmath17 . at sufficient mn concentrations ,
holes are created in the host valence band ; these delocalized carriers mediate the ferromagnetic interaction between the localized spins.@xcite gaas and ge have similar lattice constants , and since strain contributes to the impurity formation energy , it is instructive to note that the local strain around a substitutional mn impurity , denoted mn@xmath32 , is very small for both hosts the nearest neighbors distort by less than 2% from their ideal positions .
tetrahedrally coordinated interstitial mn impurities , denoted mn@xmath33 , have higher formation energies ( by 12 ev for neutral impurities ) ; interestingly , the atomic volume available at this site is the same as for the substitutional site , and consequently very little distortion is created by the mn interstitial in either host.@xcite the lattice constant of diamond is 37% smaller than that of ge , and so it is not surprising that a substitutional mn impurity creates a much larger local strain in the lattice within dft
the nearest - neighbor distortion is 12% . because of the extreme stiffness of diamond
, such a large strain is expected to lead to a relatively high formation energy .
a similar distortion occurs for mn in the tetrahedral interstitial site .
a simple way to relieve this strain is to place the mn impurity at a divacancy site i.e . to remove two neighboring carbon atoms and place the mn at their midpoint , as shown in fig .
this doubles the atomic volume available , leading to a much reduced local strain
only 2% distortion of the nearest neighbors . even in its ground - state configuration , which includes a slight off - center relaxation of the mn ion as shown in fig .
1(b ) , the local lattice distortion around this mn@xmath34 impurity is very small .
it is already widely believed that other large impurities including si , p , ni , and co preferentially occupy the divacancy site in diamond;@xcite hence our prediction that mn also prefers this site appears plausible . to make the comparison between different sites quantitative we turn now to the formation energies calculated within dft . for neutral mn impurities ,
we find the divacancy site is strongly preferred ( by 0.6 ev ) to the substitutional site ; the interstitial site is much less favorable than either ( by @xmath1410 ev ) .
figure 2 shows the formation energies for divacancy and substitutional mn as a function of magnetic moment , calculated using the fixed - spin - moment method within dft . even in the preferred divacancy site ,
the absolute formation is almost an order of magnitude larger for substitutional mn in gaas or ge , suggesting that standard methods for attaining high concentrations of magnetic dopants will probably not work for diamond .
the equilibrium magnetic moments @xmath35 in the substitutional and divacancy sites are also quite different compared to substitutional mn in gaas and ge ( @xmath36 and 3 @xmath37 , respectively ) . in the substitutional site , mn adopts a low - spin @xmath38 state , with an extremely small energy gain ( 0.1 ev ) relative to the spin - unpolarized state .
hence , we anticipate that even if mn could be forced into the substitutional site , its magnetic moment may not be sufficiently stable to facilitate magnetic ordering . in the divacancy site
two nearly degenerate moments are found ( @xmath38 and 5 @xmath37 ) with an energy difference of only 0.05 ev ; the formation energy vs. magnetic moment is symmetrical about @xmath39 3 @xmath37 .
this peculiar feature of the mn@xmath34 impurity will be explained in section iv .
the mn@xmath34 impurity has an energy - level structure that arises from the relatively weak interaction of atomic mn levels and host divacancy levels , as shown in fig .
the host divacancy defect itself has been extensively studied both theoretically and experimentally , and is well understood.@xcite the removal of two carbon atoms from the host lattice leads to a defect with @xmath40 symmetry , and thus the six available dangling - bond orbitals must form linear combinations that transform under the irreducible representations @xmath41 , @xmath42 , @xmath43 , and @xmath44.@xcite for the neutral divacancy , six electrons are available to fill these levels . in an early theoretical study , coulson and larkins@xcite predicted the ground state one - electron configuration
to be @xmath45 .
later calculations confirmed this one - electron level ordering for both silicon and diamond , and we find it here too , as shown . in fig .
3 we consider separately the interaction of the majority and minority mn levels with the four divacancy levels . under the @xmath40 crystal field ,
the 3@xmath11 level of mn splits into one @xmath41 and two @xmath44 levels .
hence , hybridization is allowed only between mn and @xmath18 levels both having either @xmath41 or @xmath44 symmetry , but no mixing is allowed between mn levels and @xmath18 levels having either @xmath42 or @xmath43 symmetry . among the calculated majority mn@xmath46 levels we find very little mixing within any level , and therefore each has a clear parentage from either mn or @xmath18 orbitals , as indicated in fig .
3 . for the minority mn@xmath47 levels
there is strong mixing between the empty @xmath18 @xmath44 level and the empty mn @xmath48 level , so that the occupied bonding combination falls well below the diamond valence - band maximum ( vbm ) . considering for the moment
only those levels that sit below the vbm , we find that seven electrons occupy majority levels and four electrons occupy minority levels .
hence , these low - lying levels carry a net `` core '' magnetic moment @xmath49 .
the highest occupied molecular orbital ( homo ) of the mn@xmath34 impurity has @xmath43 symmetry and , because it can not mix with mn states , is purely derived from the @xmath18 dangling - bond orbitals .
the two electrons in this fourfold level form a spin triplet ( @xmath50 1 @xmath37 ) as shown , but the system is energetically indifferent to whether they are aligned parallel or antiparallel to the core spin ( fig . 3 shows the parallel alignment ; when the alignment is made antiparallel the spin - up and spin - down homo levels simply switch positions ) . because of this weak coupling between the homo spin and the core spin , the total magnetic moment of mn@xmath34 can assume two possible low - energy values : either @xmath51 5 @xmath37 or @xmath52 1 @xmath37 for parallel or antiparallel alignment , respectively .
moreover , there is an energy penalty for violating hund s rule by forcing the homo into a spin - singlet state ; this is the origin of the energy increase that occurs when the total moment is constrained to 3 @xmath37 ( the core moment alone ) .
these two features the weak core - homo spin coupling , and the hund s rule penalty for constraining the homo to a spin singlet explain the unusual appearance , shown earlier in fig . 2 , of the mn@xmath34 formation energy vs. total magnetic moment .
4 we show the calculated formation energies of mn@xmath34 for charge states that are stable within the experimental 5.4-ev band gap of diamond . there are three such stable charge states ( @xmath53 ) , making mn@xmath34 formally a double acceptor . in principle
this is similar to the case of substitutional mn in ge , which is also a double acceptor , and might suggest similar electrical activity for mn@xmath34 .
quantitatively , however , the two cases are quite different .
the first two acceptor ionization energies for mn in ge have been measured experimentally to be 160 and 370 mev , relative to the valence - band edge.@xcite for mn concentrations of several percent , the width of the resulting impurity band is sufficient to create overlap with the valence band and thus to allow the holes to delocalize .
likewise , mn in gaas is a single acceptor with a measured acceptor level at 113 mev,@xcite which is accurately given by dft calculations as 100 mev .
@xcite on the other hand , the predicted first acceptor ionization energy for mn@xmath34 in diamond is an order of magnitude larger , @xmath54 1.2 ev , suggesting that the holes will remain localized on the impurity sites for any reasonable mn concentration .
for this reason alone , it appears very unlikely that there will be sufficient carriers to mediate a ferromagnetic interaction between the localized spins of mn@xmath34 impurities .
the weak coupling between core and homo spins in the isolated mn@xmath34 impurity suggests that the effective coupling between spins of two impurities will also be weak .
this expectation is confirmed in fig . 5 , where we show the results of our dft calculations for ( twice ) the heisenberg coupling constant between two mn@xmath34 impurities in a 128-atom diamond supercell .
for comparison , we show the results of similar calculations for substitutional mn in ge and si .
the results for substitutional mn in ge and si show a similar trend . when the two mn are nearest neighbors , there is a strong preference for antiparallel spin alignment . at larger separations
the interactions vary in sign ( ge ) and/or magnitude ( si ) , a consequence of the crystallographic anisotropy that arises from the strong @xmath11 character of the acceptor wavefunction in substitutional mn .
the largest ferromagnetic coupling strengths are in the range [email protected] ev .
( for si there is a shift of all the couplings toward more favorable ferromagnetic interactions ; since mn - doped ge is known to be ferromagnetic this suggests that mn - doped si might also be perhaps with a higher curie temperature ) .
the coupling between two mn@xmath34 impurities in diamond is substantially weaker : the largest ferromagnetic couplings are of order 1 mev , two orders of magnitude smaller than for mn in ge or si .
hence , any ferromagnetically ordered phase involving mn@xmath34 impurities would be characterized by a curie temperature at most on this scale , i.e. of order 10 k.
we have shown theoretically that the mn impurity in diamond is energetically more favorable in the divacancy site than in the substitutional site .
the magnetic properties of the divacancy mn impurity show nearly degenerate low - spin and high - spin configurations ; the degeneracy arises from the weak coupling of separate core and valence moments .
divacancy mn is predicted to be a double acceptor with two hyperdeep levels , suggesting poor prospects for creating the delocalized holes in the valence band that are required to mediate a ferromagnetic interaction within the zener model
. explicit calculation of the effective heisenberg coupling between mn in nearby divacancy sites confirms that mn - doped diamond shows little promise of ferromagnetism above a few kelvins
. our findings may not be unique to diamond : other semiconductors with predicted high curie temperatures have similarly small atomic volumes , which may likewise make the substitutional site unfavorable for mn doping .
comprehensive calculations of the site energetics for gan , zno , and other host semiconductors would be of great interest .
this work was supported by the office of naval research and the darpa spins in semiconductors program .
computations were performed at the dod major shared resource centers at asc and navo . | we use density - functional theoretical methods to examine the recent prediction , based on a mean - field solution of the zener model , that diamond doped by mn ( with spin @xmath0=5/2 ) would be a dilute magnetic semiconductor that remains ferromagnetic well above room temperature .
our findings suggest this to be unlikely , for four reasons : ( 1 ) substitutional mn in diamond has a low - spin @xmath0=1/2 ground state ; ( 2 ) the substitutional site is energetically unfavorable relative to the much larger `` divacancy '' site ; 3 ) mn in the divacancy site is an acceptor , but with only hyperdeep levels , and hence the holes are likely to remain localized ; ( 4 ) the calculated heisenberg couplings between mn in nearby divacancy sites are two orders of magnitude smaller than for substitutional mn in germanium . |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``High-Quality Education Act of
2009''.
SEC. 2. FINDINGS AND PURPOSE.
(a) Findings.--The Congress finds as follows:
(1) Tennessee's wide-ranging and research-intensive STAR
project began in the mid-1980's when the Tennessee legislature
funded an initial 4-year study seeking to compare achievements
for early grade students who would be assigned randomly to a
standard-sized class, a standard-sized class with a teacher
aide, or a class with reduced size. Several new analyses of the
Tennessee STAR program show that reducing class size has both
immediate and long-term benefits.
(2) Research shows that the benefits of participating in
small classes increase from year to year, both in the early
grades when classes are small and in subsequent years when
students are placed in larger classes.
(3) Further, follow-up studies of the same students show
that high-school students who were in small classes in first
through third grades beginning in 1985 were less likely to be
held back a year or suspended compared with their peers from
larger classes.
(4) The students from small classes were found to be making
better grades in high school and taking more advanced courses.
(5) The State of Wisconsin passed legislation in 1995 to
phase in reduction of classes to 15 students in low-wealth
schools. A January 2003 study of that program, called SAGE,
revealed that average test scores in smaller first grade
classes increased 12 to 14 percent more than scores of students
in regular classes.
(6) Research further shows that at the end of fifth grade,
students who were in small classes in first through third
grades were about half a school year (5 months) ahead of
students from larger classes in all core subjects--reading,
language arts, math, and science.
(7) In 1999, the Department of Education reported that
studies have consistently identified a positive relationship
between reduced class size and improved student performance.
The National Assessment on Educational Progress, the Economic
Policy Institute, RAND, the Educational Testing Service, the
American Institute of Research, and many other respected
organizations have reached similar conclusions.
(8) In smaller classes, teachers spend more time on
instruction and less time on discipline problems, reporting
that they know their students better, know where each child is
in the learning process, and can provide more individualized
instruction.
(9) Smaller classes lead to better identification of
students who need special help, increased student participation
and engagement, improved student behavior, and reduced
retention of students in the same grade.
(10) Outcomes associated with small classes are the
foundation of safe schools: improved student behavior and human
relations skills, increased participation in schooling and
school-sanctioned events, increased sense of community in small
classes, and generally improved school climate where students,
teachers, and parents feel more comfortable.
(b) Purpose.--The purpose of this Act is to assist States to
proactively attempt to lower class size in order to provide students
and teachers with an educational environment more conducive to optimal
student performance.
SEC. 3. CLASS SIZE REDUCTION MATCHING GRANT PROGRAM.
(a) Grants.--The Secretary of Education may make grants to eligible
entities to reduce the size of core curriculum classes in public
elementary and secondary schools.
(b) Eligible Entity Defined.--In this section, the term ``eligible
entity'' means any State, or any local educational agency in a State
that is not a grantee under this section, that meets the following:
(1) The State or local educational agency has in effect a
class size reduction program that--
(A) applies to all public elementary and secondary
schools served by the State or local educational
agency, respectively; and
(B) may be targeted to specific school populations
based on need, socioeconomic factors, or school-age
population.
(2) The State or local educational agency has funding in
its annual budget specifically allocated for the program
described in paragraph (1).
(3) The average core curriculum class size at schools
served by the State or local educational agency--
(A) in kindergarten through third grade, is greater
than 18 students;
(B) in fourth through eighth grade, is greater than
22 students; or
(C) in ninth through twelfth grade, is greater than
25 students.
(c) Use of Funds.--The Secretary may not make a grant under this
section unless the grantee agrees to use the grant for the following:
(1) Constructing new classroom space.
(2) Hiring additional teachers.
(3) Purchasing portable structures to replace
administrative offices converted into classroom space.
(d) Restrictions.--The Secretary may not make a grant under this
section unless the grantee agrees that funds received under the grant
will not be used for any of the following:
(1) To pay any long-term financing obligations such as
bonding.
(2) To pay any administrative costs or fees.
(e) Priority.--In awarding grants under this section, the Secretary
may give priority to eligible entities that serve schools in which--
(1) more than 17 percent of the students older than 4 and
younger than 18 years of age are from families with incomes
below the poverty line; or
(2) the average core curriculum class size is higher,
particularly in the primary grades, than the average core
curriculum class size at schools served by other grant
applicants for the fiscal year.
(f) Matching Funds.--
(1) In general.--The Secretary may not make a grant under
this section unless the grantee agrees to make available
(directly or through donations from public or private entities)
non-Federal contributions toward the costs of the activities
under the grant in an amount that is not less than $2 for each
$1 provided by the Secretary in the grant.
(2) Determination of amount contributed.--Non-Federal
contributions required in paragraph (1) may be in cash or in
kind, fairly evaluated, including plant, equipment, or
services. Amounts provided by the Federal Government, or
services assisted or subsidized to any significant extent by
the Federal Government, may not be included in determining the
amount of such non-Federal contributions.
(g) Application.--
(1) Submission.--To seek a grant under this section, an
eligible entity shall submit an application to the Secretary in
such form, in such manner, and containing such information as
the Secretary may require.
(2) Contents.--An application for a grant under this
section shall include the following:
(A) Certification of the average core curriculum
class size at schools served by the eligible entity for
each of the grade ranges that--
(i) are described in subsection (b)(3); and
(ii) will be served by the entity's class
size reduction program.
(B) Certification of the eligible entity's actual
and expected expenditures for the entity's class size
reduction program for the fiscal year involved.
(C) A description of the eligible entity's class
size reduction program and the program's goals.
(D) A description of how the eligible entity
intends to use funds received under the grant.
(E) In the case of an eligible entity that has
already received a grant under this section, the
entity's progress in achieving the goals of its class
size reduction program, particularly relative to high
poverty areas.
(3) Deadline.--The Secretary shall establish a deadline for
the submission of applications for a grant under this section.
(h) Other Definitions.--In this section:
(1) The term ``average core curriculum class size'' means
the number that is--
(A) equal to the sum of the number of students in
each core curriculum class (including for each school
term and period of instruction) divided by the total
number of such classes; and
(B) is based on the ratio of physical class rooms
to students, irrespective of the ratio of teachers to
students.
(2) The term ``core curriculum class'' means a class in any
of the following subjects:
(A) Mathematics.
(B) Science.
(C) Reading, language arts, or English, including
English for speakers of other languages.
(D) Social studies, including history, civics,
political science, government, geography, and
economics.
(E) Foreign language.
(3) The terms ``local educational agency'' and ``poverty
line'' have the meanings given those terms in section 9101 of
the Elementary and Secondary Education Act of 1965 (20 U.S.C.
7801).
(4) The term ``Secretary'' means the Secretary of
Education.
(5) The term ``State'' includes the several States, the
District of Columbia, the Commonwealth of Puerto Rico, the
Commonwealth of the Northern Mariana Islands, American Samoa,
Guam, the Virgin Islands, any other territory or possession of
the United States, and any Indian tribe (as that term is
defined in section 4(e) of the Indian Self-Determination and
Education Assistance Act (25 U.S.C. 450b(e)).
(i) Funding.--
(1) Biannual payments.--The Secretary shall make payments
to each grantee under this section on a biannual basis.
(2) Limitation.--For any fiscal year, the Secretary may not
make a payment to any grantee under this section in an amount
that exceeds the lesser of the following:
(A) An amount that is 20 percent of the total
amount appropriated to carry out this section for the
fiscal year.
(B) $200,000,000. | High-Quality Education Act of 2009 - Authorizes the Secretary of Education to award matching grants to states, or local educational agencies (LEAs) in states that do not receive such grants, to reduce the size of core curriculum classes in public elementary and secondary schools.
Requires such grants to be provided only to states or LEAs serving schools whose average core curriculum class size is greater than 18 students in kindergarten through grade 3, 22 students in grades 4 through 8, and 25 students in grades 9 through 12.
Requires grant funds to be used for: (1) constructing new classroom space; (2) hiring additional teachers; and (3) purchasing portable structures to replace administrative offices that are converted into classrooms.
Permits the Secretary to give grant priority to states or LEAs serving schools: (1) where over 17% of the students between age 4 and 18 are from impoverished families; or (2) whose average core curriculum class size is higher than the average core curriculum class size of schools served by other applicants. |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Commercial Driver Compliance
Improvement Act''.
SEC. 2. ELECTRONIC ON-BOARD RECORDING DEVICES.
(a) Amendments.--Subchapter III of chapter 311 of title 49, United
States Code, is amended--
(1) in section 31132--
(A) by redesignating paragraphs (2) through (11) as
paragraphs (4) through (13), respectively; and
(B) by inserting after paragraph (1) the following:
``(2) `driving time' has the meaning given such term under
section 395.2 of title 49, Code of Federal Regulations.
``(3) `electronic on-board recording device' means an
electronic device that--
``(A) is capable of recording a driver's duty hours
of service and duty status accurately and
automatically; and
``(B) meets the requirements under section
395.16(b) of title 49, Code of Federal Regulations.'';
and
(2) in section 31137--
(A) in the section heading, by striking
``Monitoring device'' and inserting ``Electronic on-
board recording devices''; and
(B) by amending subsection (a) to read as follows:
``(a) Electronic On-Board Recording Devices.--All commercial motor
vehicles involved in interstate commerce and operated by a driver
subject to the hours of service and the record of duty status
requirements under part 395 of title 49, Code of Federal Regulations,
shall be equipped with an electronic on-board recording device to
improve compliance with hours of service regulations under such
part.''.
(b) Effective Date.--The amendments made by subsection (a) shall
take effect on the effective date of the final regulations prescribed
by the Secretary of Transportation pursuant to section 3.
SEC. 3. RULEMAKING.
(a) In General.--Not later than 18 months after the date of the
enactment of this Act, the Secretary of Transportation shall prescribe
final regulations to carry out section 31137 of title 49, United States
Code, as amended by section 2.
(b) Performance Requirements and Certification Criteria.--
(1) Performance requirements.--The regulations prescribed
by the Secretary under this section shall establish performance
requirements that require each electronic on-board recording
device to--
(A) be integrally synchronized with the vehicle's
engine control module;
(B) identify each driver subject to the hours of
service and record of duty status requirements under
part 395 of title 49, Code of Federal Regulations;
(C) accurately record driving time;
(D) provide real-time recording of the vehicle's
location;
(E) enable law enforcement personnel to access the
information contained in the device during roadside
inspections; and
(F) be tamper resistant.
(2) Certification criteria.--
(A) In general.--The regulations prescribed by the
Secretary under this section shall establish the
criteria and a process for the certification of
electronic on-board recording devices to ensure that
such devices meet the performance requirements under
this section.
(B) Effect of noncertification.--Electronic on-
board recording devices that are not certified in
accordance with the certification process referred to
in subparagraph (A) shall not be acceptable evidence of
hours of service and record of duty status requirements
under part 395 of title 49, Code of Federal
Regulations.
(3) Additional requirements.--The regulations prescribed by
the Secretary under this section shall--
(A) define a standardized user interface to aid
vehicle operator compliance and law enforcement
reviews;
(B) establish a secure process for standardized and
unique vehicle operator identification, data access,
data transfer for vehicle operators between motor
vehicles, data storage for motor carriers, and data
transfer and transportability for law enforcement; and
(C) establish a standard security level for
electronic on-board recording devices to be tamper
resistant.
(c) Effective Date; Applicability.--Beginning on a date that is not
later than 3 years after the date of the enactment of this Act, the
regulations prescribed pursuant to this section shall apply to all
motor carriers, commercial motor vehicles, and vehicle operators
subject to the hours of service and the record of duty status
requirements under part 395 of title 49, Code of Federal Regulations. | Commercial Driver Compliance Improvement Act - Requires all commercial motor vehicles involved in interstate commerce and operated by a driver subject to both federal hours-of-service and record of duty status requirements, in order to improve compliance with federal hours-of-service regulations, to be equipped with an electronic on-board recording device meeting performance requirements and certification criteria and certain other requirements prescribed by the Secretary of Transportation (DOT). |
wild - type ( c57bl/6j ) and sod1 ( b6.cg-tg(sod1*g93a)1gur/j , stock # 004435 ) mice were obtained from jackson laboratories ( bar harbor , me , usa ) .
intraocular pressure elevation was induced by anterior chamber microbead injections as originally described by sappington et al .
however , we applied a recently described modification , in which microbead injections are followed by injection of a viscoelastic substance to thereby push the beads into the anterior chamber angle and prevent the bead reflux when the injection cannula is removed .
briefly , a 50-m glass cannula connected by tubing to a hamilton syringe ( hamilton company reno , nv , usa ) .
was first filled with a viscoelastic solution ( 10 mg / ml sodium hyaluronate ) , then 0.05 l air , and finally microbeads ( 3 10 beads per l ) .
we injected 4 l of the two - bead mixture ( equal volumes of 6 m and 1 m diameter beads ) , then 1 l of viscoelastic , as this protocol provides higher and more consistent iop elevation and greater axon loss .
intraocular pressure was measured immediately before and after injection , and twice weekly thereafter using a tonolab rebound tonometer ( tiolat , helsinki , finland ) .
the iop - time integral was used to determine the cumulative iop exposure for each mouse by calculating the area under the pressure - time curve in the ocular hypertensive eye , then subtracting this iop - time integral from that in the normotensive fellow eye ( expressed in units of mm hg - days ) . to minimize the influence of iop variability among animals , all data were analyzed in mouse eyes matched for the cumulative iop exposure between 200 and 400 mm hg - days ( corresponds to up to 50% neuron loss ) .
ocular hypertension was induced in c57bl/6j and sod1 mice after 5 months of age , and the animal age was less than 32 weeks at the end of the experimental period .
all animals were handled according to the regulations of the institutional animal care and use committee , and all procedures adhered to the tenets of the arvo statement for the use of animals in ophthalmic and vision research .
mice with unilaterally induced iop elevation received antioxidant treatment , or vehicle ( saline ) alone , over a period of 6 weeks .
tempol ( 4-hydroxytetramethylpiperidine-1-oxyl ; enzo life sciences , farmingdale , ny , usa ) , a superoxide dismutase mimetic and peroxynitrite - derived free radical scavenger that also reduces the formation of hydroxyl radicals was used for antioxidant treatment .
this multifunctional antioxidant is blood - brain barrier permeable and can readily access the intracellular compartment .
tempol ( 200 mg / kg / d ) was given by subcutaneously implanted osmotic mini - pumps ( model 2006 ; alzet , cupertino , ca , usa ) for drug delivery by constant infusion .
the mini - pumps that were used to deliver solution at a rate of 0.15 l / h and provide constant infusion for 6 weeks .
the treatment dose was chosen based on previously published studies of other disease models , our earlier in vitro study of rgcs , and in vivo dose / response experiments to provide optimum antioxidant capacity but avoid toxicity .
the selected dose is far lower than the toxic or lethal doses of tempol ( ld50 = 2 mmol / kg given by intravenous or intraperitoneal injection ) .
all animals well tolerated the antioxidant treatment with no noticeable adverse effects on systemic health status .
osmotic mini - pumps were implanted at the time of microbead injection . before implantation , pumps were primed in sterile saline at 37c .
we measured the residual volume in the pumps explanted at the end of the treatment period .
the protein lysates that were obtained from retina and optic nerve samples ( including the optic nerve head and a 2-mm segment of the optic nerve proximal to the globe ) were quantitatively analyzed for carbonyl and 4-hydroxynonenal ( hne ) levels using specific competitive elisa kits ( oxiselect protein carbonyl and hne - his adduct elisa kits ; cell biolabs , san diego , ca , usa ) , as we previously described . for the assay of protein carbonyls , protein samples adsorbed to wells of a 96-well plate react with 2,4-dinitrophenylhydrazine ( dnph ) in similar technical principal we previously used for analysis of retinal protein oxidation . for hne assay , hne - protein adducts present in the sample are probed with an anti - hne - his antibody , followed by an horseradish peroxidase conjugated secondary antibody .
a multiplexed assay kit similarly based on a standard elisa protocol ( qiagen , valencia , ca , usa ) was used to analyze retina cytokine profiles .
these multi - analyte elisarray kits allow simultaneous profiling of 12 proteins ( cytokines and chemokines ) .
a specific elisa kit was also used to analyze the dna binding activity of nf-b ( abcam , cambridge , ma , usa ) . within this assay kit
, a specific double - stranded dna sequence containing the nf-b response element is immobilized onto the wells of a 96-well plate , and binding of the nf-b in nuclear extracts can be detected by specific p65 antibody labeling .
nuclear proteins were extracted with a specific buffer containing protease and phosphatase inhibitors ( abcam ) .
detection sensitivity for the kits were low pg / ml to less than 10 g / ml . all analyses included triplicated wells and negative controls .
retina and proximal optic nerve protein samples were analyzed by quantitative western blotting that followed a methodology similar to previously described .
briefly , protein samples were separated on denaturing polyacrylamide gels ( bio - rad , hercules , ca , usa ) and transferred to pvdf membranes ( bio - rad ) . following a blocking step , membranes were probed with a phosphorylation site specific primary antibody to nf-b subunit , p65 ( phospho - ser536 ) ( 1:500 ; abcam ) .
after a second blocking step , membranes were incubated with a secondary antibody conjugated with horseradish peroxidase ( 1:2000 ; sigma - aldrich corp . , st .
immunoreactive bands were visualized by enhanced chemiluminescence using commercial reagents ( ge healthcare , pittsburgh , pa , usa ) . a beta - actin antibody ( 1:1000 ; sigma - aldrich corp . )
histological sections of the mouse retina were analyzed after specific immunofluorescence labeling with a monoclonal antibody to tnf- ( 1:500 ; abcam ) , as previously described .
in addition , specific antibodies against glial fibrillary acidic protein ( gfap ) or iba1 ( 1:500 ; santa cruz , ca , usa ) were used to identify astroglia and microglia , respectively .
a mixture of alexa fluor 488- or 568-conjugated iggs ( 1:500 ; thermo fisher scientific , waltham , ma , usa ) was used for the secondary antibody incubation .
the 4,6-diamidino-2-phenylindole , dihydrochloride ( dapi ; thermo fisher scientific ) was used for nuclear counterstaining .
slides were examined by fluorescence microscopy and images were recorded by digital photomicrography ( carl zeiss , thornwood , ny , usa ) .
negative controls were performed by replacing the primary antibody with serum or using an inappropriate secondary antibody to determine species specificity .
1 m - thick plastic cross - sections of the optic nerve ( more distal to the segment sampled for protein analysis ) were used for imaging - based axon quantification in a masked fashion as previously described .
briefly , the optic nerves excised from enucleated eye balls were fixed and then embedded in epoxy resin .
stained sections were imaged in their entirety as nonoverlapping tile images , and the captured images were analyzed for axon counts using the zeiss / zen imaging software ( carl zeiss ) .
this methodology allows axon counts representing the entire surface area of optic nerve cross - sections .
nerve outlines were manually traced on mosaics of images , and the size and shape parameters were determined to exclude intervening glia , myelin debris , and highly degenerated axons to ensure accurate counts . after image processing and axon counting , the axon loss was expressed as a ratio of axon counts in ocular hypertensive to fellow control eye .
retinal ganglion cell counting followed a similar imaging - based methodology representing the entire whole - mounted area .
whole - mounted retinas were immunolabeled for -iii - tubulin , a neuronal lineage marker that preferentially stains tubulin - rich rgcs ( 1:1000 ; abcam ) .
retinas were also double immunolabeled with an antibody to syntaxin , a marker for amacrine cells ( 1:1000 ; abcam ) . after secondary antibody incubation
, images were obtained at the focal plane of the rgc layer in whole - mounts , and these images were used to count -iii - tubulin+/syntaxin neurons in a masked fashion .
most of the syntaxin+ amacrine cells that exhibited only weak to moderate labeling for -iii - tubulin were lying the outside of the immediate focal plane and were not subject to the counting process .
an additional criterion for counting rgcs included a minimal somal size of 10 m to also eliminate dying or phagocytized rgcs .
retinal ganglion cell loss was expressed as a ratio of counts in ocular hypertensive to fellow control eye .
wild - type ( c57bl/6j ) and sod1 ( b6.cg-tg(sod1*g93a)1gur/j , stock # 004435 ) mice were obtained from jackson laboratories ( bar harbor , me , usa ) .
intraocular pressure elevation was induced by anterior chamber microbead injections as originally described by sappington et al .
however , we applied a recently described modification , in which microbead injections are followed by injection of a viscoelastic substance to thereby push the beads into the anterior chamber angle and prevent the bead reflux when the injection cannula is removed .
briefly , a 50-m glass cannula connected by tubing to a hamilton syringe ( hamilton company reno , nv , usa ) .
was first filled with a viscoelastic solution ( 10 mg / ml sodium hyaluronate ) , then 0.05 l air , and finally microbeads ( 3 10 beads per l ) .
we injected 4 l of the two - bead mixture ( equal volumes of 6 m and 1 m diameter beads ) , then 1 l of viscoelastic , as this protocol provides higher and more consistent iop elevation and greater axon loss .
intraocular pressure was measured immediately before and after injection , and twice weekly thereafter using a tonolab rebound tonometer ( tiolat , helsinki , finland ) .
the iop - time integral was used to determine the cumulative iop exposure for each mouse by calculating the area under the pressure - time curve in the ocular hypertensive eye , then subtracting this iop - time integral from that in the normotensive fellow eye ( expressed in units of mm hg - days ) . to minimize the influence of iop variability among animals , all data were analyzed in mouse eyes matched for the cumulative iop exposure between 200 and 400 mm hg - days ( corresponds to up to 50% neuron loss ) .
ocular hypertension was induced in c57bl/6j and sod1 mice after 5 months of age , and the animal age was less than 32 weeks at the end of the experimental period .
all animals were handled according to the regulations of the institutional animal care and use committee , and all procedures adhered to the tenets of the arvo statement for the use of animals in ophthalmic and vision research .
mice with unilaterally induced iop elevation received antioxidant treatment , or vehicle ( saline ) alone , over a period of 6 weeks .
tempol ( 4-hydroxytetramethylpiperidine-1-oxyl ; enzo life sciences , farmingdale , ny , usa ) , a superoxide dismutase mimetic and peroxynitrite - derived free radical scavenger that also reduces the formation of hydroxyl radicals was used for antioxidant treatment .
this multifunctional antioxidant is blood - brain barrier permeable and can readily access the intracellular compartment .
tempol ( 200 mg / kg / d ) was given by subcutaneously implanted osmotic mini - pumps ( model 2006 ; alzet , cupertino , ca , usa ) for drug delivery by constant infusion .
the mini - pumps that were used to deliver solution at a rate of 0.15 l / h and provide constant infusion for 6 weeks .
the treatment dose was chosen based on previously published studies of other disease models , our earlier in vitro study of rgcs , and in vivo dose / response experiments to provide optimum antioxidant capacity but avoid toxicity .
the selected dose is far lower than the toxic or lethal doses of tempol ( ld50 = 2 mmol / kg given by intravenous or intraperitoneal injection ) .
all animals well tolerated the antioxidant treatment with no noticeable adverse effects on systemic health status .
osmotic mini - pumps were implanted at the time of microbead injection . before implantation , pumps were primed in sterile saline at 37c .
we measured the residual volume in the pumps explanted at the end of the treatment period .
the protein lysates that were obtained from retina and optic nerve samples ( including the optic nerve head and a 2-mm segment of the optic nerve proximal to the globe ) were quantitatively analyzed for carbonyl and 4-hydroxynonenal ( hne ) levels using specific competitive elisa kits ( oxiselect protein carbonyl and hne - his adduct elisa kits ; cell biolabs , san diego , ca , usa ) , as we previously described . for the assay of protein carbonyls , protein samples adsorbed to wells of a 96-well plate react with 2,4-dinitrophenylhydrazine ( dnph ) in similar technical principal we previously used for analysis of retinal protein oxidation . for hne assay ,
hne - protein adducts present in the sample are probed with an anti - hne - his antibody , followed by an horseradish peroxidase conjugated secondary antibody . a multiplexed assay kit similarly based on a standard elisa protocol (
qiagen , valencia , ca , usa ) was used to analyze retina cytokine profiles .
these multi - analyte elisarray kits allow simultaneous profiling of 12 proteins ( cytokines and chemokines ) .
a specific elisa kit was also used to analyze the dna binding activity of nf-b ( abcam , cambridge , ma , usa ) . within this assay kit ,
a specific double - stranded dna sequence containing the nf-b response element is immobilized onto the wells of a 96-well plate , and binding of the nf-b in nuclear extracts can be detected by specific p65 antibody labeling .
nuclear proteins were extracted with a specific buffer containing protease and phosphatase inhibitors ( abcam ) .
detection sensitivity for the kits were low pg / ml to less than 10 g / ml . all analyses included triplicated wells and negative controls .
retina and proximal optic nerve protein samples were analyzed by quantitative western blotting that followed a methodology similar to previously described .
briefly , protein samples were separated on denaturing polyacrylamide gels ( bio - rad , hercules , ca , usa ) and transferred to pvdf membranes ( bio - rad ) . following a blocking step , membranes were probed with a phosphorylation site specific primary antibody to nf-b subunit , p65 ( phospho - ser536 ) ( 1:500 ; abcam ) .
after a second blocking step , membranes were incubated with a secondary antibody conjugated with horseradish peroxidase ( 1:2000 ; sigma - aldrich corp . , st .
immunoreactive bands were visualized by enhanced chemiluminescence using commercial reagents ( ge healthcare , pittsburgh , pa , usa ) . a beta - actin antibody ( 1:1000 ; sigma - aldrich corp . )
histological sections of the mouse retina were analyzed after specific immunofluorescence labeling with a monoclonal antibody to tnf- ( 1:500 ; abcam ) , as previously described .
in addition , specific antibodies against glial fibrillary acidic protein ( gfap ) or iba1 ( 1:500 ; santa cruz , ca , usa ) were used to identify astroglia and microglia , respectively .
a mixture of alexa fluor 488- or 568-conjugated iggs ( 1:500 ; thermo fisher scientific , waltham , ma , usa ) was used for the secondary antibody incubation .
the 4,6-diamidino-2-phenylindole , dihydrochloride ( dapi ; thermo fisher scientific ) was used for nuclear counterstaining .
slides were examined by fluorescence microscopy and images were recorded by digital photomicrography ( carl zeiss , thornwood , ny , usa ) .
negative controls were performed by replacing the primary antibody with serum or using an inappropriate secondary antibody to determine species specificity .
1 m - thick plastic cross - sections of the optic nerve ( more distal to the segment sampled for protein analysis ) were used for imaging - based axon quantification in a masked fashion as previously described .
briefly , the optic nerves excised from enucleated eye balls were fixed and then embedded in epoxy resin .
stained sections were imaged in their entirety as nonoverlapping tile images , and the captured images were analyzed for axon counts using the zeiss / zen imaging software ( carl zeiss ) .
this methodology allows axon counts representing the entire surface area of optic nerve cross - sections .
nerve outlines were manually traced on mosaics of images , and the size and shape parameters were determined to exclude intervening glia , myelin debris , and highly degenerated axons to ensure accurate counts . after image processing and axon counting , the axon loss was expressed as a ratio of axon counts in ocular hypertensive to fellow control eye .
retinal ganglion cell counting followed a similar imaging - based methodology representing the entire whole - mounted area .
whole - mounted retinas were immunolabeled for -iii - tubulin , a neuronal lineage marker that preferentially stains tubulin - rich rgcs ( 1:1000 ; abcam ) .
retinas were also double immunolabeled with an antibody to syntaxin , a marker for amacrine cells ( 1:1000 ; abcam ) . after secondary antibody incubation ,
images were obtained at the focal plane of the rgc layer in whole - mounts , and these images were used to count -iii - tubulin+/syntaxin neurons in a masked fashion .
most of the syntaxin+ amacrine cells that exhibited only weak to moderate labeling for -iii - tubulin were lying the outside of the immediate focal plane and were not subject to the counting process .
an additional criterion for counting rgcs included a minimal somal size of 10 m to also eliminate dying or phagocytized rgcs .
retinal ganglion cell loss was expressed as a ratio of counts in ocular hypertensive to fellow control eye .
antioxidant treatment with tempol was started at the time of anterior chamber microbead / viscoelastic injections to induce iop elevation in c57bl/6j mice .
another group of ocular hypertensive c57bl/6j mice received the equivalent volume of the vehicle ( saline ) alone .
additional groups included sod1 and wt ( c57bl/6j ) mice with similarly induced ocular hypertension .
as shown in figure 1 , tempol treatment , or sod1 , did not affect the level of iop increase or the duration of ocular hypertension over an experimental period of 6 weeks ( mann - whitney u test , p > 0.05 ) .
control groups of c57bl/6j wt or sod1 mice that received physiologic saline injection into the anterior chamber had a steady level of iop that was maintained at an average value of 10.8 1.2 mm hg through the experimental period
. however , the microbead / viscoelastic - injected mice , including both wt and sod1 animals , exhibited a transient course of ocular hypertension . also shown are the treatment groups including the wt ocular hypertensive mice that received either antioxidant tempol or the saline vehicle alone ( n = 12/group ) .
data are presented as mean sd . at the end of the 6-week treatment period , we measured the antioxidant capacity in retina and optic nerve samples by a specific assay and detected a significant increase in tempol - treated ocular hypertensive samples relative to ocular hypertensive controls that were given the vehicle alone ( p < 0.01 ) .
parallel to the increased antioxidant capacity , protein carbonyls and hne adducts exhibited a significant decrease in ocular hypertensive samples treated with tempol ( p < 0.01 ) .
figure 2 presents our data ( mean sd ) , expressed as fold - change with antioxidant treatment in ocular hypertensive mice relative to ocular hypertensive mice that received only the vehicle .
in contrast , ocular hypertensive retina and optic nerve exhibited decreased antioxidant capacity and increased protein oxidation in sod1 mice relative to wt ocular hypertensive controls ( also shown in fig .
the mouse retina ( a ) and optic nerve ( b ) protein samples were analyzed for antioxidant capacity , protein carbonyls , and hne adducts by specific assays . presented is the fold - change ( mean sd ) in tempol - treated versus vehicle - treated groups , or sod1 versus wt controls ( c57bl/6j ) .
the antioxidant capacity was increased and the oxidative stress end products were decreased after tempol treatment of ocular hypertensive mice relative to ocular hypertensive controls that received only the vehicle ( mann - whitney u test ; p < 0.01 ) . in contrast , ocular hypertensive sod1 mice exhibited decreased antioxidant capacity and increased protein oxidation compared with ocular hypertensive wt controls ( p < 0.01 ) .
we next tested the neuroinflammatory and neurodegenerative outcomes of mouse glaucoma in the study groups with decreased or increased oxidative stress .
as detailed below , tempol treatment limiting the oxidative stress resulted in a prominent decrease in neuroinflammation and neurodegeneration in ocular hypertensive mice ( relative to ocular hypertensive mice that received the saline vehicle alone ) .
however , ocular hypertension induced neuroinflammatory and neurodegenerative responses were increased in sod1 mice with defective antioxidant response ( relative to wt ocular hypertensive controls ) .
it should be clarified that although fold alterations are presented in the same graphs , tempol - treated or sod1 groups represent different experimental paradigms , having their specific controls ( vehicle - treated , or wt , ocular hypertensive groups , respectively ) .
comparison of the magnitude of effects between tempol treatment or sod1 groups would not be suitable , because tempol is a broad - spectrum antioxidant with dose - dependent outcomes , whereas the mice knockout for a specific antioxidant enzyme ( sod1 ) may potentially exhibit compensatory changes of other superoxide dismutases or other antioxidant enzymes . to determine the inflammatory status of the retina and optic nerve , we measured the cytokine / chemokine titers . among a range of cytokines measured in retina samples , proinflammatory cytokines , il-1b ( mann - whitney u test , p = 0.03 ) , il-2 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.006 ) , exhibited over 2-fold decreased titers in tempol - treated ocular hypertensive samples compared with the ocular hypertensive controls given the vehicle alone .
optic nerve samples from tempol - treated samples presented a similar decrease in proinflammatory cytokine production .
the optic nerve cytokines exhibiting over 2-fold decreased titers with tempol treatment , relative to the vehicle group , included il-1a ( p = 0.03 ) , il-2 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.005 ) .
in addition , some cytokines that may act as either proinflammatory or anti - inflammatory , including il-13 ( p = 0.006 ) in the retina , and il-4 ( p = 0.01 ) , il-6 ( p = 0.006 ) , and il-13 ( p = 0.03 ) in the optic nerve , exhibited decreased titers with tempol treatment .
in contrast to a prominent decrease in cytokine response to ocular hypertension with antioxidant treatment , the retina and optic nerve samples collected from ocular hypertensive sod1 mice exhibited a significant increase in cytokine production . compared with ocular hypertensive wt controls , ocular hypertensive sod1 retina exhibited an over 2-fold increase in il-6 ( p = 0.03 ) , il-12 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.009 ) .
the most significantly increased cytokines in the optic nerve samples from ocular hypertensive sod1 mice included il-1a ( p = 0.03 ) , il-2 ( p = 0.005 ) , il-6 ( p = 0.005 ) , il-12 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.006 ) .
bar graphs in figure 3 show the fold - change ( mean sd ) in ocular hypertension
induced cytokine production in the retina or optic nerve with antioxidant treatment ( relative to vehicle ) or sod1 ( relative to wt ) .
retina and optic nerve inflammation in ocular hypertensive mice . to determine the inflammatory status of the retina and optic nerve ,
the bar graphs show the fold - change ( mean sd ) in ocular hypertension
( a ) fold decrease in retina cytokine titers in tempol - treated ocular hypertensive mice compared with ocular hypertensive controls that received only the saline vehicle .
( b ) fold increase in retina cytokine titers in sod1 mice with ocular hypertension compared with wt ( c57bl/6j ) ocular hypertensive mice .
( c ) fold decrease in optic nerve cytokine titers in tempol - treated versus vehicle groups of ocular hypertensive mice .
( d ) fold increase in optic nerve cytokine titers in sod1 versus wt ocular hypertensive mice .
presented data represent at least six mice per group . * p < 0.05 ; * * p < 0.01 ( mann - whitney u test ) .
antioxidant treatment also resulted in a prominent decrease in ocular hypertension - induced activation of nf-b , a redox - sensitive master regulator of inflammatory mediators .
based on western blot analysis using a phosphorylation site - specific antibody to nf-b subunit ( p65 ) , and the nf-b dna binding activity assay , tempol - treated samples of the ocular hypertensive retina and optic nerve exhibited over 3-fold decreased activation of nf-b ( relative to ocular hypertensive controls that received the vehicle alone ) .
however , nf-b activation was increased 3-fold in ocular hypertensive sod1 mice relative to ocular hypertensive wt controls ( fig .
4 ) . presented data from protein analysis represent at least six mice per group .
activity of nf - kb , a transcriptional regulator of inflammation , in experimental mouse glaucoma .
( a ) for western blot analysis of protein expression , retina and optic nerve protein samples were probed with a phosphorylation site - specific antibody to nf-b subunit , p65 ( p - p65 ) .
this analysis indicated that tempol treatment of the ocular hypertensive mice ( relative to ocular hypertensive controls that received the saline vehicle alone ) resulted in a prominent decrease in p - p65 expression .
however , sod1 mice ( relative to c57bl/6j wt controls ) exhibited a prominent increase in ocular hypertension induced p - p65 expression .
( b ) nuclear factorb dna binding activity assay similarly indicated over 3-fold decreased activity of nf-b in tempol - treated ocular hypertensive samples relative to ocular hypertensive controls that received only the vehicle ( mean sd ) .
however , nf-b activity was significantly increased in ocular hypertensive sod1 mice relative to ocular hypertensive wt controls . presented
we also analyzed the extent and cellular localization of cytokine production by immunolabeling of the retina sections for an important proinflammatory cytokine , tnf-. we detected increased immunolabeling of the ocular hypertensive retina for tnf- that was localized to gfap+ astroglia and iba1 + microglia .
the ocular hypertension - induced increase in glial tnf- immunolabeling was prominently decreased after tempol treatment compared with ocular hypertensive controls that received only the vehicle .
in contrast , glial immunolabeling for tnf- was greater in the ocular hypertensive sod1 retina than wt ocular hypertensive control ( fig . 5 ) .
specific antibodies to astroglia ( gfap ) or microglia ( iba1 ) markers were used to determine the retinal localization of tnf- , an important proinflammatory cytokine .
presented include retina images from c57bl/6j wt mice with or without induced ocular hypertension , wt ocular hypertensive mice treated with tempol , and sod1 mice with induced ocular hypertension . compared with the normotensive retina ( thin arrows ) , hypertrophic astrocytes in the ocular hypertensive retina exhibited increased immunolabeling for gfap ( red ) . as seen in the image from sod1 mice , the ocular hypertension
induced glial response also included gfap immunolabeling of the mller glia located in the inner nuclear layer ( arrowheads ) . besides astroglia , the glial activation response to ocular hypertension included the microglia .
the weakly labeled microglia for iba1 in the normotensive control retina ( thin arrows ) were mainly localized around the blood vessels in the ganglion cell ( gcl ) or inner nuclear ( inl ) layers . however , ocular hypertensive retinas exhibited increased number and iba1 immunolabeling ( red ) of the microglia that were distributed throughout the inner retina .
tumor necrosis factor- immunolabeling was not detectable in the normotensive retina ; however , ocular hypertensive retinas were prominently immunolabeled for this proinflammatory cytokine ( green ) , which was remarkably decreased after tempol treatment .
the glia in the ocular hypertensive sod1 mice presented the most prominent immunolabeling for tnf- ( thick arrows ) .
the increased tnf- immunolabeling in the glaucomatous retina was localized to gfap+ astroglia and iba1 + microglia .
data represent three different samples for each group ( scale bar : 100 m ) .
we counted optic nerve axons and rgcs in tempol - treated versus vehicle - treated groups , and sod1 versus wt groups .
induced axon loss ( mann - whitney u test , p = 0.04 ) and 29% decrease in ocular hypertension induced rgc loss ( p = 0.01 ) in tempol - treated animals relative to ocular hypertensive controls that received the vehicle alone . however , in ocular hypertensive sod1 mice , axon loss increased by 34% ( p = 0.008 ) and rgc loss increased by 36% compared with ocular hypertensive wt controls ( p = 0.02 ) .
presented data ( mean sd ) represent 12 mice per group for axon counts and at least 3 mice per group for rgc counts .
( a ) analysis of optic nerve cross - sections and whole - mounted retinas indicated prominent injury to rgc somas and axons with experimentally induced glaucoma in mice .
compared with c57bl/6j wt mice , ocular hypertension induced greater injury to neurons in sod1 mice .
the red arrow indicates degenerating axons and myelin debris ; blue asterisk indicates the areas of prominent axon loss .
optic nerve axons were counted in cross - sections , and rgcs were counted in whole - mounted retinas after -iii - tubulin immunolabeling . to estimate the neuron loss in each mouse
, axon and rgc counts in the ocular hypertensive eye were adjusted to the normotensive fellow eye .
bar graphs in ( b ) and ( c ) indicate the percentage of axon or rgc loss in ( 1 ) wt ocular hypertensive mice ( relative to wt normotensive controls ) ; ( 2 ) tempol - treated wt ocular hypertensive mice ( relative to wt ocular hypertensive controls that received only the saline vehicle ) ; and ( 3 ) ocular hypertensive sod1 mice ( relative to ocular hypertensive wt controls ) .
presented data ( mean sd ) represent 12 mice per group for axon counts and at least 3 mice per group for rgc counts .
antioxidant treatment with tempol was started at the time of anterior chamber microbead / viscoelastic injections to induce iop elevation in c57bl/6j mice .
another group of ocular hypertensive c57bl/6j mice received the equivalent volume of the vehicle ( saline ) alone .
additional groups included sod1 and wt ( c57bl/6j ) mice with similarly induced ocular hypertension .
as shown in figure 1 , tempol treatment , or sod1 , did not affect the level of iop increase or the duration of ocular hypertension over an experimental period of 6 weeks ( mann - whitney u test , p > 0.05 ) .
control groups of c57bl/6j wt or sod1 mice that received physiologic saline injection into the anterior chamber had a steady level of iop that was maintained at an average value of 10.8 1.2 mm hg through the experimental period
. however , the microbead / viscoelastic - injected mice , including both wt and sod1 animals , exhibited a transient course of ocular hypertension . also shown are the treatment groups including the wt ocular hypertensive mice that received either antioxidant tempol or the saline vehicle alone ( n = 12/group ) .
data are presented as mean sd . at the end of the 6-week treatment period , we measured the antioxidant capacity in retina and optic nerve samples by a specific assay and detected a significant increase in tempol - treated ocular hypertensive samples relative to ocular hypertensive controls that were given the vehicle alone ( p < 0.01 ) .
parallel to the increased antioxidant capacity , protein carbonyls and hne adducts exhibited a significant decrease in ocular hypertensive samples treated with tempol ( p < 0.01 ) .
figure 2 presents our data ( mean sd ) , expressed as fold - change with antioxidant treatment in ocular hypertensive mice relative to ocular hypertensive mice that received only the vehicle .
in contrast , ocular hypertensive retina and optic nerve exhibited decreased antioxidant capacity and increased protein oxidation in sod1 mice relative to wt ocular hypertensive controls ( also shown in fig .
the mouse retina ( a ) and optic nerve ( b ) protein samples were analyzed for antioxidant capacity , protein carbonyls , and hne adducts by specific assays . presented is the fold - change ( mean sd ) in tempol - treated versus vehicle - treated groups , or sod1 versus wt controls ( c57bl/6j ) .
the antioxidant capacity was increased and the oxidative stress end products were decreased after tempol treatment of ocular hypertensive mice relative to ocular hypertensive controls that received only the vehicle ( mann - whitney u test ; p < 0.01 ) . in contrast , ocular hypertensive sod1 mice exhibited decreased antioxidant capacity and increased protein oxidation compared with ocular hypertensive wt controls ( p < 0.01 ) .
we next tested the neuroinflammatory and neurodegenerative outcomes of mouse glaucoma in the study groups with decreased or increased oxidative stress .
as detailed below , tempol treatment limiting the oxidative stress resulted in a prominent decrease in neuroinflammation and neurodegeneration in ocular hypertensive mice ( relative to ocular hypertensive mice that received the saline vehicle alone ) .
however , ocular hypertension induced neuroinflammatory and neurodegenerative responses were increased in sod1 mice with defective antioxidant response ( relative to wt ocular hypertensive controls ) .
it should be clarified that although fold alterations are presented in the same graphs , tempol - treated or sod1 groups represent different experimental paradigms , having their specific controls ( vehicle - treated , or wt , ocular hypertensive groups , respectively ) .
comparison of the magnitude of effects between tempol treatment or sod1 groups would not be suitable , because tempol is a broad - spectrum antioxidant with dose - dependent outcomes , whereas the mice knockout for a specific antioxidant enzyme ( sod1 ) may potentially exhibit compensatory changes of other superoxide dismutases or other antioxidant enzymes .
to determine the inflammatory status of the retina and optic nerve , we measured the cytokine / chemokine titers . among a range of cytokines measured in retina samples , proinflammatory cytokines , il-1b ( mann - whitney u test , p = 0.03 ) , il-2 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.006 ) , exhibited over 2-fold decreased titers in tempol - treated ocular hypertensive samples compared with the ocular hypertensive controls given the vehicle alone .
optic nerve samples from tempol - treated samples presented a similar decrease in proinflammatory cytokine production .
the optic nerve cytokines exhibiting over 2-fold decreased titers with tempol treatment , relative to the vehicle group , included il-1a ( p = 0.03 ) , il-2 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.005 ) .
in addition , some cytokines that may act as either proinflammatory or anti - inflammatory , including il-13 ( p = 0.006 ) in the retina , and il-4 ( p = 0.01 ) , il-6 ( p = 0.006 ) , and il-13 ( p = 0.03 ) in the optic nerve , exhibited decreased titers with tempol treatment .
in contrast to a prominent decrease in cytokine response to ocular hypertension with antioxidant treatment , the retina and optic nerve samples collected from ocular hypertensive sod1 mice exhibited a significant increase in cytokine production . compared with ocular hypertensive wt controls ,
ocular hypertensive sod1 retina exhibited an over 2-fold increase in il-6 ( p = 0.03 ) , il-12 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.009 ) .
the most significantly increased cytokines in the optic nerve samples from ocular hypertensive sod1 mice included il-1a ( p = 0.03 ) , il-2 ( p = 0.005 ) , il-6 ( p = 0.005 ) , il-12 ( p = 0.005 ) , ifn- ( p = 0.005 ) , and tnf- ( p = 0.006 ) .
bar graphs in figure 3 show the fold - change ( mean sd ) in ocular hypertension
induced cytokine production in the retina or optic nerve with antioxidant treatment ( relative to vehicle ) or sod1 ( relative to wt ) .
retina and optic nerve inflammation in ocular hypertensive mice . to determine the inflammatory status of the retina and optic nerve ,
the bar graphs show the fold - change ( mean sd ) in ocular hypertension
( a ) fold decrease in retina cytokine titers in tempol - treated ocular hypertensive mice compared with ocular hypertensive controls that received only the saline vehicle .
( b ) fold increase in retina cytokine titers in sod1 mice with ocular hypertension compared with wt ( c57bl/6j ) ocular hypertensive mice .
( c ) fold decrease in optic nerve cytokine titers in tempol - treated versus vehicle groups of ocular hypertensive mice .
( d ) fold increase in optic nerve cytokine titers in sod1 versus wt ocular hypertensive mice .
presented data represent at least six mice per group . * p < 0.05 ; * * p < 0.01 ( mann - whitney u test ) .
antioxidant treatment also resulted in a prominent decrease in ocular hypertension - induced activation of nf-b , a redox - sensitive master regulator of inflammatory mediators .
based on western blot analysis using a phosphorylation site - specific antibody to nf-b subunit ( p65 ) , and the nf-b dna binding activity assay , tempol - treated samples of the ocular hypertensive retina and optic nerve exhibited over 3-fold decreased activation of nf-b ( relative to ocular hypertensive controls that received the vehicle alone ) .
however , nf-b activation was increased 3-fold in ocular hypertensive sod1 mice relative to ocular hypertensive wt controls ( fig .
4 ) . presented data from protein analysis represent at least six mice per group .
activity of nf - kb , a transcriptional regulator of inflammation , in experimental mouse glaucoma .
( a ) for western blot analysis of protein expression , retina and optic nerve protein samples were probed with a phosphorylation site - specific antibody to nf-b subunit , p65 ( p - p65 ) .
this analysis indicated that tempol treatment of the ocular hypertensive mice ( relative to ocular hypertensive controls that received the saline vehicle alone ) resulted in a prominent decrease in p - p65 expression .
however , sod1 mice ( relative to c57bl/6j wt controls ) exhibited a prominent increase in ocular hypertension induced p - p65 expression .
( b ) nuclear factorb dna binding activity assay similarly indicated over 3-fold decreased activity of nf-b in tempol - treated ocular hypertensive samples relative to ocular hypertensive controls that received only the vehicle ( mean sd ) .
however , nf-b activity was significantly increased in ocular hypertensive sod1 mice relative to ocular hypertensive wt controls . presented
we also analyzed the extent and cellular localization of cytokine production by immunolabeling of the retina sections for an important proinflammatory cytokine , tnf-. we detected increased immunolabeling of the ocular hypertensive retina for tnf- that was localized to gfap+ astroglia and iba1 + microglia .
the ocular hypertension - induced increase in glial tnf- immunolabeling was prominently decreased after tempol treatment compared with ocular hypertensive controls that received only the vehicle .
in contrast , glial immunolabeling for tnf- was greater in the ocular hypertensive sod1 retina than wt ocular hypertensive control ( fig . 5 ) .
specific antibodies to astroglia ( gfap ) or microglia ( iba1 ) markers were used to determine the retinal localization of tnf- , an important proinflammatory cytokine . presented
include retina images from c57bl/6j wt mice with or without induced ocular hypertension , wt ocular hypertensive mice treated with tempol , and sod1 mice with induced ocular hypertension .
compared with the normotensive retina ( thin arrows ) , hypertrophic astrocytes in the ocular hypertensive retina exhibited increased immunolabeling for gfap ( red ) . as seen in the image from sod1 mice , the ocular hypertension
induced glial response also included gfap immunolabeling of the mller glia located in the inner nuclear layer ( arrowheads ) .
besides astroglia , the glial activation response to ocular hypertension included the microglia . the weakly labeled microglia for iba1 in the normotensive control retina ( thin arrows
) were mainly localized around the blood vessels in the ganglion cell ( gcl ) or inner nuclear ( inl ) layers . however , ocular hypertensive retinas exhibited increased number and iba1 immunolabeling ( red ) of the microglia that were distributed throughout the inner retina .
tumor necrosis factor- immunolabeling was not detectable in the normotensive retina ; however , ocular hypertensive retinas were prominently immunolabeled for this proinflammatory cytokine ( green ) , which was remarkably decreased after tempol treatment .
the glia in the ocular hypertensive sod1 mice presented the most prominent immunolabeling for tnf- ( thick arrows ) .
the increased tnf- immunolabeling in the glaucomatous retina was localized to gfap+ astroglia and iba1 + microglia .
data represent three different samples for each group ( scale bar : 100 m ) .
we counted optic nerve axons and rgcs in tempol - treated versus vehicle - treated groups , and sod1 versus wt groups .
induced axon loss ( mann - whitney u test , p = 0.04 ) and 29% decrease in ocular hypertension induced rgc loss ( p = 0.01 ) in tempol - treated animals relative to ocular hypertensive controls that received the vehicle alone . however , in ocular hypertensive sod1 mice , axon loss increased by 34% ( p = 0.008 ) and rgc loss increased by 36% compared with ocular hypertensive wt controls ( p = 0.02 ) .
presented data ( mean sd ) represent 12 mice per group for axon counts and at least 3 mice per group for rgc counts .
( a ) analysis of optic nerve cross - sections and whole - mounted retinas indicated prominent injury to rgc somas and axons with experimentally induced glaucoma in mice . compared with c57bl/6j wt mice ,
the red arrow indicates degenerating axons and myelin debris ; blue asterisk indicates the areas of prominent axon loss .
optic nerve axons were counted in cross - sections , and rgcs were counted in whole - mounted retinas after -iii - tubulin immunolabeling . to estimate the neuron loss in each mouse , axon and rgc counts in the ocular hypertensive eye
bar graphs in ( b ) and ( c ) indicate the percentage of axon or rgc loss in ( 1 ) wt ocular hypertensive mice ( relative to wt normotensive controls ) ; ( 2 ) tempol - treated wt ocular hypertensive mice ( relative to wt ocular hypertensive controls that received only the saline vehicle ) ; and ( 3 ) ocular hypertensive sod1 mice ( relative to ocular hypertensive wt controls ) .
presented data ( mean sd ) represent 12 mice per group for axon counts and at least 3 mice per group for rgc counts .
glaucomatous neurodegeneration has been recognized as having an inflammatory component , and resident astroglia and microglia in the retina and optic nerve play key roles in the phenotype that drives innate and adaptive immune responses with neurodestructive consequences . based on multiple evidence , oxidative stress may signal for neuroinflammation in human glaucoma and animal models .
findings of this study support the oxidative stress induced mechanisms that contribute to neuroinflammatory and neurodegenerative outcomes of glaucoma .
presented findings also point to the immunomodulatory potential of antioxidant treatment for protecting neurons from inflammatory injury during glaucomatous neurodegeneration . to determine the importance of oxidative stress for neurodegenerative inflammation in glaucoma
, this study analyzed the neuroinflammatory and neurodegenerative outcomes of mouse glaucoma using two experimental paradigms of decreased or increased oxidative stress ( by pharmacological antioxidant treatment , or sod1 , respectively ) . in the first paradigm ,
c57bl/6j mice with experimentally induced glaucoma received an antioxidant , tempol . by providing protection against multiple oxidants , including superoxide , peroxynitrite , and hydroxyl radicals , tempol treatment has the advantage of multitarget combination strategies .
our previous in vitro studies with primary cultures of isolated rgcs have also used tempol and detected its treatment effect on rgc protection against glaucoma - related stimuli .
this multifunctional antioxidant has been successfully used in various in vivo models of oxidative stress , prolonged the life span of normal mice , provided neuroprotection in brain injury models , and protected rgcs against optic nerve crush injury and light - induced retinal injury in rats .
evidently , one of the mechanisms by which oxidative stress stimulates neuroinflammation is the redox - sensitive transcriptional activation of inflammatory mediators by glial nf-b . opposing its critical roles in regulation of the neuronal survival programs , nf-b activation is known to trigger inflammation and secondary neurodegenerative processes through the transcriptional activation of pro - interleukins that are later processed into active cytokines by the inflammasome .
this redox - sensitive transcriptional program is a common regulator of the cytokine signaling , tlr signaling , and inflammasome that comediate the glia - driven proinflammatory processes during neurodegeneration in human glaucoma and experimental models . in the present study
, we detected that antioxidant treatment of ocular hypertensive mice with tempol , in comparison with the controls given the vehicle alone , resulted in decreased activation of nf-b and decreased production of cytokines in the retina and optic nerve .
the proinflammatory cytokines exhibiting a significant decrease in tempol - treated ocular hypertensive tissues included the transcriptional targets of nf-b , such as tnf- and ifn-. among the proinflammatory cytokines , tnf- has been the most studied in the field of glaucomatous neurodegeneration .
increased glial production of tnf- in the glaucomatous human retina and optic nerve has been shown to trigger pro - apoptotic caspase cascade in rgcs and induce neuroinflammatory responses during glaucomatous neurodegeneration . besides tnf- and ifn- , other proinflammatory cytokines also exhibited significant decrease after tempol treatment of ocular hypertensive mice , which included il-1b and il-2 in the retina , and il-1a and il-2 in the optic nerve .
in addition , tempol treatment affected some cytokines that may act either proinflammatory or anti - inflammatory , including il-13 in the retina , and il-4 , il-6 , and il-13 in the optic nerve .
it is important to note that cytokine / chemokine profiles ( and different sets of receptors ) determine the status of an inflammatory activation , in which dynamics of anti - inflammatory versus proinflammatory cytokines are critical for the outcome function that spans from tissue cleaning and repair to neurodegenerative inflammation .
our findings supporting the oxidative stress related proinflammatory activation in this study stimulate more focused studies to illuminate the individual contribution ( and interrelationship ) of different cytokines in inflammatory injury to glaucomatous retina and optic nerve . although the pharmacological antioxidant treatment was used to study the effects of decreased oxidative stress in mouse glaucoma , a complementary experimental strategy aimed to model increased oxidative stress .
therefore , we also studied sod1 mice to determine whether overloaded oxidative stress ( as evident by aging ) promotes neuroinflammation and neurodegeneration in experimental glaucoma .
the sod family is a major antioxidant system , and sod1 deficiency in mice results in a phenotype that resembles accelerated aging .
for example , sod1 mice , compared with wt mice , have showed a greater injury to neurons in oxidative stress
a progressive degeneration of retinal neurons in these animals has been documented by morphological and physiological criteria . despite normal iop
, sod1 deficiency has also resulted in decreased rgc counts and decreased perg amplitude along with the elevated superoxide anions in the rgc layer .
regarding glaucoma , this major antioxidant enzyme has been found to be upregulated in ocular hypertensive animal models . in the present study of sod1 mice
, we detected a stronger inflammatory response to ocular hypertension ( relative to wt ocular hypertensive controls ) that resulted in increased injury to rgcs and optic nerve axons .
compared with wt mice , neuron counts were lower in sod1 mice before iop elevation ; however , the neuron loss ratio that reflects the injury in the ocular hypertensive eye adjusted to the normotensive fellow eye supported the adverse effect of overloaded oxidative stress on ocular hypertension induced inflammatory and neurodegenerative outcomes in sod1 mice . thus ,
if there is a deficiency in the endogenous antioxidant response , as in sod1 ( or if the generated oxidative stress overwhelms the endogenous antioxidant response ) , proinflammatory activation can not be repressed and the stimulated inflammation may contribute to neurodegeneration .
the increased neuroinflammation and neurodegeneration in sod1 mice with experimental glaucoma support the involvement of sod1 in oxidative stress induced damaging outcomes .
these observations warrant additional studies to expand the information ; however , due to a wide spectrum of injuries detected in sod1 ( which may affect both neuronal and non - neuronal tissues ) , these mice do not present an informative model for further analysis . likewise ,
the sod1 group did not receive antioxidant treatment , because treatment of sod1 mice ( that may exhibit compensatory changes of other superoxide dismutases or other antioxidant enzymes ) with tempol ( that is a multifunctional antioxidant against different reactive oxygen species ) would not provide any specific information .
we hope that prospective studies using tissue / cell - targeted inducible transgenic lines or locally delivered treatments ( with rgc or glia - targeting vectors ) should help gain detailed information about the immunomodulatory potential of different antioxidants ( and the inflammatory role of different reactive oxygen species ) in glaucoma .
the accumulating evidence of oxidative stress in human glaucoma includes a decreased antioxidant potential in aqueous humor and blood samples of patients with glaucoma .
the blood samples collected from these patients also exhibit elevated levels of oxidative stress end products .
furthermore , recent proteome analysis in the glaucomatous human donor retina has indicated oxidative stress inducing cellular events and increased generation of oxidation - related end products .
more recent proteomics analysis of the ocular hypertensive human retina has also pointed to oxidative stress as a molecular risk factor distressing the physiological equilibrium toward glaucoma development .
similar to clinical or postmortem studies of human glaucoma , experimental glaucoma models exhibit a prominent oxidative stress in the retina and optic nerve , as evidenced by increased free radical production , decreased antioxidant levels , and accumulation of protein oxidation and lipid peroxidation end products .
given the neurodegenerative and neuroinflammatory consequences of oxidative stress in glaucoma , the oxidative stress
, a number of previous studies have indicated that antioxidant treatment can decrease oxidative stress and improve neuron survival in glaucoma .
for example , -luminol treatment has prevented the age - related decreases in glutamate , glutathione , and glutamine synthetase ; -lipoic acid treatment has limited the rgc death and dysfunction ; and coenzyme q10 treatment has inhibited the oxidative stress mediated mitochondrial alterations in dba/2j mice with hereditary glaucoma . in rat glaucoma , treatment with the ginkgo biloba extract ( a nitric oxide scavenger ) , or overexpression of thioredoxins , has protected rgcs , whereas the dietary deficiency of antioxidants predispose to increased rgc loss .
regarding human glaucoma , there are similar reports supporting the protective effects of ginkgo biloba extract in some patients with glaucoma .
a prospective population - based study has also revealed a protective effect of the dietary intake of antioxidant nutrients on human glaucoma . despite the studies focusing on antioxidant treatment effects on neuron survival , only one previous study of glaucoma
has examined the antioxidant treatment responses on inflammatory outcomes , which merely focused on the in vitro analysis of pig trabecular meshwork cells . in primary cultures of trabecular meshwork cells subjected to chronic oxidative stress , chronic administration of the dietary supplement of resveratrol
has prevented the increased production of reactive oxygen species and resulted in a decrease in inflammatory markers , including il-1a , il-6 , il-8 , and elam-1 . in addition , inhibition of oxidative stress by coenzyme q10 has improved the bioenergetic function of cultured optic nerve head astrocytes . as far as we are aware ,
the presented herein is the first study testing the antioxidant treatment effects on inflammatory outcomes of experimental glaucoma .
findings of this study encourage further research to value oxidative stress as an immunomodulatory treatment target to restrain neurodegenerative inflammation , as well as primarily improving the neuron survival .
respecting the widespread aspects of oxidative stress and inflammation through different neuronal compartments in glaucoma , antioxidants can provide a widely useful treatment strategy to protect rgcs and their axons , and also manipulate the inflammatory responses of neighboring glia . | purposebesides primary neurotoxicity , oxidative stress may compromise the glial immune regulation and shift the immune homeostasis toward neurodegenerative inflammation in glaucoma .
we tested this hypothesis through the analysis of neuroinflammatory and neurodegenerative outcomes in mouse glaucoma using two experimental paradigms of decreased or increased oxidative stress.methodsthe first experimental paradigm tested the effects of tempol , a multifunctional antioxidant , given through osmotic mini - pumps for drug delivery by constant infusion . following a 6-week treatment period after microbead / viscoelastic injection - induced ocular hypertension , retina and optic nerve samples were analyzed for markers of oxidative stress and cytokine profiles using specific bioassays .
we also analyzed a redox - sensitive transcriptional regulator of neuroinflammation , namely nf-b .
the second paradigm included a similar analysis of the effects of overloaded oxidative stress on retina and optic nerve inflammation in mice knockout for a major antioxidant enzyme ( sod1/).resultsincreased antioxidant capacity and decreased protein carbonyls and hne adducts with tempol treatment verified the drug delivery and biological function . among a range of cytokines measured , proinflammatory cytokines , including il-1 , il-2 , ifn- , and tnf- , exhibited
more than 2-fold decreased titers in tempol - treated ocular hypertensive eyes .
antioxidant treatment also resulted in a prominent decrease in nf-b activation in the ocular hypertensive retina and optic nerve .
although pharmacological treatment limiting the oxidative stress resulted in decreased neuroinflammation , ocular hypertension
induced neuroinflammatory responses were increased in sod1/ mice with defective antioxidant response.conclusionsthese findings support the oxidative stress related mechanisms of neuroinflammation and the potential of antioxidant treatment as an immunomodulation strategy for neuroprotection in glaucoma . |
mesons with exotic quantum numbers have long been attractive in hadron physics , among which are the @xmath6 isovector states @xmath5 , @xmath4 and @xmath3 identified in the experiments @xcite .
the construction of these states are not quite clear , four - quark states @xcite and hybrid states are most possible explanations
. theoretical studies via different methods have shown that some of these states can be considered as good light hybrid candidates . in the bag model ,
the predicted mass of @xmath0 light hybrid meson is around 1.5gev @xcite ; the mass from the flux tube model is found to be in the range 1.71.9gev @xcite ; the lattice qcd prediction of @xmath0 mass is 1.92.2gev @xcite .
calculations based on qcd sum rules @xcite have been conducted by different groups @xcite to nlo of @xmath7 contributions , and the latest versions of the predicted mass are @xmath8gev in @xcite and @xmath9gev in @xcite . although the hybrid explanation for @xmath4 is supported by previous sum rule analyses , the hybrid assignment of @xmath3 is also proposed @xcite .
thus the calculation of higher power corrections ( hpc ) of the ope is interesting and of value .
how and how much the hpc affect the mass prediction would lead to totally different conclusions . in this paper
, we focus on the mass prediction of the @xmath0 light hybrid meson using qcd sum rule method
. we will first present our calculation of the coefficients of dimension-8 condensates and then include these higher dimensional contributions in the numerical analysis . due to the possible violation of factorization of @xmath10@xmath11 condensates and variation of @xmath2 condensate
, we will consider a conservative range of the mass prediction .
we shall compare the results in d@xmath128 case with those in d@xmath126 case to show the variation of the mass prediction with inclusion of dimension-8 contributions . in order to obtain an objective conclusion
, we shall pay special attention to the fixing of the continuum threshold @xmath13 , which is not rigorously constrained in the original svz sum rules and therefore cause uncertainties . to solve the problem , some authors use the stability criterion to fix @xmath13 @xcite . in this work
, we shall fit the sum rules following the matching procedure introduced by leinweber in @xcite and successfully performed in some other works @xcite , from which the continuum threshold @xmath13 is an output parameter and an uncertainty analysis can be provided . for the explicit consideration of higher power corrections
is not seen very often in previous sum rule calculations , we will give a slightly more detailed presentation of our calculation and analysis .
we start from the two - point correlator @xmath14\right|0\right\rangle \label{eq:1}\\ & = & ( q_{\mu}q_{\nu}-q^{2}g_{\mu\nu})\pi_{v}(q^{2})+q_{\mu}q_{\nu}\pi_{s}(q^{2})\nonumber \end{aligned}\ ] ] where @xmath15 , and the invariants @xmath16 and @xmath17 correspond respectively to @xmath0 and @xmath18 contributions . in this paper , we focus on the dimension-8 corrections to the @xmath0 mass . before showing the higher power results we need to mention that coefficients of dimension-8 quark - related operators of the @xmath0 light hybrid two - point correlator have been calculated in @xcite and @xcite . in @xcite
there is only a factorized form of the total result and a complete result is given in @xcite .
we obtain a new complete result which is consistent with the former factorized form but different from the latter one . as for dimension-8 gluon operators ,
there arise ir divergences in the calculation of the quark loops as the result of setting @xmath20 before calculating the integrals .
these ir divergences can be canceled after taking operator mixing into account .
this process can partly check the calculation about dimension-8 quark and gluon operators and modify the finite part of the coefficients of gluon condensates .
some good examples for the case of @xmath21 scalar and vector currents are given in @xcite .
according to the numbers of quark operators in the condensates , dimension-8 quark condensates can be classified into two groups : two - quark @xmath22 condensates and four - quark @xmath22 condensates .
only the formers can be mixed to @xmath22 gluon condensates in lo .
we use the dimensional regularization in @xmath23 space - time dimensions , thus the @xmath24 terms of the two - quark @xmath22 condensates can be obtained , which are needed to be multiplied by the @xmath25 subtractions to modify the finite part of the quark loop calculations ( see eq . ) .
dimension-8 contributions of gluon condensates come from the calculations of quark loops . here
we give the quark propagator up to term @xmath26 needed in the calculation of the quark loops : @xmath27,\nonumber \end{aligned}\ ] ] where @xmath28 and @xmath29 . for a massless quark eq .
can be rewritten as @xmath30\nonumber \\ & + & \frac{1}{q^{8}}\{-2igq_{\gamma}d_{\gamma}\left(q^{2}\slashed j - q_{\mu}j_{\mu}\slashed q\right)+\left[-4g\left(q_{\gamma}d_{\gamma}\right)^{2 } + gq^{2}d^{2}\right]q_{\alpha}\tilde{g}_{\alpha\beta}\gamma_{\beta}\gamma_{5}+ 2ig\left(q_{\gamma}d_{\gamma}\right)^{2}q_{\alpha}g_{\mu\alpha}\gamma_{\mu}\nonumber \\ & + & 2g^{2}q_{\mu}q_{\alpha}g_{\mu\rho}g_{\alpha\rho}\slashed q+2g^{2}q^{2 } q_{\mu}g_{\alpha\rho}g_{\rho\mu}\gamma_{\alpha}+ig^{2}q^{2}q_{\alpha}\left ( \tilde{g}_{\mu\beta}g_{\alpha\beta}-g_{\mu\beta}\tilde{g}_{\alpha\beta}\right)\gamma_{\mu}\gamma_{5}\},\nonumber \end{aligned}\ ] ] where @xmath31 , @xmath32 .
eq . can also be seen in @xcite and @xcite , but the last term of is missed in @xcite and not consistent with @xcite .
we use rather than in practical calculations for is more convenient in program calculations .
k. a. olive _ et al .
_ [ particle data group collaboration ] , chin . phys .
c * 38 * , 090001 ( 2014 ) .
r. zhang , y. -b .
ding , x. -q .
li and p. r. page , phys .
d * 65 * , 096005 ( 2002 ) [ hep - ph/0111361 ] .
z. f. zhang and h. y. jin , phys .
d * 71 * , 011502 ( 2005 ) [ hep - ph/0412226 ] .
i. j. general , p. wang , s. r. cotanch and f. j. llanes - estrada , phys .
b * 653 * , 216 ( 2007 ) [ arxiv:0707.1286 [ hep - ph ] ] . h. -x
. chen , a. hosaka and s. -l .
zhu , phys .
d * 78 * , 054017 ( 2008 ) [ arxiv:0806.1998 [ hep - ph ] ] .
m. s. chanowitz and s. r. sharpe , nucl .
b * 222 * , 211 ( 1983 ) [ erratum - ibid .
b * 228 * , 588 ( 1983 ) ] ; t. barnes , f. e. close , f. de viron and j. weyers , nucl .
b * 224 * , 241 ( 1983 ) .
n. isgur and j. e. paton , phys .
d * 31 * , 2910 ( 1985 ) ; t. barnes , f. e. close and e. s. swanson , phys . rev .
d * 52 * , 5242 ( 1995 ) [ hep - ph/9501405 ] . c. michael , [ hep - lat/0302001 ] ; c. mcneile _ et al . _ [ ukqcd collaboration ] , phys .
d * 73 * , 074506 ( 2006 ) [ hep - lat/0603007 ] ; j. j. dudek , phys .
d * 84 * , 074023 ( 2011 ) [ arxiv:1106.5515 [ hep - ph ] ] .
m. a. shifman , a. i. vainshtein and v. i. zakharov , nucl .
b * 147 * , 385 ( 1979 ) .
i. i. balitsky , d. diakonov and a. v. yung , phys .
b * 112 * , 71 ( 1982 ) .
j. govaerts , f. de viron , d. gusbin and j. weyers , phys .
b * 128 * , 262 ( 1983 ) .
i. i. balitsky , d. diakonov and a. v. yung , z. phys .
c * 33 * , 265 ( 1986 ) ; j. govaerts , f. de viron , d. gusbin and j. weyers , nucl .
b * 248 * , 1 ( 1984 ) ; j. i. latorre , p. pascual and s. narison , z. phys .
c * 34 * , 347 ( 1987 ) ; j. govaerts , l. j. reinders , p. francken , x. gonze and j. weyers , nucl .
b * 284 * , 674 ( 1987 ) ; s. narison , nucl .
a * 675 * , 54c ( 2000 ) [ hep - ph/9909470 ] ; k. g. chetyrkin and s. narison , phys .
b * 485 * , 145 ( 2000 ) [ hep - ph/0003151 ] .
h. y. jin and j. g. korner , phys .
d * 64 * , 074002 ( 2001 ) [ hep - ph/0003202 ] .
h. y. jin , j. g. korner and t. g. steele , phys .
d * 67 * , 014025 ( 2003 ) [ hep - ph/0211304 ] .
s. narison , phys . lett .
b * 675 * , 319 ( 2009 ) [ arxiv:0903.2266 [ hep - ph ] ] . z. f. zhang , h. y. jin and t. g. steele , chin .
phys . lett .
* 31 * , 051201 ( 2014 ) [ arxiv:1312.5432 [ hep - ph ] ] .
d. b. leinweber , annals phys .
* 254 * , 328 ( 1997 ) [ nucl - th/9510051 ] .
f. x. lee , phys .
c * 57 * , 322 ( 1998 ) [ hep - ph/9707332 ] .
f. x. lee , d. b. leinweber and x. -m .
jin , phys .
d * 55 * , 4066 ( 1997 ) [ nucl - th/9611011 ] .
f. x. lee , phys .
b * 419 * , 14 ( 1998 ) [ hep - ph/9707411 ] .
l. wang and f. x. lee , phys .
d * 78 * , 013003 ( 2008 ) [ arxiv:0804.1779 [ hep - ph ] ] .
d. j. broadhurst and s. c. generalis , phys .
b * 165 * , 175 ( 1985 ) .
a. g. grozin , int .
j. mod .
phys . a * 10 * , 3497 ( 1995 ) [ hep - ph/9412238 ] .
v. a. novikov , m. a. shifman , a. i. vainshtein and v. i. zakharov , fortsch .
* 32 * , 585 ( 1984 ) .
s. narison , phys .
b * 624 * , 223 ( 2005 ) [ hep - ph/0412152 ] .
r. a. bertlmann , g. launer and e. de rafael , nucl .
b * 250 * , 61 ( 1985 ) .
v. a. novikov , m. a. shifman , a. i. vainshtein , m. b. voloshin and v. i. zakharov , nucl .
b * 237 * , 525 ( 1984 ) .
e. bagan , j. i. latorre , p. pascual and r. tarrach , nucl .
b * 254 * , 555 ( 1985 ) .
s. n. nikolaev and a. v. radyushkin , phys .
b * 124 * , 243 ( 1983 ) .
s. narison , phys .
b * 706 * , 412 ( 2012 ) [ arxiv:1105.2922 [ hep - ph ] ] ; s. narison , phys .
b * 707 * , 259 ( 2012 ) [ arxiv:1105.5070 [ hep - ph ] ] .
s. narison , arxiv:1409.8148 .
v. a. novikov , m. a. shifman , a. i. vainshtein and v. i. zakharov , nucl .
b * 191 * , 301 ( 1981 ) .
m. delia , a. di giacomo and e. meggiolaro , phys .
b * 408 * , 315 ( 1997 ) [ hep - lat/9705032 ] .
s. narison and e. de rafael , phys .
b * 103 * , 57 ( 1981 ) . | we calculate the coefficients of the dimension-8 quark and gluon condensates in the current - current correlator of @xmath0 light hybrid current @xmath1 . with inclusion of these higher - power corrections and updating the input parameters ,
we re - analyze the mass of the @xmath0 light hybrid meson from monte - carlo based qcd sum rules .
considering the possible violation of factorization of higher dimensional condensates and variation of @xmath2 , we obtain a conservative mass range 1.722.60gev , which favors @xmath3 as a better hybrid candidate compared with @xmath4 and @xmath5 . |
during the transpetrosal - presigmoid approach , accurate determination of the surface projection of the anterosuperior point of the transverse - sigmoid sinus junction ( asts ) is particularly important when trying to expose sigmoid sinus safely .
traditionally , neurosurgeons have regarded the squamosal - parietomastoid suture junction ( sp ) as the classic landmark to determine the asts .
however , the cranial sutures of some patients , especially the elderly , have been reported to be not obviously recognizable and palpable in craniotomy .
therefore , a more reliable as well as practical method for locating the asts precisely is needed .
recently , we proposed a reference coordinate system that was established on the lateral skull surface based on several conspicuous osseous landmarks . using this coordinate system
, we statistically analyzed the coordinates of the inferomedial point of the transverse - sigmoid sinus junction ( imts ) of forty adult skull samples .
this study aimed to use our coordinate system to analyze the distribution characteristics of the asts to explore whether the location of the asts can be estimated accurately using this system .
another aim was to compare the location of the asts with that of the sp to learn more about the differences in location between these two points .
this study was approved by the internal review board of xian jiaotong university ( no .
forty dried human adult skulls , which had clearly identifiable osseous grooves of the transverse and sigmoid sinuses and the point of the sp , were provided by the department of anatomy of medical college of xian jiaotong university .
a flexible rule was used to measure the skull circumference , which circles the outer surface of the skull through the intercilium anteriorly and the external occipital protuberance posteriorly .
the transverse - sigmoid sinus junction was defined as the transitional zone where the transverse sinus ended by the vertical descending segment of the sigmoid sinus viewed from the inside of the cranium .
thus , the asts was identified as the anterosuperior point of the junction . to project the asts to the outer surface of the skull
precisely , a vernier caliper was modified by extending the outer measuring claws to form two l - shaped arms .
the two tips of the arms correspond with each other and can remain aligned when one arm is moved away from the other arm [ figure 1 ] . when the tip of one arm was located at the asts on the inner side of the cranium , the other arm could be moved to touch the outer surface of the skull and thereby point out the corresponding site of the asts on the outer skull surface correctly [ figures 2 and 3 ] .
the two tips of the arms correspond with each other and can continue working in a line when one is moved away from the other .
ts : transverse sinus ; ss : sigmoid sinus ; asts : anterosuperior point of the transverse - sigmoid sinus junction .
after the tip of arm a was pointed at the asts on the inner side of the cranium , the tip of arm b was moved in an orthogonal direction and touched to the outer surface of the skull .
the tip of arm b pointed out the corresponding site ( open circle ) of the asts on the outer surface precisely .
therefore , we defined the junction of the squamosal suture with the extension line of the main stem of the parietomastoid suture as the sp [ figure 4 ] . a left lateral side of skull sample .
the sp ( yellow dot ) is defined as the junction of the squamosal suture with the extension line ( white broken line ) of the main stem of the parietomastoid suture .
main stem of the parietomastoid suture ; superior branch ; inferior branch ; lambdoid suture ; occipitomastoid suture ; eam : external acoustic meatus ; sp : squamosal - parietomastoid suture junction . on the lateral surface of the skull ,
a rectangular coordinate system was established by a horizontal line ( x - axis ) and a vertical line ( y - axis ) .
the x - axis was defined by points a and b. point a was located where the upper edge of the zygomatic arch ( ueza ) joins anteriorly to the frontal process of the zygomatic bone ( fpz ) , and point b was located where the ueza blends posteriorly into the supramastoid crest ( smc ) .
the y - axis was defined by a line through the tip of the mastoid and perpendicular to the x - axis . where the axes crossed ,
the origin was noted by o [ figure 5 ] . on the x - axis ,
the anterior side ( frontal side ) of the origin was defined as negative while the posterior side ( occipital side ) was defined as positive .
on the y - axis , the upper side ( rostral side ) of the origin was defined as positive and the lower side ( caudal side ) was defined as negative .
therefore , the x and y coordinates of the asts , which represented the distances from the points to the y and x axes , respectively , could be measured by a vernier caliper in this coordinate system .
the x - axis is established by the horizontal line connecting points a and b , which are located where the upper edge of the za joins anteriorly to the fpz and blends posteriorly into the smc , respectively .
the y - axis is defined by a line through the tip of the mastoid ( point c ) and perpendicular to the x - axis .
the crossing of the axes , the origin , is noted as o. fpz : frontal process of the zygomatic bone ; za : zygomatic arch ; smc : supramastoid crest ; asts ( red dot ) : anterosuperior point of the transverse - sigmoid sinus junction ; sp ( yellow triangle ) : squamosal - parietomastoid suture junction ; squamosal suture ; parietomastoid suture .
one - way analysis of variance for repeated measures was used to evaluate the differences between genders and sides .
the paired t - test was used to compare the differences between asts and sp in x and y. statistical analyses were performed with sas software version 9.2 ( sas institute inc . ,
this study was approved by the internal review board of xian jiaotong university ( no .
forty dried human adult skulls , which had clearly identifiable osseous grooves of the transverse and sigmoid sinuses and the point of the sp , were provided by the department of anatomy of medical college of xian jiaotong university .
a flexible rule was used to measure the skull circumference , which circles the outer surface of the skull through the intercilium anteriorly and the external occipital protuberance posteriorly .
the transverse - sigmoid sinus junction was defined as the transitional zone where the transverse sinus ended by the vertical descending segment of the sigmoid sinus viewed from the inside of the cranium .
thus , the asts was identified as the anterosuperior point of the junction . to project the asts to the outer surface of the skull
precisely , a vernier caliper was modified by extending the outer measuring claws to form two l - shaped arms .
the two tips of the arms correspond with each other and can remain aligned when one arm is moved away from the other arm [ figure 1 ] . when the tip of one arm was located at the asts on the inner side of the cranium , the other arm could be moved to touch the outer surface of the skull and thereby point out the corresponding site of the asts on the outer skull surface correctly [ figures 2 and 3 ] .
the two tips of the arms correspond with each other and can continue working in a line when one is moved away from the other .
ts : transverse sinus ; ss : sigmoid sinus ; asts : anterosuperior point of the transverse - sigmoid sinus junction .
after the tip of arm a was pointed at the asts on the inner side of the cranium , the tip of arm b was moved in an orthogonal direction and touched to the outer surface of the skull .
the tip of arm b pointed out the corresponding site ( open circle ) of the asts on the outer surface precisely .
therefore , we defined the junction of the squamosal suture with the extension line of the main stem of the parietomastoid suture as the sp [ figure 4 ] . a left lateral side of skull sample .
the sp ( yellow dot ) is defined as the junction of the squamosal suture with the extension line ( white broken line ) of the main stem of the parietomastoid suture .
main stem of the parietomastoid suture ; superior branch ; inferior branch ; lambdoid suture ; occipitomastoid suture ; eam : external acoustic meatus ; sp : squamosal - parietomastoid suture junction .
on the lateral surface of the skull , a rectangular coordinate system was established by a horizontal line ( x - axis ) and a vertical line ( y - axis ) .
the x - axis was defined by points a and b. point a was located where the upper edge of the zygomatic arch ( ueza ) joins anteriorly to the frontal process of the zygomatic bone ( fpz ) , and point b was located where the ueza blends posteriorly into the supramastoid crest ( smc ) .
the y - axis was defined by a line through the tip of the mastoid and perpendicular to the x - axis . where the axes crossed ,
the origin was noted by o [ figure 5 ] . on the x - axis ,
the anterior side ( frontal side ) of the origin was defined as negative while the posterior side ( occipital side ) was defined as positive . on the y - axis , the upper side ( rostral side ) of the origin
was defined as positive and the lower side ( caudal side ) was defined as negative .
therefore , the x and y coordinates of the asts , which represented the distances from the points to the y and x axes , respectively , could be measured by a vernier caliper in this coordinate system .
the x - axis is established by the horizontal line connecting points a and b , which are located where the upper edge of the za joins anteriorly to the fpz and blends posteriorly into the smc , respectively .
the y - axis is defined by a line through the tip of the mastoid ( point c ) and perpendicular to the x - axis .
the crossing of the axes , the origin , is noted as o. fpz : frontal process of the zygomatic bone ; za : zygomatic arch ; smc : supramastoid crest ; asts ( red dot ) : anterosuperior point of the transverse - sigmoid sinus junction ; sp ( yellow triangle ) : squamosal - parietomastoid suture junction ; squamosal suture ; parietomastoid suture .
one - way analysis of variance for repeated measures was used to evaluate the differences between genders and sides .
the paired t - test was used to compare the differences between asts and sp in x and y. statistical analyses were performed with sas software version 9.2 ( sas institute inc . ,
the mean circumference of male skulls was 49.85 1.29 cm , and the mean circumference of the female skulls was 49.27 1.24 cm . for asts - x
, a significant difference was found between the left and right sides ( p = 0.020 ) , but not between males and females ( p = 0.221 ) , and the interaction of gender and side was not significant ( p = 0.245 ) .
the mean asts - x was significantly higher on the right side compared with the left side in males ( 17.59 3.46 mm vs. 15.33 2.78 mm , t = 2.49 , p = 0.017 ) , but there was no significant difference between right and left sides in females .
for asts - y , there were no significant differences between males and females ( p = 0.763 ) and left and right sides ( p = 0.932 ) and the interaction of gender and side was not significant ( p = 0.522 ) [ table 1 ] . comparisons between genders and sides for the asts in this study ( mm ) asts : anterosuperior point of the transverse - sigmoid sinus junction .
on the 80 skull sides , 11 ( 13.8% ) parietomastoid sutures bifurcated into two branches before they joined to the squamosal sutures .
for the left and right sides combined , the mean atst - x and atst - y were significantly higher than the mean sp - x and sp - y , respectively ( x : 16.05 3.32 mm vs. 14.7 3.16 mm , t = 3.09 p = 0.003 ; y : 7.6 2.47 mm vs. 6.65 2.53 mm , t = 2.61 , p = 0.011 ) .
for the left side , the mean atst - y was significantly higher than the mean sp - y ( 7.59 2.41 mm vs. 6.49 2.45 mm , t = 2.12 , p = 0.041 ) , but there was no significant difference between the mean atst - x and mean sp - x .
for the right side , the mean atst - x was significantly higher than the mean sp - x ( 16.79 3.59 mm vs. 15 2.76 mm , t = 2.95 , p = 0.005 ) , but there was no significant difference between the mean atst - y and mean sp - y [ table 2 ] .
comparisons between the asts and sp in this study ( mm ) difference represented the mean of difference between the asts and sp ( astssp ) .
asts : anterosuperior point of the transverse - sigmoid sinus junction ; sp : squamosal - parietomastoid suture junction .
the mean circumference of male skulls was 49.85 1.29 cm , and the mean circumference of the female skulls was 49.27 1.24 cm .
for asts - x , a significant difference was found between the left and right sides ( p = 0.020 ) , but not between males and females ( p = 0.221 ) , and the interaction of gender and side was not significant ( p = 0.245 ) .
the mean asts - x was significantly higher on the right side compared with the left side in males ( 17.59 3.46 mm vs. 15.33 2.78 mm , t = 2.49 , p = 0.017 ) , but there was no significant difference between right and left sides in females .
for asts - y , there were no significant differences between males and females ( p = 0.763 ) and left and right sides ( p = 0.932 ) and the interaction of gender and side was not significant ( p = 0.522 ) [ table 1 ] .
comparisons between genders and sides for the asts in this study ( mm ) asts : anterosuperior point of the transverse - sigmoid sinus junction .
on the 80 skull sides , 11 ( 13.8% ) parietomastoid sutures bifurcated into two branches before they joined to the squamosal sutures . for the left and right sides combined ,
the mean atst - x and atst - y were significantly higher than the mean sp - x and sp - y , respectively ( x : 16.05 3.32 mm vs. 14.7 3.16 mm , t = 3.09 p = 0.003 ; y : 7.6 2.47 mm vs. 6.65 2.53 mm , t = 2.61 , p = 0.011 ) .
for the left side , the mean atst - y was significantly higher than the mean sp - y ( 7.59 2.41 mm vs. 6.49 2.45 mm , t = 2.12 , p = 0.041 ) , but there was no significant difference between the mean atst - x and mean sp - x .
for the right side , the mean atst - x was significantly higher than the mean sp - x ( 16.79 3.59 mm vs. 15 2.76 mm , t = 2.95 , p = 0.005 ) , but there was no significant difference between the mean atst - y and mean sp - y [ table 2 ] .
comparisons between the asts and sp in this study ( mm ) difference represented the mean of difference between the asts and sp ( astssp ) .
asts : anterosuperior point of the transverse - sigmoid sinus junction ; sp : squamosal - parietomastoid suture junction .
the transpetrosal - presigmoid approach provides an excellent corridor for neurosurgeons to deal with the petroclival lesions . in such surgical procedure ,
exposure of the sigmoid sinus from the transverse - sigmoid sinus junction to the jugular bulb remains an essential and hazardous step .
many experts have described their techniques to expose the sigmoid sinus safely without extensive bony defect . in such procedures ,
goto et al . introduced a surgical skill for safely and simply exposing the sigmoid sinus .
the authors used four key holes , including the lateral end of the transverse sinus , asts , mastoid emissary foramen , and midpoint of the transverse sinus , for guidance to complete the exposure of the sigmoid sinus .
jia et al . recommended a two - bone flap craniotomy for the transpetrosal - presigmoid approach to avoid bony defect in the periauricular area , and the first bone flap should distinctly expose the asts to facilitate dissection of the sigmoid sinus away from the inner table of the mastoid bone . in the present study , we found two more factors that would attenuate the accuracy and practicability of using sp to locate the asts . first , about 14% of the parietomastoid sutures separated into two branches before concatenating squamosal sutures , leading to an uncertainty of confirming the definite sp . second , according to the results , there were significant differences between asts and sp both in asts - x and asts - y ( p = 0.003 and p = 0.011 , respectively ) . that means sp can not represent the location of the asts precisely .
hence , it will be difficult to utilize the sp for localization of the asts accurately and universally .
some neurosurgeons preferred to use image - guided surgical planning to complete localization . those methods , including neuronavigation and others based on three - dimensional volume rendering ( 3d vr ) technique , can yield morphometric data in individual patients and overcome extreme individual variations
when neuronavigation is used , the patient should undergo high - resolution computed tomography or magnetic resonance imaging scans in combination with sinuses angiography for 3d vr of the cranial bone and the dural vasculature at the same time .
hence , it is still worth exploring an easy , quick , practical , and low - cost method for locating the sinuses precisely .
recommended using easily palpable skull landmarks ( such as zygomatic root , inion , and mastoid process ) , not cranial sutures , to identify the locations of the transverse and sigmoid sinuses .
the authors measured the distances between the three landmarks and the midpoints , and the shortest distances of the midpoints to the border of the groove for sigmoid and transverse sinuses .
moreover , the authors considered the data of the measurement could be used to avoid venous injury during posterior fossa approaches . in our previous study
, we used a rectangle coordinate system on the lateral surface of the cranium to locate the imts .
the results showed that the positioning system was a reliable and practical method for identifying the imts precisely .
moreover , it had two advantages : first , the coordinate system could be defined easily during the operation because the scalp covering the zygomatic arch , fpz , smc , and the mastoid is thin enough to palpate points a , b , and c ; second , this positioning system does not need recognition of the cranial sutures ( the lambdoidal , squamosal , and parietomastoid sutures ) which should be identified for using the traditional method to locate the imts . in the present study
, we continued to take the advantages of the coordinate system for localization of the asts . according to the results , the sds of the data were less than 4 mm .
the mean distance from the asts to the y - axis ( mean asts - x measurement ) was statistically larger on the right side versus the left side , and there was no significant difference between genders .
with regard to the mean distance from the asts to the x - axis ( mean asts - y measurement ) , there was no significant difference between genders or skull sides .
it was noteworthy that there were no interaction effects among gender and skull side for either asts - x or asts - y which meant that in this system , gender and skull side do not influence each other in localization of the asts .
in previous studies , the calibers of the transverse and sigmoid sinuses were slightly larger on the right side than left side .
the nature of the sinuses may be why the imts was located more closely to the y - axis on the right side . in the present study ,
however , the asts was closer to the y - axis on the left side than the right side . in the application of this coordinate system during the presigmoid approach , we recommended that the x - axis and y - axis should be outlined and the site of the asts should be marked on the scalp according to the data shown in table 1 before disinfection and draping of the operation area . in males on the left side ,
the asts was located approximately 15.33 mm posterior to y - axis and 7.52 mm above x - axis while on the right side , it was 17.59 mm posterior to y - axis and 7.80 mm above x - axis . in females ,
the asts was located approximately 15.29 mm posterior to y - axis and 7.65 mm above x - axis on the left side , and 16.07 mm posterior to y - axis and 7.43 mm above x - axis on the right side .
after scalp incision , the asts should be marked on the bone immediately for drilling the key hole .
because the sinuses are occasionally embedded in and adherent to the bony groove , we advised that the center of the strategic burr hole should be placed a little further away in anterosuperior direction from the asts to increase the security .
one of the limitations of this study was that since only adult skulls were used , the results may only be applied to adults .
another limitation was that sometimes , there is a high degree of individual variation in the relationship between surface landmarks and the sinuses , which will decrease the accuracy of the locating and increase the risk of sinus injury .
therefore , if possible , surgeons should utilize image - guided surgical planning technology , such as neuronavigation and other methods based on the 3d vr technique , to obtain individual morphometric data for overcoming extreme variations . in conclusion
, the craniometric measurements and statistical analyses of this study showed that our coordinate system was an accurate and practical method for identifying the asts .
the sp , which has been classically used to locate the venous junction , might be difficult to find during presigmoid craniotomy and is not always a reliable landmark for defining the asts .
this study was supported by the grant from xian science and technology program ( sf1515 - 1 ) .
this study was supported by the grant from xian science and technology program ( sf1515 - 1 ) .
| background : during craniotomies using the transpetrosal - presigmoid approach , exposure of the sigmoid sinus remains an essential but hazardous step .
in such procedures , accurate localization of the anterosuperior point of the transverse - sigmoid sinus junction ( asts ) is very important for reducing surgical morbidity .
this study aimed to create an accurate and practical method for identifying the asts.methods:on the lateral surfaces of 40 adult skulls ( 19 male skulls and 21 female skulls ) , a rectangular coordinate system was defined to measure the x and y coordinates of two points : the asts and the squamosal - parietomastoid suture junction ( sp ) . with the coordinate system ,
the distribution characteristics of the asts were statistically analyzed and the differences between the asts and sp were investigated.results:for asts - x , significant differences were found in different sides ( p = 0.020 ) ; the asts - x in male skulls was significantly higher on the right side ( p = 0.017 ) ; there was no significant difference between the sides in female skulls .
there were no significant differences in gender or interaction of gender and side for asts - x , and for asts - y , there were no significant differences in side , gender , or interaction of gender and side .
for both sides combined , the mean asts - x was significantly higher than the mean sp - x ( p = 0.003 ) and the mean asts - y was significantly higher than the mean sp - y ( p = 0.011).conclusions : this reference coordinate system may be an accurate and practical method for identifying the asts during presigmoid craniotomy .
the sp might be difficult to find during presigmoid craniotomy and , therefore , it is not always a reliable landmark for defining the asts . |
p53 is a tumor suppressor that is upregulated and activated across organ systems as a tissue protective stress response mechanism .
in contrast to p53 , both p63 and p73 exhibit cell - type - specific expression patterns and exert tissue - specific functions [ 2 , 3 ] .
relevant to this review , p63 plays an essential role in the development and maintenance of normal stratified squamous epithelium .
all p53 family members encode multiple protein isoforms that act in overlapping or opposing manners both within and across family members . given the complexity of the p53 family and the potential for the different family members to mimic or interfere with each other , the balance of p53 family isoforms in a given cellular context can impact the biological outcome . in this review , we highlight how information derived from mouse models has provided insight into molecular mechanisms of normal keratinocyte growth regulation and human cancer pathogenesis .
in particular , we focus on the p63 gene , the role of its gene products in normal epidermal development and homeostasis , and how dysregulation of p63 protein expression , which is tightly controlled under normal conditions , contributes to squamous carcinogenesis , not only of the skin , but also in other squamous epithelial cancers such as those of the head and neck .
members of the p53 family were identified based on shared homology within their major functional domains : transactivation ( ta ) , dna binding ( dbd ) , and oligomerization ( od ) ; and exist as multiple protein isoforms due to a combination of alternate promoter usage and alternative splicing [ 4 , 5 ] .
use of alternative promoters gives rise to isoforms of two classes : ta and n .
the tap63 and tap73 isoforms possess a transactivation domain with homology and function similar to that of p53 , while the np63 and np73 isoforms lack this domain and can act to block tap53- , tap63- , and tap73-mediated transcription via the mechanisms discussed below .
however , this does not imply that np63 isoforms lack transcriptional activation activity as alternate transactivation domains have been described both within the n - terminus of the np63 isoforms [ 6 , 7 ] and in exons 11 and 12 of the c - terminus ( transactivation domain 2 ( ta2 ) ) .
further analysis has suggested that the second region is unlikely to be an independent activation domain .
refined mapping studies indicate that this domain instead serves to modulate transcriptional activities associated with np63 isoforms .
correspondingly , many positive transcriptional targets of np63 have been identified , which are discussed in this review .
all ta and np63 isoforms contain the dbd and od domains but differ at the c - termini .
this additional complexity is conferred on these proteins due to c - terminal alternative splicing , which in the case of p63 gives rise to ta and n subclasses of p63 , , , , and isoforms [ 4 , 9 ] ( figure 1 ) . of these isoforms , is the longest and contains a sterile alpha motif ( sam ) protein - protein interaction domain and a transcriptional inhibition domain ( tid ) .
the tid comprises 2 subdomains , one of which binds and masks the ta domain of tap63 and the other , which is subject to sumoylation resulting in decreased intracellular p63 concentration and correspondingly to decreased activity [ 1113 ] .
degradation of p63 is also promoted by the e3 ubiquitin ligase itch via ubiquitylation at the n - terminal border of the sam domain of the p63 isoforms .
regarding the other p63 c - terminal splice variants , exon 13 is spliced out of the -isoform , which thus also lacks the sam and tid domains .
both the and isoforms of p63 contain a phosphodegron motif utilized by fbw7 e3 ubiquitin ligase in mdm2-mediated degradation .
the , , and isoforms all truncate shortly after the oligomerization domain , with each containing a unique c - terminal sequence .
thus , all three isoforms lack the sam and tid domains ( figure 1 ) . like p53 ,
the oligomerization domains of p63 and p73 , due to the presence of an additional -helix , are more similar to one another than to that of p53 .
p63 and p73 were not observed to interact with p53 through their oligomerization domains but strongly interact with one another through this domain , with the p63/p73 heterotetramers exhibiting enhanced stability over homotetramers .
while p53 does not interact with p63/p73 through the oligomerization domain , wtp53 has been shown to target np63 for caspase - mediated degradation via interactions between the dna binding domain of each protein , and mutated p53 has been shown to interact with the core dna binding domains of p63 and p73 , thereby impairing dna binding and transactivation .
dna binding is an area in which p53 family members can mimic or compete with each other .
while p63 has been shown to bind to p53 responsive consensus sequences , distinct p63 responsive elements have also been identified [ 1921 ] .
it has been reported that the global dna binding pattern of p73 does not differ from that of p63 , but intensity of binding at given sites does vary depending on the cell type profiled .
this suggests that competition between the homo- and heterotetramers of different isoforms of p63 and p73 , which are subject to cellular context , may define site occupancy . beyond interactions with one another via their oligomerization domains or their dna binding domains , and their competition at dna response elements , p53 family members have been shown to be involved in feedback loops with one another that impact expression levels [ 23 , 24 ] .
thus , at many levels dysregultion of any one family member may impact the fine balance that is involved in maintaining normal epidermal homeostasis .
p63 is critical for normal epidermal morphogenesis [ 3 , 25 ] . in the mature epidermis ,
the predominant p63 isoform expressed is np63 , and expression of this isoform is associated with the proliferative compartment .
however , it is also the np63 isoform that is overexpressed in many squamous cell cancers . as a starting point to understand how overexpression of a single isoform with ensuing disruption of the balance of p53 family members might contribute to squamous cancer pathogenesis , it is important to first understand the role of p63 both in normal epidermal morphogenesis and in homeostasis of the mature epidermis .
the criticality of p63 to normal epidermal development was highlighted by simultaneously published mouse models lacking functional p63 [ 3 , 25 ] .
the mice were developed using distinct molecular strategies and upon gross phenotypic examination appeared similar ; however , in - depth analysis of the epidermal phenotype gave rise to alternate hypotheses as to the role of p63 in epidermal development : epidermal progenitor cell maintenance versus commitment to stratification .
in the mice developed by yang et al . , exons 68 corresponding to p63 's dbd were replaced with the neomycin resistance gene . in these mice , patches of disorganized epithelial cells
positive for late markers of keratinocyte differentiation and negative for keratin 5 were evident , suggestive of a role for p63 in maintaining epidermal progenitor cells .
mice generated by mills et al . were derived using an insertional gap repair mechanism .
two strains generated by this approach , brdm1 ( truncating within exon 6 ) and brdm2 ( truncating after exon 10 ) , appeared macroscopically identical , and thus , the strains were not distinguished in subsequent experiments in the seminal paper .
microscopic analysis of these mice revealed a layer of flattened cells expressing keratin 14 at low levels with no evidence of stratification or differentiation marker expression , suggestive of a failure to commit to a stratified epidermis .
while no mrna transcripts were detected from these mice by northern blotting , the transcript in the brdm2 mouse model , which truncates after exon 10 , could in theory give rise to shortened np63 transcripts , similar to those described by mangiulli et al . .
a recent recharacterization of a line of brdm2 mice by wolff et al . revealed patches of keratinizing epidermis expressing truncated p63 at levels similar to wild type with stratification overlaying hair follicles .
based on further studies in embryos , the authors proposed these patches to be remnants of a more developed e15 epidermis 35 layers thick containing terminally differentiated epithelium that was transient in nature due to mechanical stress at birth , and suggested that the brdm2 mice were equivalent to p63/ knockout mice .
this observation and ensuing studies generated much controversy , as to whether the recharacterized mice were the same as those used by others or if perhaps a spontaneous genetic event might be at play [ 2933 ] , which to date remains unresolved .
studies of the p63-deficient mouse lines provided strong evidence for the critical nature of the p63 gene ; however , interpretation of p63 function is confounded by the existence of multiple p63 protein isoforms .
therefore , single isoform knock - in mouse models have been developed on a p63 null background to elucidate the role of specific p63 isoforms .
reconstitution of different p63 isoforms in the brdm2 mice using tissue - specific inducible mouse models generated by separate groups gave rise to opposing conclusions as to the role of np63 in initiating stratification of simple epithelium [ 34 , 35 ] . in one model , tap63 , but not np63 , was found to drive stratification and keratin 5/keratin 14 expression of the simple lung epithelium , while in the other model , np63 or np63 caused stratification and keratin 5/keratin 14 expression in the simple lung epithelium . with respect to the epidermis
, differential results were also obtained by these two groups . in the first model ,
keratin 14-driven expression of tap63 resulted in a severely hyperplastic epidermis exhibiting delayed differentiation , and based on their data the authors concluded that tap63 is the initiating switch for epidermal stratification .
in contrast , in the second model , expression of np63 or np63 under the control of the keratin 5 promoter did not result in complete restoration of epithelial integrity , but it did result in several areas of stratified epidermis , which expressed differentiation markers , indicating that the np63 and np63 can act to initiate stratification .
further support for np63 as an initiator of stratification comes from other genetic complementation studies in which np63 or tap63 , both under the keratin 5 promoter , was introduced into the p63(/ ) mice from yang et al .
[ 3 , 36 ] . in these studies , np63 was able to partially restore the epidermal basal layer , but not differentiation marker expression , whereas tap63 reconstitution resulted in a phenotype similar to p63(/ ) mice .
reconstitution of a combination of np63 and tap63 resulted in a more complete epidermis formation containing patches with a more organized structure that expressed markers of differentiation .
it is possible that differences with respect to the differentiation status of the epidermis generated by reconstitution of np63 in the later two studies could be due to the mouse model used , but in contrast to the first model discussed , partial epidermal restoration by np63 is a common feature of both .
finally , subclass - specific knockout mice have been developed as a means of exploring functions attributable to the tap63 or np63 subclasses in the presence of wild - type expression levels of the opposing subclass .
germline ablation of tap63 did not impact normal epidermal morphogenesis in the presence of np63 isoforms .
in contrast , mice in which n exon was replaced with gfp appeared phenotypically similar to p63(/ ) mice , and , like the p63(/ ) mice generated by yang et al . , retained only disorganized patches of keratinocytes expressing terminal markers of differentiation . however , in contrast to the mice generated by yang et al .
furthermore , expression of the basal transcription factor ap-2 indicated that in the absence of np63 , basal patches can form , but these were observed to have decreased ki67 staining . taken together ,
this is suggestive of a role for np63 during epidermal morphogenesis in both progenitor cell maintenance and in epidermal commitment , closing the gap between the original interpretations of the pan - p63 mouse models . in humans ,
heterozygous mutations in p63 are linked to genetic syndromes that include ectodermal dysplasia as part of the disease phenotype .
distinct phenotypes are associated with mutations in specific p63 domains , providing clues to structure / function relationships .
for example , ankyloblepharon - ectodermal defects - cleft lip / palate ( aec ) syndrome is associated with mutations in the sam domain , while ectodermal dysplasia and cleft / lip palate ( eec ) syndrome is associated with mutations within the dbd [ 41 , 42 ] .
of the syndromes , skin involvement is most pronounced and severe in aec , which is linked to missense mutations in the sam domain [ 40 , 43 ] and therefore implicates the isoforms . unlike normal skin where np63 expression is associated with the basal proliferative compartment , in aec patient skin samples
, nuclear p63 expression extends beyond the basal layer to the terminally differentiating cells and is accompanied by coexpression of differentiation markers . in vitro studies have shown that sam domain mutations , as seen in aec , block interaction between p63 and mrna splicing / processing proteins critical to direct splicing of fgfr-2 to the isoform required for normal epithelial differentiation .
characterization of the aec l514f np63 mutant in stable cell lines revealed that activation of a cryptic splice site due to loss of these interactions resulted in production of a c - terminally truncated form of np63 exclusively located in the nucleus and resistant to proteosome degradation .
mouse models have helped to further define the contribution of this genetic alteration to the phenotype of this syndrome .
a knock - in mouse model developed for the l514f mutation recapitulates the expected aec phenotype including hypoplastic and fragile skin with a transient reduction in proliferation during embryonic development .
skin fragility in these mice , and in humans with aec syndrome , was associated with altered desmosome gene expression mediated by mutant p63 . to gain insight into further pathways impacted , intact and eroded aec syndrome skin and normal skin
the findings revealed changes in expression of genes associated with epidermal adhesion , skin barrier formation , and hair follicle biology , all consistent with the clinical presentation .
thus , sam domain mutations highlight the importance of p63 and in particular np63 to normal epidermal morphogenesis / homeostasis .
maintenance of normal epidermal homeostasis involves mediation of processes including proliferation , differentiation , stem cell maintenance , senescence , viability , and cell adhesion .
evidence suggests that each of these is impacted by p63 protein expression ( figure 2 ) . in vivo , in the adult human epidermis ,
p63 is highly expressed in the basal cells with proliferative potential and is downregulated in the suprabasal layers . in vitro depletion of p63 in human
these effects were found to be mainly due to the np63 isoform . in a mouse model ,
specific knockdown of np63 in the mature epidermis resulted in severe skin fragility with erosion .
a multitude of studies , primarily in vitro , focused on the downstream targets mediated by np63 have shed light on the network of target genes implicated in these np63-mediated biological processes . while an extensive cataloguing of all of these studies is beyond the scope of this review , some of these studies , with a focus on those performed in keratinocytes ,
are discussed here to highlight the potential impact of dysregulated np63 on signaling pathways that may be assessed using mouse models of the skin .
numerous examples serve to illustrate how perturbation of np63 expression could result in altered biological outcome . in vitro , in developmentally mature murine keratinocytes , we and others demonstrated that np63 is associated with maintenance of proliferative capacity [ 4953 ] .
mimicking overexpression of np63 seen in squamous cell carcinomas blocks the normal growth arrest and induction of the cyclin - dependent kinase inhibitor p21 in response to elevated ca conditions [ 50 , 51 ] and correspondingly suppresses the differentiation markers keratin 10 and filaggrin , but not keratin 1 . the -tail of np63 is required for its suppressive effect on differentiation but not for the aberrant growth arrest response , which may be mediated at least in part by transcriptional repression of p21 by binding of np63 to its promoter .
regulation of p21 is further impacted by crosstalk between p63 and notch 1 , whereby notch 1 is negatively regulated by np63 in cells of high renewal potential but synergizes with np63 during early differentiation to induce keratin 1 .
subsequently , notch 1 downregulates np63 to permit the expression of the late differentiation marker involucrin .
this context - dependent crosstalk is implicated in maintaining the balance between keratinocyte growth arrest and differentiation .
in addition to the factors regulating p21 described above , a balance exists between np63 and many other target genes involved in proliferation and differentiation that are critical for maintenance of or for the switch between the states .
for example , the cell cycle inhibitor pten is negatively regulated by np63. depletion of either np63 or pten alone had opposite effects on colony growth in colony forming assays , but depletion of both np63 and pten at the same time had no impact , implying the balance between the two is critical to biological outcome .
another example focuses on the epidermis of mice with mutant irf6 , which is hyperproliferative and fails to undergo differentiation .
this has been attributed to a failure of a feedback loop with np63 that controls np63 expression , thereby regulating the switch between proliferation and differentiation . in this feedback loop
, irf6 is a direct transcriptional target of np63 , which when upregulated induced proteasome - mediated degradation of np63 allowing for keratinocytes to exit the cell cycle .
in addition to regulation of levels of np63 impacting biological outcome as exemplified by the previous two examples , runx1 , a transcription factor involved both in keratinocyte proliferation and differentiation , is directly differentially regulated by np63 in proliferating versus differentiating keratinocytes by binding to distinct dna binding sites on the runx1 promoter .
this represents a different mechanism of regulation , however , one that also could be perturbed by altered expression of np63. the mouse models described in section 3.1.1 support a role for np63 not only in the maintenance of epidermal progenitor cells , but also , in the commitment to stratification . at a molecular level
, np63 synergizes with notch 1 to induce keratin 1 expression during differentiation , and the np63 target gene ikk is necessary for epidermal differentiation [ 54 , 5963 ]
. however , overexpression of np63 in primary murine keratinocyte cultures blocks expression of keratin 10 and filaggrin , but not keratin 1 implying that a fine balance in levels of np63 is required for complete differentiation .
some examples of transcription factors which based on in vitro studies are thought to interplay with np63 during differentiation follow .
basally expressed keratin 14 is a known direct transcriptional target of np63 . the transcription factor skn1a ( oct11 ) blocks np63 induction of the keratin 14 promoter and promotes keratin 10 upregulation .
there is also evidence for np63 both blocking and inducing transcription factors that promote differentiation in a cell - context - dependent manner .
for instance , np63 directly represses high - mobility group box protein 1 ( hbp1 ) , a transcription factor necessary for stratification of organotypic cultures .
in contrast , in differentiating keratinocytes np63 induces znf750 , a transcription factor that is required for terminal epidermal differentiation .
interestingly , znf750 is bound by np63 in both proliferating and differentiating keratinocytes , but expression is only induced in differentiating cells , suggesting that additional cofactors are involved for distinct biological endpoints .
the contribution of cofactors is further exemplified by the case of alox12 , a granular layer protein important for epidermal barrier formation , which is induced by np63 only in differentiating keratinocytes .
np63 expression can be regulated at the transcriptional level as well as by altered protein stability , as noted above .
another means of controlling levels of np63 is by micrornas , short rna molecules that act as posttranscriptional regulators .
they recognize seed sequences in the 3utr and serve to block protein translation or decrease rna stability .
such an interaction was identified as part of a feedback loop between p63 and iaspp , an inhibitory member of the apoptosis stimulating protein of p53 family , critical for epidermal homeostasis . in this loop
, iaspp is a direct transcriptional target of p63 that positively regulates np63 via the repression of mirs 754 - 3p and 720 to allow for proliferation .
blocking iaspp expression allows for differentiation via upregulation of mirs 754 - 3p and 720 , which downregulate np63. other examples include mir203 , which directly targets p63 through its 3utr for degradation and promotes differentiation by restricting proliferative potential and promoting cell cycle exit .
mirs are also regulated by np63. mir-34a and mir-34c , associated with cell cycle withdrawal , are negatively regulated by np63 .
in contrast , mir17 , mir20b , mir30a , mir106a , mir143 , and mir 455 - 3p are positively regulated by p63 and critical for the onset of keratinocyte differentiation via modulation of the mapks .
adhesiveness and cell viability are two additional properties positively impacted by np63. epidermal - specific knockdown of np63 in mature keratinocytes in mice resulted in impaired differentiation and compromised basement membranes . in an in vitro model , fras1 , which encodes for an extracellular matrix protein ,
was identified as a np63 regulated gene important for maintaining the epidermal - dermal interface integrity . to maintain this interface
, p63 prevents nonepidermal gene expression in keratinocytes via positive regulation of bone morphogenetic protein- ( bmp- ) 7 .
the importance of np63 in maintaining epithelial - mesenchymal crosstalk was highlighted by the discovery of interleukin-1 ( il-1 ) as a p63 target gene .
il-1 induces growth factors in fibroblasts that can bind to receptors on the basal keratinocytes to promote proliferation .
cell - cell adhesiveness was found to be mediated by p63 via perp , which is a critical desmosomal component for cell - cell adhesion in normal development and in wound healing [ 75 , 76 ] . with respect to apoptosis , the proapoptotic protein , igfbp3 ,
similarly , downregulation of p63 in primary human foreskin keratinocytes was found to induce apoptosis and to reduce both 1 and 4 integrin expression , linking adhesiveness with viability .
taken together , the data presented in sections 3.2.13.2.3 demonstrate that the network of genes regulated by np63 is large and perturbation of the balance between np63 and members of this network could have adverse biological consequences .
the proliferative lifespan of cells is limited by replicative senescence during which the cells permanently withdraw from the cell cycle , yet remain viable [ 79 , 80 ] .
this phenomenon is associated with the normal ageing process of renewable tissues such as the epidermis .
p63 has been proposed as a marker of human epidermal keratinocyte stem cells that is downregulated when keratinocytes become transient amplifying cells .
consistent with these data and the hypothesis that epidermal progenitor cell exhaustion occurs in p63(/ ) mice , depletion of p63 in immature human epidermal keratinocytes resulted in reduced clonal growth .
regulation of replicative senescence in human epidermal keratinocytes involves mirs-138 , 181a , 181b , and 130b which promote senescence by targeting np63 and sirt1 for degradation .
however , in a feedback loop , these mirs are themselves targets of negative regulation by np63 ; thus , overexpression of np63 could also perturb senescence .
mouse models provide support for a role for p63 in the maintenance of stem cell proliferative capacity .
characteristics of accelerating ageing were noted in p63(+/ ) mice observed for extended periods generated by two groups using the mice developed by both yang et al . and mills et al . [ 3 , 25 , 84 , 85 ] .
germline or somatic p63 depletion under control of the keratin 5 promoter gave rise to enhanced senescence marker expression , suggesting a role for p63 in the negative regulation of senescence .
indeed , overexpression of np63 in primary mouse keratinocytes overcame replicative senescence in association with delayed and diminished induction of ink4/p16 and arf / p19 .
consistent with these findings , crossing of p63(/ ) mice developed by yang et al . with ink4/p16(/ ) or arf / p19(/ )
mice was able to partially rescue the proliferation and differentiation defects observed in p63(/ ) mice , reinforcing a role for p63 in blocking senescence .
while these mice display reepithelialization , skin from p63(/ ) mice crossed with ink4a / p16(/ ) or arf / p19(/ ) mice is fragile and easily detachable , suggestive of defective adhesion , which also can be attributed to p63 . in the mouse models described above
a tap63-specific knockdown mouse model that supports a role for tap63 in adult stem cell maintenance was generated by crossing tap63 floxed mice with germline - specific promoter cre or keratin 14-cre mice .
interestingly , overexpression of np63 under control of the keratin 14 promoter resulted in a phenotype similar to that reported in mice lacking tap63
. skin - derived precursor ( skp ) cells are multipotent precursor cells derived from the dermis that can differentiate into mesodermal and neural cells . in the tap63(/ ) mice , skp cells proliferate more rapidly than wild - type skp cells , and thus , undergo senescence more rapidly . as adult stem cell populations are not immortal , this enhanced proliferation in tap63(/ ) cells would be expected to lead to stem cell exhaustion , which is associated with accelerated ageing .
the p53 tumor suppressor gene is commonly mutated in human cancer . due to the similarity of the tap63 isoforms with p53 , it was hypothesized that mutation of p63 could provide a mechanistic explanation for tumors in which p53 was not mutated .
it was found , instead , that mutation of p63 is a rare event in human cancer cell lines , but that p63 overexpression is seen in human squamous cell cancers including esophageal squamous cell carcinoma [ 91 , 92 ] , nasopharyngeal carcinoma , and squamous cell carcinoma of the skin [ 94 , 95 ] .
overexpression of the np63 protein in primary squamous cell carcinomas ( sccs ) of the head , neck , and lung correlates with amplification of the p63 gene locus , which occurs frequently in these cancers [ 28 , 96 ] .
while there is agreement that np63 is overexpressed in lung sccs , conflicting results have been published as to whether this correlates with prognosis [ 96 , 97 ] .
in squamous cell carcinomas of the skin , a significant increase in p63 expression , both in terms of intensity and distribution , is seen relative to normal skin , as the proliferative fraction is expanded in tumors [ 26 , 95 ] .
examination of skin lesions ranging from keratoacanthoma to a grade iv spindle cell carcinoma revealed very strong p63 immunoreactivity in grade 3 scc with decrease in a single grade iv spindle scc . in these tumors ,
carcinoma in situ was characterized by p63 immunoreactivity in all layers . while np63 was shown to be the most overexpressed isoform in squamous cell tumors , careful characterization of the ta and n isoforms from different tissue and tumor types revealed that individual isoforms are differentially expressed in the neoplastic transformation of different tissue types , implying specific contributions of the isoform expressed in a context - dependent manner . while np63 is overexpressed in primary skin tumors , expression of tap63
is not a common event but has been reported to be downregulated relative to normal skin using pcr - based methods .
it is clear that np63 is overexpressed in skin sccs , however , whether it actively plays a role in tumor formation or is a bystander has been unclear .
further insight into this question has been gained by in vitro and in vivo studies , as discussed below .
in particular , in vitro studies in scc cells have provided insight into the potential signaling pathways impacted by p63 dysregulation in squamous cell carcinoma . as discussed previously ,
irf6 is involved in a negative feedback loop with np63 that is necessary for the downregulation of np63 seen with differentiation , and an appropriate balance between these factors is required for the switch between proliferation and differentiation in the normal epidermis .
reexpression of irf-6 in the context of primary human keratinocytes expressing both np63 and a mutant v - ras 12 oncogene was found to abolish the ability of np63 to promote colony growth and restore oncogene induced senescence , supporting a role for irf6 in regulating np63 as part of its tumor suppressor function . in other studies
, np63 has been shown to upregulate hsp70 , a protein colocalized with np63 in primary sccs of the head and neck ( hnsccs ) that is associated with proliferation and viability of hnscc . likewise ,
accumulation of -catenin in the nucleus and activation of downstream signaling pathways common to many cancers are induced by np63 in hnscc cells .
consistent with a role in promoting adhesion , np63 is negatively regulated by the epithelial - to - mesenchymal transition ( emt ) promoting transcription factors snail and slug , and this association is observed in primary human cervical , head and neck , and esophageal sccs .
np63 also physically sequesters yb-1 , a positive translational mediator of snail , thereby preventing both enhanced snail activity and yb1 's function in actin cytoskeleton reorganization , both of which lead to cancer cell migration and invasion .
another direct transcriptional target of np63 is the vitamin d receptor ( vdr ) , which is induced by multiple p63 isoforms .
downregulation of vdr expression results in increased cell migration of a431 epidermoid carcinoma cells , which can be rescued by np63 or vdr .
a role for np63 in preventing metastasis is further supported by the finding that antagonism of np63 by mutant - p53/smad complex allows tgf- to convert from a tumor suppressor role to a role in promoting metastases . in line with this ,
knockdown of p63 in squamous cancer cell lines , in which the predominant isoform expressed was np63 , led to an increase of mesenchymal and neural markers and upregulation of genes associated with invasion and motility .
based on the data , it is enticing to contemplate that np63 plays a role in cancer development by promoting proliferation and viability at earlier stages , while it may need to be downregulated during progression to allow for the necessary enhanced motility , invasiveness , and emt that allow metastases to form .
in which np63 was overexpressed under control of the loricrin promoter showed that downregulation of np63 is required for uvb - induced apoptosis of the epidermis .
mechanistically , degradation of np63 in keratinocytes exposed to apoptotic doses of uv was shown to be mediated by p38 mapk , which phosphorylates np63. this led to its detachment from p53-dependent promoters and results in apoptosis induction .
consistent with this report , occupancy of binding sites involved in cell cycle arrest and apoptosis switched following adriamycin or uv treatment of human epidermal keratinocytes from np63 to p53 occupancy , which would be expected to result in increased apoptosis or cell cycle arrest .
many therapeutic agents used in cancer treatment promote genotoxic stress as a means to reduce or control tumor growth .
expression of high levels of np63 predicts responsiveness of primary hnscc to platinum - based therapies . upon exposure to cisplatin , np63
is proteosomally degraded via stratifin - mediated nuclear export and rack1 targeting [ 114 , 115 ] .
an interaction between the p63 proteins and the nf-b pathway also plays a role in responsiveness to chemotherapeutics . in jhu-022
oral cavity scc cells , ikk , a known activator of rela , promotes np63 degradation in response to cisplatin . in this cell line ,
cisplatin treatment resulted in a physical interaction between rela and np63 that abrogates np63 mediated p21 promoter repression and targets np63 for proteosomal degradation .
the presence of c - abl , which has been implicated as an oncogene , in hnscc cells treated with cisplatin stabilizes np63 expression .
this stabilization of np63 leads to enhanced cell viability , which could be anticipated to result in clinical consequences .
survival of hnscc cells that overexpress np63 is dependent on the presence of np63 , which functions by blocking tap73-driven apoptosis both via promoter binding and physical interaction with p73 in a p53-independent manner . tap73 and np63 are engaged in a feedback loop involving mir-193a-5p , which is repressed by np63 and activated by tap73 and targets the p73 utr .
cisplatin treatment results in np63 degradation and tap73-mediated activation of mir-193a-5p , limiting tap73 's pro - apoptotic effects and chemosensitivity .
reimplantation in the presence or absence of a mir-193a-5p antagomir of disaggregated cells from primary mouse sccs generated by a chemical carcinogenesis protocol revealed that knockdown of this mir resulted in reduced tumor formation and enhanced chemosensitivity , indicating that a strategy targeting both np63 and mir-193a-5p might be more effective in this scenario .
hnscc cells can circumvent the requirement for np63 expression for survival by the overexpression of bcl2 .
in addition to blocking p73 to promote survival of hnscc , np63 associates with histone deacetylase 1 and 2 forming an apoptotic transcriptional repressor complex .
this complex is sensitive to breakdown by cisplatin and hdac inhibitors , in the presence of low , but not high , levels of endogenous bcl-2 indicating once again that the context of the tumor impacts the success of chemotherapy . unlike the case of tap73 described above , in hacat cells in response to chemotherapy , np63
is involved in an antiapoptotic feedback loop in which it , as well as mutant p53 , induces np63 .
thus , response to genotoxic stress is another biological endpoint that can be impacted by dysregulated np63. cancer arises as a multistep process that can be reiterated in well - established mouse models in a controlled fashion .
results of the studies presented above suggest that tap63 would harbor tumor suppressor properties and overexpressed np63 would harbor oncogenic properties . in this section ,
we highlight the use of mouse models to dissect out how altered p63 levels contribute biologically to prevention or development of cancer , either alone or in altered balance with other family members or other oncogenic pathways .
approaches discussed utilize mice with a heterozygous null mutation in p63 on a background of wild type , p53 ( + / ) and/or p73 ( + / ) ; ta - isoform - specific knockout mice ; and mouse models where the elevated levels of np63 observed in human scc are mimicked in cultured keratinocytes and transplanted to nude mice . the potential role for physiological levels of p63 acting as a tumor suppressor with respect to spontaneous tumor development
was explored by two groups in the context of alteration of other p53 family members [ 85 , 122 ] . in a mouse model in which the p63 genotype was contributed by mice developed by yang et al .
, mice heterozygous for a null mutation in both p63 and p73 displayed a higher incidence of spontaneous tumor formation relative to wild - type mice .
furthermore , mice heterozygous for p53 , p63 , and p73 developed a higher incidence and formed more aggressive tumors than mice heterozygous for the p53 null mutation alone .
these findings suggest that p63 and p73 share a tumor suppressor role as has been long established for p53 [ 1 , 85 ] . in the absence of additional genetic mutations , these p63(+/ ) mice developed squamous cell carcinomas ( 10% ) , adenomas ( 15% ) , and histiocytic sarcomas ( 20% ) at 10% , 15% , and 20% greater rates , respectively , than wild type .
in contrast , in a study using mice with a p63 genotype contributed by the mice developed by mills et al .
, p63(+/)/p53(+/ ) mice were found to be less prone to spontaneous tumors than p53 + / mice alone . additionally , these p63(+/ ) mice were shown to have decreased susceptibility to chemically induced carcinogenesis , suggesting that p63 does not contribute a tumor suppressor activity in cancer . to date
tap63-subclass - specific knockdown mice allow distinction between the ta and n subclass properties . following observation for 2.5 years
, an enhanced incidence of carcinoma , including scc of the skin and sarcoma development , was observed in tap63(+/ ) and tap63(/ ) mice relative to wild - type mice , again supporting a tumor suppressive role for tap63 .
it was noted that tumors from the tap63(+/ ) and tap63(/ ) mice were highly metastatic , and at a mechanistic level tap63 was found to positively regulate dicer , a protein critical for mir processing , and mir 130b .
reexpression of both dicer and mir130b in tap63(/ ) mefs decreased invasiveness of these cells , suggesting that tap63 's tumor suppressor role could be mediated at least in part through dicer and mir130b .
the mouse models described above focused on the tap63 isoforms and were performed at wild - type or decreased levels of endogenous p63 . however , overexpression of np63 is a common event in squamous cancers .
two independent studies have used similar approaches to mimic this overexpression with the goal of examining the in vivo functional consequences of np63 overexpression in the epidermis .
results from both lab groups support a contributory role for np63 in the cancer phenotype with mechanistic distinctions . in studies performed in our laboratory ,
wildtype primary murine keratinocytes were transduced with retrovirus encoding a v - rasha oncogene in combination with a lentivirus encoding either a control gfp construct or np63 and grafted onto the dorsum of nude mice in combination with primary dermal fibroblasts .
this model allows growth of normal keratinocytes as well as benign and malignant tumor phenotypes in the graft site .
no lesions were observed in graft sites following transplantation of keratinocytes expressing only gfp or np63 alone .
grafting of keratinocytes expressing v - ras + gfp resulted , as expected , in the formation of well differentiated papillomas , while grafting of keratinocytes expressing v - ras + np63 resulted in 100% malignant conversion to carcinoma .
although elevated levels of np63 alone are insufficient to confer a tumor phenotype in vivo , we found that np63 blocks oncogene - induced senescence by inhibiting p16/p19 pathways and cooperates with oncogenic v - ras to enhance malignant conversion in vivo .
this study supports a contributory role for np63 in cancer pathogenesis and a mechanistic link to cell survival by overriding oncogene - induced senescence through inhibition of p16 and p19 , key mediators of cellular senescence . using a similar approach , keyes et al
. demonstrated that overexpressing np63 in keratinocytes in the presence of oncogenic ras resulted in growth of malignant carcinomas following subcutaneous injection . in this study also
overexpression of np63 was further shown to enhance stem - like proliferation of keratinocytes and maintain survival of the keratin 15-positive stem cell population .
furthermore , chromatin - remodeling protein lsh was identified as a new target of np63 and as an essential mediator of senescence bypass .
although p19 was not detectable in the tumors derived from ras/np63 keratinocytes in this study , an in vitro component of the study indicated that p16 and p19 were not reduced during the initial stages of senescence bypass .
therefore , contrary to our study , it was proposed that the initiating events through which np63 inhibits senescence do not occur via p16/p19 pathways .
although the difference in p16/p19 between these two studies may be due to the different time courses used , it further indicates the complexity of the pathways interacting with p63 family members and underscores the need for additional studies to understand the role of p63 and its downstream effectors in tumorigenesis and senescence .
an oncogenic role for np63 is further supported by studies in a mouse model containing a dominant negative 14 - 3 - 3 mutation ( er/+ ) .
14 - 3 - 3 , a protein associated with keratinocyte differentiation , is a direct target for np63 repression in undifferentiated human epidermal keratinocytes .
treatment of er/+ mice on a p63(+/+ ) background with a two - stage carcinogenesis protocol resulted in the formation of tumors in which np63 was strongly expressed , while loss of function of an endogenous allele of p63 in this context , which generated ( er/+/p63 + / ) mice , resulted in reduced sensitivity to this protocol , suggestive of cooperation of np63 in ras/14 - 3 - 3-induced tumorigenesis .
a role for nf-b / c - rel in np63-mediated carcinogenesis . in a transcription factor profiling exercise , we identified activation of nf-b in keratinocytes following the overexpression of np63. the nf-b family comprises 5 members functioning as hetero- and homodimers .
only nf-b / c - rel was found to be modulated by np63 under these conditions , with nuclear accumulation of phosphorylated c - rel but none of the other nfb subunits enhanced in the presence of overexpressed np63. nf-b is associated with multiple human diseases , including cancer , for which therapeutics targeting its constitutive nf-b activation are under development [ 127 , 128 ] . of the five family members , rela , p50 , and
c - rel subunits have been implicated in the maintenance of normal epidermal homeostasis [ 129 , 130 ] , and in scc , the rela / p50 heterodimer has been shown to promote or repress malignancy in a context - dependent manner [ 131 , 132 ] .
nuclear c - rel expression is associated with both solid breast tumors and hematopoietic malignancies ; however , it had not previously been investigated in scc of the skin .
the increase in nuclear c - rel accumulation seen with elevated np63 levels was found to be critical to the ability of np63 overexpressing keratinocytes to proliferate under conditions that normally induce growth arrest .
mechanistically , this is correlated with a physical interaction between np63 and c - rel on the promoter of the p21 gene in these cells , both in vitro and in vivo , which represses p21 expression .
these findings extended to primary human hnscc , in which we found that np63 and c - rel colocalized in the nuclei throughout the tumor sections , as opposed to a more restricted expression in normal tissue . in an extension of these studies , lu et al . characterized a dynamic mechanism whereby c - rel , np63 , and tap73 , which are coexpressed in the nuclei of a subset of hnscc cell lines , control expression on binding sites including p21 , noxa , and puma .
exposure of hnscc cell line cultures to tnf- to mimic inflammation in the tumor environment was found to induce nuclear accumulation of c - rel . in the absence of this stimulus , np63 was found to physically interact with tap73 .
similar to our results in untreated primary keratinocytes upon overexpression of np63 , a physical interaction between endogenous np63 and c - rel was observed following tnf- treatment in these hnscc cell lines .
interestingly , under conditions of c - rel overexpression , the interaction between np63 and tap73 was blocked and tap73 was translocated to the cytoplasm .
chip assays indicated that this regulation occurred on the promoters of genes involved in growth arrest and apoptosis , resulting in their downregulation .
primary murine cell cultures and in vivo murine models have been instrumental in elucidating the multistep nature of carcinogenesis and in challenging the role of specific genetic alterations , such as those observed in p63 , in cancer pathogenesis [ 86 , 124 ] .
the mouse models described in this review have provided us with a clear picture of the importance of p63 to normal epidermal development and homeostasis and have highlighted the roles for specific p63 isoforms in neoplasia .
however , given the complexity of the p63 family members , their interactions , and the context - specific manner in which they can exert their effects , much remains to be defined .
mouse models with molecular alterations that allow targeting of specific gene products will be indispensible in deepening our understanding of and resolving controversy related to the role of p63 both in normal tissue and in disease .
once a pathway has been implicated , primary cultures from mouse epidermis can be readily manipulated to express or eliminate a particular protein presumed active upstream or downstream to assess the impact . applied in combination with keratinocytes from genetically altered mice , both in vitro and in vivo findings can be challenged further for the consequences of the alterations .
however , it is important to remember that all models have limitations , and a deeper understanding of the role of p63 in normal epidermal homeostasis and neoplasia will ultimately be derived from an iterative process involving in vitro observations in primary cells , cell lines and primary tumors , in vivo queries of these findings , and reexamination of the outcomes in the context of human tumors .
, the observation in primary mouse keratinocytes that c - rel acts downstream of np63 in modulating keratinocyte growth regulation led to a further novel observation that c - rel levels are enhanced in primary hnscc of humans and links this protein accumulation to altered nfb / c - rel activity in human head and neck squamous cell cancer cells .
the requirement for c - rel in these cancers can be tested by modulating c - rel and np63 independently using lentiviral gene transduction followed by grafting .
long - term overexpression of np63 has been shown to support sustained high levels of nuclear c - rel expression , and c - rel shrna lentiviruses are capable of depleting c - rel in keratinocytes for extended time ( unpublished observations ) . assessing the impact of these modulations in vivo will clarify the interplay between these alterations and their relevance to cancer development and progression . | mouse models have informed us that p63 is critical for normal epidermal development and homeostasis .
the p53/p63/p73 family is expressed as multiple protein isoforms due to a combination of alternative promoter usage and c - terminal alternative splicing .
these isoforms can mimic or interfere with one another , and their balance ultimately determines biological outcome in a context - dependent manner . while not frequently mutated , p63 , and in particular the np63 subclass , is commonly overexpressed in human squamous cell cancers . in vitro keratinocytes and murine transgenic and transplantation models have been invaluable in elucidating the contribution of altered p63 levels to cancer development , and studies have identified the roles for np63 isoforms in keratinocyte survival and malignant progression , likely due in part to their transcriptional regulatory function .
these findings can be extended to human cancers ; for example , the novel recognition of nfb / c - rel as a downstream effector of p63 has identified a role for nfb / c - rel in human squamous cell cancers .
these models will be critical in enhancing the understanding of the specific molecular mechanisms of cancer development and progression . |
acute type a aortic dissection ( ad ) is a life - threatening disorder that occurs in approximately 1 in 10,000 emergency department patients . according to reports in the literature ,
the mortality of ad is 40% on presentation , with a 1-year mortality of 90% , and aortic rupture was identified as the common cause of death in approximately one - third of patients admitted to the hospital . in recent years , the incidence of ad has been rising yearly , and the overall outcome is determined by the type and extent of dissection , the presence of associated complications , and the timing of medical intervention .
thus , early and accurate diagnosis with a noninvasive modality is of great importance for the optimal treatment and prognosis of patients with type a ad .
the purpose of this study was to preoperatively evaluate the value of aortic arch lesions by multidetector computed tomography ( mdct ) angiography in type a ad in a chinese cardiac center .
approval was obtained from the institutional review board of the university of fujian medical university , china for a retrospective review of patients with type a ad who received mdct angiography .
we reviewed the charts of 42 consecutive patients with type a ad who were admitted to our hospital between january 2013 and december 2015 and were subjected to mdct angiography .
all patients suffered from a long history of hypertension , and none received regular antihypertensive medication . during admission ,
patients presented with a classic history of acute - onset tearing chest pain radiating to the back .
some complained of a variety of other symptoms , which included syncope , hypotension , pericardium and pleural effusion , cardiac tamponade , oliguria and anuria , abdominal pain , and so on .
patients standard demographic information was also collected ( table 1 ) . among the 42 patients ,
the patients were aged 45 to 68 years ( mean standard deviation , 52.1 5.8 years ) .
their weights ranged from 48 to 85 kg ( 62.5 6.8 kg ) .
none of the patients included in the study group had a diagnosis of marfan syndrome or other connective tissue diseases .
routine examinations were performed , which included standard lead electrocardiogram , transthoracic echocardiography ( tte ) , and routine blood and biochemical tests . out of all the patients ,
the initial diagnosis was obtained with mdct angiography , and the diagnosis of ad type was made using the stanford ( types a and b ) classification .
all patients were managed conservatively with antihypertensive and analgesic therapy , according to the medical standards of care .
clinical data of patients with type a ad undergoing mdct angiography . for all patients in this study ,
mdct angiography examinations were performed with a dsct scanner ( somatom definition ; siemens , germany ) .
patients were examined while supine , and images were taken extending from the base of the neck to the thigh .
a low - dose protocol was used to reduce the radiation dose as follows : slice thickness 1 mm ; pitch 1.75 , depending on heart rate ; tube voltage 120 kvp ; and tube current 350 ma . in all patients ,
a dose of 90 ml iodinated contrast medium and iopromide 350 mgi / ml ( schering ultravist , iopromide , berlin , germany ) was injected .
the rate of injection was 4.5 ml / s , followed by 30 ml of saline at the same rate .
all images were transferred to an external workstation ( leonardo ; siemens medical solutions , forchheim , germany ) using the volume rendering technique . established radiologists with 10 years of radiology experience evaluated the data sets for each of the cases .
the location of the intimal entry site and the change of the branch blood vessels were detected by mdct angiography .
some of the parameters were measured , which included the diameter of the aortic sinus junction , ascending aorta diameter proximal to the first aortic arch branch , proximal transverse arch diameter ( between the brachiocephalic and left common carotid arteries ) , distal transverse arch diameter ( between the left common carotid and the left subclavian arteries ) , diameter of descending aorta , distance between the brachiocephalic and left common carotid arteries , distance between the left common carotid and left subclavian arteries , diameter of the brachiocephalic artery , diameter of the left common carotid artery , and diameter of the left subclavian artery .
multidetector computed tomography angiography showed the parameters that were measured , which included the diameter of aortic sinus junction , ascending aorta diameter proximal to the first aortic arch branch , proximal transverse arch diameter ( between the brachiocephalic and left common carotid arteries ) , distal transverse arch diameter ( between the left common carotid and the left subclavian arteries ) , the diameter of descending aorta , the distance between the brachiocephalic and left common carotid arteries , the distance between the left common carotid and left subclavian arteries , the diameter of the brachiocephalic artery , the diameter of the left common carotid artery , and the diameter of the left subclavian artery .
( a ) the type a aortic dissection group and ( b ) the control group .
multidetector computed tomography angiography showed the ascending aorta diameter proximal to the first aortic arch branch and the diameter of descending aorta .
( a ) the type a aortic dissection group and ( b ) the control group .
multidetector computed tomography angiography showed the proximal transverse arch diameter and the distal transverse arch diameter .
( a ) the type a aortic dissection group and ( b ) the control group .
multidetector computed tomography angiography showed the diameter of descending aorta , the distance between the brachiocephalic and left common carotid arteries , the distance between the left common carotid and left subclavian arteries , the diameter of the brachiocephalic artery , the diameter of the left common carotid artery , and the diameter of the left subclavian artery .
( a ) the type a aortic dissection group and ( b ) the control group .
in this study , 42 patients were confirmed with the diagnosis of type a ad via the surgical findings , and all patients received aortic valvuloplasty ( 1 case for valve replacement ) , ascending aorta replacement , and open placement of a triple - branched stent graft for aortic arch reconstruction .
the intimal tear site locations that were identified in all 42 patients included the ascending aorta ( n = 25 ) and the aortic arch ( n = 12 ) ; the rest ( n = 5 ) were retrograde dissections from the tear of the descending aorta .
a comparison between the type a ad group and control group ( patients with hypertension ) is presented in table 2 .
there were no significant differences in demographic characteristics . compared with the control group , the diameter of the aortic sinus junction , ascending aorta , proximal transverse arch , distal transverse arch , descending aorta , brachiocephalic artery , and left common carotid artery were significantly longer in the type a ad group ( p < 0.05 ) .
regarding the distance between the left common carotid and left subclavian arteries , compared to the control group , most cases with type a ad had a significant variation .
comparison of clinical data of the aortic arch between those patients with and without ad .
none of the patients presented with vascular complications or drug side effects when mdct angiography was performed .
the average time taken to finish mdct angiography was 3.5 to 7.5 minutes ( 4.5 1.4 minutes ) .
type a ad is the most common acute emergency condition of the aorta and often results in catastrophic results for patients , which depends on the extent of dissection and presence of associated complications .
the most common risk factor for the development of an ad is hypertension , which occurs in 60% to 90% of cases .
type a ad involves the ascending thoracic aorta and may extend into the descending aorta , and the intimal tear site is usually located in the ascending aorta and aortic arch .
some reports identified aortic rupture as the cause of death in approximately one - third of patients admitted to the hospital .
complications of type a ad include aortic valve regurgitation , aortic rupture , tamponade and compromise of the arch branches or coronary arteries leading to myocardial infarction , cerebral sequelae , aortic branch involvement , and peripheral circulation involvement .
thus , type a ad typically requires urgent surgical treatment , and early and accurate diagnosis with a noninvasive modality is required for optimal management and improvement in the prognosis of these patients .
there are a variety of inspection methods for the diagnosis of type a ad , including tte , ct angiography , and magnetic resonance ( mr ) angiography .
tte is an available , noninvasive , relatively low - cost , and easy processing examinational modality that can be repeated as frequently as necessary and has been used in the preliminary diagnostic approach to type a ad .
it has a reported sensitivity of 59% to 83% and a specificity of 63% to 93% for the diagnosis of ad .
the main purpose of tte is to determine aortic valves and root lesions , which helps surgeons to develop an aortic valve medical plan . in our study , according to the tte results that were confirmed during the operation , most of the patients with aortic valve regurgitation required aortic valvuloplasty , and few patients required valve replacement .
mr angiography is accurate and noninvasive , has excellent spatial and contrast resolution , and allows multivascular imaging phases with fast postprocessing .
although mr angiography has several advantages , including a lack of radiation and greater vessel coverage at high resolution , it may not be suitable for unstable patients due to the longer acquisition time and monitoring difficulties in an emergency situation , as well as in those patients with implanted electronic devices .
recently , mdct angiography was shown to be less invasive and time consuming and is more popularly performed in clinical practice for the diagnosis of type a ad .
its contrast - enhanced scanning can rapidly and accurately localize the intimal entry site and help assess branch vessel lesions as well as the relationship of the branch vessels , which may aid surgeons in deciding on a treatment plan with either root or aortic valve replacement , as well as intravascular stent placement .
there are several advantages in using mdct angiography for the diagnosis of type a ad , and this modality can show a high accuracy rate in assessing the severity of dissection using 3-dimensional images , which can be processed and analyzed by using several postreconstruction techniques .
the highest imaging resolution is an important reason that mdct angiography may be helpful in the preoperative imaging study of type a ad .
some information can be easily identified , including the sites of intimal tears , intimomedial flap , false and true lumen morphology , coronary and aortic arch branches , and scope of the dissection .
mdct scan can be performed in a few seconds to complete inspection , which can increase the security of the inspection process . meanwhile , mdct angiography yielded higher sensitivity and specificity and was superior to the other 2 modalities in ruling out type a ad .
some reports indicated that mdct angiography has a sensitivity and specificity of close to 100% for diagnosis of type a ad ; our results also confirmed these views .
preoperative identification of the locations and characteristics of intimal tears is one of the most important steps for surgeons to help procedural planning . to our knowledge , many studies have focused on ct angiography to determine the location and characteristics of intimal tears .
kim et al reported their study on the validation of the accuracy of ct in predicting intimal tear locations .
they concluded that sensitivity was higher for ascending aorta tears and that specificity was higher for arch tears . in our study , most of the intimal tears were located in the ascending aorta and aortic arch .
the anastomotic position of the artificial vessel depended on the location of the intimal tears and the scope of the true and false lumen . for patients with intimal tears located in the aortic arch ,
although the treatment is still controversial , we still recommend that total arch replacement can result in better long - term prognosis .
total aortic arch reconstruction for type a ad with anastomosis of the brachiocephalic vessel to a dacron tube graft or 4-branched prosthetic graft replacement of the aortic arch are popular surgical procedures .
these methods remain controversial because they are very complex and highly invasive , which makes the risk of these procedure very high . in recent years
, chen et al developed an open triple - branched stent graft placement technique for type a ad , in which total arch repair could be simply completed by inserting a triple - branched stent graft into the proximal descending aorta , arch , and 3 arch vessels through aortic incision .
their results showed that their new technique could reduce the risk and technical difficulty of total arch repair .
in addition , they found that this new technique could not be applied in most patients because the diameters of the native arch vessels and distances between the 2 neighboring arch vessels did not always match the available sizes of the triple - branched stent grafts .
they also modified the stent graft to several new generations for a good match with different diameters of the arch and branch vessels and achieved good clinical results ( fig .
6 ) . given the many advantages , their technology may have good prospects . from their new report
, they obtained encouraging short - term results ( a nearly 97.6% operation success rate , relatively short operation time , and very few complications ) .
however , it is important to preoperatively evaluate the anatomic lesions of aortic arch and branch vessels , which was the other main purpose of our study .
postoperative computed tomographic scans showed that the triple - branched vascular stent graft without kinking , the stents were well stretched in the aortic arch , and the branching artery , with satisfactory adherence to the vessel wall . from our study
, we found that mutations in the size and position of the ascending aorta , aortic arch , and branch vessels during ad had occurred . in our treatment strategy ,
the pathological ascending aorta was replaced by a dacron artificial tube graft , and the true lumen of the descending aorta , aortic arch , and brachiocephalic vessels were replaced with a triple - branched stent graft .
the diameters of the arch and descending aorta were measured by preoperative mdct angiography , which was then used to select the stent models . from our data , there were significant differences in the position change of the arch branch vessels , which was a challenge , intraoperatively , using the integration stent . compared with normal data , there were significant differences in the distance of the 3 branch vessels in patients with type a ad .
it was important for intraoperative selection and the installation of stents to preoperatively accurately measure these data .
the use of the modified triple - branched stent graft by dr chen could provide a good match with the different diameters of the native arch vessels and the various distances between the 2 neighboring arch vessels in type a ad status . like any retrospective study , ours included bias associated with data collection and incomplete data for some patients .
although the small number of patients in the study precluded reaching significance for all of the study end - points , important differences were demonstrated .
much larger numbers of patients must be evaluated to establish the results of the preoperative evaluation value of aortic arch lesions by mdct angiography .
this study was limited to 1 institution , and other institutions may obtain different results . in conclusion , mdct angiography plays an important role in the preoperative evaluation value of aortic arch lesions and guides the development of reasonable surgical plans in the clinical setting .
it is necessary to preoperatively evaluate the structures of the aortic arch and branching vessels , especially for patients who are ready for an intraoperative triple - branched stent graft .
we wish to extend our gratitude to xin - ming huang and jian - hua chen . | abstractthe purpose of this study was to preoperatively evaluate the value of aortic arch lesions by multidetector computed tomography ( mdct ) angiography in type a aortic dissection ( ad).from january 2013 to december 2015 , we enrolled 42 patients with type a ad who underwent mdct angiography in our hospital .
the institutional database of patients was retrospectively reviewed to identify mdct angiography examinations for type a ad .
surgical corrections were conducted in all patients to confirm diagnostic accuracy.in this study , the diagnostic accuracy of mdct angiography was 100% in all 42 patients .
the intimal tear site locations that were identified in patients included the ascending aorta ( n = 25 ) , aortic arch ( n = 12 ) , and all other sites ( n = 5 ) . compared with the control group ,
there were significant differences in the aortic arch anatomy among the cases .
regarding the distance between the left common carotid and left subclavian arteries , compared with the control group , most cases with type a ad had a significant variation.mdct angiography plays an important role in detecting aortic arch lesions of type a ad , especially in determining the location of the intimal entry site and change of branch blood vessels .
surgeons can formulate an appropriate operating plan , according to the preoperative mdct diagnosis information . |
spontaneous intracerebral hemorrhage is a rare and challenging condition to treat , especially in haemophiliacs .
the risk - benefit ratio that tilts the balance between conservative and surgical management is very subtle .
surgical treatment bears the risk of rebleed , whereas conservative management runs the risk of rapid deterioration and high treatment cost .
here we discuss the nuances , clinical and treatment dilemma that one faces while treating a patient , diagnosed with haemophilia , with spontaneous right subdural haematoma . here
a 32 year old doctor , diagnosed case of christmas disease , presented to the triage with sudden onset , progressive drowsiness and altered sensorium since the previous night . on further assessment , he revealed that he had holocranial headache since the last 1 week which was associated with vomiting .
on examination he had bradycardia , pulse rate of 60/min and neurological examination revealed a disoriented , drowsy patient , who was obeying simple commands with no paucity of movements .
a preliminary computed tomographic scan of the brain ( ct brain ) revealed an acute right fronto - temporo - parietal acute subdural haematoma with mass effect and midline shift of 1.6cms .
haematological workup was requested and the reports showed an elevated activated plasma thromboplastin time ( aptt55 s ) with low factor viii levels ( 4.9% ) .
the dilemma in the treatment was to weigh the benefits versus the risks of performing a craniotomy for evacuation of the acute sdh as compared to conservative management with correction of coagulation profile followed by burr hole and evacuation .
since the patient was neurologically stable a clinical judgement was made , after counselling with his relatives , to attempt at conservative management and correction of coagulation factors under continuous neuromonitoring in our neuro intensive care unit .
after consulting with the inhouse haematopathologist it was decided to start the patient on anti hemophilic factor ( ahf ) to raise the desired level to 100 iu / dl .
he was infused with the weight calculated dose for the following three days and his factor viii levels reached 153% .
follow up ct scan brain showed no significant change in the haematoma size however the patient appeared to be significantly drowsy and his bradycardia had worsened ( 45 beats / min ) on day 5 of admission .
the patient was obeying simple commands and the relatives were counselled regarding the same and decided to continue conservative line of management with ahf ( fig . 1 , fig .
2 ) . decongestants and ahf were continued and on the 7th day post admission he developed pupillary asymmetry , with deterioration of sensorium .
ct scan done revealed a right fronto - temporo - parietal subacute subdural hematoma with midline shift .
he was taken up for emergency burr hole and evacuation of haematoma under cover of ahf under general anesthesia .
postoperatively , within 6 h patient was alert , active and oriented , ct brain showed complete evacuation of hematoma and resolution of midline shift .
factor 8 infusion was continued at maintenance doses for the next 7 days and he was discharged with no complications and is on regular follow - up .
spontaneous intracranial hemorrhage is a rare complication of hemophilia , with frequency of about 2.27.8% , and a mortality of 34% .
small volume bleeds with insignificant mass effect and midline shift may be managed conservatively with ahf and close neurological monitoring , allowing spontaneous resolution of hematoma .
larger bleeds , like the current case , should be operated under the cover of ahf . in our case
we were able to successfully convert the acute subdural hematoma to a chronic subdural hematoma under cover of decongestants and ahf .
management of our cases with ahf was based on guidelines issued by the world federation of hemophilia .
factor viii concentrate , factor ix concentrate , cryoprecipitate , fresh frozen plasma ( ffp ) , desmopressin , tranexemic acid , epsilon aminocaproic acid are the products available for the management of hemophilia and bleeding manifestations . in our case
each unit of factor viii infused per kilogram of body weight increases the plasma level of factor viii by 2 iu / dl .
factor viii has a half life of approximately 812 h. factor viii requirement was calculated using the formula weight in kilogram desired concentration ( iu / dl ) 0.5 .
the prescribed level of factor viii levels for neurosurgical emergencies is 100 iu / dl and the calculated dose was 3800 iu ( 76 kg 100 iu / dl 0.5 ) .
this dose of 3800 iu was infused intravenously twice daily for 3 days .
the dose of factor viii was then reduced to achieve a maintenance concentration of 50iu ( 76 kg 50 iu / dl 0.5 ) i.e 1900 iu was infused over the next 5 days till he deteriorated and was taken up for surgery .
prior to the surgical procedure a bolus dose of 3800 iu was given intravenously and a pre op factor viii level of 200% .
the same dose was continued for 3 days postoperatively and then tapered to a level of 50 iu / dl for the next 5 days and 25 iu / dl for 3 days thereafter .
surgical indications for the management of large intracranial hematomas in hemophiliacs have been no different from non hemophiliacs in the past .
we however successfully converted an acute subdural hematoma to chronic subdural hematoma and managed it by burr hole evacuation .
the decision and favourable outcome was possible in view of the good gcs the patient presented with .
this technique not only significantly reduced the morbidity of craniotomy and rebleed but also gave a good functional outcome ( glasgow outcome score of 5 ) .
the drawbacks of the above management technique included the high costs of ahf and the ambiguity of constant deterioration of the patient .
our clinical experience has enlightened us regarding the solution to a few dilemmas one faces while treating an acute subdural in a haemophiliac .
we would like to recommend the following ; conservative management of an acute subdural to convert it into a chronic subdural when there are no financial constraints .
written informed consent was obtained from the patient for publication of this case report and accompanying images .
a copy of the written consent is available for review by the editor - in - chief of this journal on request .
| highlightsspontaneous intracerebral hemorrhage poses a risk in all patients and a treatment dilemma in patients with bleeding and clotting disorders .
the haemophiliac patient is a rare and challenging vignette to the average neurosurgeon.routine treatment would surmise with a craniotomy and evacuation of the haematoma , however this form of intervention is associated withsignificant morbidity and rebleed rates.our management involved close monitoring of the patient while we converted the acute hematoma into a chronic subdural hematoma and successfully managed it with burr hole evacuation under cover of antihemophilic factor.dosage and monitoring of ahf is described in detail . |
sputum specimens were collected from persons at high - risk for suspected tb ( previously treated case - patients and close contacts of known patients with drug- resistant cases ) in accordance with the national tb control program .
specimens that were collected at healthcare facilities in the eastern cape province were submitted to the national health laboratory service ( nhls ) in port elizabeth for tb drug susceptibility testing ( dst ) . from july 2008 through july 2009 , a convenience sample of sputum cultures , shown to be either fully drug - susceptible or resistant to at least isoniazid and rifampin ( mdr tb ) by the nhls , was submitted to stellenbosch university in cape town for subsequent genotyping .
only limited demographic and clinical data were available for each patient : a unique identifier ( assigned by the nhls ) , the date sputum was obtained , the name of the clinic / hospital where the sample originated , and the routine dst pattern . the unique identifier was used to identify the first available isolate from 309 drug - susceptible and 342 mdr tb case - patients included in the study .
this study was approved by the ethics committee of stellenbosch university , faculty of health sciences ( n09/11/296 ) .
sputum samples were processed by the nhls for routine tb diagnosis by smear microscopy and culture .
each sputum specimen was decontaminated by using the standard n - acetyl - l - cysteine - sodium hydroxide method and cultured in mycobacteria growth indicator tube ( mgit ) 960 medium until a positive growth index was observed .
dst was done by the indirect proportion method with the bactec mgit 960 system ( bd bioscience , sparks , md , usa ) , according to the manufacturer s instructions .
we initially tested resistance against isoniazid and rifampin , followed by testing for resistance against streptomycin and ethambutol if the isolate was resistant to either isoniazid or rifampin .
second - line dst was done in 7h10 medium containing 2 g / ml of ofloxacin , 4 g / ml of amikacin , or 5 g / ml of ethionamide .
dst for para - aminosalicylic acid was done at stellenbosch university in mgit 960 medium containing 4.0 g / ml , 8 g / ml , and 16 g / ml of para - aminosalicylic acid ( 15 ) .
crude dna was prepared by boiling a 200-l aliquot of a mycobacteria - positive mgit culture , and this was used as a template for subsequent pcr analysis ( 16 ) .
each isolate was spoligotyped by using the international standardized method ( 17 ) and grouped into genotypes according to previously described spoligotype signatures ( 18 ) .
atypical , according to the presence or absence of an is6110 insertion in the noise transfer function ( ntf ) region ( 19,20 ) .
the atypical beijing genotype strains were further classified by using the international standardized is6110 dna fingerprinting method ( 21 ) .
for atypical beijing strains that were drug - sensitive according to dst , sensitivity to isoniazid and rifampin was confirmed by sequencing the katg and rpob genes . in mdr
atypical beijing strains , mutations conferring resistance to isoniazid , rifampin , ethambutol , pyrazinamide , ofloxacin , streptomycin , amikacin , kanamycin , and capreomycin were identified by sequencing the inha promoter and the katg , rpob , embb , pnca , gyra , and rrs genes , respectively ( 22,23 ) .
isolates were grouped as as follows : mdr tb sensu stricto ( mdr tb ss , that is , mdr strains excluding identified pre - xdr , mdr plus additional resistance to either a fluoroquinolone or any second - line injectable anti - tb drug ) and xdr strains ) ; pre - xdr tb ; or xdr tb , according to high confidence mutations .
this method of grouping was selected because routine dst was not done for all of the anti - tb drugs on all of the isolates .
furthermore , a poor correlation was observed between high - confidence mutations and routine second - line dst .
isolates were considered to belong to the same cluster ( implying ongoing transmission ) if identical mutations were observed in all of the genes sequenced .
sputum specimens were collected from persons at high - risk for suspected tb ( previously treated case - patients and close contacts of known patients with drug- resistant cases ) in accordance with the national tb control program .
specimens that were collected at healthcare facilities in the eastern cape province were submitted to the national health laboratory service ( nhls ) in port elizabeth for tb drug susceptibility testing ( dst ) . from july 2008 through july 2009 , a convenience sample of sputum cultures , shown to be either fully drug - susceptible or resistant to at least isoniazid and rifampin ( mdr tb ) by the nhls , was submitted to stellenbosch university in cape town for subsequent genotyping .
only limited demographic and clinical data were available for each patient : a unique identifier ( assigned by the nhls ) , the date sputum was obtained , the name of the clinic / hospital where the sample originated , and the routine dst pattern . the unique identifier was used to identify the first available isolate from 309 drug - susceptible and 342 mdr tb case - patients included in the study .
this study was approved by the ethics committee of stellenbosch university , faculty of health sciences ( n09/11/296 ) .
sputum samples were processed by the nhls for routine tb diagnosis by smear microscopy and culture .
each sputum specimen was decontaminated by using the standard n - acetyl - l - cysteine - sodium hydroxide method and cultured in mycobacteria growth indicator tube ( mgit ) 960 medium until a positive growth index was observed .
dst was done by the indirect proportion method with the bactec mgit 960 system ( bd bioscience , sparks , md , usa ) , according to the manufacturer s instructions .
we initially tested resistance against isoniazid and rifampin , followed by testing for resistance against streptomycin and ethambutol if the isolate was resistant to either isoniazid or rifampin .
second - line dst was done in 7h10 medium containing 2 g / ml of ofloxacin , 4 g / ml of amikacin , or 5 g / ml of ethionamide .
dst for para - aminosalicylic acid was done at stellenbosch university in mgit 960 medium containing 4.0 g / ml , 8 g / ml , and 16 g / ml of para - aminosalicylic acid ( 15 ) .
crude dna was prepared by boiling a 200-l aliquot of a mycobacteria - positive mgit culture , and this was used as a template for subsequent pcr analysis ( 16 ) .
each isolate was spoligotyped by using the international standardized method ( 17 ) and grouped into genotypes according to previously described spoligotype signatures ( 18 ) .
atypical , according to the presence or absence of an is6110 insertion in the noise transfer function ( ntf ) region ( 19,20 ) .
the atypical beijing genotype strains were further classified by using the international standardized is6110 dna fingerprinting method ( 21 ) . for atypical beijing strains that were drug - sensitive according to dst , sensitivity to isoniazid and
atypical beijing strains , mutations conferring resistance to isoniazid , rifampin , ethambutol , pyrazinamide , ofloxacin , streptomycin , amikacin , kanamycin , and capreomycin were identified by sequencing the inha promoter and the katg , rpob , embb , pnca , gyra , and rrs genes , respectively ( 22,23 ) .
isolates were grouped as as follows : mdr tb sensu stricto ( mdr tb ss , that is , mdr strains excluding identified pre - xdr , mdr plus additional resistance to either a fluoroquinolone or any second - line injectable anti - tb drug ) and xdr strains ) ; pre - xdr tb ; or xdr tb , according to high confidence mutations .
this method of grouping was selected because routine dst was not done for all of the anti - tb drugs on all of the isolates .
furthermore , a poor correlation was observed between high - confidence mutations and routine second - line dst .
isolates were considered to belong to the same cluster ( implying ongoing transmission ) if identical mutations were observed in all of the genes sequenced .
a convenience sample of 309 drug - sensitive and 342 mdr tb isolates from patients from eastern cape province was collected during the study period .
analysis of the population structure of these isolates by spoligotyping identified 52 and 29 different spoligotype patterns among drug - sensitive and mdr tb strains , respectively . among drug - sensitive and mdr isolates ,
22/52 and 14/29 spoligotype patterns were previously recorded in the fourth international spoligotyping ( spoldb4 ) database . these represented 275 ( 89.0% ) of 309 drug - sensitive isolates and 327 ( 95.6% ) of 342 mdr isolates .
notably , 84% of mdr isolates constituted only 3 different spoligotypes ( table 1 ) , namely , beijing , lam3 , and lam4 .
these findings indicate transmission of these strains . * mdr tb , multidrug - resistant tuberculosis ; st , shared type ( 17 ) ; dst , drug susceptibility testing ; mdrss , mdr sensu stricto ; pre - xdr , pre extensively drug resistant ; xdr , extensively drug resistant .
for beijing isolates a distinction was made between typical and atypical based on the presence or absence of an is6110 insertion in the noise transfer region ( 18,19 ) .
molecular - based dst total differs from culture - based dst total , because some results were not available .
table 1 shows the classification of spoligotypes , according to the degree of drug resistance , in which drug resistance is expressed as the result of culture - based or molecular - based dst . in this study , we used molecular - based dst to define the extent of drug - resistance in routinely diagnosed mdr tb isolates .
accordingly , 119 ( 38.5% ) of the drug - susceptible isolates and 236 ( 69.0% ) of the mdr tb isolates were of the beijing genotype strain .
subclassification of beijing genotype strains showed that 11(9.2% ) of 119 drug - sensitive and 217 ( 91.9% ) of 236 mdr strains belonged to the atypical subgroup of the beijing genotype , as indicated by the absence of an is6110 element in the ntf region .
analysis of mutations conferring resistance to first- and second - line anti - tb drugs enabled grouping of the mdr isolates : 136 mdr ss , 98 pre - xdr , and 108 xdr . using these groupings
, we found that isolates with a higher degree of resistance were more likely to have an atypical beijing genotype ( drug sensitive : 11/309 [ 3.6% , 95% ci 1.8%6.3% ] , mdr ss : 29/136 [ 21.3% , 95% ci 14.8%29.2% ] vs. pre - xdr : 85/98 [ 86.7% , 95% ci 78.4%92.7% ] vs. xdr : 103/108 [ 95.4% , 95% ci 89.5%98.5% ] ) .
we analyzed dna sequencing data for the first available isolate from each patient infected with an mdr atypical beijing strain ( n = 217 ) and performed is6110 fingerprinting for a subset of these isolates ( n = 110 ) to establish whether the overabundance of the atypical beijing genotype among patients with pre - xdr tb and xdr tb strains reflected ongoing transmission .
is6110 dna fingerprinting showed that all of these patients were infected with closely related atypical beijing strains with only minor differences in the banding patterns ( technical appendix , figures 1 , 2 ) , thereby suggesting clonal dissemination .
the technical appendix table shows that 216 ( 99.5% ) of 217 of the mdr atypical beijing genotype strains harbored an identical katg ( agc315acc ) mutation , whereas 209 ( 94.9% ) of 217 had a distinctive rrs ( a513c ) gene mutation .
subsequently , resistance to rifampin , ethambutol , pyrazinamide , amikacin , and ofloxacin was acquired in various combinations .
of the 29 atypical beijing mdr ss isolates , 22 ( 75.9% ) were grouped into 4 clusters according to mutations ( mutation pattern [ mp ] ) in the inha promoter and the katg , rpob , embb , pnca , rrs , and gyra genes ( cluster size ranged from 3 to 12 cases ; table 2 : mp2 , mp17 , mp32 , mp34 ) , whereas 7 had unique mps ( table 2 : mp23 , mp25 , mp30 , mp31 , mp41 , mp44 , mp48 ) . similarly , the 85 atypical pre - xdr beijing isolates showed 11 different mps , of which 81 ( 95.3% ) were grouped into 7 clusters ( cluster size ranged from 2 to 62 cases ; technical appendix table : mp3 , mp5 , mp18 , mp26 , mp28 , mp35 , mp38 ) .
the genotype of the largest pre - xdr tb cluster was characterized by an inha promoter mutation at position 17 and the katg agc315acc , rpob gac516gtc , embb atg306ata , rrs a513c , and rrs a1401 g nucleotide substitutions as well as an insertion in the pnca gene at position 172 g .
this mp was characteristic of 81 ( 78.6% ) of 103 of the atypical beijing xdr tb isolates and , for ease of reference , will be called mp5 ( technical appendix table ) . by contrast
, only 3 of the 29 atypical beijing mdr ss isolates showed the same mutation pattern for these genes , excluding the rrsa1401 g mutation ( mp2 ) .
ten different atypical xdr beijing mps emerged from the mp5 progenitor by mutation in the gyra gene . of these , 6 mps showed clustering ( cluster size ranged from 2 to 46 cases , mp611 ) , and 4 had unique mutations conferring ofloxacin resistance ( mp1216 ) .
clustering of both the pre - xdr and xdr genotypes suggests transmission after the acquisition of additional resistance . of the remaining 22 atypical
xdr beijing isolates , 12 distinct resistance mps were observed , of which 11 isolates were clustered ( mp27 ) and 11 had unique genotypes ( mp1922 , mp24 , mp29 , mp3940 , mp4243 , mp47 ) . * cb - dst , culture - based drug susceptibility testing ; r , resistant ; mb - dst , molecular - based dst ; s , sensitive ; inh , isoniazid ; rif , rifampin ; str , streptomycin ; emb , ethambutol ; eth , ethionamide ; ofl , ofloxacin ; amk , amikacin ; cap , capreomycin .
spatial analysis of the patients origins showed that pre - xdr and xdr isolates with an atypical beijing genotype were found in 5 of 8 district municipalities ( figure ; technical appendix table ) . the largest atypical pre - xdr beijing genotype cluster ( mp5 )
was identified in 4 adjacent district municipalities ( technical appendix table ) , and the largest xdr tb cluster ( mp6 ) was identified in 3 of these districts as well as in an additional district , which suggests the past spread of these genotypes .
the presence of mutations in target genes known to confer resistance with high confidence indicated that 95.1% ( 98/103 ) of the atypical xdr beijing isolates were resistant to at least 10 anti - tb drugs : isoniazid , rifampin , ethambutol , pyrazinamide , streptomycin , amikacin , kanamycin , capreomycin , ethionamide , and ofloxacin .
the extent of drug resistance in these isolates was underestimated by routine dst ( table 2 ) .
the correlation between molecular - based drug - resistance and routine culture - based dst was 99.6% for isoniazid , 100% for rifampin , 28% for ethambutol , 92% for streptomycin , 93% for amikacin , 27% for capreomycin , 52% for ethionamide , and 86% for ofloxacin
routine dst for pyrazinamide , kanamycin , cycloserine , and para - aminosalicylic acid was not performed .
dst for para - aminosalicylic acid was done at stellenbosch university on 45 isolates ; 9 showed resistance at a level of > 4.0 g / ml .
review of routine dst results highlights the severity of the drug - resistant tb epidemic in south africa ( 4 ) and thereby emphasizes the urgent need for curbing the rising incidence of drug resistance in the country .
this result can only be achieved by implementing appropriate intervention strategies based on knowledge of the mechanisms fueling this epidemic .
recently , molecular epidemiologic techniques were used in combination with classical epidemiologic data to enhance understanding of the tb epidemic in different settings .
those studies have quantified the relative proportion of acquisition versus transmission and have described the population structure of m. tuberculosis over time ( 7,10,22,24,25 ) . using these approaches ,
we show that patients with mdr tb in the eastern cape could be divided into 2 distinct groups : isolates from patients infected with mdr ss showed diverse genetic backgrounds , while isolates from patients infected with pre - xdr tb and xdr tb showed restricted genetic backgrounds .
the finding that the pre - xdr tb and xdr tb strains are genetically distinct when compared to the mdr ss strains is counterintuitive because we would expect all mdr tb strains to have had an equal chance of acquiring resistance to second - line anti - tb drugs .
the absence of second - line resistance among a large number of different mdr tb genotypes suggests that under the current mdr tb treatment regimen , acquisition of additional resistance in mdr ss strains is reduced .
conversely , analysis of the dna sequencing data showed a significant association between the atypical beijing genotype and mutations conferring second - line resistance .
this demonstrates that this genotype has acquired resistance to the level of pre - xdr tb , which in turn has spread and thereafter has acquired additional resistance to the level of xdr tb , followed again by transmission .
an alternative explanation would be that the atypical beijing genotype acquires resistance by conferring mutations more readily than other genotypes .
however , the convergent evolution of 7 different mutations within a single genotype is highly unlikely .
analysis of the locations of the pre - xdr tb case - patients infected with this clone shows that it had a wide geographic distribution , which suggests that this genotype has been in circulation for an extended period .
this conclusion was further supported by the analysis of the evolutionary order in which resistance was acquired ( technical appendix table ) , which showed that the ancestral clone first acquired resistance to isoniazid and streptomycin .
this could be explained by the treatment regimen used in the early 1960s , which was based on the combination of isoniazid and streptomycin ( 26 ) .
a similar conclusion was drawn from whole genome sequence data which predicted that mutations conferring resistance to isoniazid and streptomycin were deeply rooted in the atypical beijing genotype ( 27 ) .
given the extent of resistance in pre - xdr tb strains and the extremely limited treatment options available , the emergence of ofloxacin resistance was inevitable .
this idea was supported by our molecular - based analysis of the xdr tb isolates , which demonstrated that resistance to a fluoroquinolone had been acquired independently on several different occasions ( several different gyra mutations were observed ) , followed by amplification through transmission ( clustering of xdr phenotypes was observed ) .
however , the true extent of acquisition may be higher than predicted , given that the xdr tb isolates were cultured from samples from patients who resided in different district municipalities , and contact was unlikely because of the long distances .
we suggest that the absence of routine second - line drug susceptibility testing and the treatment of mdr tb with an inadequate standardized regimen , according to the 2004 guidelines ( www.sahealthinfo.org/tb/mdrtbguidelines.pdf ) ( 6 months intensive phase : kanamycin , ethionamide , pyrazinamide , ofloxacin , and cycloserine or ethambutol ; 1218 months continuation phase : ethionamide , ofloxacin , and cycloserine or ethambutol ) ( 28 ) may have led to the inappropriate treatment of undiagnosed pre - xdr tb cases
. this regimen would have prolonged the period of infectiousness leading to transmission to close contacts and increased the risk of amplification of resistance ( 28,29 ) .
this problem has been recently addressed with the implementation of a revised treatment regimen ( 28 ) as well as routine second - line dst , which is now done on all isolates shown to be resistant to rifampin . however , these tests are culture - based , which exacerbates diagnostic delay and possible transmission .
this situation can be partially resolved with the implementation of a genetic - based second - line drug susceptibility test ( 29 ) .
however , the extent of resistance associated with the atypical beijing genotype makes treatment options extremely difficult as these isolates are resistant to all first - line anti - tb drugs ( isoniazid , rifampin , ethambutol , pyrazinamide and streptomycin ) and many of the second - line drugs ( amikacin , kanamycin , ofloxacin , ethionamide , capreomycin ) .
this suggests that the atypical beijing genotype clone is evolving toward total drug resistance ( defined as in vitro resistance to all first - line drugs , as well as aminoglycosides , cyclic polypeptides , fluoroquinolones , thioamides , serine analogs , and salicylic acid derivatives ) with acknowledgment of who s concern over the definition ( 31 ) .
our molecular - based results are in accordance with a recent study from the eastern cape , which documented extremely poor treatment outcomes for xdr tb case - patients ( 12 ) .
the authors found that these patients experienced a high death rate ( 58.4% ) and low culture - conversion rates ( 8.4% ) over a follow - up period of 143 days .
they concluded that only 1.7 drugs per patient could be regarded as effective on the basis of dst results , previous treatment records , or both .
given that this study was conducted concurrently with ours , it is highly likely that a large proportion of their patients were also infected with xdr tb strains with an atypical beijing genotype .
thus , the poor treatment outcome may be related to the extent of drug - resistance ; however , we can not exclude the possibility that the atypical beijing genotype contributes to illness and death .
a further concern is the knowledge that this clone is now spreading to other provinces in south africa , possibly due to migration . in western cape province ,
an estimated 55% of xdr tb case - patients harbor isolates with the atypical beijing genotype ( 32 ) .
first , clinical data were not available for this study , and thus it was not possible to establish the effects of drug resistance on treatment outcome . however , we do not believe that the strains reported by kvasnovsky et al .
( 12 ) differ from those analyzed in this study because the studies were conducted concurrently .
second , our analysis of a convenience sample may have led to an overestimation of the proportion of pre - xdr tb and xdr tb cases in eastern cape province .
third , our use of mutational data to categorize patient isolates as mdr ss , pre - xdr , and xdr is not the accepted standard .
however , genetic dst has been endorsed by who for first - line anti - tb drugs , and mounting evidence indicates that high confidence mutations accurately predict second - line drug resistance ( 33 ) .
the diagnostic dilemma facing tb control managers in eastern cape province is how to rapidly identify case - patients at risk of harboring the atypical beijing genotype to prioritize dst , ensure patient isolation , and administer appropriate treatment .
previous studies have shown a strong association between inha promoter mutations and pre - xdr tb and xdr tb ( 34 ) . given
that the genotype mtbdrplus test ( 35 ) has been implemented as the diagnostic standard in most nhls laboratories in south africa , we propose that this test could be used as a rapid screening tool to identify patients harboring drug - resistant atypical beijing strains ( 34 ) . to contain the spread of this virtually untreatable form of tb , control managers must make use of this information .
table showing the geographic distribution of atypical beijing genotype mycobacterium tuberculosis isolates and their mutation patterns , and 2 figures showing is6110 dna fingerprint patterns of a subset of atypical beijing pre
extensively drug - resistant tuberculosis isolates and of a subset of atypical beijing extensively drug - resistant tuberculosis isolates and their geographic origin , south africa , 20082009 . | factors driving the increase in drug - resistant tuberculosis ( tb ) in the eastern cape province , south africa , are not understood . a convenience sample of 309 drug - susceptible and 342 multidrug - resistant ( mdr ) tb isolates , collected july 2008july 2009 ,
were characterized by spoligotyping , dna fingerprinting , insertion site mapping , and targeted dna sequencing .
analysis of molecular - based data showed diverse genetic backgrounds among drug - sensitive and mdr tb sensu stricto isolates in contrast to restricted genetic backgrounds among pre extensively drug - resistant ( pre - xdr ) tb and xdr tb isolates .
second - line drug resistance was significantly associated with the atypical beijing genotype .
dna fingerprinting and sequencing demonstrated that the pre - xdr and xdr atypical beijing isolates evolved from a common progenitor ; 85% and 92% , respectively , were clustered , indicating transmission .
ninety - three percent of atypical xdr beijing isolates had mutations that confer resistance to 10 anti - tb drugs , and some isolates also were resistant to para - aminosalicylic acid .
these findings suggest the emergence of totally drug - resistant tb . |
the prevalence of heart failure ( hf ) continues to increase and is now the most common cause of hospitalization in the united states.1,2 routine management of patients with hf requires careful attentiveness to fluid status and diuretic treatment efficacy .
although diuretics have been in clinical use for decades , patient response and clinical effectiveness are uncertain.3 although the physical examination is a critical component for decision - making , it is limited by body habitus or subclinical hemodynamic fluid changes .
in addition to rales , edema , and elevated jugular venous pulse , clinicians measured weight , urine output , and serum creatinine on a daily basis in order to determine when euvolemia is achieved .
heterogeneity of hf and disease management present significant challenge , and often other comorbidities and conditions complicate presentation of acute decompensated heart failure ( adhf ; ie , cardiorenal syndrome).4 the two basic hemodynamic explanations for the development of cardiorenal syndrome are ( 1 ) inadequate forward perfusion typically after one or two parenteral doses of loop diuretic and ( 2 ) passive venous congestion that temporarily worsens with plasma refill from the extravascular tissues in the setting of diuresis for adhf .
daily point - of - care ultrasound is ideal to better explore these hemodynamic changes in this patient population .
assessment of cardiac structure and function is an important component in the clinical management of adhf and to understand the pathophysiology of the individual patient .
transthoracic echocardiography is the primary method of imaging individuals with hf ; however , echocardiography is used infrequently and typically not serially secondary to cost and resource utilization.5 current appropriateness guidelines do not address the use of point - of - care echocardiography in clinical scenarios of adhf to guide acute response to therapy.6 the recent availability of miniaturized ultrasound technology enables physicians to perform real - time , point - of - care ue assessment of patients.7 when applied to patients with dynamic cardiovascular disorders such as adhf , this technology allows for daily objective assessment of intravascular fluid status .
although the benefit of these devices seems obvious , little data exist on the type of information or additive benefit these devices provide in the routine care of hf patients particularly with respect to inferences concerning passive venous congestion of the kidneys .
this prospective , observational trial examined the use of handheld , ultraportable echocardiography ( ue ) by physicians in patients admitted with adhf .
the purpose of this study was to measure daily changes in ue in patients with adhf and compare those who respond to diuretic therapy to those who did not .
this prospective comparative trial examines physiologic measures of intravascular fluid volume derived from ue and explores predictors of diuretic response in adhf .
this study was conducted from december 2011 to january 2012 at genesys regional medical center ( grmc ) , a 410-bed community - based teaching hospital .
symptomatic patients admitted to grmc with the primary diagnosis of adhf who were able to provide informed consent were considered for selection during initial cardiac consultation .
subjects with adequate visualization with ue ( as determined by preliminary imaging by the echocardiologist study investigator [ tev ] ) were invited to be a part of the study .
patients were excluded if they had poor , nondiagnostic imaging on ue , unable to provide informed consent , younger than 18 years , or if a prisoner or other institutionalized individual . ultimately , 77 subjects were enrolled and were typically scanned with the ultrasound device on a daily occurrence during routine physical examination . during data analysis ,
patients were divided into two groups based on whether or not they achieved a negative fluid output of 3 l within 48 hours .
achievement of 3 l of fluid removal represented the median urine output of all study participants and was therefore selected as the criterion for patient inclusion in the diuretic responder cohort .
the ultraportable two - dimensional ultrasound device used in this study measures 3 wide by 5.3 tall and weighs < 1 pound ( vscan ; ge ) .
this pocket - size echocardiography has the capability of providing high - quality black and white imaging with doppler color - coded blood flow imaging .
the study echocardiologist , board - certified in adult cardiovascular medicine and adult echo cardiography and experienced in echocardiographic acquisition , performed all cardiac ultrasound measurements .
daily assessment of left ventricle function with standard parasternal long- and short - axis views and apical two- and four - chamber views was performed .
finally , the size and degree of collapse of the ivc and presence / size of pericardial effusions were measured .
subcostal views of the junction of the ivc , hepatic vein and right atrium ( ra ) , and ivc collapse during inspiration were also examined .
the long- and short - axis views of the ivc were obtained and measurements were obtained at end - expiration just proximal to the junction of the hepatic veins ( approximately 0.53.0 cm before the ostium of the ra ) .
these measurements were taken at the bedside with a caliper tool available on the device , and snapshots of the actual measurements were recorded in the device .
in addition , video image clips of the ivc were acquired to access ivc variability with respiration .
ivc function was subjectively graded as having no collapse ( ivc collapse score = 2 ) , ivc collapse < 20% with quiet respiration ( ivc collapse score = 1 ) , and ivc collapse ( ivc collapse score = 0 ) 20% ( ivc collapse score = 0 ) with quiet respiration .
daily measurements were recorded in the progress notes of the patient s clinical chart during routine evaluation .
study investigators collected subject data including demographic information , medical history , and standard inpatient hf clinical data with a structured database .
ultrasound measurements , subject variables , and clinical parameters were entered into a database on a daily basis .
patient demographic information collected included age , gender , weight , and height to calculate body mass index .
factors regarding patient medical history such as documented history of hf , relevant comorbid conditions listed in the medical record , social history of smoking or alcohol use , family history of heart disease , and presence of an implantable device such as a pacemaker or automatic implantable cardioverter defibrillator were obtained .
laboratory values collected included daily serum sodium , potassium , blood urea nitrogen , and creatinine , as well as serial troponin - t and brain natriuretic peptide level at admission .
variables from chest radiography included presence of pleural effusion , cardiomegaly , and pulmonary edema as indicated by the final radiology report .
data points collected from the most recent formal transthoracic echocardiogram ( within five years ) included : ejection fraction , presence and graded severity of diastolic dysfunction , left ventricular internal diastolic and systolic dimension , interventricular septum diastolic thickness , left ventricular posterior and relative wall diastolic thickness , right ventricular systolic pressure , and presence and severity of graded valvular pathology .
objective information collected daily included vital signs at the time of examination such as oxygen requirements , 24-hour fluid intake and output per nursing records , and positive findings of jugular venous distension , a third heart sound , crackles in the lungs , hepatosplenomegaly , hepatojugular reflex , and lower extremity edema .
given the small sample size and observational design , most of the data presented as continuous variables are expressed as mean standard deviation or counts with population as appropriate .
an intraclass correlation coefficient was calculated to measure the ue ejection fraction reproducibility against standard formal echocardiography on each patient .
variables with p - values less than 0.1 on univariate analysis are considered for inclusion in the multiple regression model . using forward conditional method ,
all potential explanatory variables were assessed for collinearity , and only independent variables were included in the regression model .
lemeshow goodness - of - fit test was used to measure how well the model reflects the data on which it was created and the area under the receiver operating characteristics curve was calculated .
this study was conducted from december 2011 to january 2012 at genesys regional medical center ( grmc ) , a 410-bed community - based teaching hospital .
symptomatic patients admitted to grmc with the primary diagnosis of adhf who were able to provide informed consent were considered for selection during initial cardiac consultation .
subjects with adequate visualization with ue ( as determined by preliminary imaging by the echocardiologist study investigator [ tev ] ) were invited to be a part of the study .
patients were excluded if they had poor , nondiagnostic imaging on ue , unable to provide informed consent , younger than 18 years , or if a prisoner or other institutionalized individual . ultimately , 77 subjects were enrolled and were typically scanned with the ultrasound device on a daily occurrence during routine physical examination . during data analysis ,
patients were divided into two groups based on whether or not they achieved a negative fluid output of 3 l within 48 hours .
achievement of 3 l of fluid removal represented the median urine output of all study participants and was therefore selected as the criterion for patient inclusion in the diuretic responder cohort .
the ultraportable two - dimensional ultrasound device used in this study measures 3 wide by 5.3 tall and weighs < 1 pound ( vscan ; ge ) .
this pocket - size echocardiography has the capability of providing high - quality black and white imaging with doppler color - coded blood flow imaging .
the study echocardiologist , board - certified in adult cardiovascular medicine and adult echo cardiography and experienced in echocardiographic acquisition , performed all cardiac ultrasound measurements .
daily assessment of left ventricle function with standard parasternal long- and short - axis views and apical two- and four - chamber views was performed .
the mitral and aortic valves were measured using color doppler assessment . finally , the size and degree of collapse of the ivc and presence / size of pericardial effusions were measured .
subcostal views of the junction of the ivc , hepatic vein and right atrium ( ra ) , and ivc collapse during inspiration were also examined .
the long- and short - axis views of the ivc were obtained and measurements were obtained at end - expiration just proximal to the junction of the hepatic veins ( approximately 0.53.0 cm before the ostium of the ra ) .
these measurements were taken at the bedside with a caliper tool available on the device , and snapshots of the actual measurements were recorded in the device .
in addition , video image clips of the ivc were acquired to access ivc variability with respiration .
ivc function was subjectively graded as having no collapse ( ivc collapse score = 2 ) , ivc collapse < 20% with quiet respiration ( ivc collapse score = 1 ) , and ivc collapse ( ivc collapse score = 0 ) 20% ( ivc collapse score = 0 ) with quiet respiration .
daily measurements were recorded in the progress notes of the patient s clinical chart during routine evaluation .
study investigators collected subject data including demographic information , medical history , and standard inpatient hf clinical data with a structured database .
ultrasound measurements , subject variables , and clinical parameters were entered into a database on a daily basis .
patient demographic information collected included age , gender , weight , and height to calculate body mass index .
factors regarding patient medical history such as documented history of hf , relevant comorbid conditions listed in the medical record , social history of smoking or alcohol use , family history of heart disease , and presence of an implantable device such as a pacemaker or automatic implantable cardioverter defibrillator were obtained .
laboratory values collected included daily serum sodium , potassium , blood urea nitrogen , and creatinine , as well as serial troponin - t and brain natriuretic peptide level at admission .
variables from chest radiography included presence of pleural effusion , cardiomegaly , and pulmonary edema as indicated by the final radiology report .
data points collected from the most recent formal transthoracic echocardiogram ( within five years ) included : ejection fraction , presence and graded severity of diastolic dysfunction , left ventricular internal diastolic and systolic dimension , interventricular septum diastolic thickness , left ventricular posterior and relative wall diastolic thickness , right ventricular systolic pressure , and presence and severity of graded valvular pathology .
objective information collected daily included vital signs at the time of examination such as oxygen requirements , 24-hour fluid intake and output per nursing records , and positive findings of jugular venous distension , a third heart sound , crackles in the lungs , hepatosplenomegaly , hepatojugular reflex , and lower extremity edema .
given the small sample size and observational design , most of the data presented as continuous variables are expressed as mean standard deviation or counts with population as appropriate .
an intraclass correlation coefficient was calculated to measure the ue ejection fraction reproducibility against standard formal echocardiography on each patient .
variables with p - values less than 0.1 on univariate analysis are considered for inclusion in the multiple regression model .
using forward conditional method , variables were entered into the model and the regression analysis was performed .
all potential explanatory variables were assessed for collinearity , and only independent variables were included in the regression model .
lemeshow goodness - of - fit test was used to measure how well the model reflects the data on which it was created and the area under the receiver operating characteristics curve was calculated .
there were a total of 77 patients who fulfilled study criteria and were included in this analysis .
the overall mean age was 67.0 ( sd 13.1 ) years , 58% of patients were male , and the average body mass index ( bmi ) was 29.5 kg / m .
the minimum , average , and maximum inpatient length of stay was 3.0 , 6.7 , and 14 days , respectively .
of the total 77 patients , 25 patients ( 32.4% ) presented with new - onset adhf and the remainder presented with acute exacerbation of chronic hf .
baseline demographic information of the patients are presented in table 1 . in total , with all patient days combined , the study population consisted of 544 inpatient days , in which 431 days ( 79.2% ) were spent for ue . in total , 73 of 77 patients survived to hospital discharge and one patient expired during the study .
patients with new - onset hf comprised 32.4% of the study , while 67.5% were found to have an acute exacerbation of chronic hf .
the most frequent comorbid conditions were hypertension ( 53.3% ) , hyperlipidemia ( 44.2% ) , coronary artery disease ( 41.6% ) , anemia ( 42.9% ) , and tobacco use ( 41.6% ) .
atrial fibrillation was present in 32.5% , chronic obstructive pulmonary disease was present in 11.7% , and diabetes was present in 19.5% .
overall formal echocardiography showed a decreased mean left ventricular ejection fraction ( lvef ) of 39.6% ( sd 16.7% ) .
the majority of patients ( 79.2% ) also had diastolic dysfunction and mitral valve regurgitation was another common finding .
the mean left ventricular internal diastolic dimension was 6.22 cm ( sd 1.12 cm ) , mean left ventricular internal systolic dimension was 4.89 cm ( sd 1.52 cm ) , interventricular septum diastolic thickness was 1.20 cm ( sd 0.12 cm ) , left ventricular posterior wall diastolic thickness was 1.14 cm ( sd 0.11 cm ) , left ventricular relative wall thickness was 0.38 cm ( sd 0.062 cm ) , and mean right ventricular systolic pressure was 45.5 mmhg .
of the 77 subjects , 12 patients were observed to have noticeable improvement in cardiac function during the course of the hospital stay by ue .
of the 12 patients with improved lv function , the majority of these patients had new - onset hf and most were presumed to be nonischemic cardiomyopathy ( only one patient had coronary angiography performed ) .
this patient presented with acute on chronic decompensated hf secondary to acute on chronic myocardial ischemia / infarction .
this patient had an initial lvef of approximately 45% visualized by ue , and over the next three days , the lvef deteriorated to approximately 15% .
unfortunately , the patient was deemed nonrevascularizable , and despite maximal therapy , the patient developed cardiogenic shock and expired from a malignant arrhythmia on hospital day 4 .
the diameter of the ivc was measured on each participant on day 1 of hospitalization and on subsequent hospital days . the change in ivc diameter at 48 hours
the mean ivc diameter for all subjects upon initial hospitalization was 2.04 cm ( 0.37 cm ) , the mean ivc diameter for all subjects after 48 hours was 2.03 cm ( 0.49 cm ) , and the mean 48-hour change in ivc diameter was 0.013 cm ( 0.270 cm ) .
figure 1 demonstrates a patient who was treated over four days and the change in ivc diameter and other relevant clinical variables . on average , the ivc dimension decreased by 0.23 cm ( 0.37 cm ) over the study course . in all but three patients , the ivc dimension decreased over the total examination period . in the three patients in whom the ivc dimension increased , the absolute measurement on the final day study remained within the normal range ( < 2.0 cm ) for ivc dimension . in the remaining one patient ,
the ivc measured 2.4 cm upon study enrollment and measured 2.6 cm on the last day of hospitalization ( hospital day 6 ) .
mean 48-hour urine output for the study group was 3,089 ml ( sd 1,319 ml ) , 48-hour fluid intake was 1,622 ( 348.5 ) , and 48-hour net fluid balance was 1,466 ml ( 1,406 ml ) .
a total of 29 ( 37.7% ) in the study population achieved the goal of a negative fluid balance of greater than 3,000 ml within the first 48 hours and were labeled the responder cohort .
the remaining 48 ( n = 62.3% ) participants did not achieve a negative fluid balance of at least 3,000 ml and were described as the nonresponder cohort . as described in table 1 , univariate comparisons were made between two study cohorts and atrial fibrillation and hypertension were less common in the responder cohort .
there was a greater change in the ivc diameter after 48 hours in the responder versus nonresponder cohort ( 0.2 vs. 0.1 ,
. there was higher presenting b - type natriuretic peptide ( bnp ) levels in responder cohort . on the other hand ,
the presenting systolic blood pressure was less in the responder cohort than the nonresponder group .
although it did not achieve statistical significance , the presence of new - onset hf was present with a higher frequency in the responder cohort as compared to the nonresponder cohort ( 25.6% vs. 45.3% , p = 0.073 ) .
the variables that achieved significance with p - values less than 0.10 were used to construct multiple regression model .
these included presence of hypertension , atrial fibrillation , new - onset hf , chronic kidney disease ( ckd ) , in addition to the bnp level , and change in ivc dimension .
fluid input / output measurements and pre / post ivc diameter were excluded from the multivariable model secondary to collinearity with other variables .
as described in table 3 , negative change in ivc diameter , the absence of ckd , and increased bnp value independently predicted higher likelihood of responding to diuretic therapy . based on this regression model for every 1 mm decrease in the ivc diameter at 48 hours
, there was an odds ratio of 1.62 ( 95% ci : 1.202.19 ) for responding to diuretic therapy ( > 3,000 ml of fluid output at 48 hours ) , independent of other variables .
goodness - of - fit calculation revealed that the model appropriately fit the data , and the area under the receiver operating characteristics curve was 0.85 as described in table 3 and figure 2 .
there were a total of 77 patients who fulfilled study criteria and were included in this analysis .
the overall mean age was 67.0 ( sd 13.1 ) years , 58% of patients were male , and the average body mass index ( bmi ) was 29.5 kg / m .
the minimum , average , and maximum inpatient length of stay was 3.0 , 6.7 , and 14 days , respectively .
of the total 77 patients , 25 patients ( 32.4% ) presented with new - onset adhf and the remainder presented with acute exacerbation of chronic hf .
baseline demographic information of the patients are presented in table 1 . in total , with all patient days combined , the study population consisted of 544 inpatient days , in which 431 days ( 79.2% ) were spent for ue . in total , 73 of 77 patients survived to hospital discharge and one patient expired during the study .
patients with new - onset hf comprised 32.4% of the study , while 67.5% were found to have an acute exacerbation of chronic hf .
the most frequent comorbid conditions were hypertension ( 53.3% ) , hyperlipidemia ( 44.2% ) , coronary artery disease ( 41.6% ) , anemia ( 42.9% ) , and tobacco use ( 41.6% ) .
atrial fibrillation was present in 32.5% , chronic obstructive pulmonary disease was present in 11.7% , and diabetes was present in 19.5% .
overall formal echocardiography showed a decreased mean left ventricular ejection fraction ( lvef ) of 39.6% ( sd 16.7% ) .
the majority of patients ( 79.2% ) also had diastolic dysfunction and mitral valve regurgitation was another common finding .
the mean left ventricular internal diastolic dimension was 6.22 cm ( sd 1.12 cm ) , mean left ventricular internal systolic dimension was 4.89 cm ( sd 1.52 cm ) , interventricular septum diastolic thickness was 1.20 cm ( sd 0.12 cm ) , left ventricular posterior wall diastolic thickness was 1.14 cm ( sd 0.11 cm ) , left ventricular relative wall thickness was 0.38 cm ( sd 0.062 cm ) , and mean right ventricular systolic pressure was 45.5 mmhg .
of the 77 subjects , 12 patients were observed to have noticeable improvement in cardiac function during the course of the hospital stay by ue . of the 12 patients with improved lv function ,
the majority of these patients had new - onset hf and most were presumed to be nonischemic cardiomyopathy ( only one patient had coronary angiography performed ) .
this patient presented with acute on chronic decompensated hf secondary to acute on chronic myocardial ischemia / infarction .
this patient had an initial lvef of approximately 45% visualized by ue , and over the next three days , the lvef deteriorated to approximately 15% .
unfortunately , the patient was deemed nonrevascularizable , and despite maximal therapy , the patient developed cardiogenic shock and expired from a malignant arrhythmia on hospital day 4 .
the diameter of the ivc was measured on each participant on day 1 of hospitalization and on subsequent hospital days . the change in ivc diameter at 48 hours
the mean ivc diameter for all subjects upon initial hospitalization was 2.04 cm ( 0.37 cm ) , the mean ivc diameter for all subjects after 48 hours was 2.03 cm ( 0.49 cm ) , and the mean 48-hour change in ivc diameter was 0.013 cm ( 0.270 cm ) .
figure 1 demonstrates a patient who was treated over four days and the change in ivc diameter and other relevant clinical variables . on average , the ivc dimension decreased by 0.23 cm ( 0.37 cm ) over the study course . in
all but three patients , the ivc dimension decreased over the total examination period . in the three patients in whom the ivc dimension increased , the absolute measurement on the final day study remained within the normal range ( < 2.0 cm ) for ivc dimension . in the remaining one patient ,
the ivc measured 2.4 cm upon study enrollment and measured 2.6 cm on the last day of hospitalization ( hospital day 6 ) .
mean 48-hour urine output for the study group was 3,089 ml ( sd 1,319 ml ) , 48-hour fluid intake was 1,622 ( 348.5 ) , and 48-hour net fluid balance was 1,466 ml ( 1,406 ml ) .
a total of 29 ( 37.7% ) in the study population achieved the goal of a negative fluid balance of greater than 3,000 ml within the first 48 hours and were labeled the responder cohort .
the remaining 48 ( n = 62.3% ) participants did not achieve a negative fluid balance of at least 3,000 ml and were described as the nonresponder cohort . as described in table 1 , univariate comparisons were made between two study cohorts and atrial fibrillation and hypertension were less common in the responder cohort .
there was a greater change in the ivc diameter after 48 hours in the responder versus nonresponder cohort ( 0.2 vs. 0.1 , p < 0.001 ) .
there was higher presenting b - type natriuretic peptide ( bnp ) levels in responder cohort . on the other hand ,
the presenting systolic blood pressure was less in the responder cohort than the nonresponder group . although it did not achieve statistical significance , the presence of new - onset hf was present with a higher frequency in the responder cohort as compared to the nonresponder cohort ( 25.6% vs. 45.3% , p = 0.073 ) .
the variables that achieved significance with p - values less than 0.10 were used to construct multiple regression model .
these included presence of hypertension , atrial fibrillation , new - onset hf , chronic kidney disease ( ckd ) , in addition to the bnp level , and change in ivc dimension .
fluid input / output measurements and pre / post ivc diameter were excluded from the multivariable model secondary to collinearity with other variables . as described in table 3 , negative change in ivc
diameter , the absence of ckd , and increased bnp value independently predicted higher likelihood of responding to diuretic therapy . based on this regression model for every 1 mm decrease in the ivc diameter at 48 hours
, there was an odds ratio of 1.62 ( 95% ci : 1.202.19 ) for responding to diuretic therapy ( > 3,000 ml of fluid output at 48 hours ) , independent of other variables .
goodness - of - fit calculation revealed that the model appropriately fit the data , and the area under the receiver operating characteristics curve was 0.85 as described in table 3 and figure 2 .
attributable to its novelty , no previous studies have described the use of the latest generation of ue in routine clinical management of adhf .
the data from this small observational study demonstrate the ability of ue to predict patient response to diuretics when treated for adhf . at the present time
, ue is approved by regulatory bodies for clinical use in medicine and is commercially available7 ; however , little data exist on the type of information or additive benefit these devices provide in the routine care of hf patients . when used as an extension of the daily physical examination , fluid overload can be monitored noninvasively with ultrasound measurements of global left ventricular function and change in ivc diameter.8 until recently , significant barriers to ultrasound device technology prevented their implementation for routine use .
reduction in device size , weight , and cost , with improvements in battery life , and ease of use are making inroads for this bedside tool .
factors such as time constraints , noisy intensive care units , and patient body habitus have threatened the time - honored physical examination .
this movement away from relying solely on older practices may be justifiable , as evidence - based scrutiny is lacking for many of these subjective examination techniques when applied in contemporary settings.9,10 this new era is moving ultrasound technology from the realm of formalized diagnostic imaging into the realm of a tool used to supplement the physical examination much the same as the stethoscope ( table 4).11 ue ultimately fulfills its promise by allowing us to finally visualize pathology directly than traditional methods and adds to other established examination methods ( ie , percussion , palpation , and auscultation ) .
hf is a very heterogenous clinical disorder and requires physicians to utilize multiple data points to make the diagnosis including history , physical examination , and testing .
previous literature suggests that ultrasound assessment of structures like the ivc can provide valuable supplemental data to aid in diagnosis and management.1214 as described , the significant change observed in these patients was a decrease in mean ivc size over the study period .
novel to our report , we demonstrate the ability of the ue to provide these data .
ivc diameter is an estimation of right atrial pressure and is analogous to the changes that occur with jugular venous distention in patients treated for fluid overload .
the value of sequential assessment of the jugular venous distention is that it helps monitor patient clinical status and individually tailor diuretic therapy.15 it can be very difficult to assess response to diuretic therapy within the first few days of initiation
. it can also be very difficult to predict which patients will respond favorably to diuretic therapy as evident by the lack of difference in clinical variables between the responders and nonresponders observed in this study .
as expected , impaired renal function and lower bnp levels in patients predicted less responsiveness to diuretic therapy based on the multivariate regression .
the change in the ivc diameter , however , was very robust in prediction of diuretic response .
importantly , if the ivc diameter remained relatively unchanged or increased with diuresis , it predicted a poor response in urine output over the next several days , suggesting increased plasma refill and temporary increases in passive renal congestion .
this is consistent with a previous report that bnp , ivc size , and collapsibility were able to predict 30-day readmission in adhf patients.16
our study has all the limitations of small prospective cohort studies and unblinded assessments using novel technology .
we present data from a small number of patients where clinical utility was observed ; therefore , a considerably larger study without selection bias is still needed .
this study did not capture data on the exact dose of diuretic administered , daily medication changes , and many other clinical variables that would be expected to be present in patients admitted with adhf .
patients with poor acoustic visualization were excluded , so future studies should compare conventional 3d echocardiography to its pocket counterpart to further describe limitations . showing raw data obtained from routine clinical care does not yield consistent information among all patients enrolled , particularly with variations in daily laboratories and the number of days patients scans .
it is thought that primary care providers and residents would benefit from ue,17 so further investigation is needed to support what level of basic training is necessary for reproducible results in the hf population .
while ultrasound is noninvasive and cost - effective , use of handheld echocardiography requires initial investment by the provider .
finally , we did not have advanced biomarkers of acute kidney injury ( aki ) or imaging measures of intrarenal venous congestion or intracapsular pressure , and thus , our inference on passive renal congestion and aki is indirect .
with daily ultrasound measurement , this study demonstrates that a negative change in ivc diameter , the absence of diagnosed ckd , and bnp value independently predicted higher likelihood of responding to diuretic therapy within the first 48 hours . | backgroundroutine management of patients with acute decompensated heart failure ( adhf ) requires careful attentiveness to fluid status and diuretic treatment efficacy .
new advances in ultrasound have made ultraportable echocardiography ( ue ) available to physicians for point - of - care use .
the purpose of this study is to explore physiologic measures of intravascular fluid volume derived from ue and explore predictors of diuretic response in adhf.methodsvarious echocardiography imaging measurements , particularly diameter and collapse of inferior vena cava ( ivc ) , were collected from 77 patients admitted with a primary diagnosis of adhf .
patients were divided into two groups based on whether or not they achieved a net negative fluid output of 3 l within 48 hours .
the demographic information , serum laboratory markers , and physical characteristics of the subjects were obtained to correlate with daily ultrasound measurements .
univariate and multivariate analyses were used to compare diuretic
responders to
nonresponders.resultsa
negative change in the ivc diameter at 48 hours was robust in prediction of diuretic response .
for every 1 mm decrease in the ivc diameter at 48 hours , there was an odds ratio of 1.62 ( 95% ci : 1.202.19 ) for responding to diuretic therapy independent of other variables including baseline renal filtration function and blood b - type natriuretic peptide.conclusionassessment of central venous pressure as a proxy for passive renal congestion independently predicts initial diuretic response in adhf .
future research is needed to further understand the individual variation in response to loop diuresis and to identify optimal treatment approaches that utilize anatomic and physiologic measures such as venous ultrasound . |
the fact that two - photon states generated by spontaneous parametric down - conversion ( spdc ) are entangled in transverse spatial modes with high schmidt numbers opens a possibility of encoding information in two - photon states using larger alphabets @xcite . to this end
, it is of importance to understand whether the transverse mode correlation is still present in any extent after the down - converted two - photon states have propagated through a turbulent medium . among the many possible sets of orthogonal higher - order optical beam modes , the best known are the laguerre - gaussian ( lg ) and hg modes .
lg modes are of particular interest as their helical phase front structures carry orbital angular momentum ( oam)@xcite . due to this complex spatial distribution , lg modes
can not be efficiently coupled to single - mode fibers . in order to detect higher - order modes ,
computer generated holograms shall be used to transform the higher - order modes to the zero - order ones which are further coupled to single - mode fibers @xcite .
computer generated holograms can also be used to project superposition states of lg modes to a particular state defined by the hologram necessary for verification of entanglement @xcite . as the hologram and the single mode fiber configuration is sensitive to the radial distribution of the source ( characterized by the mode number @xmath0 ) ,
measurements of only the spiral spectrum of entangled two - photon states have been carried out @xcite . in the presence of turbulence ,
the evolution of entanglement in the three dimensional lg mode basis has been observed using a single phase screen model for one of the photons , either signal or idler @xcite .
recently , an experiment on transmission of oam modes of light over a distance of 143 kilometers has been performed @xcite .
the atmospheric fourth - order correlation function for the spdc process , when the field of pump represents any of hg or lg modes as well as a partially coherent field has been calculated analytically in ref .
@xcite , showing that the joint probability for detection of the signal and idler photons in different positions is considerable after propagation for more than five kilometers . in this letter
, we go a step forward and calculate the joint probability to detect the photons in different hg modes ( see eq .
( [ final_expression ] ) ) which is a product of functions , which mixes the indices of signal and idler implying that the entanglement is preserved .
our results also show that some pairs of modes are more robust to the crosstalk due to atmospheric propagation than others which can be beneficial for free space quantum communication purposes .
full spatial entanglement has been accessed experimentally with feasible radial detection modes with negligible cross correlations in vacuum @xcite .
the expected perfectly ( anti)correlated pure state from spdc has the form @size8@mathfonts @@@#1 @xmath1 where the coefficients @xmath2 are the probability amplitudes to detect a signal photon in the @xmath3 mode and an idler photon in the @xmath4 mode .
in contrast to the azimuthal modes , their radial counterparts do not necessarily represent schmidt modes , however , there has been found non - zero quantum correlations of detected modes with different @xmath0 @xcite . instead of the basis of the lg modes , mathematically
, it is less costly to make use of the hg modes .
as the hg modes form a complete set , one can expand the two - photon state as @xmath5 where @xmath6 is the state prepared in spdc process and @xmath7 are the coefficients of expansion representing the probability amplitudes of detecting signal and idler photons in hg modes with mode indexes @xmath8 and @xmath9 , respectively .
the joint detection probability , @xmath10 , for signal and idler photons each in some transverse mode propagating in vacuum has been calculated before @xcite .
following ref.@xcite , we write the joint probability for two photons in modes @xmath11 and @xmath12 , in the representation of the configuration space variables which facilitates accounting for the atmospheric effects on the state @xmath13 where @xmath14 is the two - photon state generated by spdc @xcite , while @xmath15 represents the two photon wavefunction . experimentally , the modes @xmath16 and @xmath17 represent phase holograms , say , to be coupled with a detection system . the frequency degenerate spdc state is of our specific interest , that is , @xmath18 expression ( [ prob_transverse_modes ] ) is independent of positions of detectors due to the fact that the fields , whose modal expansion is made up of arbitrary weighted hg modes , are shape - invariant @xcite .
the shape - invariant property will no longer hold due to distortions caused by turbulence .
the two photon wavefunction @xmath19 thus can be taken in the far field approximation important for calculating the probability ( [ prob_transverse_modes ] ) by taking the effects of turbulence into account .
in this section we calculate the two - mode joint detection probability ( [ prob_transverse_modes ] ) taking into account the effects of turbulence .
to do so , we write the two - photon wavefunction in the form @xcite @xmath20\right]\\&\times \exp[\psi ( \textbf{x}_1,\textbf{r}')+\psi ( \textbf{x}_2,\textbf{r } '' ) ] , \end{split}\ ] ] where @xmath21 is a random function representing phase and amplitude distortions of signal and idler fields , @xmath22 is the wavelength and @xmath23 is the propagation distance . utilizing ( [ 2-phot - wf ] ) , the probability ( [ prob_transverse_modes ] ) takes the form @xmath24 \\&\times \left\langle \exp\left[\psi(\textbf{x}_1 , \textbf{r}')+\psi^{\ast}(\textbf{x}'_1 , \textbf{r}'')+ \psi(\textbf{x}_2 , \textbf{r}')+\psi^{\ast}(\textbf{x}'_2 , \textbf{r } '' ) \right]\right\rangle , \end{split}\ ] ] where @xmath25 the integration for a gaussian pump and hg mode functions , where the geometrical optics approximation along with the stochastic function @xmath26 as a gaussian random field were used , yields @xmath27 where @xmath28 @xmath29 @xmath30}{c_2c_3(1+p+q)(1+\mu+\nu - p - q)}\\&\times \gamma\left(\frac{2+p+q}{2}\right)%\left .
\gamma\left(\frac{2+\mu+\nu - p - q}{2}\right)\\&\times f\left(\frac{2+p+q}{2};\frac{2+\mu+\nu - p - q}{2 } , \frac{1}{2};c_4\right ) \biggr),%\right\},\end{aligned}\ ] ] @xmath31 is the hypergeometric function , @xmath32 is the binomial coefficient and @xmath33 is the gamma function .
other quantities are defined as @xmath34 here , @xmath35 measures the strength of the turbulence related to the rytov variance , @xmath36 where @xmath37 is the structure constant of the refractive index of the atmosphere , @xmath38 is the wavenumber .
the ensemble averaging in eq .
( [ prob_trans_modes1 ] ) is performed using the wiener - khinchin theorem with the tatarskii power spectrum of index of refraction fluctuations .
similar calculation can be found in ref .
being one of the main results of our paper , expression ( [ final_expression ] ) shows that the joint two - mode detection probability for signal and idler photons is a product of functions , which mixes the indices of signal and idler .
this directly implies that the entanglement is preserved . as the two - photon wavefunction in eq.([2-phot - wf ] ) is expressed in the paraxial approximation , thus not properly normalized , the sums @xmath39 do not converge to unity .
this is because the shapes of the higher and higher order modes increase , leading to a deviation from the paraxial approximation . to have better insight
, one can arrange the values of eq.([final_expression ] ) in a matrix .
below we construct the first 100 values of ( [ final_expression ] ) in a @xmath40 matrix for the vacuum case + @xmath41 + the elements @xmath42 of the matrix are double indices corresponding to mode numbers of signal and idler ranging as @xmath43,@xmath44,@xmath45,@xmath46,@xmath47,@xmath48,@xmath49,@xmath50,@xmath51,@xmath52 , where @xmath53 .
moreover , the matrix elements satisfy selection rules obtained in ref .
@xcite @xmath54 the matrix for a weak turbulence regime , more precisely , for @xmath55 and for the propagation distance @xmath56 km , the wavelength @xmath57 m and the spot size of the pump at the nonlinear crystal @xmath58 cm has the form shown in eq.([matr - turb ] ) , .
we see that all elements are different from zero : the atmosphere causes crosstalk between different modes .
the variation of the first two matrix elements with the strength of turbulence is shown in fig.[fig1 ] .
for the first line of the matrix , we compare the behavior of the probabilities for two different turbulence conditions @xmath59 , and @xmath60 with the vacuum case .
we let the propagation distance , the fresnel ratio and the spot size of the pump at the crystal to be the same .
one can see that the crosstalk between modes is not uniform : photons tend to stay in some modes , e.g. , \{00,02 } and \{00,20 } , conversely , crosstalk to some modes , e.g. , \{00,01 } , \{00,10 } is more preferred than to others , e.g. , \{00,12 } and \{00,21}. therefore , in making quantum communication with hg alphabet , one has a distinctive choice of modes that can increase the fidelity of the communication .
one should also note that this is true for quite weak turbulence conditions as demonstrated in fig.[fig2 ] .
@xmath61 fig.[fig1 ] shows that forbidden probabilities , imposed by the selection rules ( [ selection - rules ] ) , increase due to the crosstalk between modes caused by atmosphere .
accordingly , the allowed probabilities decrease to conserve the total probability . in fig.[fig2 ] , the blue and red columns represent the probabilities for the vacuum and turbulent cases , respectively .
the quantum state produced by spdc process is entangled in spatial degrees of freedom .
the entanglement in the hg transverse modes has been shown by walborn _ et _ _ al .
_ @xcite by implying restrictions on both the parity and order of the down - converted hg fields , recapped in eq.([selection - rules ] ) .
one could use this higher dimensional entanglement to make quantum communication with a large alphabet , thereby enhancing the security of the communication . for a long distance and , eventually , global quantum communication with entangled photonic states one needs to consider the effects of the atmosphere .
we obtained an analytic expression for the joint detection probability for signal and idler photons either of them to be found in an hg mode of any order .
we considered a gaussian beam as a pump and used the paraxial approximation for the down - converted fields .
our results show that for a propagation distance of 5 km there is a nonuniform crosstalk between modes : there are modes that tend to stay populated while some tend to stay empty . this feature can be used to enhance the quantum communication fidelity by selecting appropriate mode projectors at the detectors side . s. p.
walborn , a. n. de oliveira , r. s. thebaldi , and c. h. monken , `` entanglement and conservation of orbital angular momentum in spontaneous parametric down - conversion , '' phys .
a * 69 * , 023811 ( 2004 ) . | * due to the transfer of the angular spectrum of the pump beam to the two - photon state in spontaneous parametric down - conversion the generated twin photons are entangled in hermite - gaussian ( hg ) modes .
this enables one using hg modes as an alphabet for quantum communication . for global quantum communication purposes ,
we derive an analytic expression for two - photon detection probability in terms of hg modes taking into account the effects of the turbulent atmosphere .
our result is more general as it accounts for the propagation of both , signal and idler photons through the atmosphere , as opposed to other works considering one of the photons propagation in vacuum .
we show that while the restrictions on both the parity and order of the down - converted hg fields no longer hold due to the crosstalk between modes when propagating in the atmosphere , the crosstalk is not uniform : there are more robust modes that tend to keep the photons in them . these modes can be employed in order to increase the fidelity of quantum communication . * |
the system of coupled nonlinear schrdinger equations ( cnlse ) is an attractive because of several reasons . from among them
: cnlse are a soliton supporting system , the system is a proper `` a spring board '' for investigate and track the quasi - particle ( qp ) behavior of the solitary waves ; it possesses very rich phenomenology which can be extended adding new terms in the equations ; the vector structure of the system and their solutions admits to study and treat the polarization vector @xcite , @xcite , @xcite .
the initial polarization of cnlse and its evolution during the qp interaction is a very important element .
there are numerous experimental observations ( see @xcite and cited there literature ) of the effects connected with this quantity . for the full fledged cnlse with general initial polarization
, no analytic solution is available .
it can be obtained , e.g. , via adequately devised numerical scheme .
an implicit scheme of crank - nicolson type was first proposed for the single nlse in @xcite . in order to adapt it to cnsle
, internal iterations were applied in @xcite .
the latter yielded two very important advantages : fully implicit scheme and implementation of the conservation laws on difference level within the round - off error of the calculations .
the above scheme was extended to complex arithmetic in @xcite where the computer code for gaussian elimination with pivoting of @xcite was generalized for complex - valued multi - diagonal band algebraic systems .
having in mind the importance of initial polarization , we investigated in @xcite the collision dynamics for circularly polarized solitons based on @xmath0-functions and found out that there exist infinite number of manakov two - soliton solutions preceded by polarization discontinuity ( shock ) on the place of interaction . in order to extend the range of investigations in the case of general polarization we established an auxiliary conjugate system of nonlinear ordinary differential equations @xcite in order to generate numerically initial elliptically polarized soliton solutions and applied them for numerous head - on @xcite and takeover collisions @xcite . to enrich the concept of the polarization we involved into considerations linear coupling of @xmath0-like solitons which is a generator of their rotational polarization ( breathing ) and/or gain / self - dissipation @xcite . in this work
we aim to conduct series of simulations and to track the particle - like behavior of the interacted localized non-@xmath0 waves with arbitrary ( elliptic ) initial polarization .
cnlse is system of nonlinearly coupled schrdinger equations ( also called the gross - pitaevskii or manakov - type system ) : [ strong ] @xmath1\psi , \label{strongfirst } \\
{ \rm i } \phi_t & = \beta\phi_{xx } + \bigl[\alpha_1|\phi|^2 + ( \alpha_1 + 2\alpha_2)|\psi|^2\bigr]\phi,\label{strongsecond}\end{aligned}\ ] ] where @xmath2 is the dispersion coefficient , @xmath3 describes the self - focusing of a signal for pulses in birefringent media , @xmath4 ( called cross - modulation parameter ) governs the nonlinear coupling between the equations . when @xmath5 , no nonlinear coupling is present despite the fact that `` cross - terms '' proportional to @xmath3 appear in the equations and the both equations admit identical solution equal to the solution of single nlse with nonlinearity coefficient @xmath6 .
now we turn our considerations to a modified cnlse where the nonlinear coupling is trivial but is replaced by so - called linear coupling .
nevertheless the system remains nonlinear [ eq : cnlse ] @xmath7 the magnitude of linear coupling is governed by the complex - valued quantity @xmath8 .
@xmath9 governs the oscillations between states termed as breathing solitons and actually seems their frequency of oscillation , while @xmath10 describes the gain / self - dissipation behavior of soliton solutions . as it is shown in @xcite
the breathing is present free of the interaction .
the relation between the manakov - type system ( [ strong ] ) ( when @xmath5 ) and the linearly cnlse ( [ eq : cnlse ] ) is given by the substitution ( for details see @xcite and @xcite ) @xmath11 where @xmath12 and @xmath13 are soliton solutions of .
these properties and references of the solutions allow and argue us to solve ( [ eq : cnlse ] ) instead ( [ strong ] ) in order to get more information about the breathing behavior of the soliton solutions .
let us remind that in @xcite we considered the problem in question but in the particular case when @xmath12 and @xmath13 were assumed to be certainly _
sech_-solutions of . in this paper
the solutions are pulses whose modulation amplitude is of general form ( non-_sech _ ) and their polarization rotates with time .
this determines the choice of initial conditions for numerical investigation of temporal evolution of interacting solitons . as usual we concern ourselves with the soliton solutions which are localized envelopes on a propagating carrier wave .
we assume that for each of the functions @xmath14 the initial condition has the general type @xmath15\right\}}\label{eq : incond}\ ] ] where @xmath16 stands for @xmath17 , @xmath18 is the phase speed of the envelope , @xmath19 is the initial position of the center of the soliton ; @xmath20 , @xmath21 is the vector of carrier frequencies of the components ; @xmath22 is phase vector of the two components .
note that the phase speed @xmath18 must be the same for the two components @xmath23 and @xmath24 .
otherwise they will propagate with different phase speeds and after some time the two components will be in two different positions in space , and will no longer form a single structure . for the envelopes @xmath25 , @xmath26 is a polarization angle .
we are interested in solutions with initially nontrivial carrier frequencies ( @xmath27 , i.e. , with elliptic or circular polarizations .
let us emphasize that these qualities are intrinsic to non-_sech_-like solutions .
having in mind ( [ eq : incond ] ) we implement straightforward manipulations yielding @xmath28\exp{\left\{{\rm i}\left[n_{\psi } t- \tfrac{1}{2}c(x - x - ct)+\delta_{\psi}\right]\right\}}\cos(\gamma t)\notag \\+ & { \rm i } \left[a_{\phi}''+\big(n_{\phi}+\tfrac{1}{4}c^2\big)a_{\phi}+\alpha_1 \left(a_{\phi}^2 + a_{\psi}^2\right)a_{\phi}\right]\exp{\left\{{\rm i}\left[n_{\phi } t- \tfrac{1}{2}c(x - x - ct)+\delta_{\phi}\right]\right\}}\sin(\gamma t)=0,\\ & \left[a_{\phi}''+\big(n_{\phi}+\tfrac{1}{4}c^2\big)a_{\phi}+\alpha_1 \left(a_{\phi}^2 + a_{\psi}^2\right)a_{\phi}\right]\exp{\left\{{\rm i}\left[n_{\phi } t- \tfrac{1}{2}c(x - x - ct)+\delta_{\phi}\right]\right\}}\cos(\gamma t)\notag \\+ & { \rm i } \left[a_{\psi}''+\big(n_{\psi}+\tfrac{1}{4}c^2\big)a_{\psi}+\alpha_1 \left(a_{\psi}^2 + a_{\phi}^2\right)a_{\psi}\right]\exp{\left\{{\rm i}\left[n_{\psi } t- \tfrac{1}{2}c(x - x - ct)+\delta_{\psi}\right]\right\}}\sin(\gamma t)=0.\end{aligned}\ ] ] the above two equations are true if and only if the two components of the envelope are governed by the following coupled system of differential equations : [ eq : conjsys ] @xmath29 a_{\phi}''+\big(n_{\phi}+\tfrac{1}{4}c^2\big)a_{\phi}+\alpha_1\left ( a_{\phi}^2+a_{\psi}^2\right)a_{\phi}=0 .
\label{eq : conjsys_phig}\end{aligned}\ ] ] , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=75.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=75.0% ] \(c ) @xmath35\!]\>}=180^\circ$ ] we find out that this system is explicitly equivalent to the bifurcation conjugate system corresponding to manakov case with @xmath5 ( see @xcite and @xcite ) . here
we aim to trace the strong linear coupling on the interaction in conditions of general initial polarization .
after that we construct the initial conditions for @xmath16 from ( [ eq : incond ] ) as a superposition of two two - component solitary waves located at positions @xmath36 and @xmath37 and propagating with phase speeds @xmath38 and
@xmath39 @xmath40 .,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] .,scaledwidth=75.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] .,scaledwidth=75.0% ] \(c ) @xmath35\!]\>}=180^\circ$ ] .,scaledwidth=75.0% ] .,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] .,scaledwidth=75.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] .,scaledwidth=75.0% ] \(c ) @xmath35\!]\>}=180^\circ$ ] the initial distance @xmath41 is supposed to be large enough in order the solutions not to overlay in the time moment @xmath42 .
the system ( [ eq : conjsys ] ) is solved numerically and their solutions are readily used as an approximate initial condition for the unsteady computations .
our aim is to understand better the influence of the initial polarization and the initial phase difference on the particle - like behavior of the localized waves ( qps ) .
they survive the collision with other qps ( or some other kind of interactions ) without losing its identity .
the initial difference in phases can have a profound influence on the polarizations of the solitons after the interaction as well as on the magnitude of the full energy and the amplitude of breathing . before turning to the numerical investigation we mention here that the system eq .
possesses three conservation laws when asymptotic boundary conditions are imposed , namely when @xmath43 for @xmath44 . following @xcite we define `` mass '' , @xmath45 , ( pseudo)momentum , @xmath46 , and energy , @xmath47 as follows @xmath48 where @xmath49 and @xmath50 are the left end and the right end of the interval under consideration .
the conservation laws read @xmath51 which means that for asymptotic boundary conditions cnlse admit at most 3 conservation laws , i.e. , the system is non - fully integrable .
in order to be able to obtain reliable results for the time evolution of the solution , one needs to devise a difference scheme that represent faithfully the above conservation laws .
such a scheme was proposed in @xcite , and applied in @xcite .
this scheme was based on a fast gaussian elimination solver for multi - diagonal systems @xcite .
consequently , the above mentioned scheme was implemented for complex arithmetic in @xcite , where a complex arithmetic algorithms was developed to generalize the one from @xcite .
the complex - arithmetic algorithm is four times faster , and we will use it also in the present paper .
thus , for solving eqs . with the initial conditions , numerically , we use an implicit conservative scheme in complex arithmetic : [ eq : non_lin_sche ] @xmath52 - \frac{\gamma}{2 } \left(\phi_i^{n+1}+\phi_i^n\right),\label{eq : non_lin_sche_psi } \end{gathered}\ ] ] @xmath53- \frac{\gamma}{2 } \left(\psi_i^{n+1}+\psi_i^n\right),\label{eq : non_lin_sche_phi } \end{gathered}\ ] ] , @xmath54 , @xmath55 , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=68.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] , @xmath54 , @xmath55 , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=68.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] , @xmath54 , @xmath55 , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=68.0% ] \(c ) @xmath35\!]\>}=135^\circ$ ] , @xmath54 , @xmath55 , @xmath30 , @xmath31 , @xmath32 , @xmath33 , @xmath34 and different initial phase differences.,scaledwidth=68.0% ] \(d ) @xmath35\!]\>}=180^\circ$ ] \!]\>}=0^\circ$ ] corresponding to figure [ fig : clasheld180].,scaledwidth=75.0% ] .,scaledwidth=75.0% ] .,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] .,scaledwidth=75.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] .,scaledwidth=75.0% ] \(c ) @xmath35\!]\>}=135^\circ$ ] .,scaledwidth=75.0% ] \(d ) @xmath35\!]\>}=180^\circ$ ] on mesh @xmath56 with @xmath57 , @xmath58 , @xmath59 and @xmath60 , @xmath61 it is not only convergent ( consistent and stable ) , but also conserves mass , pseudomomentum , and energy , i.e. , there exist discrete analogs @xmath62 , @xmath63 and @xmath64 , for , which arise from the scheme ( for details see @xcite ) . @xmath65= { \rm const } , \nonumber \\
e^n&=\sum_{i=2}^{n-1}\frac{-\beta}{2h^2}\left(|{\psi}^{\;n}_{i+1}-{\psi}^{\;n}_i|^2 + |{\phi}^{\;n}_{i+1}- { \phi}^{\;n}_i|^2\right)+ \frac{\alpha_1}{4}\left(|\psi^{n}_i|^2+|\phi^{n}_i|^2\right)^2 + \gamma { \re}[\bar \phi_i^n \psi_i^n ] = { \rm const } , \nonumber\end{aligned}\ ] ] for @xmath66 .
these values are kept constant by the scheme during the time stepping .
the above scheme is of crank - nicolson type for the linear terms and we employ internal iteration to achieve implicit approximation of the nonlinear terms , i.e. , we use its linearized implementation @xcite . in this way
the order of approximation of eqs .
is @xmath67 .
the above nonlinear scheme is implemented via internal iterations as follows : @xmath68\nonumber\\ & - \frac{\gamma}{2}(\psi_i^n+\psi_i^{n+1,k}),\\ { \rm i } \frac{\phi^{n+1,k+1}_i - \phi^n_i}{\delta\tau } = & \frac{\beta}{2h^2 } \big(\phi^{n+1,k+1}_{i-1 } - 2\phi^{n+1,k+1}_{i } + \phi^{n+1,k+1}_{i+1 } + \phi^{n}_{i-1 } -2\phi^{n}_{i } + \phi^{n}_{i+1}\big ) \nonumber \\ & \hspace{-1.2in}+ \frac{\alpha_1}{4 } \left(\phi^{n+1,k}_i
+ \phi^n_i\right ) \big[\big(|\phi^{n+1,k+1}_{i}||\phi^{n+1,k}_{i}| + |\phi^{n}_{i}|^2 \big ) + \big(|\psi^{n+1,k+1}_{i}||\psi^{n+1,k}_{i}| + |\psi^{n}_{i}|^2 \big)\big]\nonumber\\ & - \frac{\gamma}{2}(\phi_i^n+\phi_i^{n+1,k } ) .
\label{eq : phi_scheme2}\end{aligned}\ ] ] the iterations are repeated ( stepping up the index ` @xmath69 ' ) until convergence is reached . if the internal iterations are convergent , the scheme in full steps eqs . is absolutely stable due to its conservative nature . for not very large time
steps the iteration requires less than half a dozen loops to converge .
this is a small price to pay having in mind the inextricably coupled five - diagonal complex structure of the matrix .
the time - stepping scheme needs initial conditions of the type of eq . .
in the general case of elliptic initial polarization we discretize the system eqs . in the same manner as the original evolutionary system , and
use newton s method and hermitian splines to get approximately the solution @xcite .
the result are used as initial conditions for the problem under consideration .
the above presented scheme and algorithm have been verified for different girds and time increments and the approximation has been confirmed .
this is a special elliptic polarization with polarization angle @xmath70 .
the initial configuration is generated from the auxiliary bifurcation system ( [ eq : conjsys ] ) . because the parametric space of the problem is too big to be explored in full , we choose @xmath71 , @xmath30 , @xmath31 , @xmath32 and
focus on the effects of @xmath35\!]\>}\equiv \delta_r-\delta_l$ ] .
we observe that the breathing does not interfere with the soliton collision since they are distinguished from previously obtained breathers @xcite , @xcite .
one sees the breathing " of the pulses even without any interaction .
this is the manifestation of the rotation of the polarization .
thus @xmath8 is responsible for the exchange of wave mass between the modes and we call it cross " dispersion of the signals ( see figure [ fig : massmomcird90 ] ) . , @xmath72 , @xmath73 , @xmath74 , @xmath75 , @xmath76 , @xmath31 , @xmath32 , @xmath77 , @xmath78 and different initial phase differences.,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] , @xmath72 , @xmath73 , @xmath74 , @xmath75 , @xmath76 , @xmath31 , @xmath32 , @xmath77 , @xmath78 and different initial phase differences.,scaledwidth=75.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] , @xmath72 , @xmath73 , @xmath74 , @xmath75 , @xmath76 , @xmath31 , @xmath32 , @xmath77 , @xmath78 and different initial phase differences.,scaledwidth=75.0% ] \(c ) @xmath35\!]\>}=180^\circ$ ] recall that these solutions apply specifically to the case @xmath5 .
our initial condition is valid only for this case . in figure
[ fig : clashcird180 ] we present these features for fixed set of parameters varying only the initial phase difference @xmath35\!]\>}$ ] . as we discussed in @xcite
there is no velocity shift on the place of interaction .
the individual masses start to oscillate since the same beginning with an equal period and with a phase shift and an amplitude depending on the concrete choice of @xmath35\!]\>}$ ] the total mass , however , is perfectly conserved
it is equal to 6.0683 . due to
the symmetry the pseudomomentum @xmath79 and evidently approximates 0 .
the result is the same for all considered phase differences ( @xmath80 , @xmath81 , @xmath82 ) ( figure [ fig : clashcird180 ] ) .
what happens with the energy one can see reviewing the next figure [ fig : energycird0 ] .
the magnitude of the energy depends essentially on the magnitude of initial phase difference value @xmath35\!]\>}$ ] .
the dependence is non - monotonous : @xmath83 for @xmath35\!]\>}=0^\circ$ ] ; @xmath84 for @xmath35\!]\>}=90^\circ$ ] ; @xmath85 for @xmath35\!]\>}=180^\circ$ ] .
figure [ fig : energycird0 ] demonstrates cogently the conservation properties of the used difference scheme
one observes excellent conservation of the total energy of the interacting soliton system during the whole time of evolution .
the next figure [ fig : polarcird180 ] elucidates the polarization evolution .
the individual polarizations oscillate depending on both the magnitude of linear coupling @xmath8 and initial phase difference @xmath35\!]\>}$ ] .
these oscillations do not depend on the interaction but the period depends on @xmath8 .
the magnitude @xmath35\!]\>}$ ] influences the amplitude of oscillation .
in contrast to masses ( see figure [ fig : massmomcird90 ] ) the total polarization is not constant .
it breathes also though with very small amplitude .
it is well seeing that on the place of interaction one observes a shock of both the individual and total polarization .
the last result can be interpret as a generalization of the polarization conservation law for the case of rotational polarization
it breathes in the period but it is conserved in the whole period .
\!]\>}=0^\circ$ ] corresponding to figure [ fig : clashd180ot].,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] \!]\>}=0^\circ$ ] corresponding to figure [ fig : clashd180ot].,scaledwidth=75.0% ] \(b ) @xmath35\!]\>}=90^\circ$ ] \!]\>}=0^\circ$ ] corresponding to figure [ fig : clashd180ot].,scaledwidth=75.0% ] \(c ) @xmath35\!]\>}=180^\circ$ ] .,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=0^\circ$ ] .,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=90^\circ$ ] .,scaledwidth=75.0% ] \(a ) @xmath35\!]\>}=180^\circ$ ] .,scaledwidth=75.0% ] our observations show that these interactions are independent of initial phase shift and no - phase velocity shift occurs on the place of interaction .
the trajectories of qp - centers suffers slight shift .
they were investigated and discussed in @xcite for _ sech_-profiles and initial linear polarization and we do not concern them again . in order to extend our considerations we conduct series of experiments with general initial polarization and nontrivial linear coupling . for convenience
we use the same magnitude @xmath32 . on figure
[ fig : clasheld180 ] the case of initial elliptic polarization is present for initial phase shifts @xmath35\!]\>}=0^\circ , 90^\circ , 135^\circ , 180^\circ$ ] .
our conclusion is that the linear coupling combined with the initial phase difference @xmath35\!]\>}$ ] can shift only the soliton trajectories and keeps the phase velocities unchanged .
a nontrivial phase shift is possible after involving nonlinear coupling @xmath86 @xcite .
we consider two solitons with equal initial elliptic polarization angles of @xmath87 .
the initial configuration is generated from the auxiliary bifurcation system ( [ eq : conjsys ] ) .
the above angle corresponds to the parametric set @xmath54 , @xmath55 , @xmath30 , @xmath31 .
obviously the results are qualitatively the same as in the previous case of circular polarization and they do not require a detailed discussion . on figure [ fig : ell_allenergiies ]
is plotted the energy depending on the initial phase difference .
the correlation between them is essential .
the conservation is again excellent : @xmath35\!]\>}=0^\circ$ ]
@xmath88 ; @xmath35\!]\>}=90^\circ$ ]
@xmath89 ; @xmath35\!]\>}=135^\circ$ ]
@xmath90 ; @xmath35\!]\>}=180^\circ$ ]
the breathing behavior of the total polarization is well visible as well as the affect of the initial phase difference upon the amplitude of the individual polarization angles which result to the magnitude of the total polarization angle .
figure [ fig : clasheld180 ] answers convincingly the question about the dynamics of the rotational polarization when the type of initial polarization is general .
the net conservation law is generalized as net breathing ( oscillating ) law which conserved the total polarization within one time period .
this result has not an analytic analogue and enriches the phenomenology of cnlse . among the three conservation laws about the mass , pseudomomentum and energy we found after an extensive set of numerical investigations one more net conservation law .
the pattern in takeover interaction is the same qualitatively but the required difference in the velocity magnitudes bears bigger trajectory shift of the slower soliton and slower trajectory shift of the bigger soliton ( see @xcite ) .
here we consider this kind of interaction in order to implement an interaction of elliptically polarized solitons with different polarization angles .
also such kind of evolution and interaction do not possess a symmetry .
our main goal is to check and confirm the conclusions about the net polarization realized in the previous subsection .
we choose @xmath54 , @xmath55 , @xmath73 , @xmath74 , @xmath31 , @xmath32 and focus on the effects of @xmath92 .
the above parametric set results in polarization angles @xmath93 , @xmath72 of the initial envelope configuration .
the approximate initial condition is generated from the auxiliary bifurcation system .
the solitons start with different elliptic polarizations and are an object of rotational polarization as well due to nontrivial linear coupling @xmath8 ( figure [ fig : clashd180ot ] ) .
we find out that the initial phase differences of the components play an essential role on the full energy of qps ( figure [ fig : energyd180ot ] ) .
in particular , when @xmath35\!]\>}=0^\circ$ ]
@xmath94 ; @xmath35\!]\>}=90^\circ$ ] @xmath95 ; @xmath35\!]\>}=180^\circ$ ]
just in opposite , the pseudomomentum is also conserved and does not depend on the initial phase difference .
it is not trivial because of the nonsymmetry of the qp configuration and its net values @xmath97 ( figure [ fig : massmomd180ot ] ) .
the individual masses , however , breathe together with the individual ( rotational ) polarizations .
their amplitude and period do not influenced from the initial phase difference ( figure [ fig : massmomd180ot ] ) and are conserved within one full period of the breathing .
the total mass is constant .
both the individual and total polarizations breathe and suffer a ` shock in polarization ' when qps enter the collision .
the polarization amplitude evidently depends on the initial phase difference ( figure [ fig : polard180ot ] ) .
the above quantities are conserved within one full period of the breathing . in all
considered cases of evolution and interaction the polarization angle of qps can change independently of the collision due to the real linear coupling @xmath8 .
in this work we are aiming to complete the information about the dynamical properties of the total polarization influenced by the initial parameters and , in particular , by the initial polarization of general type as well as by the nontrivial linear coupling @xmath8 and the initial phase difference @xmath35\!]\>}$ ] .
for the case of general elliptic polarization there is not available an exact initial condition concerning the shape of solitary envelopes . solving an auxiliary bifurcation system of ordinary differential equations
we construct numerically an approximate initial conditions for the full range of polarization angles between @xmath80 and @xmath81 and with non-@xmath0 shape .
let us denote that the particular cases @xmath98 ( left and right linear polarization ) when one has an exact @xmath0-like initial condition were implemented in detail in @xcite .
we consider the two main interactions head - on and takeover collisions of envelopes when only a real linear coupling @xmath8 is present ( the cross - modulation parameter @xmath5 ) .
adding an imaginary part in @xmath8 leads to gain / blow - up of the solution accompanied by a violation of the conservation laws ( see @xcite ) and we will not concern again this property in the present work .
the main conclusions can be summarized as follows * the interaction conserves perfectly the pseudomomenta and energy .
the pseudomomenta are not influenced by the initial phase difference @xmath35\!]\>}$ ] while the magnitude of the energy is strongly dependent on it .
the variation is nonmonotonous .
* the total mass is also perfectly conserved but this is realized on the inner share and exchange of local masses of both components of qp periodically in the time .
this periodicity is governed by the real part of the linear coupling @xmath8 and generates breathing of the masses among with the breathing of the solitary envelopes .
the mass breathing does not depend on the interaction and is present during the whole time of evolution .
the amplitude of mass oscillation depends on the initial phase difference . *
the individual polarizations breathe similar to individual masses but in opposite to them with a phase shift .
this is the reason the total rotational polarization to be conserved within one period . on the place of interaction the individual and total polarization angles suffer a discontinuity keeping the else functions smooth . in other words
the total polarization breathes also and a bifurcation occurs during the cross - section of the interaction . and
this is the main result of this investigation .
the amplitudes of the individual polarizations are affected by the initial phase difference .
* we found and generalized for the case of rotational polarization one more conservation law for the net total polarization .
so , the linearly cnlse possess four conservation laws : for the total mass , for the pseudomomentum , for the energy , and for the magnitude of the total polarization .
let us emphasize that the last law has not an analytic analogue and it unearths more intrinsic information for the propagating and interacting solitons as quasi - particles .
this investigation is partially supported by the science fund of ministry of education , science and youth of republic bulgaria under grant ddvu02/71 .
these results were reported on the symposium `` recent trends in nonlinear wave phenomena : achievements and challenges '' within the 6th imacs international conference on nonlinear evolution equations and wave phenomena : computation and theory , athens , ga , april 04 - 07 , 2011 .
the paper is devoted to my mentor and supervisor professor christo i. christov on occasion of his 60th birthday .
m. d. todorov and c. i. christov .
on the solution of the system of odes governing the polarized stationary solutions of cnlse . in _
3rd annual session of bgsiam , december 22 - 23 , 2008 _ , pages 8386 .
demetra ltd .
, 2009 .
m. d. todorov and c. i. christov .
collision dynamics of polarized solitons in linearly cnlse . in _ intl .
workshop on complex structures , integrability and vector fields , aip cp1340 _ ,
pages 144153 .
american institute of physics , melville , ny , doi : 10.1063/1.3567133 , 2011 . | we investigate numerically by a conservative difference scheme in complex arithmetic the head - on and takeover collision dynamics of the solitary waves as solutions of linearly coupled nonlinear schrdinger equations for various initial phases .
the initial conditions are superposition of two one - soliton solutions with general polarization .
the quasi - particle behavior of propagating and interacting solutions in conditions of rotational polarization is examined .
we find that the total mass , pseudomomentum and energy are conserved while the local masses , individual and total polarization depend strongly on the linear coupling and the initial phase difference .
we also find out that the polarization angle of the quasi - particles can change independently of the interaction .
linearly coupled nonlinear schrdinger equations ; elliptic polarization ; rotational polarization 02.70.-c , 05.45.yv , 42.65.tg |
rupture of the aorta after radiation exposure is a relatively rare but life - threatening complication of radiation therapy .
the treatment of aortic rapture involves surgery for repairing the damaged vessel . currently , thoracic endovascular therapy is the standard option for aortic diseases and has been reported to be useful in acute aortic conditions , including aortic aneurysm rupture . here
, we report a case in which we performed thoracic endovascular aortic repair ( tevar ) for aortic rupture due to radiation injury .
a 54-year - old man presented to a rural hospital with a compliant of haemoptysis . on examination , his vital signs were normal .
he had a history of lung cancer , with invasion to the mediastinum and left subclavian artery .
the cancer had been treated with chemotherapy and radiation therapy ( 72 gy/16 times ) 3 years prior to the presentation , without progression after the treatment . additionally , tumour markers became negative after completion of the treatment and there was no aortic aneurysm .
based on the findings of chest radiography on admission , pneumonia and abscess formation in the lesion of the treated lung were suspected .
enhanced computed tomography ( ct ) was performed , and it showed extravasation of contrast medium at the distal aortic arch , which was in the area that received radiation therapy previously ( fig .
his blood pressure was low ( 90/60 mmhg ) , and blood tests showed progressive anaemia ( 11.5 mg / dl in the outpatient clinic prior to admission , 10.5 mg / dl on admission , and 8.5 mg / dl currently ) .
based on these findings , we diagnosed him with aortic rupture due to radiation therapy - induced injury .
we decided to perform tevar . from the right common femoral artery , with the guidance of a stiff wire ( amplatz super stiff , 0.035 in/260 cm , boston scientific , costa rica / heredia ) , stent grafts ( relay plus 32 28 150 mm and relay plus 32 32 150 mm ; bolton medical , sunrise , fl ) were placed at the proximal landing zone 2 ( fig .
the entry point is identified distal to the subclavian artery ( arrow).figure 2:(a ) intraoperative aortography .
, stent grafts are placed between just distal to the left common carotid artery and the distal aortic arch . to achieve sufficient length of the proximal landing zone
, stent grafts are placed between just distal to the left common carotid artery and the distal aortic arch . to achieve sufficient length of the proximal landing zone
after stent graft placement , his haemodynamic condition stabilized . after confirming stable respiratory function ,
figure 3:(a c ) postoperative enhanced computed tomography ( ct ) ( a , b : axial images ; c : sagittal image ) .
the left vertebral artery is patent . ( a c ) postoperative enhanced computed tomography ( ct ) ( a , b : axial images ; c : sagittal image ) .
however , in the present case , the patient did not have an aortic aneurysm previously . in patients with lung cancer and mediastinum metastasis , direct invasion of cancer to the aorta
however , in our patient , progression of cancer did not occur after chemotherapy and radiation therapy , according to follow - up assessments .
additionally , the patient s condition improved after treatment and there was no cancer recurrence . therefore , there was no possible cause of aortic rapture , except for radiation injury .
thus , we diagnosed the patient with aortic rapture due to radiation injury at the aorta .
radiation injury to vessels has been reported to occur even 10 years after radiation therapy .
therefore , if a patient presents with aortic rapture after radiation therapy , radiation injury should be suspected , even if therapy was performed many years previously .
wolbach reported the injury as swelling of the endothelium and proliferation and obliteration of the capillary lumina as the cause of a roentgen ulcer. stone et al . reported that a large dose of radiation could cause vascular hyaline necrosis .
although elastic fibres are not feasible to radiation , a previous report mentioned that these fibres were interrupted on pathological analysis with a light microscope .
assessed radiation lesions using an electron microscope and reported irregular fragmentation of elastic fibres with non - reactive radiation necrosis in the ruptured site and slit - like space of the elastic fibre layer in radiation lesions .
lindsay et al . assessed dogs who received localized aortic radiation and mentioned that atherosclerosis was strongly localized in the segment that received radiation .
a previous study suggested that micro - vessels in the vasa vasorum are occluded by radiation , which causes hypoperfusion in the elastic fibre layer , resulting in aortic perforation .
the efficacy of tevar for thoracic aortic rupture has been reported previously . in our case ,
the entry observed on preoperative enhanced ct was small , and the lesion was limited .
the finding was consistent with the aetiology suggested in previous reports mentioned above . in our case , there were few thrombi and calcifications in the proximal landing zone , and the diameter of the aorta was normal .
we selected available grafts in the emergency setting . in order to achieve a sufficient landing zone ( 20 mm ) , we covered the left subclavian artery with a stent graft .
however , in this case of aortic rupture , we decided to stop type iv endoleak immediately .
therefore , we placed another stent graft over the first one and type iv endoleak resolved .
one year after the operation , the patient was well without aortic disease progression or lung cancer recurrence .
these findings suggest that tevar for aortic rupture due to radiation injury was performed effectively .
therefore , we believe that tevar is more effective and safe . in conclusion , we reported a case in which tevar was successfully performed for aortic rupture due to radiation injury . tevar is a useful treatment method for aortic rupture due to radiation injury in the aorta .
further follow - up of our patient is needed to evaluate the long - term outcomes .
| abstractthoracic endovascular aortic repair ( tevar ) has been reported to be an effective treatment option for aortic emergencies
. however , there are few reports about tevar for aortic rupture due to radiation injury . a 54-year - old man presented with haemoptysis .
he had a history of lung cancer , which had been treated with chemotherapy and radiation therapy ( 72 gy/16 times ) 3 years previously , and the cancer lesion did not progress . on chest radiography ,
pneumonia was suspected in the radiated lesion .
however , after admission , he presented with back pain , progressive anaemia and hypotension .
enhanced computed tomography revealed extravasation of contrast medium in the distal aortic arch .
he was diagnosed with aortic rupture due to radiation injury .
tevar was performed .
he was extubated one day after the operation , and the haemoptysis disappeared .
he was discharged from the hospital without any complications .
he is well 1 year after the surgery , without aortic disease progression or lung cancer recurrence . |
FriendFinder Networks Inc., owner of Penthouse adult magazine, plans to submit a bid for Playboy Enterprises Inc., following a $123 million offer from Playboy founder Hugh Hefner.
FriendFinder Chief Executive Officer Marc Bell said in an interview the company is “looking at alternatives” and later wrote in an e-mail it will probably make the bid today.
Playboy said yesterday that Hefner wants to take the company private, and offered to purchase the shares he doesn’t already own in Playboy, which includes the namesake men’s magazine, merchandise, and television and video content.
Hefner plans to offer $5.50 apiece in cash for the Class A and Class B shares, Chicago-based Playboy said in a statement. Hefner, 84, is partnering with Rizvi Traverse Management LLC for the transaction. The offer, at a premium of more than 30 percent, values Playboy at about $185 million.
Playboy said Hefner, who controls its voting shares, isn’t interested in a merger or sale to a third party out of concern for the company’s brand and Playboy magazine’s editorial direction. Playboy has combined units and slashed jobs to cope with a circulation plunge caused by Internet competition.
After Hefner founded the company in 1953, Playboy magazine garnered a following for its photos of nude women, its satirical cartoons, and its fiction. The first issue of the magazine included photos of Marilyn Monroe, and authors such as Vladimir Nabokov were published in Playboy’s pages.
Photographer: Rick Maiman/Bloomberg Playboy magazines are displayed on a news stand in New York, on Nov. 12, 2009. Close Playboy magazines are displayed on a news stand in New York, on Nov. 12, 2009. Close Open Photographer: Rick Maiman/Bloomberg Playboy magazines are displayed on a news stand in New York, on Nov. 12, 2009.
Expansion Years
The company expanded around the globe in the 1960s and ‘70s with Hefner at the helm. The company went public in 1971 and circulation peaked at 7.2 million in 1972. In June, the company hosted parties around the country to mark the 50th anniversary of the once-famous Playboy membership nightclubs that dotted the globe.
Playboy’s revenue has declined for the past two years as it has lost more than $200 million. At the beginning of this year, the company reduced Playboy magazine’s rate base, the total of newsstand and subscription sales guaranteed to advertisers, to 1.5 million from 2.6 million. In addition to the magazine, Playboy creates videos for its website and cable-television networks, and licenses products with its bunny-ear brand.
‘Girls Next Door’
The company last year hired Scott Flanders as chief executive officer, replacing the founder’s daughter, Christie Hefner. Christie Hefner had served as CEO for 20 years, as her father continued to personify the brand with his lifestyle at the Playboy mansion.
The Los Angeles mansion, which the company uses for television shows, photo shoots and events, is “an enormous asset to us,” said Playboy spokeswoman Martha Lindeman. “It’s a huge part of our brand.”
Hefner is currently most recognized for squiring voluptuous young women around the mansion while clad in one of his trademark silk smoking jackets. Some of the octogenarian’s most recent girlfriends star with him in the TV show, “The Girls Next Door,” and related online videos.
Hefner was sued in 2009 by an investor who said the Playboy founder scuttled potential acquisitions so he could maintain his residence at the mansion. Lindeman said she didn’t know the status of the lawsuit because it was filed against Hefner personally.
‘Billion-Dollar Brand’
Bell said that if he successfully purchases Playboy, he wouldn’t require Hefner to move out of the Los Angeles mansion. Bell, whose company includes the AdultFriendFinder.com website, said he is interested in Playboy for its online potential.
“Our interest is mostly the digital assets,” Bell said. “We have no desire to throw him out.”
Hugh Hefner couldn’t be reached for comment, according to Lindeman. Christie Hefner declined to comment, according to her spokeswoman, Deb Parry.
In a conference call last month, Flanders said that Playboy’s new strategy is to change from being an “inefficient operator of small segments of media” to becoming more of a brand management company.
Playboy, based in Chicago, is seeking partners to increase revenue from licensed goods and expand branded clubs and casinos. The moves are part of a restructuring plan that Flanders has said will result in a profit in 2011.
On last month’s call, Flanders said that investors were undervaluing Playboy stock.
“You could own the company for an enterprise value of $200 million, and we believe we have a billion-dollar brand,” Flanders said at the time.
Declining Magazine Sales
Last week, the company announced that it would downsize its organizational structure, resulting in a $3 million charge in the second quarter of this year. In recent days, Michael Dannhauser, Playboy’s senior vice president and controller since 1998, said that he was leaving the company. His duties were given to Christoph Pachler, according to Lindeman.
Hugh Hefner owns 69.5 percent of Playboy’s Class A voting stock and 27.7 percent of the Class B non-voting stock. The company said it hasn’t received a definitive offer from Hefner, and the board has made no decision about the proposal.
Playboy B shares fell 14 cents to $5.41 at 10:29 a.m. in New York Stock Exchange composite trading, after jumping 41 percent yesterday. The B shares had gained 23 percent this year before yesterday. The A shares advanced 3 cents to $5.56, after climbing 36 percent yesterday and closing at $4.06 on July 9.
Playboy magazine’s U.S. sales fell 48 percent to $7.1 million in the first quarter, reflecting the company’s decision to lower the magazine’s rate base and combine some issues. The company’s Print and Digital group lost $1.1 million in the first quarter, compared with a loss of $3.6 million in the 2009 quarter. The group’s revenue fell 30 percent to $18.2 million.
To contact the reporters on this story: Brett Pulley in New York at [email protected] ||||| Unfortunately, our website is currently unavailable in most European countries. We are engaged on the issue and committed to looking at options that support our full range of digital offerings to the EU market. We continue to identify technical compliance solutions that will provide all readers with our award-winning journalism. | – Founder Hugh Hefner wants to take Playboy private, and he mounted a bid today that values the struggling company at $185 million, Bloomberg reports. Playboy Enterprises stock closed up almost 41% and attracted interest from another party—but who would want a conglomerate that's lost $20 million in just 2 years in a world with porn available on practically every desktop? Penthouse, of course. "We always knew it would be a good fit," the CEO of FriendFinder, which owns the Penthouse brand and is readying a formal bid, tells the Chicago Tribune. It won't be easy, because Hefner owns 69.5% percent of Playboy’s Class A stock and has said he's not interested in a third-party sale. Reassuringly, FriendFinder wouldn't evict Hef from the Playboy mansion should its attempt succeed: "Our interest is mostly the digital assets,” the CEO said. “We have no desire to throw him out." |
tourette syndrome is a neurodevelopmental disorder that is characterized by both multiple motor and one or more vocal tics present some time during the illness with onset before 18 years . a large majority of the patients with gilles de la tourette syndrome are known to have psychiatric comorbidities with attention - deficit hyperactivity disorder and obsessive compulsive disorder being the most common ones , followed by mood and personality disorders . though mood symptoms are frequent in this group , the diagnosis of bipolar disorder is complicated by their inherent unreliability in children .
however , authors have reported as high as 20 - 30% comorbidity between the two .
while mood disorders might aggravate tics , the latter also has reciprocal effect on the former ; leading to spiralling deterioration .
we report an interesting case of tourette syndrome with bipolar affective disorder , which highlights these interactions and the clinical challenges encountered .
master bg , presently a 15-year - old adolescent male from lower socioeconomic class of suburban india , with unremarkable past , family , birth or developmental history , and an easy going premorbid temperament , presented to us with symptoms with insidious onset and fluctuating course of 6 years duration characterized by prolapsed mass per anum , abnormal repetitive movements , and fluctuations in mood ; with inappropriate sexual behavior and abusive behavior for last 4 - 5 months .
the symptoms started with complaints of repeated squatting and straining for passing stools at the age of 9 years . over the next few months ,
the frequency gradually rose to more than 20 per day ( with no change in consistency of stool or any other gastrointestinal symptoms ) .
there was a simultaneous deterioration in his academic performance , interaction with friends and family members , and a reduction in his interest toward leisure activities .
he was found to spend more and more time in the washroom , and after his parents noticed these changes they also found a soft , single , red , fleshy painless mass protruding out of the his anal opening .
he was treated by faith - healers and quack practitioners for next few months , but in vain . as the straining behavior improved spontaneously ,
he also started taking a step forward and two steps backward whenever he walked , walked in tandem , stomped his feet alternately , and repeated syllables of words that he spoke .
he started repeatedly blinking , spitting , and stroking his hair with his hand in a combing like fashion for no apparent reason .
this persisted for about one to 2 years , during which the mood had improved and he remained euthymic .
after around 2 years of onset , the boy developed repeated self - grooming and hand washing behavior .
these symptoms persisted for around 2 years , when the other behaviors had shown improvement .
the symptoms of elevated mood gradually deteriorated to present admission when he had prominent features of increased appetite , increased sexuality , reduced sleep , inflated self - esteem , and an elated affect . during this time
the repetitive behaviors persisted with a fluctuating course , with a few predominantly present at any given time .
he had developed repeated barking sounds around a year ago and started making pouting and sniffing gestures with his mouth , which persisted to current admission .
he was initially treated with risperidone at 0.5 mg / day in 2009 , which he discontinued within a few days due to poor perceived effect .
subsequently , he was given levodopa 100 mg+ carbidopa 25 mg per day , which he took for around 10 months .
this was discontinued for a deterioration in symptoms , and he began taking olanzapine 5 mg / day .
this resulted in some improvement in repetitive behavior but was discontinued after 3 months due to excessive sedation .
he was then seen at our institute and given oxcarbazepine 450 mg and risperidone 0.5 mg per day which he discontinued within 1 month due to poor results . following this
, he started taking sodium valproate 300 mg / day , and risperidone 2.5 mg / day , to which he responded well and continued for next 1 year .
however , all the symptoms persisted and when he stopped these medicines , they aggravated to present admission .
the boy was investigated with complete blood count , renal function test , liver function test , serum electrolytes and lipid levels , thyroid function test , urine for abnormal metabolites , electrocardiography , quantitative electroencephalography , computed tomography brain , magnetic resonance imaging brain , and ultrasonography whole abdomen , and also received a slit - lamp examination to rule out k - f rings .
all of these were within normal range . on admission , c - ybocs obsession score was 9 , compulsion score was 14 and a total score was 23 .
though the boy had 3 motor and 2 vocal tics at this time , his severity rating on ygtss revealed mild impairment ( score of 20 ) .
children global assessment scale ( cgas ) score was 44 indicating a moderate degree of interference in functioning . his iq , assessed on malin 's intelligence scale for children ( misic ) revealed a vq of 70 , a pq of 69 and full scale iq of 70 .
the boy did not give any explanation for these behaviors , but reported that if he did not perform them , it made him feel tensed .
he does not recognize them as being senseless and persisting without a cause , though he agrees to them being his own thoughts and not being imposed upon him by some external agency .
however , there is no account of active resistance to these thoughts neither are they being perceived as unpleasantly repetitive
. he does not describe any fear of harm being bestowed upon his near and dear ones if he does not perform them , any particular distress with asymmetry , or any account of repetitive images , impulses or ideas coming to his mind .
there is no history of significant head injury , seizure episodes or of substance abuse .
the boy was started on haloperidol 5 mg , and carbamazepine 400 mg per day .
after a period of 2 weeks , he started showing improvement in repetitive spitting , snorting , sniffing , and pouting .
the treatment was reevaluated , carbamazepine was increased to 800 mg per day and was subsequently augmented with lithium carbonate .
the mood symptoms showed improvement after 2 weeks on lithium , with the ymrs score reducing to 17 on serum lithium level of 0.8
simultaneous psychoeducation to the parents regarding patient 's illness and coping skills training , activity scheduling for the boy to channelize the increased physical energy , and a schedule for differential reinforcement of other behaviors ( dro ) and alternate behavior ( dra ) helped rehabilitate the boy , and he was discharged after 6 weeks with a satisfactory improvement .
although there is adequate evidence of the comorbid occurrence of gilles de la tourette syndrome and bipolar disorder from studies , the etiology of the same remains unexplained .
the two disorders may share several features such as abnormalities in neurotransmission involving noradrenaline , dopamine , and serotonin .
kerbeshian et al . , reported that the candidate region for primary genetic factors resulting in the phenotype of the two disorders could be 16q22 - 23 .
the association has also been explained by a modulation defect , in certain areas of the brain such as , the cortical - limbic system , ventral striatum , and sensory motor cortical regions .
this construct is indirectly supported by literature reporting frequent precipitation of mania or bipolar disorder following stimulant use in patients with tics .
etiology aside , our case demonstrates certain obvious hurdles that a clinician might face with this comorbidity in pediatric age group . while on one hand an account of the characteristic features of tics might not be elicited ; features of repetitive self - grooming , stomping , spitting , or other manifestations of tics might mimic motor hyperactivity of mania .
it also poses problems with management , for if the boy is not able to recognize the premonitory urges , it also precludes the use of behavioral modification techniques .
we suggest that under such circumstances , symptoms of increased appetite , hypersexuality , decreased need for sleep , and affective display might have better discriminative power . | tourette syndrome and bipolar disorder are frequent comorbidities in pediatric age group .
they provide a clinician with certain unique challenges . while on one hand the tics mask manifestation of affective symptomatology , the latter makes it difficult to elicit tics with certainty .
data suggest that they might share genetic and neurobiological basis and this is currently an area of extensive research .
these clinical and biological overlaps provide grey areas in our understanding , which not only complicates the diagnosis , but also poses problems with management . |
air pollution is a major environmental risk to health and is estimated to cause approximately 2 million premature deaths worldwide per year .
in fact , indoor air pollution levels can even be higher than the outdoor levels .
in addition to outdoor pollutants , secondhand tobacco smoke is one of the main sources of indoor air pollution .
secondhand smoke is a mixture of exhaled mainstream smoke and sidestream smoke released from a smoldering cigarette or other smoking device ( cigar , pipe , bidi , etc . ) .
scientific evidence available for more than two decades convincingly demonstrates that the exposure to secondhand smoke harms health and worsens existing health problems among non - smokers .
the adverse effects of secondhand smoke are both immediate and long term , and are felt by both children and adults .
in addition to several toxic chemicals and compounds , secondhand tobacco smoke also contains respirable suspended particles ( rsps ) .
rsps are the proportion of total suspended particulates of a size smaller than 10 m ( pm10 ) and , among them , pm2.5 particles pose the greatest health risks because they have the ability to penetrate deeply into the lungs , where they may reach the peripheral regions of the bronchioles and interfere with gas exchange inside the lungs . monitoring
the change in rsps in indoor public places is a useful tool to assess the effectiveness of smoke - free policies .
globally , the who estimates that nearly 700 million or almost half of the world 's children breathe air polluted by tobacco smoke . in adults ,
secondhand smoke increases the risk of lung cancer by 2030% and the risk of coronary heart disease by 2530% .
children are particularly vulnerable to secondhand smoke for example , exposed children tend to get more respiratory infections , ear problems and asthma .
policies requiring smoke - free environments are the most effective method of reducing shs exposure . in india ,
prohibition of smoking in public places is mandated under section 4 of the cigarettes and other tobacco products act ( which includes prohibition of advertisement and regulation of trade and commerce , production , supply and distribution ) of 2003 . as defined under 3(l ) of cotpa
public place means any place to which the public have access , whether as of right or not , but does not include any open space .
in addition , smoking is also prohibited at the open spaces that are visited by the public , like open auditoriums , stadiums , railway stations , bus stops and other such places .
the exception to this provision is that hotels with more than 30 rooms and restaurants with more than 30 seats are allowed to have a smoking area or space .
airports are also an exception to this rule as they are also allowed to have a separate smoking zone .
smoking area or space is not provided at the entrance or exit of a restaurant , hotel or airport .
smoking area is used only for the purposes of smoking and no service(s ) are allowed therein .
detailed rules prohibiting smoking in public places were notified on 30 may 2008 and came into force on 2 october 2008 .
a study was conducted to assess the implementation of smoke - free policies and its impact on indoor air quality in the city of mumbai .
mumbai ( formerly bombay ) is a large , densely populated metropolitan city ( density 22,000 inhabitants per km ) with a population of about 12 million ( census of india , 2001 ) .
the venues were sampled near railway stations and commercial areas , because the concentration of venues is much higher in these areas .
venues were then categorized into bars and restaurants ( hereafter called bars ) , restaurants , country liquor bars , hookah restaurants and pubs , as per signboards put up by venue owners . as per the indian context , these places are described as :
restaurant premises which is carried on principally or wholly the business of supplying meals or refreshments to the public or a class of the public for consumption on the premises.bar premises which is carried on principally or wholly the business of supplying alcoholic beverages ( beer , wine , whisky and cocktails , etc . ) and food to the public or a class of the public for consumption on the premises.country liquor bar premises which is carried on principally or wholly the business of supplying locally made alcoholic beverages ( fenny , toddy , etc . ) to the public or a class of the public for consumption on the premises .
these establishments are usually run - down and feature a clientele of mainly the working class people.pub a pub is an entertainment venue with recorded music played by disc jockeys and there is a provision of a back bar .
pubs in india may or may not have dancing floors.hookah restaurant the hookah restaurant is an establishment where patrons share shisha ( flavored tobacco ) from a communal hookah that is placed at each table .
restaurant premises which is carried on principally or wholly the business of supplying meals or refreshments to the public or a class of the public for consumption on the premises . bar
premises which is carried on principally or wholly the business of supplying alcoholic beverages ( beer , wine , whisky and cocktails , etc . ) and food to the public or a class of the public for consumption on the premises . country liquor bar premises which is carried on principally or wholly the business of supplying locally made alcoholic beverages ( fenny , toddy , etc . ) to the public or a class of the public for consumption on the premises .
these establishments are usually run - down and feature a clientele of mainly the working class people . pub
a pub is an entertainment venue with recorded music played by disc jockeys and there is a provision of a back bar .
hookah restaurant the hookah restaurant is an establishment where patrons share shisha ( flavored tobacco ) from a communal hookah that is placed at each table .
the sidepak uses a pump to draw air inside to measure the real - time concentration of air particles in milligrams per cubic meter .
pm2.5 is a non - specific marker for shs exposure as there may be other sources of pm2.5 .
the sidepak was zeroed prior to each use by attaching a high - efficiency particulate air ( hepa ) filter according to the manufacturer 's specification .
air sampling was carried out any time between 6:30 pm to 11:00 pm for a minimum of 60 min at each venue .
the field investigator seated himself in the central area of the venue and away from open doors , windows and kitchen entry and conducted observational monitoring , such as surveying rooms for the posting of no smoking signs and ash trays on tables .
the monitor was placed in a central location on a table near the height at which a person breathes air .
the investigators also interacted with managers , owners and waiters to assess the implementation of smoke - free policies .
data recorded in the sidepak monitor at each venue were downloaded to a computer with the help of tsi trackpro data analysis software , version 3.41 . in accordance with the global air monitoring study protocol , a calibration factor of 0.32 , which is suitable for the contribution of secondhand tobacco smoke , was applied to all data .
median and coefficient of variation of pm2.5 ( g / m ) levels were calculated separately for each venue .
for describing air quality , guidelines developed by the us environmental protection agency ( epa ) were used . the air quality index ( aqi )
ranged from 0 to 500 , with a higher value indicating a greater level of air pollution and , therefore , greater health concern .
mumbai ( formerly bombay ) is a large , densely populated metropolitan city ( density 22,000 inhabitants per km ) with a population of about 12 million ( census of india , 2001 ) .
the venues were sampled near railway stations and commercial areas , because the concentration of venues is much higher in these areas .
venues were then categorized into bars and restaurants ( hereafter called bars ) , restaurants , country liquor bars , hookah restaurants and pubs , as per signboards put up by venue owners . as per the indian context , these places are described as :
restaurant premises which is carried on principally or wholly the business of supplying meals or refreshments to the public or a class of the public for consumption on the premises.bar premises which is carried on principally or wholly the business of supplying alcoholic beverages ( beer , wine , whisky and cocktails , etc . ) and food to the public or a class of the public for consumption on the premises.country liquor bar premises which is carried on principally or wholly the business of supplying locally made alcoholic beverages ( fenny , toddy , etc . ) to the public or a class of the public for consumption on the premises .
these establishments are usually run - down and feature a clientele of mainly the working class people.pub a pub is an entertainment venue with recorded music played by disc jockeys and there is a provision of a back bar .
pubs in india may or may not have dancing floors.hookah restaurant the hookah restaurant is an establishment where patrons share shisha ( flavored tobacco ) from a communal hookah that is placed at each table .
restaurant premises which is carried on principally or wholly the business of supplying meals or refreshments to the public or a class of the public for consumption on the premises . bar
premises which is carried on principally or wholly the business of supplying alcoholic beverages ( beer , wine , whisky and cocktails , etc . ) and food to the public or a class of the public for consumption on the premises . country liquor bar premises which is carried on principally or wholly the business of supplying locally made alcoholic beverages ( fenny , toddy , etc . ) to the public or a class of the public for consumption on the premises .
these establishments are usually run - down and feature a clientele of mainly the working class people . pub
a pub is an entertainment venue with recorded music played by disc jockeys and there is a provision of a back bar .
hookah restaurant the hookah restaurant is an establishment where patrons share shisha ( flavored tobacco ) from a communal hookah that is placed at each table .
the sidepak uses a pump to draw air inside to measure the real - time concentration of air particles in milligrams per cubic meter .
pm2.5 is a non - specific marker for shs exposure as there may be other sources of pm2.5 .
the sidepak was zeroed prior to each use by attaching a high - efficiency particulate air ( hepa ) filter according to the manufacturer 's specification .
air sampling was carried out any time between 6:30 pm to 11:00 pm for a minimum of 60 min at each venue .
the field investigator seated himself in the central area of the venue and away from open doors , windows and kitchen entry and conducted observational monitoring , such as surveying rooms for the posting of no smoking signs and ash trays on tables .
the monitor was placed in a central location on a table near the height at which a person breathes air .
the investigators also interacted with managers , owners and waiters to assess the implementation of smoke - free policies .
data recorded in the sidepak monitor at each venue were downloaded to a computer with the help of tsi trackpro data analysis software , version 3.41 . in accordance with the global air monitoring study protocol , a calibration factor of 0.32 , which is suitable for the contribution of secondhand tobacco smoke , was applied to all data .
average concentration ( mean ) , median and coefficient of variation of pm2.5 ( g / m ) levels were calculated separately for each venue . for describing air quality ,
guidelines developed by the us environmental protection agency ( epa ) were used . the air quality index ( aqi ) ranged from 0 to 500 , with a higher value indicating a greater level of air pollution and , therefore , greater health concern .
a total of 50 venues were selected for the study , including five restaurants , four pubs , 27 bars and restaurants , 10 country liquor bars and four hookah restaurants ( n = 50 ) . one measurement session was carried out per venue . at the time of observational monitoring of the total 50 venues , smoking within premises
there was no smoking observed in all five restaurants and four pubs , while smoking was observed in seven of 27 bars .
the venue with the highest proportion of smoking observed was country liquor bars ( eight out of 10 ) .
in addition , the no smoking signage was seen at 33 venues , of which four were in marathi and two in hindi , commonly spoken languages in mumbai , while the remaining signages were in english
. smoking ban ( according to owner ) vs. smoking seen ( by the investigators ) at different venues table 2 shows the respective average pm2.5 ( g / m ) concentrations in the different hospitality venues included in the study .
the lowest average pm2.5 ( g / m ) level was observed in restaurants ( 55.36 g / m ) and the highest average level was observed in hookah restaurants ( 707.04 g / m ) [ figure 1 ] .
the average pm2.5 level was also higher in venues where smoking was observed ( 363.04 g / m ) compared with venues where smoking was not observed ( 97.19 g / m ) [ figure 2 ] .
average pm2.5 levels in different types of venues included in the study average pm2.5 ( g / m ) levels at different venues comparison of average pm2.5 ( g / m ) levels at garbage dumping grounds and non - smoking and smoking venues in the present study table 3 shows the aqi of all the venues in the study .
the average pm2.5 levels at restaurants and bars were categorized as moderate level of health concern .
country liquor bars and hookah restaurants however had average pm2.5 levels falling under the category of hazardous level of health concern .
this study mainly focused on assessing the implementation of smoke - free policies and its impact on indoor air quality .
seven months after the law mandating a ban on smoking in public places came into force , there were only 32 out of 50 venues where smoking within premises was not observed .
furthermore , even though no smoking signages were observed in 33 of the venues , none of these venues had signage that met the mandated minimum size of 60 cm 30 cm . according to air quality guidelines of the us environmental protection agency , an aqi value for pm2.5 particles level between 0 and 50 is considered satisfactory , and air pollution at this level poses little or no health risk . in the present study
, 20% of the venues fell under the good category [ table 3 ] .
a moderate category ( pm2.5 particle level between 51 and 100 ) indicates that air quality is acceptable .
however , for some pollutants , there may still be a moderate health concern for a small number of people . in the present study , 15 ( 30% )
venues were in this category , including nine bars , three restaurants ( average pm2.5 levels of 55.36 g / m ) and three pubs ( average 58.96 g / m ) .
average pm2.5 levels of all 27 bars ( 123.79 g / m ) fell under the category of
air quality was worse in 10 country liquor bars ( average 326.56 g / m ) and worst in four hookah restaurants ( average 707.04 g / m ) .
the level of pollution in these venues fell under the category of hazardous to health ( levels between 301 and 500 ) or higher , which has the potential to trigger emergency health conditions .
when these results were getting analyzed , a news about air quality at garbage dumping grounds created a lot of agitation in mumbai . the average level of pm2.5 ( g / m ) particles in the air of the dumping ground area in one area ( sudha park at ghatkopar ) was 148.5 g / mand 169.5 g / mat another area ( shivaji nagar , deonar ) . air quality at indoor public places where smoking was observed in this study was far worse than that at the garbage dumping grounds .
the average level of pm2.5 ( g / m ) particles in all the venues where smoking was seen despite the ban was 363.04 g / m , which was much higher than the levels found at both the dumping grounds in mumbai [ figure 2 ] . increased levels of pm2.5 ( g / m ) in these smoking areas are also harmful to the health of the customers at these venues .
the present study used a real - time aerosol monitor to measure pm2.5 levels in all venues .
our exposure metric was comparable to an average concentration of pm2.5 ( g / m ) particles reported in other studies conducted in different countries .
the levels we measured at smoking places ( mean pm2.5 363.04 g / m ) are broadly comparable with those reported by studies in indoor smoking public places in canada ( mean pm2.5 171 g / m ) , germany ( mean pm2.5 327 g / m ) , the united states ( mean pm2.5 265 g / m ) , the united kingdom ( mean pm2.5 285 g / m ) , malaysia ( mean pm2.5 181 g / m ) and pakistan ( mean pm2.5 169 g / m ) .
a recent cross - sectional study in china reported that pm2.5 levels were much higher at bars and restaurants where smoking was observed ( 208 g / m ) than where smoking was not observed ( 99 g / m ) .
the values observed in this china study were similar to those found in our study for venues where smoking was not observed ( 97.19 g / m ) , but were higher in our study for venues where smoking was observed ( 363.04 g / m ) .
we also found much higher levels among country liquor bars and hookah restaurants . a study reported from ireland showed that there was a dramatic change in the air quality of bars / pubs after the national level comprehensive workplace smoke - free law was implemented in march 2004 . as a result of this law ,
smoking at bars / pubs in ireland went down from 98% to 5% , but remained nearly unchanged in the uk ( 9897% ) , where the law was not in effect . in our study , smoking was not observed in any of the restaurants and pubs at the time of data collection , which suggests that the 2008 ban in india has been effective in these venues .
because there are no safe levels of secondhand smoke , it is important that smoke - free environment policies be as strong as possible .
the objective of the smoke - free policy is to protect non - smokers from exposure to secondhand smoke , thereby enhancing the air quality of the living environment .
although some people know that they are harming their self by smoking , they may not be aware of the negative effects on the people around them .
many people who smoke say that restricting smoking in public would be taking away their freedom but , in reality , smoking in public takes away non - smokers right to breathe fresh air .
the most serious problem with smoking in public is the negative effects it has on children .
children are the future ; therefore , instead of polluting their bodies , we should be doing everything we can to keep them healthy .
exposure to secondhand smoke is an entirely preventable cause of significant morbidity and mortality associated with tobacco use .
smoke - free public places not only protect non - smokers from the dangers of passive smoking but also encourage smokers to quit or reduce consumption and children not to take up the habit .
for smoking bans to succeed , enthusiastic endorsement by and active participation of the community and an awareness of the health consequences of exposure to secondhand smoke are needed .
our study clearly demonstrated that the average pm2.5 level was highest at hospitality venues where smoking was observed compared with those where smoking was not observed , and was especially high in hookah restaurants and country liquor bars . | background : second - hand smoke contains several toxic chemicals that are known to pollute the air and harm people 's health . in india , smoking in public places has been prohibited since october 2008 as a way to reduce second - hand smoke ( shs ) exposure .
the purpose of the present study was to assess the implementation of smoke - free policies and its impact on indoor air quality by measuring the pm2.5 levels in bars and restaurants , restaurants , country liquor bars , hookah restaurants and pubs in mumbai.materials and methods : air quality measurements at 50 venues were conducted by using a
sidepak am510 personal aerosol monitor during april to may 2009 .
average concentration of pm2.5 ( g / m3 ) particles was calculated separately for each venue.results:smoking was observed in 36% of the surveyed venues during an hour of data collection .
the pm2.5 levels ranged from 16.97 to 1101.76 g / m3 .
the average level of pm2.5 among non - smoking venues was 97.19 g / m3 and among smoking venues was 363.04 g / m3.conclusion : considerable scope for improvement in implementation of smoke - free policies exists .
the pm2.5 levels were exceedingly high in venues where smoking was observed . |
research misconduct , including fabrication , falsification , guest authorship , and plagiarism is one of the unethical behaviors in scientific research and has been of interest to the scientific society in recent years ( 1 , 2 ) .
the increased rate of various types of publication misconduct since the late 20 century has been a cause of raised concern ( 3 , 4 ) .
studies show that the percentage of scientific paper retracted due to fraud has been increasing ( 5 ) . increased publication misconduct and lack of academic honesty can encumber the production of new knowledge , waste resources , weaken public trust , and reduce motivation to participate in research and surveys ( 6 ) .
publication misconduct not only jeopardizes the author s reputation but can also create issues for the affiliated organization ( 7 ) .
an accurate estimate of publication misconduct is necessary to understand the problem and plan solutions . to estimate publication misconduct , studies use indirect methods to reduce bias caused by withholding the truth .
self - administrated questionnaires tend to be less costly and their data collection is less time - consuming . more importantly ,
their anonymity helps avoid response bias , but they are associated with an increased non - response rate , especially to sensitive questions .
in addition to lower response rates , respondents may withhold the truth or provide false responses ( 8) . a possible solution to this issue is using indirect methods in which trust is increased through randomization and aggregation , and chances of inaccurate or missing responses to sensitive questions are reduced . with aggregation , the sensitive question is placed in a list of non - sensitive questions , and respondents are asked how many of the items on the list apply to them . since not all items apply to each individual , the respondents can rest assured that they will not be identified through their response to the sensitive question .
block total response is a common aggregation technique ( 9 ) , and one of the special methods is the item count technique , the unmatched count technique ( uct ) , or the list experiment ( 10 ) . in the list experiment method , there are two lists of questions . the first one is a list of non - sensitive questions and the second one includes one sensitive question in addition to non - sensitive questions .
these two lists are presented to two groups of participants ; the baseline group ( control ) and the treatment group .
if these two groups provide truthful responses to the questions , the rate of the sensitive question can be estimated .
this estimate is the product of the difference between the average responses in the treatment and baseline groups .
if the sample respondents are randomly chosen from the target population , and other sources of bias are negligible , an accurate and bias - free estimate can be achieved . to increase the sample size and reduce estimate error
, the technique can be applied twice to the same sample using a different list of non - sensitive questions each time .
the present study was conducted with the assumption that using anonymous research tools can increase participants trust , reduce public acceptance bias , and thus reduce underestimation , and that indirect methods such as double list experiment can be an appropriate alternative to direct questionnaires . to the best of our knowledge ,
this is the first study of its kind to use the double list experiment , except for the study by jann et al . who examined the prevalence of plagiarism among students ( 12 ) .
our study objective was to use the double list experiment to assess the prevalence of publication misconduct among iranian authors who have published in iranian journals indexed in scopus .
the target population of this investigation was iranian authors who have published an article in a scopus indexed iranian journal between 2009 and 2011 .
the study was approved by the institutional review board of tehran university of medical sciences .
individuals participation in the study and responding to questions was regarded as consent to participate in the study . in the double list experiment ,
two different lists of questions ( lists a and b ) are randomly distributed between two groups of participants .
the first group acts as the treatment group for list a and the baseline group for list b. the second group acts as the treatment group for list b and the baseline group for list a ( 11 ) .
if the two groups have the same sample size , and samples are allocated to groups by random , the variance of a given estimate only depends on the variance of the two baseline lists and the variance of the sensitive item .
when the correlation between non - sensitive items in one list is negative , variance decreases , and when the correlation between non - sensitive items in two lists is positive , the inter - list covariance is increased .
the research tool in this study was anonymous questionnaires , which were developed based on the assumptions for the double list experiment model , the sensitivity of the issue , and the target population .
first , a series of non - sensitive questions with an average yes response of 0.5 and some sensitive questions concerning publication misconduct were suggested . in the questionnaires , each sensitive question was embedded within four non - sensitive questions , totally apart from the sensitive response choice item .
the five sensitive questions used in this study were :
in the past year , i have submitted / published a paper i had published before exactly as it was , after translating it , or after minimal revisions , without asking permission from the first publisher.in the past year , i have copied exact sentences ( at least 5 sentences ) from others publications to write my paper.in the past year , i have falsified or fabricated part of the research data / results for a paper i was writing.in the past year , the research methods i described in at least one of my papers were not exactly true.in the past year , my name has been listed , with my consent or to my request , as a co - author of a paper to which i did not contribute significantly ( neither the study execution nor the preparation of the article ) . in the past year , i have submitted / published a paper i had published before exactly as it was , after translating it , or after minimal revisions , without asking permission from the first publisher . in the past year , i have copied exact sentences ( at least 5 sentences ) from others publications to write my paper . in the past year , i have falsified or fabricated part of the research data / results for a paper i was writing . in the past year , the research methods i described in at least one of my papers were not exactly true . in the past year , my name has been listed , with my consent or to my request , as a co - author of a paper to which i did not contribute significantly ( neither the study execution nor the preparation of the article ) .
in addition , we consulted five experts in the field of ethics about the clarity of the questions , and used their feedback to make the final amendments . according to the respondents of this section , the clarity of the questions was 85.03% .
next , we determined the reliability of the questions . for this purpose , we ran a test retest .
questions were directed at 40 epidemiology doctoral students twice , with a two week interval , and the intra class correlation ( icc ) was determined as the reliability between them .
the icc was calculated for answers to each list ( lists a and b ) , and they ranged between 0.988 ( 95% ci : 0.951 , 0.997 ) to 0.656 ( 95% ci : 0.194 , 0.901 ) ( table 1 ) .
intra class correlation ( icc ) and 95% confidence intervals ( ci ) of each series of questions on questionnaires 1 and 2 since any question regarding participants demographics was likely to reduce their trust , no such questions were included . to measure the level of trust in the study method regarding confidentiality and difficulty
, we included the following two questions at the conclusion of the questionnaire : how did you find the instructions for completing the questionnaire ? and how trustworthy do you find this method in terms of confidentiality of your responses ? the study questionnaire was used in a pilot through electronic survey services affiliated with the tehran university of medical sciences .
implementation : we searched for papers published between 2009 and 2011 in biomedical iranian journals indexed in scopus ( approximately 50 journal titles ) .
all those with a non - iranian corresponding author were excluded from the list , and the final study population was 2321 corresponding authors with an address in iran . after retrieving their email addresses ,
a description of the study and its objectives were sent to them , and they were invited to participate in the web - based study .
corresponding authors were randomly divided into two groups and one of the two study questionnaires was sent to them . statistical analysis : in the double list experiment method , there are two question lists for each sensitive question ( for instance , lists 1 and 8 for assessing duplicate publication ) , which we shall refer to as lists a and b from now on ( table 1 ) .
for each list , one group of the participants is the baseline and the other is the treatment group . by selecting an equal sample size for each group , and using similar sensitive questions in both lists , yaik = ybik for all participants , and the total of sensitive and non - sensitive questions in these two groups would be :
yaik={1 if individual i would honestly say yes to item on the a list0 if individual i would honestly say no to item on the a list}ybik={1 if individual i would honestly say yes to item on the b list0 if individual i would honestly say no to item on the b list }
yai+k=k=1ky aikyai+k1=k=1k1y aikybi+k=k=1ky bikybi+k1=k=1k1y bik
thus , one group of participants responds to list a , not including the sensitive question , and forms the baseline group for list a , and the same group responds to list b , including the sensitive question , and forms the treatment group for list b. questions for the other group are the reverse , i.e. for list b , they are the baseline group , and for list a , they form the treatment group . assuming that participants understand the method and respond honestly , the difference in the proportion of yes responses for each list is the prevalence estimate of the sensitive question based on each given list . since the number of respondents in both treatment groups a and b was the same , the total prevalence of each sensitive question is the mean of the two estimated prevalence rates calculated for lists a and b. to determine the variance of the estimate , we added the variances of lists a and b in both groups , subtracted their covariance from the sum , and divided the results by the sample size .
the square root of the calculated variance was used as the standard error to determine the 95% confidence intervals ( 13 ) .
in the double list experiment , two different lists of questions ( lists a and b ) are randomly distributed between two groups of participants .
the first group acts as the treatment group for list a and the baseline group for list b. the second group acts as the treatment group for list b and the baseline group for list a ( 11 ) .
if the two groups have the same sample size , and samples are allocated to groups by random , the variance of a given estimate only depends on the variance of the two baseline lists and the variance of the sensitive item .
when the correlation between non - sensitive items in one list is negative , variance decreases , and when the correlation between non - sensitive items in two lists is positive , the inter - list covariance is increased .
the research tool in this study was anonymous questionnaires , which were developed based on the assumptions for the double list experiment model , the sensitivity of the issue , and the target population .
first , a series of non - sensitive questions with an average yes response of 0.5 and some sensitive questions concerning publication misconduct were suggested . in the questionnaires ,
each sensitive question was embedded within four non - sensitive questions , totally apart from the sensitive response choice item .
the five sensitive questions used in this study were :
in the past year , i have submitted / published a paper i had published before exactly as it was , after translating it , or after minimal revisions , without asking permission from the first publisher.in the past year , i have copied exact sentences ( at least 5 sentences ) from others publications to write my paper.in the past year , i have falsified or fabricated part of the research data / results for a paper i was writing.in the past year , the research methods i described in at least one of my papers were not exactly true.in the past year , my name has been listed , with my consent or to my request , as a co - author of a paper to which i did not contribute significantly ( neither the study execution nor the preparation of the article ) . in the past year , i have submitted / published a paper i had published before exactly as it was , after translating it , or after minimal revisions , without asking permission from the first publisher .
in the past year , i have copied exact sentences ( at least 5 sentences ) from others publications to write my paper . in the past year , i have falsified or fabricated part of the research data / results for a paper i was writing . in the past year , the research methods i described in at least one of my papers were not exactly true . in the past year , my name has been listed , with my consent or to my request , as a co - author of a paper to which i did not contribute significantly ( neither the study execution nor the preparation of the article ) . the validity and reliability of the questions were tested . to determine the validity ,
in addition , we consulted five experts in the field of ethics about the clarity of the questions , and used their feedback to make the final amendments . according to the respondents of this section , the clarity of the questions was 85.03% .
for this purpose , we ran a test retest . questions were directed at 40 epidemiology doctoral students twice , with a two week interval , and the intra class correlation ( icc ) was determined as the reliability between them .
the icc was calculated for answers to each list ( lists a and b ) , and they ranged between 0.988 ( 95% ci : 0.951 , 0.997 ) to 0.656 ( 95% ci : 0.194 , 0.901 ) ( table 1 ) .
intra class correlation ( icc ) and 95% confidence intervals ( ci ) of each series of questions on questionnaires 1 and 2 since any question regarding participants demographics was likely to reduce their trust , no such questions were included . to measure the level of trust in the study method regarding confidentiality and difficulty
, we included the following two questions at the conclusion of the questionnaire : how did you find the instructions for completing the questionnaire ? and how trustworthy do you find this method in terms of confidentiality of your responses ? the study questionnaire was used in a pilot through electronic survey services affiliated with the tehran university of medical sciences .
implementation : we searched for papers published between 2009 and 2011 in biomedical iranian journals indexed in scopus ( approximately 50 journal titles ) .
all those with a non - iranian corresponding author were excluded from the list , and the final study population was 2321 corresponding authors with an address in iran . after retrieving their email addresses , a description of the study and its objectives were sent to them , and they were invited to participate in the web - based study .
corresponding authors were randomly divided into two groups and one of the two study questionnaires was sent to them . statistical analysis : in the double list experiment method , there are two question lists for each sensitive question ( for instance , lists 1 and 8 for assessing duplicate publication ) , which we shall refer to as lists a and b from now on ( table 1 ) . for each list , one group of the participants is the baseline and the other is the treatment group . by selecting an equal sample size for each group , and using similar sensitive questions in both lists , yaik = ybik for all participants , and
the total of sensitive and non - sensitive questions in these two groups would be :
yaik={1 if individual i would honestly say yes to item on the a list0 if individual i would honestly say no to item on the a list}ybik={1 if individual i would honestly say yes to item on the b list0 if individual i would honestly say no to item on the b list }
yai+k=k=1ky aikyai+k1=k=1k1y aikybi+k=k=1ky bikybi+k1=k=1k1y bik
thus , one group of participants responds to list a , not including the sensitive question , and forms the baseline group for list a , and the same group responds to list b , including the sensitive question , and forms the treatment group for list b. questions for the other group are the reverse , i.e. for list b , they are the baseline group , and for list a , they form the treatment group . assuming that participants understand the method and respond honestly , the difference in the proportion of yes responses for each list is the prevalence estimate of the sensitive question based on each given list .
since the number of respondents in both treatment groups a and b was the same , the total prevalence of each sensitive question is the mean of the two estimated prevalence rates calculated for lists a and b. to determine the variance of the estimate , we added the variances of lists a and b in both groups , subtracted their covariance from the sum , and divided the results by the sample size . the square root of the calculated variance was used as the standard error to determine the 95% confidence intervals ( 13 ) .
the questionnaire was sent to 2321 corresponding authors in two groups ( n=1160 and 1161 ) ; 100 emails were undeliverable , and 813 ( 36.60 ) of the remaining responded to study questions .
first , we determined the prevalence , average , and variance of publication misconduct based on lists a and b , and then , the prevalence rates of different types of publication misconduct were determined based on the double list experiment method .
the prevalence of data fabrication was 4.15% , the rate for plagiarism was 4.90% , and rates for guest authorship , falsifying methods , and duplicate publication were 18.10% , 12.65% , and 5.40% , respectively ( table 2 ) .
prevalence of publication misconduct using the double list experiment method the instructions were very easy for 64.30% of respondents , 29.70% stated they were quite easy , 5.60% had some trouble responding , and 0.40% found it difficult to complete the survey . in terms of confidentiality ,
56.50% of respondents trusted the method and confidentiality of their responses , 34.50% stated their level of trust was average , and 6.50% did not trust the method at all .
in this study , the prevalence of duplicate publication was 5.40% , the rate of data fabrication was 4.15% , and rates of plagiarism , guest authorship , and falsification of methods were 4.90% , 18.10% , and 12.65% , respectively .
the most common publication misconduct was guest authorship and the least common one was duplicate publication .
the rate of plagiarism in this study was 4.90% . in a study concerning academic honesty among medical students of tehran university of medical sciences using the randomized response technique , the prevalence of plagiarism
was reported 31% with a confidence interval from 18% to 44% ( 14 ) . in another
study the prevalence of plagiarism among uk academics engaged in biologic research was 4.2% ( se=10.8% ) using uct ( 15 ) . in another study on 474 swiss and german students using the double list experiment ,
the prevalence rates of relative and extensive plagiarism were 9% and 4% , respectively ( 12 ) .
mcfarlin et al . published a report concerning the international journal of exercise ( ijes ) stating that 46% of submitted papers contained plagiarism ; this was seen mostly in the introduction and methodology of the manuscript , and only 3% in the discussion and conclusion ( 16 ) .
in addition to true inter - population differences in the incidence of publication misconduct , such differences in the reported rates of plagiarism are due to differences in research methodology , target populations , and definitions of plagiarism .
other misconducts we studied included fabrication and falsification , and the rates were 4.15% and 12.65% , respectively . according to a systematic review , 1.97% of authors ( 95% confidence interval : 0.86 to 4.45 ) had committed fabrication or falsification at least once ( 17 ) . in a study ,
27% of participating scholars and authors stated they had encountered papers that were suspicious in terms of falsification of methodology , data fabrication , or plagiarism ( 18 ) .
the rate of fabrication or falsification was 5.20% , and 22% of them were professors or senior scholars ( 19 ) . in a study ,
the rates of fabrication and falsification were 20% ( 95% confidence interval : 8 to 32 ) and 39% ( 95% confidence interval : 26 to 52 ) , respectively ( 14 ) . based on a comparison between our study and theirs ,
the prevalence rates of 3 publication misconducts - plagiarism , data fabrication , and falsifying the methods were higher using the randomized response technique .
the confidence intervals of these estimates were all greater than our results using the double list experiment .
considering the larger sample size and different methods , smaller confidence intervals were quite expected .
can be attributed to different target populations . in their study , the target population was medical students , but ours was iranian authors .
in addition , we only looked at publication misconduct and not all academic performances of the participants .
studied the rate of guest authorship among corresponding authors publishing original articles , reviews and editorials in high impact factor journals such as annals of internal medicine , jama , lancet , nature medicine , new england journal of medicine , and plos medicine in 2008 and compared results with the prevalence rate in 1996 ; the comparison indicated that the 2008 rate of 17.6% ( 95% confidence interval : 14.60 to 21.00 ) was not significantly different from that in 1996 .
rates were 25% in original research articles , 15% in review articles , and 11.20% in editorials ( 20 ) , which are quite comparable to our results .
the rate of duplicate publication , which is a type of redundant publication , was 5.4% ( 95% confidence interval : 4.90 to 5.81 ) . while a negative prevalence is meaningless , the computation method involved subtraction to arrive at the final estimate , and when the prevalence rate for a sensitive question is close to zero , the prevalence can turn out negative .
another reason could be providing false responses ; when respondents do not trust the study method , feel uncomfortable about sensitive questions , and fear being identified , underestimation occurs and results in a negative prevalence rate ( 12 ) . however , the question regarding confidentiality indicated that the respondents trusted that their responses would remain confidential .
one reason for the low prevalence rate could be the definition we presented for duplicate publication .
questions were designed based on a definition of extensive duplication , i.e. publishing the entire article again , while the true definition is serious overlapping material without citing the previous paper . in a cochrane review ,
the rate of redundant publication in biomedical sciences , or publishing the same material with different data was 1025% ( 21 ) . to determine the prevalence of redundant publication , susser et al .
examined various journals and found the rate had increased from 5% in 1988 to about 12% in 1990 ( 22 ) .
the present study demonstrated that the double list experiment is easy to comprehend , because it does not need additional resources for random selection .
furthermore , it can simply be implemented electronically , and thus , data collection can be done faster . in this study ,
64.3% of our participants stated the questionnaire guidelines were very easy and 29.7% stated completing the questionnaire was quite simple .
this is while in the study by mortaz hejri et al , 10% of the participants thought the guidelines were difficult , 45% thought they were average , and 44% stated they were simple ( 14 ) .
in addition , 56.5% expressed complete trust in the confidentiality of uct , and 34.5% had average trust in the method , while only 29% of the participants had trusted the randomized response technique in answering the questions ( 14 ) .
one of the strong points of our study technique was that respondents did not have to respond to sensitive questions directly which increased their trust , the questionnaire was very easy to complete and no special tool or skill was needed , and it took only 10 minutes of the participants time .
additionally , we tried to assess different types of publication misconduct to determine prevalence differences , while other studies addressed only one or two types of misconduct .
since 64% stated they had understood the methods , non - participation could be because they did not understand how to complete the survey , and since 57% stated they trusted the study , another reason for non - participation could be lack of their trust in keeping their responses confidential . in any event , the high non - response rate limits our ability to generalize findings to the general population .
in addition , considering the nature of sensitive questions and limitations of the study , we did not collect authors demographics , and thus , we were not able to do a more detailed analysis .
further studies are suggested using other indirect techniques such as the crosswise model , or the direct method with the same target population , so that the accuracy of the method is compared against other methods and differences attributable to double list experiment are determined .
double list experiment is well trustable and simple method for the academic society and can be conducted through e - surveys .
other studies using indirect methods and direct methods with control groups are suggested to assess the accuracy of this method in estimating publication misconduct .
the most common publication misconducts among iranian authors are guest authorship and falsification of the study methods . in light of the negative and maleficent impact of publication misconduct in the scientific society , we recommend raising awareness and educating authors and investigators in this
ethical issues ( including plagiarism , informed consent , misconduct , data fabrication and/or falsification , double publication and/or submission , redundancy , etc . ) have been completely observed by the authors . | background : this study was done to determine the prevalence of publication misconduct among iranian authors.methods:data were collected through an email survey of corresponding authors of papers published in iranian journals indexed in scopus during 20092011 . using the double list experiment , these individuals were indirectly questioned about committing one of the five misconducts including duplicate publication , falsification , guest authorship , plagiarism , and fabrication over the past year.results:the survey was sent to 2321 individuals ; 100 emails bounced , and of the remaining , 813 ( 36.60% ) people responded to the questions .
the prevalence rates were 4.15% for fabrication , 4.90% for plagiarism , 18.10% for guest authorship , 12.65% for falsification of the study methods , and 5.40% for duplicate publication . among respondent 56.50% trusted the method and confidentiality of the survey and 6.50% did not trust the method or confidentiality at all.conclusion:we found that the double list experiment method is simple and reliable for use in the academic community , and it can be conducted easily in an e - survey . according to our results ,
the most common misconducts among iranian authors are guest authorship and falsification of the methodology . in light of the negative and maleficent impact of publication misconduct in the scientific society ,
we recommend raising awareness and educating authors and investigators in this regard . to determine the accuracy of the method used in this study , further studies on publication misconduct using a control group and direct questioning , as well as other indirect methods
are suggested . |
the allergic response is a complex process involving the interaction of many mediators .
bradykinin ( bk ) is a potent inflammatory mediator and its actions are mediated
via specific cell surface receptors which are coupled to g - proteins .
two
mammalian bk receptor subtypes , b1 and b2 , have been reported , and the amino
acid sequence of the b1 receptor is 36% identical to the amino acid sequence of
the b2 receptor .
administration of exogenous bk into human nasal airway
causes nasal obstruction , rhinorrhea , and nasal pain [ 2 , 3 ] .
these
effects appear to be mediated by bradykinin b2 receptor because bradykinin b2
receptor antagonists abolish bradykinin - induced nasal obstruction and plasma
extravasation , whereas agonists at the bradykinin b1 receptor do not cause any
symptoms .
icatibant , a bradykinin b2 receptor antagonist , inhibits the
immediate inflammatory response to antigen in subjects with perennial allergic
rhinitis [ 4 , 5 ] .
these reports suggest that bk may
play an important role in the pathogenesis of allergic rhinitis .
the previous
autoradiografic study using i - bk has demonstrated specific i - bk
binding sites mainly exist on the small muscular arteries , venous
sinusoids , and submucosal fibers in human nasal
mucosa .
however , there has been no other report about bk receptor expression
in upper airway . in the present study ,
immunohistochemistry for bradykinin b1 and b2
receptors was
performed to confirm the expression and the distribution of these
receptors in human nasal mucosa .
human
inferior turbinates were obtained after turbinectomy from 12 patients with nasal
obstruction refractory to medical therapy .
informed consent was obtained from
all patients and this study was approved by the ethics committee of sapporo
medical university .
all were nonsmokers , and 6
patients had perennial allergy against
mites as defined by questionnaire and cap test ( pharmacia , uppsala , sweden ) .
all medications , including antibiotics , were prohibited for at least 3 weeks
prior to the study .
the nasal
mucosal specimens were immediately fixed in 10% formalin for
immunohistochemistry . for immunohistochemistry of b1 receptor , rabbit antihuman b1 receptor
polyclonal antibody against a peptide corresponding to c - terminal domain of
human b1 receptor ( catalog # ls - a3580 , lifespan biosciences , mich usa )
similarly , for immunohistochemistry of b2 receptor , rabbit
antihuman b2 receptor polyclonal antibody against a peptide corresponding to
c - terminal domain of human b2 receptor
( catalog # ls - a797 , lifespan biosciences , mich , usa ) was used at 1:100
dilutions . to identify the subsets of cells expressing each
bradykinin receptor ,
the following monoclonal antibodies were used : anti - cd68
( kp-1 clone , dako corporation , carpinteria , calif , usa )
for macrophage , anti - cd31 ( jc70a clone , dako ) for vascular endothelial cells ,
antihuman fibroblast ( 5b5 clone , dako ) for fibroblast , anticytokeratin ( ae1/ae3
clone , dako ) for epithelial cells , and antineurofilament protein ( 2f11 clone ,
dako ) for peripheral nerves .
deparaffinized sections were initially incubated with 3% h2o2 in methanol for 10 minutes to quench endogenous peroxidase activity .
after microwave
treatment ( 10 minutes at 500 watt in citrate buffer ) , the sections were
incubated in blocking solution ( 10% normal goat serum in pbs ) for 30 minutes before
incubation in primary antibody . then , the sections were incubated with
anti - bradykinin b1 or b2 polyclonal antibody for overnight at 4c , washed , and
incubated for 30 minutes with envision+ , peroxidase ( dako ) .
a further washing
in pbs was followed by developing in dab ( dako ) as a chromogen for signal
visualization .
the slides were counterstained mayer 's haematoxylin and
coverslipped using mounting medium . to identify the
subsets of cells expressing each bradykinin receptor ,
, deparaffinized sections were incubated overnight at 4c with a
combination of rabbit polyclonal antihuman bradykinin b1 or b2 antibody and one
of mouse monoclonal antihuman phenotypical makers antibody .
sections were washed in pbs and were incubated for 30 minutes
with alexa fluor 594-labelled goat antimouse igg ( diluted 1:50 ; molecular
probes , ore , usa ) and alexa fluor 488-labelled goat antirabbit igg ( diluted
1:50 ; molecular probes ) .
sections were mounted with slowfade antifade
kits ( molecular probes ) and examined under olympus bx51 microscope , dp70 ccd
camera ( olympus optical co. , tokyo , japan ) .
all images were processed with dp
controller and dp manager software ( olympus optical co ) for image analysis . using this method , bradykinin b1 or b2 receptor expressing
cells
was green , cellular phenotypical makers
were red , and the combined signal is visualized as yellow .
negative controls
were obtained by replacing primary antibodies by mouse igg1 and rabbit
immunoglobulin fraction ( dako ) .
as shown in figure 1 , the
immunoreactivity for b1 receptor was significantly detected in submucosal
glands , epithelial cells ( figures 1(a ) , 1(b ) ) , and fibroblasts ( figures 1(c ) , 1(d ) ) .
immunoreactivity for b2 receptor was significantly detected in
submucosal glands , epithelial cells ( figures 2(a ) , 2(b ) ) , vascular smooth muscle ( figures 2(c ) , 2(d ) ) , nerve bundle , and fibroblasts ( figures 2(c ) , 2(d ) ) .
specificity of the staining was also confirmed by the absence of
labeling with normal rabbit immunoglobulin ( figures 1(e ) and
1(f ) ) . in order to clarify the cell expressing bradykinin b1 and b2
receptors
as shown in figures 3 and 4 , epithelial cells , submucosal glands ( figures 3(b ) and 4(b ) ) , fibroblast ( figures 3(d ) and 4(d ) ) , vascular smooth muscle , and vascular endothelial cells ( figures 3(f ) and 4(f ) ) express both b1 and b2 receptors .
the b2 receptor was found in
nerve fibers ( figure 4(h ) ) , whereas the b1 expression was not observed in nerves ( figure 3(h ) ) .
as shown in figure 5 , the majority of cd68 positive
macrophages showed immunoreactivity for both b1 and b2 receptors .
the
expression levels of both b1 and b2 receptors on epithelial cells and
fibroblast were higher in allergic nasal mucosa ( b1
receptor : figures 1(a ) and 1(c ) ; b2 receptor : figures 2(a ) and 2(c ) ) than nonallergic
nasal mucosa ( b1 receptor : figures 1(b ) and 1(d ) ; b2 receptor : figures 2(b ) and 2(d ) ) .
the patterns of the other immunohistochemical findings in all 12
cases were remarkably similar , and we could not find any other differences of
b1 and b2 receptors immunoreactivity between on allergic and nonallergic nasal
mucosae .
it is well known that the responses to vasoactive
kinin peptides are mediated through the activation of two receptors termed b1 and b2 , which have been defined on the basis
of the structure - function relationships of their agonists and antagonists .
the natural agonists of the b2-receptor are the nonapeptide bradykinin ( bk ) and
the decapeptide lys - bk ( kallidin ) which are generated by the proteolytic action
of the serine protease kallikrein from the protein precursor kininogen .
bk
and lys - bk are weak b1 receptor agonist , however , the cleavage of these two
b2-agonists by arginine carboxypeptidases produces the high affinity b1
receptor agonists , [ des - arg9]-bk , and [ des - arg10]-kallidin ( dlbk ) , respectively ,
.
the b1 receptor is not expressed at significant levels in normal tissues ,
but its synthesis can be induced after tissue injury and by inflammatory factor
such as lipopolysaccharide and il-1 beta . on the other hand ,
the b2
receptor is constitutively expressed in many
types of the cells including smooth muscle cells , certain neurons , fibroblasts ,
and epithelial cells of the lung . in the present study
, we confirm the expression of
both bradykinin b1 and b2 receptors in human nasal epithelial cells .
bk induced
rise in [ ca ] in primary cultured human nasal epithelial cells ,
suggesting the existence of b2 receptor on human nasal epithelial cells .
b1
receptor ligand , lys - des - arg - bk activated
extracellular signal - regulated kinase ( erk ) and the transcription factor ap-1
in human airway epithelial cell lines a549 and beas-2b . taken together ,
these previous observations and our present observations suggest the functional b1 and b2
receptors in human nasal epithelial cells .
the present study indicated the significant
expression of b1 and b2 receptor expressions on nasal fibroblasts .
it has been
reported that bk stimulated il-1 , il-6 , il-8 [ 13 , 14 ] , and eotaxin
production in cultured human fibroblasts by increasing its gene expression .
tnf - alpha and il-1beta both induced an increase in b1 and b2 receptor
expressions in human lung fibroblasts .
the observation of local production
of il-1 during inflammation accompanied by b1-receptor upregulation in
several tissues has resulted in the hypothesis that this cytokine is directly
involved in b1-receptor upregulation .
the expression of bradykinin b1
and b2 receptors were found not only on
epithelial cells and fibroblasts , but also on submucosal glands in the present
study .
it has been reported that bradykinin receptors were detected over submucosal gland in
human and guinea pig airways by in vitro autoradiography .
with respect to
the effect of bk on airway submucosal glands , it has been reported that bk
directly stimulates isolated airway submucosal gland cells and induces mucus
glycoprotein and cl secretion through the activation of b2 receptor
.
also , bk induces an increase in short - circuit current across a cultured
gland cell layer from human airways with [ ca ] rise , indicating a direct
stimulation of ion transport in airway gland cells by bk . on the other
hand ,
some investigators have reported that bk had no significant effect on
mucin release from human , feline , or ferret airway explants [ 6 , 20 ] .
in contrast to significant both b1
and b2 receptor expressions on epithelial cells , fibroblasts , and submucosal
glands , b2 receptor expression on peripheral nerves , but not b1 receptor
expression , could be detected by immunohistochemistry .
b1 receptor was thought
to be generally absent in healthy tissues [ 21 , 22 ] .
in contrast , b2 receptors
are constitutively expressed in a range of cell types including sensory
neurons , and their activation results in excitation and sensitization of
sensory neurons [ 23 , 24 ] . in b2 receptor agonist ,
bk can stimulate sensory nerve
ending , causing the release of substance p and other neuropeptides .
it has
been shown that the nasal stimulation with bk causes nasal pain [ 2 , 3 ] ,
suggesting the existence of the functional b2 receptor on sensory nerves . using double immunofluorescence
technique
, we could confirm the significant expression of both b1 and b2
receptors on macrophages .
the potency of kinins to stimulate leukocytes has
been thought dependent on differentiation and especially on the
activation stage of these cells .
it has been shown that
human peripheral monocytes express a low number of kinin b2 binding sites
.
however , immature , unstimulated human monocytes - derived dendritic cells
constitutively express both b1 and b2 receptors , whereas monocytes did not
express b1 or b2 receptor protein , suggesting upregulation of b1 and b2
receptors during the differentiation of the cells . with respect to the effect
of bk on monocytes ,
bk acting via b2 receptor , increased intracelluar ca , and
stimulated the migration of immature human monocyte - derived dendritic cells
.
thus , it might be possible that local macrophages might be activated by
locally released bk during nasal allergic response .
using
immunohistochemical technique , we have demonstrated the distribution of
bradykinin b1 and b2 receptors in human nasal mucosa .
although kinins do not
appear to have major role in allergic rhinitis , our findings should be of
considerable interest for understanding the role of kinins on upper airway
diseases such as allergic rhinitis and nonallergic rhinitis . | bradykinin ( bk ) has been tobe thought a potent mediator involved in allergic rhinitis because bk was recovered from the nasal lavage fluid of allergic rhinitis patients after allergen provocation and bk receptor antagonists relief nasal allergic symptoms .
two mammalian bk receptor subtypes , b1 and b2 , have been defined based on their pharmacological properties .
we investigated the localization of these receptors by immunohistochemistry .
human turbinates were obtained after turbinectomy from 12 patients with nasal obstruction refractory to medical therapy .
the immunohistochemical study revealed that epithelial cells , submucosal glands , fibroblast , vascular smooth muscle , vascular endothelial cells , and macrophages showed immunoreactivity for both b1 and b2 receptors .
the b2 receptor expression was found in peripheral nerve fibers , whereas the b1 expression was not observed in nerves .
the results may have an important clinical implication for understanding the differential roles of bk receptor subtypes on upper airway diseases such as allergic rhinitis and nonallergic rhinitis . |
semiconductor quantum dots are now routinely obtained using electrostatic gates or etching processes to pattern a two dimensional electron gas formed in some heterostructure ( typically gaas / algaas).@xcite many of their sometimes surprising properties are now reasonably well understood from a qualitative or statistical point of view,@xcite and it is now realistic to think about using these quantum dots for some specific purpose , such as spin filtering,@xcite current or spin pumping,@xcite or in the context of quantum information.@xcite in this context , it becomes important to go beyond a qualitative or statistical description , and to develop tools able to predict quantitatively the properties of a specific quantum dot for given parameters . for isolated or weakly connected dots the coulomb blockade regime
the coulomb interaction between electrons plays an important role and has to be taken into account properly . a method of choice in this regard
is the density functional approach,@xcite which has been widely used in theoretical modeling of quantum dots . @xcite more specifically , since it is necessary to describe correctly the spin degree of freedom , we have in mind a spin density functional , where each density of spin @xmath0 , with @xmath1 corresponding to majority and minority spins , are treated as an independent variable . how this can be achieved in practice for a dot containing up to four hundred electrons , and for an @xmath2 parameter as high as four ,
has been demonstrated in a series of papers.@xcite one striking feature of these calculations , however , is that the qualitative picture which emerges is somewhat unexpected in view of previous results . indeed , within a statistical approach and assuming the classical dynamics within the nanostructure is sufficiently chaotic
, one can model the wave functions in the quantum dot using random matrix theory ( rmt ) .
if furthermore the coulomb interaction is treated within the random phase approximation ( rpa ) , it is possible to derive various statistical quantities,@xcite such as the distribution of spacing between coulomb blockade conductance peak , or the probability of occurrence of non - standard spins [ that is , not zero ( not one - half ) for even ( odd ) particle number ] .
it turns out , for instance , that the spin density functional calculations give a larger number of `` high '' spins than was predicted within rmt plus rpa modeling.@xcite such discrepancies could originate from a variety of causes , ranging from the the statistical behavior of the kohn - sham wave functions to an intrinsic failure of one or the other approach .
the goal of this paper is to clarify this issue . for this purpose , we need a way to understand , or to organize , the numbers obtained from the full - fledged spin density functional theory ( sdft ) .
this can be done using the strutinsky approximation to dft discussed in ref . , up to straightforward modifications to include the spin variable .
the strutinsky approach is an approximation scheme , developed in the late sixties in the context of nuclear physics , in which the interference ( or shell ) effects are introduced perturbatively.@xcite it has been since then used in many subfield of physics,@xcite including the calculation of the binding energy of metal clusters.@xcite standard treatments are usually limited to first - order corrections ; in this case , it is similar to the harris functional @xcite familiar to the dft literature . here ,
in contrast , we use the second - order approximation @xcite developed in ref . .
we shall see that the second - order strutinsky scheme turns out to be extremely accurate in some circumstances .
furthermore , even when it is less precise , which happens in conjunction with the occurrence of `` spin contamination '' in the sdft calculations , it still provides a qualitatively correct statistical description .
the second - order strutinsky corrections can be cast in a very natural form:@xcite in fact , they amount to taking into account the residual ( screened ) interactions between quasiparticles in a landau fermi liquid picture .
they are thus amenable to treatment by the same rmt approach as was used previously for rpa , providing an analogue of the `` universal hamiltonian '' in the case of sdft .
since within the strutinsky approximation the quantum dot properties are relatively transparent , we will then be in position to discuss the difference between sdft results and those obtained from rmt plus rpa .
the paper is organized as follows . in section [ sec : strut ] , we briefly review the strutinsky approximation as it applies to spin density functional theory . in section
[ sec : t&c ] , we consider more specifically the local density approximation from this perspective , and in particular the screened potential that it implies .
section [ sec : ksvsst ] covers in detail the specific case of a model quantum dot with quartic external confining potential .
this model is used to investigate the accuracy of the strutinsky approximation for various electron densities . in section [ sec : fl ] , we discuss how the fermi liquid picture emerging from the strutinsky approximation scheme can be used , in conjunction with a random plane wave model of the wavefunctions , to analyze the peak spacing and spin the distributions resulting from the sdft calculation .
this framework also makes it possible to discuss the mechanism of spin contamination .
finally , in the last section we come back to the original question motivating this work and make use of what we understand from the strutinsky approximation to discuss the discrepancies between sdft calculations and rpa plus rmt predictions .
in the spin density functional description of a quantum dot , one considers a functional of both spin densities @xmath3 $ ] @xmath4={{\cal t}_{\rm ks}}[n^{\alpha},n^{\beta}]+{{\cal e}_{\rm tot}}[n^{\alpha},n^{\beta } ] \ ; , \ ] ] where @xmath5 correspond to majority and minority spins , respectively . in this expression ,
the second term is an explicit functional of the densities , @xmath6\equiv\int \!d{{\bf r}}\;n({{\bf r } } ) \;{u_{\rm ext}}({{\bf r } } ) \qquad \qquad \qquad \nonumber\\ + \int \ !
d{{\bf r}}d{{\bf r } } ' \,n({{\bf r}})\,v_\mathrm{int}({{\bf r}}-{{\bf r}}')\,n({{\bf r}}')+{{\cal e}_{\rm xc}}[n^{\alpha},n^{\beta } ] \ ; , \end{aligned}\ ] ] where @xmath7 , @xmath8 is the exterior confining potential , and the precise form of the exchange correlation term @xmath9 $ ] is to be discussed in more detail in section [ sec : t&c ] .
@xmath10 is the electron - electron interaction kernel .
the presence of metallic gates can be taken into account by including an image term in addition to the bare coulomb interaction , @xmath11 where @xmath12 is the distance between the top confining gate and two - dimensional electron gas . the image term in the interaction kernel
greatly reduces classical coulomb repulsion between electrons at a distance larger than @xmath12 so that the electron density far from the boundary is quite uniform .
the bare coulomb interaction can be recovered by letting @xmath12 go to infinity .
the kinetic energy term @xmath13 $ ] , on the other hand , is expressed in terms of the auxiliary set of orthonormal functions @xmath14 ( @xmath15 ) such that @xmath16 as @xmath17 & = & { \hbar^2 \over 2 m } \int \sum_{{\sigma}={\alpha},{\beta } } \sum_{i=1}^{n_{\sigma } } \ , |\nabla\psi^{\sigma}_i({\bf r})|^2 \ , d{\bf r } \ ; .
\label{eq : def_tks}\end{aligned}\ ] ] > from the density functional eq .
( [ eq : fks ] ) , the ground state energy of the quantum dot containing @xmath18 particles of spin @xmath19 is obtained as @xmath20\ ] ] where the kohn sham densities @xmath21 $ ] minimize @xmath22 under the constraint given by the number of particles of each spin .
this in practice is equivalent to solving the kohn - sham equations @xmath23 with the spin dependent self - consistent potential @xmath24 \ ; .\ ] ] in this section , we shall give a brief description of the second - order strutinsky approximation as it applies to spin density functional theory .
up to the introduction of the spin indices , the derivation of this approximation follows exactly the same lines as the spinless case discussed in details in ref . .
we shall therefore not reproduce it here , but rather try to emphasize what exactly are the assumptions made in deriving the approximation , and then merely write down the expression we shall use in the following sections . the basic idea of the strutinsky energy correction method is to start from smooth approximations , @xmath25 and @xmath26 , to the dft energy @xmath27 and electronic density @xmath28 .
then , fluctuating terms are added perturbatively as an expansion in the small parameter @xmath29 in the original work of strutinsky @xcite various ways of constructing the smooth approximation have been considered .
the most natural choice for @xmath30 turns out to be the solution of the thomas - fermi equation @xmath31 = { \mu_{\rm tf}}^{\sigma}\ ] ] coupled with @xmath32 $ ] .
the `` generalized '' thomas - fermi functional is defined as @xmath33 = { { \cal t}_{\rm tf}}[n^{\alpha},n^{\beta}]+{{\cal e}_{\rm tot}}[n^{\alpha},n^{\beta } ] \ ; , \ ] ] with @xmath34 $ ] given by eq .
( [ eq : def_etot ] ) .
it differs from the original spin density functional only in that the quantum mechanical kinetic energy @xmath35 , eq .
( [ eq : def_tks ] ) , is replaced by an explicit functional of the density . for two dimensional systems
this takes the form @xmath36 = { { \cal t}_{\rm tf}}^{(0 ) } [ n^{\alpha},n^{\beta } ] + { { \cal t}_{\rm tf}}^{(1 ) } [ n^{\alpha},n^{\beta } ] $ ] with @xmath37 & = & \frac{1}{2 n(0 ) } \int \ ! d { { \bf r}}\big[n^{\alpha}({{\bf r}})^2 + n^{\beta}({{\bf r}})^2\big ] \label{eq : ttf0 } \\ { { \cal t}_{\rm tf}}^{(1 ) } [ n^{\alpha},n^{\beta } ] & = & \frac{\eta}{8 \pi n(0 ) } \int \!\!d { { \bf r}}\left[\frac{(\nabla n^{\alpha})^2}{n^{\alpha } } + \frac{(\nabla n^{\beta})^2}{n^{\beta}}\right ] \label{eq : ttf1}\end{aligned}\ ] ] where @xmath38 the density of states for 2-dimensional systems and @xmath39 a dimensionless constant taken here to be @xmath40 .
such a choice for the kinetic energy functional correctly takes into account the pauli exclusion principle , and thus that an increase in kinetic energy is required to put many particle at the same space location , but fails to include fluctuations associated with quantum interference . to illustrate this ,
let us for a short while the assume @xmath41 , i.e. only the first term @xmath42 of the thomas - fermi kinetic energy is taken into account .
then , one can show that the thomas - fermi density fulfills the self - consistent equation @xmath43({{\bf r}})\ ] ] where the thomas - fermi potential is defined , as in eq .
( [ eq : uks ] ) , by @xmath44\ ] ] and @xmath45({{\bf r } } ) = \int \!\!\frac{d{{\bf p}}}{(2\pi\hbar)^d}\ , \theta\left [ \mu^{\sigma}_{\rm tf } - \frac{{{\bf p}}^2}{2 m } - { u_{\rm tf}}^{\sigma}({{\bf r}})\right]\ ] ] is the weyl part of the density of states of a system of independent particles evolving under the potential @xmath46 ( @xmath47 is the heaviside step function , @xmath48 is the dimensionality , and the chemical potentials @xmath49 are chosen such as to fulfill the constraints on the total number of particles with spin @xmath50 and @xmath51 ) . from its definition , @xmath52({{\bf r}})$ ] ( and as a consequence @xmath53 ) is a smooth function , in the sense that it can change appreciably only on the scale on which @xmath8 varies , but can not account for the quantum fluctuations of the density on the scale of the fermi wavelength .
the weyl approximation is , however , only the leading term in a semiclassical expansion of the smooth part of the density of states , and higher - order corrections in @xmath54 can be added in a systematic way . the standard way to choose @xmath55 @xcite is such that eq .
( [ eq : th_sc ] ) holds , but with an approximation to the smooth density of states @xmath52({{\bf r}})$ ] which includes both the weyl term eq .
( [ eq : weyl ] ) and the first @xmath54 corrections . for two dimensional systems ,
however , the corrective term computed from this prescription turns out to be zero , when the presence of @xmath55 is actually useful in smoothing the thomas - fermi density near the boundaries of the classically allowed region .
we have therefore used the phenomenological weiscker - like term@xcite eq .
( [ eq : ttf1 ] ) which plays a similar role .
the practical implementation for the strutinsky scheme can be summarized as follows .
the first step consists in solving the generalized thomas - fermi equation eq .
( [ eq : tf ] ) , which defines a zeroth - order approximation for the ground state energy , @xmath25 , as well as an approximation to the density of particles @xmath53 . from this latter quantity ,
one derives for each spin @xmath5 the effective potential @xmath56 through eq .
( [ eq : veff ] ) .
the second step consists in solving the schrdinger equations ( again for each spin ) @xmath57 therefore , while the kohn - sham equations are both quantum mechanical in nature and self - consistent , here all the self - consistency is left at the `` classical - like '' level of the thomas - fermi equation , and the quantum mechanical wave interference aspect is taken into account without self - consistency .
one obtains in this way a new density @xmath58 it can be seen@xcite that @xmath53 is _ by construction _ a smooth approximation to @xmath59 [ this is basically the content of eq .
( [ eq : th_sc ] ) ] .
therefore @xmath60 can be considered as the oscillating part of @xmath61 , and will describe the short scale variations of the density associated with quantum interference . once the eigenfunctions and eigenvalues of eq .
( [ eq : schroe ] ) are known , corrections to the thomas - fermi energy can be added perturbatively @xmath62 the first - order correction turns out to be simply the oscillating part of the one particle energy@xcite @xmath63 with @xmath64 the one particle energy , and @xmath65 + \sum_{{\sigma}={\alpha},{\beta } } \int \!d{{\bf r}}\,{u_{\rm tf}}^{\sigma}({{\bf r } } ) \,{n_{\rm tf}}^{\sigma}({{\bf r}})\ ] ] its smooth part .
the second - order correction @xmath66 can be expressed in two different ways@xcite @xmath67 @xmath68 with @xmath69\ ] ] @xmath70^{{\sigma},{\sigma } '' } \hspace{-15pt } ( { { \bf r}},{{\bf r } } '' ) \ ; \left [ \frac{\delta^2 { { \cal t}_{\rm tf}}}{\delta n^2 } \cdot{v_{\rm bare}}\right]^{{\sigma}'',{\sigma}'}\hspace{-15pt } ( { { \bf r}}'',{{\bf r } } ' ) \ ; .\ ] ] ( the matrix inversion here should be taken with respect to both the spatial position and the spin indices . )
note that in eq .
( [ eq : vsc ] ) we can use @xmath71 and , neglecting terms involving derivatives of the thomas - fermi density , @xmath72 the first of these second - order expressions , eq . ( [ eq : de2 ] ) , involves the @xmath73 which are in principle unknown . it is therefore not useful if one is trying to avoid performing the full kohn - sham calculation . here , however , we shall also do this full self - consistent calculation in order to evaluate the accuracy of the strutinsky scheme ; we therefore know @xmath73 . in this case
( [ eq : de2 ] ) turns out to be somewhat simpler to compute than eq .
( [ eq : de2 * ] ) .
this is not , however , because of the matrix inversion in eq .
( [ eq : vsc ] ) for the case we shall consider , the screening length is much smaller than the size of the system , allowing this inversion to be done analytically .
rather , the resulting screened potential will turn out to be diagonal neither in the position nor in the momentum representation ( see next section ) , in contrast to @xmath74 which is the sum of two parts , one diagonal in the position and the other in the momentum representation .
since eq .
( [ eq : de2 ] ) and ( [ eq : de2 * ] ) are essentially at the same level of precision , we shall in the following mainly use the first one eq .
( [ eq : de2 ] ) ; we will apply eq .
( [ eq : de2 * ] ) only with an approximate @xmath75 which is diagonal in the momentum representation , thus inducing additional errors that are not intrinsic to the strutinsky scheme .
although we shall not reproduce here the derivation of eq .
( [ eq : de2 ] ) ( see again ref . for details ) , the condition of applicability of this equation can be understood easily by comparing the kohn - sham equations eq .
( [ eq : ks ] ) with the ones defined by the thomas - fermi potential @xmath46 , eq .
( [ eq : schroe ] ) .
we see there that the kohn - sham wave functions @xmath76 and their approximations @xmath77 are defined through schrdinger equations that differ only by a difference in the potential term @xmath78 with @xmath79 defined by eq .
( [ eq : vbare ] ) .
the main approximation in the derivation of eq . ( [ eq : de2 ] ) is that the @xmath80 can be taken into account by a second - order perturbative calculation .
in general , this implies that the non diagonal matrix elements @xmath81 ( @xmath82 should typically be smaller than the mean level spacing @xmath83 between one particle energies . more specifically , since the only relevant errors are ones modifying the slater determinant formed by the occupied orbitals , the actual condition is that the matrix element between the first unoccupied orbital and the last occupied orbital is smaller than the spacing between these level , that is @xmath84 a good accuracy , on the scale of the one particle mean level spacing , of the strutinsky approximation in the form eq .
( [ eq : de2 ] ) is equivalent to the above condition . now , eq .
( [ eq : de2_cond ] ) again involves @xmath85 , which is unknown .
it is therefore not possible to prove rigorously that it should be fulfilled .
it is possible , however , to show the consistency of such an assumption .
if we assume that * @xmath86 for all pairs of orbitals @xmath87 and @xmath88 , so that @xmath89 can be treated perturbatively , and * the oscillating parts of the kohn - sham densities @xmath90 do not differ significantly from @xmath91 , implying that @xmath92 , then it can be shown that * @xmath93 + which immediately yields eq .
( [ eq : de2 * ] ) from ( [ eq : de2 ] ) , and * @xmath94 and @xmath95 ^ 2 \rangle / \langle [ \delta n^{\sigma}({{\bf r}})]^2 \rangle$ ] are both negligible for a large dot for which the chaotic motion in the potential @xmath96 allows modeling of the wave functions in terms of random plane waves ( being of order @xmath97 with @xmath98 the dimensionless conductance of the dot ) .
the second order strutinky corrections , eqs .
( [ eq : de2 ] ) or ( [ eq : de2 * ] ) , involve the bare and screened interactions eqs .
( [ eq : vbare ] ) and ( [ eq : vsc ] ) . in this section
, we shall consider the particular form these interactions take for the exchange correlation term we use to perform the actual sdft calculations , namely the local spin density approximation @xmath99 \simeq \int \!d{{\bf r}}\;n({{\bf r } } ) \;{\epsilon_{\rm xc}}\big(n({{\bf r}}),\zeta({{\bf r}})\big ) \ ; , \ ] ] where @xmath100 is the polarization of the electron gas , and @xmath101 is the exchange plus correlation energy per electron for the uniform electron gas with polarization @xmath102 .
we furthermore use tanatar and ceperley s form of @xmath101 at @xmath103 and @xmath104 , and the interpolation @xmath105 $ ] for arbitrary polarization , with @xmath106 / ( 2^{3/2 } - 2)$ ] . recently ,
attaccalite et al.@xcite parameterized a new lsda exchange - correlation functional form based on more accurate quantum monte carlo calculations ( see e.g.ref . ) that include spin polarization explicitly .
we have , however , checked that for the quantities in which we are interested here , this new functional introduces only minor modifications ; we shall therefore use tanatar - ceperley s form for our discussion . from the expression of the functional @xmath9 $ ] , the bare and screened interaction potentials eq .
( [ eq : vbare ] ) and([eq : vsc ] ) , needed for the evaluation of the second - order strutinsky corrections , are easily computed .
the bare interaction is the sum of two terms @xmath107 .
the coulomb interaction @xmath108 is independent of both the density and spin .
the matrix structure here refers to the spin indices @xmath50 and @xmath51 .
the exchange correlation term is local and can be expressed as @xmath109 where @xmath110 and @xmath111 are obtained from the partial derivative of @xmath112 [ defined in eq .
( [ eq : def_exc ] ) ] . in all numerical calculations
we shall keep entirely the dependence of @xmath110 and @xmath111 on the polarization @xmath102 .
however , this latter will usually be relatively small , and @xmath110 and @xmath111 contains already second derivatives of the functional @xmath113 with respect to the polarization .
we shall therefore proceed assuming @xmath114 and @xmath115 .
the dependence of these functions on the parameter @xmath116 , with @xmath117 the 2d bohr radius , is shown in fig [ fig : xc_coef ] . and @xmath118 , which define the functional second derivative of @xmath9 $ ] [ see eq .
( [ eq : vxc ] ) ] , as a function of the parameter @xmath119.,height=249 ] turning now to the screened interaction @xmath120 , it is useful to switch to the variables @xmath121 .
the fourier transform of @xmath122 with respect to @xmath123 reads @xmath124 where @xmath125 ( again , the pure coulomb case is recovered by letting the distance to the top gate @xmath12 go to infinity ) .
this can by further simplified by diagonalizing the matrix in the spin indices : the eigenvectors are the `` charge channel '' @xmath126 and the `` spin channel '' @xmath127 .
the eigenvalues are @xmath128\}\ ] ] in the charge channel and @xmath129\ ] ] in the spin channel [ note @xmath130 .
because the screening length is short on the scale for which the smooth part of the electronic density varies appreciably , the operator @xmath131 can be inverted by treating the variable @xmath132 as a parameter , appearing thus diagonal in the @xmath133 representation .
one obtains in this way @xmath134 in terms of the eigenvalues @xmath135 } { 1 + g(q ) [ 2 v_c(q ) - ( { v_a}({{\bf r } } ) + { v_b}({{\bf r}}))]}\ ] ] for the charge channel and @xmath136}{1 + g(q)[{v_b}({{\bf r } } ) - { v_a}({{\bf r}})]}\ ] ] for the spin channel .
the @xmath132 dependence of @xmath137 and @xmath138 arises from @xmath139 and @xmath140 , and therefore from the local value of the density ( that is , of the parameter @xmath2 ) at the location the interaction is taking place .
furthermore , the function @xmath141 would just be 1 in the absence of the @xmath54 correction @xmath55 to the thomas - fermi kinetic energy term ; it prevents effective screening to take place for large momenta .
to evaluate the accuracy of the strutinsky approximation scheme , we consider a two dimensional model system for which the electrons are confined by a quartic potential @xmath142 \ ; .\ ] ] the role of the various parameters of @xmath143 is the following : @xmath144 controls the total electronic density ( i.e. the parameter @xmath2 ) , and therefore the relative strength of the coulomb interaction ; @xmath145 allows one to place the system in a regime where the corresponding classical motion is essentially chaotic ; finally , @xmath146 and @xmath147 have been introduced to lower the symmetry of the system . in the following sections , we use [ a1 ] to denote the parameter value @xmath148 ( with @xmath149 ) , and [ a4 ] for @xmath150 , which at @xmath151-@xmath152 correspond to @xmath153 and @xmath154 , respectively .
we use @xmath155 and @xmath156 in our calculations unless specified otherwise .
in addition to this 2-dimensional potential , we assume the existence of a metallic gate some distance @xmath12 away from the 2d electron gas whose purpose is to cut off the long - range part of the coulomb interaction .
this gate is placed sufficiently far from the electrons to prevent the formation of a density deficit in the center of the potential well without modifying qualitatively the quantum fluctuation . in practice , we take @xmath12 about @xmath157 for [ a1 ] , and @xmath158 for [ a4 ] .
, it was actually necessary to place the gate quite close to the electron gas to see any effect on the density , even on the classical scale .
the image charge associated with the gate is at a distance @xmath159 which is , however , still larger than the screening length within the electron gas . ]
for any set of parameters defining the potential eq .
( [ eq : qos ] ) , and for any number of up and down electrons @xmath160 , we can compute the kohn - sham energies @xmath161 $ ] and densities @xmath162 following the approach described in detail in ref . .
for the strutinsky approximation , the only part which presents some degree of difficulty is actually the thomas - fermi calculation , for which we have developed a new conjugate - gradient method which turns out to be extremely efficient.@xcite once @xmath163 are known , the effective potentials @xmath164 and the corresponding densities @xmath165 follow immediately . for a system of @xmath166 electrons ( @xmath167 ) .
from top to bottom : @xmath26 ; @xmath28 ; @xmath168 ; and @xmath169 . note that @xmath170 is a smooth approximation to @xmath171 and that @xmath168 and @xmath169 are very similar.,title="fig:",width=278 ] for a system of @xmath166 electrons ( @xmath167 ) . from top to bottom : @xmath26 ; @xmath28 ; @xmath168 ; and @xmath169 . note that @xmath170 is a smooth approximation to @xmath171 and that @xmath168 and @xmath169 are very similar.,title="fig:",width=278 ] for a system of @xmath166 electrons ( @xmath167 ) . from top to bottom : @xmath26 ; @xmath28 ; @xmath168 ; and @xmath169 .
note that @xmath170 is a smooth approximation to @xmath171 and that @xmath168 and @xmath169 are very similar.,title="fig:",width=278 ] for a system of @xmath166 electrons ( @xmath167 ) .
from top to bottom : @xmath26 ; @xmath28 ; @xmath168 ; and @xmath169 . note that @xmath170 is a smooth approximation to @xmath171 and that @xmath168 and @xmath169 are very similar.,title="fig:",width=278 ] ( solid ) and @xmath169 ( dashed ) , in units of the average thomas - fermi density @xmath170 inside the dot .
upper panel : parameters [ a1 ] ( @xmath172 ) ; lower panel parameters [ a4 ] ( @xmath173 ) .
the dot contains @xmath166 electrons ( @xmath174 ) .
the thin dashed lines correspond to @xmath169 from a less accurate choice of the thomas - fermi kinetic energy term , namely @xmath175 instead of @xmath40.,width=268 ] figure [ fig : density_a4 ] shows the densities @xmath26 , @xmath28 , @xmath176 , and @xmath169 for the ground state with @xmath166 electrons ( @xmath167 ) of the gated quartic oscillator system with parameter [ a4 ] , corresponding to an interaction parameter of @xmath177 . noting in particular the difference of scale between the upper and lower panels , one can observe that the thomas - fermi density already is a very good approximation to the exact one , and that @xmath176 is a small oscillating correction , of the same magnitude as the oscillating part of @xmath178 .
apparent also on this figure is the fact that the largest errors are located at the boundary of the dot where corrections to the weyl density of higher order in @xmath54 are the largest . to make this more visible
, we plot in fig .
[ fig : diagonal_cut ] the densities @xmath176 and @xmath169 along a cut on a diagonal of the confining potential for two sets of parameters .
this makes it clear that @xmath169 is an oscillating function only in the interior of the dot , but has a proportionally large secular component at the boundary . as a consequence ,
choosing correctly the term @xmath55 of the thomas - fermi kinetic energy term is actually important to obtain good accuracy .
we have therefore determined the parameter @xmath179 of this functional by imposing that @xmath180 $ ] oscillates around zero , rather than having a significant mean value . as an illustration ,
we also plot in fig .
[ fig : diagonal_cut ] the same quantities but for a calculation where a value @xmath181 has been used for the thomas - fermi kinetic energy correcting term .
we see that this increases significantly the error in the thomas - fermi density at the boundary , reducing the effectiveness of the strutinsky approximation . with the expressions eqs .
( [ eq : vbare_ii ] ) and ( [ eq : hatvsc ] ) of the bare and screened interactions , and using the known eigenvalues and eigenfunctions for the schrdinger equations eqs .
( [ eq : ks ] ) and ( [ eq : schroe ] ) , the strutinsky approximation for the total energy , including the order one eq .
( [ eq : de1 ] ) and order two eqs .
( [ eq : de2 ] ) or ( [ eq : de2 * ] ) corrections , can be computed for any @xmath18 .
as for the full spin density calculations , the ground state energy for a given total number of electron @xmath182 is then obtain as the minimum over @xmath18 with @xmath183 of these energies .
let us now consider these ground state energies for a choice of parameters [ a1 ] , such that the coefficient @xmath184 is still smaller than one and thus the coulomb interaction is not very large compared to the kinetic energy of the particles .
[ fig : est - eks:1 ] displays the corresponding difference between strutinsky and kohn - sham ground - state energies , in mean level spacing units , for a number of electrons ranging from 50 to 200 . for the upper panel , @xmath185 $ ]
is obtained from the expression eq .
( [ eq : de2 ] ) using the bare interaction and requiring the knowledge of the exact @xmath186 . for the lower panel , @xmath187 $ ]
is obtained from eq .
( [ eq : de2 ] ) , which involves the approximate screened interaction , but only the knowledge of @xmath188 .
( @xmath172 ) .
upper panel : @xmath185 $ ] obtained from eq .
( [ eq : de2 ] ) ; lower panel : @xmath187 $ ] obtained from eq .
( [ eq : de2 * ] ) . in both cases ,
the difference shows small fluctuations ( a few percent ) about a linear secular trend ( dashed line is fit).,width=268 ] the first observation that can be made on that figure is that the second form of the strutinsky approximation appears substantially less accurate than the first one . as mentioned earlier , this is , however , probably due to the fact that , because our code was devised to handle only two body interactions that were diagonal either in position or in momentum representation , we had to use in that calculation an approximation where , for the screened interaction , the local value of the parameter @xmath189 has been replaced by its mean value . indeed , a second feature immediately visible on fig . [ fig : est - eks:1 ] is the presence of a net trend in the energy differences between kohn - sham and strutinsky calculations .
this secular term is related to the non - oscillating component of @xmath169 and @xmath176 visible on the lower panels of figs .
[ fig : density_a4 ] and [ fig : diagonal_cut ] at the boundary of the quantum dots .
this can be checked by using a less accurate thomas - fermi approximation ( e.g. with @xmath181 for the correcting term of the kinetic energy @xmath55 ) , and noticing that this secular term in the deviation increases noticeably while the fluctuations remain less affected .
since the total density of electrons at the boundary of the dot is significantly lower than its average value , it is relatively natural that in our approach , this secular deviation is made significantly worse in the second form of our approximation .
the secular deviation is not completely negligible in terms of the mean level spacing .
the relevant scale for the smooth part of the ground energies is , however , the charging energy , compared to which these secular corrections are extremely small . to focus on the fluctuating part
, we therefore remove the secular term ( i.e. the straight lines in fig .
[ fig : est - eks:1 ] ) , obtaining in this way fig .
[ fig : est - eks:2 ] . but now with the secular trend removed .
solid : all ground states ; dots : ground states without significant spin contamination .
note the excellent agreement in the case of the first strutinsky form @xmath190 ( upper panel ) of order 1 percent when spin contamination is not present .
in the case of the second form @xmath191 , the agreement is still very good ( lower panel ) .
, width=268 ] let us consider first the upper panel , where the first form of the strutinsky approximation has been used .
we observe that the fluctuating part of the error is usually extremely small , typically of order a percent of a mean level spacing , and that this is mainly an oscillation between odd and even number of particles in the system .
nevertheless , in a few circumstances significantly larger deviations are observed , with a magnitude typically five percent of a mean level spacing and a sign which is always negative .
to understand the origin of these larger deviations , it is useful to correlate them with the occurrence of spin contamination , that is to situations where the sdft calculations break the spin rotation symmetry . since the actual spin is a somewhat ill - defined quantity in a spin density calculation , we need however first to specify what we understand by this .
indeed , in spin density functional theory the difference @xmath192 can be interpreted as twice the component @xmath193 of the quantum dot total spin .
another quantity that can be easily computed is the mean value @xmath194 of the operator @xmath195 for the slater determinant formed by the kohn - sham orbitals @xmath196 , @xmath197 , which can be expressed as @xmath198 with the `` spin contamination '' @xmath199 given by@xcite @xmath200 from this expression , one sees that if all occupied @xmath51-orbitals are identical to the corresponding @xmath50-orbitals , @xmath201 , and it is presumably reasonable to interpret @xmath202 as the system s total spin . however ,
as soon as different - spin orbitals start to differ , @xmath199 can take any positive value smaller than @xmath203 , signaling that , at least , there is some ambiguity in the assessment of the total spin of the system . in fig .
[ fig : sc ] we have plotted the ground state spin contamination @xmath204 $ ] as a function of the particle number . for [ a1 ] , the spin contamination is usually negligible , except in some few cases where @xmath205 s of order one half or so are encountered .
$ ] as a function of the number of particles .
the spin contamination is infrequent at high density ( [ a1 ] , upper panel ) , but becomes frequent and substantial for @xmath206 ( [ a4 ] , lower panel).,width=268 ] coming back to the strutinsky approximation , we can use the information from fig .
[ fig : sc ] to exclude in fig .
[ fig : est - eks:2 ] the ground states with significant spin contamination .
the remaining points correspond to the dotted symbols in this figure . in the upper panel
, we see that there is almost a one to one correspondence between larger errors and spin contamination .
turning to the lower panel in fig . [
fig : est - eks:2 ] , we see that the further approximations in treating the screening used in evaluating eq .
( [ eq : de2 ] ) do degrade the accuracy of the ground state energy somewhat .
still , st * gives the fluctuating part of the energy to within a few percent .
for the spin contamination , no particular correlation is seen , presumably again because the overall agreement is slightly spoiled by the approximation we made for the screened coulomb interaction . in lower density ( larger @xmath2 ) more realistic dots modeled by the parameter set [ a4 ] ,
spin contamination in ks ground states is much more pronounced , as shown in the lower panel of fig .
[ fig : sc ] it is , in fact , always significant . in conjunction , fig .
[ fig : est - eks - a4 ] shows that the accuracy of both st [ i.e.using eq . ( [ eq : de1 ] ) ] and
st * [ i.e. using eq .
( [ eq : de2 ] ) ] becomes worse .
as at higher density , the main error is a secular trend : in the case of st * it attains a value of several mean level spacings , due presumably to the approximations made in treating the screening . after removing the secular deviation , however , the fluctuation in the errors of st and st * ground state energy is still quite small : the rms is @xmath207 in st and @xmath208 in st*. thus for characterizing the fluctuating part of the ground state energy , st * is nearly as good as st , a property we expect to remain valid at larger @xmath2 .
in the previous subsection , we have considered the accuracy of the strutinsky approximation for individual ground state energies .
we found that as long as no significant amount of spin contamination is present in the sdft calculation , the strutinsky result provides an excellent approximation when eq .
( [ eq : de2 ] ) is used , and a good , though slightly degraded one , with eq . ( [ eq : de2 * ] ) . in this latter case , it is probable that the additional errors come mainly from the neglect of the local density dependence in the screened interaction rather than to the strutinsky approximation itself .
we shall come back to the issue of spin contamination in the next section , and sketch an extension of the theory that would make it suitable to deal with the spin contaminated case .
dot [ a4 ] .
upper panel : @xmath185 $ ] ; lower panel : @xmath187 $ ]
. the linear secular trend ( dashed line is a fit ) is now significantly larger than for [ a1 ] ( compare with fig . [
fig : est - eks:1 ] ) , but the fluctuation about this trend remains small ( of order 5 percent).,width=268 ] before doing so , however , we shall address another question , namely how well , even in the case where a one - to - one comparison of ground state energies can imply an error of a fraction of mean level spacing , are the statistical properties of the quantum dots described within the strutinsky approximation .
for instance , we have in mind the distribution of ground state spin @xmath209 $ ] or of ground state energy second difference @xmath210 = { e_{\rm ks}}[n+1 ] + { e_{\rm ks}}[n-1 ] - 2{e_{\rm ks}}[n+1]$ ] .
this latter quantity is accessible experimentally by measuring the spacing between conductance peaks in the coulomb blockade regime , and will be referred to below as the `` peak spacing '' . in fig .
[ fig : psp ] , both peak spacing and spin distributions are plotted for two interaction strength regime ( [ a1 ] and [ a4 ] ) using either kohn - sham results or one or the other form of the strutinsky approximation . in the small @xmath2 case ,
the agreement is naturally excellent , but we see that even for the higher @xmath2 case , both forms of the strutinsky approximation give a fairly good approximation certainly they provide a qualitatively correct description .
( left column ) and [ a4 ] ( right column ) . solid : even @xmath182 ; dashed : odd @xmath182 .
the statistics are obtained for @xmath211-@xmath152 with @xmath212 and @xmath213 . from top to bottom : kohn - sham , first , and second form of the strutinsky approximation .
agreement between the three methods is excellent , of course , for [ a1 ] .
but even for [ a4 ] where individual energies may be in error , the agreement of the distributions is very good .
, width=307 ]
it is not possible to develop a real landau fermi liquid theory for quantum dots because the mesoscopic fluctuations prevent any taylor expansion of the free energy in terms of occupation number .
( landau theory basically assumes that the excitation energies are the smallest energy scales of the problem , which is clearly not true for mesoscopic systems because of variation on the scale of the mean level spacing . ) however , discussing what we may call a landau fermi liquid `` picture '' , in the sense that the low energy physics is described by a renormalized weak interaction , is still something meaningful . in that sense , what eqs .
( [ eq : strut_corr])-([eq : vsc ] ) express is that sdft , in the limit where the strutinsky approximation scheme is accurate , is equivalent to a landau fermi liquid picture , where quasiparticles with spin @xmath88 evolve in the effective potential @xmath96 and interact through a residual weak interaction @xmath214 that can be taken into account as a perturbation .
the only unusual feature is the absence of an exchange - like contribution to the total energy . indeed
the main role of the exchange correlation functional @xmath215 $ ] is to make the interaction between same spin particles different from the one between opposite spins . since moreover we have chosen the confining potential in such a way that the classical motion within our model quantum dot is chaotic , we know that we can use a statistical description of the eigenlevels and eigenstates of @xmath216 in terms of random matrix theory ( rmt ) and random plane wave ( rpw ) modeling .
we are therefore in the position to follow the line of reasoning in ref . to analyse the sdft calculation .
we shall do this in this section first to get some understanding of the peak spacing and spin distributions obtained , and in a later stage to address the mechanism of spin contamination . to model the statistical properties obtained from the sdft calculations ,
let us assume that the thomas - fermi density across the dot has variation small enough that we can take the parameter @xmath2 as a constant .
we furthermore impose @xmath217 ( @xmath218 might then be half integer for odd @xmath182 , which is not a problem since at the thomas - fermi level the quantization of particle number is not playing any role ) and write the second order strutinsky correction as @xmath219 with @xmath220 the occupation number of orbital @xmath221 with spin @xmath222 , @xmath223 and @xmath224 for a chaotic system , it can be shown that the fluctuations of the @xmath225 are small ( variance of order @xmath226 ) and that their mean values are given by @xmath227 / a \ ; , \ ] ] where @xmath228 is the area of the dot , @xmath229 is 2 here since time reversal symmetry is preserved ( but would be 1 if it were broken ) , and @xmath230 is the average of the screened interaction over the fermi circle ( note @xmath231 ) .
note however that the screened interaction eq .
( [ eq : vsc ] ) is derived under the assumption that the oscillating part of the density integrates to zero , so that the total displaced charge providing the screening also does . between the reference @xmath232 configuration ( the tf case ) and the higher @xmath233 ones ,
the total number of electrons is , of course , conserved , but not the number for each spin .
it should be kept in mind , therefore , that the @xmath234 component of the density can not be screened ; this can be included simply by setting @xmath235 .
the screened interaction matrix is characterized by its eigenvalues eqs .
( [ eq : lambda_c ] ) and ( [ eq : lambda_s ] ) . in fig .
[ fig : lambda_cs ] , we thus plot the @xmath2 dependence of these quantities averaged over the fermi circle , and compare them to their bare counterparts . ] as a function of @xmath236 .
dark : charge channel .
lighter color ( green online ) : spin channel . dashed : bare interaction @xmath237 ( with a cutoff of the momentum at @xmath238 in the charge channel ) .
solid : screened interaction @xmath239 with @xmath179 .
thin dot - dashed : same but with @xmath240 . since the @xmath241 dependence of @xmath242 is entirely due to the @xmath55 correction to the thomas - fermi kinetic energy functional , it therefore disappears in this latter case .
the interaction in the charge channel is , of course , dramatically decreased by screening ; in contrast , screening increases the magnitude of the interaction in the spin channel .
, height=249 ] a few remarks are in order concerning this figure .
first , we see that , because of the divergence of the coulomb interaction at small @xmath241 , screening has a drastic effect for the charge channel . would be divergent if we did not use a cutoff on @xmath241 at the inverse of the system size .
] screening is less dramatic in the spin channel , but can still be an order one effect as @xmath2 increases . furthermore , while the screening decreases the absolute strength of the interaction in the charge channel , it actually _ increases _ it in the spin channel . indeed , since the interaction in the spin channel coming from sdft is attractive , the charges in the bulk of the fermi sea will , as long as this does not involve too much kinetic energy , move so as to increase the spin polarization .
finally , we note that for the value of the parameter @xmath39 that we use , the effect of the first @xmath54 correction @xmath55 on the screened interaction is very small in the charge channel , and only slightly larger in the spin channel .
( thick lines ) and of the mean one - particle energy cost ( thin horizontal lines ) associated with flipping the spin of one particle in the quantum dot .
solid : @xmath243 ; dot - dashed @xmath244 ; dashed : @xmath245,width=268 ] if we neglect the fluctuations of the @xmath225 , eqs .
( [ eq : hatvsc ] ) , ( [ eq : de2_rpw ] ) , and ( [ eq : meanmij ] ) imply that @xmath66 is just a function of the number of particles @xmath246 in the dot and the @xmath247-component @xmath248 of the groundstate the spin , @xmath249 the main value of this expression is how it compares to the universal hamiltonian form,@xcite and we shall come back to this point in the discussion section .
already we can see , however , that it contains almost all the information necessary to understand qualitatively the ground - state spin distributions . indeed , looking at fig .
[ fig : de2(s ) ] , which shows the difference @xmath250 as a function of @xmath2 for several values of @xmath193 , we see that for @xmath251 , the interaction energy gain and one particle energy cost of forming a triplet are equal on average , and therefore triplets should become as probable as singlets . in the same way ,
spin 3/2 becomes as probable as 1/2 at @xmath252 , and spin 2 as probable as 1 at @xmath253 . ) and ( [ eq : varmij ] ) ] and numerical calculations of the mean and variance of @xmath254 s .
the wave functions used in the numerical calculations are eigenfunctions of the effective thomas - fermi potential with @xmath166 in the quartic oscillator system .
lines ( points ) correspond to analytical ( numerical ) results , with the solid ( circle ) for @xmath255 , short - dashed ( square ) for @xmath256 , long - dashed ( up - triangle ) for @xmath257 and dot - dashed ( down - triangle ) for @xmath258 . ,
title="fig:",width=268 ] ) and ( [ eq : varmij ] ) ] and numerical calculations of the mean and variance of @xmath254 s .
the wave functions used in the numerical calculations are eigenfunctions of the effective thomas - fermi potential with @xmath166 in the quartic oscillator system .
lines ( points ) correspond to analytical ( numerical ) results , with the solid ( circle ) for @xmath255 , short - dashed ( square ) for @xmath256 , long - dashed ( up - triangle ) for @xmath257 and dot - dashed ( down - triangle ) for @xmath258 .
, title="fig:",width=268 ] to have a more precise idea of the whether the random - plane - wave model captures the main physics , we can follow the approach of ref . and make a simulation of the peak spacing and spin distributions .
we use goe distributed energy levels for the first - order correction eq .
( [ eq : de1 ] ) , and take the second - order correction in the form eq .
( [ eq : de2_rpw ] ) with the @xmath225 independent variables with mean eq .
( [ eq : meanmij ] ) and a variance which can be computed using the method of appendix a of ref . :
@xmath259 } { \delta^2 } = \frac{32}{\pi ( { k_f}l)^2 } \int_{\frac{2\pi}{{k_f}l}}^{2- \frac{2\pi}{{k_f}l } } \frac{dx}{x } \frac{1}{4-x^2 } \hat v^{{\sigma}{\sigma}'}(x ) } \\ & & \times \left [ \hat v^{{\sigma}{\sigma}'}(x ) + \delta_{ij } \big(\hat v^{{\sigma}{\sigma}'}(x ) + \hat v^{{\sigma}{\sigma}'}(0 ) + \hat v^{{\sigma}{\sigma}'}\big(\sqrt{4-x^2}\big ) \big ) \right ] \nonumber\end{aligned}\ ] ] where @xmath260 . that the random - plane - wave model correctly describe the wave function statistics
is illustrated in fig .
[ fig : mijs ] where the analytic expressions eqs .
( [ eq : meanmij ] ) and ( [ eq : varmij ] ) are compared , as a function of @xmath2 , to the result from the actual eigenfunctions derived from eq .
( [ eq : schroe ] ) . the analytic expression for the mean
is expected to be quite reliable and hence the good agreement .
the variance ( [ eq : varmij ] ) is less accurate because of the cutoff used , for instance and so we consider the agreement in fig .
[ fig : mijs ] quite good .
( left ) and @xmath154 ( right ) .
solid : even @xmath182 , dashed : odd @xmath182 .
inset : corresponding spin distribution .
, width=307 ] fig .
[ fig : level4 ] displays the peak spacing and spin distribution for @xmath261 ( corresponding to [ a1 ] ) and @xmath177 ( [ a4 ] ) coming from a simulation in which the fluctuations of level spacing and of the @xmath225 are included .
we see that the qualitative behavior observed in fig .[fig : psp ] and in particular the lower panel is very well reproduced .
thus the rmt / rpw approach using the lsda interaction is successful in comparison with the full sdft calculation .
as we saw in the previous sections , the statistical properties of the model quantum dots obtained from the full sdft computation are , at least up to @xmath262 , well reproduced by the various forms of the strutinsky approximation .
however , we also saw that spin contamination , when present in the sdft calculations , was actually degrading the accuracy of the strutinsky approximation on a case by case basis .
indeed , by construction , the strutinsky approximation as we presented it can not involve any spin contamination .
spin contamination is a way , in the sdft calculations , to lower the energy of the system without changing the total @xmath247 component of the spin @xmath193 by having different wavefunctions for the @xmath50 and @xmath51 orbitals .
however , the eigenstates implicit in the strutinsky approach are almost identical to those of @xmath263 , @xmath264 , and the @xmath264 are nearly independent of the spin . in this section
, we shall discuss how this spin contamination mechanism could be understood within this strutinsky scheme . rather than trying to consider the most general situation ,
we will limit ourselves to the case of even number of particle @xmath182 , and a ground state @xmath247 component spin equal to zero .
let @xmath265 = -\frac{\hbar^2}{2 m } \nabla^2 + { u_{\rm tf}}^s({{\bf r}})$ ] be the thomas - fermi hamiltonian defining the orbitals @xmath266 [ see eqs .
( [ eq : veff ] ) and ( [ eq : schroe ] ) ] .
what we have done is to construct a approximate solution of the sdft equations eq .
( [ eq : eks ] ) as @xmath267 plus some screening charge . in this respect , an important point was that the resulting potential change @xmath89 given by eq .
( [ eq : deltausc ] ) was such that the matrix element @xmath268 for @xmath269 was negligible , to first order in @xmath270 .
however , finding an approximate solution of the kohn - sham equation implies only that one has an extremum of the spin density functional , but not necessarily an absolute minimum .
as pointed out earlier , modifications of the wavefunctions change the electronic density only if they mix occupied and unoccupied orbitals .
therefore , when searching for a new extremum of the spin density functional , with some chance to actually get the true minimum , a natural choice is to mix the last occupied orbital @xmath271 with the first unoccupied one @xmath272 ( for @xmath273 ) . let us therefore look for approximations @xmath274 to the ks wavefunctions defined by @xmath275 for @xmath276 and @xmath277 with possibly a different value of the angle @xmath278 for the two spins @xmath88 .
for these wavefunctions , the thomas -fermi hamiltonian has a matrix element @xmath279 in terms of the thomas - fermi energies @xmath280 and @xmath281 .
this change in the wave functions produces a modification of the densities @xmath282 which , once screening is taken into account , itself generates a perturbation potential @xmath283 ( the modification of the other wavefunctions , except for screening this term , does not play a role here . ) the self - consistent condition for the angles @xmath284 is that @xmath285 in order to find matrix elements of @xmath89 , let us consider for a moment the case @xmath286 .
( [ eq : rotation ] ) implies that @xmath287 and therefore @xmath288 with @xmath289 where the last equality applies in lowest order in @xmath270 , that is , neglecting the fluctuations .
noting finally that the same reasoning can be applied to the @xmath51 orbitals , we find that to get an extremum for the spin density functional the angles @xmath290 and @xmath291 should obey @xmath292 and the analogous equation with @xmath293 and @xmath294 interchanged .
obvious solutions are ( @xmath295 ) , ( @xmath296 @xmath297 ) , ( @xmath298 @xmath299 ) , and ( @xmath300 ) .
the first one corresponds to the standard @xmath301 ( non - spin - contaminated ) solution ; the other ones involve promotion of particles from the last occupied orbital to the first unoccupied one , and so are obviously of higher energy .
however , other solutions may exist .
clearly they should fulfill @xmath302 that is , up to an irrelevant multiple of @xmath303 phase @xmath304 and therefore @xmath305 it can be checked that whenever the condition eq .
( [ eq : cont_angle ] ) can be fulfilled [ ie .
when @xmath306 , the corresponding extremum has an energy smaller by a quantity @xmath307 /a$ ] with respect to the non contaminated configuration .
in this situation , the spin contaminated @xmath308 state will be favored ( but its energy still needs to be compared to the lowest energy state with @xmath309 ) .
to summarize our findings , we have seen that up to @xmath2 values of order one ( in practice , 1.3 here ) , the strutinsky approximation yields a ground state total energy with fluctuating part reliable up to typically five percent of the mean level spacing .
furthermore , these errors can be related to the occurrence of spin contamination in the sdft calculation , which can not be reproduced by the strutinsky scheme ( in its simplest form ) . indeed , as discussed in the last section , this latter gives , by construction , an approximation to an extremum of the kohn - sham functional for which the @xmath50 and @xmath51 orbitals are nearly identical , but not necessarily an approximation to the true minimum .
nevertheless , the qualitative properties of the peak spacing and spin distribution are correctly reproduced by the strutinsky approximation ( at least up to @xmath2 of order one , for which spin contamination does not appear to change drastically the distributions ) . for a chaotic confining potential
this makes it possible to use the modeling in terms of random matrix theory ( for the energy levels ) and random plane waves ( for the eigenstates ) introduced in ref . .
within this rmt / rpw modeling , and in the limit of large dots for which fluctuations of the residual interaction term are small , the main features of the peak spacing and spin distributions can be understood as arising from the interplay between one particle level fluctuations and the spin dependence of the mean residual interaction term [ see eq .
( [ eq : de2_uh ] ) ] @xmath310 it is useful to compare this expression , as well as the corresponding distributions based on rmt / rpw modeling such as those in fig .
[ fig : level4 ] ( which actually take into account the fluctuations of the residual interaction term ) , to what is obtained following the more traditional route to the analysis of peak spacing and spin distributions for chaotic quantum dots.@xcite in these earlier approaches , the ground state energy of the quantum dot would , in a way very similar way to eq .
( [ eq : strut_corr ] ) , be described as the sum of a large non - fluctuating classical - like term , a one - particle energy contribution computed for some effective confining potential , and finally a residual interaction term @xmath311 .
this latter would , however , be understood as originating from a weak interaction @xmath312 which in the random phase approximation can be shown to be just the rpa screened potential,@xcite but should be understood more properly as the residual interaction between quasi - particles in landau fermi liquid spirit .
we shall thus refer to this latter description as the `` rpa '' approach , although this is slightly inappropriate . while the strutinsky approximation to sdft gives a residual interaction which can be understood as a first - order perturbation ( without exchange ) in terms of the spin dependent potential eq .
( [ eq : vsc ] ) , in contrast one has in the `` rpa '' approach a residual interaction arising from the perturbative corrections in some @xmath313 ( including both direct and exchange ) as well as possibly higher - order terms which turn out to be important for time - reversal invariant systems ( the cooper series ) . under this assumption and following exactly the same analysis as the one leading to eq .
( [ eq : uh_lsda ] ) , one gets for the mean residual interaction term in the rpa approach @xmath314 ( again @xmath315 but would be 1 if time - reversal invariance were broken ) . in eq .
( [ eq : uh_rpa ] ) , the parameter @xmath316 is equal to @xmath317 , where the fermi circle average is defined by eq .
( [ eq : mean_fc ] ) and @xmath318 is the fourier transform of @xmath312 . more properly however , one should understand @xmath316 as being related to fermi liquid parameter @xmath319 through @xmath320 in first - order perturbation theory , @xmath102 would be equal to @xmath316 , but screening associated with higher oder terms in the cooper channel somewhat reduces this value . an analysis following the lines of ref .
suggests that @xmath321 with @xmath322 the fermi momentum and @xmath323 the typical size of the system .
we shall assume this in the following discussion , bearing , in mind that this is true only `` up to logarithmic accuracy '' .
the remarkable point here is that @xmath324 is actually the same thing as @xmath325 , in the sense that the landau fermi liquid parameter @xmath325 can be interpreted as the second derivative with respect to the polarization , at fixed total density , of @xmath326 the exchange correlation energy per particle of the uniform electron gas .
this implies that the term quadratic in @xmath193 of eqs .
( [ eq : uh_lsda ] ) and ( [ eq : uh_rpa ] ) actually do correspond . as a consequence if we compare fig .
[ fig : level4](b ) , which is obtained from a rmt / rpw simulation with the interaction corresponding to the spin density functional , with fig .
[ fig : level3 ] , obtained in the same way but with an `` rpa''-like interaction , corresponds to an evaluation of the variance of these fluctuations for which we have assumed no screening , and is therefore rather an upper bound .
the fluctuations being in any case rather small , their magnitude does not change the peak spacing distribution drastically ( their main effect is to broaden the sharp peak for odd spacings ) , and a more detailed treatment of the effect of screening of the cooper channel on the fluctuations of the residual interaction term should not change significantly the picture . ] the differences in spin polarization and in odd / even asymmetry for the peak spacing distribution can be almost entirely associated with the different linear @xmath193 terms in eqs .
( [ eq : uh_lsda ] ) and ( [ eq : uh_rpa ] ) .
to get some further insight into the difference between the two approaches , let us consider table [ table ] which shows the spin distributions for an interaction parameter @xmath262 and various approximations discussed in this paper .
comparing different pairs of lines gives a sense of the importance of the various issues .
for instance , comparing the second line with the third gives an idea of how accurate the rmt / rpw model is for the statistical properties of the real energy levels and eigenfunctions of the quartic oscillator system , since both lines are based on the same spin dependent interaction eq .
( [ eq : vsc ] ) .
the first line compared to the second , on the other hand , is a measure of how well the strutinsky scheme approximates the full sdft calculation .
presumably , most of the difference between these two lines can be associated with the presence of spin contamination in sdft it is in some sense a measure of the effectiveness of spin contamination in lowering the total spin of the system .
going further down the table , the difference between the third and the two last lines is a measure of the impact of different linear terms in @xmath193 in eqs .
( [ eq : uh_lsda ] ) and ( [ eq : uh_rpa ] ) , without screening the cooper channel for the fourth line and with a screened cooper channel [ according to eq .
( [ eq : zeta ] ) ] for the last line of the table . from table
[ table ] , it appears that within the accuracy of the rmt / rpw modeling , which seems to be around 5% , the sdft result is compatible with an rpa - like approach if the cooper channel is not screened . in other words ,
the fact that @xmath327 is more negative that @xmath328 producing higher spins is compensated by the effect of spin contamination which favors lower spins . as seen in ref .
, this compensation between the two effects seems to exist also for higher values of @xmath2 . on the other hand ,
spin contamination is not a sufficiently strong effect to compensate for the absence of screening of the cooper channel .
it remains to decide which of the two approaches is the more correct .
this , in the end , can only be addressed by comparison with exact calculations for quantum dots ( e.g. quantum monte carlo ) .
one argument that may be considered is that in the presence of a time - reversal breaking term ( i.e. @xmath329 ) , general symmetry considerations impose that the mean value of the residual interaction term is a function of @xmath194 , but not independently of @xmath330 and @xmath233 .
expressions ( [ eq : uh_lsda ] ) clearly do not fulfill this constraint , while eq .
( [ eq : uh_rpa ] ) does .
since , however , spin contamination seems to compensate for this difference it might just be that for time - reversal non - symmetric systems , sdft and rpa basically agree .
on the other hand , the screening of the cooper channel does not seem to be reproduced by the sdft calculations , and this might be the cause of the higher spin found in this approach .
this second order strutinsky approximation has to be distinguished from second order approximations made on the the density functional itself , such as in : m. elstner , d. porezag , g. jungnickel , j. elsner , m. haugk , t. frauenheim , s. suhai , and g. seifert , phys .
b*58 * 7260 - 7268 ( 1998 ) . | we analyze the ground state energy and spin of quantum dots obtained from spin density functional theory ( sdft ) calculations .
first , we introduce a strutinsky - type approximation , in which quantum interference is treated as a correction to a smooth thomas - fermi description . for large irregular dots , we find that the second - order strutinsky expressions have an accuracy of about 5 percent compared to the full sdft and capture all the qualitative features .
second , we perform a random matrix theory / random plane wave analysis of the strutinsky sdft expressions .
the results are statistically similar to the sdft quantum dot statistics .
finally , we note that the second - order strutinsky approximation provides , in essence , a landau fermi liquid picture of spin density functional theory .
for instance , the leading term in the spin channel is simply the familiar exchange constant . a direct comparison between sdft and the perturbation theory derived `` universal hamiltonian '' is thus made possible . |
however , inflammatory processes are also involved in the onset and maintenance of many severe disorders , such as rheumatoid arthritis , asthma , chronic inflammatory bowel diseases , type 2 diabetes , neurodegenerative diseases , and cancer . the currently available repertoire of approved anti - inflammatory agents mainly consists of nonsteroidal anti - inflammatory drugs , glucocorticoids , immunosuppressant drugs , and biologicals . despite this arsenal ,
thus , the discovery of new anti - inflammatory compounds is still a great demand on scientists in academia and industry .
plants were the first source of remedies in human history . in all cultures and through all ages
different parts of a huge number of plants were used as drugs against all kinds of ailments .
needless to say , this usage was based on views that are not compatible with nowadays evidence - based medicine .
however , different traditional systems , such as european - based plant collections , the chinese traditional medicine , the kampo system , the indian ayurveda , and many more , have evolved by trial and error and have strived toward advancing the appropriate use of plants on the background of their own , specific philosophy of life .
one should be aware that in many lesser developed countries traditional medicine is still the only affordable and , thus , accessible way to meet the primary healthcare needs of a large number of patients .
the awareness that one ( or more ) chemical entity within the plant material is responsible for pharmacological actions and can be isolated for the use as single agent came up in the 19th century in the context of the emerging natural science - based medicine and pharmacy .
prominent plant - derived compounds that were isolated in this period , such as morphine , quinine , colchicine , atropine , pilocarpine , or theophylline , are still very important in current pharmacotherapy . due to the developing organic synthesis ,
plant - derived compounds were among the first lead structures in the history of drug development .
looking into the list of drugs approved within the last decades demonstrates that plant ingredients are still of importance in drug discovery .
vincristine , vinblastine , and their semisynthetic derivatives , originally isolated from the madagascar periwinkle ( catharanthus roseus ) , are highly valuable anticancer drugs .
galantamine from the caucasian snowdrop ( galanthus caucasicus ) , paclitaxel from the pacific yew ( taxus brevifolia ) , and capsaicin from chili peppers ( capsicum species ) are further prominent examples of secondary plant metabolites that made it into the clinic .
examples for plant - derived compounds that served as lead structures and/or were chemically modified are salicylic acid ( acetylsalicylic acid ) , morphine ( scores of derivatives ) , camptothecin ( topotecan and irinotecan ) , artemisinin ( artemether ) , and dicoumarol ( warfarin ) .
the number of phytochemical studies describing new substances isolated from plants is huge and rising .
preclinical reports , that is , in vitro , cell - based , and animal studies on the action of these substances , are available in an inconceivable quantity
. unfortunately , these studies are often of equivocal quality , especially in the field of anti - inflammatory compounds .
also the review literature is overwhelming and there are many comprehensive publications available that focus on the respective molecular mechanisms [ 27 ] . especially for newly isolated compounds , the knowledge is too often based on a very limited number of cell - based assays . from alterations of some prominent mediators of inflammatory processes , most frequently the transcription factor nfb ,
the compound is simply judged to be anti - inflammatory without presenting comprehensive in vivo data .
animal models are of course indispensible for the analysis of the pharmacological potential of a compound , but these models are used insufficiently and , as commonly known , do not satisfactorily reflect the situation in humans .
in contrast , prominent and well - known plant - derived compounds , such as curcumin or resveratrol , have extensively been analyzed in clinical trials and have often induced a hype in media ( even in scientific ones ) .
however , due to reasons that will be discussed in the respective paragraphs , this knowledge has as yet not led to an approved drug that advances pharmacotherapy .
this minireview will summarize the current situation of 6 selected , prominent , anti - inflammatory compounds that have been tested in humans in recent years : curcumin , colchicine , resveratrol , capsaicin , epigallocatechin-3-gallate ( egcg ) , and quercetin .
moreover , we will sum up the planned registered trials in order to provide insights into the disorders that are hypothesized to be beneficially influenced by the compounds .
curcumin ( figure 1 ) , ( 1e,6e)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione , also known as diferuloylmethane , is the main ingredient of turmeric ( curcuma longa , zingiberaceae ) .
the indian spice turmeric has been used for centuries in ayurvedic medicine against inflammatory disorders .
curcumin was identified in 1910 , is yellow in color , and represents a lipophilic polyphenol .
it exerts a great variety of actions and is amongst the most frequently investigated natural compounds .
curcumin displays anti - inflammatory , antioxidant , anticancer / proapoptotic , and antibacterial activities due to a plethora of mechanisms .
these have recently been reviewed comprehensively . with regard to its anti - inflammatory action ,
curcumin was reported ( i ) to inhibit important proinflammatory signaling cascades , such as the nfb- , mapk- , cox- , and lox - pathways [ 9 , 10 ] , ( ii ) to downregulate the secretion of prominent cytokines , like tnf , il-1 , and il-6 , and ( iii ) to block the expression of cell adhesion molecules ( e.g. , icam-1 ) , which are necessary for the interaction of leukocytes with endothelial cells .
thus , not only in regard to its anti - inflammatory profile , curcumin represents a compound with pleiotropic , multiple modes of action .
currently , 77 studies ( with known status ) dealing with diverse actions of curcumin can be found on http://www.clinicaltrials.gov/. thereof , 50 studies have been finished and 27 are in their onset ( recruiting ) phase . in pubmed ,
almost 100 clinical trials investigating curcumin in an inflammatory context are listed , of which 12 have been published in 2013 , 24 in 2012 , and 14 in 2011 .
these facts demonstrate that curcumin is still a hot topic and under intense clinical investigation .
the most prominent disorders were rheumatoid arthritis , cancer ( e.g. , colorectal , pancreatic , breast , prostate , and lung ) , and inflammatory bowel diseases ( ulcerative colitis and crohn 's disease ) , but there are also studies available , for example , on uveitis , vitiligo , or nephropathies , which reflects the pleiotropic actions of curcumin . a detailed list of these trials can be found in a recent review by gupta et al . .
the recruiting future trials will mainly deal with the action of curcumin on cognitive impairment and still ongoing different types of cancer . also inflammatory conditions will still be investigated . in these trials ,
curcumin often serves as a dietary supplement or as an adjunct treatment to the standard therapy .
the cochrane collaboration lists one systematic review ( published in 2012 ) that analyzes the effects of curcumin in ulcerative colitis [ 12 , 14 ] .
the authors conclude that curcumin may be a safe and effective therapy for maintenance of remission in quiescent ulcerative colitis when given as adjunct therapy .
however , further research in form of a large scale methodologically rigorous randomized controlled trial is needed to really confirm a benefit .
clinical trials are available ; however , they are often too weak and of poor quality to draw a clear conclusion .
the major issue is the low number of enrolled patients , which frequently ranges between 10 and 30 .
it should also be mentioned that curcumin suffers from its very low bioavailability , although considerable progress has been made to overcome this obstacle by technological and chemical approaches . whether we will see curcumin as an approved ( add - on ) option for the treatment or prevention of one of the mentioned indications depends on the performance of solid , high - quality , big cohort studies in the future . however , from the wealth of studies , it can at least be concluded that curcumin seems to have a good safety profile ; it is well tolerated and nontoxic .
the tropolone derivative colchicine ( figure 2 ) , n-[(7s)-1,2,3,10-tetramethoxy-9-oxo-6,7-dihydro-5h - benzo[a]heptalen-7-yl]acetamide , is the major alkaloid of the plant colchicum autumnale ( colchicaceae ) , commonly known as autumn crocus or meadow saffron . since ancient times ,
interestingly , the us fda has only recently ( 2009 ) approved colchicine for the treatment of familial mediterranean fever as well as for the treatment and prevention of acute gout flares . to get this approval , the applying company needed to provide new clinical data and , in return , was given an exclusive marketing agreement , 3 years for the indication gout and 7 years for familial mediterranean fever ( orphan drug status ) .
the mechanisms of action of colchicine are well investigated : the molecular target was identified ( tubulin ) , the binding site was precisely characterized , and the biological consequences of impairing microtubule dynamics were analyzed ; comprehensive reviews summarizing these findings are available [ 1619 ] .
noteworthy , colchicine played a crucial role for the initial characterization of microtubules and the tubulin subunits in the 1960s [ 20 , 21 ] . despite this huge knowledge and the fact that colchicine is already an approved drug , researchers recently have conducted several clinical studies in order to expand its fields of application .
pubmed lists a number of very interesting trials in the field of inflammation - associated pathologies with positive outcome : colchicine was tested as adjunct treatment against acute [ 22 , 23 ] and recurrent pericarditis [ 24 , 25 ] , for the prevention of atrial fibrillation after radiofrequency ablation and for postpericardiotomy syndrome prevention .
the field is still vibrant : 14 clinical trials that are open , that is , in the recruiting phase , are listed on http://www.clinicaltrials.gov/. they intend to investigate the action of colchicine mainly in the areas of cardiology and nephrology , for example , in myocardial infarction , for postpericardiotomy syndrome prevention , or in diabetic nephropathy
since the number of diseases with an inflammatory component is very large , one might speculate that colchicine will further stay an interesting , not yet fully exploited drug .
it can be found in a great number of different plants and dietary products thereof , with peanuts , grapevines , and red wine being the most prominent ones . in parallel to curcumin , resveratrol was found to exert a wealth of pharmacological actions , for example , anti - inflammatory , antioxidant , anticancer / proapoptotic , chemopreventive , and antimicrobial properties .
resveratrol is known to have a poor bioavailability , which prompted many groups to work on improvement strategies [ 3843 ] . as a consequence of these interesting in vitro and in vivo findings
, a lot of effort was put into the elucidation of the underlying mechanisms of action .
again , a large number of reviews is available and gives in - depth insights into the mechanisms : resveratrol inhibits the nfb- , ap-1- , and cox-2-pathway [ 29 , 44 , 45 ] and activates ppar , enos , and sirt1 [ 4649 ] .
however , this gigantic knowledge has as yet not been translated into an approved clinical application .
pubmed lists over 40 clinical trials on resveratrol in the broad context of inflammation - associated disorders , many of them dealing with diabetes , obesity , and coronary artery disease .
these studies often analyze inflammation - related parameters in the plasma ( e.g. , crp , tnf , il-1 , and il-6 ) and in blood cells ( e.g. , activated kinases or transcription factors ) or reported on functional parameters , such as the status of the endothelium [ 5055 ] .
however , whether this altered inflammatory status of the patients really results in a clinically relevant improvement of the severity of the diseases or , most importantly , in a reduced occurrence of disease - specific life - threatening events ( not to mention mortality ) has not been analyzed .
according to http://www.clinicaltrials.gov/ , 26 clinical trials on resveratrol are planned or are currently recruiting .
the main field of interest is type 2 diabetes / metabolic syndrome , followed by polycystic ovary syndrome , nonalcoholic fatty liver disease , and mild cognitive impairment .
research would strongly profit by conducting interventional studies with defined primary outcomes reflecting the stage and/or prevalence of the diseases on a long - term basis .
capsaicin ( figure 4 ) , ( e)-n-[(4-hydroxy-3-methoxyphenyl)methyl]-8-methylnon-6-enamide , is a very hydrophobic alkaloid produced by chili peppers ( capsicum species ; solanaceae ) and is responsible for the typical pungency / spiciness of the fruits of the genus capsicum .
it has traditionally been used as a topical rubefacient and counterirritant to relieve pain of muscles and joints .
a capsaicin 8% cutaneous patch has recently been approved by the authorities in the eu for the use against neuropathic pain in nondiabetic adults and in the us against neuropathic pain associated with postherpetic neuralgia .
interestingly , the research on capsaicin led to the discovery of the transient receptor potential channel vanilloid subfamily member 1 ( trpv1 ) , which is the direct target of capsaicin .
trpv1 is a nonselective cation channel with high preference for ca and is mainly located in nociceptive neurons .
it is activated by chemical and physical stimuli , such as heat , low ph , capsaicin , and certain inflammatory mediators .
prolonged activation of trpv1 by capsaicin is discussed to cause desensitization and , thus , reduced pain sensation . beyond pain
, some few studies also found an anti - inflammatory potential of capsaicin : it can inhibit paw inflammation in arthritic rats and ethanol - induced inflammation of the gastric mucosa in rats . moreover , capsaicin was reported to inhibit cox-2 activity , inos expression , and the nfb pathway in macrophages in a trpv1 independent way . regarding a clinical influence on inflammatory conditions ,
capsaicin was evaluated in a recent systematic review by the cochrane collaboration : topical capsaicin was reported not to be effective against osteoarthritis .
in contrast , one meta - analysis found enough evidence to conclude that capsaicin is effective in the management of osteoarthritis , although the authors pinpointed that there is a paucity of randomized clinical trials .
this is in line with a further meta - analysis reporting that capsaicin alleviates osteoarthritic pain . regarding future therapeutical enhancements ,
24 clinical trials are planned or are currently recruiting , as listed on http://www.clinicaltrials.gov/. in most of these studies capsaicin is used as a model substance to induce pain or as a diagnostic tool ( provocation test ) .
trials that investigate the therapeutical potential of capsaicin analyze its potential as preemptive ( prior to surgery ) analgesic in patients undergoing amputation of a limb and its action on neuropathic pain from critical ischemia ( predominantly in hands and feet ) and on chronic pain from artificial arteriovenous fistulae ( for hemodialysis ) in patients with end - stage renal failure .
moreover , capsaicin will be tested against persistent pain after inguinal herniotomy and against the impaired swallow response in stroke patients with oropharyngeal dysphagia .
no trial deals with anti - inflammatory effects of capsaicin . in summary , in contrast to neuropathic pain , the field of capsaicin and inflammation is not very advanced and will stay on that level in the near future due to a lack of clinical studies .
epigallocatechin-3-gallate ( figure 5 ) , [ ( 2r,3r)-5,7-dihydroxy-2-(3,4,5-trihydroxyphenyl)-3,4-dihydro-2h - chromen-3-yl]3,4,5-trihydroxybenzoate , commonly abbreviated as egcg , is an ingredient of green tea , camellia sinensis ( theaceae ) .
it is the most prominent member of the family of green tea catechins ( polyphenols ) and accounts for 5080% of all catechins in a cup of green tea .
egcg was found to exert profound anti - inflammatory , antioxidant , anti - infective , anticancer , antiangiogenetic , and chemopreventive effects [ 6569 ] .
also the knowledge about the cellular and molecular mechanisms is extremely broad : egcg promotes cell growth arrest and induces apoptosis by affecting regulatory proteins of the cell cycle and inhibition of nfb [ 6971 ] .
furthermore , it inhibits growth factor - dependent signaling ( e.g. , of egf , vegf , and igf - i ) , the mapk pathway , proteasome - dependent degradation , and expression of cox-2 [ 72 , 73 ] .
it seems to directly interact with and to modulate the character of membrane lipid rafts , which explains the ability to alter signaling processes of growth factor receptors [ 7476 ] .
furthermore , egcg inhibits telomerase , topoisomerase ii , and dna methyltransferase 1 , thereby affecting the functions of chromatin [ 7779 ] .
surprisingly , however , despite the promising preclinical findings and the thorough mechanistic insights , clinical studies in the context of inflammation are largely lacking .
one small study analyzed the action of green tea and an extract thereof on biomarkers of inflammation ( e.g. , adiponectin , crp , il-6 , il-1 , svcam-1 , and sicam-1 ) in obese patients with metabolic syndrome .
another trial reported a beneficial impact of topical egcg treatment on acne vulgaris , which might be at least in part due to anti - inflammatory effects .
interestingly , in 2006 , a green tea extract was approved as a prescription drug for the topical treatment of genital and anal warts ( condylomata acuminata ) .
17 open studies are listed on http://www.clinicaltrials.gov/. egcg will be tested for its effects on albuminuria in diabetic nephropathy as well as for its action in patients with cardiac amyloid light - chain amyloidosis , with muscular dystrophy of the duchenne type , with alzheimer 's disease ( early stage ) , with down syndrome , with fragile x syndrome , with huntington 's disease , and with multiple - system atrophy .
moreover , trials will analyze the potential of egcg on reactivation of the epstein - barr virus in remission patients and on preventing colon polyps in patients at high risk for recurrent colon adenoma .
further studies will examine whether egcg affects insulin resistance , whether gargling with egcg prevents influenza infections in teenagers , and whether topical egcg exerts an anticarcinogenic potential in patients with superficial basal cell carcinoma .
obviously , the trials will not investigate classic inflammatory disorder , although some of the mentioned diseases are associated with inflammatory processes ( e.g. , alzheimer 's disease or insulin resistance ) .
nevertheless , it is very likely that egcg will experience an expansion of its indication in the future .
quercetin ( figure 6 ) , 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one , a flavonol , belongs to the class of flavonoids , which is a large family of polyphenols representing very widely spread secondary plant metabolites .
quercetin is found in a great variety of food , such as apples , grapevines , berries , broccoli , red onions , capers , or tea . as with the above discussed compounds ,
also quercetin exerts a large spectrum of biological effects : anti - inflammatory , anti - infectious , antioxidant , anticancer / chemopreventive [ 85 , 86 ] , neuroprotective , antihypertensive [ 88 , 89 ] , and blood glucose - lowering properties have been reported .
quercetin scavenges reactive oxygen and nitrogen species , targets prominent proinflammatory signaling pathways , such as stat1 , nfb , and mapk [ 91 , 92 ] , and inhibits infectivity of target cells and replication of many types of viruses .
moreover , phosphodiesterases ( pdes ) were suggested to be affected by quercetin , as well as topoisomerases i and ii and mcl-1 .
most importantly , quercetin was identified as a broad - spectrum kinase inhibitor [ 96 , 97 ] .
several studies on inflammatory parameters in humans have been performed in the last years : one trial evaluated the effect of quercetin on biomarkers of inflammation depending on the apolipoprotein e genotype of healthy men .
although risk factors of cardiovascular disease were improved , quercetin exerted a slight proinflammatory effect ( increased levels of tnf ) .
it was reported that quercetin had no action on the levels of the proinflammatory cytokine il-6 after repeated sprint exercise . in sarcoidosis patients ,
quercetin did not alter blood leukocyte subsets , granulocyte oxidative burst or phagocytosis activity , il-6 , or tnf plasma levels . of note ,
no trial reports on the improvement of clinical parameters of inflammatory diseases ( severity and incidence ) .
almost ten clinical studies are registered on http://www.clinicaltrials.gov/ that are going to use pure quercetin as a pharmacological compound . with respect to inflammatory disorders
, quercetin will only be analyzed in two - phase 1 - 2 trials for its safety and dose - response relationship in chronic obstructive pulmonary disease ( copd ) . in the field of diabetes
, quercetin will be tested in a phase 2 study for an effect on blood glucose and blood vessel function in type 2 diabetes .
quercetin will also be given to obese patients ( with or without diabetes type 2 ) to test its action on glucose absorption ( glucose tolerance test ) .
regarding cancer , it will be tested whether quercetin modulates levels of prostate - specific antigen ( psa ) and whether it can prevent prostate cancer . moreover , in a pilot study , quercetin will be used in children suffering from fanconi anemia ( safety and pharmacokinetics ) .
thus , quercetin will undergo very interesting studies that might lead to a profound advancement of knowledge about its clinical efficacy . however , inflammatory diseases are not the main topic of current research .
state - of - the - art clinical intervention studies , that is , randomized double - blind placebo - controlled trials , are the gold standard for testing whether a substance has a therapeutical or preventive potential .
the field of plant - derived compounds often experiences hope and hype phases . opinions and assumptions about an action in humans
unfortunately , the step towards a sound and significant clinical trial is difficult , very laborious , long - ranging , and most importantly extremely expensive , which means that it is impossible in many cases .
thus , this research area often suffers from either inadequately performed or a low number of studies . in this minireview
, we did try not only to pinpoint deficiencies , but also to highlight positive developments that will hopefully lead to an advancement of prevention or therapy of diseases . | many diseases have been described to be associated with inflammatory processes .
the currently available anti - inflammatory drug therapy is often not successful or causes intolerable side effects .
thus , new anti - inflammatory substances are still urgently needed .
plants were the first source of remedies in the history of mankind . since their chemical characterization in the 19th century , herbal bioactive compounds have fueled drug development .
also , nowadays , new plant - derived agents continuously enrich our drug arsenal ( e.g. , vincristine , galantamine , and artemisinin ) . the number of new , pharmacologically active herbal ingredients , in particular that of anti - inflammatory compounds , rises continuously .
the major obstacle in this field is the translation of preclinical knowledge into evidence - based clinical progress .
human trials of good quality are often missing or , when available , are frequently not suitable to really prove a therapeutical value .
this minireview will summarize the current situation of 6 very prominent plant - derived anti - inflammatory compounds : curcumin , colchicine , resveratrol , capsaicin , epigallocatechin-3-gallate ( egcg ) , and quercetin .
we will highlight their clinical potential and/or pinpoint an overestimation .
moreover , we will sum up the planned trials in order to provide insights into the inflammatory disorders that are hypothesized to be beneficially influenced by the compound . |
according to einstein s general theory of relativity , the dynamic properties of a given spacetime are determined by its total energy content . in the cosmological context , for instance , this amounts to saying that to understand the spacetime structure of the universe one needs to identify the relevant sources of energy and their contributions to the total energy momentum tensor .
matter fields ( e.g. , baryonic matter and radiation ) , are obvious sources of energy . nevertheless , according to current observations , two other components ,
namely , dark matter and dark energy , whose origin and nature are completely unknown , are governing the late time dynamic properties of the universe .
although fundamental to our understanding of the universe , several important questions involving these dark components and their roles in the dynamics of the universe remain unanswered ( see , e.g. , @xcite for some recent reviews ) . among these questions ,
the possibility of interaction in the dark sector ( dark matter - dark energy ) , which gave origin to the so - called models of coupled quintessence , has been largely explored in the literature @xcite .
these scenarios are based on the premise that , unless some special and unknown symmetry in nature prevents or suppresses a non - minimal coupling between these components ( which has not been found see , e.g. , @xcite for a discussion ) , such interaction is in principle possible and , although no observational piece of evidence has so far been unambiguously presented , a weak coupling still below detection can not be completely excluded .
> from the observational viewpoint , these models are capable of explaining the current cosmic acceleration , as well as other recent observational results @xcite . from the theoretical point of view , however , critiques to these scenarios do exist and are mainly related to the fact that in order to establish a model and study their observational and theoretical predictions , one needs first to specify a phenomenological coupling between the cosmic components . in this concern ,
an interesting step towards a realistic interaction law was given recently by wang & meng in ref .
@xcite ( see also @xcite ) in the context of models with vacuum decay , a class of coupled quintessence in which the dark energy equation of state ( eos ) is @xmath4 .
actually , in certain sense , one may say that coupled dark energy or quintessence models are the natural inheritors of the so - called time - varying @xmath5-cosmologies @xcite .
however , instead of the traditional approach , refs .
@xcite deduced a new interaction law from a simple argument about the effect of the dark energy on the cold dark matter ( cdm ) expansion rate .
the resulting expression is a very general law that has many of the previous phenomenological approaches as a particular case . 0.1 in in this paper , we extend the arguments of refs .
@xcite to a dark energy / dark matter interaction , where the dark energy component is described by an equation of state @xmath6 ( @xmath7 ) , and explore theoretical and observational consequences of a new scenario of coupled quintessence .
differently from other interacting quintessence models , we do not consider interaction between the dark sector and the baryonic content of the universe .
we also emphasize that this process of interaction is completely different from the physical point of view from unification scenarios of the dark sector , an idea that has been widely discussed in the recent literature @xcite .
we have organized this paper as follows . in sec .
ii the interaction law and the basic field equations of the model are presented .
the influence of the dark energy - dark matter coupling on the epoch of cosmic acceleration is also discussed . in order to test the observational viability of the model , sec .
iii presents a statistical analysis involving the most recent type ia supernovae ( sne ia ) data @xcite , observations of the baryon acoustic oscillation ( bao ) peak ( measured from the correlation function of luminous red galaxies ) @xcite and the current estimate of the cosmic microwave background ( cmb ) shift parameter from wmap-5 @xcite . in sec .
iv we end this paper by summarizing our main results .
for a spatially flat , homogeneous and isotropic scenario driven by matter ( baryonic + dark ) and radiation fields and a negative - pressure dark energy component , the einstein field equations can be written as @xmath8 @xmath9 where @xmath10 , @xmath11 , @xmath12 and @xmath13 , are the energy densities of the radiation , baryons , cold dark matter and dark energy , respectively , while @xmath14 and @xmath15 are the radiation and dark energy pressures .
we will always refer to the dark matter quantities with the subscript @xmath16 , in order to distinguish them to total matter quantities , for which we will use the subscript @xmath17 .
thus , in our notation , @xmath18 . by assuming that the radiation and baryonic fluids are separately conserved , the energy conservation law for the two interacting components ( @xmath19 , where @xmath20 ) reads @xmath21 now , to complete the description of our interacting quintessence scenario we need to specify the interaction law . in principle , if the quintessence component is decaying into cdm particles , the cdm component will dilute more slowly compared to its standard ( conserved ) evolution , @xmath22 . therefore , if the deviation from the standard evolution is characterized by a positive constant @xmath1 we may write is required from thermodynamical arguments . for a discussion , see @xcite . ]
@xmath23 where @xmath1 is a constant parameter and we have set the present - day value of the cosmological scale factor @xmath24 . in what follows
we also consider that the dark energy component is described by an equation of state @xmath6 , where the constant @xmath25 is a negative quantity . 0.2 in 0.1 in now , by integrating eq .
( [ coupling ] ) it is straightforward to show that the energy density of the dark energy component is given by @xmath26 where the integration constant @xmath27 is the present - day fraction of the dark energy density . clearly , in the absence of a coupling with the cdm component , i.e. , @xmath28 , the conventional non - interacting quintessence scenario is fully recovered . for @xmath29 and @xmath30
, we may identify @xmath31 ( the current value of the vacuum contribution ) , and the above expression reduces to the vacuum decaying scenario recently discussed in refs .
@xcite . neglecting the radiation contribution , the friedmann equation ( [ fried ] ) for this interacting dark matter - dark energy cosmology can be rewritten as @xmath32 where @xmath33 , @xmath34 and @xmath35 are , respectively , the normalized hubble parameter , and the baryons and cdm present - day density parameters ( for these quantities , we have dropped the subscript ` 0 ' for convenience ) .
the parameter @xmath36 is defined , in terms of the density parameter of the dark energy component @xmath37 , as @xmath38 and , therefore @xmath39 the above expression clearly shows that the conventional ( non - interacting ) quintessence scenario is considerably modified due to the dark energy decay into cdm particles .
it is also worth noticing the importance of the baryonic contribution to this sort of scenario .
going back to high redshifts we see that the presence of an explicit baryon term redshifting as @xmath40 is well justified since the decaying dark enegy component slows down the variation of cdm density . although being subdominant at the present stage of cosmic evolution , the baryonic content will be dominant ( in comparison to cdm ) at very high redshifts
actually , it becomes subdominant just before nucleosynthesis ( @xmath41 for @xmath42 ) , so that the cdm component drives the evolution after the radiation phase .
however , even at late times , baryons have several dynamical effects .
in particular , they alter considerably the transition redshift , i.e. , the redshift where the current accelerating regime begins @xcite . to quantify this latter effect ,
let us consider the transition redshift , @xmath43 , at which the universe switches from deceleration to acceleration or , equivalently , the redshift at which the deceleration parameter vanishes . from eq .
( [ fried ] ) , it is straightforward to show that the deceleration parameter , defined as @xmath44 , now takes the following form @xmath45 some interesting features of the above expression must be explored .
first , if @xmath46 one finds @xmath47 , as expected for a flat matter - dominated model ( @xmath48 ) . note that the expression of @xmath36 has been defined by eq .
( [ def_wx ] ) . in comparison with the conventional non - interacting quintessence scenario , the coupling term ( @xmath1 ) modifies considerably the transition deceleration / acceleration . in principle , since the cdm density scales as @xmath49 , while the baryon density scales with @xmath0 , the latter becomes dynamically more important in comparison with the non - decaying scenario .
the overall baryon effect is to delay the transition epoch relative to previous cases ( including the standard @xmath50cdm model ) , which seems to be in better agreement with some recent sne results indicating @xmath51 at 1@xmath52 @xcite .
besides this effect , we also have in our model the effect of the dark energy eos @xmath25 , which introduces a new parameter relative to the decaying vacuum model @xcite .
to better visualize the effect of the dark energy eos , as well as the effect of the dark energy - dark matter interaction parameter @xmath1 , we plot in figure [ fig : qzw ] the deceleration parameter as a function of redshift @xmath53 for some selected values of the eos ( @xmath54 and @xmath55 ) and decaying ( @xmath56 ) parameters .
figures ( 1a ) and ( 1b ) show that the effect of a positive @xmath1 parameter , as required by thermodynamical arguments @xcite , is to decrease the value of the deceleration parameter , then increasing the value of the transition redshift .
the net effect of the dark energy eos , however , is not monotonic as the effect of the interaction .
we have in general , for values of the dark energy eos close to the vacuum value ( @xmath29 ) , that the present value of the deceleration parameter increases for increasing @xmath25 , although this behavior may change for values of @xmath25 much different from the standard value , or at high redshifts , as seen in figure ( 1c ) .
figures ( 2a ) and ( 2b ) show the direct effect of the @xmath1 and @xmath25 parameters on the transition redshift ( @xmath43 ) . in agreement with figure ( 1 ) , we see from panel ( 2a ) that the effect of the interacting parameter is in general to increase @xmath43 .
we can also see that the transition redshift has a maximum for values of the @xmath25 parameter a little larger than @xmath57 .
similar result can also be taken from panel ( 2b ) , although @xmath43 has a more complicated dependence on @xmath25 .
we also show in both panels the @xmath58 limits given by riess _
( 2004 ) @xcite .
it is clear that values of @xmath25 larger than @xmath57 as well as smaller than @xmath57 are favoured by these limits , whereas larger values of the @xmath1 parameter are disfavoured by these limits when @xmath59 .
this latter result is in full agreement with the results of our statistical analyses discussed in the next section .
the description of the model discussed in the previous section clearly shows that it comprises a multitude of cosmological solutions . in a model with such a wealth of different possibilities constraints on the parameter space arising from current observational data
are likely to rule out many of the possible scenarios ( combinations of @xmath1 , @xmath60 and @xmath35 ) for the evolution of the universe . in this section
we investigate such observational constraints by placing cosmological bounds on the parametric spaces @xmath61 and @xmath62 from statistical analyses involving a large set of cosmological observations . to this end
we use the most recent distance measurements to sne ia @xcite and the current estimates of the baryon acoustic oscillations found in the sdss data @xcite , as well as , the shift parameter from wmap observations @xcite . in our analysis
we fix @xmath63 also from wmap results , a value in good agreement with the constraints derived from primordial nucleosynthesis @xcite .
now , concerning the hubble parameter , it should be recalled that the estimates of @xmath64 through different methods fall on the range 62 - 74 km / s / mpc with an uncertainty of about @xmath65 @xcite . in
what follows , we consider the hubble space telescope ( @xmath66 ) key project final result , i.e. , @xmath67 @xcite , as a gaussian prior on the hubble parameter .
the predicted distance modulus for a supernova at redshift @xmath53 , given a set of parameters @xmath68 , is @xmath69 where @xmath70 and @xmath71 are , respectively , the apparent and absolute magnitudes , the complete set of parameters is @xmath72 and @xmath73 stands for the luminosity distance ( in units of megaparsecs ) . 0.1 in we estimate the best fit to the set of parameters @xmath68 by using a @xmath74 statistics , with @xmath75^{2}}{\sigma_i^{2}}},\ ] ] where @xmath76 is given by eq . ( [ mag ] ) ,
@xmath77 is the extinction corrected distance modulus for a given sne ia at @xmath78 , and @xmath79 is the uncertainty in the individual distance moduli . in our analysis
, we use a combined sample with @xmath80 sns also used by davis _
( 2007 ) @xcite .
this sample consists of the best quality light - curves sns of wood - vasey _ et al . _
( 2007 ) @xcite , which are 60 essence supernovae @xcite , 57 snls supernovae @xcite , and 45 nearby supernovae .
we also include , as in @xcite , 30 new released sne ia , classified as `` gold '' supernovae by riess _
( 2007 ) @xcite .
the baryon acoustic oscillations ( bao ) given by the acoustic oscillations of baryons in the primordial plasma , leave a signature on the correlation function of galaxies as observed by eisenstein _
( 2005 ) @xcite .
this signature furnishes a standard rule which can be used to constrain the following quantity @xcite : @xmath81^{2/3 } = 0.469 \pm 0.017 , \label{a}\end{aligned}\ ] ] where @xmath82 is given by eq .
( [ friedmann ] ) , @xmath83 is a typical redshift of the sdss sample , and @xmath84 is the dimensionless comoving distance to the redshift @xmath85 . as has been shown in ref .
@xcite , this quantity can be used for models which do not have a large contribution of dark energy at early times . a useful quantity to characterize the position of the cmb power spectrum first peak is the shift parameter , which is given , for a flat universe , by @xcite : @xmath86 where @xmath87 is the recombination redshift and the value for @xmath88 above is calculated from the mcmc of the wmap 3-yr in the standard flat @xmath50cdm model @xcite . as mentioned above
, we also include a gaussian prior on @xmath89 , as given by the final results of hst key project @xcite .
thus , in our statistical analysis we minimize the following quantity : @xmath90 in figure ( 3 ) we show the main results of our statistical analyses . as usual
, the total likelihood is written as @xmath91 , where @xmath92 is given by eq .
( [ chi22 ] ) . by marginalizing @xmath93 over the eos parameter @xmath25
, we can quantify how much the plane ( @xmath1-@xmath94 ) can be constrained by the data .
the contour levels for this analysis are shown on figure ( [ fig : projhw]a ) . at 68.3% , 95.4% and 99.7% c.l . , we have found , respectively , @xmath95 and @xmath96 with the relative @xmath97 , where @xmath98 is the number of degrees of freedom .
these results are much more constraining than those obtained in ref .
@xcite for the case @xmath4 , as we have used more recent cmb and sne ia data . while in the above reference the bounds on the interacting parameter were @xmath99 at @xmath100 c.l .
, we have found , at the same level , @xmath101 , which clearly constrains this parameter to values very close to the standard non - interacting case ( @xmath28 ) . in figure ( [ fig : projhw]b ) we show the plane ( @xmath102 ) when the total likelihood is marginalized over the density parameter @xmath94 . for this analysis ,
we have found @xmath103 whereas the bounds for @xmath1 are very similar to those found in the previous analysis ( fig .
clearly , the standard @xmath50cdm is preferred by this analysis , although much space is left for an eos distinct from @xmath57 .
the so - called phantom models ( @xmath104 ) are slightly more favoured by this analysis than quintessence ( @xmath105 ) scenarios .
the current standard cosmological model , i.e. , a flat , accelerating universe composed of @xmath106 of matter ( baryonic + dark ) and @xmath107 of a dark energy component in the form of the vacuum energy density ( @xmath50 ) , is fully consistent with a variety of observational data .
even so , given the complexity of the involved phenomena , it is clear that in order to obtain a deeper insight into the nature of the dark energy and dark matter , it is worth consider , both from the observational and theoretical viewpoint , more complex scenarios as , for instance , models with interaction between these two components . in this paper
we have discussed some cosmological consequences of an alternative mechanism of cosmic acceleration based on a general class of coupled quintessence scenarios whose interaction term is deduced from the effect of the dark energy on the cdm expansion rate .
the resulting expressions for the model , parameterized by a small positive parameter ( @xmath1 ) , are very general and have many of the previous phenomenological approaches as a particular case . in particular
, the coupled quintessense models proposed here may be thought as a natural extension of the decay vacuum scenarios discussed a couple of years ago @xcite . by combining the most recent sne ia , bao , cmb shift parameter data and the _ hst _ results on @xmath64 we have shown that strong constraints can be placed on this kind of scenario .
we have shown that the free parameters of the model are constrained to assume values very close to the standard @xmath50cdm values , i.e. , @xmath108 and @xmath109 , although space is still left for an eos distinct from @xmath57 and the interacting parameter slightly different from zero .
it is worth emphasizing that in our analysis the eos @xmath60 and interacting @xmath1 parameters have been set as constants . in a more realistic case , however , such parameters must vary with redshift .
the theoretical and observational consequences of this more realistic interacting @xmath110 scenario , as well as a full comparison with the case discussed in the present analysis , will appear in a forthcoming communication .
the authors are grateful to f. e. m. costa and j. v. cunha for helpful discussions .
jfj and rcs are supported by cnpq .
jsa is supported by cnpq under grants 304569/2007 - 0 and 485662/2006 - 0 , and jasl is partially supported by cnpq and fapesp ( 04/13668 - 0 ) .
v. sahni and a. a. starobinsky , int . j. mod
d * 9 * , 373 ( 2000 ) ; p. j. e. peebles and b. ratra rev .
* 75 * , 559 ( 2003 ) ; t. padmanabhan , phys . rept . * 380 * , 235 ( 2003 ) ; j. a. s. lima , braz .
j. phys .
* 34 * , 194 ( 2004 ) , [ astro - ph/0402109 ] ; e. j. copeland , m. sami and s. tsujikawa , int .
* d15 * , 1753 ( 2006 ) ; j. s. alcaniz , braz . j. phys .
* 36 * , 1109 ( 2006 ) , [ astro - ph/0608631 ] .
d. wands , e. s. copeland and a. liddle , ann . n. y. acad .
sci . * 688 * , 647 ( 1993 ) ; l. amendola , phys . rev .
* d62 * 043511 ( 2000 ) ; j. m. f. maia and j. a. s. lima , phys . rev .
d * 65 * , 083513 ( 2002 ) , [ astro - ph/0112091 ] ; a. nunes and j. p. mimoso , phys . lett .
b * 488 * , 423 ( 2000 ) ; w. zimdahl , d. pavn and l. chimento , phys . lett .
b * 521 * , 133 ( 2001 ) ; l. p. chimento , a. s. jakubi , d. pavn and w. zimdahl , phys . rev .
d * 67 * , 083513 ( 2003 ) ; j. a. s. lima , a. i. silva and s. m. viegas , mon . not .
* 312 * , 747 ( 2000 ) ; l. amendola and d. tocchini - valentini , phys .
d * 64 * , 043509 ( 2001 ) ; m. gasperini , f. piazza and g. veneziano , phys .
d * 65 * , 023508 ( 2002 ) ; g. mangano , g. miele and v. pettorino , mod .
a * 18 * , 831 ( 2003 ) ; w. zimdahl and d. pavn , gen .
grav . * 35 * , 413 ( 2003 ) .
w. zimdahl , int .
d * 14 * , 2319 ( 2005 ) ; x. zhang , phys .
b * 611 * , 1 ( 2005 ) ; w. zimdahl and d. pavn , gen .
grav . * 36 * , 1483 ( 2004 ) ; r .- g .
cai and a. wang j. cosm .
0503 * , 002 ( 2005 ) ; t. koivisto , phys .
d * 72 * , 043516 ( 2005 ) ; m. szydlowski , phys . lett .
b * 632*,1 ( 2006 ) ; m. szydlowski , t. stachowiak and r. wojtak , phys . rev .
d * 73 * , 063516 ( 2006 ) ; j. d. barrow and t. clifton , phys .
d * 73 * , 103520 ( 2006 ) ; s. lee , g. c. liu and k. w. ng , phys . rev .
d * 73 * , 083516 ( 2006 ) ; o. bertolami , f. gil pedro and m. le delliou , phys .
b * 654 * , 165 ( 2007 ) ; q. wu , y. gong , a. wang and j. s. alcaniz , phys.lett .
b * 659 * , 34 ( 2008 ) .
[ arxiv:0705.1006 [ astro - ph ] ] ; f. e. m. costa , j. s. alcaniz and j. m. f. maia , phys .
d * 77 * , 083516 ( 2008 ) , [ arxiv:0708.3800 [ astro - ph ] ] . historically , the possibility of a time varying @xmath5 was first advanced in the paper of bronstein@xcite .
a summary of the evolving ideas can be seen in the review papers by peebles and ratra@xcite , and lima@xcite .
m. @xmath111zer and m. o. taha , phys .
b * 171 * , 363 ( 1986 ) ; nucl .
b * 287 * , 776 ( 1987 ) ; o. bertolami , nuovo cimento soc .
* b93 * , 36 ( 1986 ) ; k. freese et al .
, nucl . phys . *
b287 * , 797 ( 1987 ) ; w. chen and y - s .
wu , phys .
d * 41 * , 695 ( 1990 ) ; d. pavn , phys . rev .
d * 43 * , 375 ( 1991 ) ; j. c. carvalho , j. a. s. lima and i. waga , phys .
d * 46 * , 2404 ( 1992 ) ; i. waga , astrophys . j. * 414 * , 436 ( 1993 ) ; j. a. s. lima and j. m. f. maia , phys . rev d * 49 * , 5597 ( 1994 ) ; j. a. s. lima and j. c. carvalho , gen .
rel . grav .
* 26 * , 909 ( 1994 ) ; j. a. s. lima , phys .
d * 54 * , 2571 ( 1996 ) , [ gr - qc/9605055 ] ; a. i. arbab and a. m. m. abdel - rahman , phys . rev .
d * 50 * , 7725 ( 1994 ) ; l. f. bloomfield torres and i. waga , mon . not .
. soc . * 279 * , 712 ( 1996 ) ; j. m. overduin and f. i. cooperstock , phys . rev .
d * 58 * , 043506 ( 1998 ) ; j. m. overduin , astrophys . j. * 517 * , l1 ( 1999 ) ; r. g. vishwakarma , class .
* 17 * , 3833 ( 2000 ) ; m. v. john and k. b. joseph , phys .
d * 61 * , 087304 ( 2000 ) .
r. g. vishwakarma , gen .
. grav . * 33 * , 1973 ( 2001 ) ; a. s. al - rawaf , mod .
a * 14 * , 633 ( 2001 ) ; r. g. vishwakarma , class .
quant . grav .
* 18 * , 1159 ( 2001 ) ; m. k. mak , j.a .
belinchon , and t. harko , ijmpd * 11 * , 1265 ( 2002 ) ; m. r. mbonye , ijmpa * 18 * , 811 ( 2003 ) ; j. v. cunha and r. c. santos , ijmp d * 13 * , 1321 ( 2004),[astro - ph/0402169 ] ; s. carneiro and j. a. s. lima , ijmpa * 20 * 2465 ( 2005),[gr - qc/0405141 ] ; i. l. shapiro , j. sola and h. stefancic , jcap * 0501 * , 012 ( 2005 ) ; e. elizalde , s. nojiri , s.d .
odintsov and p. wang , phys .
d * 71 * , 103504 ( 2005 ) ; a. friaca , j. s. alcaniz and j. a. s. lima , mon . not .
* 362 * , 1295 ( 2005 ) , [ astro - ph/0504031 ] ; i. l. shapiro , j. sola and h. stefancic , jcap * 0501 * , 012 ( 2005 ) ; j. s. alcaniz and j. m. f. maia , phys
. rev . * d67 * , 043502 ( 2003 ) , [ astro - ph/0212510 ] ; j. f. jesus , gen .
* 40 * , 791 ( 2008 ) , [ astro - ph/0603142 ] ; s. carneiro _
et al . _ ,
phys . rev .
d * 74 * , 023532 ( 2006 ) , [ arxiv : astro - ph/0605607 ] ; s. carneiro _ et al .
_ , phys .
d * 77 * , 083504 ( 2008 ) , [ arxiv : astro - ph/0711.2686 ] .
kamenshchik , a. , moschella , u. and pasquier , v. , phys .
b * 511 * , 265 ( 2001 ) ; m. c. bento , o. bertolami and a. a. sen , phys . rev .
d * 66 * , 043507 ( 2002 ) ; n. bilic , g. b. tupper and r. d. viollier , phys .
b * 535 * , 17 ( 2002 ) ; a. dev , d. jain and j. s. alcaniz , phys .
d * 67 * , 023515 ( 2003 ) .
[ arxiv : astro - ph/0209379 ] ; j. a. s. lima , j. v. cunha and j. s. alcaniz , astro - ph/0611007 . for an interacting dark energy - dark matter interpretation of quartessence
see m. c. bento , o. bertolami and a. a. sen , prd * 70 * , 083519 ( 2002 ) . c. j. dman , a. melchiorri , m. p. hobson , and a. n. lasenby , phys .
d * 67 * , 083511 ( 2003 ) ; g. steigman , ann . rev .
nucl . part .
sci , * 57 * , 463 ( 2007 ) ; v. simha and g. steigman , j. cosmol .
astropart . phys .
06 ( 2008 ) 016 .
gibson et al . , astrophys .
j. , * 529 * , 723 ( 2000 ) ; m. rowan - robinson , [ astro - ph/001206 ] ; riess et al .
, astrophys .
j. * 627 * , 579 ( 2005 ) ; j. r. mould et al .
, astrophys .
j. * 529 * , 786 ( 2000 ) ; g. a. tamman et al .
, astron . astrophys . *
404 * , 423 ( 2003 ) ; a. sandage et al .
* 424 * , 43 ( 2004 ) ; astrophys .
j. , * 653 * , 843 ( 2006 ) ; e. de filippis , m. sereno , m. w. bautz and g. longo , astrophys .
j. * 625 * , 108 ( 2005 ) ; j. a. s. lima , j. f. jesus and j. v. cunha , arxiv:0709.2195 ; j. v. cunha , l. marassi and j. a. s. lima , mon . not .
soc . , * 379 * , l1 ( 2007 ) ; komatsu et al .
, [ astro - ph/0803.0547 ] ( 2008 ) . for
a review see n. jackson , living rev .
* 10 * , 4 ( 2007 ) , arxiv:0709.3924 [ astro - ph ] . | a component of dark energy has been recently proposed to explain the current acceleration of the universe .
unless some unknown symmetry in nature prevents or suppresses it , such a field may interact with the pressureless component of dark matter , giving rise to the so - called models of coupled quintessence . in this paper
we propose a new cosmological scenario where radiation and baryons are conserved , while the dark energy component is decaying into cold dark matter ( cdm ) .
the dilution of cdm particles , attenuated with respect to the usual @xmath0 scaling due to the interacting process , is characterized by a positive parameter @xmath1 , whereas the dark energy satisfies the equation of state @xmath2 ( @xmath3 ) .
we carry out a joint statistical analysis involving recent observations from type ia supernovae , baryon acoustic oscillation peak , and cosmic microwave background shift parameter to check the observational viability of the coupled quintessence scenario here proposed . |
here we show a perturbation analysis of the transition matrix at low temperature @xmath45 in terms of the expansion parameter , @xmath128 we consider the @xmath129 transition matrix where @xmath5 is a multiples of 4 , i.e. , @xmath130 with @xmath131 .
the numerical results shown in the text correspond to @xmath132 .
the transition matrix at low @xmath45 can be expanded by @xmath133 around @xmath74 in eq .. for eq . with @xmath15
, we have [ eq : perturbation ] @xmath134 with @xmath135 where @xmath136 , @xmath137 , @xmath138 , @xmath139 , @xmath140 , @xmath141 , @xmath142 and @xmath143 are the matrices with the sizes , @xmath144 , @xmath144 , @xmath145 , @xmath145 , @xmath146 , @xmath147 , @xmath148 and @xmath149 , respectively . with the probability discussed in the main text , @xmath6 { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } = \frac{1}{4 } : \frac{1}{4 } : \frac{1}{8 } : \frac{1}{8 } : \frac{1}{8 } : \frac{1}{8 } $ ] , the numerical factors in the above matrices are computed explicitly as @xmath150 for later convenience , we define @xmath151 note that both @xmath74 and @xmath152 are reducible and non - symmetric matrices . also they have the same @xmath153 matrix in the upper left corner . because of these properties , they share 8 eigenvalues with @xmath154 .
we label these eigenvalues and corresponding left ( right ) eigenvectors of @xmath152 as @xmath155 with [ eq : t=0eigenmodes ] @xmath156 and the residual vectors , @xmath157 here the left and right eigenvectors satisfy @xmath158 .
we have chosen particular bases within the same eigenvalue as shown above for later convenience . since the sum of each columns of @xmath159 is equal to or smaller than @xmath58 , the absolute magnitude of each eigenvalue of @xmath159 is smaller than @xmath58 , so that @xmath160 in always exists . also , we have @xmath161 .
now , we consider the effects of the first - order perturbation given by @xmath162 in . since the eigenvalues @xmath163 and @xmath164 have triple degeneracy , respectively , we need to diagonalize @xmath162 in each degenerate subspace according to the degenerate perturbation theory .
then we obtain the general form of the eigenvalues , @xmath165 here @xmath166 and @xmath167 are written in terms of the matrix elements of @xmath168 .
note that the coefficients @xmath166 and @xmath167 depend on @xmath133 , since @xmath169 and @xmath159 are the function of @xmath133 . in case that we need to obtain a strict power series expansion of @xmath170 in terms of @xmath133 , further expansions of @xmath171 and @xmath172 should be made .
the eigenspace with @xmath174 in the unperturbed system is spanned by the @xmath175 eigenvectors .
then , @xmath176 is expressed by a @xmath177 matrix as @xmath178 where we used @xmath179 obtained from the symmetry of 1-cell shift .
( due to the periodic boundary condition , our model is invariant under the 1-cell shift of each column , e.g. @xmath180 { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } \to ( { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t}$ ] . with this transformation , @xmath181 is trivially invariant , whereas @xmath182 changes its sign .
therefore , the parity - odd quantity such as @xmath183 vanishes . ) together with the -perturbation by @xmath184 , @xmath185 with @xmath186 , @xmath187 and @xmath188 being the sum of the columns in @xmath141 , @xmath142 and @xmath143 respectively , we obtain @xmath189 the degeneracy between @xmath190 and @xmath191 even under the influence of @xmath176 is * removed * by @xmath184 represented as @xmath192 this leads to @xmath193 the @xmath195 eigenspace in the unperturbed system is spanned by the @xmath196 eigenvectors , @xmath197 together with the perturbation by @xmath184 , @xmath198 we have @xmath199 and @xmath200 the @xmath202 and @xmath203 perturbations on @xmath204 are obtained from @xmath205 where @xmath206 one then finds @xmath207 these eigenvalues , , , and reveal the behaviors of this markovian lattice model at low temperature .
first , the stationary distribution after a long sequence generated by eq . is given by the @xmath88 eigenstate , @xmath208 .
at the leading order , it is solely composed of the radial stripes , which directly shows the dynamical pattern selection .
the @xmath202-perturbation implies that the circular stripes decay to the radial stripes rather quickly with a lifetime of @xmath209 .
the shifts of the radial stripes ( from abab to cdcd or baba
, for example ) , corresponding to the decay of the modes of @xmath210 , @xmath211 * or * @xmath212 , are much slower than that , with a lifetime of @xmath213 . as well as
the eigenvalues discussed above , the corresponding eigenvectors also receive perturbation , @xmath214 in particular , for @xmath215 , we have @xmath216 leading to @xmath217 . because the similarity measures @xmath218 depend linearly on the state vectors , we obtain @xmath219
for @xmath221 , we can explicitly compute the matrices @xmath169 , @xmath159 , @xmath140 , @xmath141 , @xmath142 , @xmath143 and the resulting perturbative coefficients . the formula for the `` unperturbed '' eigenvectors ( including the effects up to @xmath222 )
is expanded as @xmath223 from which we can calculate the coefficients of @xmath224 expanded in terms of @xmath133 with a pretty good convergence by taking sum up to @xmath225 . substituting them into , , , and , we finally obtain the perturbative coefficients for @xmath55 as [ eq : lambdaperturb ] @xmath226 where the dots represent recurring decimals .
the true coefficients are known to be rational numbers , so that the above coefficients must be exact although obtained numerically .
we find that @xmath227 are degenerated up to @xmath203 , and the @xmath228 contributions start to break the degeneracy .
also , @xmath229 acquire nonzero real parts from @xmath228 .
we note that @xmath230 are not perturbed from @xmath164 up to @xmath228 : their absolute values should eventually become smaller than 1 in higher orders due to the perron - frobenius theorem . by simulations for @xmath220 , averaged over @xmath231 trajectories under @xmath232 initial configurations with equal weight for each temperature . ]
the analytic result can be checked from the numerical result of @xmath233 as a function of @xmath20 . shown in [ fig : w=8inplot ] are the results of simulations for @xmath231 trajectories with equal - weight @xmath232 initial configurations . corresponding initial state at @xmath54
is written as @xmath234 which leads to the coefficient @xmath235 as @xmath236 from together with and , we have @xmath237 in a range of @xmath20 satisfying @xmath238 .
therefore , we obtain @xmath239 plotted in the left panel of [ fig : fitting ] is a comparison of the analytic result of @xmath240 in and the numerical result of @xmath241 in .
they show good agreement at low temperature ( @xmath242 ) , while the the discrepancy appears for @xmath243 indicating the breakdown of the perturbative estimate at high temperature . by fitting the numerical data at @xmath244 with an ansatz , @xmath245
, we obtain @xmath246 which are quite consistent with analytic results in ; @xmath247 . for @xmath132 , it is numerically demanding to obtain the analytic formula similar to .
nevertheless , we can extract the coefficients @xmath248 and @xmath249 by plotting @xmath241 in as shown in the right panel of [ fig : fitting ] . by fitting the data at @xmath250
, we find @xmath251 these results together with lead to the temperature dependence of the decay rate of the circular stripe pattern as given in the main text .
[ cols="^,^ " , ]
to identify the essential origin of the dynamical pattern selection ( dps ) , let us consider a minimal toy - model with only 3 states ( rather than @xmath127 states discussed in the main text ) .
they represent two stable patterns ( which we call @xmath252 and @xmath253 ) and a transition state ( @xmath254 ) .
they have intra energies @xmath255 and and the inter binding energies @xmath256 and obey the markov chain with eq .. the transition matrix at zero temperature ( @xmath56 ) is given as @xmath257 where @xmath258 and @xmath9 are positive with the constraint @xmath259 .
the eigenvalues of this matrix is @xmath260 , and we define the corresponding basis vectors as @xmath261 corresponding eigenvectors in the original 3-dimensional space are @xmath270 then in the first - order perturbation theory , @xmath208 is the eigenvector of @xmath4 for the eigenvalue @xmath88 , i.e. , it represents the stationary distribution of the system . when @xmath271 and @xmath272 are of the same order , which one of @xmath252 and @xmath253 dominates the steady distribution is determined by which of @xmath273 and @xmath274 is larger than the other .
from , the magnitude of @xmath273 ( @xmath274 ) corresponds to the minimum excitation energy from @xmath252 ( @xmath253 ) .
if we define @xmath275 then @xmath276 ( @xmath277 ) indicates that @xmath278 ( @xmath279 ) , i.e. the pattern @xmath252 ( @xmath253 ) is dynamically selected .
also , the mean - number of steps @xmath280 for the unstable pattern to decay is derived from as @xmath281 although we analyzed the minimal 3-state model here , it is straightforward to generalize it to a full - scale model with a block structure , @xmath282 which includes the case of the @xmath127-state model discussed in the main text and in . in this context ,
@xmath252 ( @xmath253 ) in the minimal model corresponds to the radial stripes @xmath283 ( circular stripes @xmath284 ) .
also @xmath285 ( @xmath210 ) in the minimal model corresponds to @xmath285 in eq .
( @xmath286 in eq . ) .
then , the stability of the radial stripes is a result of @xmath287 | a markovian lattice model for photoreceptor cells is introduced to describe the growth of mosaic patterns on fish retina . the radial stripe pattern observed in wild - type zebrafish is shown to be selected naturally during the retina growth , against the geometrically equivalent , circular stripe pattern .
the mechanism of such dynamical pattern selection is clarified on the basis of both numerical simulations and theoretical analyses , finding that successive emergence of local defects plays a critical role to realize the wild - type pattern .
physical and biological implications are also discussed . [
[ introduction ] ] introduction : + + + + + + + + + + + + + arrangement of the color detecting photoreceptors ( cone cells ) on a retina is believed to be functionally important for animals to determine the spatial resolution of the color imaging @xcite . in some teleost fishes , the cone cells sensitive to green ( g ;) , red ( r ;) , blue ( b ;) and ultra - violet ( uv ;) lights with g and r forming a pair called the `` double cones '' ( gr ;) , form two - dimensional patterns : they are called the `` cone mosaics '' and have been known since 19th century ( see e.g. @xcite and references therein ) . however , the mechanism for the pattern formation is still unclear . among others ,
the cone mosaic of the zebrafish shown in [ fig : patterns ] has a prominent feature with two major characteristics ; directionality and long periodicity @xcite .
stripes of cells run radially from the central to the marginal region of the retina , and the periodicity of the pattern differs between radial and circular directions as shown in [ fig : patterns](a ) .
although the two patterns , ( a ) and its + 90@xmath0 rotation ( b ) , have the same c2 mm symmetry of the wallpaper group @xcite and have thus the same binding energy , only the pattern ( a ) is realized in nature . in this paper , we refer ( a ) as the `` radial '' ( @xmath1 ) stripe pattern since it is along with the growing direction of the retina , and ( b ) as the `` circular '' ( @xmath2 ) one . in adult fish
, a retina continuously grows through its life by generating new photoreceptors in the germinal zone of retinal margin called the ciliary marginal zone ( cmz ) .
the rearrangement of those new cone cells _
after _ cellular differentiation is considered to play a crucial role for mosaic pattern formation .
this is supported by a cell - trace experiment in which most of the cells are found not to change their subtypes after the first determination @xcite .
theoretically , cell rearrangement models for cone mosaics have been formulated on a two - dimensional square lattice : it was found that different patters ( such as the zebrafish pattern with c2 mm symmetry and the medaka pattern with p4 mg symmetry ) can be generated successfully by stochastic cell movements biased by appropriate cell - cell adhesion force @xcite .
however , such models have failed to distinguish the characteristics of directionality , such as the distinction between ( a ) and ( b ) in [ fig : patterns ] .
the main purpose of this paper is to propose a new mechanism in which the sequential accretion of new cone cells from cmz triggers dynamical pattern selection ( dps ) among those with the same binding energy .
we demonstrate it explicitly by taking the zebrafish as a characteristic example .
m ( 3 - 4 days after fertilization ) and a few @xmath3 m ( along with the retina surface ) , respectively . the ciliary marginal zone ( cmz ) where new cone cells are bone is denoted by gray area surrounding the retina . ]
[ [ markovian - lattice - model - for - pattern - formation ] ] markovian lattice model for pattern formation : + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + due to the accretion of new cone cells . the transition matrix from one column to the next
is denoted by @xmath4 .
( b ) binding energies between neighboring sites for zebrafish patterns.,scaledwidth=47.0% ] to take into account the fact that retina grows dynamically by receiving new cone cells born in cmz , we extract a rectangular region of the retina margin as indicated in [ fig : patterns ] and introduce a markovian model where cone cells are supplied stochastically from the `` cmz pool '' to the two - dimensional lattice of cells column - by - column as shown in [ fig : markov](a ) .
the radial growth of the actual retina is represented by the horizontal growth toward the right direction .
the vertical size of the lattice is denoted by @xmath5 .
possible formation of dislocations in the realistic radial growth will not be considered in this paper .
the growth is dictated by the action of a transition matrix @xmath4 whose explicit form will be specified shortly . in the cmz pool , we consider b , uv and the double cone ( rg ) with the number ratio , 1:1:2 , anticipating the possible stripe structures in [ fig : patterns](a , b ) .
then , we have six degrees of freedom on each lattice site with the probability , @xmath6 { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } : { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } = \frac{1}{4 } : \frac{1}{4 } : \frac{1}{8 } : \frac{1}{8 } : \frac{1}{8 } : \frac{1}{8 } $ ] .
the binding energies between the neighboring cells , @xmath7 with @xmath8 and @xmath9 taking either b , r , g , or uv , would be dictated by the binding proteins on the cone cell membranes , although the specific protein structures are not yet fully identified experimentally .
previous analyses of the `` phase diagram '' of cell patterns in the multi - dimensional @xmath7-space in the stochastic rearrangement models @xcite show that the zebrafish patterns , [ fig : patterns](a , b ) , are equally realized as stationary states if the three inequalities below are simultaneously satisfied : with @xmath10 taken not only for neighboring cells but also for the diagonal cells is known to be necessary @xcite .
] @xmath11 .
we take these inequalities as guide lines to choose cell bindings : our particular choice of @xmath7 is shown in [ fig : markov](b ) : @xmath12 the binding energies to the double cones are assumed to be proportional to the contact area , e.g. the side - by - side coupling between ; and ; is chosen to be @xmath13 .
therefore , in [ fig : markov](b ) , we have @xmath14 . in our analyses
below , we take a specific value @xmath15 : we have checked that essential conclusions of our paper are unchanged as long as @xmath16 . in the markov chain shown in [ fig : markov](a ) , the lattice sites are empty at the beginning and the six types of cone cells in [ fig : markov](b ) occupy the sites column - by - column in a stochastic manner .
each column with periodic boundary condition in the vertical direction has 6@xmath17 different configurations labeled by the index @xmath18 .
the probability of having the configuration @xmath19 in the @xmath20-th column is defined as @xmath21 so that the probability vector for the @xmath20-th column reads @xmath22 with @xmath23 , where @xmath24 denotes the transpose ( @xmath2590@xmath0 rotation ) .
the markov chain is generated by the @xmath26 transition matrix @xmath4 as @xmath27 where the matrix element @xmath28 with @xmath29 is nothing but the probability of having a configuration @xmath30 in the @xmath31-th column given the configuration @xmath19 in the @xmath20-th column . to model the retinal growth ,
we consider @xmath28 having a boltzmann form with an `` effective '' temperature @xmath32 : @xmath33 here @xmath34 is a sum of the intra binding energies in the configuration @xmath30 , while @xmath35 is a sum of the inter binding energies between @xmath30 and @xmath19 .
the prior probability factor @xmath36 is computed by taking into account the number ratio of the cone cells in the cmz pool : for example , @xmath37 for @xmath38 { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } ) ^\mathrm{t}$ ] . physically , @xmath32 corresponds to the mobility of the cone cells and introduces fluctuations to the cell pattern formation . since @xmath39 is a linear function of @xmath40 and @xmath41 , @xmath42 and @xmath28 can be written in terms of the dimensionless variables , @xmath43 ( reduced temperature ) and @xmath44 ( coupling ratio ) . by definition ,
the fluctuation becomes large as @xmath45 increases . for later convenience
, we introduce a bra - ket notation : each configuration @xmath30 is represented by a state vector @xmath46 , so that @xmath47 .
the eigenvalues of @xmath4 and the corresponding left - right eigenvectors are defined by @xmath48 and @xmath49 ( @xmath50 ) with a relative normalization , @xmath51 .
then , we have @xmath52 where @xmath53 s are the expansion coefficients at @xmath54 .
note that @xmath55 s are in general complex , since @xmath4 is non - symmetric . at @xmath56 ,
@xmath4 is reducible , i.e. , there appears multiple closed subspaces and @xmath57 is not unique .
correspondingly , there arises multiple eigenvectors with the eigenvalue @xmath58 . for @xmath59 ,
all the components of @xmath4 is positive , so that finite markov chain becomes irreducible and aperiodic @xcite .
consequently , there exists a unique probability vector @xmath57 irrespective of the initial vector .
moreover , the perron - frobenius theorem for positive matrix implies that ( i ) there is only one left eigenvector @xmath60 with @xmath61 , and ( ii ) the absolute values of other eigenvalues obey @xmath62 , with the sum of components for each right eigenvectors being @xmath63 due to @xmath64 .
note that the property ( i ) and @xmath65 imply @xmath66 in eq.([eq : t - p ] ) .
the essential question in dps , after all , is to identify a particular pattern which dominates the state @xmath67 at @xmath68 .
[ [ stationary - patterns - at - t0 ] ] stationary patterns at @xmath56 : + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + for zero effective temperature , the following 8 columns play crucial roles for pattern formation : ( a ) @xmath69 { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( b ) @xmath69 { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( c ) @xmath69 { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( d ) @xmath69 { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( e ) @xmath69 { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( f ) @xmath69 { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( g ) @xmath69 { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , ( h ) @xmath69 { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \cdots)^\mathrm{t}$ ] , where @xmath70 denotes the repetition .
note that ( a)-(d ) have the same intra - binding energy , a multiple of @xmath40 , while ( e)-(h ) has the same intra - binding energy , a multiple of @xmath41 . in terms of the bra - ket notation , @xmath71 , @xmath72 , @xmath73 , etc .
then , @xmath74 ( the transition matrix at @xmath56 ) in the state - space spanned by @xmath75 and the others are reducible and sparse : @xmath76 at @xmath56 ( left ) and those close to @xmath77 for @xmath78 ( right ) .
the cyan and blue points corresponds to the eigenmodes responsible for the radial stripes , while the red and orange ones are for the circular stripes . at finite @xmath45 ,
the cyan @xmath79 does not move , whereas the others go toward the inner direction . ]
due to the fact that @xmath80 , all the probability flows into the subspace @xmath81 , while it does not flow out from @xmath81 .
furthermore , the subspace @xmath81 is reducible to three closed sets , @xmath82 , @xmath83 , and @xmath84 , so that they respectively form the following stable patterns ; @xmath85 & \begin{array}{ccccc } \begin{array}{l } { \scriptstyle a\,b\,a\,b\,a\,b\ , \cdots}\\[-2pt ] { { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } { { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \\[-6.5pt ] { { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } { { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \\[-6.5pt ] { { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } { { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \;\ ; \cdots \\[-6.5pt ] { { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; 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} } \\[-6pt ] \;\vdots\;\;\vdots\;\,\vdots\;\;\vdots\;\,\vdots\;\,\vdots \end{array } , & & \begin{array}{l } { \scriptstyle c\,d\,c\,d\,c\,d\ , \cdots}\\[-2pt ] { { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; 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} } \\[-6.5pt ] { { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; 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} { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \\[-6.5pt ] { { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } { { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \\[-6.5pt ] { { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } { { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } } \\[-6pt ] \;\vdots\;\;\vdots\;\,\vdots\;\;\vdots\;\,\vdots\;\,\vdots \end{array } \end{array}. \nonumber\\[-18pt]\end{aligned}\ ] ] the first two patterns , which are equivalent under periodic boundary condition in circular direction , correspond to the radial stripe pattern of the wild - type zebrafish in [ fig : patterns](a ) , while the third one corresponds to the circular stripe pattern in [ fig : patterns](b ) . corresponding to the multi - stability due to the reducibility of , there arise eight eigenvectors @xmath86 with @xmath87 .
they have nonzero components only in @xmath81 .
such degeneracy is removed under infinitesimal fluctuation at finite @xmath45 , due to the positivity of @xmath28 .
the major eight eigenvalues for @xmath56 and the eigenvalues near @xmath88 for small positive @xmath45 are sketched in [ fig : eigenvalues ] .
the detailed analysis of these eigenvalues is given in the supplemental material i. [ [ dynamical - pattern - selection - dps - at - t - neq-0 ] ] dynamical pattern selection ( dps ) at @xmath89 : + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + let us now study dps at finite effective temperature ( finite cell mobility ) by performing a stochastic simulation with the transition matrix .
at each @xmath20-th column ( @xmath90 ) , we start with a random configuration and sweep through all the sites inside the column by @xmath91 times using the metropolis update with @xmath39
. then we fix the configuration and go to the @xmath31-th column .
this procedure gives a single pattern ( a trajectory ) for each trial starting from an initial configuration at @xmath54 . by repeating this procedure either by changing or keeping the initial condition ,
trajectories with total number @xmath92 are generated .
one may consider each trajectory as a pattern realized in individual zebrafish . mean properties of the patterns can be obtained by averaging over the trajectories .
@xmath93{t04w16frs0conf2.pdf } \\ & \includegraphics[height=0.4385\textwidth , angle=90]{t04w16frs1conf2.pdf } \end{array } \\
\includegraphics[width=0.475\textwidth]{fig4-similarity.pdf } \end{array}\end{aligned}\ ] ] @xmath93{t04w16fbs100conf2.pdf } \\ & \includegraphics[height=0.4385\textwidth , angle=90]{t04w16fbs101conf2.pdf } \end{array } \\
\includegraphics[width=0.475\textwidth]{fig5-similarity.pdf } \end{array}\end{aligned}\ ] ] shown in the upper panels of [ fig : simulationfromrandom ] are two examples sampled from @xmath94 trajectories with random initial configurations at @xmath54 with @xmath95 ( about 10% of the retina circumference ) and @xmath96 ( large enough for thermalization ) . from the simulations carried out for @xmath97 , examples at @xmath98 are displayed in the figure : although the radial stripes and circular stripes are stationary patterns equally possible at @xmath56 , the dynamical retina growth at @xmath59 selects the radial stripes observed in wild - type zebrafish irrespective of the initial random configurations . in order to quantify similarity of a configuration at given @xmath20 with the radial and circular stripes ,
let us introduce a _
similarity measure_. first , we note that the radial stripe pattern at given @xmath20 consists of the basic units @xmath99 { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } , ( { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } , ( { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } , ( { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},2*{0.36em})$ ) arc [ start angle=90 , end angle=270 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},0)$ ) arc [ start angle=-90 , end angle=90 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t}\}$ ] , while the circular stripe pattern consists of @xmath99 { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } , ( { \tikz[baseline=0.5pt ] { \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ red , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(2*{0.36em},{0.36em})$ ) arc [ start angle=0 , end angle=180 , radius={0.36em } ] ; \fill [ green , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+(0,{0.36em})$ ) arc [ start angle=180 , end angle=360 , radius={0.36em } ] ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } , ( { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t } , ( { \tikz[baseline=0.5pt ] { \fill [ black , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } { \tikz[baseline=0.5pt ] { \fill [ blue!80!cyan , inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) ; \draw [ inner sep=0 , outer sep=0 ] ( $ ( 2 * 0*{0.36em},-2 * 0*{0.36em})+({0.36em},{0.36em})$ ) circle ( { 0.36em } ) } ; } ) ^\mathrm{t}\}$ ] .
then , we count how many basic units are contained in a column at given @xmath20 . dividing the resultant number by @xmath5 and averaging it over trajectories , we obtain the similarity measures @xmath100 and @xmath101 .
they are plotted by filled stars and filled circles in the lower panels of [ fig : simulationfromrandom ] as a function of @xmath20 for @xmath102 and @xmath103 .
one finds that @xmath100 ( @xmath101 ) approaches to @xmath58 ( @xmath63 ) quickly as @xmath20 increases with weak @xmath45-dependence .
thus , [ fig : simulationfromrandom ] indicates that the radial stripe pattern is the true asymptotic configuration corresponding to @xmath57 . to check whether the circular stripe pattern is indeed unstable
, we consider circular - type ( @xmath104 ) initial configurations in [ fig : simulationfromrotated ] .
the upper panels show two cases sampled from 2048 trajectories with the @xmath105-type initial configuration . under the dynamical retina growth at @xmath59 ,
the circular stripe pattern turns into the radial stripe after certain steps .
close look at the figure shows that the transition from the circular stripes to the radial stripes is initiated by the creation and propagation of small local defects .
plotted in the lower panel of [ fig : simulationfromrotated ] are the similarity measures averaged over @xmath106-stripe initial configurations . in this case ,
approach to the radial stripe pattern becomes slower as @xmath45 decreases , as expected by the formation probability of small defects .
let us finally discuss the essential mechanism of dps in terms of the eigenvalues and eigenvectors of @xmath4 .
the similarity measure with @xmath107 can be written as @xmath108 where @xmath109 is the similarity measure of a state @xmath110 to @xmath111 , and @xmath112 . for small @xmath45 , @xmath113 and @xmath114 are close to @xmath58 , while others are close to @xmath63 ( eq.([eq : pev ] ) in supplemental material i ) .
therefore , for large @xmath20 , we have @xmath115 and @xmath116 . here
@xmath117 corresponds to the eigenvector @xmath118 which swaps the radial and circular stripe patterns .
these are consistent with what are shown in [ fig : simulationfromrandom ] and [ fig : simulationfromrotated ] .
one may also extract the transition step scale by fitting the data in these figures , @xmath119 with @xmath120 and @xmath121 ( see eq.([eq : w16-gd ] ) in supplemental material ii ) .
thus , the mean number of steps for the circular stripes to decay is found to be @xmath122 for @xmath98 .
the escape rates from the radial and circular patterns are critical for dps .
they are governed by the smallest deficit energies from the patterns ( supplemental material iii ) , @xmath123 the configuration having larger @xmath124 survives at large @xmath20 . under the choice in , we have @xmath125 which confirms the survival of the radial stripes . in . for @xmath44
being close to @xmath126 , _ global _ defects may also contribute .
this indicates the emergence of a new pattern other than the radial or circular stripes .
it is an interesting problem to be studied , but is beyond the scope of the present paper . ]
[ [ summary - and - discussion ] ] summary and discussion + + + + + + + + + + + + + + + + + + + + + + in this letter , we have introduced a markovian lattice model to describe the dynamics of cone - cell mosaic patterns in growing retina . with numerical simulations in the @xmath127-dimensional state - space ( @xmath95 ) together with theoretical analyses of eigenvalues and eigenvectors of the transition matrix @xmath4 , we found that the growing process naturally selects the radial stripe pattern observed in the wild - type zebrafish against the circular stripe pattern .
such a `` dynamical pattern selection ( dps ) '' could not be described by the previous no - growth models .
successive appearance of small defects during the growth plays a key role to transfer arbitrary patterns to the radial stripes . in the present study , we chose the cell - cell bindings @xmath7 to be characteristic values for the zebrafish , while the effective temperature @xmath45 corresponding to cell mobility was treated as a free parameter . to make further connection of @xmath45 and @xmath7 to microscopic cell dynamics
, it would be necessary to make quantitative comparison of our model predictions to in vivo experimental data for the growth rate of the pattern and also for the defect frequencies with wild - type and mutant embryos .
also , numerical simulations with round shaped retina needs to be carried out for realistic comparison with data .
direct measurements of cell - cell bindings using the atomic force microscope @xcite would also give useful information on @xmath7 .
although we have focused on cellular mosaic patterns in this letter , they have suggestive similarities with other examples in non - equilibrium physics , such as the crystal growth , patterns in granular materials , copolymerization etc , where various spatial or temporal patterns emerge due to infinitesimally small perturbations @xcite
. our theoretical approach may provide a novel insight into a universal description of dps in life and matter .
the authors thank sachihiro c. suzuki , ichiro masai , yuko nishiwaki and bernold fiedler for valuable discussions and comments .
this work was supported by riken ithes project .
99 see e.g. , j. e. cook , in _ the visual neurosciences _ , eds .
l.m .
chalupa and j.s .
werner ( mit press , cambridge ma , 2003 ) .
s. j. eglen , math .
med .
biol .
* 23 * , 79 - 99 ( 2006 ) .
a. h. lyall , quarterly journal of microscopical science , * 3.41 * , 101 - 110 ( 1957 ) ; _ ibid .
_ , * 3.42 * , 189 - 201 ( 1957 ) . + k. engstrm , acta zoologica , * 44 * , 179 - 243 ( 1963 ) .
d. schattschneider , american math .
monthly . *
85 * , 439 - 450 ( 1978 ) .
j. m. fadool and j. e. dowling , prog . in retinal and eye research ,
* 27 * , 89 ( 1999 ) .
s. c. suzuki _
et al . _ , pnas * 110 * , 15109 ( 2013 ) . s. tohya , a. mochizuki and y. iwasa , j. of theor .
biol . , * 200 * , 231 ( 1999 ) . a. mochizuki , j. of theor .
biol . , * 215 * , 345 ( 2002 ) .
s. tohya , a. mochizuki and y. iwasa , j. of theor .
biol . , * 221 * , 289 ( 2003 ) .
o. hggstrm , _ finite markov chains and algorithmic applications _ , ( cambridge univ .
press , 2002 ) .
m. krieg , y. arboleda - estudillo , p .- h .
puech , j. kfer , f. graner , d. j. mller and c .- p .
heisenberg , nature cell biology * 10 * , 429 ( 2008 ) .
j. p. gollub and j. s. langer , rev .
mod .
phys . * 71 * , s396 ( 1999 ) . * supplemental material * |
vascular complications occur in approximately a quarter of patients of pancreatitis , adding to the associated morbidity and mortality .
these include splanchnic vein thrombosis ( svt ) and hemorrhage from direct arterial wall erosion or pseudoaneurysm formation .
however , cerebral infarction from arterial thrombosis is a rare complication of acute pancreatitis ( ap ) . here
, we report a case of cerebral infarction resulting probably from left middle cerebral artery ( mca ) thrombosis in a 48-year - old male patient of alcohol related ap .
a 48-year - old male , heavy alcohol consumer for the prior 6 years , presented with complaints of severe abdominal pain , vomiting and constipation for 3 days .
there was no history of diabetes mellitus , hypertension , smoking , and previous abdominal pain .
on admission to our hospital ( on day 4 of illness ) , he was hemodynamically stable , had abdominal distention with diffuse tenderness and absent bowel sounds .
laboratory work up on day 4 revealed serum amylase : 898 u / l , lipase : 968 u / l , glucose : 116 mg / dl , na : 132 meq / l , k : 3.6 meq / l , creatinine : 1.9 mg% , calcium : 8.6 mg / dl , bilirubin : 1.4 mg / dl , aspartate transaminase / alanine transaminase : 74/28
iu / l , alkaline phosphatase : 181 iu / l , serum proteins / albumin : 7.1/2.9 g / dl , serum cholesterol : 124 mg / dl , triglycerides : 130 mg / dl , hb : 8.4 g / dl , leucocytes : 15,400/l , platelets : 98,000/l , prothrombin time : 18 s , activated partial thromboplastin time : 40 s. computed tomography ( ct ) of abdomen [ figure 1 ] carried out with intravenous contrast on day 4 revealed enlarged , diffusely enhancing pancreas , multiple peripancreatic fluid collections and bilateral pleural effusions , confirming grade e ap ( ct severity index = 4 ) . he was kept nil per orally
. continuous nasogastric aspiration , intravenous fluids , stress ulcer prophylaxis and subcutaneous unfractionated heparin 5000 units twice / day for venous thromboprophylaxis were started . on day 5
ct of brain revealed large left mca territory infarct [ figures 2 and 3 ] . electrocardiogram ( ecg ) and echocardiography of the heart were normal .
work up for hyperhomocysteinemia , protein c and s deficiency , factor v leiden , antithrombin iii deficiency and antiphospholipid antibody syndrome was negative .
he was intubated on day 8 for progressive respiratory distress and hypoxia and was shifted to intensive care unit for mechanical ventilation . on day 9 , he developed shock and was discharged against medical advice upon insistence of his relatives .
computed tomography scan of the abdomen taken after intravenous contrast showing bulky , diffusely enhancing pancreas ( indicated by white arrows ) and a fluid collection ( black arrow ) plain computed tomography of the brain showing an area of hypodensity with poor gray - white differentiation in the left parieto - occipital regions , suggesting a large left middle cerebral artery territory infarct plain computed tomography of the brain showing an area of hypodensity with poor gray - white differentiation in the left parieto - occipital regions , suggesting a large left middle cerebral artery territory infarct
splanchnic veins are most often the involved sites with a reported incidence of 1 - 2% , the consequences being portal hypertension , gastrointestinal bleeding , bowel ischemia and ascites .
splenic vein is the most common site , followed by portal and superior mesenteric veins .
thrombosis of inferior vena cava , renal veins and pulmonary thromboembolism have been reported rarely .
arterial thromboses are less common than venous thromboses , involve arteries in peripancreatic distribution namely celiac trunk , perigastric , splenic and colonic arteries .
vascular complications are more commonly reported with alcohol related than with gall stone induced pancreatitis and correlate with severity of ap .
the index patient had severe alcohol related ap as suggested by imaging [ figure 1 ] and the development of multi - organ dysfunction , but there was no evidence of svt .
neurological complications of ap include encephalopathy resulting from hypoxia or metabolic causes , uncommonly visual loss due to retinopathy or cerebral infarcts and polyneuropathy from nutritional deficiency ( vitamin e ) or prolonged critical illness .
hemiplegia due to cerebral infarction resulting from vascular occlusion is rare , as is spinal cord infarction leading to paraplegia .
earlier reports of cerebral infarction in ap have suggested fat embolism as the cause but left mca thrombosis seems to be the most probable cause in our patient as he had a large infarct in the same territory [ figures 2 and 3 ] .
cardiac source for cerebral embolism is less likely in the index patient , considering that he had sinus rhythm throughout the course and ecg and echocardiography were normal .
other risk factors for ischemic stroke ( hypertension , diabetes mellitus , obesity , smoking and advanced age ) were absent in the index case and there was no hypotension before development of cerebral infarction .
arterial thrombosis may lead to infarction of spleen , stomach and colon as well , sometimes necessitating emergency surgeries .
acute limb ischemia of both lower limbs due to arterial thrombosis has also been reported in ap .
the thrombotic tendency in ap may be related to systemic hypercoagulability resulting from inflammatory cytokines , endothelial dysfunction due to release of pancreatic enzymes into circulation , compression of vessels and direct vasculitis from surrounding inflammatory process .
the pathogenesis of fat embolism involves the release of chylomicrons and vldl into the systemic circulation from omental fat necrosis in severe ap , along with elevated c - reactive protein which induce intravascular activation of the coagulation cascade and vascular occlusion .
dual phase contrast enhanced ct of abdomen , conventional or digital subtraction angiography , color doppler ultrasonography and of late magnetic resonance angiography ( mra ) are the modalities employed to diagnose vascular complications in ap .
ct cerebral angiography / mra could not be carried out in the index case to confirm thrombosis because of worsening renal failure , progressive organ dysfunction and rapid clinical deterioration after development of cerebral infarction .
as there is increased risk of bleeding from pseudoaneurysms , frequent need for pancreatic debridement or drainage of infected collections , early anticoagulation ( heparin followed by oral vitamin k antagonists to achieve an internationally normalized ratio of around 2.0 ) for svt in patients of ap can be problematic .
spontaneous recanalization was observed in about a third of patients of svt irrespective of anticoagulation in a study .
hence , the role of anticoagulation for svt is unclear and the decision of anticoagulation has to be individualized , after considering the risk benefit ratio .
guidelines for management of arterial thrombosis are lacking , but heparin has been used in some cases .
full therapeutic dose of heparin was avoided in the index patient considering the significant risk of hemorrhage into large mca territory infarct . to conclude , cerebral infarction can be a rare complication of ap and the treating physicians should be aware of vascular thrombotic and neurological complications of ap . | peripancreatic vascular thrombosis is a known complication of acute pancreatitis ( ap ) and chronic pancreatitis .
however , hemiplegia resulting from cerebral infarction due to cerebral arterial thrombosis is a rare complication of ap . here
, we report a case of alcohol related severe ap with multi - organ dysfunction , which was complicated by large left sided middle cerebral artery territory infarct - leading to right sided hemiplegia in a 48-year - old male patient .
the neurological and vascular thrombotic complications of pancreatitis , their pathogenesis and management are discussed in brief . |
suppose that a group of individuals is voting among three candidates ( or alternatives ) , call these candidates @xmath3 , @xmath4 , and @xmath5 .
further suppose that four - ninths of the voters rank the candidates , in order of strictly increasing preference , @xmath6 , that three - ninths rank them @xmath7 , and that the remaining two - ninths rank them @xmath8 .
so five - ninths of the voters prefer @xmath4 to @xmath3 and six - ninths of the voters prefer @xmath4 to @xmath5 . a candidate such as @xmath4 , i.e. , a candidate who when paired against each other candidate is preferred by a strict majority of the voters , is called a _ condorcet winner _ @xcite .
a _ voting system _ maps from candidates and voters ( each of whose preference order over the candidates is represented by a strict , linear order ) to a winner set , which must be a subset of the candidate set . as condorcet noted in the 1700s @xcite it is quite possible that sometimes there is no condorcet winner .
the classic example is the following .
given a choice between @xmath3 , @xmath4 , and @xmath5 , one - third of a group might rank ( in order of strictly increasing preference ) the candidates @xmath7 , another third might rank them @xmath9 , and the remaining third might rank them @xmath10 .
so two - thirds of the voters prefer @xmath4 to @xmath3 , two - thirds of the voters prefer @xmath3 to @xmath5 , and two - thirds of the voters prefer @xmath5 to @xmath4 .
clearly , there is no condorcet winner .
a voting system is said to obey the _
condorcet criterion _ if it selects the condorcet winner whenever one exists .
the condorcet criterion may seem so natural that one might at first glance fail to see that many of the most widely - used voting rules do not meet it .
for instance , in the `` 4/9 , 3/9 , 2/9 '' example above , if the voters were to use plurality - rule i.e .
, a candidate is the winner if he or she receives the most first - place votes then the group would choose @xmath3 . as a second example , if instead the group were to hold an election under instant - runoff voting , @xmath5 would win and @xmath4 would be the first candidate eliminated . in instant - runoff voting ,
if no candidate is listed as the most favorite by a majority of the voters then each candidate who is listed as the most favorite by the fewest voters ( i.e. , @xmath4 in our example ) is dropped from preference lists and the election is recomputed with the edited lists ; the process ends when a majority winner emerges ( or due to ties all candidates have been removed ) .
examples where election systems fail to meet the condorcet criterion are hardly new . in the 1800
s nanson @xcite wrote on the fact that well - known voting systems , such as borda s @xcite famous rank - based point system , fail to satisfy the condorcet criterion . in 1876
the mathematician charles dodgson , whose name when an author of fiction was the now famous pseudonym of lewis carroll , devised a voting system @xcite that has many lovely properties and meets the condorcet criterion . in dodgson s system , each voter strictly ranks ( i.e. , no ties allowed ) all candidates in the election .
if a condorcet winner exists , he or she wins the dodgson election . if no condorcet winner exists , dodgson s approach is to take as winners all candidates that are `` closest '' to being condorcet winners , with closest being in terms of the fewest changes to the votes needed to make the candidate a condorcet winner .
we will in section [ sec : def ] describe what exactly dodgson means by `` fewest changes , '' but intuitively speaking , it is the smallest number of sequential switches between adjacent entries in the rankings the voters provide .
it can thus be seen as a sort of `` edit distance '' @xcite .
dodgson wrote about his voting system in a pamphlet on the conduct of elections @xcite .
it is now regarded as a classic of social choice theory @xcite .
dodgson s system was a relatively early example of a system satisfying the condorcet criterion though , remarkably , the catalan mystic ramon llull in the thirteenth century had already proposed a system that satisfies the condorcet criterion and has many other strengths ( see @xcite ) .
although dodgson s system has many nice properties , it also poses computational problems that are serious enough to make it an impractical choice for a general voting system that is guaranteed to work efficiently in any setting : the problem of checking whether a certain number of changes suffices to make a given candidate the condorcet winner is @xmath2-complete @xcite , and the problem of computing an overall winner , as well as the related problem of checking whether a given candidate is at least as close as another given candidate to being a dodgson winner , is complete for @xmath0 @xcite .
the @xmath0 level of the polynomial hierarchy can be defined as the class of problems solvable with polynomial - time parallel access to an @xmath2 oracle ( @xcite , see also @xcite ) .
more recent work has shown that some other important election systems are complete for @xmath0 : hemaspaandra , spakowski , and vogel @xcite have shown @xmath0-completeness for the winner problem in kemeny elections , and rothe , spakowski , and vogel @xcite have shown @xmath0-completeness for the winner problem in young elections .
the above complexity results about dodgson elections show , quite dramatically , that unless the polynomial hierarchy collapses there is no efficient ( i.e. , polynomial - time ) algorithm that is guaranteed to always determine the winners of a dodgson election .
does this then mean that dodgson s widely studied and highly regarded voting system is unusable ?
it turns out that if a small degree of uncertainty is tolerated , then there is a simple , polynomial - time algorithm , ` greedywinner ` ( the name s appropriateness will later become clear ) , that takes as input a dodgson election and a candidate from the election and outputs an element in @xmath11 .
the first component of the output is the algorithm s guess as to whether the input candidate was a winner of the input election .
the second output component indicates the algorithm s confidence in its guess . regarding the accuracy of ` greedywinner ` , we show that for each ( election , candidate ) pair , it holds that if ` greedywinner ` outputs @xmath12 as its second output component , then its first output component correctly answers the question , `` is the input candidate a dodgson winner of the input election ? ''
( this is an example of what we call _ self - knowing correctness _ ; definition [ d : skc ] will make this formal . )
we also show that for each @xmath13 the probability that a dodgson election @xmath14 selected uniformly at random from all dodgson elections having @xmath15 candidates and @xmath16 votes ( i.e. , all @xmath17 dodgson elections having @xmath15 candidates and @xmath16 votes have the same likelihood of being selected@xmath18-candidate elections have the fixed candidate set @xmath19 ( though in some examples we for clarity will use other names , such as @xmath3 , @xmath4 , @xmath5 , and @xmath20 ) .
so , though we to be consistent with earlier papers on dodgson elections allow the candidate set `` @xmath21 '' to be part of the input , in fact we view this as being instantly coerced into the candidate set @xmath22 . and
we similarly view voter _ names _ as uninteresting.]@xmath23 ) has the property that there exists at least one candidate @xmath5 such that ` greedywinner ` on input @xmath24 outputs @xmath25 as its second output component is less than @xmath26 .
thus for elections where the number of voters greatly exceeds the number of candidates ( though the former could still be within a ( superquadratic ) polynomial of the latter , consistently with the success probability for a family of election draws thus - related in voter - candidate cardinality going asymptotically to 1 ) , if one randomly chooses an election @xmath27 , then with high likelihood it will hold that for each @xmath28 the efficient algorithm ` greedywinner ` when run on input @xmath29 correctly determines whether @xmath5 is a dodgson winner of @xmath14 , and moreover will `` know '' that it got those answers right .
so ` greedywinner ` is a self - knowingly correct heuristic , and we will prove the above claims showing it is frequently ( self - knowingly ) correct . though the ` greedywinner ` algorithm on its surface is about _ recognizing _ dodgson winners , as discussed in section [ sec : algor ] our algorithm can be easily modified into one that is about , given an @xmath27 , _ finding _ the complete set of dodgson winners and that does so in a way that is , in essentially the same high frequency as for ` greedywinner ` , self - knowingly correct . later in this paper , we will introduce another frequently self - knowingly correct heuristic , called ` greedyscore ` , for calculating the dodgson score of a given candidate .
the study of greedy algorithms has an extensive history ( see the textbook @xcite and the references therein ) .
much is known in terms of settings where a greedy algorithm provides a polynomial - time approximation , for example @xcite , and of guarantees that a greedy algorithm will frequently solve a problem for example kaporis , kirousis , and lalas study how frequently a greedy algorithm finds a satisfying assignment to a boolean formula @xcite , and many additional excellent examples exist , e.g. , @xcite . however , each of these differs from our work in either not being about _ self - knowing _ correctness or , if about self - knowing correctness , in being about an np - certificate type of problem .
in contrast , as discussed in more detail immediately after definition [ d : skc ] , the problem studied in this paper involves objects that are computationally more demanding than mere certificates for np set membership . among earlier algorithms having a self - knowingly correct flavor , a particularly interesting one ( though
, admittedly , it is about finding certificates for np set membership ) is due to goldberg and marchetti - spaccamela @xcite .
goldberg and marchetti - spaccamela construct for every @xmath30 a modified greedy algorithm that is deterministic , runs in polynomial time ( where the polynomial depends on @xmath31 ) , and with probability at least @xmath32 self - knowingly finds an optimal solution of a randomly chosen ( from a particular , but natural , distribution ) instance of the knapsack problem .
( they call their algorithm `` self checking '' rather than `` self - knowingly correct . '' ) besides being about an np - type problem rather than a `` @xmath0''-type problem such as dodgson elections , a second way in which this differs from our work is that the running time of our algorithms does not depend on the desired likelihood of correctness .
the concept of a heuristic that is effective on a significant portion of the problem instances of some very hard ( e.g. , not even in @xmath2 unless @xmath33 ) problem and furthermore has the additional property that it can very frequently guarantee that its answers are correct is related to other theoretical frameworks .
parameterized complexity @xcite studies hard problems that have efficient solutions when instances of the problem are restricted by fixing one or more of the parameters that describe the instances .
the two most natural parameters of dodgson elections are the number of candidates and the number of voters .
it is known that with either of these parameters bounded by a constant , dodgson elections have polynomial - time algorithms @xcite .
however , we are interested in cases when no such dramatic bounding of a parameter by a constant occurs .
like average - case ( @xcite , see also the excellent surveys @xcite ) and smoothed @xcite analyses , our analysis of @xmath34 is probabilistic .
but while those methods are concerned with the expected value over segments of the problem domain of some resource of interest , typically time or a transformed version of time , we focus on a quite different property : correctness . other recent papers also focusing on frequency ( or probability weight ) of correctness for hard voting - related problems ( though not dodgson voting ) include work of conitzer and sandholm @xcite and procaccia and j. rosenschein @xcite .
those papers both assume a skewed underlying preference distribution , and in contrast our paper is focused on a uniform preference distribution .
the paper that is closest to the present paper is the independent work of mccabe - dansted , pritchard , and slinko @xcite .
the core insight there is the same as our core insight : that for appropriate numbers of candidates and voters it will hold that , if voter preferences are independent and uniform , then on a very large portion of cases one can , purely by making swaps between one s candidate of interest and people adjacently beating it within votes , make the candidate a condorcet winner ( i.e. , shift enough to precisely eliminate any shortfalls ) .
we now in the main text summarize the three major differences between @xcite and our work .
the footnotes to this summary contain additional discussion that , while important for completeness , may be safely omitted on a first reading . the first major difference between our work and that of mccabe - dansted , pritchard , and slinko is that their heuristic , dodgsonquick , outputs just a score .
although that score is correct on a large portion of inputs , their dodgsonquick does nt on any particular input ever guarantee that the score is correct .
in contrast , our @xmath35 heuristic is frequently _ self - knowingly _ correct on a large portion of inputs , it gives the right answer and guarantees that that answer is right .
mccabe - dansted , pritchard , and slinko state that their dodgsonquick is simpler than our @xmath35 .
however , this is precisely because dodgsonquick is just tossing out a score , rather than working to ensure self - knowingness .
if one changed their dodgsonquick to explicitly handle self - knowingness , it would become almost identical to our algorithm .
indeed , whenever our algorithm is self - knowingly correct , its computed score would coincide exactly with their algorithm s computed score if one modified their algorithm to correct for the `` third major difference '' mentioned below .
the second major difference regards range of application .
our analysis leaves both the number of candidates and the number of voters as variables . by doing so
, we produce a general bound flexible enough to ensure that the correctness ( indeed , the self - knowing correctness ) probability , under uniform - like inputs , goes asymptotically to one as long as the number of voters is at least some more - than - quadratic polynomial in the number of candidates . in sharp contrast , their claims cover just the subcase of this in which the number of candidates is held _ constant _ , while the number of voters increases.[multiblock footnote omitted ] a third and easy - to - miss major difference is that our dodgson score is indeed dodgson s score notion : the number of swaps needed to make the candidate a strictly beat each other candidate in a head - on - head comparison ( dodgson s crucial words relating to this are `` absolute majority '' @xcite ) , i.e. , become a condorcet winner in the standard sense of that term .
in contrast , @xcite , without mentioning that it is differing from the settled notion of dodgson score , uses as its definition of that concept a quite different score : the number of swaps needed to make the candidate _ tie or _
beat each other candidate in a head - on - head comparison . for clarity ,
let us refer to this notion as variantdscore .
( to see that this is what they define , one must carefully note their nonstandard definition of condorcet winner . )
the difference between dodgson score and variantdscore is not just an `` off by one '' in the score .
in fact , intervening candidates may have to be crossed to best close a shifted gap , and so variantdscore can vary from being the same as the dodgson score in some cases to being nontrivially smaller in other cases . on the other hand , due to the fact that both their and our algorithms focus on cases where purely adjacent swaps , at most one per voter , can triumph , this difference has just a relatively mild reflection in the formulas and algorithms of the two papers .
for example , it is this difference that results in their paper having expressions such as @xmath36 in contrast with , in our paper , expressions such as @xmath37.[multiblock footnote omitted ] like approximation algorithms , our algorithms are time efficient even in the worst case .
but approximation algorithms typically have worst - case guarantees on how far the answers they provide deviate from the optimal answers .
we by contrast are only interested in how frequently the algorithms are correct .
even when we study optimization problems , as with @xmath35 , we make no guarantees on how close actual dodgson scores are to the corresponding answers that @xmath35 provides in cases when the confidence is `` maybe . '' additionally ,
the key feature that separates our work from each of the above - mentioned related frameworks is the `` self - knowing '' aspect of our work .
the closest related concepts to this aspect of our analysis are probably those involving proofs to be verified , such as @xmath2 certificates and the proofs in interactive proof systems .
although our algorithms do not provide actual certificates , one could reasonably require a transcript of the execution of either of our algorithms .
with such a transcript , it would be easy to verify in deterministic polynomial time that the algorithm , in cases where the confidence is `` definitely , '' presented a valid proof .
put somewhat differently , our algorithms can easily be modified to give , in each `` definitely '' case , a specific set of swaps that achieve a dodgson score that is clearly optimal . by contrast ,
in interactive proof systems the methods for verifying the proofs involve a probabilistic , interactive process .
we do not consider interactive processes in this paper . in section [ sec : algor ] we discuss in more detail the differences between heuristics that find @xmath2 certificates and self - knowingly correct algorithms , but the most obvious difference is that , unless @xmath38 , the problem of verifying whether a given candidate is a dodgson winner for a given election is not even in @xmath2 .
as mentioned in the introduction , in dodgson s voting system each voter strictly ranks the candidates in order of preference . formally speaking , for @xmath13throughout
this paper we by definition do not admit as valid elections with zero candidates or zero voters a _ dodgson election _ is an ordered pair @xmath39 where @xmath21 is a set @xmath40 of candidates ( as noted earlier , we without loss of generality view them as being named by @xmath41 , @xmath42 @xmath15 ) and @xmath43 is a tuple @xmath44 of _ votes _ and a _ dodgson triple _ , denoted @xmath29 , is a dodgson election @xmath45 together with a candidate @xmath46 .
each vote is one of the @xmath47 total orderings over the candidates , i.e. , it is a complete , transitive , and antireflexive relation over the set of candidates .
we will sometimes denote a vote by listing the candidates in increasing order , e.g. , @xmath48 is a vote over the candidate set @xmath49 in which @xmath50 is preferred to @xmath51 and @xmath52 is preferred to ( @xmath51 and ) @xmath50 .
a candidate is never preferred to him- or herself . for vote @xmath53 and candidates @xmath54 , `` @xmath55 '' means `` in vote @xmath53 , @xmath20 is preferred to @xmath5 '' and `` @xmath56 '' means `` @xmath57 and there is no @xmath58 such that @xmath59 . ''
each dodgson election gives rise to @xmath60 _ pairwise races _
, each of which is created by choosing two distinct candidates @xmath61 and restricting each vote @xmath53 to the two chosen candidates , that is , to either @xmath62 or @xmath63 .
the winner of the pairwise race is the one that a strict majority of voters prefer . due to ties ,
a winner may not always exist in pairwise races .
a _ condorcet winner _ is any candidate @xmath5 that , against each remaining candidate , is preferred by a strict majority of voters . for a given election ( i.e. , for a given sequence of votes ) , it is possible that no condorcet winner exists .
however , when one does exist , it is unique .
dodgson s scores are in a sense an edit - distance notion based on the basic operation of swapping adjacent candidates in a voter s preference order . in particular , for any vote @xmath53 and any @xmath54 , if @xmath64 , let @xmath65 denote the vote @xmath66 , where @xmath66 is the same total ordering of @xmath21 as @xmath53 except that @xmath67 ( note that this implies @xmath68 ) . if @xmath69 then @xmath65 is undefined . in effect
, a swap causes @xmath5 and @xmath20 to `` switch places , '' but only if @xmath5 and @xmath20 are adjacent .
the _ dodgson score _ of a dodgson triple @xmath29 is the minimum number of swaps that , applied sequentially to the votes in @xmath43 , make @xmath43 a sequence of votes in which @xmath5 is the condorcet winner .
a _ dodgson winner _ is a candidate that has the smallest dodgson score .
this is the election system developed in the year 1876 by dodgson ( lewis carroll ) @xcite , and as noted earlier it gives victory to the candidate(s ) who are `` closest '' to being condorcet winners .
note that if no candidate is a condorcet winner , then two or more candidates may tie , in which case all tying candidates are dodgson winners .
several examples show how dodgson elections work , and hint at why they are hard , in general , to solve : consider an election having four candidates @xmath70 and one hundred votes in which sixty are @xmath71 and forty are @xmath72 . since @xmath20 is already ( i.e. , before any exchanges take place ) a condorcet winner , @xmath20 s dodgson score is @xmath73 .
thus @xmath20 is the dodgson winner .
now suppose in another election having the same candidates and the same number of voters as in the previous example that twenty voters each vote @xmath74 , @xmath75 , @xmath72 , @xmath76 , and @xmath77 , respectively . in this case
, there is no condorcet winner , so we calculate the dodgson score of each candidate
. consider candidate @xmath3 .
candidate @xmath3 beats @xmath20 by twenty votes of course , changes in the votes of as few as eleven voters can overcome such a shortfall .
candidate @xmath3 loses to @xmath5 by twenty votes .
and candidate @xmath3 loses to @xmath4 by twenty votes .
what is the fewest number of swaps needed to make @xmath3 a condorcet winner ? it might be tempting to make , for each of eleven votes of the form @xmath78 , the following transformation : @xmath79 .
but this transformation is not an allowed swap because only elements that are adjacent in the ordering imposed by the vote may be swapped at unit cost .
we can , however , make eleven of the following series of two swaps each : @xmath80 .
this can clearly be seen to be an optimal number of swaps in light of @xmath3 s initial vote shortfalls and note that every swap improves @xmath3 s standing against either @xmath4 or @xmath5 in a way that directly reduces a still - existing shortfall .
so the dodgson score of @xmath81 is twenty - two .
what makes it hard to calculate dodgson scores is what makes many combinatorial optimization problems hard : there is no apparent , simple way to locally determine whether a swap will lead to an optimally short sequence that makes the candidate of interest the condorcet winner .
for instance , if in calculating the dodgson score of @xmath3 we had come across votes of the form @xmath76 first , we might have made the following series of swaps , @xmath82 , which contain a swap between @xmath3 and @xmath20 .
but this series of swaps is not optimal because @xmath3 already beats @xmath20 , and because , as we saw , there is already a series of twenty - two swaps available , where each swap helps @xmath3 against some adversary that @xmath3 has not yet beaten , that makes @xmath3 a condorcet winner .
( however , there are instances of dodgson elections in which the only way for a candidate to become a condorcet winner is for it to swap with adversaries that the candidate is already beating , so one can not simply ignore this possibility . ) assuming that we did not at first see the votes that constitute this optimal sequence and instead hastily made swaps that did not affect @xmath3 s current standing against @xmath4 or @xmath5 , we could have , as soon as we had come across votes of the form @xmath71 , backtracked from the hastily made swaps that led toward a nonoptimal solution and , eventually , have correctly calculated the dodgson score . but as the size of elections increases , the amount of backtracking that a naive strategy might need to make in order to correct for any nonoptimal swaps combinatorially explodes . of course , computational complexity theory can give evidence of hardness that is probably more satisfying than are mere examples .
however , before turning to the computational complexity of dodgson - election - related problems , a couple of preliminary definitions are in order .
the class @xmath2 is precisely the set of all languages solvable in nondeterministic polynomial time .
@xmath0 can be equivalently defined either as the class of languages solvable in deterministic polynomial time with @xmath83 queries to an @xmath2 language or as the class of languages solvable in deterministic polynomial time via parallel access to @xmath2 .
@xmath0 was first studied by papadimitriou and zachos @xcite , received its current name from wagner @xcite , and has proven important in many contexts . in particular , it seems central in understanding the complexity of election systems @xcite .
all @xmath2 languages are in @xmath0 .
it remains open whether @xmath0 contains languages that are not in @xmath2 ; it does exactly if @xmath84 .
bartholdi , tovey , and trick @xcite define the following decision problems , i.e. , mappings from @xmath85 to @xmath86 , associated with dodgson elections .
we take the problem wordings from @xcite .
* decision problem : * @xmath87 + * instance : * a dodgson triple @xmath29 ; a positive integer @xmath88 . + * question * is @xmath89 , the dodgson score of candidate @xmath5 in the election specified by @xmath90 , less than or equal to @xmath88 ? * decision problem : * @xmath34 + * input : * a dodgson triple @xmath29 . + * question : * is @xmath5 a winner of the election ?
that is , does @xmath5 tie - or - defeat all other candidates in the election ?
bartholdi , tovey , and trick show that the problem of checking whether a certain number of changes suffices to make a given candidate the condorcet winner is @xmath2-complete and that the problem of determining whether a given candidate is a dodgson winner is @xmath2-hard @xcite .
hemaspaandra , hemaspaandra , and rothe show @xcite that this latter problem , as well as the related problem of checking whether a given candidate is at least as close as another given candidate to being a dodgson winner , is complete for @xmath0 .
hemaspaandra , hemaspaandra , and rothe s results show that determining a dodgson winner is not even in @xmath2 unless the polynomial hierarchy collapses .
this line of work has significance because the hundred - year - old problem of deciding if a given candidate is a dodgson winner was much more naturally conceived than the problems that were previously known to be complete for @xmath0 ( see @xcite ) .
in this section , we study the polynomial - time greedy algorithms ` greedyscore ` and ` greedywinner ` , which are given , respectively , as figure [ f : score ] ( page ) and figure [ f : winner ] ( page ) .
we show that both algorithms are self - knowingly correct in the sense of the following definition .
[ d : skc ] for sets @xmath91 and @xmath92 and function @xmath93 , an algorithm @xmath94 is _ self - knowingly correct for @xmath95 _ if , for all @xmath96 and @xmath97 , whenever @xmath98 on input @xmath99 outputs @xmath100 it holds that @xmath101 .
the reader may wonder whether `` self - knowing correctness '' is so easily added to heuristic schemes as to be uninteresting to study .
for example , if one has a heuristic for finding certificates for an np problem with respect to some fixed certificate scheme ( in the standard sense of np certificate schemes)e.g .
, for trying to find a satisfying assignment to an input ( unquantified ) propositional boolean formula then one can use the p - time checker associated with the problem to `` filter '' the answers one finds , and can put the label @xmath12 on only those outputs that are indeed certificates .
however , the problem studied in this paper does not seem amenable to such after - the - fact addition of self - knowingness , as in this paper we are dealing with heuristics that are seeking objects that are computationally much more complex than mere certificates related to np problems .
in particular , a polynomial - time function - computing machine seeking to compute an input s dodgson score seems to require about logarithmically many adaptive calls to sat . , among the problems that hemaspaandra , hemaspaandra , and
rothe @xcite prove complete for the language class @xmath0 is @xmath34 .
if one could , for example , compute dodgson scores via a polynomial - time function - computing machine that made a ( globally ) constant - bounded number of queries to sat , then this would prove that @xmath34 is in the boolean hierarchy @xcite , and thus that @xmath0 equals the boolean hierarchy , which in turn would imply the collapse of the polynomial hierarchy @xcite .
that is , this function problem is so closely connected to a @xmath0-complete language problem that if one can save queries in the former , then one immediately has consequences for the complexity of the latter . ]
we call ` greedyscore ` `` greedy '' because , as it sweeps through the votes , each swap it ( virtually ) does immediately improves the standing of the input candidate against some adversary that the input candidate is at that point losing to .
the algorithm nonetheless is very simple .
it limits itself to at most one swap per vote .
yet , its simplicity notwithstanding , we will eventually prove that this ( self - knowingly correct ) algorithm is very frequently correct .
our results in this section , since they are just stated as simply polynomial - time results ( see theorem [ th : grd - self ] below ) , are not heavily dependent on the encoding scheme used .
however , we will for specificity give a specific scheme that can be used .
note that the scheme we use will encode the inputs as binary strings by a scheme that is easy to compute and invert and encodes each vote as an @xmath102-bit substring and each dodgson triple as an @xmath103-bit string , where @xmath104 is the input to the encoding scheme . for a dodgson triple @xmath29 , our encoding scheme is as follows .
- : : the first bits of the encoding string contain @xmath105 , encoded as a binary string of length @xmath106,-bit strings rather than @xmath107-bit strings as we wish to have the size of the coding scale at least linearly with the number of voters even in the pathological @xmath108 case , in which each vote carries no information other than about the number of voters . ]
preceded by the substring @xmath109 .
- : : next in the encoding string are bits specifying the chosen candidate @xmath5 , encoded as a binary string of length @xmath106 .
- : : the rest of the bits of the encoding string give the votes , where each vote is encoded as a binary substring of length @xmath110 .
@xmath21 is the set of candidates .
@xmath43 is the list of votes .
@xmath46 is the candidate whose score the algorithm tries to compute .
@xmath111initialize counter variables , which represent : @xmath112 \leftarrow 0$]the number of votes by which @xmath20 is beating @xmath5 .
@xmath113 \leftarrow 0$]the number votes that may be `` greedily '' swapped against @xmath20 .
count the votes .
( each vote @xmath53 is treated as an array where @xmath114 $ ] is the least preferred candidate , @xmath115 $ ] is the second least preferred candidate , and so on , and @xmath116 $ ] is the most preferred candidate . )
@xmath117 @xmath118 \neq c$]subtract the `` pairwise votes '' for @xmath5 .
@xmath119 $ ] @xmath112 = { \mathit{deficit}}[d ] - 1 $ ] @xmath120 @xmath121$]count the opportunities to `` greedily swap . ''
@xmath122 $ ] @xmath113 \gets { \mathit{swaps}}[d ] + 1 $ ] @xmath123 @xmath124$]add the `` pairwise votes '' against @xmath5 .
@xmath119 $ ] @xmath112 = { \mathit{deficit}}[d ] + 1 $ ] @xmath125 calculate the score . if there are enough greedily swappable votes to overcome all positive deficits , then the sum over one plus half of each positive deficit ( rounded down ) is certainly the dodgson score of @xmath5 .
@xmath126 each @xmath111 [ l : begin ] @xmath112 \geq 0 $ ] @xmath127/2\rfloor + 1 $ ] @xmath112 \geq 2 \times { \mathit{swaps}}[d]$ ] @xmath128 [ l : end ] @xmath129 @xmath130 @xmath21 is the set of candidates .
@xmath43 is the list of votes .
we wish to test whether @xmath5 is a dodgson winner in election @xmath39 .
@xmath131 @xmath132 candidates @xmath111 @xmath133 @xmath134 @xmath135 @xmath136 @xmath137 return @xmath138 recall that the ` greedyscore ` and ` greedywinner ` algorithms are defined in figures [ f : score ] and [ f : winner ] .
we now describe what our algorithms do .
briefly put , on input @xmath104 , @xmath35 computes for each candidate @xmath111 the number of votes by which @xmath20 beats @xmath5 in the pairwise contest between them , and the number of votes where @xmath139 .
these numbers are stored in @xmath112 $ ] and @xmath113 $ ] , respectively .
for example , if 17 voters prefer @xmath20 to @xmath5 and 3 voters prefer @xmath5 to @xmath20 , then @xmath112 $ ] will be set to 14 . note that in that case a shift of 8 fan - of-@xmath20 voters would change the outcome to a victory for @xmath5 in this pairwise contest .
@xmath35 then takes as the dodgson score @xmath140 \geq 2 \times { \mathit{swaps}}[d]\}|| + \sum_{d \in c { \mathbf{-}}\{c\ } : { \mathit{deficit}}[d ] \geq 0 } ( \lfloor { \mathit{deficit}}[d]/2\rfloor + 1).\ ] ] @xmath35 outputs this number , paired with `` definitely '' if @xmath141 < 2\times{\mathit{swaps}}[d]]$ ] , or with `` maybe , '' otherwise .
\geq 0 } ( \lfloor { \mathit{deficit}}[d]/2\rfloor + 1)$ ] . however , for the conference version s algorithm , whenever the confidence was `` maybe '' the algorithm output a value that was a strict lower bound on the true score and so was certainly wrong .
in contrast , the above algorithm in the `` maybe '' case outputs a half - hearted stab at the score one that is sometimes too high , sometimes right , and sometimes too low . in terms of our theorems , the behavior on `` maybe '' cases does nt matter , as no promises are made about such cases . ]
turning to the ` greedywinner ` algorithm , it does the above for all candidates , and if while doing so ` greedyscore ` is never stumped , then ` greedywinner ` uses in the obvious way the information it has obtained , and ( correctly ) states whether @xmath5 is a dodgson winner of the input election . [ th : grd - self ] 1 .
[ it : scoreskc ] ` greedyscore ` is self - knowingly correct for _ score_. 2 .
[ it : winnerskc ] ` greedywinner ` is self - knowingly correct for @xmath34 .
[ it : rt ] ` greedyscore ` and ` greedywinner ` both run in polynomial time . in item
[ it : scoreskc ] s statement , as set in section [ sec : def ] in the statement of the ` dodgsonscore ` problem , _ score _ denotes the dodgson score . now , suppose that @xmath35 , on input @xmath29 , returns @xmath12 as the second component of its output .
then , as inspecting lines [ l : begin][l : end ] of the algorithm makes clear , every candidate @xmath111 for which @xmath112 \geq 0 $ ] must also have @xmath112 < 2 \times { \mathit{swaps}}[d]$ ] . in this case , note that the algorithm sets its @xmath142 variable to @xmath143 \geq 0 } ( \lfloor { \mathit{deficit}}[d]/2\rfloor + 1)$ ] . for this value of @xmath142
to actually be the dodgson score of @xmath5 , we must show ( a ) that we can by performing @xmath142 swaps turn @xmath39 into an election in which @xmath5 is the condorcet winner and ( b ) that by performing fewer than @xmath142 swaps we can not make @xmath5 a condorcet winner .
both claims depend on the following observation : let @xmath53 be a vote having some candidate @xmath20 such that @xmath139 .
then swapping @xmath5 and @xmath20 would decrease by two the difference between the number of votes where @xmath5 is preferred @xmath20 and the number of votes where @xmath20 is preferred @xmath5 .
also , @xmath5 s standing against any candidate other than @xmath20 would not be affected by this swap .
so , regarding the number of swaps needed to make @xmath5 beat some @xmath111 , let @xmath144 be the set of votes in @xmath43 in which @xmath145 .
if @xmath112 $ ] is , by line [ l : begin ] , nonnegative ( if @xmath112 $ ] is negative then @xmath5 already beats @xmath20 and the number of swaps needed is trivially 0 ) , and if @xmath146/2\rfloor + 1 $ ] , then we can make @xmath5 beat @xmath20 by choosing exactly @xmath147/2\rfloor + 1 $ ] votes in @xmath144 and swapping the positions of @xmath5 in @xmath20 in these votes .
but @xmath113 $ ] is precisely @xmath148 and is , by our @xmath112 < 2 \times { \mathit{swaps}}[d]$ ] assumption , at least @xmath147/2\rfloor + 1 $ ] .
thus , by summing over all such @xmath111 , @xmath142 is enough swaps to make @xmath5 a condorcet winner , and we have satisfied ( a ) . to see ( b )
, suppose that it is possible to make @xmath5 a condorcet winner with _ fewer _ than @xmath149 \geq 0 } ( \lfloor { \mathit{deficit}}[d]/2\rfloor + 1)$ ] swaps . then for some @xmath111 such that @xmath112 \geq 0 $ ] it must hold that at most @xmath147/2 \rfloor$ ] of these swaps are applied to @xmath5 s standing against @xmath20 .
but then , since as noted above one swap changes the deficit between @xmath5 and @xmath20 by exactly two , we do not have enough swaps to make @xmath5 beat @xmath20 .
so we must conclude under our current supposition namely , that @xmath35 returns @xmath12 as the second component of its output that @xmath142 is the optimal number of swaps needed to make @xmath5 a condorcet winner . for item
[ it : winnerskc ] , clearly ` greedywinner ` correctly checks whether @xmath5 is a dodgson winner if every call it makes to @xmath35 correctly calculates the dodgson score .
` greedywinner ` then returns @xmath12 exactly if each call it makes to ` greedyscore ` returns @xmath150 @xmath151but , by item [ it : scoreskc ] , ` greedyscore ` is self - knowingly correct .
item [ it : rt ] follows from a straightforward analysis of the algorithm .
the total number of line - executions in a run of ` greedyscore ` is clearly @xmath152 , and for ` greedywinner ` is , including the line - executions within the subroutine calls , @xmath153 .
so these are indeed polynomial - time algorithms .
time to look up a key in either @xmath154 or @xmath155 and @xmath156 time to update the associated value , and each @xmath157 operation takes @xmath158 time ) the running time of the algorithm might be more fairly viewed as @xmath159 ( respectively , @xmath160 ) , though in any case it certainly is a polynomial - time algorithm . ] note that ` greedywinner ` could easily be modified into a new polynomial - time algorithm that , rather than checking whether a given candidate is the winner of the given dodgson election , finds all dodgson winners by taking as input a dodgson election alone ( rather than a dodgson triple ) and outputting a list of _ all _ the dodgson winners in the election . this modified algorithm on any dodgson election @xmath39
would make exactly the same calls to ` greedyscore ` that the current ` greedywinner ` ( on input @xmath104 , where @xmath46 ) algorithm makes , and the new algorithm would be accurate whenever every call it makes to ` greedyscore ` returns @xmath12 as its second argument .
thus , whenever the current ` greedywinner ` would return a @xmath12 answer so would the new dodgson - winner - finding algorithm ( when their inputs are related in the same manner as described above ) .
these comments explain why in the title ( and abstract ) , we were correct in speaking of `` _ _ finding _ _ dodgson - election winners '' ( rather than merely recognizing them ) .
in this section , we prove that , as long as the number of votes is much greater than the number of candidates , ` greedywinner ` is a frequently self - knowingly correct algorithm . throughout this section ,
regard @xmath161 as a sequence of @xmath16 independent observations of a random variable @xmath162 whose distribution is uniform over the set of all votes over a set @xmath163 of @xmath15 candidates , where @xmath162 can take , with equal likelihood , any of the @xmath47 distinct total orderings over @xmath21 .
( this distribution should be contrasted with such work as that of , e.g. , @xcite , which in a quite different context creates dependencies between voters preferences . ) the main intuition behind theorem [ th : main - tech ] is that , in any election having @xmath15 candidates and @xmath16 voters , and for any two candidates @xmath5 and @xmath20 , it holds that , in exactly half of the ways @xmath53 a voter can vote , @xmath55 , but for exactly @xmath164 of the ways , @xmath139 .
thus , assuming that the votes are chosen independently of each other , when the number of voters is large compared to the number of candidates , with high likelihood the number of votes @xmath53 for which @xmath57 will hover around @xmath165 and the number of votes for which @xmath139 will hover around @xmath166 .
this means that there will ( most likely ) be enough votes available for our greedy algorithms to succeed .
[ th : main - tech ] for each @xmath167 , the following hold .
let @xmath168 . 1 .
[ it : commonsense ] let @xmath43 satisfy @xmath169 . for each @xmath28 , if for all @xmath111 it holds that @xmath170 and @xmath171 then @xmath172 .
[ it : primarybound ] for each @xmath173 such that @xmath174 , @xmath175 , ( i.e. , all @xmath17 dodgson elections having @xmath15 candidates and @xmath16 voters have the same likelihood of being chosen ) .
it : scorebound ] for each @xmath46 , @xmath176 , .
[ it : winnerbound ] @xmath177 ) } < 2(m^2-m){e^{\frac{-n}{8m^2}}}$ ] , . for item
[ it : commonsense ] , @xmath178 , so , if @xmath179 then either @xmath5 already beats @xmath20 or if not then the defection of more than @xmath180 votes from preferring-@xmath20-to-@xmath5 to preferring-@xmath5-to-@xmath20 would ( if such votes exist ) ensure that @xmath5 beats @xmath20 . if @xmath181 then ( keeping in mind that we have globally excluded as invalid all cases where at least one of @xmath16 or @xmath15 equals zero ) @xmath182 , and so @xmath35 will be able to make enough swaps ( in fact , and this is critically important in light of the ` greedyscore ` algorithm
, there is a sequence of swaps such that any vote has at most one swap operation performed on it ) so that @xmath5 beats @xmath20 .
item [ it : primarybound ] follows from applying the union bound ( which of course does not require independence ) to lemma [ l : realbounds ] , which is stated and proven below .
item [ it : scorebound ] follows from item [ it : commonsense ] and from applying item [ it : primarybound ] and the union bound to @xmath183 item [ it : winnerbound ] follows from item [ it : commonsense ] and from applying item [ it : primarybound ] and the union bound to @xmath184 ( note that @xmath185 ) .
we now turn to stating and proving lemma [ l : realbounds ] , which is needed to support the proof of theorem [ th : main - tech ] .
lemma [ l : realbounds ] follows from the variant of chernoff s theorem @xcite stated as theorem [ t : chernoff ] .
[ t : chernoff ] let @xmath186 be a sequence of mutually independent random variables .
if there exists a @xmath187 \subseteq \mathbb{r}$ ] such that , for each @xmath188 , @xmath189 then for all @xmath190 where @xmath191 it holds that @xmath192 .
[ l : realbounds ] 1 .
[ l : real - one ] @xmath193 .
[ l : real - two ] @xmath194 .
[ l : real - one ] . for each @xmath195 , define @xmath196 as @xmath197 then @xmath198 exactly if @xmath199 since @xmath200 , setting @xmath201 and @xmath202 in theorem [ t : chernoff ] yields the desired result .
[ l : real - two ] .
for each @xmath195 , define @xmath196 as @xmath203 then @xmath204 if and only if @xmath205 if and only if @xmath206 since @xmath207 , setting @xmath201 and @xmath208 in theorem [ t : chernoff ] yields the desired result .
theorem [ t : main ] captures the exact statement of our main results that , in the introduction , we promised to establish .
[ t : main ] 1 .
[ it : main : skc ] for each ( election , candidate ) pair it holds that if ` greedywinner ` outputs @xmath12 as its second output component , then its first output component correctly answers the question , `` is the input candidate a dodgson winner of the input election ? ''
[ it : main : fskc ] for each @xmath13 , the probability that a dodgson election @xmath14 selected uniformly at random from all dodgson elections having @xmath15 candidates and @xmath16 votes ( i.e. , all @xmath17 dodgson elections having @xmath15 candidates and @xmath16 votes have the same likelihood of being selected ) has the property that there exists at least one candidate @xmath5 such that ` greedywinner ` on input @xmath24 outputs @xmath25 as its second output component is less than @xmath26 .
theorem [ t : main].[it : main : skc ] follows from theorem [ th : grd - self].[it : winnerskc ] .
theorem [ t : main].[it : main : fskc ] follows from theorem [ th : main - tech].[it : winnerbound ] .
the dodgson voting system elegantly satisfies the condorcet criterion . although it is @xmath2-hard ( and so if @xmath209 is computationally infeasible ) to determine the winner of a dodgson election or
compute scores for dodgson elections , we provided heuristics , ` greedywinner ` and ` greedyscore ` , for computing winners and scores for dodgson elections .
we showed that these heuristics are computationally simple .
we also showed that , for a randomly chosen election of a given size , if the number of voters is much greater than the number of candidates ( although the number of voters may still be polynomial in the number of candidates ) , then we get with exceedingly high likelihood we get the right answer and we know that the answer is correct .
we consider the fact that one can prove extremely frequent , self - knowing success even for such simple greedy algorithms to be an _
advantage_it is good that one does not have to resort to involved algorithms to guarantee extremely frequent , self - knowing success .
nonetheless , it is natural to wonder to what degree these heuristics can be improved
. what would be the effect of adding , for instance , limited backtracking or random nongreedy swaps to our heuristics ? regarding our analysis , in the distributions we consider , each vote is cast independently of every other .
what about distributions in which there are dependencies between voters ? though definition [ d : skc ] rigorously defines `` self - knowingly correct , '' we have been using `` frequent '' more informally in uses such as `` frequently self - knowingly correct''the level of frequency is specified in each case simply by whatever frequency our results prove .
it is natural to wonder whether one can state a general , abstract model of what it means to be frequently self - knowingly correct .
that would be a large project ( that we heartily commend as an open direction ) , and here we merely make a brief definitional suggestion for a very abstract case in some sense simpler to formalize than dodgson elections , as dodgson elections have both a voter - set size and a candidate - set size as parameters , and have a domain that is not @xmath85 but rather is the space of valid dodgson triples namely the case of function problems where the function is total and the simple parameter of input - length is considered the natural way to view and slice the problem regarding its asymptotics .
such a model is often appropriate in computer science ( e.g. , a trivial such problem leaving tacit the issues of encoding integers as bit - strings is @xmath210 , and harder such problems are @xmath211 equals the number of primes less than or equal to @xmath16 and @xmath212 ) . 1 .
we say that @xmath213 is _ frequently self - knowingly correct for @xmath215 _ if @xmath216 2 .
let @xmath217 be some polynomial - time computable mapping from @xmath218 to the rationals .
we say that @xmath213 is _ self - knowingly correct for @xmath215 _ if @xmath219 since the probabilities that the above definition is tracking may be quite encoding dependent , the second part of the above definition allows us to set more severe demands regarding how often the heuristic ( which , being self - knowingly correct , always has the right output when its second component is `` definitely '' ) is allowed to remain uncommitted .
one sharp contrast between this framework and impagliazzo s @xcite notion of heuristic polynomial time is that his heuristic algorithms are not required to _ ever _ correctly assert their correctness . in his model
, one will know that one is often correct , but on each specific run one in general will have no clue as to whether the proffered answer is correct . in an undergraduate project in one of our courses , g. goldstein , d. berlin ,
k. osipov , and n. rutar proposed a more complex greedy algorithm for dodgson elections that possessed the self - knowing correctness property , and experimentally observed that their algorithm was often successful .
the present paper was motivated by their exciting experimental insight , and seeks to prove rigorously that a greedy approach can be frequently successful on dodgson elections .
we also thank the anonymous conference and journal referees for their comments , which greatly improved the clarity and readability of this article .
d. brown . a probabilistic analysis of a greedy algorithm arising from computational biology . in _ proceedings of the 12th annual acm - siam symposium on discrete algorithms
_ , pages 206207 .
acm press , 2001 .
v. conitzer and t. sandholm .
nonexistence of voting rules that are usually hard to manipulate . in _ proceedings of the 21st national conference on artificial intelligence _ , pages 627634 .
aaai press , july / august 2006 .
c. dodgson . a method of taking votes on more than two issues .
pamphlet printed by the clarendon press , oxford , and headed `` not yet published '' ( see the discussions in @xcite , both of which reprint this paper ) , 1876 .
g. erdlyi , l. hemaspaandra , j. rothe , and h. spakowski . on approximating optimal weighted lobbying , and frequency of correctness versus average - case polynomial time .
technical report tr-914 , department of computer science , university of rochester , rochester , ny , march 2007 .
p. faliszewski , e. hemaspaandra , and l. hemaspaandra .
the complexity of bribery in elections . in _ proceedings of the 21st national conference on artificial intelligence _ , pages 641646 .
aaai press , july 2006 .
p. faliszewski , e. hemaspaandra , and l. hemaspaandra .
how hard is bribery in elections ?
technical report tr-895 , department of computer science , university of rochester , rochester , ny , april 2006 .
revised , september 2006 .
faliszewski , e. hemaspaandra , l. hemaspaandra , and j. rothe .
llull and copeland voting broadly resist bribery and control . in _ proceedings of the 22nd national conference on artificial intelligence_. aaai press , july 2007 .
to appear .
a. goldberg and a. marchetti - spaccamela . on finding the exact solution of a zero - one knapsack problem .
in _ proceedings of the 16th acm symposium on theory of computing _ , pages 359368 .
acm press , april 1984 .
e. hemaspaandra and l. hemaspaandra .
computational politics : electoral systems . in _ proceedings of the 25th international symposium on mathematical foundations of computer science _ , pages 6483 .
springer - verlag _ lecture notes in computer science # 1893 _ , august / september 2000 . c. homan and l. hemaspaandra .
guarantees for the success frequency of an algorithm for finding dodgson - election winners . in _ proceedings of the 31st international symposium on mathematical foundations of computer science _ , pages 528539 .
springer - verlag _ lecture notes in computer science # 4162 _ , august / september 2006 .
a. kaporis , l. kirousis , and e. lalas .
the probabilistic analysis of a greedy satisfiability algorithm . in _ proceedings of the 10th annual european symposium on algorithms _ , pages 574585 .
springer - verlag _ lecture notes in computer science # 2461 _ , 2002 .
j. mccabe - dansted , g. pritchard , and a. slinko .
approximability of dodgson s rule . in u.
endriss and j. lang , editors , _ proceedings of the 1st international workshop on computational social choice _ , pages 331344 .
universiteit van amsterdam , december 2006 .
available online at .
m. protasi and m. talamo . a new probabilistic model for the study of algorithmic properties of random graph problems . in _ proceedings of the 4th conference on fundamentals of computation theory _ , pages 360367
springer - verlag _ lecture notes in computer science # 158 _ , 1983 . c. papadimitriou and s. zachos .
two remarks on the power of counting . in
_ proceedings of the 6th gi conference on theoretical computer science _ , pages 269276 .
springer - verlag _ lecture notes in computer science # 145 _ , 1983 .
h. spakowski and j. vogel .
@xmath221-completeness : a classical approach for new results . in _ proceedings of the 20th conference on foundations of software technology and theoretical computer science _ , pages 348360 .
springer - verlag _ lecture notes in computer science # 1974 _ , december 2000 .
h. spakowski and j. vogel .
the complexity of kemeny s voting system . in _ proceedings of the workshop argentino
de informtica terica _ , pages 157168 .
volume 30 of _
anales jornadas argentinas de informtica e investigacin operativa _ , sadio , september 2001 . | in the year 1876 the mathematician charles dodgson , who wrote fiction under the now more famous name of lewis carroll , devised a beautiful voting system that has long fascinated political scientists . however , determining the winner of a dodgson election is known to be complete for the @xmath0 level of the polynomial hierarchy .
this implies that unless @xmath1 no polynomial - time solution to this problem exists , and unless the polynomial hierarchy collapses to @xmath2 the problem is not even in @xmath2 .
nonetheless , we prove that when the number of voters is much greater than the number of candidates
although the number of voters may still be polynomial in the number of candidates a simple greedy algorithm very frequently finds the dodgson winners in such a way that it `` knows '' that it has found them , and furthermore the algorithm never incorrectly declares a nonwinner to be a winner .
= currsize [ section ] [ definition]theorem [ definition]scratch definition [ definition]corollary [ definition]lemma [ definition]side effect [ definition]proposition |
during the mid-19 century , the use of light microscopy ( lm ) in pathology grew exponentially , driven primarily by improved optics , reduced costs , and increased availability . to this day
the practice of surgical pathology is primarily interested in the analysis of tissue and cellular structures ( and alterations thereof ) and begins with a careful gross examination of the excised tissue using the naked eye .
gross examinations are followed by a more exhaustive examination of histologic preparations of tissue sections using a compound light microscope .
ancillary tools , such as immunohistochemistry , flow cytometry , and electron microscopy , are variably deemed necessary for the diagnosis of certain diseases ; however , the histologic findings are usually the most important indicator of pathologic dysfunction , and lm remains the single most used instrument and method of investigation in the arsenal of pathology tools .
regardless of the degree or index of clinical suspicion , a diagnosis of cancer can not be definitively established , and definitive therapy should not be undertaken , in the absence of a tissue diagnosis .
most hospitals , health networks , and private pathology practices have policies or regulations in place supporting this practice , and they are regularly monitored by hospital tissue committees or accrediting agencies .
thus , a pathologist 's primary tool ( i.e. , compound light microscope ) , technique ( i.e. , histologic tissue examination ) , and general workflow ( i.e. , rendering a definitive diagnosis based primarily on lm examinations of glass slide - mounted tissue sections ) have remained essentially unaltered since the second half of the 19 century .
as such , the analog realm of pathology appears superannuated compared to contemporary medical counterparts ( i.e. , radiology , surgery , and hemato - oncology ) , which have witnessed radical , technologically - driven transformations .
however , pathologists may soon be able to catch up with their tech - savvy medical colleagues , thanks to advancements in lm methods , which are already being used for the mapping of point - to - point connectivity between all anatomical regions in animal brains .
this emergent field , commonly referred to as connectomics , is leveraging automated lm instruments and computational methods in a race to complete a connectivity map of a whole - mouse brain , in hopes of providing the larger scientific community with an online atlas for viewing the entire anatomical datasets .
it has already been shown that current , automated lm methods are fully capable of creating high - resolution , high - throughput anatomic models .
traditional lm techniques utilize linear ( i.e. , one - photon ) absorption processes for contrast generation , and are therefore limited to areas at and near the tissue surface for high - resolution imaging . at tissue depths > 100 m , the effects of light scattering begin to limit the resolution and the images produced become blurry . in recent years , advanced imaging techniques and novel microscopic technologies have emerged as potential alternatives to lm .
these advanced imaging modalities , which include diffraction - limited ( e.g. , confocal , multi - photon , and 4pi microscopy ) and subdiffraction techniques ( e.g. , photo - activated localization , stochastic optical reconstruction , and stimulated emission depletion microscopy ) , are advantageous because they enable nondestructive , high - resolution , and/or ultra - sensitive imaging , down to the molecular level .
many of these imaging methods are capable of producing high - resolution , three - dimensional ( 3d ) datasets from sampled tissues .
more recently , additional computational imaging methods have been developed for microscopic analysis , including lens - free digital holographic , fourier ptychographic , and tomographic techniques .
all these methods have the capacity to exceed diffraction limits that traditionally hamper lm , and can thus produce high - resolution images .
theoretically , some of them can be combined to create low - cost imaging systems for clinical pathology ; however , none currently exist in commercial form and none of the aforementioned methods are adequately designed or optimized for high - throughput automation .
within the context of automated lm methods for 3d imaging , there are several approaches that can already be applied to clinical pathology .
they are divided into two categories , based on the method of tissue clearing : block - face / tissue - sectioning versus chemical clearing .
chemical clearing methods are beyond the scope of this review ; however , the former approach is quite similar to traditional histologic techniques , and we shall briefly review two bright - field , tissue - sectioning instruments that are currently in use .
knife - edge scanning microscopy ( kesm ) and micro - optical sectioning tomography ( most ) are both designed to perform imaging and sectioning in a single , simultaneous process : bright - field , line - scan imaging sensors and diamond - knife embedded ultramicrotomes are utilized for automated sectioning and 3d imaging of resin - embedded tissue .
the former is capable of generating 155 terabytes of data per day , while the latter has demonstrated an ability to generate > 8 terabytes of data in approximately 10 days .
most performs imaging in reflection , which requires the use of en bloc reflective stains ( i.e. , golgi stain ) that are highly specific .
furthermore , reflective stains mark numerous features that are below the diffraction limit and can not be resolved with the standard light microscopes using visible light .
kesm , on the other hand , uses transmission illumination to perform imaging , and thus it is not reliant on reflective stains .
in addition , kesm 's utilization of the diamond knife as both sectioning and optical instrument provides greater illumination near the knife edge , improving imaging speed and boosting the signal - to - noise ratio . finally , kesm is already available as a commercial service , whereas most has not yet been adapted for commercial utilization .
automated lm methods for 3d imaging are intriguing for clinical pathology because it can generate comprehensive , high - resolution , volumetric datasets of cellular architecture and morphology in a high - throughput fashion .
furthermore , many , if not all , of these 3d imaging modalities are heavily reliant on advanced cognitive technologies such as machine / computer vision and machine learning .
these advanced technologies , derived from decades of cutting - edge artificial intelligence research , are optimally suited for deployment within the realm of digital pathology because they enable algorithmic approaches to image analysis , which have been shown to be beneficial in numerous contexts ( e.g. , detection , segmentation , and classification ) .
if the resolutions , throughput speeds , and data processing pipelines of automated lm 3d imaging techniques continue to improve over time , it also holds true that these techniques will approach the levels of efficiency currently offered by contemporary histopathology and traditional lm .
sometime , in the not - so - distant future , tissue biopsies and tissue blocks from resected organs may be altogether replaced by whole - specimen or whole - organ imaging , thereby transforming the field of pathology .
the implications of automated , high - throughput , quantitative 3d lm analysis of tissue specimens will likely culminate in a major paradigm shift for the practice of pathology
| the field of pathology has used light microscopy ( lm ) extensively since the mid-19th century for examination of histological tissue preparations . this technology has remained the foremost tool in use by pathologists even as other fields have undergone a great change in recent years through new technologies . however , as new microscopy techniques are perfected and made available , this reliance on the standard lm will likely begin to change .
advanced imaging involving both diffraction - limited and subdiffraction techniques are bringing nondestructive , high - resolution , molecular - level imaging to pathology .
some of these technologies can produce three - dimensional ( 3d ) datasets from sampled tissues .
in addition , block - face / tissue - sectioning techniques are already providing automated , large - scale 3d datasets of whole specimens .
these datasets allow pathologists to see an entire sample with all of its spatial information intact , and furthermore allow image analysis such as detection , segmentation , and classification , which are impossible in standard lm .
it is likely that these technologies herald a major paradigm shift in the field of pathology . |
the question of why one person develops high blood pressure ( bp ) and another does not has long been controversial .
for example , freud in the 1930s hypothesized that keeping one 's anger in will cause bp to rise .
theories of stress and disease came a bit later , and a multitude of experimental and field studies show that stress is indeed linked , both epidemiologically and causally , to physiological dysregulation and chronic illness .
the model we present here builds on this research but attempts to take it a step further .
it is welldocumented that stress ( broadly and variously defined ) is a risk factor for hypertension ( htn ) and other cardiovascular disease ( cvd ) , including events and all - cause mortality [ 18 ] .
the mechanisms that underlie this association , however , have not been as clearly specified .
this is due , in part , to the ambiguity concerning the nature of stress .
the construct has been used and measured in many different ways , with little standardization across studies . moreover ,
the notions of chronic and acute stress , and how they relate to one another , have not been clearly delineated , with little theoretical work targeted at identifying the respective domains of each . to the extent that we believe that stress
however it is defined is indeed a risk factor for htn , it is crucial that we identify the pathways through which it may lead to sustained elevated bp if we are to develop effective interventions to reduce stress , with the aim of reducing high bp and associated long term disease risk . in this paper , we will attempt to provide specifications concerning the respective domains of acute and chronic stress and to present a model and review evidence that points to rumination
the cognitions and negative affect that stem from the experience of an acute stressor as a key mechanism through which stress exerts its pejorative effects on autonomic functioning and the resting bp level .
that is , a discrete event that stems from some aspect of one 's immediate situation , and , for the most part , has an impact on the person only to the extent that ( 1 ) it is perceived , ( 2 ) the perception leads to negative cognitions and affect , and ( 3 ) that these cause perturbations in the various physiological stress - mediating systems ( psmss ) including autonomic , hypothalamic - pituitary - adrenal ( hpa ) , and immune systems . by this definition ,
an acute stressor may also arise internally ( i.e. , a mental representation ) and provoke continuing thoughts and emotions , and , concomitantly , their effects on the autonomic and other psmss .
we have noted for the most part as some acute stressors will have effects independent of this mechanism .
for example , a pin - prick may cause such perturbations , but via different , more direct , channels not involving cognition . in this paper , we focus on those acute stressors that exert their effects on the psmss via the ruminative ( perception - negative cognition / affect ) pathway . in research examining stress effects on bp , acute stressors have mostly been defined as standardized laboratory tasks such as mental arithmetic or the cold pressor .
we and others have used an anger recall task , which we have shown is similarly effective in raising the bp and hr , decreasing heart rate variability ( hrv ) , increasing cortisol , and other outcomes including impaired endothelial function [ 913 ] .
we do not currently have a fully useful definition and circumscribed domain for chronic stress ; in the literature , it often appears to be a case of we know it when we see it .
thus , caregiver status , low socioeconomic status ( ses ) , an unpleasant low - paying job , and a stint in jail all these seem like obvious sources of chronic stress . but what are the defining characteristics ? certainly , there is a sense that part of it is the ongoingness of the situation and part is the pervasiveness of the situation .
thus , one may find oneself continuously in the midst of the situation being in prison is an extreme example , finding oneself further and further in debt with creditors calling at all hours is another .
it is not necessarily the case , however , that even under such pervasive and ongoing conditions , one is continuously attending to the situation .
thus , the individual instances or moments that do invoke the situation and do provoke a reaction the creditor 's phone call , for example , or a worry episode regarding mounting dept are intermittent , with a greater or lesser frequency depending on the nature of the chronic stressor .
and we would regard the individual instances as examples of acute stressors , per the previous section , that arise from ( are potentiated by ) the chronically stressful context .
for the purposes of this paper , as with acute stress , we define chronic stress as a situational variable . in this instance , however ,
situational refers to a background that increases the likelihood that acute stressors relating to the chronic stress situation arise .
( acute stressors may also , of course , arise from sources not related to one 's chronic stress ) .
thus , we propose that chronic stress matters largely to the extent that it consists of a background situation that gives rise to acute stressors , with these acute stressors having an impact on the psmss .
it is important to note that this chronically stressful situation may affect one 's bp via other pathways ; thus , chronic stress has effects beyond merely being the source of acute stressors .
for example , the parental caretaker may begin eating poorly and gain weight , and may increase salt intake , each of which will affect the bp via other pathways ( i.e. , health - related behaviors , in this instance , although these may arise in response to both the chronic stress background and the acute stressors that may arise ) .
so far , we have stated that acute stressors arise from environmental conditions , and often more frequently when the environmental conditions are characterized as chronically stressful .
an individual exposed to such a situation will likely be exposed to reminders of the situation such as the creditor 's phone call and may be apt to periodically recall the terrible conditions even without environmental cues .
we suggest that there is functionally no differentiation between these reminders and the effects of the acute stressors , both produce acute stress , insofar as each leads to negative cognitions and affect and perturbations in the psmss .
posttraumatic stress disorder ( ptsd ) offers an example of this , albeit an extreme one . in some cases , a single event , even a brief one , may lead to persistent effects on cognition and affect .
these effects can persist for decades as individuals with ptsd continue to deal with intrusive thoughts and emotions that recreate representations of the event ( and associated stress and other physiological responses ) .
in fact , evidence suggests that the frequency of these reexposures to the original event is strongly related to ptsd severity .
a limitation of most acute stress models is that they do not take into account the duration of exposure .
thus , a person that exhibits a larger bp response to an acute stressor is presumed to be at greater risk for htn than one who exhibits smaller responses .
stressor - related thoughts that may emerge over time as a result of ( but temporally distal from ) the acute stressor can also cause acute elevations in the psmss .
moreover , these physiological responses may persist as long as the recurring cognitions / emotions ( e.g. , anger or anxiety ) persist .
relevant to this , glynn and colleagues have shown that recall of a laboratory stressor to which the subject had been exposed in a previous session produced bp responses comparable to those which occurred when the participant was exposed to the stressor itself .
thus , the cognitive and affective sequelae of the acute stressor may have as great an effect on the psmss as the original initiating event , long after that event has occurred ( with the limits on the ruminative responses likely only constrained by the verisimilitude and intensity of the internal representation ) .
we thus broadly define rumination as affect - laden cognitions that ( 1 ) result from exposure to an acute stressor ( external in the environment or an internally generated representation ) ; ( 2 ) in most individuals cause acute activation of relevant physiological stress - mediation systems ; ( 3 ) outlast the original stimulus / acute stressor ( i.e. , the ruminative thoughts and accompanying negative affect and their effect on physiological activation persist even after the stressor itself is no longer present ) ; ( 4 ) often reemerge in some , over quite long periods of time ; ( 5 ) typically do not lead to productive solutions , but rather resemble an endless loop , that does not lead to insight or resolution of the issue .
we also note that , in addition to the term rumination , there are many other related constructs .
some are often used interchangeably , such as perseverative cognitions , whereas others imply some differences .
for example , distinct from rumination , which typically concerns past stressful events , one may experience anticipatory negative cognitions and affect concerning future events , which are often termed worry or anxiety ; these states , too , can produce sustained effects on the psmss .
it is as yet unclear whether these are distinctions that make a difference in terms of physiological consequences and/or htn risk .
we thus propose that it is largely the cumulative duration of exposure to this persistent representation of the acute stressor , with its attendant effects on , and eventual potential dysregulation of the stress - mediating physiological systems that contribute to sustained elevated bp and to htn .
that is , actual stressors are important , but that the ruminative representations ( and their consequences ) contribute more to observed psmss responses and to htn risk .
figure 1 shows a schematic of a model that illustrates these predictions and pathways .
. chronic stress ( a situational factor ) sets the stage for and gives rise to the occurrence of acute stressor incidents that , depending on their nature , may lead directly to activation of the psmss ( e.g. , a pinprick ) or may lead to ruminative thoughts and emotions that in turn may produce psmss responses .
thus , many variables that have been implicated in stress effects are accounted for before they are perceived as stressful ; and rumination is affected by the composite as a whole .
for example , the perceived availability of social support operates before appraisal and thus , in some individuals , reduces the likelihood that the stimulus will activate ruminative thoughts and affect .
the thoughts and emotions that are evoked by the acute stressor affects the psmss , causing acute perturbations in the various systems . in those who tend to ruminate ( more frequently and/or for longer duration ) , the effects on the psmss will be prolonged , and thus , the individual is exposed to the effects of the stressor for a more sustained period of time , which may lead to a resetting of homeostatic set points , including elevated resting bp .
herein , lies the critical role of duration , which many models of acute stress tend to ignore .
the dashed arrow shows a feedback mechanism such that the autonomic activation that results as a function of rumination itself becomes a stimulus that potentiates the negative emotions and cognitions ; these in turn maintain the autonomic activation , and so on .
distraction as a potential moderator of this loop leading to termination of the rumination and its effects on the psmss when a distractor of sufficient potency to drive out the ruminative thoughts and replace them with others is encountered .
we also show a moderating effect of neural inhibition by the prefrontal cortex on the association between acute stress and rumination / worry .
finally , a number of other pathways known to exist , but not addressed as central to this paper , are depicted in greyscale ( as rumination is not the only pathway by which stress may affect htn ) .
specifically , addressing these additional pathways is , however , beyond the scope of this paper .
one issue is whether the proposed model represents a mere restatement of existing theoretical formulations or offers practical and/or theoretical advance .
we are aware that many of the definitions and relationships among constructs herein have been proposed and discussed by others , many of whom developed theories that had a major impact on how stress was conceptualized .
thus , the models proposed by selye and by lazarus and folkman are progenitors of the current proposed model .
there are , as well , many other theories that address aspects of the questions at issue , and we have borrowed from some of these .
the model as we present it , however , has been informed by recent advances in the psychophysiological , health , and social psychological literatures , and addresses issues not formerly considered . moreover ,
this model is not intended to propose a general theory of stress ; rather , the goal is to understand the factors that lead chronic stress to be a substantial risk factor for htn , and the model we present focuses on this problem and the central role of rumination .
although we have been discussing rumination as a largely active process , data from several lines of research suggest that individuals may be unaware of some portion potentially a large portion of their stress - related cognitions . yet , even these unconscious thoughts and feelings can have an activating effect on the autonomic and other stress - mediating physiological systems .
( we operationalize the term unconscious as indicating only that it occurs while one 's attention is not or can not be directed toward it , or is directed elsewhere , that is , out of awareness . )
there is a rich body of research converging on the idea that implicit emotion plays a role in mental and psychosomatic disorders . in the last two decades , developments in cognitive and social psychology have strongly indicated that a great deal of cognition occurs at the unconscious ( or automatic ) level [ 19 , 20 ] . to date , several studies have shown that neurophysiological responses occur in response to threatening information that is shown subliminally , an accepted experimental model of unconscious cognition [ 18 , 21 ] . more importantly for this paper , it has also been shown that such subliminal stimuli can increase bp [ 2224 ] . regarding chronic stress
, we have found that ( conscious ) rumination was linked to cardiac activity in daily life , and this activity persisted for hours after the rumination itself had ended .
we and others [ 2629 ] also found effects of daily stress and rumination on cardiovascular activity during subsequent sleeping at night , during which conscious rumination is presumably not possible . on the basis of these findings
, some researchers [ 21 , 30 ] have recently proposed that stress research may have missed an essential phenomenon by focusing solely on the conscious tip of the iceberg of stress - related thoughts and feelings .
unconscious rumination may be responsible for a considerable portion of cardiovascular activity in one 's daily life .
pending development of appropriate measures which remains a challenge studying unconscious stress in the context of htn and other stress - related somatic conditions may turn out to be a particularly fruitful pathway for future investigation .
the perseverative cognitions that characterize rumination are thought to be under tonic inhibitory control by the prefrontal cortex [ 31 , 32 ] .
there are several conditions , including chronic stress or having an anxiety disorder , that lower prefrontal inhibition and thus render one more vulnerable to rumination as well as to prolonged and indiscriminate responses to environmental stimuli .
low prefrontal inhibition is characterized by low parasympathetic activation , which can be measured by low heart rate variability ( hrv ) .
as such , an excitatory positive feedback loop is allowed to emerge , reflected in the psychological level in hypervigilance and rumination . as a consequence ,
the normally fine - tuned ability to adjust to changing environmental factors becomes a relatively rigid , inflexible response disposition , which is in fact a continuation of the default defense response in the absence of clear threat signals .
this is reflected by a failure to recognize safe / neutral environmental signals and by responding to them as if they are threatening . in support of this idea
, patients suffering from generalized anxiety disorder have been shown to have lower tonic levels of hrv , when compared to nonanxious controls .
furthermore , people with low hrv have been shown to have an attentional bias for threatening information and interpret ambiguous situations more negatively . in sum
, we propose that low prefrontal inhibition , indexed by low hrv , predisposes people to respond with enhanced cognitive , affective , and physiological activity to stressors .
this , in combination with the psychological vulnerability factors for rumination discussed above , can cause even neutral stimuli to trigger the stress response . as a consequence , the total time that people ruminate and worry about stressful events increases , thereby adding to the total duration of exposure to stress representations and their physiological effects in daily life .
the overarching prediction derived from the model is that an important mechanism underlying the observed relationship between chronic stress and htn is rumination , which typically stems from exposure to an acute stressor .
thus , compared to individuals who show a lower tendency to regulate their angry and anxious and dysphoric thoughts using ruminative processes , high trait
ruminators should be more likely to have more frequent , intense , and longer - lasting , ruminative thoughts and emotions as well as more ( future ) reoccurrences and occurrences that persist longer into the future . in support of this prediction
, rumination has been shown to increase engagement in depressed thinking [ 37 , 38 ] , is related to negative emotions , including anxiety [ 39 , 40 ] , anger [ 4143 ] , and depressed mood [ 4345 ] , and can prolong negative affect [ 42 , 46 ] .
rumination appears to be a relatively stable characteristic , as test - retest is high for both anger and depressed rumination scales [ 47 , 48 ] ( for periods ranging from one month to one year ) .
for example , ruminators were more likely to experience a depressive episode in the ensuing 18 months than nonruminators , with a similar result found by nolen - hoeksema .
furthermore , higher tendencies toward angry rumination were related to increases in experienced and expressed anger and to decreased satisfaction with life on future occasions .
increases in rumination have consistently been linked to higher blood pressure during recovery periods [ 4954 ] .
for example , compared with nonruminators , ruminators after an anger recall incident were more likely to brood about their anger thoughts during a recovery period in which they were not distracted .
importantly , this tendency to ruminate translated - to - slower blood pressure recovery for these ruminators , demonstrating the ability for rumination to sustain high blood pressure .
other studies support this view as well ; participants induced to recall a stressor they experienced in the lab ( i.e. , ruminate about the stressor ) showed increases in blood pressure regardless of whether they ruminated about the stressor 30 minutes after it happened or one week later . in other words ,
the mental representation of the stressor increased blood pressure regardless of temporal distance from the original event .
importantly , the relationship between rumination and blood pressure is not just in the moment . compared to nonruminators ,
individuals who ruminate have higher resting [ 55 , 56 ] and ambulatory blood pressures [ 5658 ] .
for example , ottaviani and colleagues had participants engaged in an anger recall interview , which successfully raised blood pressure .
next , half of the participants were assigned to a distraction condition where rumination was abolished , while the other half was not distracted and were allowed to continue ruminating about the anger inducing incident .
pertinently , not only did this nondistracted , ruminating group have elevated blood pressure during the recovery period immediately after the anger recall , but their blood pressure remained significantly elevated compared to their baseline levels when examining their mean ambulatory blood pressure readings taken over the ensuing 24 hours . thus , there is evidence demonstrating the power of rumination to sustain elevated blood pressure not just over minutes , but hours and days .
higher blood pressure tends to beget yet higher blood pressure over time . in strictly biophysical terms , one mechanism by which the blood vessels in the body regulate blood flow
as blood pressure increases , either more blood ( i.e. , higher cardiac output ) enters the blood vessels or the blood enters the vessels with greater force ( i.e. , mean arterial pressure ) ; either way , the blood vessels must expand and contract more to regulate blood flow . over time , this process increases the thickness of the muscle around the vessels the more often a person has higher blood pressure , the more the vessels work and the faster and thicker this layer grows .
these thicker arterial walls are , however , more resistant to the force of blood flow , requiring the heart to work harder to pump enough blood hard enough for the vessels to properly regulate . with greater effort from the heart ,
this process explains how having sustained , untreated htn in one 's life is an independent predictor of cardiovascular morbidity .
this process is conceptually similar to that of allostatic load , which can be described as a resetting of the physiological set points in an attempt to maintain homeostasis and thus function , but at a new set point ( e.g. , higher blood pressure ) . in the short - run
, achieving allostasis is adaptive ( e.g. , the higher blood pressure allows the blood vessels to continue to regulate blood flow ) , but in the long term can have quite negative consequences . importantly , and supportive of the model presented here , the stressors that cause allostatic load are not major , impactful ( but infrequent )
key to this theory is that these frequent , more minor stressors have to produce sufficiently long response durations so as to lead to allostasis .
as discussed , the presence of an initial stressor does not automatically lead to the prolonged activation that causes the resetting of the body 's set point or allostasis .
rather , it is the presence and persistence of the cognitive representations ( i.e. , rumination , worry , and other perseverative cognitions ) that can later reactivate / recreate a stressor in one 's mind ; this process and the resultant physiological changes are the circumstances that characterize and explain the chronic stress - htn relationship .
we are attempting to describe a highly complex process and to understand why some are prone to ruminate and others are not , how attention clearly a key determinant of the nature of one 's conscious thoughts as well as signal detection and hypervigilance for perceived threats and insults is implicated in the process .
finally , we note that classical conditioning processes undoubtedly play a role , for example , a conditioned response to an eliciting stimulus may evoke the cognitive and affective response to past unconditioned aversive events .
consideration of these factors is beyond the scope of this paper , but will need to be addressed as our understanding of the processes increases .
there are many avenues of approach to such interventions , in part because there are several pathways by which stress may cause htn and heart disease .
thus , obvious targets are stress - related behaviors that may increase one 's risk , such as smoking , weight gain , lack of exercise , increased salt intake , and interpersonal behaviors that may cause subsequent and ongoing stressful incidents , and so on .
the model we propose suggests that an additional useful point of intervention may be the ruminative processes that can convert acutely stressful experiences into recurrent or chronic stress .
for example , one approach would be the cognitive reframing of stress - related negative thoughts and affect as a means of undermining their power to evoke subsequent negative thoughts and affect , and thus reducing the duration of exposure to sustained activation of the psmss .
even here , several strategies suggest themselves . cognitive behavior therapy [ cbt ] specifically targets such cognitions , and is a well - validated clinical technique .
enrichd has indeed used cbt as an intervention to reduce cvd risk ( in conjunction with a social support manipulation ) , but the results were largely negative .
rumination was not measured in that study , however , we would suspect that if the frequency and severity of the negative thoughts and cognitions were not reduced , such an intervention would be unlikely effective .
clinicians have developed interventions to train people to learn to forgive past perceived transgressions , and others have targeted one 's ability to let go of anger .
although intriguing , their effects on rumination and on psmss activation have been the subject of only a handful of studies and thus data are sparse for these approaches .
we hope this model spurs additional intervention work that tests a range of intervention targets , potential mediators , and a wider range of outcomes . on a final note ,
we suggest that a combination of procedures , likely targeting behavior as well as cognition and affect , may have better results than either alone .
defining chronic stress and understanding the pathways by which it may contribute to sustained elevated bp and eventual htn is a large
we have addressed one pathway , but others , including changes in risk - related behaviors and in the direct effects of chronic stress on htn , are not addressed here , nor are physiological bp regulatory systems including the angiotensin system , short term regulatory systems including the baroreflex , or the role of endogenous opioids . to eventually form a comprehensive model of the development and maintenance of pathogenically high - sustained bp resting level ,
our model attempts to make a more modest and circumscribed contribution , but we hope to integrate these potential mediators and moderators into the model in future studies . we propose that acute bp and other changes in response to experiencing an acute stressor may be less important than the continuing psmss activation that often persists after the incident itself has long ended and may reoccur when the memory of the stressor is activated .
robert sapolsky addressed this issue in his book why zebras do not get ulcers , in which he noted in his evocative example that zebras do not have the capacity to recall the stress ( the failed attack from the lion , e.g. , ) that has beset them ; therefore , they neither ruminate about the past nor worry about the future , and thus do not suffer the psmss consequences of engaging in such mental activity . and
thus do not suffer ulcers or , presumably , htn , at least not due to the pathway proposed in this paper .
( the supposition here is that these acute events occur only intermittently for the beleaguered zebra ; if they are occurring many times a day over long periods of time , the distinction between acute and chronic stress becomes blurred ) .
for some time , evolution has been shaping and perfecting the fight - or - flight response system that is designed to engage under acute threat .
awareness , or consciousness , however , emerged only a short time ago in evolutionary terms , and it was not , according to our model , until this point that mammals
humans , at least , and perhaps some infrahumans developed the capacity to self - reflect and , thus , to ruminate .
therefore , zebras do not develop ulcers , but humans do ( as well as elevated bp and htn risk ) . it is widely accepted that chronic stress must be filtered in some manner by sensation and more importantly
perceptual processes , thus leading to individual differences in response to environmental challenges or stressors .
similarly , the role of duration of exposure to the stress or , as we suggest , to the contents of one 's thoughts and emotions is , we argue , the representation of the chronic stress in its purest form ; it is , after all , those thoughts and emotions that largely affect the stress mediating physiology , which itself is a more proximal cause of htn and cvd .
do the data support the model ? as reviewed herein , parts of the model have been tested in different laboratories , often using different approaches , and the results seem to hang together to suggest that indeed , rumination is one important pathway by which the effects of chronic stress on the development of htn are transmitted .
scores of studies , however , conducted across several laboratories , have turned their attention to the role of rumination and perseverative cognition , and we anticipate that many of the blanks will be filled in as research on this topic progresses
. one important line of inquiry is to apply more intensive , within - person data capture approaches that can carefully document the temporal dynamics of these processes ( such as the initial occurrence and response to an acute stressor , and then its reoccurrence via ruminative processes and their associated responses ; see ) .
coupling ambulatory psychophysiology ( e.g. , bp ) with ecological momentary assessment techniques is one well - validated approach that holds great promise in this regard .
we believe that the model we have proposed represents an advance in the manner in which we conceptualize stress and its effects on blood pressure and cardiovascular disease .
partly , this is because of the basis it provides to develop useful interventions as well as precise targets of those interventions .
researchers have been ruminating about the nature of stress for some time ; we hope that this research will help turn these ruminations into productive ideas for further exploration . | chronic stress has been linked to hypertension , but the underlying mechanisms remain poorly specified . we suggest that chronic stress poses a risk for hypertension through repeated occurrence of acute stressors ( often stemming from the chronic stress context ) that cause activation of stress - mediating physiological systems .
previous models have often focused on the magnitude of the acute physiological response as a risk factor ; we attempt to extend this to address the issue of duration of exposure .
key to our model is the notion that these acute stressors can emerge not only in response to stressors present in the environment , but also to mental representations of those ( or other ) stressors .
consequently , although the experience of any given stressor may be brief , a stressor often results in a constellation of negative cognitions and emotions that form a mental representation of the stressor .
ruminating about this mental representation of the stressful event can cause autonomic activation similar to that observed in response to the original incident , and may occur and persist long after the event itself has ended .
thus , rumination helps explain how chronic stress causes repeated ( acute ) activation of one 's stress - mediating physiological systems , the effects of which accumulate over time , resulting in hypertension risk . |
intestinal obstruction is a common complication in patients with advanced abdominal or pelvic cancer and has a significant impact on their quality of life . in patients with inoperable malignant bowel obstruction
, the synthetic somatostatin analogue octreotide relieves nausea , vomiting and pain , and decreases drainage from a nasogastric tube . here ,
we report the use of the long - acting somatostatin analogue lanreotide autogel ( somatuline ; ipsen nv ) in the treatment of bowel obstruction in a patient with adenocarcinoma and peritoneal carcinomatosis .
in january 2012 , a 60-year - old woman presented with a 3-month history of increasing abdominal pain and a change in the stool pattern with a single episode of anal red blood loss in the past week .
an ultrasound of the abdomen showed several masses dispersed over the peritoneum , compatible with significant peritoneal metastasis .
colonoscopy revealed a large ulcerating lesion at the level of the sigmoid colon , which was diagnosed as a moderately differentiated adenocarcinoma after biopsy .
chemotherapy with 18 biweekly cycles ( 1 cycle every 2 weeks ) of folfiri and bevacizumab ( avastin , roche ) was started .
folfiri was administered according to the following schedule : day 1 , irinotecan 180 mg / m ; days 1 and 2 , leucovorin 100 mg / m , 5-fluorouracil bolus 400 mg / m and 5-fluorouracil infusion 600 mg / m .
avastin was given at a dose of 5 mg / kg every 2 weeks . if the patient had responded to this treatment , the possibility of performing debulking surgery and hyperthermic intraperitoneal chemotherapy would have been considered .
the abdominal pain disappeared after the first month of chemotherapy , while the ascites disappeared after 6 weeks .
there was also a slight regression of the peritoneal masses . during the 5th , 6th and 7th cycle of chemotherapy ,
the patient was hospitalized because of clinical signs of intestinal subocclusion ( vomiting , absence of stools and flatus ) that evolved into complete obstruction .
a ct scan of the abdomen did not reveal the cause of the obstruction or deterioration of the oncological lesions .
based on this observation , a folfiri - induced mucositis , motility disturbances due to peritoneal metastasis or a combination of these two factors were suspected . during hospitalization , fluids ,
alizapride ( litican , 300 mg / day ; sanofi - aventis ) and methylprednisolone sodium succinate ( solu - medrol , 40 mg / day ; pfizer inc . )
were administered intravenously , paracetamol ( 1 g / dose ) was administered intravenously 4 times a day and octreotide ( sandostatin , 0.5 mg / dose ; novartis ) was administered subcutaneously 3 times a day until the obstruction resolved .
oral consumption of food and fluids was withheld , and a nasogastric tube was placed . at each of the 3 hospitalization episodes ,
after the first episode of obstruction , the dose of folfiri was decreased to 75% , while the dose of avastin was not decreased .
all episodes of obstruction resolved after 3 days , and the chemotherapy was reintroduced after 12 weeks following resolution of the obstruction . after the third episode of obstruction
, we initiated treatment with lanreotide autogel 120 mg , injected deep subcutaneously once every 4 weeks .
the 120-mg dose was chosen based on our experience that the 90-mg dose has a lower efficacy .
the treatment with lanreotide autogel continued during the remaining 11 cycles of chemotherapy , and no further episodes of intestinal subocclusion or obstruction occurred . because tumor response following the 18 cycles of chemotherapy was not sufficient , debulking surgery or hyperthermic intraperitoneal chemotherapy treatment were not recommended . after a 3-month break in the chemotherapy treatment requested by the patient
the patient is currently undergoing second - line chemotherapy with folfox4 at 75% of the usual dose , administered once every 2 weeks in 12 cycles according to the following schedule : day 1 , oxaliplatin 85 mg / m at 75% ; days 1 and 2 , 75% of leucovorin 100 mg / m , 5-fluorouracil bolus 400 mg / m and 5-fluorouracil infusion 600 mg / m .
the 4-weekly lanreotide autogel injections have been continued without interruption to support the quality of life of the patient .
no new episodes of obstruction occurred until november 2013 , and the patient reported no side effects due to lanreotide autogel .
intestinal obstruction is reported in up to 51% of the patients with ovarian cancer and up to 28% of those with gastrointestinal cancer and has an important impact on their quality of life . due to contraindications such as intra - abdominal carcinomatosis , poor nutritional status or a large volume of ascites ,
surgery is not an option in a substantial portion of these patients [ 3 , 4 ] .
a nasogastric tube can be placed to drain secretions ; however , this often causes a great amount of distress in the patient as well as nasal or pharyngeal irritation , nasal cartilage erosion , occlusion of the tube or spontaneous expulsion .
short - acting somatostatin analogues such as octreotide ( sandostatin ) are antisecretory drugs used in the treatment of patients with inoperable bowel obstruction .
somatostatin was initially discovered as an inhibitor of growth hormone release , but was later found to play an inhibitory role in the regulation of several organ systems such as the central nervous system , the immune system , vessel walls , the pancreas and the gastrointestinal tract .
somatostatin analogues are valuable in the treatment of patients with malignant bowel obstruction because of their inhibitory effect on gastrointestinal motility and secretions and their ability to increase the absorption of water and electrolytes from the intestinal lumen .
the efficacy of short - acting somatostatin analogues in the management of symptoms due to malignant bowel obstruction has been reported in numerous patients , with control of vomiting obtained in more than 60% of the patients ( reviewed in ) .
reversal of malignant bowel obstruction after treatment with short - acting somatostatin analogues has also been reported .
the synthetic somatostatin analogue lanreotide has shown efficacy in the symptomatic treatment of inoperable bowel obstruction in patients with peritoneal carcinomatosis when administered in the form of microparticles . here
, we report a case of intestinal obstruction in a patient with adenocarcinoma , which resolved after treatment with octreotide
. however , new episodes of obstruction occurred , which each time led to a delay in the administration of chemotherapy . after the third episode
until november 2013 , the patient received eighteen 4-weekly injections of lanreotide autogel and did not experience any further episodes of obstruction , suggesting that lanreotide prevents recurrence of intestinal obstruction in patients with intestinal cancer .
another advantage is that while short - acting octreotide has to be administered 3 times a day , lanreotide autogel is administered only once a month , improving a patient 's quality of life .
treatment with lanreotide autogel prevented recurring episodes of obstruction , allowing the patient to continue the chemotherapy course without further delays and to start the second course . to our knowledge , this is the first report of a successful use of lanreotide autogel in the management of malignant bowel obstruction .
our results indicate that lanreotide autogel could be used as an alternative to a long - acting formulation of octreotide , which has recently shown efficacy in the symptomatic treatment of inoperable malignant bowel obstruction due to peritoneal carcinomatosis .
a long - term treatment with lanreotide , as reported herein , is further supported by the results of a study in which 3 patients with malignant bowel obstruction due to ovarian cancer received a monthly - administered long - acting depot form of octreotide ( sandostatin lar depot ) for a period of over 9 months , with no significant toxicities reported . the efficacy and safety of lanreotide in the palliative treatment of inoperable malignant intestinal obstruction
are currently being investigated in a phase ii clinical trial ( www.clinicaltrials.gov : nct01076803 ) .
| intestinal obstruction is a common complication in patients with advanced abdominal or pelvic cancer .
the synthetic somatostatin analogue octreotide can help relieve nausea , vomiting and pain in patients with inoperable obstruction . here
, we report a case of recurrent intestinal obstruction in a patient with adenocarcinoma .
although the obstruction was resolved after 3 days of treatment with octreotide , new episodes of obstruction occurred , resulting in a delay of the chemotherapy treatment .
after 3 episodes of obstruction , we initiated treatment with a longer - acting somatostatin analogue , lanreotide autogel 120 mg , administered once every 4 weeks .
the treatment with lanreotide autogel is being continued , allowing for continuation of the chemotherapy without further episodes of intestinal subocclusion or obstruction . until november 2013
, the patient received eighteen 4-weekly injections of lanreotide autogel and did not report side effects .
this case report demonstrates the successful treatment of intestinal obstruction with lanreotide autogel in a patient with adenocarcinoma . |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Teachers for Tomorrow's Careers Act
of 2005''.
SEC. 2. QUALIFIED TUITION AND RELATED EXPENSES.
(a) Extension.--
(1) In general.--Subsection (e) of section 222 of the
Internal Revenue Code of 1986 (relating to termination) is
amended by striking ``December 31, 2005'' and inserting
``December 31, 2006''.
(2) Limitations.--Paragraph (2) of section 222(b) of such
Code (relating to applicable dollar limit) is amended by
striking subparagraphs (A) and (B), by redesignating
subparagraph (C) as subparagraph (B), and by inserting before
subparagraph (B) (as so redesignated) the following:
``(A) 2006.--In the case of a taxable year
beginning in 2006, the applicable dollar amount shall
be equal to--
``(i) in the case of a taxpayer whose
adjusted gross income for the taxable year does
not exceed $65,000 ($130,000 in the case of a
joint return), $4,000,
``(ii) in the case of a taxpayer not
described in clause (i) whose adjusted gross
income for the taxable year does not exceed
$80,000 ($160,000 in the case of a joint
return), $2,000, and
``(iii) in the case of any other taxpayer,
zero.''.
(b) Expansion for Qualified Science, Technology, Engineering, or
Math Teachers and Professionals.--Subsection (d) of section 222 of such
Code (relating to definitions and special rules) is amended by
inserting at the end the following new paragraph:
``(7) Qualified science, technology, engineering, or math
teachers and professionals.--
``(A) In general.--In the case of payments made
with respect to a qualified science, technology,
engineering, or math teacher or with respect to a
qualified science, technology, engineering, or math
professional--
``(i) Dollar limitation not applicable.--
Subsection (b) shall not apply.
``(ii) Certification expenses.--Paragraph
(1) shall apply by inserting at the end the
following new sentences: `With respect to a
qualified science, technology, engineering, or
math teacher, such expenses shall include all
fees related to the initial certification of an
individual as a teacher of science, technology,
engineering, or math in the individual's State
licensing system. The deduction under
subsection (a) with respect to certification
expenses referred to in the preceding sentence
shall be allowed, in the case of any such
expense paid or incurred before or during the
taxable year in which such individual meets the
requirements of paragraph (7)(B)(i), for the
taxable year in which such individual meets
such requirements.'
``(B) Definitions.--For purposes of this
paragraph--
``(i) Qualified science, technology,
engineering, or math teacher.--With respect to
a taxable year, the term `qualified science,
technology, engineering, or math teacher' means
an individual who--
``(I) has a bachelor's degree or
other advanced degree in a field
related to science, technology,
engineering, or math,
``(II) was employed as a non-
teaching professional in a field
related to science, technology,
engineering, or math for not less than
3 taxable years during the 10-taxable-
year period ending with the taxable
year,
``(III) is certified as a teacher
of science, technology, engineering, or
math in the individual's State
licensing system for the first time
during such taxable year, and
``(IV) is employed at least part-
time as a teacher of science,
technology, engineering, or math in an
elementary or secondary school during
such taxable year.
``(ii) Qualified science, technology,
engineering, or math professional.--With
respect to a taxable year, the term `qualified
science, technology, engineering, or math
professional' means an individual who--
``(I) has a bachelor's degree or
other advanced degree in a field
related to science, technology,
engineering, or math,
``(II) was employed as a non-
teaching professional in a field
related to science, technology,
engineering, or math for not less than
3 taxable years during the 10-taxable-
year period ending with the taxable
year, and
``(III) has paid or incurred fees
during the taxable year with respect to
the enrollment or attendance of such
individual in courses of instruction
required for the initial certification
of such individual as a teacher of
science, technology, engineering, or
math in the individual's State
licensing system.''.
(c) Effective Date.--The amendments made by this section shall
apply to payments made in taxable years ending after the date of the
enactment of this Act. | Teachers for Tomorrow's Careers Act of 2005 - Amends the Internal Revenue Code to: (1) extend through 2006 the tax deduction for qualified tuition and related expenses; and (2) allow an unlimited deduction for the expenses of certified science, technology, engineering, or math teachers and professionals. |
hole - doped cuprate superconductors stand out because of the presence of an enigmatic pseudogap phase in the underdoped regime.@xcite from arpes measurements , the pseudogap is defined by the lack of a well - defined quasiparticle peak in the anti - nodal region of the brillouin zone leading to fermi arcs.@xcite among the peculiar properties in the pseudogap phase , the dichotomy between the insulating - like inter - plane resistivity along the _ c_-axis and the metallic in - plane resistivity down to @xmath7 in many underdoped cuprates is still heavily debated.@xcite this dichotomy has been considered as strong support of the spin - singlet approach to the pseudogap phase,@xcite which consider that coherent charge transport is strictly bidimensional and _ c_-axis resistivity should diverge as @xmath8 . among other models that have been proposed ,
one of these is based on incoherent tunneling between layers assisted by interplanar disorder ( see ref . and references therein ) .
finally , recent valence - bond dynamical mean - field calculations have established a clear connection between the peculiar _
c_-axis charge transport and the lack of coherent quasiparticles as the pseudogap opens in the antinodal region.@xcite this model is in good agreement with _
c_-axis optical conductivity measurements which reveal the absence of a drude peak at low frequencies in the underdoped normal state above @xmath7.@xcite + to understand _
c_-axis transport , not only must the fermi arcs observed by arpes above @xmath7 be taken into account but also the observation of quantum oscillations showing that the fermi surface ( fs ) of underdoped cuprates undergoes a profound transformation at low temperature.@xcite combined with the negative hall @xcite and seebeck coefficients @xcite at low temperature , these measurements demonstrate that the fs of underdoped yba@xmath1cu@xmath2o@xmath3 is made of small electron pockets in contrast to the large , hole - like fs of the overdoped cuprates.@xcite the underlying translational symmetry breaking , which causes the fermi surface reconstruction , has been observed in high fields nuclear magnetic resonance ( nmr ) measurements.@xcite these microscopic measurements have revealed that at low temperature and above a threshold magnetic field , the translational symmetry of the cuo@xmath1 planes in yba@xmath1cu@xmath2o@xmath3 is broken by the emergence of a unidirectional modulation of the charge density .
this conclusion is supported by a comparative study of thermoelectric transport in underdoped yba@xmath1cu@xmath2o@xmath3 and in la@xmath9eu@xmath10sr@xmath11cuo@xmath12 - a cuprate where stripe order is well - established from x - ray diffraction @xcite - which argues in favor of a charge stripe order causing reconstruction of the fs at low temperature for @xmath13.@xcite this charge stripe order can naturally be interpreted as a competing order with superconductivity akin to the smectic stripe phase observed in the archetypal la@xmath14nd@xmath15sr@xmath11cuo@xmath12.@xcite + here we directly address the consequence of the fermi surface reconstruction by stripe - charge order on _ c_-axis charge transport by measuring the _ c_-axis resistivity at low temperature in magnetic fields large enough to suppress superconductivity .
we found that the _
c_-axis resistivity becomes metallic - like at low temperature , and interpret this as a consequence of _ c_-axis coherence .
the low coherence temperature implies a small _ c_-axis dispersion and therefore a small hopping integral @xmath4 , in quantitative agreement with the splitting of the multiple quantum oscillation frequencies.@xcite the onset of this crossover coincides with the fs reconstruction leading to the emergence of a high mobility electron pocket which produces metallic - like transport both in the plane and along the _ c _ axis .
the coherence temperature decreases as the doping level decreases and vanishes at a hole doping @xmath16 , corresponding to the doping level where the electron pocket disappears.@xcite
the samples studied were single crystals of yba@xmath1cu@xmath2o@xmath3 , grown in non - reactive bazro@xmath2 crucibles from high - purity starting materials and subsequently detwinned.@xcite the superconducting transition temperatures have been obtained by resistivity measurements at zero field : @xmath7 = 57.0 k ( @xmath17 = 0.097 ) , @xmath7 = 61.3 k ( @xmath17 = 0.109 ) and @xmath7 = 66.4 k ( @xmath17 = 0.120 ) .
the doping @xmath17 of each crystal was inferred from its superconducting transition temperature @xmath7.@xcite electrical contacts to the sample were made by evaporating gold , with large current pads and small voltage pads mounted across the top and bottom so as to short out any in - plane current ( see inset of fig .
[ mrvsb]a ) .
several samples with typical dimensions ( @xmath18 ) mm@xmath19 of different thicknesses _ t _ = 0.05 - 0.15 mm were measured , each giving similar values of the absolute _ c_-axis resistivity .
the resistivity was measured at the lncmi in toulouse , france , in pulsed magnetic fields up to 60 t. a current excitation of 5 ma at @xmath20 60 khz was used .
the voltage ( and a reference signal ) was digitized using a high - speed digitizer and post - analysed to perform the phase comparison .
figure [ mrvsb ] presents the longitudinal _ c_-axis resistivity up to 60 t for the three underdoped samples of yba@xmath1cu@xmath2o@xmath3 .
below 60 k , a strong positive magnetoresistance ( mr ) grows with decreasing temperature , in good agreement with earlier high - field measurements @xcite of @xmath0 on yba@xmath1cu@xmath2o@xmath3 crystals with @xmath21 k. at very low temperature , quantum oscillations are most clearly seen in the sample with @xmath17 = 0.109 ( see fig .
[ mrvsb](b ) ) and are just above the noise level for the other two ( fig .
[ mrvsb](a ) and [ mrvsb](c ) ) .
they arise from the quantization of cyclotron orbits perpendicular to the magnetic field .
the frequencies and temperature dependence of these oscillations are consistent with previous reports.@xcite two features common to all three samples are the rise of the in - field _ c_-axis resistivity down to about 4 k , and a tendency to saturation at lower temperature .
this behavior is best captured in fig . [ rt ] where the resistivity is plotted as a function of temperature , at different magnetic fields . as _
t _ is lowered , the _ c_-axis resistivity first exhibits insulating behaviour , but instead of diverging as _
@xmath220 , it crosses over to a regime where it tends to saturate at the lowest temperatures in all three samples .
of yba@xmath1cu@xmath2o@xmath3 : ( a ) @xmath23 , ( b ) @xmath24 and ( c ) @xmath25 plotted as a function of temperature for different values of the magnetic field .
dashed lines are a guide to the eye .
the increase of the in - field _
c_-axis resistivity down to about 4 k is in part due to the strong magnetoresistance which develops at temperatures below 60 k. ] cu@xmath2o@xmath3 at @xmath26 and @xmath27 k. above a threshold field of about 30 t ( indicated by the right vertical dashed red line ) , the nernst coefficient @xmath28 ( panel a ; green curve ) saturates to its negative quasiparticle value , as demonstrated by its derivative ( panel a ; red curve ) which goes to zero as @xmath29 t. this saturation shows that the positive contribution to the nernst coefficient from superconducting fluctuations has become negligible above 30 t. above this field , the hall coefficient is almost flat ( dashed blue line in panel b ) and the two - band model fit to the _ c_-axis resistivity ( dashed magenta line in panel c ) merges with the data .
we conclude that at 10 k and above 30 t the flux - flow contribution to the transport properties is negligible , and the large magnetoresistance at high field is purely a property of the normal state at this doping level . ]
upon cooling , the resistivity drops because of superconductivity .
this drop starts at lower temperature for higher fields .
we define the threshold field beyond which the normal state is reached as the field above which @xmath30 shows no drop . to confirm that the tendency to saturation of @xmath30 at low temperature is not due to some compensation between superconducting drop ( as seen for the data below 40 t ) and insulating - like normal - state resistivity , we show that the tendency to saturation persists at fields above a threshold field down to the lowest temperatures ( see fig .
[ rt ] ) . in all three samples ,
50 t is above the threshold field down to the lowest temperatures .
therefore the magnetoresistance measured at 50 t is purely a normal - state property , at all three dopings .
+ the nernst effect is a sensitive probe of flux flow , because moving vortices make a large positive contribution to the nernst coefficient . in fig .
[ ns ] , we compare the field dependence of the nernst coefficient measured in yba@xmath1cu@xmath2o@xmath3 at @xmath26 and @xmath27 k @xcite ( fig .
[ ns]a ) with that of the in - plane hall coefficient @xcite ( fig .
[ ns]b ) and _ c_-axis resistivity ( fig . [ ns]c ) .
the nernst coefficient develops a strong positive peak above the melting line due to vortex motion in the vortex liquid phase and is followed by a gradual descent to negative values ( the quasiparticle contribution ) until it becomes almost flat as the field approaches 30 t. this saturation is best captured by the field derivative of the nernst coefficient shown by a red line in fig .
[ ns]a . above the threshold field of about 30 t ,
the hall coefficient becomes flat ( as indicated by the blue dashed line in fig .
[ ns]b ) and the two - band model used to fit the normal state _
c_-axis resistivity merges with the data ( see fig .
[ ns]c and sec .
this comparison confirms that flux - flow contribution to the normal - state transport is negligible , that is to say that the magnetoresistance is entirely due to quasiparticles , for fields greater than 30 t at @xmath31=10 k for _ p _ = 0.120 .
cu@xmath2o@xmath3 ( _ _ p__=0.109 ) measured at zero magnetic field ( black solid line ) and at @xmath32 t ( orange symbols ) .
blue solid line is a @xmath33 fit to the high temperature data up to 300 k. the saturation of the in - field resistivity at low temperature contrasts with the insulating - like behavior seen at high temperature .
the green open squares correspond to the resistivity from which the magnetoresistance has been subtracted using a two - band model to extrapolate the normal - state data of fig . 1 to _ b _ = 0 ( see section v ) . ]
the same conclusion can be drawn for the other samples thanks to hall effect measurements.@xcite the key observation is that @xmath34 , the temperature at which @xmath35 changes sign , is independent of field at high fields ( from 40 t up to 60 t ) for samples in the doping range studied here .
this shows that the temperature - induced sign change in @xmath36 at high fields is not caused by flux flow and is thus clearly a property of the normal state .
+ earlier high - field measurements of @xmath0 in yba@xmath1cu@xmath2o@xmath3 @xcite show a striking difference between the large magnetoresistance observed in samples with @xmath21 k and the absence of the magnetoresistance in sample with @xmath37 k. this can only be due to normal state transport properties and can be explained by the vanishing of the very mobile electron pocket for the low doping sample.@xcite there is no alternative explanation in terms of flux flow .
in fields of 50 t and above , where the _ c_-axis resistivity tends to saturate as @xmath38 , the non - superconducting ground state of yba@xmath1cu@xmath2o@xmath3 is coherent in all three directions at @xmath39 .
this behavior is best captured in fig .
[ fig4 ] , where the resistivities for the sample with @xmath17 = 0.109 measured at zero field ( solid black line ) and at @xmath32 t ( orange symbols ) are compared with the insulating - like high temperature behavior , where the _
c_-axis resistivity diverges as @xmath33 ( blue solid line ) .
+ the observation of _
coherent transport means that coherent bloch bands along the _
c_-axis are present at low temperature and that charge carriers are not confined to the cuo@xmath1 planes.@xcite compared to the situation in overdoped cuprate superconductors , where there is no doubt about the existence of a three - dimensional fermi surface,@xcite the
_ c_-axis coherent transport in underdoped yba@xmath1cu@xmath2o@xmath3 appears at low temperature where the fs is reconstructed .
nmr measurements performed on the same sample ( _ _ p__=0.108 ) and in the same temperature / field range where quantum oscillations have been observed,@xcite reveal an unidirectional charge - stripe order below a temperature @xmath40 k above a threshold field @xmath41 t. not surprisingly , the transition temperature @xmath42 obtained from nmr measurement coincides roughly with the temperature @xmath43 , the temperature at which @xmath35 changes sign .
t ( red circles ; left axis ) and in - plane hall coefficient @xmath36 ( blue squares ; right axis ) of a ) yba@xmath1cu@xmath2o@xmath3 ( _ _ p__=0.109 ) , b ) yba@xmath1cu@xmath2o@xmath3 ( _ _ p__=0.120 ) as a function of temperature . @xmath36
data measured at a ) @xmath44 t , and b ) @xmath45 t is taken from ref . and normalized by its value at @xmath46
k. @xmath43 is the temperature at which @xmath35 changes sign from positive at high temperature to negative at low temperature @xcite . ] in the magnetic field / temperature range where the fs undergoes a reconstruction driven by the charge - stripe order , a high mobility electron pocket dominates the transport properties . although recent specific heat @xcite measurements performed at high fields point to a fermi surface made of only one pocket per cuo@xmath1 plane,@xcite the emergence of a strong non @xmath47 mr at low temperature ( see fig . [ mrvsb ] ) is naturally explained by the fs reconstruction into electron and hole sheets , due to the ambipolar character of the fermi surface . in fig .
[ mr - rhvst ] we compare the slope of the magnetoresistance @xmath48 and the in - plane hall coefficient @xmath36 as a function of temperature measured at the same hole doping .
the onset of the mr in @xmath0 coincides with the fs reconstruction thus revealing the two roles played by the electron pocket : it enhances the orbital mr due to in - plane motion of carriers and it allows the mr to be reflected in inter - plane transport .
cu@xmath2o@xmath3 from which the magnetoresistance has been subtracted using a two - band model ( see section v ) for the three samples , as labeled .
solid lines show the resistivity measured in zero magnetic field .
dashed lines are a guide to the eye . ] to reveal that @xmath0 is metallic - like at low temperature , it is necessary to obtain the mr - free temperature dependence of @xmath30 by extrapolating the in - field resistivity @xmath48 to @xmath49 , defined as @xmath50 .
since a strong mr develops at low temperature , any smooth extrapolation to @xmath49 will give the same trend for the temperature dependence of @xmath50 , namely an initial rise with decreasing temperature turning into a drop at low temperature . to illustrate this , we extrapolate the in - field resistivity @xmath48 to @xmath49 using the same two - band model ( electron and hole carriers ) that self - consistently accounted for the temperature and field dependence of the longitudinal and transverse ( hall )
resistivities of yba@xmath1cu@xmath12o@xmath51.@xcite the transverse magnetoresistance can be fitted with a two - band model : @xmath52 where @xmath53 ( @xmath54 ) is the conductivity of holes ( electrons ) and @xmath55 ( @xmath56 ) is the hall coefficient for hole ( electron ) carriers . using the three free parameters @xmath57 , @xmath58 and @xmath59 , we were able to subtract the orbital magnetoresistance from the field sweeps and get the temperature dependence of the zero - field resistivity @xmath60 . to estimate error bars , we fitted each field sweep data set to eq .
[ mr ] between a lower bound @xmath61 and the maximum field strength and monitored the value of @xmath50 as a function of @xmath61 .
the resulting fits to @xmath48 down to 10 k for all three samples are shown in thin solid lines in the insets of fig .
[ mrvsb ] .
they yield the extrapolated zero - field resistivity @xmath50 shown in symbols in fig .
[ rtfit ] . the initial rise in @xmath50 with decreasing temperature turns into a drop at low temperature , passing through a maximum at @xmath62 k for the @xmath17 = 0.109 sample .
this is in reasonable agreement with the energy scale @xmath63 k obtained from the splitting of frequencies in quantum oscillations for yba@xmath1cu@xmath2o@xmath3 at _ p _ = 0.10 - 0.11.@xcite the same analysis for the two other compositions yields @xmath64 k for @xmath17 = 0.097 and @xmath65 k for @xmath17 = 0.12 .
cu@xmath2o@xmath3 , with the superconducting phase in zero magnetic field delineated by the transition temperature @xmath7 .
black circles mark the temperature @xmath66 below which the in - plane resistivity deviates from its linear temperature dependence at high temperature ( from data in ref . ) , a standard definition for the onset of the pseudogap phase .
the coherence temperature @xmath67 ( green circles ) is the temperature where @xmath30 peaks ( see fig . [ rtfit]).the coherence crossover splits the phase diagram into two regions : an incoherent 2d regime above and a coherent 3d regime below .
@xmath43 is the temperature at which the normal - state in - plane hall coefficient @xmath35 of yba@xmath1cu@xmath2o@xmath3 changes sign from positive at high temperature to negative at low temperature ( blue diamonds ; from ref . ) ] the coherent _
c_-axis transport at low temperature is a direct consequence of the fermi surface reconstruction occurring at a temperature scale @xmath68 . from _
c_-axis transport measurements , we define @xmath67 as the characteristic temperature for the crossover to the coherent regime at which @xmath50 peaks ( see fig . [ rtfit ] ) . in fig .
[ pd ] , we compare the temperatures @xmath67 and @xmath43 as a function of doping on the phase diagram of yba@xmath1cu@xmath2o@xmath3 .
the two phenomena trend similarly as a function of doping , both decreasing to lower _ t _ with decreasing _
p_. in addition , these characteristic temperatures extrapolate to zero at lower doping @xmath69 , where @xmath35 no longer shows any downturn ( see data for sample with @xmath7 = 44.5 k in ref . ) .
this qualitative change has been attributed to the disappearance of the electron pocket , either caused by a lifshitz transition @xcite or by a phase transition.@xcite earlier measurements of _
c_-axis transport on a sample with @xmath37 k @xcite are consistent with such a transition : the mr in @xmath30 is entirely gone and @xmath0 is now incoherent , increasing down to the lowest temperatures . in the framework of conventional theory of metals ,
c_-axis conductivity is given by @xmath70 where _ c _ is the _
c_-axis lattice parameter , @xmath71 is the relaxation time , and @xmath72 is the effective mass . for a tetragonal cuprate material and due to the crystallographic structure,@xcite the interlayer hopping integral
@xmath4 depends strongly on the in - plane momentum * k * of carriers , namely:@xcite @xmath73 ^ 2 $ ] .
it is maximum at the anti - node i.e. , at the ( @xmath74 , 0 ) ( and equivalent ) points in the brillouin zone . between the pseudogap temperature @xmath66 and the temperature characteristic of the fs reconstruction @xmath43 , the insulating - like behavior in @xmath0 and the absence of the drude peak in _
c_-axis optical conductivity measurements in the underdoped regime @xcite has been ascribed to the absence of a well - defined quasiparticle peak in the anti - nodal regions as seen by arpes measurements.@xcite + below @xmath43 and for doping levels @xmath75 , the field - induced charge stripe order detected by high - field nmr in yba@xmath1cu@xmath2o@xmath3 @xcite causes the reconstruction of the fs at low temperature .
the role of the magnetic field is to weaken superconductivity to reveal the competing stripe order . as a consequence
, there is no contradiction between the low temperature / high field electronic properties of underdoped yba@xmath1cu@xmath2o@xmath3 and the fs seen by arpes at zero field @xcite or the absence of a drude peak at low frequencies at magnetic fields below the threshold field.@xcite this fs reconstruction produces a high mobility electron pocket which dominates the in - plane transport properties @xcite and is responsible for the _ c_-axis coherence at low temperature . + taking into account the in - plane momentum dependence of the interlayer hopping integral @xmath4 , the cross - over to the coherent _
c_-axis transport suggests that either some electronic states exist close to the anti - node in the brillouin zone @xcite or that the reconstructed fs allows for assisted interlayer hopping term through 1d bands for example . in the former scenario , strong scattering at ( 0 , @xmath74 ) associated with charge fluctuations at a wavevector @xmath76=[@xmath74/2a ,
0 ] softens or freezes out when the charge order sets in at low temperature , restoring coherent quasiparticles close to the anti - node . below a doping level @xmath77
, the electron pocket disappears , probably because of a transition from a charge - stripe order ( @xmath13 ) to a phase with spin order ( @xmath78).@xcite in the absence of this electron pocket , both in - plane @xcite and out - of - plane @xcite transport properties are non - metallic - like at low temperature .
we thank a. carrington , s. chakravarty , a. chubukov , m .- h .
julien , s. kivelson , a. millis , m. norman , r. ramazashvili , t. senthil , g. rikken and m. vojta for useful discussions .
research support was provided by the french anr delice , euromagnet ii , the canadian institute for advanced research and the natural science and engineering research council .
t. timusk and b. statt , rep .
. phys . * 62 * , 61 ( 1999 ) .
et al_. , nature * 392 * , 157 ( 1998 ) .
s. l. cooper and k. e. gray , _ physical properties of high temperature superconductors iv _ ( world scientific , singapore , vol iv , 1994 ) .
d. g. clarke and s. p. strong , adv .
phys . * 46 * , 545 ( 1997 ) .
n. e. hussey , _ handbook of high - temperature superconductivity _
( springer 2007 ) . p.w .
anderson , science * 256 * , 1526 ( 1992 ) .
d. b. gutman and d. l. maslov , phys .
lett . * 99 * , 196602 ( 2007 ) .
m. ferrero _
et al_. , phys .
b * 82 * , 054502 ( 2010 ) .
d. n. basov and t. timusk , rev .
* 77 * , 721 ( 2005 ) .
n. doiron - leyraud _
et al_. , nature * 447 * , 565 ( 2007 ) .
d. leboeuf _
et al_. , nature * 450 * , 533 ( 2007 ) .
et al_. , phys .
rev . lett . * 104 * , 057005 ( 2010 ) .
f. lalibert _
et al_. , nature comm .
* 2 * , 432 ( 2011 ) .
b. vignolle _
et al_. , nature * 455 * , 952 ( 2008 ) .
t. wu _ et al_. , nature * 477 * , 191 ( 2011 ) .
et al_. , phys .
b * 83 * , 092503 ( 2011 ) . j. m. tranquada _ et al_. , nature * 375 * , 561 ( 1995 ) .
a. audouard _
et al_. , phys .
103 * , 157003 ( 2009 ) .
s. e. sebastian _ et al_. , phys .
b * 81 * , 214524 ( 2010 ) . b. j. ramshaw _
et al_. , nature physics * 7 * , 234 ( 2011 ) .
s. e. sebastian and n. harrison , phys .
lett . * 108 * , 196403 ( 2012 ) .
d. leboeuf _
et al_. , phys .
b * 83 * , 054506 ( 2011 ) .
et al_. , physica c * 336 * , 57 ( 2000 ) .
et al_. , phys .
b * 73 * , 180505(r ) ( 2006 ) . f. f. balakirev
_ et al_. , physica c * 341 - 348 * , 1877 ( 2000 ) .
n. e. hussey _
et al_. , nature * 425 * , 814 ( 2003 ) .
s. c. riggs _ et al_. , nature physics * 7 * , 332 ( 2011 ) .
n. harrison and s. e. sebastian , phys .
lett . * 106 * , 226402 ( 2011 ) .
p. m. c. rourke _
et al_. , phys .
b * 82 * , 020514(r ) ( 2010 ) . s. e. sebastian _ et al_. , proc
. natl acad .
usa * 107 * , 6175 ( 2010 ) .
o. k. andersen _
et al_. , j. phys .
solids * 56*,1573 ( 1995 ) .
s. chakravarty _
et al_. , science * 261 * , 337 ( 1993 ) . j. m. tranquada _
et al_. , phys .
b * 81 * , 060506(r ) ( 2010 ) .
a.j . millis and m. norman , phys .
b * 76 * , 220503(r ) ( 2007 ) .
s. chakravarty and h .- y .
kee , pnas * 105 * , 8835 ( 2008 ) .
et al_. , phys .
b * 84 * , 012507 ( 2011 ) .
_ et al_. , new j. of phys .
* 12 * , 105006 ( 2010 ) .
et al_. , phys .
lett . * 93 * , 267001 ( 2004 ) . | the electrical resistivity @xmath0 of the underdoped cuprate superconductor yba@xmath1cu@xmath2o@xmath3 was measured perpendicular to the cuo@xmath1 planes on ultra - high quality single crystals in magnetic fields large enough to suppress superconductivity .
the incoherent insulating - like behavior of @xmath0 at high temperature , characteristic of all underdoped cuprates , is found to cross over to a coherent regime of metallic behavior at low temperature .
this crossover coincides with the emergence of the small electron pocket detected in the fermi surface of yba@xmath1cu@xmath2o@xmath3 via quantum oscillations , the hall and seebeck coefficients and with the detection of a unidirectional modulation of the charge density as seen by high - field nmr measurements .
the low coherence temperature is quantitatively consistent with the small hopping integral @xmath4 inferred from the splitting of the quantum oscillation frequencies .
we conclude that the fermi - surface reconstruction in yba@xmath1cu@xmath2o@xmath3 at dopings from @xmath5 to at least @xmath6 , attributed to stripe order , produces a metallic state with 3d coherence deep in the underdoped regime . |
activator protein-1 ( ap1 ) is a transcription factor that consists of either homo- or heterodimers of the jun and fos family proteins .
it regulates gene expression in response to a variety of stimuli , including environmental stresses , uv radiation , cytokines , and growth factors . ap1 in turn
controls a number of cellular processes including proliferation , transformation , inflammation , and innate immune response .
the jun and fos proteins share similar amino acid sequences that comprise the basic dna - binding sequence and the adjacent leucine zipper region by which these proteins dimerize [ 24 ] .
the ap1 transcription factor binds specifically to 12-o - tetradecanoylphorbol-13-acetate ( tpa ) responsive element 5-tgag / ctca-3 which is commonly referred to as the ap1 site [ 5 , 6 ] .
c - fos and c - jun genes are autoregulated ; the transcription of c - jun is stimulated by its own product , and in contrast c - fos is negatively autoregulated [ 79 ] . ap1 has been found constitutively active in many cancers including breast , ovarian , cervical , and lung .
numerous studies have shown that inhibition of ap1 has a profound effect on the behavior of cancer cells and tumors suggesting that ap1 could be a promising target for cancer therapy .
curcumin , a dietary spice derived from the plant turmeric ( curcuma longa ) , is used as a traditional medicine for inflammatory conditions .
further , curcumin has been reported to have anti - inflammatory , anti - oxidant , and anticancer effects [ 1215 ] . in vivo administration of curcumin
was found to reduce the incidence and size of tumors in mice [ 1619 ] . moreover , curcumin was reported to inhibit proliferation and cell cycle progression in cancer cells .
curcumin suppresses constitutive ap1 activity in hl-60 , raji , and prostate cancer cell lines ( lncap , pc-3 , and du145 ) [ 2125 ] .
curcumin was also reported to suppress lps - induced cyclooxygenase-2 gene expression by inhibiting ap1 dna binding in bv2 microglial cells .
it was confirmed that curcumin directly interacts with jun - fos dimer and inhibits its binding to dna ( ap1 site ) .
some synthetic curcumin derivatives have been discovered as inhibitors of jun - fos - dna complex formation [ 2830 ] .
however , no information on the site of interaction is reported yet . in the present study
we investigate the interaction of curcumin derivatives with jun - fos complex by molecular docking studies .
to investigate the interaction with jun - fos complex , curcumin natural derivatives ( figure 1 ) , synthetic curcumin - based inhibitors ( table 1 ) , and other known inhibitors of jun - fos - dna complex formation ( figure 2 ) were drawn and 3d optimized using marvinsketch ( free academic license ) and saved in protein data bank ( pdb ) file format .
these molecules were prepared for molecular docking by merging nonpolar hydrogens , assigning gastegier charges , and saving them in pdbqt file format using autodock tools ( adt ) 1.5.6 .
x - ray crystal structure of jun - fos - dna complex ( pdb i d : fos1 ) was obtained from the protein data bank ( http://www.rcsb.org/pdb ) . for molecular docking dna and other heteroatoms ( water , ions , etc . )
gasteiger charges were assigned , and jun - fos complex was saved in pdbqt file format using adt .
grid and docking parameter files were prepared using adt , and molecular docking was performed with autodock 4.2.1 ( scripps research institute , usa ) considering all the rotatable bonds of curcumin derivatives as rotatable and jun - fos complex as rigid .
grid box size of 90 90 90 with 0.375 spacing was selected that include the whole basic dna - binding sequence and the adjacent leucine zipper region of jun - fos complex .
empirical - free energy function and lamarckian genetic algorithm , with an initial population of 150 randomly placed individuals , a maximum number of 2,500,000 energy evaluations , a mutation rate of 0.02 , and a crossover rate of 0.80 , were used to perform molecular docking .
curcumin derivative - jun - fos complex for lowest free energy of binding ( g ) confirmation from the largest cluster was written in pdbqt format and converted to pdb file format using ucsf chimera 1.6.1 .
further , these complexes were analyzed using pymol 0.99 for possible polar and hydrophobic interactions .
all the docking studies were performed at intel(r ) xeon(r ) cpu ( 3.2 ghz ) with linux - based operating system fedora 15 .
x - ray crystal structure of jun - fos - dna complex shows that arg140 , asn147 , lys153 , ser154 , arg155 , arg158 , arg268 , asn271 , arg272 , and ser278 are the key residues by which jun - fos complex binds to dna through hydrogen bonding ( figure 3 ) . to predict the interaction of curcumin derivatives with jun - fos complex , natural curcumin derivatives and other known inhibitors of jun - fos - dna complex formation
were docked over dna - binding region ( dbr ) of jun - fos complex , and results were summarized in table 2 . amongst all the natural curcumin derivatives docked to jun - fos complex curcumin sulphate bound with g of 8.20 kcal / mol and predicted ki of 976.64 nm followed by cyclocurcumin and demethoxycurcumin which bound with g of 5.75 and 5.72 kcal / mol and predicted ki of 61.42 and 63.86 m , respectively ( figure 4(a ) ) .
the binding mode of curcumin sulphate depicted that sulphate and nearby methoxy group present at one aromatic ring of the molecule were in polar contact range with lys282 ; however methoxy group present at the other side formed polar contact with side chain of lys280 ( figure 4(b ) ) .
keto group present in the linker region was in polar contact range with side chain of arg158 .
the binding mode of cyclocurcumin showed that hydroxyl group present at one aromatic ring of the molecule formed polar contact with side chain of arg155 ; however at the other side it formed polar contacts with arg158 ( figure 4(c ) ) . when demethoxycurcumin docked to jun - fos complex , hydroxyl and neighboring methoxy group present at one aromatic ring formed polar contact with side chains of arg155 and arg279 , respectively , while hydroxyl group present at other side of the molecule formed polar contact with side chain of ser276 ( figure 4(d ) ) .
in the linker region of the molecule keto and hydroxyl groups were in polar contact range with arg158 and arg279 , respectively . amongst the synthetic curcumin - based inhibitors chc011 bound to jun - fos complex with g of 9.59
kcal / mol and predicted ki of 93.25 nm followed by chc009 and chc007 which docked with g of 9.52 and 9.15 kcal / mol and predicted ki of 104.26 nm and 196.96 nm , respectively ( figure 5(a ) ) .
similar results were observed in the in vitro studies by hahm et al . in 2002 .
the binding mode studies depicted that no2 group present at one aromatic ring of the chc011 molecule formed polar contact with side chain of arg272 while at the other side of the molecule it interacted with lys282 ( figure 5(b ) ) .
when chc009 docked to jun - fos complex , keto group present in the linker region of the molecule formed polar contact with side chain of arg158 ( figure 5(c ) ) .
hydroxyl and no2 group present at one aromatic ring of the chc007 molecule formed polar contacts with backbone of arg155 and side chain of lys282 , respectively , while the hydroxyl group present in the linker region of the molecule showed polar contact with side chain of arg158 ( figure 5(d ) ) . amongst the other known inhibitors t5224 [ 3-(5-(4-(cyclopentyloxy)-2-hydroxybenzoyl)-2-((3-hydroxybenzo [ d]isoxazol-6-yl)methoxy)phenyl)propanoic acid ] bound to jun - fos complex with g of 9.96 kcal / mol and predicted ki of 49.64 nm followed by dihydroguaiaretic acid and resveratrol which docked with g of 4.43 and 4.20 kcal / mol and predicted ki of 569.58 and 829.30 m , respectively ( figure 6(a ) ) .
the binding mode studies of t5224 depicted that oxygen atom of cyclopentyloxy group formed polar contact with side chain of arg158 ; however nearby hydroxyl group formed polar contact with arg279 .
hydroxyl group of 3-hydroxybenzo [ d]isoxazol-6-yl)methoxy group formed polar contact with asn271 ; however oxygen atom of its methoxy group formed polar contact with ser278 .
acid group of the t5224 molecule was in polar contact range with lys282 ( figure 6(b ) ) . when docked to jun - fos complex neighboring hydroxyl and methoxy groups present at one side of the dihydroguaiaretic acid molecule formed polar contacts with ser278 and arg279 respectively , whereas the hydroxyl group present at the other side of the molecule formed polar contact with backbone of arg279 ( figure 6(c ) ) . when docked to jun - fos complex neighboring hydroxyl groups attached to one of the aromatic ring of resveratrol molecule formed polar contacts with ser 154 and side chain of lys282 , respectively ( figure 6(d ) ) .
we observed that curcumin derivatives form polar contacts preferentially with residues like arg155 , arg158 , lys276 , arg279 , lys280 , and lys282 when docked to dbr of jun - fos complex amongst which arg155 and arg158 are the key residues by which jun - fos complex binds to dna .
the results suggested that interaction of curcumin derivatives with residues like arg155 and arg158 could be the possible mechanism by which curcumin derivatives inhibit jun - fos - dna complex formation .
ala151 , ala275 , leu283 , and ile286 were the hydrophobic residues present at binding site contributing to hydrophobic contacts with inhibitor molecules .
the present molecular docking study provides insights into the inhibition of jun - fos - dna complex formation by curcumin derivatives .
the involvement of residues like arg155 , arg158 , lys276 , lys280 , and lys282 seems to play a key role in binding of curcumin derivatives to jun - fos complex through polar contacts which prevents its binding to dna ( ap1 site ) .
ala151 , ala275 , leu283 and ile286 were the important hydrophobic residues present at binding site .
most of the curcumin derivatives were predicted to be more potent than inhibitors like resveratrol and dihydroguaiaretic acid .
curcumin sulphate was predicted to be the most potent inhibitor amongst all the natural curcumin derivatives docked . | activator protein-1 ( ap1 ) is a transcription factor that consists of the jun and fos family proteins .
it regulates gene expression in response to a variety of stimuli and controls cellular processes including proliferation , transformation , inflammation , and innate immune responses .
ap1 binds specifically to 12-o - tetradecanoylphorbol-13-acetate ( tpa ) responsive element 5-tgag / ctca-3 ( ap1 site ) .
it has been found constitutively active in breast , ovarian , cervical , and lung cancers .
numerous studies have shown that inhibition of ap1 could be a promising strategy for cancer therapeutic applications .
the present in silico study provides insights into the inhibition of jun - fos - dna complex formation by curcumin derivatives .
these derivatives interact with the amino acid residues like arg155 and arg158 which play a key role in binding of jun - fos complex to dna ( ap1 site ) .
ala151 , ala275 , leu283 , and ile286 were the residues present at binding site which could contribute to hydrophobic contacts with inhibitor molecules .
curcumin sulphate was predicted to be the most potent inhibitor amongst all the natural curcumin derivatives docked . |
in the symbiotic recurrent nova rs ophiuchi ( hd 162214 ) , a near - chandrasekhar - mass white dwarf ( wd ) accretes material from a red giant companion ( e.g. , hachisu & kato 2001 ; sokoloski et al .
it experiences nova eruptions approximately every 20 yr ( evans et al . 2008 ) , with the most recent eruption having occurred on 2006 february 12 ( narumi et al .
fekel et al .
( 2000 ) found that rs oph has an orbital period of 455 days and give red giant and white dwarf ( wd ) masses of @xmath11 and close to @xmath12 respectively with a separation between the components of @xmath13 cm .
for the range of spectral types suggested ( worters et al .
2007 ) for the red giant in the rs oph system , its radius is smaller than its roche lobe , and accretion onto the wd may occur only from the red giant wind .
the flickering ( stochastic light variations on timescales of a few minutes with amplitude of a few@xmath14 magnitudes ) is a variability observed in the three main types of binaries that contain white dwarfs accreting material from a companion mass - donor star : cataclysmic variables ( cvs ) , supersoft x - ray binaries , and symbiotic stars ( sokoloski 2003 ) .
the flickering of rs oph has been detected by walker ( 1977 ) .
the systematic searches for flickering variability in symbiotic stars and related objects ( dobrzycka et al . 1996a ; sokoloski , bildsten & ho 2001 ; gromadzki et al .
2006 ) have shown that among @xmath15 symbiotic stars known , only 8 present flickering rs oph , t crb , mwc 560 , z and , v2116 oph , ch cyg , rt cru , o cet and v407 cyg . here
we investigate the flickering variability of rs oph in the @xmath16 bands and discuss its possible origin .
[ cols="<,<,>,>,>,>,^,>,>,^,^,^,^,>,<,^ , > " , ] [ tab1 ]
on the night of 2008 july 6 , we observed rs oph simultaneously with four telescopes equipped with ccd cameras .
the 2 m rcc telescope of the national astronomical observatory rozhen equipped with a dual channel focal reducer observed in @xmath17 and @xmath18 bands . in the @xmath17 band a photometrics ccd ( 1024x1024 px , field of view 4.9x4.9 ) has been used , and in the @xmath18 band a versarray 1330b ( 1340x1300 , 6.3x6.3 ) . the 60 cm rozhen telescope observed in the @xmath19 band ( equipped with a fli pl09000 ccd with 3056 x 3056 pixels and 5.7x5.7 ) ; the 50/70 cm schmidt telescope of nao rozhen in the @xmath20 band ( sbig stl11000 m ccd , 4008x2672 px , 16x24 ) , and the 60 cm telescope of the belogradchick astronomical observatory in the @xmath21 band ( sbig st8 ccd , 1530x1020px , 6.4x4.2 ) . on the night of 2009 july 21 , we observed rs oph simultaneously with 3 telescopes .
the 50/70 cm schmidt telescope observed in the @xmath17 band , the 60 cm rozhen telescope repeating @xmath20 and @xmath21 bands , and the 60 cm belogradchick telescope repeating @xmath18 and @xmath19 bands . on the night of 2009 july 23 , we observed rs oph simultaneously with 3 telescopes .
the 2 m rcc telescope observed simultaneously in @xmath17 and @xmath18 bands , the 50/70 cm schmidt telescope in @xmath20 , and the 60 cm rozhen and belogradchick telescopes in @xmath21 band .
all the ccd images have been bias subtracted , flat fielded , and standard aperture photometry has been performed .
the data reduction and aperture photometry are done with iraf and have been checked with alternative software packages .
the comparison stars of henden and munari ( 2006 ) have been used .
the results of our observations are summarized in table [ tab1 ] and plotted in figs.[fig1 - 1 ] , [ fig1 - 2 ] and [ fig1 - 3 ] . for each run
we measure the minimum , maximum , and average brightness in the corresponding band , plus the standard deviation of the run .
as can be seen in figs . [ fig1 - 1 ] , [ fig1 - 2 ] , [ fig1 - 3 ] and table 1 , during our observations rs oph exhibited variability on a time scale of 1 - 30 minutes with amplitude 0.3 mag in @xmath18 .
the amplitude increases to shorter wavelengths and decreases to longer .
in fig.[figcolors ] we plot the colours of rs oph versus the @xmath19 band magnitude for 2008 july 6 .
the @xmath19 band is chosen because we have the shortest exposure time . in order to relate magnitudes in different bands , taken at non - matching start times and different exposure times , we linearly interpolated the light curves .
the colours have been calculated over 3 grids with time resolutions 70 , 120 and 360 seconds , to match the poorest filter sampling in the corresponding colour relation : 70 s. for @xmath22 vs. @xmath19 , 120 s for @xmath23 vs. @xmath19 , and 360 s for @xmath24 vs. @xmath19 .
linear fits ( of type @xmath25 ) to the data points in fig.[figcolors ] give : @xmath26 the errors of the coefficients are given in brackets .
these relations are obtained on the basis of the observations from 2008 july 6 .
they are valid over the range @xmath27 mag .
the spearman s ( rho ) rank correlation gives @xmath28 ( significance @xmath29 ) for eq.1 , @xmath30 ( @xmath31 ) for eq.2 , @xmath32 ( @xmath33 ) for eq.3 .
the significance in eq.1-eq.3 is always @xmath34 indicating that all these correlations are highly significant and changes in the colours of rs oph are correlated with brightness variations .
bruch ( 1992 ) proposed that the light curve of cvs can be separated into two parts constant light and variable ( flickering ) source .
we assume that all the variability is due to flickering .
in these suppositions the flickering light source is considered 100% modulated .
following these suggestions , we calculate the flux of the flickering light source as @xmath35 , where @xmath36 is the average flux during the run and @xmath37 is the minimum flux during the run ( corrected for the typical error of the observations ) .
@xmath38 has been calculated for each band , using the values given in table 1 and bessel ( 1979 ) calibration for the fluxes of a zero magnitude star .
adopting these results , we find that the flickering light source contributes about 6% of the light in the @xmath19 band , 7% in @xmath18 , 10% in @xmath20 , and 13% in @xmath17 .
following snijders ( 1987 ) we assume interstellar extinction @xmath39 and an extinction law as given in cardelli et al.(1989 ) . using the colour relations ( eq.1eq.3 , derived in sect.3.1 ) in the interval @xmath40 mag ( in other words average @xmath41 and we calculate average values for other bands , minimal brightness in @xmath42 , and we derive minimal fluxes in other bands ) , we obtain colours of the flickering light source in rs oph as @xmath43 , @xmath44 , @xmath45 . on 2009
july 21 we obtain @xmath46 and @xmath47 .
using the entire runs in @xmath17 band from 2009 july 23 and @xmath20 and @xmath18 from 2009 july 21 ( as plotted in fig.[bb ] ) we calculate @xmath46 and @xmath48 .
the values are similar to the colours of the flickering source in 1983 july - august @xmath49 and @xmath50 ( bruch 1992 ) .
the derived @xmath51 colour corresponds to a b4v star ( @xmath52 k ) and a black body with @xmath53 k. the @xmath54 colour corresponds to an a5v ( @xmath55 k ) star and a black body with @xmath56 k. @xmath57 corresponds to a f8v star ( @xmath58 k ) .
these estimates give an approximate temperature of the flickering light source @xmath59 k. for the flickering light source we obtain magnitudes ( corrected for interstellar extinction ) : 2008 july 6 : @xmath60 , @xmath61 , @xmath62 , @xmath63 mag ; 2009 july 21 : @xmath64 , @xmath65 , @xmath66 , @xmath67 mag ; 2009 july 23 : @xmath68 , @xmath69 , @xmath70 mag .
the errors are in @xmath71 , in @xmath72 , in @xmath73 , in @xmath74 in @xmath75 .
we adopt @xmath76 kpc as given in bode ( 1987 ) . in fig.[bb ] we plot these magnitudes transformed to fluxes . using a black body fit ( @xmath77 routine of iraf ) , we calculate for the flickering light source : @xmath78 k ; @xmath79 @xmath80 ; @xmath81 @xmath6 ( 2008 july 6 ) and @xmath82 k ; @xmath83 @xmath80 ; @xmath84 ( 2009 july 21 and 23 ) . in fig.[bb]c
we plot all points normalized to the corresponding v band flux .
the fit gives @xmath85 k ; our @xmath21-band data from 2008 july 6 have considerably larger observational errors due to a technical problem which gave as a consequence a variable dark current pattern of the ccd .
@xmath17 from 2009 july 21 and @xmath20 from 2009 july 23 are short .
they are therefore not used in the black body fits nor plotted in fig.[bb ] .
there are several different estimates of the mass accretion rate in rs oph .
an estimate of @xmath86 yr@xmath87 arises from the required mass accreted on to the wd to give rise to the outburst plus the latest inter - outburst time scale of 21 years ( osborne et al . 2010 ) . assuming
@xmath88 @xmath80 ( starrfield et al . 1991 ) , this results in a total accretion luminosity @xmath89 @xmath6 .
alternatively , walder et al .
( 2008 ) explore the hydrodynamics of wind accretion in the system and find @xmath90 yr@xmath87 , i.e. @xmath91 @xmath6 ( which compares to @xmath92 @xmath6from iue observations at quiescence - snijders 1987 ) .
the spectral energy distribution of the accretion disk around the wd is similar to mid - b spectral type ( dobrzycka et al .
1996 ) with luminosity @xmath93 @xmath6 . in practice
therefore , the different estimates give @xmath94 @xmath6 , which means that 5%-35% of the total accretion luminosity is emitted by the flickering source ( in other words @xmath95 ) .
we searched for time lags between the light curves in different bands , using the interpolation cross - correlation method ( gaskell & sparke , 1986 ) , but found no delays larger than 10 sec , which is shorter than our time resolution ( the exposure times ) .
[ 2c ] represent a 2-colour diagram , @xmath51 versus @xmath54 for the flickering light source in a number of cvs and symbiotics .
the data for the cvs and t crb are from bruch ( 1992 ) .
we also plot 2 points for mwc 560 and 2 for v407 cyg , which are calculated from the data of gromadzki et al .
( 2006 ) the crosses represent rs oph .
the three crosses refer to the three epochs of observations 1983 , 2008 , 2009 .
they lie well outside the area of the cvs . to address the possible errors of our measurement
, we separated our light curves of rs oph ( plotted in fig .
[ fig1 - 1 ] ) into two parts ( from ut 19:46 to ut 20:26 and ut 20:27
21:22 ) .
we obtained for the flickering source @xmath96 @xmath97 for the first time interval , and @xmath98 @xmath99 for the second .
this indicates that for rs oph the errors are approximately equal to the size of the symbols . to search for differences between the flickering of symbiotic stars and cvs we performed a two - dimensional kolmogorov - smirnov test ( peacock 1983 ; fasano & franceschini 1987 ) , using the data plotted on fig.[2c ]
we compare colours of the flickering of the recurrent novae rs oph and t crb with those of the cvs .
the test gives a probability of @xmath100 that both distributions are extracted from the same parent population .
we also performed the same test but comparing cvs with all symbiotic stars .
the test gives a probability of @xmath101 that both distributions are extracted from the same parent population .
the number of points is not high , but sufficient , as shown in fasano & franceschini ( 1987 ) , and the difference is significant .
this result indicates that in this diagram there are clues to the cause of the differences between the flickering of these two classes of accreting white dwarfs . in the symbiotics of course
, the mass donor is a red giant and the orbital periods are @xmath102 d. in the cvs the mass donors are late - type dwarfs and the orbital periods are @xmath103 times shorter . to the best of our knowledge
this is the first evidence that flickering differs in these types of accreting wds and the physical cause of this difference warrants further investigation ( see below ) .
in quiescence rs oph varies irregulary between @xmath104 ( collazzi et al .
2009 , aavso light curves ) . this variability is observed before as well as after the 2006 outburst .
darnley et al.(2008 ) detected an increase of the brightness in @xmath20 from @xmath105 to @xmath106 mag and from @xmath107 to @xmath108 for a year after the 2006 outburst .
worters et al .
( 2007 ) detected an increase in @xmath18 from @xmath109 to @xmath110 for 2 weeks .
the brightness of rs oph at the time of our flickering observations is well inside these limits ( unfortunately , there does not seem to be any published @xmath17 light curve ) .
the derived parameters of the flickering can be considered as typical for quiescence .
after the 2006 outburst the flickering of rs oph disappeared ( zamanov et al .
2006 ) probably as a result of ( 1 ) destruction of the accretion disk from the nova explosion or ( 2 ) a change in the inner disk associated with jet production ( sokoloski et al .
the flickering resumed by day 241 of the outburst ( worters et al .
2007 ) . for the symbiotic star ch
cyg , sokoloski & kenyon ( 2003 ) observed changes in the flickering in association with the mass ejection event .
observations of ch cyg and rs oph therefore indicate that a connection does exist between the flickering behaviour and the ejection of matter from the wd .
different sites for the origin of the flickering have been discussed .
they are all related to the accretion process : * ( i ) * the bright spot ( the region of impact of the stream of transferred matter from the mass donor star on the accretion disk ) ; * ( ii ) * the boundary layer ( between the innermost accretion disk and the white dwarf surface ) ; * ( iii ) * inside the accretion disk itself .
+ the findings of bruch ( 2000 ) for ht cas , v2051 oph , ip peg and ux uma demonstrated that the flickering in these cvs can originate in both regions * ( i ) * and * ( ii)*. * ( i ) * the temperature and the size of the bright spot are derived for a number of cvs .
a few examples of temperatures are : for oy car wood et al ( 1989 ) calculated black body @xmath111 k , and color temperature @xmath112 k ; marsh ( 1988 ) for ip peg - @xmath113 k ; zhang & robinson ( 1987 ) for u gem - @xmath114 k ; robinson et al .
( 1978 ) give @xmath115 k for the bright spot in wz sge .
the temperature of the optical flickering source of rs oph @xmath116 k ( see sect.4.1 ) is similar to the temperature of the bright spot for the cvs .
the mass transfer in rs oph may not be from roche lobe overflow ( as in cvs ) , but via stellar wind accretion . as a result of the supersonic motion of the wd through the red giant wind
there should be a shock cone and an accretion wake . around the wd ,
it is likely that an accretion disk and/or a cocoon is formed . in the place where the matter flowing through the accretion wake encounters the accretion disk / cocoon a bright spot could be formed ( analogous to the bright spot formed in the case of cvs , where the mass flow from the inner lagrangian point encounters the accretion disk ) . *
( ii ) * another possible site for the origin of the flickering in rs oph is the boundary layer between the white dwarf and accretion disk .
bruch & duschl ( 1993 ) estimated the size of the boundary layer ( @xmath117 ) in rs oph as @xmath118 . in their model @xmath119
is connected with the size of the boundary layer ( @xmath120 is the the luminosity of the accretion disk , @xmath121 is the luminosity of the boundary layer ; see fig 1 in bruch & duschl 1993 ) .
if we assume @xmath122 @xmath6 , and @xmath123 @xmath6 , then we calculate @xmath124 , and the lower value agrees with the size of the boundary layer as estimated by bruch & duschl ( 1993 ) .
however , @xmath125 of rs oph as derived in sect .
4.1 is too low for a boundary layer . *
( iii ) * for uu aqr , baptista & bortoletto ( 2008 ) found no evidence of flickering generated in regions * ( i ) * and * ( ii)*. they suggested that the flickering in uu aqr is generated in the accretion disk itself and a possible reason can be turbulence generated after the collision of disk gas with the density - enhanced spiral wave in the accretion disk . the radial temperature profile of a steady - state accretion disk is : @xmath126 , \ ] ] where @xmath127 is the stefan - boltzmann constant , @xmath19 is the radial distance from the wd . using the parameters for rs oph , a temperature @xmath1289500 k ( the temperature of the flickering light source as derived in sect . [ tfl ] ) should be achieved at a distance @xmath129 @xmath80 from the wd .
if * ( iii ) * is the place for the origin of the flickering of rs oph , then it comes from @xmath19 .5ex 1 @xmath80 from the wd . to understand more fully the nature of the flickering variability of rs oph we need to acquire a set of spectra simultaneously with photometry and with time resolution @xmath130 seconds ( see also sokoloski 2003 ) .
such spectra potentially can directly give the spectrum of the flickering light source .
we report our ccd observations of the flickering variability of the recurrent nova rs oph , simultaneously with 4 telescopes in the @xmath16 bands .
rs oph has a flickering source with @xmath1 , @xmath2 , @xmath3 . for the flickering light source in rs oph ( 1 ) we estimate @xmath131 k , which is similar to the temperature of the bright spot in cvs ; ( 2 ) using a distance of @xmath7 kpc , we find size @xmath132 @xmath80 , and luminosity @xmath133 .
we find that on the @xmath8 vs @xmath9 diagram the flickering of the symbiotic stars differs from the flickering of the cataclysmic variables .
the possible sites for the origin of the flickering are briefly discussed and it is suggested that time - resolved spectroscopy should be carried out to explore this in more detail .
rkz , ag , and kas acknowledge the partial support by bulgarian nsf ( htc01 - 152 ) and slovenian research agency ( bi - bg/09 - 10 - 006 ) .
we are grateful to the referee , dr .
p. woudt , for very helpful comments on the initial version of this paper . | we report observations of the flickering variability of the recurrent nova rs oph at quiescence on the basis of simultaneous observations in 5 bands @xmath0 .
rs oph has flickering source with @xmath1 , @xmath2 , @xmath3 .
we find for the flickering source a temperature @xmath4 k , and luminosity @xmath5 @xmath6 ( using a distance of @xmath7 kpc ) .
we also find that on a @xmath8 vs @xmath9 diagram the flickering of the symbiotic stars differs from that of the cataclysmic variables .
the possible source of the flickering is discussed .
the data are available upon request from the authors and on the web www.astro.bas.bg/@xmath10 rz / rsoph.ubvri.2010.mnras.tar.gz . [ firstpage ] stars : individual : rs oph binaries : symbiotic binaries : novae , cataclysmic variables |
fibrous dysplasia is a genetic , non - inheritable bone disease due to activating mutations of subunit of stimulatory g - protein ( gs ) resulting in defective osteoblast differentiation .
when associated with endocrine dysfunction and/or caf - au - lait spots it is termed as mccune - albright syndrome ( mas ) .
the classical presentation is the skeletal involvement of long bones , ribs and craniofacial bones .
here we present two cases of polyostotic fibrous dysplasia diagnosed in adulthood with predominant spinal involvement .
we also report f - fdg pet findings and its value in assessment of fibrous dysplasia .
a 44 year old male presented with insidious onset gradually progressive symmetrical , inflammatory polyarthralgia predominantly involving small joints of hands of six months duration ; diagnosed and treated as seronegative arthritis with analgesics and methotrexate .
there was no history of bone pains , deformity of the joints / bones or systemic symptoms .
general and systemic examination was unremarkable except arthritis , of which clinical disease activity index was 32 ( maximum of 76 ; 21 indicating severe disease activity ) .
laboratory evaluation revealed a haemoglobin of 15.1 g / dl , total leucocyte count of 8,700 cells / cu.mm , normal differential count , erythrocyte sedimentation rate of 45 mm fall at one hour ( 0 - 10 ) .
all his biochemical parameters were normal except for elevated alkaline phosphatase 350 iu / l .
c - reactive protein was 12 mg / dl ( < 10 ) , rheumatoid factor was 7.0 iu / ml , anti - cyclic citrullinated peptide antibody was 4.2 iu / ml ( < 5 ) , anti - nuclear antibody was 4.8 u ( < 20 ) , anti - dsdna was 32.2 iu / ml ( < 35 ) , hla - b27 negative and anti - neutrophilcytoplasmic autoantibodies were negative . skeletal survey revealed multiple mixed lytic and sclerotic lesions in vertebral bodies and posterior elements from 8 thoracic to 5 lumbar vertebra [ figure 1 ] and expansile lytic lesions were seen in 8 , 11 and 12 rib . magnetic resonant image ( mri ) of the spine showed destructive changes in the vertebral bodies and posterior elements from 8 dorsal vertebrae to 5 lumbar vertebrae .
his bone mineral density ( bmd ) by dual energy x - ray absorptiometry ( dxa ) was normal ( t - score-0.9 and z - score-0.4 at lumbar spine ) .
serum electrophoresis did nt reveal m band and bone marrow aspiration was cellular and reactive .
oncological markers such as serum prostate specific agent ( psa ) , carcino - embryogenic agent ( cea ) and carbohydrate antigen ( ca)-19.9 were within normal limits .
an open biopsy from left 8 rib revealed the diagnosis of fibrous dysplasia in 2005 .
there was no evidence of caf - au - lait spots and his endocrinal evaluation including thyroid adrenal and pituitary function tests were normal .
radiograph of case one showing multiple osteolytic and expansile lesions in the spine anterior and posterior view of bone scan . in case
one increased uptake is seen only in lower thoracic and lumbar spine , whereas in case two spine , humerus , sternum , rib and pelvic bone is involved he was started on intravenous pamidronate , along with calcium and vitamin d supplements .
six months later he noted weight loss of 12 kgs in spite of preserved appetite .
his thyroid function test was consistent with thyrotoxicosis [ tri - iodothyronine ( t3 ) - 2.9 mg / dl ( 0.9 - 2.6 ) , thyroxin ( t4 ) -20.0 g / dl ( 5.5 - 13.0 ) and thyroid stimulating hormone ( tsh ) - 0.04 iu / ml ] .
technicium scan showed homogenous increased uptake in the thyroid with suppressed salivary uptake suggestive of hyperthyroid status .
he was also detected to have diabetes mellitus ( dm ) by oral glucose tolerance test ( ogtt , fasting 142 mg / dl and two hour 219 mg / dl ) .
there was also evidence of transaminitis ( sgot / sgpt 134/175 ) which persisted even after stopping methotrexate and test was positive for anti - hcv antibodies ; however hcv viral count was zero .
modified knodellishak score showed grade 1/18 and stage 1/6 on liver biopsy . in view of association of hyperthyroidism with fibrous dysplasia and underlying hcv infection
he developed post ablative hypothyroidism three months later and has been on thyroxine replacement since then .
once euthyroidism was achieved , result of repeat ogtt was suggestive of dm and started on metformin .
presently he is receiving zoledronic acid 4 mg twice yearly , methotrexate 7.5 mg weekly , thyroxine , metformin , calcium and vitamin d supplements .
his annual bone scans have showed stable disease . at his latest review f - fdg pet
was performed for the first time which showed both active and healed osseous lesions [ figure 4 ] .
a 27 year old man became symptomatic following repeated falls on a slippery surface with chronic low backache and neck pain for one year .
he also noticed bone pains and the severity progressed over six months to an extent that he had gross limitations of his daily activities , had to be bed bound and developed chronic insomnia .
he did nt have arthralgia , deformity of the joints / bones or systemic symptoms .
he weighed 69 kgs for a height of 170 cm ( he reported his height was 173 cm at the age of 18 years ) .
investigations revealed a haemoglobin of 14.2 g / dl ( 14 2.5 ) , total leucocyte count 7,500/cu.mm ( 4,000 - 11,000 ) , platelets 1,87,000/cu.mm ( 1,50,000 - 4,50,000 ) , erythrocyte sedimentation rate 5 mm fall at first hour ( 0 - 10 ) , fasting blood glucose 97mg / dl ( 70 - 100 ) , blood urea nitrogen 12 mg / dl ( 7 - 19 ) , creatinine 0.8mg / dl ( 0.5 - 1.6 ) , sodium 140 meq / l ( 135 - 149 ) , potassium 4.1meq / l ( 3.5 - 5.0 ) , bilirubin 0.9mg / dl ( < 1 ) , aspartate trasaminase 85 u / l ( < 40 ) , alanine trasaminase 78 u / l ( < 40 ) , alkaline phosphatase 354 u / l ( < 250 ) , protein 7.9 g / dl , albumin 4.2 g / dl , calcium 8.6 mg / dl ( 8.5 - 10.5 ) , phosphorous 3.8 mg / dl ( 2.5 - 4.5 ) , lactate dehydrogenase 811 u / l ( 230 - 460 ) and uric acid 7.2 mg / dl ( 2 - 6 ) .
crp was 6mg / l ( < 6 ) , hla - b 27 was negative .
x - ray of spine showed multiple lytic lesions with collapse of 8 dorsal vertebra and ill - defined radiolucencies in both pubic rami and ischium [ figure 5 ] . computed tomography of spine showed extensive involvement of spine , sternum , pelvis , heads of humerus and femur [ figure 6 ] .
mri spine showed extensive marrow infiltration of spine and pelvic bone and collapse of c3 , d1 and d8 vertebrae [ figure 7 ] .
he was evaluated for multiple myeloma with serum electrophoresis which was negative for m band , light chain assay was negative and bone marrow aspiration was dry and bone marrow biopsy showed extensive fibrosis ( ?
fdg - pet confirmed increased metabolic activity in above area and was suggestive of malignancy with highest suv of 7.6 in sacrum [ figure 4 ] .
parathormone ( pth ) was 13 pg / ml ( 10 - 65 ) , 25(oh ) vitamin - d was 65 ng / ml ( 30 - 150 ) and endocrinal evaluations ( thyroid , adrenal and pituitary function tests ) were normal .
bmd z - score at spine , hip and forearm were -2.6 , -0.8 and 0.5 respectively . with the suspicion of lymphoma , infective etiology , or secondary
a ct guided fine needle aspiration was done ; but was inconclusive . to obtain tissue diagnosis
an open biopsy of left sacral ala and a repeat bone marrow aspiration and biopsy from matched involved area from bone scan and ct scan at iliac spine was performed .
he was started on intravenous zoledronic acid 4 mg quarterly , calcium and vitamin d supplements .
spindle cell proliferation with immature new bone formation ( a ) and extensive fibrous tissue proliferation forming cartwheel pattern ( b ) pet - scan showing increased uptake in spine ( both cases ) , head of humerus , pelvis and head of femur ( case two ) radiograph showing multiple osteolytic lesions in the cervical , thoracic and lumbar spine and pelvis in case two ct scan of spine of case two showing multiple osteolytic lesions in cervical .
( a ) upper thoracic and sternum ( b ) lower thoracic ( c ) lumbar ( d ) sacrum and pelvis ( e ) and head of femur ( f ) mri spine showed extensive marrow infiltration of spine and pelvic bone and collapse of c3 , d1 and d8 vertebrae in case two
a 44 year old male presented with insidious onset gradually progressive symmetrical , inflammatory polyarthralgia predominantly involving small joints of hands of six months duration ; diagnosed and treated as seronegative arthritis with analgesics and methotrexate .
there was no history of bone pains , deformity of the joints / bones or systemic symptoms .
general and systemic examination was unremarkable except arthritis , of which clinical disease activity index was 32 ( maximum of 76 ; 21 indicating severe disease activity ) .
laboratory evaluation revealed a haemoglobin of 15.1 g / dl , total leucocyte count of 8,700 cells / cu.mm , normal differential count , erythrocyte sedimentation rate of 45 mm fall at one hour ( 0 - 10 ) .
all his biochemical parameters were normal except for elevated alkaline phosphatase 350 iu / l .
c - reactive protein was 12 mg / dl ( < 10 ) , rheumatoid factor was 7.0 iu / ml , anti - cyclic citrullinated peptide antibody was 4.2 iu / ml ( < 5 ) , anti - nuclear antibody was 4.8 u ( < 20 ) , anti - dsdna was 32.2 iu / ml ( < 35 ) , hla - b27 negative and anti - neutrophilcytoplasmic autoantibodies were negative . skeletal survey revealed multiple mixed lytic and sclerotic lesions in vertebral bodies and posterior elements from 8 thoracic to 5 lumbar vertebra [ figure 1 ] and expansile lytic lesions were seen in 8 , 11 and 12 rib . magnetic resonant image ( mri ) of the spine showed destructive changes in the vertebral bodies and posterior elements from 8 dorsal vertebrae to 5 lumbar vertebrae .
his bone mineral density ( bmd ) by dual energy x - ray absorptiometry ( dxa ) was normal ( t - score-0.9 and z - score-0.4 at lumbar spine ) .
serum electrophoresis did nt reveal m band and bone marrow aspiration was cellular and reactive .
oncological markers such as serum prostate specific agent ( psa ) , carcino - embryogenic agent ( cea ) and carbohydrate antigen ( ca)-19.9 were within normal limits .
an open biopsy from left 8 rib revealed the diagnosis of fibrous dysplasia in 2005 .
there was no evidence of caf - au - lait spots and his endocrinal evaluation including thyroid adrenal and pituitary function tests were normal .
radiograph of case one showing multiple osteolytic and expansile lesions in the spine anterior and posterior view of bone scan . in case
one increased uptake is seen only in lower thoracic and lumbar spine , whereas in case two spine , humerus , sternum , rib and pelvic bone is involved he was started on intravenous pamidronate , along with calcium and vitamin d supplements .
six months later he noted weight loss of 12 kgs in spite of preserved appetite .
his thyroid function test was consistent with thyrotoxicosis [ tri - iodothyronine ( t3 ) - 2.9 mg / dl ( 0.9 - 2.6 ) , thyroxin ( t4 ) -20.0 g / dl ( 5.5 - 13.0 ) and thyroid stimulating hormone ( tsh ) - 0.04 iu / ml ] .
technicium scan showed homogenous increased uptake in the thyroid with suppressed salivary uptake suggestive of hyperthyroid status .
he was also detected to have diabetes mellitus ( dm ) by oral glucose tolerance test ( ogtt , fasting 142 mg / dl and two hour 219 mg / dl ) .
there was also evidence of transaminitis ( sgot / sgpt 134/175 ) which persisted even after stopping methotrexate and test was positive for anti - hcv antibodies ; however hcv viral count was zero .
modified knodellishak score showed grade 1/18 and stage 1/6 on liver biopsy . in view of association of hyperthyroidism with fibrous dysplasia and underlying hcv infection
he developed post ablative hypothyroidism three months later and has been on thyroxine replacement since then .
once euthyroidism was achieved , result of repeat ogtt was suggestive of dm and started on metformin .
presently he is receiving zoledronic acid 4 mg twice yearly , methotrexate 7.5 mg weekly , thyroxine , metformin , calcium and vitamin d supplements .
his annual bone scans have showed stable disease . at his latest review f - fdg pet
was performed for the first time which showed both active and healed osseous lesions [ figure 4 ] .
a 27 year old man became symptomatic following repeated falls on a slippery surface with chronic low backache and neck pain for one year .
he also noticed bone pains and the severity progressed over six months to an extent that he had gross limitations of his daily activities , had to be bed bound and developed chronic insomnia .
he did nt have arthralgia , deformity of the joints / bones or systemic symptoms .
he weighed 69 kgs for a height of 170 cm ( he reported his height was 173 cm at the age of 18 years ) .
investigations revealed a haemoglobin of 14.2 g / dl ( 14 2.5 ) , total leucocyte count 7,500/cu.mm ( 4,000 - 11,000 ) , platelets 1,87,000/cu.mm ( 1,50,000 - 4,50,000 ) , erythrocyte sedimentation rate 5 mm fall at first hour ( 0 - 10 ) , fasting blood glucose 97mg / dl ( 70 - 100 ) , blood urea nitrogen 12 mg / dl ( 7 - 19 ) , creatinine 0.8mg / dl ( 0.5 - 1.6 ) , sodium 140 meq / l ( 135 - 149 ) , potassium 4.1meq / l ( 3.5 - 5.0 ) , bilirubin 0.9mg / dl ( < 1 ) , aspartate trasaminase 85 u / l ( < 40 ) , alanine trasaminase 78 u / l ( < 40 ) , alkaline phosphatase 354 u / l ( < 250 ) , protein 7.9 g / dl , albumin 4.2 g / dl , calcium 8.6 mg / dl ( 8.5 - 10.5 ) , phosphorous 3.8 mg / dl ( 2.5 - 4.5 ) , lactate dehydrogenase 811 u / l ( 230 - 460 ) and uric acid 7.2 mg / dl ( 2 - 6 ) .
crp was 6mg / l ( < 6 ) , hla - b 27 was negative .
x - ray of spine showed multiple lytic lesions with collapse of 8 dorsal vertebra and ill - defined radiolucencies in both pubic rami and ischium [ figure 5 ] . computed tomography of spine showed extensive involvement of spine , sternum , pelvis , heads of humerus and femur [ figure 6 ] .
mri spine showed extensive marrow infiltration of spine and pelvic bone and collapse of c3 , d1 and d8 vertebrae [ figure 7 ] .
he was evaluated for multiple myeloma with serum electrophoresis which was negative for m band , light chain assay was negative and bone marrow aspiration was dry and bone marrow biopsy showed extensive fibrosis ( ?
fdg - pet confirmed increased metabolic activity in above area and was suggestive of malignancy with highest suv of 7.6 in sacrum [ figure 4 ] .
parathormone ( pth ) was 13 pg / ml ( 10 - 65 ) , 25(oh ) vitamin - d was 65 ng / ml ( 30 - 150 ) and endocrinal evaluations ( thyroid , adrenal and pituitary function tests ) were normal .
bmd z - score at spine , hip and forearm were -2.6 , -0.8 and 0.5 respectively . with the suspicion of lymphoma , infective etiology , or secondary
a ct guided fine needle aspiration was done ; but was inconclusive . to obtain tissue diagnosis
an open biopsy of left sacral ala and a repeat bone marrow aspiration and biopsy from matched involved area from bone scan and ct scan at iliac spine was performed .
he was started on intravenous zoledronic acid 4 mg quarterly , calcium and vitamin d supplements .
spindle cell proliferation with immature new bone formation ( a ) and extensive fibrous tissue proliferation forming cartwheel pattern ( b ) pet - scan showing increased uptake in spine ( both cases ) , head of humerus , pelvis and head of femur ( case two ) radiograph showing multiple osteolytic lesions in the cervical , thoracic and lumbar spine and pelvis in case two ct scan of spine of case two showing multiple osteolytic lesions in cervical .
( a ) upper thoracic and sternum ( b ) lower thoracic ( c ) lumbar ( d ) sacrum and pelvis ( e ) and head of femur ( f ) mri spine showed extensive marrow infiltration of spine and pelvic bone and collapse of c3 , d1 and d8 vertebrae in case two
a year earlier mccune and albright had described association of skeletal lesion similar to fd in association with caf - au - lait spots and endocrinopathy which later was termed mccune - albright syndrome ( mas ) .
about five decades later mas and fd were shown to be due to activating somatic mutations gs ( mosaic type ) .
the presentation depends on the timing of mutation during the development of the embryo and the germ cell layer involved .
there is involvement of multiple tissues that are known to originate from the three embryonic germ layers - ectoderm ( e.g. , skin , craniofacial bone ) , endoderm ( e.g. , thyroid ) , and mesoderm ( e.g. , axial and appendicular bone ) .
the mutation in ectoderm leads to caf - au - lait spots with craniofacial fd , involvement of endoderm results in endocrinopathies and mesoderm leads to axial and appendicular fd . in our first case
there was involvement of mesoderm and endoderm whereas in second case in all probability only mesoderm was involved .
most patients with fd are diagnosed in childhood as they either present with endocrinopathy or fractures . in two largest studies isolated
leet et al . , found isolated fd in 23% of their 35 patients which included both adults and children .
adults are diagnosed to have fd when they are being evaluated for an unrelated illness or when they present with fracture .
a study from india reported that the most of their patients with fd were adult ( 68% ) and 76% of the adults had pfd .
here we have reported two cases of adult fd and both of them had predominant spinal involvement .
the distribution of skeletal lesion is classically described to involve craniofacial bones , ribs and extremities .
studies in the 1960 's reported that spine was rarely involved in pfd five of the 37 patients .
a recent study however reported involvement of spine in 39 of the 62 patients studied .
dorso - lumbar spine was the most common location followed by the sacrum and cervical spine .
in case-1 , it was during evaluation of arthritis that he was diagnosed to have skeletal lesions representative of fd which was confirmed by biopsy .
spine involvement was seen in nine vertebral segments , limited to lower thoracic and lumbar regions .
increase tracer uptake was seen in both anterior and posterior images of bone sac indicating extensive involvement of the spine .
leet et al . , reported involvement of three or more spinal segments in 23 patients with spinal pfd .
though fracture is a common complication of fd of extremities , it is rarely noted in spine .
case one developed hyperthyroidism few months after diagnosis of pfd . the most common endocrine dysfunction in mas is peripheral precocious puberty .
it can be subclinical , overt or rarely present with thyrotoxic crisis . in a study from india six of the 17 adults had endocrinopathy , the most common being acromegaly in five and hyperthyroidism in one .
these patients require definitive form of therapy for hyperthyroidism as the disease invariably recurs after anti - thyroid drugs are stopped .
. a detailed evaluation including virological and autoimmune work - up could nt point to a cause of this abnormality .
hepatic cholestasis is the most common involvement but our case had no abnormalities in serum bilirubin levels .
our case also had raised serum ldh and uric acid ; which can be explained by secondary myelofibrosis with rapid cell turnover of cells at un - involved site or extramedullary areas .
it aids in diagnosis , extent of skeletal involvement , prognostication and monitoring of therapy .
bone scan shows increased tracer uptake in the skeletal lesion either due to increased vascularity of these lesions or due to pathologic fractures .
bone scintigraphy can also pick up lesions which are not picked up by other imaging modalities and thus help in gauging the extent of disease . in case two
, scintigraphy picked up lesions which were not picked up by x - ray or mri .
however , ct scan was able to pick up the skeletal lesions similar to scintigraphy .
our cases ( one and two ) had a score of 0.66 and 12 respectively , which indicates a favorable outcome with respect to ambulation .
other imaging modalities like ct scan and mri though not necessary for diagnosis , usually done to exclude other conditions during evaluation and can be used to study the extent of the disease .
presence of lytic lesions , expansile nature , cortical disruption , sclerotic rim , decrease in body height and contour deformity can also be appreciated on ct scan .
mri shows hypointense lesions in t1-weighted sequences and hyperintense in t2-weighted sequences with occasional heterogeneous hyperintense enhancement in post - contrast images .
we were able to characterize the imaging findings on fdg - pet in both of our patients .
there have been numerous reports of fd , mimicking skeletal metastases , being diagnosed during work up of underlying malignancy . in a recent study of fdg - pet imaging in fd , the average standardized uptake value ( suv ) was 3.76 2.40 in early images and 4.51 3.07 in delayed images .
a high suv of 11.42 has been observed in fd , which is usually seen in malignancy .
it has been postulated that the increased suv could be due to metabolic turnover in the proliferating fibroblasts in the lesions . in case one
we were unable to have a baseline fdg - pet images as facilities became available recently at our centre .
the fdg - pet images taken at the latest follow up had showed both healed and active lesions , but scintigraphy had showed increased uptake in the corresponding lesion . the dichotomy between scintigraphy and fdg - pet has not been reported .
if this is confirmed in subsequent studies fdg - pet could be superior to follow the treatment response of fd .
bisphosphonate suppress osteoclast which are the target of excess interleukin-6 ( known to activate osteoclasts ) secreted by fibrous cells and postulated as possible mechanism of lytic lesions in fd .
case one was initiated on intravenous pamidronate and is subsequently receiving zoledronic acid twice yearly .
he has stable disease and in fact the latest bone scintigraphy shows regression in the some lesions .
the skeletal lesion shows mosaic pattern i.e. , both normal and abnormal cells are present .
the abnormal cells over a period of time undergo apoptosis and there is proliferation of normal cells .
this phenomenon can be clinically appreciated by the fact that the incidence of fractures decreases as the patient age increases .
hence , teriparatide may accelerate apoptosis of abnormal cells and stimulate normal cells which will enhance normal bone formation . another potential drug in treatment of fd
is tocilizumab , an anti - il6 receptor human monoclonal antibody ; as il-6 has been implicated in pathogenesis of fd .
successful vertebroplasty has been performed in cases of fd with severe kyphosis and neurological involvement due to compression by expanding fd lesions or fracture .
the main limitation of this case report is absence of genetic analysis , which could not be performed due to lack of in house facility and financial constraints .
polyostotic fibrous dysplasia is a rare disease ; which can present in adults when investigated for unrelated cause .
it usually leads to many investigations to rule out common etiology of multiple osteolytic lesions like multiple myeloma ; myelo- and lympho - proliferative disorders ; infections and secondaries from primary malignant disease .
however ; being a stem cell disease the cure of disease may lie in mesenchymal stem cell transplantation . | polyostotic fibrous dysplasia is a rare non - inheritable genetic disease due to mutation in gnas gene .
here we present two adults who were accidentally detected lytic lesions in spine and after extensive evaluation for malignancies ; was diagnosed on biopsy .
current concept of the disease and management is discussed . |
micro - swimmers are of general interest lately , motivated by both engineering and biological problems @xcite
. they can be remarkably subtle as was illustrated by e. m. purcell in his famous talk on life at low reynolds numbers " @xcite where he introduced a deceptively simple swimmer shown in fig .
[ fig : purcell ] .
purcell asked `` what will determine the direction this swimmer will swim ? ''
this simple looking question took 15 years to answer : koehler , becker and stone @xcite found that the direction of swimming depends , among other things , on the stroke s _ amplitude _ : increasing the amplitudes of certain small strokes that propagate the swimmer to the right result in propagation to the left .
this shows that even simple qualitative aspects of low reynolds number swimming can be quite un - intuitive .
purcell s swimmer made of three slender rods can be readily analyzed numerically by solving three coupled , non - linear , first order , differential equations @xcite . however , at present there appears to be no general method that can be used to gain direct qualitative insight into the properties of the solutions of these equations .
our first aim here is to to describe a geometric approach which allows one to describe the qualitative features of the solution of the swimming differential equations without actually solving them .
our tools are geometric .
the first tool is the notion of curvature borrowed from non - abelian gauge theory @xcite .
this curvature can be represented graphically by landscape diagrams such as figs .
[ fig : optstrkhh],[fig : fphieta=2],[fig : purcellcurvx ] which capture the qualitative properties of general swimming strokes .
we have taken care not to assume any pre - existing knowledge about gauge theory on part of the reader .
rather , we have attempted to use swimming as a natural setting where one can build and develop a picture of the notions of non - abelian gauge fields .
purcell s original question , `` what will determine the direction this swimmer will swim ? ''
can often be answered by simply looking at such landscape pictures .
our second tool is a notion of metric and curvature associated with the dissipation .
the `` dissipation curvature '' can be described as a landscape diagram and it gives information on the geometry of `` shape space '' .
this gives us useful geometric tools that give qualitative information on the solutions of rather complicated differential equations .
we begin by illustrating these geometric methods for the symmetric version of purcell s swimmer , shown in fig .
[ fig : symmetric - p ] .
symmetry protects the swimmer against rotations so it can only swim on a straight line .
this makes it simple to analyze by elementary analytical means . in particular , it is possible to predict , using the landscape portraits of the swimming curvature fig .
[ fig : optstrkhh ] , which way it will swim .
in this ( abelian ) case the swimming curvature gives full quantitative information on the swimmer .
we then turn to the non - abelian case of the usual purcell s swimmer which can also rotate .
there are now several notions of swimming curvatures : the rotation curvature and the two translation curvature .
the translation curvatures are non - abelian .
this means that they give precise information of small strokes but this information can not be integrated to learn about large strokes
. this can be viewed as a failure of stokes integration theorem .
nevertheless , as we shall explain , they do give lots of qualitative information about large strokes as well . .
the location of the swimmer in the plane is determined by two position coordinates @xmath0 and one orientation @xmath1 .
the lengths of each arm is @xmath2 and the length of the body @xmath3.,title="fig:",width=302 ] +
purcell s swimmer , which was invented as the simplest animal that can swim that way " @xcite , is not simple to analyze . a variant of it that is simple to analyze is shown in the fig [ fig : symmetric - p ] . and the length of the body @xmath3 .
the position of the swimmer is denoted by @xmath4 . , title="fig:",width=8 ] + the swimmer has four arms , each of length @xmath5 and one body arm of length @xmath3 , ( possibly of zero length ) .
the swimmer can control the angles @xmath6 and the arms are not allowed to touch .
both angles increase in the counterclockwise direction , @xmath7 .
being symmetric , this swimmer can not rotate and can swim only in the `` body '' direction .
it falls into the class of `` simple swimmers '' which includes the `` three linked spheres '' of najafi and glolestanian @xcite and the pushmepullyou @xcite , whose hydrodynamics is elementary because they can not turn .
let us first address purcell s question `` what will determine the direction this swimmer will swim ? '' for the stroke shown in fig . [
fig : optstrkhh ] . in the stroke ,
the swimmer moves the two arms backwards together and then bring them forward one by one .
the first half of the cycle pushes the swimmer forward and the second half pulls it back .
which half of the cycle wins ? to answer that , one needs to remember that swimming at low reynolds numbers relies more on effective anchors than on good propellers .
since one needs twice the force to drag a rod transversally than to drag it along its axis @xcite , an open arm @xmath8 acts like an anchor .
this has the consequence that rowing with both arms , in the same direction and in phase , is _ less effective _ than bringing them back out of phase .
the stroke actually swims backwards .
this reasoning also shows that the swimmer is sisyphian : it performs a lot of forward and backward motion for little net gain .
the swimming equation at low reynolds number is the requirement that the total force ( and torque ) on the swimmer is zero .
the total force ( and torque ) is the sum of the forces ( and torques ) on the four arms and body . for the symmetric swimmer ,
the torque and force in the transversal direction vanish by symmetry .
the swimming equation is the condition that the force in the body - direction vanishes .
this force depends linearly on the known rate of change of the controls , @xmath9 and the unknown the velocity @xmath10 of the `` body - rod '' .
it gives a linear equation for the velocity .
for slender arms and body , the forces are given by cox @xcite slender body theory : the element of force , @xmath11 , acting on a segment of length @xmath12 located at the point @xmath13 on the slender body is given by @xmath14 where @xmath15 is a unit tangent vector to the slender - body at @xmath13 and @xmath16 its velocity there .
@xmath17 is the viscosity and @xmath18 the slenderness ( the ratio of length to diameter ) .
the force on the a - th arm depends linearly on the velocities of the controls @xmath19 and swimming velocity @xmath10 .
for example , the force component in the x - direction on the a - th arm takes the form _
f_aj^x_j+f_a^xxx where @xmath20 are functions of the controls , given by elementary integrals [ eq : f_jk ] f_a^xx= k ( ^2_a-2 ) _ 0^ds , f_aj^x=2 k_j _ 0^s ds similar equations hold for the left arm and the body .
the requirement that the total force on the swimmer vanishes gives a linear relation between the variation of the controls and the displacement @xmath21 @xmath22 where [ eq : a - def ] a(,)= , = as one expects , the body is just a `` dead weight '' and a trim swimmer with @xmath23 is best .
.,title="fig:",width=453 ] + the notation @xmath21 stresses that the differential displacement does not integrate to a function of the controls , @xmath24 .
this is the essence of swimming : @xmath25 fails to return to its original value with @xmath26 .
for this reason , swimming is best captured not by the differential one - form @xmath21 but by the differential two - form @xmath27 @xmath28 and @xmath29 is the rational function given in eq .
( [ eq : a - def ] ) .
@xmath30 is commonly known as the curvature @xcite and its surface integral for a region enclosed by a curve @xmath31 gives , by stokes , the distance covered in one stroke .
it gives complete information on both the direction of swimming and distance .
the total curvature associated with the full square of shape space , @xmath32 is 0 by symmetry . the total positive curvature associated with the triangular half of the square
, @xmath33 is 0.274 .
this means that swimmer can swim , at most , about a quarter of its arms length in a single stroke .
@xmath30 is a differential two form and as such is assigned a numerical value only when in comes with a region of integration . by itself
, it has no numerical value . to say that the curvature is large at a given point in shape , or control , space requires fixing some a - priori measure .
for example one can pick the flat measure for @xmath26 in which case @xmath34 gives numerical values for the curvature .
however , one can pick instead the flat measure for @xmath35 one gets a different function .
a natural measure on shape space is determined by the dissipation .
we turn to it now .
the power of swimming at low reynolds numbers is quadratic in the driving : @xmath36 where @xmath37 is a function on shape space and we use the summation convention where repeated indices are summed over .
this suggests the natural metric in shape space is , in either coordinate systems , @xmath38 in particular , the associated area form is d_1d_2= d_1d_2 the curvature can now be assigned a natural numerical value [ eq : numerical - curvature ] 2 a^2(,)= 2 a^2(,)_1_2 each arm of the symmetric purcell swimmer dissipate energy at the rate [ eq : dissipation - arm ] -_0^df(s)vds & = & -k_0^ ( ( tv)^2 -2 vv)ds + & = & -k_0^ ( x^2 - 2 s^2 _
j^2 ^2_j-2(s _ j_j - x)^2 ) ds + & = & 3 ( 3x^2 + 2 _ j^2 + 6 _ j x ) and the total energy dissipation by the arms is evidently [ eq : dissipation ] 3 ( 6x^2 + 2 ( _ 1 ^ 2+_2 ^ 2 ) + 6 ( _ 1+_2 ) x ) in a body - less swimmer , @xmath23 , this is also the total dissipation , and we consider this case from now on . since we are interested in the metric up to units , we shall henceforth set . ]
@xmath39 . plugging the swimming equation , eq . (
[ eq : dx ] ) gives @xmath40 : [ eq : metric ] g()=a(,0 ) ( cc 5 - 2_2 ^ 2 + _ 1 ^ 2 & _ 1 _ 2 +
_ 1 _ 2 & 5 - 2_1 ^ 2 + _ 2 ^ 2 + ) , _ j=_j and @xmath41 is given in eq .
( [ eq : a - def ] ) . in particular
, @xmath42 is a smooth function on shape space while @xmath43 is singular at the boundaries .
one can now meaningfully plot the curvature which is shown in fig .
[ fig : optstrkhh ] efficient swimming covers the largest distance for given energy resource and at a given speed .
alternatively , it minimizes the energy needed for covering a given distance at a given speed . fixing the speed for a given distance is equivalent to fixing the time @xmath44 . in this formulation
the variational problem takes the form of a problem in lagrangian mechanics of minimizing the action @xmath45 where q is a lagrange multiplier .
@xmath21 is given in eq .
( [ eq : dx ] ) . this can be interpreted as a motion of a a charged particle on a curved surface in an external magnetic field @xcite .
conservation of energy then says that the solution has constant speed ( in the metric @xmath40 ) . for a closed path ,
the kinetic term is then proportional to the length of the path and the constraint is the flux enclosed by it .
thus the variational problem can be rephrase geometrically as the isoperimetric problem " : find the shortest path that encloses the most flux .
the charged particle moves on a curved surface .
how does this surface look like ? from the dissipation metric we can calculate , using brioschi formula @xcite , the gaussian curvature @xmath46 ( not to be confused with @xmath30 ) of the surface . a plot of it is given in fig .
[ fig : gausscurv ] . + inspection of fig .
[ fig : optstrkhh ] suggest that pretty good strokes are those that enclose only one sign of the curvature @xmath30 .
the actual optimal stroke can only be found numerically .
it is plotted in figure [ fig : optstrkhh ] .
the efficiency for this stroke is about the same as the efficiency of the purcell s swimmer for rectangular strokes of @xcite , but less than the optimally efficient strokes found in @xcite .
cox theory does not allow the arms to get too close .
how close they are allowed to get depends on the slenderness @xmath18 .
the smallest angle allowed @xmath47 must be such that @xmath48 . as the optimal stroke gets quite close to the boundary , with @xmath49 it can be taken seriously only for sufficiently slender bodies with @xmath50 , which is huge .
the optimal stroke is therefore more of mathematical than physical interest .
one can use a refine slender body approximation by taking high order terms in cox s expansion for the force .
this will leave the structure without changes , but will made eq .
[ eq : f - yosi ] and eq .
[ eq : metric ] much more complicated . from a mathematical point of view
it is actually quite remarkable that a minimizer exists . by this
we mean that the optimal stroke does not hit the boundary of shape space @xmath51 where cox theory is squeezed out of existence .
this can be seen from the following argument .
inspection of eq .
( [ eq : numerical - curvature ] ) and eq .
( [ eq : metric ] ) shows that the curvature vanishes linearly near the boundary of shape space ( this is most easily seen in the @xmath35 coordinates ) .
suppose now that the optimal path ran along the boundary .
shifting the path a distance @xmath52 away from the boundary would shorten it linearly in @xmath52 while the change in the flux integral will be only quadratic .
this shows that the path that hits the boundary can not be a minimizer .
purcell swimmer can move in either direction in the plane and can also rotate . since the euclidean group is not abelian ( rotations and translations do not commute ) the notion of `` swimming curvature '' that proved to be so useful in the abelian case needs to be modified .
as we shall explain , landscape figures can be used to give qualitative geometric understanding of the swimming and in particular can be used to answer purcell question `` what will determine the direction this swimmer will swim ? '' . however , unlike the abelian case , the swimming curvature does not give full quantitative information on the swimming and one can not avoid solving a system of differential equations in this case if one is interested in quantitative details . the location and orientation of the swimmer ( in the lab frame ) shall be denoted by the triplet @xmath53 where @xmath1 is the orientation of the swimmer , see fig .
[ fig : purcell ] , and @xmath0 are cartesian coordinates of the center of the `` body . '' .
] we use super - indices and greek letters to designate the response while lower indices and roman characters designate the controls @xmath54 .
the common approach to low reynolds numbers swimming is to write the equations of motion in a fixed , lab frame .
we first review this and then describe an alternate approach where the equations of motions are written in a frame that instantaneously coincides with the swimmer . by general principles of low reynolds numbers hydrodynamics
there is a linear relations between the change in the controls increases counterclockwise and @xmath55 clockwise . ]
@xmath56 and the response @xmath57 [ eq : linear - response ] -.1em.8ex-.6emdx^=a^_j d_j , ( summation over repeated indices implied . ) note that @xmath58 since there are two controls , while @xmath59 for the three responses .
the response coefficients @xmath60 are functions of both the control coordinates @xmath61 and the location coordinates @xmath62 of the swimmer in the lab .
however , in a homogeneous medium it is clear that @xmath63 can only be a function of the orientation @xmath1 .
moreover , in an isotropic medium it can only dependent on the orientation @xmath64 through [ eq : ra ] ^_i ( , ) = r^ ( ) a^_i ( ) ; r^ ( ) = ( * 20c 1 & 0 & 0 + 0 & & - + 0 & & + ) in the lab frame , the nature of the solution of the differential equations is obscured by the fact that one can not determine @xmath57 independently for different points on the stroke ( because of the dependence on @xmath65 ) .
the coefficients @xmath66 may be viewed as the transport coefficients in a rest frame that instantaneously coincides with the swimmer .
they play a key role in the geometric picture that we shall now describe . in the frame of the swimmer one
has [ eq : linear - response - non - ab ] -.1em.8ex-.6emdy^= a^_j d_j which is an equation that is fully determined by the controls
. the price one pays is that the @xmath67 coordinates can not be simply added to calculate the total change in a stroke @xmath31 , since one has to consider the changes in the reference frame as well . in order to do that
, @xmath67 must be viewed as ( infinitesimal ) elements of the euclidean group [ eq : euclidean ] e(y^)= ( ccc y^0 & y^0 & y^1 + - y^0 & y^0 & y^2 + 0 & 0 & 1 + ) the composition of @xmath67 along a stroke @xmath31 is a matrix multiplication [ eq : matrix - prod ] e()= _ e(dy^ ( ) ) the product is , of course , non commutative .
we denote generators of translations and rotations by [ eq : translations ] e^0= ( ccc 0 & 1 & 0 + -1 & 0 & 0 + 0 & 0 & 0 + ) , e^1= ( ccc 0 & 0 & 1 + 0 & 0 & 0 + 0 & 0 & 0 + ) , e^2= ( ccc 0 & 0 & 0 + 0 & 0 & 1 + 0 & 0 & 0 + ) they satisfy the lie algebra [ e^0,e^]=-^0e^,=0 where @xmath68 is the completely anti - symmetric tensor .
one can write eq .
( [ eq : linear - response - non - ab ] ) concisely as a matrix equation [ eq : matrix - form ] -.1em.8ex-.6emdy = a_j d_j,-.1em.8ex-.6emdy= y^e^ , a_j = a_j^e^ where @xmath67 and @xmath69 are @xmath70 matrices ( summation over repeated indices implied ) . ,
plotted with the flat measure on @xmath71,title="fig:",width=453 ] + plotted using the measure induced by dissipation , title="fig:",width=377 ] + once the ( six ) transport coefficients @xmath72 are known , one can , in principle , simply integrate the system of three , first order , non - linear ordinary differential equations , eq .
( [ eq : linear - response ] ) . this can normally be done only numerically .
numerical integration is practical and useful , but not directly insightful .
we want to describe tools that allow for a qualitative understating swimming in the plane without actually solving any differential equation .
low reynolds numbers swimmers perform lots of mutually cancelling maneuvers with a small net effect .
the swimming curvature measure only what fails to cancel for infinitesimal strokes . since reversing
a loop reverses the response , it is natural to expect , that @xmath73 for a closed ( square ) loop is proportional to the area form . integrating eq .
( [ eq : matrix - form ] ) around a closed infinitesimal loop gives y = d_1d_2 where = _ 1 a_2- _ 2 a_1 -[a_1,a_2 ] , = ^e^,_j= @xmath30 and @xmath74 are @xmath70 matrices .
@xmath30 has the structure of curvature of a non - abelian gauge field @xcite . in coordinates
, this reads ^= _ 1 a^_2- _ 2 a^_1 + ^0
( a^0_1 a^_2 - a^0_2 a^_1 ) , in the lab coordinates one has , of course , x^=^d_1d_2 , ^= r^ ( ) ^ ( ) , the curvature is abelian when the commutator vanishes .
this is the case in eq .
( [ eq : numerical - curvature ] ) and it is also the case for the rotational curvature .
the abelian curvature gives full information on the swimming of finite stroke by simple application of stokes formula .
this is , unfortunately , not the case in the non - abelian case .
one can not reconstruct the translational motion of a large stroke from the infinitesimal closed strokes @xmath74 because stokes theorem only works for commutative coordinates and @xmath74 are not .
+ for purcell swimmer , @xmath30 although explicit , is rather complicated . since the dissipation metric is complicated too , we give two plots of @xmath30 : figs .
( [ fig : fphieta=2 ] , [ fig : purcellcurvx],[fig : purcellcurvy ] ) give the curvature relative to the flat measure on @xmath71 , and describe how far the swimmer swims for small strokes . in figs .
( [ fig : fphinorm ] , [ fig : purcellcurvxnorm],[fig : purcellfynorm ] ) the curvature is plotted relative to the dissipation measure and it displays the energy efficiency of strokes . using cox theory , in a manner analogous to what was done in for the symmetric swimmer , one can calculate explicitly the force ( and torque ) on the @xmath75-th rod in the form f_a^= f_aj^_j + f_a^ x^ where @xmath76 are explicit and relatively simple functions of the controls ( compare with eq .
( [ eq : f_jk ] ) ) . the swimming equation are then given by _
a f_a^= ( _ af_aj^)_j + ( _ a f_a^ ) x^=0 this reduces the problem of finding the connections @xmath77 to a problem in linear algebra .
formally ^_j=(_a f_a^)^-1 ( _ af_aj^ ) where the bracket on the left is interpreted as a @xmath70 matrix , with entries @xmath78 , and the inverse means an inverse in the sense of matrices .
although this is an inverse of only a @xmath79 matrix the resulting expressions are not very insightful .
we spare the reader this ugliness which is best done using a computer program . picking the center point of the body as the reference fiducial point is , in the terminology of wilczek and shapere @xcite a choice of gauge .
this particular choice is nice because it implies symmetries of the connection @xmath77 @xcite .
observe first that the interchange @xmath80 corresponds to a rotation of the swimmer by @xmath81 . plugging this in eq .
( [ eq : ra ] ) one finds [ eq : symmetries - r ] a^_1 ( _ 1,_2)=\ { ll + a^_2 ( -_2,-_1 ) , & + -a^_2 ( -_2,-_1 ) , & + .
this relates the two half of the square divided by the diagonal @xmath82 .
a second symmetry comes from the interchange @xmath83 corresponding to the reflection of the swimmer around the central vertical of the middle link . some reflection shows then that [ eq : symmetries-2 ] a^_1 ( _ 1,_2)=\ { ll + a^_2 ( _ 2,_1 ) , & + -a^_2 ( _ 2,_1 ) , & + .
this relates the two halves of the square divided by the diagonal @xmath84 .
the symmetries can be combined to yield the result that @xmath85 and @xmath86 are anti - symmetric and @xmath87 is symmetric under inversion a^0_j()=-a^0_j(- ) , a^1_j()=a^1_j(- ) , a^2_j()=-a^2_j(- ) the rotational motion of purcell swimmer , in any finite stroke , is fully captured by the abelian curvature ^0 = ^0=_1 a^0_2- _ 2 a^0_1 this reflects the fact that rotations in the plane are commutative . the symmetry of eq .
( [ eq : symmetries - r ] ) implies [ eq : symmetries - r - d ] ( _ 2a^0_1 ) ( _ 1,_2)= ( _ 1a^0_2 ) ( -_2,-_1 ) and this says that @xmath88is _ ani - symmetric _ under reflection in the diagonal @xmath82 .
similarly , eq . ( [ eq : symmetries-2 ] ) implies [ eq : symmetries-2 ] ( _ 2a^0_1 ) ( _ 1,_2)= -(_1a^0_2 ) ( _ 2,_1 ) , and this says that @xmath89 is _ symmetric _ about the line @xmath84 .
( [ fig : fphieta=2 ] ) is a plot of the curvature and it clearly has the requisite symmetries . the total curvature associated with the full square of shape space vanishes ( by symmetry ) . for @xmath90 , one can see in fig .
[ fig : fphieta=2 ] three positive islands surrounded by three negative lakes .
the total curvature associated with the three islands is quite small , about 0.1 .
this means that purcell swimmer with @xmath90 turns only a small fraction of a circle in any full stroke . shown with the the tam and hosoi optimal distance stroke @xcite .
the curvature is given relative to the flat measure in @xmath71 .
, title="fig:",width=529 ] + .
the curvature is given relative to the flat measure in @xmath71 .
, width=453 ] the curvatures corresponding to the two translations of a swimmer with @xmath91 are shown in figs .
( [ fig : purcellcurvx],[fig : purcellcurvy],[fig : purcellcurvxnorm],[fig : purcellfynorm])(here we use @xmath91 for comparison with @xcite ) .
the symmetries of the figures are a consequence of eqs .
( [ eq : symmetries - r],[eq : symmetries-2 ] ) .
form the first we have [ eq : symmetries-3 ] ( _ 2a^_1 ) ( _ 1,_2)=- ( _ 1a^_2 ) ( -_2,-_1 ) , = 1,2 which implies that @xmath92 are _ symmetric _ under reflection in the diagonal @xmath82 . similarly , from the eq .
( [ eq : symmetries-2 ] ) we have [ eq : symmetries-4 ] ( _ 2a^_1 ) ( _ 1,_2)=\ { ll + ( _ 1a^2_2 ) ( _ 2,_1 ) , & + -(_1a^1_2 ) ( _ 2,_1 ) , & + .
this says that @xmath93 _ symmetric _ and @xmath94 _ anti - symmetric _ under reflection in the diagonal @xmath84 .
the curvatures for the translations is non - abelian and can not be used to _ calculate _ the swimming distances for _ finite _ strokes because the stokes theorem fails .
the landscape figures for the translational curvatures provide precise information on the swimming distance for infinitesimal strokes .
they are then also useful to characterize small strokes .
the question is how small is small ? for a stroke of size @xmath52 , the controls are of size @xmath95 and the swimming distance measures by the curvature is @xmath96 .
the error in this has terms .
] of the form @xmath97 .
this suggest that the relative error in the swimming distance as measured a finite stroke is of the order @xmath98 .
hence , a stroke is small provided @xmath99 .
clearly , a purcell swimmer swims substantially less than an arm length as the arm moves .
this says that @xmath100 and so strokes of the order of a radian can be viewed as small strokes .
the x - curvature is symmetric under inversion ^1()= ^1(- ) since both @xmath85 and @xmath86 are antisymmetric under inversion , one sees that the non - abelian part of the x - curvature is of order @xmath101 near the origin . the x - translational curvature , which is non - zero near the origin , is almost abelian for small strokes .
the y - curvature , in contrast , is anti - symmetric under inversion ^12()= -^2(- ) and so vanishes linearly at the origin .
the non - abelian part is also anti - symmetric under inversion , and it too vanishes linearly .
the y - curvature is therefore _ not _ approximately abelian for small strokes , but it is small . the swimming direction can be easily determined for those strokes that live in a region where the translational curvature has a fixed sign . this answers purcell s question for many strokes .
strokes the enclose both signs of the curvature are subtle .
purcell s swimmer can reverse its direction of propagation by increasing the stroke amplitude @xcite .
this can be seen from the landscape diagram , fig .
( [ fig : purcellcurvx ] ) : small square strokes near the origin sample only slightly negative curvature .
as the stroke amplitude increases the square gets larger and begins to sample regions where the curvature has the opposite sign , eventually sampling regions with substantial positive curvature .
the curvature landscapes are useful when one wants to search for optimal strokes as they provide an initial guess for the stroke .
( this initial guess can then be improved by standard optimization numerical methods . ) for example , tam and hosi @xcite looked for strokes that cover the largest possible distance . for strokes near the origin , a local optimizer is the stroke that bounds the approximate square blue region in fig .
[ fig : purcellcurvx ] ( in this case @xmath91 ) . the curvature normalized by dissipation , fig .
[ fig : purcellcurvxnorm ] gives a guide for finding efficient small strokes .
caution must be made , since while the displacement can be approximated from the surface area , the energy dissipation is proportional to the stroke s length and not the stroke s area . in regimes
where the gaussian curvature of the dissipation ( fig .
[ fig : gausscurvpurcell ] ) is positive - it is possible to have strokes with small length which bounds large area . in the case of purcell
s swimmer , this suggest two possible regimes : around the origin and the positive curvature island in the upper left ( lower right ) corner of fig . [
fig : gausscurvpurcell ] .
the optimizer near the origin is the optimal stroke found in @xcite , while the optimizer in the upper left corner @xcite - although more efficient ( pay attention to the values of @xmath102 in fig . [ fig : purcellfynorm ] ) , is of mathematical interest only , since it is near the boundary , where the first order slender body approximation eq .
( [ eq : cox ] ) is relevant only for extremely slender bodies . | we develop a qualitative geometric approach to swimming at low reynolds number which avoids solving differential equations and uses instead landscape figures of two notions of curvatures : the swimming curvature and the curvature derived from dissipation .
this approach gives complete information for swimmers that swim on a line without rotations and gives the main qualitative features for general swimmers that can also rotate .
we illustrate this approach for a symmetric version of purcell s swimmer which we solve by elementary analytical means within slender body theory .
we then apply the theory to derive the basic qualitative properties of purcell s swimmer . |
antioxidants are widely used in dietary supplements and have been investigated for the prevention of diseases such as cancer , coronary heart disease and even altitude sickness 1 .
vitamin c is found in high concentrations in immune cells , and is consumed quickly during infections 2 - 3 .
vitamin c has been hypothesized to modulate the activities of phagocytes , the production of cytokines and lymphocytes , and the number of cell adhesion molecules in monocytes 4 . on the other hand
, vitamin e supplementation induces a higher differentiation of immature t cells via increased positive selection by thymic epithelial cells , which results in the improvement of decreased cellular immunity in the aged .
when there is vitamin e deficiency most of the immune parameters show a downward trend , which is associated with increased infectious diseases and the incidence of tumors 5 .
some tumor cells can actually use antioxidants to protect themselves from natural cellular defense mechanisms , enabling them to survive and proliferate .
6 were investigating changes in breast cancer cells that allow them to survive without being attached to the normal extracellular matrix .
they found that treating cells with vitamin e - like antioxidants blocked the usual programmed cell death cycles , allowing the cells to survive free from their usual scaffolding by switching their metabolism to use fatty acids rather than glucose as fuel 6 .
liu and liu indicated that administration of vitamin e prevents thymocyte apoptosis in murine s180 tumor bearing mice 7 .
fodor and kunos 8 reported that subcutaneous injection of vitamin c in tumor mice resulted in a great increase in the size , whereas pollia 9 apparently did not observe a similar effect on the growth in vivo of a malignant dibenzanthracene tumor of the rat . in this work
, we conducted a comparative study of vitamin c and e in the development of sarcoma 180 in mice .
these vitamins showed significantly ( p<0.00001 ) improved great anticancer activity for dosages on the order of 100 mg / kg ( vitamin c ) and 400 mg / kg ( vitamin e ) .
transplantation of sarcoma 180 tumor was performed following the method of stock et al
10 and modified by komiyama 11 .
s180 cells ( 10 cells / mouse ) were implanted intraperitoneally into male albino mice .
data were analyzed by student 's t - test using the statistical program studyresult ( version 1.0 for windows ) .
mice were randomly divided into vitamin c and vitamin e - treated groups , respectively , to receive vitamin c ( 100 ; 200 mg / kg / day for 7 days in 1 ml of normal saline ) administered orally and vitamin e ( 100 ; 200 mg / kg / day for 8 days in 1 ml of normal saline ) by oral administration .
six days after tumor implantation , the animals were weighed , anesthetized by ether inhalation and killed by cervical dislocation , and the tumors carefully excised and weighed .
the negative control group was given normal saline ( 0.9% ) of the same volume according to body weight .
the animals were handled under the supervision of the ethics committee of the centro de cincias biolgicas ( ccb ) da universidade federal de pernambuco , recife , pernambuco , brasil .
transplantation of sarcoma 180 tumor was performed following the method of stock et al
10 and modified by komiyama 11 .
s180 cells ( 10 cells / mouse ) were implanted intraperitoneally into male albino mice .
data were analyzed by student 's t - test using the statistical program studyresult ( version 1.0 for windows ) .
mice were randomly divided into vitamin c and vitamin e - treated groups , respectively , to receive vitamin c ( 100 ; 200 mg / kg / day for 7 days in 1 ml of normal saline ) administered orally and vitamin e ( 100 ; 200 mg / kg / day for 8 days in 1 ml of normal saline ) by oral administration .
six days after tumor implantation , the animals were weighed , anesthetized by ether inhalation and killed by cervical dislocation , and the tumors carefully excised and weighed .
the negative control group was given normal saline ( 0.9% ) of the same volume according to body weight .
the animals were handled under the supervision of the ethics committee of the centro de cincias biolgicas ( ccb ) da universidade federal de pernambuco , recife , pernambuco , brasil .
the mean tumor weight of s180 in the vitamin e - treated group was lower than that in the vitamin c - treated group .
the tumoral inhibition is given by 10 : where c is the mean tumor mass of control group , t is the mean mass of treated group . from table 1 and figure 1 .
we observe that for large dosages of either vitamin c and vitamin e the mice died . for intermediate dosages
most cells express two different transporter systems for vitamin c ; a transporter system with absolute specificity for ascorbic acid and a second system that shows absolute specificity for dehydroascorbic acid 13 .
ascorbic acid is transported by the svct family of sodium - coupled transporters , with two isoforms molecularly cloned , the transporters svct1 and svct2 , which show different functional properties on different cell and tissue expression .
probably , the not linear inhibitory effect of vitamin c is caused by the saturation of svct2 and svct1 transporters inside tumor cells but only for vitamin c doses between 100 and 400 mg / kg .
however all experiments with different dosages indicates that appropriate dosages of vitamin e appear to have a better inhibitory behavior for the tumors than vitamin c. although more detailed investigation is necessary , the present results suggest that , at least for mice , 400 mg / kg vitamin e appears to be an ideal dosage for tumor inhibition .
on the other hand , there is significant statistical difference between the treatment with vitamin c and vitamin e , p < 0.00001 for tumor development in animals by student 's t - test .
our results suggest that vitamin e and vitamin c ( in a lower rate ) has inhibitory behavior on the growth of sarcoma in mice . in particular , for dosages on the order of 400 mg / kg and 100 mg / kg we obtained stronger effects .
thus , our results suggest a combatively stronger effect of vitamin e and that dosages could play an important role in the inhibitory properties of sarcoma 180 , but the mechanism remains unclear .
we suggest that stronger anti - tumor effect of vitamin e in relation to vitamin c is due to different mechanisms of anti - tumor action between these molecules .
vitamin c modulates the activities of phagocytes , the production of cytokines and lymphocytes that destroys the tumor cells . on the other hand
, vitamin e plays an important role in the differentiation of immature t cells in thymus . on the other hand ,
the dynamics of penetration of vitamins and drugs shows that a principal route of molecular penetration in cells is through lipid - rich intercellular routes 14 - 15 , the cell penetration of water - soluble vitamin c in tumors is very low . a substance having good lipid solubility diffuses well across the cells .
thus , it has been assumed that the vitamin e permeates well since this vitamin is very lipophilic . | in this work we have investigated the effects of vitamins c and e on tumors via the mice xenotransplant model of sarcoma 180 ( s180 ) in vivo .
the experimental results suggest that dosages of 100 mg / kg vitamin c and 400 mg / kg vitamin e yields a great inhibitory behavior on tumors . |
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CAIRO—A group of senior Egyptian generals landed in Washington on Sunday to try to mend one of the most serious rifts in years with the U.S.
Relations between the longtime allies have hit a new low following an Egyptian government raid on pro-democracy and human-rights groups and travel bans imposed on several of their American employees, threatening an alliance that is a pillar of U.S. strategy in the Middle East. Congress is considering slashing the $1.3 billion in annual military aid to Egypt.
The December raids on 10 nongovernmental organizations, including three American groups, were part of an investigation commissioned ... ||||| The firms had formed a joint effort called the PLM Group to advocate on behalf of the government of President Hosni Mubarak. He stepped down early last year after more than two weeks of street protests led by youth activists. According to the filings with the Justice Department, Egypt has paid PLM more than $4 million since 2007.
Photo
The severing of the contracts by the three firms comes weeks after the Egyptian government raided the offices of three American nonprofit groups that work with local organizations on election monitoring and government transparency. The groups are the International Republican Institute, the National Democratic Institute and Freedom House.
The Republican and Democratic institutes are loosely affiliated with the Republican and Democratic Parties. They were created by Congress and are financed through the National Endowment for Democracy, which was set up in 1983 to channel grants for promoting democracy in developing nations. Freedom House is a Washington-based group that promotes democracy and open elections.
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The National Endowment receives about $100 million annually from Congress. Freedom House also gets the bulk of its money from the American government, mainly from the State Department, according to tax records and budget documents.
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Officials in Egypt have long been critical of those groups, which have operated in the country without being officially registered. The work of the groups often provoked tensions between the United States and Egypt, whose leaders frequently complained that they were being undermined, according to American diplomatic cables obtained and distributed by WikiLeaks.
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Last year, The New York Times reported that several groups and individuals directly involved in the revolts and reforms sweeping the region, including the April 6 Youth Movement in Egypt, took part in training from the three groups, according to interviews and the diplomatic cables.
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Egypt, whose government gets $1.5 billion annually in military and economic aid from the United States, viewed efforts to promote political change with deep suspicion and even outrage.
Mr. Mubarak was “deeply skeptical of the U.S. role in democracy promotion,” said a diplomatic cable from the United States Embassy in Cairo dated Oct. 9, 2007.
According to a September 2006 cable, Mahmoud Nayel, an official with the Egyptian Ministry of Foreign Affairs, complained to American Embassy officials about the United States government’s “arrogant tactics in promoting reform in Egypt.” ||||| The American Embassy in Cairo on Sunday took the highly unusual step of sheltering U.S. citizens employed by nongovernmental organizations amid fears that they could be detained as part of a crackdown on pro-democracy groups, according to U.S. officials and a former NGO official.
The move comes a week after Sam LaHood, director of the International Republican Institute’s program in Egypt, was barred from boarding an international flight in Cairo. LaHood is the son of U.S. Transportation Secretary Ray LaHood. Several other NGO workers later learned that they had also been barred from leaving the country.
Moving the Americans into the neighborhood-size diplomatic compound in the center of the capital appeared to mark a dramatic worsening in Washington’s relationship with Cairo, which has been strained over the past year as the country’s ruling generals have sought to portray foreigners as agents of instability.
A senior State Department official said Sunday afternoon that a “handful of U.S. citizens have opted to stay in the embassy compound in Cairo while awaiting permission to depart Egypt.”
The official, who was not allowed to discuss the matter on the record, would not say whether LaHood was among those at the embassy, citing privacy rules. The official did not elaborate on the threat that prompted the embassy to open its doors to some of those targeted in an Egyptian investigation into the work of the organizations.
“They weren’t in immediate physical danger, that we are aware of,” the official added.
Raid on NGO offices
Egyptian authorities last month raided the offices of several U.S.-funded organizations, including IRI, the National Democratic Institute and Freedom House. The groups train Egyptian politicians and political parties and promote accountability and transparency in governance.
A former IRI official who has followed the case closely said Sunday that his former colleagues had indicated they would take shelter at the embassy only as a last resort, if they had reason to believe their arrest might be imminent. The former official spoke on the condition of anonymity because he is no longer a representative of the group.
Egyptian authorities have been examining the practices of dozens of Egyptian and foreign civil society organizations that receive foreign funding, saying they are operating without permission from the government. Such organizations have for years operated openly, but unofficially, because the government has not allowed them to register as NGOs.
LaHood said in an e-mail Sunday afternoon that he was still barred from leaving the country.
“Nothing has budged in our legal case,” he wrote. “Office still sealed, still on travel ban.”
He did not respond to an e-mail sent hours later inquiring about those who sought protection at the embassy, and his cellphone seemed to have been switched off.
IRI officials in Washington could not be reached for comment. Kathy Gest, a spokeswoman for the National Democratic Institute, said the organization’s staff in Cairo had not relocated.
The investigation has raised alarms in the Obama administration. President Obama called Egypt’s military ruler, Mohammed Hussein Tantawi, recently to express concern about the government's probe. State Department officials and U.S. lawmakers have made it clear to Egyptian officials that the crackdown could imperil future U.S. aid to Egypt, which for years has received roughly $1.3 billion annually, mostly in military assistance.
State Department spokeswoman Victoria Nuland on Friday told reporters in Washington that the United States has urged the Egyptian government to resolve its investigation promptly, lift the travel ban and develop a mechanism to allow NGOs to register.
“This harassment is counterproductive to the larger goal of Egyptians being able to get where they want to go, which is a more democratic, open, prosperous Egypt,” she said.
Low turnout at polls
Meanwhile, the Egyptian Foreign Ministry on Sunday responded to U.S. media reports that said lobbying firms in Washington abruptly dropped the country as a client over the crackdown on NGOs. The ministry said in a statement that the Egyptian government, not the lobbyists, had canceled the contract to save money.
The developments came as Egyptians cast ballots on the first day of the election for the upper house of parliament. In sharp contrast to the first day of voting for the lower house in November, when people lined up for blocks and voted in record numbers, polling stations were largely empty Sunday.
Voters and those who abstained from the polls Sunday cited a sense of weariness about the complex, staggered election process that is expected to conclude next month.
Egyptians see parliamentary elections as the first key test of the country’s transition to democracy after three decades of autocratic rule by Hosni Mubarak. But many say they have grown cynical about the promise of elections as the mood in Egypt has soured amid continuing clashes, protests and deepening economic stagnation.
Islamist parties won more than 70 percent of seats in the lower house of parliament, which was seated last week. The upper house, known as the Shura Council, is a consultative body that can weigh in on constitutional issues but otherwise has little authority. Mubarak had used the Shura Council to rubber-stamp his administration’s initiatives. Political analysts said that Islamists are widely expected to take control of the council.
“There’s a sense of resignation that Islamists will get the majority of votes,” said Mustapha Kamel el-Sayed, a political science professor at Cairo University, suggesting that feeling probably affected turnout. “There’s also election fatigue. Egyptians have been going to elections for the past six weeks, and I think they are fed up with too many elections.”
Fatma Mohammad Ibrahim, 62, was among the few voters at a polling station near the Nile around noon. “I put my country above everything,” she said, standing next to her husband. “I’m old and sick, but I’m here for my country’s sake.”
Menna el-Tohamy, 22, a university student, said she found out about the latest round of voting only on Saturday. She said she decided not to vote because she didn’t have time to learn about the candidates.
“Maybe we got depressed” after the initial phase, which saw a record turnout, she said. “We’re still in the same situation.
Wan reported from Washington. Special correspondent Ingy Hassieb in Cairo contributed to this report. | – The US embassy in Cairo has taken the extraordinary step of sheltering US citizens working for pro-democracy non-governmental organizations—ostensibly to protect them from the Egyptian government, which has raided some of their offices and prevented them from leaving the country. The move is a sign that tensions between Washington and Cairo have hit a new high, the Washington Post reports. Top Egyptian generals arrived in Washington yesterday to try to smooth those tensions over, according to the Wall Street Journal. They'll meet with officials from the State Department, Pentagon, and Congress. And while the NGOs will be a topic, State Department officials also intend to press the issue of democratic reforms, warning that US aid could be cut if they don't materialize. Meanwhile, the lobbying firms that had been representing Egypt in Washington have severed their contracts, after taking intense criticism following the NGO raids, the New York Times reports. |
despite the manifest stability of the dirac fermions in graphene against the effects of coulomb interaction,@xcite the nature of the possible broken symmetry phases at strong coupling continues to be an issue of fundamental importance @xcite .
the minimal onsite hubbard interaction , for example , when sufficiently strong , is believed to produce the antiferromagnetic nel ground state @xcite .
the universality class of the semimetal - to - nel insulator quantum phase transition can be captured by the effective gross - neveu - yukawa field theory@xcite , and studied systematically near the upper critical ( spatial ) dimension of three .
recent quantum monte carlo simulations of the hubbard model in a half - filled honeycomb lattice suggest a _
transition from the dirac semimetal to the nel state , with the critical exponents in reasonable agreement with the field - theoretic predictions.@xcite the correlated phases of graphene , nel state included , unfortunately may be laying at too strong a coupling to be realized in graphene in its pristine state , even when placed in vacuum .
@xcite in eq .
( [ hoppinglattice ] ) , which defines the modification of the hopping amplitude along each bond .
, width=330,height=226 ] the deformability of the graphene membrane may facilitate a different path towards the realization of some of the symmetry - broken phases at weaker couplings .
@xcite arguments along this line and in favor of the topological quantum anomalous ( spin ) hall insulator at weak finite - range repulsion @xcite , or of unconventional superconductors@xcite at weak attraction , have recently been put forward .
the physical reason behind this electro - mechanical phenomenon is the generic appearance of the single - particle zero - energy states in graphene under strain . upon bulging a graphene flake , the quasi - relativistic low - energy electronic degrees of freedom couple to a finite , time - reversal - symmetric , magnetic - like field.@xcite such an , and not necessarily uniform , _ axial _ magnetic field , similarly to the true magnetic field
, falls under the jurisdiction of index theorems,@xcite and as such brings a finite number of states close to the dirac point .
this creates an ideal situation for the fermions to form various particle - hole or particle - particle condensates at weak interactions .
the single - particle states at zero energy , responsible for the weak - coupling instabilities , are in the axial case , however , special:@xcite normalizability forces them to live exclusively on one of the two sublattices of the honeycomb lattice .
the remaining states in the zero - energy subspace , which would be discarded from the spectrum as non - normalizable in an infinite system , in a finite system are found near the boundary , and to be living on the opposite sublattice . of the wave - functions @xmath0 , living on a sublattice , in a system of @xmath1 sites or @xmath2 .
spatial distribution of their anti - symmetric combination @xmath3 , living on b sublattice , in the same system .
the axial magnetic field is set to be uniform here , i.e. , @xmath4 , with @xmath5.,title="fig:",width=321,height=236 ] of the wave - functions @xmath0 , living on a sublattice , in a system of @xmath1 sites or @xmath2 .
spatial distribution of their anti - symmetric combination @xmath3 , living on b sublattice , in the same system . the axial magnetic field is set to be uniform here , i.e. , @xmath4 , with @xmath5.,title="fig:",width=321,height=236 ] due to this inextricable correlation between the real - space and sublattice degrees of freedom within the zero - energy subspace the ground state of the hubbard model in strained graphene is non - trivial .
while it seems natural to expect that a short - range interaction such as hubbard s would lead to a spin - polarized hund " ferromagnetic state in the presence of a flat band in strained graphene , we show here , first via a self - consistent numerical calculations , that the ground state of the hubbard model in this system is more interesting : while it is locally displaying the expected ferromagnetic ordering , the sign of the magnetization varies in precisely such a way so that the total space - integrated magnetization in fact vanishes .
since the magnetization is tied to the zero - modes , however , its support , as well as its sign , also switches between the two sublattices when traversing the system from its bulk to the boundary , so that the nel order parameter is also finite , and of the same sign everywhere . the appearance of this unusual magnetic ordering is also supported by a quantum monte carlo calculation on the hubbard model on a half - filled strained honeycomb lattice .
we name this unconventional magnetic ordering the _ global ( edge - compensated ) antiferromagnet_. recent experimental progress in realizing the axial magnetic field in real and artificial graphene,@xcite offers hope for the detection of this unusual ground state . the paper is organized as follows . in the next section
we propose a specific modulation of the nearest - neighbor hopping amplitude that introduces a finite axial magnetic field in a graphene flake .
we also discuss and compare the zero - modes in the presence of the strain - induced axial , and true magnetic fields . in sec .
iii we introduce the on - site hubbard interaction , and discuss possible magnetic ground states in strained graphene . in sec .
iv we present the self - consistent hatree solution for the magnetic ground state in the presence of ( roughly ) uniform and well localized axial magnetic fields .
we contrast our results with the magnetic ground state in graphene in a true ( time - reversal symmetry breaking ) magnetic field in sec . v. quantum monte carlo simulation of the hubbard model in strained graphene
is presented in sec .
we summarize our findings in sec .
before delving into the effects of the electron - electron interactions , let us set the stage by reviewing the physics of zero - modes in the continuum and on the lattice , and by introducing a specific realization of the axial magnetic fields on a finite honeycomb lattice .
as well known , the low energy degrees of freedom in graphene may be collected into an 8-component dirac spinor @xmath6^\top$ ] , where @xmath7 @xmath8 @xmath9 @xmath10 @xmath11 $ ] , and @xmath12 are the two projections of electron spin along the z - axis.@xcite @xmath13 is the fermionic annihilation operator on a - sublattice , generated by the linear combination of basis vectors @xmath14 , @xmath15 , where @xmath16 is the lattice spacing , and @xmath17 is the fermionic creation operator on b - sublattice , where @xmath18 , with @xmath19 .
two inequivalent dirac points , or valleys , may be chosen as at @xmath20 , where @xmath21 .
when @xmath22 , the non - interacting low - energy hamiltonian with only the nearest - neighbor hopping takes the relativistically invariant form @xmath23 , with the first matrix acting on spin , and the second on sublattice and valley indices .
the coupling of the time - reversal - symmetric axial magnetic field @xmath24 to the low - energy dirac fermions then reads as@xcite @xmath25=\sigma_0 \otimes i \gamma_0 \gamma_j \left ( q_j - i \gamma_3 \gamma_5 a_j ( \vec{x})\right ) \equiv m(\chi ) h_d m(\chi),\ ] ] where @xmath26 , and @xmath27}$ ] .
the axial vector potential here is @xmath28 , and therefore @xmath29 .
the mutually anticommuting 4-dimensional @xmath30-matrices may be represented as @xmath31,@xmath32,@xmath33 , @xmath34 , @xmath35 .
@xmath36 are the usual two - dimensional pauli matrices . in this representation
the time - reversal symmetry operator is ( anti - linear ) @xmath37 , where @xmath38 is the complex conjugation.@xcite a random distribution of the axial gauge field in graphene , for example , results from the presence of ripples , with the net axial flux as zero .
if graphene is deliberately buckled , on the other hand , a finite total flux of the axial field may be introduced , which by index theorem would bring a finite number of states at zero energy .
these special zero - modes can be written as @xmath39(\vec{x})\ ; \propto \ ; e^{-\chi(\vec{x } ) ( \sigma_0 \otimes \gamma_0 ) } \ ; \psi_{0,n } \ ; \left[0\right](\vec{x}).\ ] ] the number of zero energy states labeled by index @xmath40 equals the total axial flux through the system .
the matrix @xmath41 in the exponent changes sign between two sublattices , whereas the function @xmath42 is a monotonic function at a large distance @xmath43 from the location of the axial flux .
the normalizable zero - energy states therefore must reside only on one of the two sublattices , which we will call the sublattice @xmath44 . on the finite honeycomb lattice ,
these are the bound states in the interior of the system , where the flux is located .
the remaining non - normalizable zero energy states , with the support on the sublattice b , on the other hand , in the continuum increase exponentially towards the infinity . on a finite lattice , however , this is tantamount to their localization _ near the boundary _ of the system .
( [ diracaxial ] ) suggests an introduction of an axial magnetic field on a lattice via the following modification of the nearest - neighbor hopping amplitude ( @xmath45 ) @xmath46 where @xmath47 , @xmath48.@xcite hereafter we set @xmath49 for convenience .
let us define a quantity , say @xmath50 , which counts the minimal number of bonds required to reach a particular site in the system from the central hexagon ( centered at @xmath51 ) in fig . 1 .
for all the six sites on the central hexagon of the system @xmath52 , for example .
we then assign the parameter @xmath53 , such that for all the sites with same @xmath50 , @xmath53 is same , as shown in fig .
1 , and the hopping between nearest - neighbor sites are modified according to eq .
( [ hoppinglattice ] ) .
otherwise , @xmath53 increases monotonically from the center towards the boundary of the system . as a result
, a finite axial magnetic field is introduced in the system .
for example , if @xmath54 the system experiences a roughly uniform axial field , whereas a bell - shaped localized axial flux around the center of the system can be realized by setting @xmath55 .
this configuration of @xmath56 is slightly different than in the previous work @xcite , with the advantage that the increase of the band width in the presence of axial fields can be somewhat better controlled here . upon introducing such modification in the nearest - neighbor hopping amplitude , the strained honeycomb lattice , shown in fig . 1 , is invariant under a @xmath57 symmetry , and thus the applied strain in our system is tri - axial . in a finite strained honeycomb lattice
there are of course no states at precise zero energy . nevertheless , irrespective of the spatial profile of the axial magnetic field , there are always a finite number of states in the close vicinity of the zero energy,@xcite which bear the signature of the axial magnetic field .
lets consider two such states @xmath58 , with the energies @xmath59 , where @xmath60 .
the symmetric @xmath61 and the anti - symmetric @xmath62 combinations of these two states live on a and b sub - lattice , respectively . in the presence of axial magnetic fields , @xmath63 lives inside the bulk , as shown in fig .
2(top ) and corresponds to the normalizable zero energy states in eq .
( [ zerostate ] ) .
the @xmath64 lives near the boundary of a finite system , as shown in fig.2 ( bottom ) , and is to be identified as the non - normalizable state in the continuum description .
hence , the bulk and the boundary of a finite graphene system become inequivalent in their sublattice structure in the presence of axial magnetic fields .
number of recent experiments have already revealed the existence of zero - energy subband in strained real@xcite and artificial@xcite graphene . in particular , when the axial ( uniform ) magnetic field @xmath65 t is introduced in strained molecular / artificial graphene , site - resolved scanning tunneling microscope ( stm ) measurements clearly indicate the existence of zero - energy states on the a - sublattice in the interior of the system@xcite . a careful examination ,
however , also shows that there are finite number of zero energy states in the close vicinity of the system s boundary , which , on the other hand , are localized on the other sublattice ( b ) .
in addition , the zero - modes residing near the boundary are predominantly localized around three of the edges of the hexagonal strained molecular honeycomb lattice , connected through rotations by @xmath66 .
all these observations are in accordance with the spatial and sublattice structure of the zero - modes , shown in fig . 2 , obtained by applying a specific modulation of the nearest - neighbor hopping amplitude ( fig .
1 ) that serves to capture the effect of the axial magnetic field in a finite honeycomb lattice .
when @xmath67 t , it becomes more difficult to discern the zero - modes on the sublattice b , although near the edge zero bias stm shows bright spots along the nearest - neighbor bonds , possibly revealing this way the overlap among the zero energy states localized on a and b sublattices .
our numerical analysis of the zero modes also exhibits the existence of such region , where the zero modes on two sublattices overlap , see fig . 2 .
it is worth contrasting the structure of the zero energy subspaces in the presence of true vs. axial magnetic field .
coupling of dirac fermions to the true magnetic field involves the same eq .
( [ diracaxial ] ) , except for the replacement of the matrix @xmath68 by the 4-dimensional unit matrix , and for taking the matrix @xmath69 to be @xmath70}$ ] .
likewise , the zero energy states in the true magnetic field still have the form of @xmath71 in eq .
( [ zerostate ] ) , but with the matrix @xmath41 in the exponent replaced by @xmath72 . as a consequence ,
the normalizable zero - modes now reside on both sublattices . in a finite graphene system in a true magnetic field ,
the near - zero - energy states , residing in the bulk , similarly populate equally both sublattices .
the non - normalizable zero - modes in the continuum , located near the boundary in a finite system , are _ also _ shared equally between the two sublattices .
hence , in stark contrast to the axial field , in the presence of true magnetic field , the interior and the boundary of a finite honeycomb lattice have the same unresolved sublattice structure .
let us focus next on the effect of electron - electron interaction in strained graphene , with the chemical potential ( @xmath73 ) tuned to the charge neutrality point .
here we consider only the onsite hubbard interaction ( @xmath74 ) among the fermions .
the standard hubbard hamiltonian is @xmath75 with the interaction hamiltonian given by @xmath76 and where @xmath77 is the fermionic number operator with spin projection @xmath12 at site @xmath78 .
the total number of electrons in the system is @xmath79 .
the charge - neutrality in the system is maintained through the constraint @xmath80 .
the usual hartree decomposition of the onsite interaction leads to an effective single particle hamiltonian @xmath81 one can rewrite @xmath82 as @xmath83 where @xmath84 respectively represents @xmath85 projections of electron s spin along @xmath86-axis .
@xmath87 corresponds to the site - dependent local deviation of the electronic density from the uniform background , and is to be determined self - consistently in a finite honeycomb lattice in presence of the axial magnetic field representing strain .
we here always take the system to be _ quasi - circular _ , and @xmath88 is a discrete variable , representing the @xmath89 ring of around center of the system . in the presence of ordering ( @xmath90 ) the overall charge neutrality of the system is achieved through the constraint @xmath91=0,\ ] ] in addition to @xmath80 .
notice that the fock decoupling of the hubbard term would yield expectation values of the components of the local magnetization that are orthogonal to the chosen ( @xmath86 ) direction , which we neglect .
depending on the relative sings of the site parameters @xmath92s , one can realize two different magnetic ground states : @xmath93 if the ground state configuration is such that all @xmath94 in the above equation , then this would correspond to an antiferromagnetic phase , whereas @xmath95 a ground state with @xmath96 , but @xmath97 would be identified as a ferromagnetic state . before we proceed with the numerical simulation of the hubbard model , it is worth pausing to compare these two magnetic phases in strained graphene .
magnetization on the two triangular sublattices points in the opposite directions when the ground state is antiferromagnetic , whereas in a ferromagnet the two sublattice magnetizations are aligned .
recall that all the zero - modes in strained graphene are localized on one sublattice in the bulk , and on the other sublattice near the boundary of a finite system .
therefore , both the nel and the ferromagnetic orders in strained graphene give rise to a finite local magnetization everywhere in the system .
however , globally the two states may be distinguished . due to the spatial separation of the zero - modes that are localized on different sublattices , the magnetization in the state with an equal sign of the nel order parameter in the entire system would need to change sign as one approaches the boundary from the bulk , so that the total magnetization could in fact vanish . in the truly ferromagnetic state , on the other hand , the sign of the magnetization in the bulk and the boundary would be the same , so that the system would develop an overall finite magnetization .
we will show shortly through a detailed numerical calculation that by taking into account the entire zero subspace in a finite system , the magnetic ground state in strained graphene is uniquely determined to be of the first variety , i. e , a global antiferromagnet with zero total magnetization .
nevertheless , the continuum picture already provides a valuable insight into the nature of the competition between the nel and the ferromagnetic states .
the order parameters of these two states read as @xmath98 , and @xmath99 , respectively . both states
split the zero - energy subspace in strained graphene , and open a gap at the dirac points .
however , the matrix appearing in the nel order parameter anticommutes with the dirac hamiltonian , and as such it corresponds to a _ chiral - symmetry - breaking _ mass - term for the dirac quasi - particles . in the ferromagnetic order parameter , in contrast , the corresponding matrix commutes with the dirac hamiltonian . as a result
, besides the splitting of the zero - energy subspace common to both orders , the nel order at the mean - field level pushes down in energy _ all _ the filled states below the chemical potential .
in contrast , the ferromagnetic order parameter splits all the energy levels equally , half up and half down in energy , and therefore only lowers the energy of the half - filled zero - energy subspace . by spontaneously developing
the nel order the system can thus more efficiently minimize the ground state energy .
we now present the results of the self - consistent calculation of the magnetic order parameters with onsite hubbard interaction ( @xmath74 ) in strained graphene .
we numerically search for the self - consistent solution of @xmath92s with two different initial ansatz for the magnetic ordering @xmath93 when @xmath94 , which can be idenified as antiferromagnet ordering , and @xmath95 @xmath100 , which corresponds to a ferromagnetic order . here ,
all the @xmath92s are kept as a function of position , and we always maintain the overall charge - neutrality of the system . in the hartree self - consistent calculation , electronic spin
is treated as ising variable , @xmath101 , and the effect of fluctuation is neglected for a moment .
later we treat the fermionic spin as @xmath102 vectors in a separate quantum monte carlo simulation of the hubbard model in strained graphene , which explicitly takes into account the effect of the fluctuations .
we here search for the self - consistent solution of the magnetic order specifically for weak hubbard interactions , @xmath103 , where @xmath104 is the zero axial field critical strength of the onsite interaction for antiferromagnetic ordering@xcite . due to the presence of a finite density of state near the zero energy in strained graphene
, ordering takes place even for onsite interaction as weak as @xmath105 , irrespective of the spatial profile of the axial magnetic field , and a spectral gap opens up at the dirac points .
the resulting magnetic ground states is insensitive to the initial ansatz @xmath93 or @xmath95 , and thus our self - consistent analysis can be considered as variational calculation . to further explore the nature of such magnetic ground state ,
we define two local order parameters as @xmath106 which correspond to local nel and ferromagnetic order parameters , respectively .
@xmath92s are as defined in eq .
( [ decomposition ] ) .
we here obtain the numerical results in a quasi - circular honeycomb lattice of @xmath107 sites or @xmath108 .
in such a system the self - consistent solutions for all the @xmath92s are essentially without any finite size effects , for all values of the sub - critical hubbard interactions , down to @xmath109 , and for both the uniform and localized axial fields ( see the captions of fig . 3 and fig . 4 for details of these parameters ) .
self - consistent solutions of @xmath110 and @xmath111 in the presence of roughly uniform axial magnetic fields and a wide range of sub - critical on - site interaction are shown in fig .
3 ( upper panel ) and fig . 3 ( lower panel ) ,
respectively . from the spatial variation of these two order parameters
we see that the local antiferromagnetic order parameter @xmath110 is off the same sign in the bulk as well as in the boundary of the system , whereas @xmath111 near the boundary is of the opposite sign from the bulk .
the total magnetization for all chosen values of the interaction and uniform axial fields is _ zero _ within the numerical accuracy @xmath112 .
therefore , the magnetic ground state is indeed an antiferromagnet , as one would anticipate from the continuum description of this problem .
the nel order in strained graphene is different from the conventional one on the honeycomb lattice@xcite as it also carries a finite local magnetization everywhere in the system .
we dub this unconventional magnetic ground state _ global (
edge - compensated ) antiferromagnet_.
we also obtained the self - consistent solution for the magnetic ground state when the graphene flake is subject to non - uniform axial fields , localized in the vicinity of the center of the system .
the spatial variation of the local order parameters @xmath110 and @xmath111 , for a wide range of sub - critical interactions , and total flux of localized axial magnetic field is shown in fig .
4 ( upper panel ) , and fig . 4 ( lower panel ) ,
respectively , obtained in a quasi - circular system of @xmath107 sites ( @xmath108 ) . from figs . 3 and 4 , it is clear that the nature of the magnetic ground state is insensitive to the exact profile of the axial field , and it is always the global antiferromagnet
however , the location where the local magnetization changes its sign depends on the profile of the axial field . in the presence of uniform axial field
, magnetization flips its sign only very close to the boundary of the system , whereas in the presence of localized fields the same change occurs in the middle of the system .
the difference in the position of the domain wall between the two signs of the magnetization is tied to the spatial distribution of the zero energy states in the system . in the uniform axial field
the zero - modes on a - sublattice are distributed over a large portion of the bulk , whereas they are highly localized in the deep interior when the axial field is peaked near the center of the system .
therefore , the local magnetization suffers a change in sign roughly where the zero energy states on a - sublattice loose their support .
the magnitude of both of the order parameters @xmath110 and @xmath111 increases with the strength of the interaction and of the axial field , as shown in figs . 2 and 3 .
the spatial distribution of the zero - modes also dictates spatial variation of the nel order parameter .
note that in the presence of uniform axial fields , the nel order parameter @xmath110 is more or less uniform in the bulk ( @xmath113 ) of the system ( see fig . 3 , the upper panel ) .
the abrupt increment in @xmath110 near the boundary of the system arises from the existence of zero - energy states on the b - sublattice in that region .
when the axial field assumes a spatially localized profile , around the center of the system , the nel order parameter predominantly develops in the region where the axial flux penetrates the graphene flake ; see fig .
4 ( the upper panel ) .
the existence of the zero - energy states on the sites of the b - sublattice near the boundary leads to the spikes in @xmath110 even when the axial field is inhomogeneous .
therefore , the spatial modulation of the nel order follows closely the profile of the axial magnetic field , resembling in this regard the spatial variation of the quantum anomalous hall insulator in strained graphene with next - nearest - neighbor interaction.@xcite ) and ferromagnetic ( black dots , with @xmath114 ) order parameters per unit cell , in the presence of uniform true magnetic field of strength @xmath115 t. right : the same quantities in a localized true magnetic field , of the strength @xmath116 t at the center of the system .
the average magnetic field at each quasi - circular ring of the honeycomb lattice decreases as @xmath117 t , towards the boundary of the system .
strength of the hubbard interaction reads as @xmath118(red ) , @xmath119(blue ) , @xmath120(dark green ) , @xmath121(purple ) .
the ferromagnetic order is identically _
zero _ for all values of @xmath74 , both in uniform and nonuniform true magnetic fields.,title="fig:",width=160,height=113 ] ) and ferromagnetic ( black dots , with @xmath114 ) order parameters per unit cell , in the presence of uniform true magnetic field of strength @xmath115 t. right : the same quantities in a localized true magnetic field , of the strength @xmath116 t at the center of the system .
the average magnetic field at each quasi - circular ring of the honeycomb lattice decreases as @xmath117 t , towards the boundary of the system .
strength of the hubbard interaction reads as @xmath118(red ) , @xmath119(blue ) , @xmath120(dark green ) , @xmath121(purple ) .
the ferromagnetic order is identically _
zero _ for all values of @xmath74 , both in uniform and nonuniform true magnetic fields.,title="fig:",width=160,height=113 ]
the conical dispersion of the dirac quasi - particles quenches into a set of well separated landau levels , when the graphene flake is subject to a uniform true magnetic field .
although the discrete quantization of the spectrum smears out if the magnetic field is spatially modulated , a finite number of states at zero energy states always persists , irrespective of the profile of the magnetic fields.@xcite finite density of states near the dirac points , here as well , catalyzes the effect of electron - electron interactions . to compare the present unconventional magnetic ground state of the hubbard model in strained graphene with the one in the presence of a true magnetic field ,
we perform the same numerical self - consistent analysis in a finite honeycomb lattice , placed in uniform and nonuniform true magnetic fields .
the orbital effect of the true magnetic field is included by incorporating the peierls phase into the nearest - neighbor hopping amplitudes.@xcite we here omit the single - particle zeeman coupling of electron s spin with the magnetic field.@xcite in true magnetic field the zero energy states are found on both sublattices in the bulk , as well as near the boundary of the system . in this situation , only the antiferromagnetic ansatz @xmath93 leads to a finite gap at the dirac point .
+ from the self consistent solution of the magnetic ground state , obtained in a finite honeycomb system of @xmath122 sites ( @xmath123 ) , we compute the two local order parameters @xmath110 and @xmath111 , defined in eq .
( [ affmop ] ) .
the results are presented in fig . 5 , when the field is uniform ( left ) and nonuniform ( once again a bell - shaped one , peaked around the center of the system ) ( right ) .
the local nel order parameter @xmath110 again follows the profile of the true magnetic field , resembling in this regard the spatial distribution of the charge - density - wave order , obtained previously for spinless fermions in honeycomb lattice with the nearest - neighbor interaction.@xcite due to the existence of a finite density of states at the dirac point , the antiferromagnetic ordering can be found for the interaction as weak as @xmath118.@xcite on the other hand , @xmath111 is _ zero _ everywhere in the system .
the dramatic difference in the magnetic ground states between the axial and the true magnetic fields arises entirely as a consequence of the distinct structure of the zero - modes .
the antiferromagnetic ground state we find in the presence of true magnetic field and at weak interaction ( @xmath103 ) is the exact replica of the one in graphene at strong interaction ( @xmath124 ) and in zero field .
+ axial magnetic fields , resulting from the modification of the hopping matrix elements between the nearest neighbors according to eq .
( [ hoppinglattice ] ) , do not break the particle - hole symmetry .
thereby , auxiliary field quantum monte carlo simulations do not suffer from the infamous minus sign problem and accurate simulations on large lattices can be carried out . here , we have used the projective zero temperature approach based on the equation , @xmath125 in which the ground state is filtered out of a single slater determinant by propagating along the imaginary time axis .
it is beyond the scope of this paper to go into the details of the implementation and the readers are referred to ref .
for an overview of the algorithm .
let us however comment on some aspects of our implementation . the axial field does not break @xmath126-spin rotation symmetry and we have found it important to impose this symmetry by opting for a discrete hubbard - stratonovitch transformation coupling to the charge : @xmath127 with @xmath128 .
we have furthermore used a symmetric trotter decomposition with @xmath129 , and the trial wave function corresponds to the ground state of the non - interacting hamiltonian . for this choice of the trial wave function projection parameters in the range
@xmath130 suffice to guarantee convergence to the ground state within the quoted accuracy .
since the monte carlo simulations do not break @xmath126 spin symmetry we have to rely on spin - spin correlations to detect the global edge - compensated antiferromagnetic state . in fig .
[ qmc ] ( upper panel ) we consider 600-site flakes at @xmath131 .
this choice of @xmath132 places us well below @xmath133 at which the transition to the antiferromagnetic mott insulating state occurs in the absence of axial field.@xcite the reference site @xmath134 is chosen to belong to the sub - lattice which hosts the ( normalizable ) _
zero_-energy modes . in the very close vicinity of @xmath135 antiferromagnetic correlations are apparent and they rapidly give way to dominant ferromagnetic correlations . for the uniform , @xmath136 , axial field
the extent of the dominant ferromagnetic correlations is considerably larger than for the localized one , @xmath137 .
finally strong antiferromagnetic correlations are present at the edge of the flake . hence the overall features present in the quantum monte carlo calculations support the mean - field picture of the global edge - compensated antiferromagnetic spin structure .
a more precise measure for the global edge - compensated antiferromagnetic state can be obtained by considering @xmath138 fig .
[ qmc ] ( lower panel ) plots this quantity for the uniform and localized axial fields and at various values of @xmath139 . owing to the singlet nature of the ground state on finite lattices , @xmath140 , when @xmath141 exceeds the radius of the flake . in the absence of axial field ( @xmath142 ) only short range
antiferromagnetic correlations are present and @xmath143 quickly decays to zero . at finite values of the axial field
@xmath144 images the global edge - compensated antiferromagnetic spin structure . for the localized field
the zero energy modes are localized around the center and @xmath143 quickly approaches a plateau value before being compensated by the edge antiferromagnetic correlations .
in contrast , for the uniform field @xmath143 builds up as a function of distance before being again compensated by the edge magnetism . in fig .
[ qmcu4 ] we consider larger values of @xmath145 . in the absence of the axial field , this choice of the hubbard interaction places us in the antiferromagnetic mott insulting phase , shown through the spin - spin correlation in fig.[qmcu4 ] ( top , left ) . as a consequence , and in comparison to the @xmath131 case , the integrated spin - spin correlations of eq.([s_r.eq ] ) show _ small _ fluctuations up to large distances .
it is interesting to note that even starting from the mott insulating state , the axial field leads to the same reorganization of the spin - spin correlations as observed at weak couplings , shown in fig.[qmcu4 ] ( bottom ) .
one will nevertheless observe substantial antiferromagnetic oscillations superimposed on the edge - compensated antiferromagnetic spin structure .
the strain induced restructure of the spin - spin correlation for super - critical interactions ( @xmath145 ) is shown in fig.[qmcu4 ] ( top ) , for roughly uniform ( middle ) and localized ( right ) axial fields .
to summarize , we proposed a specific modulation of the nearest - neighbor hopping amplitudes in honeycomb lattice that captures the coupling of the low - energy dirac quasi - particles to the ( time - reversal - symmetric ) axial magnetic fields . due to the presence of the axial magnetic field a finite number of states appears at ( near ) zero energy , which in turn enhances the effect of electron - electron interaction .
various orderings can take place this way in strained graphene even at weak interactions.@xcite .
in this paper we considered only the onsite hubbard interaction between the fermions , and studied the nature of the magnetic ground state in strained graphene . due to the special structure of the zero - energy states , which are supported by one sublattice in the bulk of the system , and by the other one near the boundary
, the magnetic ground state in strained graphene lacks any analog in pristine graphene , or in graphene in true magnetic fields . through the numerical self - consistent hartree calculation , and a separate quantum monte carlo simulation , we established that the magnetic ground state gives rise to both antiferromagnetic and ferromagnetic orders , locally , everywhere in the system .
although the antiferromagnetic order parameter is of the same sign in the entire system , the magnetization changes its sign near the boundary , so that the total magnetization is actually zero .
such ordering takes place even for weak hubbard interactions .
we named the magnetic ground state in strained graphene _ edge - compensated antiferromagnet_. in contrast , the ground state of the hubbard model on honeycomb lattice subject to true magnetic fields ( and with the zeeman coupling ignored @xcite ) is the conventional nel antiferromagnet . through the self - consistent calculation
we show that such nel ordering takes place again for weak interactions , and the order parameter closely resembles the profile of the true magnetic fields .
the magnetization is in this case , however , identically zero everywhere in the system .
the experimental detection of the global antiferromagnetic phase relies on the measurement of local magnetic moment everywhere in the system , as well as on the existence of the zero - energy states , particularly near the edge of the system .
recent stm measurements in strained molecular graphene indicate the appearance of zero - modes in the bulk and close to the boundary of the system , which are indeed living on two different sublattices@xcite , in agreement with our numerical analysis ( see fig .
2 ) . the local magnetic moment , on the other hand , can be probed by either magnetic force microscope ( mfm ) or spin - polarized stm measurement .
the latter method successfully established an anti - ferromagnetic ordering on monolayer fe , resting on tungsten@xcite , and revealed the spin structure inside a magnetic vortex core@xcite .
a systematic measurement of the local magnetic moment using the spin - polarized stm may therefore also detect the unconventional magnetic ground state in strained graphene .
the desired suppression of the real - time fluctuations of the local magnetic moment can be obtained either by increasing the system s size , or by increasing the size of the magnetic moments , which , as our analysis would suggest , can be achieved by enhancing the strength of the axial magnetic field and/or the strength of the onsite interaction .
the latter can possibly be tuned to a certain degree in the molecular / artificial graphene .
since the local ferromagnetic moment changes its sign roughly where the zero - modes loose their support on the a - sublattice , it is perhaps comparatively easier to detect the proposed global antiferromagnetic phase in strained graphene , when the axial magnetic field is localized near the center of the system .
in that situation the ferromagnetic domain wall appears somewhere in the middle of the system ( see fig . 4 ) ,
whereas , on the other hand , it would lie only very close to the boundary when the axial field is uniform ( see fig .
b. r. was supported at national high magnetic field laboratory by nsf cooperative agreement no.dmr-0654118 , the state of florida , and the u. s. department of energy .
ffa is supported by the dfg , under the grant number as120/9 - 1 and as120/10 - 1 ( forschergruppe for 1807 ) .
ifh has been supported by the nserc of canada .
we thank the jlich supercomputing centre and the leibniz - rechenzentrum in mnich for generous allocation of cpu time .
j. gonzlez , f. guinea , and m. a. h. vozmediano , `` marginal - fermi - liquid behavior from two - dimensional coulomb interaction , '' http://dx.doi.org/10.1103/physrevb.59.r2474[_phys .
b _ * 59 * ( jan , 1999 ) r2474r2477 ] .
http://link.aps.org/doi/10.1103/physrevb.59.r2474 .
t. paiva , r. t. scalettar , w. zheng , r. r. p. singh , and j. oitmaa , `` ground - state and finite - temperature signatures of quantum phase transitions in the half - filled hubbard model on a honeycomb lattice , '' _ phys .
b _ * 72 * ( 2005 ) 085123 .
d. v. khveshchenko , `` ghost excitonic insulator transition in layered graphite , '' http://dx.doi.org/10.1103/physrevlett.87.246802[_phys . rev .
_ * 87 * ( nov , 2001 ) 246802 ] .
http://link.aps.org/doi/10.1103/physrevlett.87.246802 .
d. khveshchenko and h. leal , `` excitonic instability in layered degenerate semimetals , '' http://dx.doi.org/http://dx.doi.org/10.1016/j.nuclphysb.2004.03.020 [ _ nuclear physics b _ * 687 * no . 3 , ( 2004 ) 323
http://www.sciencedirect.com/science/article/pii/s0550321304002032 .
i. f. herbut , `` interactions and phase transitions on graphene s honeycomb lattice , '' http://dx.doi.org/10.1103/physrevlett.97.146401[_phys .
_ * 97 * ( october , 2006 ) 146401 ] . http://link.aps.org/doi/10.1103/physrevlett.97.146401 .
i. f. herbut , v. jurii , and b. roy , `` theory of interacting electrons on the honeycomb lattice , '' http://dx.doi.org/10.1103/physrevb.79.085116[_phys .
b _ * 79 * ( feb , 2009 ) 085116 ] . http://link.aps.org/doi/10.1103/physrevb.79.085116 .
j. e. drut and t. a. lhde , `` is graphene in vacuum an insulator ?
, '' http://dx.doi.org/10.1103/physrevlett.102.026802[_phys .
* 102 * ( jan , 2009 ) 026802 ] .
http://link.aps.org/doi/10.1103/physrevlett.102.026802 .
j. e. drut and t. a. lhde , `` lattice field theory simulations of graphene , '' http://dx.doi.org/10.1103/physrevb.79.165425[_phys . rev .
b _ * 79 * ( apr , 2009 ) 165425 ] . http://link.aps.org/doi/10.1103/physrevb.79.165425 .
j. e. drut and t. a. lhde , `` critical exponents of the semimetal - insulator transition in graphene : a monte carlo study , '' http://dx.doi.org/10.1103/physrevb.79.241405[_phys .
b _ * 79 * ( jun , 2009 ) 241405 ] . http://link.aps.org/doi/10.1103/physrevb.79.241405
. e. v. castro , a. g. grushin , b. valenzuela , m. a. h. vozmediano , a. cortijo , and f. de juan , `` topological fermi liquids from coulomb interactions in the doped honeycomb lattice , '' http://dx.doi.org/10.1103/physrevlett.107.106402[_phys .
lett . _ * 107 * ( sep , 2011 ) 106402 ] . http://link.aps.org/doi/10.1103/physrevlett.107.106402 .
a. g. grushin , e. v. castro , a. cortijo , f. de juan , m. a. h. vozmediano , and b. valenzuela , `` charge instabilities and topological phases in the extended hubbard model on the honeycomb lattice with enlarged unit cell , '' http://dx.doi.org/10.1103/physrevb.87.085136[_phys .
b _ * 87 * ( feb , 2013 ) 085136 ] .
http://link.aps.org/doi/10.1103/physrevb.87.085136 . z. y. meng , t. c. lang , s. wessel , f. f. assaad , and a. muramatsu , `` quantum spin liquid emerging in two - dimensional correlated dirac fermions , '' http://dx.doi.org/10.1038/nature08942[_nature_ * 464 * no . 7290 , ( apr , 2010 ) 847851 ] .
http://dx.doi.org/10.1038/nature08942 .
s. sorella , y. otsuka , and s. yunoki , `` absence of a spin liquid phase in the hubbard model on the honeycomb lattice , '' http://dx.doi.org/http://dx.doi.org/10.1038/srep00992[_sci .
rep . _ * 2 * ( 2012 ) 992 ] .
f. f. assaad and i. f. herbut , `` pinning the order : the nature of quantum criticality in the hubbard model on honeycomb lattice , '' http://dx.doi.org/10.1103/physrevx.3.031010[_phys .
x _ * 3 * ( aug , 2013 ) 031010 ] .
http://link.aps.org/doi/10.1103/physrevx.3.031010 . t. c. lang , z. y. meng , a. muramatsu , s. wessel , and f. f. assaad , `` dimerized solids and resonating plaquette order in @xmath146-dirac fermions , '' http://dx.doi.org/10.1103/physrevlett.111.066401[_phys .
* 111 * ( aug , 2013 ) 066401 ] .
http://link.aps.org/doi/10.1103/physrevlett.111.066401 .
i. f. herbut , v. jurii , and o. vafek , `` relativistic mott criticality in graphene , '' http://dx.doi.org/10.1103/physrevb.80.075432[_phys .
b _ * 80 * ( aug , 2009 ) 075432 ] .
http://link.aps.org/doi/10.1103/physrevb.80.075432 .
b. roy , `` multicritical behavior of @xmath147 gross - neveu - yukawa theory in graphene , '' http://dx.doi.org/10.1103/physrevb.84.113404[_phys .
b _ * 84 * ( sep , 2011 ) 113404 ] . http://link.aps.org/doi/10.1103/physrevb.84.113404 .
b. rosenstein , h .-
yu , and a. kovner , `` critical exponents of new universality classes , '' http://dx.doi.org/http://dx.doi.org/10.1016/0370-2693(93)91253-j [ _ physics letters b _ * 314 * no . 34 , ( 1993 ) 381 386 ] .
http://www.sciencedirect.com/science/article/pii/037026939391253j .
v. n. kotov , b. uchoa , v. m. pereira , f. guinea , and a. h. castro neto , `` electron - electron interactions in graphene : current status and perspectives , '' http://dx.doi.org/10.1103/revmodphys.84.1067[_rev .
* 84 * ( jul , 2012 ) 10671125 ] . http://link.aps.org/doi/10.1103/revmodphys.84.1067 .
i. f. herbut , `` pseudomagnetic catalysis of the time - reversal symmetry breaking in graphene , '' http://dx.doi.org/10.1103/physrevb.78.205433[_phys .
b _ * 78 * ( nov , 2008 ) 205433 ] . http://link.aps.org/doi/10.1103/physrevb.78.205433 . p. ghaemi , j. cayssol , d. n. sheng , and a. vishwanath , `` fractional topological phases and broken time - reversal symmetry in strained graphene , '' http://dx.doi.org/10.1103/physrevlett.108.266801[_phys .
_ * 108 * ( jun , 2012 ) 266801 ] .
http://link.aps.org/doi/10.1103/physrevlett.108.266801 .
b. roy and i. f. herbut , `` topological insulators in strained graphene at weak interaction , '' http://dx.doi.org/10.1103/physrevb.88.045425[_phys .
b _ * 88 * ( jul , 2013 ) 045425 ] .
http://link.aps.org/doi/10.1103/physrevb.88.045425 .
f. guinea , m. i. katsnelson , and a. k. geim , `` energy gaps and a zero - field quantum hall effect in graphene by strain engineering , '' http://dx.doi.org/10.1038/nphys1420[_nat phys _ * 6 * no . 1 , ( jan , 2010 ) 3033 ]
. http://dx.doi.org/10.1038/nphys1420 .
y. aharonov and a. casher , `` ground state of a spin-@xmath148 charged particle in a two - dimensional magnetic field , '' http://dx.doi.org/10.1103/physreva.19.2461[_phys .
* 19 * ( jun , 1979 ) 24612462 ] .
http://link.aps.org/doi/10.1103/physreva.19.2461 .
n. levy , s. a. burke , k. l. meaker , m. panlasigui , a. zettl , f. guinea , a. h. c. neto , and m. f. crommie , `` strain - induced pseudo magnetic fields greater than 300 tesla in graphene nanobubbles , '' http://dx.doi.org/10.1126/science.1191700[_science_ * 329 * no .
5991 , ( 2010 ) 544547 ] , http://arxiv.org/abs/http://www.sciencemag.org/content/329/5991/544.full.pdf [ http://www.sciencemag.org/content/329/5991/544.full.pdf ] . http://www.sciencemag.org/content/329/5991/544.abstract .
j. lu , a. h. c. neto , and k. p. loh , `` transforming moir blisters into geometric graphene nano - bubbles , '' http://dx.doi.org/10.1038/ncomms1818[_nat commun _ * 3 * ( may , 2012 ) 823 ] .
http://dx.doi.org/10.1038/ncomms1818 .
k. k. gomes , w. mar , w. ko , f. guinea , and h. c. manoharan , `` designer dirac fermions and topological phases in molecular graphene , '' http://dx.doi.org/10.1038/nature10941[_nature_ * 483 * no . 7389 , ( mar , 2012 ) 306310 ] .
http://dx.doi.org/10.1038/nature10941 .
r. jackiw and s .- y .
pi , `` chiral gauge theory for graphene , '' http://dx.doi.org/10.1103/physrevlett.98.266402[_phys .
* 98 * ( jun , 2007 ) 266402 ] .
http://link.aps.org/doi/10.1103/physrevlett.98.266402 .
b. roy , `` magnetic - field induced inequivalent vortex zero modes in strained graphene , '' http://dx.doi.org/10.1103/physrevb.85.165453[_phys .
b _ * 85 * ( apr , 2012 ) 165453 ] . http://link.aps.org/doi/10.1103/physrevb.85.165453 . b. roy , z .- x .
hu , and k. yang , `` theory of unconventional quantum hall effect in strained graphene , '' http://dx.doi.org/10.1103/physrevb.87.121408[_phys .
b _ * 87 * ( mar , 2013 ) 121408 ] . http://link.aps.org/doi/10.1103/physrevb.87.121408 .
o. motrunich , k. damle , and d. a. huse , `` particle - hole symmetric localization in two dimensions , '' http://dx.doi.org/10.1103/physrevb.65.064206 [ _ phys .
b _ * 65 * ( jan , 2002 ) 064206 ] .
http://link.aps.org/doi/10.1103/physrevb.65.064206 .
b. roy and i. f. herbut , `` inhomogeneous magnetic catalysis on graphene s honeycomb lattice , '' http://dx.doi.org/10.1103/physrevb.83.195422 [ _ phys .
b _ * 83 * ( may , 2011 ) 195422 ] .
http://link.aps.org/doi/10.1103/physrevb.83.195422 .
i. f. herbut , `` so(3 ) symmetry between nel and ferromagnetic order parameters for graphene in a magnetic field , '' http://dx.doi.org/10.1103/physrevb.76.085432[_phys .
b _ * 76 * ( aug , 2007 ) 085432 ] .
http://link.aps.org/doi/10.1103/physrevb.76.085432 .
i. f. herbut , `` theory of integer quantum hall effect in graphene , '' http://dx.doi.org/10.1103/physrevb.75.165411[_phys .
rev . b _ * 75 * ( apr , 2007 ) 165411 ] .
http://link.aps.org/doi/10.1103/physrevb.75.165411 .
f. f. assaad and h. g. evertz , `` world - line and determinantal quantum monte carlo methods for spins , phonons and electrons , '' in _ computational many particle physics _ , h. fehske , r. schneider , and a. weie , eds .
739 of _ lecture notes in physics _ , pp . 277356 .
springer verlag , berlin , 2008 .
a. kubetzka , p. ferriani , m. bode , s. heinze , g. bihlmayer , k. von bergmann , o. pietzsch , s. blgel , and r. wiesendanger , `` revealing antiferromagnetic order of the fe monolayer on w(001 ) : spin - polarized scanning tunneling microscopy and first - principles calculations , '' http://dx.doi.org/10.1103/physrevlett.94.087204[_phys .
* 94 * ( mar , 2005 ) 087204 ] .
http://link.aps.org/doi/10.1103/physrevlett.94.087204 .
a. wachowiak , j. wiebe , m. bode , o. pietzsch , m. morgenstern , and r. wiesendanger , `` direct observation of internal spin structure of magnetic vortex cores , '' http://dx.doi.org/10.1126/science.1075302 [ _ science _ * 298 * no . 5593 , ( 2002 ) 577580 ] . | a novel magnetic ground state is reported for the hubbard hamiltonian in strained graphene . when the chemical potential lies close to the dirac point , the ground state exhibits locally both the nel and ferromagnetic orders , even for weak hubbard interaction . whereas the nel order parameter remains of the same sign in the entire system ,
the magnetization at the boundary takes the opposite sign from the bulk .
the total magnetization this way vanishes , and the magnetic ground state is globally only an antiferromagnet .
this peculiar ordering stems from the nature of the strain - induced single particle zero - energy states , which have support on one sublattice of the honeycomb lattice in the bulk , and on the other sublattice near the boundary of a finite system .
we support our claim with the self - consistent numerical calculation of the order parameters , as well as by the monte carlo simulations of the hubbard model in both uniformly and non - uniformly strained honeycomb lattice .
the present result is contrasted with the magnetic ground state of the same hubbard model in the presence of a true magnetic field ( and for vanishing zeeman coupling ) , which is exclusively nel ordered , with zero local magnetization everywhere in the system . |
SECTION 1. SHORT TITLE; TABLE OF CONTENTS.
(a) Short Title.--This Act may be cited as the ``Open and
Accountable Campaign Financing Act of 2001''.
(b) Table of Contents.--The table of contents of this Act is as
follows:
Sec. 1. Short title; table of contents.
TITLE I--DISCLOSURE
Sec. 101. Additional monthly and quarterly disclosure reports.
Sec. 102. Reporting by national political party committees.
Sec. 103. Increased electronic disclosure.
Sec. 104. Public access to broadcasting records.
Sec. 105. Software for filing of reports.
TITLE II--SOFT MONEY OF NATIONAL POLITICAL PARTIES AND CONTRIBUTION
LIMITS
Sec. 201. Limit on soft money of national political party committees.
Sec. 202. Judicial review.
Sec. 203. Increase in contribution limits.
TITLE III--MISCELLANEOUS PROVISIONS
Sec. 301. Prohibition of solicitation of political party soft money in
Federal buildings.
Sec. 302. Update of penalty amounts.
Sec. 303. Filing of Senate reports with the Federal Election
Commission.
TITLE I--DISCLOSURE
SEC. 101. ADDITIONAL MONTHLY AND QUARTERLY DISCLOSURE REPORTS.
(a) Principal Campaign Committees.--
(1) Monthly reports.--Section 304(a)(2)(A) of the Federal
Election Campaign Act of 1971 (2 U.S.C. 434(a)(2)(A)) is
amended by striking clause (iii) and inserting the following:
``(iii) additional monthly reports, which shall be
filed not later than the 20th day after the last day of
the month and shall be complete as of the last day of
the month, except that monthly reports shall not be
required under this clause in November and December and
a year end report shall be filed not later than January
31 of the following calendar year.''.
(2) Quarterly reports.--Section 304(a)(2)(B) of such Act is
amended by striking ``the following reports'' and all that
follows through the period and inserting ``the treasurer shall
file quarterly reports, which shall be filed not later than the
15th day after the last day of each calendar quarter, and which
shall be complete as of the last day of each calendar quarter,
except that the report for the quarter ending December 31 shall
be filed not later than January 31 of the following calendar
year.''.
(b) National Committee of a Political Party.--Section 304(a)(4) of
the Federal Election Campaign Act of 1971 (2 U.S.C. 434(a)(4)) is
amended by adding at the end the following flush sentence:
``Notwithstanding the preceding sentence, a national committee of a
political party shall file the reports required under subparagraph
(B).''.
(c) Conforming Amendments.--
(1) Section 304.--Section 304(a) of the Federal Election
Campaign Act of 1971 (2 U.S.C. 434(a)) is amended--
(A) in paragraph (3)(A)(ii), by striking
``quarterly reports'' and inserting ``monthly
reports''; and
(B) in paragraph (8), by striking ``quarterly
report under paragraph (2)(A)(iii) or paragraph
(4)(A)(i)'' and inserting ``monthly report under
paragraph (2)(A)(iii) or paragraph (4)(A)''.
(2) Section 309.--Section 309(b) of the Federal Election
Campaign Act of 1971 (2 U.S.C. 437g(b)) is amended by striking
``calendar quarter'' and inserting ``month''.
SEC. 102. REPORTING BY NATIONAL POLITICAL PARTY COMMITTEES.
Section 304 of the Federal Election Campaign Act of 1971 (2 U.S.C.
434) is amended by adding at the end the following:
``(e) Political Committees.--
``(1) National and congressional political committees.--The
national committee of a political party, any national
congressional campaign committee of a political party, and any
subordinate committee of either, shall report all receipts and
disbursements during the reporting period.
``(2) Itemization.--If a political committee has receipts
or disbursements to which this subsection applies from any
person aggregating in excess of $200 for any calendar year, the
political committee shall separately itemize its reporting for
such person in the same manner as required in paragraphs
(3)(A), (5), and (6) of subsection (b).
``(3) Reporting periods.--Reports required to be filed
under this subsection shall be filed for the same time periods
required for political committees under subsection (a).''.
SEC. 103. INCREASED ELECTRONIC DISCLOSURE.
Section 304 of the Federal Election Campaign Act of 1971 (2 U.S.C.
434), as amended by section 102, is amended by adding at the end the
following:
``(f) Internet Availability.--The Commission shall make the
information contained in the reports submitted under this section
available on the Internet and publicly available at the offices of the
Commission as soon as practicable (but in no case later than 24 hours)
after the information is received by the Commission.''.
SEC. 104. PUBLIC ACCESS TO BROADCASTING RECORDS.
Section 315 of the Communications Act of 1934 (47 U.S.C. 315) is
amended by redesignating subsections (c) and (d) as subsections (d) and
(e), respectively, and inserting after subsection (b) the following:
``(c) Political Record.--
``(1) In general.--A licensee shall maintain, and make
available for public inspection, a complete record of a request
to purchase broadcast time that--
``(A) is made by or on behalf of a legally
qualified candidate for public office; or
``(B) communicates a message relating to any
political matter of national importance, including--
``(i) a legally qualified candidate;
``(ii) any election to Federal office; or
``(iii) a national legislative issue of
public importance.
``(2) Contents of record.--A record maintained under
paragraph (1) shall contain information regarding--
``(A) whether the request to purchase broadcast
time is accepted or rejected by the licensee;
``(B) the rate charged for the broadcast time;
``(C) the date and time on which the communication
is aired;
``(D) the class of time that is purchased;
``(E) the name of the candidate to which the
communication refers and the office to which the
candidate is seeking election, the election to which
the communication refers, or the issue to which the
communication refers (as applicable);
``(F) in the case of a request made by, or on
behalf of, a candidate, the name of the candidate, the
authorized committee of the candidate, and the
treasurer of such committee; and
``(G) in the case of any other request, the name of
the person purchasing the time, the name, address, and
phone number of a contact person for such person, and a
list of the chief executive officers or members of the
executive committee or of the board of directors of
such person.
``(3) Time to maintain file.--The information required
under this subsection shall be placed in a political file as
soon as possible and shall be retained by the licensee for a
period of not less than 2 years.''.
SEC. 105. SOFTWARE FOR FILING OF REPORTS.
Section 304(a) of the Federal Election Campaign Act of 1971 (2
U.S.C. 434(a)) is amended by adding at the end the following:
``(12) Software for filing of reports.--
``(A) In general.--The Commission shall--
``(i) develop software for use to file a
designation, statement, or report under this
Act; and
``(ii) provide a copy of the software at no
cost to a person required to file a
designation, statement, or report under this
Act.
``(B) Required use.--Any person which maintains or
files a designation, statement, or report under
paragraph (11) shall use software developed under
subparagraph (A) for such maintenance or filing.''.
TITLE II--SOFT MONEY OF NATIONAL POLITICAL PARTIES AND CONTRIBUTION
LIMITS
SEC. 201. LIMIT ON SOFT MONEY OF NATIONAL POLITICAL PARTY COMMITTEES.
Title III of the Federal Election Campaign Act of 1971 (2 U.S.C.
431 et seq.) is amended by adding at the end the following:
``SEC. 324. LIMIT ON SOFT MONEY OF NATIONAL POLITICAL PARTY COMMITTEES.
``(a) Limitation.--A national committee of a political party, a
congressional campaign committee of a national party, or an entity
directly or indirectly established, financed, maintained, or controlled
by such committee shall not accept a donation, gift, or transfer of
funds of any kind (not including transfers from other committees of the
political party or contributions), during a calendar year, from a
person (including a person directly or indirectly established,
financed, maintained, or controlled by such person) in an aggregate
amount in excess of $60,000.
``(b) Aggregate Limit on Donor.--A person shall not make an
aggregate amount of disbursements described in subsection (a) in excess
of $60,000 in any calendar year.
``(c) Index of Amount.--In the case of any calendar year after
2001--
``(1) each $60,000 amount under subsections (a) and (b)
shall be increased based on the increase in the price index
determined under section 315(c), except that the base period
shall be calendar year 2001; and
``(2) each amount so increased shall be the amount in
effect for the calendar year.''.
SEC. 202. JUDICIAL REVIEW.
(a) Expedited Review.--Any Member of Congress, candidate, national
committee of a political party, or any person adversely affected by
section 324 of the Federal Election Campaign Act of 1971, as added by
section 201, may bring an action, in the United States District Court
for the District of Columbia, for declaratory judgment and injunctive
relief on the ground that such section 324 violates the Constitution.
(b) Appeal to Supreme Court.--Notwithstanding any other provision
of law, any order of the United States District Court for the District
of Columbia granting or denying an injunction regarding, or finally
disposing of, an action brought under subsection (a) shall be
reviewable by appeal directly to the Supreme Court of the United
States. Any such appeal shall be taken by a notice of appeal filed
within 10 calendar days after such order is entered; and the
jurisdictional statement shall be filed within 30 calendar days after
such order is entered.
(c) Expedited Consideration.--It shall be the duty of the District
Court for the District of Columbia and the Supreme Court of the United
States to advance on the docket and to expedite to the greatest
possible extent the disposition of any matter brought under subsection
(a).
(d) Enforceability.--The enforcement of any provision of section
324 of the Federal Election Campaign Act of 1971, as added by section
201, shall be stayed, and such section 324 shall not be effective, for
the period--
(1) beginning on the date of the filing of an action under
subsection (a), and
(2) ending on the date of the final disposition of such
action on its merits by the Supreme Court of the United States.
(e) Applicability.--This section shall apply only with respect to
any action filed under subsection (a) not later than 30 days after the
effective date of this Act.
SEC. 203. INCREASE IN CONTRIBUTION LIMITS.
(a) Increase in Individual and Political Committee Contribution
Limits.--Section 315(a) of the Federal Election Campaign Act of 1971 (2
U.S.C. 441a(a)) is amended--
(1) in paragraph (1)--
(A) in subparagraph (A), by striking ``$1,000'' and
inserting ``$3,000'';
(B) in subparagraph (B), by striking ``$20,000''
and inserting ``$60,000''; and
(C) in subparagraph (C), by striking ``$5,000'' and
inserting ``$15,000''; and
(2) in paragraph (3)--
(A) by striking ``$25,000'' and inserting
``$75,000''; and
(B) by striking the second sentence.
(b) Increase in Multicandidate Limits.--Section 315(a)(2) of the
Federal Election Campaign Act of 1971 (2 U.S.C. 441a(a)(2)) is
amended--
(1) in subparagraph (A)--
(A) by striking ``$5,000'' and inserting
``$7,500''; and
(B) by inserting ``except as provided in
subparagraph (D),'' before ``to any candidate'';
(2) in subparagraph (B)--
(A) by striking ``$15,000'' and inserting
``$30,000''; and
(B) by striking ``or'' at the end;
(3) in subparagraph (C), by striking ``$5,000.'' and
inserting ``$7,500; or''; and
(4) by adding at the end the following:
``(D) in the case of a national committee of a political
party, to any candidate and his authorized political committees
with respect to any election for Federal office which, in the
aggregate, exceed $15,000.''.
(c) Indexing.--Section 315(c) of the Federal Election Campaign Act
of 1971 (2 U.S.C. 441a(c)) is amended--
(1) in paragraph (1)--
(A) by striking the second and third sentences;
(B) by inserting ``(A)'' before ``At the
beginning''; and
(C) by adding at the end the following:
``(B) Except as provided in subparagraph (C), in any calendar year
after 2002--
``(i) a limitation established by subsection (a), (b), (d),
or (h) shall be increased by the percent difference determined
under subparagraph (A); and
``(ii) each amount so increased shall remain in effect for
the calendar year.
``(C) In the case of limitations under subsections (a) and (h),
each amount increased under subparagraph (B) shall remain in effect for
the 2-year period beginning on the first day following the date of the
last general election in the year preceding the year in which the
amount is increased and ending on the date of the next general
election.''; and
(2) in paragraph (2)(B), by striking ``means the calendar
year 1974'' and inserting ``means--
``(i) for purposes of subsections (b) and (d),
calendar year 1974; and
``(ii) for purposes of subsections (a) and (h),
calendar year 2001''.
(d) Increase in Senate Candidate Contribution Limits for National
Party Committees and Senatorial Campaign Committees.--Section 315(h) of
the Federal Election Campaign Act of 1971 (2 U.S.C. 441a(h)) is amended
by striking ``$17,500'' and inserting ``$60,000''.
(e) Effective Dates.--
(1) Except as provided in paragraph (2), the amendments
made by this section shall apply to calendar years beginning
after December 31, 2001.
(2) The amendments made by subsection (c) shall apply to
calendar years after December 31, 2002.
TITLE III--MISCELLANEOUS PROVISIONS
SEC. 301. PROHIBITION OF SOLICITATION OF POLITICAL PARTY SOFT MONEY IN
FEDERAL BUILDINGS.
(a) In General.--Section 607 of title 18, United States Code, is
amended--
(1) in subsection (a), by striking ``within the meaning of
section 301(8) of the Federal Election Campaign Act of 1971'';
and
(2) by adding at the end the following:
``(c) Definition of Contribution.--In this section, the term
`contribution' means a gift, subscription, loan, advance, or deposit of
money or anything of value made by any person in connection with--
``(1) any election or elections for Federal office;
``(2) any political committee (as defined in section 301 of
the Federal Election Campaign Act of 1971); or
``(3) any State, district, or local committee of a
political party.''.
(b) Amendment of Title 18 To Include Prohibition of Donations.--
Section 602(a)(4) of title 18, United States Code, is amended by
striking ``within the meaning of section 301(8) of the Federal Election
Campaign Act of 1971'' and inserting ``(as defined in section
607(c))''.
SEC. 302. UPDATE OF PENALTY AMOUNTS.
Section 309 of the Federal Election Campaign Act of 1971 (2 U.S.C.
437g) is amended by adding at the end the following:
``(e) Adjustment of Dollar Amounts for Inflation.--In the case of
any calendar year after 2001--
``(1) each dollar amount under this section shall be
increased based on the increase in the price index determined
under section 315(c), except that the base period shall be
calendar year 2001; and
``(2) each amount so increased shall be the amount in
effect for the calendar year.
The preceding sentence shall not apply to any amount under subsection
(d) other than the $25,000 amount under paragraph (1)(A) of such
subsection.''.
SEC. 303. FILING OF SENATE REPORTS WITH THE FEDERAL ELECTION
COMMISSION.
(a) Section 302 Amendment.--Section 302 of the Federal Election
Campaign Act of 1971 (2 U.S.C. 432) is amended by striking subsection
(g) and inserting the following:
``(g) Place of Filing.--All designations, statements, and reports
required to be filed under this Act shall be filed with the
Commission.''.
(b) Conforming Amendments.--Title III of the Federal Election
Campaign Act of 1971 (2 U.S.C. 431 et seq.) is amended--
(1) in section 304--
(A) in subsection (a)(6)(A), by striking
``Secretary or the Commission'' through ``as
appropriate'' and inserting ``Commission and Secretary
of State''; and
(B) in the third sentence of subsection (c)(2), by
striking ``the Secretary or''; and
(2) in section 311(a)(4), by striking ``Secretary or the''. | Open and Accountable Campaign Financing Act of 2001 - Amends the Federal Election Campaign Act of 1971 (FECA) to revise reporting requirements, including: (1) changing from quarterly to monthly the additional reports required to be filed with regard to the principal campaign committee of a candidate for the House of Representatives or the Senate in any calendar year during which there is a regularly scheduled election for which such candidate is seeking nomination or election; (2) requiring a national committee of a political party to file the same monthly reports designated for all political committees other than authorized committees of a candidate; and (3) directing the Federal Election Commission (FEC) to make report information available on the Internet and at FEC offices.Amends the Communications Act of 1934 to require a licensee to maintain and make available for public inspection a complete record of certain requests to purchase broadcast time that are related to legally qualified candidates.Amends FECA to require the FEC to develop, and provide at no cost, software for filing FEC reports.Limits to $60,000 the aggregate amount (indexed for inflation) of soft money per calendar year, per contributor that a national committee of a political party, a congressional campaign committee of a national party, or an entity directly or indirectly established, financed, maintained, or controlled by such committee may accept.Increases individual, political committee, and multicandidate political committee contribution limits. Revises indexing provisions. Increases Senate candidate contribution limits for national party committees and senatorial campaign committees.Amends the Federal criminal code to prohibit solicitation of soft money in Federal buildings by an officer or employee of the United States.Amends FECA to provide for the indexing of certain penalty and other amounts under enforcement provisions.Outlines provisions for filing of Senate reports with the FEC. |
the extreme inner galaxy ( eig ) has long been the subject of intense astrophysical study as it provides excellent opportunities to explore dynamics , phenomena ( from stellar to galactic scales ) and physical environments which do not exist in the large - scale galactic disk . throughout this paper
, we refer to the area inside of , and including , the 3kpc arms as the eig ( i.e. @xmath1 ) .
` inner galaxy ' is a term already used to describe the areas of the milky way inside the solar circle , likewise the term ` galactic center ' ( gc ) usually refers to the relatively small area with a galactocentric radius less than a few hundred parsecs .
useful reviews of the eig environment include @xcite and @xcite , who discuss the interstellar medium ( ism ) and structural components respectively .
radio observations of the eig region have been performed since the 1950s ( using the dwingeloo 26 m antenna , * ? ? ?
these early studies discovered large - scale hifeatures with non - circular motions @xcite , and concentrated on understanding these individual structures , or particular objects .
the eig has been extensively observed in co. molecular tracers probe denser material than neutral hydrogen ( hi ) and co is readily observed , therefore co observations allow for analysis of regions in which the ism is concentrated into structures such as arms and bars @xcite .
in contrast , observations of atomic gas trace diffuse interstellar clouds .
while hiin the eig has been well studied at low resolutions , it is only recently that high - resolution hidata which cover the entire eig region have become available ( i.e. atca higalactic center survey ( higcs ) * ? ? ?
these high - resolution hidata allow an analysis of the beginnings of the spiral arms ; the transition between orbits associated with the bar ; a comparison to high - resolution molecular observations , dynamical models and molecular transitions ; as well as investigations into the association of hiwith the galactic wind @xcite . as a result of the variation in the temperature of interstellar hydrogen , hiemission and absorption spectra probe different phases of the ism . in most emission spectra
it is the warmer components that dominate .
however , cool gas is readily observed in absorption against background continuum sources , where it may be disentangled from warmer material along the line of sight .
one advantage to studying hi absorption in the eig is that it probes this predominantly cool material , which tends to be more localised in space , and more closely confined to structural entities such as arms .
previous hiabsorption studies have been vital to our understanding of the structure , rotation and the nature of atomic gas in the eig region .
these include observations of absorption features associated with non - circular velocities , radio arc non - thermal filaments as well as particular objects including sgra * ( * ? ? ?
* and references therein ) . while high - resolution hiabsorption measurements have been made towards several bright , or otherwise interesting , eig continuum sources ( *
* ; * ? ? ?
* ; * ? ? ?
* and references therein ) a complete hiabsorption study of the eig region has not been attempted .
this present hiabsorption survey constitutes the most complete study of hiabsorption against the continuum emission from the entire sample of hiiregions known with @xmath0 .
this study is only possible due to recent hiiregion discovery surveys ( which provide a list of target continuum regions with which to measure absorption against ) and improved resolution in hisurveys that include the gc region .
in addition to providing a sample of bright continuum sources against which to measure hiabsorption , hiiregions also provide an important secondary tracer of galactic structure : the hiiregions themselves .
galactic hiiregions are the formation sites of massive ob stars , which have a main sequence lifetime of @xmath2tens of millions of years . as a result
, galactic hiiregions reveal the locations of current massive star formation , indicate the present state of the ism , provide a unique probe of galactic chemical evolution and are the archetypical tracers of galactic spiral structure @xcite . in this work
we measure hi absorption against only those hii regions with known radio recombination line ( rrl ) velocities .
this sub - sample is discussed in section [ data ] , and the method of hi absorption is described in section [ hiabs ] . we then summarise the known eig structures ( section [ gc ] ) and their locations in longitude - velocity ( @xmath3 ) space .
we plot these structures on an ` @xmath3 crayon diagram ' , and use the diagram to consider the eig @xmath3 distribution of hiabsorption , in section [ hidist ] , and later for hiiregions ( section [ hiidist ] ) .
we combine the results from sections [ hidist ] and [ hiidist ] to explore the galactic distribution of hiiregions ( section [ distances ] ) - through determining the lower limit of the line of sight distance to each hiiregion based on its hiabsorption profile and systemic velocity .
finally , a discussion of individual sources appears as appendix [ individual ] .
large scale , high resolution astronomical surveys are now publicly available in many wavelength regimes .
this work uses large - scale hidata and radio continuum maps .
radio continuum maps were sourced from the nrao vla sky survey ( * ? ? ?
* nvss ) and the southern galactic plane survey ( * ? ? ?
* sgps ) .
the nvss covers 82% of the sky ( north of @xmath4 ) at 1.4ghz , resulting in 2326 4x4 degree continuum cubes of stokes parameters and a catalog of continuum emission sources .
only the stokes i maps were used for this work .
it should be noted that the nvss maps do not include zero spacing ( u , v ) information and therefore many , larger , diffuse emission regions , particularly those in the @xcite catalog , are not detected .
for this work , hiabsorption spectra were extracted from the two sgps datasets ( @xmath5 ) and the atca higalactic center survey ( @xmath6 , higcs * ? ? ? * ) .
observations for the sgps ( i & ii ) and atca higcs were performed with the australia telescope compact array ( atca ) and supplemented with data from the parkes radio telescope .
the three surveys provide continuous coverage of the inner galactic plane ( @xmath7 ) at @xmath22 resolution .
catalogues of rrls provide systemic velocities for hiiregions .
large - scale surveys of rrls from hiiregions were performed during the 1960 s to 1980 s .
more recently , the green bank telescope hiiregion discovery survey ( * ? ? ?
* gbthrds ) covered @xmath8 and detected rrls from 448 new hiiregions , effectively doubling the number known in that longitude range .
the gbthrds is complete to 180 mjy at 9 ghz , and is able to detect all hiiregions ionised by a single o - star to a distance of 12 kpc .
in addition , the gbthrds also includes a catalog of known hiiregions as of 2010 . for the @xmath0 region
, this includes the combined works of @xcite , @xcite , @xcite , @xcite , @xcite and @xcite .
the gbthrds team carefully compiled this `` known '' catalog , removing duplicate sources through radio continuum and mid - infrared inspection .
however they note that it is `` likely to contain some residual contamination and duplicate entries '' .
the combination of this `` known '' catalog of hiiregions and the gbthrds source list , within @xmath0 , provided the sample list of regions for this work .
both the gbthrds catalog and the compilation of previous catalogs can be found at .
there are nearly 200 known hiiregions in the range @xmath9 with observed rrl velocities .
hiabsorption spectra were extracted towards a total of 151 of these hiiregions ( see figure set [ fig1 ] ) .
the remaining hiiregions were either not visible in the nvss continuum maps ( also used by the gbthrds ) , usually diffuse hiiregions from the @xcite catalog , or hiiregions with coordinates that could refer to several continuum sources - see table [ table1 ] .
therefore this study obtains hiabsorption spectra towards over 80% of known hiiregions with @xmath0 .
the ` name ' for each hiiregion is taken from the rrl catalog from which it was sourced .
.hiiregions that were _ not _ included in this work .
notes - nv : not visible at the sgps pixel scale ; ms : many continuum sources present at this location ; dc : duplicate ( in both catalogs ) .
[ cols="<,<,<",options="header " , ] diagrams showing velocity channels with significant absorption for each hiiregion overlaid onto : top panel - the ` crayon ' plot of eig features ( see figure [ fig2 ] ) ; middle panel - hiemission ( the intensity map was created from the sgps i & ii and atca higcs ) ; bottom panel - co emission ( see figure [ fig2 ] ) . ( a color version of this figure is available in the online journal . ) [ fig3 ] ] the co emission from both the near and far 3kpc arms is contained within @xmath10 @xcite , similar to the galactic latitude range of the hiiregions in this work ( @xmath11 ) .
furthermore , both 3kpc arms are thought to span @xmath12 , which includes the whole longitude range of this work .
therefore , if an hiiregion is located behind either of the 3kpc arms , hiabsorption should be visible at velocities pertaining to that arm .
figure [ fig3 ] demonstrates that significant hiabsorption is seen toward the near 3kpc arm at all longitudes ; although there is a conspicuous gap in absorption at longitudes @xmath13 , consistent with a paucity of hiiregions for which to measure absorption towards .
indeed 67@xmath14 hiiregions display absorption associated with the near 3kpc arm .
there is less absorption associated with the far 3kpc arm than with the near ( @xmath15 ) , with the site of greatest absorption for the far 3kpc arm centered at @xmath16 ( see figure [ fig4 ] ) .
the disparity in the amount of hiabsorption may be an effect of the smaller latitude extent of the far 3kpc arm , which is particularly thin in the fourth quadrant @xcite .
both the higcs and @xcite report a bifurcation in the velocities far 3kpc arm ( in @xmath3 space ) at @xmath17 .
there is limited evidence of this bifurcation at longitudes extending to @xmath18 , the best example of this is in the absorption spectrum of g007.176 + 00.087 ( see figure set [ fig1 ] ) .
the near 3kpc arm also displays evidence of bifurcation , in both the hiemission and absorption , near @xmath19 ( see , for example , g358.616 - 00.076 , g358.623 - 00.066 , g358.633 + 00062 and g359.432 - 00.086 in figure set [ fig1 ] ) .
the locus of each of the 3kpc arms , as traced by hiabsorption , in @xmath3 space was also investigated . @xcite
provide @xmath3 fits to the near and far 3kpc arms and report a velocity dispersion of 21 km s@xmath20for both arms .
however they excluded large regions of longitude , within @xmath0 , from the computation of the physical properties of each arm . in order to investigate the locus of each arm in @xmath3 space ,
a subset of absorption channels were selected for analysis ( see figure [ fig4 ] ) .
we included all channels within @xmath21 ( between @xmath22 there is ambiguity between the 3kpc arms and the circular rotation velocities and for @xmath23 there is ambiguity with the tilted disk ) , which had velocities outside the envelope of allowed circular - rotation velocities ( i.e. @xmath24 km s@xmath20 ) and were not associated with either of bania s clumps .
linear fits to these appear as equations [ nabs ] and [ fabs ] for the near and far arms respectively .
near 3kpc arm : @xmath25 in both cases , the linear fits ( @xmath26 ) of the structure as given by hiabsorption are consistent with the @xcite fits from co emission ( see figure [ fig4 ] ) . ) , the fits from this analysis are displayed in green .
( a color version of this figure is available in the online journal . )
hiiregions provide radio continuum sources to measure hiabsorption toward , but they also provide a secondary tracer of the eig region - their own systemic velocities .
the @xmath3 distribution of known hiiregions has previously been investigated by @xcite , however all hiiregions with highly non - circular motions ( i.e. those of interest to this work ) were excluded from their analysis .
the @xmath3 distribution of hiiregion rrl velocity components used in this work is shown in figure [ fig5 ] - note : for hiiregions with multiple velocity components , all are shown .
just as the distribution of hiabsorption was closely associated with known @xmath3 features in the eig region ( [ hidist ] , figure [ fig3 ] ) , the systemic velocities of hiiregions also trace these structures . ) showing the distribution of hiiregion rrl velocity components.(a color version of this figure is available in the online journal . ) [ fig5 ] ] the circular - rotation allowed velocities ( yellow envelope in ` crayon plots ' ) account for @xmath27 of the hiiregion rrl velocity components .
@xcite , in a study of 6.7 ghz methanol masers near the eig , find the same velocity range accounts for @xmath28 of their sample .
however , only @xmath29 of hiiregions with a single rrl velocity component are associated with eig features .
a list of hiiregions with rrl velocities associated with an eig structure appears in table [ table3 ] . until recently
, it was believed that there are no known hiiregions inside of the 3kpc arms , except in the tilted disk @xcite .
@xcite found no significant 6.7 ghz methanol maser emission towards the + 135 km s@xmath20 expanding arm , nor the connecting arm ; suggesting that the features are primarily gas that is not undergoing high - mass star formation .
this is in - keeping with observations of other early - type barred galaxies which show star formation in the central nuclear region and at the ends of the bar , but not in the dust lanes along the bar @xcite . using the collated hiiregion catalog of @xcite
, @xcite found no hiiregions associated with structures outside the nuclear disk within @xmath31 .
the gbthrds recorded rrl velocity components from 21 previously unknown hiiregions within @xmath31 , many ( especially in quadrant iv ) with non - circular velocities - these hiiregions are included in the target list of this work . however , as the @xcite study found , these new hiiregions are associated ( in @xmath3 space ) with the nuclear disk and looping ridge intersection .
@xcite then investigated a wider longitude range , but could not identify any dust lane associated hiiregions .
it should be noted that @xcite did not rule out the possibility of undetected ultra - compact hiiregions in the dust lanes .
one diffuse hiiregion , g007.700 - 0.079 identified by @xcite ( but not included in the @xcite catalog used in the @xcite study ) appears to have one of its rrl velocity components associated with the connecting arm .
there is also evidence of two 6.7 ghz methanol masers , tracers of current high - mass star formation , in the same part of @xmath3 space ( see figure 1 of * ? ? ?
in addition , there are four hiiregion rrl velocity components associated with the + 135kms@xmath20 expanding arm and/or bania s clump 1 ( at @xmath32 km s@xmath20 ) , as well as two 6.7 ghz methanol masers from the methanol multibeam survey ( cited in * ? ? ?
* ) , however only two of these regions have single rrl velocity components ( multi - rrl component hiiregions are probably the result of blending multiple emission sources along the line of sight ) .
therefore there is evidence of some recent star formation in these structures .
the other hiiregion of note is g002.611 + 0.135 as it is the only hiiregion that distinctly lies outside the `` crayon '' lines that delineate eig structures in figure [ fig3 ] .
@xcite suggest that g002.611 + 0.135 could be associated with either their structure j or ( see figure 4 of * ? ? ?
the latitude of the hiiregion suggests a stronger association with clump 2 .
only recently has there been evidence of significant star formation @xcite and large numbers of hiiregions @xcite in the 3kpc arms . in emission from molecular clouds the signatures of the 3kpc arms
are clearly seen @xcite , but the gbthrds was unable to discover many new hiiregions , in either of the arms . however , both arms demonstrate high - mass star formation as traced by about fifty 6.7 ghz methanol masers @xcite .
the certainty of associating hiiregions with the 3kpc arms ( in @xmath3 space ) is best in the longitude range of this study ( @xmath0 ) , as outside this limit the expected velocities of the 3kpc arms overlap with circular - motion spiral arm models and the association becomes more ambiguous @xcite . inside @xmath0
there are eleven hiiregion rrl velocity components consistent with the near 3kpc arm and two consistent with the far 3kpc arm .
this small number of rrl components does not allow for a repetition of the analysis of [ 3kpclocation ] using hiiregion rrl components rather than hiabsorption .
the analysis of an hiabsorption spectrum towards a hiiregion can constrain the line of sight distance to the hiiitself . due to the lack of a reliable rotation model for the inner @xmath23kpc of the milky way , kinematic distances to objects near , or in , the eig are the most difficult to ascertain . however
, it should be possible to provide distance constraints for hiiregions with allowed circular rotation systemic velocities , using hiabsorption associated with eig features as approximate distance indicators . in the inner galaxy , inside the solar circle
, each velocity corresponds to two degenerate solutions for the kinematic distance - each equidistant from the tangent ( subcentral ) point .
this kinematic distance ambiguity can be resolved in cases where hiabsorption is present at the velocity of a known structure - which indicates the hiiregion must be located behind the absorbing gas .
the distance arrangement of eig features , listed in [ gc ] , from the literature is assumed to be : near 3kpc arm , connecting arm , tilted disk , looping ridge , + 135 km s@xmath20expanding arm ( and bania s clump 1 ) , far 3kpc arm ( however not all structures are expected along any single line of sight , see figure [ fig2 ] ) .
therefore , if hiabsorption is seen at velocities corresponding to a particular feature , the hiiregion must lie in , or beyond that structure . in this way
, we use hiabsorption as an indicator of the lower limit of the line of sight distance , @xmath33 .
the rrl velocity of an hiiregion also hints at its location , table [ table3 ] lists those hiiregions with systemic velocities beyond the range expected by circular rotation ( see figure [ fig5 ] ) and associated with eig feature(s ) .
a discussion of each hiiregion appears in appendix [ individual ] .
clccl hiiregion & & ref .
& association + + g@xmath34 & & 2 & far 3kpc arm + g@xmath35&&3&near 3kpc arm + g@xmath36 & & 1 & near 3kpc arm + g@xmath37 & & 2 & near 3kpc arm + g@xmath38 & & 2 & near 3kpc arm + g@xmath39 & & 2 & bania s clump 1 ?
+ g@xmath40 & & 1 & bania s clump 1 ? + g@xmath41 & & 2 &
near 3kpc arm + g@xmath42 & & 2 & + 135 km s@xmath20arm + g@xmath43 & & 1 & looping ridge + g@xmath44 & & 1 & looping ridge + g@xmath45 & & 1 & looping ridge + g@xmath46 & & 3 & looping ridge + g@xmath47 & & 1 & looping ridge + g@xmath48 & & 1 & looping ridge + g@xmath49 & & 1 & looping ridge + g@xmath50 & & 1 & looping ridge + g@xmath51 & & 2 & looping ridge + g@xmath52 & & 1 & looping ridge + g@xmath53 & & 3 & near 3kpc arm + g@xmath54 & & 1 & _ blended eig features _
+ g@xmath55 & & 4 & far 3kpc arm + g@xmath56 & & 1 & near 3kpc arm ?
+ g@xmath57 & & 2 & near 3kpc arm + + g@xmath58&a&@xmath59&1 & + g@xmath58&b&@xmath60&1 & + g@xmath58&c&@xmath61&1&near 3kpc arm + g@xmath58&d&@xmath62&1 & + g@xmath63&a&@xmath64&1&+135 km s@xmath20arm + g@xmath63&b&@xmath65&1&near 3kpc arm + g@xmath63&c&@xmath66&1 & + g@xmath67&a&@xmath68&1 & + g@xmath67&b&@xmath69&1&near 3kpc arm + g@xmath70&a&@xmath71&1 & + g@xmath70&b&@xmath72&1&near 3kpc arm + g@xmath73&a&@xmath74&1 & _ blended eig features _ + g@xmath73&b&@xmath75&1 & _ blended eig features _
+ g@xmath76&a&@xmath77&1&tilted disk + g@xmath76&b&@xmath78&1 & + g@xmath79&a&@xmath80&1 & + g@xmath79&b&@xmath81&1&near 3kpc arm + g@xmath82 & a & @xmath83 & 5 & + g@xmath82&b&+151.7 & 5&connecting arm + for hiiregions with systemic velocities associated with normal circular disk rotation ( i.e. in the yellow envelope in figure [ fig5 ] , @xmath84kpc ) , a kinematic distance ambiguity resolution ( kdar ) is attempted .
if a kdar is achieved , the kinematic distance to the hiiregion can then be calculated .
kdars were achieved following these rules : * if the hiiregion rrl is consistent with normal circular disk rotation , and not with any eig feature ( see table [ table3 ] ) ( i.e. no kinematic distances are calculated for regions with @xmath85kpc ) .
* far : if the hiabsorption spectrum displays sufficient absorption associated with eig features , then the hiiregion must be located at the ` far ' kinematic location - i.e. beyond the tangent point along the line of sight . * * if @xmath86 km s@xmath20a kdar is attempted _ only _ if the hiabsorption spectrum displays absorption associated with the far 3kpc arm , this is imposed in order to avoid confusion with eig features at small velocities . *
* quality ` a ' far side kdars were awarded to hiiregions with statistically significant absorption in eig features including at least the near and far 3kpc arms . * * quality ` b ' far side kdars were awarded to hiiregions with statistically significant absorption in any eig feature located on the far side of the gc . * * quality ` c ' far side kdars were awarded to hiiregions with large uncertainties ( @xmath87 ) in their calculated @xmath33 value ( see [ errors ] ) .
* near : if the hiabsorption spectrum displays no absorption associated with any eig features , then it must be located at the ` near ' kinematic location . here
we assume that all the eig features are visible within the latitude range of the target hiiregions ( @xmath88 ) .
note that the linear scale heights of the near and far 3kpc arms is @xmath89 pc fwhm @xcite ; assuming that the far 3kpc arm is at a uniform line of sight distance of 11.5kpc , this scale height corresponds to a latitude range @xmath90 . as a result , if a hiabsorption spectrum towards an hiiregion located at @xmath91 displays no absorption associated with any eig feature , it is awarded a near kdar , of quality c. * * kdars of quality ` a ' were given to all near side hiiregions , unless * * the calculated @xmath33 value had large uncertainties ( @xmath87 ) , then a quality ` c ' kdar was given . *
no kdar was attempted for hiiregions with multiple rrl velocity components , as multiple systemic velocities suggest several ionisation sources along the line of sight .
note : multi - rrl velocity component hiiregions account for less than 10% of the hiiregions within @xmath0 , compared with 30% for the galactic plane in general ( gbthrds ) .
hiiregions with calculated kinematic distances are listed in table [ table4 ] .
four hiiregions ( g350.177 + 00.017 , g350.330 + 00.157 , g353.557 - 00.014 and g003.949 - 00.100 ) were deemed to lie at the far kinematic location , beyond the eig , following the rules above .
however , these four regions have @xmath85kpc , i.e. they are outside the bounds of the @xcite rotation model and are therefore not included in table [ table4 ] .
llcccl hiiregion & v@xmath92&ref.&q&@xmath93&@xmath33 + + g@xmath94 & @xmath95 & 3 & b & 8.6 & 16.9 @xmath964.2 + g@xmath97 & @xmath98 & 1 & a & 9.7 & 18.0 @xmath965.9 + g@xmath99 & @xmath100 & 3 & b & 8.2 & 16.5 @xmath963.6 + g@xmath101 & @xmath102 & 1 & a & 5.9 & 14.3 @xmath962.6 + g@xmath103 & @xmath104 & 3 & c & 8.8 & 23.3 @xmath96 * + g@xmath105 & @xmath106 & 1 & a & 3.9 & 12.3 @xmath962.2 + g@xmath107 & @xmath108 & 4 & c & 14.6 & 23.1 @xmath96 * + g@xmath109 & @xmath110 & 3 & c & 13.3 & 21.7 @xmath96 * + g@xmath111 & @xmath112 & 1 & c & 16.8 & 24.8 @xmath96 * + g@xmath113 & @xmath114 & 2 & c & 3.3 & 11.8 @xmath96 * + g@xmath115 & @xmath116 & 1 & c & 3.0 & 11.5 @xmath96 * + g@xmath117 & @xmath118 & 3 & c & 6.3 & 14.7 @xmath96 * + g@xmath119 & @xmath120 & 3 & a & 5.2 & 13.6 @xmath966.7 + g@xmath121 & @xmath122 & 3 & c & 7.1 & 15.6 @xmath968.9 + g@xmath123 & @xmath124 & 1 & a & 5.4 & 13.8 @xmath963.9 + g@xmath125 & @xmath126 & 3 & a & 4.1 & 12.5 @xmath962.3 + g@xmath127 & @xmath128 & 1 & a & 4.0 & 12.3 @xmath962.2 + g@xmath129 & @xmath130 & 3 & a & 6.3 & 14.7 @xmath963.5 + g@xmath131 & @xmath132 & 3 & a & 5.3 & 13.7 @xmath962.5 + g@xmath133 & @xmath134 & 3 & b & 4.6 & 12.9 @xmath962.2 + g@xmath135 & @xmath136 & 1 & a & 6.6 & 14.9 @xmath963.1 + g@xmath137 & @xmath138 & 1 & c & 12.2 & 20.6 @xmath96 * + g@xmath139 & @xmath140 & 3 & a & 3.4 & 11.6 @xmath961.9 + g@xmath141 & @xmath142 & 1 & a & 4.0 & 12.2 @xmath962.0 + + g@xmath143 & @xmath144 & 3 & c & 8.2 & 0.3@xmath96 * + g@xmath145 & @xmath146 & 3 & c & 7.6 & 0.9@xmath96 * + g@xmath147 & @xmath148 & 5 & c & 4.5 & 4.0@xmath96 * + g@xmath149 & @xmath150 & 3 & c & 6.0 & 2.5@xmath96 * + g@xmath151 & @xmath152 & 3 & c & 5.1 & [email protected] + g@xmath153 & @xmath154 & 3 & a & 4.7 & [email protected] + g@xmath155 & @xmath156 & 1 & c & 4.7 & [email protected] + if an hiiregion is awarded a far side kdar , based on the above requirements , a kinematic distance can be calculated using a galactic rotation curve model ( which assumes circular rotation ) .
the iau galactic constants have been applied in these calculations : @xmath157 km s@xmath20 .
if an hiiregion must be located at least as far as the subcentral point , then its location inside , or beyond , the solar circle is given by its systemic velocity .
in the inner galaxy , velocities are positive in the first quadrant and negative in the fourth .
the signs are reversed in the outer galaxy , such that first quadrant sources located beyond the solar circle will have negative velocities , and fourth quadrant sources in the outer galaxy will have positive velocities . throughout this work , the rotation curve of @xcite is used for regions within the solar circle . in the outer galaxy
, @xmath33 was calculated using a flat rotation model @xmath158 . caused by the choice of rotation curve , non - circular streaming motions of 15 km s@xmath20and by changing the solar circular rotation speed to @xmath159 km s@xmath20 .
blank areas are indicative of @xmath160 ( where no error analysis was carried out ) , or percentage uncertainties @xmath161 .
the eig is shaded grey ( no kinematic distances were calculated for this region ) , and the solar circle and locus of tangent points appear as the black circles .
the percentage uncertainties are mirrored for lines of sight in the fourth quadrant , here , only @xmath162 is shown for clarity . ( a color version of this figure is available in the online journal . ) [ fig6 ] ] we follow the distance uncertainty analysis method of @xcite , investigating the effects of the choice of rotation curve , streaming motions and solar rotation speed on kinematic distance calculations .
we compare all sources of uncertainty to the distances calculated from the rotation model of @xcite .
firstly we compute , for a grid of ( @xmath163 ) positions , the kinematic distance using the rotation curves of @xcite and @xcite . the standard deviation of these distances for each ( @xmath163 ) is then computed and divided by the @xcite distance to obtain the percentage uncertainty due to choice of rotation curve .
we assessed a grid of @xmath0 and @xmath164 km s@xmath20with steps of 0.1 in each unit .
this procedure is then repeated , but instead of varying the galactic rotation model , the percentage uncertainty due to streaming motions ( of 15 km s@xmath20 ) and an altered circular solar rotation speed of 255 km s@xmath20@xcite are investigated . the effect of these three sources of error
are then added in quadrature for each ( @xmath163 ) pair , before transformation onto a face - on plot ( figure [ fig6 ] ) .
it should be noted that kinematic distance errors at small galactic longitudes are intrinsically larger than for other sections of the galaxy .
equal steps in velocity map to unequal length steps in @xmath33 , such that @xmath165 .
this can be seen in figure [ fig6 ] where the percentage uncertainty is higher for smaller longitudes .
[ [ uncertainties - due - to - rotation - curve ] ] uncertainties due to rotation curve + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + in addition to larger uncertainties at small longitudes due to the velocity gradient , errors are also larger in the outer galaxy due to the uncertainty in the outer galaxy circular rotation models .
flat , rising and falling rotation curves have been suggested for beyond the solar circle @xcite .
here we have used the rotation models of @xcite and @xcite . note that the @xcite model has an applicable galactocentric range of @xmath166 kpc . as a result
the model was extrapolated to the solar circle , and a flat rotation curve was assumed for @xmath167 .
the largest discrepancy between these three models occurs at @xmath168 kpc , but even at @xmath169 the models differ significantly .
[ [ uncertainties - due - to - non - circular - streaming - motions ] ] uncertainties due to non - circular , streaming motions + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + large non - circular motions have precluded galactic astronomers from fitting a rotation curve to the eig .
smaller - scale non - circular motions are ubiquitous in the galaxy and are the result of systematic velocity fields within a source , or ordered large - scale galactic streaming motions @xcite . @xcite
suggest an uncertainty , due to non - circular motions , of 5 to 10 km s@xmath20 ; whereas @xcite assign an estimate of cloud - cloud dispersion of 5 km s@xmath20 in addition to contributions from galactic scale streaming motions of 10 km s@xmath20 . @xcite and
@xcite find hiabsorption components extending to 10 - 20 km s@xmath20beyond the systemic velocity of hiiregions . in order to promote a conservative approach to kinematic distance uncertainties , the random uncertainty due to non - circular motions
is set to 15 km s@xmath20 .
the contribution of errors due to streaming motions in relation to the total uncertainty in kinematic distance is high , especially for small longitudes .
the errors due to non - circular motions are the standard deviation of the three @xmath170 grids,@xmath170 , @xmath171 , @xmath172 divided by the @xmath170 distance , all computed with the @xcite rotation model . [
[ uncertainties - due - to - solar - rotation - parameters ] ] uncertainties due to solar rotation parameters + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + the iau values for @xmath173 kpc and @xmath174 km s@xmath20have been used throughout this work . however , here we investigate the significance of an altered solar rotation speed , as suggested by @xcite .
two @xmath170 grids were computed with the rotation model of @xcite , using @xmath175 km s@xmath20 .
the standard deviation of these two grids , at each locus , was then divided by the standard ( i.e. @xmath174 km s@xmath20 ) distance to compute the percentage uncertainty due to choice of solar rotation parameters .
note that the @xcite value for @xmath176 kpc is consistent with the iau value , and is therefore not investigated here . in order to examine the large - scale structure of the galaxy , hiiregions with successfully calculated kinematic distances
were transformed into a face - on map of the milky way ( left panel of figure [ fig7 ] ) and also superimposed onto an artist s conception of the galaxy ( right panel ) . the background image used in the right panel of figure [ fig7 ] , was created using stellar , hiand co data @xcite and was reviewed in @xcite .
in addition , the kinematic distances from @xcite are also displayed .
figure [ fig7 ] demonstrates the need for hiiregion discovery and kdar studies for galactic longitudes @xmath177 in order to further investigate the end of the bar and differentiate the norma and near 3kpc arms , as well as the sagittarius and perseus arms on the far side of the locus of subcentral points ( smaller circle in figure [ fig7 ] ) . at the end of the bar in the first quadrant ,
hiiregion kdars have been made by @xcite and @xcite - further encouragement for a fourth quadrant study .
recently , @xcite identified an extension of the scutum - centaurus arm at extreme distances from the sun , in the first galactic quadrant
. however , confirmation of this discovery requires tracing the arm over its entire longitude range .
@xcite comment that molecular gas which constitutes the section of scutum - centaurus arm behind the galactic center will be the most difficult to deconvolve . in the longitude range of this paper , hiiregions with systemic velocities opposite in sign to circular - disk rotation must be located in the eig or beyond the solar circle .
using hiabsorption features to resolve this ambiguity has allowed for seven hiiregions to be unequivocally placed in the outer galaxy .
several of these outer galaxy regions ( see figure [ fig7 ] ) appear to trace the scutum - centaurus arm .
the eig remains a difficult section of the milky way to study . in terms of galactic structure ,
kinematic studies in this region are hampered by a lack of rotation model for @xmath178kpc ( and for the outer galaxy ) .
in addition , there remains a lack of consensus regarding the number , locations and nomenclature of large - scale structures near the galactic centre ( these are discussed in section [ gc ] ) . despite this , hiabsorption associated with eig features was successfully used as a distance indicator , allowing for constraints on the line of sight distance for over 80% of the sample of hiiregions investigated , or over 60% of all known hiiregions with systemic velocities in @xmath0 . over 67% of the hiiregions
demonstrate hiabsorption associated with the near 3kpc arm ( see table [ table2 ] ) and therefore must be located at line of sight distances of at least @xmath179kpc .
a further 16 hiiregions show absorption associated with eig features assumed to lie further along the line of sight than the near 3kpc arm , therefore , over 78% of the sample hiiregions are located at @xmath180kpc .
this is in keeping with the work of @xcite who find @xmath181 of their sample of 40 eig continuum sources must be located at least as far as the near 3kpc arm . of the 151 hiiregions investigated , 54 hiiregions display absorption from eig features assumed to be on the far side of the gc ( the + 135 km s@xmath20expanding arm , bania s clump 1 or far 3kpc arm ) .
consequently , these hiiregions must be located at @xmath182kpc .
after successfully resolving the near / far kinematic distance ambiguity , line of sight distances were calculated for 31 hiiregions .
these distances suggest locations for the hiiregions in known galactic structures including the norma , sagittarius and perseus spiral arms ( see figure [ fig7 ] ) .
the 7 hiiregions beyond the solar circle are among the most distant galactic hiiregions known to exist and could be crucial to tracing the scutum - centaurus arm ; where identification of star formation with molecular tracers is extremely difficult @xcite .
errors on these line of sight distances are often large - due to the uncertainty of non - circular streaming motions , and differences in galactic rotation models - but the near / far kdar remains both valid and significant . using a summary of eig structures , and the known @xmath3 distribution of co , we construct a ` crayon diagram ' with which to investigate the distribution of hiabsorption in the eig ( figure [ fig2 ] , section [ cayondiagramsection ] ) . in section [ hidist ]
we find cold hiclouds , signified by hiabsorption , associated with the near 3kpc arm , connecting arm , bania s clump 1 , tilted disk and far 3kpc arm .
there was minimal hiabsorption associated with either the looping ridge or the + 135 km s@xmath20expanding arm .
the large amount of hiabsorption associated with each of the 3kpc arms presented an opportunity to fit a model to the @xmath3 locus of each arm ( [ hiin3kpcarms ] ) .
we find a linear fit ( in @xmath3 space ) that is consistent with the findings of @xcite , who used co to trace the arms .
the @xmath3 distribution of the rrl velocities of the 151 hiiregions was investigated in section [ hiidist ] .
like the hiabsorption distribution , the systemic velocities of the hiiregions trace galactic structures including spiral arms , features located near the galactic center and possibly the end of the bar . while most hiiregions posses rrl velocity components allowed by circular galactic rotation ( suggestive of a location outside the eig ) , smaller numbers of hiiregions are found to be associated with the hitilted disk , near 3kpc arm , + 135 km s@xmath20expanding arm , bania s clump 1 , connecting arm and far 3kpc arm . using the rrl velocity and hiabsorption spectrum of each hiiregion
, we were also able to constrain the @xmath33 for a further sample of hiiregions using only eig features as a distance indicator .
this research has made use of nasa s astrophysics data system , the nasa / ipac extragalactic database ( ned ) and the simbad database .
the hiabsorption spectrum does not give a clear indication of any absorption associated with any eig feature .
at this longitude , the velocity range of the far 3kpc arm is not clearly distinct from velocities expected by normal circular rotation .
the hiabsorption spectra clearly demonstrates absorption either side of the velocities expected by an association with the near 3kpc arm . @xcite
place the hiiregion at a line of sight distance of 6.2 kpc ( i.e. on the near side of the gc ) .
evidence of absorption in the far 3kpc arms suggests a far kdar . as with g350.330 + 00.157 ( below ) ,
the calculated @xmath93 and @xmath33 for the region are outside the bounds of the @xcite rotation model .
while the hiabsorption spectrum suffers from emission fluctuations around the rrl velocity ( @xmath183 km s@xmath20 ) , there is evidence of absorption associated with the near 3kpc arm . assuming a far side kdar , the calculated @xmath93 and @xmath33 are outside the bounds of the @xcite rotation model .
evidence of hiabsorption is seen either side of the velocities associated with the near 3kpc arm ( see g350.129 + 00.088 above ) , and is therefore located at least as far as the near 3kpc arm along the line of sight .
g350.524 + 00.960 does not demonstrate any hiabsorption outside the velocities expected by normal circular rotation .
if the near kinematic distance is therefore assumed , the hiiregion has a calculated @xmath184kpc .
as the hiabsorption spectrum of g350.813 - 00.019 demonstrates absorption in velocities associated with the far 3kpc arm , the hiiregion must be on the far side of the gc .
the positive ( small ) rrl velocity then locates the hiiregion at a line of sight distance beyond ( but close to ) the solar circle .
the hiabsorption spectrum of g351.028 + 00.155 demonstrates significant absorption at velocities corresponding to both the near and far 3kpc arms , and therefore must be located at least as far as the far 3kpc arm along the line of sight .
the positive rrl velocity then requires that g351.028 + 00.155 is located in the outer galaxy .
hiabsorption is evident in circular rotation allowed velocities only .
if the near kinematic distance is therefore assumed , the hiiregion has a calculated @xmath185kpc .
@xcite assumes the near kinematic distance , however @xcite place the hiiregion at a line of sight distance of 17.1 kpc .
g351.662 + 00.518 has a near zero rrl velocity ( -2.9 km s@xmath20 , @xcite ) which is associated with locations inside the eig region , near the solar cirle , or at a very small line of sight distance from the sun .
absorption at velocities associated with the near 3kpc arm imply a @xmath187kpc . as there is no hiabsorption associated with other eig features ( only the far 3kpc arm is expected at this longitude ) , a location within @xmath188kpc is assumed .
this hiiregion has an rrl velocity associated with the near 3kpc arm ( -88.6 km s@xmath20 , gbthrds ) .
strong absorption in the allowed circular rotation velocities and at velocities associated with the near 3kpc arm , reaffirm the location in the arm .
absorption is seen at the expected velocities of the near 3kpc arm , which is also where the rrl velocity for this hiiregion lies ( -87 km s@xmath20 , @xcite ) .
absorption up to 25 km s@xmath20beyond the rrl velocity of an hiiregion is not uncommon @xcite , therefore it is assumed that the hiiregion is located in the near 3kpc arm .
g352.611 - 00.172 displays strong absorption at @xmath189 km s@xmath20 , approximately 20 km s@xmath20beyond the known rrl velocity of the hiiregion ( -81.9 km s@xmath20 , @xcite ) . as with g352.398 - 00.057 ( above )
, g352.611 - 00.172 is assumed to lie in the near 3kpc arm .
this location , in the near 3kpc arm , is approximately the same as the line of sight distance given by @xcite ( 6.7 kpc ) .
evidence of absorption at velocities corresponding to the near 3kpc arm suggest a @xmath190kpc .
@xcite position a nearby 6.7 ghz methanol maser ( @xmath191 ) at the far kinematic location ( @xmath192kpc ) .
hiabsorption is evident in circular rotation allowed velocities only , g353.186 + 00.887 .
if the near kinematic location is then assumed , the hiiregion has a calculated @xmath193kpc .
@xcite provide a near side kdar for this hiiregion .
also the source of a variable maser @xcite , g353.218 - 00.249 has a small rrl velocity ( -8.3 km s@xmath20 , gbthrds ) and absorption present at near 3kpc arm , but not far 3kpc arm , velocities .
these are evidence for a location near the eig , and as such @xmath190kpc , @xmath194kpc is assumed .
hiabsorption is present at velocities corresponding to both 3kpc arms , suggestive of a far side kdar .
however , like the hiiregions g350.330 + 00.157 and g350.177 + 00.017 , the calculated @xmath196 fall outside the boundaries of the @xcite rotation model .
strong absorption is centered at velocities to the negative side of those expected for the near 3kpc arm ( see g352.611 - 00.172 and g352.398 - 0.057 above).@xcite were unable to determine a kdar for a nearby 6.7 ghz methanol maser ( @xmath197 ) . due to the hiabsorption associated with the near 3kpc arm @xmath190kpc is assumed .
@xcite places a nearby 6.7 ghz methanol maser ( @xmath198 ) in the far 3kpc arm .
the rrl velocity of the hiiregion ( 15.8 km s@xmath20 , @xcite ) is slightly smaller than that expected for the far 3kpc arm , but the absorption indicates the hiiregion must be located at least as far along the line of sight as the feature .
due to the positive rrl velocity , we assume that g354.486 + 00.085 is located beyond the solar circle ( see table [ table4 ] ) . a line of sight along the longitude of 354.588@xmath199 intersects the near and far 3kpc arms as well as the assumed position of bania s clump 1 .
the hiabsorption spectrum of g354.588 + 00.007 does not give conclusive evidence for either a near , nor far , kdar ; but absorption associated with the near 3kpc arm suggests @xmath190kpc .
significant hiabsorption is present before and after the velocities expected of the near 3kpc arm , as well as at far 3kpc arm velocities .
a known strong 6.7 ghz methanol maser is also in the region @xcite , with a velocity equivalent to the rrl velocity ( maser velocity : -23 km s@xmath20 , rrl velocity : -23.4 km s@xmath20(gbthrds ) ) .
@xcite suggest a poor quality near side kdar for the associated maser , but a far kinematic distance is assumed here .
no absorption is seen at the rrl velocity of the hiiregion ( 97.8 km s@xmath20 , @xcite ) , nor at velocities corresponding to the near 3kpc arm .
however , significant absorption is seen at @xmath201 km s@xmath20 , possibly associated with bania s clump 1 .
no kdar is given here , however the high rrl velocity is suggestive of a location in the eig @xcite . as with g354.665 + 00.247
, the high rrl velocity of g354.717 + 00.293 suggests a location in the eig .
the hiabsorption spectrum suffers from emission fluctuations at the rrl velocity ( 95.3 km s@xmath20 , gbthrds ) and no absorption is present at near 3kpc arm velocities .
at least two masers with high velocities ( @xmath189 km s@xmath20 ) are known to exist in the area @xcite . g354.934 + 00.327
shares a similar absorption profile to that of g354.717 + 00.293 and g354.665 + 00.247 , however it does not share a highly non - circular rrl velocity ( 14 km s@xmath20 , @xcite ) .
absorption velocities corresponding to all expected eig features requires the hiiregion to be located at least as far along the line of sight as the far 3kpc arm . due to the positive rrl velocity , the hiiregion
must then be located in the outer galaxy , beyond the solar circle along the line of sight .
hiabsorption is present at velocities corresponding to the near 3kpc arm on the near side of the gc , and there is evidence of absorption on the far side of the gc due to the far 3kpc arm and + 135 km s@xmath20expanding arm .
a far side kdar is given , but due to the positive rrl velocity , the hiiregion must be located beyond the solar circle .
absorption at the near 3kpc arm , + 135 km s@xmath20expanding arm and far 3kpc arm infer that the hiiregion is located beyond the eig along the line of sight .
the positive rrl velocity then places the hiiregion beyond the solar circle .
there are several masers in the region which are assumed to lie within 3 kpc of the gc ( see @xmath202 in * ? ? ?
this region has four known rrl velocities ( 3.8 , -22.5 , -80.6 and -41.1 km s@xmath20 , gbthrds ) , a strong indication that there are several emission sources along the line of sight .
note that the rrl velocity @xmath203 km s@xmath20is associated with velocities expected of the near 3kpc arm .
no kdar is given .
three rrl velocities are known towards the hiiregion ( + 108.7 , -76.1 and + 11.7 km s@xmath20 , gbthrds ) . as with g355.532 - 00.100 ( above ) , this is an indication of several sources along the line of sight .
no kdar is given , however the rrl velocity @xmath65 km s@xmath20is associated with the near 3kpc arm and the rrl velocity component @xmath204 km s@xmath20is associated with the + 135 km s@xmath20expanding arm .
the near zero rrl velocity ( -2.6 km s@xmath20 , gbthrds ) is indicative of a eig location , or a location near the solar circle ( either very close or at a great distance from the sun ) .
absorption in velocities associated with the near 3kpc arm and + 135 km s@xmath20expanding arm , but not at velocities corresponding to far side eig features prompts @xmath205kpc , @xmath194 kpc to be given as a distance limit for the hiiregion .
in contrast , @xcite presents a far side kdar for a 6.7 ghz methanol maser at @xmath206 which has a systemic velocity of @xmath207 km s@xmath20 .
two rrl velocities ( 3 and -79.1 km s@xmath20 , gbthrds ) suggest multiple emission sources along the line of sight , at least one of which is associated with the near 3kpc arm ( -79.1 km s@xmath20rrl association ) . at this longitude , the velocities of the near 3kpc arm and the looping ridge ( on the far side of the gc ) overlap .
no kdar is given .
g355.700 - 00.100 has an absorption profile and rrl velocity ( -76.1 km s@xmath20 , @xcite ) suggestive of a location within the near 3kpc arm or looping ridge ( as the expected velocities of these features overlap at this longitude ) .
no kdar is given .
there are multiple rrl velocities associated with g355.734 + 0.138 ( 10.7 and -77.4 km s@xmath20 , gbthrds ) .
no kdar is given , but the rrl velocity component at @xmath72 km s@xmath20is associated with the velocities expected of the near 3kpc arm or looping ridge .
the velocity ranges of the near 3kpc arm and looping ridge continue to overlap at this longitude .
two rrl velocities are known ( -31.5 , 3.1 km s@xmath20 , gbthrds ) , suggestive of multiple sources along the line of sight .
no kdar is given .
at this longitude the expected velocities of the near 3kpc arm and looping ridge are distinct ( see above )
. however , the hiabsorption spectrum of g356.230 + 00.066 does not give conclusive evidence for either a near , nor far , kdar .
absorption is seen at velocities corresponding to the near 3kpc arm and looping ridge .
it is assumed that the hiiregion is located in the + 135 km s@xmath20expanding arm ( due to the rrl velocity ( 116.3 km s@xmath20 , @xcite ) .
this is supported by absorption at velocities corresponding to the looping ridge ( on the far side of the gc , but closer to the gc than the + 135 km s@xmath20expanding arm ) .
the hiabsorption spectrum suffers from emission fluctuations in the velocity ranges associated with the near 3kpc arm and looping ridge .
as such the poor quality spectrum does not allow a kdar to be given for this hiiregion .
the hiabsorption spectrum of g357.970 - 00.169 displays absorption at velocities associated with the near 3kpc arm . as a result
, @xmath208 is assumed . the small rrl velocity , and lack of absorption corresponding to other eig features suggests a further constraint , @xmath85kpc . the hiabsorption spectrum of g357.998 - 00.159 displays absorption at velocities associated with the near 3kpc arm . as a result , @xmath208 is assumed . the small rrl velocity , and lack of absorption corresponding to other eig features suggests a further constraint , @xmath85kpc .
this hiiregion has an rrl associated with the looping ridge or tilted disk(-208.5 km s@xmath20 , gbthrds ) , however the spectrum is of poor quality and no absorption is seen at velocities pertaining to any eig feature .
this hiiregion has an rrl associated with the looping ridge or tilted disk(-208.5 km s@xmath20 , gbthrds ) , however the spectrum is of poor quality and no absorption is seen at velocities pertaining to eig features in front of the gc along the line of sight .
the hiiregion has an rrl association with the tilted disk or looping ridge .
the hiabsorption spectrum confirms absorption at velocities corresponding to the near 3kpc arm only ; further supporting a location in the eig .
absorption is also seen at velocities either side of the expected velocity range of the tilted disk .
like g358.616 - 00.076 ( above ) , g358.623 - 00.066 demonstrates significant absorption associated with the near 3kpc arm and tilted disk .
the rrl association with the looping ridge / tilted disk suggests a location in the eig .
note the bifurcation in the near 3kpc arm absorption profile , see [ cayondiagramsection ] .
hiabsorption is seen at velocities corresponding to the near 3kpc arm and the hitilted disk .
the positive rrl velocity suggests either a eig or near solar circle location : absorption corresponding to near - side eig features discounts the near - kinematic distance ; and if the hiiregion was located near the solar cirlce on the far side , there should be evidence of absorption associated with the far 3kpc arm . as a result
it is assumed that the hiiregion is located within the eig , i.e. @xmath85kpc , @xmath209kpc .
note the bifurcation in the near 3kpc arm absorption profile ( see g358.623 - 00.066 above ) .
[ [ g358.652 - 00.078-g358.680 - 00.087-g358.694 - 00.075-g358.72000.011-g358.82700.085-and - g359.159 - 00.038 ] ] g358.652 - 00.078 , g358.680 - 00.087 , g358.694 - 00.075 , g358.720 + 00.011 , , g358.827 + 00.085 and g359.159 - 00.038 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ the hiabsorption profiles of these hiiregions are all similar . and
all have highly non - circular rrl velocities which correspond to the tilted disk - g359.159 - 00.038 has two known rrl velocities ( -182.5 and -215.6 km s@xmath20 ) .
the hiabsorption spectra suffer from emission fluctuations and are generally of poor quality .
g359.432 - 00.086 has a known rrl velocity associated with the near 3kpc arm .
the hiabsorption spectrum towards the region demonstrates absorption associated with the near 3kpc arm ( and also at @xmath210 km s@xmath20 ) . at this longitude the expected velocity ranges of the near 3kpc arm and tilted disk overlap .
the hiabsorption spectrum demonstrates absorption at velocities corresponding to the near 3kpc arm , but suffers from emission fluctuations at the overlap .
the hiiregion has an rrl velocity consistent with either the tilted disk or near 3kpc arm .
absorption is present at velocities corresponding to the near 3kpc arm , but not at the expected velocities of other eig features .
it is assumed that the hiiregion is located in the eig , beyond the near 3kpc arm ; @xmath85kpc , @xmath209kpc .
g000.361 - 00.780 demonstrates hiabsorption at velocities associated with the near 3kpc arm , but no absorption at other eig @xmath3 features .
it is therefore assumed , as with g000.284 - 00.478 above that the hiiregion is located within @xmath85kpc , @xmath209kpc . with two rrl velocities ( 25.7 and 41.4 km s@xmath20 , gbthrds ) ,
the absorption spectrum is likely to have contributions from at least emission two sources along the line of sight .
absorption at the near 3kpc arm and + 135 km s@xmath20expanding arm velocities suggests that at least one of the emission sources is located on the far side of the gc .
no kdar is given .
note also that at this longitude , the expected velocity ranges of the hitilted disk and far 3kpc arm are nearly indistinguishable .
hiabsorption is present at velocities corresponding to the near 3kpc arm , but not at the velocities of other eig features .
the rrl velocity ( 45 km s@xmath20 , @xcite ) suggests an association with the far 3kpc arm .
g000.729 - 00.123 has two recorded rrl velocities ( 105.3 and 83.2 km s@xmath20 , gbthrds ) , both forbidden by circular galactic rotation .
the region was studied by @xcite who found an rrl velocity of 102 km s@xmath20 .
@xcite discussed the hiiregion as being clearly located near the eig , but not delineating the outer boundary of the galactic bar .
the gbthrds find that of their nine hiiregions associated ( in @xmath3 space ) with the nuclear disk , g000.729 - 0.103 is the only source that could be located on the red - shifted side .
the hispectrum demonstrates statistically significant absorption at velocities corresponding to both 3kpc arms , but not for the nuclear disk nor + 135 km s@xmath20expanding arm .
no hiabsorption is present at either of the rrl velocities .
no kdar is given .
the hiabsorption spectrum , which is of poor quality due to emission fluctuations , demonstrates absorption consistent with the velocities expected of each of the eig features ( near 3kpc arm , hitilted disk , + 135 km s@xmath20expanding arm and far 3kpc arm ) .
a far - side kdar is therefore awarded to the hiiregion .
@xcite remarked that the non - circular rrl velocity ( -19.7 km s@xmath20 ) and h@xmath211co at 84 and 123 km s@xmath20was typical of a eig source ; @xcite also give @xmath212kpc .
the hiiregion must be located within the eig , as absorption at eig features negates the near - side kinematic location and if the hiiregion must have a non - realistic @xmath213kpc .
g001.149 - 00.062 displays absorption at velocities corresponding to both the near and far 3kpc arms . assuming a distance of at least the far 3kpc arm , g001.149 - 00.062 must lie in the outer galaxy , beyond the solar circle ( due to the negative systemic velocity ) .
however , using a flat rotation model for the outer galaxy , the calculated @xmath33 is unrealistic ( @xmath214kpc ) .
therefore the hiiregion must lie in the eig region , but behind the far 3kpc arm .
no hiabsorption is seen at velocities corresponding to eig features , suggesting a near kdar .
however , the negative rrl velocity ( -12.7 km s@xmath20 , gbthrds ) suggests a location in either the eig or in the outer galaxy - locations that each would imply absorption by the near 3kpc arm , which is not seen .
no kdar is given .
@xcite assigns a 6.7 ghz methanol maser at the same velocity to @xmath194 kpc due to the negative systemic velocity .
absorption at velocities corresponding to the near 3kpc arm supports the @xmath194 kpc placement . for a 6.7 ghz methanol maser at the same coordinates ,
@xcite discuss that the large positive systemic velocity is most readily attributed to a location within the galactic bar .
absorption is seen at near 3kpc arm velocities , and at velocities slightly lower than the rrl velocity ( 102.4 km s@xmath20 , @xcite ) , but not at + 135 km s@xmath20expanding arm velocities ; therefore @xmath194kpc is assumed .
see section [ hiidist ] for a previous discussion of this hiiregion .
the negative rrl velocity suggests a eig or outer galaxy location .
absorption at near 3kpc arm velocities infers a @xmath187kpc ; but a lack of absorption associated with any other eig feature does not allow the eig / outer galaxy location degeneracy to be resolved . @xcite give a location in the outer galaxy .
absorption at velocities corresponding to both 3kpc arms suggests a kinematic location in , or beyond , the far 3kpc arm .
the near zero systemic velocity then suggests a location near the solar circle . @xcite
give a line of sight distance to g003.270 - 00.101 of 14 kpc .
with hiabsorption at near 3kpc arm velocities , @xmath187kpc is assumed . as the hiiregion has a near zero systemic velocity , and no absorption associated with the far 3kpc arm , then @xmath85kpc should also apply .
absorption is not seen towards any eig features , suggesting a near side kdar .
@xcite also provided a near side kdar , however , @xcite give a line of sight distance of 14.5 kpc , placing the hiiregion on the far side of the gc .
the hiabsorption spectrum of g006.148 - 00.635 does not give conclusive evidence for either a near , nor far , kdar .
however , absorption is present at velocities associated with the near 3kpc arm ; suggestive of @xmath187kpc
. the hiabsorption spectrum of g006.225 - 00.569 does not give conclusive evidence for either a near , nor far , kdar .
as with g006.160 - 00.608 , absorption is seen at velocities corresponding with the connecting arm , but not the near 3kpc arm ( which precedes the connecting arm along the line of sight ) .
again there is no absorption seen at velocities corresponding to the near 3kpc arm ( see g006.160 - 00.60 , g006.225 - 00.569 and g006.398 - 00.474 above ) , but in this case the lack of absorption is probably due to emission fluctuations .
absorption at velocities corresponding to the connecting and far 3kpc arms suggests a far side kdar .
the hiabsorption spectrum of g007.266 + 00.186 demonstrates absorption at velocities associated with the near 3kpc and connecting arms , which suggests a location @xmath216kpc .
in addition , a near zero rrl velocity ( -4.4 km s@xmath20 , gbthrds ) , and a lack of absorption at far 3kpc arm velocities suggests @xmath194kpc .
significant absorption at velocities corresponding to both the near and far 3kpc arms strongly suggests a far side kdar , however the rrl velocity ( -17.8 km s@xmath20 , @xcite ) is indicative of a location in the near 3kpc arm .
the hiiregion also presents significant absorption at @xmath218 km s@xmath20(see g006.083 - 00.117 , above ) .
@xcite and @xcite both give a near side kdar for the hiiregion .
a near side kdar is also given by this work - note that at this longitude the expected velocity range of the near 3kpc arm overlaps the expected velocities of general circular rotation .
kinematic distance analyses can be greatly affected by velocity crowding and a decrease of cold , dense hiin the eig .
for example , @xcite thoroughly investigated the high mass star formation region g9.62 + 0.20 - comprised of several hiiregions - and find from trigonometric parallax that it has a distance of @xmath219 kpc , placing it in the 3 kpc arm .
this distance is at odds with the kinematically determined distances for the region ( 0.36 and 16.4 kpc , based on the systemic velocity of the region , 4.1 km s@xmath20 ) .
inspection of the hiabsorption spectrum of g009.615 + 00.198 rules out the far kinematic distance as there is no significant absorption at the velocities of far side eig features ( i.e. the far 3kpc arm ) .
[ [ g009.925 - 00.745-g009.68200.206-g009.74100.842-and - g009.982 - 00.752 ] ] g009.925 - 00.745 , g009.682 + 00.206 , , g009.741 + 00.842 , and g009.982 - 00.752 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ anderson , l. d. , bania , t. m. , balser , d. s. , & rood , r. t. 2012 , , 754 , 62 anderson , l. d. , bania , t. m. , balser , d. s. , & rood , r. t. 2011 , , 194 , 32 anderson , l. d. & bania , t. m. 2009 , , 690 , 706 baba , j. , saitoh , t. r. , & wada , k. 2010 , , 62 , 1413 bania , t. m. 1980 , , 242 , 95 bania , t. m. , & lockman , f. j. 1984 , , 54 , 513 bania , t. m. , stark , a. a. , & heiligman , g. m. 1986 , , 307 , 350 bania , t. m. , anderson , l. d. , balser , d. s. , & rood , r. t. 2010 , , 718 , l106 bania , t. m. , anderson , l. d. , & balser , d. s. 2012 , , 759 , 96 blitz , l. , binney , j. , lo , k. y. , bally , j. , & ho , p. t. p. 1993
, , 361 , 417 brand , j. , & blitz , l. 1993 , , 275 , 67 burton , w. b. , liszt , h. s. 1983 , , 52 , 63 caswell , j. l. , & haynes , r. f. 1982 , , 254 , l31 caswell , j. l. , & haynes , r. f. 1987 , , 171 , 261 caswell , j. l. , fuller , g. a. , green , j. a. , et al . 2010 , , 404 , 1029 churchwell , e. , babler , b. l. , meade , m. r. , et al .
2009 , , 121 , 213 clemens , d. p. 1985
, , 295 , 422 condon , j. j. , cotton , w. d. , greisen , e. w. , et al .
1998 , , 115 , 1693 dame , t. m. , hartmann , d. , & thaddeus , p. 2001
, , 547 , 792 dame , t. m. , & thaddeus , p. 2008
, , 683 , l143 dame , t. m. , & thaddeus , p. 2011
, , 734 , l24 dickey , j. m. , mcclure - griffiths , n. m. , gaensler , b. m. , & green , a. j. 2003 , , 585 , 801 dickey , j. m. , & lockman , f. j. 1990 , , 28 , 215 downes , d. , wilson , t. l. , bieging , j. , & wink , j. 1980 , , 40 , 379 fux , r. 1999 , , 345 , 787 green , j. a. , mcclure - griffiths , n. m. , caswell , j. l. , et al .
2009 , , 696 , l156 green , j. a. , & mcclure - griffiths , n. m. 2011 , , 417 , 2500 green , j. a. , caswell , j. l. , mcclure - griffiths , n. m. , et al . 2011 , , 733 , 27 gooch , r. 1996 , astronomical data analysis software and systems v , 101 , 80 hachisuka , k. , brunthaler , a. , menten , k. m. , et al .
2009 , , 696 , 1981 honma , m. , bushimata , t. , choi , y. k. , et al .
2007 , , 59 , 889 jones , c . , & dickey , j. 2012 , , 753 , 62 kolpak , m. a. , jackson , j. m. , bania , t. m. , clemens , d. p. , & dickey , j. m. 2003 , , 582 , 756 lang , c. c. , goss , w. m. , cyganowski , c. , & clubb , k. i. 2010 , , 191 , 275 liszt , h. s. , 2008 , , 486 , 467 liszt , h. s , burton , w. b. 1980 , , 236 , 779 lockman , f. j. 1989 , , 71 , 469 lockman , f. j. , pisano , d. j. , & howard , g. j. 1996 , , 472 , 173 marshall , d. j. , fux , r. , robin , a. c. , & reyl , c. 2008 , , 477 , l21 mcclure - griffiths , n. m. , dickey , j. m. , gaensler , b. m. , et al .
2005 , , 158 , 178 mcclure - griffiths , n. m. , & dickey , j. m. 2007 , , 671 , 427 mcclure - griffiths , n. m. , dickey , j. m. , gaensler , b. m. , et al .
2012 , , 199 , 12 moiss , a. p. , damineli , a. , figuerdo , e. , et al .
2011 , , 411 , 705 morris , m. , & serabyn , e. 1996 , , 34 , 645 oort , j. h. 1977 , , 15 , 295 paladini , r. , burigana , c. , davies , r. d. , et al .
2003 , , 397 , 213 quireza , c. , rood , r. t. , bania , t. m. , balser , d. s. , & maciel , w. j. 2006 , , 653 , 1226 reid , m. j. , menten , k. m. , zheng , x. w. , et al .
2009 , , 700 , 137 rodrguez - fernndez , n. j. 2006 , journal of physics conference series , 54 , 35 rodriguez - fernandez , n. j. , combes , f. , martin - pintado , j. , wilson , t. l. , & apponi , a. 2006 , , 455 , 963 rodrguez - fernndez , n. j. 2011 , memorie della societa astronomica italianasupplementi , 18 , 195 roy , s. 2003 , , 403 , 917 sanna , a. , reid , m. j. , moscadelli , l. , et al .
2009 , , 706 , 464 sewilo , m. , watson , c. , araya , e. , et al .
2004 , , 154 , 553 simonson , s. c. , & madder , g. l. , 1973 , , 27 , 337 uchida , k. , morris , m. , & yusef - zadeh , f. 1992 , , 104 , 1533 urquhart , j. s. , hoare , m. g. , lumsden , s. l. , et al .
2012 , , 420 , 1656 van woerden , h. , rougoor , g. w. , & oort , j. h. 1957 , academie des sciences paris comptes rendus , 244 , 1691 wink , j. e. , altenhoff , w. j. , & mezger , p. g. 1982 , , 108 , 227 | we make a comprehensive study of hiabsorption toward hiiregions located within @xmath0 .
structures in the extreme inner galaxy are traced using the longitude - velocity space distribution of this absorption .
we find significant hiabsorption associated with the near and far 3kpc arms , the connecting arm , bania s clump 1 and the hitilted disk .
we also constrain the line of sight distances to hiiregions , by using hiabsorption spectra together with the hiiregion velocities measured by radio recombination lines . |
congenital entropion is a disease of the eyelid that is highly prevalent among oriental populations .
it has been reported that the prevalence of this condition has a rate of over 20% among 1-year - old children and that the prevalence of this condition decreases to 2% in 12-year - old children.1 it is thought that one of the causes of congenital entropion is excessive growth of the orbicularis muscle , which inverts the cilia toward the cornea .
development of an epicanthal fold also causes traction of the inner canthus area of the eyelid.2,3 in oriental eyelids , remarkable epicanthal folds are highly visible in single eyelids . the prevalence of an epicanthal fold is reportedly 70%80% in asian countries.4,5 epicanthoplasty of the superior eyelid has recently become a popular procedure in asian plastic surgery.68 however , epicanthoplasty of the lower eyelid is not common because the procedures that are used to treat congenital entropion ( ie , suturing procedures ) are often performed by ophthalmologists , while epicanthoplasty , including designing , is a rather complicated procedure .
another reason that the procedure is not common is related to a desire to avoid scar formation and changes in the appearance of the patient . therefore , we developed an easy method of preparatory designing and a surgical method that can be performed in conjunction with a modified hotz procedure .
a triangle flap that is designed on the epicanthal fold resembles the shape of the tail of a fish , so we named this resection the fish - tail resection .
between january 2010 and august 2011 , one surgeon performed congenital entropion surgery on 28 cases in the ophthalmology department of the hospital of hyogo college of medicine , hyogo , japan .
the indication for surgery was the presence of marked superficial punctate keratitis that had been determined by fluorescein staining .
we analyzed this series of 28 cases retrospectively . in total , 17 of the patients were females , and eleven were males .
ten patients with a thick epicanthal fold required epicanthoplasties that were accompanied by hotz procedures , and 18 patients with a thin epicanthal fold required only hotz procedures .
the faces of the patients were photographed at consultations before and after surgery . the degree to which an epicanthoplasty was necessary
was determined on the basis of whether a patient developed an epicanthal fold , and the effectiveness of each surgery was evaluated after the operation had been performed .
patients who were under the age of 15 years underwent surgeries that were performed under general anesthesia .
designing is the most important part of this surgery , and the surgical procedure is described in the following paragraphs .
an initial marking for a modified hotz procedure was drawn on the summit of the lower eyelid .
marks were made approximately 2 mm below the cilia where the transverse fiber of the orbicularis is prominent under the skin .
about an 18 mm - long sharp spindle - shaped marking was made that began at the inner corner of the lower eyelid and extended to the middle part of the eyelid .
second , a 2 mm - wide triangle that was adjacent to the spindle body was marked on the epicanthus .
one side of the triangle was aligned along the curvature of the epicanthus ( figure 1 ) .
the shape of the complete marking resembled the body ( spindle ) and tail ( triangle ) of a fish . after designing ,
anesthesia was administered using 1% xylocaine with 0.001% epinephrine with the aim of avoiding bleeding .
five minutes after applying the anesthetic , an eyelid pincher was used , and an initial incision was made .
the resection of the fish body was simple , but the resection of the fish tail required rather precise cutting skills using a sharp knife or blade ( eg , a no 11 blade ) .
surgeons must take care to cut through all of the layers of the dermis ( figure 2 ) .
pretarsal portions of the transverse orbicularis were observed directly above the tarsus , and approximately two - thirds of these were excised .
once the tarsus had been exposed , mattress sutures that connected the tarsus to the dermis were made using 7 - 0 vicryl sutures . in most cases ,
four or five stitches were required to convert the inverted cilia to a correct position . after the mattress sutures and reconfirmation of hemostasis had been completed , the eyelid pinch was removed .
first , we sutured the residual edge that was nearest the cilia to the corner of the epicanthus to inlay the skin precisely .
we then closed the skin edge end to end along the fish - body incision using 7 - 0 vicryl sutures .
if the patient is old enough to endure the subsequent removal of stitches , 7 - 0 nylon sutures can be used instead . at the conclusion of the surgery ,
the average age of the 28 patients was 7.6 years , and the sample population included eleven boys and 17 girls .
all 18 patients ( average age 8.3 years ) who underwent the hotz procedures alone had satisfactory results in terms of lower lid ciliary direction . however , one patient ( figure 3 ) had a recurrence 9 months after surgery .
the ten patients ( average age 6.4 years ) who underwent fish - tail resections in conjunction with hotz procedures had more successful results .
their medial canthus angles were wider than they had been prior to surgery , and the angles retained their postsurgical forms for a minimum of 6 months after surgery .
we first recognized the term congenital entropion as referring to a condition in which there is an epicanthal fold with inverted cilia ( epiblepharon ) or a congenital lower eyelid deformity with trichiasis ( true congenital entropion ) . from a public health standpoint , over 20% of 1-year - old infants in japan
have congenital entropion , but the prevalence of this condition is only 2% in junior high school students.1 the prevalence of epiblepharon decreases because of growth - induced mid - face alterations.2,9 although congenital entropion is a rare condition in western people,10,11 the 2% prevalence of it among junior high school - aged children in japan may represent the rate of true congenital entropion . during our review of a series of 28 cases ,
only two patients showed prominent lacrimal caruncles , and these two patients might have true congenital entropion .
epicanthal folds usually occur in both eyelids , and the skin around each fold covers the medial canthal area in a crescent formation , but true congenital entropion sometimes occurs unilaterally.2,10 epicanthoplasty that is performed in conjunction with a lower lid entropion procedure has been an innovative solution for the treatment of congenital entropion in asians.2,3 in 1841 , von ammon first developed surgical procedures for the correction of epicanthal folds , followed by the introduction of mustarde s flap.12 subsequently , yoon13 developed a modification of that technique that was specific to the needs of asian patients .
other methods , such as uchida s w plasty,14 the modified y - v advanced flap procedure,15 the z - plasty,5 and the modified z - plasty method,68 have been used in asian countries , but these surgical techniques are not popular among ophthalmologists .
one problem in the surgical correction of entropion is the complexity of designing the incision line for epicanthoplasty .
plastic surgeons sometimes recommend using root z - plasty3,6 instead , but that technique requires relatively strong skills in both imaging and marking .
the use of a bigger flap resulted in prominent scarring on the medial canthus because of excessive tension .
thus , the balance between the effectiveness of a flap and the size of it is important when designing the flap . in the present study
in accordance with uchida s procedure,14 a w - shaped flap is imaged on the epiblepharon . to minimize scarring
, we used only the lower triangle of this w as a flap ; the shape of this lower triangle mimics the shape of a fish tail , and it is continuous with a fish - body resection . using this method , it is easier to determine both the design and the placement of the flap in patients with epiblepharon . another common problem with epicanthoplasty
is that it changes the appearance of the eyes of the children who undergo this procedure .
some parents complain about this change in appearance , so it is important to obtain informed consent prior to surgery .
however , because of the small flap that was used in the procedure in this study , the appearance changes after the operation were not significant . the scarring was also kept to minimum . in a series of 28 patients , none of the parents had complaints about appearance changes in their children , but the patients often looked 23 years older after the surgery .
we experienced one case in which entropion recurred ( figure 3 ) ; a 13-year - old girl had a beautiful epicanthus curve , so we could not touch her epicanthal fold .
however , she had a rather thick fold ( ie , a broad development of orbicularis ) and , thus , medial ciliary entropion recurred after 9 months , and ciliary electrolysis was needed to treat trichiasis in this patient .
if we fulfilled fish - tail resection on her epicanthus , her cilia could be more everted .
our congenital entropion cases were divided into two groups on the basis of the development of epiblepharon ( severe or mild ) .
one difference between these two groups was in average age ( 6.4 years vs 8.3 years ) , which suggests that patients with severe entropion cases often need earlier surgery .
in addition , the epicanthal fold is generally thicker at earlier ages . in the series of cases that is discussed in this article , recurrence of ciliary inversion
previous reports show a recurrence rate of approximately 10% when patients are treated with bracing sutures,2,16 and about 9% of patients are undercorrected with a modified hotz procedure .
2 the hotz procedure s weak point is that it could not correct the medial part of cilia because of the tarsus location . in the present study , however , all of the patients who underwent a modified hotz procedure that either was or was not accompanied by a fish - tail resection had a lower recurrence rate .
this result is relevant to the accuracy of the surgeon s technique and the selection of the proper procedure .
because there is no existence of tarsus in the medial eyelid , we selected hotz plus fish - tail surgery for severe epiblepharon cases . during surgery , it was observed that the epicanthal fold is composed of redundant skin and is directly beneath a developed orbicularis band . at the moment that the triangular fish - tail flap was cut ,
moreover , the inlay of the medial edge increased the efficacy of widening the medial angle and correction of the medial part of the cilia .
this result demonstrates that orbicularis tension that is related to an epiblepharon is one of the causes of congenital entropion . in infant cases ,
the 7 - 0 vicryl sutures were very useful ; this type of suture is composed of an absorbable material with a tensile strength that was maintained for 6 weeks , and it can be used for both internal and skin sutures . however , it has the disadvantage of causing skin redness that can continue for between 2 months and 6 months .
therefore , in cases in which the child can endure the removal of stitches , 7 - 0 nylon sutures are a more suitable alternative and contribute to minimizing scarring .
this blepharoplasty approach is easy to design , and it facilitates the performance of the hotz procedure by removing the main cause of congenital entropion and allowing for effective correction .
it is important to determine whether there has been a development of epiblepharon in each case and to select the appropriate procedure . | prefacethe asian race has a high prevalence of congenital entropion .
it was reported that over 20% of japanese children have congenital entropion at the age of 1 year .
one of the structural causes of this condition is the development of epiblepharon , which attaches the lower eyelid to the upper eyelid , and is also common among asians .
however , designing a procedure for modifying an epicanthus flap is relatively difficult , and epicanthoplasty is not a popular procedure in japan . in the present study
, we developed an easy method of designing the surgery , and we describe both the surgical procedure and the outcome.casesbetween january 2010 and august 2011 , one surgeon performed surgery to correct congenital entropion in 28 patients .
we analyzed this series of 28 cases retrospectively .
the patients consisted of 17 females and eleven males with an average age of 7.6 years .
ten patients with a thick epicanthal fold required epicanthoplasties in addition to lower lid procedures , and 18 patients with a thin epicanthal fold required only lower lid procedures.surgical methodon the epicanthus , a small , triangular fish - tail flap that was 2 mm wide was designed and was located adjacent to a fish - body marking on the subciliary lower eyelid . after fish - tail resection ,
the residual medial edge was sutured to the corner of the epicanthus .
a c - shaped epicanthus was changed into an l - shape by means of this procedure.resultthe fish - tail resection diminished the tension of the orbicularis in the superior direction .
after a minimum of 6 months , the shape of the medial canthus remained l - shaped , and the cilia had stable orientations.conclusionthis plasty is easy to design in conjunction with a hotz procedure , and it is an effective means of correcting asian congenital entropion . recognizing the shape of a congenital entropion that is accompanied by epiblepharon is important for its radical treatment . |
we thank a. ashtekar for making us aware of ref . @xcite .
we acknowledge the compagnia di san paolo for partial support.e.v.moreva acknowledges the support from the dynasty foundation and russian foundation for basic research ( project 13 - 02 - 01170-d ) a. augustinus hipponensis , _ confessiones _ , xi , 14 ( 400 ) .
kuchar , in `` proceedings of the 4th canadian conference on general relativity and relativistic astrophysics '' ed .
g. kunstatter , d. vincent and j. williams ( world scientific , singapore 1992 ) . c.j .
isham , in `` integrable systems , quantum groups and quantum field theories '' ed .
ibort and m.a .
rodrguez ( kluwer , dordrecht 1993 ) , gr - qc/9210011 .
a. ashtekar , new j. phys .
* 7 * , 198 ( 2005 ) .
e. anderson , `` the problem of time in quantum gravity '' , in `` classical and quantum gravity : theory , analysis and applications '' , ed .
frignanni ( nova , new york 2012 ) , arxiv:1009.2157v3 .
z. merali , nature * 500 * , 516 - 519 ( 2013 ) .
dewitt , phys .
160 * , 1113 - 1148 ( 1967 ) .
j. b. hartle , s. w. hawking , phys .
d * 28 * , 2960 - 2975 ( 1983 ) .
d.n . page and w.k .
wootters , phys .
d , 27 , 2885 ( 1983 ) .
wootters , int .
23 , 701 ( 1984 ) .
page , `` clock time and entropy '' , in _ physical origins of time asymmetry _ , eds . j.j .
halliwell , et al .
, ( cambridge univ . press , 1993 ) , arxiv : gr - qc/9303020 .
r. gambini , r.a .
porto , j. pullin , and s. torterolo , phys .
d * 79 * , 041501(r ) ( 2009 ) .
a. peres , am . j. phys .
* 48 * , 552 ( 1980 ) . c. rovelli , int .
j. of theor .
phys . * 35 * , 1637 ( 1996 ) , arxiv : quant - ph/9609002v2 .
unruh , r.m .
wald , phys .
d * 40 * , 2598 ( 1989 ) .
r.gambini , l.p.g .
pintos , j. pullin , studies his .
phys . * 42 * , 256 - 263 ( 2011 ) . c. rovelli , phys .
d * 43 * , 442 ( 1991 ) .
a. einstein , ann .
* 17 * , 891 , ( 1905 ) , translated in _ the principle of relativity _
( methuen & co. , london , 1923 ) . m. o. scully , b .-
englert , h. , walther , nature * 351 * , 111 ( 1991 ) .
drr s. , nonn t. , rempe g. , nature * 395 * , 33 ( 1998 ) .
j. preskill , lecture notes at http://www.theory.caltech.edu/people/preskill/ph229 , pg .
r. gambini , l.p.g .
pintos , j. pullin , found .
phys . * 40 * , 93 - 115 ( 2010 ) .
egusquiza , l.j .
garay , j.m .
raya , phys .
rev . a * 59 * , 3236 ( 1999 ) .
bartlett , t. rudolph , w. spekkens , rev .
mod . phys . * 79 * , 555 ( 2007 ) .
wiseman , j. opt .
b : quantum semiclass . opt .
* 6 , * s849 ( 2004 ) .
m.genovese , phys .
rep . * 413 * , 319 ( 2005 ) .
d. f. v. james , p. g. kwiat , w. j. munro , and a. g. white , phys .
a , 64 , 052312 ( 2001 ) .
yu.i.bogdanov , g.brida , m. genovese , a.p .
shurupov , e.v .
moreva , s.p .
kulik , phys .
* 105 * , 010404 ( 2010 ) .
i. bogdanov , e. v. moreva , g. a. maslennikov , r. f. galeev , s. s. straupe and s. p. kulik , phys .
rev . a 73 , 063810 ( 2006 ) . | in the last years several theoretical papers discussed if time can be an emergent propertiy deriving from quantum correlations . here , to provide an insight into how this phenomenon can occur , we present an experiment that illustrates page and wootters mechanism of `` static '' time , and gambini et al .
subsequent refinements . a static , entangled state between a clock system and the rest of the universe is perceived as evolving by internal observers that test the correlations between the two subsystems .
we implement this mechanism using an entangled state of the polarization of two photons , one of which is used as a clock to gauge the evolution of the second : an `` internal '' observer that becomes correlated with the clock photon sees the other system evolve , while an `` external '' observer that only observes global properties of the two photons can prove it is static .
.45 the `` problem of time '' @xcite in essence stems from the fact that a canonical quantization of general relativity yields the wheeler - de witt equation @xcite predicting a static state of the universe , contrary to obvious everyday evidence .
a solution was proposed by page and wootters @xcite : thanks to quantum entanglement , a static system may describe an evolving `` universe '' from the point of view of the internal observers .
energy - entanglement between a `` clock '' system and the rest of the universe can yield a stationary state for an ( hypothetical ) external observer that is able to test the entanglement vs. abstract coordinate time .
the same state will be , instead , evolving for internal observers that test the correlations between the clock and the rest @xcite .
thus , time would be an emergent property of subsystems of the universe deriving from their entangled nature : an extremely elegant but controversial idea @xcite .
here we want to demystify it by showing experimentally that it can be naturally embedded into ( small ) subsystems of the universe , where page and wootters mechanism ( and gambini et al .
subsequent refinements @xcite ) can be easily studied .
we show how a static , entangled state of two photons can be seen as evolving by an observer that uses one of the two photons as a clock to gauge the time - evolution of the other photon .
however , an external observer can show that the global entangled state does not evolve .
even though it revolutionizes our ideas on time , page and wootters ( paw ) mechanism is quite simple @xcite : they provide a static entangled state @xmath0 whose subsystems evolve according to the schrdinger equation for an observer that uses one of the subsystems as a clock system @xmath1 to gauge the time evolution of the rest @xmath2 . while the division into subsystems is largely arbitrary , the paw model assumes the possibility of neglecting interaction among them writing the hamiltonian of the global system as @xmath3 , where @xmath4 are the local terms associated with @xmath1 and @xmath2 , respectively @xcite . in this framework
the state of the `` universe '' @xmath0 is then identified by enforcing the wheeler - de witt equation @xmath5 , i.e. by requiring @xmath0 to be an eigenstate of @xmath6 for the zero eigenvalue .
the rational of this choice follows from the observation that by projecting @xmath0 on the states @xmath7 of the clock , one gets the vectors and @xmath8 are the unitary time evolution operators of the clock @xmath1 and of the rest of universe @xmath2 respectively .
@xmath0 is the global state of the system which is assumed to be eigenstate with null eigenvalue of the global hamiltonian @xmath9 ( see text).,scaledwidth=50.0% ] @xmath10 that describe a proper evolution of the subsystem @xmath2 under the action of its local hamiltonian @xmath11 , the initial state being @xmath12 ( see fig . [
f : figu0 ] ) . therefore , despite the fact that globally the system appears to be static , its components exhibits correlations that mimics the presence of a dynamical evolution @xcite . two main flaws of the paw mechanisms have been pointed out @xcite .
the first is based on the ( reasonable ) skepticism to accept that quantum mechanics may describe a system as large as the universe , together with its internal observers @xcite .
the second has a more practical character and is based on the observation that in the paw model the calculations of transition probabilities and of propagators appears to be problematic @xcite .
an attempt to fix the latter issue has been discussed by gambini et al .
( gppt ) @xcite by extending a proposal by page @xcite and invoking the notion of ` evolving constants ' of rovelli @xcite ( a brief overview of this approach is given in the appendix ) . in this work we present an experiment which allows reproducing the basic features of the paw and gppt models .
in particular the paw model is realized by identifying @xmath13 with an entangled state of the vertical @xmath14 and horizontal @xmath15 polarization degree of freedom of two photons in two spatial modes @xmath16 , i.e. ( see following section ) @xmath17 and enforcing the wheeler - de witt equation by taking @xmath18 as local hamiltonians of the system ( @xmath19 being a parameter which defines the time scale of the model ) . for this
purpose rotations of the polarization of the two photons are induced by forcing them to travel through identical birefringent plates as shown in fig . [
f : schema ] .
this allows us to consider a setting where everything can be decoupled from the `` flow of time '' , i.e. when the photons are traveling outside the plates .
nonetheless , the clock photon is a true ( albeit extremely simple ) clock : its polarization rotation is proportional to the time it spends crossing the plates .
although extremely simple , our model captures the two , seemingly contradictory , properties of the paw mechanism : the evolution of the subsystems relative to each other , and the staticity of the global system .
this is achieved by running the experiment in two different modes ( see fig . [
f : schema]a ) : ( 1 ) an `` observer '' mode , where the experimenter uses the readings of the clock photon to gauge the evolution of the other : by measuring the clock photon polarization he becomes correlated with the subsystems and can determine their evolution .
this mode describes the conventional observers in the paw mechanism : they are , themselves , subsystems of the universe and become entangled with the clock systems so that they see an evolving universe ; ( 2 ) a `` super - observer '' mode , where he carefully avoids measuring the properties of the subsystems of the entangled state , but only global properties : he can then determine that the global system is static .
this mode describes what an ( hypothetical ) observer external to the universe would see by measuring global properties of the state @xmath13 : such an observer has access to abstract coordinate time ( namely , in our experimental implementation he can measure the thickness of the plates ) and he can prove that the global state is static , as it will not evolve even when the thickness of the plates is varied . and pbs@xmath20 respectively .
the blue boxes ( a ) represent different thicknesses of birefringent plates which evolve the photons by rotating their polarization : different thicknesses represent different time evolutions .
the paw mechanism ( a ) is completely independent of the thickness , whereas the gppt mechanism ( b ) allows it to be measured by the experimenter only through the clock photon ( the abstract coordinate time is unaccessible and averaged away ) ; the dashed box ( b ) represents a ( known ) phase delay of the clock photon only ; pbs stands for polarizing beam splitter in the @xmath21 basis ; bs for beam splitter.,scaledwidth=50.0% ] in observer mode ( fig .
[ f : schema]a , pink box ) the clock is the polarization of a photon .
it is an extremely simple clock : it has a dial with only two values , either @xmath22 ( detector 1 clicked ) corresponding to time @xmath23 , or @xmath24 ( detector 2 clicked ) corresponding to time @xmath25 .
[ here @xmath26 , where @xmath19 is the polarization rotation rate of the quartz plate , since the polarization is flipped in this time interval . ]
the experimenter also measures the polarization of the first photon with detectors 3 and 4 .
this last measurement can be expressed as a function of time ( he has access to time only through the clock photon ) by considering the correlations between the results from the two photons : the time - dependent probability that the first photon is vertically polarized ( i.e. that detector 3 fires ) is @xmath27 and @xmath28 , where @xmath29 is the conditional probability that detector 3 fired , conditioned on detector @xmath30 firing ( experimental results are presented in fig .
[ f : results]a ) .
this type of conditioning is typical of every time - dependent measurement : experimenters always condition their results on the value they read on the lab s clock ( the second photon in this case ) .
the experimenter has access only to physical clocks , not to abstract coordinate time @xcite . in our experiment
this restriction is implemented by employing a different phase plate a ( of random thickness unknown to the experimenter ) in every experimental run . in super - observer mode
( fig .
[ f : schema]a , yellow box ) the experimenter takes the place of a hypothetical observer external to the universe that has access to the abstract coordinate time and tests whether the global state of the universe has any dependence on it .
hence , he must perform a quantum interference experiment that tests the coherence between the different histories ( wavefunction branches ) corresponding to the different measurement outcomes of the internal observers , represented by the which - way information after the polarizing beam splitter pbs@xmath31 . in our setup , this interference is implemented by the beam splitter bs of fig .
[ f : schema]b .
it is basically a quantum erasure experiment @xcite that coherently `` erases '' the results of the time measurements of the internal observer : conditioned on the photon exiting from the right port of the beam splitter , the information on its input port ( i.e. the outcome of the time measurement ) is coherently erased @xcite .
the erasure of the time measurement by the internal observers is necessary to avoid that the external observer ( super - observer ) himself becomes correlated with the clock .
however , the super - observer has access to abstract coordinate time : he knows the thickness of the blue plates , which is precluded to the internal observers , and he can test whether the global state evolves ( experimental results are presented in fig .
[ f : results]b ) . in addition
, we also test the gppt mechanism showing that our experiment can also account for two - time measurements ( see fig .
[ f : schema]b ) .
these are implemented by the two polarizing beam splitter pbs@xmath31 and pbs@xmath20 .
pbs@xmath31 represents the initial time measurement that determines when the experiment starts : it is a non - demolition measurement obtained by coupling the photon polarization to its propagation direction , while the initialization of the system state is here implemented through the entanglement . pbs@xmath20 together with detectors 1 and 2 represents the final time measurement by determining the final polarization of the photon . between these two time measurements both the system and the clock
evolve freely ( the evolution is implemented by the birefringent plates a ) . in the gppt mechanism , the abstract coordinate time ( the thickness of the quartz plates a ) is unaccessible and must be averaged over @xcite .
this restriction is implemented in the experiment by avoiding to take into account the thickness of the blue quartz plates a when extracting the conditional probabilities from the coincidence rates : the rates obtained with different plate thickness are all averaged together .
the formal mapping of the gppt mechanism to our experiment is detailed in the appendix . as before ,
the time dependent probability of finding the system photon vertically polarized is @xmath27 and @xmath28 .
however , a clock that returns only two possible values ( @xmath32 and @xmath33 ) is not very useful . to obtain a more interesting clock , the experimenter performs the same conditional probability measurement introducing varying time delays to the clock photon , implemented through quartz plates of variable thickness ( dashed box b in fig .
[ f : schema]b ) .
[ even though he has no access to abstract coordinate time , he can have access to systems that implement known time delays , that he can calibrate separately .
] now , he obtains a sequence of time - dependent values for the conditional probability : @xmath34 and @xmath35 , where @xmath36 is the time delay of the clock photon obtained by inserting the quartz plate b with thickness @xmath37 in the clock photon path .
the experimental results are presented in fig .
[ f : resultsgp ] , where each colour represents a different delay : the yellow points refer to @xmath38 ; the red points to @xmath39 , etc .
they are in good agreement with the theory ( dashed line ) derived in the appendix .
the reduction in visibility of the sinusoidal time dependence of the probability is caused by the decoherence effect due to the use of a low - resolution clock ( our clock outputs only two possible values ) , a well known effect @xcite .
): circles and squares represent @xmath27 and @xmath28 respectively , namely the probabilities of measuring @xmath14 on the subsystem 1 as a function of the clock time @xmath32 , @xmath33 ; circles and triangles represent @xmath40 and @xmath41 , the probabilities of measuring @xmath15 on the subsystem 1 as a function of the clock time . as expected from the paw mechanism , these probabilities are independent of the abstract coordinate time @xmath42 , represented by different phase plate a thicknesses ( here we used a 957@xmath43 m thick quartz plate rotated by 15 different equiseparated angles ) .
the inset shows the graph that the observer himself would plot as a function of clock - time : circles representing the probabilities of finding the system photon @xmath14 at the two times @xmath32 , @xmath33 , the triangles of finding it @xmath15 .
( b ) super - observer mode : plot of the conditional fidelity between the tomographic reconstructed state and the theoretical initial state @xmath13 of eq . as a function of the abstract coordinate time @xmath42 .
the fidelity @xmath44 ( which measures the overlap between the theoretical initial state @xmath13 and the final state @xmath45 after its evolution through the plates ) is conditioned on the clock photon exiting the right port of the beam splitter bs .
the fact that the fidelity is constant and close to one ( up to experimental imperfections ) proves that the global entangled state is static .
, scaledwidth=50.0% ] that the upper photon is @xmath14 ( namely that detector 3 clicked ) as a function of the time @xmath46 recovered from the lower photon .
the points with matching colors represent @xmath47 and @xmath48 : yellow , red , blue , etc .
, for @xmath49 , respectively . here nine different values of @xmath50 are obtained from a 1752@xmath43 m thick quartz plate rotated by nine different angles from the vertical ( 14,16,18,20,21.5,23,25,27,29 degrees ) .
the dashed line is the theoretical value .
its reduced visibility is an expected effect of the use of imperfect clocks @xcite.,scaledwidth=40.0% ] in summary , by running our experiment in two different modes ( `` observer '' and `` super - observer '' mode ) we have experimentally shown how the same energy - entangled hamiltonian eigenstate can be perceived as evolving by the internal observers that test the correlations between a clock subsystem and the rest ( also when considering two - time measurements ) , whereas it is static for the super - observer that tests its global properties .
our experiment is a practical implementation of the paw and gppt mechanisms but , obviously , it can not discriminate between these and other proposed solutions for the problem of time @xcite . in closing
, we note that the time - dependent graphs of fig .
[ f : resultsgp ] have been obtained without any reference to an external time ( or phase ) reference , but only from measurements of correlations between the clock photon and the rest : they are an implementation of a ` relational ' measurement of a physical quantity ( time ) relative to an internal quantum reference frame @xcite . the experimental setup ( fig .
[ f : exp ] ) consists of two blocks : `` preparation '' and `` measurement '' .
the preparation block produces a family of biphoton polarization entangled states of the form : @xmath51 by exploiting the standard method of coherently superimposing the emission of two type i crystals whose optical axes are rotated of 90@xmath52 @xcite .
the measurement block can be mounted in different configurations corresponding to `` observer '' and `` super - observer '' ones of paw and gppt scheme ( fig.1 ) . in general ,
each arm of the measurement block contains interference filters ( if ) with central wavelength @xmath53 nm ( fwhm @xmath54 nm ) and a polarizing beam splitter ( pbs ) . before the pbs the polarization of both photons evolves in the birefringent quartz plates a ( blue boxes in fig .
[ f : schema ] ) as @xmath55 , where @xmath56 is the material s optical thickness .
* `` observer '' mode in paw scheme * ( fig .
[ f : schema ] , block a ) : in this mode , the polarization of the photon in the lower arm is used as a clock : the first polarizing beam splitter pbs@xmath31 acts as a non - demolition measurement in the @xmath21 basis of the polarization of the second photon , finally detected by single - photon avalanche diodes ( spad ) 1 , 2 . in this mode , the experimenter has no access to an external clock , he can only use the correlations ( coincidences ) between detectors : the time - dependent probability of finding the first photon in @xmath57 is obtained from the coincidence rate between detectors 1 - 3 ( corresponding to a measurement at time @xmath32 ) , or 2 - 3 ( corresponding to a measurement at time @xmath33 ) : appropriately normalized , these coincidence rates yield the conditional probabilities @xmath29 .
the impossibility to directly access abstract coordinate time ( the thickness of the plates ) is implemented by averaging the coincidence rates obtained for all possible thicknesses of the birefringent plates a : the plate thickness does not enter into the data processing in any way . + * `` super - observer '' mode in paw scheme * ( fig.1b ) : this mode is employed to prove that the global state is static with respect to abstract coordinate time , represented by the thickness of the quartz plates a. the @xmath58 beam splitter ( bs ) in block b performs a quantum erasure of the polarization measurement ( performed by the polarizing beam splitter pbs@xmath31 ) conditioned on the photon exiting its right port . for temporal stability , the interferometer is placed into a closed box .
the output state is reconstructed using ququart state tomography @xcite ( the two - photon polarization state lives in a four - dimensional hilbert space ) , where the projective measurements are realized with polarization filters consisting of a sequence of quarter- and half - wave plates and a polarization prism which transmits vertical polarization ( fig.4 ) .
the fidelity between the tomographically reconstructed state and the theoretical state @xmath13 is reported in fig .
[ f : results]b .
* gppt two - time scheme * here a second pbs preceding detectors allows a two - time measurement . to obtain a more interesting time dependence than the probability at only two times ,
we delay the clock photon with an additional birefringent plate b ( dashed box in fig .
[ f : schema ] ) , a 1752@xmath43m - thick quartz plate rotated at nine different angles , placed in the lower arm , and we repeat the same procedure described above for different thicknesses of the plate b. this represents an internal observer that introduces a ( known ) time delay to his clock measurements .
the results are shown in fig .
[ f : results ] . )
crystals ( placed into a temperature - stabilized closed box t ) pumped by a 700 mw ar laser , later eliminated by a filter ( uwf ) .
the basic state amplitudes are controlled by a thompson prism ( v ) , oriented vertically , and a half - wave plate @xmath59/2 at angle @xmath60 .
two 1 mm quartz plates , that can be rotated along the optical axis , introduce a phase shift between horizontally and vertically polarized photons .
the beam splitter ( bs ) is used to split the initial ( collinear ) biphoton field into distinct spatial modes .
it prepares the singlet bell state @xmath61 of eq .
( 1 ) ( using @xmath62 ; @xmath63 , and an additional half - wave plate @xmath59/2 at @xmath64 in the transmitted arm ) .
* measurement block * : we implement paw or gppt as in fig.1 . in paw superobserver mode
the final state is checked by quantum state tomography @xcite , realised by registering the coincidence rate for 16 different projections achieved through half and quarter wave plates and a fixed analyzer ( v ) .
, scaledwidth=40.0% ] in this appendix we detail how our experiment implements the gambini et al .
( gppt ) proposal @xcite for extending the paw mechanism @xcite to describe multiple time measurements .
we also derive the theoretical curve of fig .
[ f : resultsgp ] .
time - dependent measurements performed in the lab typically require two time measurements : they establish the times at which the experiment starts and ends , respectively .
the paw mechanism can accommodate the description of these situations by supposing that the state of the universe will contain records of the previous time measurements @xcite .
however , this observation in itself seems insufficient to derive the two - time correlation functions ( transition probabilities and time propagators ) with their required properties , a strong criticism directed to the paw mechanism @xcite .
the gppt proposal manages to overcome this criticism .
it is composed of two main ingredients : the recourse to rovelli s ` evolving constants ' to describe observables that commute with global constraints , and the averaging over the abstract coordinate time to eliminate any dependence on it in the observables .
our experiment tests the latter aspect of the gppt theory
. measurements of a physical quantity at a given clock time , say @xmath46 , are described by the conditional probability of obtaining an outcome on the system , say @xmath65 , given that clock time - measurement produces the outcome @xmath46 .
this conditional probability is given by @xcite @xmath66}{\int dt\;{\mbox{tr}[p_{t}(t)\rho ] } } \labell{con}\;,\end{aligned}\ ] ] where @xmath67 is the global state , @xmath68 is the projector relative to a result @xmath46 for a clock measurement at coordinate time @xmath42 and @xmath69 is the projector relative to a result @xmath65 for a system measurement and @xmath46 for a clock measurement at coordinate time @xmath42 ( working in the heisenberg picture with respect to coordinate time @xmath42 ) . clearly , such expression can be readily generalized to arbitrary povm measurements .
( a similar expression , but in the schrdinger picture , already appears in @xcite . ) the integral that averages over the abstract coordinate time @xmath42 in embodies the inaccessibility of the time @xmath42 by the experimenter : he can access only the clock time @xmath46 , an outcome of measurements on the clock system . a generalization of this expression to multiple time measurements
is expressed by @xcite @xmath70}{\int dt\;\int dt'\;{\mbox{tr}[p_{t_f}(t)p_{d_i , t_i}(t')\;\rho\ ; p_{d_i , t_i}(t ' ) ] } } \nonumber\;,\end{aligned}\ ] ] which gives the conditional probability of obtaining @xmath71 on the system given that the final clock measurement returns @xmath72 and given that a `` previous '' joint measurement of the system and clock returns @xmath73 , @xmath74 .
( this expression can also be formulated as a conventional state reduction driven by the first measurement @xcite . ) in our experiment to implement the gppt mechanism ( fig .
[ f : schema]b ) we must calculate the conditional probability that the system photon is @xmath14 ( namely detector 3 clicks ) given that the clock photon is @xmath15 after the first polarizing beam splitter pbs@xmath31 ( initial time measurement ) and is @xmath15 or @xmath14 after the second polarizing beam splitter ( final time measurement ) .
the initial time measurement succeeds whenever one of photodetectors 1 or 2 click : this means that the clock photon chose the @xmath15 path at pbs@xmath31 .
( our experiment discards the events where the first time measurement at pbs@xmath31 finds @xmath14 , although in principle one could easily take into account these cases by adding a polarizing beam splitter and two photodetectors also in the @xmath14 output mode of pbs@xmath31 . )
the final time measurement is given by the click either at photodetector 1 or 2 : the clock dial shows @xmath75 and @xmath76 , respectively . using the gppt mechanism of eq .
, this means that the time dependent probability that the system photon is vertical ( detector 3 clicks ) is given by @xmath77}{\int dt\;\int dt'\;{\mbox{tr}[p_{t_f = t_k}(t)p_{d_i , t_i}(t')\rho p_{d_i , t_i}(t ' ) ] } } \nonumber\;,\end{aligned}\ ] ] where @xmath78 is the joint projector connected to detector 3 and detector @xmath79 or @xmath80 and @xmath81 is the projector connected to the first time measurement .
the latter projector is implemented in our experiment by considering only those events where either detector 1 or detector 2 clicks , this ensures that the clock photon chose the @xmath15 path at pbs@xmath31 ( namely the initial time is @xmath74 ) and that the system photon was initialized as @xmath24 at time @xmath74 .
( in principle , we could consider also a different initial time @xmath82 by employing also the events where the clock photons choose the path @xmath14 at pbs@xmath31 . ) introducing the unitary abstract - time evolution operators , @xmath83 , the numerator of eq
. becomes @xmath84=\int dt\ ; \mbox{tr}[p_{d=3,t_f = t_k}u_{t } p_{d_i , t_i } \rho p_{d_i , t_i}u^\dag_{t } ] , & & \nonumber\;\end{aligned}\ ] ] where we use the property @xmath85 and we dropped one of the two time integrals by taking advantage of the time invariance of the global state @xmath67 ( which has been also tested experimentally in the super - observer mode ) .
gambini et al .
typically suppose that the clock and the rest are in a factorized state @xcite , but this hypothesis is not strictly necessary for their theory @xcite : we drop it so that we can use the same initial global state that we used for testing the paw mechanism .
using the same procedure also to calculate the denominator of eq . , we can rewrite this equation as @xmath86}{\mbox{tr}[p_{t_f = t_k}\bar\rho ] } \;,\end{aligned}\ ] ] where @xmath87 is the time - average of the global state after the first projection , namely @xmath88 where the averaging over the abstract coordinate time @xmath42 is used to remove its dependence from the state . in our experiment
such average is implemented by introducing random values of the phase plates a ( unknown to the experimenter ) in different experimental runs . in our gppt experiment
there are two possible values for the initial projector @xmath81 : either the clock photon is projected on the @xmath15 path after pbs@xmath31 ( corresponding to an initial time @xmath74 ) or it is projected onto the @xmath14 path ( corresponding to an initial time @xmath89 ) .
we will consider only the first case , which corresponds to a click of either detector 1 or 2 : we are post - selecting only on the experiments where the initial time is @xmath74 . in this case
, the global initial state will be @xmath90 which is evolved into the vector @xmath91 [ \cos \omega t|v\>_r+\sin \omega t|h\>_r]$ ] where @xmath92 is the global hamiltonian defined in the main text and @xmath93 is the time delay introduced by the plate b of fig . [
f : schema]b . moreover , the projectors in eq .
are @xmath94 where @xmath95 and @xmath96 .
the projector @xmath78 corresponds to the joint click of detectors @xmath97 and 3 , while @xmath98 corresponds to the click of detector @xmath97 and either one of detectors 3 or 4 . in other words ,
eq . can be written as @xmath99 where @xmath100 is the joint probability of detectors @xmath101 and @xmath97 clicking .
for example , @xmath102 is the joint probability that detector 3 and 2 click , namely that both the clock and the system photon were @xmath14 . considering only the component @xmath103 of the state @xmath104 ,
this is given by @xmath105 where we have calculated the integral over @xmath42 of eq .
using a change of variables @xmath106 . proceeding analogously for all the other joint probabilities , namely replacing the projectors into
, we find the probability for detector 3 clicking ( namely the system photon being @xmath14 ) conditioned on the time @xmath72 read on the clock photon as @xmath107 which is plotted as a function of @xmath93 in fig .
[ f : results]b ( dashed line ) . since @xmath108
, we have plotted the points relative to @xmath109 as displaced by @xmath110 with respect to the points relative to @xmath111 , so that the two curves and are superimposed in fig .
[ f : results ] . |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Clean Cookstoves Support Act of
2012''.
SEC. 2. FINDINGS.
Congress makes the following findings:
(1) Nearly half the world's population cooks their food
over open fires or inefficient, polluting, and unsafe
cookstoves using firewood, dung, or coal. Smoke from the use of
these traditional cookstoves and open fires is associated with
a number of chronic and acute diseases, including respiratory
illnesses such as pneumonia, heart disease, and cancer, with
women and young children affected disproportionately.
(2) It is estimated that smoke from cooking fuels accounts
for nearly 2,000,000 deaths annually in the developing world,
which is more than the deaths from malaria, tuberculosis, or
HIV. Millions more are sickened from the toxic smoke and
thousands suffer burns annually from open fires or unsafe
cookstoves.
(3) The amount of biomass cooking fuel required each year
can reach up to 2 tons per family. Where demand for local
biomass outstrips the natural regrowth of resources, local
environmental problems can result.
(4) Tremendous amounts of time--a burden shouldered
disproportionately by women and children--is spent collecting
and managing biomass cooking fuel resources.
(5) As nearby fuel supplies dwindle, women are forced to go
farther to find fuel to cook their families' meals. In some
regions, women and girls risk rape and other forms of gender-
based violence during the up to 20 hours per week they spend
away from their communities gathering firewood.
(6) Recent studies show that black carbon created from
biomass cookstoves significantly contributes to regional air
pollution and climate change. Black carbon emissions from
residential cookstoves in developing countries account for an
estimated 21 percent of total global inventory, and mitigation
in this sector represents a large potential public health
benefit.
(7) The Global Alliance for Clean Cookstoves is an
innovative public-private partnership led by the United Nations
Foundation that was created to enable the adoption of clean and
efficient stoves in 100,000,000 homes by 2020. The Alliance
intends to work with public, private, and non-profit partners
to raise $250,000,000 towards overcoming market barriers that
currently impede the production, deployment, and use of clean
cookstoves in the developing world.
(8) The United States Government has committed a total of
up to $105,000,000 over the first five years of the Alliance to
help it achieve its goal of spurring the adoption of clean
cookstoves in 100,000,000 households by 2020, as follows:
(A) The Department of State and the United States
Agency for International Development will commit
$11,570,000 to promote the adoption of clean
cookstoves, encourage foreign government support, and
further economic opportunities for women.
(B) The Department of Energy will commit
$12,500,000 for applied research to advance clean
cookstove technologies and designs.
(C) The Department of Health and Human Services
will commit $24,700,000 through the National Institutes
of Health and $2,180,000 through the Centers for
Disease Control and Prevention for health research and
implementation evaluation.
(D) The Environmental Protection Agency will commit
$6,000,000 to enhance stove testing and evaluation,
cookstove design innovation, and the assessment of
health benefits.
(E) The Overseas Private Investment Corporation
will commit up to $50,000,000 for debt financing or
insurance for projects that provide access to clean,
consistent, and affordable energy through the promotion
of clean cookstoves.
SEC. 3. ADVANCEMENT OF GLOBAL ALLIANCE FOR CLEAN COOKSTOVES GOALS.
The Secretary of State, in consultation with the Administrator of
the Environmental Protection Agency, the Secretary of Energy, the
Secretary of Health and Human Services, the Administrator of the United
States Agency for International Development, and the heads of other
relevant Federal agencies, and in coordination with relevant
international nongovernmental organizations and private and
governmental entities, shall work to advance the goals and work of the
Global Alliance for Clean Cookstoves, including through--
(1) applied research and development to improve design,
lower costs, promote technology adoption, conduct health
research and evaluation, and develop global industry standards
and testing protocols for cookstoves;
(2) diplomatic engagement to encourage a commercial market
for clean stoves and fuels, reduce trade barriers, promote
consumer awareness, improve access to large-scale carbon
financing, and foster women-owned businesses along the entire
business chain;
(3) international development projects to help build
commercial businesses to manufacture, market, distribute, sell,
and service clean stoves and fuels;
(4) development efforts related to refugee camps, disaster
relief, and long-term programs aimed at assisting women and
girls; and
(5) financing or insurance to support projects that provide
access to clean, affordable energy and energy savings through
the manufacture, sale, and purchase of cookstoves.
SEC. 4. AUTHORIZATIONS OF APPROPRIATIONS.
(a) Department of State and United States Agency for International
Development.--There is authorized to be appropriated out of funds
available to the Department of State and the United States Agency for
International Development not less than $11,570,000 for fiscal years
2013 through 2017 to work with the Global Alliance for Clean Cookstoves
and foreign governments--
(1) to address the harmful effects of smoke exposure from
traditional cookstoves;
(2) to support applied and operational research into how
people use improved stove technology, and how indoor air
quality and sanitation interventions can improve household
environments and promote economic opportunities for women; and
(3) to carry out other activities under this Act.
(b) Department of Energy.--There is authorized to be appropriated
to the Secretary of Energy out of available funds not less than
$12,500,000 for fiscal years 2013 through 2017 to work with the Global
Alliance for Clean Cookstoves to conduct research aimed at addressing
the technical barriers to the development of low-emission, high-
efficiency cookstoves through activities in areas such as combustion,
heat transfer, and materials development, and to carry out other
activities under this Act.
(c) National Institutes of Health.--There is authorized to be
appropriated to the Secretary of Health and Human Services out of
available funds not less than $24,700,000 for fiscal years 2013 through
2017 for the National Institutes of Health to work with the Global
Alliance for Clean Cookstoves--
(1) to support ongoing research and research training
projects, including--
(A) studies on the cookstove-related effects of
cookstoves smoke on pulmonary, cancer, and cardiac
diseases;
(B) studies on the relationship between indoor air
pollution and low-birth weight; and
(C) studies on the most effective ways to introduce
and educate users on safety and the proper use of
cookstoves;
(2) to support efforts to develop improved measuring
devices, expand epidemiologic studies, and conduct clinical
trials;
(3) to support training programs designed to help prepare
scientists in low- and middle-income countries to engage in
related research and evaluation activities; and
(4) to carry out other activities under this Act.
(d) Centers for Disease Control and Prevention.--There is
authorized to be appropriated to the Secretary of Health and Human
Services out of available funds not less than $2,180,000 for fiscal
years 2013 through 2017 for the Centers for Disease Control and
Prevention to work with the Global Alliance for Clean Cookstoves--
(1) to demonstrate the health benefits of implementing
clean cookstove programs;
(2) to promote a better understanding of the relationship
between human exposures and health outcomes;
(3) to integrate clean cookstoves and fuels implementation
with other public health programs;
(4) to evaluate cookstove program implementation; and
(5) to carry out other activities under this Act.
(e) Environmental Protection Agency.--There is authorized to be
appropriated to the Administrator of the Environmental Protection
Agency out of available funds not less than $6,000,000 for fiscal years
2013 through 2017 to work with the Global Alliance for Clean
Cookstoves--
(1) to conduct stove testing and evaluation in both the lab
and the field;
(2) to promote cookstove design innovations, possibly
including a design competition and prize;
(3) to perform assessments focused on health and exposure
benefits of clean cookstoves and fuels;
(4) to use the expertise, lessons learned, and network
developed in launching and leading the Partnership for Clean
Indoor Air to help the Alliance meet its 2020 goal; and
(5) to carry out other activities under this Act. | Clean Cookstoves Support Act of 2012 - Requires the Secretary of State to work to advance the goals and work of the Global Alliance for Clean Cookstoves, including through: (1) applied research and development to improve design, lower costs, promote technology adoption, conduct health research and evaluation, and develop global industry standards and testing protocols for cookstoves; (2) diplomatic engagement to encourage a commercial market for clean stoves and fuels, reduce trade barriers, promote consumer awareness, improve access to large-scale carbon financing, and foster women-owned businesses; (3) international development projects to help build commercial businesses to manufacture, market, distribute, sell, and service clean stoves and fuels; (4) development efforts related to refugee camps, disaster relief, and long-term programs aimed at assisting women and girls; and (5) financing or insurance to support projects that provide access to clean, affordable energy and energy savings through the manufacture, sale, and purchase of cookstoves.
Authorizes appropriations for FY2013-FY2017 to the Department of State, the United States Agency for International Development (USAID), the Department of Energy (DOE), the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Environmental Protection Agency (EPA) for work with the Global Alliance. |
Published on Aug 1, 2012
Spectacular activism fail in Tucson Arizona. Please do not post any contact info for this d-bag in the comments. I will nuke any phone numbers or email addresses that I see. Otherwise, have fun. Thanks. Also, quit sending me hate mail - I am not even the guy in the video. ||||| A former CFO is now on food stamps after a video he posted on YouTube two and half years ago criticizing Chick-Fil-A went viral and destroyed his career.
Adam Smith, 37, was the CFO of a medical device manufacturer in Arizona, until the summer 2012, when he -- and thousands of other people -- started protesting against Chick-Fil-A for the fast-food chain's anti-gay stance.
One day, Smith decided to go through the drive-thru at his local Chick-Fil-A, where he ordered a free water -- the fast food chain offers customers free water -- and videotaped himself telling the drive-thru attendant how much he despised Chick-Fil-A.
"Chick-Fil-A is a hateful corporation," Smith said, in part, to the drive-thru attendant. "I don't know how you live with yourself and work here. I don't understand it. This is a horrible corporation with horrible values. You deserve better."
Smith then posted the video on his personal YouTube channel, but when he got back to work, he received a major shock.
"I got into work and the receptionist, the first thing, big eyes, 'Adam, what did you do?' ... she said, 'The voicemail is completely full, and it's full of bomb threats,'" Smith said in an exclusive interview with ABC News' "20/20."
Play
Smith was fired that same day. He said at the time he was earning $200,000 annually and had over $1 million in stock options.
"It was taken when I lost my employment," he said.
After losing his job, Smith, his wife Amy and their four children also lost their home. They were forced to sell and give away their possessions and move into an RV. A few months later, Smith found a new CFO job in Portland, Oregon. It was the fresh start he needed.
"I felt like, 'Yeah, I got it. I am back,'" Smith said.
About two weeks later, Smith was fired from that job after his new boss discovered he was the guy from the Chick-Fil-A video. Smith told "20/20" in subsequent job interviews, he was very honest about the video and while prospective employers seemed empathetic and understanding in the end the companies would rescind the offers saying they didn't want the distraction.
Looking back at the video now, Smith said he was emotional.
"I don't regret the stand I took, but I regret… the way I talked to her," he told "20/20."
He even apologized to the drive-thru attendant he was angry with in another video posted to his YouTube channel, which also went viral. She has forgiven him. But Smith says even people who agreed with his pro-gay opinions won't hire him.
"I think people are scared," Smith said. "I think people are scared that it could happen again."
Kevin O'Leary, an entrepreneur and panelist on the hit ABC show "Shark Tank," said he always looks up potentially employees online before hiring them.
"Every time I look at hiring somebody, I go and gather their digital footprint from every source I can get," O'Leary said. "We look at who they are online, and we actually hire them in our minds before we actually ever meet them. And so the interview process is to just prove what we have already assessed online."
O'Leary warns that all the emails, texts, tweets, selfies and status updates we send out into the world can be career threatening.
Smith, with his spotty digital footprint, is still looking for a job nearly three years later, and has turned to meditation. He has also just written a new memoir, "A Million Dollar Cup of Water," detailing how his public shaming led him from riches to rags and the intensive soul search for healing.
Smith said he doesn't know if his viral video will ever go away. "It feels like it just happened," he said.
ABC News' Nick Watt contributed to this report. ||||| I confess, I had never heard of this infamous Chick-Fil-A incident until this came out last year. I was intrigued enough to look up the incident and Adam Smith and eventually got around to reading this book. Thereupon I wasn't sure what to make of it. Is this a memoir? An attempt to give sage advice on life? A personal response to The Incident? (From what I gathered from the forward, that's the best bet). My final opinion is this book's inability to decide what it wants to be makes it rather flawed, hence the three-star rating. I admittedly purchased the book with secret hopes to hate it, and in the end wanted to like it more than I did.
This personal narrative first delves into Adam's childhood, the eldest of eight in a Fundamentalist Christian family suffering from poverty and dysfunction with a father bent on atoning for the life that led to the death of his first-born son. This section is a poignant and fairly interesting account, although made too brief to be a proper memoir. Still, it's a childhood that sets the stage for Adam's adulthood. He is legally signed away from his family in his teens, marries his sweetheart Amy, attends college and becomes fairly obsessed with landing a job that would make him the most money possible--the pursuit of money becoming a strong theme in the work. His personal life continues as he and his wife build a family, wrestle with questions of religion, and get his career really going. Then enters the Chick-Fil-A incident, which I'm sure most readers would be interested in seeing. The rest of the book is the aftermath, being filled with both highs and lows as Adam's family situation is drastically changed and Adam is forced to figure out what to do next, leading to some soul-searching and greater understanding.
Handled better (I thought, more than once, after seeing excerpts of Amy's writings, why isn't she writing this book?) this would have been fine material for a finer result. Source material aside, the presentation of this book just wasn't all that polished, a problem I've seen in other similar memoirs. I finished this book vaguely thinking Adam seemed like a nice guy, but with very little significant understanding of him or his views, despite him talking about them so much. Once again, I wanted to like this book more than I did, but at some point I just wished there was more insight.
I suppose the book can work as a cautionary tale against the dangers of internet chaos and how infinitely more careful we all ought to be when expressing ourselves as the internet and social media do not forgive, though Adam focuses primarily on his reactions to his life situations; I prefer that to any incessant whine on the madness of the situation. Adam tries to share his gained wisdom, which is nice but again falls a little flat. Authentic living... what does that mean here? I appreciate his experiences, and heaven knows he and I differ on many a view, but this book wasn't eloquent enough to really change my mind or teach me anything new.
At its best, this is the story of a man who has been on a life-long journey and is still on it with all the accompanying bumps and views the reader may or may not agree with. But is it worth reading? I enjoyed it enough and even read it in one sitting, but I think it will be better appreciated by those who like the idea of the layman's memoir. | – Things haven't gone too well for the former CFO who criticized Chick-fil-A in a video he posted on YouTube. Unable to find lasting work, 37-year-old Adam Smith is living on food stamps with his wife and four kids in the RV they call home, he tells ABC News. "I think people are scared," Smith says of potential employers. "I think people are scared that it could happen again." Back in the summer of 2012, as thousands of people were opposing Chick-fil-A's stance on gay marriage, Smith rolled into a Chick-fil-A drive-thru for a free glass of water and slammed the female attendant: "Chick-fil-A is a hateful corporation," Smith told her as the filmed the exchange. "I don’t know how you live with yourself and work here. I don’t understand it." Smith posted the video before returning to work at Vante, a Tucson-based medical manufacturer—and the proverbial you-know-what had hit the fan by the time he got there. The receptionist told him "the voicemail is completely full, and it’s full of bomb threats," he says. Fired that day, Smith lost his $200,000 salary and more than $1 million in stock options. He and his family moved to Portland, where he got a CFO job, but lost it two weeks later when they realized who he was. He says he has since been honest in interviews, but companies have been too wary of fallout to hire him. "I don’t regret the stand I took, but I regret… the way I talked to her," an emotional Smith says of the worker. The interview coincides with his recent digital release of a memoir, A Million Dollar Cup of Water (a paperback version is out April 21), which chronicles his professional collapse and years of soul-searching. It's not faring so well on Amazon, which Smith addressed on the site on Friday. "Regarding the many 1-star ratings my book has received today and yesterday, I would like to note that I have only sold 17 digital copies thus far, yet there are 23 1-star ratings on my book. This fascinates me! LOL!" |
Each Monday, this column turns a page in history to explore the discoveries, events and people that continue to affect the history being made today.
The world map might look differently had the Greek volcano Thera not erupted 3,500 years ago in what geologists believe was the single-most powerful explosive event ever witnessed.
Thera didn't just blow a massive hole into the island of Santorini – it set the entire ancient Mediterranean onto a different course, like a train that switched tracks to head off in a brand new direction.
Minoan culture, the dominant civilization in the Mediterranean at the time, crumbled as a result of the eruption, historians believe, changing the political landscape of the ancient world indefinitely. Environmental effects were felt across the globe, as far away as China and perhaps even North America and Antarctica.
The legend of Atlantis and the story of the Biblical plagues and subsequent exodus from Egypt have also been connected to the epic catastrophe.
Dwarfed the atomic bomb
Historians and archaeologists have had trouble deciding on the year Thera erupted, with dates ranging anywhere from 1645 BC to 1500 BC. Studies of ash deposits on the ocean floor have revealed, however, that when the volcano did blow, it did so with a force dwarfing anything humans had ever seen or have seen since.
There are no first-person accounts of what happened that day, but scientists can compare it to the detailed records available from the famous eruption of Krakatoa, Indonesia, in 1883.
That fiery explosion killed upwards of 40,000 people in just a few hours, produced colossal tsunamis 40 feet tall, spewed volcanic ash across Asia, and caused a drop in global temperatures and created strangely colored sunsets for three years. The blast was heard 3,000 miles away.
Thera's eruption was four or five times more powerful than Krakatoa, geologists believe, exploding with the energy of several hundred atomic bombs in a fraction of a second.
An absence of human remains and valuables like metal suggest that the Minoan residents of Santorini predicted the eruption and the island was evacuated, but the culture as a whole did not fare as well.
Based on the nearby island of Crete, the powerful Minoan civilization declined suddenly soon after Thera blew its top. Tsunamis spawned by the eruption would have swamped its naval fleet and coastal villages first off, historians think. A drop in temperatures caused by the massive amounts of sulphur dioxide spouted into the atmosphere then led to several years of cold, wet summers in the region, ruining harvests. The lethal combination overran every mighty Minoan stronghold in less than 50 years.
In just a short time, their peaceful, efficient bureaucracy made way for the warring city-state system of ancient Greece to dominate the Mediterranean. The Aegean would turn out to be a fundamental building block for the history of Europe, and the Minoan decline changed its early foundation completely.
Famous legends
Thera didn't just alter the cultural make up of Europe, it has kept adventurers and treasure hunters busy too.
When the Greek philosopher Plato described the lost city of Atlantis over a thousand years after the volcanic eruption, he may have been referring to Thera folklore passed down in Greece over many generations and exaggerated like a game of broken telephone.
The eruption has also been loosely linked with the Biblical story of Moses and the exodus from Egypt. The effects of Thera's eruption could have explained many of the plagues described in the Old Testament, including the days of darkness and polluting of the rivers, according to some theories. ||||| Credit: Danny Alvarez/Shutterstock
If Aleppo's death toll is mistaken, the earthquake that hit Haiti on Jan. 12, 2010, may be a contender for the top 10 deadliest disasters. Even in a modern mass disaster, though, estimating the death toll is a tricky business.
In the year after the quake, the government of Haiti estimated that the magnitude-7.0 quake and its aftermath killed 230,000 people; in January 2011, officials revised the figure to 316,000. Those figures are highly disputed, however. A 2010 study published in the journal Medicine, Conflict and Survival put the number at around 160,000 deaths. A 2011 U.S. Agency for International Development (USAID) draft report from 2011 claimed even lower numbers — between 46,000 and 85,000.
The disparities reflect the difficulty of counting deaths even in the modern era, not to mention the political wrangling that goes on over "official" numbers. Many critics of Haiti's estimates argue that the government revised the death toll up in order to secure further international aid. On the other side of the argument, according to the Columbia Journalism Review, were those who accused USAID of leaking the report to discredit the Haitian government. | – "The single-most powerful explosive event ever witnessed" took place somewhere between 1645 BC and 1500 BC, when the volcano Thera erupted on what's now the island of Santorini. LiveScience reports its power has been likened to that of an 1883 eruption in Indonesia that could be heard 3,000 miles away and killed some 40,000 people. No such count is available for the Thera explosion, which is why it doesn't make LiveScience's list of the 11 deadliest natural disasters "for which reasonably accurate death tolls exist." It includes the 2004 Indian Ocean quake and tsunami, which hit Indonesia hardest and killed as many as a quarter of a million people overall. Here are five disasters that didn't strike so recently: 526 Antioch quake: The best estimate comes from John Malalas, a Greek chronicler from the Byzantine city where the quake struck whose writings from the time put the toll at about 250,000. A 2007 paper noted that the temblor's May timing was inopportune as the city's population was swollen with tourists there for Ascension Day, resulting in an elevated toll. 1556 Shaanxi earthquake: As far as earthquakes go, this is pretty much the worst. Believed to have been about a magnitude 8, it is said to have demolished a 621-square-mile region of China's Shaanxi province on Jan. 23 of that year, killing some 830,000 people. 1839 India cyclone: Some 20,000 ships were wiped out by the cyclone and resulting storm surge that struck the port city of Coringa on Nov. 25, but that number pales in comparison to the estimated death toll: 300,000 people. 1920 Haiyuan earthquake: The US Geological Survey believes that this quake that hit central China on Dec. 16 of that year registered as a magnitude 7.8. Landslides were a big contributor to the death toll, which researchers in 2010 estimated as 273,400. 1931 Central China Floods: Pegged by LiveScience as the deadliest of all natural disasters, this one spanned the months of July and August. The estimated ranges of those killed is a huge one, but the number is big regardless: Somewhere between 2 million and 3.7 million were killed when the Yangtze River flooded due to strong rains and melting snow, affecting some 70,000 square miles. Click for LiveScience's full list. |
Read this article in Spanish
Tokyo, Japan (CNN) -- The slaughter of bottlenose dolphins in an infamous Japanese cove took place on Tuesday.
About 500 dolphins were driven into the cove this year, a larger number than usual, according to the local Taiji fishermen's union. A fisherman who is a union board member, and who did not want to be named, told CNN that the total number of dolphins to be captured or slaughtered was less than 100, and that the rest would be released.
The yearly event is a focal point of the Taiji community's dolphin hunting season, which many in the community in southwest Japan view as a long-held tradition. The annual hunting season begins in September and runs through March, according to animal rights activists.
But the hunt is heavily scrutinized by environmental activists, who have been monitoring activities and livestreaming and tweeting about the latest developments.
In recent days, environmentalist group the Sea Shepherd Conservation Society has provided livestreams showing bottlenose dolphins splashing frantically as they tried to escape their human captors. Dolphins separated by nets into smaller partitions bobbed up and down, trying to reach other members of their pod. The group said that the dolphins appeared bloodied, and had had nothing to eat since their capture in Taiji Cove four days ago.
The union representative said that the fishermen had introduced what they considered a "more humane" method of slaughtering the dolphins, cutting their spines on the beach to kill the animals more swiftly and cause them less pain.
Defending tradition
Although the hunting of dolphins is widely condemned in the West, many in Japan defend the practice as a local custom -- and say it is no different to the slaughter of other animals for meat.
Chief Cabinet Secretary Yoshihide Suga told reporters at a news conference Monday that marine mammals including dolphins were "very important water resources."
"Dolphin fishing is one of traditional fishing forms of our country and is carried out appropriately in accordance with the law. Dolphin is not covered by the International Whaling Commission control and it's controlled under responsibility of each country."
Taiji mayor Kazutaka Sangen echoed the sentiments.
"We have fishermen in our community and they are exercising their fishing rights," he said. "We feel that we need to protect our residents against the criticisms."
He accused the Sea Shepherd of using the issue of dolphin hunting to raise funds and attract attention. The Sea Shepherd Conservation Society has been live-streaming video of events in the cove and posting frequent updates on Twitter.
The Wakayama Prefectural Government, where Taiji is located, gives an annual "catching quota." This year, the government allows for the hunting of 2,026 small porpoises and dolphins (557 are for bottlenose dolphins).
The dolphin hunt has seen some changes, Sangen said. The town wants to create a whale/porpoise study with the aim of bringing a marine park to the city. And the method of hunting has been changing, becoming less crude, he added.
On Monday, the fishermen focused on selecting dolphins to be sold into captivity at marine parks and aquariums in Japan and overseas, the conservation group said. Trainers marked the dolphins deemed unsuitable for captivity, which would be either killed or driven back out to the ocean, according to the Sea Shepherd group.
Kennedy's tweet met with criticism in Japan
Caroline Kennedy, the recently installed U.S. ambassador to Japan, tweeted that she is "deeply concerned by inhumaneness of drive hunt dolphin killing."
"I understand her statement as an expression of her concern on this debate," said Sangen. "There always are the people who say it's wrong and it's right, but what we have to see is if fishermen are hunting endangered species or not. They don't. We are fishing under the permission just like the U.S. does."
While Japanese media did not cover the dolphin hunt, several outlets reported on Kennedy's comments. On social media, Japanese users blasted Kennedy for commenting on what many consider a tradition.
One user, named @simaya tweeted: "She refers to humanitarian treatment to animals. What about the atomic bombing, Agent Orange and missiles falling on civilians in the Middle East?"
Masayhisa Sato, a Japanese lawmaker tweeted: "The dolphin hunt is also a traditional fishing culture. I wonder whether it's appropriate for ambassador to comment on this."
Captivity, death or freedom
On the days leading to the killing, divers and boats drove the dolphins into increasingly small segments of the water to select the ones that will be held in captivity.
In the days leading up to the dolphin hunting, 40 to 60 local fishermen worked with nets to divide up the dolphin pod.
"They tighten up the nets to bring each sub-group together then the skiffs push them toward the tarps. Under the tarps in the shallows is where the trainers work with the killers to select the 'prettiest' dolphins which will sell and make the best pay day for the hunters," said the Sea Shepherd Conservation Society.
Dozens of men circled around dolphins pinning them against a boat and hoisting them into black nets by pulling on their dorsal fin. When men successfully captured the dolphins into the net, they cheered "Yay!"
The Cove Guardians counted 51 bottlenose dolphins taken in the last few days, but the fishermen's union did not disclose the number of dolphins captured or killed.
Japan at center of controversy
A 2009 Oscar-nominated documentary film, "The Cove," brought the issue of dolphin hunting in Taiji to the fore with bloody scenes of dolphin slaughter.
The prefecture government has condemned the film in an online response as distorted, biased and unfair to the fishermen. "'The Cove' filmed secretly the scenes of dying dolphins, and depicted their death in a manner designed to excite outrage," according to the Wakayama Prefecture statement.
"The Taiji dolphin fishery has been a target of repeated psychological harassment and interference by aggressive foreign animal protection organizations," it said.
The Japanese practice of whale hunting has also put it in conflict with the views of much of the world.
Earlier this year, Sea Shepherd said it had chased Japan's whalers out of Antarctic waters. Japan's fleet carries out an annual whale hunt despite a worldwide moratorium, taking advantage of a loophole in the law that permits the killing of the mammals for scientific research. Whale meat is commonly available for consumption in Japan.
READ: Dolphins to be slaughtered, conservationists warned
READ: Opinion: Eat fish, kill a dolphin?
CNN's Junko Ogura and Laura Smith-Spark contributed to this report. Madison Park reported and wrote from Hong Kong. Yoko Wakatsuki reported from Tokyo. ||||| Add a location to your Tweets
When you tweet with a location, Twitter stores that location. You can switch location on/off before each Tweet and always have the option to delete your location history. Learn more ||||| 1 of 3. Fishermen hunt dolphins in the shallows of a cove in Taiji, western Japan, January 21, 2014.
TAIJI, Japan (Reuters) - Japanese fishermen drove a large group of dolphins into the shallows on Tuesday and, hiding from reporters and TV cameras behind a tarpaulin, killed at least 30 as the annual dolphin hunt that sparked protest in the West entered its final stages.
Both the U.S. and British ambassadors to Japan have strongly criticized the "drive killings" of dolphins citing the "terrible suffering" inflicted on the marine mammals.
Every year the fishermen of Taiji, in western Wakayama prefecture, drive hundreds of dolphins into a cove, select some for sale to marine parks, release some and kill the rest for meat.
On Tuesday, at least 30 dolphins out of the group of more than 200 held in the cove since Friday were herded by boat engines and nets into a killing area of the Taiji cove.
Fishermen waiting in the shallow waters by the shore, some in wet suits with snorkeling masks on their faces, wrestled the dolphins into submission and tied their tails with ropes to stop them from escaping.
Before the killing began, fishermen pulled a tarpaulin in front of the cove to prevent activists and reporters from seeing the killing. A large pool of blood seeped under the tarpaulin and spread across the cove.
"A metal rod was stabbed into their spinal cord, where they were left to bleed out, suffocate and die. After a traumatic four days held captive in the killing cove, they experienced violent captive selection, being separated from their family, and then eventually were killed today," Sea Shepherd Conservation Society activist Melissa Sehgal told Reuters.
The annual hunt has long been a source of controversy and was the topic of "The Cove", an Oscar-winning documentary that brought Taiji into the international spotlight.
Activists say that out of this year's group more than 50 dolphins were driven away to be sold to aquariums. Those not killed on Tuesday were released, they said.
"UK opposes all forms of dolphin and porpoise drives; they cause terrible suffering. We regularly raise (the issue) with Japan," said the British Ambassador to Japan, Timothy Hitchens, in a tweet on Monday. Caroline Kennedy, the U.S. envoy to Tokyo, has also said she was "deeply concerned" about the hunt.
Japan maintains that killing dolphins is not banned under any international treaty and that the animals are not endangered.
Yoshinobu Nisaka, the governor of Wakayama prefecture where Taiji is located, rejected Kennedy's concerns.
"Dietary culture varies and it is the wisdom of civilization to mutually respect other standpoints unless the world faces a lack of resources," Nisaka was quoted by Kyodo news agency as telling reporters.
The Taiji fishing union rejected Reuters requests for comment.
The dolphin hunting season runs yearly from September to March. Sea Shepherd said around 600 marine mammals had been killed this season before Tuesday's slaughter.
Monitoring is difficult, with fishermen erecting tarpaulins over their killing area and blocking access to the cove.
(Writing and additional reporting by Antoni Slodkowski; Editing by Nick Macfie) | – Japanese fishermen have wrapped up their annual dolphin hunt and slaughter in Taiji cove amid international protests. CNN reports that some 500 bottlenose dolphins were driven into the cove—a larger number than usual, though Sea Shepherd Conservation Society is sticking with its original claim that 250 or so dolphins were involved. As always, some were captured to be sold to aquariums, others slaughtered for their meat, and the rest released; a member of the local fishermen's union says fewer than 100 fell into those first two categories. But Sea Shepherd, which has tweeted and streamed video through the whole hunt, claims that "many will die at sea from the last 4 days." It claims that 52 were sold into captivity, 41 were killed, and the remaining 130 to 140 were released. Sea Shepherd has described horrific scenes as dozens of dolphins were dragged into a tent to be slaughtered, reports the Sydney Morning Herald. That tent was apparently an attempt on the fishermen's part to keep prying eyes away. Reuters reports that in advance of the killing they put a tarpaulin in place; blood streamed out from under it. The Japanese government has shrugged off criticism of the hunt from diplomats including US Ambassador to Japan Caroline Kennedy. "Dolphin fishing is a form of traditional fishing in our country," a government spokesman says. "We will explain Japan's position to the American side." (Click for another tale of marine woes involving sardines.) |
DUTCH convicted killer Joran Van der Sloot, serving a 28-year sentence in Peru for murdering a young Peruvian woman, will tie the knot in prison next month, his lawyer says.
Lawyer Maximo Altez said an official from the northern district of Ancon, where Van der Sloot is in custody, would perform the civil wedding ceremony at the Piedras Gordas maximum security prison outside Lima.
The lawyer on Thursday provided scant information about the bride-to-be however, other than to say that she is Peruvian.
"We just hope the National Penitentiary Institute (INPE) will grant us permission," said the lawyer, adding that he would be the best man and the only guest invited to the ceremony.
Van der Sloot, 25, pleaded guilty and was handed down his sentence in January 2012 for the "cruel and savage" murder of 21-year-old Peruvian Stephany Flores on May 30, 2010.
The victim had been struck, then strangled in a hotel room in Lima, where she ended up with her assailant after meeting in a casino, where they played poker.
A year ago, Peru's top court agreed to allow Van der Sloot's extradition to the United States, where he is the prime suspect in the 2005 disappearance of 18-year-old US college student Natalee Holloway on the Caribbean island of Aruba.
Van der Sloot allegedly extorted $US25,000 from Holloway's parents in exchange for information about their daughter. Once he received the money, he fled to Peru.
But Lima said it would only extradite Van der Sloot after he has completed serving his sentence there. ||||| Joran van der Sloot in the courtroom for his murder trial at San Pedro prison in Lima, Peru.AP
Joran van der Sloot, who became known around the world for the murder of Stephany Flores in Peru and for being arrested twice, but never charged, in the 2005 disappearance of U.S. teenager Natalee Holloway in Aruba, has wedding plans.
Claiming he is a changed man, he is asking to have his sentence reduced from to 28 to 20 years.
According to his lawyer, Maximo Altez, the Dutch man seeks to rebuild his life by marrying in prison, for which he is still awaiting the permission of the prison authorities.
"He is a person who has changed ... he wants to rebuild his life, wants to be a new person, and wants the Supreme Court Peru given a chance." - Maximo Altez, Van der Sloot's lawyer
Altez said the wedding could take place in 15 days.
"He wants to marry, change his life, start a new life," he said, apologizing for not disclosing the name of the bride.
According to published reports, the young woman is Leydi Figueroa Uceda, a Peruvian girl who visits in jail him often. She is said to have given birth to Van der Sloot’s son, something Altez denies.
On Wednesday, Altez filed a motion to reduce the murder sentence, claiming that Van der Sloot had collaborated with the authorities and that his rights were violated during his arrest.
"They gave him a fake lawyer that he did not pick, he never got an interpreter; a reconstruction of the facts never was never done,” Altez said to reporters on his way out from court.
"He is a person who has changed ... he wants to rebuild his life, wants to be a new person, and wants the Supreme Court Peru given a chance," said Altez.
The lawyer said that the Supreme Court will rule on his request in about 10 days.
Van der Sloot is a self-described liar, having repeatedly confessed to killing Holloway, who disappeared in 2005, and later retracting the confessions. He is the last person known to have seen her alive.
He was convicted for the 2010 robbing and killing of Flores in a Lima hotel room after meeting her in a nearby casino.
He is also wanted by authorities in the U.S. for allegedly extorting money from the Holloway family on the promise of revealing the location of her body.
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The 26-year-old Dutchman and suspect in Natalee Holloway’s disappearance—now serving time for the murder of a Peruvian girl—is set to marry, his lawyer confirms.
It’s wedding bells for Joran van der Sloot, the 26-year old Dutchman who is serving 28 years in a Peruvian prison for the murder of Peruvian college student Stephany Flores. Van der Sloot gained notoriety in 2005 in connection with the disappearance of Natalee Holloway, 19, from Alabama, who disappeared on a school trip in Aruba. Van der Sloot was the last person to be seen with Holloway on the night before she was scheduled to fly back to America. Her body was never found, but van der Sloot confessed to several different scenarios, including leaving her drunk on the beach and selling her into the sex trade. He was twice arrested but never formally charged for any crime relating to the case in Aruba. Flores was murdered five years to the day that Holloway disappeared. Van der Sloot admitted to killing Flores, but blamed posttraumatic stress disorder for being accused of Holloway’s disappearance for making him kill the Peruvian.
The Dutchman’s new bride, who can justifiably be questioned for her taste in men, is Leydi Figueroa Uced, a 22-year-old Peruvian who regularly visits van der Sloot in Piedras Gordas prison. His lawyer, Máximo Altez, confirmed the impending nuptials, which will take place in prison in early June. Last October van der Sloot told the Dutch daily De Telegraaf that his bride-to-be was pregnant with his child, but no reports of the baby’s birth have since been released. Conjugal visits are allowed in Peruvian prisons if couples register as common-law partners, as the two lovebirds are.
While no one can know for sure whether van ser Sloot and Figueroa Uced are truly in love, marrying a Peruvian and fathering her child may save van der Sloot from further punishment. In 2010, van der Sloot was charged with attempting to extort $250,000 from Beth Holloway in exchange for the exact location and details of her daughter’s death. Holloway gave him $25,000 as a down payment, but he took the money and traveled to Peru to play in a poker tournament, where he ultimately met Flores, lured her to his Lima hotel room and then killed her after she found incriminating materials relating to the Holloway case on his personal computer. He pled guilty in his trial and was sentenced to 28 years, two years short of the maximum sentence of 30 years. He was also ordered to pay the Flores family around $75,000 in damages. He faces 25 years in the American extortion case.
In 2010, Beth Holloway was able to sneak into the Peruvian jail to question van der Sloot about her daughter’s disappearance. Holloway was accompanied by Dutch investigative journalist Peter de Vries, who captured the visit on camera. Holloway was able to get van der Sloot to admit to the extortion, but not to the truth about what happened to her daughter.
Last May, an accord was reached between the United States and Peru, and van der Sloot was supposed to be extradited to face charges in the United States last year on the grounds that he was a foreign national. The extradition stalled after van der Sloot’s lawyer was able to negotiate an eleventh-hour deal to keep the Dutchman in Peru. Now, by marrying a local Peruvian, he can automatically apply for Peruvian citizenship, which will hinder America’s chances of extraditing him. | – Well, it's official: There really is someone for everyone, even literal lady killer Joran Van der Sloot. The convicted killer and alleged extortionist intends to get married next month in the Peruvian prison where he's serving a 28-year sentence, his lawyer, Maximo Altez, has announced. "He wants to marry, change his life, start a new life," Altez tells Fox News Latino. Altez will be the best man and only guest at the blessed occasion, he tells the Herald-Sun. While Altez won't divulge the name of the, er, lucky bride, reports are swirling that it's Leydi Figueroa Uceda, a 22-year-old Peruvian who, according to the Daily Beast, has registered as Van der Sloot's common law partner so she can have conjugal visits with him. The two are also rumored to have had a son together, though Altez says that's not true. |
`` beamforming is a versatile and powerful approach to receive , transmit , or relay signals - of - interest in a spatially selective way in the presence of interference and noise '' @xcite .
recently , the concept of receive and transmit beamforming has been used to enhance coverage and data rate performance in amplify - and - forward ( af ) relay networks . distributed beamforming has been applied as a coherent transceiver technique in a variety of relay network architectures , such as single - user networks @xcite@xcite . in such networks
one source transmits data to one destination .
single - user networks have been extended to peer - to - peer networks , where multiple source - destination pairs communicate directly via relays @xcite , @xcite , @xcite .
moreover , distributed systems of non - connected relays can be used for multicasting to transmit data from one source to many destinations simultaneously to avoid exhaustive individual transmissions @xcite@xcite . the task to select the optimum antenna weights in centralized beamforming systems using a connected antenna array @xcite@xcite , or in distributed beamforming systems using a non - connected array @xcite@xcite for multicasting
is highly non - trivial as it requires to form beams towards several destinations , each corresponding to a different spatial signature . in @xcite
, it has been shown that the problem of selecting the antenna weights for single - group multicasting is np - hard .
until now , no polynomial time algorithm for np - hard problems is known and it is expected that exact solutions can only be computed within exponential time . to derive adequate solutions to beamforming problems which belong to the class of non - convex quadratically constrained quadratic optimization problems ( qcqps ) , computationally efficient algorithms have been proposed which approximate the feasible set of the optimization problem @xcite@xcite , @xcite@xcite , @xcite@xcite .
outer approximation techniques replace the qcqps by convex semidefinite programs ( sdps ) which can be solved efficiently @xcite@xcite . in the latter approach ,
the weight vector is replaced by a positive semidefinite hermitian matrix .
since this so - called semidefinite relaxation ( sdr ) technique extends the feasible region , a solution matrix to the sdr problem lies not necessarily in the feasible set of the original problem .
if the rank @xmath0 of the solution matrix @xmath1 equals to one , the sdr solution is a global solution to the original problem . in practice
, however , @xmath0 might be greater than one and @xmath1 is not feasible for the original problem . especially in single - group multicasting scenarios , where many destinations demand a minimum received quality - of - service ( qos ) , it is not likely that @xmath2 .
this is a consequence of the fact that the existence of an sdr solution matrix with rank @xmath0 is only guaranteed if @xmath3 , where @xmath4 is the number of destinations @xcite . if @xmath5 , the objective value of the sdr solution is only a lower bound to the objective value of the qcqp .
the accuracy of the lower bound decreases with a growing number of destinations @xmath4 @xcite .
therefore , for multicasting with large @xmath4 , the lower bound generated by sdr can lie quite far from the true minimum value for rank - one beamforming .
recently , in the two independent works @xcite and @xcite , rank - two transmit beamforming techniques for multicasting networks have been proposed in which also _ rank - two _ sdr solution matrices are feasible . in these techniques ,
two weight vectors are used at the transmitter to process two data symbols jointly .
rank - two beamforming techniques have gained much interest in the current research as the system performance is enhanced due to the increased number of degrees of freedom resulting from the additional weight vector @xcite , @xcite@xcite . in this paper , we propose a distributed rank - two beamforming scheme for single - group multicasting using a network of amplify - and - forward ( af ) relays . in af multicasting networks , the relays forward common messages from a single source to multiple destinations .
the proposed af single - group multicasting scheme ( afms ) is a non - trivial extension of the transmit beamforming technique of @xcite and @xcite to a distributed beamforming system .
we refer to our scheme as the rank-2-afms in distinction to the conventional rank-1-afms of @xcite . as another generalization to the rank-1-afms ,
we exploit direct link connections from the source to the destinations . as the design criterion to select the power at the source and the relay weights
, we aim to maximize the minimum qos at the destinations under constraints on the transmit power in the network .
we consider constraints on the maximum transmit power of the source , on the individual power of every relay , on the sum power of the relays , and on the total power by both the relays and source . to solve the non - convex max - min fairness optimization problem of jointly determining the relay weight vector and the power split between the relays and the source , we propose a linearization - based iterative algorithm . in advantage to the sdr technique , where the number of variables is roughly squared , the number of variables is not increased for cccp algorithms .
cccp algorithms are used to approximately solve non - convex difference of convex ( dc ) programming problems .
many optimization problems that arise in the context of wireless communications are dc problems , including power allocation @xcite@xcite and beamforming problems @xcite@xcite . in contrast to the algorithms for max - min fair beamforming of @xcite , @xcite , @xcite , @xcite , and @xcite , which treat solely the optimization of beamforming vectors , our algorithm derives the relay weight vectors and allocates transmit power to the source and the relays .
the max - min fair beamforming approaches in @xcite and @xcite combine the sdr technique with one - dimensional ( 1d ) search on the maximum qos . to compare our cccp algorithm ( max - min - cccp ) with the latter sdr - based algorithms ,
we combine the sdr technique with two - dimensional ( 2d ) search on both the maximum qos and the best power split between the relays and the source . to test the rank-2-afms and the rank-1-afms under realistic conditions , we use the channel model of @xcite .
the simulation results demonstrate the performance of the proposed rank - two scheme combined with the proposed algorithm compared with the rank - one scheme of @xcite and the theoretical bound obtained by sdr .
the max - min - cccp algorithm outperforms the sdr technique for high destination numbers at a much lower runtime .
moreover , the max - min - cccp algorithm offers a good performance - runtime trade - off and achieves a minimum signal - to - noise ratio ( snr ) which is less than 1 db lower than the theoretical bound after three iterations .
the contribution of this paper can be summarized as follows : _ notation : _
@xmath6 , @xmath7 , @xmath8 , @xmath9 , @xmath10 , @xmath11 , and @xmath12 denote the statistical expectation , absolute value of a complex number , trace of a matrix , complex conjugate , transpose , real part operator , and hermitian transpose , respectively .
@xmath13 means that @xmath14 is a positive semidefinite matrix .
@xmath15 denotes a diagonal matrix , with the entries of the vector @xmath16 on its diagonal , @xmath17)$ ] is the block diagonal matrix formed from the matrices @xmath18 .
@xmath19 is the @xmath20 vector containing zeros in all entries . @xmath21 and
@xmath22 is the @xmath23 identity matrix .
@xmath24 means that @xmath25 is circularly symmetric complex gaussian distributed with mean @xmath16 and covariance matrix @xmath26 . for the complex number @xmath27
, @xmath28 denotes the phase @xmath29 .
@xmath30 denotes the rank of @xmath26 .
consider a wireless network of @xmath31 relays forwarding the signals from a single source to @xmath4 destinations . in our single - group multicasting scenario ,
all destinations demand the same information .
the source , the relays , and the destinations are single antenna devices , see fig . [ f185 ] . in the proposed rank-2-afms ,
two data symbols are jointly processed in a four time slot scheme , see fig .
[ transmissionscheme ] . in the first and second time slot of the rank-2-afms ,
the source transmits the data symbols @xmath32 and @xmath33 , respectively , which are drawn from a discrete symbol constellation @xmath34 .
both symbols are weighted by the same real - valued power scaling factor @xmath35 .
the @xmath36 vectors @xmath37}^t$ ] and @xmath38}^t$ ] of the received signals at the relays in the first and second time slot are respectively given by @xmath39 where @xmath40^t$ ] and @xmath41^t$ ] are the @xmath42 vectors of the relay noise of the first and second time slot , respectively , and where @xmath43^t } $ ] is the @xmath36 vector , containing the complex coefficients of the channels from the source to the relays .
note that all channels in the network are assumed to be frequency flat and constant over the four considered time slots .
in contrast to the system model of @xcite , we consider that there exist direct channels from the source to the destinations .
the signals @xmath44 and @xmath45 received by the @xmath46th destination in the first and second time slot , respectively , are given by @xmath47 where @xmath48 is the coefficient of the channel from the source to the @xmath46th destination and @xmath49 and @xmath50 represent the destination noise of the first and second time slot , respectively .
we make the practical assumptions that the noise processes in the network are spatially and temporally independent and complex gaussian distributed .
the noise power at the destinations is given by @xmath51 and the noise at the relays is distributed according to @xmath52 where @xmath53 is the power of the noise at the relays . here
, the relays transmit their signals over two different beams . in this fashion
, the proposed rank-2-afms enables the relays to create two different communication links from the source to each destination . in the conventional rank-1-afms of @xcite ,
the relays transmit their signals over one beam , creating a single communication link from the source to each destination .
the @xmath36 vectors @xmath54^t$ ] and @xmath55^t$ ] of the signals transmitted by the relays in the third and fourth time slot , respectively , can be expressed as @xmath56 where @xmath57 , @xmath58 , and @xmath59^t $ ] and @xmath60^t $ ] are the complex @xmath36 relay weight vectors . according to equations ( [ relaytrans ] )
, the relays transmit their received signal vectors @xmath61 and @xmath62 over the two weight vectors @xmath63 and @xmath64 .
the use of two weight vectors increases the degrees of freedom in the distributed beamformer design .
in general , the superposition of multiple symbols that are simultaneously transmitted over different beams leads to difficulties in the decoding at the destinations . in our proposed rank-2-afms
however , symbol - by - symbol detection at the destinations is facilitated by the particular spatial encoding scheme applied in equations ( [ relaytrans ] ) .
the latter encoding scheme corresponds to the popular alamouti s ostbc scheme , in which two data symbols are transmitted over two spatial channels over consecutive time slots @xcite .
in contrast to conventional ostbc schemes , which do not require the availability of channel state information ( csi ) at the transmitter , the rank-2-afms creates two `` artificial '' spatial channels which are shaped by choosing two beams with corresponding beamforming vectors that are designed based on csi . it is assumed that the perfect csi is available at a central processing node that computes the source power and the relay weights and communicates each parameter to its corresponding node .
note that according to equations ( [ relaytrans ] ) , the signals transmitted by the relays consist of linear combinations of the received signals and their conjugates .
this is also the case in distributed ostbc schemes which , however , do not use csi at the transmitter @xcite , @xcite . to further exploit the direct links from the source to the destinations
, the source transmits the signals @xmath65 and @xmath66 in the third and fourth time slot , respectively , where @xmath67 and @xmath68 are complex - valued scaling factors .
the received signals of the third and fourth time slot at the @xmath46th destination can then be written as @xmath69 where @xmath70^t \label{gvector}\ ] ] is the @xmath36 vector of the complex frequency flat channels between the relays and the @xmath46th destination and @xmath71 and @xmath72 denote the receiver noise at the @xmath46th destination in the third and fourth time slot , respectively . introducing @xmath73 as the vector of the received signals at the @xmath46th destination , @xmath74 as the vector of the noise at the @xmath46th destination , and @xmath75 as the equivalent channel matrix and making use of equations ( [ relayreceived ] ) , ( [ relaytrans ] ) , and ( [ gvector ] )
, the received signals of the four time slots in equations ( [ directpathfirsttimeslot ] ) and ( [ receivedsignal ] ) can be compactly written as @xmath76 where @xmath77^t , \\ \relax { \mathbf s } & \triangleq [ s_{1 } , s_{2}]^t , \\ { \mathbf n}_m & \triangleq \ ! \begin{bmatrix } \nu_{m,1 } \\ \nu_{m,2}^ * \\ { \mathbf w}_1^h { \mathbf{g}}_m \boldsymbol{\eta}_1 + { \mathbf w}_2^h { \mathbf{g}}_m \boldsymbol{\eta}_2^\ast + \nu_{m,3 } \\ \relax -\ ! { \mathbf w}_2^t { \mathbf{g}}_m^h \boldsymbol{\eta}_1\ ! + \ ! { \mathbf w}_1^t { \mathbf{g}}_m^h \boldsymbol{\eta}_2^\ast + \nu_{m,4}^ * \end{bmatrix } , \label{noisy}\\ \relax { \mathbf{h}}_{m } & \triangleq\ ! \begin{bmatrix
} \alpha_1 d_m & 0 \\ 0 & ( \alpha_1 d_m)^\ast \\ & \!\!\!\!\!\!\!\!\!\!\!\!\!\!\ ! \!\!\!\!\ ! \!\!\
! { \mathbf{h}}_{{\rm a},m } \end{bmatrix } , \label{hmatrix } \\
\relax { \mathbf{h}}_{{\rm a},m } & \triangleq\ !
\begin{bmatrix }
h_{m,1 } & h_{m,2 } \\ \relax -h_{m,2}^\ast & h_{m,1}^\ast \end{bmatrix } \label{hmatrix2 } \\
\relax h_{m,1 } & \triangleq \alpha_1 { \mathbf w}_1^h { \mathbf{g}}_m { \mathbf f}+ \alpha_3 d_m , \label{channelgains1 } \\ \relax h_{m,2 } & \triangleq \alpha_1 { \mathbf w}_2^h { \mathbf{g}}_m { \mathbf f}^\ast + \alpha_4 d_m , \label{channelgains2 } \\ \relax { \mathbf{g}}_m & \triangleq { \rm diag}({\mathbf g}_m ) .
\label{gmatrix}\end{aligned}\ ] ] note that @xmath78 and @xmath79 denote the equivalent scalar channel coefficients that model the flat fading channels between the source and the @xmath46th destination that are obtained from relay beamforming using weight vectors @xmath80 and @xmath81 , respectively .
according to equation ( [ hmatrix2 ] ) these channels form the matrix @xmath82 , which has the same orthogonal structure as the channel matrix of alamouti s ostbc scheme .
interestingly , if no direct source - destination channels exist , i.e. , @xmath83 for all @xmath84 and the destinations receive signals only in the third and the fourth time slot , the developed system model of equation ( [ systemmodel ] ) corresponds to the system model of @xcite and @xcite for centralized rank - two beamforming .
however , for the latter schemes , the noise at the destinations can be modeled as temporally white .
in contrast to the proposed relay beamforming approach we observe from equation ( [ noisy ] ) that the third and the fourth entry of the noise vector @xmath85 both depend on the relay noise @xmath86 and @xmath87 in the first and the second time slot , respectively . however , due to the specific orthogonal transmission format corresponding to the proposed afms it can readily be verified that the covariance matrix of the noise vector in equation ( [ noisy ] ) exhibits a diagonal structure of the form @xmath88 \right ) , \label{noisematrix}\ ] ] where @xmath89 ) .
\label{def : calg}\end{aligned}\ ] ] the spatially and temporally uncorrelated noise property expressed in equation ( [ noisematrix ] ) is essential for the use of simple symbol - by - symbol detection at the destination , which achieves maximum - likelihood ( ml ) performance as will be shown in the following . to account for the difference in the noise powers of the different time slots due to noise amplification at the relays , we transform both sides of equation ( [ systemmodel ] ) by multiplication with the diagonal scaling matrix @xmath90\right ) , \label{umatzrix}\ ] ] resulting in the equivalent model representation @xmath91
corresponding to a uniform noise power model , i.e. , @xmath92 is given by @xmath93 then , using equation ( [ ueq ] ) , the ml detection problem of finding @xmath94 can be equivalently reformulated as the least squares problem @xmath95 from equations ( [ hmatrix ] ) and ( [ umatzrix ] ) , we observe that @xmath96 , where @xmath97,$ ] where the matrix @xmath98 is chosen such that @xmath99 , i.e. , equation ( [ mlprob ] ) can be equivalently written as @xmath100 where @xmath101 and @xmath102 from equation ( [ mlprob2 ] ) , the detection of @xmath32 and @xmath103 decouples into two scalar detection problems since @xmath104 ) and ( [ bmatrix ] ) .
in other words , in the proposed four phase scheme ml detection reduces to simple symbol - by - symbol detection .
we remark that the diagonal structure of the error covariance matrix follows from the orthogonal encoding in equations ( [ relaytrans ] ) . from equation ( [ noisedistibutionreceiver ] ) , we see that the snr in @xmath105 is given by @xmath106 for both data symbols . for
the sake of convenience , let us introduce the following vector notation @xmath107^t , \label{startnot}\\ \relax \tilde{\mathbf{w}}_1 & \triangleq [ { \mathbf{w}}_1,(\alpha_3 \alpha_1)^\ast]^t,\quad \tilde{\mathbf{w}}_2 \triangleq [ \mathbf{w}_2^t , ( \alpha_4 \alpha_1)^\ast ] ^t , \\
\relax \mathbf{r}_m & \triangleq { \rm blkdiag}([\tilde{\mathbf{r}}_m,\tilde{\mathbf{r}}_m ] ) , \label{rm } \\ \relax \tilde{\mathbf{r}}_m & \triangleq { \rm blkdiag}([\sigma_\eta^2{\cal g}_m,0 ] ) . \label{endnot}\end{aligned}\ ] ] using equations ( [ noisepower ] ) and ( [ startnot ] ) - ( [ endnot ] ) yields @xmath108 let us furthermore introduce @xmath109 ) , \label{qm } \\
\relax \tilde{\mathbf{q}}_{m,1 } & \triangleq \mathbf{q}_{m,1}\mathbf{q}_{m,1}^h , ~~ \tilde{\mathbf{q}}_{m,2 } \triangleq \mathbf{q}_{m,2}\mathbf{q}_{m,2}^h,\label{matrixdefinition}\\ \relax \mathbf{q}_{m,1 } & \triangleq [ ( { \mathbf{g}}_m { \mathbf f})^t , d_m]^t , \quad \mathbf{q}_{m,2 } [ ( { \mathbf{g}}_m { \mathbf f}^\ast)^t , d_m]^t , \label{channelvectors } \relax \\ a & \triangleq 1 / |\alpha_1|^2 , \label{a_def}\end{aligned}\ ] ] where @xmath110 is a power scaling factor . with equations ( [ channelgains1 ] ) , ( [ channelgains2 ] ) , and ( [ qm ] ) - ( [ a_def ] ) , we have @xmath111 using the above identity together with equations ( [ nosevec ] ) and ( [ noiesvec ] ) , we reformulate the snr given in equation ( [ snr ] ) in vector notation as @xmath112 or , equivalently , as @xmath113
in this section , we derive an algorithm to design the weight vectors and to distribute the power between different time slots and between the source and the relays .
we consider the problem of maximizing the minimum qos measured in terms of the snr at the destinations subject to power constraints .
the power constraints include thresholds on the individual power of each relay and the source , the sum power of the relays , and the total power of the network .
maximizing the minimum snr is a practical objective , e.g. , for packet - data traffic with full buffer networks the receivers demand the largest feasible data rates rather than a certain constant data rate , provided that the average rate is satisfactory @xcite .
hence , max - min fairness is a common design criterion that has been used in @xcite , @xcite , @xcite , @xcite , @xcite , and @xcite . here
, the corresponding max - min fairness optimization problem is formulated as where @xmath114 and @xmath110 belong to the set @xmath115 characterized by the following power constraints [ powerconstraintsoriginal ] @xmath116 the positivity condition ( [ pospower ] ) results from the parameter transformation in definition ( [ a_def ] ) and ensures that the source power is a real and positive number . in inequality ( [ indpowerconstraint ] ) , @xmath117 represents the transmit power of the @xmath118th relay , @xmath119 is the maximum individual power value for the @xmath118th relay , @xmath120 in inequality ( [ sumpowerconstraint ] ) is the sum power transmitted by the relays in one time slot for which the power threshold value @xmath121 applies , @xmath122 in inequality ( [ sourcepowerconstraint ] ) is the total transmitted power at the source in four consecutive time slots with threshold value @xmath123 , @xmath124 in inequality ( [ overallpowerconstraint ] ) is the total transmit power of the network , including source and relay powers , during four time slots , and @xmath125 is the threshold value for @xmath126 . using equations ( [ relayreceived ] ) and ( [ relaytrans ] ) ,
the power @xmath117 transmitted by the @xmath118th relay in the third time slot can be derived as @xmath127 where the @xmath128 matrices @xmath129 and @xmath130 have respectively @xmath131 and @xmath132 as their @xmath118th diagonal entry and zeros elsewhere , and where @xmath133)$ ] and @xmath134)$ ] . in equations ( [ defrelay ] ) , we have used the assumption that the data symbols are independent and identically distributed with zero mean and unit variance . due to the symmetry in the transmission scheme ,
the relay power in the fourth time slot is equivalent to the relay power of the third time slot , i.e. , @xmath135 hence @xmath136 represents the relay power consumed in each time slot in which the relays transmit .
note that the inequality constraints ( [ indpowerconstraint ] ) are convex as @xmath137 in equations ( [ defrelay ] ) is expressed as the sum of the convex quadratic form @xmath138 as well as the fraction of the convex quadratic form @xmath139 and the linear term @xmath110 , which is a convex function @xcite .
the same holds true for the condition @xmath140 in inequality ( [ sumpowerconstraint ] ) , as the summation of convex functions yields a convex function .
the transmit power of the source during the four time slots is given by @xmath141 where @xmath142 is an @xmath128 matrix , having @xmath143 as its @xmath144th diagonal entry and zeros elsewhere and where @xmath145)$ ] .
note that @xmath122 is a convex function of @xmath114 and @xmath110 . as the sum powers of the relays of the third and fourth time slot are equal
, the total transmit power of the relays and the source during four time slots amounts to @xmath146 with equations ( [ defrelay ] ) - ( [ defpt ] ) , the power constraints ( [ pospower ] ) - ( [ overallpowerconstraint ] ) can be reformulated as [ powerconstraintsvec ] @xmath147 respectively .
note that @xmath148 represents the optimization problem in its general form .
we remark that the optimization procedures developed in the following for problem @xmath148 remain valid if some constraints ( [ indpowerconstraint ] ) - ( [ overallpowerconstraint ] ) are removed . introducing the auxiliary variable @xmath149 , problem @xmath148
can equivalently be written as where @xmath150 represents the minimum snr at the destinations .
the difficulty associated with solving problem @xmath151 lies in the snr constraints which can be formulated as @xmath152 where we have used the snr expression of equation ( [ snr_reformulated ] ) . due to the negative term on the left hand side of the above inequality ,
the snr constraints are non - convex in general .
the rank-1-afms can be regarded as a special case of the rank-2-afms where symbols are transmitted sequentially by a single beamformer , i.e. , choosing @xmath153 . in the rank-1-afms , each symbol is communicated in two time slots ; in the first time slot the source sends the signal to the relays and in the second time slot the relays forward their received signals to the destinations .
note that the number of time slots used to transmit one data symbol is two for the rank-1-afms ( @xmath154 ) and the proposed rank-2-afms ( @xmath155 ) . in the following we analyze the rank-1-afms and the rank-2-afms , applying sdr to problem @xmath151 .
we will prove that for both schemes , the sdr versions of @xmath151 are equivalent .
let us derive an equivalent representation of the snr at the @xmath46th destination given by equation ( [ snr_reformulated_new ] ) . defining the matrix @xmath156)$ ] , where @xmath157 , we notice from the definitions ( [ qm ] ) and ( [ matrixdefinition ] ) that @xmath158 . the unitary transformation @xmath159 exhibits the useful property that @xmath160 .
moreover , @xmath161 which follows from the definition of @xmath162 and from equations ( [ def : calg ] ) and ( [ endnot ] ) . then , using equation ( [ snr_reformulated_new ] ) , the snr constraints ( [ snr - constraint ] ) can be formulated as @xmath163 due to the quadratic forms @xmath164 and @xmath165 , the above inequality describes a non - convex set .
non - convex problems are difficult to solve and generally np - hard . to reformulate non - convex qcqps ,
the sdr technique has been proposed in the literature @xcite , @xcite . in the latter technique ,
the identity @xmath166 is exploited and @xmath167 is substituted in @xmath168 by a positive semidefinite matrix @xmath169 . substituting further @xmath170 by @xmath171 leads to @xmath172 where the constraints @xmath173 and @xmath174 are neglected and where the set @xmath175 is defined by the power constraints [ sdrpowerconstraints ] @xmath176 here the constraints ( [ constraint_a_sdr ] ) - ( [ opt : powerconstraintssdr ] ) correspond to constraints ( [ constraint_a ] ) - ( [ opt : powerconstraints2 ] ) , respectively .
note that for the rank-1-afms @xmath177 follows from @xmath178 and @xmath179 holds true .
for the rank-1-afms , the sdr problem corresponding to problem ( [ opt : maxminsdr ] ) is given by @xmath180 [ satz]theorem * ( equivalence of sdr problems ) * the optimum value @xmath181 of the problem ( [ opt : maxminsdr ] ) corresponding to the rank-2-afms is the same as for problem ( [ opt : maxminsdrafms ] ) corresponding to the rank-1-afms .
let @xmath182 be a solution to problem ( [ opt : maxminsdrafms ] ) , then @xmath183 is a solution to problem ( [ opt : maxminsdr ] ) as the constraint functions in problem ( [ opt : maxminsdr ] ) only depend on the sum of @xmath169 and @xmath184 .
on the other hand , if @xmath185 is a solution of problem ( [ opt : maxminsdr ] ) , then @xmath186 is a solution of problem ( [ opt : maxminsdrafms ] ) as the sum of positive semidefinite matrices results in a positive semidefinite matrix . as a consequence of the latter theorem ,
the sdr of @xmath187 for the rank-1-afms given by problem ( [ opt : maxminsdrafms ] ) and the sdr of @xmath188 for the rank-2-afms given by problem ( [ opt : maxminsdr ] ) are equivalent . for the rank-2-afms ,
a feasible solution for @xmath151 can be computed from the eigendecomposition of @xmath189 if @xmath190 as will be shown in the following .
let @xmath191 be a solution of problem ( [ opt : maxminsdrafms ] ) with @xmath192 and let @xmath193 with non - zero eigenvalues @xmath194 and @xmath195 and the respective eigenvectors @xmath196 and @xmath197 .
then , the solution @xmath198 of the relaxed problem is a feasible global solution of @xmath148 .
the decomposition of @xmath199 into two components is not unique and can be obtained from any vector pair @xmath200 and @xmath201 satisfying @xmath202 .
this is different from the rank-1-afms approach where a single beamforming vector @xmath200 is computed and where the sdr solution is only feasible if @xmath203 . in the proposed rank-2-afms
, the number of degrees of freedom is increased due to the introduction of two linearly independent weight vectors .
we remark that problem ( [ opt : maxminsdrafms ] ) still represents a non - convex problem , as the fractions of two linear terms in inequalities ( [ constraint_pr_sdr ] ) , ( [ constraint_pr_sdr ] ) , and ( [ opt : powerconstraintssdr ] ) represent non - convex functions .
moreover , the multiplication of the two linear terms in the snr constraints ( [ opt : maxminsdrafms ] ) results in a non - convex function .
one drawback of the sdr2d algorithm is its computational burden to solve an sdp in each iteration of the exhaustive 2d search .
another drawback is that @xmath204 in general . in this case , the corresponding optimal value @xmath181 is only a lower bound for @xmath151 ( within the grid search precision ) as @xmath205 is not feasible for problem @xmath148 since there exists no rank - two decomposition @xmath202 . for cases in which the sdr solution is not feasible for the original problem ,
randomization techniques have been applied in @xcite@xcite to generate feasible points that are suboptimal , in general . besides the sdr - based algorithms to compute vectors , recently ,
iterative algorithms have been developed which outperform the sdr - based randomization algorithms in terms of performance and computational complexity @xcite@xcite , @xcite .
the latter algorithms perform an inner approximation of the original non - convex problem and maintain the number of variables , whereas in the sdr technique , the number of variables is roughly squared . in the rest of this section
, we develop an iterative algorithm which computes the weight vector and adjusts the source power to maximize the minimum received snr at the destinations . in the max - min fairness beamforming problem @xmath151 , the left hand side of the constraints ( [ snr - constraint ] )
is the difference of @xmath206 and @xmath207
. as @xmath208 and @xmath209 are positive - semidefinite matrices , these functions are both convex since they consist of a convex quadratic form divided by a linear term and a constant divided by a linear term @xcite .
therefore , the left hand side of inequality ( [ snr - constraint ] ) is a difference of two convex ( dc ) functions and @xmath151 belongs to the class of dc programs @xcite@xcite . to solve @xmath151 approximately , we propose an iterative algorithm which generates a sequence of weight vectors @xmath210 , with iteration index @xmath211 . at iteration @xmath212
, the subsequent vector @xmath213 of @xmath210 is generated according to @xmath214 using the update vector @xmath215 as further specified below .
similarly , @xmath216 and @xmath217 are the optimization variables @xmath110 and @xmath218 at the @xmath219th iteration , respectively .
they are updated according to @xmath220 where @xmath221 and @xmath222 are the update variables as given below .
let us assume that @xmath223 , @xmath224 , and @xmath225 represent fixed feasible points of problem @xmath151 and let @xmath215 , @xmath221 , and @xmath226 denote optimization variables . if we replace @xmath227 in @xmath151 by @xmath228 , @xmath110 by @xmath229 , and @xmath149 by @xmath230 , the power constraints defined by the set @xmath231 remain convex . to derive a convex approximation of the constraints ( [ snr - constraint ] )
let us replace the concave part by its first order taylor approximation around @xmath232 , resulting in the convex constraint @xmath233 in @xcite , a similar approximation has been used for max - min fair beamforming in bi - directional relay networks .
the approximation made in inequality ( [ convexifiedconstraint ] ) is however tighter than that of @xcite in the sense that unlike the approach of @xcite , the convex quadratic - over - linear terms are not linearized . in @xcite ,
a linearization approach for max - min fair beamforming in the context of cognitive radio networks has been proposed .
the latter approach assumes a centralized system and therefore does not consider the problem of power allocation which arises in our distributed beamforming application . power allocation and beamforming optimization have been addressed in @xcite , where a cccp algorithm has been proposed to minimize the transmit power in a cooperative relay network .
an iterative algorithm for power minimization in a rank-2-afms has been proposed in our accompanying conference paper @xcite . in the referenced work , however , direct source - destination channels and power allocation have not been regarded .
[ satz]corollary let @xmath234 be feasible for @xmath151 .
the updated variables @xmath235 , obtained from a solution @xmath236 to problem ( [ opt : snr_maximizationconvexified ] ) , are feasible for @xmath151 and @xmath237 .
@xmath238 and consequently @xmath237 hold true as @xmath239 is feasible for problem ( [ opt : snr_maximizationconvexified ] ) since @xmath234 is feasible . from inequality ( [ innerapproxprop ] ) follows @xmath240 and , consequently , the snr constraints are fulfilled . as @xmath241 and @xmath242
are ensured according to problem ( [ opt : snr_maximizationconvexified ] ) , the feasibility of @xmath235 for @xmath151 is guaranteed .
the property @xmath243 ensures that the minimum snr increases or remains unchanged in each iteration . repeatedly solving problem ( [ opt : snr_maximizationconvexified ] ) for @xmath244 creates a monotonically non - decreasing sequence of minimum snr values @xmath245 with feasible weight vectors and a feasible transmit power .
the globally convergent max - min - cccp algorithm outlined in algorithm 1 starts at a random point and iterates until the relative progress @xmath246 falls below the threshold value @xmath247 + @xmath248 as the proposed algorithm is based on the linearization of the concave ( negative convex ) functions of a dc program , it belongs to the class of cccp algorithms @xcite .
note that in our algorithm , the problem ( [ opt : snr_maximizationconvexified2 ] ) is solved exactly . to reduce the computational cost
, it is possible to use an inaccurate solution @xcite .
a detailed description of an implementation is beyond the scope of this work . in our simulations ,
the subproblems that arise in every iteration of our proposed algorithm are solved exactly .
to evaluate the performance of the proposed scheme under realistic conditions , we consider a relay network , where the coefficients of the source - relay , relay - destination and source - destination channels model an urban micro scenario @xcite .
the system parameters are chosen according to the long term evolution ( lte ) standard for mobile communication @xcite .
the system is operated at a carrier frequency of @xmath249 mhz and we choose @xmath250 as the duration of one time slot .
the bandwidth is given by @xmath251 which corresponds to the bandwidth of a subcarrier in a multi - carrier lte system .
we further assume frequency flat fading channels .
we create the channel coefficients such that there is no shadow fading from the source to the relays but from the source and relays to the destinations .
the noise power is set to @xmath252 dbm .
the maximum transmit power values are chosen as @xmath125 , @xmath253 , @xmath254 , and @xmath255 , respectively . in the network ,
@xmath256 relays are placed at a distance of 250 meters around the source at equidistant angles .
the destinations are randomly distributed in between 600 and 800 meters around the source , see fig .
[ setup ] .
the source , the relays , and the destinations are placed at a height of 10 , 5 , and 1.5 meters , respectively .
we investigate the performance of the following transmission schemes , scenarios , and algorithms : the rank-2-afms combined with the max - min - cccp algorithm ( r2-max - min - cccp ) and the sdr2d algorithm ( r2-sdr2d ) .
furthermore , we consider the rank-1-afms combined with the cccp algorithm ( r1-max - min - cccp ) and the sdr2d algorithm ( r1-sdr2d ) .
moreover , we investigate also direct source - destination ( dsd ) communication , where the relays are not involved .
all results are compared with the theoretical upper bound ( sdr2d - ub ) obtained by the sdr2d algorithm , see subsection [ sr2 ] . for the sdp - feasibility problems , which are solved in the sdr2d algorithm to find a solution of problem ( [ opt : maxminsdrafms ] ) , and to solve the subproblems ( [ opt : snr_maximizationconvexified2 ] ) of the max - min - cccp algorithm , we have utilized the cvx interface for convex programming in a matlab environment @xcite . as the solver
, we have chosen mosek 7.0.0.103 under the default precision @xcite .
for the sdr2d algorithm , we search over 200 grid points to determine the power scaling factor @xmath110 and select @xmath257 as the precision in the bisection search to determine the optimum @xmath149 .
we chose @xmath258 also as the threshold value for the relative progress of the max - min - cccp algorithm .
we select @xmath259 in the problem ( [ opt : snr_maximizationconvexified2 ] ) that is solved in every iteration of the max - min - cccp algorithm . in the case
that the solution matrix to the optimization problem ( [ opt : maxminsdrafms ] ) obtained by the sdr2d algorithm is not feasible for @xmath151 , we apply the gaussian randomization procedure of @xcite . for the rank-1-afms , we select the best out of 200 random vectors , where each vector is properly scaled to meet the power constraints . for the rank-2-afms
, we create 200 random vector pairs .
each pair is properly scaled by solving a linear program using the function ` linprog.m ` of the matlab optimization toolbox @xcite . in our first example
, we examine the performance of all setups in terms of the average minimum achieved rate by solving @xmath151 .
the minimum achieved rate is given by @xmath260 ( the prefactor @xmath261 takes into account the time slots per communicated symbol ) for communications with relays and by @xmath262 for dsd , as one symbol per time slot can be communicated .
[ fig : firstexampleplot1 ] depicts the average minimum rate versus @xmath263 in the case that the direct source - destination channels are exploited for @xmath264 destinations . in our simulation results depicted in fig .
[ fig : firstexampleplot1b ] it is assumed that no direct source - destination channels exist .
both figures demonstrate that r2-max - min - cccp achieves near - optimum performance close to the theoretical upper bound .
the rank-1-afms is clearly outperformed by the rank-2-afms .
comparing fig . [
fig : firstexampleplot1 ] with fig .
[ fig : firstexampleplot1b ] , we observe that the performance improves significantly if the source - destination channels are exploited .
[ fig : firstexampleplot2 ] depicts the average minimum rate versus the number of destinations @xmath4 in the case that the direct source - destination channels are exploited for @xmath2655dbm . in fig .
[ fig : firstexampleplot2b ] the same setups are considered , assuming that no direct source - destination channels exist . both fig .
[ fig : firstexampleplot2 ] and fig .
[ fig : firstexampleplot2b ] demonstrate that r2-max - min - cccp achieves near - optimum performance close to the upper bound . for small @xmath4 ,
the sdr2d algorithm performs slightly better than the max - min - cccp algorithm due to the fact , that in most cases , the respective solution matrix has a rank smaller or equal to two .
as illustrated in table [ table1 ] , the rank of the sdr solution matrix increases with increasing @xmath4 .
this leads to suboptimal solutions generated by the randomization technique .
.average rank @xmath266 versus number of destinations @xmath4 .
[ cols="^,^,^,^,^,^ " , ] in our second example , we examine the computational aspects of the considered algorithms for @xmath264 destinations and @xmath26520dbm .
table [ table2 ] shows the average runtime in seconds of the different algorithms .
we observe that the max - min - cccp algorithm is more than ten times faster than the sdr2d algorithm .
[ fig : firstexampleplot3 ] depicts the number of iterations of the max - min - cccp algorithm for the rank-2-afms versus the minimum snr .
in this paper , a novel rank-2-afms for single - group multicasting has been proposed .
our scheme generalizes the rank - one multicasting scheme of the literature to a rank - two multicasting scheme and allows to incorporate the direct channel from the source to the destinations in the detection . to select the proper source power and to adjust the relay weights we propose an iterative algorithm to maximize the lowest snr at the destinations .
the simulation results demonstrate that the proposed rank-2-afms combined with the proposed iterative algorithm yields a performance close to the theoretical upper bound .
this work was supported by the seventh framework programme for research of the european commission under grant number adel-619647 .
z. ding , w. h. chin , and k. k. leung , `` distributed beamforming and power allocation for cooperative networks , '' _ ieee trans . wireless commun . , _ vol
. 7 , no . 5 , pp.18171822 , 2008 .
p. larsson , `` large - scale cooperative relaying network with optimal combining under aggregate relay power constraint , '' _ proc . of future telecom .
_ , beijing , china , pp . 166 - 170 , dec . 2003 .
v. havary - nassab , s. shahbazpanahi , a. grami , and z .- q .
luo , `` distributed beamforming for relay networks based on second - order statistics of the channel state information , '' _ ieee trans . signal process . _ ,
56 , pp . 43064316 , sept .
h. chen , a. b. gershman , and s. shahbazpanahi , `` filter - and - forward distributed beamforming in relay networks with frequency selective fading , '' _ ieee trans .
signal process .
_ , vol .
58 , pp .
1251 - 1262 , march 2010 . s. fazeli - dehkordy , s. shahbazpanahi , and s. gazor , `` multiple peer - to - peer communications using a network of relays , '' _ ieee trans . signal process .
_ , vol .
57 , pp . 30533062 , aug .
a. schad and m. pesavento , `` multiuser bi - directional communications in cooperative relay networks , '' _ proc .
ieee camsap11 _ , pp . 217220 , san juan , puerto rico , dec .
2011 .
a. abdelkader , m. pesavento , and a. b. gershman , `` orthogonalization techniques for single group multicasting in cooperative amplify - and - forward networks , '' _ proceedings of the fourth international workshop on computational advances in multi - sensor adaptive processing ( camsap2011 ) , _ san juan , puerto rico , pp . 225228 , december 2011 .
a. schad , h. chen , a. b. gershman , and s. shahbazpanahi , `` filter - and - forward peer - to - peer beamforming in relay networks with frequency selective channels , '' _ proceedings of the international conference on acoustics , speech , and signal processing ( icassp10 ) , _ dallas , tx , usa , pp .
32463249 march 2010 .
e. karipidis , n. d. sidiropoulos , and z .- q .
luo , quality of service and max - min fair transmit beamforming to multiple co - channel multicast groups , _ ieee trans .
signal process .
56 , pp .
12681279 , mar .
2008 .
s. ji , s. x. wu , a. m.
so , and w. k. ma , `` multi - group multicast beamforming in cognitive radio networks via rank - two transmit beamformed alamouti space - time coding , '' _ proc .
icassp13 , _ pp . 44094413 , 2013 .
a. abdelkader , a. b. gershman , and n. d. sidiropoulos , `` multiple - antenna multicasting using channel orthogonalization and local refinement , '' _ ieee trans .
signal process .
58 , pp . 39223927 , 2010 .
k. phan , t. le - ngoc , s. a. vorobyov , and c. tellambura , `` power allocation in wireless multi - user relay networks , '' _ ieee trans .
wireless commun .
, _ vol . 8 , no .
2535 - 2545 , 2009 .
h. al - shatri and t. weber , optimizing power allocation in interference channels using d.c .
programming , _ proceedings of the int .
modeling optimization mobile , ad hoc wireless netw .
, _ pp . 367373 , jun . 2010 .
k. eriksson , s. shi , n. vucic , m. schubert , and e. g. larsson , global optimal resource allocation for achieving maximum weighted sum rate , `` _ proc .
ieee global telecommun .
conf . , _ 2010 .
h. h. kha , h. d. tuan , and h. h. nguyen , `` fast global optimal power allocation in wireless networks by local d.c .
programming , '' _ ieee trans .
wireless commun .
11 , pp . 510515 , feb .
2012 . b. song , y .- h .
lin , and r. cruz , ' ' weighted max - min fair beamforming , power control , and scheduling for a miso downlink , `` _ ieee trans .
wireless commun .
, _ vol . 7 , pp . 464469 , feb .
y. cheng and m. pesavento , ' ' joint optimization of source power allocation and distributed relay beamforming in multiuser peer - to - peer relay networks , `` _ ieee trans . on signal process . , _ , vol .
60 , no . 6 , pp .
29622973 , jun . 2012 .
a. khabbazibasmenj , s. a. vorobyov , f. roemer , and m. haardt , ' ' polynomial - time dc ( potdc ) for sum - rate maximization in two - way af mimo relaying , _ proc .
ieee icassp12 , _ kyoto , japan , pp . 28892892 , mar .
a. khabbazibasmenj , f. roemer , s. a. vorobyov , and m. haardt , `` sum - rate maximization in two - way af mimo relaying : polynomial time solutions to a class of dc programming problems , '' _ ieee trans .
signal process .
10 , pp .
54785493 , 2012 . h. h. kha , h. d. tuan , h. h. nguyen , and t. t. pham , `` optimization of cooperative beamforming for sc - fdma multi - user multi - relay networks by tractable d.c .
programming , '' _ ieee trans . on signal process . , _ vol .
467479 , jan .
a. h. phan , h. d. tuan , and h. h. kha , `` d.c .
iterations for sinr maximin multicasting in cognitive radio , '' _ proc .
ieee icspcs12 , _ pp . 15 , dec . 2012
. g. dartmann , e. zandi , and g. ascheid , `` a modified levenberg - marquardt method for the bidirectional relay channel , '' available on http://arxiv.org/abs/1307.3121 , jul .
2013 .
luo and t .- h .
sdp relaxation of homogeneous quadratic optimization : approximation bounds and applications , _ convex opt . in signal process . and
d. p. palomar and y. c. eldar , eds . cambridge university press , ch .
4 , pp . 117162 , 2010 .
d. reynolds , x. wang , and h. v. poor , `` blind adaptive space - time multiuser detection with multiple transmitter and receiver antennas , '' _ ieee trans .
signal process .
12611276 , jun . 2002 .
s. zhou and g. b. giannakis , `` optimal transmitter eigen - beamforming and space - time block coding based on channel mean feedback , '' _ ieee trans .
signal process .
10 , pp . 25992613 , oct .
s. zhou and g. b. giannakis , `` optimal transmitter eigen - beamforming and space - time block coding based on channel correlations , '' _ ieee trans .
theory , _ vol .
49 , no . 7 , pp
. 16731690 , jul .
2003 .
h. a. le - thi and t. pham - dinh , `` large scale molecular optimization from distance matrix by a d.c .
optimization approach , '' _
siam j. optim .
77117 , jan .
l. t. h. an and p. d. tao the dc ( difference of convex functions ) programming and dca revisited with dc models of real world nonconvex optimization problems ,
annals of operations research , _ pp . 2346 , 2005 .
c. w. tan , m. chiang , and r. srikant , `` maximizing sum rate and minimizing mse on multiuser downlink : optimality , fast algorithms and equivalence via max - min sinr , '' _ ieee trans . on signal process . , _ vol .
12 , pp . 61276143 , 2011 .
d. cai , t. q. quek , c. w. tan , and s. h. low , `` max - min sinr coordinated multipoint downlink transmission duality and algorithms , '' _ ieee trans . on signal process .
10 , pp .
53845396 , 2012 . | in this paper , we propose a novel single - group multicasting relay beamforming scheme .
we assume a source that transmits common messages via multiple amplify - and - forward relays to multiple destinations . to increase the number of degrees of freedom in the beamforming design , the relays process two received signals jointly and transmit the alamouti space - time block code over two different beams .
furthermore , in contrast to the existing relay multicasting scheme of the literature , we take into account the direct links from the source to the destinations .
we aim to maximize the lowest received quality - of - service by choosing the proper relay weights and the ideal distribution of the power resources in the network . to solve the corresponding optimization problem
, we propose an iterative algorithm which solves sequences of convex approximations of the original non - convex optimization problem .
simulation results demonstrate significant performance improvements of the proposed methods as compared with the existing relay multicasting scheme of the literature and an algorithm based on the popular semidefinite relaxation technique .
amplify - and - forward , concave - convex programming , multicasting , rank - two beamforming , semidefinite relaxation . |
Pricey specialty drugs helped CVS Health cope with tobacco withdrawal and top analyst expectations in the second quarter.
FILE - This March 17, 2014 file photo shows a CVS/Pharmacy in Dormont, Pa. CVS Health reports quarterly financial results on Tuesday, Aug. 4, 2015. (AP Photo/Gene J. Puskar, File) (Associated Press)
But the nation's second-largest drugstore chain also narrowed its full-year earnings outlook and issued a third-quarter forecast that fell short of Wall Street's expectations.
Its stock fell 2.5 percent in trading Tuesday.
The Woonsocket, Rhode Island, company said that revenue from its biggest business, its pharmacy benefits management segment, jumped 12 percent in the second quarter to more than $24 billion, spurred in part by specialty drugs.
These complex medications treat certain forms of cancer and hepatitis C, among other conditions. They often represent treatment breakthroughs but can cost considerably more than other prescriptions. Use of these drugs is soaring, and health insurers, employers and other bill payers are relying more on companies like CVS Health to help restrain this growth.
Revenue from the company's retail drugstore segment inched up only 2 percent to $17.2 billion in part because sales from the front-end of its stores, or the area outside the pharmacy, plunged 7.8 percent, at established locations.
CVS Health runs 7,870 drugstores. The front-end figure from those stores would have been flat if CVS hadn't pulled tobacco products from its shelves nearly a year ago. The drugstore chain actually helped profitability by dumping thin-margin tobacco products, but its executives knew they would take a sales hit because smokers often grab other products when they stop in for their next pack.
The company dropped tobacco anyway because it is trying to burnish its image as a health care services provider. The drugstore chain runs nearly 1,000 walk-in clinics in its stores and has bulked up on healthy foods and the number of health care and beauty products it provides. It also plans to expand its reach into health care with a $1.9 billion deal to purchase the pharmacy and clinic business of the retail giant Target Corp.
CEO Larry Merlo told analysts that the Target deal helps expand his company's presence west of the Mississippi River "in a very, very capital efficient way," without having to build new stores.
Overall, CVS Health earnings rose 2 percent to $1.27 billion in the second quarter while revenue rose more than 7 percent to $37.17 billion.
Adjusted earnings totaled $1.22 per share, excluding costs tied to the Target deal and the company's pending $10 billion acquisition of pharmaceutical distributor Omnicare.
Analysts expected, on average, earnings of $1.20 per share on $37.16 billion in revenue, according to Zacks Investment Research.
CVS Health has scaled back the number of shares it intends to buy back this year, choosing instead to spend the money on its pending acquisitions. Partially because of that, it tightened its 2015 earnings forecast to $5.11 to $5.18 per share from a previous range of $5.08 to $5.19.
Analysts expect an average of $5.16 per share, according to FactSet.
For the current quarter, CVS Health expects adjusted earnings of $1.27 to $1.30 per share, while analysts forecast $1.37 per share.
Shares of Woonsocket, Rhode Island-based CVS Health dropped $2.86 to $109.96 on Tuesday. The stock hit an all-time high price of $113.65 last week and has increased 42 percent in the last 12 months. ||||| Sales at CVS Health are getting "smoked."
Last September, CVS became the first major pharmacy chain in America to stop selling cigarettes and other tobacco products in its stores. The drug store chain said it was the right thing to do -- even though it would hurt sales.
Now CVS (CVS) is detailing just how much the tobacco ban is impacting the company. While prescription sales continue to rise, general merchandise sales tumbled nearly 8% last quarter on a same-store basis.
CVS blamed the slump on the tobacco ban. The company said front-store sales would have been flat compared with the year before if they didn't make the change.
Conlumino analyst Stephen Ward believes that while the smoke ban was a "sensible move" for CVS's brand, it has come at a cost. "It has most certainly affected sales both directly, and indirectly, through the reduction in impulse purchases that tobacco customers made," Ward wrote in a report.
Related: Smoking is not cool. But cigarette stocks are hot
CVS stock dropped 3% on Tuesday after the company sounded cautious about the current quarter. The bar had been set very high as CVS shares have soared 40% over the past year and hit all-time highs just last week.
$2 billion hit to sales: The decline in front-store sales stands in stark contrast to the much larger prescription business. CVS said pharmacy sales jumped over 4% last quarter as Americans continue to ramp up health care spending.
The fact CVS is hurting a bit from its tobacco ban is not shocking. When CVS first announced the move in February 2014, it warned sales could take a $2 billion hit. That's just a fraction of the $139 billion in annual sales CVS generates, but it's not nothing.
"By eliminating the sale of cigarettes and tobacco products in our stores, we can make a difference in the health of all Americans," CVS CEO Larry Merlo said when the ban took effect last September.
To coincide with the smoke ban, CVS also changed its name from CVS Caremark to CVS Health.
Related: Tax the poor! States raise sales, cigarette taxes
CVS has room for improvement: CVS is clearly betting the move will improve its brand image, especially among the growing population of Americans who don't smoke. Now the company is focused on selling more profitable items like beauty products.
CVS said it once again gained market share in its health and beauty categories last quarter.
Ward, the Conlumino analyst, believes CVS can offset its tobacco challenges by taking a page out of Walgreen's (WBA) playbook. He said CVS needs to step up its game by improving the general shopping experience, especially in the beauty category.
"The trick for CVS is to match momentum in retail with the momentum it has built up in its pharmacy business," Ward wrote. | – CVS banned cigarettes from its stores last fall and last month showed it's sticking to its anti-tobacco stance, believing it's the right thing to do. The company's sales say otherwise. Though CVS' prescription sales climbed 4% in the second quarter, sales outside the pharmacy fell by almost 8%—a drop CVS attributes exclusively to its cigarette ban, reports CNNMoney. The company says it's focusing on health and beauty products, which are gaining market share, but the drug store isn't bleeding. Overall, earnings rose 2% to $1.27 billion while revenue jumped 7% to $37.17 billion, per the AP. |
At 53, Brad Pitt is more candid about his personal life than ever. In a new interview with the Associated Press, the actor reveals intimate details about the process of playing General McMahon, a fictional character based on the real-life General Stanley McChrystal. Pitt's forthcoming Netflix original movie, War Machine, is based on an original 2010 Rolling Stone story by the late journalist Michael Hastings.
The normally reclusive actor and newly single father of six also elaborates on his the flawed similarities he has the lifelong military man less than a month after revealing to GQ his struggles with alcoholism and depression. It appears that for Pitt, this role and the last year have been emotionally fraught for the actor (his split from Angelina Jolie made global headlines) as he approaches veteran status in Hollywood. Here are some things we learned about the conflicted actor and his highly-anticipated role in War Machine.
1. Pitt is aware of his God complex – and when it's out of control.
"Hubris is a trap and it's the trap of every great nation that has been number one for too long," Pitt says, inferring that military and political leaders can be reckless when making decisions from the safe distance of their own success. "You start believing your own stink," Pitt says. "Anytime I've gotten in trouble, it's because of my own hubris."
2. Pitt empathizes with General McChrystal.
"I feel for him," Pitt said. "He's a product of us. He [is] us." McChrystal, a four-star commander, retired from the U.S. Army shortly after resigning command. "We had no interest in impugning General McChrystal or any of his guys," said Pitt. "For me, the problem is more systematic ... [War Machine is] after something and we don't know where we’re going to end up. It's a delicate tightrope to walk."
3. Pitt is drawn to films that depict the complexities of power.
In 2014, Pitt visited the military medical center, Walter Reed and it inspired him to work on War Machine. "Those young men and women — who are absolutely heroic in a very harrowing situation — their lives are forever changed and so are their families. It just really made me question who is spending this currency of dedication. Who's writing the check? Who's making the order?"
4. Pitt's kids take his mind off of depression.
"I'm not suicidal or something," he said lightheartedly. "There's still much beauty in the world and a lot of love. And a lot of love to be given. It's all right. It's just life ... Kids are everything. Kids are your life," Pitt said of the children he shares with ex Jolie. "They're taking all the focus, as they should anyway."
5. Pitt is passionate about supporting U.S. troops.
"It's time to rethink what 'winning,' means," Pitt said in reference to President Trump's proposed initiative to send at least one thousands more American troops to Afghanistan. "Nothing that we've ever done has said that more troops are going to do anything but cause any more damage, more loss of life and limb ... supporting our troops is much more than giving them money and a pat on the back ... it's being responsible to how we use that ultimate dedication." ||||| FILE - In this Nov. 9, 2016 file photo, Brad Pitt arrives at the Los Angeles premiere of "Allied." Pitt stars in the new film, “War Machine,” in which he plays a slightly fictionalized version of Gen.... (Associated Press)
FILE - In this Nov. 9, 2016 file photo, Brad Pitt arrives at the Los Angeles premiere of "Allied." Pitt stars in the new film, “War Machine,” in which he plays a slightly fictionalized version of Gen.... (Associated Press)
In a recent interview, Brad Pitt spoke to The Associated Press about his new film, "War Machine," in which he plays a slightly fictionalized version of Gen. Stanley McChrystal; stepping back into the limelight for the first time since Angelina Jolie Pitt filed for divorce from him; and his future in movies. Here are excepted highlights:
___
ON ACKNOWLEDGING A DRINKING PROBLEM
I've got no secrets. I've got nothing to hide. We're human and I find the human condition very interesting. If we're not talking about it, then we're not getting better.
___
ON WHY HIS CHARACTER ISN'T NAMED GEN. STANLEY McCHRYSTAL
We had no interest in impugning General McChrystal or any of his guys. For me, the problem is more systematic. And the impetus for me was a visit to Walter Reed. Although those young men and women who are absolutely heroic in a very harrowing situation, their lives are forever changed and so are their families. I just really made me question who is spending this currency of dedication. Who's writing the check? Who's making the order?
___
ON SENDING MORE TROOPS TO AFGHANISTAN
Nothing that we've ever done has said that more troops are going to do anything but cause any more damage, more loss of life and limb. So why are we not questioning this? It seems time for some kind of hearing. I don't trust a governmental I hearing. It needs to come from the people. We talk a lot about supporting our troops but I think supporting our troops is much more than giving them money and a pat on the back. I think it's being responsible to how we use that ultimate dedication. I guess it's this idea of American exceptionalism that I question the definition of. We are exceptional is so many ways. But it doesn't mean we can just throw might at any problem. We're sending them into a culture that we don't understand.
___
ON NETFLIX AND 'WAR MACHINE'
It wouldn't have gotten made without Netflix. The reality for the studios is it just doesn't make sense for them on paper. They can take the gamble up to $35 million on a risky film. And then otherwise they focus on big tent-poles which seem to be safer and make the big payoffs. It's not their fault in any way. The numbers just don't run for them. Now with Netflix and other entities like Netflix, it becomes a whole new delivery system for these kinds of films I prefer to gamble on. For us, it's opened up a whole new world of possibilities. I'll stick work with studios, I'll always do that, at least I think so, as long as they're around. Because they are still films that deserve to have the big-screen, cultural experience.
___
ON BEST-PICTURE WINNER 'MOONLIGHT'
That's what I'm most proud of. That's Barry Jenkins' — and the cast and crew —that's their vision, but to be able to help get it over the hill — a difficult movie, a challenging film like that, that feels good. That feels really good. I like that job. | – In a new interview with the AP, Brad Pitt acknowledges he's been in some dark places lately—of his drinking problem, he says, "I've got no secrets. I've got nothing to hide"—but he insists things aren't that dark. "I'm not suicidal or something," he says, per Rolling Stone. "There's still much beauty in the world and a lot of love. And a lot of love to be given. It's all right. It's just life." He adds that his children help to keep depression at bay: "Kids are everything. Kids are your life. They're taking all the focus, as they should anyway." |
Here’s a sentence I never thought I’d type: a candidate running for president had to issue a statement insisting that he was not talking about a female journalist on her period, but instead blood coming out of her nose.
K then.
Yes, on CNN last night Donald Trump continued to rip Megyn Kelly for having the audacity to ask him tough questions at a presidential debate. And he actually, seriously said, ““There was blood coming out of her eyes, blood coming out of her… wherever.”
But the comment that politics Twitter kind of blew up over and got Trump disinvited from the RedState gathering today wasn’t what you thought, you sickos.
First, Trump tweeted these out:
So many "politically correct" fools in our country. We have to all get back to work and stop wasting time and energy on nonsense! — Donald J. Trump (@realDonaldTrump) August 8, 2015
Re Megyn Kelly quote: "you could see there was blood coming out of her eyes, blood coming out of her wherever" (NOSE). Just got on w/thought — Donald J. Trump (@realDonaldTrump) August 8, 2015
.@redstate I miss you all, and thanks for all of your support. Political correctness is killing our country. "weakness." — Donald J. Trump (@realDonaldTrump) August 8, 2015
Oh, and Trump’s full statement on the matter is even better. Here’s the highlight:
Mr. Trump made Megyn Kelly look really bad––she was a mess with her anger and totally caught off guard. Mr. Trump said “blood was coming out of her eyes and whatever” meaning nose, but wanted to move on to more important topics. Only a deviant would think anything else.
He also trashed Erick Erickson for disinviting him in the ongoing Trump cycle of 1) being honored to go somewhere or be with someone, 2) a person involved with said thing disparaging him in some way, and 3) Trump throwing a temper tantrum, doing a complete 180 and calling this person a loser, and claiming he never wanted to go in the first place.
And once again, I would just like to emphasize that we have someone running for president who had to clarify which orifice on a female journalist he believed blood was coming out of.
[image via screengrab]
— —
Follow Josh Feldman on Twitter: @feldmaniac
Have a tip we should know? [email protected] ||||| Donald Trump is once again pushing the limit, bringing Megyn Kelly’s anatomy into a feud that had already opened him to charges of sexism — and the risk of losing support among the Fox News anchor’s rabid following.
After a day of escalating hostility, Trump took his attacks on Kelly to the next level on Friday night, apparently insinuating that the moderator had been menstruating when she questioned him during Thursday’s first Republican debate.
Story Continued Below
“You could see there was blood coming out of her eyes, blood coming out of her — wherever,” he told anchor Don Lemon during an appearance on CNN.
The crudeness of the comment sparked an immediate flurry of rebukes, including from RedState.com’s Erick Erickson, who revoked an invitation for Trump to speak at his Saturday conference on the grounds that it showed he wasn’t a “legitimate” candidate.
On Saturday morning, Trump appeared to tweet a clarification of his previous remark: “Re Megyn Kelly quote: ‘you could see there was blood coming out of her eyes, blood coming out of her wherever’ (NOSE). Just got on w/thought.”
He also released a statement lashing Erickson and the decision to exclude him. “… not only is Erick a total loser, he has a history of supporting establishment losers in failed campaigns so it is an honor to be uninvited from his event. Mr. Trump is an outsider and does not fit his agenda.”
Nevertheless, Trump was a hot topic of conversation at the RedState event. Speaking there, Republican 2016 candidate Mike Huckabee said, “The Republican Party is not engaged in a war on women, the Republican Party is not engaged in saying things about Megyn Kelly,” he said. “One individual is.”
Carly Fiorina, the only female Republican presidential candidate in the race, took to Twitter to condemn Trump.
“Mr. Trump. There. Is. No. Excuse,” she wrote. “I stand with @megynkelly.”
In a tweet sent Saturday, Gov. Scott Walker also repeated the “stand with @megynkelly” line, adding, “There’s no excuse for Trump’s comments.”
Gov. John Kasich tweeted a statement, saying, “Everyone deserves respect and dignity, whether they agree with you or not. You don’t tear people down just because they disagree with you or stand up to you or question you.”
In a statement, Sen. Lindsey Graham said, “I applaud Erik [sic] Erickson for doing the right thing when he disinvited Donald Trump from a gathering of Republican activists. As a party, we are better to risk losing without Donald Trump than trying to win with him. Enough already with Mr. Trump.”
Also in a statement, Sen. Rand Paul called Trump’s statements “inappropriate and offensive.”
And then there was the nature of the target itself. Unlike undocumented immigrants, John McCain or Rosie O’Donnell, the Fox News anchor enjoys a huge following among the network’s viewers, who happen to make up the core of the Republican primary electorate. So picking a fight with Kelly — as Trump did when he chided her during a tough debate question about insults he’s lobbed at women, dissed her in the spin room, and tweeted his complaints about her — carries risks that Trump’s other feuds do not.
So does making such a gendered attack on a journalist at a time when his party is battling the perception that it’s waging a “war on women.”
But if Trump world is worried about taking on the only person who might be more popular with the Republican base than their boss is right now, they’re not showing it.
Trump’s campaign manager, Corey Lewandowski, maintained that the mogul’s willingness to take on Kelly makes him the kind of equal-opportunity brawler Republicans will need next fall.
“If the Democratic nominee is going to be Hillary Clinton, then you would want a strong person to stand up to make America great again,” he said earlier on Friday, before the “blood” comment.
Trump political adviser Roger Stone sounded a slightly more cautious note. “Certainly Fox reaches a disproportionate number of Republican primary voters,” he said, adding that as of Friday afternoon he hadn’t yet sorted out his thoughts about the matter.
Stone said Trump was satisfied with his debate performance when the two conferred last night. And Stone offered a positive assessment, if not a ringing endorsement, of his boss’s performance. “He held his own. He was fine. He made all his key points.”
But Trump and his associates clearly had a bone to pick after a debate in which Fox’s moderators, especially Kelly, trained some of their toughest questions on the controversial front-runner. Trump’s annoyance showed during the debate when he told her, “I’ve been very nice to you, although I could probably maybe not be, based on the way you have treated me” in response to a question about his name-calling of women (which he joked he’d only ever done to his longtime Twitter nemesis O’Donnell). After the debate, Trump said Kelly “behaved very nasty to me.”
It only devolved from there.
In the early morning hours on Friday, his Twitter account tweeted that Kelly was “not very good or professional”and retweeted anti-Kelly tweets from supporters, including one calling her a “bimbo.”
Trump’s deputy and surrogate, Michael Cohen, retweeted a tweet from a Trump fan (@hawaiiluvstrump) after the debate that included the hashtag “boycottmegynkelly” and the message “we can gut her.”
Cohen told POLITICO that he does not believe the tweet implied any sort of physical violence but did not back down from his beef with Kelly. “It is interesting to note that the only attacks against Mr. Trump last night came from the moderators,” Cohen said in a statement. “It appeared to all viewers that it was a coordinated effort. Megyn Kelly clearly tried the hardest and failed as Mr. Trump has been deemed the winner of last night’s debate by multiple polls and media outlets.”
Because he works for Trump Enterprises, rather than the campaign, Cohen said that his being in conflict with Kelly shouldn’t affect Trump’s political fortunes. “It doesn’t matter if I am or I’m not,” he said.
Monmouth University pollster Patrick Murray told POLITICO after Thursday’s debate that Trump’s back-and-forth with Kelly, in which he dismissed her question about insults lobbed at women as “political correctness,” could end up hurting him with female Republican primary voters, a group he is currently winning, though by a smaller margin than he’s winning men.
And despite the negative reaction of a focus group convened for Fox News by Republican messaging guru Frank Luntz to Trump’s interactions with Kelly, as well as his refusal to pledge to support the eventual Republican nominee, there were indications that his trademark Trump bluster continued to play well with important Republican constituencies.
(Trump tweeted that Luntz “is a low class slob who came to my office looking for consulting work and I had zero interest. Now he picks anti-Trump panels!” In a statement, Luntz told POLITICO, “I really enjoy him. I respect him, I respect his success as a businessman, and I respect his ability to tap into the genuine frustrations of the American people. His performance last night was Trump being Trump — and so are his attacks today.” An aide to Luntz said the messaging guru did not believe Trump himself was responsible for the “bimbo” retweet about Kelly: “We talked about that and agreed that one of his staffers had to have tweeted that she’s a bimbo. Even he wouldn’t use that word about her.”)
Attendees who gathered to watch the debate from the RedState summit of conservative activists in Atlanta cheered Trump’s performance and a highly unscientific reader poll on the Drudge Report, the news aggregation site beloved by conservatives, gave Trump an overwhelming victory in the debate, with 45 percent of respondents — more than 250,000 people as of Friday afternoon — saying he won, compared with 14 percent for the second-place Ted Cruz.
Katie Glueck contributed to this report. | – Donald Trump is getting hammered over his latest Megyn Kelly slam, but he now insists it's not as bad as everyone thinks. What Trump said: "You could see there was blood coming out of her eyes. Blood coming out of her wherever." In a tweet and statement, Trump says the "wherever" refers to her nose, with the statement adding that "only a deviant would think anything else," reports Mediaite. Meanwhile, Politico points out that Kelly has a large following on Fox News, and it rounds up some of the backlash brewing against Trump, including shots from his fellow candidates: Carly Fiorina: “Mr. Trump. There. Is. No. Excuse. ... I stand with @megynkelly.” John Kasich: “Everyone deserves respect and dignity, whether they agree with you or not. You don’t tear people down just because they disagree with you or stand up to you or question you." Scott Walker: "There's no excuse for Trump's comments." Lindsey Graham: “I applaud Erik [sic] Erickson for doing the right thing when he disinvited Donald Trump from a gathering of Republican activists. As a party, we are better to risk losing without Donald Trump than trying to win with him. Enough already with Mr. Trump.” |
Dear family and friends. Robin and I decided to start this page for our conjoined twins that we are having. Although we are learning everyday about them what we can tell you is this...They are thriving and growing well, and seem to be very active right now. They have two heads . But seem to be sharing one body. With one set of arms and legs. As for internally we still don't fully understand what is conjoined. But we are still learning more as the twins grow. Each doctors visit is some little piece of new information. We would also like to say that we are a strong Christian family. We believe that this is a gift from God no Matter what the out come is, and we want to safe guard the lives of our twins. So we will go full term. We love our babies and will go to ends of what we need to so that our babies survive. ||||| They survived a risky birth, but the conjoined Hamby twins’ heart was simply not strong enough. Asa and Eli died Friday afternoon, one day after their birth, according to their parents.
In a video posted late Friday on Facebook, Michael and Robin Hamby said their sons fought hard before they were taken off ventilators at Children’s Healthcare of Atlanta at Egleston. The twins died around 5 p.m., Michael Hamby said.
“Robin got over there and we got to hold them, love on them and sing to them,” Michael said. “I miss them, even though I have only got to be with them 24 hours. Feels like a lifetime. I don’t wish this hurt on anybody.”
At 7:32 a.m. Thursday, Robin Hamby delivered the twins at Northside Hospital by C-section. Asa and Eli arrived breathing on their own and crying, their parents said. But the boys’ health deteriorated Friday, and Robin was taken by ambulance from Northside to Egleston to be with the twins.
The Hambys, of Ladonia, Ala., have said they relied on their faith throughout the pregnancy, and remained hopeful the boys could beat the odds. Born at 37 weeks, Asa and Eli shared a torso, arms and legs.
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Conjoined twins occur once every 200,000 live births, but between 40 and 60 percent arrive stillborn, according to the University of Maryland Medical Center. Being joined side-by-side made the Hamby twins even rarer, a condition known as dicephalic parapagus.
The Hamby’s chronicled the pregnancy and the boys’ birth on Facebook, posting frequent video updates. Within hours of their births, the twins made national headlines, along with photo from the delivery room showing Robin smiling at the boys’ tiny faces.
Later Thursday, Asa and Eli were transported to Egleston for further evaluation, their parents said. The boys were holding their own until they began experiencing heart problems Friday, Michael Hamby said.
“The doctors and the nurses at Egleston were awesome,” Robin Hamby said. “They explained everything they did. They did everything they could possibly do for them.”
Though their lives were short, Asa and Eli touched many lives and won’t be forgotten, their parents said.
“They looked so much like Michael,” Robin said. “They were just the cutest little things. So, so sweet.”
In addition to their parents, Asa and Eli are survived by their 22-month-old sister, Selah, and numerous other relatives. Funeral arrangements have not been made. | – A pair of conjoined twins in Atlanta have died one day after their birth, reports the Atlanta Journal-Constitution. Dad Michael Hamby announced the news via Facebook in a video last night. “Robin got over there and we got to hold them, love on them and sing to them,” he said. “I miss them, even though I have only got to be with them 24 hours. Feels like a lifetime. I don’t wish this hurt on anybody.” Asa and Eli shared a torso, arms, and legs, and because they also shared a heart, their chances of survival were low. Still, the boys had defied the odds simply by being born—about half of conjoined twins are stillborn, and most such twins are girls, notes WXIA. “They looked so much like Michael,” said Robin. “They were just the cutest little things. So, so sweet.” The Hambys, who live in Ladonia, Ala., have a 22-month-old daughter. |
with the possibility to perform transport measurements on nano- down to atomic - scale junctions using mechanically - controllable break - junctions @xcite or scanning tunneling microscopy @xcite various fundamental questions on electron transport as well as practical problems concerning device functionality have arisen . with shrinking system size
the junctions have become considerably smaller than the mean free path of a transmitted electron , reaching the ballistic transport regime . in this regime
various effects such as the geometric arrangement of the atoms , the chemical composition , the magnetic order , vibrations , correlation effects , or the magnetic anisotropy can play an important role due to the reduced coordination number of the participating atoms . in the context of spin - dependent transport , for example , there is a strong interest in understanding how the spin - valve effect scales to systems of atomic- or molecular - scale @xcite . in nanoscale junctions ,
new transport effects can also arise such as the ballistic anisotropic magneto - resistance ( bamr)@xcite . in order to successfully address such issues a theoretical description needs to properly take into account the electronic structure of the system which is typically obtained by first - principles methods based on density functional theory .
the central experimental quantity is the measured current versus bias voltage ( i - v - curve ) or at small bias voltages the conductance .
are transmitted through a scattering region with a transmission probability @xmath2 from the left lead to the right lead .
the blue planes separate the leads from the scattering region .
while the semi - infinite leads resemble the electronic structure of a periodic system , the scattering region includes the scatterer as well as the lead - scatterer contact region.,scaledwidth=40.0% ] the theoretical method most frequently applied to describe quantum transport in such systems is the landauer - bttiker approach in which the junction is divided into a central scattering region and two leads in thermal equilibrium with contact reservoirs , fig .
[ fig : tgeo ] , resulting in the famous landauer conductance formula@xcite .
basically two different groups of techniques have been developed to solve the transport problem : wave - function and green s function ( gf ) based methods which are equivalent in case of non - interacting charge carriers@xcite . among the wave function based methods the transmission through such a quasi one - dimensional ( 1d ) system can be calculated by means of the transfer matrix method@xcite , solving the lippmann - schwinger equation@xcite , or by wave function matching@xcite .
the gf methods are usually based on keldysh , kadanoff and baym s non - equilibrium green s functions ( negf)@xcite . beyond the standard non - interacting electron approach ,
there has been work incorporating e.g. inelastic scattering on vibrations@xcite or treating correlation effects through self - energies@xcite .
an alternative way of calculating quantum transport is by using the kubo approach as formulated by baranger and stone@xcite , relating the current to the dynamical polarization@xcite .
based on these three general approaches all codes differ in the way the electronic structure is described . in the first implementations based on density functional theory ( dft ) ,
the electrodes were treated as jellium which were coupled to the scattering region @xcite .
large systems up to devices can be described using semi - empirical tight - binding methods for the electronic structure @xcite while approaches using dft for both the description of the electrodes via self - energies and the scattering region promise the highest accuracy@xcite . among these implementations
various dft methods have been applied .
transport codes based on green s functions rely on a localized basis set limiting this approach to basis sets of numerical orbitals such as gaussians@xcite , localized orbitals@xcite , or wavelets@xcite .
the application of flexible and accurate plane - wave dft methods for transport calculations is usually realized in connection with the scattering approach for the conductance @xcite .
alternatively , the efficient gf method for the transport calculation can be used if the extended states in the plane - wave expansion are mapped onto maximally localized wannier functions@xcite ( mlwfs ) .
this approach combines plane - wave calculations with the use of a minimal basis set suitable for quantum transport calculations@xcite .
when one is dealing with low - dimensional systems and subtle band structure effects such as spin - orbit coupling the accuracy of electronic structure description becomes crucial .
therefore , the application of a highly precise all - electron full - potential linearized augmented plane - wave code is desirable . to our knowledge
no such dft transport scheme has been reported and only a few codes allow to incorporate spin - orbit coupling@xcite . in this paper
we present a method to calculate transport through 1d nanoscale structures following the landauer - bttiker approach .
the underlying electronic structure of the studied system is obtained from dft within the 1d version@xcite of the full - potential linearized augmented plane - wave method ( flapw ) , as implemented within the fleur code.@xcite the 1d - flapw method is specifically tailored to treat 1d structures avoiding supercell calculations : the periodicity is explicitly taken into account only along the nanostructure s axis ( @xmath3-axis in the following ) , while the wavefunctions in the vacuum surrounding the system are forced to obey an exponential decay in - plane.@xcite since the flapw wavefunctions are intrinsically delocalized in real space we perform a mapping of the electronic structure of the system onto a set of localized wannier functions ( wfs ) , which allows to solve the transport problem in real space efficiently .
the wfs obtained from the flapw calculation ( flapw wfs)@xcite provide a minimal localized basis set which describes the _ ab initio _ electronic bands within a certain energy window with high accuracy and allows to efficiently compute the non - equilibrium green s function ( negf ) of the system needed to determine its transmission function @xmath2 .
we use and compare two different sets of wfs , namely , the maximally - localized wannier functions ( mlwfs),@xcite which are uniquely defined by fulfilling the condition of maximal localization in real space , and the so - called first - shot wannier functions ( fswfs),@xcite being much easier to obtain computationally and although non - unique , still capable of describing the transport properties of a system correctly in many cases . a special approximation we include in our transport scheme is the so - called `` locking technique '' , which allows to use separately calculated leads and scattering regions and to combine those into one quantum transport calculation , achieving an accurate treatment of leads and scattering region at reduced computational cost . as a first application we have calculated the electronic structure and the ballistic transport properties of a non - magnetic pt monowire with a single stretched bond in the middle of the chain which acts as a source of scattering . for this rather simple system
we demonstrate the quality of our mlwfs and fswfs , the locking technique to obtain the hamiltonian of the open system , and show the possibility of decomposing the transmission function in terms of orbital symmetry .
we further investigate the influence of spin - orbit - coupling ( soc ) on the transmission of the pt wire .
we find a substantial change of the conductance of one quantum of conductance at the fermi level for a perfect wire due to the strength of soc in @xmath4-transition metals such as pt . in order to include the effect of large spin - polarization we have chosen a ferromagnetic co monowire with a single stretched bond , a prototypical magnetic system , and calculate the magnetoresistance from the conductance in a parallel and antiparallel alignment of the co electrodes .
we obtain a rapid decrease of the magnetoresistance with the separation between the two co monowires which is due to the fast decay of transmission from the highly spin - polarized localized states of @xmath5 and @xmath6symmetry .
finally , we have studied scattering from a single impurity atom in a monowire due to soc .
we have chosen two configurations : ( i ) a non - magnetic pt atom in a ferromagnetic co wire and ( ii ) a magnetic co atom in a non - magnetic pt wire . in both cases ,
we have compared the conductance obtained in the scalar - relativistic approximation and upon including soc .
we find a strong influence of soc on the transmission due to the induced splitting of bands .
in addition , the conductance depends sensitively on the magnetization direction in the system being either along the wire axis or perpendicular to it .
while in case ( ii ) the resulting ballistic anisotropic magnetoresistance displays values of 7 % due to spin - orbit interaction mediated scattering into both spin - channels for the symmetry breaking out - of - chain quantization axis , in case ( i ) the values of bamr reach as much as 100% , reflecting the giant value of the ballistic anisotropic magnetoresistance of the pure co chain .
the paper is organized as follows . in sec .
[ sec : method ] we describe the theoretical basis of our approach to calculate the conductance and introduce the key quantities . in particular , the green s function method is applied to obtain the transmission function and the conductance .
the mapping of the electronic structure from the flapw method to a localized basis set is accomplished via wannier functions .
the construction of the hamiltonian for the open quantum system is described . in sec .
[ sec : results ] we present the first applications of our new transport code to several typical systems of interest .
we begin with the conductance for a non - magnetic pt wire with a single broken bond and study the transmission as a function of bond length and upon including spin - orbit coupling .
then the magnetoresistance of co monowires with a single elongated bond is discussed .
finally , the effect of spin - orbit scattering is illustrated by two examples : a pt monowire with a single magnetic co atom and a co monowire with a single pt atom .
a summary and conclusions are given in sec .
[ sec : summary ] .
we describe the transport properties of the system within the landauer - bttiker approach , dividing it into three different regions : two semi - infinite leads ( left , @xmath7 , and right , @xmath8 ) and the scattering region ( @xmath9 ) , which includes the actual scatterer as well as the lead - scatterer contact region , in which the effect of the scatterer on the properties of the leads ideally decays such that their electronic structure can be considered perfect and unperturbed inside the @xmath7 and @xmath8 regions . assuming that the interaction between the left and right leads
can be neglected the tight - binding hamiltonian of our system corresponding to such a structural division has the following form : @xmath10 where @xmath11 is the semi - infinite hamiltonian of the left / right lead , while @xmath12 describes the coupling of the scattering region to the leads and @xmath13 is the hamiltonian of the scattering region . due to the semi - infiniteness of the leads the dimension of the hamiltonian , eq .
( [ index1 ] ) , is infinite , which presents a conceptual computational problem .
an efficient method to deal with that , applicable to any system of the type depicted in fig . 1 , which can be described with a real - space tight - binding hamiltonian of the type of eq . ( 1 ) , has been developed.@xcite this method is based on the non - equilibrium green s function ( negf ) formalism , which treats the scattering region and the semi - infinite leads on equal footing , describes extractions , re - injections and excitations of electrons in the system and solves the problem of the semi - infinite leads by introducing finite - dimensional self - energies @xmath14 which include the true lead s effect on the scattering process . within the negf formalism
the system is described by means of the retarded green s function : @xmath15^{-1},\ ] ] where @xmath16 denotes the unity matrix of the dimension of @xmath17 . by neglecting at first the coupling of the leads to the scattering region and regarding just the first few layers of the leads which are actually interacting with the scattering region , it is possible to replace the leads green s function by their surface green s functions @xmath18.@xcite this can be derived by rewriting the lead s hamiltonian in a block diagonal form using square matrices @xmath19 and @xmath20 of the same dimension as the surface green s function : @xmath21 based on this description of the leads
, the surface green s function @xmath18 can be determined iteratively starting from @xmath22}_{l / r}(e)=[(e+i\epsilon)\mathbf i_{l / r}-\mathbf{h}_{l / r}]^{-1},\ ] ] with @xmath23}_{l / r}(e)$ ] being a square matrix with the dimension of interacting orbitals at the leads surfaces . the expression ( [ surfacegf ] )
can be converged to the surface green s function by recursively incorporating the inter - layer interaction sub - matrices @xmath20 with an efficient recursive scheme.@xcite by reintroducing the coupling of the scattering region to the leads as a perturbation to the system , the green s function @xmath24 of the scattering region can be obtained from the unperturbed green s function of the scattering region by the dyson equation @xmath25^{-1}.\ ] ] the whole effect of the semi - infinite leads on the conductor can be then expressed by the leads self - energies @xmath26 , which incorporate the surface green s function @xmath18 and the now finite - sized coupling matrices @xmath12 , adapted to the size of the surface green s functions : @xmath27 the self - energies are obviously finite - sized matrices of the dimension of @xmath28 .
the self - energies are related to the broadening matrices @xmath29 : @xmath30,\ ] ] which describe the effect of broadening of the states in the scattering region caused by the presence of the leads as well as the transfer rates of charge carriers from the leads into the scattering region .
the incorporation of the non - hermitian self - energies changes the nature of the description from the static steady - state picture of the open system to a dynamic transport scheme , responding to an incoming charge carrier with the energy @xmath31 .
based on these quantities the transmission function @xmath2 , describing the probability of charge carriers originating from one lead to be transmitted to the other lead , can be expressed in the following way : @xmath32.\ ] ] the current , being a natural observable in a quantum transport measurement , can then be calculated from the landauer formula : @xmath33,\ ] ] where @xmath34 are the occupation functions of the leads .
the expression for the conductance then reads : @xmath35 in case of perfect transmission , @xmath36 , this results in the well - known conductance quantum @xmath37 for a single , spin - degenerate band .
the aim of the approach introduced here is to combine the accuracy and speed of state - of - the - art dft electronic structure calculations based on the one - dimensional version of the flapw method as implemented in the ` fleur ` code,@xcite and the capability of the negf - formalism described above to treat the whole transport problem in an efficient way . especially for transport phenomena driven by magnetism or spin - orbit coupling ( soc )
a precise description of the electronic structure is necessary .
typical systems currently under scrutiny in experiment include geometries with a low coordination number which favors magnetism and gives rise to strong soc due to unquenching of the orbital moment.@xcite the major problem in combining an lapw or a plane - wave based electronic structure method with the real - space transport schemes lies in the fact that normally several hundreds of delocalized basis functions per atom are used in such codes in order to achieve the required accuracy .
in our implementation we use the machinery of wannier functions ( wfs ) , constructed out of flapw wavefunctions,@xcite which proved to be an efficient connection between the two , conceptually independent , computational methods .
the main advantage in such a `` link '' can be attributed to two factors : ( i ) using the gauge freedom of wannier functions they can be enforced to be rather localized in real space , and ( ii ) an `` exact '' mapping of the _ ab initio _
hamiltonian onto a tight - binding representation with wfs as a localized orthonormal basis set can be achieved.@xcite having at hand the converged bloch wavefunctions @xmath38 for a set of bands @xmath39 calculated on a uniform mesh of @xmath40 @xmath41-points , the orthonormal set of wannier functions can be obtained via the following transformation@xcite : @xmath42 where the number of wfs @xmath43 should be smaller than or equal to @xmath44 .
the gauge freedom of wfs manifests itself in that the matrices @xmath45 ( in the following , @xmath46-matrices ) can in principle be arbitrary . in the case
when @xmath47 and the group of bands from which we are extracting the wfs from is isolated from other bands , the @xmath46-matrices are unitary at each @xmath41-point . imposing
the constraint of maximal localization of wfs in real space determines the set of @xmath46-matrices up to a common global phase , and the corresponding set of wfs is called the maximally - localized wannier functions ( mlwfs).@xcite for the whole procedure of maximal localization we use the ` wannier90 ` code.@xcite the criterion for the localization of wfs is the smallness of their spread.@xcite the process of the spread minimization constitutes an iterative process at the end of which the @xmath46-matrices corresponding to the mlwfs are obtained .
this minimization procedure requires as a starting point a certain initial guess for the set of the mlwfs . in order to construct this set
, one chooses certain localized orbitals @xmath48 , which are projected onto the subspace of wavefunctions @xmath49 : @xmath50 and then orthonormalized : @xmath51 with the overlap matrix @xmath52 , after which the starting wfs can be generated : @xmath53 this orthonormal set of wannier orbitals we will call in the following the first - shot wfs ( fswfs ) .
the fswfs are not unique in the sense that they strongly depend on the choice of the localized orbitals @xmath54 . in many cases , however , especially when mlwfs are well - localized around atoms as in the case of certain @xmath55-orbitals in most of transition - metals and transition - metal oxides,@xcite
the difference between the fswfs , originated from the localized @xmath55-orbitals , and the corresponding mlwfs is rather small .
this allows to spare the computational time needed for the minimization of the spread , and immediately construct , e.g. , the needed effective hamiltonians in terms of fswfs .
examples , when there is a substantial difference between the fswfs and mlwfs , include orbitals for which the centers of the wfs do not coincide with the centers of atoms . in the following
we will analyze in detail the difference in transport properties calculated with mlwfs and fswfs , both in the case when there is little difference between the two sets of wfs and when the difference between them is significant . in terms of the flapw basis functions
the hamiltonian can be written as @xmath56 while in terms of wfs the equivalent expression is [ hamiltonian ] @xmath57 where @xmath58 are the hopping integrals between the @xmath59 and @xmath60 wannier orbitals at sites @xmath61 and @xmath62 . by substituting eq .
( [ ham - bf ] ) into eq .
( [ ham - hopp ] ) we find : @xmath63 thus the real - space representation of the hamiltonian in terms of localized wannier functions can be derived from the knowledge of the eigenvalues and wavefunctions of the system . in respect to wfs , for efficient evaluation of eqn .
( [ hoppingelements ] ) only knowledge of the @xmath46-matrices is required .
@xcite the correspondence in the eigenspectrum between the constructed hamiltonian in terms of wfs and the hamiltonian in terms of eigenfunctions is _ exact _ on the grid of @xmath41-points used for the wfs construction , and for this reason the set of wfs is sometimes referred to as _
basis set , or , the tight - binding basis set of _ ab initio _ accuracy .
( this is only valid within the frozen inner window of disentangled systems @xcite ) . according to eqns .
( [ surfacegf ] ) to ( [ transmission ] ) , in order to calculate the transmission function only the @xmath19 , @xmath20 , @xmath12 and @xmath28 parts of the hamiltonian are needed .
given a fleur electronic structure calculation it is necessary to construct these parts of the hamiltonian from the resulting wfs hopping elements ( eqn .
[ hoppingelements ] ) .
we focus on the correct treatment of the scattering region ( see fig .
( [ fig : locking ] ) ) . and the interaction matrices
@xmath20 between two principal layers .
the scattering region is described by the hamiltonian @xmath28 and coupled to the leads by the interaction matrices @xmath64 , extracted from a supercell calculation .
the supercell has to be large enough to reproduce the lead - scatterer contact with desired accuracy , usually larger than sketched here.,scaledwidth=40.0% ] after determination of the atoms belonging to the scattering region , it is possible to write down the preliminary result for @xmath28 , based on eqn .
( [ hoppingelements ] ) , @xmath65 where @xmath66 and @xmath67 determine the atom and @xmath59 and @xmath68 the inherent wfs . due to the real - space decay of the wfs the corresponding hopping matrix elements @xmath69 also decay as the distance in real space between the wannier functions @xmath70 is increasing . for an efficient use of the real - space wfs hamiltonian within the transport scheme described above it
is necessary to keep its matrix elements only up to a certain number of nearest neighbors ( n.n . ) , setting the rest of the elements to zero . as a result of this procedure
the hamiltonian matrix becomes sparse , which allows for a computationally inexpensive treatment . for a given number of n.n .
, the _ quality _ of the sparse hamiltonian depends on the degree of localization of the wfs . here ,
by quality of the hamiltonian we mean the correspondence between its eigenvalue spectrum to that obtained from _ ab initio _ , or , in the sense of transport , how well - converged the transmission function @xmath2 is with respect to the number of n.n . in this respect , in the following we compare and analyze the results obtained with mlwfs and fswfs , which display different localization properties . one way to deal with the exponential decay in eqn .
( [ h_s ] ) would be to manually eliminate all matrix elements beyond a certain n.n .. we propose here a flexible scheme , minimizing this effort by dividing the scattering region into principal layers @xmath71 , @xmath72 and interaction matrices @xmath73 between neighboring layers : @xmath74 the sub - matrices are set up as eqn .
( [ h_s ] ) . for the on - site matrices , @xmath71 ,
the indices @xmath66 and @xmath67 are restricted to atoms from the given layer @xmath75 . for the interaction matrices @xmath73 the index @xmath66 is restricted to atoms from layer @xmath75 and the index @xmath67 to atoms of the neigboring layer @xmath76 .. while still capable of describing the system in terms of eqn .
( [ h_s ] ) ( with @xmath77 ) , the principal layers can optimally contain the number of atoms effectively interacting , reducing the number of neglected hoppings .
typically these principal layers are chosen to contain the same number of atoms as the principal layers of the leads resulting in the same aproximation in terms of n.n .
for both regions and thereby avoids inconsistencies in the transort calculations .
furthermore this scheme allows possible future extensions , such as e.g. a combination of separately calculated scatterers into one scattering region . knowing the hamiltonian @xmath28 of the scattering region , it is necessary to determine the coupling of the scattering region to the leads . since the hamiltonians of both leads and the scattering region are partitioned into principal layers ( see eqn .
( [ leadh ] ) and eqn .
( [ matrix_h_s ] ) ) , we only need to find the hopping elements between the adjacent layers .
interactions between non - neighboring layers are neglected by construction .
the non - zero elements of @xmath78 can now be extracted from the supercell calculation ( see fig . [
fig : locking ] ) as @xmath79 where the index @xmath66 runs over the atoms of the principal layer @xmath80 of @xmath28 and the index @xmath67 runs over the principal layer of the left lead .
@xmath81 can be constructed analogously . to prevent a significant systematical error ,
it is necessary to make the original supercell large enough to screen an unphysical inter - unit cell interaction .
finally , only the hamiltonians for the leads are missing .
ideally , the calculated unit cell should be large enough in order to reproduce the properties of the bulk material far away from the scatterer and thus , the lead hamiltonian can be extracted directly from the supercell calculations in a straight - forward manner .
owing to the significant computational burden , it is , however , hardly feasible to apply this approach to large and complex systems while keeping at the same time the accuracy necessary to capture the main energy scales of the phenomena studied .
the technique we use to overcome this problem , particularly prominent for the flapw method with its complicated basis set , is discussed in the following section . up to now
no comments have been made concerning the way magnetic systems and the effect of soc are treated . for magnetic systems
the majority and minority spin channels can be regarded separately , resulting in two independent calculations of the transmission function for spin - up and spin - down channels . in the presence of soc the whole methodology holds considering that both spin channels have to be treated together , thus resulting in twice the number of wfs used simultaneously to solve the transport problem .
the accurate treatment of the leads within the approach described above constitutes a considerable challenge .
taken from a self - consistent supercell electronic structure calculation as they are , the sub - matrices @xmath19 and @xmath20 will contain deviations from `` ideal''-lead matrix elements in a large vicinity of the scattering region . while some of these deviations are definitely physical in their origin due to a large decay length of 1d charge perturbations caused by the scatterer , the rest of them will be a spurious artefact of the supercell approach owing to the fact that the leads as calculated are not intrinsically semi - infinite .
this presents a considerable problem in particular when the leads have to be described with hamiltonians beyond the @xmath82 n.n . in this case to describe the semi - infinite leads precisely one would have to go to huge supercells so that the @xmath83 atoms in the supercell describing the lead would be exactly identical , with @xmath83 being the number of atoms in one principal layer ( see eqn .
( [ leadh ] ) ) .
we found that condition impossible to achieve for non - trivial systems .
another approach of constructing a lead beyond @xmath82 n.n .
artificially from the outmost atoms of the scattering region by periodically expanding it is flawed , too , due to the unknown unperturbed hopping matrix elements beyond @xmath82 n.n .. this is a serious problem , since the lead has to be described as precisely as possible to prevent a huge systematic error .
the basic idea to work around this problem is as simple as effective , namely matching the supercell hopping matrix elements to those of the true leads . within this
so - called `` locking '' technique , the leads are replaced by the perfect wires , providing correct self - energies and fermi levels of the true infinite periodic system , while the supercell size is chosen large enough to describe the lead - scatterer interface region sufficiently well , see fig .
[ fig : locking ] . in our transport approach
this means that different parts of the hamiltonian ( eqs .
( [ h_s ] ) and ( [ h_ls ] ) ) are extracted from two different dft calculations @xcite : the @xmath28 and @xmath12 coupling matrices are taken from the supercell calculation describing the scattering region , while the @xmath19 and @xmath20 sub - matrices ( needed in eqn .
( [ leadh ] ) ) are taken from the calculation for the perfect leads . @xmath19 and
@xmath20 can be determined similar to the principal layers @xmath71 and @xmath73 of @xmath28 ( eqns .
( [ h_s ] ) and ( [ matrix_h_s ] ) ) with the principal layer @xmath75 and the neighboring identical layer @xmath76 . to achieve matching fermi levels for lead and supercell calculations , it is additionally necessary to align the diagonal elements of the matrices @xmath19 ( eqn .
[ leadh ] ) and @xmath28 ( eqn .
[ matrix_h_s ] ) .
in the following sections we present a few instructive applications which illustrate the quality and possibilities of our flapw - wf based approach to obtain the conductance in one - dimensional magnetic systems within the landauer coherent transport method . in this section
, we focus on pt monowires which possess a single stretched bond that acts as a scattering potential for electrons . starting from the construction of the wfs and the tight - binding like hamiltonian
, we discuss the transmission function and its decomposition in eigenchannels .
our results further demonstrate the applicability of the locking technique described above .
finally , we include spin - orbit coupling in our calculations and show that the obtained transmission compares well with that calculated based on the scattering approach in combination with a pseudopotential method for the electronic structure@xcite . in order to calculate the conductance within the approach described in the previous sections we need to perform two separate dft calculations and subsequent wannierizations for every system : ( i ) a calculation for the semi - infinite electrode and ( ii ) a supercell calculation which includes the scattering center . from the latter , we determine the hopping matrix elements for the coupling to the leads . for the monowires considered in the following the hamiltonian of the semi - infinite electrode can be obtained from a calculation with one atom in the unit cell . for the scattering region , we have used supercells of different size as described in the computational details section in the appendix . before proceeding into the discussion of the transmission
, it is insightful to examine the localization properties of typical mlwfs and fswfs which we use for our transport calculations . while the unique mlwfs are rather well localized in real space , this is not necessarily the case for the fswfs , which strongly depend on the choice of the initial orbitals .
if the trial orbitals do not differ very much from the final result of the localization procedure the difference in spread between the mlwfs and the fswfs can be small . for transition - metal monowires
this is the case for the localized @xmath55-orbitals of @xmath85 symmetry ( @xmath86 and @xmath87 ) and of @xmath88 symmetry ( @xmath0 and @xmath1 ) .
taking an infinite periodic pt monoatomic chain with an interatomic spacing of 4.48 bohr as an example we calculate the spreads of the @xmath85 and @xmath88 mlwfs to be 3.70 bohr@xmath89 and 2.22 bohr@xmath89 , respectively .
the calculated spreads of the fswfs , constructed with solutions of the radial equation for the actual potential obtained from the first - principles calculation @xcite , are indistinguishable from the former .
the situation is completely different , however , for the fswfs constructed from the @xmath90- and @xmath91-like trial orbitals . in this case
the difference in spread between the resulting fswfs and the @xmath92-like mlwfs is remarkable .
while values of 2.89 and 6.20 bohr@xmath89 are obtained for the spread of @xmath91-like and @xmath90-like mlwfs , respectively , the corresponding values constitute 55.78 and 319.44 bohr@xmath89 for fswfs .
this indicates that the mlwfs differ significantly from the trial functions .
the reason for the rather large spreads of the fswfs can be found by comparing the fswf centers to the mlwfs centers . in case of mlwfs
the centers of the @xmath90-like wfs are located between the atoms , forming covalent bridge - like wannier functions .
such wannier functions are hard to construct directly from the atom - centered trial orbitals .
the fswfs constructed from the @xmath90- and @xmath91-like trial orbitals are , in contrast , located on the atoms , which causes a significantly larger spread @xcite . in principle , all hamiltonians obtained by mapping to wannier functions which include the hopping matrix elements between all wfs are equivalent .
this equivalency is lifted , however , if we consider only a limited number of neighbors to set up our tight - binding like hamiltonian . in fig .
[ fig : mlwfs_vs_fswfs_bs ] , the pt monowire bandstructure based on the flapw - dft calculation and slater - koster interpolations of the bandstructure based on mlwfs and fswfs are compared .
the trial orbitals for the fswfs are in this case chosen to be @xmath90- and @xmath55-like orbitals and centered on each atom . while in first n.n .
approximation the interpolated bandstructures differ between the mlwfs and fswfs approach , especially in the bandwidth of the more delocalized @xmath90 and @xmath91 orbitals , already in second n.n .
approximation both wfs basis sets describe the flapw - dft bandstructure equally well . by further increasing the considered number of neighbors to third n.n .
approximation , the accuracy of the description increases with respect to the @xmath90-bandwidth . however , the most important part with respect to transport properties is the bandstructure in the vicinity of the fermi level , which does not improve significantly . for the more localized @xmath0 , @xmath1 , @xmath86 and @xmath87 orbitals even the first n.n .
description is sufficient as seen in the bandstructure and also from the hopping matrix elements as seen in fig .
[ fig : mlwfs_vs_fswfs_hop ] . as a function of the n.n . for a pt monowire on a logarithmic scale .
the hoppings were calculated both with mlwfs ( open red symbols ) and fswfs ( closed black symbols ) for ( a ) @xmath90 and @xmath91 orbitals , and for ( b ) @xmath0 , @xmath1 , @xmath86 and @xmath87 orbitals .
, scaledwidth=35.0% ] at least for a rather simple system such as a perfect pt monowire , the localization procedure used to obtain mlwfs obviously does not influence the localized @xmath55-orbitals mentioned above . only the @xmath90 and @xmath91 states are affected , but the decay of the hopping integrals is exponential irrespective of the description ( fswfs or mlwfs ) . for systems more complicated than a pt monowire , the initial choice of trial orbitals may not be straightforward .
in such a case the localization procedure to obtain mlwfs significantly improves the accuracy of the calculation , while for simpler systems where more intuitive choices of orbitals can be made fswfs may be sufficient .
an example that both descriptions indeed lead to very similar results with respect to transport calculations is shown below for a pt monowire with one elongated bond . note that the fswfs make the construction of the transport hamiltonian , as discussed in section [ subsection : construction ] , much more simple , expecially for systems with a more complex electronic structure .
bohr using mlwfs within the nearest - neighbor approximation for the transport hamiltonian and ( a ) a 6 atom supercell and ( b ) a 12 atom supercell for the flapw calculation of the scattering region .
the semi - infinite leads have been described using the supercell calculation ( solid lines ) or using the locking technique ( dashed lines ) , i.e. , using perfect pt monowires for the leads .
, scaledwidth=35.0% ] with the aid of the pt monowire dft calculations and the construction of wfs and the hamiltonian from the hopping matrix elements it is now possible to calculate the conductance based on the green s function method .
we start by considering the quality of the locking technique . for this purpose
, we compare the results for a rather small 6 atom supercell calculation for the scattering region with a single elongated bond of @xmath93 bohr and a calculation performed in a 12 atom supercell .
the quantum conductance obtained for both cases without applying the locking - technique , i.e. , constructing the semi - infinite leads from the supercell calculation , is similar but differs in key details such as a sharp peak just below the fermi energy ( compare fig .
[ fig : nl_vs_l](a ) and ( b ) ) .
if we replace the hamiltonian for the leads by the one constructed from the mlwfs of a periodic pt - monowire the result changes as follows : while the conductance based on the 12 atom supercell calculation is nearly independent on how the lead was constructed , the result for the 6 atom calculation improves significantly upon using the locking technique and is almost indistinguishable from the calculation in the larger 12 atom supercell .
this demonstrates the applicability and quality of the locking technique which allows to save a considerable amount of computational effort to calculate the ballistic transport properties .
while the previous test has been performed within the nearest - neighbor approximation for the tight - binding like hamiltonian we now determine how accurate the calculated transmission function is with respect to the number of neighbors included . in fig .
[ fig:1-to-3](a ) the transmission functions , calculated in first , second , and third nearest - neighbor approximation and based on the 12 atom supercell for the scattering region with one stretched bond of @xmath93 bohr are presented .
the main effect which we observe upon including more neighbors is a widening of the energy range in which the conductance is non - zero as expected from the comparison of the bandstructure obtained in the different approximations , cf .
[ fig : mlwfs_vs_fswfs_bs ] .
the conductance in the vicinity of the fermi energy which is dominated by the localized @xmath55-states is well described already using second nearest - neighbors . using only the first nearest - neighbor on the other hand results in an offset of the conductance above the fermi energy which originates from a shift of the upper edge of the @xmath85 band as seen in the bandstructure .
therefore , we use at least the second nearest - neighbor approximation in the following to construct the tight - binding like hamiltonian .
bohr based on a 12 atom supercell calculation using the first , second , and third nearest - neighbor approximation for the construction of the transport hamiltonian from mlwfs and the locking technique to attach the leads .
( b ) decomposition of the total conductance ( solid line ) for the second nearest - neighbor approximation into the contributions of the @xmath94 ( @xmath92 ) ( solid red line ) , the @xmath95 ( @xmath85 ) ( dotted blue line ) and the @xmath96 ( @xmath88 ) ( dashed - dotted orange line ) channels.,scaledwidth=35.0% ] in order to understand which states contribute to the transmission we can decompose it with respect to the orbital symmetry of the wannier functions .
the individual transmission channels can be derived from eqn .
( [ transmission ] ) , by performing the trace operation only over wfs within the same symmetry group . in fig .
[ fig:1-to-3](b ) we see that @xmath90-@xmath91 states provide an almost perfectly conducting channel in a large energy range . only far below the fermi energy the value drops below @xmath97 and in the vicinity of the fermi energy it rises due to the availability of two @xmath92 bands , cf .
the bandstructure in fig .
[ fig : mlwfs_vs_fswfs_bs ] . the more localized @xmath95 states , on the other hand , possess a much smaller transmission and their contribution is localized in a small energy window .
this effect is even more dramatic for the @xmath96 orbitals , which show a very small overlap and hopping matrix elements leading to a sharp peak in the conductance . finally , we turn to the conductance of the pt monowire as a function of the stretched bond length shown in fig . [
fig : fst_vs_mlt ] . for the conductance of a perfect pt wire , we find the expected step - function shape in which each band contributes with one conductance quantum @xmath98 per spin within its bandwidth . upon increasing the length of a single bond in the wire ,
the overlap between the wannier orbitals across the gap decreases , especially for the more localized @xmath55-orbitals , and as a result the transmission drops dramatically . accordingly
, only the contribution from the @xmath90-@xmath91 states survives at large gaps while the sharp peak originating from the @xmath96 orbitals vanishes above @xmath99 bohr .
another important result of this calculation is that the hamiltonians obtained with mlwfs and fswfs provide nearly the same results , i.e. , the radial solutions of the flapw potential are evidently a reasonable choice as fswfs trial orbitals . .
the second nearest - neighbor approximation has been used for the transport hamiltonian .
the wfs and hopping matrix elements have been constructed from a 12 atom supercell and the leads were described by the locking technique .
curves are shown for mlwfs ( solid lines ) and fswfs ( dotted lines ) for @xmath100 , @xmath101 , @xmath102 , @xmath103 , @xmath104 and @xmath105 bohr ( from left to right).,scaledwidth=35.0% ] for heavy transition metals such as pt spin - orbit coupling plays an important role and has a significant impact on the electronic structure .
evidently , the transport properties should be equally affected .
a suitable method to describe the quantum conductance in such systems has to be capable of treating soc .
the effect of soc on the electronic structure , namely the coupling of the spin quantum number @xmath106 and angular momentum quantum number @xmath107 to the total angular momentum quantum number @xmath108 can be seen in fig .
[ fig : pt_soc_bs ] . compared to the scalar - relativistic calculation , in which soc is neglected ,
[ fig : mlwfs_vs_fswfs_bs ] , the bandstructure including soc changes significantly , fig .
[ fig : pt_soc_bs ] . in the chain geometry , the states are eigenfunctions to the @xmath3-component ( chain axis ) of the total angular momentum and we can classify the bands by the absolute value of @xmath109 as shown in fig . [
fig : pt_soc_bs ] ( a ) .
thereby , spin - orbit coupling leads to several avoided crossings in the bandstructure , e.g. of a @xmath94 and @xmath110-band around @xmath111 ev below the fermi level .
with respect to the scalar - relativistic bandstructure , we also observe a significant shift of the @xmath0 and @xmath1-bands towards the fermi energy .
as this band touches the fermi energy at @xmath112 the conductance jumps from @xmath113 in the scalar - relativistic case to a value of @xmath114 .
this finding already demonstrates the importance of soc for quantum transport calculations in such systems .
( dotted line ) , @xmath115 ( dashed line ) and @xmath116 ( solid line ) n.n .
, scaledwidth=40.0% ] including spin - orbit coupling calculated within a 6 atom supercell and using locking to semi - infinite pt leads based on the hamiltonian obtained from mlwfs in second nearest - neighbor approximation . from left to right : one bond stretched by @xmath100 , @xmath101 , @xmath102 , @xmath103 , @xmath104 and @xmath105 bohr .
, scaledwidth=35.0% ] the general form of the conductance in presence of soc changes significantly , too , due to the lifted degeneracies of bands with different @xmath117-values ( see fig . [ fig : pt_soc_bs ] ( b ) ) .
while the conductance at the fermi level is enhanced upon taking soc into account , the degeneracy of the @xmath0 and @xmath1-bands in the sr case leads to a higher conductance of @xmath118 below the fermi energy .
another key difference due to soc is the larger number of steps which appear in the conductance as a result of the anti - crossings in the bandstructure , in particular , in the energy range of @xmath111 ev to @xmath80 ev below the fermi level . in fig .
[ fig : pt_soc_t ] , we also display the evolution of the conductance upon stretching a single bond in the pt monowire .
similar to the sr case , we observe a rapid decrease of the conductance due to more localized @xmath55-orbitals .
however , due to the spin - orbit split bands there is a more pronounced peak structure in the conductance . in particular , we find a sharp peak just below the fermi energy which decays more slowly than in the sr calculation where it is located slightly lower in energy .
our calculations of the conductance are in good agreement with those obtained based on fully relativistic ultrasoft pseudopotentials and a scattering approach to obtain the conductance @xcite .
another important aspect in transport through nanoscale structures is the effect of spin - polarization and magnetic order . due to the reduced coordination number in nanostructures the density of states
is enhanced and according to the stoner model the tendency towards magnetism increases .
the reduced symmetry also results in a much larger magneto - crystalline anisotropy energy ( mae ) as the orbital moments become more significant .
e.g. freestanding and suspended chains of @xmath120- and @xmath4-transition - metals become magnetic and show giant values of the mae @xcite and the effect of colossal magnetic anisotropy has been reported @xcite . here
, we demonstrate that our method allows spin - polarized transport calculations .
we consider a simple model system , i.e. , a co monowire with a single stretched bond and allow a parallel and antiparallel alignment of the magnetization on the two co electrodes .
we calculate the conductance in both configurations and determine the magnetoresistance as a function of electrode separation .
the calculations in the antiferromagnetic configuration of the co monowire can also be compared to calculations by smogunov _
based on the scattering approach and pseudopotentials @xcite .
bohr calculated within flapw ( big dots ) and fswfs in @xmath121 ( dotted lines ) , @xmath115 ( dashed lines ) and @xmath116 n.n .
( solid lines ) approximation .
, scaledwidth=40.0% ] , in ( a ) parallel and in ( b ) antiparallel alignment of the magnetization .
a supercell of 16 atoms has been used for the scattering region and the transport hamiltonian was constructed based on fswfs in the second n.n . approximation . from left to right : gap of @xmath100 , @xmath122 , @xmath123 , @xmath124 and @xmath125 bohr .
upper and lower part of the plots show the spin - up and spin - down transmission channel , respectively .
, scaledwidth=45.0% ] compared to the non - magnetic pt bandstructure , the co chain exhibits a smaller band width due to more localized @xmath126-states , and a large exchange splitting ( fig .
[ fig : co_dos ] ) .
the exchange splitting leads to a net spin moment in the unit cell of 2.13@xmath127 .
a good overall accuracy in reproducing this bandstructure based on fswfs can be achieved if we go up to third nearest - neighbor hoppings . for the @xmath55-bands and the @xmath90-@xmath91 bands around the fermi energy
even the second nearest - neighbor approximation is sufficient . from the spin - split bandstructure
we expect a larger conductance in the parallel magnetization alignment due to the overlap between minority bands of @xmath85 and @xmath88 symmetry .
this notion is confirmed by the calculated conductance in the two magnetic configurations as a function of gap size as shown in fig .
[ fig : co_p ] . at the fermi level , we observe majority and minority spin conductances of @xmath128 and @xmath129 , respectively , for a perfect ferromagnetic co monowire ( see fig [ fig : co_p ] ( a ) ) . as the central bond is stretched the minority conductance drops rapidly because it originates from the more localized @xmath130- and @xmath131-states .
the majority conductance , on the other hand , is due to @xmath94-states and decays much more slowly . in the antiparallel alignment ( fig [ fig : co_p ] ( b ) )
, the conductance is the same in both spin channels .
there is only a small energy window between @xmath80 ev and @xmath132 ev below the fermi energy in which the @xmath130- and @xmath131-states overlap and at the fermi energy , the conductance is dominated by the @xmath94-states .
the conductance in the antiparallel alignment can be interpreted as an envelope of spin - up and spin - down transmission functions calculated for the parallel case as an electron can only be transmitted if there are states of the same symmetry in both spin channels .
the conductance in this configuration is also in good agreement with that reported by smogunov _
_ using a scattering approach and pseudopotentials @xcite .
based on the obtained quantum conductance at the fermi level we can calculate the ballistic magnetoresistance ( bmr ) upon stretching the central bond .
the bmr is defined as the difference between the conductance in the parallel and antiparallel alignment divided by the antiparallel conductance : @xmath133 fig .
[ fig : co_tmr ] displays the evolution of the spin - resolved conductance as a function of gap size for the two magnetic configurations .
as noted above , the parallel alignment is characterized by a rapidly decreasing minority spin conductance and a nearly constant majority spin contribution .
however , the minority spin conductance dominates until the end of the bond length range which we considered . in the antiparallel alignment
, the conductance of both spin channels is the same and behaves similar to the majority spin channel of the parallel alignment as it is due to @xmath94-states . from this analysis of the channel contribution we can understand the fast drop of the bmr found upon stretching ( inset of fig . [ fig : co_tmr ] ) of the central bond in the monowire . for the antiparallel ( red filled circles , solid line ) and the parallel ( green solid squares , solid line ) alignment of two ferromagnetic co monowires as a function of separation . for the parallel case the decomposition into majority ( blue open squares , dashed line ) and minority ( orange open squares , dotted line ) contributions
the inset shows the bmr ratio as a function of separation .
, scaledwidth=35.0% ]
in the previous sections we applied our quantum transport code to systems with strong spin - orbit coupling ( pt monowires ) and high spin - polarization ( co monowires ) . in the following
we combine the two effects in order to study the scattering at impurities in the presence of spin - orbit coupling .
we consider two types of model systems . we begin with non - magnetic pt monowire with a single co impurity atom and calculate the dependence of the conductance on the magnetization direction of the co atom .
an analysis of the orbital decomposed transmission function allows us to study the influence of soc on the different channels .
we find that band mixing due to soc has a pronounced influence , in particular , on the contribution from the band with @xmath88-symmetry . as a second system
, we consider a ferromagnetic co monowire with a single pt impurity atom and compute the conductance for the two magnetization directions of the co wire , either along the direction of the wire or perpendicular to it . from our calculations of the conductance including spin - orbit coupling we can also determine the ballistic anisotropic magnetoresistance ( bamr ) , i.e. , the difference of transmission between a magnetization parallel to the current and perpendicular to the current . while our systems are idealized they can be seen as prototypical for experiments which may be performed for example by scanning tunneling microscopy in the contact regime @xcite or in break junctions @xcite .
scalar - relativistic calculations , i.e. , neglecting soc , in a similar geometry for a ni impurity in a au monowire have been performed before@xcite .
we begin our investigation of spin - orbit scattering at an impurity by considering a single co atom in a pt monowire .
this is the simpler of the two systems due to the nonmagnetic pt leads .
we have already discussed the conductance of pt monowires with and without spin - orbit coupling in section [ sec : results ] . here , we study the conductance for different magnetization directions of the co impurity atom in order to calculate the so - called ballistic anisotropic magnetoresistance ( bamr ) , which has been predicted based on dft calculations @xcite and
was experimentally reported for co break junctions @xcite .
before we discuss the calculated conductance , we focus on the magnetic properties of our system . from the dft calculations in the scalar - relativistic case we obtain spin moments of 2.46@xmath127 for the co atom which induces pt spin moment of a magnitude of up to 0.27@xmath127 , oscillating in sign as a function of separation from the co atom .
a similar behavior was found upon including soc in the calculations for both magnetization directions , with a co spin moment of about 2.49@xmath127 . including spin - orbit interaction in the calculations gives rise to finite values of the orbital moments of the atoms , which play an important role in determining the energetically favorable direction of the magnetization.@xcite in our system , the orbital moments of the co atoms are much larger than those of the surrounding pt atoms , and constitute 0.12@xmath127 and 0.19@xmath127 for the magnetization along the chain axis ( @xmath3 ) and perpendicular to it ( @xmath134 ) , respectively .
accordingly,@xcite this results in an energetical preference of the in - chain magnetization direction over the out - of - chain direction , with a calculated magneto - crystalline anisotropy energy ( mae ) of @xmath135 mev per magnetic atom .
we now turn to the calculated conductance presented in the three top panels of fig .
[ fig : pt - co - pt_g_vs_dos_incl_soc ] for the scalar - relativistic case and upon including spin - orbit coupling for the two different magnetization directions . for reference the orbitally decomposed conductance and the density of states ( dos ) of a perfect pt monowire
is given in each of the three plots and in the panels below , respectively .
as a general trend , the introduction of a co scatterer results in a non - perfect matching between the spin - split co @xmath126-states and the more delocalized pt @xmath4-states ( cf . the bandstructures in figs .
[ fig : mlwfs_vs_fswfs_bs ] and [ fig : co_dos ] ) . in all three cases , a clear signature of the exchange - split co @xmath85-band can be observed in the overall conductance , most clearly visible in the spin- and orbital decomposition . as expected ,
the @xmath88-bands are shifted towards the fermi energy upon including spin - orbit coupling , but due to the energetical mismatch between the co and pt @xmath88-bands in sr and for both magnetization directions with soc , this band plays only a minor role in the overall conductance .
nevertheless , there is a considerable difference between the conductance at the fermi level in the scalar - relativistic case , @xmath136 , and upon including soc either for @xmath3-magnetization , @xmath137 , or @xmath134-magnetization , @xmath138 , as seen in fig .
[ fig : bamr ] . the main reason for this large difference between sr and soc conductances
can be found in the @xmath92 band of sr pt . in this channel the dos
is reduced compared to the soc cases at the fermi energy at the pt n.n .
atoms and there is a corresponding reduction of the conductance , as shown in fig . [
fig : pt - co - pt_g_vs_dos_incl_soc ] .
the difference of @xmath139 between the two different magnetization directions can be found in the larger minority @xmath85-state contribution of the parallel aligned axis . here , the sr and the parallel soc case behave similarly .
the dos for @xmath85 majority states is small at the fermi level , the majority state conductance is reduced in comparison to the minority state contribution , as a result of the exchange splitting of the co scatterer .
interestingly this is not the case for the @xmath134 direction of the magnetization , for which majority and minority channels contribute equally to the total conductance .
this effect also occurs for the @xmath85 minority channel between @xmath140 ev and @xmath141 ev as well as for the @xmath88 conductance just below the fermi energy .
while the very sharp spin - up @xmath88-peak in the sr transmission at @xmath1420.7 ev can be traced back to a small spin - up @xmath88 peak in the dos of the central co atom at this energy , this is not the case for the mentioned regions in case of the @xmath134-magnetization , for which no majority @xmath85 and @xmath88 states are present at the scatterer .
the origin of this effect is the broken cylindrical symmetry when the magnetization points out of chain .
this broken symmetry allows for a hybridization between @xmath92 and @xmath85 bands with @xmath143 , as well as between @xmath85 and @xmath88 bands with @xmath144 . as a result an incident electron of @xmath143 ( @xmath145
) can be transmitted into a state with @xmath143 ( @xmath145 ) of different orbital character and spin .
this channel for scattering is less effective than the spin - conserving scattering for the in - chain magnetization , resulting in a larger conductance in this case .
the changes in the ballistic conductance due to ballistic spin - scattering are important for the ballistic anisotropic magnetoresistance ( bamr ) .
the bamr is defined analogously to the anisotropic magnetoresistance as : @xmath146 where @xmath147 and @xmath148 are the conductances for the magnetization along the wire axis and perpendicular to it , respectively @xcite .
the difference of @xmath149 at the fermi level in favor of the parallel quantization axis due to ballistic spin - scattering results in a small bamr of the order of 7@xmath150 , see inset of fig . [
fig : bamr ] . a small shift between the @xmath88 contributions due to a small spin - splitting of those bands for the pt atom neighboring the co scatterer ( cf
[ fig : pt - co - pt_g_vs_dos_incl_soc ] ) results in an oscillatory behaviour of the bamr when the energy is varied from @xmath151 ev to @xmath152 ev , with bamr ranging from @xmath14220% to 25% . .
, scaledwidth=35.0% ] in the previous example , we have seen that the transmission can be affected by ballistic spin - scattering , leading to a small bamr below the fermi energy and bamr oscillations due to a shift in the @xmath88 orbitals of the pt atom next to the co scatterer . in this section
, we consider a non - magnetic scatterer , a pt atom , in a ferromagnetic co monowire .
we find that this situation leads to an enhanced bamr close to the fermi level , which is crossed by the @xmath88-band . in this case
we do not expect strong ballistic spin - scattering because of the magnetic leads , since large exchange splitting prohibits scattering between the states with opposite spin .
first we consider the junction in the scalar - relativistic approximation in order to understand the main impact of the pt scatterer on the conductance .
while co atoms in the leads carry a magnetic moment of @xmath153 , the co atoms in the vicinity of the pt atom have moments in the range of [email protected]@xmath127 , and the pt atom itself is spin - polarized with a considerable moment of @xmath154 . as can be seen in the orbitally decomposed conductance , fig .
[ fig : co - pt - co_sr](a - c ) , the reduction of the transmission due to the pt impurity atom is relatively small compared to the perfect ferromagnetic co monowire .
we can understand this general behavior from the fact that the pt @xmath4-bands possess a broader bandwidth and thereby allow transmission in the entire regime of the spin - polarized co @xmath126 bands ( cf .
[ fig : mlwfs_vs_fswfs_bs ] and fig .
[ fig : co_dos ] ) . in the @xmath94-channel ,
the reduction of the transmission is similarly small for the majority and minority spin contributions due to the energetic alignment of the spin - split states of the co wire with the states of the pt impurity . in the majority spin channel ,
a significant reduction of transmission only occurs in a region from @xmath155 ev to @xmath156 ev where the perfect conductance amounts to @xmath98 . in the spin- and orbital - decomposed density of states ( dos ) ,
[ fig : co - pt - co_sr](d ) and ( g ) , we also find two resonances at the pt impurity located at @xmath157 ev , and @xmath158 ev below the fermi energy in the majority and minority spin channel , respectively . in the conductance ,
we observe a fano - type line shape due to the coupling of the @xmath92-band to these resonances .
the conductance from the @xmath85-bands displays only a reduction at the bottom and top of the band in both spin channels as the on - site energies of co and pt @xmath130-states are close in energy . the density of states of the pt atom , fig .
[ fig : co - pt - co_sr](h ) , shows that the @xmath130 states are spin - split , carry a significant part of the pt moment , and align well with the @xmath85-bands in the co monowire resulting in an efficient transport channel . the most severe change in the conductance upon introducing a pt impurity occurs in the @xmath88-band .
here , we observe a large decrease due to scattering at the pt impurity . for both , the @xmath130 and @xmath131 channels , bound states on the pt atom can be found due to the lower on - site potential at the pt site .
for the @xmath85-symmetry there are such states at @xmath159 ev for the majority band and at @xmath160 ev for both spin channels , which do not contribute to the conduction as they are below the @xmath85-band of the co leads . for the @xmath88 symmetry
there are majority states around @xmath161 ev and a paired state at @xmath162 ev with respect to the fermi level , not contributing to the majority channel transmission .
@xmath88 electrons are only transmitted in the small overlap region around @xmath163 ev for majority and around fermi level for minority states , where a very narrow band is formed in both cases .
the shape of the transmission function follows the two - peak ( majority band ) and three - peak ( minority band ) shape of the dos of the central pt atom .
( dotted red lines ) , @xmath85 ( dashed blue lines ) and @xmath88 ( solid green lines ) channels for majority spin ( positive @xmath164-axis ) and minority spins ( negative @xmath164-axis ) shows the presence of a @xmath88 minority band channel at the fermi level .
black dashed - dotted lines display the transmission of the perfect infinite co leads . , scaledwidth=49.0% ] now we turn to the effect of spin - orbit coupling on the magnetic and transport properties of the co - pt - co junction . for the perfect co monowire we found a magneto - crystalline anisotropy energy ( mae ) , i.e.
, the difference in energy for the magnetization in the chain axis and perpendicular to it , of @xmath165 mev per magnetic atom in favor of an out - of - chain magnetization and orbital moments of @xmath166 for out - of - chain and @xmath167 for in - chain direction . upon introducing the pt atom ,
this value is reduced to @xmath168 mev per magnetic atom , which is consistent with our observation in the previous section for a pt - co - pt junction favoring the in - chain direction .
the magnetic moment of the pt atom is @xmath169 for both magnetization directions and we find similar orbital moments of @xmath170 ( out - of - chain ) and @xmath171 ( in - chain ) .
characteristically , as in the case of the co leads , the orbital moments of the co atoms adjacent to the pt impurity are significantly larger for the in - chain direction ( reaching as much as 0.53@xmath127 for the nearest co atom ) , than for the out - of - chain direction ( at most 0.2@xmath127 ) .
this means that the out - of - chain easy magnetization axis in our scattering region is mainly due to the co atoms . for the transport properties including soc , the bands with @xmath85 and @xmath88 symmetry are essential .
depending on the quantization axis defined by the magnetization direction , the degeneracy of these bands is lifted .
in contrast to the pt - co - pt system , the co electrodes are ferromagnetic and therefore the splitting in the step - like conductance in the perfect co wires changes upon switching the quantization axis from along the chain axis to perpendicular to it . as can be seen from fig . [
fig : co - pt - co_soc ] , changing the magnetization direction in a perfect infinite co chain leads to a reduction of the transmission from 3.5 @xmath98 ( along the chain ) to 1.5 @xmath98 ( perpendicular to the chain ) in a very small energy window around the fermi energy , which results in a huge value of the ballistic anisotropic magnetoresistance of 133%.@xcite in a realistic situation , however , such values of the anisotropic magnetoresistance can be hardly achieved , owing to the destruction of perfect conducting channels by imperfections , impurities and disorder . ) for the co monowire with a pt impurity ( solid black line ) and for a perfect infinite co monowire ( dashed - dotted green line ) .
, scaledwidth=35.0% ] in the case of a co chain with a pt impurity , similarly to the scalar - relativistic case , we observe a reduction by roughly a factor of two in the overall conductance over the entire energy range , due to the less efficient coupling between the co wire and the pt impurity compared to an perfect co wire , especially for the @xmath85- and @xmath88-orbitals . at the fermi energy , we find majority and minority spin contributions from the @xmath92-band of about @xmath168 and @xmath172 @xmath98 for both magnetic directions
. only the minority states of the other two orbital symmetries are present due to the exchange splitting .
the minority @xmath85 band contributes almost @xmath172 @xmath98 for the in - chain magnetization , while it reveals a large dip at @xmath173 for the out - of - chain magnetization .
accordingly , the @xmath88-band conductance also changes significantly upon switching the magnetization direction , owing to the changes in the details of hybridization between @xmath85 and @xmath88 states when the direction of the magnetization is changed , see fig .
[ fig : co - pt - co_soc](b ) and fig .
[ fig : pt - co - pt_g_vs_dos_incl_soc ] ( cf .
dos of the co monowires for the two different magnetization directions ) .
these changes in the energetic structure of @xmath85 and @xmath88 states lead to a large difference between the in - chain and out - of - chain conductances , also visible for the pure co chain in the fig .
[ fig : co - pt - co_soc ] . in fig .
[ fig : co - pt - co_sr_vs_soc ] , the conductance is displayed in a small energy window around the fermi energy for the two different magnetization directions .
it is apparent that the changes arise due to the modifications of the @xmath88-band conductance between fermi level and @xmath151 ev , and @xmath85-band conductance around @xmath173 and @xmath174 ev which are subject to different band mixing from spin - orbit coupling . as a result of the fine structure of the @xmath88 and @xmath85 conductances ( see fig .
[ fig : co - pt - co_soc](b ) ) , the bamr which we obtain , shown in the inset of fig .
[ fig : co - pt - co_sr_vs_soc ] , displays a strong variation with energy .
compared to the bamr of a perfect co mw of @xmath175 a pt scatterer reduces this effect to @xmath176 , which is still considerably high .
an enhanced bamr can be found for the second peak below the fermi energy , where a @xmath88 conduction peak for the in - chain direction in coincidence with a @xmath85 conduction depletion result in a bamr increase from @xmath177 for the perfect co mw to @xmath178 when a pt scatterer is introduced .
we have implemented the landauer - bttiker method to calculate the ballistic electron transport through one - dimensional nanoscale junctions based on density functional theory calculations within the full - potential linearized augmented ( flapw ) method . in order to apply the efficient green s function method to calculate the conductance we have mapped the extended bloch states obtained from the flapw method to the minimal basis set of localized wannier functions and constructed the hamiltonian for the open system . with our approach
it is feasible to calculate ballistic transport through one - dimensional nanoscale systems including magnetism and spin - orbit coupling with the accuracy and flexibility of the flapw method .
we apply our method to calculate the conductance of non - magnetic pt monowires with a single stretched bond , including spin - orbit coupling .
already this simple example shows the key impact of soc for systems containing heavy transition metals . as a second example
, we considered a co monowire and studied the magnetoresistance upon stretching the wire at a single bond .
the decomposition of the transmission into the channels of different orbital symmetry shows the dominant contribution of @xmath90- and @xmath91-states as one moves from the contact to the tunnel regime . finally , we studied the effect of spin - orbit scattering at an impurity atom in a monowire .
we considered two model cases : ( i ) a magnetic atom in a non - magnetic wire , co in a pt monowire , and ( ii ) a non - magnetic heavy element in a ferromagnetic wire , pt in a co monowire .
we observed for both cases a distinct dependence of the conductance on the magnetization direction with respect to the wire axis .
we found for a co impurity in a pt chain , that due to the broken cylindrical symmetry for an out - of - chain magnetization direction the hybridization between states of different angular character and spin but with identical quantum number @xmath67 leads to scattering processes that do not conserve spin .
those ballistic spin - scattering processes are resulting into a bamr of 7% .
the relatively moderate values are caused by the large background conductance from bands originating from @xmath94- and @xmath130-states which are not modified much upon switching the magnetization .
on the other hand , for a pt impurity in a co chain we find that the presence of an impurity , although reducing somewhat the bamr of the pure co chain , still leads to values of bamr of about 100% , which originates from hybridization between the @xmath85 and @xmath88 states moderated via soc by the direction of the magnetization .
we acknowledge helpful discussions with stefan blgel .
funding by the dfg within the sfb677 is gratefully acknowledged .
thanks the dfg for financial support under he3292/8 - 1 .
thanks financial support from the natural science foundation of zhejiang province in china under grant no . y6100467 .
y.m . and f.f
. gratefully acknowledge the jlich supercomputing centre for computing time and funding under the hgf - yig programme vh - ng-513 .
non - magnetic ( nm ) 6 and 12 atom supercell calculations with an interatomic distance of @xmath179 bohr and the central bond stretched by @xmath100 , @xmath101 , @xmath102 , @xmath103 , @xmath104 and @xmath105 bohr .
we applied the generalized gradient approximation ( gga ) to the exchange - correlation potential@xcite . for calculations in the scalar - relativistic ( sr )
approximation , the irreducible part of the 1d brillouin zone ( bz ) was sampled by 6@xmath14210 @xmath41-points depending on the size of the supercell .
for the 6 atom supercell , we also performed calculations including spin - orbit coupling in second variation . for calculations with soc
the whole 1d bz was sampled by 24 @xmath41-points . in all calculations ,
@xmath180 was chosen to be 3.7 bohr@xmath181 , which corresponds to approximately 200 basis functions per atom .
the diameter of the cylindrical vacuum , @xmath182 , and the value of the in - plane auxiliary lattice constant , @xmath183,@xcite were set to 5.0 and 7.3 bohr , respectively . for the conductance calculations we applied the locking technique to a perfect monowire to describe the semi - infinite leads ( see sec .
[ subsection : locking ] ) . in the sr approximation fswfs and mlwfs
were generated on a mesh of 16 @xmath41-points in the whole bz starting from one @xmath184- and 5 @xmath126-orbitals per atom in the supercell , based on solutions of the radial equation of the first - principles potential as trial functions . in the calculations including soc ,
mlwfs were generated on a 24 @xmath41-point mesh in the whole bz based on 2 radial @xmath184- and 10 radial @xmath126-orbitals per atom , based on solutions of the radial equation of the first - principles potential as trial functions , due to the coupled spin channels .
the energy bands were disentangled using the procedure described in ref . [ ] .
for the sr calculations , the lowest 80 eigenstates are needed for 72 wfs for the 12 atom supercell and the lowest 44 eigenvalues per @xmath41-point for 36 wfs for the 6 atom supercell calculations . with soc
the lowest @xmath185 eigenstates per @xmath41-point for 72 wfs were used .
calculations with a lattice constant of @xmath186 bohr and a central stretched bond with stretching @xmath100 , @xmath122 , @xmath123 , @xmath124 and @xmath125 bohr
. two collinear magnetic configurations of the co monowire are considered , parallel or antiparallel alignment of the co spins on the left and on the right sides of the gap , described by performing two calculations : a 8 atom supercell constructed from two 4-spin blocks separated by a gap and aligned in parallel ( up ) , while in order to mimic the antiparallel alignment , we considered 16 atoms in the supercell with 4-spin ( up ) , 8-spin ( down ) and 4-spin ( up ) blocks , separated by two gaps with the spins antiparallel to each other at each side of the gap .
the perfect lead ferromagnetic co monowire was calculated with 24 @xmath41-points in the whole bz , using the @xmath180 of 4.1 bohr@xmath181 ( @xmath187 220 basis functions per atom ) .
for both 8 and 16 atom supercell calculations the irreducible part of the 1d brillouin zone ( bz ) was sampled by 8 @xmath41-points and @xmath180 was chosen to be 3.7 bohr@xmath181 resulting in approximately 210 basis functions per atom .
the vacuum parameters @xmath182 and @xmath183 constituted 4.3 and 6.6 bohr , respectively , in all cases .
the exchange - correlation potential was treated within the gga@xcite . for all quantum conductance calculations the locking technique ( see sec .
[ subsection : locking ] ) to a perfect fm co monowire was used . as trial orbitals for the fswfs 6 @xmath90- and @xmath55-orbitals per atom and spin in the supercell
were used , based on solutions of the radial equation of the first - principles potential . for the disentanglement procedure@xcite the lowest 58 ( 110 ) eigenstates per @xmath41-point
were used to obtain the 48 ( 96 ) wfs in the 8 ( 16 ) atom supercell calculation .
a 9 atom supercell were used for the scattering region consisting of one impurity atom ( pt or co ) and 4 monowire atoms ( co or pt ) on both sides .
the interatomic distance was chosen as @xmath186 bohr for the co monowire with a pt impurity and as @xmath179 bohr for the pt monowire with a co impurity .
the exchange - correlation potential was treated within the gga@xcite and soc was included in second variation .
all calculations were performed in the scalar - relativistic ( sr ) approximation and for two different directions of the magnetization with soc , along the chain axis and perpendicular to it . the 1d brillouin zone ( bz )
was sampled by 16 @xmath41-points and @xmath180 was set to 3.9 @xmath188 resulting in approximately 175 ( 190 ) basis functions per atom for the co ( pt ) monowire with a pt ( co ) impurity . for the case of an isolated pt impurity ,
the leads were described by a co monowire in a 3 atom unit cell in either the scalar - relativistic ( sr ) approximation or including soc for the magnetization direction along the wire axis or perpendicular to it .
the bz was sampled by 24 @xmath41-points and @xmath180 was set to 4.1 @xmath188 , resulting in approximately 210 basis functions per atom . for pt monowire with a co impurity , the lead s electronic structure was obtained from calculations of perfect pt monowires .
the vacuum parameters for all cases constituted 4.3 and 6.6 bohr for @xmath182 and @xmath183 , respectively . for all quantum conductance calculations
the locking technique wa used and the third nearest - neighbor approximation were employed . in the sr case fswfs
were generated on a 16 @xmath41-point mesh in the whole 1d - bz with 1 @xmath90- and 5 @xmath55-orbitals per atom and spin , based on solutions of the radial equation of the first - principles potential .
for the disentanglement procedure@xcite the lowest 64 ( 62 ) eigenvalues per @xmath41-point for 54 ( 54 ) wfs for pt ( co ) impurities in co ( pt ) monowires were considered .
the pt and co lead wfs were constructed as described in sec .
[ subsec : pt_sr_cd ] and sec .
[ co - compdet ] in this case .
with soc the fswfs were generated on a 16 @xmath41-point mesh in the whole 1d - bz with 2 @xmath90- and 10 @xmath55-orbitals per atom , based on solutions of the radial equation of the first - principles potential .
for disentanglement@xcite the lowest @xmath189 eigenstates per @xmath41-point for @xmath190 wfs were used .
the wfs for the semi - infinite co leads were generated on a 24 @xmath41-point mesh with the same trial functions as those used for the atoms inside the scattering region , while for disentanglement the lowest @xmath191 eigenvalues per @xmath41-point for @xmath192 wfs per spin ( sr ) and the lowest @xmath193 eigenvalues per @xmath41-point for @xmath194 wfs ( soc ) were used .
the pt lead wfs were constructed as described in sec .
[ subsec : pt_sr_cd ] . | we present an implementation of the ballistic landauer - bttiker transport scheme in one - dimensional systems based on density functional theory ( dft ) calculations within the full - potential linearized augmented plane - wave ( flapw ) method . in order to calculate the conductance within the green s function method we map the electronic structure from the extended states of the flapw calculation to wannier functions which constitute a minimal localized basis set .
our approach benefits from the high accuracy of the underlying flapw calculations allowing us to address the complex interplay of structure , magnetism , and spin - orbit coupling and is ideally suited to study spin - dependent electronic transport in one - dimensional magnetic nanostructures . to illustrate our approach we study ballistic electron transport in non - magnetic pt monowires with a single stretched bond including spin - orbit coupling , and in ferromagnetic co monowires with different collinear magnetic alignment of the electrodes with the purpose of analysing the magnetoresistance when going from tunneling to the contact regime .
we further investigate spin - orbit scattering due to an impurity atom .
we consider two configurations : a co atom in a pt monowire and vice versa . in both cases ,
the spin - orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it .
the main contribution stems from ballistic spin - scattering for the magnetic co impurity in the non - magnetic pt monowire and for the pt scatterer in the magnetic co monowire from the band formed from states with @xmath0 and @xmath1 orbital symmetry .
we quantify this effect by calculating the ballistic anisotropic magnetoresistance which displays values up to as much as 7% for ballistic spin - scattering and gigantic values of around 100% for the pt impurity in the co wire .
in addition we show that the presence of a scatterer can reduce as well as increase the ballistic anisotropic magnetoresistance . |
CLOSE SportsPulse: NFL owners voted on Tuesday to overturn the league's confusing catch rule, but will the new verbiage make a difference? USA TODAY Sports' Mike Jones thinks so. USA TODAY Sports
The Los Angeles Rams, like every other NFL team, had an all-female cheerleading squad in 2017. However, that won't be the case this season. (Photo: Kirby Lee, USA TODAY Sports)
For the first time, an NFL team will have men as part of its official spirit squad.
Quinton Peron and Napoleon Jinnies, named to the Los Angeles Rams squad this week, will be the first ones to perform the same routine as the female dancers. The Baltimore Ravens and Indianapolis Colts have men who perform stunts with female cheerleaders, but don't dance.
Peron and Jinnies are both classically trained dancers and have been performing their entire lives.
But what made them take this groundbreaking step?
"I thought, 'Why not me? Why can't I do this?' " Peron said in an interview Wednesday on ABC-TV's Good Morning America.
Congratulations to our 2018 Los Angeles Rams Cheerleaders! pic.twitter.com/gYlXtC0BOd — Rams Cheerleaders (@LARamsCheer) March 26, 2018
The men were among the 76 finalists chosen for the 40-person squad. Jinnies said the auditions were unlike any he's ever been through before.
"This one was about three weeks long and we had a bunch of rehearsals in between and an extensive interview process, but it was really humbling and amazing to be invited every time you came back," he said. ||||| LOS ANGELES (CBSLA) — For the first time in National Football League history, two men will be part of an official team cheer squad, and they’re from L.A.’s very own Rams.
Quinton Peron and Napoleon Jinnies were introduced Wednesday as part of the 2018 squad’s “rookies.”
Inside Edition reports that, while other NFL teams have males in the their stunt teams, the two classically trained dancers will be the first men to cheer alongside women.
Jinnies On Wednesday tweeted a photo of his new team saying he couldn’t believe he had made it.
Still can’t belive I’m one of the first males in history to be a pro NFL cheerleader! Everyone’s support and love has been insane! 😭 thank you and GO RAMS! @RamsNFL @LARamsCheer #LARams pic.twitter.com/srpkYiVmEI — Napoleon Jinnies (@NapoleonJinnies) March 27, 2018
In addition to appearing in all home games with the squad, Jinnies and Peron will participate in community events throughout the year.
Below is a complete list of all the other “rookies” joining the team this year: ||||| Two men are making history by becoming the first male cheerleaders in the NFL.
Quinton Peron and Napolean Jinnies are two classically trained dancers who have officially joined the ranks of the Los Angeles Rams cheerleading squad.
"I am speechless," Jinnies said in an interview moments after learning he had made the team.
While other football teams have male stunt teams, the pair will be the first men to dance alongside women on an NFL cheerleading team, reports said.
"They really just fit the bill to be a Los Angeles Rams cheerleader," Rams cheer captain Emily Leibert told Good Morning America Wednesday. "They are intelligent. They are eloquent. They are more than qualified to be ambassadors out in the community."
The contenders had to go through two rounds of preliminary auditions, an interview, three rehearsals and a final audition to make the 40-member squad.
"I cried," Peron said in an interview. "[I] am ready for this journey."
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You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more | – Quinton Peron and Napoleon Jinnies just made NFL history, CBS Los Angeles reports. They became the first men on an NFL cheer team after the Los Angeles Rams announced Wednesday they had made the squad. According to Inside Edition, Jinnies said he was "speechless" and Peron said he cried when they heard the news. "Still can’t believe I’m one of the first males in history to be a pro NFL cheerleader!" Jinnies tweets. "Everyone’s support and love has been insane! Thank you and GO RAMS!" The two classically trained dancers had to go through two auditions, an interview, three rehearsals, and a final audition to make the 40-person cheer team. They will appear at every Rams home game as well as community events. "They really just fit the bill to be a Los Angeles Rams cheerleader," Inside Edition quotes Rams cheer captain Emily Leibert as saying. "They are intelligent. They are eloquent. They are more than qualified to be ambassadors out in the community." USA Today reports the Baltimore Ravens and Indianapolis Colts have men who perform stunts with cheerleaders, but Jinnies and Peron will be the first men to dance with an NFL cheer team. |
Click here to read the latest press release about SLDN's 19th Annual National Dinner, which honored Lady Gaga for her commitment to equality with the Randy Shilts Visibility Award, or watch the video now.
Lady Gaga brings the fight to the Senate! Join our fight.
The House has spoken - again! In a historic vote on December 15th, by a margin of 250-175, the House of Representatives passed a new standalone bill (H.R. 2965) that would repeal "Don't Ask, Don't Tell." Now the ball is in the Senate’s court.
We call upon the Senate to remain in session and in Washington until they pass the House bill to repeal "Don’t Ask, Don't Tell." Show your rage for repeal and insist the Senate stay in Washington until they have finished the job.
Call both your senators at the Capitol switchboard at (202) 224-3121.
Here's a sample script for your call:
"Hello, my name is ______ and I’m a constituent from __________ (city, state).
I'm calling to tell Senator _______ to stand with Majority Leader Reid, Chairman Levin, and Senator Lieberman and vote for the House bill to repeal 'Don't Ask, Don't Tell.' Fight back against Senators John McCain and Mitch McConnell's obstructionism and pass repeal this year.
Thank you.”
Call the Capitol switchboard today!
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These senators particularly need to hear from you. Please call them today!
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--George LeMieux (R-FL);
--Richard Lugar (R-IN);
--Judd Gregg (R-NH);
--George Voinovich (R-OH);
--Kit Bond (R-MO);
--Mark Kirk (R-IL);
--Kent Conrad (D-ND);
--Joe Manchin (D-WV).
Thank you. Together we will make it to the finish line for repeal!
Spread the word on Facebook and Twitter
After you call, leave a comment below and share how your calls went!
And copy a link to your own video of calling senators, like Colorado students Lauren and Ellie, or Claire from Arizona:
Answer Lady Gaga's call for action today!
By Elizabeth Shirey, Grassroots/Policy Advocate and Paul DeMiglio, Senior Communications Manager | ||||| tv
Do You Have a Moment to Talk About Bradley Whitford’s NBC Church Choir Pilot? The Destroyer actor plays an Ivy League music professor in the comedy, formerly known as All Together Now. | – Lady Gaga is appealing directly to the Senate to urge repeal of the military's "Don't Ask, Don't Tell" policy, New York reports. In a black-and-white video, framed by the American flag, Gaga criticizes the "inconsistent and unconstitutional enforcement" of the ban on openly gay personnel, citing advocacy group SLDN's research, which she says "proves that soldiers are being searched, superiors are calling family members, operating on assumptions—ultimately, the law is being enforced using gay profiling." Click here for all things Gaga. |
Mojtaba Ahmadi, who served as commander of the Cyber War Headquarters, was found dead in a wooded area near the town of Karaj, north-west of the capital, Tehran. Five Iranian nuclear scientists and the head of the country’s ballistic missile programme have been killed since 2007. The regime has accused Israel’s external intelligence agency, the Mossad, of carrying out these assassinations.
Ahmadi was last seen leaving his home for work on Saturday. He was later found with two bullets in the heart, according to Alborz, a website linked to the Revolutionary Guard Corps. “I could see two bullet wounds on his body and the extent of his injuries indicated that he had been assassinated from a close range with a pistol,” an eyewitness told the website.
The commander of the local police said that two people on a motorbike had been involved in the assassination.
The Facebook page of the officers of the Cyber War Headquarters confirmed that Ahmadi had been one of their commander and posted messages of condolence. But Alborz users warned that the openly accessible book of condolence could harm Iran’s national security.
“Stop giving more information about him. The counter-revolutionaries will take advantage of his murder,” said one post. “It sounds like a hit job for a security officer of this importance”.
Subsequently, a statement from the Imam Hassan Mojtaba division of the Revolutionary Guard Corps said that Ahmadi’s death was being investigated. It warned against speculating “prematurely about the identity of those responsible for the killing”.
Western officials said the information was still being assessed, but previous deaths have been serious blows to Iran’s security forces. Tighter security measures around leading commanders and nuclear scientists have instilled a culture of fear in some of the most sensitive parts of the security establishment.
The last victim of a known assassination was Mostafa Ahmadi Roshan, a chemist who worked in the uranium enrichment plant at Natanz, who died when an explosive device blew up on his car in January last year.
The death of Ahmadi, a leading specialist in cyber defences, could be an extension of this campaign of subterfuge. Iran has been accused of carrying out a number of cyber attacks detected in the West. Shashank Joshi, an expert at the Royal United Services Institute (Rusi), said this was seen as a lesser threat than the nuclear programme. “Iran’s cyber attacks on Israel and elsewhere in the region are a rising threat and a growing threat, but it hasn’t yet been seen as a major and sustained onslaught, so it would be pretty novel and significant to take this step in the field of cyber-warfare at this time,” he said.
The Revolutionary Guard has also been accused of lending its expertise to Syria’s regime, helping it to hack Western targets through a body known as the Syrian Electronic Army.
The killing of Ahmadi coincides with a new diplomatic effort by President Hassan Rouhani, Iran’s newly elected leader. He has voiced the hope that Iran’s confrontation with America and the leading Western powers over its nuclear ambitions can be settled within months. ||||| Iran's Revolutionary Guard has denied reports that the commander of its Cyber War Headquarters, Mojtaba Ahmadi, has been assassinated.
In a statement posted on the Alborz website, which is closely linked to the powerful Iranian Revolutionary Guard, the group has quashed reports that one of its officials had been assassinated by two men on a motorbike:
"This statement denies all the news about assassinating one of our workers after a very sudden incident happened to him," the Imam Hassan Mojtaba division of the Revolutionary Guards Corps said.
"We are investigating the incident and the intention of the attacker or attackers." The Revolutionary Guards also issued a statement warning against prematurely assigning blame to anyone.
There was no confirmation of the person's name or rank but confirmed he had been found dead near the town of Karaj, located in northwest of the country's capital Tehran.
The statement comes 12 hours after first reports emerged in western media that the commander of Iran's Cyber War Headquarters, Mojtaba Ahmadi had been assassinated after last being seen leaving his home on Saturday on his way to work.
Assassination
The reports of the assassination also came from the Alborz website with the first report appearing in the Telegraph in the UK, before being picked up by news agencies around the world. While the report was widely reported there was never any official confirmation of an assassination by the Iranian authorities.
According to the Telegraph report, Ahmadi was last seen leaving his house on Saturday heading for work. Ahmadi was later found with two bullets in the heart in a wooded area near the town of Karaj.
"I could see two bullet wounds on his body and the extent of his injuries indicated that he had been assassinated from a close range with a pistol," an eyewitness told Alborz. Local police are reported as saying two people on a motorbike were involved in the assassination.
Since 2007 five Iranian nuclear scientists and the head of the country's ballistic missile program have been assassinated, with the Iranian regime previously pointing the finger at Israel's external intelligence agency Mossad.
Explosive device
However the US and UK have also been accused of involvement in previous attacks, the most recent of which saw Mostafa Ahmadi Roshan, a chemist who worked in the uranium enrichment plant at Natanz, killed when an explosive device blew up on his car in January last year.
The Natanz facility is the same one which was targeted by the Stuxnet computer virus which was jointly developed by the US and Israel to set back Iran's nuclear program.
The news of another high-ranking Iranian official's death comes in the same week as Israel's Prime Minister Benjamin Netanyahu told the UN General Assembly that Israel would stop Iran's nuclear arms drive single-handedly if necessary: "Israel will never acquiesce to nuclear arms in the hands of a rogue regime that repeatedly promises to wipe us out."
It also comes in the same week which saw US-Iran relations seemingly thaw, with Iran's president Hassan Rouhani and Us president Barack Obama speaking on the phone.
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This article is copyrighted by IBTimes.co.uk, the business news leader ||||| DUBAI Iran's Revolutionary Guards said they were investigating the death of an officer in a "horrific incident", but denied media reports it was an assassination.
Alborz, an Iranian website, reported earlier this week that Mojtaba Ahmadi, an official of the elite Islamic Revolutionary Guard Corps (IRGC), was found shot dead near Karaj, a town northwest of the capital Tehran.
He had left his house on Monday morning and was found a few hours later with a bullet in his heart, it said.
The London-based Daily Telegraph reported that Ahmadi was a commander of the unit's Cyber War Headquarters and quoted a local police commander as saying it was an assassination.
It speculated that the death could have been an assassination, similar to those of five Iranian nuclear scientists since 2007.
"In the wake of a horrific incident involving one of the IRGC officials ... the matter is being investigated and the main reason of the event and the motive of the attacker has not been specified," said an IRGC statement, quoted by Sepah news.
Sepah, which is operated by the Revolutionary Guard, ran its report under the headline "Denial of news reports of the assassination of one of IRGC's officials".
The statement did not identify Ahmadi but a local news website published pictures on Wednesday showing his funeral procession, along with text excerpts of the IRGC communique.
"The result of investigation will be announced through official channels and any speculation will not be appropriate before the investigation is over," an Iranian official said late on Wednesday. Western officials have not commented on the incident.
Iran has been accused of mounting cyber attacks against Western targets in recent years, and has itself been the target of suspected U.S. attacks on computer systems at its nuclear facilities using a virus called Stuxnet.
For their part, authorities in Tehran have accused Israel and its Western allies of carrying out a series of assassinations against Iranian nuclear scientists. The last such attack happened in January 2012 when one man was killed by a car bomb.
Israel regards Iran's nuclear activities as an existential threat and has applied diplomatic pressure on the West to force Iran to curb its nuclear programme. Tehran maintains it has only peaceful goals.
(Reporting by Marcus George; Editing by Jon Hemming and Mark Trevelyan) | – This much is clear: The head of Iran's "cyber war" computer defenses is dead. But how it happened is still a mystery. The Telegraph reports that Mojtaba Ahmadi was found shot to death in the woods, and it quotes a local police official as saying two men on a motorbike assassinated him. The report speculates that the killing is similar to the assassinations of several nuclear scientists in Iran since 2007, killings that Iran blames on Israel. Ahmadi belonged to Iran's Revolutionary Guard, which issued a statement denying reports of an assassination, reports the International Business Times. "In the wake of a horrific incident involving one of the IRGC officials ... the matter is being investigated and the main reason of the event and the motive of the attacker has not been specified," it said in a statement picked up by Reuters. |
the use of noncovalent molecular self - assembly
to construct materials
has become a prominent strategy offering practical routes for the
construction of increasingly functional materials .
a variety of molecular
building blocks can be used for this purpose ; one such block that
has attracted considerable attention in the past two decades is de novo designed peptides .
the exploitation of peptides
and their self - assembling properties to design hydrogels in particular
has been the focus of significant efforts due to their potential for
use in a variety of biomedical applications such as cell therapy , tissue regeneration , and drug delivery .
a number of molecular designs have been developed
for the synthesis of self - assembling peptides with the four main families
being amphiphilic peptides , short peptide
derivatives , -helix / coiled - coil peptides , and -sheet peptides .
all these designs allow the synthesis
of peptides that under appropriate conditions self - assemble to form
elongated fibers . above a critical gelation concentration ( cgc )
these
fibers entangle and/or associate to form three - dimensional networks
that have the ability to trap water , i.e. , form hydrogels .
-sheet
peptides are of particular interest as these peptides
allow the fabrication of very stable hydrogels with properties that
can be tailored through peptide design , media properties , and processing .
we have recently investigated the self - assembly and gelation properties
of a family of -sheet peptides based on the design
developed by zhang and co - workers .
this design , which is
based on the alternation of hydrophilic and hydrophobic residues ,
allows the synthesis of peptides that self - assemble into antiparallel
-sheet fibrils . because of the design used
, these antiparallel
-sheet fibrils have a hydrophobic and a hydrophilic face as
schematically shown in figure 1 .
it is thought that in order to minimize contact between
water and the hydrophobic faces , these -sheet fibrils associate
by pairing to form -sheet fibers with the hydrophobic residue
side chains buried in the fiber core ( figure 1 ) .
top : schematic representation of the self - assembling
and gelation
processes of -sheet forming peptides .
one of the most attractive properties of these systems is
their
ease of functionalization .
usually this is achieved by covalently
linking the desired functional group to the peptide to create a functional
peptide which then can be dosed as required into the system to create
functional hydrogels through self - assembly . in order to avoid affecting
the self - assembling properties of the peptides ,
their functionalization
is usually achieved by linking the functionality to one of the peptide s
chain termini .
here we are interested in looking at the possibility
to functionalize the peptide fibrils through its hydrophobic face
in order to bury the functionality in the hydrophobic core of the
peptide fiber . for this study
we have chosen the self - assembling
peptide fefkfefkk
( f9 ) ( f : phenylalanine ; k : lysine ; e : glutamic acid ) which forms stable
-sheet - rich fibers and hydrogels at ph 5.5 .
the nucleophilic thiol group of cysteine was then reacted
with 2,3-dibromomaleimide to generate the peptide
bromomaleimide
conjugate fefkc(bm)efkk ( fc9-bm ) through a straightforward
nucleophilic substitution ( figure 2 ) .
the introduction of this modification does not affect
the isoelectric point of the peptide and therefore does not affect
the ph dependency of the peptide self - assembly and gelation properties .
a ph of 5.5 was chosen for this study as it corresponds to the optimal
ph ( stability and homogeneity ) for the gelation of these peptides ,
which at this ph carry a theoretical charge of + 2 .
hybrid hydrogels
were prepared by mixing f9 and fc9-bm in the desired proportions while
keeping the overall molar concentration of peptide constant .
attenuated
total reflectance fourier transform infrared spectroscopy ( atr - ftir )
and circular dichroism ( cd ) were used to investigate how the bm modification
affected the conformation adopted by the peptide , while transmission
electron microscopy ( tem ) , atomic force microscopy ( afm ) , and small - angle
x - ray scattering ( saxs ) were used to investigate the effect on fiber
morphology and network topology .
finally , shear rheometry was used
to investigate the effect on hydrogel mechanical properties .
the
peptides used for this study fefkfefkk
and fefkcefkk were purchased from biomatik corporation ( wilmington ,
de ) with a purity > 95% ( confirmed in house by esi - ms and rp - hplc ) .
all solvents and reagents were purchased from sigma - aldrich and used
as received .
peptide fefkcefkk ( fc9 ) ( 75 mg , 55
mol ) was first dissolved in 4.5 ml of ddh2o . a solution
of 2,3-dibromomaleimide ( dbm ) ( 14 mg , 55 mol ) in 500
l of dimethylformamide ( dmf ) was added dropwise to the
fc9 solution under vigorous stirring , and then the solution was left
stirring for 24 h at room temperature .
the reaction mixture was then
lyophilized to give 79 mg ( 94% yield ) of fc9-bm as a yellow residue .
the molecular weight and purity of the product were confirmed by esi - ms
( figure esi 1 ; m / z : 1379.5 [ m +
h ] ) and rp - hplc ( figure esi 2 ; purity 95% ) ( see supporting information for detailed methodology ) .
peptide powders were dissolved in
hplc grade water by sonication at 80 khz for 30 min , and the solution
ph was adjusted to ph 5.5 by the stepwise addition of 0.5 m naoh solution .
the hydrogel was left overnight
in a fridge at 4 c to equilibrate and used the following day .
hydrogels were spread as prepared
onto the crystal surface of a bruker alpha - p ft - ir spectrometer equipped
with a multibounce attenuated total reflectance ( atr ) plate .
the transmittance
spectra were recorded ( 128 scans ) between 4000 and 400 cm with a resolution of 4 cm .
hplc grade water
was used as background and was automatically subtracted from the recorded
spectra using the opus software provided with the instrument .
peak
area relative intensity was evaluated by fitting the 1624 cm peak using a gassamp function ( origin 9.0 ) after subtraction of
a straight baseline in the amide i region ( 16001700 cm ) .
samples were placed in a 0.1 mm quartz cell ( hellma ) and spectra
recorded at wavelengths from 200 to 280 nm , with a 1 nm step size
and response time of 0.5 s. the ellipticity data acquired in mdeg
were converted to mean residue molar ellipticity in deg cm dmol residue through1where is the ellipticity
in mdeg , c the sample molar concentration , n the
number of backbone amide bonds , and l the cell optical
path length in cm .
a carbon - coated copper grid ( 400 mesh from electron microscopy sciences )
was placed on a 10 l droplet of sample for 1 min and excess
liquid drained off using lint - free tissue .
the grid was then placed
on a 10 l droplet of ddh2o for 10 s before excess
liquid was drained off .
the grid was then transferred to a 10 l
droplet of a 1% uranyl acetate solution for 30 s , and again excess
liquid was drained off .
finally , the grid was transferred to a 10
l droplet of ddh2o for 10 s before excess liquid
was drained off for a final time .
the sample was then left to dry
before imaging using a fei tecnai12 biotwin tem at 100 kev .
after 1 min excess solution
was removed and the surface washed twice with 1 ml of ddh2o .
excess water was then removed once again by wicking using whatman
no.1 filter paper .
samples were imaged by intermittent contact ( tapping )
mode in air using a bruker multimode afm with a nanoscope v controller
and a
imaging was performed using olympus
high aspect ratio etched silicon probes ( otespa ) with nominal spring
constant of 42 n m ( bruker axs s.a.s , france ) .
drive amplitude and cantilever oscillation , which varied between 300
and 350 khz , were determined by the nanoscope ( v8.15 ) software .
the
amplitude set point was adjusted to just below the point at which
tip sample interaction was lost .
height , phase , and amplitude
images with scan sizes of either 2 or 5 m were
captured at a scan rate of 1.5 hz and at a relative humidity of < 40% .
data were first - order flattened using the nanoscope analysis ( v1.4 )
software prior to image export .
rheological studies were carried
out on a stress - controlled rheometer ( discovery hr-2 , ta instruments )
equipped with a solvent trap to minimize evaporation , using a 20 mm
parallel plate geometry .
500 l of peptide hydrogel was loaded
onto the stage , and the gap between the stage and the upper plate
set to 250 m .
the loaded sample was then left for 2 min to
equilibrate at 25 c before measurement .
strain sweeps were measured
between 0.04 and 40% strain at an oscillation frequency of 1 hz .
radial
frequency sweeps were undertaken between 0.01 and 15 hz , using a strain
of 0.2% , which is within the linear viscoelastic regime ( lvr ) of all
samples .
saxs measurements were
performed at diamond light source beamline b21 equipped with a using
a biosaxs robot for sample loading and a pilatus 2 m ( dectris , switzerland )
detector .
the x - ray wavelength used was 0.1 nm corresponding to an
energy of 12.4 kev , and the sample
detector distance was 4.018
m giving an accessible q - range of 0.054.0
nm .
data were reduced , and solvent and capillary
contributions were subtracted using the dawndiamond software suite .
samples were prepared by directly at 3 mm concentration following
the methodology described above .
a series of f9/fc9-bm hybrid hydrogels were prepared at constant
overall peptide molar concentration of 30 mm by varying the ratio
of fc9-bm added from 0% ( pure f9 ) to 100% ( pure fc9-bm ) .
all samples
formed hydrogels at ph 5.5 suggesting the formation , in all cases ,
of extended fibrillar networks .
first atr - ftir and cd were used
to investigate the conformation
adopted by the peptides . in figure 3 , the atr - ftir spectra obtained for all the samples
as prepared are presented . left : atr - ftir spectra obtained for f9/fc9-bm
hybrid hydrogels
with an overall peptide molar concentration of 30 mm .
right : 1624
cm -sheet peak relative intensity vs fc9-bm
content . as expected , the pure f9 hydrogel
spectrum shows two strong absorption
peaks at 1624 and 1524 cm corresponding to the
adoption by this peptide of an extended -sheet conformation .
for the pure fc9-bm hydrogel in addition to the peak at 1624 cm a strong broad peak
the presence of both peaks suggests that the presence of the bm
side group is frustrating the adoption by this peptide of a fully
extended -sheet conformation . as can be seen from the structures
of the two peptides presented in figure 1 , the bm side group likely disrupts the overall
ordering / packing of the phenylalanine rings , resulting in a loss of
the fully extended -sheet conformation .
when the amount of
fc9-bm in the hydrogels is increased , the relative intensity ( in relation
to the overall intensity of the amide i region ) of the peak at 1624
cm decreases ( figure 3 ) , suggesting a decrease in -sheet
content .
interestingly , although the relative intensity decreases
linearly for samples with fc9-bm content higher than 25% , the sample
with an overall fraction of fc9-bm of 12.5% exhibits a lower than
expected relative intensity , pointing toward a proportionally stronger
disruptive effect of introducing small amounts of fc9-bm on the overall
content of peptide adopting an extended -sheet conformation .
this would suggest that in order to accommodate fc9-bm in the structure
the adjacent f9 peptides also lose some of their extended conformation .
as can be seen from figure 4 for the f9 sample a strong
negative band is observed at 218 nm with a strong positive signal
being observed below 205 nm .
these cd spectra features are typical
of -sheet secondary structure in proteins . when fc9-bm is introduced into the system ,
although for
12.5% and 25% samples the peak at 218 nm is unchanged , the strong
positive signal below 205 nm is lost , suggesting a decrease in -sheet
content . indeed , the cd signal associated with random coil secondary
structure in proteins presents a small positive band in the 205230
nm region but a strong negative band in the 185205 region . in agreement with the atr - ftir data ,
similar
cd signals were obtained for the 12.5% and 25% samples , suggesting
a similar -sheet content . for samples with a fc9-bm content
higher than 25% a significant decrease in the 218 nm band is observed ,
indicating a further decrease in -sheet content . an additional
band is observed at 222 nm , which in the literature has been assigned
to aromatic residues , in our case phenylalanine .
its exact origin
is still matter of debate and it is thought that it is related to
the ordering of the aromatic rings .
cd spectra
obtained for f9/fc9-bm solutions prepared by 20-fold
dilution of hybrid hydrogels with overall peptide molar concentrations
of 30 mm .
the ability of both peptides to
form extended fibrillar structures
was confirmed by tem and afm ( figure 5 ) .
clear differences in fiber morphologies can be observed
via tem . for the f9 sample thin relatively straight fibers that associate
along their length to form thicker bundles were observed .
the width
of the thinnest fibers observed was 34 nm , in good
agreement with the adoption by this peptide of an extended -sheet
conformation while fiber bundle sizes varied from 5 up to
20 nm .
for the fc9-bm sample thin kinked fibers were observed .
in this case , too , the smallest fibers observed were found to have
a width of 34 nm , but no extensive fiber association
was observed resulting in very few large fiber bundles being observed .
for the 50% f9/50% fc9-bm sample an intermediate morphology is observed .
the tem images suggest that the introduction of the bm modification
results in a change in fiber morphology from straight to kinked correlating
well with the loss of extended -sheet conformation revealed
by atr - ftir and cd .
this change in fiber morphology is thought to
result in a decrease in the ability of the fibers to associate along
their length and form larger bundles .
close inspection of the fc9-bm
tem micrograph clearly shows fibers close to each other , but due to
their kinked nature , they are unable to align and associate along
their length and form large bundles ( arrows in figure 5 ) as observed for the f9 sample .
tem ( top ) and
afm height ( bottom ) images obtained for the different
samples .
arrows in the tem of 100% fc9-bm show example of kinks in
fibers ( see text for further details ) . the reduced tendency for fc9-bm system to form extended fiber
bundles
it should be noted that tem and afm sample preparation
methods are very different .
while for tem only few fibers / fiber aggregates
are collected on the grids and imaged , in afm significantly higher
density of fibers / fiber aggregates are deposited on the mica surface ,
allowing us to observe a morphology which is closer to the overall
network topology expected for these systems . as can be seen from figure 5 much thinner features / fibers
are observed for fc9-bm sample compared to f9 sample , confirming the
tem results .
tem and afm require significant sample preparation
and give two - dimensional
images of three - dimensional structures ; therefore , saxs was used to
confirm the increased propensity for f9 to form fiber aggregates compared
to fc9-bm . in this case the samples were prepared direct at the required
concentration with no further sample manipulation . in figure 6 the scattering patterns obtained
for the three samples f9 , 50% f9/50% fc9-bm , and fc9-bm are presented .
as can be seen from the log vs log plots , at low q a clear q
behavior typical
of the scattering of fibers can be observed for the fc9-bm sample .
for the 50% f9/50% fc9-bm and f9 samples as the amount of fc9-bm decreases ,
this deviation from the
expected scattering pattern of infinitely long thin fibers is even
more evident in the ln qi(q ) vs q representations .
indeed ,
it has been shown that for thin rod - like structures ( i.e. , fibers )
for qr < 1 ( r : cross - section radius of gyration ) the scattering
intensity can be written as2as can be seen from figure 6 , a linear behavior is observed at low q only for fc9-bm , suggesting that for this sample the fibers
can indeed be considered as infinitely long thin rod - like structures .
from the fitting of the linear region r can be estimated as 1.7 0.2 nm , which corresponds to a fiber
diameter of 46 nm , in good agreement with the tem results .
for the other two samples no linear region is observed , indicating
that in this case the scattering objects can not be considered as thin
infinitely long rods . instead , a
roll - over is present ,
characteristic of asymmetric objects , which is in
good agreement with the interpretation made above of f9 favoring the
formation of fiber bundles / aggregates .
the scattering observed for
these samples becomes complex and will be a mixture of scattering
from the single fibers and fiber bundles / aggregates of different sizes .
log vs
log ( left ) and ln qi(q ) vs q representation of the
saxs scattering pattern obtained for the 100% f9 , 50% f9 + 50% fc9-bm ,
and 100% fc9-bm samples prepared at 3 mm concentration .
ftir and cd suggest that the introduction of fc9-bm
results in
a loss of -sheet conformation , which is expected to affect
the fiber intrinsic properties ( e.g. , flexibility ) .
on the other hand ,
tem , afm , and saxs suggest that the introduction of fc9-bm results
in a change in the network topology , fc9-bm sample showing a significant
lower level of fiber bundling / aggregation .
this change in network
topology is expected to affect the intrinsic properties of the network
( e.g. , elasticity ) .
the bulk mechanical properties of the hydrogels
will be a function of both the intrinsic properties of the fibers
and the intrinsic properties of the fibrillar network .
we investigated
how the introduction of fc9-bm affected the mechanical
properties of the hydrogels using shear rheometry . in figure 7
the shear moduli obtained
for the hydrogels are presented as a function of fc9-bm content .
as
can be observed , there is a significant decrease in g ( an order of magnitude ) when 12.5% of fc9-bm is introduced
in the system with an additional small decrease when the content of
fc9-bm is increased further .
the loss in -sheet conformation
as revealed by ftir and cd translates at the macroscopic level into
a significant decrease in g. the tem and
afm images suggest that the introduction of fc9-bm ultimately leads
to a change in the network topology from a network formed by thick
bundles of relatively straight fibers to a network formed by thin
kinked fibers .
one would expect indeed the latter topology to result
in a hydrogel with a lower shear modulus but a higher elasticity .
the increase in elasticity ( in other words , a decrease in brittleness )
is clearly shown by the strain sweep experiments that allow determination
of the size of the linear viscoelastic regime ( lvr ) . as can be seen
from figure 7 , the
lvr size increases significantly upon introduction of fc9-bm in the
system , pointing toward the formation of a more elastic , less brittle ,
network .
left : shear modulus ( g ) of f9/fc9-bm composite
hydrogels at 15 hz obtained from the frequency sweep experiments performed
at 0.2% strain vs fc9-bm content .
right : strain sweep experiments
for the 100% f9 ( , ) , 75% f9/25% fc9-bm ( ,
) , and 100% fc9-bm sample ( , ) ( close symbols : g ; open symbols : g ) .
all
samples had an overall peptide molar concentration of 30 mm . a number of theories that relate
topology of networks formed to
moduli of hydrogels can be found in the literature .
one such theory
was developed by jones and marques for
rigid polymer networks and relates the shear modulus to the fractal
dimension df of the objects forming the
network through the power law3where c is the concentration
of objects contributing to the network elasticity . for a network
formed by straight ( between junctions ) thin fibers df
is expected to be 1 corresponding to a power
law of c. good agreement with the jones
and marques theory was indeed obtained for the fc9-bm system for which
a power law of c was obtained
( figure 8) . for this
system as our saxs result show the system can indeed be considered
as being formed by thin straight fibers . log
log plot of
shear moduli ( g )
vs molar concentrations obtained for f9 ( ) and fc9-bm ( )
hydrogels . for the f9 system a power law
of c was obtained . as discussed
by ramzi et al .
, a higher exponent can
originate from the presence of a high number of pendent fibers ( not
connected to the network ) as the effective concentration ( concentration
of objects actively participating to the elasticity of the network )
is lower than the nominal concentration of objects . from the tem pictures obtained in our case ,
it is unlikely
that a significant number of pendant fibers are present in our systems .
on the other hand , for the f9 system the formation of large bundles
of fibers
each bundle will act as a single
element contributing to the elasticity of the network . as a result ,
the actual effective concentration of object participating to the
elasticity of the network is reduced and leads probably to a higher
exponent . this interpretation would imply that the difference in measured
and expected exponent is an indirect measure of the level of fiber
association and bundling in these systems and therefore that jones
and marques theory could be used to characterize the association and
bundling tendency of -sheet forming peptide through shear moduli
measurements .
we have investigated
the effect of functionalizing the -sheet
forming peptide fefkfefkk through the hydrophobic face by replacing
one of the phenyl ring groups with a bromomaleimide group .
our
results show that the introduction of this modification results in
a loss of the extended -sheet conformation adopted by the peptide .
this leads to a change in the fiber morphology from straight to kinked
leading to a reduced ability to associate and bundle . as a result
of these morphological changes , the macroscopic mechanical properties ,
in this case shear modulus , of the hydrogel decrease while its elasticity
increases .
the characterization of the level of association and bundling
in these systems is notoriously difficult , and here we suggest an
indirect characterization of this phenomenon through the use of the
theory developed by jones and marques . | -sheet forming peptides have
attracted significant interest
for the design of hydrogels for biomedical applications .
one of the
main challenges is the control and understanding of the correlations
between peptide molecular structure , the morphology , and topology
of the fiber and network formed as well as the macroscopic properties
of the hydrogel obtained . in this work ,
we have investigated the effect
that functionalizing these peptides through their hydrophobic face
has on their self - assembly and gelation .
our results show that the
modification of the hydrophobic face results in a partial loss of
the extended -sheet conformation of the peptide and a significant
change in fiber morphology from straight to kinked . as a consequence
,
the ability of these fibers to associate along their length and form
large bundles is reduced .
these structural changes ( fiber structure
and network topology ) significantly affect the mechanical properties
of the hydrogels ( shear modulus and elasticity ) . |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``COPS Improvements Act of 2007''.
SEC. 2. COPS GRANT IMPROVEMENTS.
(a) In General.--Section 1701 of the Omnibus Crime Control and Safe
Streets Act of 1968 (42 U.S.C. 3796dd) is amended--
(1) by amending subsection (a) to read as follows:
``(a) Grant Authorization.--The Attorney General shall carry out
grant programs under which the Attorney General makes grants to States,
units of local government, Indian tribal governments, other public and
private entities, multi-jurisdictional or regional consortia, and
individuals for the purposes described in subsections (b), (c), (d),
and (e).'';
(2) in subsection (b)--
(A) by striking the subsection heading text and
inserting ``Community Policing and Crime Prevention
Grants'';
(B) in paragraph (3), by striking ``, to increase
the number of officers deployed in community-oriented
policing'';
(C) in paragraph (4), by inserting ``or train''
after ``pay for'';
(D) by inserting after paragraph (4) the following:
``(5) award grants to hire school resource officers and to
establish school-based partnerships between local law
enforcement agencies and local school systems to combat crime,
gangs, drug activities, and other problems in and around
elementary and secondary schools;'';
(E) by striking paragraph (9);
(F) by redesignating paragraphs (10) through (12)
as paragraphs (9) through (11), respectively;
(G) by striking paragraph (13);
(H) by redesignating paragraphs (14) through (17)
as paragraphs (12) through (15), respectively;
(I) in paragraph (14), as so redesignated, by
striking ``and'' at the end;
(J) in paragraph (15), as so redesignated, by
striking the period at the end and inserting a
semicolon; and
(K) by adding at the end the following:
``(16) establish and implement innovative programs to
reduce and prevent illegal drug manufacturing, distribution,
and use, including the manufacturing, distribution, and use of
methamphetamine; and
``(17) award enhancing community policing and crime
prevention grants that meet emerging law enforcement needs, as
warranted.'';
(3) by striking subsection (c);
(4) by striking subsections (h) and (i);
(5) by redesignating subsections (d) through (g) as
subsections (f) through (i), respectively;
(6) by inserting after subsection (b) the following:
``(c) Troops-to-Cops Programs.--
``(1) In general.--Grants made under subsection (a) may be
used to hire former members of the Armed Forces to serve as
career law enforcement officers for deployment in community-
oriented policing, particularly in communities that are
adversely affected by a recent military base closing.
``(2) Definition.--In this subsection, `former member of
the Armed Forces' means a member of the Armed Forces of the
United States who is involuntarily separated from the Armed
Forces within the meaning of section 1141 of title 10, United
States Code.
``(d) Community Prosecutors Program.--The Attorney General may make
grants under subsection (a) to pay for additional community prosecuting
programs, including programs that assign prosecutors to--
``(1) handle cases from specific geographic areas; and
``(2) address counter-terrorism problems, specific violent
crime problems (including intensive illegal gang, gun, and drug
enforcement and quality of life initiatives), and localized
violent and other crime problems based on needs identified by
local law enforcement agencies, community organizations, and
others.
``(e) Technology Grants.--The Attorney General may make grants
under subsection (a) to develop and use new technologies (including
interoperable communications technologies, modernized criminal record
technology, and forensic technology) to assist State and local law
enforcement agencies in reorienting the emphasis of their activities
from reacting to crime to preventing crime and to train law enforcement
officers to use such technologies.'';
(7) in subsection (f), as so redesignated--
(A) in paragraph (1), by striking ``to States,
units of local government, Indian tribal governments,
and to other public and private entities,'';
(B) in paragraph (2), by striking ``define for
State and local governments, and other public and
private entities,'' and inserting ``establish'';
(C) in the first sentence of paragraph (3), by
inserting ``(including regional community policing
institutes)'' after ``training centers or facilities'';
and
(D) by adding at the end the following:
``(4) Exclusivity.--The Office of Community Oriented
Policing Services shall be the exclusive component of the
Department of Justice to perform the functions and activities
specified in this paragraph.'';
(8) in subsection (g), as so redesignated, by striking
``may utilize any component'', and all that follows and
inserting ``shall use the Office of Community Oriented Policing
Services of the Department of Justice in carrying out this
part.'';
(9) in subsection (h), as so redesignated--
(A) by striking ``subsection (a)'' the first place
that term appears and inserting ``paragraphs (1) and
(2) of subsection (b)''; and
(B) by striking ``in each fiscal year pursuant to
subsection (a)'' and inserting ``in each fiscal year
for purposes described in paragraph (1) and (2) of
subsection (b)'';
(10) in subsection (i), as so redesignated, by striking the
second sentence; and
(11) by adding at the end the following:
``(j) Retention of Additional Officer Positions.--For any grant
under paragraph (1) or (2) of subsection (b) for hiring or rehiring
career law enforcement officers, a grant recipient shall retain each
additional law enforcement officer position created under that grant
for not less than 12 months after the end of the period of that grant,
unless the Attorney General waives, wholly or in part, the retention
requirement of a program, project, or activity.''.
(b) Applications.--Section 1702 of the Omnibus Crime Control and
Safe Streets Act of 1968 (42 U.S.C. 3796dd-1) is amended--
(1) in subsection (c)--
(A) in the matter preceding paragraph (1), by
inserting ``, unless waived by the Attorney General''
after ``under this part shall'';
(B) by striking paragraph (8); and
(C) by redesignating paragraphs (9) through (11) as
paragraphs (8) through (10), respectively; and
(2) by striking subsection (d).
(c) Renewal of Grants.--Section 1703 of the Omnibus Crime Control
and Safe Streets Act of 1968 (42 U.S.C. 3796dd-2) is amended to read as
follows:
``SEC. 1703. RENEWAL OF GRANTS.
``(a) In General.--A grant made under this part may be renewed,
without limitations on the duration of such renewal, to provide
additional funds, if the Attorney General determines that the funds
made available to the recipient were used in a manner required under an
approved application and if the recipient can demonstrate significant
progress in achieving the objectives of the initial application.
``(b) No Cost Extensions.--Notwithstanding subsection (a), the
Attorney General may extend a grant period, without limitations as to
the duration of such extension, to provide additional time to complete
the objectives of the initial grant award.''.
(d) Limitation on Use of Funds.--Section 1704 of the Omnibus Crime
Control and Safe Streets Act of 1968 (42 U.S.C. 3796dd-3) is amended--
(1) in subsection (a), by striking ``that would, in the
absence of Federal funds received under this part, be made
available from State or local sources'' and inserting ``that
the Attorney General determines would, in the absence of
Federal funds received under this part, be made available for
the purpose of the grant under this part from State or local
sources''; and
(2) by striking subsection (c).
(e) Enforcement Actions.--
(1) In general.--Section 1706 of the Omnibus Crime Control
and Safe Streets Act of 1968 (42 U.S.C. 3796dd-5) is amended--
(A) in the section heading, by striking
``revocation or suspension of funding'' and inserting
``enforcement actions''; and
(B) by striking ``revoke or suspend'' and all that
follows and inserting ``take any enforcement action
available to the Department of Justice.''.
(2) Technical and conforming amendment.--The table of
contents of title I of the Omnibus Crime Control and Safe
Streets Act of 1968 (42 U.S.C. 3711) is amended by striking the
item relating to section 1706 and inserting the following:
``Sec. 1706. Enforcement actions.''.
(f) Definitions.--Section 1709(1) of the Omnibus Crime Control and
Safe Streets Act of 1968 (42 U.S.C. 3796dd-8(1)) is amended--
(1) by inserting ``who is a sworn law enforcement officer''
after ``permanent basis''; and
(2) by inserting ``, including officers for the Amtrak
Police Department'' before the period at the end.
(g) Authorization of Appropriations.--Section 1001(11) of the
Omnibus Crime Control and Safe Streets Act of 1968 (42 U.S.C. 3793(11))
is amended--
(1) in subparagraph (A), by striking ``1,047,119,000'' and
inserting ``1,150,000,000''; and
(2) in subparagraph (B)--
(A) in the first sentence, by striking ``3
percent'' and inserting ``5 percent''; and
(B) by striking the second sentence and inserting
the following: ``Of the funds available for grants
under part Q, not less than $600,000,000 shall be used
for grants for the purposes specified in section
1701(b), not more than $200,000,000 shall be used for
grants under section 1701(d), and not more than
$350,000,000 shall be used for grants under section
1701(e).''.
(h) Purposes.--Section 10002 of the Public Safety Partnership and
Community Policing Act of 1994 (42 U.S.C. 3796dd note) is amended--
(1) in paragraph (4), by striking ``development'' and
inserting ``use''; and
(2) in the matter following paragraph (4), by striking
``for a period of 6 years''.
(i) COPS Program Improvements.--
(1) In general.--Section 109(b) of the Omnibus Crime
Control and Safe Streets Act of 1968 (42 U.S.C. 3712h(b)) is
amended--
(A) by striking paragraph (1);
(B) by redesignating paragraphs (2) and (3) as
paragraphs (1) and (2), respectively; and
(C) in paragraph (2), as so redesignated, by
inserting ``, except for the program under part Q of
this title'' before the period.
(2) Law enforcement computer systems.--Section 107 of the
Omnibus Crime Control and Safe Streets Act of 1968 (42 U.S.C.
3712f) is amended by adding at the end the following:
``(c) Exception.--This section shall not apply to any grant made
under part Q of this title.''. | COPS Improvements Act of 2007 - Amends the Omnibus Crime Control and Safe Streets Act of 1968 to expand the authority of the Attorney General to make grants for public safety and community policing programs (COPS ON THE BEAT or COPS program). Revises grant purposes to provide for: (1) the hiring or training of law enforcement officers for intelligence, antiterror, and homeland security duties; (2) the hiring of school resource officers; (3) school-based partnerships between local law enforcement agencies and local school systems to combat crime, gangs, drug activities, and other problems facing elementary and secondary schools; (4) innovative programs to reduce and prevent illegal drug (including methamphetamine) manufacturing, distribution, and use; and (5) enhanced community policing and crime prevention grants that meet emerging law enforcement needs.
Allows COPS program grants to be used to hire former members of the Armed Forces to serve as career law enforcement officers for community-oriented policing, particularly in communities adversely affected by a recent military base closing.
Authorizes the Attorney General to make grants to: (1) assign community prosecutors to handle cases from specific geographic areas and address counterterrorism problems, specific violent crime problems, and localized violent and other crime problems; and (2) develop new technologies to assist state and local law enforcement agencies in crime prevention.
Grants the Office of Community Oriented Policing Services exclusive authority to perform functions and activities under the COPS program.
Requires grant recipients to retain additional law enforcement officers for a 12-month period after the end of the grant period.
Authorizes the Attorney General to renew COPS program grants if grant recipients can demonstrate significant progress in achieving the objectives of the initial grant application.
Increases: (1) the authorization of appropriation for the COPS program; and (2) the amount of funds available for technical assistance from 3 to 5%. Specifies amounts to be made available for hiring officers and prosecutors and for technology grants. |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Landmine Moratorium Extension Act of
1993''.
SEC. 2. FINDINGS.
The Congress makes the following findings:
(1) Antipersonnel landmines, which are designed to maim and
kill people, have been used indiscriminately in dramatically
increasing numbers around the world. Hundreds of thousands of
noncombatant civilians, including children, have been the
primary victims. Unlike other military weapons, landmines often
remain implanted and undiscovered after conflict has ended,
causing massive suffering to civilian populations.
(2) Tens of millions of landmines have been strewn in at
least sixty-two countries, often making whole areas
uninhabitable. The State Department estimates there are more
than ten million landmines in Afghanistan, nine million in
Angola, four million in Cambodia, three million in Iraqi
Kurdistan, and two million each in Somalia, Mozambique, and the
former Yugoslavia. Hundreds of thousands of landmines were used
in conflicts in Central America in the 1980's.
(3) Advanced technologies are being used to manufacture
sophisticated mines which can be scattered remotely at a rate
of one thousand per hour. These mines, which are being produced
by many industrialized countries, were discovered in Iraqi
arsenals after the Persian Gulf War.
(4) At least three hundred types of antipersonnel landmines
have been manufactured by at least forty four countries,
including the United States. However, the United States is not
a major exporter of landmines. During the past ten years the
Administration has approved ten licenses for the commercial
export of antipersonnel landmines with a total value of
$980,000, and the sale under the Foreign Military Sales program
of one hundred nine thousand one hundred and twenty-nine
antipersonnel landmines.
(5) The United States signed, but has not ratified, the
1980 Convention on Prohibitions or Restrictions on the Use of
Certain Conventional Weapons Which May Be Deemed To Be
Excessively Injurious or To Have Indiscriminate Effects.
Protocol II of the Convention, otherwise known as the Landmine
Protocol, prohibits the indiscriminate use of landmines.
(6) When it signed the 1980 Convention, the United States
stated: ``We believe that the Convention represents a positive
step forward in efforts to minimize injury or damage to the
civilian population in time of armed conflict. Our signature of
the Convention reflects the general willingness of the United
States to adopt practical and reasonable provisions concerning
the conduct of military operations, for the purpose of
protecting noncombatants.''.
(7) The United States also indicated that it had supported
procedures to enforce compliance, which were omitted from the
Convention's final draft. The United States stated: ``The
United States strongly supported proposals by other countries
during the Conference to include special procedures for dealing
with compliance matters, and reserves the right to propose at a
later date additional procedures and remedies, should this
prove necessary, to deal with such problems.''.
(8) The lack of compliance procedures and other weaknesses
have significantly undermined the effectiveness of the Landmine
Protocol. Since it entered into force on December 2, 1983, the
number of civilians maimed and killed by antipersonnel
landmines has multiplied.
(9) Since the moratorium on United States sales, transfers
and exports of antipersonnel landmines was signed into law on
October 23, 1992, the European Parliament has issued a
resolution calling for a five year moratorium on sales,
transfers and exports of antipersonnel landmines, and the
Government of France has announced that it has ceased all
sales, transfers and exports of antipersonnel landmines.
(10) On December 2, 1993, ten years will have elapsed since
the 1980 Convention entered into force, triggering the right of
any party to request a United Nations conference to review the
Convention. Amendments to the Landmine Protocol may be
considered at that time. The Government of France has made a
formal request to the United Nations Secretary General for a
review conference. With necessary preparations and
consultations among governments, a review conference is not
expected to be convened before late 1994 or early 1995.
(11) The United States should continue to set an example
for other countries in such negotiations by extending the
moratorium on sales, transfers and exports of antipersonnel
landmines for an additional three years. A moratorium of this
duration would extend the current prohibition on the sale,
transfer and export of antipersonnel landmines a sufficient
time to take into account the results of a United Nations
review conference.
SEC. 3. POLICY.
(a) It shall be the policy of the United States to seek verifiable
international agreements prohibiting the sale, transfer or export,
further limiting the manufacture, possession and use, and eventually,
terminating manufacture, possession and use of antipersonnel landmines.
(b) It is the sense of the Congress that the President should
submit the 1980 Convention on Certain Conventional Weapons to the
Senate for ratification. Furthermore, the Administration should
participate in a United Nations conference to review the Landmine
Protocol, and actively seek to negotiate under United Nations auspices
a modification of the Landmine Protocol, or another international
agreement, to prohibit the sale, transfer or export of antipersonnel
landmines, and to further limit their manufacture, possession and use.
SEC. 4. MORATORIUM ON TRANSFERS OF ANTI-PERSONNEL LANDMINES ABROAD.
For a period of three years beginning on the date of enactment of
this Act--
(1) no sale may be made or financed, no transfer may be
made, and no license for export may be issued, under the Arms
Export Control Act, with respect to any antipersonnel landmine;
and
(2) no assistance may be provided under the Foreign
Assistance Act of 1961, with respect to the provision of any
antipersonnel landmine.
SEC. 5. DEFINITION.
For purposes of this section, the term ``antipersonnel landmine''
means--
(1) any munition placed under, on, or near the ground or
other surface area, or delivered by artillery, rocket, mortar,
or similar means or dropped from an aircraft and which is
designed to be detonated or exploded by the presence,
proximity, or contact of a person;
(2) any device or material which is designed, constructed,
or adapted to kill or injure and which functions unexpectedly
when a person disturbs or approaches an apparently harmless
object or performs an apparently safe act; and
(3) any manually-emplaced munition or device designed to
kill, injure, or damage and which is actuated by remote control
or automatically after a lapse of time. | Landmine Moratorium Extension Act of 1993 - Declares that it is U.S. policy to seek international agreements prohibiting the sale, transfer, or export, and terminating the manufacture, possession, and use, of antipersonnel landmines.
Expresses the sense of the Congress that: (1) the President should submit the 1980 Convention on Certain Conventional Weapons to the Senate for ratification; and (2) the Administration should negotiate a modification of the Landmine Protocol under United Nations auspices or another international agreement to limit the sale, transfer, manufacture, and use of landmines.
Prohibits for three years after this Act's enactment: (1) sales, financing, transfers, and the issuance of licenses under the Arms Export Control Act with respect to antipersonnel landmines; and (2) assistance under the Foreign Assistance Act of 1961 with respect to the provision of such landmines. |
SECTION 1. SHORT TITLE.
This Act may be cited as ``Mynisha's Law''.
SEC. 2. FINDINGS.
Congress finds--
(1) with an estimated 26,500 gangs operating within the
United States, gang violence and drug trafficking remain
serious problems throughout the country, causing injury and
death to innocent victims, often children;
(2) on November 13, 2005, a gang-related dispute broke out
in San Bernardino, California, and gunfire sprayed an apartment
building, killing 11-year-old Mynisha Crenshaw and seriously
wounding her 14-year-old sister as they ate Sunday dinner with
their family;
(3) this tragic shooting symbolizes the struggle that so
many communities across the United States, like San Bernardino,
face in combating gang violence, and serves as a reminder of
the nationwide problem of protecting children from senseless
violence;
(4) according to the National Drug Threat Assessment,
criminal street gangs are responsible for the distribution of
much of the cocaine, methamphetamine, heroin, and other illegal
drugs throughout the United States;
(5) the Federal Government has made an increased commitment
to the suppression of gang violence through enhanced law
enforcement and criminal penalties; and
(6) more Federal resources and coordination are needed to
reduce gang violence through proven and proactive prevention
and intervention programs that focus on keeping at-risk youth
in school and out of the criminal justice system.
SEC. 3. DESIGNATION AS A HIGH INTENSITY GANG ACTIVITY AREA.
(a) In General.--A unit of local government, city, county, tribal
government, or a group of counties (whether located in 1 or more
States) may submit an application to the Attorney General for
designation as a High Intensity Gang Activity Area.
(b) Criteria.--
(1) In general.--The Attorney General shall establish
criteria for reviewing applications submitted under subsection
(a).
(2) Considerations.--In establishing criteria under
subsection (a) and evaluating an application for designation as
a High Intensity Gang Activity Area, the Attorney General shall
consider--
(A) the current and predicted levels of gang crime
activity in the area;
(B) the extent to which violent crime in the area
appears to be related to criminal gang activity;
(C) the extent to which the area is already engaged
in local or regional collaboration regarding, and
coordination of, gang prevention activities; and
(D) such other criteria as the Attorney General
determines to be appropriate.
SEC. 4. PURPOSE OF THE TASK FORCE.
(a) In General.--In order to coordinate Federal assistance to High
Intensity Gang Activity Areas, the Attorney General shall establish an
Interagency Gang Prevention Task Force (in this Act referred to as the
``Task Force'') in each such area, consisting of a representative
from--
(1) the Department of Justice;
(2) the Department of Education;
(3) the Department of Labor;
(4) the Department of Health and Human Services; and
(5) the Department of Housing and Urban Development.
(b) Coordination.--For each High Intensity Gang Activity Area
designated by the Attorney General under section 3, the Task Force
shall--
(1) coordinate the activities of the Federal Government to
create a comprehensive gang prevention response, focusing on
early childhood intervention, at-risk youth intervention,
literacy, employment, community policing, and comprehensive
community-based programs such as Operation Cease Fire; and
(2) coordinate its efforts with local and regional gang
prevention efforts.
(c) Programs.--Each Task Force shall prioritize the needs of a High
Intensity Gang Activity Area for funding under--
(1) the Child Care and Development Block Grant Act of 1990
(42 U.S.C. 9858 et seq.);
(2) the Even Start programs under subpart 3 of part B of
title I of the Elementary and Secondary Education Act of 1965
(20 U.S.C. 6381 et seq.);
(3) the Healthy Start Initiative under section 330H of the
Public Health Services Act (42 U.S.C. 254c-8);
(4) the Head Start Act (42 U.S.C. 9831 et seq.);
(5) the 21st Century Community Learning Centers program
under part B of title IV of the Elementary and Secondary
Education Act of 1965 (20 U.S.C. 7171 et seq.);
(6) the Job Corps program under subtitle C of title I of
the Workforce Investment Act of 1998 (29 U.S.C. 2881 et seq.);
(7) the community development block grant program under
title I of the Housing and Community Development Act of 1974
(42 U.S.C. 5301 et seq.);
(8) the Gang Resistance Education and Training projects
under subtitle X of title III of the Violent Crime Control and
Law Enforcement Act of 1994 (42 U.S.C. 13921);
(9) any program administered by the Office of Community
Oriented Policing Services;
(10) the Juvenile Accountability Block Grant program under
part R of title I of the Omnibus Crime Control and Safe Streets
Act of 1968 (42 U.S.C. 3796ee et seq.);
(11) the Edward Byrne Memorial Justice Assistance Grant
Program under subpart 1 of part E of title I of the Omnibus
Crime Control and Safe Streets Act of 1968 (42 U.S.C. 3750 et
seq.); and
(12) any other program that the Task Force determines to be
appropriate.
(d) Reporting Requirements.--
(1) Annual task force reports to ag.--Not later than
September 1 of each year, each Task Force shall submit to the
Attorney General a report on the funding needs and programmatic
outcomes for each area designated as a High Intensity Gang
Activity Area.
(2) Annual ag report to congress.--Not later than December
1 of each year, the Attorney General shall submit a report to
the appropriate committees of Congress and the Director of the
Office of Management and Budget and the Domestic Policy Council
that describes, for each designated High Intensity Gang
Activity Area--
(A) the specific long-term and short-term goals and
objectives of each such area;
(B) the measurements used to evaluate the
performance of the High Intensity Gang Activity Area in
achieving the long-term and short-term goals described
under subparagraph (A);
(C) the age, composition, and membership of gangs
in each such area;
(D) the number and nature of crimes committed by
gangs and gang members in each such area;
(E) the definition of the term ``gang'' used to
compile the information required under this subsection
for each such area; and
(F) the programmatic outcomes and funding need of
each High Intensity Gang Activity Area, including--
(i) an evidence-based analysis of the best
practices and outcomes from the work of the
relevant local collaborative working group; and
(ii) an analysis of whether Federal
resources distributed meet the needs of the
High Intensity Gang Activity Area and, if any
programmatic funding shortfalls exist,
recommendations for programs or funding to meet
such shortfalls.
SEC. 5. AUTHORIZATION OF APPROPRIATIONS.
There are authorized to be appropriated such sums as are necessary
to meet any needs identified by the Attorney General or in any report
submitted under section 4(d)(2). | Mynisha's Law - Authorizes any local or tribal government to submit an application to the Attorney General for designation as a High Intensity Gang Activity Area.
Directs the Attorney General to: (1) establish criteria for reviewing such applications; and (2) establish an Interagency Gang Prevention Task Force in each Area. Directs each Task Force to: (1) coordinate government activities to create a comprehensive gang prevention response, focusing on early childhood intervention, at-risk youth intervention, literacy, employment, community policing, and comprehensive community-based programs such as Operation Cease Fire; (2) coordinate with local and regional gang prevention efforts; (3) prioritize the needs of each Area for funding under specified federal community assistance and grant programs; and (4) report to the Attorney General on the funding needs and programmatic outcomes for each Area.
Requires the Attorney General to report to Congress, the Director of the Office of Management and Budget (OMB) and the Domestic Policy Council annually on: (1) the specific long-term and short-term goals and objectives of each Area; (2) the measurements used to evaluate each Area's performance; (3) the gangs and gang crimes committed in each Area; and (5) the programmatic outcomes and funding need of each Area. |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Servicemembers Insurance Relief Act
of 2014''.
SEC. 2. FINDINGS AND PURPOSE.
(a) Findings.--The Congress finds the following:
(1) When servicemembers move from one State to another they
are required to go through a burdensome process of changing
their auto insurance policies.
(2) The Servicemembers Civil Relief Act (50 U.S.C. App. 501
et seq.) allows the men and women serving in the United States
Armed Forces to keep a stable domicile with respect to auto
licensing and fees even if they are forced to move temporarily
in compliance with military orders.
(3) The Federal Insurance Office of the U.S. Department of
the Treasury, in its report of December 12, 2013, on how to
modernize and improve the system of insurance regulation in the
United States, found that ``an individual on active duty can
transfer credit cards, checking accounts, and other financial
services simply by submitting a change of address form. By
contrast, an individual moving from one state to another may be
required to obtain a new auto insurance policy on each
transfer''. Furthermore the report called on interested parties
``to identify a more accommodating approach for service members
who have personal auto policies and are required to move across
state lines''.
(4) Relief should be provided with respect to auto
insurance policies for servicemembers and their families that
are required to move in compliance with any temporary duty or
permanent change of station order.
(b) Purpose.--The purpose of this Act is to reduce the burdens and
increase the protections involved in changing auto insurance policies
for servicemembers and their families who are required to move in
compliance with a temporary duty or permanent change of station order.
SEC. 3. MAINTENANCE OF DOMICILE FOR INSURANCE PURPOSES.
(a) In General.--A member of a household of a servicemember shall
neither lose nor acquire a residence or domicile for purposes of
insuring a motor vehicle used primarily for personal, family, or
household use if--
(1) in the case of a member of the household who is a
servicemember, such servicemember has temporarily moved to
comply with any temporary duty or permanent change of station
order; or
(2) in the case of any other member of the household, such
member has temporarily moved to accompany a servicemember of
such household who is complying with any temporary duty or
permanent change of station order.
(b) Notice.--
(1) Requirement.--If a member of a household of a
servicemember notifies an insurer of a motor vehicle of such
member of a move referred to in subsection (a), such insurer
shall provide such member with a servicemembers insurance
choice notice under paragraph (2).
(2) Servicemembers insurance choice notice.--The Director
of the Federal Insurance Office of the Department of the
Treasury shall promulgate, in compliance with the rulemaking
requirements of subchapter II of chapter 5 of title 5, United
States Code (commonly known as the Administrative Procedure
Act)--
(A) a standard servicemembers insurance choice
notice that shall--
(i) summarize clearly and in plain language
the right of servicemembers and members of
their households, in addition to options
available under current law, to continue an
existing auto insurance policy as allowed by
the insurer with appropriate adjustments that
relate only to location risk factors;
(ii) include language notifying the
servicemember that the insurer to whom the
servicemember provided the notice of a move
shall explain the coverage options available to
the servicemember as a result of the move; and
(iii) include standard language that
requires no alterations or additions for an
insurer providing the notice to be fully in
compliance with paragraph (1); and
(B) standards regarding methods for transmittal of
such notice to a member of a household of a
servicemember that are sufficient to comply with
paragraph (1).
(3) Safe harbor.--Paragraph (1) may not be construed to
impose any duty on an insurer who is notified of a move
referred to in subsection (a) to determine whether the person
providing such notice is a servicemember.
(c) Limitations.--Nothing in this section shall be construed to--
(1) require a person to maintain an existing auto insurance
policy;
(2) allow an insurer to impose any penalties against a
member of a household of a servicemember based solely on a
decision to maintain or not maintain an existing auto insurance
policy, as allowed by the insurer with appropriate adjustments
that relate only to location risk factors; or
(3) require an insurer to continue providing coverage to
such a member.
(d) Preemption.--The provisions of this Act shall supersede any and
all State or local laws that conflict with this Act, including--
(1) any State or local law that requires a member of a
household of a servicemember to change the auto insurance
policy of such member;
(2) any State or local law that seeks to assert control
over the regulation of such policy other than by the State in
which the auto insurance policy was issued or renewed; and
(3) any State or local law regarding proof of insurance
that prohibits the electronic delivery of insurance documents.
(e) Liability Limits.--Notwithstanding subsection (d)(2), the
minimum security requirements for motor vehicles of the State where a
servicemember resides shall apply to an auto insurance policy of a
member of such servicemember's household.
(f) Enforcement.--Authority to examine and enforce insurer
compliance with the provisions of this Act shall be held by the State
in which the auto insurance policy was issued or renewed.
SEC. 4. DEFINITIONS.
In this Act:
(a) Member of a Household.--The term ``member of a household''
means, with respect to a servicemember--
(1) the servicemember;
(2) the spouse of the servicemember; or
(3) any dependent residing with the servicemember or the
spouse of the servicemember.
(b) Motor Vehicle.--The term ``motor vehicle'' has the meaning
given the term in section 30102(a)(6) of title 49, United States Code.
(c) Servicemember.--The term ``servicemember'' means a member of
the uniformed services, as such term is defined in section 101(a) of
title 10, United States Code, or of the National Guard or the reserve
components thereof.
(d) State.--The term ``State'' means each of the several States of
the United States, the District of Columbia, and any commonwealth,
territory, or possession of the United States.
(e) Temporarily Moved.--The term ``temporarily moved'' means, with
respect to a person, that the person has moved from one State to
another but has not decided to reside indefinitely in the State to
which such person moved. | Servicemembers Insurance Relief Act of 2014 - Declares that a member of a servicemember's household neither loses nor acquires a residence or domicile for purposes of insuring a motor vehicle primarily for personal, family, or household use if: (1) the servicemember has temporarily moved to comply with any temporary duty or permanent change of station order, or (2) the member of the household has temporarily moved to accompany a servicemember who is complying with such an order. Defines: (1) "servicemember" as a member of the uniformed services, the National Guard, or reserve components; and (2) "member of a household" as the servicemember, the spouse of a servicemember, or any dependent residing with such a servicemember or a servicemember's spouse. Requires insurers to provide a member of a servicemember's household with a servicemembers insurance choice notice if a household member notifies the insurer of such a move. Directs the Federal Insurance Office of the Department of the Treasury to promulgate a standard servicemembers insurance choice notice that: (1) summarizes the right of servicemembers and members of their households, in addition to options available under current law, to continue an existing auto insurance policy as allowed by the insurer with appropriate adjustments that relate only to location risk factors; (2) notifies the servicemember that the insurer will explain the coverage options available to the servicemember as a result of the move; and (3) requires no alterations or additions for an insurer to be in compliance with such notification requirements. Prohibits this Act from requiring an insurer to continue providing coverage to such a member. Provides enforcement authority to the states in which the relevant auto insurance policy was issued or renewed. |
SECTION 1. STUDY ON AIR FORCE TEST AND TRAINING RANGE INFRASTRUCTURE.
(a) Study.--
(1) In general.--The Secretary of the Air Force shall
conduct a study on the ability of the major air test and
training range infrastructure, including major military
operating area airspace and special use airspace, to support
the full spectrum of Air Force operations. The Secretary shall
incorporate the results of the study into a master plan for
requirements and proposed investments to meet Air Force
training and test needs through 2025. The study and the master
plan shall be known as the ``2025 Air Test and Training Range
Enhancement Plan''.
(2) Consultation.--The Secretary of the Air Force shall, in
conducting the study required under paragraph (1), consult with
the Secretaries of the other military departments to determine
opportunities for joint use and training of the ranges, and to
assess the requirements needed to support combined arms
training on the ranges. The Secretary shall also consult with
the Department of the Interior, the Department of Agriculture,
the Federal Aviation Administration, and the Federal Energy
Regulation Commission to assess the need for transfers of
administrative control of certain parcels to the Department of
Defense to protect the missions and control of the ranges.
(b) Reports.--
(1) In general.--The Secretary of the Air Force shall
submit to the congressional defense committees (as that term is
defined in section 101 of title 10, United States Code) an
interim report and a final report on the plan required under
subsection (a) not later than 120 days and 210 days,
respectively, after the date of the enactment of this Act.
(2) Content.--The plan submitted under paragraph (1)
shall--
(A) document the current condition and adequacy of
the major Air Force test and training range
infrastructure in the United States to meet test and
training requirements;
(B) identify potential areas of concern for
maintaining the physical safety, security, and current
operating environment of such infrastructure;
(C) identify potential issues and threats related
to the sustainability of the test and training
infrastructure, including electromagnetic spectrum
encroachment, overall bandwidth availability, and
protection of classified information;
(D) assess coordination among ranges and local,
state, regional, and Federal entities involved in land
use planning, and develop recommendations on how to
improve communication and coordination of such
entities;
(E) propose remedies and actions to manage economic
development on private lands on or surrounding the test
and training infrastructure to preserve current
capabilities;
(F) identify critical parcels of land not currently
under the control of the Air Force for acquisition of
deed or restrictive easements in order to protect
current operations, access and egress corridors, and
range boundaries, or to expand the capability of the
air test and training ranges;
(G) identify which parcels identified pursuant to
subparagraph (F) could, through the acquisition of
conservation easements, serve military interests while
also preserving recreational access to public and
private lands, protecting wildlife habitat, or
preserving opportunities for energy development and
energy transmission;
(H) prioritize improvements and modernization of
the facilities, equipment, and technology supporting
the infrastructure in order to provide a test and
training environment that accurately simulates and or
portrays the full spectrum of threats and targets of
likely United States adversaries in 2025;
(I) incorporate emerging requirements generated by
requirements for virtual training and new weapon
systems, including the F-22, the F-35, space and cyber
systems, and Remotely Piloted Aircraft;
(J) assess the value of State and local legislative
initiatives to protect Air Force test and training
range infrastructure;
(K) identify parcels with no value to future
military operations; and
(L) propose a list of prioritized projects,
easements, acquisitions, or other actions, including
estimated costs required to upgrade the test and
training range infrastructure, taking into
consideration the criteria set forth in this paragraph.
(3) Form.--Each report required under this subsection shall
be submitted in unclassified form, but may include a classified
annex as necessary.
(4) Rule of construction.--The reports submitted under this
section shall not be construed as meeting the requirements of
section 2815(d) of the Military Construction Authorization Act
for Fiscal Year 2000 (Public Law 106-65; 113 Stat. 852). | Directs the Secretary of the Air Force to: (1) conduct a study on the ability of the major air test and training range infrastructure to support the full spectrum of Air Force operations; (2) develop a master plan for requirements and proposed investments to meet Air Force training and test needs through 2025; and (3) submit to the congressional defense and appropriations committees an interim and final report on the master plan. |
fiber bragg gratings ( fbg ) are microstructured optical fibers that present a spatially periodic variation of the refractive index .
the combination of the guiding properties of the periodic media with the kerr nonlinearity of the fiber results in the very particular light propagation characteristic of these elements , which make them very promising for many technological applications that range from optical communications ( wavelength division , dispersion management , optical buffers and storing devices , etc . ) to fiber sensing ( structural stress measure in aircraft components and buildings , temperature change detection , etc . ) , see , e.g. , the recent review @xcite .
the amplitude equations that are commonly used in the literature to model one dimensional light propagation in a fbg are the so - called nonlinear coupled mode equations ( nlcme ) @xcite , * * * * which , conveniently scaled , can be written as@xmath0 where @xmath1 are the envelopes of the two counterpropagating wavetrains that resonate with the grating , @xmath2 is the strength of the coupling effect produced by the grating and @xmath3 is ratio of the self to cross nonlinear interaction coefficient ( @xmath4 for a cubic kerr nonlinearity @xcite ) .
the nlcme can be obtained from the full maxwell - lorentz equations using multiple scales techniques in the limit of small grating depth , small light intensity and slow spatial and temporal dependence of the field envelopes ( see @xcite for a detailed description of this derivation process ) .
it has been recently shown @xcite that light propagation in fbg can develop dispersive structures that are not accounted for in the nlcme formulation , and that , to correctly describe the weakly nonlinear dynamics of the system , the nlcme have to be completed with material dispersion terms:@xmath5 the dispersive nonlinear coupled mode equations above ( nlcmed ) are scaled as the nlcme : the characteristic length scale is the slow scale that results from the balance of the advection term with the small effect of the grating , the characteristic time is the corresponding transport time scale ( which sets to one the scaled group velocity ) , and the characteristic size of the wavetrains is the resulting one from the saturation of the small nonlinear terms .
the slow envelope assumption forces the dispersive terms to be always small as compared with the advection terms ; in other words , second derivatives of the slow amplitudes are much smaller than first derivatives . in the scaled equations
this effect is contained in the scaled dispersion coefficient @xmath6 ( which measures the dispersion to transport ratio ) and therefore , in order to be consistent with the slow envelope assumption , the nlcmed must be considered in the limit @xmath7 .
the nlcmed can be somehow regarded as asymptotically nonuniform , in the sense that the nlcmed is an asymptotic model obtained in the @xmath7 ( weakly nonlinear , slow envelope ) limit that still contains the small parameter @xmath6 .
this is the unavoidable consequence of simultaneously considering two balances of different asymptotic order : one induced by the dominant effect of the transport at the group velocity ( balance described by nlcme ) and a second one that is associated with the underlying dispersive , nonlinear schrdinger - like dynamics of the system .
the small dispersive terms in the nlcmed are essential to describe the dynamics of the system when it develops small dispersive scales @xmath8 .
as it was shown in @xcite , the nlcmed in the @xmath7 limit constitute a singular perturbation problem ( cf .
@xcite ) and the onset of the dispersive scales is not a higher order , longer time effect ; it takes place in the same timescale of the nlcme , no matter how small is the dispersion coefficient @xmath9 .
a solution of the nlcmed for @xmath10 that exhibits small dispersive scales all over the domain is represented in figure [ fig : xtchaos1 ] : note that , for short time , the dispersive structures just propagate with the group velocity but , for @xmath11 , they also interact with each other giving rise to a very complicated spatio - temporal pattern .
the initial condition used in this simulation was a uniform modulus solution with a small random perturbation that , according to the dispersion - less nlcme formulation , was a stable solution . in order ensure that the small scales in figure [ fig : xtchaos1 ] are dispersion induced scales we have repeated the nlcmed simulation but with a reduced dispersion @xmath12 .
the result is plotted in figure [ fig : xtchaos2 ] where it can be seen that the small scales fill again the entire domain , but its typical size , @xmath8 , is now approximately one half of that in figure [ fig : xtchaos1 ] ( see also the corresponding animations ` movie1.1.gif ` and ` movie1.2.gif ` ) .
space - time representation of a solution of the nlcmed exhibiting small dispersive scales all over the domain ( @xmath13 , @xmath14 , @xmath12 , and periodicity boundary conditions ) .
see the file ` movie1.2.gif ` for an animation of the onset of the dispersive scales . ]
the main goal of this paper is to show that , in addition to complex spatio - temporal patterns , the dispersion effects can also give rise to new , purely dispersive localized states , which might be of interest from the optical communications point of view .
it is interesting to note that the results in this paper apply also to bose - einstein condensates in optical lattices ( a system that has recently received very much attention @xcite ) and , in general , to any dissipation - less propagative system , extended in one spatial direction , reflection and translation invariant , and with a small superimposed spatial periodic modulation of its background , since the nlcmed are the appropriate envelope equations for the description of the weakly nonlinear resonant dynamics of this kind of systems . in order to show that light propagation in a fbg can happen in the form of dispersive pulses , we derive and solve numerically in section 2 an asymptotic equation for a family of symmetric pulses , and , in section 3
, we perform some numerical integrations of the complete nlcmed to show that some of the pulses in this family do propagate as stable localized structures .
finally , some concluding remarks are drawn in section 4 .
the starting point is the continuous wave ( cw ) family of constant uniform modulus solutions of the nlcme ( [ eq : nlcme+])-([eq : nlcme- ] ) @xmath15 where @xmath16 is the light intensity flowing through the fiber , @xmath17
$ ] measures the relative amount of both wavetrains , and the frequency and wavenumber of the amplitudes are given by@xmath18 the cw with @xmath19 and @xmath20 are approximate solutions of the nlcmed ( up to order @xmath6 corrections ) and its stability was first analyzed in @xcite and then completed in @xcite , where it was found that , for both signs of the dispersion coefficient , there are dispersively unstable cw which are stable in the dispersion less context of the nlcme .
sketch of a dispersive pulse on top of a continuous wave . ]
we now look for localized dispersive pulses propagating on top of one of the amplitudes of a stable cw , as sketched in figure [ fig : sketchpulse ] . in order to turn the background cw into a constant ,
it is convenient to first perform in the nlcmed the following change of variables@xmath21 to obtain@xmath22 a localized dispersive pulse on @xmath23 depends on the fast spatial scale @xmath24 and , according to ( [ eq : f+])-([eq : f- ] ) , in the short time scale , @xmath25 , it just propagates with the group velocity , suggesting that we have to look for solutions of the form @xmath26 with @xmath27 . inserting the above ansatz into ( [ eq : f+])-([eq : f- ] )
yields@xmath28 which means that @xmath29 remains in first approximation equal to the unperturbed cw .
similarly , the following equation is obtained for @xmath30@xmath31 where the @xmath32 ( @xmath33 ) sign corresponds to @xmath6 positive ( negative ) , together with the boundary conditions@xmath34 which ensure that the background cw is recovered away from the pulse . for dispersive pulses propagating over a zero background we have to set to zero @xmath35 , @xmath36 and @xmath37 in eq .
( [ eq : f0 + ] ) .
a standard nonlinear schrdinger ( nls ) equation is then obtained , which is known to exhibit localized pulses ( solitons ) in the focusing case of positive dispersion ( recall that @xmath3 ) .
note that in this case the effect of the grating is completely gone because it takes place only through the background state .
the only nonzero fourier spectrum components of these nls solitons correspond , in first approximation , to very large dispersive wavenumbers ( @xmath38 ) that are so off - resonance that they simply do not feel the grating .
equation ( [ eq : f0 + ] ) is a nonlinear schrdinger equation with a direct forcing term coming from the effect of the grating .
the steady solutions of this equation and their stability properties were analyzed in @xcite , where explicit analytic expressions for the steady pulses were found . in this paper
we consider the more general family of traveling localized solutions .
more precisely , we look for traveling pulses of the form@xmath39 where @xmath40 represents , in the original variables , a small correction of the group velocity .
the resulting boundary value problem for @xmath41 , after making use of relations ( [ alfa ] ) and ( [ eme ] ) and the rescaled variable @xmath42 , can be written as @xmath43 where @xmath44 and @xmath45 .
we are restricting our search to the focusing case of positive sign in eq .
( [ eq : f0 + ] ) and , in order to have a dispersively stable background cw , we have to consider only the range @xmath46 ( see @xcite ) , which implies that we have to look for pulses in eqs .
( [ eq : eqp2])-([eq : eqbcp2 ] ) only for @xmath47 . on the other hand , eqs .
( [ eq : eqp2])-([eq : eqbcp2 ] ) remain invariant under the transformation @xmath48 and @xmath49 , and therefore we can also set @xmath50 .
eigenvalues of the trivial state as a function of the parameters @xmath51 and @xmath52 .
sketches show the distribution of the four eigenvalues in each of the distinct regions . ]
the solutions of eqs .
( [ eq : eqp2])-([eq : eqbcp2 ] ) correspond to traveling dispersive pulses and can be regarded as homoclinic orbits ( in the variable @xmath53 ) connecting the trivial state ( i.e. , @xmath54 ) back to itself .
to analyze the existence of such connections we first consider the linearized system around the zero state:*@xmath55 * where @xmath56 , @xmath57 and @xmath58 are the real and imaginary part of @xmath41 , @xmath59 and @xmath60 , and the matrix @xmath61 is given by**@xmath62 * * the eigenvalues of this system are given by @xmath63 and @xmath64 , with @xmath65/2.\label{eq : eqeig}\ ] ] fig .
[ fig : eigval ] shows the behaviour of the four eigenvalues @xmath66 and @xmath67 in the @xmath68 plane .
there are four distinct regions , separated by the boundaries @xmath69 and @xmath70 : ( a ) four real eigenvalues , ( b ) two pairs of complex conjugate eigenvalues , ( c ) four purely imaginary eigenvalues and ( d ) two real eigenvalues along with two purely imaginary eigenvalues . in regions ( a ) and ( b ) the unstable and stable manifolds of the origin are two dimensional , while the equilibrium is nonhyperbolic in regions ( c ) and ( d ) where the center manifold is , respectively , four- and two - dimensional .
homoclinic orbits belong to both the stable and unstable manifold of the origin .
we investigate below the presence of homoclinic solutions in cases ( a ) and ( b ) , where these correspond to the intersections of two dimensional stable and unstable manifolds in a four dimensional space @xcite .
the problem ( [ eq : eqp2])-([eq : eqbcp2 ] ) is invariant under the symmetry @xmath71 that comes from the time reversing ( hamiltonian ) and spatial reflection symmetries of the nlcmed .
we further restrict our search for dispersive pulses to the case of reflection - symmetric pulses , i.e. , to pulses that satisfy:@xmath72 if we now set the symmetry axis to @xmath73 , we can reduce the problem to a semi - infinite interval @xmath74 with the boundary conditions @xmath75 finally , to numerically compute the profiles of the symmetric pulses , we replace the infinite interval by a finite one , @xmath76 $ ] . following @xcite ,
the resulting boundary conditions at @xmath77 are obtained by requiring that the solution projects only onto the subspace spanned by the eigenvectors associated with the decaying eigenvalues of the matrix @xmath61 ( see eq .
( [ eq : lin ] ) ) . in summary ,
the boundary value problem that we integrate numerically is given by eq .
( [ eq : eqp2 ] ) , which we rewrite as a real first order system of four equations in @xmath780,l[$ ] together with the four boundary conditions @xmath79 where @xmath56 , * @xmath80 * and @xmath81 is a matrix whose rows are the left eigenvectors of @xmath61 associated with the exponentially growing directions**@xmath82 * * for each value of @xmath51 this problem is solved using a shooting method .
we start from the known solutions for @xmath83 obtained in @xcite and apply numerical continuation techniques to locate the propagating pulses with @xmath84 . this procedure for setting the boundary conditions at @xmath77 , rather than simply imposing @xmath85 ,
allows the shooting method to converge faster , and the results obtained are found to be essentially independent of @xmath86 for @xmath87 .
( i ) the solid lines correspond to homoclinic cycles to the origin with @xmath88 for the indicated values of @xmath51 .
the dashed line bounds the regions where the origin is a saddle node ( on the left ) and saddle - focus ( on the right ) .
( ii ) spatial profiles of three pulses for the values marked in ( i ) with open circles . ] the left panel of fig . [
fig : ar_homocla ] shows several families of homoclinic orbits represented in the @xmath89 plane for different values of @xmath51 and corresponding to the case @xmath88 .
the dashed line separates the regions where the homoclinic orbit connects to a saddle point , and where it connects to a saddle - focus , while the open circles correspond to the solutions shown on the right panels . in fig .
[ fig : ar_homocla ] ii a - c the solutions can be seen to develop oscillations as we move towards @xmath90 .
this corresponds to moving along a horizontal line in fig .
[ fig : eigval ] ( constant @xmath51 ) and to the right , approaching region ( c ) ( precisely at @xmath90 , @xmath91 ) where the eigenvalues become purely imaginary .
( i ) curves of homoclinic cycles to the origin with @xmath92 for the indicated values of @xmath51 .
( ii ) spatial profiles of two pulses corresponding to the values marked in ( i ) with open circles . ]
this oscillatory behaviour , however , is not observed for the families of pulse solutions found for @xmath92 , as seen in fig .
[ fig : ar_homoclb ] . instead , these curves display turning points and , to better appreciate these limit points ,
the results have been plotted in the plane @xmath93 , where @xmath94 is the positive quantity@xmath95 in this case , as we move along the curves for fixed @xmath51 and past the turning point , the pulses develop two extra humps that tend to move away from the origin ( see fig .
[ fig : ar_homoclb ] ii ( a ) and ( b ) ) .
after having found a two parameter @xmath96 family of symmetric dispersive pulses ( dp ) that can be numerically continuated from the solutions for @xmath83 obtained in @xcite , we now proceed to study their stability .
space - time representation of the solution of the nlcmed ( @xmath13 , @xmath97 , @xmath98 , and periodicity boundary conditions ) for a unstable pulse propagating on top of a cw ( @xmath99 and @xmath100 ) .
the pulse parameters are @xmath101 and @xmath102 , and it corresponds to the point labeled ( a ) in fig . [ fig : ar_homoclb ] . see the file ` movie3.1.gif ` for an animation of this pulse destabilization . ]
the idea is not to perform a complete stability analysis of the family of dp but to show that stable dp can be found , and that the dp can thus be considered as robust realizable localized structures of light propagation in fbg . to do this we select several dp ,
place them on top of their corresponding background cw , add a small random perturbation , and use them as initial conditions for the full system of nlcmed ( [ eq : nlcmed+]-[eq : nlcmed- ] ) that we numerically integrate for a certain amount of time with periodic boundary conditions . the numerical method for the integration of the nlcmed
uses a fourier series in space with @xmath103 modes and a fourth order runge - kutta scheme for the time integration of the resulting system of ordinary differential equations for the fourier coefficients .
the stiff linear diagonal terms associated with the small dispersion coefficients are integrated implicitly , and the nonlinear terms are computed in physical space with the usual 2/3 rule to avoid the aliasing effects @xcite ( the maximum required resolution for the simulations in this paper were @xmath104 and @xmath105 ) .
unstable dp simply do not persist and their shape changes , as it can be appreciated from the spatio - temporal evolution shown in fig .
[ fig : xtpinestv05 ] , which corresponds to the pulse labeled ( a ) in fig .
[ fig : ar_homoclb ] ( see also the corresponding animation ` movie3.1.gif ` ) .
note that the size of the pulse grows , at @xmath106 it is larger than at @xmath107 , and then it decays again at @xmath108 .
a few time units later the oscillatory tails spread and the pulse structure is eventually lost ( not shown in the figure ) .
all dp explored for @xmath92 propagated over the same simple cw with parameters @xmath99 and @xmath100 ( cf .
( [ cw+])-([cw- ] ) ) , which corresponds to @xmath101 in eq .
( [ eq : eqsym ] ) , and all were found to be unstable regardless of its propagation speed @xmath109 .
space - time representation of the solution of the nlcmed ( @xmath13 , @xmath97 , @xmath98 , and periodicity boundary conditions ) for a stable pulse propagating on top of a cw ( @xmath99 and @xmath100 ) .
the pulse parameters are @xmath101 and @xmath110 , and it corresponds to the point labeled ( a ) in fig . [ fig : ar_homocla ] .
see the file ` movie3.2.gif ` for an animation of this propagating pulse . ] on the other hand , for @xmath88 and for the same background cw ( i.e. , @xmath101 ) , the dp are found to be unstable approximately for @xmath111 and stable for @xmath112 .
the evolution of two stable pulses is shown in figs .
[ fig : xtpestv13 ] and [ fig : xtpestv16 ] , which correspond to @xmath110 and @xmath113 , respectively , where the structure of the slightly perturbed pulses is seen to remain now virtually unaltered after more than @xmath114 time units ( see also the corresponding animations ` movie3.2.gif ` and ` movie3.3.gif ` ) . space - time representation of the solution of the nlcmed ( @xmath13 , @xmath97 , @xmath98 , and periodicity boundary conditions ) for a stable pulse propagating on top of a cw ( @xmath99 and @xmath100 ) .
the pulse parameters are @xmath101 and @xmath113 , and it corresponds to the point labeled ( b ) in fig . [ fig : ar_homocla ] .
see the file ` movie3.3.gif ` for an animation of this propagating pulse . ]
another very interesting feature of the dp that is worth mentioning is the fact that they are somehow transparent to each other : two dp propagating in opposite directions just pass through each other without distortion .
this is illustrated in fig .
[ fig : xtdospe ] ( see also the animation ` movie3.4.gif ` ) where two stable dp ( corresponding to those in figs . [ fig : xtpestv13 ] and [ fig : xtpestv16 ] ) are sent towards each other and after @xmath114 time units ( approximately @xmath115 collisions ) they still remain practically undistorted .
the reason of this behavior is the dominant character of the transport effect induced by the group velocity .
if we rewrite the nlcmed for a dp with short ( dispersive ) spatial and temporal scales @xmath116 and @xmath117 , they take the form of two uncoupled wave equations@xmath118 and then it is clear that dp travelling in opposite directions simply propagate through different channels , and are ( in first approximation ) completely independent . space - time representation of the solution of the nlcmed ( @xmath13 , @xmath97 , @xmath98 , and periodicity boundary conditions ) showing the simultaneous propagation in opposite directions of the two stable pulses from figs . [ fig : xtpestv13 ] and [ fig : xtpestv16 ] . see the file ` movie3.4.gif ` for an animation of this pulse interaction . ]
in this paper we have studied the effect of dispersion in the weakly nonlinear dynamics of light propagation in a fbg .
we have shown that the ( often negelected ) small dispersion terms play a crucial role in the transport dominated dynamics of light propagation in fbg .
dispersion can give rise to complex spatio - temporal chaotic states , but also to a new family of localized states ( dp ) that propagate over a cw background and do not interact with each other .
these dp are approximately advected by the group velocity , but this transport effect does not play any role in the determination of their internal structure , which results basically from a balance between nonlinearity and dispersion .
it is also important to emphasize that this type of dynamics is not contained in the standard dispersion - less nlcme formulation for light propagation in fbg .
moreover , this behavior is just the result of the competition of two effects with different asymptotic order : transport and dispersion , and this is a generic situation that applies to any propagative extended system unless some special care is taken to reduce the group velocity ( similar effects have been previously described in the context of hopf bifurcation in dissipative systems @xcite and in parametrically forced surface waves @xcite ) . , _ instabilities and soliton strucutres in the driven nonlinear schroedinger equation _ , in nonlinear world vol .
1 , proceedings of the iv international workshop on nonlinear and turbulent processes in physics , v.g .
baryakhtar , v.m .
chernousenko , n.s .
erokhin , a.g .
sitenko , and v.e .
zakharov , eds .
, world scientific , 1989 . | dispersion effects induce new instabilities and dynamics in the weakly nonlinear description of light propagation in fiber bragg gratings . a new family of dispersive localized pulses that propagate with the group velocity is numerically found and its stability is also analyzed .
the unavoidable different asymptotic order of transport and dispersion effects plays a crucial role in the determination of these localized states .
these results are also interesting from the point of view of general pattern formation since this asymptotic imbalance is a generic situation in any transport dominated ( i.e. , nonzero group velocity ) spatially extended system . |
in the last years a great number of experimental and theoretical research has been dedicated to find out how to create and extract entanglement from macroscopic interacting systems @xcite . between them
are chains of interacting spins @xcite , harmonic oscillators and harmonic lattices @xcite and macroscopic states of light @xcite .
these works intend , to respond to several aspects of the physical reality . in one hand , in some realistic experimental conditions the measurements apparatuses may not resolve single constituents composing the systems but rather global properties , thermodynamically speaking , they measure macroscopic observables rather than microscopic ones . in this case
, it is quite pertinent to ask wether the quantum correlations existent between the microscopic constituents of the systems will survive when the number of these constituents increases ? on the other hand , thermal states of interacting macroscopic systems , at finite temperature , are real classical states and the following question arises naturally : can interacting systems , initially in a thermal state , evolve to quantum entangled states ?
these kind of issues relaunch the old question of the passage from quantum to classical behavior with increasing complexity of the systems and with increasing temperature @xcite . beside this pure fundamental issue
, macroscopic entanglement may become an important physical resource to perform communication and computation tasks with efficiency not achievable classically @xcite , with the great advantage ( comparing with microscopic entanglement ) of being created and manipulated in simple and accessible macroscopic systems , at room temperature .
parametric down - conversion ( pdc ) processes have been used to visualize the quantum to classical transition at the single - mode single - photon level @xcite .
experimental techniques , developed recently @xcite , detected quantum entanglement between bright squeezed vacuum beams ( containing about @xmath0 photons ) .
this suggests that multimode pdc interactions are good candidates to study the joint effect of complexity and finite temperature , in macroscopic entanglement
. our perspective in this work will be to identify a small number of collective observables ( true physical quantities ) @xcite , that depend in the size ( number of microscopic constituents ) of the macroscopic systems and such that their measurement give information about the degree of macroscopic entanglement .
we choose for collective observables the macroscopic amplitudes of two wave - packets of finite spectral bandwidth , generated in a multimode parametric down conversion process , in two different approaches : the _ pairwise _ and the _ one - to - all _ interactions .
these macroscopic amplitudes are extensive quantities scaling with the number of the microscopic modes of the wave - packets , and are defined by the fourier transform of the amplitudes of the microscopic modes .
the corresponding observables are macro bose operators of a two dimensional continuous variable hilbert space . to measure the time dependent degree of entanglement of the bipartite macroscopic wave - packets we use the _ logarithm negativity _ and analyze its behavior in terms of the size of the wave - packets , and of the temperature of the nonlinear medium where the interaction takes place . to give a pictorial representation of the physical interactions , we associate a graph @xcite with each interaction pattern and
show that they are fundamentally different : while the graph of the _ pairwise _ interaction is composed of @xmath1 disconnected subgraphs whose vertices have degree @xmath2 , the graph of the _ one - to - all _ interaction is completely connected and its vertices have degree equal to the number @xmath1 of micro - modes in each wave - packet .
this structural difference between the two graphs will be reflected in the behavior of the degree of macroscopic entanglement .
we show that more complex is the system stronger is the macroscopic entanglement and higher is the critical temperature where it disappears .
another interesting conclusion is that , at finite temperatures , the minimum interaction time needed for the wave - packets to be entangled decreases with increasing their complexity .
our work extends previous studies with bright beams in three aspects : ( a ) our concept of a macroscopic system resides in the number of interacting microscopic modes ( degrees of freedom ) , rather than on the amount of photons produced during the interaction , and is valid for any finite number of micro - modes in each - wave packet .
( b ) entanglement between macroscopic systems is detected through collective operators that retain the global properties of the bipartite gaussian , continuous variables macro - modes rather than computing multimode entanglement , ( c ) the effect of the temperature of the nonlinear medium on entanglement is taken into account , previous results only consider the initial vacuum state .
the plan of the paper is the following : in sec.2 we introduce the hamiltonean of the nonlinear interacting wave - packets in two different approaches and derive their dynamical behavior . in section 3
we define the time - dependent collective amplitudes in terms of the microscopic ones . in section 4
we compute the macroscopic degree of entanglement and the birth time of entanglement in terms of the number of micro - modes and of the temperature . finally in section 5
we present our conclusions .
in the broadband down - conversion process @xcite the pump wave * 0 * , the signal * 1 * and the idler * 2 * , behave like short wave - packets of bandwidths @xmath3 , @xmath4 and @xmath5 , respectively , interacting in a nonlinear medium . in a discrete mode description of the electromagnetic field ( e.m . ) @xcite each wave - packet @xmath6 , is composed by @xmath7 discrete monochromatic modes of frequency @xmath8 ( @xmath9 ) where @xmath10 is the central frequency of wave - packet @xmath11 and @xmath12 is the frequency spacing between two neighbor modes .
we assume that the energy conservation condition is obeyed by the central frequencies of each wave - packet , i.e. , @xmath13 and we also assume that the spectral bandwidth of wave @xmath6 , @xmath14 , is small enough to prevent overlapping of the three waves and such that each mode interacts nonlinearly with all the others , except for those belonging to the same wave - packet .
the quantum version of the classical hamiltonean @xcite describing this nonlinear interaction is @xmath15 where the coupling constant @xmath16 is proportional to the second order susceptibility of the medium .
when the incident pump wave , is intense , the ensemble of modes @xmath17 composing the pump wave - packet can be treatead classically as a coherent undepleted field of complex amplitude @xmath18 and an arbitrary pump phase @xmath19 . within this approximation
we obtain the following _ one - to - all _ multimode parametric down conversion ( mpdc ) hamiltonean , @xmath20 where each mode @xmath21 of the signal wave interacts with every mode @xmath22 of the idler wave and vice - versa . in this approximation
the coupling parameter @xmath23 is proportional to the amplitude of the pump and @xmath24 is the interaction time that is proportional to the length of the propagation path of the e.m .
field in the nonlinear medium . when @xmath25 , mpdc hamiltonean ( [ 2waves ] ) , can be further simplified , since the coupling between the energy non conserving modes can be neglected and each mode @xmath26 of the signal interacts uniquely with mode @xmath27 of the idler , such that @xmath28 .
within this new approximation the hamiltonian @xmath29 reduces to the _ pairwise _ mpdc hamiltonian @xcite @xmath30 and @xmath31 is the hamiltonian of each pair of field modes interacting under the pdc approximation @xcite .
a better insight about the type of interaction between the microscopic modes of the two wave - packets can be achieved when a graph is associated to the interaction hamiltonians @xmath32 and @xmath33 , as we do in fig.1 . in panel ( a ) graph @xmath34 represents the interaction hamiltonean @xmath35 and in panel ( b ) graph @xmath36 is associated with hamiltonian @xmath37 . in both graphs
each vertex @xmath38 represents a microscopic mode of frequency @xmath39 and each edge @xmath40 represents the interaction between mode @xmath26 of wave * 1 * with mode @xmath41 of wave * 2*. the coupling strength @xmath42 is the same for all edges .
the degree of vertex @xmath43 is the number @xmath44 of its neighbors @xcite . in graph
@xmath45 , @xmath46 , increases with the number @xmath1 of modes in each wave - packet and , even though micro - modes of the same wave - packet do not interact directly , a common micro - mode in the other wave - packet is an interaction mediator between them , therefore , there is at least a path connecting any pair of vertices @xmath47 in graph @xmath45 , i.e. , @xmath45 is a connected graph . in graph
@xmath48 , @xmath49 for any vertex and @xmath48 is composed by @xmath1 similar , disconnected subgraphs .
these differences between the degree of the vertices and the connectivity of the two graphs must be reflected in the behavior of the degree of entanglement of the two wave - packets as we will show . and
@xmath48 represent the interaction between the microscopic modes of wave - packets * 1 * and * 2 * for hamiltonians @xmath35 , panel ( * a * ) , and @xmath37 , panel * ( b)*. each vertex represents a microscopic mode of frequency @xmath50 and each edge represents the interaction between mode @xmath26 of wave * 1 * with mode @xmath41 of wave * 2*. the coupling strength @xmath42 is the same for all edges . _ ]
when measuring wave - packets composed by several micro - modes , the measuring apparatus may not resolve and detect the individual mode amplitudes but rather the macroscopic amplitude of each wave - packet . in this case , choosing the collective operators as the physical quantities actually detected by the measuring apparatus , will enable us to relate the degree of macroscopic entanglement between wave - packets with the number of their microscopic constituents .
the frequency dependent collective operators associated with the macroscopic amplitudes of wave - packets * 1 * and * 2 * , at the initial time @xmath51 , are naturally defined by the fourier transform of the @xmath52 modes of each wave - packet @xmath53 the subscript zero refers to initial time .
these collective amplitudes obey the commutation relations @xmath54 = \delta_{ij } $ ] and @xmath55 .
the time dependent collective amplitude operators are simply given by the dynamical evolution of the initial amplitudes defined above , i.e. , @xmath56 where @xmath57 is the unitary time propagator of the composite system , that preserves the canonical commutation relations at any time @xmath24 .
let us stress that the collective amplitude operators @xmath58 are true annhilation operators of the _ macro - modes _
( wave - packets ) * 1 * and * 2*. the macroscopic quantum number operators associated with these macro - modes are naturally given by @xmath59 and their eigenvectors are collective fock states @xmath60 .
let @xmath61 be the related quadratures phase collective operators of _ macro - mode _ * j*. grouping together the operators @xmath62 and @xmath63 in a vector of operators @xmath64 , then the canonical commutation relations for the @xmath65 s at any time @xmath24 are encoded in the symplectic form @xmath66= i \omega_{i , j}$ ] , where @xmath67 are the elements of the symplectic matrix @xmath68 the initial and time - dependent quadratures phase collective operators are then related by the symplectic structure of the dynamical transformation . the time dependent amplitudes of the micro - modes , in the _ pairwise _ interaction , are given by eqs .
( [ pdc3 ] ) and ( [ pdc4 ] ) of appendix a. then , the corresponding time dependent collective amplitudes have the simple form @xmath69 @xmath70 in the case of the _ one - to - all _ interaction , the time dependent collective amplitudes are @xmath71 @xmath72 where we used the time dependent amplitudes of the micro - modes , eqs.([motion00 ] ) , ( [ motion01 ] ) derived in the appendix a. note that the bose operators @xmath73 were renamed for commodity of calculations . the expressions of the coefficients @xmath74 , @xmath75 , @xmath76 and @xmath77 , are given by equations ( [ coefficient1 ] ) and ( [ coefficient2 ] ) of appendix b.
in this work , we are interested in the amount of entanglement we can extract from the system if only the averaging collective observables @xmath78 and @xmath79 were measured and manipulated . in particular , we compute the degree of macroscopic entanglement in terms of : ( a ) the number @xmath1 of modes constituting each wave - packet , ( b ) the interaction time @xmath24 , ( c ) the strength of the coupling parameter @xmath42 and ( d ) the equilibrium temperature @xmath80 .
two physical situations , described by two different initial quantum states , have special interest when considering macroscopic correlations and entanglement in multimode parametric down conversion processes .
they are the spontaneous emission and the pair production at temperature @xmath80 . in the mpdc spontaneous emission
each mode @xmath43 composing the two wave - packets is initially in the vacuum state @xmath81 and the initial state of the composite system is the pure and separable state given by the tensor product @xmath82 .
when the nonlinear medium where the waves propagate is in thermal equilibrium at temperature t , the initial state of the wave - packets is a separable mixed state given by the density operator @xmath83 where @xmath84 is the thermal field density operator of mode @xmath85 , with @xmath86 and @xmath87 is the boltzmann constant .
the initial mean number of photons in mode @xmath85 is @xmath88 . at room temperature and
in the optical part of the electromagnetic spectrum @xmath89 , however , in the microwave part of the spectrum @xmath90 and we can not ignore the presence of thermal photons in the nonlinear medium .
both initial states we are considering are gaussian states .
since the hamiltonians @xmath91 and @xmath92 are bilinear in the field macro - modes , the overall output state is also gaussian and the separability criterion @xcite is completely characterized by the first and the second statistical moments of the collective quadrature phase operators , which will be denoted , respectively , by the vector of first moments @xmath93 and by the covariance matrix ( cm ) @xmath94 of elements
@xmath95 the first moments can be adjusted to zero by local unitary operations which leave invariant entropy and entanglement .
the time dependent covariance matrix @xmath96 for the collective observables can be expressed in terms of the three @xmath97 block matrices @xmath98 , @xmath99 and @xmath100 @xmath101 the diagonal blocks @xmath98 , @xmath99 are the local cm of wave - packets * 1 * and * 2 * , respectively
. the off - diagonal block , @xmath100 , encode the intermodal correlations ( quantum and classical ) between the two wave - packets .
the entries @xmath102 , in the _ one - to - all _ interaction , computed in the appendix b , ( eqs.([sigma11 ] ) - ( [ sigma23 ] ) ) , depend on the number @xmath1 of micro - modes in each wave - packet . making @xmath103 in these equations
we obtain the entries of the macroscopic cm for the _ pairwise _ interaction , given by eqs.([sigma11p])-([sigma23p ] ) , which are independent of the number @xmath1 of micro - modes .
this result is not surprising , since we have seen that the graph @xmath48 associated to this interaction is simply a collection of @xmath1 disconnected subgraps , each of them representing the well known two - mode pdc process .
hamiltonians that are quadratic in the bosonic operators , possess universal quantum invariants , i.e. , certain combinations of variances which are conserved in time independently of the concrete form of coefficients of the hamiltonian @xcite .
these invariants exist due to the symplectic structure of the transformation relating initial and time - dependent values of the quadrature components operators .
concerning the statistical moments , these universal invariants are @xcite @xmath104 defining the quantities @xmath105 the entanglement criterion can be written in a simple form @xmath106 for both vacuum and thermal initial states and for both interaction patterns , we prove in the appendix b , that @xmath107 with @xmath108 where @xmath109 and @xmath110 are the initial average number of photons in each wave - packet , ( see eq.([n10p ] ) ) . for the initial vacuum state ,
@xmath111 and @xmath112 .
using the entanglement criterion ( [ criterion ] ) , we conclude that the two wave - packets are entangled for interaction times @xmath113 obeying @xmath114 is an increasing function of @xmath24 .
the instant @xmath115 , such that @xmath116 is the minimum interaction time needed before macroscopic entanglement appears , for obvious reasons it will be named the _ birth time of entanglement _ ( bte ) . , over the temperature , for the dimensionless frequencies @xmath117 and for different values of the dimensionless mismatch parameter @xmath118 : @xmath119 ( triangles ) , @xmath120 ( circles ) and @xmath121 ( stars ) . _
_ ] for the vacuum initial state and for both _ pairwise _ and _ one - to - all _ interactions , @xmath122 for @xmath123 , therefore the two wave - packets are entangled since the very beginning of the interaction . on the contrary , for an initial thermal state , the condition ( [ ent ] ) is attained only after a finite time of interaction , @xmath124 , as passed .
for the _ pairwise _ interaction the _ birth time of entanglement _
@xmath125 is independent of the number @xmath1 of micro - modes .
it depends on the temperature @xmath80 , through the initial average macroscopic number of photons .
the dependence of de dimensionless bte , @xmath126 , given by eq.([birth ] ) , over the temperature is displayed in fig.2 , for the dimensionless frequencies @xmath127 and dimensionless spectral bandwidths @xmath128 .
we observe that bte increases with the temperature although this growth slows down at higher temperatures . in the case of
the _ one - to - all _ interaction is displayed as a function of the temperature @xmath80 for @xmath1 modes in each wave - packet : @xmath129 ( crosses ) , @xmath130 ( inverted triangles ) , @xmath131 ( stars ) , @xmath132 ( diamonds ) and @xmath133 ( triangles ) .
we assume the same dimensionless frequencies as in fig.2 . _ _ ] a similar behavior is found in the case of the _ one - to - all _ interaction , see fig.3 , where the bte , @xmath134 , is displayed as a function of the temperature @xmath80 for different number of micro - modes .
we observe that for a given @xmath1 the bte increases with the temperature .
we can understand the behavior of the bte with changing temperature in the following way .
the mpdc interaction produces correlated pair of photons in waves * 1 * and * 2 * and entanglement between the wave - packets starts only when the system attains the _ break - even _ , this is , when the average energy of the generated pair exceeds the average energy of the initial thermal state .
the effect of the number of micro - modes in the _ birth time of entanglement _ is displayed in fig.4 for different temperatures .
we observe that , for a given temperature @xmath80 , the _ birth time of entanglement _ decreases with increasing number of modes in each wave - packet . to quantify entanglement between the macroscopic wave - packets we use the _ logarithmic negativity _
@xmath135 @xcite given by @xmath136\ ] ] where @xmath137 is the symplectic eigenvalue of the partially transposed covariance matrix @xmath138 . since the cm in the _ pairwise _ interaction is independent of the number @xmath1 of micro - modes and
since it coincides with the cm of the _ one - to - all _ interaction for @xmath103 , we conclude that the macroscopic degree of entanglement @xmath135 , in the _ pairwise _ interaction , is @xmath1 independent and its value is the same as if there were a single pair of modes in each wave - packet , provided that their frequencies are equal to the central frequencies of the two wave - packets and their average number of photons are equal to the average number of _ macroscopic photons _ in each wave - packet . on the contrary , in the _ one - to - all _ interaction ,
the complexity of the interaction pattern is revealed on the macroscopic degree of entanglement .
we compute @xmath135 as a function of the number @xmath1 of micro - modes in fig.5 , for the initial vacuum state ( triangles ) and for a thermal state at equilibrium temperature @xmath139 ( circles ) and for the dimensionless interaction time @xmath140 . the same dimensionless frequencies as in fig.2 are assumed .
the solid lines are parallel straight lines .
we conclude that for , a given temperature , the degree of entanglement increases linearly with the number of micro - modes @xmath1 , in each wave - packet provided that the time of interaction is bigger than the bte corresponding to that temperature .
the value of the slope of the straight lines is an increasing function of the coupling parameter @xmath42 .
is plotted as a function of the number @xmath1 of modes in each wave - packet for equilibrium temperatures : @xmath141 ( stars ) , @xmath142 ( triangles ) , and @xmath143 ( circles ) .
we assume the same dimensionless frequencies as in fig.2 . _ _ ] when the initial temperature of the nonlinear medium rises , there are initially more uncorrelated thermal photons in the wave - packets .
we expect intuitively that , for a given number of micro - modes and for a given interaction time , any entanglement should vanish at large enough temperatures . to exemplify this behavior we compute the degree of entanglement @xmath135 , for the it one - to - all interaction in terms of the temperature @xmath80 , assuming @xmath144 and for : @xmath103 panel ( a ) , and @xmath130 panel ( b ) .
the same dimensionless frequencies as in fig.2 are assumed .
we observe that entanglement decreases with growing temperature until it vanishes at some critical temperature @xmath145 for @xmath103 and @xmath146 for @xmath130 . as mentioned above , the cm for the _ pairwise _ pattern coincides with the cm of the _ one - to - all _ pattern for @xmath103 and we conclude that , for a given interaction time , the critical temperature @xmath147 is independent of the number of modes in the _ pairwise _ case and increases with @xmath1 for the _ one - to - all _ case , contradicting our initial intuition that , more macroscopic are the wave - packets more classical should be their collective correlations . computed at the interaction dimensionless time @xmath140 is displayed as a function of the number @xmath1 of micromodes for the initial vacuum state ( triangles ) and for a thermal state at equilibrium temperature @xmath139 ( circles ) and for the _ one - to - all _ interaction .
the same dimensionless frequencies as in fig.2 are assumed .
the solid lines that fit the logarithmic negativity , are parallel straight lines whose equations are @xmath148 and @xmath149 . _
_ ] to connect the physical _ birth time of entanglement _ @xmath115 and the degree of entanglement @xmath135 , with the coupling parameter @xmath42 , we use the dimensionless time @xmath150 .
let us assume that for a given temperature @xmath80 the dimensionless _
birth time of entanglement _ is @xmath134 , then when the coupling constant @xmath42 increases the real _ birth time of entanglement _
@xmath115 , decreases , meaning that stronger is the nonlinear interaction faster the _ break - even _ of energy is attained . in a similar way
we show that the real interaction time @xmath113 needed to attain a given value of @xmath135 , decreases with increasing @xmath42 . , computed at the interaction dimensionless time @xmath140 , is displayed as a function of the temperature @xmath80 .
panel ( a ) @xmath103 and panel ( b ) @xmath130 , for the _ one - to - all _ interaction .
the same dimensionless frequencies as in fig.2 are assumed .
the critical temperatures are @xmath151 for @xmath103 and @xmath152 for @xmath130 . _
_ ] at a first glance the growth of the macroscopic degree of entanglement with @xmath1 and the decreasing of the bte with @xmath1 are quite surprising behaviors
. we would expect to see emerging a classical behavior with increasing number of constituents of the wave - packets , this is , with their passage from microscopic to macroscopic systems .
instead , the collective quantum behavior is insensitive to the number of micro - modes in the _ pairwise _ interaction and is enhanced in the _ one - to - all _ interaction . this behavior can be explained in the following way .
when two micro - modes are added to each wave - packet ( symmetric towards the central frequency @xmath153 ) that contains initially @xmath154 modes , the interaction energy of the system increases roughly as @xmath155 ( @xmath156 terms must be added to the interaction hamiltonean ) in the _ one - to - all _ interaction , and increases with @xmath157 in the _ pairwise _ interaction
. however , the energy contained in the modes themselves ( noninteracting hamiltonean ) increases with @xmath158 in both interaction patterns .
the ratio between the interaction energy and , the non - interacting one , increases with @xmath1 in the pattern @xmath45 and is constant in the pattern @xmath48 .
an immediate result of this energy balance is that the _ break - even _ of energy ( bte ) is attained earlier and the correlated pair production , that is responsible by the degree of entanglement , is enhanced by a factor of @xmath1 in @xmath45 and keeps constant in the pattern @xmath48 .
this is expressed in a simple way by the degree of each vertex in the graphs @xmath45 and @xmath48 . as a matter of fact , at a given temperature , the degree of entanglement for the _ one - to - all _ interaction is a linear function of the degree @xmath1 of any vertex of graph @xmath45 . in the _ pairwise _
interaction the degree of any vertex of @xmath48 is @xmath2 , independent of the number of vertices in the pattern , such as the degree of entanglement is insensitive to the number @xmath1 of micro - modes . in conclusion ,
the number of constituents of the macroscopic systems is not _
per se _ the determinant factor when computing their degree of entanglement , the determinant ingredient is no doubt the type of interaction between their constituents .
on the fundamental side our work demonstrates that , in principle , purely quantum correlations can be detected , at finite temperatures , by measuring a few number of appropriated collective observables of macroscopic systems . to illustrate this behavior we studied the macroscopic quantum entanglement of the collective amplitudes of two wave - packets of finite spectral bandwidth , generated in a parametric down conversion process in two different approaches : the _ pairwise _ and the _ one - to - all _ interactions .
we have shown that , in the _ pairwise _ pattern , the degree of collective entanglement does not depend on the number of micro - modes in the wave - packets and that , in the _ one - to - all _ pattern it increases linearly with the number of micro - modes .
this quite surprising behavior not only contradicts our naive intuition that quantum correlations are averaged out in macroscopic systems as it emphasizes that , the complexity of physical interactions between the microscopic constituents , can enhance the degree of macroscopic bipartite entanglement .
however , there is a minimum interaction time needed before the two wave - packets start to be entangled , the _ birth time of entanglement _ , which increases with increasing temperature .
moreover , for the same interaction time and the same number of micro - modes , the degree of entanglement decreases with increasing temperature , becoming zero at the critical temperature , where its first order derivative has a discontinuity . to associate
this discontinuity with a possible quantum phase transition @xcite is not clear within our model . it would be interesting , in a further work , to use the techniques developed in solid state physics to relate the polarization and the temperature of the nonlinear medium where the waves interact , with their degree of entanglement , in order to find signatures of quantum phase transitions .
since this macroscopic entanglement is higher than the corresponding microscopic one and since the measuring apparatus only needs to detect the collective behavior of the wave - packets , it could be used as a resource to perform communication and computation tasks , at room temperature , in an efficient and technically more accessible way .
in this appendix we solve the heisenberg equations of motion for the bose operators of the micromodes of the wave - packets .
the solution of the heisenberg equations of motion for @xmath159 and @xmath160 in the _ pairwise _ interaction , was derived in @xcite , and is given by @xmath161 @xmath162 the zero stands for initial time . for clarity of exposition
let us rename the bosonic operators @xmath163 in the signal wave - packet * 1 * and @xmath164 in the idler wave - packet * 2 * for the _ one - to - all _ interaction .
the correspondence is the following : for modes of * 1 * : @xmath165 and for modes of * 2 * : @xmath166 . with this new notation
the hamiltonian @xmath167 becomes @xmath168 the heisenberg equations of motion for the vector operator @xmath169 , under the hamiltonian @xmath91 are @xmath170 where @xmath171 is @xmath172 time dependent matrix . in order to obtain an autonomous system of equations
we define new annhilation operators @xmath173 where @xmath174 is a @xmath175 diagonal matrix whose elements are @xmath176 the new bose operators obey the following autonomous system of linear differential equations @xmath177 where @xmath178 is the @xmath172 matrix .
@xmath179 is a diagonal @xmath180 matrix , whose elements are @xmath181 & \mbox { if $ i = j= 1, ... ,2m+1 $ } \\ 0 & i \neq j \\ \end{array } \right.\ ] ] and @xmath182 is the @xmath180 constant matrix whose elements are @xmath183 the solution of ( [ heis5 ] ) is @xmath184 where @xmath185 is the a diagonal matrix whose elements are the eigenvalues of the matrix @xmath186 , and @xmath187 is the matrix whose columns are the eigenvectors of matrix @xmath186 .
going back to the original bose operators @xmath188 , we obtain @xmath189 more explicitly , the time dependent operators @xmath190 and @xmath191 in the _ one - to - all _ interaction are given by , @xmath192 @xmath193 in terms of the elements @xmath194 of matrix @xmath195
. the subscript zero refers to initial time .
the canonical commutation relations obeyed by @xmath196 imply that , @xmath197 @xmath198 and @xmath199 .
in this appendix we compute the elements of the cm @xmath200 of the collective operators .
the collective time - dependent amplitudes in the _ one - to - all _ interaction are @xmath201 @xmath202 where the coefficients @xmath203 @xmath204 are expressed in terms of the entries of the matrix @xmath195 .
the expressions for the elements of the symmetric collective covariant matrix for the initial thermal state , are easily computed @xmath205 | we investigate entanglement between collective operators of two wave - packets of finite spectral bandwidth , in two different approximations of the multimode parametric - down conversion ( mpdc ) process : the _ pairwise _ and the _ one - to - all _ interaction patterns . for collective operators we choose the macroscopic amplitudes of each wave - packet defined by the fourier transform of their microscopic mode amplitudes .
this approach intends , to respond to realistic experimental conditions , where measurements apparatuses may not resolve single microscopic mode amplitudes but rather the collective amplitude of the wave - packets . to quantify the bipartite macroscopic entanglement we use the logarithmic negativity .
we relate the time dependent degree of macroscopic entanglement with the complexity ( number of modes and interaction pattern ) and the temperature of the system .
our results show that the macroscopic entanglement increases linearly with the number of micro - modes in the case of the _ one - to - all _ interaction , while in the _ pairwise _ interaction it is constant . moreover , in the _ one - to - all _ pattern the _ birth time of entanglement _ and the critical temperature decrease with increasing the number of micro - modes .
we draw the graphs associated with the two interaction patterns and related the degree of collective entanglement with the connectivity and the index of each vertex ( mode ) of the graph .
we conclude that quantum information and computation tasks may be achieved more efficiently by manipulating appropriated collective operators in some macroscopic systems , then by using their microscopic counterparts .
pacs number(s ) 03.67.bg , 42.65.yj , 03.67.-a |
Image copyright Akiry Image caption Paris's Landy Tunnel is well known for smash-and-grab raids on cars.
French police are searching for three thieves who stole a handbag containing five million euros (£3.6m; $5.4m) worth of jewels in a daring Paris raid.
The owner of the handbag, a Taiwanese art collector, was stuck in traffic in a tunnel when the thieves smashed her car window.
It was not clear whether it was a targeted attack or if the thieves simply got lucky.
The 1.3km (0.8 mile) long Landy Tunnel is notorious for smash-and-grab thefts.
Some reports suggested the jewellery collection, which included a ring worth €1.7m, was due to be donated to the Paris Museum of Modern Art but the museum later denied the claim.
The unique and numbered items would be very difficult to sell on without a specialised network, a police source told France's AFP news agency.
The source said thefts in the Landy tunnel are often the work of petty crooks.
"They aren't afraid of anything, know the area and escape through emergency exits," it added.
In February 2010, Christina Chernovetska, the daughter of the then-mayor of Kiev, fell victim to a similar robbery when a handbag containing jewels worth €4.5m was stolen from her.
The theft in Paris comes two weeks after thieves pulled off a daring heist in London's Hatton Garden, stealing jewels and other valuables from safety deposit boxes worth as much as £200m.
Image courtesy of Wikimedia Commons user Akiry. ||||| Thieves often hit when cars are stationary in a traffic jam in the tunnel
A group of thieves have stolen a handbag containing €5m (£3.6m) worth of Chanel jewels from a woman on the road between Paris and Charles De Gaulle airport.
The daring robbery of the Taiwanese art collector happened on Wednesday as the taxi she was travelling in was driving through a long tunnel notorious for robbery attacks on tourists stuck in traffic.
The thieves smashed the car window and snatched the bag.
It is not known at this stage whether or not the thieves were just lucky or knew in advance that there were valuable objects in the bag, including a ring said to be worth €1.7m (£1.2m).
Police say they are keeping an open mind as they investigate the theft of the gems which were to be presented at the Paris Museum of Modern Art, a source said.
1 / 8 Gallery: Jewel Thieves Hide In Hair Salon After Heist Two men have robbed a Cartier jewellery store in Paris' Champs-Elysees shopping district
"Either it was an order or they are in the s***," the source said, adding it would be very difficult to sell the items without good contacts because of their exceptional qualities.
The 1.3km (1,400-yard) Landy tunnel is used mostly by people travelling between Paris and the airport.
Local thieves are most often the culprits.
1 / 8 Gallery: Images Of Hatton Garden Jewel Heist Suspects Police have released pictures of a van and three suspects wanted in connection with the Hatton Garden jewel heist
The police source said: "It is often local delinquency. They aren't afraid of anything, know the area and escape through emergency exits."
Christina Chernovetska, the daughter of the then mayor of Kiev, was a victim of a similar robbery in February 2010 when a bag which she said held jewels worth €4.5m (£3.2m) was stolen from her.
Even royalty is not immune.
Play video "Intruder Alarm Not Responded To" Video: Intruder Alarm Not Responded To
Saudi prince Abdul Aziz Bin Fahd, the multi-millionaire son of the late King Fahd, was the victim of a spectacular armed raid on his convoy last August in which €250,000 (£180,000) and diplomatic papers were stolen.
The robbery comes two weeks after a raid over the Easter weekend in London's Hatton Garden where thieves stole dozens of safety deposit boxes containing what is believed to be tens of millions of pounds' worth of gems and valuables. | – The Landy Tunnel that runs between Paris and Charles de Gaulle Airport is known for its traffic and, possibly as a result of that, frequent "smash-and-grab" crimes, where thieves bust car windows and snatch whatever they can from inside the car. A Taiwanese art collector stuck in the 0.8-mile tunnel Wednesday found that out firsthand when the taxi she was in was looted, with the thieves nabbing a handbag containing $5.4 million in Chanel jewelry, Sky News notes. Reported among the stolen gems was a $1.8 million ring. Police say they aren't sure if the perps targeted the victim or if they just lucked out in focusing on that car, the BBC notes. Initial reports indicated the jewels were destined for the city's Museum of Modern Art, though the museum has denied that, per the BBC. A police source tells Sky that these types of raids are "often local delinquency. They ... know the area and escape through emergency exits." But dumping the jewels for a big payday could prove difficult for the thieves: The gems were numbered, so only those with a solid contact network would be able to sell them easily, the police source adds. As a source puts it to Sky, "Either it was an order or they are in the s---." (This raid comes just two weeks after a London heist that may have netted thieves $300 million worth of stolen goods.) |
squamous cell carcinoma ( scc ) is an aggressive malignant neoplasm.1 malignancies of the nasal septum are considered rare , and squamous cell carcinoma ( scc ) comprises about 66% of such lesions.2 the treatment of choice for scc depends on the location , size , and depth of penetration of the tumor .
curettement and electrodesiccation are effective for small lesions that are not deeply invasive . for large neoplasms ,
the most commonly used treatment modalities are primary resection , radiation therapy , and mohs micrographic surgery.3 the prognosis for patients with this pathology depends on the size , infiltration and location of the lesion , presence or absence of metastatic spread , perineural invasion , rapid growth , history of previous treatment , to a certain degree the differentiation of the tumor , and etiologic factors such as burn scars , radiation , and chronic ulceration.2,4,5 facial defects secondary to the treatment of neoplasms , congenital malformations , and trauma result in multiple functional and psychosocial difficulties.6 surgical reconstruction techniques , prosthetic rehabilitation or a combination of both the methods to restore these facial disfigurements may improve the level of function and self - confidence for patients.6,7 the site , size , and etiology of the defect , patient s age , general medical condition and desire are used to determine the methods of reconstruction .
prosthetic rehabilitation can be preferred due to probability of recurrence , complexity of the surgical reconstruction procedure , radiation therapy , and esthetic importance.8,9 biomaterials such as polymethyl methacrylate and silicone have been used for prosthetic rehabilitation for facial defects .
important factors to consider when choosing silicone are biocompatibility , flexibility , translucency , color stability , and durability.10 advantages of silicones include a simplified fabrication process , optimal esthetics , light weight , and the ability to use soft flexible projections that can gently engage minor tissue undercuts to enhance retention and stability.11 retention of prosthesis in the midface region has been accomplished with anatomic undercuts , adhesives , eyeglasses and attachment to maxillary obturators,7 prosthetic connections to endosseous implants.10 when suitable conditions are provided , mechanical retention obtained by anatomic undercuts is the most advantageous .
the advantages of this prosthesis are that the techniques is noninvasive , tissue tolerant , aesthetic , comfortable to use , and easy to fabricate and clean . additionally , these prosthesis are often preferred by the patients because the weight and the cost of such a prosthesis are low .
the presence of moisture , mobile soft tissues , or lack of stable tissue support are affect the retention , these are disadvantages of anatomic retention.10,12 this clinical report describes the prosthetic rehabilitation of a patient with scc after a partial rhinectomy .
a 77-year - old woman with a partial rhinectomy ( figure 1 ) had diagnosed with scc and undergone surgery due to the disease recurred two times .
surgical reconstruction had not recommended at the time due to the need for continued observation and patient had not worn any prosthesis after the previous surgical resections .
it was noted that the right and left side of the nose and part of the nasal septum were removed .
the fabrication of a silicone nasal prosthesis was planned , and the expectation of this treatment was explained to the patient .
the patient was draped in the usual manner and petrolatum jelly was applied to the patient s eyebrows and eyelashes . after moist gauze
was packed to prevent the flow of material into the undesired areas of the defect , an impression was taken from the defect together with the adjacent tissue , using an irreversible hydrocolloid impression material ( kromopan , lascod spa , firenze , italy ) .
the impression was removed and poured in type iii dental stone ( giladur , bk giulini gmbh , ludwigshafen , rh . ) .
the prosthesis was sculpted with type i plate wax over the model , taking into account the patient s general appearance and previous photographs ( figure 2 ) .
the flask was kept in boiling water for 5 minutes so that the wax was eliminated .
prior to the patient s dismissal , the intrinsic coloration technique , which produces the most lifelike appearance of the prosthesis , was used to apply the various colors ( i-1998 extrinsic coloring kit , factor ii , inc . , lakeside , az , usa ) in multiple layers onto the textured surface of the mold.13 the platinum silicone elastomer ( a - rtv-30 v50011 a&b kit , factor ii , inc . )
mixed with intrinsic colors ( iintrinsic ii , factor ii inc . ) on a ceramic slab compared to the patient s skin color tone .
the prosthesis was removed from the mold and rinsed with water to eliminate the residues ( figure 3 ) .
finally , the prosthesis was evaluated on the patient and some extrinsic water - resistant coloration was applied ( kt-199 - extrinsic coloration system , factor ii , inc . )
nasal prosthesis must gain adhesive retention from a wide extension of the prosthesis beyond the defect , which may negatively influence the cosmetic result .
mechanical retention by extension into the defect or through contact with eyeglass may augment adhesive retention.14 in this case , the retention was highest without eyeglass , but the esthetic appearance of the prosthesis was enhanced by using an eyeglass , the skin adhesive was not used ( figure 5 ) .
the patient was scheduled for the first post - insertion adjustment one day after the insertion to ensure health of the tissues , to relieve the prosthesis for pressure areas on the tissues .
follow - up evaluation was carried out once in 3 months recall for evaluation and observation of any recurrence . | facial defects resulting from neoplasms , congenital malformations , or trauma can be restorated with facial prostheses using different materials and retention methods to achieve a lifelike look and function . for the successful result ,
a lot of factors as harmony , texture , color matching , and blending of tissue interface of prosthesis is important .
this clinical report describes treatment using a silicone prosthesis with a mechanical - retentined design for a patient who received a partial rhinectomy .
defects resulting from diseases as squamous cell carcinoma can be managed with the prosthetic rehabilitation so that the patient more comfortably and confidently resumed regular daily activity .
mechanical retention alone was sufficient to retain the prosthesis ; thus , prosthetic adhesives were not necessary . |
Health USDA shutters Foster Farms poultry plant over cockroaches Jan. 8, 2014 at 8:36 PM ET
Rich Pedroncelli / AP
The U.S. Department of Agriculture shut down a Foster Farms poultry processing plant in Livingston, Calif., Wednesday, saying it was infested with live cockroaches, which can pose a threat to public health.
The move comes even as that site and two other California chicken plants remain under heightened USDA scrutiny following two outbreaks of salmonella food poisoning in the past year, including one that is ongoing and has sickened at least 416 people in 23 states and Puerto Rico.
"Today our inspectors observed insanitary conditions in the plant," said Adam Tarr, a spokesman for the USDA's Food Safety and Inspection Service.
USDA officials said they couldn't confirm how many cockroaches were found or where in the fresh chicken production plant they were located. But a letter from the USDA to Foster said cockroaches were observed at a hand wash sink near an inspection station.
The agency pulled the inspectors from the plant, which effectively shuts down the operation.
Foster Farms officials confirmed the shut-down in a statement Wednesday, saying they temporarily stopped operations "to allow for enhanced sanitizing to take place."
"The plant treatment took place this afternoon and the company expects to fully resume operation once approved for inspection by FSIS," officials said in a statement.
Company officials later issued an updated statement in which they acknowledged cockroaches were discovered at the plant on Wednesday and four other incidents going back to September 2013. The statement said the company maintains an ongoing pest control program.
"No other facilities are affected. No products are affected. Product production has been transferred to the company’s other facilities," the updated statement said.
Cockroaches are considered pests that can carry bacteria, including salmonella. Tarr said that Wednesday's shutdown was not related to the ongoing outbreak.
FSIS in October threatened to close the Livingston plant and two others in Fresno, Calif., but agreed to allow the firm to remain open while officials put a new multi-step process in place for salmonella control.
Throughout both salmonella outbreaks, Foster Farms officials issued no recalls of potentially tainted products, instead advising consumers to handle chicken properly and to cook it thoroughly to a temperature of 165 degrees Fahrenheit.
||||| A US chicken factory, linked to a recent salmonella oubreak, has been shut down after inspectors found live cockroaches for the fourth time in five months.
US Federal inspectors halted processing at the Foster Farms plant in California following the discovery of "an infestation of live cockroaches," a suspension notice sent by the United States Department of Agriculture said.
The letter, addressed to Farm Foods CEO Ron Foster, said the latest find demonstrated that the firm had "failed to maintain an effective pest control program ... to assure that wholesome, unadulterated meat and poultry products are produced."
It said the insects had been discovered at the Livingston plant on four separate occasions between August 1, 2013 and January 8, 2014. They were found in several areas including a sink used for hand washing and a sanitiser dispenser box in meat production areas.
The plant is one of three in central California being investigated over a nationwide salmonella outbreak, newspaper USA Today reported.
According to the federal Centres for Disease Control and Prevention in Atlanta, 416 people across 23 states have been made ill by the ongoing outbreak, the newspaper said.
Studies have found that cockroaches carry viruses and bacteria, including salmonella.
In a statement, Foster Farms confirmed that the Livingston plant had been closed for "sanitisation and treatment". It said the treatment had now been completed and the factory was ready for further inspection.
The company added that the Livingston discovery was an "isolated incident" and "no other facilities were affected".
"A single incident is not acceptable, and we are committed to a zero tolerance policy," the statement said.
Foster Farms is the sixth-largest chicken processor in the United States.
:: Watch Sky News live on television, on Sky channel 501, Virgin Media channel 602, Freeview channel 82 and Freesat channel 202. | – "Cockroach" and "infestation" are two words you don't want anywhere near your dinner, but the USDA says it encountered just that at a California poultry plant that it wasted no time in shutting down yesterday. Foster Farms said that it immediately conducted "enhanced sanitizing" at its Livingston plant, and said it "expects to fully resume operation" as soon as the USDA can re-inspect the facility. It added that it was "committed to a zero tolerance policy" and that this was an "isolated incident." Ick factor aside, cockroaches are known to carry salmonella and the plant in question is one of three Foster Farms facilities linked to a salmonella outbreak that sickened hundreds of Americans last year, NBC reports. Maybe not so "isolated:" Food Safety and Inspection Services inspectors said they found the bugs on four different occasions between August and yesterday, notes Sky News. In a letter, the USDA said Foster Farms "failed to maintain an effective pest control program ... to assure that wholesome, unadulterated meat and poultry products are produced." Foster Farms is the nation's No. 6 poultry processor; NBC notes that it issued no recalls during last year's salmonella outbreak. Rather, consumers were warned to properly handle and cook their chicken. |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``American Manufacturing
Competitiveness Act''.
SEC. 2. FINDINGS.
The Congress finds the following:
(1) The competitiveness of manufacturing industries in the
United States must be a priority for the United States
Government.
(2) Antidumping and countervailing duty laws of the United
States are in the interest of the United States, when applied
in an objective and fair manner, to prevent unfair pricing and
subsidized competition.
(3) Imposing antidumping and countervailing duties may harm
United States industrial users of imported goods or domestic
like products, because those users rely on such goods to
manufacture products in the United States.
(4) Current law does not permit United States industrial
users to participate fully in antidumping or countervailing
duty cases that might affect their businesses substantially;
nor can decisionmakers in these cases consider, under United
States law, the effects on United States industrial users in
determining whether to impose antidumping or countervailing
duties.
(5) It is a matter of fundamental fairness that businesses
in the United States that may be affected by antidumping and
countervailing duties should be able to participate
meaningfully in the process by which decisions regarding those
duties are made.
(6) In order to ensure economically sound decisions and the
health of United States manufacturers, the benefits of imposing
antidumping and countervailing duties should be balanced
against the economic harm caused by imposing those duties, and
antidumping and countervailing duties should not be imposed if
the harm is greater than the benefits of imposing such duties.
SEC. 3. PARTICIPATION OF INDUSTRIAL USERS IN COUNTERVAILING AND
ANTIDUMPING DUTY PROCEEDINGS.
Title VII of the Tariff Act of 1930 (19 U.S.C. 1671 et seq.) is
amended as follows:
(1) Section 701(a) (19 U.S.C. 1671(a)) is amended--
(A) by striking ``and'' at the end of paragraph
(1);
(B) by adding ``and'' after ``merchandise for
importation,'' at the end of paragraph (2); and
(C) by inserting after paragraph (2) the following:
``(3) the Commission determines that the imposition of a
countervailing duty on such merchandise equal to the amount of
the net countervailable subsidy would result in greater
benefits to that United States industry than harm to United
States industrial users,''.
(2) Section 702(b)(4)(B) (19 U.S.C. 1671a(b)(4)(B)) is
amended by striking ``or (G)'' and inserting ``(G), or (H)''.
(3) Section 703 (19 U.S.C. 1671b) is amended--
(A) in subsection (a)(1), in the first sentence, by
striking ``and that imports of the subject merchandise
are not negligible'' and inserting ``, that imports of
the subject merchandise are not negligible, and that
the imposition of a countervailing duty on the subject
merchandise equal to the amount of the net
countervailable subsidy would result in greater
benefits to that United States industry than harm to
United States industrial users''; and
(B) in subsection (b)(3), by striking ``or (G)''
each place it appears and inserting ``(G), or (H)''.
(4) Section 704(a)(2)(B) (19 U.S.C. 1671c(a)(2)(B)) is
amended--
(A) in clause (i), by inserting ``(other than
United States industrial users)'' after ``consumers'';
(B) by striking ``and'' at the end of clause (ii);
(C) by striking the period at the end of clause
(iii) and inserting ``; and''; and
(D) by adding after clause (iii) the following:
``(iv) the relative impact on the
competitiveness of United States industrial
users, including, but not limited to, any such
impact on employment by and investment in
United States industrial users.''.
(5) Section 704(g)(2) (19 U.S.C. 1671c(g)(2)) is amended by
striking ``or (G)'' and inserting ``(G), or (H)''.
(6) Section 704(h)(1) (19 U.S.C. 1671c(h)(1)) is amended by
striking ``or (G)'' and inserting ``(G), or (H)''.
(7) Section 705(b)(1) (19 U.S.C. 1671d(b)(1)) is amended in
the first sentence, by inserting before the period the
following: ``, and whether the imposition of a countervailing
duty on the subject merchandise in an amount equal to the net
countervailable subsidy would result in greater benefits to
that United States industry than harm to United States
industrial users''.
(8) Section 731 (19 U.S.C. 1673) is amended--
(A) by striking ``and'' at the end of paragraph
(1);
(B) by adding ``and'' after ``that merchandise for
importation,'' at the end of paragraph (2); and
(C) by inserting after paragraph (2) the following:
``(3) the Commission determines that the imposition of an
antidumping duty on the subject merchandise under this subtitle
would result in greater benefits to that United States industry
than harm to United States industrial users,''.
(9) Section 732(b)(3)(B) (19 U.S.C. 1673a(b)(3)(B)) is
amended by striking ``or (G)'' and inserting ``(G), or (H)''.
(10) Section 733 (19 U.S.C. 1673b) is amended--
(A) in subsection (a), in the first sentence, by
striking ``and that imports of the subject merchandise
are not negligible'' and inserting ``, that imports of
the subject merchandise are not negligible, and that
the imposition of an antidumping duty on the subject
merchandise under this subtitle would result in greater
benefits to that United States industry than harm to
United States industrial users''; and
(B) in subsection (b)(2), by striking ``or (G)''
each place it appears and inserting ``(G), or (H)''.
(11) Section 734(a)(2)(B) (19 U.S.C. 1673c(a)(2)(B)) is
amended--
(A) in clause (i), by inserting ``(other than
United States industrial users)'' after ``consumers'';
(B) by striking ``and'' at the end of clause (ii);
(C) by striking the period at the end of clause
(iii) and inserting ``; and''; and
(D) by adding after clause (iii) the following:
``(iv) the relative impact on the
competitiveness of United States industrial
users, including, but not limited to, any such
impact on employment by and investment in
United States industrial users.''.
(12) Section 734(g)(2) (19 U.S.C. 1673c(g)(2)) is amended
by striking ``or (G)'' and inserting ``(G), or (H)''.
(13) Section 734(h)(1) (19 U.S.C. 1673c(h)(1)) is amended
by striking ``or (G)'' and inserting ``(G), or (H)''.
(14) Section 735(b)(1) (19 U.S.C. 1673d(b)(1)) is amended
in the first sentence, by inserting before the period the
following: ``, and whether the imposition of an antidumping
duty on the subject merchandise under this subtitle would
result in greater benefits to that United States industry than
harm to United States industrial users''.
(15) Section 736(c) (19 U.S.C. 1673e(c)) is amended--
(A) in paragraph (1)(C), by inserting ``United
States industrial user,'' after ``producer,'' the first
place it appears; and
(B) in paragraph (4)(A), by striking ``or (G)'' and
inserting ``(G), or (H)''.
(16) Section 751 (19 U.S.C. 1675) is amended--
(A) in subsection (b)(2)--
(i) in subparagraph (A), by inserting after
``material injury,'' the following: ``and (if
that determination is affirmative) whether
continuing the countervailing duty order or
antidumping duty order or finding would result
in greater benefits to the United States
industry than harm to United States industrial
users,''; and
(ii) in subparagraph (C), by inserting
after ``material injury'' the following: ``,
and (if the latter determination is
affirmative) whether continuing the suspended
investigation would result in greater benefits
to the United States industry than harm to
United States industrial users'';
(B) in subsection (c)--
(i) in paragraph (1), by inserting before
the period at the end the following: ``, and
(if that determination is affirmative) whether
continuing the countervailing duty order or
antidumping duty order, or continuing the
suspended investigation, would result in
greater benefits to the United States industry
than harm to United States industrial users'';
(ii) in paragraph (3)(A), by striking ``and
(G)'' and inserting ``(G), or (H)''; and
(iii) in paragraph (4)--
(I) in subparagraph (A), by
striking ``or (B)'' and inserting ``,
(B), or (H)''; and
(II) in subparagraph (B), by
inserting ``described in section
771(9)(A) or (B)'' after ``an
interested party''; and
(C) in subsection (d)(2)(B), by inserting before
the period the following: ``and that continuation of
the order, finding, or investigation, as the case may
be, would result in greater benefits to the United
States industry than harm to United States industrial
users''.
(17) Section 752(a)(1) (19 U.S.C. 1675a(a)(1)) is amended--
(A) in the first sentence, by inserting before the
period the following: ``, and (if that determination is
affirmative) whether continuation of the order or
investigation, as the case may be, would result in
greater benefits to the United States industry than
harm to United States industrial users''; and
(B) in the second sentence, by inserting ``and on
United States industrial users'' after ``industry''.
(18) Section 753(a)(1) (19 U.S.C. 1675b(a)(1)) is amended--
(A) by striking ``or (G)'' and inserting ``(G), or
(H)''; and
(B) by inserting before the period the following:
``, and (if that determination is affirmative) whether
imposition of the countervailing duty would result in
greater benefits to the United States industry than
harm to United States industrial users''.
(19) Section 771 (19 U.S.C. 1677(9)) is amended--
(A) in paragraph (9)--
(i) in subparagraph (F), by striking
``and'' at the end;
(ii) in subparagraph (G), by striking the
period at the end and inserting ``, and''; and
(iii) by adding at the end the following:
``(H) a United States industrial user, or a trade
or business association a majority of whose members are
United States industrial users.''; and
(B) by inserting after paragraph (9) the following:
``(9A) United states industrial user.--The term `United
States industrial user' means a manufacturer or producer that
uses subject merchandise or a domestic like product in the
manufacture or production of any product in the United
States.''.
(20) Section 771 (19 U.S.C. 1677) is amended by adding at
the end the following new paragraph:
``(37) Evaluation of benefits to united states industry and
harm to united states industrial users.--In considering the
potential benefits to the industry in the United States
materially injured or threatened with material injury (in this
paragraph referred to as the `United States industry'), and
harm to United States industrial users, from the imposition or
continuation of antidumping or countervailing duties under
sections 701(a), 703(a), 705(b), 731, 733(a), 735(b), 751(b),
751(c), 751(d), 752(a), and 753(a), the Commission shall weigh
harm to United States industrial users as a whole, taking into
account the following factors:
``(A) Likely harm to United States industrial users
from declines in output, sales, market share, profits,
productivity, return on investments, and utilization of
capacity in the production of downstream products,
compared to likely benefits to the United States
industry with respect to those factors.
``(B) Likely harm to United States industrial users
from negative impact on cash flow, inventories,
employment, wages, growth, ability to raise capital,
and investment, compared to likely benefits to the
United States industry with respect to those factors.
``(C) Likely negative effects on the existing
development and production efforts of United States
industrial users, including efforts to develop a
derivative or more advanced version of their products
for manufacture or production in the United States,
compared to likely benefits to the United States
industry with respect to those factors.
``(D) The effect of increased costs or prices for
the subject merchandise and domestic like products and
reduced availability of the subject merchandise and
domestic like products on the competitiveness of United
States industrial users located in the market,
including the extent to which United States industrial
users and their customers would be able to pass on
additional costs resulting from antidumping and
countervailing duties, compared to likely benefits to
the United States industry with respect to those
factors.
``(E) Such other economic factors as the Commission
determines are relevant to the potential impact of the
imposition or continuation of duties, as the case may
be, on the United States industry and on United States
industrial users.
The Commission may determine harm to United States industrial
users only if United States industrial users have presented
credible evidence of such harm.''.
(21) Section 777(h) (19 U.S.C. 1677f(h)) is amended--
(A) by striking ``and Industrial Users'' in the
subsection heading; and
(B) by striking ``for industrial users of the
subject merchandise and, if the merchandise'' and
inserting ``, if the subject merchandise or a domestic
like product''.
(22) Section 782(i)(3)(A) (19 U.S.C. 1677m(i)(3)(A)) is
amended by striking ``or (G)'' and inserting ``(G), or (H)''. | American Manufacturing Competitiveness Act - Amends the Tariff Act of 1930 to allow U.S. manufacturers that use products subject to countervailing or antidumping duty proceedings or use domestic like products (industrial users) to participate in such proceedings.
Requires the U.S. International Trade Commission, when deciding whether an antidumping or countervailing duty should be imposed or continued, to weigh harm to industrial users from such imposition or continuation, as well as (under current law) the potential benefits to the industry in the United States materially injured or threatened with material injury by a foreign countervailing subsidy. |
cystic fibrosis ( cf ) is the most common autosomal recessive disorder found in populations of european descent .
it is estimated that 70,000 individuals live with the disease around the world ( see http://www.cff.org/aboutcf/ ) with 70% of patients having the f508 mutation .
the disease is caused by a mutation in the cystic fibrosis transmembrane conductance regulator ( cftr ) gene which encodes for a chloride channel .
mutations in the gene cause decreased chloride transport out of the cell ; consequently , there is an increased absorption of sodium and reduction in the airway surface liquid .
phenotypes of cf are recurrent and chronic pulmonary infections , decreased lung function , pancreatic insufficiency , diabetes , meconium ileus , infertility in males , osteoporosis , and fatty acid defects [ 14 ] .
current therapies for cf include aerosolized antibiotics such as tobramycin , recombinant human dnase such as dornase alfa for improved mucus clearance , hypertonic saline for increases in airway surface liquid , and nonsteroidal antiinflammatory drugs ( nsaids ) like ibuprofen to decrease the inflammatory response .
cf patients take a combination of drugs to improve or maintain lung function not to mention vitamins and pancreatic enzymes and , at times , insulin for pancreatic insufficiency and diabetes . despite prophylactic treatments ,
cf patients still suffer from chronic infections and exacerbations which have psychological impacts and ultimately impact the progression of the disease .
concentrations of ceramide were found to be reduced in plasma of cf patients and mice as well as cf - related organs in mice : lungs , pancreas , and ileum .
subsequent studies have investigated the importance of ceramide in the context of cf indicating that it might be a potential target for new therapies . however , contrary to our data , certain groups have reported elevated levels of ceramide in cf tissues from patients and mice .
these contradicting results have shed light on the potential role of ceramide in cf ; however , they also bring attention to the issues surrounding the different methods of ceramide analysis .
this paper will examine why ceramide should be considered a key player in the symptoms of cf disease .
importance will be placed on the methodologies used to analyze ceramide and also the various models used to study ceramide in cf .
they are known to be involved in membrane rigidity and permeability , apoptosis and can act as second messengers signalling to cathepsin d , pkc , pp2a , and c - raf . in the cell membrane , ceramides are components of microdomains ( lipid rafts ) which are important in transmembrane signalling .
the de novo pathway occurs in the endoplasmic reticulum and begins with the conversion of serine and palmitoyl - coa to sphinganine by serine palmitoyl transferase .
ceramide synthases then transform sphinganine into dihydroceramide which is converted to ceramide by dihydroceramide desaturase . alternatively , ceramide can be synthesized through a recycling pathway with the conversion of sphingomyelin to ceramide by sphingomyelinase ( smase ) .
there are several types of smase categorized based on ph optima and localization in the cell : acidic ( asmase ) , neutral ( nsmase ) , and alkaline ( alk - smase ) .
generally a ph of 4.55.0 is optimal for asmase and it is localized mainly in lysosomal compartments in the cells as well as in membrane microdomains ( discussed later ) in the cell membrane .
neutral smases have a ph optima of 7.4 and can be located in the plasma membrane .
alk - smase is mainly found to be expressed in the intestines . considering that the deficiency in ceramides in cf can be corrected by fenretinide and the induction of dihydroceramide , the precursor to ceramide ,
can be detected , these findings suggest that the de novo pathway involving the endoplasmic reticulum is targeted by this drug in cf as it was described before in the context of cancer .
a sphingoid base is the name given to the carbon chain containing 2 to 3 oh groups and often a double bond at carbon 4 present in sphingolipids .
all ceramides have a sphingoid backbone of 18 carbons ; however , they can differ in the number of carbons in the fatty acid moiety .
the sphingoid backbone contains a double bond in ceramides which when removed forms dihydroceramide ( dhc ) often indistinguishable from ceramide when using methods based on the analysis of total ceramide levels .
ceramides can also have other molecular modifications such as the addition of glucose to obtain glucosylceramide and galactose to have galactosylceramide .
these molecules are also metabolically active and while not specifically analyzed in the studies that will be later described later on , they remain important members of the sphingolipid family .
there are several issues to consider when developing an appropriate methodology for the analysis of ceramides .
these molecules are similar in structure thus the analysis requires high level of specificity . ceramides alone represent only 1% of lipids present in the cell . therefore , a sensitive and highly specific technique must be utilized for an accurate analysis .
one of the most common biochemical assays for ceramide detection involves the use of diacylglycerol ( dag ) kinase which can convert ceramide to ceramide-1-phosphate .
the assay quantifies levels of ceramides by incubating extracted lipids with [ p ] atp and dag kinase and assessing the levels of [ p ] ceramide-1-phosphate .
there are certain caveats with this method , and there has been some question regarding the validity of the results generated with this assay [ 18 , 19 ] .
additionally , an internal standard should ideally be used to normalize the level of enzyme activity . in summary
, proper care must be taken into consideration to produce valid results , and ideally data should be verified using a more sensitive technique .
a monoclonal antibody clone 15b4 ( sigma - aldrich , oakville , ontario , canada ) was employed by our group using lipids purified by thin layered chromatography ( tlc ) in an elisa assay and by others in immunohistochemistry . a polyclonal antibody , igm - enriched mouse anticeramide antiserum ( glycobiotech , kkels germany , formerly identified as mas 0010 ) and more recently a monoclonal anticeramide antibody ( s58 - 9 , same molecule as mas 0010 sold without the addition of mouse serum , glycobiotech ) , has been used by some cf investigators [ 21 , 22 ] . both antibodies were evaluated and compared in a study by cowart and colleagues .
the study tested the affinity of the antibodies to specific species of ceramide using lipid overlay assays and it was found that each antibody recognizes different species and both recognize dihydroceramide . the monoclonal antibody ( 15b4 ) had stronger affinities to c14 and c24 ceramide than the polyclonal .
the polyclonal antibody had a strong affinity to c14 and c16 ceramides but had low detection of c10 ceramide .
the cowart study observed that variable results can be obtained when using different techniques to evaluate antibody sensitivity .
depending on the epitope exposure , the antibodies may also cross - react with other species of sphingolipids . for instance
, the authors specify that they did not compare the antibodies in the context of elisas and suggest that the recognition of ceramide species may differ using this method .
the results of dot blot assays showed that the antibody was specific to long - chain ceramides found in the skin ( ceramide-2 [ n - acylsphingosine ] , ceramide-3 [ n - acylphytosphingosine ] , ceramide-5 [ n-(alpha - hydroxy)acylsphingosine ] ) , c14 and c16 ceramides , and c16-dihydroceramide .
cholesterol could also be detected with the antibody when present in high concentrations in thin - layered chromatography assays .
dot blot assays were used to characterize the monoclonal antibody and it was found to detect weakly c16-dihydroceramide and strong sphingomyelin .
affinities to ceramides besides ceramide-1 ( [ n-(omega - acyloxy ) acylsphingosine ] ) , ceramide-2 , ceramide-3 and ceramide-5 , c14 , c16 , and c16-dihydroceramide were not assessed with the monoclonal antibody .
our group has used the monoclonal antibody in elisas only after the ceramide fraction was isolated from lipids using thin layered chromatography .
other studies have used these antibodies for immunohistochemistry detecting the amount of staining for a designated area with computer software [ 21 , 22 ] . in sum , data obtained using antibodies must be critically evaluated and should be verified with the methods able to assess the complete spectrum of detectable ceramide species and not only selected species of ceramides . with the development and refinement of separation techniques such as liquid and gas chromatography ( lc and gc ) and mass spectrometry ( ms ) ,
an accurate analysis of ceramides is now possible . using an appropriate ionization technique and lipid extraction methods , it is feasible to determine not only the concentrations of ceramides in a sample , but also to quantify the amounts of the numerous ceramide species during each analysis [ 16 , 2628 ] .
high pressure lc ( hplc ) is often used as a primary separation of lipids extracted from a given sample .
lipid species of similar molecular structure will elute off the column at similar times . upon entry into the mass spectrometer ,
it is a soft ionization technique which is not likely to cause damage to the lipid molecules and is currently the favoured method of lipid ionization . finally , to distinguish between the various ceramide species , the molecules undergo two ms analyses ( tandem ms or ms / ms ) where molecules are selected based on their mass to charge ratio or m / z . there are a few techniques used to determine amounts of ceramide at this step .
the product ion analysis method involves the detection of molecules of a specific m / z in the first ms step ( occurring in the first quadrupole or q1 ) .
finally in the second ms step , the fragments generated will be analyzed in q3 which will scan different m / z settings resulting in a spectrum of fragments issuing from the precursor ions selected for in q1 .
the q1 is set to scan a range of m / z , 500 to 670 m / z , to select for all ceramide species .
these molecules are fragmented in q2 and specific fragments are detected in the second round of ms in q3 .
ceramide molecules will be fragmented into two distinct parts : the sphingoid backbone and the carbon chain of varying lengths . in q3
, the detector is set at 264 m / z and will only detect the sphingoid backbone from the fragments generated in q2 .
to analyse sphingoid backbones of dihydroceramides , the detector must be set at 266 m / z .
however , the analysis is not limited to only one pair of precursor and product ions .
the detection can be repeated in a cycle which allows for more sensitive and rapid quantifications .
there are a few issues to consider when using the ms / ms technique .
current methods use the procedure established by folch et al . and modified later by bligh and dyer which use a 2 : 1 chloroform / methanol solution for extraction .
appropriate internal standards should be used which will elute from the lc columns and become ionized in a similar way as the ceramides molecules .
these standards should be ceramides that do not occur naturally in biological samples such as c12 or a cocktail of standards ( avanti polar lipids , alabaster , al , usa ) .
to accurately quantify the amounts of different ceramide species , standard curves must be generated and to be precise , one standard curve per analyte should be generated .
the concentration of lipids in the sample prior to analysis is also important to prevent lipid aggregation which can occur when lipid concentrations are high .
the concentration of lipids is suggested to be below 100 pmol of total lipids/l .
the previous techniques in ms / ms are incredibly accurate ; however , they can only detect known molecules .
more recently , researchers have increased their interest in assessing the full spectrum of lipids in a sample . to this end , sphingolipidomics utilizes a shotgun approach .
the lipid extraction from samples is further refined so that specific lipid classes can be isolated even before separation methods come into play .
the acidic and basic properties of lipids are used to ionize to either positive or negative ions .
this step called intrasource separation replaces the separation using lc in the previous ms / ms methods . before quantitation can occur
, a fragment ion unique to a group of lipids of interest must be found to be able to set the detector , for example , 264 m / z for ceramides .
finally , the lipids of a specific group can be quantified by comparing to the internal standard for that group .
there are a few issues that have arisen with this method , mainly that quantification of lipids in low concentrations can be compromised if signals overlap with those from more abundant lipids .
there is a lack of internal standards at the moment for certain classes of lipids , which will limit the power of lipidomics for those molecules .
recently , a survey of the lipidome from yeast using shotgun mass spectrometry has revealed that about 95% of the lipidome was covered using this approach .
cf patients are plagued with chronic pulmonary bacterial infections which are the leading cause of mortality in cf .
the majority of infections are caused by pseudomonas aeruginosa although staphylococcus aureus , haemophilus influenzae , and burkholderia cepacia are also common pathogens isolated from lungs of patients .
there are many factors in cf lungs that facilitate the chronic presence of infections such as increased inflammatory responses , thick layers of mucus , abnormal cell signalling , and defective cell death .
it is however unclear whether the abnormal expression of inflammatory genes precedes infection in patients .
a few studies have described higher levels of inflammation in infants with cf [ 36 , 37 ] and one study has described high levels of cytokines in foetuses with diagnosed cf .
hallmarks of increased inflammation in cf are mainly higher levels of il-1 , il-6 , il-8 , tnf- , while the antiinflammatory il-10 was found to be reduced in cf .
the transcription factor nf-b responsible for the transcription of cytokines has increased levels of phosphorylation in cf .
cftr was found to be a negative regulator of nf-b phosphorylation which would explain higher activation of the transcription factor when cftr is nonfunctional .
ceramides were shown to be generated under certain stimuli such as uv , heat , cytokines , oxidative stress , and lps and in turn ceramide can regulate the expression of cytokines . a study by chiba and colleagues revealed that ceramides can have different effects on cytokine expression depending on the cell type .
the pretreatment of 10 g / ml of c8 ceramide reduced the expression of il-5 , il-10 , and il-13 in mast cells in response to lps stimulation while tnf and il-6 levels were unaffected .
c8 ceramide did however inhibit tnf and il-6 in macrophages but did not alter il-10 levels .
in both cell types , the addition of c8 ceramide inhibited the transcription of cytokines in response to lps ; however , the inhibited cytokines were different per cell type .
results comparing cytokine expression between asmase deficient mice and normal controls showed a 10- to 15-fold increase in serum tnf following lps administration in asmase - ko mice .
in peritoneal macrophages isolated from asmase deficient mice , the supplementation with 30 and 60 m of c2 and c16 ceramide was able to normalize tnf expression following stimulation with lps .
il-8 expression is mainly induced by nf-b which in turn is activated by tnf , among other mediators , and also involves the activation of the mapk pathway .
ceramides were shown to activate protein phosphatase 2a ( pp2a ) , a regulator of both nf-b and mapk pathways .
using human alveolar epithelial cells , cornell and colleagues have demonstrated an increase in il-8 levels when pp2a is inhibited .
the authors found that pp2a inhibition increases the signalling through the mapk pathway by prolonging the activation of jnk , p38 , and erk and enhances the stability of il-8 mrna .
similarly , inhibition of ceramide synthesis led to a reduction in pp2a activation and consequently an increase of il-8 levels .
the authors concluded that ceramides are needed to activate pp2a in order to control and , consequently , down regulate expression of il-8 .
a recent study demonstrated that activation of p38 mapk in lungs of cf patients is greater compared to non - cf controls .
following exposure to p. aeruginosa , cells expressing the f508 mutation experienced a much greater increase in il-6 compared to cells expressing normal cftr due to the overactivation of p38 mapk .
additionally , decreases in ceramide were found to induce activation of p38 mapk which resulted in increased il-6 production .
treatment of alveolar epithelial cells with c6 ceramide prevented the increase in il-6 .
the results of these studies demonstrate the importance of ceramide in regulating excessive inflammatory responses and that a reduction in ceramide levels can result in an uncontrolled production of cytokines which is resolved by supplementation of ceramide .
additionally , the role of the recycling pathway in ceramide generation following lps stimulation seems to be a key component to the response to infections .
azithromycin , a macrolide currently used to treat cf patients , has been shown to improve clinical symptoms of cf such as lung function , improvement in bacterial clearance and attenuation of inflammation .
while the mechanism of this drug is still under investigation , it was found recently that it induces expression of certain inflammatory genes and those involved in the lipid pathways .
an older study demonstrated that total cell phospholipid content was increased following azythromycin treatment of primary fibroblasts suggesting that manipulation of phospholipids may benefit the outcome of infections in cf .
signalling following infection occurs mainly through toll - like receptors ( tlr ) found in the plasma membrane .
tlr-4 is a receptor for lipopolysaccharide ( lps ) found on the surface of gram negative bacteria .
tlr-4 expression was found to be reduced in cf patients ; however when the cftr defect was corrected in epithelial cells , higher levels of tlr-4 were detected on the cell surface .
membrane microdomains , also known as lipid rafts , are lipid aggregates in plasma membranes comprised of cholesterol , sphingolipids , and phospholipids .
they are involved in signal transduction by forming platforms for receptors activated by their ligands .
microdomains spatially organize proteins and protect them from enzymes which could prevent downstream signalling ( e.g. , phosphatases ) .
they postulated that under normal situations , cftr is a receptor for lps and induces the internalisation of p. aeruginosa , the induction of the inflammatory response , apoptosis and , during infection with p. aeruginosa , the presence of cftr increases in microdomains .
the f508 mutation in cftr prevents the localisation of cftr into the microdomains and bacterial infection is not cleared .
another member of lipid microdomains is caveolin-1 which is involved in endocytosis and cell signalling .
when caveolin-1 ko mice were infected with p. aeruginosa , increased bacterial colonization was observed compared to wt mice with higher mortality rates indicating that caveolin-1 is an important component in fighting infection .
one study has observed that caveolin-1 colocalizes with cftr and it was found to be increased in cftr - deficient macrophages inducing an inflammatory phenotype . in sum , the components of microdomains in cf seem to be abnormal , possibly leading to defects in bacteria clearance .
ceramides were found to stimulate tlr-4 . following the addition of multiple doses of exogenous c2 and c6 ceramides up to 15 m , il-8 was found to be increased in human embryonal kidney cells while cells defective for tlr-4 expression did not display any increase in il-8 levels .
the increases were dose dependent and maximum expression of il-8 was found following treatment with 1.5 m c2 and c6 ceramides .
the molecular mechanism regulating the induction of tlr-4 activation by extracellular ceramide was found to differ from that of lps as tlr-4 activation by ceramide was found to be cd14 independent .
a study by grassme and colleagues showed the importance of ceramide in membrane microdomains and infections with p. aeruginosa .
the bacteria were shown to interact with sphingolipid membrane platforms following tracheal infection of mice .
the disruption of lipid microdomains prevented p. aeruginosa - induced apoptosis and induced a 100-fold increase of il-1 gene expression compared to when microdomains remained intact .
when asmase was inhibited , human nasal epithelial cells failed to internalize the bacteria and il-1 release was increased 10-fold compared to when asmase was active .
the addition of c16 ceramide was able to correct the defects seen with asmase inhibition ; internalization , cytokine secretion , and apoptosis returned to normal .
this important study demonstrated the role of ceramide in regulating the downstream effects of bacterial infections and gives insight into potential abnormalities in ceramide levels in cf .
it is postulated that cells lacking functioning cftr display defective control of apoptosis [ 39 , 56 ] .
p. aeruginosa infection of wild - type epithelial cells was found to induce apoptosis , bacterial internalization , and caspase-3 and -6 activation , while infection of cftr defective cells did not result in apoptosis .
one hypothesis is that cftr is a transporter of glutathione , an important antioxidant able to protect cells against excessive oxidative bursts . during apoptosis , glutathione is exported out of the cell via cftr to allow an oxidative stress - induced cell death . in cf , increased levels of intracellular glutathione inhibit the induction of apoptosis .
interestingly , glutathione was found to inhibit nsmase preventing the generation of ceramide following oxidative stress .
it has been postulated that low levels of ceramides prevent the completion of apoptosis even when high dna fragmentation can be observed .
they activate signalling cascade of proapoptotic molecules such as akt , bcl-2 , prb , pkc and in some cell types can activate raf kinase and jnk . in leukemia cells , increases in tnf can cause dna fragmentation leading to apoptosis .
the addition of c2 ceramide induced dna fragmentation similar to the one observed in response to tnf increases .
many studies in oncology have involved the modulation of ceramide levels to induce apoptosis [ 6163 ] .
increases in apoptosis of various tumour cells were seen following the treatment of mice with ceramide analogs .
fenretinide treatment was used in cancer studies due to its known induction of apoptosis by increasing intracellular ceramide levels it was shown that different species of ceramide were generated following the induction of b - cell receptors leading to apoptosis . c16
ceramide levels were increased within 6 hours after apoptosis induction , while c24 levels were found to peak much later , between 12 to 24 hours after apoptosis induction , when caspases became activated .
following tnf-induction of apoptosis , only one ceramide species , c16 , was found to be induced in hepatocytes .
inhibition of ceramide induction by blocking asmase activity was shown to protect cells from apoptotic cell death .
the role of ceramide has been investigated in the context of various diseases . in oncology ,
the role of ceramide as an inducer of apoptosis has been exploited to kill tumour cells in neuroblastoma , breast cancer , head and neck cancer , and colon cancer .
defects in asmase have been shown to cause niemann - pick disease , a progressive neurodegenerative disorder .
knock - out mice for smpd1 , the gene encoding for asmase , were found to be resistant to radiation , apoptosis and tnf- due to the reorganization of membrane microdomains following the disruption of ceramide , sphingomyelin , and cholesterol .
interestingly , following infection with p. aeruginosa , 90% of knock - out ( ko ) asmase mice died while the control mice were able to clear the infection .
the role of ceramides has also been studied in other neurodegenerative diseases such as amyotrophic lateral sclerosis ( als ) where an accumulation of the sphingolipid was observed in spinal cords of patients and mice .
the current hypothesis is that ceramide levels are high due to overactivation of the de novo pathway of ceramide synthesis . in alzheimer 's disease ,
studies have found an upregulation of the enzymes responsible for the synthesis of long chain ceramides such as c18 and c24 .
these high levels were found to be mediated by high levels of ceramide produced by the de novo pathway . increased levels of ceramide in blood plasma were found to be associated with insulin resistance and diabetes .
high levels of c18 , c20 , and c24 : 1 were found in individuals with type 2 diabetes while insulin resistance was associated with low levels of c18 , c20 , c24 , and c24 : 1 .
gaucher 's disease is a known monogenic disease of altered lipid metabolism where glycosphingolipids are stored in tissues .
studies have shown that increased macrophage activation and tissue inflammation are involved in the pathology of the disease . recently
a lipidomic study revealed low levels of ceramide in patients with gaucher 's disease indicating that perhaps an impairment in one sphingolipid can alter the metabolism of others .
contradicting findings have been published about ceramide levels in cystic fibrosis ( cf ) .
we have analyzed ceramide levels in plasma samples from 10 patients with cf and 10 healthy controls by hplc / ms / ms .
our results showed that specific species of ceramide were lower in cf patients : c14 , c20 : 1 , c22 , c22 : 1 , c24 , and also dhc16 .
when looking at the total levels , cf patients were found to have an overall deficiency in ceramides .
we proceeded to analyze total levels of ceramide in tlc purified ceramide fractions using an elisa based method in plasma of 58 cf patients and 72 controls .
our analysis of ceramide levels in organs affected by cf in our mouse model had also shown defects in cf versus wild - type ( wt ) mice in plasma , lung , ileum , and pancreas [ 8 , 78 ] .
the pulmonary bacterial load of cf mice is 30-fold higher than wt mice three days post - infection with p. aeruginosa .
when treated with fenretinide , a semisynthetic retinoid used to increase ceramide in cancer studies [ 7982 ] , cf mice were able to clear infection to the same degree as wt mice . additionally , ceramide levels were increased to the levels observed in wt mice in both plasma and lungs .
mice treated with fenretinide also had a reduction in gene expression of il-1 and s100a8 , genes involved in the immune response to bacterial infections .
vilela and colleagues demonstrated an increase in il-8 levels in human tracheal epithelial cells with and without cftr expression following tnf exposure .
the study showed that fenretinide treatment on cells lacking cftr expression reduced il-8 levels after tnf stimulation . using an hplc method of ceramide detection
, they also demonstrated that intracellular levels of ceramide were increased following fenretinide treatment in cftr - deficient cells .
various studies have observed defects in smases indicating that the recycling pathway in cf is defective . in vitro studies by yu and
colleagues have revealed an impairment in the response of asmase to p. aeruginosa in bronchial epithelial cells . following infection
, s9 cells expressing cftr experienced an increase in intracellular ceramide concentrations whereas ib3 - 1 cftr - defective cells did not . silencing asmase before infection caused an increase in il-8 levels in s9 cells .
similarly , when asmase was added to ib3 - 1 cells , il-8 levels were reduced suggesting that asmase induction and ceramide generation would ameliorate the regulation of cytokine expression in the context of cf . a lower incidence of cellular apoptosis was noticed following infection of cftr - deficient cells in vitro and following p. aerugonisa infection of mice which was improved with the addition of asmase . an increase in pulmonary ceramide levels
was observed in normal mice ( c57bl/6 ) mice but not in cf mice ( cftr - tgn ) following oropharyngeal instillation of p. aeruginosa ; however , no differences were seen preinfection .
further in vitro studies by noe and colleagues in endothelial cell models revealed defects in ceramide metabolism .
pretreating the same cells with an inhibitor of cftr ( cftrinh-172 ) prevented the increase in ceramide levels .
the authors linked the defects in ceramide to the defects observed in apoptosis whereby suggesting that the lack of apoptosis seen in cf may be due to the defect in upregulating ceramide in response to oxidative stress .
in contrast , studies by the gulbins group found an accumulation of ceramide in cf .
using first two mouse models of cf ( cftr - tg and b6.129p2(cf/3)-cftr ) , ceramide levels were quantified and by liquid scintillation counting of ceramide spots run on tlc plates compared to c16 ceramide .
additionally , immunochemistry was used on paraffin embedded lungs using the s58 - 9 antibody .
the results showed elevated levels of ceramide in vesicles of epithelial cells from cf mice compared to the appropriate controls .
similar results were obtained using epithelial cells obtained from cf patients by nasal scraping and lung tissue obtained posttransplant .
the authors attributed this accumulation to the inhibition of asmase in the lysosomes due to the impairment in acidification of the vesicles .
the views on whether ph regulation in vesicles is altered in cf are still conflicting .
certain studies have shown that ph is abnormal in cf vesicles while others claim there are no differences [ 91 , 92 ] .
the authors treated mice with asmase inhibitors which resulted in the reduction of ceramide levels and improved clearance of bacterial infections .
these results agree with the studies by yu and colleagues mentioned above . when asmase is not active , ceramide levels do not increase . however , yu and colleagues observed detrimental effects during bacterial infections when asmase function is defective while the gulbins study suggests that inhibition of asmase enables increased survival of mice infected with p. aeruginosa .
the same group studied the effects of p. aeruginosa infection in macrophages from wt mice and from macrophages obtained from their cf mouse models . using
the dag kinase assay revealed higher basal levels of ceramide in cf cells compared to wt cells . using an immunofluorescence - based method , they reported increased ceramide concentrations in wt cells following bacterial infection but not in cf macrophages . in response to the infection , wt cells had increased clustering of ceramide in the plasma membrane but this response was much reduced in cf cells .
an immunofluorescence - based method was also used in another study by the same group to evaluate the levels of ceramide in alveoli from explanted lung tissue from cf patients .
concurrent to their previous results obtained with the same methods , they had seen higher staining with anticeramide antibodies in cf tissue compared to donor tissue .
finally , in a fourth study , the group utilized three methods of detection of ceramide : immunofluorescence , dag kinase assay , and mass spectrometry .
the authors looked at three specific species of ceramide : c16 , c18 , and c20 .
the levels of each of the three species were not specified in the study but their sum was higher in lungs from their cf mouse models compared to their controls .
the levels of ceramides in cf were assessed by uk investigators using lung tissues from transplant patients with cf and unused donor lungs .
the authors used two methods of ceramide quantification : immunochemistry with the two antibodies ( 15b4 and s58 - 9 ) and hplc / ms .
the immunochemistry results indicated that cf lung tissues had higher median levels of staining compared to all other lung tissue .
the authors also found variability in staining between the two antibodies although one was not systematically staining more than the other .
ceramide levels were additionally measured by hplc / ms although only four species of ceramide were analyzed .
it was found that c16 , c18 , and c20 were elevated in cf lung tissue while no difference was observed for c22 .
another study has shown a combination of the two hypothesis finding elevated levels of certain species of ceramide while others being reduced . using tlc and liquid scintillation counting ,
ceramide species were analysed in 16hbe14o(- ) cells either expressing cftr or the antisense control gene construct .
four ceramide species were found to be elevated ( dhc16 , c22 , c24 , c26 ) when no cftr was expressed while 2 species were reduced ( c18 and c18 : 1 ) compared to cells expressing cftr .
different cell types may respond differently to stress , and ceramides may act differently within each cell type .
many attempts to produce an adequate model of cf which would reproduce all phenotypes seen in patients failed due to the lack of lung disease in mice .
the first attempts at generating a ko mouse came from the university of north carolina with the disruption of exon 10 of cftr with neomycin resistance genes .
a mixed genetic background was at fault and researchers began to backcross the mice to c57bl/6j mice .
reports have described destruction of lung structure , thick mucus lining the distal airways , infiltration of inflammatory cells around the airways , and increases in inflammatory gene expression in the lungs . additionally , marked pathology in the pancreas was observed with acinar atrophy and increased inflammation .
these mice necessitate a liquid diet ( peptamen , nestle , brampton , ontario , canada ) not only to avoid intestinal blockage , a phenotype which can occur in cf patients , but to improve the absorption of nutrients without having to supplement the diet with enzymes .
other mouse models were generated to express specific cftr mutations such as f508 , g551d , and g480c but ceramide levels have not been assessed in these models as of yet . to escape the need of special diets for cf mice , other models were generated which could express cftr locally in the gut .
the cftr - tg express cftr in the gut under control of a human fatty acid binding protein ( fabp ) promoter .
although these mice show evidence of impaired alveolar macrophage function without severe intestinal pathology , there is however no description of chronic lung disease in these mice ( jackson lab site http://www.jax.org/ ) .
it is evident that different mouse models present different phenotypes of cf disease ( see review ) .
for example , defects in fatty acids such as omega-3 and omega-6 fatty acids have been shown in the b6.cftr ko mouse [ 2 , 4 ] but not in other models .
some mouse models have failed to demonstrate lung disease and it was speculated that disease modifier genes such as alternate chloride channels could exist in certain mouse backgrounds [ 94 , 102 ] .
it was verified that the b6.cftr ko mouse does not express alternative chloride channels ; however , this has not been studied in most mouse models , including the above described cftr - tg .
the latter mouse model was generated using a mixed background of 129p3/j , c57bl/6 , and fvb / nj ( see http://www.jax.org/ ) .
the issue of diet has been brought up by the gulbins group as a point contention between in vivo ceramide studies .
it has been suggested that peptamen is responsible for the reduced levels of ceramide by elevating cholesterol levels which in turn inhibit asmase activity .
however , the authors overlooked the data from cf patients presented in the same study .
the cohort of cf patients assessed in the study was not consuming peptamen in their diet , were monitored for their cholesterol levels , and none of the patients were placed on a cholesterol reducing diet .
the effect of peptamen on the levels of ceramide was analyzed in our model of cf and wt mice and no influence of peptamen diet on the level of ceramide was observed .
importantly , these findings were assessed using lc / ms / ms analysis of all detectable species of ceramides which demonstrated that several ceramide species were impaired in cf ( both in mice and cf patients ) .
this deficiency of specific ceramide species was correctable by treatment with fenretinide in mice , and we have recently obtained orphan drug status approval by the us food and drug administration ( fda ) for treatment with fenretinide of cf patients infected with p. aeruginosa .
recently , a genome - wide association study was performed on 4,400 samples collected from five european populations regarding their levels of circulating sphingolipids .
the results concluded that there are genetic variations in genes involved in the sphingolipid metabolism indicating that different populations may have varying basal levels of ceramide .
this is especially important clinically in cf as genetic variation can affect the severity of the disease , but also in terms of research , differences seen in ceramide levels between studies may be attributed to genetic differences of the populations studied .
using antibodies in the detection of ceramides can be misleading as they can bind to a selection of ceramide species and lipids in general .
while immunohistochemistry offers an opportunity to visualize staining of tissues , one must be careful to interpret the staining as pure ceramide detection since ceramides are not purified from other lipids which might cross - react with the antibodies .
using the antibodies in elisas necessitates an initial separation of lipids by tlc from which the ceramide fraction can be isolated . without purification ,
the cross - reactivity of the antibodies prevents a reliable quantification of ceramides . while this assay can reduce costs for the quantification of ceramides for many samples
, it can not provide data on the types of ceramide species nor the concentration of each species present in the sample .
dag kinase assays can be an inexpensive method for ceramide analysis ; however , only total levels of ceramide can be assessed and once again , ceramide may not be the only lipid quantified in the end .
ms offers unmistakable identification of various species of ceramides ; therefore it represents the best solution for accurate quantification .
many are turning to ms as a form of analysis ; however , it is questionable why certain studies chose to only look at a small subset of species when it is possible to look at all the known forms of ceramide .
the simple explanation would be that the cost per sample using ms is still much greater than the cost for dag kinase assays and immunodetection .
ms requires specialized equipment and knowledge in the technique which may not be available to all laboratories .
the area of lipid research is continually gaining momentum . with the improvement of sensitive quantification methods such as ms
when testing the levels of ceramides , all detectable species of ceramides ( and not only a selection of ceramide species ) have to be assessed to fully explore the role of these important mediators in various cellular and molecular mechanisms of gene expression regulation and cf physiology .
ceramides are important in the immune response and it is possible that different species have different roles . the results in the area of cf are contradicting due to the animal models used and methods of ceramide detection .
certain steps can be undertaken to resolve these issues such as the use of internal standards and clear ms protocols should be reported .
most importantly , ms should be made the gold standard for ceramide analysis since the dag kinase assays and the use of antibodies are known to not be reliable methods . however , despite contracting results , the analysis of ceramide levels remains an important subject to investigate in cf using methods which are likely to generate the most reliable results possible . | patients with cystic fibrosis ( cf ) are afflicted with many symptoms but the greatest challenge is the fight against chronic bacterial infections , leading to decreased lung function and ultimately death .
our group has recently found reduced levels of ceramides in cf patients and mice .
ceramides are sphingolipids involved in the structure of cell membranes but also participate in the inflammatory response , in cell signalling through membrane microdomains ( lipid rafts ) , and in apoptosis .
these characteristics of ceramides make them strong candidates for therapeutic intervention in cf . as more studies have come to evaluate the role of ceramide in cf ,
conflicting results have been described .
this paper discusses various views regarding the potential role of ceramide in cf , summarizes methods of ceramide detection and their role in the regulation of cellular and molecular processes . |
several species of leishmania are responsible for leishmaniasis ( 1 ) with several clinical presentations including cutaneous , mucocutaneous and visceral leishmaniasis ( vl ) ( 2 ) . although , it has been reported that vl is sporadic in iran , but in northwestern and southern areas of iran , the disease is endemic ( 3 ) and approximately 100300 new cases of vl are detected annually ( 3 ) . impaired immune responses against the leishmania parasite is the main reason for distribution of the parasite and production of vl form , also known as kala azar ( 4 ) . thus , it seems that the host immune responses against the leishmaniasis determine the infection outcome ( 5 ) .
il-10 , as the main anti - inflammatory cytokine , plays important roles in the regulation / suppression of immune responses , es - pecially during chronic infections including vl ( 6 , 7 ) .
serum levels of il-10 were increased in vl ( 8 , 9 ) , hence , it can be hypothesized that the factors , such as genetic variations , which lead to alteration in il-10 expression , can affect the outcome of leishmaniasis .
the association of a single nucleotide polymorphism ( snp ) within promoter region at -1082 position of the il-10 gene ( rs1800870 ) with altered il-10 expression has been reported by investigators ( 10 ) .
therefore , it can be suggested that the il-10 -1082 polymorphism may be associated with chronic infections including vl .
therefore , this study was designed to evaluate the il-10 -1082 polymorphism in the seropositive vl patients in comparison to seropositive and negative healthy controls .
in this cross - sectional study , the participants were divided to three groups including ; patients with clinical presentation of vl and seropositive for the leishmania ( group 1 consisting of 110 patients ) , seropositive patients but without clinical presentation ( group 2 consisting of 74 patients ) and , healthy controls ( group 3 consisting of 113 people ) .
table 1 presents the demographic data of the defined groups including mean age and sex ratios .
vl was diagnosed by an expert specialist according to medical history , clinical presentations including ; severe anemia , fever , cough , diarrhea , vomiting , fatigue , weakness , and appetite loss and finally laboratory findings .
all of the participants in the present study were selected during 2004 to 2011 from azar city ( north west of iran ) where the l. infantum is endemic ( 11 , 12 ) .
an informed consent form was filled out by the participants prior to sample collec - tion and the ethical committee of the hamadan university of medical sciences has approved the study protocol .
demographic data of study population at entry dna was extracted using a commercial kit from bioneer company ( south korea ) according to the manufacturers instruction .
the pcr - rflp technique was used for evaluation of the il-10 -1082 gene polymorphism .
pcr was performed in a final volume of 50 l containing ; 2 l of taq dna polymerase buffer ( 10x ) , 5 units of taq dna polymerase , 1 l of each dntp ( datp , dctp , dgtp and dttp in 10 mm concentration ) , 4 l of each primer ( 25 ng/l ) , 5 l of 1.5 mm mgcl2 , 2.5 l of extracted dna and sterile double distilled dnase free water . the forward primer sequence was 5'-gacaacactactaaggctcctttggga-3 ' and the reverse primer sequence was 5'-tgagcaaactgaggcacagaaat-3 ' .
the following program was used for pcr amplifications : one cycle 95c for 5 min ( denaturation ) and then 35 cycles of 30 sec at 95c , 53c for 30 sec and 72c for 40 sec using a thermal cycler ( bioneer , south korea ) . the bsli restriction enzyme ( fermentase , finland )
was used to digest the amplicon ( 315 bp ) . upon digestion of the pcr product with bsli , in the case of g allele , resulted into three fragments of 25 , 37 and 253 bp and in the case of a allele led to 37 and 278 bp .
the products were analysed by electrophoresis on a 2.5% ethidium bromide pre - treated agarose gel ( cinnaclon , iran ) .
the titration of anti - leishmania antibody was examined using a commercial kit ( qiagen , usa ) according to the manufacturer s guidelines .
briefly , the serum samples were diluted to 1/20 , 1/40 , 1/80 , 1/160 and 1/320 and the positive indirect fluorescent antibody test at each diluents was considered as the titration of anti - leishmania antibody .
the cutoff of the test has been calculated as follow : mean titration of positive sample + mean titration of negative sample /2 .
hardy - weinberg equilibrium analysis was used to confirm the validity of the raw data .
spss statistical software ( version 18 , spss , chicago , il , usa ) was used for data analysis and a p value of < 0.05 was considered significant .
the association of snp with disease and the calculation of odds ratios ( ors ) , with 95% confidence intervals ( cis ) was evaluated using analysis .
one - way ano - va test was used to analysis the differences of quantitative data between groups .
the genotype distributions between the vl patients were compared to participants without vl but seropositive and also to healthy controls by a logistic regression model controlling for age and sex .
akaike information criterion ( aic ) was estimated for three analysis models to select the appropriate model for this study using stepwise model selection ( sas ) ( 13 ) .
in this cross - sectional study , the participants were divided to three groups including ; patients with clinical presentation of vl and seropositive for the leishmania ( group 1 consisting of 110 patients ) , seropositive patients but without clinical presentation ( group 2 consisting of 74 patients ) and , healthy controls ( group 3 consisting of 113 people ) .
table 1 presents the demographic data of the defined groups including mean age and sex ratios .
vl was diagnosed by an expert specialist according to medical history , clinical presentations including ; severe anemia , fever , cough , diarrhea , vomiting , fatigue , weakness , and appetite loss and finally laboratory findings .
all of the participants in the present study were selected during 2004 to 2011 from azar city ( north west of iran ) where the l. infantum is endemic ( 11 , 12 ) .
an informed consent form was filled out by the participants prior to sample collec - tion and the ethical committee of the hamadan university of medical sciences has approved the study protocol .
dna was extracted using a commercial kit from bioneer company ( south korea ) according to the manufacturers instruction .
the pcr - rflp technique was used for evaluation of the il-10 -1082 gene polymorphism .
pcr was performed in a final volume of 50 l containing ; 2 l of taq dna polymerase buffer ( 10x ) , 5 units of taq dna polymerase , 1 l of each dntp ( datp , dctp , dgtp and dttp in 10 mm concentration ) , 4 l of each primer ( 25 ng/l ) , 5 l of 1.5 mm mgcl2 , 2.5 l of extracted dna and sterile double distilled dnase free water . the forward primer sequence was 5'-gacaacactactaaggctcctttggga-3 ' and the reverse primer sequence was 5'-tgagcaaactgaggcacagaaat-3 ' .
the following program was used for pcr amplifications : one cycle 95c for 5 min ( denaturation ) and then 35 cycles of 30 sec at 95c , 53c for 30 sec and 72c for 40 sec using a thermal cycler ( bioneer , south korea ) . the bsli restriction enzyme ( fermentase , finland )
was used to digest the amplicon ( 315 bp ) . upon digestion of the pcr product with bsli , in the case of g allele , resulted into three fragments of 25 , 37 and 253 bp and in the case of a allele led to 37 and 278 bp .
the products were analysed by electrophoresis on a 2.5% ethidium bromide pre - treated agarose gel ( cinnaclon , iran ) .
the titration of anti - leishmania antibody was examined using a commercial kit ( qiagen , usa ) according to the manufacturer s guidelines .
briefly , the serum samples were diluted to 1/20 , 1/40 , 1/80 , 1/160 and 1/320 and the positive indirect fluorescent antibody test at each diluents was considered as the titration of anti - leishmania antibody .
the cutoff of the test has been calculated as follow : mean titration of positive sample + mean titration of negative sample /2 .
hardy - weinberg equilibrium analysis was used to confirm the validity of the raw data .
spss statistical software ( version 18 , spss , chicago , il , usa ) was used for data analysis and a p value of < 0.05 was considered significant .
the association of snp with disease and the calculation of odds ratios ( ors ) , with 95% confidence intervals ( cis ) was evaluated using analysis .
one - way ano - va test was used to analysis the differences of quantitative data between groups .
the genotype distributions between the vl patients were compared to participants without vl but seropositive and also to healthy controls by a logistic regression model controlling for age and sex .
akaike information criterion ( aic ) was estimated for three analysis models to select the appropriate model for this study using stepwise model selection ( sas ) ( 13 ) .
the results demonstrated that the il-10 -1082 a / g genotype was significantly increased in group 1 when compared to either group 2 or 3 ( table 2 and 3 ) .
the prevalence of the a / a , a / g and g / g genotype as well as a and g alleles within il-10 -1082 position in the study population polymorphism association with for four different models including full genotype , dominant , recessive , and multiplicative ( for alleles ) the statistical analysis revealed that the prevalence of il-10 -1082 a and g alleles were not significantly differ among the groups ( p= 0.263 ) ( table 2 and 3 ) .
the results also showed that the vl patients ( group 1 ) ( p= 0.783 ) and participants in group 2 ( p= 0.065 ) carrying various il-10 -1082 genotypes did not differ regarding the titration of anti - leishmania antibodies ( table 4 ) .
the statistical analysis also demonstrated that the differences between the groups regarding the mean age and sex ratio were not significant ( table 1 ) .
the titration of anti - leishmania antibody in group 1 and 2 carrying various il-10 -1082 genotypes in order to show alternative effects of the variants among the four models including co - dominant , dominant , recessive and additive , a model analysis was performed .
p - values and ors of genotypes for various models are presented in table 3 .
the results revealed that the best fit model was the co - dominant model based on aic values favor .
it has been documented that il-10 up - regulation in response to infectious diseases , including leishmaniasis , leads to impaired immune responses and hence , induces chronic forms of the diseases ( 6 ) . moreover
, previous studies demonstrated that il-10 plays crucial roles in the suppression of immune responses against leishmania ( 8) .
accordingly , bhattacharya and colleagues reported that serum levels of il-10 were increased in vl patients ( 9 ) .
elevated serum levels of il-10 in indian vl patients were reported by ganguly and colleagues ( 14 ) .
saha et al . also showed that il-10 results in susceptibility to vl and post - kala - azar dermal leishmaniasis ( 15 ) .
interestingly , il-10 receptor blockade immunotherapy also led to enhanced immune responses against vl ( 16 ) .
furthermore , several studies revealed that treatment with anti - leishmania drugs resulted in decreased serum ( 1719 ) and mrna ( 2022 ) levels of il-10 .
these data proposed that il-10 as a part of immune responses participates in the pathogenesis of leishmania and its inappropriate production may be a risk factor for clearance of the parasite .
another study demonstrated that il-10 -1082 a / g genotype creates new binding sites for nuclear transcription factors and resulted in up - regulation of il-10 in patients suffering from cutaneous leishmaniasis ( 23 ) .
il-10 -1082 a / g genotype was significantly increased in group 1 in comparison to groups 2 or 3 .
thus , it may be concluded that the higher prevalence of il-10 -1082 a / g genotype in iranian vl patients may be considered as a risk factor which may lead to impaired immune responses against leishmania .
there are not yet adequate studies to describe why the il-10 -1082 a / g genotype may be responsible for increased expression of il-10 or why individuals with the a / g genotype would produce more il-10 than persons with a / a or g / g .
it may be hypothesized that a heterozygotic patient may carry epigenetic events which result in increased the efficiency of the promoter but this can not currently be identified .
however , previous investigations reported that epigenetic factors such as micro - rnas are able to alter cytokine expressions including il-10 ( 24 ) .
for instance , let-7c , as a mirna , can regulate il-10 expression in an in vitro condition ( 24 ) .
additionally , previous studies showed that there are several polymorphisms within promoter region of il-10 which may alter il-10 expression ( 25 ) , hence , it seems that several genetic and epigenetic factors are involved in the regulation of il-10 expression and evaluation of their status in vl patients can be considered for future investigations . to the best of our knowledge ,
the current study is the first investigation which evaluated il-10 -1082 gene polymorphism in vl patients in comparison to healthy controls .
our previous study on another polymorphism within -819 position of il-10 gene also revealed that this polymorphism was significantly associated with vl ( 26 ) .
another study on il-10 -819 polymorphism have shown that this polymorphism was not associated with development of post kala - azar dermal leishmaniasis ( 27 ) .
de jesus also revealed that the il-10 -819 polymorphism was not associated with cutaneous outcome ( 28 ) .
based on these studies and also the present study , it may be hypothesized that the il-10 -1082 and -819 polymorphism can be associated with vl incidence in iranian population and il-10 -1082 a / g genotype can be considered as a risk factor for vl .
our results also demonstrated that the vl patients as well as participants in group 2 with various il-10 -1082 genotypes did not differ regarding anti - leishmania antibodies ; hence , it appears that the -1082 polymorphism in il-10 gene is not associated with production of anti - leishmania antibody .
ethical issues ( including plagiarism , informed consent , misconduct , data fabrication and/or falsification , double publication and/or submission , redundancy , etc . ) have been completely observed by the authors . | abstractbackgroundimmune responses play critical roles in the leishmaniasis eradication .
il-10 is a key regulator of immune responses , and the polymorphisms within its promoter region are associated with alteration in its expression .
therefore , this study was designed to examine the correlation between polymorphism at the -1082 position of the il-10 gene and visceral leishmaniasis ( vl).methodsthe il-10 -1082 polymorphism and anti - leishmania antibody titration were examined in 110 patients with clinical presentation of vl and seropositive for the leishmania ( group 1 ) , 74 seropositive patients but without clinical presentation ( group 2 ) and 113 healthy controls ( group 3 ) using the pcr - rflp and immunofluorescence techniques , respectively.resultsthe polymorphism at il-10 -1082 ( a / g ) position was significantly associated with vl and a / g genotype was significantly higher in vl patients when compared to the groups 2 and 3 ( p < 0.001 ) .
however , the results demonstrated that the a and g alleles were not associated with vl ( p= 0.263).conclusionsprevious investigations have shown that the polymorphism at the -1082 position of the il-10 gene can influence its expression and also it has been proved that il-10 level was increased during vl .
our results suggest that the a / g genotype may be considered as a risk factor for vl . |
legionellosis is most often attributed to inhalation of contaminated aerosols from manmade water systems or , in the case of legionella longbeachae , to inhalation of contaminated potting mixes or composts [ 13 ] . from 2003 to 2004 , active population - based surveillance for atypical bacterial respiratory pathogens was performed in the province of sa kaeo , thailand , to establish incidence .
immunologic testing performed on sera of suspect legionellosis cases found 20/397 ( 5% ) adult cases exhibited a fourfold rise in titer to l. longbeachae by the indirect immunofluorescence assay .
l. longbeachae infection followed the typical legionellosis demographic , with incidences highest among adults over 34 years of age , increasing steadily with age , and infection peaking through september and october .
as rice farming is quite prevalent in this area of thailand , the extensive exposure of farm workers to moist soil would be a plausible means for transmitting l. longbeachae .
these findings , coupled with limited access to composted or processed soil , led us to investigate the presence of legionellae , specifically l. longbeachae , in indigenous soils and exposure due to agricultural practices in sa kaeo .
in 2009 , thirty - nine wet soil samples were collected from eight rural sites within sa kaeo province where prior laboratory - confirmed cases of legionellosis were identified and were shipped to the centers for disease control and prevention in atlanta for culture .
cultures were performed using a modification of the procedure used to culture legionellae from water .
five grams of soil were weighed , and mixed with 50 ml sterile dh2o .
the filtrate was then strained through sterile gauze into a 50 ml conical tube .
a 1 : 5 dilution was made of the filtrate , and 500 l of the diluted filtrate was acid treated for fifteen minutes with an equal part of kcl / hcl acid ( ph 2.3 ) .
after acid treatment , 50 l was cultured on one plate of buffered charcoal yeast extract ( bcye ) supplemented with 160 mg / l cycloheximide , two plates additionally supplemented with 100,000 u / l polymyxin b and 5 mg / l vancomycin ( pcv ) , and two plates further supplemented with 2 g / l glycine ( gpcv ) .
plates were examined at four , seven , and fourteen days to check for the presence of legionella .
any samples overgrown with non - legionella organisms were retreated with acid in fifteen - minute increments and recultured , until nonrelevant organisms were reduced enough to allow for identification of legionellae .
colonies displaying legionella morphology were checked for cysteine auxotrophy on bcye biplates with and without l - cysteine .
monoclonal antibody ( mab ) testing was used to identify l. pneumophila serogroup 1 ( lp1 ) as previously described [ 7 , 8 ] .
other l. pneumophila serogroups were determined using direct fluorescent antibody staining performed on dried , formalin - fixed suspensions using l. pneumophila serogroup - specific fluorescein isothiocyanate labeled antibody . select non - l .
all non - lp1 isolates were identified by sequencing the macrophage infectivity potentiator ( mip ) gene .
the resulting sequence was then queried against the national center for biotechnology information ( ncbi ) genbank nucleotide database using ncbi 's alignment tool basic local alignment search tool ( blast ) [ 12 , 13 ] .
sequences with a minimum of 95% identity to a known legionella species were assigned . those sequences with less than 95% identity to sequences of submitted legionella species were considered a potential novel legionella organism .
all l. pneumophila isolates were genotyped using the sequence - based typing ( sbt ) epidemiological typing scheme established by the european working group for legionella infections ( ewgli ) as previously described [ 14 , 15 ] .
eburst analysis was performed to observe the relatedness of the soil isolates to isolates from other countries previously submitted to the ewgli sbt database ( http://eburst.mlst.net/ ) .
twenty - two ( 56% ) of the 39 soil samples received were positive for legionella . in total
, we obtained 115 isolates , 87 of which were known species , 25 potential novel species , and 3 isolates that were not typable by mip sequencing ( table 1 ) .
nine of the species identified have been reported in association with human disease and represented 70% ( 80/115 ) of isolates obtained .
isolates of l. birminghamensis , l. lansingensis , l. pneumophila , l. rubrilucens , and l. sainthelensi were found exclusively in soil samples from the personal residence of suspect cases .
isolates of l. bozemanae , l. erythra , l. gormanii , l. quateirensis , l. quinlivanii , and the potentially novel species identified as legionella sp . st24644 ( ncbi accession number gu083740 ; isolated from a cooling tower in thailand ) were found only in soil samples from the workplace of suspect cases .
the highest diversity of species ( n = 7 ) was found in soils taken from the outdoor area for washing at the personal residence and within rice fields .
l. pneumophila serogroup 1 was identified in the environment ; however , none were positive for monoclonal antibody mab2 , the phenotypic subtype responsible for 65100% of lp1-caused legionellosis .
five of 112 isolates tested reacted strongly with l. longbeachae serogroup 1 antisera by direct fluorescent antibody testing .
sequence analysis , however , indicated these isolates were l. bozemanae ( n = 2 ) , legionella sp .
st24644 ( n = 2 ) , and a novel nonfluorescent legionella species ( n = 1 ) .
although the species of the three mip untypable isolates remain unknown , they were identified as legionella spp . using a pan - legionella real - time pcr assay .
slide agglutination testing found these isolates were not l. geestiana , a species in which the mip gene is known to not amplify with the primers used .
eight allelic profiles were identified by sbt analysis , seven of which were novel profiles ( as of november 2 , 2010 ) .
two of the seven novel sequence types identified were found to be related to isolates from community - acquired and nosocomial cases through eburst analysis ( as of december 14 , 2010 ; data not shown ) .
the eighth allelic profile matched the existing st260 which has been associated with community - acquired cases .
although a primary goal in this study was to identify the environmental source(s ) of the suspect causative agent l. longbeachae in the 2003/4 suspect pneumonia cases , we were unable to recover this species from these 39 soil samples .
interestingly , the water - saturated soils collected did support the growth of many other legionella species not previously associated with this indigenous soil type .
these findings suggest that the l. longbeachae seropositive - pneumonia cases documented in 2003/4 were either ( i ) due to l. longbeachae that were no longer or never present in these environments or were not found in our limited number of samples as mentioned previously ; ( ii ) due to a serologically cross - reactive strain of legionellae ; ( iii ) serological cross - reaction with another pathogen ; or ( iv ) false - positives .
cross - reactivity is an inherent problem in the use of serology for identification , and the findings of this study further highlight the need for a molecular - based method for identification [ 1922 ] .
pneumophila cases because of insufficient specificity and sensitivity of non - pneumophila legionellae antisera . for future studies , we wish to conduct prospective surveillance in sa kaeo and obtain legionellae isolates from patient samples .
a clinical isolate would allow for sequence identification of the etiologic agent and detection of any novel species responsible for respiratory disease in tropical countries such as thailand .
concurrent environmental sampling would allow identification of settings capable of transmitting these pathogens to susceptible hosts .
although l. longbeachae is widely accepted as the predominant pathogenic , soil - dwelling species of legionella , the presence of legionellae in soils has been limited to composts and manufactured potting mixes .
the findings in this study indicate native soils are a likely reservoir of multiple legionella species in regions with a geography and climate similar to sa kaeo and may play a role in human disease . | members of the gram - negative genus legionella are typically found in freshwater environments , with the exception of l. longbeachae , which is present in composts and potting mixes . when contaminated aerosols are inhaled , legionellosis may result , typically as either the more serious pneumonia legionnaires ' disease or the less severe flu - like illness pontiac fever .
it is presumed that all species of the genus legionella are capable of causing disease in humans . as a followup to a prior clinical study of legionellosis in rural thailand
, indigenous soil samples were collected proximal to cases ' homes and workplaces and tested for the presence of legionellae by culture .
we obtained 115 isolates from 22/39 soil samples and used sequence - based methods to identify 12 known species of legionella represented by 87 isolates . |
kidney biopsy specimens were procured from 22 southwestern american indians enrolled in a randomized , placebo - controlled clinical trial to evaluate the renoprotective efficacy of losartan in type 2 diabetes ( clinical trial reg .
these subjects were followed longitudinally for many years prior to enrollment in the clinical trial , and the occurrence and severity of diabetes and dn were carefully documented .
the cohort was divided into two groups according to their average albumin / creatinine ratio ( acr ) around the time of biopsy ( 6 months ) based on clinical practice guidelines and recommendations ( 5 ) .
subjects with a urinary acr of < 30 mg / g ( average , 14 2 mg / g ; range , 526 mg / g ) were placed into the low albuminuric group ( lalb ; n = 12 ) , and subjects with an acr > 30 mg / g ( average , 410 231 mg / g ; range , 342426 mg / g ) were placed in the high albuminuric group ( halb ; n = 10 ) ( table 1 ) .
the halb and lalb groups had similar hba1c levels ( 9.1 0.8 vs. 8.8 0.7% , p = 0.78 ) at enrollment .
for analysis of changes in glomerular gene expression with dn , halb was compared with lalb . at biopsy
, the two groups showed no difference in age , bmi , hba1c , fasting plasma glucose concentration , or measured glomerular filtration rate ( table 1 ) .
table 1 also shows the histopathologic features in the human cohorts at time of biopsy .
glomerular gene expression profiles obtained from living donor kidney biopsies ( nondiabetic [ nd ] ; n = 18 ) were used for halb versus nd and lalb versus nd comparisons .
in addition , glomerular gene expression profiles were obtained from patients with membranous nephropathy ( mn ; n = 21 ) and a separate cohort of nd patients ( n = 5 ) to enable comparison with an nd proteinuric disease .
all samples were processed according to the european renal cdna bank protocol ( 6 ) , and rna was isolated from microdissected glomeruli as previously described ( 3 ) .
rnas were hybridized to affymetrix human genome u133 plus genechips ( affymetrix , inc . , santa clara , ca ) and processed according to the manufacturer s instructions ( 3 ) .
phenotypic characterization of human and mouse models glomerular rna was also obtained from three mouse models of dn : low - dose streptozotocin ( stz)induced diabetes in dba2/j mice ( dba stz mice ) , a type 1 diabetes model ; homozygous leptin receptor mutation ( lepr ) on a c57blks genetic background ( bks db / db mice ) , an obese type 2 diabetes model ; and bks db / db mice with targeted deletion of endothelial nitric oxide synthase ( bks enos
db / db mice ) , an obese and hypertensive type 2 diabetes model .
dba mice were fasted for 4 h and then given intraperitoneal injections of 40 mg / kg stz or vehicle control daily for five consecutive days ( 7 ) .
bks db / db and bks enos
db / db mice became obese around 4 weeks of age and developed hyperglycemia between 4 and 8 weeks of age .
dn , as evidenced by increased albuminuria , mesangial expansion , and podocyte loss was manifest in all mouse models after 12 weeks and was more severe after 24 weeks of diabetes ( 79 ) .
standardized phenotypic analysis followed protocols established by the animal models of diabetic complications consortium ( www.diacomp.org ) ( 2 ) .
body weights , fasting blood glucose , and acr were in agreement with previously published studies ( 710 ) .
when the mice were killed , glomeruli from diabetic and control mice were iron perfused and magnetically isolated ( 7 ) .
total glomerular rna was obtained using the rneasy mini kit ( qiagen , hilden , germany ) .
gene expression profiling was performed ( 11 ) using affymetrix genechip mouse genome 430 2.0 arrays in the university of michigan microarray core facility according to the manufacturer s instructions .
these procedures were in accordance with the policies of the university of michigan and vanderbilt university institutional animal care and use committees .
verification of selected differentially expressed genes ( degs ) by quantitative real - time rt - pcr ( qrt - pcr ) was performed using taqman low density arrays ( applied biosystems ) per the manufacturer s instructions .
normalization of qrt - pcr results was performed using the geometric mean from multiple housekeeping genes for human ( n = 4 ) and mouse ( n = 5 ) samples ) ( 13 ) .
human halb and lalb samples are the same as those shown in table 1 , unless otherwise specified .
a subset of nd samples was used ( average age , 49.8 + 6.1 years ; n = 6 [ 3 males and 3 females ] ) .
diabetic and control mouse samples were also identical to those in table 1 . only cycle threshold ( ct ) values < 35 were used for analysis ; thus , eight halb samples assayed for col1a1 and kit and 11 lalb samples assayed for kit and interleukin ( il)-16 were analyzed ( 12 ) .
fold differences were calculated using the delta - delta ct method as previously described ( 14 ) .
files containing raw mrna expression data ( cel files ) were processed , normalized , log transformed , and analyzed using the chipinspector software ( genomatix software , www.genomatix.de ) ( 13 ) .
chipinspector analyzes the expression signals at single - probe level , and they are reported summarized at gene - level annotation ( 15 ) . the statistical method implemented in this software
is based on a student t test with a permuted background that enhances the original sam algorithm by tusher et al .
we used one class of exhaustive matching to detect the differentially regulated genes in the halb versus lalb , halb versus nd , and lalb versus nd human comparisons .
we applied a false discovery rate of < 1% on all datasets to detect the significantly regulated genes .
no individual - level genetic data can be publicly released from the southwestern american indian study .
the three cross - species that shared transcriptional datasets will be available for data mining using state - of - the - art systems biology tools at www.nephromine.org . to elucidate the functional relationships among the significantly regulated genes ,
transcriptional networks were generated using a natural language programming strategy ( bibliosphere module ; genomatix software suite ) .
the natural language programming scans were set to establish a connection between any two genes if they were cocited in the same sentence in a pubmed abstract . as a second level of evidence for a gene - gene interaction , information defining transcription factor
target transcript pairs was retrieved by scanning differentially regulated transcripts for binding sites of coregulated transcription factors . to compare
the large transcriptional networks comprising thousands of gene nodes from humans and mice , an algorithm implemented in tale ( tool for approximate large graph matching ) was used ( 17 ) .
tale compares the network structure and extracts overlapping conserved relations between the query and database networks . to allow a cross - species transcriptional network comparison , all mouse genes were converted to human orthologs according to the national center for biotechnology information ( ncbi ) homolog build64 and genomatix annotated ortholog database .
this resulted in a loss of 1013% of genes in the mouse transcriptional networks as no unique human orthologs could be identified for those genes .
the three mouse networks were populated into the database , and the human network was used as the query network .
next , the most important genes ( seed genes ) were identified based on the degree of connectivity within the query ( human ) network ( top 20% of total gene nodes in the network ) .
finally , a 10% mismatch parameter was used to allow for a modicum of mismatches while generating the neighborhood of the seed gene nodes as well as extending the network .
the resulting three tale cross - species networks were then evaluated for their functional enrichment using the genomatix pathway system ( geps ) from the genomatix software suite .
kidney biopsy specimens were procured from 22 southwestern american indians enrolled in a randomized , placebo - controlled clinical trial to evaluate the renoprotective efficacy of losartan in type 2 diabetes ( clinical trial reg .
these subjects were followed longitudinally for many years prior to enrollment in the clinical trial , and the occurrence and severity of diabetes and dn were carefully documented .
the cohort was divided into two groups according to their average albumin / creatinine ratio ( acr ) around the time of biopsy ( 6 months ) based on clinical practice guidelines and recommendations ( 5 ) .
subjects with a urinary acr of < 30 mg / g ( average , 14 2 mg / g ; range , 526 mg / g ) were placed into the low albuminuric group ( lalb ; n = 12 ) , and subjects with an acr > 30 mg / g ( average , 410 231 mg / g ; range , 342426 mg / g ) were placed in the high albuminuric group ( halb ; n = 10 ) ( table 1 ) .
the halb and lalb groups had similar hba1c levels ( 9.1 0.8 vs. 8.8 0.7% , p = 0.78 ) at enrollment .
for analysis of changes in glomerular gene expression with dn , halb was compared with lalb . at biopsy
, the two groups showed no difference in age , bmi , hba1c , fasting plasma glucose concentration , or measured glomerular filtration rate ( table 1 ) .
table 1 also shows the histopathologic features in the human cohorts at time of biopsy .
glomerular gene expression profiles obtained from living donor kidney biopsies ( nondiabetic [ nd ] ; n = 18 ) were used for halb versus nd and lalb versus nd comparisons .
in addition , glomerular gene expression profiles were obtained from patients with membranous nephropathy ( mn ; n = 21 ) and a separate cohort of nd patients ( n = 5 ) to enable comparison with an nd proteinuric disease .
all samples were processed according to the european renal cdna bank protocol ( 6 ) , and rna was isolated from microdissected glomeruli as previously described ( 3 ) .
rnas were hybridized to affymetrix human genome u133 plus genechips ( affymetrix , inc . , santa clara , ca ) and processed according to the manufacturer s instructions ( 3 ) .
phenotypic characterization of human and mouse models glomerular rna was also obtained from three mouse models of dn : low - dose streptozotocin ( stz)induced diabetes in dba2/j mice ( dba stz mice ) , a type 1 diabetes model ; homozygous leptin receptor mutation ( lepr ) on a c57blks genetic background ( bks db / db mice ) , an obese type 2 diabetes model ; and bks db / db mice with targeted deletion of endothelial nitric oxide synthase ( bks enos
db / db mice ) , an obese and hypertensive type 2 diabetes model .
dba mice were fasted for 4 h and then given intraperitoneal injections of 40 mg / kg stz or vehicle control daily for five consecutive days ( 7 ) .
bks db / db and bks enos
db / db mice became obese around 4 weeks of age and developed hyperglycemia between 4 and 8 weeks of age .
dn , as evidenced by increased albuminuria , mesangial expansion , and podocyte loss was manifest in all mouse models after 12 weeks and was more severe after 24 weeks of diabetes ( 79 ) .
standardized phenotypic analysis followed protocols established by the animal models of diabetic complications consortium ( www.diacomp.org ) ( 2 ) .
body weights , fasting blood glucose , and acr were in agreement with previously published studies ( 710 ) .
when the mice were killed , glomeruli from diabetic and control mice were iron perfused and magnetically isolated ( 7 ) .
total glomerular rna was obtained using the rneasy mini kit ( qiagen , hilden , germany ) .
gene expression profiling was performed ( 11 ) using affymetrix genechip mouse genome 430 2.0 arrays in the university of michigan microarray core facility according to the manufacturer s instructions .
these procedures were in accordance with the policies of the university of michigan and vanderbilt university institutional animal care and use committees .
verification of selected differentially expressed genes ( degs ) by quantitative real - time rt - pcr ( qrt - pcr ) was performed using taqman low density arrays ( applied biosystems ) per the manufacturer s instructions .
normalization of qrt - pcr results was performed using the geometric mean from multiple housekeeping genes for human ( n = 4 ) and mouse ( n = 5 ) samples ) ( 13 ) .
human halb and lalb samples are the same as those shown in table 1 , unless otherwise specified .
a subset of nd samples was used ( average age , 49.8 + 6.1 years ; n = 6 [ 3 males and 3 females ] ) .
diabetic and control mouse samples were also identical to those in table 1 . only cycle threshold ( ct ) values < 35 were used for analysis ; thus , eight halb samples assayed for col1a1 and kit and 11 lalb samples assayed for kit and interleukin ( il)-16 were analyzed ( 12 ) .
fold differences were calculated using the delta - delta ct method as previously described ( 14 ) .
files containing raw mrna expression data ( cel files ) were processed , normalized , log transformed , and analyzed using the chipinspector software ( genomatix software , www.genomatix.de ) ( 13 ) .
chipinspector analyzes the expression signals at single - probe level , and they are reported summarized at gene - level annotation ( 15 ) . the statistical method implemented in this software
is based on a student t test with a permuted background that enhances the original sam algorithm by tusher et al .
we used one class of exhaustive matching to detect the differentially regulated genes in the halb versus lalb , halb versus nd , and lalb versus nd human comparisons .
we applied a false discovery rate of < 1% on all datasets to detect the significantly regulated genes .
no individual - level genetic data can be publicly released from the southwestern american indian study .
the three cross - species that shared transcriptional datasets will be available for data mining using state - of - the - art systems biology tools at www.nephromine.org . to elucidate the functional relationships among the significantly regulated genes ,
transcriptional networks were generated using a natural language programming strategy ( bibliosphere module ; genomatix software suite ) .
the natural language programming scans were set to establish a connection between any two genes if they were cocited in the same sentence in a pubmed abstract . as a second level of evidence for a gene - gene interaction , information defining transcription factor
target transcript pairs was retrieved by scanning differentially regulated transcripts for binding sites of coregulated transcription factors . to compare the large transcriptional networks comprising thousands of gene nodes from humans and mice ,
an algorithm implemented in tale ( tool for approximate large graph matching ) was used ( 17 ) .
tale compares the network structure and extracts overlapping conserved relations between the query and database networks . to allow a cross - species transcriptional network comparison , all mouse genes were converted to human orthologs according to the national center for biotechnology information ( ncbi ) homolog build64 and genomatix annotated ortholog database .
this resulted in a loss of 1013% of genes in the mouse transcriptional networks as no unique human orthologs could be identified for those genes .
the three mouse networks were populated into the database , and the human network was used as the query network .
next , the most important genes ( seed genes ) were identified based on the degree of connectivity within the query ( human ) network ( top 20% of total gene nodes in the network ) .
finally , a 10% mismatch parameter was used to allow for a modicum of mismatches while generating the neighborhood of the seed gene nodes as well as extending the network .
the resulting three tale cross - species networks were then evaluated for their functional enrichment using the genomatix pathway system ( geps ) from the genomatix software suite .
to establish a genome - wide expression cross - species network of dn in humans and mice , we first generated four species - specific transcriptional networks from differentially expressed glomerular genes detected in the human dn cohort and three mouse dn models ( fig .
genes were represented as gene nodes with connections that indicate functional dependencies . to create the mouse - specific networks , we compared glomerular gene expression in diabetic mice with their appropriate nd controls . for the human - specific network , we compared glomerular gene expression in diabetic subjects who had halb with those who had lalb at the time of biopsy .
this approach allowed us to identify shared human mouse glomerular genes enriched for their specific contribution to nephropathy , because genes differentially regulated in human diabetes per se , in the absence of nephropathy , were excluded by this strategy .
after creation of the four species - specific networks , the human glomerular transcriptional network was overlaid on each mouse glomerular transcriptional network to identify similar , but not necessarily identical , subnetworks operational in both species . at each step of the analysis , the number of genes and gene nodes decreased , demonstrating that the analysis reduced network complexity while iteratively identifying species - specific and cross - species conserved , differentially regulated subnetworks ( fig .
1 ) . analytical strategy used to generate shared glomerular human mouse transcriptional networks .
transcriptional networks were generated from significantly regulated genes in human and mouse glomeruli using genomatix bibliosphere software .
these networks were then overlapped using tale to define cross - species shared transcriptional networks .
figure 2 graphically displays the human mouse shared transcriptional dn networks . a greater number of connections between gene nodes suggested increased network importance or centrality . in the human - dba stz ( fig .
2a ) and the human - bks enos
db / db transcriptional networks ( fig .
2c ) , there were 143 and 162 nodes , respectively , each with several high connectivity nodes ( > 70 connections ) .
the human - bks db / db transcriptional network contained fewer gene nodes ( total 97 ) , none of which had > 70 connections ( fig .
figure 2d displays the overlap between each shared human mouse glomerular transcriptional network ; 26 gene nodes were shared by all three human mouse networks ( fig .
mouse shared glomerular transcriptional networks . each circle represents a gene node , and the lines represent a connection between two gene nodes .
shared transcriptional networks for human - dba stz ( a ) , human - bks db / db ( b ) , and human - bks enos
db / db ( c ) , as defined by tale , are displayed with the most connected gene nodes in the center ( > 70 gene - gene connections ) and the least connected gene nodes at the periphery .
the overlap between the shared human mouse networks is shown in d. table 2 lists the 30 gene nodes in each shared human mouse transcriptional network with the highest number of connections ( full list in supplementary table 2 ) .
nine genes were shared among the high - connectivity gene nodes in all three networks .
for example , stat1 and stat3 , members of the janus kinase ( jak)/signal transducer and activator of transcription ( stat ) pathway , were among the top gene nodes in all three shared networks .
in addition , genes expressed by endothelial cells and associated with endothelial cell dysfunction , including cd34 , cd36 , and flt1 , were among those with the most connections in each shared network .
for example , bcl2 , fos , and fn1 were the three most - connected gene nodes in the human - dba stz and the human - bks enos
db / db networks .
however , these genes were not differentially regulated in bks db / db mouse glomeruli and were therefore not in the human - bks db / db network .
activated receptor- [ ppar ] ) and met ( hepatocyte growth factor receptor ) were found only in the human - dba stz and human - bks db / db networks , whereas nr3c1 , which encodes the glucocorticoid receptor , was shared only between human - bks db / db and human - bks enos
db / db networks .
mouse transcriptional networks were subsequently interrogated for insight into molecular mechanisms shared between the species .
first , the shared networks were examined for dependencies between gene nodes derived via natural language processing and automated promoter analysis . as an example of such analysis , fig .
3 displays each shared transcriptional network centered on stat3 and depicts key gene nodes of the tale analysis associated with jak / stat ( stat1 ) , ppar ( pparg ) , and apoptosis ( bax , bcl2 , and fos ) signaling pathways . using this method , one can input any functionally connected gene to determine its neighborhood of functionally related genes and its potential regulatory role . as a second method of network analysis
, we used pathway enrichment analysis ( geps ; genomatix ) of the gene node list from the human mouse comparison to assess the biological relevance of each cross - species network ( table 3 ) .
canonical pathways well described in dn , such as vascular endothelial growth factor receptor ( vegfr ) , fgf signaling , and hif-1 gene regulation pathways , were also enriched among all three shared networks ( 4,18,19 ) . finally , the il-7 signaling pathway was enriched in all three shared networks . to our knowledge
table 3 also lists the top canonical pathways enriched in any two networks and those unique to one human mouse shared transcriptional network .
mouse transcriptional networks centered on stat3 . focusing on any gene of interest allows for comparison of neighborhoods of functionally related genes within each shared network .
we performed this analysis using stat3 given its likely central role in the pathogenesis of dn , as suggested by previous studies .
top canonical pathways qrt - pcr analysis was performed to confirm the degree and direction of expression changes in 18 human and 19 mouse genes within the shared human mouse transcriptional networks ( fig .
all 18 human genes assayed by qrt - pcr were significantly differentially expressed by microarray in the halb versus lalb comparison . by qrt - pcr analysis , 13 of these genes demonstrated the same direction of expression .
similarly , the direction of gene expression by qrt - pcr analysis agreed with gene expression by microarray for lalb versus nd ( 6 genes out of 7 ) and halb versus nd ( 10 out of 14 ) comparisons .
for the mouse samples , the direction of expression of all genes assayed by qrt - pcr agreed with the microarray data . qrt - pcr confirmation .
qrt - pcr was performed to confirm the direction of fold change in expression ( shown as log2 fold change in human and mouse models by microarray ) .
human comparisons for halb vs. lalb ( a ) , lalb vs. nd ( b ) , and halb vs. nd ( c ) by qrt - pcr were compared with differential expression from microarray data .
mouse comparisons for dba stz vs. control ( d ) , bks db / db vs. control ( e ) , and bks enos
db / db ( f ) were also compared with significant differential expression from microarray data .
* p < 0.05 . to maximize the detection of shared pathways and cooperating genes , our initial analysis selected overlapping , differentially regulated genes without determination of the concordance of expression changes ( i.e. , when the change in expression of a human gene with dn was in the same direction as that of the orthologous mouse gene with diabetes ) . in
each shared mouse - human network , the number of genes with concordant changes in expression was lower than the number of genes with discordant changes . since gene expression during disease progression is dynamic , often nonlinear , and can be reversed due to compensatory changes , we then expanded our analysis to compare glomerular expression of these shared network genes in diabetic patients with either halb or lalb to the expression in nd living donors , comparisons more akin to the mouse diabetic versus nd comparison .
we then assessed the number of degs in each human mouse comparison that were either concordant ( changed in the same direction ) or discordant ( changed in opposite directions ) .
the examination of all degs ( tabulated in supplementary table 1 ) showed that the concordance of mouse and human expression changes increased in the diabetic to nd comparisons ( table 4 ) , especially in the lalb to nd comparison , suggesting that the gene changes from nd to early glomerulopathy in humans were most similar to those found in the mouse models .
the directionality of all degs in both the diabetic humans and mouse models was assessed ( table 5 ) .
the pattern of these changes supports the analysis of the gene changes in the shared networks . in the mouse models , the change in gene expression from nd to diabetic was positive (
increased ) in 5370% of the degs , which is similar to the percentage of degs that increased with dn in the comparison of lalb versus nd ( 64% ) and halb versus nd ( 60% ) humans , whereas the halb versus lalb comparison showed a very low percentage of increased expression , suggesting that most gene expression increases were near maximal in the lalb group and then showed a relative decline in the halb group .
concordance of human mouse gene expression within shared networks the gene expression changes reported above may have resulted from specific mechanisms activated in dn or , alternatively , from those altered in all proteinuric diseases . to determine the specificity of the gene expression profiles found in dn , we investigated changes in glomerular gene expression between the diabetic mouse models and human subjects with mn , an nd proteinuric disease ( supplementary table 4 ) .
a number of the degs found in the shared human mouse dn comparisons were also found in the human mn versus control comparison .
novel approaches that directly compare animal models to humans with dn are needed to better understand the pathogenesis of the human disease .
such comparisons will help shift the focus away from pathways that are relevant to processes in models but not in humans . in the current study , we performed an unbiased transcriptomic comparison of glomerular gene expression in diabetic humans and mouse models of dn to identify shared pathways and networks of transcriptional dysregulation in kidney glomeruli in dn . by using a human type 2 diabetes cohort with a shared environment and genetic background and by comparing human glomerular gene expression from patients with either high or low albumin excretion
, we were able to select for gene dysregulation that is likely relevant to human dn and not to diabetes alone or other nonspecific factors . by comparing these results with three well - characterized mouse models , we identified cross - species glomerular transcriptional networks shared between humans and mice that further define gene networks involved in dn .
analysis of the deg lists in the three human mouse shared networks revealed only partial overlap between any two shared networks ( 45 , 46 , and 60 gene nodes ) and less commonality among all three ( 26 gene nodes ) ( fig .
however , when similarities were mapped into canonical signaling and metabolic pathways , more than one - third of the cross - species conserved pathways overlapped between all three human mouse comparisons ( table 3 and supplementary table 3 ) .
alterations in some of these pathways have been described previously in human and animal dn ( 4,18,20 ) , especially in those related to signaling in the microvasculature ( jak / stat signaling , vegf signaling , and hif-1- activation ) , confirming our ability to identify previously identified and relevant biological targets .
however , some of the alterations were in pathways not previously associated with dn or diabetes . for example , the il-7 signaling pathway was enriched in human dn and in all three murine models .
il-7 is a cytokine important for b- and t - cell survival , proliferation , and differentiation ( 21 ) , and the change in expression of genes in this pathway suggests that the pathway may play a role as a regulator of glomerular lymphocytes or of intrinsic glomerular cells that contribute in some way to the pathogenesis of dn ( 22 ) . in addition ,
for example , the human - dba stz shared network was enriched for genes in epidermal growth factor receptor-1 ( egfr1 ) signaling .
the egfr system plays an important role in mediating renal hypertrophy in diabetes , and inhibition of this pathway attenuates albuminuria in experimental dn ( 23 ) .
these data suggest that the dba stz mouse model , but not necessarily the other models , could be useful for studying this pathway in dn . when examining the direction of gene expression changes in each human mouse shared network , we observed that a significant proportion of genes with increased expression in the murine models were decreased in the halb versus lalb human comparison ( table 4 and supplementary table 1 ) . however , when gene expression changes were analyzed in early dn ( lalb vs. normal human subjects ) , many more of these were directionally similar to changes ( usually increases ) seen in the mouse model comparisons .
although several potential explanatory factors are possible , it seems most likely that the nephropathy in humans was significantly more advanced than in the murine models . in support of this explanation ,
histopathological features of dn , such as global glomerulosclerosis and fractional interstitial fibrosis / area , were common in all subjects with type 2 diabetes studied ( halb and lalb ) , but not in nd healthy kidney donors ( table 1 ) .
in addition , the duration of diabetes and nephropathy in the human subjects was much greater than in the murine models . thus , our findings are consistent with the conclusion that mouse models , at the time points studied , demonstrate gene expression changes that are similar to those in human nephropathy before the development of microalbuminuria and therefore are most relevant to changes in very early human disease .
gene expression generally increased in the shared pathways in the murine dn models compared with controls but was mostly repressed in the human halb versus lalb comparison . when all degs were examined in both humans and mice , a similar pattern emerged ( table 5 ) , namely that differentially regulated gene expression tended to be increased in early dn in both mice and humans ( lalb vs. nd ) but then was repressed as the disease progressed in humans ( halb vs. lalb ) .
this could reflect a loss of cell number with disease progression , since a reduction in podocyte number is associated with increased proteinuria in humans ( 24,25 )
. however , this seems an unlikely explanation because the differentially regulated genes in the halb versus lalb comparison are not simply podocyte specific , and established podocyte - specific markers are not consistently repressed .
for example , in the halb versus lalb comparison , nephrin and wt-1 expression were each decreased 40% , but the expression of podocin was unchanged .
more likely , changes in cell phenotype and loss of specialized cellular functions occur with progression of nephropathy . in response to high glucose , the podocyte phenotype in mice in vivo and in vitro simplifies to a more embryonic form ( 26 ) .
cellular de - differentiation and reduction of cell - specific transcripts throughout the glomerulus occurs and contributes to disease progression .
whether this tendency toward repression of cell lineage specific genes in glomeruli would continue with even more progressive disease is unknown but would be of interest as this could represent a general pathological response .
a current challenge in dn research is the selection of the best murine model to evaluate a specific molecular pathway .
our data define the extent to which murine dn models recapitulate human dn , at least in terms of gene expression changes .
networks of the conserved genes can assist in the dynamic investigation of all networks to determine overlap between mouse models and humans with dn .
in addition , to facilitate identification of the most adequate model system for a given pathway or to screen multiple models for molecular dn mechanisms using systems biology tools , the cross - species shared datasets will be uploaded to the web - based search engine nephromine ( www.nephromine.org ) .
mouse dn comparisons were in pathways that use jak / stat signaling , which corroborates our previous report that changes in expression of jak / stat family members occurs in glomerular cells from humans with early dn ( 20 ) . in our previous report , we demonstrated an increase of glomerular jak1 , jak2 , stat1 , and stat3 in early human dn , but no changes in jak2 gene expression in glomeruli from dba stz or bks db / db models by qrt - pcr and western analysis ( 20 ) . in agreement with the previous study
, we observed no significant differential expression of jak2 in dba stz or bks enos
db / db by microarray analysis in the current study ( data not shown ) .
however , there was a modest increase in jak2 expression in bks db / db glomeruli that reached statistical significance , but did not reach statistical significance in the more extensive analysis previously reported ( 20 ) .
thus , the data in this study support the general conclusion that increased jak2 expression found in early human dn is not replicated in mouse models . similarly , socs2 and socs3 were repressed in progressive human dn but not in the mouse models .
reduction in socs gene expression would enhance stat transcriptional activity ( 27 ) , and this difference in human and mouse socs gene expression could underlie a more potent upregulation of the jak / stat signaling pathway in humans than in mice . in summary , we have discovered shared glomerular transcriptional networks , enriched for genes most likely to contribute to disease progression , in humans with type 2 dn and three frequently used mouse models of dn .
the shared networks contain genes that are members of pathways previously linked to the pathogenesis of dn as well as those in signaling pathways not previously implicated in dn .
our pathway data also suggest that the murine models , at the time points studied , demonstrate transcriptional changes that occur quite early in human dn .
indeed , multiple pathways activated early in human dn , and in the mouse models , are repressed during progression of the disease in humans , consistent with stage - specific regulation of human dn .
the results of this study thus help to unravel the complex sequence of events leading to progression of human dn and point to both the applicability and limitations of current murine models . | murine models are valuable instruments in defining the pathogenesis of diabetic nephropathy ( dn ) , but they only partially recapitulate disease manifestations of human dn , limiting their utility .
to define the molecular similarities and differences between human and murine dn , we performed a cross - species comparison of glomerular transcriptional networks .
glomerular gene expression was profiled in patients with early type 2 dn and in three mouse models ( streptozotocin dba/2 , c57blks db / db , and enos - deficient c57blks db / db mice ) .
species - specific transcriptional networks were generated and compared with a novel network - matching algorithm .
three shared human
mouse cross - species glomerular transcriptional networks containing 143 ( human - dba stz ) , 97 ( human - bks db / db ) , and 162 ( human - bks enos/
db / db ) gene nodes were generated .
shared nodes across all networks reflected established pathogenic mechanisms of diabetes complications , such as elements of janus kinase ( jak)/signal transducer and activator of transcription ( stat ) and vascular endothelial growth factor receptor ( vegfr ) signaling pathways .
in addition , novel pathways not previously associated with dn and cross - species gene nodes and pathways unique to each of the human mouse networks were discovered .
the human mouse shared glomerular transcriptional networks will assist dn researchers in selecting mouse models most relevant to the human disease process of interest .
moreover , they will allow identification of new pathways shared between mice and humans . |
NEW YORK ( TheStreet ) -- Given Microsoft's (MSFT - Get Report) global Windows- and Office-installed base, it sounds a bit nutty to claim Apple (AAPL - Get Report) killed it on Tuesday, Sept. 10. But it did.
We're in the early stages of a-like crash that, instead of taking a few years, could span decades. But it will happen.
First, there's the obvious -- Microsoft can't compete with Apple (or, for that matter) on smartphones or tablets. We're at the point where the notion of mobile competition between the companies has become farcical.
Microsoft andmade absolute fools of themselves after Apple introduced its new iPhones on Tuesday. They tweeted these ads:
Just an idiotic continuation of what we'll now know as the combined collapse of Microsoft and Nokia. Put your head down and keep your mouth shut, especially if you're Microsoft.
But the lead the media buried as it focused on the new iPhones matters more.
I'm not sure Steve Ballmer realizes just how big this is. But he'd better take a look, because there was a time when the demise of the BlackBerry sounded like a crazy prediction.
Apple will offer iWork, its productivity suite, free to buyers of all new iPhones and iPads. And don't be surprised if Apple keeps upping the ante, particularly by making Pages (its version of MS Word), Numbers (Excel) and Keynote (Power Point) better and better across platforms.
I first brought up this idea in October 2012, when I suggested Apple should improve iWork to render Office unnecessary and irrelevant to consumers and enterprises who have flocked (or desperately want to flock) to iPhones, iPads and Macs.
Apple should give iWork away for free. Everywhere. Every way. On everything. Not only could it crush Microsoft Office, but it will fend off Google's push to extend the reach of its cloud-based software and services.
Apple doesn't need to profit on iWork. It just needs to make iWork so good and so accessible, that it eliminates the one remaining factor that differentiates Microsoft from Apple, and keeps millions of individuals and businesses hooked on PCs they're hardly excited about being forced to buy. ||||| Photo by Justin Sullivan/Getty Images
For the last six years, Apple has had a simple, increasingly risky plan for selling the iPhone. Every year, the company makes only one new model, a phone that represents Apple’s platonic ideal—the one phone it thinks everybody ought to have. Apple usually sells the new phone for around $650, and wireless carriers sell it to customers for $199 with a two-year plan. To hedge its bets against low-priced competitors, Apple also keeps selling its previous models, reducing the price of each by $100. Last year, when Apple unveiled the iPhone 5, it kept selling 2011’s iPhone 4S for $550 ($99 with a contract), and the 2010 iPhone 4 sold for $450 (free with a contract).
The advantage of this strategy is clear. Unlike its competitors, which make dozens of phones every year, Apple can focus its design and manufacturing energies on a single new model, and it can push customers to purchase its highest-end, highest-margin device. But the downside is clear, too. The iPhone is Apple’s biggest business, accounting for two-thirds of its profits. By releasing only one new phone every year, Apple keeps putting more and more of its eggs in a single basket. What if that basket has a buggy antenna? What if it doesn’t seem like much of an upgrade? What if its screen isn’t big enough for some customers? What if it’s just too expensive?
This year was supposed to be different. For months now, analysts have speculated that Apple would finally do what many observers (including yours truly) have long called on it to do—to diversify its iPhone lineup. The logic seemed obvious. Samsung, Apple’s fiercest rival, has been cleaning up in developing markets like India and China by offering models that cater to every market niche, from the low end to the high end. By making a new phone that sold for around $300 to $400 without a carrier subsidy—which is how many people in developing markets buy phones—Apple would be able to compete for price-conscious phone buyers, creating a whole new class of iPhone users who currently can’t afford Apple’s shiny baubles.
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But today, Apple whiffed. At the company’s headquarters in Cupertino, Calif., CEO Tim Cook did unveil two new iPhones rather than just one. But neither of these phones is the cheap iPhone that people had been predicting. Indeed, Apple didn’t really change its pricing strategy in any meaningful way. Across the globe, it will still be charging the same for its phones as it always has. It’s not a stretch to say that instead of a good price, Apple is now offering budget-conscious consumers around the world a strange deal: OK, the iPhone isn’t any cheaper than it used to be. But hey, look, it comes in lots of colors! Colors! Even pink! How will you be paying?
The new top-of-the-line model—called the iPhone 5S—looks the same as today’s iPhone 5, but it’s got a faster processor, a better camera, and a fingerprint scanner that lets you unlock your phone much quicker than with a password. (I tried it out at Apple’s demo area and found it very easy to set up and speedy to use.) The 5S—which comes in black, white, and gold—will sell for $650, or $199 with a contract, the same as last year’s iPhone 5.
Then there’s the iPhone 5C—the long-rumored cheap iPhone that isn’t. It’s made of plastic instead of the aluminum found on the bigger iPhone. It comes in five colors: green, blue, yellow, pink, and white. Other than that, it’s got the same internals as the iPhone 5: same camera, same processor, same capabilities. And same price. Indeed, the 5C is so similar to the 5 that Apple is discontinuing that model. The 5C will sell for $550, or $99 with a contract. This isn’t a cheap phone. And if the 5C is cheaper for Apple to produce than the 5 would have been—which seems plausible given its plastic body—it might even be a way for Apple to boost its profit margins rather than scale them back.
This is a bold move. In the tech business, it’s rare—and perhaps even unprecedented—for a product to keep its prices steady year after year after year. By holding the line against lower-priced phones, Apple will be able to keep its profit margins high—and at Apple, profits are sacrosanct, considered more important than sales and market share. But refusing to give an inch on prices is also extremely risky. The next big phase of growth in the smartphone market is going to occur in places around the world where people don’t have a lot of money. What’s more, the utility of a $200 phone is quickly approaching that of a $550 phone. If you live in India and you’ve got only $300 or $400 to spend on a phone, the only iPhone you might be able to afford is the iPhone 4S—a 3-year-old device with a tiny screen. Or you can choose Google’s Nexus 4, which sells for $200, and is pretty fantastic in every way. In other words, at that price, you’d be a fool to get an iPhone.
But if the 5C is not any cheaper than the 5 would have been, why did Apple go to all the trouble to make it? Why depart from the just-sell-last-year’s-model plan if the new device is pretty much the same as last year’s, only dressed up in a colorful new shell? I suspect it’s because Apple believes the colors will prove an important selling point. Yes, really.
Two years ago, I argued that one of Apple’s underappreciated skills is the way it cunningly plays with the colors of its devices in order to make old things look new. “Apple makes us covet certain colors today, while also making us scoff at the colors it convinced us to covet yesterday,” I wrote. “Every few years, it cycles through a new palette for its gadgets—it goes from white to black to multicolor to silver and back again. As it shifts, the whole gadget world moves along, too.” I ended that piece with a prediction. Because it would become increasingly difficult for Apple to change the design of the iPhone—you can’t do much with a slab of rectangular glass—the only element left to play with was the color. “A new color, for Apple, can represent as much of a reason to upgrade as a new processor,” I wrote, predicting that we’d soon see the iPhone come in a variety of colors.
And that’s what’s happening now. The iPhone 5C doesn’t do anything different from the iPhone 5. But because it looks different—because it comes in colors—Apple believes it can sell it as something new, something worthier of your attention than last year’s model. In India and China, Apple devices are often considered to be “Veblen goods,” meaning that they are attractive precisely because they are more expensive than rivals. Part of their appeal is the fact that you can’t afford them. The 5C’s colors make that exclusivity part of the sales plan: Here’s the new iPhone. Sure, it’s just out of your price range. But it’s colorful. Everyone will notice it. Surely you can save up for blue. ||||| A year ago, Apple seemed unstoppable. Its share price topped $700. Its cash horde eclipsed the GDP of many countries. Pundits mused about a $1 trillion market cap with a straight face.
But nowadays, Wall Street sees Apple very differently — and this morning’s much-hyped iPhone announcements from the tech giant did little to stop its year-long descent into stagnation. Apple’s gold phones, 64-bit processors, and fingerprint sensors barely budged the needle on Wall Street, as shares fell more than 2 percent from the day’s opening price of $506.20.
The great slide began last September. By April of this year, Apple had shed nearly $300 billion in value, and shares bottomed out below $400. As WIRED wrote at the time, bearish sellers had plenty of reason to doubt that the post-Jobs Apple could still dazzle. Yet Apple CEO Tim Cook did little to reassure investors. As Samsung handsets gained market share and prices on Android phones fell, investors doubted Apple could keep charging the premium prices that kept its margins high.
Worst and most obvious of all, Apple failed to feed the insatiable consumer appetite for the new. As has been widely reported, its new iPhone announcements today mark the end of the longest gap in new hardware releases since at least the launch of the iPad.
As that clock ticked, shares fell or stayed flat. Even the preview of iOS 7, the most radical redesign of Apple’s mobile operating system since its initial release, failed to mollify Wall Street.
If the market’s immediate reaction is any indication — and in the era of high-speed trading, it usually is — the iPhone 5C and 5S unveiled today still don’t go far enough. As the new phones were unveiled and tech writers cooed, investors reacted with a collective “meh.” After the presentation came to a close to the strains of Elvis Costello — no iWatch or new Apple TV in sight — the company’s share price began to trickle lower.
Notably, Apple spent a lot of time at its event highlighting the high-end advances of the new 5S, dashing quickly through the less expensive 5C by comparison. Such a choice makes sense if the goal is to keep investors distracted from the margin-eating potential of less expensive phones. But the extended focus on geeked-out new features didn’t do the trick.
Though the faster, sleeker, more powerful phone is unarguably cool, the steps forward are still incremental. And incremental isn’t what the world expects from Apple. Steve Jobs’ death wasn’t an event of worldwide significance because he could craft better spec sheets. Apple’s brand is synonymous with vision, a corporate identity that was once its greatest asset. Now that asset has become a liability. | – Apple's big iPhone unveiling yesterday—in which it replaced the iPhone 5 with the similar 5S and cheaper, multicolored 5C—has pundits yawning and investors selling. Here's how people are reacting: The biggest problem is that "Apple failed to feed the insatiable consumer appetite for the new," argues Marcus Wohlsen at Wired. The 5S is a nice incremental upgrade, but the world expects more out of Apple. "Steve Jobs’ death wasn’t an event of worldwide significance because he could craft better spec sheets." Many investors were expecting a cheaper iPhone that could compete in developing countries, and the 5C misses the mark. "Apple is now offering budget-conscious consumers around the world a strange deal," writes Farhad Manjoo at Slate: "OK, the iPhone isn’t any cheaper than it used to be. But hey, look, it comes in lots of colors! Colors! Even pink! How will you be paying?" Apple may have "hit its BlackBerry moment," worries Jonny Evans at ComputerWorld, though he thinks it may have bought itself some time. He doesn't think the 5C was supposed to be a budget play, but an effort to diversify its line and give it leeway to break up its every-12-month release schedule. "This would have been a great idea. Last year." Rocco Pendola at TheStreet, meanwhile, thinks yesterday was a BlackBerry moment, too—for Microsoft. "The media buried the lead" by focusing on the iPhones, he argues. The real news was that Apple will offer its iWork productivity suite for free. That move "could crush Microsoft Office." Twitter overall reacted with apathy, CNET reports. According to the analysts at Crimson Hexagon, about 73% of social media comments were neutral, compared to 21% that were basically positive and 6% that were basically negative. |
the theory of the weak nuclear interaction aims to describe nuclear phenomena induced by the external interaction , that is mediated by the intermediate bosons @xmath4 and @xmath5 of the standard model @xcite . at low and intermediate energies ,
the strangeness conserving semileptonic nuclear interaction hamiltonian is of the current - current form @xcite-@xcite _ w =- cos _ c. [ hwn ] here the weak interaction constant @xmath6 @xcite , the cabibbo angle @xcite @xmath7 @xcite , @xmath8 is the lepton current and the operator of the weak nucleon current is ^a_w,(q_1)&=&j^a_v,(q_1 ) + j^a_a,(q_1 ) + & = & i(g_v(q^2_1)-_q_1-g_a(q^2_1)5 + iq_15 ) , [ onwhc ] where @xmath9 is the nucleon ( lepton ) mass and @xmath10 , where @xmath11 is the 4-momentum of the final ( initial ) nucleon .
the least known of the form factors entering eq.([onwhc ] ) is the induced pseudoscalar form factor @xmath12 .
the presence of this form factor in the weak nucleon current is a consequence of the intimate relation between the strong and weak interaction processes .
the contribution of the pion pole to @xmath12 is g_p(q^2_1)=-2 g_nn f_m_l ^_f(q^2_1 ) , [ gp ] where @xmath13 is the pseudoscalar @xmath14 coupling constant , ] @xmath15 is the pion decay constant , thus providing @xmath16 ; let us note , however , that @xmath17 @xcite . ] and @xmath18 is the pion propagator .
the matrix element of the axial current @xmath19 should satisfy the partial conservation of the axial current ( pcac ) ( p)q_1j^a_a , u(p)= is the pion absorption amplitude .
we also put g_a(q^2_1)=g_a f_a(q^2_1),g_ag_a(0 ) = -1.26950.0029 .
[ ga ] the value of the constant @xmath20 is taken from ref.@xcite . in order to fulfil eq.([pcac ] ) one subtracts from the induced pseudoscalar form factor a piece g_p(q^2_1)&=&-2g_nn f_m_l + & & 2mg_a m_l mg_a m_lr^2_a . [ dgp ] here
@xmath21 is a nucleon axial radius measured independently in the quasi
elastic neutrino scattering , @xmath22 @xcite , and in the charged pion electroproduction , @xmath23 @xcite . in deriving eq.([dgp ] )
, we use the goldberger
treiman relation m|g_a|=g_nn(0 ) f _ , [ gtr ] as being satisfied exactly and we assume a weak dependence of the couplings on the momentum transfer . using the constants @xmath20 , @xmath24 and @xmath13 as given above and the mean nucleon mass @xmath25
, one observes that the left- and right hand sides of eq.([gtr ] ) differ by 1.1% .
the prediction for the form factor @xmath3 , following from the above discussed material , is given for the ordinary muon capture ( omc ) in the hydrogen , ^- + p _
+ n , [ omcp ] as @xcite g_p(q^2_1=0.877 m^2 _ ) = g_a = 6.87g_a=-8.72 , [ gomcp ] whereas the correction , demanded by the pcac is @xcite g_p=0.34 g_a=-0.43 .
[ dgpomch ] this correction is obtained by using the dipole form factor for @xmath26 and the axial mass @xmath27 , extracted from the data in ref.@xcite , which is equivalent to taking the nucleon axial radius @xmath28 @xcite .
then the resulting value of the induced pseudoscalar constant , as predicted by the pcac , is g_p^pcac=6.44 g_a=-8.29 .
[ gppcac ] let us note that this value of @xmath3 , obtained from the pcac constraint , is of fundamental importance .
it is confirmed by the calculations , performed within the framework of the effective field theory @xcite that incorporates the chiral symmetry of the quantum chromodynamics .
the influence of the induced pseudoscalar form factor @xmath3 on observables and the related extraction of this quantity from experiments was studied intensively in the omc and radiative muon capture ( rmc ) in nuclei and in the electroproduction of charged soft pions .
this activity has recently been reviewed in refs .
@xcite .
let us note here first that in our opinion , the electroproduction of charged soft pions can not provide any information on the induced pseudoscalar form factor @xmath3 .
attempts to study it @xcite in the reaction e+pe+^++n , [ cpp ] at the threshold stem from the soft pion electroproduction amplitude derived from the low energy theorem .
as usually derived , this amplitude contains the current current amplitude and the weak axial nucleon current . in the next step ,
one calculates the contributions to the current current amplitude .
if one restricts oneself only to the contributions due to the nucleon born terms , one really has an electroproduction amplitude containing the @xmath3 form factor .
however , as shown in detail @xcite , the correct calculation of the contribution to the current current amplitude due to the pion and the heavy axial meson emitted in the t channel , leads to a complete cancellation of the weak axial nucleon current in the electroproduction amplitude .
simultaneously , a contact term , containing @xmath20 form factor , and the pion pole production amplitude appear , as expected from physical intuition . since the extraction of the information on @xmath3 from the data on the omc and rmc in nuclei is extensively reviewed @xcite , we restrict ourselves only to necessary comments on the rmc in hydrogen , allowing us to proceed to the material that is the subject of this review . for the omc in the hydrogen , the induced pseudoscalar form factor @xmath3 only for one value of the momentum transfer needs to be considered .
in contrast to it , the rmc in hydrogen ^- + p _ + + n , [ rmcp ] allows one to study the momentum dependence of @xmath3 in a certain interval of the values of the momentum transfer .
the rmc amplitude generally consists of two parts .
one part is due to the lepton radiation , another one is due to the hadron radiation . in the lepton radiation amplitude ,
the weak form factors depend on the four momentum transfer @xmath29 , , @xmath30 , @xmath31 is the four momentum of the neutrino , muon and photon , respectively . ] whereas the momentum dependence of the weak form factors entering the hadron radiation amplitude is given by @xmath32 . at the end of the photon spectrum , we have @xmath33 and @xmath34 .
thus one obtains the value of @xmath3 in the hadron radiation amplitude larger by a factor of about 3 in comparison with the value of @xmath3 in the lepton radiation amplitude .
this enhancement factor makes the reaction ( [ rmcp ] ) attractive for the study of the sensitivity of the high energy tail of the photon spectrum to the form factor @xmath3 .
the photon spectrum was measured in the reaction ( [ rmcp ] ) in a triumf experiment @xcite .
the comparison of the measured spectrum with the calculations @xcite provided the value of the pseudoscalar coupling constant that is by about 50% smaller than its value ( [ gppcac ] ) predicted by the pcac . in these calculations ,
a relativistic rmc amplitude was used , derived from feynman tree graphs .
this amplitude includes also the contribution from the @xmath35 excitation process .
besides , it satisfies approximately the ward
takahashi identities , generally derived in ref.@xcite .
subsequent studies , aiming to find an additional enhancement mechanism of the tail of the photon spectrum , were performed by several authors @xcite . only the model taking into account the off
shell degrees of freedom of the @xmath35 isobar is able to provide enough enhancement of the photon spectra @xcite .
one of the possible contributions to the enhancement mechanism has been studied in detail in refs.@xcite .
this is the contribution of the processes described by anomalous lagrangians .
we next provide a detailed account of the construction of such a lagrangian for the @xmath36-@xmath37-@xmath38-@xmath39 system , then we present the structure of the rmc amplitude arising from it .
we show that this part of the full rmc amplitude satisfies the pcac constraint by itself .
as in the omc , in order to calculate the capture rate , one needs to know the effective hamiltonian .
the velocity independent part of it is @xcite h^(0)_eff&=&(1- _ ) .
[ h0eff ] here @xmath40 ( @xmath41 ) are the lepton ( nucleon ) spin pauli matrices , @xmath42 ( @xmath43 ) is the unit vector in the direction of the neutrino ( photon ) momentum vector @xmath44 ( @xmath45 ) and @xmath46 is the photon polarization .
the most important form factors are @xmath47 , @xmath48 and @xmath49 .
all other @xmath50 contain at least one damping factor @xmath51 .
_ the aim of any model lagrangian of the interaction of a hadron system with an external electroweak fields is to provide the form factors @xmath50 entering eq.([h0eff ] ) .
usually , one considers processes , described by the normal lagrangians @xcite , where a natural parity of the in- and outcoming channels does not change .
the natural parity of a particle is defined for bosons only and it is @xmath52 , where @xmath53 is the intrinsic parity and @xmath54 is the spin of the particle .
the natural parity of the channel is defined as the product of the natural parities of the channel particles .
the rmc amplitude , presented in ref.@xcite , is derived from a non anomalous lagrangian of the @xmath55 system that reflects the @xmath56 hidden local symmetry @xcite .
this amplitude extends the amplitude obtained from the low energy theorem to higher values of the photon and weak current momenta . here
our goal is to construct the rmc amplitude which contributes to the anomalous processes .
let first discuss the generalities related to the construction of the necessary anomalous lagrangian . in meson physics ,
anomalous processes are defined as processes in which the natural parity is not preserved .
the value of @xmath57 for some bosons is given in table 1 .
0.2 cm table 1 .
natural parity of some bosons .
0.1 cm [ cols="<,^,^,^",options="header " , ] 0.2 cm then the vertices @xmath58 and @xmath59 are described by the non anomalous lagrangian , whereas the vertices @xmath60 and @xmath61 are anomalous and play an important role in describing the deuteron electromagnetic form factors . as we shall see soon
, the anomalous vertices @xmath62 and @xmath63 enter into the amplitudes for the process ( [ rmcp ] ) .
there exists a unique way to construct the interaction lagrangian that would violate the natural parity and would simultaneously conserve the intrinsic parity and would be lorentz invariant : the levi civita pseudotensor should be used .
so anomalous processes are defined as processes , described by a lagrangian containing the pseudotensor @xmath64 .
let us note that this definition of the anomalous processes is more general than the definition using the natural parity , as it can be extended from pure meson processes also to processes , where mesons interact also with the gauge bosons of the electroweak interaction and subsequently , with fermions .
let us note that the term `` anomalous '' refers to the axial abelian as well as non
abelian anomaly , yielding an anomalous breaking of the chiral symmetry in the theory of quantum fields @xcite .
the first such chiral anomaly was observed in the width of the decay ^0 .
[ pi0gg ] the observed decay width turned out to be enhanced by three orders of magnitude in comparison with the one derived from the models incorporating spontaneously and explicitly broken chiral symmetry @xcite .
anomalous behavior of the decay width for the process ( [ pi0gg ] ) indicates the existence of a new mechanism of the chiral symmetry breaking .
it was found @xcite that it is the regularization of the feynman one loop diagrams that produces the chiral symmetry breaking .
an elegant study of the chiral anomaly has later been performed within the path integral method in ref.@xcite .
non invariance under the chiral transformations of the measure in the path integral over the fermion fields means that the functional integral is not invariant and the chiral symmetry is broken .
this formally provides jacobi determinant different from identity .
it follows that the logarithm of such a determinant leads to an anomaly function @xcite that can be given in terms of the gauge fields of the electroweak interaction , but it does not depend on the quark fields . finally , its presence produces in the effective lagrangian the term _ ^0=-
_ f_(x)f_(x ) ^0(x ) , f_(x)=_a_(x ) -_a_(x ) .
[ lpi0gg ] this lagrangian can be qualified as anomalous in accord with both definitions of anomalous lagrangians discussed above and it provides the correct value of the decay width for the process ( [ pi0gg ] ) .
it is important to note that the form of the anomaly function is rather independent of the detailed features of the theory @xcite .
however , it should satisfy the wess
zumino consistency conditions @xcite that depend only on the properties of the anomalously broken symmetry group .
these conditions strongly restrict the form of the anomaly function , but they do not fix it uniquely . the independence of the anomaly function on the details of the theory is useful if one would like to pass from the quantum chromodynamics ( qcd ) to the low energy effective field theories given in terms of the goldstone bosons and the gauge fields of the electroweak interaction .
the consistency conditions will be the same as in qcd and it can be shown that the anomaly function will be the same , too @xcite . at the level of effective low energy lagrangians , the term , breaking the chiral symmetry , should be present in the lagrangian from the very beginning and it is called the anomalous lagrangian .
it follows from what we said above that its change under the infinitesimal chiral transformation is fixed by the anomaly function .
the form of the anomalous lagrangian for the goldstone bosons of the spontaneously broken global chiral group @xmath65 was derived in ref.@xcite . however , this lagrangian can not be given in a simple closed form @xcite , but it is possible for the anomalous action @xcite . without gauge fields ,
this action is invariant under the global transformations of the chiral group g_g=_g , [ gg ] whereas the related anomalous lagrangian is not invariant .
it is possible to extend this global symmetry to the local one by introducing the gauge fields of the electroweak interaction into the anomalous action , the fields of the photon and of the intermediate bosons @xmath66 and @xmath5 @xcite .
then the gauged wess zumino
witten action will contain terms , describing anomalous processes taking place between the @xmath36- , @xmath67- and @xmath68 mesons in the presence of the external electroweak fields , including the lagrangian ( [ lpi0gg ] ) , responsible for the decay ( [ pi0gg ] ) .
anomalous processes are important not only in the case of the goldstone bosons , but are abundantly observed in the reactions with vector mesons , such as @xmath38 and @xmath37 mesons , e.g. the radiative decay of these mesons , b+ , b=,,[rdb ] is the anomalous process , as it follows from table 1 . for an extension of the theory to incorporate the vector mesons ,
it is important to recognize that any such theory should be free of axial anomaly , as it follows from the gauge invariance @xcite . in other words ,
the anomaly functions , arising in different sectors of the theory , should compensate among themselves .
it turns out that this restriction does not allow one to incorporate the vector mesons into the anomalous lagrangians as yang
mills gauge fields .
this follows from the fact that in this case , the anomaly function , arising in the vector meson sector of the anomalous lagrangian , differs from the one , derived from the qcd .
then such a theory is in contradiction with the fundamental postulate @xcite that any effective low energy theory of hadrons should strictly respect symmetries imbedded in the qcd and the consequences following from it , including the mode in which these symmetries are broken . since the anomaly function is a direct consequence of the anomalously broken chiral symmetry of the qcd , the same anomaly function should be immanent also to any anomalous hadron lagrangian . on the contrary
, introducing the vector mesons within the framework of the hidden local symmetries ( hls ) provides a theory of the interaction of the mesons with the electroweak fields that is free of the above mentioned defects @xcite .
methodologically , the construction of the anomalous hls lagrangian does not differ from that of the non anomalous one .
the extension of the symmetry ( [ gg ] ) by the group @xmath69_l$ ] of the local transformations needs introduction both of the related massless gauge fields and non physical compensators . in the next step , after the spontaneously breaking of the extended symmetry , the compensator fields disappear , whereas the gauge fields acquire the mass .
these new gauge fields are identified with the physical vector and axial vector mesons .
then the procedure results in the appearance of the anomalous invariants , consisting of the fields of particles , which anomalous processes one would like to describe of : of the goldstone- , vector- and axial
vector meson fields and of the fields of the electroweak interaction .
in general , the anomalous lagrangian can be chosen as the sum of the wess
zumino witten lagrangian and of the linear combination of the anomalous invariants @xcite .
thus , such a lagrangian contains free parameters that can be fixed by analyzing anomalous processes , or by imposing additional semi
phenomenological conditions .
the anomalous lagrangian , containing both the vector- ( @xmath70 ) and axial vector ( @xmath71 ) mesons , was first constructed in ref.@xcite .
such a lagrangian contains 14 invariants . in ref.@xcite ,
only the electromagnetic anomalous processes were studied .
the extension of this model to the weak anomalous processes was accomplished in refs.@xcite . to carry out this step , it is advantageous to use the anomalous invariants , constructed in ref.@xcite and to express the external gauge fields using both the photon field and the boson fields @xmath66 and @xmath5 .
the most general anomalous action of the @xmath72 system reads @xcite _ an[_l,_r,_m , l , r , l , r ] & = & ^cov_wzw[u ,
l , r ] + & & + _
i=1 ^ 14_m^4c_i l_i[_l,_r,_m , l , r , l , r ] .
[ gan ] here @xmath73 $ ] is the covariant wess - zumino - witten action containing pseudoscalars and the electroweak fields .
it already satisfies the anomaly constraints .
generally , the 14 independent ( homogenous ) terms in the r.h.s . of eq.([gan ] ) are given in eqs.(3.8 ) and ( 3.9 ) of ref.@xcite .
as the terms @xmath74-@xmath75 contain at least 4 particles in each vertex , only the terms @xmath76-@xmath77 are of interest for our purpose .
the covariant wess - zumino - witten anomalous action of pseudoscalars reads @xcite ^cov_wzw[u , l , r]=-i _
m^5_tr_[^5]_covariantized , [ gcov ] where @xmath78 is the number of colors and @xmath79 is a differential one - form = ( _ u ) u^ dx _
, u(x)=exp[-i^a(x)^a / f_]^2 , and @xmath80 are the external gauge fields .
the contribution from the action ( [ gcov ] ) to the 3-point lagrangian of interest is @xcite _ wzw = i _ ( _ _ ) ( _ _ ) , [ lwzw ] where @xmath81 is an electroweak neutral field and @xmath82 is a weak vector field . in the homogenous terms
, we include both the electromagnetic and weak interactions , but we omit the field of the @xmath83 meson . keeping only the 3particle terms ,
the anomalous lagrangian of the @xmath55 system @xcite is obtained terms are . ] & & + ( g__-eb _ ) [ ( _ _ ) ( _ + e _ ) ] } , [ lb73 ] + & & + ( g__-eb _ ) [ ( _ _ ) ( g__+ _ ) ] } , [ lb83 ] + & & + ( g__-eb _ ) [ ( _ _ ) ( _ + e _ ) ] } , [ lb93 ] + & & + ( g__-eb _ ) [ ( _ _ ) ( g _ _ + _ ) ] } .
[ lb103 ] external fields @xmath84 and @xmath85 correspond to the gauge fields of ^_&=&-a^_= w^__c , [ vpm ] + v^3_&=&_+(2_w)z_= b_+z _ , [ v3 ] + a^3_&=&-z_. [ a3 ] the constants @xmath86 are @xmath87 were first determined in ref.@xcite . the progress in acquiring the data on several reactions @xcite allowed in ref .
@xcite to improve the analysis considerably .
the difference between the new data @xcite and the data @xcite is not so dramatic and only the constants @xmath88 and @xmath89 slightly changed in comparison with @xcite _
7=8.7210 ^ -3 , _
8=-1.0710 ^ -1 , _
9=9.7610 ^ -3 , _ 10=7.5910 ^ -2 .
[ ctis ] let us note that we prefer to choose @xmath90 as in @xcite , by averaging the data on the processes @xmath91 and @xmath92 , since the data on the reaction @xmath93 show clear tendency to move to the data on the charged @xmath37 meson radiative decay @xcite . having the homogenous part of the anomalous lagrangian at our disposal , we pass to the construction of the anomalous rmc amplitude .
the contribution to the rmc amplitude due to the wess zumino term ( [ lwzw ] ) is presented in fig.1 .
it reads j^a , wz_=- _ k_q_^_f(q^2_1)^a_5 , [ wzc ] where ^a_5=|u(p)5^a u(p ) .
[ ga5 ] this amplitude satisfies the continuity equations k_j^a , wz_=q_j^a , wz_=0 .
[ ccjwz ] since this amplitude contains the pion propagator , it contributes to the form factor @xmath3 .
however , @xmath94 and this contribution has no enhancement factor .
the influence of this amplitude on the photon spectrum was earlier calculated in ref.@xcite and it was found to be negligible .
+ 0.35 cm .35 cm next the contribution from the lagrangian @xmath95 is presented in more detail .
it contains eight terms |l_7&=&_i=1 ^ 8 & = & 2ig__\ { ( _ _ ) + ( _ _ _ ) .
+ & & .+e(___)}. [ lsbi ] using particular terms , the contributions to the anomalous rmc amplitude are calculated . from the vertex @xmath96 ,
one generates 3 feynman amplitudes , presented in fig.2a , fig.2b and fig.2c .
they are of the form j^a_(7,1a)&=&-2m^2_m^2 _
_ k_q_1^_f(q^2_1)^_(k ) ^_(q)^a_5 , + [ j71a ] j^a_(7,1b)&=&-im^2 _ _ k_q_q_^_f(q^2)^_(k)^_(q_1 ) ^a _ + & = & -i f_q_^_f(q^2 ) m^a_(7,1c ) , + [ j71b ] m^a_(7,1c)&=&m^2 _ _ k_q_^_(k)^_(q_1 ) ^a_. [ m71c ] here ^a_=|u(p)(_-_q_1)u(p ) .
[ gae ] both amplitudes , @xmath97 and @xmath98 , contain the pion propagator and contribute to @xmath3 .
however , only the pion propagator of the amplitude @xmath98 provides the enhancement factor @xmath99 . calculating the divergence yields k_j^a_(7,1a)&=&k_j^a_(7,1b)=0 , + [ kj71ab ]
q_j^a_(7,1a)&=&-2m^2__k_q_q_1^_f(q^2_1)^_(k ) ^a_5 , + [ qj71a ] q_j^a_(7,1b)&=&-i f_q^2
^_f(q^2 ) m^a_(7,1c ) .
[ qj71b ] relative to the index @xmath100 , attached to the photon line , the amplitudes are transverse separately .
the vertex @xmath101 generates the amplitude presented in fig.2d .
explicitly we have j^a_(7,2)&=&2m^2 _ _ k_q_1^_f(q^2_1)^_(k ) ^a_5 , + [ j72 ] k_j^a_(7,2)&=&0,q_j^a_(7,2)=-q_j^a_(7,1a ) . [ kqj72 ] again , the amplitude is transverse in the electromagnetic sector . as follows from the second part of eq.([kqj72 ] ) , the weak vector amplitudes @xmath97 and @xmath102 satisfy the cvc hypothesis . from the vertex @xmath103 we have also only one amplitude of fig.2e j^a_(7,3)&=&i m^2 _ _ k_^_(k ) ^_(q_1)^a _ , + [ ja73 ] k_j^a_(7,3)&=&0,q_j^a_(7,3)=if_m^a_(7,1c ) .
[ kqj73 ] it is seen from eq.([qj71b ] ) and eq.([kqj73 ] ) that the axial amplitudes @xmath98 and @xmath104 satisfy the pcac q_= if_m^2_^_f(q^2)m^a_(7,1c ) .
[ qj71b3 ] 0.35 cm 0.35 cm the vertex @xmath105 does not contribute to processes triggered by the charged current . in its turn
, the vertex @xmath106 generates 3 amplitudes , again represented by the graphs fig.2a , fig.2b and fig.2c j^a_(7,5a)&=&2m^2_m^2 _ _ q_q_1^_f(q^2_1)^_(k ) ^_(q)^a_5 , + [ j75a ] j^a_(7,5b)&=&-im^2 _ _ q_1 q_q_^_f(q^2)^_(k)^_(q_1 ) ^a _ + & = & -i f_q_^_f(q^2 ) m^a_(7,5c ) , + [ j75b ] m^a_(7,5c)&=&m^2 _ _
q_q_1 ^_(k)^_(q_1 ) ^a_. [ m75c ] again , both amplitudes , @xmath107 and @xmath108 , contain the pion propagator and contribute to @xmath3 .
however , only the pion propagator of the amplitude @xmath108 provides the enhancement factor @xmath99 .
the divergence of these amplitudes reads k_j^a_(7,5a)=2 m^2 _ _ k_q_q_1^_f(q^2_1 ) ^_(q)^a_5 , [ kj75a ] q_j^a_(7,5a)=0 , [ qj75a ] k_j^a_(7,5b)=-i _ k_q_1 q_q_^_f(q^2)^_(q_1)^a _ , [ kj75b ] q_j^a_(7,5b)=-i f_q^2 ^_f(q^2 ) m^a_(7,5c ) . [ qj75b ]
now the amplitudes are not separately transverse in the electromagnetic sector . on the contrary
, the weak vector amplitude @xmath107 satisfies the cvc by itself . from the vertex @xmath109 ,
one again obtains 3 amplitudes , given in fig.2f , fig.2 g and fig.2h j^a_(7,6a)=2 m^2 _ _ q_q_1^_f(q^2_1 ) ^_(q)^a_5 , [ j76a ] j^a_(7,6b)&=&-i _ q_q_q_1^_f(q^2 ) ^_^a _ + & = & -i f_q_^_f(q^2 ) m^a_(7,6h ) , [ j76b ] m^a_(7,6h)= _
q_q_1 ^_^a_. [ m76h ] in deriving these equations , we used the relation @xmath110 .
it is the amplitude @xmath111 that contains the enhancement factor .
the divergence of the amplitudes @xmath112 and @xmath111 is k_j^a_(7,6a)=2 m^2 _ _
k_q_q_1^_f(q^2_1 ) ^_(q)^a_5 , [ kj76a ] q_j^a_(7,6a)=0 , [ qj76a ] k_j^a_(7,6b)=i _ k_q_1q_q_^_f(q^2 ) ^_^a _ , [ kj76b ] q_j^a_(7,6b)=-i f_q^2 ^_f(q^2 ) m^a_(7,6h ) .
[ qj76b ] it follows from eq.([kj75b ] ) and eq.([kj76b ] ) that k_=0 .
[ kj756b ] the vertex @xmath113 yields the amplitude of fig.2e . together with the divergence , this amplitude is j^a_(7,7)=i m^2 _ _ q_1 ^_(k ) ^_(q_1)^a _ , + [ j77 ] k_j^a_(7,7)=i _ k_q_1 ^_(q_1)^a _ , + [ kj77 ] q_j^a_(7,7)=if_m^a_(7,5c ) .
[ qj77 ] combining eq.([qj75b ] ) and eq.([qj77 ] ) we obtain another pcac constraint q_=if_m^2_^_f(q^2 ) m^a_(7,5c ) .
[ qj75b7 ] from the last vertex @xmath114 , one obtains the amplitude of fig.2i .
it reads , together with the divergence , as follows j^a_(7,8)=-i _
q_1 ^_(q_1)^a _ , + [ j78 ] k_j^a_(7,8)=-i _ k_q_1 ^_(q_1)^a _ , + [ kj78 ] q_j^a_(7,8 ) = if_m^a_(7,6h ) .
[ qj78 ] it follows from eq.([kj77 ] ) and eq.([kj78 ] ) that k_=0 .
[ kj768 ] from eq.([qj76b ] ) and eq.([qj78 ] ) we have the pcac constraint q_= if_m^2_^_f(q^2 ) m^a_(7,6h ) .
[ qj76b8 ] let us note that the amplitudes that contain the @xmath38 meson propagator can be simplified at once , since it holds for the real photon with a good accuracy ^_(k)_/m^2_. [ opk20 ] summing up , the vector axial - vector ( va ) amplitudes are @xmath98 , @xmath104 , @xmath108 , @xmath115 , @xmath116 and @xmath117 . using eq.([opk20 ] )
, we have from eq.([m75c ] ) and eq.([m76h ] ) m^a_(7,5c)-m^a_(7,6h ) , [ cm5c6h ] from which it follows that j^a_(7,5b)+j^a_(7,6b)0 .
[ cj5c6b ] it also follows that in this approximation j^a_(7,7)+j^a_(7,8)0 .
[ cj78 ] then from the va amplitudes , only @xmath98 and @xmath104 survive .
since @xmath118 depends on the momentum transfer @xmath119 , we can write j^a_(7,1b)=-i _ k_q_q_^_f(q^2 ) ^_f(q^2_1)^a_,[aj71b ]
j^a_(7,3)=i _ k_^_f(q^2_1)^a_.[aj73 ] the vector vector ( vv ) amplitudes are @xmath97 , @xmath102 , @xmath107 and @xmath120 . for the weak momentum transfer @xmath121 of interest ,
the following approximation is quite acceptable ^_(q)_/m^2_. [ rpq20 ] this approximation simplifies the analysis of the vv amplitudes to a great extent , since it is clear from eq.([j71a ] ) and eq.([j72 ] ) that j^a_(7,1a)+j^a_(7,2)0 , [ cj712 ] and from eq.([j75a ] ) and eq.([j76a ] ) we have j^a_(7,5a)+j^a_(7,6a)0 .
[ cj7a56 ] it means that the vv amplitudes do not contribute to the anomalous amplitude in the approximation ( [ rpq20 ] ) . in the next step , analogous construction of the amplitudes arising from the lagrangians @xmath122 ,
@xmath123 is carried out .
it turns out that only the same amplitudes , @xmath98 and @xmath104 , result .
the full anomalous amplitude can be expressed , using eq.([lan ] ) , as j^a , an_&=&(|c_7-|c_8+|c_9-|c_10 ) [ j^a_(7,1b)+j^a_(7,3 ) ] + & = & c[j^a_(7,1b)+j^a_(7,3 ) ] , [ jan ] where = c_7+c_9=1.8510 ^ -2 .
[ tc79 ] here we have used eqs.([bci ] ) and eqs.([ctis ] ) .
the amplitude @xmath124 satisfies the continuity equations k_j^a , an_&=&0 , + [ kjan ] q_j^a , an_&=&if_m^2_^_f(q^2 ) c m^a_(7,1c ) .
[ qjan ] we now proceed to calculate the contributions to the form factors @xmath50 entering the effective hamiltonian ( [ h0eff ] ) . for this purpose ,
we multiply the amplitudes @xmath125 , eq.([wzc ] ) , and @xmath124 , eq.([jan ] ) , by @xmath126 , where the weak lepton current is @xmath127 . after the non relativistic reduction
, we obtain from the wess
zumino amplitude @xmath125 g_4,wz&=&-g^l_p , + [ wzgp4 ] g_4,wz&=&-g^l_p , + [ wzgpp4 ] g_7,wz&=&g_11,wz = g^l_p , + [ wzgpp7 ] g_10,wz&=&g_11,wz = g^l_p .
[ wzgpp10 ] here @xmath128 , @xmath129(@xmath130 ) is the photon ( neutrino ) energy , @xmath131 and the induced pseudoscalar form factor @xmath132 depends on the momentum @xmath133 .
as it has already been noted , this momentum dependence does not exhibit the enhancement factor for the photon energies at the high energy tail of the photon spectrum .
let us calculate next the contributions from the amplitude @xmath98 .
we obtain g_2,1=-(1+_v ) g^n_p , [ a1bg2 ] g_10,1=(1+_v)()^2 g^n_p , [ a1bgp10 ] g_10,1=(1+_v ) ( ) g^n_p . [ a1bgpp10 ] here @xmath134 depends on the momentum @xmath135 and it provides the enhancement factor @xmath99 in the amplitude at the high energy tail of the photon spectrum .
we have also used the approximation ^_f(q^2_1)m^-2_. [ drhoq ] the last contributions to calculate are from the amplitude @xmath104 g_2,3&=&(1+_v ) , + [ a3g2 ] g_8,3&=&-g_9,3=g_10,3=-(1+_v ) , + [ a3gp8 ] g_8,3&=&-(1+_v ) .
[ a3gpp8 ] these form factors do not contribute to @xmath3 .
however , the form factor @xmath136 is large at the high energy tail of the photon spectrum . together with the form factor @xmath137 of eq.([a1bg2 ] ) , they are by a factor @xmath138 larger than other form factors @xmath139 and @xmath140 .
it can be seen that due to the enhancement factor in the form factor @xmath137 , these two form factors are about the same size at the end of the photon spectrum . indeed ,
taking @xmath141 , we have @xmath142 .
besides , @xmath143 . on the other hand , comparing the form factors
@xmath137 and @xmath144 we have at the high energy tail of the photon spectrum -4 ^ 2 40 . [ rg2gp4 ] in deriving this ratio
, we used the kawarabayashi
suzuki fayazuddin
riazuddin relation @xmath145 .
nevertheless , the form factors @xmath137 and @xmath136 do not enhance sensibly the photon spectrum , because of the small factor @xmath146 , eq.([tc79 ] ) .
the presence of this small factor in the homogenous part of the anomalous lagrangian makes its influence approximately equal to the wess zumino term .
the numerical analysis shows @xcite that the contribution of the anomalous processes to the singlet and triplet capture rates for the rmc in hydrogen is @xmath147 % .
let us briefly discuss the double radiative muon capture ( drmc ) in hydrogen ^- + p _
+ + n. [ drmcp ] one of the possible processes contributing to this reaction is presented in fig.3 .
+ 0.35 cm the charged weak vector interaction converts @xmath148 into @xmath149 that decays into two photons .
this decay is possible due to the chiral anomaly and is described by the anomalous lagrangian ( [ lpi0gg ] ) . since in the experiment on the rmc only one photon is detected , the double differential capture rate for the process ( [ drmcp ] ) , integrated over one photon , can contribute to the measured photon spectrum .
calculations , analogous to those performed above , provide the following anomalous amplitude for the drmc process
j^a_=_k_1 k_2^_(q)^_f(q^2_1)^_f(q^2_2)(q_1 + q_2)^3ab^b_5 .
[ jdrmc ] this amplitude is gauge invariant k_j^a_=k_j^a_=0 .
[ kkjdrmc ] in the weak sector it satisfies the following ward
takahashi identity q_j^a_=_k_1
k_2 ^ 3ab^b_5 .
[ qjdrmc ] at the right hand side of eq.([qjdrmc ] ) , the amplitude of more simple double radiative process enter .
this amplitude is given at fig.1 with the wavy lines corresponding to outgoing photons .
the probability of the drmc per unit volume is dw_fi=(e^2 g_f _ c)^2_s.p .
[ mfi ] the form of the drmc rate resembles that of the single rmc rate _ drmc&=&(g_f _ c ) ^2
m^3 m_n + & & ^2 ( k_1k_2)^2 ( q_1)^2 f e_1 d(e_1)e_2 d(e_2 ) + & & _ 1 d_1 _ 2 d_2 d_2 .
[ gdrmc ] here f=[m_-2(e_1+e_2)]^2 + 4(k_1+k_2)^2 - 4[m_+2(e_1+e_2)][(k_1+k_2 ) ] , [ f ] _ 0= , [ nu0 ] @xmath150 is the fine structure constant , @xmath151 , @xmath152 ( @xmath153 ) is the proton ( neutron ) mass , @xmath154 is the reduced proton - muon mass and @xmath155 . in comparison with the single rmc rates @xcite ,
@xmath156 is suppressed by the factor @xmath157 .
this clearly indicates that @xmath156 is much smaller .
the numerical calculations yield for the triplet capture rate _
drmc , t10 ^ 3=106.710 ^ -13 s^-1 , [ dmrct ] that is damped by the factor @xmath158 in comparison with the radiative muon capture rate @xmath159 for the reaction ( [ rmcp ] ) @xcite .
besides the weak vector amplitude ( [ jdrmc ] ) , one can also construct weak axial amplitudes for the drmc .
however , they are expected to provide an effect of the same order of magnitude .
starting from the most general anomalous action of the @xmath55 system , we arrive at the 3point anomalous lagrangian , that includes the wess zumino term and four homogenous terms .
application to radiative muon capture in hydrogen is considered in order to establish possible contributions that may enhance the photon spectrum at its high energy tail . it is important to find and understand the possible sources that may explain the discrepancy between the experimental results and the conventional methods to calculate this spectrum .
the constructed anomalous amplitudes are gauge invariant and in the weak sector , the vector amplitudes satisfy the cvc hypothesis and the axial amplitudes satisfy the pcac constraint . using reasonable approximations , only two axial amplitudes result , besides the wess
zumino one .
all three terms yield corrections that turn out to be of the same order of magnitude for the high photon energies .
the numerical estimates show @xcite that they can not provide the necessary enhancement .
we have also made here an estimate of the capture rate for the double radiative muon capture in hydrogen .
this reaction is triggered by the anomalous decay @xmath160 .
the calculations show that its capture rate turns out to be strongly suppressed in comparison with the capture rate for the single radiative muon capture .
let us note finally that we have recently suggested @xcite that off
shell effects due to the isobar intermediate state can , in principle , provide an enhancement that brings the calculated results in reasonable agreement with the experiment .
this work is supported in part by the grant ga r 202/03/0210 and by the ascr project k1048102 . the research of f. c. k. is supported in part by nsercc .
donoghue , j.f . ,
golowich , e. and holstein , b.r .
dynamics of the standard model ; cambridge university press : cambridge , uk , 1992 .
weinberg , s. the quantum theory of fields , v. ii ; cambridge university press : cambridge , uk , 1996 .
adler , s.l . and
dashen , r. current algebras ; w.a .
benjamin : new york , ny , 1968 .
de alfaro , v. , fubini , s. , furlan , g. and rossetti , c. currents in hadron physics ; north holland / american elsevier : amsterdam london / new york , 1973 .
stoyle , r.j .
fundamental interactions and the nucleus ; north holland / american elsevier : amsterdam london / new york , 1973 .
walecka , j.d .
theoretical nuclear and subnuclear physics ; oxford university press : oxford , uk , 1995 .
eidelman , s. _ et al . _ .
cabibbo , n. .
ahrens , l.a .
_ et al . _ .
liesenfeld , a. _ et al . _ .
truhlk , e. and khanna , f.c . .
bernard , v. , kaiser , n. and meissner , ulf g . .
bernard , v. , fearing , h.w .
, hemmert , t.r . and meissner , ulf g .
fearing , h.w . , lewis , r. , mobed , n. and scherer , s. .
measday , d.f . .
bernard , v. , elouadrhiri , l. and meissner , ulf g . .
truhlk , e. .
gorringe , t. and fearing , h.w . .
bernard , v. , hemmert , t.r . and
meiner , ulf g . .
choi , s. _ et al . _ .
truhlk , e. .
jonkmans , g. _ et al . _ .
wright d.h .
_ et al . _ , .
fearing , h.w . .
beder , d.s . and
fearing , h.w . ;
* ibid * 1989 , 39 , 3493 .
christillin , p. and servadio , s. .
meissner , t. , myhrer , f. and kubodera , k. .
ando , s.i . and
min , d.p . .
ando , s.i . ,
myhrer , f. and kubodera , k. .
ando , s.i . , myhrer , f. and kubodera , k. .
smejkal , j. , truhlk , e. and khanna , f.c . in proceedings
sevenths international conference mesons and light nuclei 98 , prague
pr23uhonice , 1998 ; adam , j. , jr .
_ et al . _ ,
eds . ; world scientific : singapore , 1999 , p.490 ; nucl th/0110007 .
truhlk , e. , smejkal , j. and khanna , f.c . .
rood , h.p.c . and
tolhoek , h.a . .
smejkal , j. , truhlk , e. and khanna , f. c. .
bando , m. , kugo , t. and yamawaki , k. .
meissner , ulf g . .
kaiser , n. and meiner , ulf g . .
smejkal , j. , truhlk , e. and gller , h. .
adler , s. ( 2004 ) . anomalies .
arxiv : hep - th/0411038 .
bell , j.s . and jackiw , r. .
adler , s. .
fujikawa , k. .
wess , j. and zumino , b. .
t hooft , g. in recent developments in gauge theories ; t hooft , g. _ et al .
; plenum press : new york , 1980 .
witten , e. .
weinberg , s. .
fujiwara , t. , kugo , t. , terao , h. , uehara , s. and yamawaki , k. .
caso , c. _ et al .
fearing , h.w .
, lewis , r. , mobed , n. and scherer , s. . | the structure of an anomalous lagrangian of the @xmath0 system is investigated within the hidden local @xmath1 symmetry approach .
the interaction of the external electromagnetic and weak vector and axial vector fields with the above hadron system is included .
the lagrangian of interest contains the anomalous wess zumino term following from the well known wess
zumino
witten action and six independent homogenous terms .
it is characterized by four constants that are to be determined from a fit to the data on various elementary reactions .
present data allows one to extract the constants with a good accuracy .
the homogenous part of the lagrangian has been applied in the study of anomalous processes that could enhance the high energy tail of the spectrum of photons , produced in the radiative muon capture in hydrogen .
it should be noted that recently , an intensive search for such enhancement processes has been carried out in the literature , in an attempt to resolve the so called an @xmath2 50 % difference between the theoretical prediction of the value of the induced pseudoscalar constant @xmath3 and its value extracted from the high energy tail of the photon spectrum , measured in the precision triumf experiment . here ,
more details on the studied material are presented and new results , obtained by using the wess
zumino term , are provided . |
advances in cosmological observations have presented us a concordance picture that our present universe is accelerating and the dominant mass - energy components for the evolution of the universe in the standard model are non - baryonic cold dark matter ( dm ) and dark energy field ( de)@xcite . the de is identified as the engine for the accelerated expansion . the leading interpretation of such de is a cosmological constant with equation of state ( eos ) @xmath1 . while the cosmological constant is consistent with the observational data , at the fundamental level it fails to be convincing : the vacuum energy density falls below the value predicted by any sensible quantum field theory by many orders of magnitude , and it unavoidably leads to the coincidence problem , i.e. , why are the vacuum and matter energy densities of precisely the same order today ? " .
more sophisticated models have been proposed to replace the cosmological constant by a dynamical dark energy in the conjectures relating the de either to a scalar field called quintessence with @xmath2 , or to an exotic field called phantom with @xmath3 .
however , there is no clear winner in sight to explain the nature of de at the moment .
most available discussions on the de were in the minimal picture which assumed that de does not feel any significant interactions from dm .
although this picture is consistent with current observations , considering that de and dm account for significant fractions of the content of the universe , it is still natural , in the framework of field theory , to consider their interaction .
the possibility that de and dm can interact with each other has been widely discussed recently@xcite-@xcite .
it has been shown that the coupling between de and dm can provide a mechanism to alleviate the coincidence problem @xcite .
furthermore , it was suggested that the dynamical equilibrium of collapsed structures such as clusters would get modification due to the coupling between de and dm @xcite .
the influences on the growth of cosmic structure due to the coupling between dark sectors were also shown in @xcite .
observational signatures on the dark sectors mutual interaction have been found in the probes of the cosmic expansion history by using the snia , bao and cmb shift data etc @xcite .
in addition , it has been argued that an appropriate interaction between de and dm can influence the perturbation dynamics and affect the lowest multipoles of the cmb power spectrum @xcite .
recently there has been some concern about the stability of the perturbations if de and dm interact @xcite .
however , it was proved in @xcite that the stability of the curvature perturbation depends on the types of coupling between dark sectors and the eos of de .
based on the result in @xcite , we are in a position to carry out the global fitting to probe the interaction between dark sectors by using the cmb power spectrum data together with other observational data . recently the wmap data showed the deficit of large scale power in the temperature map , in particular in the cmb quadrupole . the significant contribution to the fluctuations on these scales
is the late integrated sachs wolfe ( isw ) effect which is induced by the passage of cmb photons through the time evolving gravitational potential when the universe enters a rapid expansion phase once de dominates .
the late isw effect has the unique ability to probe the size " of de .
much effort has been put into determining the eos and the speed of sound of de @xcite .
whether the late isw can give insight into the coupling between dark sectors is an interesting question . in this paper
we are going to discuss this problem in detail .
we will further employ the cmb data from ground based and satellite observations together with snia and sdss data to constrain the coupling between dark sectors .
the organization of the paper is as follows : in the following section we will review the general formalism of the perturbation theory in the presence of the interaction between de and dm . in sec.iii we will discuss the large scale cosmic microwave anisotropies and its imprint on the size " of de , especially the coupling between dark sectors . in sec.iv , we will present the global fitting result by using cmb data together with snia and sdss data and we will discuss the alleviation of the coincidence problem when de interacts with dm .
we will present our conclusions and discussions in the end .
in this section we will go over the perturbation theory when de interacts with dm .
the detailed descriptions can be found in @xcite .
the perturbed metric at first order is of the form @xmath4,\label{perturbedspacetime}\ ] ] where @xmath5 represent the scalar metric perturbations , @xmath6 is the cosmic scale factor and @xmath7 we work with general stress - energy tensor @xmath8 for a two - component system consisting of de and dm .
each energy - mementum tensor satisfies the conservation law @xmath9 where @xmath10 denotes the interaction between different components and @xmath11 denotes either the dm or the de sector . in the fourier space
the perturbed energy - momentum tensor reads @xcite @xmath12 constructing the gauge invariant quantities@xcite @xmath13'\label{invariantq}\\ \delta q_{p\lambda}^{i}&=&\delta q_{p\lambda } -q^0_{\lambda } \frac{e'}{2k}\nonumber\\ d_{g\lambda}&= & \delta_{\lambda}-\frac{\rho_{\lambda}'}{\rho_{\lambda}\mathcal{h}}\left(\phi+\frac{e}{6}\right)\nonumber\\ v_{\lambda } & = & v_{\lambda } -\frac{e'}{2k},\nonumber\end{aligned}\ ] ] we obtain the gauge invariant linear perturbation equations for dark sectors . for dm it reads , @xmath14 for de , we have @xmath15 where we have employed @xmath16 where @xmath17 is the effective sound speed of de at the rest frame , @xmath18 is the adiabatic sound speed . to alleviate the singular behavior caused by @xmath19 crossing @xmath20
, we substitute @xmath21 into @xmath22 in the above equations where @xmath23 thus we can rewrite eq ( [ dmv ] ) and eq ( [ dev ] ) into , @xmath24 @xmath25 the quantity @xmath26 is given by , @xmath27 to solve the above equations we have to specify the interaction form @xmath28 between de and dm .
however , this is a hard task , since the nature of de and dm remains unknown , it is not possible at the present moment to derive the precise form of the interaction between them from first principles .
one has to assume a specific coupling from the outset @xcite or determine it from phenomenological requirements @xcite .
for the generality , we can assume the phenomenological description of the interaction between dark sectors in the comoving frame@xcite @xmath29^{t}\nonumber\\ q_d^{\nu}=\left[-\frac{3\mathcal{h}}{a^2}(\xi_1\rho_c+\xi_2\rho_d),0,0,0\right]^{t},\end{aligned}\ ] ] where @xmath30 are small positive dimensionless constants and @xmath31 is the transpose of the matrix .
choosing positive sign in the interaction , one can ensure the direction of energy transfer from de to dm , which is required to alleviate the coincidence problem @xcite and avoid some unphysical problems such as negative de density etc @xcite .
the perturbed gauge - invariant coupling vector can be calculated by @xmath32'\ ] ] @xmath33'\ ] ] where @xmath34 .
for the reason as illustrated in @xcite , we set @xmath35 . using continuous equations to eliminate @xmath36 in eq ( [ dmu ] ) , eq ( [ deu ] ) , we obtain the perturbation equations@xcite , @xmath37 \nonumber\\ & & -9\mathcal{h}w\left(\xi_1r+\xi_2 + 1+w\right ) \phi+3\mathcal{h}w d_d+3w'\phi+3(\xi_1r+\xi_2)\phi'-ku_d-6\psi\mathcal{h}(\xi_1 r+\xi_2)\nonumber\\ & & + 3\mathcal{h}\xi_1r(d_{gd}-d_{gc } ) \label{density } \\ u_d ' & = & -\mathcal{h}(1 - 3w)u_d+kc_e^2\left\{d_{gd}-3\left(\xi_1 r+\xi_2 + 1+w\right ) \phi\right\ } \nonumber\\ & & -(c_e^2-c_a^2)a^2q^0_d\frac{u_d}{(1+w)\rho_d}+ 3(c_e^2-c_a^2)\mathcal{h}u_d+(1+w)k\psi+3\mathcal{h } ( \xi_1r+\xi_2)u_d . \label{velocity}\end{aligned}\ ] ] in solving these equations we will adopt the adiabatic initial condition@xcite @xmath38 dynamical stability of the de and dm perturbations were examined in detail in @xcite . in the general form of the phenomenological interaction , when de eos @xmath39 and we choose the coupling between dark sectors proportional to the dm energy density ( by setting @xmath40 while keeping @xmath41 nonzero ) or the total dark sectors energy density ( by setting @xmath42 ) , we observed the dynamical instability in perturbations as argued in @xcite .
however , when we choose the dark sectors mutual interaction proportional to the energy density of de by taking @xmath43 and @xmath44 , even for @xmath39 we have the stable perturbations . when eos of de @xmath45 , no matter the interaction proportional to the energy density of the individual dark sector or the total dark sectors , the perturbation is always stable .
with the formalism of the perturbation theory , we are in a position to study the cmb power spectrum . in our analysis
we will concentrate on models with constant @xmath19 and a constant speed of sound .
the temperature anisotropy power spectrum can be calculated by @xmath46 where @xmath47 gives the transfer function for each @xmath48 , @xmath49 is the primodial power spectrum and @xmath50 is the conformal time today . on large scales the transfer functions are of the form @xmath51 where @xmath52 is
the contribution from the last scattering surface given by the ordinary sachs - wolfe ( sw ) effect and @xmath53 is the contribution due to the change of the gravitational potential when photons passing through the universe on their way to earth and is called the isw effect .
the isw contribution can be written as @xmath54)e^{\kappa(\tau_0)-\kappa(\tau)}[\psi'-\phi'],\ ] ] where @xmath55 is the spherical bessel function , @xmath56 denotes the optical depth for thompson scattering . from einstein equations , we obtain , @xmath57- \mathcal{t}'\end{aligned}\ ] ] where @xmath58 and @xmath59 is the anisotropic stress of relativistic components which can be neglected in the following discussion .
the isw effect can be classified into early and late times effects .
the early isw effect takes place from the time following recombination to the time when radiation is no longer dynamically significant , which gives clues about what is happening in the universe from the radiation domination to matter domination .
the late time isw effect arises when de becomes dynamically important and has the unique ability to probe the size " of de .
when de becomes non - negligible , the gravitational potential decays .
when a photon passes throw a decaying potential well , it will have a net gain in energy and thus leads to the late isw effect .
the late isw effect is a significant contribution to the large scale power in the temperature map of cmb . in the minimal case
when there is no interaction between de and dm , the presence of de perturbations leaves a @xmath19 and @xmath17 dependent signature in the late isw source term . for @xmath39 , it was observed that the cmb temperature anisotropies on large scales got enhanced for bigger constant values of @xmath17@xcite .
it was argued that increasing @xmath17 increases the suppression of dm perturbations and therefore increases the contribution to the isw effect@xcite .
however , when @xmath45 the effect is reversed , with the perturbation initially of opposite sign , and the contribution to the isw effect increases as the sound speed of de is decreased@xcite .
the interplay between perturbations in the de and dm and the isw effect is very subtle and it is more direct to cross - correlate the late isw effect to its source term , the change of the gravitational potential@xcite . the late isw effect is a promising tool to measure the eos and sound speed of de . whether it can present us the signature of the interaction between de and dm is a question we are going to address here .
we will concentrate our discussions on three commonly studied phenomenologically interaction forms between dark sectors , namely the interaction proportional to the energy density of de , dm and total dark sectors , respectively .
when we choose the coupling between dark sectors proportional to the energy density of de , the perturbation was found stable with an eos @xmath39 as well as @xmath45@xcite . for chosen constant eos satisfying @xmath39 and @xmath60 , the result of large scale cmb anisotropies for different couplings
are shown in fig [ figone]a .
the lower set of dashed lines describes the late isw effect , the middle dotted lines show the combination of the sw effect together with the early isw effect and the top solid lines are for the total large scale cmb angular power spectra .
it is clear to see that such kind of interaction between dark sectors leaves obvious signature in the late isw effect which influences the large scale total cmb spectrum , but does not change much of the sw and early isw effects . comparing to the non - coupling case
( @xmath61 ) , the positive coupling with energy decay from de to dm enhances the late isw effect , while the more negative coupling with more energy decay from dm to de suppresses more the late isw contribution .
this can be understood from the evolution of the isw source term , the change of the gravitational potential displayed in fig [ figone]b . the bigger value of the coupling results in the further change of the gravitational potential . in fig
[ figone]c we have shown the influence of the sound speed .
it can be seen that the bigger sound speed of the de makes the difference caused by different couplings bigger in the large scale cmb power spectra .
[ cols="^,^ " , ] the likelihood of the coupling constant is shown in fig [ dm]b .
the evolution of the ratio of energy densities between de and dm for this kind of interaction is shown in fig [ eight ] . when the coupling is proportional to the energy density of total dark sectors.,width=268,height=268 ]
we have reviewed the formalism of the perturbation theory when there is interaction between de and dm .
based upon this formalism we have studied the signature of the interaction between dark sectors in the cmb large scale temperature fluctuations .
we found that in addition to disclose the de eos , sound speed , the late isw effect is a promising tool to measure the coupling between dark sectors .
when the interaction between de and dm takes the form proportional to the energy density of dm and the total dark sectors , because in these cases de and dm started to chase each other since early time , the interaction not only presents in the late isw source term but also leaves imprint in the sw and early isw effects .
these properties provide a possible way to examine the interaction between de and dm even from smaller scale in cmb observations .
we have performed the global fitting by using the cmb power spectrum data including wmap5 data and balloon observational data together with snia and sdss data to constrain the interaction between de and dm .
when the interaction between de and dm takes the form proportional to the energy density of dm and the total dark sectors , since it leaves more information in the cmb power spectra , not only just in the very large scale , the coupling can be constrained in a very precise range . in @xmath0
the coupling is positive indicating that there is energy transfer from de to dm .
this kind of energy transfer can help to alleviate the coincidence problem compared to the noninteracting case .
it is of great interest to extend our study to a field theory description of the interaction between de and dm and examine its signature in the large scale cmb power spectra .
a possible field theory model was proposed in @xcite and further investigation in this direction is called for . 99 s. j. perlmutter et al . ,
nature 391 , 51 ( 1998 ) ; a. g. riess et al . ,
j. 116 , 1009 ( 1998 ) ; s. j. perlmutter et al .
, astroph .
j. 517 , 565 ( 1999 ) ; j. l. tonry et al .
, astroph .
j. 594 , 1 , ( 2003 ) ; a. g. riess et al .
, astroph .
j. 607 , 665 ( 2005 ) ; p. astier et al .
447 , 31 ( 2005 ) ; a g. riess et al .
, astroph .
j. 659 , 98 ( 2007 ) .
m. kowalski et al . , 2008 ,
m. tegmark et al .
d 74 , 123507 ( 2006 ) .
l. amendola , phys .
d 62 , 043511 ( 2000 ) ; l. amendola and c. quercellini , phys . rev .
d 68 , 023514 ( 2003 ) ; l. amendola , s. tsujikawa and m. sami , phys .
b 632 , 155 ( 2006 ) .
d. pavon , w. zimdahl , phys .
b 628 , 206 ( 2005 ) , s. campo , r. herrera , d. pavon , phys .
rev.d 78 , 021302(r ) ( 2008 ) .
g. olivares , f. atrio - barandela and d. pavon , phys . rev .
d 74 , 043521 ( 2006 ) . c. g. boehmer , g. caldera - cabral , r. lazkoz , r. maartens , phys .
d 78 , 023505 ( 2008 ) .
s. b. chen , b. wang , j. l. jing , phys.rev.d 78 , 123503 ( 2008 ) .
b. wang , j. zang , c .- y .
lin , e. abdalla and s. micheletti , nucl .
b 778 , 69 ( 2007 ) .
w. zimdahl , int . j. mod
d 14 , 2319 ( 2005 ) .
d. pavon , b. wang , gen .
( in press ) , arxiv:0712.0565
. b. wang , c .- y .
lin , d. pavon , e. abdalla , phys .
b 662 , 1 , ( 2008 ) .
o. bertolami , f. gil pedro and m. le delliou , phys .
b 654 , 165 ( 2007 ) .
o. bertolami , f. gil pedro and m. le delliou , arxiv:0705.3118v1 .
z. k. guo , n. ohta and s. tsujikawa , phys .
d 76 , 023508 ( 2007 ) .
j. valiviita , e. majerotto , r. maartens , jcap 07 , 020 ( 2008 ) , arxiv:0804.0232 . j. h. he , b. wang , e. abdalla , phys .
b 671 , 139 ( 2009 ) , arxiv:0807.3471 w. zimdahl , d. pavon , l.p .
chimento , phys .
b 521 , 133 ( 2001 ) ; l.p .
chimento , a.s .
jakubi , d. pavon , w. zimdahl , phys . rev .
d 67 , 083513 ( 2003 ) .
e. abdalla , l.raul w. abramo , l. sodre jr . ,
b. wang , phys .
b673 , 107 ( 2009 ) arxiv : astro - ph/0710.1198 . j. h. he , b. wang , jcap 06 , 010 ( 2008 ) , arxiv:0801.4233 . c. feng , b. wang , e. abdalla , r. k. su , phys .
b 665 , 111 ( 2008 ) , arxiv:0804.0110 .
b. jackson , a. taylor , a. berera , arxiv:0901.3272 .
a. refrefier , et al , arxiv : 0802.2522 . s. das , p. s. corasaniti and j. khoury , phys . rev .
d 73 , 083509 ( 2006 ) .
l. amendola , d. tocchini - valentini , phys .
d64 , 043509 ( 2001 ) ; g. w. anderson , s. m. carroll , arxiv : astro - ph/9711288 . j. h. he , b. wang , y. p. jing , jcap 07 , 030 ( 2009 ) arxiv:0902.0660
. g. caldera - cabral , r. maartens , b. schaefer , arxiv:0905.0492 .
j. weller , a. m. lewis , mon . not .
346 , 987 ( 2003 ) , arxiv : astro - ph/0307104 .
r. bean , o. dore , phys.rev .
d 69 , 083503 ( 2004),arxiv : astro - ph/0307100 . m. doran , jcap 0510 , 011 ( 2005 ) . c. j. mactavish , et al . , astrophys .
j. 647 , 799 ( 2006 ) .
a. c. s. readhead , et al .
, astrophys .
j. 609 , 498 ( 2004 ) . c. dickinson , et al . , mon . not .
353 , 732 ( 2004 ) . c. l. reichardt , et al . ,
a. g. riess , et al .
, arxiv : astro - ph/0611572 .
p. mcdonald , et al .
, astrophys .
163 , 80(2006 ) ; p. mcdonald , et al .
, astrophys .
j. 635 , 761 ( 2005 ) .
s. micheletti , e. abdalla , b. wang , phys .
d ( in press ) arxiv:0902.0318 .
s. boughn , r. crittenden , nature 427 ( 2004 ) 45 - 47 ; m.r .
nolta , et al .
, astrophys.j . 608
( 2004 ) 10 - 15 ; p. fosalba , e. gaztanaga , mon.not.roy.astron.soc .
350 ( 2004 ) l37-l41 ; p. fosalba , et al .
, astrophys.j .
597 ( 2003 ) l89 - 92 ; r. scranton , et al .
2003 , astro - ph/0307335 ; p. vielva , e. martinez - gonzalez , m. tucci , astro - ph/0408252 ; n. afshordi , y.s .
loh , m. strauss , phys.rev .
d69 ( 2004 ) 083524 ; nikhil padmanabhan , et al .
d72 ( 2005 ) 043525 ; a. cabre , et al .
, mnras 381 , 1347 ( 2007 ) ; g. olivares , et al .
, phys . rev .
d 77 103520 ( 2008 ) ; b. m. schaefer , mnras 388 , 1403 ( 2008 ) .
j. lesgourgues , w. valkenburg , e. gaztanaga , phys , rev .
d77 063505 ( 2008 ) .
t. giannantonio , et al . ,
d77 , 123520 ( 2008 ) ; s. ho , et al .
, phys . rev .
d 78 043519 ( 2008 ) . | = 0.6 cm dark energy interacting with dark matter is a promising model to solve the cosmic coincidence problem .
we study the signature of such interaction on large scale cosmic microwave background ( cmb ) temperature anisotropies . based on the detail analysis in perturbation equations of dark energy and dark matter when they are in interaction
, we find that the large scale cmb , especially the late integrated sachs wolfe effect , is a useful tool to measure the coupling between dark sectors .
we also discuss the possibility to detect the coupling by cross - correlating cmb maps with tracers of the large scale structure .
we finally perform the global fitting to constrain the coupling by using the cmb power spectrum data together with other observational data .
we find that in the @xmath0 range , the constrained coupling between dark sectors can solve the coincidence problem .
= 0.8 cm |
the quantum theory of charge transport in one - dimensional ( 1d ) systems of interacting fermions is a fundamental building block of our understanding of electron transport in nanostructures and of a future nanoelectronics .
one - dimensional interacting fermion systems have been studied since the 1950s , beginning with the pioneering works of tomonaga and luttinger . the early work exploited the fact that the elementary excitations in these systems are charge and spin excitations of bosonic character , and led to the formulation of the method of bosonization .
@xcite this method offers a natural description of the fractionalization of the usual fermionic quasiparticles existing in higher dimensions , into spinon and holon quasiparticles in 1d . while the bosonization method is highly successful in accounting for the properties of systems in equilibrium , it is somewhat problematic when applied to transport situations .
for example , an ideal quantum wire attached to two reservoirs is expected to have a two - point conductance of @xmath2 per channel . in contradiction to this general law it was found in early work on transport in clean luttinger liquids @xcite that the conductance ( here and in the following conductance will be measured in units of the conductance quantum @xmath3 ) is given by the luttinger parameter @xmath4 , and thus depends on the interaction strength .
it was later pointed out that by carefully choosing the order of limits of frequency , @xmath5 , and wire length , @xmath6 , @xcite or else by taking into account the screening of the external field by the interacting electron system @xcite one recovers the correct value of unity for the two - point conductance .
whether the former or the latter explanation is the correct one remains disputed to this day . the more relevant case of a luttinger liquid with potential barrier has been considered first by kane and fisher @xcite and by furusaki and nagaosa , @xcite again using the bosonization method .
these authors found that interaction has a dramatic effect on the conductance : for repulsive interaction the conductance is found to tend to zero as a fractional power of the temperature @xmath7 , in the limit @xmath8 .
this was shown in the two limits of a weakly scattering barrier and a strong ( tunneling ) barrier .
in addition , results in the complete temperature range are available at special values of the interaction parameter , @xmath9 and @xmath10 .
kane1992,kane1992a , weiss1995,fendley1995,fendley1995a all these works suffer from the drawback that in the clean limit the conductance is found to tend to @xmath4 rather than @xmath11 .
it has been argued that these results may be applied to the four - point conductance .
however , the four - point conductance is expected to tend to infinity in the limit of vanishing barrier strength , a behavior not shown . for the reasons noted above we think it worthwhile to develop an alternative formulation of the transport theory of luttinger liquids , formulated entirely in the fermionic language . the fermionic representation offers the possibility to connect the fermionic degrees of freedom in the ( non - interacting ) leads smoothly with the degrees of freedom in the interacting system . in other words
, it allows to use the scattering states of the system in the non - interacting limit as a basis of description . on the simplest level , in lowest order in the interaction ,
this program has been carried out in a seminal paper by yue , matveev and glazman .
@xcite the physics of this problem lies in the scale - dependent build - up of a polarization potential around the bare barrier , induced by the friedel oscillations of the density . for repulsive interaction , the polarization potential
is found to extend farther and farther out as the temperature is lowered , until at @xmath12 it is infinitely extended , leading to a vanishing transmission probability across the barrier .
the process of gradual growth of the effective potential barrier may be described in the language of renormalization group theory applied to the transmission probability as a function of the temperature . a generalization of the approach of yue et al . to the case of two barriers
has been given in ref .
these predictions , based on the continuum version of the theory , were thoroughly checked and confirmed by the fermionic functional renormalization group method , starting from the hubbard models on a lattice .
@xcite in this paper we report on a significant extension of the work of yue et al . to the case of systems of spinless fermions in 1d interacting via arbitrarily strong forward scattering ( parameter @xmath0 ) and subject to a short range barrier potential ( width @xmath13 ) .
the principal tool we will be using is perturbation theory in the interaction , summed to infinite order . to achieve this goal , and to gain insight into the structure of perturbation theory , we map the problem first onto an effective model of interacting currents of chiral fermions .
the reformulation allows to describe the effect of the barrier potential as a local magnetic field at the position of the barrier , acting on the pseudospin vector of the chiral current .
the logarithmic corrections to this field , stemming from the fermionic interactions can be addressed in a simplified poor - man scaling approach ; however this approach becomes ambiguous in higher orders .
therefore at a later stage we will apply the callan - szymanzik type of analysis , by first introducing the counter terms to magnetic field part of the hamiltonian to compensate the effect of the interaction , and secondly requiring the `` bare '' value of the field to be independent of the high - energy cutoff .
equivalently , we may assume the scaling property of the conductance to hold , entailing the existence of a renormalization group equation for the conductance as a function of the scaling variable @xmath14 ( at finite temperature @xmath15 ) .
by comparison with the structure of perturbation theory for the conductance , which is given by a power series in the interaction and in the scaling parameter @xmath14 , one may extract the rg @xmath1-function . in this way we derive a universal renormalization group equation for the conductance as a function of the scaling parameter .
the most important consequence of the current algebra formulation is , however , to allow for an efficient organization of perturbation theory . after presenting the formulation of perturbation theory as well as a few low order results we analyze the structure of the perturbation expansion with respect to logarithmically divergent terms containing powers of @xmath16 or @xmath17 .
we identify a class of universal diagrams contributing the principal terms linear in @xmath14 and derive an integral equation resumming these contributions ( `` ladder approximation '' ) .
these terms are shown to dominate in both limits , small and large conductance .
we identify the prefactor of the terms in the perturbation series for the conductance @xmath18 linear in @xmath14 with the renormalization group @xmath1-function of the flow equation of @xmath19 .
there is , however , one important new feature : there appear scale independent terms ( from third order on ) , which lead to a correction of the conductance even at @xmath20 , the ultraviolet cutoff .
these terms must be taken into account , in order to preserve the scaling property of the conductance , and lead to a starting value of the conductance @xmath21 , different from the conductance in the absence of interaction .
the rg equation may be solved analytically in the ladder approximation , to give the conductance as a function of temperature for any interaction strength and barrier potential .
the result completely agrees with earlier work , where a comparison is appropriate we emphasize that our result for the conductance reduces to unity in the absence of a barrier .
furthermore , the effect of screening of the external field @xcite is included by omitting all polarization diagrams .
we checked the renormalizability of the theory explicitly by calculating all terms up to third order in @xmath14 and @xmath0 . at intermediate temperatures ( semi - transparent barrier )
additional diagrams contribute small corrections to the @xmath1-function .
we calculate these terms in lowest ( third ) order in @xmath0 .
a proper treatment of these contributions requires taking into account scale independent terms in a way sketched above .
we demonstrate explicitly that the resulting @xmath1-function is uniquely determined for a given physical quantity .
however , @xmath22 turns out to be a slightly different function for the two cases of interest here , the temperature dependent and the length dependent conductance .
the result of the solution of the rg - equation for the conductance , using the approximate @xmath1-function thus obtained , is found to agree quantitatively with all known results on the scaling behavior of the conductance in the limits @xmath23 and @xmath24 . in the intermediate regime @xmath25 we find small discrepancies with the results of conformal field theory in the case @xmath9 , which we can trace back to a different cutoff scheme used there and the effect of higher order terms neglected in our work . as an excellent interpolation formula between two exact limits our result goes beyond all previous works : it is valid for any interaction strength @xmath4 and any potential scattering strength .
the hamiltonian includes the kinetic energy of freely right- and left - moving ( r , l ) spinless fermions with linearized dispersion , @xmath26 , the interaction energy between the left- and right - moving densities , @xmath27 , and the impurity part decribing scattering off the barrier , placed at the origin , @xmath28 : @xmath29 \notag \\
h_{1 } & = & g_{2}\int_{-l}^{l}{dx}\;(\psi _
{ r}^{\dagger } \psi _ { r})(\psi _ { l}^{\dagger } \psi _ { l } ) \notag\end{aligned}\]]in order to regularize the theory , we assume that the region of interaction @xmath30 ( @xmath31is the fermi wave vector ) do not overlap spatially
. the length scale @xmath13 will serve as an ultraviolet cutoff in the scale dependent logarithmic corrections considered below . the last term ,
@xmath32 in ( [ genham ] ) is not explicitly specified here ( but see below ) .
we will rather take the one - particle scattering states to be known .
this means that we characterize the barrier by transmission and reflection amplitudes @xmath33 , @xmath34 , with negligible energy dependence in the energy range of interest ( here @xmath35 , @xmath36 , @xmath37 , @xmath38 are the usual components of the impurity scattering matrix ) .
notice also that we assume the system to be non - interacting in the leads , @xmath39 , which allows for an asymptotic single - particle scattering states representation .
we define the creation operator of scattering states as @xmath40with @xmath41 ( @xmath42 ) the creation operators of asymptotically right - going ( left - going ) fermions of momentum @xmath43 .
such a representation requires the kinetic energy part of the hamiltonian to be of the form @xmath44 , and the momentum , @xmath45 , before the linearization of the dispersion around the two fermi points . in appendix
a we clarify the correspondence between the scattering states representation ( [ scat - states ] ) and our linearized hamiltonian ( [ genham ] ) written in the basis of chiral fermions . for simplicity we do not consider the so - called @xmath46 part of the fermionic interaction in this work , i.e. the term @xmath47 $ ] .
for @xmath6 the @xmath46-interaction can be absorbed into the redefinition of the fermi velocity , @xmath48 .
for finite @xmath49 one can show that @xmath46 does not lead to a renormalization of d.c .
conductance , which is the quantity of interest below .
the effect of @xmath46 on the a.c .
conductance can be analyzed , following the guidelines in @xcite .
[ sec : scatteringstates ] it appears that in the case of weak potential scattering , @xmath50 , and for electrons with energies close to the fermi energy , @xmath51 , the situation is characterized two limits of the fourier transform @xmath52 of the potential : the forward scattering amplitude , @xmath53 , and the backward scattering amplitude , @xmath54 , with real - valued @xmath55 and complex - valued @xmath56 .
the fermionic hamiltonian @xmath57 in ( [ genham ] ) is then written as @xmath58 , \notag\end{aligned}\]]where the dimensionless functions @xmath59 are short - range impurity potentials , which means that @xmath60 for @xmath61 and the above amplitudes @xmath62 . in appendix
[ sec : appsmatrix ] we show that the connection between the microscopic hamiltonian and the @xmath63-matrix can be clarified in some simple cases , but requires a detailed knowledge of @xmath59 , when one goes beyond the lowest born approximation . returning to ( [ scat - states ] ) , we define fourier transforms , @xmath64 and @xmath65 .
then we have for the electron creation operator at position @xmath66 @xmath67 \right .
\notag \\ & + & \left .
\theta ( x)\left [ t\psi _ { 1}^{+}(x)+\tilde{r}\psi _ { 2}^{+}(-x)+\psi _ { 2}^{+}(x)\right ] \right\ } \ , , \label{chiralscatstates}\end{aligned}\]]with the step function @xmath68 at @xmath69 .
in bosonization technique , the chiral fermions are represented as exponentials of chiral boson fields , @xmath70 , @xmath71 . with the fields @xmath72 . here the primary field @xmath73 and its canonically conjugate momentum @xmath74 obey the commutation relation @xmath75=i\delta ( x - y)$ ] .
we have for the density @xmath76 and the hamiltonian ( [ genham ] ) , ( impham ) can be represented as @xmath77 \label{bosonham}\end{aligned}\]]one has @xmath78 and @xmath79 for free fermions , whereas the short - range interaction @xmath27 between the fermions , eq .
( [ genham ] ) , leads to the renormalized fermi velocity @xmath80 and the luttinger parameter @xmath81^{1/2}$ ] . here and
below we use @xmath82 one usually argues , that the term @xmath83 can be absorbed into a redefinition of @xmath84 ( cf .
appendix [ sec : appsmatrix ] ) . after
this redefinition one concentrates on the @xmath56 term which constitutes the boundary sine - gordon ( bsg ) problem .
a solution to this problem , in the lowest order of @xmath56 was presented in the early work .
@xcite focussing on the small - energy sector of the problem , one uses the renormalization group approach , removing the higher energy states of the problem while simultaneously rescaling the parameters of the action .
it turns out that under this procedure the amplitude of the bsg term is renormalized as @xmath85where the rg scaling variable @xmath86 . as a result ,
the conductance at small @xmath56 , given by @xmath87 , undergoes a similar renormalization @xmath88with the lower cutoff in @xmath14 defined by temperature or voltage bias , @xmath89 $ ] .
we shall confine ourselves to the the linear response regime , @xmath90 in the following . for repulsive interaction @xmath91
the conductance decreases with falling temperature . when the renormalized impurity potential becomes strong , latexmath:[$% violated and one should use a different line of reasoning .
one may think of two semi - infinite parts of the wire , connected by a weak tunneling link @xmath35 .
an appropriate rg treatment shows that the repulsive interaction leads to a further decrease of the conductance , which acquires the form @xmath93 these two regimes , eqs .
( [ condukf.high ] ) , ( [ condukf.low ] ) show different scaling exponents , which are approximately equal for small interaction @xmath94 a smooth crossover between the two asymptotes ( [ condukf.high ] ) and ( condukf.low ) was first explicitly provided for a special case of interaction strength , @xmath95 , which is known as luther - emery refermionization point .
the full curve for the conductance was obtained kane1992,kane1992a , weiss1995 in the form of a one - parameter scaling function . in subsequent works
@xcite the bsg model was analyzed at arbitrary values of luttinger parameter , @xmath4 .
the set of coupled integral equations was shown to be finite for @xmath96 and the solution for @xmath97 was derived , in particular .
corresponding scaling functions for the conductance were obtained for finite @xmath7 and voltage bias on the contact @xmath98 either by numerical solution of the corresponding integral equation or as a series in powers of the scaling parameter , see also @xcite . for practical purposes
this form of representation is not very convenient . in principle , the statement of a one - parameter scaling function for the conductance and the knowledge of its actual form provides a solution for the temperature renormalization of the barrier apparently at arbitrary strength .
however , it was noted in @xcite , that `` the strong - barrier problem which is at the end of our renormalization - group trajectory follows formally from dimensional continuation of the integrals for the weak barrier problem .
it is not in any case a generic strong - barrier problem . ''
yue , matveev and glazman @xcite have developed a theory , starting from the formalism of scattering states and taking into account the fermionic interaction in lowest order of perturbation .
they arrived at the rg equation for the transmission amplitude @xmath35 in the form @xmath99 the solution to this equation is found as @xmath100 which , in leading order in @xmath101 , agrees with eqs .
( [ condukf.high ] ) , ( condukf.low ) .
the advantage of this approach is its applicability for arbitrary strength of impurity potential .
one may thus avoid the step involving the transition from the initial hamiltonian ( [ bosonham ] ) to the observed conductance , which as we saw above can depend on the short - distance ( ultraviolet ) details of relevant quantities .
this view is further corroborated by the work by callan _
@xcite who discussed the solution of the non - interacting ( @xmath79 ) bsg theory , and arrived at a current algebra formulation similar to our formulation below .
these authors show that the connection of the initial model ( [ bosonham ] ) to the observable quantities depends on the ultraviolet regularization .
we will return to this point in our discussion below .
in the above we defined a scattering states representation ( chiralscatstates ) in chiral representation . in order to describe the effects of interaction , we need to define fermionic densities in the same basis .
one may form four bilinear density combinations out of two chiral fermions .
it is convenient to group these combinations into chiral densities or `` currents '' , according to @xmath102 we call @xmath103 the pseudocharge current and the vector @xmath104 the pseudospin current . these operators obey @xmath105 and @xmath106 kac - moody algebras , respectively @xcite , as we discuss below .
the particle density operators for incoming @xmath107 and outgoing @xmath108 particles in terms of the @xmath109 s are given by ( here and in the following @xmath69 ) @xmath110here @xmath111 is the third component of the pseudospin current vector @xmath112 rotated by the orthogonal matrix @xmath113 given by @xmath114 .
\label{defr}\]]with pauli matrices @xmath115 .
it is seen from ( [ defr ] ) that the global phase of @xmath63 drops out completely . omitting this phase , we parametrize @xmath116 in this notation , the components of interest below read @xmath117 , @xmath118 , and @xmath119 .
we see that the description of the barrier is given by the eigenmodes of the current @xmath120 , with negative and positive @xmath66 and @xmath121 . in this picture , the incoming current is given by the diagonal components of the @xmath122 matrix , and the outgoing currents correspond to the diagonal components of the rotated matrix @xmath123 . evidently , the pseudocharge component @xmath103 is not affected by this rotation .
the chiral densities introduced above satisfy the kac - moody commutation rules @xmath124 & = & \frac{i}{4\pi } \partial _ { x}\delta ( x - y ) \label{kacmoody } \\ { } [ j_{j}(x),j_{k}(y ) ] & = & \frac{i}{4\pi } \delta _ { jk}\partial _ { x}\delta ( x - y)+i\varepsilon _ { jkl}j_{l}(y)\delta ( x - y ) \notag\end{aligned}\]]with @xmath125 and totally antisymmetric @xmath126 .
the short - distance operator product expansions ( opes ) are @xmath127 in simple terms , relevant to our discussion below , one can consider ( kacmoody ) as a consequence of ( [ ope ] ) . in their turn , the opes ( ope ) simply represent fermionic green s functions , @xmath128^{-1}$ ] . a bilinear form in the currents is a product of four fermion operators ; the complete convolution of these gives a product of two two - point green s function ( modulo normally ordered operators ) , and the partial convolution produces a green s function multiplied by bilinear forms in the fermion operators , i.e. current operators .
the position argument of the latter current operators ( last term in ( [ ope ] ) ) is subject to ambiguity , but usually this concerns only less relevant terms . in our analysis below we deal with an action non - local in the currents , and to handle such an ambiguity becomes an increasingly difficult matter .
this is why we resort to the perturbative treatment in terms of chiral fermions .
the physical charge density is @xmath129 at @xmath130 and @xmath131 at @xmath69 .
a simple calculation shows that @xmath132the physical current operator is also decomposed into two parts , in the pseudocharge and pseudospin sectors .
we use the continuity equation @xmath133 $ ] to obtain @xmath134 it follows then that the pseudocharge current corresponds to the part of physical density which is even with respect to the reflection at the scatterer , @xmath135 .
the pseudospin current corresponds to the odd part of the density , @xmath136 .
this symmetry property simplifies the discussion of a voltage bias , applied to the barrier .
one sees immediately , that applying the same electrochemical potential to both leads of the wire corresponds to its coupling to the pseudocharge current .
it results in an overall increase of the fermionic density , symmetric with respect to the barrier , and not to a net physical current .
by contrast , an electric potential of the form @xmath137 , couples only to the pseudospin part , leading to a term in the hamiltonian @xmath138the physical current induced by a bias voltage is therefore given in linear response theory as @xmath139\rangle \label{def : conduc}\end{aligned}\]]a remark is in order here . strictly speaking
, the prefactor @xmath140 in the definition ( [ def : current ] ) applies for non - interacting leads . in the interacting region
we have to replace @xmath141 in ( [ def : current ] ) .
we may avoid this complication , analyzed elsewhere @xcite , by assuming in ( [ def : conduc ] ) that both @xmath142 and @xmath143 are placed outside the interacting region , @xmath144 .
the change of the limits of integration over @xmath145 in ( [ def : conduc ] ) is not important in the limit of d.c .
conductance @xmath146 , considered below .
, title="fig:",width=302 ] ( b ) ) . , title="fig:",width=302 ] it is known that fermions with linearized dispersion in one spatial dimension can be described by a hamiltonian , quadratic in chiral fermionic densities .
this observation , usually attributed to tomonaga , is the basis of the bosonization approach .
@xcite similarly to ( [ bosonham ] ) , we have @xmath147which can be represented as @xmath148the interaction part is @xmath149 in fig .
[ fig : scattering ] we show in a pictorial way our parametrization of the fermionic densities and the interaction , @xmath27 . in fig .
fig : scatteringa the @xmath0-interaction processes are shown in the usual scattering configuration . the representation in terms of the chiral currents @xmath109 ( all particles moving to the right ) is shown in fig .
fig : scatteringb and leads to a seemingly nonlocal interaction .
notice that in the case of perfect reflection , @xmath150 , we have @xmath151 and the observable densities ( see below ) form an abelian @xmath105 sub - algebra of @xmath152 .
this case of open boundary bosonization , considered by fabrizio and gogolin , allows a complete and rather simple analysis @xcite . in the next subsection
we elucidate what happens at the origin , @xmath153 . .
using the parametrization ( [ s - parametrization ] ) , one finds that @xmath154 i.e. , it is a finite rotation characterized by the dual vector @xmath155 .
we can not symmetrize the hamiltonian in the pseudospin space , reducing it to the so - called sugawara form , @xcite because the vector @xmath156 breaks the @xmath106 symmetry of the problem .
we may symmetrize the hamiltonian in the plane perpendicular to @xmath157 , but that provides little advantage .
the above formulation of the problem , incorporating the knowledge about the scatterer in the asymptotic scattering states , is equivalent to the the alternative formulation of the pseudospin current being rotated by a fictitious magnetic field @xmath157 located at the origin .
the pseudocharge sector remains unchanged and the pseudospin sector of the problem can be equivalently described by the following hamiltonian @xmath158where the operators @xmath159 , with @xmath160 obey kac - moody relations ( [ kacmoody ] ) .
the two hamiltonians , ( [ ham_0 ] ) , ( [ ham_1 ] ) and ( [ fictmagnfield ] ) , are connected by a canonical transformation @xmath161 , where @xmath162we derive the relation between @xmath163 and @xmath164 in appendix sec : appa .
equation ( [ fictmagnfield ] ) resembles the hamiltonian for the kondo problem in the current algebra representation .
@xcite however there are important differences .
the first one is the non - local interaction @xmath165 between the incoming and outgoing waves in our case .
the second difference is the classical nature of the field @xmath157 , as opposed to the quantum nature of the kondo spin @xmath166 .
the matrix green s function for chiral fermions is diagonal in pseudospin space when defined in terms of the asymptotic eigenstates .
however in terms of the usual right- and left - movers its matrix structure is evidently given by eq .
( [ s - parametrization ] ) , which shows the action of the magnetic field @xmath167 , with @xmath168 .
we will use this fact in sec .
[ sec : counterterms ] below .
let us show how the renormalization group equation for the many - body @xmath169matrix is simply reproduced in the current operator formalism .
following affleck and ludwig , @xcite we write the @xmath0 term of the @xmath169matrix in the interaction representation as @xmath170expanding the latter object in first power of @xmath0 , we find at given @xmath35 @xmath171applying ope rules ( [ ope ] ) to the last expression one finds an operator term @xmath172after eliminating the distances close to the scatterer , i.e. integrating over @xmath66 from @xmath13 to a certain @xmath173 , which serves now as new lower cutoff , we obtain the term which can be re - exponentiated to the action giving a contribution of the form @xmath174 , with @xmath175we notice further that @xmath176 , i.e. , the additional magnetic field at the origin is parallel to the above @xmath157 , and we may restrict the discussion to the change in modulus , @xmath177 . denoting @xmath178 , we obtain @xmath179 , or @xmath180which is equivalent to eq .
( [ ymg.rgeq ] ) . after this verification of the previous result in the first order in @xmath101 , we are tempted to obtain the next - order corrections to the rg equation ( rg1st ) .
it turns out however that working entirely in the current operator formalism gives no advantage in such analysis , as we explain in the next subsection .
let us return to the last term in ( [ ope ] ) @xmath181using the definition ( [ def : currents ] ) , and free fermionic green s functions , one obtains e.g. the precise relation @xmath182modulo the normal ordered part .
evidently , the numerator in ( [ preciseope ] ) is reduced to @xmath183 only in the limit @xmath184 . in other words , the relation ( [ ope ] ) is the `` short - distance '' expansion and must be used with caution .
the meaning of the relation ( [ ope ] ) becomes clearer when we compare the results obtained within the purely fermionic ( and thus unambiguous ) approach with the results provided by the use of ( [ ope ] ) .
when available , this comparison yields identical results in the limit of large ( external ) times and distances .
hence , the relations ( [ ope ] ) provide a good mnemonic rule for a quick estimate of a given contribution to a desired quantity .
however , if we want to obtain concrete prefactors and verify the renormalizability of the theory , it is better to use the standard fermionic approach , treating the currents @xmath185 as pseudospin vertices . proceeding this way below , we use a symmetry of the problem , namely the unitarity of the @xmath63-matrix related to the conservation of charge , which leads to a pure rotation of the vector current operator after the scattering event . a different attempt to explore the current structure of the theory
would be the use of the equation of motion method , which we describe in the appendices [ sec : appc ] and [ sec : appc2 ] .
if successful , this strategy would account for the influence of interaction in all orders .
the main difficulty arising in this approach is the nonlocal character of interaction ( [ ham_1 ] ) and the appearance of an infinite series of coupled equations .
we show in appendix [ sec : appc2 ] , that the attempt to truncate this series by considering the `` most relevant '' contributions leads , perhaps not surprisingly , to the restoration of the previous result ( [ solurg1st ] ) . in order to go beyond this level of consideration
, we use the regular perturbation theory in chiral fermions in the remainder of the paper .
let us first formulate the rules for the calculation of corrections to the conductance in perturbation theory in the interaction @xmath101 .
the contributions to @xmath186 in n - th order of @xmath0 may be calculated with the help of feynman diagrams in the position - energy representation ( @xmath187 is the external matsubara frequency ) .
we draw @xmath188 vertical wavy lines in parallel , each carrying the factor @xmath189 , the upper endpoint of the @xmath190-th line at @xmath191 with pseudospin matrix @xmath192 , the lower one at @xmath193 with matrix @xmath194 attached ; @xmath195 are pseudospin indices of incoming ( outgoing ) fermion lines .
the external vertices are at @xmath196 with matrix @xmath197 and at @xmath66 with matrix @xmath198 .
the vertex points are connected by green s functions @xmath199 where the @xmath200 are matsubara fequencies @xmath201 .
all internal @xmath66 -variables are integrated on the positive semi axis .
the trace over the product of all isospin matrices in each fermion loop is taken and a factor of @xmath202 is applied to each n - th order diagram .
the limit @xmath203 is taken at the end .
after this brief overview we provide further details about our calculation .
( i ) from eqs .
( [ def : current ] ) , ( [ def : conduc ] ) it follows that only two out of four correlation functions in @xmath204 are non zero .
namely , the chiral character of the currents ( [ ope ] ) leads to @xmath205 at @xmath206 . then assuming @xmath207 in ( [ def : conduc ] ) we get @xmath208\rangle\]]the first term here gives a contribution @xmath209 , it is not affected by interaction .
the second term is @xmath210 for free electrons , so that @xmath211 as expected .
\(ii ) it is this second correlation function , @xmath212 , which undergoes renormalization .
let us denote this quantity by @xmath213 : @xmath214 the decrease of the conductance can be viewed as the increase of the rotation angle @xmath215 .
below we discuss the corrections to @xmath213 .
\(iii ) in order @xmath216 , we draw a diagram which contains @xmath217 current vertices .
two currents are external , and @xmath218 come from @xmath219 pairs of currents in each interaction term .
we fix the coordinates of the interaction terms and calculate the diagrams . in the limit of external frequency @xmath220
each diagram is @xmath221 with @xmath222 , the integration over external @xmath145 in ( [ def : conduc ] ) reduces this power @xmath223 so that only the linear - in-@xmath224 contribution survives in this limit ; see also paragraph ( viii ) below .
after this procedure we have _ finite contributions _ , dependent on the positions of interaction points , @xmath193 , and should integrate over these positions .
\(iv ) these last integrals over @xmath225 ( @xmath226 ) , if taken over the entire semiaxis @xmath227 , _ diverge logarithmically _ and it is precisely at this step when we have to introduce the cutoff , as we discuss at length below .
\(v ) each current vertex has matrix structure and is @xmath228 for a current at negative coordinate ( before scattering ) and @xmath229 for positive coordinate ( after scattering ) .
we denote these matrices by @xmath230 .
corrections are generated by connecting all current vertices by green s functions .
technically , we employ _ mathematica _ and generate all possible permutations @xmath231 of vertices and make one fermionic loop , connecting these vertices in given order .
the advantage of current representation is that the information about the scattering is encoded in pauli matrices and the kinetics is given by chiral green s functions ( def : green ) .
the matrix structure produces an overall prefactor before the diagram of the form @xmath232\ ] ] \(vi ) other corrections are generated when @xmath217 current vertices are connected by more than one fermionic loop .
we denote these structurally different sets of diagrams by listing the number of current vertices in internal loops . in the zeroth order of @xmath101
we have the trivial set @xmath233 , in the first order of @xmath101 we have only a set @xmath234 . in second order of @xmath101
we have two sets , @xmath235 and @xmath236 .
in the third order of @xmath101 we have four different sets : @xmath237 , @xmath238 , @xmath239 and @xmath240 .
some of these diagrams are shown in the figures [ fig : diag1order ] and fig:3rd .
\(vii ) to exclude double counting of different graphs in this procedure , we should fix one element in each loop .
we always fix one external vertex as a first element in the first loop .
in addition , we assume that the coordinates of internal vertices are ordered , i.e. @xmath241 , etc . then .
e.g.the number of graphs in the @xmath237 set becomes @xmath242 . in the @xmath238 set
, one has @xmath243 graphs , with factor @xmath244 stemming from the necessity to fix one element in the second loop .
similarly , the set @xmath239 is obtained by taking @xmath245 permutations , then partitioning each permutation into two parts of length 4 , summing all possible diagrammatic contributions and dividing the result by factor @xmath246 to account for the necessity to fix one element in the second loop .
\(viii ) we do not explicitly require that both external vertices belong to the same loop , e.g. in the diagrams of the @xmath236 type .
however , before the final integration over the internal coordinates , we seek contributions , which are proportional to the first power of external frequency @xmath247 , this linear dependence coming from two external vertices belonging to the same loop .
if these vertices belong to two different loops , then such diagram is proportional at least to @xmath248 .
after analytic continuation @xmath249 and ( non - logarithmic ) integration over interaction region @xmath250 we have an extra factor , @xmath251 , which is small in the limit @xmath252 . in other words
, we neglect the screening of external field , which is given by rpa series where fermion polarization loops are ( 1-reducibly ) connected by interaction lines .
it is allowed when measurement times , @xmath253 , are large compared to times of travel through the interacting region , @xmath254 .
thus we find the value unity for the conductance in the absence of the barrier .
maslov1995,safi1995,oreg1995 in this subsection we discuss the general form of corrections to the conductance and outline basic ideas of the renormalization group approach , which we will use below .
starting with the conductance @xmath255 in the non - interacting limit , the corrections @xmath256 induced by the interaction take the form of a power series in @xmath101 .
more precisely , we discuss the equivalent quantity @xmath257 , equal to @xmath258 in the limit @xmath259 .
we denote the quantity @xmath213 , renormalized by interaction effects , by @xmath260 and recall that it may be represented as a power series in @xmath101 .
the coefficients of this series contain terms varying as powers of @xmath261 ( at zero temperature ) or @xmath15 at finite temperature @xmath7 in the limit of large @xmath49 . here
@xmath262 and @xmath263 are ultraviolet cutoff parameters .
accordingly , @xmath260 may be represented as a double series , @xmath264with @xmath265 functions of @xmath213 .
the terms of the form @xmath266 in ( [ expansionlog ] ) are conventionally called leading contributions , and the terms of the form @xmath267 are called subleading for @xmath268 . the first term
@xmath269 is the sum of all scale independent contributions @xmath270 naively speaking , the correction should be small @xmath271 , in order to be considered as a correction .
more precisely , the series ( expansionlog ) should be converging .
when all @xmath272 and @xmath273 , this convergence is achieved for @xmath274 which in turn imposes stricter conditions on the smallness of @xmath101 . however , assuming that @xmath275 is an analytic function of @xmath276 we expect that an analytical continuation from the region of small @xmath14 to large @xmath277 should be possible @xcite . then we can relax the requirement of the smallness of @xmath101 . rearranging the above series
we write @xmath278 where the coefficients @xmath279 are functions of @xmath213 .
if the theory is renormalizable , the following scaling relation holds : @xmath280where @xmath281 is the correlation temperature of the problem ( an analogous relation holds for the scaling with @xmath49 at zero temperature ) .
the scaling property implies the existence of a renormalization group equation @xmath282where @xmath283 is the so - called @xmath1-function . to obtain @xmath284 from perturbation theory
we take the first derivative of ( eq : rearrange ) with respect to @xmath14 and put @xmath20 @xmath285 in the last equation we have replaced @xmath213 by @xmath286 , obtained by inverting the series ( [ shifted ] ) for @xmath269 in powers of @xmath213 , which transforms the function @xmath287 into @xmath288 .
now we see that ( [ def : betafun ] ) is nothing else but the rg equation ( [ eq : rg ] ) at @xmath20 where @xmath289 .
consequently , the function @xmath290 is the true @xmath1-function . to check whether the scaling and therefore the rg equation holds
, we may integrate ( [ eq : rg ] ) to recover the perturbation series , by employing the inverse function @xmath291alternatively , noting that @xmath292 we may obtain the taylor expansion in powers of @xmath14 directly in the form @xmath293^{\prime } + \ldots \label{betataylor}\end{aligned}\]]with a prime denoting the differentiation with respect to @xmath213 . in what follows
we , firstly , verify the structure ( [ betataylor ] ) of the theory up to third order in @xmath101 , using computer algebra .
thus we show the applicability of the rg approach . secondly ,
on the basis of this analysis we propose a method of resummation of the most important contributions to the @xmath22-function in all orders of @xmath101 .
but before presenting these results we return to the significance of the scale independent terms in the perturbation theory ( the difference between @xmath294 and @xmath213 ) , as this problem has been sometimes overlooked in the literature . in the first order of @xmath101 we can absorb such finite terms into the definition of @xmath14 .
however , after this fixing of the definition of @xmath14 , higher order scale independent terms can not be removed by redefinition .
for example , we should expect a term @xmath295 with @xmath296 in the second line of ( [ expansionlog ] ) .
it is clear that in the third order we can find a corresponding multiplicative contribution @xmath297 , which contains a linear - log term and thus affects the definition of the @xmath298function in the form of ( [ def : betafun ] ) .
evidently , such terms arise only at the level of @xmath299 , or in the third loop , and do not affect the leading - log contributions . as this problem is of principal importance , we present in the following a second line of derivation of the @xmath22-function . within the callan - symanzik ( cs ) formulation of the rg method
ramond1989,higashijima1980 one may start with the perturbation series of @xmath300 in terms of the bare conductance @xmath213 , ( [ expansionlog ] ) .
the latter relation is inverted and @xmath213 is expressed in terms of the running parameter @xmath260 @xmath301with @xmath302 functions of @xmath260 .
the expansion ( [ expansioncs ] ) is the essence of the cs formulation , appropriate for our problem . here
@xmath213 is understood to be a function of the two variables @xmath303 and @xmath277 .
since the quantity @xmath213 is independent of @xmath14 we have the relation @xmath304or @xmath305 in practice , the calculation of the @xmath1-function from ( [ betacs ] ) requires the calculation of the coefficients @xmath302 from perturbation theory , which is analogous to the transformation of @xmath306 to @xmath307 discussed above .
if everything is done correctly , then the expression ( [ betacs ] ) does not depend on @xmath14 explicitly .
the cs procedure described above is different from the gell - mann low ( gl ) formulation of rg . in the latter one
considers the value of conductance used in the calculation to be defined at the scale @xmath14 ; which means @xmath308 in our notation . to eliminate the large terms involving @xmath14
one introduces counterterms into the hamiltonian ( cf .
below ) , in order to guarantee a finite value of the bare conductance , with a resulting equation similar to ( [ expansioncs ] ) .
usually the insertion of the counterterms is done in the minimal subtraction scheme , meaning that scale independent contributions are omitted .
as we show in appendix [ sec : nu ] , this gl formulation leads to ambiguities in the definition of the @xmath1-function at the level of the third loop , in contrast to the cs formulation or the scaling formulation presented in eq .
( [ def : betafun ] ) . in the perturbation theory calculation
the logarithmic factors appear at the last step , when integrating over the points of interaction . prior to this step
the calculations are straightforward .
we proceed first with the zero temperature case . in this case
the sums over discrete matsubara frequencies transform into integrals over imaginary energies , which are rather easily done by computer symbolic computation .
each diagram contains a prefactor @xmath309 with the two external vertices at @xmath310 .
integrating over @xmath145 and putting @xmath220 makes this prefactor unity .
equivalently , we may keep only the first , linear - in-@xmath224 , term in each diagram and let @xmath311 in its remaining part . in the first order of @xmath101 the correction is given by the diagrams in fig .
[ fig : diag1order ] . the vertex correction part in fig .
[ fig : diag1order]c cancels and the two first diagrams give an expression which contains @xmath312 .
this should be integrated over the point of interaction @xmath313 in the limits @xmath314 which produces a factor @xmath315 similarly , in the second order of @xmath101 we have two contributions , @xmath316 and @xmath317 , which lead to @xmath318 and @xmath319 , respectively .
we provide further details in appendix sec : appd and list here only the summary of our calculation .
contribution to the conductance .
the other three diagrams are obtained from these by reversing the direction of fermionic propagation .
, width=321 ] grouping corrections in powers of @xmath101 , as in ( [ expansionlog ] ) we have for the renormalized quantity @xmath320 : @xmath321 \notag \\ & + & g^{3}(1-y^{2})\big[-c_{\{8\}}(\lambda ^{3}-3\lambda a_{4})(y^{2}-1/3 ) \notag \\ & + & c_{\{8\}}(1-y^{2})\lambda a_{2}+c_{\{6,2\}}y^{2}\lambda ( \lambda -a_{1 } ) \notag \\ & -&c_{\{4,4\}}(1-y^{2})(\lambda ^{2}/4-a_{3}\lambda ) \notag \\ & -&c_{\{4,2,2\}}(1+y^{2})\lambda /4\big ] \label{eq : cory}\end{aligned}\ ] ] where @xmath322 .
all @xmath323 and these coefficients are shown only for reference to the underlying group of diagrams , according to the above conventions .
using the above cs scheme we come after some algebra to the rg equation @xmath324 with @xmath325 \notag \\ & + & c_{3}g^{3}(1-y^{2})^{2}+o(g^{4 } ) \label{eq : beta - general } \\
c_{3 } & = & a_{2}+a_{3}-a_{4}=\frac{\pi ^{2}}{12}-\frac{1-\ln 2}{2 } \notag\end{aligned}\]]here the value of @xmath326 is that of the @xmath12 case ( cf .
below ) . this value differs from our previously reported result @xcite , which accounted only for the set @xmath237 of third order diagrams .
here we found an aditional contribution from the @xmath239 set .
it is important to keep the scale independent contributions in the terms @xmath327 and @xmath236 in ( [ eq : cory ] ) in order to have the agreement with the result by kane and fisher in the limits of weak scattering and weak tunneling @xmath328 .
one can check that the terms with higher powers of @xmath14 in ( eq : cory ) are reproduced by eqs .
( [ betataylor ] ) and ( eq : beta - general ) .
in fact , this applicability of the rg equation is manifested already in the absence of @xmath14 in the right - hand side of ( [ eq : beta - general ] ) .
this means that , when discussing diagrammatic contributions in @xmath219th order in @xmath101 we should concentrate only on the least - leading logarithm , i.e. the terms @xmath329 .
these linear - in-@xmath14 contributions arise in two qualitatively different cases .
_ in the first case _ , the entire feynman diagram is proportional to a single logarithm .
this happens with the three first terms in ( eq : beta - general ) stemming from diagrams with the _ maximum number _ of fermionic loops . in the above notation
, these are the sets @xmath234 , @xmath330 , @xmath240 for corrections in order @xmath101 , @xmath331 , @xmath299 , respectively .
we discuss these corrections in the next section .
the finite terms , @xmath332 , do not contribute to the @xmath1-function as can be checked by the absence of coefficient @xmath333 in ( [ eq : beta - general ] ) .
in addition to these sets , there are contributions in the third order , whose leading divergence is also linear logarithmic .
they are depicted by a first skeleton graph in fig .
[ fig:3rd ] , with the _ maximally crossed _
wavy lines of interaction .
these graphs provide for one half of the value of @xmath334 in eqs .
( [ eq : cory ] ) , ( [ eq : beta - general ] ) . _ in the second case _ , the linear - log contributions arise as accompanying weaker divergence in the stronger divergent graphs . in simple cases
, it may be a combination @xmath335 ; in more complicated situations , it may be a stronger singularity at internal points , e.g. @xmath336 which is eventually removed upon symmetrization , whereas the subleading log - divergence survives and contributes to ( [ eq : cory ] ) , cf .
this second type of linear - log contributions happens in the remaining graphs in fig .
fig:3rd and provides for the rest of the value of the last term @xmath337 in ( [ eq : beta - general ] ) . , beyond ladder series .
, width=321 ] let us discuss the effects of temperature , first in the lowest order in @xmath101 . at @xmath12
the large logarithm of the theory ( [ def : lambda0 ] ) came from the integration @xmath338 over the range of interaction @xmath339 $ ] . when the integration over internal frequencies is replaced by a summation over matsubara frequencies , we find that the integrand contains the fermionic green s function @xmath340 . of the form @xmath341with an appropriate change in the definition @xmath342with the temperature correlation length , @xmath343 .
explicitly we have @xmath344 where the last relation takes place at larger temperatures , when @xmath345 . here
we introduced the ultra - violet energy cutoff @xmath346 ; one may think of @xmath347 so that @xmath348 .
the results presented below refer to this case of relatively high temperatures , @xmath349 .
we calculated the terms of perturbation theory by means of computer algebra , similarly to the @xmath12 case above .
the summary of the result is given by the same expression ( [ eq : cory ] ) , but the subleading coefficients are now given by @xmath350 . in its turn , it leads to a different numerical value of the coefficient ( eq : beta - general ) , we obtain for @xmath351 : @xmath352 let us comment on this result .
we observe that the diagrams with the maximum number of fermionic loops lead to expressions linear in @xmath14 with the same prefactors as in the @xmath12 case .
they generate the same part of the @xmath353 function , given by the first line in ( [ eq : beta - general ] ) , and correspond to one - loop rg approximation . in the next section
we show that these terms form a series which can be resummed in all orders of @xmath101 . the maximally crossed diagrams of the third order which had only linear - log divergence at @xmath12 lead to the same @xmath354 coefficient in ( [ eq : cory ] ) at @xmath355 .
let us now consider the modifications in the second order .
the complete expression for the diagrammatic set @xmath235 is given by the expression ( tempcorr(6 ) ) which shows that @xmath356 in eq .
( [ eq : cory ] ) is a smooth finite function of temperature . at finite @xmath7 each particular diagram in order @xmath299 can lead to a rather complex expression , and the resulting sum of all diagrams becomes too complicated for a brute - force approach .
the analysis can be best done in the following way .
we add all the terms of a given structural set of diagrams , thus removing the internal singularities at @xmath357 , etc .
as discussed above the leading logarithmic behavior of the set ( higher power of @xmath358 ) is determined by the rg equation .
we may hence subtract a simpler expression , with the same leading behavior , from the complicated general expression .
for instance , for the @xmath237 set we pick all diagrams proportional to @xmath359 , and notice that the zero-@xmath7 expression has a leading contribution @xmath360 with a certain coefficient .
then we expect that the finite-@xmath7 expression should have a leading term @xmath361 with the same coefficient .
we subtract this term from our expression and analyze the degree of singularity of the remaining expression .
it turns out that in the third order after the subtraction of such leading @xmath362 terms we are left with linear - log expressions .
the coefficients before these expressions are also smooth functions of @xmath7 , as we explain in the appendix [ sec : appe ] . concluding this section
, we verified the validity of the rg - equation by checking that the higher - than - linear powers of @xmath14 are generated by the linear - log terms .
this holds both at @xmath12 and at @xmath355 ; the resulting @xmath1-function is somewhat different in these cases and we discuss this difference below .
there is a part of the @xmath1-function , which is identical in both cases , and stems particularly from a sequence of diagrams with the maximum number of polarization loops .
we analyze this sequence in the next section and show that it is possible to resum it in all orders of @xmath101 .
it is important to note that the last term in ( [ eq : beta - general ] ) is vanishing in the limit when the barrier becomes fully transparent or fully reflecting , i.e. at @xmath363 . in order to see that , let us consider the case @xmath364 , then the first three terms in ( [ eq : beta - general ] ) read @xmath365 $ ] and lead to power - law scaling of @xmath18 in accordance to resutls by kane and fisher ( see below ) . at the same time
the last term in ( [ eq : beta - general ] ) is @xmath366 and does not lead to a noticeable effect in the limit considered .
it is also worth noting here , that the calculation both at @xmath12 and at @xmath367 confirms the relation between the subleading coefficients in sets @xmath237 and @xmath238 on one hand and @xmath235 and @xmath236 on the other hand .
this is seen in eq .
( [ eq : cory ] ) for the @xmath368 and @xmath333 coefficients . without this relation
the results by kane and fisher for weak and strong barrier would not be recovered .
in the previous section we saw that the corrections to the conductance are obtained as self - energy insertion into the fermionic loop , whereas the vertex corrections vanish in the dc limit @xmath369 .
this means , in particular , that the effect of renormalization in this limit can be found at the level of the one - particle green s function , or by addition of counterterms to the effective low - energy hamiltonian .
we calculate the corrections to the matrix green s function for the chiral fermions in the pseudospin sector in perturbation theory .
the rules of the diagrammatic technique remain the same .
this time we do not consider a closed fermionic loop , which described the conductance above . instead we study the matrix green s function @xmath370 connecting distant points on different sides of the barrier in the chiral representation .
the initial green s function is diagonal in pseudospin space , and the corrections to it make it non - diagonal .
we show that this non - diagonal form corresponds to additional rotation of pseudospin near the origin , in accordance with consideration of sec .
[ sec : rg - s ] . employing the cs scheme
we start with the bare barrier , characterized by the parameter @xmath215 and find the renormalized value @xmath371 as described below .
then we determine the inverse relation @xmath372 and require the independence of initial @xmath215 at the scale of consideration @xmath358 .
this provides us with the rg equation for @xmath373 the prefactor in @xmath374 is found as @xmath375 where again all @xmath323 .
the coefficients @xmath376 depend on the case in consideration .
for the zero temperature we find @xmath377 and for the finite temperature @xmath378 . in order to establish the connection to the hamiltonian we observe that the above form ( [ greenlambda0 ] ) can be represented as @xmath379 with @xmath380 this means that the effect of the interaction is indeed reduced to a change in the magnetic field @xmath381 , in accordance with sec .
[ sec : magfield ] .
we have for the value at @xmath382 @xmath383 expressing @xmath215 by @xmath384 in ( [ eq : thetar ] ) and inverting the series we obtain @xmath385 the difference @xmath386 , expressed in terms of @xmath373 , is interpreted as the counterterms to the hamiltonian , needed to compensate the divergent diagrammatic contributions . in our approach
we do not re - calculate diagrams with inclusion of the appropriately chosen counterterms , which would be problematic , given the non - abelian character of the theory and the absence of wick s theorem .
these counterterms merely reflect the structure of the corrections to the magnetic field , sec .
[ sec : magfield ] above . demanding the independence of @xmath384 on @xmath358 ,
we obtain ( here @xmath387 ) @xmath388 where @xmath389 which agrees with the above eqs .
( [ eq : beta - general ] ) , ( [ eq : c3finite ] ) .
this coincidence confirms that the vertex corrections to the conductance are unimportant in the considered dc limit .
any method of rendering the logarithmically divergent integrals finite is called a scheme of regularization .
as we explained above the contributions linear in @xmath358 get additional contributions in third order of @xmath101 from the scale independent terms appearing in the second order of @xmath101 .
we removed this ambiguity by using the scaling method or the appropriately devised cs scheme .
a part of the answer is independent of the regularization scheme and technically is obtained by summing the one - loop contributions to @xmath353-function .
one loop means here one independent integration over the internal energy , leading to a linear logarithm .
indeed the summation of the ladder series in sec .
[ sec : ladder ] amounts to a finite renormalization of the effective interaction constant , @xmath390 .
in addition to that , the quantities calculated above in the order @xmath391 included linear - log contributions stemming from diagrams with three independent energy integrations ( matsubara frequency summations ) .
particularly , the set of diagrams @xmath392 contains diagrams with vertex corrections to the polarization loops in the ladder series fig .
[ fig : ladder ] , which contribute to the regularization - dependent coefficient @xmath393 in eq .
( greenlambda0 ) and @xmath337 in ( [ eq : rgtheta ] ) .
we observe that the first three terms in ( [ eq : beta - general ] ) , ( eq : rgtheta ) are given by diagrams with maximum number of fermionic loops .
these terms are @xmath395 and therefore are important at any value of the conductance .
it is possible to resum all the contributions of this type , as we discuss below . the above
discussed linear - log contributions to the conductance with the maximum number of fermionic loops , can be viewed as a dressing of the wavy interaction line @xmath101 in fig .
fig : diag1ordera , fig .
[ fig : diag1order]b by fermionic polarization loops .
this is shown schematically in fig .
[ fig : ladder ] , with the result of the summation denoted by @xmath396 and depicted by a double wavy line .
we show below that the result of this summation is scale independent ( without logarithmic terms ) , so that using the double wavy line in first - order contributions fig .
[ fig : diag1order]a , fig .
fig : diag1orderb will produce a single logarithmic factor , while containing all powers of @xmath101 .
, describing the combined effect of interaction and barrier , and leading to a linear - in - logarithm @xmath17 contribution to conductance .
, width=321 ] in the usual situation , the rpa summation of fig .
[ fig : ladder ] is trivial after fourier transform . in our case of chiral fermion representation
, we have left - right asymmetry of the vertices whose value in pseudo - spin space depends on the coordinate . hence we always integrate over the semi - axis only , which leads , as shown below , to an integral equation of the wiener - hopf type , instead of a simple fourier convolution .
still , the ladder equation for the dressed interaction can be written and solved rather simply .
let us denote the interaction between the points @xmath397 and @xmath145 by @xmath398 where @xmath399 is the matsubara frequency along the line .
let us define the vector @xmath400 in the following way @xmath401 then the ladder summation , fig .
[ fig : ladder ] , is expressed for @xmath402 by the integral equation : @xmath403 where we used the fact that the polarization loop in the @xmath404 representation is @xmath405 . here and below the integration over coordinates is over the interval @xmath314 , it is convergent and may be extended to @xmath227 .
later we will need the integrated quantity @xmath406 , which obeys the integral equation @xmath407 % \nonumber \\ & + & + \frac{1}{2}g^{2}\omega \int d z\;\;e^{-\omega \label{equlad}\end{aligned}\ ] ] the above equation for @xmath408 is an integral equation of wiener - hopf type , and its solution can be found as follows . we differentiate both sides of eq .
( [ equlad ] ) twice with respect to @xmath66 and find that @xmath409 .
demanding that @xmath410 we seek a solution in the form @xmath411 . substituting the latter form into ( [ equlad ] ) , we determine the constant @xmath412 and find @xmath413 now we are in a position to determine the linear - log correction to the conductance stemming from the diagrams fig .
[ fig : diag1order ] where the wavy line of interaction is replaced by the double wavy line .
the equation reads : @xmath414 where the superscript @xmath49 in @xmath415 denotes ladder summation .
taking here the limit @xmath416 we find @xmath417here we defined the renormalized interaction constant @xmath396 . we observe that @xmath418 with the luttinger parameter @xmath419 . in fact ,
the expression ( [ ladcontrib ] ) already assumes the limit @xmath420 , because the prefactor @xmath421 is obtained by adding two contributions , one shown in fig .
[ fig : diag1order]b ( @xmath422 ) and another in fig .
[ fig : diag1order]a with inverted direction of fermionic lines ( @xmath423 ) .
the importance of the limit @xmath416 in the derivation of ( ladder : result ) is further illustrated by the solution @xmath424 of the initial eq .
( [ equladmatrix ] ) rather than eq .
( equlad ) . after a long and straightforward calculation ,
similar to the one described above , we find @xmath425with @xmath426 .
the first term in ( [ lxy ] ) is the bare interaction , the second one is the result of rpa summation , which is independent of the barrier transparency @xmath213 and finite even in the bulk , at @xmath427 .
the last term explicitly contains the transparency @xmath213 and decays away from the barrier . integrating over @xmath145 we get the above eq .
( [ sol : lx ] ) , and eq . ( [ lxy ] ) shows that the dressing of the interaction constant , @xmath428 , in ( [ ladder : result ] ) is not reduced to a simple multiplicative factor , but depends on the coordinates .
finally we note that @xmath429 at @xmath20 , i.e. there are no scale independent contributions in the ladder approximation , and @xmath430 in that case .
from the solution of the wiener - hopf equation for the ladder series ( ladder : result ) we then find the @xmath1-function in ladder approximation @xmath431 inverting this equation and using the definition of @xmath4 we obtain the symmetric form @xmath432 \label{eq : ladderrg}\ ] ] invariant under the simultaneous exchange of @xmath433 and @xmath434 .
this differential equation may be solved analytically @xcite .
we recall that it is asymptotically exact in the limit @xmath435 the correction term is qualitatively different in that it vanishes quadratically in the limit @xmath436 and hence is irrelevant in this limit ( considered in the early work by kane and fisher ) .
the duality property still holds , i.e. the invariance of ( [ eq : rg - y ] ) under the simultaneous change @xmath437 and @xmath438 ( or @xmath439 in ( [ eq : rgtheta ] ) ) .
based on these observations , we expect that the fourth - order terms beyond the ladder series in the rg equation will be proportional to @xmath440 .
one should keep in mind that the correction terms here have been included only to order @xmath299 .
we now discuss a further improvement .
we may perform yet one more partial resummation by dressing interaction lines as @xmath441 , where @xmath442 the @xmath326 term in ( [ eq : rg - y ] ) results from non - ladder diagrams . therefore without double - counting we can dress the interaction constant there and write @xmath443 . then ( eq : ladderrg ) receives a correction term of the form @xmath444 \notag \\ & -&c_{3}\frac{2(1-k)}{1+k+y(1-k)}+\ldots \label{eq : rg - inv}\end{aligned}\ ] ] the term proportional to @xmath326 here is of order of @xmath101 at small @xmath101 and we omitted higher order terms . integrating eq .
( [ eq : rg - inv ] ) we obtain the following result : @xmath445 we assume the initial condition @xmath446 at @xmath447 , and @xmath448 ; here @xmath326 is given by ( [ eq : c3finite ] ) for the case @xmath355 .
evidently , the renormalization stops at @xmath449 .
in this work we have presented a fermionic formulation of the transport theory of interacting electrons in a onedimensional system with potential barrier in the linear response regime .
we considered the luttinger liquid model with interaction @xmath0 ( forward scattering involving right and left movers ) , and employed a current algebra represention , leading to a substantial simplification of perturbation theoretical calculations . using the renormalization group idea in various forms we showed that the conductance as a function of temperature ( or , at zero temperature , as a function of system length ) obeys scaling , and
therefore may be obtained by integrating a renormalization group equation .
the @xmath1-function of the latter equation has been found within a ladder approximation , which becomes exact in the limit of small or large conductance , at any interaction strength .
corrections to the ladder approximation up to and including third order in the interaction , and relevant at intermediate values of the conductance , have been calculated .
these correction terms require the solution of a fundamental problem of renormalization group theory : what is the significance of and how does one treat scale independent contributions appearing in perturbation theory ? we show that these terms have to be taken into account , as they guarantee the scaling of the conductance and can lead to an important redefinition of the @xmath1-function .
in that respect our work is of general interest in the context of the renormalization group method , beyond the particular transport problem considered here .
( [ bestapprox ] ) is one of the central results of our paper .
it is in agreement with the previous findings @xcite in the limiting cases @xmath24 , @xmath23 ( i.e. @xmath450 ) , @xmath451 , except for the fact that in these previous works the conductance tends to @xmath4 , rather than @xmath11 , in the limit of vanishing barrier strength at finite temperature . in this limit ( @xmath436 )
our result is exact for any value of @xmath4 . in the intermediate regime @xmath452
there appear corrections to our result .
we have calculated these corrections in the lowest order , which is third order in the interaction strength .
the parameter @xmath326 determines the strength of these corrections .
we have shown that @xmath326 is nonuniversal in the sense that it depends on the physical nature of the ultraviolet cutoff , e.g. the temperature cutoff or the length cutoff .
we are convinced that the scaling functions of the temperature dependent conductance , @xmath453 , in the limit of infinite sample length @xmath49 and the length dependent conductance , @xmath454 , at @xmath455 are slightly different .
let us discuss the role of the factor @xmath326 in ( [ bestapprox ] ) which is new as compared to previous studies @xcite .
it is clear that @xmath456 in ( [ eq : rgtheta ] ) defines the renormalization of the conductance in the intermediate region , @xmath25 , and thus determines the coefficient relating high - temperature and low - temperature asymptotes .
we may ask the following question : what is the coefficient @xmath412 in the asymptotic expression @xmath457 ( @xmath458 ) if we fix the overall temperature scale at hight @xmath7 as @xmath459 ? from eq .
( [ bestapprox ] ) we have @xmath460 at this point it is appropriate to compare our findings to the exact results obtained within the conformal field theory ( cft ) approach to the bosonized version of the problem , sec .
[ sec : bsg ] . in these earlier works
the @xmath1-function of the rg equation was not discussed .
however results equivalent to those by fendley et al .
fendley1995,fendley1995a are presented in a recent study by lukyanov and werner @xcite , where particularly the @xmath1-function was obtained in a form equivalent to our ( [ bestapprox ] ) . according to lukyanov ( private communication ) , the coefficient @xmath461 , which deviates from our value @xmath462 and we use both values for comparison below .
unfortunately , one rarely , if ever , discusses the scheme of regularization used in obtaining the cft exact solutions .
we have to conclude that the regularization used by @xcite is different from ours .
the choice of cutoff scheme in our work is not based on mathematical convenience , but rather it is following naturally from perturbation theory . therefore , as a theoretical result to be applied to explain experimental data , our ( [ bestapprox ] ) has advantages over the cft results .
we saw above that passing from the backscattering amplitude in the hamiltonian to the conductance ( i.e. @xmath63-matrix ) may require ultraviolet regularization , i.e. certain prescriptions of dealing with short - distance singular quantities .
our observation is supported by the study of the free ( @xmath463 ) bsg theory , @xcite where the authors arrive at a current algebra formulation similar to our treatment above .
they notice that the description of the strong coupling limit @xmath464 corresponds to taking the quantity @xmath465 , ( see eq.(2.23 ) there ) , which is related to our @xmath466 and hence to the conductance .
they also notice that the connection between @xmath467 and @xmath468 begins to depend on the type of regularization chosen in the third order of @xmath469 .
on the other hand , given that the cft exact solution in the interacting case @xmath470 is expressed in terms of the scaling variable @xmath471 , we see that the implied equation @xmath472 corresponds in form exactly to our ( [ bestapprox ] )
. it would be thus desirable to understand the particular regularization used in the cft solution in more detail . .
the results of ladder summation , ( [ bestapprox ] ) with @xmath473 , are shown by dashed - dotted line ; the result of eq .
( [ bestapprox ] ) , with @xmath474 given by ( [ eq : rgtheta ] ) is shown by solid line .
the result available from cft ( multiplied by factor 2 ) is shown by pluses .
kane1992,kane1992a , weiss1995 , together with our fit by ( bestapprox ) with @xmath475 shown as dashed line .
( b ) the same plot in log - linear scale.,title="fig : " ] + .
the results of ladder summation , ( [ bestapprox ] ) with @xmath473 , are shown by dashed - dotted line ; the result of eq .
( [ bestapprox ] ) , with @xmath474 given by ( [ eq : rgtheta ] ) is shown by solid line .
the result available from cft ( multiplied by factor 2 ) is shown by pluses .
kane1992,kane1992a , weiss1995 , together with our fit by ( bestapprox ) with @xmath475 shown as dashed line .
( b ) the same plot in log - linear scale.,title="fig : " ] let us now illustrate the details of the behavior of @xmath453 in the example of the well - known case @xmath95 . both high - temperature and low - temperature asymptotes of @xmath18 are interesting from the theoretical viewpoint , but one can expect the experimental variation of the conductance to be most visible at lower @xmath7 , when @xmath476 .
it is therefore useful to consider the variation of the conductance for fixed @xmath4 and different values of @xmath326 .
we take @xmath95 and and fix the low @xmath7 behavior in the form @xmath477 , with @xmath478 and @xmath479 . we then plot @xmath480 , obtained from ( [ bestapprox ] ) for several values of @xmath481 in fig .
[ fig : conduc ] , together with the exact solution , known from @xcite @xmath482where @xmath483 the derivative of digamma function . for @xmath95 , and
the implied cft value @xmath461 we can invert ( [ bestapprox ] ) and write @xmath484 the fig . [ fig : conduc ] shows that the cft solution lies between the curve corresponding to pure ladder summation , @xmath485 , and the one with the above @xmath486 .
the proposed value @xmath461 fits the cft solution rather precisely .
this tells us that the approximation leading to ( [ bestapprox ] ) works rather well at the interaction strength @xmath95
( @xmath487 ) , provided the coefficient @xmath326 appropriate for the regularization scheme used in the cft solution is taken .
in fact , we show in the appendix [ sec : cft ] , that the overall agreement criterion using the coefficient @xmath412 , eq . ( [ eq : matching ] ) , is about 1 % in this case . for a further case reported ( @xmath97 , @xmath488 ) @xcite
the agreement is worse , about 10 % , which might be expected in this more strongly interacting situation .
finally , we emphasize again that in any comparison with experiment the correct regularization scheme is determined by the details of the corresponding experimental setup .
indications of the possible inadequacy of the regularization scheme used in the cft solutions exist .
for instance , we tend to interpret the systematic deviation of the experimental data on the conductance between the quantum hall edge states from the cft prediction at low @xmath7 in @xcite not as a shortcoming of the experiment , but rather as a consequence of choosing an inappropriate regularization . the correct regularization might lead to a different value of @xmath326 in ( bestapprox ) , providing better agreement with experiment .
we are grateful to i.v .
gornyi , d.g .
polyakov , p.m. ostrovsky , k.a.matveev , d.a .
bagrets , o.m .
yevtushenko , m.n .
kiselev , a.m.finkelstein , a.a .
nersesyan , l.i .
glazman and n. andrei for various useful discussions .
the continuum hamiltonian ( [ impham ] ) corresponds to a lattice model @xmath489 at half - filling ( @xmath490 ) and with potential present at two adjacent sites . in eq .
( [ impham ] ) we let @xmath491 . here
@xmath492 are dimensionless quantities and @xmath493 is the range of the corresponding regularization of the @xmath494-function ; at the end the limit @xmath495 will be taken .
combining the two chiral fermions into a spinor quantity @xmath496 we can write the equation of motion as @xmath497with real and imaginary parts @xmath498 .
the formal solution of ( [ eq - motion ] ) is @xmath499,\end{aligned}\]]where @xmath500 stands for the @xmath66-ordering operator . in the long wavelength limit , @xmath501
, we obtain @xmath502,\quad x<0 , \label{eq : deft0 } \\ & = & \exp [ i\omega v_{f}^{-1}\sigma _ { 3}x]\mathcal{t}_{0}\exp [ -i\omega v_{f}^{-1}\sigma _ { 3}a],\quad x>0 , \notag\end{aligned}\]]with @xmath503 depending on @xmath59 .
we assume first that the regularized @xmath494-functions in the definitons of @xmath59 are identical , which means @xmath504 . in this case
@xmath505with @xmath506 and @xmath507 .
this transfer matrix simplifies in two important cases : i ) point - like impurity , when @xmath508 and ii ) purely backward scattering impurity , @xmath509 , @xmath510 .
we have @xmath511with @xmath512 .
let us also consider two further limiting cases , when the range of the forward scattering potential @xmath513 is much longer ( shorter ) than the range of the backward scattering potential @xmath514 , i.e. @xmath515 ( @xmath516 ) .
in these two cases we get @xmath517 for @xmath518 and @xmath519 for @xmath516 . by construction ,
the determinant of the transfer matrix is unity for arbitrary @xmath59 .
the elements of the scattering matrix for the incident waves @xmath520 and @xmath521 at @xmath522 and @xmath69 , respectively , are defined by the equation @xmath523hence the scattering matrix is determined by the elements of the transfer - matrix @xmath524 as @xmath525 in the above two cases with @xmath504 we have @xmath526 whereas for model potentials of different range we obtain @xmath527 for @xmath515 and @xmath528for @xmath516 .
we see that if the forward scattering @xmath83 has wider range , than @xmath56 , then eq . ( [ smat@a1>a2 ] ) differs from the second eq .
( smat@u1=u2 ) only by the overall phase which is unimportant in physical observables . at the same time , if the model regularization of @xmath83 is narrower than @xmath56 , the resulting eq .
( [ smat@a1<a2 ] ) closely resembles the @xmath63-matrix in the double - barrier situation . @xcite expanding the reflection coefficient in powers of @xmath529 and using ( eq : transfer - b ) , ( [ smat@a1>a2 ] ) , ( [ smat@a1<a2 ] ) we have @xmath530which shows that the forward scattering amplitude @xmath83 enters the reflection coefficient in the third order , i.e. beyond the born approximation
. moreover the contribution of @xmath83 to the @xmath63-matrix depends also on the details of the microscopic hamiltonian and the regularization of the model @xmath494-function potentials .
this complication happens at the step ( [ eigenstate ] ) ; however , once the transfer matrix @xmath531 in ( [ eq : deft0 ] ) is known , the connection to the scattering state basis is straightforward . returning to ( [ scat - states ] ) , ( [ chiralscatstates ] )
, we notice that @xmath532 obeys the equation of motion for right movers , and the spinor @xmath533 is an eigenstate ( [ eigenstate ] ) of ( [ eq - motion ] ) with the above property ( defsmat ) .
we thus clarified the scattering states representation in the framework of the chiral hamiltonian ( [ genham ] ) . in the bosonization formulation , ( [ bosonham ] ) , the assumption is made that the forward scattering @xmath513 can be completely removed from the hamiltonian .
this statement is not obvious , in general .
consider the redefinition @xmath534 , which eliminates the term with @xmath83 from eq .
( [ bosonham ] ) , where the regularized sign function @xmath535 is used .
we have the backward scattering in the form @xmath536for the above cases of regularization with @xmath515 and @xmath537 , respectively .
we consider a transformation of the operators @xmath538 @xmath539with @xmath540 in our case we have @xmath541 and we may denote the direction of @xmath157 as `` 1 '' , i.e. @xmath542
. then we have the following set of equalities from the kac - moody relations ( kacmoody ) @xmath543 & = & \frac{i}{4\pi } \delta ( x - y ) \notag \\ { } [ j_{1}(y),i\int_{-\infty } ^{\infty } dx\,b_{1}(x)\theta _ { 1}(x ) ] & = & -\frac{1% } { 4\pi } b_{1}(y ) \\
j_{1}(y)u & = & u(j_{1}(y)-\frac{1}{4\pi } b_{1}(y ) ) \notag\end{aligned}\]]and for @xmath544 one has @xmath545 & = & j^{+}(x)\delta ( x - y ) \notag \\ { } [ j^{+}(x),\theta _ { 1}(y ) ] & = & j^{+}(x)\theta ( x - y ) \\ { } [ j^{+}(x),i\int_{-\infty } ^{\infty } dy\,b_{1}(y)\theta _ { 1}(y ) ] & = & ij^{+}(x)\int_{-\infty } ^{x}dy\,b_{1}(y ) \notag\end{aligned}\]]so that the relations between the operators are @xmath546the transformation @xmath547 shifts the value of @xmath548 by a @xmath549number , so that strictly speaking , the operators @xmath163 do not obey the same kac - moody algebra in the region where @xmath550 .
it is clear , though that this might affect only the physically non - observable component of the fermionic density and is therefore not important .
in this section we focus on the time evolution of the observables @xmath551 , @xmath552 , eqs .
( [ def : density ] ) , ( [ def : current ] ) , using the relation @xmath553 $ ] .
it is more convenient to use the representation ( [ fictmagnfield ] ) , with @xmath554 . in terms of operators @xmath163
one has @xmath555using ( [ kacmoody ] ) and formulas of appendix [ sec : appa ] , it can be easily shown that we have @xmath556 in the leads , @xmath39 , whereas in the interacting region @xmath557 we obtain @xmath558where we let @xmath559 . since @xmath560 is the _ observable _
density , the relation ( [ eq : motion ] ) looks deceptively close to the desired answer .
however , in the region of the barrier @xmath561 ( with @xmath562 ) we have @xmath563and the @xmath564 component comes into play .
( in other words , for the partially reflecting barrier , the observable of our problem , @xmath565 , includes the _ eigenmode _ operator @xmath566 . )
therefore it is necessary to consider also the time evolution of operator @xmath564 , which reads @xmath567at @xmath557 and @xmath568 , at @xmath561 .
the four - fermion object @xmath569 is not reduced to @xmath570 and therefore we do not obtain a closure of the equations of motion .
our situation is somewhat similar to the well - known heisenberg model of spins with pairwise exchange interaction . due to the non - commutative character of spin operators , the attempt to write the exact time evolution of spin leads to an infinite series of coupled equations , including ever increasing numbers of spins .
the approximate solutions are obtained by truncating this series at some step , according to a certain criterion , and discarding higher terms as inessential .
@xcite in magnetism , these criteria might be ( i ) low temperatures in the magnetically ordered phase , @xmath571 , ( ii ) large value of spin @xmath63 or ( iii ) wide range of interaction . in our case
, we choose the criterion of relevancy of operators , i.e. their importance in the logarithmically divergent theory .
we now briefly discuss the dynamics of @xmath572 .
the compound operator @xmath573 consists of four fermion operators and may be decomposed into the normally ordered part and a part , representing internal contractions . to clarify the notation we write @xmath574 , @xmath575
, then we have @xmath576contracting here , we get @xmath577 with ( cf .
( [ preciseope ] ) ) @xmath578which does not coincide with @xmath579 we may write @xmath580and , dropping the less relevant higher derivatives , obtain from ( eq : motion2 ) @xmath581which means that the most relevant part of the operator @xmath582 has the form @xmath583 regarding the normally ordered part @xmath584 , its time evolution is given by @xmath585i.e .
described by new operators , not reduced to simple spatial derivatives of @xmath584 .
such derivative objects ( i ) obey an infinite set of coupled equations and ( ii ) possess formal scaling dimension greater than two , and hence are irrelevant in the rg sense .
our strategy of such truncation ( [ approxo4aso2 ] ) is successful only in part , as we explain in the next appendix [ sec : appc2 ] .
taking a fourier transform in time @xmath35 , and introducing the vector @xmath586\ ] ] the above truncated set of equations can be written as @xmath587 with @xmath588 and the fermionic correlation function at finite temperature @xmath589 the solution to ( [ equ : mot_trunc ] ) is given by the @xmath590ordered exponent @xmath591 similarly to ( [ eigenstate ] ) , but now with transfer - matrix @xmath592 for densities .
the transfer - matrix in the region of the barrier @xmath561 is already known and given by @xmath593 the overall transfer - matrix over the interaction region is @xmath594 finally we observe that the definition of @xmath595 implies that the transfer matrix connecting opposite points should satisfy the boundary condition : @xmath596 @xmath597 and we should choose a solution , by demanding that the scattered component , @xmath598 , is absent in the incoming wave , i.e. @xmath599 .
we consider here only the technically feasible limit , @xmath600 . in this case @xmath601 in the leads , @xmath602 . in the interacting region @xmath603 a similar contribution on the negative semiaxis , @xmath604 ,
is obtained from ( [ transfer - g - static ] ) by the change @xmath605 .
overall we have @xmath606 solving eq .
( [ bound - cond ] ) together with the above condition @xmath607 , we find @xmath608 which is the desired solution .
let us briefly discuss it .
we observe that the d.c .
current @xmath609 is independent of @xmath66 , as it should be .
this property follows from the form of matrix ( transfer - g - static ) and condition ( [ bound - cond ] ) .
the relation of the current to the voltage bias defines the conductance of the system . in our definitions ,
the voltage bias is proportional to the difference in number of incoming left- and right - going electrons , which is @xmath610 , so that the conductance is @xmath611 which coincides with the above result ( [ solurg1st ] ) . at first glance , the result ( [ equmo - solu ] )
should thus be viewed as satisfactory .
however there are details , involved in its derivation , which spoil the significance of this approach .
first we notice that , by keeping less relevant gradient term in the above relation , ( [ approxo4aso2 ] ) , we get the appearance of @xmath612 terms in the definition of @xmath358 , eq .
( def : lambdaeqmo ) , and also in the exponents , @xmath613 , in ( transfer - g - static ) ( [ equmo - solu ] ) .
further , trying a different approximation instead of ( [ approxo4aso2 ] ) , e.g. @xmath614 , would not produce the above renormalized value of conductance .
therefore we conclude that using the equations of motion method and persisting with the current operator algebra leads to ambiguities , connected with the non - local character of the interaction .
proceeding as described in sec . [
sec : corrconda ] , we find corrections to the conductance , or to @xmath213 in ( [ def : y ] ) . in the first order of @xmath101 the correction from the diagrams of the type
@xmath234 has the form @xmath615 in the second order of @xmath101 we have two sets of diagrams for corrections to the conductance .
the diagrams containing two fermionic loops lead to the following expression : @xmath616where @xmath617 are two points of fermionic interaction .
all diagrams consisting of only one loop , @xmath235 in above notation , produce the correction @xmath618 we should mention that individual diagrams in the set @xmath235 ( and higher orders ) may contain singularities of the form @xmath619 etc . however these singularities cancel each other in the resulting expressions .
for example , one finds two particular contributions @xmath620 and @xmath621 whose sum leads to the above `` regular '' form , @xmath622 , in ( [ corr(6 ) ] ) . in the third order
, we have to analyze the following types of the diagrams : @xmath240 , @xmath239 , @xmath238 , @xmath237 .
we assume the ordered sequence , @xmath623 , in all integrals below . performing rather long computer calculations ( the stable routine in _
requires about ten hours of computation time for dual - core 3 ghz processor ) , we obtain @xmath624 \notag \\ & = & -g^3(1-y^2)(1+y^2)\frac { \lambda_0 } 4 , \label{corr(4,2,2)}\end{aligned}\]]@xmath625 \notag \\ & = & -g^3(1-y^2)^2\frac 14 ( \lambda_0 ^ 2 + 2\lambda_0(1-\ln2 ) ) , \label{corr(4,4)}\end{aligned}\]]@xmath626 \notag \\ & = & g^3(1-y^2)y^2 \lambda_0(\lambda_0 -2\ln 2 ) , \label{corr(6,2)}\end{aligned}\]]@xmath627 \label{corr(8 ) } \\ & = & g^3(1-y^2)\left[\frac{1 - 3y^2}3 \lambda_0 ^ 3 + ( 1-y^2)\frac{\pi^2}{12}% \lambda_0 \right ] .
\notag\end{aligned}\ ] ] in the final expressions ( [ corr(4,2,2 ) ] ) , ( [ corr(4,4 ) ] ) , ( corr(8 ) ) we omitted finite parts , @xmath628 , which are unimportant in the order @xmath391 .
these expressions lead to eq .
( [ eq : cory ] ) above .
in case of finite temperature we proceed in the same way as for @xmath12 , only with the integration replaced by a summation over matsubara frequencies . introducing the scaling variable @xmath14
according to ( [ def : lambda ] ) we have for @xmath629 @xmath630where @xmath617 are two points of fermionic interaction , and @xmath631 . in the last equality in the right - hand side of eq .
( corr(4,2 ) ) , we shall neglect the terms @xmath632 . instead of @xmath318 in the expression ( [ corr(6 ) ] ) for @xmath633 we now have the following integral @xmath634 \notag \\ & \rightarrow & \lambda ^{2}-\frac{\pi
^{2}}{24},\quad t\gg v_{f}/l \notag\end{aligned}\]]with @xmath635 . the integration limits in ( tempcorr(6 ) ) are @xmath636 and @xmath637 . here
@xmath638=l_{2}(-\tau _ { 0}\tau _ { l})-(l_{2}(-\tau _ { l}^{2})+l_{2}(-\tau _ { 0}^{2}))/2 $ ] and @xmath639 is the dilogarithm function .
we have @xmath638=0 $ ] in the limit @xmath640 .
in contrast to the @xmath12 case , the expressions now become extremely cumbersome in the third order of @xmath101 .
the summation over matsubara frequencies lead to expressions involving sums and products of exponents @xmath641 .
a general criterion for the correctness of intermediate expressions is the property a change of sign of each individual diagram upon performing the reflection transformation @xmath642 .
an additional check of the validity of calculation is the observation that we should get zero correction to @xmath643 in the absence of the barrier , @xmath644 , and to @xmath645 for the fully reflecting barrier , @xmath646 , for arbitrary @xmath7 .
this is not a trivial statement , because each diagram in third order contains a prefactor , either @xmath647 , or @xmath648 or @xmath649 .
we verified that the algebraic expressions canceled each other in this case .
the actual expressions are not shown here , and we describe our method of analysis below .
let us consider an expression of the form of a triple integral , relevant to our discussion in sec .
[ sec : corrcond ] @xmath650.\ ] ] we assume that @xmath651 at @xmath652 and wish to determine the coefficient @xmath653 in this asymptotic behavior . we have
@xmath654\]]here taking the limit in the integrand may lead to incorrect results .
we have two possibilities for the behavior of the quantity @xmath655=\int_{z_{2}}^{l}dz_{3}\,a\bar{f}[a , z_{2},z_{3}]$ ] , for small @xmath13 , namely @xmath656\sim a/(z_{2}+a)^{2}$ ] and @xmath657\sim 1 $ ] .
the first type of contribution , @xmath658 , is always important and survives in the limit of @xmath8 . recalling that @xmath659 $ ] is exponentially suppressed at @xmath660
, we see that the case @xmath655\sim 1 $ ] contributes to @xmath653 only at finite temperatures , @xmath661 ; typically , we find @xmath656\sim ( \xi \cosh ( 2z_{2}/\xi ) ) ^{-1}$ ] .
therefore the recipe for the determination of @xmath653 is first to determine the limiting form of @xmath662 , taking @xmath663 ; in this case the expressions are drastically simplified .
this will determine @xmath653 at @xmath8 .
to this term we should add the contribution @xmath664 $ ] , integrated over @xmath665 in the interval @xmath666 ; the sum of these two contributions gives the value of @xmath653 at finite temperatures , @xmath667 .
in a very general sense the @xmath1-function of the rg - equation is non - universal : it depends on the precise definition of the scaling quantity @xmath101 .
let the rg equation read @xmath668and consider a change of variable @xmath669 . with the same accuracy we have @xmath670which shows that only the two first two coefficients @xmath671 and @xmath672 are invariant .
since @xmath673 is associated with the three - loop contribution , one may speak about a non - universality of the@xmath674-function beyond two - loop order .
let us elucidate the origin of the eq .
( [ nu : eq1 ] ) , and compare it with the equation obtained in the callan - symanzik approach . in the gell - mann
low approach we perform our calculations with the running coupling constant @xmath675 and add counterterms to the hamiltonian in order to achieve the finite value of the bare constant @xmath676 .
one can show that the above value of @xmath677 is obtained from the expression @xmath678if we make the above change @xmath679 in the right - hand side of ( [ nu : eq2 ] ) and use the same recipe for @xmath680 , we return to ( [ nu : eq1 ] ) . in the cs approach
we fix the bare value @xmath676 and calculate the renormalized quantity @xmath681 . inverting the equation @xmath682 and using the same recipe we find @xmath683 .
one can check that @xmath684assume now that we have changed the starting value @xmath685 , according to above prescription .
evidently , the expansion for @xmath686 will be different from ( [ nu : eq3 ] ) , as well as the inverse function @xmath687 will not coincide with ( [ nu : eq2 ] ) .
one can verify however that the @xmath1-function , @xmath688 , is given by the same eq .
( [ nu : eq0 ] ) and not by eq .
( [ nu : eq1 ] ) .
this fact becomes rather obvious , when we notice that only the left - hand side of ( [ nu : eq2 ] ) is changed and it corresponds to a change in the boundary condition for @xmath689 rather than to a change in the differential equation for it .
consider the differential equation @xmath690\psi ( y)=0\]]such that @xmath691 and @xmath692 . here
@xmath693and @xmath15 . for given @xmath694 one finds a solution @xmath695 characterized by a unique value @xmath696 .
then , according to lukyanov , lukyanov2007 the conductance can be determined as @xmath697 we now fix the overall temperature scale @xmath698 by the high-@xmath7 behavior , @xmath699 , and ask what is the coefficient @xmath412 in the asymptotic low temperature expression @xmath457 . to answer this question , we slightly rewrite the differential equation . introducing
a new variable @xmath700 we have @xmath701\psi ( z)=0 \label{eq : difeqmod}\]]at @xmath702 ( i.e. @xmath703 ) the solution is a modified bessel function @xmath704 . at infinitesimal @xmath694
we seek a solution in perturbation theory as @xmath705 .
after some calculation we find the conductance @xmath706 with @xmath707 given by @xmath708\int_{0}^{\infty } { } _ { 2}f_{1}(k , k,1;-\kappa ) % \frac{d\kappa } { 1+\kappa } \notag \\ & = & { \gamma
^{4}[k]}/{\gamma \lbrack 2k]}\;.\end{aligned}\]]in the opposite limit , @xmath709 ( @xmath12 ) , we choose a variable @xmath710 and arrive at an equation @xmath711\psi ( z)=0,\]]with @xmath712 .
the solution is found similarly to ( [ eq : difeqmod ] ) and we get @xmath713 . comparing the two solutions we obtain the prefactor @xmath714 in the particular case of @xmath95 we have @xmath715 , in accordance with ref .
[ ] . for @xmath97
we get @xmath716 , a value slightly different from @xmath717 reported in @xcite , where it was obtained by numerical solution of an integral equation .
if we take @xmath461 in ( [ eq : matching ] ) , then we would obtain @xmath718 ( @xmath719 ) for the cases of @xmath95 ( @xmath97 ) , in good agreement with the above cft values .
it should be noted , however , that apart from this agreement in the matching coefficient @xmath412 , the theory in lukyanov2007 provides the value of unity for @xmath18 in the clean wire , whereas the previous works @xcite gave @xmath720 in that case . | we calculate the linear response conductance of electrons in a luttinger liquid with arbitrary interaction @xmath0 , and subject to a potential barrier of arbitrary strength , as a function of temperature .
we map the hamiltonian in the basis of scattering states into an effective low energy hamiltonian in current algebra form .
first the renormalization group ( rg ) equation for weak interaction is derived in the current operator language both using the operator product expansion and the equation of motion method . to access the strong coupling regime , two methods of deducing the rg equation from perturbation theory , based on the scaling hypothesis and on the callan - symanzik formulation ,
are discussed .
the important role of scale independent terms is emphasized .
the latter depend on the regulaization scheme used ( length versus temperature cutoff ) .
analyzing the perturbation theory in the fermionic representation , the diagrams contributing to the renormalization group @xmath1-function are identified . a universal part of the @xmath1-function is given by a ladder series and summed to all orders in @xmath0 .
first non - universal corrections beyond the ladder series are discussed and are shown to differ from the exact solutions obtained within conformal field theory which use a different regularization scheme .
the rg equation for the temperature dependent conductance is solved analytically .
our result agrees with known limiting cases . |
recent advances in fabrication technology have made it possible to realize superconductor ferromagnet ( s / f ) hybrid structures with a controlled arrangement of the ferromagnetic layers / elements .
these flux coupled and exchange coupled s / f hybrids@xcite are of fundamental interest for investigations of the nontrivial interaction between superconductivity and a nonuniform distribution of a local magnetic field ( or magnetization ) .
furthermore , s / f hybrids seem to be potential candidates for the development of tunable elements of superconducting electronics.@xcite in this paper we focus only on the planar s / f structures , consisting of a low-@xmath8 superconducting film and a ferromagnetic layer with a domain structure with a dominant magnetostatic interaction between superconducting and ferromagnetic films .
@xcite the nonuniform component of the magnetic field , induced by a ferromagnet , can modify the conditions for the appearance of superconductivity in thin superconducting films due to the effect of field compensation . the formation of localized superconductivity in the areas of compensated magnetic field@xcite results in an exotic dependence of the superconducting critical temperature @xmath8 on the external magnetic field @xmath5 , applied perpendicular to the thin film plane .
this phase transition line @xmath8 vs. @xmath5 for planar s / f hybrids becomes non - monotonous @xcite and thus , it differs significantly from the standard linear dependence of the upper critical field @xmath3 on temperature @xmath6 , which can be written as @xmath9 here @xmath10 is the critical temperature of the superconducting transition at zero magnetic field , @xmath11 and @xmath12 are upper critical field and coherence length at @xmath13 , respectively , and is the magnetic flux quantum .
such dependence given by eq .
( [ hc2 ] ) is inherent for plain superconducting films in a uniform magnetic field @xmath5 and shown by the dashed line in fig .
[ fig - pbs ] .
considering qualitatively the effect of an inhomogeneous magnetic field , which varies periodically from @xmath14 ( above positive magnetic domains ) to @xmath15 ( above negative domains ) and remains constant inside the domains , one can expect two different phase transition lines @xmath16 these two different transition lines correspond to the formation of superconductivity in the areas where the perpendicular @xmath17component of the nonuniform magnetic field is positive , eq .
( [ biased - hc2a ] ) , or negative , eq . ( [ biased - hc2b ] ) .
the phase diagram @xmath4 , composed according to eqs .
( [ biased - hc2a])([biased - hc2b ] ) , is shown in fig .
[ fig - pbs ] .
an inhomogeneous superconducting state trapped only within the areas above the domains of the opposite polarity with respect to the sign of @xmath5 , is commonly referred to as reverse - domain superconductivity ( rds).@xcite in order to guarantee the formation of such rds exclusively above either positive domains ( at @xmath18 ) or above negative domains ( at @xmath19 ) , one should satisfy @xmath20 ( i.e. , at high temperatures or / and large @xmath2 values ) .
such separated regions of rds above the domains of different signs were observed experimentally@xcite for pb / bafe@xmath0o@xmath1 , nb / bafe@xmath0o@xmath1 and al / bafe@xmath0o@xmath1 hybrid structures . upon decreasing @xmath6 and/or @xmath2 ,
inhomogeneous superconductivity above magnetic domains of both polarities ( i.e. parallel and antiparallel ) can coexist ( cf .
[ fig - pbs ] ) , since both criteria for the formation of inhomogeneous superconductivity above both magnetic domains , @xmath21 and @xmath22 , can be fulfilled simultaneously provided @xmath23 the threshold temperature @xmath24 of the crossover from simple rds to a complex state consisting of rds in the compensated regions and parallel domain superconductivity ( pds ) in the regions with enhanced magnetic field corresponds to the intersection point of the dependencies @xmath25 and @xmath26 at and can be estimated as @xmath27 .
such an inhomogeneous superconducting state , potentially observed in the @xmath5 range described by eq .
( [ h - range2 ] ) and characterized by a development of superconductivity above magnetic domains of both polarities , can be also called complete superconductivity ( cs ) . )
temperature @xmath28 " in the presence of a nonuniform magnetic field ( @xmath2 is the amplitude of the @xmath17component of the stray field ) .
the dashed line is plotted according to eq .
( [ hc2 ] ) .
the filled ( shaded ) area corresponds to inhomogeneous superconductivity above positive and negative magnetic domains , respectively , see eqs .
( [ biased - hc2a])([biased - hc2b ] ) .
here we use the notations : rds@xmath29 reverse - domain superconductivity localized above positive ( @xmath30 ) domains at @xmath18 and above negative ( @xmath31 ) domains at @xmath19 ; pds@xmath29 parallel - domain superconductivity localized above positive ( @xmath30 ) domains at @xmath19 and above negative ( @xmath31 ) domains at @xmath18 .
, width=321 ] for superconducting samples of finite lateral dimensions one can expect the appearance of surface superconductivity,@xcite i.e. superconductivity localized near the sample edges even in the presence of a nonuniform magnetic field . in the first approximation , the phase transition line for such anticipated edge - assisted ( ea ) superconductivity can be described by the shifted @xmath32 dependencies @xmath33 where the signs @xmath34 correspond to edge - assisted superconductivity above positive / negative magnetic domains , respectively .
this means that superconductivity near the sample s edges will survive until the local field exceeds the critical field of surface superconductivity @xmath35 .
furthermore , the presence of the domain walls stimulates the formation of domain - wall superconductivity ( dws ) for moderate fields , @xmath36.@xcite it has been shown that for thin superconducting films ( in the @xmath37 plane ) in a perpendicular magnetic field @xmath38 with a step - like component @xmath39 induced by a domain wall , nucleation of the superconducting order parameter along the domain wall ( at @xmath40 ) becomes possible below the phase transition line@xcite @xmath41 thus , the set of possible nonuniform superconducting solutions in flux
coupled s / f hybrids has to include the following states : domain - wall superconductivity ( dws ) , bulk " rds and pds above either positive or negative domains , edge - assisted rds and pds above either positive or negative domains , and cs above the domains of both polarities . in this paper
we present an experimental study of the temperature and field induced crossover between the different regimes of bulk and localized superconductivity in s / f hybrid structures , consisting of a thin superconducting pb film on top of a bulk ferromagnetic bafe@xmath0o@xmath1 single crystal with a well defined stripe - like domain structure . in order to exclude percolation effects and electrical shunting arising from different superconducting states , we prepared the hybrid s / f structure such that the domain walls are oriented _ across _ the superconducting microbridge . as a result , the current density is distributed over the entire cross - section of the microbridge , what allows us to detect variations of the voltage drop associated with the appearance / destruction of inhomogeneous superconductivity of various types . vs. @xmath5 ,
obtained with a vibrating sample magnetometer at @xmath42 k. the shaded area indicates the range of @xmath5 in our experiment.,width=264 ]
for the creation of a static nonuniform magnetic field with a well - defined domain structure , we used bulk ferromagnetic crystals bafe@xmath0o@xmath1 ( bfo ) . when cut along the proper crystallographic direction ,
these bfo crystals exhibit a stripe - type domain structure with dominant in - plane magnetization and a relatively small out - of - plane component of magnetization.@xcite measurements with a vibrating sample magnetometer revealed that at low temperatures the magnetization of the used crystal depends almost linearly on the applied perpendicular magnetic field , and that it saturates at @xmath43 koe ( see fig .
[ fig - vsm - magnetometry ] ) .
this means that external magnetic field @xmath44 koe , which corresponds to the range of the @xmath5-sweeps in our measurements , can only be of minor influence on the domain structure , since the variation of magnetization of the substrate is expected to be not more than 9% of the saturated magnetization .
component of the nonuniform magnetic field @xmath45 measured near a domain wall by a scanning hall probe microscope at the distance 400 nm above the ferromagnetic crystal at the external magnetic field @xmath46 ( a ) and @xmath47 koe ( b ) at @xmath48 k. the scanning area is .
( c ) one - dimensional profile of the nonuniform magnetic field @xmath49 along the direction perpendicular to two domain walls , measured by a scanning hall probe microscope for the same conditions : @xmath46 ( red circles ) and @xmath47 koe ( blue squares ) . , title="fig:",height=145 ] component of the nonuniform magnetic field @xmath45 measured near a domain wall by a scanning hall probe microscope at the distance 400 nm above the ferromagnetic crystal at the external magnetic field @xmath46 ( a ) and @xmath47 koe ( b ) at @xmath48 k.
the scanning area is .
( c ) one - dimensional profile of the nonuniform magnetic field @xmath49 along the direction perpendicular to two domain walls , measured by a scanning hall probe microscope for the same conditions : @xmath46 ( red circles ) and @xmath47 koe ( blue squares ) . , title="fig:",height=145 ] component of the nonuniform magnetic field @xmath45 measured near a domain wall by a scanning hall probe microscope at the distance 400 nm above the ferromagnetic crystal at the external magnetic field @xmath46 ( a ) and @xmath47 koe ( b ) at @xmath48 k. the scanning area is .
( c ) one - dimensional profile of the nonuniform magnetic field @xmath49 along the direction perpendicular to two domain walls , measured by a scanning hall probe microscope for the same conditions : @xmath46 ( red circles ) and @xmath47 koe ( blue squares ) .
, title="fig:",width=283 ] the spatial two - dimensional ( 2d ) distribution of the perpendicular @xmath17component of the magnetic field @xmath50 , induced by the laminar domain structure , was imaged with a scanning hall probe microscope@xcite ( fig .
[ fig - shpm - magnetometry ] ) . by analyzing the 2d patterns of @xmath51 , which corresponds to the difference between the locally measured field @xmath52 of the crystals and the external magnetic field @xmath5
[ panels ( a)(b ) ] , we come to the following conclusions : \(i ) the domain walls remain rectilinear even in the presence of an external field ; \(ii ) the effect of the external field is limited mainly to a small displacement of the domain walls as @xmath5 varies , leading to a broadening of the positive magnetic domains at @xmath19 at the expense of the negative magnetic domains , and vice versa . the 1d profile of the stray field @xmath50 along a line perpendicular to the domain walls is shown in fig .
[ fig - shpm - magnetometry](c ) .
we find that an external field of the order of 1 koe shifts the points @xmath53 at maximum 3@xmath54 m , which is much less than the equilibrium domain width of 30@xmath54 m , without substantial changes in both the shape of the domain wall and the amplitude of the built - in magnetic field .
this allows us to consider the field pattern as almost independent on @xmath5 .
_ sample preparation .
_ after polishing the cut - surfaces of the bfo crystals , we prepared lithographically an array of metallic au markers ( @xmath55 m in size ) on top of the ferromagnetic template .
the location of the domain walls with respect to the periodically positioned au markers was determined with a magnetic force microscope ( mfm ) at room temperature . a thin insulating ge layer ( 4 nm thick ) was evaporated in order to prevent exchange interaction and proximity effect between the superconducting and ferromagnetic layers . finally , two pb bridges oriented _ across _ the domain walls were fabricated by means of e - beam lithography , molecular beam epitaxy and lift - off technique in a single run on the same substrate .
these superconducting bridges have the same width ( 30@xmath56 m ) and thickness ( 40 nm ) and differ only by their lengths : 100 @xmath57 m for the short bridge and 700 @xmath57 m for the long bridge , resulting in different numbers of domain walls ( 4 and 24 , respectively ) in the narrow part of the bridges .
a combination of an optical and an mfm image of the short pb bridge is presented in fig .
[ fig - system ] . _ magnetoresistive curves @xmath58 .
_ measurements of the dc electrical resistance @xmath59 of both the short and the long superconducting pb bridges as a function of temperature @xmath6 , @xmath5 ( applied perpendicularly to the plane of the structures ) and the bias current @xmath60 , were carried out in a commercial oxford instruments cryostat using a conventional four - terminal configuration . vs. @xmath5 taken for the long pb microbridge at a fixed bias current @xmath61a and at different temperatures @xmath6 .
( b ) a single resistive @xmath58 curve at 6.10 k and the position of the critical fields @xmath62 and @xmath63 , marked by arrows : @xmath64 oe , @xmath65oe , @xmath66 oe .
two dashed horizontal lines show the levels 0.50@xmath67 and 0.98@xmath67 , where @xmath68.,title="fig:",width=302 ] vs. @xmath5 taken for the long pb microbridge at a fixed bias current @xmath61a and at different temperatures @xmath6 .
( b ) a single resistive @xmath58 curve at 6.10 k and the position of the critical fields @xmath62 and @xmath63 , marked by arrows : @xmath64 oe , @xmath65oe , @xmath66 oe .
two dashed horizontal lines show the levels 0.50@xmath67 and 0.98@xmath67 , where @xmath68.,title="fig:",width=302 ] typical @xmath58 curves measured at @xmath61a are shown in fig . [
fig - resistance](a ) .
the appearance of two symmetrical minima in @xmath58 at @xmath69 k corresponds to rds above the domains of opposite polarity .
taking the positions of the @xmath59 minima , one can estimate the amplitude of the nonuniform magnetic field @xmath2 inside the superconducting bridge to 480 oe . the observed linear increase in the width of the @xmath59 minima with decreasing temperature ( compare the curves from @xmath69 k , and to @xmath70 k ) allows us to prove the usual relationship @xmath71 ( eq . [ hc2 ] ) and to estimate both the maximal critical temperature @xmath72 k and .
contrary to the previously studied hybrid al / bafe@xmath0o@xmath1 bilayers,@xcite the estimated @xmath73 value for pb is substantially higher than @xmath2 at low temperatures .
the ratio @xmath74 gives us the temperature of the anticipated crossover @xmath75 k between rds and cs .
the @xmath58 at @xmath76 k confirms this simple estimate since the sample resistance vanishes for @xmath77 k at @xmath46 which indicates cs . considering the @xmath58 curves at rather low temperatures ( @xmath78 )
, one can see that the transition from the superconducting to the normal state upon increasing @xmath79 from zero occurs in two stages .
the first stage and an appearance of nonzero resistance can be attributed to the suppression of bulk pds above the parallel domains since the position of this anomaly corresponds to eqs .
( [ biased - hc2a])([biased - hc2b ] ) .
however , due to the presence of a continuous superconducting path along the sample edges attributed to edge - assisted superconductivity ( pds ) , the resistance increases slowly as @xmath5 increases .
the exclusive survival of rds above opposite domains at larger @xmath5 explains the rise in the total sample s resistance @xmath59 up to 50 - 60% from the normal state resistance @xmath80 ( curves 4.50 k , 4.90 k , 5.30 k and 5.70 k ) .
indeed , for the considered topology of the magnetic field , the superconducting and normal regions are connected in series and , therefore , @xmath59 should reflect the ratio between the volume of the bridge in the normal state and the total volume of the bridge .
we observe that in the developed rds state @xmath59 is not constant but slightly increases with @xmath79 .
this finding can be attributed to the external - field - induced shrinkage of the reverse domains . however , even when bulk rds is suppressed , the resistance is still lower than the normal resistance .
such a resistive state observed at low temperature and high field , can be attributed to the formation of compensated superconductivity above magnetic domains of opposite polarity but localized near the edge of the sample . in the following
, this state will be referred to as edge - assisted rds .
apparently , such states can exist until the local magnetic field above the opposite domains @xmath81 exceeds the critical field of surface superconductivity @xmath82 at a given temperature.@xcite the position of the critical fields @xmath62 and @xmath63 , which determine the shape of the magnetoresistive curve , are shown in fig .
[ fig - resistance](b ) for @xmath83 k. for instance , the experimentally determined ratio @xmath84 for @xmath83 k is close to 1.77 , supporting our interpretation . _
@xmath4 diagram .
_ a full @xmath4 diagram for the long bridge , composed from isothermal @xmath58 measurements , is presented in fig .
[ fig - experiment - pb](a ) . a similar diagram for the short bridge
is not given since both s / f hybrid samples showed almost identical behavior .
the interpretation of all distinctive regions of this diagram is given in fig .
[ fig - experiment - pb](b ) .
we explain the initial deviation of the resistance from the normal value @xmath80 by the formation of the edge - assisted rds for large @xmath5 .
such states i and ii are shown schematically in fig . [
fig - experiment - pb](c ) . for moderate @xmath5
, superconductivity can appear in the form of a complex state consisting of edge - assisted superconductivity and dws ( pattern iii ) . according to our expectations
, the localized superconductivity in the latter case ( @xmath85 ) appears above the phase transition line depicted by eq .
( [ aladyshkin - dws ] ) , since the critical temperature for dws induced by the domain walls of a finite width should be always higher than that for infinitely narrow domain walls .
interestingly , in the overcompensated regime ( @xmath86 ) , the position of the shifted @xmath32 line , eq .
( [ biased - hc3 ] ) , coincides with the level curve @xmath87 .
the next stages of decreasing resistance with decreasing temperature at @xmath88 have to be associated with the appearance of bulk rds in the compensated regions ( patterns iv and v ) .
the corresponding phase boundaries are given by eqs .
( [ biased - hc2a])([biased - hc2b ] ) and are shown by black dashed lines in fig .
[ fig - experiment - pb](b ) . for temperatures below than the transition line given by eq .
( [ biased - hc3 ] ) , in addition to rds inhomogeneous superconductivity in the form of edge - assisted pds also appears in the regions with enhanced magnetic field ( patterns vi and vii ) . inside the region viii in the @xmath4 diagram ,
where areas of inhomogeneous superconductivity for the different domains start to overlap , the total absence of electrical resistance indicates the appearance of cs .
thus , in our transport measurements , we clearly observed the switching between different regimes of localized superconductivity upon variation of @xmath5 and @xmath6 .
dependencies measured at @xmath46 ( a ) and @xmath89 oe ( b ) for the long superconducting pb bridge at different temperatures indicated in the plots .
two dashed lines correspond to the ohmic - like behavior with the resistance @xmath90 and @xmath91.,title="fig:",width=309 ] dependencies measured at @xmath46 ( a ) and @xmath89 oe ( b ) for the long superconducting pb bridge at different temperatures indicated in the plots .
two dashed lines correspond to the ohmic - like behavior with the resistance @xmath90 and @xmath91.,title="fig:",width=309 ] and @xmath92 , corresponding to the suppression of reverse - domain superconductivity ( red symbols near the top line ) , and complete superconductivity ( blue squares near the bottom line ) , respectively . for the determination of @xmath93 ( @xmath94 ) we plotted the positions of the maximal differential resistance on the @xmath95 dependencies measured at @xmath96oe ( @xmath46 )
both for the long and short bridges ; @xmath97 and @xmath98 denote the negative and positive branches of the corresponding @xmath95 curves ( fig .
[ fig - iv ] ) .
the dashed lines are guides to the eyes.,width=317 ] _ critical currents .
_ a bias current @xmath60 can suppress the different modes of nonuniform superconductivity in the considered s / f system in various ways .
the effect of @xmath5 and @xmath60 on the current ( @xmath60 ) voltage ( @xmath99 ) dependencies and on the dc resistance @xmath100 are illustrated in figs .
[ fig-2d - currents ] and [ fig - iv ] .
we observed that the state of rds is more robust with respect to current injection than the state of cs , since in the latter case the bias current can first destroy the weakly - developed superconductivity above parallel magnetic domains ( i.e. , above positive domains at @xmath19 and vice versa ) , where the local magnetic field is maximal . in order to evaluate the critical current destroying cs and rds
, we consider the effect of @xmath6 on the @xmath95 dependencies ( fig .
[ fig - iv ] ) measured at @xmath46 and @xmath101 ( i.e. close to the compensation field ) .
one can see that the state with zero resistance , which is inherent to cs , can be destroyed if @xmath60 exceeds a threshold value @xmath92 .
taking the position of the jumps in the @xmath95 curves at @xmath46 or the maximal differential resistance @xmath102 ( panel ( a ) in fig .
[ fig - iv ] ) , we plotted the the temperature dependence of the critical current @xmath92 , corresponding to the destruction of the most developed cs state at @xmath46 . for a characterization of the critical current @xmath93 , corresponding to the suppression of the developed rds at the compensation field ( @xmath101 ) , we traced the position of the jump on the @xmath95 curves at @xmath96oe upon increasing @xmath6 ( panel ( a ) in fig .
[ fig - iv ] ) .
indeed , this estimate seems to be reasonable for the describing of the current - induced destruction of inhomogeneous superconductivity under the condition when the minimal resistance of the investigated sample in the superconducting state is finite ( of the order of 50%@xmath80 ) .
the dependencies of the both estimated critical currents @xmath93 and @xmath93 as a function of @xmath6 are presented in fig .
[ fig - critcurrents ] .
in order to image the inhomogeneous superconducting states trapped by the nonuniform magnetic field we used low - temperature scanning laser microscopy ( ltslm ) . the principle of operation of ltslm can be introduced as follows.@xcite the hybrid s / f samples were mounted on the cold finger of a helium gas flow cryostat , which is equipped with optical windows to enable laser irradiation .
an amplitude modulated laser beam ( wave length 680 nm , modulation frequency 10 khz ) heats locally the superconducting sample within a spot with a diameter of @xmath103 m .
this value is determined by the diameter of the focused incident beam and by the thermal conductivity of the tested bilayer sample.@xcite the incident beam intensity power on the sample surface ( up to @xmath104w ) appears to be high enough to provide a maximum beam - induced increase in temperature @xmath105k , leading to a local suppression of superconductivity within this hot spot .
we assume that the effect of the laser irradiation should be uniform across the superconducting film thickness since the thickness of the pb film ( 40 nm ) is much smaller than the lateral spot size . in our ltslm measurements
we apply a constant bias current and measure the beam - induced voltage drop @xmath106 along the entire bridge by lock - in technique .
a set of scanning mirrors allows us to control the position @xmath37 of the spot and thus , to obtain the position - dependent 2d map of the ltslm signal : @xmath107 .
the ltslm voltage signal can be interpreted as follows .
if the laser spot heats an area of the bridge which is in the normal resistive state , the beam - induced perturbation of the local temperature causes only a very small change in the total resistance , since @xmath108 is very small .
however , if the irradiated part of the bridge is in the superconducting state and it took part in the transfer of a substantial part of the supercurrents , the beam - induced suppression of superconductivity might switch the whole sample from a low - resistive state to a high - resistive state . in other words ,
the ltslm technique makes it possible to map out the ability of the sample to carry supercurrents . comparing the ltslm responses upon varying @xmath5 and @xmath6
, one can trace the evolution of local superconducting properties in the investigated system . for the observation of the different regimes of inhomogeneous superconductivity in the long pb / bfo hybrid samples
, we applied a constant current of @xmath109a and the field was varied in the range between @xmath110 oe .
figure [ fig - ltslm-1 ] shows the ltslm images obtained at @xmath111k , which is below the crossover temperature @xmath75 k. for @xmath112oe the measured responses have no detectable variations [ see panels ( a ) , ( b1 ) and ( b2 ) ] .
apparently , at these points inside the cs state in the @xmath4 diagram , the intensity of the laser beam is insufficient for the destruction of the developed bulk superconductivity . according to our estimates , at @xmath111k ,
the depletion of superconductivity above the parallel magnetic domains should occur at @xmath113 350 oe .
this means that near the cs rds " transition line the areas above the parallel domains have to be in the _ resistive _ state , while the areas above the opposite domains are still in the superconducting state . as a result ,
the maxima in the ltslm response at @xmath114 oe should be attributed solely to the non - superconducting regions above the positive domains [ panels ( c2 ) , ( d2 ) ] .
correspondingly , at @xmath115 oe the resistive areas above negative domains are responsible for the beam - induced voltage [ panels ( c1 ) , ( d1 ) ] . at higher @xmath5 values
( i.e. deeper in the rds areas in the @xmath4 diagram ) superconductivity survives exclusively above the opposite domains and such compensated superconductivity is strong enough not to be destroyed by the laser beam of the given intensity .
however , close to the transition line rds edge - assisted rds " the reverse - domain superconductivity becomes weaker and can be affected by the laser beam .
therefore , the bright areas in the corresponding ltslm signal originate from the regions with the compensated magnetic field above the opposite domains .
the inversion of the @xmath5 sign immediately results in a switching between enhanced reverse - domain superconductivity and depleted parallel - domain superconductivity for the same areas of the superconducting bridge [ panels ( e1e2 ) and ( f1f2 ) ] .
thus , all findings concerning the migration of the maximal beam - induced voltage along the pb bridge upon varying @xmath5 are in agreement with our transport measurements .
we would like to note that the ltslm images [ panels ( c1f1 ) and ( c2f2 ) in fig .
[ fig - ltslm-1 ] ] reveal an inhomogeneity of the beam - induced voltage across the width of the bridge . indeed , the @xmath106 maxima are always located near the edges of the bridge . at the present moment
we have no reliable interpretation of this effect .
probably , it can be explained by the current enhancement near the sample edges , typical for plain superconducting bridges,@xcite or by a suppression of the energy barrier for flux entry or exit for superconductors in the developed mixed state .
another possible explanation for the pronounced edge signal is the manifestation of edge - assisted pds , since such edge - assisted pds states seem to be the states with weakest superconductivity .
finally , the edge signal can be explained by a hampered heat diffusion and , correspondingly , a larger heating effect of the beam focused near the edges as compared to that in the interior of the bridge . in any case , this issue requires a detailed theoretical treatment which is beyond the scope of the present work . at @xmath116
k , close to the crossover temperature , a voltage signal can be detected at @xmath46 .
the amplitude of the built - in magnetic field is close to the corresponding upper critical field and therefore even a weak optical influence can substantially suppress bulk superconductivity equally above the domains of both polarities . upon increasing @xmath79
we successively observe the responses from the parallel domains [ panels ( b1 ) and ( b2-c2 ) ] and from the antiparallel domains [ panels ( d1-f1 ) and ( d2-f2 ) ] , similar to that described above .
obtained by ltslm method at different @xmath6 along the line close to the lower edge of the pb microbridge : ( a ) the reference signal @xmath117 measured at @xmath118oe in order to detect the positions of the domain walls shown as vertical dashed lines .
( b ) the dependencies @xmath117 measured at different temperatures ( shown in the plot ) and @xmath46.,width=321 ] further increase in temperature above the crossover temperature could allow us to detect the domain - wall superconductivity at @xmath46 , since the masking background signal from cs and the edge - assisted rds are turned off .
the evolution of the beam - induced voltage upon increasing @xmath6 is presented in fig .
[ fig - ltslm-3 ] , where we show line scans @xmath117 along the bridge , close to the bottom edge of the bridge .
we did not find any noticeable increase in the ltslm response near the domain walls for the considered s / f system .
we would like to mention that the dws state was observed for a similar pb bridge oriented along the domain wall using the same ltslm technique.@xcite
we presented a detailed experimental study of the superconducting properties of thin - film superconducting pb microbridges in the presence of a nonuniform magnetic field of the laminar domain structure in ferromagnetic bafe@xmath0o@xmath1 crystals .
such ferromagnets generate rather strong stray fields and the parameters of this field ( amplitude and period ) are almost independent on the applied magnetic field @xmath5 in the considered @xmath5 range .
we focused on the case when the domain walls are oriented perpendicular to the bridge in order to avoid electrical shunting and masking of less developed superconducting states by more favorable states during transport measurements . it was demonstrated that , at high temperatures superconductivity appears in the form of reverse - domain superconductivity only above magnetic domains of opposite polarity with respect to the @xmath5 sign .
below the crossover temperature @xmath24 , defined as @xmath119 , superconductivity can nucleate both above antiparallel and parallel magnetic domains ( @xmath2 is the amplitude of the perpendicular component of the nonuniform field , is the temperature - dependent upper critical field ) .
indeed , at @xmath78 the regions of inhomogeneous superconductivity above positive and negative domains overlap in the @xmath4 plane , resulting in so - called complete ( or global ) superconductivity and in the vanishing total electrical resistance of the hybrid sample .
we also found experimental evidences for the regimes of edge - assisted reverse - domain superconductivity and edge - assisted parallel - domain superconductivity , corresponding to localized superconductivity near the edges of the bridge above the regions with compensated and enhanced magnetic field , respectively .
we experimentally determined the critical currents , corresponding to the suppression of the localized superconductivity above parallel and antiparallel magnetic domains in a broad temperature range .
the technique of low - temperature scanning laser microscopy made it possible to directly visualize the temperature and field - induced transitions from complete superconductivity to reverse - domain superconductivity and parallel - domain superconductivity and from these inhomogeneous superconducting states to the normal state .
this work was supported by the methusalem funding of the flemish government , the nes esf program , the belgian iap , the fund for scientific research flanders ( f.w.o.vlaanderen ) , the russian fund for basic research , ras under the program quantum physics of condensed matter " , russian agency of education under the federal target program scientific and educational personnel of innovative russia in 20092013 " , deutsche forschungsgemeinschaft ( dfg ) via grant no .
ko 1303/8 - 1 .
robert werner acknowledges support by the cusanuswerk , bischfliche studienfrderung .
b. pannetier , s. rodts , j.l .
genicon , y. otani and j.p .
nozieres , chapter in _ macroscopic quantum phenomena and coherence in superconducting networks _ , eds . c. giovannella and m. tinkham , ( singapore : world scientific ) , pp .
1724 ( 1995 ) .
equation ( [ aladyshkin - dws ] ) may be considered as an ultimate estimate of dws , since the critical temperature of the solution , localized in vicinity of the domain walls of the finite width , will be always higher than that given by eq .
( [ aladyshkin - dws ] ) . | we studied experimentally the effect of a stripe - like domain structure in a ferromagnetic bafe@xmath0o@xmath1 substrate on the magnetoresistance of a superconducting pb microbridge .
the system was designed in such a way that the bridge is oriented perpendicular to the domain walls .
it is demonstrated that depending on the ratio between the amplitude of the nonuniform magnetic field @xmath2 , induced by the ferromagnet , and the upper critical field @xmath3 of the superconducting material , the regions of the reverse - domain superconductivity in the @xmath4 plane can be isolated or can overlap ( @xmath5 is the external magnetic field , @xmath6 is temperature ) .
the latter case corresponds to the condition @xmath7 and results in the formation of superconductivity above the magnetic domains of both polarities .
we discovered the regime of edge - assisted reverse - domain superconductivity , corresponding to localized superconductivity near the edges of the bridge above the compensated magnetic domains .
direct verification of the formation of inhomogeneous superconducting states and external - field - controlled switching between normal state and inhomogeneous superconductivity were obtained by low - temperature scanning laser microscopy . |
Updated 2:39 p.m. ET
A crucial test for the Air Force’s experimental Mach 5 missile has ended in failure, according to the Air Force. Tuesday’s test is also the third time the hypersonic X-51A Waverider cruise missile has fallen short. But this time could be the last.
As first reported by Danger Room, the Waverider’s control fin failed, preventing the missile’s scramjet engine from starting. The Air Force later confirmed the result in a statement. That also corresponds to information provided by an insider familiar with the test, who said a problem with a missile’s fin caused a loss of control before the engine could kick in. The missile’s scramjet engine was supposed to power the missile at hypersonic speeds for 300 seconds. Instead, the Air Force identified a fault with the fin 16 seconds after launch. Fifteen seconds later, after the missile separated from its preliminary rocket booster — which builds up speed before the missile activates its scramjet – the Waverider broke apart.
The Air Force launched the missile over the Pacific sometime between 10 a.m. and 11 a.m. Tuesday from a B-52 Stratofortress based at Edwards Air Force Base in California. Traveling at 50,000 feet, the B-52 was to launch the missile, which would then scream across the Pacific at hypersonic speeds. The missile got away from the B-52, but then flopped uncontrollably into the ocean.
The stakes were high. So far the tests have cost the Pentagon some $300 million. True, the millions in research and testing have helped advance the field of hypersonics, but the shortage of tangible results have also helped spoil the confidence the Air Force once had in producing a working weapon. The failure also has serious implications for the military’s “prompt global strike” mission, which aims to use missiles with engines capable of hypersonic flight to wallop targets hundreds — even thousands — of miles away and do so within minutes.
The 26-foot-long X-51A was supposed to be a working candidate for prompt global strike, and a safer alternative to the Air Force’s former plan to stick conventional warheads onto intercontinental ballistic missiles, or ICBMs. Problem with using ICBMs, however, is that they look like nuclear missiles when launched, potentially provoking a devastating war. The X-51A is just a cruise missile — albeit one with an experimental scramjet engine.
It works in theory like this. After being launched from an aircraft, the X-51A fires its conventional rocket booster, which builds up subsonic speeds before the missile’s supersonic ramjet kicks in. Once the ramjet fires, the engine would begin to collect oxygen from the atmosphere and mix the air with jet fuel, burning both. The missile would next accelerate past Mach 5, staying in the air by using lift created from the missile’s shock waves.
But actually doing it is really hard. Hypersonic speed generates tremendous heat. And the missile also needs sophisticated guidance tools, sensors and navigation equipment to keep it in the air.
The X-51A’s test history is instructive. The missile’s first test flight lasted more than three minutes before a seal broke — a failure, but relatively better compared to what followed. A second test last summer lasted only a few seconds before the missile failed due to overpressure created by unexpected shockwaves. A possible solution was to tweak the timing for injecting fuel into the engine, which should also change the pattern of shockwaves. Though, it looks like Tuesday’s test didn’t last long enough for Air Force to find out if it would’ve worked.
The Air Force is currently building a fourth missile, but is short on funds for testing. And if tests keep getting worse, there may not be enough interest for another round. At the same time, the service is working on transitioning the X-51A into a serviceable missile called the “High Speed Strike Weapon.” The Pentagon’s researchers at Darpa have also been experimenting with hypersonic glider. The glider — and a potential weapons platform — is launched into near-space before zooming back to Earth at 20 times the speed of sound. Darpa wants to press ahead with another glider test after its last try-out crashed into the Pacific.
Kinda like what happened to the X-51A. Except for the Air Force’s cruise missile, there might not be another try, nor the budget and willpower. ||||| The U.S. Air Force says an unmanned experimental aircraft suffered a control failure during an attempt to fly at six times the speed of sound.
In this July 17, 2009 photo provided by the U.S. Air Force, an X-51A WaveRider hypersonic flight test vehicle is uploaded to an Air Force Flight Test Center B-52 for fit testing at Edwards Air Force Base.... (Associated Press)
The X-51A Waverider was designed to reach Mach 6, or 3,600 mph (5,800 kph) after being dropped by a B-52 bomber off the California coast on Tuesday.
But the Air Force said Wednesday that a faulty control fin prevented it from starting its exotic scramjet engine, and it was lost.
The Pentagon has been testing hypersonic technologies in hopes of being able to deliver strikes around the globe within minutes.
The first Boeing-designed aircraft achieved Mach 5 for about 140 seconds in 2010. A second flight last year ended prematurely, with the craft trying to restart its engine until it plunged into the Pacific. | – It was supposed to be a step toward ultra-quick military strikes and maybe even passenger planes that could zip from coast to coast in under an hour. Instead, an unmanned hypersonic test craft crashed into the Pacific today shortly after being released from a B-52 bomber, reports AP. The Air Force craft, called an X-51A WaveRider, was designed to reach 3,600mph, but a faulty control fin prevented its "scramjet engine" from activating, according to the report. Mach 6 will have to wait, though Wired notes that this is the third such test failure, and "this time could be the last." |
they must constantly absorb light energy and phagocyte lipid rich photoreceptor outer segment shed from neural retina due to normal physiological visual cycle .
oxidative stress refers to progressive cellular damage that contributes to protein misfolding and functional abnormalities in the rpe cells during cellular senescence .
the accumulation of this damage in the postmitotic rpe cells seems to be one of the key events in the development of age - related macular degeneration ( amd ) , the leading cause of blindness in the elderly in the developed countries .
the rpe cells ensure the survival of neural cells , rod , and cones . in senescent rpe cells ,
this ability is reduced causing secondary adverse effects on the neural retina , ultimately leading to loss of vision . both intra- and extracellular
. efficient removal of misfolded proteins from cytoplasm is critical for cellular survival and adaptation .
however , potentially toxic misfolded protein aggregates accumulate during the aging process [ 3 , 4 ] .
control of protein turnover is particularly important in postmitotic cells , since the accumulation of malfunctioning proteins may be highly detrimental to the cells .
once heat shock protein - mediated protein folding fails , the misfolded proteins are usually tagged with a ubiquitin ( ub ) moiety that directs the complex to the ubiquitin / proteasomal protein degradation pathway ( upp ) .
it is believed that the aggregation of oxidized and ubiquinated proteins is due to a decline in the proteasomal activity with age , and that this also occurs in rpe cells [ 710 ] .
protein aggregates formed in the cell periphery are delivered along microtubulus network by dynein - dependent retrograde trafficking to a juxtanuclear location where they form aggresomes [ 1113 ] .
the development of these aggresomes is part of a cellular defence mechanism against misfolded proteins , and it can be inhibited by drugs that depolymerize microtubules [ 15 , 16 ] .
tubulin undergoes various posttranslational modifications including polyglutamylation , polyglycylation , carboxyterminal cleavage , and acetylation [ 17 , 18 ] .
acetylation is unique among the known tubulin modifications , in that it occurs on the lysine 40 of -tubulin which can be found on stable microtubules in most cell types .
the deacetylation of the lysine residue in tubulin is catalyzed by enzymes called histone deacetylases ( hdacs ) .
in contrast , histone acetyltransferases ( hats ) transfer acetyl groups to lysine residue to increase acetylation of tubulin .
this results in a balance between acetylation and deacetylation states of tubulin , and any shift in this balance results in changes in the regulation of tubulin function .
. one interesting role of tubulin and tubulin modifying deacetylases is their influence on aggregation of misfolded proteins .
hdac6 contributes to the degradation of aggregated proteins because it is able to bind to both poly - ubiquitinated and dynein motor proteins as an adaptor protein to help transport misfolded proteins along microtubules into aggresomes which are finally degraded by autophagy [ 13 , 22 , 2729 ] .
hdac6 is able to sense ubiquitinated cellular aggregates and consequently induces the expression of major cellular chaperones by triggering the dissociation of a repressive hdac6/hsf1 ( heat - shock factor 1)/hsp90 ( heat - shock protein 90 ) complex and subsequent hsf1 activation .
hdac6 therefore appears as a master regulator of the cell protective response to cytotoxic protein aggregate formation .
we have recently shown that proteasome inhibition evoked perinuclear protein accumulation which then leads to the autophagy - mediated removal of the deposits . in the present study
, we demonstrate that hsp90 inhibition with geldanamycin can effectively decrease the proteasome inhibitor - induced aggregation .
increased tubulin acetylation was observed in response to hsp90 , proteasome , and hdac inhibition , but the acetylation level was not correlated with the amount of the aggregates in the arpe-19 cells .
human retinal pigment epithelial cells ( arpe-19 , from atcc , ) were used in this study .
the cells were grown in dulbecco 's mem / nut mix f-12 ( 1 : 1 ) medium ( life technologies , paisley , uk ) containing 10% fetal bovine serum ( hyclone , logan , ut , usa ) , 2 mm l - glutamine ( cambrex , charles city , ia , usa ) , 100 units / ml penicillin ( cambrex ) , and 100 g / ml streptomycin ( cambrex ) . before any exposure , the cells were grown to confluency in a standard incubator ( 10% co2 , + 37c ) .
proteasome inhibition was accomplished with 5 m mg-132 ( calbiochem , san diego , ca , usa ) .
geldanamycin ( ga , calbiochem ) , at 0.25 m concentration , was used to inhibit the function of hsp90 .
microtubules were acetylated with 1 m trichostatin a ( tsa ; sigma - aldrich , steinheim , germany ) . taxol ( tax , paclitaxel ; calbiochem ) , at 1 m concentration and nocodazole ( noc ; calbiochem ) , at 5 m concentration , were used to disrupt to function of microtubules .
the cells were exposed to the ga , tsa , tax , or noc for 24 h , simultaneously with mg-132 for 24 h or allowed to recover after 24 h mg-132 insult in medium with or without chemicals ( ga , tsa , tax or noc ) .
phase contrast microscopy photographs were taken from live cells with a nikon eclipse te300 ( nikon , tokyo , japan ) microscope . for transmission electron microscopy ( tem )
, the cell culture samples were prefixed in 2.5% glutaraldehyde ( in 0.1 m phosphate buffer , ph 7.4 ) for 2 hrs at room temperature , followed by washing ( 15 min in 0.1 m phosphate buffer ) .
the samples were postfixed in 1% osmium tetraoxide ( in 0.1 m phosphate buffer ) for 1
subsequently , the samples were infiltrated and embedded in lx-112 resin ( ladd research industries , burlington , vt , usa ) .
polymerization was carried out at 37c for 24 hrs and at 60c for 48 hrs .
the sections were examined in a jeol-1200ex transmission electron microscope ( jeol , tokyo , japan ) at 80 kv .
exposed cells were lysed in m - per lysis buffer ( thermo scientific , waltham , ma , usa ) .
whole cell extracts ( 20 g of protein ) were run in 10% or 15% sds - page gels and then wet blotted to nitrocellulose membranes ( ge healthcare , little chalfont , buckinghamshire , uk ) .
the membranes were blocked for 1 hour in 3% fat - free dry milk in 0.3% tween 20/pbs at room temperature ( rt ) .
thereafter , the membranes were incubated for 1 hour at rt with rabbit polyclonal ubiquitin antibody ( dakocytomation , glostrup , denmark , cat .
rat monoclonal hsp90 antibody ( assay designs , ann arbor , mi , usa , cat .
spa-815 ) or rabbit polyclonal lc3 antibody ( abgent , san diego , ca , usa , cat .
primary antibodies were diluted ( 1 : 500 , 1 : 5 000 , 1 : 5 000 , 1 : 5 000 , 1 : 250 or 1 : 8 000 resp . ) in 0.5% bovine serum albumin in 0.3% tween 20/pbs except for acetylated tubulin which was diluted in 1% fat - free dry milk in 0.05% tween 20/pbs . after 3 5 minutes washes with 0.3% tween 20/pbs ( for acetylated tubulin 0.05% tween 20/pbs ) the membranes were incubated for one hour at rt with horseradish peroxidase - conjugated anti - rabbit igg or anti - mouse igg antibodies or anti - rat igg antibodies ( ge healthcare ) .
the secondary antibodies were diluted ( for ubiquitin 1 : 20 000 , for hsp90 1 : 10 000 , for hsp70 1 : 40 000 , for hsc70 1 : 15 000 and for lc3 1 : 5000 , resp . ) in 3% fat - free dry milk in 0.3% tween 20/pbs except for acetylated tubulin ( 1 : 6 000 ) which was diluted in 1% fat - free dry milk in 0.05% tween 20/pbs . before detection , all of the membranes were washed as before .
protein antibody complexes were detected with an enhanced chemiluminescence method ( millipore , billerica , ma , usa ) .
the arpe-19 cells were either nonstressed , or exposed to drugs , that is , 5 m mg-132 or 0.25 m geldanamycin , 1 m trichostatin a or 1 m taxol or 5 m nocodazole for 24 hours .
in addition , the cells were treated simultaneously with mg-132 in conjunction with geldanamycin , trichosatin a , taxol or nocodazole up to 24 hours .
only a single mg-132 insult or combination treatment with taxol induced a typical perinuclear aggregation in arpe cells ( figures 1(a ) and 2(a ) ) .
hdac inhibition with trichostatin a or tubulin depolymerization with nocodazole evoked dispersed the mid - peripherical aggregation process during proteasome inhibition . with all of the insults
, cytoplasm underwent a similar effective aggregation clearance when exposed to mg-132 for 24 hours and then allowed to recover for 24 hours in normal cell culture medium ( figures 1(b ) and 2(b ) ) .
a robust elevation of hsp70 protein expression was seen in response to mg-132 or geldanamycin exposures ( figure 3 ) .
abrogation of proteasome - mediated protein degradation caused a clear increase in the amount of hsp70 which has a cytoprotective capacity in the mg-132 -treated arpe-19 cells .
the classical transcriptional heat - shock gene induction is attributable to the activation of hsf1 transcription factor . in the activation process hsp90 and hsp70 dissociate from hsf1 transcription factor [ 33 , 34 ] .
geldanamycin has been shown to bind hsp90 , to inhibit its function and to elicit the hsp90 client protein degradation in proteasomes [ 35 , 36 ] . in line with previous studies [ 3739 ] ,
the geldanamycin was found to trigger a strong expression of hsp70 , while the hsp90 response remained weaker .
the response is likely mediated through hsf1 transcriptional activation [ 33 , 34 ] .
the increase in the amount of inducible hsp70 might be one of the regulators suppressing the proteasome inhibitor - induced aggregation process , when hsp90 is simultaneously inhibited .
it has also been documented that a hsp90 inhibitor may prevent the aggregation of protein by regulating client protein posttranslational modifications .
since hsp90 inhibition has been reported to trigger autophagy clearance [ 41 , 42 ] , we wished to analyze the autophagy induction marker lc3 i / ii levels in arpe cells treated with geldanamycin or mg-132 solely or both together for 6 , 12 , and 24 hours .
our findings clearly show that proteasome inhibition mildly induced autophagy , when related to lc3 ii levels , but this was not involved in geldanamycin treatments ( figure 4 ) .
this indicates that autophagy clearance is not implicated in the suppression of protein aggregation during hsp90 and proteasome inhibition in the arpe-19 cells .
cellular ubiquitin - protein ( ub ) conjugate levels were analyzed by western blotting from cells treated as described above .
the level of ub conjugation was not changed by geldanamycin , trichostatin a , taxol , or nocodazole treatment , but a very intensive induction of ubiquitination was seen in response to mg-132 exposure whether geldanamycin , trichostatin a , taxol , or nocodazole were present or not ( figure 3 ) .
inhibition of hsp90 therefore seems to have only a minor impact on the level of ubiquitination in the arpe-19 cells , although hsp90 has been shown to regulate both proteasomal and autophagy clearance through its client proteins [ 4143 ] .
the ubiquitin levels were slightly reduced when proteasome inhibition was removed and the cells recovered either with geldanamycin , trichostatin a , taxol , or nocodazole compared to incubations of mg-132 together with these chemicals .
this is apparently explained by the autophagic clearance of proteasome - inhibitor - induced aggregates , as we have recently documented .
protein aggregates formed at the cell periphery are delivered along the microtubulus network by dynein - dependent retrograde trafficking to a juxtanuclear location where they form aggresomes [ 11 , 12 ] .
the reversible acetylation of -tubulin has been linked to the regulation of microtubule stability and function .
decreased tubulin acetylation has been shown in some reports to reduce microtubule stability [ 21 , 22 ] , but in other experiments no association was observed [ 44 , 45 ] .
hdac6 deacetylates tubulin , and hsp90 , and forms complexes with many other proteins , including ubiquitinated proteins .
hdac6 also interacts with a component in the dynein - dynactin microtubule motor complex and regulates protein aggregation trafficking [ 13 , 45 , 46 ] .
trichostatin a is a classical inhibitor of hdac deacetylase activity and thus it also blocks the hdac6 . the phase contrast and transmission electron microscopic analysis revealed dispersed cytoplasmic aggregation in response to simultaneous treatment of trischostatin a or nocodazole and proteasome inhibition ( figures 1 and 2 ) .
trichostatin a evoked a clear increase in tubulin acetylation levels , while in the situation of tubulin depolymerizator induced by nocodazole , tubulin acetylation remained at control level ( figure 3 ) .
in contrast , a tubulin stabilizer , taxol induced tubulin acetylation that was not , however , as extensive as that evoked by trichostatin a. hsp90 and proteasome inhibition evoked a similar slight increase in the tubulin acetylation levels .
the hdac inhibition by trichostatin a probably affects the dynein motor and regulates aggregation localization , but does not prevent the formation of aggregates .
moreover , the polymerization state of tubulin regulates the localization of proteasome inhibitor - induced aggregates , but this process can not be estimated by measuring total tubulin acetylation levels .
hsp90 inhibition is effectively involved in the regulation of protein aggregation that is independent of hdac inhibition or tubulin acetylation levels in the rpe cells .
these findings open new perspectives for understanding the pathogenesis of protein aggregation in retinal cells , and they may be useful in the development of therapeutic treatments to prevent retinal cell deterioration , that is , during aging . | retinal pigment epithelial ( rpe ) cells are continually exposed to oxidative stress that contributes to protein misfolding , aggregation and functional abnormalities during aging .
the protein aggregates formed at the cell periphery are delivered along the microtubulus network by dynein - dependent retrograde trafficking to a juxtanuclear location .
we demonstrate that hsp90 inhibition by geldanamycin can effectively suppress proteasome inhibitor , mg-132-induced protein aggregation in a way that is independent of hdac inhibition or the tubulin acetylation levels in arpe-19 cells .
however , the tubulin acetylation and polymerization state affects the localization of the proteasome - inhibitor - induced aggregation .
these findings open new perspectives for understanding the pathogenesis of protein aggregation in retinal cells and can be useful for the development of therapeutic treatments to prevent retinal cell deterioration . |
Kraft Foods has reached a tentative deal for a friendly takeover of Cadbury of Britain, agreeing in principle to pay about $19 billion in cash and stock for the confectioner, people briefed on the matter said on Monday.
Barring any last-minute complications — these people cautioned that the talks could still fall apart — the deal would create a global food giant that would unite Kraft and its Oreo cookies and Ritz crackers with Cadbury and its Trident gum and Dairy Milk chocolates. Together, the two companies would have more than $50 billion in revenue and a big presence in markets globally.
Over the last decade, food companies have sought to gain scale by combining with each other, most recently with Mars buying the Wm. Wrigley Jr. Company in 2008 for $23 billion.
The tentative deal for Cadbury would end a four-month battle for control of the British candy maker, one in which Cadbury executives accused Kraft of showing “contempt” with an undervalued offer.
Under the terms of the proposal, Kraft will pay 840 pence ($13.70) for each Cadbury share, while Cadbury will pay out a special dividend of 10 pence a share. The offer is about a 5 percent premium over Cadbury’s closing share price of 807.5 pence on Monday. The majority of the increase was in the cash component, which was raised to £5 a Cadbury share, from £3, a person briefed on the matter said.
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The agreement is expected to be announced as soon as Tuesday, this person said, which is the last day Kraft can raise its offer under British takeover rules.
Spokesmen for Cadbury and Kraft declined to comment on Monday.
The deal will draw to a close an often acrimonious takeover battle between the two food companies, one that began with Kraft making public an unsolicited $16.7 billion bid for Cadbury in early September. The Cadbury management quickly derided the offer as too low and dismissed the prospect of being absorbed into what it called a slow-growing food conglomerate.
Most of Cadbury’s major shareholders resisted Kraft’s original offer, with just 1.5 percent having accepted by an earlier January deadline. Many are likely to be swayed by a recommendation from Cadbury’s board now that Kraft has addressed a common complaint by raising the cash portion of its bid.
A takeover of the 186-year-old Cadbury, especially by an American giant like Kraft, will most likely send shudders throughout Britain. Politicians and unions have pointed to both a loss of jobs — the Unite labor union has estimated that as many as 30,000 jobs could be lost — and of national pride.
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Cadbury has argued repeatedly that it would prefer to remain independent, pointing to faster-than-expected success in its turnaround program. But its executives have acknowledged that Kraft’s bid put the company in play and they would consider any offer made at the right price.
From the beginning, speculation mounted among investors that another bidder could step in, forcing Kraft to raise its original offer. Representatives for Cadbury have held talks with Hershey, the American company that Cadbury had viewed as a preferable merger partner, according to people briefed on the matter.
For Hershey, buying Cadbury would prevent it from being relegated to a mostly domestic company. Hershey moved closer to making a bid in recent days, lining up more than $10 billion in financing, these people said.
Hershey had been waiting for Kraft to unveil its final offer on Tuesday before it made its final decision on a bid, but analysts have said that Hershey would most likely be unable to top the much larger Kraft in a bidding war. Other potential suitors, including Nestlé of Switzerland and Ferrero of Italy, dropped out.
Despite Kraft’s strong desire to gain control of Cadbury, its chief executive, Irene Rosenfeld, vowed to keep the company disciplined in its bidding and to maintain its investment-grade credit rating. Still, Kraft began raising its original offer earlier this month, increasing the cash portion of its bid after selling its North American frozen pizza business to Nestlé for $3.7 billion. Ms. Rosenfeld met with Cadbury shareholders in London last week to solicit their opinions.
Others have sounded notes of caution. Warren E. Buffett, whose Berkshire Hathaway is Kraft’s largest shareholder, delivered an unusually public admonishment, warning Kraft to avoid overdiluting its shareholders by issuing too many new shares.
William A. Ackman, who runs the hedge fund Pershing Square Capital Management and has been amassing a big position in Kraft, echoed concerns about shareholder dilution, though he said he supported the company’s takeover effort. ||||| Cadbury will accept defeat in its battle to stay independent today by recommending a £12bn takeover from US rival Kraft that threatens to reignite a fierce debate about the vulnerability of British industry.
The 186-year-old chocolate maker decided to throw in the towel late last night after a large foreign shareholder joined hedge funds in indicating it would accept an improved offer from Kraft, and the prospect of a rival bid from Hershey faded. Cadbury's board, led by chairman Roger Carr, will announce its decision to recommend the revised 850p-a-share bid to all shareholders through a statement to the stock exchange this morning, according to sources close to the company.
Although a board recommendation is not binding, it is highly unusual for a company to resist a hostile takeover once its management has capitulated.
The confectionery giant joins a list of British industrial names to have fallen to foreign takeovers in similar circumstances in recent years. More than 50 leading companies have gone, including BAA, Boots, Cazenove, Corus, ICI, Jaguar Land Rover, P&O, Pilkington and Scottish Power.
Until now Cadbury had fought a public campaign to preserve its independence, attracting support from Lord Mandelson, the business secretary, who warned Kraft to expect "huge opposition" from the government if it wanted to make a "fast buck" by buying Cadbury.
His intervention is understood to have rattled Kraft's chief executive, Irene Rosenfeld, who recently met shareholders in London, but the US company chose to negotiate a raised offer after calculating that the political risk was manageable.
Cadbury unions have warned that up to 30,000 jobs would be put at risk by the deal as Kraft would be weighed down by some £22bn in debt. Kraft has a record of aggressive cost-cutting, and the union Unite said that between 2004 and 2008 it shed 19,000 jobs and closed 35 sites to help reduce its debt.
Today's bid of 850p-a-share (including a 10p dividend) is an increase on Kraft's previous offer of around 770p in cash and shares, which Carr had previously described as "derisory". Nonetheless it is at the low end of many independent experts' predictions for an agreed price and comes after Cadbury's chief executive, Todd Spitzer, appeared to suggest he thought its shares were worth £10 each.
A source close to Cadbury said the decision had been taken with "a heavy heart" but followed advice from its investment bankers that any increase in Kraft's bid beyond 830p would succeed.
More than a quarter of Cadbury shares are now in the hands of hedge funds which bought them in the hope of a deal. The final straw came when Franklin Templeton, a large US mutual fund with a 7% stake, indicated it would accept 830p.
The circumstances of the defeat are likely to reopen a debate about the role of hedge funds and other investors during takeovers. Lord Myners, the City minister, has been vocal in his criticism of short-termism among institutional fund managers. Cadbury was the first big test of a supposed new mood after the financial crash and raised strong emotions because of its history as a progressive employer, supporter of fair trade and proponent of good corporate governance.
Nevertheless, its management's actions appear to have followed a well-worn path in such situations. Carr cut his teeth as chief executive of Williams, an industrial conglomerate also sold overseas, and worked with Sir Nigel Rudd, who recommended the sale of Boots two years ago.
Under Takeover Panel rules, Kraft had until midnight tonight to raise its offer. There is still a chance that Hershey may intervene, but sources close to Cadbury last night said that was unlikely. | – Kraft has won a sweet victory in its 4-month-long battle to take over Cadbury, according to sources who expect a deal to be announced today, barring last-minute complications. The British chocolate maker's board has agreed to accept Kraft's improved offer of roughly $19 billion in cash and stock in a buyout that will create a food industry behemoth with sales of over $50 billion a year, insiders tell the New York Times. The decision to stop fighting Kraft's takeover attempt was taken with "a heavy heart," a source at Cadbury tells the Guardian, but the board was left with little choice after shareholders indicated they would accept the higher offer. The takeover bid was strongly opposed by unions, who fear cost-cutting and massive job losses will result, and by British politicians who worry that the foreign takeover will dent national pride. |
the fast development of spintronics aims at making devices based on the electron spin .
semiconductor quantum dots ( qds ) are one of the promising candidates for the implementation of quantum computations@xcite because of the relative long spin coherence time , which has been proved both theoretically@xcite and experimentally.@xcite among different kinds of qds , double quantum dot ( dqd ) system attracted much more attention recently as there is an additional coupling between two qds in both vertical@xcite and parallel@xcite dqds , which can be controlled conveniently by a small gate voltage .
therefore spin devices based on dqds can be designed with more flexibility .
so far many elements of the spintronic device , such as quantum logical gates,@xcite spin filters@xcite and spin pumps@xcite were proposed and/or demonstrated based on dqd system . specially , in our previous work , a way to control spin relaxation time ( @xmath1 ) induced by the spin - orbit coupling ( soc ) together with the electron bulk - phonon ( bp ) scattering in dqds by a small gate voltage was proposed.@xcite however , according to our latest study,@xcite the spin relaxation can be controlled by other mechanisms also , if calculated correctly . in the present paper , we include all the spin decoherence mechanisms following our latest study in the single qd system , and apply the equation - of - motion approach to study the spin decoherence in dqd system . by this approach , not only the spin relaxation time but also the spin dephasing time ( @xmath2 ) can be obtained .
we show that both the spin relaxation and the spin dephasing can be manipulated by a small gate voltage in dqd system . especially , the large variation of spin relaxation still exists even at @xmath0 k. the dqd system studied here can be realized easily using the present available technology .
we organize the paper as following . in sec .
ii we set up the model and briefly introduce different spin decoherence mechanisms .
the equation - of - motion approach is also explained simply . then in sec .
iii we present our numerical results .
we first show how the eigen energies and eigen wave functions vary with the bias field in sec .
then the electric field dependences of spin relaxation and spin dephasing are shown in sec .
iiib and iiic , respectively .
we conclude in sec . iv .
we consider a single electron spin in two vertically coupled qds with a bias voltage @xmath3 and an external magnetic field @xmath4 applied along the growth direction ( @xmath5-axis ) .
each qd is confined by a parabolic potential @xmath6 ( therefore the effective dot diameter @xmath7 ) in the @xmath8-@xmath9 plane in a quantum well of width @xmath10 .
the confining potential @xmath11 along the @xmath5-direction reads @xmath12 in which @xmath13 represents the barrier height between the two dots , @xmath14 stands for the inter - dot distance and @xmath15 denotes the electric field due to the bias voltage @xmath3
. then the electron hamiltonian reads @xmath16 , where @xmath17 is the electron effective mass and @xmath18 with @xmath19 being the vector potential .
@xmath20 is the zeeman energy with @xmath21 , @xmath22 and @xmath23 being the @xmath21-factor of electron , bohr magneton and pauli matrix respectively .
@xmath24 is the hamiltonian of the soc . in gaas ,
when the quantum well width and the gate voltage along the growth direction are small , the rashba soc@xcite is unimportant.@xcite therefore , only the dresselhaus term@xcite contributes to @xmath25 . when the quantum well width is smaller than the qd diameter , the dominant term in the dresselhaus soc reads @xmath26 , with @xmath27 .
@xmath28 denotes the dresselhaus coefficient , @xmath29 is the quantum number of @xmath5-direction and @xmath30 , where @xmath31 ( @xmath32 ) is the eigen wave function of the electron along the @xmath5-direction.@xcite the electron eigen energy and wave function in the @xmath8-@xmath9plane can be obtained by the exact diagonalization approach.@xcite the interactions between the electron and the lattice lead to the electron spin decoherence .
these interactions contain two parts , one is the hyperfine interaction between the electron and the nuclei , the other is the electron - phonon interaction which is further composed of the electron - bp interaction @xmath33 , the direct spin - phonon coupling due to the phonon induced strain @xmath34 and the phonon - induced @xmath21-factor fluctuation .
we briefly summarize these spin decoherence mechanisms and the detailed expressions can be found in ref .
: ( i ) the soc together with the electron - bp scattering @xmath33 .
as the soc mixes different spins , the electron - bp can induce spin relaxation and spin dephasing .
( ii ) direct spin - phonon coupling due to the phonon - induced stain @xmath34.@xcite because this mechanism mixes different spins and also is related to the electron - phonon interaction , it can induce spin decoherence _ alone_. ( iii ) the hyperfine interaction @xmath35.@xcite it is noted that the hyperfine interaction alone only induces @xmath2 since it only changes the electron spin , but not the electron energy .
( iv ) the second - order process of hyperfine interaction combined with the electron - bp interaction @xmath36\langle \ell_{1}|$ ] , where @xmath37 ( @xmath38 ) and @xmath39 are the eigen state and eigen energy of @xmath40 , respectively .
although the hyperfine interaction can not induce @xmath41 alone , it is noted that the second - order process , combined with the electron - bp interaction , can induce both @xmath41 and @xmath2 .
the other mechanisms , including the first - order process of hyperfine interaction combined with the electron - bp scattering@xcite and the @xmath21-factor fluctuation@xcite have been proved to be negligible.@xcite due to the soc , all the states are impure spin states with different expectation values of the spin .
for finite temperature , the electron is distributed over many states and therefore one has to average over all the involved processes to obtain the total spin relaxation time . the fermi - golden - rule approach calculates the spin relaxation from the initial state to the final one whose majority spin polarizations are opposite .
however , the average method is inadequate when many impure states are included.@xcite also the fermi - golden - rule approach can not be used to calculate the spin dephasing time .
therefore , in this paper we adopt the equation - of - motion approach for many - level system with born approximation developed in ref . . when the spin dephasing induced by the hyperfine interaction is considered , as the slow relaxation of nuclear bath compared to the electron , the kinetics is non - markovian
moreover , because of the born approximation , this equation - of - motion approach can only be applied for strong magnetic field ( @xmath42t).@xcite therefore , the pair - correlation method@xcite is further adopted to calculate the hyperfine interaction induced @xmath2 for small magnetic field .
what should be emphasized is that the soc is always included , no matter which mechanism is considered .
it has been shown that its effect to spin decoherence can not be neglected.@xcite -axis @xmath43 ( @xmath44 ) and the energy difference @xmath45 _ vs. _ the bias field @xmath46 .
note the scale of @xmath47 is on the right side of the figure .
( b ) square of the absolute value of the ground state wave function along the @xmath5-axis at two typical bias fields . in the calculation , the well width @xmath48 nm , the inter - dot distance @xmath49 nm and the barrier height @xmath50 ev . , width=283,height=302 ]
following the method addressed above , we perform the numerical calculation in a typical vertically coupled gaas dqd with barrier height @xmath50 ev , inter - dot distance @xmath49 nm and well width @xmath48 nm . the gaas material parameters and the parameters related to different mechanisms are the same with those in ref .. the eigen energy and eigen wave function along the @xmath5-direction are obtained numerically . in fig .
[ fig1](a ) , the lowest two eigen energies @xmath51 and @xmath52 along the @xmath5-axis and their difference @xmath53 are plotted as functions of the electric field @xmath46 .
it can be seen that the energy difference @xmath47 increases quickly with the electric field @xmath46 when @xmath46 is larger than @xmath54 kv / cm .
the eigen wave function of the ground state along the @xmath5-axis also has large variation with @xmath46 .
it can be seen clearly in fig .
[ fig1](b ) that when @xmath46 is very small ( @xmath55 kv / cm ) , the wave function of the ground state locates at the two wells almost equally .
however , when @xmath46 is large enough ( @xmath56 kv / cm ) , the wave function of the ground state locates mostly at the quantum well with lower potential .
the physics of such bias - voltage - induced quick change of eigen energy and eigen wave function can be understood as what follows . because of the large barrier height @xmath13 and/or large inter - dot distance @xmath14 , the two quantum dots are nearly independent and the eigen wave function along the @xmath5-axis of the lowest subband spreads equally over the two qds when the source - drain voltage is very small .
therefore at this time the energy difference between the lowest two energy levels along the @xmath5-axis @xmath47 is very small .
however , with the increase of the source - drain voltage , electron can tunnel through the barrier and the wave function is almost located at one dot with lower potential and therefore @xmath47 increases quickly with @xmath46
. induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61).,title="fig:",width=192,height=158 ] induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61).,title="fig:",width=192,height=158 ] induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61).,title="fig:",width=192,height=158 ] induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61).,title="fig:",width=192,height=158 ] the spin relaxation due to various mechanisms at different magnetic fields @xmath62 and quantum dot diameters @xmath63 are plotted as functions of electric field @xmath46 in fig
. [ fig2 ] . the temperature @xmath57 k. it is seen that with the increase of @xmath46 , the spin relaxations induced by all the three mechanisms almost keep unchanged for small @xmath46 ( when @xmath64 kv / cm ) , then increase a little and reach maximums around @xmath65 kv / cm .
what is interesting is that when @xmath46 is increased to around @xmath66 kv / cm , the spin relaxations are suppressed very quickly over a small window of @xmath46 .
therefore , the total spin relaxation can be controlled effectively with a small value of the variation of the bias field @xmath67 .
for example , in fig.[fig2](a ) , the spin relaxation shows ten orders of magnitude variation when the electric field @xmath46 changes from @xmath54 to @xmath68 kv / cm .
this can be understood as following .
all the three mechanisms are related to the electron - bp scattering which is affected sensitively by the phonon wave length .
the scattering becomes most efficient when the phonon wave length is comparable with the dot size .
it is also known that the spin relaxations between the first and second subband are dominant for small electric field.@xcite therefore when @xmath64 kv / cm , as the energy difference between the lowest two subband along the @xmath5-direction @xmath47 is almost constant ( see fig .
[ fig1 ] ( a ) ) , the spin relaxation keeps nearly unchanged .
when the phonon wave length is comparable with the dot size , the electron - phonon scattering becomes most efficient .
therefore the spin relaxations show maximums .
however , with the further increase of energy difference @xmath47 by the bias voltage , the phonon wave length becomes larger than the dot size .
consequently the spin relaxation decreases very quickly over a small window of @xmath67 .
now we focus on the variation magnitude of the spin relaxation with the bias field under different conditions .
the largest variation of @xmath41 ( @xmath68 orders of magnitude ) happens at small magnetic field @xmath69 t and small diameter @xmath70 nm .
however , for larger @xmath63 ( @xmath71 nm in fig .
[ fig2](b ) ) or larger @xmath62 ( @xmath72 t in fig .
[ fig2](c ) ) , the variations of the total spin relaxation decrease by several orders of magnitude .
it is further seen that when both @xmath63 and @xmath62 are increased [ @xmath73 nm and @xmath74 t in fig .
[ fig2](d ) ] , the variations of the total spin relaxation is even smaller .
this is because the spin relaxation induced by the electron - bp interaction and @xmath61 decreases with @xmath62 and @xmath63 in the high electric field region , where electron is mostly confined in one dot .
this is similar to the single qd case.@xcite therefore to achieve large control of spin decoherence , the magnetic field @xmath62 and dot diameter @xmath63 should be small
. induced by different mechanisms _ vs. _ the electric field . in the calculation , @xmath70 nm , @xmath69 t and @xmath75 k. curve with @xmath58 : by soc together with the electron - bp scattering ; curve with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curve with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61).,width=226,height=226 ] we further investigate the electric field dependence of spin relaxation at @xmath75 k and the results are shown in fig .
it is interesting to see that the spin relaxation induced by the second - order process of hyperfine interaction combined with the electron - bp scattering ( @xmath61 ) still has large variation with @xmath46 ( @xmath76 orders of magnitude variation when @xmath46 changes from @xmath54 to @xmath68 kv / cm ) .
however , the spin relaxations induced by the other two mechanisms keep almost unchanged . this is
because when @xmath75 k , the electron only locates at the lowest orbital level and the spin relaxation happens only between the lowest two zeeman sublevels which keeps unchanged with @xmath46 .
therefore the large variations of spin relaxations induced by the soc together with the electron - bp scattering and the strain - induced direct spin - phonon coupling no longer exist .
however , for @xmath61 , which is the second - order process scattering , the middle states @xmath77 can be higher levels as the hyperfine interaction can couple the spin - opposite states in different subband along the @xmath5-axis .
the energy differences between the middle states and the initial / final states increase with @xmath46 and therefore the spin relaxation induced by @xmath61 decreases with @xmath46 quickly . and @xmath78 induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61 ) ; curves with @xmath79 : by the hyperfine interaction.,title="fig:",width=192,height=158 ] and @xmath78 induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters .
@xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61 ) ; curves with @xmath79 : by the hyperfine interaction.,title="fig:",width=192,height=158 ] and @xmath78 induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61 ) ; curves with @xmath79 : by the hyperfine interaction.,title="fig:",width=192,height=158 ] and @xmath78 induced by different mechanisms _ vs. _ the electric field at different magnetic fields and dot diameters . @xmath57 k. curves with @xmath58 : by soc together with the electron - bp scattering ; curves with @xmath59 : by the direct spin - phonon coupling due to the phonon - induced strain ; curves with @xmath60 : by the second - order process of the hyperfine interaction together with the bp ( @xmath61 ) ; curves with @xmath79 : by the hyperfine interaction.,title="fig:",width=192,height=158 ] now we turn to study the variation of spin dephasing with the electric field @xmath46 and the results under different conditions are summarized in fig.[fig4 ] .
it is seen that the spin dephasing induced by the soc together with the electron - bp scattering , direct spin - phonon coupling due to the phonon - induced strain and the second - order process of electron - bp scattering combined with the hyperfine interaction always has several orders of magnitude variation with @xmath46 at different @xmath63 and @xmath62 .
however , the spin dephasing induced by the hyperfine interaction only increases a little with @xmath46 , which suppresses the large variation of the spin dephasing induced by the other three mechanisms .
nevertheless , there is still two orders of magnitude variation of the spin dephasing when @xmath62 and @xmath63 are small ( fig [ fig4](a ) ) .
the large variation of spin dephasing induced by the three mechanisms related to electron - phonon scattering comes from the fast increase of the energy difference @xmath47 , similar to the analysis of spin relaxation .
the spin dephasing induced by the hyperfine interaction is not so sensitive with @xmath46 .
this is because for the hyperfine interaction , @xmath80 , which is obtained from the pair - correlation approach , with @xmath81 , @xmath82 and @xmath83 being the zeeman splitting energy , the hyperfine interaction parameter and the nuclear number in the quantum dot respectively.@xcite with the increase of the electric field @xmath46 , @xmath81 and @xmath82 keep unchanged and the wave function of the ground state is gradually localized on one dot with lower potential .
this means the effective quantum dot size decreases and consequently @xmath83 decreases .
however , as the effective quantum dot size decreases from two dots into one dot with the bias field @xmath46 , @xmath83 for large @xmath46 is only about a half of that for small @xmath46 .
therefore , @xmath78 for large field is about two times of that for small field due to the decrease of @xmath83 .
however , this increase of @xmath78 induced by the hyperfine interaction is very small compared to that induced by other three mechanisms ( which have several orders of magnitude variation ) .
what should be pointed out is that the variation of spin dephasing does not exist at @xmath75 k. this is because the hyperfine interaction is dominant for the spin dephasing at @xmath75 k , which keeps unchanged with @xmath46 .
in conclusion , we propose a scheme to manipulate the spin decoherence ( both @xmath1 and @xmath84 ) in dqd system by a small gate voltage .
up to ten orders of magnitude of spin relaxation and up to two orders of magnitude of spin dephasing can be obtained . to obtain large variation of spin decoherence , the inter - dot distance and/or the barrier hight
should be large enough in order to guarantee that the two qds are nearly independent for the small bias voltage . at the same time , the effective diameter and magnetic field should be small to get as large variation as possible .
finally , based on the present available experimental technology , the dqd system applied in this paper can be realized easily.@xcite this work was supported by the natural science foundation of china under grant nos .
10574120 and 10725417 , the national basic research program of china under grant no .
2006cb922005 and the innovation project of chinese academy of sciences . 10 , edited by d. d. awschalom , d. loss , and n. samarth ( springer - verlag , berlin , 2002 ) ; i. zutic , j. fabian , and s. das sarma , rev
* 76 * , 323 ( 2004 ) ; r. hanson , l. p. kouwenhoven , j. r. petta , s. tarucha , and l. m. k. vandersypen , rev .
* 79 * , 1217 ( 2007 ) ; j. fabian , a. matos - abiague , c. ertler , p. stano , and i. zuti , acta physica slovaca * 57 * , 565 ( 2007 ) .
engel , l. p. kouwenhoven , d. loss , and c. m. marcus , quantum information processing * 3 * , 115 ( 2004 ) ; d. heiss , m. kroutvar , j. j. finley , and g. abstreiter , solid state commun . *
135 * , 591 ( 2005 ) ; and references therein .
d. loss and d. p. divincenzo , phys . rev .
a * 57 * , 120 ( 1998 ) .
j. m. taylor , h .- a .
engel , w. dr , a. yacoby , c. m. marcus , p. zoller , and m. d. lukin , nature phys . * 1 * , 177 ( 2005 ) .
j. h. jiang , y. y. wang , and m. w. wu , phys .
b * 77 * , 035323 ( 2008 ) . y. g. semenov and k. w. kim , phys .
b * 75 * , 195342 ( 2007 ) .
r. hanson , b. witkamp , l. m. k. vandersypen , l. h. w. van beveren , j. m. elzerman , and l. p. kouwenhoven , phys .
lett . * 91 * , 196802 ( 2003 ) .
s. amasha , k. maclean , i. radu , d. m. zumbhl , m. a. kastner , m. p. hanson , and a. c. gossard , arxiv : cond - mat/0607110 . j. r. petta , a. c. johnson , j. m. taylor , e. a. laird , a. yacoby , m. d. lukin , c. m. marcus , m. p. hanson , and a. c. gossard , science * 309 * , 2180 ( 2005 ) . m. pi , a. emperador , m. barranco , f. garcias , k. muraki , s. tarucha , and d. g. austing , phys . rev . lett . * 87 * , 066801 ( 2001 ) . k. ono , d. g. austing , y. tokura , and s. tarucha , science * 297 * , 1313 ( 2002 ) .
d. g. austing , s. sasaki , k. muraki , k. ono , s. tarucha , m. barranco , a. emperador , m. pi , and f. garcias , int . j. of quant . chem . * 91 * , 498 ( 2003 ) .
f. h. l. koppens , j. a. folk , j. m. elzeman , r. hanson , l. h. willems van beveren , i. t. vink , h. p. tranitz , w. wegscheider , l. p. kouwenhoven , and l. m. k. vandersypen , science * 309 * , 1346 ( 2005 ) .
e. a. laird , j. r. petta , a. c. johnson , c. m. marcus , a. yacoby , m. p. hanson , and a. c. gossard , phys .
lett . * 97 * , 056810 ( 2006 ) .
p. stano and j. fabian , phys .
b * 73 * , 045320 ( 2006 ) ; _ ibid . _
* 77 * , 045310 ( 2008 ) .
n. mason , m. j. biercuk , and c. m. marcus , science * 303 * , 655 ( 2004 ) .
r. hanson and g. burkard , phys .
98 * , 050502 ( 2007 ) .
e. cota , r. aguado , and g. platero , phys .
lett . * 94 * , 107202 ( 2005 ) .
f. mireles , f. rojas , e. cola , and s. e. ulloa , j. supercond .
* 18 * , 233 ( 2005 ) .
y. y. wang and m. w. wu , phys .
b * 74 * , 165312 ( 2006 ) .
y. bychkov and e. i. rashba , j. phys .
c * 17 * , 6039 ( 1984 )
. w. h. lau and m. e. flatt , phys .
b * 72 * , 161311(r ) ( 2005 ) .
g. dresselhaus , phys . rev .
* 100 * , 580 ( 1955 ) .
j. l. cheng , m. w. wu , and c. l , phys .
b * 69 * , 115318 ( 2004 ) ; c. l , j. l. cheng , and m. w. wu , _ ibid . _
* 71 * , 075308 ( 2005 ) .
m. i. dyakonov and v. i. perel , zh .
* 60 * , 1954 ( 1971 ) [ sov .
jetp * 33 * , 1053 ( 1971 ) ] .
a. abragam , _ the principles of nuclear magnetism _ ( oxford university press , oxford , 1961 ) , chap . vi and ix .
v. a. abalmassov and f. marquardt , phys .
b * 70 * , 075313 ( 2004 ) . l. m. roth , phys . rev . * 118 * , 1534 ( 1960 ) .
w. a. coish and d. loss , phys .
b * 70 * , 195340 ( 2004 ) . w. yao , r .- b .
liu , and l. j. sham , phys .
b * 74 * , 195301 ( 2006 ) . | we propose a scheme to manipulate the spin coherence in vertically coupled gaas double quantum dots . up to _ ten _ orders of magnitude variation of the spin relaxation and _ two _ orders of magnitude variation of the spin dephasing can be achieved by a small gate voltage applied vertically on the double dot .
specially , large variation of spin relaxation still exists at @xmath0 k. in the calculation , the equation - of - motion approach is applied to obtain the electron decoherence time and all the relevant spin decoherence mechanisms , such as the spin - orbit coupling together with the electron bulk - phonon scattering , the direct spin - phonon coupling due to the phonon - induced strain , the hyperfine interaction and the second - order process of electron - phonon scattering combined with the hyperfine interaction , are included . the condition to obtain the large variations of spin coherence
is also addressed . |
allergic rhinitis ( ar ) is usually defined as the presence of at least one or more of the symptoms of congestion , rhinorrhea , sneezing , nasal itching , and nasal obstruction ( 1 , 2 ) .
the disease is an immunoglobulin e ( ige ) mediated reaction of th2-type t cell response ( 3 , 4 ) .
the disease has various effects on patients quality of life ( 5 , 6 ) .
it is divided into two aspects as seasonal and perennials and its prevalence has been increased over the last 4 decades in both industrialized and developing countries ( 7 , 8) .
based on the world health organization report in 2013 , the prevalence of seasonal and perennial nasal symptoms is estimated 30% in the united states , 20% in europe , 9% in different parts of the middle east , 36% in al - ain city ( abu dhabi ) , and 7% in the united arab emirates ( 9 ) . the prevalence of ar in iran has been reported as follows : 34.3% among high school students in hamadan city , 35.3% among 12 - 13 years old children in gorgan city , and 19.3% among high school students in kerman city ( 6 ) . in zahedan , based on a report in 2003 , a large number of allergens and high prevalence of ar disease have been recorded ( 74.5% ) among the study population that was attributed to geographical problems such as dry climate and dusty area ( 10 ) .
these allergens comprise aeroallergens such as trees , grasses , weeds , molds , air pollution ( 11 ) , house dust mites , feather , and animal dander ( 12 ) . among them ,
tobacco smoke is one of the known inhaled allergens that has been associated with high prevalence of allergic diseases and has various effects on the quality of life of smokers as well as persons who are not smoking and classified as passive smokers ( 13 ) .
tobacco contains more than 7000 chemicals , 60 known or suspected carcinogens and is responsible for approximately one - third of all cancer deaths annually . by the way ,
if someone puffs once on a cigarette , this will cause dna damage and if he wishes to continue , then this will overwhelm dna repair mechanisms , leads to genetic alterations and resulting in allergic rhinitis and other illnesses ( 14 ) .
investigations have sought to study the harmful effects of tobacco smoke on rhinitis and allergic sensitization as well as how smoking correlates with prevalence of allergic rhinitis , however the results are controversial ( 15 , 16 ) . to confirm the presence of ar disease ,
the most common diagnostic test is skin prick test ( spt ) ( 17 , 18 ) that is simple , easy , comfortable , inexpensive , safe , most reliable , and effective .
it is an appropriate diagnostic and rapid method of investigation of all type 1 hypersensitivity reaction to a specific allergen ( 17 , 19 , 20 ) .
this study was designed to understand the role of smoking in response to some aeroallergens , and to determine if there is any difference in response to some allergens between cigarette and non - cigarette smokers suffered from allergic rhinitis .
it was carried out on 478 adult patients with symptoms of allergic rhinitis referred to the immunology and allergy clinic of 2 main hospitals of zahedan city , iran between 2005 and 2012 .
the diagnostic criteria were based on standard gold criteria defined as the presence of at least one of the symptoms of congestion , rhinorrhea , sneezing , nasal itching , and nasal obstruction ( 1 ) diagnosed through physical examination by specialized physicians .
then , the patients were divided into two groups as smoker and nonsmoker based on patient s statements and their history of smoking . after taking consent letter from the patients , questionnaires , containing demographic data ,
main chief complaint , patient s history , season and duration of disease and family history of allergic rhinitis diseases were distributed among patients and completed by them .
exclusion criteria included lack of suffering from ar symptoms ; having pulmonary diseases like copd , emphysema , chronic bronchitis ; having some inflammatory diseases such as rheumatoid arthritis , inflammatory diseases of the stomach ; lack of cooperation in the project ; and transference of patients from other cities or provinces of the country . to confirm allergic rhinitis and providing an appropriate treatment ,
spt was performed with some available aeroallergens for each patient using a standard allergen extract panel ( purchased from french staller genes company ) .
aeroallergens like house dust mite , pollens , alternaria , aspergilus , cladosporium , grasses , weeds , wheat , cockroach , and feathers all were used for each patient .
the method of spt was applied on the anterior surface of the forearm and skin reactions were evaluated 20 minutes after the application of the skin test and considered positive when the reaction of redness and wheal was observed based on the reports of dogru et al . and hosseini et al .
the results were analyzed statistically by descriptive statistics method as well as odds ratio and confidence interval using univariate logistic regression model via spss software ( version 18 ) .
of 478 patients with allergic rhinitis , 278 ( 58% ) were male and 200 ( 42% ) female with ages ranged from 15 to 70 years .
additionally , the result of spt reactivity showed variable responses to different allergens among individuals as in ar smokers , the highest response was seen with aspergillus ( 79.3% ) and lowest with weeds ( 17.9% ) aeroallergens , whereas in non - smokers the highest response was seen with house dust mite ( 36.5% ) and lowest with alternaria ( 17.2% ) aeroallergens .
table 1 , lists the results of spt response to allergens in smokers and non - smokers patients based on sex , spt response , and percentage of patients .
furthermore , the result of statistical analysis of odds ratio and confidence interval with respect to sex and smoking based on univariate logistic regression model , indicated that smoking has no effect on spt results . also , there was no significant difference between male and female with respect to sensitivity to pollen and weeds aeroallergens .
however , males were significantly more sensitive than females with respect to the aspergillus , cladosporium , house dust mite , grasses , wheat , cockroach , and feather allergens ( table 2 ) .
this study was carried out to evaluate effects of smoking on spt reactivity to some allergens in male and female patients who suffered from allergic rhinitis .
little is known about the impact of smoking on reactivity to some available aeroallergens in ar smokers and non - smokers . in previous studies ,
the impact of smoking habits on allergic rhinitis and asthma diseases , has been reported ( 21 , 22 ) , but their results are controversial because some showed a significant association , whereas others did not .
accordingly as we mentioned , the potential role of cigarette smoking in allergic rhinitis is still not obscure .
in fact , the risk for the disease will be decreased more with quit cigarette smoking but still in a few patients with ar , they are more likely to develop allergic rhinitis and later asthma disease ( 23 ) . thus , association between smoking and allergic rhinitis , has been reported with a high prevalence of chronic rhinitis in both men and women and a low prevalence of allergic rhinitis in men as reported by eriksson j et al . in 2013 ( 15 ) . however , these associations have been dose dependent and remained when adjusting a number of possible confounders in multiple logistic regression analysis .
they also reported that prevalence of chronic rhinitis was the lowest in nonsmokers and highest in heavy smokers and prevalence of sensitization to common airborne allergens was lower in current smokers compared to nonsmokers .
more recently a study examined the relationship between allergic rhinitis among smokers and nonsmokers and their findings suggest that cigarette smoking is associated with allergic rhinitis ( 2 ) . on the other hand , to understand better the role of smoking on spt results in allergic rhinitis we examined the role of spt reactivity to some allergens in patients with ar .
in fact , eriksson ne and holmen a were the first in 1996 who have reported the spt results with standardized extracts of inhalant allergens in 7099 adult patients with asthma or rhinitis ( 24 ) . since that time some other investigators have studied the role of spt in young adult s ar patients with allergic rhinitis in combination with the effect of stress and anxiety on positive skin test responses ( 21 ) and some others have investigated the spt reactivity to common aero and food allergens among children with allergy ( 18 ) .
, our study has focused on the role of smoking on spt results in male and female patients with allergic rhinitis .
our results firstly confirmed that 41.4% of patients were smokers that most of them were male and statistically significant differences between gender and smokers were observed ( p < 0.001 ) .
this result is consistent with studies of hosseini et al . and saleh et al .
furthermore , our study showed that gender and smoking were related to the prevalence of allergic rhinitis among male patients and this result is also consistent with other studies ( 2 , 22 - 25 ) .
however , it is inconsistent with the study of eriksson j et al . ( 15 ) , in which the prevalence of chronic rhinitis was high whereas the prevalence of allergic rhinitis was low in male cigarette smokers .
secondly , our results showed a significant association between positive reactivity of patients to aspergillus , cladosporium , house dust mite , grasses , wheat , cockroach , and feather allergens between smoker and nonsmoker patients adjusted for male gender ( table 2 ) .
this finding has not introduced elsewhere and the reason for this may be related to the different role of tobacco smoke in health as reported by warren et al . (
in addition , there was no significant difference between male and female with respect to the sensitivity to pollen and weeds aeroallergens ( table 2 ) , but these results also are not reported elsewhere and is consistent with the study of asero et al .
in which they indicated that the clinical relevance of hypersensitivity to pollen pan allergens is similar in men and female patients suffered from pollen allergy ( 26 ) .
this result is also partially consistent in terms of gender with the study of paulose - ram r et al . who showed that cigarette smoking has been associated with some demographic parameters of smokers such as age , gender , race , and degree of education ( 27 ) .
so it can be said that aeroallergens , especially these allergens play an important role in smoker ar than in nonsmokers .
thus , for better diagnosis and treatment of patients with ar such procedures as avoiding allergens , using antihistamines , taking anti - inflammatory drugs , and following immunotherapy programs are highly recommended .
furthermore , some confounding factors in this study were included such as lack of patient cooperation in collecting accurate data on the number of cigarettes consumed , their underlying diseases , presence or absence of risk factors according to the patients statement at reception , long term study , failure to investigate some effective demographic factors associated with disease and the relatively high cost of testing ( as the test was costly , time consuming , some uncooperative patients in their next visit did not control them ) .
further study should be taken into consideration to better understand the role of aeroallergens by spt method in smoker and nonsmoker patients with allergic rhinitis .
this should be noted that other factors such as longer follow - up period , use of a comprehensive questionnaire , effect of potential confounding variables and use of statistical techniques to identify risk groups , must be investigated in future . on the other hand
, we did not examine smokers in terms of the number of cigarettes or packs of cigarettes used and also what is the effect of smoke in passive smokers and or the influence of smoking on disease intensity in smokers and nonsmokers .
our results support the effect of smoking in spt results of the patients with ar and the most effective allergens in cigarette smoker patients were aspergillus , cladosporium , house dust mite , grasses , wheat , cockroach and feather allergens compared to nonsmokers . thus we conclude that for controlling the disease in cigarette smoker patients , avoidances of such allergens following immunotherapy needs to be done . | background : allergic rhinitis ( ar ) is the most common allergic disease , affecting 30% of population around the world .
the disease is predominantly associated with exposure to some aeroallergens like cigarette smoking .
skin prick test ( spt ) is a method of detecting immediate allergic reactions and is applied for controlling disease and therapeutic modality.objectives:this study was designed to investigate the effect of cigarette smoking on spt results among male and female individuals with ar disease.patients and methods : a total of 478 patients with ar admitted to the 2 main hospitals of zahedan city from 2005 to 2012 , were recruited in this analytic - descriptive study .
categories of smokers and never smokers were used based on patient s statements and their history of smoking .
spt was performed with panel of some allergens and results were recorded and analyzed statistically .
odds ratio and confidence interval method were calculated using univariate logistic regression.results:the results of this study indicated that 41.4% of patients with allergic rhinitis was smoker with ages ranged from 15 to 70 years .
the result of this study also showed that smoking has no effect on spt results of pollen and weeds aeroallergens conducted on male and female ar patients .
however , male were significantly more sensitive than female in terms of sensitivity to the aspergillus , cladosporium , house dust mite , grasses , wheat , cockroach , and feather allergens.conclusions:our findings did not support the effect of cigarette smoking on spt reactivity to pollen and weeds aeroallergens .
however , male were significantly more sensitive than female in terms of sensitivity to some allergens . |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Regulatory Information Presentation
Act of 1998''.
SEC. 2. FINDINGS.
The Congress finds the following:
(1) There is a substantial lack of consistency in the
presentation of information explaining and supporting Federal
rulemaking actions when such information is published with
proposed and final rules in the Federal Register.
(2) This lack of consistency makes it more difficult for
the public and Congress to understand rulemaking actions and
their justification and to locate particular relevant
information.
(3) Presidential Executive Order 12866, promulgated
September 30, 1993, specifies certain analytical components for
Federal rulemaking that provide a useful design for consistent
organization of the information presented in Federal Register
rulemaking notices.
(4) Such a consistent format will facilitate congressional,
executive branch, and public review of proposed rulemaking
actions.
SEC. 3. FORMATTING OF RULEMAKING ENTRIES IN THE FEDERAL REGISTER.
(a) Significant Rules.--This section applies to each significant
rule that is published in the Federal Register as a general notice of
proposed rulemaking, or as a final or interim final substantive rule,
under section 553 of title 5, United States Code.
(b) Information To Be Included in Proposed, Interim Final, and
Final Rules.--Each agency shall, in accordance with a uniform format to
be established (after public notice and an opportunity for public
comment) by the Office of the Federal Register, include in the preamble
(the ``Supplementary Information'') to each such significant rule, both
as a proposed and as a final or interim final rule, the information
specified in this subsection.
(1) Rulemaking status.--
(A)(i) The agency shall describe whether, and if so
the reason that, the rule has been determined to be--
(I) a significant rule; or
(II) a major rule under section 804(2) of
title 5, United States Code.
(ii) If the agency determines that a rule is not a
significant rule, the agency shall provide the reasons
and justifications for such determination using each of
the factors described in section 5(3).
(B) The agency shall identify the nature and timing
of any applicable legal deadline or other good cause
for the issuance of the rule more quickly than the
normal work schedule would provide.
(C) The agency shall provide an explanation as to
whether the President, the Vice President, or any
official in the Executive Office of the President has
waived any provision of any relevant Executive order or
related policy directive applicable to the rulemaking.
If any cost-benefit analysis, risk assessment, or other
evaluation of the rule prepared by the agency displays
an important gap in the analytical information relied
upon therein, the agency shall provide an explanation
as to why it is or is not feasible or reasonable to
delay the rulemaking until those gaps in information
are filled.
(2) Regulatory policy officer.--The agency shall provide
the name, telephone number, and position of the regulatory
policy officer of the agency responsible at each stage of the
regulatory process for fostering the development of effective,
innovative, and least burdensome regulations and furthering the
principles set forth in any relevant Executive order or related
policy directive related to rulemaking.
(3) Consultation.--The agency shall describe any
consultations with stakeholders, formal advisory bodies, and
State, local, or tribal governments under title II of Public Law 104-4
(2 U.S.C. 1531 et seq.) or other applicable authority, identifying the
individuals involved and the issues discussed.
(4) Need.--The agency shall identify any applicable law
requiring the specific rulemaking and separately describe any
compelling public need for undertaking the rulemaking,
including a detailed explanation of the need for preempting, or
regulating instead of, State, local, or tribal governments.
(5) Legal authority.--The agency shall identify the
specific statutory provisions authorizing the rule, the overall
regulatory program involved, and the scope of the statutory
discretion of the agency, if any, to regulate and the degree to
which the agency is regulating. Except in cases in which the
rule has no legal effect other than to implement the literal
wording of the applicable law, the agency shall include in the
preamble a legal analysis identifying the scope of discretion
available to the agency in undertaking the rulemaking.
(6) Alternatives considered.--The agency shall identify the
principal regulatory alternatives considered by the agency
before determining which alternative to propose for public
comment, or to adopt in the final or interim final rule.
(7) Alternative selected.--Based on the criteria set forth
in title II of Public Law 104-4 (2 U.S.C. 1531 et seq.) and any
relevant Executive order or related policy directive related to
rulemaking, the agency shall identify and explain in reasonable
detail the reasons why the agency selected the alternative to
be adopted or adopted in the rule.
(8) Costs.--The agency shall estimate the direct and
indirect costs of the rule, which shall be stated to the extent
reasonably possible as monetized costs, quantified costs, or
qualitative costs, in that order.
(9) Impacts.--The agency shall identify the entities that
will be significantly impacted through compliance with the
rule, and shall evaluate and describe the nature of the impacts
that are anticipated to be caused by the costs to be imposed or
other actions the entities are anticipated to take in order to
come into compliance with the rule. The agency shall summarize
any analysis or evaluation conducted under title II of Public
Law 104-4 (2 U.S.C. 1531 et seq.) or chapter 6 of title 5,
United States Code, or if the agency did not conduct such an
analysis or evaluation, provide an explanation as to why an
analysis or evaluation was not performed.
(10) Benefits.--The agency shall estimate the direct and
indirect benefits of the rule. These benefits shall be stated
to the extent possible as monetized benefits, quantified
benefits, or qualitative benefits.
(11) Certification of compliance.--The agency shall state
whether any official in the Executive Office of the President
carried out a review of the rule under any relevant Executive
order or related policy directive related to rulemaking. If
such a review has been carried out, the agency shall briefly
describe the individuals involved, the timing of the review
process, the procedural actions taken by those involved, and
the nature of any issues raised in the course of such review.
If any such official found the issuance of the rule to be
consistent with the regulatory principles set forth in such
Executive order or related policy directive related to
rulemaking, the agency shall identify the official, and
describe the nature of the communication involved.
(c) Additional Information To Be Included in Interim Final and
Final Rules.--
(1) In general.--Each agency shall, in accordance with a
uniform format to be established (after public notice and
opportunity for public comment) by the Office of the Federal
Register, include in the preamble (the ``Supplementary
Information'') to each such significant rule, as a final or
interim final rule, the information specified in this
subsection.
(2) Significant issues.--
(A) Each agency shall provide a brief description
of the significant issues raised--
(i) by the public in a statement placed in
the rulemaking file;
(ii) in consultations described in
subsection (b)(3) by formal advisory bodies;
and
(iii) by any official in the Executive
Office of the President carrying out a review
under any relevant Executive order or related
policy directive related to rulemaking.
(B) If, under subparagraph (A)(iii), an official
did not raise any significant issue, the agency shall
provide a description to that effect. The agency shall
identify and describe any important gap in analytical
information relied upon in any cost-benefit analysis,
risk assessment, or other evaluation of the rule
prepared by the agency, and any assumptions and
justification for such assumptions that were used to
fill those gaps.
(3) Conflict resolution.--The agency shall describe in
reasonable detail, both concerning the specific review
procedures used and also the substantive concerns raised--
(A) whether the rule was returned to the agency for
reconsideration by any official in the Executive Office
of the President, the nature of any reasons for such
return, and the nature of the response of the agency to
such return;
(B) the nature of any involvement by the President
or Vice President or their respective staff in
reviewing the rule, or any earlier version of the rule,
submitted for review by any official in the Executive
Office of the President under any relevant Executive
order or related policy directive related to
rulemaking; and
(C) the nature of the resolution of any
disagreement involved in such review or return.
(4) Significant substantive changes.--
(A) The agency shall provide a brief description of
any substantive changes to the rule made--
(i) following the end of the period for
public comment and the submission of the draft
final or interim final rule for review by any
official in the Executive Office of the
President under any relevant Executive order or
related policy directive related to rulemaking;
and
(ii) during any review of the draft final
or interim final rule by any official in the
Executive Office of the President under any
relevant Executive order or related policy
directive related to rulemaking.
(B) The agency shall identify the individual
primarily responsible for suggesting any such
substantive change, if such individual is not within
the program office directly responsible for drafting
the rule.
(5) Cost-benefit determination.--To the extent permitted by
law and as applicable, the agency shall provide a reasoned
statement explaining the way in which the estimated benefits of
the rule justify its estimated costs, as described under
subsections (b)(8) and (b)(10), and any other impacts, as
described under subsection (b)(9). To the extent that the
agency relies upon qualitative benefits to justify the action
of the agency, the agency shall also describe the subjective
nature and uncertainties inherent in such a statement of
qualitative benefits.
(d) Good Cause Exception.--When the agency for good cause finds,
and incorporates the finding and a brief statement of reasons therefor
in the rule, that providing any portion of the information required by
subsections (b) and (c) is impracticable, unnecessary, or contrary to
the public interest, the agency may issue the rule without providing
such portion of the information required. The agency shall identify in
the preamble to the rule the portion of the information that is not
being provided and shall state the reasons for not providing the
preamble and when the preamble will be provided. The agency shall make
every reasonable effort to provide such information before the
effective date of the rule.
SEC. 4. PUBLIC NOTICE.
Each agency shall, on an annual basis and in accordance with a
schedule and uniform format to be established (after public notice and
opportunity for public comment) by the Office of the Federal Register,
publish a notice in the Federal Register that contains the following
specified statistics:
(1) The number of rules published as proposed, interim
final, and final rules.
(2) The number of rules under paragraph (1) that are
discretionary, in contrast to rules the contents of which were
specifically mandated by law as described under section
3(b)(5).
(3) The number of pages in the Federal Register for each
category of rule under paragraphs (1) and (2).
(4) The number of those rules that are--
(A) significant rules; and
(B) major rules under section 804(2) of title 5,
United States Code.
(5) The number of those rules reviewed under any relevant
Executive order or related policy directive related to
rulemaking, the number of rules substantively changed during
such reviews, and the number of pertinent actions taken during
such reviews.
SEC. 5. DEFINITIONS.
As used in this Act:
(1) The term ``agency'' has the meaning given that term in
section 551(1) of title 5, United States Code.
(2) The term ``rule'' has the meaning given that term in
section 551(4) of title 5, United States Code.
(3) The term ``significant rule'' means any agency
rulemaking action that is likely to result in a rule that may--
(A) have an annual effect on the economy of
$1,000,000 or more or adversely affect in a material
way the economy, a sector of the economy, productivity,
competition, jobs, the environment, public health or
safety, or State, local, or tribal governments or
communities;
(B) create a serious inconsistency or otherwise
interfere with an action taken or planned by another
agency;
(C) materially alter the budgetary impact of
entitlements, grants, user fees, or loan programs or
the rights and obligations of recipients thereof; or
(D) raise novel legal or policy issues arising out
of legal mandates, the priorities of the President, or
the regulatory principles set forth in any relevant
Executive order or related policy directive.
SEC. 6. EFFECTIVE DATE.
This Act shall take effect 90 days after the date of the enactment
of this Act. | Regulatory Information Presentation Act of 1998 - Directs each Federal agency, in accordance with a uniform format to be established by the Office of the Federal Register, to include in the preamble to each significant rule, both as a proposed and as a final or interim final rule, information concerning: (1) whether and on what basis the rule has been determined to be or not to be a significant or major rule; (2) any legal deadline or good cause for issuing the rule more quickly than normal; (3) any executive waiver of rule making policy; (4) the identity of the regulatory policy officer responsible at each stage of the regulatory process for the development of the regulations; (5) agency consultations with stakeholders, advisory bodies, and State and local governments; (6) any applicable law requiring, and any compelling public need for, the rule making; (7) the specific legal authority for the rule, the overall regulatory program involved, and the scope of the agency's discretion to regulate; (8) the principal regulatory alternatives considered by the agency; (9) the reasons for selection of the alternative adopted; (10) the rule's costs, impacts, and benefits; and (11) certification of compliance with any relevant rule making review requirements.
Requires each agency to also include in the preamble to each significant rule, as a final or interim final rule: (1) a brief description of the significant issues raised by the public, in consultations by formal advisory bodies, and by any official in the Executive Office of the President carrying out a review of the rule making; (2) a description, concerning both the specific review procedures used and the substantive concerns raised, of any reconsideration of the rule of such an official, the nature of any involvement by the President or Vice President or their respective staff in reviewing the rule, and the nature of the resolution of any disagreement involved in such review or return; (3) a brief description of any substantive changes made to the rule during specified periods and the identity of the individual primarily responsible for suggesting any such substantive change if such individual is not within the program office directly responsible for drafting the rule; and (4) a statement explaining how the rule's estimated benefits justify its costs.
Permits an agency to issue a rule without providing a portion of the information required if it determines that providing such information is impracticable, unnecessary, or contrary to the public interest. Requires the agency to: (1) identify in the rule's preamble the information omitted, the reasons for the omission, and when the information will be provided; and (2) make every effort to provide the information before the rule's effective date.
Requires each agency to publish, annually, a notice in the Federal Register that contains statistics on the number of: (1) rules published as proposed, interim final, and final rules; (2) rules that are discretionary, in contrast to mandated; (3) pages in the Federal Register for each category of rule; (4) significant rules and major rules; and (5) rules reviewed under a rule making policy directive, the number substantively changed, and the number of pertinent actions taken during such reviews. |
the facial artery musculomucosal ( famm ) flap was first described by pribaz et al in 1992.1 it consists of the mucosa and the submucosa of the cheek and a portion of the buccinator muscle .
it can be pedicled inferiorly on the facial artery and superiorly on the angular artery , depending on the site of the defect that needs reconstruction .
the superiorly based famm flap was successfully used in the reconstruction of the palate , upper vestibule , nasal cavity , and orbit.2 recent research focused on developing modifications to expand the indications of this flap.3
4 among these , xie et al5 have developed a modification of the famm flap in cadavers that increased its length by adding an extension using the fascia of the masseter for skull base reconstruction .
they demonstrated the feasibility of using this well - vascularized flap for a tension - free coverage of key areas of the skull base .
the details of the surgical technique are well described and illustrated in their study.5 in summary , this modification required a submandibular incision for dissection and ligation of the cervical facial artery .
then , the buccal and marginal branches of the facial nerve are carefully dissected from the parotidomasseteric fascia to prevent a lower facial paralysis .
care should be taken to leave the masseteric fascia in continuity with the facial artery for proper vascular perfusion of the extension flap .
the fascia and the facial artery are then transferred intraorally through a blunt dissection anterior to the masseter muscle .
the remaining steps in the harvest of the famm flap are achieved according to the standard technique.1
the use of the famm flap in posterior skull base or nasopharynx reconstruction has never been reported in a living patient .
we report the first case of skull base reconstruction using a superiorly pedicled famm flap modified with an extension to the masseteric fascia and muscle in a living patient . the defect involved the exposure of the nasopharyngeal and petrous portions of the internal carotid after an extensive surgical resection of a chordoma .
our patient is a 71-year - old man who presented at our clinic with odynophagia , dysphagia , atrophy of the left hemi tongue , and diplopia .
imaging investigations showed the presence of a voluminous lesion ( 4.8 6.5 8.7 cm ) in the left parapharyngeal space with superior invasion of the clivus , lateral process of c1 , and the left occipital condyle ( figs . 1 and 2 ) .
3 ) .
preoperative mri axial and coronal views in t2w - tse showing voluminous tumor mainly located in the left parapharyngeal space with superior invasion of the clivus , lateral process of c1 , and the left occipital condyle .
histologic sections demonstrating cords and lobules of large cells , with small , bland nuclei and abundant cytoplasm , eosinophilic or vacuolated , in a loose , myxoid stroma .
these cells are positive for the epithelial markers ( ck ae1/3 , ck818 , ema ) , vimentin and brachyury ; all other markers were negative ( s100 , rcc , ck5/6 , cea , moc31 ) .
tumor removal required an endoscopic transnasal approach combined with an open cervical approach for excision of the left parapharyngeal extension .
because adjuvant radiation therapy was planned for this patient , the defect would best be reconstructed using a robust vascularized flap .
we harvested an extended retrograde famm flap measuring 10 cm in length and 2.5 cm in width ( fig .
4 ) . the flap was transferred through a caldwell - luc fenestration to the maxillary sinus ( fig .
an endoscopic maxillary antrostomy was performed and allowed the flap to reach the nasopharynx by passing through the maxillary sinus ( fig .
5b ) . once in place , the flap completely covered the petrous portion of the exposed internal carotid and the extension island flap covered the retrostyloid parapharyngeal space .
the flap was held in place with fibrin sealant topical and petroleum gauze nasal packing to reduce the risk of retraction from the pulling gravity force .
perioperative view of the facial artery musculomucosal ( famm ) flap with an island extension to the masseter muscle ( famme flap ) .
( a ) the transfer of the superiorly pedicled facial artery musculomucosal flap through the maxillary sinus to the skull base .
( b ) postoperative mri t1w - tse c+ showing the transmaxillary passage of the famm flap pedicle .
the workhorse in skull base reconstruction is the vascularized nasoseptal flap as described by hadad et al in 2006 with the ability to lower cerebrospinal fluid leak rate to 5%.6 in this case , the nasoseptal flap or the inferior turbinate flap could not be used because of the extensive invasion of the tumor in the nasal cavity and the posterior septum .
we also anticipated that this patient would need postoperative adjuvant radiation therapy based on the size and the extent of the tumor .
a pericranial flap would have required a coronal incision leaving a very thin flap for reconstruction with limited protection for the petrous part of the internal carotid artery ( ica ) .
the use of a free flap was not considered because of the significant comorbidities of this patient .
the famm flap was ideal as it is a robust and well - vascularized regional flap .
furthermore , the need of a cervical incision for tumor extirpation also encouraged us to use this flap .
recent studies have focused on developing modifications to expand the indications of this flap by increasing its length.3
4
5 these studies demonstrated the feasibility of using this well - vascularized flap for a tension - free coverage of key areas of the skull base .
the details of the surgical technique were well described and illustrated in our previous study.5 in this specific case , a portion of the masseter muscle was harvested along with its fascia to obtain a bulkier island extension flap ( fig .
the benefit of this modification is the location of the island extension being at a certain distance from the distal famm flap , which was ideal for our two sites defects ( parapharyngeal and petrous carotid ) located at a distance from each other . at 2 weeks
postoperative follow - up , endoscopic examination showed a viable famm flap completely covering the defects ( fig .
the patient later received adjuvant radiation therapy by means of 60 gy in 30 fractions .
he fully recovered from the diplopia and was temporarily dependent on gastrostomy tube for feeding . at 49 months of follow - up
, the flap and its attached masseteric island have now mucosalized and are well perfused with no signs of retraction ( fig .
the most recent magnetic resonance imaging ( mri ) showed stability in residual disease at the clivus and retropharyngeal space ( fig . 8) .
endoscopic view of the facial artery musculomucosal ( famm ) flap 2 months postradiation therapy and 5 months postsurgery .
the dotted line denotes the course of the internal artery covered by the famm flap . * the petrous portion of the skull base .
postoperative and postradiotherapy axial mri t1w - tse c+ showing stability of intracranial and cavernous tumoral residue at 4 years follow - up .
although successful reconstruction was achieved in our patient , the retrograde famm flap should only be used as an alternative when other clinically proven options are not suitable .
this article serves as an opener to newer indications of the famm flap in head and neck reconstruction of skull base defects . | objectives the superiorly pedicled facial artery musculomucosal ( famm ) flap has been successfully used for reconstruction of head and neck defects since 1992 .
common sites of defects include the oral cavity and oropharynx .
this article presents a clinical case in which we have successfully used a newly developed modification of the famm flap for bulky nasopharyngeal and skull base reconstruction .
results our patient is a 71-year - old man who presented with a large parapharyngeal and clival chordoma . after tumor removal through combined endoscopic and cervical approach , the internal carotid artery ( ica ) in the nasopharyngeal portion was left exposed . a modified superiorly based famm flap measuring up to 10 cm in length and 2.5 cm in width was successfully harvested and used to completely cover the defect and the ica .
the flap survived local radiation therapy at the long - term follow - up .
conclusion we have developed a new modification of the famm flap , using the fascia of the masseter muscle .
this is the first reported case in the literature using a modified famm flap for the reconstruction of nasopharyngeal and skull base defect . |
a 79-year - old woman presented to our tertiary referral vascular surgical centre with an incidental finding of a thoracic aortic aneurysm on routine chest radiography . upon further investigation
, she was found to have an isolated descending thoracic aortic aneurysm secondary to a previous open aortic coarctation repair that she had undergone at the age of 38 .
she underwent a left carotid - subclavian bypass graft with left vertebral reimplantation prior to the completion of thoracic aortic stent grafting nine days later . an angiogram taken
after thoracic aortic stent grafting and a post - implantation computed tomography angiogram performed the following day demonstrated no endoleak , and she was discharged eight days later .
four months later , a small type ii endoleak was subsequently demonstrated with minimal expansion of the aneurysm sac . over the course of the following five years
catheter - directed angiography demonstrated that the right intercostal bronchial artery was communicating with the aneurysm sac , corresponding to the type ii endoleak seen on computed tomography angiography ( fig .
1 ) . onyx ( covidien , irvine , ca , usa ) was used to perform standard coil embolization , and no flow into the aneurysm sac was found after the procedure ( fig .
whilst the phenomenon of type ii endoleaks and their management is well described for the endovascular repair of infrarenal aneurysms , there is less data available about type ii endoleaks following thoracic aortic stent grafting .
the incidence of type ii endoleaks following thoracic aortic stenting can be as high as 10.6% . to our knowledge , only one similar report of a thyrocervical derived collateral causing a type ii endoleak exists , described by rivera - sanfeliz et al . .
they describe a right thyrocervical trunk bronchial collateral , which is very similar to our description of an endoleak occurring in the intercostal bronchial artery .
we strongly agree with their statement that the examination of potential anomalous or collateral thoracic pathways is mandatory when considering treatment of a type ii endoleak following endovascular taa repair .
onyx is a non - adhesive liquid embolic agent used for the pre - surgical embolization of brain arteriovenous malformations and aneurysms .
onyx is comprised of an ethylene vinyl alcohol copolymer dissolved in dimethyl sulfoxide , with suspended micronized tantalum powder to provide contrast for visualization under fluoroscopy .
the use of onyx to treat type ii endoleaks in endovascular abdominal aortic aneurysm repair was first reported in 2001 .
it is now a well - described and frequently used technique in the management of type ii endoleaks following the endovascular repair of both abdominal and thoracic aneurysms [ 58 ] .
our case further demonstrates the usefulness of onyx for type ii endoleak embolization following endovascular aneurysm repair , even in unusual cases involving aberrant anatomy . | the aetiology , incidence and management of type ii endoleaks in standard infrarenal endovascular aortic aneurysm repair is well described .
far less data is available for thoracic stent grafting .
we present a rare and interesting case of a type ii endoleak post thoracic aortic stenting and highlight the aberrant anatomy that can cause this phenomenon in such cases . |
in this prospective quasi - randomized , doubleblinded , placebo - controlled study , a total of 146 reproductive women aged between 18 - 35 years old who were referred to outpatient clinics of shahid beheshty and al - zahra hospitals from december 2009 to february 2010 for infertility treatments , having at least two of three rotterdam consensus criteria as oligomenorrhea or amenorrhoeic cycle , hyperandrogen - ism , or 10 or more follicles with size range of 2 - 10 mm on trans vaginal sonography ( aloka1000,7.5mh.z probe ) , were enrolled .
women should not have taken any hormonal or medication drugs , effective on metabolic systems for 3 months before starting the study and patients with diseases such as liver diseases , hyper or hypothyroidism , hyperprolactinemia , adrenal hyperplasia , kidney disease , cardiovascular diseases , hormonal sex - secreting neoplasm , diabetes , nervous system disorder and mentally disorders were excluded .
after approval of ethical committee of isfahan university of medical sciences with registry number 388547 and support of vice chancellor of research at this university for the funding , all patients gave their written informed consents . before any intervention , on the third day of follicular phase of spontaneous or induced menstrual cycle with medroxy progesterone acetate ,
blood samples as baseline hormonal assessment of dehydroepiandrostrone sulfate ( dheas ) , follicle stimulating hormone ( fsh ) , luteinizing hormone ( lh ) , triglyceride ( tg ) , total cholesterol , high density lipoprotein cholesterol ( hdl ) , and low density lipoprotein cholesterol ( ldl ) were collected and recorded ( tg , total cholesterol pars azmoon , tehran , iran .
the experimental group who received genistein ( bergamon , italy ) 18 mg twice a day orally and the control group taking similar capsules with cellulose as a placebo for 3 months .
patients were followed closely for 3 months and were instructed to attend our outpatient clinics if they had any problems .
4 subjects in the experimental group did not continue the study because of gastrointestinal side effects of genistein , and 5 patients from the placebo group were excluded later because of incomplete data .
patients participation diagram after 3 months of supplementation therapy blood was taken from all subjects on the third day of their follicular phase of menstrual cycle for assessment of reproductive hormones and lipid profiles .
data analysis was performed using the spss version 15.0 ( spss , inc . , chicago usa ) .
all data between two groups were compared and analyzed using anova test ( z = 1.96 , z = 0.84 ) and p value less than 0.05 was considered statically significant .
from 146 patients who enrolled in the study , 4 patients in the experimental group and 5 patients from the placebo group were excluded .
so study continued with 69 subjects in the case and 68 in the placebo group ( figure 1 ) .
no significant difference was seen between two groups regarding age , weight , and bmi .
the mean sd age of patients in genistein group was 27.11 5.76 and in the control group was 27.45 5.77 ; the difference was not statistically significant .
phytoestrogen supplementation significantly reduced lh ( p = 0.000 ) , tg ( p = 0.000 ) , ldl ( p = 0.000 ) , dheas ( p = 0.000 ) and testosterone ( p = 0.000 ) levels in patients after receiving genistein comparing with before supplementation therapy but in the placebo group they were not different . finally according to our results only ldl cholesterol was lower significantly after using genistein compared with placebo ( 120.15 10.68 vs. 126.61 14.81 mg / dl respectively , p = 0.04 ) .
comparison of clinical characteristic of the study subjects at baseline and after 3 months in genistein and placebo groups
in the current study treatment with genistein for 3 months resulted in a significant reduction in ldl cholesterol compared with placebo .
metabolic syndrome and hormonal disturbances are prevalent findings among pcos women . metabolic syndrome is a group of conditions including obesity , high blood pressure , blood fat abnormality and borderline high blood sugar and insulin levels , which together increase chances of cardio vascular disease and type 2 diabetes.14 in tehran , iran , it has been estimated that more than 30% of adults might be affected.15 some studies have evaluated the effects of nutrients on glycemic control of type 2 diabetes and metabolic syndrome .
their results have shown beneficial effects of soy protein consumption.1617 two meta - analysis concluded that isofla - vones content of soy might be responsible for its lipid lowering effect.1819 but some other studies did not confirm these results.20 therefore , because of these controversies we decided to evaluate the effect of genistein on hormonal and metabolic abnormalities in women with pcos . lissin and cooke suggested that diets containing soy - protein may provide favorable benefits in reducing ldl cholesterol and cardiovascular events.21 azadbakht et al in a randomized cross over clinical trial which was done on 42 postmenopausal women with metabolic syndrome comparing soy protein with esoy nut and controlled diet , showed that neither soy protein nor soy nut could affect weight and serum leptin levels.22 wiseman et al in a randomized cross over design compared the effect of a dietary regimen high in isoflavones with a similar product in which all of the soy was removed by alcohol .
their results showed that antioxidant effect of soy may protect against the oxidative lipid damage that is the leading cause of cardiovascular diseases and cancers.23 a study azadbakht et al indicated that soy compounds like isoflavones , fibers , phospholipids , fatty acids and its other components could have beneficial effects on cardio metabolic abnormalities such as hypercholesterolemia and lipid abnormality.24 results of our study revealed that administration of genistein not only reduced ldl cholesterol but also significantly reduced lh , tg , dheas and testosterone parameters after 3 months .
ohno et al also showed that genistein has a significant role on steroidogenesis in the adrenal gland and testis of rat , and decreasing the testosterone level.25 romualdi et al performed a pilot prospective study on patients with pcos , which revealed that treating patients with phytoestrogens result in improvement of lipid assessment , and they suggested that using phytoestrogens may have a possible advantage in improvement of lipid assessment in women with pcos.26 we also observed the same effect on improvement of lipid assessment . according to the research of kurzer soy consumption appear to have modest hormonal effects on both pre- and postmenopausal women.27 consuming 45 - 200 mg / dl isoflavones in different products like soy milk or soy flour or soy foods would decrease the midcycle fsh and lh . according to our results in genistein group , lh , testosterone , and
in conclusion , results of our study suggest that supplementation therapy with genistein that is rich of soy phytoestrogen has possible advantages in patients with pcos and may be chosen as an alternative treatment for these women and may provide favorable advantages in reduction of related complications .
we did not analyze mean of different variables between two groups at the baseline .
it seems that lh , testosterone , and dheas at the baseline , might have been different between the placebo group and genistein group .
however significant differences that were observed between results of before and after treatment in genistein group may overcome this limitation.measuring weight and body mass index in two groups was not designed in our proposal to see their impact on the results .
it seems that lh , testosterone , and dheas at the baseline , might have been different between the placebo group and genistein group .
however significant differences that were observed between results of before and after treatment in genistein group may overcome this limitation .
measuring weight and body mass index in two groups was not designed in our proposal to see their impact on the results .
we may also suggest using different doses of genistein on reproductive hormonal and lipid profiles .
ekh was responsible for data analysis , data gathering and interpretation of results and performed clinical follow - ups . | background : phytoestrogens are a group of plants derived compounds with weekly estrogen effect that appear to have protective effects on metabolic and hormonal abnormalities of women with polycystic ovary syndrome ( pcos ) . so the aim of this study was to investigate the effect of soy phytoestrogens on reproductive hormones and lipid profiles in pcos women.methods:in this quasi - randomized trial , 146 subjects with pcos were divided into two groups ; the experimental group who received genistein ( bergamon , italy ) 18 mg twice a day orally and the control group that received similar capsules with cellulose for 3 months . hormonal features and lipid profiles
were measured before and after 3 months of supplement therapy.results:after 3 months of supplement therapy there were no statistically significant differences in high density lipoprotein cholesterol ( hdl ) and follicle stimulating hormone ( fsh ) serum levels in genistein and placebo group before and after treatment ; however serum levels of luteinizing hormone ( lh ) , triglyceride ( tg ) , low density lipoprotein cholesterol ( ldl ) , dehydroepiandrostrone sulfate ( dheas ) and testosterone were significantly decreased after 3 months therapy in genistein group.conclusions:genistein consumption may prevent cardiovascular and metabolic disorders in pcos patients by improving their reproductive hormonal and lipid profiles . |
SECTION 1. SHORT TITLE.
This Act may be cited as the ``Mercury Reduction Act of 2002''.
SEC. 2. FINDINGS.
Congress finds that--
(1) mercury is a persistent and toxic pollutant that
bioaccumulates in the environment;
(2) according to recent studies, mercury deposition is a
significant public health threat in many States throughout the
United States;
(3) 40 States have issued fish advisories that warn certain
individuals to restrict or avoid consuming mercury-contaminated
fish from affected bodies of water;
(4) according to a report by the National Academy of
Sciences, over 60,000 children are born each year in the United
States at risk for adverse neurodevelopmental effects due to
exposure to methyl mercury in utero;
(5) studies have documented that exposure to elevated
levels of mercury in the environment results in serious harm to
species of wildlife that consume fish;
(6) according to the Mercury Study Report, prepared by the
Environmental Protection Agency and submitted to Congress in
1997, mercury fever thermometers contribute approximately 17
tons of mercury to solid waste each year;
(7) the Governors of the New England States have endorsed a
regional goal of ``the virtual elimination of the discharge of
anthropogenic mercury into the environment'';
(8) mercury fever thermometers are easily broken, creating
a potential risk of dangerous exposure to mercury vapor in
indoor air and risking mercury contamination of the
environment; and
(9) according to the Environmental Protection Agency, the
quantity of mercury in 1 mercury fever thermometer,
approximately 1 gram, is enough to contaminate all fish in a
lake with a surface area of 20 acres.
SEC. 3. MERCURY.
(a) In General.--Subtitle C of the Solid Waste Disposal Act (42
U.S.C. 6921 et seq.) is amended by adding at the end the following:
``SEC. 3024. MERCURY.
``(a) Prohibition on Sale of Mercury Fever Thermometers Except by
Prescription.--Effective beginning 180 days after the date of enactment
of this section--
``(1) a person shall not sell or supply mercury fever
thermometers to consumers, except by prescription; and
``(2) with each mercury fever thermometer sold or supplied
by prescription, the manufacturer of the thermometer shall
provide clear instructions on--
``(A) careful handling of the thermometer to avoid
breakage; and
``(B) proper cleanup of the thermometer and its
contents in the event of breakage.
``(b) Thermometer Exchange Program.--The Administrator shall make
grants to States, municipalities, nonprofit organizations, or other
suitable entities for implementation of a national program for the
collection of liquid mercury fever thermometers from households and
their exchange for thermometers that do not contain mercury.
``(c) Management of Collected Mercury.--
``(1) Task force.--
``(A) Establishment.--There is established an
advisory committee to be known as the `Task Force on
Mercury' (referred to in this section as the `Task
Force').
``(B) Membership.--The Task Force shall be composed
of 5 members, of whom--
``(i) 1 member shall be the Administrator,
who shall serve as Chairperson of the Task
Force;
``(ii) 1 member shall be the Secretary of
State;
``(iii) 1 member shall be the Secretary of
Defense;
``(iv) 1 member shall be the Secretary of
Energy; and
``(v) 1 member shall be the Director of the
National Institute of Environmental Health
Sciences of the Department of Health and Human
Services.
``(C) Date of appointments.--The appointment of a
member of the Task Force shall be made not later than
30 days after the date of enactment of this section.
``(D) Term; vacancies.--
``(i) Term.--A member shall be appointed
for the life of the Task Force.
``(ii) Vacancies.--A vacancy on the Task
Force--
``(I) shall not affect the powers
of the Task Force; and
``(II) shall be filled in the same
manner as the original appointment was
made.
``(E) Meetings.--
``(i) Initial meeting.--Not later than 30
days after the date on which all members of the
Task Force have been appointed, the Task Force
shall hold the initial meeting of the Task
Force.
``(ii) Calling of meetings.--The Task Force
shall meet at the call of the Chairperson.
``(iii) Quorum.--A majority of the members
of the Task Force shall constitute a quorum,
but a lesser number of members may hold
hearings.
``(F) Duties.--
``(i) In general.--Not later than 1 year
after the date of the initial meeting of the
Task Force, the Task Force shall submit to
Congress a report containing recommendations
and suggested actions concerning--
``(I) the long-term management of
surplus mercury collected from--
``(aa) mercury fever
thermometers;
``(bb) other medical and
commercial sources;
``(cc) government sources,
including mercury stored by the
Department of Defense and the
Department of Energy; and
``(dd) industrial or other
sources in the United States;
``(II) programs to test the long-
term durability of promising
technologies for sequestration of
mercury;
``(III) storage of mercury
collected or sequestered under
subclause (I) or (II), in a manner that
ensures that there is no release of the
mercury into the environment;
``(IV) reduction of the total
threat posed by mercury to humans and
the environment; and
``(V) reduction of the total
quantity of mercury produced, used, and
released on a global basis, including
whether and how--
``(aa) the quantity of
virgin mercury mined from the
ground and placed in
circulation each year can be
reduced through bilateral or
international agreements or
other means;
``(bb) the quantity of
mercury intentionally used in
products, mining, and
manufacturing can be reduced
through substitution of
mercury-free alternatives that
are safer, available, and
affordable; and
``(cc) essential mercury
needs can be met through use of
stockpiles in existence on the
date of enactment of this
section rather than through use
of virgin mercury.
``(ii) Consultation.--In carrying out this
subparagraph, the Task Force shall consult with
States, industries, and health, environmental,
and consumer organizations.
``(G) Hearings.--The Task Force may hold such
hearings, sit and act at such times and places, take
such testimony, and receive such evidence as the Task
Force considers advisable to carry out this section.
``(H) Information from federal agencies.--
``(i) In general.--The Task Force may
secure directly from a Federal agency such
information as the Task Force considers
necessary to carry out this section.
``(ii) Provision of information.--On
request of the Chairperson of the Task Force,
the head of the agency shall provide the
information to the Task Force.
``(I) Postal services.--The Task Force may use the
United States mails in the same manner and under the
same conditions as other agencies of the Federal
Government.
``(J) Gifts.--The Task Force may accept, use, and
dispose of gifts or donations of services or property.
``(K) Compensation of members; travel expenses.--
``(i) Federal employees.--A member of the
Task Force who is an officer or employee of the
Federal Government shall serve without
compensation in addition to the compensation
received for the services of the member as an
officer or employee of the Federal Government.
``(ii) Travel expenses.--A member of the
Task Force shall be allowed travel expenses,
including per diem in lieu of subsistence, at
rates authorized for an employee of an agency
under subchapter I of chapter 57 of title 5,
United States Code, while away from the home or
regular place of business of the member in the
performance of the duties of the Task Force.
``(L) Staff and funding.--
``(i) Determination.--The Chairperson of
the Task Force shall determine the level of
staff and funding that are adequate to carry
out the activities of the Task Force.
``(ii) Source.--The staff and funding shall
be provided by and drawn equally from the
resources of--
``(I) the Department of Energy;
``(II) the Department of Defense;
and
``(III) the Environmental
Protection Agency.
``(iii) Appointment of staff.--The
Chairperson may, without regard to the civil
service laws (including regulations), appoint
and terminate such staff as are necessary to
enable the Task Force to perform the duties of
the Task Force.
``(iv) Compensation.--
``(I) In general.--Except as
provided in subclause (II), the
Chairperson may fix the compensation of
the staff of the Task Force that are
not officers or employees of the
Federal Government without regard to
the provisions of chapter 51 and
subchapter III of chapter 53 of title
5, United States Code, relating to
classification of positions and General
Schedule pay rates.
``(II) Maximum rate of pay.--The
rate of pay for the staff shall not
exceed the rate payable for level V of
the Executive Schedule under section
5316 of title 5, United States Code.
``(v) Detail of federal government
employees.--
``(I) In general.--An employee of
the Federal Government may be detailed
to the Task Force without
reimbursement.
``(II) Civil service status.--The
detail of the employee shall be without
interruption or loss of civil service
status or privilege.
``(vi) Procurement of temporary and
intermittent services.--The Chairperson of the
Task Force may procure for the purposes of the
Task Force temporary and intermittent services
in accordance with section 3109(b) of title 5,
United States Code, at rates for individuals
that do not exceed the daily equivalent of the
annual rate of basic pay prescribed for level V
of the Executive Schedule under section 5316 of
that title.
``(M) Termination of task force.--The Task Force
shall terminate on the date that is 90 days after the
date on which the Task Force submits the report
required under subparagraph (F)(i).
``(N) No effect on other law.--Nothing in this
paragraph affects the regulation of mercury under--
``(i) any other provision of this subtitle;
or
``(ii) any other law.
``(2) Responsibility of the administrator for safe
management and storage of mercury.--In consultation with the
Task Force, the Administrator shall--
``(A)(i) purchase or otherwise take title to the
mercury collected under the thermometer exchange
program established under subsection (b), or collected
from any other source;
``(ii) manage (or designate a contractor to manage)
the mercury collected in a manner that ensures that the
mercury collected is not released into the environment;
``(iii) ensure, to the maximum extent practicable,
that the mercury collected under the thermometer
exchange program established under subsection (b), or
an equivalent quantity of mercury, is not reintroduced
into commerce; and
``(iv) provide to the Task Force, for inclusion in
the report of the Task Force under paragraph (1)(F)(i),
an analysis of, and recommendations relating to, the
mercury collection and management activities carried
out under this section; and
``(B)(i) identify potential mercury stabilization
technologies and long-term storage measures that ensure
minimal release of mercury into the environment; and
``(ii) conduct such research, development, and
demonstration of the technologies and measures as the
Administrator determines to be appropriate.
``(d) Relation to Other Law.--Nothing in this section--
``(1) precludes any State from imposing any additional
requirement; or
``(2) diminishes any obligation, liability, or other
responsibility under other Federal law.
``(e) Authorization of Appropriations.--
``(1) In general.--There is authorized to be appropriated
to carry out this section (other than subsection (c)(2)(A))
$20,000,000, of which--
``(A) not more than 2.5 percent shall be used to
carry out the activities of the Task Force; and
``(B) not more than 2.5 percent shall be used to
carry out subsection (c)(2)(B).
``(2) Safe management and storage.--In addition to the
amount authorized to be appropriated under paragraph (1), there
is authorized to be appropriated to carry out subsection
(c)(2)(A) $1,000,000 for each fiscal year.''.
(b) Conforming Amendment.--Section 1001 of the Solid Waste Disposal
Act (42 U.S.C. prec. 6901) is amended by adding at the end of the items
relating to subtitle C the following:
``Sec. 3024. Mercury.''.
Passed the Senate September 5, 2002.
Attest:
JERI THOMSON,
Secretary. | Mercury Reduction Act of 2002 - Amends the Solid Waste Disposal Act to: (1) prohibit the sale or supply of mercury fever thermometers to consumers, except by prescription; and (2) require manufacturers to provide clear instructions on handling of thermometers to avoid breakage and on proper cleanup in the event of breakage.Requires the Administrator of the Environmental Protection Agency to provide grants for a household mercury thermometer collection and exchange program.Establishes a Task Force on Mercury to make recommendations on: (1) the long-term management of surplus mercury collected from thermometers and from medical, commercial, government, and industrial and other sources; (2) programs to test technologies for sequestration of retired mercury; (3) storage of mercury in a manner that ensures no release into the environment; (4) reduction of the total threat posed by mercury to humans and the environment; and (5) reduction of mercury produced, used, and released.Directs the Administrator, in consultation with the Task Force, to: (1) take title to mercury collected under the thermometer exchange program or from another source; (2) manage the mercury in a manner that prevents its release into the environment; (3) ensure that collected mercury is not reintroduced into commerce; (4) provide to the Task Force an analysis of, and recommendations concerning, collection and management activities under this Act; and (5) identify stabilization technologies and long-term storage measures that prevent mercury release and conduct appropriate research, development, and demonstration.Authorizes appropriations. |
the grb 970228 and grb 980329 afterglows are among the most well observed of the afterglows detected so far .
we use observations of these afterglows to derive some of the properties of these bursts and to constrain the nature of their host galaxies .
we have determined the local galactic extinction toward the grb970228 field by comparing galaxy counts in two bands in this field to those in the hdf , and by comparing the observed broad band colors of stars in the grb970228 field to the colors of library spectra of the same spectral type .
we also estimate the extinction using the neutral hydrogen column density and the amount of infrared dust emission toward this field . combining the results of these methods
, we find a best - fit galactic extinction in the optical of @xmath0 , which implies a substantial dimming and change of the spectral slope of the intrinsic grb970228 afterglow .
further details can be found in castander & lamb ( 1998 , 1999a ) ; see also gonzlez et al .
( 1999 ) .
re - analyzing the hst images , we measure a color @xmath8 for the extended source .
we constrain the nature of the likely host galaxy of grb 970228 by comparing this color to those obtained from synthetic galaxy spectra computed with pegase ( @xcite ) , taking into account the measured extinction .
the top panel of figure [ fig5 ] shows the expected colors of an sa , an sc and an irregular galaxy with and without evolution included .
galaxies are only consistent with the observed color if they are at high redshift ( @xmath9 ) , or have active star formation ( like the evolving irr shown ) .
the bottom panel of figure [ fig5 ] better illustrates this point .
it shows that on - going bursts of star formation of duration shorter than 1 gyr produce acceptable @xmath10 colors ; longer duration bursts are disfavored for redshifts @xmath11 .
if we include the @xmath12 and @xmath13 magnitudes of fruchter et al .
( 1998 ) in our analysis , our conclusions are strengthened ( see castander & lamb 1999b for further details ) .
we conclude that the host galaxy must be undergoing star formation , in agreement with our earlier result ( castander & lamb 1998 ; see also castander & lamb 1999b ) .
if there is any extinction present due to the host galaxy , this conclusion would be strengthened .
if the extended source is a galaxy with ongoing star formation , strong emission lines are expected .
tonry et al .
( 1997 ) and kulkarni et al .
( 1997 ) have tried to obtain the spectrum of the grb970228 afterglow and its associated nebulosity .
neither observation revealed any obvious emission lines .
the lack of observed [ oii ] and ly@xmath14 emission lines suggests that the redshift of the galaxy may lie in the range @xmath15 , considering the spectral coverage of the observations .
we model the observed radio through x - ray spectrum of the grb 980329 afterglow , and its evolution through time , as follows .
we take the intrinsic spectrum to be a thrice broken power law , motivated by the relativistic fireball model , in which spectral breaks may occur due to synchrotron self - absorption , the synchrotron peak , and electron cooling ( see , e.g. , sari , piran , & narayan 1998 ) .
the spectrum that we fit is a generalization of the spectrum expected in this model , in the sense that we do not constrain the slopes of the four spectral segments , nor the ( power - law ) rates at which these segments fade , a priori .
we allow the intrinsic spectrum to be modified in the following ways .
first , we allow this spectrum to be extincted by dust and absorbed by the lyman limit at a single redshift , assumed to be the redshift of the burst and its host galaxy .
we adopt the six parameter ultraviolet extinction curve of fitzpatrick & massa ( 1988 ) and the one parameter optical and near - infrared extinction curve of cardelli , clayton , & mathis ( 1989 ) .
finally , we redshift the modified spectrum to the observer s frame of reference , and model the lyman-@xmath16 forest due to absorption by gas clouds along the line - of - sight between the burst and the observer .
the afterglow of grb 980329 is unique among afterglows observed to date in that enough measurements of it have been taken to determine all the parameters of our model . from the results of our fits
, we draw six conclusions : ( 1 ) the inferred intrinsic spectrum of the afterglow is consistent with the predictions of the simplest relativistic fireball model , in which an isotropic fireball expands into a homogeneous external medium .
( 2 ) the intrinsic spectrum of the afterglow is extincted by dust ( source frame @xmath2 mag ) .
( 3 ) the linear component of the extinction curve is flat , which is typical of young star - forming regions like the orion nebula but is not typical of older star - forming or starburst regions .
( 4 ) the @xmath3 2 mag drop between the @xmath4 and the @xmath5 bands can be explained by the ly-@xmath16 forest if the burst redshift is @xmath17 ( fruchter 1999 ) , by the far - ultraviolet non - linear component of the extinction curve if @xmath18 , and by the 2175 bump if @xmath19 ; other redshifts are not consistent with these data , given this general model .
djorgovski et al.(1999 ) report that @xmath20 based upon the non - detection of the ly-@xmath16 forest in a keck ii spectrum of the host galaxy .
( 5 ) assuming a redshift of @xmath21 for illustrative purposes , using the observed breaks in the intrinsic spectrum , and solving for the physical properties of the fireball ( see , e.g. , wijers & galama 1998 ) , we find that the energy of the fireball per unit solid angle is @xmath22 @xmath23 erg sr@xmath24 if @xmath25 and @xmath26 .
( 6 ) similarly , we find that the density of the external medium into which this fireball expands is @xmath27 @xmath28 if @xmath29 and @xmath26 .
this density suggests that grb 980329 occurred in a molecular cloud , which is consistent with the fact that the observed extinction features are characteristic of star - forming regions . | we find that the local galactic extinction towards the field of gamma - ray burst grb970228 is @xmath0 , which implies a substantial dimming and change in the spectral slope of the intrinsic grb970228 afterglow .
we measure a color @xmath1 for the extended source coincident with the afterglow . taking into account our measurement of the extinction toward this field
, this color implies that the extended source is most likely a galaxy undergoing star formation , in agreement with our earlier conclusion ( @xcite ) . in a separate analysis
, we find that the inferred intrinsic spectrum of the grb 980329 afterglow is consistent with the predictions of the simplest relativistic fireball model .
we also find that the intrinsic spectrum of the afterglow is extincted both by dust ( source frame @xmath2 mag ) , and that the shape of the extinction curve is typical of young star - forming regions like the orion nebula but is not typical of older star - forming or starburst regions .
the @xmath3 2 mag drop between the @xmath4 and the @xmath5 bands can be explained by the far - ultraviolet non - linear component of the extinction curve if @xmath6 , and by the 2175 bump if @xmath7 ; other redshifts are not consistent with the observational data , given our general model . |
there are direct and indirect observational arguments in favor of physical connection between massive or core - collapse supernovae ( sne ) and long duration gamma - ray bursts ( grbs ) , and the list of publications on the topic is ever - increasing . at first
this connection was justified by the fact that all grb host galaxies turned out to be star - forming or star - bursting galaxies with high massive star - forming rates ( e.g. , djorgovski et al .
2001 ; frail et al . 2002 ; sokolov et al . 2001 ) .
there are more and more occurences of sn signs in the grb afterglow light curves and spectra for grb 970228 ( galama et al .
1999 ) , grb 970508 ( sokolov et al .
1998 ) , grb 980326 ( bloom et al . 1999 ) , grb 990712 ( bjornsson et al .
2001 ) , grb 991208 ( castro - tirado et al .
2001 ) , grb 000911 ( lazzati et al . 2001 ) , grb 011121 ( bloom et al .
2002 ) , grb 021211 ( della valle et al .
2003 ) , grb 030329 ( hjorth et al . 2003 ; stanek et al .
2003 ) , grb 031203 ( thompsen et al .
a comprehensive analysis of sn light in grb afterglows has been recently done by zeh , klose , and hartmann ( 2004 ) , and see references therein .
if there were more cases of clear and indisputable spectral and photometric signs of association between normal core - collapse sne ( ib / c type and others ) and grbs , it would be a direct proof of the connection between grbs and massive stars .
the increasing statistics of the grb - sn associations can impose direct and strong observational constraints on grb beaming and , hence , we could have an _ observational _ estimation of a real total energy reservoir of grb sources .
the purpose of this paper is to describe the basic assumptions of a scenario of a grb source with energy @xmath2ergs : the matter is about an alternative to the ultrarelativistic fireball if _ all _ long - duration grbs are physically connected with _
normal / unpeculiar _ core - collapse supernovae ( sne ) . in section 2
it should be discussed the typical grb spectra , which is the origin of the compactness problem , and how it was solved at early stages of grb studies .
3 concerns with another attempt of solving the compactness problem , namely , the dependence of the threshold for @xmath0 pair production on the angle between photon momenta , a soft collimation and the dependence of this collimation on grb photon energy . in sect .
4 we discuss and justify observably a rather strong collimation of grb radiation ( for a small number of hard photons in grb spectra ) reaching near - earth detectors . in sect .
5 we consider the radiation pressure and how a jet or bullet arises if the reason of the relativistic jet is a powerful light pressure of the collimated / non - isotropic prompt radiation of the grb source . in section 6
we are examining in outline some possible compact mechanisms of the grb phenomenon in a compact grb model .
( concluding remarks ) concerns observational consequences of the compact " grb energy release , and what new we will see in the sky if the compact grb source model is true indeed : particulary , we would like to adduce in outline some re - analysis of the observational results of soft x - ray flashes ( xrfs ) , grbs with strong x - ray excess in spectra ( x - ray - rich grb = xrr grb ) , normal or classical grbs , obtained at first with bepposax and then with hete-2 ( amati et al .
2002 ; lamb et al .
2003a ) .
so , we will try to understand the soft ( in the meaning of photon energies ) observational grb spectrum without involving huge kinematical motions of the radiating plasma _ a priori _ , or without an enormous lorentz factor , @xmath4 .
the rapid temporal variability , @xmath5 msec , observed in grbs implies _ compact _ sources with a size smaller than @xmath6 km . but here a problem immediately arises for distant grb sources ( e.g. carrigan and katz 1992 ) : too large energy ( @xmath7 ergs ) is already released in only soft @xmath1-rays ( @xmath8 kev and up to 1 mev ) in such a small volume for the sources at cosmological distances ( @xmath9 gpc ) . for a photon number density @xmath10ergs@xmath11@xmath12 two @xmath1-ray photons with a _ sum energy _
larger than @xmath13 could interact with each other and produce electron positron pairs .
the optical depth for pair creation is given approximately by @xmath14 , where @xmath15 is the classical electron radius @xmath16 ( the cross - section for pair production is @xmath17 or @xmath18@xmath19 at these semirelativistic energies ) .
it is the essence of a so - called compactness problem " : the optical depth of the relatively low energy photons ( @xmath20kev ) would be so large that these photons could not be observed .
\1 . usually in this definition
a role of the _ high - energy photons _ is emphasized : the @xmath1-ray photons with energies larger than @xmath21 ( and @xmath22mev ) could interact with lower energy photons and produce electron - positron pairs ( piran 1996 ; 1999 ; 1999a ; 2004 ) .
the average optical depth for this process is @xmath23ergs)@xmath24 msec@xmath25 for a typical total grb energy release @xmath26 ergs in a small volume ( e.g. piran 1999 ) .
the heavy" / hard ( or high - energy ) photons are present in observational grb spectra as high energy tails which contain a significant amount of energy .
so , according to piran , the compactness problem arises because the observed spectrum contains a fraction of the high energy @xmath1-ray photons . in other words , since observations are consistent with _ a possibility _ that all grbs have the high energy tails , it must be the first and basic observational justification of the problem ( see e.g. lithwick and sari 2001 ) : the optical depth of the high - energy photons ( @xmath22mev ) would be so large that these photons could not be observed .
however , here we must make right away several specifying remarks on the typical spectra and typical photon energies in grbs , including allowance for the well known results of recent observational spectra
. yes , such high - energy photons did were observed in some cases , but far from being so always .
furthermore , photons with energies @xmath27 mev were strongly delayed after the main grb burst . for example , the 20 gev photon observed with batse / egret delayed as much as 1.5 hours relative to the grb itself .
it is obvious that in this case a physical mechanism was quite different from one creating typical prompt grb spectra .
( the grb spectra are described in a review by fishman and meegan ( 1995 ) , see also the catalogue of the spectra by preece et al .
( 2000 ) . )
typical observational grb spectra turned out to be very diverse , but yet these are mainly soft ( but not hard ) gamma - ray quanta .
it has been known since the moment of grbs discovery , when their spectra were presented in energy units : e.g. , see a review by mazets and golenetsky ( 1987 ) . at present
many authors point to the same again ( lamb et al . 2003 ; baring & braby 2004 ; liang et al .
2004 ; atkins et al . 2003 ; gialis & pelletier 2004 ) .
almost all grbs have been detected in the energy range between 20 kev and 1 mev . _
a few _ have been observed above 100 mev . in a recent review piran ( 2004 )
also has paid attention to a puzzle of the origin of narrow distribution for the typical energy of the observed grb radiation ( @xmath28kev , preece 2000 ) . besides , by 2000 it was clear that there were other two grb classes : x - ray flashes ( xrf ) and x - ray rich gamma ray bursts ( xrr grb ) ( heise et al .
2001 ; amati et al . 2002 ) .
these are grbs either _ without _ ( xrfs ) or almost without ( xrr grb ) gamma - ray quanta .
it is also discussed in detail and there are excellent illustrations in recent papers by lamb et al .
( 2003a , 2003b , 2003c ) and in other papers by this group . thus , despite the importance of the problem of the high energy ( @xmath22mev ) photons release , still there are too many lower energy @xmath1-ray photons in a small volume with @xmath29 km .
the observed fluxes give an estimate of a total grb energy release to be of @xmath30 ergs in the form of just these _ low energy _
photons , or this standard " estimation ( @xmath30 ergs ) was obtained from typical observational grb spectra of just these , most frequently observed low - energy ( target " ) photons with the _ semirelativistic _ energies , up to 1 mev , basically .
( it is natural that the photon density was estimated using the simple assumption of spherical symmetry .
see below the comments to the paper by carrigan and katz 1992 . )
further it was firmly declared , and other authors have repeated many times that grb source must be optically thin and the observed _ spectrum is non - thermal _ with certainty ( piran 1996 ; 1999 ; 1999a ; 2004 ) . now the optically thin source with the non - thermal spectrum is presented as a standard common opinion about all grbs ( postnov 1999 ) , though unlike time - averaged grb spectra , time - resolved instantaneous grb spectra are thermal ( _ black - body radiation _ with temperature @xmath31kev ) rather than power - law ones ( crider et al . 1997 ; preece et al .
1998 , 2002 ; ghisellini 2003 ; ghirlanda et al .
2003 ; ryde 2004 ) .
so far different authors have been pointing to these inconsistencies between the standard optically thin synchrotron model and observations ( e.g. preece et al . 2002 ) , and suggesting different alternative scenarios of the solution of this problem ( blinnikov , kozyreva and panchenko 1999 ; medvedev 2000 ; baring & braby 2004 ) .
it turned out that the black - body radiation with @xmath31kev is a physical model while the time - averaged non - thermal grb spectrum is merely an empirical model ( ryde 2004 , and other references therein ) .
nevertheless , if these theoretical rather than observational statements ( piran 1996 ) on the possibility that _ all _ grb spectra have high energy tails ( 1 ) and the observed grb spectra are non - thermal ( 2 ) , are true indeed , the fireball theory ( piran 1999 , 1999a ) with huge lorentz factors is the only possible theoretical alternative . it should be admitted though that the standard optically thin synchrotron shock emission theory / model explains everything , except the observational spectra of grbs themselves ( preece et al .
but for all that , it was left out of account that these target - photons " ( @xmath28kev ) are just the observed typical grbs .
so , it turns out that the main task , according to the standard model , is not the explanation of this observed soft grb spectrum in terms of photons energy / frequency , but the investigation of rare cases of release of hard quanta with energy of more than or @xmath32gev . in this connection
see the paper by lithwick and sari ( 2001 ) in which , as an alternative to the observed grb spectrum , an intrinsic spectrum " that has no cutoff at very high energies is suggested to be explained . as a result ,
the origin of the _ observed _ and substantially soft grb spectra with a big number of photons up to @xmath32mev remains not properly understood .
it is especially incomprehensible against the background of conjurations about the huge gamma factor that is supposed to solve the compactness problem .
but the question remains : why are mainly soft grb spectra observed at ultrarelativistic motions of radiating plasma supposed in the fireball model ? and what is more , sometimes the grb spectra do not contain -ray quanta at all , as , for example , xrfs known already before 2000 ( heise et al . 2001 ) .
thus , when solving the compactness problem , we somehow imperceptibly incurred another problem of strong contradiction between the ultrarelativistic loretz factor @xmath33 100 - 1000 ( with 100 mev and 10 gev photons ) and observed soft ( @xmath34 or @xmath35 mev ) -ray ( grb , xrr grb ) and x - ray ( xrf ) radiation of the most classical grbs . moreover , it is also important to point out here that the observed _
black - body _ prompt grb radiation with a temperature @xmath31kev ( ghirlanda et al .
2003 ; ryde 2004 ) is inconsistent with the loretz factor @xmath36 for the reason that the mean observed temperature can easily exceed mev in cosmological fireballs ( piran and shemi 1993 ) .
so , is there the compactness problem or not ?
if yes , then how is it solved ?
are there any alternatives of its solutions besides the fireball with its huge lorentz factor ?
particularly , can we do with semi- ( not ultra- ) relativistic approximation when explaining observed grb , xrr grb and xrf spectra ? is the strong gamma - radiation beaming necessary and to what extent can the radiation in grb , xrr grb and xrf spectra be collimated ?
this section concerns another attempt to solve the old compactness problem .
certainly , in 1998 there already were some discussions of radiation collimation , but mainly in terms of the same standard fireball theory . and it should be kept in mind that in this theory the term _ collimation _ refers to jets consisting of plasma , while the term _ beaming _ refers to radiation of the same optically thin plasma ( sari 2000 ) .
of course , we could waste not much time for the discussion of piran s approach in the previous section , if it were not a circumstance that even before 1992 ( i.e. before the batse / egret mission ) the compactness problem was mentioned in connection with the famous burst of 1979 march 5 in the large magellanic cloud .
already then a possibility of collimated @xmath1-ray radiation in explanation of observed soft spectra was not excluded because the cross - section of electron - positron pair production @xmath37 ( and annihilation also ) depends not only on energy , but on the angle between momenta of colliding particles .
then there is a comment on the paper by carrigan and katz ( 1992 ) which has not been so often cited . in fact as early as at the beginning of the 1990th a lot of interesting was said in connection with collimation of @xmath1-rays leaving the source with high photon density in it .
it seems that just the collimation solves the problem ( see below ) .
the paper by carrigan and katz ( 1992 ) tells about modeling the observed grb spectra allowing for the electron - positron pair production effects .
these effects could produce effective collimation of the flux because of kinematics of the two - photon pair production : the opacity ( @xmath38 ) is also a sensitive function of the _ angular _ and _ spectral _ distribution of the radiation field in the grb source .
because of the importance of the photon angular and spectral distribution to the opacity , below an analysis of formula ( 1 ) for the threshold of the pair production processes from the paper by carrigan and katz ( 1992 ) is given .
the argument proceeds as follows : _ two _ photons with energies @xmath39 and @xmath40 , which are above the threshold energy ( @xmath41 ) for electron - positron pair production @xmath42 may produce a pair , where @xmath43 , @xmath44 is the angle between the directions of the two @xmath1-rays , and @xmath45 .
the cross section for pair production reaches the maximum at a finite center - of - momentum photon energy : e.g. @xmath46511 kev for @xmath47 , or @xmath48700 kev for @xmath49 ) , or @xmath50 tending to infinity ( @xmath511 mev ) for @xmath52 .
if the source photon spectrum is not sharply peaked , the relatively high - energy photons ( @xmath53 ) will , therefore , form pairs predominantly with relatively low - energy photons ( @xmath54 ) .
it means that the observed / released grb spectra will be soft , since the high - energy photons will be held by the threshold of pair production . thus , because any _ reasonable _ source spectrum will contain much more low- or moderate - energy photons ( @xmath55kev ) than high - energy photons , the emergent spectrum will differ most markedly from the source spectrum at high photon energies ( @xmath56 mev ) at which it ( the emergent spectrum ) will be heavily depleted . in other words ,
the observed ( emergent ) spectrum becomes softer .
then , the @xmath0 pairs eventually annihilate to produce two ( infrequently 3 ) photons , but usually not one high- and one low - energy photon .
the result is that high - energy photons are preferentially removed from the observed spectrum .
the observation of a measurable amount of flux with @xmath57 is not expected unless the optical depth @xmath38 to pair production is equal to 1 or less , because the threshold for electron - positron pair production ( 1 ) is also a sensitive function of the angular distribution of the radiation field ( in the very source ) .
thus , the observation of a considerable number of quanta with @xmath58 mev due to the filter effect ( 1 ) is not expected , if only the optical depth for the @xmath0 pair production is not proved @xmath59 indeed .
as is seen from the paper by carrigan and katz ( 1992 ) , in 1992 it was generally accepted that typical energies of most photons in _ observed _ grb spectra are still rather small .
further in the peper , carrigan and katz adduce the estimates of distances to burst sources of such photons with the _ semirelativistic _ energies .
the matter is that the problem of a compact source ( in relation to the 1979 march 5 event in lmc ) and a surprisingly big distance arises indeed . but not because of a problem with the release of heavy " ( 100 mev , 1 gev , or more ) ultrarelativistic photons which interfere with light " ( @xmath59 mev ) target - photons observed in the grb spectra .
the powerful 1979 march 5 event in lmc was observed without any super heavy photons in its spectrum . to make sure of it one
should just look at the spectra of this burst published by mazets and golenetskii in their review ( 1987 ) . to explain why the effect of the photon
@xmath0 confinement " does not function in this grb source ( 1979 march 5 event in lmc ) , carrigan and katz discuss different possibilities . in particular , they immediately point out to the angle dependence ( 1 ) of the threshold of the @xmath0 production .
a possible loophole " exists if the source produces a _ strongly collimated _ beam of photons .
( thus , the question is about an asymmetry of the radiation field in the source . ) in this case , even high - energy photons are below the threshold for the pair production if @xmath44 is small enough .
the presence of such a window " in the opacity for _ collimated _ photons suggests that in a region opaque to pair production much of the radiation may emerge through this window , in analogy to the great contribution of windows in the material opacity to radiation flow in the usual ( rosseland mean ) approximation . the use of the words
strongly collimated " in this ( old " ) paper could be somewhat confusing . what means _
strongly _ indeed ? at that time there were no observations of grb spectra in the region of high energy @xmath60 .
heavier photons with @xmath61 mev ( beyond the peak of @xmath32 mev ) have been reliably observed only with egret / batse . in particular , from formula ( 1 ) for such photons an estimation of the collimation angle can be obtained ( without any target - photons " ) : @xmath62 it corresponds to @xmath63 less than 6 degree only .
it means that the quanta with energy @xmath64mev leaving the source within a cone of @xmath65 opening angle do not give rise to pairs , and all _ softer _ radiation can be uncollimated at all .
so the collision of 10 mev quanta with quanta of lower energy occurs at angles greater than ( @xmath66 ) @xmath67 , and softer quanta leaving the source within the cone of such opening angle do not prevent neither heavy nor ( especially ) light quanta to go freely to infinity .
thus , formula ( 1 ) demands more or less strong collimation only for _ a small part _ of the heaviest quanta radiated by the source .
if one looks at energetic spectra of typical grbs ( the same reference to mazets and golenetskii 1987 ) presented in the old way of @xmath68 vs. @xmath69 _ the number _ of photons per a time unit in an energy range unit per an area unit versus the photons energy , then everything becomes clear . only a small part or a small _ amount _ of quanta / photons observed beyond a threshold of @xmath70kev can be collimated , but within a cone of @xmath71 opening angle :) . at present , 6 degrees for 10 mev quanta would not be considered as a strongly collimated beam .
now such opening angles ( of jets ) are considered to be quite suitable in the standard " or the most popular theory of fireballs .
if one proceeds right away from an idea that it is necessary to release quanta with the energy up to 10 mev , then we would obtain at once a version of a collimated theory with the @xmath72 of @xmath64 .
but such a way in the standard fireball theory is a dead end also .
the allowing for an initial collimation of grb radiation can drastically change this model ( see below ) for the collimation arising _ directly in the source _ but not because of a huge @xmath72 of @xmath73 what would be needed to solve the compactness problem .
one way or another , the light flux is to lead to corresponding effects of radiation pressure upon the matter surrounding the source . and
if in addition the radiation is collimated , then the arising of jets ( at so enormous light flux ) becomes an inevitable consequence of even a small _ asymmetry _ of the radiation field in the source .
but the question is if
indeed , perhaps one should take into account right away this angular dependence of the threshold of the pair @xmath0 production ( 1 ) before the ultra relativistic limit , allowing for a possibility of a preferential ( most probably by a magnetic field ) direction in the burst source on the surface of a compact object the grb source .
does a preferential direction in the source sound wrong ?
but one way or another , in the model of fireball with jets the radiating plasma is to be accelerated up to enormous velocities .
what is the mechanism ? in the fireball theory this question is not solved yet , and the origin of grb spectra also remains incomprehensible . in the end , does the jet radiate itself and is it the grb source ? that is the question .
can we do without the radiating and accelerated ( nobody knows by what ) jet up to a huge value of the lorentz factor , by supposing that the source of grb radiation is _ already _ collimated by the burst source itself ? at least , the rather strong collimation of grb -rays , reaching near - earth detectors , can be observably justified .
the grbs could be the beginning of the explosions of _ usual _ massive or core - collapse sne ( sokolov 2001a , 2001b ) .
all results of photometrical and spectral observations of host galaxies confirm the relation between grb and evolution of a massive star , i.e. , the close connection between grb and relativistic collapse with sn explosion in the end of the star evolution .
( here it is already possible to adduce a lot of references : djorgovski et al .
2001 ; frail et al . 2002 ; sokolov et al . 2001 ; etc . )
the main conclusion resulting from the investigation of these galaxies is that the grb host galaxies do not differ in anything from other galaxies with close value of redshifts @xmath74 : neither in colors , nor in spectra , star - forming rates , luminosities , and surface brightness . *
it means that these are the galaxies ( ordinary " for their redshifts ) constituting the base of all deep surveys . * in point of fact
, this is the main result of _ optical identification _ of grbs with ( ordinary ) objects of already known nature : grbs are identified with galaxies up to @xmath75 st . magn . with allowing for the results of direct optical identifications this makes it possible to estimate directly from observations an average yearly rate of grb events in every such galaxy by accounts of these galaxies for the number of galaxies brighter than 26th st .
it turns out to be equal to @xmath76 .
( but most probably this is only an upper estimate , see in sokolov 2001b ) . allowing for the yearly rate of ( massive ) sn explosions @xmath77 , the ratio of the number of grbs , related with the collapse of massive stars ( core - collapse sne ) , to the number of such sne is close to @xmath78 .
most likely , this is also only the upper estimate for ib / c type sne ( sokolov 2001a ) .
porciani & madau ( 2001 ) obtained an analogous estimate : @xmath79 for ii type sne . here
we proceed from the simplest assumption , which has been confirmed from 1998 by increasing number of observational facts , that _ all _ long - duration grbs are related to explosions of massive sne . then the ratio @xmath80 should be interpreted as a very strict
@xmath1-ray beaming " of quanta _ reaching an observer _ , when gamma - ray radiation ( a part of it ) of the grb source propagates to very long distances within a very small solid angle @xmath81 another possible interpretation of the small value of @xmath80 a relation to a rare class of some peculiar sne seems to be less possible ( or hardly probable ) , since then grbs would be related only to the @xmath82th part of all observed sne in distant galaxies ( up to 28th mag ) .
these are already not simple peculiar sne , with which the paczyski s hypernova is sometimes identified ( paczyski 1999 ; fields et al .
peculiar supernovae/hypernovae " , such as 1997ef , 1998bw , 2002ap , turn out to be too numerous ( richardson et al . 2002 ; podsiadlowski et al .
2004 ) now there are already other papers ( lamb et al .
2003a , 2003b , 2003c ) , pointing out to a possibility of collimated radiation from the grb source ( 2 ) . and
the more numerous are grb / sn coincidences of type of grb 030329/sn 2003dh or grb/red shoulder " in light curves , the more confident will be the idea that grb radiation is collimated , but not related to a special class of sne/hypernovae `` .
many consider this term ( ' ' hypernovae " ) poorly defined and no longer use it .
the more so , that explosion geometry features ( sn explosion can be axially symmetrical ) make the attempts to select a class of hypernovae " more complex ( willingale et al .
2004 , see the end of their text ) .
today there are more facts for the collimation ( 2 ) , and we think that soon it will be accepted not only by lamb et al .
let us suppose that only the most collimated part of gamma radiation get to an observer , say , along a rotation axis of the collapsing core of a star with magnetic field . and
if grbs are so highly collimated , radiating only into a small fraction of the sky , then the energy of each event @xmath83 must be much reduced , by several orders of magnitude in comparison at least with a ( so called ) isotropic equivalent " @xmath84 , of a total grb energy release ( @xmath85 and up to @xmath86 ) : @xmath87 if it is just this case which is realized , and if the energy of -rays propagating in the form of a narrow beam reaching an observer on earth is only a part of the total radiated energy of the grb source ( from @xmath88 to @xmath89 ) , then the other part of its energy can be radiated in _ isotropic _
( or almost isotropic ) way indeed .
but at the spherical luminosity corresponding to a total grb energy of , e.g. , @xmath90 , no batse gamma - ray monitor detector , even the most sensitive one , would detect flux , corresponding to so low luminosity for objects at cosmological distances of @xmath91 , and if the observer is outside the cone of the collimated component of radiation ( 2 ) .
i.e. ( 3 ) can be close to the lower estimate of the total radiated energy of grb sources , corresponding to the flux measured within the solid angle ( 2 ) , in which the most collimated component of the source radiation is propagating .
( we always suppose that _ all _ long - duration grbs are related to sne . )
so , in terms of observational results known today , there is a possibility at least to considerably reduce at once the total ( bolometric ) energy of grb explosions even in the model with radiating plasma , i.e. with ultra relativistic jets in the standard fireball model .
( though we are sure that it is not plasma that radiates the grb , and the jet is a consequence , but not the cause of grbs .
more will be said below . )
then it is possible to estimate the lorentz factor @xmath72 in the same standard theory with the radiating jet ( the formula and relation with the @xmath72 are taken from the paper by piran ( 1999 ) . even in the theory with the jet radiating grb , but at the total energy of @xmath92 ergs , the lorentz factor @xmath72 turns out to be equal to : 18 , 32 , 42 , 56 correspondingly .
but we do not think the authors of the standard solution of the compactness problem will ever agree to that , though here it is possible to speculate using the closeness of this estimate to what was mentioned above for the angle of collimation and the factor @xmath72 of photons with energy of @xmath64mev ( see the end of the previous section ) .
maybe , lamb and his co - authors ( 2003a , 2003b , 2003c ) will do so , since they try to adjust the very small angle of the grb collimation with the standard theory of the radiating jet .
but in our opinion , there is only one alternative for the approach ( lamb et al .
2003c ) : the model ( a unified jet model of x - ray flashes , x - ray - rich grbs , and grbs " ) does explain observations , but with @xmath72 of @xmath341 - 10 .
then both the opening of jet and the angle of the grb collimation are to be simply equal to each other for sure , and the grb source is to be located in the very beginning , or in the point " where the jet and radiation arise ( see fig .
b. in the paper by lamb et al .
2003c ) . but
this will be quite a _ non - standard _ theory .
apparently , this question what does radiate : a point " or an extent jet ?
is crucial for any grb mechanism .
if the grb source radiation ( mainly the hard component of the grb spectrum ) is collimated indeed , then we will have to return to the old idea : the radiation ( grb ) arises _ on a surface _ ( centimeters , meters ? ) of a compact object .
( perhaps , the radiation in an annihilation line will be also found again . )
further we will try to do without an ( a priori ) assumption that it is only the jet s end " which radiates .
the jet is rather a consequence , than a cause .
it arises for sure , but because of the strong pressure of the collimated radiation on the matter surrounding a compact ( down to @xmath93 cm and less ) grb source .
certainly , this jet accelerated by photons up to relativistic velocities will radiate also , but it would be already an afterglow , but not grb itself .
if the scenario : _ massive star _ @xmath94 _ wr star _ @xmath94 _ pre - sn = pre - grb _ @xmath94 _ the collapse of a massive star core _ with formation of a shell around wr is true , then it could be supposed that the reason for arising of a relativistic jet is the powerful light pressure of the collimated or non - isotropic prompt radiation of the grb source onto the matter of the wr star envelope located immediately around the source itself a collapsing core of this star .
we can digress for a while from the problem of the mechanism of arising of the grb source itself and not discuss a question of how these collimated gamma - quanta arouse .
for example , the radiation field arising around the source can be non - isotropic axially symmetric due to magnetic field and effects of angular dependence ( 1 ) of the threshold of the @xmath0 pair production .
after all , for a while it is sufficient for us that only a part ( @xmath95 or even @xmath96 ) of the total grb energy ( @xmath97 ) may be the collimated radiation , which breaks through the dense envelope surrounding the collapsing core of the wr star .
( then the prompt radiation reaches the earth and is detected as the grb . )
the main thing now is _ the collimated flux _ of radiation from the source and a possibility of existence of _ dense _ gas ( windy ) environment pressed up by radiation from the grb source embedded in it , and this environment can be the most dense just near the source , if the density is close to @xmath98 ( the wr law for stellar wind ) . here
the distance @xmath99 is measured from the wr star itself , and @xmath100 @xmath101 ( ramirez - ruiz et al .
2001 ) . for the force of light pressure that can act on gas environment ( plasma ) around the grb source ( the wr star ) we have @xmath102 , where @xmath103 is a so called isotropic _ luminosity _ equivalent of the source ( @xmath104 erg@xmath105 s@xmath106 and more ) ,
@xmath99 is a distance from the center ( or from the source ) , @xmath107@xmath19 is the thomson cross - section , @xmath108 is the velocity of light .
it is clear even without detailed calculation that near the wr core ( @xmath109 cm ) such a force can over and over exceed ( by 12 - 13 orders ! ) the light pressure force corresponding to _ the eddington limit _ of luminosity ( @xmath110erg@xmath105s@xmath106 for 1 @xmath111 ) . in principle
, the isotropic radiation with so huge luminosity @xmath112erg@xmath105s@xmath106 ( or the light pressure ) can also lead to fast acceleration ( similar to an explosion ) of environment adjacent to the source .
but if we assume that the radiation of the grb source is non - isotropic and a part of it is collimated or we have very strong beaming with the solid angle @xmath113 , then the forming of directed motion of relativistic / ultra - relativistic jets becomes inevitable , only because of so huge / enormous light pressure affecting the _ dense _ gas environment in the immediate vicinity of the source - collapsing stellar nucleus .
naturally , the formation of jets depends also on degree of ionization , density and temperature of a medium in the immediate vicinity of the grb source an asymmetric collapsing nucleus of a massive star ( gorbatsky 2004 , private communication ) .
but we can estimate the size of the region _ within _ which such a jet can be accelerated by the radiation pressure up to relativistic velocities : + 1 .
if the photon flux producing the radiation pressure accelerating the matter at a distance @xmath99 from the center ( near the grb site ) is equal to @xmath114 , then in the immediate vicinity from the grb source ( the collapsing nucleus of wr star ) such a flux can be enormous .
it is _ inside _ this region where the jet originates and undergoes acceleration up to ultra relativistic velocities .
+ 2 . to accelerate the matter up to velocity of at least @xmath115 , at the _
outer _ boundary of this region the photon flux must be at least not less than the eddington flux @xmath116 . here
@xmath117 is the eddington limit @xmath110erg@xmath105s@xmath106 for 1 @xmath111 and @xmath118 is the size of a compact object of @xmath119 cm .
( by definition : @xmath116 is a flux _ stopping _ the accretion onto a compact source the falling of matter on the source at a parabolic velocity . for a neutron star it is equal to @xmath115 . ) from the condition that the photon flux @xmath114 at distance @xmath99 is equal to @xmath116 ( or at least not less than this flux ) , and taking into account that the luminosity or rather its _ isotropic equivalent _ of the grb radiation is @xmath112erg@xmath105s@xmath106 , it is possible to obtain an estimate of the size of @xmath120 cm @xmath121 .
at least , at this outer boundary the light pressure is still able to accelerate the initially stable matter up to sub - light velocities @xmath122 . and
_ deeper _ , at less distances than @xmath120 cm from the source , say , at @xmath123 cm ( somewhere _ inside _ the region of the size less than the characteristic size of collapsing core of the massive star ) the light accelerates the matter up to ultra relativistic velocities with the lorentz factor of @xmath64 at @xmath124erg@xmath105s@xmath106 .
it can occur in a rather small volume of the typical size of @xmath125 , which , in particular , agrees with observations of the variable absorption feature observed simultaneously with grb 990705 in its bepposax / wfc spectrum ( amati et al .
thus , inside the region of a size of less ( in any case ) than @xmath126 , a relativistic jet arises as a result of the strong light pressure onto the ambient medium .
certainly , the question about deceleration of such a jet in circumstellar medium of the star progenitor should be considered separately .
but perhaps the strong deceleration due to interaction of the relativistic shock with ambient medium does not arise ( as in the fireball model ) even at very high densities of this matter around the wr star ( up to @xmath127 @xmath12 for @xmath128 ) because the compact relativistic jet ( or bullet " ) is decelerating but not the shock , what is in the model by panaitescu ( 2001 ) , panaitescu & kumar ( 2001 , 2002 ) .
here there is no such a wide bulldozer " a shock wave raking up the matter and , correspondingly , there is no or almost no effective deceleration of the bullet " as it moves towards less dense matter ( with @xmath98 ) around the massive core of wr star .
that is why due to the small deceleration and small radiation losses ( but with a large initial momentum ) , this
bullet " can move at a relativistic speed with the same lorentz factor @xmath72 of @xmath64 all the time while the transient ( or the grb afterglow ) is observed , i.e. over all its light curve with its peaks or breaks . the shocks , which arise as the jet moves through , only heat this medium and then are radiated in x ray , in optical , in radio where this medium is still dense enough + non - uniformities in distribution of @xmath129 at distances @xmath130 cm from the source ( sokolov 2001b ) .
below is the list of basic assumptions of the scenario describing the grb source with energy of order @xmath131ergs and non - empty space near a massive star progenitor : + 1 . around the wr star progenitor of grb source , from a distance of @xmath132
cm ( the typical size of a massive star core ) up to @xmath133 cm ( the distance where the interaction between wr wind and ambient / circumstellar medium begins ) , there is a dense or windy medium an envelope resulting from the evolution of massive star .
the huge light pressure is the cause of the arising of the jet in the region of @xmath134 cm to @xmath135 cm , i.e. where the envelope density ( @xmath136@xmath12 ) is the highest , but the optical depth for tompson scattering can be already less than 1 ( @xmath137 ) .
the burst itself , probably an almost spherically symmetrical grb - explosion " , with a total energy up to @xmath138ergs arises somewhere in the volume of size @xmath139 cm , or at even a smaller depth of @xmath140 cm , i.e. where the wr law @xmath141 ( for the stellar wind ) ceases to be valid .
it is possible that the explosion / burst occurs directly on the surface of a compact object , resulting from massive star core collapse .
+ 4 ) only the most collimated radiation part of the grb source propagating within the solid angle of @xmath142sr goes to infinity , and for all that the total energy of the source is either of the same order as @xmath143rgs or about @xmath144ergs .
now we can return again to the question about collimation of photons arising on the surface of the compact object .
the pairs production will not prevent the photons with wave vectors within a solid angle of the opening of @xmath44 for from free exiting to infinity .
the threshold inside this solid angle at small @xmath44 ( for is very high , and all photons with energies below @xmath145 will freely exit through this window " in opacity for collimated photons .
an initial spectrum of the grb source is almost what is observed , still the filter ( 1 ) affects the most violently the hard range of the observed grb spectrum it was mentioned above ( carrigan and katz 1992 ) .
and one should not try to invent " at once a special mechanism of a very sharp collimation/channeling " of all photons .
it was also mentioned above .
thus , it is undoubtedly that the grb radiation is to be collimated , but the collimation ( 2 ) concerns mainly only a small part of hard quanta .
the pairs production threshold for such quanta naturally and smoothly , according to the law @xmath146 , rises with the decreasing of the angle between the direction at which the photon is radiated from the surface of the compact object and _ a selected _ direction ( e.g. the magnetic field ) on the surface . as a result , beside a soft component , the more and more hard part of the burst spectrum is passing through , and it is possible to suggest non - isotropic ( axially symmetrical ) field of radiation around the source
then , in particular , it is clear why xrf and xrr grbs are uncollimated completely or rather almost isotropic ( lamb et al .
2003 ) . and what are typical sizes accepted in the standard model ? in the paper by beloborodov ( 2004 ) namely the early stages of the grb explosion are considered .
this is just the standard view : grb afterglow is explained as emission from a decelerating blast wave .
the deceleration begins at @xmath147 cm .
it depends on the ambient density and initial lorentz factor .
so , @xmath148 is a fireball size before the deceleration begins .
and @xmath148 does not exceed @xmath149 cm .
in this theory this is actually the size of the region where the grb prompt emission (= -ray burst ) with the observed spectrum arises : @xmath150 cm .
further it is already a zone where the _ afterglow _ arises hours and days after the prompt grb .
but as was said above , allowing for the influence of the angle between photon momenta in the source on the threshold of @xmath151 pair productions , it is possible to assume that the grb radiation arises in the region 10 orders smaller .
but then there must be quite different physical conditions providing the grb source energy release .
certainly , after all , one should think about the main thing : to assume and investigate a physical mechanism explaining the grb origin on the surface or close to an object of type of neutron star ( ns ) or quark / strange star .
all possible versions of energy output onto the surface of a compact object or of explosions related somehow to this object should be considered , see the reviews by bisnovatyi - kogan ( 2003 , 2004 ) .
below we are examining in outline some of the compact mechanisms of the grb energy release .
a mechanism of the grb origin in the vicinity of a collapsing object based on neutrino - antineutrino annihilation was analyzed by berezinsky and prilutsky ( 1987 ) .
earlier grb production in a sn explosion under the action of neutrino pulse was suggested by bisnovatyi - kogan et al .
the starquake , subsequent explosion and outburst from a non - equilibrium layer in the neutron star crust , discovered by bisnovatyi - kogan and chechetkin ( 1974 ) , is accompanied by gamma radiation due to fission of the ejected super heavy nuclei .
this scenario was suggested ( bisnovatyi - kogan et al .
1975 ) as an alternative model for grbs of galactic origin , but now it can be claimed again in the compact grb model under consideration . as was obtained by brezinsky and prilutsky ( 1987 ) ,
the efficiency of transformation of the neutrino flux energy @xmath152ergs into x - ray and -ray burst is @xmath153 , with the energy output in grb @xmath154ergs .
this is in agreement with the total energy of the grb source of @xmath131ergs in the compact grb model , with accounts for strong beaming ( 2 ) .
one of quite well developed mechanisms of compact energy output in the vicinity of the collapsing object ( magnetorotational explosion ) was suggested for the sn explosion ( bisnovatyi - kogan 1971 ) .
numerical calculations of the explosion in magnetized rotating gas could give an efficiency of transformation of the rotational energy into kinetic at a level of 10 percent ( ardeljan et al .
some results of 2-d calculations of the magnetorotational explosion produced by rapidly and differentially rotating , strongly magnetized new - born ns are given by moiseenko et al .
the energy output is sufficient for the sn explosion , but seems to be low for the total standard " x - ray and -ray energy release of @xmath155ergs in the standard fireball grb model .
thus , the very idea of existence of strong global magnetic fields in the region of cosmic grbs generation has already been given many times ( see also papers by usov 1994 ; thompson 1994 ; meszaros and rees 1997 ; blandford 2002 ) . in this
connection another mechanism of compact energy output or of the origin of cosmic grbs resulting from a decay of magnetized vacuum around ns with such a field can be suggested . here
the energy of order @xmath131ergs for the source of grb in the compact grb model corresponds well to the value of vacuum energy near ns with a super strong field @xmath156 g on condition that the star surface undergoes oscillations ( gnedin 2004 ) .
one can suppose that such oscillations ( or starquakes ) occur at the moment when the ns ( or a new - born ns ) is being formed as a result of the massive core collapse of a star progenitor .
the value of the vacuum energy released in this case depends on both amplitude and frequency of such oscillations .
a possibility of decay of the vacuum in a super - strong magnetic field is now discussed rather actively ( calucci 1999 ; xue 2003 ; rojas and querts 2004 ; metalidis and bruno 2003 ) .
the idea of the decay of the strongly magnetized vacuum in the vicinity of ns with a super - strong magnetic field for explanation of the phenomenon of cosmic grb was first stated by gnedin and kiikov ( 2001 ) , and the first energy estimates were also obtained there . the energy accumulated in strongly magnetized vacuum is quite sufficient to provide the grbs energy output in the process of decay of such vacuum . here the proper oscillations of the ns surface can be a triggering mechanism of such a decay .
the result can be a perfect realization of the following chain : the collapse of a massive star core oscillations of the surface of a new - born ns the collapse of magnetized vacuum with the energy output .
but the main question remains : how the energy of magnetized vacuum is transformed into radiation ?
one of the possible solutions of this problem based on analogy with the phenomenon of sonoluminescence is suggested in the paper by gnedin and kiikov ( 2001 ) .
but the probability of such a process demands a separate special consideration ( gnedin 2004 )
. two giant flares were observed on march 5 , 1979 and august 27 , 1998 from ( so - called ) soft -ray repeaters sgr 0526 - 66 and sgr 1900 + 14 , respectively .
the peak luminosity of these flares was as high as @xmath157ergs@xmath106 ( mazets & golenetskii 1987 ; hurley et al .
it will be recalled that the problem of grb source compactness arose just in the explanation of the 1979 march 5 event ( carrigan & katz 1992 ) with the huge luminosity and with the very short observed rise time ( to @xmath158s ) .
such a bursting activity of the sgrs can be explained by the fast heating of the bare surface of a strange star and its subsequent _ thermal emission _ ( usov 2001 ) .
the heating mechanism may be , for example , the fast decay of super - strong ( @xmath159 g ) magnetic fields .
the energy output mechanism in this usov s model can be advantageously used to explain the long - duration ( cosmological ) grbs in the compact model with the small collimation of the prompt grb radiation with strong beaming ( 2 ) for -rays . in this case , grbs should be considered as a set of short bursts ( like the giant flares of the 1979 march 5 and 1998 august 27 events ) with a total grb duration of @xmath160s .
from the said above in this section it is seen that the attempts to explain grbs by physics related with a massive compact object have already a rather long history .
this experience can be used for detailed development of the compact model of grb source or grb scenario with the compact energy output allowing for what was said in the previous sections of our paper about observational and theoretical arguments in favor of such an attempt to solve the problem of the grb source compactness .
so , xrfs can be not collimated at all or slightly collimated ( xrr grb ) , but with the low total bolometric energy of @xmath161 ergs .
since most probably these are actually the explosions of massive sne at distances of 100 mpc ( norris 2003 ; norris & bonnel 2003 ) , they can be observed much more frequently than it is predicted by the standard fireball grb model .
one should try to find early spectral and photometrical sn features . then
, in general , the observational problem of xrf / xrr / grb identification becomes a special section in the study of cosmological sne .
( it will be recalled that the grb 030329/sn 2003dh was a xrr grb but not a classical grb . ) as to normal / classical grbs and especially those ones with many heavy quanta in spectra , it is possible to obtain directly from formula ( 1 ) a ( kinematical ) estimate of the limit collimation of this gamma radiation , which , in turn , independently agrees with the observational ratio ( 2 ) of the yearly rates @xmath162 .
if the matter concerns quanta with @xmath163 of distant and the most distant grbs , then from @xmath164 it follows that the radiation of such grbs turns out to be the most collimated .
such photons must be radiated in the cone of an opening of @xmath165 and be detected in the spectra of the rather distant grbs with @xmath166 and farther because of geometrical factor only .
thus , a natural consequence of our compact model of the grb source is the fact that distant bursts ( @xmath167 ) turn out to be harder ones , while close grbs " ( @xmath168 ) look like xrf and xrr grbs with predominance of soft x - ray quanta in their spectra ( though the factor @xmath169 also works ) .
naturally , the effects of observational selection due to finite sensitivity of grb detectors should be also taken into account .
for example , the soft spectral component of the distant ( classical ) grbs is cut " out by the detector sensitivity threshold . and
the isotropic x - ray burst , simultaneous with the grb , can be simply not seen in distant ( classical ) grbs because of the low total / bolometric luminosity of the source in the compact grb model ( @xmath2 ergs ) . actually , xrf and xrr grbs have lower values of @xmath84 ( so called isotropic equivalent ) , than grbs ( amati et al .
2002 ; lamb et al .
2003a , 2003b , 2003c ) . as a result
, only radiation within a narrow solid angle near a selected direction ( in the grb source ) is observable for grb detectors : the soft spectral range remainder for the prompt xrr grbs with @xmath170 ( having climbed over the equipment threshold ) and hard ( and even heavy ) quanta below the threshold of the pair production ( 1 ) for classical grbs with @xmath167 .
( close xrfs with @xmath171 can not have the @xmath1-ray quanta in their spectra at all for the definit equipment threshold ) .
though from the review by postnov ( 1999 ) it follows that typical " grbs are seen in the range of 30 kev 100 mev , but it turns out ( and it was known before ) that most grbs are much softer ( see sect .
2 ) . not without reason
lamb et al .
( 2003 ) were just amazed by this important _ observational _ result of bepposax and hete-2 missions .
we mean the detection of obvious xrfs and xrr grbs first by bepposax ( amati et al . 2002 ) and then by hete-2 . in our compact model of grb source it ( the amati law )
can be a simple " consequence of formula ( 1 ) + collimation ( most probably ) by magnetic field on the surface of the compact object . in the scenario of jet formation , which was discussed in this paper and which was also used to interpret the grb 970508 optical transient ( ot ) light curves ( sokolov 2001b ) an isotropic x - ray , optical and radio emission of the _ afterglow _ of the grb ot is possible . in x - ray lines ( piro et al .
1999 ; yoshida et al .
2001 ; piro et al . 2000 ; antonelli et al .
2000 ) it was so for sure . at
that an initial assumption was just a possibility of the small grb collimation ( 2 ) , which follows from the comparison of the rates of grbs and sn explosions in distant galaxies .
it means that the close relation between grbs and sne was taken as a basic assumption .
_ all _ long grbs are always accompanied by sn explosions , which are sometimes observed , and sometimes not ( sokolov 2001a , 2002 ) . in other words ,
the long grb is the beginning of a massive star collapse or the beginning of sn explosion , and grbs must always be accompanied by sn explosions ( of ib / c type or of _ other _ types of massive sne ) .
then in any case the total energy release at the burst in -rays can be _ not more _ than the total energy released by any sn ( @xmath172 or @xmath173ergs ) in all _ electromagnetic _ waves .
( it is interesting that the total energy release in x - ray emission lines observed with bepposax , asca , chandra for grb 970508 , grb 970828 , grb 991216 , grb 000214 is of the same order see the collected data in the paper by ghisellini et al .
( 2002 ) emission lines in grbs constrain the total energy reservoir . " ) but with so low " total energy of the grb explosion ( @xmath174 ergs ) the only possibility to see grb at cosmological distances ( @xmath167 ) is the detection of at least the most collimated part of this energy ( @xmath175% ) leaving the source within the solid angle of @xmath113 .
the rest can be inaccessible for grb _ detectors _ with a limit sensitivity of @xmath176 .
certainly , it does not concern the 10 000 times more sensitive x - ray _ telescopes _ which were used to make sky surveys with the ariel v , heao-1 , einstein satellites ( heise et al .
for limit sensitivity of @xmath177 in the band of @xmath178 kev the x - ray observatory ( einstein ) recorded fast x - ray trasients ( unidentified with anything ) at a rate of @xmath179 all over the sky .
it agrees well with an average rate of the massive sne explosions in distant galaxies , but for the present , grb - detectors see only @xmath180 part of this huge number of the distant sn explosions as grbs .
it is natural that at the total / bolometric energy of grb " @xmath181ergs and at the grb energy ( 3 ) released in the narrow cone ( 2 ) , the fireball " also looks in quite a different way . as to the compactness problem solved by the fireball model for grb energies of @xmath182ergs
, there is no such a problem for -burst " energies @xmath181ergs . in any case , allowing for the low -ray collimation from the surface of the compact object grb / xrr / xrf source , which is necessary for the angular dependence of @xmath151 pair production ( 1 ) , this problem is solved under quite different physical conditions in the grb - source than that supposed by piran ( 1999 ) . in the scenario : _ massive star _
@xmath94 _ wr _
@xmath94 _ pre - sn @xmath183 pre - grb _ , in which only a small part of the most collimated radiation with the collimation ( 2 ) goes to infinity and , correspondingly , with the total energy of @xmath184 times less than in the standard theory , the source can actually be of a size @xmath185 cm .
it means that at the energies of up to @xmath186ergs the old ( naive " ) estimate of the source size resulting directly from the time variability of grb can be quite true .
thus , the point can be that the burst energy is much less than in the standard fireball model . to the above - said we add that the suggested compact grb scenario allows also predicting the behavior of superluminal radio components ( which , e.g. ,
have been observed recently for grb 030329 ( taylor et al .
2004 ) ) . as we discussed in sect . 5 ,
most likely there is no considerable deceleration of the jet / bullet ( with the lorentz factor of order 10 ) .
hence we expect that the superluminal radio components related to the jet have the following properties : + 1 ) the radio component will move with the constant observed superluminal velocity ; + 2 ) the characteristic observed velocity of the superluminal component is of the order of the lorentz factor , i.e. of order @xmath187
. * acknowledgements . *
authors are sincerely grateful to yu .
shibanov for fruitful discussions , t. n. sokolova for the manuscript editing .
the work was supported by rfbr grants : 04 - 02 - 16300 , 01 - 02 - 17106 , 03 - 02 - 17223 , program of the presidium of ran non - stationary phenomena in astronomy " , program of russian science and education ministry .
djorgovski s.g .
, kulkarni s.r .
, bloom j.s .
et al . , 2001 , invited review in proc . gamma - ray bursts in the afterglow era : 2nd workshop " , eds .
n. masetti et al . , eso astrophysics symposia , berlin : springer verlag , p. 218
( asro - ph/0107535 ) | typical observational gamma - ray burst ( grb ) spectra are discussed and , in this connection , what is the origin of the compactness problem and how it was solved at first .
if the threshold for @xmath0 pair production depends on an angle between photon momenta , then another solution of the compactness problem is possible .
we discuss a possibility of the @xmath1-rays collimation and the dependence of photon beaming on photon energies .
the list of basic assumptions of the scenario describing the grb source with energy @xmath2ergs is adduced : the matter is about an alternative to the ultrarelativistic fireball if _ all _ long - duration grbs are related or physically connected with _
normal / unpeculiar _ core - collapse supernovae ( sne ) .
namely , we consider the questions about radiation pressure and how the jet arises on account of even small asymmetry of the radiation field in a compact grb source .
the possibility of a new approach to explanation of the grb phenomenon is shown .
possible mechanisms of their generation in regions of size @xmath3 cm are discussed ( a compact model of grbs ) .
observational consequences of the compact grb energy release are considered .
january 10 , 2005 |
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BRUSSELS—International efforts to tighten pressure on Syria intensified Monday, with the European Union placing new sanctions on Damascus while foreign ministers predicted President Bashar al-Assad was starting to lose his grip on power.
The EU confirmed it was placing an asset freeze and travel ban on 26 people—mainly army, security and intelligence officials. The EU also tightened its arms embargo and targeted three companies including Syria's flagship airline. All three companies are "closely linked to the Assad family," U.K. Foreign Secretary William Hague said.
The EU "strongly condemns the ever-increasing use of force by the regime, including use of heavy ... ||||| BEIRUT (Reuters) - Western states expressed alarm after Syria acknowledged for the first time that it has chemical and biological weapons and said it could use them if foreign countries intervene.
A week of unprecedented fighting inside the capital Damascus, including a bomb attack that killed four of President Bashar al-Assad's closest advisers, has transformed the 16-month uprising and dramatically escalated international pressure on Assad.
Damascus residents said the capital was relatively quiet in the early hours of Tuesday after a day of fighting that saw government troops storm a neighborhood.
Defying Arab foreign ministers who on Sunday offered Assad a "safe exit" if he stepped down, the Syrian leader has launched fierce counter-offensives, reflecting his determination to keep power as the uprising enters its most violent phase.
Foreign Ministry spokesman Jihad Makdissi said the army would not use chemical weapons to crush rebels but could use them against forces from outside the country.
"Any chemical or bacterial weapons will never be used ... during the crisis in Syria regardless of the developments," Makdissi said. "These weapons are stored and secured by Syrian military forces and under its direct supervision and will never be used unless Syria faces external aggression."
Damascus has not signed a 1992 international convention that bans the use, production or stockpiling of chemical weapons, but officials in the past had denied it had any stockpiles. Washington and other Western capitals rushed to warn Syria against making any threats to use such weapons.
"Given the escalation of violence in Syria, and the regime's increasing attacks on their people, we remain very concerned about these weapons," White House spokesman Tommy Vietor said.
A U.S. State Department spokeswoman said warnings against using chemical weapons extended not only to the Syrian government but to rebels and any militants who might try to obtain them.
"The warnings that we have given with regard to safeguarding this kind of absolutely horrific and dangerous weapon have been made to regime, to opposition, to anybody who might get their hands on them," she said.
Britain, Germany and other countries also said it was unacceptable for Syria to say it might use chemical arms. U.N. Secretary General Ban Ki-moon said he was very concerned Syria may be tempted to use unconventional weapons.
Western countries and Israel have expressed fears chemical weapons could fall into the hands of militant groups as Assad's authority erodes. Israel has publicly discussed military action to prevent Syrian chemical weapons or missiles from reaching Assad's Lebanese Shi'ite militant allies Hezbollah.
The Global Security website, which collects published intelligence reports and other data, says there are four suspected chemical weapons sites in Syria: north of Damascus, near Homs, in Hama and near the Mediterranean port of Latakia. Weapons it produces include the nerve agents VX, sarin and tabun, it said, without citing its sources.
Abdelbasset Seida, head of the Syrian National Council opposition group, said: "A regime that massacres children and rapes women could use these types of weapons.
"The technical infrastructure may not be suitable, but as I said, such a step could be expected from this murderous regime. The international community must prevent this," he told reporters after meeting Turkey's foreign minister in Ankara.
Arab League ministers meeting in Doha urged the opposition and the rebel Free Syrian Army to form a transitional government, Qatari Prime Minister Sheikh Hamad bin Jassim al-Thani told a news conference.
Makdissi rejected the call for Assad to step down as a "flagrant intervention" in Syria's internal affairs. "We regret that the Arab League stooped to this immoral level," he said.
On Monday the army shelled rebel forces in the northern city of Aleppo and stormed the southern Damascus neighborhood of Nahr Aisha, breaking into shops and houses and burning some of them, activists said.
Video showed dozens of men in green army fatigues massing in the neighborhood, which looked completely abandoned. Men carrying machineguns and rocket-propelled grenade launchers knocked and then kicked down doors and climbed through windows.
Assad's forces have reasserted control over several Damascus areas since they seized back the central Midan district on Friday, 48 hours after a bomb attack killed four of Assad's closest security officials.
"The regime strategy is to continue to confront the opposition, this time with much broader military response," said Ayham Kamel, Middle East analyst at Eurasia Group consultancy.
"The expectation that the regime is out of firepower or collapsing right now is misplaced."
But Assad's forces have lost ground outside cities, ceding control of four border posts on the Turkish and Iraqi borders.
Sky Television footage from the town of Azaz close to the border with Turkey showed rebel fighters parading through streets firing triumphantly after a prolonged battle with government forces.
In Aleppo, activists said thousands of residents fled the rebel-held districts of Al-Haideriya, Hanano and Sakhour after army shelling and clashes between rebels and government forces in which activists said three government tanks were destroyed.
A video posted by activists showed families crammed into taxis, vans and the back of trucks trying to flee. Dozens of other families set out on foot, carrying plastic bags with their belongings.
"This is a large scale hit-and-run battle. The whole point is to bleed the regime dry. It is a very long fight, and it will be especially long in Aleppo," said a spokesman from the Islamist rebel group the Battalions for the Free Men of Syria.
DAMASCUS FIGHTING
The fighting in Damascus, Aleppo and the eastern city of Deir al-Zor has been some of the fiercest yet and showed Assad's determination to avenge last Wednesday's bomb attack, the most spectacular blow of the uprising.
Activists reported clashes on Monday in the Damascus districts of Qadam and Kafr Sousseh. Rebel sources say the guerrilla fighters in the capital may lack the supply lines to remain there for long and may have to make tactical withdrawals.
In the northeast district of Qaboun, where Assad's forces pushed fighters back in recent days, most streets were empty, said a resident reached by telephone who visited the area from another part of Damascus. A few people were returning to check on homes, some of which were destroyed.
"I came just to pick up some of my family's belongings, I am not returning for now," one woman told the visitor at her empty-looking four-storey building.
Groups of men were removing bodies from underneath the rubble of one building. "We have removed 25 bodies so far from this area, we are burying them quickly," one said.
An activist said 24 bodies had been found outside the capital in the Daraya district of the countryside on Monday, and said they appeared to be fighters who had been executed.
The accounts could not be verified independently; Syria restricts access by journalists.
The Syrian Observatory for Human Rights, which compiles reports from anti-Assad activists, said 1,261 people had been killed across Syria since last Sunday when fighting escalated in Damascus, making it by far the bloodiest week in an uprising activists say has claimed at least 18,000 lives.
(Additional reporting by Suleiman al-Khalidi in Antakya; Writing by Dominic Evans; Editing by Peter Graff and Michael Roddy) | – Despite recent reports that Syria may be preparing to use its chemical weapons, a foreign ministry spokesperson today tried to assure the world that they will not be used on the Syrian people—officially acknowledging for the first time that the country actually has such weapons, reports Reuters. "Any chemical or biological weapons will never be used ... in the Syrian crisis, no matter what the internal developments are," he said. But they could still be used: "These weapons are stored and secured by Syrian military forces and under its direct supervision and will never be used unless Syria faces external aggression." Meanwhile, though rebels were encouraged by the assassination attack last week that killed four regime officials in Damascus, Syrian troops have now driven rebels out of the city's Mezzeh district, yesterday executing at least 20 unarmed men there, Reuters reports. Violence is also raging in Aleppo, Syria's biggest city, and Deir al-Zor. The EU issued new sanctions against Syria today, the Wall Street Journal adds; those include an asset freeze and travel ban on select Syrians, and a tighter arms embargo. The Arab League promised President Bashar al-Assad a "safe exit" if he steps down now. |
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