Massachusetts Eye and Ear Infirmary researchers have developed technology to improve the built-in zoom feature of smartphones, which many low-vision users find difficult to use due to a loss of context.
Researchers from the Schepens Eye Research Institute of Massachusetts Eye and Ear/Harvard Medical School have developed a smartphone app which helps visually impaired people who experience problems with the loss of context associated with using the zoom feature on their mobile phones.
The app projects a magnified smartphone screen to Google Glass, which people can then navigate by head movements to view a corresponding portion of the magnified screen.
The researchers have shown that the technology can potentially benefit low-vision users, many of whom find the smartphone's built-in zoom feature to be difficult to use due to the loss of context.
"When people with low visual acuity zoom in on their smartphones, they see only a small portion of the screen, and it's difficult for them to navigate around -- they don't know whether the current position is in the center of the screen or in the corner of the screen," said senior author Gang Luo, Ph.D., associate scientist at Schepens Eye Research Institute of Mass. Eye and Ear and an associate professor of ophthalmology at Harvard Medical School.
"This application transfers the image of smartphone screens to Google Glass and allows users to control the portion of the screen they see by moving their heads to scan, which gives them a very good sense of orientation."
People with low vision often have great difficulty reading and discerning fine details. Magnification is considered the most effective method of compensating for visual loss. The researchers developed the head-motion application to address the limitations of conventional smartphone screen zooming, which does not provide sufficient context and can be painstaking to navigate.
A demonstration of the technology can be viewed here.


i find the yellow/orange color that is used for many things on this new site very difficult to read. it is TOO light. is there a way to deepen it or change the color?
I agree, especially when they don't show up as unread and get darker. Why does this happen? I haven't been on in a day I know I missed a bunch of threads and I open it up this morning and everything is that same drab color.
At some point we hope to redesign CurlTalk, but we can't do it right away, unfortunately.
I'm wondering if your monitors are set properly. WOuld you mind taking a screen grab and sending to me so I can see what you're seeing?
what is a screen grab?
Thank you, glad I'm not the only one who didn't know what she meant!
On My computer there is a button with the letters "fn" with a box around it - bottom left near the ctrl key. I press that and the "prt sc" (print screen) button - upper right and a double fiuntion with the insert key. For some it's alt and the print screen button. That will capture the screen that you see. It can then be pasted into something like Microsoft paint. Just open paint and go to paste under the edit funtion. Then you can save it to email it off.
Interestingly, my fonts are the same colors they have been for the last two years. Odd.
I really like the orange and I know it's part of brand equity and consistency (I love the nc logo) but I'm also a usability professional and I realize that a certain contrast level needs to be maintained for good accessibility on any site.
There are tools that you can use to analyze whether the colors used provide enough contrast (there are web standards and guidelines around this best practice) I'd provide a link, but a quick google didn't return a really easy-to-use one, so I'll look around and add a link if I find a good one. What I did find out is that no, there isn't enough contrast between the colors used here on naturallycurly, and I'd recommend that when you do consider a redesign that you'd consider contrast when redesigning the color palette.


We would like to bring to your attention that Quick Credit has been operating at 2 Jurong East Street 21 #04-01A since 2010 and our telephone number has remained unchanged at 6899-6188. We are a licensed moneylender who abides by the rules of the Registry of Moneylenders and will not resort to sending out SMS/Whatsapp texts to market our services. We are certain that there are unethical people out there making use of our good name to deceive customers that they are our representatives. Thus, this article is just a reminder to all to be careful when dealing with moneylenders who are very pushy with loans. It is also important to be careful and read all terms and conditions clearly; especially when documents are presented to you for your signature, make sure it is legible, properly explained to you, and most importantly, accurate – printed as what had been communicated to you.
We are sure many of us have from time to time received whatsapp texts or SMSes from an unknown number that promotes moneylending services. Some are even dubious foreign numbers with the country code "+86, +81" etc. From time to time too, you might also receive such messages from local numbers. Please be aware that licensed moneylenders are not supposed to market their moneylending services like that, making it very likely that these messages could be from the "Ah Longs".
We urge all borrowers or potential borrowers to exercise caution when taking up a loan. There are currently only 166 licensed moneylenders registered with the Registry of Moneylenders.
FAQs and important information can always be retrieved from the MinLaw website. And certainly, if you are unsure about your financial status and ability to cope with a loan, feel free to contact us for a non obligatory discussion and we will always do our best to help you address your concerns.
no. business name/address licence no list of valid moneylenders registered in the republic of singapore, as at 01 april 2016 1 101 credit pte. ltd.


text:
Will McCoy Trade Make Eagles Better?
March 5, 2015 March 5, 2015 / chrismsports
LeSean McCoy, the Eagles alll-time leading rusher, is now the newest member of the Buffalo Bills. Photo by Webster Riddick
PHILADELPHIA—The first day of NFL free agency isn't until next week (March 10), but the Philadelphia Eagles are already making a lot of noise as head coach Chip Kelly begins his tenure as the man in charge of the team's personnel decisions.
On Tuesday, ESPN's Adam Schefter reported that the Birds have traded LeSean "Shady" McCoy to the Buffalo Bills for inside linebacker and former University of Oregon star Kiko Alonso. The trade can't be finalized until 4 p.m. E.T. next Tuesday.
Meanwhile, McCoy's agent Drew Rosenhaus denied that the trade has taken place via Twitter.
"I just spoke with the Eagles organization and there is no trade for LeSean at this time," he said. "There have been discussions but nothing has been finalized."
Soon to be former Bills running back C.J. Spiller told the NFL Network the Bills called him to inform him that the team was acquiring McCoy and that it told him that his services were no longer needed in Buffalo.
A source close to McCoy told ESPN that 2013 NFL rushing leader is frustrated by the proposed trade and is "not going to make it easy"—whatever that means.
The trade was no doubt a cost cutting move for the Eagles because McCoy's salary counted $11.95 million against the Birds 2015 cap. The Bills will have to pay McCoy, who is signed through 2017, $10.25 million this season.
In addition to trading McCoy, the Eagles released longtime defensive end Trent Cole, who would have counted $11.6 million against the salary cap and veteran cornerback Cary Williams whose salary was a little over $ 8 million against the cap.
Now the Eagles have to find a replacement for a running back in McCoy who ran for 6,792 yards rushing and averaged 100.2 yards from scrimmage in six seasons playing for the Birds. Last season, he was third in the NFL in rushing with 1,319 yards.McCoy had the best year of his career in 2013 when he rushed for 1,607 yards while leading the league in rushing.
The question is will the Eagles go the free agent route for a running back where you have guys like DeMarco Murray and Adrian Peterson of the market or find a new running back in the upcoming NFL draft with players like University of Wisconsin star Melvin Gordon and University of Georgia running back Todd Gurley.
Since Kelly's offense is predicated upon having a strong running game, he needs to replace McCoy's versatility at that position quickly. That's going to easier said than done. While everyone likes to say the NFL has become a passing league, you still need a difference maker at the running back position.
The Eagles are expecting Alonso to be that tough enforcer in the middle and to play with the same level of intensity he did during his rookie with the Bills in 2013. He had 159 tackles and finished second in the NFL Defensive Rookie of the Year voting.
Before the start of last season, Alonso tore his ACL and was done for the season. Because of this and Alonso's history of injuries, Birds fans are wondering if Alonzo will be the second coming of Ray Lewis, or someone that the Philadelphia 76ers would have wasted a draft pick on.
Alonso will need to be a difference maker immediately for a defense that couldn't stop snitching. The Philadelphia Eagles defense ranked a mediocre 28th in yards allowed (31st against the pass).
On the surface, this trade, along with the release of two other veterans is a sign to fans that Kelly is also maneuvering to move up in the draft to get Heisman Trophy and University of Oregon standout Marcus Mariota, whom Kelly coached.
But if he were as smart as he thinks he is, Kelly would have used McCoy as a bargaining chip to move up instead of sending him as a birthday gift to new Bills coach Rex Ryan.
This also doesn't do anything to solve the Eagles other problems. The team is looking to re-sign wide receiver Jeremy Maclin. The needs at the cornerback and safety positions are so obvious Stevie Wonder could see them.
Kelly's bold moves will either make him look like the second coming of Dallas Cowboys coach Jimmy Johnson and lead the Eagles to the Super Bowl or make him look like a colossal failure a la Nick Saban and other college coaches who couldn't make it in the pros.
But in any case, the Eagles have already won the one competition they've scored high in since Jeffrey Lurie bought the team years ago.
They have, once again, won the Salary Cap Bowl.
Buffalo Bills, Chip Kelly, Kiko Alonso, LeSean McCoy, NFL, Philadelphia Eagles, Salary Cap
← Eagles Cash in Their Biggest Chip on Alonso
Breaking it Down: Did Eagles Free Agents Moves Put Them in the Right Direction? →
One thought on "Will McCoy Trade Make Eagles Better?"
Interesting perspective ^5

redpajama_set_name: RedPajamaCommonCrawl


By Kunststoffzaun Berlin. Last changed 23 days ago.
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text:
Media releases and statements
Scientists discover shark graveyard at the bottom of the ocean
Scientists have discovered new species, a shark graveyard and megalodon teeth on the ocean floor.
Carla Howarth
Communication Advisor, O&A Comms
Contact Carla Howarth
Laboratories and Facilities
Marine National Facility
7 December 2022 News Release
4 Photos 1 B-roll Video
Scientists on CSIRO research vessel (RV) Investigator have made some exciting finds during recent voyages, including collecting a specimen of a new species of shark and discovering a shark graveyard in the deep ocean.
The graveyard even contained the fossilised teeth of the ancient ancestor of the megalodon shark.
The discoveries were made on RV Investigator – operated by CSIRO, Australia's national science agency – during biodiversity surveys in two of Australia's newest marine parks. The first was a recent voyage to the Cocos (Keeling) Islands Marine Park in the remote Indian Ocean. The second is an underway voyage to the Gascoyne Marine Park off Western Australia. Both voyages have been undertaken for Parks Australia, who manage Australia's marine parks network.
Shark expert from CSIRO's Australian National Fish Collection, Will White said one of the most exciting finds of the underway voyage was the collection of a specimen of a new species of shark.
"Early in the voyage, we collected a striking small, stripey hornshark," said Dr White.
"This species is unique to Australia, but it hasn't yet been described and named. The specimen we collected will be incredibly important to science because we'll use it to describe the species," he said.
Hornsharks include the well-known Port Jackson shark and are generally slow-moving species found in shallow waters. They spend most of the day camouflaged among rocks and seaweed on the seafloor and come out at night to feed. However, this new species lives in water over 150 m deep and we know nothing about its behaviour.
Dr White said biodiversity surveys are always exciting as you never know what you might find.
"Australia has a truly enormous marine estate that's home to some of the most diverse marine life on the planet but we still know very little about what lives beneath the waves," said Dr White.
"From the very first survey on this voyage, we've been making new discoveries and collecting data that will be vital in helping to protect and conserve the life in our oceans," he said.
Chief Scientist on the underway voyage, John Keesing from CSIRO, said the discovery of new species was quite common on biodiversity surveys such as this.
"It's been estimated that around a third of the species collected on recent biodiversity survey voyages on RV Investigator may be new to science," said Dr Keesing.
"The discoveries we make aren't just limited to new species. These voyages give us the opportunity to learn more about marine ecosystems, as well as species range, abundance and behaviour," he said.
Scientists are using a range of equipment to study marine life and seabed habitats in the Gascoyne Marine Park, including underwater towed and remote cameras. Several shark species have been captured on film during the voyage. This includes sharks taking bites of the equipment.
However, one of the more unsual finds on the previous voyage to Cocos (Keeling) Islands was the discovery of a shark graveyard on the seafloor. Scientists, led by the Museums Victoria Research Institute, made the surprising discovery during the final trawl survey of the voyage at a depth of 5400 m. The trawl brought up more than 750 mineralised (fossilised) shark teeth representing a range of predatory species.
Curator of Fishes at the Western Australian Museum, Glenn Moore is on the underway voyage and said the shark teeth came from an interesting mix of modern and ancient sharks.
"The teeth look to come from modern sharks, such as mako and white sharks, but also from ancient sharks including the immediate ancestor of the giant megalodon shark," said Dr Moore.
"This shark evolved into the megalodon, which was the largest of all sharks but died out about 3.5 million years ago," he said.
The megalodon was considered one of most powerful predators ever to have lived but is only known from fragmentary remains, such as its teeth. Its appearance and maximum size are still uncertain. The teeth collected here are likely from its closest relative, a shark which grew to over 12m long.
Dr Moore said that it was astounding that such a large number of teeth were collected from a relatively small area on the seafloor.
"We've also found a few mako and white shark teeth during the underway voyage but nothing like the numbers found during the previous voyage. It's incredible to think we've collected all these teeth in a net from the seafloor some 4 to 5 km below the ocean surface," Dr Moore said.
The discoveries emphasise the importance of marine biodiversity survey voyages and the significant contribution they make to better understanding the life in our oceans.
"From small, new, bottom-dwelling sharks, to massive ancient mega-sharks that once roamed the oceans, these biodiversity surveys give us vital insights into the life in our oceans," Dr Keesing said.
Parks Australia Head of Division, Jason Mundy said the learnings will help Parks Australia to manage the remote marine parks, now and into the future.
"It shows there is more to learn about our 60 Australian Marine Parks, especially those in deep and difficult to access environments. This is made possible through partnerships with research organisations and universities," Mr Mundy said.
RV Investigator will continue surveying the Gascoyne Marine Park, as well as the nearby Carnarvon Canyon Marine Park, until mid-December and then end its voyage in Fremantle.
This research is supported by grants of sea time on RV Investigator from the CSIRO Marine National Facility.
Multimedia assets including images can be accessed via Dropbox by clicking here.
CSIRO research vessel (RV) Investigator. Credit CSIRO: Tauri Minogue
Download image JPG 1MB
Helen O'Neill CSIRO with undescribed stripey hornshark. Credit CSIRO-Frederique Olivier
Shark teeth collected from seafloor near Cocos (Keeling) Islands at depth 5400m_Credit: Museums Victoria-Ben Healley.
Tooth from megalodon ancestor collected from seafloor. Credit: Museums Victoria-Ben Healley
B-roll video
Download video ZIP 421MB View transcript


The Bentley Map Mobile team is pleased to announce that the commercial release of "Bentley Map Mobile for Windows x64" is available here for immediate download in the Bentley SELECT Software Fulfillment Center. As noted in "What's New?", Bentley Map Mobile provides touch enabled redlining, search, locate and viewing of 2D/3D vector and raster data created by Bentley Map or MicroStation. Bentley Map Mobile i-models contain high-precision maps and business data for use by field personnel of all types, including engineers, inspectors, maintenance crews, construction crews and others.
Bentley Map Mobile - What's New?


Strengthen Skin Immunity - Not.Just.A* Konjac sponge infused with natural tourmaline powder. This mineral rich ingredient restores skin cells, enhances the immune system and improves defense mechanism.
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This magical property harmonizes the water, giving you the most desired environment for cleansing.


text:
Q: Same consumer group (s3 sink connector) across two different kafka connect cluster I'm migrating Kafka connectors from an ECS cluster to a new cluster running on Kubernetes. I successfully migrated the Postgres source connectors over by deleting them and recreating them on the exact replication slots. They keep writing to the same topics in the same Kafka cluster. And the S3 connector in the old cluster continues to read from those and write records into S3. Everything works as usual.
But now to move the AWS s3 sink connectors, I first created a non-critical s3 connector in the new cluster with the same name as the one in the old cluster. I was going to wait a few minutes before deleting the old one to avoid missing data. To my surprise, it looks like (based on the UI provided by akhq.io) the one worker on that new s3 connector joins with the existing same consumer group. I was fully expecting to have duplicated data. Based on the Confluent doc,

All Workers in the cluster use the same three internal topics to share
connector configurations, offset data, and status updates. For this
reason all distributed worker configurations in the same Connect
cluster must have matching config.storage.topic, offset.storage.topic,
and status.storage.topic properties.

So from this "same Connect cluster", I thought having the same consumer group id only works within the same connect cluster. But from my observation, it seems like you could have multiple consumers in different clusters belonging to the same consumer group?
Based on this article __consumer_offsets is used by consumers, and unlike other hidden "offset" related topics, it doesn't have any cluster name designation.
Does that mean I could simply create S3 sink connectors in the new Kubernetes cluster and then delete the ones in the ECS cluster without duplicating or missing data then (as long as they have the same name -> same consumer group)? I'm not sure if this is the right pattern people usually use.

A: I'm not familiar with using a Kafka Connect Cluster but I understand that it is a cluster of connectors that is independent of the Kafka cluster.
In that case, since the connectors are using the same Kafka cluster and you are just moving them from ECS to k8s, it should work as you describe. The consumer offsets information and the internal kafka connect offsets information is stored in the Kafka cluster, so it doesn't really matter where the connectors run as long as they connect to the same Kafka cluster. They should restart from the same position or behave as additional replicas of the same connector regardless of where ther are running.

redpajama_set_name: RedPajamaStackExchange


We are disconnected. Living in a consumer society has reduced our exposure to how products are actually made. In a continuing series, SoCo will bring you exposure: the art, the technique, the history that binds us. The small details that can make a thing more than it is. Reconnect with your past, the past of all of us, through the visual beauty of ancient art.
It's true that I've been a huge fan of India Flint's work with plants and landscape for many years, but it is only recently that I realized she's my role model for femininity. Hands and face stained by the colors of her surrounding, knee-deep in mud and muck and life and death, she wanders, she gathers, she creates. She is, simply, life. There is no pretension, no wasted matter and energy, there is only a woman who lives, completely, in her surroundings.
India Flint: botanical alchemist, working traveler, dreamer, writer, gatherer, wayfarer and the original discoverer of the eucalyptus ecoprint.
India has been an indentured artist for decades, her work progressing, growing, changing, and adapting with her education and experience. A hefty portfolio of exhibitions, residencies, and collaborations speak to her skill and dedication. And, the pile of costumes she's created sends a poor dancer's heart to palpitations.
Most of the clothing we buy today is full of dyes made from harsh chemicals, in artificially-lit warehouses, full of fumes and dismay. Our clothes cover our bodies and our bodies absorb their energy. Whether or not you are spiritual (maybe you believe in chi and chakras and maybe you don't), our skin is, definitively, a big sponge with tiny holes, and the clothing we use for cover contains toxins even tinier than those holes. Perhaps you are what you eat, perhaps not, but you definitely are what you wear.
Ms. Flint lives in South Australia and collects fallen leaves and other discarded materials and makes art from them. She plays with both form and function, and the results are original, unique, and imbued with the spirit of the land. Bones and gum leaves are pressed into fabric and boiled stains are pulled from the muck left behind. There is a simple beauty here. Fabric that wears its story, proudly yodeling of the land that birthed it.
I would never leave you hanging! India's website is a treasure trove of secret links and stark imagery to be explored on a lazy Sunday, hopefully, a stormy one. She also has the most beautiful DIY book I've ever come across called Eco Colour: Botanical Dyes for Beautiful Textiles , and for those that prefer to look but not to touch, there's a stunning coffee-table book full of the most inspiring images, Second Skin: Choosing and Caring for Textiles and Clothing .
We at SoCo believe that sustainability is not just a lifestyle – it is life. Working with the Earth, for the benefit of all, is tantamount to becoming the best society we can be. Perhaps modern technology has made things easier, but it certainly does not always make them better. In this continuing series, we aim to highlight those artists and techniques that should not be forgotten, and hopefully, are never overlooked. By remembering how we started, perhaps we can find a better way to move forward. Please let us know in the comments if there's a particular artist or technique you would like to see highlighted. This post is the third article on our "Artisan Series," you may check out posts you missed in this series using this link.
absolutely love it still create wonderful work.Thanks India.
I'm so envious! You are one lucky crafter!


text:
Thomas Fraser Rogers (born 7 February 1999) is an Australian cricketer.

Rogers has played T20 for the Melbourne Stars since the 2021-2022 season. He made his debut on 2 January 2022, as one of six replacement players called into the squad in January 2022 during the 2021–22 Big Bash League season after ten members of the original squad became unavailable due to contracting COVID-19. Rogers was subsequently ruled out of the Stars' next game against the Melbourne Renegades only one day later after testing positive to COVID-19.

References

1999 births
Living people
Melbourne Stars cricketers
Australian cricketers

redpajama_set_name: RedPajamaWikipedia


text:
\section{Introduction}

The formation of planets is a complex process that requires sub-$\mu$m dust
grains to grow over a dozen orders of magnitude in size. The smallest particles,
although they are highly-coupled to gas, can slowly drift in both radial and
vertical direction, and collide with each other. That physical collisions with
low relative velocities lead to creation of larger agglomerates~\citep{BW08}.
On the other side of the scale, $10^4$~m bodies are large enough to be almost
completely decoupled from gas dynamics and be mostly influenced by gravitational
interactions~\citep{KKI06}

\par The most problematic is the intermediate step of growing dust from cm
grains to km sized bodies, due to existence of several processes that counteract
the possible growth or pose significant time constrains. The latter is mainly
caused by a fast radial drift of the bodies that are marginally coupled to the
gas, i.e. characteristic scale of their aerodynamic drag is of the order of
their orbital time~\citep{W77}. Moreover, the characteristic relative velocities
for the bodies of sizes ranging from $1\textrm{ cm}$ to $ 1\textrm{ m}$ are of
the order of $1\div10\textrm{ m s}^{-1}$ which, during collisions, result in
fragmentation and bouncing rather than sticking~\citep{Z10}.

\par One of the possible scenarios  is a fast enhancement
of dust density via sedimentation to the midplane due to vertical component of
host star gravity. Then further fragmentation and collapse of dense dust layer
is caused by a self-gravity~\citep{GW73}. Though the sedimentation itself leads
to the rise of Kelvin-Helmholz instability~\citep{JHK06} (KHI) which prevents
forming an infinitesimally thin layer in the midplane, recent studies show that
it is not the case for massive discs with higher than solar
metallicities~\citep{L10}.

\par However, a significant flaw behind presented reasoning is a complete
negligence of disc's global turbulence, which in turn is the only mechanism that
would allow to explain observed accretion rates assuming $\alpha$-disc
model~\citep{SS73}. Even though, the most plausible mechanism responsible for
such turbulence, i.e. magnetorotational instability~\citep{BH98}, allows for
formation of local, low-level of turbulence areas due to insufficient ionization
of gas, there are still other instabilities that stir the fluids~\citep{LP10}.

\par Despite of this unfavorable circumstances there is a process that commences
to dominate dust evolution when ratio of concentration of dust particles to gas
density approaches unity. This mechanism was first presented by~\cite{YG05}
(hereafter YG05) and named the {\it streaming instability}. It appears that
combination of dust trapping in gas pressure maxima and mutual interaction
leading to dust dragging the gas, therefore enhancing the maxima even further,
results in significant dust pile-up~\citep{J11}. Even without the presence of
self-gravity, dust concentration may be risen up to the three orders of
magnitude~\citep{JY07} (hereafter JY07) which could possibly lead to
gravitationally bound objects~\citep{J07}. Recent numerical studies of
streaming instability concentrate on various physical aspects that may influence
its evolution, that includes: the influence of wide range of dust
species~\citep{BS10a}, effects of global pressure gradients~\citep{BS10b},
stratification of discs~\citep{T12}. However, all known to authors works limit
themselves to local disc approximation.

The main goal of this paper is to investigate the streaming instability in a
more realistic circumstances of radially extended discs. The essential points of
interest are:
(1) resolution studies of the streaming instability in a 2D radially extended
domain,  to see what is the minimum  grid resolution necessary to ensure growth
rates of  simulated instability modes consistent with the results of linear
stability analysis, (2) investigation of the streaming instability a in 3D
radially extended domain, in an optimal  grid resolution,  deduced from
resolution studies in 2D.

The plan of the paper is as follows: In Section~\ref{sec:eqs} we set up the
basic assumptions and equations relevant for the present paper. In
Section~\ref{sec:lsa} we perform linear analysis of streaming instability in
protoplanetary discs. In Section~\ref{sec:setup} we describe specific numerical
algorithm that were used in the performed simulations along with the initial
conditions and the basic simulation parameters. Section~\ref{sec:results} shows
the obtained results and their detailed comparison with linear stability
analysis.  Finally in Section~\ref{sec:conclusions} we discuss the outcome of
our experiments and give short outlook of the future work.

\section{Basic assumptions and equations}
\label{sec:eqs}

We investigate global dynamics of two interacting fluids -- gas and dust -- in
the protoplanetary disc. We assume that neutral gas obeys the isothermal
equation of state, whereas dust is treated as a pressureless fluid.

\begin{align}
\partial_t \rho_g &+ \nabla\cdot\left(\rho_g\mathbf{u}\right) = 0,\\
\partial_t \rho_d &+ \nabla\cdot\left(\rho_d\mathbf{w}\right) = 0,\\
\partial_t \left(\rho_g\mathbf{u}\right) &+
   \nabla\cdot(\mathbf{u}\otimes(\rho_g\mathbf{u})+P) \notag\\
 &= -\rho_g\left(\nabla\Phi +
\frac{\rho_d}{\tau_f\rho_g}(\mathbf{u}-\mathbf{w})\right),\label{eq3}\\
\partial_t \left(\rho_d\mathbf{w}\right) &+
\nabla\cdot(\mathbf{w}\otimes(\rho_d\mathbf{w})) \notag\\
 &= -\rho_d\left(\nabla\Phi + \frac{1}{\tau_f}(\mathbf{w}-\mathbf{u})\right)
\label{eq4}.
\end{align}

\noindent where $\rho_g$, $\rho_d$ are densities of gas and dust respectively,
$\mathbf{u}$, $\mathbf{w}$ corresponding velocities, $P$ gas pressure, $\tau_f$
is a friction time and $\Phi$ is gravitational potential. Our aim is to isolate
the streaming instability from the other possible processes acting in a radially
extended protoplanetary discs. In order to obtain a clear diagnostics of the
excited instability we neglect the vertical component of gravity arising from the
point mass source in the center of the reference frame, which would lead to dust
sedimentation and eventually to the onset of KHI~\citep{JHK06}.

We shall simulate disc starting from the relatively large radius (2~AU).  We
assume, following~\cite{CD93} that transition to Stokes regime occurs for
particle radius $a = 9/4\lambda_g$ where  $\lambda_g = 4.2\times 10^4\textrm{
cm} (10^{-14}\textrm{ g cm}^{-3}/\rho_g) \approx (R/1 \textrm{AU})^{2.75}$~cm is
the mean free path of the gas molecules~\citep{W77,BT09},  and $R$ is the radial
distance to the disc centre.  Under these assumptions the Epstein's regime
applies in the dominating part our domain, even for the largest simulated grain
sizes.  Therefore, to compute the friction time, we use the Epstein's law
\begin{equation}
   \tau_f = \frac{\rho_\bullet a}
      {\rho_g \sqrt{c_s^2 + |\mathbf{u} - \mathbf{w}|^2 }}
   \label{eq:tauf}
\end{equation}
where $c_s$ is the gas sound speed, and $\rho_\bullet = 1.6\textrm{ g cm}^{-3}$
is the density of the solid material.
While the term $|\mathbf{u}-\mathbf{w}|^2$ does not play any significant
role during the evolution of SI, i.e. its value never exceeds 1 per cent of
$c_s^2$ we have decided not to neglect it in our simulations for the
completeness sake.

\begin{figure*}
   \centering
   \begin{tabular}{@{}cc@{}}
      \includegraphics[width=0.49\linewidth]{figs/fig1a} &
      \includegraphics[width=0.49\linewidth]{figs/fig1b} \\
      \includegraphics[width=0.49\linewidth]{figs/fig1c} &
      \includegraphics[width=0.49\linewidth]{figs/fig1d}
   \end{tabular}
   \caption{Dust density snapshots for runs with $50$~cm grain sizes at $100$,
   $200$, $450$ and $700$~yr for upper left, upper right, bottom left and bottom
   right panel respectively. Each of the panels is divided into three subpanels
   for initial $\epsilon = 0.2, 1, 2.0$ on upper (BAh), middle (BB) and lower
   (BC) subpanel respectively. Animation of the run BBh can be found
   \href{http://youtu.be/EfQU8ixHFbU}{here}.}
   \label{fig1}
\end{figure*}
\section{Linear stability analysis}
\label{sec:lsa}
One of the aims of this paper is to validate numerical results related to the
growth of streaming instability unstable modes via the comparison to the growth
rate and mode geometry resulting from linear stability analysis. Therefore,
following the previous authors~\citep{YG05}, in this section, we review the main
steps of the linear analysis of the streaming instability in protoplanetary
discs.

The linear stability analysis relies on three essential elements: (1) finding an
equilibrium state of the system, (2) perturbing the system with small amplitude
(linear) perturbations, and (3) deriving the eigenmodes and their growth rates.
Unfortunately there is no strictly stationary solution to global Keplerian disc
consisting of two fluids coupled via the drag force.
The reason is the dust migration, implying variations of the radial disc profile.
We note however, that the characteristic timescale of radial
migration of meter-size dust agglomerates is of the order of 100 years or
longer, therefore we consider the variations of the disc profile as a
slow process, as compared to typical growth times of  streaming instability.

Another difficulty results from the fact that the wide range of the radial
coordinate in our numerical models implies radial variations of the equilibrium
state the physical parameters. In these circumstances it would be appropriate to
perform global stability analysis by means of solving the two-point boundary
value problem (see e.g. \cite{PHM04, KH06}), however the latter approach is
significantly more complex than the local stability analysis. Therefore, we
consider the local stability analysis as a first approximation to the full
analysis of streaming-instability in protoplanetary discs. The modes derived in
the framework of local linear stability analysis will serve us as a reference
solution for validation of the modes excited in the global numerical
simulations.

The most suitable local treatment of streaming instability is provided by the
"shearing-sheet" approximation~\citep{HGB95}, which is achieved by placing
Cartesian coordinate frame on an orbit of radius $R$, that corotates with
Keplerian frequency $\Omega$.  We assume that $x$ axis points radially outward,
and $y$ corresponds to the azimuthal direction, whereas $z$ is a vertical axis.
Following \cite*{YJ07} we write down the continuity and Euler equations for both
the gas and dust components
\begin{align}
\partial_t \rho_g &+ \mathbf{u}\cdot\nabla\rho_g - \frac{3}{2}\Omega x\partial_y\rho_g
 = -\rho_g\nabla\cdot\mathbf{u},\label{eqc1}\\
\partial_t \rho_d &+ \mathbf{w}\cdot\nabla\rho_d - \frac{3}{2}\Omega x\partial_y\rho_d
 = -\rho_d\nabla\cdot\mathbf{w},\label{eqc2}\\
\partial_t \mathbf{u} &+ \left(\mathbf{u}\cdot\nabla\right)\mathbf{u}
 - \frac{3}{2}\Omega x\partial_y\mathbf{u}
 = 2\Omega u_y \hat{\mathbf{x}} -\frac{1}{2}\Omega u_x \hat{\mathbf{y}} \notag\\
 &- \frac{\epsilon}{\tau_f}(\mathbf{u}-\mathbf{w}) -c_s^2\nabla\ln\rho_g
 +2\eta\Omega^2 R \hat{\mathbf{x}},\label{eqm1}\\
\partial_t \mathbf{w} &+ \left(\mathbf{w}\cdot\nabla\right)\mathbf{w}
 - \frac{3}{2}\Omega x\partial_y\mathbf{w}
 = 2\Omega w_y \hat{\mathbf{x}} -\frac{1}{2}\Omega w_x \hat{\mathbf{y}} \notag\\
 &- \frac{1}{\tau_f}(\mathbf{w}-\mathbf{u}), \label{eqm2}
\end{align}
where transport terms, such as $(3/2)\Omega x$ on the left-hand side of
equations arise due to fact that we measure all velocities relative to linear,
Keplerian shear flow in the rotating frame $\mathbf{v}_0 = -(3/2)\Omega x
\hat{\mathbf{y}}$. It is worth noting that term $-(1/2)\Omega \{u,w\}_x
\hat{\mathbf{y}}$ on the right hand side of the equations of motion
\mref{eqm1}-\mref{eqm2} is a sum of two components: $(-2\Omega \{u,w\}_x +
(3/2)\Omega \{u,w\}_x) \hat{\mathbf{y}}$ where the first one is the component of
Coriolis force and the second results from aforementioned subtraction of the
mean flow. The main difference between equations \mref{eqm1} and \mref{eqm2} is
the radial pressure gradient term influencing  the dynamics of gas only.  As
noted by YG05, it is possible, within the local approximation,  to include
consistently the disc's global pressure gradient parametrized by the
dimensionless measure of sub-Keplerian rotation

\begin{equation}
\eta \equiv - \frac{\partial_R P}{2\rho_g\Omega^2 R} \sim \frac{c_s^2}{v_K^2}.
\end{equation}

The set of equations \mref{eqc1}-\mref{eqm2} has a known equilibrium
solution~\citep{N86}

\begin{align}
\bar{\mathbf{w}} &= \left[
 -2\tau_s\xi, \frac{\tau_s^2\xi - 1}{1+\epsilon},
 0
\right]\eta v_K, \label{eq:w0}\\
\bar{\mathbf{u}} &= \left[
 2\epsilon\tau_s\xi, -\frac{1 + \epsilon\tau_s^2\xi}{1+\epsilon},
 0
\right]\eta v_K, \label{eq:u0}
\end{align}
where $\tau_s = \Omega \tau_f$ is dimensionless stopping time and
$\xi = ((1+\epsilon)^2 + \tau_s^2)^{-1}$. We linearize eq.
\mref{eqc1}-\mref{eqm2}, decomposing variables into a steady part and a
perturbation $\mathbf{q} = \bar{\mathbf{q}} + \mathbf{q}^\prime$, where
$\mathbf{q}=[\rho_d, w_x, w_y, w_z, \rho_g, u_x, u_y, u_z]$. We assume
subsequently that the perturbations are axisymmetric (independent on
$y$-coordinate in the present analysis) and can be expressed as plane waves

\begin{equation}
   \label{eq:planar}
   \mathbf{q}^\prime(x,z,t) = \tilde{\mathbf{q}}
 \exp\left[i(k_x x + k_z z -\omega t)\right]
\end{equation}

After the substitution of the linear perturbations the equations read

\begin{align}
-i(\omega- k_x\bar{w}_x)\tilde{\rho}_d &=
 - i \bar{\rho}_d(k_x\tilde{w}_x + k_z\tilde{w}_z), \label{lin1}\\
-i(\omega- k_x\bar{u}_x)\tilde{\rho}_g &=
 - i \bar{\rho}_g(k_x\tilde{u}_x + k_z\tilde{u}_z), \label{lin2}\\
-i(\omega- k_x\bar{u}_x)\tilde{\mathbf{u}} &=
 2\Omega \tilde{u}_y\hat{\mathbf{x}} - \frac{1}{2}\Omega \tilde{u}_x
 \hat{\mathbf{y}}
 -\frac{\epsilon}{\tau_f}(\tilde{\mathbf{u}} - \tilde{\mathbf{w}}) \notag\\
  &-\frac{\tilde{\rho}_d}{\bar{\rho}_g\tau_f}
  (\bar{\mathbf{u}} - \bar{\mathbf{w}})
  - \frac{c_s^2}{\bar{\rho}_g}ik_x\tilde{\rho}_g, \label{lin3}\\
-i(\omega- k_x\bar{w}_x)\tilde{\mathbf{w}} &=
 2\Omega \tilde{w}_y\hat{\mathbf{x}} - \frac{1}{2}\Omega \tilde{w}_x
 \hat{\mathbf{y}}
 - \frac{1}{\tau_f} (\tilde{\mathbf{w}} - \tilde{\mathbf{u}}), \label{lin4}
\end{align}
where $\epsilon = \bar{\rho}_d/\bar{\rho}_g$. The set of equations
\mref{lin1}-\mref{lin4} can be expressed as

\begin{equation}
 \EuRoman{A}(k_x,k_z,\omega)\tilde{\mathbf{q}} = 0
 \label{eq:linset}
\end{equation}
Nontrivial solutions of the linear system \mref{eq:linset} exist if
\begin{equation}
 \det|\EuRoman{A}(k_x,k_z,\omega)|=0
 \label{eq:disprel}
\end{equation}
We solve the dispersion relation \mref{eq:disprel} for given values of
$(k_x,k_z)$, with respect to the complex frequency $\omega$, using the
Durand-Kerner method~\citep{D60,K66}, and subsequently obtain relation between
constant amplitudes of components of the vector
$\tilde{\mathbf{q}}$~\footnote{Numerical solvers to both dispersion relation and
eigenvector calculation along with most visualization routines are publicly
available at \url{http://github.com/Xarthisius/kowalik_2012a}}.  The growth rate
of the instability is defined as imaginary part of the complex frequency $s=\Im
(\omega)$.
\begin{figure*}
   \centering
   \begin{tabular}{@{}cc@{}}
      \includegraphics[width=0.49\linewidth]{figs/fig2a} &
      \includegraphics[width=0.49\linewidth]{figs/fig2b} \\
      \includegraphics[width=0.49\linewidth]{figs/fig2c} &
      \includegraphics[width=0.49\linewidth]{figs/fig2d}
   \end{tabular}
\caption{Dust density snapshots for runs with $10$~cm grain sizes at $100$,
   $200$, $800$ and $1200$~yr for upper left, upper right, bottom left and
   bottom right panel respectively.  Each of the panels is divided into three
   subpanels for initial $\epsilon = 0.2, 1, 2.0$ on upper (AA), middle (AB) and
   lower (AC) subpanel respectively. Animation of the run AAu can be found
   \href{http://youtu.be/b7myS1PA_tE}{here}.}
\label{fig2}
\end{figure*}
\section[Simulation Setup]{Simulation setup}
\label{sec:setup}
\subsection{Algorithms}

We conduct numerical simulations with the aid of a parallel MHD code PIERNIK
using the cylindrical coordinate system.
Following \cite{M07} and \cite{SO10} we use ''angular momentum-conserving form''
of the $\phi$-momentum equation, which with respect to Cartesian geometry
introduces only one additional source term to equations~\mref{eq3} - \mref{eq4}:
$\left((\rho_g u_\phi + P) / R\right)\mathbf{\hat{R}}$ and $(\rho_d w_\phi / R)
\mathbf{\hat{R}}$ respectively.

Both components i.e. gas and dust are treated as fluids~\citep{piernik2} which
are dynamically coupled via the friction force. In order to prevent large
timestep constraint from drag force acceleration we used the semi-implicit
scheme by~\cite{TB09}. We allow the system to relax numerically (during the
period of initial $10$~yrs of the simulation) before we ''turn on'' the
aerodynamic drag force and seed dust velocities with low--amplitude random
noise. The feedback of the linear drag force scales with the density ratio of
dust to gas $\epsilon\equiv \rho_d/\rho_g$.

\subsection{Initial disc configuration}

The initial density profile for gas roughly follows prescription of Minimal Mass
Solar Nebula~\citep{H81}
\begin{equation}
   \Sigma(R) = 1700 \left(\frac{R}{1\textrm{ AU}}\right)^{-3/2}
   \textrm{ g cm}^{-2}.
\end{equation}
We assume isothermal equation of state and a constant temperature $T_0 = 170$~K
across the whole disc.
We assume gravitational field from a point mass $M=1\,\textrm{M}_\odot$, and
neglect the vertical component of gravitational acceleration towards the central
mass, implying no vertical stratification of the disc. Yet, we refer to the
vertical scaleheight $H$ to estimate  volume density of gas at given radius,
relying on the hydrostatic equilibrium density distribution in the presence of
the vertical gravity of a point mass
\begin{equation}
   \rho(R,z) =  \rho(R,0) \exp\left(-\frac{z^2}{2H(R)^2}\right),
\end{equation}
where $\rho(R,0)$ is gas density at the disc midplane and $H^2 = 2 c_s^2 R^3/
GM$.
The surface gas density is given by
\begin{equation}
   \Sigma(R) = \int_{-\infty}^\infty \rho(R,z) dz,
\end{equation}
The corresponding value of midplane gas density is
\begin{equation}
   \label{eq:rho}
    \rho(R,0) = \frac{\Sigma(R) }{\int_{-\infty}^\infty
   \exp\left(-\frac{z^2}{2H(R)^2}\right) dz}.
\end{equation}
For the chosen disc temperature $T_0$ the integral on the right hand side of
\mref{eq:rho} varies from $0.4$~AU to $2.0$~AU over the range of radii $R\in
[2,6]$~AU.
We assume for simplicity its value equal to $1$~AU.

We assume the vertical extent of the computational domain $L_z = 0.3$~AU, and
impose periodic boundary conditions at upper and lower $z$-boundaries. The
initial condition relies on a radial force balance for the gas and dust
components independently. The gas component remains in a hydrostatic equilibrium
resulting from the radial balance of gravity, centrifugal and pressure forces,
while the pressure gradient term is absent in the equation of motion for the
dust component.  Reflecting boundary conditions are set on the inner and outer
boundaries of the computational grid to prevent mass escape from the
computational domain.

\par To minimise unphysical wave reflections, we implement wave killing zones
close to the inner and outer radial boundaries. The inner wave killing zones
cover 0.5 AU near the inner and outer edges of the computational domain. In
these zones, we add an additional damping term, in the evolution equations of
each fluid variable

\begin{equation}
  \frac{\textrm{d}X}{\textrm{d}t} = - \frac{X-X_0}{T_d}f(R),
\end{equation}
together with
\begin{equation}
   \begin{split}
      f(R) &= 1 - \tanh\left(\left(R - R_\textrm{in} + 1
      \right)^{f_\textrm{in}}\right)\\ &+ \max\left\{ \tanh\left(\left(R -
      R_\textrm{out} + 1\right)^{f_\textrm{out}}\right), 0\right\},
   \end{split}
\end{equation}
where $X_0$ is the initial value of $X$ and $T_d$ is the damping timescale. We
chose $T_d$ of the order of orbital period.  The exponents
$f_\textrm{in}=f_\textrm{out}=10$ control the width of the transition layer
between the unmodified to the damped zones. Within the damped zones, the effects
of undesired wave reflection are essentially minimised.
\subsection{Simulation parameters}
We have performed a parameter sweep for the ratio of dust to gas density
$\epsilon$ and the size of particles $a$, at two different resolutions of the
computational grid in 2D, and additionally we have realized one of the models in
3D. Our choice of these parameters follows closely that of JY07, to enable
detailed comparison of the results.

The full list of simulations together with their main parameters is presented in
Table~\ref{tab1}. In all simulations the domain has height of $0.293$~AU,
for 2D it covers radii from 2 to 7~AU, whereas BB3D extends from 2 to 12~AU and
spans $\varphi\in[0, \pi/6]$.  Following JY07 we vary $\epsilon$ from 0.2 to
2.0~in order to exhibit morphologically different outcomes of nonlinear phase of
streaming instability.  We choose particle radii to be grater than $10$~cm and
less than $50$~cm so that (1) particles fall into Epstein regime in all
simulations, (2) their size could be plausibly explained by the growth processes
e.g. collisional agglomeration.

\begin{table}
   \centering
   \begin{tabular}{cccccc}
      \hline
      Run & $N_r \times N_\varphi \times N_z$ &
      $a$~[cm] & $\epsilon$ & $T_\textrm{end}$~[yr] \\
      \hline
      BB3D &  $5120  \times 128 \times 150$  & 50  & 1.0 & 500  \\
      AA   &  $5120  \times 1   \times 300$  & 10  & 0.2 & 3000 \\
      AB   &  $5120  \times 1   \times 300$  & 10  & 1.0 & 3000 \\
      AC   &  $5120  \times 1   \times 300$  & 10  & 2.0 & 3000 \\
      BA   &  $5120  \times 1   \times 300$  & 50  & 0.2 & 3000 \\
      BB   &  $5120  \times 1   \times 300$  & 50  & 1.0 & 3000 \\
      BC   &  $5120  \times 1   \times 300$  & 50  & 2.0 & 3000 \\
      AAh  &  $10240 \times 1   \times 600$  & 10  & 0.2 & 1700 \\
      AAu  &  $20480 \times 1   \times 1200$ & 10  & 0.2 & 1800 \\
      ABh  &  $10240 \times 1   \times 600$  & 10  & 1.0 & 1400 \\
      BAh  &  $10240 \times 1   \times 600$  & 50  & 0.2 & 1730 \\
      BBh  &  $10240 \times 1   \times 600$  & 50  & 1.0 & 3000 \\
      \hline
   \end{tabular}
\caption{Simulation parameters. Columns give, from left to right, name of the
   run, span of the computational domain in AU (r,z) and azimuthal angle, grid
   resolution, particle diameter in cm, solids-to-gas ratio, and total run time
   in units of years.}
\label{tab1}
\end{table}

\section{Results}
\label{sec:results}
The initial stage of streaming instability evolution is similar for all cases of
$\epsilon$ or $a$ and is governed by the dominant linear modes. Detailed
analysis of linear phase is covered in Section~\ref{simulation_analysis}. The
following two sections describe different non-linear evolution of streaming
instability in quasi-global setup with reference to similar case shown by JY07.
\subsection{Marginally Coupled Boulders ($a=50\,\textrm{cm}$, $\tau_s\approx
1.2$)\label{marg_boulders}}
As noted by JY07, streaming instability is the most prominent for $\tau_s = 1$
and exhibits fast linear growth and heavy dust clumping.  Figure~\ref{fig1}
shows temporal evolution of streaming instability for different initial dust to
gas ratios $\epsilon$. In all cases (BA, BB, BC) elongated clumps are formed.
When the saturated state is reached, due to the high vertical speed of dust
overdensities, the filaments undergo occasional fragmentation and collisions
with each other, though still following "v"-shaped trajectories that emerged
during linear phase. The most prominent differences between BA, BB and BC are:
(1) the characteristic length of local clumps is decreasing with the increase of
initial $\epsilon$ and (2) their tendency to lean in radial direction: in BB
structures are almost purely diagonal, whereas in BA and BC are much more
elongated in the vertical direction.
Similarly to JY07, in all cases (BA, BB, BC) the density peaks of the dust
component in the non-linear regime settle at levels about 2 order of magnitude
higher than initial density.

\subsection{Tightly Coupled Boulders ($a=10\,\textrm{cm}$, $\tau_s\approx 0.24$)
\label{tight_boulders}}

Since the fluid approach, contrary to the particle description, is much less
susceptible to effects of Poisson noise we were able to follow linear phase for
run AB and ABh for much longer than JY07, though in the end we also observe
sudden increase in growth rate of the instability due to spontaneous cavitation
(initial phase is caught in the middle subpanel of bottom right panel of
Fig.~\ref{fig2}).
The bubbles of void start to spawn at outer radii and greatly increase the dust
density and velocity on their edges (see Fig.~\ref{fig3}). After just
few orbital periods the accelerated instability expands to whole domain and
dominate the nonlinear evolution. Afterwards the quasi-stationary state of
vivid turbulence is achieved.
In both cases (AB, AC), the non-linear evolution leads to the enhancement
of the peak densities of dust component over one order of magnitude, which is in
close agreement with results of JY07 (see Fig.~8 in their work).

\begin{figure}
\includegraphics[width=0.98\linewidth]{figs/fig3}
\caption{Dust density snapshot for run ABh showing two "zoom-in" regions where
cavities emerge from overdensities created during linear phase of evolution
(left panel) and region totally overwhelmed by bursting void bubbles and vivid
dust turbulence (right panel). Animation of the run ABh can be found
\href{http://youtu.be/NoA5-TiQabQ}{here}.}
\label{fig3}
\end{figure}

\par In the dust dominated case (AC) our results closely follow those of JY07 up
to the point of saturation, where we achieve highly turbulent flow (lower
subpanel of upper right panel of Fig.~\ref{fig2}) and about 20 fold growth
in dust density. However, we note that secular evolution of the physical system
leads to formation of elongated dust overdensities and further growth up to 2
orders of magnitude as seen in runs with other parameters (see lower subpanel of
bottom right panel of Fig.~\ref{fig2}).

\par In the gas dominated case (AA) we observe initial overdensity growth over
two orders of magnitude in a characteristic grid-like pattern.  However, at time
1200, 440, 325 for runs AA, AAh, AAu respectively, in the course of nonlinear
evolution the dense dust filaments are abruptly smoothed out resulting in
oscillatory motion of mild overdensities that are only one order of magnitude
denser than initial dust distribution (see Fig.~\ref{fig4})

\begin{figure}
   \includegraphics[width=0.98\linewidth]{figs/fig4}
   \caption{Maximum ratio of dust to gas density for three runs with the same
      initial conditions, but different resolution. Streaming instability
      follows regular pattern of evolution: (1) fast linear growth that locally
      increases $\epsilon$ over 2 orders of magnitude (2) after reaching certain
      level of $\epsilon \approx 10$, overdensities are abruptly smoothed out
      (3) instability reaches out saturated, non-linear phase where large,
      smooth clumps of dust are only 10 times denser than initial condition.
      Varying resolution only influences the availability of shorter and faster
      growing modes, i.e. shortens phase (1).  }
   \label{fig4}
\end{figure}
\subsection{3D run}
The course of the evolution of our single 3D (BB3D) closely follows the
corresponding 2D run BB (compare Fig.~\ref{fig5} and Fig.~\ref{fig1}). During
the linear phase of growth elongated clumps or rather sheets of dense dust are
formed, as the deviation from axis axisymmetry is almost negligible.
\begin{figure}
   \includegraphics[width=0.98\linewidth]{figs/fig5}
   \caption{Snapshot of dust density distribution from run BB3D taken at
   $t=500$~yr. Upper panel shows a slice through the disc midplane, whereas lower
   panel is a part of slice perpendicular to disc plane zoom out to the region
   that corresponds to physical span of 2D simulations.}
   \label{fig5}
\end{figure}
In order to estimate whether we should expect effects of self-gravity  in the
nonlinear evolution of streaming instability, we have used {\larger\texttt{yt}}{}~\citep{yt} clump
finding facility to identify all the largest disconnected contour spanning for
minimum value of 50 computational cells in BB3D run. Then we calculated their
total mass and velocity dispersion $\sigma$ to obtain Jeans' radius:
\begin{equation}
   R_J = 2 GM / \sigma^2.
\end{equation}
Subsequently we compared the average size of each individual clump $L =
\sqrt{\sum_{i\in{\{x,y,z\}}} \max (L_i^2)}$ and found that $L < R_J$ for every
identified overdense clump, indicating that the clumps fulfill the gravitational
binding condition (see Fig.~\ref{fig6}). This indicates that in certain
situations, i.e. for dust dominated runs of the semi-global disc configuration,
streaming instability acting in a selfgravitating medium can lead to planetesimals
formation~\citep{J07}.

\begin{figure}
  \includegraphics[width=0.98\linewidth]{figs/fig6}
  \caption{
     Small patch showing projection of dust density along azimuthal axis from
     run BB3D with annotated contours of gravitationally bound clumps.}
  \label{fig6}
\end{figure}

\subsection{Comparison to the Results of Linear Stability Analysis
\label{simulation_analysis}}

In order to analyse the growth of streaming instability we extract small square
patches from various locations across the computational domain. The patches have
sizes of $0.15^2$~AU$^2$, thus are small enough so that mean values of physical
quantities do not vary significantly across them. In the case of 3D run the
patches are chosen on the {\it r-z} plane at $\varphi = \varphi_\textrm{max} /
2$.

We note that in the place of the fixed parameters  describing the unperturbed
equilibrium  in \mref{lin1}--\mref{lin2}, we use patch-averaged values of
corresponding dependent variables in equations \mref{eqc1}--\mref{eqm2}.
We calculate the spatially averaged densities of gas and dust component
$\bar{\rho}_g = \left<\rho_g\right>$, $\bar{\rho}_d = \left<\rho_d\right>$ and
their mutual ratio $\bar{\epsilon} = \left<\rho_d / \rho_g\right>$ . Mean
angular velocity $\bar{\Omega}$ is taken for the center of the patch.
Dimensionless measure of sub-Keplerian gas rotation is calculated by means of
the formula~(see YG05 eq.~(16) or JY07 eq.~(1))
\begin{equation}
   \bar{\eta} = -\frac{c_s^2\left<\partial_R \left<\rho_g\right>_z\right>_R}
      {2\bar{\rho}_g\bar{\Omega}^2 R},
   \label{eq:eta}
\end{equation}
In formula \mref{eq:eta} we average gas density in the vertical direction, then
we calculate the mean radial derivative of $\left<\partial_R \rho_g\right>$.
The expression for mean stopping time is derived from \mref{eq:tauf}
\begin{equation}
   \bar{\tau}_f = \rho_\bullet a / \left(\bar{\rho}_g \sqrt{c_s^2 +
   \left<\left|\mathbf{u} - \mathbf{v}\right|^2\right>} \right).
\end{equation}
For the sake of consistency gas and dust velocities $\bar{\mathbf{u}},
\bar{\mathbf{w}}$ are also approximated by their mean values
$\left<\mathbf{u}\right>, \left<\mathbf{w}\right>$ instead of calculating them
with the aid of \mref{eq:w0}-\mref{eq:u0}. However, we note that the mean values
that are naturally achieved during the simulation,  do not diverge from the
equilibrium solution by more than $10\%$.

To determine linear growth rates of the excited instability modes we calculate
Fourier transforms of density and velocity distributions of the dust component.
We analyse subsequently time variation of amplitudes of individual modes.
Intermediate results are shown in Fig.~\ref{fig7}.

\begin{figure}
  \includegraphics[width=0.98\linewidth]{figs/fig7}

  \caption{Temporal evolution of dust density perturbation amplitude in the
     Fourier space in the patch located at $[2.85,3.15]\times[-0.15,0.15]$~AU
     from simulation BB.  Each line represents amplitude for a given pair of
     $k_x, k_z$.  $\Delta T = T_e - T_s$ is time range when modes are fitted
     with \mref{eq:fit}.  $T_{\textrm{ref}}$ is a reference point in time used
     to identify most dominant modes using criterion of maximum amplitude value.
     Thick line is an average of amplitudes that are grater than $10^{-4}$ at
     reference time $t = T_{\textrm{ref}}$
   }
   \label{fig7}
\end{figure}

We identify time $T_s$ at which the dominating modes emerge from fluctuations
and start their linear growth phase. Similarly, we identify the end of the
linear growth phase $T_e$ when modes have grown by few orders of magnitude, and
start to saturate their growth. We fit exponential function:
\begin{equation}
   f(t) = A\exp\left(-s t\right)
   \label{eq:fit}
\end{equation}
 to the measured density amplitudes in the  period $\Delta T = T_e - T_s$.

That procedure allows us to determine the growth rate $s(k_x, k_z)$ of each
individual unstable mode, during the linear phase of the instability growth in
the numerical experiments.  We identify the most rapidly growing modes by
selecting those with the greatest amplitude at fixed point at the reference time
$T_{\textrm{ref}}$ before the saturation. We compare the growth rates $s(k_x,
k_z)$ obtained for each mode  with the solution $s_0(k_x, k_z)$ resulting from
the linear analysis for the local mean flow parameters.

In Fig.~\ref{fig8} we show temporal evolution of dust density perturbation
amplitudes for three dominating instability modes in three experiments BB3d, BB
and BBh, together with lines fitted to the phase of linear growth and  lines
representing growth of the amplitudes predicted by the linear analysis of the
streaming instability.  In the mid resolution run BB the growth rates  are
$10\div30\%$ smaller than those predicted by linear analysis, what indicates
that still higher resolution is required to resolve these modes. In the high
resolution run BBh the results of the numerical experiment tend to converge the
results of linear stability analysis.  The final saturation amplitudes seem to
be slightly smaller in high resolution runs. One should note, however, that we
have chosen the modes of the highest growth rate for each run, which are not the
same modes in terms of wavenumbers.

\begin{figure}
   \includegraphics[width=0.98\linewidth]{figs/fig8}
   \caption{Temporal evolution of the amplitudes of the dominating instability
      modes, measured in the dust density (gray line) together with the lines
      resulting from the linear analysis of the streaming instability (dashed
      line) and lines of fits of eq.~\mref{eq:fit} to the measured amplitudes
      (black lines).
      The linear solution of eq.~\mref{eq:linset} is found for the mean
      parameters of the rectangular patch at $R=3$~AU for the simulations: BB3d
      (upper panel), BB (middle panel) and BBh (lower panel).
   }
   \label{fig8}
\end{figure}

\par To extend our analysis we show in Fig.~\ref{fig9} a contour plot
(following YG05 and YJ07) of the growth rate  $s(k_x, k_z)$, resulting from
solutions of the dispersion relation \mref{eq:disprel}.  The shape of
isocontours indicates that the most unstable modes of the streaming instability,
predicted by linear analysis, form a ridge extending towards  large values of
$k_x$ and $k_z$.  The plots are constructed for the same set of the physical
parameters and the mean state parameters derived for  the domain patches at $T=T
_{\textrm{ref}}$.  We then place  $(k_x, k_z)$ of 9 dominating modes extracted
at $T = T_{\textrm{ref}}$  for simulations performed at different resolutions.

Our procedure allows us to confirm that  wavenumbers  of the modes, emerging in
presented numerical models, align with the  ridge of linear solutions at the
growth rate map.  It is apparent that dominating modes  are limited by available
numerical resolution. At lower numerical resolutions (run BB3d)  the dominant
modes locate below the contour labeled as ''$-1.000$''. At the mid resolution of
run BB some of the modes locate above the contour ''$-1.000$'', and at the high
resolution most of the modes locate above this contour. Similar tendency can be
observed for the pair of runs AB and ABh.  We anticipate that the reason for the
absence of the very short wavenumber modes is the numerical diffusivity of the
presently  used Relaxing TVD algorithm. Our estimations show that  our code
requires at least 32 computational cells per wavelength of the unstable mode, to
accurately represent the linear growth rate, which is much more than is required
by higher-order schemes~\cite{YJ07, BT09}.

\begin{figure*}
  \includegraphics[width=0.48\linewidth]{figs/fig9a}
  \includegraphics[width=0.48\linewidth]{figs/fig9b}
  \caption{
     The nine of the fastest growing modes characterized by wavenumbers
     $(k_x, k_z)$ extracted  from different simulations sharing the
     same initial conditions (left panel: BB, BBh, BB3d, right panel: AB, ABh)
     but different resolutions. Contours of growth rates $\log_{10}( s(k_x,
     k_z))$  represent solutions of \mref{eq:disprel} for the mean state
     parameters derived for  the domain patches at $T = T_{\textrm{ref}}$
  (for comparison see Fig.~2 of YG05)}
   \label{fig9}
\end{figure*}

We varied the resolution of our simulations to check how our numerical scheme
affects the obtained solutions. As the streaming instability in general
"prefers" shorter wavelengths for the optimal growth, increasing resolution
always leads to more, smaller overdensities emerging during the course of
evolution (see Fig.~\ref{fig10}). However we note that our results
follow the fastest growing, linear modes (see Fig.~\ref{fig9}) and
that most phenomena described in previous sections i.e. cavitation (see
Fig.~\ref{fig3}) or sudden growth dumping of the tightly coupled
boulders in the gas dominated regime (see Fig.~\ref{fig4}) are independent of
the size of the smallest computational cell.

\begin{figure}
   \includegraphics[width=0.98\linewidth]{figs/fig10}
   \caption{Dust density snapshots at $t = 160$~yr in two small rectangular
      patches for the two identical simulations parameters (upper: BB, lower:
      BBh) showing how the resolution affects simulation results at the linear
      and saturation phase of the instability. It is apparent that shorter
      wavelength modes dominate at the higher resolution, and that dust
      condensation structures are sharper.
   }
   \label{fig10}
\end{figure}
\section{Discussion \& Conclusions}
\label{sec:conclusions}
We performed a set of 2D simulations and 3D simulation of two mutually
interacting fluids, i.e. gas and dust in protoplanetary disc, while neglecting
vertical component of gravity. For the spectrum of grain sizes ranging from
$10\div50$~cm we observe rapid growth of unstable modes in dust component, which
are consistent with modes obtained for streaming instability within the
framework of local linear analysis.

Our model enhances previous work of other authors by taking into account the
full dynamics of protoplanetary disc, e.g. radial migration, that lead to
significant variation in physical quantities, such as gas pressure gradient, and
were previously treated as constant. Moreover instead of using a general
dimensionless stopping time parameter to couple both fluid components, we
implement specific drag law (Eqn.~\mref{eq:tauf}) which is best suited to the
physical properties of simulated fluids.

\par In the present quasi-global approach we relieved the restriction of the
fixed  radial pressure gradient, adopted for numerical modeling of the streaming
instability within the shearing box approximation.  It remains unknown how much
this term affects the non-linear evolution of the system, since the additional
term acts as an infinite energy reservoir driving the difference in azimuthal
velocities of both fluids. In the global approach, even around fixed orbit, the
parameter $\eta$, measuring the radial pressure gradient, is function of time.
While locality of shearing box fully justifies using a constant dimensionless
stopping time to calculate mutual linear drag force, that approximation is no
longer valid in the global disc.

\par The wave numbers of the fastest growing modes, extracted from numerical
models, and their positions at  the  map of growth rate  $s$ vs. $k_x$ and $k_z$
coincide with the predictions of linear analysis of streaming instability. We
reproduce reasonably well the linear growth rates, getting rapid convergence
near $\sim 32$ cells per wavelength. It is apparent, however,  that due to
diffusive nature of the Relaxing TVD scheme, PIERNIK needs high resolution to
capture linear growth phase accurately.

\par The instability saturates when dust overdensities synchronize their
velocity with the gas component. We must note that despite the steady outward
migration of the gas, dust blobs never really gain positive radial velocity and
never cease to migrate inwards (this was also noted by~\cite{JY07}). Though in
certain cases, their radial velocity is significantly slower than what is
expected from the standard estimation of the migration rate. The lack of
additional force that would keep the blobs bounded also leads to high dispersion
rate of the overdensities.

\par In our simulations we have neglected the role of stratification of the
disc, self-gravity of both fluids and also MRI induced turbulence. As each and
every of the aforementioned physical processes plays significant and integral
role in the protoplanetary disc evolution, we plan to gradually expand our setup
increasing its complexity in order to create the more complete global model.

\par We have found that nonlinear evolution of  the streaming instability forms
conditions for the formation  of gravitationally bound dust blobs in the
examined 3D semi-global discs configuration.  This indicates, in accordance with
the predictions by~\citet{J07}, the possibility  for  planetesimals formation in
accreting circumstellar discs,  and therefore we plan to incorporate selfgravity
in our future work.

\par We note that some of our runs may be underresolved, especially the
gas-dominated setups. However the nonlinear outcomes of all setups converge to
common solutions. Moreover, our initial simulation of full 3D setup, which took
0.36 MCPUh, shows that we are able to perform global simulation of streaming
instability in a convincing manner.
However, due to the severe CFL constraint on time-step imposed by the high
azimuthal velocity in 3d simulations, we consider implementing {\sc FARGO}-like
algorithm~\cite{M00} for our future work.
This is an important step towards complete model of planetesimals formation due
to combined action of various fluid instabilities postulated by~\citet{J07}.
\section*{Nullius in verba}
We would like to stress that everything that is required to reproduce results
presented in this paper is publicly available: the code
(\url{http://piernik.astri.umk.pl}), initial conditions (part of PIERNIK's
example problem set -- {\it streaming global}), analysis and visualization
routines (aforementioned github repository and {\larger\texttt{yt}}{} package). Runs in the
basic resolution took approx. 400 CPUh and can be conveniently reproduced on
small clusters or even modern workstations. KK is willing to assist inquisitive
readers with performing said simulations along with providing access to data
obtained in much more computationally demanding runs.
\section*{Acknowledgments}

This work was partially supported by Polish Ministry of Science and Higher
Education through the grant N203 511038. This work is a part of POWIEW project
supported by the European Regional Development Fund in the Innovative Economy
Programme (POIG.02.03.00-00-018/08). This research was supported in part by
PL-Grid Infrastructure. All of the post-processing and procedures described in
Sect. \ref{simulation_analysis}  was carried out using the data analysis and
visualization package {\larger\texttt{yt}}{} \footnote{\url{http://yt-project.org/}}
by~\cite{yt}.

redpajama_set_name: RedPajamaArXiv


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text:
Trump says he'll leave if the electoral college seats Biden
President Trump speaks with reporters after a video call with military leaders Thursday at the White House.
Nov. 26, 2020 Updated 7:21 PM PT
President Trump said Thursday that he will leave the White House if the electoral college formalizes President-elect Joe Biden's victory — even as he insisted such a decision would be a "mistake" — as he spent his Thanksgiving renewing baseless claims that "massive fraud" and crooked officials in battleground states caused his election defeat.
"Certainly I will. But you know that," Trump said Thursday when asked whether he would vacate the building, allowing a peaceful transition of power in January. But Trump — taking questions for the first time since election day — insisted that "a lot of things" would happen between now and then that might alter the results.
"This has a long way to go," he said.
The fact that a sitting American president even had to address whether or not he would leave office after losing reelection underscores the extent to which Trump has smashed one convention after another over the last three weeks. While there is no evidence of the kind of considerable fraud Trump has been alleging that would affect the outcome, he and his legal team have nonetheless been working to cast doubt on the integrity of the election and trying to overturn voters' will in an unprecedented breach of democratic norms.
Trump spoke to reporters in the White House's ornate Diplomatic Reception Room after holding a teleconference with U.S. military leaders stationed across the globe. He thanked them for their service and jokingly warned them not to eat too much turkey, then turned to the election after ending the call. He repeated grievances and angrily denounced officials in Georgia and Pennsylvania, two key swing states that helped give Biden the win.
Trump claimed, despite the results, that this may not be his last Thanksgiving at the White House. And he insisted that there had been "massive fraud," even though state officials and international observers have said no such evidence exists and Trump's campaign has repeatedly failed in court.
Column: Trump does his worst to make Biden's job even tougher
Let's count all the things Trump is doing that will make life difficult for his successor. It's not pretty.
Trump's administration has already given the green light for a formal transition to get underway. But Trump took issue with Biden moving forward.
"I think it's not right that he's trying to pick a Cabinet," Trump said, even though officials from both teams are already working together to get Biden's team up to speed.
And as he refused to concede, Trump announced that he will be traveling to Georgia to rally supporters ahead of two Senate runoff elections that will determine which party controls the Senate. Trump said the rally for Republican Sens. David Perdue and Kelly Loeffler would probably be held Saturday. The White House later clarified he had meant Dec. 5.
One of the reasons Republicans have stood by Trump and his baseless claims of fraud has been to keep his loyal base energized ahead of those runoffs on Jan. 5. But Trump, in his remarks, openly questioned whether that election would be fair, a move that could dampen Republican turnout.
"I think you're dealing with a very fraudulent system. I'm very worried about that," he said. "People are very disappointed that we were robbed."
As for the electoral college, Trump made clear that he would probably never concede, even if he said he would leave the White House.
"It's gonna be a very hard thing to concede. Because we know there was massive fraud," he said, noting that "time isn't on our side."
"If they do" vote against him, Trump said of the electors, "they've made a mistake."
Asked whether he would attend Biden's inauguration, Trump said he knew the answer but didn't want to share it yet.
But there were some signs that Trump was coming to terms with his loss.
Biden steps into leadership vacuum to reassure Americans with Thanksgiving address
Biden steps into the White House leadership vacuum on the coronavirus, resetting the tone in a solemn Thanksgiving address aimed at an anxious nation.
At one point he told reporters not to give Biden the credit for pending coronavirus vaccines. "Don't let him take credit for the vaccines because the vaccines were me, and I pushed people harder than they've ever been pushed before," he said.
As for whether or not he plans to formally declare his candidacy to run again in 2024 — as he has discussed with aides — Trump said he didn't "want to talk about 2024 yet."
All states must certify their results before the electoral college meets on Dec. 14, and any challenge to the results must be resolved by Dec. 8. States have already begun that process, including Michigan, where Trump and his allies tried and failed to delay the process, and Georgia and Pennsylvania.
Vote certification at the local and state level is typically a ministerial task that gets little notice, but that changed this year with Trump's refusal to concede and his unprecedented attempts to overturn the results of the election through a fusillade of legal challenges and attempts to manipulate the certification process in battleground states he lost.
Biden won by wide margins in both the electoral college and the popular vote, where he received more than 80 million votes, a record.
As coronavirus ravaged U.S. economy, Georgia Sen. Perdue saw an opportunity
Republican Sen. David Perdue of Georgia carried out a series of well-timed — and lucrative — stock transactions at the start of the COVID-19 pandemic.
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After setbacks, Biden enters year two looking to emphasize accomplishments
U.S. boosts military aid to Ukraine as Russia tensions soar
New York attorney general: Evidence shows Trump's company misled banks, tax officials
Los Angeles chosen to host Summit of the Americas, a key gathering of region's leaders
Federal website offering coronavirus tests hits some snags on its beta day
West Virginia lawmakers introduce a 15-week abortion ban
Supreme Court justices suggest Boston should have flown 'Christian flag'
Kamala Harris headed to Honduras for inauguration of country's president


text:
Batman Returns: How Culture Shapes Muddle Into Madness
David Dobbs
Neuron Culture blogger David Dobbs takes another look at the causes of tragedies like the one in Aurora.
Part of the line from the 3rd generation iPad launch in San Francisco in March of this year. Photo: Ariel Zambelich/WiredLet's try this door again.
What does it mean to say a culture shapes the expression of mental dysfunction? I bungled that question a few days ago in "Batman Movies Don't Kill, But They're Friendly to the Concept," my post about Batman movies and James Holmes. Even friends who got what I was getting at told me I hadn't really made the case well. Heeding that top item on my daily to-do list — "Do better" — I'll try to improve on it here. I'll draw on two brilliant pieces of writing that I hope will make this gin clear.
In the original piece I deliberately referred to "certain unhinged or deeply a-moral people." I left this vague for good reason: Mental health diagnoses are to a great extent social constructs. Their framing and use not only identify traits or behaviors that most observers in a given culture would agree on, but categorize a person in a way that can push that person further out of society and culture. Indeed, such diagnoses explicitly seek to identify what is different about the person -- what sets them aside, and to some extent, outside, the rest of society. Good diagnosticians do this because, at least in theory, it can help caretakers help the person. But the resulting sense of alienation can exacerbate the person's problems.
In the case of schizophrenia, for example (and I mean example, since as of this writing we have no reliable diagnosis or description of Holmes's mental state), the very diagnosis can push a person almost instantly into alienation. But it's not that way in every society. In his splendid Crazy Like Us: The Globalization of the American Psyche, Ethan Watters describes research demonstrating that the course of schizophrenia, as well as the actions of those who have it, depends enormously on culture.
Janis Hunter Jenkins and Robert John Barrett, two of the premier researchers in the field, describe the general state of affairs.*"In sum, what we know about culture and schizophrenia is… [that] culture is critical in nearly every aspect of schizophrenic illness experience: the identification, definition and meaning of the illness during the primordial, acute, and residual phases; the timing and type of onset; symptom formation in terms of content, form, and constellation; clinical diagnosis; gender and ethnic differences; the personal experience of schizophrenic illness; social response, support, and stigma; and perhaps most important, the course and outcome with respect to symptomatology, work, and social functioning."*By "course and outcome," Jenkins and Barrett are referring to that most perplexing finding in the epidemiology on the disease: people with schizophrenia in developing countries appear to do better over time than those living in industrialized nations.
A large World Health Organization study [huge PDF download], for instance, found that "Whereas 40 percent of schizophrenics in industrialized nations were judged over time to be 'severely impaired,' only 24 percent of patients in the poorer countries ended up similarly disabled.' Their symptoms also differed, in the texture, intensity, and subject matter to their hallucinations or paranoia, for instance. And most crucially, in many cases their mental states did not disrupt their connections to family and society.
Watters, curious about all this, went to Zanzibar to see how all this worked. He learned that there, schizophrenia was seen partly as an especially intense inhabitation of spirits — bad mojo of the sort everyone had, as it were. This led people to see psychotic episodes less as complete breaks from reality than a passing phenomena, somewhat as we might view, say, a friend or coworker's intermittent memory lapses.
For instance, in one household Watters came to know well, a woman with schizophrenia, Kimwana,
was allowed to drift back and forth from illness to relative health without much monitoring or comment by the rest of the family. Periods of troubled behavior were not greeted with expressions of concern or alarm, and neither were times of wellness celebrated. As such, Kimwana felt little pressure to self-identify as someone with a permanent mental illness.
This was rooted partly in the idea of spirit possession already mentioned, and partly to an accepting fatalism in the brand of Sunni that the family practiced. Allah, they believed, would not burden any one person with more than she could carry. So they carried on, in acceptance rather than panic. As a result, this delusional, hallucinating, sometimes disoriented young woman passed into and out of her more disoriented mental states while still keeping her basic place in family, village, and work life, rather than being cast aside. Almost certainly as a result, she did not feel alienated, and her hallucinations did not include the sort of out-to-get-me kind that mark paranoid schizophrenics in the West.
This, writes Watters in enormous understatement, "stood in contrast with the diagnosis of schizophrenia as [used] in the West. There the diagnosis carries the assumption of a chronic condition, one that often comes to define a person."
Can we find an example? Someone whose situation was sufficiently relevant to both Kimwana and James Holmes that it can highlight the sort of cultural effect I refer to? Yes we can.
The afternoon after Holmes shot up the theater in Aurora, and three days before I posted my assertion that culture can shape the expression of mental distress, an extraordinary young woman who goes by the pen name N described an experience that eerily parallels the one that Holmes seems to have experienced. Her story powerfully illustrates how the West's definition of and reaction to schizophrenia shapes its course, outcome, and expression. Please, if you care a whit about what happened in Colorado, about madness, about culture, read this:
I suspect it would strike most people as 'mad,' particularly perhaps, to those who know me, to identify any sort of kinship, any common bond, with James Holmes, the "Batman shooter," mass killer, and "psychotic son of a bitch," as Colorado Congressman Ed Perlmutter has put it. After all, I cry even over the deaths of the small birds my cats carry in from the deck.
And yet school shootings, or acts of extreme violence in which the perpetrator is or recently was a college student, have punctuated my life in strange & powerful ways. I was diagnosed with schizophrenia just a month after Steven Kazmierczak (quickly identified as "schizoaffective") shot six people to death on the campus of NIU, just an hour north of Chicago. Undoubtedly primed by this shooting, wary, uncertain, without enough time to think, my doctoral adviser suspended my graduate assistantship, banned me from the university, and alerted all faculty, graduate students and staff to forward all emails to her and, under no circumstances, respond. It was not until a few weeks had passed that I learned—from the Dean of Students—that she had been operating under the assumption that it had been my plan or intention to bomb one of the buildings on campus. She never apologized.
Why? Because the adviser had concluded that _N _, as she calls herself, was schizophrenic, and that this made her dangerous — a Kazmierczak waiting to happen. The effect was profound and immediate. The diagnosis didn't just marginalize this young woman a bit. It promptly cast her full out of the world that meant everything to her. She writes
Although [the adviser's] (clearly illegal) decision was reversed within a week, it set in motion a chain of events that were to forever change my life, perhaps as profoundly as the "diagnosis" of schizophrenia itself. Friends—my doctoral cohort, as is often the case, were a close and tight-knit group—abandoned me overnight. Students and faculty passed me in the halls, staring ahead blankly as if I were an undergraduate they had never seen and would never see again. Parties were announced, talked about, and I was never invited. Never again.
As if the psychosis were not enough, I developed an entirely expectable paranoia about my classmates and former adviser (and other involved faculty). I studied their schedules and timed my entrances and exits from the department with obsessive precision, forced to "hide" in bathrooms and side rooms only on a handful of occasions. I no longer attended departmental events (a fact that, with so many others, would eventually be held against me). I did not, could not, finish any of the papers from courses I had been taking, and the themes of those last lectures—the relationship between the work of Winnicott and Melanie Klein, Lacan's reading of Antigone—followed me like hungry ghosts for years.
For a while I struggled through classes, overwhelmed, perhaps in equal measure, by delusions and this new and unprecedented isolation. Voices took the places of both professors and friends. Following a hospitalization (and consequent withdrawal from a semester's worth of classes), I descended into a state of the most stunning dysfunction, unable (or simply unmotivated) even to walk from my bed to the bathroom. I could not read, I could not write—words rearranged themselves on the page, and my own thoughts became so hard to follow that I simply could not make it to the end of a sentence; suspended linguistically, suspended in life.
Then, in a harrowing annual review, she is expelled, without any warning she could discern, from her doctorate program; not given time off or compassionately offered help and room to regroup. Expelled, cast out, shunned, made irrelevant in the world that meant the most to her."I only remember bits and pieces" of this review, she relates;> within five minutes, perhaps less, I had to bite down hard, dig my nails into my forearms, to keep back the tears. First, the decision: we are dismissing you, in fact you may not, even as an unfunded student, enroll in any further classes. From a professor I had, until that point, trusted completely: "the decision strikes the committee as simple—you clearly do not have your act together and we have no reason to believe you ever will." Another professor: "you are a burden on the instructors." And then some additional reasons, faculty talking more to each other than me: "look at all the withdrawals;" "she hasn't attended a departmental lecture in almost two years;" "unambiguously uninvolved in the life of the department." Someone (I'm not looking at them) interjects: "perhaps allowing her just one more term….?" Another "…keeping in mind that if we do this she will immediately lose all her health coverage…" Then: "Absolutely not, but we can discuss the reasons after she leaves." Clearly she will not succeed. Now or ever.
Me: *Everything I have ever been told was a lie. My one way out—of poverty, desperation, madness—was never more than an illusion. And then disbelief. And then, how will I ever explain this to anyone, to family, to old mentors? *And then betrayal. No language this time, no thoughts; crying, crying for hours. Alcohol, unconsciousness, unbidden dreams. Even there: *repeating their words, over and over and over again. *Isolation so intense, there is no way I will ever bridge it. *I am lost. Days go by, weeks.
*Isolation so intense, there is no way I will ever bridge it.*This differs in deeply existential ways from Kimwana's experience. _N_ is not taken in or tolerated. She is, as one commenter at the post noted, ostracized in a way that was "a living death."She responded by fantasizing about inflicting horrid damage on herself and/or her academic mentor.
I fixated on a single vision, me, sometimes hanging, sometimes with gun in hand and a pool of blood on the floor, outside 'her' [i.e., her former advisor's] office.... Suicide, yes, obviously, but also something more: revenge.
Her obsessions and fantasies did not run to mass murder. But others who had committed mass murder in similar circumstances, such as Kazmierczak and Jared Loughner, who was much in the news then, were much on her mind. Her confusion and disorientation and anxiety — her schizophrenia — rose from complex sources. But her anger rose in large part from an alienation that came hand-in-glove with our society's definition of what she experienced -- to the mere application of the word schizophrenia. And her ideas about expressing that anger rose direclty from models of action brought to her from the media, and which expressed, in their violence and their repetitive, replicative nature — each bloody rampage imitating others — deep and multiple strains of our culture.
I hope this makes more clear that "culture shapes the expression of mental dysfunction." We see in Kimwana's experience how a different culture shaped what we all agree is schizophrenia in such a way that both its experience and expression take forms that looks foreign to us. And in N's story, we see first a medical and social culture that profoundly shaped the experience of her disoriented mind by giving it a label that cast her aside — and then see our larger culture steer the expression of her resulting anguish toward visions that would seem foreign to Kimwana but horribly familiar to Loughner or Holmes.This is what I tried to get at in my post about Holmes, his SWAT-gear mass-shooting fantasy-turned-reality, and culture.
I'm not claiming this is The Whole Answer (though many commenters virtually insisted on seeing it that way before). This is not something we're going to figure out by finding The Primary Cause, or insisting we must choose A, B, or C. Madness is an endlessly complex phenomenon and experience; mass murder is a stark but enormoously complex act. It is, pardon the language, insane to think we can explain their intersenction with math resembling a x b = c.
We need, as anthropologist Daniel Lende said in his own extraordinary, wider-ranging post about Aurora, to "expand our moral imaginations." His post and N's — the most thoughtful, risky, fully engaged, and truly provocative responses I've read, provocative in the best sense of the term, that of provoking new thought rather than reactive argument — make a good place to start.
Cited:
Batman Movies Don't Kill. But They're Friendly to the Concept.
Amazon.com: Crazy Like Us: The Globalization of the American Psyche, by Ethan Watters
maeror meror (in mourning) « Ruminations on Madness, by _N_
Inside the Minds of Mass Killers, by Daniel Lende
Many thanks to Lende, _N_, Watters, those commenters who actually tried to understand what I was getting at, and to Maggie Koerth-Baker and the commenters at BoingBoing for a rich discussion of the topic there, which provoked my thinking further and generated an earlier version of some of the material above.
Exit-door photo by jennlynndesign, used by permission. Some rights reserved. Other photos by David Dobbs.
David Dobbs, author of the Kindle Single bestseller My Mother's Lover, writes features and essays for publications including the Atlantic, the New York Times Magazine, National Geographic, Nature, and other publications. He is working on his fourth book, The Orchid and the Dandelion. You also follow his wider wanderings on... Read more
TopicsanthropologyBooksmental healthpsychologyschizophrenia


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Q: Puppet facter - How to fix Error: Could not retrieve fact='os', resolution='' On my windows server machine, just facter command gives the following error-
[stdout][0;36mDebug: Loading facts from C:/ProgramData/.../facter/windows_version.rb[0m
[stderr]Could not retrieve fact='os', resolution='<anonymous>': failed to parse display name of moniker `winmgmts:{impersonationLevel=impersonate}!//./root/cimv2'
[stderr] HRESULT error code:0x80010114
[stderr] The requested object does not exist.
[stderr]Could not retrieve fact='os', resolution='<anonymous>': failed to parse display name of moniker `winmgmts:{impersonationLevel=impersonate}!//./root/cimv2'
[stderr] HRESULT error code:0x80010114
[stderr] The requested object does not exist.
[stderr]Could not retrieve fact='os', resolution='<anonymous>': failed to parse display name of moniker `winmgmts:{impersonationLevel=impersonate}!//./root/cimv2'
[stderr] HRESULT error code:0x80010114
[stderr] The requested object does not exist.
[stderr]Could not retrieve fact='virtual', resolution='<anonymous>': failed to parse display name of moniker `winmgmts:{impersonationLevel=impersonate}!//./root/cimv2'
[stderr] HRESULT error code:0x80010108

This is happening suddenly, 2 weeks ago it was working fine.
Any idea how to fix this and what is causing these errors? Due to this, some Ruby scripts are failing.