I did not find my question answered elsewhere, so here it is.  I'm doing a project in my first optics course, and we are reading a bit about Doppler cooling. I understand that a laser is tuned to a frequency where the photon energy $E_p = h \nu$ corresponds to an energy slightly below the energy $E_{abs}$ required to excite the gas atoms, and that an atom moving towards the laser at a high speed (relative to rest of the gas) will experience a blueshift that allows the atom to absorb the photon, thus slowing down the atom.  I also understand that the photon is re-emitted in a random direction, which of course means that the atom's velocity in the direction of the laser will be decreased. What I'm not sure I understand is how the re-emission of the photon doesn't just bring the atom back to the same kinetic energy (but with a different direction of motion).  I have not been able to find a source explaining this, but here's my own attempt at an explanation (which I am not sure is correct, which is why I am asking here): The absorbed photon has an energy (in the frame of the laboratory) of $E_1 = h \nu_1$ which is slightly less than the absorption energy $E_{abs}$. But after the absorption the atom's speed is reduced, thus the photon will be emitted with a different frequency $\nu_2$ (in the frame of the laboratory). Since the speed of the atom (relative to the frame of the laboratory) has been reduced by the absorption, the energy $E_2$ of the emitted photon will be closer to $E_{abs}$, thus $|E_{abs} - E_2| > |E_{abs} - E_1|$ (the last step of the explanation only works if the atom's speed perpendicular to the laser is not greater than the speed parallel to the laser for most atoms, but since the laser is tuned to only hit the fast moving atoms, this seems improbable enough to not invalidate the explanation).  Is this explanation correct or have I made mistake? I have taken a special relativity course but no quantum mechanics yet, so please keep the quantum mechanics to a minimum if possible.

According to the first law of thermodynamics, sourced from wikipedia "In any process in an isolated system, the total energy remains the same."  So when lasers are used for cooling in traps, similar to the description here:  where is the heat transferred?    From what I gather of a cursory reading on traps, whether laser, magnetic, etc the general idea is to isolate the target, then transfer heat from it, thereby cooling it.  I don't understand how sending photons at a(n) atom(s) can cause that structure to shed energy, and this mechanism seems to be the key to these systems.


Which of the following is correct:        One in 5 people in that area are Chinese    One in 5 people in that area is a Chinese       I am confused as different resources provide a different answer.  One of the resources says that people is not the subject of the sentence. One is the subject and in 5 people is a prepositional phrase. Since “one” is singular, therefore the correct usage is “One in 5 people in that area is a Chinese.”   However, I am not convinced with this argument. I have found the other usage almost everywhere else.

Take the examples:   "One in ten children are dyslexic."  "One in ten children is dyslexic." "One in ten children has dyslexia." "One in ten children have dyslexia."   The "one" is singular so 2 and 3 should be correct. But the "one in ten" is a fraction" so 1 and 4 should be correct. And yet I think I usually say 1 and 3. Which is/are correct?!


Are charges moving around in quantum mechanics? I want to know what the standard interpretation tells us about the distribution of charge in ordinary matter. For example, in monatomic hydrogen gas, we have the 1s state and the various 2p states. I know that if I take the superposition of those two states, I see an oscillating charge distribution (some people call it a probability distribution, but for sake of argument let's call it charge). But is this what happens in an ordinary sample of monatomic hydrogen gas? or is each atom always in a pure eigenstate, either 1s or 2p, with some probability of jumping between those states? In which case (not counting the "jumps") the charge is always stationary, so there is no moving charge.  The same question applies to solids. Take the tungsten filament in a light bulb. Does quantum mechanics tell us that the charge at any given moment is stationary, with some probability of the system jumping to another state with the emission of a photon? Or is there a continuous time evolution of charge distribution, with oscillating and moving charges present throughout the tungsten filament?  I'd like to know how standard QM answers these questions.

Is there such a thing as a time-varying charge density in quantum mechanics? I am looking at the tungsten filament in a light bulb. Am I allowed to say that there is a wave function which describes that filament, and that in some sense there is a time-varying charge density (which some people call a probability) associated with the square of that wave function? There are electrons which have a probability distribution, and there are nuclei which are vibrating within the lattice, but all in all is there, or is there not, a time-varying charge distribution associated with that glowing filament? And if not, why not?  EDIT: There seems to be some question as to just what kind of charge-density fluctuations I am talking about. Let me clarify: in a hydrogen atom in the ground state, I would say there are NO charge density fluctuations. But if there is a superposition of the ground state and a 2p state, I would say the charge distribution fluctuates sinusoidally at the difference frequency of the two states. THAT is the kind of charge density fluctuation I am asking about for in the tungsten filament. Does it or doesnt' it?  I hope this clarifies the intent of my question.   RE-EDIT: In a separate (and rather hard-fought) discussion, it appears that people who know more than me agree that there is indeed an oscillating charge distribution in the hydrogen superposition as described above (see  ).  So if there is an oscillating charge in the hydrogen atom, why wouldn't there be oscillating charge in a heated tungsten filament?


I've been trying to run a .msi file in ubuntu. From what I've read, the .msi file can run on Windows natively, however, is it possible to run the .msi file in Linux(Ubuntu in my case)?

Can .exe and .msi files (Windows software) be installed in Ubuntu?


Consider the following MWE:  \documentclass[pstricks]{standalone} \begin{document} \begin{pspicture}(0,0)(5,4) \psline(0,0)(5,4) \end{pspicture} \end{document}   I can use both, TeXLive 2015 and TeXLive 2016, to successfully compile the code. However, the result of the usual latex -> dvips -> ps2pdf chain is an empty picture in the 2016 (up-to-date) case. The 2015 version of latex works just fine:  2015 PDF:    2016 PDF:    I'd like to file a bug report, any recommendation where to further look into and where to actually put the bug report?  My question is different to  as it is much more centered on the actual problem (includes an MWE) and, as such, is much more likely to be found by users encountering the same problem in the future.

The example below was downloaded from that site with pstricks examples. When I run it I get 18 blank pages. This also happens with other examples using multido. I'm using texmaker with MikTex 2.9. Do you have any idea what could be the problem?  Thank you very much.  \documentclass[pstricks]{standalone} \usepackage{pst-solides3d} \colorlet{Green}{green!100!white!40} \begin{document}  \multido{\iA=0+15}{18}{% \psset{lightsrc=viewpoint,viewpoint=30 \iA\space 20 rtp2xyz,Decran=25} \begin{pspicture}(-5,-2)(5,2) \psSolid[object=grille,grid,  fcol= /t 0 def 0 1 63 { dup dup 8 mod 0 eq { /t t 1 add def } if       t add 2 mod 0 eq { (Green) }{ (red) } ifelse } for,  base=-4 4 -4 4] \end{pspicture}% }  \end{document}


Can someone explain me, why the following doesn't work: echo hello | echo -  Just for learning purposes (don't tell me to use something else and not "echo" or why do I need it), I want to understand why it's not working. I'm trying to pipe the result of the first echo to the second echo (through stdin). Why is it not working and what can I do to make it work?

I have a file named my_file.txt whose content is just the string Hello. How could I redirect its content to the command echo?  I know I have the commands less, cat, more... but I need to do it with echo.  I tried this:   $ cat my_file.txt | echo   and also this:  $ echo < my_file.txt   But in both cases it appears only a blank in the stdout, not the content of my_file.txt.  How could I do that?


#include<stdio.h> #include<string.h> int main(){     char *a[]={"this","is","a","string"};     char temp[100];     for(int i=0;i<3;i++){                                        for(int j=0;j<3-i;j++){             if(strcmp(a[j],a[j+1])>0){                 strcpy(temp,a[j]);                 strcpy(a[j],a[j+1]);                 strcpy(a[j+1],temp);             }         }     }     for(int i=0;i<4;i++){         printf("%s\n",a[i]);     } }   The following code is for bubble sorting the strings.It gives segmentation fault.What is wrong in it?

The following code receives seg fault on line 2:  char *str = "string"; str[0] = 'z';  // could be also written as *str = 'z' printf("%s\n", str);   While this works perfectly well:  char str[] = "string"; str[0] = 'z'; printf("%s\n", str);   Tested with MSVC and GCC.


I have been stuck on this problem, I don't know where to start. The exact question is: Determine the finite-dimensional spaces $W$ of differentiable functions with this property: If $f$ is in $W$ then $df/dx$ is in $W$.  There is a hint: "Review the solutions of a homogeneous, constant coefficient differential equation: $d^ny/dx^n+a_1*d^{n-1}y/dx^{n-1}+...+a_{n-1}*dy/dx+a_n=0$"  I know that if $f$ is in $W$ then all of its derivatives must be in $W$. I understand that the exponential functions clearly are in some W. But aren't the polynomial in some $W$ too since there is always a point at which their derivative is $0$? Extending that thought, there must be an infinite number of those $W$.. Can you please put me on the track?

What are the finite-dimensional spaces $W$ of differentiable functions with this property: If $f$ is in $W$, then $\frac{df}{dx}$ is in $W$.


As far my knowledge, Linear Regression assumes that data or columns are normally distributed and doesn’t have multicollinearity amongs the features, But when I apply Shapiro test, it shows that none of the columns is normally distributed. Then how can we use Linear Regression for Boston House Price datasets

I have carried out a linear regression. The plot below shows the distribution of the response variable:    I believe the response variable is beta distributed, therefore virtually the exact opposite of normally distributed. However, when including all my predictor variables in the linear regression, the residuals turn out to be quite normally distributed, as shown in this plot:    Has my model satisfied the assumptions of linear regression? Might there be a better model to use?


I'm working with a home-grown javascript library that has event handling. At it's core is a registerEvents function:  core.registerEvents = function(evts, mod) {     if (this.is_obj(evts) && mod)     {         if (moduleData[mod])         {             moduleData[mod].events = evts;         }     } };   In this, mod is a module, moduleData is an array of modules that is in the functions parent scope, and evts is an object with named functions. Use is something like:  core.registerEvents({         "event1": function() {alert('event1');},         "event2": function() {alert('event2');}     },     myModule);   This is all working well, except that it requires all the events to be registered at once, there's no ability to register an additional event, later.  What I would like is to extend this so that when you call registerEvents(), if there are no events registered you accept the passed evts object as your events object, but if there are already events registered, then you add the functions in your evts object to your events object.  Something like this:  core.registerEvents = function(evts, mod) {     if (this.is_obj(evts) && mod)     {         if (moduleData[mod])         {             if (moduleData[mod].events)             {                 // move functions in evts to moduleData[mod].events             }             else             {                 moduleData[mod].events = evts;             }         }     } };   And I haven't a clue as to how to do it.  One complexity: Our new function, evts.event1, was defined in a particular lexical scope. When we move the function to another object, we don't want to change that scope. The variables that were in the parent scope when evts.event1 was defined should remain accessible to evts.event1, even after it's been moved to another object.  I'm at a loss. Help would be appreciated.

I need to be able to merge two (very simple) JavaScript objects at runtime.  For example I'd like to:  var obj1 = { food: 'pizza', car: 'ford' } var obj2 = { animal: 'dog' }  obj1.merge(obj2);  //obj1 now has three properties: food, car, and animal   Does anyone have a script for this or know of a built in way to do this?  I do not need recursion, and I do not need to merge functions, just methods on flat objects.


I'm trying to:   sudo echo "$USER: my message" > /dev/kmsg   to write a message to the dmesg log.  This causes a 'permission denied' error, because it is redirecting the output of 'sudo' (while no longer privileged) to /dev/kmsg.  So the 'echo' command is running as root and the writing to /dev/kmsg is running as me.  Quoting 'echo' command and ther the redirect ('>/dev/kmsg') doesn't work because the redirection is a shell service that sudo doesn't understand.  (The userid in question is in sudoers with NOPASSWD.)  Is there some Linux command that takes the file name as an option and writes its arguments out?  Like:  'tee /dev/kmsg -- My message to be logged'   I know about the 'logger' command, but that doesn't write to whatever log file 'dmesg' sees.  (I want to intersperse some of my messages in with the boot process to know when certain things happen.)  This works, but has the problem of needing to have some place to write a file to:  echo "$USER: My msg" >/tmp/foo sudo cp /tmp/foo /dev/kmsg rm /tmp/foo   Solution from ctrl-alt-delor's comment below:  echo "my message" | sudo tee /dev/kmsg >/dev/null   Although it does use piping and redirection, it occurs in the unprivileged shell.  Privileged access to '/dev/kmsg' occurs in the 'tee' command in 'sudo'.  And it doesn't need write to a disk file (which could have problems).   Also @stolenmoments solution:  echo something | sudo dd of=/dev/kmsg

I am writing a regular compiled application that needs to create a special file and write a magic cookie into it. I can’t write the file directly from the application, the system security model requires me to launch a helper tool with elevated privileges to do the trick. I can supply any number of arguments to the helper tool. Now I would like to pick some very simple system command that would serve as the helper tool and create the file for me. Something like this:  /bin/sh -c "/bin/echo -n 'magic' > /some/where/file"  Simple touch does not cut it as I need to write the cookie into the file, a simple echo without the shell wrapper does not work as it needs redirection to write the file. I don’t feel comfortable calling the shell with root privileges to do such a trivial task. Is there some really simple, constrained system command that I could call to write the file for me?


I have a spreadsheet monitoring my Stocks and cryptos etc on Google Sheets. I have a formula which 50% works and auto updates and 50% doesnt work and comes up with 'N/A : Could not fetch URL'...when multiple others are working and that one also sometimes works. The formula is; =SUBSTITUTE(IMPORTXML("https://coinmarketcap.com/currencies/"&A4,"//div[@class='priceValue___11gHJ']"), "$", )*GOOGLEFINANCE("CURRENCY:USDGBP") A4 is the title box next to it so its pulling into the box in this case 'Dogecoin'. Can someone guide me with this error please?

Google Sheets has several import functions   IMPORTDATA IMPORTFEED IMPORTHTML IMPORTXML   Sometimes the above functions returns errors like #N/A Imported content is empty and would like to be sure that there isn't a problem with the resource content to be imported.  How do I know if these functions are able to get the content that I looking to import?  I know that there also exist IMPORTRANGE but that function only is able to import content from Google Sheets spreadsheets


When I click log in to login to my user profile, the screen turns black for a fews seconds you can see a few lines (trying to start and get kick out?) and then just returns to the log-in menu. It logs me in as admin automatically. I don't have admin password either. How can i access my user profile? I am able to access the GRUB and select root but it ask for root password which i don't have. Here is the message: Give root password for maintenance (or type control-D to continue):     update I were able to reset the passwords after accessing GRUB thanks to :  but it is still looping when i try to login.      Any insight?

My Ubuntu is stuck in a login loop when trying to enter my desktop. When I login, the screen gets black and soon after that the login screen comes back.   I've read that the problem might be caused by an error depending on the graphics, here's my graphics card: ATI Radeon 7670M


Can I apply for a Schengen visa from Germany, enter there and stay for 2 days and go to Poland for 10 days and exit there? As my itinerary is dependent on a friend who's coming from US, I am assuming that this might become the case.

I'm planning on doing a Euro tour, starting with Germany. My friends and I will be travelling to a separate country each month but our stay in Germany will be the shortest. Is there any rule when applying for the Schengen Visa that states that your stay in the country of entry has to be longer than your stay in the other countries? For example: we plan to stay in Italy (third country to be visited) for two weeks but less than a week in Germany (country of entry). Will this cause any hindrances while applying for the Schengen visa?


I can hear the sound from my laptop speakers on the startup but after that when I try to play any music on VLC I don't hear any sound. I can't even hear any sound on youtube so it's not the problem with VLC. If I try running any sound by Guest user then it works.

I installed Ubuntu 12.04 a month ago and am using it till now. I failed to notice that all this time there was no sound at all while running Ubuntu, even while playing a game in Wine. The weird thing is that only the startup sound comes when I log in (Indian/African drum tone), then comes the utter silence.  I tested both Digital Output (S/PDIF) and the speakers in the sound settings but can hear nothing.  Any help?


Could anyone help me find an explicit formula for:  $$ \sum_{n=1}^\infty n^2x^n $$  We're supposed to use: $$\sum_{n=1}^\infty nx^n = \frac{x}{(1-x)^2}  \qquad  |x| <1 $$


I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?


How to rename all the files in the directory in such a way the files get added "_1" before ".txt"  apac_02_aug_2017_file.txt emea_02_May_2017_file.txt ger__02_Jun_2017_file.txt   To  apac_02_aug_2017_file_1.txt emea_02_May_2017_file_1.txt ger__02_Jun_2017_file_1.txt

I would like to change a file extension from *.txt to *.text. I tried using the basename command, but I'm having trouble on changing more than one file.  Here's my code:  files=`ls -1 *.txt`  for x in $files do     mv $x "`basename $files .txt`.text" done   I'm getting this error:  basename: too many arguments Try basename --help' for more information


after installing different drivers (rtl8812au-dkms from ubuntu apt repo, and driver from https://github.com/gnab/rtl8812au) my usb wifi receiver (802.11n) doesn't work. if i do lsusb i get: ... Bus 003 Device 002: ID 0bda:f179 Realtek Semiconductor Corp. 802.11n ...  no drivers work, so what could i do?

19 DEC 2019 - I really, really wanted to use the Cinnamon desktop to set up a new system my 83-year-old Dad could navigate. I struggled to get any USB WiFi device working with Debian using Cinnamon, gave up and installed Ubuntu, but still struggled (I think) because I had immediately changed to the Cinnamon desktop before attempting to get the WiFi device set up.  It just kept prompting for the password, no matter what fixes I tried. Not sure if Cinnamon was the problem, or if I just hadn't found the right solution online.


I am a linguistics major with background in math. I was wondering about categories arising in fields apart from mathematics,  Especially linguistics but I would appreciate examples from other disciplines as well.  Note : my background so far in category theory has been first 2 chapters of "Basic Category theory" by Tom Leinster

I apologize if this is off-topic, but I wish to know what applications have other disciplines made of category theory. I have heard that linguistics, computer science, and philosophy all make use of category theory. But due either to my own lack of familiarity with category theory or these disciplines, I'm rather ignorant of these applications.  So, what (fruitful) uses have been made of category theory, especially within philosophy, but within other academic disciplines as well?


Evaluate $$\lim_{n\rightarrow\infty}\frac{1-2+3-4+5-\cdots+\left(-2n\right)}{\sqrt{n^{2}+1}+\sqrt{n^{2}-1}}.$$   My Approach   Let $A_{n}=1+3+5+\cdots\left(2n-1\right)$ and $B_{n}=2+4+6+\cdots\left(2n\right)$, then $A_n=\frac{n}{2}\left(1+2n-1\right)=n^{2}$ and $B_{n}=\frac{n}{2}\left(2+2n\right)=n+n^{2}$. Therefore, $$\lim_{n\rightarrow\infty}\frac{A_{n}-B_{n}}{\sqrt{n^{2}+1}+\sqrt{n^{2}-1}}=\lim_{n\rightarrow\infty}\frac{-n}{\sqrt{n^{2}+1}+\sqrt{n^{2}-1}}=-\frac{1}{2}.$$ But the book mentions that the answer is $0$.

Let $\{a_n\}, {n\geq 1}$, be a sequence of real numbers satisfying $|a_n|\leq 1$ for all $n$. Define  $$A_n = \frac{1}{n}(a_1 + a_2 + \cdots + a_n),$$ for $n\geq 1$. Then find $\displaystyle\lim_{n \rightarrow \infty}\sqrt{n}(A_{n+1} − A_n)$ .    I proceed in this way  $$\lim_{n \rightarrow \infty}\sqrt{n}(A_{n+1} − A_n)=\lim_{n \rightarrow \infty}\sqrt{n}\left[\frac{1}{n+1}(a_1 + a_2 + \cdots + a_n+a_{n+1})-\frac{1}{n}(a_1 + a_2 + \cdots + a_{n})\right]=\lim_{n \rightarrow \infty}\left[{(na_{n+1}-a_1 - a_2 - \cdots - a_n})\frac{1}{\sqrt{n}(n+1)}\right]$$  Please help me to complete from here


Each magic class seems to have a stat associated with it (Int, Wis, or Cha), used to determine stats such as spell save difficulty class, or the power of certain abilities that the class has.  I think sorcerers and warlocks use Charisma. I understand how Charisma might translate to power for most warlocks (as they would be able to strike a pact with their patron and convince it that they are on track with their task more easily), but what if they made a pact with someone who doesn’t care about how their servants present themselves, but has faith in those with a high intelligence (or wisdom).  If you wanted to create a sorcerer or warlock who’s character traits make them bad at social situations, but great at their craft (or the other way around), then I’d expect this would be done by requesting to use your preferred stat instead of Charisma for your spell casting modifier, spell save difficulty class, and any other Charisma calculation that’s directly part of your class abilities (or possibly JUST your spell casting modifier and spell save DC if you wanted to make a more mixed character). How would various dungeon masters respond to this sort of request, and how would you recommend someone respond to that sort of request if they were a dungeon master?  Basically:   Are there any rules that allow players to change the stat that represents someone’s spell casting ability? (They don’t necessarily have to be official) Does the ability to do so unbalance the game in any way? (This is about changing the magic stat for a (few) specific character(s), not everyone of a class)   (...also, why would charisma be important to a sorcerer?)

With the exception of multiclassing, is there any big reason that if you were to change the spellcasting ability of a (spellcasting) class it would be a bad idea?  As a specific example: Let's say I was switching Sorcerers from Cha to Wis, what unexpected effects could this have on that class's balance? Additionally let's assume all places in spellcasting where you added your charisma modifier instead you now add wisdom (and vice-versa).


Spoiler: solution to this is . the solution was really simple. I'm trying to insert data from an external table. Here's the code I'm trying to use: INSERT /*+ ignore_row_on_dupkey_index ( consruct ( construct_id ) ) */ INTO construct        (construct_id,       n_term ,       enz_name,       c_term,       cpp,       mutations,       mw_kda) SELECT *     FROM EXTERNAL ((       construct_id NUMBER(10),       n_term VARCHAR2 (50),       enz_name VARCHAR2 (50),       c_term VARCHAR2 (50),       cpp VARCHAR2 (50),       mutations VARCHAR2 (50),       mw_kda NUMBER (7,3))      TYPE ORACLE_LOADER     DEFAULT DIRECTORY data_to_input     ACCESS PARAMETERS (         RECORDS DELIMITED BY NEWLINE         SKIP 1         BADFILE bad_files:'badflie_insert_into_construct_from_construct.bad'         FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'         MISSING FIELD VALUES ARE NULL          )      LOCATION ('CONSTRUCT.CSV')     REJECT LIMIT UNLIMITED) ext          WHERE NOT EXISTS (         SELECT * FROM construct c         WHERE c.n_term = ext.n_term         AND c.enz_name = ext.enz_name         AND c.c_term = ext.c_term         AND c.cpp = ext.cpp         AND c.mutations = ext.mutations     );  But now i get this error: Error at Command Line : 171 Column : 7 Error report - SQL Error: ORA-00957: duplicate column name 00957. 00000 -  "duplicate column name"  Line 171 is the last line of this part INSERT /*+ ignore_row_on_dupkey_index ( consruct ( construct_id ) ) */ INTO construct        (construct_id,       n_term ,       enz_name,       c_term,       cpp,       mutations,       mw_kda)  Which is clearly not a duplicate column. If I do: INSERT /*+ ignore_row_on_dupkey_index ( consruct ( construct_id ) ) */ INTO construct      (construct_id,      n_term,      enz_name,      c_term,      cpp,      mutations,      mw_kda) SELECT *     FROM EXTERNAL ((       ext.construct_id NUMBER (10),       ext.n_term VARCHAR2 (50),       ext.enz_name VARCHAR2 (50),       ext.c_term VARCHAR2 (50),       ext.cpp VARCHAR2 (50),       ext.mutations VARCHAR2 (50),       ext.mw_kda NUMBER (7,3))      TYPE ORACLE_LOADER     DEFAULT DIRECTORY data_to_input     ACCESS PARAMETERS (         RECORDS DELIMITED BY NEWLINE         SKIP 1         BADFILE bad_files:'badflie_insert_into_construct_from_construct.bad'         FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'         MISSING FIELD VALUES ARE NULL          )      LOCATION ('CONSTRUCT.CSV')     REJECT LIMIT UNLIMITED) ext          WHERE NOT EXISTS (         SELECT * FROM construct c         WHERE c.n_term = ext.n_term         AND c.enz_name = ext.enz_name         AND c.c_term = ext.c_term         AND c.cpp = ext.cpp         AND c.mutations = ext.mutations     );  I get Error at Command Line : 174 Column : 10 Error report - SQL Error: ORA-00902: invalid datatype 00902. 00000 -  "invalid datatype"  Line 171 is ext.construct_id NUMBER (10),  Background: The reason I'm listing the columns out instead of just saying insert into construct select  is because I have a virtual column in the construct table taht's defined like this: construct VARCHAR2 (200) GENERATED ALWAYS AS  (n_term || '-' || enz_name || '-' ||c_term || ' ' ||mutations) VIRTUAL, And there's no corresponding column in the csv file for it. The second column in the ERD called CONSTRUCT is defined like this:  Edit: originally, I defined datatypes for columns from the table that I was inserting into. This was a mistake and I deleted that code, replacing it with the new version for readability. It was taking up a lot of room in this post. (Edit: originally, I defined datatypes for columns from the table that I was inserting into. This was a mistake and I deleted that code, replacing it with the new version for readability. It was taking up a lot of room in this post.)

I'm trying to insert data from an external table. INSERT /*+ ignore_row_on_dupkey_index ( consruct ( construct_id ) ) */ INTO construct        (construct_id,       n_term ,       enz_name,       c_term,       cpp,       mutations,       mw_kda) SELECT *     FROM EXTERNAL ((       construct_id NUMBER(10),       n_term VARCHAR2 (50),       enz_name VARCHAR2 (50),       c_term VARCHAR2 (50),       cpp VARCHAR2 (50),       mutations VARCHAR2 (50),       mw_kda NUMBER (7,3))      TYPE ORACLE_LOADER     DEFAULT DIRECTORY data_to_input     ACCESS PARAMETERS (         RECORDS DELIMITED BY NEWLINE         SKIP 1         BADFILE bad_files:'badflie_insert_into_construct_from_construct.bad'         FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'         MISSING FIELD VALUES ARE NULL          )      LOCATION ('CONSTRUCT.CSV')     REJECT LIMIT UNLIMITED) ext          WHERE NOT EXISTS (         SELECT * FROM construct c         WHERE c.n_term = ext.n_term         AND c.enz_name = ext.enz_name         AND c.c_term = ext.c_term         AND c.cpp = ext.cpp         AND c.mutations = ext.mutations     );  But now i get this error: Error at Command Line : 171 Column : 7 Error report - SQL Error: ORA-00957: duplicate column name 00957. 00000 -  "duplicate column name"  Line 171 is the last line of this part INSERT /*+ ignore_row_on_dupkey_index ( consruct ( construct_id ) ) */ INTO construct        (construct_id,       n_term ,       enz_name,       c_term,       cpp,       mutations,       mw_kda)  Which is clearly not a duplicate column. If I do: INSERT /*+ ignore_row_on_dupkey_index ( consruct ( construct_id ) ) */ INTO construct      (construct_id,      n_term,      enz_name,      c_term,      cpp,      mutations,      mw_kda) SELECT *     FROM EXTERNAL ((       ext.construct_id NUMBER (10),       ext.n_term VARCHAR2 (50),       ext.enz_name VARCHAR2 (50),       ext.c_term VARCHAR2 (50),       ext.cpp VARCHAR2 (50),       ext.mutations VARCHAR2 (50),       ext.mw_kda NUMBER (7,3))      TYPE ORACLE_LOADER     DEFAULT DIRECTORY data_to_input     ACCESS PARAMETERS (         RECORDS DELIMITED BY NEWLINE         SKIP 1         BADFILE bad_files:'badflie_insert_into_construct_from_construct.bad'         FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'         MISSING FIELD VALUES ARE NULL          )      LOCATION ('CONSTRUCT.CSV')     REJECT LIMIT UNLIMITED) ext          WHERE NOT EXISTS (         SELECT * FROM construct c         WHERE c.n_term = ext.n_term         AND c.enz_name = ext.enz_name         AND c.c_term = ext.c_term         AND c.cpp = ext.cpp         AND c.mutations = ext.mutations     );  I get Error at Command Line : 174 Column : 10 Error report - SQL Error: ORA-00902: invalid datatype 00902. 00000 -  "invalid datatype"  Line 171 is ext.construct_id NUMBER (10),


How do we explain the logical equivalence  $$(P\rightarrow Q ) \equiv [(\neg P)\; \vee \; Q]$$ and if possible could you please give an example illustrating this equivalence. Thanks alot !!

Is there a proof for the logical equivalence of $a \rightarrow b$ and $\lnot a \vee b$?


How to calculate maximum current density(J) for a copper pcb trace.

I am currently designing a PCB layout for my team's high current, high voltage project and am having trouble with choosing my trace width.  The circuit is composed of 12 inductors placed in series with short traces connecting them together (about 5mm max length). We are feeding 10μs pulses at ~300A/1000V at a maximum rate of 10 pulses per second by discharching capacitor banks into the coils. The capacitors are recharged by an external source.  I have looked for resources on the subject, but nothing I could find applies to the level of current and voltage we are applying.  Is there a rule for determining trace width for very high current pulses?


Under what circumstances should the data be normalized/standardized when building a regression model. When i asked this question to a stats major, he gave me an ambiguous answer "depends on the data".   But what does that really mean? It should either be an universal rule or a check list of sorts where if certain conditions are met then the data either should/ shouldn't be normalized.

In some literature, I have read that a regression with multiple explanatory variables, if in different units, needed to be standardized.  (Standardizing consists in subtracting the mean and dividing by the standard deviation.)  In which other cases do I need to standardize my data?  Are there cases in which I should only center my data (i.e., without dividing by standard deviation)?


How does the aperture affect the focus area? Here are some examples:  With an 35mm(50mm)/f1.8 prime lens   What f-value will bring a group of people standing in five rows into focus? What f-value will bring the entire face and body into focus, when shooting close-ups or portraits? How do you focus on two peoples standing far from each other? How do you focus a group of players playing in ground?   Do these all differ for various physical distances between the subject and camera?

How does aperture affect my photographs?  Why should I care about the aperture with which a photo was taken?


My webpages show products. The product data (title, price, reviews, etc.) is fetched with an XHR and added to the DOM at run-time.  Does it make sense to add schema.org markup with JavaScript after the page load, or will Google completely ignore that markup?

Google show stars in Google search with JavaScript dynamically generated rich snippets?  I'm thinking about starting a widget that my users will put in their website. My widget will generate rich snippets in order to allow Google show stars on Google search.  I know that rich snippets work when they are put in static HTML.  Can they be dynamically generated via JavaScript as well?


What are he possible methods for showing that the $n$ by $n$ matrix $A$ whose coefficients are given by $a_{i,j}=\gcd(i,j)$ is inversible?

Let $A=(a_{ij})$ be a $n \times n$ matrix with $a_{ij}=\gcd(i,j) , \forall i,j=1,2, \cdots, n$ , then how do we prove $\det A=\prod_{i=1}^n \phi(i)$ ? , where $\phi$ is the Euler's phi function


I was replacing a standard light switch and noticed that the current light switch’s ground wire (green) was not being connected to anything.  It was connected to the switch on one end and to a wirenut on the opposite end, however no other wires were included in the wirenut.  The wirenut was simply terminating the single grounding wire.  This goes against my understanding of how a grounding wire should be wired, but this building is brand new construction and so must have passed inspection recently.  Is this a valid way to ground a light switch and if so, why?

I need to replace a switch that controls a single light source in a bathroom.    The switch has two wires connected to it.  I bought a replacement switch that has two screws (one for each wire), and a green ground screw.  Is it OK to connect just the two wires to the new switch and have the green ground screw unconnected?  This is not a remodel.  Just trying to replace a switch that's broken.  EDIT: strangely, I didn't see a ground screw on the original switch.  Was this permissable at some time?  EDIT 2: Picture as requested.  The left switch is for a light source and is the broken one.  Right switch is for a fan.  The two switches are on the same circuit.  The outlet is on a separate circuit.  I can't tell if the box is metal.  It seems plastic but could be painted metal I suppose.    EDIT 3: With switches and outlet pulled out.


I have programmed all night long and I can't find a mistake anymore :/ :/ If intro == 1 or 2 then do this and that.. and if intro != 1 or 2 then ask number again, till the number is 1 or 2... I can't find the mistake :/     do{         System.out.println("Enter number: ");         Scanner scanintro = new Scanner(System.in);         intro = scanintro.next();     }while (intro == ("1")|| intro == ("2"));

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


Let $R$ be a commutative ring and $I$ and $J$ be two ideals of it. We know that $I+J$ is a subset of $R$ and moreover, $I+J$ is an ideal of $R$. Question: When $I+J$ can be $R$?

I'm stuck on this exercise and any help would be well appreciated:     Let $R$ be a commutative ring with ideals $I,J$. Show that $R=I+J$ if and only if $\phi(x)= (x + I, x + J)$ is surjective from $R$ to $R/I \times R/J$.   Assuming surjectivity I got as far as to realize that I need to show $R\subset I+J$ since $I+J\subset R$ always holds (as they are both subrings of R). Now I'm not sure how to proceed.  Also, I don't even know where to begin in the direction $R=I+J$ implies $\phi$ is onto.  Again, any help, pointers or references are much appreciated.  Thanks in advance.


How do I properly use RegExp?  var text = "here come dat boi o shit waddup"; var exmaple = /[a-zA-Z0-9 ]/; // allowes a-zA-Z0-9 and whitespaces but nothing else right? example.test(test); // would return true right?  text = "%coconut$§="; example.test(text); // would return false right?  //I know this is very basic - I started learnig all this about week ago   Are JS RegExp's the same as PHP RegExp's? How do I define banned characters instead of defining allowed characters? How do I make it so that the var text has to contain 3 (or more) numbers/letters? How do I include / or ",'$ etc. in my pattern?

I don't really understand regular expressions.  Can you explain them to me in an easy-to-follow manner?  If there are any online tools or books, could you also link to them?


I am wondering if anyone can advise on issues I might run into when converting a Windows 10 Pro ASUS Zenbook to Ubuntu. I am specifically wondering if the battery life will be affected at all, if there might be driver issues, and anything else that someone on here might have experienced. I've looked at past posts and it seems like many of them are old and might be outdated. The model is UX333-FA, specs:   Intel Core i7-8565U CPU @ 1.80 GHz, 1992 Mhz, 4 cores 16GB RAM 512GB Hard drive   I'm not sure what specs would be helpful and will spare you every single detail right now but I can definitely post them if someone requests.  I recently put kubuntu on my old 2014 MacBook Air. I've noticed with my converted MacBook that the battery life kubuntu shows is the actual capacity remaining (after 5 years of wear) which is about 80% at full charge (so the charger turns green when the screen says ~80%). The battery also does not last very long and I usually just have it plugged in anyway. I sometimes experience a little bit of a lag with programs opening, but the computer is old and only has 4GB RAM so that could be part of the problem.   Are these things I should worry about on a PC? And is there anything else I might need to know before installing? (I realize it's probably impossible to know, but just wanted to put it out there.) The ASUS is about 8 months old and I think I will just put regular Ubuntu on my Zenbook. Many thanks for any help you all can offer.

I have a device on which I would like to install Ubuntu. How do I find out if Ubuntu will work on it?


Hi the question I have to solve is:  $u_x + u_y + u = e^{x+2y} \ $  where $ u(x,0) = 0$  First, I tried to solve the question of the form:  $$ u_x + u_y + u = 0$$  We know that $\dot x = 1 \ $ and $\dot y = 1 \ $. From that we can introduce s where $$x(s) = s +x_0$$ and $$y(s) = s$$. Then if $z = u(x(s), y(s))$ we have that $\dot z + z = 0$.   By setting $s = y$ we have then that $x_0 = y-x$.   Then we can get that $u(x,y) = e^{-y} \ g(y-x)$.  Now, to get $\dot z + z = e^{x+2y}$ I am completely stuck

It is asked to solve the PDE  $$u_x + u_y + u = e^{x+2y}$$  My attempt: We have that $$\frac{dx}{1}=\frac{dy}{1}=\frac{du}{e^{x+2y}-u} $$  $\Rightarrow \frac{dy}{dx}=1 \Rightarrow y=x+C_1 \iff C_1=y-x$  $\Rightarrow \frac{du}{dx}= e^{x+2y}-u \iff \dot{u}+u=e^{x+2y} \iff \\ \frac{d}{dx}(e^x u) = e^{2x+2y} \iff u = e^{-x} ( \frac{1}{2}e^{2x+2y} + C_2)$  As $u$ is constant along its characteristics:  $$u(x,y)=\frac{e^{-x}}{2}(e^{2x+2y} + 2C_2(y-x))$$  where $C_2$ is any function of one variable. But wolfram gave the following answer  $$u(x,y)=\frac{e^{-x}}{4}(e^{2x+2y} + 4C_2(y-x))$$  as you can check   What am I doing wrong?


I am revising calculus from previous years and I have one problem I had problem with. Here it is: Using the limit comparison test check convergence of $$\sum_{n=1}^{\infty}\Big(1-n\sin\Big(\frac{1}{n}\Big)\Big)$$ I tried using trigonometric identities but with no satisfactory results.

I have to study the convergence of the series $$\sum_{n=1}^\infty \left(1-n\sin\left(\frac{1}{n}\right)\right).$$ I know I should study the limit $$\lim_{n \to \infty}n^\alpha\left( 1-n\sin\left(\frac{1}{n}\right)\right).$$   But I have some troubles with this limit (and so the convergence of the series). Any ideas?


How can I introduce a conditional OR into grep?  Something like, grepping a file's type for (JPEG OR JPG), and then sending only those files into the photos folder.  For example.  I know how to send the file where I want it, and get the file type, I just need some help with the grep part.  I'm on OS X, which IMO seems to have modified/customized *nix utilities than what I'm used to in a *nix environment.  So hopefully the answers can be as generic/portable as possible.

I want to find all lines in several files that match one of two patterns. I tried to find the patterns I'm looking for by typing   grep (foo|bar) *.txt   but the shell interprets the | as a pipe and complains when bar isn't an executable.  How can I grep for multiple patterns in the same set of files?


I have a ddos protection proxy in place to deal with SYN floods and such. But http floods are still getting through. For some reason their ddos proxy is not blocking any of the flood. So there are about 500 ips connecting to the box as many times as possible and max out at about 20k connections. This is causing php to spawn 1k processes overloading the box. How can I mitigate this http flood? I thought setting up an htaccess file which required a cookie to access the site would work but rewritecond seems to be invoking php which causes the box to overload.  How can I mitigate this?

This is a  about DoS and DDoS mitigation.   I found a massive traffic spike on a website that I host today; I am getting thousands of connections a second and I see I'm using all 100Mbps of my available bandwidth.  Nobody can access my site because all the requests time out, and I can't even log into the server because SSH times out too!  This has happened a couple times before, and each time it's lasted a couple hours and gone away on its own.  Occasionally, my website has another distinct but related problem: my server's load average (which is usually around .25) rockets up to 20 or more and nobody can access my site just the same as the other case.  It also goes away after a few hours.  Restarting my server doesn't help; what can I do to make my site accessible again, and what is happening?  Relatedly, I found once that for a day or two, every time I started my service, it got a connection from a particular IP address and then crashed.  As soon as I started it up again, this happened again and it crashed again.  How is that similar, and what can I do about it?


South African on a charity visa in the UK. I need a Schengen visa. What would be the easiest to get the visa? Where would be the easiest embassy to apply? What documents are needed?

What's the quickest Schengen consulate to issue a Visa in London? Basically I want to travel as fast as possible to France, and since any Schengen visa will work, I want to go to the consulate with the shortest processing time.


Are there alternative ways to operate an open/forwarding DNS server, without having to use rate limiting or other means of traffic inspection to prevent being used for DNS amplification attacks?   Within a given network, the DNS server can be easily restricted to only answer to specified IP adresses, but given the increased usage of mobile devices I would like to avoid this restriction.  (lets ignore VPNs for this question)  Can you point me to any alternative approaches that try to prevent access to the DNS server  or amplification attacks by other means then actually keeping track of requests and client behaviour?    Are there any client-side solutions, less heavy than a VPN, to authenticate to a DNS server?  edit: as this question has been marked as a duplicate to an unrelated question, I have edited the title to include "client-side".  This is not a duplicate.  I have mentionend the traditional way to to limit the effects of an  amplification attack on the server in my question and I tried to indicate my search by mentioning the VPN based solutions.

This is a  about securing public DNS resolvers   Open DNS servers seem pretty neat and convenient, as they provide IP addresses that we can use consistently across our company regardless of where they are located. Google and OpenDNS provide this functionality, but I'm not sure that I want these companies to have access to our DNS queries.  I want to set up something like this for use by our company, but I hear a lot about this being dangerous practice (particularly in regards to ) and I want to make sure that we do this right. What things do I need to keep in mind when building this type of environment?


I am not a physicist so please excuse me if this is a dumb question. As far as I understand Relativity, as observer (in this case a photon) travels at the speed of light, time stops. So how can the photon have wave properties as it propagates through space?

Quite a few of the questions given on this site mention a photon in vacuum having a rest frame such as it having a zero mass in its rest frame. I find this contradictory since photons must travel at the speed of light in all frames according to special relativity.  Does a photon in vacuum have a rest frame?


I'm confused with javascript's Object.prototype and Anything.prototype.  In chrome console, i have code below:    My questions:   The default prototype for any function is an instance of Object. Is it right? If 1 is true. So, both Anything.prototype and Object.prototype are an instance of Object. Object.prototype is an instance with its __proto__ === null. Therefore, Object.prototype is a special instance at the top of prototype chain. Can i understand like this?

I'm not that into dynamic programming languages but I've written my fair share of JavaScript code. I never really got my head around this prototype-based programming, does any one know how this works? var obj = new Object(); obj.prototype.test = function() { alert('Hello?'); }; var obj2 = new obj(); obj2.test();  I remember a lot discussion I had with people a while back (I'm not exactly sure what I'm doing) but as I understand it, there's no concept of a class. It's just an object, and instances of those objects are clones of the original, right? But what is the exact purpose of this ".prototype" property in JavaScript? How does it relate to instantiating objects? Update: correct way var obj = new Object(); // not a functional object obj.prototype.test = function() { alert('Hello?'); }; // this is wrong!  function MyObject() {} // a first class functional object MyObject.prototype.test = function() { alert('OK'); } // OK  Also these  really helped a lot.


I was looking for a command which will allow me to trigger Ctrl + Alt + F1. This is so that I can invoke the command from the Alarm Clock app, which will ensure that I "notice" the alarm. I usually miss seeing any other window that pops up (tried xclock, etc.), and I've disabled sound, so whatever change occurs on the screen, it has to be prominent. I figured there'd be no way I was going to miss seeing the console, since it occupies the whole screen. Is there any command to trigger Ctrl + Alt + F1? Ubuntu version: 16.04 LTS.  Edit: I need a solution that doesn't require sudo.

I want to make a list of commands to install everything so it's easier the next time I do it, however, I wanted one of the commands to do CTRL+ALT+F1 for me.


I am working on a small commercial product and It is still early days, but I already try to think of ways to monetize this service. I would like to know what users prefer or in which situation the one's benefits would outweigh the other's and why.   For example, on stock resource sites, there is a clear steer towards credits, while on music subscription sites and services in general a monthly fee is charged.  Now, of course this is a bit of an extreme example because music services where you would spend credits to listen to music would not really make sense, but I think you get idea as to where I am headed.  My question specifically is, would you (maybe from personal experience) prefer going the credits route, and why ?   I think credits will bring in more money, yet the model does seem appealing to a user (I don't particularly hate credits, as a matter of fact, I really do not care too much whether a service should have been a monthly fee or not). I think about the credits route because you can really give the user control about what he intends to use in a service as opposed to using all of it for a fixed (higher) fee, if that makes sense ...  Hope I can get some advice here.

Today we were discussing our "credit system" for our website.  At our company, clients can pay us money to get credits. One credit represents one dollar. But what is the best way of represent the money given by our client?  One dollar as 1 credit or One dollar as $1.00  The discussion started because we asked ourselves if the client feels that he "lost" his one dollar when it is transformed into a credit. What are your thoughts on this question?


I am a new DBA at a company that has never had a DBA before me. SQL Servers are never upgraded unless it is part of a Windows Update on the server. Service Packs (or CUs) are never installed. We have a mix of versions from 2000 to 2014.  I'm trying to develop a policy for maintaining and upgrading the SQL Servers. How often do you upgrade your SQL Servers? Or more specifically, how up-to-date do you keep your SQL Servers and why?  For example:   SQL Servers will be upgraded when the version is not within Microsoft's Mainstream support. SQL Servers will stay within 2 (two) versions of the most recent version released from Microsoft.   What about SPs and CUs?

I'm trying to get an idea of what recommended best practices are for the .  Currently, we run on the idea of "do nothing unless an issue fixed by the CU is one we experience".  That works from an "if it ain't broke, don't fix it" approach, but I'm wondering if that's really a good idea since so many of the CUs have performance enhancements.  We're looking at perhaps adding the CU to the patches applied during our periodic maintenance cycles a month or two after the CU is released.  What do others do, and why?    As an update to the question that affects the answers below, on March 24, 2016, Microsoft's SQL Server team announced they were .  Microsoft is recommending that all users install all CUs released after January 2016:     As of January CU releases, these caution messages have been updated,   we now recommend ongoing, proactive installation of CU’s as they   become available. You should plan to install a CU with the same level   of confidence you plan to install SPs (Service Packs) as they are   released. This is because CU’s are certified and tested to the level   of SP’s. Also, Microsoft CSS data indicates that a significant   percentage of customer issues are often previously addressed in a   released CU, but not applied proactively.  More so, CU’s contain added   value over and above hotfixes. These also may contain supportability,   logging, and reliability updates enhancing the overall experience.      In addition to messaging and guidance updates, we have made updates to   the CU acquisition model.      Acquisition changes:         CUs, of course, have traditionally been made available on the “Hotfix” server (accompanied by the “cautionary language” associated   with a ‘QFE’ or ‘Hotfix’). The inconsistency here is that CUs are not   really simple quick hotfixes anymore.  The encompassed updates are   well tested at individual as well as full system integration levels   today.   Therefore, we are now placing the latest CU per mainstream supported baseline (2012 SP2/SP3 and 2014 RTM/SP1 today) on   microsoft.com/downloads, just as is done for Service Packs today   Additionally, we will soon release, and maintain, all CUs into the Windows Update Catalog to facilitate acquisition and distribution   Only interim CU ‘On-Demand’ fixes will be placed on the hotfix server moving forward   To reduce friction, downloading CUs from the microsoft.com/downloads will not require providing/receiving an email and URL   We are also evaluating offering the latest CU as an Optional update on Microsoft Update, just like Service Packs today


I have installed Ubuntu 12.04. I have installed bumblebee too, and it works fine. But my operating system is very slow. I suppose it's because the Intel video card is rendering my graphic interface. When I want to use my dedicated video card, I use the optirun command (e.g optirun firefox). How can I use optirun for graphic interface rendering?

I am considering buying a Dell XPS 15 laptop. The laptop has a Nvidia 420m card which should work with Linux but I keep reading that the Nvidia Optimus technology isn't supported on Linux. I am not really interested in switching from Nvidia to Intel to save power but need to know that the Nvidia card will in fact work if I installed Ubuntu.  If anyone has experience using a Nvidia card with Optimus technology or even better the exact laptop in question (Dell XPS 15 with 1GB NVIDIA® GeForce®  GT 420M) it would be great.  A major problem holding people back from adopting Linux is this sort of hardware issue. I am a long term Ubuntu user and supporter who can't afford to make a mistake with a purchase like this. I don't want to spend £500+ to find I have no graphics acceleration because Windows 7 is not an option.


I have an older computer and as I was pulling the graphics card my fingers slipped and I pulled this off the board... Problem is I can't find one with the same markings so I need to find a replacement... Any help that won't involve me spending a horrible amount of money on a new board (as everything else is still good) would be amazing.  Markings are: 361 100 2 5z (there is a space here between the 2 and the five)  Thanks

I need to replace an SMD capacitor on a board. The printing on it says  F1 560 2.5z  I have googled intensely but have been unable to find information on how to read such a codes.  I need to find out its capacitance and voltage. I think it could be 560uf, but I need to be sure of that and still have to find out the volatage rating.  Also would it be ok to replace an SMD  electrolytic capacitor with a standard through-hole  electrolytic one of the same capacitance and voltage rating?  I am adding picture of the relavant part below:   Inside the red square is the capacitor I need help with   Inside the red reactangle on top there are two other SMD capactor presumably from the same manufacturer. I posted these as well in the hope it may help to find out the manufacturer of the cap I need to replace.  Can somebody please help me?  Thanks.


I know that $Tor^{\mathbb z}_1(\mathbb Z, N) = 0$ for any $\mathbb Z-$module, because free modules are flat. Then because $Tor_1$ is local, we have $Tor_1^{\mathbb Q}(\mathbb Q, S^{-1}N) = 0$, which is not useful at all. How should I use localization to prove this statement?

I have the following three question about flat modules.   Why is not $\mathbb{Z}$ a flat $\mathbb{Z}$-module. Why is $\mathbb{Q}$ a flat module $\mathbb{Z}$-module. I need an example of a module which is not flat, nor injective, nor projective.    Thanks a lot!   Note:  I need only a hint to attack those problems not the complete answer.


I have this tiny little program made for fun, wanted to see how interfaces work . When I enter " iarba " onto the eatsOrNot function, for the dog object, I get true , when I am supposed to get false. What am I doing wrong in that boolean function ?   package animals;      public interface Actions {    void Sound();  boolean eatsOrNot(String s);  void guessNumberOfLegs(int x );    }    package animals;   public class Dog implements Actions {     public boolean eatsOrNot(String s)  {      if (s=="paine"||s=="morcovi"||s=="iarba") return false;      else return true;   }   public void Sound() {     System.out.println("Dog goes 'woof'"); }  public void guessNumberOfLegs(int x) {     if (x==4)          System.out.println("Right!");     else    System.out.println("Wrong!"); }              }     package animals;  public class Rabbit implements Actions {         public boolean eatsOrNot(String s)      {          if (s=="fier") return false;          else return true;      }       public void Sound() {         System.out.println("Rabbit goes bla");     }      public void guessNumberOfLegs(int x) {         if (x==4)              System.out.println("Right!");         else    System.out.println("Wrong!");     }   }    package animals;  import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.Scanner;   public class TestAnimals {      public static void main(String[] args) throws IOException {         // TODO Auto-generated method stub         Scanner in= new Scanner(System.in);         BufferedReader in1=new BufferedReader(new InputStreamReader(System.in));          Dog dog=new Dog();         Rabbit rabbit=new Rabbit();          System.out.println("Rabbit sound:" );          rabbit.Sound();          System.out.println("Dog sound:" );          dog.Sound();           System.out.println("Guess number of a dog's legs:" );            int legs=in.nextInt();            dog.guessNumberOfLegs(legs);            System.out.println("Guess number of a rabbit's legs:" );             legs=in.nextInt();            dog.guessNumberOfLegs(legs);              System.out.println("The dog eats or not : ");                 String str=in1.readLine();                dog.eatsOrNot(str);                System.out.println(dog.eatsOrNot(str));             System.out.println("The rabbit eats or not : ");            String str1=in1.readLine();            rabbit.eatsOrNot(str1);            System.out.println(rabbit.eatsOrNot(str1));             }  }

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


I was writing a document in Microsoft Word, and it flagged "less resources" as being ungrammatical and suggested "fewer resources".  I did some research, and it appears that "fewer resources" seems to be used more often, and one commenter on another English usage site said this was correct.  But this seems odd to me.  I try to be diligent about using "fewer" with countable nouns; a phrase like "The software has less bugs than it did last week" just grates on me.  But even though "resources" is a plural and thus looks like a countable noun, it doesn't seem as though it should be, logically.  If I were to write a business analysis that said "Plan A requires fewer resources than Plan B", would that mean that, say, Plan A would require only 15 resources while Plan B might require 17?  This doesn't make sense.  But is it possible for a noun such as this to be considered countable, grammatically, even though it makes no sense to use it with an actual count?

I've just received a memo which says (effectively)      As more people leave, there will be less people available.   I want that word to be fewer. Are there guidelines for which word ought to be used when?


What mechanics/objects are there in the D&D world to light fire. I'm thinking to literally light some kindling/flaming arrows etc.

One of my players is trying to invent a lighter and I was wondering if anything like that existed.    I'm aware that in D&D 5E there are many different ways to make fire, the main groups I can think of are:   Magical Racial/Class abilities Mundane equipment   I am specifically interest in how to make fire mundanely. From reading through the PHB the only real fire starter I can find is the Tinderbox.  So what equipment is there in D&D 5e to light fires, or is that it?


As seen in the image everything above the transform section is not visible and some portion in bottom is also missing. In the upper part, the cursor is also not mapping correctly, for instance when I want to select translate in transform section I actually have to hover over the rotate option as I move below it seems to work properly. I tried reinstalling different versions of blender (2.78, 2.78c, 2.77 64bit) but nothing changed. OS : Windows 10 Processor : i3 6100  GPU : intel hd 530 (tried win64_154519.4678 and win64_154514.4590) 1080p

I accidentally opened too many menus (or windows) and I want to reset them to default.  It is really annoying, and effecting my animation.  Thanks


if I am citing the reference example I get S.H. Kim & Netessine (2013) and in the second example I get Laffont & Tirole (1987). Can someone explain to me how I make the first return the second outcome? I am using \usepackage[natbibapa]{apacite}. @article{kim13,   title={Collaborative cost reduction and component procurement under information asymmetry},   author={Kim, Sang-Hyun and Netessine, Serguei},   journal={Management Science},   volume={59},   number={1},   pages={189--206},   year={2013},   publisher={INFORMS} }  @article{laffont87,   title={Auctioning incentive contracts},   author={Laffont, Jean-Jacques and Tirole, Jean},   journal={Journal of Political Economy},   volume={95},   number={5},   pages={921--937},   year={1987},   publisher={The University of Chicago Press} }  Thank you for your help.

I am writing a doctoral thesis and I am using  to set the references in APA (American Psychological Association) format. Mostly this has worked perfectly fine, but I would like to suppress the author initials from the compiled version (in-text, not in the end references section). This happens because there are multiple authors with the same name e.g.,     Smith and Jones (1992) or Wells and Smith (1901)    are typeset in-text as:      I. Smith and Jones (1992) or Wells and D. Smith (1901).   Although it may be correct to have the initial in-text in APA format, in reality I am using BPS (British Psychological Society) format, which uses an adapted APA format (and you guessed it, they don't like the initial in text). Thus in-text should look like the first example above (without initial) but looks like the second (with).  To clarify: Any ideas on how to suppress the initial in-text in apacite?  Thanks.  ps. I understand that I could do it with a different bibtex style, but my question pertains to apacite.


In the Chrome console I type:  function test() {}   Than I type:  new test()   Now Google prints "test {}" in the console. When I do:  new test() instanceof test   It prints true.  On new test().toString() it returns [object Object]. On new test().constructor it returns undefined. On new test().prototype it returns undefined. On new test().__proto__ it returns test {}.  So what is the deal?  This is just a stipped down problem of a 3rd party framework. So I can not just add a class literal, add a constructor myself, add any other fancy idea. Since Chrome already knows the correct type (name of the constructor method) I just ask myself: "How can I optain the information?".  Thanks,  Martin (Kersten)

Is there a JavaScript equivalent of Java's class.getName()?


SourceTree with iOS project with Git question.  Two files are always in unstage file:  UnserInterfaceState.xcuserstate xcschememanagement.plist   But, actually I haven't made a any change. (Maybe I just clicked one of files the in project in the Xcode window?)   Should I   commit and push those two files? just ignore them by selecting "Ignore file"? "Remove file"?   I don't want to bother other team developers.  Usually, What is the best choice for those two files?

Which files should I include in .gitignore when using Git in conjunction with Xcode?


I have installed several snaps programs on my Ubuntu 18.10 and it's taking almost 4 minutes to the computer to startup. I noticed those /loop/dev... that appears at startup and found out that those are the snaps programs loading. I never knew that, if I knew it I would never installed them as snaps. I think there are a lot of people who also do not know about it. Is there any way I could fix this? several of those programs are already set up and running just right and I did not want to have to reinstall them. Does the only way is to reinstall them as flatpak or through repository? Any suggestion of what kind of package to use so i don't have anymore unpleasant surprises like that?

After booting I ran systemd-analyze blame and here are the results:       21.596s systemd-journal-flush.service      18.658s dev-sda8.device      15.099s dev-loop33.device      15.034s dev-loop19.device      15.012s dev-loop34.device      14.989s dev-loop21.device      14.877s dev-loop15.device      14.866s dev-loop26.device      14.773s dev-loop27.device      14.684s dev-loop30.device      14.677s dev-loop32.device      14.649s dev-loop35.device      14.590s dev-loop25.device      14.267s dev-loop23.device      14.192s dev-loop24.device      14.156s dev-loop29.device      14.133s dev-loop16.device      14.065s dev-loop31.device      14.059s dev-loop28.device      13.821s dev-loop20.device      13.531s dev-loop22.device      13.495s dev-loop14.device      13.364s dev-loop18.device   What are these dev-loopxx.device (xx denotes numbers) services and why are they taking so much time? Are they related to the mounting of snaps? Can I reduce the boot time by disabling them? I'm running Ubuntu 18.04 alongside Windows 10.


Given two groups $G$ and $H$ and a homomorphism $i:G\rightarrow H$. It is clear that the image $i(G)$ is again a sub-group of $H$, if the mapping $i$ is injective.   Question: What if $i$ is not injective? Does the image still forms a subgroup? If not, why?

I have this written down in my notes, but cannot seem to find verification of it. How can I see this fact?   I believe there is a theorem, something along the lines of if a group G is isomorphic to H then, H is a group. Can anybody verify this or point me to the direction I am looking for? Thanks.


I have a sequence of recursively defined $R \times R$ real positive definite matrices: $$ \mathbf{B_{R}} = \begin{bmatrix}    R & R-1             & \cdots & 1           \\   R-1            &  & &            \\   \vdots            &  & \mathbf{B_{R-1}}  &             \\   1            &              & & \end{bmatrix} $$ and $$ \mathbf{B_{1}} = [1] $$ And I know the following numerically: $\frac{1}{4} \leq \lambda_{\min} (\mathbf{B_{R}})$ for $R \geq 2$. How to prove it? Furthermore, I know this is an asymptotically tight bound, because $\lambda_{\min} (\mathbf{B_{R}})$ is decreasing in $R$ (immediate from Cauchy interlacing) and $\lim_{R \to \infty} \lambda_{\min}(\mathbf{B_{R}}) = \frac{1}{4}$. It would be swell to prove this too. Addendum: initial examples from this sequence: $\mathbf{B_{2}} = \begin{bmatrix}  2 & 1                        \\   1            & 1            \\ \end{bmatrix}$, $\mathbf{B_{3}} = \begin{bmatrix}  3 & 2 & 1                        \\  2 &  2            & 1            \\ 1 & 1 & 1 \end{bmatrix}$, $\mathbf{B_{4}} = \begin{bmatrix}  4 & 3 & 2 & 1                        \\ 3 & 3 &  2            & 1            \\ 2 & 2  & 2 & 1 \\ 1 & 1 & 1 & 1 \end{bmatrix}$

I am handling a problem of finding a unifom lower bound ( away from zero ) of  the smallest eigenvalue of  the following real symmetric matrix  $$A =\begin{pmatrix} n & n-1 & n-2 & \cdots & 1\\ n-1 & n-1 & n-2 & \cdots & 1 \\ n-2 & n-2 & n-2 & \cdots & 1 \\ \vdots & \ddots & \ddots & \ddots & \vdots \\ 1 & 1 & \cdots & \cdots & 1 \end{pmatrix}$$  I did some simulation (simulate n from 2 to 1500 ), it shows that the smallest eigenvalue of this matrix may have a lower bound around 0.25. So I try to prove it.   First, I found there may have some results related to the problem. Such as    So I try to use   $$ \lambda_{min} \gt \sqrt{\frac{||A||_F^2-n||A||_E^2}{n(1-||A||_E^2/|det(A)|^{2/n})}} $$  or the result ( Theorem 1 ) in . But only get a trivial lower bound zero.  Then I try to use  to solve the following equivalent problem  $$\inf_{x\in \mathbb{R}^n,~\|x\|_2 = 1} x^{\top} A x$$  By some calculate, I think this problem is the following optimization  $$ \min_{x_i \in \mathbb{R}} x_1^2 + (x_1+x_2)^2 + \cdots (\sum_{i=1}^n x_i)^2~~s.t. ~~\sum_{i=1}^n x_i^2 = 1 $$  or at least find a lower bound of the object function. I tried the method of Lagrange multipliers, and the trigonometric functions to reformular the problem. But I got stuck because of the complicated calculation.   So, I wonder is there anyone may have some ideas about the problem?  Thanks!


I am trying to use the observer pattern in my GUI, and I get a NullPointerException even though the observer I am trying to add is definitely not null. here is the relevant extract of code:       private class AuditButtonActionListener implements ActionListener {     DirectoryAuditingProcessor directoryAuditingProcessor;     DirectoryAuditingAgentObserver directoryAuditingAgentObserver;      AuditButtonActionListener(){         directoryAuditingAgentObserver = new DirectoryAuditingAgentObserver();         directoryAuditingProcessor = new DirectoryAuditingProcessor();         directoryAuditingProcessor.getDirectoryAuditingAgent().addObserver(directoryAuditingAgentObserver);     }      public DirectoryAuditingProcessor getDirectoryAuditingProcessor() {         return directoryAuditingProcessor;     }      public void actionPerformed(ActionEvent ev){          directoryAuditingProcessor.process(Paths.get(selectedSourcePathTextField.getText()),null);         textAreaOutput.setText(directoryAuditingProcessor.getDirectoryAuditingAgent().                                             getDirectoryVisitingAgent().getShaOneHashAndFileProperties().toString());     } }  class DirectoryAuditingAgentObserver implements Observer {     @Override     public void update(Observable o, Object message) {         textAreaOutput.append((String)message);     } }   and the DirectoryAuditingAgent class does extends Observable. Thank you in advance for your help

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


Really just looking for honest answers from fellow users for this one.   How often do you get CAPTCHAs, and what were you doing when it appeared?  Some future scripts I'm working on may attempt actions that could at times require a CAPTCHA, which would throw a big wrench into the gears. I'm just trying to figure out when I can expect to see them, and when I can expect to avoid them.   I myself have only had to answer a CAPTCHA once, and it was on my first post ever.

I noticed that I can only perform certain actions such as commenting a finite number of times in a given period of time. Obviously, rate limiting is in place to prevent accidental misuse or intentional abuse of certain features.  Where else is rate limiting applied on Stack Exchange sites, and what are the limits?


Assuming I am a total newbie in "patisserie", what are the best ingredients and steps to be used/taken to deliver a top quality home made milk chocolate bar? I mean, those that really make a difference from low-quality/average and finest/top-quality. For instance, cocoa quality and selection, cocoa butter (or butter?), powder milk. Are there any well-known tips or techniques? Any suggestions?

I want to make plain dark chocolate at home.   The process is tricky in my experience, not simply mixing cocoa, cocoa butter, milk powder, sugar, etc.  Can you share some practical tips for doing the process and choosing the right ingredients.


Prove $ \sum \frac{\cos(n)} { \sqrt n}$ is bounded.  How can I prove $\sum \cos(n)$ is bounded. Can It be done using $\cos$ as real part of complex number as I showed in question ?

How to Prove $ \sum \frac{\cos n} { \sqrt n}$ converges Using Abel’s theorem ?  I think it can be done using $\cos n = Re(e^{in})$ { Real Part of Complex Number }  How to proceed ?


Trying to get to 14 version by updating 12.40 to 13.04 but get failed fetch error. Have tried upgrade through Software updater and get all the way through to the update prompt "you should update to 13.04" I click update get the 'release notes' window and select 'upgrade' and than i get the 'Fetching the upgrade failed. There may be a network problem.' have tried numerous things to no avail.

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


Stack Exchange sites are used on a lot of different browsers, at screen sizes ranging from huge 4k monitors to small phones, at window sizes ranging from full-screen to 1024px (sometimes smaller), on computers with resources ranging from "I never see a beachball/hourglass" to "I get by, mostly", sometimes with configuration changes for accessibility (like larger fonts or keyboard shortcuts or voice).  That's got to be a bear to test.  In the spirit of , I'm curious how SE goes about testing design changes and UI more generally.  I seem to recall from the Joel Test in past SE job posts that SE doesn't employ QA folks, and the design team isn't large.  How do y'all test the SE design in all its variant environments and still get new work done?  This question overlaps with , but that question seems to be more about implementation and automation. You can write unit tests to verify that clicking on a UI thing still works and never notice that the actual display of that thing is off, for instance. I'm really more focused on the design here and the answers might be different.

Stack Exchange is my role-model for application development.  I've tried to learn as much as possible from the blog and podcasts, from thought process to design, architecture, convention, etc etc.  I'm just about to wrap my head around TDD and am curious about how the SE team approaches it.  Is there a methodology that all team members follow, or is it more developer-driven testing where you pick complex bits to unit test as needed, or is it more about catch-all integration testing once a piece of functionality is done, or... ?  Any input would be fantastic.


I think example is worth more than words.   I want to rewrite this :   person = Person.objects.filter(email__contains="gmail.com")   somehow like this :   condition = "email__contains" person = Person.objects.filter(condition="gmail.com")   Is this possible ?

Given a class:  from django.db import models  class Person(models.Model):     name = models.CharField(max_length=20)   Is it possible, and if so how, to have a QuerySet that filters based on dynamic arguments?  For example:   # Instead of:  Person.objects.filter(name__startswith='B')  # ... and:  Person.objects.filter(name__endswith='B')   # ... is there some way, given:  filter_by = '{0}__{1}'.format('name', 'startswith')  filter_value = 'B'   # ... that you can run the equivalent of this?  Person.objects.filter(filter_by=filter_value)  # ... which will throw an exception, since `filter_by` is not  # an attribute of `Person`.


I have been having a struggle finding an explanation why $-3 \cdot (-3) = 9$. Why does this question equal a positive number? Any explanations?  And btw, if $-3 \cdot (-3) = 9$. Why does $-3 + (-3) + (-3) = -9$ and not $9$?

Someone recently asked me why a negative $\times$ a negative is positive, and why a negative $\times$ a positive is negative, etc.  I went ahead and gave them a proof by contradiction like so:  Assume $(-x) \cdot (-y) = -xy$  Then divide both sides by $(-x)$ and you get $(-y) = y$  Since we have a contradiction, then our first assumption must be incorrect.  I'm guessing I did something wrong here. Since the conclusion of $(-x) \cdot (-y) = (xy)$ is hard to derive from what I wrote.  Is there a better way to explain this?  Is my proof incorrect?  Also, what would be an intuitive way to explain the negation concept, if there is one?


Consider the action of $\mathbb{R}$ on $\mathbb{R^2}$  given by $t \cdot (x,y) = (x+t, y)$.   I am asked to find closed subsets $A \subseteq \mathbb{R}$ and $B \subseteq\mathbb{R^2}$ such that $A\cdot B$ is not closed.  there is a similar result that stats that     For any topological group $G$ acting on a space $X$, if $A \subseteq G$ is compact and $B \subseteq X$ is closed, then $A \cdot B$ is closed.   Therefore, for my example I am starting from a closed but not compact subset $A$ in $\mathbb{R}$; I have tried with unbounded intervals $[a,\infty)$ or discrete subsets like $\mathbb{N}$ or $\mathbb{Z}$. However; I can't find a suitable $B$ to get what I want.

Is there a counterexample for the claim in the question subject, that a sum of two closed sets in $\mathbb R$ is closed? If not, how can we prove it?  (By sum of sets $X+Y$ I mean the set of all sums $x+y$ where $x$ is in $X$ and $y$ is in $Y$)  Thanks!


I've been pondering this from time to time. If Aragorn is directly related to Elros, Why couldn't he have choice to become Elven like Elrond? Because he is descended from Lúthien he could have chosen, yes, or am I wrong here?  Their story in some ways, at least through the film, seems a lot like the ancient story, and there is history about Arwen being most fair and a lot of talk of her having Lúthien's bearing.  Most that was said about her was also said about Arwen. To some, Lúthien returned.  There has been information emerging about how Arwen and Aragorn meet in Mandos and get permission or are awarded to live eternally in Valinor.  I for one can see this happening, since this is one of those rare moments where such things do happen.  Now onto the lineage.  If he was related to Elros:   Did the choice end with that line?   Doesn't Aragorn have relations to more ancient heritage?  I mean, if he can be distantly but directly related to Arwen, couldn't he have this same option?   Or are most Numenoreans just simply this?

Earendil and Elwing were given the choice of kindreds after their journey to Valinor, This choice was extended to their sons (specifically sons, not daughters or grandchildren)  Elrond chose the race of the Eldar and his brother Elros chose to be counted amongst the Edain. Thus far Manwë's proclamation has been fulfilled.  There are some inconsistencies here:   Arwen was given the choice, but Elladan and Elrohir remained as Eldar in Imladris Tar-Vardamir was not given the choice The offspring of Imrazor and Mithrelas in Dol Amroth dont seem to have been given a choice   I can think of only one explanation, that the Mannish blood is dominant over the blood of the Eldar, thus, As Vardamir was the offspring of two mortals he did not fall under Manwë's proclamation despite being the son of a half elven.  However this does not seem to explain the other inconsistencies, Is it possible that Elladan and Elrohir and also the princes of Dol Amroth weren't considered important enough by Manwë or Eru to give them the choice.  Also as a side note Tolkien states there were only three unions between man and elf, but this seems to ignore Turin/Finduilas and Imrazor/Mithrelas  My question is, Why was Arwen given the choice and not the sons of Elros?


I was reading about how we can ascertain whether a cosmic object is receding from or approaching us by studying the doppler shift of its spectrum- I mean the redshift and blue-shift.  But we have no idea about the actual frequency of light emitted by the cosmic object. Then how can we say that the light is getting red-shifted or blue-shifted?  Some texts suggest that the frequency of the emitted radiation depends on the hydrogen, helium, lithium, carbon etc. content of the cosmic object. But we can at most make a guess about its percentage composition. Then how can we identify what the frequency of the emitted radiation is?  And, if the above mentioned way is not how we understand the doppler shift of the light emitted by cosmic objects, how do we confirm that the light is getting doppler shifted?  EDIT:  My question is almost similar to the duplicate question. It has solved my problem to a good extent but it doesn't totally resolve my problem.  Say we are receiving a pattern of lines from a particular star and the lines are characteristic of an element $X_1$. What happens if the red-shifted line pattern of $X_1$ resembles the pattern of lines for some other distinct element $X_2$?  How do we understand if the star is emitting light characteristic of the element $X_1$ or $X_2$?   If the question still looks unclear, you can refer to the comments section where I have tried to elaborate my query to John Rennie.

Doppler redshift of distant galaxies gave first hint that the universe is expanding. I am curious to know how this redshift is actually measured and interpreted from observation. Suppose I observe some  visible line say red with wavelength \lambda_1.  This is not enough to tell that this line is redshifted, i.e., the  original line emitted from that galaxy had a smaller wavelength. How do I know the value of that particular line when it was emitted from that galaxy? It appears that mere observation of a line is not enough. So how do we proceed?


I want to know a simple way to prove $$\sum_{k=0}^n {{n}\choose{k}} = 2^n.$$ Our teacher only gave us the combinatorial proof.

I've discovered that the sum of each row in Pascal's triangle is $2^n$, where $n$ number of rows. I'm interested why this is so. Rewriting the triangle in terms of C would give us                $0C0$ in first row. $1C0$ and $1C1$ in the second, and so on and so forth. However, I still cannot grasp why summing, say, 4C0+4C1+4C2+4c3+4C4=2^4.


I want to find questions that include a certain tag but exclude a separate, different tag.  For example, suppose I wanted to find and read all questions that include a javascript tag, but I don't even want to see any question from that set that includes a jquery tag.  How would I go about that?

I want to search for several related tags at once. When I type multiple tag-names in the search box, only one gets selected and I have to sift through a horde of non-pertinent questions.   E.g. 1: I want to find all questions where 'java' AND 'netbeans' AND 'tomcat' all are defined per question.  E.g. 2: (this may be a bit much to hope for) I want to find all questions where 'java' AND 'netbeans' BUT_NOT 'tomcat' is defined.  Alternatively, is there a way to search through the previous search results?  Is this possible?


There is an existing question  which has a complex answer, not accessible to the layman.  The point of this new question is that the electromagnetic field is mediated by photons. Yet photons emitted at the surface of a black hole (of a large enough mass) will not be able to escape beyond the event horizon.  Would a large black hole have no measurable electric field beyond its event horizon, even if it carried a high charge at its surface?

By the "No Hair Theorem", three quantities "define" a black hole; Mass, Angular Momentum, and Charge. The first is easy enough to determine, look at the radius of the event horizon and you can use the Schwarzschild formula to compute the mass. Angular Momentum can be found using the cool little ergosphere Penrose "discovered". However, I don't know how to determine the charge of the black hole.   How can an electromagnetic field escape the event horizon of a Reissner-Nordström black hole? Is there any experiment we could theoretically do to a black hole to determine its charge?


Let $F$ a field with $\operatorname{char}F\mid q$, then $\displaystyle {q \choose m} = 0$, for all $m = 1, ..., q-1$.  Comments: I'm trying to decompose q into product of primes.

It is quite easy to show that for every prime $p$ and $0<i<p$ we have that $p$ divides the binomial coefficient $\large p\choose i$; one simply notes that in $\large \frac{p!}{i!(p-i)!}$ the numerator is divisible by $p$ whereas the denominator is not (since it is a product of numbers smaller than $p$ and $p$ is prime).  My problem is with generalizing this argument for $q=p^n$. I'm looking for the most elegant and simple way to prove that $p$ still divides $\large q\choose i$.


I want to add a sentence to header of a file using bash script, I tried   echo "#define Block $i">>mypro.cpp   but it add '#define Block $i' to it's end. Thanks in advance

I want to insert text at the top of an already existing file. How can I achieve this. I tried echo and tee but was not successful.  I was trying to insert repo line at the top of sources.list file from terminal.  Note  I need an one line quick solution, because another answer's method was known to me already


I'm an international student currently living near Chicago. Tomorrow I have an appointment to get a French visa, and I have a question about one of the requirements.  According to them (), I'm required to have a travel itinerary: "2. travel itinerary: we recommend you to make a flight reservation and not purchase your airline ticket until you get your visa."  Does this phrase mean that I'm supposed to book a ticket before I show up at the Consulate General, or that it's just a recommendation and all I need is to know my route?  I would call the Consulate General, but they are closed today.

The Italian consulate website says under requirements for a Schengen visa:        Applicants for short term visas (up to 90 days) must also present an itinerary of their trip.      What does this mean? This is separate from the proof of return ticket:        Return-trip booking or proof of available means of personal transport:   ticket reservations for round-trip flights originating in our jurisdiction to Europe (and ultimately to Italy) and back, including internal entry and exit points of travel i.e. EURORAIL tickets, car rental, internal flights. The names of reservations should reflect the name on passport. The applicant may be required to show the actual ticket when picking up the visa;      When they ask for an itinerary, what documents need to be shown? Is it enough to have a plan of which places I am going to visit and where I will be staying?


Is the method of calculating determinant of $3\times 3$ matrix by diagonals, apply also on $4\times 4$ matrix?  for example:  $$\begin{matrix}2&2&1&3|\\1&4&4&5|\\5&1&1&6|\\7&1&4&5|\end{matrix}\begin{matrix}2&2&1\\1&4&4\\5&1&1\\7&1&4\end{matrix}$$  $\det = 2\cdot4\cdot1\cdot5+\dotsb+3\cdot1\cdot1\cdot4 - 7\cdot1\cdot4\cdot3-\dotsb-5\cdot5\cdot4\cdot1 = 171$  Is this valid?

Can  of finding the determinant be used for finding the determinant of matrices greater than $3\times3$, as I am unable to find any example of a matrix greater than $3\times3$ whose determinant is found by Sarrus' method?  I have tried many questions and Sarrus' method only works for $2\times2$ and $3\times3$ matrices. I have not read about Sarrus' method in any book but only from the internet, so I'm not sure about it.


So I have this command here. It's supposed to spawn a wither skeleton with a custom head and some gear.  Errors: "Data Parsing Failed: Unbalanced curly brackets"   Command:  /summon Skeleton ~0 ~1 ~0 {Equipment:[{id:iron_sword,tag:{Unbreakable:1,ench:[{id:19,lvl:2}, {id:16,lvl:1}]}},{},{},{},{id:skull,Damage:3, tag:SkullOwner:{Id:"5ee854b8-0f30-4ca6-8039-3c0cd74c7d42",Properties:{textures: [{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvMTk3ZjI4NmRmZTg3YzkyY2VhMjkyODgxNTcxZTgyNjEyNTg2NDM4Y2FiNWMwZjg0N2ZmZTBjOTFhYjlkYmUxIn19fQ=="}]}}}, CustomName:Golem,CustomNameVisible:1,Attributes:[{Name:generic.maxHealth,Base:30}, {Name:generic.movementSpeed,Base:0.7},{Name:generic.followRange,Base:40}, {Name:generic.knockbackResistance,Base:1}], ActiveEffects:[{Id:10,Amplifier:1,Duration:999999}],SkeletonType:1}

Often, when making a command block contraption, you need to set an entity's data tag. These tags can sometimes be very long, with many layers of nested curly and square brackets. For example, this is the command to summon a villager with a single custom trade:  /summon Villager ~ ~ ~ {Profession:3,Career:2,Offers:{Recipes:[{buy:{id:minecraft:diamond,Count:6b}},sell:{id:minecraft:diamond_hoe,tag:{ench:[{id:16s,lvl:10s}]}]}}   The single-line command block interface of Minecraft makes it incredibly difficult to find and fix errors, especially when it comes to mismatched brackets. In fact, for illustration purposes, I put an error in the above command.  What techniques can I use to find and fix unbalanced square or curly brackets when writing long and complicated data tags?


They are both the Capitol of their respective Galactic Empire.  Both Star Wars and Foundation trilogy have masters of the mind arts, Jedi and Psycohistorians.

In the second book of the , Foundation and Empire, written in 1953, the Mule appears, an amazing and intriguing character. Reading this book give me the sensation that George Lucas based his ideas of the Jedi and Sith orders around the influence of the Asimov tale.  Is there any evidence that Foundation series - especially the Mule - influenced Star Wars ideas of Jedi and Sith, given the multitude of acknowledged and unacknowledged-but-obvious influences that Lucas had?  UPDATE  Here's a fragment of the mule description:     One of the greatest conquerors the galaxy has ever seen, he is a mentalic who has the ability to reach into the minds of others and "adjust" their emotions, individually or en masse, using this capability to conscript individuals to his cause. Not direct mind-control per se, it is a subtle influence of the subconscious; individuals under the Mule's influence behave otherwise normally - logic, memories, and personality intact."    Can explain for example, one the Jedi/Sith main talents... and so on.


I am setting up new Ubunut machine. Stuck on setting up Java environment variable. I have tried all possible way and whatever solution I found here. None of them worked. It is still giving me blank line (see the code first line). Can anyone help me to set the variable.    me@me-ubuntu:~|⇒  echo "$JAVA_HOME"  me@me-ubuntu:~|⇒  java -version java version "1.8.0_40" Java(TM) SE Runtime Environment (build 1.8.0_40-b25) Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode) me@me-ubuntu:~|⇒   me@me-ubuntu:~|⇒  which java /usr/bin/java me@me-ubuntu:~|⇒  ls -l /usr/lib/jvm total 8 lrwxrwxrwx 1 root root   24 Mar 22  2014 default-java -> java-1.7.0-openjdk-amd64 lrwxrwxrwx 1 root root   20 Jan 27 09:22 java-1.7.0-openjdk-amd64 -> java-7-openjdk-amd64 drwxr-xr-x 7 root root 4096 Mar 31 10:26 java-7-openjdk-amd64 drwxr-xr-x 8 root root 4096 Mar 31 10:43 java-8-oracle me@me-ubuntu:~|⇒     I tried to set it in ~/.bashrc as well as in environment file but nothing work  export JAVA_HOME=/usr/lib/jvm/java-1.7.0-openjdk-amd64 export PATH=$PATH:$JAVA_HOME/bin

I only recently discovered the different JVM's on the  page and thought I'd start tinkering. Its been difficult to find documentation on how to configure Java on Ubuntu though.  Lets say I wanted to change the JRE or JDK that I'm using, I could crack open a terminal and say  sudo update-alternatives --config java   And then pick from one of the installed versions.  If I'm understanding JVM's right (which I may very well be not), You can configure the openJDK to use alternative JVM's (Eg JAMVM) and run it as such  jamvm -jar foo.jar   2 questions,  1: Do i have the concept of a JVM right? As in, is this possible?  2: If so how do i configure the JVM and switch the default to a JVM of my choosing?


Is there any software available in UBUNTU 13.10 to check line by line code execution of C programs.

I recently changed from Windows where I was using Qt Creator to Ubuntu.  The problem is that Qt Creator in Ubuntu can't properly debug due to some problem attaching ptrace to the program which was cause by a security upgrade as I found out. The only way to debug is to mess with the system settings and change the ptrace variable configuration but I'm not comfortable with this, as it compromises security.  So my question is, is there anything close to Qt Creator or Visual Studio debugger in Linux? I mean being able to track variable values and pointers, etc.  If not what's the standard debugger for Linux? I don't mind using console tools as long as they offer the same functionality


(..) those who stand to profit from our working harder,   I've noticed this pattern very often, but I don't know how or when to use it. The following      (...) those who stand to profit from us working harder,   would be right as well, right? Is there a difference in meaning? Or in context of use maybe? Thanks in advance!  For reference, the sentence is taken from the fourth paragraph from the end in .

I assume that the following sentences are grammatically correct:   He resents your being more popular than he is. Most of the members paid their dues without my asking them. They objected to the youngest girl's being given the command position. What do you think about his buying such an expensive car? We were all sorry about Jane's losing her parents like that.   I'm still getting used to this possessive gerund structure. It sounded so weird to me at first. Is the structure used in both formal and informal contexts? Are there any alternative structures that result in the same meaning and are more frequently used? (Examples taken from )


An exercise sheet of my Multivariable Calculus subject asks you to prove that a continuous function $f:\mathbb{R}^n\longrightarrow\mathbb{R}$ is uniformly continuous if $\lim_{\Vert x\Vert\to\infty} f(x) = L$. I think I have nevertheless found a counterexample: taking $n=1$, the function $f(x)=\sin(1/x)$ for $x\neq 0$, $f(0)=0$ has limit 0 as x approaches both negative and positive infinity, but it is not uniformly continuous. Is my reasoning correct? Otherwise, can you give me some hints on how to deal with this proof? Thanks in advance.

I am working on a homework problem from Avner Friedman's Advanced Calculus (#1 page 68) which asks     Suppose that $f(x)$ is a continuous function on the interval $[0,\infty)$. Prove that if $\lim_{x\to\infty} f(x)$ exists (as a real number), then $f(x)$ is uniformly continuous on this interval.   Intuitively, this argument makes sense to me. Since the limit of $f(x)$ exists on $[0,\infty)$, we will be able to find a $\delta > |x_0 - x_1|$ and this implies that, for any $\epsilon>0$, we have $\epsilon > |f(x_0) - f(x_1)|$ (independent of the points chosen). I am aware that the condition of uniform continuity requires that $\delta$ can only be a function of $\epsilon$, not $x$.   What information does the existence of a real-valued limit provide that implies $f(x)$ is uniformly continuous on this interval?


While googling myself, I found this site: . It looks like it is collecting Stack Exchange sites' questions and answers, and presenting them as its own content.  Is this legitimate?

of Stack Overflow, all content posted on Stack Exchange sites by their users (i.e. you wonderful people) has been provided to the whole universe under . For my fellow non-lawyers, that license basically means:   Anyone can use any Stack Exchange posts at any time without having to ask for permission Making money off of the copied content is permitted You don't even have to copy stuff from here verbatim; you can just use it as a starting point and make whatever edits you want There are just two rules you have to follow:   You have to provide . Simple links to the original post and author info are just fine. You have to  and allow other people to use your content, as long as they follow these very same rules. How meta!    (If you ever forget any of that, and want to refresh your memory, the license info is linked to in the footer of every page.)  There are, in fact, a lot of people who republish varying amounts of our content for assorted reasons. Unfortunately, there are some Stack Content Republishers Attributing Poorly and/or Excelling at Ranking (SCRAPERs, for short).  In this context, "attributing poorly" means any use that doesn't follow our attribution rules or make any other reasonable attempt at give credit. This can get pretty egregious; I've seen SCRAPERs that not only don't link back to SE originals, but also use fake author info and post dates to make it harder to find originals. By "excelling at ranking," I'm referring to copycat sites that end up higher in Google results than the original SE sites do for the same content. That's not necessarily wrong, but in some cases, it indicates inappropriate SEO hackery.  So, the question is: what can you do if you spot a SCRAPER?