How is it possible to suggest a change to a default site icon? I noticed a lot of sites with a default one.
Who is responsible for defining a site logo? I mean, there are moderators of the site that define it, or stackexchange defines it?
How can we recover the Newtonian gravitational potential from the metric of general relativity? The Newtonian description of gravity can be formulated in terms of a potential function $\phi$ whose partial derivatives give the acceleration:  $$\frac{d^2\vec{x}}{dt^2}=\vec{g}=-\vec{\nabla}\phi(x)=\left(\frac{\partial\phi}{\partial x}\hat{x}+\frac{\partial\phi}{\partial y}\hat{y}+\frac{\partial\phi}{\partial z}\hat{z}\right)$$  However, in general relativity, we describe gravity by means of the metric. This description is radically different from the Newtonian one, and I don't see how we can recover the latter from the former. Could someone explain how we can obtain the Newtonian potential from general relativity, starting from the metric $g_{\mu\nu}$? I am planning on spending 90 days in Schengen zone countries.  I will be taking a cruise between Lisbon and Barcelona.  Do the days at sea count against the 90 days allowed for staying in the Schengen zone? Flagging multiple comments versus flagging the whole post for moderator attention When multiple comments in a comment thread ought to be removed (especially if they're all for the same reason), should I flag each of them individually or flag the parent post for moderator attention?  I've usually adopted the former strategy - flagging each comment with the same flag reason, often a custom one copied and pasted. I had always assumed the following things that led me to follow this strategy:   Flagged comments were discretely marked as flagged in some way when the reviewer viewed the question (much like how I can see others' pending suggested edits now that I have editing privileges). By individually flagging all the comments that needed cleaning up, I was allowing the flag reviewer to see at a glance which comments needed removing, thereby providing them with useful additional information that wouldn't be available if I flagged the entire parent post. By flagging comments individually, rather than flagging the whole post, I was letting my flags be handled by anyone with 10k+ rep and access to the mod tools, rather than having to be handled by a diamond moderator.   However, I just read  (now deleted) by Shog9 that makes me suspect that approach is misguided, and question whether any of my assumptions about how comment flags work are actually true. Notably he says:     If you'd pinged me once for every comment in that thread you found noisy, I would probably be plotting my revenge instead - at very least, I would think you very rude for doing so. Yet, that's exactly what you're doing when you start flagging multiple comments in a single thread: instead of taking a few seconds to describe a problem, you're attempting to use a moderator as a tool to do your bidding, without any real effort to communicate.   He also said some more stuff on the topic - I think there was something about huge offensive boxes blotting out the UI when he views questions with multiple flags - but I now can't recover it any more because that question was deleted while I was in the process of writing this one, and it doesn't seem to be available in the Google cache.  Much of the flagging and review system is still a black box to me as a low/mid rep user, and it's difficult for me to figure out what flagging behaviors are appropriate and helpful when I have no idea what actually happens when I flag a comment. (The Privileges section doesn't mention comment flags anywhere that I can find. I don't even know who reviews them at the moment, and can't find a Meta question anywhere that addresses that.)  Could somebody provide some input on when (if ever) flagging lots of individual comments in a thread is appropriate, and when flagging the entire parent post is? A pretty screenshot of the UI of the relevant review/mod tools, demonstrating the effect of each approach, might also be helpful for understanding this, if that's not asking too much. $f$ differentiable except in $1$ point Assume we have a function $f : \mathbb{R} \rightarrow \mathbb{R}$ such that  $f$ is differentiable for all non-zero $x$, $f$ is continuous at $0$ and  $$\lim_{x \uparrow 0} f'(x) = \lim_{x \downarrow 0} f'(x) &lt; \infty. $$  Is it then true that $f$ is also differentiable at $0$?  If we drop the hypothesis that $f$ is continuous, this is not true since the signums function is a simple counterexample. But what if $f$ is continuous? I don't think this is true but I can't find a counterexample... Subtracting 2 lists in Python Right now I have vector3 values represented as lists. is there a way to subtract 2 of these like vector3 values, like  [2,2,2] - [1,1,1] = [1,1,1]   Should I use tuples?  If none of them defines these operands on these types, can I define it instead?  If not, should I create a new vector3 class? Ubuntu 14.10 folder icons missing How to echo a bang! Does C# optimize the concatenation of string literals? For instance, does the compiler know to translate  string s = "test " + "this " + "function";   to  string s = "test this function";   and thus avoid the performance hit with the string concatenation? Black artifacts when looking through many transparent objects? How to get UTF-8 working in Java webapps? Prove that for any prime p, there is a complete set of mod p residues {q1, . . . , qp}, where each qi is prime. I used the theorem {a, a+n, a+ 2n, . . .} contains infinitely many primes if gcd(a, n) = 1 but haven't got much progress. Any comment will be helpful! Why Smart's attack doesn't work on this ECDLP? I Can't receive files via bluetooth on lxde Unable to send e-mail. Contact the site administrator if the problem persists When my web form is filled and submitted, I get redirected to a page that says:     Thank you for submitting.   but theres a red warning box there that says:     Unable to send e-mail. Contact the site administrator if the problem persists.   I think its the SMTP server, but I don't know how to fix that. Are vacuum fluctuations really happening all the time? Possible Duplicate:           What book would you recommend for an undergraduate wanting to learn the basics of topology? I've come across several books that claim to give an introduction to the subject, but I wasn't sure which one(s) to pick.  Here are some of the books I came across:   Introduction to Topology - Bert Mendelson Basic Topology - M.A. Armstrong First Concepts of Topology - William G. Chinn Topology Without Tears - Sidney A. Morris Topology - James Munkres   They don't go over the exact same topics, some are more in-depth than others, some seem to target slightly different audiences etc. What would be right for me (not necessarily from that list)? To give some more background, I want to learn topology because I feel it will be somewhat helpful in the field of Computer Vision. Automatic line breaking of long lines of text? Here, it is just a example. I have a line:  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaa   Now, I want to let LaTeX automatically wrap the line according to the width of the text block/margins. How to keep VLC player in minimized mode? I'm using VLC media player which can play almost all kinds of audio and video formats. While listening to audio, I keep VLC in minimized mode and can work on other windows. But when I select to listen video songs mixing with audio songs, VLC is maximizing itself to play every video song in the playing list, which is really annoying in the middle of work.  So how can I keep always VLC player in minimized mode while playing a list of songs mixed with audio and video songs? How to add a class to a given element? I have an element that already has a class: &lt;div class=&quot;someclass&quot;&gt;     &lt;img ... id=&quot;image1&quot; name=&quot;image1&quot; /&gt; &lt;/div&gt;  Now, I want to create a JavaScript function that will add a class to the div (not replace, but add). How can I do that? I am looking for a way to delete all files older than 7 days in a batch file.  I've searched around the web, and found some examples with hundreds of lines of code, and others that required installing extra command line utilities to accomplish the task.  Similar things can be  in just a couple lines of code. It seems that something at least remotely easy could be done for batch files in Windows. I'm looking for a solution that works in a standard Windows command prompt, without any extra utilities. Please no PowerShell or Cygwin either.