Is the surface of the Earth expanding in GR?
How can you accelerate without moving?
How do I keep both the background and foreground in the image in focus at the same time? How do you have both the background and foreground in the image in focus at the same time?  Last week I was attempting a shot where I had the back of a hat in focus and in the distance you could see a mountain. I wanted both in focus, but could either focus on the mountain or the hat. I ended up taking the in-focus shots of both and merging them in Photoshop. While that isn't difficult I would prefer to shoot the shot as accurate as possible. From what I have read aperture is important in the depth of field but what are the techniques for keeping both the background and foreground in focus?  I am using a Nikon D5100 with a 18-55mm f/3.5-5.6 (standard kit lens) and a 55-200mm  f/4.5-5.6.    almost answers my question, but I am a bit confused. Can someone explain this a bit differently? Thanks! I want to draw a TikZ matrix with its border and I would like to define the distance between most external matrix nodes and matrix border. Something like a matrix inner sep. If I change inner sep in matrix options declaration, all nodes inside the matrix also change its inner separation.      I know how to do it with fit library. I just want to know if its possible without it. Do superheroes/villains like Quicksilver or Flash with super speed get tired due to running? I mean a average human can run at his full speed for 15 to 20 mins before getting tired. Trained athletes can go on running for much more time without tiring out.  Do Superheroes like Quicksilver or Flash ever get tired due to excessive running? Math symbol question: Vertical bar for ''evaluated at ...'' C program to convert Fahrenheit to Celsius always prints zero Anonymous questions and Avatars Write Python stdout to file immediately When trying to write the stdout from a Python script to a text file (python script.py &gt; log), the text file is created when the command is started, but the actual content isn't written until the Python script finishes. For example:  script.py:  import time for i in range(10):     print('bla')     time.sleep(5)   prints to stdout every 5 seconds when called with python script.py, but when I call python script.py &gt; log, the size of the log file stays zero until the script finishes. Is it possible to directly write to the log file, such that you can follow the progress of the script (e.g. using tail)?   EDIT It turns out that python -u script.py does the trick, I didn't know about the buffering of stdout. What are the options for managing multiple Ubuntu installations together and keeping them in same state Recently I got in charge of managing 2 computer labs (currently 35 workstations, could double in a month or two) in university with total control over software stack as long as I install a bunch of commonly used scientific software (Mathematica and friends).  I plan to use Ubuntu for various reasons.   Installing Ubuntu and managing updates etc by hand is certainly an option, But I want to know if there is a more efficient way to do this stuff in and a more "Don't Repeat Yourself" manner?  Tasks   Ubuntu installation Installation (duplication) of same software stack and configuration over each workstation Keeping them updated Track next Socratic badge progress Just got the  on StackOverflow and, since it can be awarded multiple times, wanted to start tracking progress to the next one, but, the badge is not shown in Available badges to track anymore:    Is it possible to track already awarded badges that can be awarded multiple times? $a+1,a-1$ invertible for nilpotent element Given a ring $R$ (with unity), prove that if $a \in R$ is nilpotent, then $a+1,a-1$ are both invertible.   Suppose $a^n=0$. Then $1=1-a^n=(1-a)(1+a+\ldots+a^{n-1})$, so $1-a$ is invertible.  If $n$ is odd we can use $1+a^n=(1+a)(1-a+\ldots+a^{n-1})$.  But what if $n$ is even? How can you profile a Python script? and other coding contests often have a maximum time to run or people boast of how fast their particular solution runs. With Python, sometimes the approaches are somewhat kludgey - i.e., adding timing code to __main__.  What is a good way to profile how long a Python program takes to run? Solve for $x$: $2^x=4x$ Given that $x$ is a positive integer. By using methods of trial and error as well as plotting two lines: $y=2^x$, $y=4x$ on a graph and find their intersection point, we can easily solve for $x$ which is equal to 4. However, I do not know how to solve this using only equation. Can anyone help me? The  EU book The Rise and Fall of Darth Vader reveals that Vader personally gave the stormtroopers the order to kill Owen and Beru Lars, and that he knew who he was condemning to death before he gave the order:  “Lord Vader,” said one of the sandtroopers, adjusting a control on his helmet so that only Vader could hear his voice.  “The Jawas sold a protocol droid and an astromech to these moisture farmers, but both droids are gone.” Moisture farmers? Intrigued, Vader examined the holograms of the kneeling couple and said, “The farmers’ names?” “Owen and Beru Lars, sir,” the sandtrooper responded. “They say they don’t know where the droids are, but it looks like a landspeeder is missing from their garage.” Owen and Beru, Vader recalled... “Tell Mr. and Mrs. Lars that they seem to have trouble keeping protocol droids on their property.”1 Not certain if he had heard correctly, the sandtrooper said, “Sir?” “Then you may extend to them every courtesy that you showed the Jawas before you continue your search. Establish checkpoints to detain any droids entering Mos Espa or Mos Eisley spaceports. And one more thing.” “Yes, Sir?” “Do not stop transmitting until I break the connection.” “Understood,” said the sandtrooper. Vader watched the sandtroopers carry out his orders on their helpless victims. He found the sight of rising flames — even holograms of flames burning millions of light years away — to be most satisfying.  I had always assumed that the stormtroopers killed the Larses on their own initiative, or in accordance with a previously given order.  The version of events in this book is interesting, but it raises the question of why it took Vader so long to figure out who Luke was. In canon, who gave the order to kill Owen and Beru Lars?  If Vader was involved, did he recognize the couple before he gave the order?  1 A reference to the fact that Anakin took C-3PO from the Lars homestead the last time he was on Tatooine, without informing the Larses that he would do so. What would you consider to be the best exception type to throw when an extension method is called on a null instance (where the extension method does not allow it)? Since extension methods are nothing but static methods you could argue that it should be ArgumentNullException, but on the other hand they're used like instance methods so it might be more natural to use the NullReferenceException. Let's take the following example:  public static string ToInvariantString(this IFormattable value, string format) {     return value.ToString(format, CultureInfo.InvariantCulture); }   This way a NullReferenceException will be thrown if the value parameter is null.   The other example would be:  public static string ToInvariantString(this IFormattable value, string format) {     if (value == null) throw new ArgumentNullException("value");     return value.ToString(format, CultureInfo.InvariantCulture); }   EDIT: In some of the answers you have pointed out that an extension methods can be called like a static method and in those cases a null reference exception would be wrong, which is a great point, and actually one of my concerns, not sure why I forgot to mention that in the question in the first place.   Someone also pointed out that it's wrong to throw a NullReferenceException, and yes, it is. That's why I don't throw it, I just let it happen (let the CLR throw it) by not guarding the method.  I think I favor the ArgumentNullException (that's what I've use so far) but I still think there is at least room to argue for an against the NullReferenceException since it seems more natural in most places where the method is going to be used. proving of inequality $(n!)^2 \leq n^n\cdot n!\leq (2n!)$, where $n\in \mathbb{N}$ How can we prove the inequality $(n!)^2 \leq n^n\cdot n!\leq (2n!)$, where $n\in \mathbb{N}$  $\bf{My \; Try}$::  $1\leq n$  $2\leq n$  $3\leq n$  ....  ....  $n\leq n$  So $1\cdot 2 \cdot 3 ..n \leq n^n$  So $n!\leq n^n\Rightarrow (n!)^2 \leq n^n\cdot n!$  But  did not understand how can we prove $n^n\cdot n! \leq (2n!)$  Help me  Thanks How to share data between forms? The following is an Exercise of Conway's Functional Analysis.   Prove that $X$ is a $\,Banach$ space iff whenever $\{x_n\}$ is a sequence in $X$, such that $\sum \| x_n \| &lt; \infty$, then $\sum x_n$ converges.   I easily can show that if $X$ is a Banach space then $\sum x_n$ converges. My problem is showing that $X$ is a Banach space. For this I suppose that $\{s_n\}$ is a Cauchy sequence in $X$, then I want to make a series. For this I do not have any idea. Please help me. How to make /sbin/shutdown, /sbin/reboot etc. require sudo again in 16.04? For whatever reason, we do no longer need to be root (or using sudo) to run /sbin/shutdown, /sbin/reboot etc.  This seems to be because those executables are now symlinks to /bin/systemctl which handles everything as normal user.  However, what if I want shutdown and reboot to require root authentication again? How can I achieve this? How to change user in WinSCP? I'm using WinSCP to access Unix computers. How can I change user after I have logged into a Unix server using WinSCP?  E.g. I have personal account in Unix computer A. I can log into this computer using PuTTY and then change user to root user  $sudo /usr/bin/su - rootuser   How can I do the same thing using WinSCP? I don't know the password for rootuser. Evaluate the integral: $\int_{0}^{1} \frac{\ln(x+1)}{x^2+1} \mathrm dx$