Stuck in US due to coronavirus - travel visa will expire before flights are available
What to do when visa admission expires during lockdown?
I sometimes get files from my clients that have the wrong file extension. For example, the name is image.jpg but the file is actually a TIFF image. In many cases I can clarify it by opening the file in a text editor, looking at the first few bytes, then deducing which file type it is.  This works for me with JPEG, TIFF, GIF and PDF files. However there are many more file types out there.  Is it possible to automate identification of the correct file type by analyzing the containing data? Physical meaning of this integral in $k$-space I am trying to solve an integral in $k$-space where I want to calculate the ratio of the average energy of an arbitrary electronic band ($E(k)=k^n)$ to the square of average group velocity of electrons($v_g   = k^{n-1})$ approximately in the form of this expression given by $$L=\frac{\frac{\sum_{\mathbf{k}}k^{n}}{\sum_{\mathbf{k}}1}}{\left(\frac{\sum_{\mathbf{k}}k^{n-1}}{\sum_{\mathbf{k}}1}\right)^2}\;.$$  Now, I want to do this for $d$-dimensions, so I convert this sum to integral.  $$L=\frac{\dfrac{\int_{0}^{k_f}k^{n} d^d k}{\int_{0}^{k_f}1d^d k}}{\left(\dfrac{\int_{0}^{k_f}k^{n-1}d^d k}{\int_{0}^{k_f}1d^d k}\right)^2}$$ where $d^dk  = \dfrac{d \pi^{d/2}}{\Gamma(\frac{d}{2}+1)}k^{d-1}dk$ is the volume element in $d$-dimensional space.  I want to get a simple expression for $L$ and how it depends with $k_f,n$ and $d$. any physical insight into this integral could also be helpful. I have these two CREATE TABLE statements:   CREATE TABLE GUEST (   id int(15) not null auto_increment PRIMARY KEY,   GuestName char(25) not null );  CREATE TABLE PAYMENT (   id int(15) not null auto_increment   Foreign Key(id) references GUEST(id),   BillNr int(15) not null );   What is the problem in the second statement? It did not create a new table. "#include" a text file in a C program as a char[] How to share an encrypted storage on Windows, Mac OS X and Linux in a secure way I got a 2 TB drive that I have to use with both Windows 8.1 / Windows 10 and Yosemite to OS X / OS X El Capitan and maybe even on Linux.  I need to encrypt the volume. Or rather, I want to create two partitions: a 1.7 TB encrypted and unencrypted the remaining space.  Now I use Windows BitLocker to 512bit. On Mac and Linux nothing, obviously.  What do you recommend?  I saw TrueCrypt (and I read about all the confusion created after May 2014), of VeraCrypt, of GNUPG, Disklocker to read BitLocker on Unix.  But I feel lost and without a good idea.  And if I use TrueCrypt 7.1a waiting for new solutions such as precautions to prevent memory dumps and other potential crack?  And then how should I use TrueCrypt to format the drive? In GPT? MBR? Journaled? FAT? Prove that $\mathbb Z^n$ is not isomorphic to $\mathbb Z^m$ for $m\neq n$ Prove that $\mathbb Z^n$ is not isomorphic to $\mathbb Z^m$ for $m\neq n$.   My try:  Let $\mathbb Z^n\cong \mathbb Z^m $. To show that $m=n$.  Case 1: Let $m&gt;n$. Now that $\mathbb Z^m$ has $m$ generators whereas $\mathbb Z^n$ has $n$  generators and an isomorphism takes a generator to generator ; that is the contradiction.  Please correct me if I am wrong.  The case  $m&lt;n$ also follows similarly. Cannot log into Area 51 with OpenID Resolve the error "An illegal choice has been detected..." In a dual boot system, how does the BIOS choose which bootloader to run? I have a dual boot of Windows and Ubuntu. When I switch on the machine, the BIOS does POST and after that the bootloader starts.  I want to understand how the BIOS chooses which bootloader to run. I want to know the process going on between the BIOS and the bootloader in a dual boot computer. "I wish I didn't do" vs. "I wish I hadn't done" Unique quadratic subfield of $\mathbb{Q}(\zeta_p)$ is $\mathbb{Q}(\sqrt{p})$ if $p \equiv 1$ $(4)$, and $\mathbb{Q}(\sqrt{-p})$ if $p \equiv 3$ $(4)$ Difference between the i386 download and the amd64? What is the difference between standard i386 download and the amd64 download of Ubuntu 11.04? I am currently running the i386 on an amd machine, would my system work better with the amd64 download instead? (my machine was running Windows 7 64bit, but I neglected to look at that prior to installing Ubuntu). doesn't has to /have to How to do integer & float calculations, in bash or other languages/frameworks? Using echo "20+5" literally produces the text "20+5".  What command can I use to get the numeric sum, 25 in this case?  Also, what's the easiest way to do it just using bash for floating point? For example, echo $((3224/3807.0)) prints 0 :(.  I am looking for answers using either the basic command shell ('command line') itself or through using languages that are available from the command line. I'm running Bash scripting, but sometimes I get confused which of these commands I use belong to who. Sometimes man xxx works, sometimes doesn't, so I use --help or info, mostly one of these works to show description of the command. Can anyone tell me how I would know what command belongs to what? Bash builtin, GNU utility, etc. I am Indian passport holder living in Hungary for 4 years and I have been issued a Temporary residence permit (EU Schengen).  Can I go to visit Dublin without any visa, or do I need to apply for a UK visa? I know Ireland still in Schengen but part of United Kingdom. How do I prevent the blank screensaver when using keyboard shortcut to lock the computer? Quantum teleportation - the alternative to destroying atoms Can't you just disassemble, not destroy our atoms and transport them to another teleporter via networking or telecoms?  This is my thinking of how to keep the same person, not an exact copy of him/her, alive when teleporting.  Please answer to tell me if it's possible or not. How are Clash of Clans multiplayer battles determined Are battles determined by level or trophies? Just curious. Limit- almost finished, however hint needed.