How are physics theorems so accurate, relative to fixed measurement systems?
Why isn't it $E \approx 27.642 \times mc^2$?
Do I need a transit visa in Zurich on the way to India? I am travelling from US to India, with an Indian passport but expired F1 visa and going there to get my H1B visa stamping. I have a stop at Zurich for 2 hours while flying to India. Do I need a transit visa for my trip? How to do version numbers? My company is building a product. It's going to be versioned by SVN. It's a webapp so basically there will never be a version out which doesn't have some features in them and thus could always be labeled as beta. But since it's going to be a corporate product I really don't want the "unstable watchout" on there. So how would you go about versioning? Is 1.0 stable? Should the build date be in the version number? Tell me what you guys think! Is it possible to batch import Wavefront .obj to blender? I'm working on 2.69. If I select multiple .obj files, only one gets imported. Also if I hit A on file selection window to select all files (.obj and .mtl) I get an error, nothing gets imported. I have to import several hundreds of .obj into the blender file, is this possible? Oscillation of air particles and speed of sound wave A sound wave is essentially air particles oscillating parallel to the direction of travel of the wave.  We learnt that $v = f\lambda$, where $v$ is the speed of the wave, $f$ is the frequency of the wave and $\lambda$ is the wavelength of the wave.  Suppose the air particles oscillate with a frequency of $f_{particle}$. Is there any relationship between $f_{particle}$ and $v, f, \lambda$ of the entire sound wave?   I thought about this because intuitively, if the air particles vibrated faster, then the wave should travel faster, but I am unable to come up with any formula that describe this relationship (if it is even true!). Is there any function that converts an escaped Url string to its unescaped form? System.Web.HttpUtility.UrlDecode() can do that job but I don't want to add a reference to System.Web.dll. Since my app is not a web application, I don't want to add a dependency for only using a function in an assembly.  UPDATE: Check  about the same issue. Ackermann Function primitive recursive I am reading the wikipedia page on ackermann's function,   And I am having trouble understanding WHY ackermann's function is an example of a function which is not primitive recursive.  I understand that the ackermann function terminates, and thus is a total function. So why is it not primitive recursive? The only information that i can find on the wikipedia page is      [Ackermann's function] grows faster than any primitive recursive function and is therefore   not primitive recursive   Which isn't a good example of why it is not primitive recursive.  Could anyone explain to me how exactly ackermann's function is NOT primitive recursive please? I caught an Eevee, which of its evolutions will it evolve into? So I just caught an Eevee. Now, I need 25 candies to evolve it. The fact is that in the GameBoy color versions, that Pokémon needed a stone to evolve instead of experience. Depending of the stone he was fed with (thunder, water or fire), he was evolving in a different Pokémon.   Is the stone feature also in Pokémon Go? If not, what decide the evolution of this Pokémon?   Bonus point : If it's possible, how can I get a stone? General solution to the PDE $xU_x+yU_y=0$ Solve the equation $xU_x+yU_y=0$.   From Partial Differential Equations: An Introduction, 2nd Ed. (Strauss, pg. 10). There are no boundary conditions.  Solution: The PDE can be written $(x,y)\cdot\nabla U(x,y)=0$, implying that the vector $(x,y)$ is tangent to the PDE's characteristic equation. Then I can write $dy/dx=y/x$, and to solve this ODE,  $$\frac{dy}{dx}=\frac yx \\ \ln y=\ln x+c_1 \\ y=cx \\ y/x=c$$  Hence, the PDE is dependent on $c$ and I can write $U(x,y)=f(y/x)$ for some function $f$, solving the problem.  Question: Is this solution correct? The hint for the question (supplied by the professor) said I should use a substitution of variables, but this seems reasonably valid. '\r' added end of the script command This is my script:  #!/bin/bash hd='pwd' cd $hd   When I try to run it, it fails with:  line 3: cd: $'pwd\r\r': No such file or directory   What is going on? underbrace matrix inside brackets I would like to put an underbrace below the matrix like this:  $$\left(\underbrace{ \left[\begin{array}{ccc}     a&amp;b&amp;c\\     d&amp;e&amp;f\\     g&amp;h&amp;i \end{array}\right]}_{A} \left[\begin{array}{c}     x_1\\     x_2\\     x_3 \end{array}\right]\right)$$     But I don't want the outer brackets \left( and \right) to stretch vertically. I want them to remain as if there was no underbrace. How to achieve that behaviour? When I search for similar questions that I am going to ask, I usually can't find anything through the search box on Stack Overflow. But when I enter my question on the &quot;Ask Question&quot; page, the questions suggested through the &quot;Questions with similar titles&quot; box are usually relevant. Do you experience the same thing? Have red shifted photons lost energy and where did it go? I am able to parse strings containing date/time with time.strptime  &gt;&gt;&gt; import time &gt;&gt;&gt; time.strptime('30/03/09 16:31:32', '%d/%m/%y %H:%M:%S') (2009, 3, 30, 16, 31, 32, 0, 89, -1)   How can I parse a time string that contains milliseconds?  &gt;&gt;&gt; time.strptime('30/03/09 16:31:32.123', '%d/%m/%y %H:%M:%S') Traceback (most recent call last):   File "&lt;stdin&gt;", line 1, in &lt;module&gt;   File "/usr/lib/python2.5/_strptime.py", line 333, in strptime     data_string[found.end():]) ValueError: unconverted data remains: .123 # ~/.profile: executed by the command interpreter for login shells. # This file is not read by bash(1), if ~/.bash_profile or ~/.bash_login # exists. # see /usr/share/doc/bash/examples/startup-files for examples. # the files are located in the bash-doc package.  # the default umask is set in /etc/profile; for setting the umask # for ssh logins, install and configure the libpam-umask package. #umask 022  # if running bash if [ -n "$BASH_VERSION" ]; then     # include .bashrc if it exists     if [ -f "$HOME/.bashrc" ]; then     . "$HOME/.bashrc"     fi fi  # set PATH so it includes user's private bin if it exists if [ -d "$HOME/bin" ] ; then     PATH="$HOME/bin:$PATH" fi   Can anyone explain the contents of the ~/.profile file? So when you enter into the ~/.profile file what does all the writing mean? Suppose $ \alpha, \beta&gt;0 $. Compute:   $$ \int_{0}^{\infty}\frac{\cos (\alpha x)-\cos (\beta x)}{x}dx $$   Here is what I do: $$\begin{align} \int_{0}^{\infty}\frac{\cos (\alpha x)-\cos (\beta x)}{x}dx &amp;= \int_{0}^{\infty}dx\int_{\alpha}^{\beta}\sin (yx)dy\\ &amp;=\int_{\alpha}^{\beta}dy\int_{0}^{\infty}\sin(yx)dx\\ &amp; \\ &amp;   \qquad\text{let $ yx=u $}\\ &amp; \\ &amp;=\int_{\alpha}^{\beta}\frac{1}{y}dy\int_0^{\infty}\sin u du\\ &amp;=\int_{\alpha}^{\beta}\frac{1}{y}dy\left( -\cos u|_{\infty}+\cos u|_0 \right)\\ &amp;=\log\frac{\beta}{\alpha}(-\cos(\infty)+1)\\ &amp;=\log\frac{\beta}{\alpha}-\cos(\infty)\log\frac{\beta}{\alpha} \end{align}$$  But $ \cos(\infty) $ does not exist right? Does it mean the integral actually diverse?  Edit: The question comes from   Who can point out my mistake in the above deduction? Is it possible to keep publishing under my professional (maiden) name, different from my married legal name? Lower bound on energy is potential minimum Suppose we have a particle of mass $m$ that is in an eigenstate $|\psi\rangle$ of the Hamiltonian $\hat{H}=\hat{T}+\hat{V}$, where $\hat{T}$ is the kinetic energy operator and $\hat{V}=V(\hat{r})$ is the potential energy operator. If the potential has lower bound $V_0$, then is it necessary for the energy eigenvalue $E$ of $|\psi\rangle$ to be greater than $V_0$? Classically this is true, since we regard negative kinetic energy as physically unrealizable/meaningless. However, I don't know if I can necessarily say the same in the quantum case. For example, what I'm tempted to do is write  $$\langle\psi | \hat{T}|\psi \rangle = \langle\psi | E-\hat{V}|\psi\rangle$$  and say "If $E&lt;V_0$, then the RHS is necessarily negative, implying the LHS is as well, which we will regard as physically meaningless. If $E=V_0$, then $|\psi\rangle$ is trivial.", but I'm not sure if that's right.   Confused by that, I then wanted to show that, if $E&lt; V_0$, then a non-trivial $|\psi\rangle$ is non-normalizable. However, I'm not entirely sure how to do this. I have a matrix which is kind of symmetrical with the other diagonal, i.e., something like  $$A = \left[ \begin{array}{c c c c}    a &amp; b &amp; c &amp; d \\    e &amp; f &amp; g &amp; c \\    h &amp; i &amp; f &amp; b \\    j &amp; h &amp; e &amp; a  \end{array} \right]$$  Does this matrix have a special name in literature? What are it's properties?  And a matrix that is symmetrical by both diagonals   $$A = \left[ \begin{array}{c c c c}    a &amp; b &amp; c &amp; d \\    b &amp; e &amp; f &amp; c \\    c &amp; f &amp; e &amp; b \\    d &amp; c &amp; b &amp; a  \end{array} \right]$$  What's the name of it? Any interesting properties? Dual boot => Triple boot A 256GB SSD has Windows-10 and 16.04 installed.  BIOS not UEFI.  A charity I work with requires me to use Quickbooks Desktop on Windows.  The plan is to ghost the existing system to a 512GB or larger SSD and create a third bootable Windows 7  partition for performing charity activities.   Is this possible to have a third partition? Is there a good example you have used as a guide? Is triple booting with two Windows partitions different from 2 Linux partitions?   If you have done this before ( with GRUB) please indicate this in your response: lessons-learned are appreciated.  Thank you how to reset gnome panel? I think my gnome-panel is messed up because I alt+right click it and nothing pops up.  I'm on 12.04, classic gnome desktop.  so I used locate and found gnome-panel in .gconf somewhere, how do I clear just gnome-panel's settings so that I can add things to my panel again?   edit:  matt: ~/.gconf $ find|grep -iw panel ./desktop/ibus/panel ./desktop/ibus/panel/%gconf.xml ./apps/gnome-settings/gnome-panel ./apps/gnome-settings/gnome-panel/%gconf.xml