What is the unit vector in electric field formula?
Find the Unit Vector of a Three Dimensional Vector
What is the difference between "var=${var:-word}" and "var=${var:=word}"? cardinality of the Borel $\sigma$-algebra of a second countable space Second countability by itself doesn't restrict the cardinality of a topological space, since every set with the trivial topology is a second countable space, but it seems natural to ask whether second countability restricts the cardinality of the Borel $\sigma$-algebra of the space.  Can the cardinality of the Borel $\sigma$-algebra of a second countable space be arbitrarily big? If this is the case is there a simple construction for a second countable space with an arbitrarily big Borel $\sigma$-algebra? Why does my DIY "solar panel circuit" show battery voltage and not solar panel voltage? Calculate the uncertainty in velocity of electron I got this question in one of my periodic test in coaching, I (seemingly) solved the question but later recognised what mess I did.  So, the question is :      Calculate the uncertainty in velocity of an electron. If the uncertainty in its position is ${10^ {-15}} \; \mathrm m$.   By simple calculations one can see that the answer would be ${5.79\times{10^{10}}} \; \mathrm{m/s}$. However, as one can see, the uncertainty in velocity is greater than the velocity of light then how is that possible or there is some other way to handle such problems.  P.S. I know the concept of dynamic mass but I am not very familiar with it. (I think that would work here, but don't know how?) Can a matrix have a null space that is equal to its column space? I had a question in a recent assignment that asked if a $3\times 3$ matrix could have a null space equal to its column space... clearly no, by the rank+nullity theorem... but I have a hard time wrapping my head around the concept of such a matrix, no matter what size, even existing. How could this be possible, and does anybody have an example of such a $m\times n$ matrix? If you look at this picture, how would you describe the mood and the eyes of the character?  I would not say she's angry. I would say she is concentrating to cut the object. However there are many kinds of concentration, and thus the eye expression can differ. This one gives me the feeling that she doesn't accept the existence of the object, and thus must kill it. Cannot install Ubuntu in VirtualBox due to "this kernel requires an x86-64 CPU, but only detects an i686 CPU, unable to boot" error I was trying to install Ubuntu 12.04 in VirtualBox 4.2.12r84980. I see    this kernel requires an x86-64 CPU, but only detects an i686 CPU, unable to boot   But I am using a 64 bit Windows 8, and trying same .iso for trying Ubuntu. Then what is the problem? How do I withdraw a paper from a journal after it was accepted but before it was fully published? On the advice of a senior colleague, I decided that I do not want to publish the paper anymore and with that journal. I wrote the editor several times; he has received the emails, but refuses to reply. I know he gets the emails because if its on other matters he has replied but not on the paper. I am ready to forfeit the processing fee I gave them but they refuse to reply and have already published the abstract of the paper to their site but not the full paper. Is legal action an option and do I have the right to sue? What are the guidelines in matters like these? I've seen this message several times whenever someone has a problem installing, upgrading or removing some piece of software, but I wonder, what does it mean, and more importantly, is possible to solve it?  (Reading database ... 81657 files and directories currently installed.)  Removing mongodb-10gen ...  arg: remove  invoke-rc.d: unknown initscript, /etc/init.d/mongodb not found.  dpkg: error processing mongodb-10gen (--remove):   subprocess installed pre-removal script returned error exit status 100  invoke-rc.d: unknown initscript, /etc/init.d/mongodb not found.  dpkg: error while cleaning up:   subprocess installed post-installation script returned error exit status 100  Errors were encountered while processing:   mongodb-10gen  E: Sub-process /usr/bin/dpkg returned an error code (1)   (the above is just an example, not my actual problem) What is the capacity of this circuit? I simply can't figure out what the capacity of this circuit is.  I can do the math myself, I just need a hint how to create an equivalent circuit where it is obvious what is parallel and what is in series... What is the most efficient way given to raise an integer to the power of another integer in C?  // 2^3 pow(2,3) == 8  // 5^5 pow(5,5) == 3125 Can I programmatically open the devtools from a Google Chrome extension? Similar Matrices and Linear Transformations Cauchy principle value of $\int_{-\infty}^{\infty}\sin(x)/(x-a)dx$ FTP and Apache permission issues How can I solve this quantum mechanical "paradox"? Is there a term for words that when reversed, form other words? I'm aware of what a palindrome is. What do you call words that, when reversed, form other words, such as ton (not) and part (trap)? Unchained Flurry of Blows with Natural Weapons and Feral Combat Training using natural attacks as primary Reading the target of a .lnk file in Python? I'm trying to read the target file/directory of a shortcut (.lnk) file from Python. Is there a headache-free way to do it? The  is way over my head. I don't mind using Windows-only APIs.  My ultimate goal is to find the "(My) Videos" folder on Windows XP and Vista. On XP, by default, it's at %HOMEPATH%\My Documents\My Videos, and on Vista it's %HOMEPATH%\Videos. However, the user can relocate this folder. In the case, the %HOMEPATH%\Videos folder ceases to exists and is replaced by %HOMEPATH%\Videos.lnk which points to the new "My Videos" folder. And I want its absolute location. On my Toshiba Encore 8 Tablet I noticed that the CPU usage is very high. In Taskmgr / ProcessExplorer, I can see that OneDriveSetup.exe is hogging 1 CPU cores heavily for hours.    How an I solve this hang and finish the OneDrive Update?