How to do email address validation using Javascript (without JQuery)?
How to validate an email address in JavaScript
What are recommended, general strategies to start block-cipher design and/or analysis? I (and many others for that matter) have always been fascinated by the inner workings of the modern building block of cryptography: block ciphers.  Now, the ressources on the "black art" of design and analysis of these ciphers are sparse; especially for the entry level. Available information like  seems to be somewhat outdated (due to its age).  What's the general consensus of the “best” (read: recommended) strategy to start designing and/or analyzing modern cryptographical block ciphers?    Nota bene: Think of this as a general, wiki-alike question – for learning purposes only. (Besides that, this Q&amp;A would represent a place we can point people to when alike algorithm design questions arise.) Ubuntu 14.04: very slow UI in Oracle VirtualBox Short summary: 14.04 is much slower than 12.04 even with more RAM assigned.  I'm using latest VirtualBox 4.3.10 on Mavericks 10.9.2. How can I make it faster? How to dynamically create a local variable? Find the maximum value of the expression ${\frac {x}{1+x^2}} + {\frac {y}{1+y^2}}+{\frac {z}{1+z^2}}$. Find the maximum value of the expression :   $${\frac {x}{1+x^2}} + {\frac {y}{1+y^2}}+{\frac {z}{1+z^2}}$$   where $x,y,z$ are real numbers satisfying the condition that $x+y+z=1$.   Taking $x=y=z=\frac {1}{3}$, I get the expression as $\frac {3x}{1+x^2}$, which is equal to $\frac {1}{1+{\frac{1}{9}}}$ or $\frac {9}{10}$.  How can I actually solve the problem without making unnecessary assumptions ? How long does it usually take for published articles to show up on Google Scholar? The title pretty much says it all - what's the typical delay with which Google Scholar indexes newly published articles? (Note I'm not talking about citations, but about the article showing up at all.)  Edit: the article in question went for over six months after being published (in a well-regarded Springer journal with its own Wikipedia page) without appearing on Google Scholar, until it received a citation, at which point it was added to Google Scholar almost immediately. One more motivation to write papers that get cited. :)  Edit 2: Another article in an even more mainstream journal took a little over seven weeks. Redirect everything from old domain to new domain I need to (permanent) redirect all of the following:   www.example.com www.example.com/folder sub.example.com sub.example.com/folder   Basically, all URLs that are reachable without being intended to: www.new-example.com, I want to do this within Apache and using the mod_rewrite module via the .htaccess file. What does it mean to "program to an interface"? I have seen this mentioned a few times and I am not clear on what it means. When and why would you do this?   I know what interfaces do, but the fact I am not clear on this makes me think I am missing out on using them correctly.   Is it just so if you were to do:  IInterface classRef = new ObjectWhatever()   You could use any class that implements IInterface? When would you need to do that? The only thing I can think of is if you have a method and you are unsure of what object will be passed except for it implementing IInterface. I cannot think how often you would need to do that.   Also, how could you write a method that takes in an object that implements an interface? Is that possible? One page website - Effect on SEO I'm considering re-designing my personal website to promote my web services in my local area.  My issue is whether to do a one page website with a scroll-to navigation system. What effect does this have on SEO. As i understand it, you set stuff like h1's and meta description on specific page content. How does this work when all of your different content is on one page? How can I measure the execution time of a terminal process? I'm trying to measure the execution time of a process that I call via the command line (i.e., I want to find out how long it takes to for the process to finish). Is there any command that I can add to the command calling the process that will achieve this? As my question says,   $$\frac 1{1.2.3}+\frac 1{2.3.4}+\frac 1{3.4.5}+...$$  As far as $\frac 1{1.2}+\frac 1{2.3}+\frac 1{3.4}+...$ is concerned, we can write it as $\frac 1{n-1} - \frac 1{n}$ What can we do here? How to do joins in LINQ on multiple fields in single join Can the default font be changed? I have been playing with the settings for the text object recently, and every time I add a new text object, I need to change the font to my favorite one. (Eurostile LT ExtendedTwo) Is there any way to change the default font so I do not need to change it every time I add a new text object?   Example: All Stack Exchange data dumps The original ClearBits link to the September 2011 data dump has broken. How can I access it and other previous data dumps? The Internet Archive only has . How do I get from Terminal 1 to Terminal 5 in Fiumicino Airport? I realise it's unlikely that posting the file would cause a problem. However, since I know nothing about what a what's in a minidump file I thought I should check. How can I center a too wide table? I have a document containing a table which is slightly too wide for the page. But instead of growing to the right side only, I would like to have it centered on the page.  I have tried to use the center environment but this doesn't seem to help. The error: "mount: only root can do that" while mounting a partition I've installed Ubuntu 12.04 along with Windows 8.1. When I tried to open the C: drive in Ubuntu a window is popping out saying to run this command:  mount -t ntfs-3g -o remove_hiberfile /dev/sda2 /media/2A36EE3236EDFEA7   After running the command I'm getting the error mount: only root can do that.   What should I do? I am comfortable with the different sizes of infinities and Cantor's "diagonal argument" to prove that the set of all subsets of an infinite set has cardinality strictly greater than the set itself. So if we have a set $\Omega$ and $|\Omega| = \aleph_i$, then (assuming continuum hypothesis) the cardinality of $2^{\Omega}$ is $|2^{\Omega}| = \aleph_{i+1} &gt; \aleph_i$ and we have $\aleph_{i+1} = 2^{\aleph_i}$.  I am fine with these argument.  What I don't understand is why should there be a smallest $\infty$? Is there a proof (or) an axiom that there exists a smallest $\infty$ and that this is what we address as "countably infinite"? or to rephrase the question "why can't I find a set whose power set gives us $\mathbb{N}$"?  The reason why I am asking this question is in "some sense" $\aleph_i = \log_2(\aleph_{i+1})$. I do not completely understand why this process should stop when $\aleph_i = \aleph_0$.  (Though coming to think about it I can feel that if I take an infinite set with $\log_2 \aleph_0$ elements I can still put it in one-to-one correspondence with the Natural number set. So Is $\log_2 \aleph_0 = \aleph_0$ (or) am I just confused? If $n \rightarrow \infty$, then $2^n \rightarrow \infty$ faster while $\log (n) \rightarrow \infty$ slower and $\log (\log (n)) \rightarrow \infty$ even slower and $\log(\log(\log (n))) \rightarrow \infty$ even "more" slower and so on).  Is there a clean (and relatively elementary) way to explain this to me?  (I am totally fine if you direct me to some paper (or) webpage. I tried googling but could not find an answer to my question) Silencing "Your disk is almost full" notification Linear Transformations: Proving 1 dimensional subspace goes to 1 dimensional I am having trouble understanding this whole question, and how to prove it.  Let $F:\mathbb{R}^n\to\mathbb{R}^m$ be a linear transformation. Prove that if $L$ is a $1$-dimensional subspace of $\mathbb{R}^n$, then  $F(L)=\{y\in\mathbb{R}^m: y=F(x)\text{ for some }x\in L\}$  the image of $L$ under $F$ is a subspace of $\mathbb{R}^m$ with dimension $1$ or $0$. Hence prove that if the kernel of $F$ is $\{0\}$, then the image of $L$ is a $1$-dimensional subspace of $\mathbb{R}^m$ (and so, in this case, $F$ takes lines in $\mathbb{R}^n$ to lines in $\mathbb{R}^m$).