Intuitively proof that intensity of a wave is proportional to the square of its amplitude
Why is energy in a wave proportional to amplitude squared?
Excel function that evaluates a string as if it were a formula? How to download a file using Selenium's WebDriver? Basically I want to at least check that a download-able file exists / download link works and preferably get stuff like the file size too. Here's an example: link = self.browser.find_element_by_link_text('link text') href = link.get_attribute('href') download = self.browser.get(href) print download  That fourth line prints &quot;None&quot;, presumably because I haven't manually clicked the Save button, and even if I had, I doubt WebDriver would be able to &quot;see&quot; the file. Any ideas? I'm using Firefox as my browser-under-test, and I understand that the file handling for downloads is somewhat browser and/or OS-specific. Getting inverse of a transposition key How do I get the icon associated with a file type? I have a form that displays file information in a TabControl, and I'd like the pages to have the file's icon in their tab.  How do I get the icon associated with a file type?  I'd prefer solutions that don't involve looking things up in the registry, but if that's the only way then so be it. alias fo rm command ( cp comand issue ) In the double-slit experiment of electrons (observed by photons), is it correct to say the collapse is caused by the momentum of the photons? I'm working off the article, . I think it's well-written, but I'm not convinced about this part:     So what is causing the change in the particle’s behaviour?      In the example given above, when electrons are fired at a fluorescent screen, when we bombard the electrons with photons the interaction changes the state of the system catastrophically as, despite lacking mass, photons do carry momentum.   Here the author strongly implicates the momentum of photons as being responsible for the collapse. But is that correct to say?  I have read that the  verified that obscuring which-way information restores wave-like behavior. So it feels to me it's more about some "outer" state (perhaps well-characterized as "information") that we don't yet understand that collapses the system, not per se the photon-electron interaction.  Or am I wrong, and in fact for example, the process of obscuring in the quantum eraser experiments somehow "undoes" the photon-electron interaction or restores the quantum state through another interaction? Person, Persons, People, Peoples Minimum Length Regular Expression Is Ubuntu based on Debian unstable or Debian testing? which of the two it is? A mysterious app named &quot;10102&quot; shows up in my data usage. It bears only the standard Android app icon (the Bugdroid logo with a cube on its torso). From what the graph tells me, it has used 36 megabytes of data in the background and zero on the foreground. I think I haven't uninstalled anything for months. Is it malware? I haven't sideloaded anything and only authorized my laptop as a USB debugger. If it's malware, how do I remove it? I have no idea how to find its package name and 10102 isn't in the list of downloaded apps in settings. I'm running stock &amp; never-been-rooted Android 4.4.4 on Nexus 4. I have written an essay last year, as a personal exercise. I now have a course at uni on the topic and could basically just hand in this essay now, the topic fits perfectly. I have also never submitted this essay to any other course or so.  Could I just hand in this essay, or would I violate some rules with that? Is this maybe already self-plagiarism? Solve for $f(x)$ if $f(f(x))=6x-f(x)$ If $f: [0,\infty) \rightarrow [0,\infty)$ and   $f(f(x))=6x-f(x)$ $f(x)&gt;0$ $  \forall x \in (0,\infty) $   Find f(x) show that every continuous real-valued function defined on $S_{\mathbb{\Omega}}$ is eventually constant We've been talking a lot about the efficacy of community self-evaluations lately, both internally on the Community Team and out in the open . Lots of ideas were tossed around, but the underlying theme of these discussions has been that site self-evaluations are not useful in their current form. The review queue format hampers discussion, the meta thread posted by the Community user is trivially ignored, and the sample question size is far too small to be useful, but big enough to be non-trivial for participants. They also don't provide much in the way of useful information to community managers behind the scenes.  So we're going to shut them down this week, and we'll be using the time it saves us to digest the ideas y'all have thrown out in the previous discussions and figure out where to go from here.   I'll be going over the previous threads with a fine-toothed comb to try and suss out what worked well and what was broken and determine a more useful mechanism - if one is required at all. I'd also welcome continued suggestions from the communities about how to continue capturing what the evals accidentally did right - encouraging communities to stop and examine how they're doing at somewhat regular intervals.   So: if you have ideas on how to get communities to monitor their own Q&amp;A quality and get a little introspective, feel free to sound off in the answers.  Update: with a creative application of per-site feature toggles, we've shut down evaluations except on a handful of sites where they're currently running. Once those evaluations run their course, no new ones will be started anywhere on the network. Why are imported PDFs blurry in InDesign? Show that $f$ is differentiable on $(−1, 1)$. Let $f$ be a function defined on the interval $(−1, 1)$ such that for all $x, y \in (−1, 1)$, $$f(x + y) = \frac{{f(x) + f(y)}}{{1 - f(x)f(y)}}.$$ Suppose that $f$ is differentiable at $x = 0$, show that $f$ is differentiable on $(−1, 1)$.  Need your kind guidance and help. Thanks in advance! What does it mean when Git says 'rewrite' or 'rename' in a commit message? Isomorphism of quotient modules implies isomorphism of submodules? Let $A$ be a commutative ring, $M$ an $A$-module and $N_1, N_2$ two submodules of $M$.  If we have $M/N_1 \cong M/N_2$, does this imply $N_1 \cong N_2$?  This seems so trivial, but I just don't see a proof... Thanks! Help me understand Bayesian prior and posterior distributions In a group of students, there are 2 out of 18 that are left-handed. Find the posterior distribution of left-handed students in the population assuming uninformative prior. Summarize the results. According to the literature 5-20% of people are left-handed. Take this information into account in your prior and calculate new posterior.    I know the beta distribution should be used here. First, with $\alpha$ and $\beta$ values as 1? The equation I found in the material for posterior is   $$\pi(r \vert Y ) \propto r^{(Y +−1)} \times (1 − r)^{(N−Y +−1)} \\ $$  $Y=2$, $N=18$  Why is that $r$ in the equation? ($r$ denoting the proportion of left-handed people). It is unknown, so how can it be in this equation? To me it seems ridiculous to calculate $r$ given $Y$ and use that $r$ in the equation giving $r$. Well, with the sample $r=2/18$ the result was $0,0019$. The $f$ should I deduce from that?  The equation giving an expected value of $R$ given known $Y$ and $N$ worked better and gave me $0,15$ which sounds about right. The equation being $E(r | X, N, α, β) = (α + X)/(α + β + N)$ with value $1$ assigned to $α$ and $β$. What values should I give $α$ and $β$ to take into account prior information?  Some tips would be much appreciated. A general lecture on prior and posterior distributions wouldn't hurt either (I have vague understanding what they are but only vague) Also bear in mind I'm not very advanced statistician (actually I'm a political scientist by my main trade) so advanced mathematics will probably fly over my head. How to really clear the terminal? I can issue the clear command or press Ctrl + L to clear the current Ubuntu terminal, but this just shifts previous output upwards and if you use mouse scroll or PgUP and PgDown keys it's hard to distinguish where the output of previous command ends and output of current command begins.  Is there a way to really clear the terminal so I won't see previous command results?