If electron (or other charged particle) is accelerated by gravity (a very weak force), it should emit electromagnetic radiation. Is there any experimental evidence that gravity does indeed cause such emissions?
A charged particle undergoing an acceleration radiates photons.  Let's consider a charge in a freely falling frame of reference.  In such a frame, the local gravitational field is necessarily zero, and the particle does not accelerate or experience any force. Thus, this charge is free in such a frame. But, a free charge does not emit any photons. There seems to be a paradox. Does a freely falling charge in a gravitational field radiate?
Is there a way to retrieve the user id of @mention user from chatter post in Apex? We can write a before insert trigger on feeditem, but when we display the body (which has @mention user) it simply displays as text. Is there any workaround for this? Right now  is fairly broken -- it's a simple descending sort by views. As Joel said , it is &quot;a self-fulfilling prophecy.&quot; But this is not intentional, it's only because we haven't had time to improve it yet! As I sit down to write a better algorithm, I thought you guys might have some insight into what would make a good formula to determine the &quot;hot&quot; questions -- over the last 24 hours, the last week, the last month, and all time. Here are the variables we have to work with:  Votes [aka Score] Views Answers Answer Votes [aka Score] Whether the question has an accepted answer or not Time question was originally asked Time of last activity on question Reputation of asker Reputation(s) of answerers  Joel cited the reddit formula as an example, but I think our site is a little different than just a basic link submission site. Plus, we have more variables and data to work with. I found a  describing a few formulas: Y Combinator Hacker News  (p - 1) / (t + 2)^1.5 p = votes (points) from users t = time since submission in hours  Reddit  t = (time of entry post) - (Dec 8, 2005) x = upvotes - downvotes y = {1 if x &gt; 0, 0 if x = 0, -1 if x &lt; 0) z = {1 if x &lt; 0, otherwise x} log(z) + (y * t)/45000  Thoughts? Ideas? I don't want to overthink this; I just want the &quot;hot&quot; questions to be relevant and useful to us. So the simpler the algorithm the better! Based on my analysis of the above and the comments so far, here's the second version of what I have implemented so far. This might suck. I don't know:  (log(Qviews)*4) + ((Qanswers * Qscore)/5) + sum(Ascores) -------------------------------------------------------- ((QageInHours+1) - ((QageInHours - Qupdated)/2)) ^ 1.5  Note that accepted answers weight not at all in hotness. This is intentional, as I feel accepted answers are a fine social contract, but not a good data point for question or answer quality. This algorithm will heavily favor questions with LOTS of answers, as the sum(Ascores) are now included -- one assumes if there are lots of answers, there will be a lot more voting on the answers, too. Update: Note that this formula is what is used on the  linked from the homepage of each site. It is not the formula used to determine the  list. See . Alternative ways to say "if and only if"? There are some scenarios about which I would like to get some confirmation:   when defining a concept A,      We call A, if ... [definition of   concept A]   Does "if" here mean equivalence instead of just sufficiency? Is it incorrect to replace "if" with "if and only if"?    For precisely what condition is    B satisfied?   Does "precisely" mean asking for necessary and sufficient condition for B? Some other ways to say "if and only if" / "necessary and sufficient"?   Some references that summarize some standard terminologies in Mathematics  such as this one?  Thanks and regards! How do I install wine? "Examine whether the given progressions converge (eventually improperly) and determine their limits where applicable.  (a) $$(a_n)_{n\in\mathbb{N}}:=\frac{n^n}{n!}$$  [...]"  I am having problems getting this homework done as I have no clue about convergency at all. Through Mathematica I know that $\lim\limits_{n\to\infty}a_n=+\infty$ however I don't know how to proove it! During my research I found out that for sufficient big $n$ the inequality $x^n\leq n!\leq n^n$ for $x\in\mathbb{R}$ and $n\in\mathbb{N}$ is true. However this doesn't help me at all. Having a look at our lecture notes I developed the following statement: every $x^n$ with $|x| \geq 1$ diverges as $x^n$ is unbounded and therefore has the improper limit $\lim\limits_{n\to\infty}x^n=+\infty$. Furthermore it seems obvious to me that I need to express the terms in a simpler way, like fractions converging to 0 etc, but I don't know how. Neither some work with the $\varepsilon$-definition of limits in combination with the triangle inequality helped me out. Any suggestions or hints?  Information: This is "Analysis for computer scientist" and therefore we haven't "officially" learned any fancy tricks like L'Hôpital's rule etc. just basic properties of $\mathbb{R}$ and some inequalities as this is an introductory lecture. Extra }, or forgotten \right My MWE:  \documentclass{report}  \usepackage{amsmath}  \begin{document}  \begin{align} y &amp;= a \\ =&amp; -2c_1\bar{z}_1^2 + 2\bar{z}_1\bar{z}_2 + 2\bar{z}_2 \left ( -\bar{z}_1 -c_2z_2 - \frac{3\epsilon}{2}\bar{z}_2 -\sigma_{2,1}\cos(x_1)\Delta x_1 \notag \right. \\ \left. &amp;- \sigma_{2,2}\Delta x_2 -\sigma_{2,3} \Delta u +c_2 \chi_2 \vphantom{\frac{1}{1}} \right ) - 2\gamma \sigma_{2,1}^2\cos^2(x_1) \Delta x_1^2 - \gamma \sigma_{2,2}^2 \Delta x_2^2   - 2\gamma \sigma_{2,3}^2 \Delta u^2 \end{align}  \end{document}   The error I get:  Extra }, or forgotten \right.   The expected result: Moving status bar in iOS 7 A word that means stage-fright, but for a person? Suppose you met a famous person, and you were shy and anxious and almost overwhelmed by them.   Is there a word for describing that? Similar to getting stage fright, or "choking", except in this case for a person?     When he said hello to me, I couldn't respond. I (was) __________. Lie Algebra of U(N) and SO(N) U(N) and SO(N) are quite important groups in physics. I thought I would find this with an easy google search. Apparently NOT! What is the Lie algebra and Lie bracket of the two groups? Rotate photo in moderncv I'm doing my CV with the template ModernCV Classic. I want to rotate my picture but the command used is \photo I don't know how to do that.  \documentclass[11pt,a4paper,sans]{moderncv}  \moderncvstyle{classic} \moderncvcolor{blue} \nopagenumbers{}  \usepackage[utf8]{inputenc}  \usepackage[latin1]{inputenc} \usepackage[T1]{fontenc} \usepackage[francais]{babel}  \usepackage[scale=0.75]{geometry}  \name{John}{Doe} \title{...} \address{adress}{Town}{Country}  \extrainfo{age, nationality} \phone[mobile]{54466145745} \email{john.doe@mail.com} \photo[80pt][0.4pt]{Photo.jpg} \quote{Objectifs: ...} What PDF Editors are available on Ubuntu? I was wondering if there is a pdf reader-writer-publisher-editor that can add text, highlight, shapes and general edit an existing pdf document.  Something like Nitro in windows. How are bones & armatures connected to the rest of a model? Let's say I'm really new to Blender, and have just barely figured out what keyframes are for. Explain a Blender skeleton to me like I'm five. Do I need to use it, and how exactly does it connect to the rest of the model? Color Transfer from colored image into grayscale image Best lens for taking pictures of surfers C# difference between == and Equals() VSE isn't multi-threading Whenever I render a video using the blender video editor only one core is ever used at any time. I have an 8 core CPU(FX-9590) yet regardless of whether blender is set to auto detect or a fixed 8 threads only one core ever sits at 100% at any given time. The rest of the cores sit and really low usage as if blender is completely ignoring them. I'm running blender 2.77a on Linux. I'm using Theora as the codec with an ogg container and Vorbis audio. How do I get blender to use all my cores? Is it physically possible to build a long zoom (17-300 mm for example) at an aperture value of around 1.4 or 1.2? I'm curious if the physics allow a company to build such a lens of course with good IQ, minimal color aberration, maximum sharpness, and little to none lens vignetting or edge softness Is there any simple method to calculate $\sqrt x$ without using logarithm Suppose that we don't know logarithm, then how we would able to calculate $\sqrt x$, where $x$ is a real number? More generally, is there any algorithm to calculate $\sqrt [ n ]{ x } $ without using logarithm? More simple techniques would be nice.  Here is a simple technique used to approximate square roots by :  For example: $\sqrt {78}\approx 8\frac { 14 }{ 17 } $ , where $8$ is the nearest integer root of $78$, $14 = 78 - 8^2$, $17 = 2 \times 8 + 1$.  if $n=2^k$ we can use the method above.   For example, for $k=2$ Lets calculate $\sqrt [ 4 ]{ 136 } $: $$\sqrt [ 4 ]{ 136 } =\sqrt { \sqrt { 136 }  } \approx \sqrt { 11\frac { 136-{ 11 }^{ 2 } }{ 11\times 2+1 }  } =\sqrt { 11\frac { 15 }{ 23 }  } \\ \sqrt { 11\frac { 15 }{ 23 }  } \approx 3\frac { 11\frac { 15 }{ 23 } -{ 3 }^{ 2 } }{ 3\times 2+1 } =\frac { 544 }{ 161 } =3.38\\$$ The exact result is$$ \sqrt [ 4 ]{ 136 } =3.4149\cdots$$ The method approximates well, but it is working for only $n=2^k$ as I know. I have two questions. First, which command lists files and directories, but lists directories first?  Second question: I want to copy a list of files into a single directory, but make the target directory the first filename in the command. How to select distinct field values using Solr?