Is electric current just the rate of flow of charges?
Displacement currents, aren't really currents?
Should 'Hi', 'thanks', taglines, and salutations be removed from posts? I edit a lot of posts every day. I often run across posts with 'Hi' and 'Thanks' on the top and the bottom of the post respectively. I also run across things like:     --User   Should these items be removed during the editing of the post by an editor? How do I use the 'scientific' mode in the Calculator? A question about long exact sequence of finite dim vector spaces The plural of "person" is "people".  The plural of "people" is "peoples". Person-people-peoples is the only sequence like this that I know of, but I'm looking for another.  (The equivalent question is, is there another plural noun which has become a singular countable collective noun?)  EDIT  For those of you that think that people is nothing but a collective noun (and not an irregular plural, like mice), I urge you to consider:   Do you treat other collective nouns as plurals?  One person, two people, but one star, two galaxy? Do you treat other plurals as collective nouns?  You can certainly say "a galaxy of stars" but do you say "a mice of mouses"?    For those of you that think the customary plural of person is persons, try it on the next three, uh, persons you see: "Finish this sentence: 'one person, two _ ?' " How come unpolarized light does not undergo destructive interference? Assume $R=(\mathcal{U}_n)_n$ is a sequence of distinct ultrafilters on some set $X$. Since every Hausdorff space has an infinite discrete subspace, there is a subsequence $R=(\mathcal{V}_n)_n$ of $R=(\mathcal{U}_n)_n$ such that $\{\mathcal{V}_n|n \in \mathbb{N} \}$ is a discrete subspace of $\beta X$. In particular, there is a sequence $(A_n)_n$ of sets with $A_n \in \mathcal{V}_m$ if and only if $m =n$. If we let $B_n=A_n - (A_0 \cup...\cup A_{n−1})$, then the sequence $(B_n)_n$ is pairwise disjoint and $B_n \in \mathcal{V}_m$  iff $m=n$. If we let $B =\cup_n B_{2n}$, then $B \in \mathcal{V}_m$ if and only if $m$ is even. In other words, if $B =\{ \mathcal{V} \in βX|B \in \mathcal{V}\}$, then $B$ is a clopen set with $\mathcal{V}_m \in B$ iff $m$ is even. Therefore, we conclude that the sequence $(\mathcal{V}_m)_m$ cannot converge to any point, so the sequence $(\mathcal{U}_n)_n$ cannot converge to any point either.     I would like to know that:      (1) Why "$B_n \in \mathcal{V}_m$  iff $m=n$"? And " $B =\cup_n B_{2n}$, then $B \in \mathcal{V}_m$ if and only if $m$ is even "?      (2)$B$ is a clopen set with $\mathcal{V}_m \in B$ iff $m$ is even Email from IOS with attachments larger than 7.5Mb gets stuck in outbox and constantly tries to resend. Costs us hundreds in data fees Why does this cloth go down past the top surface of the cube? I was following a , and the presenter said that he did not change the default options other than enabling self-collision and increasing the collision object's friction from 5 to 10. His looks like the first image below, but when I tried that, the cloth goes down past the top surface and stops at the bottom surface (second and third images below). Why is it so?   I had a previous problem with cloth, and it was due to the objects' small size. This time, I made sure that both the cloth and the cube are large enough. (Cloth=7.68*8.22*1.99m, cube = 7.68*7.68*0.897m)  The project file can be . Physically Identify the failed hard drive I have a Category entity which has a Nullable ParentId field. When the method below is executing and the categoryId is null, the result seems null however there are categories which has null ParentId value.  What is the problem in here, what am I missing?  public IEnumerable&lt;ICategory&gt; GetSubCategories(long? categoryId) {     var subCategories = this.Repository.Categories.Where(c =&gt; c.ParentId == categoryId)         .ToList().Cast&lt;ICategory&gt;();      return subCategories; }   By the way, when I change the condition to (c.ParentId == null),  result seems normal. How do i make my ubuntu server public? I want to know how to make my ubuntu server ip public. I'm not asking for a domain, if people would be able to access my website by ip, it would be great! (just for now) Does someone have an idea how to do this? What is the purpose of LongLength for .Net Arrays? To make Latin-letter variables bold I can use e.g. \mathbf{a}, but while putting Greek letters or symbols such as \nabla inside \mathbf doesn't cause any errors or warnings, it also doesn't do anything else.  What is the best way to make bold math symbols, in particular Greek letters and \nabla? Starting services in batch file on windows 7 How to insert code with accents with listings? I'm trying to insert source code in LaTeX with using listings, but my code has accents and pdflatex gives me this error:  Unicode char \u8:�\expandafter not set up for use with LaTeX.   This is a code the reproduces the error.  example.tex  \documentclass{article} \usepackage{listings} \usepackage[utf8]{inputenc} \usepackage[spanish]{babel}  \begin{document}  \lstinputlisting[language=C++]{code.cpp}  \end{document}   code.cpp  // Código con una tilde   What can I do to generate the PDF correctly? Show that for any prime $ p $, there are integers $ x $ and $ y $ such that $ p|(x^{2} + y^{2} + 1) $. If we allow that the energy to allow quantum tunnelling through a potential barrier has been borrowed by the Heisenberg energy-time uncertainty relation, from the vacuum energy. How is the borrowed energy paid back? facing difficulty to create dynamic xpath for City field of UTest website I am beginner in automation field, I am trying to automated one of the module, I have tried many different XPATH to fetch proper XPATH for City field o UTest site. Im trying to automate registration module as one of my assignment. I have tried my different xpath example below:  //xpath="//body/div[@class='pac-container pac-logo']/div/span[2]/span" //div[@class='pac-item']/span[3] //div[@class='pac-item']/span //div[@class='pac-container pac-logo']/div/span[2]/../span[3]   the following code written:  //xpath to send data in field @FindBy(xpath="//input[@placeholder='Enter a location']") WebElement city;  //xpath for list to appear @FindBy(xpath="div[@class='pac-item']/span") List&lt;WebElement&gt; City;  public void EnterSignupTwo(String CiTy) throws Exception {     city.clear();     city.sendKeys(CiTy);     Thread.sleep(3000);     System.out.println("the size of List " +City.size());//printing list size      for(int i=0; i&lt;City.size(); i++ ) {         String cities = City.get(i).getText(); //storing list element in String         System.out.println("Converted value of city :"+cities); //print of total list      if(cities.contains(CiTy)) //if parameterized match with Available then click     {         System.out.println("enter specific value of city :"+City.get(i).getText());         City.get(i).click();         break;     } }   kindly refer the I have a shapefile and I want to change the order of the features. Is that possible? I want to sort the features in the shapefile because I'm embedding this shapefile in a mobile app. The app will display a list of features, and although I could do the sorting at load time, I'd prefer to have them sorted. mysql select from n last rows I have a table with index (autoincrement) and integer value. The table is millions of rows long.  How can I search if a certain number appear in the last n rows of the table most efficiently?