A fundamental question about charge and speed of a particle
Massless charged particles
Quadratic substitution question: applying substitution $p=x+\frac1x$ to $2x^4+x^3-6x^2+x+2=0$ By using the substitution $p=x+\frac{1}{x}$, show that the equation $$2x^4+x^3-6x^2+x+2=0$$ reduces to $2p^2+p-10=0$.  I can't think of anything that produces a useful result, I tried writing p as $p=\frac{x^2+1}{x}$ and finding areas to substitute but have come with no progress. Could someone offer a slight hint on how to proceed?  Thanks Importing Nodes to D7 with all custom fields I've got a Drupal site with an obscene about of content that has been given to me in CSV format. I'm toying with the idea of building a module to let me do this but if there's one already out there that I can use to just get this site out of the way that would be awesome.  My question is: Is there anything out there that allows you to import a CSV file into D7 that will populate the node table and all the custom fields tables as well?  Thanks. How to change keyboard layout in Lubuntu 15.10? I have recently upgraded my PC from Lubuntu 14.10 to 15.10. Before the upgrade my keyboard layout matched my Danish keyboard. But after the upgrade I probably have a standard English/US layout.   Preferences/Language Support, doesn't let me configure the keyboard layout. Preferences/Keyboard and Mouse, only let me configure stroking delay and similar.    I don't know about iBus and fcitx, as far as the tooltip infomation tells me, its for more complex languages such as Chinese.  I don't have a US icon in the taskbar, no keyboard and/or language icon at all.  Things I have tried:   Running the following in a terminal works, but only until the next reboot:  setxkbmap -layout dk  I got the following parameter in the file /etc/default/keyboard:  XKBLAYOUT="dk"  Installing and running the app Lxkeymap changes the keyboard to Danish when I run it, but rebooting will change the layout back to US.   I don't want anything fancy, I just want to set my keyboard layout to Danish. How can I do that? A friend has been kind enough to lend me a DSLR for a few months.  It's my first foray into DSLR photography, or indeed any kind of photography beyond simply aiming my Canon IXUS at something and clicking the button.    Over the last few weeks, I've been busy studying, practising and trying to learn as much as possible ahead of a planned trip to Norway where I hope to see, and get some photos of, the Aurora Borealis.  I currently have:   Canon Rebel Xsi (450D) Canon 50mm f/1.4 L  Canon 18-55m kit lens Aluminium full height tripod with ball head Cable release Spare battery &amp; memory cards   I'm prepared to spend the night wrapped up outdoors, in the hope that they will make an appearance. I'd like some advice on how to get the most out of this kit for the trip:   How should I go about setting up to get pics of the Aurora?  How might I achieve optimum focus? From what I've read, I'll need to use the tripod and cable release, with IS turned off, on continuous shooting mode with long exposure times. But I'd like some more specific tips in terms of which aperture and ISO settings might work best? Should I use one of the lenses above, or would it be worthwhile renting a better, wide angle lens; if so, which would you recommend? $[S]$ means linear span of S. Then $[S] = [[S]]$ My definition of span:   Suppose a vector space $(V,+,\cdot)$, and       $$S = \{u_1,\cdots,u_n\}$$      (and $S$ is a subset of $V$, not a subspace)      $$[S]=:\bigcap_{W\subset V, W\supseteq S} W$$      In other words, $[S]$ is, by definition, the intersection of all $W$,   such that $W$ is a subspace of $V$ and $W$ contains $S$.   Well, then I need to prove that   $$[S] = [[S]]$$  My strategy:  $[[S]]$ means the intersection of all subspaces that contain $[S]$. If all the subspaces contains $[S]$, so does their intersection. Therefore, $[S]\subset[[S]]$  However, I'm having trouble proving the converse:  $$[[S]]\subset[S]$$  Any hints? I was recently granted German refugee status with a travel document and, in my interview, I told them I would never go back to my home country, Iraq. Now, someone I loved died in my country.  Is it possible for me to leave and return to the Schengen area, using my Iraqi passport? Would German Immigration notice and would it revoke my refugee status?  Would I be able to use both my Iraqi passport and my German travel documents? Would the German authorities know if I did this? What’s the point in having “www” in a URL? Other than for historical reasons, is there is reason to have “www” in a URL?  Should I create a permanent redirect from www.xyz.com to xyz.com, or from xyz.com to www.xyz.com? Which one would you suggest and why? Here's a pickle: reference style links in markdown are fantastic. Numbered footnotes, however, can be a pain. Named references are a beautiful solution, but the editor seems to choke on them in certain contexts, throwing an error:  your post appears to contain code that is not properly formatted as code...  I've looked at a  and tested it out quite a bit and I'm pretty sure line breaking isn't the problem, named references are valid , and I can get multi-word named references to work basically every time (in this post, even). Is there a reason for named references to be seen as improperly formatted code in certain contexts? At the risk of being verbose (but for the sake of completeness), here's the source of the specific question I was trying to post when I encountered the problem: I'm trying to build a [Google Apps Script] that integrates with [Trello], the idea being to use it to push information from spreadsheets and forms into the [Trello API] and create cards on a `pending` list on a certain board.  I found this [question] on here that pointed me in the right direction, and added in OAuth based on the [GAS OAuth Documentation]. The problem is I can't post the the board. I run the script, the OAuth prompt fires, and the script completes with no errors. I can also `GET` data from the private board, so I assume the authorization is working properly.  So, what am I doing wrong that prevents my script from `POST`ing to Trello?  Here's the code I'm working with:      var trelloKey = [Trello API key];     var trelloSecret = [Trello API key secret];     var trelloList = [the id of the list we're posting to];      var oauthConfig = UrlFetchApp.addOAuthService('trello');         oauthConfig.setAccessTokenUrl('https://trello.com/1/OAuthGetAccessToken');         oauthConfig.setRequestTokenUrl('https://trello.com/1/OAuthGetRequestToken');         oauthConfig.setAuthorizationUrl('https://trello.com/1/OAuthAuthorizeToken');         oauthConfig.setConsumerKey(trelloKey);         oauthConfig.setConsumerSecret(trelloSecret);      function createTrelloCard() {        //POST [/1/cards], Required permissions: write       var payload = {'name': 'apiUploadedCard',                       'desc': 'description',                       'pos': 'top',                       'due': '',                       'idList': trelloList};        var url = 'https://api.trello.com/1/cards'       var options = {'method' : 'post',                      'payload' : payload,                      'oAuthServiceName' : 'trello',                      'oAuthUseToken' : 'always'};        UrlFetchApp.fetch(url, options);     }  [Trello]: http://trello.com [Google Apps Script]: https://developers.google.com/apps-script/ [Trello API]: https://trello.com/docs/ [other question]: http://stackoverflow.com/questions/18710641/trello-api-how-to-post-a-card-from-google-apps-script-gas [GAS OAuth Documentation]: https://developers.google.com/apps-script/guides/services/external#making_requests_to_services_with_oauth  If I'm being a complete dunce, please let me know. It seems like one of those errors where it's either a hardcore backend bug or a really stupid user mistake and I'm ready to admit to the latter. What does a "real" quantum computer need for cryptanalysis and/or cryptographic attack purposes? The cryptographic world has been buzzing the word "quantum" for a while now (even the NSA is currently preparing itself for a post-quantum crypto world) and quantum-related hardware engineering is evolving constantly. For example: the 5-qubit quantum computer created at MIT by using the technique of ion traps succeeded in prime-factorizing 15. Does that mean that since it succesfully managed that, that it is a all-purpose quantum computer which could be used for cryptanalysis and/or cryptographic attacks?   If that's not the case, what exactly would a "real" quantum computer need (think: rough description of expected technical abilities, aka specs) to enable its users to use it for cryptanalysis and/or cryptographic attack purposes? And - ignoring rumours about potentially existing but confidential governmental projects - does any such system already exist today? I always thought water sources were called taps in kitchens, bathrooms etc, but a Google search only returned outdoor taps.  So my question is, what are indoor taps really called? Like this one: I'd like to update the label of an operator when it's called. But this :  def execute(self,context):     self.bl_label = "good night"   ... apparently doesn't work if the bl_label property has already been defined. Am I wrong ? What's the best way to develop old, exposed film? A friend of mine just found 3 rolls of exposed 135 (i.e. 35mm) film. They are at least 10 years old. He'd like to know if it is even worth taking them to the local hour photo lab but also if he should give them any special instructions. How to maximize any of the views in quad view? I am new to blender. Pressing &#9096; Ctrl&#9095; AltQ opens the quad view. How to maximize any one of the four views of the quad view? I'm using a BooleanToVisibilityConverter in WPF to bind the Visibility property of a control to a Boolean. This works fine, but I'd like one of the controls to hide if the boolean is true, and show if it's false. How can I attach a file to a post? I want to attach some files to a post on one of Stack Exchange sites. What is the best way to do this? I am taking a course in Mathematical Methods for physicsPhysics (Junior Level).   We are working from   > Mathematical Methods for physicists, George B.Arfken .    I just need online resources covering ( Matrices, Determinants, Vector Analysis, Tensors and differential forms and Vector spaces...etc) to study and understand from. Is there any way to add an ePub book to iBooks without iTunes? I purchased a book and have it in ePub and PDF formats. I can easily add the PDF to iBooks from Safari. However, I can't find a method to get an ePub book into iBooks without iTunes. I'm away from my laptop with iTunes where my iPhone syncs, so that's not an option at the moment.  Is there anyway to add an ePub book to iBooks without iTunes? How to prove that $\lim\limits_{\epsilon\rightarrow 0}\int_{-\infty}^{\infty}f_\epsilon(x)g(x)dx=g(0)$ (Dirac delta function)) I'm currently studying the Dirac delta function using a textbook which unfortunately provides only partial solutions to its explanations. Why does $\lim\limits_{\epsilon\rightarrow 0}\int_{-\infty}^{\infty}f_\epsilon(x)g(x)dx=g(0)$ if $ f_\epsilon=\frac{1}{2\epsilon}e^{-\frac{|x|}{\epsilon}}$? Any help is very much appreciated. What JavaScript keywords (function names, variables, etc) are reserved? Showing $\sup \{ \sin n \mid n\in \mathbb N \} =1$