How do I make an application's user settings persist from one version to the next?
How do you keep user.config settings across different assembly versions in .net?
Relation between magnetic moment and angular momentum -- classic theory How do I prove the relation between the vectors of magnetic moment $\vec\mu$ and angular momentum $\vec L$, $$\vec\mu=\gamma\vec L$$  ?  Many text books and lecture notes about the principles of magnetism show the relation of $\mu$ and $L$ as scalars only and then just state that the relation holds also for the vectors. An example:   $$\mu=I\cdot A = \frac{q}{t}\pi r^2 = \frac{qv}{2\pi rm}m\pi r^2$$  ($I=q/t$: current, $A$: area of a loop, $q$ charge, $t=2\pi r/v$: time of 1 rotation, $v$: velocity of particle, $m$: mass )  The angular momentum is $\vec L = \vec r\times\vec p$ or $L=mrv$ and therefore $$\Rightarrow \mu = {\frac{q}{2m}} L = \gamma L.$$  Why is this also true for the vectors? Is there a general explication by classical physics without the need of quantum theory? Is it the "Stack Exchange Network" or the "Stack Overflow Network"? How to make GRASS and SAGA tools capable to use in QGIS？ I installed QGIS, GRASS and GDAL by OSGeo4w package, and as I finish the installation, I want to use GRASS tool, I face this problem：    But I already installed GRASS and SAGA, how to make those tools in QGIS to be used？ Natural number solutions to $\frac{xy}{x+y}=n$ (equivalent to $\frac 1x+\frac 1y=\frac 1n$) I have a question about the following problem from a Putnam review:  Let $n\in \mathbb{N}$. Find how many pairs of natural numbers $(x, y)\in \mathbb{N}\times \mathbb{N}$ solve $$ \frac{xy}{x+y}=n. $$  I have found some solutions for all $n$, such as $(2n, 2n)$ and $(n+1, n(n+1))$, but I feel as though this is the wrong approach, as the question is only asking for the number of solutions to the equation.  I don't really want a complete solution, but any hints would be greatly appreciated. Why is everybody so concerned about etc/passwd? Here is the content of my vagrant machine of this particular file:  root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/us$ nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin syslog:x:100:103::/home/syslog:/bin/false   Could anybody explain me why it is bad if some evil guy could get this file of my production server? Why is "cupboard" pronounced with a silent "p"? Passing Javascript variable to If gravity is a pseudoforce in general relativity, then why is a graviton necessary? Prove that for every prime $p$, there exists a solution to $(x^2-2)(x^2-6)(x^2-3) \equiv 0 \mod(p)$ So far: I know that$\mod(p)$ is a field thus one of the factors in the expression has to equal $0$ $\mod(p)$ for some $x$. However I just don't know where to continue from this point? How do I approach a congruency like this? Are there any general tips for problems like these?  Thanks for all the help. How To Create A 'Two-Sided' Unique Index On Two Fields? How can I efficiently create a unique index on two fields in a table like this: create table t (a integer, b integer);  where any unique combination of two different numbers cannot appear more than once on the same row in the table.  In order words if a row exists such that a=1 and b=2, another row cannot exist where a=2 and b=1 or a=1 and b=2.  In other words two numbers cannot appear together more than once in any order.  I have no idea what such a constraint is called, hence the 'two-sided unique index' name in the title.  Update: If I have a composite key on columns (a,b), and a row (1,2) exists in the database, it is possible to insert another row (2,1) without an error.  What I'm looking for is a way to prevent the same pair of numbers from being used more than once in any order... When do merchants start paying the actual value of items without bonus effects and perks? So in the image below there are two circles, how can I remove the internal vertices between them without messing up the outside shape. I'm working on a gun and this is just a simple way to illustrate the issue I'm dealing with. If I where to go in and delete the internal faces it would leave holes on the outside of the object, is there a fast way to get around this? An image alt="" text should contain information about that image in the context of the page, so for instance if you have an article about cats on skateboards and then a photograph of the cat on his skateboard you'd probably give it the alt text of alt="Fluffy pulling some mad tricks on his pimped-out board".          &ndash; Wireframes created with   However, what should happen when that image is a link to a page (such as the Wikipedia cat page)?  I don't think there is any point using the title attribute here because screenreaders just ignore that when an alt attribute exists - the only people who would see the title attribute are mouse users who hover over the image, so that excludes keyboard only users too. It's not really any benefit to accessibility to include a title in this situation (Overall the title attribute is a bit useless really).  So, what should the image ALT text say in this case?   states:     Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.    Therefore giving it the alt text of cat article page on Wikipedia is incorrect because that doesn't describe the image, neither does skateboarding cat image that links to the wikipedia article because the alt text should refer to the image itself, not the link associated with it. Send Ctrl+Alt+F1, Crtl+Alt+F7 into VirtualBox My WordPress website currently uses this custom permalink structure: %author%/%year%/%monthnum%/%day%/%postname%  In this case, %monthnum% instantiates numbered dates with a leading zero -- e.g., "09" for September. So, a sample URL might look like this: mywebsite.com/username/2012/09/12/post-name  Is there a function I can add or .htaccess change that I can make which will remove the leading zeros from my permalink stucture? So, using the example above, my URLs would ideally look like this: mywebsite.com/username/2012/9/12/post-name  Thank you! I've read up on WordPress' structure tags documentation (http://codex.wordpress.org/Using_Permalinks), but I can't find any solutions or plugins for the above-mentioned problem. What's the difference between iterating over a file with foreach or while in Perl? I am looking for a textbook that treats the subject of Special Relativity from a geometric point of view, i.e. a textbook that introduces the theory right from the start in terms of 4-vectors and Minkowski tensors, instead of the more traditional "beginners" approach. Would anyone have a recommendation for such a textbook ?  I already have decent knowledge of the physics and maths of both SR and GR ( including vector and tensor calculus ), but would like to take a step back and expand and broaden my intuition of the geometry underlying SR, as described by 4-vectors and tensors. What I do not need is another "and here is the formula for time dilation..." type of text, of which there are thousands out there, but something much more geometric and in-depth.  Thanks in advance. Using OPENQUERY to execute a script I have a SQL Server 2008 instance which I want to use to import data from an Oracle server.  I have set up a linked server that works correctly when running simple queries like SELECT * FROM table. However, if I declare a variable or loop through the rows in a table or anything else inside the OPENQUERY, I get errors.  Is it possible to do this using OPENQUERY? Do I need additional permissions? What is the most convenient way to change options for Graph[] objects? Prove by induction $\sum_{i=1}^ni^3=\frac{n^2(n+1)^2}{4}$ for $n\ge1$ Prove the following statement $S(n)$ for $n\ge1$:  $$\sum_{i=1}^ni^3=\frac{n^2(n+1)^2}{4}$$  To prove the basis, I substitute $1$ for $n$ in $S(n)$:  $$\sum_{i=1}^11^3=1=\frac{1^2(2)^2}{4}$$  Great. For the inductive step, I assume $S(n)$ to be true and prove $S(n+1)$:  $$\sum_{i=1}^{n+1}i^3=\frac{(n+1)^2(n+2)^2}{4}$$  Considering the sum on the left side:  $$\sum_{i=1}^{n+1}i^3=\sum_{i=1}^ni^3+(n+1)^3$$  I make use of $S(n)$ by substituting its right side for $\sum_{i=1}^ni^3$:  $$\sum_{i=1}^{n+1}i^3=\frac{n^2(n+1)^2}{4}+(n+1)^3$$  This is where I get a little lost. I think I expand the equation to be  $$=\frac{(n^4+2n^3+n^2)}{4}+(n+1)^3$$  but I'm not totally confident about that. Can anyone provide some guidance?