Quantum Field interaction transferred via "exchanging fermions"
Is there some special case where a fermion can mediate a force?
How do amortization schedules work and when are they used? Specifically, I notice that on a mortgage statement, my payment is "amortized" so that at the beginning of the loan, I am paying almost entirely interest and very little principal.  However, on a credit card balance, it seems interest is only charged on the balance.  Why do amortization schedules work the way they do, and are they typically used for most loans, and why? Uniform convergence of $f_n(z)=nz^n$ in the set $|z|<\frac{1}{2}$ I'm loading an XML document in my C# application with the following:  XDocument xd1 = new XDocument(); xd1 = XDocument.Load(myfile);   but before that, I do test to make sure the file exists with:  File.Exists(myfile);   But... is there an (easy) way to test the file before the XDocument.Load() to make sure it's a valid XML file?  In other words, my user can accidentally click on a different file in the file browser and trying to load, say, a .php file causes an exception.    The only way I can think of is to load it into a StreamWriter and simple do a text search on the first few characters to make sure they say "  Thanks!  -Adeena Best way to find all factors of a given number I want to copy a live production database into my local development database.  Is there a way to do this without locking the production database?  I'm currently using:  mysqldump -u root --password=xxx -h xxx my_db1 | mysql -u root --password=xxx -h localhost my_db1   But it's locking each table as it runs. Bake Simple Deform animation into mesh for Unity3D export? I'm trying to use a .blend file with a keyframe animation on the angle of a Simple Deform modifier in Unity3D. Unity3D however does not know how to handle modifiers and hence cannot play the animation.  How can I bake/save the animation to the .blend file so that Unity3D can play it? Initial capitalization of foreign surnames when starting a sentence Alternative for Notepad++? Accessing the index in 'for' loops? I'm using an old iBook G4 (PowerPC) running Tiger to serve iTunes to the house. For the past week or so, the mac boots fine, and then sometime during the day starts generating   An unexpected error occurred (error code -50).   errors when iTunes attempts to save its library file.  Checking reveals that the boot drive (main drive, in the laptop) behaves as if it is write-protected - I get the same error code when I attempt to create a folder on the desktop, for instance. If I attempt to create files via the terminal, e.g. via     ls > foo.txt I get an "invalid argument" error.   I've set the iBook to run in Target Disk Mode and run Disk Utility to repair the disk (from a Macbook running Snow Leopard) and get "The volume appears to be ok".   I don't have the option in Disk Utility to Repair Permissions in Target Disk Mode. When I ran Repair Permissions on the iBook itself, it came back with no errors, no permissions corrected, but did not in fact fix the problem.  Rebooting always solve the problem - for the next 5-10 hours or so.   Would Disk Warrior help, or some other software fix, or is it time to buy a new drive? (And, in any case, what's going wrong?) making a big summation sign How can I make a big summation sign?   ‎\begin{align}‎ ‎\cos x‎ ‎=‎ ‎‎\sum\limits‎_‎{n=0}^{‎\‎‎infty‎} ‎\frac{(ix)^{2n‎}}{(2n)!}‎‎ \end{align}‎   this is the code which I'm using for summation Who were the other two heroes with Superman in the newspaper article who left? In Justice League, we see a newspaper article showing three heroes who died (left to their home planets) but it was too fast that I missed catching the faces.   Who were the other two heroes who are dead? Programmatically Create X509 Certificate using OpenSSL Configuring dpkg stops processing when calling an HTTP request to Adobe Flash Player I recently moved to Linux, and I am in love with the experience. Opinions apart, I am having problems when running sudo dpkg --configure -a  My computer stops processing the command here:  You may know Adobe Flash Player is no longer supported, and I believe that could be why the command is unable to load pepperflashplugin-nonfree. I have tried fixing the problem by checking older posts here, but none of them was able to fix this problem. I've made a simple snowfall particle simulation (using gandalf3's solution: ). Is there a way to loop the animation, so the transition between last frame and first frame is not visible? Is there a setting to do it? Showing that $a^n - 1 \mid a^m - 1 \iff n \mid m$ Let $a\ge 2$ be an integer. Show that for positive integers $m,n$, we have $a^n - 1$ divides $a^m - 1$ if and only if $n$ divides $m$.   I am having trouble showing this. I've seen a similar problem on here but it only shows one direction for the proof. I would like to see both directions.  This is what I have so far: Let $m = nq + r$, then $a^m - 1 = a^{nq + r}- 1 = a^{nq}a^r - 1 = a^{nq}a^r - a^r + a^r - 1 = a^r(a^{nq} - 1) + a^r - 1$. Since $0\le r\lt n$, $r = 0$ then $a^m - 1$ = $a^{nq} - 1$ so $a^m$ = $a^{nq}$ . Thus $m = nq$ hence $n\mid m$. Is there a way to give promo/coupon codes for people to download your app for free? Why $f(x) = \sqrt{x}$ is a function? For me at least,  has answers that are not sorted by score:    Is this normal?  I've tried refreshing the page a few times, but the order doesn't change... Unicode identifiers in Python?