New top-bar really doesn't know maths
Reputation items in the achievements dropdown don't add up
Does metric signature affect the stress energy tensor? Applications of ultrafilters I'm looking for some interesting applications of ultrafilters and also everything of interest involving ultrafilters. Do you know some applications or interesting things involving ultrafilters?  I'm at the beginning, so I'd prefer some applications that also a beginner could read. I've been trying to play with a rigid body simulations.  I prepared a project of a building made of domino tails. I've placed all objects very tight, but as soon as I start animation it looks like there was some tiny gap between objects, so they all fall down a little bit. For a high building it leads to a construction disaster as the whole building colapses.  Here is an example:  (I'd suggest to use 0.25x speed).  How can I fix it? Do I need to have antivirus software installed? I thought that there was no need to scan for viruses either in Ubuntu or any Linux distros until I found virus scanner packages clamtk and klamav in Ubuntu software center yesterday.  This leads to the following questions:   How do viruses differ between Linux and Windows? How do the strategies for protection differ between Linux and Windows? Should a virus scanner package be installed on my system? If so, which would be a better option? How can I get a history of running processes Data Recovery - How to Restore Deleted / Formatted Files on HD Micro SD Card Background:    I put in a friend's SD Card to format it because it was having problems. Then I put mine back in and I think my phone formatted my SD Card. I had a ton of pictures on there that are now gone! I put the card into the computer and there's only 2mb of cache files on there and none of the original directories.   I already tried the following freeware recovery applications:         Neither of them were able to retrieve any files. Undelete took 1minute to scan for files and came up with 0 files.  Recuva took 10 minutes for their "deep scan" which doesn't seem thorough enough at all for this 8GB SD Card. I need something that's a lot more heavy duty.  I don't mind paying for an application to get the data back if necessary...   Questions:     Which application can I use to recover my deleted picture files from my 8GB HD Micro SD Card?   Why did Anroid format my SD card?   How can I tell if it's a phone problem, data problem, or SD Card problem? Is any quotient of a Euclidean domain by a prime ideal a Euclidean domain? Let $R$ be a Euclidean domain, i.e., a ring with a norm $N : R \rightarrow \mathbb N$ such that for any $a,b\in R$ with $b\not=0$, we may write $a = qb + r$ for some $q,r \in R$ with $N(r) &lt; N(b)$. Let $I$ be a prime ideal of $R$, so $R/I$ is a domain. Must $R/I$ in fact be a Euclidean domain?   I know that this is true if we replace "Euclidean domain" with "PID", and false if we replace it with "UFD", so there is no clear intuition to be gained from similar concepts. My first attempts at a proof was to borrow a construction from analysis and define a norm on $R/I$ by  $N(a + I) = \inf\{N(a+i) : i\in I\}$  but this didn't really get me anywhere.   So, this fact true? If so, how can I prove it? If not, whats a counterexample? How strongly can a 1mo be rocked? My 1 month old baby only seems to quiet down when I vigorously rock her (while I carefully hold her head). Can I cause her some (brain?) damage if I rock her too hard? I'm looking for the title of a Sci-Fi story (probably pre-1990) where a group is sent off into deep space and I believe unbeknownst to them it's a one-way journey.  In the course of the journey they all become very intelligent, they make psychoactive drugs from the plants on board, I recall that they discovered it's a one-way journey to test the affects of space travel, and they redesign/refit their engines and return to Earth.  Lame recall, sorry, that's all I got. Any help appreciated. Faster language/keyboard swapping I like making a habit to use the different languages I study, to keep that knowledge fresh. So I like typing in those languages when I get the chance. But swapping keyboards under OSX is just a little too cumbersome.  For example, I was just typing the name of one of my co-workers in its original 汉子 form instead of as an English transliteration. It's nice. It reminds me to pronounce her name properly, with tone, etc., which otherwise doesn't come naturally. The transliteration of her name is especially misleading. Everyone at the company is pronouncing it wrong.   But to swap into writing 汉子 I have to mouse up to the top menu bar, select a new keyboard, type, mouse back up to the top bar, and then select back into English. I know there's a keyboard shortcut, but with 5 different keyboards active in my menu, cycling through 5 to get to the one I want feels just as cumbersome.  Is there a way to attach a hotkey to a specific keyboard, or some other way to make swapping character sets lighter? What five odd integers have a sum of $30$? Should seemingly arbitrary things like "play piano for Church" or "intramural badminton" go on M.S. or PhD applications in sciences/engineering? And if they should, I assume that these things should go on a resume under something like "Activities and Community Service". I mean I consider being able to sight read music to play at my Church as a significant feat (how many people can do that?) and might sway one person on an admissions committee if he or she enjoys music and understands how hard one must have worked to accomplish this.   Badminton?.... perhaps not so much How will people upgrade from 12.10 to later releases after 13.04 is EOL? Is Cyclops’ mutant power just an organic version of Iron Man's repulsor tech? They occupy the same universe so we have to assume the same physics apply. Iron Man's repulsor tech is described as an inertia-less one-way kinetic blast. At higher energy levels, it can can even disintegrate matter in front of it. Cyclops’ eye beams are described exactly the same way. Is there any place in comics or the animation where the two beams are shown to have different powers? $\{\emptyset\}$ is a set containing the empty set. Is $\{\emptyset\}$ a subset of $\{\{\emptyset\}\}$?  My hypothesis is yes by looking at the form of "the superset $\{\{\emptyset\}\}$" which contains "the subset $\{\emptyset\}$". How can I stop applications and services from running? How would I go about creating a 3D MMORPG Mouse Look? How would I go about creating a 3D MMORPG Mouse Look? I have created a 3D Space Rpg that is almost finished with success so far. However, I didn't have a clue, how I would attempt to make a Mouse Look method where if a user right clickes and then holds the right mouse button and moves it around the camera moves around with the mouse. The camera can not move away from your character/ship, it should act as if the character/ship is it's origin and that it rotates all around the origin.  I don't mind coding this with python either. Advice is welcome! How can I create launchers on my desktop? Algebra of LDA. Fisher discrimination power of a variable and Linear Discriminant Analysis Apparently,     the Fisher analysis aims at simultaneously maximising the   between-class separation, while minimising the within-class   dispersion. A useful measure of the discrimination power of a variable   is hence given by the diagonal quantity: $B_{ii}/W_{ii}$.     I understand that the size (p x p) of the Between (B) and Within-Class (W) matrices are given by the number of input variables, p. Given this, how can $B_{ii}/W_{ii}$ be a "useful measure of the discrimination power" of a single variable? At least two variables are required to construct the matrices B and W, so the respective traces would represent more than one variable.  Update: Am I right in thinking that $B_{ii}/W_{ii}$ is not a trace over a trace, where the sum is implied, but the matrix element $B_{ii}$ divided by $W_{ii}$? Currently that is the only way I can reconcile the expression with the concept. bi-directional sync with rsync