I've always heard of such statements as $SU$ group describing our world even before I seriously learned physics.   When learning about spin, someone spoke of $SU(2)$ but did not seriously explain. When learning isospin and hypercharge for particles made of $u, d, s,$ someone spoke of $SU(3)$ but did not give detailed explanation. When talking about the discovery of J/ψ, teacher (a experimentalist) say, well now with the charm quark, we need $SU(4)$.   I am crazy, $SU$ is just special unitary matrix group, what are they talking about when relating these matrix with spin or particles? I hope someone could give me a detailed explanation about how these group is related to real world substances or recommend a book.
I was hoping someone could give an overview as to how the Lie groups $SO(3)$ and $SU(2)$ and their representations can be applied to describe particle physics?  The application of Lie groups and their representations is an enormous field, with vast implications for physics with respect to such things as unification, but I what specifically made these groups of physical importance and why there study is useful.  I have just started studying these two groups in particular, but from a mathematical perspective, I'd very much appreciate understanding some sort of physical motivation.
I see questions/information online about how to get rid of corpses but I'm not sure what the consequences to having them lying around are.  I know that I can use a morgue to store them and that they will eventually be taken away in a hearse. However, I've always just left them lying around. This doesn't seem to have any obvious consequences.  Do they upset prisoners or staff (e.g. increasing the danger level beyond what death normally does)? Make them sick? Slow down pathing? Is this something that's not implemented yet or is leaving dead bodies all over the place meant to be completely fine?  The wiki's pages for  and  don't shed any light on this. All I'm finding is the how of getting rid of corpses/glitches related to it but not why it matters in the first place. All I've seen that's related is that apparently prisoners can loot guard corpses for keys, but there's no obvious consequences for prisoner corpses which are what I tend to end up with.  So why not just leave them in the corridors? Short Story/Novella in Which People Living in What they Think is Small Town Fifties America Find Look Magazine and Don't Recognize Anything in It This is probably from the mid-to-late fifties.  It involved families living in what seemed to be normal, small town America of the time.  But two boys found in a garbage dump or in a nearby landfill a copy of "LOOK" magazine from their time period (1955? 1957?).  Their problem was that they and their families didn't recognize any of the people or events that were reported in the magazine.    The tone of the articles in the magazine matched their actual lives in that the magazine reported world events, trouble spots, celebrities, politics, and had advertisements for cigarettes and TVs, etc. but the facts were completely different. I think the magazine was a magazine from 'real' America and they were living in a 'fake' America, i.e., they had been brought up in a separate isolated environment with everything different but now had found something from the 'real' world. The tone of the story was that they were never supposed to know about any of this. Maybe, just maybe, part of it was a story about Marilyn Monroe but none of the people had ever heard of her. I can't remember much more than that but I have a nagging thought that they were part of some controlled environment experiment by the US Military. Storing Images in DB - Yea or Nay? So I'm using an app that stores images heavily in the DB. What's your outlook on this? I'm more of a type to store the location in the filesystem, than store it directly in the DB.  What do you think are the pros/cons? Cumulative Sum without Script Can you enter the Schengen area with a UK visa? A "non-believer" of C# was asking me what the purpose to extension methods was. I explained that you could then add new methods to objects that were already defined, especially when you don't own/control the source to the original object.  He brought up "Why not just add a method to your own class?" We've been going round and round (in a good way). My general response is that it is another tool in the toolbelt, and his response is it is a useless waste of a tool... but I thought I'd get a more "enlightened" answer.  What are some scenarios that you've used extension methods that you couldn't have (or shouldn't have) used a method added on to your own class? Free GIS workshops, tutorials, and applied learning material This Q&amp;A lists free as in $0 workshops in GIS and related fields that have their material available to view or download online. The list is not limited to FOSS GIS, as GISers usually use a combination of open and closed source tools to accomplish their tasks. Some of these tools are easier than others and some are better documented. This list will be a great benefit to the community especially for new comers to the field. General GIS   from   from   from   from   Open-source GIS   from   from   from   from   from   ESRI Products   from   from   Transportation These links include either theoretical or applied transportation knowledge in transportation planning          Disaster Management    Databases   from   Geo Statistics    from "done" vs "have done" How would I solve the following problem involving elementary matrices? Let $A=\begin{pmatrix}0&amp;5\\ 7&amp;4\end{pmatrix}$.      1) Write $A$ as a product of $4$ elementary matrices.      2) Write $A^{-1}$ as a product of $4$ elementary matrices.   My work. I have managed to find $A^{-1}$, which came out to be this:  \begin{pmatrix}-\frac{4}{35}&amp;\frac{1}{7}\\ \frac{1}{5}&amp;0\end{pmatrix}  However, I am struggling to figure out how I would split each of these matrices into $4$ elementary matrices. Any help? I want to get the following:    I tried the following  \[    a(i,k) \leftarrow     \min\Big\{0, r(k,k) + \sum_{i^{'} | i^{'}\notin \{i,k\}}\max\{0, r(i{'},k)\}\Big\} \]   and got    How can I make the part under the summation extend to left and right without making a space between plus and max as in the first figure? How can I run a DSLR from AC power? My wife has a Nikon D3100 that I've been using to film, but the battery typically won't last through long shoots.  I've gathered from searching around that I can't charge the camera with USB, but I wondered if there's ANY way to do that. It seems at least possible that an adapter could exist that would fill in for the battery and plug into the wall, but I haven't been able to find such a thing.  Is there such a product or technique? It would be nice to not buy a second battery, I'm really hoping for a "set it and forget it" solution. Python and regular expression with Unicode I need to delete some Unicode symbols from the string 'بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ'  I know they exist here for sure. I tried:  re.sub('([\u064B-\u0652\u06D4\u0670\u0674\u06D5-\u06ED]+)', '', 'بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ')   but it doesn't work. String stays the same. What am I doing wrong? I'm going through MSIL and noticing there are a lot of  instructions in the MSIL.  The MSDN article says they take no action and are used to fill space if the opcode is patched. They're used a lot more in debug builds than release builds.  I know that these kinds of statements are used in assembly languages to align later instructions, but why are MSIL nops needed in MSIL?  (Editor's note: the accepted answer is about machine-code NOPs, not MSIL/CIL NOPs which the question originally asked about.) Odds made simple How can particles be emitted from particles? In a scene with two particle system configured as boids and boids brain set to fight, one swarm attacks the other. I would like to emit child particles as lines (laser or something) to visualize some fighting action. I couldn't find a way to setup the line emitting particle system, either they are created from the plane or further cones will be added. Is there a way to do this as I saw on a  but I didn't get the trick? Blend file   At blendersushi  the author says:  PARTICLE INSTANCE MODIFIER &gt; PARTICLES With this stacking thing, we can now pretty much emit Particles from emitted Particles, &gt; if you know how to set it up. Not very obvious, but basically you Instance some meshes &gt; (using Instance Modifier) and then add Particle System to the object with Instance &gt; Modifier. Make sure you have &quot;Use Modifier Stack&quot; turned on.  But I can't get this to work. What would you call someone who makes no lasting impression? How do I prove that $f(x)f(y)=f(x+y)$ implies that $f(x)=e^{cx}$, assuming f is continuous and not zero? This is part of a homework assignment for a real analysis course taught out of "Baby Rudin."  Just looking for a push in the right direction, not a full-blown solution.  We are to suppose that $f(x)f(y)=f(x+y)$ for all real x and y, and that f is continuous and not zero.  The first part of this question let me assume differentiability as well, and I was able to compose it with the natural log and take the derivative to prove that $f(x)=e^{cx}$ where c is a real constant.  I'm having a little more trouble only assuming continuity; I'm currently trying to prove that f is differentiable at zero, and hence all real numbers.  Is this an approach worth taking? Use counter before its value is set I'd like to use a counter in the text which however is only set at a later point. Like so:  \newcounter{howmany} There are \thehowmany items in this list: \begin{enumerate}   \item one   \item two   \item three \setcounter{howmany}{\theenumi} \end{enumerate}   And it should say "There are 3 items in this list". But that doesn't work. Well, sure. I need to use \refstepcounter to get that save-functionality. But \refstepcounter only increments it by one, and there doesn't seem to be a \refsetcounter ;) Any suggestions? A loop after the enumerate over \refstepcounters? Redefining \item to include \refstepcounter? There gotta be a simpler way, no?  Thanks! Significant predictors become non-significant in multiple logistic regression When I analyze my variables in two separate (univariate) logistic regression models, I get the following:  Predictor 1:    B= 1.049,    SE=.352,    Exp(B)=2.85,    95% CI=(1.43, 5.69),    p=.003    Constant:    B=-0.434,    SE=.217,    Exp(B)=0.65,                            p=.046  Predictor 2:    B= 1.379,    SE=.386,    Exp(B)=3.97,    95% CI=(1.86, 8.47),    p&lt;.001    Constant:    B=-0.447,    SE=.205,    Exp(B)=0.64,                            p=.029   but when I enter them into a single multiple logistic regression model, I get:  Predictor 1:    B= 0.556,    SE=.406,    Exp(B)=1.74,    95% CI=(0.79, 3.86),    p=.171 Predictor 2:    B= 1.094,    SE=.436,    Exp(B)=2.99,    95% CI=(1.27, 7.02),    p=.012    Constant:    B=-0.574,    SE=.227,    Exp(B)=0.56,                            p=.012   Both predictors are dichotomous (categorical). I have checked for multicollinearity.  I am not sure if I have given enough info, but I cannot understand why predictor 1 has gone from being significant to non-significant and why the odds ratios are so different in the multiple regression model. Can anyone provide a basic explanation of what is going on? uint color;  bool parsedhex = uint.TryParse(TextBox1.Text, out color);  //where Text is of the form 0xFF0000 if(parsedhex)    //...   doesn't work. What am i doing wrong?