I was wondering a bit after I got a Santa Lucia Hat from several different SE-pages. For getting the SL-Hat you have to vote on 15th of december, but for example I got the SL-Hat on meta, even if I created the account here on 16th of december (according to my time zone). So, what is the relevant time zone for hats? And even if the time zone is UTC, I am in UTC +1, so that should not be the answer...
During Winter Bash, users can earn hats. But sometimes it seems that a hat was awarded even though its requirements weren't (yet) met, or vice versa.  What could be the reason for this?
Are there any galois fields which consist of product of two primes, as in $\mathrm{GF}(2\cdot 3) = \mathrm{GF}(6)$? If a superconductor has zero resistance, does it have infinite amperage? I have a Asus ROG G551VW laptop and I'm trying to install Ubuntu 16.04 on my laptop, but when i try to load the installer, my laptop just freezes and its fan starts working for no reason. I have tried to install Ubuntu 14.04 on my laptop and the installation went smoothly. What should I do if I want to install Ubuntu 16.04 on my laptop?  Any help would be greatly appreciated. Is it possible to use `find -exec sh -c` safely? I'm trying to use find to echo 0 into some files, but apparently this only works with sh -c:  find /proc/sys/net/ipv6 -name accept_ra -exec sh -c 'echo 0 &gt; {}' \;   But using sh -c with find -exec makes me feel very uneasy because I suspect quoting problems. I fiddled a bit with it and apparently my suspicions were justified:   My test setup:  martin@dogmeat ~ % cd findtest  martin@dogmeat ~/findtest % echo one &gt; file\ with\ spaces martin@dogmeat ~/findtest % echo two &gt; file\ with\ \'single\ quotes\' martin@dogmeat ~/findtest % echo three &gt; file\ with\ \"double\ quotes\" martin@dogmeat ~/findtest % ll insgesamt 12K -rw-rw-r-- 1 martin martin 6 Sep 17 12:01 file with "double quotes" -rw-rw-r-- 1 martin martin 4 Sep 17 12:01 file with 'single quotes' -rw-rw-r-- 1 martin martin 4 Sep 17 12:01 file with spaces  Using find -exec without sh -c seems to work without problems - no quoting necessary here:  martin@dogmeat ~ % find findtest -type f -exec cat {} \; one two three  But when I'm using sh -c {} seems to require some kind of quoting:  martin@dogmeat ~ % LANG=C find findtest -type f -exec sh -c 'cat {}' \; cat: findtest/file: No such file or directory cat: with: No such file or directory cat: spaces: No such file or directory cat: findtest/file: No such file or directory cat: with: No such file or directory cat: single quotes: No such file or directory cat: findtest/file: No such file or directory cat: with: No such file or directory cat: double quotes: No such file or directory  Double quotes work as long as no file name contains double quotes:  martin@dogmeat ~ % LANG=C find findtest -type f -exec sh -c 'cat "{}"' \; one two cat: findtest/file with double: No such file or directory cat: quotes: No such file or directory  Single quotes work as long as no file name contains single quotes:  martin@dogmeat ~ % LANG=C find findtest -type f -exec sh -c "cat '{}'" \; one cat: findtest/file with single: No such file or directory cat: quotes: No such file or directory three    I haven't found a solution that works in all cases. Is there something I'm overlooking, or is using sh -c in find -exec inherently unsafe? Given the Lie algebra, what is the systematic way to construct the matrix representation of the generators of the desired dimension? I ask this question here because it is the physicists for whom representation of groups is more important than mathematicians.   Let us, for example, take $SU(2)$ for concreteness. Starting from the generic parametrization of a $3\times 3$ unitary matrix $U$ with $\det U=1$, and using the formula of generators $$J^i=-i\Big(\frac{\partial U}{\partial \theta_i}\Big)_{\{\theta_i=0\}}$$ one can find the $3\times 3$ matrix representation of the generators.  However, I'm looking for something else.    Given the Lie algebra $[J^i, J^j]=i\epsilon^{ijk}J^k$, is there a way that one can explicitly construct (not by guess or trial) the $3\times 3$ representations of $\{J^i\}$? Will the same procedure apply to solve other Lie algebras appearing in physics such as that of $SO(3,1)$ (or $SL(2,\mathbb{C})$)? Seeking QGIS tutorials and web resources? I wish to familiarize myself with the capabilities of QGIS up to and beyond QGIS version 3.0.   Can you recommend some good web resources and tutorials that would show me QGIS' capabilities?   I am interested in both using QGIS through its GUI and in developing applications using QGIS. How to typeset subscript in usual text mode? Showing that a map is bijective and finding its inverse Let $S$ := {$(x, y) ∈ \mathbb R^2: x^2 + y^2 = 1$} be the unit circle. Let $p = (0, -1)$ ∈ $S$. Define a map $F$ from $\mathbb R$ × {$0$} to $S$ as follows: Given $(t, 0)$, let $F((t, 0)) = (x, y)$ ∈ $S$ be the intersection of $S$ with the line through $p$ and $(t, 0)$. Derive a formula for $F$. Show that $t$ → $F((t, 0))$ is a bijective map from $\mathbb R$ to $S$ \ {$p$}, and also derive a formula for its inverse.  If we express $S$ in polar coordinates: $$S:=\{(r,\varphi):r=1,\varphi∈(-\frac\pi{2},\frac{3\pi}{2})\}$$ then, from simple trigonometric relations, the inverse function $\Phi$ is: $$\Phi(\varphi)=\tan\frac{\frac\pi2-\varphi}2$$ and its inverse $F$ is: $$F(t)=\frac\pi{2}-2\arctan t$$ After changing coordinates back to cartesian, $F$ will look like: $$F(t)=(\cos(\frac\pi{2}-2\arctan t),\sin(\frac\pi{2}-2\arctan t))$$ which can be further simplified to: $$F(t)=(\frac{2 t}{t^2 + 1},\frac{1 - t^2}{t^2 + 1})$$ Is this the formula of $F$? Is it correct? And I know that to show that $\phi$ : $\mathbb R$ →  $S$ \ {$p$} is a bijective map, I have to show that $\phi$ is injective and surjective. But how do I do that? Can someone please help me show that $\phi$ is bijective? and how can I derive a formula for its inverse? How do I change the plymouth bootscreen? Changing isometric drawing's constraint angles in Illustrator How to remove film from stainless steel pan I have an unsightly film around my stainless pan as shown here:    What is causing this to happen?  And how can I remove the film? I have soaked it in soapy water, scraped it with a plastic scraper, and run it in the dishwasher several times, but I can't seem to get rid of the film.   UPDATE: the pan is an All-Clad stainless, fully-clad frypan: When Ron broke his wand, why didn't he apply for Hogwarts financial aid? We know, from Book Six, that Hogwarts has a financial aid for students in need. It's supposed to cover all expenses regarding materials and school supplies, so it certainly covers wands. So why didn't Ron simply apply for this fund when he broke his wand in Book Two, since his family could not afford a new one?  Seems absurd that no teacher would notice that Ron had a broken wand and inform him there's a school fund. Plot hole?  Obs.: Even if Ron could afford a new wand, one could ask how we would purchase it (you must experiment personally to find a wand that chooses you). It turns out that there's a local branch of Ollivander in Hogsmeade. I'm sure that, under those circumstances, a second-year student like Ron would be allowed to visit Hogsmeade to purchase a new wand. How does the Ranger's Extra Attack feature work with Two-Weapon Fighting? I think I know the answer to this one but I'm double checking.  At the 5th level the Ranger gets Extra Attack, which lets them attack a second time during the Attack action. If they are fighting with 2 weapons, the second weapon normally uses their bonus action.  Does this mean when using the Extra Attack and using two weapons, a ranger can attack twice during the Attack action, and still make 1 extra attack as a bonus action, for a total of 3 attacks? How to use Alt+Shift to switch keyboard layouts? I recently upgraded to Ubuntu 13.10, with the new keyboard handling system. The little "switch keyboard" option does not let me set it to Alt+Shift. How can I get this keyboard binding, as I have absolutely no interest in using the Mac-esque Super+Space combo? Is it possible to scale up an image to increase the the pixel density? I have taken a picture whose resolution is less. I can resize the image easily (i.e I can scale to higher resolution) but the image quality goes for a toss, which is true because the image might not have enough pixels to scale properly.   Is resizing a means of increasing the resolution of the image ? Is it possible to increase the pixel density of the image and then resize, so that quality of the image is not affected much?   I mainly use GIMP and Picasa. How do I prove this function is bijective? $$ v(s,p)=2^{p-1}(2s-1). $$ The domain is natural numbers and the codomain is also the natural numbers.  And this one: $$ f(s)=2s-1. $$ The domain is the natural numbers, and the codomain is the odd numbers in the natural numbers.  With this one I would do this to show it's injective: $$ \begin{align} v(s)&amp;=v(s_1)\\ \implies 2s-1&amp;=2s_1-1\\ \implies (2s_1)/2&amp;=(2s_2)/2\\ \implies s=s_1 \end{align} $$ So it's injective since if $v(s)=v(s_1)$ then $s=s_1$.  And to show it's surjective $f(s)=y$: $$ \begin{align} y&amp;=2s-1\\ \implies s&amp;=(y+1)/2 \end{align} $$ Then the function must be surjective since every $y$ is the same as the codomain for $f$.  Am I correct? Massless charged particles Javascript - alert("zoo">"house") returns true Unexpected workspace change? My friend who has only recently downloaded blender has come across a workspace issue. He said he accidentally pressed a button and it has entirely changed his user interface/ Workspace. He can't open, save or do anything with the change.    This is a full window image! I understand that people explain (in layman's terms at least) that the presence of mass "warps" space-time geometry, and this causes gravity. I have also of course heard the analogy of a blanket or trampoline bending under an object, which causes other objects to come together, but I always thought this was a hopelessly circular explanation because the blanket only bends because of "real" gravity pulling the object down and then pulling the other objects down the sloped blanket. In other words, to me, it seems that curved space wouldn't have any actual effect on objects unless there's already another force present.   So how is curved space-time itself actually capable of exerting a force (without some source of a fourth-dimensional force)?  I apologize for my ignorance in advance, and a purely mathematical explanation will probably go over my head, but if it's required I'll do my best to understand.