Why we can't see other than visual light??
While explaining to my nephew about the physics of light, I told him we cannot see infrared color, and he kicked back with a very simple question: why can't we see it? I could not tell him. Is the human eye unable to sense such light or can it indeed but the brain can't understand the signal? any other reason?
Any nice, stable ways to keep a window 'Always on top' on the Mac? I am looking for a stable way to keep any window 'always on top' on OSX.  , an app that does that requires SIMBL/easySIMBL, which it seems is not very stable.  Are there any better solutions? It's actually surprising that there is no native way to implement this. Construct a fourth circle tangent to 3 circles forming a tangency chain How can I make a time delay in Python? I would like to know how to put a time delay in a Python script. Flight reservation for Schengen visa Currency formatting in Python I am looking to format a number like 188518982.18 to £188,518,982.18 using Python.  How can I do this? I have three partitions on my drive, arranged something like the following:   ___________ | 1 |  2 | 3| -------------   I wish to merge partitions 1 and 3.  Is there a way to do this, or do I have to manually "slide" partition 2 over to partition 3, and then merge the newly open space where partition 2 used to be?  Note: I do not have the space to copy partition 2 to partition 3 (2 is 200GB and 3 is 65GB). Everyone knows that Wolverine's adamantium claws are super-sharp — sharper than even a razor — and virtually indestructible. What puzzled me the first time I saw Wolverine is: how do the claws stay in his body?  As it is shown, Wolverine's flesh and skin are human in strength, but the healing factor makes it superhumanly durable and strong. Still, when Wolverine slashes something, or someone, extremely hard, dense, or thick (as he has to use great amount of force), the claws don't tear through his hand and leave his hand through the opposite side of the palm (because of the action having equal and opposite reaction). How do I give text or an image a transparent background using CSS? Newcommand + Stepcounter I'm trying to come up with a command which should increase a counter and return a string including the current value of the counter.  Have a look at the following minimal example:  \documentclass{article}  \newcounter{mycounter} \newcommand{\mystepFAILS}{\stepcounter{mycounter}foo\themycounter} \newcommand{\mystepWORKS}{foo\themycounter}  \begin{document}  \section{\mystepFAILS}  \section{\mystepWORKS}  \end{document}   Why does the command with \mystepFAILS throw an error? What is so special about \stepcounter? Any ideas? Is there any way to include an animated GIF directly? Is there any way to include an animated GIF directly in either PDFLaTeX or XeLaTeX? I realize the animate package can include animations in a PDF, but it doesn't support animated GIFs and you have to split them up manually into EPS or PNG files as far as I can tell. How to make shortcuts on Ubuntu 17.10? Suppose that $f$ is analytic on a close curve γ. Prove or disprove $\int_\gamma \overline{f(z)}f'(z)dz$ is purely imagine. Suppose that $f$ is analytic on a close curve γ. Prove or disprove   $$\int_\gamma \overline{f(z)}f'(z)dz$$  is purely imagine.  I know that $f$ is analytic on a close curve, then   $$\int_\gamma f(z) dz=0$$  I tried an example with $\gamma =e^{it}$ with $0\leq t\leq 2\pi$, I often get the real part of the integral equal zero.  I tried let $f=u+iv$ so $f'=u_x+iv_x$. Since $f=u+iv$, $\overline{f}=u-iv$  $$\overline{f(z)}f'(z)=uu_x+vv_x+i(uv_x-vu_x)$$  But this doesn't get me anywhere. Any help would be greatly appreciated. I have been using Ubuntu 12.04 for quite a while and have never had a problem come at me out of the blue like this. I'm trying to install python 3.2 on my Ubuntu system and every time I run the code to compile the python source, I get this error:  'Command 'sudo' is available in '/usr/bin/sudo' The command could not be located because '/usr/bin' is not included in the PATH environment variable. sudo: command not found'   I've also tried running gksudo command to view what my environment shows but I pretty much get the same error. How to extend summations to fractional orders? List has no row exception: Queryerror I have below line placed in controller that fires list has no row exception. I just need to show a custom message instead when the query returns no value.   Apex code:  Id CI=[select Compliance_Incident_abv__c from Compliance_Incident_Transaction_abv__c where Name=:selectedCIT].Compliance_Incident_abv__c ;  //**This line throws error**     system.debug('CI@@'+CI);         if(cond != '')             cond += ' and';           else             cond += ' where ';                                        if(CI!=null)          cond += ' Id = \'' + CI+ '\''; Help with Spivak Calculus Ch3 Problem 6a Yet again I find myself stuck on a Spivak question. This time it is simply the question that isn't clear to me. It states:  If $x_1, ..., x_n$ are distinct numbers, find a polynomial function $f_i$, of degree $n-1$ which is 1 at $x_i$ and 0 at $x_j$ for $j\neq i$. Hint: the product of all $(x-x_j)$ for $j\neq i$, is 0 at $x_j$ if $j\neq i$. This product is usually denoted by: $$\prod_{\begin{smallmatrix}{j=1}\\ {j\neq i} \end{smallmatrix}}^n(x-x_j)$$  To be honest I don't know where to begin. I understand how to create a polynomial equation for a given set of results but this is quite strange. I'm not sure exactly what the author is expecting.  The answer book shows:  $$f_i(x)={\prod_{\begin{smallmatrix}{j=1}\\ {j\neq i} \end{smallmatrix}}^n(x-x_j)}/{\prod_{\begin{smallmatrix}{j=1}\\ {j\neq i} \end{smallmatrix}}^n(x_i-x_j)}$$  Which I have expanded out just fine but don't know what to do with. One frequent aspect of pdflatex output that could be improved is to what extent one can select text output from the generated pdf-file and copy-and-paste it. This is essentially an issue of having the right output encoding. There are at least two important aspects to this:   In the ideal case, Unicode would be the output encoding. Ligature glyphs (such as ﬁ) are ideally de-ligated in the output (here: "fi").   It seems that output encodings are specified through the fontenc package. What is the range of possible output encodings, and most importantly: Is there a way to specify a Unicode output encoding and one that deals with ligatures in the intended way?  (Note: It is important to distinguish output from input encodings. How to use different input encodings in LaTeX has been documented widely. My understanding is that this is best handled by the inputenx package, as it supersedes the inputenc package.)    Quick guide to the solutions: The information in the answers and answer threads is a bit distributed, so here the short summary: one approach is to use \input glyphtounicode together with \pdfgentounicode=1; the other approach is to use cmap/mmap.  Addendum: Sometimes one will need to load the package accsupp and enclose one's macro definition in \BeginAccSupp{method=hex,unicode,ActualText=&lt;codepoint&gt;}[...]\EndAccSupp{} to generate a specific code point. See the caveat about non-BMP code points  and the fix (starting from accsupp version v0.4, 2012/11/18) , which provides the new unichar package option. Is there a limit to the number of magic rings a character can wear on one hand? C# HttpWebRequest with XML Structured Data I generally defrost meat on the kitchen counter. A friend of mine suggested that this was dangerous and suggested that I defrost meat in the refrigerator. I am no biologist but it seems to me that as long as the meat doesn't get warm defrosting it on the counter should be safe.  Generally, I remove the frozen items from the freezer and place them on a plate on the counter in the packaging they were frozen in. When they are mostly / completely thawed I place the meat in the refrigerator.  Am I wrong and should I be defrosting in the refrigerator?