Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? I understood the basics but please don't hesitate to go deeper into the concept. Also, If you happened to have an elegant explanation please drop it here if you can.
When light waves enter a medium of higher refractive index than the previous, why is it that:  Its wavelength decreases? The frequency of it has to stay the same?
How do I sort a list of dictionaries by a value of the dictionary? I have seen this a lot but i ran into this question today:    And the answer (while good) has 83 upvotes which seemed a little over the top.  I see dozens of answers of this caliber every week that only seem to get a few upvotes.    Was there some sort of SO policy that encouraged people to upvote more during this period?  Am I just imagining that answers from this period received more votes than comparable ones now? Referencing subfigures in main caption (with \subfloat and \subref) I've used subfloat to include subfigures, with their relevant labels but with empty captions. what I'm going to do is to reference these figures with \subref in the main caption of the figure. But what I get is only ?? signs in the caption [main caption]. I can't figure out what's the problem. this is what I have:  \begin{figure} \centering \subfloat[][] { \includegraphics[scale=0.55]{signal} \label{signal_model} } \subfloat[][] { \includegraphics[scale=0.55]{amplitude} \label{amplitude_mod} } \caption{phase noise variability: \subref{signal model} some text \subref{amplitude_mod} some other text} \end{figure} Can I enter the Schengen area with a German long-term visa through a different country? I am an Indian national. Right now I am staying in Israel. I will be moving to Germany on the last week of this month with german national visa directly from tel aviv. Ticket price of direct flight is high. So I am thinking to buy either Air France or LOT for travelling having layover at Paris or Poland. Am I allowed to do that? I mean is it mandatory to enter in Germany first? May I travel with these airlines with proper transit visa? Assuming String a and b:  a += b a = a.concat(b)   Under the hood, are they the same thing?  Here is concat decompiled as reference. I'd like to be able to decompile the + operator as well to see what that does.  public String concat(String s) {      int i = s.length();     if (i == 0) {         return this;     }     else {         char ac[] = new char[count + i];         getChars(0, count, ac, 0);         s.getChars(0, i, ac, count);         return new String(0, count + i, ac);     } } Proving a graph has no Hamiltonian cycle If I said, &quot;I will run, not if it is snowing, if I my shoes are comfortable.&quot; Does the &quot;if my shoes are comfortable&quot; modify the &quot;I will run&quot; clause? I agree the sentence would be clearer with the addition of &quot;and&quot; in place of the comma. However, without the &quot;and&quot; is it still clear that the &quot;if my shoes are comfortable&quot; clause modifies the &quot;I will run&quot; clause? How to redirect output to screen as well as a file? My aim is to log all output from a script into a directory that the script is going to create.  For example, I have:  ~/.abc.sh:  #! /bin/bash rails new myapp   When I run...  cd ~/code . ~/.abc.sh   ...that will create a new Rails app in directory ~/code/myapp.  When Rails is creating an app, it outputs a whole lot of text that I want to capture and store in a log file in the same directory the rails command newly created. I also want to display that text in the terminal as well.  How do I go about doing this? How is it, that $\sqrt{x^2}$ is not $ x$, but $|x|$? Can Cycles use multiple UV layers? I'm trying to match Cycles to a Blender-Internal material setup and I didn't see a way for cycles to have an image reference more then one UV map.  Is it possible to have a node setup with 2 image textures, each using a different mesh UVLayer? How can I create an association list from 2 lists? "IllegalFormatConversionException: d != java.lang.String" when padding number with 0s? With services like Google Finance or Yahoo Finance it is very convenient to find the historical stock price metric of a listed company, but if the company is not listed, I can't find the data.  For example, I want to see the price metrics for Macromedia, which had been listed in 1993 on NASDAQ (MACR), then acquired by Adobe in 2005. How could I find its historical price metrics? Where to find the checksums of Ubuntu ISO images? I just downloaded the ubuntu-10.10-desktop-i386.iso, and am having a hard time burning it, so I'd like to check that the file is intact, but I cannot find the md5sum of the file.    Is there a URL or official FTP mirror which includes the md5sum of the Ubuntu disk images? Call a javascript function after 5 sec of last key press " java.lang.IllegalArgumentException: uri.getScheme() == null! " error using JavaFX to play audio How to prove that $d \sin(x)/dx = \cos(x)$ without circular logic such as L'Hôpital's rule? Yesterday I was copying a single, 8 GB file to a USB with a slow, 7 MB/s write speed, while my RAM is 3 GB. While copying the system froze, to the point where I couldn't even move the cursor.  I managed to log into the text console, and ran iotop, it showed that a process named kswapd0 was taking 99.99% of IO.  Are there workarounds so copying a large file doesn't make my system unusable? Prove that neither $A$ nor $B$ is divisible by $5$ When is the Laplace transform of a function continuous? Are there any general conditions on a function so that its Laplace transform is continuous? e.g. what conditions on $f:\mathbb {R} \rightarrow \mathbb {R}$ guarantee that its Laplace transform  $$F\left(s\right)=\int_{0}^{\infty}f\left(t\right)e^{-st}dt$$ is continuous? It seems to me that if $f$ has compact support and is bounded, then it ought to be. The idea I have is that we get  $$\left|F\left(s'\right)-F\left(s\right)\right|\leq\int_{0}^{y}\left|f\left(t\right)\right|\left|e^{-st}\right|dt$$ by making $s'$ and $s$ close enough, it seems we can make the RHS arbitrarily small. I haven't been able to complete a proof. Additionally, can we change the assumptions? Are there more natural assumptions to get continuity?