For example We know that some television manufacturers have the limited IR-based remotes which cannot be seen by our eyes directly but while playing when I just put my camera in front of my TV remote I just saw light but I can't see it directly. So why is it visible through camera rather than our eyes directly ?  I just took one image to show what I saw!
I know that if you held an infrared remote in front of a digital camera, it'll flash a blue/purplish light when you press the buttons. Why?    (Image by  .)
I would like to try a different video display driver, but I'm not sure which one I'm currently using.    What's the simple way to see what driver my system is using currently? Cost Distance Analyst In QGIS? Are there any tools, plugins or methods in QGIS which allows for an analysis of the best path between two points using least cost path method? As shown below ArcGIS has several distance tools. Self-references in object literals / initializers WebView loading Url It's been some weeks now, whenever I try to used my Youtube app, it tells me it's impossible to connect to Youtube. Since it's an iPad 1, I have had trouble finding information online.  Did Google or Apple stop supporting the app? Is it finally obsolete? Is there another app I could use that works on iOS 5?  Just to be clear, I did not tinker with my device. I did not change its parameters, I did not jailbreak it, it connects to the Internet just fine and I've tried the app on different Internet connections. Also, this is not a login problem, the app just refuses to let me browse videos, whether I'm logged in or not.  Thanks for your help. "This product is good value" vs "This product is of good value" in a sentence 1.This product is good value. 2.This product is of good value.    Are there any difference in meaning between "good value" and "of good value"? Counting the occurrences / frequency of array elements Given  $N\geq30$ i.i.d. $X_n\approx\mathcal{N}(\mu_X,\sigma_X^2)$,  and $\mu_X \approx 0$, looking for:   accurate closed form distribution approximation of $Y_N=\prod\limits_{1}^{N}{X_n}$ asymptotic (?) approximation of same product    This is a special case $\mu_X \approx 0$ of a more . While adding to an Answer to  question, I needed to use the above phrase, and I suddenly realised I was unsure whether to write "is" or "are".   There is more than one way to skin a cat. If there are more than one species of cat, we will flay each species differently.   I don't think that second example above sounds quite right to me (disregarding the meaning - sorry!), but in my original Answer I felt "is" would have been even worse.  Is "are" always wrong here? If so, what exactly is the rationale? If not, is there a case where it's unquestionably preferred – and why is that?    Note that in both the problematic Answer and my example attempting to mimic the same context more briefly, the writer doesn't know how many there are. There may be one, more, or even none.  Getting even more specific, the writer might have an opinion on how many there might be, and wish to convey his leanings by choice of verb form if language allows this to be done succinctly. Getting started with ArcObjects? What is the best route or place to get started with ArcObjects if one is not a developer and not aiming to become a developer?  I've been using gis professionally for a long time, almost two decades, arcinfo/arcgis for most of that; I'm pretty good. I'm learning software development, and even have a modestly successful small python application used in a public project; I'm not good! I don't want to become a full fledged software developer but I keep running into things I just can't do without programming (). In the arcgis world this puts me pretty squarely in the python camp, which is fine by me since I like python, however python does not have straightforward access to ArcObjects. (Python and ArcObjects , but it's an unsupported route. This question is about following a beaten path.)  I need to get started, but where?  to get started with the  but $1500/yr is definitely not in my budget, and sounds like using a sledge hammer to swat mosquitos. And which language .NET, Visual Basic, or Visual C++?    UPDATE: Thank you everyone for the wonderful answers. In light of them I realise  I unecessarily narrowed the scope of my question be pre-supposing "ArcObjects" is the direction I need to go in. A more open ended formulation is more along the lines of:     I keep running into problems I just   can't solve with arcgis and python   alone. What else can I learn/use to   solve problems like X? I've no   interest or intention of becoming a   software developer. I just need to do   a couple things which aren't exposed   to the arcgis python modules. Need a matrix to seventh power which is the identity but the original is not or the negative identity The question on the homework wants a $2\times2$ matrix $R$, but $R$ not equal to positive or negative identity, that when you raise to seventh power you get the identity.  $R^7=\operatorname{Id}$.  I thought it would have to be some ones and negative ones,  it no luck, then tried some ones and some $.5$.  Just using an online matrix calculator to do brute force.  We just started talking about eigenvalues with visual example, so assuming wouldn't need that since we have not talked about how to find them yet.  Any hints or ideas to get me back on track? Proving the limit of a function of a sequence is equal to the function of the limit of that sequence Suppose $f$ is a continuous function at $x = c$ in $[a,b]$.  Prove that for any sequence ${x_n}$ in $[a,b]$ converting to $c$, the sequence $\{f(x_n)\}$ converges to $f(c)$.  That is, $$ \lim_{n\to\infty}f(x_n)= f\left(\lim_{n\to\infty}x_n\right)$$    This proof seems simple but there are a few things that I need to know first. If $\{x_n\}$ converges to $c$, is it sufficient to substitute $c$ in for $\lim_{n\to\infty}x_n$?  Also needing some guidance on the structure of this proof.  Thanks! I  that there are two folders for unit files (not in user mode). /usr/lib/systemd/system/: units provided by installed packages /etc/systemd/system/: units installed by the system administrator  Conflicting with this understanding is the answer to this question: . Can someone fill in the missing information so that I understand what is going on? (UPDATE: The answer has been updated, and my understanding no longer conflicts with it.) Also, it seems that the scripts are organized in subfolders within the /etc/systemd/system/ folder: getty.target.wants multi-user.target.wants  In another location I read that there are other locations. It seems these are for user-specific services. /usr/lib/systemd/user/ where services provided by installed packages go. /etc/systemd/user/ where system-wide user services are placed by the system administrator. ~/.config/systemd/user/ where the user puts its own services.   Update 2015-08-31: For the sake of others, here is a link to a related question I recently asked: UK visa: unsigned application form Can someone give me some example code that creates a surface with a transparent background in pygame? Consider a particle on the ground. This particle is raised by a force of magnitude $mg$ to a height $h$ above the ground. At this point, the work done on the particle by the force is $mgh$, which is equal to the potential energy of the particle. But, during this period, the force of gravity also acts on the particle and is displaced by $h$, and so does a work of $-mgh$ on the particle. Shouldn't  the two cancel and no net work should be done on the particle?   If they don't cancel, then where did the energy that came from the work done by the force of gravity go? How can I install Windows software or games? Fast way to find period-n points of a tent map? I need to find a period-3 orbit for a tent map defined by $$T(x)=\begin{cases}2x &amp; 0\le x\le0.5 \\[2ex] 2-2x &amp;0.5 &lt; x \le 1 \end{cases}$$  So, what is a fast and efficient way of finding it? I only know how to do it by guessing-and-checking. For example, I picked a random point, $x = \frac{2}{7}$ and found that $$T\left(\frac{2}{7}\right)=\frac{4}{7}\\[4ex]T\left(\frac{4}{7}\right)=\frac{6}{7}\\[4ex]T\left(\frac{6}{7}\right)=\frac{2}{7}$$ which is a period-3 orbit. Is there any better way of finding a period-3 orbit , more specifically, a period-3 point? How can I combine multiple rows into a comma-delimited list in Oracle? I have a simple query:  select * from countries   with the following results:  country_name ------------ Albania Andorra Antigua .....   I would like to return the results in one row, so like this:  Albania, Andorra, Antigua, ...   Of course, I can write a PL/SQL function to do the job (I already did in Oracle 10g), but is there a nicer, preferably non-Oracle-specific solution (or may be a built-in function) for this task?  I would generally use it to avoid multiple rows in a sub-query, so if a person has more then one citizenship, I do not want her/him to be a duplicate in the list.  My question is based on the similar question on .  UPDATE: My function looks like this:  CREATE OR REPLACE FUNCTION APPEND_FIELD (sqlstr in varchar2, sep in varchar2 ) return varchar2 is ret varchar2(4000) := ''; TYPE cur_typ IS REF CURSOR; rec cur_typ; field varchar2(4000); begin      OPEN rec FOR sqlstr;      LOOP          FETCH rec INTO field;          EXIT WHEN rec%NOTFOUND;          ret := ret || field || sep;      END LOOP;      if length(ret) = 0 then           RETURN '';      else           RETURN substr(ret,1,length(ret)-length(sep));      end if; end; More than one 'Open xxxxx here as Administrator' I want the option to open a Command window or Powershell window as Administrator from the drive and directory context menus in Windows.   I can have either by creating and populating the special 'runas' registry keys shown below, but is there a way I can have both listed on the context menu and have both run as Administrator?  [HKEY_CLASSES_ROOT\Drive\shell\runas] ... [HKEY_CLASSES_ROOT\Drive\shell\runas\command] ... [HKEY_CLASSES_ROOT\Directory\shell\runas] ... [HKEY_CLASSES_ROOT\Directory\shell\runas\command] ... [HKEY_CLASSES_ROOT\Directory\Background\shell\runas] ... [HKEY_CLASSES_ROOT\Directory\Background\shell\runas\command] ...