Why can't I connection the anode of a battery to the cathode of an other battery and get a current flowing?
Why does connecting a battery's positive terminal to the negative terminal of another battery not create a short circuit?
When I save a file (e.g. Images) to a folder which already exist there, Chrome adds a (N) where N is first available number. This causes I have multiple copies of same file! How can I disable Chrome's auto file renaming?   Thanks I have a UK Refugee passport. Do I need a visa to go to France?   I want to go for two days with my husband, but I'm not quite sure if I can go without a visa. How to install bicycle pedals without a notch on the spindle? I bought a pair of bicycle pedals that to my surprise had no notches on the pedal spindle to use when tightening them. I managed to screw them in by hand, but they are not quite tight since I can't use a spanner on them. So what would be the correct way to tighten them? Are there any special tools or similar that I'm supposed to use?  The offending pedals can be seen below. The spindle is, as you can see, completely smooth. How to keep VLC player in minimized mode? I'm using VLC media player which can play almost all kinds of audio and video formats. While listening to audio, I keep VLC in minimized mode and can work on other windows. But when I select to listen video songs mixing with audio songs, VLC is maximizing itself to play every video song in the playing list, which is really annoying in the middle of work.  So how can I keep always VLC player in minimized mode while playing a list of songs mixed with audio and video songs? Would Beetee's electrocution plan work and kill the tributes in the lake? In , the second episode of the Hunger Games trilogy, one of the characters (Beetee) proposes a plan to kill some of the remaining tributes. He proposes wrapping a special wire that he has designed to withstand the vast energy of lightning around a tall tree and running it down to a salt water lake. Then when lightening strikes the tree (which it does predictably every twelve hours) anyone in the lake will be killed. (N.B. This is not Beetee's real plan, but it is the one he wants his allies to believe.)  I don't think his plan would work at all. Assuming that his wire can carry the enormous current delivered by a lightening strike (this is fiction after all) surely the current would short to ground through the salt water rather than taking a path through anyone standing or swimming in the water. The analogy I have in mind is that of birds standing untroubled on live electricity wires. They are unharmed because they do not provide a path to earth. But another analogy might be dropping a mains electric heater into a bath when you are in it. I think that kills you (though I'm not sure why.) Show that $\arctan\frac{1}{2}+\arctan\frac{1}{3}=\frac{\pi}{4}$ Show that $\arctan\frac{1}{2}+\arctan\frac{1}{3}=\frac{\pi}{4}$.   Attempt:  I've tried proving it but it's not equating to $\frac{\pi}{4}$. Please someone should help try to prove it. Is anything wrong with the equation? If there is, please let me know. How to make a FPS-like camera in BGE sudo apt-get upgrade installs all updates, not just security updates. I know that I can use Update Manager to select only important security updates, but is there a way to do this from the command line? Neatest proof that set of finite subsets is countable? I am looking for a beautiful way of showing the following basic result in elementary set theory:     If $A$ is a countable set then the set of finite subsets of $A$ is   countable.   I proved it as follows but my proof is somewhat fugly so I was wondering if there is a neat way of showing it:  Let $|A| \le \aleph_0$. If $A$ is finite then $P(A)$ is finite and hence countable. If $|A| = \aleph_0$ then there is a bijection $A \to \omega$ so that we may assume that we are talking about finite subsets of $\omega$ from now on. Define a map $\varphi: [A]^{&lt;\aleph_0} \to (0,1) \cap \mathbb Q$ as $B \mapsto \sum_{n \in \omega} \frac{\chi_B (n)}{2^n}$. Then $\varphi$ is injective hence the claim follows. (The proof of which is what is the core-fugly part of the proof and I omit it.). Should you declare methods using overloads or optional parameters in C# 4.0? I was watching , and it got me thinking about when optional parameters are available in C# what is going to be the recommended way to declare methods that do not need all parameters specified?  For example something like the FileStream class has about fifteen different constructors which can be divided into logical 'families' e.g. the ones below from a string, the ones from an IntPtr and the ones from a SafeFileHandle.  FileStream(string,FileMode); FileStream(string,FileMode,FileAccess); FileStream(string,FileMode,FileAccess,FileShare); FileStream(string,FileMode,FileAccess,FileShare,int); FileStream(string,FileMode,FileAccess,FileShare,int,bool);   It seems to me that this type of pattern could be simplified by having three constructors instead, and using optional parameters for the ones that can be defaulted, which would make the different families of constructors more distinct [note: I know this change will not be made in the BCL, I'm talking hypothetically for this type of situation].  What do you think? From C# 4.0 will it make more sense to make closely related groups of constructors and methods a single method with optional parameters, or is there a good reason to stick with the traditional many-overload mechanism? Handling Calls to Remove a Moderator This discussion informed our process for seven years, but eventually required updates and augmentation. For discussion regarding the successors to this process, please see:    Stack Exchange has some of the best Moderators around — seriously — and that is due in no small part to the communities who scrutinize and vote in our Moderator elections.  We have a rather formal process for electing moderators, but up until now  has been quite informal. On those rare, rare occasion when things just aren't working out, you can see why it becomes such a sticky business to remove someone from a democratically elected position. Our current process is one of &quot;we've got your back.&quot; The Community Team routinely monitors moderator activities, so if a moderator violates the  or fails to uphold the , we can and do intervene. If the disputes and problems persist without resolution, eventually we can ask someone to step down. That's not good enough. We need a much more transparent and prescribed process for when — and more importantly how — to intervene when on-going problems are going unresolved. In urgent situations, we'll step in to protect a site, but ideally the process should be impartial and not subject to accusations of Stack Exchange simply applying undue influence over a community when the whim strikes. The Question: Before we start bouncing around ideas internally, I'd like to hear what you think. What process should be in place to add some checks and balances to deal with higher issues like possible impeachment of a moderator? When and how would such a process come into play? How should such situations be resolved? How do we keep it from being abused? Have at it. This is a round table vetting of ideas. states:  Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants.  However if the class/method/function that I am importing is only used in rare cases, surely it is more efficient to do the import when it is needed? Isn't this: class SomeClass(object):      def not_often_called(self)         from datetime import datetime         self.datetime = datetime.now()  more efficient than this? from datetime import datetime  class SomeClass(object):      def not_often_called(self)         self.datetime = datetime.now() As  says:     [...] the kinetic energy of a non-rotating object of mass $m$ traveling at a speed $v$ is $\frac{1}{2}mv^2$.   Why does this not increase linearly with speed? Why does it take so much more energy to go from $1\ \mathrm{m/s}$ to $2\ \mathrm{m/s}$ than it does to go from $0\ \mathrm{m/s}$ to $1\ \mathrm{m/s}$?  My intuition is wrong here, please help it out! Why are integer GCDs positive? [unit normalization of GCDs] The definition in my text reads, An integer $d$ is said to be the greatest common divisor of two non-zero integers $a$ and $b$ iff,  $d|a$ and $d|b$ and if $k$ is any other common divisor of $a$ and $b$ then $k|d$  Now here's the thing, if $d|a$ and $d|b$ then surely $-d|a$ and $-d|b$ as well, also $k|-d$ What I take from this? GCD is not unique! That is if $\mathrm{gcd}(12,8)= 4$ then by the definition, $\mathrm{gcd}(12,8) = -4$ as well. Yet I never ever seen a negative gcd. Someone please explain. Maybe, $4&gt;-4$, and we want the &quot;greatest common factor&quot; so...? But that still doesn't justify the definition. How to migrate from test environment to production environment? The migration is from the local environment to the production environment. The production environment has run some time and created a lot of articles.   In order to add new things to my site, I added a custom theme and installed CCK, Views and other modules in my local test environment. Now that the local test environment is finished, how do I migrate it to the production environment, without destroying the content of its database? I currently have an Ubuntu-Windows Dual boot. However, I would like to try out a new OS so I burned Linux Mint to a USB stick.   I would like to install Linux Mint and remove Ubuntu while still keeping my windows dual boot. I've already backed up my Ubuntu setup so I can wipe it out.   In the Linux Mint installer, should I choosing the "install alongside windows" option do this? How do I get label of the selected item from a lightning:select drop down list? I would like to get the value of the label of the selected drop down item.  In this case, the label is the Name of the Contact.  &lt;aura:component&gt;  &lt;aura:attribute name="contacts" type="Contact[]"/&gt;  &lt;lightning:select label="Contact" aura:id="contactList" name="contactList"&gt;     &lt;aura:iteration items="{!v.contacts}" var="c" indexVar="index"&gt;        &lt;option value="{!c.Id}"&gt;{!c.Name}&lt;/option&gt;    &lt;/aura:iteration&gt;  &lt;/lightning:select&gt;  &lt;/aura:component&gt;   I know how to get the value:  component.find("contactList").get("v.value");   But how do I get the label? Search in favorited questions? I'd like to create a chart where the column titles are rotated, as per this toy example:    I used the rotating package to generate the above. It has certain shortcomings: the rotate command doesn't leave space for the titles, so I have to manually space things to prevent overlaps. The turn command, by contrast, creates too much space, where each column is the width of the entire rotated column title.  There is also no easy way to have long titles be split into multiple lines.  Is there a package for creating tables of this sort, or at least one that would relieve some of the manual placing and spacing that goes into creating such a table?    This question is more to make sure I don't miss any easy way of doing what I want than seeking help on manually doing it, but the code for above is included anyways:  \begin{tabular}{r|ccc} &amp; \begin{rotate}{60} Property 1 \end{rotate} &amp; \begin{rotate}{60} Property 2 \end{rotate} &amp; \begin{rotate}{60} Property 3 \end{rotate} \\ \hline System 1        &amp;       &amp;       &amp;  X    \\  System 2        &amp; X     &amp; X     &amp;  X    \\ System 3        &amp; X &amp;   &amp;  X    \\ \hline \end{tabular} Listen for incoming request on port on Linux, then run command I am after as lightweight as possible solution to listen on a port for a specific request, then run a command should the port be hit and the correct request be recedved.  Eg. Send a request to 192.168.0.10 on port 5432 with the string my_token. On the host (eg. 192.168.0.10), then run a command should that port be hit and the string matched.  I was initially thinking of using netstat (eg. nc -l 5000) then running the command on change. However, ideally a string or token of sorts would be ideal alongside this or similar, but without using a full-blown webserver - essentially something that can run in the background with few resources.