Can I use a 12 V DC power supply for an 9V AC gadget? Does it get too hot? Or can it work safely? I tried it already and it seemed to work.  Is it safe? The gadget is a telephone.
Power supplies are available in a wide range of voltage and current ratings.  If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify?  What if I don't know the device's specs, but am replacing a previous power supply with particular ratings?  Is it OK to go lower voltage, or should it always be higher?  What about current?  I don't want a 10 A supply to damage my 1 A device.
To explain the expansion of space I have often heard people saying that space is continuously created. This picture is usually applied to cosmological scales but I`m nevertheless curious if some microscopic description of this process could be found (or probably is already available?).  The first thing which comes into my mind by thinking about this is that in theories like loop quantum gravity, there is an idea that space is quantized. Would space expansion then be explained as the creation of new quanta in loop quantum cosmology? Or are there other different ideas, such as the quanta themselves changing properties? Do people actually working on this already have some interesting results? Converting FLV to MP4 Using FFMPEG and Preserving the Quality Im trying to use ffmpeg to convert my flv files to mp4 to play them on iOS devices but the converted video has a much worse quality than the original one.  Here is the command i use:  ffmpeg -i input.flv -ar 22050 output.mp4   I would really appreciate if someone could provide me with the best settings for flv to mp4 conversion. This is purely a curiosity, but I'm fascinated by mid-word pluralization, even if the word in question is a compound word.  For example, passersby or standersby.  No others have occurred to me. Can you provide other examples, or a link to a resource that enumerates them?  I'm particularly interested in compounds that do not include spaces or hyphens. Java: Load class from string What is the opposite of postpone? Why is find not accepting '-exec cp {} dir +'? I have a directory, dir1 which contains many files whose names end in either .jpg or .png. I want to copy all the .png files to dir2 which is empty.  This command works:  find dir1 -name '*.png' -exec cp {} dir2 \;   but this command doesn't:  find dir1 -name '*.png' -exec cp {} dir2 + find: missing argument to `-exec'   I also tried:  find dir1 -name '*.png' -exec cp {} -t dir2 + find: missing argument to `-exec'   and:  find dir1 -name '*.png' -exec cp {} dir2 \+ find: missing argument to `-exec'   After looking at , I even tried:  find dir1 -name '*.png' -exec cp {} dir2 {} + find: Only one instance of {} is supported with -exec ... +    says that:     -exec {} + was added in [version] 4.2.12 in 2005   My version of find is 4.4.2.  What am I doing wrong? Nobody owner (99 99) in FTP caused by php functions? Nvidia driver updated - mixed versions of 304.88 and 319.32 My problem is that after trying to update my driver through the additional drivers GUI I can't boot Ubuntu with GUI anymore, since Xorg says the kernel module is of version 304.88 (The old version before I updated) but the driver components are of version 319.32 (The new version)  This is the output of dpkg -l | grep nvidia  dkpg -l | grep nvidia ii nvidia-304 : 304.88-0ubuntu0.0.3  NVIDIA binary Xord driver, kernel module and VDPAU library ii nvidia-319 : 319.32-0ubuntu0.0.1  NVIDIA binary Xord driver, kernel module and VDPAU library ii nvidia-common : 1:0.2.44.2  Find obselete NVIDIA drivers ii nvidia-current : 304.88-0ubuntu0.0.3  Transitional package for nvidia-current ii nvidia-settings : 304.88-0ubuntu.0.0.3  Transitional package for nvidia-settings ii nvidia-settings-304 : 304.88-0ubuntu.0.0.3  Tool for configuring the NVIDIA graphics driver ii nvidia-settings-319 : 319.32-0ubuntu.0.0.1  Tool for configuring the NVIDIA graphics driver   That's the output of that file.  The message startx gives me is:  NVIDIA: API mismatch: the NVIDIA kernel module has version 304.88, but this NVIDIA driver component has version 319.32. Please make sure that the kernel module and all NVIDIA driver components have the same version.     Fatal server error:    no screens found   I understand that something went wrong during the update, so I wonder how to fix this so that the remaining parts of 304 are removed and replaced with 319. I don't know hwere to start because I thought that nvidia-current was the one that would update to 319 and so reinstalling that didn't work. And I googled and found that somebody said to try to install/reinstall/uninstall this package: nvidia-current-updates-dev  But I didn't have that package installed so it did not help. Other than that, I am clueless. I hope the information I provided will be enough so I can get an answer soon.  EDIT:  lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 12.04.3 LTS Release: 12.04 Codename: precise  uname -a Linux SQuad 3.2.0-52-generic #78-Ubuntu SMP Fri Jul 26 16:21:44 UTC 2013 x86_64 x86_64 x86_64 GNU/LINUX LIGO has announced the detection of gravitational waves on 11 Feb, 2016. I was wondering why the detection of gravitational waves was so significant?   I know it is another confirmation of general relativity (GR), but I thought we had already confirmed GR beyond much doubt. What extra stuff would finding gravitational waves teach us? Is the detection of gravitational waves significant in and of itself, or is there data which can be extracted from the waves which will be more useful? $\newcommand{\P}{\mathbb{P}}$Is it valid to interpret $\P(B|A)$ as "infinite probability" when $\P(A) = 0$? Is it possible to take an image from the clipboard and output it to a file (using X)?  I can do this with text easily:  $ xclip -selection c -o &gt; file.text   But when I try the above with an image nothing is written.    The reason I want to do this is I don't have an image editor installed, and it got me thinking whether I could do this without installing one. Does "until [date]" mean "before that date"? I know that Dirichlet function has uncountable many discontinuities. I think they are removable, because the discontinuities can be removed by redefining the function values of the rational numbers as 0.  So Dirichlet function is a function that has uncountable many removable discontinuities, then my question is can we construct a function with uncountable  many jump discontinuities? If not, how do we prove it is impossible? Thank you.  An odd but similar question is can we have a function that has uncountable many infinite discontinuities? Jordan normal form for a characteristic polynomial $(x-a)^5$ Write down all the possible Jordan normal forms for matrices with characteristic polynomial $(x-a)^5$. In each case, calculate the minimal polynomial and the geometric multiplicity of the eigenvalue $a$. Verify that this information determines the Jordan normal form.  I found this question in a textbook that I'm using for a test I have tomorrow. I think that I need to use the method for finding the Jordan normal form of a matrix but I can't see how to apply it and I don't have much intuition about the answer...  I'm guessing that there are 5 possibilities since the minimal polynomial can be any factor of the characteristic, but I don't know how to prove this.  Some help would be great for my test tomorrow! Thanks Existence of elements of order $p^k$ in a finite group By Cauchy's theorem, if a prime number $p$ divides the order of a group $G$, then there is an element $g$ in $G$ whose order is $p$. In addition, if $|G|$ admits a prime decomposition with a factor $p^k$, then Sylow's theorem tells us that a subgroup of order $p^k$ must exist.   My question is the following. If $|G|$ admits a prime decomposition with a factor $p^k$, does this imply that an element of order $p^k$ must exist in $G$?   Update: As explained in Mindlack's answer (among others), the implication does not hold and simple counterexamples exist. In the comments, Mindlack discusses special cases where such an element exists. I've created a new user by using "User Accounts" in "System Settings". How do I grant rights so that this new user can have the same level of access as root? The following is the residuals vs predicted scatter plot for a regression model with two IVs.   Initially, I thought it was evidence of heteroskedasticity. But, I reasoned that although there is a visible pattern in the plot, the variance across different levels of predicted values is same.  To clear my doubts, I saved the standardized residual and predicted values and ran a bi-variate correlation test. The correlation is zero, as expected. I am, nevertheless, intrigued by this observation. Any idea why I might have obtained this pattern?  PS:- My dependent variable is a sum of two likert-type items (Response scale: 1-5). So, it's theoretical range is 2-10 and it has no absolute zero value. Why can't Mathematica integrate this? A Lebesgue measure question Possible Duplicate:          Is there a measurable set $E \subset [0,1]$ such that for any $0 &lt; a &lt; b&lt;1$, the Lebesgue measure $$m(E \cap [a,b])= \frac{b-a}{2}?$$  I am stumped and have no idea. How to derive $E=mc^{2}$? Is there some way to derive ? I can understand that energy in something is proportional to its mass, but the $c^{2}$ part. I have no idea. It seems like the way the units are going it would end up as $kg*(m/s)^{2}$, which I think is the unit for Newtons, not energy. And why is there no constant of proportionality $k$? Did Einstein just set it up perfectly so that there wouldn't be one?