Today while installing a 12v LED strip on my windows with the power adapter plugged but the LED turned off, I noticed the led that I pushed down against the wall got turned on partially. It wasn't right. My finger shouldn't have enough resistance to turn on those led with 12v. Right away, I tested the DC adapter output line with a 90-1000vac surveyor and found out that the 12vdc line from the DC adapter carries a high voltage AC. When testing with a meter, it measures about  12vdc, and unstable AC range from 38-0Vac. ( properly higher AC voltage, since my meter may not be fast enough.)  1, Is it safe to use this power adapter? ( It powers up the LED strip fine. I have also found a 5V usb charger that carries a HIGH voltage AC before, of which I discarded right away.)  2, What is the cause of this HIGH voltage AC? ( Is it because it's not isolated? or it's not filtered properly at the output end? I can't open the case, as it's sealed completely with no screws. )
I'hv seen every 2 pin SMPS AC to DC adapters shows a little high voltage respective to the ground on the out put, on both + and GND wires(or more if more wires present).  This voltage is high enough to light small neon bulbs or a line tester, but very low current, barely could be felt. This voltage vanishes if I connect the output to ground somehow, e.g. touch it while standing on floor bare foot.  As the size of the adapter increases, the AC voltage and current increases. When laptop adapters are powered from a ungrounded AC outlet, they gives reasonable shock from the 19V DC(or whatever else) output.  Perhaps this is the reason why many 3 pronged laptop adapter carries a warning CONNECT ONLY TO GROUNDED OUTLET Connecting to a grounded outlet magically vanishes the high voltage.  I am aware about the EMI filtering capacitor connected between high voltage and low voltage ground, I tried to solve this by removing them, but this trick is not working.   Why and how this mysterious AC voltage is created ?  Is it harmful to sensitive electronics components ? Is there any way to solve this without grounding the DC output side ?
Prove: $$ (a+b)^\frac{1}{n} \le a^\frac{1}{n} + b^\frac{1}{n}, \qquad \forall n \in \mathbb{N} $$ I have have tried using the triangle inequlity $ |a + b| \le |a| + |b| $,  without any success. How would I remove the border from an iframe embedded in my web app? An example of the iframe is:  &lt;iframe src="myURL" width="300" height="300"&gt;Browser not compatible.&lt;/iframe&gt;   I would like the transition from the content on my page to the contents of the iframe to be seamless, assuming the background colors are consistent. The target browser is IE6 only and unfortunately solutions for others will not help. RELATED,ESTABLISHED state in iptables What do the words 'RELATED' and 'ESTABLISHED' individually signify in RELATED,ESTABLISHED state in iptables? Positive and negative complex numbers? Can there be such a thing as positive and negative complex numbers? Why or why not?   What about positive or negative imaginary numbers?   It seems very tempting to say $+5i$ is a positive number while $-2i$ is a negative number. On an Argand diagram (complex plane) $+5i$ would be represented by a point above the horizontal axis while $-2i$ is a point below the horizontal axis. I want to turn my system on automatically every day. So I use the below code in my Python script, but sudo asks me for a password every time:  os.system('sudo sh -c "echo date \'+%s\' -d \'+ \        24 hours\' &gt; /sys/class/rtc/rtc0/wakealarm"')   How can I run this script without sudo asking for the password every time? Finish an activity after a time period Reprojecting raster from lat/lon to UTM in R? i have to turn it into a  UTM in order to make the buffer functional.  wets&lt;-readOGR(dsn=".",layer="shapefile") r.raster &lt;- raster() extent(r.raster) &lt;- extent(wets) res(r.raster) &lt;- 100   wets.r &lt;- rasterize(wet,r.raster) plot(wets.r) wetsbuf&lt;-buffer(wets.r,width=500)   During the buffer creation which is the last line of code, it gives this warning:  Warning message:   In couldBeLonLat(x) :   raster has a longitude/latitude CRS, but coordinates do not match that   here's the info    summary(wets.r)           layer  Min.        1  1st Qu.     1  Median      2  3rd Qu.     9  Max.       11  NA's    52629  summary(wets)    Object of class SpatialPolygonsDataFrame Coordinates:       min       max  x  683705  714088.8  y 4326266 4343768.0  Is projected: TRUE   proj4string :  [+proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=500000 +y_0=0 +datum=GGRS87  +units=m +no_defs +ellps=GRS80 +towgs84=-199.87,74.79,246.62]  Data attributes:    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.      0.0     2.5     5.0     5.0     7.5    10.0         wets.r  class       : RasterLayer  dimensions  : 175, 304, 53200  (nrow, ncol, ncell) resolution  : 100, 100  (x, y) extent      : 683705, 714105, 4326268, 4343768  (xmin, xmax, ymin, ymax) coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0  data source : in memory names       : layer  values      : 1, 11  (min, max) attributes  :    ID FID  from:  1   0  to  : 11  10   I have to change the prjection in order to be possible to do the buffer. How to fake a package version installed? Being an early adopter and using 11.04 daily builds I sometimes meet a situation when some packages require earlier versions of other packages than those I have installed. Usually newer (but refused) versions of needed packages provide all the functionality of their older versions.  If I use dpkg -i --force-depends-version to install dependent packages everything works fine, I've never seen a problem.  Instead of manually downloading and installing every package, can I just make the system pretend there is a specific package version installed when there is a newer? Or is there a --force-depends-version key equivalent for apt-get? Approximating a $\sigma$-algebra by a generating algebra Theorem. Let $(X,\mathcal B,\mu)$ a finite measure space, where $\mu$ is a positive measure. Let $\mathcal A\subset \mathcal B$ an algebra generating $\cal B$. Then for all $B\in\cal B$ and $\varepsilon&gt;0$, we can find $A\in\cal A$ such that $$\mu(A\Delta B)=\mu(A\cup B)-\mu(A\cap B)&lt;\varepsilon.$$  I don't think there is a proof in this site. It's a useful result for several reasons:  We know what the algebra generated by a collection of sets is, but not what the generated $\sigma$-algebra is. The map $\rho\colon \cal B\times\cal B\to \Bbb R_+$, $\rho(A,A')=\mu(A\Delta A')$ gives a pseudo-metric on $\cal B$. This makes a link between generating for an algebra and dense for the pseudo-metric. We say that a $\sigma$-algebra is separable if it's generated by a countable class of sets. In this case, the algebra generated by this class is countable. An with the mentioned result, we can show that $L^p(\mu)$ is separable for $1\leq p&lt;\infty$, which makes a link between the two notions. In ergodic theory, we have to test mixing conditions only an a generating algebra, not on all the $\sigma$-algebra. Interpreting the Kretschmann scalar How to recover a removed file under Linux? By accident, I used rm on a file I didn't want to delete. Is there a way that I can get it back under Linux? top x% in [tag] : rules for the tag to be taken into account? How do you get the index of the current iteration of a foreach loop? Is there some rare language construct I haven't encountered (like the few I've learned recently, some on Stack Overflow) in C# to get a value representing the current iteration of a foreach loop?  For instance, I currently do something like this depending on the circumstances:  int i = 0; foreach (Object o in collection) {     // ...     i++; } What is the best way to add options to a select from a JavaScript object with jQuery? What is the best method for adding options to a &lt;select&gt; from a JavaScript object using jQuery?  I'm looking for something that I don't need a plugin to do, but I would also be interested in the plugins that are out there.  This is what I did:  selectValues = { "1": "test 1", "2": "test 2" };  for (key in selectValues) {   if (typeof (selectValues[key] == 'string') {     $('#mySelect').append('&lt;option value="' + key + '"&gt;' + selectValues[key] + '&lt;/option&gt;');   } }   A clean/simple solution:  This is a cleaned up and simplified :  $.each(selectValues, function(key, value) {      $('#mySelect')           .append($('&lt;option&gt;', { value : key })           .text(value)); });   Changes from matdumsa's: (1) removed the close tag for the option inside append() and (2) moved the properties/attributes into an map as the second parameter of append(). How can I stop Steam from loading when I start my computer? Every time I boot into OSX or Windows, Steam automatically starts.  Is there a way to stop Steam starting whenever I boot up my computer? How can I get Gnome3 to remember my session? I am running Gnome3, but I had the same problem with Unity, on Ubuntu 12.04.  I have a fairly elaborate setup I enjoy using day-to-day. A LibreOffice spreadsheet with everyone's extension numbers; a window with reference data I use regularly; two mulit-tabbed Konsole/Terminal windows with several remote systems sessions, firefox with a set of open tabs, and so on. But whenever I log out, when I return, I must set up everything from scratch. I remember the good 'ol days, when I rebooted, I'd re-log in, and all my windows came back up in the same places as they were when I logged out, and my Konsole/Term would come up with the same remote logins as before.... I'd have to re -setup  some of my programs, but that's better than having to move every win into place, and resize them, etc.  How do I get this functionality back? Many LaTeX “hacks” begin with \makeatletter and end with \makeatother. What do these commands do? Compute $E(X\mid X+Y)$ for independent random variables $X$ and $Y$ with standard exponential distributions Failed to load map. Error contacting Google servers. This is probably an authentication issue Make your own .sty files Sorry to start a subjective question, but want to understand "own.sty" file.  Other than all \usepackage{} what sort of other commands can be added to the makeyourown.sty file.  Can you include \let command, and \newcommands in it.   What sort of precaution / structure newbies should follow.