Perpetual motion machine
Can magnets rotate infinitely?
Removing las2dem streaks from raster DEM? I've created a series of DEM files using the  tool from LAStools; however since I don't have a licensed version they have black streaks running across them. Does anyone know a good method for removing these streaks? How do I restore the default repositories? Comparing $\pi^e$ and $e^\pi$ without calculating them How can I  compare (without calculator or similar device) the values of $\pi^e$ and $e^\pi$ ? Why can't I log into minecraft with a mojang account? I created a Mojang account and downloaded the Minecraft launcher, but when I started it up, I couldn't log in. Since the log in fields did not require a username, I tried typing in my email, and still couldn't log in. I've tried after resetting my password, but that didn't work either. What am I supposed to do to log in and play? The  defines multiple padding schemes for signature generation/verification ( and ),  and encryption/decryption ( and the less safe ).   Which attacks are possible on signature generation/verification and encryption/decryption if no padding mechanisms are applied, i.e. if raw RSA is used over the plaintext or hash? If I have a legendary creature out, and I make a copy of it (such as by enchanting it with  or making a ), do I get enters-the-battlefield effects from the creature before I have to sacrifice it to the legend rule? Auto confirm when running bash scripts? Where did the Q come from, before the Q Continuum? In the Star Trek Universe where did the Q come from? I mean before they were Q in the Q Continuum? In Star Trek Voyager you learn that the race is somewhat intolerant of individualism (in the episode of the Q Civil War) but Q also suggest they have always been Q. Is that statement true, have the Q always been the Q? or were they a race that evolved into omniscience? How to find patches with data in Raster and then how to extract those patches? I have a single band raster file as drawn in the labeled image attached.  The size of raster is around 4k pixel in each x and y axis. Large part of this raster is empty. Only in small portions of the raster contains data as labeled. Is there any efficient way I can extract rectangular patches around the data portions of the large tif raster file? Any pythonic way using gdal or rasterio or some other package. What I have done so far: I have followed from sklearn.feature_extraction.imageway to extract 2D patches where there is data as follows. from sklearn.feature_extraction.image import extract_patches_2d im = imageio.imread(largeFilePath) # reading the large image x, y = np.nonzero(im) # taking xy locations with non zero values  # determining xleft, xright, yleft and yright of the non zero area in  raster  xl,xr = x.min(),x.max()  yl,yr = y.min(),y.max()   #Extraing the non zero area from my original raster only_desired_area = im[xl:xr+1, yl:yr+1]  # my desired window to extract  window_shape = (480, 480)  # 2D Ptaches extraction B = extract_patches_2d(only_desired_area, window_shape, max_patches=100)  Issue: This doesn't have georeference information because I haven't used gdal or rasterio How to correctly assess the correlation between ordinal and a continuous variable? I'd like to estimate the correlation between:  An ordinal variable: subjects are asked to rate their preference for 6 types of fruit on a 1-5 scale (ranging from very disgusting to very tasty) On average subjects use only 3 points of the scale.  A continuous variable: the same subjects are asked to quickly identify these fruits, which results in an mean accuracy for the 6 fruits.   Is Spearman rho the best method to analyze these data and/or are there other good methods I could consider? How does the Mac choose which connection to use when both Wifi and Ethernet are connected? When I'm connected to two networks with separate routers using Wifi and Ethernet, how does my Mac know what connection to use when I visit a website? How to diagnose computer lockups and freezes? I built a desktop computer a couple years back with the following specs:  CPU: Intel  Yorkfield 2.5GHz 6 MB L2 Cache LGA 775 95W Quad-Core Processor BX80580Q9300 Motherboard:  LGA 775 NVIDIA nForce 680i SLI ATX Intel Motherboard Video Card: Two  GeForce 8600GT SCC 256 MB 128-bit GDDR3 PCI Express x16 SLI Supported Video Card PSU: SeaSonic S12 Energy Plus  ATX12V V2.3 / EPS12V V2.91 SLI Certified CrossFire Ready 80 PLUS Certified Active PFC Power Supply Memory: Two G.SKILL 4 GB (2 x 2 GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory   Since its inception, the machine has periodically locked up, the regularity having varied over the years from once a day to once a month. Typically, lockups happen once every few days. By &quot;lockup&quot; I mean my computer just freezes. The screen locks up, I can't move the mouse. Hitting keys on my keyboard that normally turn LEDs on or off on the keyboard (such as Caps Lock) no longer turn the LEDs on or off. If there was music playing at the time of the lockup, noise keeps coming out of the speakers, but it's just the current frequency/note that plays indefinitely. There is no BSOD. When such a lockup occurs I have to do a hard reboot by either turning off the computer or hitting the reset button. I have the most recent version of the NVIDIA hardware drivers, and update them semi-regularly, but that hasn't seemed to help. I am currently using Windows 7 x64, but was previously using Windows Server 2003 x64 and having the same lockup issues. My guess is that it's somehow video driver or motherboard related, but I don't know how to go about diagnosing this problem to narrow down which of the two is the culprit.  Additional information re: cooling Regarding cooling... I've not installed any after-market cooling systems aside from two regular fans I scavenged from an older computer. The fan atop the CPU is the one that shipped with it. One of the two scavenged fans I added it located at the bottom tower of the corner, in an attempt to create some airflow from front to back. The second fan is pointed directly at the two video cards.  SpeedFan installation and readings Per studiohack's suggestion, I installed , which provided the following temperature readings:  GPU: 63C GPU: 65C System: 76C CPU: 64C AUX: 36C Core 0: 78C Core 1: 76C Core 2: 79C Core 3: 79C   Update #3: Another Lockup :-( Well, I had another lockup last night. :-( SpeedFan reported the CPU temp at 38 C when it happened, and there was no spike in temperature leading up to the freeze. One thing I notice is that the freeze seems more likely to happen if I am watching a video. In fact, of the last 5 freezes over the past month, 4 of them have been while watching a video on Flickr. Not necessarily the same video, but a video nevertheless. I don't know if this is just coincidence or if it means anything. (As an aside, each night before bedtime my 2 year old daughter sits on my lap and watches some home videos on Flickr and, in the last month, has learned the phrase, &quot;Uh oh, computer broke.&quot;)  Update #4: MemTest86 and 3DMark06 Test Results: Per suggestions in the comments, I ran the MemTest86 overnight and it cycled through the 8 GB of memory 5 times without error. I also ran the 3DMark06 test without a problem (see my scores at ). So... what now? :-) Any further suggestions on what to check? Is there some way to get a stack trace or something when the computer locks like that? Resolution I have never did figure out the particular problems, but based on the suggestions here and elsewhere, I'm presuming it was a motherboard issue. In any event, I recently upgraded my system, buying a new motherbeard, PSU, CPU, and RAM, and that new rig has been working splendidly the past several weeks. I am using the same graphic cards as in the old setup, so I think it's safe to reason that they weren't the cause of the problem. Complement property of DES I'm supposed to show the complement property of DES ($c=DES(p,k) =&gt; \bar c = DES(\bar p, \bar k)$).  My idea was to just start the algorithm with $\bar p$ and see what happens (ignoring the initial permutation for now). I looked at it step by step and got the the point where $R1 = \bar L1 \oplus f(\bar k1, \bar R0)$. So I figured I had to show that $f(\bar k1, \bar R0) = \bar f(k1,R0)$. Is that even right so far? Because I got stuck at the point where the S-Boxes are used. Why would $S(\bar x) = \bar S(x)$?  Somewhere else I read something about a formal prove using induction, but I don't know how I would do that either... How to respond to "How much funding will you bring?" as an interview question for a faculty job? Why is OpenJDK 10 packaged as openjdk-11-*? While looking to compile OpenJDK from source, the newest General Availability version () insists on OpenJDK 9 or 10.  JDK 11, however, is not due to be released until .    However, to my surprise, when I do apt search openjdk the result is:  ... openjdk-11-jdk - OpenJDK Development Kit (JDK) ... openjdk-8-jdk - OpenJDK Development Kit (JDK) ...   No OpenJDK 9 or 10!  And wait, is that OpenJDK 11?  Maybe a Beta release?  Nooo....  So I looked at apt show openjdk-11-jdk:  Package: openjdk-11-jdk Version: 10.0.1+10-3ubuntu1 ...   Why has OpenJDK 10 been packaged as openjdk-11-*?? Do gravitational lenses work on gravitational waves? Copy from Evernote to Paste to Wordpress preserving formating Is it possible to post texts directly from the Windows desktop Evernote application to Wordpress, and retain the formating? Simple copy/past leads to format break. Why are only certain shutter speeds or apertures available? I've tried almost any method to root my ASUS ZenFone Live, but no one seems to work. Also I only need root, no unlocked bootloader (don't want to wipe data) or custom recovery (not essential ATM). Suppose there are $2$ permutations given by $p$ and $q$. I need to check whether $p$ belongs to the group generated by $q$, and if so, it's representation in a power of $q$. In other words, I've been given $p$ and $q$, I need to check whether $\exists i \in \{ 0,...,|q|-1 \} \text{ such that } p = q^i$ I know that if $m = \gcd(i, |q|)$, then $|q^i| = \frac{|q|}{m}$. Now, say that such an $i$ exists. Then, $$ |p| = \frac{|q|}{\gcd(i, |q|)} \Rightarrow \gcd(i, |q|) = \frac{|q|}{|p|} $$ Thus, a necessary condition for such an $i$ to exist is: $|p|$ divides $|q|$ Say that this holds, and $\frac{|q|}{|p|} = r$, where r is an integer. Then we just have to solve $\gcd(i, |q|) = r$ for $ i \in \{ 0,...,|q|-1 \}$. Can this be done? If not manually, then by some efficient algorithm? (Note: Just looping over all values of $i$ is not efficient as $i$ may be very large) Edit: Another way I can think of solving this is by writing both $p$ and $q$ as product of disjoint cycles: $$ p = c_1c_2\ldots c_k \text{ and } q = d_1d_2\ldots d_l $$ And thus, as disjoint cycles commute: $$ p^i = c_1^ic_2^i\ldots c_k^i $$ How to proceed after this?