I've had (and abused) for over 4 years: sandy gigs, pretty harsh drops, 2 failing hard drives, and it still runs fine EXCEPT for random freezing, no bsod; only way to get it moving is to keep the power button pressed or remove power. I've noticed that it is definitely heat related. Living in a big city the dust is a huge problem, I have to clean it out and replace the thermal paste every 2 months or so because the issue gets out of hand and the freezes become more and more frequent.   I've ruled out RAM and hard disk problems, so I figure it's either the CPU or GPU. Is there a way that I could rule out GPU? I've read that CPUs will start doing this if they have so many uptime hours, and this thing has definitely ran for hours on end almost every day for the past 4 years - but I could replace it and even perhaps upgrade it if I knew it was the cause of this problem.
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.
Using the same variable as a fixed and random effect in Mixed Effect Models Bottom to top explanation of the Mahalanobis distance? I'm studying pattern recognition and statistics and almost every book I open on the subject I bump into the concept of Mahalanobis distance. The books give sort of intuitive explanations, but still not good enough ones for me to actually really understand what is going on. If someone would ask me "What is the Mahalanobis distance?" I could only answer: "It's this nice thing, which measures distance of some kind" :)   The definitions usually also contain eigenvectors and eigenvalues, which I have a little trouble connecting to the Mahalanobis distance. I understand the definition of eigenvectors and eigenvalues, but how are they related to the Mahalanobis distance? Does it have something to do with changing the base in Linear Algebra etc.?  I have also read these former questions on the subject:       I have also read .  The answers are good and pictures nice, but still I don't really get it...I have an idea but it's still in the dark. Can someone give a "How would you explain it to your grandma"-explanation so that I could finally wrap this up and never again wonder what the heck is a Mahalanobis distance? :) Where does it come from, what, why?   UPDATE:   Here is something which helps understanding the Mahalanobis formula: I note that the installation of qgis completed successfully. However, the log procedure returns this message:     "...... Estrazione: wvhpgn.gsb Estrazione: wyhpgn.gsb Cartella di   destinazione: C:\Programmi\Quantum GIS Lisboa Creato il programma di   disinstallazione: C:\Programmi\Quantum GIS Lisboa\Uninstall-QGIS.exe   Crea cartella: C:\Documents and Settings\All Users\Menu   Avvio\Programmi\Quantum GIS Lisboa   Impossibile accedere al file. Il file Š utilizzato da un altro processo. Running postinstall grass64.bat... Running postinstall   msvcrt.bat... ......"      System parameters: Quantum GIS Lisboa 1.8.0  Microsoft Windows   Professional, Versione 2002, Service Pack 3   The message:      Impossibile accedere al file. Il file Š utilizzato da un altro   processo   translates as      Unable to access the file. The file used by another process   I then get the following error:     "Impossibile trovare il punto di ingresso locale_charset della   procedura nella libreria di collegamento dinamico iconv.dll"   which translates as:     Can not find the entry point of locale_charset procedure in the   dynamic link library iconv.dll Quotient ring of Gaussian integers Italian keyboard: entering tilde (~) and backtick (`) characters without changing keyboard layout I haven't had the chance to take any serious low-level programming courses in school. (I know I really should get going on learning the "behind-the-scenes" to be a better programmer.) I appreciate the conveniences of Java, including the ability to stick anything into a System.out.print statement. However, is there any reason why you would want to use System.out.printf instead?   Also, should I avoid print calls like this in "real applications"?  It's probably better to  to print messages to the client's display using some kind of UI function, right? How to remove the Unity Amazon package in 16.04? I was able to go to the ubuntu software center before and remove it and now it doesn't show up since the switch to the gnome software store. Trying the terminal method of removing the shopping lens doesn't work in this release. Algebra of LDA. Fisher discrimination power of a variable and Linear Discriminant Analysis Apparently,     the Fisher analysis aims at simultaneously maximising the   between-class separation, while minimising the within-class   dispersion. A useful measure of the discrimination power of a variable   is hence given by the diagonal quantity: $B_{ii}/W_{ii}$.     I understand that the size (p x p) of the Between (B) and Within-Class (W) matrices are given by the number of input variables, p. Given this, how can $B_{ii}/W_{ii}$ be a "useful measure of the discrimination power" of a single variable? At least two variables are required to construct the matrices B and W, so the respective traces would represent more than one variable.  Update: Am I right in thinking that $B_{ii}/W_{ii}$ is not a trace over a trace, where the sum is implied, but the matrix element $B_{ii}$ divided by $W_{ii}$? Currently that is the only way I can reconcile the expression with the concept. Random number generation and probability Trying to make aliases that open the last modified file One thing that I frequently do is edit the most recently modified files, so instead of typing "ls -lr" and then "vim lastfile", I thought I would make some shortcuts in my ~/.bash_profile file:  alias via="vim `ls -rt | tail -1`" alias vib="vim `ls -rt | tail -2 | head -1`" alias vic="vim `ls -rt | tail -3 | head -1`" alias vid="vim `ls -rt | tail -4 | head -1`" alias vie="vim `ls -rt | tail -5 | head -1`"   The problem is that, weirdly enough, these commands don't work.  They open some file that isn't one of the last, or even a file was deleted from the current directory (I wonder if there's some kind of file cache updating issue in the directory.  This occurs on both my local machine and the cluster I work on).  However, if I type vim `ls -rt | tail -1` directly, without using the alias, it works every time. How can I suspend/hibernate from command line? How can I suspend or hibernate my laptop using command line, without installing additional software? grub2 wont load Ubuntu on dual boot Having an issue with a dual boot setup that is being run from Windows boot manager. I can successfully load into grub2 from Windows boot manager, however it seems that grub2 cannot locate to the Kernel or something, as it is dropping me right into a shell with the following output:  [ Minimal BASH-like line editing is suported. For the First word, TAB list the posible command completion. Anywhere else tab list the posible completions of a device/filename,]  grub&gt;   I have used Easybcd in the past and successfully loaded a Linux grub through Windows bootloader, but this was when both operating systems were on the same partition, but since my OS installationd are now on separate partitions it seems EasyBcd cant work its magic.   ONe encouragement is that I was able to get Easybcd to load a working Grub if I used the Neo grub bootloader and edit the confg with:  title Ubuntu 14.04 find --set-root /boot/vmlinuz-3.19.0-61-generic kernel /boot/vmlinuz-3.19.0-61-generic ro root=/dev/sdc initrd /boot/initrd.img-3.19.0-61-generic   however this loads in Grub4DOS which is very slow, and as of today this method stopped working See  for details).  Here is the output of EasyBcd Settings for all the different methods I have tried for the Ubuntu 14.04 installation:  Default: Windows 7 Timeout: 30 seconds Boot Drive: C:\  Entry #1 Name: Windows 7 BCD ID: {current} Drive: C:\ Bootloader Path: \Windows\system32\winload.exe  Entry #2 Name: Ubuntu 14.04 Legacy BCD ID: {a4f127cf-3150-11e6-8aaf-408d5cb9e442} Drive: C:\ Bootloader Path: \NST\nst_linux.mbr  Entry #3 Name: Ubuntu 14.04 Grub2 BCD ID: {a4f127d0-3150-11e6-8aaf-408d5cb9e442} Drive: C:\ Bootloader Path: \NST\AutoNeoGrub0.mbr  Entry #4 Name: Ubuntu Neo Grub BCD ID: {a4f127d1-3150-11e6-8aaf-408d5cb9e442} Drive: C:\ Bootloader Path: \NST\NeoGrub.mbr   *It seems that none of the paths seen above are pointing to my dev/sdc2/ partition which would be considered DISK1 on my Windows Volume manager.     EDIT - In the confusion of attempting to get a working bootmanager for Ubuntu/Windows, you will see that grub and Windows Boot manager have all been installed in numerous locations. Below are the present locations and contents of all bootmanager &amp; Grub installations:  dev/sdb Windows7 drive  /dev/sdb1 - 512 MB fat32 partition which is currently empty  /dev/sdb2 - 110 GB ntfs partition containing Windows7 installation. This partition contains a 'Boot' folder which contains BCD files and a whole wack of langauage folders. THIS IS The FOLDER THAT WINDOWS BOOTLOADER uses.  /dev/sdb4 - 121.53 ntfs partition containing storage for media    dev/sdd - Ubuntu Drive  dev/sdd1 - 512 MB partition containing a 'EFI' folder, inside of which are two folders 'grub' and 'Ubuntu', both of which contain the exact same files (grub.cfg, grubx64.efi, MokManager.efi, shium64.efi)  dev/sdd2 - 48.83 GB ext4 partition that contains the '/' folder and Ubuntu instalation.   dev/sdd3 - 69.91 GB ntfs partition containing storage for media  what do I need to do so that the Grub shell I am being dropped into will load up Ubuntu? HOw can I get this machine to dual boot out of Grub? Why do cars gain lift while going at a high speed? I've been researching the physics involved with spoilers and I've just been turning up the same information about spoilers giving the back wheels of a car more traction by acting as an up side down airfoil.   So my question is, what exactly causes the car to apparently gain lift while moving quickly, so as to merit the use of a spoiler, and is this entirely due to the aerodynamics of the vehicle in question?   Edit: Clarity of question. Lots of questions are very generic, &quot;share an experience&quot; kinds of questions. In these cases, I am quite often interested in specific answers that may not have gotten that many upvotes. These questions also tend to elicit lots of responses, so going back to find the answers I'm interested in somewhere in the middle of a sea of responses is a pain. Is there a way to favorite or bookmark these answers? How does the 2009 Star Trek film mesh with Enterprise canon? All of the events in the 2009 Star Trek movie would have taken place after the adventures of Captain Johnathan Archer and company.  So, unless J.J. Abrams and friends decide to completely hand-wave that bit of history as well, all of the events in Enterprise should (in theory) still be able to line up with this new timeline.  Are there any points of conflict in this?  How about any time-travel episodes in the Enterprise series which may have happened differently after the interventions of Nero?  Are there possible good explanations for such conflicts, or are there some which are irreconcilable?  NOTE:  I'm not arguing here whether or not ST2k9 is a part of Star Trek canon.  In fact, this question is specifically granting that it is.  I just want to know if there's any conflicts between the new movie and the existing Star Trek history that remains applicable to it. Playing a remote movie on the remote computer I have two computers (a desktop and a laptop) running linux connected to my local area network. I like to ssh from my laptop over to my desktop and run programs there, and sometimes listen to music on my desktop, which is connected to my stereo system. Lately, I've been wanting to play movies on the desktop and desktop screen, but cue them from my laptop across the room.   Unfortunately, I cannot play a movie in the current X session running on my Desktop on from my laptop. What is odd about this is that I can listen to the audio coming from the speakers that are hooked up to my desktop, by playing the audio files over ssh! This tells me that there must be a way to send the movie to that Xsession, from the ssh shell that I am connected to.  Does anyone have any ideas about this? Create a new cmd.exe window from within another cmd.exe prompt An infinite subset of a countable set is countable In my book, it proves that an infinite subset of a coutnable set is countable. But not all the details are filled in, and I've tried to fill in all the details below. Could someone tell me if what I wrote below is valid?  Let $S$ be an infinite subset of a countable set $T$. Since $T$ is countable, there exists a bijection $f: \mathbb{N} \rightarrow T$. And $S \subseteq T = \{ f(n) \ | \ n \in \mathbb{N} \}$. Let $n_{1}$ be the smallest positive integer such that $f(n_{1}) \in S$. And continue where $n_{k}$ is the smallest positive integer greater than $n_{k-1}$ such that $f(n_{k}) \in S$. And because $S$ is infinite, we continue forever. Now consider the function $\beta : \mathbb{N} \rightarrow S$ which sends $k \rightarrow f(n_{k})$.   So in order for $S$ to be countable, $\beta$ would have to be a bijection. $\beta$ is injective since if $f(n_{k}) = f(n_{j})$, then $n_{k} = n_{j}$ because $f$ is injective. We also can conclude $k = j$ because the various $n_{i}$ chosen were strictly increasing.   Edit: $\beta$ also needs to be surjective. So for every $r \in S$ there exists a $q \in \mathbb{N}$ such that $\beta(q) = f(n_{q}) = r$. We know that $f^{-1}(r) \in \{n_{1}, n_{2}, ..., n_{k} ... \}$, so we can let $f^{-1}(r) = n_{d}$. Thus $\beta(d) = f(n_{d}) = r$. just after the Big Bang and before inflation the currently observable universe was the size of a coin. One millionth of a second later the universe was the size of the Solar System, which is an expansion much much faster than speed of light. Can space expand with unlimited speed? I want to update Acrobat Reader for Firefox, but the download has the .bin extension. How can I install it?