Wikipedia:Reference desk/Archives/Computing/2010 August 27

= August 27 =

Compile error in hidden module: AutoExec?
The message "Compile error in hidden module: AutoExec" shows whenever I start my Word 2000. After clicking OK I can use it normally, but the message shows again when I close it. It seems to be no more than an annoyance. Any idea what this means, and how I can fix it? 24.92.78.167 (talk) 00:39, 27 August 2010 (UTC)
 * There is an article about this on the Microsoft Support web site; have you seen it yet? http://support.microsoft.com/kb/307410 PleaseStand (talk) 01:10, 27 August 2010 (UTC)

Built in Anti-virus programs
I was highly displeased at all the flame I got for my last post, now my question is what are the antivirus programs that come with lets say a mac laptop or a pc from either 6 years ago or now. I'm not talking about program trials either, my cousin just got a new mac and want to know if he's properly protected by built in antivirus programs if any. Thanks in advance. Wikiholicforever (talk) 00:40, 27 August 2010 (UTC)
 * General information: Most PCs come with only trial subscriptions to antivirus programs (6 months or so), and Macs come with no antivirus software at all. That has not changed much in the past several years. However, there are far fewer malware programs for Mac versus PC. PleaseStand (talk) 01:08, 27 August 2010 (UTC)

Thank you for the answer, so from what I got your answer is that the majority of pc's don't have any permanent antivirus programs at all??? Are there at least very simple detecters that come packed in?? And I did'nt know that the mac was so badly protected, I'm kind of surprised! I really appreciate the answer, thanks again! Wikiholicforever (talk) 01:22, 27 August 2010 (UTC)


 * Unless the particulars of the deal included the vendor installing a full version of some anti-virus program, your cousin's Mac doesn't have any anti-virus software on it. They don't come with any from Apple.  That said, in the 18 years that I've been using Macs, I've never once had a virus or other malicious program on my systems.  Partially because there are significantly fewer viruses written for Macs as well as the fact that I'm careful about where I go on the net and what I click on.  It's not that Macs are badly protected when sold it's that, for the most part, it's just not necessary.  It's like someone who lives in the United States getting a malaria shot.  The chances of getting malaria in the US are so low that nobody bothers getting immunized for it.  Dismas |(talk) 01:26, 27 August 2010 (UTC)


 * Windows Vista comes with Windows Defender. Mac OS 10.6 (released in 2009) also comes with a hidden anti-virus program. All versions of Windows also automatically download the Windows Malicious Software Removal Tool. So, in summary, if he's using an older version of the Mac OS, he isn't protected by an anti-virus program by default.--Best Dog Ever (talk) 02:23, 27 August 2010 (UTC)
 * That basic protection, though, is very limited. The Windows MSRT only scans for specific prevalent families of malware once a month, so it cannot prevent infection by malware. The Mac OS X 10.6 "file quarantine" only applies to files downloaded using Safari, iChat, etc. and only scans for a small set of Mac trojan horse programs. It won't prevent the user, for example, from spreading a Windows virus or macro virus, or spreading a virus via flash drive (if a Mac virus were to spread that way). So I wouldn't consider it a "substitute" for antivirus software, applying security updates to the operating system, web browser, and all browser plug-ins, and avoiding unsafe links. PleaseStand (talk) 03:18, 27 August 2010 (UTC)

Thanks for all the answers, I really appreciate it. Over the past two days I've been testing to see if a keylogger would be blocked by a number of computers. What I found out was very similar to your answers. It was detected on 3 out of the 5 computers with just built in antivirus, the keylogger was'nt detected on a mac and another pc. When I went home to see if the keylogger was working, nothing came up so obviously it was'nt written for mac and I don't know what happened with the pc... Wikiholicforever (talk) 22:07, 27 August 2010 (UTC)
 * Using real malware for testing to see if an antivirus program is working isn't a good idea. The EICAR test file, in contrast, is a safe file specifically designed for the purpose. PleaseStand (talk) 22:41, 27 August 2010 (UTC)
 * Keyloggers are pretty harmless if they are under your own control and don't have a "phone home" feature, and you remember to delete all your logged passwords, but the very simple EICAR file (X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*) is much safer. Just save it as a text file and see how long it takes your anti-virus software to detect it.    D b f i r s   02:29, 29 August 2010 (UTC)

Error Box when Googling
My PC runs Windows XP Professional "Version 5.1.2600 Service Pack 3 Build 2600" and IE Version 7.0.5730.13 (data from System Information) Recently while using Google the search results appear, but I have also had an error box come up several times saying:
 * "Internet Explorer cannot open the Internet site
 * http://www.google.com.au/search?hl=en&source=hp&q=Chris+Madden+hockey&rlz=1R2GGLJ_en&aq=f&aqi=&aql=&oq=&gs_rfai=
 * Operation aborted"

The box has a red cicle with a white X on the left, and an 'OK button' at the bottom to click on.

Refreshing the screen (F5) does not always seem to make the search work. It only seems to have been happening the last week or two. Any ideas what may be causing this? Perhaps a simple failure to acccess Google for some reason? But the search results are appearing so it seems it is accessing the Google site. 220.101 talk\Contribs 03:43, 27 August 2010 (UTC)


 * Some cursory Googling suggests it's an IE problem. IE is attempting to contacting Google, fails, and just gives up. This MSDN forum post suggests a number of different potential fixes. My suggestion is to upgrade to IE 8, or a better browser like Chrome, FireFox, Opera, Safari. --—Mitaphane Contribs 15:50, 27 August 2010 (UTC)


 * Thanks for your reply, Mitaphane. I'll take a look at what the links say and go from there. I'll also take a look at some of the other browsers. Thanks! 220.101 talk\Contribs 15:10, 28 August 2010 (UTC)

Implementing a lock for a socket stream
Hello! I'm developing a Java application that uses network sockets to transfer s between two computers over TCP though  s. My problem is I can't figure out what's the best way to implement a lock for the socket's   and  s so that when one computer wants to transfer an , the other is listening. The easiest way seems to be use two sockets and two threads per computer (an up-down socket and a down-up socket, and a thread blocking to read or write on the designated side), but that sounds really inefficient (though I'm not that familiar with socket application, so if that's the way it's usually done, I wouldn't know). I've experimented with interrupting threads blocked in I/O operation for similar tasks in the past, and they seem to ignore the interruption. (It seems like the Java API specifies a different behavior with every subclass of  for interrupts, which gets very confusing and difficult with sockets.) I'd appreciate any related information, especially specific to Java. Thank you!--el Aprel (facta-facienda) 03:49, 27 August 2010 (UTC)
 * One socket is sufficient for bidirectional communication; you can "simultaneously" send and receive (on both ends). In other words, both ends of the socket implement an InputStream and OutputStream.  Writing to the output streams, as defined in the java.io interface, is non-blocking - so you can write data, and it will get buffered on the other end until the other program is ready to read.  When reading, just be sure to check if bytes are available, and only read that many (guaranteeing that you won't block indefinitely); or set up a read-timeout or channel for non-blocking reads.  The Java socket API abstracts this for you; you don't have to worry about locking the socket for bidirectional communication to work.  (Whether the data is actually flowing both directions simultaneously is entirely dependent on your network card driver; if it doesn't support this, the JVM or the operating system will buffer and serialize the datastreams; TCP sockets guarantee that data will never be lost because of such buffering at any point in the network).  In terms of efficiency - well, if you're sending and receiving, you're increasing your network traffic - so if your hardware is maxxing out on bandwidth, you'll be able to measure the slow-down; but it will only affect performance, not functionality.  If you implement multiple sockets, (and your hardware and operating system support it), each socket could map to a different IP and network interface, parallelizing the data flow, so that could conceivably benefit you; but only if you actually have multiple IPs and network cards per machine.  Nimur (talk) 03:58, 27 August 2010 (UTC)
 * Thank you for the rapid (less than 10 minutes!) and informative reply, Nimur. I didn't know that sockets supported two-way communication—it sure makes a lot of things easier! Your note about checking available bytes before reading them was also helpful, as it led me to check the documentation for 's constructor, which blocks and was part of my problem. Now everything is working fine.--el Aprel (facta-facienda) 05:32, 27 August 2010 (UTC)
 * I haven't done any Java socket programming, but OutputStream.write must block because the alternative is too horrible to contemplate. Writes to a TCP stream have to block when the write buffer fills just as reads block when the read buffer empties. If the write buffer were allowed to grow indefinitely, you could exhaust all available memory by sending a 10GB file on a socket at 30MB/s when the recipient happens to be on a 1MB/s DSL line.


 * If I understand correctly, you want each computer (call them A and B) to act as an object server for the other. Abstractly, you have four unidirectional message types: requests A→B, responses B→A, requests B→A, and responses A→B. Your original idea of two TCP connections gives you four unidirectional streams, one for each of the message types. Nimur's suggestion is to use one TCP connection and multiplex requests and responses onto the same stream. That would be somewhat harder to implement and I'm not sure if you'd see a performance benefit. If you processed each stream sequentially, you could see a degradation in performance, since a request from B to A couldn't go through while a request from A to B was pending.


 * You also need to think about deadlock. Is it possible that satisfying the other machine's request for an object will require requesting an object from the other machine? If so, consider what happens if B requests X from A and, to satisfy that request, A needs Y from B. If you're using a single TCP connection and everything is sequential, you're doomed at this point, because the request for Y can't go down the wire until X has been sent. If you use two TCP connections, you're okay in that case, but then consider the possibility that B needs X' from A in order to satisfy the request for Y. The only way to deal with this in general is to implement out-of-order responses. -- BenRG (talk) 20:12, 27 August 2010 (UTC)


 * Thank you for your concerns. My socket application is pretty basic (using it as practice—and I'm lucky if I can get a String transmitted successfully!), and uses a server-client relationship (client only asks for objects, and server only sends objects), so I think this avoids most of the problems you mention. As I develop more sophisticated application, I'll keep your advice in mind. I'm a little confusion about your comment "If you processed each stream sequentially, you could see a degradation in performance, since a request from B to A couldn't go through while a request from A to B was pending." Could you explain a little more? Does sequentially mean processing the stream on a single thread per computer?--el Aprel (facta-facienda) 23:10, 27 August 2010 (UTC)
 * 'Sequentially' in this case means that if A requests an object, it cannot make another request until B has responded with said object, and vice versa. It's essentially a 'conversation': one speaker at a time, and with one TCP connection you are limited to this. It can decrease performance, if a long response or network latency blocks the connection when a new request needs to be made. If you go for an implementation with two connections, both computers can send requests whenever they need to. The two separate connections aren't automatically synchronized in any way, which might cause other design problems. I hope this helps. Zigorney (talk) 16:58, 28 August 2010 (UTC)

AJAX/JavaScript problem.
I'm something of a JavaScript newbie (although I have a bazillion years of programming in other languages under my belt). So it may be necessary to speak loudly and use short words!

I'm trying to write a JavaScript application that essentially does the following:


 * 1) Issue an XMLHttpRequest "POST" to launch a CGI program 'A' on the server using xmlhttp.onreadystatechange to register an event handler function. ('A' is a honking great C++ program).
 * 2) Program A will start up and work for ~8 seconds before sending it's response "AJAX-style" using:
 * printf ( "Content-Type:text/plain\nFromA: ...60kbytes of ASCII data...\n" ) ;
 * 1) The instant the JavaScript gets the reply from A, it will return to step (1) and re-issue the post.
 * 2) Should it not get a response within 20 seconds, the JavaScript code re-issues the post on the assumption that something went wrong.

That much works GREAT. I get a solid 8 second 'heartbeat' update from the server.

Now I need to complicate matters.

When the user clicks a button, (at any time during the 8 second cycle), I need to kick off a second program 'B' on the server...which need not respond at all - but which (I strongly suspect) is required to send some sort of response to avoid browser hangups. So 'B' responds immediately with a different AJAX-style response:


 * printf ( "Content-Type:text/plain\nFromB:HelloWorld\n" ) ;

With the "FromB:" part letting me know that this is a junk message from B and not an interesting one from A.

The trouble seems to be that JavaScript forgets the onreadystatechange handler that's waiting for the message from 'A' whenever the message from B arrives...so the heartbeat stops coming back and my 20 second timeout is invoked every time I click the button. (At least, I suspect that's the reason).

Is there some reason why it might be impossible to have multiple AJAX-type queries going on at the same time? Can I have multiple XMLHttpRequest objects working at the same time?

(I need this to work in FireFox, Safari, Chrome and (ideally) Opera - but InternetExplorer is already a lost cause for a dozen other things it doesn't do right!)

TIA SteveBaker (talk) 05:17, 27 August 2010 (UTC)


 * The keyword in AJAX is asynchronous - so yes, you can definitely have multiple independent queries in-flight at any time, going to the same or different programs on the server-side. (This is the whole point of AJAX!)  If it isn't working, it may be some kind of a bug in the order that data is returning ("asynchronous" of course means that there's no guarantee on timing or re-ordering of queries - your server could be doing "smart" things at the HTTP layer, etc.).  Have you considered wrapping your data and responses in JSON (a very lightweight and simple text-based data object format)?  Then, you can easily tag every transaction with its source program (A or B) and some kind of unique transaction ID to ensure it's processed in the correct place / order.  This will make it easier to parse your queries and responses and guarantee that data goes where you intended (to the right server-side program / client-side javascript function, and so on).  Nimur (talk) 06:20, 27 August 2010 (UTC)


 * HTTP/1.1 specifies a connection limit of 2 connections per server. Although browsers recently started increasing this limit for better Ajax responsiveness, you might still run into this depending on what else your application/other tabs are doing. Other than that, multiple XMLHttpRequest objects shouldn't be a problem, and then I'd suspect that somehow your completion handler for B is interfering with the xhr object for A. Do you reuse A and B's XHR object, or create a new one for every request? I've had to work around some odd (mostly IE bugs) with XHRs by calling abort and resetting the readystatechange handler every time I reused a XHR object. Unilynx (talk) 06:23, 27 August 2010 (UTC)


 * Number of connections per server can be set by the server configuration; but that's something to check. On reading Steve's code a bit more carefully, I wonder if he's using the same variable name (xmlhttp) for both transactions.  This is one of those things that you know not to do in C++.  But Javascript makes this problem even more acute, because scope in Javascript is so complex.  You can almost always assume that "it's a global variable."  I would check closely: are you over-riding Transaction A 's registered callback by assiging xmlhttp.onreadystatechange during the initiation of Transaction B?  You're probably mucking with the first transaction object!  In other words, Transaction B isn't a new instance of xmlhttp: it's the same object!  Check carefully; for safety, use clean, new names for each object; and if that fixes it, good.  Follow-up by with some web-searches on "scope in Javascript" - this is a very common programmer-error because JS is so different from normal languages, it's almost impossible to have a "locally-scoped" variable.  Nimur (talk) 06:33, 27 August 2010 (UTC)
 * Number of connections is a client-side restriction too (and there is no standard way for the server to communicate a limit, expect by using HTTP/1.0 instead of /1.1) and requires a configuration change to modify, see eg here where IE7 defaults to 2 and requires a registry change. JavaScript local variables work fine, as long as you properly use the var keyword or put them in objects, and realise that even 'var' variables in JavaScript have function-scope, not block-scope as they would in most other languages. But the issues Nimur mention remain relevant - how exactly do you pass the XMLHttpRequest object to your completion callbacks? Through global variables or closures? Unilynx (talk) 10:19, 27 August 2010 (UTC)


 * &lt;drumroll&gt;...and the winner is...Nimur! Yes, I had goofed up the scope of my XMLHttpRequest and was using the same object for both transactions.  (I really, deeply, truly **HATE** JavaScript!)  Giving each request a different name fixed the problem.  Many thanks folks!
 * @Unilynx: Now you have me worried about the transaction limits! I expect to have 50+ people using this site at the same time - and that means that there will typically be 50 connections to program A - all waiting for their 8 second heartbeat - plus some random number of connections to program B...so there could easily be 50 connections to the server - and perhaps as many as 100.  When you say "a connection limit of 2 connections per server" - I hope you mean "two connections TO EACH CLIENT per server" or something - not a total system limit of two connections...right?
 * I don't intend to support Internet Explorer (it can't run this stuff for LOTS of other reasons) - and I also don't need to support older versions of any of the other browsers either, but I need it to work with the latest HTML-5 versions of Chrome, Firefox, Safari and Opera (actually, the upcoming as-yet-unreleased versions of those four browsers) - and also on Android & iPhone4 cellphone browsers. SteveBaker (talk) 14:14, 27 August 2010 (UTC)
 * 2 per server, per client, yes, so no need to worry unless you did something explicitly to your server to limit connections per IP. As far as I know, no browser actually fully implements HTML5, but that shouldn't matter, as XmlHTTPRequest predates HTML5 anyway - HTML5 is just the first HTML spec to standardize it. (In fact, XmlHTTPRequest is a IE/Exchange invention). Unilynx (talk) 22:31, 27 August 2010 (UTC)

XP Spanned Volumes
I'm running Windows XP and have three 250 GB disks in my machine. I spanned two of them in Disk Management to create one dynamic NTFS drive (D:). If I reformat the system disk (C:) and reinstall the OS, will this affect my spanned volume? matt (talk) 08:16, 27 August 2010 (UTC)
 * No, because you have two logical partitions (one extended) and XP sees only the logical partition you choose when installing which you can ask XP to (quick)format. It will not touch or attempt to change any of your partitioning during installation. Sandman30s (talk) 21:38, 27 August 2010 (UTC)


 * Nonetheless, you should backup all of the data on your (D:) drive. While formatting your and reinstalling your operating-system on (C:) drive normally will not affect any other drives/partitions on the same computer, if something goes wrong, one of your other two disks could be wiped - I presume that by spanning, you mean that (D:) partition resides on two HDDs in a RAID 0 array, in which case the data on both disks is lost even if one disk is wiped. Keep in mind that anytime you're formatting any drive/partition in a computer, you should be prepared to lose all of the data on every partition on every HDD in that computer. Good luck. Rocketshiporion  08:15, 1 September 2010 (UTC)

Nuclear Physics-Package Simulation Software
Hi. I am seeking simulation-software which can be used to simulate the deformation and detonation of nuclear physics-packages. It should be able to: Does anyone here know of any simulation-software (preferably free and/or open-source, but commercial is also acceptable) which meets these criterion? Any information or pointers would be useful. The available double-precision computational power for running this software would be about 2.06 teraflops, scalable if necessary to a maximum of 4.12 teraflops. Thank you to everyone. Rocketshiporion Friday 27-August-2010, 2:45pm GMT.
 * 1) Accept input of shape, size, dimensions, mass, etc. of the fissile core, neutron reflector, explosive lenses and package-wall.
 * 2) Visually simulate deformation of all parts of the physics-package (fissile core, neutron reflector, explosive lenses and package-wall) upon detonation.
 * 3) Output numerical values for the following at the moment of detonation;
 * 4) tonnage (TNT equivalent),
 * 5) nett energy release (in newtons),
 * 6) nett force (in Pascals) at various distances from the epicenter,
 * 7) temperature (in either kelvin or celsius) at various distances from the epicenter,
 * 8) and percentage of fissile material wasted (i.e. which did not undergo fission).
 * 9) Support designing with the following materials:
 * 10) Fissile Material: Uranium, Plutonium, Americium, Curium, Californium, Protactinium & Radium.
 * 11) Neutron-reflector: Beryllium, Titanium, Tungsten, Osmium, Steel, Graphite, Gold, Lead & Uranium.
 * 12) Explosive Lenses: Trnitrotoluene, Cyclotrimethylenetrinitramine, Cyclotetramethylenetrinitramine, Octanitrocubane, etc.
 * 13) Package-Wall: Titanium, Tungsten, Duralumin, Iron, Steel, Carbon, etc.


 * I would strongly suspect that software packages with the level of detail you describe are mostly or entirely the property of national governments and classified as state secrets. If you are employed by such a government, then you might get access to their software.  Otherwise, you'd probably have to develop your own software.  I suspect that one could probably find public information on things like models of various explosives, or neutron response curves for various materials.  However, the data to comprehensively validate a nuclear detonation model is probably also a state secret since only governments have ever been able to test bombs.  Dragons flight (talk) 14:56, 27 August 2010 (UTC)


 * The hard part is not simulating, it is simulating accurately. For example, AutoCAD and several of its commercial and 3rd-party plugins can do deformation finite-element modeling.  And if you home-brew your own full-fledged CAD tool and numerical modeling software, you can do your best to estimate all the necessary parameters, and visualize the output however you like.  But do the equations used to estimate the dynamics and the material properties apply to the unique situation of nuclear detonation?  The only way you can know this is if you have access to both the software (and all the mathematics behind it) AND access to empirical nuclear test data.  As you know (if you use or design CAD tools), accurate equations of state suitable for predicting and modeling are very complicated and are rarely developed from first principles of physics.  They are highly-parameterized and tuned for specific experimental conditions.  Only a few places - say, Lawrence Livermore National Laboratory and Los Alamos National Laboratory will be able to have access to these sorts of parameters; and there is an entire profession dedicated to the validation of nuclear weapons physics-packages through computational simulation.  And, as Dragons Flight points out, because of the sensitive nature of nuclear weaponry, these sorts of career-tracks invariably require access to confidential and controlled information.  Your best chance to get such software is:
 * Begin the long and arduous process of studying an advanced technical field, like computer science, mathematics, physics, or nuclear engineering
 * Apply for an advanced-degree program related to the computer modeling of nuclear weapons
 * Establish good citizenship in a country with a solid nuclear weapons research program, and establish good standing in that country, beyond a reasonable doubt
 * Apply for a position at one of the national laboratories that specialize in weapons maintenance and validation
 * Obtain a Department of Energy clearance to authorize access to the data and software you want (in the United States, this is called "Department of Energy Q")
 * Find yourself in a project team with access to the software.
 * Realistically, asking here at Wikipedia, this is the best kind of answer you'll get. Such tools are not freely or commercially available.  You can always go for "baby physics" versions - in fact, almost any nuclear engineering textbook homework-problems will apply the equations that solve for energy and material dynamics - but do those equations apply accurately enough to model system dynamics for the case of a specific configuration?  Nimur (talk) 15:20, 27 August 2010 (UTC)


 * ... Or you can ask Oak Ridge on Facebook. They're having a conference in Tennessee on October 11, it is not too late to register.  Nimur (talk) 15:24, 27 August 2010 (UTC)


 * I had wondered if the question was meant to test our no-criminal-assistance-answers guideline. Comet Tuttle (talk) 16:15, 27 August 2010 (UTC)


 * It is not criminal to be a nuclear weapons researcher, unfortunately. But it does rouse suspicion.  Anyway, like most complicated systems, nuclear weapon design is not merely about having access to the technology - you need hundreds (thousands, perhaps) of talented individuals to assist in managing the complexity of the engineered system.  I have a feeling Rocketshiporion could receive fully documented schematics, blueprints, software, and all the necessary materials, and still be unable to construct a weapon with them.  I suspect he or she has a long road ahead - starting with learning that "nett energy" is not measured in units of newtons.  Nimur (talk) 17:22, 27 August 2010 (UTC)


 * And just as an aside: I posted the link to the SCALE conference because they are actually involved in the design of nuclear-engineering software, and actually offer training courses. If the OP is serious, that is a reasonable line of inquiry. But if this is an "elaborate hoax to test the limits of Wikipedia," well... all I can say is: do not "joke" with Oak Ridge National Laboratory.  That would be tantamount to walking into a rifle store and "jokingly" asking for schematics to build your own assault-rifle.  You may find yourself way over your head.  These things are not "jokes," they are weapons.  Nimur (talk) 17:33, 27 August 2010 (UTC)


 * Technically, in the United States, if you do research that involves Restricted Data, regardless of whether it is officially or privately derived, you are subject to the legal requirements of the Atomic Energy Act of 1954. (Our article on classified information does not really explain RD very well. It is not really a classification category in the same sense that "secret" and "confidential" are. It basically means "anything to do with nuclear weapons design which has not been explicitly declassified by the DOE", and carries with it heavy requirements for regulation under the Atomic Energy Act.) Lots of things are declassified — but a lot you would need for the above is not. (Like, say, the equation of state for plutonium under pressure.) Which means that you can't tell anybody about it, basically, or keep it in an insecure location. So it is kind of criminal to be a freelance nuclear weapons researcher, if you are generating RD and communicating it to others in any way. But this is not enforced very often. --Mr.98 (talk) 22:21, 29 August 2010 (UTC)


 * I will try asking at Oak Ridge National Laboratory for either the software or atleast all past empirical test-data. I don't realistically expect to be successful with Oak Ridge, but it wouldn't hurt to try. My specific interest is in designing small-diameter physics-packages for interplanetary (not interstellar) spacecraft propulsion, definitely not weaponry or warfare. As for the measurement of nett-force, I was under the impression that the SI unit of force is the newton, although the kilogram (equivalent in my understanding to 9.80665 newtons) has also been used as a unit of force, as has the pound. So which unit of force is used in the simulation of nuclear detonations? Rocketshiporion  Friday 27-August-2010, 10:54pm GMT.


 * Before you dive into such details, you might want to read the difference between a nuclear reactor, an RTG, and a physics package - you specifically asked about detonation (which shouldn't happen if you're only generating energy for propulsion). Check your earlier post - you seem to have confused energy, force, pressure, etc.  Nimur (talk) 23:20, 27 August 2010 (UTC)


 * Rocketshiporion's name would suggest that he's interested in an application similar to Project Orion (nuclear propulsion), which did propose using (lots of) nuclear explosives for spacecraft propulsion. -- Finlay McWalter ☻ Talk 23:24, 27 August 2010 (UTC)


 * He? Nil Einne (talk) 11:43, 28 August 2010 (UTC)


 * There isn't an all-in-one package like that. You can't actually do it from first principles (accurately), you need weapons codes data (derived from nuclear testing), and those are highly classified. The stuff you are asking for is also computationally non-trivial. This report tells about the kinds of crazy computers that the US government uses to try and simulate nuclear weapons designs, and the difficulties of scaling things from the quantum level up to the macroscopic. The physics that happens inside a detonating nuclear weapon is exceedingly complicated. It is more like the sorts of processes that happen inside stars than anything that happens on earth, and yet it is not quite so big as a star that you can generalize so readily about it. Predicting the yield of any given design, for example, is considered to be one of the hardest things to do even for an experienced designer.
 * The only software I know that would be useful at all for any of this is KB, a "comprehensive educational package of computer codes and reference documents for modeling model materials at high temperature and pressure." If you know what you are doing with the relevant physics, this kind of thing would be useful, but you'd still need to know, for example, the equation of state for plutonium at very high densities, which is, predictably, classified.
 * Oak Ridge not only won't help you, they legally cannot. The information you are asking for is restricted data; if someone there were to give it to you (presuming you do not have a Q-clearance), they would face decades of prison time! --Mr.98 (talk) 22:21, 29 August 2010 (UTC)


 * I don't know enough yet about nuclear weapon engineering, but I fail to understand why nuclear detonations cannot be accurately simulated ab initio. I have submitted the Request Form on the KB Product Webpage. As for the computational power required to simulate nuclear weapons designs, the ASC Platform 2007 document indicates that Sandia possess computational capacity of hundreds of teraflops. As I have 2.06 teraflops (scalable if necessary to 4.12 teraflops via addition of another four modules) of double-precision computational power, I should be capable of running Sandia's nuclear weapon simulation-codes, albeit a few hundred times as slowly. Rocketshiporion  02:33, 30 August 2010 (UTC)


 * You can use KB, for example, to simulate various kinds of explosion overpressures and things like that. You can use very rough scaling laws to tell you what a kiloton of TNT will give you in terms of blast, thermal, and radiation. None of this is very precise, and none of it can be adjusted for arbitrary design differences, much less the kinds of free-form designs you're imagining this for. This is true even for the labs. The holy grail since 1945 has been to be able to accurately simulate a nuke from first principles. They can't do it yet. It's just too large an equation, one where you are running everything from quantum mechanical effects (tunneling, inverse Compton, etc.) and then running them all the way up to give you results with a 10 mile diameter and so on. It just turns out to be very, very hard to do that, even if you know quite a lot about all of the physics, chemistry, metallurgy, engineering involved. The labs today can only do it to a reasonable amount of uncertainty because they have the data from thousands of nuclear tests that tell them, "what happens if you use this as a reflector, and this as the core, and this as the radiation channel" and so on, which they can then use to calibrate their models. Even then they have only limited confidence, hence Livermore's interest in NIF and Los Alamos' interest in DARHT — tools that let you fill in some of the "what happens when..." questions without actually setting off a nuke. An interesting read regarding why nukes are hard to simulate and code for is Stober and Hoffman's A Convenient Spy (esp. chapter 3), about Wen Ho Lee. (Lee was accused of giving the codes to the Chinese, so there was a lot of discussion about what these supposedly were and why they were vitally important both to the US and to China, who has not done as much nuclear testing.) --Mr.98 (talk) 12:41, 30 August 2010 (UTC)


 * A previous RefDesk back-of-the-envelope demonstrated that we can't even model a grain of sand from first principles. --Sean 17:37, 30 August 2010 (UTC)


 * Just to clarify about not even the labs being able to accurately simulate nuclear weapons from first principles. Is this because
 * the equation is not known in its entirety (i.e. hasn't yet been derived), or
 * the labs simply lack sufficient computational power to solve for all of the variables in the equation?
 * Rocketshiporion 02:56, 1 September 2010 (UTC)


 * Certainly number one; potentially number two? They certainly don't know enough of the basic physics to reliably model from first principles — if you look at the Stober and Hoffman book, it describes how they get by with fudge factors based on experimental data. I doubt they have the computational power to actually simulate from first principles anyway. As I understand it what they do at the moment is just consider each "stage" of the problem separately — look at the quantum/atomic stage, look at the chemical separately from that, look at the metallurgical separately, look at the engineering, etc. One of their reports on that site I linked to, I cannot remember which one, has a nice graph showing each of their stages of consideration, with the end goal (probably unattainable without more nuclear testing) to be able to go from the tiniest to the largest in one step. But you're talking about a gigantic simulation, if you are really trying to model the whole thing at the atomic level. Billions and billions of atoms and all. It's non-trivial.
 * None of this is to say that they can't do back-of-the-envelope, or come up with pretty good guesses. I wouldn't be surprised if, at this point, they could pretty accurately simulate most "standard" changes to the stockpile bombs. (E.g., substitute one type of material for another, or take into account the effects of aging on a different material.) But they don't use one program for that — they have lots and lots of codes that simulate different parts of it. And they always have to compare it against experimental data. And they don't totally understand (at a deep theoretical level) why the experiments give some of the results they do. It's very hard to see what happens inside a bomb as you are setting it off, for obvious reasons. You have to infer a lot based on somewhat indirect evidence (yield, neutrons, "Teller light", etc.) --Mr.98 (talk) 00:11, 2 September 2010 (UTC)

What is 32kb of "used space" on an empty USB pendrive?
I've plugged an empty USB2 pendrive into my computer. I had previously deleted everything on it and reformated. But when looking at the properties of the drive in WinXp, it shows 32kb as "used space". What is this "used space" used for? Could anything sinister be lurking there? Thanks 92.15.21.39 (talk) 19:31, 27 August 2010 (UTC)

it will be the space containing information about the drive. I can't think of the name for it (like the 'reserved' space on a cd) but someone will fill you in on the blanks. There's a certain amount of space lost between the advertised size and the size itself (though this is slightly different to that I believe). ny156uk (talk) 20:14, 27 August 2010 (UTC)


 * It could be firmware used by the pendrive itself (which would be in hidden files so you can't delete them) - I had a pendrive with an LCD display on it that had a startup Logo that was stored as a file on the drive itself that you couldn't erase or overwrite no matter what.
 * It could be directory space and free space map for a FAT filesystem (this is by far the most likely thing).
 * It could (maybe) be bad "sectors" that it's mapped to prevent you from using them. Flash memory does eventually 'wear out' and stop working - and fancy flashdrives know to 'lock out' that worn out space so you don't use it again and corrupt a file.  Cheap flashdrives don't do that (at least, not that I've noticed).
 * OTOH, I don't think it's a difference between advertised space and real space as Ny156uk suggets.  (eg hard drive manufacturers quote "Megabytes" meaning 1,000,000 bytes and not 1024x1024=1,048,576 bytes so it looks like they have more space than they really do).   The reason I don't believe that is because the "used space" that WinXP measures will be in self-consistent units with "total space" and "free space" - there wouldn't be a discrepancy.  However you might well seem to have less free space on the drive than it implies on it's case for those kinds of reasons.  However, I don't think flash drive manufacturers do the god-awful things that hard drive vendors do.  When they say "4Gb", they really do mean "4x1024x1024x1024" - minus the things I listed above. SteveBaker (talk) 20:37, 27 August 2010 (UTC)
 * Actually flash memory device (cards, USB sticks and I think SSDs) manufacturers do use decimal based bytes. This always surprised me, since the flash memory internally would seem to be in binary bytes, but I read that it's primarily because the extra space is used for wear levelling, binary prefix now mentions this as well Nil Einne (talk) 22:37, 27 August 2010 (UTC)


 * Windows Explorer doesn't report the size of FAT16/FAT32 metadata ("directory space and free space map"), so it's not that, unless the volume is formatted as NTFS, in which case the used space would be much larger than 32K. 32K is too small for FAT as well except in unusual circumstances (a very small USB drive formatted as FAT16 might qualify). USB flash drives manage bad sectors internally and don't report them to the OS (ditto modern hard drives), so it's not bad sectors. It can't be an undeletable firmware file because USB drives behave as block devices to the operating system; they can't control what the operating system does at the filesystem level. It's not a difference between advertised and actual size because drives just have one size; they don't know what it said on the retail box.


 * It could be the RECYCLED/RECYCLER/$Recycle.Bin folder and possibly a desktop.ini file inside it. Each of those will take one cluster on a FAT filesystem. Try configuring Explorer to show hidden and protected operating system files and see if you see anything. -- BenRG (talk) 23:07, 27 August 2010 (UTC)
 * Actually, now that I think about it, it's almost certainly the root directory, if this is a FAT32 volume. Explorer counts used clusters. In FAT16/FAT12 the root directory is stored in a special zone before cluster 0. In FAT32 it's stored in clusters like any other directory. In NTFS all of the metadata is stored in clusters, which is why the reported used space is so much larger. -- BenRG (talk) 23:18, 27 August 2010 (UTC)

About this theme
Can anyone tell me which theme (http://i33.tinypic.com/20k39qd.png) it is? I want to use that theme. Please help me to find it out. Thanks.--180.234.34.141 (talk) 19:54, 27 August 2010 (UTC)


 * Unless I'm missing something, that's the default Windows Vista/Windows 7 Aero theme. I don't think the theme is available for XP -- Ferkelparade &pi; 20:30, 27 August 2010 (UTC)
 * But I am using Windows 7, can't find that theme in OS. Also that theme contains colorful menus, which is absent in Windows default theme. —Preceding unsigned comment added by 180.234.34.141 (talk) 21:17, 27 August 2010 (UTC)
 * If you're talking about the menus with red icons in the "Catalyst Control Center" window, those are peculiar to that program. A theme won't add icons to ordinary menu bars. -- BenRG (talk) 23:11, 27 August 2010 (UTC)

Printing multiple slides per page in powerpoint (Office 2010)
Hello, I am trying to print 2 slides per page in powerpoint. I can do it. But, it's small and there is a lot of white space that I would prefer be filled up with bigger slides instead. I did Alt F P to print and where I select to print 2 slides, I select "Scale to fit paper" and it gets a bit bigger. But, there is still an inch between the two slides and 1.5 inches at the top and bottom and 2 inches on each side. I'd love to at least make the slides take up an extra .5 inches each in height. Is this possible? I can't find margin settings any where... thanks. StatisticsMan (talk) 21:59, 27 August 2010 (UTC)


 * I have had a look at this, though in PowerPoint 2007. I assume you are printing in the 'Handouts view' ?. Try "Design" → Page Setup" → "Slides sized for" and select "Custom". You may be able to set it for larger slides, but when you print it may give an error rmessage as it expects the larger paper to be loaded in the printer. You may (again!) be able to tell it to continue and it will print assuming you have loaded the larger paper. (maybe!)
 * If you are trying the 2 slides per page via the printer's own setup software, then how it's done will depend on the printer and it's driver software.
 * You could probably paste the slides into a Word document and manually resize them, a lot of work though! 220.101 talk\Contribs 10:36, 29 August 2010 (UTC)
 * Okay, thanks. I will check this out tomorrow at school.  As far as pasting it into Word, way too much work.  I'm printing off slides for a class.  For example, I have 49 slides just for the first chapter and there are like 15 chapters covered in the class.  When I print 2 per page, they are big enough, so not worth any big amount of trouble.  But, bigger would be better so if I can do it that would be great.  Thanks again. StatisticsMan (talk) 03:10, 30 August 2010 (UTC)

Can't log into facebook!!
Ok, so here's what happened. I created my facebook acount in the united states, and I later moved to British Colombia in Canada. When I tried to log in, it said something like "your location is unfamiliar with this acount,yada,yada,yada...", so then Facebook made me do a little quiz, where I had to Identify pictures of people on my friends list. The problem is that I have over 450 friends on facebook, and I don't know who all of them are...in fact most of them are random ppl I've met on the internet. Now my question is "is there any way to bypass this, or at least to trick facebook into thinking I'm still in the united states??". Would masking my ip help???? If so how do you mask an ip address??? Any help would really be appreciated, since I really need to log in! Thanks in advance! Wikiholicforever (talk) 22:14, 27 August 2010 (UTC)
 * I've never used Facebook so I'm unfamiliar with their policies, but searching google for "facebook proxy" lists a lot of sites which will mask your ip to (usually) a US address. Whether this will solve your problem I don't know. You could also try asking at their help page 82.44.54.25 (talk) 22:27, 27 August 2010 (UTC)


 * In case you're interested in the technical details, Wikiholicforever, see proxy server. You aren't simply "masking" your IP address when you use one of these; you are actually routing all your data through a computer in the US.  Facebook sees an IP address that appears to be in the US, and thinks everything's fine.  Comet Tuttle (talk) 22:42, 27 August 2010 (UTC)


 * I have two questions: 1)so you guys can confirm that this will work?? and 2) Could you guys provide some links to some good facebook proxy sites, I was trying to find a few but I'm afraid I might stumble upon a phishing site... Thanks for all the help and support! Wikiholicforever (talk) 02:52, 28 August 2010 (UTC)


 * I could be wrong here, but I was under the impression that it literally means location as in the the IP/block of IPs that you're connecting from. I don't think it's necessarily a country check, but rather the the IPs you would normally connect from. I'm happy to be proved wrong though, I only wanted to mention it incase you do use a US proxy and it still doesn't work.  ZX81    talk  05:33, 28 August 2010 (UTC)


 * I'm not exactly sure what zx81 was saying but the proxys did work for one of my acounts, not for the other two... I'm still trying to figure out why its not working.... Wikiholicforever (talk) 16:14, 28 August 2010 (UTC)


 * I just meant that I don't think being in the same country is enough, I think it has to be from the same block of IPs (at least the same Internet provider) as those which had previously logged into the account. If not it throws up the check.  ZX81    talk  17:36, 28 August 2010 (UTC)

I see what you're saying now, I think you might actually be right... In that case does anybody know a proxy that mask my ip to pensilvania???? Thanks a bunch guys! Wikiholicforever (talk) 19:47, 28 August 2010 (UTC)


 * Hi. Just search Google for "anonymous proxies." If you go to Start --> Control Panel --> Internet Options --> Connections --> LAN Settings and check the box that says, "Use a proxy server..." you can enter in the IP address of the proxy. Then, Internet Explorer will connect to the Internet using that proxy. You can also use WHOIS (Google that, as well) and enter in the IP address of the proxy to determine where it is located.--Best Dog Ever (talk) 22:41, 28 August 2010 (UTC)


 * The OP should probably also be aware that all their data, including all text and photos that they and their friends post "only visible to friends", as well as their passwords, is being re-routed through a proxy run by a random stranger. Only you can make the call as to whether you think this is an acceptable risk. Marnanel (talk) 15:38, 29 August 2010 (UTC)

Thats why I said I was afraid of phishing sites. Wikiholicforever (talk) 22:03, 29 August 2010 (UTC)

Flash video (in embedded player) restarting computer
Hello,

I had something quite odd happen to me the other day: a Flash video in a player embedded on a web page (see link below) caused my computer to spontaneously restart (what Microsoft apparently refers to as a blue screen/stop error). Once Windows had started again, the "your system has recovered from a serious error" information box was displayed. No damage appeared to have been done, so I tried to watch the video again and the same thing happened again (at the same point in the video).

I've checked the integrity of my hard drive using CHKDSK and scanned for viruses using both MBAM and Symantec Antivirus and there don't seem to be any problems on either front.

I watched some other videos that use the same embedded player on the same site and they all played without incident. Today, my brother was watching a video on a completely different site that (as far as I can tell) uses a different embedded player and the same thing happened. In both cases, this was in Firefox (version 3.6.8).

So, does anyone have any idea what might be causing this? Could it be video card drivers? Firefox? Giant squirrels from the future? It's not really a major problem, but it's pretty strange.

Information


 * First video that caused the problem: "Everybody plays a part" (TVO video that teaches kids about civics)
 * Note that other videos on the same site did not trigger restarts
 * Second video that exhibited the same problem: "Thor" (the first video on the page, described as "Tom Hiddleston tells MTV News ...")
 * Computer: Windows XP SP3, 2.4 Ghz Q6600, 2 GB RAM, ATI Radeon HD 5770
 * Browser: Firefox 3.6.8

Any ideas about what's causing this would be appreciated - I'm pretty curious about how an embedded Flash video could trigger a system restart.

Thanks,

- Hiram J. Hackenbacker (talk) 22:15, 27 August 2010 (UTC)


 * Neither of those videos cause my computer to restart. Click here. What version does it say you're using? You should be using at least version 10.1 of the Flash Player. You probably should uninstall it and then re-install it even if it's up to date, though.--Best Dog Ever (talk) 22:25, 27 August 2010 (UTC)


 * It's probably the video driver. Try upgrading to the latest version. -- BenRG (talk) 23:12, 27 August 2010 (UTC)


 * My version of Flash is 10.1.82.76, which that site indicates is the most recent version. I'll try removing it and re-installing it, though, and check for updates to my video driver as well. Thanks for the suggestions. - Hiram J. Hackenbacker (talk) 00:42, 28 August 2010 (UTC)


 * Well, updating the video drivers fixed the problem - now I can finally find out how little things we do in everyday life bolster our democratic society! Thanks for the tips, everyone. - Hiram J. Hackenbacker (talk) 01:10, 28 August 2010 (UTC)

Batch download
How can I make my computer/Adobe PDF download all PDF files of an URL of a set format with one minor different? —Preceding unsigned comment added by 76.229.159.12 (talk) 22:27, 27 August 2010 (UTC)


 * If you mean you want to download stuff like http://foo.com/document_0001.pdf, http://foo.com/document_0002.pdf, http://foo.com/document_0003.pdf, etc., then I'd recommend you write a script in the scripting language native to your platform (probably Windows PowerShell if you're on Windows, bash if you're on *nix) to generate the list of URLs, then feed that to wget to download them. -- Finlay McWalter ☻ Talk 22:31, 27 August 2010 (UTC)


 * Free Download Manager has an option for batch downloading similar urls which should work. 1230049-0012394-C (talk) 22:31, 27 August 2010 (UTC)

Merge PDFs?
OK< this is kind of related, kind of unrelated to the above. I've got some PDF documents of the same format and stuff that I need merged into a single big PDF document. How do I do that? 76.229.159.12 (talk) 22:45, 27 August 2010 (UTC)


 * pdftk does this. -- Finlay McWalter ☻ Talk 22:48, 27 August 2010 (UTC)


 * Since pdftk is a command-line program, you may want to get the GUI version instead (GUI stands for graphical user interface). If you are looking for a commercial software program, Adobe Acrobat (the full version that is quite expensive) and Nitro PDF (another commercial software program) will merge/split PDF files among other things. PleaseStand (talk) 01:51, 28 August 2010 (UTC)


 * What you're looking for is PrimoPDF. Just install PrimoPDF as a printer, then open and print each file (which you want to merge) to PrimoPDF. As you print each file, save it with the same name in the same location. You will be asked whether you want to replace the current file or append to the end of it - select Append. Rocketshiporion  08:32, 1 September 2010 (UTC)

Download trouble
This is related to the 2nd post up, not so much to the one right up. I followed the instructions in the first and installed download manager, put in my URL, etc. But the download manager keeps logging a "redirecting" and the files don't work. They are too small and when I try to open them in PDF Reader I get the message "Adobe reader could not open [filename.pdf] because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded". PS: This site requires a username/password so I gave the manager my username/password and checked the box and logged in; it still didn't work. Sorry for all the questions, I need to get these files loaded and there are about 800, so manual downloading won't work. Thanks for your patience 76.229.159.12 (talk) 23:51, 27 August 2010 (UTC)
 * When you log on to the site using a web browser, does it show a pop-up window just like or ? If not (the log-in screen is in the same window as everything else), the site is probably using HTTP cookie authentication, which your download manager likely does not support, rather than basic access authentication. PleaseStand (talk) 01:01, 28 August 2010 (UTC)
 * Actually, the download manager uses the cookies from Internet Explorer; did you make sure to leave the site open in that browser? A post on the Free Download Manager forum gives some information on getting it to work (although that post is specific to the RapidShare website, the general concept is the same). The username and password boxes in the download manager itself are irrelevant.
 * Alternatively, if the site works in Mozilla Firefox, the DownThemAll! download manager extension for that browser might work. It has a "Manager" tool accessible from the Firefox tools menu that allows you to add multiple URLs by replacing the number with, where start is the first number and end is the last number. Since that download manager is integrated with a web browser, it has access to that browser's cookies. PleaseStand (talk) 01:28, 28 August 2010 (UTC)