How do Star Fleet officers command the computer? Sometimes they just speak commands, other times they also add a code like "Picard epsilon 7 9 3".  I presume the computer authenticates commands by voice recognition (now a real world technology). However that's vulnerable to replay attack (someone could record a command voiced by Picard, then play it back later).   Is that why they use the keys? If they were single use, that would thwart a replay attack. I guess they must be one-time only, else Picard wouldn't say his key loudly on the bridge.  In Ship in a Bottle Moriarty conducts a man in the middle attack. Picard believes he is giving his code to the Enterprise's computer, but he is really in conversation with the sim-Enterprise created by Moriarty. Moriarty then using Picard's code to take command of the real Enterprise.  Does Star Fleet ever introduce a defence against that?

In Star Trek franchise there are command codes that seems to give you access to the ships systems, can you change or at least disable them?  In one episode of ST:VOY the captain, B'Elana and Tuvok are assimilated but something goes wrong and and the Borg Queen gains access to Tuvok's memories including his access codes?  So can you change or disable access codes or is the crew of ST:VOY totally stupid?


I am at the end of the quest given by the Daedric Prince Clavicus Vile, and I have done this quest in another profile so I know about the option at the end where you can either keep The Rueful Axe or get the Masque of Clavicus Vile.   My question is: Can you keep both the axe and the mask somehow? I have tried to figure out how but I have had no luck - anybody got an idea how I could keep them both?

Is there a way to keep the Rueful axe and get Clavicus's Mask?  I thought you could kill Barbas after receiving the mask, but he is a statue now.  Did I miss my chance?


Note that this is not the same as  because that question is about deliberate misspellings, whereas this one is about unwitting misspellings.  Many people unknowingly spell an English word exactly as they would pronounce it, which can lead to a misspelling. Examples:  1.Elifant or Elifent for elephant. "She ran away on seeing the elifant." 2.Shiwawa for Chihuahua. "Their dog is a "  This is related to not knowing the correct spelling of the word, and is a common type of mistake made even by native speakers of English, though probably not with 'elephant'; for instance I remember a native speaker cuttingly reject some good advice from a moderator at a car audio forum with the sentence:  You need not lekcher me about the rules of this forum. I am no neofite here.  Sample sentence for SWR:  Writing 'elifent' for 'elephant' unwittingly, based on its pronunciation would be an example of ______________.  The correct term is not transliteration, and google search did not prominently turn up a pointer to such a word:  So what is the English word for "misspelling words based on their pronunciation?"  A very good option already suggested kindly by @Lawrence is "phonetic spelling" (or ) but can someone find a single word to express the same meaning?

For example,      Night -> Nite   Through -> Thru   The -> Da   Though -> Tho     Nite even appears in some dictionaries as having the same meaning as night.  What is it called when words are deliberately written incorrectly but the pronunciation and meaning are kept unchanged?


I've built a few drupal sites, and always end up creating a content type for Home Page so that I can have a custom template for my home page content, however it seems excessive to have a whole content type just for this. Is there a better way to have a custom home page template?   Wordpress has the front-page template, is there something like that for Drupal?

How do I create a theme for the front page only? I only want to change what is in the content area but leave the rest of the stuff the same from page.tpl.php.


On a page like , after scrolling for a little while, the sidebar will suddenly fling to the bottom of the screen and remain fixed:

When post a question ("Ask Question") the side bar's position is not fixed while scrolling the page. There are some extra spaces are displaying in the top.  GIF for the same:    Update: This issue occurs in the  page too when scrolling the page.


Class(Knight, Consular, Smuggler, Trooper, Warrior, Inquisitor,Bounty Hunter, Agent)/Faction(Republic or Empire) -Starter Planet (Korriban, Tython, Hutta, Ord Mantel) -Chap. 1 Planets -Chap. 1 Final Planet -Chap. 2 Planets -Chap. 2 Final Planet -Chap. 3 Planets -Chap. 3 Final Planet -Interlude Quest Planets -RotHC Planet(s) -Interlude Quest Planets -SoR Planet(s) -Interlude Quest Planets -KotFE -KotET -Interlude Quest Planets -ONSLAUGHT

A friend and I are starting new characters.  which planet each class starts on, but we were wondering what happens after that.  Do the higher-level planets continue to cater to the same pairs of classes? Is there a point where all four classes meet up, or the classes swap which planets they have quests on?  Which planets have story quests for which classes?


What package and command do I have to insert to write letter V in a handwriting style using Inline Math Mode?  Below is the result I want to obtain:

I know what my symbol or character looks like, but I don't know what the command is or which math alphabet it came from. How do I go about finding this out?


I just started working with arrays.My code is supposed to keep asking for the user to enter words/alphabets.However,if the words entered are similar for 2 consecutive entries,the program should display a message as shown below.The following was my hypothesis to compare 2 consecutive string elements.However,my program does't work.       import java.util.*;  public class StringArrays {     public static void main(String[]args)     {          String[] list=new String[50];         for( int i=0;i<50;i++)          {               Scanner a=new Scanner(System.in);             System.out.println("Enter something: ");             list[i]=a.next();              if(list[i]==list[i+1])             {                 System.out.println("Stop!");              }             else             {                 System.out.println("Smart!Continue..");             }          }     } }   I'm just wondering what's the correct way to inspect 2 consecutive elements of a string array. Thanks for all your help :)

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


Surely there are many many questions on this topic, But I've a reason to believe that this is different.  Things that I've already tried   Formatting from Nautilus Formatting from Gnome-Disks Creating a new partition table from Gparted Formatting from Gparted  chown to get ownership remounting with rw forcefully remounting wit ntfs-3g     outputs (mounting)  $ sudo mount -o remount,rw /dev/sdc1 mount: cannot remount /dev/sdc1 read-write, is write-protected $ sudo mount -o remount,rw '/media/sumeet/4CCF-3379' mount: cannot remount /dev/sdc1 read-write, is write-protected $ sudo mount -t ntfs-3g -o uid=$(id -u) /dev/sdc1 /media/sumeet/4CCF-3379 Mount is denied because the NTFS volume is already exclusively opened. The volume may be already mounted, or another software may use it which could be identified for example by the help of the 'fuser' command.   Chown  $ sudo chown -R sumeet:sumeet /media/sumeet/4CCF-3379 chown: changing ownership of '/media/sumeet/4CCF-3379/LOST.DIR/134797': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/LOST.DIR': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/.android_secure': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/.cache/tb': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/.cache': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/.log': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/app': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/music': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/video': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/photo': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/misc': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/backup': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/doodle/.nomedia': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/doodle': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya/folder': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379/zapya': Read-only file system chown: changing ownership of '/media/sumeet/4CCF-3379': Read-only file system   dd  $ sudo dd if="/dev/zero" of="/dev/sdc1" bs=1M count=10  dd: error writing '/dev/sdc1': Operation not permitted 1+0 records in 0+0 records out 0 bytes copied, 0.000825744 s, 0.0 kB/s   hdparm  $ sudo hdparm -r0 /dev/sdc  /dev/sdc:  setting readonly to 0 (off)  readonly      =  0 (off)   Creating new partition  $ sudo fdisk /dev/sdc  Welcome to fdisk (util-linux 2.29). Changes will remain in memory only, until you decide to write them. Be careful before using the write command.  fdisk: cannot open /dev/sdc: Read-only file system   Still isn't working    Device info  Bus 002 Device 008: ID 0781:5567 SanDisk Corp. Cruzer Blade

After I used dd to make a USB drive from an Ubuntu ISO, I am unable to format it for normal use. I ran: sudo dd if="ubuntu-16.04-desktop-amd64.iso" of="/dev/sdb" bs=4M  In order to create a bootable USB drive. However, after I was done with it, I wanted to format it as FAT32 and use it like a normal USB drive. No problem, should be easy, right? WRONG. I have tried:  Using the included Disks application to format it. It threw an error about corrupt GPT tables and wouldn't give me an override option. Using Gparted the erase the current partition table and write a new MBR table [completed successfully] After that I created a FAT32 partition spanning the entire volume, and remounted. [Showed up in Files, good so far] Attempted to copy a file to it. It thre an error saying the medium was read-only. Erased the partition table again in Gparted and this time created an NTFS partition spanning the entire disk. [Same RO error when attempting to copy a file onto it] Repeated the procedure trying this time with EXT4 [Same RO error] Repeated procedure trying a GTP table instead of an MBR table. {Same error]  Finally, I tried running: sudo hdparm -r0 /dev/sdb  And remounted. Still the same error. Keep in mind that I remounted it after formatting it each time. I am at a total loss. Has dd bricked my USB drive?


We know that \begin{align*} \frac{|GL_n(\mathbb{F}_q)|}{|\mathcal{M}_N(\mathbb{F}_q)|} &= \frac{\prod \limits_{k=0}^{n-1} (q^n - q^k)}{q^{n^2}} \\ &= \prod_{k=1}^n \left( 1-q^{-k} \right) \\ &= \left(\frac{1}{q}, \frac{1}{q} \right)_n, \end{align*} where the last expression denotes the . How can we generalize this to $m\times n$ matrices. I mean what is the ratio of matrices which have full rank to total number of matrices. Thanks.

$F$ is a finite field of order $q$. What is the size of $\operatorname{GL}_n(F)$ ?  I am reading Dummit and Foote "Abstract Algebra".  The following formula is given:  $(q^n - 1)(q^n - q)\cdots(q^n - q^{n-1})$.  The case for $n = 1$ is trivial.  I understand that for $n = 2$  the first row of the matrix can be any ordered pair of field elements except for $0,0$. and the second row can be any ordered pair of field elements that is not a multiple of the first row.  So for $n = 2$  there are $(q^n - 1)(q^n - q)$ invertible matrices.  For $n\geq 3$, I cannot seem to understand why  the formula works.  I have looked at Sloane's OEIS A002884.  I have also constructed and stared at a list of all $168$ $3\times 3$ invertible matrices over $GF(2)$.  I would most appreciate a concrete and detailed explanation of how say $(2^3 - 1)(2^3 - 2)(2^3 - 2^2)$ counts these $168$ matrices.


I'm looking for a story I read in the late 80s or early 90s that featured a guy living in his car in the future. The best thing I remember about it was that the car could never dip below a a certain speed in miles per hour (I think it was around 100). I believe he was also in competition or conflict with other cars somehow. It would have been in one of those sci fi anthologies but it might have been a best of a year's science fiction type thing.   It's possible the car or a computer in it was the protagonist. Sadly I don't remember that detail.  Also the roads were somehow built for these cars or the cars were designed for these freeways and the cars never left them. I believe it would have been set in the United States.

I'm trying to locate a short story, probably written in the 1970s but likely before the oil crisis, about a day in the lives of two officers and one medic on a patrol car riding the highways of the U.S. and Canada at speeds of over 400 miles per hour.  They eat, shower and sleep in their vehicle as they patrol, rescue and arrest drivers over hundreds on miles of road. It's either a multi-national patrol or the two countries have merged in some fashion. I probably read this in an anthology, possibly in the 1980s or 1990s.


Would it be theoretically possible to implement C++ keywords, classes syntax etc. using a C library with right macros? (i.e. prepare a library which would make any C++ code compile using C compiler). I guess the answer is probably "no", but I wonder if you can prove it.

What are some ways to write object-oriented code in C? Especially with regard to polymorphism.    See also this Stack Overflow question .


Why does it advertise free for 3D tour of ancient Jewish temple then when I try to install the app it asks for credit card details

Ever since adding an iTunes gift card to my account, I'm getting verification requests like crazy. I can't even download free apps. It takes me to my payment info and when I try to select none, I continually get a message under the payment info that says "you must verify your payment info to continue"  I don't want a credit card on file and would really like the none option to work. My ID shows I still have iTunes credit.


Prove that if $G/Z(G)$ is cyclic then $G$ is abelian. Using this fact and $G$ is a nontrivial group of prime power order, deduce that a group of order $p^2$ , $p$ prime, is abelian.

I am looking for a correct proof of this statement: If $G$ is a group such that $G/Z(G)$ is cyclic, then $G$ is commutative.  Proof: $G/Z(G)$ is isomorphic to $\operatorname{Inn}(G)$ and is cyclic, and then for every $a$ and $b$ in $G$ the inner isomorphisms $\gamma_a$ and $\gamma_b$ satisfy $\gamma_a \gamma_b = \gamma_{ab} = \gamma_{ba} = \gamma_b \gamma_a$, and therefore for every $a,b \in G$, $ab = ba$.  Is that proof complete, or am I missing something? Thanks a lot for the help.


I've already asked a similar question yesterday (is there a well-order such that $X$ has a largest element). Can one prove the existence of a well-order on an infinite set $X$ such that $\forall x \in X \exists y \in X: x \leq y$?

According to the well ordering theorem "". Whenever we have a well ordering on a set, it is not difficult to construct a new well ordering with a largest element. My question is:     For a given infinite set, can we find a well ordering on it such that there is no largest element?


Two sides of an acute triangle are 8 and 15. How many possible lengths are there for the third side, if it is a positive integer?  I'm not sure if the word "acute" affects the problem.  If not, is the answer 15?  I tried using triangle inequality.

In the triangle shown, $n$ is a positive integer, and $\angle A > \angle B > \angle C$. How many possible values of $n$ are there?      Two sides of an acute triangle are 8 and 15. How many possible lengths are there for the third side, if it is a positive integer?   Thanks!


PROBLEM: In the past couple of weeks - around mid-May 2015, I found a folder named "Hacked" in my Recycle Bin and in another recent case, several Files and shortcuts that I had previously emptied from my Recycle Bin show up back in my Recycle Bin.  Up until a few weeks ago, I have not had this problem or any other problem.   ACTIONS: I emptied my recycle bin when the "Hacked" folder showed up and emptied the recycle bin when the previously deleted files showed up and the folder & files were removed.    QUESTIONS:  1. Why did this "Hacked" folder end up in my Recyle Bin and why are these previously deleted files showing up in my Recycle Bin? 2. What can I do to prevent this type of behavior from happening again?  3. What can I do to determine if my system has been hacked and in need of a cleaning?  I run a full McAfee scan regularly - at least weekly if not more.   SYSTEM: I have an HP - Pavilion 23" Touch-Screen All-In-One Computer - AMD A6-Series, running Windows 8.1 and has had McAfee installed from day 1.  The system was purchased in April of 2014.  I use this system for email and web browsing.  I do not goto suspicious sites (i.e. porn) and don't consciously download files or open email from unknown sources.   Thank you for any replies.

What should I do if my Windows computer seems to be infected with a virus or malware?  What are the symptoms of an infection? What should I do after noticing an infection? What can I do to get rid of it? how to prevent from infection by malware?   This question comes up frequently, and the suggested solutions are usually the same. This community wiki is an attempt to serve as the definitive, most comprehensive answer possible. Feel free to add your contributions via edits.


I want to solve :    I think the inclusion $H \subset HK$ and the projection $HK \to HK/K$ are both group homomorphisms and so is their composition $H \to HK/K$. May be we should find the kernel of this map. But I am not sure how to write the complete proof for this.

Let $H$, $K$ be subgroups of $G$. Prove that $o(HK) = \frac{o(H)o(K)}{o(H \cap K)}$.  I need this theorem to prove something.


I've been reading about this everywhere all day, and from what I've gathered, TIME_WAIT is a relatively harmless state. It's supposed to be harmless even when there's too many.  But if they're jumping to the numbers I've been seeing for the past 24 hours, something is really wrong!  [root@1 ~]# netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n   1 established)   1 Foreign  12 CLOSE_WAIT  15 LISTEN  64 LAST_ACK 201 FIN_WAIT2 334 CLOSING 605 ESTABLISHED 816 SYN_RECV 981 FIN_WAIT1 26830 TIME_WAIT   That number fluctuates from 20,000 to 30,000+ (so far, the maximum I've seen it go is 32,000). What worries me is that they're all different IP addresses from all sorts of random locations.  Now this is supposed to be (or was supposed to be) a DDoS attack. I know this for a fact, but I won't go into the boring details. It started out as a DDoS and it did impact my server's performance for a couple minutes. After that, everything was back to normal. My server load is normal. My internet traffic is normal. No server resource is being abused. My sites load fine.  I also have IPTABLES disabled. There's an odd issue with that too. Every time I enable the firewall/iptables, my server starts experiencing packet loss. Lots of it. About 50%-60% packets are lost. It happens within an hour or within a few hours of enabling the firewall. As soon as I disable it, ping responses from all locations I test them from start clearing up and get stable again. Very strange.  The TIME_WAIT state connections have been fluctuating at those numbers since yesterday. For 24 hours now, I've had that, and although it hasn't impacted performance in any way, it's disturbing enough.  My current tcp_fin_timeout value is 30 seconds, from the default 60 seconds. However, that seems to not help, at all.  Any ideas, suggestions? Anything at all would be appreciated, really!

This is a  about DoS and DDoS mitigation.   I found a massive traffic spike on a website that I host today; I am getting thousands of connections a second and I see I'm using all 100Mbps of my available bandwidth.  Nobody can access my site because all the requests time out, and I can't even log into the server because SSH times out too!  This has happened a couple times before, and each time it's lasted a couple hours and gone away on its own.  Occasionally, my website has another distinct but related problem: my server's load average (which is usually around .25) rockets up to 20 or more and nobody can access my site just the same as the other case.  It also goes away after a few hours.  Restarting my server doesn't help; what can I do to make my site accessible again, and what is happening?  Relatedly, I found once that for a day or two, every time I started my service, it got a connection from a particular IP address and then crashed.  As soon as I started it up again, this happened again and it crashed again.  How is that similar, and what can I do about it?


Can anyone shed some light on the following aspect?  By 5 PM I gave him the book.  By 5 PM I had given him the book.  In both the sentences the book was given before 5 PM and no later than 5 PM. But I can't understand then what the difference between them is. a Also is it right to use simple past with 'by' at all? If yes, then why and if not, then why is it incorrect to use simple past with 'by'?

I gave him the money by 6 PM.   I had given him the money by 6 PM.   I can't spot the difference between them and both seem right, but I was told the first one is wrong. Can anyone say, why?  Here is a another set of sentences with the same issue:     By 5 PM I gave him the book.   By 5 PM I had given him the book.   In both the sentences the book was given before 5 PM and no later than 5 PM. But I can't understand then what the difference between them is.   Is it right to use simple past with 'by' at all? If yes, then why and if not, then why is it incorrect to use simple past with 'by'?


This is a piece of my function with the question in it:  function deletePost() {     var ask = window.confirm("Are you sure you want to delete this post?");     if (ask) {         window.alert("This post was successfully deleted.");          /* How to redirect to another page on confirm? */      } }   Pure Javascript needed.

How can I redirect the user from one page to another using jQuery or pure JavaScript?


We are Indian passport holders, with valid visas for Canada. Plan is to take the EgyptAir flight Mumbai to Toronto, via Cairo. Problem is Egypt embassy website says we don't need Transit Visa if transit is up to 12 hours but here transit is 14 hours.    Has anyone with a Indian passport traveled this route? What was your experience at Cairo? Did you need a transit visa?

In a couple weeks, I will have a long layover in Cairo on a trip from Mumbai to Toronto. I get to Cairo on Sunday at noon and leave for Toronto on Monday at about 1 AM.  I am travelling on EgyptAir business class. While browsing for people who have experiences with a similar itinerary, some people seemed to have said they they were put up ina  hotel by the airline. However, I did not see anything about this when I booked my ticket.   allows me to enter my status (i.e. citizenship etc.) which results in a .  It doesn't appear like I need a transit visa- however it specifies that:     Leaving the airport is permitted for passengers with transit time   between 6 and 12 hours   My transit time 13.5 hours.  Now for my questions:   Is it an issue that my transit time is longer than 12 hours? Can I still leave the airport? What are my options with regards to airport hotels, etc.? Any other recommendations about how I could best utilize my time while in Cairo?


A simple question.   What proof will be sufficient for the existence of God? (where God is someone who is all capable ,all knowing , all  present)

"Scientific" theories require proof, and there are certain guidelines and standards for the proofs to be acceptable to the "scientific" community in that domain (Algebra, Computer Science, etc.). Hence I am keen to know: What can suffice as a "scientific" proof for the existence of a monotheistic God? to what domain can such a proof belong to?    And Is "science" mature enough to come up with scientific instruments and methods that can assess such a proof as we are dealing with a thing which is supposedly more complex then the Atom which physicist are still struggling to understand ?


I have a dataset of 300 observations with 7 predictor variables with 1 continuous response variable.  The response is strongly skewed to the right and there are no significant correlations among any of the predictors or the response.  I have attempted several different models including XGBoost, random forests, etc. Even transforming of the response hasn't helped.  Any advice on how one should approach a problem like this would be greatly appreciated.

Imagine a standard machine-learning scenario:     You are confronted with a large multivariate dataset and you have a   pretty blurry understanding of it. What you need to do is to make   predictions about some variable based on what you have. As usual, you   clean the data, look at descriptive statistics, run some models,   cross-validate them etc., but after several attempts, going back and   forth and trying multiple models nothing seems to work and your   results are miserable. You can spend hours, days, or weeks on such a   problem...   The question is: when to stop? How do you know that your data actually is hopeless and all the fancy models wouldn't do you any more good than predicting the average outcome for all cases or some other trivial solution?  Of course, this is a forecastability issue, but as far as I know, it is hard to assess forecastability for multivariate data before trying something on it. Or am I wrong?   Disclaimer: this question was inspired by this one  that did not attract much attention. It would be nice to have detailed answer to such question for reference.


I'm trying to use a template from online and when I upload the zip into Texmaker it gives the following error   "! Fatal fontspec error: "cannot-use-pdftex" ! ! The fontspec package requires either XeTeX or LuaTeX to function. ! ! You must change your typesetting engine to, e.g., "xelatex" or "lualatex" ! instead of plain "latex" or "pdflatex". ! ! See the fontspec documentation for further information. ! ! For immediate help type H ."  What I have tried  I've looked at several posts in this forum, but none seem to have worked. I tried making a custom command for both XeLatex and LuaLaTeX, but neither has worked. I think maybe I don't have something properly downloaded? My custom commands look like this   XeLaTeX: xelatex --interaction=nonstopmode %.tex  LuaLaTeX: lualatex --interaction=nonstopmode %  Possibly these are wrong though. When I run either command, it just says  "Error : could not start command"  Thanks for the help, and once again I've read most of the threads related to this, but to no avail, so I think I'm doing something else wrong.   Below is what my texmaker preferences look like...let me know how to change them in order for this to work. Running quick build or my custom command doesn't work and results in the same error

I use TeX Live 2010 and my editor is Texmaker Bidi. It was working probably good but from 2 months ago I've encountered with the error:   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! ! Fatal fontspec error: "cannot-use-pdftex" !  ! The fontspec package requires either XeTeX or LuaTeX to function. !  ! You must change your typesetting engine to, e.g., "xelatex" or "lualatex" ! instead of plain "latex" or "pdflatex". !  ! See the fontspec documentation for further information. !  ! For immediate help type H <return>. !...............................................   when I'm trying to load xepersian LaTeX.  but I do not know how can I change pdfLaTeX to XeLaTeX.    This is the second edit of my question .   the code is :    \documentclass{article} \usepackage{pstricks} \usepackage{pst-bezier} \usepackage{xepersian}  \settextfont{XB Zar}  \setlatintextfont{Junicode}  \setdigitfont{XB Zar}  \begin{document}  !سلام دنیا \begin{pspicture}(3,3) \psbcurve(1,2)(5,7)(2,2)(12,3) \end{pspicture}  \end{document}   but the output does not include the shapes .


I've tried mimicking the proof in case of $\mathbb Q$ to deal with the characteristic zero case, but can't do the characteristic $p$ case. Can someone give a solution to that end?

Let $F$ be a field and $F^\times$ be its group of units. If $F^\times$ is cyclic, then show that $F$ is finite.  I'm a bit stuck. I know that I can represent $F^\times = \langle u \rangle$ for some $u \in F^\times$ and that we must have that $|F^\times| = o(u)$, where $o(u)$ denotes the order of $u$ in $F^\times$.  I tried assuming $o(u) = \infty$, but I'm not sure exactly where to go from there. I was wondering if I could get a hint.


I bought a cheap HP laptop just for the internet. Well, the hard drive is only about 30 gigs. Big problem, because so is Windows 10 with new updates. In fact there's not enough room on the drive to even update the operating system.  I thought, well, Ubuntu is much smaller. But I read I need 25 free gigs of disk space to install. Windows took up all that.  Is there a way to install over Windows or use an external drive, or USB?  Incidentally, I detest Windows 10 and want to move to an all-free platform with all free programs. That's something I can really believe in.

I would like to see a full how-to guide on how to install Ubuntu.


I am trying to evaluate $$\lim\limits_{n \to \infty}{2^3-1 \over 2^3+1}{3^3-1 \over 3^3+1}\dots{n^3-1 \over n^3+1}$$ It seems to be the perfect candidate for a factoring formula, however, I get stuck rewriting the fractions. Do you have any suggestions?

Calculate $$\lim_{n \to \infty} \frac{2^3-1}{2^3+1}\times \frac{3^3-1}{3^3+1}\times \cdots \times\frac{n^3-1}{n^3+1}$$ No idea how to even start.


It could be argued that only native speakers of English from England are true native speakers. Other countries that have adopted English as their primary language (America, Australia, Canada) have cultural and language differences, spelling, pronunciation etc.

Who is considered a native speaker of English? I am a little confused by the various answers found online.


I'm doing a master's thesis about quadratic fields and I know that for squarefree m, the ring of integers for the quadratic field $\mathbb{Q}(\sqrt{m})$ is $\mathbb{Z}[\sqrt{m}]$ if $m \equiv 2,3 \pmod{4}$ and $\mathbb{Z}[\frac{1 + \sqrt{m}}{2}]$ if $m \equiv 1 \pmod{4}$. My question is this: Why is the ring of integers in $\mathbb{Q}(\sqrt{m}) = \mathbb{Z}[\frac{1+\sqrt{m}}{2}]$ when $m \equiv 1 \pmod{4}$ instead of just $\mathbb{Z}[\sqrt{m}]$?   EDIT: I have seen some of your posts and I know that it has to do with integral closure. My confusion comes when I see that the minimal polynomial of $3 + 6\sqrt{5}$ is $x^2 -6x -171$ even though $3 + 6\sqrt{5}$ does not seem to be an element of $\mathbb{Z}[\frac{1+\sqrt{5}}{2}]$. What I'm looking for is an element of $\mathbb{Z}[\sqrt{m}]$ which is not a quadratic integer. i.e. one whose minimal polynomial has a non-integer coefficient.

Quadratic integer ring $\mathcal{O}$ is defined by \begin{equation}    \mathcal{O}=\begin{cases}       \mathbb{Z}[\sqrt{D}] & \text{if}\ D=2,3\ \pmod 4\\       \mathbb{Z}\left[\frac{1+\sqrt{D}}{2}\right]\  & \text{if}\ D=1\pmod 4    \end{cases} \end{equation} where $D$ is square-free.   I understand $\mathbb{Z}\left[\frac{1+\sqrt{D}}{2}\right]$ is not closed under multiplication if $D=2,3\pmod 4$. But still, isn't it more natural to define $\mathcal{O}=\mathbb{Z}[\sqrt{D}]$ for all square-free $D$? (in that case, it really seems like 'quadratic integer') I wonder what is the motivation of this definition.


I currently have a VM where the user is locked down and i am unable to find any flags. I have tried to use sudo but the account is not a sudoer. I have tried "nano /etc/sudoers" but i received a permission denied message. Any other ideas on how to become root?  Also, this is for a class. Its a basic CTF, and he completely locked down his VM it seems...

I clean-installed Ubuntu 11.10 today, and then installed VirtualBox.  This required me to add myself to the vboxusers group, and since 11.10 seems to no longer have a graphical app to add users to a group, I ran the following command:  sudo usermod -G vboxusers stephane   This is a problem.  I now see what I should have run instead is:  sudo usermod -aG vboxusers stephane   The end result is I'm no longer in the groups I should be in.  Including whatever group is required to run "sudo".  When I run any command as sudo now, I get the following:  $ sudo ls [sudo] password for stephane:  stephane is not in the sudoers file.  This incident will be reported.   Is there a way to fix this, or do I need to re-install from scratch again?


For some reason my iMac keeps turning off around 5 to 10 minutes into boot.  Also just recently it turns on but has shaded lines going down the screen. I have not installed any weird programs and i have not used it in around 3 months.   Any ideas on what the issue is, i don't have any other information about the issue besides whats happening when i use it.  The image i'm showing you was found on google but this looks exactly like mine does.  The model of my imac is the late 2011 model.

I've got a 27 inch iMac made in 2011 that displays 5 pink vertical bars on the screen. It won't boot properly. I ran the Apple Hardware Test and it came up clean.   Machine Specs:  Apple Subfamily:    Mid-2011  Apple Model No: A1312 (EMC 2429) Model ID:   iMac12,2


Quoting the accepted answer from :     There may be an exception where all that is needed is a one letter fix. However it is a huge exception, not a rule.   Isn't this an exception? Within code snippet sib and sob means two different things (input / output).  Why can't an edit be just one character? Typos usually are one character...  For example in , sib should be sob in line #6  Saying that I should make more changes as to have more than 6 characters doesn't make sense as this is the one (rather important) change I want to make. Also, I'm aware that you need 2K points to edit freely - but I can't see how to suggest an edit without flagging it for a moderator.. am I missing something?

On Stack Overflow, there was a question with an incorrectly formatted list, which lacked a newline before it and thus came out like this: 1. Hello 2. Something else 3. Goodbye  I changed it to the right formatting by inserting a newline:   Hello Something else Goodbye   And I got the "Edits must be at least 6 characters" error message. Is there an OK way to trick this rule?


I have a mid 2010 MacBook Pro and want to install a new hard drive but I'm not sure how to restore my Time Machine back ups (Yosemite) with a new hard drive.

I am going to upgrade my MacBook Pro hard-drive, but before doing so I'm trying to figure out how to restore OS X on it. My DVD drive doesn't work so I cannot re-install from the DVD.  I have a recent Time Machine backup, is that enough to restore the OS? And in that case, what would be the procedure? Also, in case the Time Machine restoration fails, is there any way to re-install OS X from a USB or external hard-drive? Any suggestion would be much appreciated.


I'm wondering why we use entities for some cases, when we can use nodes. When we use nodes we can use lots of modules to use for almost any purpose.. The above sentence is my main question, while I was planning to make an election system. Here is my case: I want to write a simple voting system that users become candidates, then an admin authenticate them, then for a period of time othef users come and vote to number of candidates(number of candidates is defined by admin)  The structure I planned is to make outside of drupal world is to have three tables 1. A table for elections, containing information about the election itself for example election for choosing manager this year! 2. A table for candidates containing election reference( no 1 ), user id , accepted status, and votes. 3. A table for keep track of election containing the voter id, and candidate id , and election id.  I was thinking these can be fields of nodes, that we only work with these values by php codes in template for example. But I want to make a drupal module. But I'm confused that what is the best DRUPAL WAY to do that?  Thanks

What is the benefit to creating new entity types over just building a new content type?    It seems a bit overkill to do all of the custom coding that is required to create a new entity when you have all of the CRUD and Views functionality already built into content types.


I would like to know how I can align a group of vertices at an angle without having to resort to scaling to zero on an axis. in the picture below how would you make it the vertices circled in green line up the same angle the end points? I know I could just dissolve them and add them again but that would require reconnecting everything again.

On a line, I need to line up the bottom vertex points in relation to a top reference vertex point. How could I reset the X Y and Z coordinates of these vertex points to essentially line them up all through use of the vector of the reference point vertex.  I do not have access to Mesh -> Transform -> Scale on Axis for aligning vertices along a line.


Will my archer tower defend in clan war during their upgradation?

If a war is started and some of my defensive buildings are being upgraded, are they able to defend my base during war?  I know they don't function in normal play until the upgrade is finished, but war bases are different to some degree.


63  git clone https://github.com/LionSec/katoolin.git    64  cp katoolin/katoolin.py /usr/bin/katoolin    65  chmod +x /usr/bin/katoolin    66  sudo katoolin sudo: katoolin: command not found   This about sums it up I hope. I am running a relatively fresh install of Ubuntu 18.04 Xfce Desktop Enviroment.  Architecture:        x86_64 CPU op-mode(s):      32-bit, 64-bit Byte Order:          Little Endian CPU(s):              4 Model name:          Intel(R) Core(TM) i5-2320 CPU @ 3.00GHz

I think everyone has known - we need to install katoolin to use Kali Linux Tools on Ubuntu. Before did anything I had looked through the internet and also found out these solutions: ,   So here are my steps:  apt-get install git git clone https://github.com/LionSec/katoolin.git && cp katoolin/katoolin.py /usr/bin/katoolin chmod +x  /usr/bin/katoolin sudo katoolin   Then, to add Kali Linux repositories and update them, I selected option 1 from the katoolin Menu  Then, to view the available categories and install all available tools, I selected option 2 from the main menu of katoolin and then pressed 0.   But after that I got this:    What do you want to do ?>    1) Add Kali repositories & Update  2) View Categories 3) Install classicmenu indicator 4) Install Kali menu 5) Help   kat > 2  ************************** All Categories **************************  1) Information Gathering                      8) Exploitation Tools 2) Vulnerability Analysis                     9) Forensics Tools 3) Wireless Attacks                           10) Stress Testing 4) Web Applications                           11) Password Attacks 5) Sniffing & Spoofing                        12) Reverse Engineering 6) Maintaining Access                         13) Hardware Hacking 7) Reporting Tools                            14) Extra  0) All   Select a category or press (0) to install all Kali linux tools .  Furthermore, I got an error in Software Updater - it didn't let me do anything. Ubuntu just hung up. I solved this problem by deleting kali linux repositories in katoolin and then in Software Updater.  Does anyone know how to install Kali Linux tools in Ubuntu 16.04 in a proper way?


I'm attempting to add three social media icons through CSS. The company logo was added to the website through CSS (images/logo.png).   I've attempted extensions by adding commas, but that causes the entire logo to disappear.  Any CSS advice here would be greatly appreciated.  Update  The "duplicate" in question didn't address the position overlap issue I was having.  The multiple images issue is now resolved. The only issue I'm running into now is applying individual links to each social media button.  Any advice?  #heading h1 {     text-align: left;     font-weight: normal;     margin: 0px 0px 0px 0px;     padding: 0px 0px 0px 0px;     height: 92px;     background:#396ba5 url(images/logo.png) no-repeat 495px 0px; }

Is it possible to have two background images?  For instance, I'd like to have one image repeat across the top (repeat-x), and another repeat across the entire page (repeat), where the one across the entire page is behind the one which repeats across the top.  I've found that I can achieve the desired effect for two background images by setting the background of html and body:  html {     background: url(images/bg.png); }  body {     background: url(images/bgtop.png) repeat-x; }   Is this "good" CSS?  Is there a better method?  And what if I wanted three or more background images?


Is there a way to make some graphical elements to be non-printable, i.e. prints as white, while staying fully visible on screen? Here's a MWE to play and have fun with: \documentclass[11pt,letterpaper,twoside]{book} \usepackage[T1]{fontenc} \usepackage{lmodern} \usepackage[total={6in,10in},left=1.5in,top=0.5in,includehead,includefoot]{geometry} \usepackage{microtype} \usepackage{amsmath} \usepackage{mathtools} \usepackage{eso-pic} \usepackage{xcolor} \usepackage{showframe}  \newlength{\distance} \setlength{\distance}{0.0in} \newlength{\rulethickness} \setlength{\rulethickness}{0.5in} \newlength{\ruleheight} \setlength{\ruleheight}{\paperheight} \newlength{\xoffset} \newlength{\yoffset} \setlength{\yoffset}{0pt}  \AddToShipoutPicture{%     \setlength\fboxsep{0pt}%     \ifodd\value{page}%         \setlength{\xoffset}{\distance}%     \else         \setlength{\xoffset}{\dimexpr\paperwidth-\rulethickness-\distance}%     \fi     \AtPageLowerLeft{%         \put(\LenToUnit{\xoffset},\LenToUnit{\yoffset}){%         \colorbox{lightgray}{\parbox[b][\ruleheight][c]{\rulethickness}{%         \centering         \ifodd\value{page}%             \rotatebox[origin=cB]{90}{\color{red}{\large{\normalfont\textsc{Copyright notice}}}}%         \else             \rotatebox[origin=cB]{90}{\color{blue}{\huge{\normalfont\textsc{Some Title}}}}%         \fi     }}}}% }  \begin{document}  Test \newpage Another page  \end{document}  This code draws a gray vertical bar in the inner margins, with some copyright notice.  I need it to stay visible while reading the PDF document on screen.  But I would also like it to turn completely invisible when printed on paper.  Is that possible with some LaTeX commands?  EDIT: Oups !  This question appears to be a duplicate of this one :

I'm creating a fancy header with hyperlinks () for a large document. However, if/when this document is printed, this header is not useful and uses up ink and space. Is it possible to include an element in a pdf file such that it is not actually printed to paper but does display on screen?


I want to filter the contents of all the views of my website. This should happen before the views pager is built. I guess I need a Views plugin then. First of all I want to create a views filter plugin, which will be recognized by Drupal.  On my way I have found an article about creating a views display extender. However this one is a display extender. I want to create a "filter extender". But I have no idea what I should specify in the annotation of the class, which resides in the      Drupal\my_module\Plugin\views\filter   namespace.   I have tried this:  /**     * Filters views content.     *     * @ingroup views_filter_handlers     *    *     * @Plugin(     *   id = "my_filter_name",     * )     */   But the filter won't get recognized by Drupal after a cache clear. I was setting a few breakpoints there and the class is never invoked. Has anybody a hint or a good tutorial about creating a custom "views filter plugin"?

In Drupal 8, I have a view that gathers all the nodes built in my Gallery Hours content type.  The content type has a field called View Order that I use for another view that displays the list of gallery hours in that order.  What I am trying to do is to build another view that checks for the gallery hours for today.  For instance, today is Tuesday, so I would like the view to display the gallery hours for Tuesday.  My thought was to create a custom filter option that compares the numeric value of a field, such as my View Order field which is set to 1=Sunday, 2=Monday, etc., with DATE_FORMAT(NOW(),"%N"). This is my first foray into custom Drupal module development and am spinning my wheels.  Any and all suggestions welcome.  The one thing I think I have correct are my yaml files.  todaysdate.info.yml   name: Todays Date Filter module description: 'Creates a filter to search by todays day of the week.' type: module core: 8.x package: SMA Modules     todaysdate.routing.yml   todaysdate:   defaults:     _controller: Drupal\todaysdate\Plugin\Filter\todays_date_handler_filter_numeric::operators   requirements:     _permission: 'access content'     Where I am really confused is where to go from there.  I am trying to piece together a class that extends the NumericFilter and add a new operator that then add to the WHERE expression with the dateformat I'm looking for.  Anyhoo, this is my attempt at creating the filter.  I am not getting any errors, but I am also not getting the new operator on my numeric fields in my view.  todays_date_handler_filter_numeric.php   <?php  /**  * @file  * Provides views filter option for the Todays Date module.  */  namespace Drupal\todaysdate\Plugin\Filter;  use Drupal\views\Plugin\views\display\DisplayPluginBase; use Drupal\views\Plugin\views\filter\NumericFilter; use Drupal\views\Plugin\views\filter\InOperator;  class todays_date_handler_filter_numeric extends NumericFilter {   function operators(){     $operators = parent::operators();     $operators += array(       'todays date' => array(         'title' => $this->t('Is this day of the week'),         'short' => $this->t('todays date'),         'method' => 'op_day_of_week',         'values' => 0,       )     );     return $operators;      function op_day_of_week($field) {       $this->query->addWhereExpression($this->options['group'], 'DATE_FORMAT(NOW(),"%N")');     }   } }     Thank you all in advance for any assistance you can provide.  I can't tell you how many times StackOverflow has helped me in the past.


I saw you waited for the bus. (wrong unless add that)   I saw that you waited for the bus. (correct)         I saw a house destroyed on the road.  (wrong unless add that)   I saw that a house destroyed on the road. (correct)     But most of us omit “that” am I right?

I searched for  and found many example where "that" is omit. So my question is, is "that" unnecessary when paired with "what happened is?" Example sentence (with a small tense change):  What happened was (that) I got into an argument with my co-workers, so I headed back home alone.


public class Bucket  {      int rows,cols,blocked,open,full;      public void initialize()     {         rows=0;         cols=0;         blocked=0;         System.out.println("You were here");     }     public void open()     {         blocked=1;     } }   I am getting a null pointer exception when I am running the percolation class, I don't have any clue, how to get rid of it, any help will be very thankful.  public class Percolation {      //public Percolation(int N)     public static void main(String args[])throws Exception     {         try         {             int N=5;             Bucket[][] barray=new Bucket[N][N];             for(int i=0;i<N;i++)             {                 for(int j=0;j<N;j++)                 {                     barray[i][j].initialize();                     //barray[i][j].cols=0;                       //barray[i][j].blocked=0;                            }             }         }         catch(Exception e)         {             System.out.println(e);         }     }   }

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I will be soon joining a Top-50 school for a PhD in High Energy Theory. They have some very good professors who have published top quality journal articles in their area of expertise (even with some Nobel Laureates as co-authors). They are not as famous as Nathan Seiberg, Leonard Susskind, etc. though. I would like to know, given the job scenario in academia (especially in high energy theory), is it worth transferring to a top school like Harvard or Princeton after performing very well at my current school ? I mean, is their any huge advantage in the academic job market to be at a Top-10 school compared to a Top-50 school ?   I do not really care about going to a brand name school as far as my studies are concerned. I just want to make sure that if I work hard and succeed, I do not face problems in getting an academic job just because I did not attend Harvard or Princeton. Academically, my current school is very good too but it doesn't have that IVY kind of brand. My concern is only about the people in the hiring committees otherwise I am happy going to my current school.  Also, I have earlier worked with Professors who graduated from such top schools and they say that famous advisors are like "King-Makers" who get their students well placed in academia after PhD since they have influence in the field. Personally, I have no issues being at my current school if I get good people to work with. Also, is it ethically good to change schools like this ?

What I'm trying to understand is, to what degree does the status/rank of the University (where one completes his/her Ph.D) matter while shaping his/her career after graduation? I would like to know the weight given to one's school in both the following cases:   While applying for post-docs/faculty positions in academia While applying to industrial research labs   For instance, I've read on some forums (I can't locate the link now) that while considering prospective applications for tenure-track faculty positions, very few Universities accept a candidate who has completed his/her Ph.D from a lower ranked school having a lesser "brand" value, irrespective of the fact whether he/she has published equally original work as his/her counterpart from an Ivy league college. How much truth is in this statement? It would be really great if someone already in academia, either as a newly-accepted faculty or someone on the Faculty Hiring committee could share their experiences/statistics on this regard. I'm simply interested to know the answer, without commenting at all on whether such a practice is justifiable.  Similarly, what about recruitment to internationally acclaimed research labs (like  or ) - what importance do they place on the pedigree of a candidate's college, before taking into consideration what they published ?  I'm personally interested in answers related to the field of Computer Science (theory), but the question is applicable to any prospective grad student in any discipline in my opinion. Feel free to share your personal experiences post-Ph.D in detail, as that would give me (and future viewers of this question) about what its like to carve a career once you are out of school!


I edited this phrase:  the farther the negative from the lens, the more light needed to expose it properly and the longer the exposure  to read:  the farther the negative from the lens, the greater the amount of light needed to expose it properly and the longer the exposure  I am sure the former is not grammatical but I am having a hard time explaining why the edit is necessary. Can someone help?

What is the type of sentence exemplified below called? Is it appropriate to use it in a scientific paper and formal written English in general?     1. The more pronounced the variation, the   more the waste.      2. The more you give, the more you get.      3. The longer I live, the more I realize the impact of attitude on life.


Trying to prove or disprove this statement: For all real numbers A, B, if $AB$ is rational and $A+B$ is rational, then $A^2$+$B^2$ is rational Ive hit a wall as Im assuming A and B must either be rational or irrational in order for A+B to be rational (ex. A = $\sqrt2$ and B = $-\sqrt2$, or just A = 2 and B = 3), but that's not really getting me any further into proving or disproving the statement

Knowing that $z + \frac{1}{z} = 3$ ($z \in \mathbb{R}$), prove that $z^n + \frac{1}{z^n} \in \mathbb{Q}$ ($n \in \mathbb{N}$ and $n \geq 1$).  I've tried to find a general formula for $z^n + \frac{1}{z^n}$. $$\left(z + \frac{1}{z}\right)^n = \binom{n}{0}z^n + \binom{n}{1}z^{n-2} + ... + \binom{n}{n-1}z^{2-n} + \binom{n}{n}z^{-n}$$ $$\left(z + \frac{1}{z}\right)^n = \binom{n}{0}(z^n + z^{-n}) + \binom{n}{1}(z^{n-2} + z^{2-n}) + ...$$  However, this formula seems to be wrong and I currently have no idea how to correct it and what to do next.  Thank you in advance for your help!


Minimum requirements statistics do not provide enough accurate info to new and prospective users trying to determine a suitable flavor for their machine. People need to know if an OS will run smoothly on their hardware. We need the ability to easily compare Ubuntu flavors in terms of resource usage and management.   Points of interest include:  Performance   responsiveness under load (e.g. Firefox open with 10 tabs) menu/dash speed    Resource usage   memory usage hard drive usage 3D graphics requirements   This data could be depicted using bar graphs and with different versions (13.04, 13.10, 14.04, etc) in separate graphs but most important are the latest versions.  How do they compare under standard use case scenarios such as using Firefox, LibreOffice, or watching full screen flash videos or Netflix? Will my machine be snappy and responsive running Ubuntu or am I better off with Lubuntu or Xubuntu? What are the minimum system requirements for a reasonable speedy and responsive system? Official minimum hardware requirements specifications do not provide this info.

What different Ubuntu derivatives are there? And what is special with them?


I want to show that $(n+1)^{n-1}<n^n$ using the binomial theorem. I have done the following:\begin{align*}\left (n+1\right )^{n-1}&=\sum_{k=0}^{n-1}\binom{n-1}{k}n^{n-1-k}1^k=\sum_{k=0}^{n-1}\binom{n-1}{k}n^{n-1-k}\\ & <\sum_{k=0}^{n-1}\binom{n-1}{k}n^{n-1}=n^{n-1}\sum_{k=0}^{n-1}\binom{n-1}{k} \\ & =n^{n-1}\cdot 2^{n-1}<n^{n-1}\cdot n^{n-1}=n^{2n-2}\end{align*} This is not correct. What could I change to get the correct result?

How would one prove that  $$(n+1)^{n-1}<n^n \ \forall n>1$$  I have tried several methods such as induction.


I'm trying to set up vnc4server on an Ubuntu 16.04 (Xenial Xerus) server version system.  I can currently vnc into the computer no problem, but I can't view my running applications - only my terminal. How can I view my running application on the device?  This is what I see:    Here is my ~/.vnc/xstartup file:  #!/bin/sh  # unset SESSION_MANAGER # unset DBUS_SESSION_BUS_ADDRESS # exec /etc/X11/xinit/xinitrc startxfce4 &  [ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup [ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources  xsetroot -solid grey vncconfig -iconic & x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" & x-window-manager &  gnome-panel & gnome-settings-daemon & metacity & nautilus &

I have a server running Ubuntu 12.10 and need to be able to remote to this server without being logged-in.  I have found many solutions, but none seem to work with 12.10.  Can anyone give me step-by-step instructions on how to configure x11vnc to start as a service (prior to user login) so that when connecting with VNC I will be presented with a graphical login screen?  I'm new to Linux so please give as much detail as possible in your responses/comments.  Thanks


I am a dual Canadian and British citizen with only a British passport. The new Canadian immigration system requires British citizens to have an eTA (Electronic travel authorization) however you can not apply for one if you are a Canadian citizen. Does this mean I can no longer visit Canada using my British passport and will have to get a Canadian passport? An eTA costs $7 and a passport $160.

Some countries (e.g., U.S., Israel) require their citizens to present themselves as such when entering the country - that is, they cannot enter using another country's passport.  In Canada there is no such requirement:  Currently, , if they have one.  Starting March 15, 2016, , except for U.S. citizens.  On the , it says:     Reminder      You cannot apply for an eTA if you are:         a Canadian citizen or a dual Canadian citizen, ....      Does this mean that when the eTA requirement takes effect, it will become illegal for Canadians to enter Canada by air using a passport from any visa-exempt country other than Canada or the U.S.?  If a Canadian citizen obtains an eTA using their foreign passport and enters Canada with it, what law or regulation will they be violating?


Four frogs are located at the corners of a square on the plane. At each step a frog jumps over another frog and lands in the symmetrically opposite location.   Question: Can the frogs find a way to jump over each other (in any order, even the same frog several times) such that their final places will form a square of larger side (not necessarily parallel to the original square)?  Well, I think this is not possible, I'm not sure yet how to prove it, but just jumping over each other it's simple to show that they can form same size square as they started (just in different place), other than that, I have no clue how to show that it's not possible.

You are given four points (on a Euclidian plane) that make up the corners of a square. You may change the positions of the points by a sequence of moves. Each move changes the position of one point, say p, to a new location, say p', by "skipping over" one of the other 3 points. More precisely, p skips over a point q if it is moved to the diametrically opposed side of q. In other words, a move from p to p' is allowed if there exists a point q such that $q = (p + p') / 2$.  Find a sequence of moves that results in a larger square. Or, if no such sequence is possible, give a proof of why it isn't possible. (The new square need not be oriented the same way as the original square. For example, the larger square may be turned 45 degrees from the original, and the larger square may have the points in a different order from in the original square.)  I've tried many different combinations and still haven't gotten anything more than 3 points in the right position and one point completely off. Is this possible?


I am trying to calculate the areas of some polygons and i want to use the field calculator to measure the area. The result i got using this method is different from using the QGIS measurement tool. I am confused on which is correct. How can i do this correctly? Also is it possible to change the measurement unit of the field calculator to give result in meter square?

Using QGIS, if I load a polygon layer and make a new column, how do I fill that column with the:   area of each polygon and another column with length of the perimeter of each polygon?


I have a question on the variational formulation of electromagnetism.   I read that the action is given by   $\mathcal{S}_{EM} = \int d^4x\  F_{\alpha \beta} F^{\alpha \beta}$ (1)  and the source term is given by   $\mathcal{S}_{source} = \int d^4x\  A_{\alpha} J^{\mu}$ (2)  My question is on how one obtains the above two actions. Here is the explanation that I read.   A.) For expression (1), by the Lorentz invariant of electromagnetism, the Lagrangian must be of the form   $c_1 F_{\alpha \beta} F^{\alpha \beta} + c_2(F_{\alpha \beta} F^{\alpha \beta})^2 + c_3(F_{\alpha \beta} F^{\alpha \beta})(F_{\sigma \tau} F^{\sigma \tau})+...$ (3)  Furthermore, we assert that the higher order terms (i.e. the terms including and after the second term) are all small, experimentally. (Alternatively, we can assert that they are small when we work in Plank units.) Therefore, we are left with the form of the action as in equation (1).    B.) We get equation (2) as follows. We want $\mathcal{S}_{EM} + \mathcal{S}_{source}$ to be invariant under the gauge transformation $A_{\alpha} \to A_{\alpha} + \partial \Lambda$ for any smooth scalar function $\Lambda$. Furthermore, under this gauge transformation, we get $\delta A_{\mu} = \partial_{\mu} \Lambda$, so   $\delta(\mathcal{S}_{source}) = -\int d^4x\ \Lambda \partial_{\mu} J^{\mu} + \text{boundary terms}$  We get gauge invariance if $\partial_{\mu} J^{\mu} = 0$ holds, i.e. if the charge conservation holds. Thus, we get equation (2).   In summary, equation (1) follows from Lorentz invariance and experimental evidence. Equation (2) follows from gauge invariance and conservation of charge.   The above formulation seems unsatisfying to me for the following reasons.    Argument A.) relies on experimental evidence which seems to not follow from general principles. Is there a way of coming up with this using only knowledge in, say Purcell?  All argument B.) seems to do is check whether equation (2) satisfies gauge invariance and charge conservation, and in particular, it does not help us come up with equation (2).    My question: is there a more intuitive way of "seeing" equation (1) and (2)? (For instance, in classical mechanics, the Lagrangian of a system is fairly easy to see since we can just take the difference of the kinetic and potential energies which in turn follows from undergraduate Newtonian mechanics.)   What I have tried: I noticed that $F_{\alpha\beta}F^{\alpha\beta} = \frac{1}{2}(\mathbf{E}^2 - \mathbf{B}^2)$, and I also recalled that the energy density of an electromagnetic field is $\frac{1}{2}(\mathbf{E}^2 + \mathbf{B}^2)$.  This seems to be analogous to $L=T-V$ and $E = T+V$ from classical mechanics. I am not sure if this analogy is just a coincidence.    I tried Googling all of the above of course, but I could not find anything that satisfied me.

So I know that for an electromagnetic field in a vacuum the Lagrangian is $$\mathcal L=-\frac 1 4 F^{\mu\nu} F_{\mu\nu},$$ the standard model tells me this. What I want to know is if there is an elementary argument (based on symmetry perhaps) as to why it has this form. I have done some searching/reading on this, but have only ever found authors jumping straight to the expression and sometimes saying something to the effect that it is the "simplest possible".


Why do SD cards and USB drives have less space than advertised? This is even after accounting for unit prefixes defined in powers of 1024.  For instance I have an SD card from SanDisk that was advertised to contain 8 gigabytes of storage. The total number of 512-byte sectors available for use is 15523840, which is equal to 7948206080 bytes. Now, that's close to enough to 8000000000 to get there by rounding to the nearest gigabyte, but it is still 51793920 bytes less than that value.  Is the missing 51793920 bytes of space there but not exposed by the card's microcontroller or is it just not there at all?

I just got a new Lenovo Laptop which has been installed with Windows 7 and is supposed to have 250 GB hard disk.   Windows 7 reports that the hard disk drive has two parts: 221 GB C: and 9.76 GB Lenovo Recovery. The sum of the two parts is 230.76 GB.  If I remember correctly, if divide 250 GB by 1024 three times, I will get 232.8 GB, which should be what the OS reports as the hard drive size. But why the sum 230.76 GB of the two parts of hard drive is still smaller than 232.8 GB?


I'm a newbie to c# and i'm trying to follow a youtube tutorial and the code will not run. It's coming up with several errors  Severity   Code    Description Project File    Line    Suppression State Warning CS0642  Possible mistaken empty statement   WindowsFormsApp1        36  Active Error   CS0103  The name 'RecipeTable' does not exist in the current context    WindowsFormsApp1        44  Active Error   CS0103  The name 'stRecipes' does not exist in the current context  WindowsFormsApp1        44  Active Error   CS0103  The name 'stRecipes' does not exist in the current context  WindowsFormsApp1        43  Active Error   CS0103  The name 'stRecipes' does not exist in the current context  WindowsFormsApp1        42  Active Error   CS0103  The name 'RecipeTable' does not exist in the current context    WindowsFormsApp1        41  Active Error   CS0103  The name 'adapter' does not exist in the current context    WindowsFormsApp1        41  Active Error   CS0117  'DataTable' does not contain a definition for 'RecipeTable' WindowsFormsApp1    40  Active Error   CS0210  You must provide an initializer in a fixed or using statement declaration   WindowsFormsApp1    37  Active Error   CS1503  Argument 1: cannot convert from 'string' to 'System.Data.SqlClient.SqlCommand'  WindowsFormsApp1        37  Active Error   CS1002  ; expected  WindowsFormsApp1        44  Active Error   CS1002  ; expected  WindowsFormsApp1        43  Active Error   CS1002  ; expected  WindowsFormsApp1    42  Active  using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; using System.Configuration; using System.Data.SqlClient;   namespace WindowsFormsApp1 {     public partial class FrmMain : Form     {         SqlConnection connection;         string connectionString;         public FrmMain()         {             InitializeComponent();               connectionString = ConfigurationManager.ConnectionStrings["WindowsFormsApp1.Properties.Settings.CookbookConnectionString"].ConnectionString;          }         private void FrmMain_Load(object sender, EventArgs e)         {             PopulateRecipes();                  }         private void PopulateRecipes()         {              using (connection = new SqlConnection(connectionString)) ;             using (SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM Recipe"), connection)             {};             {                 DataTable.RecipeTable = new DataTable();                 adapter.Fill(RecipeTable);                 firstRecipes.DisplayMember = "Name";                 firstRecipes.ValueMember = "Id";                 firstRecipes.DataSource = RecipeTable;              }         }     } }

I was working with a new C++ developer a while back when he asked the question: "Why can't variable names start with numbers?"  I couldn't come up with an answer except that some numbers can have text in them (123456L, 123456U) and that wouldn't be possible if the compilers were thinking everything with some amount of alpha characters was a variable name.  Was that the right answer?  Are there any more reasons?  string 2BeOrNot2Be = "that is the question"; // Why won't this compile?


Can anyone help me figure out how to convert an iso into a dmg file..  I'm sure it has something to do with the dd command,  but I'm really not sure how to go about it..  I need to make a bootable ubuntu disk for an imac, and it is not reading any of the hundreds of burnt iso disks i have..  I'm at a total loss..  everything i can find about the process is done on a mac, and since my imac has been broken for about a year, I'm kind of stuck..  Thanks in advance. Max

I have an intel Imac (early 2006).  I recently decided to install ubuntu on it as the sole OS as it was running 10.4.11 and was unable to meet my current needs.  The optical drive on it is broken,  so I downloaded the ubuntu iso,  converted it to a DMG and created a bootable flash drive.  Everything seemed to be going great.  I used gparted to wipe the hard drive and than began running the installer from the live enviro.   That's when things took a turn for the worst..  Half way through the installer crashed.  I attempted it a few more times,  but it eventually just froze solid.  I asked around what to do and was told to just reboot and try again.  Now it is not seeing the flash drive, and there is no OS to boot to,  so I'm just getting the ol' grey screen with a flashing question mark..    I bought a new 500gig external that I can format for a mac..  I'd like to try and install ubuntu on it and see if I can maybe boot the mac off it to try and fix and finish the install..    I mainly want to know how to convert an iso to a dmg using my other ubuntu machine,  but failing that,  I'm open to any suggestion.


I have been struggling with this all day-long and can't find a suitable method yet. I defined my arrays as follows:       public String month()     {         return birth.substring(3, 5);      } public int beers()     {     return nbBeer;     }   Then I put this in my public class      static int julyBeer(Personne[] perso, int nbElem)                 {                     int i;                     int k = 0;                     for(i=0; i < nbElem; i++)                         if(perso[i].month() == "07" && perso[i].beers() >= 1)                             k++;                     return k;              public static void main (String[] args){               Personne[] pers = { new Personne("10/07/1999", 3), new     Personne("19/02/1993", 2), new Personne("22/10/1988", 5), new         Personne("10/06/1994", 4),  new Personne("02/07/1990", 2)};  int nbElem = pers.length;     int beerMin = 1;  System.out.printf("Beer in July: %d", julyBeer(pers, nbElem));                 }     }   And the outcome is:  Beer in July: 0, and it's supposed to return 2.

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


Prove that for every integer $ n \geq 1$, we have  $\displaystyle \sum_{j=1}^n j^3 = \left(\dfrac{n(n+1)}{2}\right)^2$  I know how to prove an induction proof, but I just can't get the algebra down on this problem. Can anyone help?

How can I prove that     $$1^3+ 2^3 + \cdots + n^3 = \left(\frac{n(n+1)}{2}\right)^2$$    for all $n \in \mathbb{N}$? I am looking for a proof using mathematical induction.  Thanks


Given an entire function which is real on the real axis and imaginary on the imaginary axis, prove that it is an odd function i,e $f(-z)= -f(z)$ My attempt :  Here two cases will be possible $1.$ when $z= x$ $2.$ when $z = ix $ I have no any issue when $z=ix$  and solution is alreaday given  but i have some issue when $z=x$ $$f(x) = \overline{ f(\bar x) }$$ $$\sum_{n=0}^{\infty}a_nz^n=\sum_{n=0}^{\infty}\bar a_nz^n \implies a_n=\bar a_n$$ \begin{align} f(x)=\sum_{n=0}^{\infty}a_nx^n&=\sum_{n=0}^{\infty}a_{2n}x^{2n}+\sum_{n=1}^{\infty}a_{2n+1}x^{2n+1} \end{align} Here  $f(x)$  is both  even and odd so here  we are getting  contradiction that  $f(z)$  is odd that mean $f(x)$ is not even function

Let's say we have an entire complex function $f(z)$ such that:  $f(z)$ is real when $z$ is real $f(z)$ is purely imaginary when $z$ is purely imaginary.  SO basically this entire function maps real/im axis to itself. The question asks me to show this function is an odd function and I have no clue.


Ubuntu Server 16.04 is now released.  I have Ubuntu (server) 14.04.4 LTS, but when I try to do a do-release-upgrade it tells me that there are no upgrades available.     Why? How can I upgrade my server so I get the new awesomeness?     lizzard@lounge:~$ uname -a Linux lounge 4.2.0-34-generic #39~14.04.1-Ubuntu SMP Fri Mar 11 11:38:02 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux  lizzard@lounge:~$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description:    Ubuntu 14.04.4 LTS Release:        14.04 Codename:       trusty  lizzard@lounge:~$ do-release-upgrade  Checking for a new Ubuntu release No new release found

I'm following the , but on launching the upgrade tool I get this response:  Checking for a new ubuntu release No new release found   Am I doing something wrong? Is there a workaround?


I am adding a background worker process to my dll to report progress back to the gui. I have the following problem   I am getting the following errror :     Severity  Code    Description Project File    Line    Suppression State   Error   CS0120  An object reference is required for the non-static field, method, or property 'Program.slate_ExportReportProgress(object, SlateExportContext.ProgressArgs)' SlateExportApiTest  C:\Projects\fhsslateexport\SlateExportApiTest\Program.cs    24  Active   This is my implementation  //update the progress to the client   public EventHandler<ProgressArgs> ReportProgress;  // Eventargs to contain information to send to the subscriber public class ProgressArgs : EventArgs {     public int Percentage { get; set; }     public string Message { get; set; } }  public void TransferToSlateBackground() {     var worker = new BackgroundWorker();     worker.DoWork += DTOBackGroundWorker;     worker.ProgressChanged += worker_ProgressChanged;     worker.RunWorkerCompleted += WorkDone;     worker.RunWorkerAsync("input"); }  public void DTOBackGroundWorker(object sender, DoWorkEventArgs e) {     e.Result = e.Argument.Equals("input");     DTOCaseObject(); }  private void worker_ProgressChanged(object sender, ProgressChangedEventArgs e) { }  public void WorkDone(object sender, RunWorkerCompletedEventArgs e) {     var result = (bool)e.Result; }   The code that raises the ReportProgress event is:  int step = 100 / CaseAssets.Count(); int i = 0;  // Report progress if somebody is listening (subscribed) if (ReportProgress != null) {     ReportProgress(this, new ProgressArgs { Percentage = i, Message = "Exporting to Slate   " + caseid.ToString() }); }   But it is when I am calling the code from the gui / console app i have the problem.  here i wire my event handler   _slateExport.ReportProgress += slate_ExportReportProgress;  public void slate_ExportReportProgress(object sender, ProgressArgs e) { }   But I am getting the error above  Edit 2  I don't believe this is the main problem the problem I am facing is with an event not a property or a form control

Consider:  namespace WindowsApplication1 {     public partial class Form1 : Form     {         public Form1()         {             InitializeComponent();         }          private void button1_Click(object sender, EventArgs e)         {             //int[] val = { 0, 0};             int val;             if (textBox1.Text == "")             {                 MessageBox.Show("Input any no");             }             else             {                 val = Convert.ToInt32(textBox1.Text);                 Thread ot1 = new Thread(new ParameterizedThreadStart(SumData));                 ot1.Start(val);             }         }          private static void ReadData(object state)         {             System.Windows.Forms.Application.Run();         }          void setTextboxText(int result)         {             if (this.InvokeRequired)             {                 this.Invoke(new IntDelegate(SetTextboxTextSafe), new object[] { result });             }             else             {                 SetTextboxTextSafe(result);             }         }          void SetTextboxTextSafe(int result)         {             label1.Text = result.ToString();         }          private static void SumData(object state)         {             int result;             //int[] icount = (int[])state;             int icount = (int)state;              for (int i = icount; i > 0; i--)             {                 result += i;                 System.Threading.Thread.Sleep(1000);             }             setTextboxText(result);         }          delegate void IntDelegate(int result);          private void button2_Click(object sender, EventArgs e)         {             Application.Exit();         }     } }   Why is this error occurring?     An object reference is required for the nonstatic field, method, or property 'WindowsApplication1.Form1.setTextboxText(int)


I researched this problem on various sites and questions here on stack overflow, but I could not find a solution that solved my problem. I am struggling with this problem for some time now but just can't solve it..  I have two activities and a fragment. The first Activity (Overview) should add the Fragment in t's onCreate with different text then the default one. The second Activity (AddCity) sends this text data to Overview with an Intent and a Bundle. In Overview the Data is available and i send it to the Fragment with myfragment.setArguments(bundle), but when I try to access the Textview in onCreateView with Bundle bundle = getArguments() i get the following error:  FATAL EXCEPTION: main      Process: com.myapp.www, PID: 19690      java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference   The exception occurs at the following line in StatusFragment:  TextView cityText = (TextView) getView().findViewById(R.id.city_name);   I already tried the approach using a own constructor for that, but as far as i know you should avoid a custom constructor other than the empty default constructor in a fragment, and it didn't work either.  My classes are:  Overview:  protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_overview);          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);         setSupportActionBar(toolbar);         getSupportActionBar().setIcon(R.drawable.myicon);         // Create the adapter that will return a fragment for each of the three         // primary sections of the activity.         mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());          // Set up the ViewPager with the sections adapter.         mViewPager = (ViewPager) findViewById(R.id.container);          if(getIntent().getExtras() != null){             Bundle extras = getIntent().getExtras();              StatusFragment newFragment = new StatusFragment();             newFragment.setArguments(extras);              mSectionsPagerAdapter.addFragment(newFragment, extras.getString("city"));         }else{             Log.w("Overview-Bundle", "No Bundle Data");         }          mViewPager.setAdapter(mSectionsPagerAdapter);     }   AddCity:  This class uses a method to receive a JSON string and parse it to get the data i need to send to the fragment. This works fine, so I only give the relevant code where I put together the Intent. obj is the JSON object. (let me know if you need more code)  Intent i = new Intent(AddCity.this, Overview.class);                     Bundle bundle = new Bundle();                     bundle.putString("city", obj.getString("user_city"));                     bundle.putString("country", obj.getString("user_ country"));                     i.putExtras(bundle);                     startActivity(i);   StatusFragment:  public View onCreateView(LayoutInflater inflater, ViewGroup container,                              Bundle savedInstanceState) {         View view = inflater.inflate(R.layout.fragment_for_overview, null);          setUI(view);          return view;     }      public void setUI(View view){         if(getArguments() != null) {              Bundle bundle = getArguments();              String city = bundle.getString("city");             String country = bundle.getString("country");              TextView cityText = (TextView) getView().findViewById(R.id.city_name);             TextView countryText = (TextView) getView().findViewById(R.id.country_name);              cityText.setText(city);             countryText.setText(country);          }else{             Log.w("Arguments", "no arguments");         }     }   I would be grateful for every answer. Let me know if I should post more code.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I'm traveling from Macao to India with Air Asia and have an 8-hour transit in Kuala Lumpur.  I do not plan to leave the airport, but I'm wondering if I need a transit visa for Malaysia.

I am an Indian passport holder travelling from China to India via Kuala Lumpur, on Air Asia tickets bought separately. The layover is 4 hours and 30 minutes.  Do I need a transit visa?


Such as in "that item is 86, we need to buy more"

What does it mean when someone or something is referred to as being "86'd"?


Prove that if $[.]$ is Greatest integer function then $$\left[\frac{[x]}{n}\right]=\left[\frac{x}{n}\right]$$ $\forall$ $n \in \mathbb{Z}$  My Try is i have used both LHS and RHS:  Case $1.$ if $x \in \mathbb{Z}$ proof is trivial  Case $2.$ if $x=q+f$ where $q \in \mathbb{Z}$ and $ f \in (0 \:\: 1)$  Then $$\left[\frac{x}{n}\right]=\left[\frac{q+f}{n}\right]$$  Now by euclid's algorithm for some positive  integer $p$ we have $$q=np+r$$ where $0 \le r \lt n-1$  So $$\left[\frac{x}{n}\right]=\left[\frac{q+f}{n}\right]=\left[\frac{np+r+f}{n}\right]=p+\left[\frac{r+f}{n}\right]$$  Now since $$0 \le f \lt 1$$ and $$0 \le r \lt n-1$$  we have  $$ 0 \le r+f \lt n$$  So $$\left[\frac{r+f}{n}\right]=0$$  hence  $$\left[\frac{x}{n}\right]=p \tag{1}$$  Now  $$\left[\frac{[x]}{n}\right]=\left[\frac{[q+f]}{n}\right]=\left[\frac{q}{n}\right]=\left[\frac{np+r}{n}\right]=\left[p+\frac{r}{n}\right]=p+\left[\frac{r}{n}\right]$$  Now since  $$0 \le r \lt n-1$$ we have  $$\left[\frac{r}{n}\right]=0$$  So  $$\left[\frac{[x]}{n}\right]=p \tag{2}$$  From $1$ and $2$ we have the required proof.  is there a better way please share

I'm trying to prove rigorously the following:  $\lfloor x/a/b \rfloor$ = $\lfloor \lfloor x/a \rfloor /b \rfloor$   for $a,b>1$  So far I haven't gotten far. It's enough to prove this instead  $\lfloor z/c \rfloor$ = $\lfloor \lfloor z \rfloor /c \rfloor$   for $c>1$  since we can just put $z=\lfloor x/a \rfloor$ and $c=b$.


Below program returns 0.009999999999999998. My question is why it does not return .01.       double a = 0.02;     double b = 0.03;     double c = b - a;     System.out.println(c);   I know BigDecimal will return expected output but i want to understand By what logic  answer is 0.009999999999999998 in double ?

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


Anybody know what the leading "F" means on these brushes?

First, I know that clicking the '+' button on the right side of the material list makes an empty material slot, and after clicking the 'New'-button it adds a new material. But isn't it the same as just only clicking the 'New'-button (without clicking the '+' button first = empty slot)?   Second, I know that clicking the '+' button at the bottom next to the 'F'-button copies this material and makes it as a new node. Activating the 'F'-button will not delete unused material after closing the file. What exactly does the '2' button do (when 'F' button activated)? Is it the same as just clicking the '+' button (at the bottom, next to 'F' button)? So what exactly does the 'F' button and '2' button do?


The energy-time uncertainty principle, given by, $$\Delta E\Delta t\geq\frac{\hbar}{2},$$  can be used to explain the existence of virtual particles which violate the law of conservation of energy. That is, the smaller the uncertainty in time, $\Delta t$, the greater $\Delta E$ that is needed to ensure that this relation holds. My question however is this: What is stopping both the uncertainty in time and the uncertainty in energy being large simultaneously?   From what I can tell, a simultaneously large $\Delta t$ and $\Delta E$ would not violate this relation, so why do virtual particles have such short lifetimes?

I (as a middle-school student) was wondering how virtual particles even conserve energy of the entire system? I don't mean just the particle's energy, but conservation with respect to the surroundings?  Let me explain more, Einstein proved that $E = mc^2$ and equivalently, we can say $m = \frac{E}{c^2}$ . We however know mass causes curvature in space-time (gravity well). Now that statement being completely valid we can use Quantum Fluctuation, implying energy and time can be related by the relation:  $\Delta{E}\Delta{t}\approx\frac{\hbar}{2}$ and by that simple relation we can make the following points:   As the energy increases, the time allowed to be "borrowed" decreases, before it gives it back to the universe. As time increases, the energy allowed to be "borrowed" decreases.    These are completely satisfactory points I've made, I believe.  Now, I have read that the vacuum is filled with constantly bubbling virtual particles that get created from the energy "borrowed" by the above relation and is destroyed again, which satisfies the energy conservation laws.   This seems to imply that  in the short time the virtual particle exists, they must have a very small mass which is: $m_{1} = \frac{\Delta{E}}{c^2}$ and using basic classical mechanics rather than GR (for sake of simplicity) we calculate that the gravitational force mediated by this short-lived virtual particle;  $F_{g}= G\frac{m_1 * m_x}{r^2}$   where $m_x$ is an particle\mass in question. Nevertheless since we know the force set upon an object moves the object in a direction, we can say it would increase its kinetic energy by this factor: $F_g = \frac{1}{2}mv^2$ which is equal to $G\frac{m_1 * m_x}{r^2} = \frac{1}{2}mv^2$.  Surely, this implies that every time quantum fluctuations happen, energy of real-particles\masses increases and therefore violates energy conservation, but what prevents this violation from taking place?  If virtual particles are not really present and interact with objects like I thought, how can Hawking radiation (currently a large concept in black hole physics) then be accepted in physics community?


Is it true that if $X$ and $Y$ are sets and there is a bijection between $\mathcal{P}(X)$ and $\mathcal{P}(Y)$ then there is a bijection from $X$ to $Y$ ?. I believe this should be obvious, but I can't see why this is so. A proof or a counter example would be highly appreciated.   Thanks.

A friend of mine told me that $X \cong Y \Rightarrow 2^X \cong 2^Y$ ($X$ and $Y$ being sets), which is very easy to prove, but he was wondering about the converse in ZF, i.e., can one take logarithms? Since the (apparently) simpler question of whether it is possible to divide by a natural number is not particularly trivial without assuming the axiom of choice (see Doyle, Conway: ), I would imagine that this problem doesn't have an easy answer either.


I am a casual user of stack overflow and frequently end up here from Google searches.  Recently it seems that most of the questions I stumble upon have been 'closed as not constructive' by moderators despite protesting users who have heavily up-voted a 'this question helped me allot' comment.  (See  and  for examples).   I think I speak for a large part of the SO user community when I say that 'opinion' questions like:   What is the best library for doing FOO What are things to avoid when coding in language BAR What are some good reference materials to learn library FOOBAR   are very helpful, perhaps the most helpful questions on stack overflow.  Choosing a technology/library happens early in the development pipeline and is expensive to fix if you get it wrong.    I would love to see SO change it's policy on this type of question, because I deeply appreciate the advice the wisdom of the intelligent user community.  It has personally saved me countless hours and I hope that this can continue in the future.

I frequently come across a really useful answer on StackOverflow which has been closed because it doesn't match the Q&A format.  Examples include  ,  ,   ,  and there are others.  Where should this information be exchanged if it's not on stackoverflow?  It seems the moderators are often somewhat overzealous...  ---edit  When I say best, I mean they are informative and useful for someone who's looking for an answer to them.  Even if they do become a bit of a discussion, I value other people's opinions on the relative merits of the different JPA frameworks.  I come here looking to choose one and the answer helps me.  So what if it's not a definitive answer?  ---edit  I don't care how popular a question is, nor how interesting it is.  Users are interested in stuff that's useful to them.  Plenty of those were useful (as judged by the upvotes on the answers: 'This answer is useful'), but closed because they didn't have a definitive answer, as far as I can tell.  ---edit  Seems I'm not the first person to think this: there are various similar questions to mine like this one:   In it the user lists lots of other useful questions which have been closed:                    So isn't there a place on stackoverflow for these questions?  A discussion section, maybe?


Full error messsage: Could not load file or assembly 'LimitlessSoft.Buffer, Version=4.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. A strongly-named assembly is required. (Exception from HRESULT: 0x80131044) First of all I have looked at these questions and all of their answers:      I haven't found any solution that is working for me. Here is my situation. I have winform .NET Framework 4.0 project (no I cannot update to higher version). I had some code in it which I wanted to separate in dll so I can use it in some other project. I have created new .NET Framework 4.0 Class Library project which has only one class and it looks like this: using System;  namespace LimitlessSoft.Buffer {     /// <summary>     /// Used to buffer data     /// </summary>     /// <typeparam name="T"></typeparam>     public class Buffer<T>     {         /// <summary>         /// Delegate that returns object that is buffered         /// </summary>         /// <returns></returns>         public delegate T SetBuffer();         /// <summary>         /// SetBuffer that returns object that is buffered         /// </summary>         private SetBuffer UpdateBuffer;          /// <summary>         /// Indicates when has buffer been updated last time         /// </summary>         public DateTime LastUpdate { get; set; }         private T Value { get; set; }           /// <summary>         /// Initializes new buffer         /// </summary>         /// <param name="updateBuffer">Delegate that returns object being buffered</param>         public Buffer(SetBuffer updateBuffer)         {             UpdateBuffer = updateBuffer;         }           /// <summary>         /// Gets item from buffer that has been last time updated not greater than maximumObselence.         /// If it cannot be found, he will do as updateIfNotFound says.         /// If it cannot be foudn after updateIfNotFound, you will get default(T)         /// </summary>         /// <param name="maximumObselence">Maximum obselence for buffered item</param>         /// <param name="updateIfNotFound">Indicates if buffer need to be updated if it has not been found at given period</param>         /// <returns></returns>         public T Get(TimeSpan maximumObselence, bool updateIfNotFound = true)         {             if (Value != null)                 if ((LastUpdate - DateTime.Now).TotalMilliseconds < maximumObselence.TotalMilliseconds)                     return Value;              if (updateIfNotFound)             {                 Value = UpdateBuffer();                 LastUpdate = DateTime.Now;                 return Value;             }              return default(T);         }         /// <summary>         /// Sets item into buffer         /// </summary>         /// <param name="item"></param>         public void Set(T item)         {             Value = item;             LastUpdate = DateTime.Now;         }         /// <summary>         /// Updates data in buffer         /// </summary>         public void Update()         {             Value = UpdateBuffer();             LastUpdate = DateTime.Now;         }     } }  When I import this class library in my project it drops error. Then I created new empty .NET Framework 4.0 winform application, imported this dll, initialized class, called function from it and poof it is working. Why does same dll works in new empty project but drops error on other one?

I have a Windows forms project (VS 2005, .net 2.0). The solution has references to 9 projects. Everything works and compiles fine on one of my computers. When I move it to a second computer, 8 out of the 9 project compile with no problem. When I try to compile the 9th project (the main project for the application - produces the .exe file to execute the application), I get the following error:   'Error 3: A strongly-named assembly is required. (Exception from HRESULT: 0x80131044)'   The file location for the error is is listed as "C:\PATH-TO-APP\LC".   I have checked in the project properties and all of the projects are set to build in Debug mode, none of them are supposed to be signed. In the project that is failing, the only assembly that it references that is not in any of the other projects is Microsoft.VisualBasic (a .net 2.0 assembly). So I am at a loss to find what ids causing this error (the file referenced above in the error message - "LC" - does not exist.   Anyone know how I can force the project to accept all unsigned assemblies, or to determine which assembly is the culprit?  The only meaningful difference between the dev environments between the dev environment where this worked and the current one is that the first was XP and this is Vista64. However, a colleague of mine who is using XP is getting the same error.  Third-party assemblies being used:   ComponentFactory.Krypton.Toolkit ComponentFactory.Krypton.Navigator VistaDB.NET20   All of these are referenced in other projects in the solution which build with no problems, so it doesn't look like these are the problem.  So far I have tried deleting the suo file, Rebuild All, unloading and reloading projects from the solution, removing and readding referenced assemblies. Nothing has worked.


In my physics class we were doing problems such that we set $N$ (normal force) $= mg$. I understand that by Newton's Third Law, if I exert a force on the ground, then the ground will exert an equal and opposite force on me. However, the part that I am slightly confused about is that when the Earth rotates, and thus I rotate too, I am accelerating with the centripetal force towards the center of the earth (assuming I am at the equator). How am I doing this if the normal force equals $mg$? If the normal force doesn't equal mg then why isn't the ground exerting an equal and opposite force?

Let us say a block of mass is placed on the surface of earth. Then while drawing the forces on that body, we say:   Force $F = mg$ acting towards the center of Earth. Normal reaction $N$ offered by the surface of Earth.   If no other forces are acting, we say $F=N$. But what about the centrifugal force $m\omega^2R$ . Why don't we ever bring that into picture? What am I missing?


public partial class JobDataDuplicatorForm : Form {     public JobDataDuplicatorForm(IJobDataDuplicatorEngine engine)     {         _engine.CopyStartedEvent += GetEventHandler(OnCopyStarted);         _engine.CopyEndedEvent += GetEventHandler(OnCopyEnded);         ...     }      private static EventHandler GetEventHandler(Action action)     {         return (sender, args) => action();     }      private void OnCopyStarted()     {         copyStatus.Text = "Copy progress: ";         generateButton.Enabled = false; // Cross-thread operation not valid     } }   I have the following exception:  Additional information: Cross-thread operation not valid: Control  'generateButton' accessed from a thread other than the thread it was created on.   Can I fix the exception by changing GetEventHandler() instead of wrapping each button in different places like this   Invoke((MethodInvoker)delegate {         generateButton.Enabled = false;         }); ?  How can I do this?

I have a scenario. (Windows Forms, C#, .NET)   There is a main form which hosts some user control. The user control does some heavy data operation, such that if I directly call the UserControl_Load method the UI become nonresponsive for the duration for load method execution. To overcome this I load data on different thread (trying to change existing code as little as I can)   I used a background worker thread which will be loading the data and when done will notify the application that it has done its work.   Now came a real problem. All the UI (main form and its child usercontrols) was created on the primary main thread. In the LOAD method of the usercontrol I'm fetching data based on the values of some control (like textbox) on userControl.    The pseudocode would look like this:  CODE 1  UserContrl1_LoadDataMethod() {     if (textbox1.text == "MyName") // This gives exception     {         //Load data corresponding to "MyName".         //Populate a globale variable List<string> which will be binded to grid at some later stage.     } }   The Exception it gave was     Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on.   To know more about this I did some googling and a suggestion came up like using the following code  CODE 2  UserContrl1_LoadDataMethod() {     if (InvokeRequired) // Line #1     {         this.Invoke(new MethodInvoker(UserContrl1_LoadDataMethod));         return;     }      if (textbox1.text == "MyName") // Now it wont give an exception     {     //Load data correspondin to "MyName"         //Populate a globale variable List<string> which will be binded to grid at some later stage     } }   BUT BUT BUT... it seems I'm back to square one. The Application again  become nonresponsive. It seems to be due to the execution of line #1 if condition. The loading task is again done by the parent thread and not the third that I spawned.  I don't know whether I perceived this right or wrong. I'm new to threading.  How do I resolve this and also what is the effect of execution of Line#1 if block?  The situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread.   So only accessing the value so that the corresponding data can be fetched from the database.