Why is the spectrum of the $\beta$-decay continuous?

the spectrum of the Gamma and Alpha decays are both discrete, i.e. the $\alpha$-particles and the $\gamma$-rays take on only discrete values when emitted from a decaying nucleus.  Why is it then, that the $\beta^{\pm}$ can take on continuous values?  The main thing that distinguishes the beta decay from the other two is, that it is a three body problem, i.e. the nucleus does not only decay into an electron/positron, but also into a electron-neutrino/antineutrino. I don't see yet how this immediately implies that the spectrum of the electrons is continuous though.  The way I understand the two body decays is, that the initial nucleus spontaneously decays into the two bodies, i.e. a smaller nucleus and a gamma or alpha particle. As the energy levels in both the nuclei are quantized, only certain values for the energy of the photon and the Helium core are allowed, sine Energy and momentum need to stay conserved.  Does the third particle change things in the way that there basically are two things (i.e. the electron and the neutrino in the beta decay) that are not restricted by an inner energy level hierarchy in the way the nuclei are, thus allowing the energy given by the nuclei to be split arbitrarily (and continuously) between the electron and the neutrino?  If this is the wrong explanation, please correct me.


Introduction Even within a site's relatively focused range of topics (it's unlikely anybody on SO will think  refers to the solar system's star), some tags are inherently ambiguous. There are currently two unsatisfying options:  Declare that the tag is only to be used for one of the possible meanings, write a tag wiki explaining it, and link from there to the newly created tags for the other meanings, and keep cleaning up the tag whenever someone ignores the tag wiki popup explaining the tag. Use alternative tags for all meanings (e.g. cd-command and compact-disk, instead of cd), and keep removing the undesired tag whenever it pops up again. And it will. The  is not deterring users from creating unnecessary or redundant tags.  Blacklisting tags is a complicated ritual occurring once in a blue moon, at most, and involves a dragon, a team member, and sacrifices to be burnt. It also makes those other, unambiguous tags not easier to discover, if it were applied to ambiguous tags. I don't consider this to be a viable option in this case. Proposal Here's the proposed : Just like a tag can be declared a synonym of another tag, basically changing all references to the synonym to references to that other, canonical tag, it should be possible to make it a disambiguation tag (or ambiguous tag) for multiple other tags. It's a logical progression from "You entered a term with the same meaning as this other term" to "You entered a term with the same meaning as one of these other terms, please choose the correct meaning". Use of the tag should force the user to choose one of the alternatives presented:  ", did you mean  or ?" ", did you mean , , or ?" "You entered 'vm', did you mean  or ?" "You entered 'sas', did you mean  or ?" "You entered 'kvm', did you mean  or ?" "You entered 'mono', did you mean  or ?" "You entered 'dsl', did you mean  or ?"  Not all of these examples might be good (I'm not sure e.g. about the first two SO examples), but that's not really the point here anyway — they should just convey how this could be used. Note how some of these tags would probably never be used if users had to type them, and yet everything shorter is ambiguous. This could probably be mostly solved by extending the synonym/tag wiki excerpt dropdowns shown when a user enters the tags, proposing the alternatives for an ambiguous tag entered by the user (like a synonym suggestion, but with multiple options). If ignored, the user could still be shown an error message like with blacklisted tags, but by designing the selection dialog well, it should be possible to prevent that in most cases.  Related topics   This topic is related, but the user seems to have accepted the inclusion of tag wiki excerpts in the tag suggestions drop-down as sufficient.   This requires extensive discussion and team involvement (i.e. the status quo)   This topic has no real solution, except manual retagging.


How do I install the latest version of Matlab?

When I tried to install Matlab using the Software Center, it prompted me for the Location of MATLAB installation(s). Since I am trying to install it, I don't know what to do.


Area of a spherical cap across an intersection

I have a sphere with radius $r$ that equally divided in to two hemisphere P and S. There is a plane that separate two different zone A and B. Upper zone called A and lower zone called B.  $\alpha$ is the contact angle. So $\alpha $ larger means sphere is more in zone A and vice versa. Range of $\alpha $ can go between $[0,\pi]$The angle $\beta$ defines the orientation of the sphere which is an angle between z axis (vertical) and a unit vector. Range of $\beta $ can be $[0,2\pi]$. The  Schematic representation of this is below.  To calculate the area of $P$ portion of the sphere into $A$ is given by following equation $$ \mathrm{Area}_{P@A}=  r^2\int_{\theta=\frac{\pi}{2}-\beta}^\alpha  \int_{\phi=\arcsin(1/(\tan\theta \tan \beta))} ^{\pi -\arcsin(1/(\tan\theta \tan \beta)} \sin\theta\; d\theta d\phi. $$  After solving this equation we can get the following solution.  $$ \textrm{Area}_{P@A}= 2 r^2 \left\{ \cos (\alpha) \sin ^{-1}(\cot (\alpha) \cot (\beta)) -\tan ^{-1}\left(\frac{\cos (\beta)}{\sqrt{\sin ^2(\beta)-\cos ^2(\alpha)}}\right)\right\}+\pi  r^2 (1-\cos (\alpha)). $$  Note that the solution is defined as a function of $\alpha$ and $\beta$. If we change the value of $\alpha $ and $\beta$, the area of P into A will change eventually.     Now consider more complex case where $P$ and $S$ are not equal hemisphere.         Question:   If $P$ and $S$ are not equal hemisphere rather they are spherical cap, then what I need to consider to calculate the area of $P$ into zone $A$ as a function of $\alpha$ and $\beta$? Here $\gamma$ defines size of the spherical cap and r1 is the radius of the base of the cap. Do I need to introduce any other parameter?


Children's fantasy book where two boys enter a parallel world through the principal's office where math and poetry were magic

Read this as a kid in the early 80s.  Two boys in our world get in a fight at school, but when they enter the principal's office they are transported to a parallel world. As I recall, they had to work together to save that world by finding several magic items (one was a thread, I think?). And in that world math and poetry were magic?  Anyone remember this?


, thanks for the time invested at resolving my issue :)


I want recommendations about which CMS to go for where should I ask it

I am a developer seeking recommendations for an open source CMS.  I had an age old question on SO with 20+ upvotes asking for recommendations for a book but it was recently deleted for being off topic.  I then asked for my CMS recommendation question on programmers and was told recommendations are off topic but there are other places on stack exchange i could ask it.  I know the basis of SE sites is questions and answers and discussions are discourage but I would like some feedback from the development community about what they have used and that fits my specific requirements.  I am not looking for a discusion or a which is best or to start a forum style thread.  I just want "I have used this it has the following features you have requested, I have also found these other features useful.  Bearing in mind i want to know from a developer's point of view, is there a place on SE that I can ask this kind of question and if so where.


How to compute minimum shallowness of quantum well to have at least one bound state?

Given a potential $V$, how does one compute how shallow the potential can be such that it allows at least one bound state?


Twitter Bootstrap uses these break points for responsive design:  Large Display: 1200px Default: 980px Tablet: 768px Mobile: 480px  A client said they are using 1280px for their Large Display breakpoint.  Is there an industry standard for these or are they just made up as we go right now?


Javascript: When I use the same code but outside of a function it works

I'm doing a program which converts currencies and measures. To make the code more reusable I've created a function which shows the symbols on a dropdown and get the rate from an API. This is the code: const firstDropdown = document.querySelector('.first-value'); const secondDropdown = document.querySelector('.second-value'); const firstSymbol = document.querySelector('.first-symbol-button'); const secondSymbol = document.querySelector('.second-symbol-button'); const firstInput = document.querySelector('.first-value-input'); const secondInput = document.querySelector('.second-value-input');   //FUNCTIONS const showSymbolsAndGetRates = (event, symbol, rate) => {     if(event.target.tagName === 'A'){         symbol.innerText = event.target.innerText;         rate = currencies.rates[event.target.innerText];     };     return rate; }  //get symbols and rates let firstRate = 'ciao'; let secondRate = 'ciao';  firstDropdown.addEventListener('click', e => {     e.preventDefault();     showSymbolsAndGetRates(e, firstSymbol, firstRate);      // if(e.target.tagName === 'A'){     //     firstSymbol.innerText = e.target.innerText;     //     firstRate = currencies.rates[e.target.innerText];     //     return firstRate;     // };     console.log(firstRate) }); secondDropdown.addEventListener('click', e => {     e.preventDefault();     showSymbolsAndGetRates(e, secondSymbol, secondRate);     // if(e.target.tagName === 'A'){     //     secondSymbol.innerText = e.target.innerText;     //     secondRate = currencies.rates[e.target.innerText];     // }     // return secondRate;     console.log(secondRate) });  As you can see the code in the function showSymbolsAndGetRates  is the same as the commented code, which was the original code. The problem is that when I use the commented code the rate is returned without problems but when I use the function the rate does not change, so the console shows 'ciao' instead of the real rate. I'm new at programming and I have no idea of how to solve this problem without having to write code for every event.


Text is printed at weird positions in some (sub)sections

I'm writing a realively normal document. I just adjusted it to print it double sided. Now a few pages have weird placement of text and images. Notice that the text should be directly under the section header and the image directly below it.   The source for the page:  \subsection{Cartridge} The newly designed cartridge is half the height of proof of concept's cartridge while holding the same amount of plastic tube. The force needed to pull the plastic out of the cartridge is the same, as described in chapter \ref{subsec:des2_cart}. The difference between size is shown in figure \ref{fig:cartimprove}. The cartridge does not damage the plastic bag. The cartridge is found to be easy to replace thanks to the sliding the mechanism, although it is advised to test this mechanism with other test subjects. It should, however, be noted that there is quite some space needed between to cartridge and the sealer mechanism to get the cartridge out. This space is needed because the opening between the seal beams is too small for the cartridge to pass through. So to get the cartridge out you will need to tilt it quite a bit. Figure \ref{fig:carttilt} visualizes this.\\  \begin{figure}[H]     \begin{center}         \includegraphics[width=0.8\textwidth]{img/cartimprove.PNG}         \caption{Size reduction of new cartridge}         \label{fig:cartimprove}     \end{center} \end{figure}   and my preamble:  \documentclass[12pt, twoside, openright, titlepage]{article} \usepackage[T1]{fontenc} \usepackage[utf8]{inputenc} \renewcommand{\familydefault}{\sfdefault}   \usepackage[margin=2cm, twoside]{geometry} \usepackage{amsfonts, amsmath, amssymb} \usepackage[none]{hyphenat} \usepackage{fancyhdr} \pagestyle{fancy} \usepackage{float}  \usepackage{multicol}  \usepackage{siunitx}  \usepackage{pdfpages} \usepackage{pdflscape}  % References % \usepackage{hyperref} \usepackage[ backend=biber, citestyle=numeric, sorting=none, hyperref=true ]{biblatex} \addbibresource{ref.bib}  % Images %  \usepackage{graphicx} \usepackage{caption} \usepackage{subcaption} \usepackage{wrapfig}  % pro and cons lists* \newcommand*\MyPitem{% \item[\textbf{\color{green}\scalebox{1}{+}}]} \newcommand*\MyCitem{% \item[\textbf{\color{red}\scalebox{1.1}{-}}]}  % Page layout%  \fancyhead{} \fancyfoot{} \fancyhead[RO, LE]{\slshape title} \fancyhead[LO, RE]{\slshape name} \fancyfoot[LE, RO]{\thepage} \renewcommand{\footrulewidth}{0pt}  \parindent 0ex \usepackage{tikz,amsmath, amssymb,bm,color} \usetikzlibrary{calc,patterns,decorations.pathmorphing,decorations.markings,shapes,arrows} % needed for BB \usetikzlibrary{calc}  \begin{document} \includepdf[fitpaper=false, pages=-, noautoscale=true]{inc/frontpage.pdf}  \cleardoublepage


INVALID_TYPE Error When Creating a Custom Object With SOAP

I am getting errors when attempting to 'Create' a custom "O2C_Alert__c" object with a SOAP request.  My request is:  <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:enterprise.soap.sforce.com" xmlns:urn1="urn:sobject.enterprise.soap.sforce.com">    <soapenv:Header>       <urn:SessionHeader xmlns:urn="urn:enterprise.soap.sforce.com">          <urn:sessionId>SESSION_ID</urn:sessionId>       </urn:SessionHeader>    </soapenv:Header>    <soapenv:Body>       <urn:create>          <!--Zero or more repetitions:-->          <urn1:sObjects>             <!--Zero or more repetitions:-->             <urn1:type>O2C_Alert__c</urn1:type>                 <urn1:CreatedDate>20151231</urn1:CreatedDate>                 <urn1:Alert_Code__c>STD</urn1:Alert_Code__c>                 <urn1:Status__c>New</urn1:Status__c>                 <urn1:Customer_Id__C>0123456789</urn1:Customer_Id__C>                 <urn1:Name>Kroger</urn1:Name>                 <urn1:Order_Id__c>0123456789</urn1:Order_Id__c>          </urn1:sObjects>       </urn:create>    </soapenv:Body> </soapenv:Envelope>   The response I am getting back is:  <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:sf="urn:fault.enterprise.soap.sforce.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">    <soapenv:Body>       <soapenv:Fault>          <faultcode>sf:INVALID_TYPE</faultcode>          <faultstring>INVALID_TYPE: Must send a concrete entity type.</faultstring>          <detail>             <sf:InvalidSObjectFault xsi:type="sf:InvalidSObjectFault">                <sf:exceptionCode>INVALID_TYPE</sf:exceptionCode>                <sf:exceptionMessage>Must send a concrete entity type.</sf:exceptionMessage>                <sf:row>-1</sf:row>                <sf:column>-1</sf:column>             </sf:InvalidSObjectFault>          </detail>       </soapenv:Fault>    </soapenv:Body> </soapenv:Envelope>   Thanks for any and all help.


prove that for $n\geq 8$ exist $p,q\epsilon\mathbb{N}$ so that $n=5p +3q$

I ve been asked to prove that for $n\geq 8$  exist $p,q\in \mathbb{N}_0$ so that $n=5p +3q$ anyone who could help and explain too?


Units (invertibles) of polynomial rings over a field

If $R$ is a field, what are the units of $R[X]$?   My attempt: Let $f,g \in R[X]$ and $f(X)g(X)=1$. Then the only solution for the equation is both $f,g \in {R}$. So $U(R[X])=R$, exclude zero elements of $R$.  Is this correct ?


Is this a valid proof for $\gcd(a^m - b^m, a^n - b^n) = a^{\gcd(m, n)} - b^{\gcd(m,n)}$?

$ \newcommand{\Mod}[1]{\ (\mathrm{mod}\ #1)} $  Prove that, if $\gcd(a,b)=1$ and $a>b>0$, then $$      \gcd(a^m - b^m, a^n - b^n) = a^{\gcd(m, n)} - b^{\gcd(m,n)}, \quad 0 \leq m < n . $$ (All variables are integers.)  Let $d>0$ be an integer so that $d = \gcd(a^m - b^m, a^n - b^n)$ and therefore, by definition, $d \backslash (a^m - b^m)$, $d \backslash (a^n - b^n)$. By definition of modular congruence, if $m > 0$, then $a \equiv b \Mod{m}$ if and only if $m \backslash (b - a)$, we get \begin{equation*}     b^m \equiv a^m \Mod{d} \; , \quad     b^n \equiv a^n \Mod{d} \; . \end{equation*} According to the Bézout's lemma, there must exist integers $x$ and $y$ so that $mx + ny = \gcd(m, n)$. We can raise both sides to the power of $x$ or $y$: \begin{equation*}     (b^m)^x \equiv (a^m)^x \Mod{d} \; , \quad      (b^n)^y \equiv (a^n)^y \Mod{d} \; . \end{equation*} We can "combine" and simplify them as following: \begin{gather*}      (b^m)^x \cdot (b^n)^y \equiv (a^m)^x \cdot (a^n)^y \Mod{d} \; , \\     b^{mx + ny} \equiv a^{mx+ny} \Mod{d} \; , \end{gather*} and further as \begin{equation*}     b^{\gcd(m, n)} \equiv a^{\gcd(m,n)} \Mod{d} \;. \end{equation*} If follows that \begin{equation}     d \backslash (a^{\gcd(m,n)} - b^{\gcd(m, n)}) \; . \tag{1} \end{equation} Moreover, we can factor \begin{gather*}      a^n - b^n = (a^{\gcd(m,n)} - b^{\gcd(m,n)})(a^{n-\gcd(m,n)}b^0 + a^{n-\gcd(m,n)-1}b^1 + \ldots + a^0 b^{n-\gcd(m,n)}) \;, \\     a^m - b^m = (a^{\gcd(m,n)} - b^{\gcd(m,n)})(a^{m-\gcd(m,n)}b^0 + a^{m-\gcd(m,n)-1}b^1 + \ldots + a^0 b^{m-\gcd(m,n)}) \; . \end{gather*} Here we can see that $(a^{\gcd(m,n)} - b^{\gcd(m,n)}) \backslash (a^n - b^n)$, $(a^{\gcd(m,n)} - b^{\gcd(m,n)}) \backslash (a^m - b^m)$, and therefore \begin{equation}     (a^{\gcd(m,n)} - b^{\gcd(m,n)}) \backslash \gcd(a^m - b^m, a^n - b^n) \;. \tag{2} \end{equation} (1) and (2) together imply \begin{equation*}     \gcd(a^m - b^m, a^n - b^n) = a^{\gcd(m, n)} - b^{\gcd(m,n)} \; . \end{equation*}


Android Java NullPointerException when trying to see if GPS is enabled

I'm a noob to Android (and not too hot on Java either). I am trying to make sure GPS & internet are enabled before launching the map activity in my app.  I'm getting a null pointer exception when calling CheckGPSStatus() in the code below and cannot resolve it. (I've been pulling my hair out for the last 2 days trying to solve this; I've read loads of questions similar to this already & still can't solve it.   I've also cut and paste a different programs code and while it works in its own project, when i practically copy it into my project it doesn't work in mine). Any and all help gratefully received! Error: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference at com.example.racewatch.MainActivity.CheckGPSStatus(MainActivity.java:64) at com.example.racewatch.MainActivity$1.onClick(MainActivity.java:46)  MainActivity.java  import android.app.ActivityManager; import android.content.Context; import android.content.Intent; import android.location.LocationManager; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.Toast; import java.util.List;  public class MainActivity extends AppCompatActivity {           Button launch_button;     boolean gps_enabled = false;     boolean internet_enabled = false;     Context context;     LocationManager lm;       @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          launch_button = findViewById(R.id.launch_button);          launch_button.setOnClickListener(new View.OnClickListener(){             @Override             public void onClick (View view){                 CheckGPSStatus();                 CheckLocationStatus();                  if (gps_enabled && internet_enabled) {                     Intent i = new Intent(getApplicationContext(), Route.class);                     startActivity(i);                 } else {                     Toast.makeText(MainActivity.this, "Please enable Date & GPS Location", Toast.LENGTH_SHORT).show();                 }             }   // end of OnClick          // TODO: need to check for older build versions          });  // end of onClickListener     } // end of onCreate method       public void CheckGPSStatus() {         lm = (LocationManager)context.getSystemService(Context.LOCATION_SERVICE);         gps_enabled = lm.isProviderEnabled(LocationManager.GPS_PROVIDER);     }      public void CheckLocationStatus() {         lm = (LocationManager)context.getSystemService(Context.LOCATION_SERVICE);         internet_enabled = lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER);     }    } // end of class```


Malleability attacks against encryption without authentication

Suppose there is a message that is encrypted with AES-128-CBC.  The message is as follows, new lines are used to delimit the 16 byte boundary for each block:  Wire funds from: Alice to Bob in   the amount of $ 1   Because this message is encrypted using CBC mode,  any modification of the first block of cipher text would propagate throughout the message.   However, the amount of the fund transfer falls in the last block.  I am under the assumption that an attacker can use the property of  to alter the last block and produce a valid amount that is greater than \$1 in far fewer than $2^{128}$ operations.   Is this a correct assumption?  Is there a name for this attack or do you know of a real world example?    My instinct is that if you just need one byte of the 16 byte block to be of a specific value then it would only require $2^8$ operations because the other 120 bits of the plain text could be any value. For example lets say we wanted the last block of cipher text to decrypt to 9\0 (where \0 denotes a single null byte, and the message would be interpreted as \$9), then it would take only $2^{16}$ operations to find this cipher text block.  Is there something I am missing?


Would it make sense to take a loan from a relative to pay off student loans?

Together my wife and I have about $80,000 in student loans. My mother in law is in the process of selling her house. We proposed the idea of borrowing ~$50000 from her, once she sells, so that we could pay off our loans with higher rates. We offered to pay her back with an interest rate of 5%. Our idea was that we would be able to pay off all of the loans with a rate over 5%, and she would get a (nearly*) guaranteed 5% return rate.  Does this plan make sense to all parties involved?  Loan amounts  and rates (from a couple of months ago, may update when I have more time):  $10,541.19      8.63% $16,966.98      8.38% $ 6,423.44      6.55% $ 6,341.26      6.55% $14,715.64      6.50% $ 7,107.64      4.41% $ 2,126.34      4.25% $ 3,637.38      3.61% $ 3,438.88      3.61% $ 2,779.82      3.61% $ 4,131.47      3.15% $ 3,482.91      3.15% $   697.95      3.15%   Some other relevant information:   We've already bought a house  We own both our vehicles (actually have a third we need to sell) We're currently bringing in a little more each month than our monthly expenses, but can (and probably will) cut back in certain areas to have extra to pay off loans with even faster   * I only say nearly as you never know what could happen, but we have every intention of paying it all back at that rate.


switching keys and values in a dictionary in python

Say I have a dictionary like so:  my_dict = {2:3, 5:6, 8:9}   Is there a way that I can switch the keys and values to get:  {3:2, 6:5, 9:8}


Can one tell, just by looking at a picture, if it's a sunset or a sunrise?

I was wondering, is there any inherent difference between a still of a sunset and one of a sunrise, if you have no further context?  That is, without knowing the time when the picture was taken, where in the world it was, which way the photographer was facing etc. Just from elements in the picture itself. Is it possible to tell the difference?  For instance, if the earth rotated a lot faster, I assume you would be able to tell by the light trail (or, of course, if it was a long exposure photograph).  Ideas?


Effect of Gate Voltage on conductivity - MOSFET

I have this formula for the current based on conductivity but I cannot see the influence when applying the gate voltage. What does it change ? My assumption is that I have to change the conductivity as the conduction edge is shifted by e*Vgate.   Thanks


Will forcing integrated GPU mode prevent GPU panics? If so, how to do that?

Context: My mid-2010 MBP 15" has started to get random GPU panics:  Anonymous UUID:       84FEDF51-A1D6-EDC2-CC8C-6B53B7959874 Thu Feb  5 09:29:06 2015 *** Panic Report *** panic(cpu 2 caller 0xffffff7f9bbb0f63): "GPU Panic: [<None>] 3 3 7f 0 0 0 0 3: NVRM[0/1:0:0]: Read Error 0x00000100: CFG 0xffffffff 0xffffffff 0xffffffff, BAR0 0xd2000000 0xffffff8134a1d000 0x0a5480a2, D0, P3/4\n"@/SourceCache/AppleGraphicsControl/AppleGraphicsControl3.8.6/src/AppleMuxControl/kext/GPUPanic.cpp:127 Backtrace (CPU 2), Frame : Return Address 0xffffff8137c5b590 : 0xffffff8018f2fe41   My system has two graphics subsystems: the built-in Intel HD Graphics and the NVIDIA GeForce GT 330M.  I've heard anecdotally that the NVIDIA 330M is problematic.  (I also heard that I just missed the deadline for an Apple warranty repair for that very problem...sigh.)    So I'd like to try forcing the system to always use the Intel HD Graphics and see if that makes the problem go away.  My questions:   Will forcing the system to use the Intel HD Graphics will cure the panics? If so, is the  app the recommended approach?


Is it possible to decrypt an encrypted SD card without rooting the Android phone? (How to get the .key file of /data/misc/vold?)

I'd like to encrypt my SD card for Android conveniently, safely and in a cross-platform way so that it can also be used on other devices. I asked about that .  As of right now there doesn't seem to be a way to do that (an app on FDroid or Playstore which doesn't put data at risk and is secure and very convenient/easy/fast to use).  This is why I decided to keep using the Android's default way of encrypting the SD card. However, this way it's not possible to access the data from other devices.  it has been described how data of the SD card can be decrypted from other devices but that way requires rooting the Android phone. Is it possible to do this without rooting the phone? In specific how could one get the .key file in /data/misc/vold?


Configuration needed so that sudo doesn't have to be typed before commands

How would I go about setting up my system so that sudo doesn't have to be typed before commands. For example instead of typing sudo apt-get install I would only have to type apt-get install. Now I know I can run sudo -i but I end up forgetting to do it half of the time. Is there a more permanent way of doing it?  EDIT: For clarification I am not wanting to know how to do it without a password I already have that setup. I want to do it without typing the word sudo I want to remove the need to even type the word sudo.


I'm running Windows 10 version 1607 (OS Build 14393.693)  Recently after restarting my computer, all icons have either gone missing or not getting displayed properly. Have a look at the following screenshots:      I have tried rebuilding the Icon cache. I have also started the PC in safe mode and rebuild icon cache. But it's all same for me.   Any help would be highly appreciated. Thanks


I've completed the Nether and reached the end (the sign) while digging. There is, apparently, no more things to do except buying the plane, which is very expensive.  The next step is, then, amass a lot of "money" to buy the plane? Or I'm supposed to do anything else? I have the lava bucket, which maybe can be used to make the X potion.


How to replace the content of specific column with awk? Tab Delimited File

Here's a similar question but I ran into a problem that was not addressed in the question.   I want to do something similar, however my file is tab delimited instead of space delimited.  I want to change field 3. Lets say my file looks like this:  NAME\tNUMBER\tID\tSEQ\t...\t...\t...    Lets say I want to change field 3 to AD  awk '{$3 = "AD"; print}' infile > outfile   my output is  NAME\tNUMBER\tAD SEQ ... ... ... ... ... ...   my tabs turn into spaces after the replaced  I'm sure I can just tr the output file but I want to know what causes awk to change the field delimiter.  expected output:  NAME\tNUMBER\tAD\tSEQ\t...\t...\t...\t


Chromium "New Tab" page stays blank. No search bar, no icons, nothing. When it happened for the first time, it showed a error message on the screen. But now it stays completely blank. Browsing works completely fine. No problem with the internet connection. My Chromium version : 88.0.4324.96 (Official Build) snap (64-bit) Ubuntu version : Ubuntu 20.04.1 LTS x86_64 When I opened up the console on the new tab page it showed two errors. GET chrome://new-tab-page/modules/dummy/foo_proxy.js net::ERR_FAILED GET chrome://new-tab-page/modules/dummy/module.js net::ERR_FAILED


How to make two people play at the same time?

My brother owns Skyrim on steam. We use Steam Family Share, but we were wondering how both of us could play it at the same time?


Python list slice syntax used for no obvious reason

I occasionally see the list slice syntax used in Python code like this:  newList = oldList[:]   Surely this is just the same as:  newList = oldList   Or am I missing something?


Identify story wherein special glass slows time

Sorry I don't recall much about this at all. A friend, who had recommended many other books/authors I ended up liking, told me about a story in which a scientist develops some kind of special glass, that had some property like slowing down light by a factor of a trillion, or something else odd like that, adventure ensuing. He's since moved away, and now I'm wondering what this book might have been.


Why does Vi add the letters ABCD when I press arrow keys in insert mode?

I am using Ubuntu 16.04 LTS. I have a file I open in the terminal with vi abc.txt, and to edit/insert some text into it I press the insert button.  When I press the arrow keys ↑/→/↓/←  it inserts the letters A/C/B/D respectively instead of moving the cursor. Even if I type backspace ⌫ to delete the inserted letter it doesn't get deleted.   Why is this happening? Why are these letter added instead and why are they not getting deleted when I press backspace?


I just got started on Stack Exchange. What happens to your reputation after deleting a question on a Stack Exchange website?  Do you lose the reputation associated with the deleted question? If yes: If you go below a privilege threshold, do you lose that privilege too?


How do I find out the user name and password for an existing account?

MY site was created and maintained from a developer I cannot contact, and I need to know the username/password the developer used to access the site.  How can I achieve this?


Is there a way to create a Yahoo! account without having a cell phone that can receive SMS messages?

I'd like to create a Yahoo! account. The signup page won't let me proceed without entering a cell phone number, and it won't recognize my Google Voice number as a valid cell phone number. Is there a workaround to be able to create a Yahoo! account without having a cell phone that can receive SMS messages?


Can't reset my JAVA_HOME to new Open JDK 11 Java installation

OS: UBUNTU 18.04  I had installed Oracle Java 8 earlier. But decided to switch to open JDK 11. it's successfully installed. java -version openjdk version "11.0.2" 2019-01-15 OpenJDK Runtime Environment (build 11.0.2+9-Ubuntu-3ubuntu118.04.3) OpenJDK 64-Bit Server VM (build 11.0.2+9-Ubuntu-3ubuntu118.04.3, mixed mode, sharing)  Then I set the JAVA_HOME sudo nano /etc/environment  File changes: PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/$ JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64/"  Then executed: source /etc/environment  echo $JAVA_HOME /usr/lib/jvm/java-11-openjdk-amd64/  But the moment I exit the terminal and then launch the terminal again: I get this output:  ▶ echo $JAVA_HOME /usr/lib/jvm/java-8-oracle  which you can see is not what is expected. Please help me out


is it true if $f,\overline f$ are both analytic in a domain $\Omega$ then $f$ is constant? I am not able to  find out what property of holomorphic map I need to apply. please help.Thank you.  $f(z)=u(x,y)+iv(x,y)$, $\bar{f}(z)=u(x,y)-iv(x,y)$


How do I install LINE messenger in Ubuntu?

After few hours of trying, I registered here to ask you.. I want to install Line messenger on my Ubuntu 12.4. Among other things, I tried to do this:    But it just doesn't work. Is there any way that Line works in Ubuntu, or I really have to switch to Windows because of this :/


Canon D30 4.3V powered with PSP charger 5.3V

I do not want to charge the battery but make a long video. I want to use the Canon D30 camera without battery, but with a PSP charger which has the same plug but 5.3V. The Canon D30 needs 4.3V.    Found a solution: a $5 DC to DC Converter like this    I cut off a normal USB and a PSP loading cable. Tested and works fine. Voltage is around 3.8.


Does the set  {$ 1,\frac{1}{2},\frac{1}{4},\frac{3}{4},\frac{1}{8},\frac{3}{8},\frac{5}{8},\frac{7}{8},\frac{1}{16},\frac{3}{16},....$} dense in [0,1].  I am not sure about that.   I think it is not dense in [0,1] because the set contains rationals of the form $\frac{m}{2^n}$, where $m,n\in N$.   Am i correct? If not please give me a proof and also help me to gain intuition. I want intuition and hint rather than proof. Please leave the proof for me. My question in different from the previously asked question because I'm in need of intuition and the answers there doesn't give me enough satisfaction.


Ubuntu 18.04, Gnome. I'd like to hide my drive that's dedicated to windows, in my Nautilus file explorer, under other locations.   I already used "disks" app to edit mount options of that disk and unchecked "show in user interface" and "mount at system startup". Rebooted. Same issue.


Check if an automatically created div has been clicked

I have a JSON file with a list of elements. For each element in this list a container gets created. This is the code:  $.getJSON('/data/risks.json', function(data) { var html = '';  $.each(data.risk, function(key, value){     html += '
';     html += '

'+value.name+'

'+value.description+'
';     html += '
'; }); $('#list').html(html); });   Now I need to know which container was clicked by the user. This:  $('.elementlist').click(function(){ var chosenRisk = $(this).text();      console.log(chosenRisk); });   works for the container that is already on the page but is for the ones that are created based on the JSON file.  What would be the best way to do this?  Greetings


I've looked to another example but struggle to adapt it to my needs. Tikz is new to me.    \begin{center}   \begin{tikzpicture}[every edge/.style={shorten <=1pt, shorten >=1pt}]   \draw (0,0)  node [below] {0} -- (1,0) node [below] {1};   % draw the tick marks   \coordinate (p) at (0,2pt);   \foreach \myprop/\mytext [count=\n] in {0.06/$p_1$,0.06/$p_2$,0.06/$p_3$,0.06/$p_4$,0.06/$p_5$,0.15/$p_6$,0.13/$p_7$,0.14/$p_8$,0.15/$p_9$,0.13/$p_10$}   \draw [decorate,decoration={brace,amplitude=2}] (p)  edge [draw] +(0,-4pt) -- ++(\myprop,0) coordinate (p) node [midway, above=2pt, anchor=south] {\mytext} ;   \path (1,2pt) edge [draw]  ++(0,-4pt); \end{tikzpicture} \end{center}     Latex squeeze all the values together instead of spreading them over the 0 to 1 axis.


Recovering an account without knowing the email address

Over a year ago, I first started out on Stack Overflow thinking I was just going to use it once, and then leave, so I created an account using one of those temporary email addresses. Yesterday, my hard drive started dying, forcing a reformat, etc, and long story short, I don't remember the email address I used for signing up, even though I know the password. Is there any way for me to find the email address?  I'm not overly miffed about the whole situation, but I was in the middle of a question, and now, even with a new account, I can't make a comment to say that I won't be able to continue with my question for the time being, because I need a minimum of 50 reputation.  If it is possible to find the email address, would it also be possible to change the email address to the account I'm currently using?


Broadcom BCM43142 WiFi drivers with AP mode to create hotspot for android devices

I want to create WiFi hotspot for android device using Broadcom BCM43142 chipset. OS : 14.0.4but I am stuck at a STEP which says your Wireless card should support AP mode!The current  driver: wl0 which I am using does not support AP(access point) mode.     iw list    Result :  Supported interface modes:        * IBSS        * managed   I found many drivers for other broadcom chipset like BCM4312 that support AP mode ex : b43 driver but failed to find for BCM43142.  Is their any driver available for Broadcom BCM43142 that support AP mode? OR  Is their any other way I can create hotspot for my android device using Broadcom BCM43142 card (os : Ubuntu 14.0.4)?  Thanks.


I'm using Ubuntu 14.04. For some time I haven't been able to run more programs simultaneously. This is what df -h gives:  Filesystem      Size  Used Avail Use% Mounted on /dev/sda1        29G   25G  3.4G  88% / none            4.0K     0  4.0K   0% /sys/fs/cgroup udev             16G  4.0K   16G   1% /dev tmpfs           3.2G  724K  3.2G   1% /run none            5.0M     0  5.0M   0% /run/lock none             16G   59M   16G   1% /run/shm none            100M   40K  100M   1% /run/user /dev/sda2       438G  138M  416G   1% /scratch AFS             8.6G     0  8.6G   0% /afs   and of df -i:  Filesystem       Inodes   IUsed    IFree IUse% Mounted on /dev/sda1       1875968 1875968        0  100% / none            4106915      11  4106904    1% /sys/fs/cgroup udev            4103190     499  4102691    1% /dev tmpfs           4106915     524  4106391    1% /run none            4106915       3  4106912    1% /run/lock none            4106915     122  4106793    1% /run/shm none            4106915      27  4106888    1% /run/user /dev/sda2      29138944     709 29138235    1% /scratch AFS             9000000       0  9000000    0% /afs   I have also tried the suggestion here:  , does not help, actually it makes it worse. Now, if I enter the terminal and partially write the name of a folder ,I press Tab  and get:  cd Pybash: cannot create temp file for here-document: No space left on device   where I just wanted to write   cd Python   Edit: The output of sudo du -hxd1 / is :  1.5G    /var 22G /usr 18M /etc 16K /lost+found 36K /home 349M    /opt 68K /tmp 9.7M    /bin 4.2M    /libx32 12K /.config 2.5M    /root 4.0K    /mnt 4.0K    /lib64 13M /sbin 81M /boot 505M    /lib 3.5M    /lib32 12K /media 4.0K    /srv 25G /


Interpreting output of importance of a random forest object in R

After running a Random Forest Classifier on the Iris data set, I get an output that looks like this:                setosa  versicolor virginica MeanDecreaseAccuracy MeanDecreaseGini SLength     1.277324  1.632586   1.758101   1.2233029           9.173648 SWidth      1.007943  0.252736   1.014141   0.6293145           2.472105 PLength     3.685513  4.434083   4.133621   2.5139980          41.284869 PWidth      3.896375  4.421567   4.385642   2.5371353          46.323415   While I understand the last 2 columns, I don't understand what the numbers in the first 3 columns (the classes) are.  Can someone help me understand what the number 1.277324 (SLength, setosa) means please?


Getting the ID of the element that fired an event

Is there any way to get the ID of the element that fires an event?  I'm thinking something like:    $(document).ready(function() {   $("a").click(function() {     var test = caller.id;     alert(test.val());   }); }); <script type="text/javascript" src="starterkit/jquery.js"></script>  <form class="item" id="aaa">   <input class="title"></input> </form> <form class="item" id="bbb">   <input class="title"></input> </form>     Except of course that the var test should contain the id "aaa", if the event is fired from the first form, and "bbb", if the event is fired from the second form.


I need to create a banner that is 18 feet wide by 2.5 feet high.  What would be the best way to go about planning this as it is going to be made in Illustrator and every element will be a vector.  Would my best bet be to create the document in its native size and then scale it down in Illustrator to keep the ratio but reduce the file size?  I've come across this before working at large sizes but not quite this large.


If a photon doesn't experience time, how can it have a frequency?

It is said that photons, moving at c, do not experience time. But then, if a photon doesn't experience time, how can it have a frequency?


Eigenvalues of a nxn matrix without calculations

I have a question about the following matrix:  $$         \begin{bmatrix}         1 & 2 & 3 \\         1 & 2 & 3 \\         1 & 2 & 3 \\         \end{bmatrix} $$  Find the eigenvalues without calculations and define your answer. Now, I was thinking about this problem. And I thought, yeah ok if you try the vector (1,1,1), you can find 6 as one eigenvalue (and I know you have a double multiplicity 0 too). But than you are doing sort of guessing/calculation work.  I see that the columns are linearly dependant. So I know the dimension of the column space and of the null space.  Thank you in advance.  EDIT: follow up question:  Ok, so you find that the dimension of the null space is 2, so there are 2 eigenvectors when the eigenvalue is 0. Now my question is, can the dimension of the eigenspace be bigger than the amount of eigenvalues? I guess not. I know it can be smaller


How to delete a file with the name of an apostrophe (')?

I unintentionally saved a file with vim with an apostrophe and now when I attempt to use my cli to remove it doesn't allow me to do it because Linux can't recognize it.  eg  $ rm ' >


Order of a map $\Bbb F_{p^n}\to \Bbb F_{p^n}$which maps $x$ to $x^{p} -x$

Let $\Bbb F_{p^{n}}$ be the field of order $p^{n}$. Define a map $\phi: \Bbb F_{p^{n}}\to\Bbb F_{p^{n}}$ by $x \mapsto x^{p} -x$. My question is what is the order of im$(\phi)$?  I already know Frobenius automorphism $\sigma: \Bbb F_{p^{n}}\to\Bbb F_{p^{n}}$ via $x \mapsto x^{p}$ has order $n$. But it seems that any work with $\sigma$ does not involve $\phi$.  Any help would be much appreciated.


number of groups with fixed number of conjugacy classes

why is there only finite number of (finite or infinite)groups with a fixed number of conjugacy classes? I know this is classical ,so plz give me a reference if you have. thank you


Why  does an accelerated charged particle emit electromagnetic waves?  I have already seen a proof but I am looking for a more intuitive qualitative answer, such as conservation of energy etc.  Thank you!


Why did Arthur Weasley prefer Portkey rather than Apparition?

The Weasleys along with Harry and Hermione could have Side-Along Apparated to the Quidditch World Cup, There are four licenced and professional practitioners (Arthur, Bill, Charlie, Percy) in Weasley's.   Why did they use a less comfortable way of Portkeys to the  Quidditch World Cup?     “Some Apparate, of course, but we have to set up safe points for them to appear, well away from Muggles. I believe there's a handy wood they're using as the Apparition point.”      - Harry Potter and The Goblet of Fire, Chapter 6-The Portkey   We can see that underage wizards can Side-Along Apparate without any mess with Ministry of Magic from Harry's Apparition with Dumbledore      “You have not, of course, passed your Apparition Test,” he said.      “No,” said Harry.      “I thought you had to be seventeen?”      “You do,” said Dumbledore.      “So you will need to hold on to my arm very tightly. My left, if you don’t mind — as you have noticed, my wand arm is a little fragile at the moment.”   Harry gripped Dumbledore’s proffered forearm.      “Very good,” said Dumbledore. “Well, here we go.”      - Harry Potter and the Half-Blood Prince, Chapter 4-Horace Slughorn


How to increase open files limit mysql in linux

i want to increase "open files limit mysql" to 2084. what are the commands to run through ssh?


I'm trying to solve this integral but I don't know where to start.  $\int_{0}^{\infty}\frac{x\sin(x)}{x^2+16}dx$


To determine multiplicity of $2$ in $n!$

Is there a general formula for determining multiplicity of $2$ in $n!\;?$  I was working on a Sequence containing subsequences of 0,1. 0 is meant for even quotient, 1 for odd quotient.  Start with k=3, k should be odd at start, if odd find (k-1) /2, otherwise k/2. This subsequence goes on until we reach 1.  Assign 0,1 accordingly as quotient is even, odd respectively. k(n+1) =k(n) +2, k(n) is odd, n>=1.Do this for all k>=3.1 is added before each subsequence as subsequence is generated by odd integer>=3.This sequence goes on like this: 11, 101, 111, 1001, 1101, 1011, 1111, 10001, 11001, 10101, 11101, 10011, 11011, 10111, 11111,..  The subsequences with increasing k are replica of the subsequence with steps to reach 1 minus one step or no of bits minus one with one extra bit of 1,0 depending on k.  Example-for k=5 the subsequence is 101 as quotient in first step is 2, and in second step is 1.  I want to find what is sequence at nth step?  Also can this sequence help in determining what is multiplicity of 2 in n! ?


I'm prepping a hexcrawl-style game, my first sandbox game ever, and I'm expending all the online resources I can to learn how to run them and prep them. I'm actually having a lot of fun (and work) doing it; I've completed the map, placed key locations, also created landmarks for dungeons and adventure hubs. I have 3 settlements (being a post apocalyptic fantasy I don't plan to add more), 1 secret village, 13 dungeons, 12 monster lairs, 10 ruins. The world is highly hostile and most encounters will be combat based.  So, as I've been investigating, people often uses "don't prep too much" as tip, however this beign my first time on a sandbox campaign I don't know how much prepping is "too much".  My fear is that my players run into something I haven't prepared yet, since I'm terrible improvising adventures. I can easily improvise wilderness encounters, however I don't know what I'd do if my players run into a dungeon I haven't mapped yet so I'm mapping pretty much "everything" beforehand, which makes me wonder if I'm doing it "right".  My players aren't the "cooperative" type when it comes to world creation (tho I love my group), so, any tips to know when to stop and what to do to avoid "prepping too much" on games like this?


Problem:  Ajax suggest-search on [n] ingredients in recipes. That is: match recipes against multiple ingredients.  For instance: SELECT Recipes using "flower", "salt" would produce: "Pizza", "Bread", "Saltwater" and so forth.  Tables:  Ingredients [     IngredientsID INT [PK],     IngredientsName VARCHAR ]  Recipes [     RecipesID INT [PK],     RecipesName VARCHAR ]  IngredientsRecipes [     IngredientsRecipesID INT [PK],     IngredientsID INT,     RecipesID INT ]   Query:  SELECT     Recipes.RecipesID,     Recipes.RecipesName,     Ingredients.IngredientsID,     Ingredients.IngredientsName FROM     IngredientsRecipes      INNER JOIN Ingredients     ON IngredientsRecipes.IngredientsID = Ingredients.IngredientsID      INNER JOIN Recipes     ON IngredientsRecipes.RecipesID = Recipes.RecipesID WHERE     Ingredients.IngredientsName IN ('salt', 'water', 'flower')   I am currently constructing my query using ASP.NET C# because of the dynamic nature of the WHERE clause.  I bites that I have to construct the query in my code-layer instead of using a stored procedure/pure SQL, which in theory should be much faster.  Have you guys got any thoughts on how I would move all of the logic from my code-layer to pure SQL, or at least how I can optimize the performance of what I'm doing?  I am thinking along the lines of temporary tables:  Step one: SELECT IngredientsID FROM Ingredients and INSERT INTO temp-table  Step two: SELECT RecipesName FROM Recipes joined with IngredientsRecipes joined with temp-table.IngredientsID


I'm new to Stochastic Processes, in general. However, I see that they come in varying forms of complexity. A gaussian process (and gaussian process regression) are quite complicated and can easily fit non-linear trends in data. When I read about Poisson processes, the author starts and stops by deriving the Poisson distribution from the binomial. (But nothing more.) Examples typically include estimating the number of events in a time interval, so it seems to boil down to parameter estimation. I thought anytime "process" came up, there could be an infinite-dimensional problem where you estimate parameter functions, not just scalar parameters. Could anyone elaborate? (My job almost exclusively uses Bayesian methods, so if you have a resource that discusses PP in terms of Bayesian computation, that's not a deal breaker for me.)


I have a data stream that may contain \r, \n, \r\n, \n\r or any combination of them.  Is there a simple way to normalize the data to make all of them simply become \r\n pairs to make display more consistent?  So something that would yield this kind of translation table:  \r     --> \r\n \n     --> \r\n \n\n   --> \r\n\r\n \n\r   --> \r\n \r\n   --> \r\n \r\n\n --> \r\n\r\n


I have a script, which starts the execution of multiple C++-programs. I have to execute those with sudo, as they use some "restricted" linux libs/files(probably not the right nomenclature, but you get what i mean). Now i would like to write a shell-script which calls those binaries one after the other, but i do not know how to do this:  #!/bin/bash ./main a > out/output2DFloat.csv  ./main a a > out/output3DFloat.csv  ./main a a a > out/output2DDouble.csv  ./main a a a a > out/output3DDouble.csv   and call this with sudo? Or append Sudo before each and call it with sudo...  My fear is, that the sudo timer runs out, before even one is finished, which would lead to big problems, if the next ones then need sudo-rights ...


Planck mass is about the mass of one eyebrow hair

Unlike most  named after "Planck" such as Planck length, Planck temperature, etc, the  seems more closed to daily life. It is about $10^{-5}$g, same order of magnitude of one eyebrow hair or a flea egg.  I am just wondering is there any interesting explanation about the relation between Planck mass and the mass of small lives such as flea.


evaluate $\lim_{n \rightarrow \infty} \sqrt[n]{2^n+3^n}$

I am interested in evaluating the following limit: $$\lim_{n \rightarrow \infty} \sqrt[n]{2^n+3^n}$$ I realize it should be 3 because as $n$ approaches infinity, $3^n$ gets significantly larger than $2^n$. But numerically: $$\lim_{n \rightarrow \infty} \sqrt[n]{2^n+3^n}= \lim_{n \rightarrow \infty} \sqrt[n]{\frac{2^n+3^n}{1}}= \lim_{n \rightarrow \infty} \sqrt[n]{\frac{(\frac{2}{3})^n+1}{\frac{1}{3^n}}}$$ which is $\sqrt[\infty]{\frac{2}{0}}$ ..? Where is my mistake?


How to combine these funcions (FILTER + IMPORTRANGE) in one?

I have all data in one sheet and I need to filter the imported data to another sheet. How can I do that in one function?  Function to filter data which I use:  =FILTER(A7:C,RIGHT(A7:A,7)="?id=999")   so how to combine this filter function with importrange function?  =IMPORTRANGE("URL", "Template!A16:C")


Answerers Should not be able to vote/comment on other Answers to the same question

Why are answerers allowed to comment/vote on one another's posts? We can infer that answerer's already disagree with one another which is why they wrote their own answer. Or they wanted to contribute to the other answerer.  It seems answerers think their own answer is better and will downvote other answers just because they want their own answer to be the best.  If an answerer wants to respond to another's answer they could do it in their own answer (ie "Other answerers have said X but I believe Y").  This is not a duplicate. Other questions ask about etiquette. I am asking why it still exists.


Proof verification: Set of partial limits of a sequence is closed

I wanted to prove this claim but I'm not sure if this proof is okay. Please let me know what you think! 🌻  Let $\{a_n\}_{n=1}^{\infty}$ be a sequence, and let the set of its partial limits be $PL(a_n)=A=\{a|\exists a_{n_j}\rightarrow a\}$.  Let $a_0$ be an accumulation point of A, so, exists a sequence $\{x_n\}\subset A=PL(a_n)$ such that $x_n\rightarrow a_0$. But $\{x_n\}$ is a sequence of $a_n$'s accumulation points, (Edit) so for any $\epsilon>0$ There are infinitely many terms of $a_n$ in $(x_j-\epsilon,x_j+\epsilon)$, for any $j\in \Bbb N$.   Also, for any $\epsilon>0$,  exists $J\in \Bbb N$ such that for every $j\ge J$, $x_j$ is in the $\epsilon$ neighborhood of $a_0$, so and there is an infinite number of $a_n$'s terms in $(a_0-\epsilon, a_0+\epsilon)$.   It follows that (Edit) for any $\epsilon$ exists $\epsilon '$ such that $(x_j-\epsilon', x_j+\epsilon')\subseteq(a_0-\epsilon,a_0+\epsilon)$ so there are infinitely many of $a_n$'s terms in the $\epsilon$ neighborhood of $a_0$. This goes to show that $a_0$ is a limit point of $x_n$, so $a_0\in PL(a_n)$ so it is closed.


Why is it uncommon for import statements to be placed inside functions?

I am maintaining a few Python packages, and on systems where dependencies are not fully satisfied, functions which may otherwise work, fail due to global scope imports:  import numpy as np  def lala(in):     out = max(in)     return out  def fufu(in):     out = np.mean(in)     return out   So for instance here I cannot use lala() if I do not have numpy, ven if lala does not use numpy. Of course, ideally dependencies would be managed correctly, still, it would make for a more robust package if functions failed only when they had to fail.  Is there any reason why imports are almost never done in function scope? Is this reason just reducing the number of lines?


Encode each $n_1,n_2,n_3,...∈N^N$ by an inﬁnite sequence of 0s and 1s with inﬁnitely many 0s, and give a proof that $N^N$ is equinumerous with $R$.

Encode each $n_1,n_2,n_3,...∈N^N$ by an inﬁnite sequence of 0s and 1s with inﬁnitely many 0s, and hence give a proof that $N^N$ is equinumerous with $R$.  Background: Here the set $N^N=N \times N \times N \times N \times...$ is the set of finite sequences of positive integers. Each inﬁnite sequence $n_1,n_2,n_3,...$ of positive integers gives an irrational number (with a infinite continued fraction) between 0 and 1, because each rational has a ﬁnite continued fraction. Conversely, each irrational number between 0 and 1 has a continued fraction of the above form, and hence gives an inﬁnite sequence of positive integers. Thus, we immediately have a bijection between $N^N$ and the irrational numbers in (0,1). The latter set is equinumerous with (0,1), and hence with $R$.  So far I tried to encode each n in N^N as either ones and zeros, where comas are represented as zeros. For example <3,2,3,0,1> ---> 1110110111001   TIA


I was running out of space for Windows 10, so I deleted my Ubuntu partition and then combined the free space and added it to the Windows 10 partition into a single partition (the boot partition was untouched). Now all I get when I turn on my computer is:  Error no such partition. >grub rescue   I have tried rebooting, but it did not work. Is there any way to fix it? My idea is that if i reinstalled Ubuntu it may fix it, but I'm not sure. I don't have a Windows repair disk, and I can't make one, but I do have a 4GB USB flash drive.


Finding sum to infinity: $\sum\limits_{n = 1}^{ \infty}\frac{n^2}{n!}$

I am trying to find what this value will converge to $$\sum_{n = 1}^{ \infty}\frac{n^2}{n!}$$  I tried using the Taylor series for $e^x$ but couldn’t figure out how to manipulate it to get the above expression, can someone help me out.  Edit: I have seen the solution, the manipulation required didn’t come to me, is there any resource that you guys can tell me about where I can find/practice more questions like this?


Installing extra packages of Debian Wheezy from terminal (after a net install)

I've installed the small image of Debian Wheezy from  but had to skip the mirror install of the extra packages.  Now that I have the command line how do I get the rest of the stuff?  When I tried apt-get install ssh-server, it told me to insert the CD.


How can I create automatically expiring user accounts?

This is what I'd like to be able to do:  After a user's account is created, they should be able to ssh-tunnel, but their account is automatically removed after 30 days unless the countdown is reset by the root user.  How can I automate this? I'll have to handle around 15 users.


How do we prove the set of bounded and continuous functions between metric spaces is a complete subspace from the set of bounded functions?

Let $(X,d_{X})$ be a metric space, and let $(Y,d_{Y})$ be a complete metric space. The subspace $(C(X\to Y),d_{\infty})$ is a complete subspace of $(B(X\to Y),d_{\infty})$. In other words, every Cauchy sequence of functions in $C(X\to Y)$ converges to a function in $C(X\to Y)$.  MY ATTEMPT  Here, $B(X\to Y)$ represents the set of bounded functions from $X$ to $Y$, $C(X\to Y)$ is the set of bounded and continuous functions from $X$ to $Y$ and $d_{\infty}$ is the sup norm distance.  I was thinking about proving that $B(X\to Y)$ is complete, whence we conclude that $C(X\to Y)$ is complete, since it is already closed.  However I am not able to do so. Could someone provide a proof based on such line of reasoning? Any other approach is welcome as well.


Command/macro name cannot include numbers and symbols

I would like put picture into table, and my idea is define new command as below>   \newcommand{\EJ471}{\includegraphics[scale=0.150]{EJ_471.jpg}}   But compiler reports an error. If I use the command name for example \EJa, everything is all right. I've read similar questions as      But still I don't understand why it does not work.


Does wave-particle duality exist for gravitational waves?

For electromagnetic waves there exists a wave/particle duality: light sometimes behaves as a wave, and other times as a particle (photons).  Does such a duality exist for gravitational waves? In other words would we expect gravitational waves to sometimes behave has particles (gravitons)?


How do I interpret the Mann-Whitney U when using R's formula interface

Say we have the following data:  set.seed(123) data <- data.frame(x = c(rnorm(50, 1, 1), rnorm(50, 5, 2)),                    y = c(rep('A', 50),    rep('B', 50)))   Which yields the following boxplot (boxplot(data$x ~ data$y)):    Now let's say I want to test if the two samples have the same location parameters (median and/or mean). In my real case, the data are clearly not normal, so I've decided to run the Wilcoxon-Mann-Whitney test, like this:  wilcox.test(data$x ~ data$y)   However, I would like the alternative hypothesis to be that B, data$y's "second" factor, comes from a distribution with higher position parameters. I've tried setting the alternative parameter to "greater" and "less", but apparently the alternative hypotheses are not what I'm looking for. For example, alternative = "greater" tells me "alternative hypothesis: true location shift is greater than 0"; alternative = "less" tells me "alternative hypothesis: true location shift is less than 0".  How can I tweak the wilcox.test() function in order to have the alternative hypothesis I want (B comes from a distribution with higher position parameters than A)? Or should I just use another test instead?


I was wondering about finding expected value of dice throw. I know that in case of single dice throw,the expected value is 3.5 = ((1+2+3+4+5+6)/6). So for purpose of betting the base price could be 3.5 to ensure no profit and no loss scenario. But how can I extend this logic for double dice throw or N dice throw. I though that for case of double dice out of the 36 cases, I could take the maximum value for each pair which would give 6 eleven times, 5 nine times, 4 seven times, 3 five times , 2 three times and 1 once. But this gave expected value to be 4.47, whereas the correct answer in book is 4.25. How can I determine the fair value in this case?


How do I round to exactly 2 decimal places in Python?

Not to print, I want the actual value with less precision. For example if I say:   numb = 1.23456789123456789 print "num %0.2f" % numb   then it'll display it as having only 2 decimal places   num 1.23   but in reality the value for numb will remain the same. How do I convert numb so that it will actually have the value of 1.23?   The purpose is that I'm trying to send this value into an api and the value is too precise for the api which is causing an error, the only things I can find online are about displaying a less precise value but not actually changing the value.   Edit: I wanted to clarify that I want it rounded down. I know math.floor would do that but it only rounds to integers. Is there a function that rounds down but with decimals as well?  Note: I'm new to Python so code samples are preferred, thanks!


Looks like the design has changed on the Users page

Suddenly, the design of the /users page changed like this:    Other pages, such as /questions or /tags, haven't changed at all, which makes me think this might have been a premature or accidental change.  Was this change purposeful or not? Is it part of a network-wide design changing process?  Please note that this is most probably unrelated to , as the screenshot is from . Also,  looks like a dupe at first, but this question focuses on reasoning, not a specific issue.


Digital save file compatibility for Bloodborne

So I got the vanilla version of Bloodborne when it was on PS+ and got the DLC as well but because of economical reasons I have not been able to continue with PS+. I was in the Old Hunters and my roommate still in the game but looking forward to playing the DLC as well. Since we both work we did not think getting PS+ for a short time (ie. a month or three) would be good because we know we would end up having to renew it several times. But...the complete bundle is available on the PS network for roughly the same price as three months PS+ and it would only be a one time payment. However we need to know if we could access our save files. I have seen this addressed for disk to disk and digital to disk but not when both versions are digital.   Anyone know if it would be no issue to keep playing on our files or would we have to start over?


How calculate the probability density function of $Z = X_1/X_2$

Let $X_1$ and $X_2$ be two continuous r.v., my question is: what is the p.d.f of $Z=X_1/X_2$?


A proof of the Axiom of Choice --- where am I wrong?

I am trying to understand the Axiom of Choice. However, I found a proof of the Axiom. Let $A_i, i\in I$ be a set of mutually disjoint nonempty sets. We will construct a set that contains exactly one element in common with each of the sets as follows. Consider arbitrary $i\in I$ and fix it. Since the set $A_i$ is nonempty, $\exists x$ such that $x\in A_i$. Now we use the existential instantiation and write $x(i)$ for a new symbol (just a symbol) such that $x(i)\in A_i$. Consider one-element sets $\{x(i)\}$ and let $A=\bigcup_{i\in I}\{x(i)\}$. Then $A$ is a set and $A$ contains exactly one element in common with each $A_j$. Where am I wrong? Please help me.


"gstreamer1.0-libav" Package dependencies cannot be resolved

I am in Ubuntu 14.04 amd64, I have met all updates available, but also I am getting these errors in media codecs. First I got this error:      gstreamer1.0-libav:i386: Depends: libavcodec-extra-54 (>= 6:9.13) but 6:9.16-0ubuntu0.14.04.1+fdkaac is to be installed                  Depends: libavformat54 (>= 6:9.1-1) but 6:9.16-0ubuntu0.14.04.1+fdkaac is to be installed                  Depends: libavutil52 (>= 6:9.1-1) but 6:9.16-0ubuntu0.14.04.1+fdkaac is to be installed                  Depends: libc6 (>= 2.7) but 2.19-0ubuntu6.3 is to be installed                  Depends: libglib2.0-0 (>= 2.37.3) but 2.40.0-2 is to be installed   After getting this error I tried to install those libraries, i then did      sudo apt-get install libavcodec-extra-54   That went good, and i could download that package. But any other packages were not installed, terminal said they were already installed.  But again I am getting this error.      The following packages have unmet dependencies:    libavcodec54:


Do we have $\lim_{h\to 0^+}\int_0^\infty|f(t+h)-f(t)|dt=0$?

Let $f:\mathbb{R^+}\to\mathbb{R}$ be an integrable function ($f\in L^1(\mathbb{R}^+,\mathbb{R})$). Do we have $$\lim_{h\to 0^+}\int_0^\infty|f(t+h)-f(t)|dt=0$$ ? How can we prove it ?


In a previous question, it was brought to me that LEDs do not obey the Ohm's law. (See )  Simply put: how is that?  What makes them behave so differently? How should we treat them in a circuit and calculations?  Are there other components with similar behavior?


Air travel between Schengen countries and single-entry Schengen visas

I applied for schengen visa via Norway embassy. I got a single entry visa (even though I asked for multiple entry). Now my plan actually is to land in France (Paris), travel through Belgium to Amsterdam by road and then fly from Amsterdam to Bergen in Norway. I am curious to know whether flying from Amsterdam would be considered as exiting the Schengen state even though I am flying to another Schengen state?   I know it is OK to travel from one Schengen member country to another within the visa tenure and without exiting the Schengen states. I did it before last year by entrying into Austria and traveled through Czech Republic, Germany and then reaching Switzerland (all by road) and then flew back to Dubai where I reside.  But I am really unsure of air travel that how is it taken when you fly from one Schengen state to another?


Why is observing 100 heads for a fair coin flips surprising?

Assume that we have a fair coin. We flip it 100 times. The outcome is all heads. Why is it surprising? Doesn't all outcomes have the same probability? Any particular outcome, including irregular ones, would have the same very small probability. Why is it that observing an irregular outcome is less surprising to us than a regular one?


How can I stop PayPal from setting up automatic payment to vendors?

I find that often when I pay a bill with PayPal somehow the vendor is able to create an automatic payment. Then I have to go and cancel it. This is extremely annoying.  How can I prevent PayPal from setting up automatic payments unless I explicitly authorize it?


What is difference in this javacascript function definition syntax?

I'm a beginner in javascript programming and I notice that there are some cases where a function is defined as   myfunc : function() {...},   and other cases where it is defined as:  function myfunc(){...}   Can someone explain what the difference is, and when should one be used over the other.


Let A be a subset of {1, 2, 3 ... 2n-1, 2n} containing n + 1 elements. (Full Question below)

Let A be a subset of {1, 2, 3 ... 2n-1, 2n} containing n + 1 elements Show that:  a) some two elements of a are relatively prime b) some two elements of a have the property that one divides the other  I am assuming that we have to use the pigeon-hole principle here but I have no idea how to use it in this particular situation.


Calculating the capacitor values to control ceiling fan speed

I have an old ceiling fan motor that runs with a 1.5µF run capacitor, at what I believe is, its full intended speed.  With the help of some folks here at StackExchange I've wired everything up as in the image below, also refer to the schematic further down this question. The motor seems to be running well.    The next step is to add a 4 way rotary switch that selects between off and 3 different speed settings. I need to figure out the capacitor values I can use in C3 and C4 in the schematic below to achieve the slightly slower speeds for speed settings 1 and 2, with 3 running at full speed.      I do believe that the capacitors need to be in parallel for the capacitance to add up, and slow the motor down, please do correct me if I'm wrong. As far as I can understand the capacitance shifts the phases apart further in the two coils.  The simplest approach might be to go and buy some 1µF to 1.5µF caps and play around with different configurations. I already know I need a 1.5µF to get and keep the motor running.  Is it safe to say I can just add another +/-1µF/1.5µF in parallel for my 1st speed setting, and another 1µF for the 2nd setting to slow the motor down? Thus, I have the following configurations:  Speed = 1 : 1.5µF  Speed = 2 : 1.5µF + (C2)1µF = 2.5µF  Speed = 3 : 1.5µF + (C3)2µF = 3.5µF  If this bit of information helps, our supply is 220V at 50Hz, and the motor has, what appears to be 14 coils, according to my counting through the holes in the motor casing.


Single Quote Escape in PDO Prepared Statement Parameters

So I understand PDO Prepared Statements should protect from SQL injection and ' escapes. But when I attempted the following...  if ($_SERVER["REQUEST_METHOD"] == "POST" && isset($_POST["id"])) {        $id = $_POST["id"];      //$id = "2' AND name='Entry2";     $someinfo = "updated";      ...DB Stuff...      $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $dbpassword);      $stmt = $conn->prepare("UPDATE testdb SET info=:someinfo WHERE id=:id");      $stmt->bindParam(':id', $id);     $stmt->bindParam(':someinfo', $someinfo);     $stmt->execute();      $conn = null;      exit(); }   Then the row with id=2 and name=entry2 would be updated. Now it doesn't seem like this can be used to escape into other SQL queries, and I assume I can take precautions to ensure this kind of escape can't really do damage. But I wanted to be sure that there wasn't some other way to prevent ' escapes making unexpected changes to SQL query parameters. (Worth noting, I tried something similar in SQLi and got pretty much the same result.)  Is there something I'm missing? Or is this just the way Prepared Statements work.


Is separate DS-160 form needed for spouse for US B1/B2 visa?

I'm going to travel with my spouse to the US for visiting. and I want to apply for B1/B2 visa. I filled an application for myself. Do I need to fill a separate DS-160 form for her? If so, how can I link these two applications?


Are all hyper-algebraic numbers algebraic?

I know an algebraic number is any complex number that is a root of a non-zero polynomial in one variable with rational coefficients (or equivalently – by clearing denominators – with integer coefficients).  So Let  hyper-algebraic number  be any complex number that is a root of a non-zero polynomial in one variable with algebraic coefficients    My question   : are all hyper-algebraic numbers algebraic ?     for example :   let define $x_0$ as the root of   $x^5+x=10$  something like $x_0≈1.53301...$   I wonder :  if $y_0$ is any root of $y^5+x_0^2y=(1+{\sqrt x_0})$  (this polynomial has algebraic coefficients) then  is $y_0$ algebraic ?  I mean is there any polynomial with integer coefficients (may be we cannot find it , but it exists ) that  $y_0$ is its root ?


Create filter on Gmail for BCC to myself

I run a startup and we send quite a lot of emails. I've started to BCC these emails that my software sends to myself as an alias. For example:  layke@example.com might be my main email and I'm now sending them to  layke+blind@example.com as a bcc to field, (in addition to the clients email as the main "to" field).  The problem is that I can't seem to create a filter for these emails in my Inbox. I want to archive them immediately, but it doesn't appear as though there is a way to do this.   If I search for emails, I can't see them. I guess this is because Gmail doesn't store the BCC field (even if it's sent to you).     Headers of email:    I think my only option is to create a fully fledged inbox JUST for these BCC's as I can't find any way to identify and label them.


Can I pre-purchase more luggage allowance on Qatar Airways flights?  I am traveling with Qatar Airways from Stockholm, Sweden (ARN) to Bangkok, Thailand (BKK) and I will be carrying one additional bag beyond the carry-on and standard check-in bag.   Am I able to pre-purchase allowance for this additional bag or is it always counted as excess luggage according to the fee list on their website?  And if so are there different rules for different routes (i.e transatlantic fares or such)?


How to record desktop screen with audio?

I have seen this question:   The answers given here is to install recordmydesktop. I have installed it but it does not work. It gives a error message just after selecting the screen area.  Also I have many screen recorder applications but none works perfectly. Some records the screen but not the audio. eg EasyScreenCast. I would like to know how to record screen with audio.


How do you style an input type="file" button?


Proof that $$\sum_{k=1}^n (-1)^kk^m{n \choose k} = 0$$ for every $n>m$ and $m>1$.  I tried to use properties of ${n \choose k}.\;$ I tried to use $${n \choose k} = {n-1 \choose k} + {n-1 \choose k-1}$$ and using induction got stuck here $$\sum_{k=1}^t (-1)^kk^m{t-1 \choose k-1} = 0$$, where $t = n - 1$.


Correct password cannot be authenticated to run Synaptic Package Manager GUI

I cannot access my synaptic package manager(in GUI) due to authentication error. Even though I enter the correct user password, it always say that "Your authentication attempt was unsuccessful. Please try again."  I also configured the sudoers file and add/edit my user priveleges:  maximus ALL=(ALL:ALL) ALL   below the root priveleges.   Is there any other way to access or any other configurations to access it in GUI?


Default cmake version of 14.04 is 2.8. How can I install cmake 3.2 and replace the default one? Or how can I upgrade 2.8 to 3.2?


Run app from removable drive without sudo

I want to run apps like Google Chrome in my lab PC where I don't have administrator access meaning I can't run sudo command to do any thing. Is it possible to make apps run from removable drive like the portable apps in windows? Is there any way of doing so?


My android comes with 3 different solid wallpapers. I have found more in the market but its paid. How to get a black wallpaper for free?


IID Random Variables that are not constant can't converge almost surely

I am trying to prove the following.  If $\{ X_n \}$ are iid random variables and not constant, then $R:=P\{ \omega \mid  X_n(\omega)\text{ converges} \}=0$  Using independence I know that by Kolmogorov's 0-1 law, that if $R$ is not $0$ then $R=1$.  So I think the way to do this proof is by contradiction.  So I am trying to show $R=1$ implies the $X_n$ are constant using their identical distribution but sadly it is not working.  Help would  be appreciated.  Thanks!


How do I delete the first n lines of an ascii file using shell commands?

I have multiple files that contain ascii text information in the first 5-10 lines, followed by well-tabulated matrix information.  In a shell script, I want to remove these first few lines of text so that I can use the pure matrix information in another program.  How can I use bash shell commands to do this?    If it's any help, I'm using RedHat and an Ubuntu linux systems.


How can I make my website appear in the top position of Google?

I have added some of the keywords in a meta tag, but my site is still not in the top position when Googled. How can I achieve this?


In the movie Arrival the aliens say that they will need help in 3000 years. What for? Is it implied or mentioned in the movie because I didn't catch that part. Is it mentioned in 'Story of Your Life' that is the short story the movie was based on?


C++ - set base class vptr without constructor?

I've written a memory manager in C++. The details aren't important, but when set up it allocates a large byte array from the heap, and when its allocate function is called, it clears some free memory bytes to 0 and returns a pointer to them. So an example of use would be:  memoryManager->initialise(1024); //Allocates 1024 bytes T* t = memoryManager->allocate<T>(); //Prepares sizeof(T) bytes and returns a ptr   This works great, I've thoroughly tested it and it works exactly as intended. However, since it just makes a "fake" pointer, the object's constructor doesn't get called. This falls apart when I try to allocate a class that inherits from another - its vptr never gets set, since that's done at the start of the constructor and hidden from the programmer. So as soon as I call a base class function, the program crashes with a seg fault.  Is there any way around this? Can I set it myself?  Edit: to anyone else looking for a way to do this, do a search for "placement new". Read comments for more info.


Following program:  #include <stdio.h> #include <stdlib.h>  int main() {     int *array;     array = malloc(sizeof(int)*100);      for(int i=0; i<sizeof(array); i++) {     printf("%d\n",i);     }     free(array); }   It display 0-3. But I expected 0-399. I thought the size will be calculated through 4*100.


What is the time of impact of a dropped item at a very high altitude

I'm trying to automate a landing at a specific spot in Kerbal Space Program and to do that I need to know when the estimated time of impact will be. In short, I'm trying to solve the following question:  Given a planet without an atmosphere with a gravitational parameter $\mu$, radius $r$ and an object with mass $m$, an initial velocity of $v=0$ and a distance $d$ between their centers, what will be the time of impact?  An example: Given a spherical earth without an atmosphere and a brick at an altitude of $100.000$km, how long after release will the brick hit the surface?  I've tried using conservation of energy but that left me with a differential equation I'm unable to solve:


xkb: editing keyboard layout/map in Ubuntu 16.04

I edited the file /usr/share/X11/xkb/symbols/fi but I can't take those modifications into use.   The folder /var/lib/xkb is empty apart of the file README.compiled which contains this:     The X server uses this directory to store the compiled version of the   current keymap and/or any scratch keymaps used by clients.  The X server   or some other tool might destroy or replace the files in this directory,   so it is not a safe place to store compiled keymaps for long periods of   time.  The default keymap for any server is usually stored in:        X-default.xkm   where  is the display number of the server in question, which makes   it possible for several servers on the same host to share the same    directory.      Unless the X server is modified, sharing this directory between servers on   different hosts could cause problems.   So I suppose this folder should contain the compiled xkm file, but in the filesystem there is no xkm files anywhere.  How can I take my modifications into use?  Update, a little progress:  I added this to /usr/share/X11/xkb/symbols/fi:  partial alphanumeric_keys    xkb_symbols "oma2" {     include "fi(kotoistus)"     key <AE00> { [  braceleft,       braceright,       NoSymbol,              NoSymbol              ] };    name[Group1]="Finnish (oma2)"; };   And this to evdev.xml:      <variant>       <configItem>         <name>oma2</name>         <description>Finnish (oma2)</description>       </configItem>     </variant>   I can now select the new variant Finnish (oma2), but I can't still see any change in the actual keyboard. I believe/hope I added the new definition correctly...


I got an assignment to prove that in a straight homogeneous rod, you can always choose a coordinate system in such a way that   $\int_S x_1dx_1dx_2=0 $  $\int_S x_2dx_1dx_2=0 $  $\int_S x_1x_2 dx_1dx_2=0$  where S is the cross section of the rod  Now, intuitively, I can understand that the first two expressions basically state that if you find the mass center of the rod, then all you have to do is to put the origin of the coordinate system in the mass center, and the integrals turn out to be zero. What I'm curious about is whether or not this is a good enough of an explanation, and also, a hint on how to obtain the third equality.


After purging AirVPN wifi is still not working - how can I remove all traces of the changes made to my system by this software?

How does a person remove/purge residual files after uninstalling/purging an application?   After uninstalling AirVPN Eddie client via   sudo apt-get remove --purge airvpn   I still have the affected (corrupted?) conf files in the /etc directory. I'm looking for other files that remain that are keeping my wifi from working. See this question:    Right-clicking and deleting these files doesn't work. What is the proper command to take ownership of hidden and system files and delete them?


Is it possible to bypass the permission bit and execute software downloaded from a website?

I want to know if it's possible to run software that has been downloaded from the internet. Ubuntu does not allow that but is it possible to set the executable permissions required for ? I recently downloaded software but it wont work due to this reason. Does anybody know of a way?


Confusion over QM Free Particle Propagator - Shankar 5.1

I am working through Shankar's Principles of Quantum Mechanics and I am confused about his derivation for the propagator of a free particle from the Schrodinger Equation (Section 5.1).  He states that the propagator is given by the following equation (in terms of an integral over $p$):  $$U(t) = \int_{-\infty}^\infty \lvert p\rangle\langle p\rvert \exp(-ip^2t/2m\hbar)dp\tag{5.1.9}$$  and in Exercise 5.1.1 he states that the propagator, in terms of an integral over $E$, is:  $$U(t) = \sum_{\alpha = \pm} \int_0^\infty \biggl[\frac{m}{\sqrt{2mE}}\biggr]\lvert E, \alpha\rangle\langle E, \alpha\rvert e^{-iEt/\hbar}dE \tag{1}$$  However, from 4.3, the propagator appears to be defined as a sum over $E$ (the eigenvalues of the Hamiltonian):  $$U(t) = \sum_{E} \lvert E\rangle\langle E\rvert e^{-iEt/{\hbar}}\tag{4.3.13}$$  which, when $E$ is continuous, can presumably be written in integral form:  $$ U(t) = \int_{-\infty}^{\infty} \lvert E\rangle\langle E\rvert e^{-iEt/\hbar}dE \tag{2}$$  I am having difficulty reconciling these two forms of the propagator (1 and 2 above), as they appear to contradict. Surely, based on the definition given in 4.3, the propagator for a free particle should be given by:  $$U(t) = \sum_{\alpha = \pm} \int_0^\infty \lvert E, \alpha\rangle\langle E, \alpha\rvert e^{-iEt/\hbar}dE$$  and the extra $\bigl[\frac{m}{\sqrt{2mE}}\bigr]$ term should be present in the $p$ version of the equation?  Note 1:   I am aware of an existing question   that is similar. However, I find the accepted answer not very satisfactory. It's quite brief and doesn't seem to explain the whole story. It suggests there should be an additional term in the propagator integrand to account for a 'Density of States'.   So, what is happening here? Has Shankar glossed over this, in his earlier description of the propagator? If so, why would he do that? Does he address this point anywhere else in his book (as it seems fairly important)?  Can anyone explain more clearly why this Density of States is required and where it comes from? I thought the degeneracy of $H$ was being accounted for by summing over the +/- values of $p$. Why would an extra term be required?  Note 2:   Also, to clarify, I am aware that the extra term comes from changing the integral from $dp$ to $dE$:  $$p = \pm (2mE)^{1/2}$$ $$dp = \frac{m}{(2mE)^{1/2}}dE$$  However, I am confused as to why this factor appears in the integral over $E$, rather then the integral over $p$.


I am reading Berkeley Physics Course vol. 4 (Quantum Mechanics) , chapter 4 (photons). (1)  Section 46: book says: consider a typical photon emitted by  the source. It can be regarded as a a wave train of finite duration, spreading out in all directions in space and carrying a total energy $\hbar\omega$. If this is true, a photon emitted by a star which is few light years away, would have spread over a sphere of radius of few light years. Then it is not possible to "detect" that photon using a detector.  Then  why does the book say like this?  In section 47, the book gives same example of photon spreading over light years. But in this section, it says that how the people can use this as a paradox; and clarifies that paradox by saying that classical expression for "energy density" refers to a large number of photons, and not for single photon.  So does photon really spread in all directions?   (2)  In Section 38 book says: almost monochromatic photons can not be split into 2 photons of the same frequency which carry only a fraction of the energy of the original photon. While in section 48, it says (with reference to double-slit diffraction experiment) photon came through BOTH the slits.  Does a photon REALLY goes through both the slits? Doesn't it indicate that a single photon can be split into two photons of same frequency ?   Any help will be appreciated. Thanks


I'm running xelatex installed from TeXLive 2013 running on Cygwin, and it works fine compiling from the commandline with xelatex input.tex or latexmk, but for some reason running the same file through AUCTeX's compile command with C-c C-c with TeX-engine set to xetex crashes xelatex with the output of the log file:   This is XeTeX, Version 3.1415926-2.5-0.9999.3 (TeX Live 2013/W32TeX) (format=xelatex 2014.4.9)  9 APR 2014 22:55 entering extended mode  restricted \write18 enabled.  %&-line parsing enabled. **\input input.tex  ! Emergency stop.  \input input.tex  *** (job aborted, file error in nonstop mode)   Here is how much of TeX's memory you used:  2 strings out of 493918  17 string characters out of 6151720  52462 words of memory out of 5000000  3428 multiletter control sequences out of 15000+600000  3640 words of font info for 14 fonts, out of 8000000 for 9000  1144 hyphenation exceptions out of 8191  4i,0n,3p,1b,8s stack positions out of 5000i,500n,10000p,200000b,80000s No pages of output.    C-c ` just says:   Error occurred after last TeX file closed.  Does anyone know of any additional configuration I need to do to get AUCTeX working under windows? Or is there a way to run the AUCTeX compile command with some flags to get some more info about why xelatex is exiting?   The relevant parts of my emacs configuration are as follows:   (setq TeX-auto-save t) (setq TeX-parse-self t) (setq-default TeX-master nil) (setq TeX-engine 'xetex) (setq TeX-PDF-mode t)   I would appreciate any help as it would be nice to not have to switch back to the commandline to compile everytime I make changes. Also, if there are more relevant lists or boards I should post this to in order to get help, I would love to know.


I am displaying post tags like this:
<?php the_tags('Tags' , ' '); ?>
   It works fine, but if the post does not have any tag, then it adds empty div

   So, how can I use the condition to check if post has any tag, then display above.


When I try to send a HTML encoded email from PHP, if the subject line contains special chars like "Here's the information you requested", PHP encodes it to read "Here&#039;s the information you requested."  How do I fix this?    Here's what the code looks like using PHP mail():  $headers  = 'MIME-Version: 1.0' . "\r\n"; $headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";  $headers .= 'To: ' . $mod_params['name'] . '<' . $mod_params['email'] . '>' . "\r\n";  $headers .= 'From: <do_not_reply@a4isp.com>' . "\r\n";    $email_to = $mod_params['email'];  $email_sub = "Here's the Information You Requested";  $body = html_entity_decode("" . $email_html_body . "");  mail($email_to,$email_sub,$body,$headers);   It gives the same error as running it through the SugarPHPMailer class.


Find a number by the decimal part of its square root

I have a math problem consisting of two questions:   can we find a number N knowing only the decimal part of its square root up to a precision (only an approximation of the decimal part because the decimal part never ends) is the answer unique? which mean that we won't find two integer whose square root decimal values are equal (the first 50 for example).   Example:  if we have $0,4142135623730950488016887242097$, can we find that it's the decimal part of square root of 2 or $0,418286444621616658231167581$ for $1234567890$   The answer for the second question is pretty easy because, let's say we have 50 decimals, the number of possible integer's square root is much more than the 10^50-1 possible values of the decimals parts, so there will be more than one answer. but is there a pattern or example getting one from another  I am very grateful for your help or any research track.


Did everyday Americans really speak like they did on the radio?

When you listen to old radio broadcasts such as the War of the World or this Dick Tracy radio feature, you can hear Americans having the kind of fast talking and inflections you associate with old-time radio:    Did people really talk like that? On the Honeymooners, you can see similar things when Norton speaks. It's not always as fast, but the focus of the topics, the way they interrupt each other, etc. is very different from today. Did everyday people speak like this?  In your answers, if you could link to some youtube videos or soundcloud recordings of how regular Americans used to speak in the past, and comment on the differences between that, radio and current speech patterns, that would be great.


Regex: how to match all character classes and not just one or more

I'm struggling with a regex. I'm giving the possibility to pass human-readable set of rules to be internally translated in a regex inside a validation function I'm writing.  I've mapped some small patterns to some made up names like "letters" for [a-zA-Z]+ and the likes and users can also define a list of must-have of these to say, for example, "check if string has letters AND numbers AND hyphens".  Now, when I get to assemble the regex, a simple [PUT_ALL_CLASSES_HERE]+ pattern with all the classes into it would match anything having class1 OR class 2 OR ... but I need this to match only a string having class1 AND class2 AND ... in it.  The way I've brutally solved this was to execute a separate regex match for every class name, where every pattern was a simple [CLASS_NAME]+.  I'm sure there's some obvious way to do it as I don't know much about regex but please help!


Interpretation of Weinberg-Witten theorem

The  states that  A 3 + 1D QFT quantum field theory with a conserved $4$-vector current $J^\mu$ which is Poincaré covariant does not admit massless particles with helicity  $|h| > 1/2$. A 3 + 1D QFT with a conserved stress–energy tensor $T^{\mu \nu}$ which is Poincaré covariant does not admit massless particles with helicity $|h| > 1$.  This theorem is interpreted to mean that the graviton cannot be a composite particle. However, I do not quite follow this interpretation. My understanding is that the massless graviton of spin $2$ ought to have a Poincare-covariant conserved stress-tensor (and Poincare-covariant conserved $4$-vector currents associated to other symmetries). So the Weinberg-Witten theorem means the graviton is not allowed to exist at all. That the graviton is not allowed to be a composite particle appears to be a weaker conclusion.


What if I assume an ideal gas in a cylinder having frictionless piston and perfectly insulated walls with a perfectly conducting base is kept on a reservoir at temperature $T$ which is greater than the temperature of gas. The gas inside the cylinder would expand due to heat gained and the piston would rise in proportion to keep the temperature constant. All I essentially did was describe an isothermal process which is mathematically, $dU = dQ - dW$ Which in our case would be, $dQ = dW$ Since the temperature stayed constant and thus the internal energy as it is an ideal gas. Does it not mean that all of the heat that I'm supplying to the system is being used to do work which is a direct violation of the statements:  All of the heat can never be converted to work. Or 100% of heat can never be converted to work. (Which is just one of the variations of second law of thermodynamics I suppose, nevermind if not)  Or is there something else I need to know.


How do I include a gnuplot graph in a beamer frame?

I'm using the beamer class to create a presentation. I'd like to include a gnuplot graph, but inside the frame environment, that seems to be impossible. When running pdflatex, I get the error  ! File ended while scanning use of \next.   which I don't understand. Can you tell me how I solve this?  Example:  \documentclass{beamer} \usepackage[T1]{fontenc} \usepackage[utf8]{inputenc} \usepackage{lmodern} \usepackage[miktex]{gnuplottex}    %I'm using miktex \usepackage{epstopdf} \usepackage{graphicx}  \begin{document}  \begin{frame}\frametitle{Gnuplot in Beamer Class} \begin{figure}[htbp] \centering \begin{gnuplot}[terminal=cairolatex] plot [0:2*pi] sin(x) with lines title 'sine' \end{gnuplot} \caption{A plot.} \end{figure} \end{frame}  \end{document}


Circuit breaker wiring: put source current on side marked with X or side with switch?

I am trying to wire an electrical panel in a standard manner.  I have several automation devices that take 120 Vac power.  In order to protect them, I have purchased a 2-pole circuit breaker, .  I am now trying to wire it to an outlet.  I plan to put the breaker on L and N of the 120 Vac source.  The circuit breaker's schematic is shown in the below image.  Pins 1 + 3 connect to an X, pins 2 + 4 connect to what looks like a SPST switch.  Questions   What do the X's mean? Where should I put power inlet?  On pins 1 + 3, or pins 2 + 4?   Any additional advice is welcome, I am looking to comply with industry standards.  Thank you in advance for your help!


Prove That $6^n -1$ is composite $\forall n>1 \in \mathbb{N}$


Are the $C$-points of a simply connected algbraic group simply connected?

Let $G$ be a simply connected algebraic group defined over $C$.   Note : I see the definition of simply connected as "Every isogeny to $G$ is an isomorphism" as given in Hochschild's  "Basic Theory of Algebraic Groups and Lie algebras".   $C$ is an algebraically closed field.   Please help me realise the follwoing things provided they are true:   $G_C$ (the $C$-points of $G$) is simply connected as well. $Lie(G) \cong Lie(G_C)$    Thanks !


Shell error when trying to install R from .exe

I'm having trouble installing R. I remember on my old computer I just double-clicked on the EXE (R-3.6.3-win.exe) and no issues. I am getting the following error when I double click: ShellExecuteEx failed; code 31. A device attached to the system is not functioning.  If I right-click to Run as Administrator, I still get the "A device attached to the system is not functioning." error. Restarted my computer a couple times of course. Not sure if it is related, but I get the same error when I try to uninstall Adobe Flash... should have done that last year I guess...


Is my proof for the sum of two square roots being irrational correct?

Prove that the following number is irrational:  $$\sqrt { 5 } +\sqrt { 3 } $$  Steps I took:  Proof by contradiction: let us assume that $\sqrt { 5 } +\sqrt { 3 } $ is rational.  If $\sqrt { 5 } +\sqrt { 3 } $ is rational, so is $(\sqrt { 5 } +\sqrt { 3 } )^{ 2 }$  $$(\sqrt { 5 } +\sqrt { 3 } )^{ 2 }=5+2\sqrt { 15 } +3= 2\sqrt { 15 } +8$$  However, this is a contradiction since $\sqrt { 15 } $ is irrational.   Is my proof good? What needs to be added and how can it be made more complete if it already isn't. Please note that I already proved that $\sqrt { 15 } $ is irrational in part (a) of the problem. This is part(b). That is why I didn't bother to prove it again. I guess you could say the irrationality of $\sqrt { 15 } $ was given when I started the proof.


I'm getting E: The repository 'http://ppa.launchpad.net/deadsnakes/ppa/ubuntu hirsute Release' does not have a Release file. While running sudo apt update in a LTS 20.04 server, I'm currently trying to install python3 but it seems it's not being found either. Not sure what to do. Any assistance?


Notification on questions on which a user comments

Whenever I comment on a question like to post a fiddle or give more explanation on the problem statement, unless the OP does not mention my name I do not receive the comment what the OP or others might have commented. Can a feature be added for the same as I would be interested in that question and if I had commented from my mobile their should be a way that I get the response for that question.


I want to convert list into string with unix command. X is a variable and store in new variable Y. X =  ['8922','9292','3220'] to '8922,9292,3220' How can I do this. Please suggest.


I have a system whose entropy is specified by three variables: Salinity $S$, pressure$p$, and density$\rho$. I have the following partial derivative: \begin{equation}   (\frac{\partial\eta}{\partial p})_{\rho,S}= -(\frac{\partial\eta}{\partial \rho})_{p,S}(\frac{\partial\rho}{\partial p})_{n,S} \end{equation} Where $\eta$ is the specific entropy: My question is where does the minus sign come from? I though it just was a chain rule but I can not explain this sign. Thanks


Can my cars in my game look like real cars?

We are making a game filled with thousands of cars. We were wondering if we need a licence to use body designs of lets say a Lamborghini, Ferrari, Impala. etc. We do not want to pay money to use the designs in our game, of course we are going to make our own car brands though. Can we use a similar body design??


Seeking again your expert opinion on how to remove dynamic elements using jquery? Im currently working on a php page with forms with functionality to add and remove new section. Now im having issues when im trying to remove the newly added section using jquery. As the hyperlink doesn't get triggered.  HTML page:
     File upload
       <input type="file" />       <textarea required placeholder="Description of the document" class="form-control" name="description-of-incident" id="description-of-incident" rows="2"></textarea>

       Add another

   and this is the jquery i used:    $(document).ready(function() {       $('input[type="radio"]').click(function() {              if($(this).attr('id') == 'peopleinvolvedyes') {                   $('#involvement-section').show();              }               else {                   $('#involvement-section').hide();              }          });        $("#addanother").click(function(){         $("#container").append('
File upload
<input type="file" /><textarea required placeholder="Description of the document" class="form-control" name="description-of-incident" id="description-of-incident" rows="2"></textarea>

Remove

');       });        $(".remove-document-upload").click(function(){           alert("dasdasdas");         //$(this).closest('.addanother').remove();       });     });   Whenever, i get click on the the 'Remove' hyperlink, the jquery function doesn't get triggered.  Comments and suggestions are high appreciated.  Thanks, Nhoyti