Do package managers check the hashes of packages?
How is the authenticity of Debian packages guaranteed?
How can I send an email by Java application using GMail, Yahoo, or Hotmail? Is it possible to send an email from my Java application using a GMail account?  I have configured my company mail server with Java app to send email, but that's not going to cut it when I distribute the application. Answers with any of using Hotmail, Yahoo or GMail are acceptable. Maya is sister of dhara who is doctor. Maya is sister of dhara, who is doctor.   In both statements who is used for which person??? We have no mention of Voldemort in Harry's sixth year. So, I was wondering- what could Voldemort have been doing? No upgrade available for 19.04 from 18.10 I'm pretty new to running linux, but I know that 19.04 was released today and I wanted to upgrade from my current 18.10. However, when I follow the release notes here:  I get the message "The software on this computer is up to date". I made sure that my update settings are set to "any new version" and "normal" in the /etc/update-manager/release-upgrades file.   What am I doing wrong?  Thanks for the help!  Side note: I had to disable this PPA:  because it would cause errors in apt updating. Do I need to re-add it? If so how do I do so without it giving me an error?  Edit: I have followed the procedure recommended in the documentation which is identical to the suggested duplicate, but I am not given the option to upgrade. I have not yet tried the   do-release-upgrade -d    option as I don't want to upgrade to the developer version. How to choose the number of hidden layers and nodes in a feedforward neural network? Is there a standard and accepted method for selecting the number of layers, and the number of nodes in each layer, in a feed-forward neural network? I'm interested in automated ways of building neural networks. Shortest path from points in one layer to points in another layer via roads in QGIS notify-send not working under ssh Maybe this is answered somewhere else, but I didn't see it.  I am running Ubuntu 14.04. When I SSH into my machine, for example:  ssh &lt;user&gt;@&lt;machineip&gt; notify-send "Hello"   I don't see anything on the monitor where I am logged into the machine. If I prefix notify-send with DISPLAY=:0.0 or DISPLAY=:0 nothing different happens. I just never see any notification on the current session.  Is there some trick/switch to getting this working?  In case this isn't clear, allow me to reiterate: From Computer A, I SSH into Computer B. Within the SSH session, I wish to execute notify-send to run on Computer B. I expect a growl-type notification to appear on the monitor of Computer B. Let $a,b,c\in \Bbb R^+$ such that $(1+a+b+c)(1+\frac{1}{a}+\frac{1}{b}+\frac{1}{c})=16$. Find $(a+b+c)$ What does the Canonical Commutation Relation (CCR) tell me about the overlap between Position and Momentum bases? Number of labeled trees which have one vertex of degree 4 How many labeled trees which have one vertex of degree 4 can we have? A tree with $10$ vertices has $9$ edges, so the sum of the degrees of the vertices is $2\cdot 9=18$. If there is one vertex of degree $4$, the sum of the degrees of the other $9$ vertices must be $14$. I don't know what to do next. Should I count all possible vertex degrees? Can we add Markdown support for tables? Since a while, 2 weeks, Dropbox does not startup anymore on my laptop running Ubuntu 12.04 LTS with GNOME shell.  When I run dropbox start -i in the console I get the following output.    Starting Dropbox...Traceback (most recent call last):   File "/usr/bin/dropbox", line 1387, in &lt;module&gt;     ret = main(sys.argv)   File "/usr/bin/dropbox", line 1376, in main     result = commands[argv[i]](argv[i+1:])   File "/usr/bin/dropbox", line 1247, in start     if not start_dropbox():   File "/usr/bin/dropbox", line 731, in start_dropbox     stderr=sys.stderr, stdout=f, close_fds=True)   File "/usr/lib/python2.7/subprocess.py", line 679, in __init__     errread, errwrite)   File "/usr/lib/python2.7/subprocess.py", line 1249, in _execute_child     raise child_exception   OSError: [Errno 8] Exec format error   I already removed Dropbox and reinstalled it. What should I do to fix this? Run a program X times In  (scrolled to 5:55) there's a claim that replacing an AC high voltage transmission line with a high voltage DC transmission line allows for having seven times fewer powerlines (the video shows how seven lines evaporate, then one line appears and the cutting in the forest gets narrower).  How is that possible? I've read the  and it claims that     The power delivered in an AC system is defined by the root mean square (RMS) of an AC voltage, but RMS is only about 71% of the peak voltage. The peak voltage of AC determines the actual insulation thickness and conductor spacing.   but that doesn't explain seven times less power lines.  How is such massive (seven times) saving possible when switching from AC to DC transmission? Set String via String.prototype function without return was created on Server Fault, answered on Server Fault, I upvoted some of those answers on Server Fault, and then moved by consensus to Super User.  Now that the question is on Super User, I can upvote the same answers I previously upvoted on Server Fault. 17.10 Super key to open applications (Google) Title of page not updated, everything else did My website changed significantly this month.  Amongst the changes was the website's title.  Two weeks ago, I finally used Webmaster Tools and submitted the page.  So far, Yahoo and Bing have updated the title in the search results, but not Google.  I've resubmitted via Webmaster Tools the website, and the bots have crawled the page, and have added "content keywords".  But the title still doesn't match.  The "content keywords" lists many of the words in the new title (but contains keywords of the existing title also).  Must say that 4 of the top 5 key words in the "significance" list are the new title's.  Still, no change.  Any remedies for this problem?  Is adding the "alt" tag for the logo significant enough to trigger the change?  There isn't an appropriate place to put the company name between  tags on the front page.  Any suggestions?  Thanks. What is the reasoning that leads one to postulate this second form for the relativistic particle action? The action for the free relativistic particle with worldline $\gamma : I\subset \mathbb{R}\to M$ is  $$S[\gamma]=-m\int d\lambda\sqrt{-\dot{\gamma}^a(\lambda)\dot{\gamma}_a(\lambda)}\tag{1} $$  Now, one may postulate a second action  $$S'[\gamma,\eta]=\frac{1}{2}\int d\lambda \bigg(\eta(\lambda)^{-1}\dot{\gamma}^a(\lambda)\dot{\gamma}_a(\lambda)-\eta(\lambda)m^2\bigg).\tag{2}$$  These are classically equivalent actions.  My question is: usually what we have is (1) and we have a problem both with the square root and with the massless limit. Given this, how could we think about postulating (2)? In other words, how can we reach (2)?  Usually some people answer this by saying: "it doesn't matter, actions are postulated, you postulate it, compute the equations, prove it works and its over".  Now I beg to differ. I want to know how could someone reason exactly in order to know what to postulate.   I am perfectly comfortable with computing the equations of motion. I want to know is how given (1) we would have the idea to postulate (2).  Is it some special case of some general procedure that deals with constraints? I'm trying to show that if $f$ is a continuous function on $[0,1]$ and $\int_0^{1} f(x)e^{nx}\,{\rm d}x = 0$ for all $n = 0, 1, 2, \dots$, then $f(x) = 0$.  I'd like to use Weierstrass approximation theorem to find a sequence of polynomials $p_m$ that converge uniformly to $f(x)$. Then we could say $\lim\limits_{m\to \infty} \int p_m(x)e^{nx}\,{\rm d}x = \int f(x)e^{nx}\,{\rm d}x = 0$, but I'm struggling to deduce that then all the $p_m$ are zero which would give the result.