What is the difference between FTPS and SFTP?
FTPS versus SFTP versus SCP
Storing Images in DB - Yea or Nay? So I'm using an app that stores images heavily in the DB. What's your outlook on this? I'm more of a type to store the location in the filesystem, than store it directly in the DB.  What do you think are the pros/cons? How to avoid bad box with long words with no hyphenation? Why isn't my website in Google search results? The following problem came up from a though I had while reading:  Let's say we have $M=\mathbb{Z}^n$ and we have another free $\mathbb{Z}$-module, $N$, inside of $M$ also with rank $n$.  We know we can make a matrix $A$ that changes $N$ to its representation in $M$ (ie has as columns the basis $N$ expressed in coordinates coming from the basis of $M$). If the index of $N$ in $M$ is $m$, I am pretty sure just from tinkering that the determinant of $A$ should also be $m$, however, I have not been able to show this.  It is unclear to me how to proceed. I though maybe I could do something related to the points in $\mathbb{Z}^n$ that are within the unit box of $N$, but I cannot really make sense of this.  Thank you for any help or direction. Factoring $-3x^2 - 2xy + 8y^2 + 11x - 8y - 6$ dpkg-divert: error: rename involves overwriting `/usr/lib/xorg/protocol.txt' with different file `/usr/lib/xorg/protocol-precise.txt', not allowed I just installed Ubuntu (12.04.4) and I upgraded to 13.10  I have no idea how to fix this :/  $ sudo apt-get install -f  Reading package lists... Done Building dependency tree        Reading state information... Done The following packages will be REMOVED:   xserver-common-lts-saucy 0 upgraded, 0 newly installed, 1 to remove and 2 not upgraded. 1 not fully installed or removed. After this operation, 1,718 kB disk space will be freed. Do you want to continue [Y/n]? y (Reading database ... 175174 files and directories currently installed.) Removing xserver-common-lts-saucy ... Removing 'diversion of /usr/lib/xorg/protocol.txt to /usr/lib/xorg/protocol-precise.txt by xserver-common-lts-saucy' dpkg-divert: error: rename involves overwriting `/usr/lib/xorg/protocol.txt' with   different file `/usr/lib/xorg/protocol-precise.txt', not allowed dpkg: error processing xserver-common-lts-saucy (--remove):  subprocess installed post-removal script returned error exit status 2 Errors were encountered while processing:  xserver-common-lts-saucy E: Sub-process /usr/bin/dpkg returned an error code (1) Last digits, numbers Can anyone please help me?  1) Find the last digit of $7^{12345}$   2) Find the last 2 digits of $3^{3^{2014}}$.  Attempt: 1)  By just setting the powers of $7$ we have $7^1 = 7$, $7^2=49$, $7^3=343$, $7^4 = 2401$, $7^5 = 16807$, $7^6 = 117649$, $\dots$  After the power of $4$, the last digits will repeat. Then by noticing the pattern the digits will end in $7,9,3$ and $1$.  Then we can divide the exponent $(12345)$ by $4$ since this is the cycle that makes it repeat. Then $12345 : 4$ has remainder $1$. So $7^1 = 7$ is the unit digit to $7^{12345}$.   So the last digit is $7$.   I know how to do it like this, the problem does not state how to find the last digit, but I know it has something do do with Euler's theorem.  for part $2$) I don't know how to start. Can anyone please help me?   Thank you for the help. Custom plugin giving: wp-admin/admin-ajax.php 400 (Bad Request) I am having trouble debugging an issue with a plugin that I'm writing. I want to do an Ajax request when a user changes the option on a select input. The thing is it was fully working as expected yesterday, then when I test the website today (no code changes were made at all since yesterday) I'm getting an:   domain.com/wp-admin/admin-ajax.php 400 (Bad Request)  message in my Chrome console. If I try in Internet Explorer/FireFox it doesn't give the error in console but the Ajax request is still not working.  The plugin I'm creating is on a DigitalOcean droplet which was made using their one click app for WordPress.  Here is the barebones code I'm using on the plugin for the ajax:  //This is in a class' constructor method add_action('wp_enqueue_scripts', array($this, 'plugin_prefix_scripts'));  //PLUGIN_URL is a constant created earlier in the plugin public function plugin_prefix_scripts() { wp_enqueue_script('plugin_prefix_scripts', PLUGIN_URL . 'scripts/frontend_script.js'); wp_localize_script('plugin_prefix_scripts', 'js_object',   array(     'ajax_url' =&gt; admin_url('admin-ajax.php')   ) );   }  frontend_script.js:  $('#plugin-prefix-option-one, #plugin-prefix-option-two').on('change', function() {     var data = {         'action': 'plugin_prefix_page_change',         'option_val': 'some_val',     }      $.post(js_object.ajax_url, data, function(response) {         console.log(response); });   Back in the class:  add_action('wp_ajax_plugin_prefix_page_change', array($this, 'plugin_prefix_page_change'));  public function plugin_prefix_page_change() {     $arr = array(1, 2, 3, 4, 5);      wp_send_json($arr);      //I've also tried wp_die() and no die call at all but same outcome     die(); }   I'm unsure how to debug this further. Any help is much appreciated.  Thanks Why doesn't the Moon fall onto the Earth? Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body? Improving upon ArcGIS Buffer/Dissolve performance? Are there strange attractors whose coordinates are "almost integers"? I am wondering if the mass density profile $\rho(\vec{r})$ has been characterized for atomic particles such as quarks and electrons. I am currently taking an intro class in quantum mechanics, and I have run this question by several professors. It is my understanding from the viewpoint of quantum physics a particle's position is given by a probability density function $\Psi(\vec{r},t)$. I also understand that when books quote the "radius" of an electron they are typically referring to some approximate range into which an electron is "likely" to fall, say, one standard deviation from the expectation value of its position or maybe $10^{-15}$ meters.  However it is my impression that, in this viewpoint, wherever the particle "is" or even whether or not the particle "had" any position to begin with (via the Bell Inequalities), it is assumed that if it were (somehow) found, it would be a point mass. This has been verified by my professors and GSIs. I am wondering if its really true.  If the particle was truly a point mass then wherever it is, it would presumably have an infinite mass density. Wouldn't that make electrons and quarks indistinguishable from very tiny black holes? Is there any practical difference between saying that subatomic particles are black holes and that they are point masses? I am aware of such problems as Hawking Radiation although at the scales of the Schwarchild radius of an electron (back of the envelope calculation yields $\tilde{}10^{-57}$ meters), would it really make any more sense to use quantum mechanics as opposed to general relativity?  If anyone knows of an upper bound on the volume over which an electron/quark/gluon/anything else is distributed I would be interested to know. A quick Google Search has yielded nothing but the "classical" electron radius, which is not what I am referring to.  Thanks in advance; look forward to the responses. Copy over ssh and execute commands in one session How come unpolarized light does not undergo destructive interference? As far as I know, unpolarized light is defined as light which has no clear axis of polarization, but electric field vectors in all directions. However, I also know that electric fields can be superpositioned. So this leads me to the conclusion that if unpolarized light has equal $\vec E$ vectors in all directions, they should cancel.   Obviously, though, this is wrong (we've got light!). What's the explanation? The probability that an initial quantum state $|\psi_i\rangle$ becomes the final quantum state $|\psi_f\rangle$ is given by  \begin{eqnarray} P(i \rightarrow f) &amp;=&amp; |\langle\psi_f|\psi_i\rangle|^2 \tag{1}\\ &amp;=&amp; \langle\psi_f|\psi_i\rangle^*\langle\psi_f|\psi_i\rangle \\ &amp;=&amp; \langle\psi_i|\psi_f\rangle\langle\psi_f|\psi_i\rangle. \end{eqnarray}  Equation (1) seems to show that the probability for the transition ($i\rightarrow f$) can be interpreted as the system both moving forward in time ($i\rightarrow f$) with amplitude $\langle\psi_f|\psi_i\rangle$ and backward in time ($f\rightarrow i$) with amplitude $\langle\psi_i|\psi_f\rangle$ simultaneously.  Does this reasoning help to explain the Born rule? (Is it like the Transactional Interpretation of QM?)  I guess we must experience the macroscopic direction of time ($i\rightarrow f$) in accord with increasing entropy in an expanding universe whereas microscopically QM works both forwards and backwards in time.  Addition  This is an improved version of the argument including time-evolution operators.  The probability that an initial quantum state $|\psi_i\rangle$ evolves to become the final quantum state $|\psi_f\rangle$ is given by  \begin{eqnarray} P_{i \rightarrow f} &amp;=&amp; |\langle\psi_f|U_{i \rightarrow f}|\psi_i\rangle|^2 \tag{2}\\ &amp;=&amp; \langle\psi_f|U_{i \rightarrow f}|\psi_i\rangle^*\langle\psi_f|U_{i \rightarrow f}|\psi_i\rangle \\ &amp;=&amp; \langle\psi_i|U^\dagger_{i \rightarrow f}|\psi_f\rangle\langle\psi_f|U_{i \rightarrow f}|\psi_i\rangle \\ &amp;=&amp; \langle\psi_i|U_{f \rightarrow i}|\psi_f\rangle\langle\psi_f|U_{i \rightarrow f}|\psi_i\rangle \end{eqnarray} where $U_{i \rightarrow f}$ is the forward-time evolution operator and $U_{f \rightarrow i}=U^\dagger_{i \rightarrow f}$ is the corresponding backward-time evolution operator.  Equation (2) seems to show that the probability $P_{i\rightarrow j}$ can be interpreted as the system first evolving forwards in time and then evolving backwards in time.  Perhaps this is an example of Murray Gell-Mann's  that "Everything not forbidden is compulsory"? At the quantum level, below observable probabilities, there is nothing to stop time flowing both forwards and backwards. If column matches another file, print every line with match (awk/grep) I’m taking two input files, one with certain ID numbers, and another with a large list of ID numbers and additional columns. The latter file contains multiple lines for each ID number and I need to extract all lines that match an ID from the first file. Those lines then must be printed in a new file.  Edit 1: Replaced sample files with excerpts from actual  Edit 2: Removed extra spaces that were in excerpt, but not actual file. Files likely need to be sanitized in some way, but how is unclear.  file1:  AT1G56430 AT3G55190 AT3G22880   file2:  AT1G01010|GO:0043090|RCA AT1G56430|GO:0010233|IGI  AT1G56430|GO:0009555|IGI  AT1G56430|GO:0030418|IGI   expected output  AT1G56430|GO:0010233|IGI  AT1G56430|GO:0009555|IGI  AT1G56430|GO:0030418|IGI   [[  I have tried:  awk -F'|' 'NR==FNR{c[$1$2]++;next};c[$1$2] &gt; 0' file1 file2 &gt; output.txt   and:  grep -Ff file2 file1 &gt; output.txt   I’m aware that there are many somewhat similar questions posted in these forums and others. However, these don’t mention how the output is handled… nor do they mention duplicates. I’ve tried solutions from 4 of them, have been messing with this for many hours and keep getting the same problem: a blank output file.   I’m new to awk and I greatly appreciate the help. Sorry if this is a simple problem with syntax etc; please let me know. Thanks for the help. $\displaystyle\sum_{n=1}^\infty \frac{1}{n^s}$ only converges to $\zeta(s)$ if $\text{Re}(s) &gt; 1$.  Why should analytically continuing to $\zeta(-1)$ give the right answer? Motion Tracking objects that go out of frame and re-enter later I am motion tracking a video in which the camera turns away from one scene and then shortly returns to it. However, the segments that went off-screen lose their track and do not continue tracking once the camera returns. I am wondering if there is a manual way to tell a segment where and when to continue looking for it's tracking target. Is this possible to do? Is every dense subspace of a separable space separable? Determine group G as cyclic If $G$ has no proper subgroup, prove that $G$ is cyclic of order $p$, where $p$ is a prime number.     I know that since $G $is a group with no proper subgroups, $g \in G$ is not just the identity. I don't know where to go from there.