Unable to access LastViewedDate on Account object SQL
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How are questions in the 'hot' tab on a site selected? I know questions on the "hot" tab of a site homepage are based on some sort of views/velocity criteria, but does anyone know the actual algorithm used?  Background: I was considering a feature-request about the "hot" tab, but I don't have enough information to speak about it intelligently. Proof of centripetal acceleration formula ($a_c = v^2/r$) for non-uniform circular motion The formula for centripetal (radial) acceleration is well known, and there exist many proofs for it: $$||a_c|| = \frac{||v||^2}{r}$$  However, all the proofs I've seen rely on the fact that it is uniform circular motion and the magnitude of the tangential velocity vector does not change. For instance, take the classic proof using similar triangles — the similarity can only be established if the final tangential velocity vector and the initial one are of the same length.  In addition, take  calculus based proof from Khan Academy, outlined as follows:     For this proof to work, $(d\theta / dt)$ must be considered a constant, $\omega$, that does not depend on time. In the case of non-uniform circular motion, however, this is not always true as since there exists a tangential acceleration along with a radial one, $\omega$ must depend on time and is not necessarily a constant value.  Intuitively I understand that the centripetal/radial acceleration depends only on the difference in orientation between two tangential velocity vectors, and that their magnitudes do not matter -- hence the formula intuitively holds true in the non-uniform case. However, how would you go about modifying either of the proofs presented so that they are still valid in this case? Or alternatively, is there another proof that holds valid even when there exists tangential acceleration?    As per the suggestion of one of the answers, I let $\omega$ vary with time and took its derivative as $\alpha(t)$. This is my work so far. Unfortunately, I am stuck after the last step.  \begin{align} \overset{\rightharpoonup }{p}(t) &amp;= r \cos (\theta (t))\cdot\hat{i}+r \sin (\theta (t))\cdot\hat{j} \\ \overset{\rightharpoonup }{v}(t) &amp;= -r \sin (\theta (t))\cdot\omega(t)\cdot\hat{i}+r \cos (\theta (t))\cdot\omega(t)\cdot\hat{j} \\ \overset{\rightharpoonup }{a}(t) &amp;= (-r \cos(\theta(t))\cdot\omega(t)^2 - r \sin(\theta(t))\cdot\alpha(t))\hat{i} \\ &amp;+ (-r \sin(\theta(t))\cdot\omega(t)^2 + r \cos(\theta(t))\cdot\alpha(t))\hat{j} \end{align}     From here on, $\theta(t)$ is represented as just $\theta$ for brevity   and clarity   $$\overset{\rightharpoonup }{a}(t) = -\omega(t)^2(r \cos\theta\cdot\hat{i} + r \sin\theta\cdot\hat{j}) -\alpha(t)(r \sin\theta\cdot\hat{i} - r \cos\theta\cdot\hat{j})$$ What is the difference between $* and $@? Change ViewPager animation duration when sliding programmatically Force NTFS permissions inheritance for newly created files Do different "Picture styles" affect RAW output? I was  the manual of my camera (Canon 50D, but I am sure that each DSLR offer the same kind of functionality, albeit I don't know the exact names adopted) and noticed the issue of Picture styles which I had overlooked in my first reading.   In short I think that they are a collection of various calibration settings (more or less enhanced colours, things like that...). Those that are available on my camera are:   Standard Portrait Landscape Neutral Faithful  Monochrome 3 user definable modes.   These styles are so important to deserve a direct button just under the LCD screen of the camera (I guess this is useful for simplifying the use of the camera in the basic modes as opposed to manual / less automated ones).  And now for the question:   These settings obviously affect the appearance of the picture "as it comes out of the camera". But given the raw file I assume that they are all equivalent, a style is not applying a destructive transformation to the raw data, isn't it?  Shooting raw, is there a reason to favor one of these styles (Neutral?) over the other? Up to now I have been using Standard.   As a bonus (don't know if it deserves a separate question, in which case I will ask it again), what is the difference between Neutral and Faithful? A worker carries two bags. Each of the bags initially contains N nails. Whenever the worker needs a nail, he takes it from a bag picked at random. At some point the worker picks an empty bag. Find the probability that the other bag contains exactly m nails.  My reasoning:  The desired probability: $C_2^1 \cdot P(|A| = 0\ and\ |B| = m)$, where A, B - sets of nails in each bag. Then we can "divide" this probability (I suppose that I deal with independent events):  $P(|A| = 0\ and\ |B| = m) = P(|A| = 0) \cdot P(|B| = m);$  $P(|A| = 0) = (\frac{1}{2})^N$, where $|A| = |B| = N$ (initial condition).  $P(|B| = m) = (\frac{1}{2})^{N - m}$  Result: $C_2^1 \cdot P(|A| = 0\ and\ |B| = m)$ = $C_2^1 \cdot (\frac{1}{2})^{2N - m}$  Am I wrong or it is correct? how to install the DDE to the ubuntu 20.04? I have installed the Ubuntu 20.04, and want now I want to install Deepin Desktop Environment (dde)  My steps are:   add the ppa and install using apt  sudo add-apt-repository ppa:leaeasy/dde sudo apt-get update sudo apt install dde    But during the command sudo add-apt-repository ppa:leaeasy/dde I get the following error:  $ sudo add-apt-repository ppa:leaeasy/dde  You can install deepin desktop environment by run  sudo add-apt-repository ppa:leaeasy/dde sudo apt-get update apt-get install dde ------ Ubuntu Bionic: https://drive.google.com/file/d/1xkQPb4tWocknuYeY-t41W--kz-9SSL0V/view?usp=sharing ------ Important Issue: Q: Can dde on Ubuntu 16.04? A: Sorry, the dde depends on qt version above than 5.6.      If you want to install dde, please upgrade to 17.04 or above.  More info: https://launchpad.net/~leaeasy/+archive/ubuntu/dde Press [ENTER] to continue or Ctrl-c to cancel adding it.  Hit:1 http://in.archive.ubuntu.com/ubuntu focal InRelease Hit:2 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease                                      Hit:3 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease                                    Ign:4 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal InRelease                                      Hit:5 http://security.ubuntu.com/ubuntu focal-security InRelease            Err:6 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release             404  Not Found [IP: 91.189.95.83 80] Reading package lists... Done E: The repository 'http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.   I get the similar error with sudo apt-get update :  $ sudo apt-get update Hit:1 http://in.archive.ubuntu.com/ubuntu focal InRelease Hit:2 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease                                       Hit:3 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease                                     Ign:4 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal InRelease            Hit:5 http://security.ubuntu.com/ubuntu focal-security InRelease Err:6 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release   404  Not Found [IP: 91.189.95.83 80] Reading package lists... Done E: The repository 'http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.   How can I install dde ? Structure of ideals in the product of two rings $R$ and $S$ are two rings. Let $J$ be an ideal in $R\times S$. Then there are $I_{1}$, ideal of $R$, and $I_{2}$, ideal of $S$ such that $J=I_{1}\times I_{2}$.  For me it's obvious why $\left\{ r\in R\mid \left(r,s\right)\in J\text{ for some } s\in S\right\}$ is an ideal of $R$ (and the same for $S$) so I can prove $J$ is a subset of the product of two ideals and also that the product of these two ideals is an ideal. But I can't see how to prove equality without assuming existence of unity or commutativity. Trying basically to show that if $\left(r,s\right)\in J$ then also $\left(r,0\right),\left(0,s\right)\in J$. Thank you for your help! Sort on a string that may contain a number I need to write a Java Comparator class that compares Strings, however with one twist.  If the two strings it is comparing are the same at the beginning and end of the string are the same, and the middle part that differs is an integer, then compare based on the numeric values of those integers.  For example, I want the following strings to end up in order they're shown:   aaa bbb 3 ccc bbb 12 ccc ccc 11 ddd eee 3 ddd jpeg2000 eee eee 12 ddd jpeg2000 eee   As you can see, there might be other integers in the string, so I can't just use regular expressions to break out any integer.  I'm thinking of just walking the strings from the beginning until I find a bit that doesn't match, then walking in from the end until I find a bit that doesn't match, and then comparing the bit in the middle to the regular expression "[0-9]+", and if it compares, then doing a numeric comparison, otherwise doing a lexical comparison.  Is there a better way?  Update I don't think I can guarantee that the other numbers in the string, the ones that may match, don't have spaces around them, or that the ones that differ do have spaces. For which values does the Matrix system have a unique solution, infinitely many solutions and no solution? Given the system:  $$\begin{align}  &amp; x+3y-3z=4 \\   &amp; y+2z=a \\  &amp; 2x+5y+(a^2-9)z=9 \end{align}$$  For which values of a (if any) does the system have a unique solution, infinitely many solutions, and no solution?    So I am getting that it has: infinitely many solutions at: (-1)    No solution at (1)    Unique solution at (-1,1)    AM I RIGHT?? In a bash script, how can I redirect all standard outputs to a log file and tee the output on the screen using exec ?  log_file="$HOME/logs/install.txt-`date +'%Y-%m-%d_%H-%M-%S'`" [ -f "$log_file" ] || touch "$log_file" exec 1&gt;&gt; $log_file 2&gt;&amp;1   This code redirect all the log to the log file but not to the screen . Knowing the interface of ubuntu and editing them Where are the files for the desktop or the interface that appears on the screen stored? And how can we edit them. How are they programmed?  What programming language is used to built the interfaces? I have a bunch of external and internal HDDs that I use on a Linux system. I only have Linux systems, so using a Linux file-system would only make sense, right? However I'm currently using NTFS everywhere, because it gives me the most usable space out of HDDs.  I would like to switch to Linux file-systems now though, mostly because of permissions and compability (e.g. I can't get my LUKS encrypted NTFS partition to resize under Linux, keeps telling me to chkdsk under Windows).  However when I formatted those HDDs I tried out a bunch of different filesystems and every Linux filesystem, even ext2 which as far as I know has no journaling, used a lot of space for itself. I don't recall exact values, but it was over 100GB that NTFS got me more on a 2TB HDD, which is a lot.  So my question is: Is there a way to make ext-filesystems use less space for themselves? Or is there another filesystem (I've tried ext2, ext3, ext4, NTFS and vfat - None of them came even close to the usable space NTFS offered me) with perfect Linux support and great usable space?  I'd love to hear about how and why filesystems (especially ext2 which has no journaling) use that much more space than NTFS and I don't know where else to ask. I'd mostly prefer a way to use ext4 without journaling and anything else that uses up this much space, if that's possible. Can I buy a plane ticket from A-B-C but get on the plane at B? I get the point of having a minimum reputation to use the new chat feature. However, I was hoping my 2K reputation from Stack Overflow would be enough - but it looks like I need to acquire 20 rep here on Meta Stack Exchange.  So my question is - should this restriction be moved? How exactly does one “control for other variables”? Here is the article that motivated this question:   I liked this article, and it nicely demonstrates the concept of “controlling for other variables” (IQ, career, income, age, etc) in order to best isolate the true relationship between just the 2 variables in question.    Can you explain to me how you actually control for variables on a typical data set?      E.g., if you have 2 people with the same impatience level and BMI, but different incomes, how do you treat these data?  Do you categorize them into different subgroups that do have similar income, patience, and BMI?  But, eventually there are dozens of variables to control for (IQ, career, income, age, etc)  How do you then aggregate these (potentially) 100’s of subgroups?  In fact, I have a feeling this approach is barking up the wrong tree, now that I’ve verbalized it.  Thanks for shedding any light on something I've meant to get to the bottom of for a few years now...! Syntax error on print with Python 3 How to increase the width and height of the Rich Text area field in Visual force Page? I know this question has been asked earlier. but did not see proper responses so asking again.  &lt;apex:pageBlockSection title="Preview Pane" columns="1"&gt;     &lt;apex:inputTextarea richtext="true" id="EmailBody" label="EmailBody"            cols="1" ondblclick="false" disabled="false"           value="{!emailTemplateSelected.htmlValue}"/&gt; &lt;/apex:pageBlockSection&gt;   I have tried to set the column value for the pageblock section. As well as for the inputtextarea. Still the column width dose not span the entire page.    &lt;apex:inputTextarea richtext="true" id="EmailBody" label="EmailBody" cols="1"     ondblclick="false" disabled="false" value="{!emailTemplateSelected.htmlValue}"     style="height:200px;width:200px;"/&gt; How to implement "select all" check box in HTML?