Rendering an animation only returns blank images
Render result is completely blank
During U-substitution, is the $du$ that we use as the infinitesimal in $\int f(u) \ du$ changing size? I am familiar and comfortable with the following definition of an integral (defined as the the Riemann Sum where n approaches infinity).    I have circled in red two terms to emphasize a concept that I was taught: the $\frac{b-a}{n}$ term effectively becomes the $dx$ term. This intuitively makes sense to me.   Additionally, I am familiar with the following statement (as expressed here: )    However, I have boxed in red something that I find rather confusing when trying to interpret it through the understanding that $\frac{b-a}{n}$ sorta kinda equals $dx$...  Specifically, the $du$ value appears to be changing throughout the interval $[ g(a), g(b)]$. To reframe this in the "Riemann Sum" version,we would have something like: $\text{ "value that varies depending on where you are"} * \frac{g(b)-g(a)}{n}$  This is very confusing to me...because, if this is the correct interpretation, I'm not quite certain I understand why this is allowed. Create default home directory for existing user in terminal How do I do this? I created a user without a home directory and now I want to create one. Not just a folder called new_user, I want the default home directory with all it's folders and hidden files, etc. How is evolution possible in contemporary humans? I would like to know if evolution is continuing to happen in modern humans, assuming things like existence of the nuclear family structure, fidelity to one partner, etc. It seems to me the answer would be NO because evolution depends on differential reproductive rates, but in the modern world, all male humans have roughly 2.5 (or whatever the number) kids. Add in the process of culturally modified selection pressure, and it seems to me that even an "unfit" male would end up having a couple of offspring. The fittest male (or female) is no better off than his or her contemporaries because of this "leveling" effect.   However, the impression I get from the popular science media is that scientists think evolution is continuing to happen. I would like to know what the actual scientific consensus is, and why. Thanks. Map matching links and ideas? I'm using OpenStreetMap and its vectorial road network and I'd like to implement a map matcher algorithm.   Currently I'm able, for each GPS position, to retrieve the nearest road segment and calculate the projection of this position to that segment, like on this image (Red pin is the pure GPS position, in blue the mapped segment and in Green the mapped position):    However, due to the lack of accuracy of the GPS, sometimes the mapped position jumps from segment to another and can provide some inconsistent mapped position from time to time.  My current algorithm is very basic : from the pure GPS position, I get the nearest segment and decide that the mapped matched position is on this one. I know that this can be really improved.  I can imagine that taking the vehicle direction into account will improve the map matching but do you know any other approach that would enable me to improve my map matcher ?  I seek any link, and/or open source software? When to switch to a CDN? I am often logged in several SSH sessions at once. To logout from several sessions, I press CTRL+d, until I am back on my local machine. However, I occasionally press it once too many, and my terminal exits. Is there a way to make CTRL+d unable to close my terminal ? I am using terminator as my terminal emulator. I am trying to evaluate the following:  $\displaystyle \int_{0}^{\infty} \frac{1}{1+x^a}dx$, where $a&gt;1$ and $a \in \mathbb{R}$  Any help will be much appreciated. Taking ownership of comments on migrated questions When a question is migrated to a SE site that I'm not registered to, I can't claim ownership of my comments. An example question:   I registered only after the question was migrated and can't delete my comments. I always like to perform some garbage collection of noise comments made by me. (like on the example question)  Would it be possible to claim ownership of comments in this scenario? Is this a bug? Reputation block layout after earning new privilege On the mobile web after new privilege is earned, reputation block contains some design issues:   no margins poor text color inside bar         By tapping on "track the next one" link, page have been refreshed:   no margins empty block in the middle obscure content         Only after manual refreshing, page looks fine again:        It is hard to reproduce because you need to earn next privilege which takes a lot of time. But I believe it's no too hard for developers :) CS0120: An object reference is required for the nonstatic field, method, or property 'foo' Consider:  namespace WindowsApplication1 {     public partial class Form1 : Form     {         public Form1()         {             InitializeComponent();         }          private void button1_Click(object sender, EventArgs e)         {             //int[] val = { 0, 0};             int val;             if (textBox1.Text == "")             {                 MessageBox.Show("Input any no");             }             else             {                 val = Convert.ToInt32(textBox1.Text);                 Thread ot1 = new Thread(new ParameterizedThreadStart(SumData));                 ot1.Start(val);             }         }          private static void ReadData(object state)         {             System.Windows.Forms.Application.Run();         }          void setTextboxText(int result)         {             if (this.InvokeRequired)             {                 this.Invoke(new IntDelegate(SetTextboxTextSafe), new object[] { result });             }             else             {                 SetTextboxTextSafe(result);             }         }          void SetTextboxTextSafe(int result)         {             label1.Text = result.ToString();         }          private static void SumData(object state)         {             int result;             //int[] icount = (int[])state;             int icount = (int)state;              for (int i = icount; i &gt; 0; i--)             {                 result += i;                 System.Threading.Thread.Sleep(1000);             }             setTextboxText(result);         }          delegate void IntDelegate(int result);          private void button2_Click(object sender, EventArgs e)         {             Application.Exit();         }     } }   Why is this error occurring?     An object reference is required for the nonstatic field, method, or property 'WindowsApplication1.Form1.setTextboxText(int) As it was suggested  I am using cat command to concatenate several .mp3 files into one .mp3 file. Imagine, I have following .mp3 files in the current folder: 001001.mp3 001002.mp3 001003.mp3 001004.mp3 001005.mp3  or, like this: 096001.mp3 096002.mp3 096003.mp3 096004.mp3  I need to concatenate these .mp3 files in there ascending sequence, i.e.  001001.mp3+001002.mp3+001003.mp3+etc. In order to join these .mp3 files into one I am executing following command in the current folder: cat *.mp3 &gt; final.mp3  I tested the final .mp3 file and it is what I am expected, but I need to be sure that above command picks files in there ascending sequence. Can I be sure that above command always concatenates files in the ascending sequence? Thank you Sir! Should we MAC-then-encrypt or encrypt-then-MAC? Most of the time, when some data must be encrypted, it must also be protected with a , because encryption protects only against passive attackers. There are some nifty encryption modes which include a MAC (, ...) but let's assume that we are doing old-style crypto, so we have a standalone encryption method (e.g. AES with CBC chaining and PKCS#5 padding) and a standalone MAC (e.g.  with SHA-256). How should we assemble the encryption and the MAC?   MAC-then-Encrypt: Compute the MAC on the cleartext, append it to the data, and then encrypt the whole? (That's what  does) Encrypt-and-MAC: Compute the MAC on the cleartext, encrypt the cleartext, and then append the MAC at the end of the ciphertext? (That's what SSH does) Encrypt-then-MAC: Encrypt the cleartext, then compute the MAC on the ciphertext, and append it to the ciphertext? (In that case, we do not forget to include the initialization vector (IV) and the encryption method identifier into the MACed data.)   The first two options are often called "MAC-then-encrypt" while the third is "encrypt-then-MAC". What are the arguments for or against either? list files and store it in variables I'm new with shell programming. My goal is to give the user a selection which file should be run. I catch all available scripts in one var with:  var=$(find script*)   so far so good, this is the output:      echo $var     script1 script2 script3 scr...   now I want to store each file in a singel variable to run it in later selection  select SEL in script1 script2 script3 .......... case $SEL in         $Script1) echo ($Script1 will start) &amp;&amp; ./$script1 ;;         $Script2) echo ($Script2 will start) &amp;&amp; ./$script2 ;;         $Script3) echo ($Script3 will start) &amp;&amp; ./$script3 ;;         $Sc..) echo ($Scr.... will start) &amp;&amp; ./$scrip.... ;;         $Sc...) echo ($Sc...... will start) &amp;&amp; ./$scrip..... ;;         *) echo "choose on of the availabel files";;     esac done   I don't have a clue how should I should separate all files if I don't know how many and the exactly length of each file.  I tried to split with echo ${var[1]} and echo $var[1] but this dosn't work. I recive either a empty output or the whole string. What does this phrase from The adventures of Tom Sawyer sentence mean: "True, the knife would not cut anything, but it was a "sure-enough" Barlow, and there was inconceivable grandeur in that -- though where the Western boys ever got the idea that such a weapon could possibly be counterfeited to its injury is an imposing mystery and will always remain so, perhaps."  Thank you! We've all wanted to express certain questions, rhetorical or not, with annoyance, excitement, surprise, frustration and so on. What better way than with both a question mark (?) and an exclamation mark (!), right? I've seen two ways of punctuating such questions:  Where is this place?!    Who do you think you are!?  (Things like ?!?, !?!, ?????!!!!!, ??!?!!?!?!!??, etc are irrelevant here.) Which is the proper way to order the two symbols? Or does each of the above two have a distinct and grammatically correct meaning? Or is the interrobang (‽) the clear winner here? ;) QM and Renormalization (layman) I was reading Michio Kaku's Beyond Einstein. In it, I think, he explains that when physicsts treat a particle as a geometric point they end up with infinity when calculating the strength of the particle's field as you approach the particle.  First, did I get that part right?  Second, how does (in very simple terms) renormalization try to fix this in Quantum Mechanics? If you can include some type of word picture that would be great. Accepted answer will go to the clearest explanation.  Update  I got a little further in the book (lol) and Kaku talks about using symmetry to remove the divergences in the math. I'd appreciate an answer that incorporates this also. Thanks guys! $f$ strictly increasing does not imply $f'>0$ We know that a function $f: [a,b] \to \mathbb{R}$ continuous on $[a,b]$ and differentiable on $(a,b)$, and if $f'&gt;0 \mbox{ on} (a,b)$ , f is strictly increasing on $[a,b]$. Is there any counterexample that shows the converse fails?   I have been trying to come up with simple examples but they all involve functions that are discontinuous or has derivative $f'=0$ which does not agree with the hypothesis hmmm What would be the associated wavelength of the particle if its velocity is zero? What free Remote Desktop (server) solutions are there? I know Ubuntu comes with a "Remote Desktop" option that appears to be a straightforward VNC server, and I'm trying to understand the alternatives. Here are the possibilities I've heard about so far:   VNC  VNC + SSH Tunnelling NX Server, free edition FreeNX NeatX X2Go X11 Forwarding over SSH xrdp    I'm coming at this from a Windows user's perspective: To the best of my experience, RDP (aka Terminal Services) is a reasonably secure (barring mitm/server spoofing), efficient desktop sharing protocol with well-supported clients, that can be exposed to the internet when necessary without major fears of intrusion. To the best of my knowledge straight VNC is none of those things, which is where I get confused - why wouldn't a better desktop sharing technology be developed or used in the open-source world? I know VNC can be wrapped with SSH, but that seems beyond the reach of a casual user. X11 forwarding over SSH may be more or less efficient, I have no idea, but is definitely even more complicated, and doesn't (as far as I know) give you access to already-running stuff (no desktop sharing as such, just remote application running).  So, I'd like any feedback/preferences amongst these or any other "Free" desktop sharing options, using these criteria and/or any others:   Security (esp. for access across internet) Efficiency (bandwidth usage, responsiveness, etc) Free-ness, as in Speech (not sure where RDP or FreeNX lie for this) Free-ness, as in Beer (are there any commercial solutions with usable dependable free offerings?) Ease of use (server and client side) Cross-OS Client availability Cross-OS Server availability Support for independent sessions and shared (and/or "Console") sessions Ongoing support/maintenance/development   Thanks! I have been reading about the new Salesforce async triggers. Currently, I tend to handle these sort of needs with a trigger that passes data to a 'Handler class' that would evaluate if a certain change has occurred. If it has then we pass those Ids to a queueable class for further processing.   What advantage do CDC and async triggers offer over using queueable or batch apex?