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Black body radiation and spectra lines My understanding was that all objects emit light of continuous spectrum when hot ( black body radiation) but then you see discreet wavelengths in spectra lines and I am confused. I know I am making a mistake somewhere but not able to point it Function returns None without return statement Is there a way to retrieve the user id of @mention user from chatter post in Apex? We can write a before insert trigger on feeditem, but when we display the body (which has @mention user) it simply displays as text. Is there any workaround for this? Possible to click on an object in the viewport and the object list hierarchy automatically goes to that object also? It shows no question owner, not even a simple name (without link).   What happened? Too many blanks between summation symbol and its associated expression mysql select from n last rows I have a table with index (autoincrement) and integer value. The table is millions of rows long.  How can I search if a certain number appear in the last n rows of the table most efficiently? How to create a GUID/UUID in Python How do I create a GUID in Python that is platform independent? I hear there is a method using ActivePython on Windows but it's Windows only because it uses COM. Is there a method using plain Python? Is there any simple method to calculate $\sqrt x$ without using logarithm Suppose that we don't know logarithm, then how we would able to calculate $\sqrt x$, where $x$ is a real number? More generally, is there any algorithm to calculate $\sqrt [ n ]{ x } $ without using logarithm? More simple techniques would be nice.  Here is a simple technique used to approximate square roots by :  For example: $\sqrt {78}\approx 8\frac { 14 }{ 17 } $ , where $8$ is the nearest integer root of $78$, $14 = 78 - 8^2$, $17 = 2 \times 8 + 1$.  if $n=2^k$ we can use the method above.   For example, for $k=2$ Lets calculate $\sqrt [ 4 ]{ 136 } $: $$\sqrt [ 4 ]{ 136 } =\sqrt { \sqrt { 136 }  } \approx \sqrt { 11\frac { 136-{ 11 }^{ 2 } }{ 11\times 2+1 }  } =\sqrt { 11\frac { 15 }{ 23 }  } \\ \sqrt { 11\frac { 15 }{ 23 }  } \approx 3\frac { 11\frac { 15 }{ 23 } -{ 3 }^{ 2 } }{ 3\times 2+1 } =\frac { 544 }{ 161 } =3.38\\$$ The exact result is$$ \sqrt [ 4 ]{ 136 } =3.4149\cdots$$ The method approximates well, but it is working for only $n=2^k$ as I know. My question is how I can intergrate Salesforce with different FTP servers in real time. I have read some articles about it, but to be absolutely sure I thought it would be a good idea to post a question here.  I want to be able to send and receive data from Salesforce as a csv file to a ftp server. How I'm thinking about doing this is listed below.  Send the data:  Create a apex class which query the necessary data in Salesforce and create a csv file. I guess this is trivial? Then send the file to a web service created in Salesforce, just by calling it in the apex code. Create a web service in Salesforce which receives the data from the apex code. This web service should in some way send the data to the appropriate ftp server. I guess I can simply modify some of the code provided by Salesforce to make this work? The file is sent. Receive the data  This one is a bit trickier. I guess I have to pull the data from the FTP server by using my web service, which then send the file collected to the appropriate apex class. Or, the FTP server could send the data to the SFDC web service, I don't know if this is possible? The web services on the other side that sends the data to the ftp server, could send it directly to the SFDC web service, which then again forward it to the apex class. I guess the web service will use the remote site url to connect to the SFDC web service? What is this triangle icon [Samsung Galaxy S9+]? Nothing shows up in the terminal when I type my password When I'm about to install a program in the terminal it wants the password:  [sudo] password for xxx:   But when I start to type my password nothing happens. What should I do? Show bounded and convex function on $\mathbb R$ is constant Printing labels along with equation numbers Working with documents with huge amount of equations it becomes cumbersome to go back and remind yourself what you labeled a certain equation to (I try to name them in a smart way, but there are too many).  Is there a convenient way to have equations print the label along with the tag/number, so that I can easily check the label in the compiled document?  Something like this would be perfect:  x = y               (14.1) eq:my_label The set of homotopy classes Epsilon Delta Proof: How do I use the definitions to prove Why can’t the Doctor’s companions understand babies and horses? The Doctor claimed to speak both horse and baby. The reason human companions can understand every language is because the TARDIS translates. So why can't anyone else understand babies and horses? Can you explain the sentence structure 'In a hole in the ground there lived a Hobbit'? Why put the verb before the subject? The opening sentence to The Hobbit by J.R.R. Tolkien reads,     In a hole in the ground there lived [verb] a hobbit [subject].   I wonder if there are accepted stylistic purposes for such a structure.  When is it natural, and when is it unnatural? When is $\sin(x)$ rational? Why don't the White Walkers take the sea route to Westeros