How can I use += operator in PHP for String
How to combine two strings together in PHP?
Strange issue with the right side margin How to cite a book chapter written by an author who is not the editor or author of the book with BibTeX? I don't know how to cite a chapter written by an author who is not the editor or author of the book.   How can I get the following citation?     Grandstrand, O. (2004), 'Innovation and Intellectual Property Rights', in J. Fagerberg, D.C. Mowery and R.R. Nelson (Eds.), Oxford Handbook of Innovation. Oxford University Press: Oxford. Issue in evaluating the performance of my "clustering algorithm" using NMI, ARI when the "ground truth" is available? Can I read the hash portion of the URL on my server-side application (PHP, Ruby, Python, etc.)? Why did the Jedi want to bring balance to the Force? During the Prequel trilogy, the Jedi wanted to bring balance to the Force, in accordance with a prophecy.  There seemed to be a general agreement that this was a 'good thing', but a disagreement with the assertion that Anakin was the one to do it.  Why did the Jedi Council believe it was good to bring balance to the Force?  The Republic was mighty (in theory), the Council was established as THE source of Force users, the Sith were thought extinct, and the number of Dark Jedi was apparently very, very low.  It seemed, for all intents and purposes, as if the Force was strongly imbalanced in favor of the Light side...so why did the Council want to 'balance' it? how to reset gnome panel? I think my gnome-panel is messed up because I alt+right click it and nothing pops up.  I'm on 12.04, classic gnome desktop.  so I used locate and found gnome-panel in .gconf somewhere, how do I clear just gnome-panel's settings so that I can add things to my panel again?   edit:  matt: ~/.gconf $ find|grep -iw panel ./desktop/ibus/panel ./desktop/ibus/panel/%gconf.xml ./apps/gnome-settings/gnome-panel ./apps/gnome-settings/gnome-panel/%gconf.xml Display only the penultimate (second last) row of a text I have a sprite sheet from a classic video game (if you're curious, Final Fight) that I'd like to be broken up into indivual images to be used in . However, the images aren't on an even grid, and all have a different amount of space between them.  Is there an automated way to export images based on contiguous pixels or something like that? Evaluating the integral $\int_0^\infty \frac{\sin x} x \,\mathrm dx = \frac \pi 2$? A famous exercise which one encounters while doing Complex Analysis (Residue theory) is to prove that the given integral: $$\int\limits_0^\infty \frac{\sin x} x \,\mathrm  dx = \frac \pi 2$$ Well, can anyone prove this without using Residue theory?  I actually thought of using the series representation of $\sin x$: $$\int\limits_0^\infty \frac{\sin x} x \, dx = \lim\limits_{n \to \infty} \int\limits_0^n \frac{1}{t} \left( t - \frac{t^3}{3!} + \frac{t^5}{5!} + \cdots \right) \,\mathrm  dt$$ but I don't see how $\pi$ comes here, since we need the answer to be equal to $\dfrac{\pi}{2}$. Is there a proof from the first principle that the Lagrangian L = T - V? Is there a proof from the first principle that for the Lagrangian $L$,    $$L = T\text{(kinetic energy)} - V\text{(potential energy)}$$  in classical mechanics? Assume that Cartesian coordinates are used. Among the combinations, $L = T - nV$, only $n=1$ works. Is there a fundamental reason for it?  On the other hand, the variational principle used in deriving the equations of motion, Euler-Lagrange equation, is general enough (can be used to to find the optimum of any parametrized integral) and does not specify the form of Lagrangian. I appreciate for anyone who gives the  answer, and if possible, the primary source (who published the answer first in the literature).      Notes added on Sept 22: - Both answers are correct as far as I can find. Both answerers were not sure about what I meant by the term I used: 'first principle'. I like to elaborate what I was thinking, not meant to be condescending or anything near to that. Please have a little understanding if the words I use are not well-thought of. - We do science by collecting facts, forming empirical laws, building a theory which generalizes the laws, then we go back to the lab and find if the generalization part can stand up to the verification. Newton's laws are close to the end of empirical laws, meaning that they are easily verified in the lab. These laws are not limited to gravity, but are used mostly under the condition of gravity. When we generalize and express them in Lagrangian or Hamiltonian, they can be used where Newton's laws cannot, for example, on electromagnetism, or any other forces unknown to us. Lagrangian or Hamiltonian and the derived equations of motion are generalizations and more on the theory side, relatively speaking; at least those are a little more theoretical than Newton's laws. We still go to lab to verify these generalizations, but it's somewhat harder to do so, like we have to use Large Hadron Collider. - But here is a new problem, as @Jerry Schirmer pointed out in his comment and I agreed. Lagrangian is great tool if we know its expression. If we don't, then we are at lost. Lagrangian is almost as useless as Newton's laws for a new mysterious force. It's almost as useless but not quite, because we can try and error. We have much better luck to try and error on Lagrangian than on equations of motion. - Oh, variational principle is a 'first principle' in my mind and is used to derive Euler-Lagrange equation. But variational principle does not give a clue about the explicit expression of Lagrangian. This is the point I'm driving at. This is why I'm looking for help, say, in Physics SE. If someone knew the reason why n=1 in L=T-nV, then we could use this reasoning to find out about a mysterious force. It looks like that someone is in the future. So this is something I just found out about that I find odd:   Opportunity attacks—trigger off of movement that uses the creatures movement (action, move action, bonus action, reaction.)  Sentinel—Whenever a creature within 5 ft of you makes an attack at a creature other than you.   Booming blade—If the target willingly moves.   Mental Prison spell—if it moves, attacks through it, or reaches any part of body out of it.   So the “willingly” is different than other rulings for how effects related to movement works. However what exactly fits willing?   Cause fear—nope magic is having them move. Dissonant whispers—same thing. They have to immediately move.   So the creature has to want to move completely of its own accord.   Crown of Madness—Humanoid creature you choose must make a wisdom saving throw. On a fail it is charmed by you. (Next is flavor text so skipping.) While charmed in this way the target must make an attack on a creature other than itself that you mentally choose on each of its turns before moving.  It can act normally if you choose no creature or if none are within reach.   Crown of madness isn't making them move but doesnt specifically say willing.  And if the ruling for willing is movement not caused by magic what about magic causing situations where you take damage if you don't move. Would a creature shimmering with evocation energy be spared because he moved out of the magical blender that is cloud of daggers? If no, then what is the go-to rule for willing movement that I should be using?  In short, what movement counts as willing, and where can it be found? Is moving out of obvious danger caused by magic, willing? Is moving away from an ally so you don't hit them, willing?   If there isn't any actual ruling on willing, that's fine; I'll go back to running it with my interpretation, so that it has same wording as AOO. If there is an actual 5e term or explanation for willing (that isn't Sage Advice), please let me know. I just don't see why it was necessary to put a term in the spell that isn't used anywhere else. I understand it could have been overlooked since it was in a splatbook or has just been ignored since most people probably assume that there is "Forced " and "Willing" movement, with the willing being defined as: any movement from an action, move action, bonus action, or reaction. In same way AOO work. How does Austria's suspension of Schengen affect travellers (both EU and non-EU)? I'm an Italian citizen. Next Sunday I'm going to Austria. I have a national ID card but no passport. Recently Austria suspended Schengen. So can I enter Austria? About embryonic and genetic evidence of evolution? My question here is about evidence for evolution from Embryology and from Genetics.  Mammals do have similar Embryos, but is it the case that for each species there is an embryonic development that occurs in earlier species, has such relationship been observed? What I mean for example if we generally conceive of having species$Sp_1,Sp_2,...,Sp_n$ where each $ Sp_{i+1}$ being evolved from $Sp_i,$ then is it the case that the embryonic development stages of $ Sp_{i+1}$ contains some of the embryonic development stages of all of its ancestor species.  Similar question to 1 but regarding Genetics, is it the case that every species has a genetic thumbprint of its ancestors that lie there in the non-functional sections of its DNA, i.e. is it the case that all the genetic history of our evolution is recorded in the non-functional section of our DNA. So do human DNA have some portions of the DNA of some dinosaurs for example? How do I properly use the "Not an Answer" flag? What is the "Not an Answer" flag and what is its purpose? When should I use this flag? When should I not use this flag? But I'm still not sure if I'm using the flag correctly... An answer is "Not an Answer", but the flag was declined or disputed!   See also: Google Drive storage mismatch Is there any way to index my Github account to google search. I see that many people's account show up as soon as I type their name, but mine doesn't show up even after I type my name followed by github n search. I have a large file and I would like print from each sequential 50 lines , the 15th and 25th lines.  sed -n '15,25p' inputfile   How to modify this command to print only lines 15 and 25 and to loop over each 50 lines in the file. Suppose I have BaseClass with public methods A and B, and I create DerivedClass through inheritance.  e.g.  public DerivedClass : BaseClass {}   Now I want to develop a method C in DerivedClass that uses A and B.  Is there a way I can override methods A and B to be private in DerivedClass so that only method C is exposed to someone who wants to use my DerivedClass? Execute function when post is published I try to use this function i have created when a post is published for the first time.  function a_new_post($post){   $post_id = $post-&gt;ID;    if ( !get_post_meta( $post_id, 'firstpublish', $single = true ) ) {       // ...run code once       update_post_meta( $post_id, 'firstpublish', true );   } } add_action( 'draft_to_published', 'a_new_post' );   I can't see anything wrong with it, but when i try to create some sample posts i check the database and the field "firstpublished" has not been created.  Does anyone see anything wrong? This image from wikipedia, explains that there occurs a potential drop across a , and an electric field confined to the depletion region.  I already know the reason for the existence of this drop and the calculation of the difference but I have two questions regarding this drop.    1) If the  regions are externally connected using a perfectly conducting wire, why will not any current flow? Connecting the two regions should equalize their potentials (since wire is a resistance less) conductor, and therefore the gradient at the junction is destroyed resulting in a  which is obviously against conservation of energy as the semiconductor has non-zero resistivity. Where will extra potential drops will be created so that Kirchoff's voltage rule holds without any current and the built-in potential difference $V_o$ of the juction persists?    2) (probably naive) If an external Bias is applied, of say $|V|&lt;|V_o|$, then the pn potential difference across the junction will just reduce by that amount ($|V|$). Assuming that the external voltage source is ideal without any resistance, what will be the potential drops which would sum to zero in this case? Will drop due to the resistance of semiconductor play a par in it? If yes, then there cannot be any ideal resistance-less semiconductor junction, can there?