SAT in some DTIME always via a constructive proof?

Question: Why can the statement $SAT \in DTIME(n^3)$ not be proven through a non-constructive proof? Intuitively a proof would be a turing machine, which solves this problem in $DTIME(n^3)$, but there are non-constructive proofs like the following:
https://cs.stackexchange.com/questions/367/how-can-it-be-decidable-whether-pi-has-some-sequence-of-digits
Comment: Because it's very probably not true?
Comment: To clarify: Assume there is a proof for $SAT \in DTIME(n^3)$. Can this proof be nonconstructive?
Comment: See Levin's universal optimal search  algorithm.
Comment: @user20264 Why specifically SAT and cubic time? You could equally ask something like, "Can there be a non-constructive proof of the four-colour theorem" or anything else.
Comment: Why is this question downvoted?
Comment: It is always an option to come to my office and discuss any problem. (I admit that I was not available yesterday afternoon.)
Answer: I would like to elaborate on Kaveh's answer because I see people wondering about the constructive status of $P = NP$.
Levin's algorithm performs a dove-tailing parallel execution of all Turing machines on the given SAT instance. If and when any machine terminates, it is verified whether its output is a solution to the SAT instance. If so, Levin's algorithm terminates, otherwise it keeps going.
The algorithm solves SAT because there is a Turing macine that solves SAT, and so eventually Levin's algorithm emulates enough of it to find a solution. Moreover, with careful programming the dove-tailing technique incures at most a polynomial slowdown of any particular simulated machine, so if there is a machine solving SAT in polynomial time, then Levin's algorithm does it in polynomial time as well.
Now let us consider the logical complexity of the statement *"Levin's algorithm runs in polynomial time". It is a specific algorithm whose Gödel code is some number $\ell$. The statement that it runs in polytime can be expressed in first-order arithmetic using Kleene's predicate $T$:
$$\exists C, k. \forall m . \exists n < 2^{C \cdot m^k}. T(\ell, k, n).$$
This can be read as: "There are $C$ and $k$ such that for every (Gödel code of a) SAT instance $m$ there is (a Gödel code of) an execution trace $n$ of $\ell$ running on input $k$, and the length of execution trace does not exceed $C \cdot m^k$."
The predicate $T$ is primitive recursive, and so is the inner formula as its quantifier is bounded by a primitive recursive function. If I am not making a mistake here (please correct me if I am, or provide a reference as I cannot be the first person noticing this), this means that we can express $P = NP$ as a $\Sigma^0_2$-formula. Thus, by negating the formula we can express $P \neq NP$ as a $\Pi^0_2$-formula. By Friedman's conservativity result we therefore have

If Peano arithmetic proves $P \neq NP$ then Heyting arithmetic proves $P \neq NP$.

In other words, this shows that in the context of first-order arithmetic $P \neq NP$ has a constructive proof if it has a classical one.
Am I making a mistake somewhere?
Comment: I have seen this argument about PA and HA but don't recall where. I personally feel a bit uncomfortable to interpret this result as "if P=NP is provable then it is constructively provable" since it interprets provable as provable in PA.
Comment: I agree that we should not confuse provable with provable in $PA$, which is why I always wrote "in the context of arithmetic". On the other hand, it would be rather stunning if $P=NP$ were independent of $PA$.
Comment: @AndrejBauer: Looks right to me. I wasn't aware of Friedman's conservativity result, and this is quite an interesting consequence (which I had also not heard of)! Might be worth a short note on ECCC (or maybe even a ToC Note, or IPL?)...
Comment: Google found [this post on FOM](http://www.cs.nyu.edu/pipermail/fom/2010-August/015000.html) by Harvey but I am sure there are earlier references. ps: I looked around a bit but I couldn't find a good reference to cite. It can be a good idea to write and post it somewhere more accessible than a FOM thread.
Answer: It is not entirely clear what you mean by a nonconstructive proof of P=NP.
I am guessing that you are asking if it is possible to prove that there is a polynomial time algorithm for SAT without providing one. That cannot be the case because we can prove that Levin's universal search algorithm for SAT has optimal running time, if P=NP is true (even if it is not provable at all) his algorithm will be polynomial time and will solve SAT.
On the other hand, the proving that Levin's algorithm (or any algorithm for SAT) runs in polynomial time may require nonconstructive concepts and axioms.


Mental Disability and Exemption from Mitzvot

Question: To what extent are the mentally disabled exempt from mitzvot, and what mitzvot are they exempt from?  At what level of mental disability does this exemption kick in if it exists, and is it gradual depending on the level of mental handicap, or is it all at once when a certain threshold is reached?
Comment: There have been several articles on this in the *Journal of Halacha and Contemporary Society*. If I can track one of them down I might post an answer.
Answer: See Does Down Syndrome make one a Shoteh? .
Generally, they are obligated in whatever mitzvot their consciousness can support.
If someone's actions indicate they're completely disconnected from reality (hard to define), then they could reach the threshold of a shoteh and be exempted from everything.
There are 50 places in Rambam's code where he takes for granted that a Shoteh (insane individual) is exempt from all mitzvot. He then writes that a Shoteh cannot serve as a witness, "as he is not bound by mitzvot." Additionally, "the exceedingly simple who cannot determine that two concepts are mutually exclusive" are disqualified from serving as witnesses, "and the exact gradation can't be described in writing, each rabbi has to make his own determination."
Rabbi Moshe Feinstein, like many others, read Rambam as saying that the "exceedingly simple" is not a Shoteh per se, but that there is a mental-fitness disqualification for witness eligibility, even if one is obligated in some other mitzvot. (Some suggest that such testimony never bears the risk of perjury, as he could always explain, "I didn't understand what I was saying." Rabbi Feinstein suggests that the Torah requires a witness to have a consciousness that supports all 613 mitzvot.)
There's a responsum of ... the Shevet Sofer, I think? about committing an individual to an institution that will help increase his cognitive function. The issues involve the availability of kosher food, and his ability to leave for his bar mitzva. Rabbi JD Bleich (in a yutorah mp3, and a J. Halacha & Contemporary Society article) observes from the language that the individual was developmentally challenged, not insane.
Comment: Great answer. I wonder why (in your last paragraph) the two considerations highlighted were kosher food and bar mitzvah, rather than the individual's ability to do other mitzvot (within his capacity) while in the institution. Can you shed any light?


AVL tree worst case height proof

Question: The worst case height of AVL tree is $1.44 \log n$. How do we prove that?
I read somewhere about Fibonacci quicks but did not understand it.
Comment: Can you recall where you read about Fibonacci quick? Have you tried proving it by yourself? Please edit the question to show what research you have done and how much progrogress you have made.
Comment: Possible duplicate of [AVL trees are not weight-balanced?](https://cs.stackexchange.com/questions/421/avl-trees-are-not-weight-balanced). Although the two questions are different, the answer to that question contains a nice explanation of the worst-case height of an AVL tree.
Answer: We want to show that the number of nodes $n$ in a height-balanced binary tree with height $h$ grows exponentially with $h$ and at least as fast as the Fibonacci sequence.
Let $N_h$ denote the minimum number of nodes in a height-balanced binary tree having height $h$.  Recall that in a height-balanced binary tree of height $h$, the subtree rooted at one of the children of the root has height $h-1$, and the subtree rooted at the other child of the root has height $h-1$ or $h-2$.  Thus, $N_h > N_{h-1} + N_{h-2}$.  Thus, $N_h$ is at least $f_h$, the $h$th term of the Fibonacci sequence, where $f_h \approx \phi^h / \sqrt{5}$ and $\phi$ is the golden ratio $\frac{1+\sqrt{5}}{2}$.
So, if $n$ is the number of nodes in an AVL tree of height $h$, we have $n \ge \phi^h / \sqrt{5}$. Taking $\log_2$ of both sides, we get $h \le \frac{\log_2 n}{\log_2 \phi} + c = 1.4404 \log_2 n + c$, for some constant $c$. Thus, an AVL tree has height $h = O(\log n)$
An easier proof, if you don't care about the constants as much, is to observe that $N_h > N_{h-1}+N_{h-2} > 2N_{h-2}$.  Hence, $N_h$ grows at least as fast as $\sqrt{2}^h$.  So the number of nodes $n$ in a height-balanced binary tree of height $h$ satisfies $n > \sqrt{2}^h$.  So $h \log_2 \sqrt{2} < \log n$, which implies $h < 2 \log n$.
Answer: Try and create the "worst" AVL tree, that is, the AVL tree in which the height is as large as possible, with as least nodes as possible.
Once you get to the Fibonacci sequence (the answer to the question above), you can use the fact the the $n$-th Fibonacci number is  $O(\phi ^n)$ (where $\phi = 1.618\ldots$), it should be easy to conclude that the worst case height of the tree is  $\log_\phi n = O(\log n)$.

AVL tree worst case height proof


How long did inflation take to happen?

Question: If inflation happened, it ended about 13.7 billion years ago. But how long was inflation going on before that? Was it just a short burst of time so that it's really okay to say that the age of the universe is 13.7 billion years, or was it going on for a long time before it ended (maybe forever?)?
Answer: As the introduction to the wikipedia article states, inflation is generally considered to have occured $10^{-36}$ to $10^{-32}$ seconds after the big bang. This is extremely extremely tiny period of time. It is okay to say that the universe is probably approximately 13.7 billions years old.
Answer: The answer to this question is very hard to give without a theory of the start of inflation. There is no firm consensus, because the details of inflation are shrouded in mystery.
Standard new inflation
The way in which you find the approximate time which inflation happens is to integrate the slow-roll conditions. Slow roll means that the inflaton field is sliding down the potential well like a ball immersed in honey sliding down an incline, and you can tell how it slid from the shape of the potential. So you go back until you get to some Planck-scale cosmological constant or field value.
The Wikipedia estimates I presume, are for standard inflation models with a scalar and a polynmially rising potential. Then the time-scale for inflation is on the order of the doubling time at the inflation scale determined by CMB observations.
Stringy inflation
In the string-theory plausible brane inflation, some branes slide toward each other, then annihilate. In this situation, the situation where the branes are far apart is the initial condition, and it doesn't necessarily terminate on a singular big bang, but in another regime. To figure out what happens at the big-bang in these types of theories, you need to know the exact string solution and the exact brane configuration before annihilation.
Universe nucleation
There are other situations where you start the universe in an inflating state just as an initial condition. This is the Hartle-Hawking idea--- the universe tunnels into existence as a small sphere (a small inflating de-Sitter space), and there is no time near the beginning, so  it is impossible to ask how long inflation lasted, because the concept of time breaks down.
Eternal inflation
In the theory of eternal inflation, the universe never stops inflating, creating new bubbles all the time. This type of theory doesn't have a backward singularity, because it replenishes the regions where inflation is going on by using the notion of an enormouse volume of space outside the cosmological horizon is. In this theory, inflation never started.
In my opinion, this type of theory can be excluded by the general principles of logical positivism, which forbid us from speaking about things we cannot observe, like an eternally inflating region permanently outside our horizon. The proponents of eternal inflation hope that some sort of statistics on the eternal volume will give observable consequences to observations in our patch.
But in eternal inflation, the "likeliest" volumes of the universe are inflating for as long as possible. This gives rise to paradoxical consequences, noted by Guth. The paradox is that the amount of universe which inflates for 1 more second is vastly larger by volume than a region where inflation stopped one second ago. So imposing the final condition that we are here, we conclude that, if we are in a typical space-time volume, then we should have emerged as quickly as possible, to allow the inflation to go on as long as possible. This is absurd, because it requires improbable conspiracies in our history, like having the solar system and planets emerge as quickly as possible, etc, etc, with each second of time saved weighted by a factor of 10 to the bazillion.
These types of paradoxes can be avoided by restricting attention to one causal patch in cosmology. This point of view has been recently explicitly stated by Susskind, and it has also been advocated by Polchinski, but I think it should really be classified as some old holographic principle folklore.
Comment: Thanks! I didn't realize there were so many possibilities.

How long did inflation take to happen?


Why don't we have Ubuntu membership here?

Question: Why don't we offer Ubuntu membership for helpful members here with good bounties?? Like they do in www.ubuntuforums.org with a new membership icon and an email ID?
Comment: Related (but probably not a duplicate): [Has there been any suggestion to encourage AU members to become Ubuntu Members?](http://meta.askubuntu.com/questions/2458/has-there-been-any-suggestion-to-encourage-au-members-to-become-ubuntu-members)
Answer: It sounds like you're confusing two things — or at the very least the two are tangled in your question:

Ubuntu membership is open to all. Anybody can apply for it and their work here on Ask Ubuntu can contribute towards that membership application (speaking as an Ubuntu Member who got through almost wholly on his AU work).
We don't offer membership because we do not have a community council just for us. IRC and UF both have their own councils with which to create members. AU users step through the traditional regional membership boards.
To pre-empt why don't we have a council?, I think there are three main reasons:

Moderatorship and Council member election work completely differently. Moderatordom is permanent (until you die or give it up) while community councils need to be regularly re-elected, with open nominations.
In short, there could easily be a conflict between the two groups.
It's more work its members. CCs are supposed to resolve conflicts, they need to hold regular meetings and in the case of sub-boards (as we would be), we would need to report to a higher board once a month. Assuming this would be moderator lead (at least to begin with), we'd just be wrapping what we already do in a ton more red tape.
Do we even need it?

For the purpose of becoming a member, you can go through the standard channels.
For resolving a dispute you can either come to meta, or if it's deeply personal with one moderator you can go to the Ubuntu Community Council or Stack Exchange. We moderators are already accountable to both groups.
For anything else (planning, whatnot) you can just use meta to discuss it.

We don't display membership slang next to users because the only thing that gets displayed next to the username is the post date and their reputation data. That's internal to Stack Exchange and that won't change.
Ubuntu members are more than free to advertise their membership on their profile.
Comment: Just a note. The IRC users and the forums members do have their own separate channel for obtaining the membership.. [IRC council](https://wiki.ubuntu.com/IRC/Membership)and the [forums council](https://wiki.ubuntu.com/Forums/Membership).
Comment: @jokerdino hmm that's an interesting point. I was trying to find those pages last night when I was writing this (but clearly failed so assumed the opposite).
Answer: Don't we? Don't you have to apply for an Ubuntu membership, telling about how you've contributed?
See details here about Ubuntu membership. (This question might also help, as well as this meta question.)
I think users who have contributed extensively on Ask Ubuntu, even if they aren't significantly active anywhere else in the Ubuntu community, surely would be eligible for Ubuntu membership.
However, I should add that usually membership is granted based on contribution in multiple areas (see Marco Ceppi's meta answer explaining this).
Comment: They are eligible, lots of people here have gotten Ubuntu membership via AU contributions, including all the moderators!
Answer: Small answer, but...
As Oli and other pointed out, Ubuntu Membership is unrelated to Ask Ubuntu.  However, in your application for Ubuntu Membership, activities here can be used as part of the "I'm contributing" proof, as contributions here still technically count towards supporting the Ubuntu community.  There's just no Ask Ubuntu specific membership track, you apply through one of the regional boards is all.


How does facial recognition work?

Question: I'm interested in learning about how facial recognition works.  I'm especially interested in the algorithms or approach that is used.  What are the leading methods for facial recognition?  Is there a good overview or source to learn about a few of the most widely used algorithms for facial recognition?  What would be the best handful of research papers to read first?
Comment: We have closed many questions like this as "too broad" (and never mind that it's a list question). What makes you think this one is better suited?
Comment: Did you already read [the Wikipedia article](https://en.wikipedia.org/wiki/Facial_recognition_system) and the references it provides?
Comment: Yeah, I've read Wikipedia.  @Raphael, if you think it's too broad, feel free to close it.  My thought was that there might be a good answer of the form "The standard approach today is to use Eigenfaces with X or Y with Z; you can read an introduction to those two techniques in papers A, B, and C." (and if that is the case, then it doesn't seem too broad to me)  But I'll be glad to defer to your judgement about whether this is suitable.
Answer: The simplest Face Recognition 101 would be run a PCA on the data, followed by a K-nearest neighbor classification.
but now there are more advanced techniques that you pick along, it might be using "better" classifiers like SVMs or Neural Networks or apply Bayesian learning, but then, as you move up the knowledge tree, you will realize you need your data itself to be more robust.. so you will then want to learn about about SIFT and other techniques.
One of the nice places you can start looking for papers and algorithms is face-reg
Have fun learning :)

How does facial recognition work?


How to make flavoured rice like uncle ben's chinese rice?

Question: What can I add to my rice cooker to create a similar flavour? Also I find, rice comes out quite dry even when I put more water? There's a slight oily sheen to it. Will this help?
Thanks heaps!
Comment: You'll probably want to ask this as two questions -- one about it drying out even after additional liquid, separate from the attempt to recreate the boxed mix.
Comment: I've never read it, but there's a [rice cooker cookbook by Roger Ebert](http://www.amazon.com/The-Pot-How-Use-It/dp/0740791427)  (yes, the film critic).  It's possible that there might be something similar in there.
Comment: Does your rice cooker have an automatic shutoff? I wonder if it's just shutting off too late, so that if you add more water it just cooks it off.
Comment: When you say your rice is too dry, what do you mean? Is the rice still crunchy from being undercooked, or has the rice cooked fully and then begun to dry out?
Answer: The ingredients on Uncle Ben's Chinese Fried Rice are:

LONG GRAIN PARBOILED RICE, SOY SAUCE (SOYBEAN, WHEAT, SALT), DEHYDRATED VEGETABLES (RED BELL PEPPER, CARROT, PARSLEY, ONION, GARLIC), MODIFIED CORN STARCH, GLUCOSE SOLIDS, HYDROLYZED PLANT PROTEIN (WHEAT, SOY), MALTODEXTRIN, AUTOLYZED YEAST EXTRACT, FLAVOUR, SPICES, HYDROGENATED VEGETABLE OIL (SOYBEAN, COTTONSEED), SILICON DIOXIDE, SALT, CARAMEL, VINEGAR SOLIDS.

First off, the rice: In a rice cooker, I wouldn't use parboiled. Just get regular long grain white rice, but be sure to rinse it pretty well. Extra starch left on the rice can cause it to come out sticky. When you complain about your rice being too dry, I'm not sure what you mean, so perhaps leaving a bit of starch in would help?
You can easily just add a bit of soy sauce to the water that you'll cook the rice in.
As for the vegetables, if you can find dehydrated vegetables, great. Otherwise, I'd just saute fresh veggies and fold them in at the end.
Next we have some industrial ingredients that will be harder to replicate at home. The corn starch I'd skip. Glucose solids can be replaced with a pinch of sugar. Hydrolyzed plant protein and autolyzed yeast extract could be replaced with a bit of nutritional yeast or some liquid seasoning like Maggi or Kitchen Bouquet.
Flavour and Spices get a bit tricky. I'd guess a bit of black pepper and a dash of sesame oil, which can be thrown into the water at the beginning. You'll need to adjust those to taste, of course.
Hydrogenated vegetable oil can be replaced with whatever you saute the veggies in and the sesame oil you threw on the rice.
Silicon dioxide is just an anti-caking agent to keep it from clumping up in the package, so you can skip it.
Salt, caramel, and vinegar solids: Your liquid seasoning (Maggi, Kitchen Bouquet) should provide these. You should, of course, salt it to taste though.
Answer: If you're Canadian and talking about the Chinese Fried Rice, see sourd'oh's answer. But if you're from the UK (or maybe other places?) and are asking about the Chinese Style Rice...
The UK site has an ingredient list!

Steamed long grain rice with sesame oil, soy sauce, garlic & ginger
Ingredients: Pre-steamed LOng Grain Rice (85%), Onions, Red Peppers, Sunflower Oil, Flavour, Sugar, Garlic, Ginger, Chives, Salt, Toasted Sesame Oil, Soy Sauce, Chili Oil, Spices

You've got some of the main ingredients you'll want there: soy sauce, sesame oil, red pepper, onion, garlic, ginger, and chili oil. By far the simplest thing would be simply to mince the red pepper, onion, garlic and ginger and toss them in along with all the other seasonings (soy sauce, sesame oil, and chili) to cook with the rice. For the chili, you could use some kind of ground chili powder instead; it's just there to add some heat. If you want this to be really easy, you could try paprika, onion powder, and garlic powder instead. The flavor will be a little different, though. (Ground ginger is very different from fresh, though, that's harder to substitute for.)
For "flavor" and "spices", you may not need too much, but I'm guessing you'll want some umami - you could try a bit of fermented soybean paste (or a premade Asian sauce containing plenty of it), nutritional yeast like sourd'oh suggested, or whatever your favorite is.
As for the rice drying out, I'm not sure. My best guess would be that your rice cooker is just going a bit overboard and overcooking your rice. That'd explain why adding more water doesn't help - it just automatically cooks it longer with similar results. If that's it, you might have to just try to time it and shut it off a bit sooner than it wants.
Answer: I am an engineer by training; if I can't give you an exact answer, I give you the information you need to do functionally the same thing.  As such, this is not a perfect answer, but it will help you get rice cooked (and edible) and it will help you make the dish in question.
Cooking Rice
I avoid rice cookers.  Every time I use them, the rice is always too dry.  This doesn't seem to happen for multitudes of roommates I've had who use them though.
When I make white rice (any length, but not arborio rice) I usually use 1 part rice to 2 parts water.  Bring the water to a boil, add the rice, cover it with a lid and simmer for 20 minutes.  Do not open the lid until the 20 minutes are up; rice needs pressure to cook correctly.  If it comes out dry or crispy, turn down the heat, and it doesn't hurt to add a little extra water.
Brown and wild rices will cook differently.  If you use the above cooking method on them, you'll probably have to throw it away (it can be salvaged, but it takes some knowledge).
Making Fried Rice
As far as Uncle Ben's Chinese rice goes...I've never had it.  I've started learning how to cook various Asian dishes at home simply because I love Asian food enough that I want to know anything and everything about it.
That being said, making fried rice from scratch isn't too hard once you figure out the sauces/flavors you want in it.  Frequently, I will use sesame oil instead of olive oil (I never cook with vegetable oil, particularly in a wok where temperatures are higher, which breaks down vegetable oil relatively easily).  Not only is sesame oil safer with high temperatures, but it also adds a distinctly Asian flavor.  After I'm done with all the cooking, I like to add a little teriyaki sauce, Hoisin sauce or Five-spice powder (also known as Chinese five spices) depending on my mood.  I've even had roommates who will throw in a splash of rice wine while it's cooking.  (These are not necessarily authentic uses for these flavors; I am not even Asian by association.)
Take left over rice.  If it's cold from the fridge, even better, although not necessary.  Put 1-2 tablespoons of sesame oil in a large frying pan or wok and add some heat.  Before the oil gets way too hot, put the rice in and try to evenly coat it in the oil while heating it up.  Add bits of cooked meat, tofu, vegetables, or whatever else you'd like in your fried rice.  Once the rice is warm enough (you can even brown it a little if you'd like) and the vegetables are cooked to your liking, take it off the heat and add any additional sauces you'd like.  Be sparing with the sauces though; you don't want to over power the flavor of the food and a lot of sauces are potent and chalk full of sodium (even MSG depending on where you get it).  You can even sprinkle some green onions and/or sesame seeds on top.
Uncle Ben's website also has a handful of Asian recipes, although most of them look like normal rice with something prepared served on top.
Comment: I'm not sure that this is functionally the same thing. You're focusing on fried rice, which is not what the OP is asking about. And while the question does ask about the rice drying out too much, it's definitely interested in the flavor, which as you say, you don't actually know. So this is a lot of good advice that's sort of related to the question, but I'm not sure how useful it is as an answer. (Note that whoever downvoted can come to those sorts of conclusions even if they don't know the "correct" answer - there's nothing wrong with downvoting.)


Why is it 'Elm' in 'A Nightmare on Elm Street'?

Question: What does Elm depict in A Nightmare on Elm Street? Does Elm tree represent something bad in the horror context?
Answer: Elm Street is one of the most common street names in the United States. If you exclude numbers (because numbers in a title are strongly connoted to having several in a series, whether it's streets or movies), the most common names are Park, Main, Oak, Pine, Maple, Cedar, Elm. So "Elm Street" has a "generic street" feel to it.
In fiction, Elm and Pine have traditionally dominated over the other tree names that are more popular in real life. Park is even above, but the word "park" has connotations (of nature, empty spaces, that kind of stuff) that "elm" doesn't have. This points towards Elm or Pine as a generic street name for a movie.
Comment: Also "Park" has connotations of Park Place in Monopoly and Park Avenue in NYC, which both lend "Park" a more upscale feeling that doesn't seem like just down the road from anywhere.
Answer: I've always seen it as just a very generic suburban name. There's a complete difference in tone and setting between (for example) A Nightmare on 5th Ave, A Nightmare in the Bronx, and a nightmare in peaceful suburbia.
To my knowledge there's nothing deeper to it, and my guess is that it just helps set the tone.
Answer: The wiki page says that maybe a 1968 student film project made by students of Craven's at Clarkson University inspired the movies. The student film parodied contemporary horror movies, and was filmed along Elm Street in Potsdam, New York.
I'm not sure if it's true or not, maybe it was just for the tone, like Stephan Muller said.
Answer: I was watching the video of the assassination of JFK tonight and the street where it happened was called Elm Street, which may bring back the memories of the people who lived in that time and for those who follow history.  Could be a clever way of marketing a movie title.
Comment: Rolling Stone, Oct. 30 2014, quotes Wes Craven: "Elm Street is the name of the street that ran past the book depository where Kennedy was shot. To me, it was where the innocent world ended."  The article is an oral history (that is, excerpts from longer interviews), and there's no context given.  We can assume, I think, that JFK was one of the reasons for the naming.  Note: Craven was 24 in Nov. 1963.
Comment: @professor_feather - You should post that as the answer
Answer: Craven decided to make A Nightmare on Elm Street after reading a series of L.A. Times articles about a group of teenage Khmer immigrants who, after moving to the U.S. from refugee camps, died in their sleep after suffering from disturbing nightmares.
There was also sleep paralysis experiments conducted in the 1970's by a doctor named Ravenscroft that lived on Elm Street.


How would one monitor an address for a transaction and 1 confirmation in PHP?

Question: I have a small PHP script with my static bitcoin address shown. When someone sends any btc to that address, how can I get the PHP script to check if the transaction has had 1 confirmation? Do I have to run something on cron to have it check every second? Or is there another elegant way to do this in PHP? Any examples?
Answer: Cron Jobs and 3rd Party API:
You could try with cron jobs, but I wouldn't run it every second, that's rather exhaustive. Maybe every 5 or 10 minutes, and then have it check the current total received vs the previous amount using a database.
$addy = "1somebitcoinaddress";
$bcinfo = json_decode(file_get_contents("https://blockchain.info/address/".$addy."?format=json"), true);
$balance = $bcinfo["total_received"];
$query = $db->prepare("SELECT previous_balance FROM address WHERE address = :addy");
$query->bindParam(':addy', $addy);
$query->execute();
$result = $query->fetch(PDO::FETCH_ASSOC);
$prevBal = $result["previous_balance"];
   if($balance > $prevBal){
   //balance changed, do something
   }

That way seems rather less than elegant though, and it's not instant.
3rd Party Webhook:
A better way would be with a webhook. Blocktrail offers a free webhook service, and you can even do it all in their UI after creating an account. Just sign up as a developer, then once logged in click on the webhooks tab and then create a new webhook that monitors your bitcoin address. It will ask for a callback url, that's where you provide a link to your PHP script to run.  When you provide the callback url I would add a secret to help prevent unauthorized calls like: yourdomain.com/callback.php?secret=12345
Your callback PHP script can look something like this:
$secret = "12345";
$verify = $_GET["secret"];
if($secret != $verify){
die();
}

$data = json_decode(file_get_contents("php://input"), true);

//get estimated value of transaction
$amount = $data["data"]["estimated_value"];
$confirm = $data["data"]["confirmations"];

if($confirm >= 1){
//do something, like send an email notification
$email = "email@example.com";
$sub = "New Transaction";
$body = "Amount: ".$amount;
mail($email, $sub, $body);
}

Bitcoind and Wallet Notify:
Lastly, there's run bitcoind and use walletnotify.
Make sure the address you are monitoring is imported into your bitcoind wallet. Set wallet notify up in your bitcoin.conf
walletnotify=curl https://yourwebsite.com/script.php?txid=%s

Now anytime there is activity on your bitcoind wallet your script will run, with the transaction id stored in a GET under ["txid"] and then you can do a script like:
require("easybitcoin.php");
$bitcoin = new Bitcoin("someusername", "somepassword");

$txid = $_GET["tx"];
$txinfo = $bitcoin->gettransaction($txid);
$details = count($txinfo["details"]);

for($i=0;$i<$details;$i++){
$check = $txinfo["details"][$i]["address"];
$addy = "1SomeAddressToMonitor";
    if($check == $addy){
    //activity on your address, do something
    }
}

Comment: Not sure if Blocktrail still operates as it used to, but I've personally used both https://www.blockchainwebhooks.com/ and https://blockcypher.com for webhooks - both work reliably and have free plans
Answer: Depending on your trust model there are various ways to do this. Firstly you may consider subscribing to a well known API service that notifies you of a transaction confirmation. That requires trust in a third party. If that is not suitable then you'll have to run a full node or spv node connected to the Bitcoin network and implement the interface to said node in your script.
Finally you can run this script of yours in background to prompt you of the transaction confirmation.
Comment: which api service is best?
Comment: Any block explorer API should do the job. (i.e. http://dev.blockcypher.com/)


Is wireless wake on lan possible?

Question: I don't really have much to add to the question in the title.. Is it possible to wake a computer via a wireless network card? (Assuming that a wireless card doesn't consume enough power to make putting it to sleep not worth it)
Answer: Yes it is, so long as you have a fairly new wireless card - Intel vPro branded machines  do have this feature. You could also use Intel AMT (which can be made available over Wireless) to power up machines.
Technically, WoWLAN support within the operating system needs to be present as well - Windows 7 comes with this kind of support.
http://www.intel.com/network/connectivity/resources/doc_library/tech_brief/wowlan_tech_brief.pdf
Answer: There is no technical block to WOL working with wireless, it's all down to whether it is implemented in the hardware and whether the wireless NIC is active when the machine down. For machines with built-in wireless NICs this is quite easily implemented but historically hasn't been for a number of reasons. One such reason is the fact historically only portable devices operated wirelessly and it would generally be considered quite undesirable to have the device woken up remotely. With more and more fixed systems using wireless we can expect to see an ever increasing number of such devices with WOL support.
Answer: Unfortuantly not.  Although you could get a wireless bridge so your computer actually sees ethernet yet your wireless bridge remains on so you could use wake on LAN.
Comment: This answer is not correct, or partially correct. As of Linux 3.0 WoWLAN is supported for certain network cards.
Comment: This is no longer true. There are many shipping systems that support Wake on Wireless LAN now.
Answer: The only solution I have is that any computer that needs wake on lan is wired to the network. You can send wake on lan over the wireless part of the network into the wired part but that's about it.

Is wireless wake on lan possible?


Recovering from Oracle host OS disk failure (options)?

Question: If an Oracle host OS has a complete disk failure and the host can be restored (assuming from a recent clone of the host OS disks) from backup, is it possible to then point the host to the existing Oracle datafiles on a SAN, as they were before the host disk was lost, and bring the database back up?  This is assuming we are using Oracle ASM and that there were no OS or Oracle configuration changes made on the OS between the imaging of the host drive(s) and the drive failure.
Answer: There is nothing 'magical' about Oracle and its recover ability. As long as you have your ASM metadata somewhere available, you can import it on a spare host and use that in a fresh installation to attach your SAN hosted files/LUNs and use that to continue your run on. Important is to know that all your data is in ASM and all your ASM disks are on the SAN. If you do happen to have some files containing application data are left on the Server that ran your databases before it crashed, it might cause an extra challenge.
Knowing that it is technically possible is one thing, the ability to perform such a recovery is an other one. The only way to gain that ability is to train for it. Each OS has some things that make it more or less easy to do. This is for any failure scenario.
Comment: "Knowing that it is technically possible is one thing, the ability to perform such a recovery is an other one." there speaks painful experience? :)
Comment: Yes, I have seen quite a few recoveries being messed up.
Answer: Yes, certainly, assuming your controlfile and spfile are in ASM too and therefore survive the failure intact.
This is the kind of thing you need to test in your own environment to give confidence you will be able to pull it off for real when disaster strikes - there really is no substitute for testing your DR procedures to make sure you are not making any invalid assumptions such as:

my tape really has data on it
I really am cloning the correct disks
my spare disks on the shelf really do work
etc etc


Run xampp on external hard drive on XP and Windows 7

Question: I've installed XAMPP on an external hard drive. My Windows XP desktop can run XAMPP fine from the external. But when I plug the external into my Windows 7 laptop, XAMPP doesn't run. I run the control panel. It says Install(er) Directory: No Installer Package Found. When I click Start next to Apache and MySql it says Apache / MySql started but the Running green message does not appear, or appears for a split second then disappears. Localhost is unavailable.
Does anyone have any ideas?
Thanks,
HR
Answer: Go to control panel>administration tools and select IIS Management Services. Once opened right click on the root of IIS (your PC's name) and select stop.


How to remove full disk encryption?

Question: I want to learn Linux so after lot of research I choose Elementary OS to start with. I installed it using USB as my primary and only os, after first time installation everything was fine and running smooth but I wanted to create partitions. But this time I choose to encrypt my disk. After installation every thing was fine but then I tried to create some folders in my drives and it was giving permission denied flags. I can create folders and copy paste files with root using terminal but its hard for me as non linux and first time user. I tried to complete reinstall but still can't get rid of it. I tried to create diffrent size of partitions but still no luck, I even installed windows 7 and cleaned all the partitions, but again after installing elementary os I can't get rid of it.
Please help me I really want to learn, and sorry for my week English.
Answer: It seems that the only way to remove disk encryption it to reinstall elementary os. Just make sure to back up all your files on an external drive before you do.
Sorry there is no other way :(

How to remove full disk encryption?


What are safe, effective practices for smoking salmon in a commercial smoker?

Question: We have been smoking salmon in an electric smoker (a Master Built) for about 6 months now, using a dry rub brine recipe containing salt, brown sugar, garlic and other flavorings (sometimes brandy, sometimes smoked red pepper powder).  We have tried to adjust the temperature and time to gain a safe, but moist and smoky tasting end result.  We have been using mesquite wood chips. I have read that the authentic way to smoke meat is very slow over a smoky fire and can last longer than what is possible in a commercial smoker. How can I achieve the best results with my smoker?
Comment: Great question!
Comment: Welcome. Good question. A link to the type of smoker you have might be helpful to some people who are familiar with smoking, but not the type of smoker you are using (like me). When you say commercial do you mean for consumers or professionals? Are you trying to hot smoke or cold smoke your salmon? Cold smoked would be like the salmon you'd traditionally put on a bagel or buy at the grocery store as smoked salmon.
Comment: Some what similar question with interesting book link in an answer: http://cooking.stackexchange.com/questions/6409/hot-smoked-salmon-on-big-green-egg
Comment: The type of smoker that I have is a Master Built. I used the recipe from http://www.salmonuniversity.com/rs_htss01_index.html
this site. I am hot smoking for hours, rather than for a short period of time as suggested by the answer given.  I wonder - does the brining for 24 - 36 hours  along with the 20 minutes of cold smoking suffice for adequate (safe) cooking time? Also, it seems that this type of smoked salmon would be very perishable. Roux is correct that I want more moist and succulent salmon.
Answer: I am projecting here, perhaps, but I think the question you're asking is "why doesn't my salmon come out moist and succulent like what I get at the store?"
A couple reasons.
First: you want to properly cure the salmon for at least 24 hours beforehand. 36 is better. To cure, you will need two whole sides of salmon (or one cut in half), with the skin on. Rub your cure into the flesh--so 2:1 salt:sugar, plus whatever other spices you care to use. The addition of brandy sounds lovely; I like tequila or a nice peaty/smoky Scotch myself, or maple syrup (but obviously nix the sugar if you're doing that). Place the two pieces together, flesh to flesh, optionally including herbs between. Wrap very tightly in plastic, completely sealed, bung into your fridge to let it cure.
Second: when the fish is cured, remove from the wrap, rinse off the cure.
Third: time to smoke. If you want dry and flaky, hot smoke--this seems to be what you're doing and what you don't like. Therefore, it's cold smoke time. The two basic ways to do this are either to add LOTS of trays of ice to the smoker itself, or to route the smoke through a cooler filled with ice and then back into your smoking chamber. A quick Google should provide you with diagrams for doing so.
Do not over-smoke. Fish picks up flavours quite readily, and will dry out if oversmoked, even if cold. Really for salmon I don't think you need much more than 20 minutes of cold smoke.
Comment: I will definitely try the shorter cooking time, along with a longer curing time, with your suggested steps,  the next time we smoke. I may try hot smoking at 185 - 200 as yossarian suggests at least once again. Then if I still get too dry a produck and  I feel adventurous, I will try cold smoking.  Thank you for your answer!
Answer: I think you are cooking your salmon for too long. When I hot smoke salmon, I'll do a 1 1/2 lbs salmon fillet at 180F to 200F for about 35 - 45 minutes. Depending on the size of the fish you may need shorter or longer. This is sufficient to get a nice smokey flavor and properly cook the fish. Cooking for hours will make the fish very dry. It sounds like your only real issue is the length of time you are cooking it for.
This assumes that you are smoking the salmon to serve and not as a preservation method to keep for a long period of time. I don't know how long this method will preserve the salmon, but my guess is no longer than normal cooking methods.
Of course, you may still prefer cold smoked, the end product is quite different. But I don't think it's time to write off hot smoked yet.
Answer: There is no need to cold smoke to get juicy salmon. The trick is to properly dry it after brining overnight. I put the salmon in my fish dryer till it has a nice pellicle forms, then it's ready for smoking.


What is the difference between "nevermind" and "never mind"?

Question: I never remember the appropriate use of either of nevermind and never mind. What's the difference and how can I remember?
Comment: Thank you all for the very helpful answers. I am chagrined to realize that I have been using "nevermind" incorrectly all these years.
Answer: Nevermind is an album by Nirvana. "Never mind" means don't bother with something.
Comment: There is no "incorrectly" for art.
Comment: So you are suggesting that Nirvana used the word incorrectly?
Comment: Same with the movie name `Inglorious basterds`
Answer: The only time I can think of that "nevermind" is written as one word is when it's used as a noun in the colloquial idiom "Pay me no nevermind" (or "Don't pay me no nevermind"), which as you might theorize means "pay no attention to me."
Comment: But "nevermind" in that expression is definitely dialectal. It's not in my dialect, and to me has a strongly American flavour.
Comment: I agree with Colin Fine. The single word form is an American colloquialism that really just means "attention". Slang often has superfluous negations, as in the relatively common phrase *it don't make no nevermind*.
Comment: many people use *nevermind* when typically *never mind* "should" be used. i suspect both will become accepted usages.
Comment: @FumbleFingers The OED attests [nevermind](http://www.oed.com/view/Entry/255396) as a noun dating from 1924, which it labels as *U.S. regional*. Here's its first sense: "A matter of interest or relevance; one's business or concern. Chiefly in negative contexts, as ***to make no nevermind***: to make no difference, to be of no significance."
Comment: Chiefly in negative contexts? I would have expected *only* in negative contexts.
Answer: As Robusto clearly pointed out, Nevermind is the name of a rock album written and performed by the late (and great, depending on who you ask) grunge rock band, Nirvana. However, the legacy of the term "Nevermind" doesn't end there.
Nevermind is also an album name written / recorded by a popular Philly (Philadelphia, PA) punk band named Clockcleaner. You can check it out at Amazon here. It is, unfortunately, out of stock. No doubt because the fan-base didn't warrant a huge number of units. I am sure the album can be found elsewhere.
Nevermind is also a video game produced by SCE Studio Liverpool. Back in "the day", the development company was named Psygnosis and it was a subsidiary of that development company, called Psyclapse, that originally wrote the game and released it in 1989. It is a 3D isometric arcade puzzle game, which actually got quite a following from Amiga-heads. The game was distributed on Amiga computers in the UK, much like Window's minesweeper. You can check out the game over at Retrogames.co.uk
Nevermind is also a song written by the Red Hot Chili Peppers. It appeared on the album Freaky Styley which was released by EMI in 1985. Now, THAT, makes me feel really old.
Nevermind is also a song written / recorded by a band named Violet and it appeared on their album, The Birthday Massacre. The album was released through Metropolis records in 2004.
Nevermind is also the name of a children's book written by Edward Irving Wortis (who prefers to be called Avi...just Avi). The eccentric man has written quite a few different titles in quite a few different genres.
Nevermind is, yet another, song name written / recorded by the underground cult group named Sonic Youth. It was the only single released from their 13th studio album called NYC Ghosts & Flowers. The album has an interesting history to it. The sound and production was very different from their norm. The interesting part is the reason for the "new sound". Evidently, the album was a direct retaliation to the theft of their instruments in 1999! The album is based on beat poetry and the music is riddled with crazy sound effects. They literally used anything they could get their hands on that would make noise.
And finally, for the boring answer. The term "Nevermind", when used in conversation, is a negation to attention and/or responsiblity. Some examples from dictionary.reference.com:

Pay him no nevermind.
It's no nevermind of yours.

It boils down to being the noun usage for the verb phrase "never mind", which originated in the early 1930's.
Well, this was my first answer. It was fairly fun, except for the editor messing up half the links. I had to fix them manually only to be denied and restricted to only posting two links. Sorry!
Answer: I was always under the impression it was a derivation/corruption from

Never you mind

and that it was idiomatic at best. Perhaps I've got the order reversed?
Comment: I believe that the "you" is unnecessary to make it a sentence. The imperative case doesn't need a subject to be correct because the 2nd person is implied, like when yelling "stop that!" The same applies to the phrase "never mind that."
Comment: @Joe I agree and concur, just that I always thought that the original form was the one I quoted and the asked about form was the one that came later, after the one I quoted.
Comment: Ah, I see what you're saying. :)
Comment: Seems unlikely, since "Never mind" is, as JoeCool says, grammatically normal. "Never you mind", on the other hand, though undoubtedly an idiom, is grammatically rather odd: it seems still to be an imperative (declarative would be something like "Never shall you mind") but "you" is anomalous there.
Comment: @Colin so if we can show that it is imperative with an unspoken `you`, does that help a non-native English speaker?
Comment: @drachenstern: I don't understand what you are asking. The imperative in modern English very rarely has an explicit "you" (and if it has, the "you" is usually stressed, marking an opposition: you as opposed to me or somebody else).
Answer: It's never mind. It would be written never-mind if it would be used as modifier.

? It's a never-mind talk.
Comment: I don't think I've ever seen that second use you mention. I have, however, seen it used as @Hellion mentions ("nevermind" as a noun in the colloquial idiom, "pay me no nevermind").
Comment: @Viktor Haag: That is why the sentence is preceded from a _?_; I didn't mean that _never-mind talk_ is a set phrase, or it is used.
Answer: You use "nevermind" in the same context that you would, alternatively, use "payattention."
Comment: I appreciate the wryness, but not quite enough to vote it up.  It's not the most helpful answer for someone who is struggling with English and just here to learn.  That said, I don't find this answer mean or objectionable either.
Answer: OK I realize this thread is really old by now, but I would like to add my 2¢ worth:
(I'm English-speaking American, raised mostly in California. (spent a couple years in Jolly Olde England, about age 3-5, Arizona, Washington State, and finally California around age 8.)
Anyhoo (!), here's my take on what "nevermind" means contrasted with my understanding of "never mind".
To me, "Nevermind" is used to convey that one wishes to withdraw just-uttered words, "Did you pick up the dry cleaning––?[notices dry cleaning hanging in bedroom doorway] Oh. Nevermind."
Another use, also to withdraw a question or statement, would be during a discussion or argument: "What the heck is that supposed to mean? ...Nevermind" (She realizes the futility in trying to get him to UNDERSTAND.)  Or, she could ask what that's supposed to mean, and HE responds, "Nevermind", meaning, "forget it" (this conversation is going nowhere), or "FORGET IT!" (you are too dim to grasp the concept).  I think stomping out of the room is required when the meaning is that last one.
On the other hand, I have only used the "never mind" (with a space) when making a statement such as, "When someone offers me cream for my coffee instead of milk, I never mind."  LOL.  I'm saying I've never seen it printed that way, but worth noting: while typing this post on my iPad just now, at some point I goofed up and auto-suggest suggested, both "never mind" and "never-mind", NOT plain ol' "nevermind".  So there's that.  I have to add that i saw the hyphenated one here today for the first time.
Oh, and by the way, "Don't pay him no nevermind" sounds horribly wrong, breaking the "Don't never use no double negatives!" rule.  LOL. I would say that is a sort of regional saying, while acknowledging people move from region to region all the time.  They tend to exchange their hometown habits for those of their new home, if they are there for very long, I would say.  People want to sound like the locals.
A more widespread way of saying the same thing, might be "Oh, Opie, your Pa didn't mean to hurt your feelings; pay him no mind."  I think Aunt Bea meant for Opie not to think about that particular problem, that it would be wasteful to use up energy worrying about a non-problem, if you see what I mean.  (for those of you who are not yet 100 years old(!), you could probably look up "Aunt Bea, Andy of Mayberry" on Google or YouTube, and see what that final example is about.)
Comment: I would downvote this if I could. One should use "never mind" for all the paragraphs except the last one.
Answer: It is said (in a 2001 biography of Cobain) that Nirvana's breakthrough 1991 album Nevermind was tentatively titled Sheep, as a joke on consumerism. As recording completed, Cobain grew tired of that title and renamed it Nevermind, as a metaphor for his attitude on life, and because it was a common misspelling of the phrase "never mind".
The word "nevermind" (spelled as one word) does not exist in the 2015 New Oxford American Dictionary, nor in the online American Heritage Dictionary or Merriam Webster.
Spelled as two words, the phrase means (from NOAD):
<code>1 used to urge someone not to feel anxiety or distress.
2 used in refusing to answer a question.
3 used to indicate that what has been said of one thing applies even more to another.
</code>
See also AHD's definition or MW's definition of the two-word version.


Why are hollow cathode lamps used for atomic absorption spectroscopy?

Question: In 1955, it was proposed that hollow cathode lamps are good emission sources for monochromatic radiation, and thus for atomic absorption spectroscopy (AAS).  In looking into the topic, I've read that "continuum radiation is not preferred in AAS." Why not?
Answer: Atomic absorption lines are very narrow.
For the Beer-Lambert law to be applicable, the bandwidth of the source should be narrow in comparison with the width of the absorption peak. Otherwise, the signal-to-noise ratio and the slope of the calibration curve would be low; the resulting sensitivity would be poor.
Continuous radiation sources use monochromators; however, even good monochromators have effective bandwidths that are significantly greater than the width of atomic absorption lines.
Therefore, the use of line sources with bandwidths even narrower than the width of absorption peaks is preferred.
Answer: One of the strengths of atomic absorption and other ionizing elemental analysis techniques using optical detection (ICP-OES is the main other one I know of) is that the optical absorption and emission properties at particular wavelengths are highly element-specific.
Despite this, the reasons for desiring monochromatic, element-specific AAS light sources are as follows:

Most detectors used in AAS / OES are broad-spectrum: they report just about any light that strikes them within their respective ranges of sensitivity, which usually span several hundred nanometers.
While the "fingerprint" wavelengths of each element are highly specific, they often sit at wavelengths close to those of other elements.
In AAS, any light that is passed through the sample has the potential to be absorbed by anything present in the sample.

Therefore, the use of a continuum light source in AAS would obliterate the analytical specificity afforded by the technique: anything present in the sample that absorbs light in the region of overlap of (a) the emission wavelength range of the light source and (b) the wavelength range of sensitivity of the detector would be recorded in a given measurement.
Comment: Yes, thanks but I need a more specific answer than the oliteration of analytical specificity by the continuum light source, for example: how does it have to do with the optical width ? Optical width of the absorbtion line is small, 10 times less than the optical width of the monochromator. Continuum sources in tiny spectral regions can affort not so much energy. I don't clearly understand these relations above I read in my book.


Why change in enthalpy is negative?

Question: I noticed that the enthalpy of the products of an exothermic reaction (bonds formed are stronger than bonds broken) is lower than the enthalpy of the reactants. Enthalpy equals internal energy plus $PV$. In a constant pressure environment, change in enthalpy equals to change in internal energy as $PV$ in constant. Internal energy consists of $E_k$ (kinetic energy) of particles and $E_p$ (potential energy) of bonds between particles. When stronger bonds are formed, $E_p$ is bigger. And the energy of the heat released to environment equals to the energy gained in form of potential energy, so why is the internal energy lower?
It would be helpful if someone shows me my mistake :)
Comment: Frequently the convention is $KE$ and $PE$ or if you have a physics bent, $T$ and $U$, instead of $E_{k}$ or $E_{p}$, respectively.
Comment: These are simply conventions. For more grasp, consider it like this: energy goes from high to low, that is energy flow is downwards, which means a negative enthalpy change
Answer: Bonds actually have negative potential energy. Think about it this way: in order to break a bond you have to expend energy so when a bond is created, energy must therefore naturally be released. Hence internal energy is lower.
Answer: <code>When stronger bonds are formed, *Ep* is bigger.
</code>
I take issue with this statement.  When stronger bonds are formed, the internal energy becomes more negative, not just "bigger".  It is this decrease in internal energy that makes the products' bonds so strong, since now the activation energy will be very large for a reaction to occur.
This link might help to explain: http://www.rsc.org/Education/Teachers/Resources/cfb/energy.htm
My favorite passage from this link is, looking at a one-step exergonic reaction: "The height of the peak from the reactants side is a measure of the strength of the bonds in the reactants and the height of the peak from the products is a measure of the strength of the bonds in the product. Thus we can consider the bonds in the product to be stronger than the bonds in the reactants."
If PV constant, this means Ek is the same.  Ep gets more negative.  So naturally enthalpy decreases (negative sign).
Answer: When energy goes off from a molecule, we take the sign as negative - this implies that the sign of PE which we are considering in formation of stronger bonds is MORE, albeit WITH NEGATIVE SIGN, hence, it is going down in energy coordinate.
The magnitude of change in PE, with formation of stronger bonds is more, this will lower the Internal Energy.
Answer: The change in enthalpy is negative in an exothermic reaction because energy is "lost" through the reaction (because there is more energy on the products side than on the reactants side).
Another way to think about this is by calculating the enthalpy before and after a reaction, for example - and this is a synthesis [and exothermic] reaction:
$$\ce{2H2 + O2  <=> 2H2O}$$
The ΔH [change in enthalpy] is -484 kJ (you can calculate this using standard enthalpy of formation numbers).
You can also think back to the definition of enthalpy - disorder: When two molecules that were 'freely' moving around, come together, there is less disorder [so the disorder in the system has decreased, and consequently is negative].

Why change in enthalpy is negative?


Odd birthdate surprise

Question: Last year, just before my birthday in February, I noticed something unsual. The last two digits of my birth year were the same as my age. How old was I then and was this an unusual occurrence?
Comment: When you say last year I assume you mean 2013?
Comment: Yes, my age prior to my birthday in 2013
Comment: this has a name: Beddian birthday (go ahead, search on it) after Bobby Beddian http://markbialczak.com/2014/03/19/fallen-firefighter-bobby-beddian-discovered-the-magical-match-of-birth-year-age/
Comment: Wow that was an interesting story! And I am pleased to find someone else was fascinated with the age/year quirk. Also that it now has a name. Thanks Bobby Beddian. http://markbialczak.com/2014/03/19/fallen-firefighter-bobby-beddian-discovered-the-magical-match-of-birth-year-age/
Comment: I'm kind of sad that this won't happen to me until 2086, and that I don't even know if I'm going to live that long.
Answer: Generally, people born in $1900 + n$ will have this birthday in the year $1900 + 2n$, when they are $n$ years old. The same can be applied to any century. You'll notice this is an even number; the year in the question is odd because you noticed this just before your birthday. That is, the Beddian birthday (see Kate Gregory's link in the quetion) was in 2012, but you noticed the phenomenon in the next year, 2013.
Working backwards, if this year is $c + m$ (where $c$ is a century such as 1900 or 2000 and $m$ is  even and less than 100), those with a Beddian birthday this year were born in $c + \frac{m}{2}$ or $(c - 100) + \frac{m + 100}{2} = (c - 100) + \frac{m}{2} + 50 = c + \frac{m}{2} - 50$.
You can obtain the second option by "going back" a century, making $c - 100$ the new century part and $m + 100$ the new "$2n$" part from the first paragraph. Since $m < 100$, $\frac{m}{2} + 50 < 100$, and so the year is valid. You can't go back another century, or else the "$m$" portion will be more than two digits, which wouldn't make any sense.
Thus, for the year 2012:
$$
c = 2000, m = 12\\
\text{birth year is } \boldsymbol{6}=\frac{m}{2} \text{or } \boldsymbol{56}=\frac{m}{2} + 50
$$
As Rob Watts notes, you're more likely to have been 56 than 6. Additionally, this happens every even year for those born turning $(year ~mod~ 100)/2$ and the same age plus or minus 50.
Comment: Well that was a very thorough analysis of probabilities. Impressive.
Answer: You were born in either 1956 or 2006 and were 56 about to turn 57 or 6 about to turn 7. I'm guessing that you're not 8, so you were 56 about to turn 57.
As for how unusual it is for this to happen, it is very common - everyone born in 1956 and 2006 (except for those born on January 1st) were all 56 and 6 respectively on January 1st, 2013. It is a little less common toward the end of a century though. For example, in 1989 people who were 44 or 94 could have noticed the same thing. The only reason it was less common then is because fewer people live to be 94.
Comment: I should live 66 more years if I want it!
Comment: Yes. I was born in 1956. I hadn't thought of the other option!

Odd birthdate surprise


What is difference between Stack Overflow and Pro Webmasters?

Question: What kind of questions that matters about web(HTML, CSS, PHP, SEO, CMS, ... ) should posted at Stack Overflow and what at Pro Webmasters?
Comment: Have you read the FAQ for both sites?
Comment: @TheEstablishment Yes. I have, but i didn't see clear difference between explanations.
Answer: I bumped into this the other day where some folks were trying to close a question about CSS and have it migrated to Pro Webmasters.
The FAQ states:

If your question generally covers the operation of websites which you
  control, then you're in the right place to ask your question!
Please note that if your question is about detailed HTML, JavaScript,
  or CSS coding, it might be a better fit on Stack Overflow.

As a moderator, these are some guidelines I work with based on my interpretation of the FAQs and site-specific meta discourse:
CSS, HTML, Javascript, general markup are basically "Domain Specific Languages" and so can be considered as programming languages.
SEO however is on-topic for Pro Webmasters. Pro Webmasters is geared towards running a site as a "Webmaster/Administrator" i.e. site operations but not the minutia of the code or markup itself.
CMS questions are tricky. We already have two sites that deal specifically with WordPress and Drupal questions and answers so where to ask these questions is reasonably clear cut.
Other CMS systems where you have questions that are programming related should probably be asked on Stack Overflow.
CMS/E-Commerce App questions about the operation, administration and maintenance of your application are a bit of a grey area.
For example, questions about how to set tax rates, managing stock or maintaining content are very application specific and I'd say probably don't have a home anywhere on the Stack Exchange network at this time. There have been a number of Area51 proposals for different CMS applications but none of these on their own have gained enough traction to reach any reasonable critical mass to survive. See: CMS/BLOG proposals MERGER.
On the other hand, questions about sites that happen to have a CMS or E-Commerce application where you're asking an "operational" question about the site overall are probably on-topic.
The bottom line is, check a site's FAQ first. Then if you still can't decide, don't hesitate to ask on a site's meta about whether a question is acceptable.
Answer: From what I understand, StackOverflow is for the programming (actual development) for the sites, and ProWebmasters is for when the site is up-and-running. Don't forget there are other semi-related web SE sites, like WordPress Answers.


Question on energy mass conversion

Question: I have a question regarding the energy-mass conversion. Well, when a particle starts moving with a speed comparable to that of light, its (relativistic) mass increases that means some matter is created and that too of the same particle...energy being converted to mass is ok but how does energy perceive what atoms it has to form? Say I take a stone to a high speed, then constituents of stone is formed. And if I perform same thing with another substance, its constituents are formed..How? Energy can be converted to mass but a mass of what? Does that mean we can create matter of any desirable substance?
Comment: There is no matter created. A single particle, say an electron, at high speed will remain a single electron.
Comment: The mass $m$ of a particle is constant. It does not depend on the speed of the particle. For massive particles, the energy and the momentum depend on the mass and the speed : $E = \dfrac{mc^2}{\sqrt{1- \dfrac{v^2}{c^2}}}, \vec p = \dfrac{m \vec v}{\sqrt{1- \dfrac{v^2}{c^2}}}$
Comment: This question (v2) seems spurred by a confusion between rest/invariant mass and relativistic mass. See e.g. [this](http://physics.stackexchange.com/q/8610/2451) Phys.SE post, and a couple of paragraphs down on [this](http://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence) Wikipedia page.
Answer: The basic constituents of matter are the components of the Standard Model.

These elementary particles have a fixed mass, called rest mass always. It is given by the measure of the four momentum vector, in analogy to the length of a three vector
 , in units where c=1
No matter how much energy is given to them, their rest mass is an invariant of the Lorenz transformation.
The relativistic mass involved in the famous E=mc**2 is a concept that describes the inertial behavior of a fast moving relativistic particle, but is confusing when one does energy budgets, answering "how" new particles can form.
If you look at the table you will see that the basic elementary particles are accompanied by quantum numbers. In any interaction some of them have to be conserved. Particularly in the strong interaction all of them have to be conserved, and together with conservation of energy and momentum the allowed particle creation channels are opened.
To form a proton, the quarks in the primordial quark gluon plasma have to be of low enough momentum to fit in the solution that characterizes a proton. To form a hydrogen atom the electron has to have low enough energy so that it can bind with the proton. Sequentially up to higher atomic number nuclei.

Does that mean we can create matter of any desirable substance?

Let us ask a simpler question. In order to conserve all the quantum numbers not only energy has to be taken into account but also momentum conservation at the center of mass. Is it possible to create a hydrogen antihydrogen pair from gluon gluon scattering, for example?  All quantum numbers are conserved together with momentum conservation. Theoretically it can happen, but the probability is very very low as the electromagnetic constant enters in powers , because the hydrogen and antihydrogen have an electron bound to the proton. So the electron and positron have to be created coherently with a proton antiproton at the exact energy levels for binding into a hydrogen and antihydrogen.
We create antihydrogen in the lab by cooling antiprotons and letting them capture positrons. Hard though it is, the probability of making it is finite and people have succeeded to do it.
In conclusion , converting energy to mass can only happen if all quantum numbers of elementary particles are conserved and this has a measurable probability to happen in simple two body interactions, and usually in particle antiparticle pairs.
Answer:
"how does energy perceive what atoms it has to form"

May i correct you here energy will not create new matter(or new atoms as you mentioned) in the case you mentioned. It will just increase the mass of the existing matter. For if you accelerates an electron from rest to a speed comparable to speed of light what you will get is the same electron with an increased mass. Similarly if you accelerates a stone to a speed comparable to $c$ the number of atoms in the stone will remain the same but the mass of each atom will be increased.
If you are interested in creating matter you should consider something like pair production. It would be more precise to use the word relativistic  mass if you consider mass as an amount of matter
Comment: @Nandan I didn't really got you.There's an adequate explaination on wikipedea. e.g read the last lines of the first paragraph written here:http://en.wikipedia.org/wiki/Mass#Special_relativity
Answer: If you accelerate a stone to relativistic speeds, no new atoms are created in the stone. There is constant amount of atoms. If new atoms were created, that would mean than these atoms have to disappear when you decelerate the stone. And now think about someone accelerating together with the stone. From the perspective of accelerating observer, the stone does not get heavier. So from their perspective no new atoms would be needed.
The quantity that is increasing during acceleration is the total energy. Relativistic mass (that's the "mass" which is increasing) is in fact nothing else but the kinetic energy. The amount of atoms is unchanged. The kinetic energy can be calculated into kilograms with the relation E=mc^2, but such result is not really useful. What matters is the energy. That's why the concept of relativistic mass (which increases with speed) is not used. Only the rest mass (whcih does not change with speed) is important.
The increase of energy manifests itself as higher resistance to further acceleration, which somehow vaguely relates that to mass (inertial mass namely), but using the concept of relativistic mass is not useful. The total energy is what matters.

Question on energy mass conversion


Shower base installation: screws through the flange, or not?

Question: I'm about to install this acrylic/fiberglass shower base. It's going on top of a wooden subfloor, with 2x4 walls behind it, then tile on the walls. The  instructions that came with the base say to lay down a bed of mortar and set the base on top of it, with the flange right against the studs; they don't say anything about screwing the flange to the studs, but I've seen it done. Would the screws be overkill?
Answer: I wouldn't put holes there unless you carefully waterproof them and are 100% sure they won't show. Some panels don't sit down tight on the bottom. You'll also want to be sure not to crack the flange if it's not tight. Use shims if needed.
The mud base, floor caulk and plumbing combined will keep it from moving.
Comment: Pans designed to be fastened at the lip usually have slots (to allow movement without cracking) and recommend galv. roofing nails not driven tight. Waterproof wall membrane to lap over the lip and fasteners.
Comment: If clamping to the wall would be necessary probably it would be stainless steel screws driven above the flange so the head of the screw would engage the lip, but even this might be a stress point leading to cracking. Unless the mfgr says to do this, or some expert who has had experience with these bases says to do it, then I would not do it.
Comment: The flange will be completely hidden by the tiles and caulk, so yes, I'm sure the holes wouldn't show. I was mainly worried about structural integrity, and the possibility of cracking the base. Following the manufacturer's directions is usually the best option, I just wanted to see if anybody has a different opinion.
Answer: If you have specific questions about the installation of a specific product, and the installation instructions do not address your question, the infinite wisdom of these fine random people on the internet is not the place to start.
Call or email the manufacturer and ask them for guidance.
In general, products without factory pilot holes will use a clip for anchoring, or they will use a shower surround that captures the lip and provides the anchoring.
Drilling holes in that lip will invite water into the wall cavity.


Is there a chat room for Wordpress.stackexchange.com?

Question: Some stackexchange sites like StackOverflow have chat page. Does WordPress.stackexchange.com have something similar?
Answer: As soon as I posted that I found the link in the footer. In StackOverflow the chat link is on the right side column.
Link to chatroom.
Comment: we mostly chat in The Loop, the other chatrooms are mostly just people who had lots of comments and were prompted to move discussion to chat by the site
Comment: The link can also be found on the site-switcher from the top-right SE icon.


Is it possible that Kakashi and Obito are brothers?

Question: Is it possible that Kakashi and Obito are brothers? Neither of their mothers are mentioned, and it would explain how Kakashi awakened the Kamui after his eyes were taken.
Comment: Also, Kakashi and Obito are really close in age, so it would have been hard for the same woman to give birth to them around the same time.
Comment: Just because their moms are not mentioned, does not mean anything. Also Obito's mom has been mentioned, a little, by his grandmother which said she died alongside her husband, Obito's dad, while protecting him. While on the other hand we know nothing whatsoever about Kakashi's mom, so I guess we either have to assume she died while giving birth to him (that or she died with something else), or just left Kakashi and Sakumo, Kakashi's dad. Which I'm pretty sure she wouldn't do.
Comment: The only reason Kakashi's Mangekyo awakened was because Obito awakened it when Spoilers:         he saw Rin die.
Answer: No, they are not brothers. Obito's sharingan has the ability to use Kamui. Since both Obito and Kakashi share that sharingan, both were able to unlock Kamui.
Obito gives Kakashi his left eye, which has the ability to use long range Kamui. Obito gets to use his right eye, which can only use short range Kamui. That's why Kakashi was able to unlock Kamui. (Specifically the long range variant).
Also, Kakashi is from the Hatake clan, while Obito is from the Uchiha clan.
Comment: Are there any references to long range and short range Kamui? Kakashi is able to use Kamui both at long range (Ex: against Deidara) or even short range (Ex: against Pain and Madara). I think Both are capable of using Kamui at both ranges.
Comment: @VarunRao Obito is best known for using kamui on his own body. You can read about the variations of kamui here:http://naruto.wikia.com/wiki/Kamui
Comment: Wow!! Thanks for the information. I did not know that
Answer: Since Kakashi is from Hatake clan and Obito is from Uchiha clan so I don't think they can be brothers.
Also in wiki it states that :

Kakashi teaches the importance of teamwork, a lesson he, like the
  Sharingan, received from his childhood friend, Obito Uchiha.

So its pretty much clear that Obito was Kakashi childhood friend not more than that.
Answer: No, they are not brothers. Obito is from the Uchiha clan, while Kakashi is from the Hatake clan.
Furthermore, them being brothers would not explain why Kakashi was able to activate his Sharingan or Mangekyou.
Sharingans work even after having been transplanted, and that is why Kakashi was able to use his — however, it is worth noting that it puts much more strain on him than it would on a "native" Sharingan user. As with any other Mangekyou users, Kakashi's and Obito's Mangekyou were awakened once they experienced great loss of someone close to them (Rin, in their case) — it has nothing to do with them being related by blood.


Host multiple domains with Apache

Question: Is there a way to host multiple domains with Apache web server without making any changes to the DNS server?  I have full control over the Apache server and no control over the DNS server.
Answer: Do the DNS records for those domains all point to your Apache server?  If so, then the answer is yes.  If all of the domains should serve the same content, then there's nothing more you need to do.  If you want them to serve different content, then you need to set up name-based virtual hosts.
If the domains don't resolve to an IP address of your Apache server, then you need the cooperation of the servers where they are currently pointing to, to proxy (or failing that, redirect) the requests to your server.  Otherwise, your server will never see the requests, and there's nothing to be done.
Answer: Figured it out.  I use django with mod_wsgi, and this is how I ended up getting it to work
<code>NameVirtualHost *:80

<VirtualHost *:80>
ServerName b2m1.int.---.com
WSGIScriptAlias / "C:/portal/django.wsgi"
Alias /static/ "C:/portal/inspections/static/"

<Directory "C:/portal/">
Order deny,allow
Allow from all
</Directory>
</VirtualHost>

NameVirtualHost *:8000

<VirtualHost *:8000>
ServerName b2m1.int.---.com
WSGIScriptAlias / "C:/dailyplanning/django.wsgi"
Alias /static/ "C:/dailyplanning/plans/static/"

<Directory "C:/dailyplanning/">
Order deny,allow
Allow from all
</Directory>

</VirtualHost>

NameVirtualHost *:8080

<VirtualHost *:8080>
ServerName b2m1.int.---.com
DocumentRoot "C:/portal/redirect/"

<Directory "C:/portal/">
Order deny,allow
Allow from all
</Directory>
</VirtualHost>
</code>

Host multiple domains with Apache


Is there a difference between cold brewing in the fridge vs room temp?

Question: I use a Toddy and wanted to know if there is a difference and what in cold brewing and placing it in the fridge for 20-24 Hours versus the counter at room temp (65-70 deg)?
Answer: Well if you put it into a fridge, all you are doing is slowing down the process. Cold brew is one of the hardest things to mess up if you ask me, so I would just brew it room temperature. If you extend a brew process in time - than you generally have a larger interval of time where the coffee will still taste great, but since it's already hours long I really wouldn't worry about it. All the shops i've ever worked at brew room temperature. Hope this helps!
Comment: This is supported by the [Seattle Coffee Gear temperature test](https://www.seattlecoffeegear.com/blog/2015/05/20/cold-brew-temperature-test/). Spoiler alert: they liked the room-temperature brewed batch better. It seemed to extract more (darker in color, anyway) over the same period of time, and was described more positively as stronger and more full-bodied than the fridge-brew.
Answer: I don't really think there is a big difference in terms of taste, but the brew process time will be slower in fridge mode.


How can I determine if a CA Cert can be used for DPI-SSL

Question: I would like to know if a CA Cert I installed can be used to perform DPI-SSL decryption without my knowledge. Would there be any indication? Can you look at the cert properties to determine if it can be used for this purpose?
Answer: DPI-SSL works by doing a man in the middle attack: it frames the right server by dynamically generating a fake certificate for that server. This works only if the corresponding CA (the one which issues the fake certificate on-the-fly) is "trusted" by the client. By definition, this CA "looks like" any other CA It is different from the "normal" CA only in that the private key is owned by some system which does the DPI, but this is not written on the certificate itself.
What you can do is compare the certificates that your machine trusts with that from the "root CA" store of a generic desktop system; compare the "thumbprints" (these are the hash values computed over the root certificates themselves). Presumably, the default root CA are not involved in DPI; any extra certificate is then a potential suspect.


Making a delayed havdallah from Motzei Shabbos on the night of Rosh HaShanah

Question: The Biur Halacha in Siman 299 brings an interesting opinion from the Magen Avraham. If someone was fasting (and had taken on to fast for a few days) and wasn't able to make havdallah Motzei Shabbos and when it came "lyl gimmel" it was also Rosh HaShanah the Magen Avraham says that the person should make havdallah on one cos and kiddush on another cos (and not to make them on one cos.) The Biur Halacha has a very difficult time with this and says how can someone make the bracha of havdallah and end off "bein kodesh l'chol" when it's right now Yom Tov? To say bein kodesh l'kodesh he says one also couldn't say. The biur halacha leaves this din b'tzrich iyun gadol. Were there any other poskim that discussed this Magen Avraham and perhaps offer an explanation or discuss (and possibly answer) the questions of the Biur Halacha?
Comment: I've tried to make the title more specific. Question, though: is this only when somebody has been fasting? What about if somebody was just sick?
Comment: related https://judaism.stackexchange.com/questions/86034/
Answer: Rav Dovid Feinstein was asked this question and he answers in the sefer L'Torah V'Horaah pg.28
The person asked what should he say since the Biur Halacha ends with a tzarich iyun.
Rav Dovid answered ,it seems to be reliant on a machlokes Rishonim.Is it a tashlumim or do we say a chyiuv is on him still.He brings the Rosh from perek mi shameisu siman 2 that one who is a onein on motzai shabbas does he say havdsllah or not.The Rosh brings the Ri who says that it is a tashlumim and if he was patur then he doesn't say it,the Rosh is maskim to this.However,he brings the Ram who says he is obligated in havdallah and the Maadnei Yom Tov os 3 holds the time is extended up until the third day and the Mechaber paskens in YD 341:2 that he should make havdallah.In the Mishna Brurah siman 71:1 its mashmah a little that he paskens not to say havdallah even though from the מלבושי שרד its mashmah lav davkah.
Rav Dovid then writes ,it seems to me that if it is a tashlumim then its shayich to say Ben Kodesh lchol but if the chiyuv is straight then it should be Ben Kodesh lkodesh and the issur of eating is still on him .The MA writes in 299:17 that it is assur to eat all times until one makes havdallah.It seems to me that is not like the MA ,but what can we do,since the MA paskened this way we have to go like him.
wrote from my phone,please fix mistakes,and read inside.
Comment: This is answered in the seder Vedbartah Bam shailos and tshuvos siman 81 pg.167


Why the surname 유 (Yoo) is translated as 刘 instead of 余 or 于?

Question: 유창혁 (Yoo Changhyuk) is translated as 刘昌赫 in Chinese. Is there any reason that 유 is translated as 刘 instead of 余 or 于?
Comment: FYI: In South Korean dialects, if a word starts with **ry-** it gets shifted to **y-**, that is, the「ㄹ」sound gets omitted. So, in North Korea,「劉」is pronounced as「류」(**Ryoo**).
Answer: I don't think it is translated as much as it is that every Korean family actually has their own Hanja.
According to Wikipedia's List of South Korean surnames by prevalence

유

can be one of four Chinese characters:

柳, 劉, 兪, 庾

Most Koreans have Hanja names & they would certainly know which their surname is.

If you check out Wikipedia's Appendix:Korean surnames you can see that

여

is the Southern Korean equivalent of

余

while

우

equates to

于, 禹
Answer:
Do you know what it is? It is a Korean newspaper printed in 1920. It is printed in Korean language, not Chinese. The Chinese characters in that newspaper are actually "Korean Chinese characters", known as hanja in English. Hanja is still the official script of Korean language, alongside Hangul.
Hanja has not been abolished in South Korea, but few Korean people use it today. Most of Korean people only write Hangul today, except their names. Korean names are still in Hanja.
Have a look at South Korean identity cards. Korean names are still printed in Hanja. As a result, we never translate Korean names into Chinese. We only copy the Chinese characters into Chinese.

Therefore, the real question should be:
Why is the Chinese character 刘 (劉) pronounced 유 (yoo) in Korean?

Why the surname 유 (Yoo) is translated as 刘 instead of 余 or 于？


What is geckodriver? How to use it in Selenium Webdriver?

Question: What is geckodriver? How to use it in Selenium Webdriver?
Comment: Good question. Did you try search that on the web?
Comment: I was searched, But  still confuse between geckodriver and Marionette.
Comment: So it would be good if you put up an appropriate question. Current question is likely to get closed!
Comment: This maybe?  https://www.youtube.com/watch?v=vTS917o7_f8
Answer:
GeckoDriver:

A Proxy for using W3C WebDriver-compatible clients to interact with Gecko-based browsers. Geckodriver provides HTTP API described by the WebDriver protocol to communicate with Gecko browsers, such as Firefox version above 47.

Marionette:

Marionette (the next generation of FirefoxDriver) is turned on by default from Selenium 3. Even if you are working with older versions of Firefox browser, Selenium 3 expects you to set a path to the driver executable by the webdriver.gecko.driver
For more details on Marionette click here.

Note: If you are using Selenium version below 2.53, you don't need gecko additional driver.

If you are not doing so, it will throw exception:
"java.lang.IllegalStateException: The path to the driver executable must be set by the webdriver.gecko.driver system property;"

How to use it?

If you are using Selenium 3.0 and you are running your test on Firefox; in this case, you have to download and set the path of the geckodriver as like chrome in selenium 2.0.
System.setProperty("webdriver.gecko.driver","path of/geckodriver.exe");
WebDriver driver = new FirefoxDriver();

with RemotWebDriver:
System.setProperty("webdriver.gecko.driver","path of/geckodriver.exe");
DesiredCapabilities capabilities=DesiredCapabilities.firefox();
capabilities.setCapability("marionette", true);
WebDriver driver = new FirefoxDriver(capabilities);

Comment: +1; It looks like the perfect answer for this question with proper explanation and desired code to launch firefox using Selenium 3.0.
Answer: I'm not sure if you had googled it before you post your question here.
Anyway, first you need to know what Gecko is. Gecko is a web browser engine used in many applications developed by Mozilla Foundation and the Mozilla Corporation. Where Gecko Driver is the link between your tests in Selenium and the Firefox browser.
GeckoDriver is a proxy for using W3C WebDriver-compatible clients to interact with Gecko-based browsers, in this case, Firefox.
As Selenium 3 will not have any native implementation of Firefox, we have to direct all the driver commands through Gecko Driver.
How to use it in Selenium? Check this link out.
Answer: Lot of article are present on internet regarding GeckoDriver and Selenium 3.
Gecko is a webbrowser-engine used in many applications developed by Mozilla Foundation and the Mozilla Corporation
Gecko Driver is the connection between your tests in Selenium and the Firefox program. compatible clients to interact with Gecko-based browsers i.e. Mozilla Firefox for this situation. As Selenium 3 won't have any local usage of Firefox, we need to direct all the driver through Gecko Driver. Gecko Driver is an executable record that you need in one of the framework way before beginning your tests. Firefox program actualizes the WebDriver convention utilizing an executable called GeckoDriver.exe. This executable starts a server on your system. All your tests communicate to this server to run your tests. It translates calls into the Marionette automation protocol by acting as a proxy between the local and remote ends
I had created some demo on Selenium 3 using Gecko driver using Java. Github code link is provided in blog. Check out my blog for demo code
Comment: Can the manual download be avoided somehow? On Windows, we have `System.setProperty("webdriver.gecko.driver", "C:/Users/asst/Desktop/geckodriver.exe");` and this is not portable at all.


Shnayim Umeya - mi yodeya?

Question: Who knows one hundred two?
Please cite/link your sources, if possible. At some point at least twenty-four hours from now, I will:

Upvote all interesting answers.

Accept the best answer.

Go on to the next number.
Answer: The number of chapters in Kav HaYashar. The word "kav," with a gematria of 102, hints to this fact. It also corresponds to the gematria of the author's first name, "Tzvi." (His second name, "Hirsh," is hinted in the word "HaYashar," which has the same letters.)
In the same vein, Rabbeinu Chananel (cited by Rosh, Eruvin 4:2) says that the rule which states that the halachah follows R' Eliezer ben Yaakov because his teachings are "kav venaki" (few in number but pure), is actually limited to 102 -- "kav" -- of his teachings.
Comment: Some more info: http://en.wikipedia.org/wiki/Kav_ha-Yashar
Comment: Similar: http://judaism.stackexchange.com/questions/8191.
Answer: 102 are the years that Lubavitcher Chassidus was headquartered in the town of Lubavitch (Cheshvan 5574/1813 - Cheshvan 5676/1915).
R' Shalom Dovber Schneersohn (the then Lubavitcher Rebbe) commented, upon his departure, that this number represents the numerical value of the word יסוד (foundation, basis) plus the 22 letters of the Hebrew alphabet, symbolizing the idea that "Lubavitch, during these 102 years, built a strong foundation with the 22 letters."
(Likkutei Dibburim, vol. 1, pp. 29-30)
Comment: I believe so, yes. (The yeshivah actually remained in Lubavitch a couple of more years; it moved to Kremenchug in the summer of 1918.)
Comment: And R' Yehuda Chitrik zt'l was the last remaining Lubavitch chossid who'd studied in Lubavitch, no?
Answer: Avraham was 102 at Yitzchak's weaning party
Answer: Yefes was 102 when Shem begat Arpachshad
Answer: Eved Hashem(yukeyvavkey) is 102 and the word emuna(alef mem vav nun hey) is 102 thus we learn from this that a true eved hashem will and must have emuna.
Answer: Nusach S'farad says psalm 27 102 times a year as part of the prayer services: during shacharis and mincha daily from 1 Elul through Sh'mini Atzeres.
I'm told Nusach Haari also says it 102 times: at shacharis and mincha from 30 Av through Hosha'na Raba.

Shnayim Umeya - mi yodeya?


May one use the name of an avodah zara?

Question: What is the source for not using the proper name of an avodah zara? How far does this halacha extend? For instance if thousands of years ago people worshipped an avodah zara named "XYZ" but no longer do so, may I use that proper name when referring to it? What about if only a select few people nowadays actually worship something as avodah zara, may I not use its proper name (let's say 7 people decide to worship, for example Bill Cosby, would I no longer be able to use his proper name even though the amount of people that worship him is miniscule)?
Comment: Adding in a source for your premise that one may not use the name of an _avoda zara_ will improve the quality of your question.
Comment: masechet avodah zara uses names for idols and idol-ologies that are manipulations of the names (turning them into insults) such as kulis to kilus. I knew that choosing to learn A"Z this summer would pay off.
Comment: [Shemot 23:13](http://www.mechon-mamre.org/p/pt/pt0223.htm#13)
Comment: @Dan ...in this world and the world to come! But what's the surprise? We say that every morning!
Comment: I don't have a source right now, but any Avodah Zarah that is mentioned in the Torah is allowed to be said. - Also, as an example, I know people who say Harei Krishnif, or something like that.
Answer: There is a prohibition against mentioning the name of a foreign deity. (Shulchan Aruch, Yoreh Deah 147).
However, according to the sources cited there by the Gra (YD 147:2), the prohibition  only applies if the name was given for the purpose of idolatry. If the name is an ordinary name which has no inherent implication of divinity and which was not given for the purpose of deification, then there is no problem with using it.
In a very interesting teshuva, R' Esriel Hildesheimer details two additional limitations on the prohibition:

The prohibition applies only to speech, not to writing.
The prohibition does not apply to speech for the purpose of Torah study or psak halacha.
Answer: I once was told I couldn't even spit at an idol, lest it's mistaken as a form of service. Better to err on the side of caution rather than look like an idolater.
Comment: Spitting (which might be a form of avoda zara - thus forbidden) and using the name of avoda zara are different things. It is not clear from your answer why one would apply to the other

May one use the name of an avodah zara?