Coffee will make you lean?

Question: I'm 25 , Coffee lover, I always start my day with my coffee like many of you. I will have at least 3 cups of coffee a day. I am very lean but not weak. Few people of my circle and some internet articles says that coffee will make us lean even though we eat healthy. Can someone throw light on this ? Is it true?
Answer: I think caffeine can´t make you lean if you eat well & health food, and of course doing some exercises, gym, jogging etc. Caffeine is most consumed psychoactive drug, legal of course(more at wiki). Also, I like to start day with warm cup of coffee. :)
Btw, about year ago I use caffeine pills (200mg pure caffeine per pill , it really have effect, adrenaline increases, you feel energy). Than and today, when I don´t consumed this pills anymore, I have almost same weight.
A suggest you to eat food which contains proteins, avoid too much (white) sugar etc.
Answer: Correct. It (caffeine) can make you lean. But just a bit. It increases the overall speed of the metabolism, thus the body burns more fats. However, I don't think its effect is overwhelming.
Also, think of other ingredients in coffee.
Each cup of coffee includes its own fat and hydrocarbons from the beans even if you don't add any cream and sugar into it. I didn't mention the fancy toppings, here.
Here you can find a quick Google search result on caffeine and metabolism.
Please, check other related discussions on health tag.
Comment: Straight coffee (black) has 1 calorie.  It's misleading to say it "includes its own fat and hydrocarbons".  It's also misleading to say it "can make you lean" even with the waffle statements "just a bit" and "effect is [not] overwhelming" - there is no proven connection *at all* between caffeine intake and weight.
Comment: @Lyrl Coffee, of course includes hydrocarbons and fats. That's why we extract some of its aroma to taste it. [This paper](http://link.springer.com/article/10.1007/s10661-005-3547-7) refers the hydrocarbons it contains and [this one](http://www.sciencedirect.com/science/article/pii/S0963996999000162) refers the lipids. These are just the first papers I've encountered on Google scholar. Still, it may be correct that the dietary Calorie (1 Calorie = 1000 calorie) is still in the range to cover such energy. So, you are right. Caffeine still increases overall metabolism speed without doubt.
Answer: I don't have any factual evidence. Just two observations.

If there was a strong correlation between caffeine and weight loss then it would be all over the news.
Everybody in my office drinks 3+ (or is it 10+) cups of coffee per day. Most are not slim. Those that are in good shape walk the stairs, eat well, but they don't drink more coffee than those that aren't in good shape.
Answer: It does suppress appetite which could contribute to being lean, though adding sugar and cream would definitely counteract the calories lost by that side effect.
Answer: I can tell from my own experience that coffee does affect loosing weight. When I am on diet I use coffee more than usual.
Comment: That doesn't necessarily suggest a link to weight loss, though as it's a bit of a goose and egg problem. For example, you could be drinking more coffee because the reduced caloric intake causes you to feel tired more often, and to self-treat that tiredness with more coffee.
Answer: Caffeine is a stimulant, in the same family that "diet pills" are in.  It boosts metabolism and energy (the stimulant effect), and suppresses appetite.  So, yes, in a certain sense, ingesting caffeine, whether in the form of coffee or otherwise, can, potentially act like popping a diet pill.
Drinking a coffee heavily flavored with high-calorie creams, sugars, etc. will probably add more calories than you'd burn from the caffeine.
Having that coffee before a morning workout is a good way to jump start the metabolism for both a better workout and increased metabolic effects, I've read, but that might be a bit dated (Robert Haas' "Eat to Win").
Answer: Coffee can promote good gut bacteria and create a more favorable condition for weight loss.  Dr. David Perlmutter's book, Brainmaker, goes into some depth about pre-biotic foods, or foods that nourish a healthy gut bio culture.  A healthy gut bio culture is a negative indicator for obesity, and in fact, some obese patients have been successfully treated with a fecal matter transplant to adjust the gut culture.  There is conjecture that the really efficacious part of a gastric bypass surgery is the gut reboot that happens afterwards rather than the actual surgical procedure.
So yes, there is growing evidence that pre-biotic foods like coffee can help you lose weight through better gut health.  This is not a caffeine related effect, but actually dependent on some of the coffee solids working their way into your gut.
http://www.drperlmutter.com/coffee-pour-cup/
(But see http://nymag.com/scienceofus/2015/06/problem-with-the-grain-brain-doctor.html before you make up your mind about Dr. Perlmutter.)
Answer: It can help on a short term. That's why there is a bunch of people that drinks coffee regularly without any effect.
Please check this article from Authority Nutrition:

Even though caffeine can boost your metabolism in the short term, this effect is diminished in long-term coffee drinkers due to
  tolerance.
If you're primarily interested in coffee for the sake of fat loss,
  then it may be best to cycle it to prevent a buildup of tolerance.
  Perhaps cycles of 2 weeks on, 2 weeks off.
Of course, there are plenty of other great reasons to drink coffee,
  including the fact that coffee is the single largest source of
  antioxidants in the western diet, outranking both fruits and
  vegetables, combined.

Coffee will make you lean?


Unable to bind to 0.0.0.0:8333 on this computer. Bitcoin is probably already running

Question: I installed bitcoin-qt and my wallet was all synced, everything working as it should. I sighed up for slush's pool and was trying to connect the 2 and I think I may have clicked the box to run SOCKS proxy (if I am remembering right)  Now my wallet will not show up on my desktop and when I click the icon I get 2 errors:

Unable to bind to 0.0.0.0:8333 on this computer. Bitcoin is probably already running.
Failed to listen on any port. Use -listen=0 if you want this.

I am running Fedora 18.  I tried to uninstall/reinstall and ended up with the same issue, i'm assuming I did not uninstall ALL of the initial package/program.
Can someone help PLEASE!!
Thank you!!
Answer: Are you sure that betcoind is not running?
<code>Bitcoin is probably already running.
</code>
You can try to restart your computer...
Comment: how to change the port to 8334?


Screen zoomed after removing external monitor

Question: Hi I am having an issue after disconnecting from an external monitor that my display is enlarged the windows run off the screen so I can open catalyst control or
settings->display to try and see what the problem is.  I'm thinking its from unplugging from my monitor but Ubuntu is usually smart enough to figure that out.  Any one whose had a similar problem or anyone with suggestions I'd greatly appreciate your help
Answer: I have no solution but I can confirm this.
I've experienced the same problem a couple of times. I plug in the TV from time to time and sometimes I am stuck with a 3000+resolution after!
I disable the TV. It goes away after restart, but it is really annoying.


Why didn't people of the Leaf Village want to get closer to Naruto if he is the son of the 4th Hokage?

Question: Naruto was always discriminated against by the people of the Leaf Village because he had the Kyuubi inside. However, he is the son of the 4th Hokage and he was the one who sealed it inside him. Why, then, did they discriminate against him if it was in order to save the village?
Comment: [Related](http://anime.stackexchange.com/q/561/49)
Comment: it didn't show when i was composing this question....
Answer: The details of how Minato sealed the Kyuubi inside Naruto, and the fact that Naruto is Minato's son was kept hidden from the villagers. The villagers believed that Naruto is the reincarnation of the Kyuubi, who killed their beloved Hokage. Having experienced the Kyuubi's attack on Konoha, they were also frightened about going near Naruto. Even the people who knew that the Kyuubi was sealed inside Naruto were worried about their own safety, and wanted to stay away from Naruto.
Comment: what an answer.. :)
Answer: The Masked Man pretty much nailed it. For future reference, even the fact that Naruto's mom, kushina was giving birth was kept secret, as the seal on kyuubi is weakest during child birth. So, if someone told the villager's that Naruto was the son of Minato and Kushina, when no one knew she was even going to give birth, it could be hard to believe. Especially, when only a few people knew about it. Furthermore, it was probably safer for Naruto if people didn't know that he was the Hokage's kid. That title brings a lot of enemies. Even Konohamaru had people following him 24/7.


After 1.e4 e5 2.Nf3, is 2...Nf6 safer and easier to learn than Nc6?

Question: I am an amateur player and do not have much time to study and memorise complicated opening lines. Am wondering after 1.e4 e5 2.Nf3, if 2...Nf6 is a safer and simpler option for black than 2...Nc6. My database shows that after 1.e4 e5 2.Nf3, the move which gives white the lowest winning percentage is 2...Nf6 instead of 2...Nc6.
Comment: Nf6 indeed is easier to learn. Not as many different lines after Nf6 compared to Nc6. Also, openings such as the scandinavian defense does not have much things to memorize, if that's your aim.
Answer: As an amateur player, you should know the connotation that 2...Nf6  (The Petrov defense) has a reputation of being more boring and more of a draw than 2...Nc6 (leading to the Ruy Lopez, Italian, and Scotch games). However, this really doesn't apply at the amateur level. In fact, you're much more likely to win or lose than draw, unlikely to the masters' database showing that certain lines have a drawish tendency.
So my suggestion, as unexciting as it is, is play what you like! Try out Nf6, try out Nc6, and see what pawn structures/middlegames you're getting in your games. Do you like them? Do you prefer one or the other? Play that one more often!
Comment: The Caro Kann has been seeing some games in professional games with the current WCC even choosing it against the best of the best. If you prefer the Caro Kann to 1...e5, then definitely play the Caro instead.
Comment: @Zuriel, a reason to switch from Caro Kann to 1...e5 would be to learn about different position types, or just curiosity, but objective strength of these openings is about the same for vast majority of chess players.
Comment: @Zuriel Unless you are rated 2500+ you won't feel the difference in the strength of 1...c6 vs 1...e5
Comment: Thanks! I personally like Caro Kann better but am not sure if 1...e5 is slightly better than 1...c6 and if it worths switching
Answer: Objectively speaking, 2...Nc6 is the strongest reply. That's why it's preferred by most top players. 2...Nf6 is an interesting alternative, but it often leads to more drawish positions after 3.Nxe5 d6 4.Nf3 Nxe4, but White can also go for 4.Nxf7!?, which is an inferior line, but very sharp and it can put you in big trouble if you don't know it well.
So it all boils down to what you feel more comfortable with. Both moves are perfectly playable but you need to figure out what type of position you understand better.
If you want to play 2...Nf6, you'll have to be ready for the 4.Nxf7 line, and also understand how to play in those positions with the open "e" file. White can also try 3.Nc3, with a transposition to the four knights opening after 3...Nc6, which is its own story but still not as hard to learn as 2.Nc6 as White has lost a lot of its flexitiblity (most lines in the Italian or Spanish openings play a c2-c3 push at some point.
On the other hand 2...Nc6 will need you to be ready for (mainly) 3.Bb5, 3.Bc4 and **3.d4, all of them being very complex openings with a lot of theory on them.
Finally, even if your skill level doesn't directly play a role on which one to choose, it will definitely have an impact on the time that is worth dedicating to openings. If you're not a particularly strong player, you may want to play 2..Nf6 just to need less studying and move on to things like tactics and strategy, but in that case you may also want to play a completely different defense.
Comment: Correct on all points. And if it were coming from a chess teacher, the students would get nowhere with that correct advice. Well, no, that's not true. Student would get a lot of mileage from the part about having to be practiced tactically in order to deal with things like Cochrane's knight sacrifice.  I just don't know what I'm talking about.
Comment: @friscodelrosario this does not intend to be an explanation of a complete repertoire on these defenses (that would take an entire book), but rather a general guideline about what to research
Answer: The Petrov is a sound opening but the problem is that white can basically force a queen trade in a symmetrical position. For example- 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4
5. Qe2 Qe7 6. d3
That's okay for a GM but bad for a developing player for two reasons:

You aren't going to get better playing these types of positions. There aren't a lot of tactics and the endgames are going to be boring attempts to draw rather than learning how to win.

If the Petrov is your only defense to e4 that means you're going to have a lot of situations where you're playing someone rated 500 points below you and you can't find a way to win because they're just trading pieces.

A good starter opening is the Scandinavian. If you know the line 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 and understand a few general ideas you can get a playable game against anyone.
When you get a little better and want to expand your rep then look at 2...Nc6. The Ruy Lopez is really all you have to worry about. You can equalize against the other lines fairly easily. Against the Ruy you have a lot of choices. If you don't play 3...a6 you cut out 90% of the theory. My favorite is the classical (3...Bc5). Black has an active and solid position but without a lot of theory. There's other options too like 3...d6, 3...Nge7, 3...Nd4 etc. 3...g6 is rarely played but probably fine. There's other options to avoid theory even after 3...a6. Just find a line you like that gives you reasonable chances. You won't see it that often anyway until you start getting pretty good.
After you get around 18-1900 you can look at other openings and start narrowing your rep. Below that point, theory isn't all that important. Most games don't go more than 4 or 5 moves deep into theory and you're just looking to get a playable position against the guy who memorized a single line 30 moves deep or the guy who learned a couple of traps. What you learn from the types of positions you get is the most important thing. The openings that will make you better are the ones that give you sound, active positions while avoiding theory and drawish positions.
Answer: For practical reasons, 2...Nf6 is better for you than 2...Nc6, because 2...Nc6 does not make a threat, and your opponent won't have to think about anything. But if you counterattack with 2...Nf6, then your opponent has to think, and that's what you want: your opponents thinking for themselves.
That's in practice. In theory, 2...Nf6 can be safer than 2...Nc6, can also be wilder. Depends on where the players take it, in practice. Your opponent has 50 percent of the say about whether your moves are safe.
Is it easier to learn? What does that even mean?
If you think "learning an opening" will help your results, that's nonsense. The best chess teacher ever, Cecil Purdy, said: "Some players think they could play a good game 'if they only knew the opening'. This is just crazy."
Why do you think you need to learn an opening? This is the dumb idea that 99% of chessplayers have. Your only real job in the opening is to reach a playable middlegame, one with rough equality in center control, development, and king safety. You can get there playing whatever you want, as long as you're mindful of the general principles of the opening, and especially of the tactics. Chessplayers are pretty dumb about this: They think they lose in the opening because they're bad at the opening. They lose in the opening because they're bad at tactics.
Let's say you want to be dumb about it, like your friends and neighbors, and you think you absolutely must know something about 1. e4 e5 2. Nf3 Nf6 to survive your next session of play. Here's what they will tell you here on StackExchange: It's more important to know the ideas behind an opening than memorizing the moves in that opening. That is actually code for: Give me fewer things to remember.
Chessplayers sort of figure out through experience that memorizing strings of moves gets them nowhere. Their opponent will vary from their book knowledge, then they are floundering. Or they reach the end of their book knowledge with a magical +=, but then what? Then they're wandering around lost in the middlegame. So chessplayers say "if you learn the ideas, you can find moves based on the ideas". And because there are fewer ideas to learn than strings of moves, chessplayers think they've got opening learning figured out. This doesn't drill down deep enough. What if — instead of knowing the ideas behind one opening — you knew the ideas behind all the openings? This will save you untold hours of study time, understanding that if you're playing to maintain at least one pawn in the center, maintain roughly equal development, and tuck your king as safely as his, you'll be OK.
I already said that people who "learn" openings get lost in the middlegame, rendering their opening knowledge moot. It helps your opening play if you know what your rooks are doing during the middlegame. Purdy said: "The real test of one's opening is the play it gives the rooks." Primarily because of what grandmaster Fine said about favorable middlegames: If you have emerged from the opening with better center control, better development, and better king safety, you clearly have a superior middlegame position. And from a superior middlegame position, attack the enemy king by opening files for your rooks.
But sometimes you can't checkmate them, and it's impossible to avoid an endgame. The endgame is inevitable. You cannot put pieces back on the board to the second move and play 2...Nf6 all over again, you will reach endgames. So it is imperative that you know what a favorable endgame looks like and what an unfavorable endgame looks like. Otherwise you will never know during the middlegame whether you want to swap units to simplify the position or to preserve units on the board to keep things complicated.
In other words, you can get through the opening with pretty much anything. Purdy said it's impossible to play a perfect opening, but it's pretty easy to play a decent one. And no matter what happens in the middlegame, you have to judge whether or not you want to head toward that endgame that's on the horizon. So learn endgames. You have to. A mistake in the opening will not kill you. A mistake in the endgame turns a win into a draw, a draw into a loss. Mistakes at the end are far more costly than whether Stockfish says one move in the opening is .35 better than some other move in the opening.
The beauty of this is that endgame can be learned, while the opening cannot. You can learn how to play perfectly every position with three units on the board. Then you add a unit, and learn how to play all the positions with four units on the board. Perfectly doable. And work your way backward. It took me 50 years; I'm still working on positions with four units on the board. So isn't it logical and common sense that if learning positions with few units on the board is more valuable and more doable, then that's far more important than wondering what to do at move 2 with 32 units on the board?
This might be LOTS more than you wanted to know, but if you want to get good at this, you have to know it, the sooner, the better. And by telling you, I get to tell everyone else reading it.
Comment: And then what? You can take a complete library of openings literature to the board, and play with an open book. Take your laptop with you, consult master databases of millions of games. You will eventually have to find a move yourself. Play two moves, three moves, 13 moves perfectly in the opening, *doesn't help you a bit*. Play 13 moves perfectly in the ending, you have won the game you were supposed to win, or drew the game you were supposed to draw. Sticking to "I can learn openings" is what bad players live by. If you don't buy into what I said, believe Purdy. Even Fischer believed Purdy.
Comment: @friscodelrosario I don't think oversimplifications are bad, but statements such as "What if — instead of knowing the ideas behind one opening — you knew the ideas behind all the openings? This will save you untold hours of study time" are ridiculous and massively unhelpful. How on earth do you think getting a deep understanding of the game is easier by studying _all_ openings in the abstract, rather than a few concretely? The value of studying openings is not as a shorthand to concrete moves, but rather to gain ideas for the middle-game and apply similar ideas to other opening lines.
Comment: A music student was frustrated with learning a new piece. He'd play from the top, reach an unfamiliar part, then slow down, stumble, stop. Takes it from the top, slow down, stumble, stop. Professor said : Learn the last measure first. Then learn the next-to-last. 2nd-to-last, and so on. That way, you're always headed toward the part of the song you already know. Chessplayers who are confident in endings feel better i middlegames, because they're inevitably heading toward the part of the game they know. Music professor had no clue what he was talking about,
Comment: Thank you for your very, very detailed answer! I am curious about your comment that "endgame can be learned, while the opening cannot" and your supporting arguments. In fact, I can learn how to play the first moves perfectly (just play 1.e4 or 1.d4 or 1. c4 or 1. Nf3 as white and as black, know a perfect reply to white's every possible move). It should not take me very long to learn how to play the first two moves perfectly. Three moves? Possible, except for some very rare lines. So at least learning the first few moves is a reasonable task.
Comment: If I can consult master databases, I can likely end up with a very comfortable, maybe sometimes winning midgame (for example,  1. d4 d5 2. c4 e5 3. dxe5 d4 4. e3 Bb4 5. Bd2 dxe3 6. Bxb4 exf2 7. Ke2 fxg1=N ) and if my opponent is not much stronger than me, I will have a great chance of winning such games.
Comment: You asked about openings. I said: Here is all you have to know. You said: But I *could* learn as many moves in the opening as I could in the endgame. I said: It won't help. You said: Here, I have an opening trap! I told you all I know about the opening, do what you will, and have fun. When chess is not fun, do something else.
Comment: Your penultimate paragraph really shows you have no clue what you're talking about
Comment: @friscodelrosario what fun is there in learning n-men tablebases?
Comment: Purdy's most famous saying is "Pawn endings are to chess as putting is to golf". Some part in the late middlegame -- the transition to the ending, chessplayers say, but that's too elegant a term for some occasionally easy simplification -- is the approach shot to the grain. The drive off the tee is the opening. Hit it 350 feet, center fairway, and you still have to get up on the green and down in the cup. Drive for show, putt for dough, the golfers say. Maybe that really shows they have no clue what they're talking about.
Comment: Tarrasch said: "Before the endgame, the gods have placed the middlegame". He was talking to chessplayers who think they can get their += from  perfect opening play (or maybe more than that against a gambit player), and carry that to the ending. But there's the middlegame. Kasparov loves that Tarrasch line. Kasparov and Tarrasch don't know what they're talking about?
Comment: This answer only applies to beginner-intermediate level players. Past this stage, poor opening knowledge definitely can and WILL land you in a lot of trouble because you're starting to play against opponents who are good enough to exploit opening advantages.
Comment: Quite right. Where is that line, do you think?
Comment: Not sure whether you're replying to me with your last comment, but I'd say that the line is somewhere between 1900-2000 Elo. Before this you can get by somewhat decently without much beyond the basic opening principles. In general, I find this answer to be lacking, since it contains both oversimplifications as well as some blatant misunderstandings. I'm honestly surprised that it has so many upvotes.
Comment: I used to think that line was around 22 or 2300, but it's different these days; 20-2100, I think. Sorry, but I oversimplify many things because I talk in front of many people, not all of 'em as smart as you, recognizing blatant misunderstandings so easily as to be impressive.
Comment: I do get the point that openings should not be the focus of study for a beginning chess player. But surely you can get that point across without spreading misinformation?
Comment: @Discretelizard Yeeh, you're right. I got caught up in my grandiloquence there.
Comment: @Zuriel, if I could win all the winning games, I'd at least be an IM now. Yet I stuck at 1900. For non-titled players, it's not as easy as you think to actually win a winning game. The game still boils down to a few tactical shots and/or endgame blunders.


message when responses are made to questions you have upvoted

Question: If I have upvoted a question, I would appreciate notification (for example, in the message window under the StackExchange upper left) when there is a post or comment to that question.  Do others feel that way?
Comment: To add on Zev's answer, SE is a platform which encourages voting very often (note for the badges given for using all your voting in a single day, as well for voting competing answers and on many questions). This makes your request - while reasonable - impractical. A slight modification which is in order for your request is to replace the word "upvoted" with "favored".
Answer: Personally, I think that there are far too many questions I've upvoted for notifications of activity on all of them to be practical to keep track of - I'd be swamped! Besides, the current setup of getting notifications of activity on precisely those questions which one has favorited is strictly better because it gives one the ability to disconnect "I want to get notifications of activity on this question" and "I want to vote on this question" (and these notifications are somewhat "quieter", because they are not in one's inbox, but only in the favorites tab of one's profile).
Comment: I'm having trouble getting a clear description too. I found [this](http://meta.stackexchange.com/questions/45360/subscribing-to-questions-and-comments-that-dont-belong-to-you/52093#52093), and my understanding of it is that edits or new answers light up the "activity on a favorited question" indicator, but comments do not. This matches my personal experience: even with [all of my favorites](http://math.stackexchange.com/users/264/zev-chonoles?tab=favorites), my activity indicator only goes off once in a while, while I would guess that comments occur on them occur more frequently than that.
Comment: I never used the favorite question feature. What kind of activity triggers a notification? Comments to the question and newly posted answers, I presume, right? Is there a detailed description of that somewhere, I couldn't locate it on meta.SO (I admittedly didn't try very hard, though)?


structural result

Question: what exactly is the meaning of "obtaining a structural result" in mathematics, for example in graph theory?
Comment: I've heard of a constructive proof.  Never heard of a structural result.  Example?  Domain?
Comment: In graph theory, it usually means a result that somehow describes the *structure* of the graphs in question.
Answer: There is no exact meaning of the term "structural result" across mathematics (or even across graph theory).  In fact, I fear it is one of these impressive sounding terms which means very little apart from what the writer wants it to mean in any particular case (cue Humpty Dumpty and the obligatory reminder that Lewis Carroll's day job was mathematics professor).   Or at least there is relatively little that it can be counted on to mean.  For many mathematicians (including me) it does call something to mind, and indeed this and similar terminology appears in some of my papers and notes.
Let me to try to give an example.  Consider the problem of determining whether a finite graph is planar.  Perhaps the graph is given to me as an immersed planar graph, i.e., with edges crossing each other.  In this case, one could ask about algorithms for making the graph planar possibly by changing the original diagram in a minimal way (in some sense).  [Note that there is a game which is based upon solving this problem: planarity.] One could imagine very nice -- and certainly, very useful -- results of this kind, but somehow they are not "structural" in the sense that they are paying too much attention to the particular representation of the graph one starts with rather than its abstract structure as a graph.  On the other hand, the theorem of Kuratowski-Wagner that a finite graph is planar iff it does not have $K_5$ or $K_{3,3}$ as a graph minor is more structural: it manifestly depends only on the isomorphism class of the graph.
This example is not fantastic.  If I wanted to criticize it, I would start by pointing out that an immersed planar graph is a graph with additional structure of a certain kind.  But I guess the idea of the nonstructuralist approach is that one does not make that additional structure explicit and try to prove theorems which mention the structure explicitly.  A structuralist would say exactly what kind of metric / differential geometric object an immersed graph is, try to construct moduli spaces of such things and then study their properties, and so forth...
Comment: For another example with a rather different flavor, look at SPQR tree on Wikipedia.
Comment: @Yuval: I had never heard of such a thing until I saw your comment, but I looked just now and it does indeed seem relevant.  Perhaps you should consider parlaying your comment into an answer?
Answer: Here is a nice structural result for general graphs.
Every graph is the disjoint union of its connected components.
Every connected graph is a tree of biconnected components. A biconnected component is one in which the removal of any one edge leaves the graph connected. An edge disconnecting the graph is known as a bridge. Removing all bridges, we get a collection of biconnected components. It's easy to see that if we shrink all biconnected components to a dot, then the original graph becomes a tree.
Every biconnected component is obtained from triconnected components (those requiring the removal of at least three edges to disconnect the graph) using two specific constructions, "series" and "parallel"; see SPQR tree for more details.
Recent results in the same vein concern the structure of claw-free graphs (Seymour and Chudnovsky) and bull-free graphs (Chudnovsky); the same method (and a lot of hard work) was used to prove the Strong Perfect Graph Theorem.
And let's not forget the Graph Minor Theorem, which is (in some sense) a vast generalization of Kuratowski's theorem.

structural result


Difference between Turing machine and Universal Turing machine

Question: I've read what a Turing machine and a UTM are, but I don't get the difference. What can a UTM do which a normal Turing machine can not?
Answer: A universal Turing machine is just a Turing machine whose programming simulates other Turing machines.  That is, the input to the UTM is a description of a Turing machine $T$ and an input for $T$, and the UTM simulates $T$ on that input.
It's universal in the sense that, for any problem that can be solved by Turing machines, you could either use a Turing machine that directly solves that problem, or you could use a UTM and give it the description of a TM that directly solves the problem.
If you like, a UTM is an interpreter for (all) Turing machines.
Comment: I don't think so. After all, it wasn't even thought of as a computer at all. Or rather, it was thought of as what was at that time called a computer, namely a human who computes logarithm tables etc. by hand. That's how Turing came up with his model: a pen, a piece of paper, a (limited) vocabulary, a (limited) memory, and a (limited) set of rules.
Comment: It is also (one of) the first description(s) of a stored-program computer.
Comment: @JörgWMittag Good point. Was it thought of in those terms in the 1930s?
Answer: A UTM can run any Turing machine on some input.
A Turing machine can be compared to a program. It takes some input and generates some output.
A UTM can be compared to a computer. It can take any program and run it with some input and generates some output.
The UTM is a Turing machine in itself, so the interesting idea here is that any Turing machine can be encoded as input understood by another Turing machine.
Comment: I think you have to be careful with this analogy. A Turing machine feels more like a special-purpose computer, to me: it's a "physical" device. But I suppose that part of the point is that these devices can be described as something like programs.
Comment: @DavidRicherby, by "special-purpose computer" do you mean a fixed-program computer? Would it be correct to say that the difference between a Turing machine and the UTM is analogous to the difference between a fixed-program computer and a stored-program computer?
Answer: Every TM does just one task. It sums two input numbers, or it scans the input for some symbol, or it looks for a counterexample of Goldbach's conjecture ...
... or it (let us call it TM#1, since we will have a 2nd one shortly) gets two parts of input, where the first describes a TM, TM#2 (think of a (fixed) TM as a finite number of states and transitions and stuff like head directions) and next to the description of TM#2 a description of input to TM#2.
So TM#1 receives the pair ("TM#2" "input#2") as its input#1. And then TM#1 runs on this input#1 and behaves (to the outside, after termination!) as if it was TM#2 working on input#2. In case TM#2 would not halt, TM#1 won't do either.
Such a TM#1 is called a UTM, since it can behave like/fake/simulate any other TM you give it as TM#2. Think of a virtual machine (TM#1), a simulated program (TM#2), and an input to the simulation (input#2). The VM takes longer, but the results are the same.
Even TM#2 = TM#1 is possible ... then input#2 = ("TM#3" "input#3") and TM#1 is a UTM and now simulates another UTM (TM#2) which in turn meta-behaves as TM#3 on input#3, in symbols:
TM#3(input#3)
= TM#2("TM#3 input#3") since we took TM#2 to also be a UTM
= TM#1("TM#2  'TM#3 input#3'")
Again: Behaviour is in terms of eventual final output, if and when halting, certainly not in terms of tape contents at any time, number of time steps etc., simulation takes (much) more time than doing it directly.


Are there any good tools to figure out the correct gamma corrections for equal appearence?

Question: Every display device has a different characteristic in regards of how the colours are shown. This can be adjusted by the gamma correction. Are there any good tools that help with finding the right gamma correction?
Answer: The "best" solution is to use a colorimeter to accurately calibrate the screens.
Some screens do have ICC colour profiles that you can obtain from the manufacturer as well, which can give acceptable results.
Answer: You want a hardware display calibrator. I have a Huey Pro, I believe. You need to adjust a lot more than the gamma, and it's extremely difficult to do this by eye.


Deploying Branding as a Feature across multiple site collections

Question: I'm Junior dev trying to get my head around SharePoint so I was hoping someone might be able to help me out with some issues I'm having.
I'm in the process of complying a new branding solution for our internal intranet as my company has recently changed their logos/color palettes etc. We have numerous different color palettes that can be used and I've been asked to develop it in a way such that teams can pick and choose between which ones they want to use.
The easiest solution I've been able to come up with is having multiple web scoped features, one for each of the available color palettes, which on activation while update the site's css/masterpage/images as appropriate.
The problem I'm running in to is that when I attempt to activate the web scoped feature on sites in different site collections I'm getting a "File Not Found" error message from SharePoint.
Now I'm assuming this because the .wsp when deployed is deployed to a specific site collection and the files aren't available outside of the collection while the feature is still visible due to it's scope.
Could anyone offer me some insight in to how I might deploy my solution in such a way that I can retain having my branding features work across multiple site collections.
Thanks.
Comment: To which kind of site collection templates,  you looking to apply branding to? Team sites, publishing etc.
Comment: Trying to apply to team sites.
Answer: I solved it this way:

Create a site collection feature which is responsible for deploying font/spcolor files, master page, Background Image etc.
Create a web scoped Feature which sets the theme, masterpage, font and the Background image in FeatureActivated-Method.
Establish a Feature dependency, so the web Feature can only be activated when the site collection Feature is already activated.
Implement Feature stapling: so every new Sub web sites activates the web Feature automatically.


When analyzing a parallel algorithm, how do you take communication costs into account?

Question: My question is related in spirit to "Is algorithmic analysis by flop counting obsolete?".  Counting the number of computational operations in an algorithm is commonly used as a first-order model to aid in understanding the computational costs of an algorithm. However, the unit cost (in, say, time per operation) of data movement is greater than that of a processor cycle (see Peter Norvig's table of approximate timings for operations on a PC at this link). Is there any type of analysis for communication similar to the analysis done for computational operations? If not, is coding up an algorithm and running it the only (or most effective way) to determine the costs of communication?
Comment: Do you mean "Can you do an $O(N^a)$ type analysis of communication costs?" If so, I think there is again the challenge—as mentioned in Norvig's table—of determining what kind of movement you're talking about, as I suspect that the prefactor is of huge importance here.
Comment: Yes. I also suspect that the prefactor may be of huge importance here. I suspect the answer to this question is, "We know some strategies are bad because of personal experience," followed by lists of good and bad things. My experience with parallel computing is limited to a semester of a parallel computing class. I'd like to know how people who work on supercomputers figure out effective strategies for parallelism. I also suspect that GPU programming faces a similar hurdle with memory movement.
Comment: For GPU computing, I think communication and memory accessing (the latter, of course, a big subject in the linked question) are equally important issues.
Comment: Communication and memory access patterns are of fundamental importance when cosndiering GPUs as they work as co-procesing units. Either you move all data to reside on the GPUs to reduce the latency connected with transfers of data between a CPU (host) and a GPU (device) through a PCI express link. For algorithms with high arithmetic intensity (high flops/transfer rates) the GPUs can excel performance due to number of ALUs when operations are data-parallel. However, most algorithms would be memory bound algorithm because of the memory wall (increasing gap between processing speed and bandwidth)
Answer: It's fairly common to construct performance models of parallel codes that include FLOPS, memory bandwidth, and communications.   A real world example of modelling performance of such a code is here, for the POP (v2) ocean code; it's just the first that came up in a google search.   I've given a simple example of how it works in my answer to this question: How can I reduce the communication bottleneck of a parallel explicit finite difference scheme?
The communication part of these performance models generally count the number and size of messages, and use latency and bandwidth to estimate the time taken by point-to-point messages, with some logarithmic factor for collectives.
As with any modeling exercise, you can go nuts adding more terms to your model -- making communications on-node less expensive, and off-switch more expensive, including load imbalance, etc -- but even a fairly simple model gives you a fairly strong understanding of what is going on in your code, and allows you to quantitatively answer questions like "is infiniband vs. ethernet likely to make a difference for this simulation", etc.
As to your last question, "If not, is coding up an algorithm and running it the only (or most effective way) to determine the costs of communication?" -- experiment always trumps theory, of course, but theory can be a useful guide.
Answer: The Hockney model is an excellent simple model for communication: the time to send a single message of $m$ words from one process to another is
$$
T(m) = \alpha + \beta m
$$
where $\alpha$ is the so-called latency cost, and $\beta$ is the inverse bandwidth. Typically, the larger the machine, the larger $\alpha$ is. Clearly the Hockney model does not take into account more subtle issues like network congestion, but it's hard to stress exactly how much mileage one can get out of this model.
If you would like to see an analysis of various algorithms for MPI collective communication using the Hockney model, I highly recommend Collective Communication: Theory, Practice, and Experience. It discusses various algorithms for broadcast, reduce, scatter, gather, allgather, reduce-scatter, and allreduce on various network topologies.
Answer: This is a hard thing to do and there is nothing as general, well defined and powerful as complexity analysis that includes memory movement.  Memory complexity is at least a start.  Kung and others have done relevant work in this area (H. T. Kung. Memory requirements for balanced computer architectures. In Proceedings of the ACM Int'l. Symp. Computer Architecture (ISCA), Tokyo, Japan, 1986) and Jim Demmel's group at Berkeley has recently worked explicitly with complexity theory that include communication, but "memory movement " theory has far to go until it is as versatile as traditional complexity theory and analysis.
Answer: According to the book "Parallel Programming in C with MPI and OPENMP" (2004) by M.J. Quinn, you can think of parallel programs in the "task-channel" model.  In it, the critical thing to understand is that "a task may only send one message at a time, but it can receive a message at the same time it is sending a message" (Quinn, 2004, pg 76).  So, you only need to consider how many messages are sent simultaneously at each iteration.  Also, communication is never instantaneous: there is always a latency period before even 1 bit is sent through a channel (think of it as though the processor needs to "warm up" before it can send a message).  We can usually assume that this is a constant, independent of the message length.  In general, we do not consider too many other "hardware-dependent" factors into the algorithm analysis such as bandwidth, network topology, or cache hit rate.  This is part of the reason why a parallel implementation does not perform as predicted by the algorithm analysis. It is also not uncommon for programmers to not know these parameters about the machine they are testing their code on, which makes experimental testing much more convenient.


Can a PDF file contain a virus?

Question: Could a PDF file contain any type of malware?
Comment: Check this site: http://canarytokens.org
Answer: There are many features in the PDF that can be used in malicious ways without exploiting a vulnerability.  One example is given by Didier Stevens here.  Basically he embeds an executable and has it launch when opening the file.  I am not sure how today's versions of readers handle this but its a good method of using PDF features in malicious ways.
Comment: Would such a PDF be dangerous only on OS'es like Windows? Would the permission system of Mac/Linux be able to prevent such PDF's from running executables automatically?
Comment: @Nav executing code has little to do with the OS, and everything to do with the reader.  Executing code is allowed to execute other code.  Basically you have to trust the reader to not do something stupid like allowing a PDF to execute an application.
Comment: @Nav It's entirely feasible that a SELinux policy would block a pdf reader from executing _any_ programs.
Comment: The PDF links in that blog no longer work.
Comment: @SteveSether I would reword to sth like "do the standard readers that come with major OS'es guard against running executables"
Comment: @Magnus That doesn't have a lot of meaning.  I honestly don't know what a major OS is, or what a standard reader is.  It's also a moving target.  Maybe that's true today, but not tomorrow?
Answer: Yes it can. PDF is a rich format that aside from static content, can contain dynamic elements. The latter can for example contain JavaScript, and other elements. Modern PDF viewers tend to warn the user about potential malicious activity though.
If you want an example malware, check out pidief.
And generally PDF malware will predominantly be just the dropper, not the payload itself.
To learn more on the vulnerabilities associated with pdf files and ways of detecting them before they do any damage read this kali documentation on peepdf.
Answer: Yes it can.
Whether a file is malicious or not, does not depend on the file extension (in this case PDF). It depends on the vulnerabilities in the software which will be parsing it. So for example, PDF reader that you are using potentially contains a buffer overflow vulnerability, then an attacker can construct a special PDF file to exploit that vulnerability.
Consequently, to guard against such attacks is also easy, just ensure your PDF reader is up-to-date.
A simple google search landed me up on the SANS Institute's overview of PDF malware, which seems to be good to start with.
Comment: For Adobe Reader, which is likely what you use if you didn't consciously choose something else, the bulletins at http://helpx.adobe.com/security/products/reader.html list the numerous fixed vulnerabilities, with no or little detail.
Comment: @Jor-el unsurprisingly this page is now serving a 404 error. Would you care to re-find it and summarise it in your answer?
Comment: (edit: I updated the link -- still, the proper thing to do would be to summarise the content).
Comment: "Guarding by constantly updating" is not necessarily 'easy', nor is it a guarantee that you won't fall prey to an unpatched vulnerability.  Yes, it's a good thing to do, but it requires constant discipline.  Adobe Reader has so many vulnerabilities that they include an automatic updater - do you really think they've all been found yet?

Can a PDF file contain a virus?


How can I keep gravel from moving out of my driveway during winter?

Question: I have a gravel driveway going horizontally across a hill, and have trouble keeping the gravel in the driveway, especially during snow. This is because every time I shovel out the driveway, stones get picked up by the shovel and thrown into the grass. Of course, this takes a long time to pick up. Big rainstorms also wash out gravel. It is crushed limestone in the 1/2-1" diameter range. I can't pave it because I haven't got the money, and there are some nice trees over it which would be bothered by pavement. How do I keep gravel where it belongs?
Comment: Ah, the springtime ritual of raking gravel from the lawn back onto the driveway...
Comment: Washout and rain could be handled with small channels (to keep the gravel in easy to move places) or by dropping the height of the drive a few inches. As for snow, then I think you need a new way of clearning the drive - or a new drive. Both are expensive. :-(
Comment: You got snow this winter?  In south-central NH we got around 8 inches for Halloween, and nothing to speak of since.  Throw the snow uphill when feasible.  It will be easier to rake them back, or gravity will do it for you.  If you keep the driveway fairly level, just keep the shovel handle low and leave the bottom inch of snow.  This works best, I think, with a standard-design cheap plastic supermarket shovel - my favorite anyway.
Comment: A gas powered back pack blower or hand held is far better than a rake!
Answer: Two traditional methods which work but may not agree with you are:
1) tar the surface.  I believe you could get a local construction company to do this as spraying hot tar may not be a chore you want to do
2) If your driveway is already compacted and drains well this is my preferred solution:
Crusher run or
Crushed stone: this is generally limestone or dolomite that has been crushed and graded by screens to certain size classes. It is widely used in concrete and as a surfacing for roads and driveways, sometimes with tar applied over it. ... A special type of limestone crushed stone is dense grade aggregate, or DGA, also known as crusher run, or colloquially as "crush and run". This is a mixed grade of mostly small crushed stone in a matrix of crushed limestone powder.
This should be available in bulk at good prices from any quarry or landscape supplier. Spread in a layer so the top of the existing gravel and compact with a roller and apply water to harden.
For spots where it could wash out mix with Portland cement.
Average Coverage
*1 cu. Yd. will cover approximately 100 sq. ft. at 2" deep
If you are going to go to the effort of doing this you should also do some grading on the uphill side to add a ditch and add piping to let the water through from one side to another.
Comment: Here is my math, Kevinsky.  Square footage divided by 81 gives you the yardage necessary to cover at 4" depth; 100 sq. ft. / 81 = 1.2 yards and that would be a 4" depth.  I could have fried my brain, just want to make sure I am telling people the correct math.  If I wanted 2" depth I divide by 2 and I get .6 yard to cover 100 sq. ft. with 2". I've used sq. ft. divided by 81 to get the yardage of gravels, mulches I want at 4".   This isn't matching what you are saying and by golly I am worried...you are almost always right, especially with math.
Comment: Crushed gravels with minus compacted are the only way to go in my opinion.  Never had a problem even on slopes losing gravel.  All my gravels were edged with pt 2X4 and a gas powered blower kept all in check.
Answer: I found a product called Stone Man Stay Put. The manufacturer is Ivy League Landscape LLC. Found it at Ace but I'm sure Home Depot has it too. Simple water like mixture. Put it in your sprayer and apply a thin coating. You literally cannot tell there is anything holding the stones together, but they do not move. It's been two years and I have not had to rake a single pebble. Has no effect on your sprayer either. I still use the same sprayer for Roundup.
Answer: Try using a gravel stabiliser! I used one on my driveway, which was also on a slope.
The one I used was called COREgravel Coredrive, and it has really helped. It's from the UK, but you can probably find something similar wherever you live.
I saw another forum which said these grids must have a weed membrane already attached, so when I was hunting for a grid coregravel popped up a lot, and I must say the weed membrane is helping a lot.
While we were doing the drive we also did a couple paths leading to the house, which this grid could also help with!! Bonus!
It was very inexpensive, but I'd check prices for yourself.


What's the actual relationship between deflation, spending and saving?

Question: I am pretty confused with this concept. Since deflation is a result of decreasing prices, it means that the demand for goods and services rise therefore stimulating more spending. But on the other hand it is also a matter of fact that it encourages people to save (see potential in the increasing value of money over time).
Answer: Think about the permanent income hypothesis. People's spending is dependent not just on present income, but also the future stream of income. A deflation usually indicates a recession. The central bank is trying to optimize monetary policy subject to a short run Phillip's curve.
$$\min_{u, \pi} V(u, \pi) = -(u^2 + \pi^2)$$
such that
$$u = u^* + k(\pi^e - \pi)$$
where $u$ is unemployment, $u^*$ is the natural rate of unemployment, $k$ is the sensitivity of the tradeoff, and $\pi^e$ is the market expectation of inflation.
If you find a Nash equilibrium for this game with credibility in the model, then the Federal Reserve will want to target a constant steady rate of inflation. If the economy falls into recession, they will in return try to raise inflation, because in the short run it serves as a tradeoff with unemployment, so though the Fed is causing more inflation, hopefully they will stop too many people from losing jobs (note the loss function for the Fed in this case is convex). If the Fed tries out monetary policy and still sees deflation, then you can tell the recession is pretty rough, if that makes sense.
So even though the price of goods falls, wages on average will fall, and production will fall. So demand in the economy will fall. Those who do still have a good job are doing better on average than those who become unemployed, and they might dissave in periods where expected income in this recessionary period might be lower than future periods where the economy is doing well, but in reality, most people will be liquidity constrained and will be saving what little they can while drastically cutting back on spending. Usually. There are exceptions (think of payday loans).
Answer: We need to get cause and effect clear.
It is incorrect that "deflation is a result of decreasing prices".
In fact, the price level at a given time is determined solely by the preferences of the people (to the extent the society is cooperative, i.e., not coercive.)  At a higher price level than the actual one at a given time, there would be more suppliers who prefer money to goods than there were buyers who preferred that amount of goods to that amount of money. The market sets the price to the level where supply equals demand.  For the moment we are assuming for simplicity that people don't want to save, only consume.
What causes deflation?  Since deflation is a decline in the price level, from the above we see that it must be caused by a change in human preferences.  The (aggregate) preference for goods and services relative to money must have decreased.  Last year I was willing to produce a pumpkin and trade it for 2.00, but not 1.90.  This year I will produce and sell it for 1.90.
So, the correct cause-and-effect relationship is: deflation is caused by a change in human preferences for money relative to real wealth.
It is also incorrect to say that deflation causes changes in spending ( quantity supplied, which equals the quantity purchased.)  Both the aggregate quantity level and the price level are determined by human preferences: the quantity and price both adjust to the level at which the market is cleared, where supply = demand at that price.
Likewise, deflation (price level) does not cause the level of saving.  Saving level is the result of the aggregate of human preferences, in this case the preference for current goods over future goods.


What does "chrome" mean in Microsoft design guidelines?

Question: One of the most important principles in Microsoft Design Guidelines is:
put content before chrome.
What does chrome refer to? Just like action items?
Comment: I believe it's referring to the visual 'wrapper' of the content. Loosely translated:
"Function over form."
Answer: Per Nielsen Norman:

Chrome is the visual design elements that give users information about
  or commands to operate on the screen's content (as opposed to being
  part of that content). These design elements are provided by the
  underlying system — whether it be an operating system, a website, or
  an application — and surround the user's data.

What this means in practice
An example would be: If a user is looking at a table of photos, and they want to move a photo from the bottom row to the top row, they can simply click, hold, and drag that photo to where they want it, instead of having to click a button that says "move this photo". That is putting "content before chrome", because you are not cluttering the screen up with extra commands like "move this photo"-- the user is simply interacting directly with the content.
Here's another great article by Luke Wroblewski to reference about putting "content first": http://www.lukew.com/ff/entry.asp?1598
Answer: In the guideline they define chrome
Do more with less
This principle limits your app to its core functions and no more. Think content, not chrome. Content takes many forms: pictures, emails, news articles, and so on. Remove chrome to leave only the most relevant elements on-screen. And, make navigation elements from the content itself where you can. Let clean, immersive experiences rule. Every element on the screen must have value and a clear purpose.
This principle doesn't mean that you should sacrifice intuition. A design is successful if navigation elements guide the user to discover how to interact with the app. Great design balances intuition with reduction and yields a clean, beautiful final product.
Content, not chrome
Let the user interact directly with content. By removing the chrome and taking advantage of font, scale, and color, content surfaces more easily. In this example, names and titles are easier to read.
Microsoft design principles


Create Windows AMI with instance storage

Question: I have a business use case and workflow where local/instance/ephemeral storage for an EC2 instance is ideal.  Unfortunately I'm coupled to a Windows platform for this particular task and the EC2 Windows offering appears to have some deficiencies related to AMI creation.
In essence, I'm trying to figure out if there's a way to attach local instance storage to a Windows EC2 instance using the typical command line interface (because the Amazon Website GUI doesn't support it) and then to somehow create an AMI based upon that.  I've tried creating a snapshot and then creating a Windows AMI based upon the snapshot, but of course the docs say this is unsupported and makes an unbootable AMI.
In short, here's what I'm trying to do:

Be able to run a Windows instance (EBS/S3 instance doesn't matter)
Attach local instance storage as drive D:
Persist that configuration as an AMI such that I can start lots of them as necessary from   either the GUI, command line, or REST API.
Be able to take a launched instance, update software, shutdown, and create another AMI based upon that.
Wash, rinse, repeat.

One other potential option which isn't horrible, but isn't ideal is to create an AMI which has 2 EBS volumes already attached (system+apps and data).  Essentially, every time I startup an instance based upon the AMI it'll create 2 new EBS volumes of pre-determined size.  I'm trying to avoid that scenario if possible.
Comment: Have you tried just using "Create AMI Image" on your Windows instance?
Answer: After much research, it looks like Windows-based AMIs are all backed by EBS with no possibility to convert to S3/instance storage. While the instance/ephemeral disks can be added as at startup via the command line interface, there's no way to make this happen out of the box.


Effect on abs: leg raises vs crunches

Question: What is the difference for my abs between raising my legs, and raising my body?
I've heard that the whole lower abs/upper abs training is BS. It's like trying to train the lower or upper biceps.
Answer: First let's see how the exercises square up on the whole.
Studies have been performed regarding the EMG (electromyography) activity for various abdominal muscles in a variety of exercises. You will find the results for the exercises in stimulation of the rectus abdominis and obliques, relative to the traditional crunch, in this Wikipedia section: https://en.wikipedia.org/wiki/Abdominal_exercise#Types_of_abdominal_exercises_and_effectiveness
For the durability of this answer I'll reproduce the table here:
<code>Activity in rectus abdominis                      Activity in obliques
Exercise                  Mean activity      Exercise                  Mean activity

Bicycle crunch            248%               Captain's chair           310%
Captain's chair           212%               Bicycle crunch            290%
Exercise ball             139%               Reverse crunch            240%
Vertical leg crunch       129%               Hover                     230%
Torso track               127%               Vertical leg crunch       216%
Long arm crunch           119%               Exercise ball             147%
Reverse crunch            109%               Torso track               145%
Crunch with heel push     107%               Crunch with heel push     126%
Ab roller                 105%               Long arm crunch           126%
Hover                     100%               Ab roller                 101%
Traditional crunch        100%               Traditional crunch        100%
Exercise tubing pull      92%                Exercise tubing pull      77%
Ab rocker                 21%                Ab rocker                 74%
</code>
From this study, the highest mean activity is to be found in the captain's chair exercise (also known as power tower or knee raise station) and the bicycle crunch maneuver, which exceed the other activities rather dramatically on the rectus abdominis.
There has also been some tests done by Bret Contreras, who looked at a larger number of exercises, but did all tests himself meaning there's far less data points to extrapolate from. Here is the article: https://www.t-nation.com/training/inside-the-muscles-best-ab-exercises
The conclusion here was that chin-ups, hanging leg raises and the ab wheel had the highest mean activity for the rectus abdominis, ab wheel (from feet and from knees) and body saw for internal obliques and ab wheel (from feet), hanging leg raises and bodysaw for external obliques.
As you can see there doesn't seem to be a consensus amongst there articles, although I'd say the actual study would be the most reliable. The hanging leg raise and captain's chair are very similar and an excellent workout provided you focus on using your abdominal muscles and not just the hip flexors.
From the data it seems like the reverse crunch (raising your legs) is a better option than the traditional crunch (especially for the obliques), and leg raises or captain's chair an all-around superior option.
Now as for upper/lower muscle groups, the Wikipedia article claims that a crunch with the arms stretched out over your head (effectively lengthening the moment arm) will result in increased activation of the upper abs, although I'm a bit wary of the reference.
The Bret Contreras article references previous tests of his that claim that different exercises do vary between the ratio of upper/lower ab recruitment.
A study referenced in this article shows activation of lower and upper rectus abdominis: https://www.acefitness.org/prosourcearticle/4934/can-you-train-upper-and-lower-abs-separately
There are big differences between the general activation for various exercises but insignificant differences between upper and lower ab activation.
All in all, there doesn't appear to be much evidence that exercise choice will greatly affect upper/lower activity ratio, but there is evidence that there's a big difference between exercises in general utility.
EDIT: I've done some more digging and am going to have to revise my above answer. I've found two studies (which are very similar) that deal with this question:

Journal of Sports Science and Medicine, 2011, 10, 322-327. "Selective activation  of the rectus abdominis muscle uring low-intensity and fatiguing tasks"
"Muscle Activity in Upper and Lower Rectus Abdominus During Abdominal Exercises"

Links, in order:

http://www.leb.usp.br/andfkohn/SELECTIVE%20ACTIVATION%20OF%20THE%20RECTUS%20ABDOMINIS%20MUSCLE%20DURING%20LOW-INTENSITY%20AND%20FATIGUING%20TASKS.pdf
http://www.archives-pmr.org/article/S0003-9993%2896%2990195-1/pdf

In these studies there is a comparison between a supine trunk raise (or curl up, a crunch where the chest is raised towards the knees while maintaining leg position) and a posterior pelvic tilt exercise (a lying leg raise, where the pelvis is tilted towards the chest while maintaining upper torso position). The conclusions seem to be that separate portions (upper/lower) of the rectus abdominis can, at least in part, be individually activated. Furthermore, the ratio of the upper rectus abdominis activity to that of the lower, was much greater for the curl up exercise than for the leg raise.
So not only do certain exercises seem much more effective than the traditional crunch, it does appear that you can indeed train specifically for upper or lower abdominals, at least where the rectus abdominis is concerned. It seems possible that any exercise where posterior pelvic tilt is favored (which is the case for the captain's chair exercise and reverse crunch) will put emphasis on the lower RA, while exercises favoring the upper trunk (like the traditional crunch) would emphasize the upper RA. I should hasten to say that the studies can't be generalized like that (it's speculation on my part) and also that this concerns relative recruitment of the upper and lower portions. The leg raises still worked the upper RA considerably.
Comment: Screw my answer, this is the best!
Comment: @JJosaur Actually, it wasn't. I was too hasty because I had to leave. I've searched some more and found studies that speak against my first conclusion, which are a better reference for the specific question. I've updated my answer with references and conclusions. It appears some upper/lower rectus abdominis focus in training is in fact possible.
Answer: In terms of developing the strength of your abdominals, both will work.
Different exercises activate different muscles more or less. Generally, you cannot split out upper and lower abdominals by exercise and both mentioned exercises will activate both.
Answer: From personal experience, albeit without professional experience or references to back it up, crunches tend to feel like they're only really working the front of the abdomen, while leg lifts always feel like they engage more of the sides, possibly due to differences of stability and how far off of straight legs can go versus the torso.
Comment: +! Agree completely, leg lifts require you to hold your leg weight central and work your obliques (sp?) harder than rolling up into a crunch. I have heard crunches are bad for backs but cannot find peer reviewed evidence to support this.
Comment: @JJosaur: FWIW, I asked after that at http://fitness.stackexchange.com/questions/19327/are-situps-actually-harmful
Answer: Anything that either causes your ribcage to curl down towards your pelvis, or or pelvis to curl up towards the ribcage will work primarily the abdominals, with support from the obliques and hip flexors. If the spinal column doesn't flex, you're not really using the abdominals except as in support.
By that I mean that if by leg raises you mean keeping your legs straight and just lifting them (as seen in this picture), then you are only minimally using the abdominals as support, and the primary motivation for the exercise comes from the hip flexors.

Effect on abs: leg raises vs crunches


When is it better to get gold per 10 items instead of saving for something else?

Question: I know supports usually get Philosopher's Stone and Heart of Gold, but what about other roles? Also would getting a 3rd gold per 10 item on the support such as Kage's Lucky Pick be a good idea or would it be better to get one of the other support items?
Comment: Due to season 4, this has definitely changed.
Answer: I like to build 3 GP10 items on my supports because when coupled with all the gold generating runes and masteries, you get 3.525 gold per second. That's a Sight Ward every 21 seconds or an Oracles Elixir after 1:54 seconds.
Being a warding machine by about 20 minutes into the game is so valuable that I would rather hold onto these 3 GP10 items for as long as possible and not worry about what they upgrade to.
Answer: The point of gold per 10 items is to increase that gold generation early since you will not be getting creep score.  You get a philosopher for mana regeneration and heart of gold for health bonus for your survivability.  Generally you want to build a gold per ten on a character if it is beneficial for you in what it builds into generally.  Stone builds into Shurelya's Reverie, heart finally into something useful, Locket of the Iron Solari.  These are both useful to a team as a support.  Kage's pick only builds into deathfire, not as benificial to team, and Avarice Blade also gives gold per ten but builds into ghostblade which only gives benifits to holder again.  You would want to sell pick and avarice blade later on for other items due to this fact which is not very viable.  From the league wikia, the items pay for themselves after roughly 12 minutes.  The gold you have to put in is locked up for 12 minutes each so there are more viable options to buy.
Answer: depends on the player but typically support build 2 gper10 items and wards oracles etc just because the game might not be 50mins long when you have enough money you can then upgrade the gold per 10 items in late game team fights assists is where your income will come from.


Is that normal to have many idle connections in MySQL (without persistent parameters)?

Question: But we didn't use any persistent connections. Why are there many idle connections? We noticed that by using 'show processlist' command and the time was about 4000-8000 seconds. Those connections looked like always 'sleep'. We're using Nginx with PHP in fast-cgi mode, and we use PDO library. Any suggestions?
Comment: Did you find anything on this?
Answer: That sounds like a client isn't closing its connections properly, so the server keeps them hanging around until they time out. If a client just opens a connection, then runs a query and then abandons the connection, it is NOT closed (even though the client can't access it any longer after throwing the handle away). My understanding is that the web server should close these connections when the page completes. Looks like this isn't happening. As to why, I don't know.
The default timeout setting on the server is 6 hours, which means that on a web server this can easily build up to several thousand connections waiting for a timeout.
Answer:
Disable persistent MySQL queries in your php.ini configuration file.
Edit your /etc/my.cnf file and set some additional limits.

set-variable    = long_query_time=120
set-variable    = wait_timeout=28000
set-variable    = connect_timeout=25
Answer: hmmm, it depends.
Certainly the DBMS won't invent these connections on its own. While the overhead in creating a connection to mysql is low, there's still going to be a gap between creating the connection and firing a query off, and between the query completing and the results being polled completely, and then a further gap before the script closes down the connection. These will be even more pronounced if your code opens the connection before its needed, and/or waits too long before closing the connection.
However in the absence of persistent connections, no web based software should be holding a connection open for more than a couple of seconds. If you have mysql replication enabled then this will show as a thread running since startup.
What does
<code>SHOW FULL PROCESSLIST
</code>
(from the mysql shell) show?
Comment: those connections were always 'sleep', seems they did not do anything~
Answer: I noticed you tagged fastcgi. I suspect thats your problem.
PHP (assuming thats what your doing this with) only terminates the connection once the interpreter has exited and cleanup starts, meaning the connection remains open as idle until garbage collection. FastCGI typically doesn't 'terminate' as it runs as a service which is why your experiencing these long sleep times.
The best way to fix this it to explicitly declare a mysql_close() at the end of your code. Anyway, its best practice to clean up after yourself! But as a kludge workaround you could set a wait_timeout in mysql to destroy the connections.


Can we infer how the Fifth Holy Grail War would have ended had Gilgamesh not intervened?

Question: In the Unlimited Blade Works scenario, Gilgamesh intervenes in the Fifth Holy Grail War, kills Berserker, and seizes Ilya. If he had not gotten involved, can we guess based on knowledge from other scenarios what might have happened?
Comment: My first thought was to close this, but the Fate series is deep and well developed enough that I do think there could be a reasonable answer to this. I also dislike our current trend of closing any question with a complex answer that isn't entirely well posed. Perhaps the OP could add some information? It seems you're asking about Unlimited Blade Works, is that correct?
Comment: I'm inclined to leave this open, seeing as this is the sort of thing that Nasu is fond of making word-of-god pronouncements about (and he's made a lot of them, though I don't know whether or not about this particular topic).
Comment: I'm not a huge fan of the fate/stay series but I doubt that they had a working roster of who would defeat who before they made the Gilgamesh edit. Or if that was even the case. There is a high possibility that this alternative was never considered IMHO this is like asking could Goku have beaten Cell if Gohan was defeated?
Answer: Scenario 1: The Einzberns cheated....again! and thus win
the Einzbern family were at one point holders of the 3rd Magic, Heaven's Feel, which is what the Holy Grail War was original for, reclaiming this magic that at some point the Einzberns lost. Zouken had interest in Heaven's Feel himself because of how his soul was rotting and the Tohsaka only sought to use the Grail to reach the Root.
However the Einzberns have had a somewhat unfair advantage, the Greater Grail's "soul" if you will is that of Justeaze Lizrich von Einzbern and the Einzberns have always had the components needed to finish the war.

the Lesser Grail which origianlly was a cup but after the 3rd war being the form of a Homunculus similar to Justeaze because if damaged would end the war as was the case in one of the wars and one needs the Lesser Grail to use the Greater Grail to have their wish granted
the Dress of Heaven which can control the Greater Grail

and in different versions of the third Holy Grail War the Einzberns use their knowledge of the System to create a new Servant to get the upper hand, either replacing Beserker with Avenger (which failed horribly) or summoning Ruler to be the absolute authority.
in this answer i explain what i believe the Einzbern's plan was in regards to Ilya. since she's the Lesser Grail if she was killed (being a Master) then no one gets their wish. it's like the Einzberns taking away the ball from the ballgame if things don't go the way they want, but instead of taking the ball away they make every other player destroy it. (it's for this reason Kotomine and Gilgamesh needed Ilya (or at least her heart) for their purposes)
Scenario 2: Angra Mainyu is born and no one wins
in the 3rd war the Einzbern Family summoned Angra Mainyu in the Avenger Class but was quite weak and was killed off early. his death contaminated the Greater Grail.
Kiritsugu concluded after his encounter with Angra Mainyu (talking to him via the radio, TV and appearing as Irisviel) that any wish would lead to destruction, even if Kotomine and Gilgemesh didn't have their own plans and a Master or Servant were able to get a hold of Ilya as the Lesser Grail for their own use and make their wish this would release the six billion curses of the world which Angra Mainyu now embodies.

The materialization of Angra Mainyu brought forth by truly opening the Holy Grail is an ichor that will consume every human being, 6 billion curses flowing out from the gate to hell. Gilgamesh specifically mentions 5.6 billion curses for an unknown reason. It is a reaper that will strike down all humans equally, an endless darkness that is born from humans and massacres them.

Source: Avenger - Abilities - All the World's Evil
in the Fate and Unlimited Blade Works routes of Fate/Stay Night even before anyone makes a wish the mud from the grail is already spilling and corrosive. in Fate when Shirou fought Kotomine he has to take care to avoid being hit my the mud Kotomine shoots at him as at one point he is grazed by it and is almost succumbed to the curses.
in Unlimited Blade Works Saber stops Rin in wading into the Mud Pool to reach the deformed Shinji because of what it would do to her (if i recall it was Saber's abilities which gave her some protection but it was describing that it was eating away it her)
Sakura as the Lesser Grail
while Sakura is also a lesser Grail thanks to Zouken infusing fragments of the one from the 4th war into his Crest Worms that are inside her Sakura's connection to the Greater Grail is to that of Angra Mainyu itself.
before she realized she was The Shadow it was already consuming people and Servants and unleashing Saber-Alter and Blind-Berserker. while Zouken might have been able to control Sakura for years in the end The Shadow wasn't under his control. it would have only been a matter of time before it controlled Sakura as the ribbons that's seen on The Shadow make up Dark Sakura's dress which was then used to bind her after her's and Rin's fight near to the end of Heaven's Feel.
Answer: I get the impression Illya would've agreed to team up with Shirou & Rin temporarily (Despite one of her goals being to kill Shirou) Kotomine would've then not order Lancer to help Rin, and waited towards the end of the war before he intervened.
Illya, Rin, Shirou, Berserker would then arrive at the church, to defeat Caster, Archer would then have to take on Berserker 1v1.
This fight could go one of two ways, Beserker could overwhelm him, since Archer has no form of terrain advantage, or Archer could spam noble phantasms(like Gil albeit slightly slower), buy enough time to summon UBW, then sword spam the rest of his lives away(Quicker than Gil). I'm assuming Illya will stay with Berseker though, when Shirou and Rin go to take on Kuzuki and Caster. I'll assume Archer wont sword spam in case he hurts Illya.
So i'll just say Berserker kills Archer, although Archer is at the very least taking 6 labors ... Which incidentally will make Shirou useless for the remainder of the route, since he can't gain anymore of his abilites/knowledge, and his projections are poor without understanding UBW.
Rin/Shirou VS Caster/Kuzuki continues as normal, until Berserker bursts in and kills Caster & Kuzuki. At this point Illya probably cares a bit more for Shirou and doesn't want to outright murder him, HOWEVER as a master she'll probably decide this is a good time to take out Saber. Rin will probably also want to seize this opportunity, and will taunt Illya, into allowing her to make a contract with Saber. Saber may object a bit, but she'll see it as the only way to save Shirou and Rin, Shirou will instantly agree to it...
They then agree to fight OUTSIDE of the church (pretty much for the sake of plot, but i'm sure the Berserker/Archer fight, and Berserker breaking into the scene would've caused significant damage to the structure, so it's unfavorable for all combatants) Saber can compete with Beserker since she has a compotent master, holds her own, defeats him with Excaliblast when the oppertunity presents itself. Illya then teams up with Rin, Shirou, Saber.
Illya gets kidnapped by Kotomine from Emiya household. Taken to Fuyuki temple, used as lesser grail (killed). Saber defeats Lancer, Rin & Shirou defeat Kotomine. Then it ends like the Sunny day ending of UBW :)
Comment: What evidenice backs any of this up? where does this impression you mention at the very beginning come from? this seems to read like a malformed version of just one route which you admittedly say *"ends like the Sunny day ending of UBW"*
Comment: Meh it's ALL complete speculation but i don't see a reason to get rid of Saber. Especially since Rin didn't have to give a large proportion of her mana to Shirou


Secondary Fermentation

Question: I've only started brewing Wine a year ago and have been keeping the subtle complexities of making a good wine as simple as possible, only to level up when I feel confident. So, consequently I've only been brewing wine from fruit concentrate.
From what I've learned about the various reasons why secondary fermentation is needed when brewing with fruit, I don't see the benefits of racking into a carboy prior to bottling, other than letting the particulates settle, which, with time will occur anyhow.
Can anyone enlighten me of a minute point I've missed, or shed light on a small detail I've missed?
Comment: I haven't made wine, but I'd assume it is for similar reasons as beer brewing; letting particulates settle out. It is also good for bulk-aging away from the majority of the yeast cake, or for flavor additions (fruit or hop additions in beer brewing). It's worth pointing out that in homebrewing, it was historically encouraged to use a secondary, but has since fallen out of style.
Answer: Generally secondary has a couple benefits.

Racking to a secondary removes the product from the loose fluffy trub that makes a clear product difficult if bottling right from primary. The secondary then gets a nice compact trub that doesn't disturb as easily.
If primary is over an extended time that results in yeast death (several weeks). A secondary will reduce bad esters that get released when the cell wall ruptures. Whether from autolysys or from age.

Secondary has fallen out of favor with brewing since many styles can ferment out before #2 is an issue and we write off #1 as volume loss leaving behind enough beer not to disturb the trub.
Answer: My experience is mostly with fruit wine, not so much with grape wines. When you make (fruit) wine, you can

use syrup
juice the fruit (e.g, blackberries)
just mash the fruit (e.g., for strawberries, where you hardly can squeeze any juice out)

Each of these leaves with you with more solids in the fermenter. (For example, after fermentation strawberries are all pale and mushy.) After fermentation, you rack the wine to another fermenter (or bucket) to get rid of the sediment at the bottom of the first one; the wine can clear and clarify.
If you're happy with the cloudiness / clearness of your wine, skip the secondary.

Secondary Fermentation


Favourited questions credit

Question: Do users who ask questions that are favourited a lot (by other users) get any sort of credit e.g. badge etc or is this just a convenience for those reading the question?
Comment: You can find the full list of badges here: http://programmers.stackexchange.com/help/badges
Answer: There are two badges for having your question favorited. You get a silver "Favorite Question" badge if 25 people favorite your question and a gold "Stellar Question" badge if 100 people favorite your question. Both badges can be awarded multiple times.

Favourited questions credit


What is the difference between Canon's Remote Switch and Remote Control?

Question: I own a Canon Rebel T3i and on the accessories page on Canon website there is a Remote Switch (Cable Switch) and Remote Control. What is the difference between both (they are the same price) and if I got one do I really need the other one?
Comment: If you want a wired remote control for the shutter and auto-focus, there are many third party products that are much, much cheaper than the Canon part. I bought a number of them from assorted vendors. The one I like the best is http://flashzebra.com/products/0218/index.shtml
because it uses a standard 2.5 stereo headphone cord. You can get extensions to any length you want. I found that the remotes with fixed length cables were too short for self portrait work.
Answer: The remote switch (RS-60E3) is a wired shutter release switch that allows for the activation of the shutter via a cabled interface. Your location is limited by the length of the cable.
The remote control (RC-6) is an infra-red shutter release device that allows the shutter to be activated using an infrared signal. Because the RC-6 uses infra-red to communicate with the camera and the sensor is on the front of the camera, this means the remote must be in front of the camera to trigger it, with a direct line-of-sight to the receiving sensor. It is possible to reach over the camera and trigger it whilst standing behind it. The RC-6 also offers a 2 second timer.
They perform the same function with the difference being wired vs. infra-red.
Comment: Same function but perhaps different **purpose**. Don't know about the T3i but I bought the wired shutter release switch for my T1i because the salesman said it can be used behind the camera.  He said the wireless switch had to be used from in front of the T1i. I wanted an external shutter switch for steadier time exposures of e.g. lightning, not pictures with me in them.
Comment: These are not really the same thing at all, the shutter cable essentially gives the same functionality as the shutter release button including half press it to focus and meter. The wireless remote control activates a two second timer based release on the camera same as activating the two second timer when the shutter release is pressed. So not the same function at all.
Comment: @MarkJerde I don't know if this is true for T3i but sounds like a valid reason cause the remote control receiver is in the forehead of the camera


Definition of Absolute Risk Aversion

Question: In its Wikipedia article, absolute risk aversion is defined as
$ARA = -\frac{u''(c)}{u'(c)}$. However, I have alternatively seen absolute risk aversion
defined as half the decrease in consumption that an investor is willing to accept to avoid a gamble $\varepsilon$, where $E[\varepsilon] = 0$, $E[\varepsilon^2] = 1$, and $\varepsilon$
is independent of consumption:
$$
U(C - ARA/2) \equiv E[U(C + \varepsilon) \mid C].
$$
Using the latter definition, how can I show that $ARA = -U''(C) / U'(C)$?
Comment: why is there a lowercase $c$ and conditional expectation on the right? and don't we need to specify that this is an infinitesimal gamble, rather than having a constant variance 1?
Answer: Set $y \equiv c+\varepsilon$. So $y$ represents changed consumption around and "close" to a given level $c$. Take a 2nd-order Taylor expansion of the function $E[u(y)\mid c]$  around $c$, which is treated as fixed since we condition on it :
$$E[u(y)\mid c] \approx E[u(c)\mid c] + E[u'(c)(y-c)\mid c] + E[\frac12u''(c)(y-c)^2\mid c]$$
But $y-c = \varepsilon$
so
$$E[u(y)\mid c] \approx E[u(c)\mid c] + E[u'(c)\varepsilon\mid c] + E[\frac12u''(c)\varepsilon^2\mid c]$$
Due to the conditioning, and the independence of $\varepsilon$ from $c$ the expected value distributes and applies only to $\varepsilon$:
$$E[u(y)] \approx u(c) + u'(c)E[\varepsilon] + \frac12u''(c)E[\varepsilon^2]$$
Since we assume
$$E[\varepsilon] = 0 \Rightarrow {\rm Var}(\varepsilon)=E[\varepsilon^2] =1$$
we obtain
$$E[u(c+\varepsilon)] \approx u(c) + \frac12u''(c)  \tag{1}$$
Now consider $u(c-\frac 12 ARA)$, with $ARA \equiv -\frac{u''(c)}{u'(c)}$, and take a 1st-order Taylor expansion in this case, again around $c$:
$$u\left(c-\frac 12 ARA\right) = u(c) + u'(c)\cdot (c- \frac 12 ARA - c) = u(c) - \frac 12 u'(c)\cdot ARA $$
Using the definition of $ARA$ to replace it we obtain
$$u\left(c-\frac 12 ARA\right) \approx u(c) - \frac 12 u'(c)\cdot\left (-\frac{u''(c)}{u'(c)}\right)$$
$$\Rightarrow u\left(c-\frac 12 ARA\right) \approx u(c) + \frac 12 \cdot u''(c) \tag{2}$$
The right-hand sides of equations $(1)$ and $(2)$ are equal therefore, approximately, so  are their left-hand sides or,
$$E[u(c+\varepsilon) \mid c] \approx u\left(c-\frac 12 ARA\right)$$
which is valid as long as $ARA$ is defined the way it is. QED.
If the variance of the gamble is not unity but $\sigma^2 \neq 1$, then the more general equation is
$$E[u(c+\varepsilon) \mid c] \approx u\left(c-\frac {\sigma^2}2 ARA\right)$$
Answer: @Alecos's answer is great. For pedagogical purposes, I'm just going to rephrase some of the steps.
We want to show that $ARA = -u''(c)/u'(c)$ given that ARA is defined such that
$u(c - ARA/2) = E[u(c + \varepsilon) \mid c]$. So, following Alecos' answer, take a 2nd-order Taylor expansion to get
\begin{equation}
E[u(c + \varepsilon)\mid c] \approx u(c) + \frac 12 u''(c).
\end{equation}
Then by definition,
$u(c - ARA/2) \approx u(c) + \frac 12 u''(c)$.
Now, taking of 1st order Taylor series expansion of the left-hand side of this expression, we see that
\begin{equation}
u(c - ARA/2) \approx u(c) - u'(c) \cdot \frac{ARA}{2},
\end{equation}
which implies that
\begin{align}
u(c) - u'(c) \cdot \frac{ARA}{2} &\approx u(c) + \frac 12 u''(c) \\
ARA &\approx -\frac{u''(c)}{u'(c)}.
\end{align}
Comment: this is certainly right and well-written, but I still don't think it's a good idea to do this with $E[\epsilon^2]=1$; in that case, the relation holds only as an approximation, and it may be a very poor one depending on the relative levels of $c$ and $\epsilon$. In the limit $E[\epsilon^2]\rightarrow 0$ it holds exactly, and that's the clearest way to define risk aversion here (in the limit, as a coefficient that relates the variance of an infinitesimal gamble to its consumption equivalent).
Comment: I'm sorry, I'm just not understanding. So, you would define ARA such that $\lim_{\sigma^2 \rightarrow 0} E[u(c + \varepsilon) \mid c] = \lim_{\sigma^2 \rightarrow 0} u(c + \frac{\sigma^2}{2} ARA)$?
But in this case, doesn't $\lim_{\sigma^2 \rightarrow 0} u(c + \frac{\sigma^2}{2} ARA) = u(c)$ regardless of the value of ARA?
Comment: Thanks for the comment. I was wondering about this. So, just to clarify, are you saying that for this reason, it's usually better to just define ARA as -u''/u' ?
Comment: well, that's the more convenient way, but it's equally valid to define ARA as the limit, as you take $\sigma^2=E[\epsilon^2]\rightarrow 0$, of twice the ratio of the consumption equivalent to $\sigma^2$. For it to be a precise definition it needs to be explicit about this limit, though, rather than taking a finite $\sigma^2$ as given.
Comment: yes, the limits are the same, so it's about the derivative. Suppose $\epsilon$ has mean 0 and variance 1, and define the certainty equivalent $z(c,\gamma)$ implicitly as the $z$ satisfying the equation $E[u(c+\sqrt{\gamma}\epsilon)] = u(c-z)$. Then the derivative of $z$ with respect to the variance $\gamma$, at $\gamma=0$, is $ARA(c)/2$. In principle, this can be used as a definition of $ARA$. (Btw, if we want to write $z$ in terms of sd $\sigma$ rather than variance $\gamma=\sigma^2$, then we need to talk about the second derivative. Also see MWG problem 6.C.20, which is related.)

Definition of Absolute Risk Aversion


Upgrading a PERC h310 to a PERC H710 mini RAID controller on a Dell R620

Question: I have an ESXi 5.0 Free license host using an internal Datastore (RAID 5, 5 Disk) that was configured with a Dell PERC h310 RAID controller.  The disk performance was very poor, so I upgraded to the PERC H710 Mini.  The IT Tech installed the controller and powered the host back on.  I had to rescan the controller and the datastore appeared.  Should any settings be changed in the RAID BIOS, or should the default settings be sufficient?  Is they anything to be aware of when performing this type of upgrade in order to achieve the maximum performance?
Answer: Congrats! Sounds like you worked at a low level, and successfully made the jump.
At this point, you should leave everything alone and make sure the system is stable.
Most of us leave those PERC cards at stock config. There is rarely any benefit from changing the config.
The #1 issue your config will have is that it is RAID5. If you want real perf improvement, especially for writes, you need to move to RAID10.
Answer: Yes you should change settings - read and write cache is probably disabled, back sure you have a UPS then go and enable write back caching and adaptive read caching (CTRL R on boot up, F2 for operations on the vdisk)
Comment: You'll also want a RAID controller battery, and a method to cleanly stop writing in the case that power loss is imminent, etc.