Is this about Physics, or just theoretical armchair physics?

Question: Because when it comes to real practical advice on specialist experimental techniques I may as well be talking to myself. It seems to be singularly useless.
Comment: Also, the tone you've taken here is not going to help your case. You've got *me* miffed and I should be a natural ally: getting more experimenters and more experimental questions is one of my long-term goals for the site. Note also that tpg2114 (who answered you below) is a practical hands-on type as well.
Comment: @DirkBruere Nobody is forcing you to play the game side of it. Focus on asking good questions, and posting good answers to good questions, and ignore the crap and the noise. If you don't like the game, don't play. But that doesn't mean you can't participate if you choose to do so.
Comment: Dirk, don't be a dick.  Those that regularly participate here do so because they get some value from answering questions they find interesting, not because they're standing by for Dirk to ask some questions on *specialist* experimental techniques.  This is the way things work.  You should be smart enough to understand that.  Why aren't you?
Comment: hi   you state _Because most people here do not seem to be paid for their physics knowledge in real life. Correct me if I am mistaken._  no offence intended but thats a logical fallacy, an appeal to authority is implied here. Your argument here seems to me to be "If a person is  paid for what they do, then they know more than you do". I found out the hard way, getting my car brakes "fixed", by a paid trained mechanic, that this ain't necessarily so :)  I self study, love doing it  and find this site extremely useful.    regards
Comment: Why do you say armchair?
Comment: Some more link you might want to read: http://meta.physics.stackexchange.com/q/2948/ http://meta.physics.stackexchange.com/q/5129/ http://meta.physics.stackexchange.com/q/6266/
Comment: @dmckee Thanks for digging up those links. Also suggested reading (in particular how to walk the fine line between experimental (good) and engineering (bad) questions): http://meta.physics.stackexchange.com/q/65/ http://meta.physics.stackexchange.com/q/6135/ http://meta.physics.stackexchange.com/q/5553/ http://meta.physics.stackexchange.com/q/4535/
Comment: Although I think it's probably true that most of us here "do not seem to be paid for their physics knowledge", there are in fact quite a few of us who are, especially on the theoretical side. I up-voted your question, because although I agree with others that your tone is off, the question of how to attract and be welcoming toward experts in other sub-fields than the ones we already have is an important issue. (It seems to be a difficult issue for Stack Exchange sites in general for some reason.)
Comment: The problem is that people who self study are studying, not doing experimental physics. It's a lot easier to read a book than find a well equipped lab and get access to it for research that takes hundreds of hours of input. There is a huge difference between reading about something and then trying to do it. You come across all kind of problems too trivial for the book to cover but which are show stoppers when it comes to doing. "First prepare your sample to within 1 milliKelvin of the desired temperature...".
Comment: Because most people here do not seem to be paid for their physics knowledge in real life. Correct me if I am mistaken.
Comment: I just seriously dislike the whole gamification thing which encourages trivia and idiots while marginalizing the rest. When I first came on here I tested the theory by posting one or two seriously crap questions and got most of my 2800 points that way.
Comment: Sorry - 3800 points
Comment: As for people standing by to answer my questions, when I do get answers I take time out to answer other people's questions. But it has to be two way.
Comment: Maybe it's just me, but I have a tough time imagining self-study and experimental physics overlapping, unless the questions that come from it are just idle curiosities about how one might actually conduct an experiment. My guess is if you are trying to do an experiment outside the confines of a well-funded lab, you're not going to be capable of (or have a need to) get your temperature to within 1 milliKelvin (to continue your example). Self-study of theory seems plausible because all you really need is some pen and paper, maybe a computer to do some crunching.
Comment: And so people doing self-study-experiments may not be asking the right question or the one that will be the most helpful to them if they dropped in to ask how to get to 1 mK accuracy. Just like somebody asking me a computational question about how to solve for the flow around an airplane would get a radically different answer if that person only has their laptop at home or has access to every machine in the Top 500.
Answer: It's always amusing when (insert branch of physics here) complains about how few (insert branch of physics here) experts there are and we're just overrun with (insert opposite branch of physics here) questions/people. The theoretical folks complain(ed) all the time there was too much applied physics and not enough theory. The people who want homework help complain there is too much advanced physics. Experimentalists complain there's too much theoretical physics. Maybe if I get motivated, I'll go through meta in the past 2 years and pull together all the various times this comes up.
Anyway, I'll address the idea you are raising rather than the (albeit mild-mannered) rant in the text.
Yes, there are disappointingly few experimental physicists on the site. And many experimental questions go unanswered or get threatened with close reasons as being too engineering, or not about physics, or whatever by people who don't conduct experiments.
It's unfortunate for sure, but we want experimental physics questions just as much as other areas. We simply don't have the people here yet in a critical mass to make it work well. We have the tags for it, we have a few people excited to answer questions about it, but it also has to be questions about experiments we can answer. I would love to answer questions about experiments in fluids (analyzing results, measurement techniques, etc) but I would be completely useless to answer particle physics experiment questions.
So there are two things that people who want to discuss experimental work should do. First, get other people who conduct experiments involved. If you are actually conducting experiments, odds are good that you have colleagues you share lab space/equipment with. Get them on the site too so that way we start building an experimental sub-community.
In the mean time, the second thing you can do is be proactive in defending your question and make sure you include the experimental-physics on it. Don't say:
"What kind of filter should I use to record XXXnm wavelengths?"
and leave it at that. Because to many people, that would be off topic (and to the rest of us, a poor question). Instead, say:
"I am designing an experiment to measure Y under conditions X. I know it radiates at A, B, C frequencies and I want to capture phenomenon D which occurs primarily at wavelength XXXnm. How do I set up my camera to record this?"
because then it clearly communicates that you're looking for an answer to a physics experiment and not just trying to come up with some new app that's a Instagram-Clash of Clans-selfie stick integration tool (this post hereby counts as me establishing priority for copyright on such a tool!).
It opens up some good avenues of discussion because experts can give advice on the experiment overall -- maybe there's better ways to set it up or other things to consider (like maybe all the glass in the world happens to filter that particular wavelength and you need to do something special). And experimentalists who are researching how to conduct similar work can find the answer here and say "Wow, a place to ask/answer experimental questions? Awesome!"
Having an awesome repository of questions and answers is what draws theoretical (and for better or worse, homework) questions and experts, so let's build up the same repository for experimental ones.
Comment: @DirkBruere: You are implying that all professional physics is experimental physics. This is wrong, and an insult to theoreticians. Whether [tag:experimental-physics] should be used or not (it is kind of a meta tag, after all) is a tangential issue, but it certainly would raise visibility of experimental questions if more questions started to appear in that tag. Once it is sufficently populated with *good* questions, we could discuss abolishing it in favour of more specific tags.
Comment: @DirkBruere Ideally that tag wouldn't be needed because it is a meta tag. But my recommendation to add it is really just a suggestion to be proactive until the sub-community is established and there are reviewers within it who can take care of experimental-type questions in the review queue. Until that happens, help out those 3000+ rep users by making it very, blatantly obvious that you are asking a question about experimental methods and that you're aware of the differences between experimental and engineering, that you've read the policies, and so your question is on-topic.
Comment: Maybe you could also tag your questions with the "research-level" tag, if they are for research. The tag does not limit to theoretical physics and seems to describe your problem: very specialized knowledge needed.
Comment: I did not expect to have to tag something "experimental physics" any more than anyone else tags their stuff "theoretical physics". It should be obvious from the question. Maybe a different tag is needed: "professional physics" for those whose questions need answers for real life applications rather than just curiosity or fun.
Comment: A friendly, passive-aggressive "Hey look, this is an experimental question!" through using the tag is a much better idea than angry ranting when close votes start showing up because people think you're looking for shopping advice or something.
Comment: @DirkBruere *"I am currently working, right this second, on stuff directly related to questions I post"* I actually think that this may be one of the reasons for the site attracting relatively few active experimenters. The stuff that comes up predictable we already know how to handle. It's the surprises that send us looking for outside help, and we'd like to find it faster than the site can reliably provide it without more experimenters participating. Cue chicken and egg, or vice versa.
Comment: @DirkBruere [We've talked about what motivates people](http://meta.physics.stackexchange.com/questions/6567/why-do-users-answer-questions) before and we've also [talked about why most experts don't ask questions](http://meta.physics.stackexchange.com/questions/4571/question-self-destruction-why-dont-experts-ask-more-questions) and I think you're just in an unfortunately place where you fall into the "I come here to get answers to my questions" category of user but there aren't enough "experts who do nothing but answer questions" in your area to help yet.
Comment: Cool answer, I respect your patience.
Comment: Probably. But I am currently working, right this second, on stuff directly related to questions I post. Bottom line being, if the answers I can supply are better than the ones I'm getting (assuming I am getting any at all), it's not worth my time.
Comment: There's not a problem with being a user who consumes answers more than contributes answers, but it's just unfortunate in your case that there aren't enough producers to help you. So like I said in my answer, you can work to raise the number of contributors to build up the critical mass needed, or you can give up on trying to build the community. You wouldn't be the first, nor the last, to move on and I doubt anybody would fault you for it.
Comment: I can't explain in too much detail what I am doing for commercial reasons, but I have managed to measure the time of flight of a sound pulse in gas to 1 part per million over 60mm and we are now investigating effects of milliKelvin temperatures on the results. In length terms we are measuring to around 50nm


ABRSM exams for adult beginners

Question: I have been playing piano for five years as an adult beginner, and recently passed my ABRSM grade 5. I am determined to pass all eight grades but I realize that the higher the grades the more difficult the process will be, but I am determined to master this instrument to the best of my ability.  Will it be possible for someone who started as an adult to go all the way through the grades? I like the structure that studying for the exams provides, and use the syllabus as a guide with my piano teacher. I would love to hear from other adult beginners who are taking ABRSM exams.
Comment: I would quibble with the idea that it is easy to achieve such an aim. Does anyone really think it is an easy task to get to the stage of mastering pieces such as fugues from the Well-Tempered Clavier, as required for level 8 on the ABRSM syllabus?!
Comment: Of course it is possible! Unless there is some restriction due to age, you can easily achieve this goal and even aim for something higher.
Comment: My mind gets blown every time I see a piano score. I agree nothing about it seems easy to me.
Comment: It is certainly possible, since it has been done by someone I know - and has probably been done many times. I am trying something similar, but only 2 years into the project.
Comment: @Shevliaskovic there are no age restrictions for the ABRSM exams.
Answer: The problem with adults is they have a lot of other stuff on their plates. Kids are in a great position, with relatively few draws on their time, in reality, and probably some financier there as well. Go for it. There will always be other things to pull you away from having some practice time, but force these things into the background.
If you have the desire, then make time to get the music flowing. it will take time - and don't forget, you'll need grade V theory under your belt, too. Just do it. Later, you'll look back with pride, and have all that experience to fall back on - plus a nice piece of paper that proves you are a great player.
Your teacher must think it's achievable too. I used to run an exam centre, and the most nervous candidates were the adults. There again, nerves aren't such a bad thing, as they tend to concentrate the mind better.Kids are taking tests on an almost daily basis, so a piano exam is just another test to do for a lot of them.As long as you're enjoying playing keep going till you pass grade VIII.
Answer: There's a degree of truth in the idea that you have to start young to achieve full mastery of instruments such as violin or piano.  But that's about concert soloist level.  Grade 8 is no mean achivement, but it IS achievable by anyone with aptitude who is prepared to put in the work.  And - and this is why so many adults make excellent initial progress then give up - who is prepared to be patient when the early spurt slows down.
Be aware that the ABRSM seems to have succumbed to the modern "no-one fails" philosophy. You need a Merit or Distinction.  A plain Pass must be considered close to failure.
Answer: Your age should not be the problem. What can be a problem is the realities of adult life. If you have a job and a demanding family life then it is probably going to be hard to find several hours a day to practice your instrument. There is nothing about your age that makes it impossible, just the higher demands on a person time that seems to come from being an adult.
That being said there is some possible advantages. You can probably get more done in less time as an adult. You are mature enough to see the skill of your teachers and may very well take their teachings more seriously. There may be less of the superfluous nonsense that teachers have to deal with children.
So don't get too hung up on the age. Put the hours in and you will get the results.
Comment: Well, sort of.  Many adults manage to find plenty of regular time to pursue a hobby, craft or sport.  The particular issue with music is that spectatular early progress has to settle into a period of consolidation. A child just labours on.  An adult gets impatient and drops out.
Comment: @LaurencePayne - a child just labours on. Usually because some pushy adult who's footing the tutoring bills makes it! Adults don't usually have that kind of pressure.

ABRSM exams for adult beginners


What happens to bounties when a question is moved to another Stack Exchange site?

Question: Just wondering what happens to the reputation.
Answer: As far as I can tell the rep the answer gained after winning a bounty get's migrated along with it.
If you're referring to moderators migrating a question with a bounty attached to it, this bounty has to be removed (thus returning to the user who asked the question) before migration.
Comment: Ah, yes, that was my question. I answered a question with a 200 bounty and it was migrated to Severfault :) I was just kind of curious to if the rep just disappeared or was refunded.
Comment: I suspected that was the cause, I removed the bounty and migrated it to Server Fault, because it was likely to get you a better answer for free!
Comment: Totally understandable :) Was just curious.


What is the meaning of 近いほうが here?

Question: I came across this phrase in a passage and I am not quite sure what it means. It seems unlikely that it is used for comparison, but I could be wrong. The Chinese translation following it seems to translate it to "not only". There is no grammatical explanations in the book, and searching online hasn't been helpful either. So someone please illustrate the appropriate grammar here.
Answer: 生に近いほうが can be broken down as 生に近い + ほうが. 生に近い means to be close to raw. Presumably close because you do some preservation, just not cooking. ほうが is used as a judgement/comparison. This example, which I copied from here, illustrates this:

部屋{へや}は、広{ひろ}いほうがいいです。

This example means As for rooms, wider/more expansive ones are better. The ほうが is used to make the judgement that wider ones are better. In your example, 生に近いほうが means that the speaker is about to make a judgement/analysis about things that are close to raw. In your case the speaker says that they let you understand the original taste and don't destroy the (original) nutrients.
As for why the Chinese translates that as not only, I imagine it's because the Japanese clause ends with ~し, which is a grammar that can be used to list things/reasons.
Comment: Thank you so much for your comprehensive explanation. However, I do still have one question. The Chinese translation completely ignored this phrase and it made sense. So is translating it necessary? If yes, what should be the appropriate translation? and if not, why?
Comment: @Zeyuan I think in the Chinese there is an implicit comparison to non-raw food as well. But I'd say that translating that part isn't necessary because I think it's just drawing attention to the unique characteristics of raw food and it could be replaced by 生に近いのが (I'm not a native speaker though so I could be wrong).

What is the meaning of 近いほうが here?


What cheeses work well for pizza that will be refrigerated and reheated?

Question: I make pizza pretty frequently, and I always have leftovers. I have a few go-to crust recipes that reheat well after being refrigerated, but I'm never happy with the cheese upon reheating. Usually I use freshly grated, part-skim, grocery store mozzarella and the leftover pizza never gets good and melty again. What other cheeses might give me better results when I reheat the pizza after a day or two in the fridge? I'm open to outside-the-box choices; I can tweak the other ingredients to complement the cheese. What I am looking for is a texture in the reheated pizza that is as pleasant (although, not necessarily the same) as it was fresh from the oven.
Answer: It isn't a perfect match for the flavor and texture of regular pizza cheese, but soy cheese (Daiya mozzarella shreds, specifically) reheats beautifully and is even good cold. We switched cheeses because of a dairy intolerance, but found the storage properties to be a great side benefit.
It does end up being a noticeable change to a pizza's flavor profile, but may be less of an impact if there are lots of other toppings on your pizza. If you find the flavor and texture of the Daiya cheese acceptable when the pizza is fresh, it will still taste the same when reheated.
Comment: I'll give it a shot, but I'm suspicious of vegan cheese. The reviews are encouraging, and local grocery stores carry it.
Comment: It is definitely outside-the-box, but you asked for that ;) One of the best "upgrades" that we (accidentally) discovered is adding pepperoni on top, which emits a bit of grease and gives a more familiar look and taste to the cheese.
Comment: What types of pizza crusts have you used with this cheese? For a pan pizza I would use a lot more cheese than I would for a thin Neapolitan style. I could go either way – load up on cheese or use it more sparingly?
Comment: Generally Neapolitan (often just buying dough from the store when we're in a hurry), we've been looking for a good deep-dish recipe but haven't had a chance to try one yet. A relatively sparse layer of cheese tends to work better, because it does take it a while to melt and we haven't had any success with really thick, gooey layer (the crust burns before the cheese fully melts!)
Answer: While there are many cheeses to choose from, I find that provolone both heats and reheats well. Also, the flavor profile works nicely with most Italian dishes, pizza included. I've used smoked, unsmoked, mild, and sharp. Whether smoked or not, the mild tends to be a little "meltier", and more suited to the flavor I'm looking for.
Answer: I've found that lower fat cheeses tend not to reheat particularly well. Full-fat mozzarella would be better than part skim. Also, keeping the cheese in bigger chunks gives better results than shredding, so slicing may be a better way to go. I use full-fat soft mozzarella which I pull apart or slice rather than shredding, and it has a much better texture when cooled and reheated than hard mozzarella, which tends to get a waxy look and texture.
I've been thinking that the reason for this is water loss, and that the reason for the texture of shredded cheeses and lower fat cheeses after cooking is that they get dried. It may be worth trying semi-skimmed cheese in strips or thin slices and see whether that fixes your problem rather than changing cheeses. Maybe next time do half shredded, half sliced and see what you think.
Comment: "Waxy" describes it pretty well.


Do you get penalized for writing a title very similar to other blogs?

Question: Do you get penalized if you use somebody's post title with few words changed in the title to match your post?
Answer: No. What I do when I decide to write is search for my proposed title and look for the results shown in the top spot. I get their link and use AdWords to search for keywords. Then I take those keyword into the content of my own post.
Answer: No. There are lots of pages out there using similar or identical page titles. There's a finite number of them available and its unreasonable to expect them all to be different.
What does matter is if the page's contents are very similar or identical. In this case that is low quality content and bad for SEO.


how to connect android phone(client) to laptop using only one ip address(static)?

Question: I am doing a android project. I want to connect my client(android phone) using ip address to my laptop(server). I am using ip address of wireless modem(MTS). Each time i reconnect the ip address changes. So how can I keep this ip address constant so that only one ip address can be used for connection via wireless internet connection?
Answer: If client IP is fix then here's an approach
1)Write a code listening to port in android client
2)In the server, write a client to connect to android port send the server IP to the android
Then you can continue with your normal approach
OR
You can use UPNP for your case where upnp server broadcast its info to all the clients in the network.But implementation will be a bit extensive in this case.
Answer: The ip-address of your modem is given by your provider and will most likely change everytime you reconnect.
So my answer would be you can´t. This makes the question far off topic, you might wanna take it off.


How to convince my boss to use SCRUM

Question: We are 7/8 person in the development team. I would like to convince my boss to use agile technics(SCRUM). He told me to present a bit of documentation, in order to evaluate it. He has an economy background but he is very open to "new tecnologies" and to experience. I can not present a big amount of documentation otherwise he will never read it. Can anyone suggest something?
Answer: Articulate how Scrum will improve the one thing most important to your boss
In addition to @zsolt's success stories, find out which one of the following is most important to your boss. It is easier to say they want all of them, but one of these may be more important than others based on your organization's current situation and their role in the organization. Try to articulate how Scrum  will improve that specific item of interest to your boss:

Improve customer satisfaction: If your customer is frustrated with the painful change control process, this may be of interest. Also, they get to see a working product much sooner.
Minimize risk: By deploying a minimal application early and adding  features to it every sprint or every few sprints, you get faster feedback and minimize risk of the project needing major rework.
Improve team morale and retention: Scrum improves team morale by channeling all prioritization through one person (the Product Owner), by encouraging self-organization (as against command-and-control) and by providing opportunities for team members to learn new skills (cross-functional).
Increase productivity: By reducing context switching, by removing impediments, by improving teamwork and by keeping team size manageable.
Improve quality of output: While Scrum does not require any specific engineering practices (such as TDD or continuous integration) by requiring a shippable increment at the end of each sprint it pushes you to adopt good engineering practices. Also, by making the team agree on a definition of done and by continuous improvements through retrospectives it improves the quality of output.
Comment: I'd also add shared work meaning there is less dependence on individual developers availability (or sticking around) to get certain tasks done. This one thing can be a big  deal for a manager in my experience.
Answer: You can pitch success stories, and this collection might be a good start: https://www.scrumalliance.org/success-stories, or you can ask for a month to do it, and show him/her the benefits from your own experience.
Comment: A month sounds a bit short, going from an adhoc development cycle to a bit more structured Agile cycle might add overhead in the first few itterations.
Comment: I kind of agree, however, it is very rare that a manager let teams to try out something for more than a month without any prospective results.
Answer: Ask your boss if he is willing to read a book about the subject. I think this is the best way to get most of the needed information and a better understanding of the concepts then some slides and summaries will give. I believe any manager should continuously read books about their respective industries processes and tooling.
The newest book of Jeff Sutherland "Scrum The Art of Doing Twice The Work In Half the Time" reads like a novel and anyone should be able to finish it in a couple of evenings.
If your boss is more skeptical, maybe the book "This is Agile" of Sander Hoogendoorn might be a nice alternative. Sander writes about his Agile experiences and it does not focus on a single framework like Scrum. His years of experience are a nice and complete read from general Agile concepts to implementation.
Pushing Agile bottoms up is a start, but for it to work I think you also need to push top-down. The whole organization needs to understand why you want to be Agile and should support this, else it will be a hard ride.

How to convince my boss to use SCRUM


Difference between "mas" and "más"

Question:
What's the difference between mas and más?
What rules should I follow to know which one to use?
Could you provide examples showing their uses?
Comment: Interesting(?) note, 'mas' also means 'but' in Portuguese, I'm no etymology expert though, so just pointing out the connection.
Comment: @Kage so is in Spanish as well; but that's not the only meaning it has.
Comment: @aparente001 I observe (https://spanish.stackexchange.com/tags?tab=new) you have created several tags lately, with no description of use in its wiki page, nor tagging other questions with them. This is not very useful. Let's use Meta to regulate tags and agree on how to use them when it is not trivial.
Answer: Más means 'more'

No quiero más comida (I don't want more food)

Mas means 'but', usually it can be replaced by 'pero'

Fui a casa, mas estaba vacía (I went home, but it was empty)

They both have the same pronunciation(*) despite the accent, the accent is here to make clear what meaning is actually used. Note that 'mas' is uncommon in a casual conversation, it is mostly used in literature.
(*) That's only true if they are alone. In a complete sentence, the pronunciation may vary. As written in some comments:

They are pronounced in the same way when they are alone.
Mas is "átona" and más is "tónica", so they're not pronounced exactly the same.
Words that are "tónicas" are stressed in the context of a sentence while the "átonas" are linked to whatever "tónica" word appears next in the sentence (forming a group that is treated like a "whole word" in pronunciation). Here is a good article about that: blog.lengua-e.com/2011/palabras-tonicas-y-palabras-atonas
Comment: @MikMik yeah you're right. They are just pronounced in the same way when they are alone. The "tónicas" are stressed in the entonation of a sentence while the "átonas" are linked to the next "tónica" word (forming like a "whole word" in pronunciation). Here is a good article about that: http://blog.lengua-e.com/2011/palabras-tonicas-y-palabras-atonas/
Comment: I don't think their pronunciation is the same. `Mas` is "átona" and `más` is "tónica", so they're not pronounced exactly the same. But I don't know how to explain the difference, really.
Comment: "Mas" can mean "pero" but also "sino". But "mas" is a very formal way for both meanings; for that reason people tend to use the other options.
Answer: "Mas" is rather unfrequent - at least in every day speech, here in Argentina, but I suspect it's the same in many other places, based on movies, TV, books, etc. It even sounds a bit archaic.
You almost always will see and want to use "más", not "mas" (most of the times you read "mas", it's probably a "más" missing an accent).
How to tell them apart? A quick rule (that I'm making up right now so it's obviously not thorughly tested!) is remembering that "mas" means "but". So if you can replace it with "pero", it's "mas"; otherwise, it's "más".
A dumb example of both words in a sentence:

Las dos son palabras perfectamente válidas, mas una se usa mucho más
  que la otra.
Comment: Agreeing with Juan, I never heard 'mas' as in 'but' once when I was in Argentina.
Comment: It doesn't make any sense comparing "más" and "mas" in the frequency of use. They don't mean the same! It would be like saying that "hello" is more frequent than "helo" in English. You can say that "pero" is much more used than "mas" (they mean the same).
Comment: "más" and "mas" is not the same. "Más" is a comparative adverb while "mas" is a adversative conjuction.
Comment: The usage comparison was comparing the frequency of 'mas' and 'pero'
Answer: When you use "más" it means more.
When you use "mas" you are contrasting ideas, like "but".

Difference between "mas" and "más"


Hedgehog AP Bio question

Question: Could someone please explain this AP Biology question? I know the answer is C but I do not understand why. Doesn't Smo prevent gene transcription? If you "block its activity" then wouldn't it cause gene transcription, whereas the goal of treating cancer is to prevent transcription? Please help!
Comment: Reread the line: "When Hedgehog is absent, Ptc inhibits another protein known as Smo"; Hedgehog is present in the cancer cells, so what you want to do is to *mimic Hedgehog's absence*. The question is hard because there is a lot of inhibitory and disinhibitory activity in this pathway, so that's what you have to do, try to follow all those +s and -s; it might be helpful to draw the whole thing out as a block diagram, and to take that approach with similar questions in the future.
Comment: Thank you! This was actually helpful, I think the information was worded a little weirdly - "When Hedgehog is absent, Ptc inhibits another protein known as Smo, which, in turn, blocks the activation of a group of proteins..." I think I was thrown off by the end of this sentence, because the way the sentence is constructed makes it seem like when Smo is inhibited it blocks the activation of a group of proteins, when it was actually the opposite idea!
Answer: I'm just going to outline the alternatives, I'll leave validating why choice C to you.
Choice A. If the new molecule acts in the same fashion as Hh, the results will be identical. If the new molecule bound to Pct but did not effect a response, that might work.
Choice D. Addition of Ci into the nucleus initiates transcription which seems to be the issue here.
Choice B. Best wrong answer! Can you inject enough stem cells to make a difference? Will the cells have some adverse effect? More importantly, the binding of messengers to receptors is a reversible process. The Hh will be able to detach from Ptc on the stem cells and eventually interact with Ptc on the native cells.
So, what effect will Hh have if the Smo in unable to respond?
Comment: Thank you! This was great! Especially your justification for B and explanation that binding to receptors is a reversible process. Now I why that choice was incorrect! :)

Hedgehog AP Bio question


Are there other sites such as Rome2Rio?

Question: I have been solely relying on Rome2Rio (click the link for a quick explanation of what Rome2Rio is) for planning transportation around Europe. However, only recently have I noticed that it doesn't provide complete information. For example, some TGV routes aren't included and I've had to find routes through other websites. Are there other websites similar to Rome2Rio or is there a more complete version of such a site?
Comment: You can't assume we all know this site, or know it as well as you do. You should tell us briefly what it does and especially what features it has (or lacks) are the ones you need.
Comment: it's not really the same (there is no mix trains/planes) but to have tgv routes, try http://mytripset.voyages-sncf.com/#/search/FR_fr
Comment: TGV routes will soon be available through SNCF OpenData portal: http://www.nextinpact.com/news/93038-la-sncf-va-mettre-ses-horaires-tgv-en-open-data.htm
Answer: I'm Chris from Rome2Rio, if you don't mind sharing your experience we'd be keen to find out which TGV routes and European routes in general you have found are missing from Rome2Rio results. This would help us review and improve our results in future. If you prefer you can send the details to email@example.com
If you are looking for alternatives to Rome2Rio you could also try routerank along with the Voyage SCNF site already mentioned.  Also there are a couple more German focused sites with similar concepts GoEuro and Waymate in the future they may expand to feature other European countries in their data.
Some other sites that you may already be aware of that I'd recommend would be Bahn a comprehensive schedule planner along with Seat 61 which has good references and guides to travelling by train in Europe.
There also several nice sites using the Rome2Rio API, but as it is generally the same dataset as Rome2Rio you may not be as interested in those :)
Comment: +1, Love it when site owners come and engage in a useful manner, and aren't afraid to show alternatives.
Comment: When I travelled in the Balkans, I found some bus routes missing from Rome2Rio database. I wrote to them with all the information needed and Chris answered that they appreciated the info. Unfortunately, **they have not added anything to the database 3 months since**.
Comment: I also recently heard of https://www.kenavo.com/
Answer: I think adding GoEuro for europe is important, specially because you can do booking. Note that I work for the company.
Comment: Hi and welcome. Are you in any way affiliated with GoEuro?

Are there other sites such as Rome2Rio?


Confusion over VLAN tagging

Question: My question is, if I have a Cisco switch with a particular port kept in default VLAN 1 and the native VLAN of the trunk port is changed to 2. When a frame arrives at the trunk port from that port it will be an untagged frame, right? If yes, then the trunk port will tag this untagged frame with its own native VLAN (VLAN 2) before sending it over to other end of trunk, right?
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it.
Answer: VLAN tags are placed on frames leaving a trunk port except for frames in the native VLAN for that port.
Access ports, despite being a port for a particular VLAN, do not tag frames, and, depending on the switch, a received tagged frame may be dropped on an access port.
A frame coming into an access port will not have a tag.  It will be tagged as it leaves the switch on a trunk port (assuming it is not in the native VLAN for that port), but it will not be tagged if it leaves the switch on another access port.
Comment: Hi Ron,so this means VLAN tagging occurs only at trunk ports.Now if I have only a single switch with multiple VLANs but no trunk port as I am not connecting any other switch or router,then in this case how will traffic separation between VLANs on same switch take place as there is no VLAN tagging in frame to carry VLAN information?
Comment: VLANS create virtual switches inside the switch. The ports on the switch are configured for the VLAN the port serves. Single switch, multiple VLANs, no trunks: Frames come into the ports with no tags, and are either forwarded to the correct port in the same VLAN as the port on which it arrived, or it ends up flooded to all the ports in that same VLAN, except the port on which it arrived. Tags are applied only on trunk frames. Most access devices don't understand tagged frames.
Comment: The exception (although, not actually an exception) to the no tags on access ports is the case of an access port configured for both VoIP and data when a VoIP phone is connected to it. The link discovery protocol (CDP or LLDP) will discover the VoIP phone and negotiate a trunk with the VoIP phone acting as a switch. It's not really an exception since the port ends up being a trunk port despite being configured as an access port.
Comment: yes...exactly...so in case Single switch, multiple VLANs, no trunks:frames dont carry any VLAN information....The traffic separation  between different VLAN s is solely done  by switch intelligence .Its only when I have Trunk ports and multple connected switches that I require frames to  actually carry VLAN information so that VLAN  tagging can be done at trunk port.Hope I am right .....
Comment: @SreejitMenon, based on your last comment, you appear to understand how and where tags are applied.
Answer: No.
The native VLAN on a trunk means that:
A) Any untagged frame arriving on the trunk will be treated as being in the native VLAN (regardless of what VLAN it was in on the sending switch).
B) Frames on the native VLAN will cross the trunk untagged.
In your example a frame arriving on the default VLAN (VLAN 1) will be forwarded out the trunk port on VLAN 1. Since VLAN 2 is the native VLAN that means the frame on VLAN 1 will be tagged.
The only way a layer-2 switch will ever move a frame from one VLAN to another is if something is misconfigured. You could misconfigure it intentionally but in my opinion it would still be wrong.
Comment: oh yes....I got it now....But even when i configure either ends of trunk link with different VLAN(intentional mismatch) ,it is seen that trunk port gets blocked with message "Mismatch found in local pvid"....still I got my question cleared...thanks a ton
Answer: The switch receives it and since there is no tagging will threat it as if it was on VLAN 2 (in your example). So if it receives a broadcast on this port, it will forward it out of all ports configured with VLAN 2 (still untagged doh).
Comment: So acc. to this ,all frames from VLAN 1 will be treated by untagged ?
Comment: no, all untagged frames will be treated as if they were from VLAN2 (in your example with native vlan 2)

Confusion over VLAN tagging


Question about metta

Question:
Does metta mean that we should not ignore people?
Is it possible to forcefully and assertively tell people their wrong doings? What about scolding?
My reservation: If one always remains kind it's likely that people will do whatever they want with you which will result in more problems or not stating one's concerns sufficiently
Comment: Why (in what situations) would you want to tell people "forcefully" (and is "forceful" really a good description for speech, what does it mean, or do you mean something related but slightly different like angry, intimidating, persuasive, loud)? And why would "stating one's concerns sufficiently" be difficult without "remaining kind"? This question might be clearer if it were more specific and personal (i.e. why are you asking, what problem[s] are you facing), otherwise answers might be general but irrelevant to your concern..
Comment: My question can be generalized since metta in Buddhism is also generalized and should applied in any situation. If for example somone treats us (repeatedly) wrongly and does not want to stop. Wouldn't assertive speaking to him be more effective? Human are emotional beings and they usually change if you forcefully and again repeatedly tell them a new way of behaving. Or let us take life threatening situations  or child abuse.. How is kindness helpful in these instances?
Answer: Human are emotional beings and they usually change if you forcefully and again repeatedly tell them a new way of behaving.
People can also be (or learn to be) bullies -- and unless you are able and willing to be the biggest bully on the block, I suggest that trying to persuade people using "force" is the wrong way to go about it.
To be honest, i.e. to avoid concealing a fact that appears to contradict my thesis, the suttas describe the Buddha has having a "lion's roar" ... and being like a bull among men ...  but,

Perhaps (I'm not sure) that's not relevant to use of force -- for example:

The Pali Commentaries explain that there are two kinds of lion's roar: that of the Buddha himself and that of his disciples. The former is sounded when the Buddha extols his own attainments or proclaims the potency of the doctrine he has realized; the latter, when accomplished disciples testify to their own achievement of the final goal, the fruit of arahantship.

See also Did the Buddha ever 'thunder' during a Fire Sermon?
The Buddha can be trusted to know when what and how is appropriate -- for example:

In the case of words that the Tathagata knows to be factual, true, beneficial, but unendearing & disagreeable to others, he has a sense of the proper time for saying them.

What about scolding?
I don't know (exactly what "scolding" is), according to the dictionary it's "an angry rebuke or reprimand".
So that seems to get into the question of whether and when anger is appropriate.
There was a topic What is a wrathful Buddha? from Vajrayana where an answer describes that as being like a parent pretending to be angry with their children in order to protect them -- and/or transmuting the energy of anger in a skillful way.
I'm not convinced that everyone is able to be so skillful, though; I think of anger as associated with a loss of skill (like a regression to one's infancy), and generally something to steer clear of. The Dhammapada:

Na hi verena verani
  sammantidha kudacanam
  averena ca sammanti
  esa dhammo sanantano.

Hatred is, indeed, never appeased by hatred in this world. It is appeased only by loving-kindness. This is an ancient law.

Another possibility might be that "scolding" implies telling someone something repeatedly or endlessly. I'm not sure that's effective though -- if it were effective, ought you need to repeat it?
Or let us take life threatening situations
I think you might go to the police, or the courts, or use physical force yourself (though this may not have been true everywhere, my personal experience of police leaves me admiring their ability to arrest a person "with overwhelming force" and yet still "without violence" -- like you might restrain a young child near something dangerous).
Or consider a drug addict, for example, asking you to help them to continue their habit.
I think you'd be within your rights to reply, "No, I won't. It's not good for you." (though I'm sympathetic to the fact that people do help addicts).
And I think that when you say "No" like that it doesn't have to be forceful (though it may need to be repeated), nor unkind -- the kinder the better, in my opinion. The kindness may be an even more important part of the message than the "no" (the "no" closing a door but the kindness opening one).

There's also an expression that I thought might be relevant -- i.e., "It's not the size of the dog in the fight, it's the size of the fight in the dog" -- that might help to explain how larger people can be bullied by smaller.
My experience of dogs tells me that's superficially true, e.g. that to deter a cowardly dog attacking a smaller dog, I may to need to be loud and explosive i.e. bark and not remain silent myself: to show it that I have a bigger bark than it does -- that there is (contrary to first appearances) a 'big dog' in me (or "in the fight"), i.e. that I'm the bigger dog.
Among humans, though, it may be more a matter of perseverance than intensity -- unless you can (and are willing to) sustain anger for hours, days, years, you may lose an anger-based competition -- anger is unreliable as a motive (but may fuel your opponent's opposition).
And so, I don't recommend it, I think it's the wrong avenue to pursue or to set off on.
Answer: Does metta mean that we should not ignore people?
Metta is loving kindness or the wish for others to be happy. If you can ignore people while maintaining the wish for them to be happy, then there is no contradiction. Introspect and see if this is possible. To be clear, I'm not saying it is or isn't. You should investigate yourself and see.
Is it possible to forcefully and assertively tell people their wrong doings? What about scolding?
Can you be forceful with people and assertive while wishing them nothing but happiness? Again, introspect and see! If you can do this, then there is no contradiction whatsoever.
My reservation: If one always remains kind it's likely that people will do whatever they want with you which will result in more problems or not stating one's concerns sufficiently
It is not about acting kind. What matters is what is in your mind and in your heart. If you can maintain a mind of calm and a heart full of nothing but the wish for them to be happy, then whatever you do will be motivated by loving kindness. Is it possible to be forceful and assertive towards another being motivated with nothing but the wish for them to be happy? Again, introspect and find out. Is it possible right now for you? Is it possible that if you keep training your mind in metta that it could become possible for you? These are good questions to experiment with :)
Comment: +1 "Find out for yourself" usually seems to me an unsatisfactory, insufficient answer; and yet I like this answer.
Answer: When you do metta, simply concentrate on sending good wishes to people. I use mantras for this purpose. They are very effective and practical. By singing mantras of loving kidness (e.g. "May all human beings be happy!") you build up positive impressions of loving kindess in your mind and slowly transform.
You don't need to concetrate on ingoring people because this just distracts you from metta. Bad people will gradually go away. This is one of the benefits of doing metta, that fire (mening anger or angy people) will not touch you (read Mettanisamsa Sutta for the list of full benefits).
Answer:
Does metta mean that we should not ignore people?

In my opinion metta and ignoring people or not are two different things altogether. They don't relate at all. You can abide in metta and still ignore people. Ignoring people doesn't mean that you no longer have a 'metta-mind'.

Is it possible to forcefully and assertively tell people their wrong doings? What about scolding?

One can be assertive. That again doesn't mean that one has no metta.

My reservation: If one always remains kind it's likely that people will do whatever they want with you which will result in more problems or not stating one's concerns sufficiently

I think that a better translation of metta is well wishing instead of loving kindness. I did a metta retreat this year with a nun and she spoke of well wishing as a better translation. To me it makes more sense indeed.
If you work with well wishing as translation for metta you'll see that it's not a problem to be assertive towards other people, that you could even scold (the Buddha did), that it doesn't mean that you let other people walk all over you. It just means that you don't wish harm for other people.
Reacting with "I wish you break your neck" if someone hurts you, is not metta for instance. Reacting with metta in this situation would be to walk away, give yourself room, distance, safety. Make a wish for yourself to not give rise to anger, fear or whatever. You can also make a wish for the other person: "May (s)he be able to let go of this/that behaviour."
As the nun told me it's important to take care of one's own safety. That's also part of metta practice. You don't have to wish another person happiness. I tried that with one person of the 'enemy category'. Guess what, it doesn't work. It felt insincere. But, as she told me, that's not necessary. I wished him: "May he be able to live his life skilfully." According to her that was metta, it was well wishing.
I'm not sure I'm making sense.
(Hope you understand what I want to convey; English is not my first language.)
Comment: Indeed, I also try not to globally judge them as being bad rotten and also try to wish them all best, since all human beings have to face vicissitudes like loss of others, sickness, aging, death, mental suffering etc.

Question about metta


Selenium RC : How to handle drop down list while automating?

Question: How to handle  the drop down by using  selenium RC. While I am automating Gmail  registration page the birthday section giving error
Answer: You need to show us:

HTML code
Your code
Your error message

Having said that, I assume you are talking about Month dropdown list from Gmail registration?
From what I can see:

Month dropdown list, you can click to open it by using span id = "BirthMonth"
After this list is expanded, you can get a list of items by using div class = "goog-menu goog-menu-vertical", looking for its child elements div class = "goog-menuitem", each div class = "goog-menuitem" represents a month respectively.
Comment: Ohk.... I am just adding the same


What's the difference between the 'Burning', 'Poisoned', and 'Disoriented' status debuffs?

Question: What's the difference between the 'Burning', 'Poisoned', and 'Disoriented' status debuffs? I know for sure that Burning and Poisoned deal a damage over time effect to affected teammates and enemies, but is that all? What does Disoriented do?
Answer: Looking at the XCOM Mod Buddy, there are several statuses that prevent abilities from being used: Disoriented, Burning (Acid is burning too), Carrying Units, Bound, Confused, and Stunned.
Here's the other thing - every single action is an ability, including firing -- but since the game wants you to be able to fire while burning, they added in exceptions for particular abilities and particular statuses. So rather than list every ability that's blocked, I'm going to list every ability that isn't blocked (it's a much smaller list!).
Burning

Is cleared upon entering water
Damage Over Time (varies, depending on source)
Prevents use of all non-passive Abilities except: Interact, Hunker Down, Medkit Heal Use, EVACing, Melee Attacks, Gremlin Heal commands, and Shooting.

Disoriented

-20 Aim
-30 Will
-6 Mobility (Tiles)
Prevents use of all non-passive Abilities except: Overwatch, Reload, Looting, Hunker Down, EVACing, Suppression, Rupture(!?), Lightning Hands, and Shooting.

Poisoned

-30 Aim
-4 Mobility (Tiles)
Damage Over Time (can vary, depending on source)
Spreads to Adjacent Units (Yes, even Vipers'. I realize this makes no sense)

Poisoned and Disorient aim and movement penalties are defined by the defaults, which I believe correspond to .ini files that I haven't found yet, so if someone knows the default values, I'll happily add those in.
Comment: Thanks, most of my answer was purely anecdotal but thanks for the super in-depth answer :)
Comment: The .ini values you're looking for are in XComGameCore.ini under XComGame.X2StatusEffects. Lots of good info there, such as the fact that being disoriented gives you -30 will.
Comment: Even though this was not part of the question, you could also add "Acid Burn" and "Crysalid Poision" to the list for sake of completeness.
Comment: @Philipp in the first line i mention that acid burn is another form of burning. I'm not sure chyrssalid poison behaves differently from regular poison.


How do I add a hyperlink in a card to a document on my server?

Question: How do I add a hyperlink in a card to a document on my server? For document version management, I need the members to work on the document saved in my local server.  How do I create a link to my server?
Comment: Please note that this site is for questions about all kinds of web applications, not just Trello. You need to tag your question accordingly so that the people who can answer can find your question.
Answer: The answer depends upon what kind of network you have.
The link success your users will have will be determined by the permissions they each have as well as their connectivity to the server.
Meaning, if a user is not connected directly to your server or does not have access to the file location, they will receive an error message.
With that in mind, all you need to do is provide the link in a Card description.
For a MS Windows network, you would use the "UNC" version of the file location.
Example:
Latest file: \\servername\path\folder\subfolder\file
For a cleaner look, you can use Markup in the card description
Example:
To edit the current version of the file, click here.
Will look like:
To edit the current version of the file, [click here]
If your filename includes spaces, enclose the entire link in quotes ("\server.....ext")


Do I need a transit visa to visit Istanbul on my layover? Do airlines offer any city tours?

Question: I have a Bangladeshi passport but is currently living in UK with a student visa. Can I enter Turkey at my transit without a Turkish  visa? I will be travelling with Turkish Airlines and have a layover at Ataturk Airport.
I also read somewhere that Turkish Airline offers city tours in long transits. Is that true?
Answer: As stated in the website of Ministry of Foreign Affairs of Turkey, ordinary Bangladeshi nationals are required to have a visa to enter Turkey. However, since you have a UK residence permit, you are eligible to apply for a single entry e-Visa which is valid for one month.
Turkish Airlines, does offer guided tours in Istanbul for layovers of at least 6 hours. You can find more details on How To Apply on their website.
Comment: Good answer. One small note for brevity. Min 6 hours and Max 24 hours. And no application required, just clear immigration and go to Hotels Desk next to Starbucks. That's it. Even the meal on the tour is free. You only have to pay for anything you might want to buy from shops on the tour. If not, there are no costs other than the possible cost of eVisa
Answer: As stated in Timatic, the database used by Airlines:

Visa required, except for Holders of normal passports issued
  to nationals of Bangladesh holding a visa valid on arrival,
  issued by Ireland (Rep.), USA or United Kingdom or a Schengen
  Member State can obtain a visa or an e-visa on
  arrival, for a max. stay of 1 month. Fee: USD 30.-, EUR 25.-
  or GBP 20.-. The e-visa can also be obtained online prior to
  departure at www.evisa.gov.tr.

So you can either apply for an electronic entry Permit HERE, or you can get it at a Kiosk at Istanbul Airport.
Comment: The only problem with getting it at the Kiosk at airport is that right next to you the passport control queue keeps growing and growing and growing and those 3 minutes seem like eternity
Comment: @HankyPanky Makes sense. The two times I flew into Atatürk I had to queue for 10-15 minutes despite being the first person to leave my all-but-empty plane (I don't need an e-visa)


How does compass calibration work?

Question: I am wondering how compass calibration works / why e.g. drawing an 8 or rotating the phone to all 3 axis works (or at least shall work) - I mean I would understand the calibration process, if an application would say me: Point to north, then press that button down there, but you can start at basically zero knowledge for the app, just by rotating your phone! How is that done? Also, do I need to enter a special calibration mode or can I draw these figures (like the 8) directly in Google Maps? How does Google Maps know that I am not just really moving the phone but want to calibrate the compass? Thanks for any hint!
Comment: Moving an object through a magnetic field can induce an electric current, which I'm guessing is being measured in this case.  The figure 8 ensures that the phone is moving along every possible vector in a 2D plane, which ought to allow it to distinguish north from south.  I think.  As for Maps sensing it, that one's easy -- what other time do you make such an absurd motion with your phone?  It's quite different from normal movements and ought to be simple to detect.
Comment: Technical information: http://electronics.stackexchange.com/questions/22144/magnetometer-shaped-calibration
Comment: Flagged as dupe, please don't post two separate questions for the same problem. Edit your existing question with new information; http://android.stackexchange.com/questions/30328/compass-configuration-file
Comment: @bigbadonk420 This is not a duplicate, it's a completely different question.
Answer: The purpose of calibration is to figure out how to compensate for how the components in your phone (screws, speaker magnets, etc.) interfere with the measured magnetic field.
The calibration process is based on the fact that you can separate the internal and external contributions to the magnetic field by looking at how the field changes as the phone is rotated. For example, in one orientation the magnetic field from the magnet in the speaker will add on to the Earth's field; but when the phone is oriented in the opposite direction, the two fields will partially cancel out.
As you wave the phone around, the magnetometer records how the magnitude of the measured field changes and uses this to calibrate the x, y, and z magnetic field sensors. See geometrikal's answer to a similar question for more details on this process. Note that this calibration does not let you compensate for the influence of other external objects (e.g., your refrigerator) on the magnetic field.
Regarding the implementation in Google Maps: I believe that Google Maps has no control over the compass calibration because there is no such functionality  in the Android API. The magnetometer is probably calibrating itself continuously, and Google Maps is just asking you to rotate your phone so that the magnetometer can collect the data it needs to get an accurate calibration.
In other words, you can calibrate your compass any time the magnetic field sensor is being used just by waving your phone – there is no "calibration mode".
Comment: But how does the android OS decide when to change it's calibration values, i response to movement or at regular intervals or both?
Comment: Android must just maintain a history of readings and keep applying the [_hard-iron_](https://www.sensorsmag.com/components/compensating-for-tilt-hard-iron-and-soft-iron-effects) correction on them. This is even [specified in the documentation](https://source.android.com/devices/sensors/sensor-types#magnetic_field_sensor).
Answer: Compass calibration works by detecting the magnetic field intensity of earth. But sometimes due to strong interference from other electronic devices like transformers, compass sensor may get wrong idea about the magnetic poles of earth and can point in wrong direction.
So to ensure that, it asks users to recalibrate compass by rotating in figure-8 direction so that it can judge the magnetic intensity in all directions. From that data, it deduces the actual poles of earth.
Comment: This is actually a wrong answer.  Calibration can only cancel out the distortions coming from objects affixed to the device (thus rotating with the device during calibration). If the objects are in the environment, the phone will observe a fixed magnetic field and it will have no idea how far away from true North it's directed.
Answer: At any point in space, the magnetic field strength and direction is the net effect of all the magnetic field sources affecting that point.  The earth's magnetic field is one of them.  Magnetized screwdrivers, cars, refrigerator magnets, etc. all produce fields.  Fields are also produced by current flowing through wires.  It's like pouring water into a glass from multiple sources.  Once it's in the glass, you can't tell where it came from.
There is no instrument that can determine the "actual poles" of the earth by measuring the magnetic field at a point. What the phone can do, however, is sense the point where the phone axis is parallel to the N/S magnetic force line and determine which end of the phone is north-pointing.  If you do your dance far away from objects that might be magnetized, like cars and steel fences, the field the phone is measuring may be primarily the earth's field and hence the phone compass will be properly calibrated. If you then put the phone into a magnetized car, however, it will point the wrong direction for north. The steel in every car is magnetized to one degree or another.
High-precision compasses such are used on aircraft and serious maritime vessels actually have tiny correction magnets that are adjustable with screws for N/S and E/W errors. They are calibrated after installation by turning the vehicle onto known headings (a compass rose painted by a surveyor on a taxiway far from metal buildings, for example) and fussing with the magnets until the compass error is minimized. Then the residual errors are recorded on a "compass correction card" for use in correcting the indicated readings.  Search "compass correction card" to see the images.
In theory, the GPS could be used to calibrate the compass when walking or driving since the instantaneous GPS track is accurate. I have not heard of this being done, though it possibly is common.  It would work even in a magnetized car. However, in an airplane or a ship, this wouldn't work because the vehicle's heading is to one degree or another usually crabbed slightly into the wind and the GPS has no knowledge of this.
Comment: This doesn't seem to tell how and why the common calibration procedure in Android works.
Answer: I've tested the compass fields measurments provided by Android phone and found out, that if I rotate the phone by 180 degrees, the field doesn't change to exactly opposite, which must be the case if the sensors are correct. This might be due inner magnetism of the phone  details or sensor reading inacuracy.
If you don't compensate for that and just use reading as is and try to calculate the North direction, you'll find out that they are incorrect: rotating phone by 90 degress around vertical axis doesn't lead to rotating measured magnetic field by the same angle (that is true for any angle, it's just easier to check it with 90 degrees).
So the aim of calibration is to develop compensation formula which will transform wrong readings from magnetic sensor to more realistic values, from which we can calculate the correct bearing. My guess is that it is looking for optimal shift of zero for each axis which will give the result magnetic vector length independent on the phone orientation (that must be the case in ideal situation but is not the case when the zero is shifted on any axis).

How does compass calibration work?


I have 1635 inbound and one outbound connection on my relay is that normal?

Question: I am running a middle relay on a raspberry pi b+ its been up for about two weeks now and until last night was averaging 50MB downloads a day. Now its finally sped up, hope im not doing something wrong my relay has HSDIR tag on it not sure what that means.
Comment: I'm seeing something similar on my relay-only server. I increased my max bandwidth rate to 8Mbps (from 4 Mbps) and the number of incoming connections (in ARM) went waaaay up....but the number of outgoing connections actually went down. I'm currently sitting on 2114 incoming and 72 outgoing. I'll wait and see if it settles down. But the imbalance does seem odd. Why so many incoming....but so few outgoing? Yours was a generic question about the perceived balance / imbalance between incoming and outgoing connections. The previous responder missed the point of it, I think.
Answer: You're not providing enough information to answer the question but you can always take a look at the status of your relay at Globe or Atlas. Familiarize yourself with what each of the flags mean, that will help you diagnose if there are issues. HSDir means that you are hosting a portion of the hidden service distributed hash table or the Hidden Service Directory.
You can also make manual circuits to confirm that you can indeed use your relay as a node. This is pretty easy if you're using STEM.


Reversibility of a Markov Chain

Question: Rephrased question: Is it ever possible for a reducible Markov chain to be reversible?
Answer: Yes. Consider the Markov chain with just two states and no transitions between them. This is reducible, and any distribution is stationary and satisfies the condition for reversibility, since both sides of the detailed balance condition are zero.
Answer: Reversibility implies that if the Markov chain can go from $x$ to $y$ in finite time with positive probability, the same holds for $y$ and $x$. Hence the only way to be reducible is that there exists some states $x$ and $y$ such that the chain cannot go from $x$ to $y$ neither from $y$ to $x$. In other words there exists a partition of the state space such that the Markov chain starting from a state in a given class stays in this class forever with full probability and such that the Markov chain restricted to this class is irreducible.
In other words, one considers a collection $(Q_i)_i$ of reversible irreducible transition kernels on disjoint non empty state spaces $(S_i)_i$ with stationary measures $\mu_i$. The state space of the Markov chain is the union of the spaces $S_i$ and while in $S_i$, the chain uses the kernel $Q_i$. Every barycenter of the stationary measures $(\mu_i)_i$ is stationary and the chain is reversible but reducible as soon as there is more than one state space $S_i$.

Reversibility of a Markov Chain


Which lenses typically don't focus properly on the Canon 60D?

Question: I currently have the 18-200mm kit lens for my canon 60D. I am thinking of getting the 10-22mm wide angle lens as a second lens. So far with my kit lens I havent experienced any focusing problems or needed any adjustments (so far as I can tell). Will the 10-22mm give me problems and need to be adjusted? Are there certain lenses to stay away from on the Canon 60D since it lacks the micro-adjustment feature?
Answer: Generally speaking I think the concept of "lenses that don't focus well on body X" is a misconception. All mechanical and electronic gear is manufactured to certain tolerances...and usually, the more expensive, the tighter the tolerances. If you get two pieces of equipment that are at opposing ends of their range of tolerance, you might end up having to adjust one or the other to get a proper "fit".
In the average case, most consumer-grade equipment is within a tolerance divergence that you won't need to do any adjustment at all most of the time, and it would only really be on the off-chance that you end up with a particularly poor match that you actually do need to adjust even to be moderately useful/acceptable. If you find that you regularly encounter lenses that need adjustment, its probably better to adjust the camera rather than the lenses, as its probably the camera that is near the limit of its tolerance range. Additionally, if you are really looking for a perfect fit with less chance of even a need to tune either the camera or a lens, you should probably be looking at more expensive equipment. Both lenses you listed are from Canon's consumer line of lenses, and are generally not manufactured to the stringent tolerance levels that the L-series lenses are. (The 10-22mm is a pretty solid lens, but its not an L-series lens, so I wouldn't expect it to have as stringent of manufacturing quality.)
Sadly, the 60D is the first of the Canon XXD line that I know of recently that doesn't seem to offer any micro-adjustment. My standard recommendation when people ask whether they should get a 60D or a 7D, given the moderate price difference, is to get the 7D. Not only does it have AF microadjustment, but it is packed full of a ton of other useful features as well.
Comment: Yea, the 50D was the only in that line that ever has had micro adjust.
Comment: @dpollitt: I think the 40D and 30D also had it via firmware upgrades, though.
Comment: My 40D has the newest firmware(almost 3 years old now), and it does not have micro adjust. If you know how I can get it, that would be awesome though! I have v1.1.1.
Comment: Guess it may have just been someone poking around in the firmware that noticed something about AF, but it seems it was never actually enabled: http://chdk.wikia.com/wiki/40D
Answer: I have the 10-22mm lens on a Canon 60D and it works just fine.  As mentioned on the previous answer, because of the wide angle there is quite a margin for error in most circumstances — which won't show up on the finished photo.
The only lens I've had any focus problems with on the 60D is the Samyang 85mm f/1.4 (manual lens) fitted with the 'EURO' AF-Confirm chip.  This fires the confirm-beep slightly short and while the chip is configurable, the steps between adjustable values are large and hitting the nail on the head at f/1.4 is difficult.  In the real world, it's annoying but easily overcome by short-focussing the lens, pressing the button half-way, rolling the focus forward until it beeps and then rolling back just a hair.  This does rule the lens out for high-speed action shooting, but I've found very little reason to take a f/1.4 portrait lens on a sports-shoot.  Decreasing aperture helps, though (as it will on all lenses that don't get the AF quite right), and while it would be nice to have focal adjustment on the 60D, its other benefits still put it above the 7D in my mind.
If in doubt, tell your lens retailer what camera your lens is for when you buy it and ask them if it will work perfectly with that model.  If they say yes, get a receipt and you have strong grounding to return the lens for a full refund if you have problems (as the reason you bought it was the seller's guarantee it would work, so if it doesn't then it's "not fit for purpose"). Good luck!
Answer: I haven't heard of any problems with the 10-22 (or with the 60D in general) but even if I did I wouldn't worry with the 10-22, as long as you're not shooting at the minimum focus distance your depth of field will be huge so accurate focusing is not a worry. In fact I once left my 10-22 set to manual focus all afternoon, I didn't notice because I was still getting focus confirmation beeps whatever I pointed it at (meaning things were in focus within the tolerance of the AF chip).
Answer: I got back focus problem with the EF 50mm f/1.4 prime lens on my 60D. It happens with auto focus, even with a tripod. The focus (I use the center point focus) always fall to the back of the subject. The actually subject is always blur.
And 60D doesn't have AF micro adjustment which makes me very disappointed in Canon.


Is the price per person affected by searching a flight for more than one person?

Question: When I search for a flight for more than one person I usually search the flight for one so that I can easily have the total amount per person.
I wonder if there are cases in which searching for more than one person would result in a cheaper fare per person.
Comment: On full-fare tickets, when booking with some higher end travel agents (eg American Express), it's sometimes possible to get reduced rates when booking two tickets. Last time I looked, it basically brought the cost of two fully-flexible business tickets down to not much more than two non-flexible business ones, which is a large discount, but one not all that useful to many travellers...
Comment: What I know is, price _might_ be less when you are booking for a group, and a group for the airlines is 9 people or more.
Comment: If you travel with children, their price might be less (have seen them knock 10% off the price), so the per ticket ends up smaller.
Answer: The main case where the price-per-person will be different when searching for more than one person is when there is only one seat left at the cheapest fare. In such a case, the search engine (or at least every one I've ever seen) will search for the cheapest fare where all passengers can travel at the same fare.  That might mean bumping all passengers to business class, or taking an entirely different route.
For sufficiently large groups, you might be eligible for a group discount, too, but I think you won't find those discounts on most online search engines. You'd likely need to go through a travel agent.
Comment: Makes sense. I want to add: I've been a flight search engine developer (Spain, Portugal, Brazil), and - during countless tests against various airline and OTA APIs - I never once recall seeing a cheaper price when booking multiple passengers. Theoretically, of course, there could be group discounts. Airlines have different pricing policies. For example, I recall one "family-friendly" Brazilian airline that offered lower prices for children, although they still occupy a full seat.
Answer: They are unusual in the West, but there are some airlines that offer cheaper seats when booking for multiple people.  In particular, Singapore Airlines and Cathay Pacific both offer "GV2" and "GV4" fares, available only to groups of 2 or 4 passengers respectively.  For example, in this randomly Googled travel agent page, the single passenger price for a Singapore-Chennai/Kolkata return is S$700, while the GV2 fare is $600 and the GV4 fare is only $500.  These show up automatically when booking online for the appropriate number of people, no travel agent needed.
Of course, even in SQ's case, these fares are not offered on all routes or all flights.  When they're not, you may still be better off following Alessandro's suggestion and booking separately to get the best possible fare classes.
And before you ask, despite living in Singapore for >7 years, I was never able to figure out what "GV" stands for!  Probably "Great Value" or something equally naff.
Comment: @RossPresser Fare classes are single letters: GV2 is 'Q', GV4 is 'N'.
Comment: "GV2" is a combination code -- G for group, V for value, 2 for 2 people. From [this answer](http://travel.stackexchange.com/a/20253).
Answer: My experience confirms Flimzy answer, so I won't repeat that.
I would like to add a suggestion to get a cheaper price per person: when such situations arise just buy tickets separately and then share the total equally between each person. Try to find out which is the number of available tickets at the lowest fare and buy them in one transaction, then buy the others at higher fare. For example Ryanair website tells you how many seats are available with a given fare.
If you are quick enough (and maybe have 2 credit cards at hand) you can save some money.
I've personally used this trick a few times :-) but cannot guarantee that it will always work.
Answer: I can confirm one scenario where it makes difference - when you travel with kids. We used it this summer when travelling to Europe and it knocked off around $200 for the kids tickets. But not all airlines do it. But if you search e.g. on Kayak, there is under dropdown next to Search button this list of options:

Adults 18-64
Seniors 65+
Youth 12-17
Child 2-11
Seat Infant under 2
Lap Infant under 2

You can specify number of passengers for each age group and and then the price that Kayak shows is average price per passenger (so e.g. when price per adult only is $1400, with kids Kayak will start show $1300 per passenger) - and it also allows you to sort by it.
Comment: In fact for French families travelling within France with Air France (I know that is a lot of restrictions), you can benefit from specific discounts: "Special fares are available when you travel as a family or with children on flights in metropolitan France.
Parents/grandparents with at least one young child/grandchild (from 12 to 24 years of age) or a student (25-26 years of age). You must show proof of family relationship upon boarding: a French livret de famille or an official document showing the relationship."
Answer: It does change. Airlines sell tickets in blocks, so lets say one block cost $300 per ticket and next block is $400 per ticket.
Assume you want to buy 2 ticket but there is only one left in $300 block then you will be paying a total of $700 as the second one will be priced at $400 - meaning $350 per ticket!
Comment: If you want two tickets, and there's only one $300 ticket left, most airlines would actually sell you two $400 tickets at $800.


Screenshot Quality

Question: Is there a way to increase the quality of the screenshots that are taken by the default Screenshot application, the pictures have a very low quality especially when they are zoomed. I have a screen resolution of 1366x768
Answer: You can not tweak the quality of your screenshot, it only captures your screen or region (as is, the only quality adjustement you can use is the filetype used when you save your document).
If you need to modify your screenshot, you should use additional softwares such as Gimp or Krita
(I do not see your issue in the provided capture.)
Nicolas

Screenshot Quality


I can't inflate tire. Should I look for another pump?

Question: Hello to everyone in the community. I used to own a mountain bike which used 26" tires and I was able to inflate them after changing the tube while on the road. It wasn't perfect but allowed me to keep riding.  I have since switched to a road bike which uses narrower 700 tires and so far everytime I have tried to inflate them I find it impossible to do it properly. The pressure is just not enough to ride the bicycle and I am forced to just hire some professional to fix it. Has anybody experienced this? At  1.79m and 64kg I am certainly scrawny but I was thinking maybe with a different pump I could be able to inflate the tires.
Anyway, thanks for reading and any advice will be much appreciated.
Peace
Comment: Tire pumps have a maximum pressure that they can produce.  In particular, "compact" pumps, designed to be carried on a bike, are often short and hence cannot develop as much pressure as a longer pump.  But some pumps are designed to overcome this problem through several mechanisms.  You need to look at the specs of the pump.
Comment: Note that a "fat tire" pump will be designed to produce a higher volume than a pump for a thin-tired road bike, trading off pressure for volume.  So it's not surprising that your old pump doesn't work.
Comment: It sounds like you're trying to get to full pressure with a portable pump?  You'd be better off with a "floor pump", saving the portable pump for roadside emergencies / tube swaps.  Also, have you checked your valve types?  it may be that you're used to one type and have another on your new tires.
Comment: A CO2 cartridge is the best thing for a 700C tyrre.
Comment: We need more information. What kind of pump are you using? What pressure are you trying to achieve?
Answer: Most average small/hand pumps are in the 'high volume, low pressure' category. That means they have a big air chamber and are good for inflating a high-volume tire like on a mountain bike with a relatively small number of strokes, but once you reach a certain pressure, often in the realm of not enough for a road bike but maybe around enough for a hybrid, it can become impossible or impractical to go further. Small/portable pumps that work on road bikes do exist. Traditional frame pumps are one example, as are the "mini floor pump" type like the Topeak Road Morphs and its copies. There are also some decent true road mini pumps these days; the Lezyne Road Drive is one that works well. Of note is that many road mini pumps have proven to be basically bad products that don't work very well, and all of them, even the good ones, share the characteristic of needing a high number of strokes and being generally on the tiring side to use.
Most people with road bikes settle on having a floor pump at home, which makes it easy to reach high pressures because your body weight is behind it, and then carrying either one of the above options or a CO2 inflator. If you need a new pump and can only get one, one of the mini floor pump variety is often a good choice, because of the portable pump choices they're the easiest to reach full pressure with, plus they usually have gauges (which most portable pumps don't.)
Comment: Yeah, I have a loooong "frame" pump (roughly 20" long) on my bike.  It can generally get the tire up to 80 psi or so (if I don't wear myself out pumping first), but I have to get home (or to the sag wagon) to use a floor pump to get up to my normal 100 psi.
Answer: Are both sets of wheels using the same valve types?
I recently made a similar transition from mountain to road bike and I had trouble with my floor standing pump. The pump had so much resistance I could lift both feet off the floor and balance 100% of my weight on the pump without it going down all the way. I had assumed it had to do with the higher pressure needed for road tires. Days later I found out I wasn't converting my pump between its presta and schrader configuration correctly. Once I had the parts flipped around correctly my 63kg self had no problem with the pump.
As for my compact pump, it converted between valve types fine but it takes so long to get the tires up to pressure that I quit once it is around 80% of the tires' recommended pressure. Then I carefully ride home to my floor standing pump or to my local bike shop (one happens to be between where I work and where I live) to finish the job. As far as I know, that's just a compromise you have to make when using a compact pump. They take longer.
Comment: There is floor pump and floor pump. Those with short big cylinders that can also be used with car tyres are quite useless with racebikes. They produce pressures that don't normally exceed 4-5 bar. You'll need a typical track pump with a long slender cylinder to reach up to 12 bar.


How does heat get transported between the surface layer, twilight zone, and the deep ocean?

Question: Just as importantly, how do we measure the heat that's transported from the surface layer into the twilight zone and deep oceans?
Answer: I think the simplest answer is through water mass formation, the resulting thermohaline circulation, mixing caused by wind predominantly in shallow regions, and through downwelling processes. The heat exchanged with the atmosphere in the surface layers determine the temperature of the near-surface water. From there, mixing (caused by wind, for instance) will transfer some of the heat to lower layers in the ocean. In the case of areas of water mass formation, the sinking of surface waters is usually enhanced. When the water masses are away from the ocean boundaries (surface and bottom), then the thermohaline circulation controls the transport and exchange between water parcels and thus the heat transfer.
Answer: Solar uv is an extremely effective means of heating a body of water, the atmospheric temperature in comparison is ineffective.
Water has a high heat capacity, as uv Penetrates deeper into the water it's acts on a greater volume and transfers a lot of energy.
The ARGO drifting bouy programme has data accessible to the public which gives us data down to 2000m pretty much worldwide. This is a great resource! But in terms of deep ocean I think we are pretty much in the dark.
Thermohaline circulation is indeed a major route for surface water to overturn to the depths. Ssta and argo will give a good idea of what is heading down there.


How exactly is ERC721 tokens non-fungible?

Question: What makes them unique as compared to the ERC20? Is it the owner's address as  included in the form of token id? So what makes them unique is the historical chain of addresses attached to it?
Answer: As you can see for example in this implementation, ERC721 contracts keep track of an owner (identified by its address) for each single token (identified by its token ID, a 256 bit number):
mapping (uint256 => address) internal tokenOwner;

Consequently, to transfer a token, a sender, a receiver, and the ID of the token to be transferred have to be provided:
function transferFrom(address _from, address _to, uint256 _tokenId) public canTransfer(_tokenId) {
    ...

    removeTokenFrom(_from, _tokenId);
    addTokenTo(_to, _tokenId);

    ...
}

For comparison, the corresponding lines of this ERC20 implementation look like this:
mapping(address => uint256) balances;
function transfer(address _to, uint256 _value) public returns (bool) {
    ...

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);

    ...
}

So here, there are no identifiable tokens, but for each user a balance is stored which is increased or decreased by a value. Transfers from different sources simply add up and it's impossible to distinguish them afterwards.
Comment: Just one more question, how is this token ID generated? There is no token ID for the ERC20 tokens?
Answer: The ERC-721 Standard explains the requirements of an ERC-721 token.
Each token has its own unique token ID, which never changes throughout the life of the token. Any given token can only belong to one person at a time, and tokens are transferred individually. Your token contract should keep track of who owns which specific tokens at any givevn time.
Tokens may have other metadata attached to them, depending on your needs.


2000 Dodge Intrepid electrical problem

Question: I accidently let the battery power cable touch the frame of the car and it sparked. Now my car does not light up dashboard or anything type of power. I tried jumping the car and still no sin of life. I checked the fuses and nothing is blown out. I checked the relays and nothing is blown. Can anybody help? IS it the battery, I just bought this 2 weeks ago.
Answer: Does the car have a big "master fuse" somewhere in the engine bay? If so, that is probably your culprit... There may also be a second fuse box in the engine bay as well as the main one in the cabin.
If you have access to a multimeter, a decent battery should put out just over 12v when the car is switched off, however I doubt that a quick short like the one you describe would ruin the battery.

2000 Dodge Intrepid electrical problem


How can I stop my iMac's remote management connection from defaulting to wifi?

Question: I have two Mac computers that I connect to using Screen Sharing and when the Mac Mini's wifi is disabled I get great performance out of it. The problem that occurs is when I enable wifi on the Mac Mini and use screen sharing it appears to bypass the ethernet connection and use wifi instead to connect resulting in a slow connection. Is there any way to force the iMac to connect to my Mac Mini via ethernet instead of wifi when wifi is enabled on the Mac Mini?
Answer: In System Prefereces > Network set Ethernet above Wifi. That should do the trick.
Answer: Use the System Preferences > Network > Action (cog) menu > Set Service Order to alter the default network.
You can change the Service Order of your network connections. The order tells Mac OS X to prefer one network connection over another.
Drag your Ethernet connection above your Wi-Fi connection:


What is the Ubuntu Server's relationship to LAMP?

Question: Alright, I don't know if it's a good idea to challenge these two, is there any relation between them?
I understand LAMPP: it's the installation of Apache, MySql, PHP and Perl (or Python) on Linux.
But I don't quite understand what the Ubuntu server is.
Please, explain me what I can do with Ubuntu server and if it has any relation with LAMPP. (if yes, is it better than LAMPP?).
Thank you.
Answer: The Ubuntu Server is the 'L' in 'LAMP'; that is to say, Ubuntu Server is a Linux-based Operating System (L) on which people run the Apache HTTP Server (A) with MySQL or MariaDB for data storage (M) and Python, Perl, or PHP for scripting (P).
People also run Debian, CentOS, and RedHat as their L. Ubuntu is growing pretty popular as a LAMP OS because of its quick installation and deployment, as well as five years of free LTS (Long Term Supported) support from Canonical.
Comment: Ubuntu also provides the *A*, *M*, and *P* components of *LAMP*. They are all Ubuntu packages.
Answer: L -- Linux
Ubuntu is a Linux distribution.
A distribution has a standard protocl for installing and removing applications, libraries and dependant files. This is called a packaging system.
Ubuntu uses Debian( another linux distribution) packaging system and apt tools to package and install the tools and applications used in the linux ecosystem more graphically user friendly and better integrated.
Ubuntu Server is the same linux distribution with packages tuned for deployment as a server. When using ubuntu server, one could get support from Canonical and have the benefits of tools like landscape for monitoring.
The main difference between having ubuntu server packages and using any other LAMPstack like would be the ease of upgrading and downgrading based on availability of packages.
Yes, using ubuntu server is better than using a LAMPstack. Better documented technique of hosting an application , more secure way of organising the filesystem and finally, the possibility of getting support from canonical support staff.


Sum of $n$ consecutive numbers divided by $n$

Question: I was trying to write a poker program yesterday, and trying to figure out a way to tell the computer how to detect a straight. I realized that if you add $5$ consecutive numbers and divide by $5$, you'll get no remainder. I tried for $6$ consecutive numbers, but it didn't work. It turns out it only works for odd numbers. Really silly question, but does this 'method' have a name? Has it been proven that for all odd $n$, the sum of any $n$ consecutive numbers divided by $n$ yields a remainder of zero?
Comment: 1+2+....+n = n(n+1)/2. That should answer your question :)
Answer: Yes, If $n=2k+1$, write the numbers as
$a - k, a-(k-1), \dots,a-1, a, a + 1, \dots, a+(k-1), a+k$
Adding gives you $na$ which is divisible by $n$.
Try something similar for even $n =2m$ and you see that the sum is $m \mod n$, which is not divisible by $n$.
Answer: This page have a proof for the same.It also includes the the prove that when $n$ is even then this is not true.
Answer: HINT $\ $ The sum is $\rm\ 0 + 1 +\:\cdots\:+\: n-1\ \ (mod\ n)\:.\: $ Pairing each summand $\ne 0\:$ with its negation shows that the sum is $\rm\: \equiv 0\ \ (mod\ n)\:.\ \ $ Note: $\rm\ - x\ \equiv\ x\ \Rightarrow\ 2\ x \equiv 0\ \Rightarrow\ x\equiv 0\ \:$ since $\rm\:n\:$ is odd.
If $\rm\:n\:$ is even then the above argument demonstrates simply that the sum reduces to the sum over the fixed points of the negation map, viz. $\rm\ 0,\ n/2\:.\ $ Therefore the sum is  $\rm\:\equiv n/2\ \ (mod\ n)\:.$
This is a special case of Wilson's theorem for groups, e.g. see here and here -
which highlight the key role played by the reflection / involution symmetry (here negation $\rm\ x\to -x\:$).


Can I add unsweetened cocoa to a store-bought white cake mix to make chocolate cake mix?

Question: I know that buying a chocolate cake mix would be the easiest, but there is a white cake mix whose flavor I like...
Answer: A small amount will be fine, but if you try to add enough to make it significantly chocolate flavored, you'll throw off both the wet/dry ratio and the acid chemistry of the mix, and probably end up with an unsatisfactory cake.
Answer: What may be easier is to get unsweetened chocolate (Baker's is the most common brand around here). Melt it (I do it in the microwave) and stir it into the batter once it's made. Minor stirring will make it marbled, and major stirring will give you chocolate cake. This can solve the problem of throwing off the wet/dry ratio Michael mentioned.
Answer: In a scratch white cake recipe, you could replace part of the flour with an equal amount of unsweetened cocoa. However, that's not possible with a cake mix, which already has the sugar and flour mixed together.
I would recommend either adding a small amount of melted unsweetened chocolate (no more than 2oz) or you could add chocolate extract.
Answer: Yes. Use a little if color's the only thing you care about. If you want more chocolate taste, you may require additional tricks.
Answer: For the added chocolate, put the Hershey's powdered chocolate in the dry mix, mix well; go from there. You got your chocolate. No problem
Comment: This doesn't really address the question - this is exactly what the OP was asking if he could do, and as you can see from the other answers, it's not as simple as this.
Answer: consider adding hot chocolat mix instead of coca, and add some extra liquid, if you add more than 1/4 c total ingredients you might need to adjust the spices and levening (powder/soda)