Why are some airplane wings not painted?

Question: Why is it that some wings are not painted on commercial jets? Couldn't they paint them the same color as the fuselage or would it be a waste of money?
Comment: Almost every aircraft wing I've ever seen was painted. They're just usually painted white.
Comment: Airbus requires paint on all surfaces, including the wing. Usually, Airbus wings are painted light grey.
Comment: [Painting robots](http://www.itc.mb.ca/robots/boeing-automating-777-wing-painting-other-manufacturing/) at Boeing, Airbus [decorated](http://www.airliners.net/photo/157054/L/) wings.
Comment: Related: [Why are planes generally pained white?](http://aviation.stackexchange.com/q/2354/755)
Answer: Fuselage present a large vertical surface with greater length than height. Wings are a large horizontal surface that is shorter in the direction of travel. So...
The fuselage paint job is clearly visible on the ground, painting on the wings only if you are above or below the plane. This is probably the main reason. Simple geometry. It would be waste of money.
Sun will heat a large horizontal surface more than a large vertical surface, so making the wings white is more useful than making the fuselage white. While I am not sure that wings would be structurally weaker if heated, the heat would cause thermal expansion, which would indirectly result in increased drag by making maintaining optimal shape more difficult.
Paint has significant effect on drag, more specifically it affects when the boundary layer transitions from laminar to turbulent. In the very long fuselage the difference is probably insignificant and you can paint them as you wish, but for wings the paint should be as smooth as you can make it. While I doubt white paint is smoother than paint of any other color, keeping it simple is probably a good idea.
Comment: @RockPaperLizard I think I can guess what that is about, and if so, it shouldn't normally be an issue on commercial jet liners.
Comment: "...but for wings the paint should be as smooth as you can make it".  You may want to double-check that with physics and aerodynamics experts.  I've heard that if you make it too smooth, it can add drag due to the complexities of physics that are beyond my knowledge.
Answer: A number of aircraft manufacturers do paint the wings; only that the color is more neutral (like white or gray) rather than the flashy aircraft liveries as found in the fuselage and vertical tail. According to Boeing, the wings are indeed painted:

Wing skins are made of bare aluminum and are protected by an impact-resistant paint system.

Modern wings are composite and are protected by paint anyway:

Protective paint is used in certain areas to prevent corrosion, and it is used on all composites to prevent erosion and moisture ingress.

It appears that the wings of Airbus aircraft are also painted:

... operate within the Airbus UK wing production facility, painting all narrow-body wing sets.

As for painting in airline livery, it would add another coat of paint, adding weight (For example, paint in A380 weighs half a ton already). Not a lot of people is going to see the wing paint anyway.
Answer: American Airlines didn't paint many of their older aircraft, leaving them mostly bare metal, to save weight and thus fuel. However, their newer aircraft are painted because it's required to protect composites.
Regarding colors of paint, most planes are mostly white because it absorbs the least heat, doesn't fade and makes leaking fluids or corrosion more obvious. Any other colors used are typically the minimum required for branding.
Answer: In some military aircraft, like the P-51 Mustang, the wings were often not painted. This is because the rough camouflage paint made the P-51 Mustang go about 8 miles slower. I don't know if this is the same reason for commercial planes, but it was for the P-51 Mustang and other military planes.
Many commercial planes actually do have paint on the wings, but the paint is white, or light grey.


FFT of size not a power of 2

Question: My question is regarding the input size of a signal which is not a power of 2 and we have to take the fft of it. Some solutions say that suppose  if we want to take the fft of 1800 we should zero pad it till the length of 2048 to make it power of 2 and then apply the radix 2 algorithm. But there are other solutions as well which applies a combination of different algorithms without zero padding and then calculating the required FFT. My question is Does zero padding a signal to length of 2048 in case we have to take fft of 1800 makes any difference in results , if we use a combination of different algorithms to calculate the fft of size 1800. Would there be any difference or the result would be same.
Comment: Assume your data is in `x`.  Form `X = fft(x,123456);` (or some other strange length).  Find `xx = ifft(X);`.  See what `sum(abs(x-xx(1:length(x))));` is.
Comment: The resulting FFT will be different: instead of calculating the FFT at the frequencies $2\pi n/1800$ for $n=0\ldots 1799$, you will be calculating them at $2\pi n/2048$ for $n=0\ldots 2047$. However, there is no degradation of the information.
Comment: So, it means both approaches are correct? But which one you recommend to be more good in terms of practicality ?
Comment: Yes, both approaches are correct. I'd use the "minimum energy solution" (i.e. the simplest, the laziest solution).  This would usually be using the 2048 length transform.
Comment: I have seen in the literature and books people are recommending that zero pad it to make it power of 2.. Why they never insist on implementing some combination of other algorithms for good results.
Comment: Probably because people didn't know about decent non-radix-2 algorithms, such as those available in [FFTW](http://www.fftw.org/) and other libraries.
Comment: One last question regarding you 1st comment. You mentioned that there is no degradation of the information. How can I see this in Matlab that there is no degradation in information if we do zero padding.
Comment: @PeterK. I recommend you combine most of this set of comments into an answer
Comment: @lxop Done!!!!!
Answer: The resulting FFT will be different: instead of calculating the FFT at the frequencies $2\pi n/1800\ \ $ for $n=0\ldots 1799\ \ $, you will be calculating them at $2\pi n/2048\ \ $ for $n=0\ldots 2047\ \ $. However, there is no degradation of the information.
Both approaches are correct: using 1800 or 2048. I'd use the "minimum energy solution" (i.e. the simplest, the laziest solution).  This would usually be using the 2048 length transform.
People tend to use radix-2 transforms because they don't know any better. There seems to be much mis-information about FFTs HAVING to be power-of-2. There is no such constraint.  Also, they probably don't know about about decent non-radix-2 algorithms, such as those available in FFTW and other libraries.
To see that the FFT of any length is information-preserving:

Assume your data of length 1800 is in x.  Form X = fft(x,2048); (or some other  length different from 1800).
  Find xx = ifft(X);.
  See what sum(abs(x-xx(1:1800))); is.

See also this question and its answers.
Comment: When i do it ... it just gives me a number but no comparison through graphs. I am sorry but i am not very good in matlab because I implemented everything in C.
Answer: One needs to understand that since the result (and the source) are discreet, FFT is not really a Fourier transform, but is in reality Fourier Series development. This means that the result of any FFT is not the the transform of a single block of data, but is the tranform of a periodic signal consisting of an infinite concatenation of the same block of data, with or without a separation consisting of the padding length. (Assuming that my analysed data looks like «m», the transform will be the the development of «...mmmmm...» or of «... m  m  m  m  m ...», which are not the same signal.)
As a consequence, having no padding means one will implicitly add or remove the high frequency glitch in the source data coming from the discontinuity in the joining of the end of one bloc and the beginning of the next one (which is the same). The extreme example would be to analyse a block containing all the same value. Padding of not padding will make the difference between a continuous signal and a rectangular one.
The other consequence of this, is that the longer the padding, the nearer the result will be from the transform of a single burst of data, and the higher will be the resolution of the transform. It is not completely accurate to say that wathever the passing, there will be no degradation of information. There will (in a limited way), because of the rounding errors and using a longer buffer might help prevent it (again, in a very limited way).

FFT of size not a power of 2


If we want to know what the Bible says about an issue, what methods can help us to find all the relevant scriptures?

Question: If we want to know what the Bible says about an issue, what methods can help us to find all the relevant scriptures? Particularly if someone is looking for a "clear, unambiguous, direct statement in Scripture" (source). A sola scriptura perspective is sought.
Comment: @fredsbend this question always seemed to me "what tools do I use?" That's basic- but also completely answerable.
Comment: This question has been re-edited slightly in an attempt to re-open it. See http://meta.christianity.stackexchange.com/questions/3830/off-topic-are-you-guys-serious for further discussion.
Comment: disclaimer: this question was prompted by this particular answer - http://christianity.stackexchange.com/a/30538/10486
Comment: Isn't this just like "How can we prove the non-existence of something?" That leaves this as a general philosophical question, which is off-topic. At best, this is "What do we do if the Bible is silent?" which a sola scriptura perspective cannot handle, by definition.
Comment: Just because something is on topic for another site doesn't make it off topic for this one. Likewise, this is information that Christians use in understanding doctrine.
Comment: @fredsbend I don't think it is - you will either find relevant scripture passages or after an exhaustive search you won't and then can declare with confidence that the bible is silent on the issue.  Of course the hermeneutic you apply and the manner of your search will make a differnce, but I think it's a fundamentally different task to "proving the non-existence of something".
Comment: @AffableGeek It's not about Christianity then. It is about the process of Biblical exegesis. That would open this site into a new area, that I think BH handles, that I am not sure would be very useful, but I don't think it would be harmful either. Maybe we need a meta post.
Comment: [This question and a broader topic about this question type are being discussed in meta.](http://meta.christianity.stackexchange.com/q/3830/3961)
Answer: The following tools are good for determining what the bible says about a matter.  Take, for example, this question about pets going to heaven.  If you wanted to know the answer, you should consult:
1. A Concordance
The first tool that just about any pastor is going to use to answer a question such as this is a concordance. A concordance is nothing more than an index of words in Scripture, arranged in dictionary form.  The best concordance, of course, is the one in our heads.  The next best one is one in a book.
The classic work here is Strong's Concordance, which originally indexed the KJV bible. Other editions look at the Greek and Hebrew words underneath, or use other tricks to better index the words. Using google, by the way, is another easy way to find verses you sort of know, but don't know where they are.
Searching for 'pets' you will find nothing.  Searching for 'dogs,' you will find that it is usually an insult to a person, not anything about the animal. (Clearly, the writers misguided cat-o-philes, I suppose. ) Regardless, the point is that if you look up any of the words you might think are useful, you just won't find anything.
One word of warning: It is tempting to think a concordance can answer everything. It can't. And, references always need to be read in context.  But, it is a good place to start.
2. A Topical Dictionary of the Bible
Sometimes, a word might not appear in Scripture, but an idea does.  The word 'Trinity' for example, appears nowhere in Scripture - BUT the idea certainly permeates the whole.  For concepts, a topical dictionary like Nave's or one of these are useful.
In these dictionaries, key words will be explored, and centuries of Christian knowledge will be summarized, as a useful starting point for where you are heading.  Again, you need to read what they write in context, but it will show you where to focus your study.
Nave's lists Pestilence (hey some people keep spiders as pets!), Peter, and Pethiah - so, yeah, maybe not.
3. A Systematic Theology
Finally, for larger topics, one should consult a systematic theology.  Several (if not most!) theologians will write books that seek to put a propositional order to everything in Scripture.  Typically, this means they will start with questions like "The Nature of God," "The Nature of Man," "The Nature of the Bible," etc...  If you know what transubstation or predestination ante praevisa merita is, you jump straight there and learn a lot - but more likely, you need to be exposed to the terms and directed as to why these things are important.  That's what a systematic theology would do for you.
In this case, looking at the nature of the soul, the curse of the law, and the need for redemption only when there is transgression, one could begin to formulate questions around whether or not animals have souls, whether or not the "image of God" is a necessity for heaven, and the like.  But that takes work!
And, that ultimately, is where all of the tools need to be placed in perspective. Each of these tools is a map to a microscope.  If you don't have an overall picture, these tools won't provide a lot of light. But, with regular reading, the overall map takes shape and you will be able to find these answers.
Answer: There are no shortcuts to the process you appear to be asking about. I say that through personal experience, and from many Bible enthusiasts I have known and collaborated with over the years.
There are some excellent aids to enhance your Bible study free on the internet, some are online Bible study, and for the novice there are some excellent interactive sites available. A simple Google search will give you thousands of sites for each of these, but I suggest that you add any qualifiers you may think appropriate, otherwise the return list can be quite extensive (as in the millions).
For someone who is fairly familiar with Scriptures, as I feel I was, after having read the Bible from Genesis through Revelation approximately ten times maybe more. I have downloaded two excellent free Bible Study Programs to my computer and use both extensively in my study and for research for this site. Even though they are free I have found them so valuable that I have donated to keep them free.
These two programs are "/the word" available at http://www.theword.net/
and E-Sword available at http://www.e-sword.net
Along with the study programs there are many Bible translations, commentaries, and books that can be downloaded for the programs.
There are also some useful aids that can be downloaded to your computer to enhance your study, one that I have found very helpful is 'What the Bible says. It is free to try, and very inexpensive to buy. This program has a list of topics on the left and on the Right it lists all of the Scriptures which address that topic.
Comment: This question has been re-edited slightly in an attempt to re-open it - you may wish to re-edit your answer as well to reflect the change. See http://meta.christianity.stackexchange.com/questions/3830/off-topic-are-you-guys-serious for further discussion.
Comment: +1 for adding digital tools. Online tools, such as bible.is and youversion could be mentioned also. These will read the text while displaying it, and there are many more sites with multiple bibles, interlinears, and complete libraries of aids.
Answer: Absolute certainty probably isn't attainable (whether absolute certainty is or should be considered attainable by humans at all might be a worthwhile question), but as brought up in Affable Geek's answer to the inciting question, you can get pretty close through use of a good concordance and topical Bible dictionary.
Concordances are lists of words used. You can think of them as a giant index at the back of a book, or the Bible reorganized so that each word is alphabetically ordered. Often, a concordance will distinguish between the words in their original language and assign a number to the original term. Here's an example of a concordance entry for the Hebrew word that's often translated as "stranger" or "foreigner." Keep in mind that when you're looking based on English words, there is a disconnect between the English translation and the original language, and sometimes the same work in (for example) Greek can be translated different ways, even in the same Bible translation. A concordance in English is going to be based on a particular translation/version of the Bible, too, so make sure you pay attention. A New International Version concordance is not going to coincide as well with a King James Version of the Bible! (Side note: A lot of the work of a concordance is crunching through the data. There's been some really good work on getting computers to help out with that.)
A topical dictionary, on the other hand, is an attempt by its creators to lump together passages by topic. There's more interpretation done by the creators of the dictionary here. I've seen a topic like "beauty" that only included references to physical human beauty, for example.
I'll also throw in that a major reason for academics to publish and circulate papers comes from an older tradition, seen in seminaries as well as classical Greek dialogues, of viewing any particular argument as part of a larger discussion, in which we engage with others, trusting that "Iron sharpens iron, and one man sharpens another." (Proverbs 27:17).
Comment: This question has been re-edited slightly in an attempt to re-open it - you may wish to re-edit your answer as well to reflect the change. See http://meta.christianity.stackexchange.com/questions/3830/off-topic-are-you-guys-serious for further discussion.
Comment: Honestly, I think my answer stands as well now as it did before, though @affable-geek's answer is more thorough.

Even with the notion of certainty removed from the question, I think it's important to remember that this is a "Zeno's Paradox" sort of endeavor. You might be 50% more sure with each successive study, but it's important to remember that there's always a hair's chance that you're missing something.
Comment: Yes I recognize that - hence the somewhat radical change from 'know for sure' to 'help'; that semantic shift aside though, the main subject of the question hasn't changed so you're right, your question doesn't really require re-editing (in my opinion at least).
Comment: Okie dokie, then! Didn't mean to imply that you missed my point or disagreed with it, but for the secondary audience of any future readers, I felt it worth leaving in.
Answer: A program which you might try is http://bibleresources.org/bible-answers/ it has research in a variety of Bible including Hebrew and Greek plus several other languages


How was your experience learning to type in Hangeul on the keyboard?

Question: What was it like for you to learn how to type in Korean on a keyboard?  I'm two semesters so far in my Korean classes.  One of my keen challenges has been typing in Korean on my smartphone and computer.  Google's 10-key is easy enough.  However, using a keyboard makes me feel like I'm in grade school learning to touch type all over again.  Your story?  Recommendations?  Tips?
Comment: I would advise against "romaja" if you're serious about learning Korean - Hangul is different enough from Latin alphabet that you will end up with a lot of ad-hoc rules for disambiguation.  E.g., how would you disambiguate 시비/십이 or 갔다/갖다/같다.
Comment: What about typing romanization? On a macbook there is an input method called "HNC Romaja" that lets you do this. (Sorry I have no idea what HNC actually stands for.) Personally it took no more than a week for me to get completely used to it.
Comment: At this point in my learnings, I have to absolutely agree!  Romanization, even though carefully systematic, is something I had to wean off from.  Haha, I love your examples of ambiguity.
Answer: First I'm Korean.
I think my keyboard layout same as yours.
left hand controls 모음(ㄱ,ㄴ,ㄷ,...,ㅎ)
right hand controls 자음(ㅏ,ㅓ,ㅗ,ㅜ,...,ㅣ)
So, almost Hangul type sequence like left, right, left, right.
Practice typing in Korean helps you get used to it.
Comment: I've found Hangul to be beautifully designed because it makes sense!  Unlike so many things in English... keyboard layout too!  Matter of practicing then I suppose.
Answer: Practice, practice, practice.
But! Practice smart. Despite other's recommendations, I would highly discourage anyone from buying stickers or Korean keyboard – typing is supposed to be in your muscle memory, any good touch typing course will tell you not to look at the keyboard at all.
If you don't know how to touch type properly in English yet, I'd recommend doing that first, the time investment is small and the returns are huge, both in terms of learning to type other languages and other implications in life. (Good and free English touch typing course I liked typingclub.com.) Start with Korean shortly after you learn to which keys each finger belongs to. You can proceed without any specialized exercises and you'll pick up confidence and speed naturally, both in English and in Korean. (But don't look, ha!)
Practice – if you don't know the Korean layout yet, have an image open, but try to look as little as possible. (Obviously when starting you'll be only looking, that's ok though.)
Practice sites:

typeracer.com – full sentences, unfortunately accuracy score doesn't work for Korean (my favorite)
10fastfingers.com – only basic words, no punctuation, good for beginners
memrise.com – Memrise is an SRS (spaced repetition software, i.e. learning words), but the main part of their process is a type of exercise that allows you to type the words – this has helped me a ton personally

I knew how to type English before, but I properly relearned to touch type last year about two months before I started learning Korean. After a year of learning Korean I get the result of 39 WPM on Typeracer and 50 WPM on 10fastfingers (both in Korean of course).
(I am not sponsored by any of these sites.)
Comment: When I first bought stick-on Hangeul covers for my keyboard, it was painful AF haha.  But, I remembered how awkward it was too when I was first learning to touch type in junior high.  Suppose there is no special trick; just gotta practice like you said!
Answer: I recommend getting a cover for your keyboard, but it's really important that you don't look unless you absolutely need to (muscle memory). Really it comes down to practicing every day, starting slow by typing little things. I've used the Practice section on the TypeRacer website for some guidance. It's just a website where you practice typing quotes as fast as possible, the beauty of it is you can practice alone or compete with strangers and it's a minute. If you do it once a day when you get home from classes then you'll be proficient in no time.
edit: 없 is the hardest thing to type, ever.
Comment: Got some stick-on covers for my keyboard !
Answer: If you don´t have a Korean physical keyboard, I would recommend you to buy one online or add those Hangul stickers to yours and practice like @Salvatore DePalma said. This can help for a while.
But in my opinion, the crucial thing is to memorize the position of the keys so that you can type in Korean as fast as you would in your native language using any type of keyboard. Finally after years of typing Korean really slowly, I am now able to type anything, even using a standard international keyboard without the Hangul markings.
I used the excellent mnemonics from this page (https://www.90daykorean.com/typing-in-korean/). You can check the Step 3: Memorize the Korean Keyboard Layout. Once you master the consonants (which are on the left side of the 두벌식 keyboard, you only have to memorize 3 sentences), start memorizing the vowels on the right side, for those I really did not need any special sentences because I memorized that K equals ㅏ, H equals ㅗ and so forth. After you are familiar with these tricks, start practicing a lot with a regular international keyboard and don´t use the cover for a while. Eventually you will know by heart the position of most/all keys.
Answer: If you have an iPad you can add languages to your keyboard. Then you can press on the globe at the bottom left of your keyboard and a dialogue box or drop down menu appears and you can select what language you want to type.
Go to settings, type keyboard in the search box at the top, the keyboard page will show with more than likely English as the keyboard language. On the bottom of that page it says, 'Add new keyboard' press that and a selection shows up in the drop down menu alphabetized. You can then select Korean or 한글. I have 4 languages added. Hope this helps. Once you have the keyboard, just memorize it. Only takes 2/3 weeks.


Input-output economics and stability of general equilibrium

Question:
Here, I will start with a simple expression for an
  input–output system with $x(t)$ representing the vector of outputs and
  $A$ the input–output matrix. Then, the simplest possible linear
  discrete time model of multi-commodity production with no fixed
  capital, perfect thrift, and no technical change is: $x(t+1) = Ax$.
  For this system to grow stably over time, there has to be a stable
  rate of growth a at which all sectors grow: $x(t+1) = (1+\alpha)\cdot x(t)$. These two equations yield $((1+\alpha)\cdot I -A)\cdot x(t) = 0$ - This is only consistent with non-zero output levels if
  $|(1+\alpha) \cdot I -A|=0$. This is the crucial relationship that
  basically determines the results to follow, since the stability of a
  linear difference equation is determined by the dominant eigenvalue of
  the matrix (the largest root of the polynomial $|(1+\alpha) \cdot I -A|=0$). If this dominant eigenvalue exceeds zero (for a continuous time system) or one (for a discrete time system, such as this
  example), then the equilibrium of the system will be unstable.

Can anyone explain this - because I can't understand how the whole things are going on. Like why $A$ must have all eigenvalues smaller than 1 to be stable and so on.
Answer: You can find answer to your question on wikipedia:
http://en.wikipedia.org/wiki/LTI_system_theory#Discrete-time_systems


Why are my dimmer switches malfunctioning?

Question: I have two dimmer switches that have started malfunctioning.  They are in the same box with two other standard switches.  Each controls a set of three small flood lights.   There is no other way to control these floods except with the dimmer switch.   They were working fine last week.   Now, when I slide the dimmer, it sometimes works and sometimes doesn't.   I know it isn't a circuit breaker problem since the other switches are on it as well and they work.   These were installed about 6 years ago.   I will need to call an electrician to fix this but would like to have an idea, if possible, of what the problem could be.
Comment: Dimmers have maximum ratings (usually 300 watts or 600 watts). If you exceed the max, they may burn out. Also if they are mounted next to each other, part of the heat sink face plate is usually trimmed off, reducing their wattage max.
Comment: In my experience, dimmers seem to fail relatively frequently compared to switches.
Comment: Thanks for your replies. I don't trust myself to do anything electrical. I will call my electrician to check it out and replace them.
Comment: I don't know which type of construction you have, but if the sliding part is attached to some variable resistor, that may simply be dirty and/or worn out. It will probably be more economical to get new ones than to pay an electrician to take one apart and clean this place, though – even if that would be slightly cheaper, the problem will resurface, probably sooner than with a new one.
Comment: When it "sometimes doesn't" work, do the lights come on at all?
Comment: Have you changed the bulbs to a different type or wattage recently?
Answer: Sounds like a simple case of a bad switch.
Note: a squirt of WD-40 into the right place in the sliding mechanism can help, or even fix the problem at least temporarily by lubricating the internal sliding electrical contacts.  But getting the location right requires experience, and if you have to bring out an electrician anyway, they'll prefer to replace.
Do this with the power off by the way.  And it's far better to take it apart and lubricate, compared to the squirt and hope method.
Consider upgrading to a dimmer model with a remote control, CFL compatibility, or other features.
Comment: WD-40 is flammable. Spraying it into a light switch is probably not a good idea.
Comment: WD-40 is bad for plastic, use contact cleaner if you must.
Comment: With the power OFF.
Comment: True, I have wrecked dot-matrix printers by wetting dried-out ribbons with WD-40.
Answer: Your dimmer was probably damaged by excessive heat and maybe more load than it is rated for. Solution:replace bad dimmer with one that is rated at or above the amount of watts you are controlling with it if one dimmer is a 3 way you may be able to put that one on the other end and a regular 3 way switch at that box. Otherwise you may be able to change your lamps to dimmable led s that will reduce the load and also the heat. But still replace the dimmer they are not repairable.
Comment: I'm not aware of anything prohibiting it. Most dimmers have heat sink fins that can be snapped off for higher density installs, however every fin that is snapped off reduces the wattage rating of the dimmer per the manufactures specs. So it really has more to do with load on the dimmers then the number of dimmers in a box.
Comment: Can you point to the section in the National Electrical Code that prohibits multiple dimmers in a single box?
Comment: No sense in asking for a code reference because it does not exist. As Steven says, it is clearly explained in the instructions how to break off the fins if dimmers are to be ganged.
Comment: Sorry I knew I had read that somewhere it must have been in the manufacturer's instructions for a dimmer that I have used in the past . one that I was just looking at describes a reduction in wattage per number of dimmers ganged.


How do I get better at writing questions?

Question: Every time I post a question to the main site, it always seems there is something that I missed when posting it. How do I catch these issues?
Answer: Use the sandbox
Even for the most experienced challenges writers, catching all open questions and potential issues of a challenge can be difficult. That's what the Sandbox for Proposed Challenges is for: get help from the community to catch these things before going live on the main site.
As a rule of thumb, I saw that you used the sandbox once before, but sandboxing your challenge for less than two hours isn't terribly effective, as almost nobody will have seen it by then. I suggest waiting at least until your proposal has dropped of the first page (sorted by activity) or until a week has passed, whichever happens earlier.
Comment: @HyperNeutrino That's not entirely true.  The sandbox still provides valuable feedback on issues that are specific to your challenge.  You may have misinformation about your topic, or you hadn't considered a brute force solution that you would have wanted to disallow, or there's some edge case you hadn't considered.  Sure, perhaps another run-of-the-mill [tag:kolmogorov-complexity] might not need it, but most posts do.
Comment: @bushdid911 Patience is a virtue :P It takes a while to get accustomed to the details of this site, and you need to be patient with others' suggestions to get better at writing good challenges. After writing a bunch of challenges, you eventually won't even need the sandbox anymore once you've gotten the hang of it :D
Comment: im not a very patient guy
Comment: @NathanMerrill You're absolutely correct. I phrased my point a bit incorrectly; I mostly meant that after getting the hang of it, some challenges you can skip sandbox (like what you said with the kolmo challenges).
Comment: If I have a challenge idea that I consider too simple to need the sandbox, I sandbox it anyway just in case. It's worth it for the times it turns out I overlooked something.
Answer: Use the FAQs
In addition to Dennis' answer to use the Sandbox, we also have two FAQs related to challenge writing --
Things to avoid when writing challenges
Things to consider when creating a challenge
Answer: Write more questions
As it is with many things the best way to get better is to practice, and question writing is no exceptions.  Every time you make an error or a misstep you learn to avoid it.
There is a lot that other users can do to help you, in the sandbox, in chat and through the FAQs, but there is also a great value in getting the feel of a fun clear question.  Forming your own intuitions and systems for writing and proof reading questions can be extremely valuable.
Read more questions
It's practically a cliche at this point, but they say that to become a better writer you ought to read more.  And I think this is true of questions as well.  Reading more questions will also help you build the same skills as writing questions.
This works especially well if you spend time to think about how the question works.  Here is my checklist for reading challenges

Try the challenge.  Even if just a bit try the challenge to see how it feels when you are solving it.
Form an opinion.  Do you like the challenge?  What parts do you like what parts do you think are bad?
Ask yourself "How would I write this challenge?"  You don't have to write up a whole draft but thinking about this can help you to get practice at writing challenges.
Comment: This is excellent advice. I'd add a similar point: reading through the feedback that other people's sandbox posts receive is a great way to accelerate that learning process.
Answer: I would agree with all of the sandbox suggestions and would add to leave your challenge there until there is at least some feedback. May be 2 days or may be a month. There is no rush to put the challenge live and waiting and getting it right can save a lot of downvotes. There is no rule that says we have to go to the sandbox and give feedback but many of the more experienced members have helped me there with previous challenges. I thank them for that. I have also written (not particularly golfed) reference implementations for all of mine. This helps me understand any ambiguities in what I am asking. Works for me and hopefully will help you too.
Comment: I know a lot of people find it difficult to wait a week for feedback when they are keen to get on with posting a challenge. One way I deal with this is moving on to draft another sandbox challenge while I wait for feedback on the first. I see no problem with having a number of sandbox posts, posting them to main in the order they become ready, rather than in their original order.


Relationship between karma and science

Question: How can science support or challenge the concept of Karma?
Comment: Is this like a [tag:comparative-religion] question. of the type we're not sure we like on this site? See [Can we ban "comparative-religion" questions?](https://buddhism.meta.stackexchange.com/q/353/254)
Answer: They are perfectly compatible. The teaching of Karma is about latent (potential) result of our actions and choices. Science is in complete support with the idea of potential energy, latent results etc. It's just normal causation, albeit its subtle/hidden aspect, nothing magical.
It's like, when you act like a jerk, it leaves aftertaste with people, and then it comes up in the middle of other situations sooner or later. Or, you keep rushing in your daily life and leave simple things not taken care of, like taking out garbage or paying bills - and then these little things accumulate and really interfere with your life. It is stuff like that. Our actions, our intents leave residue, they create some little tensions in our mind, in other people mind, in the fabric of everyday things - and that stuff eventually comes up as some funky result downstream. I repeat, it's not magic, it is totally normal stuff - just hard to see because it's subtle.
Comment: Newton's third - 'for every action there is an equal and opposite reaction', seems a nice parallel!
Answer: If you need scientific explanation to Kamma and Vipaka is all about probability and possibility due to chain of causes and relative effects. There are different type of kamma some are generate vipaka at same moment and some take longer time. E.g 1. if you hit a person you will be get the respond within seconds. 2. Think that your house full of rats and you keep some poison to get rid of it and if you have a child in your home there is a great risk of consume poison by child as unaware of it and will be fatal.( I have read news article few months ago. Incident was there are product to kill rats looks like a chocolate and eaten by child and killed.) 3. If you cut a tree today you will not get vipaka sooner. When cut trees collectively long period the vipaka will be generated gradually with the time. So this is about probability of chain of causes and effects. There is no mystery about Kamma and Vipaka. If Kamma and its relevant vipaka are linked to privious life to this life (as rebirth or reincarnation process) is more close to mythical and speculative. It's like saying "Don't kill butterflies as colors of rainbow will fade away". If you mention "Don't cut down trees as earth will burn by sun" is more wise statement and scientific.
Answer: The word 'kamma' means 'intentional action' and has no explicit relationship to ideas of reincarnation. The teachings attributed to the Buddha say:

Intention, I tell you, is kamma. Intending, one does kamma by way of body, speech & mind.
AN 6.63

From intentional actions (kamma) there arise 'results', called 'vipaka'.
For example, you have an intention to have & maintain a romantic relationship & enter into & engage in such a relationship. This is kamma. Then later, due to certain causes relating to incompatibility, the relationship ends, which is contrary to your intentions. As a result (vipaka), you suffer from sorrow & unhappiness due to not getting what you want. This is 'kamma-vipaka', which science obviously does not deny.
The following link explains kamma: Kamma in Buddhism
Comment: This is very practical and "closer to facts"answer. I think this is what buddha states "come and see". Additions to your example "vipaka" not always suffering. If someone can advance romantic relationship to better understanding and best compatibility it can lead happy marriage life. So this proves "vipaka" has positive and negative aspects. Also as you mention there is no relation to reincarnation or rebirth. Kamma and Vipaka here and now.
Answer: According to my opinion...
When a child born, he weeps, plays, through his legs without knowing how to do, why to do and what to do. This action of doing things is called karma. After some couple of years, the child gets to know, how to do the things, why to do the things, what to do for them is called the science. In this scenario, to do the things or execute the things is karma, and to doing or execute the thing with rhythm, sequence, a manner is called science. It can be in many forms like psychology, sociology, physics, maths etc... Karma did not tell us how to do, it just an action without knowing anything but science gives us a method of doing things...
Answer: There is a reaction after action good or bad , simply karma like reaction for our good or bad action.
compare this with science .. :)
Comment: Maybe you could elaborate a bit on the science part.
Comment: @Lanka - if someone taking about science, we have to think he/she knows about science.
Previous comment - Newton's third - 'for every action there is an equal and opposite reaction', seems a nice parallel! – Ilya Grushevskiy
Comment: Can any one tell me the correctness of my answer ? who set the minus points should know the correct answer .

Relationship between karma and science


Why is rock sugar used in Chinese cooking?

Question: Why do some Chinese dishes, namely braises and soups often call for rock sugar instead of regular sugar. Does rock sugar have any properties that would make it behave differently than regular granulated sugar?
Answer: while all of the above answers are correct, I want to provide a perspective as a native Chinese. Rock sugar is better used (than granulated sugar) when you try to make dishes involving coloring the ingredient (by caramelization, dishes like braised pork belly (Hong Shao Rou need this step) mostly because of the shape difference. Rock sugar has less surface area touching the oil while granulated sugar immerses itself in, which makes it react faster, and more likely to get burnt.
Answer: No, it doesn't, really. Once it is dissolved, it behaves exactly the same. Eaters won't know the difference when eating the finished product. So, tastewise, there is no special reason to use rock sugar.
This answer assumes that you are adding sugar to a polar solvent (water, broth, alcohol...). It doesn't cover techniques of adding the sugar to oil or other occasions where it is not dissolved.
Comment: This is not exactly true. If you stir fry powered sugar in hot oil, more likely than not it would be overcooked and turn bitter, so taste wise, there really is a difference...
Comment: @xuq01 I haven't considered techniques in which the sugar is being stirred into oil. You are right, if the oil is very hot and you use powdered (not crystalized) sugar, it would probably burn very quickly. Is this really done with soups in Chinese cuisine? Do you stir fry the vegetables with the sugar first?
Comment: Not really soups, but in braises, yes. This is a very common braising technique ("red braise") used in almost all parts of China for a variety of ingredients.
Comment: The point of stir-frying the sugar in oil is to give a red color, BTW (hence the name of the technique). You put the sugar in before anything else.
Comment: @xuq01 thank you for clarifying that. I added a paragraph to the answer saying that it is only valid for cases where you dissolve the sugar in something, and doesn't cover the case you meantion.
Answer: In China, highly refined granulated sugar like we find in US is somehow uncommon. The most common form of sugar is soft white sugar that is less pure and contains a few percent of syrup and other sugar family substance. These imperfections sometimes affect cooking.
Rock sugar has a relatively larger market in China than the rest of the world for precisely this reason: over there it's the most common highly purified and refined form of sugar, because if it's not pure, it won't crystalize so large. Crystalization is the further refinement process.
As a result, if a Chinese chef feel the need for highly purified sugar, he/she calls for rock sugar. This logic is sometimes carried on by chefs that works with granulated sugar regularly that is truly indistinguishable form crushed rock sugar.
So, if your regular sugar is already crystalized high purity granulated sugar, then no need for rock sugar.
Answer: According to this, it is less sweet than regular white sugar which can be used if rock sugar is not available.
Even if it can/ has a brown/golden-ish color, it is not brown sugar which has a more distinct flavor.
Comment: That information is incorrect. White rock sugar is made of the same chemical compound as regular granulated sugar.
Comment: not so fast.  Rock sugar comes from sugar cane, while granulated sugar can be made from other stock.  Cane sugar and beet sugar (for ex) have different flavors.  There is also a difference in how they carmelize.  In theory both are pure sucrose, but in practice there are differences which any competent. chef knows to utilize.
Answer: My answer is based on experience;I'm not sure of the underlying science.  Rock sugar is not as sweet as granulated sugar.  It has a broader, less intense sweetness which works well in savory dishes.  It lacks a sweet "punch" which is more suited to desserts.  I use the white kind, though I'm sure the yellow/brown sort has some additional flavor.


Do countries have to run on deficits? What is their possible economic future?

Question: Do countries have to run on deficits? Is their future to behave and act like big companies that produce goods and services?
Answer: One of the main reasons for the general tendency to run deficits is political economy. Governments are elected for a limited period and try to stay in power by benefiting their electorate. An alternative explanation is that high debts reduce the scope for the subsequent government. So there are good reasons to impose some restrictions to the deficit into the constitution.
I find the comparison to big companies misplaced. Governments fulfil different purposes than companies. Many of their 'products' are public goods (public infrastructure, education, defense, social security) which cannot be provided by private actors due to external effects. A strictly profit-oriented view of public services therefore falls short of what governments are supposed to do (which does not say there is probably lots scope for efficency-enhancing in most administrations). As a sidenote, running huge deficits is not uncommon to big companies, especially in digital services. As long as creditors are convinced these debts will be paid, companies can be run on losses for quite a while.
Comment: But goverments are not competing in a market with other entities they will get their cut(taxes) whether they have done their job htrough services or not because they can apply force to you if you are not gonna pay, they operate like a mafia. Generally they are not doing their job for example. I live in Greece and all the free services like healthcare or police their not doing their job or their doing it poorly and as a result most people have to go to a private hospital or to hire a private investigator. Tech companies i think they have much more cash than their liabilities.
Comment: OK, Greece is obviously an example for excessive deficit and corruption and patronage apparently played (or still play) their role. Greece was forced to reduce their deficit by the troika, thereby harming growth and boosting unemployment. This should not come as a surprise if the largest source of demand is cut back. This again is another major difference between private and public debt. Reducing spending makes a lot of sense for private actors when in debt. If governments reduce spending, the consequences are much more severe.
Answer: Based on modern macroeconomic theory a country does not have to run deficits, but often chooses to. From a Macroeconomic perspective, a country runs a deficit when G is greater than T (Government purchases outweighs Tax revenue). This is not limited to the public sector (Government), but private individuals can also run deficits when consumption outweighs private savings such as in the United States. When a country has both private and public deficits we call these "twin" deficits, such as in countries like the United States.
In theory a country can run a surplus or a deficit, so to answer your question "no a country does not have to run a deficit". A country can increase savings, reduce investment, and have positive NX (net exports). Of course, the reduction in investment means less consumption in the short-term, which is not politically desirable.
The impact of public and private deficits is theoretically less consumption in the future. This is why economists call running large deficits "borrowing from the future." At some point, the money borrowed to finance the deficit must be paid back, which will reduce future consumption, raise interest rates, and force more savings. Another impact of deficits is a crowding out effect if the government is running the deficit. This decreases savings, which decreases the pool of savings for private parties to borrow. A surplus on the other hand can lead to an increased pool of savings that can be drawn down upon in the future for consumption.
Answer: According to Keynesian theory, if a country does not run a budget deficit of at least 1 percentage point greater than GDP growth, this will cause sunspots to appear, thus causing their economic future to be bleak.
This can be contrasted with private markets where saver/borrower status of non-governmental agents is assured to enable rational optimization without succumbing to animal spirits.


Why was Marvin called "the paranoid android"?

Question: Marvin, from The Hitchiker's Guide to the Galaxy, is clearly depressed, but there are not any indications that I recall (from the books, at least ) that he is paranoid. Yet both in-universe and out-of-universe, he's very often referred to as "Marvin the paranoid android" (Wikipedia even lists this as an alternate name for the character). Why is this? Is the character in the original radio show more paranoid?
Comment: @CodesInChaos I believe it's at least indicated that he's generally person-shaped. He has a head and legs.
Comment: Is Marvin even an android?
Comment: Since you mention Wikipedia, I'll note that the article does have [a section on his name](http://en.wikipedia.org/wiki/Marvin_%28character%29#Name) which specifically calls out that he "does not actually display signs of paranoia"
Comment: Probably because of Zaphod's delivery of the line - it just stood out so well in the moment. Doesn't hurt that it rhymes nicely.
Comment: @Tacroy Which does nothing to explain why he's given that name...
Comment: http://www.douglasadams.eu/en_h2g2_interviews_stephen_moore.php
Comment: http://marvin.cat-v.org/songs/reasons-to-be-miserable
Answer: Quite simply because it rhymes.
There is no suggestion that Marvin is clinically paranoid anywhere in the series.
Zaphod Beeblebrox is the first person to use the epithet in the radio series.  Also, he calls Marvin many things as the series progresses.  However, it is the Paranoid Android that sticks.  Most characters refer to Marvin as a Robot, not as an Android.  There aren't so many snappy phrases that use the word robot.
Zaphod often uses nicknames for other characters.  They aren't always good descriptions.
Comment: Fun fact, in the german translation Zaphod used to call Marvin a "manisch-depressiver Roboter" (i.e. a bipolar robot), despite the fact that Marvin was uniformely depressive and did not show any upswings in mood  that would normally be part of a bipolar disorder.
Comment: He calls himself that at one point ("What are you supposed to do if you are a manically depressed robot", in response to Ford's question "what are you supposed to do with a manically depressed robot") - you'd think with a brain the size of a planet, he'd know better.
Comment: @DanielRoseman I rather think that he does know better, Marvin secretly delights in showering other "intelligent", living, artificial, or otherwise, beings with his particular brand of depression.
Comment: @EikePierstorff I remember one upswing in his mood from the book. There is a chapter where he utters the words: "I think, I feel good about it."
Comment: @EikePierstorff IIRC, the English version also called him "manic depressive" at a couple of points, despite the distinct lack of manic symptoms.
Comment: Zaphod delivers the same epithet in the 1981 TV series as well.
Answer: It might have something to do with the amount of pessimism Marvin displays.  He's convinced terrible things will come of just about everything, and that people are going to treat him poorly, hence him being paranoid.
As noted there are also a number of points where he's referred to as being very depressed.
Overall though... this is Douglas we're talking about, his MO is inconsistency, contradiction and throw away jokes.  I am quite comfortable accepting the notion that he went along with labelling Marvin paranoid just because it sounded nice.  Need I remind people of the story behind Zaphod's third arm and second head and just how much trouble that caused when they tried to make the TV series? ;)
Comment: @KyleStrand: It's mentioned in the footnotes in the (sadly out of print) [Original Hitchhiker's Radio Scripts](http://www.amazon.com/The-Original-Hitchhiker-Radio-Scripts/dp/0517559501).  IIRC, Zaphod's third arm and second head were both mentioned first either in ad libs, or at the very least, throwaway jokes added to the script at last minute.  When the TV show was produced, Adams insisted on fidelity to the way the characters were depicted in the radio series (the latter being the closest thing to canon in the Hitchhiker's universe), including the ruinously expensive extra arm and head.
Comment: I'd appreciate the story about Zaphod's extraneous anatomy and the TV series; I've never heard it.
Comment: @SteveIves except they weren't CGI... they were radio controlled animatronics, definitely state-of-the-art at the time but completely unreliable sadly.  The tales basically said that the head would often stop working after 10 minutes.  The arm would be swapped around so that both arms on that side were shown working some of the time heh.
Comment: @Kaithar - I was being slightly tongue-in-cheek. I thought the head and arm were actually papier-mâché and controlled by strings! Very much a budget special effect!
Comment: I remember the original TV series - the CGI work that went into that head and arm was state-of-the-art at the time...
Answer: As mentioned before, the term comes from Zaphod.  His own psych profile is "He's just zis guy".  Don't expect a proper psychiatric diagnosis from him.
Comment: I believe his *full* profile is "He's just this guy, *you know?*." :P
Comment: Ok, lets's get the quote right... "Zaphod's just zis guy, you know?" was Gag Halfrunt's catch phrase in the radio show.  Halfrunt was Zaphod's "Personal Brain Care Specialist".


Front tires hitting struts

Question: 2006 Mazda 5 Sedan front tires are hitting while traveling. There is lots of clearance when not moving. We just put 4 brand new tires on 4200 miles ago. Drivers side rubbed a little on the side but it was the top of the tire hitting the strut bracket that cut it up like a lathe. Causing it to blow. The passenger side is just hitting the top and cutting through bad enough to show the metal cords. The old tires are the same size as the new. So would it be the struts or could it be the tire manufacturer. Or possibly something else.
Comment: Can you clarify - is there clearance when the steering is forward but not when turning? Or is it the shocks compressing that makes the tire hit? Either way it's not the tire manufacturer - as long as you have the right size tire on, the manufacturer is irrelevant. Photos would be a useful help
Answer: If you've got plenty of space when stationary, then something is allowing the wheel to move more than it should - most likely a failed bush or joint. Jack the car up and support it on axle stands, then check the suspension for movement. Try to shake the wheel in various directions, and try getting an assistant to turn the steering wheel from one side to the other while you watch the wheel and suspension. This should reveal the culprit...

Front tires hitting struts


There is no menu bar on Mac OS 10.7.3

Question: I installed the latest version of QGIS on Mac OS 10.7.3 with 2 additional frameworks (GDAL Complete and GSL) but there is no main menu bar (not at the top of screen, not at the window of QGIS).
Where is the menu?
Answer: Context: I believe this is a Mac issue. I had the same thing with QGIS 1.8.0 and HEAD (d68524) built with homebrew on OSX 10.7.5. It appeared after rebooting for the first time in a long time (initially the shutdown hung, so I did hard power off and booted up, then rebooted a second time, cleanly).
Symptoms: After this the menu bar at the top of the screen (the normal Mac one) was missing for QGIS. It would just show the menu of whatever application I used before I selected the QGIS window. Uninstalling and reinstalling didn't help (I tried two versions). Command-Tab application switching didn't show an icon for QGIS. Doing Exposé's "show all windows" showed the QGIS window as a thin vertical line.
The solution for me was:

Delete preferences: rm ~/Library/Preferences/org.qgis.QGIS* (probably not necessary, but it was one of the steps I took).
Exit all applications and shut down machine, with "Reopen windows when logging back in" unchecked.
Boot back up, log in and start QGIS.

There is no menu bar on Mac OS 10.7.3


Beliefs about the 14th Dalai Lama

Question: What are the Tibetan Buddhist beliefs of the Dalai Lama being an incarnation of the Bodhisattva Avalokiteshvara? Do all Buddhists agree with this idea?
Answer: The institution of the Dalai Lama, as an emanation of the Bodhisattva Avalokiteśvara, is officially recognized only by Tibetan Buddhism.
The concept of tulku where teachers like the Dalai Lama, Panchen Lama and Karmapa, may intentionally reincarnate again and again as custodians of certain religious lineages, is only found in Tibetan Buddhism. It's not clear if other Vajrayana traditions also have tulkus.
The Bodhisattva Avalokiteśvara is found prominently in many Mahayana sutras, and has the ability to incarnate as any kind of being, including human, to help and teach others. But the Mahayana sutras do not identify the Dalai Lama as an emanation of Avalokiteśvara.
The Bodhisattva Avalokiteśvara, though present in temples in Theravada countries (probably due to Mahayana influence), is not found in the Pali Canon.
Answer: The Pali suttas teach a monk is to be scrutinized for mental states of greed, hatred & delusion.

There is the case, Bharadvaja, where a monk lives in dependence on a certain village or town. Then a householder or householder's son goes to him and observes him with regard to three mental qualities — qualities based on greed, qualities based on aversion, qualities based on delusion....
Canki Sutta

Therefore, all Buddhists do not agree the Dalai Lama being an incarnation of the Bodhisattva Avalokiteshvara.

The Dalai Lama's administration acknowledged today that it received $1.7 million a year in the 1960's from the Central Intelligence Agency, but denied reports that the Tibetan leader benefited personally from an annual subsidy of $180,000.
By THE ASSOCIATED PRESSOCT. 2, 1998

Comment: You might like this: [Trimondi](http://www.trimondi.de/SDLE/Index.htm). Insider knowledge.

Beliefs about the 14th Dalai Lama


Parental Controls Always Allow does not work for Avid Media Composer

Question: I've enabled Parental Controls on a new Nov 2012 iMac being used in a school for public access (OS X 10.8.2 Mountain Lion) and have restricted the applications this account can use. Everything works fine with the exception of Avid Media Composer (the main reason we purchased the iMacs...). Avid Media Composer is marked as an application that the account is allowed to use in the parental control settings.
When I try to start Avid Media Composer under this account, a message pops up saying that this user doesn't have permission to use the application, giving the following three options:

Always Allow...
Allow Once...
OK

When clicking Allow Once, I have to enter the admin account username and password and the app starts without problems. But when I click Always Allow, it asks for the admin account as well, but then pops up the same message again and again. I have verified that I'm using the right admin account username and password, but it's still refusing to run the application.
When I disable parental controls, everything works, but the moment I turn it on again, it fails, despite having Avid Media Composer in the list of allowed applications for this account.
In the Console application, I can see the following error message whenever this happens:

com.apple.launchd.peruser.504: ([0x0-0x1de1de].com.avid.mediacomposer[2033])
  Job failed to exec(3) for weird reason: 13

Has anybody else experienced this or knows how to fix this?
Answer: I found this problem too!
Turn off parental control and it works fine.
Interesting as I have two Mac Pros and one with PCs on does allow MC to work.
The other with the PCs on and it does not.
I suppose best answer is to turn off Parental Controls for an separate account just for users whom use AVID.


Ubuntu 12.04 launcher icons missing

Question: I just notice that the icons in the launcher are all missing. The launcher  is there, but it is empty. Now I have to use Alt+Tab to switch between opened applications. I don't know what happened. I am just opening a lot of chrome tabs. Can someone help me with it?
Answer: Are you using intel graphics?  This may be an annoying bug that was only recently fixed in February in the precise-updates repository.  See:
https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/1024768

Ubuntu 12.04 launcher icons missing


SYN Flooding kernel message

Question: Hi I'm getting this type of message repeatedly from the kernel:
<code>[1697692.076962] possible SYN flooding on port 80. Sending cookies.
</code>
Any idea of what this means? It is on an EC2 host if that makes it easier.
Thanks
Answer: It means that you're being attacked by someone who thinks that the state of the art of network stacks was reached in the late 90s.  "SYN flooding" is a way of denying service by half-opening a huge number of TCP connections, which is supposed to exhaust the resources on the server by needing to hold state for all those half-opened connections.  It was quickly realised that the state of these half-open connections could be stored in the ACK packet itself, which is what is meant by "Sending cookies".
Plenty of information can be found by searching the Internet for "Syn flooding" and "Syn cookies".
Answer: You have SYN cookies enabled, your server's table of pending TCP connections is full, and your server received another connection attempt (SYN packet).
This can be due to SYN flooding (a type of denial of service attack), but it could also be due to poor configuration (too small a size for the SYN-recv table, too long a timeout / retry count for SYN packets, etc.).
The up-shot is that while you are receiving these messages, some of your normal / actual users may be experiencing sub-optimal behavior.  This would typically be a higher sensitivity to packet loss, mostly resulting in the failure to connect for a small fraction of connections that would otherwise have succeeded.
There are LOTS of posts on what this is all about, many on this site.  If you search for the log message or even just SYN, you will almost certainly learn everything useful there is to know.

SYN Flooding kernel message


Direct products of closures of subgroups

Question: Let $H$ be subgroup of a topological group $G$. Suppose $H$ is the (internal) direct product of two of its subgroups $K_1$ and $K_2$. Does it follow that $\bar{H}$ is the direct product of $\bar{K_1}$ and $\bar{K_2}$?
Answer: Well, depends on which direct product you mean, but if you mean only group product, you can find a very simple example.
Let $G=(\mathbb{R},+)$.  Let $K_1=\mathbb{Z}$ and $K_2=\alpha\mathbb{Z}$ where $\alpha$ is irrational.  Then $H = \{u+v\alpha: u,v\in\mathbb{Z}\} \cong K_1\oplus K_2$.  But $H$ is dense in $\mathbb{R}$, so $\bar{H}=\mathbb{R}$, but $K_1$ and $K_2$ are closed in $\mathbb{R}$.
In this case $H$ is not homeomorphic to $K_1\times K_2$ as a topological space.  I'm not sure what you can say if you require that the group isomorphism between $H$ and $K_1\oplus K_2$ is also a homeomorphism.
Comment: Yes this is what I meant. Thanks for the example.
Answer: I think some topological abelian groups have dense free abelian subgroups, but are not themselves free. A direct factor of a free abelian group is free, and a direct product of two free abelian groups is free, so this would give a counterexample.
A specific example should be the direct product (with product topology, I think, but I could be wrong) of copies of the discrete infinite cyclic group.  The result is not a free abelian group, but the direct sum of those copies of the discrete infinite cyclic group is dense (in the appropriate topology).
I think lots of "algebraically complete" abelian groups should have similar properties, but I have never really considered the topology, just the algebraic versions that sometimes use topological words.  The p-adic integers should be another example, but I was even less sure I had the topology right there.


What is the point of a cover letter in journal submission?

Question: Many journals do specify that cover letters are optional. From my experience, most people write cover letters in journal submission, but I am also aware that articles can also be published without the cover letter. Therein arises the question: why are cover letters written if they are not necessary for the publication process?  My guess is that perhaps it helps to prevent the desk-reject from the editor.
Comment: Not the same question, but a related one I asked: https://academia.stackexchange.com/questions/82811/effect-of-bland-cover-letter-for-journal-submission-in-biology
Answer: Prior to online submission forms, cover letters let the authors communicate information to the editors. Information I have included in covers includes:

Why the manuscript fits into the journal (if i recall correctly, Ecological Indicators explicitly requires a statement of what "indictor" you are addressing in the manuscript)
Potential reviewers and blocked reviewers
A statement that the manuscript is not under review elsewhere
Other pertinent information for the editor such as why the manuscript is timely (for example, perhaps you are studying a species that is under consideration for listing as an endangered species, and the information may be public, but not widely known)
Responses to reviewer comments
How I am meeting the journal's open data/open code requirements

With current online journal submissions, all of this information can be captured in online forms. Hence some journals either no longer require cover letters or outright do not allow authors to upload them. Conversely, I have seen other journals that still require cover letters.
I suspect journals use of cover letters depend upon the history of the journal, their current online publishing system, and the culture of the editorial team and office.
Comment: This is the best answer to the question because it addresses the "historical" aspect of cover letters.
Answer: I like to see the cover letter as the 'meta' part of your paper. What constitutes as meta is essentially anything beyond the purely scientific aspect of the paper, which can be easily gleaned by reading the abstract (in theory).
This is your chance to speak to the editor personally about your paper. Most basic advice about cover letter writing is emphasizing writing about why (1) your work is important and (2) why it is suitable for this journal in particular.
Even if your handling editor is an expert in your sub-field (and in my experience it rarely is - this is especially the case for general-interest journals), it is not always immediately obvious why your results are important, or even interesting. All scientists know about the 'hot topics' in their field, usually because they are published in high impact journals. But how did these topics get published in the first place without getting the recognition first? Usually some degree of convincing is needed.
There can also be other reasons for including a cover letter. Perhaps you may have spoken to the editor at a conference and you want to remind him that this is the paper you were talking about for submission. Or perhaps your paper was transferred from another journal and you want to inform him about the comments from the reviewers there. The cover letter can also be the place where you recommend reviewers for your paper.
It is easy to think for the writer that the merits of one's paper is obvious, or why waste your time? But this is not immediately obvious for the editor, who generally has a limited time to make a decision.
Comment: This aptly summarizes many of the best justifications for a cover letter. In my experience, the cover letter is most critical for submissions at high-profile journals where the editor may reject the paper without input from referees. The Nature Methods summary is very good about this: http://blogs.nature.com/methagora/2013/09/how-to-write-a-cover-letter.html
Comment: Isn't the abstract the place to emphasize why the work is important?
Answer: Cover letters can be used to specify information which is relevant for the editors, but doesn't belong into the title and abstract. For example, if the paper is submitted upon invitation for a contribution to a special issue, that goes into the cover letter.
Answer:
I am also aware that articles can also be published without the cover
  letter.

The cover letter is not intended for the reader.

Therein arises the question: why are cover letters written if they are
  not necessary for the publication process?

There is far more to the publication process than what sees print.
The point of a cover letter is to introduce your paper to the editor of the journal and (potentially) the reviewers. It helps to frame the paper - why you think it's interesting, why you think it's interesting to that journal, and if there's any relevant information that might weigh on the decision to publish, or how to go about publishing it - for example, in biomedicine one might occasionally make a request for expedited publication for information relevant to an ongoing outbreak, or attempt to coordinate a publication's release date with the presentation of the paper at a major conference.
Some journals also use cover letters as a place to put in some boilerplate assurances, like the paper not being under consideration elsewhere.
Answer: There is no point in these letters per se.
I presume they are there because of historical reasons, where people were actually submitting the manuscript with a physical letter, so obviously, you would need, back then, to have a cover letter to explain what is the intention of the parcel. But now we can communicate the same information with an email or an electronic form, serving by itself as a cover letter, i.e., giving possible important information to the editor in charge.
Answer: Depending on the journal and/or field of research the title and abstract may not indicate clearly the topic or area of interest addressed by the submitted paper. Also consider that the editor may not be expert in the area that the paper addresses.
Are you submitting a paper to a journal that publishes a range of topics?
Are you submitting to a journal that publishes exclusively in one field?
Are you submitting to a journal that publishes exclusively in one area of one field?
Highly sought-after journals such as Nature and Science publish across a wide range of fields, so you would need to provide some specifics as to why you seek to be published in that journal. Also, why they should consider your submission (is it ground-breaking?).
You could submit to a journal that publishes exclusively for one field (physics, biology, chemistry, education...) but with so many areas of research in these fields you could not expect the editor to just know whether your paper is relevant, or which reviewers to assign.
So a cover letter can help define this for the editor - why you have selected that journal, the importance/relevance/originality/defining outcome of your paper, why they should publish/consider publishing your paper. It gives you a chance to give an outline with detail that may not be relevant in the abstract but goes towards background information so that they don't need to read some/all of the entire paper to make a decision.
Actually, if they need to read the whole paper first they may reject it without review, since at the least they may need to read title, abstract and introduction. A cover letter can save them time, which will be appreciated and help your chances of getting the paper reviewed.
Comment: I must say don't find this argument very convincing. If after reading my abstract the editor has no idea what I am writing about, there is a big problem either with the abstract or my choice of editor/journal.
Comment: We must have very different contexts in mind, then. I am used to journals in which the editor is a "peer, colleague, researcher in my field". The editor is a good prototype of a "typical reader", at least for the journals I am used to.
Comment: @FedericoPoloni OP asks why are cover letters written... Your abstract is written for your peers, colleagues, researchers in your field and other interested readers - your audience. You cannot automatically assume the editor is in that circle but they do have to make the decision why to accept your paper over the (possibly) hundreds of similar submissions.
Comment: @FedericoPoloni Fair enough. I would say the same about the editors where I have published. I tried to be broad in my answer since the OP didn't give specifics.


My phone doesnt find my PC on Bluetooth

Question: My phone is a Sony Ericsson j10i2 , the windows system is Windows 8.
I can send files from PC to phone but not vice versa, because my phone doesn't find my PC, and Bluetooth settings are correct "allow Bluetooth devices to find this computer"
Comment: Are the bluetooth versions compatible? I'm not sure if Bluetooth 1.0 will work with 2.0, 3.0 etc.
Comment: how can I know ? and how to fix it if it does ?
Comment: There's no way to fix it if the bluetooth versions are incompatible other than installing a new BT chip. To find out which versions google "(your computers manufacture and model number) bluetooth version"
Answer: If you can send files from PC to phone, it means the both devices have already been paired up. So, you don't need to find your PC at all whether its discoverable or not. Just look in the list of paired devices on your phone (I am not familiar with interface of phone, so I can't help with this). Also remember, Object Push Profile (OPP) is required on phone to send files (verify this in "About Bluetooth" section).
Another way to fetch files from the phone: In bluetooth software of PC, you can see "Browse files from the device". Use it & right-click on files/ folders you want to fetch (OBEX FTP Bluetooth profile is needed on the phone for that).

My phone doesnt find my PC on Bluetooth


How to get rid of an Ad bot?

Question: The issue started due to setting up a proxy server on a PC connected to my network. I then realized that all of my devices that connected to the network, including PCs and phones, are all infected by an ad bot that redirects me to ads websites whenever I click on any link. I then installed Malwarebytes, Adware Cleaner and other AV softwares to clean up my PCs but not any of them have detected anything. I thought that this maybe some kind of router hacking so I made a hard reset to my router and re-configured it with my ISP, then the problem solved on all of my PCs. However, it remained on my phone. I then made a reset to factory settings, formatted everything, all apps deleted but the problem still exists and I'm being redirected to ads websites, I almost tried every AV app on the playstore but they didn't catch anything. What should I do in this situation? I don't know any other way to solve this problem. I have to mention also that this bot works only on my phone when I'm connected to my router and it doesn't work when I switch to the mobile data. On the other hand, if it is still a hacking on the router, it should also affect the other PCs. Any suggestions guys? I really appreciate any idea.
Answer: What you've described sounds like your router's DNS settings have been changed to use servers under the control of your attackers.  You can confirm this by disabling the proxy server.  If you disable the proxy and the problem goes away then wipe the proxy machine and start again - it's the only way to be sure.
You can reset the DNS server settings to what they should be (your ISP can tell you what they should be, your router may be able to get them automatically or you can use a third-party service like Google or OpenDNS) to fix the initial problem for the local network.
Then you also need to prevent the attack from happening again.  Measures to do that include:-

performing a factory reset to clear any settings left by the attackers
installing the latest router firmware
using a strong password on the configuration interface
limit access to the configuration interface to appropriate places (wired, local connections, not the internet)
log out of the configuration interface after use (and do not tick 'save password' on your browser when configuring the router)
changing the IP addresses used and supplied by the router (for example change from 192.168.1.1 to 192.168.123.1)

The location of settings varies by model and if you're not sure how to check these settings then check with the manufacturer of the router, your ISP's helpdesk or bring in a professional.  Some of those options may not be free of charge but will be worth it.
Answer: I agree with everything that the first person to answer your question has said -- this is likely a router DNS hack, UNLESS there is persistent malware on some other endpoint (say, your child's computer) within your local LAN (the one whose IP addresses start with "192.168" etc. etc.) that is attacking the rest of your local infrastructure faster than you can clean it.
Don't forget -- the people who do this kind of thing are ruthless criminals, the lowest of the low. They are stealing the use of your infrastructure and will continue stealing it until you forcibly eject them. Unfortunately, this is the situation on the Internet today -- the minute you plug in to it, you are exposing yourself to every miscreant, literally around the world, who wants to steal from you.
And this gets to the only other thing I have to add, to the previous poster's comments : before you do ANYTHING with your router, your ADSL / cable modem, your PC, etc. -- UNPLUG COMPLETELY FROM THE INTERNET. You need to be cut off physically from ANY data path that the attacker could use to re-compromise your local LAN, while you are trying to "sanitize" it.
Some of these cyber-criminals have botnets with a "heartbeat" function -- if they see a node (in this case, "your router") momentarily drop off the botnet, they conclude "the legitimate owner is trying to get rid of my malware -- can't allow THAT, now can we?) and it triggers an auto-attack script to bombard your infrastructure (e.g. your public IP address) with various exploits until one of them gets through and you're back to Square One.
So the rule is simple : DISCONNECT FROM THE INTERNET, clean everything up and then only reconnect devices, one by one, that you are sure have been completely cleaned and "hardened", to stop these sleazebags from trying to again get a toe-hold on your LAN... because, at the end of the day, it IS "your" LAN... not, "theirs".
Good luck!
Comment: A factory reset on most routers will usually isolate the LAN from the outside.  Although disconnecting would ensure it.
Answer: Id just get a dynamic IP or buy a new router and get a new phone or buy a burner phone copy all of the files on your current one onto the new phone and see if it persists.

How to get rid of an Ad bot?


What is the maximum safe storage temperature for a bike?

Question: I like to keep my bike in the car on days I drive to work, in case I need it to get to a meeting in another building.  However, I'm concerned that it gets too hot some days.  Is there a temperature at which bike components might overheat or be damaged?
Comment: What about leaving a used 50$ beater at your regular office, e.g. in a storage shed, the corner of a production hall, the bottom of a staircase or wherever?
Comment: Agree with arne.  I would get cheap single speed with some larger tires (so you can run at a lower pressure).  It will also load and unload easier.  A cars interior does not melt.
Comment: Get a cheap folder and keep it in the trunk where temperatures aren't as brutal as the main cabin.
Answer: I've heard of tyres exploding if inflated close to their limit when cold, then left in a hot confined space. But unless you're running your tyres at 100 PSI and up, I wouldn't be too worried. But perhaps someone with more knowledge will chime in; I'm just hazarding a guess about that. I don't think there's anything else on a bike you'd need to worry about though, not as far as temperature goes, anyway.
Carbon fibre doesn't like UV. Most if not all carbon fibre products use UV-protective resins in their construction to avoid delamination from prolonged exposure to sunlight. I'd be a bit suspicious of cheap n cheerful carbon parts.
To be on the safe side, let your tyres down a bit and keep a white sheet over the bike when it's in the car. Probably a good move anyway; a bike is a good reason for a car thief to break in... it doesn't matter if your car's alarmed; they're stealing the perfect getaway vehicle!
Comment: Going from say 20C to 80C inside a hot car will increase tire pressure by about (60/300K) 20%. If left in direct sunlight, the surface temp can exceed 120C. Its not really the increase pressure that causes the tire to go, but the tire losing strength from the heat. As advised, let the tires down but also cover the bike. Once you take the bike out of the car and start riding, the tires will cool off quickly and loose a lot of pressure, so you may want to over inflate them a bit just before heading off, or check them after 10 minutes or so.
Comment: Thanks! It would be interesting to know if heat also degrades things like chain lube, or cables over time.
Answer: Possibly carbon bikes are a problem, but a regular steel/aluminum bike will have no trouble with "reasonable" heat (such as the inside of the average parked car) for a few hours.  The biggest dangers are blown tires (if they were near their pressure limit to begin with) and melted plastic parts.
If left in a regularly hot place for weeks/months/years, however, eventually the grease in the bearings will break down and ooze out, plus the heat will take a toll on paint, tires, and plastic parts.  And electronic parts are apt to be damaged.


How to get cat pee smell out of a camera

Question: Yes, you read it right!  I was staying with friends and their rotten little furball peed in my handbag.  Anything soft, like my cloth wallet, was a write-off.  Anything hard, like keys, just needed a good rinse with soap.  But I don't know what to do about my camera.  It was in its case so escaped any real damage and it still works fine.  But it smells terrible and I'm not sure what's the safest way to clean it without damaging it.
Comment: Cat pee is the worst.  Had to rip up an entire floor and 2 ft of drywall to try and get rid of the smell in one room.  What kind of camera is it?  Some types might allow for removal of the shell, which could be soaked or treated more harshly than the whole device.
Answer: There is Electrical Cleaner that is a solvent used to clean electronics without risking damage by corrosion.
However, before processing with that route... I would advise to wipe the external shell of your camera as much as you possibly can to make sure you haven't missed a spot of residue. It does not take much urine to have a strong smell stick to your camera (clean cracks and crevices)
If the problem still persist, you may need to take the camera apart (or to camera shop) and have them clean it with solvent used for electrical components. Look up "Electrical cleaner" in google to find many useful products with reviews.
Comment: It might be safe to put the camera in a container with household ammonia (dilute ammonium hydroxide), **but not in contact with the liquid**, for a few minutes to see if the ammonia reacts with the odorant. If that doesn't help, you could try vinegar. Don't leave it for too long, though.
Comment: Urine contains ammonia already.  It takes vinegar to counteract ammonia smells.
Comment: These chemicals could damage the camera beyond repair.


Basis for the hydrophobic effect?

Question: I'm confused about why hydrophobic molecules, which do not have high polarity, would have a tendency to attract and cluster with themselves. It is easier to understand the hydrophilic as long as one believes that positive charges attract negative charges. Anyone have any insights?
Comment: related: http://chemistry.stackexchange.com/questions/26544/how-do-transmembrane-protein-alpha-helixes-bind-to-the-membrane
Answer: The driving force behind the hydrophobic effect is entropy. Suppose I put several hydrophobic molecules in water. These molecules have two choices. (1) The molecules can stay separate from each other and randomly move around in solution. (2) They can group together and form a cluster. It turns out that it is entropically favorable to cluster. The reason is that it takes more water to individually solvate the separate molecules. It takes less water to solvate a cluster of the molecules. When water solvates these molecules, it is ordering itself. In fact, it is believed that water forms cages around hydrophobic molecules in solution. Therefore, if the molecules cluster, less water will have to order itself. Less ordering means greater entropy (randomness).
It also true that London dispersion forces will occur in these clusters. However, this is not the driving force for the hydrophobic effect. The driving force is entropy.
Answer: There are other intermolecular forces besides dipole-dipole forces (which is what polar molecules primarily use) that allow molecules to come together. For nonpolar molecules, they use dispersion (London) forces. Dispersion forces come from random movements of electrons which cause temporary dipoles. Due to the large amount of electrons in the molecules, lots of these temporary dipoles exist at all times, keeping the molecules together.

Basis for the hydrophobic effect?


tool to analyze MSSQL schema and current values

Question: Is there a tool out there that will go through a schema, compare the current values, and return a report of what columns are near the capacity of their data type? I am looking for a tool that can give me insight into limitations that may be reached soon. An example would be forewarning that I am at 60% of reaching the limit of an INT on a column).
Answer: I don't know of a tool to purchase, but you could create a SQL job that could analyze things for you. I'd hoped that the Redgate software would do it, but that's pretty much for comparing schema of databases between servers (I suppose you could use it to find all the INT columns in all tables, but you can look that up yourself in system tables)
Have the script look at each Column you're concerned about and check its value against the max value. Use conditional statements that only send an alert when the value is relatively high.


How does a lower pH change the alcohol concentration of wine?

Question: I have been told it that when the pH of wine is lowered the alcohol concentration will decrease because of Le Chatelier's Principle. Which states; if a  equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. How can I best expand on this?
Comment: Possible duplicate of [How does a lower pH affect the alcohol concentration of wine?](http://chemistry.stackexchange.com/questions/51600/how-does-a-lower-ph-affect-the-alcohol-concentration-of-wine)
Answer: This is a slightly broad question, but ill try to assist some. Google has a large assortment of articles describing pH, Le Chatelier's Principle, and EtOH.
Im not sure if you mean altering the pH during the fermentation process or altering the pH of the final product? It also makes a difference on the types of yeast you use. Some yeasts can handle different conditions and produce a different amount of alcohol.
Here is a great response from last year on the Stack Exchange, regarding fermentation without the addition of commercial yeast, using the change in pH as a catalyst for fermentation.
With the production of wine that uses commercial yeast for fermentation (which is most commercial wines), altering the pH too far outside of it's "designated" range will cause it to produce less alcohol. Some connoisseur winemakers will alter the pH slightly sometimes, varying on the types of grapes, to alter the terpene profile present. Different variables, equals different systems of equilibrium.
Comment: For my chemistry EEI I decreased the pH of my varied fruit wine just before fermentation. I have quite a lot of information about Le chatterer's principle but am still unsure of how it causes the alcohol concentration to decrease if pH is increased?