After a diffie hellman key exchange, what is the common secret used for?

Question: What is the common secret that is established used for? What types of interactions are now possible?
Comment: Common secret is generally used as a key of a symmetric encryption algorithm.
Answer: It can be used as a key for a symmetric key algorithm.
It can be used to derive a key via a standard key derivation mechanism.
Answer: There are many protocols that require a common secret between the two communicating parties. An obvious example is the establishment of a confidential channel between them, with respect to eavesdroppers: once the DH key exchange takes place and a common secret exists, it can be used to derive a secret symmetric key (as Kodlu mentions in the answer) that feeds a symmetric encryption algorithm protecting the communication channel. Note that this protocol does not protect against active attackers, nor provides authentication.
Comment: As I understand it dh alone doesn't provide authentication but you can digitally sign the messages to perform an authenticated key exchange.
Answer:
What is the common secret that is established used for?

That of course depends on the protocol definition.
In general it is used to establish secret session keys between the two parties to communicate. Generally you need one or two keys for either party; a key for encryption and a key for message authentication. Nowadays authenticated modes of encryption are becoming popular, meaning that the encryption key is also used for authentication, reducing the number of keys to two.
I'm assuming 2-way communication for above.

What types of interactions are now possible?

This allows secure communication to take place. This means confidentiality, integrity and authenticity of the messages that are send/received.
This kind of construction can also be used for asymmetric encryption using DH primitives. An example of this is ECIES which stands for for Elliptic Curve Integrated Encryption Scheme. This hybrid scheme uses Elliptic Curve Diffie-Hellman keys internally.

Although the master secret can often be used directly as key material, usually a Key Based Key Derivation Function (KBKDF) is used to derive session keys.
This allows full use of the entropy contained within the master secret. It also allows to generate any number of keys using labels, and possibly information and salt. Nowadays HKDF is becoming popular which explicitly contains a key extract and expand part (first extracting the entropy, then expanding to the right key size).
Note that the KBKDF function is simply called a PRF in TLS 1.2 transport security. TLS 1.3 (draft) uses HKDF.


How does universal inflation fit with the Planck length?

Question: If the universe is undergoing inflation, and there is a minimum scale that things can exist at (the Planck length), does that mean that new Planck-sized domains have to be continuously popping into existence? If not, does that mean that the Planck length is constantly changing?
Comment: This is the problem of the [Big Snap](http://physics.stackexchange.com/q/15571) as explained by Tegmark.
Answer: This question is very puzzling. Why can volumes of space keep growing without limit, when we think there is a graininess somewhere down there?
To understand it best, you should go to other places where volume space keeps popping up out of nowhere like this. The best example is near a black hole horizon. In this case, if you trace back outgoing light rays, you will find that they all emerge from an infinitesimally thin skin right next to the horizon. This is obvious, because light rays on the horizon are stopped, so two light rays that peel off the horizon at two different late times were squished very close together earlier.
So the entire exterior volume of a black hole is peeling off a thin skin next to the horizon. This property, when it is considered as a property of outgoing Hawking radiation is called the "transplanckian problem". Outgoing modes, which have normal wavelengths by the time they get away from the black hole, are traced back to impossibly compressed wavelengths near the horizon.
This is not a problem classically, but if you imagine some sort of graininess to space, you run into trouble. How do you get the grains to appear as you have this expansion going on?
The resolution to this, as to all problems of quantum gravity, is the holographic principle. You need to change point of view regarding the domain of quantum gravity. The gravity doesn't live in the bulk of spacetime, but on holographic surfaces, and the bulk is reconstructed. Any graininess is boundary graininess not bulk.
This reconstruction means that new space can be created, it is not paradoxical, so long as the boundary degrees of freedom that describe the new space are the same as they were previously. For the case of the black hole, the geodesics peeling off of the horizon may keep on making new space-volume, but any physical matter which they contain loses it's identity and merges with the black hole degrees of freedom once you trace it back to close to the horizon.
Similarly, in deSitter space, there is a cosmological horizon all around you. As the universe inflates, geodesics separate exponentially and go to join the cosmological horizon. But this horizon is not doing anything, it is just sitting there, so any putative holographic description of the space doesn't involve producing new degrees of freedom, it just means that the old degrees of freedom have a finite time before they reach the horizon and, from the point of view of the holographic description, they thermalize.
This is one of the properties of classical GR which really cries out for holographic interpretation. If you take a naive space-time graining, without holography, the constant creation of space from horizons and inflation is very mysterious.
Comment: "Why can volumes of space keep growing without limit, when we think there is a graininess somewhere down there?"  Quantization is not necessarily graininess. Photons have a continuous spectrum although bound states produce them with graininess.
Answer: This Wikipedia article on the Metric expansion of space might provide a better answer, but here goes my understanding, good or bad.
I don't think it makes sense to think that new Plank domains come into existence. After all, the Plank distance is just a unit of measure. The distance between objects in the Universe does grow, so expressing the distance between them will require an ever-increasing number of Plank distances, but nothing new has been created. The Plank length, as a unit of measure, is the same as it was. There was an early time when everything fit in a Plank-distance-sized Universe.
Easier: you measure the diameter of a baloon with a long ruler. As you inflate it, it will take more and more centimeters to express its diameter, but no new space is created.
Comment: This analogy is not great--- the question is more fundamental than this.


What's the evolutionary reason behind feeling 'sorrow'?

Question: As it's established that life's design is a product of evolution, what advantage does emotions like sadness play in the life of an individual/species ?
Comment: @david yes every emotion had better have an evolutionary advantage otherwise it is is really difficult to explain why humans have it.
Comment: Do you really think you there is a concrete evolutionary advantage to every human emotion? And if you do, do you think that anyone knows for certain what it is. All you will get is subjective speculation. This is a question and answer site, not a discussion site. I have voted this off topic.
Comment: @John — So there is no such thing as a neutral mutation being propagated? Yes the things that make us human attract us to others and we mate with them. Is that anything more than common sense. Except in Sparta or in Gengis Khan's army...
Comment: Won't answer your question, but if your name is an indication of another problem I may be able to help you there.
Comment: Basic emotions like sadness are wide spread basic behavior in multiple species, with strong  effects on behavior, they are not neutral effects, drift will not explain them.
Answer: I'll answer from a perspective I've been studying in Psychology, but can't provide sources. If this is not within the scope of this SE, I'd kindly ask to either add appropriate sources to my answer or close it.
Sorrow is an emotion that has specific cues and expressions like tears, distinct micro-facial cues (which are stable over practically all cultures according to studies of Paul Ekman et al.), a general tendency to withdraw from social settings.
This can be understood as communicating to other members of your group the need for consolation and social closeness, which would count as an evolutional gain.
Update:
I found an extensive article on the subject: http://www-personal.umich.edu/~nesse/Articles/Nesse-EvolutionBereavement-2005.pdf
Answer: First sadness and sorrow are not necessarily the same thing. Many consider them quite distinct and thus have different functions.
In the case of sadness it is currently believed that sadness functions to drive you to change disadvantageous behavior. Example 1. Bob insults Betty, Betty will not talk to Bob, Bob feels sad and depressed about this and learns to stop alienating potential mates and allies. Example 2. Lela the wolf takes too long to in sneaking up on what would be easy prey and the prey wanders off Lela feels sadness, a negative stimulation, at the loss and the behavior leading up to it and quickly learns to sneak faster. Source
Sorrow on the other hand is a bit more difficult because it is not clear what you mean by sorrow. Separation sorrow may function to maintain connection in anticipation of the return of a partner or ally. Source Michi's anwer explores some other possible advantages in more intelligent social species. This a a far more tentative explanation than sadness which is not surprising as we see signs that sorrow exists in far fewer organisms and thus is far more difficult to define or study.
Answer: This is just a thought......... overtime the animal brain has developed and became more sophisticated. Included in this process has been the development of emotions, such as love, need to perpetuate the genetic line, ability to feel a sense of loss and hence, sorrow and the need to belong. This emotional growth has contributed in no small way to the ongoing perpetuation of the species.  The ability to experience a variety of emotions enables us to feel both wonderful highs but also mind numbing lows. If we were incapable of feeling emotions and never knew was it was like to be happy or sad our subconscious yearning to perpetuate the species might not be so strong. In other words, I think there is a direct link between our capacity to feel and the innate need to perpetuate the species. If animals, including humans, didn't experience a range of emotions why bother to perpetuate the species?
Comment: We represent a science stack and thoughts or opinions are not really what we're after - we ask answers to be properly founded and backed up by references.


CSGO - Banned competitive or a penalty of a few months / years?

Question: I think I'm banned in competitive csgo, I was wondering when I'm banned, they block the competitive line? or you can throw at it, only without earn points, how it works? why this happened to me only, I was "Banned" at the time did not read the VAC message, I am now playing legitimate competitive because I can still join the queue, without fraud, but I do not earn points to climb, silver for 2 always. If anyone knows of a solution or what really happened. Sorry English, Google Translate, I hope you can understand the text.
Comment: Was it a VAC ban? If so I *think* that means you're essentially banned from all official servers, and any third party server that is VAC secured, which is most of them.
Comment: You mention you can still play competitive with no problems but you aren't seeing a rank increase.  Just because you win some games doesn't necessarily mean you will rank up immediately and see results.  It takes a lot of wins and points to earn a rank up.
Answer: There are a few reason why you might be unable to connect to a competitive round:
Competitive Ban
You can receive this ban for doing any of the following:

Too much damage to teammates. (3 warnings)
Harming a teammate at the start of the round (Instant ban)
Leaving a match after you have pressed the ACCEPT button.
Abusing the kick system.

Keep in mind that a matchmaking ban will be issued regardless of whether or not an infraction was intentional.
VAC Ban
VAC is Valve's anticheat system, it is very accurate and there are almost no false positives.
FACT: There has only been one false ban, and this was due to a game having a broken DLL.
You will be VAC Banned for the following reasons:

Cheating! D:

You will not be VAC banned for any other reason, face it you cheated and got caught. You will no longer be able to connect to any other VAC Secured server!
Source: Valve Knowledgebase
Comment: That link should say "Valve Knowledgebase"
Answer: TLDR at bottom
There are many reasons to not being able to connect to CSGO competitive matches.
COOLDOWNS
you will receive a Competitive cooldown of varied length depending of the amount of infractions which you have committed. An Competitive cooldown is issued when you:

Dealing over 300 team damage
Killing 3 Teammates
Abandoning the match
Failing to reconnect within 3 minutes of disconnecting
Being Kicked for a certain amount of times
Kicking too many players

BANS
If a user has reported you, and after reviewing the footage of that specific match, you are found to be guilty, you will be issued 1 of the two bans, or in some cases, both.

Minor Disturbance Bans
You will attain one of these bans if you are reported for Griefing, Abusive Voice Chat, Or Abusive Text Chat, and are found guilty of doing so. Your account will be banned for a large amount of time (Unsure about exact duration).
Major Infraction Bans
These bans are attained if you are reported for Aim Assistance, Visual Assistance, and Other Assistance, or the VAC system catches you cheating. These will result in a permanent ban from competitive matches, and a VAC ban will even prevent you from entering any official Valve server.

ACCOUNT GLITCH
For some users, your PC/game cache might be glitched, causing you to not be able to connect to matches, despite not having committed any infractions. A very common case of this is the "Appear Button" not appearing. There many solutions to this, and I am not going to list them here, but the solution that solved this problem for my PC was simply to reinstall the game.
Hopefully this clarifies any of your questions. I can attempt to further help you if you provide further details into your problem.
After re-reading your text, it seems like you have previously received a ban, (Possibly VAC ban) and after the ban has expired, you can no longer rank up. I doubt that this has occurred before, but maybe, if you try some more, you can rank up. Maybe it's not anything having to do with your ban, maybe you're just stuck. I can't help you to rank up, sorry.
If you provide more details of your problem in better English, I might be able to help you better.
TLDR

explained cooldowns and bans
seems like he cannot rank up from silver 2
cannot really help him if it's not glitch
if better message is provided I will try to help


What information does a lightning network node hold?

Question: Just setup my first lightning network node, what information exactly am I downloading when syncing?
Answer: When syncing the bitcoin node (a prerequisite to running Lightning securely), you are downloading the entire blockchain and validating all historical transactions, which takes a while and a over couple hundred GiB of information. Having a full validating node means that you are always receiving valid transaction information yourself, and you are not relying on third-parties who could present false information, or where you may have privacy leaks by requesting information about transactions from others.
The bitcoin node will continue to receive new blocks and transactions as they occur on the network, and each block acts as a synchronization point approximately every 10 minutes.
When initially syncing the Lightning node, you are receiving the most recent information about online nodes, open channels, and the policies by which you can send payments through those channels with Lightning's onion routing. By default, this information is limited to the previous 2 weeks only, so historical information about nodes and channels is not transmitted or stored.
After the initial sync, your node will constantly receive and rebroadcast new information about nodes and channels over Lightning's gossip network. Each node broadcasts information about itself or its channels each 2 weeks if there have been no changes and the channels are still active. Any changes to channel or node states are broadcast immediately, but nodes may limit the frequency of updates they accept to prevent potential DoS which would degrade the network. These broadcasts are also timestamped and signed.
Comment: Thanks a lot that answered my question, appreciate the quick reply also!
Comment: How does the the gossiping work? Is there situations where this doesn't occur effectively ? Say if I have an issue routing a payment through nodes due to incorrect data?
Comment: Gossiping is staggered each 60 seconds between nodes to prevent information duplication, so it spreads through the whole network within minutes. However, in the case where you attempt to route information and something has changed since the last information you received, there is a failure message forwarded as a reply to your payment request, which contains the most up-to-date information in it so you can try again with that updated information immediately.


What can be done about Closed Questions spoiling the questions page?

Question: I find it irritating to see a closed question on the questions page. It shouldn't be there, it spoils the smooth running of the site. It makes me want to... trample all over it. Perhaps a  tag could be put on the question and it put at the bottom of the questions queue so that people can find closed questions if they want. Perhaps there's another more elegant solution?
Answer: Closures can be reversed (by a moderator or by 5 users with 3k+ reputation) and they do happen error, so it is proper that they should receive some attention.
Comment: I agree that they deserve _some_ attention but the OP's point remains: surely we could find a more elegant solution.. Actually I feel this is one small aspect of **a more drastic overhaul of the site's organizational structure** that IMO is getting more and more overdue.
Comment: OK, so perhaps a subtle link on the main page to closed questions would be a better compromise.
Answer: I would support closed questions to be tagged as closed, so people can put them into their ignored tags. If the question is reopened, the tag can be removed.
Comment: The team are [firmly against "meta tags"](http://blog.stackoverflow.com/2010/08/the-death-of-meta-tags/), and [closed] would be exactly that.
Comment: ok i see. seems reasonable.


What's a good minimal pair to highlight interrogative prosody in English?

Question: I want to show my students how intonation contours in Praat can help identify English interrogatives. An obvious example is "He's coming." vs "He's coming?" -- but perhaps those of you more familiar with prosody or intonation have better ideas in mind.
Answer: It is often helpful to avoid voiceless sounds as much as possible in prosody stimuli, to get a clearer pitch track. For example, "Mary will win" has no voiceless sounds (from: Pierrehumbert, J. (2000). Tonal elements and their alignment. In Prosody: Theory and experiment (pp. 11-36). Springer Netherlands.).
For demonstration purposes, you may also want to use a longer sentence.
Comment: Yep. And among voiced sounds, you'll want to avoid voiced fricatives, which are not handled well by the pitch analysis.


How to construct a pythagorean scale?

Question: I am trying to understand how to construct the pythagorean scale. I have gathered, that the basic idea is to use only the 3/2 ratio starting from some base frequency. As this takes you out of the octave quickly, using the 1/2 ratio (=one octave) you move back into the original octave. The video

 explains this quite well. However for the last step he suddly starts from the base frequency with a 4/3 ratio and calls this "the oddball one".
Using the same approach as all notes before and starting from the previous note would take you (in this example) to 372.525 Hz. This is not the same but within the octave so i do not understand why the approach is suddenly different for the "last" note (This is another question: where to stop).
Comment: Maybe the [wiki article](https://en.wikipedia.org/wiki/Pythagorean_tuning) on this, which is pretty complete could also help?
Comment: My problem with the wiki article is twofold: it starts out with already naming notes ("A is tuned such that its frequency equals 3/2 times the frequency of D") while my understanding is that Pytagoras had no knowlege of note names so would not be able to say "ok, now i have all 12 notes and i am done". Also, the only part where the article actually talks about scale construction using frequencies, they also "suddenly" change the approach without explaination just suddenly "Starting from the same point working the other way"
Comment: This tuning tries to stay as tuned as possible compared to the base note. Starting from there, you can see it this way: pick one step up, one step down, and so on. There is no sudden change, you go back and forth above and under the base note (3/2 then (2/3)^-1 and scale back to one octave). At some point, you get two frequencies that are very close (G# and Ab on the wiki) which is a good point to stop. The first time such a close set happens is after 12 iterations. You can obviously go higher, that's why they are usually denoted pythagorean scaleS.
Comment: The fact that, in the video he is going several steps one way, before getting the other way is a bit confusing, and I agree sounds a bit "out of the hat". The good way of constructing is to alternate. I hope I did clarify things a bit… If you want I can make it an answer…
Comment: The answers firm here : https://music.stackexchange.com/questions/110699/from-the-piano-tuners-viewpoint-what-needs-to-be-done-in-order-to-achieve-equ might also be of help!
Answer: The combination of Information from the comments made it much clearer. I actually used this method to calculate the resulting frequencies starting with 440Hz and you can see quite nicely how two frequencies (618.05Hz and 626.48Hz) are really close to each other and "mess up" the otherwise almost equal distribution.
Comment: Neat! I guess the key point was to see that you need to alternate up and down around the base note.
Answer: This approach is suddenly different for the last note, because the last note, the subdominant of the scale, does not exist in the harmonic series of the tonic. 4/3 is not a harmonic of 1.  You could also construct the scale only using 3/2 ratios (and bringing down into one octave) by starting on the subdominant (say, F in a C major scale) and going up from there. This is because the subdominant is the "flattest" note in a major scale.
And do check out the wiki that Tom suggested.

How to construct a pythagorean scale?


What are the best practices for DOF stacking?

Question: What are the best practices for DOF stacking? How do you get the frames with focus just right amount apart? How do you stack them in post processing?
Answer: If you are taking photos of something stationary, then a focusing rail will allow you to do them perfectly.  If you are talking about moving things, like insects, then all you can do is take a lot of photos.  If you aren't able to focus reliably without a tripod and rail, then you can use burst mode.  But, with some practice, you can get to the point where you can reliably click the shutter when specific portions of the shot are in focus and capture a series that way instead.
Comment: What about post processing?
Comment: I agree with that remote is a must.
Answer: There is a good article over at DPS about focus stacking which documents one way of doing it including post processing in Photoshop.
Answer: There is a good article about focus stacking using command line tools align_image_stack and enfuse (both included in Hugin).
Answer: A friend of mine recommended ImageJ in combination with the Stack Focuser plugin for combining the images into a single image with an extended depth of field. He mainly uses it for microscope images.
I've also found good references for CombineZP. Although there's not much info on the site there is a yahoo user group for it for more information and this (old) article describes a complete workflow using CombineZP.
Answer: I think it is worth mentioning that if you are a Canon person, Magic Lantern has a great focus stacking utility that will let you set the number of shots in front and the number behind as well as the size of the focus shift for each shot. It will take the series of shots and even generate a little script that can be used with Hugin to merge.


Conservation of kinetic energy in perfectly Elastic collision

Question: Suppose two bodies of mass $m_1$ and $m_2$ moving with velocity $u_1$ and $u_2$ and they collide (perfectly elastic collision) and after collision their velocities are $v_1$ and $v_2$.
Then by law of conservation of linear momentum.
$$m_1u_1 + m_2u_2 = m_1v_1 + m_2v_2$$
And if I am given only this information is it possible to prove that the initial kinetic energy of the system is equal to final kinetic energy of the system, or the information is insufficient?
Any help would be appreciated.
Comment: Are you given all the specific values of initial velocities, final velocities, and masses? Are there any unknowns?
Answer: By the very definition of an elastic collision, both kinetic energy and momentum are conserved. If it were any collision, you are certain that if no net external forces are acting on the system, the initial momentum equals the final momentum. However, only in perfectly elastic collisions is the kinetic energy conserved.
Comment: We define the perfectly elastic collision is one in which the kinetic energy is conserved. It is the basis of further analysis of this type of collision.
Comment: does that mean there is no mathematical proof of the conservation of *kinetic energy* in perfectly elastic collision?
Answer: Conservation of linear momentum doesn't equate to collision being elastic ,so no you can't prove energy conservation using that equation
Comment: Sorry I forgot to mention that the collision is perfectly elastic.Also I need the mathematical proof of conservation of kinetic energy.
Comment: Suppose the particles were moving towards each other with u1 and u2 and after collision they move in opposite direction of their initial velocity with speed v1 and v2 .  Then u1 + u2 = v1 + v2 (sorry for my bad editing ) use this equation along with conservation of momentum you can easily prove energy conservation.
Comment: you said that for elastic collision the coefficient of restitution becomes 1 but this is proved by the conservation of kinetic energy and that is my question.
Comment: I think I made it look confusing collision is elastic iff energy is conserved,this is by definition. About coefficient of restitution e = relative velocity of separation/ relative velocity of approach
Answer: The equation for the conservation of momentum does not imply that kinetic energy is equal before and after a collision - oftentimes, it is not. For any input parameters $m_1, m_2, u_1, u_2$, there are an infinite number of possible $v_1$ and $v_2$ that will satisfy the equation and the conservation of momentum. There are few solutions that will also satisfy the conservation of kinetic energy. The fact that a collision is elastic by definition implies conservation of kinetic energy, but the mere conservation of momentum does not imply conservation of kinetic energy (inelastic collisions conserve momentum but not KE).
Comment: Thank you for your answer I understood the concept very clearly.
Answer: Let's suppose two bodies collide the total kinetic energy from the encounter is equal because of the elastic net conversion K = 1/2 m v2
which is adequate and satisfies the law of conservation in kinematics as well as in non-linear dynamics hence I would say the total energy is conserved throughout unless it were to be acted upon otherwise, so in technicality this would be a perfect frame that we discuss of to have it be conserved. I hope I gave you a bit more of a grasp on the coefficient and those parameters!
Comment: Welcome to [Physics.SE]!  I don't think this answers the question, though;  it seems to boil down to "kinetic energy may be conserved", but the question was asking whether it *must* be conserved.
Answer: If for a system:$$\sum F_{external}=0$$
Then  $$\sum_i(m_iv_i)=constant$$
Or simply $m_1u_1+m_2u_2=m_1v_1+m_2v_2$ ; for a two body system. But we cant conclude about $KE=constant$, simply from this equation.
So here we use concept of elasticity.
In elastic collisions, kinetic energy remains constant while in inelastic collision it doesn't remains constant.
For checking nature of collision we use Newton's coefficient of restitution ($e$), which is defined as:
$$e=\left|\frac{\Delta v}{\Delta u}\right|$$
Here, $\Delta v$ is velocity of seperation (after collsion) and $\Delta u$ is velocity of approach (before collision).
So we can clearly see that $e\in [0,1]$.
So for, $e=1$, collision is perfectly elastic and kinetic energy remains conserved.
For other values of $e$, we have inelastic collsion, and energy is wasted in form of friction, heat, sound or other forms of energy. So, for our real non-idealistic world, $e\in (0,1)$.


IP packet reading

Question: Just got an simple question.Its abt reading a plane IP packet. In a standard IP packet RFC 791, there are multiple fields, the IP packet header size is 20 bytes.  Now when i look at following packet and see the highlighted sections i see Version is IPv4 and header length is 20 bytes (which is true and we ack that).However the binary values on the left side are confusing .  For the version the binary value is 0100 which is decimal  is 4 and is true (IPv4) but for Header length  the binary is 0101 which should be 5 but it shows 20 bytes!!!! How? Also since the IHL (IP header length) field in IP header is only 4 bits the max decimal value can only be 15 (if 1111). Now how come it can show the header length as 20. Now sure what u am missing but i request experts to take a moment to answer this.
Comment: RFC 791, p.11 -- You didn't read.
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 could provide and accept your own answer.
Answer: The unit used in the Length field is not bit nor even byte but 32bits words.
So the value 5 correspond to five 32 bits words = 160 bits = 20 bytes.
And the max value is then 15 x 32 bits = 60 bytes (40 for options).

IP packet reading


Axiom of choice - to use or not to use

Question: I was wondering if there are examples of results in mathematics that were first proven using axiom of choice and later someone found a proof of the result without using the axiom of choice.
Comment: The title of your question does not seem related to the question itself...
Comment: @Mariano: I was just trying to sound Shakespearan.
Comment: Super far from the answer to your question, but a question from MO that I really like and I think you might like also is http://mathoverflow.net/questions/3557/where-are-some-interesting-places-where-the-axiom-of-choice-crops-up-in-category/3623#3623
Comment: There are probably tons of examples historically considering the axiom of choice wasn't explicitly singled out until relatively recently in history, but I don't think they'll be easy to find since mathematicians were not likely to have pointed out their usage of it before then.
Comment: I think that asking for examples should be under big-list, and even if not then community wiki for sure.
Answer: Cantor-Schroder-Bernstein theorem was first proved by Cantor using the axiom of choice.  Proofs without using it came later.
Comment: This is probably the best possible answer to this question.
Comment: To say a bit more, the point is that in his proof of this theorem, Cantor introduced the Axiom of Choice for the first time, and people were indeed rather skeptical.
Comment: @Pete: Thanks! I really like the proof this theorem.
Answer: The issue is complicated by the fact that many (most?) "mainstream mathematicians" are not really keeping track of whether they are using some form of AC in their arguments.  Moreover, they often do not write their proofs in such a way which makes clear either whether they are using AC or whether this use of AC is really necessary.
Here is an example from my own experience.
Theorem (Luther Claborn): For every abelian group $A$, there exists a Dedekind domain $R$ such that the ideal class group of $R$ is isomorphic to $A$.
I know of three proofs of this theorem.

Claborn's original 1966 proof:

http://alpha.math.uga.edu/~pete/claborn66.pdf

C. Leedham-Green's 1972 proof:

http://alpha.math.uga.edu/~pete/leedhamgreen.pdf

My 2008 proof:

http://alpha.math.uga.edu/~pete/ellipticded.pdf
Of these, the only one I am truly familiar with is my own.  My proof uses transfinite induction.  To be quite honest, I was pretty tickled by this: it was maybe the fourth time in my life that I had written down a transfinite induction argument and the first time that it was for any serious purpose.
Anyway, I soon heard from the eminent mathematician Bjorn Poonen (then at Berkeley) that he had been thinking about this very result because a student of Eisenbud's had recently given a seminar talk on Leedham-Green's proof (which I would describe as "clever and complicated").  The proof I had given was much more up his own alley, and he immediately found a way to recast / improve it.  Among other things, his recasting completely avoided use of the Axiom of Choice.  (But I hasten to add that there was more to it than that.)
We speculated briefly on the possibility that this modified argument was the first proof of Claborn's theorem to avoid AC.  I asked whether Leedham-Green's proof used AC and he told me that indeed it was also a transfinite induction argument.  So then I looked back at Claborn's paper and asked my student about it.  We were able to point to some part of Claborn's argument (which, if you look at the paper, you'll see is rather terse: I wish the paper were more than four pages long!) which we thought used AC.  But I don't remember what that was, and I am only moderately confident that we were right: if you told me otherwise, I wouldn't be too surprised.
And now I must tell you that I didn't include in my paper any hint that Poonen's modification would give an AC-less proof (and possibly the first such proof!)
of Claborn's theorem.  I felt that Poonen's argument was so nice that it deserved further exploration in its own right: I wanted to use it -- and still do -- to give a characterization of all abelian groups which can be the group of rational points on some elliptic curve over some field.  So in essence I have been keeping to myself the fact that this theorem of Claborn (which lots of people know about) can be proved independently of AC.  Sorry!
Comment: Thanks for the interesting anecdote.
Answer: This  article is an example of sorts where Doyle and Conway prove without using AC that for any two sets $A,B$ such that there is a bijection between the sets $3\times A$ and $3\times B$, where $3=\{0,1,2\}$, there is a bijection between $A$ and $B$. http://www.math.dartmouth.edu/~doyle/docs/three/three.pdf
This should be relatively easy to prove using well ordering principle which is equivalent to axiom of choice.
Comment: Oh, please. Conway is a great man, but let's not forget that Tarski proved (without AC) a much more general result in 1949. Namely, if $k$ is a nonzero finite cardinal, and $a,b$ are arbitrary cardinals, then $$ka\le kb\implies a\le b$$ and $$ka=kb\implies a=b.$$ (Of course, the second implication is a corollary to the first implication, by virtue of the Cantor–Schröder–Bernstein theorem.) Reference: A. Tarski, Cancellation laws in the arithmetic of cardinals, Fund. Math. 36 (1949), 77–92.
Answer: If $G$ is a locally compact abelian group, then there exists a unique measure $\mu$ on the Borel sets of $G$ such that:

$\mu(G)=1$,
For every measurable $A$ and $x\in G$: $\mu(A)=\mu(A+x)$,

We can slightly enlarge the Borel sets to include all the subsets of measure zero sets, and thus have a complete measure.
This measure is called Haar measure. In the case of $\mathbb R$ this is exactly the Lebesgue measure.
Haar (the mathematician) proved its existence on separable compact groups in 1933, and von Neumann proved the uniqueness shortly after.
The general case for locally compact Abelian groups was proved by Weil and relied on the axiom of choice. Henri Cartan later proved both existence and uniqueness of the general case without the axiom of choice.
Comment: @Asaf:  One should not expect "unique up to isomorphism" shows AC is not needed.  Merely "unique".
Comment: (Warning: this comment contains egregious name-dropping.)  I had dinner with Richard Borcherds and Stephen DeBacker about ten years ago and listened to the latter tell the former that he had supervised an honors (undergraduate) thesis on the construction of the Haar measure without AC.  Borcherds's immediate reaction was that the **uniqueness** of the Haar measure was a big clue that AC should not be required.  I found that to be a nice insight worth remembering.
Comment: @Pete: While true and important, remember that the uniqueness of an algebraic closure does require [some of] the axiom of choice. Indeed this is a whole different case here, but not everything unique is essentially "choice free".
Comment: A few remarks: $\mu(G) = 1$ can only hold if the group is compact. Haar assumed second countability, but neither compactness nor commutativity and while his proof used a little choice, his argument can without problems be adapted to avoid it in the second countable case. Weil and JvN proved uniqueness independently. Cartan's contribution was to modify Weil's argument to avoid AC in the general case. A nice account of Cartan's argument is [here](http://www.mscand.dk/article.php?id=1667) and [here](http://www.math.ku.dk/kurser/2004-2/mat3re/haarintegral.pdf) for a traditional account.
Answer: Things come full circle:  Constructive proofs of the Hilbert Basis theorem.
Click with all of your justice.
Comment: Constructive/not constructive is not the same dichotomy as not using the Axiom of Choice / using the Axiom of Choice.  So far as I know, the standard proof of HBT does not use the Axiom of Choice in any way.  (Nor does the word "choice" appear in the article you link to.)
Comment: Tbh, why would somebody care about AC if they weren't worried about constructiveness of some or another proof?
Comment: From personal experience: There are many reasons why people interested in set theory may want to keep track of uses of choice that have nothing to do with whether something is constructive or not.
Comment: Also, the axiom of choice is not necessarily non-constructive. For example, full choice is valid in constructive type theory.

Axiom of choice - to use or not to use


Regular expression for a binary number that includes "10" and has an odd number of 0's

Question: I have been struggling trying to write a regular expression for a binary number that includes "10" and has an odd number of 0's, so far I have (1) * (00) * 10(1010)   * (00) * (1) * but it doesn't accept 0100 for example or 010101 etc, also if I write a finite automata for this how do I prove its correctness ?
Comment: I would produce an automaton and then [convert it to a regular expression](http://cs.stackexchange.com/q/2016/9550).
Comment: Please restrict yourself to one question per post; you are posing two very different ones. David gives you a good hint; the usual proof strategy is induction. See [here](http://cs.stackexchange.com/questions/11315/how-to-show-that-l-lg) for an introduction to such proofs for grammars; since NFA are basically the same as (right-)regular grammars, the principles carry over.
Answer: You can write a regular expression directly:

First ignore the odd number of zeroes. You can easily write an expression for this modified language, based on the fact that you can choose to particularize the first occurence of $10$ (namely $0^*1^*10(0+1)^*$ is a valid expression).
Now you want to modify the first part ($0^*1^*$) and the second part $(0+1)^*$ to take into account the odd number of zeroes. Since these two parts have to agree (have the same parity of zeroes) there are two disjoint cases: either you have even numbers of $0$'s before and after the $10$ pattern, or an odd numbers:

To have an even number of $0$'s before the pattern, simply write $(00)^*1^*$. For an even number after the pattern, this is simply an expression for a word with an even number of zeroes: $1^*(01^*0)^*1^*$ (each $0$ has a friend). Together, this gives you the expression: $(00)^*1^*\ 10\ 1^*(01^*0)^*1^*$.
To have odd numbers, you can re-use modified versions of the expressions in 1.: Before the pattern, you add a first $0$ in front: $0(00)^*1^*$; After the pattern, you need a first $0$ but also $1$'s in the middle: $1^*01^*(01^*0)^*1^*$. Together: $ 0(00)^*1^*\ 10\ 1^*01^*(01^*0)^*1^*$.

Globally, you have the disjunction of the two cases:
$$(00)^*1^*\ 10\ 1^*(01^*0)^*1^* + 0(00)^*1^*\ 10\ 1^*01^*(01^*0)^*1^*$$
This is not meant to be the smallest possible expression, but at least it shows how you can construct one. For instance, you can factorize the common parts to obtain
$$ (00)^*(1^*10+01^*101^*0)1^*(01^*0)^*1^*.$$


Can a Demon be possessed by Spirits?

Question: I assume a demon cannot be possessed by a spirit.  Is this correct?
I'm not finding it in any of the rule books.
Answer: No, a Demon cannot be possessed by a Spirit
I'm frustrated that I can't find a passage - I thought there was an explicit "Demons can't be mentally/spiritually influenced by any external forces," but I'll assume I was thinking of classic WoD Demons.
DtD p182, "Total Control"

A demon never expresses a thought or emotion involuntarily... This precise trait makes it almost completely impossible to read his true intentions.

Demons are, by their nature, unemotional. They can emulate emotions, they can even trick themselves into feeling emotions (Flowers of Hell, page 25), but they cannot be influenced by emotions.
The problem is, that's most spirits' angle of attack; the Demons offer nothing Resonant to Open up, so to speak.
Even in the case of say, a mechanical Spirit, wherein it could be argued an innate resonance exists with Demons, the situation would be far more akin to having your Spam folder flooded with all caps directives to paint your living room, rather than waking up after a three hour blackout with paintbrush in hand.
It's also worth considering the Possession Exploit - DtD, page 171. While naturally Demons and Spirits have different mechanisms for the act of possession, the effects are by and large the same - the invader gains total control of the victim, does not have to keep burning fuel to retain control, etc. In some ways, the Demonic method is stronger - using her own traits and possibly using some of the victim's Skills, not counting lack of restrictions on Embeds and Exploits.
This Exploit specifically says it targets "human beings" - meaning Demons can't be victim to this arguably stronger version of possession.
And, to circle back, since a Demon's true motives are inscrutable, it bears to reason that even if a Demon was able to be possessed by a Spirit, it'd be a meaningless endeavor - like a court order prohibiting a person from flying without mechanical assistance. Most people can't do that - and for those who could, why would they obey such a piece of paper?
Comment: Thanks.  I couldn't find anything that said it specifically either in DtD, FoH or DSG.  However, I haven't read each book cover to cover so I might have missed. it.
Comment: @Ghostdriver I still would have preferred something more explicit, but it makes sense that an answer can be derived via extrapolation; Demons are very logical, after all.
Comment: The entire premise of this answer is wrong. Demons are not unemotional robots, they are robots who have emotions and can conceal them perfectly.
Comment: @user10063 My answer is merely trying to say "A demon is always in full control of his emotions" paired with "Spirits possesses via emotional manipulation (at least, initially)" imply that the possession wouldn't work. I did not mean to imply that Demons don't feel emotions.
Answer: There is no rule that makes demons immune to becoming Possessed by ephemeral beings.
Ironically, yes, a demon could also even be possessed by an angel, technically.
It may merely be somewhat more difficult for the Possess Manifestation to succeed, on par with trying to possess more powerful supernatural beings, as unlike others, demons in human guise use their morality/sanity stat, Cover, as their Supernatural Tolerance. And it's much higher even for novice demons (Cover 7) than their Supernatural Potency stat (Primum 1).

Living subjects contest the roll with Resolve + Composure + Supernatural Tolerance.

Before it can use the Possess Manifestation, the ephemeral being just needs the target to have the Open Condition. For spirits, this means first advancing from the prerequisite Resonant Condition. If that involves a specific emotion, so be it, because demons feel emotions just as keenly as everyone else. Hell, emotion is almost inevitably involved in what caused their Fall in the first place.

Demons are really good at lying: Very true. Demons are
  masterful liars, the consequence of being an inhuman machine-
  creature wearing a human body. Demons feel emotions — they
  feel them just as deeply as humans — and can express themselves
  by angry shout or tender whisper, but the disconnection
  between what a demon thinks and his human body means that
  they don't show involuntary signs of emotion. Every demon
  has an iron-clad poker face and magical attempts to sense their
  emotions usually fail.

The fact that demons feel emotions, even as they hide them from mundane observation, is repeatedly alluded to throughout the book -- even still-enslaved angels have them, to some degree.

For good or ill, angels don't experience emotion in their
  bodies. Everything is intellectual for them. A hunter angel
  might feel contempt for the demons he is sent to destroy, but
  he doesn't hate them, not with the bone-deep, venomous hatred
  that humans are capable of. His hate exists purely in his mind,
  a pseudo-emotional circuit placed there by the God-Machine to
  ensure that the angel completes its mission.
When an angel Falls, the barriers of emotional objectivity
  falls with it. A demon is fully embodied in the world. She
  feels her emotions as fully and viscerally as any human being
  (though they don't necessarily express them normally — see
  p. 44 for details). This comes as a shock to most demons, but
  they usually adapt quickly. Not all demons Fall because their
  non-physical emotive thoughts were enough to overcome their
  programming, but it's a sufficiently popular motivation that
  demons are generally friendly to the idea of passion.
Torn from the God-Machine's control, a Falling angel
  experiences a tumult of new emotions and thoughts, its
  previously clear mind wrecked by an explosion of sensation.
  For a terrifying instant it doesn't exist — it isn't part of the
  God-Machine any more and the universe has no place for it —
  but the remains of its protective Infrastructure wrap around it
  and reality warps to accommodate the newcomer.
anyone who can see into the Shadow might notice
  the spirits of passion who are drawn to a demon's newfound intense emotions.
They feel emotions as deeply as any
  human. What they don't do, however, is express these emotions
  unconsciously. A demon might lash out in anger, but no one
  around her will see it coming. Her interpersonal self-control is
  perfect.
For
  example, if a human psychic tries to read a demon's aura, the
  demon can spoof the psychic's ability to detect that she isn't
  human, but not his ability to read her emotional state. She
  might, however, get a contested roll against the power.

Can a Demon be possessed by Spirits?


Minimum water temperature for swimming workout

Question: What is the minimum water temperature for swimming workouts, like 1-2 km swims? I love swimming in lakes and rivers and am generally okay with cooler water (especially if swimming intensely), but I'm concerned about under-cooling my organs (most of all prostate and kidneys). Of course, if it feels too cold or I start freezing, I get out immediately.
Answer: It depends on your body and acclimation. I had a friend who was an excellent swimmer who died after being stranded in Lake Michigan when it was 45F. I was at a 1 and 2 mile race once where the water temperature was 68F, and it was early season so people had only acclimated with warm pool swimming. Out of 500 or so people, 3 women without wetsuits became hypothermic. They recovered with warm showers and ER visits. No men had issues and no one wearing a wetsuit had issues. I swam with no wetsuit and was fine. Men on average have more mass and about twice the muscle mass in proportion on average, and this helps them. People who are both strong and have a fat layer may also have an advantage. I have heard of people swimming distance in the San Francisco Bay daily without a wetsuit, and that is quite cold. I recommend that with boat support you start with very short swims and see how you react, and this will also allow your body to acclimate.
Comment: Recent research suggests that you do not generally become ill or get infections from being in the cold unless you are near hypothermia. At that point your body may divert energy from immunity to immediate survival, making you more prone to pneumonia and a number of other infections. The immediate risk is hypothermia, which can happen to anyone on a bad day even in warmer water. Once hypothermic, you may lose rational thought and strength it could kill you. Have support from someone dry or well insulated, such as a kayak escort, or a larger boat if you are further from shore.
Comment: Thanks for the reply, I see you have some experience in this. Have you heard of cases where chronic (read: long-term negative effects) damage has occured because of the habit of swimming in cold water?


Cannot install mysql gem / ruby-dev

Question: I'm trying to install ruby mysql gem. After gem install mysql I get:
Building native extensions.  This could take a while...
ERROR:  Error installing mysql:
ERROR: Failed to build gem native extension.

    /usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from extconf.rb:5:in `'

Gem files will remain installed in /var/lib/gems/1.9.1/gems/mysql-2.9.1 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/mysql-2.9.1/ext/mysql_api/gem_make.out

I found this answer recommending installing ruby-dev, but after either apt-get install ruby1.9.1-dev or apt-get install ruby-dev I get:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
ruby1.9.1-dev : Depends: libruby1.9.1 (= 18.104.22.168-8.1ubuntu2) but 188.8.131.52-8.1ubuntu2.1 is to be installed
                Recommends: ruby1.9.1 (= 22.214.171.124-8.1ubuntu2) but 220.127.116.11-8.1ubuntu2.1 is to be installed
E: Unable to correct problems, you have held broken packages.

1) How can I fix this problem?
2) Even more interestingly: as the problem occurs on a fresh xubuntu installation, what causes this type of errors? Have I managed to break something unknowingly? I'll appreciate a link to a resource which will help me get some understanding about the ways of the Ubuntu package manager and dependencies under Linux.
Comment: did you installed build essentials?
Comment: Yes, I have the build-essential package installed.
Comment: I'm the same situation. Did you solved in some ways?
Comment: @ilpaijin, No - I used different versions of Ruby and the gem, but despite trying multiple times, I was not able to make it work.
Answer: I meet the same problem on Ubuntu 14.04. I remove all the ruby ,ruby-1.9 ,ruby-dev package and re-install ruby and ruby-dev. It seems that I can install ruby software by gem now.

Cannot install mysql gem / ruby-dev


Do publications outside your primary field of study help or hinder your early career?

Question: I'm an interdisciplinary PhD student and I've heard conflicting reports on your publication record in your early career. Some members of my host department say that you should stay focused while others outside the department say it can help. Given that my dissertation is by publication and I've got one core field and two secondary, what would a hiring committee expect my CV to look like? Would publications in tertiary field (as primary author) be looked upon negatively?
Answer: If you have 5 publications in 5 different areas, I would be concerned that you might become the eternal prodigy or that you are not willing to perform some long term research. However, if you have a clear focus and can document that you are working continuously on one project, then activities outside your core area indicate that you are able to work together with very different people. So you won't be hired because you have many publications, if there is no area where you are really convincing. But among applicants, which are similar in the area the position is aiming at, other activities become a significant advantage.
Answer: TL;DR: If you just start your PhD, it's better to stay focus on one topic.
You can imagine yourself as an employer (whether in academia or in industry), looking for a candidate to work on topic X. There are two CVs, one has 5 papers on X, and the other also with 5 papers but on X, Y, Z... Which one do your prefer?
After PhD, you are supposed to be an expert, having deep knowledge on a (very narrow) topic. You need to make sure that you have enough publications to prove this. If you wrote your thesis as a monograph, you would need to tell a story, and only the papers relating to that story should be included in the thesis.
I have no idea how a compilation thesis looks like, but I imagine you still need to write an introduction, which summarizes all the papers, and how they are related together.
Moreover, focusing on one field will make you more productive. If you can publish 5 papers in 5 different field, then you might be able to publish 10 papers in 1 field.
Comment: This seems like the traditional approach, how does this apply in interdisciplinary situations?
Comment: @anonymous did you ask your advisor if there is any specific requirements, e.g. number of papers in each field etc?
Comment: The requirements are largely set by my committee and my advisor wants to make sure I can demonstrate satisfactory competency with the literature. For my dissertation my committee wants me to publish as much as I can that is within the bounds of the research project. So the secondary publications are effectively a requirement for the degree since we are developing new methods in the side fields in order to be able to conduct the research. So the issue really isn't what my dissertation is going to look like as it is how search committees are going to view it once it get done.
Answer: There are a couple aspects of this to consider:

Some members of my host department...

They are your host department, but you're an interdisciplinary PhD student. There is not promise that your host department now will be the kind of department you end up sending job applications to. I can tell you, in addition to my "primary" field, I applied heavily to positions in other areas, and when it came down to it, it was one of these applications that landed me my current position. Papers that are slightly off your main topic area help signal that you can do work outside that area. It gives people in those fields something to grip onto and evaluate while they consider you, etc.

...you should stay focused...

The key here is not to let side-projects distract you so much that they start obstructing your actual progress. They are, inherently, side projects. You should have some way to tie them into your main research agenda (even in different fields, what you do should have a coherent theme) and participating them should be holding you back. But a paper or two in adjacent fields likely won't hurt your chances overall, and in some cases may help.
Answer: Everything else equal, publications outside your primary area are unlikely to hurt.  If you have a strong record — e.g., good publications, evidence of teaching excellence, a clear scholarly identity, and a great letters — publications outside of your area aren't going to disqualify you. Some departments are more method focused and interdisciplinary in ways that might even cause "side" publications to be helpful to some degree.
Generally, publications outside your field will help much less than articles in your field. Hiring and promotion committees will have a much easier time evaluating your work in your area. They know the prestige of different journals, for example. Additionally, publications within an area help build a consistent scholarly identity which is helpful when you're selling yourself to employers and you're fighting to build a name for yourself. Fantastic letters often say things like, "X is among the best young scholars working in the area of Y anywhere." That's hard to write if your scholarship is all over the map. You have limited time and energy to work on publications. Use it well!
In the absence of a strong scholarly identity and clear evidence of excellence, "side publications" might be seen interpreted as evidence of a lack of a focus. Hiring and promotion decisions are not made based on a single criteria. Although publications from an outside area are not likely to hurt on their own, they might be taken seen as additional evidence of — or an explanation for — weakness in your application. If you haven't published very much in your primary area, folks are going to think your side publications might be why. If your commitment to your discipline isn't clear from the rest of your record, publications outside your discipline won't help.


Which heroes beaten up by Garou died?

Question: Garou has beaten many heroes, but some of them at least in their first beating survived, such as Tank Top Vegetarian. Which heroes beaten up by Garou died?
Answer: As far as I know, no hero that Garou defeated ever died in the manga. As noted here:

Although Garou is a villain and considered evil by most, he possesses a sense of morality: he fights heroes in a way without killing them, but he is okay with others killing heroes.
Comment: @Pablo Yep. In later scenes, Charanko and Tank Top Master was seen talking to Saitama (in the hospital). The Tank Top Army is also not listed as deceased nor dead in the wiki. If they were dead, then it would at least be shown in the manga since subordinates' deaths would inevitably have an effect on Tank Top Master.
Comment: When Bang found Charanko and the other heroes lying on the floor the next day, they all seemed dead. Were they alive? Tank Top Master and Mumen Rider werent there.

Which heroes beaten up by Garou died?


can I recover the change of a TX?

Question: I was reading and I have a question, if you please can help me. I send 0.00335 BTC in this TX: bf3eedc1929042444e62badaf885a8dd49333c31ff40d023175a90da241ec2e0
and I see the 0.00335 as spent, but the change (that I didn't specify the address where to put it) went to another address, and it appears as unspent. What can I do to recover it? Thanks a lot for your suggestions.
Answer: Your wallet software will handle all of this for you. Your wallet software generated the change address and stored its private key. When you want to spend more Bitcoin, it will still know about the change and can spend from it. Your balance in your wallet should still include the change. There is nothing you have to do in order to spend the change, and there is no "recover" required.
Comment: Thanks a lot, you was very clear! I hope to continue learning about Bitcoin and help to other in the future.

can I recover the change of a TX?


Does dukkha apply to name-and-form?

Question: That is to say, anicca and anatta obviously apply to all 5 skandhas, but 'stress/suffering' is a psychological phenomenon. Is it the 'name' within name-and-form that links it back to dukkha?
Answer: 'Dukkha' as one of the three characteristics is not a psychological phenomenon (unlike 'dukkha' in the four noble truths). As one of the three characteristics, 'dukkha' means 'unsatisfactoriness', namely, the inherent inability of impermanent conditioned things to bring lasting happiness.
For example, apples, motor cars & cocaine are 'unsatisfactory' because there is no characteristic within those things that can bring lasting happiness.
The following correct translation makes the different usages of 'dukkkha' clear:

Sabbe baṅkhārā dukkhā'ti yadā paññāya passati Atha nibbindati dukkhe esa maggo visuddhiyā.
"All conditioned things are unsatisfactory" — when one sees this with wisdom, one turns away from suffering. This is the path to
  purification.
Dhammapada 278 translated by Acharya Buddharakkhita

As for 'nama', for Buddhist purposes, it is defined in the suttas (SN 12.2; MN 9; etc) as the 'mentality' or 'mental faculties' of feeling, perception, intention, contact & attention and also mindfulness, zeal, energy, decision, etc (MN 111).
'Nama' for the purpose of converting & teaching Brahmans (eg. DN 15, DN 11, SN 7.6), namely, 'name', is not for Buddhist purposes & should be ignored by those wanting to comprehend Buddhism.
In other words, in the context of Buddhist suttas such as SN 12.2, MN 9, etc, 'name-form' is an incorrect translation. The correct translation here should be 'mentality-materiality'.
'Name-form' is only a correct translation for Brahman suttas, such as DN 15, DN 11, SN 7.6, etc.
Thus, in terms of the three characteristics, nama-rupa is dukkha (unsatisfactory); just as SN 22.85 states the five aggregates of a Buddha are unsatisfactory (dukkha).
However, in terms of the four noble truths, nama-rupa is not dukkha because the 1st noble truth summarises all psychological dukkha as attachment (upadana) to the five aggregates.
Comment: Of course. It is the experience of unsatisfactory-ness that results in liberation via the destruction of craving. Its like being in love with a girl who has left you & you can't get over her. But then you learn she poisoned her previous five lovers. & stole all their money. When you realise how unsatisfactory that girl was, you are completely liberated from her. Because all conditioned things are totally unsatisfactory for an arahant, the arahant has no desire towards those unsatisfactory things, as explained in SN 22.59. It is a total victory. regards
Comment: Thanks for the answer.. On a small note though, would an Arahant, having cut off suffering still experience unsatisfactory-ness? That seems like it would be a bit of a half victory!
Answer: In Conditioned Genesis (Paticca- samuppada),  consciousness leads to mentality & materiality (Nama Rupa).  Feeling, perception, intention, contact & attention are called 'name/mentality' or nama and the body dependant on the four great elements (Earth, fire, water & air - 'Patavi', 'Apo', 'Thejo', 'Vayo') is form/ materiality or rupa). The Buddha taught that nominal and physical things (nama rupa dhamma) which are subjected to the three characteristics of existence impermanence, suffering and soullessness, are nothing but a state of Conditioned Genesis (Paticca- samuppada) which exists without a doer or causer.  Those causes and effects are subjected to cessation on the same spot and thus manifesting this state of cessation from within oneself, can attain the state of Extinction, the Nibbana. Thus all of these are Suffering (dukkham) and arising of Suffering (dukkha samudayam).
Answer: Nama is vedhana, sangna, sankhara, vingnana. Rupa is solid, liquid, gas and heat. This is pancha upadhanakkandha.
Pancha upadhakkandha is by definition dukkha, a noble truth.

Does dukkha apply to name-and-form?


How can I get $\sum_n e^{i a_n} |n\rangle$ from $\sum_n a_n |n\rangle$?

Question: Suppose that I have a normalized quantum state $\sum_n a_n |n\rangle$, is there a quantum operation/circuit so that I can get $\frac{1}{N} \sum_n e^{i a_n} |n\rangle$ at output? How?
Comment: I strongly suspect that this is not a unitary map, which means that it can't be implemented by a quantum circuit. Have you checked this?
Answer: It's not unitary, so it's impossible because all quantum transformations have to be unitary.
Consider the states
$$
\frac{3}{5} |0\rangle + \frac{4}{5} |1\rangle \quad \mathrm{and} \quad \frac{3}{5} |0\rangle - \frac{4}{5} |1\rangle. $$
These get taken to
$$
\frac{1}{\sqrt{2}}\left(e^{3/5 i} |0\rangle + e^{4/5 i} |1\rangle\right) \quad \mbox{and}\quad \frac{1}{\sqrt{2}}\left( e^{3/5 i} |0\rangle + e^{-4/5 i} |1\rangle \right). $$
The inner product between the first pair of states is $-\frac{7}{25} = -0.28$, while the inner product between the second pair of states is $\frac{1}{2}(1+e^{8/5 i} )\approx 0.4585 +0.4998 i.$
Since unitary operations preserve inner products, this is not unitary.
Answer: I wouldn't think so. I'm assuming your $a_n$'s are normalized, i.e. that $||\sum_n a_n |n\rangle|| =1$. But then your wish output is not normalized since $$||\sum_n e^{ia_n} |n\rangle|| = \sqrt{\sum_n |e^{ia_n}|^2} = \sqrt N$$ where I assume there are $N$ terms in the sum. Quantum (unitary) operations have to preserve the norm so there can't be one that maps the first state to the second one.
Comment: Yeah, but that's not the point. I have edited my question to make clear my intentions.


Measurement for 3 sheets of crushed graham cracker

Question: My receipe calls for 3 sheets of crushed graham cracker. I bought pre-crushed graham cracker. What is the cup measurement for 3 crushed sheets?
Answer: Jefromi answered this related question How much is a cup of graham cracker crumbs in crackers and weight? with the information that there are 7 or 8 crushed crackers in a cup. So, 3 crackers would be about .4 cup crushed.
Comment: I'm closing as a duplicate, because there is really no sense in answering it for 1 cup, 2 cups, 3 cups... etc. once the ratio has been established.


Can I sell a handpainted large scale 3D model of a copyrighted 2D concept art?

Question: The art in question is https://www.instagram.com/p/CIfsO2ZD7Rj/ . I Think the concept artist, Jean Giraud, is dead.
Answer: While better fitted to our friends at law.SE, the general gist is: No.
Art is protected by copyright, and any adaption (derivative work) requires the OK from the right holders per se. Only 70-75 years after the death of the author (or publication for company works), a work enters the public domain and the copyright expires.
There are some exceptions (fair use/fair dealing/...), but media transformation is not one of them.
Giraud died in 2012, his estate or heirs - or whoever he/they sold the commercial rights to - own the right to ok derivative Works till around 2087.
Comment: Yes, better asked at law se, however, if the work is a 3d model inspired by a 2 image then it can be argued that it's a new work. This concept came up when people were thinking about selling 3d prints of existing sculptures; in that case, the answer was a definite no.
Comment: @user77232 *inspired by* is ok, but  *3d representation of a 2D art* is not. There is a rather blurry line between *inspiration* and *derivative*
Comment: yes; and this is why we have lawyers  :)
Answer: This is something that might have a precedent, where the line is blurry, someone might have already tried, and in that case the judge's decision in that court case is the official interpretation of the law towards that specific scenario.
There might also be definitive laws regarding "derived works"...
Like the others, I would ask the Law SE for help.


Evaluating a function in matlab

Question: I have expanded sin function into a Taylor series. Now I want to evaluate it at specific point. I get strange "MuPAD" errors in matlab. What am I doing wrong?
function r1=taylor_sine
syms x;
mysine = taylor(sin(x), 63, 0);
r1 = funm(220, mysine);

Answer: I'm not 100% familiar with the syntax you're using, maybe the inline function syntax is slightly different from the expanded syntax, however it looks like your function doesn't have a cleary defined input and output. A non-inline matlab function should look like this:
%Comment
function [ theta ] = FunctionName( alpha, beta )
theta = alpha + beta;
end

Try to create your function in a separate .m file (filename the same as the function name). After you've created the .m file make sure that it's located in the search path of MatLab (check if the autocompleter shows your function name when you type it in partially).
As for the actual body of your function, I see a few weird things. What is "syms x" supposed to do? I would replace this line with "x = -pi:0.001:pi;"  (have x be a vector from -pi to pi with increments of 0.001). or something analogue to that.
Also for normal Taylor aproximation I would use taylor(sin(x), 63)  (the overload with 'v'- does a Maclaurin approximation).  Also I wouldn't do a Taylor approximation up to the 63-1th order, that's way too high, maybe MatLab crashes on that.
In the following picture you can see that the 7th order approximation is already extremely good between -pi and pi.
Answer: Did you really mean 220?  Or did you mean 220 degrees in which case you should use 220*pi/180?
I think it should be subs not funm
r1 = double( subs(mysine, x, 220*pi/180) );

Comment: Actually what did help me was "subs".
Comment: @Artium, thanks. You're right, it is "subs" not "sub". Sorry, I use Octave and not Matlab.

Evaluating a function in matlab


How does Original Sin come back in man even after being washed at the time of baptism?

Question: According to Catholic thought, if we are washed of Original Sin at the time of baptism, why do we transmit Original Sin to our children? In other words, how is it that my child is born with Original Sin when I was freed from Original Sin at the time of my baptism?
Answer: I think you misunderstood the role of Baptism in Catholicism.
Cathecism of the Catholic Church-1263 says

[1263] By Baptism all sins are forgiven, original sin and all personal
  sins, as well as all punishment for sin. In those who have been
  reborn nothing remains that would impede their entry into the Kingdom
  of God, neither Adam's sin, nor personal sin, nor the consequences of
  sin, the gravest of which is separation from God.

It doesn't say original sin is washed away, it says it is forgiven. Forgiven doesn't mean you don't have original sin anymore; it only means your sins are forgiven.
Our sins cannot be washed away by merely washing with water nor any kind of Baptism. Only the blood of Jesus Christ can wash away our sins.

1 John 1:7 (NIV) But if we walk in the light, as he is in the light,
  we have fellowship with one another, and the blood of Jesus, his Son,
  purifies us from all sin.
Revelation 7:14 (NKJV) And I said to him, "Sir, you know." So he said
  to me, "These are the ones who come out of the great tribulation, and
  washed their robes and made them white in the blood of the Lamb.
Revelation 22:14 (DRA) Blessed are they that wash their robes in the
  blood of the Lamb: that they may have a right to the tree of life, and
  may enter in by the gates into the city.
Answer: Original sin is a state of human nature passed to all mankind, but it is not like a gene passed on from our immediate parents. It affects the nature of all humans. The Catholic Catechism discusses this in and around paragraphs 396 to 408.
In paragraph 404 talks a bit about what Original Sin is and its source:

But we do know by Revelation that Adam had received original holiness and justice not for himself alone, but for all human nature. By yielding to the tempter, Adam and Eve committed a personal sin, but this sin affected the human nature that they [Adam and Eve] would then transmit in a fallen state. It is a sin which will be transmitted by propagation to all mankind, that is, by the transmission of a human nature deprived of original holiness and justice.

In paragraph 405 talks about what Original Sin is and the effects of Baptism on it:

Although it is proper to each individual, original sin does not have the character of a personal fault in any of Adam's descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin — an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ's grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.

On the effects of Baptism, paragraph 978 says:

"When we made our first profession of faith while receiving the holy Baptism that cleansed us, the forgiveness we received then was so full and complete that there remained in us absolutely nothing left to efface, neither original sin nor offenses committed by our own will, nor was there left any penalty to suffer in order to expiate them. ... Yet the grace of Baptism delivers no one from all the weakness of nature. On the contrary, we must still combat the movements of concupiscence that never cease leading us into evil "

Finally, in talking about Baptism of Infants in paragraph 1250:

Born with a fallen human nature and tainted by original sin, children also have need of the new birth in Baptism to be freed from the power of darkness and brought into the realm of the freedom of the children of God, to which all men are called. The sheer gratuitousness of the grace of salvation is particularly manifest in infant Baptism. The Church and the parents would deny a child the priceless grace of becoming a child of God were they not to confer Baptism shortly after birth.
Answer: Not being a Roman Catholic, I cannot give you an answer from the RC perspective and tradition.  I can, however, give you a brief overview about what the Bible has to say about Christian baptism.
As a wise man once told me,

"Baptism doesn't make you a Christian; it marks you as a Christian."

As good as infant baptism may be as a way for Christian parents to "sanctify" their offspring through a well-established rite (which exists in both the Catholic and Protestant traditions), nowhere in the New Testament is there any indication that infant baptism cleanses the infant from "original sin."  If the RC church teaches this, all I can say is, the teaching is not biblical.
On the basis of Scripture, I say confidently but lovingly, the physical act of being baptized neither forgives us of sin nor frees us from sin.  To say otherwise is to contradict the clear teaching of Scripture.  If, however, Scripture is not the ultimate guide for your life and practice, then none of the following will be of help to you, and will certainly not answer your question--though I am glad you asked it!
There are two baptisms in the New Testament, each having two aspects, both spiritual and literal/physical.  The first is the baptism of John.
John the Baptizer fulfilled two roles: the first as a herald for the Messiah, and the second as a forerunner for the Messiah.

(1) John as a herald.  In John's day, just as the king's servant who preceded his king during royal tours from city to city would announce in a loud voice, "The king is coming, the king is coming, get ready for the coming of your king," so too did John announce the coming of the King Jesus, the Messiah.

John, however, shouted

"Repent, the kingdom of heaven is at hand, the kingdom of heaven is at hand, the kingdom of heaven is at hand" (Matthew 3:2).

John certainly attracted the attention of the people with his announcement of the coming kingdom, and they came to him in great numbers.

(2) John as a forerunner.  Historically, when a king was scheduled to enter a city, he was not only preceded by a herald, but he also sent servants called forerunners ahead of him to remove any obstacles such as rocks, tree branches, or potholes--anything that would impede his path as he was being carried by litter into the city.

What was hindering the entrance of Jesus the Messiah into the hearts of the people?  Sin.  John therefore had to tell the people

"'Make ready the way of the LORD, Make His paths straight'" (Matthew 3:3; Isaiah 40:3).

Just as the forerunners of old were responsible to remove obstacles from the road, so too was John responsible to get people to repent of their sins, removing anything that would hinder the entrance of Messiah into their hearts and lives.
John's message to the crowds who came to hear him was a simple one:

"Repent"

And repent the crowds did!   Repentance is simply a change of mind resulting in changed behavior.  It's doing an "about face":  you are going in one direction, but you make a 180-degree turn and go in the opposite direction.

" . . . and [the people from Jerusalem and the surrounding areas] were being baptized by him in the Jordan River, as they confessed their sins" (Matthew 3:2,6).

Before a watching world, the people baptized by John were declaring openly in the waters of the Jordan River--that's the literal/physical part of baptism--what had transpired inside their hearts--that's the spiritual part of baptism; namely, that they were turning their backs on their sins in preparation for the appearance of the coming Messiah, whose coming John foretold.
Being baptized did not cleanse anyone of sin, it merely bore witness to their repentance.  On the other hand, the baptism of the Messiah was completely different.  As John himself said of Jesus, the coming Messiah and king:

". . . this is the One who baptizes in the Holy Spirit" (John 1:33).

The second baptism, then, is Christian baptism.  Like John's baptism, it has both a literal/physical aspect and a spiritual aspect.
The physical aspect is the outward act of being immersed in (or sprinkled by)
actual water in the presence of witnesses, and

". . . in the name of the Father and the Son and the Holy Spirit" (Matthew 28:19).

The spiritual aspect is the inward process of conversion by the Holy Spirit, which takes place before we are baptized.  Call it regeneration, as in

". . . the washing of regeneration and renewing by the Holy Spirit" (Titus 3:5),

or call it being born again or born from above, as in Jesus' words,

"Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God. . . . [and] unless one is born of water and the Spirit he cannot enter into the kingdom of God" (John 3:3,5).

Christian baptism is for believers in Jesus Christ who have been regenerated within their spirits by the Spirit of Christ, whom Jesus called a "Helper," "the Spirit of truth" who "teaches us all things," and the presence of Christ within us "forever" (see John 14:16 and ff.).  Believers who are indwelt by the Holy Spirit want to bear witness to that transformation by obeying the command of our Lord to be baptized.  To this day, in some countries of the world, being baptized openly and publicly is to invite persecution and even death!
As Paul tells us in Romans 6, Christian baptism is a symbol of our having died to our old way of life.  When we die, we need to be buried.  Baptism, then, is a picture of burial that is enacted symbolically by immersing ("burying") a person in water.  As the person comes up out of the water, symbolically he is coming alive in the Spirit of God, just as Jesus came alive in His glorious resurrection from the dead (vv.3-5 and ff.).
Does being baptized mean we will never sin again?  No.  Neither an infant who has been baptized nor a person who has experienced the new birth and has been baptized will cease to sin (see 1 John 1:8-10).  We can, however, have victory over sin in our lives, since as believers in Jesus

". . . our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin" (Romans 6:6).

Furthermore, we have the responsibility as baptized believers (literally and spiritually) to

". . . consider [ourselves] to be dead to sin, but alive to God in Christ Jesus";
"not [to] let sin reign in [our] mortal body so that [we] obey its lusts";
"[to] present [ourselves] to God as those alive from the dead, and [our] members as instruments of righteousness to God";
"[because] sin shall not be master over [us], for [we] are not under law but under grace" (Romans 6:11-14).

In conclusion, being baptized with water neither cleanses us from sin nor takes away our ability to sin.  It is, however, a way of telling both God and man that we have become new creatures in Christ, that

"the old things passed away; behold, new things have come" (2 Corinthians 5:17).


NNJoin aborted with error "worker: no geometry"

Question: I have a series of points in a csv file, with lattitude, longitude  in WGS84, and I want to know to which country they belong. These points are on the shore, not inside a country, that's why I'm using NNJoin plugin to have the distance to the nearest country.
The shapefile for countries is the one provided by natural earth ( ne_10m_admin_0_countries.zip downloaded here https://www.naturalearthdata.com/downloads/10m-cultural-vectors/).
When I run NNJoin, I get the error "worker: no geometry" and aborted error. It doesn't provide any more information in the log. It happens on QGIS 2.18 and 3.0
Any idea of what I am doing wrong ?
Answer: I found the error ! latitude and longitude were empty in one line...


Why did the solution turn green?

Question: I mixed L Arginine with l Citrulline in Hibiscus and green tea water which was red in color. Once the red liquid hit the mix of powdered Aminoacids the solution changed green. Can someone tell me why? Thanks so much for any info!
Answer: Both citrulline and arginine are nitrogen-rich, basic amino acids. A basic acid sounds confusing, but that's the way it is.
The colour change indicates a change in the pH of the solution (the tea mix).
The pH indicator that changes the colour is in the hibiscus flower and belongs to the class of the anthocyanes.
Under acidic conditions, the dye exists as a deeply-red flavylium cation. At a slightly higher pH, the dye is reversibly converted to a colourless form. Here, the colour of the mixture is determined by the other ingredients. When more base (read: more amino acid) comes to action, further colour changes are conceivable and the double deprotonated form of some anthocyanes are known to be bluish-green.
Comment: Dear Klaus,thank you so much for answering my question. So does this mean that the mixture created is now more acidic? Also since I am drinking this do you see any problems or should I just drink the Amino acids with water? Thank you so very much,Jeff
Comment: Jeff, actually it should be just the opposite: the amino acids make the tea is more alkaline. Yes, alkaline (basic) amino acids are confusing, I'm a bit reluctant to answer the medical part oft the question, that's not really my field of work. but since the amino acids are a food supplement, I'd try to drink the with water and check if the taste of the tea is better then. Btw, if you think that the answer was helpful, you might have to accept it. Please have a look at [this](http://chemistry.stackexchange.com/help/someone-answers) for the background.

Why did the solution turn green?


Transform/Distort Image points to new positions in Photoshop

Question:
How do I transform the 4 points A B C D to 1 2 3 4 respectively so that the individual planes AB, BC, CD and DA are mapped and stretched evenly across into 1-2, 2-3, 3-4 and 4-1?
Answer: I guess you ae out of luck in Photoshop. Normal warp is useless, you cannot get the edges and corners both right (tried), Distort in pieces breaks the image to displaced pieces (tried), Puppet warp needs a half hundred nails at edges and they still look out jagged (tried). A math transformation would do it, but that needs a programmer which I'm not.
Something quite nearly right is available with visual tools in Affinity Photo. It's Warp Mesh is incredibly loyal. Here the wanted area is made rectangular. It's not a big deal to stretch it bigger.

The same should be possible in Illustrator (=Envelope distort with mesh)
BTW. You did not specify how evenly it must be made. You should declare upper limits for local stretch and rotation somehow. Warping this way surely doesn't scale lines AB and BC linearly. Math transform is the only way have exact control.


find-grep-dired equivalents for ack and ag

Question: Is there an equivalent find-grep-dired using ack or ag? With the ability to specify the directory where the search starts? The Dired output itself is not so important (in fact I prefer the ack-mode result output). The closest thing I found is a Projectile ag/ack integration where the prefix argument prompts for the directory, but I was looking for something more general.
Comment: Sorry for not being clear. Here is another try : the projectile ag/ack integration supports prefix argument, which when used prompts for the directory. So it works similar to the _find-grep-dired_. But that works only within a projectile project (projectile mode is on). I'm looking for ag/ack version of _find-grep-dired_ that can be used _outside_ of the projectile too.
Comment: Can you elaborate on what you mean by more general? The way this question is phrased now makes it unrelated to emacs.
Answer: The ag package (available on MELPA) has the ability to run ag only within your specified folder or in project root. Check out its README on its github for more info.
Here are some of the answers from this stackexchange the elaborate on the use of ag in emacs:

What is the easiest way to search all useful files inside a single project?
Is there a way to use query-replace from grep/ack/ag output modes?
Answer: Here is small function that does what I was looking for; perhaps useful to someone else too. The function prompts for the directory and invokes the ag search-term. When invoked with the prefix argument the search-term is interpreted as regular expression.
(defun find-ag (dir search-term)
  "Run an ag search with SEARCH-TERM in the directory.

With an optional prefix argument ARG SEARCH-TERM is interpreted as a
regular expression."
  (interactive "DFind-ag (directory): \nsFind-ag (ag expression): ")
  (if (fboundp 'ag-regexp)
      (let ((ag-command (if current-prefix-arg 'ag-regexp 'ag))
            ;; reset the prefix arg, otherwise it will affect the ag-command
            (current-prefix-arg nil))
        (funcall ag-command search-term dir))
    (error "Ag is not available")))

Answer: You can use helm-ff-do-grep invoked in helm-find-files to grep any directory you want. It has a demo in there; the grep in Helm is incremental: it returns results for every character you type, effectively provides live feedback. Or use helm-projectile that is capable of invoking grep in any directory of selected file or directory in a helm-projectile-find-file or helm-projectile-find-dir. See the helm-projectile guide here.


I got error low space memory on my Lumia 520

Question: How do I move my music, pictures and apps et cetera from my phone's memory over to an SD card which I had to buy? I fitted the SD card into the phone (Nokia Lumia 520 - running Windows Phone 8) only to be repeatedly told thereon that I still need space and I should move some stuff over to the SD card but I'm at a loss as to how that's done. Can you help please?
Answer: You should be able to transfer data to your new SD card using the Storage Sense app - you'll also see that there is the option to save new items (photos/videos/etc.) to the SD card, as well as the option to install new apps to the SD card.
Not all apps allow themselves to be installed on an SD card, and some may need to be moved back if the developer enforces that for an app as part of an update.
Answer: Go to the Microsoft store and download the Files app. This is a file manager application. Use that to browse through, and manage the files on both your phone, and your Micro SD card.
Comment: How is this content different from the answer that I posted earlier?
Answer: Try moving them manually using e.g. either the Files app or (Windows 10 built-in) File Explorer app.
Comment: Why the down vote?


What happened to Hampnie Hambart in Episode 3?

Question: When Hampnie Hambart died, was it because his wish came true AND he succumbed to his wounds, or would he have died whether he was wounded or not because his wish came true? I'm asking because I don't recall him being that terribly wounded. It seemed like the group that captured him was just getting started.
Comment: You have no need to add a spoiler warning in the title. If you feel that something might be spoilerish add `>!` before the sentence or paragraph, to hide the spoiler content until a user mouses over it. With that being said, your title implies a spoilers so you don't really need to include one if you don't want to.
Comment: Thank you for @Krazer! In the past I've written a spoilery title and didn't want it to happen again, but also I wanted to make sure I wrote a proper title for this question.
Answer: It's hard to know for sure, but it makes sense why he would die if we accept Hampnie Hambart's own theory for what God is doing. He believes that God thinks he is granting humans their wishes. In that case, Hampnie Hambart's own wish, to die happy with his family, was granted. Until that point, he was unable to die because it would go against his wish. However, once those conditions were met, he could die just as any other human.
As for his wounds not being very severe, this is a matter of how you interpret the scene. My personal guess he was probably at the level that an ordinary human would die, but being immortal himself, he could withstand more than the average human. Another possibility is that after his conditions were met, his wish being his own death, God granted him that wish right away. What exactly the group does to him isn't depicted much so we can't know for sure whether it would kill a normal person. There may be more information in the light novels, but I haven't read them.
Of course, we don't really know what God is doing (at least not yet), so there could be a different explanation, but this makes sense given all that we know so far by episode 3 of the anime.
Comment: Very true! I believe that he died when his wish was granted. His wish was to die with his family, which is why he was searching for Hana. He would not be able to die unless he knew what happened to her. Once he found out she passed away, and that he still has family who will remember him and mourn his death, he could finally die with content and rest in peace.
Comment: Hampnie's wish included dying with a pang of regret. His wish wouldn't have come true if he hadn't thought, "I don't want to die now..."
Comment: This is probably it, although it is a bit strange because when he was dying he said something like *"I don't want to die now..."* (he wanted to stay with Ai). Either he wished this too late or God is fed up with his requests.


Why didn't Tony Stark order Jarvis to save Pepper Potts?

Question: In the beginning of Iron Man 3 when Extremists  attack on his house, he uses his suit to save Pepper's life. The same could be done in the end part of the movie when Pepper Potts was falling from 200 feet. Why didn't he do it?
Comment: I'm not 100% sure, but was that suit present at the battle at that time? I thought it showed up later.
Comment: Yah! When Pepper was about to fall ,suits were presents and fighting with other extremists.
Comment: A lot of suits were present, yes, but they were the suits from Tony's basement. Suit #42 may not have been there yet.
Comment: @AdamV Certainly #42 came at the last moment. But I think other suits too were capable of fulfilling any command by Tony.They were saving Tony ,why couldn't they save  pepper (If only she was not injected with Virus). :-)
Answer: The suits were under the command to engage and eliminate all Extremists. The suits considered Pepper too as an Extremist as she had been injected with the virus. Therefore, the suits would try to destroy her rather than save her.
And, IMO issuing a new command to save Pepper Potts would had taken time and moreover be seen as an ambiguous instruction by the suit's system.
Comment: is "this could be the reason" or "this is the reason"?
Comment: and why didn't the suit destroy pepper potts ,while she was hanging?
Comment: @user2509211: If I say "this is the reason", do you have anything to refute the claim. But no, this is all logical inference. And my guess is that the suits did not destroy Pepper then because the virus had yet not been activated.
Comment: Ok ,So As Pepper was injected with virus ,and that virus could have been  activated at any moment...Tony thought It's safe to keep Jarvis away from pepper. :-) I accept your ans. Good thought.
Answer: The MK42 was a prototype, thus it was the only one that he had that he could send onto her body or summon to his own. The only one that had those gesture controls from when he injected himself with transmitters in the beginning of the movie. After pepper falls is when he is up top with Aldrich and he says "The prodigal son returns." meaning MK42 was in bound. MK42 then crashed and fell into pieces and he never put it on again. But he wasn't able to order any other suits to attach to her in that period of time. The only way he ever got caught in a suit was from timing his jumps and Jarvis having his back. But there were a lot more suits at that point.
Comment: I think this is the correct answer. The other suits couldn't work with Pepper, as per Tony's earlier exchange with Rhodey: "Colonel James Rhodes: Give me a suit. Tony Stark: Sorry, they're only coded to me. Don't worry, I got you covered." (source: https://m.imdb.com/title/tt1300854/quotes)
Answer: The Extremis was created as a way of recovering and rebuilding a body. It could activate when a body got injured. Maybe that's why Jarvis' systems started considering Pepper as an Extremist and didn't try to save her when she was falling and attempted to kill her when the virus activated. As for me, though, I was expecting the suit to catch Pepper till the end)))


hightraffic dns ttl record

Question: Whats bestpratice TTL for hightraffic www sites? Should there be a high TTL to make dnsservers around cache longer so the dnsserver wont have to get requests to often?
Answer: I can't tell you what TTL value to set, you can set it quite high (let say 1 day) but take care that if a day you need to do a maintenance and want to switch the resolution to a new IP . Until the TTL expire you may have request on the old IP. In some case it is OK because both IP will still work, in some case the old IP is not available after maintenance. In this last case you will probably want to decrease the TTL value before you maintenance to reduce the downtime for users.
So take care of this, if you think you could have to reduce TTL someday your dns server need to be able to enough powerful to handle that.
Comment: So if my dns servers handle it i may want to have a low TTL incase of emergency-maintenance etc.
Comment: Probably, but do not set it to low.. it's faster for users if ISP DNS Cache can reply directly. From my point of view 30m is a good mean to have quite good caching and low outage in case of emergency change

hightraffic dns ttl record