Is it possible to have a spherical object with only hexagonal faces?

Question: If so, what would be the most efficient algorithm for generating spheres with different number of hexagonal faces at whatever interval required to make them fit uniformly or how might you calculate how many hexagonal faces are required for each subdivision?
Comment: Consider a sphere with a hexagon drawn on it. This surface is spherical along with two faces, both of which have six edges and six vertices. Yes?
Comment: CoryG: I've responded to the title question in my answer.  For a reasonable approximation using pentagons and hexagons, look at @pjs36's link to Goldberg polyhedra in the comments to my answer.
Comment: @AgnishomChattopadhyay: See the comments below my answer for more thoughts on this suggestion (made independently by DavidK).
Answer: No, not even if we permit non-regular hexagonal faces.  (We do, however, preclude hexagons that are not strictly convex—where interior angles can be  $180$ degrees or more—since those permit degenerate tilings of the sort David K mentions in the comments.)  The reason is more graph-theoretical than geometrical.
We begin with Euler's formula, relating the number of faces $F$, the number of vertices $V$, and the number of edges $E$:
$$
F+V-E = 2
$$
Consider the faces meeting at a vertex.  There must be at least three of them, since it is not possible in a solid for only two faces to meet at a vertex.*  Thus, if we add up the six vertices for each hexagonal face, we will count each vertex at least three times.  That is to say,
$$
V \leq \frac{6F}{3} = 2F
$$
On the other hand, if we add up the six edges for each hexagonal face, we will count each edge exactly twice, so that
$$
E = \frac{6F}{2} = 3F
$$
Substituting these into Euler's formula, we obtain
$$
F+V-E \leq F+2F-3F = 0
$$
But if $F+V-E \leq 0$, then it is impossible that $F+V-E = 2$, so no solid can be composed solely of hexagonal faces, even if we permit non-regular hexagons.

*ETA (2022-05-17): This is a concession to geometry; the argument isn't strictly graph-theoretical. If you permit situations where only two faces meet at a vertex, then it is possible to create a polyhedron with only hexagons. For instance, start with a cube, and describe a circuit around the faces. (One such circuit goes along the faces of an ordinary die in numerical order.) Then on the edge adjoining two faces in this circuit, add an additional vertex in the middle. Each face will have two new vertices, converting each square into a "hexagon" of sorts. But I think most people would agree this isn't a very interesting positive response to the original question.

If we now restrict ourselves to regular faces, we can show an interesting fact: Any solid with faces made up of nothing other than regular hexagons and pentagons must have exactly $12$ pentagons on it (the limiting case being the hexagon-free dodecahedron).
Again, we begin with Euler's formula:
$$
F+V-E = 2
$$
Let $F_5$ be the number of pentagonal faces, and $F_6$ be the number of hexagonal faces.  Then
$$
F = F_5+F_6
$$
The only number of faces that can meet at a vertex is three; there isn't enough angular room for four faces to meet, and as before, solids can't have only two faces meet at a vertex.  If we add up the five vertices of each pentagon and the six vertices of each hexagon, then we have counted each vertex three times:
$$
V = \frac{5F_5+6F_6}{3}
$$
Similarly, if we count up the five edges of each pentagon and the six edges of each hexagon, then we have counted each edge twice, so
$$
E = \frac{5F_5+6F_6}{2}
$$
Plugging these expressions back into Euler's formula, we obtain
$$
F_5+F_6+\frac{5F_5+6F_6}{3}-\frac{5F_5+6F_6}{2} = 2
$$
The $F_6$ terms cancel out, leaving
$$
\frac{F_5}{6} = 2
$$
or just $F_5 = 12$.

I've heard tell that any number of hexagonal faces $F_6$ is permitted except $F_6 = 1$, but I haven't confirmed that for myself.  The basic line of reasoning for excluding $F_6 = 1$ may be as follows: Suppose a thirteen-sided polyhedron with one hexagonal face and twelve pentagonal faces exists.  Consider the hexagonal face.  It must be surrounded by six pentagonal faces; call these $A$ through $F$.  Those pentagonal faces describe, at their "outer" edge, a perimeter with twelve edges and twelve vertices, which must be shared by a further layer of six pentagonal faces; call these $G$ through $L$.
There cannot be fewer than this, because the twelve edges are arranged in a cycle of six successive pairs, each pair belonging to one of $A$ through $F$.  No two faces can share more than one edge, so the twelve edges must be shared amongst six faces $G$ through $L$, but "out of phase" with $A$ through $F$.
However, these pentagonal faces $G$ through $L$ cannot terminate in a single vertex—they would have to be squares to do that.  Hence, they must terminate in a second hexagon.  Thus, a polyhedron of the type envisioned cannot exist.
Likely the above approach could be made more rigorous, or perhaps there is a more clever demonstration.
Comment: @pjs36: No, you're right; strictly speaking, they don't need to be regular.  We just need to cap the number of faces meeting at a vertex to three.
Comment: If you admit partitions of the sphere that do not have corresponding polyhedra, a simple partition into two spherical hexagons is to put six vertices around a great circle and connect them with the obvious arcs of the great circle. You can even displace alternating vertices to opposite sides of the great circle if you want "real" vertices, although that makes the hexagons non-convex. You can insert additional hexagons by dividing a hexagon in two by connecting opposite vertices with a three-edge path. This isn't very "uniform", however.
Comment: Similarly, one can show that a solid composed of only square and hexagonal faces must have exactly six square faces.
Comment: @Wildcard: Of course a sphere can be composed of spherical polygons. For example take a platonic solid and project it from the center onto the enclosing sphere. Although I think he simply meant an object whose vertices are all located on a sphere.
Comment: Are you sure regularity of hexagons is required, or even possible? I'm thinking of these [Goldberg polyhedra](https://en.wikipedia.org/wiki/Goldberg_polyhedron); I think it's purely combinatorial, coming from $V - E + F = 2$ alone. EDIT: Ah, I see where regularity is used. Sorry about that! I'll still link to Goldberg polyhedra, 'cause they're cool :)
Comment: @Wildcard: I understood the OP to be speaking of a polyhedron.  Note that I refer in my solution simply to a solid, not a sphere.
Comment: @pjs36, and [here](http://dmccooey.com/polyhedra/DualGeodesicIcosahedra.html) is a pretty nice site about them!
Comment: I'm lost.  Since when could it even be *considered* a possibility that a sphere could be composed of polygons?  What definition of a "sphere" are we using here?  Perhaps a link would be in order; the question is only tagged "geometry."
Comment: @celtschk, "an object whose vertices are all located on a sphere"—this makes perfect sense; thank you.  "...spherical polygons..."—what on earth is that supposed to mean?  Ah, I see; you mean "formed on the surface of a sphere."  Now the question makes sense.
Comment: @BrianTung Thanks, this is what I was looking for, you were right in that I was thinking of a polyhedron - my background is in computing and physics not math (the math is something I only really delve into for graphics programming and experiments.)  I appreciate the leniency in interpreting the terminology used.
Comment: I guess by a "solid" you mean a convex body, right? Otherwise I don't see why your argument that "the only number of faces that can meet at a vertex is 3" is valid.
Comment: Can you run those numbers again, only this time with octagons as the primary component of the sphere?
Answer: If a compromise is acceptable, the $2p, 4p, 8p, ... $ subdivisions of  each side of an icosahedron in Buckminster Fuller domes  leave behind 12 pentagons at each of its 12 vertices.
Else, possible by means of a stereographic projection of a flat regular hexagonal net (a node of which touches south pole and other nodes/junctions connect to north pole), the curvilinear hexagon boundary cells shrink to zero towards north pole according to standard stereographic scaling. They can be seen on POV Ray image provided by user PM 2Ring below. A part of spiral has been traced connecting opposite vertices of some hexagons.

It is a collection of log spirals centered at south pole that  isogonally ( i.e., conformally) project to rhumb-lines (loxodromes constant inclination to meridians at $\pm \pi/6$) with corresponding latitude circles drawn.  I could make an image later if you wish to see. Since these loxodromes are not overtly seen on the above image,  some segments are indicated across some hexagon diameters.
Comment: Speaking of stereographic projections, here's a mapping of a hexagonal net onto the Riemann sphere, rendered using POV-Ray: [RiemannHex](https://i.stack.imgur.com/59qvd.png)
Comment: Thank you very much. I searched for it but could not find one.
Comment: Feel free to embed that image in your answer, if you want.
Answer: You can do it if you allow your sphere to have a hole through it, i.e. be a torus.  See image here.  Then the Euler characteristic, as described in Brian Tung's excellent answer is 0, not 2.
You might also be able to do it for non-convex polygons; convexity is a requirement of the Euler characteristic.  See, e.g., the octahemioctahedron.  I couldn't find one with just hexagons though.
Comment: The thing about a torus is it *isn't* a sphere.
Comment: @JollyJoker:  I'd think that it would be hard, if not impossible, to use  [Penrose tiles](https://en.wikipedia.org/wiki/Penrose_tiling) to cover a torus.  Anything that covers a torus should be able to cover the plane, though, as the torus can be viewed as the plane with periodic identifications made;  basically, you can unwrap the torus into a rectangle and clone it to cover the plane.
Comment: Technically this is is a tiling of the punctured sphere - the point at the north pole is missing, and does not have a defined color.
Comment: Am I correct in assuming anything that tiles a plane can tile a torus and vice versa? Would that hold for anything with Euler characteristic 0?
Comment: @MichaelSeifert Right, a tiling of the torus obviously must be periodic and non-periodic plane tilings exist. Thanks, I learned something!


Is there any way to use just year and month as timestamp in org-mode?

Question: Specifically, I'd like to sort a column in a table in org-mode. However, the column only has year and month information, like 2016-02 or May 2016. It can't sort for now as it's not recognised as timestamp. How can I make it to work properly?
Answer: An org-mode timestamp must have a day.  However if you give the months in the form "2016-02" then time sorting and alphabetical sorting are the same (so long as you're careful to keep everything padded to the same length).


How to find a paint color that corresponds to pantone swatch?

Question: I have a fabricator who needs me to send paint colors that match the pantone shades i'm using in an illustrator document. The colors are 7495c 60% tint and 611 20%tint. Is there an easy way for me to match these colors, or am I going to need to sort through a bunch of paint samples?
Comment: Take a Pantone color chip to a local paint store, ask them to match it and provide you with the formula used.... often you can purchase small sample pints of paint fairly inexpensively. So match, get a sample pint, and test to be certain it's correct when it dries.
Comment: I wouldn't start with an 80 or 20% pantone. I'd start with a 100% of an actual pantone tint [ie, plus white] of your desired colour . Less margin for error, assuming everything else is properly calibrated.
Comment: I agree that using tints of two Pantone colors seems like a pity if you have the possibility to choose lighter colors and use them at 100% instead. Looks much better as solids and easier to communicate to others when trying to find the right RAL color.
Comment: Paints are RAL coded, there is a bunch of Pantone to RAL converter online to find, if its what you mean.
Answer: Converting Illustrator's Pantone tints to solid paints looks quite a lottery. I guess you have nothing physical, only a file, but you need the tint as paint and want a simple mixing formula like "20% tint = 20% solid color and 80% white, shake 2 minutes"
You will not get it here - Tints in Illustrator try to imitate the look when solid color is printed on white paper with a dense raster and by leaving white between colored dots. Knowing usual print methods and how inks and papers behave makes possible to create somehow acceptable prediction of the result. But the result of mixing liquid paints depends heavily on the used paint materials and no general rule exists for the color of the mixing result.
I continue guessing: Your best option is to search for the most same looking solid Pantone by browsing the color book in Illustrator and making comparison tests. Have side by side a rectangle colored with the tint an another which you color with solid Pantones until a close enough version is found.
Know that uncalibrated screen very likely shows something different than what can be seen in a real Pantone color book (sold by Pantone). That book shows the actual meanings of Pantone codes. If possible, check also the found solid color in the real Pantone book.
If you like the found solid Pantone color you can pick it's code and find a good RAL color paint with a web Pantone code to RAL code converter as suggested already by others.
Theoretically you can go to a paint shop with a real Pantone book and say "I want this color made of paint material XXX(right for the job)". Do not try it if you have only the Pantone code, but not the real Pantone book. In that case you have better possiblilities if you have a good RAL code to tell.
Some paint webshop probably can mix for you something (no guarantee nor experience what it would be) if you tell the wanted Pantone code. If you find one who advertises "Pantone matching paints" it can be worth asking. Check also with the Wayback Machine how long they have survived with it.
Comment: It might be worth trying the ColorSnap app from Sherwin-Williams. Snap the pantone chip and see if it comes up with anything close to matching.  'Course, it's only good with Sherwin-Williams paints.
Answer: I would use a spectrometer or colorimeter. The official from Pantone is insanely expensive.
https://www.pantone.com/pantone-capsure
So start looking at probably one that can read printed samples in some color space that you can convert on Illustrator.
Then take it to the print shop and start measuring samples of paint.
You can find some in Amazon that gives you a Lab color and at a decent price. So take a look.

One additional problem you have is that you need to target a tint, and you will have trouble with that because normally you will find solid colors. Probably you need to print a sample of the tones.
If you did that as an identity branding... you did it wrong, because an identity color guide should be mainly on solid colors.
There is a chance you can get the % tones with transparent ink, and not screening the tones.
Take a look at this: so you can sort of finding a Pantone equivalent to a shaded one: Printing photographs when job is a 2 spot color job

Updated sometime later.
Here is a website that has and compares different paint systems. https://www.myperfectcolor.com/


Do I get to keep medals/fruit if I quit out of a level?

Question: I'm going to need to do some backtracking to get my Rainbow medals. If I get a medal and quit out of a level do I get to keep that medal or will I keep it? I know I get a "you'll lose progress" message but different games interpret "lose progress" differently so I don't really know if I'll still have that medal unlocked (and I haven't been brave enough to try it).
Answer: No, you have to finish the level to get the medals.


How is sheet music conventionally conveyed among professional musicians?

Question: At my university, we carry around sheet music in black folders in backpacks. I imagine this practice is not the same among professional musicians, such as those in an orchestra or a big band. How do professional musicians normally carry around music?
Comment: I only carry my music (written on parchment paper) in an elk-leather satchel that is twice daily flown to me by my falcon.  If you're asking why my falcon doesn't just carry my music, my answer is that I wouldn't be able to carry it in my elk-leather satchel.
Comment: How else would you carry it?
Comment: My most recent experience was that I was sent a pdf as an email attachment, I sent it to my printer, and then I put the loose sheets in my case for the first rehearsal.  For the next rehearsal, I had the sheets in a 1/2 " black 3-ring binder, where I had done a little bit of scotch taping to deal with some awkward page turns.  I carried the binder in one hand and the instrument with the other into the venue.
Comment: I tend to commit it to memory. Then all I need to remember is my head...
Answer: It is very typical for musicians to have a folder or binder for whatever sheet music they are using. It is also not uncommon nowadays to see musicians using and iPad or a tablet to store digital copies of their sheet music and using it in place of a binder or folder.
Comment: Yes, all the bands I play in use ring binders. In the brass band where we sometimes play in tents or outside the separate sheets are all in plastic covers, the kind with holes so they go in ring binders. This is of course a pain to get organised the first time, but it's worth it if you have a lot of gigs. In the Big Band we use the big binders exactly the same, but for a gig we'll take the sheets out and organise them in the right order in a little binder. I like to keep using the plastic covers, so they don't fly away, but some people won't. Have some clothes pegs handy to keep them fixed!
Answer: In the big band, a flight case holds all of the orchs, which get set up by the band leader or one of his minions, on the music stands on the bandstand/stage. That way, no-one ever forgets their music, or brings the wrong folder, and the dots never get lost.
For personal use, there is a special sort of leather case, which has a metal bar to close it over. Never found why it was designed like this, but musos still occasionally use one. 50 or so yrs ago, most musos would use one.
Comment: Do most big band ensembles do this, in your experience?
Comment: @Anthony - most of those I've worked with, yes. A set of orchs for one piece may consist of 18 separate parts, quite expensive to buy, earlier stuff irreplaceable, and losing just one part is inconvenient at the least. So it's a safe, tried and tested method. Till someone steals the vehicle that they get left in - as happened - then it's catastrophic!


C# Dynamic types

Question: I just read a chapter in a programming book about Dynamic types. Although they are quite neat I cant think of a single real world example where I would use them. Does anyone here actually use them and for what?
Comment: See my question f.e.: http://stackoverflow.com/questions/6883741/generic-static-class-retrieving-object-type-in-run-time - the difference between Jon's solutions for 4.0 and 3.5. What I needed it for was feeding business objects with data from parsed CSV, whose format I wouldn't know beforehand. It could be [id][name][category][id][category][name] or whatever, so I'd just recognize the type of the busines object that was needed and then used a generic class for assembling them, making sure that the 1st occurence of attribute X goes to the 1st instance of class Y, the 2nd - to the 2nd etc.
Answer: I've used dynamic to evaluate logical expressions represented in an object graph, where using the dynamic keyword allowed me to largely ignore the types of the operands.
For example, if my expression graph was an arithmetic expression with a multiplication operator (e.g. 12 * 1.3), I would use dynamic to store the operands 12 and 1.3, and dynamic again to catch the result from the multiplication.
Without dynamic I would be forced to deal with concrete numeric types (int/long/decimal/float, etc...) and the resulting code bloat. My dynamic solution requires very little code and is much easier to grasp and maintain.
My initial idea was to turn my logical expressions into snippets of Python or Ruby, then run these snippets through IronPython or IronRuby to evaluate the result. It struck me all I required from Python or Ruby was their dynamic typing, so I was very happy to see that dynamic affords Python-like typing for C#.
Comment: Numeric calculation is a great idea.
Comment: This sounds like a good idea, but I'm having trouble getting my head around it. How was dynamic better than using decimal for everything?
Comment: @pdr: using dynamic avoids all casting and fewer casts make source code cleaner and easier to maintain.
Comment: @Ed: I mean, why are they all different types to start with? Where are they coming from? Is there not a risk here of dividing a decimal by a double and ending up with inaccuracies you didn't expect?
Comment: @pdr: the real answer to your questions requires more space and time than I can provide right now. The quick answer is that most of the expression are user input, so it's the problem of user if expression produces inaccurate results or even fails to evaluate.
Comment: Just to note it: using `dynamic` for math-operators can have its own issues.  For example, `3/2` can evaluate to being about `1` or about `1.5`, depending on the types.  Usually it'd be safest to convert the values to an intended type, then do the math there.
Answer: In addition to previous answers relating to dynamic languages, dynamic typing in C# also eases a lot of pain when doing COM interop - e.g. see this MSDN article , or scroll down to the bottom of this post on Chris Burrows' blog.
Answer:
I cant think of a single real world example where I would use them

It's a framework, it isn't always about you. In the case of dynamic alot of the backing came from the need to support more dynamic languages in the CLR, such as F# or IronPython. The fact that it helps cut down on code in other ways is an added bonus.
Comment: @Wyatt Barnett even if I dont use them I would still like to know what they are used for
Comment: What do you mean, 'it isn't about you'?
Comment: added the quote to help it make sense.

C# Dynamic types


C'est la fête du slip

Question: How would you translate or explain « la fête du slip »? Is it often used in French and in which situation? Is it a very rude expression? (I already know what « fête » and « slip » mean.)
Answer: After a quick googling (e.g. https://dico-des-mots.com/definitions/la-fete-du-slip-ou-craquage-de-slip.html) one finds:

[Expression imagée] fête du slip (étymologie) :
(Familier) (Ironique) Décrit un comportement sans-gêne, une situation qui dégénère ou devient absurde, un relâchement total.
[That is, it describes a behavior without embarrassment, a situation that degenerates or becomes absurd, a total relaxation.]

An example of a sentence:

Avec ce gouvernement, c'est vraiment la fête du slip tous les jours !

(cf. wiki)
More information about the origin of the expression is provided below:
http://www.linternaute.com/expression/langue-francaise/13975/fete-du-slip/
[An attempt to translate:]

A popular expression among young people, it derives its meaning from
chamber music organizations. The organization and storage must be
impeccable and nothing should exceed (especially not underwear!).
However, when the end of the service arrived, the military rebelled
against the authority by organizing "underpants", decorated the
garrisons of underwear and had absurd behavior to challenge the
military.

For still more information concerning the so-called event (!) "Fête du slip" described in the last paragraph see the link below:
http://www.feteduslip.org/origine-definition
Comment: I didn't think it could be in a dictionary. Thank you for your help, your last link feteduslip.org is certainly not to be taken seriously though.
Comment: Based on this, I think the Americans would talk about a "dumpster fire".
Comment: I think you missed the "Is it often used in French ?" in your answer ;)
Comment: @Random  N'étant pas locuteur natif, je ne peut y répondre:-)1
Answer: To supplement Dimitris' excellent answer

Is it often used in French and in which situation?

It is not an expression you will hear all the time, but it is used form time to time. This to say that it is not a dying expression, just one you would use judiciously.
To give you an idea, in a professional setting I heard it a few times over the last years, and used it once or twice.

Is it a very rude expression?

No it is not rude. It is intended to be funny, in a circle you know. Macron would not say it on TV, he may use it during a closed meeting.
Answer: "slip" means underwear in French. "Fête du slip" can be translated as underwear celebration. It can be construed as the celebration of something absurd and senseless, where common sense is forcefully banished. This is a typical criticism of governmental decisions nowadays, local bureaucracy or network-propelled idiots in organizations

C'est la fête du slip


How is the Controlled Z Gate implemented?

Question: How are 2 qubit Controlled Z gates (1 control / 1 target) typically implemented? Do we seek physical realizations of this gate, or have an alternate decomposition?
Comment: This will generally be hardware dependent. Do you have a specific platform in mind?
Comment: No - I was curious if there was a typical realization with CNOTs / Pauli gates. I'd also be interested on which platforms CZs can be directly implemented.
Answer: On IBM QX architectures, the only entangling gate is the controlled not (CX), so controlled Z gates with control qubit $n$ and target qubit $m$ are decomposed into $CZ^n_m = H_m CX^n_m H_m$.
Although this is QX-specific, it demonstrates a principle that will likely hold on any architecture -- That the general method is to use a similarity transform to rotate Z onto the most conducive rotation axis for the hardware, perform that rotation, and rotate Z back into place.


Android scanning app media files

Question: My M8 is scanning all the app media files so music and images and icons from apps are showing up in gallery and music apps, I'm not sure which directories these are coming from so I can't add the .nomedia file, and when I did try to add it it wouldn't allow me to save the file with that name. So how can I stop android from processing the images and music from apps I just want it to use the music and pictures files where music and photos are saved
Answer: The media scanner scans everything on your S.D. card. Adding a .nomedia to any of the subdirectories will allow the media scanner to skip everything in that sub-tree.
Your S.D. card will be F.A.T.-formatted so there are no permission restrictions. If you are receiving access denied on the S.D. card then it may be locked read-only due to damage to the card, or worse some malware you have installed. There isn't enough information to say for certain. You can scan the card properly by connecting it to a computer and running fsck (Linux and other *nix) or chkdsk (Windows). Remember to back up any important files before doing so.
Applications can access a directory on the S.D. called Android, and sometimes just data. Add a .nomedia file to those directories to stop those directories from being scanned.
The command for doing so in a terminal emulator would be:
touch /path/to/SD/Android/.nomedia
touch /path/to/SD/data/.nomedia

where /path/to/SD/ varies depending on your version of Android. To do the same under Windows would be something along the lines of "Create new blank file" from within Explorer.

Android scanning app media files


What's a good source of information about how the structure of english sentences has evolved over time?

Question: There is a lot of information about the evolution of English vocabulary since Anglo-Saxon times, but I am looking for examples of how English sentence construction has changed over time.
Comment: I vote to leave this question open.
Comment: This is indeed broad but a good question on the other hand. I vote to leave this question open.
Answer: Ian Roberts's 1993 book Verbs and Diachronic Syntax has a good amount of (comparative) information on the history of English (and French) sentential structure. It's couched in late-GB terms, but I don't remember it being too over-the-top theory-heavy. I used it in a Historical Syntax class and remember liking it.
Answer: There's a recent textbook by Bettelou Los which deals with exactly this topic. Not too pricey, either, by academic book standards.


How/why did animals/humans started showing kindness?

Question: Every emotion must had a reason when it was evolved into existence and genetically. Why did animals/humans started showing kindness to the other 'kind', when there was nothing they can gain by feeling 'kind'ness with other individual.
Comment: This is a scientific question. But why do you assume there was nothing to gain by showing kindness?
Comment: To me, this question is relatively meaningless without a working definition of 'kindness'.
Comment: @fileunderwater My definition of kindness was something in the lines of being generous or helping etc. I got the answer anyhow.
Answer: Keep in mind that genes are causally related to phenomena occurring in many levels at the same time: molecular, cellular, systemic, individual, social, even environmental. The interplay of all these different levels is not without attrition. More often than not, the existence of a particular trait cannot be reduced to a single explanatory principle.
Your premise - that there's nothing to be gained from positive affections on the individual level - is probably unwarranted in itself, but also suffers from a limitation in perspective, as the best utilitarian explanations for the existence of emotions are probably those that investigate the phenomenon at the social level.
Answer: Evolution works at the species level, not at the individual level. Altruism evolved because it gave certain groups advantages aver other groups competing for the same resources. If an individual sacrifices their own personal needs for the group so that the group as whole thrives, the end result is still the propagation of that individual's genetic information (as a subset of the group genetic information), and evolution is driven by genes.
An extreme example of this are female worker ants and worker bees: These individuals do not mate at all, only the queens in their colonies/hives do, and yet they spend their whole lives dedicated to the well being of the group.
See the SEP article on altruism for further information.
Comment: I could manage to read few paras from the article you mentioned. Rest I will read tomorrow. But, it's very good one. Exactly what I am looking for. Thanks for sharing!
Comment: I am a bit skeptical of that. Altruistic societies are tend to be "free-loaded" by selfish individuals. Selfless organisms that are more vying than others then tend to defect, leading to decrease in overall benefits by altruism. The species may or may not benefit overall but selfish individuals sure do, which is bound to increase their proportion in population. So while a completely selfish society may not sustain itself, a society with a ratio where selfishness and selfness are balanced would probably be most "stable". That means that a section of population will be selfish genetically......
Comment: Does this scenario occur in reality? I don't think so.


Is it better to reschedule workout than skip it?

Question: I go to gym 3 days a week on Tuesday, Thursday and Saturday (chest, shoulders, biceps/back, triceps/legs). This Friday, however, I'm going to leave the city till the next Tuesday. Is it better to reschedule Saturday's workout to Friday, or, increase the amount of Thursday's training? Or, should I do some kind of exercises during the trip? What is the general advice for inevitable training skips?
Answer: Whatever you decide to do should be dependent upon your training goals (eg. Training for a competition or race, etc.). Missing a training day is not the end of the world as long as it does not become a habit.  Life happens, and, sometimes it impacts your training.  Often, this results in "training guilt" especially if you're a person that regularly trains.  You might feel uneasy/guilty about missing a session when, in fact, a short training break may be just what you need.  So, take a look back at your recent training history, and, see if you've been pretty strict about it. If so, I would just skip the workout and perform some light training on your trip.  Then, pick up your training when you return.
Comment: I agree with this answer; if no competition is around the corner, it's not mandatory to reschedule. Of course, if you're gonna make yourself neurotic over skipping a workout, then reschedule it to give yourself peace of mind. Fitness goal is a long-term goal; you become fit as long as you keep working on it :).
Comment: I mean, it's only my 3rd week of training and I'm not going to have a "training guilt". I just want to know what solution would be more effective in terms of my overall progress
Comment: @Herokiller - Meh. Either skip it and move on, or double up as marten suggests. Either way, it's not really going to make much of a difference. If you want, since it's on a trip, you could do a day of body weight exercises.
Answer: I'll just answer this from my own experience.
For my job I often have to leave for a few days and can't access any strength training facilities. Worse (or better?) my job is physically demanding so I come back to town and I'm pretty beat up, sleep deprived, and didn't eat so well. It's a real drag because I can't maintain the progressive strength training schedule I'd like to. How I handle it:

I try to do about 3 intermediate training program cycles (Texas method) during the winter when I have more control over my schedule. I can usually manage a couple of months without much interruption and make a lot of progress.
During the summer when my job is more active, I stay in maintenance mode. I try to lift two days a week, one day at 80% of my 5RM and the other as close to 100% as I can get. If I go a couple of weeks without training it's okay, strength losses usually only show up after 3-4 weeks of no training.

I've had to understand that physical fitness (to me) is about having my body in a good-enough shape to do whatever I throw at it. I don't really lose size or strength during the summers. The only downside is that two weeks off and then 80% of my 5RM makes me wicked sore for a couple of days. Still, it's worth it.
Answer: I would increase the amount of exercise BEFORE the trip, since you know have a slot for recovery. Whatever workout you would do at the time of the trip, do it before instead, together with whatever you would do otherwise.
Comment: so, like 3 hours of back/triceps/legs is okay? not too much?
Comment: No, the whole "you shouldn't work out more than 45 minutes" is a myth. It's all about total workout volume and your recovery period.
Answer: Exercise during the trip even though its not necessary in this case. Start now to get into the habit of it. Reschedule is better than doubling up. I go for hitting some performance highs if I skip a work out, and generally don't regret it.


What are the "User Mode" tools in kubernetes lens?

Question: I have been using kuberentes lense and noticed under the cluster settings page an optional package called "user mode".  Does anybody know what this means?
Answer: I have not used it, but the description in your image is understandable. It is adding RBAC (user permission) so that any user (also non-admins) can list namespaces (e.g. see all namespaces that exists within the cluster).
But it should not mean more than that, e.g. a user can not create a Deployment in a namespace he is not granted to.


Migratory aptitude in pinacol pinacolon rearrangement

Question: Out of ortho-methoxyphenyl and para-methoxyphenyl which one has more migratory aptitude in pinacol-pinacolon rearrangement?
Answer: Groups with higher electron density have a greater tendency to migrate. So, o-methoxy phenyl should be the answer but due to steric factors p-methoxy phenyl can always be an equally likely answer.  It can only be found out accurately by experimentation and considering other reaction conditions.


Has Veda Vyasa seen Lord Krishna?

Question: It is said that Lord Krishna was a human being with qualities of God, thus Lord Krishna has a special place in sanatana dharma. I would like to understand, if Veday Vyasa has written Mahabharata, whether he has seen Lord Krishna and therefore he was able to write so much about Lord Krishna in Mahabharata and later in Bhagavatham. I also have read that Veda Vyasa is also known as 'Krishna Dwaipayan'. Does it mean that Veda Vyasa himself is krishna?
Comment: The name 'Krishna Dwaipayan' has nothing to with Lord Krishna. It was just that he was dark in complexion so the name Krishna which means Dark and as he was born on an Island therefore the name Dwaipayan which means born on a dweep(island)
Comment: Krishna and Vyasa met on several occasions in the course of the Mahabharata, but that had nothing to do with Vyasa's composition of the Mahabharata and the Srimad Bhagavatam.  Vyasa was able to compose these and other works because he was a Trikalajnani, i.e. one wh can see past, present, and future.  It's similar to how Valmiki met Rama and Sita, but that isn't what gave him knowledge of Rama's life; see my answer here: http://hinduism.stackexchange.com/a/760/36
Comment: @Aby I am enlightened about 'Krishna Dwaipayan' now. Thanks.
Comment: @Keshav: Information about meeting of Vyasa and Krishna is new to me. It is a little hard to believe that Krishna had nothing to do with the Mahabharata or Bhagavatam, because the story contains the very Lord krishna who you are saying, Veda Vyasa met!.
Comment: @KurioZ7 It's just like how Rama and Valmiki met, but their meeting had nothing to do with causing Valmiki to compose the Ramayana.
Comment: Hinduism exist today because of lord veda vyasa, Name any root scripture (18 puranas, Gita, Brahma Sutra) Arranging Vedas and Upanishad. All can be attributed to Veda vyasa, so he is non another than Sriman Narayana himself..
Answer: Yes. Vyasa saw and met Sri Krishna many times but this wasn't how Vyasa wrote Mahabharata.  One such meeting happened during Brahmastra episode of Arjuna and Aswathama. Indeed, Kauravas are biological descendants of Vyasa.
Vyasa with his Trikaladarshi powers analyzed Vedas and taught Puranas to his disciples. Here is what Chapter one of Adi Parva of Mahabharata says:

The son of Satyavati having, by penance and meditation, analysed the
  eternal Veda, afterwards composed this holy history, when that learned
  Brahmarshi of strict vows, the noble Dwaipayana Vyasa, offspring of
  Parasara, had finished this greatest of narrations, he began to
  consider how he might teach it to his disciples.

Similarly, later Vyasa dictated Slokas of Mahabharata to Ganesha and Ganesha composed them as discussed here. Refer this answer to know  about Jaya, Bharata and Mahabharta in detail.
Vedavyasa is Avatar of Lord Vishnu. He was named "Krishna Dwaipayana" as he was born on island and black in complexion. Adiparva of Mahabharata says

And it was thus that Vyasa was born of Satyavati through Parasara. And
  because he was born in an island, he was called Dwaipayana (Dwaipa or islandborn). And the learned Dwaipayana, beholding that virtue is
  destined to become lame by one leg each yuga (she having four legs in
  all) and that the period of life and the strength of men followed the
  yugas, and moved by the desire of obtaining the favour of Brahman and
  the Brahmanas, arranged the Vedas. And for this he came to be called
  Vyasa (the arranger or compiler).

Since Krishna Dwaipayana Vyasa is Vishnu and Krishna is also Vishnu, you can consider Vyasa as Krishna though they differ in some qualities or attributes.
Answer: Yes he did. There is an interesting story of how Vyasa saw Krishna.
First, Vaishampayana explains that Vyasa was son of Narayana.

Vaisampayana said, "I bow unto that great Rishi who is the dispeller of darkness, and whom Satyavati bore to Parasara in the midst of an island, who is possessed of great knowledge and who is endued with great liberality of soul. The learned say that he is the origin of the Grandsire Brahma; that he is the sixth form of Narayana; that he is the foremost of Rishis; that he is endued with the puissance of Yoga; that as the only son of his parents he is an incarnate portion of Narayana; and that, born under extraordinary circumstances on an Island, he is the inexhaustible receptacle of the Vedas. In the Krita age, Narayana of great puissance and mighty energy, created him as his son. Verily, the high-souled Vyasa is unborn and ancient and is the inexhaustible receptacle of the Vedas!"

Janamejaya asked how Vyasa was son of Narayana.

Janamejaya said, "O best of regenerate persons, it was thou that saidst before this that the Rishi Vasishtha had a son of the name of Saktri and that Saktri had a son of the name of Parasara, and that Parasara begot a son named the Island-born Krishna endued with great ascetic merit. Thou tellest me again that Vyasa is the son of Narayana. I ask, was it in some former birth that Vyasa of immeasurable energy had sprung from Narayana? O thou of great intelligence, do tell me of that birth of Vyasa which was due to Narayana!"

Vaisampayana told how he had the same question to Vyasa.

Vaisampayana said, "Desirous of understanding the meaning of the Srutis, my preceptor, that ocean of penances, who is exceedingly devoted to the observance of all scriptural duties and the acquisition of knowledge, dwelt for some time in a particular region of the Himavat mountains. Endued with great intelligence, he became fatigued with his penances in consequence of the great strain on his energies occasioned by the composition of the Mahabharata. At that time, Sumanta and Jaimini and Paila of firm vows and myself numbering the fourth, and Suka his own son, attended on him. All of us, O king, in view of the fatigue our preceptor felt, waited dutifully upon him, engaged in doing all that was necessary for dispelling that fatigue of his. Surrounded by these disciples of his, Vyasa shone in beauty on the breast of the Himavat mountains like the Lord of all the ghostly beings, viz., Mahadeva, in the midst of those ghostly attendants of his. Having recapitulated the Vedas with all their branches as also the meanings of all the Verses in the Mahabharata, one day, with rapt attention, all of us approached our preceptor who, having controlled his senses, was at time rapt up in thought. Availing ourselves of an interval in the conversation, we asked that foremost of regenerate persons to expound to us the meanings of the Vedas and the Verses in the Mahabharata and narrate to us the incidents as well of his own birth from Narayana. Conversant as he was with all topics of enquiry, he at first discoursed to us on the interpretations of the Srutis and the Mahabharata, and then set himself to narrate to us the following incidents relating to his birth from Narayana.

He recounts how Vyasa told about his former birth

After this, the original Creator of the universe once more uttered the syllable, Bho, causing the atmosphere to resound with it. From this syllable of speech (Saraswati) arose a Rishi of the name Saraswat. The son, thus born of the Speech of Narayana, came to be, also called by the name of Apantara-tamas. Endued with great puissance, he was fully conversant with the past, the present, and the future. Firm in the observance of vows, he was truthful in speech.

Later, he even said how Apantaramas in the kalpa named after the self-born arranged the vedas which gratified Vishnu.

Unto that Rishi who, after birth, had bowed his head unto Narayana, the latter, who was the original Creator of all the deities and possessed of a nature that was immutable, said those words: Thou shouldst devote thy attention to the distribution of the Vedas, O foremost of all persons endued with intelligence. 2 Do thou, therefore, O ascetic, accomplish what I command thee.--In obedience to this command of the Supreme Lord from whose Speech the Rishi Apantaratamas sprang into existence, the latter, in the Kalpa named after the Self-born Manu, distributed and arranged the Vedas. For that act of the Rishi, the illustrious Hari became gratified with him, as also for his well-performed penances, his vow and observances, and his restraint of the senses or passions.

Vishnu said how Apantaramas will take birth as Vyasa in the lineage of Vashishta.

Addressing him,--Narayana said,--At each Manwantara, O son, thou wilt act in this way with respect to the Vedas. Thou shalt, in consequence of this act of thine, be immutable, O regenerate one, and incapable of being transcended by any one. When the Kali age will set in, certain princes of Bharata's line, to be called by the name of Kauravas, will take their birth from thee. They will be celebrated over the Earth as high-souled princes ruling over powerful kingdoms. Born of thee, dissensions will break out among them ending in their destruction at one another's hands excepting yourself. O foremost of regenerate persons, in that age also, endued with austere penances, thou wilt distribute the Vedas into diverse classes. Indeed, in that dark age, thy complexion will become dark. Thou shalt cause diverse kinds of duties to flow and diverse kinds of knowledge also. Although endued with austere penances, yet thou shalt never be able to free thyself from desire and attachment to the world. Thy son, however, will be freed from every attachment like unto the Supreme Soul, through the grace of Madhava. It will not be otherwise. He whom learned Brahmanas call the mind-born son of the Grandsire, viz., Vasishtha endued with great intelligence and like unto an ocean of penances, and whose splendour transcends that of the Sun himself, will be the progenitor of a race in which a great Rishi of the name of Parasara, possessed of mighty energy and prowess, will take his birth. That foremost of persons, that ocean of Vedas, that abode of penances, will become thy sire (when thou wilt take birth in the Kali age). Thou shalt take thy birth as the son of a maiden residing in the house of her sire, through an act of congress with the great Rishi Parasara.

Vishnu also said that he will see him as Krishna and in his next birth as Krishna-Dwaipayana Vyasa, he will have no doubts of past, present, and future.

Doubts thou wilt have none with respect to the imports of things past, present, and future. Endued with penances and instructed by me, thou wilt behold the incidents of thousands and thousands of ages long past away. Thou wilt see through thousands and thousands of ages also in the future. Thou shalt, in that birth, behold me, O ascetic,--me that am without birth and death,--incarnated on Earth (as Krishna of Yadu's race), armed with the discus. All this will happen to thee, O ascetic, through the merit that will be thine in consequence of thy ceaseless devotion to me. These words of mine will never be otherwise. Thou shalt be one of the foremost of creatures. Great shall be thy fame. Surya's son Sani (Saturn) will, in a future Kalpa, take birth as the great Manu of that period. During that Manwantara, O son, thou shalt, in respect of merits, be superior to even the Manus of the several periods. Without doubt, thou shalt be so through my grace.

This is how Vyasa was able to see Krishna.

Has Veda Vyasa seen Lord Krishna?


Searching for installed App by name

Question: I used to have a HTC Hero with had it's own search button. When being in the application selection menu I could press the button and then search for an app by typing it's name.
Is there similar way to access apps in Android 4.x without a specific search button?
Answer: The Google Search app is able to search the applications on your phone. On 4.1+ this can be done through a Google Now search. On many devices, this is accessible by swiping upwards from the home button in the navigation bar.
When you search for the app on your phone, you can use the bar along the bottom to scroll to "Phone" to search your phone rather than the web.
You can also search "start " so for example if I had an app called (in your case) "Battery", if I typed into the search bar "start battery" it would give me a card showing the app name and icon with a button below saying "Open App"
Comment: If I search "Battery" in 4.4.4 it doesn't show me the App that I installed that named "Battery" but suggests a websearch.
Comment: When you start a search along the bottom of the screen you should see "Web Images Maps..." etc, if you scroll through that list, one of them should be "Phone" usually the last one. then you will get a section called "Apps" that shows all the apps with your search term in the title of the app.
Comment: Also if you type "start " it will give you a card with the option to open the app. So in your case search "start battery" and the top card should say the app name "battery", with the icon on the right, and a button below saying "Open App"
Answer: Try  google gesturesearch using this you can  not only search for  an application but also contacts,music and bookmarks.
This has a cool feature that you can use natural hand writing to type the app name and keypad is not needed.
Answer: There is an option in Google Search / Now settings to allow you to search through apps as well as web (Go to Google Now settings, there you'll see phone search, open it and tick Apps)

Searching for installed App by name


Sun's power density compared to a compost heap

Question: According to Wikipedia the Sun's "power density" is "approximately 276.5 $W/m^3$, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb." My question is, so why is the Sun's core so hot (15.7 million K)? Using a gardener's (not a physicist's intuition) it seems apparent that you can't keep on increasing the temperature of a compost heap just by making the heap larger.
Comment: Any intuition about human-scale objects is likely to be invalid for something as big as the Sun.
Comment: The main limit to the compost heap's size is the onset of nuclear fusion in its core ;-).
Comment: The reason you can't keep increasing the temperature of a compost heap by making it larger is that a lot of the heat is generated by biological activity - microorganisms &c - which die if it gets too hot.  But they do catch fire sometimes: https://www.gardeningknowhow.com/composting/basics/overheated-compost-piles.htm
Comment: My gardener's intuition neglected to consider gravity.
Comment: @Octopus The Sun's diameter is roughly $1.4\times 10^9$ meters, and its mass is roughly $2 \times 10^{30}$ kilograms. "Human scale" intuition is trained on objects roughly 0.1–10 meters in diameter and 0.01–100 kg in mass, and objects only a couple orders of magnitude bigger (cars, I-beams, heavy crates, etc) behave surprisingly enough that you have to have special safety training to work with them, so for me it seems more intuitive to say that human-scale intuition _won't_ scale all the way up to the Sun.
Comment: @zwol, but why? That's not intuitively the case.
Comment: @Peter A. Schneider, but the question points out that the energy density is not like a thermonuclear bomb.
Comment: @Octopus Yes, I know; a star-sized compost heap would have approximately twice the energy density of the sun -- half of it is the anearobic fermentation (hey, it works in vacuum!), the other half comes from the hydrogen in the organic matter fusing in the heap's core.
Answer: Your (gardener's) intuition is wrong. If you increase the size of your compost heap to the size of a star, then its core would be as hot as that of the Sun. All other things being equal (though compost heaps are not hydrogen plus helium), the temperature of a spherical compost heap would just depend on its total mass divided by its radius$^{*}$.
To support the weight of all the material above requires a large pressure gradient. This in turn requires that the interior pressure of the star is very large.
But why this particular temperature/density combination? Nuclear reactions actually stop the core from getting hotter. Without them, the star would radiate from its surface and continue to contract and become even hotter in the centre. The nuclear reactions supply just enough energy to equal that radiated from the surface and thus prevent the need for further contraction.
The nuclear reactions are initiated once the nuclei attain sufficient kinetic energy (governed by their temperature) to penetrate the Coulomb barrier between them. The strong temperature dependence of the nuclear reactions then acts like a core thermostat. If the reaction rate is raised, the star will expand and the core temperature will cool again. Conversely, a contraction leads to an increase in nuclear reaction rate and increased temperature and pressure that act against any compression.
$*$ This relationship arises from the virial theorem, which says that for a fluid/gas that has reached mechanical equilibrium, that the sum of the (negative) gravitational potential energy and twice the internal kinetic energy will equal zero.
$$ \Omega + 2K = 0$$
The internal kinetic energy can be approximated as $3k_BT/2$ per particle (for a monatomic ideal gas) and the gravitational potential energy as $-\alpha GM^2/R$, where $M$ is the mass, $R$ the radius and $\alpha$ is a numerical factor of order unity that depends on the exact density profile. The virial theorem then becomes total kinetic energy
$$ \alpha G\left(\frac{M^2}{R}\right) \simeq 2\left(\frac{3k_BT}{2}\right) \frac{M}{\mu}\ ,$$
where $\mu$ is the mass per particle. From this, we can see that
$$ T \simeq \frac{\alpha G\mu}{3k_B}\left( \frac{M}{R}\right)$$
Comment: @Krumia I meant exactly what I said. Exactly half the energy released by gravitational contraction is radiated away (see https://physics.stackexchange.com/questions/249679/gravothermal-catastrophe-looking-for-simple-explanation/249813#249813 ). The other half goes into increasing the temperature of the core. That is also a consequence of the virial theorem. Without nuclear reactions, "stars" would continue to contract and their internal energy would continue to rise. The process is only halted (or slowed) when electron degeneracy kicks in because then the star can cool without contraction.
Comment: @Krumia Another way of seeing that is just to look at the final equation in my answer. The mass is fixed, so if the radius gets smaller then $T$ goes up. But this equation relies on the assumption of perfect gas pressure. Once degeneracy pressure dominates, things change.
Comment: "The Boltzmann constant ($k_B$) ... is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas."
Answer: Another way of seeing that the Sun's power density must be rather low (or that very large compost heaps get very hot) and also to see the temperature-radius relationship is to calculate what the surface temperature should be, for a given power density.
So, we can model the Sun as a sphere with radius $R$, and a power density of $\rho$.  The total volume of the Sun is then
$$V =\frac{4\pi R^3}{3}$$
and the total power output is
$$P =\rho V = \rho\frac{4\pi R^3}{3}$$
The surface area of the Sun is then
$$A = 4 \pi R^2$$
So the power flux through the surface of the Sun is
$$f = \frac{P}{A} = \rho \frac{R}{3}$$
(Notice that this is going like $R$: the bigger the star, the higher the flux for a given power density.)
And we can use the Stefan-Boltzmann law which relates surface temperature to flux, assuming the Sun is a black body
$$f = \sigma T^4$$
And putting this together we get
$$T = \left(\rho\frac{R}{3\sigma}\right)^{1/4}$$
Where $T$ is the surface temperature of the Sun.  This formula tells you that large objects which are generating power get much hotter than small ones with the same power density: the surface temperature goes as the fourth root of the radius.
Plugging in the numbers this gives a surface temperature which is much too high, from which I conclude that the power density of the Sun is in fact much lower than the Wikipedia figure: that figure is probably for the part of the Sun where fusion is occurring only, not the whole volume.
Answer: If the heap was self-gravitating then the larger the heap, the warmer its center. The idea behind is that at the core the material will feel the pressure exerted by all the layers above, and you probably know that if you put pressure on something, it will heat up.
What is interesting here is that all the outer layers of your self-gravitating "heap" will tend to collapse towards the center (that's what gravity does best), and as a result the pressure will continue increasing and so will the temperature at the core. If the mass of it is large enough, the temperature reached through this mechanism is so high that molecules split, atoms ionize, and nuclei merge, thus generating thermonuclear energy.
This energy, generated at the center, will travel outwards and generate a pressure on the collapsing material. The result is that the system reaches equilibrium, where the hydrodynamical pressure is balanced by the radiation pressure coming from fusion at the center. It is possible to do the math and calculate what is the temperature required to merge Hydrogen into Helium: the result is 15.7 million K.


SQL Server 2000 clustering

Question: I have a SQL Server 2000 2000 box that has a Active/Passive Cluster. My network guys are changing the IP address for private IP on both nodes db01 db02 to 192.168.0.1 and 0.2 and also, removing the BACKUP network resource from cluster admin. I have to do the failover after they change the configuration on Cluster Admin. Can anyone please tell me the steps to do the failover? I would really appreciate this, Since this is my first time doing the failover.
Thanks.
Answer: this link provides some really good information.hih

SQL Server 2000 clustering


toning down the fresh chilli picquancy

Question: I like to use green finger chillies in my curries more for the flavour than for the heat, but in order for me to be able to cook out the rawness of the chillies, I end up with the chillies all "melted" in the pan, looking more like leaves, i.e they lose shape. I was wondering if there are any tricks to make fresh chilli less hot and thus needing less cooking time in order for the chilli to be less picquant.
Answer: Most of the heat in a chili pepper is concentrated on the ribs and membrane that holds the seeds.
By cutting out those parts, and using only the fleshy part of the fruit, you will get less heat.
The heat can also be mitigated by dairy or fatty ingredients in the dish in which you incorporate the chili, as they tend to help wash away the hotness in the mouth.
Comment: Of course, you can always use less...    and there is the option of exploring different peppers whose flavor you might like but which are not as hot.  If you are using them whole, don't cut them open--that will help keep the heat inside, by physically trapping it there.
Comment: I should have added that I don't intend to deseed the chillies as I consider that to be part of the shape that I want to preserve. :)
Comment: I don't know what to say; those goals are contradictory.  If you use the seeds and membranes, they will bring the heat along with them.  BTW. cooking them longer doesn't really reduce the heat; capsaicin, the hot chemical in chili peppers, is not that heat sensitive (it requires about 400 C to break it down).  So cooking them down thinking it will reduce the heat is not going to work for you.
Answer: If you want chili flavor rather than heat then add the chilis in whole, they will keep their shape well. Just be careful about eating them, they will be fearsomely hot!
Answer: Advance warning: I haven't tried this.
It seems that you don't want to remove the ovaries because that would affect the shape, but you do want to remove the capsaicin from them. It's soluble in fat and alcohol, so you could try making a small hole in the bottom and pumping a light vegetable oil or vodka through from the other end using a syringe. Obviously you're likely to end up with some solvent trapped inside, and you might also wash away some of the flavours you're trying to preserve, so experimentation would be necessary.
Comment: Since the integrity of the fruit is not compromised, you probably would not wash away good flavors.  But without being able to expose the interior to a large volume of solvent, I am not sure how effective this would be.
Answer: I've seen hot chilies blended with red bell pepper (seeds in) to add volume without impacting heat. This works well for Harissa sauce, where tomato is unwelcome.
Whole chilies are used in Indian dishes, but cooks advise care. Breaking the peppers will seriously overheat the dish.
I suspect blending hot and mild chilies is the best approach, but I'm looking forward to other suggestions.

toning down the fresh chilli picquancy


Is it tough to make a robotic workshop of your own

Question: I want to make a robotic workshop.. I recruited 10 members to work...  Please give some tips about robotic workshop
Comment: Related:  http://robotics.stackexchange.com/questions/2215/how-do-robotics-startups-work
Answer: I'm going to completely disagree with previous answers stated. Robotics consists of two major parts: 1.Hardware and 2.Software. Mechanical and  electrical are generally subclasses of hardware. Software is a subclass of, you guessed it, software. Software encompasses programming of course, however some argue that it also encompasses algorithm analysis and computational processing.
Nonetheless, the difficulty of starting a robotics workshop, as you call it, depends on the skills and backgrounds of the people you recruited. If everyone is a software engineer, you're going to have problems, the same applies for if everyone is a mechanical engineer. The hardest part of robotics comes from  understanding how all the encompassing disciplines and their respective principles come together to function in a single system. You have to be able to look at individual  subsystems and then understand how these subsystems interact with each other to create the main top-level system.
Anyway digressing from that tangent, if you are looking for a starting point look at arduino and at raspberry pi. The great thing is that they are open source, so you can look at other projects, make your own, and ask for help here and on their very active respective forums. Look at a website called seedstudio.com it has a large variety of arduino and raspberry pi compatible parts you can order and use for whatever you want.
As for programs, for 3d cad user solid works or autodesk inventor. For PCBs eagle or tinycad are good. For programming the arduino ide or visual studio are good. And there's a site called opensourcehardware.com that has all the tutorials on arduino programming and interfacing with digital electronics. I would definitely encourage you to look at those.
Good Luck.
Answer: It is tough if you don't have any knowledge on programming or electronic.
There are three parts related to Robotics:
Mechanical part, Hardware part and Software part.
You should focus on one or more parts of them.
Usually programming is the key thing. Because you can buy existing equipment(mech or hw) instead of designing your own and build them but you have to program by yourself.
So if you really know nothing, buy some devices like Arduino and using them to teach MCU/EmbeddedSystem programming.
Advanced, try to design circuit yourself. Either breadboard or designing PCB using Eagle or Altium Designer.
More advanced and if possible, design the mechanical part by yourself. Design the  joint and structure by Solidworks and produce what you draw using 3d printer or other ways.
Comment: Yup i am studying software engineering
Comment: Thanx for the answer


How many years did Amatzyah rule over the kingdom of Yehuda?

Question: How long was he king? Aside from being taken captive by Yehoash (king over Israel kingdom) he also stayed 15 years in Lachish. My question is how long did he actually rule - till he was taken captive.
Comment: Are you asking what year in his 29-year reign was he taken captive?
Comment: I'm asking how long was he king. Are you saying he was king for 29 years? Does 29 years include the 15 years he was in Lachish?
Comment: Yes, it includes the years in Lachish.
Comment: See at length in Radak Kings 2:14:22
Answer: Seder Olam states that Amaziah reigned for 29 years until he died in Lachish. Rashi states that the last 15 years of his life, he spent in Lachish though he was still technically king and this was included in the 29 years.
II Melachim 14:2

He was twenty-five years old when he became king, and he reigned in
Jerusalem twenty-nine years. His mother's name was Jehoadan of
Jerusalem.

SederOlam

2915  -845    2   Amaziah son of Joash reigns II Kings 14:1   Y2 Jehoahaz
2917  -843    17      Jehoahaz son of Jehu dies   II Kings 13:1   reigned 17Y
2917  -843    40  Joash is murdered by 2 servants II Kings 12:22  reigned 40Y
2919  -841        Black Obelisk of Shalmanezer III    Historical
2929  -831    16      Jehoash son of Jehoahaz dies    II Kings 13:10  reigned 16Y
2929  -831    14      Jeroboam son of Jehoash reigns  II Kings 14:23  Y15 Amaziah
2940  -820    -16 Azariah son of Amaziah born II Kings 14:21,15:2 reigned 16Y old
2944  -816    29  Amaziah flees to Lachish; killed there  II Kings 14:2,17    reigned 29Y
2956  -804    27  Azariah son of Amaziah reigns   II Kings 15:1-2 Y27 Jeroboam

Thus we see that Amaziah reigned from 2915 to 2944 which is 29 years. However, Rashi says that this 29 years includes the 15 years that he spent in Lachish.
II Divrei Hayamim 25:25

25 And Amaziah the son of Joash the king of Judah lived fifteen years
after the death of Joash the son of Jehoahaz the king of Israel.

II Divrei Hayamim 25:27

27 And from the time that Amaziah turned away from following the Lord,
they conspired against him in Jerusalem, and he fled to Lachish. And
they sent after him to Lachish and assassinated him there.

RASHI

and he fled to Lachish: a fortified city against which Sennacherib waged war. He fled to Lachish, where he remained fifteen years until
they followed him to Lachish and assassinated him there. And during
those fifteen years that he was in Lachish, Jecoliah, Uzziah's mother,
reigned in his stead. This is how it appears to me. In the commentary
of Rabbi Joseph (Kara), I saw that during those fifteen years that he
was in Lachish, Uzziah his son reigned in his stead, but it is
incorrect to interpret it in this manner, for it is written
immediately following (26:1): "who was sixteen years old." We find
that when his father fled, he was only one year old. Moreover, if this
is the case, it should say, "took Uzziah and made him king instead of
his father during his lifetime." Rather, Scripture intimated that he
did not reign during his father's lifetime.
Comment: Note that those dates are according to the conventional chronology, which at least ostensibly contradicts that of Chazal (see https://judaism.stackexchange.com/questions/92617 and other questions linked there). The traditional dates of Amatziah's reign would be 3101-3129 (660-632 BCE).
Comment: @Meir There are various reasons given for the 165 year difference involving the second temple. See my writeup at [Rabbi Leibtag shiurim: The Hebrew Calendar and its Missing Years- Parts 1 - 3](https://sabbahillel.blogspot.com/2015/05/rabbi-leibtag-shiurim-hebrew-calendar.html) which goes into this in detail. In any case, the number of years of Amatziah's reign remain unchanged.
Comment: That I know (some of those reasons are mentioned in the question I referenced and the other ones linked there). I just figured it ought to be pointed out.


Multi Agent Deep Reinforcement Learning for continuous and discrete action

Question: I am looking to have a cooperative multi agent reinforcement learning framework where one agent has a discrete action space and another agent has a continuous action space. Is there a way to do this as most papers I have seen will only handle one or the other.
Comment: you might want to google "parametrized action reinforcement learning" and "parametrized Markov decision process"
Comment: Thanks Sanyou seems like what I have been looking for.  I just didn't really know the correct terms to google were
Answer: Seems like what you are looking for is Parametrized RL to train an agent for a Parametrized Markov Decision Process. You can look up both terms to find courses/readings about it.
Anyway, one existing RL framework for it is the Multi-pass Parametrized DQN (MPDQN) which is proposed in this paper, and if google enoug you can even find the author's dissertation on MP-DQN which preliminaries section might help you a lot. In short, the Agent uses Actor-Critic arhitecture in which the Actor will predict the continuous parameters of all actions given the current state, and the Critic will predict the action-value of each action given the states concatenated by the predicted values of the continuous parameters. The final discrete action is chosen by sampling the action-value or using argmax.
In P-DQN, the state concatenated with all the continuous parameters' values are passed to the Critic. However, it is shown that by passing all continuous parameters at once to the Critic, the unused action's parameters will affect the gradient thus affecting the Actor's parameters, which is not expected. Therefore, the parameters of each action are passed separately into the Critic in MP-DQN (unrelated action parameters' are zeroed). With good design, you can implement it so you can pass all the parameters and state in a single pass (multi-pass) as shown in MP-DQN. Other alternative for Parametrized RL is the hybrid-PPO and parametrized DDPG.
Finally, based on my personal experiments, I still have difficulty on controlling the scale of the continuous parameters values prediction so that it stays in a certain predefined range. There are 2 ways to do it, first is using softmax or using gradient inverting (changing the gradients' sign depending on the current predicted parameter values). However, I still eventually produced Actor that output only extreme values (either upper or lower bound) of the continuous parameters.
Comment: Hi sanyou I have been working my way through the implementation of MPDQN in the github and it seems like they only handle the case where there is one discrete action possible and then many continuous actions.  I am in the case where I have a multi-discrete space and continuous actions.  Do you think this method would be able to handle this?
Comment: yes it can, if you look closely at the agent class definition, there's an intricate masking operation to differentiate which continuous parameters are related to which discrete action.
Comment: I can see how they are handling the parameterized action spaces in `env.action_space ` where the first space is a Discrete that describes the total number of actions and then the rest are box spaces that hold the high and low value information.  However I am not certain how to define my action space in these terms since I have some actions that are just completely discrete.  For example I have one action that is just a discrete action between 5 choices and then also 2 other actions that are continuous.  All of these actions can be used at a step together.
Comment: for the discrete action, just don't use any of the continuous parameter, so that no grad will be backpropagated. While for the continuous actions, that's what the discrete action/label is for, to point what action you choose, and you just so happen to choose a continuous action. Note that, while the continuous actor give you real values, the discrete critic just give you which action to do, right? so no problem with the continuous actions.


Google is showing cached results for a website, and I cannot view the results with any cache

Question: I tried accessing the results by typing cache:(website) in Chrome, didn't work. Tried typing http://webcache.googleusercontent.com/search?q=cache:(website). Didn't work. Wayback machine has the site archived, but only the front page. Also, Bing can find other topics and such on the website, and so can the mobile Google search. I just can't access the cached pages of the site at all, but Google and Bing are crawling the site and showing search results. Does anyone know why?
Comment: It would be much easier to accurately answer this question if you said what "website" is. For example, search engines can index websites even if they are robots-excluded. That would mean no caching and no Wayback, which appears to fit what you're saying.
Answer: The searched website cached content will be available in the drop down option near to the search link available as shown in the image below. Please check whether the cached content is showing for the website.
click the


drupal commerce calculator

Question: I have a webshop made with drupal commerce kickstart and use it as a POS in a bar. The people pay with cash. What i want is a calculator with 2 input fields: field 1: the "Order total" from checkout automatic comes in this field. Field 2 is the amount of cash the customer pays with. So i can see how much i have to return to the customer.
I have webform calculator installed. But the big question is how to automatic place the value from Order total in the calculator.
Answer: If you already have a calculator that you like and the commerce portion is working the way you want it, the best thing to do is probably to change as little as possible. My first thought is to use a simple javascript that looks for the field where commerce stores the order total and copy it into your webform field. In my kickstart staging environment, there is a field called "ajax-item-price". So you could do a jquery one-liner like
<code>$('#name-of-your-webform-field').val($('#ajax-item-price').html());
</code>
Comment: Thx for the quick response. It looks like a good solution. But how do i put that jquery in the webform field? I am notgood with writing code. But is it something like: http://jamestombs.co.uk/2012-09-24/create-new-webform-element-drupal-7
Comment: Ah, sorry: With a drupal_add_js() call in your hook_form_alter() implementation. But it sounds like you already have a different way of doing it.
Answer: I found a solution myself.
I have 3 fields in the webform calculator:
Field 1: payed with (the amount the customer pays with, for example he pays with 20 Euro)
Field 2: with token: [site:current-cart-order:commerce-order-total:amount_decimal] it fills the field automatic
Field 3: a formula {payed-with}-(name of field 2}
Thats it. Now i have a working cash register for a Drupal webshop.

drupal commerce calculator


How important are camera settings when shooting RAW?

Question: I would like to start shooting RAW instead of jpeg. I am wondering if i need to still worry about setting ISO, aperture and shutter speed. If so, why?
Comment: The aperture and shutter speed selected also affect the contents of the image in many situations. You can't undo the blur caused by using too slow a shutter speed on a moving subject. You can't take an image with a shallow depth of field and make it sharp from front to back, etc.
Comment: Kim, basically RAW allows more latitude (room for error) in exposure, so if you get ISO, aperture or shutter speed a bit wrong, you have a better chance at recovery.  But those settings absolutely still affect how much light hits the sensor, so affect your final image.  Get those wildly wrong and you will have unrecoverable highlights or shadows
Answer: Yes. You still need an exposure. RAW is not magical, it is just the sensor data for a certain exposure.
You must choose the aperture according to the depth-of-field you want, the shutter-speed according to the motion you want to capture and the ISO to balance between them which will set the gain on the sensor to make a balanced exposure. Sure, RAW is more permissive if you do not get it perfect but anything clipped on either side is gone forever.
Of course, you can let the camera choose some for you in a automatic or semi-automatic mode but it will still choose an exposure which determines way get captured and therefore what gets stored in the RAW file.


Continuous use of outdoor outlet

Question: I have a friend who wants to run a heater  in his van during the winter (MO).  Heater will be on continuously.  Outdoor outlet (not GFCI)...what type of electrical system should I set up? Or NOT...
Comment: The largest concern I can think of would be to make sure you use a heavy extension cord 16 awg absolute minimum if it is short 15' or less. If longer 14 gauge would be needed.
Comment: Thanks.  The heater in the van will be just to keep the temp around 40 degrees.  He has carpet cleaning equipment in there....I am not sure this is a good idea at all.  Older wiring in house...van probably about 15 feet from outdoor outlet.  Not sheltered area.
Answer: The first piece of information you will want to know is the power requirements of the heater. It is common for an electric "personal" heater to be about 1500 watts, which is also a very good figure for a blowing-type hand-held hair-dryer.
Rough calculation means that 1500 watts on a 110 volt home system in the USA will draw about 15 amperes of current.
For this application, it is a good idea to have a dedicated circuit for the outlet that will provide power and use wiring and a breaker appropriate for 20 ampere current. Circuits are typically designed for eighty percent capacity. A twenty amp circuit would then provide safely sixteen amperes for the heater, but would have no reserve capacity.
No GFCI may not be a problem if you have no water contact involved (sheltered area?) but code may require otherwise.
You suggest that the heater will be on continuously, but a 1500 watt heater will generate enough heat that it is likely to cycle on and off to maintain a comfortable temperature.
Note also that many of these heaters will have low-grade power cords which may get hot and pose sufficient risk, regardless of the other portions of the circuit.

Designs such as the one pictured above will also have tip-off safety switches, although contact with oil-filled heaters are not as serious as contact with exposed resistance element type heaters.
Comment: What service type and ampacity of flexible cord would you propose the user select for connecting the 1500W heater to the 20A receptacle?  Would it make a difference if the van were over 50 feet away from the house? Should they install permanent wiring to a point closer to the van?
Comment: when it comes to high current applications, closer is better. If closer is not practical, bigger conductors as referenced in Ed Beal's comment is also a wise option.
Comment: A 1500w heater draws 12.5 amps. A 15 amp circuit can handle this load with no problem.

Continuous use of outdoor outlet


Do all cultures have "taboo language"?

Question: In english, taboo language may be realized as swear words--though I could see some languages not having "swear words" in the english sense, while maintaining "vulgar expressions". All cultures have taboos. However, do all cultures have linguistic taboos?
Comment: What is a "linguistic taboo"?
Comment: What do you mean when you say «though I could see some languages not having "swear words" in the english sense»?
Comment: How would you know, since they're not saying those things in front of you?
Answer: First, there's no clear dividing line between culture and language when it comes to idiomatics and usage rules (as opposed to say phonology). So how do we determine that if a culture has a taboo, that it's not linguistic or does not have a linguistic component?
Second, how do you know that 'all cultures have taboos'? It sounds like a reasonable assumption but so was that all cultures have creation myths or all cultures have religions. The first one has been disproven and the second one is debated because of the lack of clarity over what is religion when you don't start from a Christian perspective. China, India, Japan, certain Amazonian tribes all have things that may look like religions but they are not very similar to the traditions that gave rise to the concept in the first place.
Equally, it's not clear what a taboo is. The original concept came from certain religious prohibitions but has since been extended to things like what one does not do in polity society. While it is extremely likely, that all cultures have the latter, it is not clear that they have the former.
In summary, I suspect that all languages have things that are proscribed in certain contexts. And that these exist at the intersection of language and culture. But without a clear definition of what you're talking about when you say 'taboo' and an extensive survey of a large sample of languages, you cannot really answer this question. Given the difficulty of what formulating the question, I doubt it's worth going to the trouble of trying to come up with an answer.
Answer: There is something like that in Berber, see: Destaing, E., « Interdiction de vocabulaire en berbère», Mélanges René Basset, Paris, Leroux, 1925, p.177-277. You can read it here: https://www.scribd.com/document/114584799/Interdiction-de-vocabulaire-en-berbere-E-Destaing

Do all cultures have "taboo language"?


Normalising data with multiple methods

Question: When training a neural network, I appreciate that data normalisation helps training. However, is it a good idea to normalise the data in multiple ways. For instance, is it a good idea to apply z-score normalisation on min-max normalised data? That is if the input data is already normalised to [0, 1], is it a good idea to train on the z-scores of that?
Answer: Depends on the dataset, and what you're looking for.
It is possible to do multiple data transformations. Standardization is often the safest choice, but only when the data is normally distributed.
If you have normalized the data, you can always apply standardisation. Standardization does not mutate the data set, but rescaling does create a new data set. From the standardized data set you can go back to the original data set.
Answer: I've not seen any paper about that but based on what I've faced till now, normalizing data intuitively is just for assigning same importance to different features which their raw values do not have a same range. Take a look at here. Also, you can take a look at here that professor says that you just need to employ a technique and it's not really important which technique. Also, take a look at here.

Normalising data with multiple methods


About studying econometrics in undergraduate

Question: I'm currently undergraduate student studying economics and mathematics. I took econometric class and mathematical statistics class last semester. So during the vacation, I decided to study econometrics more because I'm planning to do Phd in economics in the future and I thought it will be helpful. But, come to think of it, I feel like I made a wrong choice. I don't know what the exact reason is, but whenever I study econometrics, I find that I'm just 'reading' a book. And I think that's because of my lack of statistics and other math ability. So now I'm considering to study mathematical statistics more deeply and other maths, and postpone studying econometrics. One of my professor said that it's fine not to study econometrics now deeply because I will study during Phd course, but it's crucial to fully study and understand maths, statistics before Phd. What do you think?
Answer: If you are looking to understand how Econometrics are and should be grounded in Statistics, read Aris Spanos "Probability Theory and Statistical Inference: Econometric Modeling with Observational Data". Be prepared for a bit of a shock.
As for Mathematical Statistics, they are a difficult subject, and there is no magical textbook that has ever succeeded in making them "accessible".
Comment: Thank you. But I have a Hogg's "Probability and Statistical Inference", which was a main textbook last semster. What about this book? By the way, what's the difference between mathematical statistics and probability theory? Is it neceesary to study real analysis & set theory before probability thm? (Someone told me they are necessary but I'm not sure. I want to study probability theory after mathematical statistics if the prerequisites are only like calculus and linear algebra )
Answer: A really good textbook for introductory econometrics for me was Essentials of Econometrics by Damodar Gujarati. The problem is, it is quite old (mine was from 1992), so it does not even mention some of the more recent breakthroughs like cointegration analysis. But it really gets you into the subject.
I would say that for me at least, study of econometrics looks relatively useful and interesting precisely because I have moderate knowledge of different economic theories, so I know how and where to put those methods to good use (to test wether models based on one or other theory fits the real world data better).
Other than that, stats and math is also important to grasp the deeper aspects of econometric methods.
Answer: Econometrics in undergraduate curriculum is often presented as a black box. "Run these regressions in R and check the results". If you really want to understand what you're doing with econometrics, then yes you should approach it from the bottom up. Learn the math so you can understand the black boxes.
Answer: Econometrics at the PhD level requires a few specific skills you should really cultivate. First, extensive undergraduate training in Probability Theory and Mathematical Statistics is essential. Applied statistics courses are not going to help you because they take the underlying econometrics as given and just tell you how to push the buttons. You should take Linear Algebra and study it as hard as you can- I just did the bare minimum in LA and I really, really regretted it. You want to be able to eat,sleep, and breathe:

Matricies and Matrix Operations, especially rank and determinant conditions, and inversion.
Linear Projection- understand the geometry of this thoroughly, not just in the tiny little bites you'll get in most books. You should be extremely comfortable with projections and orthogonal complements.
Summation Operators- you should feel extremely comfortable manipulating summations, breaking things into double summations, etc.

Econometrics I usually consists of a very thorough coverage of linear techniques (linear in parameters, that is). Metrics II generally goes into MLE, Logit, Probit, and other more advanced techniques. You will also have a graduate stat course prior to this, which covers much of the same material as Prob Theory at a higher level. To get a taste of this, my stats class used "Statistical Inference" by Casella and Berger, and my Econometrics class used Bruce Hansen's Econometrics text, available on his site here: https://www.ssc.wisc.edu/~bhansen/econometrics/
A word of advice- self study is only ever effective toward a specific end. You need a fire under your proverbial behind. I taught myself a lot of convex analysis- but only after I realized I needed it to prove something in my first project. Your brain is designed to forget that which is not used. If you really want to learn it, you should do each and every practice problem, and be hard on yourself about getting them wrong- a live and let live attitude of "it doesn't matter really because this isn't a class" tells your brain not to remember.


Getting invalid verification code for email confirmation

Question: I am using Craft CMS as a backend for react Next app. On our live site we are sometimes getting complaints from the user about error when user try to verify code sent in the email.
This case doesn't happen with every user but very for random users. For this reason I am not able to find the reason for the issue and fix it.
Everytime I see following information in the log file.

2020-05-27 10:17:35 [-][-][-][warning][craft\services\Users::isVerificationCodeValidForUser] The verification code (gqkZpvgTZDMNSXRyNuXE4ksxpNOlBOl) given for userId: 99965 does not match the hash in the database.
  2020-05-27 10:17:35 [-][-][-][info][application] $_GET = [
      'p' => 'ACT/craft-rest-api/user/verify-email'
      'code' => 'gqkZpvgTZDMNSXRyNuXE4ksxpNOlBOl'
      'id' => 'ef2156d6-306b-4a88-80bb-25ca26562702'
  ]

Here is the information about the system.
PHP version 7.4.5
OS version  Linux 3.10.0-1127.el7.x86_64
Database driver & version   MySQL 8.0.20
Image driver & version  GD 7.4.5
Craft edition & version Craft Pro 3.4.21
Yii version 2.0.35
Twig version    2.12.5
Guzzle version  6.5.4
Imagine version 1.2.3-dev
Plugins:-
Amazon S3   1.2.8
Architect   2.3.3
CKEditor    1.0.0-beta.3
Comments    1.5.6
Contact Form    2.2.7
Craft-Rest-Api  1.1.0
Enforce password    1.0.0
Image Resizer   2.0.9
Klaviyo Connect 220.127.116.11
Redactor    2.6.1
SendGrid    1.2.0
Comment: What's ``verificationCodeDuration`` set to?
Answer: Those codes are valid for as long as whatever verificationCodeDuration is set to (24 hours by default).
Guessing the users that are getting that are hitting expired verification codes.


In Poker tournament, when we need to start Hand in Hand (Bubble)?

Question: Suppose, in tournament we have Prize Payout is 10 and 20 Player left on 4 tables. Out of 20 Player, 10 go allin in 2 tables and in rest 2 table game are just to start, so in that case do we need to start the bubble? If yes, then what if only 3 player eliminate from the tourney, do we need to continue with bubble or just stop the bubble ? If we stop the bubble then we create bubble in tournament multiple times.
Please give your pro-level feedback, which is as per industry standard.
Comment: You seem to be a bit confused. The bubble is not hand for hand play, but rather the point when the last person  busts out without winning a prize.
Comment: This might be a useful clarification on this issue, but I think the Q needs to be edited to be clearer.
Answer: < TL;DR >

Bubbles and Hand-for-hand play are not the same thing, although hand-for-hand play is most often imposed right before the bubble bursts.
You shouldn't have 20 players over 4 tables, unless it's a 6-max tournament.
I wouldn't expect H4H to begin on the basis of any number of players being all in, just based upon the number of players remaining in the tournament.
There's no fundamental problem with a tournament entering H4H multiple times, but I wouldn't expect it in the way you describe (starting H4H because a lot of players are all in, then cancelling it once very few/none of them bust).

< /TL;DR >
Firstly, as Herb Wolfe mentions in his comment, there is some confusion here around the terminology, so let's clarify:
Bubble
In its purest sense, the bubble is the point in a tournament at which the next player eliminated will be the last player to receive no prize. So if you're tournament pays 10 players and you have 11 players remaining, the tournament (and therefore the 11 remaining players) is/are "on the bubble".
The term has been expanded over time to also include other milestones in a tournament, such as the point where the next player eliminated will be the last to receive a certain level of payout, or the last to not make the final table (known as the "final table bubble").
Hand-for-hand
This is a mechanic to allow for easier administration of player exits at key points in a tournament, including often on some of the bubbles described above.
The concept of hand-for-hand play is that all tables complete the current hand before proceeding to deal the next hand. This ensures that the speed of play at one table or another does not affect the number of hands seen in a given time and therefore provide a benefit or disadvantage to anyone.
For example, without hand-for-hand play, a short stacked player on the bubble may decide to take a long time with every decision, resulting in other tables playing more hands and so increasing the chances of someone else busting on the bubble instead of him. A lack of hand-for-hand play at key points in a tournament can lead to this behaviour occurring at multiple tables (or even all tables) and the tournament therefore grinding to a halt, which is obviously not in the interest of the venue providing the tournament as they have to allocate staff to run the tournament (dealers, floor etc) and the longer the tournament runs, potentially the more it costs them to run it.
Hand-for-hand play also makes it easier for tournament directors and their staff to identify the order in which players have been eliminated, which is important around any prize jumps and the pure bubble itself to make sure that people get paid the right amount.
So, now on to your question:
Firstly, you ask us to presume there are 20 players left on 4 tables. This should never happen in a well run tournament (unless it is a 6-max tournament) as tables should be broken as soon as it is possible to do so, keeping the number of tables to a minimum. This is both for the benefit of the players (balanced and maximum numbers of players on each table) and the venue (reduced running costs). So with 20 players remaining, I would expect there to be 2 tables (10 players on each) if playing 10 handed or 3 tables (two with 7 players and one with 6 players) if playing 9 handed.
Putting this aside, you then essentially ask:

What should happen if enough players are all in across some subset of the tables remaining such that if they were all eliminated, the bubble would be broken? Specifically should play at the other tables be halted in preparation for hand-for-hand play?

The exact criteria/rules for making the decision of when to start hand-for-hand play varies from venue to venue and even between tournaments within the same venue sometimes. However, the general approach is usually the same:

Start hand-for-hand play as soon as it becomes apparent that a significant point in the tournament could likely be reached within the next few hands.

So, if you have 11 players at 2 tables remaining and are playing to a final table of 10, it would be appropriate to start hand-for-hand, as when the next player is eliminated, the two tables will be merged into one, seats re-drawn for at least some of the players, etc.
Equally, if you're running a $100 tournament and there are 33 players remaining, with 33rd place paying $1000 and 32nd paying $1500, this could also be considered a significant point and thus hand-for-hand should commence.
In your specific example, I would suggest that play at other tables should not be halted until the outcome of the hands where 10 players are all in has been established. You can then judge whether you are close enough to the bubble to justify moving to hand-for-hand play. This also answers the second part of your question, about whether hand-for-hand should then be revoked if only a small proportion of the all-in players bust, as you wouldn't start hand-for-hand until you knew how many busted from those hands.
If the rather unlikely scenario you describe occurs and all of the players who were all in are eliminated, you obviously have no problem and there is no need for hand-for-hand, as the bubble has been burst exactly. The only exception would be if shortly after this bubble there is a significant pay jump or a final table bubble, in which case, hand-for-hand play may be imposed anyway.
With regards to:

If we stop the bubble then we create bubble in tournament multiple times.

If by "bubble" you actually mean "hand-for-hand play", then this is fine. It's common for a single tournament to enter hand-for-hand play multiple times at different points, especially if the tournament is very large.