Wikipedia:Reference desk/Archives/Science/2014 October 30

= October 30 =

Cygnus CRS Orb-3
Why did the rocket explode? --EditorMakingEdits (talk) 02:48, 30 October 2014 (UTC)


 * At this time, the root cause is not known. The most informative report presently available is NASA's press conference from October 28.  According to NASA's press office, the FAA is overseeing and Orbital's accident team is currently leading the investigation.  It is probable that in the weeks that come, there will be additional independent investigations by NASA, the NTSB, and the State of Virginia.  For now, it's not really useful to speculate on the cause: very few facts are available to the public.
 * The first real data-driven information is not expected to become public for at least a few weeks, and the investigation will probably continue for a lot longer.
 * Nimur (talk) 04:02, 30 October 2014 (UTC)


 * It's only speculation at this stage - but one "expert" I was listening to on the radio this morning said that this was the first launch with their Antares-130 rocket - which uses circa 1965 ex-Soviet NK-33 motors modified by AeroJet. AeroJet bought 36 mothballed NK-33's for about $1.1 million each.  These are really rather weird motors - and their design elements aren't widely used elsewhere, so they are certainly somewhat suspect.


 * If I were guessing, a 50 year old soviet junker would be the first place I'd look.


 * SteveBaker (talk) 04:24, 30 October 2014 (UTC)
 * There's definitely appeal to that conclusion. In fact, in the press briefing, NASA's own "social media" contact mentions that this Russian engine is the number one concern brought to NASA's attention by the general public at large, via Twitter and "social media."
 * Orbital's flight director addresses this pretty directly: at this time, we do not even know whether the engine was involved in the explosion. There are a lot of parts to a rocket - not just its power plant.  It is premature to speculate that the engine was the problem.  Given that this answer comes from a literal rocket scientist who has access to data that the outside world does not, I am tempted to suggest that the rampant speculation by the public at large (many of whom are not rocket scientists) ought to be set to the side until we have real facts.
 * I've built some pretty big rocket engines in my life; I can think of a dozen reasons why a rocket can explode; but I also know that rockets are subject to incredibly extreme environments - structural, chemical, thermodynamic, mechanical, ..., and simple intuition is not a good way to deduce cause-effect relationship. We need to wait for expert analysis of video and telemetry information.
 * The "general public" is really bad at performing analysis of catastrophic rocket failure. As a perfect example: why did the Challenger explode during STS-51-L?  Everybody seems to recall the famous O-ring problem.  Everyone also seems to recall Richard Feynman's public demonstration of the O-ring dunked into a glass of ice-water to show how it becomes brittle.  Everyone seems to recall that Feynman's dissenting opinion was "the O-rings got brittle when cold, the rocket exploded."  Few people have actually read Prof. Feynman's dissent opinion in the appendix of the Rogers Commission report, in which he puts forth the real reason that he believes the disaster took place: because mission-critical facts were obfuscated by the complex social organization structure that surrounded the manned space flight program, a sort of pathology of "group-think" that enabled incorrect and faulty decision-making based on invalid scientific data.  In fact, Feynman enumerated more than a dozen engineering defects - the O-ring was only one of many problems he found! - in the Space Transportation System.  The general public blames the O-ring, and probably will continue to do so for the rest of recorded history.  The details of the rocket-science got lost for the exact reason Feynman explained - a crowd mentality is a terrible way to evaluate factual evidence!
 * Nimur (talk) 04:59, 30 October 2014 (UTC)
 * Steve, while this was indeed the first launch of the 130 variant, only the upper stage has changed, the lower stage is unchanged, they've flown the duel NK-33 (AJ-26) setup four times before. That '50 year old Soviet junker' that you so easily dismiss is still a higher preforming kerolox engine than anything the US has ever produced, so I wouldn't dismiss it so rashly. Oxygen rich staged kerolox combustion is something the Russians mastered a long time ago, and is still being used as well on the RD-171 on the Zenit and the RD-180 on the Atlas V (for now, due to be changed). Not to say the engines aren't to blame of course (they had one undergo a RUD on the test stand no too long ago), but until we have data it's all speculation. Fgf10 (talk) 09:05, 30 October 2014 (UTC)
 * ("RUD"=&gt;"rapid unscheduled disassembly"=&gt;BIG EXPLOSION) SteveBaker (talk) 14:55, 30 October 2014 (UTC)
 * And "It's only speculation at this stage" were the first six words of my answer! I agree, but still - circumstantial evidence is there:  One of these engines did explode during a test back in May, and Space-X's CEO Elon Musk said Antares "honestly sounds like the punch line to a joke." (although I'd be the first to admit that Mr Musk does tend to be a bit aggressive in his statements - and he's hardly in an unbiassed position - but it's also true that he was offered those exact same engines and chose not to buy them).   These motors were built in the 1960's for the Russian manned moon mission - all four test launches of that rocket ended in failure (one of which caused the largest accidental explosion in human history!)...but it's not thought that the engine design itself was the problem.  The design dates back to the late 1950's...so these are hardly modern machines - or even classically bullet-proof Russian engineering with a great track-record.
 * So, yeah - we don't know the cause, and there are a great many other things that it could be...but it's clear that this is a strong candidate. SteveBaker (talk) 14:52, 30 October 2014 (UTC)


 * No.It is not clear. Have to agree with Fgf10 sentiments. Soviet engineers are very conservative. They over- engineer stuff so that reliability is more important than maximum efficiency. During the Second wold war their basic tanks where more reliable, easier to maintain, etc. than the NAZI's high-tech equivalents. This is not a political comment, rather than one coming from an editor that is a qualified engineer. It may have well been an engine failure but as this rocket is still work-in-progress there is in my my mind, no reason at this stage, to single out and  speculate, that is was down to one of these old, well tested engines. From the fireworks display, it looked to me as thought the  first stage  was manually annihilated (for safety reasons) and maybe that was the major cause for the rapid disassembly before it it the ground. Even a few second after launch it would have been  traveling fast and its kinetic energy could be sufficient to send in into a populated area unless it was totally dissembled in mid air.--Aspro (talk) 15:45, 30 October 2014 (UTC)


 * Steve, get your facts straight, the N1 never launched with NK-33s, all the launches used NK-15s. The NK-33s were planned for the never flown N-1F upgraded version. Also, note that the Musk quote was from 2012, before Antares had even flown.
 * Aspro, the FTS was apparently fired, though the timings are unclear. Best evidence is that is was at or near the ground. The exclusion range is large enough for it to take a considerable time to exit it. Post-accident photos suggest that the impact site is only tens of metres from the pad (which is remarkably intact, by the way).
 * Generally speaking, the engines are most likely to be the root cause of many failure, as they are necessarily run to very tight tolerances in a very hostile environment. My problem here is that I think the Russian origin of the engines is leading a lot of people to be very keen to blame them first..... Fgf10 (talk) 16:08, 30 October 2014 (UTC)
 * I wondered, because at the moment of the first visible sign of trouble, there were streaks of what I thought could be burning aluminium or magnesium alloy, (possibly made pyrotechnic on the account that it could have been ejected at very high speed   by a charge of high explosive attached  to it), (by the scale of the rocket they must have been travelling fast to move so far in so  few frames). I can't think of any components in the fuel deliver systems that are pyrotechnic ( I am willing to be corrected here).  From just googling around in the last few minutes, both this and the SpaceX lift vehicles do seem to have  a autonomous self destruct system to knock out further propulsion. Thus, this could have initiated before any visible malfunction could be witnessed. It seem reasonable to think that to destruct the whole contrivance in the air so soon after launch would possible spread the debris over a lager area. Better to let it come down in as large bit as possible.  The engines may be Soviet but isn't all the fuel delivery systems non-Soviet? There is a lot more to go wrong there.  Also, to get a good telemetry record one needs the engines to be the most reliable part of the whole issue. If they blow apart on the launch pad there is no chance to see how all the other systems perform in flight – how ever short that might be.  So as these engines are the widgets  which have the longest flight history, I am putting their failure as less probable.  Anyway, one failure in five isn't bad for a new rocket. Orbital shares have suddenly had a drop. Maybe this is a good time to buy some of their stock. So in answer to the OP's question: Nobody knows yet!--Aspro (talk) 18:08, 30 October 2014 (UTC)
 * In the high temperature oxygen rich preburner gas, pretty much anything will burn, normal steel will just melts away (coping with the metallurgical side of this is why the Russian rule at kerolox staged combustion, US can't as yet match). So if it's a engine issue, it doesn't need to be aluminium or magnesium. The first stage/tankage is Ukrainian, don't know where the Ukrainian ends and the Soviet starts. Regarding FTS, from the initial NASA/Orbital presser the day of the incident, it was stated that the FTS was activated, from context probably from the ground rather than autonomous, and it was activated approximately 10-12 seconds after launch, coinciding roughly with the vehicle staring to lose altitude. (Working from memory, presser is probably to be found on the NASA website somewhere). The TEL avoidance manoeuvre of the vehicle was probably what caused the vehicle to come down next to the pad, rather than on top of it.  — Preceding unsigned comment added by 82.21.7.184 (talk) 19:32, 30 October 2014 (UTC)
 * High temperature sintered rocket engines, may (in parts) glow bright yellow but once blown always, they don't leave white smoke trails as seen in the video footage. So those bits where not engine fragments.--Aspro (talk) 23:57, 30 October 2014 (UTC)
 * About the timing issue, see this discussion Talk:Cygnus CRS Orb-3. There seems to have been different times reported and it hasn't always been clear what that time referred to. One thing which does not seem to be disputed is the Range Safety Officer initiated the termination. Nil Einne (talk) 20:52, 30 October 2014 (UTC)
 * Here is a photo from NASA's aerial survey of the launch pad, and yes, it shows much less damage than I would have expected.
 * And here is a nasaspaceflight.com article with a good description of the 130 variant of the Antares. -- ToE 16:24, 30 October 2014 (UTC)


 * It was a manually-activated destruct order. ←Baseball Bugs What's up, Doc? carrots→ 23:07, 30 October 2014 (UTC)


 * Thanks for that link Bugs, That's was my first thought (see above). However, until the post mortem is released, I am always ready to be corrected.--Aspro (talk) 23:42, 30 October 2014 (UTC)
 * For sure. Details will come out over time. And how fitting is it that an object called "Cygnus" took a swan dive? ←Baseball Bugs What's up, Doc? carrots→ 04:55, 31 October 2014 (UTC)

Dose any ampule contain substances which shouldn't meet the air?
I've heard that the reason medicine are put in the ampules is because these specific medicines should be protected of the air (maybe of the oxygen). That's right? anyway it's really interesting to know why are medicines put just into the ampules. Thank you.149.78.45.113 (talk) 04:44, 30 October 2014 (UTC)
 * Ampoules are hermetically sealed, thus offering increased protection from air or other contamination compared to other containers such as capped vials. Mihaister (talk) 07:15, 30 October 2014 (UTC)
 * Air is just great at making things stale, i think the primary mechanism is simple oxidation. Almost ALL medicine, ampule or not, will be hermetically sealed. Most medicine in tablet form comes in blister packs, with cautions to discard any pills whose seal has been prematurely broken.Vespine (talk) 00:50, 31 October 2014 (UTC)
 * Indeed, even food is packed in nitrogen these days, and medicine has been for decades. Oxygen is really very reactive over time, and plays havoc with very many if not most organic molecules and almost any formerly living tissue. 71.215.67.106 (talk) 07:47, 31 October 2014 (UTC)
 * It's also possible that the ampoule is there to shut out light from the medicine. Lots of chemicals break down when exposed to light. SteveBaker (talk) 17:22, 31 October 2014 (UTC)
 * Only if the ampule is dark or tinted glass. Otherwise, it's to provide a really airtight seal over a compound which might attack or be contaminated by a polymer or rubber membrane, as in many injectable medication vials.
 * When I was on daily octreotide therapy, the daily doses were sealed in individual glass ampules, which was a pain in the neck - I had to draw the medication out of the ampule with a filter needle (one which incorporated a fine-pore ceramic filter in the needle bore) into a disposable syringe to strain out any very small glass splinters from the ampule after the neck was snapped open, then switch to a narrow-bore needle to inject myself. All in all, I'd rather have been in Philadelphia. loupgarous (talk) 00:25, 4 November 2014 (UTC)

non-orientable matter
I recently read The Shape of Space by Jeffrey Weeks, an introduction to 2– and 3-manifolds. The last part is about the topology of the Universe, and what kinds of evidence would help us choose among the candidates. (Soon after it was published, the suggestion was raised that the Universe is a Poincaré homology sphere.)

Weeks doesn't discuss the implications, if any, of non-orientability, i.e. the existence of closed paths in space such that a traveler comes back with reversed chirality. I have the impression that such reversal creates antimatter, with consequences I needn't discuss; but it may be that I got that idea only from Doorways in the Sand, which is not a reliable source for physics. So: is there consensus among Real Scientists about what happens to particles on an orientation-reversing path? —Tamfang (talk) 05:12, 30 October 2014 (UTC)


 * Antimatter particles are not related to their matter counterparts only by a simple inversion of chirality. Among other properties, charge would also have to become inverted.  So, a closed path that inverts chirality is not sufficient to create antimatter - irrespective of whether such a closed path can even meaningfully exist in the physical world.  (In addition to being a geometric conundrum, such a path implies symmetry-breaking, i.e. violation of several well-established conservation laws - which runs counter to everything we normally observe, at least in ordinary conditions).  Nimur (talk) 06:13, 30 October 2014 (UTC)


 * It's hard to find references for this, but as far as I can see, if a theory has both P and CP symmetries (like QED does) then you can pick either one when gluing the space together—the electrons might come back as electrons (P) or positrons (CP). The Standard Model has no P or CP symmetry, so you can't make a Standard-Model Klein-bottle universe at all. However, only the P asymmetry is built into the theory at a deep level. The CP asymmetry is "accidental" and controlled by two continuous parameters. If you set them to zero (which is inconsistent with experiment) or allowed them to vary with position (which could be consistent with experiment), you could probably construct a world where electrons came back as positrons. I don't think they could come back as electrons. -- BenRG (talk) 06:24, 30 October 2014 (UTC)


 * The symmetries show whether you can have a normal region of space and a reverse region of space that obey the essentially same physical laws. I think it is another step entirely to posit whether one could have a continuous path that connects one such region to an opposite sense region, or more extreme, a closed loop such that a particle could return to the original position with inverted properties.  For parity issues, I think it is possible to have such paths if space can be imagined to twist in Mobius / Klein bottle configurations.  It is less obvious how you would do that for charge reversal.  Perhaps that is a failure of my imagination.  To give a simplified example, suppose there exists a straight line from point A to point B, and at point A a particle acts like an electron and if you move the particle to point B it acts like a positron.  It would seem like if you measure the electric force on a positive test charge at point A due to such a particle, then at some point on its journey it must exert no force and appear to have no charge.  In addition, if charge inversion can be accomplished via closed paths it would also seem that there are issues with energy conservation and other fun things.  As I said, maybe it is just a failure of my imagination, but I have trouble figuring out how one could create a sensible looking universe that allowed particles to move from charge to anticharge simply as a result of the path traveled.  Dragons flight (talk) 22:04, 30 October 2014 (UTC)


 * I think it's fine. Instead of thinking of physics on a Klein bottle, you can imagine tiling the plane with its fundamental polygon Klein Bottle Folding 1.svg, which gives you a pattern like

RRRRRRRR ЯЯЯЯЯЯЯЯ RRRRRRRR ЯЯЯЯЯЯЯЯ
 * where each R is an image of the same world. If there's an electron in one R, there's a lattice of alternating electrons and positrons filling the plane. If transport them up by the lattice distance, you now have positrons where there used to be electrons and vice versa. You can think of this as a single electron coming back to the same place as a positron. Everything is continuous and there's no violation of conservation laws. The positron was always out there at a distance equal to the lattice separation; you could have detected it by its electric field. -- BenRG (talk) 23:03, 30 October 2014 (UTC)


 * You've drawn pretty image (and kudos on the backwards R), but you haven't really explained what happens at the boundary. When a single particle moves from R to Я what does it experience?  What do test charges stationed at R and Я perceive happens to the field if a single electron is moved from R to Я?  Maybe there is a way to make sense of those questions.  However, also note that the original question was about non-orientable surfaces (e.g. Mobius strips).  A lattice of R and Я spaces stitched together isn't actually an example of that.  A true non-orientable manifold has closed paths that take travelers from R to Я.  The charge analogy would be if you could get in normal spaceship, fly around in some way, and come back to Earth in an antimatter spaceship (from the perspective of people who stayed on Earth).  That's the kind of universe that seems particularly primed for weird consequences.  Dragons flight (talk) 23:56, 30 October 2014 (UTC)


 * Try this image: Take a universe mathematically described by a 2-sphere – with two space-like dimensions and no time-like dimension – except that every particle has its antiparticle at the antipodes.  This is just a mathematically convenient description for visualization: the particle and its antiparticle at the antipodes are really the same thing at same point in the "real" space, which is half the size of this spherical model.  Now when an object travels half-way around the sphere, the antimatter form arrives where it departed from.  You'll see that there is no boundary at which the character changes from "electron" to "positron", only that it is one or the other depending on where on the path you look at it from. in this picture, also, any consistent definition of total charge is inherently zero. This universe is actually the real projective plane with a metric: elliptic geometry. The same idea can be extended to our 3+1 dimensions to produce a non-orientable geometry. —Quondum 00:27, 31 October 2014 (UTC)


 * I think Quondum's example is better than mine, but to clarify, I was talking about the Klein bottle as a quotient space of the plane. My universe is still a Klein bottle, not a plane—it's just a different way of looking at it. There are no boundaries at which anything special happens. -- BenRG (talk) 05:33, 31 October 2014 (UTC)


 * Stitching together multiple "fundamental polygons" like you did, without looping them back, produces a plane, not a Klein bottle. You need to specify how you loop them into a Klein bottle still. I suspect you mean to do this via identifying the polygons all as the same polygon. Agreed, this is different from the projective plane. —Quondum 14:21, 31 October 2014 (UTC)


 * Yes, that's why I said they were images, not copies. Although in a deterministic classical world you could just as well think of them as copies, since they'll all evolve in lockstep anyway. This question doesn't need quantum mechanics, so if calling them copies makes the example easier to understand, that's fine. In a quantum world you'd have to also stipulate that random measurement outcomes are the same in all of them. -- BenRG (talk) 17:56, 31 October 2014 (UTC)


 * Ah, gotcha. I evidently skimmed your description too quickly. —Quondum 18:46, 31 October 2014 (UTC)

Thank you. —Tamfang (talk) 07:18, 30 October 2014 (UTC)

See also here. Count Iblis (talk) 18:11, 30 October 2014 (UTC)

Disclaimer: what follows is strictly OR There is CPT symmetry. This is preserved geometrically as well in a four-dimensional non-orientable projective geometry, satisfying de Sitter relativity. The Copenhagen interpretation does not sit comfortably with the time-reversal implied by circumnavigation of the universe, but I expect that aside from layering further counter-intuitive ideas on top of quantum mechanics, this is actually consistent with modern quantum theory. So to answer the original question: following an orientation-reversing closed path (possibly necessarily a non-causal i.e. space-like path) may result in antimatter with time-reversal. But under the Many-worlds interpretation, don't expect to see yourself departing when you arrive, or that entropy considerations present an obstacle. —Quondum 21:15, 30 October 2014 (UTC)

spacetime
Weeks also doesn't touch on the topology of spacetime as a 4-manifold. Does the asymmetrical metric signature of Minkowski spacetime assure us that it is (topologically) the product of time and a 3-manifold? —Tamfang (talk) 07:18, 30 October 2014 (UTC)


 * "Antisymmetrical" is not a term I'd use in this context. I presume you mean indefinite. No, while the assumption that a 4-manifold has a continuous metric tensor free of singularities (e.g. changes in metric signature), I strongly doubt whether this would produce a constraint to the simple product that I think you mean.  In particular, see my counterexample of a non-orientable space above. —Quondum 21:27, 30 October 2014 (UTC)


 * By "asymmetrical" I meant only that one of these things is not like the others. I understood your antipodal example (for spacelike space) before I posted the question; please help me see how it answers this question. —Tamfang (talk) 22:11, 31 October 2014 (UTC)


 * The antipodal example works almost unchanged with one time and one space dimension. Take the previous sphere, and slice off the top and bottom caps at latitudes ±45° and discard them. At every point we have the usual light cone of special relativity (light travels on great circles tangent to "both" boundaries).  As we move along a spacelike path to the antipodes (which is also the point we started from), the future light cone is the original past light cone, and particles are their antiparticles. The boundary is infinitely far, so this manifold is open (unbounded).  Topologically this is a punctured projective plane. This is not the trivial product (i.e. trivial bundle) of a space-like manifold with time; it is a Möbius strip (or a four-dimensional analogue when you add the other two spatial dimensions) that flips the direction of time when smoothly travelling along a suitable path. Hence my answer: No, we do not have the assurance you seek (assuming you meant trivial product). —Quondum 23:46, 31 October 2014 (UTC)
 * An afterthought: if you stipulate that the universe be simply connected as well, the conclusion may change, but I see no compelling argument to suggest that it should be so. —Quondum 00:51, 1 November 2014 (UTC)
 * I quite agree with that last point. —Tamfang (talk) 08:33, 3 November 2014 (UTC)

parity
I've been feeling a lot of confusion whenever trying to gather what parity really means in physics. We have chirality (physics), which explains well the difference between chirality and helicity, but not much else. For example, our article on Standard Model (mathematical formulation) explains that the mass of an electron is really the coupling between a left-handed electron and a right-handed electron, which is the antiparticle of a left-handed positron... say what? I'm getting the feeling this has nothing to do with whether the electron in a 1s hydrogen orbital has spin +1/2 or -1/2, but why not... I'm not so clear on. And that's not even getting into weak isospin -- left-handed fermions have a value of 1/2, right-handed fermions have a value of 0 why? My feeling is that this topic is the pons asinorum that is so far doing a great job of guarding the juicy meat of the Standard Model from my comprehension. Wnt (talk) 21:48, 30 October 2014 (UTC)


 * It's always true in a relativistic quantum field theory that a massive particle X is a coupling between left-handed (=counterclockwise polarized) and right-handed (=clockwise polarized) X fields, and the left-handed (resp. right-handed) X is the antiparticle (CPT dual) of the right-handed (resp. left-handed) anti-X.
 * In the case of the standard-model fermions, only one of the two polarizations exists. There are no mass couplings because there's nothing to couple to. However, you still have equal numbers of left- and right-handed fields because everything still has a CPT dual, and there are three-way interactions involving the Higgs field, one left-handed fermion field, and one right-handed fermion field. Probably the most important thing to understand is that the left-handed and right-handed fields are not designed to go together. They're a priori unrelated chiral particles that end up stitched together in this Frankensteinian construction at low energy that resembles a massive mirror-symmetric particle. They have different SU(2) and U(1) charges because the Higgs field is charged and the three-way interaction has to conserve charge. -- BenRG (talk) 00:06, 31 October 2014 (UTC)

Sunrise or sunset ?
Just curious - Is it possible to deduce if a photo is of sunrise or of sunset ? What clues (other than the caption of the photo and the metadata :-) ) can we look for to arrive at an answer with reasonable accuracy ? WikiCheng | Talk 09:13, 30 October 2014 (UTC)


 * I think one important difference between sunrise and sunset is the air temperature, which at sunrise tends to be much lower that at sunset. This means that the chances of fog are higher at sunset sunrise. Additionally the temperature of the air may impact its refractive index for certain wavelengths, meaning that some colors are seen more or less depending on temperature. I don't know if this effect is significant enough to be noticeable though. - Lindert (talk) 09:40, 30 October 2014 (UTC)
 * You mean "the chances of fog are higher at sunrise" don't you? ... or am I thinking of mist which is much more common at sunrise?    D b f i r s   11:31, 30 October 2014 (UTC)
 * Yes, thanks for the correction. It goes for both fog and mist, because fog is just dense mist. - Lindert (talk) 12:04, 30 October 2014 (UTC)


 * Some more suggestions in the archives.--Shantavira|feed me 12:06, 30 October 2014 (UTC)


 * Another suggestion not included in the thread linked by Shantivara above, is that if you know the location of the photograph, it might be possible to work out if the camera was pointing east or west. Alansplodge (talk) 15:05, 30 October 2014 (UTC)


 * Our Sunset article says "Sunset colors are typically more brilliant than sunrise colors, because the evening air contains more particles than morning air."...and provides a bunch of references for that statement. However, the word "typically" is key here.  If there are days when the colors aren't more brilliant, then that's only one clue.   There are likely to be clues of other kinds - cloud formations might result from warmer daytime weather conditions than nighttime, fog at dawn as the sun starts to evaporate off dew - so there are likely to be other clues there.    Yet more things are that in one case you're looking east and the other, west - so you may see other features of the landscape that offer clues, moss grows predominantly on the north side of trees in the northern hemisphere - so if you see moss on the right-hand side of trees in your photograph, then the camera was pointed to the west and it's a sunset.   But that assumes you know which hemisphere you're in - which may require more clues such as looking at the species of trees present in the image.   Maybe you can see stars in the sky?   Maybe you can find a distinctive landmark?   There could be any number of clues for a careful observer.


 * But I doubt that it's possible to do this with 100% certainty - and for sure there is no one, single rule that will get you a high success rate - but by examining all of the evidence, it ought to be nearly always possible with enough effort.


 * SteveBaker (talk) 15:14, 30 October 2014 (UTC)
 * Knowing the location certainly helps - although one has to be careful with such pictures from the parts of Panama where sun rises in the Pacific and sets in the Atlantic. ←Baseball Bugs What's up, Doc? carrots→ 15:57, 30 October 2014 (UTC)
 * Considering the width of the isthmus and the fact that the Pacific is generally to the south of the country, are there any such points? You'd need a high elevation somewhere in the middle part of the country where the canal is, and the reason they put it there was that the elevation wasn't high. --174.88.134.249 (talk) 05:14, 2 November 2014 (UTC)

Why ionizate equation of weak base are written as single step.
The ionizate equation of weak acid, are written as multiple steps: e.g. H2CO3 <--> HCO3- + H+, HCO3- <--> CO32- + H+. But Cu(OH)2 <--> Cu2+ + 2OH-. They both by two steps, acid's are split, base' are not. --Qqqqtgffg (talk) 11:35, 30 October 2014 (UTC)
 * Because all metal hydroxides are (to the extent that they dissociate) are always strong bases. The difference between a strong acid/base and a weak acid/base is the ratio of particles in solution.
 * For a strong acid/base, there are NO undissociated particles in solution. That is, if you got a really strong magical microscope, and looked at a solution of, say, HCl, you would see essentially zero actual molecules of HCl floating in that solution.  You would only find H+ ions and Cl- ions.
 * For a weak acid/base, you would find a mixture of dissociated and undissociated particles in solution. For example, if you had a solution of acetic acid (HC2H3O2) and again looked at it with your super-powerful microscope, you would see mostly HC2H3O2 molecules floating in solution, and only a small amount (about 1 out of every 5000 molecules or so) of them would have broken up into H+ and C2H3O2-.
 * Here's the deal with Cu(OH)2: when you get your super powerful magic microscope, and look at a solution of it, you don't find any undissociated Cu(OH)2 particles in solution All you see are Cu+2 ions and OH- ions. By definition, that means it is NOT a weak base.
 * Now, as a mostly unrelated matter, the Cu(OH)2 is only very slightly soluble in water. If I add a scoop of it to water, most of it settles to the bottom of the container, and very little dissolves.  But the only thing that matters with regards to acid/base behavior, is what is in the solution after it dissolves.  Solid Cu(OH)2 sitting at the bottom of the container has no effect on the acid/base behavior.
 * So, we treat Cu(OH)2 as a strong base, and don't do a "step-wise" dissociation because that's how it behaves: whatever is actually in the solution is fully dissociated already, so we don't do a step-wise (or split) dissociation to calculate the concentration, as we have to do with partially dissociated acids and bases. All metal hydroxides are essentially strong bases.  Weak bases are usually your nitrogenous bases.  Something like hydrazine would be a good example of a weak base which you would need to do a step-wise calculation, a different value for protonating each nitrogen.  I hope that helps! -- Jayron  32  16:28, 30 October 2014 (UTC)

Fea modelling
What are the main things to check if your mesh density study for an fea steady state heat transfer model isn't converging? I've checked the dimensions, added load parameters. — Preceding unsigned comment added by 194.66.246.44 (talk) 11:45, 30 October 2014 (UTC)

If you have a dynamo but what a specific output
If you have a dynamo or hand crank (or some other form of irregular output, like photo-voltaic) but want a specific output for your charging a battery or an electronic device (which is not a lamp, but something more sensitive, like a computer). How could you filter the irregular output into something that won't damage the receiving device (battery or gizmo)? — Preceding unsigned comment added by Senteni (talk • contribs) 18:32, 30 October 2014 (UTC)


 * Well, there are plenty of simple voltage regulators that will take an irregular DC voltage and turn it into a voltage within some fixed range.  The simplest is probably to use a resistor and a zener diodes - which will prevent voltages higher than a certain threshold from passing.  (See Zener_diode)...but there are many other possibilities of varying complexity and efficiency. SteveBaker (talk) 19:44, 30 October 2014 (UTC)


 * Possibly the most effective solution is just to put a big battery in the circuit. Irregular current inputs will keep it charged, and the battery will provide the the constant voltage.  A little bit of control circuitry might be necessary, depending on the input, to check that you are not overcharging or gradually draining the battery.    D b f i r s   12:43, 31 October 2014 (UTC)


 * The OP seems to want a regulated DC output from a fluctuating DC input. This avoids the need for a rectifier to transform AC to DC. A diode might still be useful to keep the capacitor or battery from feeding power back to the input device. In addition to the regulator that SteveBaker mentioned, a large capacitor would be helpful to maintain the output voltage when the input voltage dips momentarily. If the input drops for a long time or extremely low, then the battery Dbfirs mentioned would be useful. To design such a power conditioning circuit, you would need to carefully specify the power demands of the device you are powering, as well as the input variations. Then it is a straightforward circuit design problem. Without knowing how the input can vary, you really have no way to select the battery/capacitor etc. If you could avoid the battery it would likely save weight and cost. Photovoltaic panels in many climates have very unpredictable output. I would plan on a battery with a charge controller. If I were powering something with dynamo which had something continuously turning it I would probably skip the battery and use a capacitor based power conditioner to smoth out variations, since it would not be stopping and starting. You could use the solar panel or dynamo to charge the battery integral to a laptop or other electronic device, perhaps with circuitry to avoid overcharge or too-fast charging.  Edison (talk) 16:13, 31 October 2014 (UTC)

What is the difference between stochastic model vs statistical model
If you are modelling a process, like spread of an epidemic, or stock prices or language, can you say a model is statical but not stochastic, or, the other way round, stochastic, but not statistic? — Preceding unsigned comment added by Senteni (talk • contribs) 18:54, 30 October 2014 (UTC)
 * Stochastic is not the antonym of statistical. Stochastic is the antonym of deterministic.  The difference between stochastic and deterministic is thus: if you predict a relationship between some events, that is "If I do X, then Y will happen", the system is deterministic if Y happens 100% of the time, while the system is stochastic if Y happens at no better rate than random chance.  For example, picture you are holding a rugby ball (or American football) in your hand: If I let it go, I can predict it will fall towards the ground.  The result is deterministic: every time I let the ball go, it goes in exactly the same direction (towards the ground) every time.  Now, after it hits the ground, predicting where it will bounce is highly stochastic: the shape of the ball makes it fiendishly difficult to predict where it will bounce.  If I dropped it 100 times, 100 times it will fall towards the earth (a deterministic result) but I would expect no way to predict the direction it would bounce (a stochastic result).  Both deterministic systems and stochastic systems obey certain rules of statistics.  With the football example, for instance, even the stochastic result (the bounce of the ball) will result in a pattern which is statistical in some way: the result of any one bounce is random, but over a large number of results, you'll find the results forming a rough circle around where it lands.  This is the same sort of thing, for example that allows us to predict the shape of atomic orbitals: the location of an electron is truly stochastic: there is absolutely no way to predict the location of an electron at any one time, however we can reliably predict the areas around the nucleus we are likely to find electrons.  This sort of statistical results from stochastic events is the study of things like chaos theory and quantum mechanics and other studies that deal in predicting the behavior of random systems with what is known as the Law of large numbers.  Thus, while the behavior of the price of any one stock, or of the market on any one day may be stochastic, the behavior of the entire market over a long period of time may show predictive patterns. -- Jayron  32  19:42, 30 October 2014 (UTC)
 * That description does not quite sound right to me. For one, stochastic and deterministic should not be regarded as antonyms, since a deterministic process may be described as a stochastic process in which the random variables describing the evolution of the system have zero uncertainty. I think the key difference between statistical and stochastic is a nuance: the former describes an outcome, the latter a process. —Quondum 20:55, 30 October 2014 (UTC)
 * Yes, confusingly, we can model deterministic processes via stochastic models (and vice versa), and in certain circumstances, that can be quite productive. Nevertheless, "stochastic" is usually considered an antonym to "deterministic" as adjectives referring to the same class of things. Generally, a model cannot be both stochastic and deterministic, nor can some physical process be both. Interestingly, some stochastic processes have certain aspects that are deterministic, the classical example being the brownian bridge. Though we cannot predict with certainty what path will be taken, we know the process will return to zero! We can also show that a simple random walk on the 2D lattice will return to the origin infinitely often. So again, a stochastic process can have some attributes that are not up to chance (well, almost surely, but that's a whole different can of worms :) SemanticMantis (talk) 21:08, 30 October 2014 (UTC)


 * We have an article on statistical models, and stochastic models. But I would caution against taking those definitions as absolutely authoritative (remember, WP is not a reliable source!). I can draw a distinction between the two, but the concepts are closely related and researchers in different fields may draw slightly different distinctions. In practice, statistical models are usually about finding a probability distribution that describes some observations. This can be done without any time component In practice, "stochastic model" is usually used for a dynamical systems approach where there is some stochastic component, and, as our article points out, a stochastic process doesusually describe some sort of time evolution of a system. So, something like fitting a general linear model to observed data is a statistical model. Something like a stochastic differential equation or a stochastic difference equation could be used to dynamically model things like stock markets or population growth. There are definitely models that are stochastic but that we would not normally call statistical models. An example might be a simple random walk -- this is a stochastic and dynamic model. It wouldn't exactly be incorrect to say it was a statistical model, but most researchers wouldn't call it that. And that leads to another distinction: statistical models tend to be descriptive, but not necessarily explanatory. The classic example is that shoe size and knowledge have a significant relationship, and would could make a nice statistical model to describe it. However, this only means that adults tend to know more than children. In contrast, stochastic models often attempt to describe a mechanism of action, so that stronger conclusions can be drawn, compared to the "X explained 82% of the variation in Y" that is common of statistical models. SemanticMantis (talk) 21:08, 30 October 2014 (UTC)


 * Another note, since Jayron mentioned chaos theory- "Stochastic" came to be used to distinguish a certain kind of variability and indeterminism from other vaguely "random" types of behavior in the 1930s . "Chaos" can also loosely mean "random" in English, but chaos theory of e.g. the logistic map is often called "deterministic chaos" simply to reinforce the point that the variation and unpredictability are not due to stochastic processes. Prior to a few synergistic findings, mathematicians and scientists did not know that such unpredictable behavior could be the result of a deterministic process, and that's why we have a handful of technical terms that all pertain to the loose concept of "randomness". SemanticMantis (talk) 21:32, 30 October 2014 (UTC)

How do 32 electrodes transmit a complex behavior?
I'd welcome commentary on this article, specifically how a fairly small number of electrodes manage to apparently train a mouse. See also, , and the target article to improve if you can, prosthetic hippocampus. Wnt (talk) 21:52, 30 October 2014 (UTC)