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September 16

Lesch–Nyhan syndrome

Lesch–Nyhan syndrome causes a mess of problems: the patient cannot produce a specific enzyme, produces too much uric acid, experiences intellectual disability severe enough to prevent speech and ambulation, and is susceptible to a raftload of self-harming behaviors. I get the impression that the enzyme absence causes the overproduction of uric acid somehow, but what causes the rest? The article seems to suggest that the hyperuricemia is responsible for everything, yet that seems unlikely (why would too much of a toxic acid cause compulsive self-harming?) — but then I've looked over the "Pathophysiology" section without understanding much of anything after the first three paragraphs. Nyttend (talk) 03:35, 16 September 2017 (UTC)[reply]

From the article: "The etiology of the neurological abnormalities remains unknown." Ruslik_Zero 08:13, 16 September 2017 (UTC)[reply]

Nonetheless, it might be useful to research purine autism, which also involves hyperuricemia. Purine autism is interesting in that it is a kind of autism said to respond to allopurinol treatment, though I would have expected much more confirmation of that by now if it were reliable. [1] Note that autism can also cause self-harm activity and is mentioned in this regard in our Lesch-Nyhan article. Wnt (talk) 11:32, 16 September 2017 (UTC)[reply]

Hm, I didn't realise that "etiology" meant "origin" or "cause". Nyttend (talk) 12:33, 16 September 2017 (UTC)[reply]

Aquo complex versus hydrated compound

Is there a clear demarcation between an aquo complex and a hydrated compound; or does it simp.ly depend on context; or does it depend on the particular author? I am not talking about water of crystallization when I say 'hydrated compound'. Case in point: tetraaquocopper(2+) sulfate versus copper(2+) sulfate tetrahydrate. Does it have anything to do with the degree of lability of the aquo ligands, or perhaps whether the complex is homoleptic? Plasmic Physics (talk) 07:03, 16 September 2017 (UTC)[reply]

At the level of one of my freshman chemistry textbooks (General Chemistry by Ralph H. Petrucci 5th edition 1985, p.911) and this website [2] (Washington University at St. Louis), both would appear to be non-standard names for coordination complexes, although the first is close. Standard nomenclature would be tetraaquacopper(II) sulfate, indicating copper 2+ coordinated to 4 waters and not coordinated to the sulfate counter ion. "Copper(2+) sulfate tetrahydrate" would mean CuSO4.4H2O to me, which would be an example of water of crystallization. An example of where you have seen this would be helpful, but using CuSO4.4H2O terminology would be necessary in instructions for a copper sulfate solution preparation to get the right mass of starting reagent for the desired concentration of copper sulfate.--Wikimedes (talk) 17:45, 16 September 2017 (UTC)[reply]

Using the ionic charge instead of the oxidation state when constructing additive names seems to be the preffered alternative convention according to the latest IUPAC nomenclature conventions. From what I've read, when 'hydrate' appears in the name, it can refer to either an aquo complex or w.o.c. introducing vagueness. From your your concluding remark, I gather that which one to choose, depends more on the context? If that is the case, what defines the context in which either use would be appropriate? Plasmic Physics (talk) 23:28, 16 September 2017 (UTC)[reply]

Standard nomenclature seems unambiguous, and you probably can't go wrong by choosing the standard way of saying or writing things. (2+ vs. II or aquo vs. aqua wouldn't impede understanding and is just a tangential nitpick.) One of my fields is solid state chemistry; I'm not up on common variations of standard nomenclature in coordination chemistry and can't recall much anecdotally.--Wikimedes (talk) 02:29, 17 September 2017 (UTC)[reply]

(My appologies, it appears it is actually supposed to be 'aqua'). Solid-state chemistry? Interesting... How can you tell expermentally or theorhetically, if an atom is bound to a neighbouring atom in a bulk phase? Plasmic Physics (talk) 03:03, 17 September 2017 (UTC)[reply]

Experimentally, X-ray crystallography would be choice for crystalline compounds, and can give some information about amorphous solids as well. There are also the related neutron and electron diffraction. Solid-state NMR gives information on the proximities of NMR-active nuclei. According to table 3.1, p.48 of Solid State Chemistry and its Applications by Anthony R. West 1984, most types of spectroscopy give information on local structure, though you would have to do some research to find out which technique is best used for a particular situation. Theoretically, according to p.20 of the January 2017 edition of the MRS Bulletin, "... (molecular dynamics) simulations are routinely used to model the structure of materials with steadily increasing accuracy".--Wikimedes (talk) 18:58, 17 September 2017 (UTC)[reply]

Breaking boards

How much force does it take to perform a power break on an unpegged stack of 4 standard 1-inch-thick boards made from seasoned pine, dimensions 12x6 inches, grain along the 6-inch edge? How much more force is needed if the stack is increased to 6 boards with all the other parameters remaining the same? (This is NOT homework -- this is me trying to gauge my own strength!) 2601:646:8E01:7E0B:3DB7:8D6E:A762:14CC (talk) 08:02, 16 September 2017 (UTC)[reply]

You don't break them with force (at least, not in karate), you use impulse to do it. This is the product of force and time (strictly, their integral). There are two impulses under consideration here, the impulse given to the moving hand by the body, and the impulse the moving hand then transfers to the boards. Much of karate training is about increasing the impulse given to the hand, in the short time available. Considering human muscle generally, we're "strong but slow" - a mediocre performer in pure strength sports can produce more force than most karetaka can, but they can't deliver anything like the same impulse. The ultimate demonstration of this being of course the "inch punch" techniques.

This also indicates why an empty hand technique is limited (for pure striking effect) against anything with a weighted glove, or a kick (legs are heavier than arms). Human muscles are better at loading impulse into things slightly heavier than a single hand.

Then there's the matter of transferring the impulse into the board. It takes a certain amount of energy to fracture a brittle material like dry cross-grain timber, so six boards will need at least

6/4

as much as four. But, one must also couple the impulse of the hand effectively into the boards. This is very difficult to model as a physical process, because it's fast and the materials (mostly hands) are flexible, so they turn the energy of the moving hand into compressed and displaced flesh, rather than bending (and breaking) the board. This is the second matter of karate training: which part to strike with and how to keep the hand rigid enough.

Then there's the physics of breaking boards. The easiest boards to break are a stack of moderately thin boards, already touching at the impact point. It is hard to break the same boards with spacers at their edges. If they're spaced apart for visibility, they sometimes have a 'coupler' in the middle too. It's very hard - soon impossible - to break a single board of the same thickness. Also don't demonstrate against a carpenter who gets to choose which boards to use, because there's visible and selectable variations in their strength. Boards are broken by exceeding their strain, not their stress. It's not applying a force greater than their ability to resist, it's bending the board past their linear ability to extend (why the materials broken are chosen for being brittle, i.e. having a poor resistance to strain, even if strong against a stressing force). If the boards are too thick, you can't bend them enough to achieve this strain - you may put a Herculean dent into the top, but they don't snap. If they're too thin, they become simply flexible and all you will do is bend them down and have them spring back afterwards - this is some of the theory behind composite materials. If the boards are in a spaced stack, then there is considerable bending in the upper boards (absorbing your impulse), but there isn't enough left for the lower boards to break them. Bending the upper boards downwards to touch the next board absorbs energy and this energy is lost to the strike when the board breaks (it turns into sound or an acceleration of the board halves starting to move independently). So a spaced stack of boards will require an impulse that increases more than the number of boards. Exactly how much more is tricky to work out, as it depends on many factors - such as the relative energy needed to bend a board down vs. the energy to break it. A stiff board in a spaced stack (such as tiles) is very hard to break.

Boards and tiles are broken for demonstrations because they demonstrate the effect of impulse over force. To show simple force strength (and not highlight the effects of speed), then punching a swinging bag and seeing how far it moved would show this better - and the karetaka would probably lose to Indian wrestlers. Andy Dingley (talk) 09:39, 16 September 2017 (UTC)[reply]

@Andy Dingley: I am suspicious you are thinking of something else besides impulse here. The impulse is force x time, and causes an acceleration of the target object. In other words, the swinging bag would be a perfect measurement of impulse. What you are describing seems more like simple speed, or perhaps some other quality, that allows the board to be pulled far off center before it has much of a chance to push back on the hand i.e. to apply its impulse to the hand. But I know nothing of how to break multiple boards with a hand, so I am likely wrong. Wnt (talk) 11:39, 16 September 2017 (UTC)[reply]

Would it be rate of transfer of impulse (= rate of change of momentum) that is important here? Dbfirs 12:05, 16 September 2017 (UTC)[reply]

And if so, that would be the force! (F*t)/t=F 2601:646:8E01:7E0B:3DB7:8D6E:A762:14CC (talk) 12:17, 16 September 2017 (UTC)[reply]

So it would! I've never tried to break boards (at least not seriously). Presumably, one needs both a large impulse and a fast rate of transfer (speed of strike; force) to achieve the effect. There is some discussion here but I'm not convinced by the approximations in the mathematics. Dbfirs 12:27, 16 September 2017 (UTC)[reply]

The link loops back to Wikipedia: Breaking (martial arts) for a source. Our article there has some data (also shows some signs of personal stress, like the uppercase link to SCIENCE). I am still not convinced it is very simple. For one thing, the displacement of the board depends on the force, but force is a tricky thing. Suppose you contrast my hand, modelled by a heavy sausage wrapped in confectionary marshmallow, versus the hand of a martial artist, modelled by the sausage wrapped in horn. Well, if I had a rocket booster handy to get my hand up to the same speed as the artist, the impulse would be the same. But the force wouldn't be the same because the whole mass of the marshmallow has to squish up (OUCH!) before all the momentum is transferred; but the horny hand of the artist presumably is more rigid and conducts that impulse rapidly upon the first few millimeters of contact (and impulse/time = force). Bent off center more rapidly by the increased force, perhaps the board breaks sooner, and therefore has much less time to transfer impulse back to the hand of the artist. So how much is speed, needed to build up the hand's impulse, and how much is rigidity, to deliver it? And what else have I forgotten? Wnt (talk) 18:07, 16 September 2017 (UTC)[reply]

So, anyone find an approximate number value for the force involved? 2601:646:8E01:7E0B:3DB7:8D6E:A762:14CC (talk) 07:44, 18 September 2017 (UTC)[reply]

Force is the wrong measure. Andy Dingley (talk) 10:13, 20 September 2017 (UTC)[reply]

Shortest Nobel Prize-winning paper

Today I learned that Watson & Crick's paper announcing their discovery (or at least, their part in the discovery) of the structure of DNA is a mere 834 words - exceptional brevity for such a significant finding. Is that a record? I appreciate Nobel Prizes aren't for papers but for research generally, but using published papers which described Nobel-winning research as a metric has anyone ever bettered 834 words? 51.9.138.245 (talk) 10:10, 16 September 2017 (UTC)[reply]

Watson & Crick's paper was so short largely because they were in such a hurry. Much of the background work was already known. Pauling had already published one postulated structure, which was largely held to be unworkable. They thought that others (i.e. Pauling) would reach their own conclusions for themselves if given much more time. Watson & Crick had two ideas, the double helix (rather than a triple structure) and also the "zipper" idea for replication. They wanted to be Wallace, not Darwin. Their paper wasn't publishing the results of long years of research and careful study (that was mostly out there already, or was filled out later) it was throwing two wild ideas out to claim clear priority on them, even if they turned out to be wrong later. The specific paper is a brilliant hypothesis, not careful research. Andy Dingley (talk) 10:36, 16 September 2017 (UTC)[reply]

Since Watson and Crick were mentioned, Rosalind Franklin must be mentioned too. Fgf10 (talk) 11:39, 16 September 2017 (UTC)[reply]

One of the justifications for Franklin not being mentioned on this paper has been that the paper was based on the two "wild guesses" that were so urgent to make publicly visible and so to claim precedence for. Franklin's work had been the painstaking careful research that led up to this. Sadly and IMHO wrongly, the Nobel Prize was awarded for the narrow paper, and overlooked Franklin's contribution to making it possible to have those ideas. Andy Dingley (talk) 12:42, 16 September 2017 (UTC)[reply]

Franklin is acknowledged in the paper (as well as Wilkins). --69.159.60.147 (talk) 22:14, 17 September 2017 (UTC)[reply]

I fully agree that Franklin should have been given more credit by the scientific establishment, but it's difficult to see how the Nobel Committee itself could have: Nobel Prizes are never awarded posthumously, and Franklin had died in 1958, 4 years before the award to Watson, Crick and Maurice Wilkins. Watson himself suggested that, had she lived, she might also have shared the award.

Perhaps those three should themselves have made more of her contribution, which Franklin may never have been fully aware of, as Wilkins had shown her critical 1952 photo to W & C in 1953 without her knowledge, and after she herself had moved on to a different college and different areas of research. {The poster formerly known as 87.81.230.195} 90.200.137.12 (talk) 16:06, 16 September 2017 (UTC)[reply]

Well her also sharing the award with Watson, Crick and Wilkins, if she had lived was surely about as likely as her getting the award after she died, i.e. really unlikely. Prize rules limiting a single prize to 3 people would have required either there were 2 awards in two separate categories or years, or there was something weird like the Randall X-ray diffraction lab. Mind you, I'm not sure anything but the Nobel Peace Price can be award to an organisation. Our article suggests so but the cited source doesn't really seem to say this and the closest I can find on the Nobel site is that in some places they mention the Nobel Peace Price has been awarded to organisations etc. Anyway, if they had wanted to award to an organisation in memory of her, I don't see that her death really stopped that. And if they were going to award 2 prizes, they could have simply said no living person deserved the second, although that may seem a little weird since more likely no living person and Wilkins should share the second prize. Mind you the no 3 people and posthumous rules [3] don't really seem to come from Nobel's will anyway [4]. Also although that clearly says the award is divided equally, among the recipients, [5] suggests it isn't always. I guess most likely this arises when 2 separate works receive an award, in which case the one work with 2 recipients gets 1/2 share which is divided among the 2 people, and the other gets 1/2 share which goes to that single awardeee. Nil Einne (talk) 17:48, 16 September 2017 (UTC)[reply]

My assumption is that Franklin would have been jointly awarded the Prize instead of Wilkins. Both of them had been working on DNA crystallography, and Franklin had been recruited by their mutual boss John Randall to either collaborate with Watkins (as he believed) or to take the work over and forward it (as she believed – Randall's poor management of them led to their misunderstanding). Franklin's improved data was crucial to Watson and Crick, but with her dead, it was not unreasonable to include Watkins as the "next biggest player" in the discovery. {The poster formerly known as 87.81.230.195} 90.200.137.12 (talk) 19:46, 17 September 2017 (UTC)[reply]

Here is the paper, and as you see, Franklin is acknowledged (as well as Wilkins).

Possibly. However your original comment said also without any mention of excluding any recipients so I was replying to that. Nil Einne (talk) 05:06, 18 September 2017 (UTC)[reply]

Acknowledgement isn't an authoring credit though. Andy Dingley (talk) 10:16, 20 September 2017 (UTC)[reply]

The assumption I've heard is that if Franklin had survived and been able to promote her work (and that of her doctoral student Raymond Gosling), there would probably have been two prizes: Watson and Crick would have won the Nobel Prize in Physiology (for working out the reproduction mechanism of DNA) and Wilkins, Franklin (and maybe Gosling) would have won the Nobel Prize in Chemistry or maybe Physics (for pioneering x-ray crystallography methods that uncovered the structure of DNA). Smurrayinchester 10:18, 20 September 2017 (UTC)[reply]

Conway famously published a paper with the title "can n^2+1 unit equilateral triangles cover an equilateral triangle of side > n, say n + e" with the substantive body of "n^2 + 2 can" accompanied by two diagrams. — Preceding unsigned comment added by 2A01:E34:EF5E:4640:35DC:A78A:A81D:9CA4 (talk) 15:32, 16 September 2017 (UTC)[reply]

The question was about Nobel Prizes, though. --69.159.60.147 (talk) 22:14, 17 September 2017 (UTC)[reply]

Infinity

Jean-marie Adragna Vancouver B.C Canada

Everybody thing at the infinity at the space in expansion. For my the description of the Infinity is the ( The wave of the Big-Bang forever increase ) Sorry but I don't have any background in science ,i this possible the somebody told me if is possible For my ( fiery ). Sin cerement J-M.A — Preceding unsigned comment added by 70.79.181.150 (talk) 14:57, 16 September 2017 (UTC)[reply]

Yes, there are many infinities. There's infinitely large, infinitely small, infinitely forward in time, and infinitely backwards in time, for example. You might also be interested in the infinite worlds hypothesis. StuRat (talk) 15:06, 16 September 2017 (UTC)[reply]

Some people regard "infinitely small" as a contradiction in terms. The usual term is Infinitesimal. Mathematically, there is a hierarchy of infinities (see Stu's link above). For example, there are more real numbers than there are whole numbers, but the number of fractions is the same as the number of whole numbers. Dbfirs 16:40, 16 September 2017 (UTC)[reply]

But no matter how you slice it, "infinity" is not a quantity, it is not a number. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:33, 16 September 2017 (UTC)[reply]

It's actually a cardinality. Dbfirs 19:36, 16 September 2017 (UTC)[reply]

Yes, there are different "cardinalities" of infinity. Hence the terms "countably" infinite vs. "uncountably" infinite. But infinity is infinity. As Carl Sagan said, no matter how large a number you can imagine, you are no closer to infinity than is the number 1. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:58, 17 September 2017 (UTC)[reply]

Did you read the article on cardinality? Dbfirs 06:25, 17 September 2017 (UTC)cardinality[reply]

The term "infinitesimal", which is used to mean "infinitely small", is essentially a way of saying "infiniteth", as compared with "tenth" or "hundredth" or "thousandth".[6] ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:07, 17 September 2017 (UTC)[reply]

Nothing is infinite (with one exception). Everything is by design or definition infact finite as a concept of science. The only exeption is the literal Nothing in Sense of empty space which is the only "thing" that can be regarded as infinite without braking our laws of physics. --Kharon (talk) 03:21, 17 September 2017 (UTC)[reply]

Or breaking. But braking works too. :) And if space is "finite but unbounded" then your premise remains true. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:00, 17 September 2017 (UTC)[reply]

The metric expansion of space should be braking, but isn't, so the Americans are apparently the only ones to put the brakes on something metric. :-) StuRat (talk) 04:29, 17 September 2017 (UTC) [reply]

Ofcourse i meant Breaking. Im German but my englisch was always very, very good. No idea how that got so wrong in my head - or out of to be more precise. I promise I'll take more care for my writing. --Kharon (talk) 05:06, 18 September 2017 (UTC)[reply]

I'll give you a break and assume your misspelling and improper capitalization of "English" was intentional. :-) StuRat (talk) 16:49, 18 September 2017 (UTC) [reply]

What's the diff between a straight-A student, her teacher, and Ford Proving Grounds ? One breaks the curve on a test, the next curves the test on a break, and the last tests the brakes on a curve. StuRat (talk) 16:43, 18 September 2017 (UTC) [reply]

Empty space is not literally nothing, neither ontologically nor physically. See virtual particle. μηδείς (talk) 20:50, 18 September 2017 (UTC)[reply]

What does D. Œ. A. V. stand for?

In working on the history of glaciology, I'm finding references to "D. Œ. A. V.", such as this: "Le succès des sondages de 1899 encourageant les plus grands espoirs pour la réussite du levé complet par la même voie, d'un profil transversal du glacier, le Comité central du D. Œ. A. V., qui avait subventionné les premiers travaux, consentit avec la plus louable munificence à faire les frais d'une nouvelle campagne de sondages dans ce but." which Google translates as "The success of the surveys of 1899, which encouraged the greatest hopes for the success of the complete survey by the same route, of a transverse profile of the glacier, the central committee of the D. Œ. A. V., which had subsidized the first works, consented with the most laudable munificence to pay the cost of a new survey campaign for this purpose." I also see this abbreviation in some old citations. Can anyone tell me what it stands for? The "Œ" quite probably stands for "Österreich" or some variation, since we're talking about the Alps; the A might derive from the Alps. Googling the abbreviation and searching Google Scholar for the cited papers hasn't gotten me anywhere. Any other way to find out? Mike Christie (talk - contribs - library) 16:24, 16 September 2017 (UTC)[reply]

Possibly Deutscher und Österreichischer Alpenverein. Cheers ✦ _hugarheimur 16:46, 16 September 2017 (UTC)[reply]

That's sure to be it. Thank you very much! Mike Christie (talk - contribs - library) 16:50, 16 September 2017 (UTC)[reply]

D. Œ. A. V. and D.Œ.A.V. now created as redirects. Nyttend (talk) 23:24, 17 September 2017 (UTC)[reply]

Atmospheric pressure

My Thermodynamics professor drew a free-body diagram for a lid being lifted by boiling water in the pot below. Applying downward force is gravity and atmospheric pressure, he said, while vapor pressure provides the lift. But doesn't the air inside the pot provide a lift as well due to an equal amount of atmospheric pressure as the air above? Thank you. Imagine Reason (talk) 16:49, 16 September 2017 (UTC)[reply]

It could be that your professor is assuming that water vapor has displaced all the air in the pot. Your professor is the best authority on the assumptions s\he has made in his/her model; this would be a good question to ask him/her.--Wikimedes (talk) 17:05, 16 September 2017 (UTC)[reply]

Until the lid is lifted, the gas underneath it should be at atmospheric pressure plus the water vapor pressure. So yes, the atmospheric pressure on both sides of the lid cancels out. StuRat (talk) 17:13, 16 September 2017 (UTC)[reply]

Since the sides of the pot are not involved in the scenario, should I assume that the lid has been lifted? In that case, will the vapor have completely displaced all the air? Thank you. Imagine Reason (talk) 23:13, 16 September 2017 (UTC)[reply]

After a little more thought, I see it this way: If the water is boiling, it means that the gas above the water in the pot is at (or less than) the vapor pressure of water for the temperature of the water. On the stove top, heat is put in until the water temperature rises to the point where this pressure starts to push off the lid. This upward pressure is equal to the downward pressure on the lid caused by gravity acting on the lid and the external gas pressure on the lid, which is atmospheric pressure.

Another way to look at it is that the gas inside the pot is isolated from the atmosphere outside the pot (and the weight of the ~100km column of air that causes atmospheric pressure), so there's no reason to expect atmospheric pressure to be a factor inside the pot.--Wikimedes (talk) 00:42, 17 September 2017 (UTC)[reply]

The Temperature vs. specific entropy diagram of Steam

The air is not displaced. Infact it will not be displaced but to the contrary remain and get saturated (with steam) in dependence of its temperature and pressure, in an multicomponent (Water and Air (Nitrogen, Oxygen Argon Carbon dioxide etc.)) Vapor–liquid equilibrium commonly named and known as "Steam" (See Steam T-s-diagram in added picture on the right). --Kharon (talk) 03:00, 17 September 2017 (UTC)[reply]

Ask the professor, but a possible simplification would start with the lid directly atop the water with no air under it, and with no air dissolved in the water. As it happens, in real life before boiling starts there will be air under the lid and air dissolved in the water, but the total amount of air is small in proportion to the amount of steam that is generated, so its effect is mathematically negligible in a sufficiently large container.-Arch dude (talk) 04:03, 17 September 2017 (UTC)[reply]

I don't want to ask the professor because he introduced concepts like gage pressure without much explanation and refused to answer a student who asked about it. He didn't mention anything about cooking a vacuum. Also, if the atmospheric pressure from the air inside the pot is negligible, then so is the atm outside, no? Imagine Reason (talk) 04:46, 17 September 2017 (UTC)[reply]

You are at the start of thermodynamic lessons obviously, else you had not asked your question. It will be answered later on. You will learn to use the Gas constant, learn about Bernoulli's principle etc. Your professor probably tried to tease you to get you interested and wanting to learn. You still have to learn, to understand, which obviously seems much more boring then trying to bend your mind around it with what you already believe to understand. Have some patience, do your lessons and you answer this question and other new ones yourself. --Kharon (talk) 05:40, 17 September 2017 (UTC)[reply]

If the atmospheric pressure from the air inside the pot is negligible, then the atmospheric pressure from the outside should be neglected as well, no?

It's not really a matter of atmospheric pressure inside the pot being negligible (i.e. so small it can be ignored). Atmospheric pressure is caused by the weight of the atmosphere. After the lid is put on, the gas inside the pot is isolated from the weight of the atmosphere, so it doesn't make sense to use the weight of the atmosphere to model the pressure inside the pot (except perhaps when the lid is first put on and nothing has changed inside the pot yet). Outside the pot, however, the weight of the atmosphere is still pushing down on the lid (even after the pot heats up), so atmospheric pressure must be taken into account.--Wikimedes (talk) 19:43, 17 September 2017 (UTC)[reply]

The partial pressure contribution of the air molecules is negligible because they are a negligible percentage of the total gas in the pot after it commences boiling. Essentially all of the gas is steam, as the steam molecules increase while the number of air molecules remains fixed. ("air molecules": the usual mix of gases. "steam molecules": H₂O). -Arch dude (talk) 20:34, 17 September 2017 (UTC)[reply]

Forgive me for still not understanding. Right after you close the lid, the air inside the pot is lifting the cover with 1 atm of pressure. Then you apply heat to the contents of the pot. The air inside then should contribute more than 1 atm of pressure now, thus canceling the weight of the air on top of the cover. Imagine Reason (talk) 03:28, 18 September 2017 (UTC)[reply]

When the air inside the pot is contributing more than 1 atm of pressure, it no longer exactly cancels the external atmospheric pressure. At this point you have to consider them as separate forces acting on the lid, rather than ignoring them.--Wikimedes (talk) 05:09, 18 September 2017 (UTC)[reply]

See Dalton's law. If the gas under the lid is 50% air and 50% steam, then the equilibrium pressure of the mixture will be that of the steam, which will be given by the Vapour pressure of water. HTH, Robinh (talk)

Feynman Lectures. Exercises. Exercise 14-15 JPG

. .

...
14-15. A certain spring has a force constant k. If it is stretched to a new equilibrium length within its linear range, by a constant force F, show that it has the same force constant for displacements form the new equilibrium position.

— R. B. Leighton , Feynman Lectures on Physics. Exercises

In Solutions they write: Let the spring is stretched by the force F₀. The displacement can be found from F₀ = k x₀. Let's stretch the spring more by x. Then new force is : k(x₀ + x) = k x₀ + kx = F₀ + kx. So extra force is the same as if the spring is stretched from undisturbed state.

But the Solution' author uses k=const from beginning of the proof. If k is some function of x, and F = k(x)•x only for very small x, then how to prove the exercise? In other words, we have the undisturbed spring length L₁ and we know the law for it: F_I = k₁ x for small x. And we have the stretched spring length L₂ and the law F_II = k₂ x for small x. From these two laws it is clear that F≠k₂(L₂ - L₁)≠k₁(L₂ - L₁). Username160611000000 (talk) 19:02, 16 September 2017 (UTC)[reply]

If a spring has a force constant, then k should be a constant.

It is ridiculous that we are asked to prove k = const, and this is given under the statement of the problem. No, I think we should not use k = const. Besides the exercise is to Lectures 13,14 "Work and Potential Energy".Username160611000000 (talk) 08:14, 17 September 2017 (UTC)[reply]

I think you're being asked to prove the constant is constant from the new position. Yes, it's pretty elementary, I mean, k(x+dx) - kx = kdx or something. They can't all be stumpers. Wnt (talk) 18:15, 17 September 2017 (UTC)[reply]

If k increases in the spring stretched under force, it seems apparent the new k will be the "force constant" for very small deviations, if the function derivative is continuous. i.e. FII = k2(x +- delta x) for small delta x. Wnt (talk) 19:35, 16 September 2017 (UTC)[reply]

It is not impossible, e.g. k = sin (x). Then for x = 0.5π, 1.5π etc. the derivative = 0 and so k(x) = k(x+dx).Username160611000000 (talk) 08:14, 17 September 2017 (UTC)[reply]

yeah, but ... if k = 0 at 1.5 m, how is the pendulum going to stay there when it's under some continuous force? Also, this isn't really an exception = for this FII = 0 (x +- delta x). For small deviations it's not a spring, but it's not an exception. Wnt (talk) 09:34, 17 September 2017 (UTC)[reply]

ancient glacial features

It's easy to point to valleys that were shaped by glaciers in the last million years. But what are the oldest known glacial features? Are there glacial valleys in continents that were near the poles in Mesozoic times? —Tamfang (talk) 20:35, 16 September 2017 (UTC)[reply]

Note that land didn't need to be near the poles to have glaciers. Glaciers covered much of Europe and North America in the most recent ice age, for example. StuRat (talk) 20:53, 16 September 2017 (UTC)[reply]

See here. Count Iblis (talk) 21:17, 16 September 2017 (UTC)[reply]

Global glaciations and atmospheric change at ca. 2.3 Ga. Count Iblis (talk) 22:14, 16 September 2017 (UTC)[reply]

As others have noted about, we have seen signs of ancient glaciations going back billions of years. That said, features like carved valleys will be eroded and changed over time. Given 10-20 million years or so, most features won't be easily recognizable as glacier derived except by detailed study from experts. Dragons flight (talk) 09:11, 17 September 2017 (UTC)[reply]

September 17

Vaccination boosters

Why are adults, other than those at high risk, not offered a booster for the chickenpox vaccination if the dose given at childhood doesn't last a lifetime? 90.198.254.50 (talk) 09:08, 17 September 2017 (UTC)[reply]

You didn't say where but I see from your ip it is the UK. My guess is because the NHS is being stretched far too far by austerity and have far more important things to spend their money on. But even if it was offered it probably wouldn't be worth it till people were 60 and their immmune systems started to get weaker and they got more liable to get shingles, there's enough chickenpox around still anyway to keep the immune system primed normally. If we were halfway towards eradicating chickenpox it probably would be worthwhile doing booster shots more generally until it was totally eliminated - but that isn't viewed as any sort of important target at the moment. There have been efforts to eliminate measles but those have been stymied by stupidity and ignorance in the developed world in refusing the MMR vacine. Dmcq (talk) 12:30, 17 September 2017 (UTC)[reply]

In the case of testing for bowel cancer every patient is written to every two years between the ages of 65 and 70 I believe, and the letters say that those over 70 are welcome to request a self - test pack. So far as I know, testing and vaccination for common diseases is given on request - I wouldn't like the OP to think (s)he can't have a vaccination if (s)he wants one. If you've had shingles once you can get it again, and vaccination does not provide complete protection. 82.14.24.95 (talk) 12:54, 17 September 2017 (UTC)[reply]

Varicella vaccine is given two times not just one. It is often given on the same schedule (1 year and 4-6 years) as the vaccinations against measles, mumps and rubella (MMR). There are even combined quadrovalent vaccines for these diseases. The third adult (or booster) dose is not given by the same reason as for MMR: it is generally considered pointless. The vast majority will remain immune for life after two doses. So, returns are diminishing quickly for any additional dose. Ruslik_Zero 18:59, 17 September 2017 (UTC)[reply]

The Zoster vaccine article discusses the various US, UK, and European recommendations. It's basically a high-dose chickenpox vaccine for adults, either over 60 or at risk. -Arch dude (talk) 20:22, 17 September 2017 (UTC)[reply]

There is a confusion here with zoster vaccines. They serve a different purpose and are give to those who are already infected. The question was about a vaccine to prevent the primary infection. Ruslik_Zero 20:28, 17 September 2017 (UTC)[reply]

Our varicella vaccine article seems to me to discuss the issue well. What do you think is not adequately answered by the article? --47.138.161.183 (talk) 05:41, 18 September 2017 (UTC)[reply]

Well I personally know of at least one person that contracted shingles just weeks after receiving a chicken-pox/zoster vaccine a few years back so (just a guess but) maybe that sort of occurrence has become common enough to motivate health officials to refrain from recommending the scheduling of that shot for all but the highest risk categories? My overall take on the whole thing basically this: a correctly prepared and properly stored vaccine administered at the right time to a person whose state of health is sufficiently "just so" will most likely experience positive-to-neutral results, otherwise there is always the inherent risk that comes with injecting foreign (and potentially dangerous) agents into one's system. And you can't necessarily rely on the conclusions reached in peer-reviewed studies because most are directly/indirectly funded by the health-care industry itself which is naturally in the business of selling stuff and minimizing legal liability. So look at the raw data and be very wary of interpretive statistics. For example, when the question comes up as to why adults are not typically offered a booster for the chickenpox vaccination, suppose you eventually come across papers such as this one [7] (which unequivocally asserts that there is "no evidence of a statistically significant change in the rate of increase [of shingles onset] after introduction of the varicella vaccination program") take careful note of the the highly-presumptive interpretation and then draw your own conclusions accordingly using just a bit of logic and reasoning. 73.232.241.1 (talk) 12:57, 19 September 2017 (UTC)[reply]

Exactly what in all that conspiracy theory contradicts what I said above? I said there was enough chickenpox around to keep up the immune system primed normally. However older peoples immune system can be weaker and need a bigger jolt to keep in order. Dmcq (talk) 17:30, 19 September 2017 (UTC)[reply]

Is it true to say that "in every disease the entire body is involved"?

I'm reading now a medical book which stays "in every disease the entire body is involved". Now, I am not sure if every disease involves every system in the body. 93.126.88.30 (talk) 15:09, 17 September 2017 (UTC)[reply]

Yes, that does seem a bit silly. Acne doesn't normally effect your pancreas, for example. Perhaps they could say "potentially could become involved", as an infection that starts from, say, acne, could eventually spread to, say, the pancreas. StuRat (talk) 15:45, 17 September 2017 (UTC)[reply]

What do you mean by "medical" here? It's clearly starting from the point of holistic medicine, but the woo woo is strong is such fields and the risk is that it can easily diverge into nonsense such as homeopathy. Discussion and rational coverage of such fields is forbidden at WP, and any detailed coverage of them is just blanked with a redirect to a single simple bucket of ridicule, as if all are equally unworthy of consideration. Andy Dingley (talk) 15:55, 17 September 2017 (UTC)[reply]

If I get a severe cold or flu, it certainly "seems like" the entire body is involved, but to turn that experience into some kind of generalized truism seems highly suspect. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:08, 17 September 2017 (UTC)[reply]

The OP needs to cite title, author, edition and page if he wants any sort of real help. And presumably the author has defined his terms and that sentence does not sit alone, but is found within an argument. I wouldn't come here with the sentence from one of my favorite books, "Now it's broken and needs to be fixed", and expect comment if I didn't give the context so that editors could make sense of its significance. μηδείς (talk) 17:46, 17 September 2017 (UTC)[reply]

Pedantic and off topic.

The following discussion has been closed. Please do not modify it.

Not everything requires context. "Elephants are a kind of fish" is just plain wrong, regardless of context. On the other hand, "whales are a kind of fish", could be correct, in some contexts, like "According to the archaic classification system of X, whales are a type of fish". StuRat (talk) 19:24, 17 September 2017 (UTC)[reply]

But elephants are fish, at least cladistically... it's in the lead section of the article. Wnt (talk) 19:39, 17 September 2017 (UTC)[reply]

Yes, Wnt, I had to laugh when Stu laid that whopper. Stu also thinks a graphic from the US Forestry Service hosted at the Boston Globe showing the reforestation of the Eastern US since 1900 is right-wing hate speech. Oh, well. A little knowledge is a dangerous thing. μηδείς (talk) 20:39, 17 September 2017 (UTC)[reply]

No, your misrepresentation of what it said was right-wing misinformation, not hate speech. StuRat (talk) 20:49, 17 September 2017 (UTC)[reply]

Well, no, that's not what you said either, but I knew I could count on you to take the bait. Here's the link to your original suggestion that a Forestry Department report at the Boston Globe was misinformation from a right-wing website. You have to understand, Stu, that some of us are actually credentialled in some of the fields we comment on, and know what sources to go to to prove our point, rather than just immediately answer every question posted on these desks based on some Faygo-intoxicated guess. μηδείς (talk) 01:41, 18 September 2017 (UTC)[reply]

That's exactly what I said and I stand by it. If you want to debate it, that was the place, not here. That link DOES NOT SAY, AS YOU CLAIM "According to the trend from 1850 to 1920, according to this government map, the US would be entirely void of trees at this point." That's you just making crap up. StuRat (talk) 01:56, 18 September 2017 (UTC) [reply]

I'm all for correcting people to be excessively pedantic, but not just to make a case against them (I'm not directing this at any particular party). We should return to the topic. Wnt (talk) 02:17, 18 September 2017 (UTC)[reply]

Agreed. Hatted. StuRat (talk) 02:26, 18 September 2017 (UTC) [reply]

I think the idea is pretty much correct -- at least, if we take "involved" to mean potentially affected during the future course of disease, rather than noticeably damaged. For example, acne might cause dermatillomania, depression, and apparently on some famous occasions can lead to septicemia and even death. Obviously, an intact and well-functioning immune system should keep the acne contained, but then again a truly well-functioning immune system probably ought to have stopped the acne to begin with.

I would anticipate that the moral of the story might be the need for a complete medical history... no matter what. Wnt (talk) 18:11, 17 September 2017 (UTC)[reply]

The difference between "involved" and "could potentially become involved" seems rather critical in a medical context. If a doctor said "your pancreas is involved" instead of "could potentially become involved", that would be malpractice. StuRat (talk) 19:21, 17 September 2017 (UTC)[reply]

Every disease might be an overstatement, but the great majority of diseases activate either a stress response or the immune system, both of which cause changes pretty much throughout the body. Looie496 (talk) 19:06, 17 September 2017 (UTC)[reply]

"normally closed" relays

Please could you tell me what consumer electronics are likely to contain "normally closed" relays. I know microwaves contain "normally open" relays which switch to "normally closed" when power is applied. Thanks for your time. — Preceding unsigned comment added by 36.85.29.51 (talk) 18:17, 17 September 2017 (UTC)[reply]

Some type of overheat switch which opens when the device overheats, then you hit the reset button to close it again ? For example, a hair dryer might have this. StuRat (talk) 19:11, 17 September 2017 (UTC)[reply]

I think my first electronic experimenter kit as a kid had at least one of each ... I would make those things buzz... the FCC probably had a van out looking for me. ;) Wnt (talk) 19:43, 17 September 2017 (UTC)[reply]

An un-interruptable power supply (UPS) might have a NC relay on its mains input. The mains will be connected to the UPS output unless the UPS actively decides otherwise and disconnects the mains by energizing the relay coil. (In fact, the relay will probably be SPDT with the mains on the NC input and the inverter on the NO input) -Arch dude (talk) 20:17, 17 September 2017 (UTC)[reply]

Sounds like you already got some good answers, but to be clear, most general purpose relays have both a normally open and normally closed pin making it a SPDT (single-pole double-throw) switch. As far as applications, they're all over the place. A magnetic door lock for example, and as mentioned anything that during a power loss, you want it to close a connection (probably to some other system), so you see them a lot in safety type applications where you need a "cut-off" of some sort. As just a fun fact, you can use a DPDT relay to make a forward / reverse controller for a motor. When the relay is activated, the motor goes forward, when de-activated, it reverses the polarity, see these in kid's electric cars a lot. Drewmutt (^ᴥ^) talk 02:13, 20 September 2017 (UTC)[reply]

Walking/running downhill energy consumption

Walking/running downhill: what consumes more energy for a human?--Hofhof (talk) 21:08, 17 September 2017 (UTC)[reply]

Considering the high amount of energy we burn just standing still, whatever gets you to the bottom fastest would "stop the clock" and thus reduce the total amount of energy burnt for the trip. That would be running. However, if you phrase the Q differently, such as "What method will get you to the bottom of the hill and consume the least energy, over the course of an hour", then a slow walk would probably be better, since the clock no longer stops when you get to the bottom. The temperature would figure into it, though. If it's so cold that mere walking results in shivering, then running may conserve energy. StuRat (talk) 21:14, 17 September 2017 (UTC)[reply]

There are actual sources for this on line. These are rather basic: http://healthyliving.azcentral.com/burn-many-calories-running-downhill-18961.html https://www.verywell.com/how-many-more-calories-do-you-burn-walking-uphill-3975557. Both show that it is easier going downhill either way, and you save about 6% walking downhill. The amount saved depends on the incline, and past a certain point the calories saved decreases as the slope gets steeper. Neither of those sources gives any charts or formulae or much in the way of detail, but if the popular press is covering this, I expect their are more formal studies as their sources. μηδείς (talk) 01:33, 18 September 2017 (UTC)[reply]

The steepness is also relevant if you're having balance problems: if it's so steep that you risk falling down the hill, your effort to balance yourself and stay on your feet might take a bit of energy, and of course you're likely to be steadier (and thus require less balancing effort) if you're going more slowly. Of course, if you fall down on a steep slope, you may expend no energy (other than the basal metabolic rate) in descending the rest of the hill, but that might cause the expenditure of energy for other purposes. Nyttend (talk) 01:55, 18 September 2017 (UTC)[reply]

According to the laws of physics downwards should be far easier and with lower energy consumption. However it seems to be the opposite, with walking, in reality. Not because of physics but because of lake of training, humans are not used to constantly decelerate bipedal motion, thus usually very ineffective in doing that and thus, physically paradox, need more energy walking downhill. --Kharon (talk) 05:15, 18 September 2017 (UTC)[reply]

I used to do a lot of hillwalking and the descent phase always gave me sore quadriceps femoris muscles. A lot of walkers get knee pain from descents, [8] a condition called Iliotibial Band Syndrome. It's the stress of controlling the speed of your footfall, a problem that is going to be worse if you're running; more speed equals greater kinetic energy. I have seen people lose control when descending too fast, a jog turns into enormous strides, turns into head-over-heels tumbling. Quite comical unless you meet any large rocks on the way. Alansplodge (talk) 10:14, 18 September 2017 (UTC)[reply]

When I climbed Mount Kinabalu on the standard guided tourist route from Timpohon Gate, I had a similar experience. Ascending was fairly tiring. Normally done over two days which is what I did, I think that's mostly because if you want to do it over 1 day you have to make good time and also may not reach the summit at the best of times (it can cloud over sunrise) and also for commercial reasons. Unless you're fairly fit and making good time, on the first phase you'll have porters speeding past you with large gas bottles etc on their backs, which at very least means you probably aren't going to moan when you see the food prices in Laban Rata (even despite recognising the porters aren't getting much from that). The second phase from Laban Rata is not as long although I think steeper on average (the vertical ascent is less than the first phase but the distance is even less) and with more tricky terrain and also generally done mostly when it's dark and given the altitude you may get mild altitude sickness. The descent follows on from the second phase of the climb (i.e. the total climb is over 2 days). From memory, the descent is not quite so tiring overall but boy can you feel it in the legs as most information guides note [9], probably for days afterwards. And this was as a ~19 year old albeit not that fit. IIRC my travel companion actually read stuff suggesting that some people found jogging or running down was actually kinder on the legs, but it's not something I researched myself. This source for example [10] suggest other things and on another issue it notes that doing it may seem to reduce pain on descent, but actually increase the required recovery time. Nil Einne (talk) 12:34, 18 September 2017 (UTC)[reply]

User:Kharon, the sources I cited said you always expend less energy walking or running down hill, but that at steeper slopes the energy saved is less because the stride becomes irregular. At some point you are simply climbing downhill, and using your legs to break a fall, but at that point it's not really walking or running anymore.

User:Alansplodge, one of the sources actually recommends running down hill as a good way to build quadriceps muscle, hence your soreness on doing this--its a different type of exercise. μηδείς (talk) 20:44, 18 September 2017 (UTC)[reply]

Note to self - always read the references that you link :-) Most older hillwalkers in the UK use trekking poles in an attempt to reduce the impact on their knees. Another point is that when planning a route using Naismith's rule, you add time for ascent (usually 1 minute for every 10 metres up) but don't add time for descent. Alansplodge (talk) 10:13, 19 September 2017 (UTC)[reply]

Perhaps we should start using Tobler's hiking function instead of Naismith, though the spike in its graph makes it look rather implausible to me. AndrewWTaylor (talk) 16:28, 19 September 2017 (UTC)[reply]

But if you would use an ebike that has an recuperation capable controller, you could even fill up your batteries on the way. So be smart, buy your very own ebike asap!:D --Kharon (talk) 21:49, 19 September 2017 (UTC)[reply]

Civil engineering asset management

Is asset management and ongoing maintenance in civil engineering generally more closely aligned to civil engineering design and consulting as opposed to construction? 90.198.254.50 (talk) 22:30, 17 September 2017 (UTC)[reply]

Civil engineering is a huge field of Work and civil engineers are typically "jack of all trades" since they have to recon with everything that may happen to their construction, design or planning. So ofcourse asset management and maintenance seems to have no direct connection to design, construction and its planning but since it usually is an essential part of all that is designed, constructed and planned, they have to learn how that is done too. --Kharon (talk) 05:33, 18 September 2017 (UTC)[reply]

September 18

Disability-affected life years from falls

According to this map, in 2004, Iraq had by far the world's worst statistics for disability-adjusted life years related to Falling (accident). It accurately reflects its source, according to which, 50 of the 192 countries tracked had a score of 200+, with 28 being 200-299, 13 being 300-399, 6 being 400-499, and the top three countries being Yemen at 524, Sri Lanka at 649, and Iraq at 1002. Why would Iraq have such horrid statistics? Is this merely an artifact of damage to the medical infrastructure during the ongoing war? It seems a bit extreme, especially since Afghanistan and Somalia, which both had less medical infrastructure in 2000 than Iraq, were tied for eighth at 417, and another country with a war during the data collection, Liberia, had just 133. Nyttend (talk) 01:53, 18 September 2017 (UTC)[reply]

ISIS has a habit of throwing people off roofs (homosexuals): [11]. If those are included in the data, that might explain it. StuRat (talk) 02:06, 18 September 2017 (UTC)[reply]

I strongly doubt that ISIS is at all relevant, since this map relies on figures published in 2004. Nyttend (talk) 02:26, 18 September 2017 (UTC)[reply]

Good point, but such violent practices did not begin with there with ISIS. Their predecessors were also quite violent. StuRat (talk) 02:29, 18 September 2017 (UTC)[reply]

And they were really good at making it look like an accident? Of 19 (talk) 22:37, 18 September 2017 (UTC)[reply]

Somehow I doubt if there was much of an investigation when they found a body on the street under a tall building with fall injuries there, unless the victim was a friend or relative of whoever was in charge at the time. StuRat (talk) 23:01, 18 September 2017 (UTC)[reply]

Those awful DALY things from the beginning included an absolutely arbitrary curve claiming that young adults are more important than anybody else; they were then immediately used to show that more funding emphasis should be put on treating diseases of young adults. Think of a slavemaster prioritizing his stock. Scientific fraud is almost too kind a description for this.

That said, the article says that some sources have stopped using the arbitrary curve (though this indeed is its own kind of arbitrary decision, and another value judgment ...) The figure points straight at an Excel spreadsheet as its source ... it might be worth looking into. My thought is that if Iraq is a war zone that has chased out all the old and young people, it may have more people per capita, by DALY standards, than other countries. Wnt (talk) 02:14, 18 September 2017 (UTC)[reply]

According to http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0131834, in Iraq the majority of falls occur in houses, and the majority of victims are women. Only a small fraction are fatal. The causes are not clarified, but I suspect that one of them is the fact that the great majority of Iraqis sleep on their roofs during most of the year -- so they spend a lot of time going up and down stairs while sleepy. Looie496 (talk) 02:53, 18 September 2017 (UTC)[reply]

Holy.... what's wrong with Motherland. Do they think they're cats or something. "See, Ivan, 5 storeys isn't high. Hold my beer..." 78.53.109.203 (talk) 03:16, 18 September 2017 (UTC)[reply]

Stud finder

Yesterday I had to do some assembly work that required drilling into the wall, and my fancy-schmancy $50 stud finder indicated a wall stud just where I wanted one to be, but when I drilled into that "stud", there was only drywall with nothing behind it! What could have caused this gadget to give me the false positive, and (more importantly) how can I prevent this from happening again? 2601:646:8E01:7E0B:3DB7:8D6E:A762:14CC (talk) 07:47, 18 September 2017 (UTC)[reply]

1. How some work: http://www.nytimes.com/2001/04/12/technology/how-it-works-detectors-can-find-just-the-right-spot-to-drive-that-nail.html

2. How to lessen chance of false positives: http://zirconcorp.custhelp.com/app/answers/detail/a_id/28/~/is-the-stud-you-found-really-a-stud%3F-minimize-false-positives. 129.55.200.20 (talk) 13:09, 18 September 2017 (UTC)[reply]

Thanks! So the key is to look for regular intervals, right? 2601:646:8E01:7E0B:EDA1:6DA2:2F4C:8E0A (talk) 05:43, 19 September 2017 (UTC)[reply]

Most stud finders find a difference, not a stud. If there is a 4 inch air gap next to a 2 inch air gap, that is a difference. It will beep or light up when you are over the difference. When you find a stud, the indicator goes off on each side of the stud. Mark both sides. It should be about 1.5 to 2 inches wide, depending on what is used for the stud. Move to both sides. You should find another stud on each side about 14 or 15 inches away. They are normally set 16 inches to the center of each stud, leaving about a 14 to 15 inch gap between studs. If you find that, you likely have a stud. If you don't, you need to keep looking. Also, don't assume there is a stud. When people do work themselves, they do all kinds of silly things like putting up drywall without any studs behind it. 209.149.113.5 (talk) 13:02, 19 September 2017 (UTC)[reply]

Most studs in your house are vertical and run from floor to ceiling. Therefore, you can cross-check the stud location by looking for it at several heights on the wall. If these separate heights disagree, be suspicious of a false reading or an unusual situation. Find the same stud from both sides at each height. -Arch dude (talk) 14:48, 19 September 2017 (UTC)[reply]
It's worth noting that most stud finders out there are "edge" stud finders. As previously mentioned, they sense change, so it's important that when you initially start scanning you do so in place known not to have a stud, for calibration. Or, you can do as I do and use a strong magnet to find the screws that anchored the drywall to the stud. Drewmutt (^ᴥ^) talk 02:21, 20 September 2017 (UTC)[reply]

Do tree trunks really bend at 32 miles per hour?

That's what the Beaufort scale implies. How much could a deciduous trunk bend before breaking? (though in some cases it would uproot before that happens). Why is the Beaufort scale 12 description "devastation" while the Category 1 hurricane description doesn't seem as bad? (and Floridians even drive over bridges in that). Sagittarian Milky Way (talk) 09:59, 18 September 2017 (UTC)[reply]

The best reference I could find is Trees, regardless of size, all break at the same wind speed. Here’s why. from the American Association for the Advancement of Science.

Anecdotally, a youth activity centre in Essex used to have a wooden abseiling wall attached to an old sweet chestnut coppice (before the days of health & safety obsession) which had three large trunks each of more than 2 metres circumference. Even in a light breeze, the top platform which sat between the three trunks would sway rather alarmingly and had to be closed on windy days. Although the trunks weren't bending visibly, the swaying motion could only have been caused by the flexion of the trunks. Alansplodge (talk) 10:35, 18 September 2017 (UTC)[reply]

That article actually says the wind speed required does vary a bit, but not by much, for the factors they considered (wood elasticity and tree size). They also didn't look at the effects of leaves. A tree with lots of leaves (that stay on during the storm) will absorb more wind than a leafless tree. And some tree forms, like palm trees, with only a small clump of leaves at the top and a massive trunk, seem like they evolved to resist tropical storms better, too. StuRat (talk) 23:14, 18 September 2017 (UTC)[reply]

Tree trunks would bend at any wind speed, just not noticeable so at low speeds. For that matter, any material would bend, with crystals bending perhaps the least, but still a tiny bit. Buildings bend and sway, too. StuRat (talk) 23:04, 18 September 2017 (UTC)[reply]

Presumably the person who extended the scale to land meant "visible to the naked eye" when he said whole trees in motion = 7, large branches in motion = 6. In our tropical storms I'd been so distracted by trying to get "air" from sprinting downhill with umbrellas and seeing how many degrees I could lean that I forgot to test the whole trees in motion thing. Sagittarian Milky Way (talk) 23:49, 18 September 2017 (UTC)[reply]

Yes, the point of those notes is that a layman can assess the wind speed without any specialist knowledge or technical equipment. Out article says it was adapted "in the 1850s". Alansplodge (talk) 10:18, 19 September 2017 (UTC)[reply]

activated charcoal effect on carbohydrates, proteins and fats

The activated charcoal article specifically states that it does not work on alcohol. What about the other macronutrients; carbohydrates, sugar/glucose, proteins and fats? Does it bind to those and prevent their absorption by the gastrointestinal tract? I've tried researching this on my own but I can't seem to find an answer one way or the other. I realize that carbohydrates, proteins and fats are not poisons but how would activated charcoal differentiate between a poison and a macronutrient? I would assume that it would bind to all of them. Thanks for your help. — Preceding unsigned comment added by 62.16.22.76 (talk) 11:32, 18 September 2017 (UTC)[reply]

You didn't say so, but are you asking because of one of the activated carbon diet and/or "detox" fads? If so, I'd suggest you save your time and money. By weight, in a pure solution, you may need 10 or 100 times as much activated charcoal as the substance you want to adsorb before you can capture most of it. For small quantities of poison, that may not be too hard to accomplish, but for bulk foods the corresponding quantities involved are likely to be impractical or even dangerous. Dragons flight (talk) 13:48, 18 September 2017 (UTC)[reply]

I'm not following any kind of fad diet, I was just curious when reading the article because the article specifically mentions activated charcoal does not work on alcohol but omits to mention any of the other macronutrients. I wondered if that was because activated charcoal does indeed work on the other macronutrients, so I searched for answers but found nothing helpful. Still curious, I then came to the reference desk to ask in the hope that someone more knowledgeable and better at finding references than me could shed some light onto the question. I hope that is okay. 62.16.22.76 (talk) 14:38, 18 September 2017 (UTC)[reply]

The "Mechanism of action" section of that article is woefully unreferenced, if some kind editor has time to take a look at it. shoy (reactions) 15:05, 18 September 2017 (UTC)[reply]

I doubt if much of any of those would pass through an activated charcoal filter. They would quickly clog it. As for consuming activated charcoal, you'd need a huge quantity to bind to all that, which would make you sick. BTW, if you want a fat binder, try Orlistat (but be prepared for "anal leakage"). StuRat (talk) 16:29, 18 September 2017 (UTC)[reply]

Does normal charcoal have any poison absorbing properties?

I understand that activated charcoal greatly increases the surface area of charcoal to make it effective at absorbing poisons. But does normal charcoal have any poison absorbing properties? Again, I did try researching this myself but everything I found was about activated charcoal. I want to know if normal charcoal can bind to poison or not. Thanks for your help. 62.16.22.76 (talk) 11:50, 18 September 2017 (UTC)[reply]

Yes, but they work by adsorbing material onto their surface, rather than absorbing it into their bulk. Activated charcoal is just charcoal produced by a process (either thermal or chemical and thermal) which increases this surface area. Andy Dingley (talk) 12:32, 18 September 2017 (UTC)[reply]

How useful is the telescopic sight on a rifle

When shooting a rifle with a telescopic sight, the bullet will drift due to the wind and gravity to one side and down. Since it will never hit the crosshair, would it be any difference if the shooter had some binoculars attached to his face or helmet?--Hofhof (talk) 17:12, 18 September 2017 (UTC)[reply]

It will hit the crosshair. The turrets on the side of the sight allow the crosshair position to be adjusted, to compensate for bullet drop, windage etc. When the sight is 'dialed in' for the range and conditions, the bullet should go where the crosshair indicates.

Although simple "crosshairs" aren't the only form of reticle available. Some have a scale on them, so that the shooter chooses an aim point on that scale, rather than adjusting the turrets. Andy Dingley (talk) 17:18, 18 September 2017 (UTC)[reply]

Should a marksman use head-mounted binoculars he would have to sight the bead of the rife which would end up looking fuzzy at short short focal distances. The bead is also rather large and can be larger than the target at 400 yards on some rifles. Of course, he may have infinity focus binoculars – if there are such things. P.S. Why do we call them cross hairs. All my sights up until I gave up shooting used spiders web ( with the exception of a laser sight which I borrowed). Think also, that AD was over simplifying things. On a 2500 range with a 303 one need little flags all down the range to show moment to moment fluctuations in crosswind. It is nearly one and a half miles and the round takes several seconds to miss the targets I was hopefully aiming at, regardless of where the scope was pointing at. Aspro (talk) 19:07, 18 September 2017 (UTC)[reply]

For an example of actual-hair "hairs", see Mary Babnik Brown. DMacks (talk) 19:21, 18 September 2017 (UTC)[reply]

Articles: Telescopic sight, Reticle. Blooteuth (talk) 23:19, 18 September 2017 (UTC)[reply]

Can sniper rifles be automated ?

I've often thought that sniper rifles should be automated. Some reasons:

1) The shooter's movements make it difficult to maintain aim. If the operator was instead seated some distance away, or even on the other side of the world, controlling the apparatus remotely, this variable would be removed. Also, the shooter could then be hidden from snipers in the opposing army.

2) An automatic correction method could be used, where the target is painted with a laser (possibly IR, to keep it hidden), then each shot would be tracked (perhaps tracer rounds would be needed for this) and the error corrected for each subsequent shot. I would suggest 2 or 3 rifles in an array, all precisely aimed the same, yet physically isolated so as to not be affected when another fires. This would allow multiple shots in rapid succession, each correcting for the previous error, without allowing the target time to flee.

I would suspect that this setup could significantly extend the effective range, and require far less training and experience to use effectively. Also, fewer snipers would be needed, since the same one could operate weapons in multiple locations without needing to travel from location to location (somebody else could roughly position them). So, has anyone done this ? If not, why not ? StuRat (talk) 20:40, 18 September 2017 (UTC)[reply]

The US already have semi- automated sniper rifles. The operator identifies the target's thermal infra-red signature and if the target should lean against a tree, suggesting he may be there long enough for the round to reach him/her/it – gun goes off (no need to squeeze the trigger) . Should target move earlier than expected – well EXACTO will correct the trajectory in-flight. This type of technology is what your tax dollars are paying for. When the 3rd world war comes, just follow me into a cave and let Arnold Schwarzenegger and Linda Hamilton sort it all out for us, so that we can look forward to a sequel, providing of course that they win, in a real war. Aspro (talk) 21:25, 18 September 2017

Articles: Sniper, Narcissistic personality disorder, Serial killer. Blooteuth (talk) 23:07, 18 September 2017 (UTC) (UTC)[reply]

I've heard that bolt-action rifles tend to be the most accurate, with the design (not sure how, but...) being more accurate overall than semiautomatic rifles; no source, but it's something to look into. Remember that with a sniper rifle the point is being supremely accurate and delivering sufficient firepower in the perfect spot, not delivering a ton of firepower to the general area; it's like using smart bombs versus carpet-bombing. Also, "fewer snipers" — part of the point of having lots of snipers is redundancy: individual snipers are vulnerable, having lots of snipers means that you can cover the enemy from lots of angles, and eliminating one sniper doesn't do the enemy much good if he can't get rid of the rest. Nyttend (talk) 23:21, 18 September 2017 (UTC)[reply]

A couple of problems with this proposal: (1) The loss of the datalink between the operator and the rifle positions (such as through enemy jamming) will make the latter useless; (2) A remotely-controlled rifle cannot change position unless mounted on a mobile platform, and even then, such a platform cannot conceal its movements as well as a human sniper (i.e. it will be easier for the enemy to see and destroy, or at least get out of its line of fire). 2601:646:8E01:7E0B:EDA1:6DA2:2F4C:8E0A (talk) 05:41, 19 September 2017 (UTC)[reply]

This "mobile platform" could be made rather stealthy. Place it in position when no enemy is around (or perhaps they are distracted by an attack from elsewhere), put the equivalent of a ghillie suit over it, and have it move slowly enough that nobody spots the movements. No need for breaks for food, water, the toilet, etc., should then make it less noticeable over the following days, as should a lack of IR light leaking out. As for the datalink, you could do a direct shielded wire to somebody in a bunker nearby, and they could take over if jamming occurs. StuRat (talk) 17:44, 19 September 2017 (UTC)[reply]

While you're at it ... what has kept them from putting sniper rifles on drone aircraft? I mean, obviously the bombs are more powerful, but having some drone far away -- potentially solar powered, even -- making virtually unlimited shots would be damned demoralizing, emphasis on the damned. Wnt (talk) 08:59, 19 September 2017 (UTC)[reply]

That's the Autonomous Rotorcraft Sniper System. There are technical issues to be dealt with. To shoot a bullet instead of a missile implies stronger recoil. You'll need a more solid base. You'll need a bigger drone. This defies the purpose of shooting bullets for having a small drone. Since bullets are not guided, your sniper drone would also need to be more stable in flight. (also implies bigger drone, with maybe a longer wings or tail). Modern drones like the Predator drones fire AGM-114 Hellfire, which are bout 100 lb and can be used to disable armored vehicles, bridges and so on. Jihadi John was killed inside a vehicle by one of these. That would be hardly possible with a mere bullet. B8-tome (talk) 12:35, 19 September 2017 (UTC)[reply]

(edit conflict) Wild speculation from my part, but it could have to do with the altitude. Killer drones fly high to avoid detection by potential targets; Unmanned_aerial_vehicle#Military pointed me to this page saying one of the earliest killer drones flies at an altitude of 26,000 feet (7,900 m), I am going to assume it is higher for more modern stuff. On the other hand, Sniper#21st_century gives a record sniping distance of 3.5km. Supposedly deviations in the air and the like prevent accuracy at larger distances; I doubt^{[citation needed]} that a flying drone could beat a grounded human for steadiness of the aim. If so, maybe sniper drones would lose much of the operational advantage because of the required approach distance. Tigraan^{Click here to contact me} 12:49, 19 September 2017 (UTC)[reply]

Of course it could be automated! But if both sides of a war automated their rifles, what would be the point of shooting?

“

Besides which, gentlemen, the exigencies of war compel us to remember one thing. A man is much more dispensable than a computer.

”

— Isaac Asimov, The Feeling of Power

Nimur (talk) 14:21, 19 September 2017 (UTC)[reply]

I can indeed imagine a time when warfare is only between drones. Once one side's drones destroy all the other side's, they would need to surrender or be wiped out. StuRat (talk) 17:34, 19 September 2017 (UTC)[reply]

On 2: Sniper Rifles are already on the edge of still being mobile. For example the .50 caliber M96, broadly used in US Services, has a hefty Weight of 11.35 kg. Unloaded, with no scope attached! If you would add laser targeting and automatic aiming that Weight would easily triple or go beyond. A "mobile" BGM-71 TOW-Launcher weights 92.5 kg, to give you some direction what "mobile laser targeting system" only may add. If it was practical some army would have it today. But actually most armies already have what you imagine. Infact the Germans invented this in WWII. On some of their Infantry fighting vehicles (originally called "Schützenpanzer" which could be translated to "Snipertank"). --Kharon (talk) 21:00, 19 September 2017 (UTC)[reply]

Btw. German Engineers perfectly implemented your imagination already in 1960. They called it Flakpanzer Gepard. In case you are interested in a promotional video impression: [12]. On top it was capable to operate autonomously without crew (stationary), only wired by cable to a hidden command post - in principle like a drone. Tho with its 50 tons weight hardly confused with todays drone "toys" ofcourse. --Kharon (talk) 04:04, 20 September 2017 (UTC)[reply]

There was a demo on TV of a remote-controlled small tracked vehicle with a rifle which could shoot more accurately than a human gunman. A remote-controlled rifle on a rooftop would have an easier time staying still all day than a guy in a gilly suit. As far back as WW1 the Brits, French and Germans had excellent hiding places such as a fake tree stump made of iron which could be erected in darkness on a hillside facing the enemy so an observer could report by phone back to a command post, without being detected by the enemy, and even with some protection against stray rounds. Some were built to look like actual tree trunks so no one would notice a "new tree" at dawn. Today they would hacve to have IR emission/reflection like the real thing. Emitting any IR would be a bad idea and would likely be detectable and draw mortar/RPG/artillery fire. It would be easy to hide a remote-controlled sniper rifle on a rooftop or in a highrise window, or in a pile of rubble. It could similarly resemble an air conditioning unit or chimney. The Washington DC sniper was undetectable firing through a hole cut in the trunk of his car. But once the device starts firing it would likely get high-powered counterfire, since a video camera or IR detector could catch the muzzle flash. A sniper weapon could be a camo version of existing Sentry guns which could acquire and kill targets automatically, but which typically require human permission to fire. Edison (talk) 16:16, 20 September 2017 (UTC)[reply]

September 19

Black hole vs. white hole

A thought occurred to me: if a black hole is a region of spacetime from which nothing may leave, and a (wholly theoretical) white hole is one in which nothing may enter, what does the math say about what would happen if one of each of these objects were to meet? Thanks! – Clockwork Soul 01:01, 19 September 2017 (UTC)[reply]

For as simple an answer as possible... Any object approaching a white hole will fall towards the event horizon around the white hole, but not enter the event horizon until it is a black hole. Because "any object" includes black holes, black holes falling towards a white hole won't reach the white hole event horizon while it is a white hole. 209.149.113.5 (talk) 12:54, 19 September 2017 (UTC)[reply]

I've just about given up on this stuff. One of the better? sources for our article [13] says that white holes spew out matter, yet the matter they spew out will self-collapse from gravitation. So why doesn't it collapse before it comes out...? Hell, I still don't really understand Kruskal-Szekeres coordinates or why it looks like the black hole event horizon is moving out at the speed of light endlessly so that (apparently) everything will fall into it. Wnt (talk) 20:13, 19 September 2017 (UTC)[reply]

Every normal, active Sun is a "white hole" if you like. Our Sun has a surface temperature of 5.000.000 degree Kelvin btw. I dare you to propose anything (exept another Sun) that could manage to fly near or even past aka enter that. --Kharon (talk) 21:17, 19 September 2017 (UTC)[reply]

I'm not sure what "5.000.000" is suposed to mean. The actual, referenced value from our article Sun is 5,772 °K. The term White hole has a meaning in Cosmology entirely different from a Star. {The poster formerly known as 87.81.230.195} 90.197.25.72 (talk) 15:44, 20 September 2017 (UTC)[reply]

Caffeine allergy

Can a caffeine allergy really kill someone who consumes even a small amount of caffeine? (Question inspired by the 4th case in Criminal Case: Pacific Gay.) 2601:646:8E01:7E0B:EDA1:6DA2:2F4C:8E0A (talk) 05:47, 19 September 2017 (UTC)[reply]

It's possible. The medical consensus is that anaphylaxis and death can be caused by very small amounts of any antigen.^[1] That said, caffeine allergies are rare, and I can't find any reports of deaths due to a caffeine allergy. C0617470r (talk) 07:15, 19 September 2017 (UTC)[reply]

References

^ "Common Questions | Food Allergy Research & Education". www.foodallergy.org.

Some may also confuse allergic reaction with the inability to metabolize caffeine. The latter could result in cardiovascular issues and death but without anaphylaxic shock (using a caffeine quantity that someone else could tolerate). Some animals are also more sensitive to caffeine because of that reason, like cats and dogs. —Paleo Neonate – 07:39, 19 September 2017 (UTC)[reply]

This is a common confusion; that people confuse the meanings of a Food allergy with a Food intolerance. Food allergies always are immune system responses to an ingested substance, such as anaphalaxis, hives, or the like. Food intolerances can include things like excess gas, indigestion, acid reflux, feelings of bloating, or other responses which are not immune system responses. --Jayron 32 10:45, 19 September 2017 (UTC)[reply]

A well-known example being lactose intolerance, which is caused by the body being unable to digest lactose. --47.138.161.183 (talk) 05:41, 20 September 2017 (UTC)[reply]

How many pages of information for a science degree?

How many pages are needed to put all knowledge for a college degree? (for reading and as look-up material like dictionaries). Interested in computer science, mechanical engineering, physics.--Hofhof (talk) 16:06, 19 September 2017 (UTC)[reply]

Much of that knowledge (nay, perhaps the bulk of it) is practical knowledge which is not learned through written material, but through direct instruction, lecture, labs, practice, etc. Also, "science degree" is far too vague, there are hundreds of different kinds of science degrees. Thirdly, I have no confidence this is the sort of thing anyone has ever bothered to study before (given my second point) which makes searching for such non-existent data fruitless. --Jayron 32 16:47, 19 September 2017 (UTC)[reply]

For an alternative link that is blue see experiential knowledge. Looie496 (talk) 21:38, 19 September 2017 (UTC)[reply]

I did perhaps half of an Applied Physics degree by understanding four books (I bought maybe just six textbooks over the course, then I read those until the ink wore out). The rest was dipping into books and journal papers in the library. Those four books though (Bleaney & Bleaney? [14], Solymar & Walsh?) represented serious effort to understand them. You could also just try counting how many pages there are in a copy of Feynman.

I did physics partly because it involves hard reading of few books, rather than something like palaeontology where the corpus is perhaps less terrifying on a line-by-line basis, but much larger. Andy Dingley (talk) 17:04, 19 September 2017 (UTC)[reply]

My answer gets in the same lines as the answers above. It's not enough to do the reading, but if you read thoroughly one good book per course, it would be reasonable to read 25 to be at graduate level.B8-tome (talk) 18:00, 19 September 2017 (UTC)[reply]

1000-1200 pages would do. When you memorized, understood and than can apply that much science, you earned your degree! In case its specialized Science it could be less. For example a Metallurgist could probably find everything in "Donald R. Askeland - The Science and Engineering of Materials, 2011" (only 896 pages thin). --Kharon (talk) 21:25, 19 September 2017 (UTC)[reply]

I suspect that this has changed, and much of the need to memorize info has been replaced by the ability to access it instantly, when needed. Of course, this doesn't apply to all info. For example, I suspect a chemist still memorizes the atomic numbers, weights and electron configurations of the most common elements, but not the rarer elements and isotopes of each. StuRat (talk) 23:56, 19 September 2017 (UTC)[reply]

The majority of my physics course was taught with Tipler's Physics for Scientists and Engineers. This is 1172 pages, and it covers everything on the core syllabus. Of course, there are also elective modules which adds more (a random example: my biophysics module used Philip Nelson's Biological Physics, which is 600 pages, although we didn't cover every chapter) and there's stuff from other fields that overlapped (for instance, I needed a roughly 300 page linear algebra textbook and a C programming book), and many lecturers gave us 50-100 pages of notes. 2000 pages seems like a decent estimate. Smurrayinchester 08:36, 20 September 2017 (UTC)[reply]

Common cold and temperature.

It is often said that being in the cold has nothing to do with catching a common cold but people do catch a cold after being in the cold. Furthermore staying out in the cold seems to make it worse. I understand that viruses cause a cold but there must be an indirect way in which the low temperatures increase the chances of catching a cold. The old wives tale can't have survived this long if it's not true. 90.198.254.50 (talk) 17:17, 19 September 2017 (UTC)[reply]

Yep, cold, dry air causes chapped skin, including in the respiratory tract, and breaks in the skin allow microbes in. There could also be effects on people spending more time inside, close together, causing more spread of disease. Vitamin D production from sunlight may also be down, but I don't know that this vitamin has an effect on colds.StuRat (talk) 17:23, 19 September 2017 (UTC)[reply]

Scientists have done experiments to prove that being cold is not a direct cause of a cold (because a cold is always caused by a virus), but that doesn't mean it is not an indirect cause, as explained above. Often, being cold (a drop in core temperature) just allows existing viruses to gain a hold when they had previously been inhibited by the immune system. Dbfirs 18:17, 19 September 2017 (UTC)[reply]

The problem is caused by being afraid of the cold. There are many people who turn on the heating when it gets colder than 20 C in their homes and who dress for winter when the outside temperature dips below 15 C. Their bodies stay acclimatized for tropical conditions all year round even in winter when it's -5 C outside. When they go outside in winter, their blood flow to their body extremities, their noses etc. shuts down. The immune system then becomes less active in their airways, making them susceptible to catching the cold. Another contributing effect here is that these people tend to not be outside for long during the cold periods. If they do regular exercise they prefer to do that indoors rather than outdoors, they hate the idea of running outside at, say 2 C. Weeks before many people get hit by the cold, the cold virus will already be there in Nature, if you run outside every day for an hour, you're likely to breath in that virus but in low concentrations that will lead to immunity without making you ill. Also, it may be a less virulent version of the virus that will later cause severe cold symptoms in many people. Count Iblis (talk) 20:43, 19 September 2017 (UTC)[reply]

It's true, those who cringe at the thought of acclimating to the discomforts of environmental changes often seem to be the most susceptible to illness. Reminds me how I was once dared to dive into an ice-cold swimming pool situated next to a hot-tub. Several people there advised against it on the grounds that I might catch a cold, have a heart attack, etc. I did it anyway (several times) and exhausting as it was I actually felt quite invigorated for days after that. Another friend made a half-hearted attempt but quickly retreated out of discomfort and swears to this day that it only resulted in stiff muscles for him. I've always wondered though if that would have been the case had he truly been willing to "take the plunge"? 73.232.241.1 (talk) 05:06, 20 September 2017 (UTC)[reply]

Hence the concept of a Sauna, popular in some cultures, where one alternates hot and cold phases. {The poster formerly known as 87.81.230.195} 90.197.25.72 (talk) 15:50, 20 September 2017 (UTC)[reply]

A cold happens when rhinoviruses implant in the nasal mucosa and manage to reproduce fast enough to outrun the immune response for a while. There is a good bit of evidence that extended exposure to cold air can cool the nasal tissues enough to weaken or delay the immune response there. However many doctors are skeptical that this mechanism plays more than a minor role in seasonality. Looie496 (talk) 21:33, 19 September 2017 (UTC)[reply]

The low temperatures not only make the immune response less effective. The low temperatures also allow the viruses to remain virulent for a longer time outside the body (see e.g. [15]), facilitating the transmission. Dr Dima (talk) 22:19, 19 September 2017 (UTC)[reply]

See also There is A Scientific Reason That Cold Weather Could Cause Colds from the Smithsonian Institution and Why common cold may thrive at low temperatures from the UK National Health Service. Alansplodge (talk) 16:59, 20 September 2017 (UTC)[reply]

What exactly is "Thermally activated delayed fluorescence"?

I've seen the term used many times, typically with regard to materials for OLEDs, and I'm not quite sure what it means. OrganoMetallurgy (talk) 17:31, 19 September 2017 (UTC)[reply]

Delayed fluorescence sounds like phosphorescence, but the "thermally activated" bit sounds like it only emits light at certain temperature ranges. StuRat (talk) 17:37, 19 September 2017 (UTC)[reply]

This paper has a relatively decent intro, depending on your ability to read scientific papers, as well as keywords to feed to your bibliographic search. For instance, I suspect this paywalled chapter would be interesting to read (but I cannot go through the paywall). Tigraan^{Click here to contact me} 17:48, 19 September 2017 (UTC)[reply]

I'm not sure myself! Years since I did anything like this. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence (2014) is a reasonable start (I think it's one of the first and canonical papers on it). In OLEDs, a cause of inefficiency is that some of the excited states are singlet states, from which they can transition and emit a useful photon, but others are triplet states which don't. Excitation to triplet states is a wasted, inefficient use of energy for the OLED.

There are three generations of OLED tech. The first were based on fluorescence, then the second on phosphorescence and now a third generation using this TADF. Fluorescent were inefficient, as they only put 25% of their energy into the fluorescent singlet states (I think that 25%'s a pretty fundamental limit from the 1:3 ratio). The phosphorescent ones managed to be efficient emitters by adding noble metal dopants which made the triplet states into practical emitters too, but these were expensive to make. The new generation doesn't need these metals, but potentially offers similar efficiencies. It overlaps with here: Intersystem crossing. They work by eliminating the triplet states, by converting them to useful singlets. This up-conversion obtains its energy thermally. Current SotA is here: "Photophysics of thermally activated delayed fluorescence molecules". Methods Appl. Fluoresc. 5 (1): 012001. 9 March 2017. doi:10.1088/2050-6120/aa537e. {{cite journal}}: Unknown parameter |authors= ignored (help)

(And why am I telling anyone with a username like that how to suck eggs?) Andy Dingley (talk) 18:10, 19 September 2017 (UTC)[reply]

As an aside: Thermoluminescence dating is a form of thermally activated delayed fluorescence. Aspro (talk) 20:35, 20 September 2017 (UTC)[reply]

strange equation in physics class

My daughter is taking physics II in college. She has the equation $C={\frac {k\cdot \epsilon _{0}\cdot A}{d}}$

(Sorry, I'm not too familiar with TeX), where C is capacitance, epsilon_0 is the permativity constant, A is the surface area and d is the distance. Usually k is Coulomb's constant, but she is wondering if k is something else here. I say that the equation doesn't make sense because in $k\cdot \epsilon _{0}$ the physical units cancel out, leaving Farads on the left and meters on the right. Does she have something wrong in this equation? Bubba73 ^{You talkin' to me?} 23:44, 19 September 2017 (UTC)[reply]

May we see the units you are using for each term ? StuRat (talk) 23:52, 19 September 2017 (UTC)[reply]

These are from her writeup of her notes. She has C in Farads, epsilon_0 in Farads/meter. She has

$k={\frac {1}{4\pi \epsilon _{0}}}{\frac {N\cdot m^{2}}{C^{2}}}$

and I suppose area in m^2 and distance in meters. With this equation for k, the epsilon_0 cancels out in the first equation. Bubba73 ^{You talkin' to me?} 00:04, 20 September 2017 (UTC)[reply]

This looks like Capacitance#Capacitors and Capacitor#Parallel-plate model. And it looks like there is some confusion over which epsilon is used for which context (permittivity or dielectric constant of whatever the material is vs the electric constant (an actual "constant"). If she's using epsilon_0 as the dielectric constant of the material in F/m, that's already confusing, but that would mean k is the Vacuum permittivity but without the units? Or else is she using epsilon_0 as the vacuum permittivity in its usual F/m units, with k being the dielectric constant of her material? DMacks (talk) 02:07, 20 September 2017 (UTC)[reply]

Yes, k is a dimensionless constant here, representing the relative permittivity of the dielectric material that separates the plates. It is 1 for empty space, and larger than 1 for any other material. Looie496 (talk) 02:37, 20 September 2017 (UTC)[reply]

To add to this, that's the equation for the capacitance of a parallel plate. It is a notable equation and she should understand its derivation and what it means. ε₀ is the permittivity of vacuum, which has the lowest possible permittivity. So the equation says that if you have a better dielectric, you will have a better capacitor. And that's because the dielectric resists the electric field, so you will have a lower voltage difference for a given amount of charge, so you can store more charge in the capacitor at a given voltage. (Tangent: another practical reason to use a dielectric instead of air is to increase the dielectric strength. Dielectrics including air will break down and become conductive at high enough voltages, and we want that upper limit as high as possible.) C0617470r (talk) 03:06, 20 September 2017 (UTC)[reply]

So the k in the equation at the top is NOT Coulomb's constant? In her notes, she has

k={\frac {1}{4\pi \epsilon _{0}}}=8.99*10^{9}

(and SI units), which is Coulomb's constant. Bubba73 ^{You talkin' to me?} 03:18, 20 September 2017 (UTC)[reply]

She talks about an example the teacher did "a 4.2 nF capicitor has an area of 2.8 m^2 and a separation of 12mm. What is the dielectric constant?" He used the equation at the top, solved for k, getting k=2.03. So this k is the dielectric constant, not Coulomb's constant? Bubba73 ^{You talkin' to me?} 04:42, 20 September 2017 (UTC)[reply]

Right, it is not Coulomb's constant. Unfortunately they share the same symbol. C0617470r (talk) 04:46, 20 September 2017 (UTC)[reply]

Coulomb's constant is usually written

k_{\text{e}}

- she apparently failed to write down the subscript, leading to the confusion. Bubba73 ^{You talkin' to me?} 04:53, 20 September 2017 (UTC)[reply]

It is also notable that "k" stands for a bewildering number of constants in scientific equations, to the point where the best assumption about its meaning is "whatever constant is used in this particular equation". Besides the aforementioned Coulomb's constant, there's also (just think off the top of my head, I am certain this list isn't exhaustive) reaction rate constant, the spring constant in Hooke's law, the Boltzmann constant, the generic proportionality constant, etc. etc. --Jayron 32 10:59, 20 September 2017 (UTC)[reply]

Some other big ones in physics: wave number, and momentum when "p" is already in use (especially off-shell momenta in quantum field theory). And it's also very often used as a summation or integration variable. --Link ^(t•c•m) 22:25, 20 September 2017 (UTC) [reply]

The dimensional analysis emphasizes that relative permittivity is a dimensionless ratio - permittivity of a substance compared to vacuum. The original equation can be written nF = ? * F/m * m^2 / m, with ? representing k, and we see indeed it has no units. But constants without units are aggravating because they imply you actually have to remember a formula. Maybe it would be useful to think of the (relative permittivity * permittivity of vacuum) as a subunit here, because then you can think of it as a conversion factor relating the other data you have available. Wnt (talk) 12:08, 20 September 2017 (UTC)[reply]

September 20

Unknown plumeria leaf disease

Well, it's a long shot, but figured I'd ask the smartest folks I know. My plumeria plant is having leaves die off, and I have no idea what's causing it. If it's helpful, I'm pretty close to the coast in southern California. They get maybe 75% sun and I only water them when they look like they need it. The plant as a whole looks healthy, although it's growing very slowly. I've had this problem with other plants, which were also in containers on my deck. Anywho, thanks in advance! Drewmutt (^ᴥ^) talk 06:15, 20 September 2017 (UTC) [reply]

That looks like a problem with growing conditions, I can see no evidence of an external disease like insects or fungus. This could be a normal process where leaves mature and then fall. Is the plant being irrigated with water that may be slightly alkali, from a tap for example? Do you feed the plant regularly? Richard Avery (talk) 07:49, 20 September 2017 (UTC)[reply]

Richard Avery Thanks so much for the quick reply. It's a good question about the water, it's possible, and I have some litmus papers handy (which good Wikipedian doesn't), so I can check tomorrow. Regarding feeding, I thought the same thing, since it presents itself like a K deficiency, so I got me a nice tame 5-5-5 organic fertilizer (not opposed to non-organic, btw) with limited success. Maybe it's just the wrong season? But I would expect them to just go yellow and fall as opposed to becoming necrotic. Drewmutt (^ᴥ^) talk 08:09, 20 September 2017 (UTC)[reply]

I wouldn't expect dramatic results with that fertilizer, not within a few weeks. A shot of miracle gro or similar (almost) never hurts, provided you test it at 1/2 strength first, and since that has plenty of soluble K I would expect it to show faster results (of course the damaged leaves won't rejuvenate, but you should stop seeing them turn). For fun, you can easily make up a batch of your own potash. But don't just go adding all the NPK willy nilly, many of the nutrient problems are not due to lack of presence in the soil, but due to lack of availability, due wrong pH, being bound up with something else, etc. SemanticMantis (talk) 20:28, 20 September 2017 (UTC)[reply]

According to this, it may be a disease such as rust or black tip fungus (for which I cannot find a Wikipedia article). --Jayron 32 10:54, 20 September 2017 (UTC)[reply]

If so, see Black Tip Fungus from the Valley of the Sun Plumeria Society. Alansplodge (talk) 17:03, 20 September 2017 (UTC)[reply]

The shape of the patterns looks far more like a deficiency (and probably K) than a rust or fungus. Andy Dingley (talk) 17:11, 20 September 2017 (UTC)[reply]

Yes, most plant pathogens have a more distinctive patterns [16], including birds-eye, stripes, etc. As for deficiencies, it also be Iron_deficiency_(plant_disorder) or Manganese_deficiency_(plant). I'd apply a light dose of organic fertilizer and test soil pH. (For those, who, like me, had a momentary lapse of nomenclature, Andy is talking about Potassium_deficiency_(plants), not Vitamin_K_deficiency ;) SemanticMantis (talk) 20:23, 20 September 2017 (UTC)[reply]

Iron or manganese deficiencies tend to lead to chlorosis, where cells remain viable but don't produce enough chlorophyll, so the leaves turn yellow (often away from the ribs first). Potassium causes the cell structure to fail, so cells shrivel and turn dry and brown. Fungal problems often cause black spots, but the spots are more irregular (or circular, rather than following the leaf structure) and may give damp, mushy patches. Andy Dingley (talk) 22:12, 20 September 2017 (UTC)[reply]

[1] "Common Questions | Food Allergy Research & Education". www.foodallergy.org.

[1]