Revision as of 01:55, 7 November 2016

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

• WP:RD/S

Main page: Help searching Misplaced Pages

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

How do I answer a question?

Main page: Misplaced Pages:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

• Teahouse
• Help desk
• Village pump
• Help manual

November 2

What could you drill into that would make sparks?

If you wanted to make sparks from a substrate while drilling into it with an ordinary metal or masonry drill bit, what could you choose to drill into? Flint stone? Fire steel? ----Seans Potato Business 12:11, 2 November 2016 (UTC)

Flint will do it. The sparks you see are tiny bits of burning steel from the drill. There are not many things you could drill into with a masonry drill that will provide sparks of themselves, because few such things hard and resistant enough to generate the heat will then burn.

Drilling wood can often give a fire. Produce easily flammable thin shavings as tinder, then either frictional heating (especially with a blunt drill) or friction heating against a screw or nail hidden in the wood can cause a fire, if not sparks.

There are a few metals which are sufficiently close to being pyrophoric in powders or thin sections that just drilling them can give a risk of fire, from hot swarf igniting itself. Andy Dingley (talk) 15:18, 2 November 2016 (UTC)

If you are interested in other easy ways to make a lot of sparks for show, demonstration or experimentation, an angle grinder is a common tool of choice, as in e.g. various "grinder girl" acts. SemanticMantis (talk) 15:59, 2 November 2016 (UTC)

An angle grinder isn't a drill. It has a hard, vitreous grit (thus an easy source of high temperature), often used on a metal. You're mostly seeing the metal burning, not the disc. If you grind the disc into stone you will see "sparks" too, but these are mostly incandescent stone grains (and dimmer) rather than grains that are actually burning, thus would be brighter.

I've made angle grinder underwear for stage use. It's thin titanium sheet over (wider) rubber, over underwear. Rubber, with canvas reinforcing as used for conveyor belts, is relatively grinder proof. Don't slip though.

Motorcycle "knee slider" pads are plastic (hockey puck material) pads to go on the knees of a racing suit. They can have titanium studs set into them, for extra sparkinesss. Andy Dingley (talk) 16:47, 2 November 2016 (UTC)

Human (How far can a human eye see?)

How far can a human eye see — Preceding unsigned comment added by Orochiha (talk • contribs) 14:24, 2 November 2016 (UTC)

The Andromeda Galaxy is visible to most people. It is 2.5 million light-years away. --Jayron32 14:55, 2 November 2016 (UTC)

• Expanding on the answer above, there is no real distance limit to human vision (only the observable universe), only a brightness limit. Things aren't too far away, they're too dim. We can see galaxies from millions of lightyears away, but in a completely unlit room, you can't see something even if it's right in front of your eye. In the atmosphere, things like haze and other atmospheric disturbances don't help either. The human eye is pretty remarkable, it can detect a single photon, and will signal after only a few of them in succession. (Convinced I posted this before, but seems to have disappeared...) Fgf10 (talk) 16:06, 2 November 2016 (UTC)

  The other thing to remember is that vision also involves the brain. Because of the process our brains do known as Neural adaptation, vision adjusts based on the environment, not just on the specific stimulus. The classic example is olfactory fatigue, where you stop "smelling" an odor after you've been accustomed to it. Vision works the same way, as well: A tiny spark in a completely darkened room will appear brighter than the same spark in a well-lit room. Even if the same number of photons strike your retina as a result of that same spark in both sets of conditions; you will register them as being of different brightness because of the environment that they are in. The limits of human perception and senses are highly contextual, and not based solely on absolutes. --Jayron32 17:26, 2 November 2016 (UTC)

As far as being able to spot a distant object, Brian Skiff has explained here how you can observe the galaxy Messier 81 at a distance of 11.8 million lightyears with the naked-eye. Now, as mentioned here people with very good night vision can see stars up to magnitude 8.5. Galaxies need to be a lot brighter than this to be spotted because they are extended objects. The most distant objects that are in theory visible to the naked eye are not galaxies, but gamma-ray bursts, the current record is held by GRB 080319B at a distance of 7.5 billion lightyears which was visible for 30 seconds if you happened to look in the right direction. The peak magnitude was 5.8, so in principle one can have even more distant naked-eye visible gamma-ray bursts. Count Iblis (talk) 18:33, 2 November 2016 (UTC)

Obscuration haze limits how far you can see to distant mountains. It's more noticeable if you are looking to the horizon. On that note, see horizon distance for how far the horizon is; its related to your distance above sea level. LongHairedFop (talk) 19:54, 2 November 2016 (UTC)

• See visibility. It's an extrinsic limit, but still relevant, and much more of a life and death question than some other issues. :μηδείς (talk) 18:04, 3 November 2016 (UTC)

The question should be how far photons can travel. Hofhof (talk) 20:28, 3 November 2016 (UTC)

Wrong. The visible universe is much smaller than the entire universe, and photons can travel where we cannot see them. μηδείς (talk) 03:19, 4 November 2016 (UTC)

Technically, there are only two places in the entire cosmos where you can see a photon. :) Wnt (talk) 12:34, 5 November 2016 (UTC)

Feynman Lectures. Lecture 32. Ch. 32-4, 32-5

32–4Independent sources

...

Another case in which the interference averages out is that in which, instead of having only two sources, we have many. In this case, we would write the expression for A2R as the sum of a whole lot of amplitudes, complex numbers, squared, and we would get the square of each one, all added together, plus cross terms between every pair, and if the circumstances are such that the latter average out, then there will be no effects of interference. It may be that the various sources are located in such random positions that, although the phase difference between A2 and A3 is also definite, it is very different from that between A1 and A2, etc. So we would get a whole lot of cosines, many plus, many minus, all averaging out.
So it is that in many circumstances we do not see the effects of interference, but see only a collective, total intensity equal to the sum of all the intensities.

32–5Scattering of light

The above leads us to an effect which occurs in air as a consequence of the irregular positions of the atoms. When we were discussing the index of refraction, we saw that an incoming beam of light will make the atoms radiate again. The electric field of the incoming beam drives the electrons up and down, and they radiate because of their acceleration. This scattered radiation combines to give a beam in the same direction as the incoming beam, but of somewhat different phase, and this is the origin of the index of refraction.

But what can we say about the amount of re-radiated light in some other direction? Ordinarily, if the atoms are very beautifully located in a nice pattern, it is easy to show that we get nothing in other directions, because we are adding a lot of vectors with their phases always changing, and the result comes to zero. But if the objects are randomly located, then the total intensity in any direction is the sum of the intensities that are scattered by each atom, as we have just discussed. Furthermore, the atoms in a gas are in actual motion, so that although the relative phase of two atoms is a definite amount now, later the phase would be quite different, and therefore each cosine term will average out. Therefore, to find out how much light is scattered in a given direction by a gas, we merely study the effects of one atom and multiply the intensity it radiates by the number of atoms.

Explain, please , why if atoms are randomly located only cosines average out?? If phase differences are not definite, phases are also all different. So whole vectors (Fig. 29–9) must average out. In Ch. 32-5 Feynman says that vectors can average out, but only in solids with beautiful pattern. But in beautiful pattern (say cubic lattice) all phase differences of adjacent layers are constant and phases of single layer atoms' oscillations are also constant.

In Ch. 32-4 does Feynman mean that phases of vectors are constant in time?Username160611000000 (talk) 15:57, 2 November 2016 (UTC)

I don't see him saying the light is scattered non-uniformly there - he gets to the blue sky on the basis that light at different frequencies is scattered by different degrees. The bluer light moves the electrons in any given atom around more (per unit energy) than the redder light; therefore, it is scattered more. I think.

There's actually something more intriguing in this chapter - the statement in 32-1 that it is unknown what the force from an electron pushes against when it resists acceleration due to its electromagnetic radiation. I find myself wondering if it might push against the same thing an Emdrive pushes against. Wnt (talk) 21:43, 2 November 2016 (UTC)

But what can we say about the amount of re-radiated light in some other direction? Ordinarily, if the atoms are very beautifully located in a nice pattern, it is easy to show that we get nothing in other directions, because we are adding a lot of vectors with their phases always changing, and the result comes to zero. - It seems some materials can absorb radiation from side face of crystal, I'm not sure. But I still don't understand in case of sky (where atoms are randomly located), why does not initial phase of atoms average out? If atoms are located randomly, then incident light reaches each atom in different time, so drives electrons with different initial phase(actually initial phase is same as initial phase of incident wave but at any moment of time every atom will have absolutely random total phase as function of its random position). Then according to Fig. 29–9 we should add all vectors. Each vector has random angle from 0 to 360°. When cosines average out, then we get (Total Intensity) = (Intensity from one atom)•(Number of atoms) or A_R=A₁+A₂+...=A • N . So the resultant sum vector must have length √(Number of atoms). Is there some rule that adding many vectors of equal length (say 1 unit) with random angles, sum-vector's length must be √(Number of vectors) units?? Maybe, random walk could be applied? Username160611000000 (talk) 06:44, 3 November 2016 (UTC)

Oh boy, that's a tough one after all. I mean, the spots on a piece of film used for crystallography are not mathematical points - there's some fuzziness about it, and I was thinking that meant it wasn't truly zero when misaligned, but a source like does very little to encourage such thinking. Intuitively, I'd think that if you take a crystal and smash it into a bunch of little pieces before you do the crystallography, you have the little dots scattered out all over the film with the limit case of a universal low background of scattering. But why would the phases in a misaligned crystal be more random and cancel out better than the phases in a smashed crystal? I wonder if it has to do with them not being random - in the misaligned crystal you have atoms in a neat series, with every phase represented equally, whereas in a gas I suppose by chance you might have more at one phase than another. But that's probably not it... hmmm... Wnt (talk) 01:04, 4 November 2016 (UTC)

November 3

Strabismus and Amphetamine use?

Our article on Strabismus says nothing about amphetamines, but a broad google search gets over a megahit. The main ones seem to be anecdotal. Is there any RS about this phenomenon? Thanks. μηδείς (talk) 04:33, 3 November 2016 (UTC)

A quick scan of the professional literature doesn't turn up anything major about amphetamines and strabismus in adults, but interestingly there are several papers describing increased occurrence of ocular problems in children born to addicted mothers (perhaps not surprising). Fgf10 (talk) 09:46, 3 November 2016 (UTC)

Reasons for immune response in food allergies

I've browsed food allergy and food sensitivity and it seems neither describes the underlying causes of why exactly in some cases an otherwise healthy immune system reacts to harmless stuff. Food_allergy#Pathophysiology says in particular that "The IgE antibodies identify the allergenic proteins as harmful and initiate the allergic reaction". What's the reason for such false positives? Could they be a vestigial reaction left evolutionarily from our ancestors who could not digest some foods? Institute of Food Research says here that "We do not know what makes some proteins, and not others, food allergens", so I'm wonder whether this is indeed unknown. Curiously enough, non-seafood meat seems to be a very rare allergy trigger. PS: I'm not seeking a medical advice. Brandmeister 21:50, 3 November 2016 (UTC)

The IFR link (funny to see them linked to, I used to work next door to them) is still current as far as I'm aware. There's a lot of theories, including evolutionary ones as you mention, but no evidence to favour one over the other. There may be a small genetic component, as there is some family risk, but that doesn't tell us that much more yet. Fgf10 (talk) 07:51, 4 November 2016 (UTC)

There is no reason for this. Viruses and bacteria and other pathogens are constantly trying to evolve ways of slipping past the immune guards, so the immune system needs to respond very broadly to capture as many as possible. Tuning it so perfectly that it responds to all pathogens and no non-pathogens is functionally impossible -- inevitably some pathogens slip by and some non-pathogens generate responses. These are failures of the system. Failures have causes but they do not have reasons. Looie496 (talk) 19:00, 4 November 2016 (UTC)

November 4

Physics: Black hole inside a larger black hole

I've read there could be black holes inside of black holes.

1.Smaller black holes evaporate faster than bigger black holes, according to Hawking. So if a black hole contains a smaller black hole, then the smaller one would seem likely to evaporate first(though I don't know for sure, maybe time passage is so messed up by gravity and general relativity that time goes slower for the one inside, so it ends up lasting longer), so what happens when the one inside does evaporate? Will this be in any way observable to us on the outside?(yes I've heard that in principle you can't get any information of what's happening inside, but I thought this could be an extreme case where that principle no longer holds or rather, gets modified, just as when something's going near the speed of light, newton's laws are modified.)

2. Could the craziness of black holes inside black holes cause the space or spacetime nearby it to be nonorientable topologically? thanks. 155.97.8.203 (talk) 00:56, 4 November 2016 (UTC)

A black hole merger has some weird predicted properties, like the area of the event horizons remains constant. But you're right that in a supermassive black hole, some say a person could fall in and not even notice it. (Others say a firewall (physics) or fuzzball (physics) intervenes, and what happens is something altogether more dramatic) If indeed nothing happened, you'd think that if you were orbiting a small black hole and fell past the horizon, you'd still be orbiting it after you fell in. But no matter what explosion happens if the small black hole decays, nothing should make it out past the supermassive black hole's event horizon, since nothing can. Wnt (talk) 01:10, 4 November 2016 (UTC)

The general governing principle here is the so-called no-hair theorem, which basically states that virtually nothing that happens inside a black hole is observable from outside it. John Archibald Wheeler expressed this idea by saying, "A black hole has no hair." Looie496 (talk) 15:09, 5 November 2016 (UTC)

Hidden wire

Is it possible to locate a hidden wire inside a wall without having to tear it up (similar to how it's possible to find wall studs inside the drywall)? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 00:57, 4 November 2016 (UTC)

If it is conducting electric current it should produce a magnetic field, so a magnetometer ought to do it. A metal detector might detect eddy currents in even a wire without current. You could look straight through the wall with a terahertz scanner - I remember reading a couple years ago that a "terahertz app" on a phone would be coming out any time but find myself rather skeptical that mere peasants, the inferiors of cheap machines, will ever be allowed to have their grubby hands on that technology - anyone heard an update? Wnt (talk) 01:16, 4 November 2016 (UTC)

Can I buy any of these goodies at my local hardware store? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:58, 4 November 2016 (UTC)

Ask for a stud finder that will also detect AC wires, like maybe one of these. Sjö (talk) 06:53, 4 November 2016 (UTC)

Thanks! This is even better -- it will find both the wall studs (to drill into) and the wires (to avoid)! So it's two for the price of one! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:10, 4 November 2016 (UTC)

The sources you linked to don't describe a "terahertz app" which normally refers to simple software. It described the possibility of a cheap CMOS chip which functions as a transceiver of terahertz EM. This chip could potentially be integrated into a phone, or attached as an accessory (but on the later point, it could also and likely more easily be attached to a laptop or just be attached to a simple portable device with its own software etc, as some sources mention). You can't magically make a phone without such a chip and with no accessory function that way, and it isn't because of any major conspiracy. Nil Einne (talk) 08:04, 4 November 2016 (UTC)

True, that was a silly word to use. There are some political issues playing on my consciousness in regard to the tendency of surveillance tech to show up in phones yet be useless to the user, e.g. where people are spied on with GPS yet don't know where they are themselves. Wnt (talk) 11:17, 4 November 2016 (UTC)

I don't know what stud detectors are like, in fact this is the first time I've heard that term, but I've had a combined metal an voltage detector for years and always use before drilling any holes in the wall. The one I've got seems to be only good to a few inches in the wall so it might be worth checking for something better if you want to use it for anything big like bolts in an outside wall. Dmcq (talk) 08:40, 4 November 2016 (UTC)

Agreed, finding a wire that's not near the surface would be difficult, as closer metal objects, like nails and brackets, would give a much stronger return. StuRat (talk) 21:00, 4 November 2016 (UTC)

Our article on test lights (also known as voltage detectors) describes at length how this can be done if the wire is active and carries line voltage. These devices are generally available for a few bucks at your local hardware store. Looie496 (talk) 15:24, 5 November 2016 (UTC)

Belief perseverance

The article on Belief perseverance talks about people clinging to beliefs despite evidence to the contrary. I've been wondering if there is some good term for what I think of as the WMD effect where people were even more convinced that Saddam was hiding weapons and was even more evil and devious than they originally thought. Basically that the evidence against their belief makes them become quite extreme in their belief. I think there is the same effect with these Clinton emails - lots of people are now shouting kill the bitch as time goes on and successive inquiries come up with nothing of note. Is there a good reason why evidence against something should actually accentuate belief and is there an entry about it? Dmcq (talk) 09:00, 4 November 2016 (UTC)

• It sounds just like a particular form of confirmation bias. Tigraan 10:13, 4 November 2016 (UTC)

That didn't sound strong enough but I found a bit there which I think covers what I mean. Thanks. "The backfire effect is a name for the finding that, given evidence against their beliefs, people can reject the evidence and believe even more strongly". It has some references but says nothing much more about it that I can see. The link has more about it and summarizes it as “When your deepest convictions are challenged by contradictory evidence, your beliefs get stronger.” It's pretty sad news if the Cinton hate business is part of some core belief. Dmcq (talk) 11:29, 4 November 2016 (UTC)

is good too with lots of examples. Though I don't see how something like whether 0.9999... is 1 or not can be part of a core belief or deepest conviction. Certainly worth an article I think.. Dmcq (talk) 11:52, 4 November 2016 (UTC)

There seems to be another term for it as well 'motivated reasoning', see which gives hope that there are ways to reason with people even when they are deeply committed to a point of view. However that seems to be more in common with 'belief perseverence' rather than the way contradictory data actually confirms the opposite in backfire effect. Dmcq (talk) 12:01, 4 November 2016 (UTC)

Trying to convince someone that their belief is wrong is typically a futile effort. It will be taken as a personal attack, and will only make them more defensive. The essence of it is "I'm right and you're wrong". All of us are guilty of it from time to time, and it generally doesn't work. ←Baseball Bugs carrots→ 13:08, 4 November 2016 (UTC)

Jonathan Swift once wrote "Reasoning will never make a man correct an ill opinion, which by reasoning he never acquired..." which is often paraphrased as "You cannot reason a person out of a position he did not arrive at via reason." --Jayron32 15:19, 4 November 2016 (UTC)

cognitive dissonance. Count Iblis (talk) 18:14, 4 November 2016 (UTC)

Thanks for that. It does seem very strange. I didn't get a good idea of what might be behind it all, laziness in thinking does not explain why a person would be even more confirmed in their beliefs. I guess in Blair's case there might be a bit of him feeling he had to defeat any challenge. Dmcq (talk) 23:36, 5 November 2016 (UTC)

This logic often applies to a conspiracy theory:

1) P is "obviously true".

2) Organization Q should therefore acknowledge the truth of P.

3) Therefore, the fact that organization Q did not do so indicates that they must be in on the conspiracy, and the conspiracy is even bigger than we thought.

Note that the only flaw in the logic is the false assertion that P is obviously true. In a case where P really is obviously true, like Galileo's assertion that the Earth revolved around the Sun (obvious to anyone who studied it), this logic does prove that there was a conspiracy to hide the truth. StuRat (talk) 21:02, 4 November 2016 (UTC)

That logic stream is a good example of what a math teacher once told us: "If you start with incorrect assumptions, you're liable to get 'interesting' results." ←Baseball Bugs carrots→ 00:17, 5 November 2016 (UTC)

Another way to state that mathematically is that extrapolation greatly magnifies any slight errors in the initial conditions. StuRat (talk) 00:43, 5 November 2016 (UTC)

In the case of Hillary's emails, the problem is worse because there is a grain of truth there. If the birther nonsense can survive for years without any facts to back it up, you can see how something which is partially true is far harder to dismiss. StuRat (talk) 21:35, 4 November 2016 (UTC)

Full meaning of:" 66.038 ± 0.025/0.049 Ma " in Science (journal)

Hello women and men! We are having problems in the equivalent of this reference desk in French (we call it "The Oracle"), here and more specifiquely here . No need to read French; the problem is how to understand several figures in this paper , coming from Science Magazine about the date of the Cretaceous–Paleogene extinction event. Several figures as "66.032 ± 0.058/0.072 Ma" or "66.038 ± 0.025/0.049 Ma" (6 series of such figures) are written.
For example: concerning "66.038 ± 0.025/0.049", somebody proposed the following explanation, standard deviation = sigma = 0.025 thus probability(m-1.96*sigma < age < m+1.96*sigma) = (66.038-0.049 < age < 66.038+0.049) = 95% because 1.96*25 = 49 (these 1.96 and 95% are known figures coming from ).
But this explanation does not fit for "66.032 ± 0.058/0.072" because 0.058*1.96≈0.114≠0.072
SOS. Who can rescue our French team? I never was a scientist, but I can understand some things about statistics and about Radiometric dating. Thank you a lot for the time you took reading this question.--Jojodesbatignoles (talk) 17:56, 4 November 2016 (UTC)

This detail of notation will be buried somewhere in Science's Information for Authors. Hopefully we can narrow down to a more specific publication-requirement.

Nimur (talk) 18:00, 4 November 2016 (UTC)

There are two relevant footnotes in the article:

9. Uncertainties here and throughout are stated at the 68% confidence level.

11. Uncertainties given as TX/Y refer to values excluding (X) and including (Y) systematic sources as defined in the supplementary materials.

Footnote 9 seems self-explanatory to me; 68% corresponds to 1 standard deviation if the values have a normal distribution. I did not read the supplementary materials, but an example of random vs. systematic errors would be making measurements with a tape measure. Some of the (most likely) random errors in making measurements would be reading values when the length of an object falls between divisions, deciding where an object begins and ends when the shape is irregular, etc. A systematic error would be a tape measure that is 0.1 % too short, or not supporting the tape measure all along its length while using it, and failing to account for the sag. So the authors of this paper were able to identify certain error sources as systematic, and provided uncertainties with just the random errors, and with the combined random and systematic errors. Jc3s5h (talk) 18:16, 4 November 2016 (UTC)

See Experimental uncertainty analysis for our (very detailed) article on the subject. Measurement uncertainty is perhaps more accessible to the general reader. Tevildo (talk) 21:04, 4 November 2016 (UTC)

Transitional epithelium and urothelium

What is the precise relationship between the terms transitional epithelium and urothelium? My current hypothesis is that they are effectively synonyms, since both terms describe the epithelial lining of the renal pelvis, the ureters, the bladder, and (the proximal parts of) the urethra. But since "transitional epithelium" describes the morphology of the epithelium, and "urothelium" describes the location of it, it would also make sense to say that "transitional epithelium" is a hypernym of "urothelium".

But if the terms are really synonyms, why do Misplaced Pages have two separate articles on them?

What do you say? --Andreas Rejbrand (talk) 21:00, 4 November 2016 (UTC)

The article says the latter is a subset of the former. ←Baseball Bugs carrots→ 00:14, 5 November 2016 (UTC)

Presumably a proper subset, or they could indeed be identical. StuRat (talk) 01:12, 5 November 2016 (UTC)

So the difference is the transitional epithelium found in prostatic ducts, which cannot be described as urothelium? Any sources? --Andreas Rejbrand (talk) 12:21, 5 November 2016 (UTC)

According to Pawlina, Wojciech (2015). Histology: A Text and Atlas (With Correlated Cell and Molecular Biology) (Seventh, International Edition). Wolters Kluwer. China (2015). ISBN 978-1-4698-8931-3, the terms are synonyms. --Andreas Rejbrand (talk) 23:18, 6 November 2016 (UTC)

Is this static electricity?

In m room I have two short walls that protrude part way across. The first is shorter than the second and has no electrical in it. The second has a regular light switch. If I touch the light switch first I get the usual static electricity, the blue spark, crack sound and minor shock, that is common in dry houses in winter. If I put the palm of my hand flat on the first wall I get a greenish glow around it, no noise and no shock. However, this only works when I get out of bed and never if I walk into the room from the corridor. What am I seeing? Is it just a different form of static? Could it be caused by the paint on the wall? The bed and door are next to each other so it's not caused by walking. I tried with and without socks, changed the blanket and sheets but that doesn't make any difference and I get a kick out seeing the glow. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 22:54, 4 November 2016 (UTC)

You should probably mention the climate in the room. If you are still in Cambridge Bay I am guessing the humidity is very low now, unless you have a humidifier. That affects static electricity. Could the green glow be many tiny sparks ? The getting out of bed part does make me think that you collect static electricity when you drag yourself past the blankets.

Also see St. Elmo's fire. Not that it's what you are experiencing, but it may be a related form of corona discharge. And check out Kirlian_photography, a way to photograph coronal discharges. StuRat (talk) 00:28, 5 November 2016 (UTC)

I suspect that the paint on the wall contains something electroluminescent. Looie496 (talk) 14:58, 5 November 2016 (UTC)

Thanks both. I need to try and get a picture of it. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 04:32, 6 November 2016 (UTC)

November 5

Protrusions in lower jaw?

Recently I was at the dentist getting a cleaning, and the technician mention that I have a somewhat uncommon feature just behind my lower front teeth (on either side, underneath the tongue), which I understand to be bone protrusions, just underneath the gum, that are like two little bumps in the gum in that area (almost like two recessed lower "fangs" that have not formed). She only mentioned it because she was having difficulty positioning the mouthpiece for the x-ray. I didn't really follow up with her about it (it seemed of no concern, and because, you know, at the dentist it's somewhat hard to have a conversation), but I wonder if someone could provide the name of this dental feature so that I can get more info, just out of curiosity. Thanks! Ditch ∝ 00:54, 5 November 2016 (UTC)

Doesn't sound like a bone spur (osteophyte) or enthesophyte. StuRat (talk) 01:03, 5 November 2016 (UTC)

No, I don't think so. From the context of our conversation, it seemed like a "normal" dental trait, just not one she sees a whole lot. She had a clinical name for it. I just can't remember. Ditch ∝ 01:06, 5 November 2016 (UTC)

Wait, I think I found it: Bilateral Mandibular Tori. We have an article, somewhat less specific than what I have, but basically the same thing Torus mandibularis. Seems like I grind my teeth too much, which is unfortunately true. Ditch ∝ 01:17, 5 November 2016 (UTC)

What, that's a medical condition? I thought everyone had them...(edit) Looking at some better images on Google than are in our article, looks like quite a variety of shapes and sizes can occur. Someguy1221 (talk) 02:30, 5 November 2016 (UTC)

Manganese Poisoning

How much Hemp Milk would you have to drink for Manganese poisoning? JoshMuirWikipedia (talk) 04:48, 5 November 2016 (UTC)

This nutrition information for Hemp Milk does not indicate any manganese. This site indicates some manganese in whole hemp seeds, but I cannot see that any significant amount of manganese in the hemp milk. If you know how much manganese is in the hemp milk you are drinking, you can find information on the LD-50 of manganese from an Materials Safety Data Sheet. --Jayron32 04:53, 5 November 2016 (UTC)

This source suggests that 200mg/kg per day of manganese dissolved within food may decrease rodent lifespan. Studies disagree on how toxic oral manganese is, and means of manganese consumption may influence the results, but let's just stick with this value. According to this, hemp seeds have 10mg of manganese per 100g of seeds. And according to Hemp milk, the are at least 8 grams of hemp seed extract in every 100grams of hemp milk. Now we have everything we need to make an educated guess. The average adult human male is 70 kilograms, so it will take chronic consumption of 14 grams of manganese per day to have some problems. That's 1,400,000 grams of seeds a day, or 17.5 million grams of hemp milk, or over 4000 gallons of hemp milk, every day. Someguy1221 (talk) 08:28, 5 November 2016 (UTC)

Is it possible to control heart rate directly as we can control our breathing?

Iv'e heard a professor who said that it's possible to control heart rate directly, by control some part of the brain, and the results are that if we put the stethoscope on the chest we don't listen any voices as it should in normal heart which beats. Is that true? and Generally is that possible to control heart rate directly? 93.126.88.30 (talk) 09:17, 5 November 2016 (UTC)

See Biofeedback. Rojomoke (talk) 11:05, 5 November 2016 (UTC)

In spite of some things you might read, it is not possible to alter your heart rate by simply willing it to change. There is however an inhibitory pathway from the brain to the heart, traveling through the vagus nerve, and its activity is affected by emotion. In other words, you can alter your heart rate to a degree by thinking about things that alter your emotional state. Looie496 (talk) 14:52, 5 November 2016 (UTC)

Don't forget physical state. Avoid any movement, to lower your heart rate. StuRat (talk) 15:30, 5 November 2016 (UTC)

Our Freediving article states "Before competition attempt, freedivers perform preparation sequence, which usually consists of physical stretching, mental exercise and breath exercise. It may include sequention of variable length static apnea, special purging deep breaths, hyperventilation. Result of preparation sequence is slower metabolism, lower heart rate and breath rate, lower level of CO2 in bloodstream"(my bold). DrChrissy 20:45, 5 November 2016 (UTC)

why do people get sickness and diseases in the winter more than in the summer?

First of all is that true that people get sickness in the winter more than the summer? (apparently it seems so, because of the differences at the emergency rooms in these two times) and if it is true, what is the reason for that? 93.126.88.30 (talk) 09:48, 5 November 2016 (UTC)

One explanation I've seen suggested is that in winter people congregate together in spaces that are less well ventilated than in summer, thus providing more opportunity for transmission of communicable diseases. There may well be other factors, and perhaps someone else can provide some references. Dbfirs 12:16, 5 November 2016 (UTC)

Common_cold#Weather mentions several possible reasons (with refs), some of which may also apply to other illnesses. The British NHS thinks that a range of diseases may be triggered by cold weather. Henry 13:21, 5 November 2016 (UTC)

Yes, this research suggests that "seasonal exposure to cold air causes an increase in the incidence of upper respiratory tract infections due to cooling of the nasal airway" and "inhalation of cold air causes cooling of the nasal epithelium, and ... this reduction in nasal temperature is sufficient to inhibit respiratory defences against infection such as mucociliary clearance and the phagocytic activity of leukocytes." Dbfirs 13:50, 5 November 2016 (UTC)

Don't forget the health effects of low humidity, also found in winter. Chapped lips are a visible sign, and microbes can gain entry to the blood stream via any breaks in the skin like that. StuRat (talk) 15:32, 5 November 2016 (UTC)

Yes, infectious disease is more common in winter, such as the common cold (cited by Henry) and influenza. In fact, in the US, all-cause mortality is 15-20% higher in winter than summer, due in large part to the impact of seasonal diseases on already vulnerable populations (e.g. the elderly). Dragons flight (talk) 13:58, 5 November 2016 (UTC)

Nuclear attack

If a 25-megaton atom bomb is detonated at optimal height, what would be the destructive radius based on blast effects and thermal effects? (More specifically, if detonated over the geometric center of Qatar, would it destroy everything within Qatar's borders?) Is it true that for an explosion of this size, thermal effects will dominate? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 10:24, 5 November 2016 (UTC)

Please do your own homework.

Welcome to the Misplaced Pages Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Dolphin (t) 10:50, 5 November 2016 (UTC)

This doesn't seem like a homework question, but an interesting hypothetical scenario. But looking at the article it says "If detonated at optimal height, the B-41 would generate a fireball approximately 4 miles (6.4 km) in diameter, it would have been able to destroy reinforced concrete buildings 8 miles (13 km) from ground zero, and it would have been able to destroy most residential structures 15 miles (24 km) from ground zero, while producing third degree burns 32 miles (51 km) from ground zero.", so it seems like someone's already given us a lot of this information in the article. Now... if only they had a source for that statement there we'd be in business; otherwise, we can do somebody's alleged homework and fix a sourcing problem at the same time. :) Unfortunately none of the three refs there seem to cover any of this. Actually, one issue - looking at the development schedule they do cite - is that the bomb's components apparently weren't tested above 5 MT. Since it says the 25 MT version was a "dirty" nuclear bomb with heavy fallout, this is a good thing. But it means this is a guess or a simulation with computers from 1960 by an army with a track record (e.g. Castle Bravo) of badly misestimating the yield, including a fizzle during the testing of that weapon. So I feel like this Misplaced Pages-induced hallucination, wherever it came from, can't possibly be relied on, though it's as good a guess as any. Our article on nuclear weapon yield gives a figure of 3.7 km for a 15 MT bomb (well, the figure shows half that, but our legend says the figure is wrong. Typical.)

Meanwhile Qatar is 4467 square miles, and no matter how you push that around, I don't think you're going to fit it under that nuke. (Well, unless you count the fallout) But I like the direction of your mind. :) Wnt (talk) 12:25, 5 November 2016 (UTC)

Absolutely NOT homework -- I don't think they teach about nuclear weapon effects in school (or even in college, unless it's at West Point)! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 01:00, 6 November 2016 (UTC)

See here for an estimation. I'm not sure I'd want to be anywhere near a school where estimating nuke effects is part of the curriculum....! Fgf10 (talk) 08:52, 6 November 2016 (UTC)

Thanks! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:07, 6 November 2016 (UTC)

Generating electricity from domestic water pressure

The incoming mains water to my house is 4 bar via a 15mm copper pipe. I do not have a water meter so pay a set charge no matter how much I use. If I connected the incoming water supply to some kind of contraption that turned an alternator or dynamo, how much electricity would I be able to generate? Jinpingwoo2 (talk) 15:48, 5 November 2016 (UTC)

This Q has been asked before, and I believe the answer was that it would be too little electricity to pay for the equipment over it's projected life. If this wasn't the case, everyone would do it, and then nobody would provide unlimited water at a set charge. Also, note that you can get "free electricity" from solar panels, although it's similarly not free when you consider the cost of the equipment, amortized over the projected life. In fact, it's usually more expensive than regular electricity. StuRat (talk) 16:08, 5 November 2016 (UTC)

We'd like to assume this is a thought problem only, i.e. the pressure doesn't drop below 4 bar when the water is running. Otherwise you may get more energy from the heatedness of your town's reaction. :) Let's see where that gets us... Then you have a pressure of four bar = 400 kPa, where 1 Pa = 1 kg m-1 s-2 = 1 J m-3 energy density. Now you have this energy density over an area of pi (0.015 m/2)^2 = 0.0001767146 m^2, so we now have a figure of oh, 70.7 J/m. Meaning what? Well, I guess for every linear meter of water in the pipe you decompress you get 70 J. But how much power is that in watts? Well, depends on how many meters you decompress every second. Which implies we *need* to know that rate of flow, which we know intuitively can't be infinite. I have no idea how to calculate it, but you could measure how many buckets you fill, and get a figure, and convert that to m^3 of water and figure it out, or somehow measure how fast the water flows for a m/s reading in the pipe. Just take 400000 J/m^3 * x m^3 = 400000 x J/s or 70 J/m * x m/s and get 70x J/s.

Now of course, even after the water is decompressed, it might deliver more energy. You might have a cliff outside your house and you can drive a water wheel with it. Or maybe the municipal sewer is a way down and that too is unmetered... Of course, don't do this because it's mad; the city will get curious where the leak is and find it, or you'll flood your basement, or something. Wnt (talk) 16:18, 5 November 2016 (UTC)

XKDC has already worked out the math: .

Here are some vendors who will sell you a Micro-hydro generator. Enough to recharge a cellphone or maybe a laptop if you have water and no electricity.

Here is a clever fellow who proposes extracting energy from the temperature difference between his city water and outdoors, then pumping the water back, reversing his water meter: http://www.eagle-research.com/cms/blog/free-energy/generating-electricity-using-household-water-pressure-or-heat --Guy Macon (talk) 18:07, 5 November 2016 (UTC)

@Guy Macon: xkcd draws a pretty comic, but it's the same calculation. With the notable omission that, although they admit the flow rate is a crucial part of the calculation, they never say what it is. But since they come up with 200 watts of power, you can divide that by 400000 J/m^3 to get 200 /400000 m^3 = 50 cm^3 (ml) of water per second to produce that power (they use almost the same pressure, 4 atm instead of 4 bars and who's really measuring?). I'm getting that it takes 40 seconds to fill up a 2-liter bottle that way, which is believable for a bathroom tap; mains are probably better. Wnt (talk) 00:05, 6 November 2016 (UTC)

Try another version: Call it a spherical cow,back of the envelope calc: my house has faucets which will each supply 3 gallons per minute. The water pressure is about 40 pounds per square inch. 3 gpm times 40 psi divided by 1714 yields .07 horsepower or 52 watts mechanical input to a generator. But my mains are engineered to furnish three baths, a laundry and a kitchen,as well as an outside hose bib implying that with a 20% pressure drop when running them all, a generator directly connected to the main might supply 18 gpm at 32 psi, or 0.33 HP or 246 watts. As a side note, some 19th century phonographs were powered from the kitchen tap via a rubber hose to a little water motor with a return hose to the sink. Edison (talk) 20:02, 5 November 2016 (UTC)

See Hydraulic power network for our article on Edison's sidenote, incidentally. Tevildo (talk) 23:20, 5 November 2016 (UTC)

Feynman Lectures. Lecture 33. Ch. 33–6 The intensity of reflected light

It is possible to go on with arguments of this nature and deduce that b is real. To prove this, one must consider a case where light is coming from both sides of the glass surface at the same time, a situation not easy to arrange experimentally, but fun to analyze theoretically. If we analyze this general case, we can prove that b must be real, and therefore, in fact, that b=±sin(i−r)/sin(i+r). It is even possible to determine the sign by considering the case of a very, very thin layer in which there is reflection from the front and from the back surfaces, and calculating how much light is reflected. We know how much light should be reflected by a thin layer, because we know how much current is generated, and we have even worked out the fields produced by such currents.

I want to ask again . What does this part of the Lecture mean? How can we use thin layer? In thin layer refracted light beam will infinitely reflect. Second reflected beam will have amplitude ${\displaystyle b^{*}\cdot a}$, where ${\displaystyle |b^{*}|^{2}={\tfrac {\sin ^{2}\,(r-i)}{\sin ^{2}\,(r+i)}}}$. — Preceding unsigned comment added by Username160611000000 (talk • contribs) 18:11, 5 November 2016 (UTC)

Feynman Lectures. Lecture 33. Ch. 33–7 . Fig. 33–7

I think image (b) of Fig. 33–7 is not correct, because atoms must oscillate vertically, so secondary waves must be perpendicular to image, producing something like cylindrical surface. There is some component of the field in other directions according to formula (29.1), but it is much smaller. — Preceding unsigned comment added by Username160611000000 (talk • contribs) 18:21, 5 November 2016 (UTC)

We can split vector E into components situated only in plane perpendicular to direction of propagation (like is shown in Ch. 33–1). We cannot represent vector E as superposition of one vector perpendicular and the second vector parallel to optical axis of crystal. Is it correct? Username160611000000 (talk) 10:21, 6 November 2016 (UTC)

November 6

Thermally unstable compounds

Are there techniques for finding properties of a thermally unstable compound (TUS) beyond temperatures at which significant decomposition takes place? For example, even though mercury(II) hydride readily decomposes at approximately -125 degrees Celsius, is it practical to heat a sample faster than it can decompose and still be able to determine whether or not the decomposition temperature coincides with the melting point? How would I go about detecting a phase chance on the molecular scale under such dynamic conditions? Plasmic Physics (talk) 09:52, 6 November 2016 (UTC)

For higher temperatures this is certainly possible, and you may be able to overheat by some tens of degrees if you do it fast. However the decomposition products will contaminate your product and disturb the properties. Another issue is that heat is released during the decomposition, there will be positive runaway feedback, and it likely explodes. Perhaps you can subject the solid to high pressure, or high pressure under hydrogen to try to reverse the decomposition. Perhaps a thin layer on some substrate will be more stable. You may be able to use X-rays, Raman spectroscopy, optical dispersion, mechanical properties (eg the sound of the explosion), or even Neutron diffraction or Positron annihilation spectroscopy to find some properties. To see if the liquid is intrinsically unstable you could try dissolving your product in suitable liquids (liquid nitrogen, liquid xenon) and see if it can be recrystalised. Graeme Bartlett (talk) 10:52, 6 November 2016 (UTC)

Phase changes don't happen instantly. Whether this makes sense depends on a comparison between the time scale of decomposition and the time scale of the phase change. I believe that in most cases the decomposition will happen faster. Looie496 (talk) 14:37, 6 November 2016 (UTC)

• That exactly. Steel is "unstable" at room temperature (it demixes very very slowly into Fe and Fe3C) but there are tons of tables for its mechanical properties. Tigraan 17:20, 6 November 2016 (UTC)

Borrachero tree

Borrachero tree should redirect to Brugmansia aurea or simply to Brugmansia? This article suggests the second option for example. —  Ark25  (talk) 10:38, 6 November 2016 (UTC)

That article describes a plant with yellow or cream flowers, growing in Colombia. When you eliminate the species with red flowers, and those which don't grow as far north as Colombia, you are reduced to either B. aurea or B. arborea. Wymspen (talk) 11:48, 6 November 2016 (UTC)

Thanks. I don't understand what's with the red flowers though. —  Ark25  (talk) 16:57, 6 November 2016 (UTC)

What is the scientifical explanation for that phenomenon?

I saw in this video on youtube (and also on facebook) a group of Indian people who makes some things which look like dangerous things (such as: getting a lot of beats which normal body can not survive after them and getting an heavy hammer into the chest or one of them was run over by car and motorcycle at the same time - on the torso and the head and laying on standing nails with naked upper bodies), but after that in the past I asked here about phenomenon of putting hand into boiled oil by Indian you linked me the trick behind it and then I saw that every one can actually do that, so then I started to cast doubt in any exceptional phenomenon. What is the explanation in this case? 93.126.88.30 (talk) 15:18, 6 November 2016 (UTC)

The usual explanation for many of these things is the difference between force and pressure. The human body can withstand a great deal of force, so long as it is distributed over a wide area. The bed of nails provides many not-so-sharp nails, to spread the force over a wide area. The hammer also spreads the force out. Replace that with a pick, then apply the same force, and it would cause major damage. StuRat (talk) 15:35, 6 November 2016 (UTC)

See also our Bed of Nails article. CodeTalker (talk) 16:31, 6 November 2016 (UTC)

And see Leidenfrost effect for the "boiling oil" phenomenon. Tevildo (talk) 22:13, 6 November 2016 (UTC)

Main Battle Tank

Hello , what is the highest speed of a target that tanks with the best fire control system can hit ? 149.200.231.84 (talk) 16:21, 6 November 2016 (UTC) In other words can tanks hit the opponent tanks driving at 45 km/hr speed ? 149.200.231.84 (talk) 16:45, 6 November 2016 (UTC)

In theory a tank can hit a target going at any speed - even a jet aircraft flying past at low level. However, the faster the target, the greater the element of chance in actually scoring a hit. Wymspen (talk) 16:52, 6 November 2016 (UTC)

Are there any dinosaur museums in BC?

I would like to see some dinosaur fossils. Drumheller in Alberta is kinda far. Swancat (talk) 01:55, 7 November 2016 (UTC)

• Misplaced Pages resources for researchers
• Misplaced Pages help forums
• Misplaced Pages reference desk