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November 22

Steel mill type

Judging by [1], Google aerial view at 41°34′24″N 84°2′35″W, and my picture, what kind of facility is the North Star BlueScope Steel mill near Delta, Ohio? Trying to figure out which subcategories of Commons:Category:Steel production I should use for the image. Nyttend (talk) 00:05, 22 November 2015 (UTC)

"Since 1997, North Star BlueScope Steel LLC has been providing hot rolled bands...". They also have furnaces (including an electric arc furnace) that input pig iron and other raw materials. That would make it a refinery, a foundry, and a rolling mill: it's a facility that takes in ore and raw material, melts it and mixes it to produce steel, and finally hot rolls the output steel to produce coiled sheet metal. Nimur (talk) 02:02, 22 November 2015 (UTC)

preserving ornamental squashes

Perty much every year I buy ornamental squash / pumpkins in mid-october as gifts. They are solid, hard, weigh only a few ounces each, and seem to be wax covered. Nevertheless, the ones I buy my mother are almost always mold-ridden by Thanksgiving. (I give the others away to store clerks I deal with regularly, they don't report on their demise.) Is there some way to preserve them by washing or heating or the like? Thanks. μηδείς (talk) 00:49, 22 November 2015 (UTC)

Regular washes in a dilute bleach/water solution (like a capful of Clorox bleach in a kitchen sink full of water)? When we buy fruit we do that to make it last longer, at my estimate we can about double the shelf-life of a 3 pound bag of mandarin oranges that way. --Jayron32 01:29, 22 November 2015 (UTC)

The enemy here is moisture. If the skin is not damaged and no part of the squash is exposed to constant moisture, it should last months without getting moldy. Looie496 (talk) 13:05, 22 November 2015 (UTC)

Location (location, location) is probably the key here. Just move your mom to Canada and the pumpkins will easily last from mid-October to Thanksgiving! Okay, more seriously, only getting a month on squash seems awfully short. Per Looie, moisture is the problem, so the place of storage is going to be key; keeping them in a bowl in the kitchen is a high-risk activity. Moisture from cooking and dishwashing will inundate the place (and roll out an invite for mold). You may also want to make sure that she's not sticking it in a bowl with fruit, such as apples or bananas. They outgas ethylene quite vigorously, aging the squash prematurely. 99.235.223.170 (talk) 13:28, 22 November 2015 (UTC)

Think the above have laid out the gist of the problem. Fruit waxing is a cheap and easy way to get produce from field to market but does not let the produce breath. Also, it allows the farmer to harvest before produce is fully ripe. I don't know if your familiar with Marrow (vegetable), my father used to grow them and keep them for winter. Pick only when ripe (when the skin has matured and hardened -and marrow skins are very thin), wash (bleach is OK – hydrogen peroxide may be better than chlorinated but I don't have any references) and store at a low temperature – not in the house. He placed them in a string-bag so that air could circulate and thus not encourage mold. Suggestion: Find a supplier from which to buy un-waxed squash. Bleach, dry, place in string bag and store at or below 10º centigrade. Just a little bit of salt and white pepper (not black pepper in this case) brings out the subtle flavor. Do please, let us know next year how you get on.--Aspro (talk) 17:27, 22 November 2015 (UTC)

Thanks for the above answers. Yes, I did actually consider the Canadian solution. And yes, she does keep them in a bowl on the kitchen table, but the bowl already has carved wooden 'fruit' in it, and the squash sit on top, and do not touch each other. Humidity is not a huge issue, since the house is rather dry--I have never seen any condensation. Most years the squash last until Christmas. I suspect the real problem is that they were allowed to get moldy at the store. I was going to buy some bigger and very bizarrely shaped bumpy multicolored melons, but they were already moldy on the stand. Next year I will wash them and dry them before putting them on the table. That might have prevented these going bad so unexpectedly quickly. Oh, and interesting about the marrow. We call them zucchini here. μηδείς (talk) 18:46, 22 November 2015 (UTC)

As was mentioned before, it can be more humid in the kitchen than the rest of the house, and it doesn't need to get to the point of condensation to promote mold. I'd make sure the ones you buy are rock hard. Also, you might consider getting fake squash to go along with the other fake fruit. Keeping live squash in the fridge when not on display might also help. StuRat (talk) 18:58, 22 November 2015 (UTC)

They are a rather cheap novelty item, so it is not a big deal. I was simply surprised they went so quickly this time. There were eight. Of the four still left I have noticed they are all getting soft on the bottom, so I expect they'll be gone by Turkey Day. I've never cut one open, so if there is one left perhaps I'll dissect it. Thanks. μηδείς (talk) 00:53, 23 November 2015 (UTC)

Waitaminnit. The "ornamental" nomenclature is just because they're neat to look at - why aren't you cooking them and eating them? I don't think I've ever found any that weren't perfectly edible, though some of them are difficult to cook evenly due to their odd shape. 99.235.223.170 (talk) 02:06, 23 November 2015 (UTC)

You can keep the same squash for several years if you dry them properly [2] [3]. SemanticMantis (talk) 15:25, 23 November 2015 (UTC)

Thanks. The drying methods linked to are basically for edible gourds grown at home. These gourds are very small (smaller than commercially sold apples) and have been "waxed" and the stems are dry; I suspect drilling holes in the bottom and hanging them outside might work. They are so small I doubt there would be enough pulp to eat; the smaller the fruit, the more rind and seeds in proportion. Perhaps I will cut one open after Thanksgiving dinner. I did give a rather large grapefruit-sized gourd to my physical therapist on my last day with her, she said that she would cook and eat it, but it easily massed 10 times what the ones I got for Mom's dinner table do. μηδείς (talk) 18:46, 23 November 2015 (UTC)

What would it feel like to stand on a planet with a really high speed of rotation?

Can anyone describe what it would feel like, for an average human, if one were standing at the equator on a planet the size of Earth, but this planet is rotating on its axis many orders of magnitude faster than Earth's rotation? Would one 'fly off into space'? Would one get squashed by inertial forces? Would there be any physical effects at all? Or would the person just see the stars whizzing by really fast? -- œ^™ 06:43, 22 November 2015 (UTC)

If Earth were to spin at more than about 18 times its present rate, nothing on the equator would stay down. I don't know what you mean by "squashed by inertial forces". —Tamfang (talk) 08:01, 22 November 2015 (UTC)

Actually the higher centrifugal force at the equator causes the spheroid to deform - expanding at the equator (increased oblateness) to maintain hydrostatic equilibrium. -- Roger (Dodger67) (talk) 08:48, 22 November 2015 (UTC)

Yes, exactly. The Earth shouldn't be considered as a solid 'thing' - it's a relatively loose collection of stuff held together by gravity. If the rotational speed were to increase, the particles at the equator that are experiencing more centrifugal force will move outwards somewhat and material from the poles would move inwards a little to fill the void. The earth would go from being a perfect sphere to becoming squashed a little. In fact, this has already happened and the earth is about 44 kilometers wider than it is tall.

So with increased spin, the shape of the earth would flatten more and more. The experience for someone standing at the equator would indeed feel like a reduction in gravity...and that's true right now. If you currently weigh 100lbs at the north pole, you'd only weigh 99.65lbs at the equator.

But even one order of magnitude increase in spin rate would be catastrophic...the shape of the planet would change drastically...and much more than that would cause the whole thing to break apart - there would be catastrophic consequences long before a person would fly off of the surface. SteveBaker (talk) 16:09, 22 November 2015 (UTC)

The increase in spin speed might make you feel lighter, but the increased mass of rock underfoot would increase gravity, right? Gravity varies locally depending on what's underfoot - surely a more greatly deformed earth would affect that as well? 99.235.223.170 (talk) 16:32, 22 November 2015 (UTC)

That's why I linked hydrostatic equilibrium. Roger (Dodger67) (talk) 16:36, 22 November 2015 (UTC)

Steve's 99.65 lbs. isn't exactly right. You feel lighter at the equator for two reasons. One is the direct effect of the centrifugal force (i.e. centripetal acceleration of the Earth away from you). This is given by v²/r and works out to about 0.35% of 1 g-force, so I assume that's what Steve had in mind. But the other reason is because you are farther from the center of the Earth. If the Earth was a sphere, the force of gravity would be proportional to 1/r² and you would be about 0.71% lighter for that reason, compared to the poles; but the whole point of this calculation is that the Earth is not a sphere, and so you will feel additional weight due to the equatorial bulge, reducing the effect I just described. Perhaps someone can cite a reference that provides the correct value. --70.49.170.168 (talk) 16:51, 22 November 2015 (UTC)

Probably the easiest way to get an estimate is this: the effective gravitational potential in the rotating frame should be roughly constant over the Earth's surface (because any variation is a hill and at large distance and time scales there will be a downhill flow that equalizes it again). The potential at the center of the Earth is constant because it's just one point. Therefore the average acceleration (= first derivative of the potential) along a straight line from the pole/equator to the center will be larger/smaller by an amount equal to the ratio of the path lengths. If that difference is distributed uniformly over the length of the path, then equatorial acceleration / polar acceleration ≈ polar radius / equatorial radius ≈ .9967.

However, Gravity of Earth#Latitude says "effective gravity increases from about 9.780 m/s² at the Equator to about 9.832 m/s² at the poles", which is a ratio of .9947, so something is wrong with that argument, possibly the assumption that the difference is distributed uniformly. -- BenRG (talk) 19:19, 22 November 2015 (UTC)

I heard on a science podcast that I listen to, that if the earth stopped spinning gently, you could walk around the equator on dry land, since the water there now is due to the bulge caused by the earth's rotation. I must admit I haven't looked for a source to confirm this claim. 00:09, 23 November 2015 (UTC)

If there was a cat orbiting the sun, what would its name be?

See headline.

There are many cats orbiting the sun. We don't know what their names are, only what their owners choose to call them. SteveBaker (talk) 15:58, 22 November 2015 (UTC)

Cats don't have owners, they have slaves. Roger (Dodger67) (talk) 16:35, 22 November 2015 (UTC)

And anyway, the naming of cats is a difficult matter; it isn't just one of your holiday games. --70.49.170.168 (talk) 16:53, 22 November 2015 (UTC)

To get back to the OP's question, the technical term is Small Solar System body - meteoroid is also a possibility, although we'd have to use the definition of "metal" as "anything other than hydrogen or helium" for this particular case. See also Asteroid#Terminology. Tevildo (talk) 16:40, 22 November 2015 (UTC)

I rather disagree. You're absolutely correct that some stellar physicists would call a cat a metal, because its metallicity is quite high. But, it's premature to assume we ought to use that specialized jargon when we write about orbital cats.

First, let's describe the composition of a cat. To draw on the science-fiction series Star Trek, carbon-based life forms are termed "ugly bags of mostly water." You can read a more encyclopedic breakdown of the typical mass composition of an ordinary mammal here: Composition of the human body. For stoichiometric purposes, a cat and a human are nearly identical. By mass, a cat (like most mammals) is mostly liquid water; a small fraction is made of organic molecules - largely carbon, nitrogen, and oxygen, with traces of a few other elements like sodium, sulfur, calcium, and so forth.

For the purposes of stellar physics, those materials including carbon and oxygen are, indeed, "metals." But, an orbital cat is not a star: it does not exhibit any indications of nuclear fusion; it does not incandesce; it hardly self-gravitates; it certainly is not in hydrostatic equilibrium. So, a cat is not a star; it is not a planet; if it orbits the sun, it is a "non-planetary" body.

It is much more likely that we would apply the terminology that is commonly reserved for non-planetary worlds that exist within our solar system: comets, asteroids, and meteoroids. The classification schema for non-planetary bodies distinguishes between many types of objects. First are icy worlds (water, ammonia, and methane are common); a cat is not made of frozen water or methane ice. The next general category are the "metallic" bodies: these are mostly iron and nickel asteroids, consistent with the chemical spectrum we associate with the Iron peak. A cat is not primarily made of these materials. The last category, which is the "catch-all" for everything else floating in our solar system, is the term "chondritic". This includes other solid bodies that would be neither a metallic nor an icy world - so a cat would be a chondrite - even more specifically, a carbonaceous chondrite.

If a chondritic body were discovered in orbit of our Sun, and we learned that it did contain organic chemicals, it would be a high priority for our best space scientists to study this object. The NASA Astrobiology Roadmap highly emphasizes our ongoing search for organic macromolecules and amino acids on extraterrestrial worlds.

Nimur (talk) 20:43, 22 November 2015 (UTC)

I'm not sure what you're disagreeing with, I'm afraid. Are you saying that a cat can't possibly be a meteoroid as it's not metallic in the geological as opposed to astrophysical sense? In that case, would it be an asteroid? Or, are you saying that the "rocky or metallic" qualification isn't necessary for it to be a meteoroid? In that case, our meteoroid article needs to be corrected. Tevildo (talk) 21:15, 22 November 2015 (UTC)

Sorry, my opening sentence was not clear: I do not think we would call a cat "metal" simply because it is mostly non-hydrogen/helium. After re-reading your comment, I see that you weren't actually suggesting we do that. Nimur (talk) 01:31, 23 November 2015 (UTC)

Surely, in the absence of life support systems, an isolated cat would be made of mostly frozen water in fairly short order? MChesterMC (talk) 10:23, 23 November 2015 (UTC)

It would probably not survive - interplanetary space is not suitable for unprotected mammals for many reasons. However, objects in space are not necessarily very cold: the temperature at which they equalize primarily depends on their radial distance from their parent star. In practice, not all objects actually reach thermal equilibrium - it all depends on their material properties, rotation rate, and so forth. If an object rotates slowly, relative to its thermal conductivity and thermal capacity, its day-side may remain hot, while the night-side remains colder, and a thermal gradient may be set up throughout the object.. Nimur (talk) 01:34, 24 November 2015 (UTC)

Sol. StuRat (talk) 19:00, 22 November 2015 (UTC)

That answer is open to a charge of affirming the consequent, though. The OP may be interested to know that the French did have an active space program for cats in 1963. Tevildo (talk) 19:39, 22 November 2015 (UTC)

Was it a catastrophe ? StuRat (talk) 01:03, 23 November 2015 (UTC)

Swcharzschild limit

What unit of measurement is used in the Swcharzschild limit? In other words, is the big Rs at the end of the equation measured in cm or m or km or what?Megaraptor12345 (talk) 18:01, 22 November 2015 (UTC)

It's spelled "Schwarzschild" BTW. The r has the same units as the c in the equation. The G and the m should also match the units in c. Basically the output unit is the same as the input unit. Ariel. (talk) 18:19, 22 November 2015 (UTC)

Thank you, Ariel. Sorry about the spelling mistake! It is a hard word to spell!:)Megaraptor12345 (talk) 22:31, 22 November 2015 (UTC)

For those of you playing along at home, Schwarzschild radius is the article on this topic. DMacks (talk) 04:05, 23 November 2015 (UTC)

It depends on which version of the equation you're looking at. There is a tendency in physics to use natural units, in which case various constants (usually at least c and ħ) are set to 1, but even then authors tend to have their own preferences (e.g. some authors set G=1, while others don't). This is extremely confusing if you aren't familiar with the subject matter (especially when authors neglect to state which convention they're using), but it really saves time when you get the hang of it. In any case, the SI-compatible expression for the Schwarzschild radius is R_s=2GM/c². This gives R_s in metres if you enter G in metre cubed per second squared per kilogram, M in kilogram, and c in metre per second. --Link ^(t•c•m) 22:33, 23 November 2015 (UTC)

Physicists normally work in SI units, which means distance will be measured in metres unless otherwise stated. You could use any distance unit though, but you would have to be consistent in the rest of the equation. For example, you could measure the distance in furlongs, but would therefore have to measure the speed of light in furlongs per time unit (say, fortnight) and the speed of light in furlongs per fortnight]]. This would also change the value of G. Iapetus (talk) 17:32, 24 November 2015 (UTC)

Serrula, Rastellum, Fovea; What?

Hello, I would like to ask a few questions about some of these spider-related terms. I have looked up these terms: rastellum, serrula, fovea, tegular; and not found anything that fits the context (which was in relation to Tarantulas). So what do these mean?Megaraptor12345 (talk) 22:40, 22 November 2015 (UTC)

Wait, I have found out what Tegular means, sorry! Still, I do not know what the others mean.Megaraptor12345 (talk) 22:46, 22 November 2015 (UTC)

Does fovea help ? StuRat (talk) 22:56, 22 November 2015 (UTC)

[ec] It looks as though Spider anatomy and Glossary of arachnology terms need some additions. For rastellum, see Trapdoor spider. For serrula, see wikt:serrula. Fovea is a general anatomical term - according to this site, a spider's fovea is "a depression in the middle of the carapace which is the internal attachment point for thoracic muscles". Tegular means "of or resembling a tile", and the various tegular apophyses are mentioned in our spider anatomy article. Tevildo (talk) 23:01, 22 November 2015 (UTC)

November 23

The difference between cavity and sinuses

Someone wrote on Facebook that the difference is that "the 4 sinuses contain only blood and limph but the cavity is empty space which organs occupy". Is that true? I tried to find any source for that claim and I couldn't. I would like to get some help to verify it. 92.249.70.153 (talk) 05:55, 23 November 2015 (UTC)

Maybe they were referring to the dural venous sinuses, which apparently are lined with lymph vessels [4]. However, our article lists more than four. --NorwegianBlue ^talk 08:59, 23 November 2015 (UTC)

Thank you. They're refereeing to the paranasal sinuses rather than to those sinuses that you mentioned that are not exist in the bones. 92.249.70.153 (talk) 09:29, 23 November 2015 (UTC)

Is a bone considered as an "organ"?

Is it every bone considered as an "organ"? according to what, we can determinate what is organ or what is not? Can it be that we have 206 bones that each one of them considered an organ? 92.249.70.153 (talk) 08:51, 23 November 2015 (UTC)

Well, organ (anatomy) gives a broad enough definition to make a bone a type of organ, and bone describes a bone as an organ. On the other hand, on this page a medical professional gives a more restrictive definition by which bones are not organs. --70.49.170.168 (talk) 09:14, 23 November 2015 (UTC)

bone marrow has a good claim to be an organ (although bone marrow is not totally separable from the bone itself), and it forms part of the lymphatic system. Smurrayinchester 09:26, 23 November 2015 (UTC)

But bon marrow is found in all the bones? 09:30, 23 November 2015 (UTC) — Preceding unsigned comment added by 92.249.70.153 (talk)

Does rust accelerate corrosion?

If an iron surface had some rust and then was coated with an effective isolating paste without removing the previous rust, will this rust continue even in the absence of humidity?--82.114.170.222 (talk) 09:08, 23 November 2015 (UTC)

Humidity doesn't cause rust, oxygen does. Water would accelerate the reaction by acting as a sort of catalyst. --Jayron32 15:30, 23 November 2015 (UTC)

Jayron is correct that water by itself doesn't cause rust because rust requires oxygen. But that would be in the more theoretical case of pure water. Most water found in the world has a bunch of dissolved oxygen in it - so water does cause rust as a practical matter. Notice how, for example, the brand new, rust-free Titanic, has rusted away, despite being kept a bazillion feet away from the air, deep under the Atlantic ocean.

The presence of rust does tend to accelerate additional rusting because it's a very rough material and it traps moisture better than smooth, bare metal. If you first remove all of the moisture, THEN coat it with something waterproof, you'll certainly slow down the rate of corrosion. But just painting over rust may not help much. That's why people generally try to remove all existing rust before painting - because doing so removes any traces of trapped moisture.

SteveBaker (talk) 19:40, 23 November 2015 (UTC)

Also, painting over thick rust doesn't work. The rust breaks off in chunks, and takes the paint with it. StuRat (talk) 20:38, 23 November 2015 (UTC)

Physical equivalent of asymmetric key algorithms

Is there an actual physical equivalent of asymmetric key algorithms ? Like how (only) the public key can decrypt something which was encrypted with a private key, are there physical locks which can be locked with one key but can be opened with only another key (with a different set of cuts or serrations)? - WikiCheng | Talk 11:02, 23 November 2015 (UTC)

The only physical analogy I can think of is a yale-type lock on a door, where someone already inside can open the door and it will lock when they close it. I have been able to say to a visitor who needed to leave while I was at work "close the door behind you, but make sure you have everything as you won't be able to get back in", after he'd left only someone with a key could get in. I know its not exactly the same. -- Q Chris (talk) 11:35, 23 November 2015 (UTC)

Yes. Also similiar are the pad locks which can be locked by pressing. This amounts to using one key (no key) to lock and another key (the actual key) to open. But I was wondering if there are any locks which require one key to lock and another to open :-) -- WikiCheng | Talk 11:58, 23 November 2015 (UTC)

Ha Ha - in googling I found a lovely poetic analogy "only the right one can unlock the key to my heart". (I know that it is not what you were looking for, but felt it was worth sharing) - Q Chris (talk) 12:05, 23 November 2015 (UTC)

(Not answering the question but..) Simon Singh's The Code Book uses the analogy of padlocks (the kind that can be clicked shut without a key): Alice sends Bob an open padlock (her public key) to her friends, and he can send her a secret message by putting it in a box and locking it with the padlock. Alice (and no one else) can open the box with her (private) key and read the message. AndrewWTaylor (talk) 12:17, 23 November 2015 (UTC)

A physical mailbox? Anyone who has physical access to it can throw messages into it. Only the owner of the private key can get the messages.

The problem with the pad lock analogy is that once someone uses it, further uses cannot lock it again. It forces a different use. 13:44, 23 November 2015 (UTC)Denidi (talk)

I think that's just because physical objects can't be duplicated the way data can. Probably any physical analogy for data will fail on that count. -- BenRG (talk) 18:10, 23 November 2015 (UTC)

A close analogy would be a combination lock with a fixed public unlocking state and a "dial" that only supports irreversible moves, like this cube. For any sequence of moves that returns the cube to its original state, the first half and second half of the sequence could function as a public and a private key respectively. You could plausibly construct a puzzle like this where it's easier to come up with complete move sequences of that type than to find the second half of one given the first half. Also, if the puzzle has enough symmetry that flipped moves in a reversed order also return it to its original state (as this cube probably does), then the same key pair could also be used for "signing", as is possible with RSA. -- BenRG (talk) 18:10, 23 November 2015 (UTC)

This is a loopy idea, but I keep wondering how complicated magnetic field lines can get. Sometimes the Sun seems to get them so tangled up and then spew the lot out into space, but I don't really understand it; I don't understand if ball lightning has a really tangled layout either. "Braided magnetic fields" are a thing [5] - in a conductive plasma, is it possible though to somehow braid a magnetic field in such a way that untangling it takes a prohibitively long time, sort of like decrypting from a public key by brute force, and to "solve" that field by some other complex manipulation? Wnt (talk) 20:00, 23 November 2015 (UTC)

@Wnt: Maybe not so terribly loopy. Or rather loopy in a way that others have been very interested in. The braid groups can be used in cryptography, see e.g here [6] for a recent-ish work, with lots of previous refs. I don't think the authors have a physical instantiation in mind, but at a skim I don't see any reason why it couldn't work. (It would be very very slow, and need some sort of adamantium wire, but the concepts don't demand non-physical braids) SemanticMantis (talk) 22:20, 23 November 2015 (UTC)

@SemanticMantis: I was thinking if you have a perfect conductor (not a superconductor because that pushes magnetic field lines out of itself, but apparently that's not strictly a requirement; maybe stanene? - see [7]) then you can have magnetic field lines inside it that cannot cross one another (thus the adamantium) and which are generated by controlling twists in the magnetic field at the surface of the perfect conductor, then you might be able to add operations per the braid group diagram from either surface, and keep them stably stored somewhere in the middle. This would depend only on how fast you can twist a magnetic field at the surface, I think. (But then again, I have a really poor sense for how twisting magnetic fields really works) Wnt (talk) 12:52, 24 November 2015 (UTC)

+-+ |A| c +-+ | / a |A| |/| s | / / | e |/| |B| ==/ |== ==\ |== p |B| |\| l \ | | \ u |\| |C| g | \ +-+ |C| +-+ +-+ |K| +-+ | | |K| | | +-+ +-+

I wonder if a standard pin tumbler lock could do it by cutting the shear points (the places where the key pins and driver pins meet) on on an angle tilted "up or down" compared to the shear line instead of flat. It would mean the key could only turn in one direction when the pins are engaged. For example, if the top of the key pin were cut "lower-left to upper-right" as facing the lock, it could only turn clockwise after being inserted and only for a key cut to the "upper-right" height. Turning this way, shear line aligns at the start (the key is correct), and turning pushes the driver pin higher (shear pushes against its angled cut). This key can then turn back to start and be removed, but not overall counterclockwise because the shear line does not align with the side of the pin on the left side (the key is not correct). A key cut to the height of the "lower-left" height would not work (the key is "correct" but does not turn) because that motion would make the shear try to push the key pin further down onto the key. A second shear line could be cut on the opposite angle (upper-left to lower-right)...a different key that would only turn in the opposite direction after being inserted. Result: two different keys, one for "lock" other for "unlock". DMacks (talk) 23:13, 23 November 2015 (UTC)

For example, the left diagram has the key (K) that pushes the pin (ABC, with a spring beyond A) up to the extent that the left edge of AB is at the shear line (==). The plug cannot turn clockwise because the right AB edge does not align. Even though the shear line aligns on the left, the key cannot turn left because the shear makes the case push down on B, a motion that is blocked by the key. Only when the key is correct for the correct angle direction can the it turn. In the right diagram, the plug cannot turn clockwise (shear line does not align on right edge of pin) but can turn counterclockwise because doing so makes the plug push up on B, which is just pushing up A and the spring. The pin can always and only slide up, so the plug motion is only allowed in the direction such that the angle of the pin/pin surface transfers a component of the turning motion in towards the spring. DMacks (talk) 23:44, 23 November 2015‎ (UTC)

Another real-world analogy is the drop safe (which we do not seem to have an article on!). The ones in retail establishments, any cashier can drop money into. The ones on the outside of banks for night deposits, the night depositors need an (ordinary, low-security) key to open, But only an Authorized Person with a higher-security key can get the deposited money back out. —Steve Summit (talk) 00:41, 24 November 2015 (UTC)

I would call that a night safe, but that link only goes to a disambiguation page with no onward links. AndrewWTaylor (talk) 08:55, 24 November 2015 (UTC)

There are locks like this where you can push the bolt in and lock it in place with the small key. When you release the bolt (with the small key) and close the door it's locked and you can only open it with the larger key. Sjö (talk) 06:16, 24 November 2015 (UTC)

Thanks everyone -- WikiCheng | Talk 07:08, 24 November 2015 (UTC)

Another example would be a shaft that has two ratchets that only allow motion in opposing directions. As it stands, it cannot turn because one direction is blocked by one pawl and the other by the other (each prohibits turning in the only direction the other allows). Have a key-lock that pulls the pawl back from its gear, a separate such mechanism for each pawl. Now each of the two keys unlocks one but not the other direction of motion of the shaft, and separate keys unlock the two different directions. DMacks (talk) 07:18, 24 November 2015 (UTC)

Obtained electricity or heat as result of a chemical reaction

What kind of reactions would produce heat, and what kind would produce an electrical current? Does burning also generate electricity? Or could burning generate electricity too? At least electrons are moving around. --Scicurious (talk) 15:12, 23 November 2015 (UTC)

To address the first question, see Exothermic reaction. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 15:22, 23 November 2015 (UTC)

If I got it correctly both reaction types, generating heat or electricity, are exothermic. It is not necessary to generate heat in the narrow sense. Just releasing energy makes the reaction exothermic.--Scicurious (talk) 16:05, 23 November 2015 (UTC)

To address the second question, see galvanic cell, electrochemistry, electrochemical cell and redox. --Jayron32 15:27, 23 November 2015 (UTC)

And could we use fossil fuel to implement a kind of gasoline/diesel-air battery? Could we put a membrane between both elements? fuel would be the anode, and air the cathode. --Scicurious (talk) 16:05, 23 November 2015 (UTC)

See Fuel cell and Direct methanol fuel cell. Yes, in other words. Tevildo (talk) 18:54, 23 November 2015 (UTC)

It's all energy, when you get down to it. You can convert heat to electric current and vice versa; electricity generation is mostly done by harnessing heat to heat water that then turns turbines. The reason why we choose one method over another is a question of engineering. A hypothetical perfect fuel cell would be more efficient for electrical generation than burning fuel to heat water, but real-world fuel cells have numerous issues that limit their usefulness. --71.119.131.184 (talk) 19:24, 24 November 2015 (UTC)

Would a hypothetical perfect fuel cell be better than hypothetically perfect conventional combustion, where 100% of the energy released goes into heating the water ? StuRat (talk) 08:20, 26 November 2015 (UTC)

That's irrelevant in the case cited: 71.119 said "for electrical generation than burning fuel to heat water". The question is: how efficiently can hot water be made to generate electricity, and the answer is "not very".--Phil Holmes (talk) 11:57, 26 November 2015 (UTC)

What is this electronic component?

It came off the power supply board of an old piece of test equipment. It's the same size as a standard fuse. My guess is something like this. The resistance between the terminals is 10K.

— Preceding unsigned comment added by Cash4alex (talk • contribs) 15:12, 23 November 2015 (UTC)

Applying the duck test, I'd say it's a Fuse (electrical).--Denidi (talk) 15:27, 23 November 2015 (UTC)

The picture is a bit out of focus. What does the red line in the middle appear to be made of? Smurrayinchester 15:33, 23 November 2015 (UTC)

I don't know... there are clearly markings from 0 to 10 - this is a 'fuse' with a scale of some sort, and a heavy-duty resistance. My guess is that it has to be some kind of thermometer, measuring the electrical current by the heat generated??? An issue is that the power dissipation (VI = I²R) isn't linear ... something like mercury is ... that isn't consistent with what I see, but then again, I'm not taking how the heat is dissipated into account. Wnt (talk) 15:47, 23 November 2015 (UTC)

A "temperature fuse" is commonly called a "thermal cutoff" and it doesn't look like that. When using inline leads, they tend to look like fat resistors - no glass - no temperature markings. Therefore, I doubt this is related to both "temperature" and acting as a "fuse." Further, temperature of 0 to 10 is a very small range. 209.149.114.197 (talk) 16:18, 23 November 2015 (UTC)

Here's a better picture (not taken with a mobile phone this time...).

It looks like there is a fat glass tube inside, with a small bore with the metal (mercury?) running through. The red part looks like it might be coloured plastic behind the glass. Cash4alex (talk) 17:08, 23 November 2015 (UTC)

An electrochemical hour meter - full explanation here: http://www.vintage-radio.net/forum/showthread.php?t=116566 — Preceding unsigned comment added by 86.130.12.61 (talk) 18:46, 23 November 2015 (UTC)

^^^ That's the answer. I found another ref here [8] - they're also called "elapsed time indicator". The principle is that there is a small blob of electrolyte somewhere in the middle; a small amount of electric current causes mercury to dissolve at one end and electroplate onto the other. As noted above, the high resistance of the device limits its power consumption to what is barely necessary - this is of course going to be wired in parallel (like a voltage meter) rather than in series (like a fuse) to the main circuit. They are still made [9] but now in a mercury-free variant - I didn't see the details of the new device operation. Others are digital and look more different. Wnt (talk) 19:55, 23 November 2015 (UTC)

It could also be a mercury-based coulombmeter. They can be used as run-hour meters. 62.56.60.78 (talk) 18:54, 24 November 2015 (UTC)

Maybe it's the missing Mercury link from the Tardis (very old reference). {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 18:12, 25 November 2015 (UTC)

Lack of large marine browsers

The largest land animals (elephants, giraffes, rhinos, hippos, moose) eat leaves or are at least herbivores. So why isn't this the case for marine animals ? Baleen whales do eat plankton, but that includes zooplankton, so they aren't herbivores. The largest marine herbivore I can think of is the dugong. So, what limits the size of marine herbivores ? I wouldn't think it would be the food supply, as the Sargasso Sea has plenty of seaweed, for example. StuRat (talk) 20:48, 23 November 2015 (UTC)

Temperature is a likely limiting factor, see scholarly articles here [10] and here [11]. The former discusses latitudinal gradients in herbivore size and temperature as an important driver. The latter also discusses temperature, and also engages the Metabolic_theory_of_ecology, which relates biophysical and biochemical stoichiometry to ecology and evolution of organisms' life history traits. I think it's no fluke that the manatees and whales are so big - they are endotherms (while most of the ocean's critters are ectotherms), and so their growth rates are not so constrained by ambient temperatures. The great Simon Levin thinks that dimensionality is additionally important, see page 158 onward here [12]. The basic idea is that a pelagic herbivore living in a 3D world is constrained to foraging on macrophytes that predominantly grow on a 2D surface. SemanticMantis (talk) 22:13, 23 November 2015 (UTC)

But land herbivores are also constrained to foraging on plants that predominantly grow on a 2D surface. StuRat (talk) 04:53, 24 November 2015 (UTC)

Right, an elephant is basically living on a 2D surface, most of which can provide food. Pelagic ocean critters live in a 3D world, only a small portion of which can grow macrophytes. This plays into the gross metabolic processes of the individuals and populations, and offers an explanation of why body size of oceanic herbivores is often smaller than their terrestrial counterparts. Also it gives a rationale for why baleen whales and other eat lots of pelagic plankton instead of looking for macrophytes, but then they end up eating animals too, and you don't want to consider them herbivorous. SemanticMantis (talk) 15:19, 24 November 2015 (UTC)

(Also - perhaps User:Obsidian Soul has some additional comments or refs? SemanticMantis (talk) 22:23, 23 November 2015 (UTC))

• Steller's sea cow μηδείς (talk) 23:13, 23 November 2015 (UTC)
• See Manatee#Diet. --Jayron32 02:00, 24 November 2015 (UTC)
• See Dugong#Feeding. --Jayron32 02:01, 24 November 2015 (UTC)
• See Green_sea_turtle#Diet. --Jayron32 02:04, 24 November 2015 (UTC)

Probably the largest marine animals eat plankton because plankton is the most abundant food source in the oceans, and the largest land animals eat plants because plants are the most abundant food source on land. It might not be any more complicated than that.--Wikimedes (talk) 08:05, 24 November 2015 (UTC)

• Perhaps a silly question, but how exactly is a whale supposed to filter the phytoplankton from the zooplankton? The plankton mix freely and I can't see any obvious evolutionary advantage to not digesting zooplankton. Phytoplankton are the main photosynthesizers in the ocean, and I'd argue that anything that eats them counts as a grazer even if they also consume zooplankton. Incidentally, seaweed doesn't have leaves - it's a colony of algae (a group to which most phytoplankton also belong). Smurrayinchester 09:05, 24 November 2015 (UTC)

Sargasso Sea gets to Sargassum, which points to mostly unhelpful Herbivorous fishes, but this can be unravelled to Algae eater. Sargassum is brown microalgae, so I suppose that makes anything that eats it an algivore. They are not notably huge animals, but the pictures don't make this seem that surprising. Large herbivores live on endless plains with grass up to your ass (until they eat it all, that is); these fish have to deal with little clumps that occasionally get big enough to impress - though I'd speculate the contrasting demands of cold-blooded versus warm-blooded metabolism and the modes of locomotion might have something to do with it also. Truly large herbivores like elephants go after more than just grass, but can take down trees. My impression, perhaps false, is that large dinosaurs had even more impressive foliage to munch on. Wnt (talk) 13:49, 24 November 2015 (UTC)

It seems to me that this question could be asked in the opposite way and get to the same answer... Why don't elephants hunt and eat other animals? Could an elephant catch a gazelle? Could a giraffe hunt effectively? It should be rather obvious that it is difficult for large animals to be hunters. It isn't impossible - just difficult to not notice the huge elephant trying to sneak up on you. As for whales... I specifically remember an article from last year discussing how whales hunt giant squid and that it was an unknown practice because it takes place in the deep ocean where whales are not monitored. 209.149.113.52 (talk) 20:50, 24 November 2015 (UTC)

Toothed whales are pack hunters, basically lions of the sea. The article on pack hunters specifically notes both dolphins and orcas in this ecological role. --Jayron32 01:23, 25 November 2015 (UTC)

Another electrical device needing identification

• 
  Array of them at upper left
• 
  Front detail view
• 
  1/4 side view
• 
  Broader 1/4 view

This is in the old pump room of the Ballard Locks. Maybe some sort of heat sink? Something that can be cut in and out of the circuit so that the shift isn't too sudden when power to the pump is turned on and off? The otherwise knowledgeable person giving a tour of the locks wasn't sure. - Jmabel | Talk 23:42, 23 November 2015 (UTC)

Looks like a high-power resistor bank. Googling around, they are (or at least were) a component of pumping stations and other facilities for motor control. DMacks (talk) 00:08, 24 November 2015 (UTC)

Thanks! - Jmabel | Talk 00:23, 24 November 2015 (UTC)

November 24

What causes certain pathogens to be only transmitted orally or nasally or topically or urogenitally?

Why can't astroviridae spread urogenitally? Why can't trichomonas parasite be transmitted by food contamination or by swimming in contaminated pond water? Does it have to do with finding the right receptors or favorable location in a host body? 140.254.70.25 (talk) 14:49, 24 November 2015 (UTC)

The two examples are

• Urogenital spread of Astrovirus (virus)
• Trichomonas spread by food/nasal (protist)

With viruses, one reason is that they are very small and simple. Humans don't have a gene for an arm and another for a leg, but viruses typically have just a few genes whose products physically make them up (though they may have some extras to mess with the host). There are exceptions like smallpox, which probably has a fully functional kitchen sink hidden away somewhere in its massive innards, and even larger megaviruses. But when a typical virus only has a few genes, it can't really do more than a few things. Finding a receptor which may have limited distribution is one of those things. If a virus does manage to pick up a new gene for a new receptor, then it's not the same virus any more.

For protists, it's a more complex question. Some of it is a matter of ecological niche, I suppose. Trichomonas vaginalis ought to be clever enough to figure out a way to infect other areas, but the body is a tough opponent and it would face many well-established competitors. You can see from the broader Trichomonas link though that they don't all work the same way, so it's not impossible. Wnt (talk) 15:32, 24 November 2015 (UTC)

Part of it has to do with the fact that your skin itself is pretty tough stuff. The Stratum corneum is a layer of relatively impermeable material on the outside of your skin which stops most pathogens from entering. However, many surfaces such as mucous membranes of the nose or genitals, the lining of the mouth, etc. don't have this layer, making them more susceptible to pathogens. Otherwise, however, there are many infections which are not specific to the genitals, exclusive of other ways of entering the body. For example, most herpes infections can infect the eyes, mouth, nasal passages, or genitals in equal measure, the actual pathogen is the same regardless of its method of entry. It just can't get through ordinary skin. --Jayron32 15:39, 24 November 2015 (UTC)

Or, putting it another way, different organisms find different environments hospitable. One organism will like a high pH, another a low pH. Some like a relatively warmer temperature. Some "like" a certain humidity or level of oxygen. And so they are only found in environments that permit their growth. And nose, vagina, lungs, skin, and urethra differ in those and other ways. - Nunh-huh 03:18, 25 November 2015 (UTC)

Dark matter "hairs" (gravitational lensing of distant dark matter sources)

NASA points to current/future Astrophysical Journal, which means I look up Arxiv.

The premise is that there are sources of dark matter which are subject to gravitational lensing. Because the dark matter moves through planets, it is focused to different degrees in dense and less dense material, forming "hairs" from a low altitude "root" to a high altitude "tip". They say for the Sun these roots and tips are hidden inside it. For their Earth calculation, the root seems to be 1.1 million km and the tip at perhaps 2.4 million km. For Jupiter, 0.21 million km and the tip at 0.9 million km.

However, all this assumes "weakly interacting particles streaming at 220 km/s (the approximate orbital velocity of the solar system around the galactic center (Karachentsev and Makarov 1996)) through a compact body". What I don't get is why. If the dark matter particles are coming from some source, or currently exist as a "fine-grained stream" at a fixed location, doesn't that source or stream have to be revolving around the galaxy itself, perhaps originating somewhere close by? Then the "hairs" might come right down to the Earth's surface, no? And if they are truly a diffuse cloud that has been orbiting the galaxy from the beginning, shouldn't they be spread out homogeneously, with no particular roots or tips in any direction?

Another thing I wonder is if any of the other planets project these "hairs" onto Earth. I suppose Venus, like Jupiter is out - being similar to the Earth, the 2.4 million km just shouldn't reach. But maybe something smaller like Mercury, Mars, or Titan, could focus (weaker) streams to a longer distance? Time for NASA to start up an astrology department, perhaps. :) Wnt (talk) 15:12, 24 November 2015 (UTC)

The dark matter streams are something that you have to think of in phase space. They don't necessarily come from a nearby source, they depend more on the merger history of the galaxy and may exist for a very long time. In the simplest model of a dark matter halo, where there are no streams, you'd expect WIMPs near Earth to have completely random and uncorrelated positions and velocities (including direction). If there are streams, that gives you dark matter particles that are moving together (same velocity and direction) but not clumped spatially (at least on the scale of the solar system). When this kind of stream interacts with a mass like Earth, some of the clustering in velocity turns into a spatial concentration. (Again this is easiest to think about in phase space). For one planet to focus one of these "hairs" onto Earth, you'd have to have an alignment of the direction of the stream with the direction of the other planet. This would be very unlikely and also wouldn't last very long. --Amble (talk) 19:18, 24 November 2015 (UTC)

@Amble: I'll admit I don't really have this phase space thing in my head. Especially not where they talked about six-dimensional phase space! But does this differ from looking at stars? The light from a star isn't clumped into a stream, but we still look out and see it in one direction, and its gravitationally lensed image is in the other. Looking at a single particle of dark matter, I'm thinking if it is stationary relative to the galactic center it has to fall straight toward the galactic center from here, while to be coming at Earth from a perpendicular angle it has to have a speed relative to the center of the galaxy that is comparable to Earth's, and I suppose if it has a speed faster than Earth's then it should be bound for some higher apogee. Dark or not, phase space or whatever, it's still gotta orbit, right? And if particles have a speed comparable to that of Earth, and if the "hairs" project in all directions, then why isn't there a "hair" from particles overtaking Earth at virtually the same speed as Earth, that focus to a root somewhere close to the surface? Now I'll admit that it makes sense that most of the particles are in some galactic orbit not similar to that of Earth's and so they're indeed moving really fast relative to it, and so most of the hairs are 185 times the surface of the Earth away, but the few exceptions ought to be a lot easier to study. :) Wnt (talk) 21:01, 24 November 2015 (UTC)

@Wnt: Yes, any particular orbit will be in some orbit, but not necessarily a circular orbit or one in the galactic plane. So it can be traveling in any direction relative to our solar system. There won't be hairs projecting in all directions. A hair only exists if there's a stream of dark matter coming from some particular direction and making up a large fraction of the local dark matter density. So you could have a stream that's in a similar galactic orbit to our Sun, such that the particles would pass by Earth at much lower speeds than 220 km/s and the hair's "root" would be close to the ground. This is what you're suggesting, right? I believe that's possible, but not a great detection target for a few reasons:

• There's a lot less phase space available for the stream to match the solar system's orbit than for the stream to have a very different orbit, making it unlikely for such a stream to exist. It would have to be an extreme "lucky shot", while the case considered in the paper is a typical sort of dark matter stream (assuming that such things exist at all).
• Detecting dark matter depends on the number of particles passing through per unit time. If the relative velocity is small, then the number of WIMPs per unit time going through your detector is also small (proportional to v).
• Detecting dark matter may depend on detecting the energy from a dark matter particle scattering in a detector. (Certainly for WIMP detection this is the case). If the velocity is small then the energy available is small and it will be very hard for the signal from a single interaction to be larger than the energy threshold for a realistic detector.

I don't see a discussion in the paper of possible low-velocity streams (unless I've missed it), so the considerations above are the ones that I think are likely relevant. If you want to know the author's reasons for this choice, you could try emailing him directly. --Amble (talk) 22:47, 24 November 2015 (UTC)

These are good points, and of course I can't really argue against an explicit assumption. I suppose what I was really wondering is if the Gravity Field and Steady-State Ocean Circulation Explorer or something similar might have picked up one or more fixed anomalies on east-west ley lines under the sign of Scorpius (sorry, I couldn't help myself!), but I suppose that's probably too much to hope for. Wnt (talk) 14:41, 25 November 2015 (UTC)

The local dark matter density is something like 5×10^-25 g/cm³, so even with a huge enhancement you won't see it as a gravitational anomaly. The idea with the "hairs" is that it will boost the rates enough to help with direct detection. --Amble (talk) 17:06, 25 November 2015 (UTC)

Wow. I'm always getting tripped up on some paradox with dark matter ... I was thinking since it's invisible but has mass and makes up most of the matter in the universe (excluding dark energy), you could detect it gravitationally more easily than by directly imaging it. I guess not! The paper says 10E+7 enrichment, so that's 5x10E-18 g/cc = 5x10E-12 g/m³ ... yeah, that's not going to stand out much against the ocean currents! Dang how can something be so prevalent and so hard to find! Wnt (talk) 20:26, 25 November 2015 (UTC)

Annoying, isn't it? ;-) One way to think about this that I find somewhat helpful is to turn the vastness of empty space (as described by Douglas Adams) on its head. The remarkable thing is not that there are great empty distances between things, but instead, the remarkable thing is that a small fraction of the baryonic matter has somehow made itself incredibly densely concentrated -- by a factor of something like ×10³⁰!. A lot of open questions in astrophysics and cosmology have to do with how such a thing could have happened at all. The "default" behavior would be to stay spread out and nearly undetectable (and this is true not only of the nonbaryonic dark matter, but most of the hydrogen too). So what we think of as ordinary matter is actually very special stuff that has somehow figured out a way to make itself mind-bogglingly concentrated in a few places here and there.

If you do ask the paper's author about nearer hairs from low-velocity streams, I'd be curious to hear his response as well. --Amble (talk) 20:45, 25 November 2015 (UTC)

As a side note to the refdesk / more importantly for the encyclopedia, we really ought to have an article on dark matter direct detection. Started a draft Draft:Direct detection of dark matter split from dark matter; feel free to edit. --Amble (talk) 21:06, 25 November 2015 (UTC)

Fossil crinoids of Ireland

Hello! I would like to ask for some link to a website with a key to Irish and English fossil crinoids right down to the species level. I searched before and could not find anything!:( And if anyone suspects that this is for homework,... It is not. Megaraptor12345 (talk) 17:31, 24 November 2015 (UTC)

Not a key, but there is a review article here: Donovan, Stephen K.; Harper, David A. T. (January 2003). "Llandovery Crinoidea of the British Isles, including description of a new species from the Kilbride Formation (Telychian) of western Ireland". Geological Journal. 38 (1): 85–97. doi:10.1002/gj.934. Let me know if you can't find a copy of that article. Graeme Bartlett (talk) 20:32, 24 November 2015 (UTC)

Another review is here: Paul, Christopher R. C.; Donovan, Stephen K. (2011). "A review of the British Silurian cystoids". Geological Journal: n/a–n/a. doi:10.1002/gj.1287. Graeme Bartlett (talk) 20:57, 24 November 2015 (UTC)

Yet another really old one is here: Bather, F.A. (April 1890). "XLIII.— British fossil Crinoids". Journal of Natural History Series 6. 5 (28): 306–334. doi:10.1080/00222939009460837. It has a nice diagram summarising all the species, but since it is so old is sure to miss many. Graeme Bartlett (talk) 21:04, 24 November 2015 (UTC)

Are not Cystoids different from Crinoids? I am not ungrateful, but I do want the right thing;) Megaraptor12345 (talk) 14:30, 25 November 2015 (UTC)

They look to be different groups, but they are hard to distinguish, so it depends on exactly why you want this information. See Cystoid. Graeme Bartlett (talk) 19:42, 25 November 2015 (UTC)

It's a Gothic horror set in England, but any fan of krynoids needs to see The Seeds of Doom. μηδείς (talk) 22:11, 25 November 2015 (UTC)

November 25

Induction cooking, and induction charging

Is the physics behind induction heating a pan and induction charging a smartphone (aka wireless charging) basically the same? Except for the fact that the devices (pan or phone) are different. One is designed to resist and get hot, the other to let the current flow through a coil and get charged? I don't get though why you can place the smartphone in any orientation on the charging pad, and why its components don't get hot.--Scicurious (talk) 02:19, 25 November 2015 (UTC)

The saucepan needs a fairly big chunk of metal to set up a big eddy current. Small pieces will net get much voltage across them, and less current with heating much much smaller. Graeme Bartlett (talk) 09:36, 25 November 2015 (UTC)

We have pretty good articles on induction cooking, induction heating, inductive charging, and see also conductive wireless charging. SemanticMantis (talk) 15:18, 25 November 2015 (UTC)

I took a look at those, but still... It's quite a mystery for me that you can orient the smartphone in any direction. Shouldn't the coils be parallel? Does the charger or phone adapt internally? --Scicurious (talk) 16:00, 25 November 2015 (UTC)

Some of the simpler inductive chargers do demand a specific orientation, like the Nokia one mentioned here [13]. This patent [14] explains a bit about the proper orientations are achieved, and this blurb [15] talks about some methods to allow for multiple orientations or devices. Qi_(inductive_power_standard)#System_overview has some info and refs about how orientation-independent charging can be handled. SemanticMantis (talk) 17:31, 25 November 2015 (UTC)

Gaining/losing weight too fast

Any associated health risks with either one? If any? What's the maximum rate for someone's height? Theskinnytypist (talk) 04:50, 25 November 2015 (UTC)

Yes, there can be major health risks for either. But the factors that come into play are too complex for me to try to summarize. Looie496 (talk) 15:53, 25 November 2015 (UTC)

I doubt the rate can be calculated precisely.

A crash weight-loss diet can imply loss of water, loss of muscle mass (including heart), lack of nutrients, saggy skin, among others. A crash weight-gain diet could imply too much fat is built up. Or, if you are trying to build muscle, fatigue and injuries.

Any one of both are long-term goals.--Scicurious (talk) 16:05, 25 November 2015 (UTC)

• Is there a list of notable people who died of crash diets? Laird Cregar is one, and I recently saw a more recent actor mentioned but forget who. —Tamfang (talk) 04:54, 26 November 2015 (UTC)

• Not to be insensitive, but hunger strike and list of hunger strikes would be related. 64.235.97.146 (talk) 16:53, 26 November 2015 (UTC)

Orientation of solar system ecliptics to galactic ecliptic

Without going into specifics - is there any relationship between the orientation of the ecliptic planes of individual solar systems, and that of the parent galaxy? Or is there no reason to assume such, and solar ecliptics are likely to be oriented every which way relative to the galactic plane? Gut feeling says that since ecliptic planes at both scales are the result of similar mechanics, there might well be some correlation, but I haven't been able to find a statement either way.-- Elmidae 12:43, 25 November 2015 (UTC)

As far as I know, there is no significant correlation. Methods of detecting exoplanets and Kepler_(spacecraft)#Objectives_and_methods seem to assume random orientation. And, anecdotally, the Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit), according to Milky Way. --Stephan Schulz (talk) 16:05, 25 November 2015 (UTC)

Too bad. If alignment were commonplace, Kepler (spacecraft) would work better. Jim.henderson (talk) 17:46, 25 November 2015 (UTC)

Or worse, depending on where you point it. In particular, Kepler "points to a field in the northern constellations of Cygnus, Lyra and Draco, which is well out of the ecliptic plane, so that sunlight never enters the photometer as the spacecraft orbits". If all orbits were aligned, Kepler would need point along the ecliptic, too, and that would be very bad for the 1/30s of its orbit where the sun would be directly in its field of view, and probably quite bad at other times when it points closely to the sun. --Stephan Schulz (talk) 18:46, 25 November 2015 (UTC)

Actually, I just realized that the very orientation of the Milky Way in the night sky at the equator (incl. range of seasonal precession) shows a significant departure from the solar ecliptic. Heh. - Seems the far-fetched SF plot device I was trying to falsify is Go *rubs hands* Cheers, people! -- Elmidae 19:41, 25 November 2015 (UTC)

One could also say "And, anecdotally, the Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit)" ;-). --Stephan Schulz (talk) 20:07, 25 November 2015 (UTC)

I suspect that there IS a relationship, but it's at such a large scale that it's only revealed on the galactic level, i.e. that if you add up ALL the solar systems' orientations, they "add up" to the orientation of the galaxy. However on an "individual level" the solar systems would form up every which way. Vespine (talk) 23:32, 25 November 2015 (UTC)

I take back the above. Reading articles such as these it is possibly just random, up to chaos theory. Vespine (talk) 06:01, 26 November 2015 (UTC)

That does sound pretty definite, thanks!-- Elmidae 07:41, 26 November 2015 (UTC)

Little Boy and Fat Man detonation timings

According to Little_Boy#Fuse_system, the detonation was supposed to occur at the most destructive altitude, similarly to Fat Man. Why it was decided not to detonate both bombs upon ground impact or at very lower altitudes (via different timer and altimeter settings) where damage would be the greatest? 93.174.25.12 (talk) 21:37, 25 November 2015 (UTC)

Note: I have changed the heading to Little_Boy#Fuze system. A fuse is typically just a piece of some sort of cord that burns; a complicated detonator is a fuze. So the original poster's link will no longer take you to the right section; use the one I posted instead. --Trovatore (talk) 21:47, 25 November 2015 (UTC)

One factor may well have been that they didn't know what altitude would produce the most damage, so wanted to try various altitudes. StuRat (talk) 21:45, 25 November 2015 (UTC)

Against non-hardened targets like an ordinary city, damage is the greatest when the weapon detonates above the ground as an air burst (as the bombs used on Japan were). Think about the physics of an explosion. An explosion expands roughly spherically. A ground burst directs much of the weapon's energy (the bottom part of the sphere) into the ground. In an air burst, the explosion is free to expand over a wider area. Sometimes a ground burst is desirable, like when the target is underground, or you want to maximize fallout. --71.119.131.184 (talk) 21:56, 25 November 2015 (UTC)

Definitely the premise that a ground detonation or very low altitude detonation is the "most destructive" is mistaken. The topic is discussed here Effects of nuclear explosions. Vespine (talk) 23:24, 25 November 2015 (UTC)

Yes, anything in a city pretty much directly under an air burst is going to be wiped out anyway. An air burst will spread the destruction over a wider area. Bubba73 ^{You talkin' to me?} 02:41, 26 November 2015 (UTC)

The Linear thermal expansion of technetium

Where can I find data for the linear thermal expansion of technetium at temperatures from room temperature up to the melting point? — Preceding unsigned comment added by 77.247.29.84 (talk) 22:40, 25 November 2015 (UTC)

Our article Technetium gives a figure of 7.1 μm/m⋅K, cited to this paper. This is only for the range 0 - 100°C, though. Tevildo (talk) 23:12, 25 November 2015 (UTC)

Why do humans live so long?

Why does it take 20 years for a human being to reach sexual maturation and even longer for cognitive maturation? Why do other animal species have shorter life cycles? With the push to delay marriage at later ages, is it ever possible to delay puberty as well and prolong childhood, so that childhood is from 0-20 years, adolescence is from 21-29 years, and adulthood is from 30-death? 71.79.234.132 (talk) 22:44, 25 November 2015 (UTC)

Sexual maturity occurs far earlier than 20 in most people, although near starvation can delay it substantially. The reason for long human life spans seems to be related to our intelligence, in that it takes decades to learn everything we need to know for optimal survival chances. And prolonging childhood seems to be important for learning, as the more maleable child brain learns more easily, but also isn't sufficient for survival without assistance. As for delaying puberty, yes, there are drugs to do that. I think you have a good idea there, and venereal diseases, teen pregnancies, and teen violence could all be reduced by delaying puberty until people are mature enough to handle it. StuRat (talk) 22:51, 25 November 2015 (UTC)

(EC) Lots to address here. Let's start with the last: puberty in humans is occurring earlier now than in the past, Puberty#Historical_shift. For animals' life spans, see Life_history_theory#Reproductive_value_and_costs_of_reproduction and r/K selection. For our relatively slow maturation times, see altricial, Neoteny#Neotenic_traits_in_humans, and Observational_learning. For our longer lifespans, see Grandmother hypothesis. Somewhere in there the Obstetrical dilemma comes in. Parental_investment is also relevant. SemanticMantis (talk) 22:55, 25 November 2015 (UTC)

Also, we live long compared to some other common "small" animals, but we're not even in the top 10 longest lived animals. Vespine (talk) 00:44, 26 November 2015 (UTC)

• No warmblooded animal our size has a similar longevity or such a delayed adolescence. Neoteny and kin selection, specifically the importance of grandparents in raising children while the parents work and passing along folklore exhibit a large selection pressure in favor of longevity. μηδείς (talk) 04:57, 26 November 2015 (UTC)

No terrestrial warmblooded animal, perhaps. See Bowhead_whale#Lifespan. --NorwegianBlue ^talk 15:41, 26 November 2015 (UTC)

November 26

Genetics of the Kalash people

Is there anyone with a little understanding of the genetics of human populations? I need an opinion on a recently added text to the wikipedia article on the Kalash people (of Pakistan) that says:

The studies show the oldest estimated date (990-210 B.C.) of DNA mixing by Western Eurasian sources most probably by Scottish sources originated from regions comprising modern day Germany and Austria, which coincides with Alexander's expansion into Central Asia around (356 to 323 BCE).

Although I can see where in the referenced Science magazine article the bit in bold might have come from it strikes me as particularly nonsensical. Is it just me?— Preceding unsigned comment added by Uanfala (talk • contribs) 23:53, 25 November 2015 (UTC)

Why do you think it is non-sensical. Ruslik_Zero 13:30, 26 November 2015 (UTC)

The bit about Scottish sources is misleadingly worded at best. Scots are the modern group that accounts best for the admixture event, but that's undoubtedly because the Scots correlate best of the modern groups with the Celtic/Pictish people who dominated much of Europe before the Germanic invasions. It doesn't at all mean that the geographic source was Scotand. In fact the Science article say: "Distinct, ancient and partially shared admixture signals (always dated older than 90BCE) are seen in six groups, including the Kalash, whose strongest signal suggests a major admixture event (990-210BCE) from a source related to present-day Western Eurasians, though we cannot identify the geographic origin precisely.". Looie496 (talk) 14:16, 26 November 2015 (UTC)