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September 24

What's happened with the PHYTOME project?

Have there been any new processed meat products with phytochemicals sold in the marketplace ever since the project was finished in 2016? — Preceding unsigned comment added by 184.67.108.46 (talk) 10:45, 24 September 2018 (UTC)[reply]

filtering salt out of seawater

"The teenager only had a few days worth of supplies and survived by catching fish, burning wood from his hut to cook them, and sipping seawater through his clothes to minimize his salt intake."[1] Can one filter out salt by sipping seawater through the textile of one's clothes? Bus stop (talk) 14:12, 24 September 2018 (UTC)[reply]

No, that will not work - but it doesn't mean he didn't try it (or that the news report was inaccurate).

From a scientific point of view, salt water is a chemical solution - the salt has dissolved into the water and is present as individual ions of sodium and chloride. Many textbooks define a solution as a mixture that cannot be separated by filtration. Cloth isn't even a good filter - so it's not going to have any effect at removing the salt - not even in ideal laboratory conditions.

From a practical, survival point of view: this isn't a standard procedure either. Almost all sources agree: in a survival situation at sea, it's better to drink nothing than to try to drink seawater. For reference, I pulled out the Army Survival Manual, which you can purchase online in reprint. They make it pretty clear: do not drink seawater, unless you have a real desalination kit. "By drinking seawater, you deplete your body's water supply, which can cause death." Nimur (talk) 14:23, 24 September 2018 (UTC)[reply]

It's pretty clear this is the way it has to work since seawater has more salt than the body's solutes. (almost 4 times as much in fact) Sagittarian Milky Way (talk) 14:56, 24 September 2018 (UTC)[reply]

What about using a funnel, and covering it with a piece of paper, into a bottle. Then constantly pouring the water from a bottle back to the funnel. Well, the easy answer to check is if you see salt piling up in the paper funnel, then you're getting progress. 67.175.224.138 (talk) 02:56, 25 September 2018 (UTC).[reply]

I think I read something about getting the fluid from the eyes and spine of fish but no other fluid from them and not eating and that would keep you going for a while. Rather desperate but needs must I guess. Dmcq (talk) 14:37, 24 September 2018 (UTC)[reply]

They may be incorrectly describing a solar still. --47.146.63.87 (talk) 21:20, 24 September 2018 (UTC)[reply]

In the original language of the article, it says that he squeezed sea spray from his clothes and drank that. He didn't filter the water through his clothing. I'm not claiming that is better. It is just not the same thing. 216.59.42.36 (talk) 18:11, 26 September 2018 (UTC)[reply]

Baker Dam

Which Baker Dam, upper of lower, uses Pelton turbines?Rossroderick (talk) 15:02, 24 September 2018 (UTC)[reply]

I don't think you need to repeat the same question every other day: You can simply continue an opened thread. From all the posts in the last one ( https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#Baker_Dam_turbines,_continued_dialog ) I got the impression that there are no sources stating what kind of turbines are mounted in the Baker Dams, so there is no answer to your question, even if you ask it a fourth and a fifth time. 194.174.73.80 (talk) 13:58, 25 September 2018 (UTC) Marco Pagliero Berlin.[reply]

@Rossroderick: If you're in the area, you can try Free tours of Baker River Hydroelectric Project, or try "Contact us. We welcome your questions and comments!" —107.15.157.44 (talk) 15:58, 25 September 2018 (UTC)[reply]

I've been reading this discussion for a few days. The link Andy Dingly gave after your first question clearly tells (if anybody had taken the effort of actually reading it...) that the new Lower Baker Unit 4 has a Francis turbine. Lower Baker 1 and 2 no longer exist. It doesn't tell anything about Lower Baker 3, but at the same head and higher flow than Lower Baker 4, it's probably a Francis turbine too. Pelton wheels are more common for high head, low flow. No source has been found for Upper Baker. It has slightly higher head and lower flow than Lower Baker, so it could be either type of turbine.

BTW, the fish-friendliness of Lower Baker 4 is all about fish-friendly management of downstream waterlevel. PiusImpavidus (talk) 17:11, 25 September 2018 (UTC)[reply]

Where in the deepest bedrock in the world?

Where is the strongest? (lb/in² before a load slowly placed directly on a leveled part of the top of the bedrock damages it) Sagittarian Milky Way (talk) 15:54, 24 September 2018 (UTC)[reply]

I'm not clear on what you're asking - bedrock goes from the base of superficial deposits down 10s of km. The strongest part of the crust is at the brittle–ductile transition zone, beneath which higher temperatures promote crystalplasticity. Mikenorton (talk) 17:18, 24 September 2018 (UTC)[reply]

I was asking about the top of the bedrock. Sagittarian Milky Way (talk) 17:31, 24 September 2018 (UTC)[reply]

Do you mean "How far down is the deepest from the surface one has to go to reach bedrock?" --Jayron 32 17:41, 24 September 2018 (UTC)[reply]

If you are this paper seems to have all of the data you need. And then some. --Jayron 32 17:45, 24 September 2018 (UTC)[reply]

That paper implies that there is a place in the US where the rockhead (that's what the top of bedrock is called) is more than 3 km below the surface. That seems a little high in my view, although I can't see the data that was used to give that value, presumably a borehole record. There are plenty of places globally that have hundreds of metres of superficial deposits however, especially in areas that were once close to the front of ice sheets (during the last glacial maximum), where the mass of sediment coming from the ice sheet infilled any existing topography - valleys, lakes etc. Mikenorton (talk) 19:24, 24 September 2018 (UTC)[reply]

Actually, if you read the paper, they actually made your exact point years before you thought to write it. --Jayron 32 03:44, 25 September 2018 (UTC)[reply]

Three km deep sediments are not rare, for example the Po river delta in Italy and the Brandenburg region in Germany are said to lie on three km of sand. But you don't need a three km depression at the beginning: the weight of few hundred metres of sediments can sometime cause the crust to sink into the mantel, so as to give place for even more sediment to accumulate and so on. 194.174.73.80 (talk) 14:50, 25 September 2018 (UTC) Marco Pagliero Berlin[reply]

Is it possible for sediments to break through the crust when it was thinner or in the far future if they accumulate enough? Maybe if the sediments continental drift to a place where 4+km of ice form on top? Sagittarian Milky Way (talk) 15:37, 25 September 2018 (UTC)[reply]

Sediments (more properly sedimentary rock) can be pushed under the crust at subduction zones. But no, there's nothing to "break through". It's not like the crust is sitting over nothing, there's dense, plastic solid mantle underneath. --Jayron 32 16:04, 25 September 2018 (UTC)[reply]

As Jayron says, we're dealing with sedimentary rock, not unconsolidated sediment, as once we have a thick enough accumulation (and therefore high enough temperature and pressure) the process of lithification starts. That's why I balked at 3 km to bedrock, because the bottom of such a sequence would have become lithified and therefore would form part of the bedrock itself (and of course part of the crust). There are a some places where unconsolidated sediments were deposited directly onto exhumed (if somewhat altered) mantle, non-volcanic passive margins, but that's because during continental break-up the crust has been thinned away to nothing before the mantle part of the lithosphere has given way - this has been proved by the Ocean Drilling Program (e.g. hole 637). Mikenorton (talk) 18:38, 25 September 2018 (UTC)[reply]

September 25

Global Warming in Mexico

Under the various global warming scenarios, does it seem possible/likely that Mexico will become uninhabitable except for mountainous regions?Rich (talk) 00:55, 25 September 2018 (UTC)[reply]

See here: "A 2010 study concluded that under a worst-case scenario for global warming with temperatures 12 °C (22 °F) higher than 2007, the wet-bulb temperature limit for humans could be exceeded around much of the world in future centuries.[10] A 2015 study concluded that parts of the globe could become uninhabitable.[11] An example of the threshold at which the human body is no longer able to cool itself and begins to overheat is a humidity level of 50% and a high heat of 46 °C (115 °F), as this would indicate a wet-bulb temperature of 35 °C (95 °F).[12]". Count Iblis (talk) 04:01, 25 September 2018 (UTC)[reply]

However, that's speaking of global effects of a staggering 12 degrees Celsius of warming, which would take centuries even with unabated emissions. In the tropics and subtropics, which includes Mexico, things will start getting dire much earlier. If you believe this analysis, originally published in New Scientist, at 4 degrees of warming much of Mexico would indeed be close to uninhabitable. And depressingly we have a good chance of hitting 4 degrees by the end of the century if we continue with our present policies. If you haven't read "The Uninhabitable Earth", do so, though you won't be upbeat afterward. --47.146.63.87 (talk) 04:31, 25 September 2018 (UTC)[reply]

Technology can help adapt to the worst conditions. The Inuit adapted to the extreme cold near the north pole, the Tuareg adapted to the extreme heat of the Sahara desert. Walipinis seem a working technological adaption in South America. --Kharon (talk) 04:50, 25 September 2018 (UTC)[reply]

There is a limit. The problem is not just heat but humidity—wet-bulb temperature reflects both. At a wet-bulb temperature of around 35 Celsius, the atmosphere no longer convects heat away from your body, and you quickly cook to death. The tropics are famously humid, as contrasted with dry deserts (including polar deserts). Also there's the minor issue of sustaining a modern agricultural society. The Inuit and Tuareg are historically nomadic, but to keep alive 7.6 billion people and growing, you need to grow food, you need water supplies, and so on. We could debate the exact definition of "uninhabitable", but it's not really important for analyzing the potential future, because people will start evacuating long before the point of "you drop dead if you go outside during the day". --47.146.63.87 (talk) 07:56, 25 September 2018 (UTC)[reply]

Not a strictly scientific answer, but an interesting fictional consideration of almost exactly the OP's area of interest is to be found in Paolo Bacigalupi's 2015 science fiction novel The Water Knife. {The poster formerly known as 87.81.230.195} 2.221.81.75 (talk) 08:43, 25 September 2018 (UTC)[reply]

Yes, that lethal combination does not exist on Earth - the eastern United States comes closest. 92.31.140.53 (talk) 13:07, 25 September 2018 (UTC)[reply]

Really? What about Arabia and the Persian Gulf when the wind comes from the water? The Upper Midwest can actually get surprisingly close, it can reach the mid-110s in Minnesota and all the crops drying out makes the air ~115 and not very dry. Sagittarian Milky Way (talk) 13:39, 25 September 2018 (UTC)[reply]

Lunation and tropical year in 5000 BC

Nowadays, around AD 2000, the value of the mean synodic month is about 29.5306 mean solar days, and that of the mean tropical year, 365.2422 mean solar days, where a mean solar day is about 86,400 SI seconds. I was wondering about their variation over the millennia, and what their values would have been around, say, 5000 BC or AD 5000. — 79.113.236.200 (talk) 13:30, 25 September 2018 (UTC)[reply]

The Wikipedia article titled year has information on the variation of the length of a year, and even has a handy table which, while it doesn't have 5000 BC listed, does have several different years. There are 4 references just before that table, you perhaps could use those to help you in your research. --Jayron 32 13:35, 25 September 2018 (UTC)[reply]

Year length varies from year to year. I am interested in an average, for a few centuries around the given date. Is that what the table is supposed to represent, or does it merely show the length of the specific year in question ? — 79.113.236.200 (talk) 18:30, 25 September 2018 (UTC)[reply]

In Year#Numerical value of year variation it states "Mean year lengths in this section are calculated...". Reading the cited sources confirms that the values are mean values near the stated year, not the length of the individual stated year. Jc3s5h (talk) 17:10, 27 September 2018 (UTC)[reply]

Correction: 86,400.002 seconds. Sagittarian Milky Way (talk) 13:43, 25 September 2018 (UTC)[reply]

Two milliseconds over the course of a year fits within the allowable parameters of "about". --Jayron 32 13:48, 25 September 2018 (UTC)[reply]

86,400 seconds is a day but yeah, it's pretty similar. Sagittarian Milky Way (talk) 13:58, 25 September 2018 (UTC)[reply]

The Babylonians used a mean synodic month of 29d 12h 44m 03 1/3s. The modern value is 29d 12h 44m 02.87s. Although the moon is slowing down (due to the tides) the increase in the length of the day caused by the tides slightly overcompensates. Thus although the month is getting longer, in terms of mean solar days it is diminishing. The length of the mean tropical year diminishes by about 1/2 second per century - you can't really differentiate between mean solar days and ephemeris days (those are the ones that consist of 86,400 SI seconds). 92.31.140.53 (talk) 14:06, 25 September 2018 (UTC)[reply]

Just courious, but how can we know to the third of a second what duration the Babylonians attributed to the synodic month? Or to any month for that matter? Is there any Babylonian text stating such a thing, and if, how did they express "44 minutes and 3.33333 seconds"? Thank you. 194.174.73.80 (talk) 16:05, 27 September 2018 (UTC) Marco Pagliero Berlin[reply]

I'm not up in Babylonian units of measurement. However the Jews (who had a long sojourn in Babylonia and still use their calendar) assign the length of 29d 12h 793 halachim to the month. There are 1080 halachim to the hour and 18 to the minute, so ... 44m 3.33 (recurring) seconds. 86.131.233.235 (talk) 09:46, 28 September 2018 (UTC)[reply]

More on this [2]. 86.131.233.235 (talk) 10:50, 28 September 2018 (UTC)[reply]

September 26

Neutron star cooldown time

According to the article on neutron stars the majority of the examples in our galaxy are already cold (or at least cold enough to not be detectable), but according to the article on white dwarfs, that type of star is not expected to cool down for at least trillions of years. Why do neutron stars cool down so much faster than white dwarfs? 182.0.151.47 (talk) 10:07, 26 September 2018 (UTC)[reply]

Maybe because while a white dwarf has radius on the order of ~~3000~~ 6000 kilometres, a neutron star has a radius on the order of 10 kilometres? 194.174.73.80 (talk) 10:39, 26 September 2018 (UTC) Marco Pagliero Berlin[reply]

If anything, shouldn't a larger surface area lead to faster cooling, as you can get a greater heat flux through it? 139.194.67.236 (talk) 10:42, 26 September 2018 (UTC)[reply]

Of course not. A drop of molten steel gets cold faster than a ton of molten steel. Can you imagine why? 194.174.73.80 (talk) 11:51, 26 September 2018 (UTC) Marco Pagliero Berlin[reply]

Could it have something to do with the ratio between volume and surface area not being linear? 216.59.42.36 (talk) 18:05, 26 September 2018 (UTC)[reply]

The reason a droplet of steel cools faster than a ton of steel is because the surface area to mass ratio is greater in the droplet than in the ton due to square cube law. That will only work for comparisons of objects of similar densities. The neutron star (with a mass of about 1.5 solar masses) has far greater thermal energy to fit through its tiny surface area, compared to a white dwarf with its surface area several orders of magnitude greater, but a smaller mass of around 1 solar mass. So, the comparison of the radii doesn't answer the question. It just makes it more puzzling. 114.124.239.108 (talk) 23:29, 26 September 2018 (UTC)[reply]

You are right, I didn't think of this and IP139, I beg your pardon. So it can be that heat conduction in a neutron star is much faster and the whole star cools quickly, or in the opposite, conduction is very slow, so the surface cools while the core stays very hot. 194.174.73.80 (talk) 15:07, 27 September 2018 (UTC) Marco Pagliero Berlin[reply]

PS Neither nor: neutrino emission from the core cools the neutron star very quickly: https://academic.oup.com/mnras/article/324/3/725/1025405

"After a period of intense accretion the neutron star surface cools on a time scale of years." Source: Thermal and transport properties of neutron star matter.[3]

--Guy Macon (talk) 04:07, 27 September 2018 (UTC)[reply]

Thermal conductivity is roughly proportional to density. A neutron star has ~1×10⁸ times the density of a white dwarf, which contributes greatly to its ability to cool down much faster than a white dwarf. Dragons flight (talk) 19:44, 27 September 2018 (UTC)[reply]

Wouldn't the conductive heat loss be zero? It seems like the heat loss would be 100% radiative. BTW, do we know what neutronium looks like? I keep imagining shiny silver, but now that I think about it I am pretty sure that I got that from Larry Niven's books. Is a neutron star a black body radiator? --Guy Macon (talk) 21:41, 27 September 2018 (UTC)[reply]

From the surface it's presumably (almost) 100% radiative, but the heat has to get to the surface. Radiation isn't going to move far inside a neutron star. --Trovatore (talk) 21:43, 27 September 2018 (UTC)[reply]

Ah, but of course neutrinos can, as in Marco's link above. I guess that's "radiative", more or less? --Trovatore (talk) 23:41, 27 September 2018 (UTC)[reply]

Manhole cover in space?

Assuming that the shaft steel plate cap of the Pascal-B nuclear test actually survived its launch (it was never found), where would it be now? Is that fast enough to leave the solar system? Be ahead of Voyager? It would be ironic if the first contact an alien race had with humans was to be hit by a giant manhole cover travelling at 150,000 mph. SpinningSpark 17:21, 26 September 2018 (UTC)[reply]

So close to a nuclear explosion everything simply gets evaporated in some nanoseconds by the heat. The physical expansion is rather slow in comparison. Little Boy exploded 580 metres (1,900 ft) above the city of Hiroshima and caused temperatures of 6000 C° in a cone beneath it on the ground. The nuclear core is so hot that it starts rising up by heating the air around it so viciously that the resulting Convection airflow takes the core with it up. That is how the typical nuclear mushroom forms. --Kharon (talk) 18:15, 26 September 2018 (UTC)[reply]

No, that's rubbish (as usual for your comments). Andy Dingley (talk) 18:17, 26 September 2018 (UTC)[reply]
No, that's rubbish (as usual for your comments) II. --Doroletho (talk) 10:24, 27 September 2018 (UTC)[reply]

It was definitely faster than Earth escape, definitely slower than Solar escape. However no-one knows how it would survive passing through the atmosphere. If it stayed in one piece, it's probably now in a solar orbit. If it broke in two, it probably broke further and burned up on ascent. Andy Dingley (talk) 18:16, 26 September 2018 (UTC)[reply]

Well thanks but no thanks for the flowers Andy. Even a 500 ton Tungsten (wolfram) plate would evaporate faster that the physical blast could reach it. Nuclear cores heat up to 100,000,000 C° in their chain reaction. If you put anything close enough to a chain reaction to theoretically push it to 66 km/s, it wont get pushed but turned to its Plasma (physics) state. --Kharon (talk) 18:32, 26 September 2018 (UTC)[reply]

The first frame of the high-speed film taken at the time has the thing airborne (that's how they got the lower bound on the speed) so that kind of makes you, well ... wrong. SpinningSpark 18:41, 26 September 2018 (UTC)[reply]

I doubt that but since there is no physical evidence (1 frame is no prove), you believe what you like. All i know is that 100,000,000 C° evaporates everything close to it faster than a 1957 highspeed camera can record. --Kharon (talk) 19:04, 26 September 2018 (UTC)[reply]

Wrong. Not even close to being correct. Read the reference that you yourself cited: "Two pulses of thermal radiation emerge from the fireball. The first pulse, which lasts about a tenth of a second, consists of radiation in the ultraviolet region. The second pulse which may last for several seconds, carries about 99 percent of the total thermal radiation energy."

In 1957 high speed cameras were commercially available that took 600 pictures per second, and the fastest cameras took 4.5 million pictures per second.[4]

Last time I checked 1/600 of a second is less than either 1/10 of a second or several seconds.

The force that blew the lid off, on the other hand arrived at the speed of sound. Nobody who understands the physics thinks that the nuke vaporized the lid. The question is whether it was traveling fast enough for atmospheric friction to vaporize it before it exited the atmosphere. If the answer is no, then a manhole cover beat Sputnik into space. --Guy Macon (talk) 20:32, 26 September 2018 (UTC)[reply]

Even if vaporization of the object does have time to proceed significantly before the shock wave reaches it, that will kickstart the acceleration of the object due to ablation, so no matter which way you slice it the object starts traveling very fast. 114.124.239.237 (talk) 23:48, 26 September 2018 (UTC)[reply]

If you're that interested, you can read my work (and many others, originally Peter Hagelstein) in the '80s on X-ray lasers and the production of them via irradiation of thin metal foils by either lasers or nuclear devices. See the underground Excalibur tests. And these were thin foils, not manhole covers. So please don't give me this crap about 500 ton tungsten manhole covers turning instantly to plasma without moving. Andy Dingley (talk) 11:34, 27 September 2018 (UTC)[reply]

The Escape velocity from Earth's gravity is 11.186 km/s and from the Sun's gravity 617.5 km/s. Designer Dr. Robert Brownlee estimated that the explosion accelerated the plate to six times the former, which would not allow its remains to escape the Solar System. The Voyager space probes had escaped from the Sun's gravity by 1980 after flying past Jupiter, see [5]. DroneB (talk) 19:05, 26 September 2018 (UTC)[reply]

Sorry, this is plainly wrong. The velocity necessary to leave the Solar System from the Earth' surface is minimum 16.6 km/s though it depends on direction. This is so called total escape velocity. You need to learn some basic physics before making such claims. Ruslik_Zero 19:42, 26 September 2018 (UTC)[reply]

With the initial velocity of 66 km/s the final velocity upon leaving Solar System will be 85 km/s if the initial velocity was in the direction of the Earth's orbital motion. If it was launched in the direction opposite to the Earth's orbital motion, it will now orbit Sun in the retrograde direction somewhere between Earth and Mars. The real situation is more messy, of course. Ruslik_Zero 19:58, 26 September 2018 (UTC)[reply]

I am no nuclear physicists so i may have overlooked something in my "vaporizing"-answer. Luckily we have good articles to cite from like Effects of nuclear explosions:

(cite) "Energy from a nuclear explosive is initially released in several forms of penetrating radiation. When there is a surrounding material such as air, rock, or water, this radiation interacts with and rapidly heats it to an equilibrium temperature (i.e. so that the matter is at the same temperature as the atomic bomb's matter). This causes vaporization of surrounding material resulting in its rapid expansion." (cite end). So the "blast" is clearly just a secondary phenomenon of the vaporization, or rapid change to a plasma state, given the just 100 MILLION DEGREES Celsius or Kelvin(273.15° difference doesnt matter anymore at such numbers). The only chance that this "Manhole cover" had is when it was far enough away and shielded from the radiation. I concluded for an impulse from 0 to 55Km/s it must have been very close. --Kharon (talk) 02:45, 27 September 2018 (UTC)[reply]

With on object like a manhole cover, the radiation is first incident on the top layer of object, heating it directly and very, very quickly. This causes that layer to immediately vaporize and expand as a cloud of hot gas (a process known as ablation), pushing the remaining non-vaporized portion of the cover in the direction away from the blast. With the top layer of the manhole cover removed, the second layer is now irradiated and vaporized, which accelerates the bulk of the manhole cover further. As the cover moves further from the blast, the degree of radiation it is subject to is reduced very rapidly (due to the inverse square law). This allows the object to be accelerated to a very high speed without the bulk of its matter being heated to vaporization. 202.155.85.18 (talk) 03:27, 27 September 2018 (UTC)[reply]

There are too many factors involved to sum this up in a simple answer. First of all, when talking about heat, we're talking about energy. When talking about vaporization, we're talking about energy transfer. How that energy transfers all depends on the method of transfer and the material it transfers to (ie: absorption and dissipation). The initial release of energy comes in the form of a blast from the detonation charges, followed by an intense radiation (light) wave that outruns the supersonic shockwave. At enough intensities, this light exerts more pressure than heat, and this is especially true for reflective objects like metal. (There are actually laser meters that measuer power by the pressure the beams exerts on the mirror.) In close enough proximity, this light blast will arrive at roughly the same time as the concussion, and, since the metal does not absorb radiation well, nor the thermal heat fast enough, it is conceivable it would absorb most of that energy as kinetic and become airborne.

At mach 2 you can expect to be heated to around 200 degrees F. At mach 5 you're up to about 1325 degrees, hitting 4000 by mach 8. Temperatures of the nose of the Apollo capsules reached up to 19,800 degrees (the temp of a blue star). While it is extremely plausible such a thing could be blasted far from the explosion, that it would survive traveling through the atmosphere for any distance before ablating to death or exploding itself like that meteor over Russia a few years ago, is highly unlikely. (Or that it would retain it's energy long enough, as the atmosphere will dissipate it quickly for such a small object. Remember, skin pressure goes up dramatically once you go supersonic, because the air just can't get out of the way fast enough. Zaereth (talk) 03:25, 27 September 2018 (UTC)[reply]

You can clearly see at 1:00 on this video: https://www.youtube.com/watch?v=KQp1ox-SdRIt=60 that the expanding blast wave hits nearby objects first (you can see it expanding at the speed of sound) and that the high temperatures come a fraction of a second later (you can see this when the fireball becomes much brighter). Thus a manhole cover that is blown into space by the blast wave is long gone before the high temperatures you keep SHOUTING ABOUT IN ALL CAPS AS IF WHAT MATTERS IS HOW HOT AND NOT HOW SOON reach the place where the manhole cover used to be. And of course you assumed that "the speed of a 1957 highspeed camera" was much lower than the actual figure of 4,500,000 FRAMES PER SECOND.

The distance between the bomb and the cover was 500 feet.

The camera was recording 1 frame per millisecond.

The blast wave hit the manhole cover 506 milliseconds after the bomb went off. Note that being at the bottom of a shaft magnifies the blast wave compared to a free-air detonation, but does little to concentrate the thermal effects, most of which end up vaporizing a big hole 500 feet down.

The welds held for some short amount of time, allowing the pressure to increase, then the manhole cover was launched at a calculated velocity of 180 feet per millisecond.

By the time the thermal maximum happened, roughly 1000 milliseconds later, the manhole cover is calculated to have been roughly 35 miles up and still climbing, having passed through the stratosphere and into the mesosphere.

The scientist who did that calculation concluded that it was going too fast to burn up before reaching outer space: "I was in the business and did my own missile launches. I realized that that piece of iron didn’t have time to burn".[6] This is easily confirmed by examining nickle-iron meteorites that are considerably smaller and faster than the manhole cover, and arrive on the ground icy cold with zero evidence of surface melting.

All of which is just a long-winded way of saying "Kharon is wrong". Zaereth, on the other hand, is likely to be right. It would be very interesting to see the calculations for a gun attempting to fire a metal projectile into space. We have an article on this: Space gun. --Guy Macon (talk) 04:15, 27 September 2018 (UTC)[reply]

Not sure if you're talking to me, but you make a good point. You also have to take into account that air pressure and speed all play a role. Meteors that are traveling fast enough may explode before ever reaching the ground, such as the one in Tunguska, or those that hit Jupiter a few years ago. Those that are small enough may ablate completely. Ablation transfers little to almost no heat to the main body, which is why it is used for cooling space vehicles. These are typically 80,000 mph +, and not every meteor is traveling that fast relative to the Earth. Then there is the physical stress of accelerating that at that rate, which I know from experience can lead to an object completely spalling before traveling more than a few yards. It seems entirely plausible either way, but, like I said, too many factors involved to sum it up so simply. I do agree that vaporization from heat of the blast is the least likely. Zaereth (talk) 04:13, 27 September 2018 (UTC)[reply]

For whatever it is worth, my physicist's intuition is that the scenario described would not be capable of reaching orbit, too much atmospheric drag relative to the mass and speed of the projectile. However, when I tried to do a rough estimation of the drag forces involved, my calculation made it seem like a much closer thing than I had expected. For 900 kg disk 1.2 m across and 60 km/s initial velocity, I estimated that it would reach an apex of more than 35 km in altitude, which is rather quite a lot. In my rough calculation, the disk slows from 60 km/s to only 2 km/s by 2 seconds after launch, but has already hit an altitude of 10 km by that point. Though the cover would likely be somewhat ablated by the initial explosion and the subsequent hypersonic drag, if the initial acceleration of the launch doesn't tear the cover apart, I would guess that the cover would remain mostly intact until it returned to the Earth. Dragons flight (talk) 14:14, 27 September 2018 (UTC)[reply]

My educated guess is that if the steel was brittle it would break up, but if it was ductile it would stay intact, possibly bent or even folded. My uneducated guess is that is went tens of kilometers up and then came down somewhere, but don't ask me to prove it. --Guy Macon (talk) 15:53, 27 September 2018 (UTC)[reply]

My physicist's intuition leads me to a slightly different result. Since 66 km/s vastly exceeds the speed of sound in the air, the air in front of the disk will be simply compressed and accelerated. This process will look like an inelastic collision between the disk of 900 kg with the air column above it with about 11000 kg mass. The momentum conservation means that the final speed will be around 5.5 km/s with about 88% of the kinetic energy dissipating into heat. This is about 17 170 MJ per kg. The naive calculation using 600 J/kg/K thermal heat capacity of the air leads to about ~~30,000~~ 300,000 K temperature. In reality (taking into account the increase of thermal capacity with temperature and ionization) it will be probably lower - around ~~10,000~~ 50,000 K. Ruslik_Zero 21:05, 27 September 2018 (UTC)[reply]

That sounds about right to me. Do you have any guesses as to why space guns aren't rejected at the planning stage for the same reasons? --Guy Macon (talk) 21:47, 27 September 2018 (UTC)[reply]

I actually made an error: it should be around 170 MJ per kg. And all guns that I heard of involved velocities less than 4 km/s, which means that my assumption about inelastic collision may not be right. Ruslik_Zero 18:00, 28 September 2018 (UTC)[reply]

1) Project Orion found that coating the pusher plate with oil resulted in almost no ablation so I wonder if they could have gotten that (much smaller) plate to survive with a little such preparation. 2) the space gun design that I read about a while back used a pointy projectile with an ablative coating. Energy and momentum transfer was modelled as elastic collisions between air molecules and the oblique projectile surface. 3) Streak cameras and rotating mirror cameras (High-speed_photography#Rotating_mirror) even in the 1950s could film at millions of fps so it's unfortunate that they didn't set up something like that. 173.228.123.166 (talk) 04:36, 29 September 2018 (UTC)[reply]

Fascinating story. I followed back two refs from the article to the blog (well, pre-blog) that everything is based on: [7] Note of course that the calculation he cites was either manual or damn near, so it is possible now to do far more elegant numerical simulations that might shed some light on the topic. Alas, I found nothing in ArXiv about "Pascal B". Anybody good at computer science and wanna get published? Wnt (talk) 23:41, 29 September 2018 (UTC)[reply]

Plant identification help

Unidentified plant

The flower

The leaves

Could anyone please help identify this plant, growing in a Sussex garden in September? The stalk is a distinctive red, matching the colour of the flowers. Shallow, chalky soil, full sun, facing south. This specimen is about 2'6" tall. DuncanHill (talk) 18:34, 26 September 2018 (UTC)[reply]

This plant is Leycesteria formosa, known commonly in the UK as Himalayan honeysuckle or Pheasant berry. Richard Avery (talk) 07:10, 27 September 2018 (UTC)[reply]

Splendid, thank you. DuncanHill (talk) 14:29, 27 September 2018 (UTC)[reply]

Dutasteride and erectile dysfunction

Please consult your doctor or pharmacist -- we don't answer this kind of question here

After how many days of daily Dutasteride 0.5 mg administration will the erectile dysfunction become irreversible? — Preceding unsigned comment added by 2401:FA00:C:702:DC27:9C1A:E16F:22E3 (talk) 21:21, 26 September 2018 (UTC)[reply]

Didn't you ask that question already? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:38, 26 September 2018 (UTC)[reply]

This is a different one and the previous question was not answered in a satisfactory manner. — Preceding unsigned comment added by 2401:FA00:C:702:DC27:9C1A:E16F:22E3 (talk) 23:02, 26 September 2018 (UTC)[reply]

When are you going to see your doctor about this? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:23, 27 September 2018 (UTC)[reply]

September 27

Plutonium density

According to the article allotropes of plutonium, the least dense phase is the δ phase, and it has a face centered-cubic structure. But a fcc structure is one of the two most dense packings possible, the other being hexagonal close-packing. How is it that the most dense packing structure gives the least dense allotrope? 202.155.85.18 (talk) 06:39, 27 September 2018 (UTC)[reply]

The article matches the refs, even though it seems extraordinary. (A negative thermal expansion coefficient for a crystal? Come on...) Ref #2 lists (p. 294) your remark as "unusual property" #5 and ascribes it to nonstandard behavior of the 5f electrons (p.296 and following give an explanation but I find it hard to follow); in other terms, the "rigid spheres with a constant atomic radius" model is too wrong to apply it here. Tigraan^{Click here to contact me} 07:18, 27 September 2018 (UTC)[reply]

Hmmmm...actually that makes a lot of sense. The Goldschmidt correction for actinide series elements is probably much larger due to the lanthanide contraction, so as the coordination number is increased going to more and more close packed structures, the metallic radius increase is so great it leads to overall lower densities. Thanks! 202.155.85.18 (talk) 07:26, 27 September 2018 (UTC)[reply]

I don't know what the bloody hell you two are on about but that was great. It almost made me want to follow the links. (I always found physical chemistry banal). — Preceding unsigned comment added by Greglocock (talk • contribs) 09:56, 27 September 2018 (UTC)[reply]

Exoworlds with glowing vegetation

I believe that exoworlds with colorful glowing plants covering much of the world exist like Pandora from Avatar. What do you guys think? Glowing plants are obviously very uncommon on Earth with the most common species being sea-dwelling kelp. Planet Star 21:11, 27 September 2018 (UTC)[reply]

See article Bioluminescence for the glowing and its functions. Contrary to your assumption the Abyssal plains (depths below 3,000m) actually cover more than 50% of the Earth’s surface! Since there is hardly any sunlight reaching these deeps - even the Macropinna microstoma, that uses giant eyes pointing upwards to detect prey against the light from the surface, prefers much higher zones around 1000m depth - and Bioluminescence is pretty common in these deeps, we actually have masses of glowing lifeforms here at "home". Just no "jungles" full of it because all food sources are way to scars that deep, to feed so much life.

One interesting revelation, since you cite the Movie Avatar as reference, is that the Director of that movie, James Cameron, actually became an expert on deep-sea exploration and thus certainly saw lots of Bioluminescence down there himself, which probably inspired him to add this to his computer generated jungle world Pandora and its biosphere. --Kharon (talk) 22:12, 27 September 2018 (UTC)[reply]

James Cameron seeing bioluminescent lifeforms deep below the ocean's surface inspired him to generate jungle of bioluminescent plants, both on land and underwater in the Avatar movie, which in turn inspired me to ask question about the real life existance of such a jungle on alien worlds by watching it. Although bioluminescent plants and animals are abundant deep in the ocean, why is bioluminescence so uncommon on land plants and animals? Isn't Earth unusual for a life-bearing planet to not have land bioluminescence in abundance? Planet Star 21:18, 28 September 2018 (UTC)[reply]

In most cases bioluminescence is rather faint. There are some "surface" plants like Schistostega pennata where bioluminescence seems to have a benefit but our earth vegetation actually thrives great without it. Avatar is just a fantasy movie. You certainly will not find flying mountains anywhere in our universe for example. But they look spectacular of course - like bioluminescent jungles or elegant 3.5 meters high blue-coloured humanoids with huge shiny eyes do. Again, it's a movie. Don't read too much into it, especially when it's from the Sci-fi or fantasy genre. --Kharon (talk) 12:28, 29 September 2018 (UTC)[reply]

Isn't Earth unusual for a life-bearing planet to not have land bioluminescence in abundance? How could we know, since we've not discovered life anywhere else yet?

—Paleo Neonate – 19:37, 30 September 2018 (UTC)[reply]

Fireflies put on an impressive display, but a fairly dim one; nature can be stingy. (pure speculation:) Still, I'm thinking that the abyssal plain is always dark, but the Earth, even at night, is often moonlit. Perhaps a planet without a moon would encourage more investment in bioluminescence? Another issue for plants is that their potential mates can neither see the display nor respond to it; they could signal to pollinators but other methods might be cheaper. But, what if another planet developed somewhat mobile plants with some degree of color vision? In truth, of course, we know nothing at all about other biospheres, nor can we predict them with any confidence. Wnt (talk) 00:38, 30 September 2018 (UTC)[reply]

I know Pandoran jungles seem fantastical, well, who knows, alien biospheres can be fantastical too. From my point of view, why isn't the Earth covered in Pandora-like glowing jungles and forests on land, while from Cameron's POV why isn't plants glowing deep underwater cover much of the land too? Maybe it's just the way the Earth's evolution went. My sister said had evolution gone in a slightly different direction, we would possibly see land forests/jungles of glowing plants. Of course it's far more likely to see these than flying mountains. Sci-fi never even look into rocks that fly, at least from my point of thought. Planet Star 03:02, 30 September 2018 (UTC)[reply]

If you think rocks don't fly, watch a volcanic eruption sometime. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:23, 30 September 2018 (UTC)[reply]

Uuuuhhh, that's right! I could now say rocks don't have feathery wings and aren't self-aware. Planet Star 19:29, 30 September 2018 (UTC)[reply]

Gecko in or out of house?

Background: I live in a large house in Algeria, where daily outside temperatures are typically from ~ 17 to ~ 27 C. There are cats in one room of the house (don't ask). The population of flies in the house seems fairly minimal to me. I see adult geckos outside the house, and occasionally find baby ones inside (not in the room which has cats, but they could get under the door). I typically transfer the babies outside, in the basis that they're more likely to live long and happy lives there.

My question: am I right, or am I just providing food for various predators? I realise refdeskers can't calculate the odds of a particular gecko being stood on / eaten by cats / freezing to death, but in general terms, is there a scientific basis for thinking they're better off in or out? 105.235.137.66 (talk) 21:12, 27 September 2018 (UTC)[reply]

It's typically 17-27 but they might freeze to death? I assume this is not the low desert? Sagittarian Milky Way (talk) 00:11, 28 September 2018 (UTC)[reply]

How does one freeze at 17C?--Jayron 32 00:30, 28 September 2018 (UTC)[reply]

OP says "Daily outside temperatures are typically from ~ 17 to ~ 27 C".

Our article says "on the steppes of the High Plateaus winter temperatures hover only a few degrees above freezing". Rojomoke (talk) 04:46, 28 September 2018 (UTC)[reply]

The IP geolocates to Algiers, which has Csa sub-climate classification. Regarding the original question, it is essentially a matter of opinion, which this reference desk doesn't provide (stop laughing!). That being said, I'd be inclined to let nature take its course; if the geckos manage to find enough bugs to eat in your house -- great! Otherwise, they just might leave the way they came in (or end up being a nutritious cat snack). In many places it is considered good luck to have a gecko in the house (Hawaii, Indonesia, etc.). —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 06:00, 28 September 2018 (UTC)[reply]

Thanks, 2606, for not completely ignoring the question. Re: temperatures, I should have specified currently (could also have specified that dying of cold does not necessarily require temperatures literally below freezing). Re: opinion, I was hoping for (e.g.) some animal welfare society guidelines, which would be based on expert knowledge. All I find online is about caring for captive gecks. 105.235.137.247 (talk) 07:09, 28 September 2018 (UTC)[reply]

I never heard of "geckos" before. I only came across the word in a description of a browser using Chrome/Internet Explorer where it says "like gecko". What does that mean? 86.131.233.235 (talk) 09:39, 28 September 2018 (UTC)[reply]

See Gecko. Or watch some Geico TV commercials. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:08, 28 September 2018 (UTC)[reply]

While it's possible that your decision to take a pro-active vs. laissez-faire approach may have a massive impact on any one gecko (one may, as you fear, be snatched up by a predator instantly), as a probabilistic matter it is unlikely that your habit of removing them has a substantial net effect one way or another (that is, if you remove a hundred of them in a given year, probably close to the same number will meet their end shortly after their encounter with you). Young geckos, like most juvenile lizards, have a higher ounce-to-ounce metabolism than adults as they develop and specimens of almost all species likely to be in your house utilize a lot of energy in movement. Consequently, those individuals from species which have not developed a mechanism for storing energy in fat reserves (there are numerous of these, such as the fat-tailed gecko and the leopard gecko) need to eat fairly consistently, and they rely very much upon the conditions of their ecological niche for predation. This means that most geckos who end up in your house, particularly the young ones, will quickly begin to feel the pangs of hunger. That said, while there may be the occasional home which has features that make it likely to confuse a gecko guest such that they become trapped, by and large they will not have much difficulty in finding their way out again when circumstances prompt them to--so provided there are no environmental hazards inside the house (of the feline variety or otherwise), they should be fine if you leave them be.

Of course, this all assumes that the effort you are going to exert is limited to walking them to the door. If you really want to give the best possible chances to your reptilian boarders, you should identify the exact species, learn which flora provide them the best hunting and defense opportunities and deliver them to the nearest acceptable specimen. Most adult geckos will also be more than happy to accept mealworms or crickets, if you can find a supplier that provides them and have the patience to set the gecko up in a vivarium for a while--if you were really dedicated to giving them a leg up on their way out the door. Sorry I can't find a suitable source for all of this; I did look but couldn't find anything particularly on point--this is just a summary of various details I happen to know regarding lizard physiology and ethology. Snow ^{let's rap} 09:45, 28 September 2018 (UTC)[reply]

Thanks, that's useful. To clarify, when you say if you remove a hundred of them in a given year, probably close to the same number will meet their end shortly after their encounter with you, do you mean just that most baby geckos don't survive long, or the ones I find are most likely already in bad shape? I'll try to identify the next one, in case I can do better by him. 105.235.137.247 (talk) 10:38, 28 September 2018 (UTC)[reply]

Well, survival rates will vary by species and location, but what I meant is that over a large enough sample size, your decision to remove them or not remove probably will not have a significant impact on the longevity of the Gecko's in that particular group, collectively. That is, you will probably not have a big impact on their fortunes (on average) whichever approach you land on (again, assuming you are just taking the ones you remove to the door).

Incidentally, there is another consideration I didn't think to mention before that I'll emphasize now; as a cat owner, you may wish to remove the geckos just to reduce the likelihood that they may come into contact with your feline roomates; lizards oftentimes carry parasites, some of which your kitties could possibly contract from ingestion. Small mammals are more likely to operate as this sort of vector than reptiles, but better safe than sorry. It's also a really bad way to go for the lizard; domestic cats typically do not hunt out of hunger, if they are owned and properly fed, so they drag the affair out to excruciating length before eating just bits. As someone who has done some wildlife rehabilitation, I can tell you that there's little that's more difficult to deal with than an animal a cat had a hold of for half an hour--but refused to finish off, because it was entertained by the movement. Geckos probably go a bit faster from abdominal puncture wounds, because of their size relative to a cat, but still, a miserable end. And sure, no problem--happy to help. :) If you need assistance in identifying the species, let us know, and feel free to ping me. Snow ^{let's rap} 10:54, 28 September 2018 (UTC)[reply]

Good points. The cats are completely inept hunters, which would probably prolong things even if they didn't want to. As long as I'm not clearly sending the little guys to their deaths, I think I'll continue with my transfer policy, while trying to find an optimal drop-off point. 105.235.137.247 (talk) 15:26, 28 September 2018 (UTC)[reply]

If you've got little geckos slithering their way into your house, what other, smaller creatures might be invading also? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:02, 28 September 2018 (UTC)[reply]

I think that carrying capacity is the relevant concept here. It is very difficult to predict, short term, the effect of releasing a few extra geckos into a wild population. They might, after all, be momentarily low in numbers for some reason, so that the introduction of new blood helps them to recover faster. Or, they might be near a population crash where a few extra mouths help them all to starve. But if you come back in fifty or a hundred years, the number of geckos each year will follow some random pattern that will depend in no significant way at all on how many you released. What this means is that for every gecko you lovingly feed, nurture, and defend as it makes its way into the wild, there is another gecko which is pushed aside by your newcomer and crawls off to some unwatched corner of the wild to die.

The situation in your house may be the same; in that you may be relatively inefficient at catching geckos so that the "predation" imposed by your good intentions (plus the doorway to the room full of cats) actually has little real influence on the total population. Much likea properly managed hunting or fishing season in the wild would be. On the other hand, you certainly could catch every single last gecko and put up a Great Wall of Trump to keep out any future invaders, and leave the stray bits of kitty kibble to be dealt with solely by some other member of the ecosystem (bacteria, mold, cockroaches, or Roomba). Then, there would genuinely be some lost gecko-hours of home enjoyment lost forever to history.

I think the reason why this seems surprising to our expectations is that with humans there is a culture. We expect that if there are more people, eventually they discover plows, domesticate plants and animals, or do genetic engineering trying to improve the carrying capacity of the environment, also they may actually limit their own fecundity, all of which means that increasing their numbers now doesn't automatically guarantee exterminating the same number in the future. (Though it scarcely rules it out either) Wnt (talk) 19:39, 28 September 2018 (UTC)[reply]

Interesting! In this particular case, geckos here suffer from religious persecution (not every day you get to write that), so perhaps carrying capacity is not the limiting factor. 105.235.137.251 (talk) 22:27, 28 September 2018 (UTC)[reply]

I couldn't help but take that bait: [8][9][10][11][12]. I didn't come to any strong conclusions, but it's interesting. Wnt (talk) 23:27, 28 September 2018 (UTC)[reply]

Mainly this. There may be a pragmatic origin related to e.g. parasites, but basically it's superstition. 105.235.137.251 (talk) 06:17, 29 September 2018 (UTC) [reply]

What I was referring to was this sentence in my browser configuration details:

AppleWebKit/537.36/KHTML, like Gecko

I googled the term but there is nothing listed. What does it all mean? 86.131.233.235 (talk) 17:34, 29 September 2018 (UTC)[reply]

Gecko (software) is the "browser engine" that displays a document in the web browser, after it has somehow been obtained. It explains at the first article how Apple made its own version in 2001, back when Netscape was a popular browser, but one that took a long time to start up on account of all the "software bloat" it had accumulated. Wnt (talk) 18:26, 29 September 2018 (UTC)[reply]

Now I understand why they call it a "search engine". I had always wondered. Thanks. 86.131.233.235 (talk) 18:53, 29 September 2018 (UTC)[reply]

September 28

Flexible tubing resistant to ~350 C (660 F)

There's a desoldering tool whose main feature seems to be a piece of silicone tubing which the manufacturer claims can be in contact with the soldering iron. A typical soldering iron temperature is 350-370 °C (~660-700 °F). I figured I could buy some silicone tubing and put it on my cheap desoldering tool but I can't find any that is good up to 350 °C. Is it actually possible? If so, does anyone know how I might find it or alternatively some other small-diameter tubing that's as flexible and heat-resistant? 185.230.100.66 (talk) 03:01, 28 September 2018 (UTC)[reply]

Your google fu is weak https://core-electronics.com.au/replacement-tubes-for-professional-silicone-tip-solder-sucker-ss-02.html Greglocock (talk) 04:36, 28 September 2018 (UTC)[reply]

Thanks! — Preceding unsigned comment added by 185.230.100.66 (talk) 05:45, 28 September 2018 (UTC)[reply]

Solder sucker tips are usually made of PTFE (Teflon) that melts at 327°C. Although our article about Silicone rubber quotes an upper use temperature of 300°C (and an O-ring manufacturer quotes a limit at 450°F=232°C[13]) the "fancy" transparent silicone tube for solder sucking is claimed[14] to be heat resistant to 350°C. The term silicone can cover a large group of Elastomers in which vinyl-methyl-silicone is the central ingredient, with chemical inertness and high temperature resistance attributable to the stability of their Si-O-Si atomic backbone. DroneB (talk) 15:03, 28 September 2018 (UTC)[reply]

There are several factors to take into account, because heating an object has a lot more involved than just temperature. There are also things like thermal conductivity, thermal diffusion, and heat capacity to consider, to name a few. Temperature, for example, you can think of as being a surface quality, because you can only measure it at the surface or extract energy from it at the interface of a surface.

Most polymers (plastics) have low melting temperatures. As far as common polymers go, Teflon, is the highest, although some exotic polymers do exist that reach temps up to 850 degrees F, these are mostly used in the aerospace industry. However, if your polymer is a thermoplastic and not a thermoset, it will melt, but it will melt like glass rather than a crystalline like ice or metal. Before it melts it crosses through the glass transition (T_g), and starts to be come pliable and rubbery. The more you heat the softer it gets, until it crosses the glass melting temperature (T_m). A thermoplastic's damage threshold is often (but not always) lower than the glass transition and much, much lower than the glass-melting temp. Teflon, being a semi-crystalline, is one of those exceptions. It's T_m is 626 degrees F (330 C) while its T_g is -166 F (-110 C). (This is what gives it its combination of rigidity and pliability.) However, above 527 F (275 C) the material begins to lose that rigidity sharply, thus the damage threshold is kept 50--100 degrees lower as a safety margin.

Elastomers (elastic polymers) like silicone are different, because these are usually thermosets, and thus will not melt. Instead, above their damage-threshold safety margin, they begin to burn instead. For high-temp silicone, this will be at around 500 F (260 C), which is the highest temp you can find in a common elastomer. (Although there are some exotic ones like Kalrez that can go higher.) For much higher temps you may need to use a fabric, or even a glass fabric that can get you up over 1000 F (540 C).

Fortunately, this really only applies if you're holding it at that temp for extended periods of time, such as in an oven. In a solder sucker, the plastic only contacts the molten metal for a short time. Because the plastic has poor conductivity and high capacity, it doesn't absorb this heat very fast, so it never actually reaches the temp of the molten metal. (This also keeps the metal from cooling too quickly and hardening on first contact.) So, for intermittent use like this, a plastic or polymer with a lower melting point than the metal can work just fine. Zaereth (talk) 19:34, 28 September 2018 (UTC)[reply]

The OP whose IP address is located in the UK posed a question with temperatures primarily in degrees Celsius, the unit used by all countries except the United States, the Bahamas, Belize, the Cayman Islands and Liberia. It would be a courtesy to give answers in the same units rather than imposing a superfluous conversion from a unit of local use in the United States, the Bahamas, Belize, the Cayman Islands and Liberia. DroneB (talk) 22:13, 28 September 2018 (UTC)[reply]

Sorry, I will keep that in mind. The OP asked using both, and for that reason it didn't occur to me to convert from the numbers I know by heart. Zaereth (talk) 23:08, 28 September 2018 (UTC)[reply]

Courteous behavior is what you do and not just something you think about doing some time in the future. Do you wish anyone to help edit your post with appropriate units? DroneB (talk) 23:59, 28 September 2018 (UTC)[reply]

If you wanted me to change my post all you had to do was ask. My time is very limited, but I thank you for the lesson in courtesy and how to deliver it with condescension and equivocation. (Suddenly, I remember why I don't respond here.)Zaereth (talk) 06:05, 29 September 2018 (UTC)[reply]

Ref. desk rules differ from Wikipedia mainspace in that I am not allowed to change what another has posted, so I only suggested how and why your post might be edited. Thank you for acting on my suggestion and for all your work here. DroneB (talk) 14:47, 29 September 2018 (UTC)[reply]

Actually, here in the U K we are familiar with both scales. The papers will say that temperatures will reach 95° and we all know what that means. If they said they were expected to reach 35° we would have to think about it. — Preceding unsigned comment added by 86.131.233.235 (talk) 19:03, 29 September 2018 (UTC)[reply]

On wikipedia, you can just write {{convert|95|°F|°C}} or {{convert|35|°C|°F}}, which will display as "95 °F (35 °C)" or "35 °C (95 °F)" respectively. You state what you have, and the template converts it to the other one automatically. Then we can spend our time more productively, arguing about which to should be the main vs parenthesized units. DMacks (talk) 04:14, 30 September 2018 (UTC)[reply]

For what it is worth, I gathered everything I have that is made of silicone -- around a dozen different items. I then applied my soldering iron. At 350/375/400 °C (my normal soldering temperatures) the silicone laughed at me. At 450 °C I was able to make a mark on a cheap scrubbie ( https://www.amazon.com/gp/product/B01MREBZ2V/ ) but not on any of the other items. --Guy Macon (talk) 11:12, 30 September 2018 (UTC)[reply]

Antimatter

In space, are there naturally occurring accumulations of antimatter in significant amounts (say, 300 lbs. or more)? 2601:646:8A00:A0B3:19E8:E4E1:14EA:832C (talk) 06:18, 28 September 2018 (UTC)[reply]

As far as we know, the answer is no. If they do exist, they must be quite rare. If there were large clumps of antimatter in our universe, these would be expected to sometimes encounter ordinary matter, which would result in colossal explosions. The fact that we haven't seen the signs of large matter-antimatter explosions indicates (at the very least) that any macroscopic accumulations of antimatter must be extremely rare. Dragons flight (talk) 07:15, 28 September 2018 (UTC)[reply]

I'm not an expert, but from the sort of explanation given in Chronology of the universe, it is believed that all of space was filled with a nearly homogeneous plasma for quite some time. As such, it is difficult to imagine that nucleosynthesis or subsequent processes would have permitted the assembly of 300-pound lumps of antimatter in the middle of space at random; they should have been annihilated. Every once in a while I read about people hunting for antimatter islands in the cosmos, but my understanding has been they are looking for very large regions (very, very far away) which might be indicative of how the overall asymmetry got started. That said, then there's stuff like this. Dragons flight was correct to take the empirical approach, but I just wanted to heads-up a little on the theoretical aspects. Wnt (talk) 19:24, 28 September 2018 (UTC)[reply]

In the very beginning of the Big Bang there was neither matter nor antimatter, but the primordial ingredients for both. It is really a mystery as to why one formed but not the other, but it could have been as simple as the grain of rice that tips the scales. What we do know, and most people don't consider, is that space is not a total vacuum, but is filled with dust and gases; in some places at extremely low pressures and others extremely high. In fact, our local region of space, through which the heliosphere travels, is one of those extremely low-pressure areas compared to the surround galaxy. Even so, far greater vacuums have been created here on Earth than are found in space. According to Chakrabarti, the closest thing you can find to a total vacuum is near the event horizon of a black hole, where matter enters with the speed of light. Thus, it is highly unlikely that any quantities of antimatter exist, and if they do, it would most likely be extragalactic. Zaereth (talk) 22:43, 28 September 2018 (UTC)[reply]

Oh yes, by "very, very far" I meant "large Hubble constant". Even so, that antimatter-detecting instrument on the ISS at least seems to be finding something. I think your description of the heliosphere and outer space in general is inaccurate but I don't have the figures to argue it. The asymmetry has something to do with the failure of CT symmetry, so it's probably not just random. Wnt (talk) 23:51, 28 September 2018 (UTC)[reply]

Average density in the area of Earth is around 0.25 particles per square centimeter, which is a mixture of neutral atoms (mostly hydrogen and helium) and ions traveling outward from the sun at supersonic speeds. However, at that distance, the gas pressure is not nearly as high as the ram pressure (the inelastic, supersonic column of pressure described a few sections above), which is roughly equivalent to the magnetic or radiation pressure. The pressure gets very high as the flow goes from supersonic to subsonic, forming a shockwave we observe as the bubble of the heliosphere. The shock dissipates the energy until the pressure in the shockwave reaches an equilibrium with the surrounding local interstellar medium (LISM), which has a density of about 0.07 to 0.015 particles per square centimeter, although this tends to be lower than the density in the surrounding local interstellar cloud.

I think it's likely antimatter exists out there, but find it doubtful it does in large quantities within the interstellar medium. (There is an interesting theory that the accelerating expansion of the universe may be powered by a pressure differential between it and the total vacuum that may be outside the universe (where laws like the speed of light may not even apply). It may be entirely possible that gas densities between galaxies are even higher than in certain areas within them, like water whirlpooling around a drain or air in the capture-zone of a fan. Or they may be lower. These are all just hypotheses at this point.) The problem is that the original question is one of cosmology, thus all we have are best guesses. Zaereth (talk) 01:29, 29 September 2018 (UTC)[reply]

Our article Local Bubble is somewhat relevant. Long story short: the Solar system and a few nearby stellar systems sit within an irregular bubble whose interstellar medium of gas and dust has around 1/10th of our galaxy's average, caused by one or more nearby supernovas within the last 20 million years. As a formerly active astronomer and science textbooks editor, I concur with Zaereth's initial and subsequent descriptions, which perhaps Wnt initially misread. {The poster formerly known as 87.81.230.195} 90.217.102.65 (talk) 10:11, 29 September 2018 (UTC)[reply]

There's a Larry Niven story Flatlander about a planet made of antimatter. Spoiler:

It was as if he'd screamed. I could hear that word echoing from side to side in my skull.

Elephant's booming voice was curiously soft. «Antimatter?»

«Of course. We have no excuse, of course, but you should have realized it at once. Interstellar gas of normal matter had polished the planet's surface with minuscule explosions, had raised the temperature of the protosun beyond any rational estimate, and was causing a truly incredible radiation hazard. Did you not even wonder about these things? You knew that the system was from beyond the galaxy. Humans are supposed to be highly curious, are they not?»

173.228.123.166 (talk) 02:58, 29 September 2018 (UTC)[reply]

Hawking radiation

How big must a black hole be in order for its evaporation to create a 20-kiloton explosion? 2601:646:8A00:A0B3:19E8:E4E1:14EA:832C (talk) 06:20, 28 September 2018 (UTC)[reply]

Since the blackhole's entire rest mass is released as energy as it evaporates, the mass of the black hole that causes a release of 20kT(

8.37\times 10^{13}J

) will be given by

m={\frac {E}{c^{2}}}

i.e.

9.298\times 10^{-4}kg

. Then we can use the relationship between the Schwartzschild radius and the mass (

r_{s}={\frac {2GM}{c^{2}}}

where G = 6.674×10⁻¹¹ N·kg^–2·m²) to determine that such a black hole would have a Schwartzschild radius of

1.38\times 10^{-30}m

. 202.155.85.18 (talk) 08:55, 28 September 2018 (UTC)[reply]

Thanks! Would it be possible to create such a black hole artificially (e.g. in a particle accelerator), or would the energy requirement be prohibitive? 2601:646:8A00:A0B3:D843:FF23:EE04:4F41 (talk) 11:25, 28 September 2018 (UTC)[reply]

Today I learned the largest fossil fuel power plants burn a Hiroshima of energy each in ~2 hours. No wonder there's global warming. Sagittarian Milky Way (talk) 18:45, 28 September 2018 (UTC)[reply]

I wasn't talking about the biggest power plant, but about the biggest particle accelerator (or whatever other means there might be of creating black holes artificially). The reason is, there's been a scare a few years back about the possibility the Large Hadron Collider might create a black hole which would then suck in the whole Earth -- which is an impossibility given that small black holes evaporate so fast, but I thought that maybe such a scenario could create the hazard of a nuclear explosion instead? 2601:646:8A00:A0B3:D843:FF23:EE04:4F41 (talk) 09:30, 29 September 2018 (UTC)[reply]

If a micro-black hole was created in a particle accelerator, there is no guarentee that it would evaporate, since Hawking radiation is postulated, but not proven. On the other hand, it's totally impossible for a micro-black hole to "suck in the whole Earth". A micro-black hole of a given mass doesn't have any more gravitational pull than any other object of the same mass. In other words, a ~1g micro-black hole such as the one that would give a 20kT blast if it does in fact evaporate, would exert no more gravitational pull on the matter around it than a 5 carat diamond. 2400:D400:9:1268:306:200:0:10B0 (talk) 09:58, 29 September 2018 (UTC)[reply]

True, but my question is, would it even be possible to create a 1g black hole in the first place, or would the amount of energy required be too out of this world? 2601:646:8A00:A0B3:D843:FF23:EE04:4F41 (talk) 10:40, 29 September 2018 (UTC)[reply]

That's really difficult to say with any degree of accuracy, but we can make a ballpark guess. The compressibility of nuclear matter is very roughly 300MeV based on theoretical calculations [15]. If we wanted to compress a proton into a space smaller than its Schwartzschild radius, we'd be reducing its volume by 38 orders of magnitude. To a first order approximation (and assuming this type of classical mechanical calculation is even valid for this quantum system) that would take around 337 Joules. That's not a prohibitive amount of energy for us to come up with, but it's probably very difficult for us to focus that amount of energy as a compressive force on a single proton. Since the Large Hadron Collider is not some kind of quantum scale diamond vice, it's hard to imagine a situation where a micro-black hole would be created. Maybe where the forces of acceleration on a given particle are so great that it experiences enormous compression on a time scale too short for it to relax through expansion in the dimensions perpendicular to the acceleration. Though when day dreaming about what fantastical properties a subatomic scale black hole might have, it's good to keep in mind that electrons already display many of the properties of a micro-black hole.139.194.67.236 (talk) 12:29, 29 September 2018 (UTC)[reply]

My impression is that the black hole electron idea involves a mass and singularity that doesn't fit within the Schwartzschild radius (the position is simply too uncertain!). Yet if it doesn't ... how is it a black hole? Hmmm. I wonder if anyone has tried to model a super-extremal fuzzball (string theory)?? Our article says those have a volume equal to black holes, but are made up of strings, which are quarks. I'm not clear on whether each of the six types of quark has a volume in string form that is proportional... the part about them getting less dense the more they are is also curious ... but if you can take those quarks and somehow shave them down to something with a -1 charge and a mass much less than that of a quark, that would take the game, set and match! Wnt (talk) 00:28, 30 September 2018 (UTC)[reply]

Electric-field equivalent of Lenz's law?

I note that the article on Lenz's law states that "the direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field". This is useful heuristic for getting the sign on the magnetic field right on boundary condition. Is there a corresponding law for electric fields? If so, what is it called? If not, why not? I admit that I might be missing some understanding, here, so comments/help are welcome. Attic Salt (talk) 17:25, 28 September 2018 (UTC)[reply]

As there are no magnetic charges and therefore "magnetic" conductors, there is no "Lenz's" law analog for electric field. Ruslik_Zero 18:30, 28 September 2018 (UTC)[reply]

Hmm, I guess I was thinking of something different from that. Insofar as magnetic discontinuities are supported by current sheets, for example, at surfaces, I would think that a (possible) electric Lenz's law would involve surface charge -- something consistent with Maxwell's equations and Ohm's law. I just don't quite know how to phrase it or if someone has it named after him/her. Attic Salt (talk) 18:57, 28 September 2018 (UTC)[reply]

Two urine streams from pressure

I get the experience when I often lay belly down on the floor or bed and putting pressure on my urethra, it seems that is cause me whenever I pee it usually comes out in two streams or one wide stream rather than one thin stream. Other times when I get away from home and not laying on the floor for hours, I usually pee it out in one solid stream afterwards. Is it true that pressing urethra on the floor or bed causes it to pee it out in two streams? Planet Star 22:19, 28 September 2018 (UTC)[reply]

You should see a doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:31, 28 September 2018 (UTC)[reply]

LOL, this is a deep male secret that no woman should be permitted to learn, so here goes. ;) Humans do not form vaginal plugs, but wankage is not always entirely traceless. Wnt (talk) 23:54, 28 September 2018 (UTC)[reply]

Not funny. Meatal stenosis or narrowing of the opening of the urethra that causes abnormal direction of the urinary stream is commoner among circumcised males due to lack of a protective foreskin. A urologist (whom the OP should consult) may carry out a Voiding cystourethrography (VCUG) test if a physical exam, e.g. using ultrasound, indicates an incorrect urine flow or Urinary tract infection that could put the bladder or kidneys at risk. DroneB (talk) 00:30, 29 September 2018 (UTC)[reply]

Semen does get sticky when it congeals, no? Anyway, what you describe sounds like a long-term/medical situation, but what I'm suggesting is an issue that, once understood, is readily attributable, and in any case (dis)solves itself. Wnt (talk) 01:30, 29 September 2018 (UTC)[reply]

See Nozzle. Bus stop (talk) 01:13, 29 September 2018 (UTC)[reply]

The one reference source more comprehensive than Wikipedia has an article about this.[16] 173.228.123.166 (talk) 04:25, 29 September 2018 (UTC)[reply]

Despite the fact that I have pointed out on multiple occasions that no Wikipedia policy or guideline exists against giving medical advice except in the fevered imagination of a few people who do not understand the concept of "disclaimer" -- and that only an idiot pays any attention to medical advice from random strangers on the Internet -- this is a situation where I really think that User:PlanetStar should see a doctor. It doesn't happen to me when I lay down the same way, nobody here has come out and said that it happens to them, and it just might be either [A] something minor but still worth asking a doctor about, or [B] something serious that is just starting to show the first symptoms. (Medical disclaimer.) --Guy Macon (talk) 04:29, 29 September 2018 (UTC) [reply]

Yet another off-topic attempt to enforce an imaginary rule that does not appear in any Wikipedia policy or guideline. --Guy Macon (talk) 02:18, 1 October 2018 (UTC)[reply]

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

Wikipedia:Medical disclaimer is the policy or guideline. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:47, 29 September 2018 (UTC)[reply]

Even if I accept your dubious claim that a disclaimer is a policy, that page would be a "policy" that utterly fails to say that we cannot give medical advice. The lawyers who wrote the disclaimer were invited to set a policy (which they are allowed to do; see Wikipedia:Office actions) that we are not allowed to give medical advice. They declined to do so.

Wikipedia:Medical disclaimer says that when we give medical advice, no warranty is made that the advice is accurate, true, correct, precise, or up-to-date. It doesn't say that we can't give medical advice. It says that when we give medical advice, our advice cannot substitute for the advice of a medical professional. It doesn't say that we can't give medical advice. It says that when we give medical advice, even if our advice is accurate, it may not apply to you or your symptoms. It doesn't say that we can't give medical advice. It says that when we give medical advice, we do not take any responsibility for the results or consequences of any attempt to follow our advice. It doesn't say that we can't give medical advice. It says that when we give medical advice, it should not be construed as an attempt to engage in the practice of medicine. It doesn't say that we can't give medical advice.

All of which is lawyer talk saying the same thing I said in plain English above: only an idiot pays any attention to medical advice from random strangers on the Internet.

Baseball Bugs, please stop citing imaginary policies.

For the pedantic who really want to know what the rules are: some medical advice is forbidden under the general rule prohibiting disruptive comments, but not all medical advice. For example, the following medical advice is allowed:

Don't do crystal meth. It will screw up your health. Don't bother asking a doctor if crystal meth is good for you. It isn't. There. I just provided medical advice, and while I did make a point, I did so without being disruptive. There are some who believe that Wikipedia has a policy against giving medical, legal, and business advice, but no such policy or guideline exists except in the fevered imagination of a few people who do not understand the concept of "disclaimer" (If you are about to cite the reference desk guidelines, please read WP:LOCALCON and then show me where the Wikipedia community approved them).

Feel free to report my behavior at WP:ANI if you believe that I have violated any Wikipedia policy or guideline.

Did I mention that Wikipedia:Medical disclaimer doesn't say that we can't give medical advice? Because it doesn't. --Guy Macon (talk) 09:52, 29 September 2018 (UTC)[reply]

Advising someone to obey the law does not constitute professional advice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:31, 29 September 2018 (UTC)[reply]

Actually, In my comment above I gave medical advice. To expand on my medical advice (which I remind you, I advise you to ignore because I am unqualified to give medical advice), don't become a meth addict even if the Libertarians win enough seats to control congress and legalize meth, heroin, etc. It will still be bad for your health. --Guy Macon (talk) 06:29, 30 September 2018 (UTC)[reply]

Recommending not ingesting illegal drugs does not qualify as medical advice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:44, 30 September 2018 (UTC)[reply]

Also, since you've stated this same hypothesis a number of times, have you run it by the WMF to get the opinion of the owners of this website? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:46, 29 September 2018 (UTC)[reply]

By my count, five individuals have asked WMF legal to issue a ruling that says that we are not allowed to give medical advice such as "don't do meth". WMF legal has declined to do that. Feel free to do your own asking. I am not going to ask because the WMF medical disclaimer (which, I remind you, does not say that we can't give medical advice) seems clear to me. --Guy Macon (talk) 06:29, 30 September 2018 (UTC)[reply]

User Guy Macon pastes yet again his purported "allowed medical advice" in what looks like an opportunistic attempt to filibuster and provoke. The last time he did it [17] I pointed out[18] the error in his advice about crystal meth (which is Methamphetamine and is sometimes a legitimate medical prescription). Guy Macon defies suggestion that his rhetoric amounts to soapboxing[19] while he much more credibly admits ""When it comes to medical topics, an electronics engineer like myself is pretty much lost" [20]. I wish to distance myself from, and to reject as unacceptable and dangerous any medical advice like Guy Macon's that contains the phrase Don't bother asking a doctor.... DroneB (talk) 17:10, 29 September 2018 (UTC)[reply]

...Which, of course, you are free to do. In fact, I highly recommend ignoring (as opposed to rejecting; that would lead you to taking crystal meth) my medical advice, and doing your own research if you are considering taking crystal meth. I would even advise (which you should ignore) that if you are so dimwitted that you can't figure out that becoming a meth addict is bad for you without a M.D. telling you, then go ahead and waste your doctor's valuable time asking him whether to take crystal meth, and while you are at it, have him check your cognitive abilities, based upon your inability to figure it out without him.

Please do ignore any medical advice I give you. Please do not make claims about imaginary "policies" that do not exist.

Please do report me at WP:ANI if you honestly believe that my repeatedly correcting editors who fabricate imaginary policies and guidelines is disruptive. --Guy Macon (talk) 06:29, 30 September 2018 (UTC)[reply]

Please see Wikipedia:Reference desk/Guidelines/Medical advice "Any question that solicits a diagnosis, a prognosis, or a suggested treatment, or any answer that provides them, is considered inappropriate for the reference desk." Dmcq (talk) 10:22, 29 September 2018 (UTC)[reply]

Please show me where the Wikipedia community demonstrated a consensus for the above "policy". Until you do, per WP:LOCALCON (which is a WP:POLICY), the refdesk guidelines "have not formally been approved by the community through the policy and guideline proposal process, [and] thus have no more status than an essay". --Guy Macon (talk) 06:29, 30 September 2018 (UTC)[reply]

(...sound of crickets...) --Guy Macon (talk) 02:36, 1 October 2018 (UTC)[reply]

The disclaimer presumably gets the WMF off the hook legally. But does it get YOU off the hook legally? If you post medical advice, someone takes it, and something bad happens, might YOU be sued? That's the question to ask the WMF. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:41, 30 September 2018 (UTC)[reply]

Go ahead and ask it. They will either ignore you or tell you that it is the WMF's job to insure that the WMF won't be sued, not to insure that I personally won't be sued. And it shouldn't be your concern either -- especially while you are in the process of evading any discussion about the established fact that you keep making up fake Wikipedia policies.

I would really, really enjoy having someone try to sue me for telling people that crystal meth is bad for them. --Guy Macon (talk) 02:36, 1 October 2018 (UTC)[reply]

That's not medical advice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:50, 1 October 2018 (UTC)[reply]

Double streaming may be caused by a strand of hair across the orifice. This has no medical significance. Whether this is a problem for the circumcised but not the uncircumcised I am not in a position to say. 86.152.81.16 (talk) 12:03, 29 September 2018 (UTC)[reply]

It might be, or it might not be. Only a doctor can tell the OP. No one here is qualified to. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:29, 29 September 2018 (UTC)[reply]

I am with Bugs on this. Only a doctor can tell the OP. No one here is qualified to. All I can add is that it seems like the sort of thing one should see a doctor about. --Guy Macon (talk) 06:29, 30 September 2018 (UTC)[reply]

According to Pastry bag "Though a circular nozzle is quite useful for making round shapes and for filling pastries such as profiteroles, many differently shaped nozzles are commonly used to produce star, leaf, and flower-petal shapes." Bus stop (talk) 13:25, 29 September 2018 (UTC)[reply]

This is getting grosser by the minute. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:28, 29 September 2018 (UTC)[reply]

Might I suggest there are a couple of piss artists involved in the discussion. Dmcq (talk) 14:40, 29 September 2018 (UTC)[reply]

I don't know what that means, but it can't be good. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:47, 29 September 2018 (UTC)[reply]

See Wikt:piss artist. Alansplodge (talk) 17:22, 29 September 2018 (UTC)[reply]

Must be a British thing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:37, 29 September 2018 (UTC)[reply]

I would be tempted to use the term wanker, but as you might infer from my non-medical explanation above, I'm in no position to talk, as such usage would formally make them wankers' wankers, which is to say not wankers at all. The drolls are calling and they want the Internet back - the bureaucrats have tried and tried, but they don't know how to wring any real pleasure from it! Wnt (talk) 23:49, 29 September 2018 (UTC)[reply]

Speaking of wankers, some Yankees haters call this team "Wankees". In the AL Wild Card Game to be played on Wednesday between A's and Yankees, some A's fans would call the opponent team Wankees. If Yankees win and play the Red Sox in the ALDS, some Red Sox fans would call them Wankees.

Two of the good places to post medical questions are Quora and Yahoo! Answers, which already have a lot of them. Planet Star 19:44, 30 September 2018 (UTC)[reply]

I see someone is asserting there is no consensus support for WP:Reference desk/Guidelines/Medical advice. This is untrue. At WT:Medical_disclaimer#RFC_for_deprecation_of_this_policy overwhelming support for the policy and guideline were shown. People should not go around saying a policy or guideline is not supported without raising the matter there or on WP:VPP first and getting the matter resolved, deliberately misquoting policy is a serious business. Dmcq (talk) 11:03, 1 October 2018 (UTC)[reply]

Why does ocean water get colder as you go deeper

When you go deeper in soil/rock, you reach higher temperatures because you approach a strong source of heat (Earth's core). But if you go deeper in ocean, temperatures decrease. Obviously I'd expect upwelling of warm water to carry off some heat from the bottom layers and lessen the temperature gradient, but how can they become even colder than the top layers? How does this not violate the second law of thermodynamics? 93.136.121.252 (talk) 23:30, 28 September 2018 (UTC)[reply]

There's a flaw in your logic. Whether you're on the dry surface or at the bottom of the ocean, you're on the Crust (geology). As suggested in Thermocline, the surface of the ocean is heated by sunlight and air temperature, and is fairly active. The farther down you go, the less active it is, so the warmer water does not mix in. Generally, the bottom of the ocean is calm and cold, because there is almost nothing to heat it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:44, 28 September 2018 (UTC)[reply]

The OP has a decent argument, but has neglected that ocean currents travel vast distances over long periods between different climates. See thermohaline circulation. It is true that the ocean is heated from below to some degree, but the water is gradually replaced with new water from the poles. I don't have any idea whether it would be theoretically possible to maintain a cold layer at the bottom of an ocean in a completely homogeneous climate by periodic (nightly) cooling with downwellings from the surface layer; I'm skeptical, but I think relevant data might exist from smaller seas and lakes in the tropics. Wnt (talk) 01:57, 29 September 2018 (UTC)[reply]

Yes, ocean currents make sense, I forgot that they might replenish cold water faster than the hot crust/mantle can transfer heat. Thermocline says that in polar waters temperature often doesn't decrease with depth. If there's sea ice then the surface should actually be colder (<4C), so that's probably where the cold at the bottom of warm seas comes from. Still, I'm pretty amazed that oceans can cool the Earth so much. In a shallow lake the day/night cycle can be significant, but when you look at deep oceans, even the 0-30C difference pales in comparison with the temperature differential at equivalent continental crust depth. 93.136.121.252 (talk) 04:07, 29 September 2018 (UTC)[reply]

I have heard that the pressure at those depths made the water reach its maximum density, which occurs at 4 degrees C. So the temperature at the bottom of a very deep lake is supposed to be that. I'm not convinced though, and I've wondered about it. 173.228.123.166 (talk) 04:28, 29 September 2018 (UTC)[reply]

Nope. Nothing about the pressure cools the water. And if the water was completely still, the heating from the core would be greater than it it is in deep mineshafts, because the crust is thinner at the bottom of the sea. Wnt got it right. The water isn't still, and whenever there is a difference in temperature (such as near the poles) the colder water sinks and then spreads out when it hits the bottom. https://oceanservice.noaa.gov/facts/coldocean.html explains it all. --Guy Macon (talk) 10:01, 29 September 2018 (UTC)[reply]

That's not the point. But water at 4°C is at its densest, so that's what sinks to the very bottom. In lakes, where there's no sideways ocean current, this becomes a stable layer. Andy Dingley (talk) 12:11, 29 September 2018 (UTC)[reply]

The Wikipedia article I cited earlier states that while the crust at the bottom of the sea is vertically thinner, it's also more dense. And the other article says the bottom of the sea is calm. I wouldn't take that to mean there's no circulation at all, but much less than there is higher up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:42, 29 September 2018 (UTC)[reply]

Not really the point, but it is worth noting that the 4 C density maximum only applies to fresh water. For typical ocean salinity, the maximum density of sea water actually occurs at its freezing point (approximately -2 C). Dragons flight (talk) 18:38, 29 September 2018 (UTC)[reply]

I was puzzling over that, since I always understood that the zero point on the Fahrenheit scale was the freezing point of brine. However, the article indicates that the "salt" referred to is actually ammonium chloride. 86.131.233.235 (talk) 19:16, 29 September 2018 (UTC)[reply]

Water actually has one of the highest thermal capacities of all substances. Also water has the highest "volumetric heat capacity". That means it can store allot of (heat) energy but also takes or gives allot of energy when changing 1°. It also has a very good thermal conductivity for fluids. So it needs a constant high energy input to stay at or around some heat level.

That is the main secret behind the seemingly paradox about deep sea cold streams. The heat input from the earth core is barely enough to keep the water from freezing while the sun, nomatter it "heats" only half the time, manages to even warm up the top sea streams so much that they start to vaporize considerably. --Kharon (talk) 20:35, 29 September 2018 (UTC)[reply]

it needs a constant high energy input to stay at or around some heat level. Sorry, what? The most generous reading I can make of the above is that because water has high conductivity it transfers heat faster to close areas, thus gets to equilibrium quicker, thus needs higher incoming flux to match the outgoing flux. However, it is wrong on multiple levels. One: the relevant variable would be thermal diffusivity which is actually fairly low for water (about 100 times less than air, for instance), precisely because the thermal capacity is so high. Two: in most fluids of large dimensions, the dominant phenomenon of heat transfer is not diffusivity but convection; maybe that is different at the bottom of the sea because of anomalous density effects, but you cannot just blather about conductivity effects without discussing that first. Oh, also, "heat level" is not a thing. Try temperature or maybe internal energy.

The second paragraph's mumbo-jumbo seems to imply that the lower sea bed is kept liquid by heat from the Earth's core. Let's say I would like to see a source for that. Tigraan^{Click here to contact me} 09:56, 1 October 2018 (UTC)[reply]

September 29

Are there any pathogens where the fraternal birth order effect makes a difference?

It's been established that the more older brothers a boy has, the more likely he is to be gay:

http://www.pnas.org/content/early/2017/12/05/1705895114

This fact, combined with Greg Cochran's theory about a pathogen being response for male homosexuality, makes me wonder:

Are there any pathogens where the fraternal birth order effect makes a difference? Specifically, are there any pathogens where the more older brothers a boy or man has, the more likely he is to be affected by this pathogen?

Basically, I am asking this question in order to get a rough idea of the likelihood of Greg Cochran's theory actually being correct. Also, No, I'm certainly not trolling; rather, I am trying as best as an amateur can in figuring out the truth behind this issue. Futurist110 (talk) 01:11, 29 September 2018 (UTC)[reply]

It doesn't sound like much of a "theory" where Cochran is concerned, but the association of homosexuality with a female anti-neuroligin 4 Y-linked (NLGN4Y) antibody is fascinating. This makes it sound like the antibody could be a simple case of an Rh factor like phenomenon; however, bear in mind that evolutionarily this "problem" could easily be "fixed" (women could express NLGN4Y anywhere in their bodies - big toe, salivary gland, wherever - and then it would end up being recognized as a self antigen and homosexuality would go away). This would indicate that far from being some insoluble design issue, homosexuality has been preserved by natural selection even in the face of a readily available mutation (putting some random enhancer on the DNA next to it). Which would mean that some very immediate selective benefit for homosexuality has to exist from the perspective of the mother.

That said, Cochran's speculation isn't necessarily wrong -- anything is possible in biology, always. One can imagine that a foreign antigen could influence rejection of some other protein, like lone star tick causing meat allergy. The antigen could, in theory, be just about anything - mosquito saliva, rose thorns, or a virus. But the problem is, I am not aware of any demonstration that homosexuality has ever not existed in any human society, so how can it be an environmental factor?

It could be interesting to look into whether this particular neuroligin is responsible for the specificity of synapses between potential pheromone receptors (some orthologs are allegedly pseudogenes, but I'm suspicious of selenocysteine involvement) in the vomeronasal organ, and GnRH-expressing neurons that pass through the terminal nerve to the hypothalamus. If this antibody response can alter the determination of which odor is a pheromone, then it should be able to condition recognition of one sex rather than another. Wnt (talk) 01:50, 29 September 2018 (UTC)[reply]

Here is a list of possible ways that natural selection can select for homosexuality as a trait that increases the success of an individual in reproducing and passing their genes on to the next generation: [ https://sites.psu.edu/evolutionofhumansexuality/2014/03/05/selection-for-homosexuality/ ]. --Guy Macon (talk) 04:38, 29 September 2018 (UTC)[reply]

Relevant articles: biology and sexual orientation and environment and sexual orientation. --47.146.63.87 (talk) 22:12, 29 September 2018 (UTC)[reply]

@Guy Macon: That article looks like a good review of at least most of the leading ideas. Problem? (a) Heterozygous advantage implies there is a "gay gene", which would have been mapped and cloned by now. People have tried hard and failed to map any one locus on the chromosome. (b) Altruism seems iffy in the article itself, as it is hard to explain how the homosexual can improve transmission of his genes that much in third parties; but see below. (c) A polygenic trait seems like a winner --- however, if women can simply express this neuroligin to prevent this antibody effect, then they can have a single gene trait that overrides it all, which is why I got excited to see the article. And (d) antagonistic pleiotropy only would make sense if the antibody response could also improve reproductive success (how?)

However, this paper introduces another possibility, which is that the mother could be selecting for her success, not the offspring's. It is always easier to tell somebody else to be altruistic than to be altruistic yourself, and so I think this might change some of the numbers, but I haven't looked into the math of altruism. Wnt (talk) 00:05, 30 September 2018 (UTC)[reply]

Diamond valuation

Is there someplace online where you can get a general idea of the value of a daimond (or even minor gemstones like, say, citrine)? I was reading about the 4Cs and am trying to figure out valuation by altering certain digits. Say how much would something like this cost? Color: I; Clarity: SI2; CTW: 0.200; Cut: RoundLihaas (talk) 09:41, 29 September 2018 (UTC)[reply]

This was the first hit on google for "diamond valuation", and puts your diamond's value at $147.42. 2400:D400:9:1268:306:200:0:10B0 (talk) 10:12, 29 September 2018 (UTC)[reply]

It's not clear from your post whether you're buying or selling. The price of a synthetic gemstone will generally be much lower than that of a "natural" one. Whether buying or selling, if you want a "natural" stone, you will likely get widely varying prices from different establishments; the market is intentionally opaque and full of collusion so you'll give up and just take whatever price is offered. (For instance, several of the largest U.S. jewelry store chains are owned by the same company.) --47.146.63.87 (talk) 22:07, 29 September 2018 (UTC)[reply]

This is a very old article but still relevant.[21] 173.228.123.166 (talk) 22:19, 29 September 2018 (UTC)[reply]

There is a company called the Jewelry Exchange in Redwood City, California that advertises "diamonds guaranteed to appraise for double". That ridiculous slogan indicates that diamond prices are mushy and subjective, as opposed to gold prices, for example. Cullen³²⁸ Let's discuss it 22:23, 29 September 2018 (UTC)[reply]

That's what I head, especially if they are lab made vs. natural.

Thanks, anywasy, yall.Lihaas (talk) 22:59, 29 September 2018 (UTC)[reply]

We have an article, though it's in bad shape. (No Cal resident? As the article says, their headquarters are down here, so here their ads always tout "The Jewelry Exchange in Tustin". I think they've been running the same TV ad for over 20 years.) --47.146.63.87 (talk) 08:11, 30 September 2018 (UTC)[reply]

September 30

Pianos vs motor vehicles: moving parts

A dear friend of mine, who's a highly experienced piano teacher, has told me that a piano has more moving parts than a motor car. I wonder if this would depend on the type of piano and the type of car. Or maybe it's absolutely correct. Or maybe not. Can someone shed light on this for me? -- Jack of Oz ^{[pleasantries]} 00:19, 30 September 2018 (UTC)[reply]

It could well be true. Start counting the moving parts in a typical car, and they might fall short of 88, or whatever the magic number would be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:38, 30 September 2018 (UTC)[reply]

I can tell you it's way more than just the 88 keys. And I'm sure any car would have way more than 88 moving parts. -- Jack of Oz ^{[pleasantries]} 02:06, 30 September 2018 (UTC)[reply]

Have you asked your friend to "prove it"? Or might that be a sensitive issue? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:13, 30 September 2018 (UTC)[reply]

Do you count the cams on a cam shaft or the wheel weights on the wheel? Technically, every part on a car is a moving part if the car is moving, no??? ;) Wnt (talk) 01:59, 30 September 2018 (UTC)[reply]

A piano can also be moved via its wheels, but I'm not so sure the basic chassis of either a car or a piano would count as a "moving part". ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:13, 30 September 2018 (UTC)[reply]

These items claim that a piano has about 12,000 while a car has about 10,000. Piano and [22] ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:16, 30 September 2018 (UTC)[reply]

Our piano article cites a promotional website from Steinway & Sons, a piano building firm of international repute. The source claims: "There are 12,116 individual parts that make up a Steinway grand piano." This is not the same as 12,000 moving parts.

In any event, the number of parts - moving or otherwise - is a poor proxy for the mechanical complexity of a system. Not all moving parts are equal in complexity.

Personally, I find the non-moving part of the piano to exude more complexity: for example, the curved hardwood that forms the distinctive casing, or rim, of a grand piano commands a five-figure premium over the straight wall of an upright piano; and in both types of piano, the soundboard must be crafted in a manner that simultaneously satisfies strict engineering requirements and artful imprecision. As discussed in our article on piano acoustics, it is the inharmonicity of a piano - "not because of a lack of precision" - that give each instrument it timbre - and why it takes so much effort for electronic synthesizers to produce an authentic piano sound!

Nimur (talk) 03:24, 30 September 2018 (UTC)[reply]

Nobody mentioned complexity. Just numbers of moving parts. -- Jack of Oz ^{[pleasantries]} 03:43, 30 September 2018 (UTC)[reply]

{{ec}} with Nimur (had trouble tracking down the piano-article ref to verify) As a quick guesstimate, I count 15 moving parts in the action of a grand piano key, which gives 1320 total. That does not include the mechanism of shifting the set of hammers for the soft pedal, holding up all the dampers for the sustain pedal, etc. but those are likely^[SWAG] only a few tens each for the whole instrument or at most a few extra per key. DMacks (talk) 03:54, 30 September 2018 (UTC)[reply]

Cars would generally be seen as having more, because the manufacturing processes used involve assembling together smaller parts. Consider a piano action vs. an engine cylinder. 88 keys, 11 parts in a piano action per key; 8 cylinders (or 4) - we can simplify this to "Does a car have more than 11 moving parts per cylinder?" Maybe 22 in Europe. Now the parts of that action are largely wooden, with many separate holes drilled into a piece of wood for each lever. The levers are few, but complex. But the car has separate parts, each staying separate until assembled by a mechanic in a garage (I'm counting parts which would be separated during repair as being "separate parts"). We have as many parts as a piano action just for each engine valve on an OHV engine. If you start counting balls in ball bearings, then it's far more. Andy Dingley (talk) 09:49, 30 September 2018 (UTC)[reply]

Small numbers of parts are replaced in routine car maintenance but a full restoration that considers all its parts happens only rarely, if ever, to a car or a piano. One cannot meaningfully compare counts of "moving parts" without an even-handed definition of what constitutes a moving part. Some extreme views are possible e.g.

Every separable part that moves relative to another separable part when the piano/car is taken into use. The count includes screws holding the piano lid to its hinge, and every ball in the car wheel bearings.

Literally every separable part because pianos and cars both have continual motions, both vibratory and planetary, relative to the fixed stars. The count includes every screw on both sides of the piano lid hinge and every chassis fastener in the car.

A conceptual moving part counts as a single part regardless of its actual construction. For piano, key+hammer+string counts as 3, for car drivechain+camshaft+valve counts as 3.

A moderate view can be to count Every saleable replaceable part that moves in contact with another saleable replaceable part during normal continual use of the piano or car. For the car, the dealer's parts list is a guide. We may assume that a piston (with rings, gudgeon, connecting rod and big end shells) or a wheel bearing (preassembled with rollers and oil seals) count each as one. A piano key action should be separated into parts than a qualified repairer would consider replacing. This piano repairer estimates 12,000 action components. DroneB (talk) 19:59, 30 September 2018 (UTC)[reply]

Every component of every link in the timing chain would give you about a thousand moving parts. Your excellent attempt at stratifying the terminology is important, in this trivial problem.Greglocock (talk) 22:53, 30 September 2018 (UTC)[reply]

That's the 2nd example of intellectual snobbery on this thread. It says more about the writers of such things than anything else. -- Jack of Oz ^{[pleasantries]} 08:47, 1 October 2018 (UTC)[reply]

Berry

What berry is it? Grows this month along a public sidewalk in Warsaw, quite small, about the size of a blackcurrant. I'm planning to pick them for eating, if they're non-toxic, so would like to know the species with absolute certainty. Brandmeister^talk 15:51, 30 September 2018 (UTC)[reply]

Looks a bit like a cotoneaster - if so the berries are not considered edible. Mikenorton (talk) 20:49, 30 September 2018 (UTC)[reply]

I agree, looks very like a cotoneaster to me. DuncanHill (talk) 23:57, 30 September 2018 (UTC)[reply]

I disagree. The leaves in the picture are obtuse - not "ovate to lanceolate in shape". The fruits are borne singly or pairs close to the stem in the pictures - not on a corymb. I will try to track down a better candidate. 196.213.35.147 (talk) 13:37, 1 October 2018 (UTC)[reply]

Looks like it could be a cotoneaster after all. I'm going with Cotoneaster microphyllus var. glacialis 196.213.35.147 (talk) 14:01, 1 October 2018 (UTC)[reply]

Why do tinyish spiders often rappel when chased indoors?

Why don't they just jump off without expelling silk? They probably can't fall as fast as freefall while making silk and such a small creature might not even be injured by terminal velocity. Or did blowing away in the wind on a 1-thread parachute save more spider lives than "freefall and run" in its original outdoor habitat and the instinct remains? Sagittarian Milky Way (talk) 20:01, 30 September 2018 (UTC)[reply]

Our article ballooning (spider) may help. Mikenorton (talk) 20:57, 30 September 2018 (UTC)[reply]

You refer to "its original outdoor habitat". I very much doubt whether a spider, whether spiderling or adult, has either any concepts of "outdoors" and "indoors", or the perceptual abilities to tell the differences bearing in mind their size relative to a human-dimensioned structure. {The poster formerly known as 87.81.230.195} 90.217.102.65 (talk) 09:33, 1 October 2018 (UTC)[reply]

It goes without saying, as it is implied in OP's "and the instinct remains".

But even if spiders could distinguish indoors from outdoors (which should be possible, as there are so many differentiating factors they could evaluate: average wind speed, temperature, direction and intensity of infrared radiation and polarized light, smell), why should they just jump off without expelling silk? How could this be a selective advantage? Freefall speed is not the only relevant factor, another would be for example that the thread gives the spider a chance to withdraw from any less than optimal landing place, like water or perhaps the vicinity of predators and carnivorous plants or fire. 194.174.73.80 (talk) 13:31, 1 October 2018 (UTC) Marco Pagliero[reply]

If you really are asking how it could be a selective advantage, that's obvious: freefall speed could be the most important factor. I've no idea whether it is, but for what it's worth, the ballooning article doesn't seem to give any indication that the spiders can direct their flight. That would seem to imply that the other factors you mention are not significant. Henry ^Flower 14:49, 1 October 2018 (UTC)[reply]

Please, you apparently did not read carefully the original question: it asks, why do small spiders "often rappel when chased indoors". Rappel has nothing to do with ballooning but instead describes a spider dropping e.g. from the ceiling on a line of silk. Even if the spider has no control on the direction, the thread allows it to stop and even to reverse the fall if it wishes so. In the context of rappel (not ballooning), my suggestions are of course significant.

And secondly you did not read carefully my own question, which read: "How could it be a selective advantage for a spider to just jump off without expelling silk?", this is the opposite of the question you seem to believe you are answering.

While for your post to be significant at all you should prove or at least make credible that such small animals as "tinyish spiders" can indeed be damaged when free falling from any height (We are not talking of Migale or Tarantula). 194.174.73.80 (talk) 16:35, 1 October 2018 (UTC) Marco Pagliero Berlin[reply]

"Migale"? Is there an article? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:40, 1 October 2018 (UTC)[reply]

Sorry, "Migale" is not English, you are looking for Mygalomorphae 194.174.73.80 (talk) 16:51, 1 October 2018 (UTC) Marco Pagliero Berlin[reply]

File:Amrum.grass.jpg

Location known, but wanted to check something. The grass here gives way to a different cover, over what I am thinking is the landward portion of dunes?

Which articles should I look at to epxand the description? — Preceding unsigned comment added by ShakespeareFan00 (talk • contribs) 22:52, 30 September 2018 (UTC)[reply]

The green and purple stuff? Heather - so see Ericaceae, Erica, and Calluna vulgaris. DuncanHill (talk) 23:54, 30 September 2018 (UTC)[reply]

October 1

Silicone max temperature resistance

[https://cpc.farnell.com/velleman-sa/as11/soldering-mat/dp/SD02170?mckv=sfa5L1aKf_dc%7Cpcrid%7C224654335881%7Ckword%7C%7Cmatch%7C%7Cplid%7C%7Cslid%7C%7Cproduct%7CSD02170%7Cpgrid%7C50784539401%7Cptaid%7Cpla-371097198385%7C&CMP=KNC-GUK-CPC-SHOPPING&gclid=Cj0KCQjwi8fdBRCVARIsAEkDvnLQ-6XCWQu7cjQ-2LUabIqbXpPnPDVz7xz2MTd_tbgc7KPPpQm22_4aAroVEALw_wcB This soldering matt suposedly has a resistance up to 500 °C but I heard the no silicone can withstand even 400. Must this be a lie? 185.230.100.66 (talk) 16:53, 1 October 2018 (UTC)[reply]

Toluene, water and isopropanol miscibility

I mixed one part toluene with one part 70% isopropanol and it separated into two phases. How do I determine what is in the lower phase? I'm guessing it's the water? — Preceding unsigned comment added by 185.230.100.66 (talk) 16:56, 1 October 2018 (UTC)[reply]