Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

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

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

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

June 2

Nuclear bombs and the Tunguska event

I'm all confused about mt and kt etc. In a nuclear war, would the bombs be as bigger or smaller than the Tunguska event?

Links:

Many thanks, Anna Frodesiak (talk) 04:17, 2 June 2018 (UTC)[reply]

In the modern era probably smaller but higher destruction per megaton due to carpet bombing each city with many small hydrogen bombs instead of the giant Tunguska plus bombs of a long time ago. Firing the world's arsenals is much worse than Tunguska both in destruction and sum of megatons but there's asteroids much worse than a nuclear war. Sagittarian Milky Way (talk) 04:38, 2 June 2018 (UTC)[reply]

Did you just say carpet bombing with hydrogen bombs? Tell me you didn't say that. Anna Frodesiak (talk) 05:09, 2 June 2018 (UTC)[reply]

A big nuclear war would be thousands of warheads, if it's important to hit metro area X it's going to get sent many (partially to try to overwhelm missile defense systems)). Sagittarian Milky Way (talk) 06:12, 2 June 2018 (UTC)[reply]

Smaller, much smaller. There was a time when very large nuclear weapons were actually in service (many of the largest explosions were just tests). The B41 nuclear bomb was the largest ever fielded by the United States, a 25 mt bomb of which 500 were built, serving from 1961 to 1976. So during this time, sure, a nuclear war could see the use of bombs about as powerful as the Tunguska Event. The US also had around 340 of the B53 nuclear bomb with a 9 mt yield. This was served from 1962 until 1997, but it was actually intended as a bunker buster, not a strategic weapon - it would actually detonate on the surface for maximum energy transmission to the ground, rather than in the air for maximum blast radius. Though it could also be used as a strategic weapon if desired.

With both of those phased out, the largest bomb in service in the US is the 1.2 mt B83 nuclear bomb. As SMW said, the modern strategy is many smaller bombs. In part it's just more efficient, since the actual goal is usually to take out specific military targets rather than entire metropolitan areas, and also modern bombs and missiles are far more accurate. See for instance the B61 nuclear bomb which replaced the B53 has a yield of only 340 kt, not even 4% of its predecessor. It can get away with this because the bomb can delivered virtually on top of its target. The "many smaller bombs" strategy also makes anti-missile defense a lot harder. Someguy1221 (talk) 05:07, 2 June 2018 (UTC)[reply]

You say in the past a big bomb would be about as big as the Tunguska Event, understood. You also say that targets today are not cities, but military targets. That's a bit of good news, at least. Anna Frodesiak (talk) 05:12, 2 June 2018 (UTC)[reply]

Even in the past, the targets were always theoretically military. Even in the bombings of Hiroshima and Nagasaki, military value of the targets was considered, though of course the shock value was most important. But regardless, there was a problem with delivery. At the time, an error of half a kilometer was not unusual for an aviation bomb under poor conditions, and good conditions for bomb delivery tended to also be good conditions for shooting a plane down. Since military targets are likely to be much more heavily built (i.e. thick, reinforced concrete, and large underground sections), the effective radius of a nuclear weapon for destroying a military structure is much smaller than its radius for destroying civilian structures. This meant the bombs had to be enormous to catch the target in its blast radius despite the inaccuracy, especially if you wanted to strike multiple military targets at once, and cities just become collateral damage. All factors considered, it was simply unlikely for a large city to not be close enough to a military target that it would be annihilated by a strategic weapon. Once you had better technology, as well as other reasons to favor small weapons, that changed. I can use a real example.

I grew up near a retired Air Force base (part of Project Nike) that was only 10 miles from New York City. We learned after the Cold War ended that our town was indeed a subject of Soviet satellite surveillance, and was possibly on a target list at one point. A 25 mt air burst detonation over my house would flatten several towns and cities, and the Big Apple itself would be in flames, but buildings possibly left standing. However, if you could accurately deliver a 340 kt weapon directly to the base and detonate it on the ground, the blast would still annihilate my town, but there would be little destruction beyond. Still sucks for me, though. Someguy1221 (talk) 05:32, 2 June 2018 (UTC)[reply]

10 miles from the edge or 10 miles from the center? Cause even 20 miles from the center can still be inside New York City. Sagittarian Milky Way (talk) 06:18, 2 June 2018 (UTC)[reply]

10 miles from downtown Manhattan. Ish. Someguy1221 (talk) 06:37, 2 June 2018 (UTC)[reply]

Nike sites were Army, not Air Force. -Arch dude (talk) 18:38, 3 June 2018 (UTC)[reply]

You are correct! Wow, I'd always assumed that since it was a nuclear missile, it was Air Force. But yes, the base was operated by the US Army and the Army National Guard. Someguy1221 (talk) 23:19, 3 June 2018 (UTC)[reply]

ICBMs have also gotten more accurate. In the table at Comparison of ICBMs, the last column "CEP" stands for Circular error probable: the radius within which 50% of shots fired are expected to land. Early launch systems had a CEP measured in kilometers. (The first successful Soviet ICBM, the R-16, had a CEP of 2.7 km.) If a 'good' shot is one that doesn't land more than a couple of miles from where it was aimed, there are two ways to make sure you still destroy your target: launch lots of missiles, or use really big warheads. As our ability to aim precisely improved, the bombs tended to get (relatively speaking) smaller. TenOfAllTrades(talk) 13:51, 2 June 2018 (UTC)[reply]

The Soviets started development on an actual "Doomsday device", but they apparently decided that it actually was an insane idea. [1], [2], [] -- I haven't got the time to check the details from these articles, but it would have been perportedly sufficient to literally blow-up the earth. —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 22:29, 2 June 2018 (UTC) -- Postscript: those articles relate to a system that the Soviets and/or Russians possibly actually did develop; there's a project that was cancelled (forgot name) that would have consisted of the largest-bomb-ever, on a barge -- there was a PBS documentary on it (mid-'90s?) -G2G:2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 22:42, 2 June 2018 (UTC)[reply]

"Literally blow up the Earth" is not something that humans can do. The Chicxulub crater was created by a 100 teratonne explosion (that is 100,000,000 megatons), and while that killed 90% of living animals, as you can see the Earth is still here. Someguy1221 (talk) 22:54, 2 June 2018 (UTC)[reply]

But that is why we need to develop the Solaronite, so that we will be able to! --76.69.118.94 (talk) 23:50, 2 June 2018 (UTC)[reply]

Until the development of the MIRV, an ICBM delivered only one warhead, so an ICBM directed at a city needed a really big weapon. A bunch of smaller weapons with the same total mass is a whole lot more effective, even though the bunch has a lower total megatonnage. For the earlier aircraft-delivered bombs, You pretty much wanted to have one big bomb because the aircraft was likely to be shot down. You sent ini as many aircraft as you had, and each tried to reach its one target. It was MAD. -Arch dude (talk) 18:35, 3 June 2018 (UTC)[reply]
Your question is "in a nuclear war". If you mean a nuclear war today, the bombs are clearly smaller than the Tunguska event. If you mean a theoretical past nuclear war, then a very few of the bombs might have approached the size of the Tunguska event, but probably not: we don't have complete knowledge of all bombs ever developed, and some might theoretically be of that size. If you mean future nuclear wars, there are multiple possible ways to use really big bombs and there is not much to constrain the size of the weapons. -Arch dude (talk) 20:53, 3 June 2018 (UTC)[reply]

Thank you all for the very thoughtful and informative answers. They are much appreciated.

If aliens come now, we are going to look so stupid. Never mind the nukes. We will literally all die of embarrassment. Anna Frodesiak (talk) 23:02, 3 June 2018 (UTC)[reply]

June 5

Terrorist Explosions and Tyres

I know that vehicle tyres are made out of quite tough rubber. But having seen numerous bomb explosions in India, I am amazed to see that while toughest of material twisted by sheer force of modern plastic explosives like RDX's action (stoutest metals like barrels of SLRs twisted to "U" shaped things). But strangely tyres of the vehicles turned upside down (or lying on their sides) - due to awesome force of the bomb which should have melted or even vaporized the rubber of both tyre and the tube inside it (most models like Ambassador still use the traditional airtube-inside-the-tyre instead of "tubeless" system which I think is today the standard in the west), but as I have seen both in media and even live, they are not even reduced to sherds but were as good as they were before the bombing, while the body of the rest of the vehicle was twisted and turned like a tin-can stepped upon by an elephant, it's armoured-plates in doors, roof and all now a part of the mess. Can someone please explain why nothing happens to the tyres ? Jon Ascton (talk) 04:48, 5 June 2018 (UTC)[reply]

Your post seems to contain two incorrect preconceptions about things work (leading to the apparent paradox). I would say clearing those is not a clear "answer" though since (as is often the case) fully solving the question requires horribly complex calculations of 3D phenomena.

During quick combustion events (such as a bomb exploding), while the gas temperature rises a lot (by thousands of degrees), the temperature of solids nearby does not rise that much. One of the best-documented examples is the internal combustion engines, where during combustion the engine walls rise by 10 to 50°C, but that happens only within the first mm or so of metal (see for instance this classic article (paywall)). It is hard to compare with the bomb case (on the one hand there is more energy per unit of time, on the other hand it is probably not a confined medium so gas temperature may still be lower) but I very much doubt that anything would get melted or even vaporized, temperatures should stay relatively low.
Rupture mechanics can be deceiving; it happens that softer materials bend but do not break while harder materials resist and eventually break, depending on the exact constraint applied. If you apply the same stress (= pressure) to both metal and rubber, then what matters is the yield strength and that is going to be much smaller for rubber than for metal (this source gives about 25MPa for rubber when it is in the hundreds for most common alloys). However, if you force a certain strain (= deformation) then metals deform reversibly "only" up to 10-20% while elastomers can deform reversibly up to 700% (according to our article, I didn't check the ref).

Tigraan^{Click here to contact me} 07:25, 5 June 2018 (UTC)[reply]

...For example, whacking a car with a sledge hammer makes a big dent, but whacking a tire (aka: tyre) with same force does nothing much. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 04:33, 6 June 2018 (UTC)[reply]

When there is a risk of bomb attacks, it's best to dress up like Michelin Man. Count Iblis (talk) 11:59, 6 June 2018 (UTC)[reply]

Michelin Man doesn't work as a bomb suit, as the blast goes between the tyres. Bomb suits are more like the Dendra panoply. Although the overlapping plates being staggered outwards and downwards must have made this an armour that was susceptible to anyone stabbing downwards, it's how the usual Felix suit is arranged. Andy Dingley (talk) 12:44, 6 June 2018 (UTC)[reply]

Felix suit → [3] —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 02:04, 7 June 2018 (UTC)[reply]

[4] Andy Dingley (talk) 17:27, 7 June 2018 (UTC)[reply]

Tyres are damn near indestructible. This is just one problem with recycling them. They're a composite material of a soft rubber and many high tensile cords. They have an enormous resistance to blunt impacts - why they survive bombings, why they're used as fenders on tugboats. Andy Dingley (talk) 12:44, 6 June 2018 (UTC)[reply]

Etymology of Zeuctherium

Hello. What could the first half of the name Zeuctherium mean? Thanks.--Leptictidium (mt) 15:13, 5 June 2018 (UTC)[reply]

The original paper describing the fossils (from the journal Vertebrata PalAsiatica) is available online, but it's (mostly) in Chinese, and is only a scanned version so Google translate etc can't cope with it. If you can find someone who reads Chinese they might be able to identify the etymology. AndrewWTaylor (talk) 15:49, 5 June 2018 (UTC)[reply]

I would ask that in the Wiktionary Tea room. --31.0.121.29 (talk) 15:53, 5 June 2018 (UTC)[reply]

Preemptive therapy

What is the defintion of it? --31.0.121.29 (talk) 15:36, 5 June 2018 (UTC)[reply]

Basically it seems to mean "giving the treatment before the illness" - for example see here (first Google hit for the phrase), which is about its application in transplant surgery, and the prevention of rejection. AndrewWTaylor (talk) 15:52, 5 June 2018 (UTC)[reply]

That article has a great overview of the terminology for various related prophylactic approaches. DMacks (talk) 18:15, 5 June 2018 (UTC)[reply]

June 6

Golden-mantled ground squirrel or Palmer's Chipmunk?

I uploaded the photo at right to Commons, believing it was a Palmer's Chipmunk; it was taken at 8500 feet in the Spring Mountains, three miles away from Charleston Peak, which I believe to be prime territory for that species. Looking at images on Golden-mantled ground squirrel, I'm questioning that identification, but I'm not sure enough one way or the other to have the image renamed. Can someone help identify this individual?--Prosfilaes (talk) 19:31, 6 June 2018 (UTC)[reply]

Definitely looks like a Golden Mantle Ground Squirrel to me, especially when comparing to the Palmer's Chipmunk photo. But I'm not an expert. --Trovatore (talk) 22:06, 6 June 2018 (UTC)[reply]

I found some images of the Palmer's Chipmunk via the Clark County, NV government website, and it certainly looks much different (lighter tail coloration, a more reddish face) than your photo. --UltravioletAlien (talk) 03:58, 7 June 2018 (UTC)[reply]

Thanks; I had it renamed on Commons.--Prosfilaes (talk) 20:22, 7 June 2018 (UTC)[reply]

Honestly I'm not sure there's enough evidence either way. --Trovatore (talk) 20:36, 7 June 2018 (UTC)[reply]

The Golden-mantled ground squirrel article says "This species is distinguished from similar ground squirrels by a black-bordered white stripe down each side of the back" In this photo we see a black-bordered white stripe on one side. By contrast, the Palmer's chipmunk we display [5] appears to have a black-bordered white stripe dorsally, but no black border on the lateral white stripe that I can see. Also notice a very different coloration around the eyes. Wnt (talk) 15:03, 8 June 2018 (UTC)[reply]

June 7

Except for adrenal gland and kidney are there another organs with cortex and medulla?

Except for adrenal gland and kidney are there another (parenchimal) organs with cortex and medulla? --93.126.116.89 (talk) 01:26, 7 June 2018 (UTC)[reply]

The brain. See cerebral cortex and medulla oblongata.--Jayron 32 01:52, 7 June 2018 (UTC)[reply]

That's different, in the brain it's not like everything that's inside the cortex is medulla, like in the kidney, in fact the medulla isn't inside the cortex at all. Fgf10 (talk) 08:14, 7 June 2018 (UTC)[reply]

Some of these might be excluded by your question, but ovaries, the thymus, lymph nodes, bones and hair. Adrian J. Hunter^{(talk•contribs)} 02:25, 7 June 2018 (UTC)[reply]

It's actually not a very meaningful question, unless you are asking about the words, in which case the answers above are correct. "Cortex", derived from the Latin for "bark", simply means a layer of tissue covering the surface of an organ, and "medulla" means a mass of tissue in the interior of an organ. Many organs/organ systems have that sort of structure, and, as Adrian said, those specific words are used for a number of them. Looie496 (talk) 12:18, 7 June 2018 (UTC)[reply]

Guns etc. and hi-explosive

I think material-science has progressed so much nowadays, remember space-vehicles, fighter-aircraft, submarines (temperature and pressure they must tolerate!)

My question is that why don't they still use RDX or any other hi-explosive in military rifles's cartridges, don't they already use it in heavy-artillery shells ? Jon Ascton (talk) 12:06, 7 June 2018 (UTC)[reply]

An explosive weapon generally uses high explosive to project blast and/or fragmentation from a point of detonation. The article Explosive material gives details of types and properties of a long list of materials.

World War II saw an extensive use of new explosives (see List of explosives used during World War II). In turn, these have largely been replaced by more powerful explosives such as C-4 and PETN. However, C-4 and PETN react with metal and catch fire easily, yet unlike TNT, C-4 and PETN are waterproof and malleable.

The term RDX metioned by the OP is a relic of British security naming "Research Department Explosive" of an organic compound (O₂NNCH₂)₃ also known as cyclonite, hexogen, T4, and, chemically, as cyclotrimethylenetrinitramine. It has been widely manufactured and used as a military explosive component since WW2 (see illustration) as reported at RDX#Usage. Lately FOX-7 is offered as a low-sensitivity replacement for RDX. DroneB (talk) 14:56, 7 June 2018 (UTC)[reply]

For further reading: "greener charges", (2015): "Engineers at Picatinny Arsenal are developing a new propelling charge for the family of 105mm artillery cartridges that are safer for the warfighter by eliminating the use of lead and other toxic substances present in the current charge." Replacing the lead bag liners with bismuth was a minor but important change, and it's not even modifying the energetic compound chemistry!

I think it's fair to summarize that in this century, engineers aren't making significant changes to high explosive chemistry: the body of knowledge developed since 1900 is fairly thorough, and we know how to make explosive chemicals that are safe, nonvolatile, effective, compact, lightweight; that remain functional when exposed to heat, cold, humidity; water, salt, jungle mud, desert sand, chemical weapons, biological contaminants, nuclear radiation, and the nasty cleaning processes to wash off all that other stuff...; that can be transported by sea, air, land; that can be handled without going off unexpectedly; ... I mean, those very important scientific and technical advances were already mature by the 1940s, and by now we're pretty much just in "maintenance mode."

The big explosive chemistry news, which is almost ten years old, was IMX-101, the new explosive mix designed to replace TNT. Here's a Sandia report, "Interactions Between Ingredients in IMX-101".

If you're really interested in what's new in explosive technology, here are a few more websites to peruse:

Sandia Research Magazine
Poulter Lab, at SRI
Armed with Science, the official United States Department of Defense Science Blog

Why is all this scary, accurate, and specific information about high explosive chemistry available for zero cost on the internet? Because generally, scientists who study such things know that having easy access to dangerous information via the internet is not actually very likely to stimulate violent extremism.

On the other hand, if we have an informed public, we might make scientifically-sound, well-guided decisions, like funding research-efforts to reduce the hazardous materials used in our incredibly-massive defense industry; and we might be more inclined vote for people who use fact, knowledge, and critical thinking to guide policy-decisions, especially pertaining to unpleasant subjects.

Nimur (talk) 15:59, 7 June 2018 (UTC)[reply]

As an answer to OP's question, I recall hearing that high explosives are not suited to propel bullets down the barrel of a handgun or rifle because they are too explosive. Gunpowder burns slow enough to accelerate the bullet down the entire length of the barrel, whereas a more explosive chemical is a worse propellant. Anyway, I didn't bother looking this up, but I'm pretty sure. Abductive (reasoning) 17:41, 7 June 2018 (UTC)[reply]

Yes. See the difference between propellant, explosive, high explosive, deflagration, detonation et al (some disambig needed).

Explosives are of little use as propellants for guns, either small arms or artillery. They make them explode. Some, such as blackpowder, are on the borders between. In large, solid grains (with a limited surface area to volume) they may be restricted to burning slowly enough that they can be used as propellants. If that goes wrong (such as mechanically damaged grains), the effects can be explosive and dangerous (at the wrong end).

Explosives too have a similar distinction (and a big one on cost too). ANFO, ammonium nitrate and TNT have low V_det and are used for mining (either meaning) and demolition of masonry (and they're cheaper). Those used for quarrying (where the stone needs to be released in good condition) might use watergels, which are even lower, or traditional coarse gunpowder. In contrast, RDX / C4 et al. have high brisance, a high V_det and produce shock waves. They can thus be used to make shaped charges too. This makes them useful for the controlled demolition of steelwork (with very small charges) where the steel is cut in a narrow plane, either by jet of hot material, or by shock wave. The rest of the steel needn't be disturbed (and you don't need to pay for the explosive that would have been needed to move the rest). Militarily that also makes them suitable for other devices, such as HESH (more shock waves). Andy Dingley (talk) 18:04, 7 June 2018 (UTC)[reply]

Either Abductive or I is misunderstanding you — Abductive took you to mean the use of explosives as propellant, while I take you to mean the use of explosive bullets. This happens in the cartoons (pretty sure I've seen Wiley Coyote use them, for example), but for most purposes it doesn't work or is unnecessary; bullets generally work because they're dense and fast (there's tons of momentum being applied at a specific location), so they can do lots of damage before they leave the body or lodge somewhere in the body. And if you have reason to have the bullet explode, this can be done with the structure of the bullet itself (no explosives needed); see Expanding bullet. Finally, remember that bullets' high momentum and piercing power would be lost in some cases if they exploded; expanding bullets can't pierce walls, for example, and a bullet filled with explosives wouldn't be able to go as far into something as a non-exploding bullet would. Nyttend (talk) 00:15, 8 June 2018 (UTC)[reply]

antigen Vs. pathogen

I googled it and found different opinions about the difference between antigen and pathogen. Some say that pathogen is a microrganism and some say that it can be any substance that trigger the immune system. But others say the same about antigen. So the difference between them isn't clear to me. Then my question here is what's widely accepted? --93.126.116.89 (talk) 23:30, 7 June 2018 (UTC)[reply]

A Pathogen is anything that causes a disease, whether it's a microorganism or a substance, whether or not the disease triggers an immune response.

An Antigen is a molecule that triggers an immune response, whether or not this is caused by a disease or something else (like pollen). Ian.thomson (talk) 23:42, 7 June 2018 (UTC)[reply]

"gen" means "to create" or "to give birth to". A "patho"gen is a substance that creates a disease (patho- meaning disease or sickness, c.f. pathology) and an "anti"gen creates an oppositional response (anti- meaning opposed to). --Jayron 32 01:04, 8 June 2018 (UTC)[reply]

(ec)The way I read antigen and pathogen, an antigen is a molecule, whereas a pathogen is a microbe such as a bacterium or a virus. If the articles were written based on the best sources, then they should reflect what is generally accepted. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:44, 7 June 2018 (UTC)[reply]

There are pathogenic molecules as well, i.e. prions. --Jayron 32 01:04, 8 June 2018 (UTC)[reply]

The "broad 1880s" sense at the beginning of pathogen is essentially never used in current discussion. For example, polonium-210 or dioxin or Novichok agents are not called "pathogens". Note also that that broad sense is not the same as the "any substance that can trigger the immune system" mentioned above, which is much closer to the meaning of antigen. (If there is any difference from 'antigen', it would be related to how haptens are interpreted in that phrase) There are a few substances which are toxic and trigger the immune system which are therefore classifiable both as "antigen" and as "pathogen" in that archaic sense but which are not replicating disease-causing agents, notably the drug that idiots at TeGenero dosed according to its chimp-human cross-reactivity in their trial, therefore cratering its chances and their company and the poor saps injected with it as well. Wnt (talk) 10:55, 8 June 2018 (UTC)[reply]

June 8

Mold or fungi?

Hi. I have a food case that I haven't opened for several months, and it seems that the food case had grown something. Can someone tell me, is it a mold or a fungi, and what type is it? I want to use it to illustrate about mold, but I am quite unsure.--Jeromi Mikhael (talk) 14:13, 8 June 2018 (UTC)[reply]

Mold are fungi, in case you are not aware. --OuroborosCobra (talk) 14:58, 8 June 2018 (UTC)[reply]

(ec) Have you read mold and fungus (fungi is the plural)? That definitely looks like mold in your picture (although I'm no expert). You can see the hyphae on the lump in the top right. Rojomoke (talk) 15:05, 8 June 2018 (UTC)[reply]

@OuroborosCobra and Rojomoke: Can you help me use the picture in mold or fungus article?--Jeromi Mikhael (talk) 04:23, 9 June 2018 (UTC)[reply]

Sorry but in my opinion this picture is not suitable as an illustration for anything. An illustration should give an idea of the intended item, but I would never have recognise any mold in your photo without you telling us: my first impression of the picture was of an aerial view of a bay with the moon reflecting in blue waters and in the background some dark islands in front of a rocky coast. And I would not recognise any actual molds on the basis of it, I think 194.174.76.21 (talk) 11:10, 11 June 2018 (UTC) Marco Pagliero Berlin[reply]

"Cell" cooling towers

Hi experts,

I would like to know whether "cell" type coolers at industrial or power plants are always induced draft cooling towers?

--DCKH (talk) 14:49, 8 June 2018 (UTC)[reply]

The last one looks like a Crossflow cooling tower: [6]. See also Induced draft vs. forced draft at that link. —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 15:43, 8 June 2018 (UTC) ... Btw, they call them "modular" cooling towers.[reply]

If they're in small cells like that (1,2,4) they're nearly always fan-blown, not induced draught. Andy Dingley (talk) 15:58, 8 June 2018 (UTC)[reply]

Most smaller units have a passive mode that is purely water flow, and then the fan kicks on at some point as water flow increases. Small units always have a fan, you need a large tower to induce enough draft to dispense with the fan entirely. Acroterion (talk) 01:31, 9 June 2018 (UTC)[reply]

Crookes radiometer

Hi, I'm confused by this claim: "Finally, if light pressure were the motive force, the radiometer would spin in the opposite direction, as the photons on the shiny side being reflected would deposit more momentum than on the black side where the photons are absorbed."

On my own, I'd think the other way: (1) the black side gets 100% of photon momentum, (2) while the shiny side only gets a fraction thereof, (3) so there is more push on the black side, (4) so the mill should spin shiny-side forward.

What's wrong? And couldn't the article be a little more explicit about that claim? 82.227.203.82 (talk) 16:08, 8 June 2018 (UTC)[reply]

Here's a video of a radiometer in action.[7] It's pretty clear, especially at the very beginning, that the black side of each "leaf" is the side being pushed by the sunlight. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:21, 8 June 2018 (UTC)[reply]

The white side is pulled by angels. - Nunh-huh 16:30, 8 June 2018 (UTC)[reply]

(2), and hence (3) and (4), is incorrect. The black side gets 100% of photon momentum when it absorbs one, but the shiny face gets not a tiny fraction but 200% (assuming the photon comes and goes perpendicularly to the surface - you can do the funky math assuming non-perpendicular reflexion but the idea is that whatever the result is, it is twice as much as the black side result). Momentum is a vector quantity, and the photon leaves with opposite speed hence momentum (again in the perpendicular case), so the difference in momentum between photon-before and photon-after is larger in the reflection than in the absorption case. Tigraan^{Click here to contact me} 16:43, 8 June 2018 (UTC)[reply]

Conceptually for such a radiometer in a vacuum, the white side absorbs the photon and then emits a photon in the reverse direction. It gains momentum in the forward direction for both. The black side absorbs a photon and then emits a lower-frequency photons with the same total energy in random directions, so the total forward momentum gain is lower. -Arch dude (talk) 18:30, 8 June 2018 (UTC)[reply]

That makes sense, thanks! I like Arch dude's two-step version better, but Tigraan's 200% vs. 100% point is good reinforcement. 82.227.203.82 (talk) 18:40, 10 June 2018 (UTC)[reply]

How is estradiol synthesized through Marker degradation?

The sources I've found all seem to think it's "trivial" and are overly focused on male steroids (as expected of articles predominantly written by male scientists), but what is the major exact route to estradiol from diosgenin?? Why can't I seem to find this anywhere? (I have a biochemistry degree, so the devil is in the details!) Yanping Nora Soong (talk) 19:54, 8 June 2018 (UTC)[reply]

Testosterone→estradiol was Carl Djerassi's graduate thesis. Oxidative aromatization of an enone really is trivial in a conceptual chemical sense, even if the exact details were thesis-worthy especially with what chemistry was known at that time. Careful to avoid letting your own emotion create biases on behalf of others, but instead (as a scientist) do a dispassionate literature search. You may find it is indeed a trivial reaction--this route to the "first" hormone was possibly the difficult/lynchpin stage that allowed diverse derivatives. Oxidative cleavage of the acyl on the D-ring to get the C-17 hydroxyl of testosterone looks more difficult than oxidizing the A-ring. DMacks (talk) 22:00, 8 June 2018 (UTC)[reply]

Genetic speech impediment

Speech impediment and related articles mention plenty of causes for impediments, but they're all either psychological, or the result of developmental problems, or the results of injuries. Are there any documented examples of genetic impediments? Counterexample — many second-language learners don't pick up unique sounds, e.g. the typical idea of a German or Frenchman who can't get ð and þ (cf. the German Coast Guard video), or apparently most Westerners can't pick up the 'ayin of Semitic languages, but the German's children raised in an anglophone environment and the Western kids raised with Arabs will pick up those sounds quite fine, so it's not genetic. I'm imagining a sound that requires a certain mouth or vocal-cord movement that some populations' genetics don't enable them to perform. In such a situation, a kid from population A, raised from infancy in an exclusively B-speaking context, would still be unable to pronounce a certain sound. Nyttend (talk) 23:12, 8 June 2018 (UTC)[reply]

See this. Ruslik_Zero 05:00, 9 June 2018 (UTC)[reply]

Well, the first thing to do in answering your question is to point out that you have conflated a few different discrete phenomena here. There is a big difference between the role genetics play in normal language acquisition between populations of healthy and neurotypical persons and genetics as they impact upon speech disorders. So those two topics must be disentangled before anything meaningful can be said in response to your inquiry. That said, the state of research in both areas is substantial, so it's easy to provide concrete elucidation on both points.

As to the notion of populations who have a physiological inability to acquire the phonological repertoire used by some other population (whether by defect in the vocal tract, places of articulation, or the neurological structures which impart language facility), the answer is no: no such phenomena has ever been observed anywhere in the world. The normal rules regarding language acquisition which you allude to (environmental feedback in early development causing a person to gain facility with distinguishing and pronouncing certain phonemes, generally to the exclusion of others, as per the needs of their first language or languages) are pretty much universal to all neurologically healthy human beings. This is not to say that there is zero variance between individuals with regard to how long into development the brain stays plastic and how readily said individual may pick up the ability to distinguish phonemes in a new language. But as regards regular language acquisition, there is no such thing as a population that is genetically incapable of pronouncing a certain sound which other populations regularly use; both the physiology of the voice box and the fitness of the language organ are more or less uniform across our species. Some relevant articles here are first language acquisition, phonology, and articulatory phonetics.

Are there however familial lines of heredity in which defects to the normal use of language (such as your example of a speech impediment) can be carried by virtue of herditary mutation? Yeah, of course. It's not common, because such severe difficulties with language production are (relatively speaking) quite rare, and usually they are (as you noted) caused by developmental issues, which means they are better understood as an issue of epigenetics than straight-forward lineal genetics. But there certainly are cases where language deficiency can be passed from parent to offspring. It's more likely to be a purely neurological issue, a disorder of neuromotor or muscular function in the maxillofacial region, or a deformity of the structure of the nasal or oral cavities, though; malformations of the voice box are not a common deformity, and a variety which affects only that portion of the airway and no other is rarer still. There are also uncommon motor disfunctions which affect the voice box, but here too, defect in ability with an articulator is more common. Snow ^{let's rap} 06:57, 9 June 2018 (UTC)[reply]

Excellent answer. A quick example of a genetic condition affecting the ability to speak and form normal sounds: Down syndrome. As this paper points out, however, it's not 100% clear how much is genetic (versus epigenetic or other). Matt Deres (talk) 14:23, 10 June 2018 (UTC)[reply]

I'm sorry, but I apparently chose the wrong terms; this isn't at all what I was asking about. Imagine that tongue rolling is genetic, as until recently I'd always understood it to be. Next, imagine that population A is 100% capable of tongue rolling, and their language includes sounds that require it. Meanwhile, an unrelated population B is 100% incapable of tongue rolling. This isn't considered a speech impediment among them, or among those with whom they're in contact, because tongue-rolling-influenced sounds aren't parts of any of their languages. However, were B people placed into population A (even if placed as pre-vocal infants), they'd never be able to speak A fluently, and they'd be considered to have a speech impediment, because they'd be physically incapable of producing one of its sounds. My question Has this kind of situation ever been documented? Nyttend (talk) 21:20, 10 June 2018 (UTC)[reply]

Are you referring to the ability to trill? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:43, 10 June 2018 (UTC)[reply]

That article doesn't say anything about physiological (in)ability, so apparently not. Nyttend (talk) 21:51, 10 June 2018 (UTC)[reply]

No, as I said in my answer above (though perhaps I was not as clear as I thought), this scenario does not happen and has never been observed in the history of modern scientific inquiry into human language and physiology. All populations of human beings are constituted almost entirely of persons who, if raised in the right environment with the right exposure, would have zero difficulty enunciating the full stock of phones of the local language. Again, there are many conditions which cause individuals to have difficulty with language production, but in the rare case where these conditions are genetic, they are particular to specific lineages, not the broader population. I'll rephrase one more way to be clear: for any population of people (beyond the family unit) anywhere on planet Earth, if you took the average and healthy individual from that population as a baby, you could put them into any other population anywhere in the world, speaking any known human language, and they would grow up speaking that language without difficulty of pronunciation. There are many conditions which can cause individuals to have general difficulty with language production, and some of them hereditary and thus may be common to a small kin group, but there is no such thing as a "population speech impediment", such that an entire population would be physiologically incapable of exercising a particular place of articulation. The physiology of all speech organs is more or less identical between all populations of humans. Snow ^{let's rap} 03:37, 11 June 2018 (UTC)[reply]

Incidentally, Nyttend, you may find this fascinating given your general interest here: every language is pretty much comprised of human beings that use the vast majority of all possible phones; it's just that only a subset of the distinctions between these sounds are phonemic in a given language. So, for example, I'm sure you know that in Chinese [mā], [má], [mǎ], and [mà] (ponounced here) are four different words, differing only by tone, whereas in English, there is merely one word (albeit with different homophonous meanings): [ma], colloquial for "mother" and/or a pronunciation of "my" in certain dialects. But it's not that we don't say [mā], [má], [mǎ], and [mà]; we simply don't distinguish between them phonemically). So suppose you are Jed Clampett responding to "Ma" Clampett's" telling him what to do: "Ah, maaaaa!" (probably pronounced [má]) or "Yes ma." (probably pronounced either [mà] or [mā]). You use the sounds, but they are not phonemic to you as the two pronunciations have the same exact received meaning (other than perhaps an emotional subtext). It's the same with most other sounds that human beings regularly make for the purposes of meaning with their voice box and speech organs; most of them get used in every language, but go relatively unnoticed and uncommented upon.

Returning to the original topic, one of the reasons I am taking care to be super explicit here is that there is a racist history that underlays the topics to which your question is reaching (though needless to say, I recognize your interest is a purely empirical one). There was a time when white colonialists (quite predictably) assumed that language ability was not uniform and that there were significant differences in the basic mechanics and complexity of the languages of white races, and those of others (including folk theories about the differences in the anatomy of the speech production, such as you are inquiring about). But it just turned out not to be the case, at all. And thankfully, experts began to recognize this quickly, because linguistics as a field started to gain its empirical early in the era of modern science, in part because of the brilliance of some of it's foundational figures, who often (though certainly not always) resisted the kind of rampant racial bias that was common in that era to other burgeoning sciences regarding the human mind, body, and faculties thereof.

And one last little sidenote: it's worth mentioning that even with conventional, individual speech impediments, the difficulty is caused by neurological irregularity, rather than a deformity with an articulator. Hope some of this is of assistance or interesting! Snow ^{let's rap} 04:56, 11 June 2018 (UTC)[reply]

June 9

X polysomy

I have seen the following question on internet and the answer is A: "Clinical presentations of a woman allowed provisionally diagnosing her with X polysomy. Cytogenetic method is applied to clarify the diagnosis. The diagnosis will be confirmed if the patient’s karyotype is: A. 47, ХХХ B. 48, XXXY C. 48, XXYY D. 47, XXY E. 46, XX". My question why is this (47, XXX) the answer? why it cannot be XXY for example? (Based on this article: "45,X, 47,XXX, 47,XXY, and 47,XYY collectively occur with an incidence of approximately 1 in 400 newborns"). --93.126.116.89 (talk) 01:27, 9 June 2018 (UTC)[reply]

It isn't a great question IMO. But read the question especially the first few words and your source carefully. Of if your source isn't clear enough for you, try our articles XXXY syndrome+Klinefelter syndrome and Triple X syndrome or these two sources [8] [9]. Remember also with MCQs you should always choose the answer which best fits, regardless of whether you can argue another answer also fits. Nil Einne (talk) 05:16, 9 June 2018 (UTC)[reply]

Maybe see also [10] [11]. In the particular case of XXY, it's perhaps also worth considering the technicalities of the definition of Polysomy and so X Polysomy (as opposed to sex chromosome polysomy). Nil Einne (talk) 11:00, 9 June 2018 (UTC)[reply]

The word "woman" rules out all the answers that have a Y in them. If there is a Y chromosome, you have a man. Looie496 (talk) 14:16, 9 June 2018 (UTC)[reply]

That's true. Thank you!--93.126.116.89 (talk) 16:10, 9 June 2018 (UTC)[reply]

Normally, but not always, true. The Y chromosome (normally) carries an active SRY gene, the X carries an inactive version. People can have a XY karotype, but with an inactive SRY gene. They are physically female; this is called Swyer syndrome. Likewise people can have an XX karotype, and be physically male; this is called XX_male_syndrome. ---- 20:46, 9 June 2018 (UTC)

Ecoregions

Where can I find a map which shows both the ecoregions of the United States and southern Canada (as defined by the EPA)? 2601:646:8A00:A0B3:75BF:B7E1:4F33:DA1C (talk) 09:25, 9 June 2018 (UTC)[reply]

I think the resources on this page will be more or less ideal to your needs. Incidentally, the EPA's mandate pertains to domestic policy only, for the most part, so it is doubtful that the cash-strapped and heavily constrained agency spends a whole lot of effort surveying the bioregions of other countries (where they are not contigous with the U.S. or are at least somehow marginally relevant to a regulatory scheme), except for the fact that they coordinate with the Commission for Environmental Cooperation to compile their own data on region identification with that of their counterparts in Canada and Mexico. So the better article for you on the topic is List of ecoregions in North America (CEC). Though, again, the maps you specifically requested are found at the external EPA-hosted link. I must admit, I am getting lost in them myself right now. Snow ^{let's rap} 09:49, 9 June 2018 (UTC)[reply]

Perfect! I was looking for some way to find the ecoregions of all the places I've ever been! Just one question, though: Is Vancouver considered part of ecoregion 7.1.6 (Pacific and Nass Ranges), or 7.1.7 (Strait of Georgia/Puget Lowland)? 2601:646:8A00:A0B3:D47E:7D12:20FE:2672 (talk) 02:14, 11 June 2018 (UTC)[reply]

Main Battle Tank

Hello , I once saw a video on Youtube by an unknown person that says that there was an incident in which an M1 tank was passing over a bridge in Iraq and the bridge collapsed due to the extreme weight of the tank . My first question is that true ? My second question if that was true then can we conclude that all 70 ton tanks which are the Abrams ,the challenger 2 and the Leopard 2 cannot be delivered to the cities of middle eastern countries ? 149.200.165.63 (talk) 14:46, 9 June 2018 (UTC)[reply]

Heavy equipment including tanks have been collapsing bridges and other structures since their invention, whether or not this particular incident occurred. No you cannot conclude that all MBTs are unusable in all cities. The engineers can in general figure out something. I suspect that narrow streets are a more universal problem than weak bridges. -Arch dude (talk) 16:29, 9 June 2018 (UTC)[reply]

I'm disinclined to believe this anecdote unless evidence is presented. People who drive tanks literally go to school where they learn not to drive the 70-ton, $10-million weapon system into an easily-avoidable hazardous situation. Combat engineers are probably the greatest experts in the world when it comes to the science and practical engineering of evaluating whether a bridge is sturdy enough to use for a specific purpose, like supporting a 70-ton armored vehicle during combat. Neither bridges, nor the waterways and land features they bridge across, spring up unexpectedly; during planning of a strategic or tactical deployment, a commander would generally know in advance whether a bridge needs to be crossed, or built, or inspected, before sending the armored unit in. There are entire agencies of the United States Government whose sole purpose is to accurately map the geography, and the bridges and transportation infrastructure, of every part of this planet - so there should be no reason for a tank crew to become surprised when they encounter an unexpected weak bridge as they sally forth on their merry way to warfare.

A lot of people would have to be sleeping on the job for an American tank to drive onto a bridge and then cause the bridge to collapse.

Here's a review thesis, The Relevance of Armor in COIN, which I found on the CARL library website. In thirty pages of summary of American armored forces in Iraq, there is no mention of an accident while operating on a bridge.

There was an accident in the very first days of the Iraq war in which an M1A1 operated by the Marines drove off a bridge in Nasiriya. The bridge did not fail. Evidently, somebody - the driver - fell asleep on the job.

Nimur (talk) 18:33, 9 June 2018 (UTC)[reply]

Great so it`s not an issue of weight , thanks for help both of you .212.34.7.236 (talk) 21:04, 9 June 2018 (UTC)[reply]

Cardiac arrests

Does the heart ever just completely stop suddenly or does it always go into ventricular fibrillation first? If it can, does defibrillation do anything in such scenarios? 90.192.115.154 (talk) 16:06, 9 June 2018 (UTC)[reply]

https://health.stackexchange.com/a/15131/856 Count Iblis (talk) 16:11, 9 June 2018 (UTC)[reply]

Is syn-Propanethial-S-oxide stable enough for it to be stored for some time at room temperature?

syn-Propanethial-S-oxide is formed when onions are cut, it causes our eyes to water. The question is if it is possible for large quantities of this compound to be stored in a pressurized cylinder for use as a non-lethal chemical weapon? Count Iblis (talk) 17:10, 9 June 2018 (UTC)[reply]

It dimerizes (doi:10.1021/ja960722j). DMacks (talk) 20:43, 9 June 2018 (UTC)[reply]

Why are so many places' all-time record high temperatures near the world record?

So many places have been within a handful of degrees of the highest reliable temperature of 129.2°F. There doesn't seem to be a weather station with a big advantage over the rest of the world. Is there a physical reason for this given the current configuration of the continents? (that the Mediterranean shore would be kilometers lower if Africa moved enough to close the Strait seems to suggest plate tectonics that enable desert kilometers below sea level isn't exceptional (mediocrity principle). If the watershed was a little more south at Sahara latitudes instead well the lowest point is 17,280 feet below sea level. Which I assume would enable sick lapse-rate induced temperatures that make Death Valley look like an air conditioner) Sagittarian Milky Way (talk) 23:16, 9 June 2018 (UTC)[reply]

If the air were hot at the surface it would absorb lots of watervapor, get less dense, and buoyantly shoot up until it cooled and formed clouds. Neat negative feedback. It does rely on there being water to absorb. Cites? any thermodynamics transport tables. http://admin.cambridge.org/academic/subjects/engineering/thermal-fluids-engineering/thermodynamic-tables-si-metric-units for example. Greglocock (talk) 23:31, 9 June 2018 (UTC)[reply]

Adiabatic lapse rate can give us a reasonable estimate of temperature when heat is mostly exchanged with the surroundings by air flowing in or out of the valley. When an area has a very large surface area compared to its circumference, like the dried-up Mediterranean, heat exchange largely happens through radiation directly from or to space, which doesn't strongly depend on elevation (elevation can have some influence on this via the greenhouse effect). Our article on Messinian salinity crisis#Relationship to climate says the the climate in the dried-up Mediterranean is unknown and mentions temperatures up to 80°C due to lapse rate, but is unsourced. Outgoing radiation increases with the fourth power of absolute temperature, which is fast and makes it hard to get temperatures much above the equilibrium temperature as expected from radiation alone. Those extremely hot places like Death Valley and the Danakil Depression are all relatively small, so that heat is largely exchanged via wind. Now if you find some 4000m deep valley that's only 40km wide, you can expect some extreme temperatures, but such valleys may be rare. PiusImpavidus (talk) 10:32, 10 June 2018 (UTC)[reply]

I guessed the fourth power law might be at least part of it. The Death Valley weather station is only ~0.08 kilometers below sea level so per dry adiabatic lapse rate that should only give it about a 0.8°C advantage over sea level deserts which isn't a lot. The Dead Sea's lower but perhaps the geography of the area might not be as favorable? (is it Israel mountains protecting it's basin less than California? Mediterranean moisture rains in Jerusalem enough to farm after all and its basically the brim of the Dead Sea depression) Sagittarian Milky Way (talk) 16:05, 10 June 2018 (UTC)[reply]

June 10

Coldest city housing a major university

"Major university" being defined as the main campus of any university listed in the "big three" university rankings (ARWU, QS, THE). So far I've found the University of Alaska Fairbanks, which probably takes the cake as Fairbanks has a subarctic climate and is also far from the ocean.—azuki (talk · contribs · email) 14:38, 10 June 2018 (UTC)[reply]

Surely someplace in Asia. The climate data for Novosibirsk looks colder than Fairbanks, and the city has a bunch of universities. Since I don't know what those ranking initials mean I cannot check. -Arch dude (talk) 16:53, 10 June 2018 (UTC)[reply]
Murmansk State Technical University looks like a contender. --Wrongfilter (talk) 17:07, 10 June 2018 (UTC)[reply]

Don't get me wrong - Alaska can be really cold - but I've visited UAF at Fairbanks in the summer time, and it was muggy and hot - in the sense that Californians were walking around in shorts and tee-shirts.

And when it gets cold, it gets really cold - to the extent that human survival requires specialized knowledge. A few miles down the way - (well, as the Alaskans measure it - it's a several-hour automobile journey) - you'll find the Cold Regions Testing Center, where the Army makes sure that you and your ballistic-missile-interceptors still work correctly "...in the snow, extreme cold, and sub-arctic natural environment." Just imagine what wet snow and extreme thermal cycling will do to carbon-fiber composite or rocket propellant - let alone semiconductor electronics!

Fairbanks' climate is quite complicated to summarize. Have a look at their winter and summer weather records!

The science of the polar region is amazing, and being immersed in it can help draw focus to the realities of Earth's climate and atmosphere. It's why UAF is such a great place to study climatology.

Nimur (talk) 18:13, 10 June 2018 (UTC)[reply]

There was a discussion on similar lines on the Humanities desk last year:

In my time at university (some obscure place in the East Anglian Fens which was bleeding cold in January when the wind blew in from Siberia), lectures were entirely voluntary. You were expected to attend several "supervisions" (tutorials) per week at which you had to discuss the essay you had submitted a few days earlier, and would get into serious trouble if you didn't attend these. I think scientists had to attend lab sessions as well. I think now a lot of universities require students to attend and keep a log.Paulturtle (talk) 23:31, 19 April 2017 (UTC)[reply]

I'm intrigued. Did you attend the University of East Anglia, whose campus is north of Norwich (a fine city where it never seems to stop snowing in winter) or did you just go to Cambridge? 86.168.123.128 (talk) 09:29, 20 April 2017 (UTC)[reply]

— Preceding unsigned comment added by 2A00:23C1:3180:6501:C141:A0C2:E530:A34 (talk • contribs)

And of course, there are the secret Tech tunnels, used by engineers and scientists alike to avoid the ~~sunlight~~ harsh winters of the other Cambridge!!

Nimur (talk) 19:23, 10 June 2018 (UTC)[reply]

The coldest I have found is North-Eastern Federal University in Yakutsk. It has about 16,000 students, more than the University in Fairbanks, and the mean daily temperature across the year is about 16 degree F, about 10 degrees F colder than Fairbanks. Fairbanks is colder on average than the other places mentioned here, such as Murmansk and Novosibirsk. Looie496 (talk) 20:53, 10 June 2018 (UTC)[reply]

June 11