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December 28

Hammer and nail

Am I right in assuming that when a hammer head hits a nail, there is an almost instantaneous conplete transfer of momentum (assuming the hammer does not recoil) from the hammer head to the nail and that the transfer takes a very small amount of time. in other words, is it an inpulsive transfer of energy?? 80.2.23.3 (talk) 01:07, 28 December 2018 (UTC)[reply]

It will be quick but not quite an "instant" or zero time. The transfer of momentum will continue as long as the nail is being driven in, or it is being deformed by the impact. Our hammer article could do with more physics in it. Graeme Bartlett (talk) 03:04, 28 December 2018 (UTC)[reply]

That is entirely dependent on the timeframe or -resolution you choose to look at. There will be all the normal physical deformations in the nail but since it is very well constructed for its purpose of course the energy in the hammer will be mostly "transfered" to achieve the meant result. Btw., in physics the base concept of your "transfer of momentum" is Elastic collision. Since the main energy is then used for Deformation (mechanics) its a little more complicated to describe correctly. --Kharon (talk) 07:41, 29 December 2018 (UTC)[reply]

reducing methane emissions from hydroelectric power plants

how can methane emissions from hydroelectric power plants be reduced? — Preceding unsigned comment added by Tokk.Tokk (talk • contribs) 02:38, 28 December 2018 (UTC)[reply]

One way would be to switch to nuclear. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:48, 28 December 2018 (UTC)[reply]

~~Here's a report on the general subject.[1]~~ ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:50, 28 December 2018 (UTC)[reply]

Well that was a report on natural gas plants. Hydroelectric power plants will have a dam that could have anaerobic conditions where methane is produced. One way to reduce emissions would be to remove organic matter before the dam is filled with water, eg cut down the trees, scrape off the undergrowth and soil. Graeme Bartlett (talk) 02:53, 28 December 2018 (UTC)[reply]

This article from 2014 says scientists are in the "early stages" of study of this phenomenon, but the causes are plainly obvious, and square with what Graeme says.[2] ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:44, 28 December 2018 (UTC)[reply]

Sounds like fixing at the wrong end. Most "artificial" methane comes from the flood of manure all the lifestock produces that we keep to produce all the cheap meat we want. --Kharon (talk) 07:00, 29 December 2018 (UTC)[reply]

Again huh? Do you actually have a source for this? I'm not disagreeing that livestock are a big contributor to methane. Although not so much from manure, which is a problem but AFAIK isn't a major contributor to methane, instead most methane comes from cow belches. More importantly, the above source explicitly says

Scientists are searching for answers to that question, as they study how much methane is emitted into the atmosphere from man-made reservoirs built for hydropower and other purposes. Until recently, it was believed that about 20 percent of all man-made methane emissions come from the surface of reservoirs. New research suggests that figure may be much higher than 20 percent, but it’s unclear how much higher because too little data is available to estimate.

and

Methane emissions from livestock are the second-largest source of methane emissions in the U.S., behind crude oil and natural gas, according to the U.S. Environmental Protection Agency. But the EPA’s greenhouse gas emissions estimates do not yet account for methane emissions coming from man-made reservoirs. Part of the reason is that, generally, very little is known about reservoirs and their emissions, especially in temperate regions, such as in the U.S., where few studies have been conducted. In 2012 study, researchers in Singapore found that greenhouse gas emissions from hydropower reservoirs globally are likely greater than previously estimated, warning that “rapid hydropower development and increasing carbon emissions from hydroelectric reservoirs to the atmosphere should not be downplayed.” Those researchers suggest all large reservoirs globally could emit up to 104 teragrams of methane annually. By comparison, NASA estimates that global methane emissions associated with burning fossil fuels totals between 80 and 120 teragrams annually.

The NASA estimate link still works although it isn't maintained. And it says "Animals contribute about 80 Tg methane per year".

Nil Einne (talk) 12:35, 31 December 2018 (UTC)[reply]

Again what? Are you demanding that i add sources to anything i write here now? Btw. I was refering to "man made" aka "artificial" methane, since the question was about "artificial pools" generating methan. Not about natural deposits getting accessed.--Kharon (talk) 17:50, 31 December 2018 (UTC)[reply]

(cite)"Identifying it as “a major threat to the environment” (FAO 2006), the FAO found that the animal agriculture sector emits 18%, or nearly one-fifth, of human-induced GHG emissions, more than the transportation sector. (Steinfeld et al. 2006).
::Our objective was to outline the animal agriculture sector’s share of global GHG emissions by synthesizing and expanding upon the data reported in Livestock’s Long Shadow (FAO 2006) with more recent reports from the IPCC, data from the U.S. Environmental Protection Agency (EPA), and studies on GHGs from agriculture and mitigation strategies [Cederberg and Stadig 2003; International Federation of Organic Agriculture Movements (IFOAM) 2004; IPCC 2007a, 2007b, 2007c; McMichael et al. 2007; Ogino et al. 2007; U.S. EPA 2007a; Verge et al. 2007]. We also investigated links between this sector and the far-reaching impacts of climate change on conflict, hunger, and disease, while underscoring the roles of animal agriculture industries, policy makers, and individual consumers in mitigating this sector’s contributions to climate change and global warming.
"(citeend)(Environmental Health Perspectives, May 2008

This is the reference desk, so yes you should be providing sources for anything you write here, especially when it's something which isn't obvious and is probably incorrect. Someone has been topic banned from here in the past in part due to their persistence in never providing sources. Your response is largely unrelated to anything I've said. You explicitly claimed that 'Most "artificial" methane comes from the flood of manure all the lifestock produces that we keep to produce all the cheap meat we want'. This is disputed by the source already linked which suggests emissions from reservoirs could actually exceed that from livestock. I already acknowledged that methane production from livestock, mostly cattle is a serious concern. However as I also said, this doesn't mean, as your first response claimed, that methane from hydropower reservoirs is not a concern. You've provided zero evidence it is not a significant concern, whereas the evidence suggests it is a significant concern. BTW, GHG emissions from animal agriculture are not simply methane. Note also that methane emissions from fossil fuels related to human activity are generally counted as an anthropogenic source of methane per the NASA source, whether or not you want to count it as artificial, although as said this is largely besides my point. Nil Einne (talk) 22:53, 31 December 2018 (UTC)[reply]

BTW, I had a little time to look into methane from animal manure and found [3] [4] [5]. Based on these, I will refine my earlier comment from "Although not so much from manure, which is a problem but AFAIK isn't a major contributor to methane, instead most methane comes from cow belches." to "Although not so much from manure, which is a problem but AFAIK is a far smaller contributor to methane then enteric process i.e. most methane from livestock comes from cow belches not manure." as methane from manure is higher than I had thought. Nil Einne (talk) 23:33, 31 December 2018 (UTC)[reply]

Happy to learn something every day. --Kharon (talk) 12:07, 1 January 2019 (UTC)[reply]

December 29

Biochemistry factors

The image and caption are copied from the Haemophilus influenzae article. The body of the article has comparatively little information: it says Bacterial culture of H. influenzae is performed on agar plates, the preferable one being chocolate agar, with added X (hemin) and V (nicotinamide adenine dinucleotide) factors at 37 °C in a CO₂-enriched incubator, but neither hemin nor NAD appears elsewhere in the article. In this context, what is a factor, what do these chemicals do in their roles as X and V factors, and in general what are X and V factors? I see from the NAD article that it's a Cofactor (biochemistry), but we don't have a Factor (biochemistry) article. I tried X factor, but that's a TV show, and X Factor (disambiguation) doesn't have anything relevant, while V factor doesn't exist. (I get a sense of NAD's general activities from its article, but I'm not clear if its redox activities make it a factor, or if it's something else.) If I've missed an answer that's provided in a linked article, this is probably because I don't have much chemistry background and didn't understand something crucial. Nyttend (talk) 05:38, 29 December 2018 (UTC)[reply]

PS, I found Factor X and Factor V, but neither hemin nor nicotinamide appears in either one of them, and it looks like they're related to the clotting process in blood; I didn't see anything seemingly relevant to unicellular organisms. There is no Factor W or W Factor article, and W factor began This theory about time travel is correct and uses logic that is being constantly proven... Nyttend (talk) 05:43, 29 December 2018 (UTC)[reply]

I went to PubMed and searched "factor X" hemophilus and found nine papers, the earliest of which is [6]. Because this is an exercise in psychoanalyzing the person who came up with the name rather than science per se, there might really be no alternative to know for sure but to go back and get the German paper and see what its references were or if it named the factors itself. But one of the other references might let the reason slip. That said, I would make a wager that X and V are Roman numerals. Probably one thing and another were isolated and named in numerical (Roman) order as things that seemed to help the growth rate, then on rescreening maybe some of them didn't pan out or turned out to be the same thing in different forms or whatever, until they got down to two "essential" things, both of which could be supplied from catalase [7] though without reading I don't know if that happens always never or somewhere in between. (You should see from this idea though how the number of factors could vary, especially in early days of research)

Cofactors, in general, are things proteins rely on to "help" their activity. The individual protein made by some gene (or made of polypeptide protein subunits each made by a gene if you want to be anal about it) would be the "factor", and then the "cofactor" is what is needed so the factor works. Typically, modern biology seems to find that proteins work well for most things, but whenever you run across something really ancient and important, that's when "RNA world" hangovers tend to turn up. So like ribosomes are made out of RNA decorated with proteins, and in this case, proteins have prosthetic groups (another term for cofactor, apparently implying that the protein with its 21 amino acid choices + modifications is "crippled" and needs help to do things). Really, something like NADH with its 5'-5' linkage and odd nucleotide base structure looks like it might be a relic from an era before DNA and RNA were standardized, let alone cells, but it is hard to think of a way to prove or disprove any such idea. Wnt (talk) 15:16, 29 December 2018 (UTC)[reply]

The relevant paper is "Studies on Bacterial Nutrition: II. Growth Accessory Substances in the Cultivation of Hemophilic Bacilli (June 1921)" and can be found here [8]. "V factor" was so-called for behaving like the (newly discovered!) vitamins, and "X factor" was simply poorly understood. Choess (talk) 03:16, 30 December 2018 (UTC)[reply]

How much time does it take for a bacterium to produce 1 ng of botulinum toxin

Couldn't find any reliable information on this simple factum here or elsewhere online.--TMCk (talk) 22:05, 29 December 2018 (UTC)[reply]

It will depend on which bacterium and which botulinum toxin, but to get started, I'll just use the number our article has in the infobox ( 149,321 g/mol ) as a molecular weight. Calculating

(1 ng) * (1 g / 10^9 ng) * ( 1 mol / 1.49321 x 10^5 g ) * (6.022 x 10^23 molecules / 1 mol) = 4.03 x 10^9 molecules. So you're asking how long it takes for a bacterium to make 4 billion molecules of botulinum toxin. My guess is that an individual bacterium won't make that many; but if you can use multiple bacteria, it should be trivial to have a few billion of them (advertently or not). So I'm not quite sure how to answer that one. Also, I didn't quickly find the "protein copy number" per bacterium looking as I intended, because all I get is people who care how many it takes per human cell to do something bad. Let us know which way you want to go from here. Wnt (talk) 04:56, 30 December 2018 (UTC)[reply]

I looked at a bunch of the original (late 1920s) reports of the isolation and analysis of the toxin from cultures. While they report yields and concentrations of the product, and the time and other incubation parameters, they don't seem to report the starting or ending colony size. DMacks (talk) 17:32, 30 December 2018 (UTC)[reply]

December 30

Like a speeding arrow?

We all know that the English longbow is the ultimate weapon of all time, the Gatling gun of its age, and that a well-aimed bodkin arrow can easily pierce mail and plate at any range. Indeed, El Alamein would probably have been decided in hours had the English only thought about using their longbows against German tanks. However, when watching the Battle of the Bastards episode of Game of Thrones, I was wondering how plausible Ramsey's shot at Rickon was. Of course, he had plot on his side. But, having shot (weak and inferior modern) bows, I noticed that arrows have a significant flight time - as kids, shooting straight up, we had plenty of time to step out of the way of the arrow before it came down. This would make it basically impossible to aim at an erratically moving target at any but quite short distances. So if the intrepid English longbow men loose a volley of irresistible feathered death against the quivering French in their useless armour, how long exactly does it take for the arrow to cross, say, 100 or 200 yards (or meters ;-), and wreak havoc? --Stephan Schulz (talk) 12:50, 30 December 2018 (UTC)[reply]

Initial speed is roughly 100 meters per second. But you need to pull back hard enough to lift like 150 pounds without the help of multiple pulleys. Sagittarian Milky Way (talk) 13:42, 30 December 2018 (UTC)[reply]

Kids shooting arrows straight up, confident that two seconds is long enough to get out of the way. What could possibly go wrong? Well, Daddy might accidentally run over the bow with his SUV three or four times while backing out of the garage, then replace it with a puppy... Wnt (talk) 14:28, 30 December 2018 (UTC)[reply]

I'm too old for daddy to have had an SUV. And while I agree in principle that replacing an SUV with a puppy is a good idea, I don't quite see the motivation here - do you think driving over the bow might damage the vehicle that much? --Stephan Schulz (talk) 15:31, 30 December 2018 (UTC)[reply]

Arrows shot straight up at a papingo slow right down before falling again, the archers keep out of the area the arrow's expected to land but also watch it in case they do have to get out of the way of a stray shot. Blunt tips these days, but still rather dangerous. . . dave souza, talk 17:18, 30 December 2018 (UTC)[reply]

Arrows don't speed, agreed. In the timescale of GoT (i.e. the period of European history which its technology most closely resembles) the arrow had become regarded as a bulk weapon, where many archers would engage with large attacking forces as a form of attrition, and also as an area-denial weapon. They didn't go through plate armour (your ability to fire off plate-piercing bodkins is much less than when firing lighter arrows and a lighter pull), but they stopped the archers being rushed by a horde of angry grunts.

Where a single arrow was intended as a means of assassination, then that arrow had become a crossbow bolt instead. Their greater draw weight gave them a higher velocity and a flatter trajectory, giving better aim, much better aim in crosswinds, and also a faster flight (as mentioned here). This was one of the reasons why the medieval crossbow was regarded so badly at times, with its users being regarded as somewhere between pirates and war criminals. Their disadvantage was their slow rate of fire, compared to the bow. Not a problem for single shots, and also less so when repellng sieges. Andy Dingley (talk) 15:22, 30 December 2018 (UTC)[reply]

Thanks a lot, all! --Stephan Schulz (talk) 15:31, 30 December 2018 (UTC)[reply]

Actually 100 meters/yards per second/200 mph is bows designed for distance and mph [9], Medieval English longbows used heavier arrows (maybe Asia had less metal for armor?) and were more like 200 feet per second. Sagittarian Milky Way (talk) 17:43, 30 December 2018 (UTC)[reply]

Regarding "the English longbow is the ultimate weapon of all time" - I doubt that the average bomb would be bothered much by an arrow. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:25, 31 December 2018 (UTC)[reply]

Since OP's post was positively drooling in sarcasm I think you may have been sucked into a transatlantic troll's ambush. Greglocock (talk) 10:29, 31 December 2018 (UTC)[reply]

I almost got the point. It was an arrow escape. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:19, 31 December 2018 (UTC)[reply]

Oh, archer the funny one. DroneB (talk) 14:19, 31 December 2018 (UTC)[reply]

From my dealings with internet and politics, I would say... Newer users of the internet have trouble telling when they are reading sarcasm. More experienced users have trouble telling when they are writing sarcasm. Wnt (talk) 05:36, 1 January 2019 (UTC)[reply]

The Technological Development of the Bow and the Crossbow in the Later Middle Ages, Ph.D. Thesis by Stuart Gorman "In 1998, the Royal Armouries published a series of experiments led by Thom Richardson. These tests involved a wide range of [replica] weapons from the Middle Ages and earlier... The 72 and 90 lbs longbows both fired a bodkin headed arrow with average speeds of 41.65 metres per second (93 mph) and 43.47 metres per second (97 mph) respectively... The steel crossbow fired two different bodkin headed bolts built by different fletchers. These bolts travelled at an average speed of 44.6 metres per second (100 mph) and 43.9 metres per second (98 mph).... All of these weapons were also fired at a 2 mm thick piece of steel, but none of them was able to penetrate the sheet" (p. 59). He says a bit earlier on that arrows have a terminal velocity, so increasing the power of the bow may not increase the velocity very much - some of the longbows from the Mary Rose have been controversially rated at up to 140 lbs draw. There have been several other experiments but none seem to have made replica arrows fly as fast as 50 metres per second; you can read it yourself if you have time on your hands. The answer therefore is that it takes a war arrow a little more than two seconds to fly 100 metres but you're pretty safe if you've put your armour on properly. Alansplodge (talk) 22:05, 1 January 2019 (UTC)[reply]

I think you give distance weapons of the middle ages tomuch credit. Everyone, especially Army-Commanders and Knights knew about their potential and thus used siege shields aka Mantlets and alike protection to close in on an enemy army, camp, city or castle. In close combat or with cavalry hunting, anyone just wielding a bow, or worse a heavy clumsy crossbow, was toast in seconds. Also these where units the enemy cavalry usually went after first because they where so vulnerable. So against an prepared enemy these distance weapon where totally useless, often just Cannon fodder. --Kharon (talk) 21:15, 2 January 2019 (UTC)[reply]

Missile weapons become relevant for "targets of opportunity". For example, consider Battle of Lechaeum - not archers, not medieval, but it illustrates the idea that what seems like a "nuisance" in the military sense of the term can turn into a problem given half a chance. Or the Siege of Rome (537–538) where the deficiency of planning made for some moments of amusement. I imagine the persistent threat of a shaft sprouting from some uncomfortable place during any unguarded moment must have made medieval sieges seem even longer than they would otherwise. Wnt (talk) 17:30, 3 January 2019 (UTC)[reply]

December 31

Weapons of REAL mass destruction

Is it possible to cause the Baltic Sea and/or the Caspian Sea to explode? If so, about how big of an explosion (in megatons) could happen in this scenario, and how much damage on Russian soil could it cause? Is it possible to do the same thing with permafrost? 2601:646:8A00:A0B3:F484:63E7:CDC0:1004 (talk) 10:53, 31 December 2018 (UTC)[reply]

Well, the Schuylkill River and the Cuyahoga River have caught fire at various times, so anything's possible. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:17, 31 December 2018 (UTC)[reply]

Hydrogen sulfide produced from the microbial breakdown of organic matter may be delivered in small amounts from sewers to the seas mentioned but it is not explosive, merely smelly. DroneB (talk) 14:15, 31 December 2018 (UTC)[reply]

I think the OP might be thinking of the Lake Nyos disaster, which depended on carbon dioxide release - once an area started bubbling up, it had a positive feedback until a large amount of CO2 headed toward the village. Laboratory mice are euthanized the same way (also occasional hip kids who try dry ice in a hot tub). Hydrogen sulfide can be emitted during such events; I remember it, or other gases (I see our article mentions methane clathrates) was an explanation given for the Permian extinction but there were a lot of horses in that race and I haven't looked at the standings in some time. I remember long back reading the Black Sea has a high CO2 content deep down, so the idea using a shipload of dry ice to gas Turkey was an old fave, but I wouldn't bet on it. Most of these events are blamed on volcanism that has been priming waters to the point of a catastrophic turnover for some time, which is to say, they are repeated events; if you don't see that a body of water has done it before, I doubt puny humans can easily make it happen a first time. Wnt (talk) 15:18, 31 December 2018 (UTC)[reply]

Actually, I was thinking of the Status-6 first-strike nuclear torpedo which the Russians have developed (along with other ideas of theirs, such as nuking Yellowstone to make it erupt, or blowing up Iceland to disrupt the Gulf Stream), and looking at ways we might do the same things to them in retaliation -- my idea was to explode a nuclear weapon (say, a B83 fitted with a hydrostatic fuze) just below the halocline in the Gotland Deep and/or in the Caspian Sea in order to disrupt the halocline and cause massive outgassing of hydrogen sulfide (hopefully creating an explosive fuel-air mixture which the fireball would promptly detonate, hopefully causing a self-sustaining chain reaction which would cause most of the dissolved hydrogen sulfide to explode and create a veritable (and radioactive) tsunami heading toward St. Petersburg and Astrakhan and hopefully far inland). 2601:646:8A00:A0B3:F484:63E7:CDC0:1004 (talk) 02:55, 1 January 2019 (UTC)[reply]

How nice. Please find a forum somewhere else on the Internet for such ghoulish speculation. Acroterion (talk) 03:02, 1 January 2019 (UTC)[reply]

Please cite Wikipedia policy which prohibits discussion of this subject on here, or else retract your comment. 2601:646:8A00:A0B3:F484:63E7:CDC0:1004 (talk) 03:10, 1 January 2019 (UTC)[reply]

"The reference desk is not a chatroom, nor is it a soapbox for promoting individual opinions" and "The reference desk is not a place to debate controversial subjects." To extend, the refdesk isn't a forum for gleeful spitballing about "hopefully" creating radioactive tsunamis to destroy Russia in speculative forum-style posts. Your initial question has been answered, as far as I can tell, take the fictional speculation elsewhere. Acroterion (talk) 03:32, 1 January 2019 (UTC)[reply]

In that case, I have 2 specific questions here which have to do with science: (1) In the scenario I outlined above, will the gas (hydrogen sulfide or methane) detonate? (2) If so, will this detonation cause a self-sustaining and self-propagating chain reaction? 2601:646:8A00:A0B3:F484:63E7:CDC0:1004 (talk) 05:29, 1 January 2019 (UTC)[reply]

There are some things I don't know about this ... to be honest, I never even realized the Baltic Sea was brackish, even what our article calls "borderline freshwater", until now. (Except for the salty deep region described [10]) But what I do know is that H2S and H4C will not "detonate", because detonation implies that all the ingredients for a chemical reaction are present. Whether they could or would burn is another question, which I don't know the answer to. Methane, of course, is more dangerous if it doesn't burn, hence natural gas flare stacks. Creating a tsunami is a dicey proposition, since colossal energies from earthquakes often fail to produce one even when they are feared, and no nuclear weapon I know of can register 8 or 9 on the Richter scale. Supervillains might take heart that the source of a catastrophic tsunami might be predicted and manipulated, but if you look at a map of a feared feature [11], it's not like it has a "just push here" sign; who knows if even a lot of nukes would do it? Additionally, a radioactive source for a tsunami does not produce a radioactive tsunami, since a gravity wave does not literally mean that water propagates from source to destination, only that its displacement propagates. Wnt (talk) 16:16, 1 January 2019 (UTC)[reply]

So the answer is "probably not"? 2601:646:8A00:A0B3:F484:63E7:CDC0:1004 (talk) 01:37, 2 January 2019 (UTC)[reply]

The simplest way is to let an asteroid impact the target. NASA is investigating methods to avert asteroid strikes by changing the course of potential impactors, but the same methods can be used to steer an asteroid to hit a target on Earth. The asteroid that will be made to hit Earth doesn't have to be targeted directly, one may seek out a smaller asteroid whose course can be changed to hit a larger asteroid that will in turn hit the Earth. For the purpose of avoiding collisions with the Earth, I've shown here that this method to target smaller asteroids to hit the larger asteroids of interests, can be more practical than trying to deflect the larger asteroid directly. Count Iblis (talk) 19:27, 2 January 2019 (UTC)[reply]

Is superheated water a unique phase of water?

If the phase transition to superheated water only occurred when water temperature exceeded 100°C, then water would never superheat. Boiling would PREVENT superheating. Therefore, water must completely convert into the phase that can superheat BEFORE water can superheat.

Certain transitions between phases do not necessarily require latent heat. The phase transition from water with a 100°C boiling point to water that can superheat occurs when pure water is not in a scratched container and is vibration free. Conversely, vibration or a scratched container can convert the phase that can superheat into the phase with a 100° C boiling point.

“However, once the water is disturbed, some of it violently flashes to steam, potentially spraying boiling water out of the container.”

Disturbing the superheated water triggered conversion to the phase with the 100°C boiling point. The vapor is 100°C because the phase with the 100°C boiling point is vaporizing.

The phase that can superheat is not boiling. If superheated water itself indeed boiled, its vapor temperature should be the same as its water temperature and boiling should occur at the rate external heat is added.

“Even when the water temperature was over 105°C, the steam temperature was only a few tenths of a degree over 100°C (Marcet 1842, 404-405).”

The phase that can superheat has a lower melting point than the phase that boils at 100°C. Likewise, there are 18 known solid crystalline phases of water, each with their own phase transition temperatures and pressures.

“Extremely pure, supercooled water stays liquid below 0°C and remains so until applied vibrations or condensing seed doping initiates crystallization centers. This is a common situation for the droplets of atmospheric clouds.” — Preceding unsigned comment added by Vze2wgsm1 (talk • contribs) 11:30, 31 December 2018 (UTC)[reply]

Vze2wgsm1 (talk) 11:32, 31 December 2018 (UTC)[reply]

Superheated water isn't a different phase but there is evidence that liquid water is really strange in that there are two phases of liquid water with a crossover between 40°C and 60°C. Dmcq (talk) 13:23, 31 December 2018 (UTC)[reply]

@Dmcq: do you want to say more about that? I don't know what you mean. --Trovatore (talk) 01:44, 1 January 2019 (UTC)[reply]

[12], in particular there are some studies linking this to the temperature at which proteins denature if you look at the papers citing it. Dmcq (talk) 02:04, 1 January 2019 (UTC)[reply]

Boiling does prevent superheating. When you heat pure water past its proper boiling point on that phase diagram (100 C at 1 atm), then logically two things can happen. Either it turns into a gas, in which case you say it boils, or it stays liquid, in which case you say it superheated. The key fact that matters here is that boiling doesn't happen on a single-molecule level; it requires nucleation. Think of an angry mob facing off against a line of cops -- there has to be somebody to throw the first stone. If your water isn't very pure, there will be some "troublemakers" around to make sure that happens as soon as it can, but if it is totally homogeneous then you can see some stranger behavior. You can be at a point where a large bubble would get bigger, but no bubble exists to begin with. I recall an intro chem lab where my entire reaction in petroleum ether abruptly took to the air - bumping (chemistry) - leaving reactants/product all over the benchtop and what was almost immediately a dry Erlenmeyer behind. Wnt (talk) 15:26, 31 December 2018 (UTC) Does not apply. Petroleum ether is not a pure compound. Vze2wgsm1 (talk) 02:11, 1 January 2019 (UTC)[reply]

For all pure compounds, boiling occurs at temperature and pressure combinations where added thermal energy converts into heat of vaporization, instead of increasing enthalpy. Each of these temperature/pressure combinations are precise.

A given pure chemical compound has only one normal boiling point, if any, and a compound's normal boiling point and melting point can serve as characteristic physical properties for that compound, listed in reference books.

A requirement for nucleation sites would make boiling points imprecise. Therefore, no pure compound requires nucleation sites to initiate boiling.

Superheated water contains more enthalpy than water that boils at 100 C, without becoming less stable than a vapor molecule. The phase of water that boils at 100 C becomes less stable than a vapor molecule if temperature exceeds 100 C. Therefore, water that can superheat is a different pure chemical compound than water that boils at 100 C.

Note: The boiling point of a pure compound is not necessarily a function of surface tension. Adding surfactants to change water’s surface tension does not necessarily lower water’s boiling point.

“They found that adding surfactants to the water jet did not change the incipient boiling point.” Vze2wgsm1 (talk) 01:34, 1 January 2019 (UTC)[reply]

I think you're probably getting confused by that paper, 'supercritical' is not the same as 'superheated'. Dmcq (talk) 12:03, 1 January 2019 (UTC)[reply]

In the paper, the author used the word supercritical was with respect to Nusselt numbers, not to the phase of water with the high Nusselt numbers. The water in the supercritical region was (initially) subcooled.

“Boiling was not present in the supercritical region of flow partly because water entered the channel as a subcooled liquid, and partly because the supercritical flow field had high enough heat transfer coefficients to keep the disk surface below the level of superheat needed to induce boiling.”Vze2wgsm1 (talk) 14:48, 1 January 2019 (UTC)[reply]

What are sweet peas?

This is related to my seeing Popeye (film) for the first time. When I went to Sweet pea I was expecting a plant that we can eat, but the article says we shouldn't eat it. However, I have heard for years about "sweet peas", including a product by that name that was related to a pricing game on The Price Is Right. Nothing in the pea article seems to suggest there is such a thing that we can eat.— Vchimpanzee • talk • contributions • 18:21, 31 December 2018 (UTC)[reply]

Pisum sativum, regular garden peas, vary in their sugar content according to cultivar, ripeness, and processing. The sweeter ones are called sweet peas. Abductive (reasoning) 19:01, 31 December 2018 (UTC)[reply]

Could this be the snow pea? Its scientific name is P. sativum var. saccharatum, i.e. "sugared" or something like that; in German it is called de:Zuckererbse, i.e. "sugar pea". --Wrongfilter (talk) 19:34, 31 December 2018 (UTC)[reply]

I don't know. Snap pea comes closer but I don't see anything in the article calling it "sweet pea".— Vchimpanzee • talk • contributions • 20:13, 31 December 2018 (UTC)[reply]

It's called sugar snap pea per our article or simply sugar pea [13] [14] [15] [16] en:wiktionary:sugar pea sometimes. I guess it's possible some people may call it sweet pea, but I doubt it's very common. Nil Einne (talk) 22:42, 31 December 2018 (UTC)[reply]

Our article on the Popeye character Swee'Pea states that the name derives from sweet pea (Lathyrus odoratus). The name "sweet pea" in horticulture normally refers to this plant, rather than to a sweet-tasting edible pea. My guess is that the "sweet" part of the common name is referring to the scent of the flowers, not the taste of any fruit (peas). PaleCloudedWhite (talk) 23:07, 31 December 2018 (UTC)[reply]

As with the flowering plant called Sweet William. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:50, 1 January 2019 (UTC)[reply]

To confirm PaleCloudedWhite's guess, the OED says that the Sweet Pea was 'formerly called sweet-scented pea'. AndrewWTaylor (talk) 10:23, 1 January 2019 (UTC)[reply]

What CO2 percent is needed to boil the ocean?

If you added it in a climatological instant like a year. How long would it take to start and finish boiling? How long after that before thermal equilibrium? Would any carbonate rocks survive? How hot would Challenger Deep and Mount Everest get? Sagittarian Milky Way (talk) 22:48, 31 December 2018 (UTC)[reply]

I'm assuming you mean, 'what CO₂ percent in the atmosphere...'? PaleCloudedWhite (talk) 23:19, 31 December 2018 (UTC)[reply]

"Numerical climate models as well as carbon isotope measurements from preserved Ordovician soils suggest that atmospheric levels of carbon dioxide during the period were 14–16 times higher than today... How continental glaciation could have formed when carbon dioxide levels were so high has been a paradox."[17] If you look at the various theories, you will find a vigorous debate about glaciers forming vs. glaciers melting during this high CO2 period, but the debate is about temperatures slightly above freezing vs, temperatures slightly below freezing, never about temperatures near boiling.

As our article on Runaway climate change says, "an extreme moist greenhouse might cause an instability with water vapour preventing radiation to space of all absorbed solar energy, resulting in very high surface temperature and evaporation of the ocean. However, simulations indicate that no plausible human-made greenhouse gas (GHG) forcing can cause an instability and baked-crust runaway greenhouse effect." --Guy Macon (talk) 00:38, 1 January 2019 (UTC)[reply]

The following is a lot more speculative, but our article on Snowball Earth says "The carbon dioxide levels necessary to unfreeze Earth have been estimated as being 350 times what they are today, about 13% of the atmosphere."

Also our article on Carbon dioxide in Earth's atmosphere says "Concentrations of CO2 in the atmosphere were as high as 4,000 parts per million (ppm) during the Cambrian period about 500 million years ago to as low as 180 ppm during the Quaternary glaciation of the last two million years... Global annual mean CO2 concentration has increased by more than 45% since the start of the Industrial Revolution, from 280 ppm during the 10,000 years up to the mid-18th century to 410 ppm as of mid-2018." The earth has never experienced boiling oceans since the time during and shortly after the surface was molten lava, but we have seen periods of little or no glaciation, alternating with ice ages. --Guy Macon (talk) 00:51, 1 January 2019 (UTC)[reply]

Note the relevant article/term is runaway greenhouse effect or runaway climate change. It seems to be relatively out of favor as a possibility lately, but some do say it could happen. I've been waiting for old artifacts from Venusian exploration missions to turn up and provide some insight on this... really was holding out some hope for the Dawn mission... Some of the NASA maps I've seen lately put Earth right at the inner edge of the Sun's habitable zone, FWIW. Note that the question is difficult and would require simulation because to get to the boiling of oceans implies not just a few degrees of heating but a "runaway" proper, i.e. that the increased water vapor acts as a greenhouse gas more than the increased clouds act to cool the planet. At the same time, the remarkable CO2 levels quoted from long ago have to be taken in context of the faint young Sun paradox; it isn't clear nearly that much would be needed now. Wnt (talk) 05:27, 1 January 2019 (UTC)[reply]

Very roughly, a runaway moist greenhouse might start about 47 C in the global mean temperature according to runaway greenhouse effect. That's about 33 C warmer than today. Assuming a climate sensitivity of ~3 C/doubling of CO2, that would imply something like 2000 times as much CO2 as today. Which translates to adding enough CO2 that roughly 1/2 of the atmosphere would be CO2 (assuming other constituents stay the same). At that level, all macroscopic oxygen-dependent life would suffocate before they had a chance to boil. Dragons flight (talk) 11:21, 1 January 2019 (UTC)[reply]

If tenths of a bar of CO2 was suddenly added would enough of the locked-up methane be released before its atmosphere residence time to matter? Sagittarian Milky Way (talk) 14:24, 1 January 2019 (UTC)[reply]

@Dragons flight: That article describes an effect per "doubling", but as far as I see they only look at the one data point of double some baseline. I don't think they're making a claim for a logarithmic effect, are they? At least, I don't see why the effect would be logarithmic, though I don't know it wouldn't be either. Given the degree of uncertainty for even one data point, in any case, I would be skeptical that the curve of many can be predicted beyond the parameters of existing simulations. Wnt (talk) 16:04, 1 January 2019 (UTC)[reply]

The radiative forcing of CO2 is approximately logarithmic. For more complete expressions, I would refer you to Table 6.2 of this IPCC chapter [18]. The logarithmic response arises (primarily) because the radiation absorption on the wings of the CO2 absorption bands evolve approximately exponentially with distance from the center on the band. The climate response (e.g. 3C) to a given radiative forcing is quite uncertain (due largely to various feedbacks), but the radiative forcing part as a function of CO2 actually isn't very uncertain (at least not at normal concentrations). I would however assume that there is a very large uncertainty with extrapolating to thousands of times modern CO2 levels, but then I also assume that SMW isn't really in need of a very precise answer. Dragons flight (talk) 18:02, 1 January 2019 (UTC)[reply]

Thanks! That chapter looks like the Real Deal for understanding this stuff, and quite a lot of it. Wnt (talk) 20:53, 1 January 2019 (UTC)[reply]

January 1

Are large rings of pure oxygen possible?

What about this? Sagittarian Milky Way (talk) 19:32, 1 January 2019 (UTC)[reply]

Solid oxygen describes allotropes of four and eight oxygen atoms per molecule. The graphic you have is some sort of crown ether, but with all those oxygens on each carbon atom (gem-diol) I would be very skeptical about its stability. Wnt (talk) 20:59, 1 January 2019 (UTC)[reply]

Long chains of oxygen are endothermic at standard pressures. Energy is released to make dioxygen. They may be stable at low temperature. Trioxygen difluoride and bis(trifluoromethyl) trioxide both exist. For your "what about" there are organic esters of tricarbonate. Your structure will rapidly turn into water and carbon dioxide unless you can freeze it. Under high pressure carbon dioxide may behave more like silica. Graeme Bartlett (talk) 21:04, 1 January 2019 (UTC)[reply]

Cyclic and linear polymers of -CH₂-O- are known (see polyoxymethylene and Formaldehyde#Forms of formaldehyde). Various analogs with chains or functional groups instead of the H on the C are known also, but gem-diols (especially the hydrate of a carbonate ester) are quite unstable. DMacks (talk) 14:37, 2 January 2019 (UTC)[reply]

January 2

Animals with head first delivery preferred?

What animals other than humans have the preferred delivery being head first (as opposed to for example a cow, for which the front hooves is the preferred first part of the animal to deliver.Naraht (talk) 01:18, 2 January 2019 (UTC)[reply]

Well, the other great apes and indeed a majority of simians. This is actually an interesting evolutionary matter, as live birth is believed to have evolved independently in various parts of the tree of life on at least a couple hundred occasions, and the variations on the physiological morphology are remarkable as a result. There are a number of different factors which are believed to have influence which species evolved head-first birthing (meaning superior portion of the body first, which a strong but by no means absolute majority of live birth species use), but by far the most significant is cephalo-pelvic ratio: basically, the higher this ratio the more likely the species is to require this form of birthing, and then at the high end of that spectrum (especially where mammals are concerned) are mostly clustered the cranial-first species. Of course we must also account for aquatic live-birth species, of which there are quite a few, most of whom have no legs to compete with the head. Snow ^{let's rap} 12:06, 2 January 2019 (UTC)[reply]

Thank you very much. I am excluding the aquatic in this. What is the split within the simians?Naraht (talk) 14:59, 2 January 2019 (UTC)[reply]

You're very much welcome. As to your further inquiry, I'm unaware of an obvious single source that aggregates that data, and could not immediately find one, but it's likely to be out there somewhere. Here are a few sources which at least provide detailed consideration of the relative physiological proportions in various simian species, though a majority of them are behind paywalls which may restrict your access depending on your research portal resources: [19], [20], [21], [22], [23], [24].

My suspicion, based upon what I do know about parturition across mammalian species, is that the vast majority of all simians birth cranium first. Of course, you should take that uncited statement with a grain of salt, but there's actually a generally reliable test for figuring out which species are going to birth which extremities in which order: Because childbirth is an exceptionally risky process for both parent and offspring in most all species, there is a substantial selective pressure to ease and expedite the process to the extent the morphology of the child allows. As such, in mammals there is a pronounced, almost universal preference for births to proceed in the order which minimizes the maximal circumference to which the vagina will be stretched, thus minimizing potential trauma to the mother and child. So obviously with most bipeds, allowing the hands and arms to come out extended alongside the cranium would increase the radius and also put dangerous pressures upon parts of the body already tightly constrained by pressure that is already at the high end of all animal parturition. Whereas with most livestock species, to borrow your example from above, the most complicated and problematic method would be too have the legs pressed downwards against the trunk of the body, which is why most all avoid this by having the forelegs precede the head. Now this is not an absolute rule, because there are other considerations and many species actually have room to spare in the vagina (well, at least compared against humans, who are at an extreme end of the spectrum), including some simians. But as a general rule, you can look at a species, consider it's biomechanics (which way the extremities most naturally flex and which profile would allow for a minimal demand upon increase in the diameter of the birthing canal) and make a rough reliable guess for whether they are likely to come out cranium first or superior limbs first. Snow ^{let's rap} 23:16, 2 January 2019 (UTC)[reply]

January 4

Is there any evidence that biology is reducible to physics

Reductionism has worked very well for technology but why do so many people assume everything can be reduced to subatomic particles? There are intractable problems like how the first cell formed, consciousness, free will, if reductionism is to be believed. Is there any research along the lines of "strongly emergent" behaviours of complex systems? By strongly emergent i mean something that's not predicted to exist given the laws governing the constituents, i.e. something completely new comes into existence at sufficient complexity. Have people tried to calculate how the simplest bacterium behaves according to laws governing atoms? — Preceding unsigned comment added by Money is tight (talk • contribs) 04:25, 4 January 2019 (UTC)[reply]

As mentioned in this talk, for simple microbes there does exist a complete description. But, with hundreds of thousands of different enzymes, the "flow chart" of a microbe is huge, it fills tens of thousands of pages. Count Iblis (talk) 04:49, 4 January 2019 (UTC)[reply]

Bear in mind that reductionism is not necessarily about arriving at the most efficient description of a given phenomenon--it's just an attempt to isolate and definite its constituent features, ideally in terms of universals that can be used for all other like phenomena, or (when it comes to physical reductionism, potentially all phenomena). So, to answer the query of your first sentence, the effort is based not so much in an "assumption" that everything can be reduced to a discussion of such constituents--no sensible empiricist working from first principles would operate their inquiry in that way--but rather upon a testing of that hypothesis. And so far, with one deeply perplexing exception, all biological functions have proven amenable to description in terms of physics. The one exception, which you allude to in your inquiry, is something we have such a difficult problem even conceptualizing, that we can;t reliably say whether it is a property (emergent or otherwise) of biology or physics--although we have a profound propensity/bias to frame it in those terms. I am, of course, talking about consciousness. Because it is (not just in terms of biology or psychology, but indeed the entirety of science and empirical human inquiry) the one phenomena that has never been captured or explained by a physical model in any concrete fashion, at any level, this quandry has been given (rather appropriately, I feel) the forbiding title of the the hard problem. And it is indeed something so incredibly different and alien to the empirical method, that some philosophers and cognitive scientists surmise that it is in some sense illusory (whatever Descartes would say to that) or something so far beyond the parameters of what our mental organs are designed to grapple with, that we will never understand it in even a rudimentary fashion. But as to everything else, reductionism works as well for biology as for any other physical system--the complexities simply require a broader canvas to orient and make sense of, with a lot of work still to be done to fill in the gaps--a task which may realistically span eons, if it is resolvable at all. Snow ^{let's rap} 05:41, 4 January 2019 (UTC)[reply]

Really? There has been calculation of the trajectories of each atom in a cell and it agrees with the observed movement? May I see a reference?

Just as an addendum, OP, despite my comments above, which might reasonably be received as a full-throated defense of reductionism, I do not mean to suggest it is the only (or even the most effective) empirical model for physical systems, only that there is not fundamental reason why, as a per se matter, it cannot describe all biological phenomena. However, for an alternative model, you might consider looking into systems theory, which is very much in the vein of describing emergent properties of complex systems. Fritjof Capra, one the populizers of this field of thought, wrote a number of popular science works surveying its development, and one of them is focused on biology in particular. Alas, we have no article for it (perhaps I should fix that), but the title is Web of Life; it could be a good place to start regarding your interests in this area. Snow ^{let's rap} 05:55, 4 January 2019 (UTC)[reply]