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.

December 12

Fluorine (and neon) 2s shell

Resolved

Normally, we talk about fluorine as having 2s and 2p as valence orbitals, for seven valence electrons. However, there's a huge difference in orbital energies between these two, and actually fluorine 2s has a lower energy than the core 5p orbitals in the lanthanides. So, how significant is the contribution of fluorine's 2s shell to chemical bonding? And what about neon? Double sharp (talk) 08:10, 12 December 2022 (UTC)[reply]

The matter has apparently been discussed on Chemistry Stack Exchange. Some MO diagrams for SF₆ and HF are given to support fluorine 2s as inactive. But that doesn't prove that fluorine 2s is always inactive, only that it is in those compounds. Looking at orbital energies throughout the periodic table, I'd expect it to be more possible in something like BrF+6 and indeed this paper finds some fluorine 2s bonding contribution there.

So I suppose I managed to track down an answer for my original question and the natural follow-up has become "OK, so what are the valence orbitals of neon"? Double sharp (talk) 09:03, 12 December 2022 (UTC)[reply]

Well, this distinguishes 2p vs 2s in solid neon as the outer vs inner valence regions. I guess this gives the answer to "what are the valence orbitals of neon" in a natural context when that question is meaningful. Double sharp (talk) 09:51, 12 December 2022 (UTC)[reply]

uploading unpublished government technical reports

I would like to know if documents pertaining to a Wikipedia page can be uploaded as pdf files. These are government technical reports which have not been formally released for various reasons. Rdhara (talk) 21:49, 12 December 2022 (UTC)[reply]

The Help desk is better prepared for this type of question. 136.56.52.157 (talk) 23:51, 12 December 2022 (UTC)[reply]

December 13

Starting the engine of military vehicles

Random thing that someone was wondering about in the bar tonight. Do tanks, fighter planes and attack helicopters have a set of keys for the doors and the ignition? — Preceding unsigned comment added by 146.200.126.234 (talk) 00:04, 13 December 2022 (UTC)[reply]

I don't have a general authoritive answer, but keys have long been used in private ownership vehicles because of theft. Industrial vehicles such as bulldozers have traditionally needed no key for starting, as practically nobody wanted to steal them.

My father bought a World War 2 surplus British made tank. There was no key - anybody could enter and start it. It had an aircraft-style ignition lever switch - off/one/two/both (the engine had 2 spark plugs per cylinder- you are supposed to test running on one set of plugs at a time, to prove both work) and a push-button to crank it.

Last year, a former iron curtain country had some sort of celebration in which their state museum supplied a restored Russian made tank (T54 or similar). Leaving it on public display, they took the battery out, thinking this would immobilise it. A couple of old guys, probably a somewhat drunk, showed up and they had served years before in the same sort of tank. They knew it had an emergency air start system in case of a dead battery. So they started the tank using the air system and drove off with it.

Our army sold of a few old Armoured Personnel Carriers (APC). I inspected one (M113 or similar) at the dealer's yard. They invited me to start it - it needed no key. It had a simple lever on/off switch for electrical power, and a push-button to activate the starter motor.

There are a number of military aircraft start procedure videos on YouTube. There's no key.

One can imagine a scenario: "We are under overwhelming fire. Quick, corporal, start the truck and let's get out of here!" "Uh, sorry Sarge, I dropped the keys in the mud. Can't find them now." Dionne Court (talk) 00:54, 13 December 2022 (UTC)[reply]

This article in ARMY Magazine, criticising the US Commercial Utility Cargo Vehicle or M880 (a military pick-up truck), cites the provision of a common ignition key as a disadvantage; "Imagine trying to bug out and having to fumble for a key to start the truck". Alansplodge (talk) 22:21, 13 December 2022 (UTC)[reply]

Hello user with IP 146.200.126.234, nope, most military vehicles and airplanes in general (not just military) don't use keys, i've heard that humvees don't use keys, nor do tanks, as shawn nelson proved, most aircraft don't use keys, aside from smaller GA aircraft like the Cessna 172 and bushplanes that have a keyed magneto switch, as those aircraft are more likely to be kept in an unsecure airport, military and civil aircraft are always always kept in very secure airports, often having more then a few hundred CCTV and thermal CCTV cameras, these aircraft also relies on a rather complex procedure to start and prep for take off, people have stolen unkeyed aircraft before, but it's often a little twin prop, not sure if anyone has ever stolen a 737 for instance.

Military aircraft are the same, no keys, but good luck getting into a military base, and then there's starting it.

Vintage fighters like the spitfire had their own security feature, huge prop torque that even experienced pilots have trouble handling. OGWFP (talk) 21:59, 16 December 2022 (UTC)[reply]

Exactly what I was going to say -- there's no need for military vehicles to have keys to get in and/or to start, because these vehicles are (supposed to be) guarded whenever not in use! 2601:646:8A81:6070:CC33:2635:A453:3355 (talk) 06:31, 19 December 2022 (UTC)[reply]

Examples Where Genetics was used to determine definitions of genus and species

I recall that there were examples where the definition of a species, genus, etc. were redefined based on genetic analysis. E.g., we thought that Chimp was a species but we changed it to be a genus or we thought a Sea Horse was a fish but we changed it to an Anthropod (I'm making that last one up but I think the first one might be true). I can't remember where I read this though and I've looked through Wikipedia and my books and can't find anything. Would appreciate any examples and refs. MadScientistX11 (talk) 00:59, 13 December 2022 (UTC)[reply]

Here are some examples; there are probably countless more.

The Arctic warbler was formerly thought to include various populations that breed in Asia, but these are all now considered distinct species.
The black Sumatran langur was formerly considered a subspecies of the brown long-eared bat, but is now treated as a separate species.
The black-and-white langur was formerly considered a subspecies of the black-crested Sumatran langur, but is now treated as a separate species.
The Calabria pine vole was formerly considered a subspecies of Savi's pine vole, but is now treated as a separate species.
The East Sumatran banded langur was formerly considered a subspecies of the Raffles' banded langur, but is now treated as a separate species.
The European green toad was formerly thought to include various mainly Asian populations, but these are now considered distinct species; together they have been assigned a new genus, Bufotes.
Imaizumi's red-backed vole was formerly considered a subspecies of the Japanese red-backed vole, but is now provisionally treated as a separate species.
The Japanese long-eared bat was formerly considered a subspecies of the Sumatran surili, but is now treated as a separate species.
The Siberut langur was formerly considered a subspecies of the Mentawai langur, but is now treated as a separate species.

--Lambiam 07:56, 13 December 2022 (UTC)[reply]

For an example regarding some species of gulls, see Larus#Ring species. Long story short – we thought they were a Ring species, but a recent genetic study (linked as a reference) has shown that it's even more complicated than that. {The poster formerly known as 87.81.230.195} 90.213.188.15 (talk) 14:21, 13 December 2022 (UTC)[reply]

Metallising fluorine

Resolved

Has anyone ever measured the pressure necessary to form an expected high-pressure metallic phase of F₂? Or calculated what it theoretically ought to be? Double sharp (talk) 03:07, 13 December 2022 (UTC)[reply]

According to this 2020 paper, it apparently has never been experimentally found (well, no surprise given that it seems like a safety nightmare), but that doesn't exclude it having been calculated. Double sharp (talk) 04:14, 13 December 2022 (UTC)[reply]

Per this 2020 paper there have been experiments (with inconclusive results) and the theoretical metallisation pressure for fluorine is 2500 GPa (with a novel tetragonal P4₂/mmc structure). So I've once again answered my own question. Double sharp (talk) 04:18, 13 December 2022 (UTC)[reply]

Updated metallization pressure (and also the French article). Don't think anyone has calculated it for radon. Double sharp (talk) 04:35, 13 December 2022 (UTC)[reply]

Scientific articles about beef versus Impossible Burger that are not commissioned by the latter?

I've been seeing a lot of the 89% statistic about "global warming potential" from the life cycle analysis that Impossible Foods commissioned from Quantis. This number seems to be repeated commonly, and so I was looking for other studies/scientific articles about the same topic that were not commissioned by Impossible Foods so I could further evaluate the claim. 777burger ^{user talk} ^contribs 03:49, 13 December 2022 (UTC)[reply]

Producing an adequate life-cycle assessment of a product in conformance with the ISO 14040 and 14044 framework and guidelines is a substantive effort of a type that does not help one to earn scientific brownie points. Such a study is unlikely to be undertaken by a scientific establishment unless specifically commissioned. Prior to publication, the LCA was reviewed by an independent panel of academic experts, who found no major issues. In particular, it found that that the methods used are scientifically and technically valid. The report produced by Quantis can be downloaded from the Web,^[1] and is detailed enough that anyone who is interested can check that data from other studies have been properly cited and reproduced and can check the computations. It would be interesting to make a comparison with other "fake meat" products, but I bet that for most one would find very similar results. The report can be read more as an indictment of run-away meat production than as an ad for specifically Impossible Foods. One might even say that beef is the more impossible food. --Lambiam 07:26, 13 December 2022 (UTC)[reply]

What is thirtylone?

Transferred from Computing desk

i wanna do some research about What is thirtylone?if you have the idea about you can help me in my research Elsiewright343 (talk) 13:44, 13 December 2022 (UTC) — Preceding unsigned comment added by 95.145.0.90 (talk) [reply]

As far as I can tell, it's whatever anyone wants it to be. There doesn't seem to be any single real chemical compound with that name, and nothing recognized as such with a CAS number. It seems to usually be used for various forms of amphetamines or analogs of MDMA, but basically as a name it gets used by the illicit designer drug community for whatever new compound they come up with in these families as existing compounds get banned. Don't buy it, don't do research on using it, as you have literally no idea what you are getting. You don't know what compound they are even promising, let alone whether it is actually containing that compound, in what purity, what else it is mixed with, and I guarantee zero research or testing on safety. --OuroborosCobra (talk) 15:52, 13 December 2022 (UTC)[reply]

@Elsiewright343 It is here on Chemspider and here on wikipedia. I wouldn't touch it with the proverbial barge-pole. Mike Turnbull (talk) 16:18, 13 December 2022 (UTC)[reply]

I found this and am providing this as is, no comment. --Ouro (blah blah) 04:57, 17 December 2022 (UTC)[reply]

Help

What was the most recent common ancestor of dinosaurs and mammals? Allaoii ^talk 19:31, 13 December 2022 (UTC)[reply]

It would have been whatever animal existed when Sauropsids (reptiles, dinosaurs, and birds) and Synapsids (mammals and their reptile-like ancestors) diverged, probably living sometime in the Pennsylvanian, likely earlier than 306 million years ago, when the oldest known synapsid evolved. --Jayron 32 19:39, 13 December 2022 (UTC)[reply]

You are looking for a basal amniote. -- Verbarson ^talk_edits 19:43, 13 December 2022 (UTC)[reply]

i remember reading something that named a specific creature, im trying to find its name Allaoii ^talk 20:01, 13 December 2022 (UTC)[reply]

I'm not sure we know it down to that level of precision. The vast majority of species have been unidentified. It seems unlikely in the extreme that the specific species that was the MRCA is known. --Jayron 32 21:11, 13 December 2022 (UTC)[reply]

well it was star trek... Allaoii ^talk 21:27, 13 December 2022 (UTC)[reply]

Ah, the Voyager episode "Distant Origin." It claimed that MRCA to be eryops, which is probably not correct, since it is an amphibian that lived after the first reptiles evolved, and so isn't an ancestor of either dinosaurs or us. Also, the organism they pictured in the episode is not an eryops at all. According to Memory Alpha, the pictured animal is likely a gorgonops, which is already a mammal like reptile. It might be among our ancestors, as a stem group leading to all mammals, but that would already put it after the split between sauropsids and synapsids. So, yeah, Star Trek got this wrong in a lot of ways. --OuroborosCobra (talk) 21:35, 13 December 2022 (UTC)[reply]

...wanna be nerd friends? Allaoii ^talk 21:37, 13 December 2022 (UTC)[reply]

that reminds me, is the "most evolved dinosaur" they showed real, and if so, what is it? Allaoii ^talk 20:38, 14 December 2022 (UTC)[reply]

"Most evolved" is meaningless. All organisms alive on Earth at the same time are equally evolved. --User:Khajidha (talk) (contributions) 16:52, 16 December 2022 (UTC)[reply]

in the episode im talking about they showed a dinosaur that was "most evolved" toward humanoidness Allaoii ^talk 20:15, 16 December 2022 (UTC)[reply]

well most evolved before they died off Allaoii ^talk 20:16, 16 December 2022 (UTC)[reply]

The idea that dinosaurs would evolve toward "humanoidness" reminds me of an ecology concept that is being reevaluated called monoclimax, which I apparently need to write a page for now. Anyways, the idea seems to ignore the value of biological diversity. Etippins (talk) 16:30, 18 December 2022 (UTC)[reply]

I think here on the Reference desk we're required to say seagulls. – b_jonas 15:30, 19 December 2022 (UTC)[reply]

Try this. Alansplodge (talk) 22:39, 13 December 2022 (UTC)[reply]

read the other replies before commenting Allaoii ^talk 22:51, 13 December 2022 (UTC)[reply]

Yes. I was providing a reference, this being a reference desk. Alansplodge (talk) 15:07, 14 December 2022 (UTC)[reply]

one of the other replies already answered my question. Allaoii ^talk 17:17, 14 December 2022 (UTC)[reply]

This is the reference desk, not the answer desk. Alansplodge did exactly what they were supposed to. --Jayron 32 19:52, 14 December 2022 (UTC)[reply]

December 14

Gamma decay.

So the shortest wavelength in the EM spectrum are gamma rays, then x-rays. It appears to me that gamma rays are called gamma rays because they have only been gamma rays emitted. If they can emit wavelength in the x-ray range, then they can get a name change. Have scientists been working on finding gamma decays to emit in the x-ray range? Also, if I look at gamma decay, and sort the shortest gamma ray, to the longest gamma ray, what is the pattern, from the decaying point of view? Nucleus mass? Do scientists predict they can 1 day have decay emit x-rays? And maybe win a Nobel prize if someone discovered a way. 67.165.185.178 (talk) 01:25, 14 December 2022 (UTC).[reply]

The total energy released in radioactive decay is the energy equivalent of the difference in mass (by ⁠

E=mc^{2}

⁠) between the parent nuclide and daugher nuclide(s). The energy of a photon is given by the Planck relation, ⁠

E=hf={\frac {hc}{\lambda }}

⁠, which implies that longer gamma rays carry less energy and shorter gamma rays carry more energy. Indeed, very low energy decays can produce x-rays or even ultraviolet rays in the case of the remarkably low-energy nuclear isomer thorium-229m (Sources: [2] [3]). ^Complex/_Rational 01:56, 14 December 2022 (UTC)[reply]

Excellent. And all these gamma rays, are ionizing. Can this thorium-229 or so, release the radiation that are non-ionizing? 67.165.185.178 (talk) 03:42, 14 December 2022 (UTC).[reply]

The excitation energy of Th-229m is less than 10 eV, which is commonly used as a threshold for ionising radiation. So, yes, it would emit non-ionising radiation by this definition. Though usually the gamma vs X-ray (or in this case UV!) distinction is by origin rather than wavelength. Double sharp (talk) 03:47, 14 December 2022 (UTC)[reply]

Double sharp's last sentence is important. An alternate and fairly common distinction between the two types of radiation is for "X-rays" to be the result of electronic reactions vs "gamma rays" coming from nuclear reactions, rather than a bright-line (ha!) delineation of wavelengths. X-ray#Energy ranges has a discussion. DMacks (talk) 03:58, 14 December 2022 (UTC)[reply]

It depends on whom you ask. The people who generate their own radiation (like radiologists) discriminate between X-rays and gamma rays by source, i.e., the apparatus they need to generate it. The people who only observe the radiation (like astrophysicists) discriminate only on energy, putting the threshold at something like 100 keV. PiusImpavidus (talk) 09:54, 14 December 2022 (UTC)[reply]

Yeah, I'm used to the nuclear-physics convention that anything coming out of a nucleus is gamma (even if by wavelength it's UV in the case of Th-229m), but indeed definitions vary between fields. Double sharp (talk) 14:54, 14 December 2022 (UTC)[reply]

Oh, and what does the m symbolize, in thorium-229m? 67.165.185.178 (talk) 04:01, 14 December 2022 (UTC).[reply]

What did you learn when you clicked on the thorium-229m link? DMacks (talk) 04:03, 14 December 2022 (UTC)[reply]

Oh okay, it stands for metastable. 67.165.185.178 (talk) 04:08, 14 December 2022 (UTC).[reply]

I want to underline something that several commenters here have said from different points of view:

Gamma rays and X-rays are the same thing. They're both just photons. Classifying photons by wavelength, energy, or source can be very useful for a number of reasons, but it's important to remember that these are still just sub-categories (with somewhat conflicting definitions) of the same fundamental thing. PianoDan (talk) 16:45, 14 December 2022 (UTC)[reply]

Just to really drive home the point that PianoDan is making above, the different "kinds" of electromagnetic radiation (gamma rays, X-rays, UV, light, IR, microwaves, radio waves) are all the same thing. There is no difference between any of them on a fundamental level except the wavelength, but in every other way, they are exactly the same phenomenon. When we use words like "gamma rays" or "X-rays" or "visible light" to describe certain ranges of wavelengths, we're largely doing so to make it convenient for us to explain how we use those forms of EM radiation, and in some cases are really just historical artifacts to a time when we didn't understand this stuff as well as we do now. When we named, for example, X-rays and gamma rays, we didn't really know what they were. X-rays have that "X" at the front because because Wilhelm Conrad Röntgen, when he first described them, didn't know what they were, so he used the standard placeholder "X" meaning "unknown" for the name, and it kinda just stuck. When gamma radiation was named, it was named because it was the third time of nuclear radiation (which is to say, radiation given off during nuclear decay discovered. No one really knew what it was, but since alpha radiation (the first so discovered) and beta radiation (the second so discovered) already had names, Paul Ulrich Villard, who discovered this third type, just kept the pattern going. Notice, however, that none of these names has anything to do with what the radiation actually was. It turned out that X-rays and gamma radiation were basically the exact same thing, so for mostly historical reasons, we differentiate the name by the process that produces it, rather than by any fundamental difference in the particles themselves. You see the same thing all the time; for example alpha particles are just helium 4, beta particles are just electrons. It's certainly no different than you calling your mother "Mom", but her brother calling her "Susan" or whatever. Different names in different contexts don't mean they are different things. The same thing can have multiple names. --Jayron 32 18:11, 14 December 2022 (UTC)[reply]

Collisions at railroad crossings

Statistically, does California experience a disproportionately high number of collisions between trains and pedestrians and/or road vehicles at level crossings (when compared to other states)? If so, does the number remain disproportionate if corrected for the main confounding factors (namely, (1) the amount of population living in communities with active railroad tracks running through them, (2) the number of trains operating daily within the state and (3) the number of ungated railroad crossings and/or the mileage of street running)? If so, what are the possible reasons why the number is so high? (Because it certainly seems that way -- a person I know who rides Caltrain regularly told me that he experienced delays almost every week on average (!!!) due to either his train or another train ahead of him hitting someone or something on the tracks, and when I rode the Coast Starlight up to Salem a couple months ago, I experienced these delays personally -- the northbound train pulled into San Jose a full 4 hours late due to having run over some stupid hobo in Salinas, whereas the southbound train got to Salem exactly on time and kept going as far as Oakland without delay, but between Emeryville and Jack London Square we had an emergency stop due to some idiot driver pulling onto the tracks right in front of the train without looking (fortunately we were going dead-slow and therefore didn't collide, so we were only delayed 10 minutes or so). So, is California really that bad in terms of collisions at railroad crossings, and if so, why might that be? 2601:646:8A81:6070:8D7A:87F9:2C1B:94A0 (talk) 08:03, 14 December 2022 (UTC)[reply]

According to Operation Lifesaver which exists to prevent these types of collisions, Texas is #1 in the number of collisions and California is #1 in deaths caused by such collisions. This is not surprising since those are the two most populous states with California being most populous. The death rate in California per 100,000 residents is close to the national average. This is a nationwide problem although 234 deaths a year in a country of 332 million people is not a major cause of death. Pancreatic cancer, for example, kills about 50,000 Americans each year. As a long term resident of the Bay Area, I am well aware that Caltrain has a bad reputation for this type of disaster, since it is a heavily used commuter rail line between San Francisco and San Jose, with plenty of grade crossings and ample opportunities for pedestrians to engage in dangerous behavior. This article from 2000 reports 90 deaths in the previous eight years, which would be less than one a month but would certainly have an impact on daily commuting. Many of those deaths were suicides. Talking about "stupid hoboes" is pretty much guaranteed not to be useful. There are obvious safety improvements that should be made, such as eliminating grade crossings, but that would cost many billions of dollars and take decades. That is part of the California High-Speed Rail program, which is behind schedule and over budget. Cullen328 (talk) 10:17, 14 December 2022 (UTC)[reply]

For comparison, 5 people were killed at UK level crossings in 2020/21, [4] 2 in 2019/20 and 2 in 2018/19. [5] The population of the UK is 67 million, nearly double that of California, with a much denser rail network. Alansplodge (talk) 15:04, 14 December 2022 (UTC)[reply]

But California has over 10,000 level crossings, almost twice as many as the UK. To compare them properly you'd need to analyze both places in terms of the number of road vehicles and the number of trains that use the crossings daily. I'm not searching, but I doubt that those statistics will be easily found. --174.89.144.126 (talk) 15:32, 14 December 2022 (UTC)[reply]

Good point. The UK deaths were all pedestrians, mostly using rural footpath crossings. I suspect that the safety infrastucture of British vehicle crossings is rather better - crossings without automated barriers and/or warning lights are very rare and only in remote areas. Alansplodge (talk) 12:06, 15 December 2022 (UTC)[reply]

UK level crossings appear pretty safe then. In the Netherlands, we have about 12 accidental deaths among road users on level crossings per year (in addition to about 200 suicides), which amounts to one accidental death per level crossing per 200 years. That's about 98% of all accidental rail fatalities and 2% of all accidental road fatalities. Assuming the average level crossing sees about 6 trains per hour during the day (most see 4 or 8 per hour, some over 20 per hour, some only 2 per week), that's one accidental death per 8 million train passages. That may be a more useful statistic, but you still have to compensate for road traffic density and that the rush hour on road traffic may or may not coincide with peaks in rail traffic. Ideally, you take the number of trains at a level crossing in an hour, multiply with the number of road users at that crossing during that hour, integrate over a year, sum over all level crossings and then divide the number of accidental deaths or the number of collisions by that number. It's still not a fair number: as the most heavily used level crossings, with the most elaborate warning signals, get replaced by grade separated crossings, accident rate drops, but the average safety of the remaining level crossings drops too. PiusImpavidus (talk) 12:48, 15 December 2022 (UTC)[reply]

wormholes

hello i would like to ask if resonant tunneling antenna diodes can generate wormholes. thanks very much. 2607:FEA8:BCE0:D500:75E8:5E73:E7C8:DE4 (talk) 15:38, 14 December 2022 (UTC)[reply]

No. --Wrongfilter (talk) 15:44, 14 December 2022 (UTC)[reply]

More specifically, quantum tunnelling and wormholes are not the same thing. --OuroborosCobra (talk) 16:02, 14 December 2022 (UTC)[reply]

from internet searches i found macroscopic and electromagnetic quantum tunneling can generate wormholes. is that this correct. 2607:FEA8:BCE0:D500:D9DA:4F2F:3CE:E4B6 (talk) 17:42, 14 December 2022 (UTC)[reply]

Please read the Wikipedia articles you have been sent to read. Wormholes and quantum tunnelling are entirely unrelated phenomena, and have nothing to do with each other. Wormholes are a consequence of gravity, and are thus explained by general relativity. Quantum tunnelling, as the name implies, is a result of quantum mechanics. It is not an electromagnetic effect, per se, but rather due to the way that all elementary particles behave. The quantum tunnelling article actually has a nice, lay-person level explanation in the "Introduction to the concept" section.--Jayron 32 17:59, 14 December 2022 (UTC)[reply]

Water's boiling point

One of the things that allow life to exist on Earth is that liquid water is available in large numbers. This is because of the distance to the sun, but also because of our atmosphere and its pressure, that allow a wide temperature range for liquid water (from 0º to 100º). If Earth was in the same orbit but had a lower atmospheric pressure, that range would be way more limited. And IIRC, with no atmosphere water would sublimate from ice to vapor directly.

This is something I simply know, but I would need a proper source for it. I'm listing in a sandbox all the reasons that allow life to exist on Earth, from an astronomical perspective, but all the sources I find that explain our liquid water attribute it only to the goldilocks zone, making no mention to the atmospheric pressure. Cambalachero (talk) 19:06, 14 December 2022 (UTC)[reply]

What you're looking for is a phase diagram of water, or even more simply the triple point of water. The pressure at the triple point is the lowest pressure at which a liquid could exist, so any pressure less than about 0.006 atm (0.6% of the earth's atmospheric pressure) would not be able to support liquid water. The relationship between pressure and boiling point is seen on any phase diagram as the liquid-solid line on the graph. If you want a text description, it's really basic stuff taught in any first-year chemistry class. Here it is in LibreText Chemistry and Here it is on OpenStax Chemistry, for two free entry-level chemistry textbooks. I can't imagine that literally every entry-level chemistry text book doesn't discuss the relationship between pressure and phase changes. It's REALLY basic stuff. --Jayron 32 19:49, 14 December 2022 (UTC)[reply]

If the motivation here is to explore limits of alternative "Goldilocks zones," we might need to freeze the discussion (sorry, bad pun) and revisit exactly what that zone is.

If we're reducing it to a few words of sound-bite, we might say that a planet is in the Zone if liquid water exists on that planet.

But hang on - we also want to say, "... and we're looking for liquid water because..." ... it's an important part of every form of plausible biochemistry that we're interested in - even the plausible alternative xenobiology that borders on the speculative!

At the same time, the so-called "habitable zone" also has other requirements. If the liquid water is in equilibrium at an ambient temperature that is so hot that it's denaturing proteins, then protein-based biology won't work: that's "not the habitable zone." If it's so cold that metabolism is chemically unsustainable, that's also "not the habitable zone." We can imagine biochemistries that are very different from our fundamental earth-like biochemistries - and we can even test some of this in a lab - but there are still limits! And so we can traverse down the speculative, alternative, plausible sorts of "habitable" zones for speculative, alternative, plausible sorts of non-Earth-like life forms, ... just bear in mind that as you stray farther afield, even the requirement for liquid water will also evaporate (sorry, bad pun).

Here's a NASA website that talks about the Kepler Occurrence Rate, and here's the SETI study that goes into the boring details; and if I may editorialize a bit - NASA had to make some "clarifying editorial updates" to their press release in order to keep things more science-y and less fiction-y.

Real scientists do care about this stuff, but they have to mince words, define terms, and tread very carefully. Speculation is fine as long as we are still making meaningful scientific statements - which fundamentally boils (sorry) down to falsifiability and testability.

Nimur (talk) 21:12, 14 December 2022 (UTC)[reply]

Just as (relatively analogous to water) examples of plausible alternative biochemistry: ammonia has long been suggested as a possible water substitute, being another 2p element hydride with hydrogen-bonding benefits and a good solvent. I've similarly wondered about hydrogen fluoride for some years, and that possibility is explored in this paper. Going much farther afield, some early transition metals form some intricate structures and make a plausible high-temperature biochemistry (at which point we've left analogies to water very far behind). Double sharp (talk) 03:01, 15 December 2022 (UTC)[reply]

@Cambalachero, this is somewhat addressed at Rare Earth hypothesis#Requirements for complex life, specifically in the subsection A terrestrial planet of the right size (which is tied to atmospheric pressure, as well as longevity of that atmosphere). You could check out the references there for more. 199.208.172.35 (talk) 21:15, 14 December 2022 (UTC)[reply]

December 15

Most intense wind

What is the most intense natural wind on Earth? ✶Mitch199811✶ [Talk] 04:06, 15 December 2022 (UTC)[reply]

Possibly tornado. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:14, 15 December 2022 (UTC)[reply]

We have a List_of weather records#Wind speeds. DMacks (talk) 07:36, 15 December 2022 (UTC)[reply]

Here is an article about the strongest wind ever recorded. Who knows about unrecorded winds? Cullen328 (talk) 08:23, 15 December 2022 (UTC)[reply]

1999 Bridge Creek–Moore tornado. Cullen328 (talk) 08:27, 15 December 2022 (UTC)[reply]

Thank you! ✶Mitch199811✶ [Talk] 12:51, 15 December 2022 (UTC)[reply]

Tornados produce very fast air movements, but they are gusts, not sustained winds. A tornado doesn't stay at the same force and exactly the same position for ten minutes. Very high sustained windspeeds are produced by tropical cyclones and have been recorded at up to 185 kn (95 m/s; 343 km/h; 213 mph) during Hurricane Patricia, which is a one minute average (as Americans tend to calculate such things). Katabatic winds can get very strong too. A piteraq on Greenland in 1970 was recorded at 90 m/s (170 kn; 320 km/h; 200 mph). That would be a ten minute average (as the rest of the world tends to calculate such things). One minute averages tend to be about 14% higher than ten minute averages, so that wind on Greenland was probably stronger than the wind in hurricane Patricia. PiusImpavidus (talk) 20:58, 15 December 2022 (UTC)[reply]

Almost certainly the jet streams. 2A01:E34:EF5E:4640:4210:3448:E6A9:8778 (talk) 22:21, 15 December 2022 (UTC)[reply]

The article only says 250 mph while the tornado at least is higher. ✶Mitch199811✶ [Talk] 03:31, 16 December 2022 (UTC)[reply]

Cullen above made an important point. Strong winds destroy recording equipment, so we may never really know the answer to this question. See Cyclone Tracy#Meteorological history. (Final paragraph.) HiLo48 (talk) 22:44, 15 December 2022 (UTC)[reply]

I know I'm always being a weeny for strict definitions, but the original question asked for the "most intense" wind.

Does anybody know what the word "intense" means in a meteorological context?

The way I learned things, "intensity" is a property of a storm, and not a measure of wind or wind velocity. "Intensity" is a quantitative, numerically predicted product of most modern weather forecast models - notably these "Track and Intensity Models" used by the National Hurricane Center.

We can find many definitions for the word "intensity" - including a perfectly precisely-defined meaning in the physical sciences ... or like, fifteen other totally different but equally-perfectly-precisely defined meanings in the physical sciences, but ... I bet our original question meant to ask about "maximum wind velocity." And I bet they were implying "standard" measurement methods for wind speed near Earth's surface (or, say, "1.5 meters above the ground," which is one of the most common standards - like the standard measurement used by NOAA for the Climate Reference Network, which matches most standards used for standard surface observation stations like the ASOS. And I bet we were all implying that we're all talking only about wind-moving-horizontally-and-totally-ignoring-vertical-velocity. And, we're probably all implying a standard observation of the sixty-second average with peak gusts. And ...

Look, we have to define terms carefully if we want to meaningfully understand what a record-setting wind even means, let alone when and where it happened!

My textbook - Aviation Weather - tells me that tornadoes are the most "violent"; "the most intense of all atmospheric circulations" - and the latest edition (AC 00-06B) goes into detailed discussion about the Enhanced Fujita Scale, detailing why the way they measure wind differs from the way we measure the wind. "Note: The Enhanced F Scale is a set of wind estimates (not measurements) based on damage. The 3 second gust is not the same wind as in METAR/SPECI surface observations."

Lately, microbursts have been a hot topic. "Although microbursts are not as widely recognized as tornadoes, they can cause comparable, and in some cases, worse damage than some tornadoes produce. In fact, wind speeds as high as 150 mph are possible in extreme microburst cases."

To me - for my concerns - I care just as much about the vertical wind speed as the horizontal windspeed in the microburst. The vertical downdraft wind velocity is not measured or reported by most common wind reporting stations! By the time the vertical column of wind hits the surface, it starts spreading out radially, which means that those "EF-1 tornado" winds they measure are just one little tiny horizontal component of the pi-r-squared flux that's spreading away from the central vertical downdraft.

Nimur (talk) 18:17, 16 December 2022 (UTC)[reply]

On the other hand, if something is the definition that is used by most non-specialist sources like the weather report on the news, that should always be presumed to be the definition that non-specialists mean when asking such a question. Your points are at once valid and irrelevant to answering the most likely question the OP asks, which unless the specific, should be read to be "what is the strongest winds (as measured and reported by whatever means I am used to hearing such things reported)." If that's not a complete measurement or give a full picture, or as interesting as these other tangents are to you is mostly irrelevant as that's not really useful in answering the question the OP asked for. --Jayron 32 18:43, 16 December 2022 (UTC)[reply]

Feedback taken! Nimur (talk) 19:12, 16 December 2022 (UTC)[reply]

The weather report on the news, at least where I live, makes a distinction between wind speed and gust speed (and is usually presented by an actual meteorologist). This wind speed follows the WMO standard for surface wind speed, a 10 minute average at 10 metres above the ground, so I answered with fast, sustained surface winds. From the comments by the OP it appears that gust speed is fine too, whatever is higher.

What about the slipstream of a supersonic meteor falling through the stratosphere? It's natural and pretty fast. PiusImpavidus (talk) 19:20, 16 December 2022 (UTC)[reply]

AFAIK, both average wind speed and gust speed are taken from data from actual physical weather stations that contain an anemometer, which AFAIK, just measure horizontal wind speed at the standard height of the weather station (which is where I believe Nimur above got the 1.5 meter standard for "surface winds"); with gust speed being merely like local maxima and average speed being, well, the average. This describes the specific procedures for averaging the wind speeds. The measurement itself is not terribly complicated, and it's been largely standardized for decades, probably at least a century at this point, with the exception of the data being transmitted digitally now. --Jayron 32 19:34, 16 December 2022 (UTC)[reply]

I'd drop the subject and walk away, but I keep seeing the discussion fixing back on "surface winds..." which are categorically not where we would find the "most intense natural wind on Earth." The question can't be answered properly if we're couching its answer in a conceptually-invalid framework! Wind occurs in three dimensions, and we now measure it at many places, including above the surface!

Winds at high altitudes are now regular outputs of forecasts and computer models; and these winds are also directly and indirectly observed using airplanes, RADAR, and satellite.

I wish I could simply concede that this was "irrelevant" to the original question, except that winds at high altitudes are substantially more intense than surface winds. Even tornados - "the most intense of all atmospheric circulations" - do not always contact the ground!

As far as the history goes - some of this is new science! Meteorological science did not have coherent theories, let alone any measurements, pertaining to high altitude winds, before aircraft began regularly flying at high altitudes - the exact place on our planet where the winds are most intense! The density of the 3D observations and forecasts have improved a lot in recent decades - so much that the textbook I cited above had to be updated in 1954, 1965, 1975, and most recently in 2016. Gosh, the Enhanced Fujita scale - which quantified "intensity" - the exact word in the original post - was only conceived in this millenium and has only been in use since 2007! I must respectfully disagree with the assertion that this type of wind speed measurement has been unchanged for decades - especially when we're talking about measurements at the extreme intensity ranges.

Even I am old enough to have seen the transition from wind reports that looked like this to pictures like this to animations like this. Low level wind shear RADAR - providing ultra dense local measurements of extreme wind phenomena - evolved from theoretical physics in the 1970s into a standard system in 2013. Dense wind measurement data and forecasts didn't exist when I was born - not even in computer weather research laboratories at NASA!

In a very precise and specific sense, we (scientists and the general public) have learned new things about wind intensity even in the last couple years. The nature of what we have learned has changed scientific understanding of wind in a substantial way.

Personally, I think this is a pretty big deal: there are recent, fundamental shifts in the conceptual framework that scientists use for understanding how wind works, how it interplays with climate and earth systems, and how we have to understand it as a 3-D interaction of air flowing everywhere at all parts of the global climate system.

These ideas are important - even if we want to reduce it to a factoid like a "wind speed record" for consumption by the general public.

Nimur (talk) 14:23, 17 December 2022 (UTC)[reply]

Big whirls have little whirls, that feed on their velocity... AndyTheGrump (talk) 14:38, 17 December 2022 (UTC)[reply]

December 16

Regeneration of the body

Is there a method to stimulate collagene proliferation in the body? 2A02:908:424:9D60:1D3E:5FB6:8A8A:44A6 (talk) 18:22, 16 December 2022 (UTC)[reply]

Not sure, but this article may give you some leads for your research. --Jayron 32 18:39, 16 December 2022 (UTC)[reply]

Collagen is a collective noun for a large class of proteins with very different characteristics, from the smooth and elastic cartilage found in joints to the tough ossein in the bone matrix. If collagen production is stimulated artificially, it should be of just the right type in just the right place by just the right amount; of the many disorders associated with collagen, a large number is caused by overproduction. In cases caused by a genetic disorder, gene therapy may offer a spot of light on the horizon. Severe nutritional deficiency can contribute to low collagen production, but will then generally also result in many other problems. For otherwise healthy individuals, a balanced diet does more to stimulate healthy collagen production than available collagen supplements. This article on WebMD contains some nutritional suggestions. --Lambiam 09:17, 17 December 2022 (UTC)[reply]

Definition of dead

Why is circulatory determination of death abbreviated as DCDD rather than CDD? — Python Drink (talk) 22:16, 16 December 2022 (UTC)[reply]

I've only seen DCDD used in the context of death-determination for purposes of organ donation, with phrases like "donation after circulatory determination of death". So the first "D" seems like "donation". DMacks (talk) 22:21, 16 December 2022 (UTC)[reply]

Indeed; see this. Alansplodge (talk) 12:37, 17 December 2022 (UTC)[reply]

December 17

small electrical generators

I wonder what the obstacles are (i.e. why can't we get them) to making small electrical generators or fuel cells, e.g. for portable outdoor use. It's easy to get a 1 kilowatt generator that weighs 30 pounds, so why not a 100 watt generator that weighs 3 pounds? Things like this are on the internets now and then, but are always just around the corner, never "order now". Thanks. 2601:648:8200:990:0:0:0:497F (talk) 00:43, 17 December 2022 (UTC)[reply]

Gasoline and diesel gensets don't scale linearly. For example, I own a Chinese made 2 kW generator and a Chinese made 3.3 kW generator. They look identical, and occupy the same volume, but actually there are 2 key changes - the 3.3 kW unit has a larger cylinder bore, such that it is 215 cc capacity whereas the 2 kW unit is 185 cc. The 3.3 kW unit has a larger frame size generator. The difference in total weight is small - about 10%, due to the difference in generator frame size.

Honda Japan used to make a 300 Watt gasoline powered generator - it weighed about half of what my 2 kW unit weighs.

Basically, to make a gasoline engine half the power of another one, you basically need to halve the cylinder displacement volume. To do that, each length, width, and height dimension needs to be reduced by only the cube root of 1/2, i.e., reduce 20%. Stresses remain about the same (for instance, to run efficiently on standard gasoline, the compression ratio must stay about the same), so mass only comes down 20%. Similarly, to make an engine of 1/10 the power, it will end up reduced by the cube root of 0.1 i.e., dimensionally reduced by 53%.

As far as fuel cells go, they are like nuclear fusion power stations - i.e., they have been reported as just around the corner for almost as long as I have lived, which is 75 years. The trouble with fuel cells is that unless they are constructed with ultra pure materials, and fuel them with ultra pure fuel, they soon clog up with detritus. Dionne Court (talk) 02:47, 17 December 2022 (UTC)[reply]

And while combustion-powered generators get lower power-to-mass ratio (and lower efficiency) as you scale them down, this doesn't apply to batteries, which are therefore more attractive at small size. In particular as they don't produce noise and nasty fumes. It gets ever easier to recharge batteries as mains power sockets appear everywhere to charge our phones, e-bikes and electric cars, so I don't expect the minimum size of petrol-powered generators to drop. PiusImpavidus (talk) 11:34, 17 December 2022 (UTC)[reply]

Fusion is a few decades from now for 70 years cause no one ever throws them enough bones of money to make one big enough. Cube-square law. Sagittarian Milky Way (talk) 15:02, 17 December 2022 (UTC)[reply]

Although they've done something in the past few days that's never been done before [6]. 146.199.206.38 (talk) 17:10, 17 December 2022 (UTC)[reply]

Yeah - they have now and then been announcing they've done something new ever since the Soviets invented the tokamak in the 1950's, followed by British confirmation of improved Soviet tokamak results in the 1960's. Don't hold your breath for the world being saved from being cooked by emissions from fossil fuel burning. Unless WW3 sends us back to another Dark Age. Dionne Court (talk) 00:52, 18 December 2022 (UTC)[reply]

The Sn–Sb system

Are Sn–Sb alloys generally metallic conductors or semiconductors? (With no other metals added. I know for example that type metal was historically Pb–Sn–Sb, but that's not what I'm asking about.) Double sharp (talk) 13:51, 17 December 2022 (UTC)[reply]

Sn (tin) with 5% Sb (antimony) is used as a lead-free solder, so would need to have metallic conduction. Tin has a valency (number of outer shell electrons) of 4 and antimony has a valency of 5. For a binary alloy to be a semiconductor, the "median" valency would need to be 4, as in combining a valence 5 element with a valence 3 element, as with gallium (valence 3) and arsenic (valence 5).

There is a simple formula for calculating the resistivity of binary metallic alloys from the resistivity of each element and the ratio present, but I can't think of it right now. Maybe another poster will know. Dionne Court (talk) 15:11, 17 December 2022 (UTC)[reply]

Thanks! I wasn't sure because germanium arsenides (one row further up the periodic table) are semiconductors (10.1002/pssb.201552598), despite the wrong "median" valency. True, tin at ambient conditions is a metal (whereas germanium isn't), but grey tin becomes the stable state not too far below room temperature, so I thought it was better to ask. :) Double sharp (talk) 03:56, 18 December 2022 (UTC)[reply]

I'm not going to pay $12 to access 10.1002/pssb.201552598, nor travel to my university to access it for free, but I think you'll find that germanium arsenide is only a semiconductor at low fractions of arsenic, so that germanium's valency of 4 predominates. As the concentration of arsenic approaches 100%, it cannot be a semiconductor. Dionne Court (talk) 14:49, 18 December 2022 (UTC)[reply]

That paper calculates that GeAs and GeAs₂ are semiconductors and says that agrees with experiment, so it seems possible at quite high As fractions. But it seems to be a close thing, since they calculate that with a few Ge vacancies these can metallise (OTOH, with even more they can become semiconductors again). Anyway, pure As has both metallic (grey) and semiconducting (black) allotropes. Double sharp (talk) 16:19, 18 December 2022 (UTC)[reply]

Missing centers of the United States

We have mean center of United States population, median center of United States population, mean center of United States land and mean center of contiguous United States land, in all cases counting the land or people of the 50 or 48 states plus DC as a whole (including islands). Where are the missing centers? (the mean and median center of the contiguous population and the median center of the land and land minus Alaska and Hawaii, same definitions as the other 4). Are the 51 median land centers of the states+DC online anywhere? Or the 51 mean population centers and 51 median population centers? We have the 51 mean land centers. Sagittarian Milky Way (talk) 16:54, 17 December 2022 (UTC)[reply]

Note that there are different, non-equivalent definitions of "median centre".^[7] The cited source identifies the one used by the United States Census Bureau as following the "British tradition". It has the unappetizing property of being sensitive to isometric transformations and thereby ambiguous. --Lambiam 17:27, 17 December 2022 (UTC)[reply]

Apparently mean is minimal sum of distances squared and geometric (other) median is minimal sum of distances. While the British tradition is sensitive to rotation and translation (i.e. the British median of an equilateral triangle of 3 people moves as it rotates, the middlemost people of an even number of ppl probably has an ambiguous gap in between) it also has the awesome property of "half on each side" in both latitude and longitude and in practice land is infinitely divisible and for large lands of millions population almost is: any gap for the whole country would be feet at most and smaller than any realistic error for a Census where the sum of double counts and missing people is c. millions. I've found some things like a map of the state population medians and a pause-able animation of cumulative county populations by latitude and longitude which allows figuring out the 2018 contiguous population median to county-level accuracy. Sagittarian Milky Way (talk) 22:37, 17 December 2022 (UTC)[reply]

So after trying many times to get it to successfully fall on exact right county out of 3,143 it appears the centers of median population are almost too close to tell signifying lots of persons near these meridians and parallels (i.e. Chicago metro area) and the median contiguous land is circa 2 counties south of the mean contiguous land and ~1-2 counties east. So maybe the north and west halves have better leverage or they're using a map projection where parallels sag in the middle. Sagittarian Milky Way (talk) 07:35, 18 December 2022 (UTC)[reply]

Patagopelta, Kelumapusaura, Notoceratops, Labocania, Alamosaurus...

I am really wanting to know what is the deal with this faunal interchange between dinosaurs of North America and South America. CuddleKing1993 (talk) 19:06, 17 December 2022 (UTC)[reply]

What you're interested in is biogeography and according to this paper there was probably a link between North and South America during the Campanian (Late?), via a line of volcanic islands, allowing "a dispersal route for hadrosaurids and other vertebrates". Mikenorton (talk) 22:56, 17 December 2022 (UTC)[reply]

December 18

Is it safer to run washer + dryer in same strip outlet, or same wall outlet?

And if you run a washer and dryer at the same time, on the same strip outlet, if something happens, more like the appliance will be damaged and break a circuit, than the strip outlet, right? Also, older washing machines spin horizontally and newer washing machines spin vertically, do the new 1s who spin vertically use less amps than the older 1s? Not because of spinning, but less water use, which would make spinning easier. 67.165.185.178 (talk) 14:49, 18 December 2022 (UTC).[reply]

Before anyone can give you an answer about your wiring you need to specify which country you are in. As regards the washing machines, they should have pumped all water out before the spin starts, so it depends upon the fabrics within and how much water they retain. Martin of Sheffield (talk) 15:24, 18 December 2022 (UTC)[reply]

Ah yes, if voltage is the issue then it's worse in the UK, but since this is about amps, would be worse in U.S. 67.165.185.178 (talk) 15:58, 18 December 2022 (UTC).[reply]

It's also about how houses are wired. The term "strip outlet" makes me guess that you are in the USA where ring mains are rare/unknown. Martin of Sheffield (talk) 16:50, 18 December 2022 (UTC)[reply]

The IP geolocates to Chicago, and I expect there are many wiring possibilities in that city. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:49, 18 December 2022 (UTC)[reply]

If the simultaneous use of the appliances results in an overcurrent, a circuit breaker should step in and shut off the power, thereby grinding the appliances to a halt. Such appliances are designed to withstand sudden power interruptions, so this should by itself not damage them. If the wiring has been done properly and modern circuit breakers are used, the breakers should just trip and be easily reset – which should only be done after disengaging one of the appliances. If the wiring has been done improperly or disfunctional circuit breakers are used, overcurrent engenders a house fire risk because of overheating wires, by itself much worse than the risk of damaged appliances. To stay on the safe side, make sure the combined power is not more than nominally supported by the outlet and breakers. --Lambiam 21:27, 18 December 2022 (UTC)[reply]

If I have a bowl of water with salt and sugar in it...

Is it possible to filtrate out the salt without the sugar, or filtrate out the sugar without the salt? So I think the answer is osmosis and reverse osmosis. Osmosis is where you filtrate out the solute from the water, reverse osmosis is where you filtrate out the water from the solute. So for this case, you 1st have to osmosis/revere osmosis the salt 1st, then sugar. (Because salt is smaller than sugar.). Otherwise, filtrating out the sugar, sucks salt with it. Note that if salt and sugar crystals are initially the same size, then you stir the water until the salt dissolves into ions, which sugar will not. Otherwise, not possible if they are the same size. But is this method accurate, and, are there other methods? And I don't think doing osmosis or reverse, is easily done at home, because for 2 containers separate by a membrane, you need to find a way to increase/decrease the pressure of 1 container, are stuff like this already made? 67.165.185.178 (talk) 20:10, 18 December 2022 (UTC).[reply]

How about you speak to the washer-dryer question first, before posing another one? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:21, 18 December 2022 (UTC)[reply]

The simplest sweet sugars, glucose, fructose, and galactose, have a molar mass of about 180 g·mol⁻¹, while that of kitchen salt is just shy of a third of that, at about 58 g·mol⁻¹. When sugar dissolves in water, the molecules remain intact; only the weak bonds between different molecules are broken. But when salt dissolves in water, each salt molecule turns into a sodium and a chloride ion, both much smaller than a sugar molecule. Therefore I expect that there are ion-exchange membranes with pores of a size that will block sugar molecules from passing through yet allow the passage of sodium and chloride ions. After filtration, the result should be a low-salt sugar solution on one side, and a very diluted salt solution on the other side. --Lambiam 21:59, 18 December 2022 (UTC)[reply]

I think it should be possible to make a membrane that blocks salt but allows sugar through too, based on the charge of sodium or chloride ions. You only have to block one of them, the other ion will be blocked by the electric field after a few have diffused to the other side. Or there may be some solvent in which salt or sugar dissolves, but the other doesn't. Solubility of sugars in water is generally better than the solubility of kitchen salt (you didn't mention exactly what sugar and salt you're dealing with), so by concentrating the solution you may be able to get the salt out, partially at least. Or evaporate the water, melt the sugar and filtrate (or does salt dissolve in molten sugar?), but that risks pyrolysis of sugar. Or evaporate the water and try to get giant crystals of sugar and salt, which can be separated by hand. Or try some chemistry trick to replace the chloride ions by some other ion, then try one of the above tricks. But a filter based on size sounds simplest and may be commercially available. Probably still not worth the effort, though. PiusImpavidus (talk) 12:01, 19 December 2022 (UTC)[reply]

December 19

Vortex ring state

Are helicopters with coaxial rotors (like Kamov helicopters) less susceptible to vortex ring state? 2601:646:8A81:6070:CC33:2635:A453:3355 (talk) 06:39, 19 December 2022 (UTC)[reply]

They are clearly capable of entering VRS: see this (rather technical) paper on modelling the phenomenon in a Kamov Ka-32. [8] Given the physical causes of the phenomenon, and the layout of such helicopters, I can't see any obvious reason why they should be less susceptible in principle. AndyTheGrump (talk) 06:52, 19 December 2022 (UTC)[reply]