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December 3

How long is this problem in molecular biology?

In 2016, DeepMind turned its artificial intelligence to protein folding, a long-standing problem in molecular biology.

How long is this problem in molecular biology? Source HarryOrange (talk) 10:20, 3 December 2024 (UTC)

Even before the process of protein biosynthesis was discovered, it was known that small changes in the amino acid sequence could lead to major changes in protein structure. How the amino acid sequence determined the protein structure was an open question, but at the time one with no practical relevance, initially drawing little theoretical interest. That changed in 1969 when Cyrus Levinthal published the paper that gave rise to the term Levinthal's paradox. With the possibility to edit genes and synthesize proteins in the lab, it has now also become a problem of high practical relevance, but 1969 is a good starting date for the standing of the problem.  --Lambiam 15:05, 3 December 2024 (UTC)

I just came across this YouTube video: "How AI Cracked the Protein Folding Code and Won a Nobel Prize". It also gives the history of the problem.  --Lambiam 09:20, 6 December 2024 (UTC)

December 5

Birds with white cheeks

• 
  Silver-eared Mesia
• 
  White-cheeked Starling
• 
  Great Tit
• 
  White-cheeked Bushtit
• 
  White-cheeked Bullfinch
• 
  White-cheeked Bulbul

What is the evolutionary advantage - or purpose - of white "cheeks" on these disparate birds? Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 14:54, 5 December 2024 (UTC)

In great tits, the immaculateness of the black border of white cheek patches predicted social status and reproductive success, but there was no clear evidence that it played a role in mate choice (Ferns and Hinsley 2004).

Bird Coloration, Volume 2 (p. 186)

Alansplodge (talk) 15:47, 5 December 2024 (UTC)

Here's recent a review article about what's known about the genetics of bird color patterning. We know a lot less about this topic than about the genetics of patterning in insect wings. It strikes me that all birds follow that same general pattern scheme, with only the colors varying. So in a bird that is all one color, the scheme is there, but not apparent. As for the face, there are many selection pressures that could be occurring–or that might have occurred in the past–to be tested. First, if the pattern is found only in males, there's a good chance it is sexually selected (some trait is getting sexually selected for, but the face color might just be genetically or developmentally tied to it and just along for the ride). In some species, fights between males drive selection, and drawing one's opponents to peck somewhere other than the eyes would be strongly selected for. If female choice is strong, then costly-to-maintain signals are selected for. But there is also selection for confusing predators (such as about the size and position of the eyes), and for confusing prey. Finally, the feathers near the beak get a lot more wear and tear, so need to get replaced more often. Skipping adding color might make this process faster and/or cheaper. All this is guesswork on my part so make of it what you will. Abductive (reasoning) 19:09, 5 December 2024 (UTC)

Time dilation

I can't seem to get a straight answer: How many parts per trillion between Earth's most time travelly places+where are they? (1 answer for all points a "stationary" non-"antigraviting" (i.e. helicopter/airship) human could be that exist now (i.e. Mammoth Cave/the Chunnel/2 WTC's temporary roof but not the much higher place the permanent roof's planned to be or 10ft below the deepest ice dig a human could put their body. Humans could theoretically go 10ft lower but not as is), 1 answer for if under liquids also doesn't count Mariana Trench=sea level)

Some ppl say everywhere on an equipotential surface has the same speed of time from the 2 dilations canceling out. So Everest+Mariana should be extremest? Or the Kidd Creek Mine if under liquids doesn't count. I haven't been able to reproduce cancellation with the formulae or calculators though. Some gravitational dilation calculators want distance to center which is NOT geopotential (Chimborazo's furthest, Arctic seabed closest, or North Pole if has to touch air), some want g-force???. It's not g-force unless that calculator only works for the surfaces of spheres. Earth's gravitational dilation's strongest at the base of the gravity well where you'd be weightless. Google AI dumbass can be made to say both ellipsoid+geoid for the equal dilation surfaces. Some human who might know says it's the geoid. Some probably different human I don't remember says it's only equipotential on one of rotating vs inertial reference frame. How the hell can it depend on reference frame? Clocks can't both be later than each other when they reunite (very slowly to infintesimalize kinematic dilation from the trip). Some clock pair has to be most disparate when they reunite. Maybe it can still depend in some way without violating this logic? Presumably Cayambe's the place with the most kinematic time dilation? Furthest point of Earth's surface from the axis. Presumably axis points avoid more kinematic time dilation than any other points of the planet? Sagittarian Milky Way (talk) 00:20, 6 December 2024 (UTC)

Although the Earth can be considered a rotating sphere, I think the effect of its rotation on gravitational time dilation is small. Using the formula at Gravitational time dilation § Outside a non-rotating sphere, I compute that the fractional difference is about 1.1 × 10⁻¹⁶ per metre height difference (above sea level). The fractional difference of time dilation by the velocity difference between the poles and the equator is about 1.2 × 10⁻¹², so this will beat gravitational time dilation.  --Lambiam 02:41, 6 December 2024 (UTC)

How is Rainbow considered as application ?

How is Rainbow considered as application ? Source

I believe Rainbow is just a Rainbow, not a something to use. HarryOrange (talk) 22:42, 5 December 2024 (UTC)

The Okapi Framework has an app named "Rainbow", which we describe by, "Rainbow — a toolbox to launch a large variety of localization tasks." (Other than this I know nothing about Okapi and its app.)  --Lambiam 01:48, 6 December 2024 (UTC)

The link to the article about rainbows has been in the "applications" section from the start, in this edit, where the applications listed were Rainbow, Cosmic microwave radiation, Laser, and Laser fusion. The first two of those are phenomena, not technologies, so it's certainly unclear how to apply equations to them - with what end in mind? Subsequently Radio wave, Gravitational lens, and Black-body radiation joined the list. Although radio waves are phenomena there are many technological things we might seek to do with them, and in the course of trying to make things work we might need numbers that come from an equation. In other cases the application might simply be to obtain numbers, to study a phenomenon like radiation. But I agree, I can't imagine in what way we could even investigate a rainbow with these equations, and so I don't understand how it's an "application". I think it might be a reference to this Feynman lecture. Near the bottom is a discussion of rainbows:

“While I’m on this subject I want to talk about whether it will ever be possible to imagine beauty that we can’t see. It is an interesting question. When we look at a rainbow, it looks beautiful to us. Everybody says, “Ooh, a rainbow.” (You see how scientific I am. I am afraid to say something is beautiful unless I have an experimental way of defining it.) But how would we describe a rainbow if we were blind? We are blind when we measure the infrared reflection coefficient of sodium chloride, or ...”

Then

“On the other hand, even if we cannot see beauty in particular measured results, we can already claim to see a certain beauty in the equations which describe general physical laws. For example, in the wave equation (20.9), there’s something nice about the regularity of the appearance of the x, the y, the z, and the t. And this nice symmetry in appearance of the x, y, z, and t suggests to the mind still a greater beauty which has to do with the four dimensions, the possibility that space has four-dimensional symmetry, the possibility of analyzing that and the developments of the special theory of relativity. So there is plenty of intellectual beauty associated with the equations.”

So, OK. But it's tenuous, and would be better removed or explained.  Card Zero  (talk) 05:15, 6 December 2024 (UTC)

The disambiguation page for Rainbow treats the various uses of the word equitably without over indulgence in any isolated usage such as the artistic to the unfair extent of shunning the physical reality that the electromagnetic wave understanding of light is the physicist's most applicable tool and that for this its equations are fundamental. Philvoids (talk) 11:47, 6 December 2024 (UTC)

OK? But this question is about Electromagnetic_wave_equation#Applications (which is easily missed, since it's hidden under the word "source"). Should that really list "rainbow" as an "application"?  Card Zero  (talk) 12:37, 6 December 2024 (UTC)

I agree not, and others in the 'Applications' list are also inappropriate ('black hole'?). Perhaps a further list of 'Phenomenon' (or similar) should be created? {The poster formerly known as 87.81.230.195} 94.1.211.243 (talk) 13:20, 6 December 2024 (UTC)

That's Black-body radiation, but yeah.  Card Zero  (talk) 15:03, 6 December 2024 (UTC)

That stuff was added on Feb 9, 2006,[1] by a user who's no longer active. But if their email is available, someone could try sending them a note. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:42, 6 December 2024 (UTC)

December 6

Geodesics for Massive and Massless Particles

In general relativity, do massive and massless particles follow the same geodesic? Why or why not? Malypaet (talk) 23:19, 6 December 2024 (UTC)

According to the Einstein field equations, the worldline traced by a particle not subject to external, non-gravitational forces is a geodesic. Each particle follows its own worldline. Two particles that share their worldline are at all times at the same location and so have identical velocities.  --Lambiam 08:46, 7 December 2024 (UTC)

A massless particle must follow a null geodesic and massive particle must follow a time-like geodesic (in my limited understanding). catslash (talk) 22:20, 7 December 2024 (UTC)

So a massive particle with a velocity infinitely close to that of a photon (under the influence of a massive object) will have a geodesic infinitely close to that of the photon, right? Or is there another explanation and which one? Malypaet (talk) 22:11, 9 December 2024 (UTC)

I believe that is correct (perhaps there is an expert to hand who could confirm this?). catslash (talk) 23:42, 9 December 2024 (UTC)

In some frame of reference, the massive particle is at rest and so its spacetime interval along its geodesic is as spacelike time-like as can be (and thereby as non-null-like as can be for a non-tachyonic particle). So it depends on the point of view of the observer. Simplifying the case to special relativity and considering a particle traveling with speed $v$ in the x-direction, the spacetime interval $\Delta {s}$ between two events separated by a time $\Delta t$ is given by:

$(\Delta s)^{2}=(\Delta ct)^{2}-(\Delta x)^{2}=(\Delta ct)^{2}-(\Delta vt)^{2}=(c^{2}-v^{2})(\Delta t)^{2}.$

In frames of reference in which $v$ approaches $c,$ the interval can become arbitrarily small, making it experimentally indistinguishable from that of a massless particle.  --Lambiam 07:40, 12 December 2024 (UTC)

@User:Lambian, could you re-read the spacetime interval section? I reckon that if there exists a frame of reference in which an interval is purely a time difference, then it is time-like, and if there exists a frame of reference in which the interval is purely a difference in location, then it is space-like. catslash (talk) 10:14, 12 December 2024 (UTC)

Yes, I used the wrong term, now corrected.  --Lambiam 07:30, 13 December 2024 (UTC)

December 7

Source

The articles Radium dial and Radium Girls blithely speak of the element as though infinitesimal quantities of pure metal were employed, whereas the iron law of economics dictate that some partially processed yellowcake with a minuscule (and difficult to extract) percentage of some radium salt would be the raw material. Does someone have this information? Doug butler (talk) 22:02, 7 December 2024 (UTC)

The paint, marketed as Undark, was a powdery mixture of radium sulfate, zinc sulfide and phosphor.^[2] The young women had to mix this powder with water and glue before it could be applied. The radium-226 percentage had to be high enough to produce sufficient luminosity. For its pernicious effect, its chemical form is immaterial.  --Lambiam 23:19, 7 December 2024 (UTC)

the chemical form is mostly immaterial. Radium sulfate is insoluble enough that it's unable to get a hold in the physiology and so has only minimum effects. 176.0.131.138 (talk) 09:45, 8 December 2024 (UTC)

Because radium is not an actinide it can be easily separated from the other elements. So the economic pressure is not to give away something to a customer what you can sell to another customer. 176.0.131.138 (talk) 09:52, 8 December 2024 (UTC)

December 8

Unit questions

1. How widely is the metric system used in the Philippines? Do people there use metric for both short and long distances? Is centimeter a widely used unit in the Philippines? Does Philippines use metric mass and volume units almost exclusively?
2. How widely is the metric system in former British colonies in Africa (Gambia, Sierra Leone, Ghana, Nigeria, Rwanda, Uganda, Kenya, Tanzania, Malawi, Zambia, Zimbabwe, Botswana, Namibia, South Africa, Eswatini, Lesotho)? Are there still some applications for which some people might use imperial units?
3. How widely is the metric system used in Caribbean island countries? Do these countries use imperial system widely?
4. Is there any application that commonly uses fractions with metric units?
5. Can exact one-third of a meter be measured in most devices, as its decimal representation contains just repeating threes? --40bus (talk) 20:56, 8 December 2024 (UTC)

It's worth pointing out that item 5 is one reason the English System is preferable, because feet, yards and miles, as well as acres, are easily divided by 3. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:19, 8 December 2024 (UTC)

This Australian, having now worked with the metric system for two thirds of his longish life, has never screamed "I wish this unit was divisible by three!" HiLo48 (talk) 06:58, 9 December 2024 (UTC)

Is there any metric unit, other than units of time, which is easily divisible by 3? --40bus (talk) 06:14, 9 December 2024 (UTC)

1 metre is easily divided by 3. A third of a metre is 1/3 meter. Do you mean 1/3 meter cannot be precisely written in decimal form? Just use fractions. problem solved. 2001:8003:429D:4100:186E:C147:C792:1055 (talk) 09:25, 9 December 2024 (UTC)

The Metric system article lists the basic units. For several of them, division by 3 doesn't seem like it would be all that useful. Temperature, for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:28, 9 December 2024 (UTC)

1. Have you read Metrication? The article says The Philippines first adopted the metric system in 1860 because of the Spanish Colonial government; imperial units were introduced by the American Colonial government; however, the metric system was made the official system of measurement in 1906 through Act No. 1519, s. 1906. US customary units still in use for body measurements and small products while the metric system is used for larger measurements; e.g. floor area, highway length, tonnage. Shantavira|^{feed me} 09:30, 9 December 2024 (UTC)

December 9

I'm collecting examples of a purely "physical property of a physical property" (of a body).

By (purely) physical property, I mean any measured property whose measurement depends on (purely) physical [dimensions usually measured by physical] units. A few examples of physical properties include: momentum, energy, electric charge, magnetic charge, velocity, and the like (actually the elementary particles carry plenty of purely physical properties).

However, by purely (physical property), I mean that it's not also a mathematical or geometric property, i.e. excluding: numeric value (size) of a physical property, density of energy ("density" is also a mathematical concept - e.g. in density of primes), center of mass ("center" is also a geometric concept), and the like. But I do consider velocity to be a purely physical property, because its description invloves (e.g.) the temporal dimension (which actually "flows" - whereas the way time "flows" can't be described by any mathematical equation. Anyway this "flow" is another issue I don't want to discuss in this thread).

So, for finding a purely "physical property of a physical property" (of a body), I've thought about one example so far: the physical units dimensions of any physical property.

I'll be glad for any additional examples. 2A06:C701:746D:AE00:ACFC:490:74C3:660 (talk) 11:22, 9 December 2024 (UTC)

The physical units in which physical quantities are expressed (such as erg, eV, foe, joule, therm) are somewhat arbitrary social constructions. The dimension of a physical quantity is a much more purely physical property. It is a point in an abstract vector space. One may argue that there is some arbitrariness in the choice of the basis of this space. The SI standard uses time (${\mathsf {T}}$), length (${\mathsf {L}}$), mass (${\mathsf {M}}$), electric current (${\mathsf {I}}$), absolute temperature (${\mathsf {\Theta }}$), amount of substance (${\mathsf {N}}$) and luminous intensity (${\mathsf {J}}$) as the basis, but other choices for the base physical dimensions span the same vector space.  --Lambiam 12:42, 9 December 2024 (UTC)

Yes, I really meant "dimensions" of a physical property, thank you. 2A06:C701:746D:AE00:ACFC:490:74C3:660 (talk) 14:24, 9 December 2024 (UTC)

December 10

Proton decay and cosmic expansion

A friend's physicist father opined that the phantom energy causing more and more rapid cosmic expansion will never be as strong as the attraction of the strong force, so protons will not be ripped apart in the big rip. Be that as it may, if the phantom energy is counter to the strong force, however weakly, wouldn't protons, consisting of quarks held together by the strong force, have an increased rate of decay in the far future? I have heard that the theories that protons do undergo decay at all have not yet been supported by experiments, though. Rich (talk) 13:41, 10 December 2024 (UTC)

We have to suppose quite a few things to get to the question: suppose there is some form of proton decay, suppose there is phantom energy, and suppose that the phantom energy reaches some plateau before getting to an energy scale high enough to create a quark-gluon plasma. Would protons then decay at a faster rate? I don't think that's necessarily the case. Proton decay is not the same kind of process as making a quark-gluon plasma. I believe the answer depends on what kinds of operators lead to the hypothetical proton decay. --Amble (talk) 22:49, 10 December 2024 (UTC)

Thanks, nice clarification of the issues. You've thought through the issues more clearly and knowledgeably than I did. That's a valuable answer. But having said that, is there more information available about current speculations and theoretical work by physicists concerning proton decay interacts with cosmic expansion? I can't be the only one wondering about it and many of the people wondering about it would be physicists.Rich (talk) 07:30, 13 December 2024 (UTC)

The nearest paper I came across is [3], but there "proton decay" actually means p⁺ → n + e⁺ + ν and not p⁺ → e⁺ + 2γ. --Amble (talk) 20:22, 13 December 2024 (UTC)

December 13

What is the most iconic tornado photo

Request for opinions
The following discussion has been closed. Please do not modify it.
What photo of a tornado would you say is the most iconic? I'm researching the history of tornado photography for an eventual article on it and I've seen several specific tornadoes pop up over and over again, particularly the Elie, Manitoba F5 and the "dead man walking" shot of the Jarrel, Texas F5. Which would be considered more iconic? ApteryxRainWing🐉 | Roar with me!!! | My contributions 17:21, 13 December 2024 (UTC) At the top of this page is a bullet point stating "We don't answer requests for opinions, predictions or debate": this reads to me like a request for subjective opinions. Perhaps you would like to consider what quantifiable and referenceable metric would answer what you want to know? Presumably you also want only real tornadoes considered? Otherwise some might nominate the the twister from The Wizard of Oz, or from more recent tornado-related movies – Sharknado, anyone? :-). {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 18:07, 13 December 2024 (UTC) "Swegle Studios" has a couple of YouTube videos dedicated to the backstories of famous tornado photos and video; you might find them useful in your research. Photos, Videos. Matt Deres (talk) 18:40, 13 December 2024 (UTC) I googled "most iconic tornado photo" and a bunch of different possibilities popped up. I don't see how you could say that any given photo is the "most iconic". ←Baseball Bugs What's up, Doc? carrots→ 18:57, 13 December 2024 (UTC)

December 15

help to identify File:Possible Polygala myrtifolia in New South Wales Australia.jpg

possible w:Polygala myrtifolia in New South Wales Australia

Did I get species right? Thanks. Gryllida (talk, e-mail) 06:56, 15 December 2024 (UTC)

related: https://species.wikimedia.org/wiki/Wikispecies:Village_Pump#help_to_identify_species Gryllida (talk, e-mail) 06:57, 15 December 2024 (UTC)

FWIW, I can't detect any visible differences between the plant in this photo and the ones illustrated in the species and the genus articles. However, the latter makes it clear that Polygala is a large genus, and is cultivated, with hybrids, so it's possible that this one could be a close relative that differs in ways not visible here, such as in the bark or roots. That may or may not matter for your purposes. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 10:11, 15 December 2024 (UTC)

How to address changes to taxonomy

Hi all, I am a biology student brand new to wiki editing who is interested in cleaning up small articles/stubs for less known taxa. One that I've encountered is a mushroom that occurs in the pacific northwest (Fomitopsis ochracea). The article mentions that this fungus is occasionally mistaken for another fungus, Fomitopsis pinicola.

However, the issue I've run into is that F. pinicola used to be considered a single species found around the world, but relatively recently was split into a few different species. The original name was given to the one that occurs in Europe, and the one in the pacific northwest (and thus could be mistaken for F. ochracea) was given the name Fomitopsis mounceae.

The wiki page says

Historically, this fungus has been misidentified as F. pinicola. When both species are immature, they can look very similar, but can be distinguished by lighting a match next to the surface of the fungus.[1] F. pinicola will boil and melt in heat, while F. ochracea will not.[1]

Since the source says pinicola (as likely do most/all other sources of this info given the change was so recent), and since technically it's true that they used to be mistaken for it... what would be the most appropriate way to modernize that section?

My questions are: Should I replace F. pinicola with F. mounceae? Or is that wrong because the source doesn't refer to it by that name? Would it be better to write something like (now known as/considered F. mounceae) next to the first mention of the species? Or is that a poor choice because it implies all the members of F. pinicola were renamed F. mounceae?

Any advice on how to go about updating this section is incredibly appreciated
TheCoccomycesGang (talk) 10:21, 15 December 2024 (UTC)

First, take these sorts of questions to the relevant Wikiproject, in this case Wikipedia talk:WikiProject Fungi. I am not as familiar with the consensus at WP:FUNGI, but it seems like they defer to Species Fungorium/Index Fungorium and Mycobank to decide. Those sources presently seem to consider Fomitopsis pinicola a good species. Also, be careful about "replacing", there are rules to ensure the continuity of the article history. By the way, there is a hilarious but unencyclopedic/copyvio recipe appended to the Fomitopsis mounceae article. Abductive (reasoning) 11:09, 15 December 2024 (UTC)

Thanks for the tips, I didn't know about projects so I'll go read up on that. And thanks for the warnings about replacing things. I've been reading a lot of help pages, but I'm still in the process of learning the all conventions and what mechanics break if you do things the wrong way.

I actually saw the recipe ages ago before I made my account and completely forgot about it... it was one of many things that prompted me to get into wiki editing. TheCoccomycesGang (talk) 23:12, 15 December 2024 (UTC)

Does stopping masturbation lead to sperm DNA damage?

I'm looking for information on the potential link between the frequency of ejaculation (specifically through masturbation) and sperm DNA damage. I've come across some conflicting information and would appreciate it if someone could point me towards reliable scientific studies or reviews that address this topic.

Specifically, I'm interested in whether prolonged periods of abstinence from ejaculation might have any negative effects on sperm DNA integrity. Any insights or links to relevant research would be greatly appreciated. HarryOrange (talk) 17:08, 15 December 2024 (UTC)

Only males may abstain from sperm-releasing Masturbation that serves to flush the genital tract of old sperm that in any case will eventually dissipate. No causal relationship between masturbation and any form of mental or physical disorder has been found but abstinence may be thought or taught^{1 2 3} to increase the chance of wanted conception during subsequent intercourse. Philvoids (talk) 00:51, 16 December 2024 (UTC)

There's many rumors about that topic. One is that not ejaculating frequently increases the risk of developing prostate cancer. Abductive (reasoning) 01:02, 16 December 2024 (UTC)

Nothing really conclusive but there's some evidence that short periods are associated with lower DNA fragmentation, see

• Du, Chengchao; Li, Yi; Yin, Chongyang; Luo, Xuefeng; Pan, Xiangcheng (10 January 2024). "Association of abstinence time with semen quality and fertility outcomes: a systematic review and dose–response meta‐analysis". Andrology. 12 (6): 1224–1235. doi:10.1111/andr.13583. ISSN 2047-2919.
• Hanson, Brent M.; Aston, Kenneth I.; Jenkins, Tim G.; Carrell, Douglas T.; Hotaling, James M. (16 November 2017). "The impact of ejaculatory abstinence on semen analysis parameters: a systematic review". Journal of Assisted Reproduction and Genetics. 35 (2): 213. doi:10.1007/s10815-017-1086-0. ISSN 2047-2919. PMC 5845044. PMID 29143943.
• Ayad, Bashir M.; Horst, Gerhard Van der; Plessis, Stefan S. Du; Carrell, Douglas T.; Hotaling, James M. (14 October 2017). "Revisiting The Relationship between The Ejaculatory Abstinence Period and Semen Characteristics". International Journal of Fertility & Sterility. 11 (4): 238. doi:10.22074/ijfs.2018.5192. ISSN 2047-2919. PMC 5641453. PMID 29043697.

for example. Alpha3031 (t • c) 02:12, 16 December 2024 (UTC)

Mature sperm cells do not have DNA repair capability.^[4] Inevitably, as sperm cells get older, they will naturally and unavoidably be subject to more and more DNA damage. Obviously, freshly produced spermatozoa will, on average, have less DNA damage. It is reasonable to assume that the expected amount of damage is proportional to the age of the cells, which is consistent with what studies appear to find. Also, obviously, the more the damage is to a spermatozoon fertilizing an oocyte, the larger the likelihood that the DNA repair in the resulting zygote, which does have DNA repair capability, will be incomplete. The studies I've looked at did not allow me to assess how much this is of practical significance.  --Lambiam 09:40, 16 December 2024 (UTC)

December 16

Abelian sandpile model

Thanks to those who answered my last question, I think it should be added to a disambiguation page. If anyone wants to help me write that, reach out.

A sandpile seems disorganized and inert, but these are critically self-organizing. Do the frequency and size of disturbances on sand dunes and snowy peaks follow power law distribution? Gongula Spring (talk) 01:18, 16 December 2024 (UTC)

Shouldn't this be at the Math Desk? Abductive (reasoning) 05:12, 16 December 2024 (UTC)

If the question is not about the model mentioned in the heading but about the physical properties of sand dunes and snowy peaks, this here is the right section of the Reference desk.  --Lambiam 08:51, 16 December 2024 (UTC)

I await a non-mathematical answer. Abductive (reasoning) 09:23, 16 December 2024 (UTC)

It depends is probably a fairly reasonable non-mathematical answer for these kinds of systems. For sand dunes anyway, sometimes avalanche frequency is irregular and the size distribution follows a power law, and sometimes it's close to periodic and the avalanches span the whole system. It seems there are multiple regimes, and these kinds of systems switch between them. Sean.hoyland (talk) 09:35, 16 December 2024 (UTC)

Hi, this is an interesting and somewhat open question! A lot of work is done on these models but much less on careful analyses of real dunes. I did find this dissertation that is freely accessible and describes some physical experiments and how well they fit various models. The general answer seems to be that the power law models are highly idealized, and determining the degree to which any real system's behavior is predicted by the model ahead of time is very difficult. Update: This is one of the earlier important works on the topic and it does include discussion of how well the model fits experiments.SemanticMantis (talk) 17:21, 16 December 2024 (UTC)

Polar night

Are there any common or scientific names for types of polar night? The types that I use are:

• polar night - meaning a day when sun's altitude remains below horizon entire day (there is no daylight at solar noon, only civil twilight), occurring poleward from 67°24′ north or south
• civil polar night - meaning a day when sun's altitude remains below -6° entire day (there is no civil twilight at solar noon, only nautical twilight), occurring poleward from 72°34′ north or south
• nautical polar night - meaning a day when sun's altitude remains below -12° entire day (there is no nautical twilight at solar noon, only astronomical twilight), occurring poleward from 78°34′ north or south
• astronomical polar night - meaning a day when sun's altitude remains below -18° entire day (there is no astronomical twilight at solar noon, only night), occurring poleward from 84°34′ north or south

These names were changed on Polar night article, and I wnat to know whether these named I listed are in use in any scientific papers, or in common language. (And I posted that question here and not in language desk because I think that this is not related to language very tightly.) --40bus (talk) 18:56, 16 December 2024 (UTC)

Some definitions at The Polar Night (1996) from the Aurora Research Institute. Alansplodge (talk) 22:55, 16 December 2024 (UTC)

These seem to be generalizable as: X polar night is a period, lasting not less than 24 hours, during which the sun remains below the horizon and there is no X twilight. The specific definitions depend then on the specific definitions of civil/nautical/astronomical twilight. These can be defined with a subjective observational standard or with an (originally experimentally determined) objective standard.  --Lambiam 10:36, 17 December 2024 (UTC)

FWIW, I as a former amateur astronomer have never previously thought about the question of Polar twilight and night nomenclatures, but immediately and completely understood what the (previously unencountered) terms used in the query must mean without having to read the attached descriptions. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 16:34, 17 December 2024 (UTC)