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January 6

Does the energy belonging to an electromagnetic field, also belong (or is considered to belong) to the space carrying that field?

HOTmag (talk) 18:41, 6 January 2025 (UTC)

It would be unusual to express the situation in such terms. Since the notion of energy "belonging to" some entity is not itself a physical concept – any practical approach to energy bookkeeping that satisfies the law of conservation of energy will do – this cannot be said to be wrong. It is, however, (IMO) not helpful. Does an apple belong to the space it occupies? Or does that space belong to the apple?  --Lambiam 23:37, 6 January 2025 (UTC)

First, I let you replace the notion of energy "belonging to" some entity, by the notion of energy "attributed to" some entity, or by the notion of energy "carried by" some entity, and the like. In other words, I'm only asking about the abstract relation (no matter what words we use to express it), between the energy and the space carrying the electromagnetic field, rather than about the specific term "belong to".

Second, I'm only asking about what the common usage is, rather than about whether such a usage is wrong or helpful.

The question is actually as follows: Since it's accepted to attribute energy to an electromagnetic field, is it also accepted to attribute energy to the space carrying that field?

So, is your first sentence a negative answer, also to my question when put in the clearer way I've just put it? HOTmag (talk) 03:28, 7 January 2025 (UTC)

The answer remains the same. It would be a highly unusual use of language to "attribute" electromagnetic energy to a volume of space, in quite the same way as it would be strange to "attribute" the mass of an apple to the space the apple occupies. But as long as an author can define what they mean by this (and that meaning is consistent with the laws of physics), it is not wrong.  --Lambiam 13:21, 7 January 2025 (UTC)

An electromagnetic field that we may (even tenuously) conceive to have the form of a massless photon has, like the aforementioned apple (a biological mass) its own unique history, that being a finite path in Spacetime. I reject apparent effort to give spacetime any kind of identity capable of owning, or even anticipating owning or remembering having owned anything at all. Concepts of owning, attributing or whatever synonymous wordplay one chooses all assume identification that can never be attached to the spacial location of an em field. The energy of the photon is fully accounted for, usually as heat at its destination, when it is absorbed and no lasting trace remains anywhere. I am less patient than Lambian in my reaction to this OP who under guise of interest in surveying "what is commonly accepted" returns in pursuit of debate by patronisingly "allowing" us to reword his question in abstract "words that don't matter" to make it purportedly clearer and worth responders' time. Philvoids (talk) 14:55, 7 January 2025 (UTC)

chill outRich (talk) 02:15, 17 January 2025 (UTC)

Thank you Lambiam for your full answer. I always appreciate your replies, as well as your assuming good faith, always. HOTmag (talk) 15:08, 7 January 2025 (UTC)

January 8

Australian for double-decked bridge?

On a topographic map (or on any other kind of map, like a track diagram), what symbol represents a railroad bridge which is directly above and collinear with another railroad which is either on a lower deck of the same bridge, or else is at grade (as in, for example, a narrow-gauge line on a coal trestle above a standard-gauge one)? 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 06:35, 8 January 2025 (UTC)

Our List of multi-level bridges#Australia article only lists two multi-level bridges in Australia, neither of which seem to fit your criteria. Alansplodge (talk) 19:16, 8 January 2025 (UTC)

Clarification: in this case, "Australian" is meant figuratively (as in that Fosters ad) -- what I was really asking was the representation of such a bridge on a map. 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 01:03, 9 January 2025 (UTC)

What Fosters ad? That link doesn't help, and Australians don't drink Fosters, so won't have seen any ad for it. HiLo48 (talk) 01:15, 9 January 2025 (UTC)

Nonsense. I have it on good authority—Fosters own ads on TV in the US two decades ago—that all Australians do nothing but drink Fosters all day because it is the one true Australian beer. DO NOT ARGUE WITH YOUR CAPITALIST OVERLORDS' CULTURAL APPROPRIATION! Um, I mean, Foster's Lager had a bunch of ad campaigns promoting their image as being Australian. See its article for details. Search youtube for fosters australian to see some examples. DMacks (talk) 01:28, 9 January 2025 (UTC)

HiLo48, I think it's drunk a little here; sometimes I'll collect containers for the deposit money, and some weeks ago I found an empty Foster's can. Nyttend (talk) 09:50, 13 January 2025 (UTC)

Nit pick, at grade means at the same height, you mean grade separated. Greglocock (talk) 05:32, 9 January 2025 (UTC)

It's all grade-separated (rail-line vs rail-line). I assume they mean one rail-line is on the ground (in contrast with being on a bridge as the first example). The term is annoying, but we're stuck with terms like at-grade railway. DMacks (talk) 05:38, 9 January 2025 (UTC)

Yes, in this case "at grade" means at ground level -- with the narrow-gauge line on the trestle directly above it! 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 06:25, 9 January 2025 (UTC)

Only example of a multi-level bridge or viaduct I've found so far in the world having a WP article is Highline Bridge (Kansas City, Kansas). DMacks (talk) 06:32, 9 January 2025 (UTC)

There is one on the Driving Creek Railway (no photo of this detail in the article, but a few in c:Category:Driving Creek Railway). I've seen mentions of some others that are long-gone (or have one or both levels now used for other modes). Lots of pictures of old New York City have an el with rails in the street under it, but nothing still existing or in-use. DMacks (talk) 07:25, 9 January 2025 (UTC)

DMacks did your pictures come from Googling Manhattan el? That island has almost no elevated rail left but had a whole 4 route el system by 1880 that coexisted with the subway (of 1904-2025+) till the 1940s/50s/last gasp in the Bronx 1974 so el's less commonly used than Chicago (Chicago also says L which is a specific line in NY that doesn't leave the tunnel till pretty far out). The Manhattan el system was sort of it's own thing didn't share track with subway trains in Manhattan while the 4 els shared the same downtown terminus (South Ferry)+split & re-merged as a coherent system. Nevertheless 40% of NYC subway track is elevated & very few of the dozens of subways (ABCDEF<F>GJLMNQRSSSSWZ123456<6>7<7>) are 100% tunnel there's even elevateds in Manhattan (the BDNQ entering the island on a road-rail bridge diving underground before it even stops, the JMZ doing the same thing, the Grand Central trains going from plateau tunnel to slope orifice to lowland el to river bridge, the 1 train crossing an ex-stream valley aboveground for 0.5 miles for slope reduction, the 1 going aboveground for the last ~mile before the river bridge & the elevated parts of the West Side Freight Line that haven't been turned into an aerial park). There are places in New York City with multiple co-linear rail levels above a street they're just not famous. There's even multiple co-linear levels of subway platforms with fare stuff underneath then a street below that. An interesting article about the ancient (1868) Manhattan els. Maybe the closest real thing to a steampunk subway system (steam locomotives for decades till electrification) Sagittarian Milky Way (talk) 04:38, 15 January 2025 (UTC)

There are a several parallel-stacked underground rail platforms and tunnels in the New York Subway system that are currently in-use, such as the Lexington Avenue–63rd Street station and continuing through the 63rd Street Tunnel. I'm not sure if other large and/or old subway systems have them, but I wouldn't be surprised if Boston or others do. Unlike a raised line, underground is the issue of the cross-sectional geometry of the tube to be strong and minimize construction cost for a given number of lines. Track-maps seem to illustrate them as dotted lines. See for example that 63rd St staion at , where the "top" is one of the two F and one of the two Q, and the "bottom" is the other of each of them. DMacks (talk) 07:55, 17 January 2025 (UTC)

NYC subways stacked is less common above-grade than below-grade, below-grade it's nothing special. Though not ideal you could cram so much stuff without being so deep you can go under skyscrapers. The 6th Avenue stack has 6 tracks (PATH not shown) could fit 8 tracks 4 express, the Lexington Avenue stack fits 4-track 2-platform express stations between the foundations of skyscrapers only 75 feet apart which'd otherwise need 100ft or almost I don't know exact number. Here's a photo of one of the stacked elevated subways. Shown near the bottom with dotted/dashed lines on that track map site. Sagittarian Milky Way (talk) 22:36, 17 January 2025 (UTC)

Right, so how would one show such a bridge on a map? 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 22:51, 9 January 2025 (UTC)

Exactly the same as a map would indicate a railway under a roadway or a roadway under a railway (or anything under anything), of which there are numerous examples on maps, i.e. the lower railway disappears under the upper railway and then reappears at the other end of the bridge. Shantavira| 10:27, 10 January 2025 (UTC)

Thanks! Which would actually make it easier if the two railroads are of different gauges and one of them is at grade, as in my (fictional) example (I'm currently mapping the station layouts on the North Western Railway for a possible scenario pack for Train Sim Classic and/or Train Sim World, and there's a setup just like I describe at Arlesburgh West -- the narrow-gauge Arlesdale Railway goes up on a coal trestle above an at-grade siding of the North Western) -- in that case, the standard-gauge line goes under the ends of the bridge lengthwise and disappears, while the narrow-gauge line remains continuous on the bridge deck, and because they have different symbols there's no confusion! 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 22:11, 10 January 2025 (UTC)

January 11

Pork belly and microwaves

Why does pork belly always seem to pop in a microwave whenever I cook it in there? It also splatters, too, which creates a mess I have to clean up. Kurnahusa (talk) 02:53, 11 January 2025 (UTC)

Boiling of intracellular fluid? 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 07:10, 11 January 2025 (UTC)

I agree with the IP. Also food in a microwave should always be covered. Microwave plate covers are widely available. Shantavira| 09:52, 11 January 2025 (UTC)

Pork belly contains a layer of fat. Fat tends to heat up very fast in the microwave. This brings watery fluids in contact with the hot fat quickly to a boil, well before the boiling temperature would have been reached in lean meats. The splattering happens when internal steam bubbles under high pressure force their way out and pop.  --Lambiam 09:17, 12 January 2025 (UTC)

Thank you! Have always wondered why my food pops in the microwave sometimes. Kurnahusa (talk) 19:59, 14 January 2025 (UTC)

Hence the "bang" part of bangers and mash? ←Baseball Bugs carrots→ 01:46, 16 January 2025 (UTC)

When you're microwaving them, of course, lol. Generally I think any type of a fatty cut of meat will pop in there. Kurnahusa (talk) 00:45, 19 January 2025 (UTC)

Which bird species?

I found this picture on Commons. Is this really a mallard (Anas platyrhynchos)? We have lots of mallards here in Sweden where I live, and nor male or female looks like that.

I'm sure it belong to Anseriformes, yes... but what kind of bird species?

// Zquid (talk) 21:48, 11 January 2025 (UTC)

A female gadwall seems most likely, although a lot of female dabbling ducks are rather similar. Mikenorton (talk) 23:31, 11 January 2025 (UTC)

Which primate species?

I found this picture on Commons. Description says Purple-faced langur, and so did the category. I changed the category to Semnopithecus vetulus, but I'm not sure the picture shows Purple-faced langur/Semnopithecus vetulus.

Can someone tell me what kind of primates?

// Zquid (talk) 21:59, 11 January 2025 (UTC)

Going by the long nose and concave facial profile, that looks to me like a macaque. In fact, based on the ludicrous hairstyle, the first second last on the list, Toque macaque, is indicated. It is endemic to Sri Lanka like the Purple-faced langur. These individuals in the picture do have very purple faces, I must admit. Perhaps it was mating season and they go like that? But monkeys tend to send that kind of signal via the butt, not the face. Our article says "With age, the face of females turns slightly pink. This is especially prominent in the subspecies M. s. sinica", so I suppose that could be it.

It was convenient that this species was wrongly sorted to the top of the alphabetical list.  Card Zero  (talk) 01:30, 12 January 2025 (UTC)

Flying off to infinity in a finite time

In "Newton's law of motion", chapter Singularities we find this text: "It is mathematically possible for a collection of point masses, moving in accord with Newton's laws, to launch some of themselves away so forcefully that they fly off to infinity in a finite time."

How can one write such a thing, when by definition infinity has no limit and whatever the speed of a point mass, it will therefore never reach infinity, that is to say a limit that does not exist? Malypaet (talk) 22:07, 11 January 2025 (UTC)

Did he actually refer to his own work as "Newton's laws"? ←Baseball Bugs carrots→ 23:16, 11 January 2025 (UTC)

Looking at the citation, we find an article entitled "Off to infinity in finite time". I didn't find it at all answers your question, though. What does it mean? --jpgordon 02:48, 12 January 2025 (UTC)

I would assume it means there's some finite time ${\displaystyle T}$ in the future such that, for any natural number ${\displaystyle n}$, there's a time ${\displaystyle t<T}$ such that the object is more than ${\displaystyle n}$ meters away at every time between ${\displaystyle t}$ and ${\displaystyle T}$.

What happens to the object after time ${\displaystyle T}$ seems to be unspecified. Maybe it's just gone? --Trovatore (talk) 05:36, 12 January 2025 (UTC)

If the point mass flies off to infinity in finite time, its velocity must be infinite. But simply having infinite velocity in itself isn't a real problem, if the velocity is held for an infinitesimal period of time. Therefore the statement is made in terms of distance.

Newtons laws occasionally give some infinities if you put in zeros at the wrong place. What it really tells us is that there're no point masses in real life – as far as Newton is concerned. PiusImpavidus (talk) 11:21, 12 January 2025 (UTC)

No, the velocity does not have to be infinite. You can have finite velocity at every moment before the time at which the distance approaches infinity. You just need the integral of the velocity to diverge to infinity. --Trovatore (talk) 18:26, 12 January 2025 (UTC)

Trovatore, the cited source states: "To develop a flavor for how the “wedges” of initial conditions are found, notice that, in the limit, m3 has to move infinitely fast from m1, m2 to m4, m5 ; this happens only when m3 starts arbitrarily close to m1 and m2 while m4, m5 already are close together. Consequently, the limiting configuration is a m1, m2, m3 triple collision with a simultaneous binary collision of m4, m5. ". Apparently, it is this infinite speed in the limit that is behind the "Flying off to infinity" claim. Nevertheless, it is still an example of finite-time singularities as I noted below in my response to this query. Modocc (talk) 18:46, 13 January 2025 (UTC)

(ec) The bit you should have emphasized is "in the limit". The authors here are (slightly imprecisely) rephrasing "the limit of the speed is infinite" as "moves infinitely fast in the limit". But at any time before the singularity, the speed is finite, and at or after the singularity, I doubt it really makes sense to talk about the speed (I'd have to examine this point a little more closely).

Anyway, what I wrote above is correct, with no modification required. --Trovatore (talk) 18:51, 13 January 2025 (UTC)

I don't disagree with your valid points... I'm just pointing out the authors' various claim(s)... such as "...a m1, m2, m3 triple collision with a simultaneous binary collision of m4, m5." Modocc (talk) 19:09, 13 January 2025 (UTC)

In addition, we seem to be in agreement (far more than we differ). For example, the authors assert that "...m3 has to move infinitely fast...", echoing what PiusImpavidus said, in the limit. In other words, the infinities at the singularities are arrived at with the integrals, in theory at least. Modocc (talk) 20:13, 13 January 2025 (UTC)

The question should be raised at Talk:Newton's laws of motion instead of on this desk where the OP extracts an incomplete statement about Newton's laws of motion#Singularities. Important provisos lack and we are left in doubt about what is happening that may involve launching by unspecified agency, and whether "fly off to infinity in a finite time" means (i)"start in a finite time on an infinite outward path" or (ii)"travel to infinity in a finite time". The OP sees meaning (ii) and queries it as untenable. The alternative (i) can be taken to mean achieving Escape velocity.

I propose the following rewording to clarify the article text.

Singularities

Mathematicians have investigated the behaviour of collections of point masses that may approach one another arbitrarily closely, possibly collide together, and move in accord with Newton's laws. In simulations that impose no relatavistic speed limit, singularities of unphysical behavior are observed. For example, a particle velocity can accumulate through successive near-collisions to the extent of theoretically departing the system to infinity in a finite time. Philvoids (talk) 15:23, 12 January 2025 (UTC)

None of the references talk about simulations (certainly not the article linked to above , and apparently none of the others). Singularities, and things flying off to infinity, are not (easily) simulatable. Your interpretation (i) also doesn't seem very plausible. Interpretation (ii) simply means that the integral ${\displaystyle T=\int _{0}^{\infty }{\frac {ds}{v(s)}}}$ converges and yields a finite value. The (rather weak) mathematical condition is that the velocity ${\displaystyle v(s)}$ increases with distance faster than linear. The question now is whether such a velocity can be achieved given the Newtonian ingredients, in addition to point particles and the lack of a speed limit that involves the gravitational field, which of course vanishes at infinity, but diverges for ${\displaystyle r=0}$. To the extent that I understand the article, the authors set up a situation where a particle bounces between two very carefully set-up and timed binaries (near-colliding) which causes the particle to bounce fast enough for it to cover an infinite distance in a finite time. This some way to answering the question but not all the way because the motion of the particle is still bounded between the two binaries and does not go off to infinity. Unfortunately, the article then loses me by going into Cantor sets and whathaveya, and I'm not sure whether they manage to generalise to the actual situation that they promise in the title. In any case, the exercise is a mathematical curiosity and clearly not physically realisable. --Wrongfilter (talk) 16:36, 12 January 2025 (UTC)

"cover an infinite distance in a finite time": covering an infinite distance never ends by definition, whatever the velocity, so there can be no finite time. If we consider the problem posed textually, this is as true in mathematics as in physics. In addition, I am not sure that the integral posed here is the right one, because the distance interval whose sum goes from 0 to infinity is a variable if the velocity is increasing non-linearly for a constant time interval ds. Malypaet (talk) 22:36, 12 January 2025 (UTC)

Sorry Malypaet, you're incorrect in your first statement above. --Trovatore (talk) 00:12, 13 January 2025 (UTC)

Would you like to comment at Talk:Newton's laws of motion on a new version of the following sentence?

Version #1: In simulations that impose no relatavistic speed limit, singularities of unphysical behavior are observed.

Version #2: In studies that assume no relatavistic speed limit, singularities of unphysical behavior are predicted.

Philvoids (talk) 22:37, 12 January 2025 (UTC)

ok Malypaet (talk) 22:43, 12 January 2025 (UTC)

T= distance/velocity Malypaet (talk) 22:41, 12 January 2025 (UTC)

I changed the article as proposed. Malypaet, Baseball Bugs, jpgordon, Trovatore, PiusImpavidus and Wrongfilter you are welcome to comment further at Talk:Newton's laws of motion. Philvoids (talk) 14:40, 13 January 2025 (UTC)

ObSMBC --Trovatore (talk) 19:25, 12 January 2025 (UTC)

Malypaet, this is an example of a finite-time singularity and these infinities are theoretical and unphysical. The assertion that it is "mathematically possible" is true, and it's also true that it does not happen. As I understand this paradox, one sums an infinite number of infinitesimal smaller time intervals. For example, consider the graph of the function x=(1-t)^-1. It has a vertical asymptote at time t=1. The distances traversed by the confined particle(s) become infinite at t=1; the work due to increasing kinetic accelerations as their separations, d, approaches 0 becomes infinite too. In actuality, every closed-system's mass-energy does not deviate (from when their separations are infinite instead); the particles' total KE cannot exceed their total energies (PE + KE). Modocc (talk) 15:15, 13 January 2025 (UTC)

But point masses have infinite available PE, since they can approach arbitrarily closely. Point masses are surely unphysical though. catslash (talk) 11:00, 14 January 2025 (UTC)

Infinite available PE? I suppose, if it can be found. :-) Atoms, protons and neutrons are not point-like and their binding energies are fixed. But electrons and positrons have equal masses and according to scattering experiments appear to be point-like. Between them the Coulomb force is many orders stronger than gravity, yet instead of binding they annihilate and conserve their energies in the process. Even black holes don't whip up infinite PE because of mass-energy conservation. Which was my point. Classically, there are infinities, but in every case, energy conservation prevents them. If there are no radiative losses or gains, the total energy (KE + PE) of every mass remains constant. This is true for ideal pendulums and our satellites. In other words, when an apple falls from a height its PE is said to be "converted" to KE based on the work principle and which maintains the underlying energy conservation, which is pretty ubiquitous. That said, there is no reason that two high-energy electrons could not be forced to scatter against each other with an equally energetic PE. But, obviously, we never have any infinite KE at hand. Modocc (talk) 14:58, 14 January 2025 (UTC)

Your function goes to ${\displaystyle +\infty }$ at t=1 and to ${\displaystyle -\infty }$ at t=1+dt.

How is this possible for a point mass, even in mathematics?

Is the x dimension on a kind of infinite circle where ${\displaystyle +\infty }$ joins ${\displaystyle -\infty }$? Malypaet (talk) 22:37, 16 January 2025 (UTC)

The function itself is simply undefined at the asymptote due to division-by-zero. Still, according to the article section about finite-time singularity, it is the functions' behavior close to or near these that is of interest.. Modocc (talk) 23:06, 16 January 2025 (UTC)

I want to believe it, but if we consider the elements of the mathematical set, here defined by inspiration from Newton's mechanics, we have 3 spatial dimensions, 1 time dimension, and a mass dimension. By definition, a point mass approaching ${\displaystyle +\infty }$ in a finite time t*, at t* +dt cannot then end up at ${\displaystyle -\infty }$. The reasoning of the article leads us to a contradiction.

Reductio ad absurdum: the reasoning that put a point mass at ${\displaystyle +\infty }$ in a finite time is false. Malypaet (talk) 22:13, 17 January 2025 (UTC)

Rubbish. The article simply describes what the finite-time singularity is: that in finite time, from t=0 to t=t₀, an "output variable" increases to infinity. That's all it describes, and the article mentions a number of examples. As for my example, restrict the function's domain to t<1 because the article also plainly states that "...infinities do not occur physically, but the behavior near the singularity is often of interest." Modocc (talk) 23:53, 17 January 2025 (UTC)

And this does not happen mathematically if we respect the rules of the mathematical set defined here. Malypaet (talk) 14:17, 18 January 2025 (UTC)

Mathematically, the output increases towards infinity. Moreover, the integral (a summation of the output variable between t=0 and t=t₀ (exclusive) ) diverges; its summation is infinite, whether or not it is ever physical. Modocc (talk) 14:49, 18 January 2025 (UTC)

January 12

Wind speed definitions of SW Indian Ocean cyclones?

Is km/h, knots, or something else used for wind speeds, to define the strength of South-West Indian Ocean tropical cyclones? More details and sources at Talk:Tropical cyclone intensity scales#South-West Indian Ocean, Very intense tropical cyclone definition. -- Jeandré, 2025-01-12t14:19z

January 13

Geologic map age percentiles

Something that seems hard to find online is how many % of Earth's land area's older than each Phanerozoic period+Cenozoic epoch on those maps of which period/epoch is the top layer. Google AI dumbass says 88% Precambrian which is clearly just how much of the yrs the acres isn't 88% craton shield. Sagittarian Milky Way (talk) 03:58, 13 January 2025 (UTC)

SMG, I've been deciphering (and sometimes answering) your queries since you started here (since I've been here longer), and I know a little bit about geology, but I'm not sure exactly what you're asking with this semi-incoherent stream-of-consciousness.

Can I suggest that you think more about your question, re-write it one step at a time, without irrelevant asides about AI, and re-read it (or get someone else to) before re-posting to ensure it makes sense to the rest of us? {The poster formerly known as 87.871.230.195} 94.8.29.20 (talk) 20:24, 13 January 2025 (UTC)

OK I re-write: How many % of Earth's land km² pre-date various geologic time divisions? The question's way simpler than you fear. Sagittarian Milky Way (talk) 01:23, 14 January 2025 (UTC)

OK, I understand now. I don't know the answer; I could probably work it out with anything from an hour to a day of concentrated research (see last paragraph), but this evening I'm meeting a friend who is a professional geologist and planetologist, so I'll ask her if she wants to answer.

(I am assuming that answers are not available via simple websearch queries, since of course you will already have tried that.)

You ask with reference to "various geologic time divisions". Those could be Eons (of which there are 4), Eras (10), Periods (22), Epochs (37), or Ages (96), so her or anyone's answer will depend on how much effort they want to expend. {The poster formerly known as 87.81.230.195} 94.8.29.20 (talk) 10:41, 14 January 2025 (UTC)

Physical Geology 2nd Edition from BC Open Textbooks and An Introduction to Geology from Salt Lake Community College don't seem to say either. Sagittarian Milky Way (talk) 20:10, 14 January 2025 (UTC)

Dua's layer

Dua's layer is sourced mostly to the paper in which it was announced, and to other publications from around the same time (2013). The latest-published source is from 2015. Has the subject been addressed in 2020s publications? Just looking for scholarly journals, of course. Nyttend (talk) 09:55, 13 January 2025 (UTC)

https://scholar.google.com/scholar?as_ylo=2021&q=%22dua%27s+layer%22: there seem to be 187 results on Scholar since 2021. HansVonStuttgart (talk) 12:36, 13 January 2025 (UTC)

Squeeze bulb transfer pump

Anyone know if these things are any good for pumping water, i.e. from a lower container to a higher one (opposite of siphoning), with energy input by squeezing the bulb over and over? If I can have two or three feet of lift and transfer 1 gallon of water in a few minutes without my hand getting too tired, I'm satisfied. Even 1 foot of lift is ok really. I could buy one and try it but would rather avoid a useless purchase if it's not suitable. I know there are fancier ones but this one is very lightweight and simple and ISTM that not much can go wrong with it. Thanks. 2601:644:8581:75B0:0:0:0:5FED (talk) 10:02, 13 January 2025 (UTC)

On the Harbor Freight pages you can see hundreds of reviews by customers who have bought the things and used them. Generally you get just what you pay for. Philvoids (talk) 13:56, 13 January 2025 (UTC)

Out of 1202 reviews, 237 (almost one fifth) gave a 1-star review, the lowest rating possible. Many of those are titled "Junk", "Doesn't work", or "Waste of money". The other review titles are mostly variants, such as "Trash", "Defective", and "Not worth buying". There appears to be a no-return policy.

There are also (more) reviews by satisfied customers, so it may be the case that most of the units sold are fine, but roughly 20% is defective. More likely, though, many of the dissatisfied buyers wanted to transfer a liquid from a lower container to a higher one. One happy buyer opines in their review, "I think the negative comments come from people who don't know how to use the pump properly." Their advice: "Once you see the hose filling up with fluid, insert it into the container and let gravity take over and it works like a BOSS." This advice presumes the pump is used for siphoning.  --Lambiam 23:12, 13 January 2025 (UTC)

Thanks, I might opt for one of the fancier ones then. A high defect rate is discouraging since a simple thing like this would seem almost foolproof. Some tubing, and a squeeze bulb with a flap valve at each end. Oh well. 2601:644:8581:75B0:0:0:0:5FED (talk) 09:59, 15 January 2025 (UTC)

Added: my current idea is to give up on pumps and just use a large syringe. I want something lightweight and foolproof more than I'm concerned with speed. 1 atmosphere = 15 psi = 32 feet of water and the cross sectional area of that syringe is roughly 10 sq inches, so to lift the water 3.2 feet I would need 15 pounds of pulling force, right? I think I can manage that. 2601:644:8581:75B0:0:0:0:5FED (talk) 22:22, 15 January 2025 (UTC)

Atmospheric pressure is not involved as long as your containers are not sealed, which would obviate siphoning. A syringe used to lift water is a force multiplier comparable to a hydraulic lever. If the syringe piston area is ten times the cross section area of the input then 0.1 gram force would lift 1 cc water volume. However the friction of the syringe piston seal must first be overcome by a force of many grams that can be found by experiment and is usually greater in a dry syringe than one whose inside wall is wet. Your water lifting project requires you to deliver by hand an amount of work {1 gallon X (water density) X 3.2 feet} plus whatever energy your procedure wastes. If you are patient as you say, you may minimise your force exerted by using a small syringe....or consider a teaspoon? Philvoids (talk) 13:39, 16 January 2025 (UTC)

Towel on radiator

If I put a towel on a radiator, will the room be cooler, and/or will the heating of the room be less efficient? Thanks. 2A00:23C7:518:7B00:AC19:4850:B9D:6299 (talk) 18:16, 13 January 2025 (UTC)

Without actually running numbers, just going by experience . . . the room will be marginally cooler until the towel dries (because a little of the heat will be evaporating the water rather than heating the air and room surfaces), but by so little that it wouldn't be perceptible.

However, the humidity of the room's air will be increased, which may well be perceptible depending on the size and content of the room – the smaller the room, the more humid it will be, and a 'non-absorbant' room with tiled walls etc., like a bathroom, will likely show condensation, whereas a room with (dry) furniture, carpets and curtains will be able to absorb a fair bit of moisture.

Increasing the humidity will likely make the room feel warmer, because it reduces the rate that one's sweat can evaporate to cool one's body. {The poster formerly known as 87.81.230.195} 94.8.29.20 (talk) 20:37, 13 January 2025 (UTC)

Placing a towel over a radiator reduces its effective surface area. Radiators are designed to maximize the contact between air molecules and the hot surface, which helps transfer heat from the radiator to the surrounding air. By limiting this heat transfer, the radiator's efficiency is decreased. --136.56.165.118 (talk) 14:04, 14 January 2025 (UTC)

While I do not disagree that some of the heat will be taken by the water molecules during evaporation, the rest of the heat will go into the room. The net heat to the room is positive, heating up the room. So, the room will not be cooler, but the effect of the radiator on the room will temporarily be reduced. Of course, all that energy absorbed for evaporation will be released on condensation. Assuming it condenses in the room, a substantial amount of the heat will remain in the room. But, everything eventually becomes heat. This is related to a question I saw here many eons ago which asked what type of light bulbs produce a higher ratio of light to heat and all of the answers were that light becomes heat, so all bulbs produce 100% heat. So, it is possible to get stupidly pedantic. 12.116.29.106 (talk) 15:29, 14 January 2025 (UTC)

May not a bulb shed light on a Solar cell? Philvoids (talk) 17:03, 14 January 2025 (UTC)

To be fair (if pedantic), compared to a fluorescent or LED that produces the same amount of visible light, an incandescent does release a lot of heat that doesn't become (visible) light, so overall the incandescent does have a lower ratio of light to heat even if it does eventually all become heat. -- Avocado (talk) 17:12, 14 January 2025 (UTC)

[Clarification: I assumed when answering above that the room has already reached a stable temperature before placement of the towel, so that some of the heat maintaining this equilibrium will be diverted to evaporating the water in the towel. I agree that if the towel is placed while the room is still warming up, it will do so a little more slowly until the towel is dry.

Strictly, I also assumed that the towel is wet, though the OP did not explicitly stipulate this. {The poster formerly known as 87.81.230.195} 94.8.29.20 (talk) 17:37, 14 January 2025 (UTC)]

The towel, radiator, and room, if left long enough, will all eventually reach their new thermodynamic equilibrium state with each other. Thermodynamics 101: heat flows, hot → cold. The radiator "system" (whatever is feeding heat into the radiator to keep it at a set temperature) will have to work slightly harder to keep the room at a set temperature, as you are decreasing the effective surface area of the radiator and thus its rate of heat transfer into the room. (If the radiator just runs "always on" and has no thermostat control, the room will become slightly colder, ceteris paribus, since the room's rate of heat loss to the outside remains the same.)

There's also the separate issue that this is not necessarily the safest thing to do. Depending on what kind of towel it is you might start melting the material (e.g. polyester) and/or approaching its autoignition temperature, or that of something else in the room which could come into contact with the heated towel. If dry winter air is bothering you, get a humidifier. --Slowking Man (talk) 06:35, 15 January 2025 (UTC)

January 15

The moment everything changed

Can anyone tell at a glance what this picture is trying to show? It may have something to do with climate change. I'm unable to read the comment thread without making an account on X and logging in, which I don't want to do. Thanks. 2601:644:8581:75B0:0:0:0:5FED (talk) 09:56, 15 January 2025 (UTC)

According to comments on the tweet it's showing the Cretaceous–Paleogene boundary, formerly know as the K-T boundary, which is associated with the extinction event that killed off the non-avian dinosaurs. AndrewWTaylor (talk) 10:35, 15 January 2025 (UTC)

You can read an explanation here on Threads or here on Bluesky, also without an account.  --Lambiam 16:23, 15 January 2025 (UTC)

Dependent personality disorder

What version of the DSM and ICD was the first to include this personality disorder? Bit dissapointed that the article didn't already had this answer Trade (talk) 13:37, 15 January 2025 (UTC)

Regarding DSM that would be DSM III :S0272735813001311, "presence in the DSM for the last 32 years" (a 2013 article). More on the DSM and its evolution in https://www.sciencedirect.com/science/article/abs/pii/S0272735898000026. This https://www.ncbi.nlm.nih.gov/books/NBK606086/ discusses Clusters as in DSM 5, one ref I've lost possibly one of those three states dpd was almost about to be excluded as too divergent from other disorders from Cluster C. --Askedonty (talk) 00:39, 16 January 2025 (UTC)

Male lion hunting

Do African male lions without a pride get food mainly by hunting or mainly by confiscating dead prey from other carnivores like hyenas?Rich (talk) 23:42, 15 January 2025 (UTC)

Our Lion#Hunting and diet article has the details. Male lions do hunt, but "carrion is thought to provide a large part of lion diet". Alansplodge (talk) 12:18, 16 January 2025 (UTC)

Are you sure? I still don't see that sentence at all. I did read the article before asking.Rich (talk) 01:53, 17 January 2025 (UTC)

Last paragraph of the section. Tip: use +f to search for key words or phrases in a page. {The poster formerly known as 87.81.230.195} 94.8.29.20 (talk) 05:00, 17 January 2025 (UTC)

I have read of instances where a young adult male lion expelled from his parental pride (which is normal) but not yet accepted into another, teams up with one or two other young males (sometimes his sibling/s) to hunt. {The poster formerly known as 87.81.230.195} 94.8.29.20 (talk) 12:41, 16 January 2025 (UTC)

January 16

A list of all species

Is there a database of binomial names where I can see all species with a particular specific epithet? For example, I type in "nigra" and it gives me Populus nigra, Sambucus nigra, Comatricha nigra, Actia nigra, etc. Surtsicna (talk) 22:07, 16 January 2025 (UTC)

I suggest you try WikiSpecies.-Gadfium (talk) 22:55, 16 January 2025 (UTC)

Well, that should certainly do the trick. Thank you! Surtsicna (talk) 22:57, 16 January 2025 (UTC)

If there is another website where I could order the species alphabetically by generic name, I would appreciate a link :) Surtsicna (talk) 22:59, 16 January 2025 (UTC)

You can use POWO for plants. gracilis is the most common epithet for plants, with 599 accepted species (and 2,146 names listed). User:Jts1882 put together this program for me that arranges POWO data taxonomically and even checks if a Misplaced Pages article exists. Abductive (reasoning) 07:06, 17 January 2025 (UTC)

January 17

Turquoise and copper

Do turquoise and other green stones tend to show up near copper deposits? Gongula Spring (talk) 00:35, 17 January 2025 (UTC)

If you check out the Turquoise article, you can see that the answer is yes. But the deposits may not be worth mining. Copper is not super rare and is found in living organisms, and sediments in small amounts. Graeme Bartlett (talk) 05:45, 17 January 2025 (UTC)

January 18

moves infinitely fast in the limit

In a previous topic, @trovatore writes:"rephrasing "the limit of the speed is infinite" as "moves infinitely fast in the limit." But what does "moving fast" mean? What I have found is:"full of rapid action and sudden changes In his latest movie." I prefer the original one because speed or velocity is linked with a constant time interval, so you have just to compare the distance between each consecutive interval to use the good adjective: "fast" or "slow." Achile is moving fast relative to a tortoise but slow relative to a rocket (see zeno paradox Achiles and the tortoise). And what is strange here, not to say absurd (Reductio ad absurdum), is to associate a limit to something that has no limit by definition (infinity), the same for moving or speed. Malypaet (talk) 14:09, 18 January 2025 (UTC)

This seems to me something you and Trovatore should discuss on your, or his, Talk page. You are apparently debating the multiple common meanings of words in an effort to extract variant understandings of topics in physics/mathematics, where the meanings they are assigned are firmly defined, and in which the mathematics should predominate over everyday speech. Though I myself have studied Physics to undergraduate level (and am a native Englissh speaker), I generally find your paraphrasings within this topic unclear. Just my 2¢. {The poster formerly known as 87.81.230.195} 94.8.29.20 (talk) 17:41, 18 January 2025 (UTC)

While I struggle to follow what Malypaet is trying to say exactly, to be fair, the rephrasing in question was not Malypaet's (or mine), but the original authors'. Quote:

To develop a flavor for how the “wedges” of initial conditions are found, notice that, in the limit, m3 has to move infinitely fast from m1, m2 to m4, m5; this happens only when m3 starts arbitrarily close to m1 and m2 while m4, m5 already are close together.

— http://www.ams.org/notices/199505/saari-2.pdf

I suspect that some readers were tempted to understand this as claiming that there is a limit time at which m3 is moving infinitely fast, but if you read it carefully you can see that it is not claiming this. It would be awkward to reword the passage in terms of the limit of the speed of m3, which is presumably why the authors didn't. --Trovatore (talk) 21:11, 18 January 2025 (UTC)

The 5 bodies are point masses. What does "arbitrarily close to" mean between points that are infinitely small? Since we are in Newtonian motion, I assume the initial distances, initial velocities, and masses, along with values ​​and their unit scale, are given. I specify that the motion of m3 is an oscillation on the z-axis between the two binaries. Malypaet (talk) 22:51, 18 January 2025 (UTC)

Yeah, actually I haven't quite figured out what they mean by "arbitrarily close to" in this passage. If I get around to it I might try to work it out and let you know. --Trovatore (talk) 23:22, 18 January 2025 (UTC)

Nothing can move "infinitely fast". ←Baseball Bugs carrots→ 18:16, 18 January 2025 (UTC)

That's why it says "in the limit". This means that it may never be actually reached.  --Lambiam 23:27, 18 January 2025 (UTC)

As t->(1/0) v->(1/0) but dv/dt->0. Greglocock (talk) 23:09, 18 January 2025 (UTC)

With the article Off to Infinity in Finite Time, the gravitational force, thus the accelerations , f/m=a=dv/dt, between arbitrarily close masses gets arbitrary larger not smaller (as you are indicating). I believe its increase is why there is a finite-time singularity according to the authors. But it does makes sense there should also be a decrease in their accelerations in the limits, such that their energy is constant. In this case, since their KE is still without an upper limit then their PE must be too. However, there are no known n-body systems with infinite mass. :-) Modocc (talk) 23:28, 18 January 2025 (UTC)

There is a point in space between the far binary and the near binary where the acceleration of m3 is zero. At this point, the gravitational forces cancel each other out, and after their resultant reverses on the z axis, causing a deceleration. Malypaet (talk) 09:48, 19 January 2025 (UTC)

With respect to near-zero accelerations it's also important to note that their point masses don't appear to become unbonded since they are aiming for a finite-time singularity: "Of importance to our tale is the highly oscillatory nature of a noncollision motion that was established for the argument of . It turns out that particles must approach other distant particles infinitely often and arbitrarily closely. The intuition is that a particle flying off to infinity by itself has nearly zero acceleration, so the velocity remains essentially constant. As a constant velocity precludes any possibility of reaching infinity in finite time, the acceleration needs to be boosted, and this requires a close visit by another particle." Modocc (talk) 02:33, 19 January 2025 (UTC)

Yes, but what about oscillating and "approach other distant particles infinitely often," and about inertia when m3 changes direction to return to the other binary? Malypaet (talk) 09:39, 19 January 2025 (UTC)

Your question(s) are about their closed orbits, but they are vague. It's unclear what you are asking. Note: I tweaked my comment to make it clearer that I was referring to their orbits. Modocc (talk) 13:10, 19 January 2025 (UTC)

January 19

Observatory

From what I've read, this building in the background is some unspecified observatory rather than lighthouse. The photo is no later than 1991, around 1986. Do we know what observatory exactly? Assuming it's the same building, also this. Brandmeister 09:56, 19 January 2025 (UTC)

I don't see how anyone can tell given the lack of context, and I don't think they are the same building. They are very small so probably belong to a school or college. Shantavira| 12:20, 19 January 2025 (UTC)

I'm pretty sure that both pictures were taken at Calar Alto Observatory. The second one is the 2.2m telescope , the first one probably the 1.23m telescope . --Wrongfilter (talk) 12:36, 19 January 2025 (UTC)

Bodies reflecting light are to stars, what (...?) are to black holes.

Black holes can, in some sense, be described as antistars, insofar the latter emit light, whereas the former absorb it. Various celestial bodies, such as planets and satellites, or comets and meteors, reflect starlight, thereby becoming secondary light sources. What (theoretical) astronomical objects relate to black holes, in a manner analogous to the one to which the latter relate to stars ? — 86.125.205.116 (talk) 13:15, 19 January 2025 (UTC)

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