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September 27

Autumn foliage

Is there any information of dates of beginning, peak and ending in different regions in Europe? And does the foliage come at all to southeastern Europe such as Croatia, Serbia, Romania and Bulgaria? The Finnish Wikipedia says that in southern Finland, the foliage begins in mid-September, peaks in early October and ends in late October and early November. In Central Europe (such as central Germany, southern Poland, Czechia, Slovakia and western Ukraine), the foliage begins in early October, peaks in early November and ends in early December. In northern Italy it begins in mid-November, peaks in early December and ends in early January. Is there any any information about that? --40bus (talk) 14:19, 27 September 2023 (UTC)

Some leads at Deciduous. Click the "59 languages" tab to access information from many countries. 2A02:C7B:113:1E00:8EC:E016:111:57CE (talk) 14:57, 27 September 2023 (UTC)

But it tells nothing about Europe. Where can I find information about that? --40bus (talk) 15:24, 27 September 2023 (UTC)

The Bulgarian, Croatian, Romanian and Serbian words for "deciduous" are respectively широколистни, listopadne, foioase and Листопадни. Typing those words into the search boxes of the relevant Wikipedias (bg, hr, ro, sr) brings up many hits. 2A02:C7B:113:1E00:8EC:E016:111:57CE (talk) 16:23, 27 September 2023 (UTC)

I found Substantial variation in leaf senescence times among 1360 temperate woody plant species

The results suggest that, in contrast to the broader temperature effects that determine leaf out times, leaf senescence times are probably determined by a larger or different suite of local environmental effects, including temperature, soil moisture, frost and wind.

So I'm not sure that you;re going to find a definitive answer.

You may be interested in Climate crisis making autumn leaves fall earlier, study finds.

Alansplodge (talk) 22:01, 27 September 2023 (UTC)

Planck's constant

In wikibook Introduction to Theoretical Physics , chapter 4.5.2 Planck's constant.

You read:

"If you know h (Plank's constant), and you know the frequency of the light, then you can calculate the energy delivered over a certain period of time. For instance, if a beam of light illuminated a target for 3 seconds, and the light frequency was 540 × 10¹² hertz, then the energy delivered would be h × 3 × 540 × 10¹² joules."

So can we replace "3 seconds" by the period associated with the frequency and write "then the energy delivered would be h joules", if not, why not ? Malypaet (talk) 21:40, 27 September 2023 (UTC)

The answer is NO! Your quotation suggests “Introduction to Theiretical Physics” has got it seriously wrong. The frequency of the light multiplied by Planck’s constant gives the energy of one photon of light of the nominated frequency. Dolphin (t) 21:57, 27 September 2023 (UTC)

The quoted sentence implies that h is a dimensionless quantity, while in actuality it has dimension ${\mathsf {M}}{\mathsf {L}}^{2}{\mathsf {T}}^{-1}.$  --Lambiam 07:17, 28 September 2023 (UTC)

Difficult to correct this book on wikibooks which is an offshoot of Wikipedia.

However this sentence raises a question, as a Planck resonator emits a beam of elementary radiation with an energy quanta "E=hv", that this beam can be cut into pulse over a time interval, how many photons emits a resonator in 1 second? Malypaet (talk) 07:20, 28 September 2023 (UTC)

If $P$ is the power output and $\nu$ the wavelength frequency, divide $P$ by $h\nu \,{\text{s}}.$ Note, though, that you cannot just equate quanta with photons. The beam does not consist of individually countable photons – you can only count particles, and these only come into play upon wave function collapse.  --Lambiam 16:47, 28 September 2023 (UTC)

ν is the frequency, not wavelength.

So the number of quanta "nq" in Δt=1s is:

nq=P.Δt/h.ν

And now how can we get the number of resonators emitting this beam with power P ? Malypaet (talk) 21:15, 28 September 2023 (UTC)

Looking at the original Wikibooks entry, that entire section is a disaster from start to finish.

Planck's constant is the constant of proportionality between the energy of a single quanta of electromagnetic radiation and its frequency, as observed by others here. I considered trying to edit the Wikibook, but the more I looked at that page, the more I realized the entire thing needs to be burned to the ground, and I have other stuff to do. PianoDan (talk) 03:29, 29 September 2023 (UTC)

What do you mean by: "a single quanta of electromagnetic radiation" ? An elementary emission from a Planck resonator, or what else? Malypaet (talk) 05:44, 29 September 2023 (UTC)

I mean a photon. "Planck resonators" are not really a modern concept - Planck used them when he was developing his theory, but it's not language anyone uses now. Electromagnetic radiation comes from a variety of sources, but it always consists of photons. PianoDan (talk) 15:03, 29 September 2023 (UTC)

Yes, but the photon is what is emitted. I am more interested in the emitter which is always matter as in thermal radiation. Thermal energy is indeed the agitation of particles in matter and in this case we can very well find the synchrotron effect with its electrons, right? For a radio antenna too, we have electrical energy which is transformed into radiation energy, synchrotron effect too? You replace the virtual Planck resonator object with what in modernity?

Can you list for me the main sources emitting photons? Malypaet (talk) 22:00, 30 September 2023 (UTC)

See Light § Light sources.  --Lambiam 05:47, 1 October 2023 (UTC)

September 28

Weighing less than nothing in Don Rosa's comic (continued)

I asked a question about this before. I have now read Don Rosa's comic The Universal Solvent again, and can verify that there is indeed a scene where the Ducks have travelled close to the centre of the Earth inside a shaft, and they notice that gravity is now working upwards instead of downwards because, as the Ducks cite, "more of the Earth's mass is above them than below them". I could even take photographs of the pages and upload them to Wikipedia but I don't think copyright reasons would allow this.

I remember that the last time I asked, there was a reply that this shouldn't work like this, as the entire other half of the Earth is still below the Ducks from their point of view.

Am I therefore correct that Don Rosa made a mistake in how physics work here? JIP | Talk 09:13, 28 September 2023 (UTC)

Either a mistake or literary license. Comic books are not necessarily reliable sources for science. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:05, 28 September 2023 (UTC)

For reliable science, you ask random strangers on the Web, as any fool knows. —Tamfang (talk) 17:14, 4 October 2023 (UTC)

See shell theorem for the real answer (gravity always points inwards, goes down linearly with radius, and is zero at the center). —Kusma (talk) 11:10, 28 September 2023 (UTC)

The shell theorem was also referred to the previous time this question was posed. Earth's mass distribution is not perfectly symmetric, so there will be some discrepancy between the centre of mass centre of gravity, where the intrepid explorers are weightless, and the centre of symmetry of the Earth spheroid, where they experience a force towards the mass centre.  --Lambiam 16:34, 28 September 2023 (UTC)

For a general asymmetric mass distribution, I don't see why the centre of mass should necessarily be a point of weightlessness. —Kusma (talk) 17:07, 28 September 2023 (UTC)

Simplest 1d example: Two point masses a and b at -1/a and 1/b have centre of mass at 0. Gravity there is -1/a^3+1/b^3, which is nonzero unless a=b. —Kusma (talk) 19:22, 28 September 2023 (UTC)

You're reading a comic about talking ducks with human-level intelligence, and you're worried about the accuracy of an obscure aspect of gravity? {The poster formerly known as 87.81.230.195} 90.212.130.182 (talk) 16:30, 28 September 2023 (UTC)

Short of asking Don Rosa, you can read his thoughts about related questions in the archives of the Disney Comics Mailing List. See threads from April 1995, particularly [1] and [2]. --Amble (talk) 18:49, 28 September 2023 (UTC)

September 29

Extremes in standard redox potential table

C is the known strongest oxidising agent (criteria:C should be neutral chemical species, or "normal" chemical compound/chemical element, not a moiety, radical or supramolecule) and in various reactions the corresponding common reduction product is C*. So what is the chemical formula/ structural formula of C, and what is the electrode potential value for the couple C/C* (by convention, in volts, measured in standard conditions of environment)? I find out that C cannot be the fluorine gas, but may instead the reactive fluoride compounds of certain transition metals or noble gases, for example ("known" means that the candidate chemical species must have been synthesised in lab and reliably detected by any means). What about the similar case: B is the known strongest reducing agent, in various reactions the corresponding common oxidising product is B*- forms the electrochemical couple B*/B?. Again, there are many mistakes and misconceptions on the Internet as they said that B is nothing other than the alkali metals. I find out that B is more likely one of these compounds: the alkalide and electride compounds, the complexes of various low-valent actinide elements, the lowest carbonyl complexes of transition metals or the metallic compounds of group 13 elements in -5 oxidation state. In a nutshell, what I need is the correct chemical formulae for the coumpound C and compound B, along with the reliable and good sources for the data on the (estimated) reduction potential values of their couples. 2402:800:63BC:EE1A:35EE:814F:BDD:42B4 (talk) 14:43, 29 September 2023 (UTC)

While this isn’t necessarily my designated area of expertise, I looked into this and I think - as a fellow scientist - I have a pretty solid understanding of what you’re asking. The fluoridated electrode potential would be a function of the voltage B* given in relation to valency with respect to the redox potential of a metal, where that redox potential is basically a constant according to electrochemical carboxide tables. It’s actually pretty basic. In a closed system, current potential (i.e. voltage) would be determined by the chemical species, meaning that halide valencies would be dependent on differential charge coupling. More can be found here, here, here, here, here, here, and here. Buckrune (talk) 22:44, 30 September 2023 (UTC)

October 1

Variables affecting national fertility rates

I have a proposal for a scientific study, but I don't know enough about statistics to do the study myself. Specifically, I am wondering if it can be shown that the prevalence or legal status among worldwide nations of birth control, pornography, homosexuality, and other sexual behaviors historically considered 'non-traditional' have any effect on national fertility rates. How could I go about forwarding this idea to someone who can do a study? Wiki Crazyman (talk) 01:54, 1 October 2023 (UTC)

This is not at all a simple question, and I think you are probably going about this the wrong way/a way impossible to get meaningful results. You are going to need to speak to, work with, and get data not only from sociologists, anthropologists, and historians (these first three might also have something to say about throwing around words like "non-traditional" about the variables you listed), but also experts in fields like fertility health, epidemiology throughout history, and many, many other fields. Not only are all of the things you have listed happening at the same time, but potentially far greater other variables as well. For example, how much of a population is reaching adulthood to even have children? If many die before adulthood, then there will be pressures to have higher birthrates. That's just one example. How about a war having a huge impact on the population of one biological sex? What about the impacts of famines or climatic events? It is generally difficult to determine correlation or causation when you have more than one changing variable, very difficult when you have three, and even more difficult when trying to do so while attempting to control for a myriad of other outside influences like those I've listed. I would remind you that a "traditionally conservative" (and that's a bad use of the term) country, Russia, experienced a marked decline in its fertility rate at the very same time that the Russian Orthodox Church was massively returning to general public life with the fall of the Soviet Union. There were many other confounding variables, such as a sharp collapse in the economy, lowered support for public healthcare, the loss of a portion of its male population at normal child raising age due to war, and many other issues that all had impacts on birthrate. You aren't likely to get a meaningful result by setting out already deciding what your independent variables are going to be (indeed, it is even worth asking if those practices you listed are independent variables with fertility rate depending on them, or if their incidence and practice are the dependent variables that respond to the fertility rate of a given population; you can't just assume it's one way or the other). You are better off first studying things like historical trends and working to determine what influenced those specific trends, instead of starting already thinking you know. --OuroborosCobra (talk) 03:06, 1 October 2023 (UTC)

Meta-answer: very few (if any) scientific fields are lacking in "study ideas". The hard part is actually making the study in a proper way.

The first step in any of these is "look up if others have not already done it". A 30 second Google Scholar search turns up this article which did (attempt to) disentangle the various effects of economics, religious views, and so on. Any serious research should take that previous publication (and others) into account - either attempting to replicate its results, question implicit hypotheses, or study something else entirely. Tigraan^{Click here for my talk page ("private" contact)} 13:21, 4 October 2023 (UTC)

Crustaceans becoming insects

If crustaceans have 10 legs and insects developed from crustaceans, how did they end up with only 6 legs?? Did 4 legs evolve into anything?? If so, what did they evolve into?? Georgia guy (talk) 14:28, 1 October 2023 (UTC)

Does Arthropod#Segmentation help? Martin of Sheffield (talk) 14:52, 1 October 2023 (UTC)

Lots of crustacians have many legs or ten legs. And caterpillars have lots of legs too. The common ancestor of crabs and flies was perhaps twice as long ago as the rise of the dinosaurs and didn't have to look particularly like anything today. A lot of things can happen in deep time. NadVolum (talk) 15:19, 1 October 2023 (UTC)

• As a general principle, it's a bad idea to say "<current group> evolved from <other current group>". They may both have evolved from the same thing, but that last common ancestor can be a lot different to either. Also there are some body structure (leg pairs on arthropods being an example) where it's just not that hard for the total number to vary (over evolutionary time). Andy Dingley (talk) 17:30, 1 October 2023 (UTC)

  Our article Pancrustacea states that several molecular studies support a phylogeny in which hexapods, including insects, are derived from crustacean ancestors, so then cladistically insects are crustaceans, just like birds are dinosaurs.  --Lambiam 20:44, 1 October 2023 (UTC)

• But is our hypothesised Pancrustacean ancestor a crustacean? Was it (by any stretch of the imagination) "a crab"? A common mis-implication from cladistics, especially when the names are similar like this, is my original point: although it's true that the ancestor is a pancrustacean, this shouldn't be taken to mean that it resembles anything like what we'd regard today as a modern example crustacean. Morphologically modern birds are far closer to coelurosaurs. Andy Dingley (talk) 21:34, 1 October 2023 (UTC)

  Regardless of the answer to these questions, the statement vindicates the OP's contention that insects developed from crustaceans. The clade Pancrustacea would have been named just "Crustacea" but for the fact that in traditional taxonomy, mainly based on morphology, Hexapoda were excluded from Crustacea. Look at the phylogenetic diagrams in Pancrustacea and note that not a single one contains a subphylum "Crustacea". Note also that in each of these diagrams Hexapoda is a subsub...subclade.  --Lambiam 06:45, 2 October 2023 (UTC)

• Segmentation, including in arthropods, is often governed by HOX genes. A very small alteration in HOX genes can easily result in a different number of legs, just as long as the number is still even. It can even result in some fun things, like legs growing out of where you would expect antennae. --OuroborosCobra (talk) 21:29, 1 October 2023 (UTC)

• The arthropod head problem Andy Dingley (talk) 21:34, 1 October 2023 (UTC)

Hashtag: Very High Energy, Particle accelerator, Blueshift

Besides the well-known device - which "accelerates particles" to ultra-velocity and above - in order to charge them with very high energy, is there also an analogous device - which "shifts the color of photons" to ultra-violet and above - in order to charge them with very high energy?

2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 23:30, 1 October 2023 (UTC)

Not that I can think of. If you want to make high energy (i.e. high frequency, which is the same thing) photons, you generate them at the desired frequency, rather than trying to add energy to existing photons. The Hermes III experiment at Sandia National Laboratory claims to be the most powerful gamma ray generator in the world.[3] PianoDan (talk) 03:20, 2 October 2023 (UTC)

Thanks. It seems that Hermes III is weaker than Z Pulsed Power Facility, which is the successor of the former, isn't it? 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 08:10, 2 October 2023 (UTC)

This is a tough thing to do. very small changes can be done via Optical modulators using electro–optic effects. Nonlinear optics using multiple photons, can do Second-harmonic generation or Third-harmonic generation to generate ultraviolet. And it appears that High harmonic generation can generate X-rays. Graeme Bartlett (talk) 03:32, 2 October 2023 (UTC)

Thanx. 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 08:11, 2 October 2023 (UTC)

Thank you all. Assuming the very high velocities generated by particle accelerators have no upper bound (at least theoretically), do you think gamma ray generators (like those built in Sandia National Laboratory) can also generate any chosen frequency (at least theoretically)? 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 08:19, 2 October 2023 (UTC)

No, a human engineered system will have limits. For natural gamma rays see Ultra-high-energy gamma ray which says that 1.4 PeV is the highest energy detected so far. A 100,000 PeV photon would interact with the Earths magnetic field to produce a pair of particles. For an even bigger imaginary limit, if the whole mass energy of the universe was used to make one photon, its energy could not be exceeded. Some consider that the Planck energy is a limit. Graeme Bartlett (talk) 10:16, 2 October 2023 (UTC)

Please notice that I've added "theoretically", just to make sure that one should not consider any practical limits human engineered sustem usually has. As for the Planck energy, It's approx. one billion Joule, so it can't be a limit, because there are many objects whose energy exceeds this limit. Just as the Planck momentum, being approx. six kg m/s only, is not a limit of momenta in the universe. So it seems that the only theoretical limit is the energy of the whole universe, right? What about intermediate exact values of energy, like pi (3.14...) Joule? Again, I'm asking theoretically. 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 11:24, 2 October 2023 (UTC)

The velocities produced by particle accelerators absolutely have an upper bound, namely the speed of light. Electrons approach this limit so quickly that all you're basically doing to the velocity as you add energy to electrons in an accelerator is adding "9"s to the end of 0.999...*c. PianoDan (talk) PianoDan (talk) 15:01, 2 October 2023 (UTC)

I'm referring to a limit of energy. 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 15:16, 2 October 2023 (UTC)

Using the mass–energy equivalence, the mass of a photon with an energy of 3.5 GJ (about 22×10²⁷eV) is such that the corresponding Schwarzschild radius is larger than its wavelength. Does this give a limit on the energy of a photon?  --Lambiam 22:32, 2 October 2023 (UTC)

You can always transfer to a reference frame where this photon's energy is below that value — nothing happens in that reference frame, therefore nothing happens in the original frame. This is a good example of why the mass-energy relation should not be applied to centre-of-mass motion (or whatever you'd call it in the case of a photon). A limit would have to come from considerations about the emission process, or generally about the interaction of photons/the electromagnetic field with matter. --Wrongfilter (talk) 06:18, 3 October 2023 (UTC)

1. Do you think you can calculate the limit you suggest? This may help.

2. As for user:Lambiam's comment you have rejected, I think the core of Lambiam's quesion is simple: Does a photon's wavelength have any lower bound, e.g. the Planck length (being approx. 10^-35 m)? Please notice this question is quite equivalent to my original question about whether a photon's energy (in a given reference frame) has any upper bound. Maybe this important question, at least about the wavelength, deserves a thread of its own. 2A06:C701:7446:D900:1D55:57C:4F3F:3A51 (talk) 07:36, 3 October 2023 (UTC)

ad 1.: I do not know what that limit would be. I only know that it cannot come from the photon in isolation.

ad 2.: My answer is no, based on the theory of relativity. Again, interactions, possibly with the quantum structure of spacetime or more simply with the matter distribution in the Universe, could change the answer. It might be that the photon picture is too simplistic, however, and there might be more in the full theory of quantumelectrodynamics.

I was mainly challenging the argument with the Schwarzschild radius. If that radius depended on "relativistic mass", it would be frame-dependent. What would it look like anyway? Spherical? In which frame? The event horizon of an ordinary (non-rotating) black hole is spherical only in its rest frame, but non-spherical in a frame where the BH is moving (same for its gravitational field). --Wrongfilter (talk) 08:11, 3 October 2023 (UTC)

Do you think a photon's wavelength may be less than the Planck length (being approx. 10^-35 m)?

A photon's relativistic mass depends on the photon's momentum only, hence on the photon's wavelength only. Are you sure this momentum/wavelength, the photon has, depends on the reference frame? 2A06:C701:7446:D900:1D55:57C:4F3F:3A51 (talk) 10:45, 3 October 2023 (UTC)

Around the Planck length, quantum gravity effects become important. Perhaps the speed of photons like this will be lower than the speed of light. In reference frames that move with respect to each other, there can be a Doppler shift that affects the frequency measured, and thus wavelength, momentum and energy. In a gravitational field, the photons will also change energy and be shifted. Graeme Bartlett (talk) 11:15, 3 October 2023 (UTC)

OP's recent thought: If no wavelength can be shorter than the Planck length, then no photon can have energy higher than 12.3 billion Joule (hence no photon can have a relativistic mass higher than 0.13675 milligram), so no gamma ray generator can generate a photon whose energy is higher than that limit. 2A06:C701:7446:D900:1D55:57C:4F3F:3A51 (talk) 17:37, 3 October 2023 (UTC)

October 2

"I do it because it feels good"

Jane Doe knows that aromatherapy has no basis in science, but she engages in it for psychological reasons: she's been really sad lately, so she thinks the nice smells can help her feel happier.

When we do something medically useless because it's pleasant, like Jane Doe is doing here, what's a term for it? The placebo effect discusses something different, where you seemingly improve when taking something that you think might be effective — not where you intentionally do something even though you know it won't directly have an effect. Nyttend (talk) 10:39, 2 October 2023 (UTC)

Recreational drug use? It doesn't have to involve harmful substances. -- Verbarson  ^talk_edits 12:25, 2 October 2023 (UTC)

So, how does exposing oneself to pleasant smells conceptually and physiologically differ from exposing oneself to pleasant sounds, such as birdsong or music? Or pleasant sights such as a garden, park, or seascape? These are hardly describable as 'recreational drugs'.

I see what Nyttend is getting at here, and it seems to me to be a common human behaviour: there's surely a name for it.

Deliberately and knowingly using (what for the moment I will call) the placebo effect on oneself, exploiting one's own unconscious but known-of psychological and physiological reactions, is a major aspect of the 'craft' aspect of modern witchcraft [says this Wiccan]. {The poster formerly known as 87.81.230.195} 90.212.130.182 (talk) 17:44, 2 October 2023 (UTC)

Our articles at Subject-expectancy effect and Self-fulfilling prophecy seem germane, but at some it becomes about proving that relaxing things relax people. Jane enjoys smelling nice things, Bob enjoys listening to white noise, Ahmed likes watching birds. I'm not sure further explanation is really needed. Matt Deres (talk) 18:37, 2 October 2023 (UTC)

The question does not ask for an explanation, but for a name.  --Lambiam 21:33, 2 October 2023 (UTC)

This feels like a false premise scenario. I realize this is a ref desk and not an article, but what are your sources that say that nice smells can't improve someone's mood? Who says that something that is pleasant is medically useless? --Onorem (talk) 18:45, 2 October 2023 (UTC)

Jane engages in a therapy in spite of her belief that it lacks a scientific basis. For the question whether there is a linguistic label for such behaviour, it is not relevant whether her belief is correct. I have met people taking holy water for ailments while well aware that no scientific test can discern a difference with tap water.  --Lambiam 21:30, 2 October 2023 (UTC)

There are lots of things which are pleasant but uncorrelated with medicine ("medically useless") and Jane is presumably undertaking aromatherapy because she likes, or expects to like, it. There are many terms for engaging in pleasant non-medical activites. 2A01:E0A:D60:3500:2E65:7281:7004:C5D0 (talk) 11:33, 3 October 2023 (UTC)

Hedonism may not be the best term but that article covers much of what has been discussed here. Mike Turnbull (talk) 11:41, 3 October 2023 (UTC)

This appears to be a form of "chilling out" [4]. 2A02:C7B:10C:3200:A89E:70FA:13B5:5106 (talk) 11:53, 3 October 2023 (UTC)

At least in the UK, oncologists are generally supposed to be supportive of medically useless (and harmless) activities, even while medical treatment is ongoing. This comes under Alternative medicine and Complementary medicine, and there are lots of types. There may well be pschological benefits, which may be significant. Johnbod (talk) 15:19, 3 October 2023 (UTC)

October 3

Heating any metal makes it red??

I find a number of Internet sites saying that a metal can become red when it is very hot. How hot to be specific?? I want a lower limit and an upper limit. The same sites also say that metals can become yellow or blue if heated even further. Can anyone reveal exact temperatures?? Georgia guy (talk) 00:08, 3 October 2023 (UTC)

Hello, Georgia guy. Please read Incandescence. That article says In practice, virtually all solid or liquid substances start to glow around 798 K (525 °C; 977 °F), with a mildly dull red color, whether or not a chemical reaction takes place that produces light as a result of an exothermic process. Cullen328 (talk) 00:15, 3 October 2023 (UTC)

I bet that repeating Draper's experiment with a range of human subjects will produce a bell-shaped curve for the temperature where the subjects start perceiving a glow, rather than a sharp transition precisely at 977 °F.  --Lambiam 07:41, 3 October 2023 (UTC)

Probably right, but I guess the deviation will be quite small. Basically receptors are mostly identical, which leaves pupil diameter, lense transeparency and receptors prevalence as actual factors. Leave out extreme cases like severe cataract and the resulting variance will be small. Zarnivop (talk) 13:54, 4 October 2023 (UTC)

Another good read would be black body radiation. --OuroborosCobra (talk) 00:48, 3 October 2023 (UTC)

Also Pyrognomic, Thermal radiation and Planckian locus.  --Lambiam 07:20, 3 October 2023 (UTC)

No exact temperatures, as the changes from invisible to red to orange are gradual. There are lava lakes that appear grey in daylight but clearly glow red at night. And where is the boundary between red and orange?

All hot, dense materials glow. So of the metals, mercury is out, as it evaporates before being hot enough. In normal gases, the density is so low that interactions between particles are too weak to create continuum emissions.

Most metals have a fairly flat reflectivity over the visible spectrum, so they are close to blackbody emitters. Copper and gold are notable exceptions, which have a high reflectivity (and therefore low emissivity) in red. PiusImpavidus (talk) 07:57, 3 October 2023 (UTC)

798 K is well below the critical point of mercury (our article says "1750 K, 172.00 MPa"), so presumably if you can keep the pressure high enough you could keep it as a liquid. Calculating using NIST's Antoine equation parameters suggests a minimum of about 11.25 barr. DMacks (talk) 15:04, 3 October 2023 (UTC)

Plot of spectral radiance vs wavelength of blackbody radiation for selected temperatures

@Georgia guy: It doesn't have to be metal. Anything at a given temperature emits blackbody radiation, though some materials emit or absorb spectral lines (due to electronic transitions) that overwhelm the blackbody radiation. Though the peak wavelength depends on temperature, other wavelengths including red are emitted, as in this graph or this visualisation. Whether our eyes interpret it as red depends on various psychological and psychological effects. As other respondents have replied, the boundaries are inexact and depend on observer, material and viewing conditions. Cheers, cmɢʟee⎆τaʟκ 12:17, 3 October 2023 (UTC)

You might also want to look at this particular chromaticity diagram that include color temperatures: https://www.luxalight.eu/sites/default/files/inline-images/CIE_ledtuning_1.jpg Dhrm77 (talk) 14:50, 4 October 2023 (UTC)

Why do car wheels have an odd number of spokes?

Wheels (besides bicycle ones with thin tensioned ones) often have five spokes (or ten, comprising five pairs). Some I've seen have three.

https://engineering.stackexchange.com/a/14606 claims it's "because having directly opposed spokes causes problems with residual stress distribution as the casting cools and shrink". Is that true? If so, why do having opposed spokes have this issue. What other reasons might there be?

Thanks,
cmɢʟee⎆τaʟκ 12:28, 3 October 2023 (UTC)

In 5 spoke wheels, any one spoke has two directly opposing spokes that will reduce the effect of torsional vibration. With 6 or 8 spokes, there is a directly opposing spoke that creates a henge point. This henge point leads torsional vibration around the two opposing spokes. In addition, having an even number of directly opposing spokes causes problems with the residual stress distribution of the wheel as it cools and shrinks. This is highly evident in cast iron handwheels having "S" shaped spokes. With an even number of spokes, you have a directly opposing spoke that creates a henge point, so you can get torsional vibration around the two opposing spokes. [5]

However, the exact definition of "henge point" eludes me at present, but I'm sure one of the sages here will be able to enlighten us. Alansplodge (talk) 13:59, 3 October 2023 (UTC)

A typo for 'hinge point', surely? AndyTheGrump (talk) 14:03, 3 October 2023 (UTC)

I'd agree to some extent about the cooling issue, the torsional one sounds like at best one bizarre pre FEA case that got generalised. I was design engineer on a 5 spoke and a 3 spoke. https://www.carsguide.com.au/car-reviews/used-car-review-ford-falcon-eb-1991-1993-13217 and https://bringatrailer.com/2017/06/03/little-red-orphan-1993-mercury-capri-xr2-turbo-5-speed/ Greglocock (talk) 22:47, 3 October 2023 (UTC)

According to this source, wheels with 3 and 4 spokes didn't sell well, people preferred 5 spokes. So the reason could simply be esthetics. Prevalence 14:08, 3 October 2023 (UTC)

Internal stress in a solid object such as a car wheel is greatest with a possibility of breakage when road vibrations match a Mechanical resonance of the wheel. Therefore a wheel designer is concerned about the Normal modes of vibration in which all parts of the wheel move sinusoidally with the same frequency and with a fixed phase relation. Ernst Chladni invented a technique to show Chladni figures which are nodal lines that divide parts of a plate that resonate in opposite directions. This lead to the study of Cymatics of objects of various shapes. The Chladni figure of a car wheel that has an even number of spokes is dominated by a full diameter nodal line that indicates a fundamental vibration mode that could lead to catastrophic breakage and is therefore avoided. Philvoids (talk) 15:52, 3 October 2023 (UTC)

Interesting theory, but in that case disc like (unspoked) wheels would break, whereas in fact they are the strongest. Greglocock (talk) 22:49, 3 October 2023 (UTC)

It may be spoked that a one-spoke disc is odd. Philvoids (talk) 09:54, 4 October 2023 (UTC)

Perhaps the vibrations would be dissapated throughout the disc, rather than being channelled along an individual spoke? Alansplodge (talk) 12:12, 4 October 2023 (UTC)

Who appointed you spokesman? —Tamfang (talk) 17:18, 4 October 2023 (UTC)

When did recycling start in your countries?

In the U.S., I heard someone say that recycling started after the Environmental Quality Improvement Act of 1970, signed by President Nixon. But in Illinois and California, the garbage truck takes black or green garbage bins, and the recycling is a blue bin. But as a kid in the 1990s, I never saw the blue bins, but I see it now. So I think recycling came much later than 1970, but maybe it depends on jurisdiction? 170.76.231.162 (talk) 16:00, 3 October 2023 (UTC).

Recognizably-colored bins are probably a much later innovation, as are having separate bins out in public places (or for pickup adjacent to trash). When I worked a community recycling project around 1990, the local government dropped off a few regular dumpsters at some mass-transit parking lots on Saturdays, with informal signs "paper", "clear glass", "steel", etc. and I vaguely recall a regular compactor trash-truck that we used for plastic bottles. Residents could drive in and drop off their household materials--most were either loose in their trunks or in whatever box/bin/bag they happened to have at their house. I have no idea what the county did with those dumpsters-full of each type of material. But weekly curbside pickup was solely headed to the landfill, as were the only bins anywhere in public. DMacks (talk) 16:12, 3 October 2023 (UTC)

In the UK, charities used to collect old newspapers for recycling in the 1970s and 1980s. The reward was IIRC, about £20 per Imperial ton, which was pretty much a roomful. In the 1990s aluminium drinks cans were also collected. which required less space (but more wasps). Both income streams were lost when local councils began recycling.

This article dates local authority recycling in the UK to the Environmental Protection Act 1990 and in the US to a similar timeframe, with a few cities leading the way in the late 1980s according to this source. Alansplodge (talk) 16:31, 3 October 2023 (UTC)

Another form of newspaper recycling was done by fish-and-chip shops, which at that date used newspapers for the outer wrappings. If you were known to the chippy and trusted that the papers would be in clean condition, you could trade a couple of week's broadsheets for a bag of chips and batter scraps. Great for the walk home from the pub. Martin of Sheffield (talk) 16:38, 3 October 2023 (UTC)

There were a series of recycling (then called "salvage") campaigns in Britain during the Second World War, perhaps the best known being the collection of aluminium pots and pans, which housewives were assured would be turned into Spitfires. Another less productive effort was the collection of Victorian iron railings which adorned the front gardens of many urban houses; the iron recovered was of such poor quality that heaps of railings remained at steel works until the 1970s, others were used as ballast in ships or [allegedly] just dumped in the sea. [6] [7] Alansplodge (talk) 16:47, 3 October 2023 (UTC)

Not just houses, also businesses and churches. Martin of Sheffield (talk) 16:56, 3 October 2023 (UTC)

I remember collecting the aluminium foil tops from glass milk bottles, in the late 60s/early 70s. I have a vague thought that they were given to a charity which could sell them, presumably for recycling? -- Verbarson  ^talk_edits 18:10, 3 October 2023 (UTC)

In America, "paper drives" were a thing at least as far back as World War I. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:35, 3 October 2023 (UTC)

See also History of bottle recycling in the United States. And I remember wrapping piles of newspaper in twine & taking them to be recycled on Long Island circa 1970. Pretty sure there we also brought in aluminum cans. - Jmabel | Talk 04:02, 4 October 2023 (UTC)

For what it's worth... when I moved into a house here in Toronto, Canada, in 1983, garbage was collected twice a week. Then in 1988 every household was given a blue box to be used to recycle glass and plastic bottles; they changed one of the garbage collections to a blue-box collection. Recycling of other materials followed over the next few years and has continued to expand, now using wheelie-bins instead of open boxes. The original poster said "in your country", but here this stuff is all organized at the municipal level. --142.112.221.246 (talk) 06:52, 4 October 2023 (UTC)

Zabbaleen: Around the 1910s, a group of Muslim migrants from the Dakhla oasis in the Western desert of Egypt relocated to Cairo in an area known as Bab El Bahr, which is situated between Attaba and Ramses square in downtown Cairo.[2][17][18][19] These people are known as the Wahiya (singular: wahi), which means people of the oasis.[18][19] The Wahiya assumed the sole responsibility for the collection and disposal of Cairo's household waste under the framework of contracts with building owners in Cairo. In this system, the Wahiya paid the owners of buildings an initial sum and then collected monthly fees from the tenants for their services.[17][18][20]

--Error (talk) 15:11, 4 October 2023 (UTC)

October 4

EMT's taking EEG

Adventure (fanfic) novel (chapter 34).[8] Guy gets hit by some kind of energy beam, falls down, paralyzed, no heartbeat, eyes not responsive to light, stiff as a board, seemingly dead, or else tonic immobility. Medics arrive and they find a normal EEG, i.e. the guy is alive despite the paralysis.

Would paramedics/EMT's usually carry EEG equipment and know how to use it? EKG maybe, but I thought EEG was much more sensitive and anyway there is no CPR analog for head injuries. So this EEG seemed a bit out of place. Of course it's fiction, but it is generally pretty careful about stuff like this. Thanks. 2601:644:8501:AAF0:0:0:0:86EA (talk) 09:41, 4 October 2023 (UTC)

Help identifying a biological database

Hi, I'm trying to identify a biological database. I recall a scientist from the EU (I think) talking about a database (which is available only to researchers) which has been collecting samples over the past few decades from healthy volunteers - the same people every period of time - and their DNA, RNA and proteins were sequenced. They also collect other health measures. This allows retrospective research, say an individual was diagnosed with a certain disease, the researcher can look back and see when things started to go wrong. Does anyone have any clue which database this might be? Or maybe a publication that used such data? 2A01:6500:A042:E362:5864:707B:9DB7:B12A (talk) 12:38, 4 October 2023 (UTC)

I don't know about the EU but the UK has a large project of that type called UK Biobank. Mike Turnbull (talk) 13:21, 4 October 2023 (UTC)

UK Biobank, in fact. See also Biobank for general information and pointers to other specific organisations. -- Verbarson  ^talk_edits 13:24, 4 October 2023 (UTC)

Thank you Mike Turnbull & -- Verbarson , it looks like this is what I was trying to find. 2A01:6500:A042:E362:5864:707B:9DB7:B12A (talk)