Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

September 21

Becquerels released in nuclear explosions

https://en.wikipedia.org/wiki/Becquerel#Examples states

“ The nuclear explosion in Hiroshima (an explosion of 16 kt or 67 TJ) is estimated to have injected 8×10²⁴ Bq (8 YBq, 8 yottabecquerel) of radioactive fission products into the atmosphere. ”

whereas https://www.sciencedirect.com/topics/earth-and-planetary-sciences/fission-weapon states

“ …atmospheric testing of more than 500 atomic and thermonuclear weapons between then and the end of the 1970s. The fallout from such weapons amounted to a total of ∼250 EBq (2.5×10⁺²⁰ Bq)… ”

How is it possible that a small nuclear explosion release over 30000 times more becquerels than all atmospheric tests combined?

Thanks,
cmɢʟee⎆τaʟκ 00:04, 21 September 2023 (UTC)

According to Nuclear weapons testing, "Nuclear explosions close enough to the ground to draw dirt and debris into their mushroom cloud can generate large amounts of nuclear fallout due to irradiation of the debris. This definition of atmospheric is used in the [1963] Limited Test Ban Treaty, which banned this class of testing along with exoatmospheric and underwater." That would explain at least part of it. Clarityfiend (talk) 13:18, 21 September 2023 (UTC)

No, it's some sort of dumb error. Abductive (reasoning) 15:17, 21 September 2023 (UTC)

Which part do you think is in error, @Abductive:? cmɢʟee⎆τaʟκ 16:02, 21 September 2023 (UTC)

Lessee, the article on says Little Boy had 64 kg of highly enriched uranium, and added 8 YBq to the environment. The article on the Chernobyl disaster says "8.5×10¹⁶ Bq equals 24 kilograms of caesium-137". These are, what, 7 orders of magnitude apart? Something's wrong. And it looks like it might be Wikipedia. Abductive (reasoning) 18:06, 21 September 2023 (UTC)

Even "highly enriched" uranium is not very radioactive. U-235 has a half-life of around 700 million years, whereas U-238 has a half-life of 4 billion years, and HEU is still mostly U-238. On the other hand cesium-137 has a half-life of about 30 years, so it's something like 8 orders of magnitude more radioactive than HEU per unit mass.

But of course the radioactivity from Little Boy didn't come (mainly) from the HEU, but from its fission products, which were immensely more radioactive. Direct comparison is challenging based just on this. --Trovatore (talk) 19:00, 21 September 2023 (UTC)

7 orders of magnitude. Abductive (reasoning) 19:47, 21 September 2023 (UTC)

7 orders of magnitude sounds too small to me. Why do you seem to think that it is too big? (If I understand your position correctly.)Liberté2 (talk) 20:31, 21 September 2023 (UTC)

As can be seen below, the huge number for Hiroshima in the Becquerel article is grotesquely inflated by counting all the energy released as if it was radioactive fallout. Abductive (reasoning) 02:08, 22 September 2023 (UTC)

According to our article, Little Boy's uranium was 80% U-235.

At what time you measure this radioactivity also matters. Little Boy injected quite a lot of radioactivity into the atmosphere one second after detonation. Within minutes, much of that had already decayed to stable isotopes. If you measure fallout, you're talking about the radioactive materials that make it back to the ground in the weeks after detonation. You can get the number for the Hiroshima explosion almost as high as you want by counting the very short lived fission products. Which makes the number meaningless. PiusImpavidus (talk) 20:01, 21 September 2023 (UTC)

Oh, I bet that's it. Sure, if you look at the first second after detonation, then you've got all those nuclides with half-lives on the order of a second, disintegrating at a furious rate. Doesn't mean much for humans compared to the direct radiation from the bomb, but technically it's ultra-high radioactivity for that short time. --Trovatore (talk) 20:39, 21 September 2023 (UTC)

@Trovatore,@PiusImpavidus,@Liberté2,@Clarityfiend,@Abductive: Thanks for your explanations. Does that mean Becquerel#Examples should be changed in any way? Thanks, cmɢʟee⎆τaʟκ 09:10, 24 September 2023 (UTC)

Absolutely, yes. While you could theoretically estimate the distribution of isotopes at the moment of the Hiroshima explosion and estimate the activity of each one, and then make a (horribly complicated) table of all the daughter products and their quantities at any given time after, that's NOT a useful example for understanding the concept of the unit, even if the number given is accurate. I'll change it. PianoDan (talk) 23:12, 25 September 2023 (UTC)

Thanks, @PianoDan:. cmɢʟee⎆τaʟκ 11:08, 28 September 2023 (UTC)

Intelligence and Biases

Which biases are correlated with intelligence (g)? Which are positive, which are negative, and which are independent? 2A02:8071:60A0:92E0:418B:548F:263F:56D7 (talk) 18:31, 21 September 2023 (UTC)

Your question is way too vague. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:06, 21 September 2023 (UTC)

There is a very long list of biases at bias and bias (disambiguation). I suggest you consult those articles or clarify your question. Shantavira|^{feed me} 08:39, 22 September 2023 (UTC)

From what I've seen there is very little connection between intelligence and the amount or type of biases. More intelligence just makes for better rationalization. And unfortunately as far as AI sytems are concerned it seems the better ones are also getting better at not only incorporating biases but also at having the same types of failure of reasoning as people. As to whether they are good or bad - that's what I'd call a moral or policy question rather than a science one. NadVolum (talk) 13:41, 22 September 2023 (UTC)

RESCUE REQUEST (Sorry, I misspoke last time ; addition of a sentence)

Trolling
The following discussion has been closed. Please do not modify it.
🆘 I CAN'T STAND IT ANYMORE, cryonics is said to be too neuron-destroying for the technologies of the future to do anything. I did come up with a process to do something for all these people, but given the previous recital, we need to focus on preserving neurons in good conditions. I need a process (cold or otherwise) that works. Could you please send a message "Extreme urgency: current Cryonics destroy too many neurons and vitrifixation does not preserve the excitability threshold of synapses and is said to destroy neurons too, could you please immediately launch research into finding a satisfactory process" to the authorities, public services and non-profit organisations. What we are going to do is, instead of using classic cryonics followed by dismantling of the brain into individually excited neurons by computer (thanks to a computer simulation (based on the data collected during dismantling)) - to do this we would also have to dismantle each neuron into each of its parts in order to recover information about (among other things) the excitability threshold of the synapses - use vitrifixation with preservation of the excitability threshold of the synapses and with non-destruction of the synapses and neurons (a process yet to be invented); This will allow us, thanks to the downloading of data from the mind, to simply dismantle the brain by removing the neurons one by one without having to dismantle them themselves, which makes this operation much easier. Could someone here please take the administrative steps to organise a march in Washington DC ? 2A01:CB0C:C45:E000:94D6:C59A:5856:535F (talk) 18:58, 21 September 2023 (UTC)

combinatorics of chromosome

In a discussion with friends, the topic of how some conditions, such as autism and ADHD, are more common for males. For example, Sex and gender differences in autism.

Someone brought up the XX vs XY issue:

Women have two X chromosomes, and men have one X and one Y chromosome. This changes the combinatorics of recombination (meaning: the likelihood of various combinations of genes appearing together over generations of reproduction). 

I don't know much about genetics. Is this actually a factor?

On the one-hand, it sounds perfectly reasonable and there's no reason to doubt it. On the other hand, it also sounds very "pop-sci". Liberté2 (talk) 20:30, 21 September 2023 (UTC)

This is the idea that having only one X chromosome unmasks recessive genes responsible for autism, as seen in color blindness, right? I think that there isn't much evidence for it. Abductive (reasoning) 01:58, 22 September 2023 (UTC)

The reasoning is sound, and it works because each chromosome has its own allele for each gene, meaning that in the case of X and Y chromosomes, there are effectively four in total. Since there are four gene alleles, there is a greater chance that one of them will be affected. Another consequence of having four alleles is that the severity of the autism is variable depending on how many alleles are affected. With the Y chromosome being as small as it is, there is little opportunity for meiotic exchange of material and thus it tends to be affected more frequently in a heterozygous state. Hope this helps. Buckrune (talk) 04:02, 22 September 2023 (UTC)

I am not sure where Buckrune gets the idea of FOUR alleles, nor the argument about a greater chance of being affected the more copies there are. In a diploid species like humans each individual has TWO alleles per locus (if the gene lies on an autosome, i.e. not a sex chromosome). If one chromosome has a defective allele, usually the allele on the sister chromosome will not be defective and that one copy will be sufficient to maintain function, hence masking the defect. But in the case of a defect in a gene on the X chromosome, in men the Y chromosome would not have this "backup" copy to maintain function. It is more complicated in women, because in each cell one X chromosome is inactivated and which it is tends to be inherited by daughter cells; this causes the patchiness of colouration in tortoiseshell cats. That is the principle behind sex-linked genes. But whether any of the genes involved in autism are sex-linked is another issue that I cannot answer. Mostly the reasons for correlations between between phenotype and sex are not because the genes involved are on the sex chromosomes. JMCHutchinson (talk) 08:58, 22 September 2023 (UTC)

The thing is, the genes on the X being fully expressed in males means that natural selection takes a cold, hard look at them every time. Aside from fragile X syndrome, there aren't many genes implicated in autism on the X. And there are hardly any genes at all on the Y. As to the idea that recombination itself has anything to do with an increased likelihood of autism or any other disease or condition, that's not how recombination works. Abductive (reasoning) 09:57, 22 September 2023 (UTC)

Good points, but I would add that although selection indeed ought to weed our defects on the X chromosome quicker than those on autosomes, a number of X-linked diseases are not so rare, including haemophilia and Duchenne muscular dystrophy. JMCHutchinson (talk) 06:40, 23 September 2023 (UTC)

There's an argument that particularly devastating conditions that affect children are not selected against as strongly as one might suppose. Instead, the selection pressure is a wasted pregnancy – a stillbirth that lives for a while. Abductive (reasoning) 12:44, 23 September 2023 (UTC)

Blacklight/UV light

Browsing through Amazon, it seems like there are two main types of UV/black lights: those in the 395-400 nm band and those at 365-370 nm. What is the functional difference between the two? The ad copy seems largely the same. Am I right in thinking the 365 nm one is not functionally visible unless it's fluorescing something, while the 395 nm will appear purple? Anything else? Matt Deres (talk) 21:33, 21 September 2023 (UTC)

Here are a couple of pages from lighting manufacturers discussing the differences: 1 2 CodeTalker (talk) 23:47, 21 September 2023 (UTC)

Thank you - very helpful! Matt Deres (talk) 11:10, 22 September 2023 (UTC)

September 22

Mucosal layer peeling off

I've noticed that when my soft palate is scalded with some hot meal, there's a feeling of some mucosal layer peeling off or shrinking in the affected area. How that layer and related process is called anatomically/physiologically (other than thermal burn)? 212.180.235.46 (talk) 12:30, 22 September 2023 (UTC)

See oral mucosa and, more generally, mucous membrane. We cannot provide medical advice, but if you think your mouth has been injured, a visit to your doctor is in order. Matt Deres (talk) 17:44, 22 September 2023 (UTC)

Bell AH-1 Expert arround? Why a wide-chord rotor blade?

The fact that when the Bell AH-1 was created, "components of the Bell 204 UH-1 were used as far as possible" to keep costs low (for example, rotor, gearbox and turbines) can be read widely distributed in many places within Wikipedia.

However, why exactly a special rotor blade was developed for the Cobra is nowhere explained. Perhaps an expert reads this and spends some time for an educated statement?

Thanks in Advance --46.114.5.151 (talk) 14:56, 22 September 2023 (UTC)

It appears that the wide-chord rotor in general was being adopted at that time, as it provided more stability. Abductive (reasoning) 21:52, 22 September 2023 (UTC)

Googling around, it seems that the UH-1C (developed immediately before the AH-1 but only 750 were built) also had wide-chord blades, intended to increase speed. I couldn't pin down whether exactly the same rotors were used on both, or if those used on the AH-1 were a further development. Other sources state that wide blades are quieter as well. Alansplodge (talk) 18:23, 25 September 2023 (UTC)

Universal principles show that the planform area of a wing or rotor is largely determined by the weight of the aircraft/helicopter. Noise levels and general flying qualities of a helicopter are partly determined by the airspeed of the tip of the advancing blade. If two different helicopters have the same maximum weight but different maximum speeds, they will have the same rotor blade planform area but the faster of the two must have a smaller rotor diameter if the two are to have the same blade tip speed when flying at maximum speed; this dictates that the faster helicopter must have blades with a wider chord, or a greater number of blades.

The UH-1 and AH-1 have the same maximum take-off weight - 9,500 lb. The UH-1 has a maximum forward speed of 110 knots and a rotor diameter of 48 ft. In the case of the AH-1, these parameters are 149 knots and 44 ft. Seeing both helicopters have the same number of blades, the wider chord of the AH-1 blade is exactly what is expected from these universal principles. Dolphin (t) 22:35, 25 September 2023 (UTC)

Attention deficit disorder

What is the difference between attention deficit disorder (ADD) and attention deficit hyperactivity disorder? Why does Wikipedia only have a single page for both and say only that ADD was an older name of ADHD? 207.114.136.166 (talk) 21:02, 22 September 2023 (UTC)

Wikipedia say that ADD was an older name of ADHD because it was. There is no difference. AndyTheGrump (talk) 21:15, 22 September 2023 (UTC)

September 23

How to simultaneously fire every neuron?

Trolling
The following discussion has been closed. Please do not modify it.
Hello, I am working on the concept phase of a device that I intend to expand brain power by firing every neuron at the same time. We currently use no more than 15% of our brain’s processing capacity, leaving the other 85% of neurons idle. This device would bring that number up to 100%, thus improving overall speed and performance. What kind of stimulation would cause all neurons to fire simultaneously? It seems like some pharmaceuticals unlock brain power, but I imagine something immediate, like electrical or possibly magnetic energy that would basically flip one switch for all neurons to activate. Gliffor32XD (talk) 03:53, 23 September 2023 (UTC) It was never true to claim that "We currently use no more than 15% of our brain’s processing capacity". HiLo48 (talk) 04:15, 23 September 2023 (UTC) Yes, that has been soundly debunked. As to how to fire all the neurons at once, I'm thinking that might happen in an electric chair. ←Baseball Bugs What's up, Doc? carrots→ 04:24, 23 September 2023 (UTC) This question was previously asked and answered at Wikipedia:Reference desk/Archives/Science/2023 February 11#Increasing brain power.-gadfium 04:26, 23 September 2023 (UTC) Asked by a sockpuppet of a globally locked former contributor. Not much brainpower here... AndyTheGrump (talk) 05:31, 23 September 2023 (UTC)

soil bearing capacity

Hi. This US site[1] lists soil bearing capacity ranging from 2000 PSI to 12000 PSI, which is 13789 kPa to 82737 kPa in metric units.

This UK site[2] lists soil bearing capacity ranging from 75 kPA to 600 kPa.

Clearly they are using very very different measurement methods, and thus resulting in two very very different scales. These two scale are not directly comparable to each other (as far as I can see).

What is the difference in the measurement method that results in such a large difference in the resultant scale?

(Obviously these scales are arbitrary so there is no right or wrong here. I am not suggesting that one of these scale is somehow better than the other, or that one of them is more preferable than the other. I just want to know why they are different.) Liberté2 (talk) 18:04, 23 September 2023 (UTC)

Doesn't the US one give pounds per square foot? 12,000 pounds per square foot is 574.6 kPa. Abductive (reasoning) 20:51, 23 September 2023 (UTC)

Right you are. That was a terribly embarrassing mistake on my part, haha. Liberté2 (talk) 22:39, 23 September 2023 (UTC)

Resolved

Liberté2 (talk) 22:39, 23 September 2023 (UTC)

air concrete

Hi. I know nothing about concrete (as clearly evident by my embarrassing question above).

Before today, I was under the (uninformed) impression that air in concrete is a very bad thing. Then today I came across this PDF[3] which explained that air is intentionally kept in concrete in some regions. I did not know that before. This is also covered in the WP article Air entrainment.

Roughly in which region or states in the US is this done? The PDF is from the Federal Highway Administration and they build highways all across the US, so presumably they have some sort of map or list or guidance on where this should or should not be done.

I googled "Air-Entraining Admixtures map", "Air-Entraining Admixtures states", and "Air-Entraining Admixtures region" and nothing useful came up. Liberté2 (talk) 22:55, 23 September 2023 (UTC)

• For any topic as broad as "concrete", it's a fair guess that everything that is possible is done sometimes, for some purpose, and will have some (maybe very narrow) usefulness in some obscure situation.

Concrete is dense. So there are many situations where a lighter concrete, formed by the inclusion of gas bubbles, is useful. It might lose strength, yet gains strength / weight ratio, so is still useful. This is becoming a major (major!) topic in the UK at present, as we finally act on the amount of RAAC (Autoclaved aerated concrete is the more useful article) which is reaching its end of life.

In the situation you link, it's an even more obscure case. Trading off a few % loss in strength gives a useful increase in longevity against Winter freeze-thaw damage, a major problem for civil engineering in the more northerly states. Andy Dingley (talk) 08:41, 24 September 2023 (UTC)

They should definitely have done better checks on how well protected the steel rods inside were before using it so widely rather than now having to replace it all. Concrete is used for everything is about right though! I remember how surprised I was when I was told a dredging barge I was looking at was made of concrete! And it had been happily working away for nearly a century. The reinforcement in that was much better done than in those buldings made fifty years ago. NadVolum (talk) 10:32, 24 September 2023 (UTC)

Even the Romans used concrete, some of which survives to the present day.... Mike Turnbull (talk) 14:16, 24 September 2023 (UTC)

According to a recent YouTube video made by an experienced builder, problems with RAAC installations in the UK, particularly those from the 1960s and -70s, are not due to the material itself, but to its use for less appropriate purposes (like unpitched roofs, which inevitably leak and allow water into the porous concrete to rust the steel rebar) and to hasty inaccurate building work that resulted in many horizontal RAAC panels being inadequately supported at their ends by walls an inch or more out of true, leading to excessive shear forces that cause them to crack.

The presenter contrasted these with Rome's Pantheon, a huge unsupported dome built, skilfully, with Roman concrete nearly 2000 years ago that is still sound and safe today (which is why Mike Turnbull's post above reminded me of the video). {The poster formerly known as 87.81.230.195} 51.198.107.25 (talk) 15:24, 25 September 2023 (UTC)

There are concretes such as kiln brick where air bubbles are intentionally incorporated into concrete for temperature insulation. Such concrete is usually structurally very brittle while allowing a thousand degrees of temperature difference to room air temperature right next to it (either Fahrenheit or Celsius, take your pick). 85.76.21.190 (talk) 14:58, 27 September 2023 (UTC)

• Air in concrete is of little consequence, but moisture (resulting from rain water) certainly is. Of course, this applies to all construction materials: Wet timber decomposes, wet steel rusts, etc.
• Wet masonry (Stone Henge, Cheops Pyramid, Gothic cathedrals) generally is not critical. The lintels atop the sarsen stones on Salesbury Plain have not - well, not all - collapsed in 3.4 millennia.
• The problem is reinforced concrete, a compound material where steel bars / meshes are embedded in concrete (= an aggregate of sand and pebbles bound by cement). In the case of aerated panels these structural elements also contain air bubbles to decrease the weight / reduce thermal transmission.
• When water is absorbed, there may be two results:

1 Cement, which acts like a glue to the aggregate, is - simplified - washed out.

2 Reinforcing rods will oxidise / rust.

• As a result, the load bearing capacity of the structural element is reduced and the item fails under structural load. Generally, aerated concrete is used for panels which simply support their own weight. This weight suffices to cause damage and injuries.

--Cookatoo.ergo.ZooM (talk) 16:31, 27 September 2023 (UTC)

Music lost to time

Hi all. Listening to Mazzy Star's "Fade into You" got me thinking just how nicely it captured that 90s feeling. Then I wondered if people would be able to listen to it a thousand years down the line. Let's assume for a second that streaming platforms will exist in 3000: would our successors be able to listen to Hope Sandoval the way I do now? Will the server have to re-upload a fresh recording some time between now and 3000 for millions to stream? Where and how is the initial studio recording stored? Does the recording decay? If the record is copied for preservation to another device, will the quality greatly diminish for the copy of a copy's copy? What's the best medium to save a music file and is it financially viable?

Too many questions condensed into one: If records do fade away and their near-eternal storage is financially unsound, or future technology is unable to reproduce current media just like we're already struggling with VHS, will the majority of present-day music eventually become lost to time?

Thank you. Splićanin (talk) 23:05, 23 September 2023 (UTC)

I take it you're talking about digital recordings. What about older technologies, like 78 RPM phonograph records? They were being produced as recently as the 1950s, but it's pretty hard to find a machine that will play them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:48, 24 September 2023 (UTC)

A quick search on Amazon returns: 'over 6,000 results for "78 rpm record player"'. Pretty well all turntables I've see recently are 33/45/78. You make a fair point for digital media however. Martin of Sheffield (talk) 08:46, 24 September 2023 (UTC)

You're asking for speculation, which we can't really do here. However, the general concept you're looking for can be researched on a number of articles, including Digital preservation and Data preservation, Digital permanence, Media preservation, and many others. In other words, it's something that a lot of people have thought about (including the Norwegians). I'm 99% sure we have an article specifically on the specific struggle with the obsolescence of the software/hardware used to read the data (e.g. VHS tapes), but it's evading me. Matt Deres (talk) 02:46, 24 September 2023 (UTC)

Digital dark age and media preservation talk about the issues of hardware and software obsolescence to some extent although the former not in relation to VHS tapes. Nil Einne (talk) 03:32, 24 September 2023 (UTC)

When you look at the history of music, what has kept certain music alive through the centuries without technology is not just sheet music, but also its status as part of a musical repertoire. It is also quite common for popular music to fall out of this repertoire and go missing and unheard, only to be brought back a century or so later. Even without technology to preserve this music, I can assure you, the music behind "Fade into You" doesn't belong solely to 1994 (although it certainly felt like it at the time, because you couldn't escape it). It belongs to the sphere of the mind, which means as long as musicians are still around in the future, it is likely that many of them will cover the tune and keep it alive. As odd as this might sound, it's not unheard of. A lot of music is known to contain bits and pieces of melodies and arrangements from older folk music. Much of that folk music is now lost, but survives in part through its incorporation into newer pieces. Given the simplicity and general tone of "Fade into You", that's how it will likely survive as well, and newer musicians will rediscover it and call it their own, as they always do. Viriditas (talk) 21:45, 24 September 2023 (UTC)

Products of culture, like books, films, architecture, paintings, drawings and the like, including music, tend to inevitably get lost as time goes by. It is inevitable, sadly. Very few thought about long-term preservation of such products of culture hundreds of years ago, and right now there are countless of probably interesting and maybe groundbreaking works that have been lost. It is impossible to keep and save everything, sad as it might be. --Ouro (blah blah) 17:34, 26 September 2023 (UTC)

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)

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)

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 [4] and [5]. --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)