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November 18

Open-air dust explosions

Dust explosion#Conditions required says There are five necessary conditions for a dust explosion. It even has a pointless diagram that arranges the five conditions in a pentagon with "dust explosion" in the middle. Condition 5 is confinement. But further down the page, Dust_explosion#Mechanism has a series of photographs demonstrating a dust explosion in open air. And thermobaric weapons, although more effective at killing people in confined spaces, seem to explode just fine in the open. So is condition 5, as a "necessary condition", plain wrong, perhaps an exaggeration of the fact that confinement makes a dust explosion more likely?

Supplementary question: I hear residents of Lahore and Delhi are wondering if their very sooty smog might one day explode. Is this at all plausible?  Card Zero  (talk) 00:09, 18 November 2024 (UTC)

Pointless? It is a five-pointed diagram.  --Lambiam 06:53, 18 November 2024 (UTC)

In general, not only for dust, for detonation to occur, a mix of fuel and oxygen within the explosive limits has to be present in a compact largish volume. Upon detonation, the pressure in this volume will rapidly increase tremendously within (typically) microseconds. If the volume is not confined by an enclosure, the gases resulting from the combustion will expand supersonically with a shock wave that may or may not cause damage, depending on the power released and the environment. If the volume is confined by an enclosure, the enclosure may be able to withstand the pressure and contain the gases – possibly with controlled release through safety valves. (See e.g. Pyréolophore.) Otherwise, if the enclosure is broached, the gases will also expand explosively.

The OSHA fact sheet that is the source of our five-pointed list of conditions is actually about another scenario. It considers the case in which ignition merely leads to deflagration, which is much more likely to occur – the mix only has to be within inflammability limits. The combustion is much slower and does by itself not cause a shock wave. However, although the pressure rises less rapidly, the rise is still dramatic, especially if the volume is contained by an enclosure. If the enclosure cannot withstand the pressure, the gases will also expand explosively, as before.

So I think a fuel–oxygen explosion can occur in open air, but for this to be an explosion in the strict sense of causing shock waves, the right conditions will only very rarely be fulfilled accidentally. (In thermobaric weapons, they are fulfilled by design.)  --Lambiam 09:05, 18 November 2024 (UTC)

But in the conditions there is no requirement of an accidental event?! 176.3.66.65 (talk) 15:10, 22 November 2024 (UTC)

The OSHA fact sheet does not deal with ways to mitigate the risk of intentional explosions, such as may be caused by weapons. You are free to see this as an omission; I doubt though they will agree.  --Lambiam 12:00, 23 November 2024 (UTC)

Delayed onset muscle soreness

How long does it last and how to recover from it? CometVolcano (talk) 16:53, 18 November 2024 (UTC)

According to the article: "It peaks from 24 to 72 hours, then subsides and disappears up to seven days after exercise." --Amble (talk) 17:11, 18 November 2024 (UTC)

From the top of this page: We don't answer (and may remove) questions that require medical diagnosis... AndrewWTaylor (talk) 14:15, 19 November 2024 (UTC)

It is said that the soreness is helped by consuming protein. Abductive (reasoning) 10:27, 20 November 2024 (UTC)

November 20

John Balbus and Steven Balbus

Are Steven Balbus (Oxford University astrophysicist) and John Balbus (Head of Office of Climate Change and Health Equity in Biden's HHS) related? 178.51.16.158 (talk) 19:43, 20 November 2024 (UTC)

Given their mutual association with Philadelphia and their strong physical resemblance, it seems very likely, but I haven't been able to find any source confirming it with a cursory web search, so this might take some deep digging (better suited to someone in the USA, not Europe). John Balbus, incidentally, seems to me to be a good candidate for a Wikipedia article. {The poster formerly known as 87.812.230.195} 94.1.211.243 (talk) 02:13, 21 November 2024 (UTC)

They are brothers, with a third brother named Peter.^[1] Here on p. 33 is a photo of Steven en John side by side. Their father was Theodore G. Balbus,^[2] a radiologist, and their mother Rita S. Frucht.^[3] A bio of the father is found here, where you can also find that Peter runs a consulting firm called Pragmaxis.  --Lambiam 10:09, 21 November 2024 (UTC)

November 21

Griffiths in math and physics

There's something called the Griffiths phase. If you search for griffiths phase activity so, you'll find things with similar names. A Griffiths singularity, Griffiths effects, there's probably more than one thing people call Griffiths' formula since there's a physicist called Phillip and two named David J. Griffiths. How many things are we dealing with under this name? Is there a book where they're all listed right next to each other? Gongula Spring (talk) 19:37, 21 November 2024 (UTC)

The concept of a Griffiths phase is named after theoretical physicist Robert B. Griffiths, who was the first to describe the appearance of such phases in an Ising model of ferromagnetism.^[4] He is also the eponym of the Griffiths inequality. Most uses of Griffiths singularity and Griffiths effect appear to be related. "Griffiths' formula" is a very general name that may refer to various formulas found by mathematicians with the surname Griffiths, such as Griffiths' integral formula for the Milnor number of an isolated hypersurface singularity, found by pure mathematician Philip A. Griffiths, also the eponym of the Griffiths group. See also Griffiths' theorem, named after yet another Griffiths.  --Lambiam 23:43, 21 November 2024 (UTC)

That formulation seems at least superficially be leading to references to Alan Arnold Griffith. Formulas like ohmic or non ohmic dissipation in metallic griffiths phases used at the National High Magnetic Field Laboratory then tend to appear ambiguous to that effect too. Most other examples are deeply plunging into statistical quanta states thus unambiguously associated with Robert B. Griffiths instead. --Askedonty (talk) 00:13, 22 November 2024 (UTC)

The bracketing is not as in ((Griffith phase) field theory) but like (Griffith ((phase field) theory)), a theory of fracture, based on a phase-field model, developed by Griffith.  --Lambiam 08:47, 22 November 2024 (UTC)

The interesting thing is that those approaches are leading us very near of a (a least to me ) finally rather satisfying view of the problematics induced by the idea of Action at a distance. --Askedonty (talk) 10:51, 22 November 2024 (UTC)

So much that you only have to think about it and what do you get? Long distances in apparent contradiction to.. --Askedonty (talk) 11:00, 22 November 2024 (UTC)

I'm not sure if these long distances anticipate my next question, which is what does "long-range" mean in the search results above?

Gongula Spring (talk) 15:54, 22 November 2024 (UTC)

Perhaps, as in #16 from that request as I get it "Temporal disorder in discontinuous non-equilibrium phase transitions: general results". The "long distances" discussion above being from 2002 by contrast. --Askedonty (talk) 16:39, 22 November 2024 (UTC)

Number 16 uses "temporal" and "critical" terms, are we getting toward ideas about long-range temporal correlations in critical brain dynamics? Are they spooky?

Gongula Spring (talk) 17:05, 22 November 2024 (UTC)

I don't think so. Or not so directly anyway. Number 16 seem to be about logic and geometry: distance in that context is fact, and can also be manipulated. Relevant quote if there was one regarding our subject - but their process define a temporal Griffiths inactive phase some time - relevant would be (see their pdf):

Disorder due to spatial or temporal inhomogeneities is almost an unavoidable ingredient in many real systems, it is then desirable to understand their effects on these phase transitions. For continuous phase transitions, it was earlier recognized that spatial and temporal disorder changes the critical behavior whenever the generalized Harris criterion is violated [11, 12]: quenched spatial disorder is relevant whenever dν⊥ > 2 is violated while temporal disorder is relevant when νk = zν⊥ > 2 is violated; with ν⊥, νk and z being critical exponents of the clean phase transition and d being the number of spatial dimensions. Since the critical exponents of the directed percolation universality class violate the Harris criterion, it was then argued that this was the reason why it was never seen in experiments [13] (see however Ref. 14).

(They describe their purpose as: Non-equilibrium phase transitions have constituted a rich and lively topic of research for many years. They occur in a wide variety of models in ecology [1], epidemic spreading [2], sociophysics [3], catalytic reactions [4], depinning interface growth [5, 6], turbulent flow [7], among other fields [8–10].) [8–10] refer to Nonequilibrium Phase Transitions in Lattice Models. Sociophysics is a product of Positivism#Logical positivism ( perhaps note there a spooky "component not derived from observation" ) --Askedonty (talk) 21:03, 23 November 2024 (UTC)

November 22

Heat of chillies

How hot, in terms of Scovilles, does a chilli need to be before a parrot can feel the burn? I just saw a video on Facebook of a macaw eating a ghost pepper without the slightest care. From what I read, parrots are extremely resistant to the capsicum from chillies. Or is it because we have thousands of taste buds and parrots have tens, which is also true. 146.90.140.99 (talk) 01:27, 22 November 2024 (UTC)

“The seeds of Capsicum plants are dispersed predominantly by birds. In birds, the TRPV1 channel does not respond to capsaicin or related chemicals but mammalian TRPV1 is very sensitive to it. This is advantageous to the plant, as chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, whereas mammals have molar teeth which destroy such seeds and prevent them from germinating.”  Card Zero  (talk) 03:22, 22 November 2024 (UTC)

Yes, as Card Zero says, birds have different TRPV receptors (for vanilloids like capsaicin) than mammals. I guess chillis want their seeds distributed far and wide by birds. On the other hand, I've never seen anything eat the chillis that accidentally grow in my garden. Interestingly, my dog appears to have different TRPV receptors than me as they don't seem to notice very spicy chilli seeds on food and they won't be damaging the seeds. Sean.hoyland (talk) 03:32, 22 November 2024 (UTC)

Indeed, one of the most effective ways to keep squirrels off my bird feeder is to sprinkle the birdseed with chilli powder. Shantavira|^{feed me} 09:23, 22 November 2024 (UTC)

My entire home crop of capsicums (bell peppers to Americans), and some chillis disappeared in one night last summer right after a colony of fruit bats arrived in my local park. Fruit bats, of course, are mammals. HiLo48 (talk) 10:08, 22 November 2024 (UTC)

That's interesting because there are many bats here. They often sleep individually or in small groups inside young banana leaves that haven't unfurled yet. They sometimes crash into me at night if I'm moving. I guess in bat-world tree-like things don't move. They seem to have a chilli-free diet but might eat some of the other fruit. Plenty of insects to eat. Bat teeth seem to be quite diverse molar-wise. Chilli is the only thing that survives the wildlife. It's a multi-belligerent fruit-based forever war over resources with the birds, squirrels, rats, countless insects, fungi, bacteria and viruses. Sean.hoyland (talk) 15:50, 22 November 2024 (UTC)

Insect eating bats are very different from the fruit bats. There's a theory that peppers have the same sort of relation to fruit bats as chillis do to birds so I can easily imagine a fruit bat being partial to a couple of chillis even if it does find them rather hot. NadVolum (talk) 21:23, 25 November 2024 (UTC)

November 23

Before Puberty, sex organs are not functional?

How do sex organs function in both genders before puberty in humans? Not after Puberty. HarryOrange (talk) 07:24, 23 November 2024 (UTC)

Sexual maturity is only reached during puberty. Before it is reached, the sex organs are not (or not yet fully) functional. See also Sex organ § Development and Precocious puberty.  --Lambiam 11:51, 23 November 2024 (UTC)

They're functional. It's just that their functions are generally under the headings of "basic maintenance" and "not atrophying". Abductive (reasoning) 09:39, 24 November 2024 (UTC)

To my understanding (which may be deficient), testicles prior to puberty are secreting some levels of androgens (including testosterone) and estrogens, which contribute to the male body's normal development, even though these levels are well below what they become during and after puberty. I imagine (perhaps wrongly) that similar considerations apply to the ovaries.

Our immediately relevant articles seem not very informative about pre-pubertal operations of the sex organs. Perhaps someone more knowlegable could take a look at them. 94.1.211.243 (talk) 09:46, 24 November 2024 (UTC)

I did take a look, I always do before answering a question. Here is a representative article; The immature human ovary shows loss of abnormal follicles and increasing follicle developmental competence through childhood and adolescence. The word "competence" means that in vitro the ovary tissue does a better job of taking on adult functionality the older the girl, but in vivo such activity is suppressed. Abductive (reasoning) 10:08, 24 November 2024 (UTC)

Nevertheless, if I've understood the peripheral hints I've encountered, those pre-pubertal levels of androgen and estrogen (and steroid, etc.) secretions are necessary at the time (the pre-pubertal period) for ongoing normal development, which is kinda what the OP asked about. Of course, all this is well above my pay grade. {The poster formerly known as 87.81 230.195} 94.1.211.243 (talk) 13:36, 24 November 2024 (UTC)

This discussion seems to have focused on the testicles and ovaries but the penis is also a sex organ and is capable of an erection before puberty. This is mentioned in our erection article in a sort of weird way given the flow on sentence. Ejaculation however only happens after puberty. I assume there is similarly some level of function in female sex organs. As mentioned in our masturbation article it's normal in children even in infancy and may even happen in the womb and is only a concern when there are indications it may relate to sexual abuse. Nil Einne (talk) 20:46, 24 November 2024 (UTC)

The penis as such is able to "ejaculate" well before puberty (somewhat dependent on definition) but because the prostata doesn't produce anything, there is nothing to ejaculate. So it's going through the motions way before the other organs are functional. 176.0.132.86 (talk) 05:20, 29 November 2024 (UTC)

November 25

Is there a cryonic company that will freeze me while I'm still alive and healthy, and reanimate me 15 years later? If I arrest the aging process for 15 years this way, could I then pass for a Gen Z?

Could I have myself cryofrozen (without dying of another reason first) in 2025 with instructions to reanimate me in 2040 so that I could more convincingly pass for and live like someone born in the Gen Z generation?

What companies cryofreeze people who ask for it while still alive and healthy?

Or does such a cryonic plan and company exist anywhere in the world?

I wanted to be born in 2000, not the year I was actually born in. So if I get cryofrozen for enough years, I'll look as young as a Gen Z when I'm reanimated.

Lastly, Reddit's r/Cryonics subreddit's automoderator keeps glitching out because it keeps autoremoving any content of mine from there. I tried posting this question and above summary to other subreddits but their automod keeps autoremoving it too. Their persistent glitches kept bugging me enough to dust off the Wikipedian reference desk and post here again for the first time in many years. I used to be a regular on the refdesk, then moved to Reddit, and now I'm back. --2600:100A:B005:AFD5:B08A:71E6:8521:5D8E (talk) 01:48, 25 November 2024 (UTC)

Short answer: No. As currently freezing a human adult, results in their death, as no resuscitation is possible. It would be some kind of murder to perform this, so only a crime syndicate would be willing. And then could you trust them for 15 years? Graeme Bartlett (talk) 01:59, 25 November 2024 (UTC)

In 15 years, you'd be just as deceased, pushing up daisies, no more, pining for the fjords. So what's trust got to do with it? Clarityfiend (talk) 08:34, 25 November 2024 (UTC)

At this point I feel bound to recommend that you watch Sleeper.Shantavira

Terraforming a planet around some distant star and setting up a population there sounds far easier and actually doable to me. Perhaps in the far future it'll be possible to create a new body and copy the brain fom one of those frozen blocks for it, or maybe set up an android with an artificial copied brain - but why would any people who could do that bother with anyone from this time, would it be ethical for us to try and make a Neanderthal clone? NadVolum (talk) 21:15, 25 November 2024 (UTC)

By way of a reference, try 'We don't yet have the know-how to properly maintain a corpse brain': Why cryonics is a non-starter in our quest for immortality. Alansplodge (talk) 11:53, 26 November 2024 (UTC)

Can any insurance company make a cryonics bankruptcy insurance policy for companies that preserve bodies in cryogenic preservation vats so that even when the company goes bankrupt, their insurance policies will keep these vats running and bodies preserved?

...So that we can continue the hope and possibility of reanimating these bodies back to life when medical science advances and finds cures to reverse whatever they died from?

This topic was also autoremoved from r/Cryonics so that's why I'm bringing it here too. Thanks in advance. --2600:100A:B005:AFD5:B08A:71E6:8521:5D8E (talk) 01:48, 25 November 2024 (UTC)

An insurance policy defines the amount of money to be paid to the holder of the policy when a specified contingency occurs. If the contingency is bankruptcy and the idea is to keep the company running, the amount should be larger than the prospectively unknowable debt to preferential creditors. It should be obvious that no insurance company can offer a policy with an unlimited payout. Apart from this, even an insurance for a sufficiently large amount cannot guarantee that the company or trustee will use the money paid out for the intended purpose.  --Lambiam 02:53, 25 November 2024 (UTC)

Who would be a creditor? They're all dead and have no rights. NadVolum (talk) 21:00, 25 November 2024 (UTC)

Creditors of Instant Immortality (the bankrupt cryonics company, for short II) could be: (1) the tax office; (2) II's bank; (3) the company from which II hired its cryogenic equipment; (4) II's provider of liquid nitrogen; (5) II's lawyers; (6) scores of estates of frozen clients, legally presumed dead, who won a class action lawsuit against II.  --Lambiam 11:43, 26 November 2024 (UTC)

Wow, is it April 1 already? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:00, 26 November 2024 (UTC)

Cryonics is such a blatant scam I don't understand how it is legal. Shantavira|^{feed me} 09:33, 26 November 2024 (UTC)

More blatant than (also legal) homeopathy? Clarityfiend (talk) 10:06, 26 November 2024 (UTC)

A marginally better idea might be to create a testamentary trust fund, if you could find a willing trustee. I'm not sure how far into the future you might want this to extend (do frozen corpses have a "best before" date?) but a legal expert might advise on how to extend the trust beyond the lifetime of the trustee, and what incentives might be required for another person to accept that role. Alansplodge (talk) 11:45, 26 November 2024 (UTC)

Where to verify a chemical compund name synonyms?

The ARM390 compound has multiple IDs, (some of?) which can be found at PubChem here:

https://pubchem.ncbi.nlm.nih.gov/compound/9841259#section=Synonyms

There are two among them, which differ with one zero only: AR-M1000390 and AR-M100390. The difference seems too small to be just a coincidence, it looks like one must be a typo modification of the other.

Is there any way for a non-chemistry/medicine-professional to trace the origin of those specific symbols and learn whether they are actually the same, or genuinely different? --CiaPan (talk) 08:09, 25 November 2024 (UTC)

PS. The motivation for publishing this question here is it's not only me in doubt – another user called for discussion at Redirect discussion: AR-M100390. The sources refer to both names, so from the Wikpedia point of view both are valid, but... Out of curiosity, I just would like to know: are they independent, truly different? CiaPan (talk)

Usually, I would trust ChemSpider to validate such synonyms and that's where I'd send a non-expert. In this particular case, Chemspider seems to prefer AR-M1000390 but one possible source of misinformation/typo is this paper, which consistently uses AR-M100390 in the text but AR-M1000390 in the citation #23, which is correct at doi:10.1016/S0024-3205(03)00489-2. Mike Turnbull (talk) 12:14, 25 November 2024 (UTC)

The earliest use of the name AR-M1000390 seems to be in a PhD thesis from 2003.^[5] The same name was used in a 2003 journal article in Life Sciences describing the results of this PhD thesis.^[6] The substance was synthesized by researchers from AstraZeneca R&D; their paper describing the design, synthesis, and pharmacological evaluation of the drug, published in 2000, does not use this name, but only the systemic name N,N-diethyl-4-(phenylpiperidin-4-ylidenemethyl)benzamide.^[7] Plausibly, the "AR" bit is short for "AstraZeneca R&D" and the whole was originally a code for internal use in the AstraZeneca lab. Subsequently:

• AR-M1000390 was deposited on 2016-02-05; the source was the IUPHAR/BPS Guide to PHARMACOLOGY,^[8] which references the 2003 Life Sciences article.^[9]
• The synonym ar-m100390 was deposited on 2017-09-13 by Springer Nature.^[10]
• Yet another synonym: AR-M 1000390, deposited on 2024-11-14 by a chemical vendor.^[11]

--Lambiam 20:02, 25 November 2024 (UTC)

Thank you both, Mike Turnbull and Lambiam, for detailed info. CiaPan (talk) 07:24, 26 November 2024 (UTC)

November 27

Right whales and Left whales

Why are there right whales, but not left whales? Someone who's wrong on the internet (talk) 09:05, 27 November 2024 (UTC)

Perhaps there's a naming dispute in the whale courts over brand names, a left vs wrong case. Sean.hoyland (talk) 09:32, 27 November 2024 (UTC)

You're thinking of the Narwhal. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:00, 27 November 2024 (UTC)

Not right versus left, but right versus wrong. This was the right species to catch. PiusImpavidus (talk) 10:10, 27 November 2024 (UTC)

Th answer is in the article you linked: Right_whale#Naming. Shantavira|^{feed me} 11:27, 27 November 2024 (UTC)

If a member of a group of whales manages to beach itself, and the others swim on, then the one on the beach would be a left whale. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:11, 27 November 2024 (UTC)

What is a wrong whale exactly? Someone who's wrong on the internet (talk) 23:19, 27 November 2024 (UTC)

The ones that don't fit the definition given in the article. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:42, 27 November 2024 (UTC)

There's also this:[12] ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:45, 27 November 2024 (UTC)

Maybe Gregory and Syme got to them. Iapetus (talk) 12:01, 28 November 2024 (UTC)

Lawson Criterion: calculating energy density W

Lawson Criterion

The article states:

Ion density then equals electron density and the energy density of both electrons and ions together is given by

$W=3nT$

where $T$ is the temperature in electronvolt (eV) and $n$ is the particle density.

However, there is no clear explanation given as to why the energy density equals 3nT, rather than 2nT or just nT. If the electrons and ions are in equal parts within the plasma, shouldn't it equal 2nT?

Is there any source that clears this up? — Preceding unsigned comment added by Shouldputsomethinginterestinghere (talk • contribs) 11:28, 27 November 2024 (UTC) Shouldputsomethinginterestinghere (talk) 11:27, 27 November 2024 (UTC)

The energy density of a monoatomic gas is $E={\frac {3}{2}}nT$. Both electrons and ions can be considered monoatomic gases, so the total energy density is double of that value. Ruslik_Zero 20:56, 27 November 2024 (UTC)

Depends on what n is precisely. If n is the ion density (equal to the electron density), then $2\cdot {\frac {3}{2}}nT$ is correct. If taken literally as "particle density" (i.e. ions and electrons combined), then it should still be ${\frac {3}{2}}nT$. I assume that the former is meant, but the formulation seems ambiguous. --Wrongfilter (talk) 21:39, 27 November 2024 (UTC)

stage 4 breast cancer

I'm not seeking medical advice, but stage 4 cancer means you're gonna die from it imminently, can someone confirm? Or is it wait, what?? Maybe I'm confused. Thanks. 2601:644:8581:75B0:0:0:0:6B00 (talk) 22:22, 27 November 2024 (UTC)

• According to breast cancer classification, Stage IV means the cancer has metastasized, that is, tumors that have "broken off" of the original tumor have appeared elsewhere in the body. "Metastatic breast cancer has a less favorable prognosis." Abductive (reasoning) 06:52, 28 November 2024 (UTC)
• "While there is no cure for metastatic breast cancer, it is possible to control it with treatment for a number of years. The cancer can also go into remission."^[13] So "imminently" is not generally correct.  --Lambiam 15:17, 28 November 2024 (UTC)

November 28

Are there any volatile gold compounds?

Title. Let's say "boiling point under 500°C" counts (as long as it actually boils and doesn't decompose). :) Double sharp (talk) 03:11, 28 November 2024 (UTC)

Gold(III) fluoride apparently undergoes "sublimation above 300 °C". Tracing the dewiki article's data suggests this comes from CRC 10th ed. doi:10.1016/0022-328X(87)80355-8 is a lead article about volatile gold compounds, but these (and others I found) are generally about transferring as a vapor for CVD, nanoparticle formation, or other short-timeframe processes, so probably low pressure and maybe not highly stable in the vapor phase. DMacks (talk) 03:58, 28 November 2024 (UTC)

The compound [Me₂AuOSiMe₃]₂ sublimes at 40 °C (0.001 mmHg) without decomposition. (doi:10.1002/anie.196706831) --Leiem (talk) 04:24, 28 November 2024 (UTC)

Closure, does it exist in physics?

In mathematics, closures are pretty common, e.g. a sum of positive/negative numbers is a positive/negative sum - respectively, and a space of two/three dimensional bodies is a two/three dimensional space - respectively, and so forth.

I wonder if closures also exist in physics, i.e. when the closed properties are physical rather than mathematical, i.e. I'm not interested in applying mathematical properties - like a sum or a space - in physics: e.g. when we say that "a sum of two electric forces is an electric force": It's a bad example for closures in physics, because a "sum" is a methematical property, whereas I'm only interested in purely physical examples.

The above-mentioned example for closures in physics is bad also for another reason: Whereas there is a concrete difference between an electric field and a magnetic field (e.g. by how they influence a stationary body), there is no concrete difference between an electric force and a magnetic force: They influence a given body by the same way, e.g. if their value is 1 kg N they will accelerate a given body by the same acceleration, so the only difference (if at all) between an electric force and a magnetic force and a gravitaional force is "historical", i.e. it only tells us whether the source of that force, was an electric field or a magnetic field or a gravitational field.

HOTmag (talk) 08:35, 28 November 2024 (UTC)

1 kg is the unit of mass and not of force for which physicists have another unit Newton (the force to accelerate 1 kg at 1 m/s²⁾ and your Greengrocer uses a scale that displays W(kg)=mg. Mathematical Addition (or summation), whether of scalar or vector quantities, is defined in abstract symbols. Those symbols may represent any physically real quantities and the summation result is equally real. That is no set-limited exercise or example-setting in Set theory and physical science is well enough aware that that there can be four (not just 3) fundamental forces viz. gravity, electromagnetism, weak interaction and strong interaction that act in combination and cease to be explicitly separable in the result. Philvoids (talk) 13:40, 28 November 2024 (UTC)

Yes, I really meant Newton (sometimes people tend to replace weight by mass, but this mistake is so widespread - mainly in daily life, that it should be forgiven when readers understand what the speaker meant). Additionally I didn't want to mention the other forces becuase they are not useful in daily life.

As for your main response, I didn't fully understand the bottom lime: Do you eventually claim that there don't exist purley physical closures (although there are purely mathematical closures)? HOTmag (talk) 14:08, 28 November 2024 (UTC)

Are Symmetry (physics) and Conservation law what you're after?

Not necessarily, but could you give a concrete example? HOTmag (talk) 14:27, 28 November 2024 (UTC)

In mathematics, a closure is always the closure if a set. The set of positive numbers is closed under addition. The concept of closure requires the notion of an operation such as addition that can be performed on elements of the set. What is closed is not a property but a set.  --Lambiam 15:08, 28 November 2024 (UTC)

A property is usually interpreted as a set. E.g. the property "Asian" is the set of all Asian objects, and when we say that a given object is Asian we only mean that it belongs to that set.

Here is a surprising example of closure: "a space of two/three dimensional objects is a two/three dimensional space - respectively". It really points at a closure because: on one hand, the operation is "to collect objects in a space": the result of this operation is the space in which those object are collected. On the other hand, the property is "two/three dimensional" (choose one option): this property is represented by the set of all two/three dimensional objects (respectively).

My original question was, if there was any physical property (i.e. a set of physical objects sharing an indentical physical property), closed under a physical operation. HOTmag (talk) 17:59, 28 November 2024 (UTC)

Do you mean, in lay terms, 'is there any physical property of a physical object that can never be changed?' (I assume by a physical process – I don't think changing the host's accident by transubstantiation counts.)

I'd guess that Dark matter can't be changed into Baryonic matter and vice versa, but I might well be wrong. {The poster formerly known as 87.81.230.195} 94.1.211.243 (talk) 10:01, 29 November 2024 (UTC)

Active galaxys

What are active galaxies? NoBrainFound (talk) 17:29, 28 November 2024 (UTC)

See Active galactic nucleus, first paragraph. Perhaps there should be a redirect for this topic. -- Verbarson  ^talk_edits 18:11, 28 November 2024 (UTC)

Oh. There is one: Active galaxy. It's a bit annoying that the search bar does the redirect invisibly. -- Verbarson  ^talk_edits 19:10, 28 November 2024 (UTC)

November 29

Where can I find counterintuitive phenomenons list in Science?

Examples:

Asymptotic freedom - We'd normally expect forces to increase as objects get closer, but surprisingly, the strong nuclear force between quarks decreases as they get closer together.

Mpemba effect - The phenomenon where hot water can sometimes cool and freeze faster than cold water

Ultraviolet catastrophe

Pioneer anomaly HarryOrange (talk) 16:19, 29 November 2024 (UTC)

The ultraviolet catastrophe is not actually a phenomenon (that's the point). 19th-century classical physics theories predicted it should happen and, because it doesn't, were superceded by improved, quantum theories. {The poster formerly known as 87.81.230.195} 94.1.211.243 (talk) 18:45, 29 November 2024 (UTC)

There are some examples at List_of_paradoxes#Physics AndrewWTaylor (talk) 19:12, 29 November 2024 (UTC)

A list of counterintuitive phenomena can never be universally applicable because "intuitive believability" i.e. credibility is subjective and depends on a person's experience and education, that can both change. It is counterintuitive (for some) that the Earth can be spherical and yet have oceans that do not immediately drain off down the sides. It is incredible that my car registration number has the same digits as the winning lottery ticket of someone who knew a friend of a cousin of mine who lives in a different country because what are the infinitesimal chances of that happening? If apes can evolve into humans as we are told, why are there still apes around? Philvoids (talk) 16:54, 30 November 2024 (UTC)

In medical school, a lot of facts you have to learn by rote, since there is no overarching theory from which you can rationally deduce those facts. tgeorgescu (talk) 18:21, 30 November 2024 (UTC)

November 30

Displacement receiver v. transducer v. sensor

I'm working on the Displacement receiver page, which formerly had no citations, and the going is difficult because few things actually talk about displacement "receivers" rather than sensors/transducers/etc.. Does anyone know if these three terms refer to the same thing? The initial article talked about a carbon microphone as a displacement receiver because it responds to displacement internally, although what it measures is sound waves, whereas this book says displacement transducers measure the distance between a sensor and a target, and this one says they measure movement and the "occurence of a reference position", whatever that means. It doesn't seem like carbon microphones fit those definitions. But I've also seen e.g. this conference paper use "displacement receiver" to refer to a contact sensor measuring its change in distance from a concrete block to measure stress waves, which is an application actually measuring distance. The article defines it as "a device that responds to or is sensitive to directed distance", which also matches the concrete definition.

Does anyone know if a carbon microphone is really a displacement receiver? And is a displacement transducer the same as a displacement sensor? Mrfoogles (talk) 19:56, 30 November 2024 (UTC)

Smelly plasterboard

This BBC News article about a smelly landfill site quotes a chemist as saying "One of the materials that is particularly bad for producing odours and awful emissions is plasterboard". I thought that plasterboard was a fairly inert substance. Why would it cause bad odours in landfill? (I assume that this is not faulty plasterboard suffering from the in-use 'emission of sulfurous gases' mentioned in the WP article.) -- Verbarson  ^talk_edits 21:07, 30 November 2024 (UTC)

When mixed with biodegradable wastes like manure and sewage, gypsum can produce hydrogen sulphide gas, which is odorous and toxic, and a threat to public health.

Plasterboard Disposal: What You Need to Know

Perhaps somebody who understands the chemistry could add something to our article? Alansplodge (talk) 22:35, 30 November 2024 (UTC)

Well, gypsum is CaSO4·2H2O, which has a significant amount of sulfur and hydrogen in it, and hydrogen sulphide is just HS -- I imagine it's not too hard for a chemical reaction to release hydrogen sulphide gas and therefore as they occur they do. Probably there's a paper somewhere that goes over the various reactions that happen. Mrfoogles (talk) 01:07, 1 December 2024 (UTC)

Hydrogen sulfide (however you like to spell it:) is H₂S. According to our article about that chemical, it arises from gypsum by the action of sulfate-reducing microorganisms that are active "moist, warm, anaerobic conditions of buried waste that contains a high source of carbon". 11:48, 1 December 2024 (UTC) DMacks (talk)

1990s Cathode-ray TV questions.

In the late '90s / early 2000s I remember as a kid looking closeup to the TV screen. For The Simpsons, their yellow skin was red green red green lights next to each other to make yellow. You can't do this with the modern TVs now anymore, but what did cathode-ray TVs use for pink? Would it be dim red by itself, or all 3 colors? How do they make brown? And if Cathode rays can do red green red green, can they do for example, red red green, red red green? Thanks. 2603:8001:5103:AF08:2477:8D7F:1D4B:D0 (talk) 22:41, 30 November 2024 (UTC).

Current screens also describe colors mostly in RGB (red,green,blue) format, although I don't know the details of how they display it (see LCD for one method) -- this webpage lists some color codes for various shades of pink. It looks like they use full red, plus moderate levels of green and blue. Sort of like red + white. Mrfoogles (talk) 01:03, 1 December 2024 (UTC)

OLED displays use a variety of methods; see OLED § Color patterning technologies.  --Lambiam 03:08, 1 December 2024 (UTC)

Brown is basically a darker shade of orange. Whether this is perceived as brown depends strongly on the context. There is no such thing as a brown light; only surfaces of objects can appear brown.  --Lambiam 03:18, 1 December 2024 (UTC)

In photochemistry/photophysics, we can use dyes to make chemicals fluoresce non-spectral colors. Whether or not there is a brown dye is another question. But I believe pink dyes are known. 2603:8001:5103:AF08:2477:8D7F:1D4B:D0 (talk) 05:45, 1 December 2024 (UTC).

In straightforward terms, most human eyes have three color receptors — red, green and blue. The eye can be tricked into seeing any color of light by the right proportions of those three pure colors. The devil is in the details. Doug butler (talk) 06:41, 1 December 2024 (UTC)

It works out mathematically, but one of those details with a devil is that for some colour mixes you may need a negative amount of one of the primary colours – which is physically impossible. That's why some screens use a fourth colour in the mix. PiusImpavidus (talk) 10:35, 1 December 2024 (UTC)

Please see Gamut before declaring devilry. Philvoids (talk) 14:37, 1 December 2024 (UTC)

The colours are still red, green and blue, mixed in varying proportions. The exact hue may vary a bit and some screens add a fourth colour. The dots are pretty small though (maybe smaller than before; resolution has increased, but so have screen sizes) and you may no longer be able to watch them from as close as when you were a kid. Try a magnifying glass. PiusImpavidus (talk) 10:23, 1 December 2024 (UTC)

You're maybe thinking of printing, where the fourth color is black. Way off topic. The really cool thing about color tubes is how the manufacturer deposits the bunches of three phosphors on the inside of the glass screen. The (iron) shadow mask, with its millions of holes, is spaced a few mm back. Spray guns for each color, located where the electron guns will be located in the final manufacturing stage, blast their phosphors so a trio of dots get through each hole in the mask. Electrons from each gun that get through the mask will hit its respective phosphor. Costly, wasteful and inefficient but it worked. Doug butler (talk) 17:07, 1 December 2024 (UTC)

I remember a TV manufacturer telling they added yellow to the standard blue-green-red to be able to make more intense yellows. It makes sense, as the alternative would be driving the blue component to negative.

Professional printers, like those printing food packaging, often use around 6 colours, chosen specifically for the task. PiusImpavidus (talk) 09:32, 2 December 2024 (UTC)

December 1

Fusion power critics

I've stumbled upon a few freak Russian critics in the internet who still allege that fusion power is principally impossible. Perhaps the most notorious seems to be Soviet-era physicist Igor Ostretsov, who published an article in a Russian scientific journal, "On the Lawson Criterion in Thermonuclear Research". Since Ostretsov's criticism is too technical for me, I started to wonder how much weight does it carry, if any. Ostretsov writes in particular:

"It is perfectly clear to every competent physicist that thermonuclear plasma, i.e. plasma at temperatures at which a thermonuclear reaction occurs, cannot be transparent. At thermonuclear temperatures, most of the energy is concentrated in radiation. In the article, I cited Zeldovich on this subject: “In complete thermal equilibrium, a significant portion of the energy is converted into radiation; this circumstance limits the equilibrium average energy of charged particles to a threshold of 5–15 keV, which is completely insufficient for a fast nuclear reaction. A slow nuclear reaction of light elements at an average energy of about 10 keV is practically impossible because the removal of energy by radiation during a slow reaction will lead to a rapid drop in temperature and a complete cessation of the reaction.” If the engineers of thermonuclear fusion in magnetic traps "secretly" assume not a thermonuclear reaction, but the synthesis of hydrogen isotopes in high-energy beams, then this is how the problem should be formulated and consider its "efficiency" as extremely ineffective. The Lawson criterion has nothing to do with that problem, since it was obtained for the Maxwellian distribution of particles by velocity, which is shown in my article".

In a letter to physicist Valery Rubakov Ostretsov further asserts that

1. The Lawson criterion was obtained for the Maxwellian distribution of particles by velocity, which is established as a result of dissipative processes (collisions). 2. As shown in my article, the particle velocity distribution function in magnetic "thermonuclear" traps is determined only by external constant and variable fields, and therefore is not Maxwellian. Due to points 1 and 2, the Lawson criterion has no relation to modern "thermonuclear" research.

Ostretsov also claims that the "during thermonuclear fusion reactions, high-energy neutrons constantly fly into the inner walls of tokamak" and "it's difficult to withstand such bombardment, while a thermonuclear reactor must operate for many years". Is anything of it true? Brandmeister^talk 16:57, 1 December 2024 (UTC)

Check who cites the article and see what they say. Abductive (reasoning) 19:23, 1 December 2024 (UTC)

There is an article about him in Russian Wikipedia. Based on it, he looks like some kind of freak. So, I think that his opinions can be safely ignored. Ruslik_Zero 20:40, 1 December 2024 (UTC)