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January 18

Lanthanum and Actinium

These 2 elements are d-block or f-block? Simple google search says f-block, but other sources, I have, say d-block. Both present their claim with confidence. ExclusiveEditor _{Notify Me!} 15:47, 18 January 2024 (UTC)

This issue is discussed at Periodic table#Group 3 and Group 3 element. La and Ac were thought to be d-block back when electron configurations were first being measured: in 1927, Friedrich Hund thought that the usual trivalency of rare earths meant the configurations of La through Lu were 4f^0–145d¹6s², so that La would be d-block, Ce-Lu would be f-block, and then Hf-Hg would continue the d-block. Since then it became known that this doesn't happen (in fact, almost all 4f elements lack a 5d electron as gaseous atoms), and that the relationship between electron configuration and chemistry is not so simple: transition elements are better thought of as having different configurations depending on their environment. Since at least 1965 (doi:10.1119/1.1972042) it has been suggested that La is really an f-element, as it has chemically accessible f-orbitals that are implicated in bonding, and later authors who focused on this issue have tended to agree. More generally, the elements that can use f-orbitals for bonding are La-Yb and Ac-No, so those are the most natural choice for the f-elements, and Lu and Lr are best treated as the first members of the subsequent d-series. With that said, many textbooks still persist in the old version with La as a d-element – probably as a result of a long string of copying back to Sargent–Welch.

(The same issue of course applies to actinium, but it was naturally studied less due to its radioactivity. That it is an f-element was confirmed by calculations last year: doi:10.1002/jcc.26929.)

P.S. I collected a lot of links to papers about this at User:Double sharp/Group 3 sources. Double sharp (talk) 16:39, 18 January 2024 (UTC)

@ExclusiveEditor: forgot to ping you. Double sharp (talk) 17:16, 21 January 2024 (UTC)

January 19

White Cap Budgies Info

Can someone help me find sources for my draft on whitecap budgies Klajjur (talk) 01:38, 19 January 2024 (UTC)

Wouldn't it be better to add the information to the Budgerigar colour genetics article? If you create a stub for this mutation, it will get very few pageviews. Budgerigar colour genetics gets 53 pageviews a day on average. Abductive (reasoning) 04:37, 19 January 2024 (UTC)

January 20

Old book cover material

Cover material of a 1978 book

Comparing modern and older book covers, I've noticed that their characteristic rugged material, common particularly in the 1960s and 1970s, is hard to find in modern covers (meaning it was probably phased out at some point and replaced by smoother materials, both for hardcovers and soft covers). My WP:OR suggests it was either buckram or leatherine (or both), but could someone confirm? 212.180.235.46 (talk) 14:58, 20 January 2024 (UTC)

Bookbinding#Hardcover binding and Book cover may lead to some relevant information.

As a collector for some decades, mainly of paperback books but also having two or three thousand hardbacks of all kinds and ages, I can say that a great variety of harback cover materials have been used over the years, though this has never been a focus of my collecting, so it's difficult to generalise. {The poster formerly known as 87.81.230.195} 176.24.47.60 (talk) 20:05, 20 January 2024 (UTC)

(Esperanto, sorry, (eo) postvivado / "survival" )

Saluton, mi nepre bezonas metodon por konservi la cerbon sufiĉe bone, ke la teknologioj de la estonteco povu fari ion por la koncerna persono, sed kiu funkcias. Resume, mi havas la komencojn de vojo: vitrifixation kun 2 novigoj: la sojlo de ekscitiĝo de la sinapsoj dum vitrifixation devas esti konservita, kaj la sinapso ne devas esti detruita dum vitrifixation. Ĉu ni povus modifi la artikolon pri krioniko, por informi pri la absoluta urĝeco direkti esploradon al ĉi tiuj 2 aferoj, mi petas? Mi nepre bezonas ĝin. 78.242.18.218 (talk) 21:25, 20 January 2024 (UTC)

This is the English language Wikipedia. Your question may be enthralling and make perfect sense - but to a simple anglophone like me it is as comprehensible as Madarin Chinese. Please rewrite it so that us poor editors understand you. Martin of Sheffield (talk) 21:37, 20 January 2024 (UTC)

Google Translate says:

Hi, I really need a method to preserve the brain well enough that the technologies of the future can do something for the person in question, but that works. In short, I have the beginnings of a path: vitrifixation with 2 innovations: the threshold of excitation of the synapses during vitrifixation must be maintained, and the synapse must not be destroyed during vitrifixation. Could we modify the cryonics article to inform about the absolute urgency to direct research to these 2 issues please? I absolutely need it.

Wikipedia articles are based on cited reliable sources, not a place to propose new ideas or to report your own research projects. Even opinions and analysis of previous work or the value of future direction needs to be cited. DMacks (talk) 21:48, 20 January 2024 (UTC)

Hello,

here are a few sources (most of them in French), but I can't remember if it was in them or elsewhere that a specialist said that the data of the mind was not in the way neurons are linked together, but in the threshold of excitability of synapses. She concluded immediately afterwards: "what's not just hot air is that they're going to kill people" [with vitrifixation, which has to be carried out while the person is still alive]. So I concluded that the first priority was to direct research towards preserving the excitability threshold of synapses during vitrifixation. Secondly, the synapses must be preserved.

https://www.begeek.fr/une-start-up-promet-de-telecharger-votre-cerveau-dans-le-cloud-apres-votre-mort-267146

https://www.letemps.ch/economie/cyber/une-startup-americaine-promet-limmortalite-numerique

https://www.radiofrance.fr/franceinter/podcasts/c-est-deja-demain/une-start-up-americaine-veut-sauvegarder-notre-cerveau-2272910

https://cmte.ieee.org/futuredirections/2018/05/08/jumping-into-the-void-vitrifixation/

https://www.01net.com/actualites/cette-start-up-promet-de-telecharger-votre-cerveau-dans-le-cloud-apres-vous-avoir-ote-la-vie-1396344.html

• ^ https://www.fightaging.org/archives/2018/03/large-mammal-brain-preservation-prize-won-using-a-method-of-vitrifixation/
• ^ https://www.medicalnewstoday.com/articles/321235
• ^ https://www.basicthinking.de/blog/2018/03/20/wuerdet-ihr-euer-gehirn-in-der-cloud-speichern-lassen/
• ^ https://de.1in4mentalhealth.com/your-brain-could-be-backed-up-for-a-F5R

2A01:CB0C:585:DC00:8C6C:A642:3FC:97EE (talk) (former 78.242.18.218) 12:38, 22 January 2024 (UTC)

[Translation]

Hello,

I'm taking the liberty of contacting you again because I need to find a source to back up the 2 emergencies so as to alert, on the WIkipedia "Cryonics" page, the urgent need to direct research towards what is necessary for the process to work and thus save people. 90.110.182.248 (talk) (former 78.242.18.218) 21:38, 23 January 2024 (UTC)

[Translation]

Hello, could we complete, just after the word 《quackerism》of the article《Cryonics》

《, use vitrifixation instead, but 2 improvements urgently need to be made: there must be preservation of the synapse excitability threshold and non-destruction of the original synapse. 》with as source the expert who warned that it was necessary, please? 37.165.144.188 (talk) (former 78.242.18.218) 23:44, 24 January 2024 (UTC)

survival, question about reference desk

[translation]

Hello, why hasn't anyone replied to the last 3 messages in the "survival" section on January 20? Has the source not been found? I managed to find "https://usbeketrica.com/fr/article/nectome-veut-vous-euthanasier-avant-de-vous-rendre-immortel" 90.110.182.248 (talk) ((former 78.242.18.218)) 10:00, 26 January 2024 (UTC)

We're all volunteers here. Take your pick: nobody understands the question, nobody has found a good ref, nobody has had time to look at it, nobody has an interest in it. etc. I gave up because it's not clear what is being asked. Remember: this ref-desk is not a place to debate ideas and Wikipedia articles are strongly oriented towards mainstream science that has already been published in reliable other sources. There is no deadline, and specific proposals for article changes (as supported by cited sources) should be discussed on the talkpage of those articles themselves. DMacks (talk) 10:07, 26 January 2024 (UTC)

Apparently no one here has found a method for what you need. The simplest explanation is that no such method has been developed yet, very likely because it is just not possible with current technology.  --Lambiam 10:59, 26 January 2024 (UTC)

[translation]

Hello, I don't understand,

1) I had read somewhere on the Internet a sentence in French stating that [what was needed for the mind] was the preservation of the threshold of excitability of the synapses. I did a search on Google, in French ""vitrifixation" seuil d'excitabilité des synapses" and strangely, I didn't find the text / site in question, among the 3 sites found by Google. How odd!

2) I had read somewhere on the Internet a sentence in French declaring "ce qui n'est pas du vent, c'est qu'ils vont tuer des "[personnes], and by typing on Google "vitrifixation" followed by this sentence, the only result found was not the one in question... 90.110.182.248 (talk) 21:00, 27 January 2024 (UTC)

January 21

Photon gas

Richard A. Mould, claims in his book "Basic Relativity" (New York, Springer-Verlag, 1994), p.119, that although a photon gas has no rest mass, it has [been empirically proven to have] a positive relativistic mass. Can anyone supply an evidence for that claim? By the way, here is what he exactly states about the photon gas:

"Its passive gravitational mass is equal to its relativistic mass (which equals its total energy divided by c^2), so that when it is placed on a scale in a gravitational field g, its weight is equal to its total energy divided by c^2 times g. Furthermore, if the gas is accelerated horizontally [that is, without moving away from/to the gravitational field] it will display inertial properties also equal to the total energy divided by c^2, even at non-relativistic accelerations."

HOTmag (talk) 17:36, 21 January 2024 (UTC)

Consider two photons of equal energy E flying in opposite directions along the x-axis. The 4-momentum of the first photon is (E, p, 0, 0) = (E, E, 0, 0), its mass is $m^{2}=E^{2}-p^{2}=0$ (I'm using units where c=1). The 4-momentum of the second photon is (E, −p, 0, 0) = (E, −E, 0, 0), its mass is $m^{2}=E^{2}-(-p)^{2}=0$. The 4-momentum of the two photons combined is (E+E, p+(−p) , 0, 0) = (2E, 0, 0, 0), its mass is $m^{2}=4E^{2}$ or $m={\frac {2E}{c^{2}}}$ with c put back in. Therefore, a system consisting of two photons has finite mass even though the photons individually have zero mass. This is true for any two photons as long as they don't travel in the same direction. Now generalise to a photon gas and you have. I've said it many times before: Relativistic mass applies to systems that have internal degrees of freedom. It does not apply to elementary particles without substructure. And don't give me any of that "semantics" stuff, I'm tired of hearing that. --Wrongfilter (talk) 18:04, 21 January 2024 (UTC)

This discussion seems to be confusing invariant mass with relativistic mass. The photons individually have zero invariant mass, but the invariant mass of the system of the two photons is nonzero.

Relativistic mass, on the other hand, seems to be out of fashion as a category. There's nothing really wrong with it; it's just not generally found to be the best bookkeeping method for describing things.

But why in the world you would use it, but then exclude elementary particles, makes no sense to me whatsoever. Wrongfilter, I really think you owe more explanation than "I've said it many times before", because I think you're simply incorrect here. --Trovatore (talk) 19:21, 21 January 2024 (UTC)

Let's throw out the term "relativistic mass" entirely then, and call it "invariant mass", fine with me. What I meant is mass that can arises from energy in internal degrees of freedom (which is a relativistic effect), but maybe the wrong term is stuck in my aging brain. I'd be happy with simply calling it "mass", anyway, since mass is invariant (to changes of reference system or, equivalently, centre-of-mass motion). Apart from that, the explanation is in the maths above. --Wrongfilter (talk) 19:28, 21 January 2024 (UTC)

Thank you for your detailed response.

As for your answer (except your two last sentences which I didn't understand): Please notice the equations you've used refer to the invariant mass only. So yes, it's a well known fact that a given system consisting of two photons that move in opposite directions has a positive invariant mass, even though each photon in that system has no invariant mass.

But I didn't ask about the invariant mass, but rather about what Mould (the author whose book I've quoted from) had meant: It seems he had made a distinction between an invariant mass and a relativistic mass, claiming an empirical claim, that even though a gas photon has no invariant mass it does have a relativistic mass. For us to get better what Mould had meant, let me quote from Max Jammer's book: "Concepts of Mass in Contemporary Physics and Philosophy" p. 56, about what Mould had meant: "he [Mould] illustrates it in terms of a photon gas, which has a rest mass equal to zero but, contrary to what is commonly thought, is not weightless", and then Jammer quotes exactly what I've quoted from Mould's book in my first post. So it seems Mould hadn't used the equations you've used, but rather had relied on an empirical evidence, and that's why I asked if anybody could explain what Mould had meant.

As for your two last sentences (in your first response to me): I didn't understand what you were talking about, because I don't remember I've ever given "semantics" staff. HOTmag (talk) 19:43, 21 January 2024 (UTC)

You did, a few months ago. No you didn't, see below. I apologise. --Wrongfilter (talk) 10:37, 22 January 2024 (UTC) I don't know Mould's book so I can only rely on the passage quoted above; my response is informed by the courses that I've taken and books that I've read (with Schutz' "First course in general relativity" probably the biggest influence). As I understand it Mould always talks about the mass of the gas, never about the mass of any individual photon. In light of that, Jammer's looks like a misunderstanding, but I can't tell without more context. Direct empirical evidence for the mass of a photon gas would seem hard to come by, that'd be a very difficult experiment; I'd like to see that though, if it has been done. However, the mass of a proton arises from essentially the same principle. --Wrongfilter (talk) 20:01, 21 January 2024 (UTC)

Although in case of proton it is gluons, not photons. Ruslik_Zero 20:12, 21 January 2024 (UTC)

Doesn't matter. It's energy in internal degrees of freedom that contributes to the mass of the composite system. --Wrongfilter (talk) 21:12, 21 January 2024 (UTC)

Re. your estimation that Jammer misunderstood Mould: Actually that's what I had suspected before I posted this thread, but if we stick to the way Mould phrased his idea - using the term "relativistic mass", I'm not quite sure Jammer was wrong (even though I still suspect).

Maybe you confuse with someone else? I do remember, that I asked (some months ago) a question about the neutrino's mass, and that I found your reply very thorough and helpful. I also remember someone else asked a question about the neutrino in the same month, and that you had a long conversation with that user. Anyway, I don't think I've ever used the word "semantics" in my posts here or anywhere. HOTmag (talk) 21:39, 21 January 2024 (UTC)

Mould didn't state, in this quote of him, that a photon gas has no mass or invariant mass! Of course laser light's mass-energy should gravitate (has a gravitational field) any counter-propagating light and all matter. For example, see this recent paper which references this one. Modocc (talk) 23:11, 21 January 2024 (UTC)

Thank you for this link. I appreciate that. HOTmag (talk) 09:00, 22 January 2024 (UTC)

Those very interesting references delve into general relativity, whereas I think Mould talks about special relativity (in his quote the gravitational field is external). In GR the source of the gravitational field is not simply the mass itself, but the energy-momentum tensor, which includes energy density (including particle mass, but also kinetic and other internal energy components), pressure, stress (zero for a radiation field) and energy flow. The latter is interesting because it means that the gravitational field depends on the state of motion of the source (relative motion between source and observer, more precisely). This is due to the fact that the gravitational field itself is frame-dependent and has to be transformed between the rest frames of the source (problematic for a light beam, I know) and the observer. --Wrongfilter (talk) 10:01, 22 January 2024 (UTC)

Thank you for this comment. HOTmag (talk) 15:26, 22 January 2024 (UTC)

I loss 1h00 in finding your pb with 2E/c^2 in your text (may be a masked char). Otherwise, it was impossible for me to put latex formula in my question today. In this answer it is impossible too, a mystery. Malypaet (talk) 18:27, 22 January 2024 (UTC)

Can't you find ${\frac {2E}{c^{2}}}$ in his text? HOTmag (talk) 18:41, 22 January 2024 (UTC)

Looks like I forgot the slashes in the closing tags. I need a vacation (in fact, I am on vacation, of sorts). --Wrongfilter (talk) 18:53, 22 January 2024 (UTC)

banned user
The following discussion has been closed. Please do not modify it.
(edit conflict) I'm sorry to hear about your aunt's passing. Maybe Wrongfilter is alluding to 2A06:C701:7469:5D00:79A0:4F6B:4303:B768's reference to "syntax" on 27 December, or even Modocc's 18 November reference to "synthesis" in relation to a comment by 2A06:C701:7463:9900:11BA:FAE2:6F7E:5413. 2A00:23D0:DB9:C701:71A7:949A:7ABB:10F1 (talk) 10:24, 22 January 2024 (UTC) My sincere apologies to HOTmag — it was indeed that lengthy IP 2A06:C701:7463:9900:11BA:FAE2:6F7E:5413 in a comment on 16 November in this thread. --Wrongfilter (talk) 10:37, 22 January 2024 (UTC) I will say no more than that the IP geolocates to Israel. 2A00:23D0:DB9:C701:71A7:949A:7ABB:10F1 (talk) 10:48, 22 January 2024 (UTC) I missed it (15:06, 16 November). 2A00:23D0:DB9:C701:71A7:949A:7ABB:10F1 (talk) 10:53, 22 January 2024 (UTC)

January 22

bad weather drones

This question is inspired by the recent incident[1] of a guy freezing to death in the White Mountains (New Hampshire) in very windy, bad weather conditions because SAR helicopters couldn't fly safely in the storm, and rescuers couldn't get to him either.

'm wondering if there are drones that can fly in such conditions, or alternatively, whether there are serious technical obstacles to building them. Note that while in principle they should be expected to not crash during missions, the point of using a drone is that the risk tolerance is higher than it would be for a copter carrying humans. Also the drone can be smaller, and doesn't have to land in the snow: if it can drop a 5kg or 10kg payload at the location, that is probably enough to deliver some Duraflame logs and matches, or whatever else it would have taken to keep the person warm til the next day. While it was unusually cold for New Hampshire (single digit Fahrenheit, or well below 0 with wind chill), compared to say a Mount Everest expedition it sounded mild. I.e. from my uninformed perspective it seems like the guy would have been ok with the right gear.

I'm not connected to any SAR stuff or to the victim. It's just about understanding a news story. Thanks! 2602:243:2007:9330:15DA:CAD1:28F4:E61E (talk) 03:08, 22 January 2024 (UTC)

I searched for bad weather military drones and found this one. Modocc (talk) 06:04, 22 January 2024 (UTC)

British mountain rescue teams are beginning to work with drones, but as this paper points out, they are limited by law to only operate drones within Visual Line of Sight (VLOS), which rather negates their effectiveness. Alansplodge (talk) 12:16, 22 January 2024 (UTC)

The majestic and steadfast Saint Bernard is famous for rescuing travelers in peril on the snowy slopes of the Swiss Alps. Here are mountain dog breeds that may reach places that drones cannot reach. Philvoids (talk) 14:56, 22 January 2024 (UTC)

Civilian drones are limited to unobstructed visual sight here in the US too, but perhaps one of our delivery services will build drones that are equipped and operated safe enough to be exempt, especially for SAR uses. Last year, four companies applied for exemptions with the FAA. Modocc (talk) 18:37, 22 January 2024 (UTC)

Amount of elements in universe and Earth

Does the sequence of the atomic number of elements sorted by the amounts in the universe from high to low be 1, 2, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 3, 4, 21, 22, 23, 24, …? How about in the Earth? In the Earth the sequence seems to be 8, 14, 13, …?

Also, which elements occur as free state in nature, and which elements occur as chemical compound in nature? I think that the only elements which occur as free state are 2, 7, 8, 10, 16, 18, 36, 44, 45, 46, 47, 54, 76, 77, 78, 79, 86, am I right? Since even some elements with low activity such as 14 and 29 also occur as chemical compound in nature. 36.233.233.71 (talk) 13:48, 22 January 2024 (UTC)

This table of the elements will help anyone investigate your question. The sequence that you assume applies in Earth is Oxygen, Silicon, Aluminium. Philvoids (talk) 14:42, 22 January 2024 (UTC)

More commonly we refer to elements by their names, rather than atomic number. And our article on this topic is "Abundance of the chemical elements". This has a different order for cosmic abundance. Your Earthly figures match those in "Abundance of elements in Earth's crust". For your second part of the question see native element mineral for occurrences in pure form. For gases they may be mixed even if the molecules only contain one kind of element, eg oxygen, nitrogen, and noble gases in the air. Even element 1 occurs as natural hydrogen on Earth. Graeme Bartlett (talk) 21:59, 22 January 2024 (UTC)

The native element mineral article looks pretty hard to read and seems to include things other than 'free state'. Better might be native metal. Note that both of these include alloys. Is that considered "an element in its free state, mixed with other things", for purposes of this discussion? DMacks (talk) 17:28, 24 January 2024 (UTC)

Max Planck and intensity of radiation

Reading "The theory of heat radiation"[2] from Max Plank, I found the formula (9):

K=$\int _{0}^{\infty }d\nu (K_{\nu }+K_{\nu }')$

Then Max Plank write about this formula "it is seen that the quantity K$_{\nu }$, the intensity of radiation of frequency $\nu$, and the quantity K, is the intensity of radiation of the whole spectrumn are of different dimensions."

K being in watts per square meter, what is the dimension of K$_{\nu }$ and what kind intensity is it?

Malypaet (talk) 18:39, 22 January 2024 (UTC)

K_ν is the "specific intensity" and has units of Watt per square meter per Hertz (or equivalent). --Wrongfilter (talk) 18:46, 22 January 2024 (UTC)

Ok, indeed we have $d\nu K_{\nu }$ in Watt per square meter, because $d\nu$ is in Hz. Malypaet (talk) 23:00, 22 January 2024 (UTC)

Bare electrode stick welding

I want to learn about bare electrode stick welding, ie without flux. Wikipedia tells us that coated electrodes were invented around 1900. So for nearly 100 years they welded without flux, yet I can find almost no information on this older technique. All I can find is this one forum thread from 2004 which talks about using a pine block to provide shielding to the bare electrode, and various other scattered mentions of "old timers" welding with car batteries and coat hangers. Can anyone point me towards old books from the era or whatever that discuss this method in detail? Gkarkp (talk) 19:09, 22 January 2024 (UTC)

The article you point to says "there was little development in electrical welding until Auguste de Méritens developed a carbon arc torch that was patented in 1881" and that "in 1885, Nikolay Benardos and Stanisław Olszewski developed carbon arc welding". So at most for 19 years people suffered with whatever that method entailed until "around 1900, Arthur Percy Strohmenger and Oscar Kjellberg released the first coated electrodes". I would guess that previous efforts involved mechanical means of feeding flux and/or shielding onto the growing weld. Abductive (reasoning) 02:47, 23 January 2024 (UTC)

Time zone questions

These questions are questions that I have thought quite a long time and are not homework.

1. Why Belarus switched to Moscow time in 2010? Why they don't use Eastern European Time?
2. Why western Russia (St. Petersburg) has always been in UTC+3, rather than its natural time zone UTC+2? Why St. Petersburg has always been in same time zone as Moscow? --40bus (talk) 19:32, 22 January 2024 (UTC)

Belarus stopped doing the Summer Time/DST thing in 2010, and went on the equivalent of year round EEST. Here's a neat map of deviations between solar time and standard time. http://blog.poormansmath.net/images/SolarTimeVsStandardTime.png --jpgordon^{𝄢𝄆𝄐𝄇} 21:20, 22 January 2024 (UTC)

That's a really neat map! Thanks for posting it. DMacks (talk) 17:13, 24 January 2024 (UTC)

Data mittens

What are data mittens? Thank you. 86.187.226.242 (talk) 22:52, 22 January 2024 (UTC)

Wired gloves AKA datagloves? Modocc (talk) 23:09, 22 January 2024 (UTC)

Or mittens to handle data kittens?  --Lambiam 08:50, 24 January 2024 (UTC)

"Handy" if you take a virtual walk through Beatrix Potter land? Martinevans123 (talk) 09:56, 24 January 2024 (UTC)

Cheap knockoffs of data gloves, probably made by Guccy. Clarityfiend (talk) 13:30, 25 January 2024 (UTC)

January 23

Simple fluid question

I take some fluid(liquid) in glass, with sides perpendicular to base. At the horizontal plane at height 'h', I take two planes at different angle. The layer above plane 1 exerts pressure P1 on that one point it intersects horizontal with, and Layer 2 above plane 2 exerts P2. Is P1=P2?

I have made a simple figure of this question:

https://i.postimg.cc/QC0Kp5qL/Question.png

If necessary, take liquid as incompressible, non viscous and homogenous. Also this is not a homework question, so don't tag it unnecessarily. Thank You. ExclusiveEditor _{Notify Me!} 12:59, 23 January 2024 (UTC)

Pressure at any point in a fluid is isotropic i.e. it does not vary with angle. Assuming a vertical pressure gradient due to gravity, P1=P2. Philvoids (talk) 15:14, 23 January 2024 (UTC)

January 24

Physical dimension of frequency per speed

in the formula x=${\frac {\nu }{c}}$ where $\nu$ is a frequency and $c$ a speed what is the resulting dimension of x? Malypaet (talk) 10:13, 24 January 2024 (UTC)

Inverse length, 1/L. --Wrongfilter (talk) 10:21, 24 January 2024 (UTC)

Thank's, and for y=${\frac {\nu ^{3}}{c^{2}}}$ ?

. Malypaet (talk) 11:52, 24 January 2024 (UTC)

1/(L²T). In units 1/(m² s), or something equivalent. I don't see any direct physical meaning for this combination.--Wrongfilter (talk) 16:10, 24 January 2024 (UTC)

Multiply by E as energy in joule and you get Watt per square meter, isn't it ?

But as there is a frequency in this equation, how do you tel Watt per square meter + something for indication the frequency, in system units or physical dimension? Malypaet (talk) 17:07, 24 January 2024 (UTC)

Perhaps the table and formula in the Irradiance article will help, especially since it has a section on the time-average of the component of the Poynting vector perpendicular to a surface. Modocc (talk) 17:59, 24 January 2024 (UTC)

I don't find anything satisfactory there. We often find watt per hertz with dimension $ML^{2}T^{-2}$ which corresponds to the joule, as in electrical billing for KW-h where we remove the time. An electromagnetic wave is a flow of energy modulated in amplitude, therefore in the same unit of time an energy flow and a cycle flow. A power and a frequency which share the same unit of time, how to write it with x as energy value and y as cycle number in the frequency: ${\frac {x\ joule}{y\ cycle\cdot seconde}}$?

So, in the same fraction, one has the power and frequency value, and x/y gives the energy per cycle.

. Malypaet (talk) 22:08, 24 January 2024 (UTC)

I have no idea what you're trying to say here. I'll just point out that Watt per Hertz is not the same as Joule. Although both have the same dimension, they describe very different physical quantities (specific power vs. energy). This is an instance of the the confusion I warned about earlier (see below). — Where did you see the combination $\nu ^{3}/c^{2}$? --Wrongfilter (talk) 22:44, 24 January 2024 (UTC)

As a classic example of two very different physical quantities with the same dimension, take torque and work. Dimensions can be a useful tool, but they don't tell everything. PiusImpavidus (talk) 10:35, 25 January 2024 (UTC)

Yes but in my case, dimensions correspond to my feeling. I have an example with a constant flow of spheres of mass M crossing an area at speed c and all lines off spheres at the same frequency $\nu$ Malypaet (talk) 14:02, 25 January 2024 (UTC)

Thank you all, this discussion allowed me to find my solution, even if it does not appear directly here. Malypaet (talk) 22:03, 25 January 2024 (UTC)

(edit conflict) @Malypaet: With (my simple way of showing) working: frequency (Hz)/speed (m⋅s⁻¹) = s⁻¹/m⋅s⁻¹ = 1/m. Bazza (talk) 10:28, 24 January 2024 (UTC)

A little bit of nitpicking: dimension and unit are not the quite the same thing. In connection with frequencies, this occasionally causes confusion. In this case, it might help to introduce a dimensionless (pseudo-)unit "cycles", so that frequency is measured in cycles per second, and the quantity x in cycles per meter (x is wavenumber). --Wrongfilter (talk) 10:39, 24 January 2024 (UTC)

@Wrongfilter: Thanks; nitpicking is always welcome as a bit of free education. My view of the world is not as precise as others', hence my inclusion of a qualifier on my response above. I had also linked Hz which conveniently gives its SI base unit equivalence (s⁻¹) in the first paragraph, but the link's not obvious. Bazza (talk) 10:49, 24 January 2024 (UTC)

Eo vs. Paleo prefix in geologic time

Why does the Eoarchean precede the Paleoarchean, but the Eocene follows the Paleocene?

Did the naming body (the ICS?) consider the inconsistency and disregard it, or not consider it at all? 140.147.160.45 (talk) 15:31, 24 January 2024 (UTC)

The term eocene was coined in 1831, 143 years before the ICS was formed. The term Eoarchean appears to have been used by Willem Nieuwenkamp already in 1965,^[3] also well before the genesis of the ICS. This must have been in his article "Geschichtliche Entwicklung der heutigen petrogenetischen Vorstellungen", Geol. Rundschau. 55: 460–478,^[4] presumably in the German form Eoarchaikum. It seems to me that the ICS gave its seal of approval to terms that were already widely used in the literature, with the senses as established there. This may have been a wise approach, similar to that of the king on the first planet visited by the Little Prince after biding his farewell to the rose.  --Lambiam 22:53, 24 January 2024 (UTC)

(after ec)The epochs of the Cenozoic are named for the amount of "new" life (compared to the present day) that was present at that time. Eocene is the "dawn" of new life and the Paleocene is the old part of the Eocene, according to our article, a bit clumsy perhaps, but the names have been around for well over a hundred years. The Eoarchean is a much more recent coining, derived from "dawn" of the "ancient" (world), the very beginning of the Archean. The Paleoarchean is the "old" part of the "ancient", formerly it was the "early Archean". Mikenorton (talk) 22:56, 24 January 2024 (UTC)

What's the rarest level of human hospital?

There are probably many different classifications of hospitals for humans like teaching hospital, poison control center, Level I Trauma Center, burn center, state certified, AMA (or whoever does that) national accredited, maybe each board or subspecialty of MD and DO and the few paramedical degrees like nursing and podiatry have their own thing? Which has the fewest members? Sagittarian Milky Way (talk) 15:46, 24 January 2024 (UTC)

Might be a stand-alone ophthalmology hospital, if any still exist. Abductive (reasoning) 17:11, 24 January 2024 (UTC)

See Moorfields Eye Hospital. Alansplodge (talk) 18:28, 24 January 2024 (UTC)

Category:Eye hospitals has 50 articles, though obviously some might be not "stand-alone" or no longer exist. DMacks (talk) 18:31, 24 January 2024 (UTC)

Wouldn't the highest certification or accreditation or whatever they call it of eye hospital (I wouldn't know what that is) also include at least a few not just eyes hospitals like the Mayo Clinic? Sagittarian Milky Way (talk) 18:35, 24 January 2024 (UTC)

Having the criterion be "specialty hospital" vs. "department of a larger hospital", this a problem with the question. Even in that case, there are way more, say, children's hospitals than eye hospitals. Perhaps hospital ship is truly the rarest? Abductive (reasoning) 18:46, 24 January 2024 (UTC)

What would you classify as a hospital in this sense? In the US consumers get health services termed usually primary, express, urgent, and emergency. A "hospital" as a consumer thinks of in the US may sometimes only be defined as such if it offers emergency care, whereas the next level may be termed an urgent care clinic. However, the CDC and WHO definitions of hospital do not require emergency care. (I mention this all only because in the US this sense of scale can be a common consumer definition.)

Taking the CDC or WHO definition, there are several inpatient mental/behavioral health and physical therapy programs that may take place in an ordinary-looking house in an ordinary-looking neighborhood, where patients sit down to home-cooked meals at the table and do their own chores. This is different from a halfway house, but even the latter could/should/is be seen to be on the spectrum of specialized health care facilities (namely if there is any 24/7 medical/nursing/EMS staff). If your intended definition is open to these possibilities, the amount of unitary microscopically specialized care facilities may surprise you. SamuelRiv (talk) 18:48, 24 January 2024 (UTC)

I don't think the demarcation is so much whether it has an emergency room as whether it admits inpatients. --Trovatore (talk) 19:13, 24 January 2024 (UTC)

Ok. The WHO uses that in its definition. The AHA does not, nor do many subset classifications listed at the CDC. That's why I provided sources and asked OP for the definition they intended. SamuelRiv (talk) 19:27, 24 January 2024 (UTC)

Hmm? Your own link says According to the American Hospital Association (AHA), hospitals are licensed institutions with at least six beds.... --Trovatore (talk) 19:36, 24 January 2024 (UTC)

Unfortunately or not I've been infected with an American view that hospitals and standalone clinics, methadone clinics, doctors offices, simulated or real/converted houses, rehabs and nursing homes are different things. I've seen lists like this is the official list of all the poison control centers (some states having very few, obviously any hospital is better than no hospital but it's better to go to the poison control center if there's enough time or they're equal minutes away), these are all the burn centers and wonder which the country has the fewest of. Sagittarian Milky Way (talk) 20:09, 24 January 2024 (UTC)

I'm pretty sure poison control centers just take phone calls. Abductive (reasoning) 08:46, 25 January 2024 (UTC)

And would also wonder what's the fewest that's not that regional if the answer's something very regional like a certified gila monster treatment center or something, the only place that has gila monster antivenom 24/7/365. Sagittarian Milky Way (talk) 20:17, 24 January 2024 (UTC)

This is a bit of a digression, but our Gila monster article doesn't mention any such centers or even any such antivenom. It seems that bites are pretty rare, and rarely fatal even when they happen. --Trovatore (talk) 21:36, 24 January 2024 (UTC)

I don't know if such certification or antivenom exists. Searching snake antivenom center gives a top result of list of Hospitals with CroFab Antivenom. Quickly find hospitals near you that stock CroFab (crotalidae polyvalent immune fab). crofab.com so maybe there's no official list but CroFab will tell you who has CroFab. Sagittarian Milky Way (talk) 21:50, 24 January 2024 (UTC)

London is well endowed with specialist hospitals. There is a Royal National Orthopaedic Hospital in the west end, and the Royal National Ear, Nose and Throat Hospital near King's Cross (older directories switch "ear" and "throat"). Nearby is the Eastman Dental Hospital. 86.142.1.84 (talk) 09:53, 25 January 2024 (UTC)

Not forgetting the Hospital for Tropical Diseases, the Western Eye Hospital and the Royal Marsden Hospital which is a specialist cancer treatment hospital, as well as three children's hospitals. Alansplodge (talk) 14:56, 25 January 2024 (UTC)

According to Google we only seem to have dental clinics, a tropical clinic (New York Center for Travel and Tropical Medicine) and a New York Eye and Ear Infirmary but not just eyes. There's an orthopedic Hospital for Special Surgery, NYU Langone Orthopedic Hospital, Manhattan Eye, Ear and Throat Hospital (which I joked as a kid Eye, Ear, Nose, Mouth, Throat, Butt), Memorial Sloan Kettering Cancer Center (which is a hospital) and a few children's hospitals, one children's hospital even advertised(ses?) on over-the-air TV. Sagittarian Milky Way (talk) 23:51, 26 January 2024 (UTC)

<- I wonder how many high-security psychiatric hospitals there are. The UK seems to have 4 apparently. Sean.hoyland (talk) 10:15, 25 January 2024 (UTC)

Locked wards are a feature of all psychiatric hospitals, but of course patients who are not the subject of a detention order under the Mental Health Act are free to come and go at any time. The level of security varies. The highest is where the exit door is accessed by a corridor. There may be a handle on the outside allowing people to enter but no handle on the inside, meaning staff intervention is needed to leave. Opportunist patients may follow a delivery man out when he leaves, or, if conditions are right, vault the food counter and exit via the kitchen if it leads to the ward's outer door with handles on both sides. When a patient does this it leads to a meticulous search of the entire ward. 2A00:23C7:9C86:4301:6418:B7B2:105:23FE (talk) 10:30, 25 January 2024 (UTC)

To clarify, in the UK at least, "high-security" has a formal definition in this context and only 4 hospitals have that designation. Sean.hoyland (talk) 10:39, 25 January 2024 (UTC)

(edit conflict) There are three high-security psychiatric hospitals in England providing services to England and Wales: Ashworth Hospital, Broadmoor Hospital and Rampton Secure Hospital. There is one high security hospital in Scotland, the State Hospital in Carstairs providing services to Scotland and Northern Ireland. These four are equipped to deal with dangerous individuals such as Ian Brady ("Moors murderer") or Peter Sutcliffe ("Yorkshire Ripper"). Martin of Sheffield (talk) 10:52, 25 January 2024 (UTC)

Like the Magdalene Laundries in Ireland, psychiatric hospitals can be a dumping ground. A case history: [5]. 2A00:23C7:9C86:4301:6418:B7B2:105:23FE (talk) 10:50, 25 January 2024 (UTC)

People held in the "hospitals for the criminally insane" tend to be returned to prison. Peter Sutcliffe was last held at HMP Frankland in County Durham. 2A00:23C7:9C86:4301:6418:B7B2:105:23FE (talk) 11:16, 25 January 2024 (UTC)

No sooner had I pressed "Save" on the above edit than this appeared on the screen [6]. If AI is involved it's pretty impressive. 2A00:23C7:9C86:4301:DDA8:3416:7CEB:4CEA (talk) 11:30, 25 January 2024 (UTC)

No AI - laptops do unexpected things, and on this occasion it decided to access a link posted earlier. 2A00:23C7:9C86:4301:140E:5EAC:2D72:8A9E (talk) 13:12, 26 January 2024 (UTC)

It posted the above comment before I had even pressed "send". 2A00:23C7:9C86:4301:140E:5EAC:2D72:8A9E (talk) 13:14, 26 January 2024 (UTC)

In Australia we have Bush Nursing Hospitals. Wikipedia doesn't (yet) have an article on them, but they are mentioned in several, such as the one on Ian Turpie, a one time boyfriend of Olivia Newton-John. While there are only a handful left, there used to be many. They served as hospitals in rural towns. They employed nurses, but no doctors, and existed to service patients of the local doctors, who would visit to attend to those patients. HiLo48 (talk) 01:39, 27 January 2024 (UTC)

There's a standalone burn hospital in Poland's Siemianowice Śląskie, I think it's the only one of its kind in Poland, see website. --Ouro (blah blah) 16:17, 27 January 2024 (UTC)

(edit conflict) The words "hospital" and "clinic" appear to be interchangeable. Yesterday's Evening Standard reports:

The London Clinic opened in February 1932 after a group of Harley Street doctors set out to "establish a new kind of hospital that would set a standard of healthcare for generations to come."

If "clinics" are included the number of "specialist hospitals" (in Harley Street and elsewhere) is greatly expanded. News reports overnight say "Charles is doing well" and "the queen is by his side." While I wish him a speedy recovery, she is nothing of the kind. You may recall that a litigant filed a case in the High Court challenging her use of the title because English law specifically prohibits members of the royal family from marrying in register offices. The court office wrote back months later (target time for reply is five working days) to say the papers would be hurled into the wastebin if a court form declaring the case to have no prospect of success was not filed. Naturally they would hold on to the expensive court fee. The Civil Procedure Rules Committee examined the form and declared it to be a forgery. Also overnight it is reported that a jury has ordered Donald Trump to pay 83 million dollars in damages. His lawyer says she will appeal. Even Trump does not attempt to prevent his opponents having their day in court. 86.150.238.95 (talk) 16:37, 27 January 2024 (UTC)

Childrens' hospitals seem to be generalised [7]. 86.150.238.95 (talk) 16:37, 28 January 2024 (UTC)

January 25

Using acoustic extinguishing equipment to change the wavelengths of visible light

Greetings!

I've been reading some web articles concerning acoustic extinguishers, viz., devices that put out small fires by changing the sound waves surrounding them. These devices do not blow air like a fan, but merely emit a very loud sound imperceptible to humans.

I cannot help but wonder, though: Can such a device be jury-rigged to alter the properties of visible light?

Picture a cubic box, 30cm × 30cm × 30cm, closed on 5 sides but open on the 6th. Could an acoustic device be made so that the open side become blurry, pixelated, or opaque—so as to make impossible to see inside the box?

EDIT: reworded the question.

Thank you! Pine (talk) 06:41, 25 January 2024 (UTC)

See Acousto-optics and linked articles. Perhaps not blurred but may add a spectral affect. Graeme Bartlett (talk) 07:04, 25 January 2024 (UTC)

January 26

What's the mean or median air pressure at the Empire State Building observatory?

The International Standard Atmosphere gives an answer but also gives average sea level 101325 pascals and 59.0F when the weather station's roughly 101750 pascals corrected to sea level and 56.?F plus 0.499F environmental lapse rate (6.5C/km) from 0 feet to 140. Should its pressure for 1106' above sea level (nostril height) be increased by 101750/101325? Sagittarian Milky Way (talk) 03:20, 26 January 2024 (UTC)

Multiplying the pressure from the standard atmosphere at that altitude with 101750/101325 takes care of the non-standard sealevel pressure. That's a 4‰ (note: per mille) increase in pressure. The lower than standard temperature increases the pressure lapse rate by about 5‰, so that lowers the pressure at the observatory by 5‰ of the difference between there and sea level. That's a smaller correction. A non-standard humidity also affects the lapse rate: higher humidity gives a lower lapse rate. If the top of the building is in the clouds, pressure lapse rate is increased. When some of the water vapour in the air condenses, the volume decreases and density increases. The pressure lapse rate is simply the density of the air divided by gravity. Both temperature and humidity vary from day to day. To be really sure, you'll have to measure it. PiusImpavidus (talk) 08:52, 26 January 2024 (UTC)

I forgot to think of that (denser column should thin faster). Why is ISA humidity zero at all altitudes, shouldn't they have at least a simple function fitted to the avg humidity of each altitude? Do you know where NOAA or National Climate Data Center or NWS or whoever gives its pressure averages? ~1017.5 from a (old?) El Dorado Weather map but ~1017.0 from a different map of known averaging period 1981-2010. I found current maps 1991-2020 but only even integers weird un-interpolatable shape.Sagittarian Milky Way (talk) 20:59, 26 January 2024 (UTC)

I don't know why the ISA is the way it is. I suppose temperature and humidity are so variable that choosing a more realistic standard value doesn't give a significant improvement. With humidity set to zero, you don't have to deal with cloud formation.

On the website of my national meteorological institute I can simply download all validated hourly air pressure readings of all weather stations in my country since 1900. Is there no such option in the US? PiusImpavidus (talk) 14:32, 27 January 2024 (UTC)

30-year average pressure is harder to find than most other things (even pressure for a specific hour decades ago). Sagittarian Milky Way (talk) 05:07, 28 January 2024 (UTC)

Yes, it may not be listed because no-one (until you, now) may have wanted to know it. You might just have to download all the individual values and work out the averages yourself. {The poster formerly known as 87.81.230.195} 90.205.103.187 (talk) 19:50, 28 January 2024 (UTC)

January 27

Neurotransmitters, part 2

Does oxytocin reduce the level of and/or counteract the effects of dopamine within the brain? 2601:646:8080:FC40:3118:F122:673F:8204 (talk) 14:59, 27 January 2024 (UTC)

I'm afraid that there are only 53,000 results on Google Scholar for "oxytocin dopamine interactions". Abductive (reasoning) 20:25, 27 January 2024 (UTC)

Activation of the amygdala and hippocampus by oxytocin can induce penile erection and elevate extracellular dopamine levels in the nucleus accumbens in rats.as per study of Melis MR et Harvici (talk) 06:17, 28 January 2024 (UTC)

So, follow-up question: how does oxytocin affect the action of dopamine specifically on the D4 receptor? 2601:646:8080:FC40:3118:F122:673F:8204 (talk) 12:14, 28 January 2024 (UTC)

Research of 2010 (this study ) indicates that oxytocin cells located in the MPOA, SON, and PVN contain dopamine D2, D3, and D4 receptors. This finding suggests the possibility of direct influence by dopamine on hypothalamic oxytocin neurotransmission through D2-like receptors. Harvici (talk) 13:18, 28 January 2024 (UTC)

And of oxytocin on dopamine neurotransmission specifically through D4 receptors (particularly in an antagonistic manner)? Or does it not go the other way? 2601:646:8080:FC40:3118:F122:673F:8204 (talk) 17:30, 28 January 2024 (UTC)

This study suggests that there may be modulation and interactions between the two neurotransmitter systems during penile erection, but the exact nature of these interactions, especially through D4 receptors, is not definitively outlined. The study shows that oxytocin receptor blockade can inhibit dopamine agonist-induced penile erection, indicating a role for oxytocin in modulating dopamine pathways or oxytocin may itself be able to modulate central dopamine neurotransmission. Harvici (talk) 18:22, 28 January 2024 (UTC)

I can't find any mention particularly in an antagonistic manner Harvici (talk) 18:23, 28 January 2024 (UTC)

Well, this study does seem to mention one specific antagonistic interaction between oxytocin and dopamine -- so, if I understood it correctly, it makes a lot of things clear! (Just FYI, this is for a research project I'm doing on my own time about introversion -- a topic of interest to me, since I'm an introvert from the very deep end of the scale myself, and specifically having a very low excitement-seeking score on the ocean test (a measly 4 out of 20) -- and the starting point is that we introverts have super-sensitive D4 receptors, so stimulating them causes stress, and therefore we like things which inhibit them instead! And this study, if I understood it correctly, sheds light in particular on the reason why I love physical affection and tender, romantic sex but find casual and/or rough sex repulsive -- and also on why I, a man, need lots of romantic, loving foreplay to get myself ready, almost like a woman! Oh, and for the record, this is not medical advice -- I'm not trying to find any information on how to change any aspect of myself which is related to introversion, I wouldn't change it even if I could, all I'm trying to do is to find out what makes me tick!) 2601:646:8080:FC40:3118:F122:673F:8204 (talk) 03:33, 29 January 2024 (UTC)

Well , I am an introvert too,so it's nice to meet someone who is an introvert too and interested in medicine stuff.😉. Harvici (talk) 05:22, 29 January 2024 (UTC)

January 28

1/r² law with area for source and reception

For radio waves, the radiated power responds to the law 1/r$^{2}$ for the power received at the distance r into a receiving antenna. This rule applies to transmission and reception as a theoretical point. But if the power is measured for a surface near the emission and a surface near the reception in watt/m2, wouldn't we have a rule in 1/r$^{4}$ or something else? Malypaet (talk) 10:04, 28 January 2024 (UTC)

no you would not. r is the distance between the transmitter and the receiver, not the side of a square at both receiver and transmitter. You could measure the strength of the wave at the receiver in watts per square meter, but the power transmitted is measured in watts. Graeme Bartlett (talk) 11:09, 28 January 2024 (UTC)

Also, when you are measuring the power, the surface used for the measuring assumes the role of the receiver, so then r is the distance between the transmitter and that surface. The law can easily be understood as a steady amount of power being emitted in concentric spherical shells centred on the emitter, all equally (infinitesimally) thin. The surface of these shells is proportional to r², so the amount of power per unit of surface area decreases inversely.  --Lambiam 13:19, 28 January 2024 (UTC)

If you were to measure the power per unit area (power density) at a surface near the emission and another surface near the reception, the power density at the receiving surface would still follow the inverse square law. The power received per unit area would decrease with the square of the distance from the source. Harvici (talk) 13:19, 28 January 2024 (UTC)

The 1/r² law assumes a point-source, or at least a source that is small compared with r (the wavelength also needs to be small compared with r). One can indeed consider radiation out to an intermediate surface between the source and receiver, followed by radiation onward from the surface to the receiver. This is the surface equivalence principle, a variant of Huygen's principle. However radiation from the intermediate surface is not bound by the 1/r² law (measured from the surface), since the surface is an extended source, not a point source. catslash (talk) 23:53, 28 January 2024 (UTC)

In acoustics we divide the radiating field up into two parts. In the far field intensity falls as 1/r^2. In the near field there is no such relationship, and with an intensity probe you can trace the energy flux of the waves as it loops back on itself. The reason for this is the radiating body can only emit energy into the general far-field atmosphere in a way that is compatible with the physical properties of air, but the radiating body has a different set of properties, so the complex resulting sound energy pattern resolves the differences between the two. The same will happen with radio waves. Greglocock (talk) 21:31, 29 January 2024 (UTC)

Planck's thoughtlessness

On 1901 Planck article: "Ueber das Gesetz der Energieverteilung im Normalspectrum"[8] One find a conjuring trick:

$u=\theta ^{5}\cdot {\frac {c}{\nu ^{2}}}\cdot \psi ({\frac {c\theta }{\nu }})$

According to Kirchhoff-Clausius law, the energy of a temperature ϑ and the number of vibrations ν, when emitted by a black surface per unit of time into a diathermic medium, is inversely proportional to the square $c^{2}$ of the propagation speed. So the spatial energy density u is inversely proportional to $c^{3}$, and one gets:

$u={\frac {\theta ^{5}}{\nu ^{2}c^{3}}}f({\frac {\theta }{\nu }})$

So, constants of the function f are independent of c. Instead, one can write if f denotes a new single-argument function each time, including in the following:

(7) $u={\frac {\nu ^{3}}{c^{3}}}f({\frac {\theta }{\nu }})$

What is this Kirchhoff-Clausius law ?

Why Planck don't use Wien's Displacement law with $\theta =b{\frac {\nu _{m}}{c}}$ where $\nu =\nu _{m}$? Then in the first equation replace directly $\theta ^{5}$ with $b^{5}{\frac {\nu ^{5}}{c^{5}}}$ to get directly the equation (7) ?

. Malypaet (talk) 18:37, 28 January 2024 (UTC)

Kirchhoff-Clausius law is likely a combination of two important principles in thermal radiation: Kirchhoff's law of thermal radiation and the Stefan-Boltzmann law.

And ,If I am correct, Planck's work on blackbody radiation actually predates the development of Wien's Displacement Law,so that's why Planck didn't use Wien's Displacement law . Harvici (talk) 05:26, 29 January 2024 (UTC)

Can you give me a pointer of this Kirchoff-Clausius law ?

And sorry, but here Panck begin with a Thiesen formula which is the result of applying the Wien's Displacement law to Wien's approximation (${\frac {1}{\lambda ^{5}}}f_{1}(\lambda \theta )=\theta ^{5}f_{2}(\lambda \theta )$).

Also how can you have ${\frac {\theta ^{5}}{\nu ^{2}}}=\nu ^{3}$?

. Malypaet (talk) 10:16, 29 January 2024 (UTC)

The Kirchhoff-Clausius law deals with the energy emitted by a black surface at a specific temperature and frequency.It asserts that the energy emitted per unit of time into a diathermic medium is inversely proportional to the square of the propagation speed (c^2).

Planck formulated an expression for spatial energy density (u) based on this law. He introduced a function, denoted as ψ, to represent the spectral distribution of energy. The ultimate expression (equation 7) involves the frequency (ν) raised to the power of 3, divided by the cube of the propagation speed (c^3), and multiplied by the function f(θ/ν).

About why Planck didn't directly use Wien's Displacement Law, the Planck's objective was to derive a formula accurately describing the energy distribution in blackbody radiation. While Wien's Displacement Law offered a practical empirical relationship, it fell short of explaining the complete blackbody radiation spectrum, particularly at longer wavelengths.

To sum up, Planck's work surpassed the limitations of Wien's Displacement Law. I hope you understand. 😊. Harvici (talk) 11:22, 29 January 2024 (UTC)

The equations above are (variants of) Wien's displacement law. Originally, this law was a sort of scaling law for the entire intensity distribution, which at the time was of course unknown. Additional assumptions were needed to turn this scaling law into the actual distribution. Now of course we know the distribution and have no more use for the scaling law, and "Wien's displacement law" has been reduced, so to speak, to the behaviour of the maximum of the intensity. --Wrongfilter (talk) 11:47, 29 January 2024 (UTC)

Wikipedia is an encyclopedia, so if the Kirchhoff-Clausius law exists, it must be referenced there. I can't find it and no one here has given me the reference. The only Kirchhoff's law referenced in wikipedia is the equality of emitted and absorbed radiation power of a black body at thermal equilibrium. Your statement has no value if it is not referenced and associated with an experiment. Malypaet (talk) 12:32, 29 January 2024 (UTC)

And to:

${\frac {\theta ^{5}}{\nu ^{2}}}=\nu ^{3}$?

Have you a serious explanation ?

. Malypaet (talk) 12:56, 29 January 2024 (UTC)

Wien displacement law => $\theta ^{5}={\frac {\nu ^{5}}{c^{5}}}b^{5}$

So ${\frac {\theta ^{5}}{\nu ^{2}}}={\frac {\nu ^{3}}{c^{5}}}$ not $\nu ^{3}$

. Malypaet (talk) 13:11, 29 January 2024 (UTC)

The Kirchhoff–Clausius Law perhaps ought to be referenced in Wikipedia, but this requires someone actually to write the article. It is not a law of the universe that this would already have happened if the Law exists – Wikipedia is incomplete, always will be, and we can only do our best to make it less so.

In an effort to address your original query, I web-searched "Kirchhoff–Clausius law", and found very few results, none of which gave a satisfactory definition, so perhaps it is not surprising that no-one has written an article about it yet. Are there sufficient RS to do so? Could it instead be made a section of an existing article? {The poster formerly known as 87.81.230.195} 90.205.103.187 (talk) 19:06, 29 January 2024 (UTC)

The law of Kirchhoff-Clausius states that at equilibrium the specific intensities of radiation of a certain frequency in two media are in the direct ratio of the squares of the indices of refraction in those media.^[9]  --Lambiam 10:55, 29 January 2024 (UTC)

Ok:

"The law of Kirchhoff-Clausius states that at equilibrium the specific intensities of radiation of a certain frequency in two media are in the direct ratio of the squares of the indices of refraction in thoses media. See, e.g. Planck 1906..."

Only a one more Planck reference.

Where does $c^{2}$ intervenes here, as the indice of refraction is dimensionless ? Malypaet (talk) 12:50, 29 January 2024 (UTC)

The speed of light in a medium depends on the refractive index: $c_{\mathrm {med} }=c_{\mathrm {vac} }/n$, which is why Planck can turn the law from refractive index to propagation speed. The law doesn't seem to be very well known, at least not under that name. --Wrongfilter (talk) 13:43, 29 January 2024 (UTC)

Yes not under that name.

There is only one law giving specific intensity inversely proportionnal to the speed of light squared:

The planck's law !

Planck knew the result before making the demonstration. In my opinion, he stalled in his research and invented a Kirchhoff-Clausius law, which has since fallen into a quantum well.

It's like replacing

$u={\frac {\theta ^{5}}{\nu ^{2}c^{3}}}f_{1}({\frac {\theta }{\nu }})$ by (7) $u={\frac {\nu ^{3}}{c^{3}}}f_{2}({\frac {\theta }{\nu }})$

whithout justification.

But hey, he gets the desired result.. Malypaet (talk) 21:43, 29 January 2024 (UTC)

May be here [10]Gesammelte abhandlungen; von Kirchhoff (1882) p.594. But in german and poor quality.

This line "$I'=n^{2}I$" ??? Malypaet (talk) 22:37, 29 January 2024 (UTC)

Why do you make your contributions sound as if the physics community is after you? From an article published in 1900, well before Planck's article:

Bereits Kirchhoff hat in seiner 1860 erschienenen berühmten Abhandlung den Satz bewiesen, dass die Strahlung vollkommen schwarzer Körper in verschiedene Medien den Quadraten der Brechungsexponenten dieser letzteren proportional ist und ein Jahr später fand Clausius denselben Satz.^[11]

 --Lambiam 00:22, 30 January 2024 (UTC)

The article in de Gesammelte Abhandlungen is apparently a revised version, published in 1862, of the berühmte Abhandlung from 1860 published in Annalen der Physik; they have identical titles.  --Lambiam 00:36, 30 January 2024 (UTC)

Ok, so who can put this into an equation for me and then derive the equation for the inverse of the speed of light squared? Kirchhoff-Clausius laws: "the radiation of completely black bodies in various media is proportional to the squares of the refraction exponents of the latter." Malypaet (talk) 10:30, 30 January 2024 (UTC)

If you accept Kirchhoff's result, then ${\frac {I_{\mathrm {med} }}{I_{\mathrm {vac} }}}=n^{2}=\left({\frac {c_{\mathrm {vac} }}{c_{\mathrm {med} }}}\right)^{2}$, therefore $I\propto {\frac {1}{c^{2}}}$ (with c the propagation speed in the medium). --Wrongfilter (talk) 12:30, 30 January 2024 (UTC)

So, if I consider the thermal intensity of a black body wall equivalent to a light intensity $I'$ which will be converted into light intensity $I$ in a vacuum, we obtain the

Kirchhoff-Clausius law:

$I={\frac {1}{c^{2}}}(I'C'^{2})$.

Then with $(I'C'^{2})$ as a function with energy related to the temperature of the black body wall.

. Malypaet (talk) 14:01, 30 January 2024 (UTC)

Hey here is a mention of Kirchhoff-Clausius law in BSBM varying-alpha theories, on page 7 Harvici (talk) 13:41, 31 January 2024 (UTC)

Science is not a religion. If this law exists with well-demonstrated equations, I will add an article in Wikipedia: "Kirchhoff-Clausius law".

There is a first law: “If the boss is wrong, the boss is always right.” But it's a joke at work. Malypaet (talk) 11:45, 30 January 2024 (UTC)

January 30

Why is the following value, relativistically invariant?

Here is a simple thought experiment: A photon and a massive particle, both being in a moving train, begin a race, starting from the rear of the train to its front, i.e. in the direction of the train's movement. When the photon arrives at the end of the race (i.e. at the train's front), the photon comes across a mirror, so the photon is reflected back, i.e. it bounces backward, on the same route but in the opposite direction, until this photon meets the massive particle - still on its way to the train's front.

The point at which the photon and the massive particle meet, specifies a part of the train's length. This part is a actually a proper fraction, i.e. its value is between 0 to 1. Intuitively and apparently, this fraction is relativistically invariant, i.e. it does not depend on the reference frame measuring that fraction.

David Mermin (in his book "It's about Time: Understanding Einstein's Relativity", p.37, in the first new paragraph of the page.), wants to assume (rather than to prove) that the fraction is indeed invariant, because he wants to use this assumption for - proving the relativistic velocity-addition formula without using the Lorentz transformations. Apparently Mermin regards this assumption, either as an axiom, or (more likely) as a conclusion of the principle of relativity, because this principle is mentioned (p. 29) as one of his two assumptions, the second one being the constancy of the speed of light.

But I'm looking for a more rigorous justification for his assumption (about the invariance of that fraction), again without relying on the Lorentz transformations nor on the relativistic velocity-addition formula. Unless someone explains to me how Mermin's assumption rigorously follows from the principle of relativity (if it really does). HOTmag (talk) 13:14, 30 January 2024 (UTC)

I'm not sure what you mean by "relativistically invariant" in this case. "X is invariant with respect to Y" means that the value of X doesn't change when Y does. What's Y in this case? Are you saying that the fraction is the same regardless of the speed of the train? Of the initial speed of the massive particle? Both? Something else? PianoDan (talk) 18:22, 30 January 2024 (UTC)

I mean exactly what you mean when you say that the speed of light is relativistically invariant, i.e. it does not depend on the reference frame measuring the speed of light. The same is true for the fraction: it does not depend on the reference frame measuring the fraction. HOTmag (talk) 18:52, 30 January 2024 (UTC)

Ah, OK. What you're looking for here, then is the concept of "Spacetime Interval", given for one dimension as: ${\textstyle (\Delta s)^{2}=(\Delta ct)^{2}-(\Delta x)^{2}}$. For any reference frame the computed value of delta s will be the same for two events, even though the values of delta x and delta t may vary from frame to frame.

Say you're in the reference frame of the train, and you observe the photon to collide with the particle at point P (relative to the train, so P is just the fraction in the problem times the length of the train). The two events here are "photon reaches point P" and "particle reaches point P"

In the reference frame of the train, delta x between those two events is zero, and delta t is ALSO zero. As such, the invariant spacetime interval between those events is also zero, which means it is zero in all frames.

To put it even more simply - events which are separated in space can be perceived to be simultaneous or not, depending on the frame of the observer. But events which are NOT separated in space have a well-defined meaning of "simultaneous," and are simultaneous in all reference frames.

This is also necessary for causality. If shoot a bullet at a pumpkin, different observers can disagree over precisely how long it takes between the shot and the pumpkin exploding. But the fact that the bullet hits the pumpkin AT ALL can't change depending on the motion of the observer, or you get nonsense.

PianoDan (talk) 23:00, 30 January 2024 (UTC)

Thanks. Let me quote you:

"The two events here are 'photon reaches point P' and 'particle reaches point P'...the invariant spacetime interval between those events is also zero, which means it is zero in all frames...events which are NOT separated in space have a well-defined meaning of 'simultaneous', and are simultaneous in all reference frames".

I still want to find out the logical way your argument quoted above can be used for proving that the fraction does not depend on the reference frame, although your argument can't be used for proving the same for the length, so first let me put your argument in my own words:

A given length involves its two endpoints, being two different "events" separated in space by a non-zero interval. However the fraction (I'm asking about) is only specified by a single point (e.g. the one indicating the part of the train's length), while this point is not separated in space by any pair of different points/events.

That said, your argument must still rely on the principle stating that: If all reference frames agree that a given event occurs at a single point in spacetime (e.g. a meeting point), then all of them agree about the exact value of this point, hence about the exact fraction specified by that point. But, what's the exact source/origin of this principle? Does it directly follow from the principle of relativity, if we don't want to rely on the geometrical formula you've indicated at the beginning of your response? HOTmag (talk) 09:17, 31 January 2024 (UTC)

The fraction is determined by three events, not one. It is the ratio of two lengths, each determined by two points, with one point (the collision event) in common. For the fraction to be frame-dependent those two lengths would have to be transformed differently, i.e. length contraction would have to depend weirdly on direction. You may want to look at the derivation of the Lorentz transform from the two axioms and see if there is a shortcut without going via the full transforms. The invariance of the zero-interval is the second axiom (invariance of speed of light). --Wrongfilter (talk) 09:54, 31 January 2024 (UTC)

Thanks. How does the invariance of the zero-interval, follow from the second axiom (invariance of speed of light)? HOTmag (talk) 10:20, 31 January 2024 (UTC)

For light, ${\frac {dx}{dt}}=c$, or $c^{2}\,dt^{2}-dx^{2}=0$. If the speed of light is the same in all reference frames then light follows zero-interval trajectories in all reference frames. --Wrongfilter (talk) 11:01, 31 January 2024 (UTC)

Thank you @Wrongfilter: Regardless of your "principle of existence" (which I find helpful here), do you think the invariance of the zero interval can be used - and is sufficient - for concluding that the fraction is invariant? HOTmag (talk) 11:40, 31 January 2024 (UTC)

"If all frames agree that an given event occurs at a single point, then all of them agree about the exact value of the point" is a tautology. It doesn't need to be derived further, because the two halves of that sentence say the same thing. PianoDan (talk) 15:41, 31 January 2024 (UTC)

It's not a tautology. Think about our meeting yesterday. All of the reference frames agree it was held, at a single point, and at a single moment. However, there may still be a dispute over whether this point at which we met was my home or your home. The same is true for my original question: All agree that the photon and the massive perticle met at a single point and at a single moment. However, perhaps there may still be a dispute over whether this point was at the half of the train's length, or at the quarter of the train's length. Indeed, I'm not claiming there is really a dispute, but I'm still asking if you can prove there isn't one, without your relying on the Lorentz transformations, nor on the Minkowski invariant distance in spacetime, nor on the velocity-addition formula. HOTmag (talk) 17:18, 31 January 2024 (UTC)

There are likely to be other postulates that are implicitly used. For more detail see postulates of special relativity. This thought experiment relies on spatial homogeneity. You can imagine marking the side of the train with tick marks every 1 cm. The number of tick marks between the rear of the train and the meeting point is invariant; the number of tick marks between the meeting point and the front of the train is also an invariant. The distances themselves are not invariant, because the 1 cm spacing is not invariant. Then the question is: in any given frame, are all the tick marks equally spaced? Or is there a frame where some spacings are wider and some are narrower? Spatial homogeneity says that in any frame, the tick spacing must be uniform across the length of the train. And that guarantees the invariance of the fraction you asked about. --Amble (talk) 20:59, 30 January 2024 (UTC)

There needs to be an assumption that the train is not accelerating.  --Lambiam 23:46, 30 January 2024 (UTC)

Thanks. Let me quote you: "the number of tick marks...is...invariant". What basic principle does this assumption follow from? HOTmag (talk) 08:47, 31 January 2024 (UTC)

Not sure how to phrase it — invariance of existence? --Wrongfilter (talk) 09:54, 31 January 2024 (UTC)

Thanks, but it's not only the invariance of existence alone, but rather the invariance of the number of tick marks. My question is, why should we regard this number as invariant? Maybe because this number is dimensionless? HOTmag (talk) 10:20, 31 January 2024 (UTC)

The number can only change if one or more tick marks vanishes or appears. Therefore "invariance of existence" is equivalent to "invariance of number". --Wrongfilter (talk) 10:47, 31 January 2024 (UTC)

Thanks. HOTmag (talk) 11:40, 31 January 2024 (UTC)

x tick marks has the dimension of tick marks. Unlike the velocity-dependent magnetic field, which vanishes leaving only the electric field whenever v=0, the marks are presumed to all be physically present in all reference frames. Modocc (talk) 10:53, 31 January 2024 (UTC)

Thanks. HOTmag (talk) 11:40, 31 January 2024 (UTC)

OP's summary: To sum up, regardless of the Lorentz transformations, and of the Minkowski invariant distance in spacetime, and of the relativistic velocity-addition formula, what's the simplest intuitive principle one had better rely on, for concluding that the fraction I've been asking about is relativistically invarinat, in your opinion?

Actually, what still bothers me is the following fact: a ratio between two velocities - does depend on the reference frame, so how can it be intuitively justifiable to assume that lengths are different from velocities, i.e. that a ratio between two lengths - does not depend on the reference frame? HOTmag (talk) 11:40, 31 January 2024 (UTC)

Because everything that matters for that is linear. In any reference frame an object or photon goes twice as far in twice the time. NadVolum (talk) 13:11, 31 January 2024 (UTC)

Your response has involved time, while my question has not (regardless of the velocity of the reference frame). Let's think about my hand's length and your hand's length. No time is involved (regardless of etc.). So why should we think that the ratio between those lengths (involving no time) does not depend on the reference frame, although a given length per se does depend, and although a ratio between velocities does depend? Can you explain how your argument ("everything that matters for that is linear") explains the difference between the invariant ratio between lengths, versus the variant length per se, or versus the variant ratio between velocities? HOTmag (talk) 14:19, 31 January 2024 (UTC)

So if A, B, C are three points along a lines along a line you're wondering why AB/AC should be the same in one reference system as another? Linearity in the transformation between one reference system and another is what is required for this. Time and distance are transformed linearly in that doubling in one system doubles in the other. It does not matter that velocity changes. AB/AC will be the same in any system and the time for anythng going at a constant speed from A to C to get to B will be AB/AC of the time it takes to get to C. Assuming a physical system leaving A and meeting up at B are the same event in every system and B is the same point. How velocities change given this and the invariance of the speed of light is what one would next come to but the basic asssumption is the linearity of distance and time after transformation. NadVolum (talk) 15:05, 31 January 2024 (UTC)

I take your three words "linearity of distance" as stating that any ratio between two given lengths does not depend on the reference frame. Now I'm asking, if this fact about the ratio is a third postulate of special relativity, or one can derive this fact from any of Einstein's two declared postulates (Principle of relativity and the constancy of speed of light), or one must rely on the spatial homogeneity for deriving this fact, or on...what? Of course without relying on the Lorentz transformations, nor on the Minkowski invariant distance in spacetime, nor on the velocity-addition formula. HOTmag (talk) 17:28, 31 January 2024 (UTC)

Any two distances along the same line. Yes this would have been assumed, the special theory of relativity was a minimal change needed to Newton's laws to accomodate that the speed of light is a constant. Everything changes when one get to general relativity. NadVolum (talk) 21:14, 31 January 2024 (UTC)

Your first sentence is an important correction. Thanx. HOTmag (talk) 22:36, 31 January 2024 (UTC)

What do smartphone strips do?

Thin strips attached to the phone under the cover possibly always glued to the phone. Not the ones that look like it serves no purpose besides an internals protector or loudspeaker membrane. Sagittarian Milky Way (talk) 15:45, 30 January 2024 (UTC)

I don't see how anyone can answer this without more information. Which strips and which brand of phone? Can you supply a pic? The strips around the outside are the antennae. Shantavira|^{feed me} 16:24, 30 January 2024 (UTC)

It seems like you're describing Antenna Strips or NFC Antenna or Wireless Charging Coil or Vibration Motor or some Biometric Sensor Components , can you use a pic? Harvici (talk) 13:45, 31 January 2024 (UTC)

Not wireless charging or biometric. They're actually small tabs of a matte black sheet. One tab covers what looks like a very small port (what the hell is that?). The glue side of the tabs is NOT matte black.Sagittarian Milky Way (talk) 22:00, 31 January 2024 (UTC)

Evolution and most efficient solutions

Many people seem to believe that evolution leads to the most efficient solution to a problem.
Is there any scientific evidence that confirms this? 2A02:8071:60A0:92E0:0:0:0:B32D (talk) 20:51, 30 January 2024 (UTC)

Sounds a bit pointy. Define evolution in context and define efficient. Darwin talked about fitness, not efficiency. Not surprisingly Evolution probably answers your questions. Greglocock (talk) 21:55, 30 January 2024 (UTC)

For any selection criterion, an evolutionary process consisting of many steps of small changes, retaining only changes that correspond to improvements, is like a combination of a random walk in the design space (also called a drunkard's walk) with the optimization technique of hill climbing. If it converges, it does so on a local maximum. There may be a much higher maximum that can only be reached by traversing a valley; local search methods such as hill climbing will not find it. Therefore, the belief appears to be unwarranted.  --Lambiam 23:37, 30 January 2024 (UTC)

Evolution is a pretty good way of finding solutions, but for instance it is pretty unlikey any vertibrate will ever develop eyes without a blind spot like other creatures for example cephalopods have. In computing the 'evolution' can be run past some points where in effect a real creature would quickly die so it can be a very effective ways of finding good solutions - but we have no guarantees of most efficient except in very simple circumstances. NadVolum (talk) 13:22, 31 January 2024 (UTC)

The Recurrent laryngeal nerve seems to be a good example of a non-optimal solution (though each step in its evolution may have been). AndrewWTaylor (talk) 13:55, 31 January 2024 (UTC)

I wonder how many is many in "Many people seem to believe...". Most of biology seems to be non-optimal working solutions at all scales, work in progress, but not necessarily to optimize efficiency. Sean.hoyland (talk) 14:28, 31 January 2024 (UTC)

You might look at our article on genetic algorithms#Limitations. But amongst all the reasons why natural selection is not expected perfectly to optimise, let's not lose sight of the fact that many biological structures seem to be extremely well "designed" for the job they perform. I suppose that there are some nice examples from biomechanics but the example I am more familiar with is the excellent quantitative fit between predicted and observed sex ratios.JMCHutchinson (talk) 18:41, 31 January 2024 (UTC)

There are important distinctions to make between biological evolution and genetic algorithms used in engineering. In biology, there is no teology, it is very chaotic, a mutation that does not select negatively enough but can be considered useless may be preserved, elements of selection are unpredictable, etc. In engineering, the designer is everywhere: the constraints, processes and efficiency evaluations for selection are designed with a purposeful goal. This also means that when trying to find a solution, many iterations can be run and reset. The most efficient one can then be used for the intended application. These methods are only used for problems where it is useful. —PaleoNeonate – 23:56, 31 January 2024 (UTC)

Wien's Displacement curves

Stephan-Boltzmann law gives:
$B=T^{4}\sigma$ in watt per square meter.
Expressed to all spectrum in wavelength, you have:
$B=\int _{\lambda =0}^{\infty }B_{(\lambda ,T)}d\lambda$
$B_{(\lambda ,T)}d\lambda$ is in watt per square meter, like $B$.
In frequency you have:
$B=\int _{\nu =\infty }^{0}B_{(\nu ,T)}d\nu$
$B_{(\lambda ,T)}d\lambda =B_{(\nu ,T)}d\nu$ both in watt per square meter, like $B$.
With Planck's law:
$B_{(\lambda ,T)}d\lambda ={\frac {2hc^{2}}{\lambda ^{5}}}\cdot {\frac {1}{e^{\frac {hc}{\lambda k_{b}\theta }}-1}}\cdot d\lambda$
$B_{(\nu ,T)}d\nu ={\frac {2h\nu ^{3}}{c^{2}}}\cdot {\frac {1}{e^{\frac {h\nu }{k_{b}\theta }}-1}}\cdot d\nu$
For $d\lambda =x$, ${\frac {c}{\nu ^{2}}}d\nu =x$
You have:
$B_{(\lambda ,T)}d\lambda ={\frac {2hc^{2}}{\lambda ^{5}}}\cdot {\frac {1}{e^{\frac {hc}{\lambda k_{b}\theta }}-1}}\cdot x$
$B_{(\nu ,T)}d\nu ={\frac {2h\nu ^{5}}{c^{3}}}\cdot {\frac {1}{e^{\frac {h\nu }{k_{b}\theta }}-1}}\cdot x$
So, you see that for a fixed value for x and T, with $\lambda$ from 0 to $\infty$ and $\nu ={\frac {c}{\lambda }}$ you get the same curves for:
$B_{(\lambda ,T)}d\lambda$ and $B_{(\nu ,T)}d\nu$
(when $\lambda =0$, $\nu =\infty$ on the same abscissa, and vice versa),
and, of course, that $\lambda _{peak}$ and $\nu _{peak}$ have the same coordinates.
I specify that in the black body experiment, the power is measured by a bolometer, $\lambda$ and $d\lambda$ are obtained by a crystal filter, therefore of a finite value. One is unable to measure the frequency, it is deduced from the wavelength.

Can you tel me what is wrong in there ?

Malypaet (talk) 23:44, 30 January 2024 (UTC)

If $\lambda$ and $\nu$ are related by the invariant relation $\lambda \nu =c,$ and it is given that, universally,

$\int _{\lambda _{0}}^{\lambda _{1}}B_{\lambda }(\lambda ,T)d\lambda =\int _{\nu _{1}}^{\nu _{0}}B_{\nu }(\nu ,T)d\nu ,$

it follows that the functions $B_{\lambda }$ and $B_{\nu }$ are related by

$\lambda B_{\lambda }(\lambda ,T)=\nu B_{\nu }(\nu ,T).$

This is just mathematics, independent of any physical interpretation. Is this what you mean by "getting the same curves"? (For the rest I didn't understand what you are trying to say; perhaps other editors are more successful in interpreting it.)  --Lambiam 11:51, 31 January 2024 (UTC)

How can you write that, knowing that $\lambda$ and $\nu$ are linked by $\lambda ={\frac {c}{\nu }}$, and $d\lambda$ and $d\nu$ are linked by $d\lambda ={\frac {c}{\nu ^{2}}}d\nu$?

From Planck 1901 article:

Therefore, designate the spatial density of the energy of the radiation belonging to the spectral region $\nu$ to $\nu$ + d$\nu$ by u∙d$\nu$. One must write u∙d$\nu$ instead of E∙d$\lambda$, c/$\nu$ instead of $\lambda$, and c∙d$\nu$/$\nu ^{2}$ instead of dλ.

What I want to write is if you use or not d$\lambda$ and d$\nu$, you get the same curves or different curves.

But which one correspond to experiment?

So, to the nature or reality based on experiment? Malypaet (talk) 13:26, 31 January 2024 (UTC)

Plancks goes from:

$\int _{\lambda _{0}}^{\lambda _{1}}B_{\lambda }(\lambda ,T)d\lambda =\int _{\nu _{1}}^{\nu _{0}}B_{\nu }(\nu ,T)d\nu ,$

to:

${\frac {4\pi }{c}}B_{\lambda }(\lambda ,T)d\lambda ={\frac {4\pi }{c}}B_{\nu }(\nu ,T)d\nu ,$

that is the same as:

$Ed\lambda =ud\nu$

If you have:

$\int _{\lambda _{0}}^{\lambda _{1}}B_{\lambda }(\lambda ,T)\lambda =\int _{\nu _{1}}^{\nu _{0}}B_{\nu }(\nu ,T)\nu ,$

What do you get out of it?
Malypaet (talk) 18:53, 31 January 2024 (UTC)

The latter formula makes no sense, mathematically.  --Lambiam 22:01, 31 January 2024 (UTC)

With me:

$B_{(\lambda ,T)}d\lambda ={\frac {2hc^{2}}{\lambda ^{5}}}\cdot {\frac {1}{e^{\frac {hc}{\lambda k_{b}\theta }}-1}}\cdot d\lambda$

With you:

$B_{(\lambda ,T)}={\frac {\nu }{\lambda }}{\frac {2h\nu ^{3}}{c^{2}}}\cdot {\frac {1}{e^{\frac {h\nu }{k_{b}\theta }}-1}}$

$={\frac {2hc^{2}}{\lambda ^{5}}}\cdot {\frac {1}{e^{\frac {hc}{\lambda k_{b}\theta }}-1}}$

The difference is related to physical dimension:
$B_{(\lambda ,T)}d\lambda$ and $B_{(\nu ,T)}d\nu$ are equal and of the same dimension as B.

When $B_{(\lambda ,T)}$ and $B_{(\nu ,T)}$ have different values and dimension , each of them and to B.

So, how can you put them on the same graph, to compare their curves?

In mathematics, you don't mix cabbages with carrots, do you?
Malypaet (talk) 22:44, 31 January 2024 (UTC)

January 31

Actual drawing of the Pentalobe screw profile

Hi. While repairing some electronics, I came across the Pentalobe screw. I noticed that Wikipedia, and many other sites[12] , use a black-and-white generalized image to represent the Pentalobe screw profile. This image is made using 5 circles, with each circle's centre located at one vertices of a regular pentagon[13].

I don't know whether it's an optical illusion or not, but this "5 circles diagram" looks vastly different than the actual profile of the Pentalobe screw. It's more apparent if you look at a zoomed in image of the screw or screwdriver[14].

If the Pentalobe screw profile is indeed different than the "5 circles diagram", is there somewhere that I can find this profile?

Anything would be extremely helpful, even non-official sources, because right now the best thing I found is just a zoomed in image of a screwdriver tip, which is less than ideal. Liberté2 (talk) 02:41, 31 January 2024 (UTC)

c:Category:Pentalobe screws has photos and diagrams of several different variations. One important variable is the size of the circle relative to the pentagon. If the circles are tangent to each other or overlap, there is a point where they meet, like File:Pentalobular.svg. If the circles are small enough that they don't touch, like File:Medida de un tornillo pentalobular.svg, what should be the profile in the space between them? A second is an apparent difference of design: starting with a circular hole, do the five circles expand it (bumped-out curves) like File:Pentalobular.svg, or contract it (bumped-in) like File:Torx plus tamper.jpg? Is there an overlap of terminology between 'pentalobe' and 'torx variant with 5 points'? DMacks (talk) 09:56, 31 January 2024 (UTC)

The shape of the indentation of (Apple-specs conforming) Pentalobe screws should be more determinative than the heads of some screwdrivers capable of turning them. As seen here for bottom case screws of a MacBook, the circles clearly overlap.  --Lambiam 10:26, 31 January 2024 (UTC)

Are free radicals electrophile?

Are free neutral radicals, like CH3 electrophile? Their are differing and opposite answers to all on internet, some saying "Free radical is neither a nucleophile nor an electrophile because it does not seek out positively or negatively charged reactants", others say "Since methyl radical contains 7 electron ( 4 from C and 3 from H) and needs 1 more electron to complete its octet, so it will accept electron from some species and will behave as Lewis acid." and others say "I don’t think that methyl free radical is a Lewis acid. According to the definition of Lewis acid, Lewis acids accept a pair of electrons". ExclusiveEditor _{Notify Me!} 17:19, 31 January 2024 (UTC)

Methyl radical can indeed accept an electron and form unstable methyl anion, which (but not the radical!) is a Lewis base. Ruslik_Zero 19:26, 31 January 2024 (UTC)