Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

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

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

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

January 23

Exceptional configurations

I was puzzled by the fact that chromium and copper have five and ten electrons in 3d orbitals rather than four and nine. Now I have come to know from Dr. Wayne Breslyn's video that half-filled or completely filled d orbitals are more stable than those with one electron less. However, I found a few more exceptions in 4d orbitals, i.e., niobium, ruthenium, rhodium, and palladium, which are neither half-filled nor completely filled. What may be the explanation for the exceptional electronic configuration? Huzaifa abedeen (talk) 06:32, 23 January 2022 (UTC)[reply]

Check out the article on Aufbau principle. The "Exceptions" headings are particularly relevant. Search the web for Madelung rule exceptions. The neat math rules for calculating atomic shells do not work in all cases in the real world. The math is an approximation that does not always match real world experiments. If you can find the quantum (and beyond that) physics answer, please do write an article here about it. Perhaps even collect your Nobel Price when you do that. 85.76.87.150 (talk) 15:57, 23 January 2022 (UTC)[reply]

Atomic orbital and electron configuration also have some useful information. As they discuss, when you start getting to large atoms with complex orbitals, the energies of different subshells can be very close or overlap. Nature always tries to fill the lowest-energy subshells first. There are also complicated effects that can come into play from electron-electron interactions, with electrons of different orbitals repelling each other (due to their negative electric charge) or one orbital "screening" the positive charge of the nucleus from another. --47.155.96.47 (talk) 05:04, 25 January 2022 (UTC)[reply]

"Nature always tries to fill the lowest-energy subshells first" as the whole statement, with then a bunch of exceptions and such, leads to my students thinking Nature is mostly exceptions. Instead, "Nature always tries to reach the lowest overall energy configuration." Then there are just a set of details what causes higher vs lower energy. DMacks (talk) 05:34, 26 January 2022 (UTC)[reply]

How different type of species were discovered before 1970s?

Omicron virus discovered through Genome Sequencing method used not before 1970s. How different type of species were discovered before 1970s? Rizosome (talk) 06:41, 23 January 2022 (UTC)[reply]

Please note that the Omicron variant is not considered a species of its own, but one of the variants of the SARS-CoV-2 species. Our article Virus classification explains how viruses are classified as species, most of which does not depend on genome sequencing but can be done by inspecting electron microscope images (for the phenotypic characteristics) and observing its macroscopic effects (host organisms and disease symptoms). --Lambiam 12:47, 23 January 2022 (UTC)[reply]

As the virus classification article states, the classification of viruses can be inconsistent and is very much an unsettled question. This is on top of the more general uncertainty of the species concept. People like nice, neat classifications with exact places to put everything and consistent rules for doing so. Nature is a LOT messier. --User:Khajidha (talk) (contributions) 16:07, 23 January 2022 (UTC)[reply]

Messy as it may be, such classifications may have a practical usefulness, from conservation efforts for vulnerable species to developing effective medication for diseases with identifiable pathogens. --Lambiam 21:58, 23 January 2022 (UTC)[reply]

"Conservation efforts for vulnerable species"? I think the vulnerable species is man, not some <nasty word> virus! Martin of Sheffield (talk) 22:02, 23 January 2022 (UTC)[reply]

I reacted to a contribution referring to "the more general uncertainty of the species concept" – which even applies to proposed extinct (sub?)species in the genus Homo. --Lambiam 13:39, 24 January 2022 (UTC)[reply]

Along with the ongoing question about whether viruses are really "alive" or not. --←Baseball Bugs ^{What's up, Doc?} carrots→ 16:51, 23 January 2022 (UTC)[reply]

This line solved my doubt: Our article Virus classification explains how viruses are classified as species, most of which does not depend on genome sequencing but can be done by inspecting electron microscope images (for the phenotypic characteristics) and observing its macroscopic effects (host organisms and disease symptoms). Rizosome (talk) 07:04, 24 January 2022 (UTC)[reply]

Resolved

Adhesive for use on skin

I mean the stuff on band-aids and adhesive tape, not surgical adhesive. Any idea what it is that they use, and where to get it? Somehow separating it from adhesive tape might be a possibility if there's no other way. Application is strapless n95 masks, which stay on with adhesive (look up "Readimask"). They apparently work pretty well on first use, but aren't easily re-usable because the adhesive loses its stickiness. Thus, the is to find a way to add more. The masks seem like a nice idea but they are on the expensive side. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 08:11, 23 January 2022 (UTC)[reply]

Our article Adhesive bandage has this to say: "The adhesive is commonly an acrylate, including methacrylates and epoxy diacrylates (which are also known as vinyl resins).^[2]" --Lambiam 12:53, 23 January 2022 (UTC)[reply]

Thanks, I should have looked there. I also found a less expensive source of strapless masks. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 02:26, 24 January 2022 (UTC)[reply]

January 24

Why were much of Japan's deciduous forests replaced with conifer plantations?

As mentioned in the article Japanese wolf. What purpose do the plantations serve? ZFT (talk) 06:48, 24 January 2022 (UTC)[reply]

Not sure it gives a good reason, but see Afforestation in Japan#History for some background. Clarityfiend (talk) 07:32, 24 January 2022 (UTC)[reply]

This chapter titled "Japanese Forestation Policies During the 20 Years Following World War II" gives an explanation:

During World War II, the area cut annually in Japan exceeded the area planted, and cutover land was common. Within approximately 10 years of the end of the war, however, forestation on cutover land was almost complete. In the 10 years that followed, forestation policies targeted increasing coniferous tree plantations to secure industrial roundwood. Forestation plans and legal systems were developed, and organizations such as the Prefectural Forestry Corporations and Forest Development Corporation were founded to promote the planting of coniferous trees.

Clarityfiend (talk) 07:36, 24 January 2022 (UTC)[reply]

"The softwood derived from conifers is of great economic value, providing about 45% of the world's annual lumber production. Other uses include the production of paper and plastic from chemically treated wood pulp." (Quoting Conifer#Economic_importance.--Shantavira|^{feed me} 09:12, 24 January 2022 (UTC)[reply]

A similar drive for domestic softwood production in the UK (in this case following WWI) resulted in the Forestry Commission. Alansplodge (talk) 09:44, 24 January 2022 (UTC)[reply]

drum in front of a military military (WW I)

What is the name and the purpose of this "oil barrel" mounted in the very front? --Mateus2019 (talk) 16:56, 24 January 2022 (UTC)[reply]

It is probably a mine roller. Nimur (talk) 17:32, 24 January 2022 (UTC)[reply]

(ec)Not sure about the drum but it appears to be a Somua MCG-4 or MCG-5 artillery tractor (or possibly an earlier version). Lots of descriptions of this vehicle but I can't find an explanation for the drum. Mikenorton (talk) 17:38, 24 January 2022 (UTC)[reply]

Also found on other half-tracks, such as the M3 and the Unic P107 (File:Unic P107 , Musée des Blindés, France, pic-2.JPG). Mikenorton (talk) 17:53, 24 January 2022 (UTC)[reply]

Explanation with useful diagram found here, to quote "the roller worked to prevent the front bumper from digging in when at too severe of an angle of approach. Its contact would lift the front wheels". Mikenorton (talk) 18:59, 24 January 2022 (UTC)[reply]

And it turns out that WP:WHAAOE wins again - see unditching roller. Mikenorton (talk)

Thanks Mikenorton! I agree, it's more likely to be an unditching roller (it's positioned a little close to the engine-block to be useful as any kind of mine flail or mine roller). Nimur (talk) 20:12, 25 January 2022 (UTC)[reply]

Ice age meat conservation

I read long ago maybe in Scientific American about archeology, maybe in the USA or Canada, where they escavated a well or shaft finding some vertical pole and round each pole several rather heavy stones. They reconstructed it so, that hunters in the past were filling intestines of some large game with meat and some stones, then wrapped the filled intestines round some poles inserted under water in a pond, the stones helping to sink the meat. The cold water would conserve the meat for several months, maybe helping lactic fermentation.
I cannot find references any more. Can you help please? Thank you. 2003:F5:6F0E:8B00:4002:87CF:C1C1:20DB (talk) 22:00, 24 January 2022 (UTC) Marco PB[reply]

It wouldn't work for long in the current summer climate of central USA but in places or ice ages when the average annual temperature is colder, like fridge or freezer cold, then the very bottom of a deep enough water body might be the temperature of the densest temperature of water (4°C). If it is very deep like contemporary Lake Superior the acceptably cold layer thickness might be many many meters. Sagittarian Milky Way (talk) 02:58, 25 January 2022 (UTC)[reply]

That doesn't sound like a very effective way to preserve meat. Maybe I'm misunderstanding what you're describing? If you left the meat hanging in an empty, dry well or shaft, especially if it had been initially smoked or salted, you would have a kind of larder. But if you then put that meat into a pond, all you'd end up with is some very happy fish. Matt Deres (talk) 14:53, 25 January 2022 (UTC)[reply]

Depends if you can make fish unwilling or unable to pierce intestines or not. With mammals you can coat it with sticky high-capsaicin stuff, with birds that doesn't work, with fish I don't know. And maybe whether you make the intestines waterproof is important too. And if you can MacGyver a vacuum pump with a mouthpiece and one-way flap or something maybe even better. Sagittarian Milky Way (talk) 15:38, 25 January 2022 (UTC)[reply]

The OP is asking about an archaeological site; what are you going on about with vacuum pumps and capsaicin? Matt Deres (talk) 19:39, 25 January 2022 (UTC)[reply]

If you have a Stone Age way to deter animals from underwater meat intestines that would be more realistic. Maybe there's a way, some gardeners deter herbivory with a dried blood bag from the garden store (USA deer don't want to eat anything that smells like a light dusting of pulverized blood) Sagittarian Milky Way (talk) 20:51, 25 January 2022 (UTC)[reply]

Thank to everyone. Someone tried actually and let some meat in a pond under cold water and it was still edible after several months, althought with an unusual smell (but people eat Surströmming, don't they?). On the other side I don't think fish to be a real problem in isolated subglacial bog ponds.

But yes, I was looking for references about this particular archeological site, but it was no full article but instead a short message under news so it is not a surprise even googl doesn't know of it. 2003:F5:6F0E:8B00:B4DB:248B:38E7:9C7E (talk) 20:33, 25 January 2022 (UTC) Marco PB[reply]

Is it anoxic down there? That might help. Sagittarian Milky Way (talk) 20:51, 25 January 2022 (UTC)[reply]

It occurred to me too, that the anoxic environment deep in the water of a pond could be relevant, I'm thinking for example about the so called Bog Bodies, dead people or animals conserved during up to some millenia in the anaerobic, acidic environment of peat bogs. But how far they are still edible is an open question. 2003:F5:6F0E:FD00:3110:6631:C3BB:E9DB (talk) 17:47, 26 January 2022 (UTC) Marco PB[reply]

Anecdotally (meaning I haven't looked for references), it seems to be the case for some samples of Bog butter. {The poster formerly known as 87.81.230.195} 90.213.224.157 (talk) 18:15, 26 January 2022 (UTC)[reply]

You have it. That could be a practical solution for the European surplus butter problem. 2003:F5:6F14:DE00:D0F0:4D6E:90B2:D717 (talk) 17:53, 27 January 2022 (UTC) Marco PB[reply]

January 25

What technology used in Bluetooth?

In Bluetooth it says: Bluetooth uses a radio technology called frequency-hopping spread spectrum.

But in Phase-shift keying, it says: It is widely used for wireless LANs, RFID and Bluetooth communication.

Is it PSK or Frequency-hopping spread spectrum? Rizosome (talk) 07:30, 25 January 2022 (UTC)[reply]

Our article on Bluetooth also says "Originally, Gaussian frequency-shift keying (GFSK) modulation was the only modulation scheme available. Since the introduction of Bluetooth 2.0+EDR, π/4-DQPSK (differential quadrature phase-shift keying) and 8-DPSK modulation may also be used between compatible devices". Someone like Nimur could explain better I'm sure but AIUI, there's no contradiction here since these don't refer to the same thing Bluetooth uses FHSS and either PSK or FSK. Similarly Bluetooth Low Energy uses DSSS and FSK. Nil Einne (talk) 09:44, 25 January 2022 (UTC)[reply]

Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. Phase-shift keying (PSK) causes modulation sidebands close to the carrier frequency but is not itself a spread spectrum method. Philvoids (talk) 18:09, 25 January 2022 (UTC)[reply]

I think we have to disentangle the terminology: "spread-spectrum" can be used as a qualitative description of the frequency behavior, and this description can be applied (qualitatively) to many different kinds of transmissions.

From this perspective, the description "spread-spectrum" is not exclusive of other descriptions: any particular scheme can be both PSK and spread spectrum.

At the same time, "spread-spectrum" can be used to specify a particular technical detail about a particular piece of the technology implementation.

Whether BlueTooth actually satisfies either adjective might depend on who you ask. But of course, this is the reference desk - so we have to find a reliable source! The canonical, authoritative source is the BlueTooth SIG (Special Interest Group); they publish most of their detailed technical specifications and basic technology summaries at zero-cost.

From Learn About BlueTooth - Technology Overview - the set of technologies branded as "Classic" BlueTooth are described in this way:

Channel Usage - Frequency-Hopping Spread Spectrum (FHSS)
Modulation - "DQPSK" (and others)

So the distinction about which adjectives they apply depend on which layer of abstraction you're evaluating. Like everything in modern wireless communication, it helps to think about the radio as part of a protocol stack: and BlueTooth is a sophisticated stack! The low level radio control layers - those portions that select the frequency - are conceptually different from the slightly-less-low-layer radio modulation control, where the encoding or "keying" scheme is implemented. And these are, in the common model-abstraction, at a "lower layer" than the BlueTooth communication protocols that sustain various higher-level features. If you're looking at the signal strictly in the context of its radio frequency spectrum, you'll probably see big bursts of noisy energy - it'll be challenging to describe the power-spectrum at all, because that spectrum will vary as many system-parameters change. Even the keying-scheme can be changed during normal use.

Nimur (talk) 20:27, 25 January 2022 (UTC)[reply]

So both PSK and Frequency-hopping spread spectrum (FHSS) are used in bluetooth technology? Rizosome (talk) 00:59, 26 January 2022 (UTC)[reply]

Yes, much the same as both motors and wheels are used in car technology. They serve different functions. --Lambiam 09:20, 26 January 2022 (UTC)[reply]

I got the answer from this line: Yes, much the same as both motors and wheels are used in car technology. Rizosome (talk) 06:51, 27 January 2022 (UTC)[reply]

Resolved

Solar panels silicon nitride coating

Hi, I've been reading and searching for information related to solar panels made of monocrystalline silicon. I read about silicon nitride coating. I'm sure that such a coating must have it's disadvantages (material-wise), such as degradation over time. The problem is that I can't find any specific source for explanations - I can't point out those problems With proper information. I would appreciate your help 87.70.11.210 (talk) 16:56, 25 January 2022 (UTC)[reply]

Monocrystalline silicon and silicon nitride are very different things. Are you asking about the pros and cons of using silicon nitride coatings in general, or for using them specifically on solar panels (presumably in comparison to other ceramic coatings used for solar panels), or even more specifically on solar panels made of monocrystalline silicon? --Lambiam 09:41, 26 January 2022 (UTC)[reply]

I'm specifically interested in the pros and mostly cons of using silicon nitride coatings on solar panels made of monocrystalline silicon. No need for comparisons :) 87.70.11.210 (talk) 13:40, 26 January 2022 (UTC)[reply]

Here are a few links to research articles: [1], [2], [3], [4]. An issue mentioned in some articles on silicon nitride coatings in general, not in connection with solar panels, is a difficulty in applying them by conventional thermal spray processes, due to silicon nitride decomposing under a high temperature (2173 K). However, other spraying processes appear to work well.^[5][6] Benefits mentioned by a firm that has a financial interest in the issue (but not contradicted by others) are low density, high temperature strength, superior thermal shock resistance, excellent wear resistance, high hardness and toughness.^[7] Si_xN_y coatings subjected to micro scratching have been reported to undergo adhesive failure with loads above 214 mN;^[8] I have no idea if that signals high durability. --Lambiam 21:44, 26 January 2022 (UTC)[reply]

Thank you so much!! 84.228.239.26 (talk) 13:49, 28 January 2022 (UTC)[reply]

Spin states of planets in S-type circumbinary orbits

Wikipedia defines "S-type" orbit as follows: When you have a binary star i.e two stars (here called "A" and "B") in a common orbit, a planet (here called "b") that has its own orbit around just one star (hereby called "B") is an "S-type planet" [in contrast to "P-type planets" which have an orbit around both "A" and "B"]. I have been looking for research on how tides would influence the spin state of planet b when it is close enough to B that tidal acceleration would play a role, but where the gravitational influence of "A" cannot be disregarded. I can't find any research that discusses the scenario of a S-type planet. Jo-Jo Eumerus (talk) 17:08, 25 January 2022 (UTC)[reply]

Courtesy link: Habitability of binary star systems. —Tamfang (talk) 06:31, 28 January 2022 (UTC)[reply]

If the gravitation of A is so strong that effects the rotation of the planet then its orbit is likely to be unstable. Ruslik_Zero 20:39, 25 January 2022 (UTC)[reply]

Hair Loss Restoration

Biotin, or Vitamin B7, is a natural substance frequently touted for restoration of hair loss or for increase in density of hair. In the footnotes to the Wikipedia article explaining it are two references (footnotes 29 and 34) regarding studies of subjects to evaluate the efficacy of Biotin for this purpose. One of those footnotes refers to a product called Viviscal which was found effective in restoring hair loss for women but when I searched Wikipedia for Viviscal no such page is found. I and perhaps many others would like to know what Viviscal is and where to find it. Probably millions would thank you.Bruce1939 (talk) 20:41, 25 January 2022 (UTC)[reply]

Wikipedia is not for product advertising. However, a Google search brings up lots of stuff, e.g. the Healthline article Viviscal Hair Growth Treatment: Does It Really Work? Clarityfiend (talk) 22:08, 25 January 2022 (UTC)[reply]

...which follows Betteridge's law of headlines.

The wording of the biotin article is In the US, biotin as a non-prescription dietary supplement is sold in amounts of 1 to 10 mg per serving, with claims for supporting hair and nail health, and as 300 mg per day as a possibly effective treatment for multiple sclerosis. That section explains why some screening tests can be affected, but it does not say it is efficient for its purpose; indeed, the "research" section of the same article says the evidence is very poor. (Why )

Bruce1939, generally speaking, you should not take any dietary supplement that has not been prescribed to you by a medical professional. (By which I mean a doctor or dietetician with a license to practice issued by the local governmental authority, not a "dietary supplement expert" from the Board of Dietary Supplements.) Also, one study can almost never "find [something] effective". Why is a long story, but as a start, 32% to 56% of the best-cited studies cannot be reproduced - the rate is likely up to 80% at least for the stuff that is produced with the marketing department (rather than other researchers) as the reader target. Tigraan^{Click here for my talk page ("private" contact)} 14:49, 28 January 2022 (UTC)[reply]

January 26

Maximum no. of compounds

The elements which form the most compounds are carbon, which most of the compounds of carbon have hydrogen in them, and hydrogen, which is the element which can form compounds with almost all of the elements in the periodic table. If hydrogen forms the maximum number of compounds, why is a whole branch of chemistry dedicated to the compounds of carbon? Maximum number of compounds are formed by Which element? Carbon, hydrogen, or any other Huzaifa abedeen (talk) 06:17, 26 January 2022 (UTC)[reply]

Organic chemistry is interesting because of its practical applications in biological processes. "Life chemistry" is also something of a historical accident, as in the past people held the idea that living matter had some kind of a mystical life force that made it fundamentally different from non-living matter.

We could invent a specific field of study of hydrogen for purely intellectual interest, and invent a name for that, but what can be said about hydrogen is already pretty well covered by general chemistry.

The number of different molecules that can be formed is pretty much an open-ended question because there are big molecules that can not be readily counted, such as DNA and proteins and other macromolecules. 85.76.87.150 (talk) 08:52, 26 January 2022 (UTC)[reply]

Structure of ethanol

(edit conflict) If you look at the structure of compounds, like that of ethanol or benzene, you can see that the carbon atoms can form chains and rings, and thereby the backbone of a compound. Hydrogen can only appear as fringe. --Lambiam 09:14, 26 January 2022 (UTC)[reply]

Per Lambiam for the same reason that the study of human biology spends more of its energy on your internal organs than your hair, organic chemistry is more concerned with the carbon than the hydrogen. The carbon provides the primary structure and function of organic molecules, while the hydrogen, while there is a lot of it, is just kinda "there". You have more hairs than hearts, but I dare say your heart's function is more vital to your life than that of your hair. --Jayron 32 11:51, 26 January 2022 (UTC)[reply]

85.76.87.150, if you think that living and non-living matter are not fundamentally different, I suggest you do some more reading. Start with life. -- Jack of Oz ^{[pleasantries]} 21:40, 26 January 2022 (UTC)[reply]

See Wöhler synthesis, in particular the "Debates" section. See also Vitalism. Martin of Sheffield (talk) 21:50, 26 January 2022 (UTC)[reply]

As Martin implies above, there is nothing special about the atoms, compounds, molecules, etc. that make up living things that makes them different than the exact same molecules as made from non-living sources. If you created DNA from carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur atoms, each of which came from non-living sources, then that DNA would behave exactly like DNA created inside of your cells. The now long-debunked theory that there was some special "life force" that made living matter somehow different from non-living matter is called vitalism, and it's not a thing. The work of Friedrich Wöhler and Hermann Kolbe put an end to that thinking. --Jayron 32 12:49, 27 January 2022 (UTC)[reply]

Sure, life is different from non-life. Life has, depending on your definition, properties such as (1) birth, (2) death, (3) metabolism, (4) reproduction. The definition differs depending on who you ask.

If you send a probe to Mars to find "life" you need to think pretty hard about what that word means, and how to differentiate between "life" and "non-life" ground samples.

But at the molecular lever making a stand between living and not-living molecules is magical thinking. Compounds that contain carbon are not magically different those that do not.

Thank you for your suggestion of "doing more reading". I genuinely non-sarcastically do try to do that. 85.76.87.150 (talk) 17:01, 27 January 2022 (UTC)[reply]

The CAS database has at least 3 orders of magnitude more carbon compounds than non-carbon. Sagittarian Milky Way (talk) 21:59, 26 January 2022 (UTC)[reply]

Carbon § Compounds: Carbon is so special because carbon atoms can bind to each other to form long chains, and these bonds between carbon atoms are strong and stable. This is why all known life is based on carbon chemistry. No other element can do this to the degree that carbon can. At Earth surface conditions, the only stable hydrogen-only compound is dihydrogen, a gas. --47.155.96.47 (talk) 00:46, 27 January 2022 (UTC)[reply]

The strong desire to form 4 bonds, ability to bond the most common non-hermit atoms in the universe (H=1 C=4 N=3 O=2) and semi-common FClBrI (1 bond) and PS (multiple) atoms, and the ability for 1 or 2 or 3 or even "1.5" of those bonds to be used up on the same atom pair also help. Sagittarian Milky Way (talk) 01:57, 27 January 2022 (UTC)[reply]

Tar sands tailings

Which metals are concentrated to a significant degree in the tailings from tar sands processing? In particular, do they contain high levels of metals from groups 4-6, 12 and 14? Is there a comprehensive list of metals in tar sands tailings somewhere out there? 69.181.91.208 (talk) 12:41, 26 January 2022 (UTC)[reply]

It would, of course, depend on which tar sands are being looked at, but this has some promising leads to help with your research. --Jayron 32 12:44, 26 January 2022 (UTC)[reply]

Excellent! So, we have titanium, zirconium, vanadium, rare earths (great!), mercury (not quite what I was looking for, but still useful), arsenic (same), lead and iron (useful, but not as exciting as the first four) -- anything else? (For example, I've read somewhere that these tailings have high levels of columbium and tantalum -- any confirmation on this?) 2601:646:8A81:6070:ADA7:93DA:4B41:EBF (talk) 02:35, 29 January 2022 (UTC)[reply]

January 28

Why characteristics graphs of p–n junction and Zener diode are similiar?

See characteristics graphs of p–n junction : click here

See characteristics graphs of Zener diode : click here Rizosome (talk) 01:49, 28 January 2022 (UTC)[reply]

Because they are the same! See the first line of Zener diode: "A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" when a certain set reverse voltage, known as the Zener voltage, is reached." You can use any diode as a zenner but: (1) the Zener voltage will not be accurate, and (2) you may well destroy the diode doing so unless you are very careful. The difference is in the fine details of the physical structure. That's why the symbols are nearly identical, but with the two little "wings" which change the bar into a "Z" for Zener (or it is sometimes said it reflects the characteristics). Martin of Sheffield (talk) 09:52, 28 January 2022 (UTC)[reply]

(ec) Their current/voltage chracteristics are similar because P-N junction diodes, whether specified as rectifiers or for a specific reverse breakdown characteristic, are all similarly constructed. There is a wide spread of characteristics in mass produced diodes and individual diodes are selected to meet specification from this continuum. So a diode selected as a rectifier such as 1N4001 must satisfy a published forward current-voltage specification. It will also have a reverse breakdown voltage, but as long as it is more than the guaranteed value (50V) for this diode, its actual value is neither important nor guaranteed. Conversely diodes intended for use as zener diodes are produced with heavier doping of the P-N junction that encourages a low breakdown voltage (especially values below 5.6V) but they must be tightly selected from production for exact reverse voltages e.g. 4.7V for type 1N4624. Philvoids (talk) 10:45, 28 January 2022 (UTC)[reply]

I got the answer: Their current/voltage chracteristics are similar because P-N junction diodes, whether specified as rectifiers or for a specific reverse breakdown characteristic, are all similarly constructed. Rizosome (talk) 07:51, 29 January 2022 (UTC)[reply]

Resolved

January 29

Dark matter and quasars

One of the original reasons for the postulate that most of the matter in the universe is dark matter is that in the solar system, the inner planets like Mercury have a higher velocity than the outer planets like Neptune, however, the stars in galaxies do not exhibit the same phenomenon - the velocity of the outer stars is roughly the same as the inner stars. This article deals with the phenomena, https://en.wikipedia.org/wiki/Galaxy_rotation_curve, and it mentions a halo-effect, however, I don't think it specifically considers the effect of mass ejected by quasars. Quasars often eject matter perpendicularly to the galactic plane. If the matter from quasar jets were ejected in opposite directions perpendicularly to the galactic plane a significant portion of the radius of the galaxy, it could have a significantly greater inward pull on stars in the outer edges of the galaxy than it would on stars close to the centre of the galaxy because the forces on the inner-stars would mostly cancel-out (one component of the net force exerted on stars by the ejected matter would be the sine of the angle between the centre of mass of the ejected matter and the axis of rotation of the galaxy, which could easily more than offset the inverse square gravitational law).

The thing that I'm not sure about is whether or not over billions of years, the total amount of matter and energy ejected by quasars would be enough to have a dramatic effect on the relative speed of stars close to and far from the galactic centre.

The image in this article - https://cosmosmagazine.com/space/quasar-jets-are-thousands-of-light-years-long/ - based on an article published in the journal Nature, reveals the hidden truly massive extent of some quasar jet emissions, and I think it's worth re-examining the galactic orbital velocity & dark matter thesis in light of it.

MathewMunro (talk) 08:12, 29 January 2022 (UTC)[reply]

(Re-formatted to remove absurdly long heading. Bazza (talk) 09:59, 29 January 2022 (UTC))[reply]

The matter in the jets of an active galactic nucleus is ejected by the magnetic field in the inner part of the accretion disk. Whatever that matter is (it's just ordinary atoms), it must be able to interact with other matter electromagnetically. We also know that we can't see the matter that explains the fast rotation of galaxies (that's why it's called dark matter), so it can't interact electromagnetically, or only very weakly. If that dark matter were gas, we would have seen it with our radio telescopes. So that unknown matter cannot be the gas ejected by a quasar. Anyway, the gas wouldn't stick around for billions of years. If it pulls on the matter in the disk to make it rotate faster, the matter in the disk would pull back (Newton's third law), causing the matter to fall back into the disk. So whatever this dark matter is, it must be massive, gravitationally bound to the galaxy and able to fall through the disk without interacting in any way other than by gravity. Gas doesn't work. PiusImpavidus (talk) 10:15, 29 January 2022 (UTC)[reply]

Firstly, thanks for your reply. I'm not aware of what our radio telescopes can and can't see, but wouldn't the gas "go dark" after millions of years, after it radiates its heat? And in regard to it not sticking around for billions of years, true, but it also wouldn't just stop once it falls to the galactic plane - it would orbit in ellipses that gradually went from being very long in the perpendicular direction to being very much shorter in the perpendicular direction and longer in the galactic plane direction, I think. Also, given that it takes 230 million years for our solar system to orbit the galaxy, it could receive successive boosts (relative to the inner stars) from long-since faded quasar emissions. I just don't know if the amount of the effect would be enough to account for observations. MathewMunro (talk) 10:43, 29 January 2022 (UTC)[reply]

Space isn't in thermal equilibrium. The gas in the galactic halo is still bathing in the light of all those stars, which has a low intensity, but a fairly high energy. A very low density hydrogen and helium gas is a pretty poor radiator of infrared, but still pretty good at absorbing the ultraviolet light from those stars, so it doesn't get really cold.

Any cloud launched from the centre of the galaxy will be on an orbit still intersecting that centre, and if we were to put a lot of gas clouds on wide orbits around the galaxy, the shell theorem tells us they wouldn't affect gravity inside. So those gas clouds are on orbits (if indeed they are bound to the galaxy) intersecting the disk of the galaxy. But this is very low density gas. The density of the gas in the halo is certainly not much higher (in fact, much lower) than the density of the interstellar gas in the disk. That means that your gas cloud cannot pass through the disk; instead, it will collide. Halo stars can pass through, similar to how a bullet can travel for kilometres through air, but a cloud of smoke can't. PiusImpavidus (talk) 12:58, 29 January 2022 (UTC)[reply]

The vast majority of galaxies does not have an active galactic nucleus. Yet, for example, the Triangulum Galaxy, aka Messier 33, has a galaxy rotation curve that cannot be explained by its visible matter. The observed curve even shows an increase in speed as the distance from the centre increases. Matter ejected from the centre perpendicularly to the galactic plane should remain near the axis of rotation. Even if all gravitational matter is concentrated in a very long cylinder coinciding with the axis, the speed should still decrease with the distance. --Lambiam 13:09, 29 January 2022 (UTC)[reply]

'Even if all gravitational matter is concentrated in a very long cylinder coinciding with the axis, the speed should still decrease with the distance.' - I'm not convinced of that. Rigorously disproving it is well beyond my capability, however, I note that the matter in the central column that's perpendicular to the galactic disk may spend more time far away from the galactic core, as it's initially travelling extremely fast, and presumably when it eventually falls back in and crosses the galactic plane, it would likely be travelling at a tremendous speed once more, whereas when it's far away, it's going slower, and if it just so happens that the average distance from the galactic centre is something like two times the galactic radius, then the obviously stars close to the galactic nucleus would experience lower net inward pull than stars further out. Even comparing a star on the edge of the galaxy to one half way between the galactic centre and the edge, (setting the galactic radius to 1): sin(tan^-1(1/2))/(1^2+2^2) > sin(tan^-1(0.5/2))/(0.5^2+2^2). Granted that's a very sketchy argument with some questionable assumptions, but I think it demonstrates that it's at least possible for matter ejected in quasar jets to accelerate outer stars more than inner ones.

As for M33, a possible explanation is in the Wiki article: 'M33 is linked to M31 by several streams of neutral hydrogen and stars' - that may have an effect like an AGN plume of providing greater orbital acceleration to outer than inner stars? MathewMunro (talk) 19:14, 29 January 2022 (UTC)[reply]

January 30

How did NASA know that JWST reach L2 point beforr deploying its high gain antenna?

JWST reached L2 points then after few hours, it deployed its high gain antenna.

But NASA released statement about reaching L2 point even before deployment of high gain antenna. How did NASA without using its antenna? Rizosome (talk) 01:38, 30 January 2022 (UTC)[reply]