Wikipedia:Reference desk/Archives/Science/2021 December 15

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December 15

What makes asbestos fire resistant?

Basically that's it: what are the physical/chemical properties of asbestos that make it so good at resisting fire?

Does it have to do with the fibrous structure? Fiberglass insulation apparently is also fire resistant, so do tiny fibers generally resist fire well?

2601:401:100:FBF:7175:62A5:1F1A:F138 (talk) 05:15, 15 December 2021 (UTC)

Having the fibres enables air to be trapped, and also makes it very hard for heat to conduct. The substance is also resistant to heat, unlike polyester wadding or cotton wool. Graeme Bartlett (talk) 05:52, 15 December 2021 (UTC)

I think the question is why it resists combustion rather than heating, and that is simply because it is an inorganic mineral and therefore noncombustible. And no, not all fibrous materials resist fire -- cotton wool is very combustible (in fact, if wetted and then allowed to dry out it can even self-ignite!) 2601:646:8A81:6070:CD89:937C:428D:CE7D (talk) 06:02, 15 December 2021 (UTC)

Tiny fibres can burn very well. Steel wool contains tiny fibres (and is inorganic) and it burns, in contrast to steel in other forms. But the various forms of asbestos have in common that they consist of oxides. Generally, you can't burn (oxidise) an oxide, because it is already the product of such oxidation. The same is true for glass wool. PiusImpavidus (talk) 10:02, 15 December 2021 (UTC)

To be very simplistic, asbestos (there are many different types) are types of rock, and lots of kinds of rock are fire resistant. The question should be, why has asbestos been used so extensively for this purpose (and other purposes)? Its fibrous nature means it can be processed and incorporated within other materials, thus changing the properties of them. The fibres of asbestos are also particularly persistent and enduring within an application - years ago I was told be someone who worked in a lab that tested things for asbestos contamination that the fibres can easily be split longitudinally into finer and finer fibres, but they are more resistant to being degraded into shorter fibre lengths; it is this property that gives asbestos its usefulness, but also makes it so hazardous to the lungs, because the fibres do not degrade and instead persist and irritate and cause inflammation for a very long time, leading to illness. PaleCloudedWhite (talk) 18:48, 15 December 2021 (UTC)

• Fiberglass insulation apparently is also fire resistant - assuming you meant glass wool, not really. It is true that fiberglass does not burn (unlike some other materials used in similar applications). However, glass wool is not fire resistant - although the fiberglass itself can stay put up to 650°C or so, the glass wool structure is held together by a binder, which is often a polymer that will degrade at 200°C or so. (After that, fibers fall over and you lose the thermal insulation properties that come from the air-trapping structure.) Tigraan^{Click here for my talk page ("private" contact)} 11:38, 17 December 2021 (UTC)

What do you get if...

...you cross a bulldog with a Shih tzu? No, seriously -- asking a cynologist for an expert opinion, what would happen? My own non-expert guess is that you won't get anything good in this scenario -- but just how bad would it be? 2601:646:8A81:6070:CD89:937C:428D:CE7D (talk) 05:58, 15 December 2021 (UTC)

The appearance of the puppies is unpredictable. They tend to have serious health problems, in particular brachycephalic airway obstructive syndrome (BAOS). For more, see the section "Shih Tzu Bulldog mix health" on this web page.  --Lambiam 10:45, 15 December 2021 (UTC)

Thanks! 69.181.91.208 (talk) 12:53, 16 December 2021 (UTC)

Resolved

69.181.91.208 (talk) 12:53, 16 December 2021 (UTC)

Are the standard and vertebrate mitochondria codon tables "well-designed"?

Is it worse if most things had 3 codons and the rest had 2 and "start but only put methionine if methionine is the next one" had 3 codons? Sagittarian Milky Way (talk) 06:24, 15 December 2021 (UTC)

What? --OuroborosCobra (talk) 19:17, 15 December 2021 (UTC)

Also, they aren't "designed" in the first place. They seem to function rather well, though, yes. --OuroborosCobra (talk) 19:18, 15 December 2021 (UTC)

You are right, but as an evolutionary biologist I would be comfortable about using the term "well designed" here. It is not taken to imply teleology or that there is a Maker, but rather to compare what has evolved against the product that a hypothetical clever designer would create to accomplish the same purpose with the same materials. "Well adapted" is an alternative, but not quite the same thing, because it implies merely reaching a local adaptive peak, whereas something well designed should be at the global optimum. The giraffe's recurrent laryngeal nerve functions well, but is not well designed. Jmchutchinson (talk) 20:14, 15 December 2021 (UTC)

(edit conflict) That's why I put designed in quotation marks. Or rather I should've asked "is it a good table?". Does it not matter much that the first amino acid is always methionine? Isn't that limiting? Maybe a start codon (that doesn't "print") isn't needed but why is only one amino acid able to start? Does it not matter much that some amino acids have 6 tags each and others have only 1? This may be good if the code allocation we got is fitter. Which may or may not be the same thing as maximizing fidelity and minimizing the amount of amino acid mutations that break the protein.

Also I've got 2 more questions about the process: Are there "forbidden letter sequences" (no longer than the longest correctly-formed natural chain) that can't pass the folding step without breaking?

Are there any amino acids that can't touch each other cause they don't fit or play nice? Probably not. Sagittarian Milky Way (talk) 21:37, 15 December 2021 (UTC)

You will find lots of relevant studies by googling "optimal genetic code". A good start is this. Jmchutchinson (talk) 20:14, 15 December 2021 (UTC)

I'll go read that now, thank you. Sagittarian Milky Way (talk) 21:37, 15 December 2021 (UTC)

So it looks like the oddities could be naturally-selected features then. Sagittarian Milky Way (talk) 22:59, 15 December 2021 (UTC)

They're as well-designed as anything created by natural selection can be. --←Baseball Bugs ^{What's up, Doc?} carrots→ 21:23, 15 December 2021 (UTC)

Nasal test kit use for other conditions...

(Medical disclaimer acknoweleged)

Currently the UK use Lateral Flow tests in testing for a specfic pathogen related to the current pandemic.

Do any of the contributors on the Reference Desk, know if a simmilar rapid result test kit has been deploy in respect of screening for other conditions, (the obvious one prior to the current pandemic would be MRSA screening in Healthcare environments.)? Ideally citations to appropriate media or journal articles would be preferable. ShakespeareFan00 (talk) 13:47, 15 December 2021 (UTC)

For years prior to the current pandemic, I had had nasal swab tests done as a test for influenza. From my memory, the test worked exactly like the current Covid tests do. --Jayron32 18:58, 15 December 2021 (UTC)

It depends on where an infection is likely to be found. For respiratory infections, such as SARS-CoV-2, there is obviously a fairly good chance of finding shed viral particles in the nasal passages. For other infections, including MRSA, that may not be the case. Staph is already not uncommon to find in nasal passages of healthy people, it's more of a problem when it becomes a skin infection or even worse. So... a nasal swab test won't be as useful for MRSA. A UTI is hopefully not going to be found anywhere near the nose (though I do not judge people for their consensual fetishes). --OuroborosCobra (talk) 19:15, 15 December 2021 (UTC)

Atrioventricular Node Ablation (AV Node Ablation)

From Mayo Clinic:[1] "AV (atrioventricular) node ablation is a treatment for an abnormally fast and disorganized heartbeat called atrial fibrillation. It uses heat (radiofrequency) energy to destroy a small amount of tissue between the upper and lower chambers of your heart (AV node). If you have AV node ablation, you will need a permanent device implanted to control your heart rhythm (pacemaker)."

Related: Electrical conduction system of the heart

Before I ask my specific question, do we already have an article on this that I am not finding? Searching Wikipedia for atrioventricular nodal catheter ablation returns "Did you mean: atrioventricular nodal catheter abortion?" Why does Wikipedia have a "did you mean" link to a term that doesn't exist, has no article, and is never searched for?

I did find the related article Catheter ablation, but that article makes no mention of the concept of purposely destroying the cardiac pacemaker and replacing it with an artificial cardiac pacemaker. Could someone please create a stub article on Atrioventricular Node Ablation and a redirect from AV Node Ablation using the info[2] from Mayo?

OK, so here is my actual question: If their heart's natural pacemaker is completely replaced with an artificial pacemaker, I can see how that would result in a steady beat instead of however the old system was screwing up (Ventricular tachycardia, Arrhythmia, Fibrillation, Bradycardia etc.), but how does the pacemaker know to slow down the Cardiac output when resting and speed it up when exercising? Artificial cardiac pacemaker#Permanent transvenous pacing defines the term "Rate-responsive pacemaker" but the reference does not mention rate-responsiveness at all, much less giving details. 76.216.220.191 (talk) 14:27, 15 December 2021 (UTC)

To your first comment, the article Atrioventricular block#Management mentions pacemakers and has sources. I guess that would be the place to add anything on ablation and maybe then create redirect(s). I don't think that a new stub is needed. Mike Turnbull (talk) 16:35, 15 December 2021 (UTC)

Rate-responsive pacemakers mimic the normal, moment-to-moment changes in heart rate that would be provided by a normal heart rhythm. An activity sensor, which detects body movement increases your heart rate when you are more active. A breathing sensor, which measures your rate of breathing increases your heart rate when you breathe faster and are presumably more active. Philvoids (talk) 17:41, 15 December 2021 (UTC)

Thanks! Great answer. I wondered about whether it sensed movement. That would show jogging or swimming, but not bench pressing weights. The breathing detection would catch any exercise, even if it didn't make the torso move around. 76.216.220.191 (talk) 18:21, 15 December 2021 (UTC)

Flaps behind aircraft

Hello! So while looking at the aircraft carrier article, the shown image has some sort of flap behind the aircraft that are on the ship's "runway". I looked through the article to try and figure out what they were but it made no mention of anything that pops up behind aircraft preparing to take off. So does anyone know what they are and what their purpose is? I'm asking here since this is sort of an engineering question. ― Blaze The Wolf^Talk_{Blaze Wolf#6545} 18:03, 15 December 2021 (UTC)

Jet blast deflector. AndyTheGrump (talk) 18:07, 15 December 2021 (UTC)

Yes, see the second image in that article, which has the caption: "An airman services a jet blast deflector (JBD) before flight operations aboard an aircraft carrier". Martinevans123 (talk) 18:09, 15 December 2021 (UTC)

Thanks for the answer! I think it's rather interesting that the aircraft carrier article makes no mention of them, even though they are a part of aircraft carriers. ― Blaze The Wolf^Talk_{Blaze Wolf#6545} 18:16, 15 December 2021 (UTC)

You could fix that. :) --←Baseball Bugs ^{What's up, Doc?} carrots→ 19:41, 15 December 2021 (UTC)

Yep. I know. I just don't know where to put it.― Blaze The Wolf^Talk_{Blaze Wolf#6545} 20:02, 15 December 2021 (UTC)

They go behind the aircraft. 😀 Martinevans123 (talk) 21:32, 15 December 2021 (UTC)

Ho, ho, ho! I have added it to Aircraft carrier#Postwar era. Alansplodge (talk) 22:36, 15 December 2021 (UTC)

You beat me to it! Oh blast. Martinevans123 (talk) 23:16, 15 December 2021 (UTC)

Solar panel longevity in relation to experienced intensity of light

Are solar panels that are installed further from the equator and therefore receiving less solar radiation expected to last proportionally longer, all other factors being equal? — Preceding unsigned comment added by 88.111.0.124 (talk) 22:26, 15 December 2021 (UTC)

According to https://www.paradisesolarenergy.com/blog/solar-panel-degradation-and-the-lifespan-of-solar-panels (which lists https://www.nrel.gov/docs/fy12osti/51664.pdf as a source) the effects of wind and temperature play a larger role in degradation, after initial decrease in efficiency from UV exposure this slows compared to the others. So I expect the difference in longevity due to UV based on latitude alone would be small. Rmvandijk (talk) 07:53, 16 December 2021 (UTC)

"all other factors being equal". I'll take that literally. You've got cooling/heating on the panels so the thermal stresses are the same, you throw the same amount of water on each panel, and so on. (The point I'm making is that all other factors being equal is very hard to do). There is one failure mechanism I know of which is a function of total insolation, and that's migration of metal across the pn junction, which is likely to be a positive function of time*insolation power^2 at a guess, that is, a short period of bright sunlight will do much more damage than the same energy received over a longer period. Most other failure modes are related to corrosion or thermal cycling, so this rather long term effect is likely to be dwarfed by other failure modes. Greglocock (talk) 08:00, 16 December 2021 (UTC)