Wikipedia:Reference desk/Archives/Science/2022 January 17

= January 17 =

Sample and hold
From here: The original signal is retrievable from a sequence of samples, up to the Nyquist limit, by passing the sequence of samples through a type of low pass filter called a reconstruction filter.

What's the purpose of "retrieving the signal back" after sampling process? Is it referring to demodulation? Rizosome (talk) 00:36, 17 January 2022 (UTC)


 * For audio playback etc. Funny terminology. Greglocock (talk) 01:31, 17 January 2022 (UTC)
 * I've changed the wording in the article to "The original signal can be reconstructed from a sequence of samples, ...". --Lambiam 09:22, 17 January 2022 (UTC)

I got clear idea from this line: For audio playback. Rizosome (talk) 12:23, 18 January 2022 (UTC)

Transhumanism
Hello,

thank you to the volonteers

I'm stressed, may I know the informations about Vitrifixation, please ? 37.164.32.245 (talk) 04:36, 17 January 2022 (UTC)
 * What are you talking about? --←Baseball Bugs What's up, Doc? carrots→ 05:12, 17 January 2022 (UTC)
 * Paying a company a butt ton of money to glassify your corpse as fast as possible after death and store you in Arizona in the hope that you'll wake up in a 21-year old body that cannot age or at least get to relive the nursing home till some aspect of aging they can't cure kills you again. For a mini-butt ton of money they can freeze just your head but you have to hope the future can recapitate too. Sagittarian Milky Way (talk) 06:51, 17 January 2022 (UTC)


 * perhaps we need a way of flagging questions as "you can google weird shit/nonsense just as well as we can"Greglocock (talk) 09:06, 17 January 2022 (UTC)


 * Or you could even look up Vitrification in cryopreservation in Wikipedia.--Shantavira|feed me 09:29, 17 January 2022 (UTC)


 * Less weirdly, the OP might be asking about the method of embryo cryopreservation; see What is the vitrification technique?. But some clarification required. Alansplodge (talk) 13:28, 17 January 2022 (UTC)


 * The heading Transhumanism makes this is not about standard applications of cryopreservation techniques, but about an application to human brains – designated with the neologism vitrifixation – to preserve them until ways have been found to upload their information content to the cloud. Apart from the minor detail that the process involves killing the customers, there is no guarantee that it will actually preserve that content in a potentially interpretable way. There is not even a glimmer of light on the technicological horizon of a method that might hold a promise for retrieving the content, so the frozen brains may need to be kept in uninterrupted cold storage for centuries or millenia.  --Lambiam 20:56, 17 January 2022 (UTC)
 * I stand corrected, Alansplodge (talk) 22:46, 17 January 2022 (UTC)
 * Reminds me of that thing where they bleed a real corpse, add an equal volume of some transparent liquid, freeze it, immobilize it to a blue floor with foot glue and photoshopped-out vises or something and take thousands of pictures. First the nude guy seen from the top, then they polish his head a little, take a photo, shave a bit more and repeat the process till just a few pieces of foot skin are left. Then let the anatomy-curious public browse all the slices online. If the guy cared then the ice shavings that the vacuum cleaner or broom or whatever cleaned after each slice are carefully collected into a 70 kilogram pile so they can be melted and cremated. Sagittarian Milky Way (talk) 00:31, 18 January 2022 (UTC)

What percentage of wild budgerigar chicks are born blue and white?
The genetic mutation that causes a budgerigar to have blue and white plumage is a simple and common recessive gene that prevents production of yellow psittacofulvin pigments (blue + yellow = green), and as far as I'm aware, if you were to take some budgies from the wild and breed them in an aviary, it wouldn't take long before some of the chicks emerged with blue feathers, instead of green. The reason you don't see many of them in flocks of wild budgies being that a blue budgie is a more obvious target for predators than a green one, so they get picked off early, or the other budgies chase them from the flock because they realize that a blue bird in the flock draws negative attention to the flock.

Has there ever been a study into the prevalence of blue budgerigars, at hatching? I'd quite like to add that info somewhere... --Iloveparrots (talk) 18:32, 17 January 2022 (UTC)
 * I'll bet the answer is, we don't know. Doing such a thing in the wild is a great way to fail to get your PhD. See Polly Wants a Genome: The Lack of Genetic Testing for Pet Parrot Species. Also, there is a lot of info, with some links at the bottom, at Budgerigar colour genetics, which makes it pretty clear that the Dutch run this particular show. Your best bet is to ask some of them. Abductive  (reasoning) 10:54, 18 January 2022 (UTC)

Hot air
Since "hot air rises", how come the temperature at higher elevations are colder than at lower elevations? It probably has to do with less dense air, but doesn't that mean that more of the Sun's rays reach the surface? 2603:6081:1C00:1187:D94:75F0:870E:13A2 (talk) 20:19, 17 January 2022 (UTC)
 * Please, see lapse rate. Ruslik_ Zero 20:27, 17 January 2022 (UTC)
 * That article mostly explains how. As for why, the best that I could glean is that energy becomes dispersed as the air expands (becoming less dense).  Is that the gist, or am I missing something? 2603:6081:1C00:1187:D94:75F0:870E:13A2 (talk) 02:01, 18 January 2022 (UTC)
 * Hot air rises, but it's more accurate to say that air with a higher specific entropy rises. At the same pressure, higher specific entropy means higher temperature, but lower pressure also leads to higher specific entropy. As the air rises, the pressure drops, causing the air to expand adiabatically. The air does work in its surroundings (pushing air away), causing it to loose energy and cool down, but the specific entropy stays the same. This adiabatic cooling explains why the air higher up is colder, and as long as this cooling with altitude isn't faster than the cooling of a bubble of air rising, then rising air will not equalise the temperature. In other words, an atmosphere with the warm air at the bottom is stable as long as the air with higher specific entropy is at the top. PiusImpavidus (talk) 10:33, 18 January 2022 (UTC)


 * To add to the above, very excellent answers, the idea that "hot air rises" is broadly true, but that doesn't mean it stays hot as it rises. In a sufficiently small, relatively closed system, with a localized heat source, you will get convection currents as warm air rises and cool air sinks, and you can measure and track such movement of air, especially where such a system has a relatively uniform air pressure throughout.  In other words, it works fine when describing say, your house.  However, for any system as large and complex as the entire atmosphere of the earth, you aren't going to see such a temperature gradient.  The above descriptions of adiabatic cooling and specific entropy are very apt here.  -- Jayron 32 17:19, 18 January 2022 (UTC)