Wikipedia:Reference desk/Archives/Science/2021 October 30

= October 30 =

Analog to digital conversion process
I didn't understand the portion: Sampling in Analog to digital conversion process.

I read this sentence from here: To sample the input signal the switch connects the capacitor to the output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across the capacitor is practically equal, or proportional to, input voltage. In hold mode the switch disconnects the capacitor from the buffer. The capacitor is invariably discharged by its own leakage currents and useful load currents, which makes the circuit inherently volatile, but the loss of voltage (voltage drop) within a specified hold time remains within an acceptable error margin for all but the most demanding applications.

It mentioned "input signal" clearly, but it didn't mention term output signal anywhere in the paraphrase. It didn't even mention output signal is binary type. So how binary type here achieved ? Rizosome (talk) 04:36, 30 October 2021 (UTC)
 * The description you give is just for sampling. A sample of the input voltage appears on the capacitor. This then allows measurement of a constant value, rather than the time varying input. You could say that the output is the voltage of the capacitor. To convert to binary, you need the analog to digital converter. (perhaps you can compare the capacitor voltage, to a voltage ramp, and measure the time it is equal. ) Graeme Bartlett (talk) 11:15, 30 October 2021 (UTC)
 * To be more explicit, the process of transforming an analog input signal to a digital output signal is best understood as a two-step process. The amplitude of the input signal is a continuous function of continuous time to a continuous range of values. In the output signal, both the time domain and the range are discrete. Sampling only makes the time discrete and leaves the range continuous. Using R for a continuum and Z for a discretum, and "→" as is usual for the direction of a mapping from domain to range, we have:
 * input signal:    R → R
 * sample:           Z → R
 * output signal:  &thinsp;Z → Z
 * Our article Sample and hold describes only the first step. --Lambiam 11:47, 30 October 2021 (UTC)

Can non lipid ointments diffuse into the skin?
Can non lipid ointments diffuse into the skin?

Maybe there is an article about such non lipid ointments/creams/lotions/Colloids?

Thanks, 182.232.129.86 (talk) 05:54, 30 October 2021 (UTC)


 * Calling a substance an ointment suggests that its main ingredient is a lipid. Glycolic acid is used in skin-care products for its capability to penetrate skin. A non-lipid solvent that is known for its ability to penetrate the skin without damaging it is dimethyl sulfoxide (DMSO), which can be used for topical delivery of solutes. Its use has several hazards, some of which can be serious; see the section . Our article Absorption (skin) does not discuss any specific substances other than DMSO, and I did not find an article with a more general treatment of non-damaging skin penetrating substances. --Lambiam 11:23, 30 October 2021 (UTC)
 * Very many substances are toxic by skin absorption and this reference for acetonitrile is typical. Hence most lab chemists handling solvents wear appropriate gloves of nitrile rubber or other similar material. The OP's term "ointment" is, as said, normally reserved for things that are intended to be rubbed on the skin, not necessarily to penetrate it, otherwise described as topical applications. Mike Turnbull (talk) 12:12, 30 October 2021 (UTC)

Drag on Satellites
To quote from an article in "New Scientist" ; "...a warming planet might ..reduce.. the drag on satellites, keeping them in orbit for longer." This seems to imply that as the atmosphere warms it causes less drag on orbiting satellites. I can't understand how this could be. Wouldn't the upper atmosphere reach further into space if it warmed up and expanded? And wouldn't this cause MORE drag on satellites in low earth orbit, bringing them down sooner? Any references or comments on this would be much appreciated!! 49.197.130.6 (talk) 07:01, 30 October 2021 (UTC)
 * A warmer atmosphere would presumably become less dense (unless additional atmospheric gases were released from the lithosphere and/or hydrosphere), and atmospheric material that expanded higher than the orbit in question would no longer exert a net gravitational attraction on a satellite in it; perhaps these would more than offset increased drag in some circumstances.
 * Can you cite the issue and/or date and page? I subscribe to New Scientist (in paper form) and would like to study the full passage in context. {The poster formerly known as 87.81.230.195} 90.200.65.29 (talk) 07:16, 30 October 2021 (UTC)

(OP) it's in the leader of the latest edition, 30 october 2021 49.197.130.6 (talk) 07:31, 30 October 2021 (UTC)
 * I'm having trouble finding the article (I only have an database subscription, can't easily browse a whole issue). But is an explanation of an anomalous cooling in the upper atmosphere as a result of CO2 released at lower levels. The cooling causes contraction: pulling the atmosphere "down" a bit leaves it less dense (==less drag) up where the satellites are. DMacks (talk) 07:48, 30 October 2021 (UTC)
 * Ah, right! The New Scientist leader points to a Features article on pp 42-46, 'Space Jam' by Robin George Andrews, which I hadn't yet reached (my copy arrives no earlier than Friday).
 * The relevant passage (p 44) reads:
 * "One saving grace so far has been that space junk often gets dragged into the lower atmosphere and burns up. Unfortunately, as we have recently discovered, climate change means the rate at which this happens may decline, making orbital overcrowding worse.
 * In the upper atmosphere, the sun's extreme ultraviolet radiation splits molecular oxygen into two oxygen atoms that collide with carbon dioxide molecules, releasing infrared energy. Adding more carbon dioxide to the upper atmosphere increases this effect. As more infrared energy is released, it escapes into space and so the upper atmosphere cools. In this more frigid environment, the particles lose energy and the upper atmosphere contracts.
 * This phenomenon was predicted in 1989, and has been observed for some time. But [Hugh Lewis, a space debris expert at The University of Southampton, UK] and his colleagues recently realised it is influencing the lifetime of space junk. When falling orbital debris meets atmospheric particles, the object experiences drag. This causes the size of its orbit to shrink, bringing it closer to the denser, lower atmosphere in which it will eventually be incinerated. The climate change-induced contraction of the upper atmosphere will reduce the drag that debris experiences as it spirals towards us. This means it will stay in orbit for longer.
 * A recent paper, co-authored by Lewis, found that objects in low Earth orbit will stay up there for 30% longer even if we restrict carbon dioxide emissions to successfully keep the global average temperature rise to 1.5°C this century."
 * Hope this is useful. {The poster formerly known as 87.81.230.195} 90.200.65.29 (talk) 12:17, 30 October 2021 (UTC)
 * You compare Earth with Venus, which has CO2 atmosphere. Whereas Earth has a hot thermosphere with the temperature in excess of 1000K, at Venus the thermosphere is rather cool at 300-400 K during day and at about 100K at night. As a result the atmosphere of Venus is rather compact. Ruslik_ Zero 20:18, 30 October 2021 (UTC)

Grinding plant-parts with oils
If we want to use certain natural products available in plants, a good way to do that is to grind relevant plant-parts (flowers/fruits/roots/seeds, etc.), often after drying them, with some oil.

Are some oils better at capturing the natural product out of the plant-part better than others?

For example, should "saturated" oils be better than "non saturated" oils and alike?

The purpose of the question is to understand if some oils are better than other for creating cosmetics grade / food grade essential oil products by means of fragrance/flavor/nutritional content.

Thanks, 182.232.129.86 (talk) 09:24, 30 October 2021 (UTC)


 * It is hard to discuss in generality – what is the nature of the "natural products available in plants" you want to "capture", and what is the purpose to which they will be put after extraction? The process of extraction by immersion in a liquid is known by the more technical name "maceration". If you want to extract essential oils, used for example in aromatherapy, this article on how essential oils are made contains a detailed description of extraction by maceration, but mentions, generically, using carrier oils as solvent. The absence of a discussion of which oils to use as carrier suggests that it does not make a big difference. This article states that commonly used solvents are olive oil and sunflower oil. Another carrier oil, advocated if the product is to be rubbed in the skin, is jojoba oil.  --Lambiam 10:54, 30 October 2021 (UTC)
 * For interest, Shea butter is also used as an ointment base, as well as on its own. {The poster formerly known as 87.81.230.195} 90.200.65.29 (talk) 12:30, 30 October 2021 (UTC)
 * It is likely that vegetable oils are selected on the basis of their having little to no odor of their own, and not being too quick to go rancid. The color of the oil may also be important. Abductive  (reasoning) 01:27, 31 October 2021 (UTC)


 * This recipe for chili oil says "High temperature oil can simulate the strong aroma while lower temperature oil brings us the bright red color". Alansplodge (talk) 12:51, 1 November 2021 (UTC)