Wikipedia:Reference desk/Archives/Science/2022 January 25

= 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)
 * Our article on Bluetooth also says "". 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)
 * 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)


 * 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)

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

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)

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)
 * 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)
 * 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)
 * Here are a few links to research articles:, , , . 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. 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. SixNy coatings subjected to micro scratching have been reported to undergo adhesive failure with loads above 214 mN; I have no idea if that signals high durability. --Lambiam 21:44, 26 January 2022 (UTC)
 * Thank you so much!! 84.228.239.26 (talk) 13:49, 28 January 2022 (UTC)

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)


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


 * 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)

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)


 * 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)
 * ...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 )
 * , 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)