Wikipedia:Reference desk/Archives/Science/2021 October 29

= October 29 =

Afterglow lifetime change
Hi, I was looking for some references about afterglow lifetime. What may be the reasons that the lifetime of a sample changes from long to short, or short to long? For example, when the sample is synthesized, its lifetime is 1.0 s. After 2 hours, it's 1.5 s. After 8 hours, 1.4 s, and 16 hours, 1.3 s. Then it gradually stablizes at ~1.2 s. --Leiem (talk) 03:52, 29 October 2021 (UTC)
 * Which Afterglow (disambiguation) are you talking about? ←Baseball Bugs What's up, Doc? carrots→ 09:41, 29 October 2021 (UTC)
 * The reference to a synthesized sample strongly suggests a chemical substance, in which case "afterglow" is probably phosphoresence. Depending on the type of phosphoresence, the glow of persistent phosphoresence may last for hours after excitation, so the question is probably about short-lived triplet phosphorescence. I doubt the question allows for a uniform answer, but may depend on the nature of the synthesized material. Is it a polymer? Does the material have structure defects or impurities that can trap charges? Is there temperature dependence? If the temperature is not constant, this may already account for such variation. --Lambiam 13:02, 29 October 2021 (UTC)
 * Thank you for your reply. It is phosphoresence lifetime of a coordination polymer and the temperature is constant. --Leiem (talk) 14:15, 29 October 2021 (UTC)
 * I can't think of another reason than spontaneous changes in the crystallization structure, where molecules at the boundaries of regions may still switch their alliance before eventually stabilizing. If true, it should imply that charting afterglow lifetime versus real time gives graphs that are not correlated between different samples, and also that at a lower temperature reaching stabilization takes longer. --Lambiam 22:26, 30 October 2021 (UTC)

Sequenced inoculation
In Spanish flu, I find What is sequenced inoculation? The article Inoculation is concerned mainly with smallpox. From what I understand, it is infecting healthy people and hope for the best. In the case of smallpox, it uses viruses from mild cases and it is done on the arm so that it is less agressive.

How was it done in the 1918 flu? What does "sequenced" mean here? Thanks. --Error (talk) 11:54, 29 October 2021 (UTC)


 * This contains several good sources, such as this one that defines "sequenced inoculation" as the avirulent strain was applied 2h before the virulent one. This is contrasted with co-inoculation, in which the two strains are administered at the same time.  -- Jayron 32 12:09, 29 October 2021 (UTC)
 * Thanks. Those results are mostly about yeasts or symbiotic bacteria where the inoculates produce a desirable effect which can be synergized by sequenced inoculation or co-inoculation of different variants. Reading https://eu.usatoday.com/in-depth/news/nation/2020/11/21/covid-and-thanksgiving-how-we-celebrated-during-1918-flu-pandemic/6264231002/ and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2862332/ tells me that there were vaccines against influenza, but since virology was very primitive, they were actually against bacteria found in flu patients. They may have helped or not. So this "sequenced inoculation" was not about flu viruses, which was one of my puzzles. Still our article about inoculation is very centered on smallpox and says nothing of inoculating plants with bacteria or other uses. --Error (talk) 15:19, 29 October 2021 (UTC)
 * Influenza vaccine describes some success with the use of blood transfusions from recovered patients, presumably either the inactivated virus in their own blood or the antibodies themselves helped provide some vaccine-like protection to those so inoculated. -- Jayron 32 15:34, 29 October 2021 (UTC)


 * The 1918-19 Spanish Influenza Pandemic and Vaccine Development says:-
 * Certainly none of the vaccines described above prevented viral influenza infection – we know now that influenza is caused by a virus, and none of the vaccines protected against it. But were any of them protective against the bacterial infections that developed secondary to influenza? Vaccinologist Stanley A. Plotkin, MD, thinks they were not... the vaccine developers had little ability to identify, isolate, and produce all the potential disease-causing strains of bacteria circulating at the time.
 * Alansplodge (talk) 18:15, 29 October 2021 (UTC)

Reduction potential
1. What is the reduction potential of (HgCl4)2- in seawater? 2. What is the reduction potential of mercury in seawater? — Preceding unsigned comment added by Horus1927 (talk • contribs) 12:44, 29 October 2021 (UTC)

Sound in non-expanding universe
In a purely theoretical thought experiment, would it be correct to state that without the universe expansion, matter density would gradually rise to the point where it would conduct sound waves from cosmic processes (Sun's activity, supernova explosions, etc)? Can Friedmann equations handle this? 212.180.235.46 (talk) 15:17, 29 October 2021 (UTC)
 * So, in a steady state universe, density would not be increasing (by definition, the universe is at a steady state and not contracting or expanding). In that case, meaningful sound would not be possible.  In a contracting universe (perhaps caused by Gravitational collapse), ala the big crunch, then matter density would gradually increase, though whether anyone would be around to hear such a sound would make it moot, but presumably, at some point, such a universe would be able to maintain pressure waves one could define as sound; of course in the real universe, such a state did exist in the past, shortly after the Big Bang.  See, for example, this article, which discusses what such an early universe would have sounded like.  -- Jayron 32 17:32, 29 October 2021 (UTC)
 * The assertion "the density of matter in the expanding universe remains unchanged due to a continuous creation of matter" in the steady state universe looks self-contradictory to me. How can a continuous creation of matter not increase the density of matter? If cosmological processes, such as nucleosynthesis and supernova explosions, continuously produce more elements, why the average matter density would not increase? Thanks. 212.180.235.46 (talk) 21:24, 29 October 2021 (UTC)
 * Jayron's initial sentence above is incorrect. Hoyle's steady state universe was expanding (because the expansion had already been observed and shown to conform to Einsteinian theory), but (as Amble says below) new matter, supposedly in the form of individual hydrogen atoms) was being continually created in intergalactic space at a rate that maintained the Universe's overall density. It was the states of density and the overall homogeneity and space-time isotropism of the universe (see Perfect cosmological principle) that were "steady", not its space-time dimensions, which were presumed to be infinite. {The poster formerly known as 87.81.230.195} 90.200.65.29 (talk) 23:09, 29 October 2021 (UTC)
 * Nucleosynthesis, supernova explosions, etc. don't create new matter; they transform lighter elements (mostly hydrogen) into heavier ones. The steady state universe supposes there to be some additional, unknown mechanism for creating new matter out of nothing, so that space and matter grow together and keep the ratio constant. --Amble (talk) 21:43, 29 October 2021 (UTC)
 * Insert picture of Fred Hoyle frantically waving his hands. Clarityfiend (talk) 22:28, 29 October 2021 (UTC)

Calculating sidereal time
I'm trying to calculate sidereal time by following chapter 12 in Astronomical Algorithms by Jean Meeus.

He gives example 12.a, mean sidereal time at Greenwich on April 10, 1987, at 0H UT. He gives two equations (in seconds):


 * theta0 = 100.46061837 + 36000.770053608 * T + 0.000387933 * T2 - T3 / 38711000.0 (Eq. 12.3)
 * theta0 = 280.46061837 + 360.98564736629 * (JD - 2451545.0) + 0.000387933 * T2 - T3 / 38710000.0 (Eq. 12.4)

He uses equation 12.2 and gets (rounded to the second) theta0 = 6 hours 41 minutes 50 seconds - 1099864 seconds.

I don't see how he gets these figures or where the 1099864 seconds comes from.

Then he says to add multiples of 86400 seconds (the number of seconds in a day) to get it in range, but he adds 23335.8 seconds and gets 13 hours 10 minutes 46 seconds.

My JD (Julian Date) and T (time in centuries from 1/1/2000) agree with his exactly: JD = 2446895.5 T = -0.127296372347707

but I get:

theta0 = -4482.306804892 (22 hours 45 min 18 sec) (by 12.3) theta0 = -1678122.30680491 (13 Hr 51 Min 18 sec) (by 12.4)

These are both far different from what he gets, and I don't know why. Am I missing something? Bubba73 You talkin' to me? 23:04, 29 October 2021 (UTC)
 * Your theta0 values are correct -- but they are in degrees. Divide by 15 to get hours. --Amble (talk) 23:18, 29 October 2021 (UTC)
 * theta0 = (6 hours plus 41 minutes plus 50 seconds minus 1099864 seconds) = negative 12.something days, he added 13 days, not 23335.8 seconds. Sagittarian Milky Way (talk) 01:22, 30 October 2021 (UTC)


 * Thanks! All of these units in astrometry are driving me crazy!


 * Local time, universal time, sidearal time
 * most of the equations are in degrees, but they have to be converted to radians for the trig functions
 * Time is measured in seconds, hours, or centuries
 * angles are in degrees, hours, or radians. Bubba73 You talkin' to me? 02:16, 30 October 2021 (UTC)
 * I like to turn everything into Cartesian coordinates and work in matrix transformations. That way, you only ever need to handle the various spherical coordinate conventions on the way in and the way out. —Amble (talk) 03:16, 30 October 2021 (UTC)
 * I'm following the book by Meeus. That must have been how they did the calculations back in the day, even though the first edition was written in 1991.  Some early computers didn't have floating point.  Meeus has a lot of things in integers.  Then he says "divide these by 1,000 and these by 1,000,000.  Bubba73 You talkin' to me? 03:28, 30 October 2021 (UTC)
 * No floating point in 1991 is not surprising. Every time they say "x light years" or a planet orbit is x years they mean the Julius Caesar calendar. Sagittarian Milky Way (talk) 03:47, 30 October 2021 (UTC)
 * Even if some CPUs did not come with inbuilt floating point arithmetic, surely there were software libraries in 1991 implementing it. I find it hard to imagine a manufacturer marketing a CPU without a C compiler, in 1991 ANSI C. --Lambiam 12:28, 30 October 2021 (UTC)
 * The Sinclair Specrum (in 1982) had floating point capabilities and earlier computers certainly had, too. I recall using the Titan (1963 computer) in 1970, programmed in Fortran IV, and that language had had floating point for many years. Mike Turnbull (talk) 15:12, 30 October 2021 (UTC)
 * Did floating point have enough benefits for Jean Meeus to convert the book? Sagittarian Milky Way (talk) 15:51, 30 October 2021 (UTC)
 * In 1991 (or say the 1970s or 1980s when the recipes would have been written down) you could expect to have single precision floats. These recipes don’t just have the right offsets and coefficients, they also have the right precision in the right step. Trying to simplify it all with 32-but floats would get you simpler code and (usually) the wrong answer. —Amble (talk) 16:40, 30 October 2021 (UTC)
 * Intel 8087 (1980) implemented 64-bit (double-precision) float. DMacks (talk) 18:03, 30 October 2021 (UTC)
 * Local apparent solar time, local mean solar time, local civil time (AKA local mean solar time at the time zone's nominal longitude), Greenwich mean time (can be almost 1 second unaligned with Universal Time), Besselian New Year (10 degrees of Earth orbiting after the December solstice, not rounded, I don't know if this became obsolete with the switch from B1950.0 coordinates to J2000.0 (B for Besselian, J for Julian, even though it's New Year 2000 on the Gregorian calendar)), 2000.0 starts on January 1 noon but 1900.0 starts on January 0th noon ... Also 1 second of time is 15 seconds of arc, 4 seconds of time is 1 nautical mile (~6,080 feet) after multiplication by the cosine of the latitude, angle used to go signs (30 degrees), degrees, minutes, seconds, thirds and fourths, lunar months used to go 29 days (29), hours (12), and parts (793, 793 1080ths of an hour) and time used to go hours, minutes, seconds, thirds and fourths (AKA 5/18ths of a millisecond, imagine if high-tech astronomy said things like 54⁗ instead of 0.015"/15 milliarcseconds and camera shutter knobs were marked in thirds and fourths)... Sagittarian Milky Way (talk) 03:35, 30 October 2021 (UTC)


 * Well, I got my program to calculate the altitude and azimuth of the Moon working. But I could look that up - the reason for the program is to do reverse look-ups.  (1) Given several locations, when will the Moon be near a specified altitude and azimuth, (2) from a certain location, when will the Moon rise south of a given azimuth, and possibly (3) given an altitude and azimuth, when and where do you have to be.  Bubba73 You talkin' to me? 15:35, 3 November 2021 (UTC)
 * Sounds good! It might be interesting to add the phase of the moon to those search parameters. --Amble (talk) 16:09, 3 November 2021 (UTC)


 * The method to do that is in the book. I'll probably add it because one thing I'm interested in is days near the full moon.  Bubba73 You talkin' to me? 00:39, 4 November 2021 (UTC)


 * a little background (skip this if you aren't interested) When there was a supermoon in November 2016, I got a tight photograph of it shining through the glass of a lighthouse.  I was going to do a similar photo last month, but not as tight, and a day or two before the full moon to have more sunlight on the lighthouse.  I was near where I was in 2016, and I had freedom to move around to line things up.  But the Moon came up too far to the south!  There was nowhere I could get in order for the Moon and the top of the lighthouse to line up.  That's why I decided to write the program.  Bubba73 You talkin' to me? 03:21, 4 November 2021 (UTC)
 * @: This is because an October full moon rises like an April sun and a November full moon rises like a May sun: 180 degrees of ecliptic longitude out-of-phase. Your program will be more accurate than watching sunrise(s) c. 182.5 days in advance of course (I forsee an error of a few tenths of a degree if you don't make a short lookup table of refraction amounts at each altitude range and add them to the altitudes). These kinds of photos are progressively harder the nearer you are to the tropics cause very near the pole you can just watch the last 23 degrees of setting all week as it overflies every compass direction once per 25 hours and only an extremely rare cloud or breaking your leg or something could stop you (it's also always the first full moon of spring or maybe slightly beyond). At the equator it rises 1 Moon diameter in about 130 seconds with almost no sideways slant at all. Sagittarian Milky Way (talk) 20:54, 4 November 2021 (UTC)