Wikipedia:Reference desk/Archives/Science/2024 April 11

= April 11 =

Gender benders
Re this comment in an earlier discussion:

...As I understand it, Rishi agreed to ban, for example, mechanical restraints that prevent natural development and cripple young women, and hormone treatments that oppose it. That is because girls of this age are immature and in many cases young women who were crippled in this way later said that their lives had been ruined by what was done to them. So is Stonewall saying that Rishi agreed to the opposite of what he agreed to? 92.10.96.64 (talk) 11:07, 1 November 2023 (UTC)

Last night's Evening Standard carried this harrowing report:

The most high-profile case of "detransitioning" is that of Keira Bell, who began taking puberty blockers aged 16 before transitioning to a male. She later decided to reverse treatment, claiming she never should have been given the medication and that the Tavistock clinic should have challenged her more.

I'm no medical expert, so can someone explain what physical (as opposed to intellectual) aspects of adulthood have not been reached by age sixteen? The process begins at age seven. 92.28.114.98 (talk) 10:56, 11 April 2024 (UTC)


 * We have an article on Bell v Tavistock. According to this article, the complainant had a double mastectomy at the age of 20, which to me seems a mature age in terms of both physical and mental development, so this would hardly be a relevant case concerning gender-conforming care for children.
 * An intended effect of the most commonly used puberty blockers is diminished sex-specific physical characteristics, which should no longer be an issue at age sixteen. A potential risk for patients having a change of heart at a later age is compromised fertility; I have not investigated for which age class this may be an issue. --Lambiam 14:40, 11 April 2024 (UTC)

Luminosity of air plasma
Is there some empirical formula or theory that describes the expected (optical) luminosity of a plasma? Say depending on ionization rate and/or ion density. JoJo Eumerus mobile (main talk) 13:43, 11 April 2024 (UTC)


 * Are you asking about the black body radiation, atomic emission (or ionic, as it may be), or the combination of both? --OuroborosCobra (talk) 13:48, 11 April 2024 (UTC)
 * Both, really - I wonder less about the mechanisms and more about the quantities. JoJo Eumerus mobile (main talk) 15:41, 11 April 2024 (UTC)
 * You can't have the quantities without an understanding of the mechanisms. Our article on black body radiation does a good job explaining the necessary mathematics for that aspect. As for atomic emission, that is far less trivial (to the extent that black body radiation can be considered "trivial" to calculate to a given quantitative accuracy). As for atomic emission, that gets far more difficult. For a hydrogen-like atom, i.e. an atom with only one electron, this isn't terribly difficult to solve using the Schrödinger equation. However, once you start having more than one electron, you now have a many-body problem. We do not have exact solutions to the Schrödinger equation for many-body systems. These require approximation methods, such as the Hartree–Fock method, density functional theory, coupled cluster method, etc. That's not even getting into the issue of things like spin–orbit interaction, or relativistic effects that come into play once you start getting to large numbers of electrons around a single nucleus. If we go to molecules, then we may need to consider other effects and make other approximations, such as the Born–Oppenheimer approximation. So... it kind of matters what you are looking at and what you want out of it. --OuroborosCobra (talk) 19:23, 11 April 2024 (UTC)
 * The degree to which these issues are relevant depend on the composition of the plasma, density, temperature and the degree of ionisation. Even for astrophysical plasmas (that I am somewhat familiar with) the conditions vary quite a bit. As the intro to bremsstrahlung explains, the emission mechanisms can be classified into free-free, free-bound and bound-bound processes. A very hot plasma, such as the intracluster medium in clusters of galaxies, the free-free process of thermal bremsstrahlung dominates: an electron is scattered, i.e. accelerated, in the electric field of an ion and emits radiation. The resulting spectrum is a continuous spectrum, but not a black-body spectrum (electrons and ions are in thermodynamic equilibrium but the radiation is not). In cooler plasmas, free-bound radiation becomes more important; this is emitted when an ion captures an electron (this is called recombination) and again results in a continuous spectrum. The recombined electron often lands in an excited energy level of the resulting atom (or ion) and can then cascade to lower levels or the ground level. This then leads to bound-bound radiation, which happens in distinct emission lines (for example the reddish glow of an HII region around a hot star is from the Hα line of neutral hydrogen, following recombination of a proton (H+) with an electron). There are computer programmes that can compute the full spectral energy density for a specified plasma; I could dig out some formulas for the luminosity of a cluster of galaxies but I suspect that is not what you're actually after. --Wrongfilter (talk) 21:59, 11 April 2024 (UTC)
 * I am mostly looking at air plasma and gas-discharge lamp, not astrophysical things. The plasmas I am interested in have a low ionization fraction and low temperature, and I want to know how bright they would be to the naked eye (or not, if the luminosity is way too low) for a given energy input/ionization rate. I guess that recombination radiation is the most important component. Jo-Jo Eumerus (talk) 07:05, 12 April 2024 (UTC)