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December 10

Maxwell's third and fourth equations

Using Formulation in SI units convention and ignoring the conventional current term of Ampere-Maxwell equation (focusing solely on the displacement current term), we have: ${\begin{aligned}\oint _{\partial \Sigma }&\mathbf {B} \cdot \mathrm {d} {\boldsymbol {\ell }}==\mu _{0}\varepsilon _{0}{\frac {\mathrm {d} }{\mathrm {d} t}}\iint _{\Sigma }\mathbf {E} \cdot \mathrm {d} \mathbf {S} \\\end{aligned}}$

So my question is: why is the Maxwell-Faraday equation in the following form: $\oint _{\partial \Sigma }\mathbf {E} \cdot \mathrm {d} {\boldsymbol {\ell }}=-{\frac {\mathrm {d} }{\mathrm {d} t}}\iint _{\Sigma }\mathbf {B} \cdot \mathrm {d} \mathbf {S}$ and not in the following form: $\oint _{\partial \Sigma }\mathbf {E} \cdot \mathrm {d} {\boldsymbol {\ell }}=-\mu _{0}\varepsilon _{0}{\frac {\mathrm {d} }{\mathrm {d} t}}\iint _{\Sigma }\mathbf {B} \cdot \mathrm {d} \mathbf {S}$ ?

Many thanks, 173.209.130.10 (talk) 21:29, 10 December 2022 (UTC)

The units wouldn't match. The SI unit of the electric field is $[E]=1\,\mathrm {\frac {N}{As}}$, of the magnetic field $[B]=1\,\mathrm {\frac {N}{Am}}$. With that the unit of the left hand side is $\mathrm {{\frac {N}{As}}\cdot m} =\mathrm {\frac {Nm}{As}}$, of the right hand side it is $\mathrm {{\frac {1}{s}}{\frac {N}{Am}}\cdot m^{2}} =\mathrm {\frac {Nm}{As}}$, i.e. the same, as it must be. The factor $\varepsilon _{0}\mu _{0}=1/c^{2}$ with unit $\mathrm {\frac {s^{2}}{m^{2}}}$, and if you insert that as you propose, you mess up the units of the right hand side. --Wrongfilter (talk) 21:47, 10 December 2022 (UTC)

Using natural units in which $c=1,$ the identities take on a more symmetric appearance.  --Lambiam 05:13, 11 December 2022 (UTC)

December 11

When a high-speed alpha particle hits a gold nucleus, does the gold nucleus remain stationary?

In the Geiger-Marsden experiments, the alpha particle can receive the entire changes of momentum if the gold nucleus remains stationary.

$\Delta p=F\Delta t=k\cdot {\frac {Q_{\alpha }Q_{n}}{r^{2}}}\cdot {\frac {2r}{v_{\alpha }}}$

Otherwise, the KE gained by the gold nucleus must equal the KE lost by the alpha particle. Vze2wgsm1 (talk) 12:29, 11 December 2022 (UTC)

It's not at all clear what your question is. The equation you've posted IS the change of momentum in the alpha particle under a classical mechanical description of the collision as an elastic one between two spheres. There is ALSO a change in momentum of the gold atom, and a corresponding change in kinetic energy of each. And yes, as long as you consider this an elastic collision, then kinetic energy is conserved. PianoDan (talk) 18:03, 11 December 2022 (UTC)

Rutherford's gold foil experiment, performed by Geiger-Marsden, is the basis of believing an atom has a nucleus. Rutherford used the above equation to claim that an alpha particle collision with a gold nucleus can reverse the alpha particle's momentum. In other words, Rutherford may have made a false assumption. The alpha particle's deflection by more than 90 degrees may have been via collision with a multi-atom molecule, instead of a collision with the nucleus of a single gold molecule. Vze2wgsm1 (talk) 22:46, 11 December 2022 (UTC)

Gold molecules? Au₃O₄? Given a model for the atom, one can compute the predicted distribution of the angles of deflection of the emerging alpha particles. This is not about the occasional stray particle, but about substantial numbers. If the observations differ too strongly from the theoretical model, and experimental or calculation errors can be ruled out, the model was wrong.  --Lambiam 01:46, 12 December 2022 (UTC)

The calculation predicting the angles of deflection assume that gold nucleus (q_n) remains stationary while the alpha particle approaches and leaves the gold nucleus.

$s={\frac {Xnt\csc ^{4}{\!\left({\tfrac {\phi }{2}}\right)}}{16r^{2}}}\cdot {\left({\frac {2Q_{n}Q_{\alpha }}{mv^{2}}}\right)}^{2}$

Acceleration of q_n removes KE from the alpha particle and changes the angle of deflection Vze2wgsm1 (talk) 02:47, 12 December 2022 (UTC)

I don't get what you are trying to argue, other than that you seem to think Rutherford and his team (and the many teams who replicated the experiment) were stupid and overlooked something big, like the presence of Blue Meanies imparting motion to the gold nuclei.  --Lambiam 05:18, 12 December 2022 (UTC)

If you think that Rutherford's calculations of alpha particle deflection do not assume a stationary gold nucleus, then either mathematically prove your point, or show how a gold nucleus can indeed remain stationary while a high-speed alpha particle approaches. I wish you luck. Vze2wgsm1 (talk) 09:54, 12 December 2022 (UTC)

It's called an approximation, and it's made because a gold nucleus is about 50 times as massive as an alpha particle. Do you think that approximation is unjustified and therefore everything we know about atoms and nuclei is wrong? Because nobody's done any more experiments since Geiger-Marsden? Or done any more sophisticated analysis of scattering experiments than Rutherford in the last hundred years? --Wrongfilter (talk) 10:17, 12 December 2022 (UTC)

Thanks PianoDan. I appreciate your comment on the equation. Another equation from the Geiger-Marsden experiments article indicates the alpha particle receives the entire change of momentum when an alpha particle approaches a gold nucleus. When a high-speed alpha particle hits a gold nucleus, does the gold nucleus remain stationary?

$::\theta \approx {\frac {\Delta p}{p}}<k\cdot {\frac {2Q_{\alpha }Q_{n}}{m_{\alpha }rv_{\alpha }^{2}}}::$ Vze2wgsm1 (talk) 11:39, 12 December 2022 (UTC)

It remains stationary enough. Remember a couple of things about the transfer of momentum of the alpha particle to the gold atoms in the experiment 1) the alpha particle is 1/50 the size of the gold nucleus, so that needs to be taken into account. But MOST IMPORTANTLY, 2) the gold atoms are bound up in a solid crystal lattice. Yes, if the gold atoms were in the gas phase, we would expect a transfer of kinetic energy on something like a one-to-one relationship. However, the gold atoms are bound up with each other in a solid matrix. What that means effectively is that the transfer of energy is distributed across the entire sheet of gold foil rather than to 1 gold atom. A single alpha particle, even a really fast moving alpha particle, transferring some of its momentum to trillions upon trillions of gold atoms has essentially no effect on the gold. We can treat the gold atoms as stationary, because they essentially are; any displacement of the gold nucleus by interaction with an alpha particle is so many orders of magnitude smaller than the size of the nucleus itself, it is functionally nil. --Jayron32 12:56, 12 December 2022 (UTC)

I'm not so sure about the lattice argument. Atoms in a crystal do oscillate about their mean positions, and a collision will excite crystal vibrations (phonons on a quantum level). The transferred energy will ultimately dissipate away, and the momentum transfer to the entire gold foil is obviously negligible, but that does not make it necessarily so in the individual scattering process, which is what is relevant here. I'm not well versed in crystal and solid state physics, but my gut feeling suggests that it ought to be more appropriate to treat the gold nuclei as free particles rather than being fixed in a crystal lattice (actually, do nuclei know that they live in a crystal?). Which brings us back to the mass ratio of 50 that again makes a stationary gold nucleus a good approximation. --Wrongfilter (talk) 14:57, 12 December 2022 (UTC)

Yes, but the important thing is it will not excite one single atom alone; such excitations are dispersed through the lattice of gold atoms. The OP sounds like their major objection is that the fact that when interacting with the alpha particle, the singular gold atom would experience some kind of measurable displacement in order to itself redirect the alpha particle; the fact that the specific gold atom does not itself appreciably change momentum means that something is wrong with Rutherford's theory. I was explaining why that was at fault; the momentum transferred to any one gold atom is dissipated through the system via the chemical bonds between gold atoms; yes that dissipation does all sorts of complex things to the lattice of gold atoms; but that's irrelevant. The OP's statement "Rutherford used the above equation to claim that an alpha particle collision with a gold nucleus can reverse the alpha particle's momentum" is based on some sort of model of the gold nucleus as a gas particle of some sort, the assumption the OP makes is that Rutherford's model presupposes the gold nucleus absorbs the alpha particle's momentum without itself doing anything with that momentum, violating the law of conservation of momentum. This assumption on the part of the OP seems to be that the interacting gold nucleus is not dissipating the absorbed momentum through the lattice (in all the ways I glossed over but that you describe). That's what they are not understanding here. That's why the gold nucleus remains stationary; or at least can be treated like it remains stationary, even if at levels below the level of measurement, it probably does shimmy a little bit.--Jayron32 15:23, 12 December 2022 (UTC)

I still disagree: the dissipation happens on a time scale that is longer than the time scale that is relevant for the individual scattering process. Staying classical (and we'd need to get quantitative to see whether that is justified), in my view the nucleus ought to be treated as a free particle which does absorb a bit of momentum (not enough to significantly alter Rutherford's conclusions, mind!). This is then transferred to the electron shell of the atom and then to the lattice as a whole. But when this happens the alpha particle is already on its way and is not affected any more. For the time scales I'd look at the speed of the alpha particle vs. the sound speed in the crystal. --Wrongfilter (talk) 15:35, 12 December 2022 (UTC)

That's fair. I concede. Still, it is perplexing that, for the second time in as many weeks, the OP thinks that with almost no in-depth reading of the physics involved in the Rutherford/GM experiment and its conclusions, they're somehow going to play "gotcha" and take down over 100 years of atomic theory so simply. --Jayron32 16:12, 12 December 2022 (UTC)

I'll also point out that if atoms don't have nuclei, then I'm out of a job, since I work in nuclear medicine, and my entire livelihood is based on confirming every single day that our understanding of the nucleus is more or less correct. :) PianoDan (talk) 15:31, 12 December 2022 (UTC)

How do you define nucleus and what is your best evidence that an atom has a nucleus? If you define nucleus as the thing that is left over after all electrons are stripped away from an atom, then I agree with you. The thing that is left over can have volume and chemical reactivity of an atom or molecule.

If you define nucleus as a small structure within an atom, then I wonder how adding a single electron to a stripped nucleus can convert the stripped 'nucleus' into a small structure within an atom? Vze2wgsm1 (talk) 13:27, 13 December 2022 (UTC)

Thanks Jayron32. The gold can ionize, which is an inelastic collision. Typical of high-speed alpha particle collisions. Vze2wgsm1 (talk) 21:56, 12 December 2022 (UTC)

Thanks Jayron32. When an alpha heads toward a stationary gold, and if both the gold and the alpha are free, then during every instant, and at every distance between them, the repulsive force between the alpha and the gold is EQUAL and mutual.

$m_{1}a_{1}=m_{2}a_{2}$

The mutual force causes the KE lost by the alpha to equal the KE gained by the gold, regardless of the difference in mass. The alpha simply loses KE. Vze2wgsm1 (talk) 20:42, 12 December 2022 (UTC)

That is simply Newton's third law of motion. PianoDan (talk) 21:20, 12 December 2022 (UTC)

The point is that a high-speed alpha will not reverse direction when the alpha approaches a free gold nucleus, regardless of the difference between alpha mass and gold mass. Rutherford had to assume a stationary gold, to get Newton's third to reverse the direction of the alpha. Vze2wgsm1 (talk) 05:38, 13 December 2022 (UTC)

Yes, it will reverse direction. Let's look at the one-dimensional problem, central collision of point particles, forward or backward scattering only. We need to satisfy conservation of momentum and of energy, and we write the energies and momenta before and after the collision at infinite separation (large enough that the Coulomb energy is negligible). First, momentum:

$m_{\alpha }v_{i}=m_{g}v_{g}+m_{\alpha }v_{f}$, i.e. $v_{g}=r(v_{i}-v_{f})$,

where I've defined the mass ratio $r=m_{\alpha }/m_{g}\approx 1/50$. Now for energy (the factors 1/2 cancel, and I won't bother to write them out):

$m_{\alpha }v_{i}^{2}=m_{g}v_{g}^{2}+m_{\alpha }v_{f}^{2}$.

Inserting $v_{g}$ and rearranging gives the quadratic equation

$(r+1)v_{f}^{2}-2rv_{i}v_{f}+(r-1)v_{i}^{2}=0$.

This has two solutions. The first is $v_{f}=v_{i}$ and $v_{g}=0$, which corresponds to no collision, this is uninteresting. The second solution is

$v_{f}={\frac {r-1}{r+1}}v_{i}$, hence $v_{g}={\frac {2r}{r+1}}v_{i}$.

With $r\approx 1/50$, the velocity $v_{f}$ of the alpha particle is negative, i.e. reversed. The velocity of the gold nucleus is $v_{g}\approx 0.039v_{i}$, so it does pick up a bit of velocity, which is of course reflected in the fact that the speed of the alpha particle is a bit lower than initally, $|v_{f}|<|v_{i}|$, but clearly in the opposite direction. This is very basic physics. --Wrongfilter (talk) 11:31, 13 December 2022 (UTC)

@Wrongfilter's analysis is correct. And if you want to just visualize it - if you put a bowling ball on an ice covered pool table and hit the cue ball towards it, would you REALLY be surprised if the cue ball came back towards you? Because that is more or less exactly what is happening here. And yes, the bowling ball DOES move a bit away from you in that case. PianoDan (talk) 17:14, 13 December 2022 (UTC)

Thanks Wrongfilter.

1. KE is conserved, due to conservation of energy. Momentum is not necessarily conserved.

2. If gold is free and initially stationary, then the KE lost by the alpha will equal the KE gained by the gold, regardless of the difference in mass. If alpha KE somehow became zero (before reversing direction), then the gold would contain total KE. Afterwards, adding KE to the alpha requires removing KE from the gold.

3. If gold remains stationary, then when the alpha particle slows to zero (before accelerating in the opposite direction) total KE equals zero. Vze2wgsm1 (talk) 22:11, 13 December 2022 (UTC)

Momentum is, in fact, necessarily conserved. TOTAL energy is also conserved. If this were an elastic collision between two solid spheres, then kinetic energy would also be conserved at all times, yes. In that (simplified) model, you would have an instantaneous transfer of (some) energy from the alpha particle to the gold nucleus at the moment of collision, and an instantaneous change of direction.

Worth pointing out, however, that in the nuclear case, there is also POTENTIAL energy to be considered, in the form of the Electric potential energy between the positively charged alpha particle and nucleus, which stores energy as the two particles approach, and returns it to the two particles as they separate. PianoDan (talk) 23:01, 13 December 2022 (UTC)

Thanks PianoDan.

1. Conservation of momentum requires an environment not acted on by external force. The electrostatic force between the alpha and the gold is an external force.

2. Nobody assumed collisions or other instantaneous changes of direction. Electrostatic repulsions are not necessarily collisions.

"If this were an elastic collision between two solid spheres, then kinetic energy would also be conserved at all times, yes. In that (simplified) model, you would have an instantaneous transfer of (some) energy from the alpha particle to the gold nucleus at the moment of collision, and an instantaneous change of direction."

3. You do realize that Rutherford's calculations are based on the electric potential energy between an alpha particle and a gold nucleus.

"there is also POTENTIAL energy to be considered, in the form of the Electric potential energy"

Vze2wgsm1 (talk) 01:17, 14 December 2022 (UTC)

The electrostatic force between alpha and gold is an internal force in the system that we consider here. External forces might come from the gold lattice, for instance, but we've discussed at length why those forces can be neglected here. You might worry, incidentally, about alpha particles that excite gold atoms. In this case, kinetic energy would be lost to internal degrees of freedom and that would have to taken into account. But: these inelastically scattered particles are not measured in the Geiger-Marsden experiment, only the elastically scattered ones are. I also explained why potential energy did not appear in the energy equation that I used. There is no need to consider the dynamic details of the scattering process (aka collisions), we only need to look at the initial and final states. --Wrongfilter (talk) 06:18, 14 December 2022 (UTC)

Thanks Wrongfilter. Forces like gravity and electrostatic are both external and internal. When force causes acceleration, then KE and momentum change. Momentum = mass x velocity. Vze2wgsm1 (talk) 11:08, 14 December 2022 (UTC)

So what? --Wrongfilter (talk) 11:16, 14 December 2022 (UTC)

PianoDan's assumption of conservation of momentum conflicts with acceleration due to electrostatic force.

$m_{\alpha }v_{i}^{2}=m_{g}v_{g}^{2}+m_{\alpha }v_{f}^{2}$

Are you claiming that alpha particle deflection is indeed governed by conservation of momentum? Vze2wgsm1 (talk) 11:40, 14 December 2022 (UTC)

Yes, of course it is. And if you think it isn't then any further discussion is useless. --Wrongfilter (talk) 12:08, 14 December 2022 (UTC)

I accidently put PianoDan's KE equation instead of his momentum equation in my previous post. I should have used the following equation to show that PianoDan indeed assumed conservation of momentum:

$m_{\alpha }v_{i}=m_{g}v_{g}+m_{\alpha }v_{f}$, i.e. $v_{g}=r(v_{i}-v_{f})$

An example that shows momentum is not conserved is:

When the alpha has high velocity, the alpha has high momentum and gold has zero momentum and remains stationary. When the alpha stops while reversing direction, the alpha will have zero momentum and the gold will have zero momentum. Total momentum was initially high, and then became zero.

Note: If you cannot defend your conservation of momentum idea, then my next step is alteration of the Geiger–Marsden experiments article to highlight Rutherford's assumption of zero gold velocity. Vze2wgsm1 (talk) 12:52, 14 December 2022 (UTC)

I wrote down that equation, not PianoDan. And your example is utterly wrong. Any momentum lost by the alpha particle is taken up by the gold nucleus, so that total momentum is conserved. Do not edit the article, any changes you make will be reverted. --Wrongfilter (talk) 13:06, 14 December 2022 (UTC)

Ok, what can I say and what can't I say? Vze2wgsm1 (talk) 13:21, 14 December 2022 (UTC)

If you wish, I can use the talk page. I request participation from uninvolved, interested editors. Vze2wgsm1 (talk) 13:28, 14 December 2022 (UTC)

Your comment: "Any momentum lost by the alpha particle is taken up by the gold nucleus" conflicts with the stated condition that gold nucleus remains stationary. Please explain.

Does your comment: "Do not edit the article, any changes you make will be reverted" indicate that Wikipedia found justification to ban me from making any comments on article? What was the justification? Vze2wgsm1 (talk) 14:17, 14 December 2022 (UTC)

The gold nucleus gains momentum in the same way that a brick wall takes up momentum when you hit it with your fist. Conservation of momentum is not negotiable. However, as has been said before, the resulting speed of the nucleus is small because of its high mass. As an approximation it is therefore justified to neglect that speed and to assume that the nucleus remains stationary. As regards the article: you can of course put in anything that is properly sourced with reliable external references, anything else not. --Wrongfilter (talk) 14:29, 14 December 2022 (UTC)

Any movement of the brick wall conflicts with the (absolutely) stationary gold criteria. If the gold remains stationary, then the KE of the alpha converts entirely into electrostatic potential energy by the time the alpha becomes stationary. Otherwise, the alpha KE would be divided between gold KE and electrostatic potential energy.

I will make sure that any edit I make to a Wikipedia article contains the proper references. Vze2wgsm1 (talk) 15:16, 14 December 2022 (UTC)

You keep missing the point, so I'll try to restate it, as others have, yet again. There is a difference between "doesn't move enough to factor into our calculations, so we'll treat it like it is stationary" and "really-for-real-honest-to-God-didn't-move stationary". As everyone here keeps telling you, when we (and everyone else except you) are saying "stationary", we're referring to the first situation, NOT the second. You keep hearing us tell you the first, and keep arguing against the second, which no one except you is claiming. Yes, the gold nucleus absorbs some of the momentum of the alpha particle. However, it does not absorb enough to make a difference, so we treat it like it's stationary. The mosquito that slams into my car windshield while I am driving down the road also imparts a momentum on my car, but I'd be stupid to spend any effort calculating how much it altered my car's speed. --Jayron32 16:01, 14 December 2022 (UTC)

To provide evidence that a gold nucleus can act like a free particle, I present the following video. The video contains the math for deflection of an alpha particle and a FREE gold nucleus.

https://www.youtube.com/watch?v=5V_1oVbrWLs

Note: I do not claim that deflection from electrostatic repulsion is the same as deflection via a collision. Vze2wgsm1 (talk) 19:47, 14 December 2022 (UTC)

That video does indeed contain the math for the interaction between a free nucleus and an alpha particle, because that is a simple problem to solve, and the video is a solution to a problem in a first year college physics textbook. It is not evidence that a gold nucleus can act like a free particle, because that is taken as a starting assumption of the problem. PianoDan (talk) 23:36, 14 December 2022 (UTC)

Also, since PianoDan has made the point that a contrived problem for the purpose of demonstrating how to do a calculation is not a statement on how the physics of the Rutherford gold foil experiment actually worked, I will just note that "deflection from electrostatic repulsion is the same as deflection via a collision" is a nonsensical statement. Collisions are electrostatic repulsions; whether we're talking two balls rolling on a billiards table and colliding (where the force of the collision is mediated by the electrostatic repulsion of the electron clouds of the atoms at the surface of each ball) or where we're talking about the collisions of fundamental particles, where the collision is described by Quantum electrodynamics and things like Feynman diagrams and Path integral formulation and the like. --Jayron32 13:48, 16 December 2022 (UTC)

If I drop a heavy and a light ball from the leaning tower of Pisa, both hit the ground at the same time, with the heavy ball gaining the most KE.

The force on the alpha and the gold is mutual and the total time the force is applied is the same. Vze2wgsm1 (talk) 13:35, 16 December 2022 (UTC)

The video got it right. because both the gold and the alpha got equal KE. The answer to my question was that gold indeed acquires KE equal to alpha. The Geiger-Marsden experiments article contained calculations that use force at a particular distance for an increment of time to calculate change of momentum. The change of alpha momentum could be a function of if the gold gained KE or not.

The leaning tower of Pisa is another complication of how forces act. Equal gravitational force acting on particles with different masses can continuously give more KE to the heavier mass. Equal electrostatic force between particles with different masses can continuously add equal KE to both particles. Vze2wgsm1 (talk) 15:13, 16 December 2022 (UTC)

Correction: Some say electrostatic force causes equal KE, others say equal momentum. Not picking sides. The alpha particle's change of momentum is a function of the gold's change of velocity.

$\Delta p=F\Delta t=k\cdot {\frac {Q_{\alpha }Q_{n}}{r^{2}}}\cdot {\frac {2r}{v_{\alpha }}}$

Vze2wgsm1 (talk) 15:53, 16 December 2022 (UTC)

I have no idea what you are talking about with "some say". There are no sides here - there's just physics.

Momentum is conserved. The total momentum of the system is the same before and after the collision.

Kinetic energy is conserved. The total kinetic energy of the system is the same before and after the collision.

The statement "Equal gravitational force acting on particles with different masses..." doesn't make sense, because the gravitational force between two objects is DEPENDENT on their mass, and is therefore not equal for particles of different masses in the same field. (See the article on gravity). The reason the acceleration for two objects dropped off a twoer is the same, is that the mass of the body in the equation of motion ${\textstyle F=m_{obj}a}$ is cancelled by the mass of the body in the equation of the force of gravity ${\textstyle F=G{\frac {m_{obj}m_{earth}}{r^{2}}}}$.

So ${\textstyle a=G{\frac {m_{earth}}{r^{2}}}}$ in all cases where the change of r can be neglected (i.e., any tower you care to drop a ball from in Renaissance Italy), even though F (and therefore the change in momentum and kinetic energy) is dependent on the mass of the object.

And it's also completely unclear what dropping balls off a tower has to do with the gold foil experiment. PianoDan (talk) 17:00, 16 December 2022 (UTC)

Where in digestion does salt and sugar separate?

Human urine is 95% water, then urea at the next largest, followed by the salt ions of sodium, chloride, and potassium. And so, urine is salty, even if you eat lots of sweet food doesn't make urine more sweet. So that means sugar goes the other route. Sugar is covalent, so covalent foods go the other route, ionic foods go to the urine. Where is that separated? In the liver, blood vessels? Thanks. 67.165.185.178 (talk) 14:19, 11 December 2022 (UTC).

Sugar is metabolized by insulin. The presence of sugar in urine is a symptom of diabetes. Acroterion (talk) 14:22, 11 December 2022 (UTC)

So that happens in the pancreas? And the salt continues to the blood vessels, then to kidneys? 67.165.185.178 (talk) 14:33, 11 December 2022 (UTC).

No, the pancreas supplies the insulin, which is used throughout the body. Read carbohydrate metabolism, digestion, kidney and pancreas. Acroterion (talk) 14:44, 11 December 2022 (UTC)

Okay, so there is selectivity? (Insulin can metabolize sugar without metabolizing salt?) Or, is salt already separated out when the time the insulin meets the sugar? 67.165.185.178 (talk) 14:56, 11 December 2022 (UTC).

Salt is not metabolized, and it is not a source of energy. It is an essential nutrient. See sodium in biology. Acroterion (talk) 17:02, 11 December 2022 (UTC)

Since sugar is covalent, then there must be other things that are covalent like sugar, that insulin also metabolizes that might get in the way? 67.165.185.178 (talk) 17:37, 11 December 2022 (UTC).

Covalence is a property of bonds between atoms, not of compounds such as sugars. The kidney has a filtration system that can separate small ions from larger molecules; see Ultrafiltration (kidney) § Selectivity.  --Lambiam 19:45, 11 December 2022 (UTC)

The glucose is fact filtered into primary urine and then re-absorbed in renal tubules. Ruslik_Zero 20:12, 11 December 2022 (UTC)

I'm looking at Digestion#Carbohydrate_digestion, which states sucrose is broken down by sucrase, and elsewhere it says it happens in the small intestine. Then, carbohydrate_metabolism says insulin and glucagon are the primary hormones involved in maintaining a steady level of glucose in the blood. I also see proteins are being digested in the stomach and small intestines. Now, I'm not seeing anything for salt, so Googling "how does the body digest salt" yields "Sodium is absorbed from the gastrointestinal tract, always bringing water along with it." So something from the intestines can go into the kidneys. And both salt and sugar make it to the small intestines. I'm wondering what is the next place for salt and sugar after the small intestines, directly into the kidneys? And then, kidneys filter out sugar into the renal tubules, salt does not? 67.165.185.178 (talk) 00:53, 12 December 2022 (UTC).

Sugar is a carbohydrate, which is digested. Salt is a mineral/essential nutrient, which is absorbed. One is metabolized, the other is not. There are two distinctly different processes involved,and bio;logically the two substances have drastically different roles and processes. You appear to be proceeding from false assumption of similarity. Acroterion (talk) 01:01, 12 December 2022 (UTC)

But in the small intestines, if you have salt and sugar in water, then the process to suck out salt 1st, from water, then there must be selectivity. Salt ions are smaller than sugar molecules so that should be some amazing selectivity. So it might be the salt are going through pores, like channels. 67.165.185.178 (talk) 02:43, 12 December 2022 (UTC).

Sodium absorption is complex and happens at multiple places along the digestive system. this briefly describes some of them. --Jayron32 12:49, 12 December 2022 (UTC)

I like Lambiam and Ruslik's reference to the kidney articles. The link Jayron provided doesn't mention anything about kidneys, though it appears to me not much sugar is put into the kidneys. But Jayron's link has the professor's e-mail for questions, so I am e-mailing that. 67.165.185.178 (talk) 05:30, 16 December 2022 (UTC).

Sounds waves vs. light waves.

Can sound waves emit light and can light waves emit sound? Also, note that light-waves is a duality. The particle equivalent of light waves is photons, is there a particle-equivalent of sound waves? Thanks. 67.165.185.178 (talk) 14:46, 11 December 2022 (UTC).

Read Sound wave and Light wave. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:08, 11 December 2022 (UTC)

Read sonoluminescence, acousto-optics and phonon. Also not a good answer, but hopefully a little more to the point. --Wrongfilter (talk) 17:23, 11 December 2022 (UTC)

A 3rd question is are light waves and sound waves actually the same wave, then, can waves emit sound and light at the same time? (And what would you call that.). Unfortunately, those 2 articles don't seem to connect to each other. 67.165.185.178 (talk) 17:52, 11 December 2022 (UTC).

Maybe Bugs' articles are indeed more for you. Now it's unclear to me what you think light and sound waves actually are. --Wrongfilter (talk) 18:03, 11 December 2022 (UTC)

Yes. I never heard people associate sound waves with photons, for example. 67.165.185.178 (talk) 19:24, 11 December 2022 (UTC).

Light waves and sound waves are very definitely not manifestations of a common underlying physical phenomenon. Light waves are waves in the electromagnetic field. Sound waves are waves propagating in a fluid medium consisting of material particles such as molecules. In the vacuum of outer space, there is no sound, but light traverses it without problem. The speed of light is independent of the relative velocity of an observer, which cannot be said for sound waves (see Doppler effect). Even when abstracting from the physical context, these waves have different characteristics. Light waves are strictly transverse, while sound waves usually have a strong longitudinal component. In that respect, stadium waves are more like light waves.  --Lambiam 19:34, 11 December 2022 (UTC)

Tiny correction: Sound waves propagate in all phases of matter, not just the fluid ones. See acoustics. If they didn't, you wouldn't be able to hear them, as at least part of your hearing apparatus in your ear are solid bones (see ossicles).--Jayron32 12:42, 12 December 2022 (UTC)

Hello user with IP 67.165.185.178 and welcome to the science reference desk, as a licenced amateur radio operator i can tell you that while they seem similar, light (electromagnetic) and sound waves are two different kinds of wave, sound waves are movements of air often arising from physical vibrations, and electromagnetic waves are a different form of energy that has a very wide spectrum so depending on the frequency, an EM wave could be a radio wave, heat, IR, or visible light, from what i know all EM radiation uses the same force carrier, photons, just like how sound propagates through air, so i wouldn't think there is such thing as a sound particle, physical vibrations are exactly that.

As for the conversion of light to sound, or vice versa, it's very possible at least with electronics and is commonly done, some music visualizers are simply light sources that are amplitude modulated by the music, or more advanced a spectrum analyzer, a spatial representation of the frequency spectrum, and the same is true the other way round, read about fibre optics and bells photophone, not only do we convert a form of invisible light into sound whenever we listen to a radio, but whatever modulation can be applied to a radio wave can also be applied to light waves, meaning that light, when modulated, can carry sounds and even data! OGWFP (talk) 21:36, 15 December 2022 (UTC)

Walrus's family

If you learned it in high school, it's probably oversimplified, like this diagram

Wikipedia's walrus article says walruses are the only living member of their family, but dictionaries often define a walrus as being "of the seal family". Any 2 biological concepts it is important not to confuse?? Georgia guy (talk) 15:15, 11 December 2022 (UTC)

Our article says

Order: Carnivora

Clade: Pinnipedia

Family: Odobenidae

Genus: Odobenus

Species: O. rosmarus

Pinnipedia include seals too. Dictionaries may be using the term 'family' more loosely. See the cladogram on the Pinniped article for the relationship. AndyTheGrump (talk) 15:31, 11 December 2022 (UTC)

When Illiger introduced the phylonym Pinnipedia, he defined it both as a family and a one-family order.^[1] The taxons of the usual taxonomic hierarchy correspond to cutting up the phylogenetic tree in layers. As far as I can see, there is no clear scientific criterion for where these cuts are made, and cladistics has multiplied the number of reasonable cutting points, obliterating any notion of comparing the cutting point levels in different trees in a sensible ranking system and leading to new taxon names such as suborder and superfamily. The traditional rank names for given clades, such as order, family (not a rank in the original taxonomy of Linnaeus) and genus, are based more on tradition than anything else.  --Lambiam 18:37, 11 December 2022 (UTC)

It's rather arbitrary whether one calls the odobenidae a family and the pinnipedia a clade between order and family, or calls the pinnipedia a family and the odobenidae a clade between family and genus. Declaring a clade with a single species doesn't make a lot of sense, but there could be extinct relatives.

The whole idea of a ranked system made a lot of sense to Carl Linnaeus, who lived a hundred years before Charles Darwin, studied current animals and plants and noted that some were more similar to each other than others, and it still makes a lot of sense to those who study the organisms alive today. From an evolutionary point of view it makes no sense. What at one point in time is a genus of two closely related species may a hundred million years later have evolved into an entire order of hundreds of species. PiusImpavidus (talk) 10:07, 12 December 2022 (UTC)

To reiterate what PiusImpavidus said above in slightly different terms: You are rarely taught all the details of a complex subject in an introductory-level course like one has in high school or early college. Few people make it further into taxonomy than is taught in high school biology, and the classic hierarchy taught in such a class is extremely oversimplified and super-outdated. The modern system of cladistics is much more useful, but also much more nuanced and complex, which is why most people don't learn it. --Jayron32 12:36, 12 December 2022 (UTC)

What is added to wood, to prevent sunlight damage?

As in color change from sunlight. 2 answers I heard of are polyurethane and mineral oil. But, that strikes me as stuff that is easily wiped off, or does it get stuck inside the wood? 67.165.185.178 (talk) 20:50, 11 December 2022 (UTC).

Traditionally in Australia cedar homes are painted with used motor oil. It soaks in. Good thing we don't have bushfires Greglocock (talk) 21:58, 11 December 2022 (UTC)

While there is an article on Photodegradation, there is no section for wood. Search for wood photo-degradation yields results. I personally have used catalyzed polyurethane and added an automotive UV inhibitor (probably HALS) for use on a wooden table; kinda expensive, but that was in the '70s, and it still looks like new. 136.56.52.157 (talk) 23:54, 11 December 2022 (UTC)

Wood preservation article might be helpful. 136.56.52.157 (talk) 00:21, 12 December 2022 (UTC)

There are wood preservation products, some use something called Trans-Oxide® which the manufacturer claims are manufactured to have needle-shaped particles that will not scatter light even when fully dispersed in the coating or vehicle. This makes them completely transparent and yet still able to impart high color tint strength, weather resistance and UV-barrier properties.^[2] Exterior Danish Oil UV^[[3] includes UV inhibitor compounds [...that] absorb harmful ultraviolet light wavelengths and emit them harmlessly in the infrared range as heat. They don't say what the "compounds" are, but probably includes metallic oxides. 136.56.52.157 (talk) 01:08, 12 December 2022 (UTC)

For not-too-expensive general use see: tung oil. 136.56.52.157 (talk) 01:17, 12 December 2022 (UTC)

I immediately thought of creosote which is cheap and widely used on wood in fences and other outdoor settings. Mike Turnbull (talk) 11:59, 12 December 2022 (UTC)

FYI: Creosote is banned in many jurisdictions, you'll have to put up with substitutes like CreoCote™. They claim to be as good as the original. Martin of Sheffield (talk) 15:41, 12 December 2022 (UTC)

• Keeping wood from changing colors is often done via the use of wood sealants. The main options for wood are varnish and lacquer. Generally three things can degrade the color of wood; being water, oxidation (air), and light. Good sealants will stop water and air from fading the wood; and some will have materials that absorb UV light, which will additionally block most of the oxidative effects of sun. --Jayron32 14:20, 12 December 2022 (UTC)

Enteroctopus date: 1887 or 1889?

Most sources state the genus Enteroctopus was created by Alphonse Tremeau de Rochebrune and Jules François Mabille in 1889; however this is not entirely correct; It was published in 1889 in Mission scientifique du cap Horn, 1882-1883 but the very same book affirms it was created two years before, in 1887. So, what is the correct date? -- Carnby (talk) 21:25, 11 December 2022 (UTC)

Wasn't the genus created on the Fifth day of Creation? :) Generally, one goes by the publication date.  --Lambiam 01:27, 12 December 2022 (UTC)

The 1889 article indeed gives the taxonomic authority of the binomial name Enteroctopus megalocyathus as Rochebrune & Mabille 1887. As a confusing side issue, nowadays we would write "Enteroctopus megalocyathus (Gould, 1852)" because Gould had come up with the species name already, but Rochebrune & Mabille here coined the generic name and they wrote themselves as the authors of the combination of the two names (a bit like the rules botanists still follow). The 1887 date is erroneous. It seems that their intention was to indicate that this name was new in their current work, and that they were both authors of this description. Presumably they expected their manuscript to be published in 1887, but in fact it appeared in 1897 1889 and nobody changed the date in the meantime. It is the actual date of publication that now counts. https://doi.org/10.11646/zootaxa.2723.1.2 probably explains more but is behind a paywall. Jmchutchinson (talk) 23:42, 13 December 2022 (UTC)

December 12

Fluorine (and neon) 2s shell

Resolved

Normally, we talk about fluorine as having 2s and 2p as valence orbitals, for seven valence electrons. However, there's a huge difference in orbital energies between these two, and actually fluorine 2s has a lower energy than the core 5p orbitals in the lanthanides. So, how significant is the contribution of fluorine's 2s shell to chemical bonding? And what about neon? Double sharp (talk) 08:10, 12 December 2022 (UTC)

The matter has apparently been discussed on Chemistry Stack Exchange. Some MO diagrams for SF₆ and HF are given to support fluorine 2s as inactive. But that doesn't prove that fluorine 2s is always inactive, only that it is in those compounds. Looking at orbital energies throughout the periodic table, I'd expect it to be more possible in something like BrF+6 and indeed this paper finds some fluorine 2s bonding contribution there.

So I suppose I managed to track down an answer for my original question and the natural follow-up has become "OK, so what are the valence orbitals of neon"? Double sharp (talk) 09:03, 12 December 2022 (UTC)

Well, this distinguishes 2p vs 2s in solid neon as the outer vs inner valence regions. I guess this gives the answer to "what are the valence orbitals of neon" in a natural context when that question is meaningful. Double sharp (talk) 09:51, 12 December 2022 (UTC)

uploading unpublished government technical reports

I would like to know if documents pertaining to a Wikipedia page can be uploaded as pdf files. These are government technical reports which have not been formally released for various reasons. Rdhara (talk) 21:49, 12 December 2022 (UTC)

The Help desk is better prepared for this type of question. 136.56.52.157 (talk) 23:51, 12 December 2022 (UTC)

December 13

Starting the engine of military vehicles

Random thing that someone was wondering about in the bar tonight. Do tanks, fighter planes and attack helicopters have a set of keys for the doors and the ignition? — Preceding unsigned comment added by 146.200.126.234 (talk) 00:04, 13 December 2022 (UTC)

I don't have a general authoritive answer, but keys have long been used in private ownership vehicles because of theft. Industrial vehicles such as bulldozers have traditionally needed no key for starting, as practically nobody wanted to steal them.

My father bought a World War 2 surplus British made tank. There was no key - anybody could enter and start it. It had an aircraft-style ignition lever switch - off/one/two/both (the engine had 2 spark plugs per cylinder- you are supposed to test running on one set of plugs at a time, to prove both work) and a push-button to crank it.

Last year, a former iron curtain country had some sort of celebration in which their state museum supplied a restored Russian made tank (T54 or similar). Leaving it on public display, they took the battery out, thinking this would immobilise it. A couple of old guys, probably a somewhat drunk, showed up and they had served years before in the same sort of tank. They knew it had an emergency air start system in case of a dead battery. So they started the tank using the air system and drove off with it.

Our army sold of a few old Armoured Personnel Carriers (APC). I inspected one (M113 or similar) at the dealer's yard. They invited me to start it - it needed no key. It had a simple lever on/off switch for electrical power, and a push-button to activate the starter motor.

There are a number of military aircraft start procedure videos on YouTube. There's no key.

One can imagine a scenario: "We are under overwhelming fire. Quick, corporal, start the truck and let's get out of here!" "Uh, sorry Sarge, I dropped the keys in the mud. Can't find them now." Dionne Court (talk) 00:54, 13 December 2022 (UTC)

This article in ARMY Magazine, criticising the US Commercial Utility Cargo Vehicle or M880 (a military pick-up truck), cites the provision of a common ignition key as a disadvantage; "Imagine trying to bug out and having to fumble for a key to start the truck". Alansplodge (talk) 22:21, 13 December 2022 (UTC)

Hello user with IP 146.200.126.234, nope, most military vehicles and airplanes in general (not just military) don't use keys, i've heard that humvees don't use keys, nor do tanks, as shawn nelson proved, most aircraft don't use keys, aside from smaller GA aircraft like the Cessna 172 and bushplanes that have a keyed magneto switch, as those aircraft are more likely to be kept in an unsecure airport, military and civil aircraft are always always kept in very secure airports, often having more then a few hundred CCTV and thermal CCTV cameras, these aircraft also relies on a rather complex procedure to start and prep for take off, people have stolen unkeyed aircraft before, but it's often a little twin prop, not sure if anyone has ever stolen a 737 for instance.

Military aircraft are the same, no keys, but good luck getting into a military base, and then there's starting it.

Vintage fighters like the spitfire had their own security feature, huge prop torque that even experienced pilots have trouble handling. OGWFP (talk) 21:59, 16 December 2022 (UTC)

Examples Where Genetics was used to determine definitions of genus and species

I recall that there were examples where the definition of a species, genus, etc. were redefined based on genetic analysis. E.g., we thought that Chimp was a species but we changed it to be a genus or we thought a Sea Horse was a fish but we changed it to an Anthropod (I'm making that last one up but I think the first one might be true). I can't remember where I read this though and I've looked through Wikipedia and my books and can't find anything. Would appreciate any examples and refs. MadScientistX11 (talk) 00:59, 13 December 2022 (UTC)

Here are some examples; there are probably countless more.

• The Arctic warbler was formerly thought to include various populations that breed in Asia, but these are all now considered distinct species.
• The black Sumatran langur was formerly considered a subspecies of the brown long-eared bat, but is now treated as a separate species.
• The black-and-white langur was formerly considered a subspecies of the black-crested Sumatran langur, but is now treated as a separate species.
• The Calabria pine vole was formerly considered a subspecies of Savi's pine vole, but is now treated as a separate species.
• The East Sumatran banded langur was formerly considered a subspecies of the Raffles' banded langur, but is now treated as a separate species.
• The European green toad was formerly thought to include various mainly Asian populations, but these are now considered distinct species; together they have been assigned a new genus, Bufotes.
• Imaizumi's red-backed vole was formerly considered a subspecies of the Japanese red-backed vole, but is now provisionally treated as a separate species.
• The Japanese long-eared bat was formerly considered a subspecies of the Sumatran surili, but is now treated as a separate species.
• The Siberut langur was formerly considered a subspecies of the Mentawai langur, but is now treated as a separate species.

 --Lambiam 07:56, 13 December 2022 (UTC)

For an example regarding some species of gulls, see Larus#Ring species. Long story short – we thought they were a Ring species, but a recent genetic study (linked as a reference) has shown that it's even more complicated than that. {The poster formerly known as 87.81.230.195} 90.213.188.15 (talk) 14:21, 13 December 2022 (UTC)

Metallising fluorine

Resolved

Has anyone ever measured the pressure necessary to form an expected high-pressure metallic phase of F₂? Or calculated what it theoretically ought to be? Double sharp (talk) 03:07, 13 December 2022 (UTC)

According to this 2020 paper, it apparently has never been experimentally found (well, no surprise given that it seems like a safety nightmare), but that doesn't exclude it having been calculated. Double sharp (talk) 04:14, 13 December 2022 (UTC)

Per this 2020 paper there have been experiments (with inconclusive results) and the theoretical metallisation pressure for fluorine is 2500 GPa (with a novel tetragonal P4₂/mmc structure). So I've once again answered my own question. Double sharp (talk) 04:18, 13 December 2022 (UTC)

Updated metallization pressure (and also the French article). Don't think anyone has calculated it for radon. Double sharp (talk) 04:35, 13 December 2022 (UTC)

Scientific articles about beef versus Impossible Burger that are not commissioned by the latter?

I've been seeing a lot of the 89% statistic about "global warming potential" from the life cycle analysis that Impossible Foods commissioned from Quantis. This number seems to be repeated commonly, and so I was looking for other studies/scientific articles about the same topic that were not commissioned by Impossible Foods so I could further evaluate the claim. 777burger ^{user talk contribs} 03:49, 13 December 2022 (UTC)

Producing an adequate life-cycle assessment of a product in conformance with the ISO 14040 and 14044 framework and guidelines is a substantive effort of a type that does not help one to earn scientific brownie points. Such a study is unlikely to be undertaken by a scientific establishment unless specifically commissioned. Prior to publication, the LCA was reviewed by an independent panel of academic experts, who found no major issues. In particular, it found that that the methods used are scientifically and technically valid. The report produced by Quantis can be downloaded from the Web,^[4] and is detailed enough that anyone who is interested can check that data from other studies have been properly cited and reproduced and can check the computations. It would be interesting to make a comparison with other "fake meat" products, but I bet that for most one would find very similar results. The report can be read more as an indictment of run-away meat production than as an ad for specifically Impossible Foods. One might even say that beef is the more impossible food.  --Lambiam 07:26, 13 December 2022 (UTC)

What is thirtylone?

Transferred from Computing desk

i wanna do some research about What is thirtylone?if you have the idea about you can help me in my research Elsiewright343 (talk) 13:44, 13 December 2022 (UTC) — Preceding unsigned comment added by 95.145.0.90 (talk)

As far as I can tell, it's whatever anyone wants it to be. There doesn't seem to be any single real chemical compound with that name, and nothing recognized as such with a CAS number. It seems to usually be used for various forms of amphetamines or analogs of MDMA, but basically as a name it gets used by the illicit designer drug community for whatever new compound they come up with in these families as existing compounds get banned. Don't buy it, don't do research on using it, as you have literally no idea what you are getting. You don't know what compound they are even promising, let alone whether it is actually containing that compound, in what purity, what else it is mixed with, and I guarantee zero research or testing on safety. --OuroborosCobra (talk) 15:52, 13 December 2022 (UTC)

@Elsiewright343 It is here on Chemspider and here on wikipedia. I wouldn't touch it with the proverbial barge-pole. Mike Turnbull (talk) 16:18, 13 December 2022 (UTC)

I found this and am providing this as is, no comment. --Ouro (blah blah) 04:57, 17 December 2022 (UTC)

Help

What was the most recent common ancestor of dinosaurs and mammals? Allaoii ^talk 19:31, 13 December 2022 (UTC)

It would have been whatever animal existed when Sauropsids (reptiles, dinosaurs, and birds) and Synapsids (mammals and their reptile-like ancestors) diverged, probably living sometime in the Pennsylvanian, likely earlier than 306 million years ago, when the oldest known synapsid evolved. --Jayron32 19:39, 13 December 2022 (UTC)

You are looking for a basal amniote. -- Verbarson  ^talk_edits 19:43, 13 December 2022 (UTC)

i remember reading something that named a specific creature, im trying to find its name Allaoii ^talk 20:01, 13 December 2022 (UTC)

I'm not sure we know it down to that level of precision. The vast majority of species have been unidentified. It seems unlikely in the extreme that the specific species that was the MRCA is known. --Jayron32 21:11, 13 December 2022 (UTC)

well it was star trek... Allaoii ^talk 21:27, 13 December 2022 (UTC)

Ah, the Voyager episode "Distant Origin." It claimed that MRCA to be eryops, which is probably not correct, since it is an amphibian that lived after the first reptiles evolved, and so isn't an ancestor of either dinosaurs or us. Also, the organism they pictured in the episode is not an eryops at all. According to Memory Alpha, the pictured animal is likely a gorgonops, which is already a mammal like reptile. It might be among our ancestors, as a stem group leading to all mammals, but that would already put it after the split between sauropsids and synapsids. So, yeah, Star Trek got this wrong in a lot of ways. --OuroborosCobra (talk) 21:35, 13 December 2022 (UTC)

...wanna be nerd friends? Allaoii ^talk 21:37, 13 December 2022 (UTC)

that reminds me, is the "most evolved dinosaur" they showed real, and if so, what is it? Allaoii ^talk 20:38, 14 December 2022 (UTC)

"Most evolved" is meaningless. All organisms alive on Earth at the same time are equally evolved. --User:Khajidha (talk) (contributions) 16:52, 16 December 2022 (UTC)

in the episode im talking about they showed a dinosaur that was "most evolved" toward humanoidness Allaoii ^talk 20:15, 16 December 2022 (UTC)

well most evolved before they died off Allaoii ^talk 20:16, 16 December 2022 (UTC)

Try this. Alansplodge (talk) 22:39, 13 December 2022 (UTC)

read the other replies before commenting Allaoii ^talk 22:51, 13 December 2022 (UTC)

Yes. I was providing a reference, this being a reference desk. Alansplodge (talk) 15:07, 14 December 2022 (UTC)

one of the other replies already answered my question. Allaoii ^talk 17:17, 14 December 2022 (UTC)

This is the reference desk, not the answer desk. Alansplodge did exactly what they were supposed to. --Jayron32 19:52, 14 December 2022 (UTC)

December 14

Gamma decay.

So the shortest wavelength in the EM spectrum are gamma rays, then x-rays. It appears to me that gamma rays are called gamma rays because they have only been gamma rays emitted. If they can emit wavelength in the x-ray range, then they can get a name change. Have scientists been working on finding gamma decays to emit in the x-ray range? Also, if I look at gamma decay, and sort the shortest gamma ray, to the longest gamma ray, what is the pattern, from the decaying point of view? Nucleus mass? Do scientists predict they can 1 day have decay emit x-rays? And maybe win a Nobel prize if someone discovered a way. 67.165.185.178 (talk) 01:25, 14 December 2022 (UTC).

The total energy released in radioactive decay is the energy equivalent of the difference in mass (by $E=mc^{2}$) between the parent nuclide and daugher nuclide(s). The energy of a photon is given by the Planck relation, $E=hf={\frac {hc}{\lambda }}$, which implies that longer gamma rays carry less energy and shorter gamma rays carry more energy. Indeed, very low energy decays can produce x-rays or even ultraviolet rays in the case of the remarkably low-energy nuclear isomer thorium-229m (Sources: [5] [6]). ^Complex/_Rational 01:56, 14 December 2022 (UTC)

Excellent. And all these gamma rays, are ionizing. Can this thorium-229 or so, release the radiation that are non-ionizing? 67.165.185.178 (talk) 03:42, 14 December 2022 (UTC).

The excitation energy of Th-229m is less than 10 eV, which is commonly used as a threshold for ionising radiation. So, yes, it would emit non-ionising radiation by this definition. Though usually the gamma vs X-ray (or in this case UV!) distinction is by origin rather than wavelength. Double sharp (talk) 03:47, 14 December 2022 (UTC)

Double sharp's last sentence is important. An alternate and fairly common distinction between the two types of radiation is for "X-rays" to be the result of electronic reactions vs "gamma rays" coming from nuclear reactions, rather than a bright-line (ha!) delineation of wavelengths. X-ray#Energy ranges has a discussion. DMacks (talk) 03:58, 14 December 2022 (UTC)

It depends on whom you ask. The people who generate their own radiation (like radiologists) discriminate between X-rays and gamma rays by source, i.e., the apparatus they need to generate it. The people who only observe the radiation (like astrophysicists) discriminate only on energy, putting the threshold at something like 100 keV. PiusImpavidus (talk) 09:54, 14 December 2022 (UTC)

Yeah, I'm used to the nuclear-physics convention that anything coming out of a nucleus is gamma (even if by wavelength it's UV in the case of Th-229m), but indeed definitions vary between fields. Double sharp (talk) 14:54, 14 December 2022 (UTC)

Oh, and what does the m symbolize, in thorium-229m? 67.165.185.178 (talk) 04:01, 14 December 2022 (UTC).

What did you learn when you clicked on the thorium-229m link? DMacks (talk) 04:03, 14 December 2022 (UTC)

Oh okay, it stands for metastable. 67.165.185.178 (talk) 04:08, 14 December 2022 (UTC).

I want to underline something that several commenters here have said from different points of view:

Gamma rays and X-rays are the same thing. They're both just photons. Classifying photons by wavelength, energy, or source can be very useful for a number of reasons, but it's important to remember that these are still just sub-categories (with somewhat conflicting definitions) of the same fundamental thing. PianoDan (talk) 16:45, 14 December 2022 (UTC)

Just to really drive home the point that PianoDan is making above, the different "kinds" of electromagnetic radiation (gamma rays, X-rays, UV, light, IR, microwaves, radio waves) are all the same thing. There is no difference between any of them on a fundamental level except the wavelength, but in every other way, they are exactly the same phenomenon. When we use words like "gamma rays" or "X-rays" or "visible light" to describe certain ranges of wavelengths, we're largely doing so to make it convenient for us to explain how we use those forms of EM radiation, and in some cases are really just historical artifacts to a time when we didn't understand this stuff as well as we do now. When we named, for example, X-rays and gamma rays, we didn't really know what they were. X-rays have that "X" at the front because because Wilhelm Conrad Röntgen, when he first described them, didn't know what they were, so he used the standard placeholder "X" meaning "unknown" for the name, and it kinda just stuck. When gamma radiation was named, it was named because it was the third time of nuclear radiation (which is to say, radiation given off during nuclear decay discovered. No one really knew what it was, but since alpha radiation (the first so discovered) and beta radiation (the second so discovered) already had names, Paul Ulrich Villard, who discovered this third type, just kept the pattern going. Notice, however, that none of these names has anything to do with what the radiation actually was. It turned out that X-rays and gamma radiation were basically the exact same thing, so for mostly historical reasons, we differentiate the name by the process that produces it, rather than by any fundamental difference in the particles themselves. You see the same thing all the time; for example alpha particles are just helium 4, beta particles are just electrons. It's certainly no different than you calling your mother "Mom", but her brother calling her "Susan" or whatever. Different names in different contexts don't mean they are different things. The same thing can have multiple names. --Jayron32 18:11, 14 December 2022 (UTC)

Collisions at railroad crossings

Statistically, does California experience a disproportionately high number of collisions between trains and pedestrians and/or road vehicles at level crossings (when compared to other states)? If so, does the number remain disproportionate if corrected for the main confounding factors (namely, (1) the amount of population living in communities with active railroad tracks running through them, (2) the number of trains operating daily within the state and (3) the number of ungated railroad crossings and/or the mileage of street running)? If so, what are the possible reasons why the number is so high? (Because it certainly seems that way -- a person I know who rides Caltrain regularly told me that he experienced delays almost every week on average (!!!) due to either his train or another train ahead of him hitting someone or something on the tracks, and when I rode the Coast Starlight up to Salem a couple months ago, I experienced these delays personally -- the northbound train pulled into San Jose a full 4 hours late due to having run over some stupid hobo in Salinas, whereas the southbound train got to Salem exactly on time and kept going as far as Oakland without delay, but between Emeryville and Jack London Square we had an emergency stop due to some idiot driver pulling onto the tracks right in front of the train without looking (fortunately we were going dead-slow and therefore didn't collide, so we were only delayed 10 minutes or so). So, is California really that bad in terms of collisions at railroad crossings, and if so, why might that be? 2601:646:8A81:6070:8D7A:87F9:2C1B:94A0 (talk) 08:03, 14 December 2022 (UTC)

According to Operation Lifesaver which exists to prevent these types of collisions, Texas is #1 in the number of collisions and California is #1 in deaths caused by such collisions. This is not surprising since those are the two most populous states with California being most populous. The death rate in California per 100,000 residents is close to the national average. This is a nationwide problem although 234 deaths a year in a country of 332 million people is not a major cause of death. Pancreatic cancer, for example, kills about 50,000 Americans each year. As a long term resident of the Bay Area, I am well aware that Caltrain has a bad reputation for this type of disaster, since it is a heavily used commuter rail line between San Francisco and San Jose, with plenty of grade crossings and ample opportunities for pedestrians to engage in dangerous behavior. This article from 2000 reports 90 deaths in the previous eight years, which would be less than one a month but would certainly have an impact on daily commuting. Many of those deaths were suicides. Talking about "stupid hoboes" is pretty much guaranteed not to be useful. There are obvious safety improvements that should be made, such as eliminating grade crossings, but that would cost many billions of dollars and take decades. That is part of the California High-Speed Rail program, which is behind schedule and over budget. Cullen328 (talk) 10:17, 14 December 2022 (UTC)

For comparison, 5 people were killed at UK level crossings in 2020/21, [7] 2 in 2019/20 and 2 in 2018/19. [8] The population of the UK is 67 million, nearly double that of California, with a much denser rail network. Alansplodge (talk) 15:04, 14 December 2022 (UTC)

But California has over 10,000 level crossings, almost twice as many as the UK. To compare them properly you'd need to analyze both places in terms of the number of road vehicles and the number of trains that use the crossings daily. I'm not searching, but I doubt that those statistics will be easily found. --174.89.144.126 (talk) 15:32, 14 December 2022 (UTC)

Good point. The UK deaths were all pedestrians, mostly using rural footpath crossings. I suspect that the safety infrastucture of British vehicle crossings is rather better - crossings without automated barriers and/or warning lights are very rare and only in remote areas. Alansplodge (talk) 12:06, 15 December 2022 (UTC)

UK level crossings appear pretty safe then. In the Netherlands, we have about 12 accidental deaths among road users on level crossings per year (in addition to about 200 suicides), which amounts to one accidental death per level crossing per 200 years. That's about 98% of all accidental rail fatalities and 2% of all accidental road fatalities. Assuming the average level crossing sees about 6 trains per hour during the day (most see 4 or 8 per hour, some over 20 per hour, some only 2 per week), that's one accidental death per 8 million train passages. That may be a more useful statistic, but you still have to compensate for road traffic density and that the rush hour on road traffic may or may not coincide with peaks in rail traffic. Ideally, you take the number of trains at a level crossing in an hour, multiply with the number of road users at that crossing during that hour, integrate over a year, sum over all level crossings and then divide the number of accidental deaths or the number of collisions by that number. It's still not a fair number: as the most heavily used level crossings, with the most elaborate warning signals, get replaced by grade separated crossings, accident rate drops, but the average safety of the remaining level crossings drops too. PiusImpavidus (talk) 12:48, 15 December 2022 (UTC)

wormholes

hello i would like to ask if resonant tunneling antenna diodes can generate wormholes. thanks very much. 2607:FEA8:BCE0:D500:75E8:5E73:E7C8:DE4 (talk) 15:38, 14 December 2022 (UTC)

No. --Wrongfilter (talk) 15:44, 14 December 2022 (UTC)

More specifically, quantum tunnelling and wormholes are not the same thing. --OuroborosCobra (talk) 16:02, 14 December 2022 (UTC)

from internet searches i found macroscopic and electromagnetic quantum tunneling can generate wormholes. is that this correct. 2607:FEA8:BCE0:D500:D9DA:4F2F:3CE:E4B6 (talk) 17:42, 14 December 2022 (UTC)

Please read the Wikipedia articles you have been sent to read. Wormholes and quantum tunnelling are entirely unrelated phenomena, and have nothing to do with each other. Wormholes are a consequence of gravity, and are thus explained by general relativity. Quantum tunnelling, as the name implies, is a result of quantum mechanics. It is not an electromagnetic effect, per se, but rather due to the way that all elementary particles behave. The quantum tunnelling article actually has a nice, lay-person level explanation in the "Introduction to the concept" section.--Jayron32 17:59, 14 December 2022 (UTC)

Water's boiling point

One of the things that allow life to exist on Earth is that liquid water is available in large numbers. This is because of the distance to the sun, but also because of our atmosphere and its pressure, that allow a wide temperature range for liquid water (from 0º to 100º). If Earth was in the same orbit but had a lower atmospheric pressure, that range would be way more limited. And IIRC, with no atmosphere water would sublimate from ice to vapor directly.

This is something I simply know, but I would need a proper source for it. I'm listing in a sandbox all the reasons that allow life to exist on Earth, from an astronomical perspective, but all the sources I find that explain our liquid water attribute it only to the goldilocks zone, making no mention to the atmospheric pressure. Cambalachero (talk) 19:06, 14 December 2022 (UTC)

What you're looking for is a phase diagram of water, or even more simply the triple point of water. The pressure at the triple point is the lowest pressure at which a liquid could exist, so any pressure less than about 0.006 atm (0.6% of the earth's atmospheric pressure) would not be able to support liquid water. The relationship between pressure and boiling point is seen on any phase diagram as the liquid-solid line on the graph. If you want a text description, it's really basic stuff taught in any first-year chemistry class. Here it is in LibreText Chemistry and Here it is on OpenStax Chemistry, for two free entry-level chemistry textbooks. I can't imagine that literally every entry-level chemistry text book doesn't discuss the relationship between pressure and phase changes. It's REALLY basic stuff. --Jayron32 19:49, 14 December 2022 (UTC)

If the motivation here is to explore limits of alternative "Goldilocks zones," we might need to freeze the discussion (sorry, bad pun) and revisit exactly what that zone is.

If we're reducing it to a few words of sound-bite, we might say that a planet is in the Zone if liquid water exists on that planet.

But hang on - we also want to say, "... and we're looking for liquid water because..." ... it's an important part of every form of plausible biochemistry that we're interested in - even the plausible alternative xenobiology that borders on the speculative!

At the same time, the so-called "habitable zone" also has other requirements. If the liquid water is in equilibrium at an ambient temperature that is so hot that it's denaturing proteins, then protein-based biology won't work: that's "not the habitable zone." If it's so cold that metabolism is chemically unsustainable, that's also "not the habitable zone." We can imagine biochemistries that are very different from our fundamental earth-like biochemistries - and we can even test some of this in a lab - but there are still limits! And so we can traverse down the speculative, alternative, plausible sorts of "habitable" zones for speculative, alternative, plausible sorts of non-Earth-like life forms, ... just bear in mind that as you stray farther afield, even the requirement for liquid water will also evaporate (sorry, bad pun).

Here's a NASA website that talks about the Kepler Occurrence Rate, and here's the SETI study that goes into the boring details; and if I may editorialize a bit - NASA had to make some "clarifying editorial updates" to their press release in order to keep things more science-y and less fiction-y.

Real scientists do care about this stuff, but they have to mince words, define terms, and tread very carefully. Speculation is fine as long as we are still making meaningful scientific statements - which fundamentally boils (sorry) down to falsifiability and testability.

Nimur (talk) 21:12, 14 December 2022 (UTC)

Just as (relatively analogous to water) examples of plausible alternative biochemistry: ammonia has long been suggested as a possible water substitute, being another 2p element hydride with hydrogen-bonding benefits and a good solvent. I've similarly wondered about hydrogen fluoride for some years, and that possibility is explored in this paper. Going much farther afield, early transition metals form some intricate structures and make a plausible high-temperature biochemistry (at which point we've left analogies to water very far behind). Double sharp (talk) 03:01, 15 December 2022 (UTC)

@Cambalachero, this is somewhat addressed at Rare Earth hypothesis#Requirements for complex life, specifically in the subsection A terrestrial planet of the right size (which is tied to atmospheric pressure, as well as longevity of that atmosphere). You could check out the references there for more. 199.208.172.35 (talk) 21:15, 14 December 2022 (UTC)

December 15

Most intense wind

What is the most intense natural wind on Earth? ✶Mitch199811✶ [Talk] 04:06, 15 December 2022 (UTC)

Possibly tornado. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:14, 15 December 2022 (UTC)

We have a List_of weather records#Wind speeds. DMacks (talk) 07:36, 15 December 2022 (UTC)

Here is an article about the strongest wind ever recorded. Who knows about unrecorded winds? Cullen328 (talk) 08:23, 15 December 2022 (UTC)

1999 Bridge Creek–Moore tornado. Cullen328 (talk) 08:27, 15 December 2022 (UTC)

Thank you! ✶Mitch199811✶ [Talk] 12:51, 15 December 2022 (UTC)

Tornados produce very fast air movements, but they are gusts, not sustained winds. A tornado doesn't stay at the same force and exactly the same position for ten minutes. Very high sustained windspeeds are produced by tropical cyclones and have been recorded at up to 185 kn (95 m/s; 343 km/h; 213 mph) during Hurricane Patricia, which is a one minute average (as Americans tend to calculate such things). Katabatic winds can get very strong too. A piteraq on Greenland in 1970 was recorded at 90 m/s (170 kn; 320 km/h; 200 mph). That would be a ten minute average (as the rest of the world tends to calculate such things). One minute averages tend to be about 14% higher than ten minute averages, so that wind on Greenland was probably stronger than the wind in hurricane Patricia. PiusImpavidus (talk) 20:58, 15 December 2022 (UTC)

Almost certainly the jet streams. 2A01:E34:EF5E:4640:4210:3448:E6A9:8778 (talk) 22:21, 15 December 2022 (UTC)

The article only says 250 mph while the tornado at least is higher. ✶Mitch199811✶ [Talk] 03:31, 16 December 2022 (UTC)

Cullen above made an important point. Strong winds destroy recording equipment, so we may never really know the answer to this question. See Cyclone Tracy#Meteorological history. (Final paragraph.) HiLo48 (talk) 22:44, 15 December 2022 (UTC)

I know I'm always being a weeny for strict definitions, but the original question asked for the "most intense" wind.

Does anybody know what the word "intense" means in a meteorological context?

The way I learned things, "intensity" is a property of a storm, and not a measure of wind or wind velocity. "Intensity" is a quantitative, numerically predicted product of most modern weather forecast models - notably these "Track and Intensity Models" used by the National Hurricane Center.

We can find many definitions for the word "intensity" - including a perfectly precisely-defined meaning in the physical sciences ... or like, fifteen other totally different but equally-perfectly-precisely defined meanings in the physical sciences, but ... I bet our original question meant to ask about "maximum wind velocity." And I bet they were implying "standard" measurement methods for wind speed near Earth's surface (or, say, "1.5 meters above the ground," which is one of the most common standards - like the standard measurement used by NOAA for the Climate Reference Network, which matches most standards used for standard surface observation stations like the ASOS. And I bet we were all implying that we're all talking only about wind-moving-horizontally-and-totally-ignoring-vertical-velocity. And, we're probably all implying a standard observation of the sixty-second average with peak gusts. And ...

Look, we have to define terms carefully if we want to meaningfully understand what a record-setting wind even means, let alone when and where it happened!

My textbook - Aviation Weather - tells me that tornadoes are the most "violent"; "the most intense of all atmospheric circulations" - and the latest edition (AC 00-06B) goes into detailed discussion about the Enhanced Fujita Scale, detailing why the way they measure wind differs from the way we measure the wind. "Note: The Enhanced F Scale is a set of wind estimates (not measurements) based on damage. The 3 second gust is not the same wind as in METAR/SPECI surface observations."

Lately, microbursts have been a hot topic. "Although microbursts are not as widely recognized as tornadoes, they can cause comparable, and in some cases, worse damage than some tornadoes produce. In fact, wind speeds as high as 150 mph are possible in extreme microburst cases."

To me - for my concerns - I care just as much about the vertical wind speed as the horizontal windspeed in the microburst. The vertical downdraft wind velocity is not measured or reported by most common wind reporting stations! By the time the vertical column of wind hits the surface, it starts spreading out radially, which means that those "EF-1 tornado" winds they measure are just one little tiny horizontal component of the pi-r-squared flux that's spreading away from the central vertical downdraft.

Nimur (talk) 18:17, 16 December 2022 (UTC)

On the other hand, if something is the definition that is used by most non-specialist sources like the weather report on the news, that should always be presumed to be the definition that non-specialists mean when asking such a question. Your points are at once valid and irrelevant to answering the most likely question the OP asks, which unless the specific, should be read to be "what is the strongest winds (as measured and reported by whatever means I am used to hearing such things reported)." If that's not a complete measurement or give a full picture, or as interesting as these other tangents are to you is mostly irrelevant as that's not really useful in answering the question the OP asked for. --Jayron32 18:43, 16 December 2022 (UTC)

Feedback taken! Nimur (talk) 19:12, 16 December 2022 (UTC)

The weather report on the news, at least where I live, makes a distinction between wind speed and gust speed (and is usually presented by an actual meteorologist). This wind speed follows the WMO standard for surface wind speed, a 10 minute average at 10 metres above the ground, so I answered with fast, sustained surface winds. From the comments by the OP it appears that gust speed is fine too, whatever is higher.

What about the slipstream of a supersonic meteor falling through the stratosphere? It's natural and pretty fast. PiusImpavidus (talk) 19:20, 16 December 2022 (UTC)

AFAIK, both average wind speed and gust speed are taken from data from actual physical weather stations that contain an anemometer, which AFAIK, just measure horizontal wind speed at the standard height of the weather station (which is where I believe Nimur above got the 1.5 meter standard for "surface winds"); with gust speed being merely like local maxima and average speed being, well, the average. This describes the specific procedures for averaging the wind speeds. The measurement itself is not terribly complicated, and it's been largely standardized for decades, probably at least a century at this point, with the exception of the data being transmitted digitally now. --Jayron32 19:34, 16 December 2022 (UTC)

I'd drop the subject and walk away, but I keep seeing the discussion fixing back on "surface winds..." which are categorically not where we would find the "most intense natural wind on Earth." The question can't be answered properly if we're couching its answer in a conceptually-invalid framework! Wind occurs in three dimensions, and we now measure it at many places, including above the surface!

Winds at high altitudes are now regular outputs of computer models, and these winds are directly and indirectly observed using airplanes, RADAR, and satellite.

I wish I could simply concede that this was "irrelevant" to the original question, except that winds at high altitudes are substantially more intense than surface winds. Even tornados - "the most intense of all atmospheric circulations" - do not always contact the ground!

As far as the history goes - some of this is new science! Meteorological science did not have coherent theories, let alone any measurements, pertaining to high altitude winds, before aircraft began regularly flying at high altitudes - the exact place on our planet where the winds are most intense! The density of the 3D observations and forecasts have improved a lot in recent decades - so much that the textbook I cited above had to be updated in 1954, 1965, 1975, and most recently in 2016. Gosh, the Enhanced Fujita scale - which quantified "intensity" - the exact word in the original post - was only conceived in this millenium and has only been in use since 2007! I must respectfully disagree with the assertion that this type of wind speed measurement has been unchanged for decades - especially when we're talking about measurements at the extreme intensity ranges.

Even I am old enough to have seen the transition from wind reports that looked like this to pictures like this to animations like this. Low level wind shear RADAR - providing ultra dense local measurements of extreme wind phenomena - evolved from theoretical physics in the 1970s into a standard system in 2013. Dense wind measurement data and forecasts didn't exist when I was born - not even in computer weather research laboratories at NASA!

In a very precise and specific sense, we (scientists and the general public) have learned new things about wind intensity even in the last couple years. The nature of what we have learned has changed scientific understanding of wind in a substantial way.

Personally, I think this is a pretty big deal: there are recent, fundamental shifts in the conceptual framework that scientists use for understanding how wind works, how it interplays with climate and earth systems, and how we have to understand it as a 3-D interaction of air flowing everywhere at all parts of the global climate system.

These ideas are important - even if we want to reduce it to a factoid like a "wind speed record" for consumption by the general public.

Nimur (talk) 14:23, 17 December 2022 (UTC)

December 16

Regeneration of the body

Is there a method to stimulate collagene proliferation in the body? 2A02:908:424:9D60:1D3E:5FB6:8A8A:44A6 (talk) 18:22, 16 December 2022 (UTC)

Not sure, but this article may give you some leads for your research. --Jayron32 18:39, 16 December 2022 (UTC)

Collagen is a collective noun for a large class of proteins with very different characteristics, from the smooth and elastic cartilage found in joints to the tough ossein in the bone matrix. If collagen production is stimulated artificially, it should be of just the right type in just the right place by just the right amount; of the many disorders associated with collagen, a large number is caused by overproduction. In cases caused by a genetic disorder, gene therapy may offer a spot of light on the horizon. Severe nutritional deficiency can contribute to low collagen production, but will then generally also result in many other problems. For otherwise healthy individuals, a balanced diet does more to stimulate healthy collagen production than available collagen supplements. This article on WebMD contains some nutritional suggestions.  --Lambiam 09:17, 17 December 2022 (UTC)

Definition of dead

Why is circulatory determination of death abbreviated as DCDD rather than CDD? — Python Drink (talk) 22:16, 16 December 2022 (UTC)

I've only seen DCDD used in the context of death-determination for purposes of organ donation, with phrases like "donation after circulatory determination of death". So the first "D" seems like "donation". DMacks (talk) 22:21, 16 December 2022 (UTC)

Indeed; see this. Alansplodge (talk) 12:37, 17 December 2022 (UTC)

December 17

small electrical generators

I wonder what the obstacles are (i.e. why can't we get them) to making small electrical generators or fuel cells, e.g. for portable outdoor use. It's easy to get a 1 kilowatt generator that weighs 30 pounds, so why not a 100 watt generator that weighs 3 pounds? Things like this are on the internets now and then, but are always just around the corner, never "order now". Thanks. 2601:648:8200:990:0:0:0:497F (talk) 00:43, 17 December 2022 (UTC)

Gasoline and diesel gensets don't scale linearly. For example, I own a Chinese made 2 kW generator and a Chinese made 3.3 kW generator. They look identical, and occupy the same volume, but actually there are 2 key changes - the 3.3 kW unit has a larger cylinder bore, such that it is 215 cc capacity whereas the 2 kW unit is 185 cc. The 3.3 kW unit has a larger frame size generator. The difference in total weight is small - about 10%, due to the difference in generator frame size.

Honda Japan used to make a 300 Watt gasoline powered generator - it weighed about half of what my 2 kW unit weighs.

Basically, to make a gasoline engine half the power of another one, you basically need to halve the cylinder displacement volume. To do that, each length, width, and height dimension needs to be reduced by only the cube root of 1/2, i.e., reduce 20%. Stresses remain about the same (for instance, to run efficiently on standard gasoline, the compression ratio must stay about the same), so mass only comes down 20%. Similarly, to make an engine of 1/10 the power, it will end up reduced by the cube root of 0.1 i.e., dimensionally reduced by 53%.

As far as fuel cells go, they are like nuclear fusion power stations - i.e., they have been reported as just around the corner for almost as long as I have lived, which is 75 years. The trouble with fuel cells is that unless they are constructed with ultra pure materials, and fuel them with ultra pure fuel, they soon clog up with detritus. Dionne Court (talk) 02:47, 17 December 2022 (UTC)

And while combustion-powered generators get lower power-to-mass ratio (and lower efficiency) as you scale them down, this doesn't apply to batteries, which are therefore more attractive at small size. In particular as they don't produce noise and nasty fumes. It gets ever easier to recharge batteries as mains power sockets appear everywhere to charge our phones, e-bikes and electric cars, so I don't expect the minimum size of petrol-powered generators to drop. PiusImpavidus (talk) 11:34, 17 December 2022 (UTC)

The Sn–Sb system

Are Sn–Sb alloys generally metallic conductors or semiconductors? (With no other metals added. I know for example that type metal was historically Pb–Sn–Sb, but that's not what I'm asking about.) Double sharp (talk) 13:51, 17 December 2022 (UTC)