Wikipedia:Reference desk/Archives/Science/2020 April 17

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April 17

Whitcomb rule for cars?

is the Porsche 911 GT1 designed according to Whitcomb rule? is it of any value at these speeds? thanks! --RM

The Whitcomb area rule, also called the transonic area rule, is a design technique used to reduce an aircraft's drag at transonic and supersonic speeds, particularly between Mach 0.75 and 1.2 (575 to 920 mph, 926 to 1482 kph), see Area rule. A Porsche 911 GT3 manages at most "only" 193 mph (311 km/h) and the GT1 is slower, so No and No. DroneB (talk) 01:18, 17 April 2020 (UTC)

Quiz question. One GT3 can manage Mach 0.25. How much can four GT3s manage?  --Lambiam 08:18, 17 April 2020 (UTC)

Quiz answer: by exchanging fuel they can send one car twice as far. Cars #1..4 set off in parallel. When cars #1 & #3 consume 50% fuel they stop and instantly (this part is magic) give their remaining fuel to cars #2 and #4 respectively. When cars #2 and #4 again have 50% fuel, car #2 stops and (magic again) gives its remaining fuel to car #4. Car #4 now has full fuel tank again and completes the trip. DroneB (talk) 15:39, 17 April 2020 (UTC)

Car #1 is driving on the roof of car #2, car #3 on the roof of car #2, and car #4 on the roof of car #3. Net result is car #4 much greater than Mach 0.25 in the frame of an observer outside the car-stack. Sadly even if we do this as plain vector addion, neglecting all aerodynamic, acceleration-distance, and wobbly-stack concerns, we can only get up to Mach 13.25, as the next Mach 0.25 increment is missing. DMacks (talk) 15:56, 17 April 2020 (UTC)

At User:DroneB's request, I have small'ed my US-centric ancient pop-culture humor. DMacks (talk) 02:24, 20 April 2020 (UTC)

Ooh! Ooh! ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:51, 20 April 2020 (UTC)

Dare I say, the speed and aerodynamics of four cars driving near each other at high velocity are governed by difficult nonlinear equations? 16:14, 17 April 2020 (UTC)

The hell they do. DMacks (talk) 16:20, 17 April 2020 (UTC)

We have a Whitcomb area rule article. DMacks (talk) 14:51, 17 April 2020 (UTC)

thanks! --RM

What is the color of iron(II) selenate???

I'm don't sure that iron(II) selenate will have green colored (penta- and hepta- hydrate). So what is color of this compound??? (Sorry if you don't understand, because my English is not good).--Ccv2020 (talk) 09:55, 17 April 2020 (UTC)

It appears to be a compound without nearly any commercial application; indeed I can't find anything more than confirmation that it is possible to make it. There is not even an MSDS for it [1] which is a dead giveaway that you literally can't buy it anywhere, which will put a crimp on finding pictures of it to check out the color. As such, it is super rare to find anything about it online; the Wikipedia article iron(II) selenate has only one non-print reference, but even that is a scan of a 1918 paper describing its synthesis. I can't find anything at all about it more recently than a few random papers that mention it from the mid 1990s. Your question may not be easily answerable from available information. --Jayron32 12:40, 17 April 2020 (UTC)

Could one estimate it computationally through ligand field theory? Yanping Nora Soong (talk) 14:59, 17 April 2020 (UTC)

Could one? Maybe. Has one? Probably not. --Jayron32 15:02, 17 April 2020 (UTC)

Tutton in the 1918 paper mentioned describes the mother liquor as green but the crystal were very hard to obtain, decomposing quickly with heat and air and he never seems to actually state the color of the crystal itself but notes the red and brown opaque contamination as they decompose. Green is most likely. Having worked on similar crystals, modern inert atmosphere techniques and vacuum systems as well as ice baths would seem to make the synthesis much simpler today but his story of waiting for a record cold snap in a severe winter to run the successful double salt reactions makes for an amusing story. Rmhermen (talk) 04:53, 18 April 2020 (UTC)

I agree green makes sense. Selenate probably adds little too the color, and iron (II) compounds are often a pale green in color.--Jayron32 18:00, 18 April 2020 (UTC)

Why do some scientists keep calling the Warburg effect and aerobic fermentation "inefficient"?

I've been a little confused by these two articles. We're covering these topics in grad school and almost all my lecturers take it as a given that aerobic glycolysis promotes accumulation of biomass (e.g. anabolism) rather than oxidation of carbon-carbon bonds to carbon dioxide (i.e. catabolism). I'm aware there are many nuances, including apoptosis and particular molecular targets or mediators, but overall, this seems like such an obvious driving force. Why do some scientists keep calling aerobic fermentation "inefficient"? Oxidative phosphorylation efficiently produces ATP, but it does not efficiently produce fatty acids to expand the lipid bilayer or new amino acids. Much of our assigned readings and reviews argue that in fact aerobic glycolysis is very efficient at incorporating biomass, just not that efficient at conserving ATP in times of starvation, emphasizing parallels between the "well-fed state" and the "starvation state" at both the systemic and cellular levels. Yanping Nora Soong (talk) 09:57, 17 April 2020 (UTC)

I think they're just alluding to the fact that aerobic respiration releases much more energy per molecule of substrate. At least for most animals I believe fatty acids and amino acids are obtained from the diet if possible; anabolic pathways are mainly used to convert one type into another as needed. De novo synthesis is done mainly to store excess nutrients or when needed in the fasting state, and essential nutrients can't be synthesized de novo at all. Not sure exactly how that goes in other organisms. I mean, I think you're right that calling it "inefficient" is probably an oversimplification. It sounds like people calling it that are thinking in terms of whole multicellular organisms rather than the cellular level.

Side note, but at least for most mammals, anabolism is linked to the well-fed state by insulin. When you're well-fed, high insulin levels promote uptake of nutrients and tissue repair and growth. --47.146.63.87 (talk) 22:54, 17 April 2020 (UTC)

Yes, but for T-cells, yeast and cancer cells alike, who are rapidly proliferating, glucose is a much faster way of obtaining biomass than capture of fatty acids AFAIK. Yanping Nora Soong (talk) 11:34, 20 April 2020 (UTC)

Yes, they're explicitly talking about the inefficient production of ATP per molecule of glucose. Honestly it strikes me as weird to talk about fermentation as being a better route toward biomass accumulation, since this necessarily ignores its last step, which leaves that carbon trapped in a toxic byproduct. And this can't explain the preference for fermentation when carbon is not a limiting factor to growth. But in that case, fermentation still has the advantage of being significantly faster in terms of atp production per unit biomass per unit time. That is, even though respiration generates 16 times the usable energy per glucose, fermentation is so much faster that it can overcome that. Though even that can't fully explain the preference. It's pretty complicated, not fully understood, and numerous models are still being debated. I'd point you to [2] What is generally agreed on is that when a cell is uptaking glucose very quickly, the use of fermentation leads to faster accumulation of biomass, though does not require that fermentation is even the pathway through which the biomass is being accumulated. Someguy1221 (talk) 13:41, 18 April 2020 (UTC)

Proliferating T-cells show Warburg effect-like metabolism ... indeed, any proliferating cell. Does the sheer amount carbon of glucose end up in pyruvate? What about the pentose phosphate pathway? Yanping Nora Soong (talk) 11:34, 20 April 2020 (UTC)

Depends on the cell of course, but most of it leaves as lactate, with glutamine instead being used as a source of carbon for making new molecules. [3]. A lot of microbes also prefer this arrangement. Someguy1221 (talk) 13:12, 21 April 2020 (UTC)

Scientific evidence of possibility of lab theories (Coronavirus)

Is there any scientific basis currently in the politicians claims that the SARS-COV2 could have been accidentally released from a lab? 90.198.251.144 (talk) 11:33, 17 April 2020 (UTC)

It depends on the politicians. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:06, 17 April 2020 (UTC)

No. it is a bullshit conspiracy theory. You should pay it no mind, and become highly suspicious of anyone who claims such nonsense as credible.[4]. In the U.S., the main sources of the "theory" seem to be 1) Fox News 2) the New York Post (basically the print arm of Fox News) and 3) The Trump Administration, who started making public statements about it after Fox News began floating the idea (this is a standard pattern for statements by the Trump administration). In China, a similar theory is that it was created by the U.S. and released in China as a sort of bioweapon.[5]. Both of these are bullshit theories. Nearly all actual reliable sources make it clear two things 1) we don't know much about it at all, and making definitive statements are hard and 2) what we do know seems to lean towards a zoonotic origin, likely a market in Wuhan. See [6] for example. This is probably the best non-press summary about the current understanding. Scientists who are studying the disease most intently have a pretty clear consensus this is of natural origin. The "Made in a lab" bullshit is only coming from news organizations with sketchy reputations and non-scientific government officials with axes to grind. --Jayron32 12:53, 17 April 2020 (UTC)

It is not helpful to conflate "Made in a lab" conspiracy theories with the "naturally occurring virus accidentally released by lab which was studying it" question asked here. For the latter, see Misinformation related to the 2019–20 coronavirus pandemic#Accidental leakage. -- ToE 13:44, 17 April 2020 (UTC)

It's still a bullshit conspiracy theory. You'll note that you linked to the "misinformation" article. --Jayron32 15:01, 17 April 2020 (UTC)

I think it is incorrect to call it a "conspiracy theory" if the theory involves no conspiracies – except for the authorities not coming clean about it, which however is a ubiquitous phenomenon with people in power. Also, it is not impossible; the lab in question studies coronaviruses obtained from wildlife. Accidents happen, and the lab is situated close to the market. However, there is not a thread of non-circumstantial evidence, and specific allegations brought forward that seemingly support the theory appear, on closer inspection, to be made up or in any case incorrect. There is even no certainty that the wet market (or its close surroundings) were the source; it can have been a highly focal but secondary source.  --Lambiam 17:57, 17 April 2020 (UTC)

I agree, it's not a conspiracy theory. However, it's then a bit strange that the accidentally released virus happens to be such a massive problem for us now. If a lab collected coronaviruses from nature for study, then how did they end up with such a problematic virus for us? So, if it really happened this way, then the lab would likely have done experiments like e.g. mixing SARS with other viruses to see if a virus that is more infectious to humans than SARS could arise in nature. Count Iblis (talk) 19:37, 17 April 2020 (UTC)

"Naturally occurring virus accidentally released by lab which was studying it" would be easy to prove if that had happened. Scientific research, including at labs like that in Wuhan, is well documented. Early in working with a virus like this, they would have sequenced its genome (which, in fact, the Chinese did do early on in the outbreak, as there was no genome before the outbreak). That would be a very early step used then to classify any other results they made while studying this viral strain in comparison to other coronaviruses, such as SARS-CoV-1 and MERS. So... where's the documentation? All of the documentation out of Wuhan studying coronaviruses have different genomes than SARS-CoV-2, different enough that it clearly isn't a release from their lab. In my own lab, I could tell you the genome of the strains of infectious bacteria that I work with. I don't just know that I work with Staphylococcus aureus, but I know down to monoclonal strains, such as S. aureus Newman D2C NCTC 10833 or USA-300 strain of MRSA, etc. If the SARS-CoV-2 strain wasn't in their laboratory, they can't have accidentally released it. However, we HAVE found almost identical strains of coronavirus in bats and pangolins, which is why we think they are the likely zoonotic vector (most recently I have seen pangolins to bats to humans). There is a lot of piling evidence for the zoonotic vector, and zero evidence for an accidental lab release. It is still a conspiracy theory, as in order for it to be true, there would have to be a well organized conspiracy to suppress the evidence of a lab release. --OuroborosCobra (talk) 19:44, 17 April 2020 (UTC)

This. --Jayron32 20:09, 17 April 2020 (UTC)

Trump says it's plausible because "that bat wasn't in that area". Count Iblis (talk) 23:47, 17 April 2020 (UTC)

That is a really phenomenal example of an either-or fallacy. Someguy1221 (talk) 13:51, 18 April 2020 (UTC)

Conveniently ignoring the fact that bats fly and pangolins (also involved and the more likely final animal-to-human vector in this case) get moved around by people as part of the food and "traditional medicines" trades. {The poster formerly known as 87.81.230.195} 90.203.117.240 (talk) 03:30, 18 April 2020 (UTC)

If anyone is interested in shaping how our articles cover or don't cover this, they may want to participate in Talk:2019–20 coronavirus pandemic#Leaked from lab, in particular Talk:2019–20 coronavirus pandemic#Break. Nil Einne (talk) 11:39, 18 April 2020 (UTC) 02:55, 19 April 2020 (UTC)

Could presession (rosette-shaped orbits) be explained by gyroscopic effects, due to the orbiting body's spin?

Could presession (rosette-shaped orbits) be explained by gyroscopic effects, due to the orbiting body's spin?

Gyroscopic effects make it harder to change the direction of motion of a spinning object. Correct me if I'm wrong, but I believe this effect would affect the motion of a rotating body that's in an elipse-like orbit, more, when it's furthest from the object that it orbits, where gravity is much weaker, causing the far end of the eliptical orbit to be wider, thus causing presession.

What makes me think of this is the recent news report of confirmation of pressession of a star in an excentric orbit around our galaxy's supermassive black-hole. https://www.abc.net.au/news/2020-04-17/chile-astronomers-discover-star-dancing-einstein-theory/12158154

Secondarily, I'd like to know if it might also be because there's more drag closer to the black-hole due to electromagnetic forces or more dense dust-clouds.

I'm aware of possible relativity-based causes, of presession, however the exact mechanism by which this would cause presession has not been well explained in anything I've read thus-far. MathewMunro (talk) 14:18, 17 April 2020 (UTC)

I don't think so. As long as its mass can be considered equivalent to a mass concentrated in the orbiting body's centre of gravity – which is true if its diameter is small compared to its distance at periapsis from the host body – Newton’s laws govern the orbit (if the local spacetime geometry is flat). Gravity is the only force acting on the point mass.  --Lambiam 15:08, 17 April 2020 (UTC)

Lambian, do you believe that the orbit of a rapidly spinning object will be exactly the same as that of one that doesn't spin? I thought that the additional angular momentum of the rotation of a body around its axis would exert forces on its centre of gravity when it is in a gravitational field. Intuitively, if you try to turn an object like a rapidly spinning bicycle wheel, you notice that there are resistive forces that are not present when the wheel isn't rotating. MathewMunro (talk) 21:39, 17 April 2020 (UTC)

Gyroscopic effects make it harder to change the direction of the spin axis of a rapidly spinning object, but have no effect on the motion of the centre of mass. The spin frequency of an orbiting body can affect the apsidal precession (by creating a gravitational quadrupole moment as the object deforms and by relativistic frame dragging), but that's a very small effect and has nothing to do with gyroscopic effects. Read apsidal precession. Note that the general relativistic part of the apsidal precession in that article is not related to frame dragging. PiusImpavidus (talk) 09:15, 18 April 2020 (UTC)

"Gyroscopic effects make it harder to change the direction of the spin axis of a rapidly spinning object, but have no effect on the motion of the centre of mass." Thanks PiusImpavidus (and Lambian) for clearing up that misconception of mine. MathewMunro (talk) 20:58, 18 April 2020 (UTC)

"as the object deforms" - do you mean essentially tidal effects causing an exchange of angular momentum between the orbiting object and the body it orbits? MathewMunro (talk) 19:09, 18 April 2020 (UTC)

Not really. On the one hand there's tidal deformation of the planet orbiting a star (or a star orbiting a supermassive black hole). The tidal forces don't depend on the spin of the object, but the resulting deformation does. On the other hand there's the equatorial bulge of a spinning body. For symmetry reasons it must work both ways, but usually we can ignore the equatorial bulge of the secondary. With these deformations the body is no longer spherically symmetric and equivalent to a point mass, so apsidal precession will result. PiusImpavidus (talk) 09:58, 19 April 2020 (UTC)

Regarding the equatorial bulge of the central body due to spin, if an equatorial bulge were distributed equally on both sides of the line between the centres of mass of both objects, I don't think it would cause a deviation from elliptical motion. However, if the orbital plane & the central body's axis of rotation were oriented such that the equatorial bulge is sometimes off-centre, it would cause a deviation from elliptical motion, however such a bulge is not necessarily going to be offset by the same amount each time like a tidal-bulge is, so it wouldn't cause consistent apsidal precession. MathewMunro (talk) 13:07, 19 April 2020 (UTC)

Consider a spinning planet with its spin axis perpendicular to its orbital plane. The equatorial bulge moves mass from the poles to the equator. Some of this mass ends up at the terminator, sunset or sunrise. This is at the same distance from the star as the poles, so it doesn't affect gravity. Some of it ends up at the places where it's noon or midnight. This moves the mass towards the star or away from it, in the same way as tidal bulges do. The mass moving to the noon side cause a larger increase in gravity than the decrease coming from the mass going to the midnight side, and the effect is stronger when the planet is closer to the star. The effect does not rely on a misalignment between the axes of the ellipsoid of the planet and the line connecting the planet to the star. Redistributing the mass from a point at the centre of the planet to a spherically symmetric shell around it does not have this effect, as most of the surface area of the shell is further away from the star than the centre is, which exactly compensates for the larger increase in gravity for the parts that get closer to the star. PiusImpavidus (talk) 10:31, 20 April 2020 (UTC)

Thanks again PiusImpavidus. What would be the effect of equitorial bulge in the secondary on its orbit? I'm guessing that it would accelerate near the periapsis more than a non-rotating body would, which I'm guessing would swing it wide (negative aspidal presession), and increase eccentricity (although of course, other effects may dominate, and probably do, as most talk seems to be of positive rather than negative aspidal presession).

I'm also guessing that a body in an eliptical orbit, even a non-rotating one, would experience a torque for reasons similar to the ones you describe above (due to the side that is closer to the primary being pulled more strongly than the other side, and the net force being mis-aligned with the centre of mass of the secondary other than when it's travelling perpendicularly to the primary, at the apsis). I'm guessing that in the case of positive aspidal presession, due to asymmetry, there would be a net torque in one direction, I'm guessing it's in the counter-orbital spin direction. Your thoughts? MathewMunro (talk) 11:50, 21 April 2020 (UTC)

Also, since scientists are able to calculate the theoretical effect of spacetime curvature on the orbit very precisely (see Two-body problem in general relativity), the observed precession is adequately described by the theory (but perhaps not by anything you've read).  --Lambiam 15:20, 17 April 2020 (UTC)

Does the OP mean Apsidal precession, Axial precession, or Nodal precession? --Jayron32 15:14, 17 April 2020 (UTC)

The recently observed precession using the Very Large Telescope is reportedly apsidal.^[7]  --Lambiam 15:20, 17 April 2020 (UTC)

The star in question, S2, is at periapsis still 18 billion kilometres away from the black hole. For comparison, that is four times the distance of Neptune from the Sun. It is not plausible that dust clouds have a significant (observable) effect. If they did, causing the orbiting body to lose kinetic energy, the effect would not be precession but inward spiraling.  --Lambiam 15:30, 17 April 2020 (UTC)

Lambian, you wrote that "the effect [of gas-drag] would not be precession but inward spiraling", but might it be counterbalanced by a phenomenon known as "tidal despinning and orbital expansion", as described in this article: https://www.planetary.org/blogs/guest-blogs/2016/1017-rapidly-rotating-regular-satellites-and-tides.html (written by an orbital dynamicist and Associate Professor of Physics). "our own Moon is thought to have been mostly formed at a distance of ~3 Earth radii... Tides are then invoked to move it to its current position at ~60 Earth radii." MathewMunro (talk) 21:28, 17 April 2020 (UTC)

Lambian, there may be much more gas in the vicinity of the galactic centre than you think, even extending out to the range of S2's orbit. Refer to: https://www.mpg.de/8777573/gas-cloud-galactic-centre and https://www.sciencealert.com/strange-objects-have-been-found-orbiting-our-galaxy-s-supermassive-black-hole

The first article shows a picture of the massive gas clouds G1 & G2 whose orbit took them across the path of S2. The second article mentions that in passing close to the galactic centre, they shed outer layers of gas. It also refers to four other similar gas clouds, and suggests that binary star orbits may be destabilised by proximity to the supermassive black-hole, resulting in relatively frequent creation of gas clouds.

Another factor that might be relevant is solar-wind density being greater closer to the galactic centre. MathewMunro (talk) 00:57, 18 April 2020 (UTC)

Tidal locking is caused by a drag-like effect within the rotating body. It has nothing to do with drag caused by the interstellar medium. 93.136.29.149 (talk) 20:20, 18 April 2020 (UTC)

93.136.29.149, S2 would not be in tidal lock with the supermassive black hole. Tidal acceleration (or retardation) likely affects its orbit though. Tidal acceleration would speed-up an object in an eliptical orbit more at the periapsis than at the apoapsis, and if it's in a prograde orbit, that would cause retrograde apsidal presession (however S2 was observed to exhibit prograde apsidal presession), as well as making the orbit larger and more excentric, whereas a retrograde orbit, would have the opposite effect.

It's hard to know what the effect of interstellar medium would have higher average momentum in an outward direction due to sling-shot effects, imparting a net positive kinetic energy and gravitational potential energy to S2, or it may generally cause drag, and more so nearer the periapsis. It clumps and its density varies in a non-systematic way.

Accretion-disk radiation-pressure, would also be greater closer to the black-hole, by a factor greater than the square of the distance between the bodies, because the radiation is not only spreading-out in an inverse-squared way, but also being reduced in intensity as it climbs against gravity. It would also be offset from the black-hole's centre of mass to the approaching side of the accretion disk (presuming it's rotating as most are thought to), due to red or blue-shifting, which would contribute to apsidal presession, consistently.

And there's an inverse r to the sixth power involved in the tidal formulas. So these things may combine in a way that causes apsidal presession without noticable orbital expansion or contraction.

Without knowing the magnitude of all these things, I think it's jumping to conclusions to say that the apsidal presession of S2 proves General Relativity as the mass-media tends to. MathewMunro (talk) 10:57, 20 April 2020 (UTC)

I think we can safely say that electromagnetic effects are negligible. The accretion disk of the supermassive black hole in our Galaxy isn't particularly bright. PiusImpavidus (talk) 09:58, 19 April 2020 (UTC)

I don't know. The radiation pressure article says: "had the effects of the sun's radiation pressure on the spacecraft of the Viking program been ignored, the spacecraft would have missed Mars' orbit by about 15,000 km". Sagitarius A* has been described as "very bright" in radio frequencies. How does it compare to the sun for typical total electromagnetic energy output? MathewMunro (talk) 14:14, 19 April 2020 (UTC)

When I take the mass of the Viking probes and divide it by surface area pointing towards the Sun, I get about 200 kg/m². When I do this for star S2, I get about 5E11 kg/m². Radiation pressure acts on the surface turned towards the radiation source, gravity acts on the mass. So the effect of radiation pressure on the Viking probes, compared to gravity, was about 2.5 billion times stronger than on a star like S2 under the same circumstances. Add to this that Sgr A* is a particularly strong source of gravity (a few million times stronger than the sun). Sgr A* is a strong radio source, but there's little energy and momentum in radio waves. It's also a significant X-ray source, but that's relative: the entire Galaxy is quite dim in X-rays. In optical, you can't even see Sgr A* in images where you can see S2. PiusImpavidus (talk) 10:31, 20 April 2020 (UTC)

Thanks PiusImpavidus, nice. I wonder if the huge mass of Sgr A* would also make tides (and possibly even its own equatorial bulge) relatively less significant in a similar way? And is the mass of the accretion disk likely to be significant? MathewMunro (talk) 11:05, 20 April 2020 (UTC)

If you take a look through this user's contributions, they've come here before to push their pet physics "theory" that totally demolishes relativity. They appear to be here to just ask questions, not to learn. --47.146.63.87 (talk) 22:15, 17 April 2020 (UTC)

47.146.63.87 I deleted your irrelevant and rude contribution once already, as it was not worthy of a reply. Please kindly desist your disruptive editing. MathewMunro (talk) 01:03, 18 April 2020 (UTC)