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November 11

Cleveland rat-squirrel ?

There seems to be a new species of rodent just SE of Cleveland, Ohio. It looks mostly like a squirrel, but is smaller, has a less fluffy tail, and is more aggressive towards humans. Any idea what it is ? SinisterLefty (talk) 06:49, 11 November 2019 (UTC)

Look like this? -- The source is dubious, but they call it a "sqrat". 2606:A000:1126:28D:25BA:5B02:33E7:A409 (talk) 09:04, 11 November 2019 (UTC)

Yea, that looks like it. The 2 useful suggestions there were that it was mange or that the squirrels plucked their tails for nesting material. The mange theory doesn't explain why it's only the tail. Maybe there's a new squirrel-tail mange mite that specializes in just that ? That might also explain the smaller size, if the parasites drain them of nutrients. But when I've seen mangy animals it's typically patchy hair loss, not as uniform as this. As for the plucking for nest material theory, that doesn't explain why there are so many more like that recently. Neither theory explains why they would be more aggressive towards humans. SinisterLefty (talk) 11:28, 11 November 2019 (UTC)

sorry, but this irresistibly draw this to my mind Gem fr (talk) 15:01, 11 November 2019 (UTC)

• Here's an article about them that seems pretty solid. --Jayron32 12:43, 13 November 2019 (UTC)

What size of sink is needed to truely demonstrate Coriolis effect at the equator?

There are these bogus demonstrations where two sinks are a meter apart with the equator between them, and water rotates one way in the north and the other way in the south.

What size of sink will really demonstrate it? — Preceding unsigned comment added by 77.124.56.240 (talk) 21:10, 11 November 2019 (UTC)

Somewhere between the size of the Great Lakes and the size of an ocean ? I say this because the Great Lakes [1] don't show the same rotation as ocean currents. Now the shape of the sea floor and beaches, and inflow and outflow points, do contribute, but still I'd expect to see more rotation than I do, if the Coriolis effect was a major factor in lake currents. SinisterLefty (talk) 22:00, 11 November 2019 (UTC)

See[2] where it says:

Coriolis forces are best observed at a large scale...In your tub, such factors as any small asymmetry of the shape of the drain will determine which direction the circulation occurs. Even in a tub having a perfectly symmetric drain, the circulation direction will be primarily influenced by any residual currents in the bathtub left over from the time when it was filled. It can take more than a day for such residual currents to subside completely. If all extraneous influences (including air currents) can be reduced below a certain level, one apparently can observe that drains do consistently drain in different directions in the two hemispheres.

You can estimate the magnitude effect by applying conservation of angular momentum. For simplicity assume that the basin of water is the same shape as the plug hole (circular) and that the hole is central. For more simplicity let the experiment initially be performed at the north or south pole of the earth (which will maximize the effect).

Before the plug is pulled, the basin and water are rotating with the earth, once in just under 24 hours. When the plug is pulled, the water moves towards the centre and the radius of rotation of each particle of water ultimately decreases in proportion to the radius of the hole to the radius of the basin - say a factor of 1/n. Conservation of angular momentum demands that the angular velocity increases by a factor of n², so the period of rotation decreases by a factor of n². Thus, if the radius of the basin is 100 times that of the hole, the water ends up rotating once in about 24hr/100² ~ 8.6sec - not hugely fast, but possibly discernible.

If the experiment is performed at a lower latitude, the period of rotation is multiplied by (probably) the sine of the latitude (see Foucault pendulum). catslash (talk) 00:24, 12 November 2019 (UTC)

Further to the above, note that the original poster asked about bogus demonstrations with sinks "a meter apart with the equator between them". Now one nautical mile is defined as 1,852 m and corresponds pretty nearly to one minute of latitude. Therefore a position 0.5 m from the equator corresponds to a latitude of 0.5/1,852 of a minute north or south. According to units this angle is equal to about 1/12,700,000 of a radian, and therefore, using the small-angle approximation, its sine is also about 1/12,700,000. So the force is so slight that no such practical demonstration is possible using anything smaller than a sizable lake. (And of course, a sizable lake would have to be farther from the equator to be all one one side of it, requiring a new calculation. But even at say 100 km from the equator, the sine of the latitude is about 1/64,000.) --76.69.116.4 (talk) 09:49, 12 November 2019 (UTC)

In OR, an actual bath tub filled nearly to the top, at above 52°N and drained after standing for a few days showed no obvious rotation. The water appeared to go straight down, right to the dregs. catslash (talk) 00:34, 12 November 2019 (UTC)

Thanks for that. I've never tried leaving the water to stand like that and the bath water has always had a vortex one way or the other for me - except for one time when it disappeared straight down the plughole just like you describe. I was really astonished. It emptied far faster than usual. If somebody could get it to happen again and take a video they'd have a winner. Dmcq (talk) 19:40, 13 November 2019 (UTC)

• Look at Rossby number for a way to quantify this. It's the ratio of the forces for the inertial and Coriolis forces. If Coriolis is greater, then rotation follows the relevant direction for each hemisphere, otherwise it depends on the initial conditions instead. For weather systems, the larger they are, the more likely they are to follow the Coriolis direction. Smaller systems can (and do) go either way. Andy Dingley (talk) 01:12, 12 November 2019 (UTC)

OP here, I am confused. I do not feel ashamed to admit the math and physics in the articles are above me. Is there any straight answer? — Preceding unsigned comment added by 77.124.56.240 (talk) 10:04, 12 November 2019 (UTC)

• We really do need better coverage in the weather articles which shows a comparison list of low-pressure system by their size, so that we can easily see how their behaviour changes according to size. Most large scale weather arises through a similar means, warm air cooling down and its pressure dropping, but what that then turns into depends so much on how big a mass of air is acting as one.

You need to get to the point of having an idea what Rossby number means (even without the maths). It's the ratio between the non-Coriolis forces and the Coriolis forces. The Coriolis forces are weak, but increase with size of the system. So small systems ignore Coriolis, large ones (hurricane and upwards) are affected by it. Middle-size ones might be. Your bathroom sink is so much smaller than any of this that Coriolis is just insignificant.

Smaller than a hurricane (and that includes tornadoes) and they rotate either way, depending on the starting conditions. Try a circular bathroom sink in the UK. Sometimes you can demonstrate this as "Hot water rotates one way, cold water rotates the other". The trick is that in the UK we still mostly have two separate taps, not single mixers, and that water enters the basin with pre-existing spin, depending on which side the tap was mounted. This rotation continues for enough time for you to then pull the plug and demonstrate rotation during emptying, with either direction of rotation, and predictably.

There's also the ice skater effect. The rotational energy stays mostly constant (it's lost, but only slowly) and so if a rotating system shrinks in diameter, then it has to speed up. So in your "big funnel by the side of the equatorial road" sideshow example, it might start off with no discernible rotation in the water, but as it approaches the plughole it speeds up so obviously - we've all seen this in the bathroom. Now what you're seeing there is conservation of angular momentum, not Coriolis, but it's great sideshow patter to present it that way. Andy Dingley (talk) 11:21, 12 November 2019 (UTC)

As Andy Dingley explains, it won't work with a draining sink. The forces are just too small, especially near the equator. These forces are strongest at the poles and zero on the equator. At higher latitudes the effect can be seen from a Foucault pendulum (if you have patience, at my location it is takes over a day). Rmvandijk (talk) 12:55, 12 November 2019 (UTC)

What with, say, 500Km sink (well, reservoir). The question came form an argument I had with guys who saw this YouTube vid. So for the sake of the argument i wanted to say what terribly large "sink" will be required.

I think I got the general idea of this Mossby number: Larger than 1 - Coriolis not effective. lower than one - effective. But to get proper answer I need to do calculation like the angles sinus from above, and even than I will surely mess things up. If you guys can lend a hand that will be great. Just think of enlighting the uneducated... — Preceding unsigned comment added by אילן שמעוני (talk • contribs) 13:35, 12 November 2019 (UTC)

Did some moss grow on the Rossby number ? :-) SinisterLefty (talk) 13:46, 12 November 2019 (UTC)

• It depends on the relative density of air and water too. But for air you need something the size of a hurricane, so even though denser water allows you to do the same at a smaller scale, that's still bigger for "the sink" than any building to put it in.

Also, as noted, the Equator itself (nearby to it on either side) is just the wrong place to do this, as it's where the forces are smallest.

I've built Foucault's pendulums myself. They're not trivial either, but you can do it for a school science project, if you have a way to hang a weight from the top of a gym roof. One of mine is still running in a science museum - that's about 50 lbs of concrete in an oil drum, dressed up on the outside. Andy Dingley (talk) 15:23, 12 November 2019 (UTC)

I'm trying to get to the point where I can say confidently "Sure mate, you only need like 500Km (approx. 300 miles) wide sink and it will work out just fine...". With air it wouldn't have that impact. — Preceding unsigned comment added by אילן שמעוני (talk • contribs) 17:36, 12 November 2019 (UTC)

It's not going to have a sharp cut-off, due to all the factors listed, but 500 km would be a fine approximation. SinisterLefty (talk) 17:39, 12 November 2019 (UTC)

November 13

Fungus eggs?

Clathrus ruber "eggs"? No they are not pretty, sorry. No really... These ones are called "Stinkhorn baskets" (baskets are the cute ones)

Hallo, various species of fungus produce what are called "eggs" or sometimes "fruiting body". What is the proper term for that? Sporocarp (fungus) and spore don't specifically cover it. ~ R.T.G 00:28, 13 November 2019 (UTC)

Fruiting body or "sporocarp" is the correct name. They don't all resemble eggs. Many resemble flowers. And then there are mushrooms. I don't see anything obvious missing from the the article. SinisterLefty (talk) 01:10, 13 November 2019 (UTC)

In my unqualified opinion, they seem to be unique enough to require a further categorisation and seem to be called "eggs" so often I checked to see if I couldn't start an article, but I just wanted to find something focused specifically on the "eggs". It feels like they are mentioned endlessly but without any deep focus. Might still be possible, but so much easier if I found a book or two called "This is what a fungus egg is!" xP ~ R.T.G 01:29, 13 November 2019 (UTC)

Functionally they are the same, whether egg-shaped, flower-shaped, or mushroom-shaped. So, the shape isn't all that important to mycology. SinisterLefty (talk) 01:39, 13 November 2019 (UTC)

See puffball. 85.76.45.42 (talk) 09:59, 13 November 2019 (UTC)

Now wait. This thing is not like a sporocarp or a puffball. This thing doesn't spray. It seeds[fruits]. Birds [Insects] eat this stuff and spread it. ~ R.T.G 19:38, 13 November 2019 (UTC)

Are you sure about that ? I'm not aware of a fungus with spores able to survive digestion. SinisterLefty (talk) 04:19, 14 November 2019 (UTC)

Sorry, not birds, but "flies, other insects, and, in one report, a scarab beetle," (according to Wikipedia..). It's called the Clathrus ruber. The word spore conjures me an image of a floating dust particle, but in fact, that's not what a spore is. According to Spore#By_mobility, some spores swim. Also according to that article, "the difference between a "spore" and a "gamete" is that a spore will germinate and develop into a sporeling, while a gamete needs to combine with another gamete to form a zygote" and ""The main difference between spores and seeds as dispersal units is that spores are unicellular". These statements are unreferenced. Should we be changing it? ~ R.T.G 10:36, 14 November 2019 (UTC)

Birds nest peridioles

Cannonball peridioles

It imitates rotting flesh instead! I suppose an article is possible, but I don't want to give it a COMMONNAME like fungal "eggs". There are others. "Birds nest fungus" Nidulariaceae#History says, "these fungi were the subject of some controversy regarding whether the peridioles were seeds, and the mechanism by which they were dispersed in nature. ... French botanist Jean-Jacques Paulet, ... proposed the erroneous notion that peridioles were ejected from the fruiting bodies by some sort of spring mechanism." (also Cyathus) In fact, water from raindrops splashes them out, and that is called a peridiole (not a spore). Even the BBC are calling the calthrus version an "egg" (they all using the quotations, hence my over-quotation). Cannonball fungus flicks the peridiole out with a spring. According to Ambrosia beetle, some fungi are clonal. Still reckon there is a suitable name for that egg. ~ R.T.G 11:39, 14 November 2019 (UTC)

Note that I don't believe all fungi spores dispered via insects are eaten see e.g. [3] [4]. Some may simply on sticking to the insect, ala pollen. That said, some do. However I'm not particularly aware of any that rely on birds, at least by themselves. There is this [5], but it sounds like it's rely on the plant to attract the bird rather than attracting the bird itself. Which highlights a key point, for this measure to be successful, the fungi will need to be able to attract some bird, so I'm wondering which do that? Rotting meat smell doesn't sound like something which would attract birds. Even 'Rafflesia' and similar attract insects not birds. Not all do that, e.g. I don't think it's accurate to say the truffle relies on a rotting meat smell but it's still something which is unlikely to attract birds. Nil Einne (talk) 00:41, 15 November 2019 (UTC)

There are carrion-eating birds. SinisterLefty (talk) 01:12, 15 November 2019 (UTC)

Nl Einnes second link here says there is "plenty of evidence" regarding birds dispersing so I suppose I got that reading an external link, and these links are great and comprehensive, however they still don't focus on the somewhat unique stinkhorn "egg". I suppose they are peridiolum and they only look unique to me because of the lattice. Not seen anything quite like it, unappealing though it is. ~ R.T.G 13:40, 16 November 2019 (UTC)

There are (plant) flowers which simulate rotting flesh to attract insects for pollination, or to eat them. SinisterLefty (talk) 20:41, 16 November 2019 (UTC)

Effects of sensory deprivation tank (floating) without tank or drugs

Good Day

I am wondering if it is possible to have similar effects like in a sensory deprivation tank (“floating”) without the use of a tank or drugs.

Thank you very much for your answers!

With kind regards--2A02:120B:C3E7:E650:18C8:AAB0:523A:9250 (talk) 01:09, 13 November 2019 (UTC)

To some extent. A soundproof, lightproof room will help. Still, there will be odors, and slight wind currents, and you will feel pressure points where you are sitting or lying down. When stimuli are few, those that do exist seem to grab your attention. SinisterLefty (talk) 01:20, 13 November 2019 (UTC)

Spending an evening with an insurance salesman could do the trick. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:35, 13 November 2019 (UTC)

I suppose the ultimate in sensory deprivation would be to sever the nerves going to the brain, being careful to leave those coming from the brain intact. That would be foolhardy, now, as there would be no way to reconnect them all correctly. But, with future technology, this might be possible, and even desirable, say for burn patients with pain throughout their body. SinisterLefty (talk) 03:40, 13 November 2019 (UTC)

Meditation will do this, though for most people those states require competent teaching and a lot of practice.--Shantavira|^{feed me} 08:59, 13 November 2019 (UTC)

Toward the end of Surely You're Joking, Mr. Feynman!, the chapter Altered States memorializes the experiences of one famous physicist on exactly this topic, including his experiences with sensory deprivation tanks and the altered state of mind he experienced. For the most part, Mr. Feynman did not participate in heavy drug use, because he respected the physiology of his own brain, and did not "want to screw up the machine."

I would not endorse everything that Mr. Feynman tried: he initially documents his sensory deprivation efforts while completely sober, but he also participated in sensory-deprivation tanks under the influence of prescription drugs including ketamine. Although that might be an ill-advised life-choice for the recreational physicist - consult your personal physician! - we can at least learn from Feynman: "I got this strange kind of feeling which I've never been able to figure out when I tried to characterize what the effect was." The chapter then proceeds to describe his experiences and non-experiences with the sensory deprivation tanks, including what he calls "hallucination" and out-of-body experiences.

When I want to get high and float - "without the use of a tank or drugs" - I prefer to separate myself from the surface of the Earth. With enough discipline, this can be safely conducted in compliance with good medical self-care and all local, state, and federal laws; and it's a lot safer than playing with psychoactive chemicals. On the other hand, it's probably more expensive than a sensory-deprivation tank.

It is said that astronauts experience the overview effect - a "cognitive shift." If I may wax a bit poetic, at the expense of a little bit of accuracy: that grandeur described by the astronauts is simply the most severe form of the psychological disorders related to hypoxia; and with enough effort, we can all experience it in small doses ... and with the right type of vessel, we can even make ourselves float.

And so far as sensory deprivation: there is probably no more effective way to isolate a human from their sensory perception than night IMC. If you can imagine nothing - you are nearly there; and it is absolutely an altered state of mind that fuses the most intense cognitive focus with the most intense absence of meaningful sensory stimuli. As described by Shantavira, this type of scenario absolutely requires "competent teaching and a lot of practice," especially if you plan to ever get out of it. To directly quote one of our books of great wisdom and knowledge: "disregard your sensory perceptions." (17-10.8).

Nimur (talk) 15:05, 13 November 2019 (UTC)

• List of bodies of water by salinity. ~ R.T.G 01:26, 14 November 2019 (UTC)

Insularia Canaria

From one of our foreign language Wikipedias, Did you know that the Canary Islands are not named after birds but rather after dogs as the Latin Insularia Canaria translates to Islands of Dogs. While interesting this reminded me that when I was there I took a boat trip around one of the islands and noted that there were no birds. No birds anywhere on the island. Also there was no sign of birds such as guano on the rocks. I asked the tour guide who was able to confirm that he had never seen a bird there but that he had not really noticed until I pointed this out and that he was not able to explain the absence of birds. One would expect that like most oceanic islands, it would have a healthy population of birds, yet they are conspicuously absent. Why? Thank Anton 81.131.40.58 (talk) 15:16, 13 November 2019 (UTC)

Maybe the dogs ate them all? No, actually there are plenty of birds. See Category:Birds of the Canary Islands. I suspect your tour guide was just pulling your drumstick. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:37, 13 November 2019 (UTC)

Introduced species, like house cats, can decimate bird species on an island. I don't know if this happened there, though. Eventually, either the native species of birds would adapt to survive, or new bird species, which are able to survive with predators around, would move in. One important adaptation would be nesting in trees instead of on the ground (cats can generally only climb the trunk, not out on branches). SinisterLefty (talk) 16:57, 13 November 2019 (UTC)

The article Atlantic canary indicates it was named for the islands, and by implication it is quite common there - except for a couple of the islands in the chain where it is much less common. Maybe one of them is the island you were touring? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:07, 13 November 2019 (UTC)

Having just come back from Tenerife, I can confirm that we saw both seabirds (gulls, I think) and songbirds (unidentified species ;-), though maybe less than you would expect. --Stephan Schulz (talk) 00:16, 14 November 2019 (UTC)

Birdwatching Spain says: "Birding trip to the Canary Islands: You won’t see a large number of birds but that is not the point as these beautiful islands hold a nice combination of endemic birds, Macaronesian specialities and African species... The endemic birds list includes: Laurel Forest Pigeon, Bolle's Pigeon, Fuerteventura Stonechat, Canary Islands Chiffchaff, Tenerife Goldcrest and Blue Chaffinch". Alansplodge (talk) 17:16, 14 November 2019 (UTC)

On a trip to Tenerife two years ago I saw the local chaffinches, chiffchaffs, goldcrests and blue tits, no end of canaries, Sardinian warblers and the occasional buzzard. The number of species is less than for some islands, although migrants are quite common, but the Canaries are quite remote, and the birds have to get there. Mikenorton (talk) 22:08, 14 November 2019 (UTC)

The OP needs to get back here and explain some things. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:08, 14 November 2019 (UTC)

Not sure what you want me to answer. When I went to Tenerife I saw no birds whatsoever and hence my question. Please see WP rules about being nice, Bugs and Jayron. Bullying is not appreciated and could see you banned. Anyone is allowed to ask a question, and anyone is allowed to answer. Anton 81.131.40.58 (talk) 12:17, 15 November 2019 (UTC)

You answered it: Tenerife. And as others have noted here, there are birds at Tenerife. For whatever reason, you didn't see them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:53, 15 November 2019 (UTC)

Yes, they should be nicer. Also, you might be more careful in how you ask questions. In this case instead of saying there were "No birds anywhere on the island" say "I didn't see any birds anywhere on Tenerife". The first statement is false, while the second is presumably true. Many people here are sticklers for details like that. SinisterLefty (talk) 18:55, 15 November 2019 (UTC)

Maybe what the OP didn't see are migratory birds. Tenerife has a hot and desertly dry climate in summer. It might be a good target or stopover for Europe's plentiful migratory birds in winter, but in summer these would be in Europe. If OP visited in summer he would only be able to see year-round birds. 93.136.94.213 (talk) 06:36, 17 November 2019 (UTC)

November 14

Enthalpy of fusion

A solid crystal (such as ice) is a more ordered state than water, so one would expect that when transitioning from water to ice extra energy is expended to order the atoms in the ice crystal lattice. When ice melts back into water, I would expect that that energy that had been bound into the system gets released, so melting would be an exothermic reaction. Yet it seems that melting a solid actually binds energy. The example in the article clearly states that it takes 333.55 kJ/kg extra energy just to move from 0C solid to 0C liquid water. Why is that so? Where is the fault in my conceptual model? 93.136.57.235 (talk) 00:09, 14 November 2019 (UTC)

In a simple form, the answer is right there in the article: ``The liquid phase has a higher internal energy than the solid phase. This means energy must be supplied to a solid in order to melt it and energy is released from a liquid when it freezes, because the molecules in the liquid experience weaker intermolecular forces and so have a higher potential energy (a kind of bond-dissociation energy for intermolecular forces). `` This is true for all solid-liquid transitions (unless quantum-mechanical effects become dominant and stabilize the liquid phase even at T = 0K, but that's irrelevant for this discussion). The volume may increase (normal transition) or decrease (anomalous transition, as water has at about 1 atm of pressure) but the key is that the internal energy of a liquid is always higher than that of a solid. Hope this helps. Dr Dima (talk) 00:55, 14 November 2019 (UTC) . To add, I don't really like the "weaker intermolecular forces" formulation in the article because, first, the enthalpy of fusion is positive for all materials undergoing first-order solid-liquid transition: metals, molecular solids, etc.; and second, because the forces are not necessarily weaker per se, but rather because the melting causes the atoms / ions / molecules to move against those forces, that is, to perform work (for which the energy must be supplied from outside), hence the positive enthalpy of fusion. Dr Dima (talk) 01:04, 14 November 2019 (UTC)

Yes I see that it has a higher internal energy, but why? It's a more disordered state. I see an analogy with a tower of bricks arranged one atop of another, which obviously has more "energy" (in this case gravitational potentional energy) than a pile of collapsed bricks, which is obviously the opposite of what is the case with states of matter. What analogy works here instead? 93.136.57.235 (talk) 01:16, 14 November 2019 (UTC)

Hmm I thought about this some more, thank you for reminding me that in a crystal atoms have to first overcome the forces holding them in stable symmetry to create the disorder that is a liquid. But when you look at it from the opposite side, the freezing, then energy is obtained from the system by binding it in this highly organized and improbable state? Why isn't that a violation of the law that entropy always increases? 93.136.57.235 (talk) 01:27, 14 November 2019 (UTC)

Its called Phase transition and water is a special case. See Liquid-liquid critical point.--Kharon (talk) 04:41, 14 November 2019 (UTC)

Are we talking about the same thing? The article Enthalpy of fusion lists positive enthalpies for a bunch of substances and only helium is mentioned as an exception (which I was taught in school never freezes). 93.136.94.213 (talk) 06:29, 17 November 2019 (UTC) (OP)

Water molecules have two positively charges hydrogen atoms and one negatively charged oxygen atom. In ice the molecules are arranged such that the hydrogen atoms of one molecule point at the oxygen atom of its neighbour. This gives lower internal energy. Our article on ice I_h has a picture attempting to show the crystal structure.

You forgot about the containment of the bricks in your brick analogy. Take a vertical tube and neatly stack the bricks inside. Now take an identical vertical tube and randomly throw the same number of bricks into it. The second pile of bricks will be higher. Or, starting from a random pile of bricks, reorder them on the same surface area in a regular pattern, like a road surface. You'll get them in a lower energy state.

The Second Law only tells us that entropy can never decrease in a closed system. A bucket of water being frozen isn't a closed system. Heat is flowing out of it, along with entropy. PiusImpavidus (talk) 11:09, 14 November 2019 (UTC)

Yeah, I forgot that entropy can decrease in one place while increasing in another, of course that makes sense. I've come up with a way of conceptualizing the positive heat of solidification: as the avg kinetic energy drops, at some temperature particles encountering a crystal formation don't have enough energy to escape being bound into it, and that energy is when moving a good bit faster than zero speed (which would be necessary to get stuck if there were no binding forces). But this drop into a lower energy state means some heat must be created, maybe particles knocking into the crystal transfer their momentum while being bound into it and increase its own temperature so that little crystals quickly blow apart if the temperature is a little too high. On the other hand big crystals maybe dissipate energy from collisions amongst its particles better so take extra energy input in form of even faster-moving than freezing-speed particles to melt (kinda like launching something out of a gravity well, you need to make it move faster than the speed you want it to move at when it's out of the well, which is here the enthalpy of fusion).

Is my model realistic? That would explain seed crystals phenomenon and why for example water freezes quickly but snow melts slowly at the same ΔT from freezing point. 93.136.94.213 (talk) 06:29, 17 November 2019 (UTC)

Your "model" is not too wrong, but it is not entirely correct either. At the molecular level there is no such thing as "dissipating energy from collisions" (i.e. inelastic collisions), and there is no "collision" in solids except for a very weird definition of the term.

As for the kinetics of melting/freezing, that is mostly due to nucleation problems (see subcooling and supercooling). The basic model for supercooling is that small crystals are unstable because they have a small volume to surface ratio hence surface tension effects (which do not like the solid/liquid interface) are higher than the energy win from a better organization in the bulk; hence you need to go through an energy barrier to create a "germ" i.e. a crystal above the critical volume. (Yet more nitpicking: critical germ size is usually about a few hundred atoms so "surface tension" is not really a thing at this scale either.) Tigraan^{Click here to contact me} 10:56, 18 November 2019 (UTC)

Separate question
So water boiling to steam (at boiling point) and melting of ice (at room temp) are both endothermic? And water is a rare exception? What other compounds/molecules fit this criteria? 67.175.224.138 (talk) 15:31, 16 November 2019 (UTC).

• Melting#As_a_first-order_phase_transition says that melting is endothermic except for two pathological cases (helium close to absolute zero), and so is boiling. Water is no exception here. Water does have a pathological phase diagram (as the article says: Water is an exception which has a solid-liquid boundary with negative slope so that the melting point decreases with pressure., which is not usual - but the enthalpy of fusion is still positive). Tigraan^{Click here to contact me} 10:37, 18 November 2019 (UTC)

Relativistic jets and black holes

Reading the article on relativistic jets, I get the impression that they can be produced by black holes. But black holes absorb all matter with nothing escaping. What's the relationship between relativistic jets and black holes? How are relativistic jets produced? 5225C (talk) 00:58, 14 November 2019 (UTC)

They are created by the accretion disk, which is outside the event horizon of the black hole (the point of no return). SinisterLefty (talk) 03:23, 14 November 2019 (UTC)

My layman's impression is that it's a situation similar to the gravity assist. Matter is attracted from somewhere else to the vicinity of the black hole, does a pirouette outside the event horizon and gets accelerated and focused in a narrow beam by some mechanism. You'll have to ask someone else what that particular mechanism is. I suspect it's extracting work from the rotation in case of a rotating black hole, but no idea for when the hole isn't rotating. 93.136.57.235 (talk) 03:53, 14 November 2019 (UTC)

Obviously some black holes dont absorb everything. Quasars have already been found in the 1960s to typically develope these jets. So science knows for 60 years now that black holes dont absorb everything. --Kharon (talk) 05:14, 14 November 2019 (UTC)

If you google "black hole accretion disk magnetic field" you can find lots of articles and images and mathematical models of the magnetic fields around a black hole. The black hole itself is expected to have little to no innate magnetic field, but the accretion disk around the black hole can have a strong one. These magnetic fields are what accelerate charged particles, successfully launching some of them away. Someguy1221 (talk) 06:01, 14 November 2019 (UTC)

To elaborate: matter only gets "absorbed" into a black hole if it passes the event horizon. Outside the event horizon, a black hole behaves just like any other massive object; matter can orbit the black hole, or fall towards it and get flung away, as long as its trajectory does not cross the event horizon. Black holes aren't "cosmic vacuum cleaners", any more than stars are. --47.146.63.87 (talk) 11:01, 14 November 2019 (UTC)

Last and maybe least - there is a maximum rate to a black hole matter consumption. The maximum input is a single neutron layer with in the density of a neutron star, all around the event horizon. anything beyond this will either accumulate or flung away. אילן שמעוני (talk) 15:14, 14 November 2019 (UTC)

Yes, think of it like water trying to go down a drain, or the The Three Stooges all trying to get through the same doorway at once [6]. :-) SinisterLefty (talk) 17:07, 14 November 2019 (UTC)

The saying is that "black holes are messy eaters". [7] --Amble (talk) 17:57, 14 November 2019 (UTC)

Like so [8]. :-) SinisterLefty (talk) 18:02, 14 November 2019 (UTC)

"medical oxygen"

What's the concentration level of oxygen in a standard medical oxygen gas which is normally found in ambulances or hospitals? Should it contain some percent of nitrogen too? 93.126.116.89 (talk) 20:14, 14 November 2019 (UTC)

I'm an EMT and administer oxygen to patients routinely. We always treat it, and do calculations, as if it's 100% oxygen. Of course, minor amounts of nitrogen or other harmless gases wouldn't matter. Oxygen used in various chemical operations probably has to meet different specifications. Jc3s5h (talk) 20:17, 14 November 2019 (UTC)

Note that the percentage of oxygen in the tank isn't the same as the percentage which reaches the lungs. Even in a healthy individual there would be mixing of the old air and the new, with carbon dioxide continuously being released into the lungs by the body. But in somebody with breathing problems (an obstruction, fluid in the lungs, not breathing, etc.), the proportion reaching the alveoli could be considerably less. SinisterLefty (talk) 20:37, 14 November 2019 (UTC)

Prolonged exposure to high partial pressure of oxygen can cause oxygen toxicity. I think medical oxygen in ambulances is close to 100% oxygen, but on the understanding that it will only be administered undiluted to a patient for a short period. Dolphin (t) 21:05, 14 November 2019 (UTC)

See Explanation On PSA Medical Oxygen Generator Purity 93±3%. It seems that nobody minds a bit of argon but halogen is a bad idea. Alansplodge (talk) 21:56, 14 November 2019 (UTC)

Thank you all for the answers, but I don't understand it yet properly. in the last reference it's mentioned that "United States Pharmacopoeia (USP) Oxygen 93% Monograph has specifications as “not less than 90.0% and not more than 96.0%” for PSA oxygen". So EMTs use 100% against it? or maybe I miss something? 93.126.116.89 (talk) 01:17, 15 November 2019 (UTC)

Also, if the standard medical oxygen which found in ambulances is 100% concentration, so how could it be that AHA (see here paragraph No.6.2.1) states: "In term and late-preterm newborns (≥35 weeks of gestation) receiving respiratory support at birth, the initial use of 21% oxygen is reasonable". How could it be? or maybe it's a specific oxygen found in hospitals in neonates department? 93.126.116.89 (talk) 01:18, 15 November 2019 (UTC)

21% oxygen is just normal air. EMTs are trained to avoid giving 100% (or whatever the concentration of medical oxygen is) to newborns whenever possible. You will notice the guidelines you quoted indicated to start with 21% oxygen, and titrate to achieve acceptable oxygen saturation in the blood, measure with pulse oximetry. Jc3s5h (talk) 02:47, 15 November 2019 (UTC)

• It's important to distinguish between concentration and partial pressure. Humans suffer from long-term oxygen toxicity if the partial pressure is too high. This can be caused by too great a proportion of oxygen at atmospheric pressure (or, less commonly, by the same proportion at an increased hyperbaric pressure (divers have to switch to technical mixes)). But if the overall pressure is also reduced, then increased oxygen isn't a problem, even up to pure oxygen. The partial pressure is then no more than it would be for the standard atmosphere (twice the proportion at half the pressure). This is the case for military pilots, or even the first astronauts (although see Apollo 1 fire, and the risks if this is at atmospheric pressure).

Medical oxygen is either acute use, through a mask, which is pure [sic] oxygen. As the exposure is short, there's no problem. Or else long-term use is through a nasal cannula and there's a dilution effect. The masks used for long-term use have similar effects and can give oxygen levels up to about 50%. Paediatric oxygen therapy is done through incubators which are at atmospheric pressure, so again there's an issue with an excess partial pressure if the concentration would be too high. Andy Dingley (talk) 02:06, 15 November 2019 (UTC)

To explain the 100% vs. 90-96% standards (it's already been mentioned by I'll make it clear), these are based on where the oxygen came from, as this has an effect on the contaminants present. Pressure swing adsorption is a technology that can be used to generate up to 96% oxygen with 4% argon. Commercially available systems using this technology cannot presently generate 100% oxygen. Another method of obtaining high concentrations of oxygen is with a cryogenic oxygen plant. This technology has different contaminants present in the final product, and to ensure that these are at a low enough level to not cause health problems of their own, it is recommended that the oxygen be at least 99.5% pure. Someguy1221 (talk) 03:36, 15 November 2019 (UTC)

We could do with an article on cryogenic production of oxygen, why this was so common pre-WWII as the general workshop cryofluid (despite the obvious fire risk!) and why it was supplanted by the rather safer liquid nitrogen, post-WWII. Andy Dingley (talk) 10:01, 15 November 2019 (UTC)

Medical-grade oxygen is almost pure, almost-100% O₂. The only commercially-available oxygen bottles that are more pure are Aviator's Breathing Oxygen. Here's a standard, for those who need technical details: AS8010C from SAE. The chief difference is the complete, certified, removal of trace water vapor, to reduce the risk of water-ice formation when the bottle gets abnormally cold due to aviation environmental factors; and mechanical considerations for the safe storage and delivery of the breathing gas.

As such, I would posit that most medical oxygen in nearly pure oxygen with trace water-vapor as the primary contaminant - and that interested readers should talk to their oxygen vendor for specific source and quality information.

From DTIC, here is a nice archived review study: SAM-TR-76-44: Aviator's Breathing Oxygen Specifications, which gives detailed breakdown of allowable contaminant gas, and common values for various sources that can be procured industrially. With water vapor removed, the chief remaining contaminants in the breathing gas bottle appears to be methane, at extraordinarily low concentration.

Nimur (talk) 14:24, 15 November 2019 (UTC)

"Medical oxygen" has two standards for it, by use if not a formally defined standard. That produced by cryogenic fractional distillation is as you describe. But increasingly these days, especially for chronic care at home, it's produced at low pressure and not stored in bulk, by use of a PSA concentrator. These don't separate out the argon. But as argon is about as inert as it gets, that "impurity" is inconsequential. Yet that oxygen is only 90+% purity. The actual purity varies a bit depending on machine: some offer lower purity (more argon) as it's technically simpler and more efficient, and the resulting product is just as good. Andy Dingley (talk) 15:59, 15 November 2019 (UTC)

See oxygen therapy: the actual concentration of oxygen delivered to the patient's lungs depends on flow rate, method of administration, and other factors. --47.146.63.87 (talk) 04:09, 16 November 2019 (UTC)

November 15

Alkali metals solubility in liquid hydrazine, phosphane and diphosphane

What data are there regarding the solubility of alkali metals like sodium, lithium, etc, in liquid hydrazine and liquid phosphanes like phosphane PH3 and diphosphane P2H4? This question re solubility of alkali metals has as starting point the (comparison with) solubility of sodium in liquid ammonia (azane)! Thanks!--185.53.196.75 (talk) 18:11, 15 November 2019 (UTC)

Standard practice would be: "find a less dangerous process!" Rmhermen (talk) 18:06, 18 November 2019 (UTC)

November 16

RF scanners and cards.

I recently had a card blanked out. It wasn't a credit/debit card, but 1 used for public transportation, with a magnetic strip. I recently started a part-time job where I go through security every day, a metal detector and use of RF scanners, like the ones used in airports. Could that interfere with the magnetic strip of cards? 67.175.224.138 (talk) 14:52, 16 November 2019 (UTC).

It's all about distance, but also frequency. In general, no. It is very hard to wipe magnetic tape with either an RF field, or a permanent magnet. This changed somewhat when the far more powerful rare earth magnets appeared. Magnetic key cards in the 1980s often had small magnets embedded in them, but these disappeared from use (in favour of mag stripes or RFID) because they would wipe stripe cards if placed alongside them in a wallet. Your most likely "everyday" field of interest is some piece of power mains equipment, such as a transformer or an electric motor. Some metro trains have been known to do this if you put a bag on the floor above the traction motors on the wheels.

I'd ask around. If the scanner is wiping cards, you won't be the first to suffer. Andy Dingley (talk) 15:20, 16 November 2019 (UTC)

Re: "such as a transformer or an electric motor." Does the electric motor have to be turned on? 67.175.224.138 (talk) 15:45, 16 November 2019 (UTC).

Yes.

TBH, cards are fragile, they fail for many reasons and without walking through your workplace - maybe even carrying a field strength meter - it's impossible to say, "Yes, the coffee machine did it". But RF scanners aren't noted for doing this and the magnetic devices which might do it are only powerful enough to do this at short range.

Sadly I know of no published and citeable work on this, since an IBM paper in the 1960s on the safe transport of magnetic tapes. Which was a little surprising for finding that permanent magnets just didn't have any effect so long as they were outside the carrying case. Andy Dingley (talk) 16:31, 16 November 2019 (UTC)

I've always wandered why the cards slot in wallets are not coated with metal to produce Faraday cage. I made my own from aluminium foil after several cards were wiped out simultaneously. אילן שמעוני (talk) 18:20, 17 November 2019 (UTC)

• A Faraday cage is a shield against electrostatics, somewhat against RF fields. It has almost no effect against a magnetic field. If you make a shield of mu-metal, that would help against magnetism, but it's likely to need to be very thick. Andy Dingley (talk) 18:42, 17 November 2019 (UTC)

(sigh) Thanks. It seems I just have to avoid putting my wallet mindlessly on electric motors. אילן שמעוני (talk) 19:38, 17 November 2019 (UTC)

CO2 2018 engine cars

On a recent documentary I watched it said that a 2018 petrol engine car on a 35Km journey would usually produce 4.8 Tons of CO2. How many Tons of CO2 would a 2018 diesel engine car on a 35Km journey usually produce? I hope this is the right place to ask. (78.16.154.120 (talk) 17:16, 16 November 2019 (UTC))

• Two things.

First of all, that's nonsense. How much fuel does a car burn in that distance? Maybe a gallon? Now, how do you produce "4.8 tons of CO₂" with just a gallon of fuel? Let's say (wild assumptions, not looking up anything) and that's 5kg of fuel, which we'll call "pure carbon", which is then reacted with twice as many moles of oxygen from the air. I can't remember the atomic masses, so assume they're the same, and now you have 15kg of CO₂ produced. Which is so far from "4.8 tons" that I'm just going to stop there.

Next thing is the actuality. It turns out that cars vary a lot in how much CO₂ they produce. This varies with their engine design, how they're driven, but perhaps most significantly how new they are, and which set of emissions standards they meet. Because that has a large influence on how much they produce, and it has fallen significantly in recent years. This [9] is brief, readable and worth a look.

It's also noteworthy that being diesel or petrol doesn't make a significant difference in CO₂ emissions. It does, but it's dwarfed by the greater reduction imposed by the emission standards. This is why the "terrible, filthy, lying Volkswagens" are actually still some of the cleanest and lowest emission cars around. The emission standards are 130 g/km at present, 95 g/km in a couple of years. About 50% more for light vans. So that's a required emission level of 4.55 kg for your 35 km journey (and I think we can see what the error was now) for a "new" car, reducing to 3.325 kg if you buy a 2021 car. This is the same for petrol or diesel. They might vary, but they both have to get under this limit. Andy Dingley (talk) 17:29, 16 November 2019 (UTC)

• Yes, the strange combo of metric "Km" (abbreviated that way instead of the standard "km") and non-metric "tons" makes me suspect that some unit must be wrong. Does Km mean something like "thousand miles" in this abbrev ?

• What the original poster heard as "tons" may have been metric tons, also known as tonnes. (This does not change the argument that the statement is nonsense if "35Km" does indeed mean 35 kilometers.) --76.69.116.4 (talk) 21:13, 16 November 2019 (UTC)

• Carbon dioxide produced will be proportional to the amount of either gasoline or diesel fuel used, so just look at the MPG to figure out which pollutes more. You may have heard that diesel pollutes more, but that is not carbon dioxide they are talking about, it's other pollutants, like sulfur compounds. Perhaps a chemist can comment on if there is any difference at all between gasoline and diesel, in carbon dioxide production. That is, does a vehicle which uses 20 MPG of gasoline produce the same amount of carbon dioxide as one that gets 20 MPG on diesel ? SinisterLefty (talk) 19:11, 16 November 2019 (UTC)

I've driven a few thousand mile journeys. I've never driven a 35 thousand mile journey. Certainly not on one tank. Andy Dingley (talk) 19:58, 16 November 2019 (UTC)

Yes, it would be quite a journey, something like visiting every city in Eurasia. SinisterLefty (talk) 20:34, 16 November 2019 (UTC)

The Rutan Voyager traveled around the entire Earth without stopping for fuel, and they only made it to 26,366 statute miles. Nimur (talk) 16:51, 18 November 2019 (UTC)

diesel pollutes more

Diesel pollutes less. Also less CO₂. But what it does produce are particulates. Which are the fashionable demons of popular paranoia this week. They're a problem, but also they're fixable by filtration. For NO_x there's AdBlue. Andy Dingley (talk) 20:06, 16 November 2019 (UTC)

How much less carbon dioxide ? As for diesel being clean, before they switched to the low sulfur formulation in the US, the clouds of black smoke pouring from diesel truck engines would make me choke and make my eyes water, so it's not just paranoia. They are better now, but by no means clean. SinisterLefty (talk) 20:36, 16 November 2019 (UTC)

"Clouds of black smoke" has nothing to do with fuel, that's a fault in either the fuel pump or the injectors. Either wear with age, or it's a smal engined Ford car. See rolling coal, BTW.

Sulphur is why Volvos smelled of eggs in 1990 (their particular catalysts, combined with certain fuels like the high-sulphur semi-synthetic VIP petrol in NE England), but that's a petrol issue. Andy Dingley (talk) 20:45, 16 November 2019 (UTC)

I'm talking about big trucks when I say clouds of black smoke. Apparently making them burn cleaner robs them of horsepower, so if laws don't require it, they don't bother. See [10] and note that the Class A (and B ?) trucks in that race put out lots of black smoke. SinisterLefty (talk) 21:04, 16 November 2019 (UTC)

Diesels get a bum rap because diesels are cheap to maintain so cheap people and cheap companies buy diesels. They can also take a harder beating, you'll run a poorly maintained gasoline car to the chopping block in no time. Their advantages also get bigger when it comes to hauling heavy loads. That's why when a transportation company is aching for that extra % in savings (and which one isn't), using legal minimum catalysts, doing poor maintenance and MacGyvering broken parts, the smoke they'll be blowing in your radiator can only come from diesel fuel. 93.136.94.213 (talk) 05:33, 17 November 2019 (UTC)

I feel I must add an important reservation to Andy Dingley answer. While true that diesel engines produce less CO2, they produce way more poisonous particles than gasoline engines. There is a going dispute how to evaluate both pollution types against each other. אילן שמעוני (talk) 18:12, 17 November 2019 (UTC)

Particulate matter is toxic (it certainly is not the "fad of the month" to study that effect and try to alleviate it), but not "poisonous" as they do not act by chemical reaction.

I am not sure what "going dispute" you refer to. Pretty much everyone knows that CO2 emissions are a global problem whereas PM are a local problem - on the one hand, high concentrations of vehicles in densely-populated cities cause a uptick in respiratory diseases even when said vehicles are equipped with countermeasures; on the other hand, container ships all use low-grade diesel with an engine optimized for consumption and not PM minimization, but nobody cares because their emissions gets diluted over large distances before they reach the population. If there is a dispute, it's political (what levels of PM are deemed acceptable in a given city/country), not technical. Tigraan^{Click here to contact me} 10:06, 18 November 2019 (UTC)

The dispute I mentioned is from the public health point of view. Naturaly, you are right to point that ocean going ships are out of this debate. What is within the debate is the classification of emission ratings for cars. If you will insist I will try to fetch a source or three. אילן שמעוני (talk) 15:23, 18 November 2019 (UTC)

The pollution from ships is a concern from multiple POVs. There's the effect on the workers aboard the ships. And there's the effect on ports, especially when they run their engines while in port, to provide electricity and heat. This can be solved by providing electrical cables from the port to the ship, but not all ports are so equipped. Also note that dilution alone doesn't actually solve the problem, since, if it stayed in the air forever, it would just accumulate until it was a danger worldwide. But dilution followed by natural cleaning of the air, from precipitation, for example, can solve the problem, or at least convert it into a problem of water pollution (acid rain and such). SinisterLefty (talk) 16:32, 18 November 2019 (UTC)

• The answer to the question "does diesel get more miles per gallons / kilometers per liters than petrol" is "yes" but it involves three separate effects.

One is explained at Diesel_fuel#Fuel_value_and_price: a gallon (or liter, or...) of diesel is not equivalent to the same volume of gasoline because diesel is more dense. Both fuels have the same heat of combustion in joules per kilogram, but for a given volume diesel contains ~10% more mass hence energy (well, enthalpy to be precise).

The other is the difference in ratio of mechanical work recovered to fuel energy (i.e. the energy efficiency). That is due the technology difference (diesel engine vs. petrol engine have very different combustion processes) which causes efficiency to be higher for diesel than petrol - the most significant difference is due to the higher compression ratio (good article even though lacking in sources), which itself is due to complex considerations (the oversimplified summary is that a short fuel autoignition delay is good for diesel but bad for petrol so petrol needs lower chamber temperatures hence CR). In general diesel has a better energy efficiency than spark-ignition, but the variation within each combustion mode is significant depending on engine speed, load, engine design etc. - a rough order of magnitude would be an average of 35% for petrol and 40% for diesel for 2019 engines.

The third is how much mechanical work you need to push your vehicle a given distance. This depends on vehicle aerodynamics and traffic conditions (which are roughly the same for diesel and petrol cars) as well as vehicle mass (which is a tad higher for diesel, the engine being heavier). Tigraan^{Click here to contact me} 10:30, 18 November 2019 (UTC)

This is quite comprehensive, but misses a small point. Diesel fuel contains on average longer-length carbon chains, and hence a slightly higher ration of C to H in the fuel. So not only is Diesel denser, it also produced a bit more CO2 (and less water), proportionally, than petrol. On the third hand, petrol will be more highly refined, so there may be more CO2 emission during production of the fuel. --Stephan Schulz (talk) 14:31, 18 November 2019 (UTC)

Original poster. The figure is 35 Kilometres. The 4.8 Tons of CO2 was how much was produced making the documentary & the text at the end said it was equivalent to a 2018 petrol engine car for 35 Kilometres. Petrol & diesel are often lumped together & was wondering which was worse for the environment. (78.16.154.120 (talk) 16:20, 18 November 2019 (UTC))

Which one is worse for the environment depends very much on the exact details, and which factors you consider. For CO2, Diesel engines are slightly better than equivalent petrol engines, but this is not a big differences. CO2 emissions cannot reasonably be avoided - burning of fuel is the way the engine works. The other two big emissions considered are usually NOx and small particulates. As written above, these mainly affect the local area, and can cause health issues. Diesel engines normally produce more of both (more NOx because the engine works at higher temperatures and pressures, more particulates because of the higher sulphur and carbon content of the fuel), but there are filter/converter technologies for both, and a Diesel engine with modern exhaust processing is much cleaner than a petrol engine without equivalent equipment. So it really comes down to the emission standards the car was built for. And no, I don't think there is any street-legal vehicle that will produce 4.8 tons of CO2 for 35 km of driving. It would need to burn roughly 2 tons of fuel for that distance. I'm sure there are rocket engines like that, and the Queen Elizabeth-class aircraft carriers seem to burn about 1 ton of fuel per 5km, but neither of these are road-worthy. --Stephan Schulz (talk) 17:29, 18 November 2019 (UTC)

Remote sensing, Terrain mapping and supercomputers

Could a type of computer, like a supercomputer, map terrain without relying on input from a satelite? Furthermore, how powerful would a supercomputer have to be to map out one ace of terrain each nanosecond, creating a slideshow of maps? déhanchements (talk) 22:02, 16 November 2019 (UTC)

Are you asking whether it was possible to make terrain maps (I guess you mean topographic maps) before the deployment of satellites? Yes, the history of cartography indicates that such maps existed long before Sputnik or computers. The 19th century Great Trigonometrical Survey of India is a famous example of such a mapping project. Satellite measurements are just another form of surveying which was traditionally done with ground-based instruments. You'd take a bunch of surveyed measurements and convert them into a map. Computers help but it was historically also done without them. As for mapping one acre per nanosecond (10⁹ acres/sec or about 1.5 million square miles/sec), that depends on the resolution of the map and the measurements, of course. You have to be more clear about what you want. 67.164.113.165 (talk) 22:32, 16 November 2019 (UTC)

The techniques for managing geographic data, that may be obtained from satellites or manual land surveying, are described in the article Geographic_information_system (GIS), particularly about map making. A human typically uses minutes to examine a finished map and the source data is seldom collected in real time but comes from sources (e.g telemetry downlink, photograph scanning or data file reading) that may have low speeds. Computer speed is seldom a limiting factor in matching the source to the viewing requirement (unless a specially complex processing step is required) and large area GIS projects can make use of Parallel computing. The Nanosecond which is about the time for light to travel 1 foot is too short a time unit to be meaningful here.

See also Supercomputers will start building a 3D map of the world. DroneB (talk) 01:30, 17 November 2019 (UTC)

Mapping has become a ideal task for satellites because of the developments in sensors! A "Supercomputer" is idealy suited to do simulations or scan giant data sets for expected and/or unexpected data.

So "Supercomputers" have little to no use for the scanning/collecting geographic data, which will at best become a near real static Interpolation. Satellites can go far beyond because their sensors and filters give them not only the ability to collect real geographic data but other realtime valuable data like temperatures, moisture, movement, etc. continuously, which for example enabled a total revolution for Agricultur, Geology, Archaeology and many other scientific fields - last not least Astronomy. Satellites are the superior scientific tool at the moment. --Kharon (talk) 19:25, 18 November 2019 (UTC)

November 18

Cytotoxic CD4 T cells

[11] I looked at the abstract of this and can't make head or tail of it, even after looking at our article Cytotoxic T cell. Is the implication that very old people's cells change to make them more likely to get autoimmune disorders? Or that they have somehow already gotten autoimmune disorders that cause them to develop these cells? Or what? Thanks. 67.164.113.165 (talk) 07:13, 18 November 2019 (UTC)

Nothing about autoimmune disorders is implied. In fact, the authors explicitly have no idea what these CD4 CTLs are programmed to do. The main finding is simply that these cells (previously reported as very rare in healthy individuals) are found in very high numbers in healthy supercentenarians. They also show that these cell populations are stable over time, and to the extent testable, the cells appear to be functional cytotoxic cells, meaning that they can probably kill their target cells, whatever those are. Someguy1221 (talk) 07:46, 18 November 2019 (UTC)