Wikipedia:Reference desk/Science: Difference between revisions
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::: Careful: "things that start off at a higher temperature wind up getting to a higher temperature" doesn't really prove a whole lot, and "liquid water gets hotter faster than ice" is actually ''completely consistent'' with what Guy just said. We are obviously not operating at equilibrium conditions. [[User:DMacks|DMacks]] ([[User talk:DMacks|talk]]) 14:43, 30 November 2019 (UTC) |
::: Careful: "things that start off at a higher temperature wind up getting to a higher temperature" doesn't really prove a whole lot, and "liquid water gets hotter faster than ice" is actually ''completely consistent'' with what Guy just said. We are obviously not operating at equilibrium conditions. [[User:DMacks|DMacks]] ([[User talk:DMacks|talk]]) 14:43, 30 November 2019 (UTC) |
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::::I generally refrain from responding to Andy Dingley, because I have never seen him change his opinion when faced with evidence against it. For those who doubt what our [[Microwave oven]] article says ('''"Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted"''') it is a simple matter to confirm at home that microwaves do indeed heat ice. Simply place an ice cube in a microwave, heat it on high, and see how long it takes to melt. Now repeat the experiment without turning the microwave on. It is also interesting to try dry sugar and pure cooking oil, but be careful; it is easy to make a hard-to-clean mess. And if anyone still thinks that microwaves only heat water, buy one of these [ https://www.amazon.com/dp/B01D9V8Z9O/ ], [ https://www.amazon.com/dp/B07BDK7BZY/ ] (or just read the customer reviews for them). --[[User:Guy Macon|Guy Macon]] ([[User talk:Guy Macon|talk]]) 16:58, 30 November 2019 (UTC) |
::::I generally refrain from responding to Andy Dingley, because I have never seen him change his opinion when faced with evidence against it. For those who doubt what our [[Microwave oven]] article says ('''"Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted"''') it is a simple matter to confirm at home that microwaves do indeed heat ice. Simply place an ice cube in a microwave, heat it on high, and see how long it takes to melt. Now repeat the experiment without turning the microwave on. It is also interesting to try dry sugar and pure cooking oil, but be careful; it is easy to make a hard-to-clean mess. And if anyone still thinks that microwaves only heat water, buy one of these [ https://www.amazon.com/dp/B01D9V8Z9O/ ], [ https://www.amazon.com/dp/B07BDK7BZY/ ] (or just read the customer reviews for them). --[[User:Guy Macon|Guy Macon]] ([[User talk:Guy Macon|talk]]) 16:58, 30 November 2019 (UTC) |
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::::: Actually Guy, what you usually do is post insulting and personally targetted cartoons. And a bit of pontification has always been your way. BTW - WP articles are ''not'' reliable sources. [[User:Andy Dingley|Andy Dingley]] ([[User talk:Andy Dingley|talk]]) 18:48, 30 November 2019 (UTC) |
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= November 30 = |
= November 30 = |
Revision as of 18:48, 30 November 2019
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November 23
nuclear fission bombs inside white dwarfs
As heavier elements sink to the core of a white dwarf, does enough uranium, radium, etc, become concentrated to start a chain reaction and explode? In a bomb on Earth made by humans, the material needs to be concentrated very rapidly to prevent the chain reaction from pushing itself apart too soon. But the might not be needed inside the pressure and gravity of a white dwarf, and any sinking of heavy elements might happen very fast, fast enough to make a bomb. If such a bomb went off, the debris might be stifled by pressure and gravity, causing sudden extreme compression and maybe a nova?Rich (talk) 15:53, 23 November 2019 (UTC)
- AFAIK, white dwarf, being lighter than Chandrasekhar Limit, does not fuse anything heavier than iron. אילן שמעוני (talk) 18:29, 23 November 2019 (UTC)
- Nuclear reactions in ordinary stars, including white dwarfs, never create anything heavier than iron. But the heavy metals could have been present in the material that the star formed from in the first place: the same reason that they exist in our solar system. See nucleosynthesis. The question is whether they could be present in sufficient quantity to react in this way, and what would happen if so. I have no information about that. --76.69.116.4 (talk) 20:11, 23 November 2019 (UTC)
- This is wrong. In ordinary stars s-process creates elements heavy than than iron, though not radioactive staff like uranium. Ruslik_Zero 20:46, 23 November 2019 (UTC)
- The heavy elements will eventually concentrate in the center of the white dwarf. However their mass is very low - about a few thousandth parts of percent, So, any fissile explosion will have negligible influence on the white dwarf (or more likely the black dwarf). Ruslik_Zero 20:54, 23 November 2019 (UTC)
- Nuclear reactions in ordinary stars, including white dwarfs, never create anything heavier than iron. But the heavy metals could have been present in the material that the star formed from in the first place: the same reason that they exist in our solar system. See nucleosynthesis. The question is whether they could be present in sufficient quantity to react in this way, and what would happen if so. I have no information about that. --76.69.116.4 (talk) 20:11, 23 November 2019 (UTC)
- No, to make a fission bomb you need weapons grade uranium or plutonium, which is made by removing unwanted isotopes which spoil the prompt critical reaction. A star will have these isotopes present. (Stars are where they're all made in the first place.) For an implosion-type bomb, you also need the core to be compressed extremely rapidly, or you just get a "fizzle". I don't think this would happen outside of a stellar core collapse, which already makes a really big boom. --47.146.63.87 (talk) 01:56, 24 November 2019 (UTC)
- All fissile materials would have probably decayed long before there had concentrated in the center as their life-times are rather short. Ruslik_Zero 13:53, 24 November 2019 (UTC)
How vinegar can be salt substitute?
According to this article: "vinegar is kick ass salt substitute you should be using". Now, logically when I think about it, it's difficult for me to understand the mechanism of it, since the feeling of saltiness is caused by tongue sensors of salts (or maybe NaCl only). Now, vinegar is acidic, and it should cause a sourness rather than saltiness. Isn't it? ThePupil (talk) 20:23, 23 November 2019 (UTC)
- The article is talking about using salt (or vinegar) in sufficiently small quantities that it doesn't make the food taste actually salty (or saltier). Used at such low concentrations it instead has the effect of enhancing the other tastes present in the food, a usage called seasoning.
- As the Wikipedia article Seasoning suggests, vinegar used for seasoning does not give a result identical to that of salt, but it does enhance other food tastes in a broadly similar way. Quite how either of them do this is beyond my ken, though I suspect that it has something to do with modifying sensory threshold processes (see also the links in that article's 'See also' section). {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 22:22, 23 November 2019 (UTC)
- I doubt it would be widely effective. One of the reasons why salt enhances other flavors is that many of the receptors involved in flavor make use of sodium co-transport. Vinegar won't make up for the lack of sodium ions for co-transport. Sodium acetate would. --OuroborosCobra (talk) 23:33, 23 November 2019 (UTC)
- ...Or more commonly, sodium diacetate. 2606:A000:1126:28D:144E:A9EA:EDD2:AB72 (talk) 04:09, 24 November 2019 (UTC)
- Thank you all for the answers. 05:49, 25 November 2019 (UTC)
- ...Or more commonly, sodium diacetate. 2606:A000:1126:28D:144E:A9EA:EDD2:AB72 (talk) 04:09, 24 November 2019 (UTC)
- I doubt it would be widely effective. One of the reasons why salt enhances other flavors is that many of the receptors involved in flavor make use of sodium co-transport. Vinegar won't make up for the lack of sodium ions for co-transport. Sodium acetate would. --OuroborosCobra (talk) 23:33, 23 November 2019 (UTC)
November 24
Memory foam for sleeping - real science or marketing gimmick?
I came here from a now-defunct conversation in Talk:Memory foam#Steady-state behavior which was less about improving the article and more about science.
Is there any actual research showing a benefit of memory foam mattresses over regular open-cell foam? In a steady state, any open-cell foam ("memory" or not) doesn't compress like a spring; it exerts a fairly constant force that is nearly independent of displacement, over a range of displacement.[1][2]
Why would it matter if the mattress is viscoelastic open-cell foam or just regular open-cell polymer foam? Each point on the foam still exerts a constant force on the object laying on it, if the foam is compressed within its constant-force range. In fact, memory foam seems less desirable because it resists changing shape, making it hard to change position or roll over during the night.
The "memory" feature of retaining a deformity for a short period seems, to me, to be nothing more than a marketing gimmick. It makes for nice photographs of impressions left by pressing a hand into it. So what? What is the advantage?
Any search I do for gets muddled by results that take it for granted that a benefit exists. Even the patent on memory foam mattresses relies on speculation and uncited tests for its claims of being a benefit to sleeping. Where are the comparisons to open-cell foam that isn't viscoelastic?
My sleep therapist suggested I look into getting a mattress pad, and in my search, knowing the compression characteristics of open-cell foam, I got stuck on this question: why not just a pad of open-cell foam? What is better about memory foam? ~Anachronist (talk) 17:51, 24 November 2019 (UTC)
- " Sleep specialist Donna L. Arand, PhD, says that objective studies supporting the claimed benefits of memory foam -- or the effects of any particular type of sleeping surface -- are lacking." -- [3]
- --Guy Macon (talk) 19:40, 24 November 2019 (UTC)
- @Guy Macon: Thanks for that. "Lacking" indeed! That confirms my observations.
- However, that article does say that memory foam changes shape not only in response to pressure, but also to body heat. I'm skeptical that body heat makes any difference, or that its response is unlikely to be different from normal open-cell foam. ~Anachronist (talk) 16:35, 27 November 2019 (UTC)
- You could confirm your suspicion by putting a hot water bottle full of cold water on some memory foam and then repeating it with the same weight of hot water.
- Here is what I suspect happened. NASA realized that if someone is sitting on normal foam at 1G and suddenly gets a 20G jolt, the astronaut hits the metal frame of the chair as if the foam wasn't there. Memory foam doesn't have that problem. Then the marketing elves started selling it for a completely unrelated application, and you are the first person who thought about it and realized this makes no sense. --17:58, 27 November 2019 (UTC)
- "In fact, memory foam seems less desirable because it resists changing shape, making it hard to change position or roll over during the night." I can offer anecdotal evidence for this particular annoyance of using a memory foam pillow for headrest. We now use it to support feet at the coffee table. 93.136.178.2 (talk) 21:53, 29 November 2019 (UTC)
Penultimium and ultimium compounds
We know that element 119 is currently being worked on testing. The article (currently titled ununennium) says that +1 and +3 compounds of this element are going to be equally stable. This would mean all of the following:
- Penultimium fluoride (PnF)
- Dipenultimium oxide (Pn2O)
- Penultimium trifluoride (PnF3)
- Dipenultimium trioxide (Pn2O3)
Also, let's add the same info on element 120 (the article is currently at unbinillium.) It says +2 and +4 compounds are the most stable, which means these compounds are valid:
- Ultimium difluoride (UlF2)
- Ultimium oxide (UlO)
- Ultimium tetrafluoride (UlF4)
- Ultimium dioxide (UlO2)
Any info on what compounds of these elements are most likely besides the above?? (Please note that the terms I'm using for these elements are intended to be interpreted as meaning that I feel sure that these are the last 2 chemical elements that will ever get an official name; elements 121 and up will always have their systematic names.) Georgia guy (talk) 19:34, 24 November 2019 (UTC)
- Have these compounds been shown to exist and be stable (I doubt that, given that the elements haven't been synthesized), or are you assuming that from the proposed stable oxidation states? Also, what does "I feel" mean and why do you think heavier elements 121 and beyond will always have systematic names? What source do you have for the name "penultimium," since the official IUPAC designation is still the temporary "ununennium"? What do you mean by "element 119 is currently being worked on testing?" Currently all work is on basic synthesis of the element, and so it isn't being "worked on" as there is none to "work on". --OuroborosCobra (talk) 21:28, 24 November 2019 (UTC)
- Currently, all work is on basic synthesis of the element. This means we're in the early part of working on the elements. The source of the 2 names I'm using is simply my enthusiasm. Georgia guy (talk) 21:49, 24 November 2019 (UTC)
- No work is being performed upon this element as this element does not exist. You also said they were doing tests. They cannot be doing tests on something that does not exist. Please see WP:OR. Basically, no one here is likely to be in any position to even begin to speculate on your questions, and your use of a name that you've made up also makes your question difficult to answer. Your question itself isn't based on real science, but your imagination (fun as that may be). --OuroborosCobra (talk) 01:50, 25 November 2019 (UTC)
- Currently, all work is on basic synthesis of the element. This means we're in the early part of working on the elements. The source of the 2 names I'm using is simply my enthusiasm. Georgia guy (talk) 21:49, 24 November 2019 (UTC)
- Here is a fairly extensive article on the subject. I haven't read it fully, but it looks to provide a good introduction, and may help you with your research. --Jayron32 13:44, 25 November 2019 (UTC)
- You could predict that these things exist. But it could be original research. If the element decays very rapidly, it may not be possible to make a solid form, as either there will be too much energy for it to solidify, or not enough time for sufficient chemical bonds to form before the element atom is decayed to something else. Perhaps you could form a single molecule of the element. However then you will have to compare them to gaseous CsF or BaO for example. Graeme Bartlett (talk) 20:31, 25 November 2019 (UTC)
- Yeah, I've noticed that our articles frequently make predictions about bulk properties of substances so radioactive that any bulk quantity of them would instantly vaporize. It's a little bit fantastical.
- That said, radioactive decay is a random process, so you're free at least to ask what would happen if, just by chance, not very many of the atoms happened to decay. This could be made precise. There's a big multidimensional probability distribution, and you can restrict to points with some limited number of decays in them. Even though this is a tiny fraction of the measure of the whole event space, it's nonzero, and you could then marginalize it to get conditional probability distributions of things like what color it would appear to be or what pH it would have in aqueous solution.
- I guess this is meaningful after a fashion, though as Homer Simpson said when he thought he was being congratulated on his job at the bowling alley, it's getting a little abstract.
- In the case of just forming chemical bonds with oxygen or fluorine, though, that doesn't take very long. I don't know exactly how long, but the half-lives listed in the article strike me as ample for those compounds to exist in a more everyday sense. I would be interested to hear more details on that. --Trovatore (talk) 21:21, 25 November 2019 (UTC)
- Well, there are likely more stable isotopes that we haven't yet made. If you get a half-life of about a millennium, as is predicted for the most stable isotopes of copernicium (we know the element, but not the isotopes in this predicted most stable region), you've got an opportunity for actually finding bulk properties. And, as you said, you can ask what the behaviour would be if by chance there were no or very few decays in some time span. ^_^
- The theoretical limit for chemistry is 10−14 seconds, as that's how long you need for the nucleus to get an electron cloud (see Extended periodic table). So we definitely have long enough half-lives to do it in theory, but doing it in practice currently requires something more substantial (around a second). And indeed, there have already been chemical experiments on nuclides like 284Nh (half-life 0.91 seconds) and 287Fl (half-life 0.48 seconds). With current methods, it ought to be possible to do chemical experiments up to moscovium (element 115) with the isotopes we already know; the only isotopes we know of the last three are too short-lived. Double sharp (talk) 17:13, 26 November 2019 (UTC)
- One of the key things here, that no one is mentioning, is the role of computational chemistry in predicting the properties of as-yet-undiscovered elements. The methods of computational chemistry for this purpose are old indeed, one could even make a decent claim that Dmitri Mendeleev was the father of such applications, the use of basic computational techniques was key in the assembly of his periodic table, in the creation of early forms of the periodic law for element properties, and the use of those to predict the properties of then unknown elements. Even in the late 1800s, Mendeleev was able to get (what was for the time) shockingly good predictions for such elements, his his predictions were very close to the actual properties of those unknown elements. Considering that, today, we have powerful supercomputers working on the complex calculations, and Mendeleev had pencil and paper and his own brain, we've only gotten more accurate. The expected properties of elements 119 and 120, at least on the level of precision the OP is talking about, as predicted by the calculations, are unlikely to be very wrong. --Jayron32 13:41, 26 November 2019 (UTC)
- I'd be careful making this comparison with computational chemistry. It's not as simple as you are making it out to be, and your comparisons with Mendeleev are just plain wrong. What method was he using with a pen and paper? Perturbation theory? Variational method? Hartree-Fock? I doubt he was using any, since he wouldn't have had a Hamiltonian operator to work with, and the Schrödinger equation wasn't proposed until 1925, 22 years after Mendeleev died. Computational chemistry techniques generally depend on quantum mechanics as well, which also basically didn't exist as an accepted science during Mendeleev's life. Classical techniques, like molecular dynamics, won't cut it for the properties being discussed. Coming up with general trends based on a nascent concept of orbitals (itself still not proposed in his lifetime, so he didn't even fully understand what it was his model was based upon) is not comparable to computational chemistry. It definitely was a step forward in our understanding, but it isn't computational chemistry. In terms of modern applications, I'm sure we would love if quantum chemistry was as simple as "tell the computer to model my element X and give me accurate results," but it isn't. Different computational methods suffer from different issues. Hartree-Fock omits electron correlation, for example. So, which post-Hartree Fock method are you going to use? Møller–Plesset perturbation theory? Configuration interaction? Or are you going to go a completely different direction and use density functional theory? What type of functional will you use? local-density approximation or generalized gradient approximation? If the latter, which GGA functional? BP86? PBE? Or a hybrid HF-DFT method, like B3LYP? Then, even once you have a computational method, you need a basis set. Are you going to use an effective core potential? Will your results be more or less accurate by accounting for relativistic effects? Do you even have a constructed basis set to use, or will you have to make your own? I don't see any basis sets on Basis Set Exchange that include elements 119 or 120. Slater type orbitals, or gaussian type orbitals? This all ends up getting extremely complicated, and there will be competing solutions. Now, oftentimes there may be experimental values to compare with, be them the directly observed systems you are computing, or similar enough models that allow you to validate your method. However, this would be very difficult to do when you don't actually have the element in question in existence to validate against, and you are having to construct a basis set from scratch not around any observation of said element. It's not easy, and you'll probably end up with computational chemists debating in the literature as to who has the most accurate model, rather than having a definitive answer that you want. --OuroborosCobra (talk) 23:06, 29 November 2019 (UTC)
+4 for element 120 has been suggested, but I don't really believe much in it: I do believe +3 for element 119 should be possible, but surely not as stable as +1 (which the article does not, in fact, claim). As noted in the articles, the major oxidation states for E119 and E120 are probably +1 and +2 respectively as you'd expect. The possibility for higher oxidation states is because the energy gap between the (n−1)p3/2 and ns subshells shrinks relativistically. I did some literature reviewing (coupled with a bit of extrapolating myself from the data, because that's a talk page, but it should be clear what's what) at Wikipedia_talk:WikiProject_Elements/Archive_34#Meitnerium through oganesson, so I'll quote myself:
Chemically, they are obviously going to be strong metals with 1 and 2 marked in blue [basic oxidation states; the colouring is about the periodic table poster Droog Andrey and one of his colleagues produce] respectively: the ionisation potentials are predicted as about 2.7 V and 3.0 V respectively for the 119+/119 and the 1202+/120 couples (10.1088/0031-8949/10/A/001). The main interesting question here is if the 7p3/2 electrons might also be ionisable to give oxidation states higher than 1 and 2 respectively. For E119, the difference between the 1st and 2nd ionisation energies is similar to that of Cu, Ag, and Mc, suggesting that element 119 may have some group IB-like properties in the same way that element 165 may have some group IA-like properties. I think we can therefore seriously expect a minor +3 oxidation state as predicted by Hoffmann et al. (10.1007/1-4020-3598-5_14), which like the +3 oxidation states of those three elements would probably show amphoteric behaviour (which would be consistent with colouring Og2+ in as amphoteric, continuing the trend from a perhaps basic Ts+ [well, later we discussed that with Droog Andrey, and agreed with his conclusion that TsI should not have much oxygen affinity to be called basic or amphoteric or acidic]). Annoyingly I have not found values for 3rd and higher ionisation potentials of E120, but Hoffmann et al. likewise predict a minor +4 oxidation state for it. Nonetheless reading the graph Fricke gives of the predicted DFS energy eigenvalues predict the energy gap between 8s1/2 and 7p3/2 for E120 to be more than that between 7p3/2 and 7p1/2 for Lv as the 7p3/2 electrons rapidly retreat into the core, so that while E119 might show higher oxidation states I am doubtful that E120 would. (Similar reading of his figures seem to suggest the possibility of a +3 state for E165 but not a +4 state for E166).
And Droog Andrey went on to agree with my suggestion that E119 should have a major oxidation state of +1 (basic) with a minor one of +3 (amphoteric), whereas E120 should be stuck at +2 (basic) always. Since he is a computational chemist (one of his papers), I have some faith that this is likely to be more or less right. ^_^
So we could guess that 119F and 1192O should be possible (I'd rather guess the superoxide 1192O2 to be formed when you expose a hypothetical chunk of metallic element 119 to air, like for rubidium), and since fluorine and oxygen are strong oxidisers we may be able to think of 119F3 (there is AgF3, after all) and perhaps even 1192O3 (since there is silver(I,III) oxide). But for element 120 I'd guess that there's only going to be 120O and 120F2 among your suggested compounds. In general, you can think of 119 and 120 as being more or less homologues of Rb and Sr (the trend does an about-face after Cs/Ba towards lower reactivity as the outermost s-shell is stabilised by relativistic effects), with some group 11 and 12-like character bringing them a bit closer to Cu/Ag and Zn/Cd respectively. So, although it is rather OR-ish, you could probably come up with many plausible compounds of E119 and E120 by looking at what rubidium and strontium do respectively.
Also, there seems to be no reason except the limits of current technology why we couldn't proceed beyond E120. Technology may well improve enough to make the early superactinides reachable within another generation, although it will get more and more difficult with lower cross-section and half-lives measured in microseconds. E121 should be more or less like actinium with its only important oxidation state +3 (basic), for instance. You can look at Extended periodic table#Chemical and physical properties for predictions on what happens next, all the way to the probable next noble gas at E172 and a few glimpses beyond. ^_^ When E119 and E120 are discovered, anyway, they are almost surely not going to be called "penultimium" and "ultimium". For one thing, that last name was already considered for plutonium (element 94, which at that time was suspected to be the last possible element – link is to an interview with Glenn Seaborg, who with his team discovered Pu; how wrong that turned out to be, with another 24 elements trailing behind on today's periodic table!). Double sharp (talk) 17:26, 26 November 2019 (UTC)
Flexible Hydraulic Arm
Would a flexible arm that can have a huge range of motion utilizing hydraulic power be possible? Maybe it would be made of rubber and use hydraulics on the inside? I don't know much about hydraulics.173.119.71.63 (talk) 21:07, 24 November 2019 (UTC)
- Yes, this is a topic of considerable current development. See soft robotics. One question is whether such an arm would have a rigid internal skeleton, even a "spine" of many short "vertebrae", or else would it be entirely soft? Worms, such as annelid worms, have provided a model for how this could be achieved. Andy Dingley (talk) 21:53, 24 November 2019 (UTC)
- See the 'Ladder Climbing with the Snake Robot' video at YouTube: https://www.youtube.com/watch?v=kN9AIQQZRw4
This robot seems electric rather than hydraulic, but certainly it is quite flexible.... --CiaPan (talk) 22:10, 24 November 2019 (UTC)
- See the 'Ladder Climbing with the Snake Robot' video at YouTube: https://www.youtube.com/watch?v=kN9AIQQZRw4
- Actually allot of Arthropod (insects, arachnids, myriapods, and crustaceans) use hydraulic systems for movement very successful for many millions of years. A flexibility is however mostly realized by a combination of many hydraulic elements like a leg of multiple connected segments or even a Hydrostatic skeleton in many Worms as Andy Dingley already mentioned. There are however huge differences in the precision between of for example slow bugs and Jumping spiders. --Kharon (talk) 22:30, 24 November 2019 (UTC)
- Related: Hydrostatic skeleton and Water vascular system. Also see [ https://www.youtube.com/watch?v=K2G7L5hcEt8 ] --Guy Macon (talk) 07:45, 25 November 2019 (UTC)
November 25
Planet axis configuration and seasons
I can't remember if I have asked this before or not, but I was curious anyway.
We all know the change of seasons on the Earth happens because the axis is tilted in relation to the orbit. So I thought of three alternate configurations for a planet:
- Axis is exactly perpendicular to the orbit, pointing "up" and "down" on the orbit plane: No annual change in seasons. Temperature depends only on latitude and time of day.
- Axis is parallel to the orbit: No seasons. Temperature depends only on time of day.
- Axis points towards and away from the sun: No seasons. One side experiences permanent sunlight and the other experiences permanent darkness.
I know there might be local weather changes that might affect the temperature and sunlight but I'm ignoring these here for the sake of simplicity.
Have I understood these scenarios correctly, and is it possible they might actually occur (not on our Earth but on some other planet)? JIP | Talk 10:54, 25 November 2019 (UTC)
- 2 and 3 do not work like that due to conservation of angular momentum: The axis of rotation is fixed in space and therefore changes its direction with respect to the sun as the planet orbits around it. In the solar system, Uranus has its axis closely within the orbital plane and it does experience seasons much more extreme than ours. Scenario 1 works; if you want to remove diurnal variation, too, you need tidal locking. --Wrongfilter (talk) 11:29, 25 November 2019 (UTC)
- Some seasonal effects also result from orbits being not exactly circular, but rather elliptical as is nearly always the case. The degree of effect is proportional to the degree of ellipticality, or eccentricity, of the orbit in question.
- Earth's orbit is only modestly eccentric (with aphelion (furthest distance from the Sun) being in July and perihelion in January), so the resultant effects are mostly swamped by the greater ones of its axial inclination (they tend to ameliorate the Northern and intensify the Southern hemisphere's seasons, but only slightly). They are however readily observable on rocky planets like Mars and Pluto which have greater orbital eccentricities. Similar effects are detectable, though less obvious, on the gas and ice giant planets of our Solar system.
- For an entertaining (and extremely well written) fictional examination of the effects on an Earth-like planet with a very eccentric orbit, see the Helliconia trilogy by my old acquaintence Brian Aldiss. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 13:38, 25 November 2019 (UTC)
- So, "seasons" are a higher-order climate phenomenon and it's really hard to extrapolate from our Earthly experience... they obviously involve the planet's orbit and its axial tilt, but they also involve its atmospheric dynamics and its average temperature and so on.
- The first-order item to consider, if we're speaking of a generic planet in a generic orbit - is the insolation - incoming solar radiation - and the equation of time that describes how insolation changes over a long period of time - let's call that a "year" cycle or a single orbit. If the planet is earth-like, its day-night cycle occurs hundreds of times per orbital-revolution; its axial tilt precesses very slowly (thousands ir millions of years go by with no meaningful precession); the orbit is nearly perfectly circular; and so on; the dominant "seasonal" change is caused by axial-tilt only.
- If the planet is Venus-like - meaning that its day-night cycle is more like its orbital period - everything "seasonal" that we infer about its axial tilt gets dwarfed by other factors. If the planet is Jupiter-like, its nine-hour atmospheric rotation is so hard to describe that the variability in gas circulation probably affects local long-term temperatures and weather more than the orbit. Uranus, as we now know it, rotates prograde and nearly perpendicular to the rest of our solar system; and its temperature profile against latitude indicates that solar radiation does not directly dominate the seasons: the hottest parts of the planet get the least sunlight. Gas convection is really complicated when the gas blob is the size of an entire world and self-gravitates! And if the planet is as eccentric as Pluto, or Halley's Comet, the variable insolation due to orbital radius change - direct distance from the Sun - has a bigger impact than axial tilt. On certain moons of the big gas-giants, like the moon Io, the most severe long-term climate cycles are caused by tidal heating, and not by the variable Solar radiation itself.
- The summary, then, is that every world is very unique; it happens that on Earth our dominant seasonal variation is caused by our orbit's weirdest peculiarity; but other worlds have their own weird peculiarities. The task of the planetary scientist is to rigorously and open-mindedly study which parameters, out of all the zillions of parameters into all the equations of physics, predominantly define the nature of any particular celestial body.
- Nimur (talk) 15:52, 25 November 2019 (UTC)
- The other thing with the potential on the seasons for the outer planets is that the seasons are caused by the variance in solar radiation due to axial tilt, and that variance is a function of the amount of solar radiation to begin with. The less overall solar radiation a planet receives, the less axial tilt "matters" to variances in solar radiation. If the earth were located out by Jupiter's orbit, with the same axial tilt, it would get less variation in its seasons. --Jayron32 19:22, 25 November 2019 (UTC)
November 26
What kind of innervation does human heart have?
Does heart has innervation to the SA node only for influence on the rhythm only (sometimes) and not for pain sensation, or it has innervation inside it for pain sensation too? Theoretically, if a physician cut an heart of his patient without any anesthesia. Should the physician expect for pain from the heart? (assuming the the patient doesn't have any other pain, for example because it section were done by catheter or by local anesthetic for the opening of the chest). If it doesn't have innervation, so why people with MI feel so strong chest pain as if it the most innervated? 93.126.116.89 (talk) 06:19, 26 November 2019 (UTC)
- Angina may explain. ←Baseball Bugs What's up, Doc? carrots→ 08:08, 26 November 2019 (UTC)
- The electrical conduction system of the heart (which includes the SA node) only makes the heart beat, by producing the action potentials that make the heart contract. In general throughout the body, there are separate afferent and efferent nerve fibers; afferent fibers transmit stimuli from the body to the central nervous system, while efferent fibers transmit from the CNS to the rest of the body. The heart does have efferent innervation, but this only serves to regulate the heart rate up or down. The heart itself generates its own action potentials. The heart has afferent innervation as well, and this is what transmits pain sensations to the brain. These nerves are separate from the heart's conduction system. Note that heart attacks don't always produce the "traditional" symptom of chest pain, and also, because the sensations are poorly "mapped" in the brain, pain from the heart can be referred to other parts of the body. --47.146.63.87 (talk) 08:18, 26 November 2019 (UTC)
Immune system and antimicrobial resistance
Why pathogens (fortunately) do not develop resistance to human immune system as quickly and intensely as to antibiotics? It seems that as they encounter immune system more often than antibiotics, the evolutionary pressure would be even greater. Also, since antimicrobial resistance states that it "threatens the world as we know it, and can lead to epidemics of enormous proportions", would immune system effectively offset the threat? 212.180.235.46 (talk) 22:09, 26 November 2019 (UTC)
- Because any chemical that kills pathogens without killing the person taking them is necessarily less effective than the person's own defenses, which are alive and which adapt to new pathogens. See Immune system. --Guy Macon (talk) 00:02, 27 November 2019 (UTC)
- I would say that is wishful thinking. The real reason pathogens don't develop resistance to immune systems is that a pathogen that kills its hosts before the hosts can spread the pathogen is selected against. Consider these counterexamples: Anthrax is quite lethal but avoids this problem by being non-contagious. Instead, it forms spores in the carcasses of its dead hosts and hopes to spread that way. Rabies is 100% fatal, and avoids the problem by getting its hosts to salivate, and bite new hosts. Abductive (reasoning) 09:40, 27 November 2019 (UTC)
- You should tell this to the people who died of AIDS. HIV is known to quickly develop resistance to any immune responses eventually exhausting the immune system and killing its host. Ruslik_Zero 11:00, 27 November 2019 (UTC)
- We're getting off track with the HIV and Rabies, since they are viruses. But note that HIV does not kill its hosts quickly. Abductive (reasoning) 11:57, 27 November 2019 (UTC)
- Whether we're getting off track depends somewhat on the OP I guess. They asked about antimicrobial resistance but then seemed to talk about antibiotic resistance. As per the article, antimicrobial resistance is a broader category than antibiotic resistance. The article indeed talks about antiviral resistance including HIV Antimicrobial resistance#Viruses. I admit I found this a bit weird at first since of course in a strict biological sense viruses are often not considered microbes nowadays as they are not generally considered living. But it seems to be the same as the WHO [4] and the NZ MOH [5]. Possibly they consider it doesn't make sense to put viruses in a special category for monitoring etc and microbes is the best fit. (And indeed as our article mentions, viruses are normally studied as part of microbiology.) True the US CDC seems to use the term interchangeably with antibiotic resistance [6] like the OP. But then again they do track both fungal and bacterial resistance under this and specifically mention they don't include viruses or parasites in their report suggesting they don't think it's obvious [7]. And they do include viruses in the papers they list [8]. (And elsewhere they call viruses microbes [9].) It's true of course that antiviral resistance is not any where as much as a threat as antibiotic resistance or even antifungal resistance, but that's a different point. And on that point, while I didn't read the WHO report where the OP's quote came from, I strongly suspect they probably were at least concerned about anti-fungal resistance and probably anti-parasite resistance and not just antibiotic resistance. Nil Einne (talk) 13:29, 27 November 2019 (UTC)
- We're getting off track with the HIV and Rabies, since they are viruses. But note that HIV does not kill its hosts quickly. Abductive (reasoning) 11:57, 27 November 2019 (UTC)
- You should tell this to the people who died of AIDS. HIV is known to quickly develop resistance to any immune responses eventually exhausting the immune system and killing its host. Ruslik_Zero 11:00, 27 November 2019 (UTC)
- I would say that is wishful thinking. The real reason pathogens don't develop resistance to immune systems is that a pathogen that kills its hosts before the hosts can spread the pathogen is selected against. Consider these counterexamples: Anthrax is quite lethal but avoids this problem by being non-contagious. Instead, it forms spores in the carcasses of its dead hosts and hopes to spread that way. Rabies is 100% fatal, and avoids the problem by getting its hosts to salivate, and bite new hosts. Abductive (reasoning) 09:40, 27 November 2019 (UTC)
- This is a good question! The immune system has a diverse arsenal to attack pathogens: from antibodies to the complement system to the respiratory burst and more. It's harder for a pathogen to develop resistance to a bunch of things than to one. For instance, some bacteria develop resistance to penicillin by acquiring a modified penicillin binding protein that isn't inhibited by penicillin. For this reason, there is increased use of multi-drug regimens, such as co-amoxiclav, trimethoprim/sulfamethoxazole, and the regimens for tuberculosis and malaria. With that said, some pathogens do have a good ability to resist the immune system; examples include some Salmonella, Helicobacter pylori, and the aforementioned tuberculosis and malaria pathogens. Logically, if no pathogens could withstand the human immune system, no one with a healthy immune system would die of infectious disease or develop a chronic infection. There's a constant evolutionary arms race between disease-causing organisms and the organisms they infect. --47.146.63.87 (talk) 09:36, 27 November 2019 (UTC)
- First, resistance to many classes of anti-microbials have existed in the nature for millions years. Bacteria only need to acquire necessary genes, which can be easily done by multiple routes. So, nothing to develop in the first place. Second, bacteria do develop or acquire resistance to immune responses. One notable example is acquisition of toxin genes (or other virulence factors), which are used as chemical weapons against cells of the immune system. Bacteria can also avoid expressing some proteins, which serve as targets for the immune system. One example is appearance of strains of Bordetella pertussis that lack pertactin protein, which is used in acellular vaccines. Ruslik_Zero 11:18, 27 November 2019 (UTC)
- The immune system is more like a weapon factory than a weapon, and it takes no prisoners, even attacking the body cells. For instance, it can produce an infinite range of antibodies, and if a pathogen develops resistance to one though changing antigen, it creates a new pattern for which the immune system could very well be already ready. This is obviously harder to fight back that a single specific molecule. Gem fr (talk) 04:29, 29 November 2019 (UTC)
November 27
Helicopters spending more fuel hovering
Helicopters spend more fuel (much more actually) while hovering (per unit of time) than while flying. Is that something that happens due to helicopters being the way that they are or can we generalize this to any self-propelled flying vehicle due to physical laws? That is, is hovering always less efficient than flying, in the same way that going uphill is less efficient than going downhill? Or, is this per design, in the same way that, say, that an engine can have maximum torque at 2,000 RPM and others at 5,000 RPM? --C est moi anton (talk) 17:12, 27 November 2019 (UTC)
- Who told you that Helicopters use much more fuel hovering than flying? Do you have a source for this claim? --Guy Macon (talk) 18:00, 27 November 2019 (UTC)
- The graph of fuel consumption versus the velocity and altitude of the helicopter flight?C est moi anton (talk) 18:08, 27 November 2019 (UTC)
- Any vehicle is likely to have an optimal fuel consumption range. ←Baseball Bugs What's up, Doc? carrots→ 18:59, 27 November 2019 (UTC)
- And how many vehicles spend less fuel while moving than while quiet?--C est moi anton (talk) 19:43, 27 November 2019 (UTC)
- Any vehicle is likely to have an optimal fuel consumption range. ←Baseball Bugs What's up, Doc? carrots→ 18:59, 27 November 2019 (UTC)
- The graph of fuel consumption versus the velocity and altitude of the helicopter flight?C est moi anton (talk) 18:08, 27 November 2019 (UTC)
- Note that this isn't a sudden increase when in the hover itself, it's more of a gradual shift from when below moderate airspeeds.
- It's the asymmetry of the rotor moving in a moving airstream, vs. a still airstream. This depends on the airspeed of the rotor, which of course stays constant around the rotor disc (proportional to radius), during a hover in still air. If there is some forward airspeed, then the rotor airspeed (and drag) when the blade is moving sideways (forwards or rearwards position) is just the same. But at the same time, the airspeed on the advancing rotor blade is increased (rotational speed + airspeed) and the airspeed on the retreating blade reduces (rotational speed - airspeed). Near the centre of the rotor, on the retreating side, where the blade's linear speed is least, this can reduce to zero and even becomes negative. That reduces the drag on the blade, but also reduces lift. To avoid the helicopter rolling, the incidence of the blades has to be adjusted as they rotate, so as to compensate. Overall, there's a non-linear effect. Efficiency gains more from the increased airspeed on the advancing side than it loses on the retreating side, so overall there's a gain with airspeed.
- There's also a smaller effect from the tail rotor. In the hover, this is needed to counteract torque reaction and avoid yaw, entirely by itself. However when the helicopter is moving forwards, the static tail surface also assists.
- Other effects may apply, depending on the shape of the helicopter. Streamlining is optimised for performance in the cruise, less so below this. That's important for helos because not only is the airflow faster, but it changes direction from the pure vertical of a hover to something more astern. There may even be a dynamic lift effect for some (if there's any sort of stub wing shaping) and they can give lift from airspeed rather than the rotor disc, which tends to be a more efficient way to do it. Andy Dingley (talk) 19:25, 27 November 2019 (UTC)
- I think the helicopter is designed to work best when moving, and that include
- The cabin intercept and hinder the downward flow of air when hovering, more than it does moving (the airflow is then somewhat rearward
- aerodynamics of the craft is designed for a forward movement
- it may incluse some feature of a fixed wing, delivering better lift that the rotor (as evidenced by the better performance of planes Vs helicopters)
- Now, you could design it otherwise, with best aerodynamics when hovering. It just isn't very useful
- Gem fr (talk) 21:46, 27 November 2019 (UTC)
- I agree with the answers above, but there is another factor which can play part in this. Many helicopters use a turbine engine. These are usually optimized to work best at a cruise speed and may work much less efficient at low inlet speeds, see Propulsive_efficiency#Jet_engines. Rmvandijk (talk) 10:51, 28 November 2019 (UTC)
- You right, I forgot this obvious one: the engine produce some forward thrust, and you have to fight it back to hover Gem fr (talk) 04:40, 29 November 2019 (UTC)
- That wasn't the effect I meant, I suppose that one happens too. I meant that, if we assume a fairly constant outlet speed, the efficiency of the engine goes to zero (at zero inlet speed). That would mean no suction, which is wrong and violates the conservation of mass, but the idea works for low airspeeds relative to the exhaust speed. Rmvandijk (talk) 09:23, 29 November 2019 (UTC)
- You right, I forgot this obvious one: the engine produce some forward thrust, and you have to fight it back to hover Gem fr (talk) 04:40, 29 November 2019 (UTC)
- The above explanation sounds expert is probably right, but I'm not surprised more fuel is used when a helicopter is still. I'd have though the air would circulate down through the rotor then up outside to the top again. If the rotor was stopped there would be a wind pushing the helicopter down until the circulatio stopped compared to what would happen if going through still air. Dmcq (talk) 12:31, 29 November 2019 (UTC)
More power is required by the rotor to hover (airspeed zero) than to fly forwards with non-zero airspeed. There are complicating effects due to proximity to the ground, so I will say more power is required to hover out-of-ground-effect (OGE) than to fly forwards slowly at the same height above the ground. Fuel efficiency is usually unaffected by a helicopter’s airspeed so I can say rate of fuel consumption is greater in the hover OGE than flying forwards slowly at the same height. The short explanation for this phenomenon is lift-induced drag.
When we investigate the power required by a helicopter rotor there are two competing processes. Firstly, as the speed of the helicopter increases up to its maximum forward speed, the parasite drag on the rotor blades and the fuselage increases, necessitating progressively increasing power. This is the same process that necessitates progressively increasing power from the engine of any road vehicle or ship.
Secondly, there is an opposing process that requires increasing power as the forward speed of the helicopter decreases! This is counterintuitive and has no counterpart in road vehicles or ships. It is due to the phenomenon of lift-induced drag. Fortunately, it can be illustrated by some simple arithmetic. Imagine a helicopter hovering out of ground effect. Let’s examine the rotor blade elements 75% of the distance out to the tip of the blade. Let’s imagine these blade elements have a speed of 300 knots due to the speed of the rotor. The angle of attack on the rotor blade is controlled by the pilot so that the lift on the rotor exactly matches the weight of the helicopter and causes the height above the ground to remain constant.
Now let’s imagine that the helicopter has accelerated to a forward speed of 30 knots. On the advancing blade our blade element at 75% is experiencing an airspeed of 330 knots; but on the retreating blade it is experiencing only 270 knots. The mean of these two speeds remains unchanged at 300 knots so it is tempting to imagine that the rotor will produce the same lift at the same angle of attack, but that is incorrect.
The lift on every blade element is directly proportional to the square of the airspeed. Assuming no change in angle of attack, the lift on our blade element on the advancing blade is proportional to 330/300 squared, or 1.21 of its original value, an increase of 21%; the lift on our blade element on the retreating blade is proportional to 270/300 squared, or 0.81 of its original value, a decrease of 19%. An increase of 21% and a decrease of 19% means a net increase of 2%. This increase in lift would cause the helicopter to accelerate upwards. The pilot wishes to maintain a constant height so she lowers the collective lever to reduce the angle of attack on the rotor blades and eliminate that 2% net increase.
Reducing the angle of attack is associated with a reducing lift coefficient; and a reducing lift coefficient causes the component of the drag coefficient associated with lift-induced drag on the rotor blades to also reduce. As lift-induced drag reduces, the power required to turn the rotor at constant RPM also reduces, and so too does the rate of fuel consumption.
As the helicopter leaves the hover and begins to accelerate forwards, the reduction in lift-induced drag is more pronounced than the increase in parasite drag. These two effects become equal in magnitude and cancel each other at the speed for minimum power. As forward speed increases even further, the increase in parasite drag on the rotor is more pronounced than the reduction in lift-induced drag. Dolphin (t) 13:12, 30 November 2019 (UTC)
How much alcohol?
The other day I was going down the production line filling up the little water bottles we use to wet sponges for cleaning soldering iron tips. Because of past experience with the water turning green I put a glug of alcohol in the water. We have Isopropyl, Methanol and Ethanol available; I usually use Isopropyl.
This got me to thinking: what is the minimum percentage of each kind of alcohol needed so that nothing - no germs, algae, mold, yeast, tribbles, politicians, etc. -- grows in the water?
I am guessing that for Ethanol the percentage will be about that of the strongest available wine. I believe that windshield wiper fluid is 50% Methanol but I suspect that is for the antifreeze effect. --Guy Macon (talk) 18:11, 27 November 2019 (UTC)
- Who told you tribbles grow in water? --C est moi anton (talk) 18:44, 27 November 2019 (UTC)
- You forgot about the politicians. ←Baseball Bugs What's up, Doc? carrots→ 18:59, 27 November 2019 (UTC)
- Politicians grow everywhere like weeds.C est moi anton (talk) 19:32, 27 November 2019 (UTC)
- I recall reading about Nicolae Ceaușescu who, because of pathological fear of poisoning or infection later in life, asked his hands to be sanitized with 90% alcohol, presumably ethanol. Perhaps the real minimum percentage needed to kill all germs is somewhat lower. Brandmeistertalk 21:43, 27 November 2019 (UTC)
- Politicians grow everywhere like weeds.C est moi anton (talk) 19:32, 27 November 2019 (UTC)
- You forgot about the politicians. ←Baseball Bugs What's up, Doc? carrots→ 18:59, 27 November 2019 (UTC)
- Antiseptic concentration vs. killing power is not a linear or direct relationship. For example, 60-70% isopropyl alcohol is a more effective disinfectant than 90-95%. And nothing will kill everything. - Nunh-huh 00:27, 28 November 2019 (UTC)
- You don't see a lot of things growing in whiskey bottles do you? (smile.) Bottles of isopropyl alcohol also tend to be notably lacking in thing growing in them. --Guy Macon (talk) 05:26, 29 November 2019 (UTC)
- If things didn't grow in whiskey, there wouldn't be any alcohol in it. And bourbon makers need to be aware of which bacteria are contaminating their product. Pediococcus, lactobacillus and other bacteria change the flavor of the end product in different ways. And it's best not to read about the alcohol tolerant features of E. faecium before drinking... - Nunh-huh 23:08, 29 November 2019 (UTC)
- I linked that microbe in your post, to help others not-read about a meaning of "shitty beer" other than what I drank when I was a poor college student. DMacks (talk) 23:12, 29 November 2019 (UTC)
- Here, when you have a strong drink outdoors in summer, especially in a cafe (where there's always a healthy supply of alcohol drinkers), don't be surprised when tiny flies arrive to feast on what you didn't drink (or if you're drinking too slowly). 60% brandy doesn't seem to faze them at all... 93.136.178.2 (talk) 21:30, 29 November 2019 (UTC)
- You're talking about beverages created, or at least bottled, under sterile conditions as sterile products. You don't generally see much growing in bottled water if bottled under the same conditions, and that's 0% alcohol. What you are observing is more the fact that spontaneous generation doesn't exist, so a bottle sealed under sterile conditions with sterile contents won't grow anything. 70% ethanol (or isopropanol) is what is used in biosafety laboratories as a disinfectant. That and 10% bleach. --OuroborosCobra (talk) 22:43, 29 November 2019 (UTC)
- If things didn't grow in whiskey, there wouldn't be any alcohol in it. And bourbon makers need to be aware of which bacteria are contaminating their product. Pediococcus, lactobacillus and other bacteria change the flavor of the end product in different ways. And it's best not to read about the alcohol tolerant features of E. faecium before drinking... - Nunh-huh 23:08, 29 November 2019 (UTC)
- You don't see a lot of things growing in whiskey bottles do you? (smile.) Bottles of isopropyl alcohol also tend to be notably lacking in thing growing in them. --Guy Macon (talk) 05:26, 29 November 2019 (UTC)
Why does this peripheral drift illusion stop working when rotated 45°?
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Primrose_field_peripheral_drift_illusion.svg/220px-Primrose_field_peripheral_drift_illusion.svg.png)
When viewed fullscreen, moving waves appear on this checkerboard. Yet when I rotate it 45 degrees, such as on a mobile phone, the illusion stops working for me. It works again when rotated 90 degrees. Is there a reason for this?
Thanks,
cmɢʟee⎆τaʟκ 20:05, 27 November 2019 (UTC)
- For me, it even stops if I turn the head about 45 degrees. Very interesting. I second this question ;-). --Stephan Schulz (talk) 20:40, 27 November 2019 (UTC)
- Chirality is conditioning most everything we experience (test yourself on the picture with shells at the bottom of the article) --Askedonty (talk) 21:04, 27 November 2019 (UTC)
- Try doing this closing one eye. Gem fr (talk) 21:25, 27 November 2019 (UTC)
- Rather reading Popeye. It's Screen reading and Vision span (which could be improved). we are highly trained to exercise viewing along recurring patterns. --Askedonty (talk) 21:30, 27 November 2019 (UTC)
- Works just as well for me when I rotate 45 degrees. Dmcq (talk) 11:59, 29 November 2019 (UTC)
- It seems to work best on me when the picture is moving, like if I'm zooming in with my head or scanning around with the eyes. When I'm simply staring at the center of the picture it only seems to ripple when my stare wanders a little involuntarily. At 45 degrees only the connections between perpendicular lines ripple. 93.136.178.2 (talk) 21:34, 29 November 2019 (UTC)
What are these creatures?
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/%E5%AE%9D%E5%AE%89%E8%A5%BF%E6%B9%BE%E7%BA%A2%E6%A0%91%E6%9E%97%E5%85%AC%E5%9B%AD_2.jpg/220px-%E5%AE%9D%E5%AE%89%E8%A5%BF%E6%B9%BE%E7%BA%A2%E6%A0%91%E6%9E%97%E5%85%AC%E5%9B%AD_2.jpg)
I saw these little animals in a mangrove forest in Shenzhen. They're maybe 2-3 cm long and look something like fish, but I didn't see them swimming, just sitting on the rocks, using their short fins to crawl, and skipping across the surface of the water. I couldn't get a picture from up close, because they jumped away when I approached. Any idea what they are? —Granger (talk · contribs) 23:49, 27 November 2019 (UTC)
- To my untrained eye they look to be in the family that includes Mudskippers. Other editors may have a more accurate link for you Granger. MarnetteD|Talk 23:53, 27 November 2019 (UTC)
- That looks right—thank you! If anyone can identify a genus or species that would be great, but I'm also satisfied with the general identification. —Granger (talk · contribs) 00:10, 28 November 2019 (UTC)
- Hard to be sure, but barred mudskipper looks likely. Mikenorton (talk) 08:37, 28 November 2019 (UTC)
November 28
Nostrils
Why do human nostrils have their opening pointing down compared with chimps, and other mammals who have them sticking out normal to the plane of their face.,? Ie forward. 86.8.202.181 (talk) 00:29, 28 November 2019 (UTC)
- This article[10] discusses the question. ←Baseball Bugs What's up, Doc? carrots→ 01:12, 28 November 2019 (UTC)
- As does the following:
- Cimons, Marlene (March 16, 2017). "Climate may have shaped the evolution of the human nose". Popular Science.
- ...which references the following journal article:
- Thomson, Arthur; Buxton, L. H. Dudley (1923). "Man's Nasal Index in Relation to Certain Climatic Conditions". The Journal of the Royal Anthropological Institute of Great Britain and Ireland. 53: 92–122. doi:10.2307/2843753. ISSN 0307-3114.
- —2606:A000:1126:28D:9417:2118:29F3:6E25 (talk) 01:31, 28 November 2019 (UTC)
- I must admit I find the explanations rather unsatisfactory. If it is so much less efficient evolution would have acted against it, after all they're saying evolution has changed it going from warmer to colder climates. It would ha eto be somethng reasonably important like aiding swimming or persistence hunting or countering disease. Something a bit better than what thy say I'd have thought. Dmcq (talk) 12:19, 29 November 2019 (UTC)
Who is a climate scientist?
where I can find definition? — Preceding unsigned comment added by 61.68.141.189 (talk) 02:46, 28 November 2019 (UTC)
- You could start by reviewing List of climate scientists. ←Baseball Bugs What's up, Doc? carrots→ 03:19, 28 November 2019 (UTC)
- See also: Climatology (a scientist who studies climate is a climatologist; also related: paleoclimatology) —2606:A000:1126:28D:9417:2118:29F3:6E25 (talk) 03:57, 28 November 2019 (UTC)
- Since underwater military (Submarines) became a very important focus in the last century and science was very surprised by the huge impact of earthe's Oceanography on it's atmosphere, very specialized sciences like Bathymetry have become a thing you can actually study and make your profession. --Kharon (talk) 03:52, 29 November 2019 (UTC)
Cybertron is the size of Saturn
In the Transformers comics, Cybertron is said to be the size of Saturn. Cybertron is obviously a solid planet, consisting almost entirely of rock and metal, not a gas planet like Saturn. Now ignoring the fiction that it's all populated by sentient living robots, could a rocky planet of such a size exist in the first place? JIP | Talk 11:07, 28 November 2019 (UTC)
- This is all very hypothetical. What's the biggest planet which could form? Would it be rocky? What happens if it's bigger?
- Kevin C. Schlaufman has written on this https://iopscience.iop.org/article/10.3847/1538-4357/aa961c
- His work is mostly based on observation (we see evidence for things up to the mass of 10 Jupiters, but not bigger). We do see bigger things, but they mostly become luminous as stars.
- In our limited Solar experience, larger planets have been formed as gas giants: once they had a large rocky core, they then accreted lighter elements and so their main volume remains gaseous. But could a large rock have accreted, if the materials were there?
- Schlaufman's paper takes the accepted view that large bodies form either by core accretion (as planets do), or by gravitational instability (as stars do). But these both form objects in a range of masses, and those mass ranges don't overlap. So "planets" aren't found with more than 10 Jupiter masses (which would be a problem for something as dense as a rocky planet that diameter). Andy Dingley (talk) 12:56, 28 November 2019 (UTC)
- List of transiting exoplanets has several planets with estimated densities that are larger than Earth's, including planets of several Jupiter masses. This high density is presumably not sufficient to characterise them as rocky planets, though. --Wrongfilter (talk) 13:29, 28 November 2019 (UTC)
- We can set an upper limit by assuming that somebody would have noticed it if Cybertron was a Neutron star or a Black hole... --Guy Macon (talk) 17:03, 28 November 2019 (UTC)
- List of transiting exoplanets has several planets with estimated densities that are larger than Earth's, including planets of several Jupiter masses. This high density is presumably not sufficient to characterise them as rocky planets, though. --Wrongfilter (talk) 13:29, 28 November 2019 (UTC)
- According to our article Hot Jupiter the biggest planetary mass cannot be greater than approximately 13.6 Jupiter masses, because then the planet would start burning deuterium and become a brown dwarf aka a star. However the search for exoplanets is still a very young science field and we know there are "gazillion popillion" of stellar objects out there waiting to be found. --Kharon (talk) 03:19, 29 November 2019 (UTC)
- Though if it was made of rock, deuterium would be low level, and thus it may not be a brown dwarf. The problem may be to get a lot of rock together without getting too much gas, otherwise you would get something like Neptune. Graeme Bartlett (talk) 03:32, 29 November 2019 (UTC)
- If you're big enough, you become a vacuum cleaner for the light elements too, and thus you not only accrete rock, but you acquire the gaseous layers of Jupiter or Saturn. Do it on a big enough scale, and you also get the deuterium and tend towards starhood. It's not simply that "you might or might not acquire fusible materials", it's that if you're big enough, you will. Schlaufman also ties this to the mechanism by which the body forms. Andy Dingley (talk) 16:28, 29 November 2019 (UTC)
- Though if it was made of rock, deuterium would be low level, and thus it may not be a brown dwarf. The problem may be to get a lot of rock together without getting too much gas, otherwise you would get something like Neptune. Graeme Bartlett (talk) 03:32, 29 November 2019 (UTC)
- According to our article Hot Jupiter the biggest planetary mass cannot be greater than approximately 13.6 Jupiter masses, because then the planet would start burning deuterium and become a brown dwarf aka a star. However the search for exoplanets is still a very young science field and we know there are "gazillion popillion" of stellar objects out there waiting to be found. --Kharon (talk) 03:19, 29 November 2019 (UTC)
Let's go back to the beginning assumption. The question at the top of this thread says
- "Cybertron is obviously a solid planet, consisting almost entirely of rock and metal"
but our article on Cybertron says
- "Cybertron is described in the first issue of the Marvel comic book as being the size of Saturn, which would logically mean it possessed incredibly dense gravity, and yet it did not, possibly as a result of its hollow structure, honeycombed as it is by tunnels. However, in later depictions the art suggests Cybertron is much smaller..."
So that answers the question for Cybertron. But the more general question of very large planets is still interesting. Assuming a large planet made of the same stuff as a Stony-iron meteorite, and assuming that it is far enough way from the star to not be torn apart by tidal forces, is there an upper limit to size other than the neutron star and black hole limits? --Guy Macon (talk) 05:39, 29 November 2019 (UTC)
November 29
Pluto
The description of this image of Pluto (right, top) on Wikimedia Commons says:
This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope (HST). The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 2.6 billion miles (4.4 billion kilometers) from Earth; or nearly 30 times the separation between Earth and the sun.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Pluto_in_True_Color_-_High-Res.jpg/220px-Pluto_in_True_Color_-_High-Res.jpg)
If it's the clearest view yet, then where did the second image (right, bottom) come from? Or is it because the description is apparently from 1998 and hasn't been updated since then? JIP | Talk 14:09, 29 November 2019 (UTC)
- Thanks. So why does the description of the first image say "This is the clearest view yet of the distant planet Pluto" when the New Horizons image is clearly clearer (pun intended)? JIP | Talk 14:55, 29 November 2019 (UTC)
- It also goes on to say"...and its moon, Charon" May I suggest that the first image is that of Charon. Though the top image resembles neither, and the appropriate moon article has a better picture. Another option is that the first image is mislabelled. Anton 81.131.40.58 (talk) 15:02, 29 November 2019 (UTC)
- copied from JPL's description. It's pluto.—eric 15:07, 29 November 2019 (UTC)
- Also the description needs to be updated as Pluto is no longer considered a planet. It is a dwarf planet. Dja1979 (talk) 15:37, 29 November 2019 (UTC)
- (ec) Check the description on commons (eric's first link): The image was created in 1998, uploaded to en.wikipedia in 2008, transferred to commons last week, obviously without changing the text, which was accurate in 1998 and 2008, but not any more. --Wrongfilter (talk) 15:38, 29 November 2019 (UTC)
- It also goes on to say"...and its moon, Charon" May I suggest that the first image is that of Charon. Though the top image resembles neither, and the appropriate moon article has a better picture. Another option is that the first image is mislabelled. Anton 81.131.40.58 (talk) 15:02, 29 November 2019 (UTC)
- Thanks. So why does the description of the first image say "This is the clearest view yet of the distant planet Pluto" when the New Horizons image is clearly clearer (pun intended)? JIP | Talk 14:55, 29 November 2019 (UTC)
- I have made some updates to the 1994 picture's description. ←Baseball Bugs What's up, Doc? carrots→ 18:15, 29 November 2019 (UTC)
- Apparently someone copied the caption from the NASA page, but only part of the image. The one in question does not show Charon at all, so the caption is nonsense as applied to it. Maybe the complete image is somewhere on Commons as well; I haven't searched. --76.69.116.4 (talk) 06:43, 30 November 2019 (UTC)
- @JIP: Please feel invited to correct/update or mark such entries yourself right away on its own page. Worst thing that can happen is that it will be re corrected instead of drawing 20-30 people into a missplaced discussions. Please read WP:MAINT. --Kharon (talk) 08:21, 30 November 2019 (UTC)
- If it was on Wikipedia rather than Commons I might, but I don't know how to call attention to such things over there. Feel free to do so yourself. --76.69.116.4 (talk) 12:06, 30 November 2019 (UTC)
ANS receptors
Why do Beta 2 receptors of the Sympathetic ANS relax blood vessels of the skeletal muscles but Alpha receptors also part of the Sympathetic ANS constrict the same blood vessels of the skeletal muscles? --217.97.100.184 (talk) 18:16, 29 November 2019 (UTC)
- Links: adrenergic receptor, alpha-1 adrenergic receptor, alpha-2 adrenergic receptor, beta-1 adrenergic receptor, beta-2 adrenergic receptor. It looks to me from those articles that under physiological stimulus (as opposed to synthetic agonists), the effect of beta adrenergic receptors is stronger than that of alpha receptors, and so adrenergic stimulus overall causes vasodilation of blood vessels supplying skeletal muscle. Additionally, alpha-1 receptors are downregulated in muscles under stress. This causes increased vasodilation in muscles being heavily used, which shunts more blood to those muscles as opposed to inactive ones. This is likely the primary evolutionary purpose. --47.146.63.87 (talk) 07:34, 30 November 2019 (UTC)
Microwaving food
I've noticed that some foods, such as rice, heat up faster in a microwave than other foods, such as meat, and end up taking all the heat while the latter remain lukewarm. Why is that so and why is cooked meat in particular so hard to rewarm? 93.136.178.2 (talk) 21:00, 29 November 2019 (UTC)
- Meat is likely to be a lot more dense than rice. ←Baseball Bugs What's up, Doc? carrots→ 21:25, 29 November 2019 (UTC)
- The microwave wavelength is chosen so that it's absorbed effectively by water. Dry food isn't heated by it, nor is ice. IMHE, rice isn't heated well by a microwave. When reheating it, I always sprinkle it with some extra water.
- There used to be a problem of poor energy distribution within the oven cavity, hence the turntables. But modern microwaves are much better for this.
- If you make some cup-shaped icecubes specially, you can do the experiment of boiling water in an ice cube. Andy Dingley (talk) 21:30, 29 November 2019 (UTC)
- Interesting, for me rice heats up the fastest, while watery food such as a soup or a stew needs the extra hard setting. Maybe my microwave has the wrong wavelength? 93.136.178.2 (talk) 21:43, 29 November 2019 (UTC)
- Your soup may be gaining a lot of heat, but still staying at a low temperature. It's coupling the microwave energy in pretty well, but water also has a remarkably high specific heat capacity, thus takes a lot of energy to warm up. Andy Dingley (talk) 22:12, 29 November 2019 (UTC)
- And soup is mostly water, whereas rice is mostly not (and also has lots of air pockets, so the "cup of rice" has even less heat capacity than "a grain of rice". It also depends what other ingredients are present on the rice, meat, soup. Added salt or certain other chemicals can increase microwave absorption. DMacks (talk) 22:23, 29 November 2019 (UTC)
- "Added salt or certain other chemicals can increase microwave absorption. "[citation needed]
- pmid:17249886. And "Microwave heating of alkaline or salt solutions in open or closed vessels will concentrate these solutions, causing precipitation of salts and formation of crystal deposits on vessel walls. These crystal deposits will absorb microwave energy, causing localized heating which may char and damage vessel components, leading to possible failure." from [11] to get started. [12] is too technical for me to grasp the implications at a casual read. DMacks (talk) 22:45, 29 November 2019 (UTC)
- "microwaves of 2.5-20 GHz frequencies,"
- Mine's 2.45GHz. So's yours. So's everyones. To get those frequencies, I have to go in the workshop and get the radar bits out. Salted water might improve absorbtion at 2.45GHz, but not crystals. Andy Dingley (talk) 22:52, 29 November 2019 (UTC)
- The cem.com URL is 2.45 GHz. Sorry, I wasn't clear that the quote is from the subsequent link, not the PMID link. I don't have access to doi:10.1080/00207217908938675, but it seems like it might have useful info. I won't have time to run those sorts of controlled experiments (for example, T-vs-t plot for constant power at various [NaCl]) for a week or two. DMacks (talk) 23:00, 29 November 2019 (UTC)
- pmid:17249886. And "Microwave heating of alkaline or salt solutions in open or closed vessels will concentrate these solutions, causing precipitation of salts and formation of crystal deposits on vessel walls. These crystal deposits will absorb microwave energy, causing localized heating which may char and damage vessel components, leading to possible failure." from [11] to get started. [12] is too technical for me to grasp the implications at a casual read. DMacks (talk) 22:45, 29 November 2019 (UTC)
- "Added salt or certain other chemicals can increase microwave absorption. "[citation needed]
- And soup is mostly water, whereas rice is mostly not (and also has lots of air pockets, so the "cup of rice" has even less heat capacity than "a grain of rice". It also depends what other ingredients are present on the rice, meat, soup. Added salt or certain other chemicals can increase microwave absorption. DMacks (talk) 22:23, 29 November 2019 (UTC)
- Your soup may be gaining a lot of heat, but still staying at a low temperature. It's coupling the microwave energy in pretty well, but water also has a remarkably high specific heat capacity, thus takes a lot of energy to warm up. Andy Dingley (talk) 22:12, 29 November 2019 (UTC)
- Interesting, for me rice heats up the fastest, while watery food such as a soup or a stew needs the extra hard setting. Maybe my microwave has the wrong wavelength? 93.136.178.2 (talk) 21:43, 29 November 2019 (UTC)
- More general answer: microwave ovens work primarily by heating water. Heat is transferred to the rest of the food by thermal conduction. This means foods with a higher water content get heated more quickly and evenly. This is also why microwave cooking directions often advise you to let food sit after microwaving, and sometimes to stir it between cooking stages, or to use lower power settings. This allows the heat to diffuse from the water. --47.146.63.87 (talk) 07:39, 30 November 2019 (UTC)
- Good microwave ovens offer multiple automatic heating programs that use predefined heating and heat dispatching phases to warm and/or melt up food. Of course thous are more expensive than the cheapest ones and they need more time and a little more energy to achieve the task. --Kharon (talk) 08:06, 30 November 2019 (UTC)
- Please don't pass on the misinformation that microwaves only heat water or that they don't heat ice. From Microwave oven#Principles:
- "Water, fat, and other substances in the food absorb energy from the microwaves... It is a common misconception that microwave ovens heat food by operating at a special resonance of water molecules in the food... Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted... Compared to liquid water, microwave heating is less efficient on fats and sugars (which have a smaller molecular dipole moment)... However, due to the lower specific heat capacity of fats and oils and their higher vaporization temperature, they often attain much higher temperatures inside microwave ovens." --Guy Macon (talk) 08:13, 30 November 2019 (UTC)
- Go boil some water in an ice cup, then come back and say that. Andy Dingley (talk) 14:11, 30 November 2019 (UTC)
- Careful: "things that start off at a higher temperature wind up getting to a higher temperature" doesn't really prove a whole lot, and "liquid water gets hotter faster than ice" is actually completely consistent with what Guy just said. We are obviously not operating at equilibrium conditions. DMacks (talk) 14:43, 30 November 2019 (UTC)
- I generally refrain from responding to Andy Dingley, because I have never seen him change his opinion when faced with evidence against it. For those who doubt what our Microwave oven article says ("Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted") it is a simple matter to confirm at home that microwaves do indeed heat ice. Simply place an ice cube in a microwave, heat it on high, and see how long it takes to melt. Now repeat the experiment without turning the microwave on. It is also interesting to try dry sugar and pure cooking oil, but be careful; it is easy to make a hard-to-clean mess. And if anyone still thinks that microwaves only heat water, buy one of these [ https://www.amazon.com/dp/B01D9V8Z9O/ ], [ https://www.amazon.com/dp/B07BDK7BZY/ ] (or just read the customer reviews for them). --Guy Macon (talk) 16:58, 30 November 2019 (UTC)
- Actually Guy, what you usually do is post insulting and personally targetted cartoons. And a bit of pontification has always been your way. BTW - WP articles are not reliable sources. Andy Dingley (talk) 18:48, 30 November 2019 (UTC)
- I generally refrain from responding to Andy Dingley, because I have never seen him change his opinion when faced with evidence against it. For those who doubt what our Microwave oven article says ("Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted") it is a simple matter to confirm at home that microwaves do indeed heat ice. Simply place an ice cube in a microwave, heat it on high, and see how long it takes to melt. Now repeat the experiment without turning the microwave on. It is also interesting to try dry sugar and pure cooking oil, but be careful; it is easy to make a hard-to-clean mess. And if anyone still thinks that microwaves only heat water, buy one of these [ https://www.amazon.com/dp/B01D9V8Z9O/ ], [ https://www.amazon.com/dp/B07BDK7BZY/ ] (or just read the customer reviews for them). --Guy Macon (talk) 16:58, 30 November 2019 (UTC)
- Careful: "things that start off at a higher temperature wind up getting to a higher temperature" doesn't really prove a whole lot, and "liquid water gets hotter faster than ice" is actually completely consistent with what Guy just said. We are obviously not operating at equilibrium conditions. DMacks (talk) 14:43, 30 November 2019 (UTC)
- Go boil some water in an ice cup, then come back and say that. Andy Dingley (talk) 14:11, 30 November 2019 (UTC)