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November 22

Fat burning

If a person is predominantly burning fat in his/her body, rather than carbs, due to a low carb diet, does he/she smell any different from other people who are predominantly eating more carbs? If so, how does it smell. Is it pleasant or unpleasant.? 86.8.200.208 (talk) 01:41, 22 November 2019 (UTC)[reply]

Define "pleasant" and "unpleasant". -- Baseball Bugs 01:47, 22 November 2019‎ (UTC)

Is it 'deemed' pleasant or not by the general mass of people, during the normal working or relaxing day/evening in the bar or at home or on the train etc,who are smelling it? 86.8.200.208 (talk) 02:13, 22 November 2019 (UTC) Ok. If you want to be awkward, just what does it smell like?[reply]

You are probably thinking of the smell associated with the ketogenic diet. Our article doesn't seem to say anything about it, but you could try a web search with those search terms. 173.228.123.207 (talk) 04:05, 22 November 2019 (UTC)[reply]

I am aware of "keto breath" (see https://www.healthline.com/health/keto-breath and https://www.webmd.com/oral-health/features/low-carb-diets-can-cause-bad-breath ). I did a google search on [ ketone body odor ] and found a lot of sites talking about it, but I didn't see any reliable sources. I would like to see a WP:MEDRS source that talks about it, and especially whether it is temporary until you adapt to the diet. --Guy Macon (talk) 17:08, 22 November 2019 (UTC)[reply]

What the mechanism by which vinegar has a cooling effect while eating it?

"The effect of vinegar was astringent, but it was also used frequently because of its soothing and cooling effects". It states that Ruth was bidden to dip her bread into vinegar (Ruth ii. 14). See here. Is it scientific true that vinegar can cool a body by eating it? What the mechanism by which vinegar has a cooling effect while eating it? ThePupil (talk) 02:56, 22 November 2019 (UTC)[reply]

Your source doesn't specify that the cooling effect is from consuming it. More likely, it is applied topically. The source also mentions that "it might be employed for dandruff, and even for dressing wounds". 2606:A000:1126:28D:144E:A9EA:EDD2:AB72 (talk) 06:37, 22 November 2019 (UTC)[reply]

I left below the sources that I forgot to added. You'll find there what I stated. ThePupil (talk) 20:52, 22 November 2019 (UTC)[reply]

Also for treating sunburn.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:01, 22 November 2019 (UTC)[reply]

Surely vinegar mentioned here not as a cooling food, but, still, it is still mainly water, and as such WILL cool by ingesting. The energy of acetic acid can be used inside the body, releasing 875 kJ mol−1 / 14,58 kJ g−1, but this is too low to offset the cooling effect of water. So, it IS scientific truth that vinegar can cool a body by eating it, the mechanism by which vinegar has a cooling effect while eating it is just the same as water's. Gem fr (talk) 08:22, 22 November 2019 (UTC)[reply]

Does it mean that the they have the same level of effect? If so, why did they use vinegar for this purpose, while water is cheaper and tastier?ThePupil (talk) 20:52, 22 November 2019 (UTC)[reply]

Water (and food!) was a killer at the time (and remained so, well, pretty much until 20th century, AFAIK) , unless you are very sure of its purity, or disinfect it in some way. Physical mean like boiling it would do. Chemical mean such like adding vinegar also would, and could be more practical and cheaper, especially when you don't want heat; it seems that this was pretty common in the space-time you are interested in. Gem fr (talk) 22:58, 22 November 2019 (UTC)[reply]

Water always was a source of infections, and it's still. But it didn't avoid people to consume water ever. So the explanation you suggested doesn't make sense not only because the bible is full of descriptions of people who drunk water as an habit, but mainly because a few verses above in the same chapter (which describes that they dipped the bread in the vinegar (not drunk it!) there is a verse which mentions that they drunk of that which they have pumped (from the well, i.e. water). ThePupil (talk) 00:02, 23 November 2019 (UTC)[reply]

It could also be perceptive effects. After all, mint doesn't lower the temperature of your mouth, but it activates sensors in your mouth to make you perceive a sensation of coolness. That may be what they are talking about. --Jayron 32 13:13, 22 November 2019 (UTC)[reply]

@Gem fr: The energy of acetic acid can be used inside the body, releasing 875 kJ mol−1 / 14,58 kJ g−1, but this is too low to offset the cooling effect of water (emphasis added) citation or calculation please, because I strongly suspect that affirmation is somewhere between "wrong" and "not even wrong". Tigraan^{Click here to contact me} 14:55, 22 November 2019 (UTC)[reply]

water cools you mainly through evaporation, taking away (more or less; not exact because starting temperature, different pressure, etc.)2257 kJ/kg of evaporated water, so you need to turn ~155g of acetic acid entirely into heat to offset that. Common vinegar would have, like, 3x or more less acetic acid, AFAIK, so, too low to offset the cooling effect of water. Gem fr (talk) 17:47, 22 November 2019 (UTC)[reply]

You are simultaneously addressing energy released from ingestion and energy used for evaporation. Ingested substances do not seem likely to under go evaporation. DMacks (talk) 18:01, 22 November 2019 (UTC)[reply]

ingested water IS likely to undergo evaporation when cooling is needed (less so when cooling is not required, of course). Now, if you claim that ingested water won't cool you, well, you crossed my limit. Gem fr (talk) 18:25, 22 November 2019 (UTC)[reply]

OK, not even wrong then. The calculation (enthalpy of combustion of acetic acid) - (latent heat of water) may well yield a negative number, but drinking an amount X of water will not increase body evaporative cooling proportionally to X (see Homeostasis#Fluid_balance, Thermoregulation, etc.).

I was thinking of the calculation (enthalpy of combustion of acetic acid) - (heat capacity of water × temperature difference between ingested water and body) which yields almost surely a positive number (which makes the argument "wrong"); it probably is not too wrong for the heat capacity part, but physiology considerations would still apply to the combustion part (ingested organic matter is not entirely released as a mix of CO2, H2O and nitrates, so you cannot assume the combustion is close to complete). Tigraan^{Click here to contact me} 13:24, 25 November 2019 (UTC)[reply]

Oh dear. congratulation, you just proved that you cannot rely on drinking water (or, even worse, hot sweetened tea) to cool you. That, or you missed the point. Your choice. Gem fr (talk) 14:02, 25 November 2019 (UTC)[reply]

The article about vinegar which I cited earlier also points out that cool water also helps relieve the sting of sunburn. So it might indeed be the water in vinegar which is doing the job, equal to or more so than the pungent parts. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:40, 22 November 2019 (UTC)[reply]

Here is a group of interpretators of the bible that say: vinegar consumption has a cooling and refreshing effect. I'd like to ascertain it scientifically. ThePupil (talk) 20:46, 22 November 2019 (UTC)[reply]

Original Research, but I have personally observed that adding a small quantity of vinegar to tap water (which by law is of potable quality in my country) makes the water more palatable and "refreshing", masks any harmless but unappealing tastes resulting from water treatment, etc., and therefore encourages one to drink more of it.

In a Biblical context, I would observe that the alcohol in wine (and other alcoholic beverages like beer) exposed to the air turns partially to vinegar (the word literally means "sour wine") which was likely how most vinegar was anciently manufactured, and partly soured wine has been claimed to have been called vinegar, and commonly drunk, by Roman soldiers. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 13:24, 23 November 2019 (UTC)[reply]

I don't like the smell of vinegar (and so dislike most things with enough vinegar that you can smell/taste it e.g. vinegar chips). So adding it to water is unlikely to make me drink more water. I've never had a problem drinking most tap water, even in Malaysia where it can sometimes be quite chlorinated although the norm there is to boil water and so there is a standing period which reduces it somewhat. OTOH, I do find even during winter I actually prefer ~4 degrees C water from the fridge compared to 10-20 degrees water from the tap and it probably makes me drink more. Nil Einne (talk) 15:53, 23 November 2019 (UTC)[reply]

The amount of vinegar I employ is a few drops in, say, 1/3 of a pint of water, nowhere near enough to smell, or to actually taste of vinegar. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 22:03, 23 November 2019 (UTC)[reply]

Thank you all for the participation and sharing your interesting opinions in this discussion. ThePupil (talk) 05:52, 25 November 2019 (UTC)[reply]

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)[reply]

AFAIK, white dwarf, being lighter than Chandrasekhar Limit, does not fuse anything heavier than iron. אילן שמעוני (talk) 18:29, 23 November 2019 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

...Or more commonly, sodium diacetate. 2606:A000:1126:28D:144E:A9EA:EDD2:AB72 (talk) 04:09, 24 November 2019 (UTC)[reply]

Thank you all for the answers. 05:49, 25 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.[2][3]

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)[reply]

" 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." -- [4]

--Guy Macon (talk) 19:40, 24 November 2019 (UTC)[reply]

@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)[reply]

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)

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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. --Jayron 32 13:44, 25 November 2019 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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. --Jayron 32 13:41, 26 November 2019 (UTC)[reply]

+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)p_3/2 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 7p_3/2 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 Ts^I 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 8s_1/2 and 7p_3/2 for E120 to be more than that between 7p_3/2 and 7p_1/2 for Lv as the 7p_3/2 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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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. --Jayron 32 19:22, 25 November 2019 (UTC)[reply]

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)[reply]

Angina may explain. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:08, 26 November 2019 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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 [5] and the NZ MOH [6]. 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 [7] 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 [8]. And they do include viruses in the papers they list [9]. (And elsewhere they call viruses microbes [10].) 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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

Any vehicle is likely to have an optimal fuel consumption range. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:59, 27 November 2019 (UTC)[reply]

And how many vehicles spend less fuel while moving than while quiet?--C est moi anton (talk) 19:43, 27 November 2019 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

Who told you tribbles grow in water? --C est moi anton (talk) 18:44, 27 November 2019 (UTC)[reply]

You forgot about the politicians. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:59, 27 November 2019 (UTC)[reply]

Politicians grow everywhere like weeds.C est moi anton (talk) 19:32, 27 November 2019 (UTC)[reply]

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. Brandmeister^talk 21:43, 27 November 2019 (UTC)[reply]

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)[reply]

Why does this peripheral drift illusion stop working when rotated 45°?

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)[reply]

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)[reply]

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)[reply]

Try doing this closing one eye. Gem fr (talk) 21:25, 27 November 2019 (UTC)[reply]

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)[reply]

What are these creatures?

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)[reply]

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)[reply]

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)[reply]

Hard to be sure, but barred mudskipper looks likely. Mikenorton (talk) 08:37, 28 November 2019 (UTC)[reply]

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)[reply]

This article[11] discusses the question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:12, 28 November 2019 (UTC)[reply]

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)[reply]

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)[reply]

You could start by reviewing List of climate scientists. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:19, 28 November 2019 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

November 29