Wikipedia:Reference desk/Archives/Science/2019 November 24

= November 24 =

Memory foam for sleeping - real science or marketing gimmick?
I came here from a now-defunct conversation in Talk:Memory foam 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.

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." --
 * --Guy Macon (talk) 19:40, 24 November 2019 (UTC)
 * 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)


 * 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)


 * 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.  -- Jayron 32 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, 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 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)


 * 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)