Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

January 1

Are large rings of pure oxygen possible?

What about this? Sagittarian Milky Way (talk) 19:32, 1 January 2019 (UTC)

Solid oxygen describes allotropes of four and eight oxygen atoms per molecule. The graphic you have is some sort of crown ether, but with all those oxygens on each carbon atom (gem-diol) I would be very skeptical about its stability. Wnt (talk) 20:59, 1 January 2019 (UTC)

Long chains of oxygen are endothermic at standard pressures. Energy is released to make dioxygen. They may be stable at low temperature. Trioxygen difluoride and bis(trifluoromethyl) trioxide both exist. For your "what about" there are organic esters of tricarbonate. Your structure will rapidly turn into water and carbon dioxide unless you can freeze it. Under high pressure carbon dioxide may behave more like silica. Graeme Bartlett (talk) 21:04, 1 January 2019 (UTC)

Cyclic and linear polymers of -CH₂-O- are known (see polyoxymethylene and Formaldehyde#Forms of formaldehyde). Various analogs with chains or functional groups instead of the H on the C are known also, but gem-diols (especially the hydrate of a carbonate ester) are quite unstable. DMacks (talk) 14:37, 2 January 2019 (UTC)

January 2

Animals with head first delivery preferred?

What animals other than humans have the preferred delivery being head first (as opposed to for example a cow, for which the front hooves is the preferred first part of the animal to deliver.Naraht (talk) 01:18, 2 January 2019 (UTC)

Well, the other great apes and indeed a majority of simians. This is actually an interesting evolutionary matter, as live birth is believed to have evolved independently in various parts of the tree of life on at least a couple hundred occasions, and the variations on the physiological morphology are remarkable as a result. There are a number of different factors which are believed to have influence which species evolved head-first birthing (meaning superior portion of the body first, which a strong but by no means absolute majority of live birth species use), but by far the most significant is cephalo-pelvic ratio: basically, the higher this ratio the more likely the species is to require this form of birthing, and then at the high end of that spectrum (especially where mammals are concerned) are mostly clustered the cranial-first species. Of course we must also account for aquatic live-birth species, of which there are quite a few, most of whom have no legs to compete with the head. Snow ^{let's rap} 12:06, 2 January 2019 (UTC)

Thank you very much. I am excluding the aquatic in this. What is the split within the simians?Naraht (talk) 14:59, 2 January 2019 (UTC)

You're very much welcome. As to your further inquiry, I'm unaware of an obvious single source that aggregates that data, and could not immediately find one, but it's likely to be out there somewhere. Here are a few sources which at least provide detailed consideration of the relative physiological proportions in various simian species, though a majority of them are behind paywalls which may restrict your access depending on your research portal resources: [1], [2], [3], [4], [5], [6].

My suspicion, based upon what I do know about parturition across mammalian species, is that the vast majority of all simians birth cranium first. Of course, you should take that uncited statement with a grain of salt, but there's actually a generally reliable test for figuring out which species are going to birth which extremities in which order: Because childbirth is an exceptionally risky process for both parent and offspring in most all species, there is a substantial selective pressure to ease and expedite the process to the extent the morphology of the child allows. As such, in mammals there is a pronounced, almost universal preference for births to proceed in the order which minimizes the maximal circumference to which the vagina will be stretched, thus minimizing potential trauma to the mother and child. So obviously with most bipeds, allowing the hands and arms to come out extended alongside the cranium would increase the radius and also put dangerous pressures upon parts of the body already tightly constrained by pressure that is already at the high end of all animal parturition. Whereas with most livestock species, to borrow your example from above, the most complicated and problematic method would be too have the legs pressed downwards against the trunk of the body, which is why most all avoid this by having the forelegs precede the head. Now this is not an absolute rule, because there are other considerations and many species actually have room to spare in the vagina (well, at least compared against humans, who are at an extreme end of the spectrum), including some simians. But as a general rule, you can look at a species, consider it's biomechanics (which way the extremities most naturally flex and which profile would allow for a minimal demand upon increase in the diameter of the birthing canal) and make a rough reliable guess for whether they are likely to come out cranium first or superior limbs first. Snow ^{let's rap} 23:16, 2 January 2019 (UTC)

FYI: Apparently, hyenas have a very high mother-and-infant mortality rate during childbirth, but a low post-partum chld mortality rate, becasue the fetal hyena develops farther and larger in utero than most other mammals. The latter is alluded to in the wiki hyena article. (I read about this someplace years ago (perhaps Tuesday NYTimes Science section?), but don't now have a reference.) Acwilson9 (talk) 21:27, 7 January 2019 (UTC)

January 4

Is there any evidence that biology is reducible to physics

Reductionism has worked very well for technology but why do so many people assume everything can be reduced to subatomic particles? There are intractable problems like how the first cell formed, consciousness, free will, if reductionism is to be believed. Is there any research along the lines of "strongly emergent" behaviours of complex systems? By strongly emergent i mean something that's not predicted to exist given the laws governing the constituents, i.e. something completely new comes into existence at sufficient complexity. Have people tried to calculate how the simplest bacterium behaves according to laws governing atoms? — Preceding unsigned comment added by Money is tight (talk • contribs) 04:25, 4 January 2019 (UTC)

As mentioned in this talk, for simple microbes there does exist a complete description. But, with hundreds of thousands of different enzymes, the "flow chart" of a microbe is huge, it fills tens of thousands of pages. Count Iblis (talk) 04:49, 4 January 2019 (UTC)

Bear in mind that reductionism is not necessarily about arriving at the most efficient description of a given phenomenon--it's just an attempt to isolate and definite its constituent features, ideally in terms of universals that can be used for all other like phenomena, or (when it comes to physical reductionism, potentially all phenomena). So, to answer the query of your first sentence, the effort is based not so much in an "assumption" that everything can be reduced to a discussion of such constituents--no sensible empiricist working from first principles would operate their inquiry in that way--but rather upon a testing of that hypothesis. And so far, with one deeply perplexing exception, all biological functions have proven amenable to description in terms of physics. The one exception, which you allude to in your inquiry, is something we have such a difficult problem even conceptualizing, that we can;t reliably say whether it is a property (emergent or otherwise) of biology or physics--although we have a profound propensity/bias to frame it in those terms. I am, of course, talking about consciousness. Because it is (not just in terms of biology or psychology, but indeed the entirety of science and empirical human inquiry) the one phenomena that has never been captured or explained by a physical model in any concrete fashion, at any level, this quandry has been given (rather appropriately, I feel) the forbiding title of the the hard problem. And it is indeed something so incredibly different and alien to the empirical method, that some philosophers and cognitive scientists surmise that it is in some sense illusory (whatever Descartes would say to that) or something so far beyond the parameters of what our mental organs are designed to grapple with, that we will never understand it in even a rudimentary fashion. But as to everything else, reductionism works as well for biology as for any other physical system--the complexities simply require a broader canvas to orient and make sense of, with a lot of work still to be done to fill in the gaps--a task which may realistically span eons, if it is resolvable at all. Snow ^{let's rap} 05:41, 4 January 2019 (UTC)

Just as an addendum, OP, despite my comments above, which might reasonably be received as a full-throated defense of reductionism, I do not mean to suggest it is the only (or even the most effective) empirical model for physical systems, only that there is not fundamental reason why, as a per se matter, it cannot describe all biological phenomena. However, for an alternative model, you might consider looking into systems theory, which is very much in the vein of describing emergent properties of complex systems. Fritjof Capra, one the populizers of this field of thought, wrote a number of popular science works surveying its development, and one of them is focused on biology in particular. Alas, we have no article for it (perhaps I should fix that), but the title is Web of Life; it could be a good place to start regarding your interests in this area. Snow ^{let's rap} 05:55, 4 January 2019 (UTC)

Really? There has been calculation of the trajectories of each atom in a cell and it agrees with the observed movement? May I see a reference? — Preceding unsigned comment added by Money is tight (talk • contribs) 09:23, 4 January 2019 (UTC)

You're confusing the question of whether a model is in principle capable of describing a phenomena with the question of whether one has the ability to perform a given calculation--two very different matters. From the start through the finish of your original post, you framed the biological question as fundamentally different from other physical phenomena in terms of whether or not they could be reduced into fundamental constituents governed by the same basic physical laws as the rest of matter. And unless you are looking for some sort of answer steeped in quasi-mysticism, there's just no reason to believe that's so, and there's nothing in modern theoretical physics (whether it is reductionist or systems based) which suggests as much. The only difference between the only two examples of application you raise--the vaguely defined "technology" and a human cell--is the orders of complexity involved in the specific object or process observed. Again, that's a matter of calculation restraints, not any flaw of the model itself, and I believe I made it pretty clear in my first response that the distinction is between efficiencies when one compares more or less reductive methods of description of a given closed system against others. But more to the point, friend, if you want to be snidely dismissive of an answer that isn't the one you wanted, seconding your opinion of how limited a fundamental ontological branch of physics is, I'll just leave you to the assistance of all of the other people who have rushed to take some time out of their day to give you a considered answer and point you to some resources.... Snow ^{let's rap} 10:50, 4 January 2019 (UTC)

Oh, but I see from reviewing your contrib history that this is not a topic you were looking for information on, but in fact a topic you are persistently trying to create a debate around, across numerous spaces on this project over the course of years. Please understand that the RefDesk, and Wikipedia broadly, are WP:NOTAFORUM for you try to use to argue your metaphysical perspectives on. This desk is for genuine inquiries, not your efforts to set up someone to espouse a perspective you disagree with, so you can attempt to score a discursive victory. This has already been explained to you previously, I now see. Please respect the scope and purpose of this space. There are plenty of forums online for you to advance and argue your beliefs at length--this is not one of them. Snow ^{let's rap} 11:10, 4 January 2019 (UTC)

I was genuinely asking for a link about any strongly emergent process, after watching this https://www.youtube.com/watch?v=GVL2Y5z2jLU and knowing the severe problems with reductionism. All you did is link me to biophysics article and claim all of biology except for consciousness has already been proven to be derivable from interactions between atoms. I ask for link then you get so hurt that you spend the time to go through my posts just to cook up some insults so you can feel better about yourself... All I can do is lol. — Preceding unsigned comment added by Money is tight (talk • contribs) 11:54, 4 January 2019 (UTC)

There is an article "Reductionism in Biology" in the Stanford Encyclopedia of Philosophy. There is no proof that biology can be reduced to physics but there is no proof it cannot. I suppose the reason that people assume reductionism is possible is that organic objects have been observed to respond to physical actions in the same way as inorganic ones. It requires the same effort for example to transport organic and inorganic cargo of the same weight. There seems to be implicit in your question whether a resolution of this issue would have any metaphysical implications, specifically whether it could prove or disprove religious claims. The answer is no. (PS - please sign your posts.) TFD (talk) 13:43, 4 January 2019 (UTC)

The point is, this space is for people seeking information, while your previous history of getting into fights about the nature of an immaterial existence beyond the body all across the project as basically your only activity here for years makes it clear that that you are actually here to find opponents/a debate--and you're not going to get either here. You very clearly were asking about something you expected responders not to be able to provide to your satisfaction: you ask your queries with the vague "Have people tried to calculate how the simplest bacterium behaves according to laws governing atoms?", to which the obvious answer is "yes, of course" at which point you get to swoop in with "Oh come on, obviously no one has tracked the motion of every subatomic particle in a cell", which is something you clearly already knew and just wanted an excuse to say. Again, this space is for people who are requesting new information on a topic, not an excuse to argue about spiritual or philosophical beliefs for which they already know the standard arguments, which they want to engage in a WP:BATTLEGROUND over.

Your question was disingenuous and you're just trying to re-engineer the same debate you apparently have everywhere you go on Wikipedia--on talk pages for articles about near-death experiences to those about metaphysics and indeed, on this very page previously--despite being told this project isn't the place for that kind of engagement. It is WP:disruptive to the point of being a form of WP:NOTAFORUM trolling, since you clearly know this is, under our policies, not an acceptable use for a talk space and yet it is all you are here to do. Please desist. Snow ^{let's rap} 17:14, 4 January 2019 (UTC)

If this isn't a forum, this isn't a moot court either. There are some good answers here but please, take the nastiness and WP:SILLYTERMS to talk or something. Wnt (talk) 22:03, 4 January 2019 (UTC)

Wnt, this isn't about nastiness, it's about WP:NOTHERE and WP:DENY. And why would I take this talk; I'm not trying to give an opening to any guideline skeptics to open that TP's five-hundreth tedious, no-consensus debate about liberalizing our WP:NOTAFORUM standards. I commented here because this is where this user is engaged (for the moment) and therefore this is the appropriate place to tell him this is not what the RefDesks are for. Aside from that, I'd said what I intend to say on the matter, but I'll add this: I really suggest you look through the diffs before you consider feeding this user's behaviour--you'll not be doing the desks any favour and you'll be steering them that much closer to a block or topic ban. Snow ^{let's rap} 01:24, 5 January 2019 (UTC)

Can blood vessels damaged by hypertension repair themselves?

I personally think the damaged inner lining of artery in which inducers like hypertension left cracks on the vessel wall that later allowed buildup of plaque (lipids) can eventually heal on their own if the inducer such as hypertension is no longer present just like how a bleeding-wound healing works when we don't rub it or irritate it. If a cut or damaged vessel can't be regenerated, then those bleeding wounds on the skin involving much broken vessels we have all ever had in childhood shouldn't have been able to heal.

I wonder which article to read in Wikipedia that gives in-depth introduction to damaged blood vessel wall recovery? Thanks! --It's gonna be awesome!✎Talk♬ 13:52, 4 January 2019 (UTC)

I would try to start at wound healing or Regeneration in humans and check out ongoing links there. For more specific Information you may have to search the WWW.

Anyway, since the exact cause of Atherosclerosis (plaque builds up inside your arteries) is still considered to be unknown to science, some answers to that part of your questions may be more speculation than science. --Kharon (talk) 15:33, 4 January 2019 (UTC)

Thank you for the productive response! --It's gonna be awesome!✎Talk♬ 16:11, 4 January 2019 (UTC)

Everything in your body, including your arteries are constantly being repaired in response to damage done. Biological systems are dynamic systems not static systems that gradually wear down. Any long term degradation of a system in your body is the result of the net balance between wear and tear and the repairs being slightly negative. So, if you remove a source of wear and tear in your body then usually the system will improve. E.g. atherosclerosis is not simply the result of a long term deposition of plaque on artery walls, it is the dynamic equilibrium between plaque buildup and plaque removal being shifted too much toward plaque buildup. Under normal circumstances both processes occur at quite high rates, but plaque removal is more effective so arteries of animals tend to not have any plaque. When the first heart-lung machine was invented, the medical scientists were surprised to find that blood circulating in the pipes of the machines had a large amount of blood clots in them after just a few minutes. This shows that the blood vessels in your body are not simply inert pipes. This is why people who get angioplasty and are fitted stents need to get anti-platelet medication for the rest of their lives. Count Iblis (talk) 19:43, 4 January 2019 (UTC)

Yes, but the process of wounding and healing is inefficient, which is why scaring is a thing. The repair the body makes in response to stress, damage, injury, etc. is almost always inferior to what would have been there had the damage not occured in the first place. In general, the microscopic accumulation of these processes of damage and repair is senescence, and most living multi-cellular organisms undergo these problems to one extent or another. The body cannot go one forever, because the processes that created the body are not the same processes that repair the body. --Jayron32 20:38, 4 January 2019 (UTC)

Thanks both of you for the informative replies. --It's gonna be awesome!✎Talk♬ 09:27, 5 January 2019 (UTC)

Australian Snakes - Origin ?

How did the ancestors of modern Australian snakes get to Australia across Wallace's Line? It is my understanding that snakes are thought to be a monophyletic clade, so that the ancestral reptiles either evolved elsewhere and went to Australia or evolved in Australia and went elsewhere. Wallace's Line has been a barrier to placental mammals since before the evolution of placental mammals. (When Europeans "discovered" Australia, it had two placental species, C. dingo and H. sapiens, and we know which of them built boats.)

This would seem to imply either that snakes are older than placental mammals and crossed to Australia when there was a land bridge across what is now Wallace's Line, or that there is some alternate explanation. The alternate explanations that come to my mind are that aquatic snakes crossed to (or from) Australia and evolved back to terrestrial life, or that snakes arrived by rafting or similar accidental transport. Robert McClenon (talk) 20:58, 4 January 2019 (UTC)

• Rafting. Abductive (reasoning) 21:13, 4 January 2019 (UTC)
• (ec) The argument is not conclusive - it may be that placental mammals did not migrate to Australia for some other reasons (e.g. unsuitable climate, or origin in a very different location and not having spread there before the Wallace Line became a barrier). Indeed, Wallace Line says that the deep water channel has been a barrier for "over 50 million years", while "true placentals may have originated in the Late Cretaceous around 90 MYA, but the earliest undisputed fossils are from the early Paleocene, 66 MYA, following the Cretaceous–Paleogene extinction event" (from Placentalia#Evolution). Snakes go back at least 90 million years, so probably could have spread to Australia long before the Wallace Line became a barrier. Indeed, a lot of interesting continental movement happened during the time snakes have been around - it's hard to imagine 1e8 years... --Stephan Schulz (talk) 21:19, 4 January 2019 (UTC)

• Naw, just rafting. Abductive (reasoning) 21:48, 4 January 2019 (UTC)

As I said, either rafting or a land bridge. No suggestion of swimming. Robert McClenon (talk) 23:39, 4 January 2019 (UTC)

There are variety of families, but none endemic to Australia. This means it can only, only, only be rafting. Abductive (reasoning) 01:44, 5 January 2019 (UTC)

This paper may be of interest, although it deals with all snakes, rather than just Australian ones. The "biogeographic reconstruction" section on page 19 discusses the likelihoods of snakes crossing water barriers of various different sizes. Mikenorton (talk) 21:52, 4 January 2019 (UTC)

Thanks. Robert McClenon (talk) 23:39, 4 January 2019 (UTC)

Robert McClenon, "two placental species", and the rest. cygnis insignis 22:26, 4 January 2019 (UTC)

User:Cygnis insignis? What do the two placental species have to do with the snakes? The snakes were already there. If you mean that how H. sapiens arrived is just another oceanic dispersal, that is one way of viewing things. Robert McClenon (talk) 23:39, 4 January 2019 (UTC)

Robert McClenon, excuse me being unclear, there are many placental mammals (Placentalia). Lots of them, the statement at the outset is incorrect. cygnis insignis 23:44, 4 January 2019 (UTC)

What other placental mammals were there in Australia at the time of its "discovery" by Europeans? Robert McClenon (talk) 01:42, 5 January 2019 (UTC)

I assume bats would have made it to Australia, as they did to more remote NZ.-gadfium 03:04, 5 January 2019 (UTC)

Okay, thank you. Two land placental species, then. Robert McClenon (talk) 04:51, 5 January 2019 (UTC)

According to Fauna of Australia#Placental mammals, there were at least two families of bats (it's a little unclear from the article how many were present prior to European influence), and many species of rodents, with 14 genera from five million+ years ago, and another seven species of rats from only one million years ago.-gadfium 05:17, 5 January 2019 (UTC)

Then the rodents presumably arrived by rafting. Robert McClenon (talk) 08:32, 5 January 2019 (UTC)

Robert McClenon, inside snakes being carried by bats between rafts during the Eocene (sometime before Europeons arrived) cygnis insignis 21:21, 5 January 2019 (UTC)

I haven't put in the effort to answer this properly, but for example Elapidae has members in and out of Australia. The genus also includes sea snakes, but I don't know how rapidly ancestral forms might have developed the ability to cross the ocean. This list of "ten deadly snakes" [7] are all venomous elapids; I haven't figure out, but if the continent was colonized by something akin to a sea snake I suppose it would explain why so many of its snakes are deadly. Wnt (talk) 15:07, 6 January 2019 (UTC)

Flightless Birds - Origin?

Now that we have discussed the arrival of snakes in Australia, I will ask about the arrival of the emu in Australia. There are large flightless birds known as ratite birds in Africa, South America, and Australia. Did the emu arrive in Australia by rafting, or by land bridge, or are the flightless birds paraphyletic, so that their ancestors flew, and they then evolved species that were too large to fly? Robert McClenon (talk) 23:44, 4 January 2019 (UTC)

• The ratite article seems to cover this. Abductive (reasoning) 01:42, 5 January 2019 (UTC)
• Robert McClenon I would recommend this article by zoologist Darren Naish [8]. To directly answer your question, their ancestors are thought to have flown there and then evolved into emus and cassowaries. Now, the ratite lineage (moas, kiwis, emus, ostriches, cassowaries, rheas, and elephant birds) is a monophyletic group, with the exception of tinamous being deeply nested within them, sister to moas, but almost all of these lineages seemed to have independently evolved flightlessness (including kiwis and moas - the former are closest to elephant birds). Lusotitan (Talk | Contributions) 22:30, 6 January 2019 (UTC)

January 5

Species identification

There's a picture I need to add a caption to, identifying the species in the pic. What kind of hummingbirds are these?

Please provide link(s). Thank you.    — The Transhumanist   01:33, 5 January 2019 (UTC)

Another one...

What kind of hummingbird is this?    — The Transhumanist   01:36, 5 January 2019 (UTC)

There could be three species in those photos. Abductive (reasoning) 01:45, 5 January 2019 (UTC)

For the first picture, of the two in New Mexico, I'm not sure we can see the birds clearly enough to identify them. I found a list of NM hummingbirds (with pictures) here. For the one on the left, all I can really make out for certain is the iridescent green on the back. There are multiple species in NM to have this, including the Broad-tailed hummingbird and Ruby-throated hummingbird (and probably others; please check through the list). According to that site, neither is very common in NM, though our article confirms that the broad-tail at least passes through while on migration. The picture was taken in May, though, which doesn't seem to be when they migrate. Sorry, maybe someone else can do better.

For the bird from San Fran, I think it's a Rufous hummingbird. Matt Deres (talk) 15:54, 5 January 2019 (UTC)

FYI, I've converted your images to thumbnails so they'd sit more easily on the page; I'm not sure why you'd set them as banners instead of thumbnails, but it was distracting. Matt Deres (talk) 19:07, 5 January 2019 (UTC)

I was looking at the articles about, and they say that the broad-tailed hummingbird has a white eye ring that can be used in identification, which I think I see in the first image. The article shows a summer range including much of New Mexico as I would interpret the graphic. Our article on Rufous hummingbird says that it is very difficult to distinguish from Allen's hummingbird and it might come down to exactly where and when the picture was taken. Wnt (talk) 14:03, 7 January 2019 (UTC)

Good point. I thought the tail was diagnostic, but I guess not. Unfortunately, the photo is only dated as "2006", so there's no saying whether it was summertime or not. Maybe the blooms would lend a clue? If they're not typically open while Allen's is there, that would support my proposal of Rufous. Matt Deres (talk) 21:21, 7 January 2019 (UTC)

Can organic chemistry reactions be calculated on a computer?

I've seen computer-generated videos showing what happens in some of these complex organic chemistry reactions, but can computers actually calculate what is happening? Computational chemistry doesn't say anything about organic chem. Bubba73 ^{You talkin' to me?} 08:39, 5 January 2019 (UTC)

3D-Visualisation of a Photosynthetic reaction centre (cytochrome subunit)

If you count PET/CT-Systems as computers, they can even be set up to track marked molecules in a body in realtime and that way track and measure biological processes in a living organism. Computers are also frequently used in fields like Process simulation or Chemical reaction engineering or simply as a 3D-Visualisation to understand more complex molecules or find key structures faster. Beyond that i doubt computers are successful in finding anything meaningful with purpose beyond their search pattern or to put it more precise realize when they find something special. --Kharon (talk) 16:44, 5 January 2019 (UTC)

I'm mainly asking about using physics to calculate how organic chemistry reactions work. Bubba73 ^{You talkin' to me?} 18:34, 5 January 2019 (UTC)

Like Folding@Home? Sagittarian Milky Way (talk) 19:35, 5 January 2019 (UTC)

Yes, I think that counts. Bubba73 ^{You talkin' to me?} 01:16, 6 January 2019 (UTC)

Tetrahydrocannabinol

Chemistry and especially Biochemistry or organic chemistry gets to complicated to fast and unpredictable if and how it interacts with other chemicals. Just compare the famous 2 drug Tetrahydrocannabinol THC and Cannabidiol CBD, which are a) almost identical and b)still very small molecules but they cause totally different effects in organisms and influence each others effects. A few years ago a study found CBD may be a Antidepressant[9].

If you could calculate even reactions of simple molecules, we would probably have drugs and medicine for every known illness and for future ones aswell today. Unfortunately we cant, not even with that very promising project Folding@Home that Sagittarian Milky Way thankfully linked. But nomatter its impressive 135 petaFLOPS calculation power apparently the best it manages to do is find "interesting Candidates" that have to be further evaluated by scientists for their potential.

So no. Computers cant calculate organic chemistry. Even with the power of a big commercial data center they need years to sort gazillions of possible combinations of molecules and their possible 3D structures for a "hey that one looks interresting". --Kharon (talk) 01:24, 6 January 2019 (UTC)

I'm not talking about calculating their effect, it is more about how the molecules operate on the molecular level, like DNA reproducing would be an example (probably one of the more complicated ones). Bubba73 ^{You talkin' to me?} 02:09, 6 January 2019 (UTC)

The level of sophistication I'm seeing here doesn't greatly impress me with its accuracy. But I don't know this area of research and I could be missing better efforts. Wnt (talk) 02:07, 6 January 2019 (UTC)

Astronomer vs. astrophysicist

It seems to me that more and more the general public is calling astronomers "astrophysicist". To name one, J. Allen Hynek - in the introduction he is listed as an astronomer but in the box to the right he is listed as an astrophysicist. He sounds like an astronomer to me. (I could name others.) Is this distinction getting blurred? Bubba73 ^{You talkin' to me?} 18:41, 5 January 2019 (UTC)

I think that in the twentieth and twenty-first centuries the distinction is probably one of self-identification by the scientist. Astronomy, by etymology, is the description of the stars. In early modern times it came to be the description of the telescopic observation of the planets and stars, first by Galileo and then by others. In the eighteenth and nineteenth centuries, after Newton showed that universal gravitation accounted for the orbital Kepler ellipses, astrophysics was the mathematical analysis of the orbits of the planets. In the twentieth and twenty-first centuries, astrophysics also includes the nuclear physics of what goes on inside the stars. Robert McClenon (talk) 20:04, 5 January 2019 (UTC)

In the case of amateurs, they are more likely to be called astronomers, especially if their research does not involve physics. They have long played a role of astronomy because of their willingness to spend time in observation. TFD (talk) 20:57, 5 January 2019 (UTC)

I had two astronomy teachers in college. One's research was in the interior of stars. I had him for celestial mechanics, and other things. Definitely an astrophysicist. The other's research was in observing galactic structure. He would be an astronomer in my mind. Bubba73 ^{You talkin' to me?} 21:32, 5 January 2019 (UTC)

I think that is the distinction people make, but it is becoming less distinct. As I remember, astronomy as the subject was called was part of the physics department and completion of the course fulfilled any requirements for high school physics. (That is if a course required prior completion of high school physics, then it was waived upon completion of an astronomy course. But there was also a separate "gee wiz" astronomy course that did not involve physics and did not count as a physics prerequisite.) TFD (talk) 01:21, 6 January 2019 (UTC)

Traditionally an astronomer was someone who named the stars -- observed what was in the sky. But now nobody reports that they "spotted a speck of light" at such and such a location; they have to try to explain what it is. And just explaining what it is involves things like Hubble's law and emission and absorption bands and if they are observing an orbital period and so on. So my feeling is that there is a lot of physics in any modern astronomy. Wnt (talk) 02:14, 6 January 2019 (UTC)

January 6

All-weather fighters

What was the first American or Nato fighter jet to have true all-weather capability (take off, intercept and destroy the target in any weather, and then land in any weather from an ILS coupled and/or manual approach and/or a PAR approach)? Is it true that the F-102 was capable of this? What was the first Soviet fighter jet to have the same capability? 2601:646:8A00:A0B3:74C8:E1A4:A5D:7436 (talk) 07:49, 6 January 2019 (UTC)

PAR approach is the correct wikilink. DroneB (talk) 11:04, 6 January 2019 (UTC)

It should be noted that "all weather" really means "most weather". The procurement specifications for "all weather" aircraft don't include the ability to fly into category 3, 4 or 5 hurricanes, severe icing, or H5 and larger hail. --Guy Macon (talk) 15:40, 6 January 2019 (UTC)

Also see: Lockheed WP-3D Orion. --Guy Macon (talk) 15:44, 6 January 2019 (UTC)

Indeed, it's more useful to consider the gradual improvement in aircraft capability. One useful metric is the percentage of operations that had to be scrubbed (cancelled) due to weather: you can compare how that percentage varied with time across aircraft types. Bear in mind that this analysis would be fraught with confounding variables, like the actual weather variability with time and geography of operations; and improvements to the infrastructure around the aircraft; and so on.

Personally, I consider the A-6 Intruder to be a significant milestone: its electronics and avionics look and feel very similar to modern aircraft. It even had computer screens in the flight deck!

Since the early days of aviation, pilots and engineers have been increasing the capability of the aircraft's control and navigation performance, marching toward operations in "all" weather. But even today, pilots use a healthy dose of Aeronautical Decision Making - that is, the scientific process of risk management (and specifically including quantitative analysis of the weather during the flight operation). If the sum total of all risks, including weather risks, exceeds a reasonable threshold, the flight must be scrubbed!

Nimur (talk) 17:35, 6 January 2019 (UTC)

And while we're digging into winter all-weather history, this was the front-page story on the All Hands digital edition during November/December last year: story about a now-famous F-9F flight - a specific mission launched in 1952 over a geographic region that today is either Korea, China, and/or Russia - the Navy pilots flew through a blizzard-condition snowstorm because their orders came from the cryptography division known in 2019 as the National Security Agency. When there's a reason to go, they can fly Panthers into snow...

This was an aircraft that was not "designed" for an all-weather role; its on-board systems and its pilot training regimen probably meant that it was not fully-prepared for combat operations in blizzard white-out. But, as long as you have a working compass, a working altimeter, and at least one additional instrument such as a turn coordinator, it is possible for a skilled pilot to keep their head up ... even though we'd all surely prefer an attitude indicator.

Nimur (talk) 17:50, 6 January 2019 (UTC)

The F-15 and F-16 both got an update to allow full allweather operation. I only read for the F-15 that the "F-15E" was the first version that was allweather but i guess the F-16 got updated at the same time. Likely it was mainly software since both fighters already had very capable, modern computers. --Kharon (talk) 18:38, 6 January 2019 (UTC)

General Dynamics F-16 Fighting Falcon says this: "it evolved into a successful all-weather multirole aircraft" (note piped link) and later this: "The first C/D version was the Block 25 with improved cockpit avionics and radar which added all-weather capability with beyond-visual-range (BVR) AIM-7 and AIM-120 air-air missiles." Martinevans123 (talk) 18:48, 6 January 2019 (UTC)

Thanks Martinevans123. I also just read the F-16 was the first manufactured with an advanced Fly-by-wire-System. Quite a package if you compare all that in the F-16C/D for ~19 million $ compared to the new fighters which are somewhere beyond 100 million $ a piece. --Kharon (talk) 19:28, 6 January 2019 (UTC)

It's a widely-known fallacy to compare costs on a unit-basis for such extraordinarily large Government acquisitions that span multiple decades. Consider reading Metrics to Compare Aircraft Operating and Support Costs in the Department of Defense, an extensively-researched economics policy whitepaper published by RAND and ... made available to the general public at zero-cost. Another relevant recent RAND Monograph, specifically as pertains to a total program cost comparison between F-16 and F-35, is MG-1225: Do Joint Fighter Programs Save Money? And if you're really following the news closely, here's RAND Report 2063 from July, advising whether a 24-month block-buy is a net cost savings between now and 2021; put simply, if we buy the same number of airplanes in 2021 and pay for them in 2021, they cost quite a different amount than if we pay for them in 2019, or if we pay for them in 2023; and if we decide in 2020 that we want to buy a different number of airplanes, the cost per airplane will also change! As you can surmise, this whole cost-per-airplane stuff is pretty heavily scrutinized by lots of experts!

Economics - it's a real thing with implications!

Of course, if you don't believe me, you can always hop on to Trade-a-Plane.com, where you, the discerning airplane-cost-expert, may purchase jets for discount prices, as long as you disregard the hidden costs of acquisition, transport, operation, training, airworthiness, maintenance, storage, fleet management, legal and regulatory items, taxes, tariffs, ... you know, the small details. I understand that as of January 2019, they even have MiG-29 listed on behalf of the owner.

Nimur (talk) 19:52, 6 January 2019 (UTC)

• Some time before the F-102. Either the Gloster Meteor NF.11 (UK), the F-94 Starfire (US) or the CF-100 (Canadian). All of these first-gen jet fighters were of fairly limited performance compared to what came only a few years later, but they had the basics. and were really just intended as stop gaps before the Gloster Javelin, F-102 or CF-105 became available.

At this early time, there was little distinction between 'all-weather' and 'night fighter'. Both involved deploying on-board radar. The airframes were largely interchangeable, even if deployed aircraft might be long-term tasked to either one or the other.

The 'basics' here were to have radar, a second seat (as these early sets needed an operator who wasn't busy piloting) and two engines. This was mostly to lift the weight of a heavier radar-equipped, twin-seater aircraft with large fuel capacity (adequate endurance in the days before in-flight refuelling) – engines of this era were low thrust, so two were needed. A second engine was also needed for reliability in the real all-weather case. The F-94 was sngle-engined, but also had a lighter weight radar set than the others, of limited range. It used this radar for interception and gunnery, but search and acquisition was performed by ground radar (and the SAGE system).

ILS was still in its infancy at this time but was developing both rapidly and in gradual stages. It didn't 'suddenly appear' in one go. Andy Dingley (talk) 20:31, 6 January 2019 (UTC)

"All-weather" fighters was an outgrowth of night fighters. The Germans worked on night/all-weather version of their Me262, but since the OP ask about US and NATO jet aircrafts;

• North American F-86D Sabre, first flight 1949 (developed as an all weather fighter)
• Douglas F3D Skyknight, first flight 1948, entry into service 1951 (developed as a naval all weather fighter)
• Avro Canada CF-100 Canuck, first flight 1950, entry into service 1952 (developed as a long range all weather fighter)
• Gloster Meteor NF.11, first flight 1950, entry into service 1951 (modified from a "day fighter" as an interim night fighter)
• de Havilland Vampire NF.10, first flight 1949 (modified from a "day fighter" as an interim night fighter)
• Gloster Javelin, first flight 1951, entry into service 1956 (developed as an night & all weather fighter)

All of the above was capable of taking off, navigating, conducting combat and return to base (and land) in darkness and inclement weather. WegianWarrior (talk) 20:36, 6 January 2019 (UTC)

@Nimur So the F-16 from 1998 was US$18.8 million and the F-35B from 2018 is US$115.5 million. That is a 600% rise in just 20 years or a bit under 30% inflation per year. I dont need a lesson in economy and even less some made up science paper or study to see something went wrong there. Besides i remember even Mr. Trump had some talks about that with Lockheed Martin. Btw. the russian Sukhoi Su-57 aka T-50 will be US$50 million according our articles. Bet it has all the latest technology an F-35 has, so new technology is not the factor for these crazy (600%) developements, not is time. --Kharon (talk) 21:16, 6 January 2019 (UTC)

@Kharon: I wasn't following the whole discussion, but your math doesn't take into account that inflation per year is multiplicative (like compound interest). You want 6.00^(1/20) = 1.0937, or 9.4% increase per year. Of course, this doesn't change the total amount the price has increased! Wnt (talk) 00:06, 7 January 2019 (UTC)

[un-indent] Thanks, all! So the conclusion (for the first question) is that by the end of 1950, the USA already had several interceptors with this capability. Now for the other question: when did the Soviets acquire the same capability? 2601:646:8A00:A0B3:74C8:E1A4:A5D:7436 (talk) 04:07, 7 January 2019 (UTC)

For several reasons (language and security, to mention two) the information on early Soviet all weather capable interceptors are harder to come by, but the earliest I'm aware of is :

• Yakovlev Yak-25, first flight 1952, entry into service 1955
• Sukhoi Su-9, first flight 1956, entry into service 1959

It is commonly accepted - as far as I can tell - that the development of Soviet avionics and airborne radar lagged western development by several years. This - and different strategic and tactical considerations - explains why NATO forces fielded all weather jet fighters several years ahead of the Soviets. WegianWarrior (talk) 04:35, 7 January 2019 (UTC)

Thanks! So as far as the Soviets were concerned, this song (recorded 1951) was at the time just empty bragging and actually described the capabilities which would have been used against them, just as I thought?  :-) 2601:646:8A00:A0B3:940E:B215:E6AD:437C (talk) 03:31, 8 January 2019 (UTC)

Why are carbonate esters so obscure?

Carbonate esters have been promoted as "green solvents" (dimethyl carbonate), but aren't something I've heard much about. Probably this reflects a very limited role in biology, hence few sources of cheap bulk carbonate ester compounds -- even though there should be a carbonate analog for almost every ketone. I know that carbonic acid and bicarbonate are everywhere in the body, and I see a report about a catalytic antibody able to catalyze a relevant reaction [10] and apparently their stability isn't all that different from esters [11]. Artificially, people make polycarbonate plastics out of them. But I really see very little about them in the biological literature! What is the big obstacle that prevents biology from making free use of them? Wnt (talk) 18:42, 6 January 2019 (UTC)

• The article Carbonate ester alludes to "the problem of high viscosity...". Abductive (reasoning) 06:36, 8 January 2019 (UTC)

Source of medical opioids like Percocet, Percodan, and OxyContin.

Could the pill manufacturers rely absolutely on synthetic production means, or do they have to use the poppy (the plant) proper for producing their medicines? --Doroletho (talk) 23:54, 6 January 2019 (UTC)

According to [12] "Synthetic opioids may be sub-divided into five chemical classes: phenanthrenes (including levorphanol and butorphanol), benzomorphans (including pentazocine and loperamide), phenylpiperidines (including fentanyl and its derivatives), diphenylheptanes (including methadone), phenylpropyl amines (including tramadol, tapentadol)." Those are fully synthetic; the others are either natural, or (mostly) semi-synthetic (natural materials that are chemically modified, like modifying morphine with acetic anhydride). Most of the semi-synthetic opioids still have a phenanthrene chemical structure.

I imagine that reference probably missed some more obscure classes from current research - it seems like somebody comes out of the woodwork with some yet more potent opium analog all the time nowadays. There are also cases like kratom where the classification is up for debate, and that too might be the case for obscure research chemicals. Wnt (talk) 02:09, 7 January 2019 (UTC)

January 7

Chief Engineer at Hughes Aircaraft at end of WWII

I have read that the Chief Engineer at Hughes Aircraft at the end of WWII suggested to Howard Hughes that he transition the company from the building aircraft to an electronics company (specifically focusing on radar, at least initially). If so, I think this fact and naming the Chief Engineer would make a significant contribution to the current article on Hughes Aircraft which at present simply states that after WWII the new Aerospace Division was headed by Ramo and Woolridge. The Chief Engineer made a significant contribution to redirecting Hughes from an aircraft company to an electronics (and ultimately) and Aerospace company. — Preceding unsigned comment added by Martyw999 (talk • contribs) 06:07, 7 January 2019 (UTC)

Maybe, if you can find a valid source. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:59, 7 January 2019 (UTC)

Have you checked the full-length books listed in our article's further reading material? Like articles on many subjects, our summary does not go into as much depth as a full-length scholarly textbook - nor even as far as a light-reading non-fiction book.

A few weeks ago, I picked up A Brief History of The Boeing Company. Now, I've read a lot of encyclopedias and a lot of books on aircraft and history, but this one book was among the most comprehensive and readable summaries of Boeing history I've found yet.

It would be wonderful if Hughes had ever published such a thorough history; but on account of their tumultuous reorganizations, it's probably unlikely that you'll even find a good summary on the corporate websites of the conglomerates that acquired the various branches of the former Hughes.

Some years ago, a co-worker had created a big wall-chart of M&A dating back to the early 20th century. I don't recall where they got their data, but I think it must have been superset material from the Commission on the Future of the United States Aerospace Industry. If you dig through the archived copies of that report, you can find an abbreviated wall-chart in Table 7-4; here's a PDF from archive.org.

Nimur (talk) 16:56, 7 January 2019 (UTC)

Straight lines on the ocean floor

What is this? Is it something to do with the photo? Thank you. Anna Frodesiak (talk) 17:16, 7 January 2019 (UTC)

According to Google, these so called "ship tracks" are an artifact of the measuring process, and the incomplete data on ocean depth, see Google blogpost. - Lindert (talk) 17:27, 7 January 2019 (UTC)

[Edit Conflict] I think it likely that Google Maps display the topography of the ocean floor according to the best data available. For most of it, this will be limited to satellite surveys whose resolution is comparatively poor and which therefore yield a somewhat smoothed appearance. However, where marine survey ships have deployed with sonar or lidar arrays the resolution will be much finer and will show the ruggedness of the ocean floor better. These linear tracks will therefore be the paths where survey ships have operated; their varying widths will be as a result of different systems having different capabilities it terms of how far sideways they are able to scan. Further details may be found in of through Seafloor mapping. {The poster formerly known as 87.81.230.195} 90.217.251.247 (talk) 17:35, 7 January 2019 (UTC)

See also Seafloor mapping and Bathymetry. Unfortunately, the first article is heavily weighted towards modern methods like satellites, which are of limited utility in mapping the deepest parts of the ocean, which still basically involves driving a boat across the surface of the water and sending soundings of some sort (usually something like a Multibeam echosounder) to do the measurements. Because of this, measurement artifacts get picked up in things like Google Maps. --Jayron32 17:35, 7 January 2019 (UTC)

That's exactly what the nazi alien ghost pirates in their undersea bases want us to believe... --Guy Macon (talk) 18:29, 7 January 2019 (UTC)

Ah-ha. More swastikas. Just like on the moon. Martinevans123 (talk) 19:40, 8 January 2019 (UTC)

The lines are artifacts of determining depth using marine seismic soundings (sort of a glorified SONAR, only a lot bigger and more powerful).

A very thorough mathematical treatment of the ship track problem is reviewed in Eliminating Noise and Ship Tracks, an online excerpt from the excellent book Geophysical Image Estimation By Example (Claerbout, 2008). That webpage is the jumping-off point into a lot of difficult math and software, and cites a whole lot of research papers. If you're unfamiliar with marine sounding geometry, chapter 1 of Basic Earth Imaging covers that in great detail. We also have an illustrated article section, marine survey acquisition.

Professor Claerbout used to make all the summer-students design and implement physics-based image-processing algorithms to remove ship track artifacts from sea survey data. Regrettably, his students all graduated to lucrative careers in geophysical image-processing, instead of getting snagged by Google or its ocean map data vendor - so the ocean maps you see at zero cost on the internet are ... sub-standard. (Interestingly, when Google bought the remnants of the completely unrelated technology designed by the software engineering legend, James Gosling, he quit Google to go play with underwater acoustics, before he got bought out by Boeing). He wrote a lot about this on his blog, NightHacks.

Nimur (talk) 19:17, 7 January 2019 (UTC)

Thank you very, very much everyone!!! Anna Frodesiak (talk) 19:20, 8 January 2019 (UTC)

Need access to a scientific journal

Hello. I write and edit science articles in Wikipedia, and there is one subject I want to update in the light of a new research paper, but the paper is behind a paywall. I wonder if Wikipedia has access to it on special bases. If so, which WP project may be doing this? The article and journal I need is:

• Chlorate brines on Mars: Implications for the occurrence of liquid water and deliquescence. J. D. Toner, D. C. Earth and Planetary Science Letters, Volume 497, 1 September 2018, Pages 161-168. doi:10.1016/j.epsl.2018.06.011

Thank you, Rowan Forest (talk) 22:20, 7 January 2019 (UTC)

I'm not aware of any special access for WP, but sci-hub can pirate it if you're okay with that. Lusotitan (Talk | Contributions) 22:22, 7 January 2019 (UTC)

Actually, I don't need it any more. Thank you. Rowan Forest (talk) 22:32, 7 January 2019 (UTC)

You go to a library of a major University. They typically have electronic subscriptions for a host of scientific journals, show your credentials, talk to a nice young female librarian and she gives you an access to their computer and database. You must have a google email account. Thanks, - AboutFace 22 (talk) 23:20, 7 January 2019 (UTC)

• Try emailing the authors directly. Most authors have the rights to distribute copies individually and are happy to help you out. Andy Dingley (talk) 23:40, 7 January 2019 (UTC)
• Wikipedia has Wikipedia:WikiProject Resource Exchange. This is totally legally different from Sci-Hub in that ... well, I have no idea, copyright isn't my religion. Wnt (talk) 03:08, 8 January 2019 (UTC)

For clarity: the Reference Desk endorses the use of proper channels to obtain permission for access to publications. We do not endorse piracy. We do not promote copyright infringement. Rather, we promote free access to free information.

Wnt, if you need an analogy to understand the difference: first, recall that there is a distinction between zero-cost and zero-restrictions. Imagine, by analogy, that you were queued in line to get some, shall we imagine, free beer; but while everyone else queued politely, you stand up, insisting that you're entitled to your free beer, that you don't respect anyone who pays for beer, and that you will take your beer with or without the permission of the people who are offering it to you at zero cost, because you admire piracy and renegade culture.

This would make you a boor, and it wouldn't really ingratiate you to all the people who are being nice, giving something away for zero cost, and the others who are all pleasantly partaking in an otherwise zero-cost exchange. I'm not sure where you are, geographically; but around my parts, boors can pay for their own beer.

Nimur (talk) 16:57, 8 January 2019 (UTC)

January 8

Strength of ice at colder temperatures?

Can buildings like 30-stories be built on ice instead of steel or concrete at colder temperatures? For example, absolute zero is at -459 F, so imagine a city of ice buildings from -10 F to -100 F, all the way down to absolute zero. Can ice be strong enough? 67.175.224.138 (talk) 01:48, 8 January 2019 (UTC).

Icebergs can extend 75 meters above the sea, according to that article. Nine tenths of the iceberg is beneath the water, but I'm not sure this counts because of buoyancy (the compressive force does not increase below the waterline). Our article on ice hotels says that SnowCastle of Kemi is the largest and maxes out at 20 meters. Further cooling seems like a useful tactic, but I am hesitant to make any guesses about the engineering of what has never been built. Keeping a skyscraper standing is more complicated than just measuring compression strength. Ambitious people can plan remarkable accomplishments with what we think are limited materials -- see List of tallest wooden buildings for example. Wnt (talk) 03:25, 8 January 2019 (UTC)

Seriously, they even proposed turning an iceberg into an aircraft carrier! 2601:646:8A00:A0B3:940E:B215:E6AD:437C (talk) 03:35, 8 January 2019 (UTC)

The links you want there are for pykrete (a composite mixture of water ice and sawdust) and Project Habakkuk (the proposed aircraft carrier). Are we allowed to make an ice-based composite for the purposes of this question, or are we limited to the properties of pure water ice? TenOfAllTrades(talk) 03:44, 8 January 2019 (UTC)

Imagine a city with buildings on a foundation of ice which starts to melt. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:00, 8 January 2019 (UTC)

We don't really have to just imagine it—climate change is already making buildings at high latitudes vulnerable to melting permafrost. The linked article touches on some of the passive and active strategies used to attempt to avoid the worst effects, from insulation and passive ventilation through to installation of subsurface refrigeration systems. TenOfAllTrades(talk) 05:13, 8 January 2019 (UTC)

I think you've just effectively answered the OP's question. It's a No. It might work on Pluto, but not here. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:23, 8 January 2019 (UTC)

Well, not quite. The OP isn't asking if it's possible here on Earth. They're asking about the strength and suitability (for construction purposes) of ice at lower – and potentially regulated – temperatures. I took a quick stab at trying to answer that question by looking for data on the compressive strength of water ice under various conditions, but I was flooded (ahem) with data about natural ice at 'normal' Earth temperatures only.

And it's worth noting that as far as the (different) question you're answering goes, the source I linked to doesn't say we can't build on permafrost even here on Earth, it's just that it adds significant cost and complexity, e.g.

“The Arctic foundations are considerably more expensive in permafrost areas,” said Streletskiy. “For example, for large residential apartment buildings in Russia, the cost of the foundation can be as high as 30 percent of the structure.”

One hospital in Alaska went to extremes to make sure the ground would stay solid. The Yukon-Kuskokwim health facility in Bethel refrigerates the ground with temperature-controlled probes installed in the ground.

Unfortunately, none of that gets back to the original question about the physical strength of ice at very low temperatures. TenOfAllTrades(talk) 14:17, 8 January 2019 (UTC)

It would be interesting to dunk an ice cube into liquid nitrogen and see if it becomes brittle. — Preceding unsigned comment added by Baseball Bugs (talk • contribs) 15:35, 8 January 2019 (UTC)

Water-ice does not have an abrupt glass transition, the way many common materials do; so the ice won't behave significantly differently during such an experiment. The brittleness you often see when other items are chilled to very low temperature is not solely because of the cold temperature: it also depends on their material properties and in some cases their composite structure. Here are some notes for setting up a lab experiment, suitable for high-school or early college students, from Wright State University's college of engineering. Nimur (talk) 16:22, 8 January 2019 (UTC)

At conditions on the Earth, ice subject to stress flows in a glacier. But if the temperatures is much lower it becomes more rigid, eg on Pluto. Graeme Bartlett (talk) 09:50, 8 January 2019 (UTC)

This is an engineering question. So I don't think stuff like tensile strength for ice at colder temperatures is known. Imagine if there was a 20-story ice building at -50 F, and then the temperature is raised to 15 F (still below freezing) and then it would be interesting to see if the building would collapse. I'm also trying to find out about hydrogen peroxide as a solid. All the literature tends to be about it as a liquid (like density as a liquid) but no data like density as a solid. 67.175.224.138 (talk) 16:08, 8 January 2019 (UTC).

Anyways my question arises as a comparison - we know steel and concrete is strong enough to build skyscrapers - far below their melting point - and so therefore I wonder if something like ice can be just as tough also at far below its melting point. So I wonder if stuff like tensile strength gets stronger at colder temperatures? 67.175.224.138 (talk) 16:20, 8 January 2019 (UTC).

The trump question is, how do you keep it from melting? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:21, 8 January 2019 (UTC)

Water ice also suffers the unique property that it can melt (and deform!) at contact when under compressive load - which is very bad for structural integrity. The minutiae of these details are argued on an almost monthly basis in our article section on the physics of ice skating; but here's a reference from Physics Today: Why Is Ice Slippery? (2005). Water, and its crystalline ice state, are strange substances; the atypical relationship between density and temperature are the major reason why ice floats over liquid water, instead of sinking.

If you've been watching the news, you've surely seen the beautiful photographs of this year's Harbin International Ice and Snow Sculpture Festival; in Harbin, and in other places, artists sculpt and construct enormous building using ice, snow, and water (which then freezes). So, it is possible to build elaborate structures suitable for humans; but if you analyze this art with the bland rigor of a civil engineer, you'll see that the ice structures have poor performance for things like structural load, cantilever performance, and so on - even if we disregard concerns about melting. For many of the same reasons, we have the ability to construct homes and offices using sandbags, but we don't build many of those structures when other materials are readily available. When compared to these exotic alternatives, the cost and the structural limitations favor building with conventional materials.

On the other hand, a small niche of builders do use exotic material like ice (or earthworks); in some areas, the material is readily available; the aesthetic can be pleasing; and across the world, many ice hotels are both commercially viable and fascinating places to stay. It's unlikely, however, that we'll see permanent ice construction of tall megastructures, because there are better and safer construction materials to work with.

Nimur (talk) 16:29, 8 January 2019 (UTC)

St. Paul constructs buildings of ice every year about this time.[13] They're nice and sturdy. But they eventually melt. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:33, 8 January 2019 (UTC)

• Here is an article about the mechanical properties of ice at various temperatures; it will help the OP research some of their question. In terms of actual examples of building on ice itself, Ice shantys are used in ice fishing; I've known people to drive recreational vehicles as large as a Winnebago onto a frozen Lake Winnepesaukee in the winter; and there are places that get MUCH colder. See ice roads. which regularly support the weight of very large vehicles. People also regularly build large structures of ice, and not just igloos. See Ice hotel for example. --Jayron32 17:40, 8 January 2019 (UTC)

• Does everyone here already know about Pykrete? --Guy Macon (talk) 19:01, 8 January 2019 (UTC)

  Presumably, since someone brought it up 16 hours ago, we've all been familiarized. But thanks for the reminder. --Jayron32 19:09, 8 January 2019 (UTC)

pH measurement

For a 20% citrate solution, does direct pH measurement with a pH meter give accurate results, or does such a solution require some other means of pH measurement? 2601:646:8A00:A0B3:940E:B215:E6AD:437C (talk) 03:59, 9 January 2019 (UTC)