Wikipedia:Reference desk/Archives/Science/2017 July 20

= July 20 =

Simulation of persistence hunting among humans in industrialized societies
I know hunter-gatherer societies would sometimes do persistence hunting, whereas in industrialized societies, humans can just buy meat at the grocery store. So, assume a very chubby human lives about 4-5 miles from the grocery store with a lot of traffic lights along the journey. The human is not accustomed to vigorous physical exercise but decides to stop driving to the grocery store. He uses his legs to run there as fast as possible. After running, I think the body will take about a day to rest and recover. If that human runs every other day, then he will likely build muscle. My question is, is counting calories really necessary? Why can't humans just work on building a lot of muscles and let the muscle raise the basal metabolic rate? 50.4.236.254 (talk) 00:31, 20 July 2017 (UTC)


 * Wikipedia has an article titled exercise. It should answer your question.-- Jayron 32 01:02, 20 July 2017 (UTC)


 * They can and should, but people who don't habitually exercise fear that exercising will be boring, physically unpleasant and will take up more time than they think they have available, so they look for easier alternatives. Such opinions may be subtly reinforced by advertisers who wish to sell products (in the form of "diet"-promoting books and other media, and "special foods" and/or "dietary supplements"). Much of the contents of the more downmarket "Women's magazines" is made up of advertisements, "advertorials" and "factual" articles of possibly dubious scientific accuracy in support of this "industry".
 * In your scenario. it wouldn't be necessary for the person to run as hard as possible. Merely walking as fast as felt comfortable would be positively beneficial, and over time the speed of "comfortable" would increase to the point where other exercise would also become more bearable and even positively attractive. {The poster formerly known as 87.81.230.195} 2.218.12.40 (talk) 15:00, 20 July 2017 (UTC)


 * See for a balanced look at the underlying notions behind this question.  Neon  Merlin  09:46, 22 July 2017 (UTC)


 * Actually counting calories isn't a particularly successful dieting strategy, as the math required and even getting the true calorie count from restaurants make this approach painful and difficult. Better to eat healthy foods, and avoid junk food, and get lots of exercise.  While it's possible to become or remain obese while doing all of these, it's unlikely. StuRat (talk) 15:42, 23 July 2017 (UTC)

"Hand laser cutter for nuclear decommissioning"
See this gif HERE. What is this death ray looking tool (more specifically)? What is meant by "nuclear decommissioning" Decommission of nuclear generators? Why must a laser cutting tool be used instead of say, a plasma cutter or any other type of cutting tools? 64.170.21.194 (talk) 01:30, 20 July 2017 (UTC)


 * First, our article Nuclear decommissioning defines the term as "the process whereby a nuclear facility is dismantled to the point that it no longer requires measures for radiation protection." In other words, taking a nuclear plant apart and removing and securing the radioactive material in it to the point that it's not necessary to take special care not to be exposed to above-normal levels of radiation.


 * I traced the video back to its original post on YouTube and found this link to a document published by The Welding Institute (TWI) located in the United Kingdom, "The laser alternative to nuclear decommissioning".


 * This paper summarizes the answer to your question this way:
 * "'As the nation's power stations reach the end of their working lives the problem of their demolition has prompted engineers to look at implementing novel techniques in many aspects of nuclear decommissioning."
 * "Using one laser, configured in two different ways, TWI's team has shown that both tube cutting for size reduction and concrete scabbling for removal of contaminated surface layers can be conducted in a safe, remote and efficient manner."
 * "In March 2009, the UK's Nuclear Decommissioning Authority awarded TWI a contract to develop prototype equipment for demonstrating the twin processes of concrete scabbling and tube cutting, and how these technologies might be implemented for remote use in nuclear decommissioning environments. The goal of the project was to allow Site Licence Companies and supply chain companies to evaluate the technology in terms of both process capability and operating costs, mindful that the underlying technical issues had already been addressed.'"


 * So, the Welding Institute is reporting that they have shown how laser cutters can be used to decommission (take apart) nuclear power stations by scabbling (breaking up) concrete and cutting metal tubing, two materials commonly found in nuclear power plants.  According to the paper, the advantages to using laser cutters are that they are portable, quick, efficient, don't spread contamination from cutting or breaking up contaminated tubing or concrete as much as other demolition tools, and can be used by robots for remote decommissioning of old nuclear power plants (reducing exposure of human workers to radiation). loupgarous (talk) 02:19, 20 July 2017 (UTC)


 * They're mostly for dismantling medium-sized structures with high contamination: so fuel reprocessing and research plants, rather than large power reactors. Plasma cutting is favoured, as it's cheaper and simpler, but it needs the torch to be placed very close to the cut and also it generates a lot of heat and oxidised materials as a further waste product. Using a laser mainly has the advantage that the torch can be further away - an advantage when it might have to be held by a waldo manipulator, or through a heavy-gloved suit. Andy Dingley (talk) 11:12, 20 July 2017 (UTC)
 * Wow. I can't believe this guy is blasting apart a big metal apparatus with a ray gun!  But how does he avoid beads of molten metal reflecting the thing back at himself causing him to have a bad day? Wnt (talk) 21:59, 20 July 2017 (UTC)


 * A welding helmet would be in order, along with leather gear. StuRat (talk) 20:50, 23 July 2017 (UTC)

61905-2Z vs 6905-ZZ
Is there any difference between a 61905-2Z bearing and a 6905-ZZ bearing? They appear to have the same dimensions, and some shops even advertise both models on the same page (though most don't). Are these two different designations for the same items? Or two mutually compatible items? Covfefe beans (talk) 01:32, 20 July 2017 (UTC)


 * They are the same. As far as I know, SKF has its own naming convention with the extra "1" --195.145.95.2 (talk) 06:58, 20 July 2017 (UTC)
 * "Z" is the Suffix for Gap seal and thus -ZZ and -2Z bearings should be the same with gap seals on both sides. However only -2Z and -Z (for only one side gap seal) are mentioned as Suffix on the pages from Schaeffler (FAG bearings). Maybe ist an old suffix nolonger used. --Kharon (talk) 18:11, 20 July 2017 (UTC)

Machining
Are there things which can be made on a shaper but cannot as easily be made on a milling machine? 2601:646:8E01:7E0B:1AA:EC88:6F1A:C659 (talk) 10:55, 20 July 2017 (UTC)
 * Keyways and splines, particularly internal keyways. Otherwise they're not a popular machine. They cut very slowly, they're hard to set up. As power is easily available these days, it's more common to see broaching (multi point, multi-step tools) used for these linear cuts. Andy Dingley (talk) 11:14, 20 July 2017 (UTC)
 * The only advantage is they can fabricate sharp edges in dead end inner forms which milling machines never can because they cut by rotation and thus can only fabricate a radius in such ends edges. Besides that ofcourse shapers are very simple, cheap machines, exeptionally fit to teach early apprentices the foundation basics of mechanized cutting! I believe they are not build anymore today. Their limited, very specific advantage is covered by Electrical discharge machining today. --Kharon (talk) 12:02, 20 July 2017 (UTC)
 * I can see a couple of advantages for them, in some contexts. Firstly, they are very simple. The level of tech is no higher than that of a power hacksaw. Secondly it is entirely feasible to grind the cutting tools yourself. But yes, slow and of very limited special capabilities. I haven't seen one for 39 years. Greglocock (talk) 12:25, 20 July 2017 (UTC)
 * Thanks! So I gather there's no real need for shapers anymore, given that splines and keyways can now be made by broaching and sharp edges by spark erosion? 2601:646:8E01:7E0B:A51C:A8E5:DDE4:3E35 (talk) 06:08, 24 July 2017 (UTC)

Why do we have split forearms?
Circumstances led me to ask a question I cannot answer: Why do we have split forearms?. A putative answer is that it is better for pronation and supination. Is it true? But at the same time it is a very ancient feature. It seems all vertebrates have them. A reptile skeleton shows the ulna and radius in a giant lizard. A legend for the picture of some obscure dinosaur mentions both forelimb bones. I don't think it helped them with pronation. What would happen if two bones of the forearm (ulna and radius) are replaced with one bone. It is important for me to find the answer. Thank you, --AboutFace 22 (talk) 16:44, 20 July 2017 (UTC)
 * If not for the two bones in the forearm, you would have to rotate your entire arm to rotate your hand. ←Baseball Bugs What's up, Doc? carrots→ 17:09, 20 July 2017 (UTC)
 * Yes, he said exactly that. So you just repeated him.  However, split bones have existed in vertebrates for much longer than vertebrates have had arms.  His question is "what evolutionary advantage does having two bones in that specific limb segment".  -- Jayron 32 17:16, 20 July 2017 (UTC)
 * One not obviouse anymore today but shurely very valuable advantage of two bones instead of one is the joint-size, since a single bone ofcourse would have only on joint to the hand, and both would be bigger, making it more difficult to search for insects, small animals or even eggs and alike in holes and gaps. --Kharon (talk) 17:49, 20 July 2017 (UTC)
 * Pronation_and_supination.jpgmical_terms_of_motion. But Bugs is still right, as far as I can tell. If OP User:AboutFace 22 isn't convinced by the image I just placed, I'm not sure what will. It's kind of obvious. All else being equal, the hand would not be able to have the same range of rotation with a single bone. But obviousness is no reason to not explain things. Toward that end, here  are a few relevant and freely accessible scholarly articles that speak to the importance of these bones for hand motion, and here  is another that will require access to read beyond the abstract. For any evolutionary question, "why" is always a very fraught question, and the correct but unsatisfactory answer is always "because this trait conferred more benefits than detriments to lifetime reproduction of ancestors." But in this case we do have lots of good research on the function of the joints involved, and what motions they allow. SemanticMantis (talk) 20:48, 20 July 2017 (UTC)
 * Surely we have two bones in our forearms because our ancestors had split bones in their forelegs, and we've not found cause to change it.
 * So any strong reason to favour it is going to come from its role as a leg, not as an arm. Andy Dingley (talk) 17:52, 20 July 2017 (UTC)
 * Actually the radius and ulna date back before terrestrial life . So their adaptive role, if any, must relate to how they are useful to fish.  But when dealing with questions like this it's important to remember that not all characteristics are adaptive.  CodeTalker (talk) 17:59, 20 July 2017 (UTC)
 * In that case, the branching aspect could possibly be looked at. Moving from the body outward, the limbs go 1->2->5 in terms of number of bones, that naturally lends itself to a fan shape which many fins take.  -- Jayron 32 18:05, 20 July 2017 (UTC)

Thank you much, but I still don't feel I have an answer. Deep down I hoped that somebody working in a med school anatomy would try to attach a flat bone to a skeleton instead of ulna and radius and see if it allows locomotion and what the limitation might be. I may try to do it virtually, there are programs but it will take a lot of time for sure. --AboutFace 22 (talk) 19:44, 20 July 2017 (UTC)


 * You seem to be asking a different question now. The original question (why do we have two forearm bones) is a question of evolutionary history -- we have two bones because our ancestors had two bones.  Now you're asking, is it possible for a forearm with a single bone to have the same mechanical characteristics of the joints as our existing forearms?  Undoubtedly that's possible, although with significantly different joints at the wrist and elbow (eg. it might require a ball and socket joint at the elbow).  Just "attaching a flat bone" to a skeleton without joint modifications certainly isn't going to work since the elbow and wrist are designed for two forearm bones.  — Preceding unsigned comment added by CodeTalker (talk • contribs) 20:36, 20 July 2017 (UTC)

@CodeTalker, it was the part of the OP post: "What would happen if two bones of the forearm (ulna and radius) are replaced with one bone" Everything you say is contributing, although it is not the full answer yet. Perhaps it is impossible now to get the complete answer. Thanks, --AboutFace 22 (talk) 20:51, 20 July 2017 (UTC)

@SemanticMantis, are you saying that true pronation and supination require two forearm bones? --AboutFace 22 (talk) 20:54, 20 July 2017 (UTC)


 * RightHumanPosteriorDistalRadiusUlnaCarpals.jpg The branching is 1->2->3->4->5 --catslash (talk) 20:56, 20 July 2017 (UTC)
 * No. I'm saying that they allow for much more freedom of motion, especially rotation, compared to a one-forearm-bone case where the wrist is otherwise similar. In principle we could have a ball and socket joint for our elbow, and all kinds of other fantastical things. But in practice, if you somehow replaced your radius and ulna with one bone, you couldn't move your hand very well, especially in pronation/supination. There is a reason why you see that as the standard explanation, and I'm honestly somewhat confused as to why you seem to want to reject it. Ven fish get a lot of use out of that kind of motion, as shown by Wnt's good references below. SemanticMantis (talk) 22:58, 20 July 2017 (UTC)

It is all very interesting. Thank you very much. I think I am close to a solution. --AboutFace 22 (talk) 21:02, 20 July 2017 (UTC)


 * The function is inherited from fish . There are specific functions for pronation and adduction? of at least the pelvic fin, which is the precursor to the leg ; of course the arms have a similar plan.  That article seems to suggest that pronation is a general feature of ray fins of fishes.  The gonopodium (specialized anal fin) of a fish can also pronate .  To be clear, I'm not sure that all these "pronations" are the same as human "pronation", because the basic body plan and terms used for humans and fishes have some differences; nor am I sure it is always because of the two bones.  I might know better if I actually read these papers...  my guess certainly would be that if you wanted to design something with a fin in the water you would certainly want to be able to control what angle it is pointed, that fish arranged that, and that nothing since that has a use for limbs at all has found a way to dispense with this function. Wnt (talk) 21:54, 20 July 2017 (UTC)

@Wnt, it is absolutely incredible, almost teleological in design. There is a way to download a virtual skeleton and I plan to do it and investigate the joints of the arm and hand closely. I need it for a project. I thought I could simplify the structure by replacing two forearm bones with one but it may not be possible without sacrificing some degrees of freedom. Thank you --AboutFace 22 (talk) 23:29, 20 July 2017 (UTC)

@SemanticMantis, I tried to understand if an artificial arm I may eventually design could function with one bone instead of two. That would have saved money and production time but I cannot sacrifice the function of the artificial hand and need to make the latter exactly matching the real hand. --AboutFace 22 (talk) 23:37, 20 July 2017 (UTC)


 * Well, an artificial limb is different. Rotating locomotion in living systems is notably underpopulated in examples, but it is quite easy to make an artificial limb rotate as far as you want at a single joint.  Of course, such a mechanism doesn't directly mimic the biological arm, but if you put a few "epicycles" into the computerized control mechanisms, figuratively speaking, by which I mean, to compensate for any irregularities of this mechanism with additional movable elements, it is possible that the positions of the fingers might work out exactly as you expect, and even an artificial skin conceivably could be made to match the motion of the biological.  The situation with prosthetics now is pretty medieval, so it is truly a wide open field for the skilled artisan. Wnt (talk) 01:08, 21 July 2017 (UTC)
 * Yep, now that I understand more where OP is coming from, it makes more sense. Bioinspiration and Bio-inspired_robotics are great, but lots of robotic arms don't use two forearm bones. Robots have different limitations that quadruped evolution does/did, and if you get to change a lot about an arm, there is no strict requirement that two bones are necessary to achieve a nimble extremity. Here's some arms that use one-piece forearms, here's some that use a double-bone forearm , but it's not even used for pronation, just for flexion! In robotics, lots of designs are possible. In the actual history of human evolution, we only have one. SemanticMantis (talk) 02:54, 21 July 2017 (UTC)
 * Actually, bioinspiration is not that great; designers often begin with it, suffer failures, then make the thing work but quite differently from their biomodels (e.g. History of aviation). Biology miss rolling-element bearing, and use flexion instead; on the other hand, we often find it hard to construct things with as much flexibility as found in living beings. Gem fr (talk) 09:49, 21 July 2017 (UTC)

Again many thinks to @SemanticMantis, @Wnt and @Gem fr. Your contributions and musings are super important to me. @Wnt, especially wrote something that gave me shivers since this is what I am planning to do eventually: "...the positions of the fingers might work out exactly as you expect, and even an artificial skin conceivably could be made to match the motion of the biological." Unfortunately I cannot go into many details, some patents are still pending, but I feel I got everything I could hope for from this post. Thank you, - --AboutFace 22 (talk) 15:12, 21 July 2017 (UTC)
 * The article Animatronics may be helpful. Blooteuth (talk) 12:51, 22 July 2017 (UTC)

@Blooteuth, Yes, it may be useful. I am taking notice of it. I wonder if Latex 74 or another grade might be flexible enough in the dry state? Thanks, - --AboutFace 22 (talk) 15:06, 22 July 2017 (UTC)


 * I might have missed it, but I haven't yet seen anybody point out that we have two bones in the distal part of our legs as well as our arms. So if there is a basic mechanical reason it must apply to legs as well.  But in fact it is mostly likely that this is just one of many features that go so far back in evolutionary history that it is "locked in" to our design.  It appears in salamanders and even in the fins of lungfish. Looie496 (talk) 20:13, 22 July 2017 (UTC)
 * Search "pelvic" in my answer above. Wnt (talk) 23:20, 22 July 2017 (UTC)

I did not mention the legs because they are out of my interest and I did not want to distract attention from the main subject: radius an ulna. Thanks, - --AboutFace 22 (talk) 18:19, 23 July 2017 (UTC)