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May 27

Feynman Lectures. Exercises PDF. Exercises 4-1...4-16

I have a general question. In exercises for Lecture 4 a principle "if system is in balance it is reversible machine" is used. But why is it true?
If a reversible machine is balanced it doesn't mean that anything else balanced is a reversible machine.
If Feynman uses this argument, then why doesn't he say that frankly in Lecture 4 (He says only "If we say it is just balanced, it is reversible and so can move up and down")?
But even with this argument there is a problem: at the moment of Lecture 4 we do not know that balanced system is a system without acceleration, because we do not know what acceleration is yet. Therefore, we can't know what a "balanced system" means. So we can't say is the reversible machine in Fig. 4–1 balanced or not at each moment of its operation.

We have:
1) Statement "balanced system is reversible machine" is unproven.
2) Statement "reversible machine is balanced system" is unproven.
3) Statement "if all reversible machines are balanced then all balanced systems are reversible machines" lacks logic. Username160611000000 (talk) 08:10, 27 May 2017 (UTC)

That part isn't quite as clear as the rest, but it does make sense. If you have a "machine" in the classical sense, specifically an inclined plane, with weights on the incline and vertically, then if one end pulls down i.e. it is unbalanced, it is not reversible. Presumably this is in the sense that once the one weight hits the ground, its energy is dissipated and (by conservation of energy) there's no way to reset the whole thing how it was without putting some energy back in. He is taking conservation of energy on blind faith, to be sure. Now, if you have the same machine and it is precisely balanced, then you can push it either way as you like, because, well, I think that's what balanced means. But ... yes, balanced is an imprecise term. After all, a screwdriver can be balanced on its tip, and in theory, you could have it sitting like that and with a push send it one way or the other, yet that is not reversible. The key distinction there though is that the screwdriver doesn't stay balanced. The inclined plane example, in theory, you can give it a little teeny weeny itsy bitsy push, and if it's a perfectly reversible machine, watch it creep down or up, one way or the other, over months and years and whole precessions of the earth, and yet, if you give it a little more push, or push it a little back the same way, it will then go at that new rate the same way. And so you see there that because it remains continually balanced, it never is in the point of giving up its energy, i.e. it does no mechanical work on the weights to get them moving this way or that, beyond what you yourself have put in. Wnt (talk) 20:12, 27 May 2017 (UTC)

@Wnt: He is taking conservation of energy on blind faith -- No. He takes the impossibility of the perpetual motion (in the sense of continual supply of extra energy) on blind faith (later in the Lect.4 he says that experiment confirms the impossibility, so it's not a blind faith). And from that he derives the conservation of energy law (for reversible machine and for gravitation potential energy only). Reversible machine is a machine that can lift 1 unit weight 1 meter by lowering N units weight X meters, and can lift N units X meters by lowering 1 unit 1 meter.
Username160611000000 (talk • contribs) 12:22, 30 May 2017 (UTC)

I'm pretty sure he's using the term "balance" here to mean what is often termed "equilibrium" in the physical sciences. Chemical equilibrium, for example, is closely tied to the concept of the reversible reaction. In general, a system that is at an equilibrium resists changes in its status by returning to equilibrium (see Le Chatelier's principle for the chemical law), and by definition is reversible. That is, if something is in an equilibrium state "A" and some action puts it in state "B", then it will spontaneously return to state A. That's a reversible system. With the screwdriver example, if you balance the screw driver on its tip, it is NOT in equilibrium, because a small changes causes it to leave its initial state, not return to it. By contrast, a screwdriver lying on its side IS in equilibrium, because a small change causes it to return to its initial state. By definition, all equilibrium systems are reversible. The opposite statement is NOT necessarily true, however, not all reversible systems are in equilibrium; in the screw driver example BOTH processes are reversible, but only one is in equilibrium. --Jayron32 12:51, 30 May 2017 (UTC)

@Jayron32: That is, if something is in an equilibrium state "A" and some action puts it in state "B", then it will spontaneously return to state A. I don't understand. According to Feynman a reversible machine is a machine capable of equally willingly passing from state A to state B and from state B to state A:

...
A very simple weight-lifting machine is shown in Fig. 4–1. This machine lifts weights three units “strong.” We place three units on one balance pan, and one unit on the other. However, in order to get it actually to work, we must lift a little weight off the left pan. On the other hand, we could lift a one-unit weight by lowering the three-unit weight, if we cheat a little by lifting a little weight off the other pan. Of course, we realize that with any actual lifting machine, we must add a little extra to get it to run. This we disregard, temporarily. Ideal machines, although they do not exist, do not require anything extra. A machine that we actually use can be, in a sense, almost reversible: that is, if it will lift the weight of three by lowering a weight of one, then it will also lift nearly the weight of one the same amount by lowering the weight of three.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume IAnd with the screwdriver, it's not a machine at all. It seems it's like Unstable equilibria from this article [1], but I do not think that this has something to do with lecture 4. Username160611000000 (talk) 16:58, 30 May 2017 (UTC)

It sort of depends on how you set up your systems. For example, in the case of chemical equilibria, a system is only at chemical equilibrium if its temperature is held constant; the equilibrium conditions (related to the equilibrium constant) is tied to a specific temperature. If you let temperature vary freely, you get a truly reversible chemical processes. In Feynman's case, he's established a reversible system because it can be run in both directions with small inputs of energy; and it's balanced (equilibrium) because small changes in any direction will self-correct. His example may be simplified by imagining a lever with the fulcrum offset to one side, such that there is, say, one meter of lever on side A and three meters of lever on side B. If we THEN put 3 kilograms of weight on side A and 1 kilogram of weight on side B, we have our simple, balanced (equilibrium) machine. We can do work in either direction with similar effort (that is, I can push down either side, and get the opposite side to lift up). That's a simple machine which is also a reversible machine. It's also a balanced machine (more properly it is at "equilibrium") because it is self correcting; if I nudge the lever and let it go, it returns to level on its own. --Jayron32 04:40, 31 May 2017 (UTC)

if I nudge the lever and let it go, it returns to level on its own. Why? Actually (what we do not yet know at the moment of Lect.4) to accelerate the machine to some speed we must apply a force. And when the machine gains speed, we turn off the force, then the machine continues movement forever . Username160611000000 (talk) 12:46, 31 May 2017 (UTC)

---

I think I understand. Reversible machine is a machine for which a very small push (or as Feynman says "extra") brings it to movement (0.5 cycle). So before that push the machine is idle (v=0). If machine is stationary it is balanced, because one of the criteria of "balanced" is fact v=0 (second is v=const). Username160611000000 (talk) 16:53, 31 May 2017 (UTC)
All info about thermodynamics, temperature, screwdrivers, chemical equilibria is unknown (at Lect.4) , off-topic and complicated. Username160611000000 (talk) 17:00, 31 May 2017 (UTC)

Typical revolutions per minute of a fidget spinner

Not a specialised one designed to go ridiculously fast. Just a normal, hand-spun one. What sort of ballpark are we talking? 10rpm? 1000rpm? Amisom (talk) 21:05, 27 May 2017 (UTC)

This is still a very new field of research so there won't yet be much published literature on this particular aspect.----Seans Potato Business 21:57, 27 May 2017 (UTC)

A Fidget spinner is a type of stress-relieving toy. A video of children playing with the toy shows it spins at a rate a child can easily start and stop, apparently similar to a Gramophone record i.e. 16 to 78 r.p.m.. Blooteuth (talk) 22:55, 27 May 2017 (UTC)

A fidget spinner is hand spun to about 1000rpm in this YouTube video (1:06 minutes in). --Modocc (talk) 23:01, 27 May 2017 (UTC)

About 20,000 rpm or more to get failure. Count Iblis (talk) 23:54, 27 May 2017 (UTC)

Is there any pattern to warning symbols?

I see sometimes common warning symbols in orange squares or white diamonds with red outlines or yellow triangles with black outlines or white triangles with red outlines. Is there some situation where one is preferred? Can an nuclear trefoil, for example, be put in any of these?

See the article about [Hazard symbol]s. Their use of hazard symbols is often regulated by law and standards organisations who direct different colors, backgrounds, and borders. The radiation Trefoil symbol was originally majenta on a yellow or blue background but is now internationally recognized drawn in black, see Hazard symbol#Ionizing radiation trefoil warning symbol. See the article Warning sign about national traffic hazard signs. Blooteuth (talk) 22:44, 27 May 2017 (UTC)

See also Globally Harmonized System of Classification and Labelling of Chemicals and GHS hazard pictograms. Also Hazchem used in some Commonwealth countries. Alansplodge (talk) 23:18, 27 May 2017 (UTC)

May 28

If babies are never weaned, then will they be able to digest lactose at later ages?

I know babies are weaned from breastmilk. But what happens if they are never weaned? Will babies continue to feed on breastmilk and be able to digest breastmilk at later ages? 50.4.236.254 (talk) 02:07, 28 May 2017 (UTC)

Most people can digest milk their entire lives. Why would this matter? --DHeyward (talk) 02:28, 28 May 2017 (UTC)

It may be true in D's country, but it is not true in general that "most people can digest milk their entire lives". --69.159.60.50 (talk) 02:40, 28 May 2017 (UTC)

Agreed. Most people of the world live in Asia, and Asians, with exceptions of North Asians, are largely lactose-intolerant. 50.4.236.254 (talk) 03:22, 28 May 2017 (UTC)

Fine, but the question seems to be, if they never stop drinking milk, can they avoid the onset of lactose intolerance? I think the answer is "no", but I'm not really sure, and it's an interesting question. --Trovatore (talk) 03:39, 28 May 2017 (UTC)

I agree I think the answer is no. First, I don't see any reason to think breast milk will make a difference so without ruling it out, I'll let someone else look for any evidence about that. While I couldn't find a source specific placesspecifically commenting on the issue, remember in plenty of places cow milk consumption is fairly common from weaning or before. Most sources like [2] [3] discussing lactose intolerence refer to differing ages of onset etc. They don't say anything about how people can avoid it if they make sure they always consume milk. Note that although people who regularly consume milk may have less symptoms of lactose intolerance [4], according to [5] which is from the dairy industry of Canada, there's no evidence that this is due to increased lactase production and actually they acknowledge they don't know for sure why there seems to be this adaptation, but just that there is evidence does. This doesn't rule out a higher level of lactase production in people who have always consumed milk (nor for that matter that there really is no increased production in people who start to later regularly consume milk even if they lack the various known lactase persistence alleles), still it makes it seem less likely. Nil Einne (talk) 04:26, 28 May 2017 (UTC) 07:04, 28 May 2017 (UTC)

If I'm reading your question right, you're not talking about any old milk (like from cows or goats) but from human breastmilk. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:46, 28 May 2017 (UTC)

There is a specific gene (MCM6) which has the role of switching off lactase production after weaning: it generally kicks in when the child is about four, and had an evolutionary advantage, in that it prevented the older child from hogging the mother's milk, and let the next baby get its share. The mutation which changed Europeans, and some other populations, means that this gene does not work: we continue to produce lactase, so can continue to digest lactose. Without that mutation, the gene is going to switch of lactase production: a child will stop wanting to breast feed because it will start getting bad tummy aches. Wymspen (talk) 10:26, 28 May 2017 (UTC)

Actually re: my answer above, I intentionally didn't link to or check out our articles because I assumed the OP had read them. It seems this was a mistake and I'm now assuming they didn't. While Lactose intolerance isn't that helpful (that I noticed), we also have an article Lactase persistence which specifically covers the issue "While a variety of genetic, as well as nutritional, factors determine lactase expression, no evidence has been found for adaptive alteration of lactase expression within an individual in response to changes in lactose consumption levels.[1]". I haven't checked the source, so I'm not sure if it specifically comments on continuous lactose consumption, I think the evidence is now fairly strong that it's unlikely it will ward of the development of lactose malabsorption/intolerance.

About your comment, I believe we covered the question of why lactase nonpersistence is the norm recently. While it's possible it did provide an evolutionary advantage in some species including humans, for the reasons you stated, I would be careful about assuming that this is a significant factor. Lactase nonpersistence seems to be the norm in most mammal species so it's not clear that preventing older offspring from hogging the milk would be a significant factor.

Nil Einne (talk) 11:32, 28 May 2017 (UTC)

Reading a bit more, I see I missed this part:

Multiple studies indicate that the presence of the two phenotypes "lactase persistent" (derived phenotype) and "lactase nonpersistent (hypolactasia)" is genetically programmed, and that lactase persistence is not necessarily conditioned by the consumption of lactose after the suckling period.[11][12]

Nil Einne (talk) 11:36, 28 May 2017 (UTC)

Decades ago I read a book about a European's life among the Inuit. It may well have been "Arctic Adventure" by Peter Freuchen. In it the author told of a custom among the local Inuit of mothers continuing to breastfeed their offspring into adulthood, such that a grown man would proudly take a suck from his old mother's breast. I wonder if lactose intolerance is common among the Inuit? (PS) I found the actual passage, confirming what was stored in my memory from 50 years ago! [6]. Edison (talk) 13:09, 28 May 2017 (UTC)

Hmmmm... I may have contributed to confusion here before. I went on recently about lactase being inducible in humans, being sure I'd read something to that effect, yet now as you say there are sources being cited to the contrary. Looking at it this time, I ran across a curious bit of data: [7] says that "The mean level of lactase activity among subjects with C/C-13910 genotype was 6.86 ± 0.35 U/g, with C/T-13910 genotype 37.8 ± 1.4 U/g, and with T/T-13910 genotype 57.6 ± 2.4 U/g protein" So at this key genetic locus, it is less than a ten-fold difference in level - and homozygotes and heterozygotes, differing by 2-fold, are taken to be essentially the same. That paper also concludes that lactase levels have to be less than 10 U/g for lactase intolerance to occur. Now that strikes me as a really small difference in enzyme activity, when we consider that some of us are afraid to put milk in coffee and others of us will kill an entire container of ice cream in no time! I also ran across an indication that intestinal flora contribute to lactase levels in rats [8] but haven't looked into this further. There's something I don't understand here... Wnt (talk) 00:10, 29 May 2017 (UTC)

Effect of bovine milk and human milk on human babies

Humans probably agree that human babies should be fed human milk. But in case the mother dies in childbirth, has HIV, or (A) just doesn't want to or can't breastfeed for some reason, (1) how good is unpasteurized, grass-fed, raw bovine milk as a replacement for human breast milk? (B) Human breast milk may be flavored with whatever food the mother eats. So, (2) does that mean if the mother eats crappy doughnuts and soda, the child will grow up to eat crappy doughnuts and soda? (C) And if the mother eats fruits and vegetables, then her veggie-flavored or fruit-flavored breast milk will cause the child to eat fruits and vegetables and reject crappy doughnuts and soda because they are too sweet to be palatable? (3) What about the breast milk of the biological mother compared with the breast milk of the adoptive mother or wet nurse? 50.4.236.254 (talk) 17:17, 28 May 2017 (UTC)

[I have lettered your premises and numbered your questions to facilitate others' who may wish to address them. Please be aware that (A) elides the fact that many mothers find themselves unable to breastfeed their infant(s), no matter how much they'd like to – glossing over this fact can cause offense and distress. {The poster formerly known as 87.91.230.195} 90.200.129.108 (talk) 20:07, 28 May 2017 (UTC)]

I made small adjustments by adding the word "can't". 50.4.236.254 (talk) 20:23, 28 May 2017 (UTC)

(1). Cow's milk compared to human breast milk contains too little iron, retinol, vitamin E, vitamin C, vitamin D, unsaturated fats or essential fatty acids for human babies. It also contains too much protein, sodium, potassium, phosphorus and chloride which may put a strain on an infant's immature kidneys. In addition, the proteins, fats and calcium in whole cow's milk are more difficult for an infant to digest and absorb than the ones in breast milk. United States Centers for Disease Control report 148 outbreaks, 2,384 illnesses (284 requiring hospitalizations) as well as 2 deaths due to unpasteurized dairy products between 1998 and 2011.

(2) There is no evidence of eating habits being inherited through breast milk.

(3) What about it? Wet nursing is not widely practiced now. A more acceptable substitute is screened, pasteurized, expressed milk (or especially colostrum) donated to milk banks, analogous to blood banks. Blooteuth (talk) 19:40, 29 May 2017 (UTC)

What does the word "refractory" in "refractory period" refer to?

I know what it means "refractory period" (both, absolute and relative) in the action potential graph, but I don't understand what the meaning of "refractory" in this context is. What is it refractory for? 93.126.88.30 (talk) 12:49, 28 May 2017 (UTC)

See refractory. Refractory is an adjective usually used around high-temperature resistant materials, indicating that they are unaffected by outside influences, such as heat. This is extended by analogy to physiology, to where there is a time period during the potential graph, during which this too is unaffected by further outside stimuli. Andy Dingley (talk) 13:07, 28 May 2017 (UTC)

Also see meaning 4 in the Wiktionary entry: wikt:refractory. Looie496 (talk) 14:05, 28 May 2017 (UTC)

Thank you. I found the answer here. "After repolarization there is a period during which a second action potential cannot be initiated, no matter how large a stimulus current is applied to the neuron. This is called the absolute refractory period, and it is followed by a relative refractory period, during which another action potential can be generated, but only by a greater stimulus current than that originally needed. This period is followed by the return of the neuronal properties to the threshold levels originally required for the initiation of action potentials." 93.126.88.30 (talk) 14:45, 28 May 2017 (UTC)

• This is really a language question. The word "refractory" means "very difficult to change." See refractory (disambiguation) for several non-metallurgical examples.-Arch dude (talk) 22:45, 28 May 2017 (UTC)

Re: whale death due to ship strike. Why not attach a beeping horn to the ships bow to provide warning to whales in imminent danger?

Blue whale gets hit by big ship and dies. Question: Would some kind of underwater horn that emits a warning sound towards the area of travel help whales avoid getting hit by the ship? My guess is, this would have been tried already and found to be unhelpful. But I'd like to know why it wouldn't work?

Thanks, --InverseSubstance (talk) 15:48, 28 May 2017 (UTC)

• I'm sure it has not been tried. Abductive (reasoning) 17:49, 28 May 2017 (UTC)

• Ships already make a large amount of noise, and whales not only have excellent hearing but also have natural sonar. The problem is that the whales make little or no attempt to avoid being hit by ships.[9]. The currently favored technology to reduce whale strikes is a combination of reduced ship speed,[10] routing shipping lanes away from where whales are most common,[11] and sonar and other alarms so that the ships can avoid the whales.[12] --Guy Macon (talk) 18:31, 28 May 2017 (UTC)

Whales evolved for tens of millions of years in an environment which did not include large, hard, fast counter-current-moving surface objects. They likely lack the cognitive ability to understand the ramifications of such objects, in the same way that many land mammals fail to cope with the characteristics of motor vehicles and end up as roadkill. Some of the latter may to some extent be evolving instincts helping to avoid traffic, but are evolutionarily aided by greater numbers and shorter generation lengths. {The poster formerly known as 87.81.230.195} 90.200.129.108 (talk) 20:17, 28 May 2017 (UTC)

The research papers are helpful. Thanks for that. I agree, the whales that avoid ships will be selected in, and the ones that don't will get selected out. There are deer whistles sold that one puts on the front of one's truck, and its supposed to warn deer to get out of the way. Maybe just another gimmick, eh? I have an idea! How about a giant airbag that inflates at the front of the ship to cushion the blow? Or maybe some powerful jets of water to give a warning? Just thinking out loud here... --InverseSubstance (talk) 20:34, 28 May 2017 (UTC)

Whalebags? Sagittarian Milky Way (talk) 20:42, 28 May 2017 (UTC)

Its very, very unlikely whales collide with ships because the oceans are really huge areas and shipping lines only use a tiny tiny fraction of the space. Also whales, especially as in this case a blue whale, usually avoid humans. Strangely in this case there are no reports about evidence like huge wounds or broken bones, far as i have read. So i wonder how this "ship collission"-Story made it to the news. Would not shock anyone if it turned out that someone boldly made it up just to fill some space and everyone else started copying it, would it? --Kharon (talk) 20:45, 28 May 2017 (UTC)

See here: "The entire left side of the whale was damaged from a boat strike, and the whale had 10 broken ribs and 10 fractured vertebrae from close to its tail to mid-body, according to Halaska. The whale was identified through photographs of its tail in a database of the Cascadia Research Collective. It was spotted 11 different years beginning in 1999, most often off Santa Barbara. The carcass will be left on the beach to decompose and be eaten by birds. A reef along Agate Beach would make towing the carcass back out to sea difficult." Count Iblis (talk) 00:30, 29 May 2017 (UTC)

[13] mentions "“It’s an unhappy coincidence,” Irvine says. Over a 2-week period in 2007, for example, at least three blue whales were killed by ships striking them near California’s Channel Islands. (Two other blue whale carcasses were spotted during the same 2 weeks, but the scientists weren’t able to study them.)" So actually it seems in the more reliable sources at least, when they say struck by a ship they mean we studied the carcass and decided it was most likely struck by a ship. This blog [14] by someone who seems to be a nature photographer is similar circumspect, it does have the photos if you want to check them yourself. Although interesting, the author does specifically note it was in an area with high shipping traffic. That was in Sri Lanka and [15] notes it's particularly an issue there (the claim is it's a leading cause of death). The first source suggests it is possible but less certain, it's also problem along the Californian coast. (Although the certainty may relate more to who's talking since one was a scientist studying whales whereas the other is an advocacy group.) I suspect some of the sources linked above by others before you posted also discuss the evidence blue whales are being struck by ships. Nil Einne (talk) 07:11, 29 May 2017 (UTC)

I think that a ship coming into port with a dead whale draped over its Bulbous bow is pretty good evidence that ships hit whales. -Guy Macon (talk) 14:47, 29 May 2017 (UTC)

There's several obvious flaws in your hypothesis. First, you can't say random chance is unlikely simply by saying the ocean is big, you need to determine what percentage of the ocean is covered by blue whales (in general) over a defined time period, e.g. ten years. If it's something like 0.00000001% then yes, random chance seems unlikely. But even at 0.1% it's starting to seem possible. Maybe you have some idea what this is based on evidence but that hasn't been presented here. And while I admit it seems likely it'll be small to me, you need to actually have some evidence (even OR) before you can just assume random chance isn't enough.

The bigger flaw though seems to be in assuming random chance. It's possible shipping lanes and the areas blue whales tend to swim in overlap for some reason e.g. favourable ocean currents or location near but not too near certain coasts. Maybe also favourable feeding/fishing grounds (yes I know blue whales are filter feeders but krill etc are eaten either directly or indirectly by some of the fish we eat); although shipping lanes was mentioned above I'm not sure if it's certain this was a cargo vessel (and of course if there is, it would be because the wounds etc have been carefully studies, as it seems they have been per Count Iblis). Maybe size would make it unlikely to be one but some Factory ship aren't exactly small. And these are a lot of assumptions, how well have you considered each one. To give a related example, if I see my neighbour on the bus in the morning on my way to work/uni/whatever regular activity and then see them on the way back as well, and then see them again tomorrow; thinking stalker is generally (but not always) silly regardless of there being many buses in Auckland. An even closer example, it's no surprise that whale watching ships can encounter whales somewhat regularly.

Also for the claim that "especially" blue whales avoid humans, I briefly looked but couldn't find any source discussing this. And what is meant by humans? Swimming humans? Large ships? There's a fair chance the whales aren't going to see these as the same thing, as others have indicated. (Actually the view including from people who actually study blue whales seems to be the opposite, blue whales don't avoid ships.)

Nil Einne (talk) 06:55, 29 May 2017 (UTC)

P.S. Especially in light of my other comment above, I should also point out if shipping lanes and the grounds some blue whales tend to inhabit overlap in at least one instance, it's interesting but ultimately irrelevant when it comes to considering the likelihood of collisions; why there's this overlap. Nil Einne (talk) 07:16, 29 May 2017 (UTC)

So you mean, That's a Whale of a Story! --InverseSubstance (talk) 20:49, 28 May 2017 (UTC)

I agree with Guy Macon: the ships are already really noisy. Underwater noise pollution is widely thought to contribute to deaths from cetacean stranding and so forth. The ship could start beeping when it detected a whale, but how would a whale understand that is in reference to it? Still, the wildcard here is whale language. If someone can figure out something to play that means "MOVE IT!", and broadcasts that when a whale is detected, maybe you have a winner. But without the experiment, that's just pure hot air on my part. Wnt (talk) 00:17, 29 May 2017 (UTC)

[16] Sagittarian Milky Way (talk) 19:21, 29 May 2017 (UTC)

The interested reader may find the following to be helpful; Amazon has a bunch of reviews of the book How to Avoid Huge Ships by those who have successfully avoided huge ships (and a few cautionary tales by those who failed to do so). The reviews are here:[17] --Guy Macon (talk) 15:00, 29 May 2017 (UTC)

• There are about 9,000 blue whales in the world. About 2,900 of them hang out off the California coast. Containerships from China usually visit Los Angeles and then Oakland before heading back to China, so there are a large number of very large ships in these coastal waters. On my only containership trip in these waters (in 2009), we saw two Blue whales fairly close up, and the officers said that this was routine: they see them more often than not. For some reason 2017 appears to be a record year for whale sightings. Containerships travel at 20 knots or more. Their enormous propellers are directly coupled to the engines and rotate very slowly at 100 RPM or so. -Arch dude (talk) 21:30, 29 May 2017 (UTC)

May 29

What is shame from an evolutionary perspective?

It seems to me that a large part of shame has to do with the fear of social rejection. So, one requirement may be that the organism needs to be able to predict the future or remember the past. Another requirement may be that the organism needs to fear social rejection. Another requirement may be recognition of the self. Ay, there seems to be so many factors that I wonder if humans are the only creatures that can experience shame. 50.4.236.254 (talk) 02:24, 29 May 2017 (UTC)

Well, dogs show behaviors that look a whole lot like it. Looie496 (talk) 03:01, 29 May 2017 (UTC)

That makes sense. Dogs are social animals. I bet one of the requirements of shame is fear of social rejection. An animal can remember the past and be self-aware, but does not really depend on social approval and acceptance. 50.4.236.254 (talk) 03:32, 29 May 2017 (UTC)

Your bet is as good as ours. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:40, 29 May 2017 (UTC)

Dogs are social, but behave much differently if raised by dogs instead of humans. Human-like behavior (such as the puppy-dog eyes) doesn't happen in the wild. Around humans, dogs learn very quickly that specific behavior results in preferential treatment. Humans reward human-like behavior, so dogs exhibit human-like behavior without any need to fully comprehend what that behavior means. 209.149.113.5 (talk) 11:47, 30 May 2017 (UTC)

Social systems in the natural world involve a pecking order, so I would guess that it evolved to help to assess if your current position is at risk of being challenged. Count Iblis (talk) 05:54, 29 May 2017 (UTC)

Why speculate when there is Google?

Evolutionary Neurobiology of Shame

Why humans evolved to feel shame

On the biological and cultural evolution of shame

Evolving Concepts of Evolution: The Case of Shame and Guilt

A little bed-time reading. Alansplodge (talk) 17:55, 29 May 2017 (UTC)

Charles Darwin, in his book The Expression of the Emotions in Man and Animals, described the effects of shame. Roger Scruton, in "Modern Sex: Liberation and its Discontents" wrote "the real purpose of shaming is not to punish crimes but to create the kind of people who don't commit them". See the article Shame that suggests the emotion stems from comparison of the self's state of being with the ideal social context's standard. Blooteuth (talk) 19:09, 29 May 2017 (UTC)

@50.4.236.254: Your question is an interesting one, but one which had led to anthropomorphic and anthropocentric answers. Most ethologists today would accept that vertebrates and some invertebrates are conscious and therefore may experience emotions. However, this is just about where the agreement stops, mainly because of our human inabilities to ask questions of animals about these matters in a scientifically robust and biological meaningful way. DrChrissy ^(talk) 20:47, 29 May 2017 (UTC)

Personally I've become suspicious that shame is simply the physical sensation of vasoconstriction somewhere near Broca's area, curtailing verbal communication, and further that the facepalm might be a physical reaction to this. I meant to try to figure out if facepalms had a left-side bias for this reason, but there are, well, some issues with trying to figure that one out. ;) Wnt (talk) 16:56, 30 May 2017 (UTC)

Domestic irradiator instead of a refrigerator?

Could an irradiator be an economically-viable alternative to a refrigerator? Would it require too much shielding? --78.148.98.254 (talk) 12:43, 29 May 2017 (UTC)

Irradiator is supposedly a device that heat things instead of cooling them? Ruslik_Zero 13:37, 29 May 2017 (UTC)

No - I imagine it is a machine using beta or gamma radiation as a means of food preservation - Food irradiation. I don't think I would want one in my kitchen. Wymspen (talk) 14:07, 29 May 2017 (UTC)

Well then, first step would be to know whether food irradiation is comparable to refrigeration as a way to preserve food. Our article on decomposition seems to say that abiotic decomposition is possible. Tigraan^{Click here to contact me} 16:02, 29 May 2017 (UTC)

Then this might be why this was not tried in the 50s. Sagittarian Milky Way (talk) 18:22, 29 May 2017 (UTC)

Irradiating food to preserve it between uses (which is what we use refrigerators for in kitchens) would require an impractical amount of shielding, yes. According to our article Food irradiation, 1000 Gray is considered a "low dose" for food irradiation, while a 5 Gray dose of whole-body radiation is considered lethal to humans within 14 days.

Apart from that, it's not just microbes responsible for food spoilage which are changed by food irradiation. While a one-shot dose of gamma radiation retards spoilage of food enough to permit, say, fresh produce to be economically shipped very long distances (between continents) for sale, repeated irradiations intense enough to keep food from spoiling between uses (in the way we, say, keep a jug of milk in the refrigerator to keep it from spoiling) would also change many foods enough to make them not taste good. Milk and eggs are good examples of complex foods we refrigerate and which would not survive many irradiations without being made unpalatable. loupgarous (talk) 18:26, 29 May 2017 (UTC)

Indeed, spoilage is not a purely biological process, but also a chemical one. Irradiation will e.g. do nothing to reduce the rate at which fats go rancid. Cooling reduces the rate of chemical reactions. As a rule of thumb going from 24°C (not an implausible temperature for a room or the environment) to 4°C (a typical fridge temperature) will reduce the rate of reactions by a factor of 4, and thus keep food fresh longer. --Stephan Schulz (talk) 21:07, 29 May 2017 (UTC)

Deinococcus radiodurans would have 37% viability after a 15,000 Gray dose. Then it would spoil the food. Edison (talk) 17:59, 30 May 2017 (UTC)

Looking at food irradiation I'm not feeling the idea is all that far-fetched. I mean, anywhere from 1000 Gy to 25000 Gy whether the intent is to hinder spoilage a little or to sterilize, with some apparently nontoxic damage to the food at higher levels. Some bacteria may be selected to thrive in the niche but they ought to be containable, or at least, have low odds to be good pathogens. A key distinction between commercial irradiation and home irradiation would seem to be that you don't have to do it all in a few minutes at home; you can apply that 1000 Gy over the course of a day, and if you keep the food 25 days, then you've given it more of a sterilizing dose. So I'd think you can settle on a dose that is not that high and can be sustained in your chamber pretty much as long as desired. Now to be sure, 1000 Gy a day is still more than 40 Gy an hour, which is lethal, and more than 0.5 Gy a minute - it is highly disapproved to linger in front of the irradiator mulling over what to eat today. Still, it might make for a laugh riot if folks in a postapocalyptic film use the elevator to the surface as a storage space to keep their food fresh. ;) Wnt (talk) 18:28, 30 May 2017 (UTC)

While it wouldn't wholly replace a fridge, it might be a useful device to have in addition. Great for those of us too lazy to go to the market every other day for fresh fruit. ...But it's not going to happen any time soon.

The equipment to do this sort of thing is dangerous and tightly regulated. You simply couldn't make a safe one.

here is an accident report about someone who was fried in a large-scale device, but it also gives a good overview of how the machines work. They use Cobalt-60 which you absolutely should not have in your house.

Imagine all the problems that would come from mass-producing a device with Cobalt-60 in it. Firstly, the amount of cobolt-60 in use would go up dramatically, increasing the risk of accidents in production. Then, the manufactured machines would be shipped to appliance stores all over the world, some of these would be destroyed in shipping accidents. Once they were in consumer homes, any fire, earthquake, or other disaster would risk destroying the machines, presenting a significant risk to residents and first responders. A certain number of them would break down and, no matter how many warning stickers you put on them, some idiots would decide to try to fix them, with bad results. And finally, five-to-ten years later, when people want to upgrade to a newer, more stylish model, you'll have a serious waste disposal issue. (You'd need to replace or reload the machine at least once a decade anyway. But the old,used Cobalt-60, would be far from "dead".)

As handy as they might be, I don't see it becoming practical any realistic time soon.

Food irradiation is one of those things that has to be done by professionals or not at all.

The Goiânia accident involved a medical irradiation machine, but it's an illustration of how badly things can go wrong when such machines are left unattended. ApLundell (talk) 14:38, 31 May 2017 (UTC)

Cobalt-60 is a poor choice for irradiating food at home. Better to use X-Rays.[18]

It isn't all that hard to build your own X-Ray source suitable for irradiating food.

• How to Build an X-ray Machine
• How to X-Ray
• An Inexpensive X-ray Machine
• Homemade X-ray Machine

You can easily cast a lead enclosure from lead salvaged from old car batteries. By placing your irradiation chamber inside a refrigerator or large freezer, you can have long exposure times, which allow for a weaker X-Ray source. --Guy Macon (talk) 20:16, 31 May 2017 (UTC)

Help with understanding a U-series dating method

I'm working on ice core, and have found a reference in Landais 2012 (p. 192) to a U-series dating method, cited to Aciego 2010. The latter is an appendix to the proceedings of a conference, without much discussion, but the reference in Landais, which just calls it "a promising study", makes it worth a one-sentence mention (and I've seen it cited elsewhere in introductions to journal articles on this topic). However, I don't understand the method and was hoping someone here could enlighten me -- I don't want to cite something I don't understand. It looks like Aciego et al are discussing U-series decay in dust that falls on the ice core, but what exactly are they measuring, and how does it determine age? Thanks for any help. Mike Christie (talk - contribs - library) 14:17, 29 May 2017 (UTC)

It looks like they are discussing uranium-uranium dating and uranium-thorium dating. Double sharp (talk) 14:47, 29 May 2017 (UTC)

You may find this paper useful. Mikenorton (talk) 15:35, 29 May 2017 (UTC)

That does help, but I'm not sure what Aciego is referring to by "recoil products from dust into ice". Is she saying that the alpha decay in dust grains of ²³⁸
U leads to the product, ²³⁴
Th (or a later alpha daughter product in the decay series) recoiling into the ice, and that analysing the ice itself for daughter products, eliminating the dust, can be used to determine the age via the given equation? I looked through Mike Walker's Quaternary Dating Methods to try to get a better understanding of how U-series dating works, and it looks like it depends on an event that causes a disequilibrium, which can be dated by determining the extent to which the decay has returned to secular equilibrium. I don't see what is going on here that would allow that method to work. Mike Christie (talk - contribs - library) 16:10, 29 May 2017 (UTC)

"Recoil products from dust into ice" seems to refer to an impact. Meteor (especially bolide in the geological sense of the term) impacts in parts of the Earth where uranium is relatively abundant in the mantle which release much dust into the atmosphere could create such a disequilibrium. See Uranium–lead zircon systematics in the Sudbury impact crater-fill: implications for target lithologies and crater evolution by Petrus et al for an example of studies of such phenomena which use uranium dating. loupgarous (talk) 19:48, 29 May 2017 (UTC)

I don't have access to the paper, but from the abstract I don't think that can be the explanation. Aciego is talking about dust in ice cores with miles of ice below them; there's no possibility of an impact being on anything but ice. Micro meteorites are found in ice cores, but that doesn't seem to be it either. Mike Christie (talk - contribs - library) 20:09, 29 May 2017 (UTC)

• Does ice exhibit a phenomenon like a Radiohalo? (The Radiohalo is a real phenomenon. The whacko creationist stuff is pseudoscience.) With a radiohalo, you detect a physical change in the substrate instead of attempting to detect the daughter product itself. -Arch dude (talk) 21:11, 29 May 2017 (UTC)

  I've never read that it does, but it's possible. Aciego doesn't use the term. The calculations Aciego gives is this: The activity of 234U in the ice is due to (1) the recoil out of the dust plus (2) the decaying initial 234U dissolved in the precipitation plus (3) the accumulation from the decay of 238U dissolved in the precipitation. These three terms are functions of t, the time since deposition; she re-arranges to isolate t and calls t "the recoil age of the ice". I can see that if you can measure all three of those terms you can solve for t, but what is "the recoil out of the dust", and why does she call t "the recoil age"? Mike Christie (talk - contribs - library) 21:36, 29 May 2017 (UTC)

  Aha. They are measuring 234U in the ice, where ice is defined as "not dust." There are 3 ways a 234U atom can find its way into (non-dust) portion of the ice: it's in the precip already, or it decays from the 238U in the precip, or it gets kicked out of a dust particle when a 238U atom in the dust fissions. -Arch dude (talk) 01:39, 30 May 2017 (UTC)

  Yes, that seems to be it. I think that's clear enough that I can use it in the article with a clear conscience. I still don't know what "recoil age" means, but I don't think it matters for the purposes of the ice core article. Mike Christie (talk - contribs - library) 02:25, 30 May 2017 (UTC)

Which plant?

Which plant is this?

• 

--Pyrophyt (talk) 16:43, 29 May 2017 (UTC)

To my eye, it resembles some type of bean plant. Alansplodge (talk) 17:46, 29 May 2017 (UTC)

I agree that it's probably a legume, the location and date of the photo might help narrow down the possibilities. Roger (Dodger67) (talk) 18:41, 29 May 2017 (UTC)

Google suggests that the "Father Richert Farming Project" is at St. Rupert Mayer's High School, Makonde in Zimbabwe. Alansplodge (talk) 23:47, 29 May 2017 (UTC)

And it ain't alfalfa, clover, pea, lentil, lupin bean, mesquite, carob, soybean, peanut or tamarind, which pretty much leaves beans in the legume department, as far as I can tell. Alansplodge (talk) 23:52, 29 May 2017 (UTC)

This seed company says that "the most popular bean varieties are of the speckled sugarbean type." We do have an article on sugar beans, but it's just a re-direct to general Lima/Butter beans, and not much specific on the speckled sugar bean grown in Africa. This page [19] discusses several bean varieties grown in Zimbabwe. Here's nice pamphlet on growing sugar beans from N2AFRICA, "a large scale, science-based “research-in-development” project focused on putting nitrogen fixation to work for smallholder farmers growing legume crops in Africa. SemanticMantis (talk) 02:34, 30 May 2017 (UTC)

Frequency of solar eclipses at a given place

"Total solar eclipses are rare events. Although they occur somewhere on Earth every 18 months on average, it is estimated that they recur at any given place only once every 360 to 410 years, on average."

So, do we know whether there's a place in the inhabited part of the world that has historically experienced more solar eclipses (not necessarily total) than any other place? And what would explain this? Sorry if this has been asked before. -- Jack of Oz ^{[pleasantries]} 21:44, 29 May 2017 (UTC)

Barring Viganella, which can't experience a solar eclipse in the winter because it can't see the sun in the winter at all (and probably experiences fewer in the summer, since the mountains hide the sun before sunset and after sunrise), I'd point you to the map in my question just down below. It looks like eclipses are most common in equatorial regions. Nyttend (talk) 21:52, 29 May 2017 (UTC)

Totality is more common in the Northern Hemisphere than the South because the June solstice is almost aphelion. Maybe the peak is somewhat north of the 0th parallel? Sagittarian Milky Way (talk) 06:56, 30 May 2017 (UTC)

Solar eclipse at the poles

Attempting to answer the eclipses-in-Toronto question led me off onto yet another rabbit trail: solar eclipses in general. File:Central eclipses 2001-2020.png makes it clear that during this two-decade time, they're much more common in equatorial regions, decreasing with latitude increases, and they're virtually nonexistent at the poles. But maybe that's the result of a too-small sample (i.e. a time span of 200 years would show different results from this time period of 20 years), or maybe because it's a Mercator projection that simply doesn't show the poles well. Can all parts of the world experience a total eclipse, even the poles? Nyttend (talk) 21:49, 29 May 2017 (UTC)

Yes. Total solar eclipses can occur at any latitude. The polar regions are of course smaller targets in real life than on the map. The paths being widened by foreshortening helps the poles see more umbra than they would otherwise and being further from the Moon hurts somewhat but not a ton. Maybe the fact that half the year the poles are immune to umbras being blocked by the ground and instead just stand still waiting to be hit helps them but maybe other things like never getting eclipses in winter cancels that out. Sagittarian Milky Way (talk) 21:55, 29 May 2017 (UTC)

Yes, these effects cancel. The sun is visible (weather permitting) at the poles about half the time, the same as at other latitudes. It's just that that "half the time" is 24 hours a day for half the year, rather than an average 12 hours a day for all the year as in most of the world. (Other latitudes in the Arctic or Antarctic are intermediate between the two cases.) It's not exactly half, because the Earth's orbit is not circular, but close enough. --69.159.63.238 (talk) 06:10, 30 May 2017 (UTC)

So does foreshortening cancel? An x "milligamma" slice of the Earth will be less miles of Earth's surface wide at 0 gamma because it isn't foreshortened but it'll be longer. Sagittarian Milky Way (talk) 06:39, 30 May 2017 (UTC)

A recent one. Count Iblis (talk) 22:17, 29 May 2017 (UTC)

I'm thinking that at a zero-order approximation, the risk should be the same. I mean, every point on Earth is, on average, in the sun half the time, and on average, the risk of a moon shadow crossing the point is random at any given time and place. So if a polar area is bent away from the passing shadow and have less likelihood of being hit by any given pass, when a pass does hit its shadow should go a long way along the ground, like you're looking at your shadow at sunset. If you want to do a higher order simulation, you have to model the exact north-south distribution of the moon in its orbit, the exact reach of the cone of the umbra and how the Earth's curve away from it decreases the chance of totality and so on. That is a big project. There's also the wildcard of whether any kind of precise repetition could emerge at high level number crunching of the periodicities of eclipses - see [20] - so far as I know at the highest level it is just considered "secular variation" i.e. everything is hit eventually, but maybe there's some kind of NSA astrology you can do to show that there's no real randomness in the long run? It'd be funny if there turns out to be some spot in South America that never gets eclipsed because of a 9040:17337 resonance with Jupiter or something. ;) But I know of absolutely no such thing! Wnt (talk) 18:41, 30 May 2017 (UTC)

A place being immune seems about impossible since Saroses make ~36 slices from highest gamma to lowest or vice versa then die, there are many Saroses at the same time, and Earth's rotation is delayed by 32*centuries² seconds, a rate which itself varies with isostatic rebound (24 hours minus 1.7 milliseconds/century long day now, 2.3ms/century if the Ice Age had never happened). Sagittarian Milky Way (talk) 22:20, 30 May 2017 (UTC)

Does superluminal communication through a (traversable) wormhole inherently imply time travel?

The article on wormholes mentions that "In 1988, Morris, Thorne and Yurtsever worked out explicitly how to convert a wormhole traversing space into one traversing time by accelerating one of its two mouths". But would a causality violation occur if I merely used a wormhole traversing space as a data link?

Perhaps more succinctly, is traversing a wormhole inherently a form of time travel? What if didn't accelerate either end of the wormhole?--Jasper Deng (talk) 22:19, 29 May 2017 (UTC)

That's a good question. I have no idea what the answer is, but it reminds me: how do you accelerate the mouth of a wormhole anyway? I mean, I assume if you hit it with a baseball bat you get a ... distorted baseball bat. Does the mouth of a wormhole fall like an ordinary physical object in a gravitational field? Or does the far end somehow ... apply a rigid force on it? Good question. Well, I did the web search and here it is ... now all I have to do is understand that ... give me a minute........ Wnt (talk) 22:55, 29 May 2017 (UTC)

While a good paper for an introduction to 4D wormholes, that paper doesn't answer many questions. It explains the questions. I have one answer. I've been Googling to see if I can find the thesis that used this specific method of explaining it, but I can't find it anywhere. So, here is a plagiarized answer until I find the proper attribution: Imagine time is a highway. We are all driving down the highway in the same direction side by side. Now, you create a wormhole in the highway by bending the road so it curves and hooks up with itself. Suppose you get mile marker 100 to join with mile marker 50 in a big loop. Now, at mile marker 75, you purposely sideswipe another vehicle. No problem. You just take the loop at mile 100, go back to mile 50, and this time you don't sideswipe the other vehicle when you get to mile 75. This works if time is like it is in the movies. Every time you take the loop, all the cars are back in the same position and travel from mile 50 to mile 100 again. But, what if that isn't the case. What if when you branch off at mile 100, all the other cars continue driving down the highway? You loop back to mile 50 and an entirely new set of cars is there. You can't go back in miles and kill yourself. You can't change events that happened on a previous trip. You simply merge into an entirely new set of traffic. The causality argument vanishes because, if we go back to time travel, going back in time doesn't let you meet your younger self. It lets you meet an entirely different universe traveling on the same timeline, just traveling behind ours. 209.149.113.5 (talk) 16:47, 30 May 2017 (UTC)

Would'nt a wormhole swallow itself aka one end "jump" to the other aka implode in the first femtosecond of its existence? --Kharon (talk) 18:26, 30 May 2017 (UTC)

In ER=EPR entangled particles are connected via wormholes. But also the wormhole connection lengthens at the speed of light. So don't expect any useful communication. Graeme Bartlett (talk) 01:32, 31 May 2017 (UTC)

May 30

The good, the bad, and the immunocompromised

Can the immune systems of immunocompromised individuals distinguish "good bacteria" from "bad bacteria"? Do they get sick because of the immune cells are overwhelmed by opportunistic pathogens, or do they get sick because of the failure of the "good bacteria" to protect by creating a barrier? In regards to the microbiota of the gut, do these individuals have trouble with absorption of nutrients too? 50.4.236.254 (talk) 04:06, 30 May 2017 (UTC)

As far as absorbtion goes - yes. Very much so. See Crohn's_disease. My sister has it. 196.213.35.146 (talk) 12:06, 30 May 2017 (UTC)

Immunocompromised conditions form a spectrum that can run from mild to severe, and whose impact can vary depending on what component(s) of the immune system have been affected. That being said, it is not really possible to give a complete answer that covers all possible immune conditions. However, I will give one example. For patients with severe neutropenia (a kind of failure of the innate immune system) the most common problem is often from ubiquitous bacteria already present on or in the body that start to grow out of control or migrate to tissues where they would not ordinarily reside. Obviously, such a patient is also at risk from new pathogens, but often the most immediate risk is from the body's inability to continue to control normal bacteria. Dragons flight (talk) 07:19, 31 May 2017 (UTC)

About Amader Electronics a popular Bengali Educational website and blog

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

---

I would like to know about Amader Electronics website but I haven't found any wiki page regarding this. As like who the founders are, what is there motto, what they want to do... etc.

I know that i can know more about them by going on to there site but I am looking a neutral point of view from fellow wikipedians.

Regards --Syed.raiyan (talk) 09:24, 30 May 2017 (UTC)

I'm not finding many sources for this, and it's not a topic currently covered in the English Wikipedia. I did find that you have a page bn:ব্যবহারকারী:Syed.raiyan/খেলাঘর. Are you looking for help expanding that article? —Guanaco 09:29, 30 May 2017 (UTC)

GuanYes actually I'm seeking help to translate and possibly neutral point of view article written about this site. --Syed.raiyan (talk) 12:26, 30 May 2017 (UTC)

"Amader" is a common word in Bangladesh that means "Ours". Amader Electronics: Here is their website (in Bengali), reportedly[21] owned by Syed Raiyan of Amader Electronics and hosted by CloudFlare Inc.; their web shop (in English and Bengali) offers a wide range of electronic components and a few kits; and their Facebook page offers design and writing services. Since Nov. 2007 Amader Electronics have uploaded to their YouTube channel videos about amateur electronic projects. The OP has been reminded that Wikipedia does not allow advertising. Blooteuth (talk) 15:11, 30 May 2017 (UTC)

Thanks for the detailed info Blooteuth. Appreciate it. But actually I'm seeking help regarding writing an article about that site which will not violate any "RULES" of wikipedia and also which will not be a promotional material. If you go to my bn:ব্যবহারকারী:Syed.raiyan/খেলাঘর there you will find an article as Guan said. --Syed.raiyan (talk) 07:12, 31 May 2017 (UTC)

@Syed.raiyan: Please read WP:COI, which basically says you, as the site owner, should not be the one creating the article. It should be mentioned that I can't find sufficient independent reliable sources to establish notability, however, so in any case, Amader Electronics is not eligible for a Wikipedia article at this time. Please read this as well: Wikipedia:An article about yourself is nothing to be proud of.--Jasper Deng (talk) 15:50, 31 May 2017 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Cancer spreading through the blood

Our article Metastasis says

Some cancer cells acquire the ability to penetrate the walls of lymphatic or blood vessels, after which they are able to circulate through the bloodstream (circulating tumor cells) to other sites and tissues in the body.

It seems to me that this implies that if a metastisized cancer patient donated blood, the recipient would acquire the cancer. But this site says

The only situation in which cancer can spread from one person to another is in the case of organ or tissue transplantation. A person who receives an organ or tissue from a donor who had cancer in the past may be at increased risk of developing a transplant-related cancer in the future. However, that risk is extremely low.

Why isn't metastisised cancer contagious through blood donation? Loraof (talk) 13:43, 30 May 2017 (UTC)

Blood is often classified as a tissue. See for example [22] and [23]. So, the quote from cancer.gov does not exclude blood. --Jayron32 14:00, 30 May 2017 (UTC)

The American Cancer Society writes that there have been no reports of cancer transmission by blood transfusion. The American Red Cross allows most people who have had cancer to donate blood if the cancer was treated at least 1 year ago and the cancer has not come back. Blooteuth (talk) 14:34, 30 May 2017 (UTC)

The same site also notes "You cannot donate blood for other people if: You are being treated for cancer, Your cancer is spreading or has come back, You have had leukemia or lymphoma as an adult (including Hodgkin’s Disease), You have ever had Kaposi sarcoma" Which would indicate that they consider active or metastisized cancer to be a reasonable enough risk that they remove such people from the donation pool; they also exclude people with any history of blood cancers. "There have been no reports of cancer transmission by blood transfusion" could mean "our system does a good job of stopping it from happening" rather then "it cannot happen". --Jayron32 14:41, 30 May 2017 (UTC)

Foreign cancer cells in the blood are very likely subject to immediate immune system attacks. Organ donors are well-matched, and patients still require massive immunosuppression. Red blood cells (the ones usually transfused) have a much simpler immune response (mostly due to the ABO blood group system and the Rh blood group system). --Stephan Schulz (talk) 14:46, 30 May 2017 (UTC)

Red blood cells also don't have nuclei and wouldn't be reproducing anyway. -Nunh-huh 15:05, 30 May 2017 (UTC)

The reason is probably because of the immune system of a recipient quickly destroys cancer cells. These is because (i) The recipient's immune system is less tolerant of cancer cells then the donor's immune system (ii) the immunological differences between different people are significant. This may lead to a transplant rejection but is protective against an infection with cancer cells. Ruslik_Zero 14:52, 30 May 2017 (UTC)

P.S. Stephan Schulz answered faster them me. Ruslik_Zero 14:53, 30 May 2017 (UTC)

Do you guys have any additional reading on that? --Jayron32 15:45, 30 May 2017 (UTC)

Our core article is blood transfusions, which describes both some of the immunological aspects and the modern practice of using only selected blood components. --Stephan Schulz (talk) 17:05, 30 May 2017 (UTC)

It has been well documented that melanoma can exhibit trans-placental malignancy, see e.g. [24]. There seems to have been considerable research into whether a sub-clinical melanoma in blood donors can affect the blood transfusion recipients (see e.g. [25]) but I certainly wouldn't speculate as to what the consensus in the field currently is or how well the donors are screened for melanoma in various jurisdictions. Dr Dima (talk) 16:27, 30 May 2017 (UTC)

A key factor here is tissue rejection. Basically, the body has a cell mediated immunity, immune cells that examine other cells in the body and reject them if the major histocompatibility complex isn't right. Cancer cells are foreign cells, and so they get rejected just like a foreign finger or liver would be rejected. Persons on immunosuppressant drugs to prevent tissue rejection therefore may be at higher risk not to reject a cancer from someone else. In general, clonally transmissible cancer is rare, with the notable exception of devil facial tumor disease. It is, however, not impossible - nothing is really impossible in biology. Wnt (talk) 16:33, 30 May 2017 (UTC)

In a Swedish study, 3% of 354 094 blood donations were given by donors with an undiagnosed cancer. There was no excess risk of cancer among the 12,012 recipients of such units. See: Risk of cancer after blood transfusion from donors with subclinical cancer: a retrospective cohort study. Edgren, G. et al., Lancet 2007 PMID 17512857. --NorwegianBlue ^talk 21:58, 30 May 2017 (UTC)

Effect of purified vitamins orally and topically vs vitamins in foods orally or topically

Is there a difference in the effects? Is there a difference between putting on retinol skin creams and eating a carrot? 140.254.70.33 (talk) 16:14, 30 May 2017 (UTC)

Retinol also known as Vitamin A₁, is a vitamin found in all these foods and used as a dietary supplement. Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision. and it serves a role as retinoic acid (an irreversibly oxidized form of retinol), which is an important hormone-like growth factor for epithelial and other cells. Vitamin A skin creams reportedly show a reduction in lines and wrinkles, control acne, and relieve psoriasis. However intake via the skin is too uncertain to count against the recommended dietary allowance. Blooteuth (talk) 11:33, 31 May 2017 (UTC)

May 31

Bbits per second

Can you calculate the rate of bits per second at which a human learn? — Preceding unsigned comment added by 31.177.96.46 (talk) 15:44, 31 May 2017 (UTC)

@31.177.96.46: No, because this is not a well-defined quantity (yet). For example, how many bits of information is learning an Axel jump and at what point in time does it become fully "learned"? We can't answer the former and the latter does not admit a natural definition.--Jasper Deng (talk) 16:01, 31 May 2017 (UTC)

Since even world-class figure skaters fall on jumps, the question of when they "fully" learn it might be answered "never". ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:47, 31 May 2017 (UTC)

And yet you can safely assume that most senior-level skaters have "learned" it in the everyday sense of "learned", even if they cannot do it 100%, because they know all the different components of the move and (usually) can demonstrate it to others. Hence the point remains that there is no natural definition of "learned" suitable for a calculation like the OP asks for. Also, to be a bit clearer, my statement about "learned" is intended specifically for each bit of information. Even if we could model a learning process as a stream of bits entering the mind, at what point does each bit become learned? "Learned" does not obey the law of the excluded middle.--Jasper Deng (talk) 21:21, 31 May 2017 (UTC)

Figure skating is fun, but this discussion is distracting from the pedagogical purpose of bringing it up.

Doing back-to-back jumps and having to skate several minutes are handicaps. A 10 second routine with 1 jump would be easier and even female skaters seem to do double jumps like they're a piece of cake. Maybe some human has in fact become practically immune to falling from a single Axel (assuming fair conditions. Not drunk, tired etc, no wind, earthquakes but no mulligans). No one will ever do a centuple Axel without cheating. Sagittarian Milky Way (talk) 21:41, 31 May 2017 (UTC) @Sagittarian Milky Way: Next time, make sure you don't overrun my comment!--Jasper Deng (talk) 23:32, 31 May 2017 (UTC)

Human senses and the human brain, or Neurons in general are far beyond binary math. If you would try to brake this down into the binary system you could count all the nerve cells and multiply the number with 256 kbps, which is known as near real "resolution" in mp3-audio. On one hand the result would probably be much to high but on the other your Question is alike much to wrong. --Kharon (talk) 20:10, 31 May 2017 (UTC)

You can, however set an upper limit by calculating the rate at which the human retina transmits data to the brain (around 10 million bits per second, which is close to an Ethernet connection) and repeating for hearing, touch, etc.[26][27] You can't learn any faster than that, but you can learn a lot slower. Judging by some of the people I come in contact with, learning can sometimes be as slow as several bits per year, or can even go negative. --Guy Macon (talk) 20:25, 31 May 2017 (UTC)

• This article deserves to be shared every time this question comes up. The OP should read it daily until it becomes ingrained. --Jayron32 23:35, 31 May 2017 (UTC)

Is sweetness intensity associated with sucrose quantity?

Is sweetness intensity associated with sucrose quantity? Is there a sucrose quantity upper threshold at which the sweetness "tastes the same"? Or is sweetness perception variable from individual to individual? Is there a point at which sweetness becomes unbearable, or is that subjective? All I know is, I've never liked the icing and fillings of bakery goods. They are too sweet for me. It's one reason why my favorite type of doughnut is the plain glazed doughnut, eaten with water to dilute the sweetness. I think this low-sweetness-tolerance threshold is genetic, because my father and mother also prefer mildly sweet things so icings, fillings, jams and fruit preserves, fruit juices, fruit smoothies are rarely consumed in the house. 50.4.236.254 (talk) 23:13, 31 May 2017 (UTC)

The Wikipedia article with the surprising title of sweetness gives the common scale by which sweetness is measured, with pure sucrose given a sweetness value of "1.00" Concentrations of sucrose less than pure will, of course, have values less than one. Here are some external sources which go into more detail on methods for determining sweetness. --Jayron32 23:20, 31 May 2017 (UTC)

It's difficult to separate genetic and environmental factors in such cases. You may have inherited genes making you more sensitive to sweetness, or you may have become habituated to a lower level of sweetness because you were raised in a family culture, and retain those behaviours, exposing you to lower levels of sugar that the average, or both may be true. ObPersonal, but when in the past I cut down the amount of (cane) sugar I consumed in, for example, tea, at first it tasted insufficiently sweet, but after a few weeks became the new normal, and tea with the previous amount of sugar tasted unpleasently sweet. I have no doubt that if I were to reverse that change, the reverse would occur. {The poster formerly known as 87.81.230.195} 94.9.8.213 (talk) 23:37, 31 May 2017 (UTC)