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January 8

Negative coefficient of friction

I was reading the article on friction in the section about negative coefficients of friction, where it discussed the force of friction decreasing with an increase in the normal force. However, shouldn't these mean that the force of friction is inversely porptional to the normal force? A negative coefficient of friction would mean the force of friction would be negative (which in terms of vectors would mean working in the same direction as the applied force), but it would still increase with an increase in the normal force. Am I wrong here? Thanks, --T H F S W (T · C · E) 04:34, 8 January 2015 (UTC)

I agree with your interpretation. However, as far as I know, that doesn't exist in the real world, while what they described does. One example that comes to mind is ice skating, where the friction is reduced once the pressure builds in the area under the blade and melts the ice, so the skater is then gliding on water on ice. I'd call that a "negative change in the coefficient of friction". Of course, that's more of step function than a continuous case. StuRat (talk) 04:58, 8 January 2015 (UTC)

It is true that there is high pressure under a skate blade, which lowers the freezing/melting point, but it's a myth that this results in melting that makes skating possible. Artificial ice rinks are normally maintained at temperatures below the lowered freezing point. The truth is more complicated and involves other factors. --65.94.50.4 (talk) 05:09, 8 January 2015 (UTC)

Great link. I love it when myths are busted. 196.213.35.146 (talk) 10:08, 8 January 2015 (UTC)

Well, if it was due to friction that the ice melts, then you'd expect it to be very hard to get started moving on skates, since there's no frictional heating until after movement begins. Note that the pressure lowers the melting point, but the increase in pressure also heats the ice. As to the argument that water takes up less volume and therefore the pressure would decrease when it melts, this ignores the fact that the skater will simply sink down by a microscopic amount into the ice, to restore the pressure. StuRat (talk) 19:02, 8 January 2015 (UTC)

I agree that it's a misleading heading. I've put "negative" in quotes until someone comes up with a better way to express the concept. Dbfirs 09:45, 8 January 2015 (UTC)

It may be misleading, but for better or worse a lot of scientific terminology is misleading to the uninitiated, no? That doesn't mean we get to change it on WP, we should be consistent with the literature. The authors of the cited paper say in the abstract "This leads to the emergence of an effectively negative coefficient of friction in the low-load regime." - I don't think it's our place to change the terminology that has been accepted in a Nature publication. It is unclear to me whether your solution of scare quotes is better than calling the section "effectively negative coefficient of friction" - any thoughts from the group? SemanticMantis (talk) 16:20, 8 January 2015 (UTC)

If we quote something which is believed to be in error, we should put "(sic)" after it, to show this. StuRat (talk) 16:58, 8 January 2015 (UTC)

Sure, as a general practice, but I don't believe this specific case to be an error, and in general I would doubt our understanding before I would doubt the findings of Nature paper (sure, they occur, but much more rarely than errors in WP). SemanticMantis (talk) 20:09, 8 January 2015 (UTC)

Note that it is the coefficient of friction that is negative, not the force of friction. The coefficient relates the normal force to the frictional force, and is dimensionless. In this case, the coefficient is negative, because increasing normal force decreases friction (in at least one very special scenario) - read the abstract of the paper cited in our article here [1]. I actually think the article is fine how it was - it makes sense if you've read and understood everything up to that point. SemanticMantis (talk) 16:20, 8 January 2015 (UTC)

(ec) Note that a negative coefficient of friction invariable would lead to a negative frictional force:

Ff = μFn

-Ff = (-μ)Fn

StuRat (talk) 19:00, 8 January 2015 (UTC)

Yes, what SM said. It's not as counter-intuitive as you would first think, because there is adhesion involved; there is a resistance to sliding even under zero normal load. The slip resistance is a constant (adhesion) plus a coefficient of friction times the normal force, and in this case that coefficient would be negative. But this is just decreasing the adhesion under increased vertical load; no one is saying that this could overcome the cohesion and start "pushing" in the same direction as the applied load. --Floquenbeam (talk) 17:02, 8 January 2015 (UTC)

Floquenbeam's explanation makes sense. But, there still can't be a fixed negative coefficient of friction, as that would indeed eventually lead to a frictional force, at high normal force ranges, which surpasses the adhesion force. So, the coefficient of friction must be variable, and only negative at certain low ranges of normal forces. StuRat (talk) 17:05, 8 January 2015 (UTC)

Yes, as SM already stated above, it's an "effectively negative coefficient of friction in the low-load regime." It's variable, and no one is saying it continues this behavior at higher loads. --Floquenbeam (talk) 19:07, 8 January 2015 (UTC)

I've changed the wording to an exact quote of the source, but left the scare quotes in the heading. Will this suffice?
I've also moved the section to its proper place after the table of conventional positive values. Dbfirs 19:41, 8 January 2015 (UTC)

Thanks, that's better. I personally don't like the scare quotes, because it seems to me the coefficient is literally negative under the specific regime studied. But I don't feel strongly enough about it to argue or change it :) SemanticMantis (talk) 20:06, 8 January 2015 (UTC)

If I'm not mistaken, it still opposes the applied force. The proportion of opposition gets smaller as more force is applied. I think a hydrofoil can be modeled as a negative coefficient of friction. Motion lifts it, drag is reduced, efficiency increases. It can be modelled other ways with more conventional positive coefficients but it's not as cool. --DHeyward (talk) 02:49, 9 January 2015 (UTC)

Snow Extrusion

Though the illustration might not demonstrate it very well, I'm interested in the natural phenomena of when snow forms an extended extrusion-like structure growing from behind of objects like trees or fences. I assume it has something to do with wind, but how exactly does it work? 176.14.195.212 (talk) 12:36, 8 January 2015 (UTC)

This is a very interesting question, and it turns out to be very difficult to describe and understand all the things snow and wind can do! Here are some nice descriptions of how snow interacts with snow fences - [2] [3]. I don't know of a specific term for the influence of trees/fences on snow, but Penitentes is a word for spire-like snow formations - these form from wind but also due to interactions with temperature and dew point. The general concept that would apply to snow/fence interactions is Aeolian_processes (sometimes spelt 'Eolian'). These processes can also cause pattern formation and have can have some degree of self organization. Behavior of snow due to wind is an active area of research, and there is a lot we still don't understand. Here is an example of a recent empirical paper on snow/wind dynamics [4], and here is a nice overview from the USGS [5]. There are also lots of simulation models and theoretical mathematical treatments, but those can get pretty heavy and might not be that useful for a general audience. An unrelated but interesting water 'extrusion' is ice spike. Both this and the photo you show (and the formation of snow flakes themselves]] are examples of dendritic growth.

If you have any more specific questions I might be able to find more suitable references. In the meantime, let's all enjoy these beautiful photos that we get searching /eolian snow pattern/: [6] or simpley /penitentes/ [7] :) SemanticMantis (talk) 16:06, 8 January 2015 (UTC)

Winter mountaineers in UK call this "rime ice" but we have an article on the same subject called Hard rime. On the hills, you can determine the prevailing wind direction (useful for avalanche prediction) because the ice grows into the wind. See Avalanche, the Basics - Part 2: Staying Safe; "Rime Ice is caused when super-cooled water vapour hits a freezing object (rocks, fence posts etc). Counter-intuitively, rime grows into the wind rather than away from it, so the direction it points is another handy indicator of recent wind direction" (just over halfway down the page). I rather like this picture. Alansplodge (talk) 16:32, 8 January 2015 (UTC)

Just what kind of person would be so easily impressed as to take such an interest in structures that arise out of snow anyway... Snow talk 11:22, 9 January 2015 (UTC)

The kind of people that try to avoid having your electricity supply or mobile phone cut off in Winter, or ensure cars going across bridges don't get impaled by falling icicles. Or any people who are generally interested in strange phenomena. Dmcq (talk) 12:00, 9 January 2015 (UTC)

@Dmcq: Just so you don't walk away with the wrong impression of me, can I trouble you to take a look at my full user name? Snow talk 16:28, 9 January 2015 (UTC)

Ha, until any sarcasm punctuation becomes commonly available, this is a situation where a sarcasm tag might have helped (e.g. '/s', '</s>', '/sarcasm', etc. :) SemanticMantis (talk) 16:45, 9 January 2015 (UTC)

I had considered that, but the problem is that it wouldn't necessarily have delineated that the sarcasm was self-effacing and I hoped that keeping my name at full scale would make that point more clearly. Oh well, just a reminder as to one of numerous reasons I don't attempt humour here as a general rule. :) Snow talk 02:47, 10 January 2015 (UTC)

Human only (or close) diseases.

According to their articles, both Smallpox (Variola Major) and Polio are found in nature only in Humans. (It apparently is possible to give smallpox to a primates, but no cases have been observed in the wild). Any idea where I could find a list of diseases that (like these) are more or less restricted to humans?Naraht (talk) 15:54, 8 January 2015 (UTC)

Would you include mental diseases ? I imagine many of those are human-only, as more complex brains are prone to more complex disorders. StuRat (talk) 16:55, 8 January 2015 (UTC)

Lots of zoo animals develop mental disorders, Stereotypy_(non-human) covers one common symptom. Even stuff like schizophrenia, which seems very human-centric by definition, is studied by Animal_models_of_schizophrenia. It's not clear to me if it's fair to say these rodents and primates "have schizophrenia". SemanticMantis (talk) 20:03, 8 January 2015 (UTC)

Unfortunately, Wikipedia seems to be a little deficient here - there are 219 entries in Category:Zoonoses, but only 216 entries on List of infectious diseases. Ideally, the diseases the OP is looking for would be those which are on the second list but not the first. Tevildo (talk) 19:57, 8 January 2015 (UTC)

If you're willing to include parasites, then several of these are human-specific, e.g. Louse#Lice_in_humans. SemanticMantis (talk) 20:03, 8 January 2015 (UTC)

You can look at Eradication of infectious diseases as a human infectious disease can only eradicated if it is human specific. Ruslik_Zero 20:21, 8 January 2015 (UTC)

That's a very good point, thanks! However, Malaria is on that list, and it definitely lives in mosquitoes as well as humans, though it doesn't give them the same symptoms. SemanticMantis (talk) 20:36, 8 January 2015 (UTC)

Plasmodium can not reproduce in mosquitos and humans are the only secondary hosts. Ruslik_Zero 20:54, 8 January 2015 (UTC)

That's not necessarily true; you could eradicate it both in the human population and any other carrier populations (though unfortunately for members of that other species, the likely approach would be (and has at times historically been) to eradicate the carrier population itself. In any event, it's quite likely there's never truly been a human-specific pathogen; all infections to which humanity has been subject have arrived in the human population through zoonoses at some point or another, and there's no way of knowing with any degree of certainty that there's even so much as a single pathogen which entered the human ecological niche and then mutated into a form that has never since infected another member of any other species. Certainly there might have been cases where the only per-existant animal vector(s) disappeared to extinction, but these are surely a great rarity as well. Non-communicable diseases are of course another matter entirely, but I rather suspect Naraht was excluding them by principle. Snow talk 11:18, 9 January 2015 (UTC)

This is a difficult topic especially regarding viruses. There are closely related viruses that have different effects on hosts. SIV and HIV are closely related. AIDS is mostly human though. Rabies in bats is quite the different story for humans. The flu moves through swine, avian and human hosts that all contribute and affect each differently. I suspect the "human only" might be symptom related rather than antibody related and it would surprise me a bit to find a symptomless carrier in insects, birds or mammals that are simply unknown. --DHeyward (talk) 04:26, 10 January 2015 (UTC)

Beaver poo

Mice don't "hold it in" but rather urinate and defecate more or less constantly. Is this also true of larger rodents, such as beavers ? StuRat (talk) 17:25, 8 January 2015 (UTC)

According to [8], beaver droppings are found in the early morning at the water's edge. I don't know if that means they do it overnight and it's only found when the sun rises, or if they do the business at first light, but it implies they hold it in through daylight hours. Mogism (talk) 17:31, 8 January 2015 (UTC)

Thanks. Anyone else ? StuRat (talk) 06:32, 12 January 2015 (UTC)

Are siblings the most genetically similar people to a person?

And if so... if one sibling is smart, and their sibling(s) is/are dumb, does that not demonstrate that the factors that determine smartness and dumbness are predominantly environmental and not genetic? 69.121.131.137 (talk) 22:32, 8 January 2015 (UTC)

As for the first question, apart from identical twins, the closest genetic relationship is that between two siblings or that between a parent and his/her child. A child has inherited 50% of its genome from each of its parents, so is 50% identical in its genome to either parent. Likewise you can calculate that two full siblings share on average 50% of their genome.

As for the second question, no, that does not logically follow, at least not from just a few cases. Children can inherit different genetic material from their parents, and so they need not share between them any of the genes which influence intelligence. In fact theoretically they need not share any genes. On average, they share 50% of their genes, but in individual cases it may be 60% or 45% or even 0% (though this would be exceedingly unlikely). - Lindert (talk) 22:45, 8 January 2015 (UTC)

(ec) Usually this is addressed with a twin study. Twins who are genetically identical are compared to those who share 50% of their genes, and the difference is considered. Of course, it might not be foolproof (what if the smart twin was sneaking in and takes tests for the dumb one, affecting how they are later treated, or if the teachers have a visually driven bias) but it's a pretty good way to look at it. Wnt (talk) 22:49, 8 January 2015 (UTC)

(ec) Siblings have 50% genetic overlap, the same as the overlap between a parent and child. That isn't enough to determine whether differences are due to environment or genes. However, identical twins have 100% genetic overlap, so the differences between them are much easier to interpret. The most powerful test of environment-versus-genes is to compare identical twins reared apart with identical twins reared together. It's hard to find good data, because the number of identical twins reared apart is quite small, but the data that exists is extremely useful. Looie496 (talk) 22:51, 8 January 2015 (UTC)

Because the exact proportion of "shared" genes in siblings can theoretically vary between 0% and 100% (though with an average of 50%) it is possible to have more "shared" genes with other people than with your sibling. (Note that these percentages refer to the genes that can vary between two people (i.e. your parents), and not to genes that you "must" have in order to be human rather than some other species). Your question about the factors determining intelligence is not yet resolved, though scientists are hard at work on it. Geneticists talk of the heritability of different traits. As you will see from our article on the heritability of IQ the best estimate of the heritability of intelligence seems to be about 50%. That is, about half of the variability of intelligence among the human population at large can be explained in terms of a genetic component. However, this figure refers to the population as a whole, and, because we don't know the proportion of genes you share with your sibling, we can't reach any conclusions about the relative impacts of nature and nurture in your particular case. RomanSpa (talk) 00:41, 9 January 2015 (UTC)

I saw my doppelganger at a train station a few years back. Looked nothing like my brother. Can't speak for the genes beneath the skin, but my resemblance was uncanny. InedibleHulk (talk) 00:48, January 9, 2015 (UTC)

• Looie's answer is the correct one in general, but both male and female children bear their mother's mitochondrial DNA, so are slightly closer to each other and their mother than their father in that respect. There's also the question of the Y chromosome. Since the Y carries fewer genes than the X, again, children are closer to their mother, but two brothers, each carrying the same Y, are thereby closer to each other and their father than to a sister not carrying the identical Y. Ex chromosomes cross over, so the exes inherited by sisters are not necessarily identical, while the wyes carried by brothers are.μηδείς (talk) 01:33, 9 January 2015 (UTC)

Sisters do have identical X-chromosomes, since their father only has X-chromosome. Both sisters necessarily inherit all of the genetic material in their father's single X-chromosome (unless some genes could cross over between the father's X and Y). Of course the X-chromosomes they inherit from their mother could be quite different, but in that respect they are no different from two brothers either. - Lindert (talk) 09:59, 9 January 2015 (UTC)

There actually is a portion of the Y chromosome, the pseudoautosomal region, that can recombine with the corresponding portion of the X chromosome. It only comes to about 5% of the Y chromosome, though. Looie496 (talk) 16:31, 9 January 2015 (UTC)

One thing to clarify: First, let's ignore things that can alter the 50% from each parent (the things Medeis mentions, but also genetic disorders like XXY or XYY, etc), and focus on the simplified 50/50 model of genetic inheritance from each parent for alleles in nuclear DNA. Now, a parent is guaranteed to share 50% of your alleles ( not genes, let's be precise here :), and cannot share any more or less unless you get into edge cases. We don't know exactly which alleles are shared, in part due to recombination. In contrast, a sibling shares 50% as an expected value. So the situation is this - if you want a "safe bet" for most shared alleles, pick a parent, you'll never be far off from 50%. If you want to potentially maximize the shared alleles, pick a sibling, who will share more than 50% of alleles roughly half the time. As Lindert points out above, a sibling has the potential to share much more than 50% with you, but can also be lower, and this makes for some interesting differences, depending on our motive for finding a highly similar person. SemanticMantis (talk) 16:41, 9 January 2015 (UTC)

January 9

Trustworthy sources of Windows builds of open source software?

Some of the open source software I use is hosted at Sourceforge. I've stopped downloading Windows installers from SF since reports came out in 2013 that installers hosted there were bundled with extra/unwanted software. Are there trustworthy alternative sites for Windows builds of open source software, ones that don't bundle extra stuff in the installers?

Are there ways to confirm that no unwanted extras are bundled with an installer? --134.242.92.2 (talk) 16:02, 9 January 2015 (UTC)

Are you talking about malware, or just spam-like junk? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 9 January 2015 (UTC)

Not sure about what's bundled in the case of SF, but I do want to avoid both categories.

*** I inadvertently posted the question here instead of the Computing RD. I've moved the question there. Please post follow-up there. --134.242.92.2 (talk) 16:26, 9 January 2015 (UTC)

";" issue

Can some review this section please (https://en.wikipedia.org/wiki/Human_evolution#Divergence_of_the_human_clade_from_other_great_apes). Iss ";" in the end of the last word, an error? -- (Russell.mo (talk) 16:58, 9 January 2015 (UTC))

Yes, that was a typo, and I fixed it. I'm now a little confused by the styling of "Ardipithecus ramidus" as "Ar. ramidus" - normally we only use the first letter of a genus name when describing the species, and the article for A. ramidus just says "A. ramidus" as I would expect. Our style guide Wikipedia:Manual_of_Style#Scientific_names is silent on the issue. Before I change these to single letter abbreviations for genera does anyone want to defend the abbreviations as they are currently used in this section? I can see the desire to avoid confusion with e.g. Australopithecus, but the two-letter genera still looks wrong to me... SemanticMantis (talk) 17:12, 9 January 2015 (UTC)

Ok I've found this style advice that says the two letter abbreviations are to be avoided but are tolerable in some publications to avoid ambiguity: [9], citing "Butcher’s Copy-editing" as the style guide. SemanticMantis (talk) 17:17, 9 January 2015 (UTC)

Thank you for clarifying the issue. In regards to the point you mentioned, I'm not a science student, whatever knowledge I acquired so far, is from Wikipedia. Personal point of view: I think "A." is used for the Australopithecus, well this is what I've come across so far in my readings. -- (Russell.mo (talk) 10:49, 10 January 2015 (UTC))

Resolved

Damages caused by too much staring at a screen (be it TV, computer or smartphone)

What could happen to my eyes, when we spend many hours starring at a screen? (I mean a modern TFT or LED backlight, not that old TVs.). Is this associated with any illnesses, poor vision or whatever? How can I know whether High-energy visible light is real or just a urban legend? How can I know if screens will cause another illness down the road? After all we didn't evolve starring at an illuminated screen. — Preceding unsigned comment added by Noopolo (talk • contribs) 18:25, 9 January 2015 (UTC)

At the very least, there's the problem of literally "staring" (not "starring") at a screen too much, be it TV or your computer screen, in that you might not blink enough, and your eyes might tend to get dry. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:20, 9 January 2015 (UTC)

See eye strain, computer vision syndrome, and this link from the Mayo clinic [10]. SemanticMantis (talk) 21:10, 9 January 2015 (UTC)

Oh and you can tell that high-energy visible light is not an urban legend because you can check the references at High-energy_visible_light#References - many of which are peer-reviewed scientific literature. You can also presumably see the color blue. SemanticMantis (talk) 21:12, 9 January 2015 (UTC)

One problem is always having the same focal distance to the screen, which means you don't exercise the focusing muscles in your eyes and they atrophy. StuRat (talk) 22:31, 9 January 2015 (UTC)

Source please? This is simply not how the physiology of this organ works. Snow talk 02:41, 10 January 2015 (UTC)

See vision therapy. There is some evidence that exercising the eyes helps, but more is needed. StuRat (talk) 05:10, 10 January 2015 (UTC)

That article is not at all relevant to the issue here, or the mechanism of atrophy you proposed. Vision therapy is for those who have per-existent conditions (such as motor disorders or those involving binocular coordination) not for people whose muscles "atrophied" because they weren't focusing at enough different varieties of distance, as you speculate. That's an absurd suggestion for many more reasons than I'm going to take the time to address here, but I will point out this much: the eyes are constantly in motion and constantly making minute changes to focus that we are not consciously aware of. As you stare at your monitor reading this message, your eyes are actually darting back and forth and focusing at/upon different points on the screen even when you are not willing them to. What we see and what we think we see are two very different things, as the visual cognition centers of the brain are applying many layers of filters to compose a perceptual image around that tiny little space that your eyes are focused on at any given time; the brain takes previously acquired optical information and uses color and shading ques and a huge array of assumptions to create the composite your conscious mind perceives as the field of vision you are experiencing -- but the truth is that, at any given instant, you are only "seeing" (in the sense of receiving visual information directly from that eye in that instant) a fraction of what you perceive yourself to be seeing, and the eyes themselves are almost never at rest to any significant degree (even when you have your eyelids closed).

Regardless, you're not going to find a source out there supporting your guess that any issues with vision that arise from starting at monitors too long proceeds from atrophy. Quite the opposite, in fact -- the eye strain involved comes from the manner of exertion, not the lack of it. Stu, please, we've been down this road a million times; please don't post outright speculation in responding to issues upon which you have no first-hand knowledge and no sources to back you up. Snow talk 05:38, 10 January 2015 (UTC)

Here's one source: [11]. Not a very good source, but it does show it's not just me making up stuff, as you seem to think. I heard this from multiple sources, so will try to track down some better ones. StuRat (talk) 05:54, 10 January 2015 (UTC)

Convergence insufficiency is also somewhat related. StuRat (talk) 06:14, 10 January 2015 (UTC)

That ref is not just a mediocre source, it's a three paragraph non-scientific fluff piece in a fad health e-mag recommending "eye yoga" that doesn't even discuss the physiology of the eye or even really relate to this topic. Even that description somehow doesn't do justice to how silly virtually every word in it is and how much it is working against you here in establishing that you aren't speculating wildly. As for convergence insufficiency, it is another example of a motor condition which has nothing to do with atrophy. Look, if you heard this from multiple sources I can only guess that it must be a piece of folk science making the rounds, because the physiology of the eye is not an area of trivial interest for me and I'm telling you that what you are suggesting is not consistent with the actual science. CVS is simply not caused by atrophy -- again, it's much closer to the opposite. Snow talk 11:16, 10 January 2015 (UTC)

Apparently, Medieval teenagers were also the demographic to stare at illuminations all day until they grew too old and blind. But at least they were reading. InedibleHulk (talk) 02:53, January 10, 2015 (UTC)

Haha, that first link made my day, Hulk. That's some funny marginalia, a rare thing. Snow talk 12:10, 10 January 2015 (UTC)

What's the problem of putting metal objects into a microwave oven?

I get that a sharp object will release sparks, but what would happen if I put a metal bowl with a metal top and water inside into the microwave? Would it get hot and heat the water, while blocking the microwaves that won't heat the water directly?--Noopolo (talk) 19:49, 9 January 2015 (UTC)

Microwave oven explains the consequences of putting metal objects in the microwave. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:17, 9 January 2015 (UTC)

On rare occasions, you can also get the same arcing without metal. I managed to get it with a saltine with a jalapeno pepper and cheese on top. StuRat (talk) 22:27, 9 January 2015 (UTC)

Olives make cool sparks and jump around, if it's just them in there. InedibleHulk (talk) 03:02, January 10, 2015 (UTC)

I'd love to see an explanation for how certain nonmetallic objects cause arcing in the microwave oven. Salty brine seems to be one necessary ingredient. StuRat (talk) 05:01, 10 January 2015 (UTC)

If you cut a grape almost in half, so that the two halves are connected with a thin strip of skin and lay them with the cut faces uppermost in a microwave, you get quite impressive sparks. I'm sure there is some salt in a grape - but hardly very much. You can see it in a rare example of a YouTube video that isn't faked: https://www.youtube.com/watch?v=DrY0aC81wxI

The stuff that happens in a microwave is frequently hard to figure out - so unless the specific situation you're thinking about has been written about, I doubt we could come up with a definitive answer. SteveBaker (talk) 05:59, 10 January 2015 (UTC)

There are many (not quite scientific) experiments about what happens to a variety of things in the oven at Is It a Good Idea to Microwave This? InedibleHulk (talk) 00:05, January 11, 2015 (UTC)

Yes, if you build a Faraday cage in a microwave, it will prevent EM radiation from entering. But water already does that and is a reason it heats. A microwave oven has numerous TE and TM modes of standing waves inside the cavity (the oven is much larger than half a wavelength). Low resistance metal forces the field to be zero and the field gradient can be large (causing arcs) and also causing electrical current in the metal. See TEM mode but only TE and TM modes are excited in the cavity. --DHeyward (talk) 05:57, 11 January 2015 (UTC)

January 10

Butterfly Flight

How does a butterfly flap its wings and change direction while in flight?--75.171.82.75 (talk) 01:11, 10 January 2015 (UTC)

They use muscles on their abdomen to flap the wings, and changing direction, I suppose, involves flapping one side harder than the other. Another possibility is wing warping. StuRat (talk) 01:21, 10 January 2015 (UTC)

The aerodynamics of butterfly flight has been the subject of multiple scientific studies - it is more complex than it might at first seem, and may involve different mechanisms for different phases of flight. This [12] Nature paper is unfortunately behind a paywall, but is well worth looking at if you can access it. AndyTheGrump (talk) 01:40, 10 January 2015 (UTC)

Here is a full text version of the paper. Mikenorton (talk) 10:37, 10 January 2015 (UTC)

Thanks to all for your time and effort to provide an answer to my question. I just read the Nature article referenced by AndyTheGrump, through the link provided by Mikenorton. Andy, your comment "is more complex than it might at first seem" is a major understatement. I am left thoroughly amazed at the potential complexity of the techniques these small creatures can utilize while in flight - and all by virtue of instinct. I highly recommend using this link to all who have an interest in the mechanics of insect flight. Thanks again guys for this incredible eye-opener!75.171.82.75 (talk) 18:40, 10 January 2015 (UTC)

Welch's

The method of pasteurizing grape juice to halt the fermentation has been attributed to a British physician and dentist, Thomas Bramwell Welch (1825–1903) in 1869. I am not happy with the wording and lack of a source. Wasn't pasteurization known before? Are there any specifics to that method? Isn't "has been attributed to" classic weasel wording that should be avoided? --92.202.13.41 (talk) 03:16, 10 January 2015 (UTC)

That doesn't indicate that he invented it, only that he used it. According to Louisization Pasteurization, the process was invented in 1864 , initially for milk of course. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:58, 10 January 2015 (UTC)

Reading the article you just linked to shows that "initially for milk of course" is quite incorrect; the process was for wine and beer -- "it would be many years before milk was pasteurized". --jpgordon^{::==( o )} 16:32, 10 January 2015 (UTC)

D'oh! You're right. I was more concerned with the date, which was five years before Welch applied the process. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:41, 10 January 2015 (UTC)

Welch's history page shows in the 1869 entry Bramwell and a couple of labels for his "unfermented wine". It looks legit. --Mark viking (talk) 04:56, 10 January 2015 (UTC)

PG-1302-possibly a pair of black holes close to colliding

The news article I just read said these 2 black holes will probably collide in a million years. It also said the energy released at that time could be as much as 100 million supernovae, with spacetime warping effects. My questions are 1) Even allowing for the very great distance, billions of lightyears, could that released energy, a million years from now, still damage the life on Earth, assuming life on Earth then is similar to life on earth now? 2) Could the spacetime warping be large enough, even with the very great distance, so that in ordinary life,(not just when using sensitive scientific instruments) a human's senses could notice definite effects on spacetime, assuming humans exist then? thanks.2601:7:6580:5E3:9138:4390:6740:EBCC (talk) 03:41, 10 January 2015 (UTC)

There are masses of binary star systems in every galaxy and most even seem stable. Given the fact that "black holes" are very small stellar objects it seems near impossible that two such black holes will ever come into contact. They will always miss eachother and that way develope into one (exeptional) binary system. --Kharon (talk) 04:27, 10 January 2015 (UTC)

These are very massive black holes, perhaps millions or much more of solar masses. Read the recent Michael Franco at CNET or Dennis Overbye at New York Times.2601:7:6580:5E3:9138:4390:6740:EBCC (talk) 05:16, 10 January 2015 (UTC)

It's always an interesting calculation to identify the event horizon or Schwarzchild radius for objects with the mass of the sun or earth. "Small" isn't quite the right word when it physically warps space into itself. A black hole with the mass of the sun wouldn't be "smaller" but the rulers would be longer. --DHeyward (talk) 07:11, 10 January 2015 (UTC)

Ok, but these aren't small in any case. theyre not stellar black holes, they seem to be supermassive black holes, two galaxies may be colliding.2601:7:6580:5E3:4D7:335A:100B:7C6B (talk) 09:23, 10 January 2015 (UTC)

Coorbiting black holes are predicted by Einstein to lose energy via gravitational radiation. This causes their orbit to decay and makes a collision inevitable for compact binary systems. Dragons flight (talk) 20:11, 10 January 2015 (UTC)

Back of an envelope calculation - 100 million supernovae at a distance of 3.5 billion light years is equivalent to one supernova at a distance of 350 thousand light years (inverse square law). That is about 3 times the diameter of our own galaxy. So it doesn't sound like we need to be worried about this. Gandalf61 (talk) 13:30, 10 January 2015 (UTC)

Chemicals used to enhance flavor in food?

No, I am not talking about complex chemicals called "spices". I am talking about monosodium glutamate and other flavor enhancers. I watched a documentary, and one part said that there are actually various flavor enhancers in food (i.e. citrate?). I do not remember the specifics, so can anyone list all the flavor enhancers that have been used in modern times to enhance the flavor of processed foods? 71.79.234.132 (talk) 05:20, 10 January 2015 (UTC)

Plain old sodium chloride (table salt) is the most common one. StuRat (talk) 05:23, 10 January 2015 (UTC)

Capsaicin is what makes peppers hot, and that's added to many foods as a flavor enhancer, although too much overpowers every other flavor. StuRat (talk) 05:25, 10 January 2015 (UTC)

No, it was not capsaicin or table salt. It was a chemical with a very scientific name and no common name. Capsaicin and table salt are not part of the list. 71.79.234.132 (talk) 05:34, 10 January 2015 (UTC)

Monosodium glutamate?129.178.88.82 (talk) 09:40, 12 January 2015 (UTC)

List of food additives, Category:Flavour enhancers. Mr.Z-man 05:58, 10 January 2015 (UTC)

Why does new york city have a continental climate?

If new york city is right beside the ocean, why does it have a continental climate? — Preceding unsigned comment added by 199.119.235.169 (talk) 06:38, 10 January 2015 (UTC)

The prevailing wind direction is critical here. If the wind blows off the continent, then you get a continental climate. StuRat (talk) 06:52, 10 January 2015 (UTC)

It's a little more complicated than that, but you're right that prevailing wind direction is crucial. Let me add a pointer to our continental climate article. Looie496 (talk) 16:58, 10 January 2015 (UTC)

I think the oceans are naturally warmer for New York than other countries at the same latitude. Compare swimming season for New York vs. Northern California, Europe, Japan at the same latitude. Pure anecdotal evidence so could be wrong. --DHeyward (talk) 08:41, 10 January 2015 (UTC)

The large-scale oceanic gyres are clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere, because of the differing sign of the Coriolis parameter. This means ocean currents in both hemispheres tend to be relatively warm off the east coasts of continents (e.g., New York) and relatively cold off the west coasts. Short Brigade Harvester Boris (talk) 18:56, 10 January 2015 (UTC)

• Who says it does have a continental climate? The NYC article certainly doesn't. μηδείς (talk) 20:55, 10 January 2015 (UTC)

• • Try Climate of New York. Very first sentence. Short Brigade Harvester Boris (talk) 23:29, 10 January 2015 (UTC)

You've confused two very different things, User:Short Brigade Harvester Boris. Look at the first sentence of this thread. μηδείς (talk) 00:18, 11 January 2015 (UTC)

Ah. Right. The NYC metropolitan area has an average January temperature right around 0 C. This puts it into the C Koeppen primary classification rather than the D classification that applies to most of the state, knocking it out of the Df "humid continental" range.

More complete response to OP: Keep in mind that the names for the Koeppen classifications are somewhat arbitrary and there's no agreed upon quantitative definition of "continental." Over the years there have been various indices proposed for continentality. A fairly well known one is the Conrad index. Using the Conrad index NYC (Central Park) has a continentality of 39. This compares to a value of 13 for London and (perhaps surprisingly) is not much below the value of 42 for Moscow. Short Brigade Harvester Boris (talk) 01:26, 11 January 2015 (UTC)

Yes, having lived in Philly, Atlantic City, New Brunswick, NJ, NYC, Ithaca, NY, as well as briefly in places like Hempstead, NY, Cape Cod, Binghamton, NY, Melrose, MA, Long Beach, NY, I can assure you NYC is humid subtropical, and much milder than inland continental climates. Indeed, I don't believe I have ever worn a jacket in NYC before Thanksgiving, while interior NJ can be inbearable both in summers and winters. μηδείς (talk) 01:48, 11 January 2015 (UTC)

does re-enamel toothpaste work?

Hi,

I was wondering if we had an article on re-enamel toothpaste, and also whether in general the consensus is that it works? I was surprised there's no Colgate Total + re-enamel for example? Despite the Triclosan controversy, the Triclosan ingredient is the reason I use colgate total products only (and I know about the cancer risk or whatever, and just take it as a given.) But I wonder why it is not combined in a re-enamel version? Do these things not work? Colgate does have re-enamel but not under its Total brand - despite the Total brand including lots of other sub-things, like a version for fresh breath, a version with whitening, and. All of these are popular: http://www.colgatetotal.com/toothpaste

but no re-enamel version. why not? Does that stuff not actually work / rebuild mineral into your teeth?

Thanks for any information.

212.96.61.236 (talk) 08:57, 10 January 2015 (UTC)

The active ingredient in such toothpastes is Amorphous calcium phosphate. Our article contains several references which indicate it does have some beneficial effect, although probably not as dramatic as the advertisments suggest. The first part of the question can only be answered by Colgate-Palmolive's marketing department, and I'm sure they keep their decision-making process highly confidential. See Brand management for our general article on the subject. Tevildo (talk) 09:43, 10 January 2015 (UTC)

But note that calcium and phosphate are already abundant in saliva and if you want more calcium phosphate, a good glass of milk will do the trick for non-vegans (it wasn't just old school dairy propaganda, milk really is pretty good for teeth, especially during development). Our (frankly kinda promotional-reading) amorphous calcium phosphate article seems to suggest it is the most ideal form of calcium phosphate and though I did not look into the ncbi articles it references in detail, I'm willing to buy that it might have some marginal advantages. But I will say that generally speaking the advantages of toothpaste are more in prevention than in repair. Tooth enamel will repair itself to an extent in healthy contexts, and fluoride is the real hero of toothpaste in this regard, so in this sense most all modern toothpastes are "re-enamel" toothpastes. I tend to be skeptical of any benefits from "amorphous" calcium phosphate being beyond (or even comparable to) to fluoride's. There's actually a journal specifically devoted to topics in this area, Cares Research and its website hosts abstracts for every article, and I couldn't find a single mention of calcium phosphate within it, though research found therein and elsewhere has deconstructed the efficacy of toothpaste from nearly every possible angle. Still, with enough persistence, one could probably find some relevant research therein. Snow talk 11:53, 10 January 2015 (UTC)

Guys, thank you. I found this incredibly helpful. As a non-expert, my impression had been that alternative toothpastes (Enamelon) figured out a way to remineralize teeth. It seemed to me that following this, it was incorporated into other products (this is Colgate's explicit offering, outside it's total brand: http://www.colgateprofessional.com/products/colgate-enamel-health/overview .) But what I didn't get is why it wouldn't ALSO include all the normal total stuff? Is it because they interfere with the remineralization process? Then why not brush with total first, for all its benefits, then rinse and use an enamelon-type product?

Now that I've seen your references though, my impression is different. My impression is that Enamelon or other enamel-building categories didn't discover anything new. It's not a truly new category. It isn't something Colgate actually adopts or can use. Because it doesn't really work, it's just an invented fad. So, with this conclusion it makes perfect sense for Colgate to just add "enamel" to its list of benefits on normal Total products, without explicitly making an enamel-building version. (Which doesn't work or exist measurably better than its normal total properties.) At least, this is my impression today. Here is a cateogry of all toothpastes that are branded into this new fad: https://www.google.hu/search?q=enamel+building+toothpaste&tbm=isch in 2010 the wsj seemed skeptical: http://www.wsj.com/articles/SB10001424052748704141104575588374178767514 and they basically repeated what you've said above. In essence then, I think I fell for the idea that the popping up of that whole category (which is an area of the toothpastes section in every drug store) actually reflects something. It simply doesn't (in my current impression). Like if there were Night Time skin creams section with SPF 20+ factors. Sure.  :)

Thanks for all of your work and references, Tevildo and Snow Rise. It was greatly appreciated. 212.96.61.236 (talk) 15:42, 10 January 2015 (UTC)

Not at all, it's what we're here for. Toothpaste advertising is not a good example of objective scientific research - I saw a poster a few weeks ago that promised "Up to 100% less plaque!", which I think counts as "not even trying". Tevildo (talk) 17:03, 10 January 2015 (UTC)

As Telvido says, not a problem. I wouldn't go as far as to say that there haven't been developments in efficacy for toothpaste in recent times, by the way, but I think your skepticism about the branding is well-advised; for many consumer products relating to the body, diversification in the product field is as much or more the result of increased marketing efforts as genuine innovations in the products themselves -- a fact of which you are clearly aware. There's even a marketing term for the process by which competitors (or even a single company which own multiple brands) tend towards greater and greater differentiation in their branding and product claims, even if the product itself is identical, though I forget the term just now. I'm not willing to speculate that this is definitely the case with your re-enameling tooothpaste, but let's just say I'm not going to discourage you from the the belief either. Certainly the product line offerings raise the question that you point out: why not make a composite containing all of the elements that confer health benefits and other valuable properties (whitening and so forth); that's often the inconsistency a lot of companies have to just have to hope they won't be called on with regard to their massively diversified branding -- luckily the consumer is usually willing to meet them more than half way in suspending disbelief with regard to the "unique" properties of a particular variant of a product. Snow talk 20:49, 10 January 2015 (UTC)

See also Recaldent. Johnuniq (talk) 09:03, 12 January 2015 (UTC)

Structural system

http://www.retrotogo.com/2010/12/for-sale-grade-ii-listed-1950s-modernist-apartment-in-langham-house-close-ham-surrey.html What is the structural system of these types of flats often seen around the suburbs of major cities in the UK. I've seen much larger versions of these with multiple floors, up to 5 or 6. 90.194.54.111 (talk) 17:17, 10 January 2015 (UTC)

Hard to tell for sure, but it looks to be steel reinforced concrete with decorating/insulating bricks (a concrete exterior doesn't look very "homey" or keep you very comfortable inside). StuRat (talk) 18:12, 10 January 2015 (UTC)

Normal steel reinforcement or prestressed? 90.194.54.111 (talk) 18:25, 10 January 2015 (UTC)

Can't tell that from the pics. StuRat (talk) 21:37, 10 January 2015 (UTC)

What distribution are the most common?

Somehow this distribution is pretty common in nature and society, and I suppose it's the most common (correct me if I am wrong). Besides this, what are some distributions that arise everywhere and why? (I suppose the normal dist. is the result of several binary options.) --Noopolo (talk) 20:49, 10 January 2015 (UTC)

The Gaussian distribution, aka "normal distribution", is the most common. That's a consequence of the central limit theorem, which says that if you start with essentially any probability distribution with finite variance, and take the average of N independent samples, the larger N gets, the closer the probability distribution of the sample average to a Gaussian distribution. Probably the next most commonly encountered distributions are the Poisson distribution,the binary distribution, and the continuous uniform distribution. Looie496 (talk) 21:03, 10 January 2015 (UTC)

I see multimodal distributions frequently in my day job. Often, these are simple linear superpositions of n gaussian distributions with different parameters. Sometimes they are more pathological. Nimur (talk) 21:27, 10 January 2015 (UTC)

I think the most common continuous distribution is indeed the Normal distribution, also known as the Gaussian distribution. However, the most common distribution encountered by most people in their daily lives is probably the Bernoulli distribution, because so many things either happen or don't with some probability. This is so common that most people don't even notice it, but every time they say something like "the car might crash" or "this cake might be delicious" or "the bus will probably be here in a moment" there's a Bernoulli distribution involved. Other discrete distributions evolve naturally out of the Bernoulli distribution, and these in turn lead naturally to consideration of their continuous equivalents. RomanSpa (talk) 21:59, 10 January 2015 (UTC)

Edibility/healthfulness of shellfish parts

What exactly are these shellfish parts? Are they safe/healthful to eat?

• The soft, pasty part at the back of a cooked shrimp's head
• The dark-colored, non-muscular part of a cooked mussel
• The blister-like part of a limpet above its "foot"

--96.227.60.16 (talk) 22:42, 10 January 2015 (UTC)

In the case of shrimp, that's their hepatopancreas. Quite edible; perhaps an acquired taste in some cultures, but I think it's yummy. --jpgordon^{::==( o )} 23:00, 10 January 2015 (UTC)

In shellfish, the stuff is called tomalley when eaten as a food stuff. The tomalley of lobster is a common enough delicacy. Shrimp have a lot less of it, but it is of course just as edible. I'm not sure which part of the mussel you're asking after; perhaps the Byssus, also called the "beard", which is not edible. Not sure on the limpet. Never eaten those. --Jayron32 01:56, 11 January 2015 (UTC)

I've not eaten limpets either. I've seen 2 YouTube videos in which limpets were collected, cooked, and eaten. In both cases, the presenters cut of the top part of the limpet bodies, consuming only the disc-like "feet". --96.227.60.16 (talk) 03:49, 11 January 2015 (UTC)

January 11

Can a goat really eat and digest a tin can?

Question as topic. I've found comments from goat owners online who say that they've never seen it happen for real. I know that goats, with their famously resilient stomachs, can and do eat things like newspaper, cardboard boxes, clothing and shoes without an apparent problem. I've even seen videos of them eating lit cigarettes without seeming to give the slightest damn. Anyone have a definitive answer? --Kurt Shaped Box (talk) 01:43, 11 January 2015 (UTC)

I doubt they could digest it. The greater question is whether they could pass it. Even humans can (and do) eat lots of undigestible stuff. If it is small enough, it will just show up in the stool later. --Jayron32 01:57, 11 January 2015 (UTC)

I suspect they were just eating the labels off the tin cans, which might involve putting cans in their mouths as they work the labels loose with their tongues. StuRat (talk) 02:00, 11 January 2015 (UTC)

That's what they used to teach us, decades ago - that they are, if anything, eating the label and the tasty glue. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:16, 11 January 2015 (UTC)

(EC) No,goats do not eat tin cans. It seems implausible that a typical tin can (actually tin coated steel) such as one I am looking at`which is about 3 inches in diameter by 4 3/8 inches high would pass through the esophagus of a goat, without killing the goat. It also seems implausible that it would pass through that esophagus if it were flattened. It also seems implausible that a goat's teeth could tear it into fragment small enough to swallow. A goat will certainly chew on a tin can, either to get the food residue on the inside or to eat the paper label on the outside, or to eat the glue..I recall an old published psych experiment, probably from the 1960s wherein goats were the subjects being conditioned, and the reward was the opportunity to chew on a length of chain, so they definitely are not averse to chewing on iron. Edison (talk) 02:10, 11 January 2015 (UTC)

Interesting question. A quick web search turns up some sources like Modern Farmer magazine that weigh against it ( [13] ). There's not really any general theory of biology that can honestly tell you a goat can't eat a tin can with any confidence; on all things goaty I'd trust a farmer's experience over a biologist's prediction any day.

The mention of goats chewing on a chain makes me wonder if there could be some "germ of truth" based on a sort of pica for them to obtain trace metals. I don't know if modern pet goats get too many vitamins/minerals or too good a diet to show some of that behavior. One thing that's clear, though, is that calling on YouTube for goat tin can gets lots of items that reflect the presence of the meme... yet no video of goats actually eating cans, or even chewing on them a bit. There's a curious example of one eating a page out of a book [14] which might reflect on the label eating behavior suggested above, but the video stops before we see whether it swallows or not. Wnt (talk) 00:40, 12 January 2015 (UTC)

Goats use their mouths to examine things in the same way that we use our hands, so people often think they are eating something when they are just investigating it. For example, they will pull clothes off a washing line to see what they are and check if they are worth eating, but then drop them and move on. What is surprising is that they will eat thorny bushes, brambles etc. without any problem, so they must have very tough mouths and guts. Richerman (talk) 07:31, 12 January 2015 (UTC)

Yep. Just makes more sense for them. Hooves and horns are useful, but are about the clunkiest and least sensitive things any mammal has. With those crazy lips, they can eat the leaves from around the thorns so nimbly, you'd swear they were crazy. Just magicians, though. InedibleHulk (talk) 08:27, January 12, 2015 (UTC)

They have very nimble lips and can eat round thorns but I've also known then to eat brambles with no problem. According to this it's all down to their hard palate - and presumably a very leathery tongue. I suppose they chew them up well before swallowing. Richerman (talk) 10:02, 12 January 2015 (UTC)

Helps to have a rumen, too. InedibleHulk (talk) 00:35, January 13, 2015 (UTC)

Climate change vs. Global Warming

Is it true that the term, "global warming" was changed to, "climate change" as a euphemism to respond to arguments presented by conservative pundits who denied global warming existed simply because sometimes it got really cold outside? ScienceApe (talk) 02:09, 11 January 2015 (UTC)

Yes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:14, 11 January 2015 (UTC)

Well, "global warming" isn't such a good term anyway, because the globe is only warming on average, with parts warming a lot, and other parts not at all, or even cooling a bit. Also, climate change includes things like changes in humidity, rain, and drought patterns, along with more numerous and more intense storms (hurricanes, tornadoes, cyclones, etc.). StuRat (talk) 02:41, 11 January 2015 (UTC)

The pundits and politicians who denied (and who continue deny) global warming based on the fact that "it sometimes still gets cold outside" aren't going to be satisfied anyway; a change in terminology isn't going to satisfy someone who makes a living from conflating "anecdote" and "data". One could argue that the terminology change is more useful (and perhaps more effective) in communicating the important or significant effects to the general public, however. "Climate change" – more extreme weather events like hurricanes, droughts, floods, etc. – is something that has a more conspicuous, tangible, visceral, and even economic impact than "global warming"—so what if it's a couple of degrees warmer? TenOfAllTrades(talk) 03:18, 11 January 2015 (UTC)

They don't mean the same thing. Global warming is an increase in the global average temperature, and climate change is a change of weather patterns. The former is one possible cause of the latter.

Google Ngram Viewer doesn't appear to support the claim that "climate change" has replaced "global warming" in more recent years. If that graph is to be believed, there was never a time when "global warming" was used much more than "climate change". Interestingly, the American English and British English trends are quite different from one another. -- BenRG (talk) 03:25, 11 January 2015 (UTC)

(edit conflict) Through the mid-2000s, "climate change" was essentially the European term for "global warming" as used in the U.S. Usage goes back and forth so that now "climate change" is seen a little more commonly in the U.S. than it was before. This happened in no really systematic way and there was never a conscious decision to replace "global warming" with "climate change." After all, the IPCC -- the Intergovernmental Panel on Climate Change -- was constituted way back in 1988. Short Brigade Harvester Boris (talk) 03:31, 11 January 2015 (UTC)

No. In the 1970's the term was "inadvertant climate modification" because they didn't know if it was warming or cooling. "Global warming" was coined in the 1970's in a paper that advocated that the climate change would be one of warming. In 1979 the Charney report was released and Charney adopted Broecker's usage. When referring to surface temperature change, Charney used "global warming." When discussing the many other changes that would be induced by increasing carbon dioxide, Charney used "climate change." Scientists maintain the distinction while clueless journalists (and Wikipedia articles) do not.[15]. --DHeyward (talk) 05:00, 11 January 2015 (UTC)

Until the late 1980s, the common term was actually "climatic change" comparitive Ngrams, used for both changes in the geological past and those taking place recently. Mikenorton (talk) 08:34, 11 January 2015 (UTC)

See Frank Luntz about him advising republicans to say climate change instead of global warming as a survey found it less worrying. So basically the opposite to the implication in the question. Both terms seem okay to me, people kow what they mean. Dmcq (talk) 10:43, 11 January 2015 (UTC)

"Climate change" is preferred by many climate scientists and atmospheric scientists, in part because many local regions could get cooler, or have more rain, or have less rain, or get warmer, etc. The local effects of CC are hard to predict, but several impacts will be more notable to people than simply "warmth." See also global weirding, and Effects_of_global_warming#Projected_impacts. Many of the most negative impacts of CC are not directly due to warmth, but warming is still indirectly responsible, e.g. speculation of the shutdown of some ocean conveyors would make the UK very cold, even though warming could be the cause. Same goes for more frequent storms and more frequent droughts, etc. SemanticMantis (talk) 16:12, 12 January 2015 (UTC)

What is the reason that the saturation (oxygen) rises after smoking?

Today someone showed me by the oxymeter that BEFORE he smoked he had 94% saturation, but AFTER he smoked it raised to 98%. What is the explanation for that? 213.57.31.194 (talk) 02:56, 11 January 2015 (UTC)

I don't know if it applies to smoking, but in general, carbon monoxide attached to hemoglobin can deceive oxygen saturation sensors. Jc3s5h (talk) 03:00, 11 January 2015 (UTC)

Indeed; see this paper: "... Pulse oximetry is unreliable in estimating O2Hb saturation in CO-exposed patients and should be interpreted with caution when used to estimate oxygen saturation in smokers." TenOfAllTrades(talk) 03:08, 11 January 2015 (UTC)

There are other factors as well including vascular and circulation changes from nicotine or changes in temperature (i.e. smoking outside). The pulse oxymeter is really not very useful except to correlate other clinical signs (i.e. congestion, labored breathing and low readings in a controlled setting like a hospital). 94% is relatively low number for awake and healthy patients but really a blood gas analysis and lung function test would be needed to show that it is abnormal. I've seen emergency pediatric doctors require the sleeping SpO2 to be above 90% before discharging asthmatic children but also at the same time, tell parents to throw their own pulse oxymeter away because the real signs are in behavior and type of breathing. They say the oxymeter should not be used to decide whether intervention is necessary and the number doesn't add any value. YMMV. --DHeyward (talk) 06:36, 11 January 2015 (UTC)

Attached with nails

Why do nails work? Is it solely friction? Push a pin into a pincushion, and you can pull it right out, but hammer a nail into a block of wood, and there's no way to pull it out without using the hammer or some other tool. Does the hammering process disrupt bits of wood that block the nail from being pulled? I understand why screws work (they bore thread-shaped holes in the wood, and the space between the threads provides significant resistance), but just as a stripped screw can easily be pulled, a nail "should" be easy to pull, but it's not. Nyttend (talk) 05:55, 11 January 2015 (UTC)

The nail compresses the wood around it, the compressed wood presses back against the nail, and there's your source of friction. --65.94.50.4 (talk) 06:06, 11 January 2015 (UTC)

Framing nails also have a coating of glue that melts from friction of driving it and then binds it to the wood. I believe it also protects the nail from rust so they don't have to be galvinized. --DHeyward (talk) 06:39, 11 January 2015 (UTC)

For wood, Young's modulus and the bulk modulus are sufficiently high that when the wood is compressed by action of the intruding nail it applies a large compressive stress to the nail. The friction force that must be overcome if the nail is to be extracted is numerically equal to the coefficient of friction applicable to a wood/steel interface, multiplied by the normal force at work between the nail and the wood. The normal force is very large, thanks to the large compressive stress that exists between the wood and the nail. The coefficient of friction between wood and steel is also high. Consequently, to extract the nail a large force must be applied to overcome the force of friction that resists movement of the nail.
For a pin cushion, Young's modulus and the bulk modulus are many orders of magnitude smaller than they are for wood. Consequently, compressive sress in the pin cushion's filling is almost zero and normal force is almost zero. I suspect the coefficient of friction between the cotton filling and steel is also less than for wood and steel.
If the nail is driven into a pre-drilled hole, the wood surrounding the hole does not need to be compressed as much as when the nail is driven without the aid of a hole. Consequently the wood is not compressed as much, the normal force is less, and the friction force is less, allowing the nail to be extracted with less force. Dolphin (t) 10:23, 11 January 2015 (UTC)

Another point here is that in most structures where nails are used, the forces applied to the structure are generally at right angles to the long axis of the nail. Imagine, for example, hammering a nail into a wall and hanging a picture on it. So the forces applied to the nail aren't pulling it out of the hole so much as deforming the nail - or forcing it to break through the wood along it's entire length. When overloaded, what generally happens is that the nail bends - and then pulls out relatively easily because some of the force is now directed along the length of the nail rather than at right angles to it. When nails are required to resist a pull at 90 degrees to the surface of the wood, they are generally hammered in at an angle for precisely that reason. SteveBaker (talk) 16:23, 11 January 2015 (UTC)

Decent large nails usually have little ridges near the top to help with the friction aspect - see this image. Alansplodge (talk) 22:44, 11 January 2015 (UTC)

Agree with the above, that it's more about the material than the fastener here. Try pushing a nail into a pincushion, and you will be able to easily pull it out (but it will likely leave a large hole behind). If you could manage to drive a pin into wood, it would also be quite difficult to extract. The thinness of the pin would make it nearly impossible to drive it into wood without it bending, though. Perhaps a high speed, like from a tornado, would make this possible. StuRat (talk) 04:18, 12 January 2015 (UTC)

With any slender body, including a pin, that is to be driven into a solid material such as wood, the failure mechanism is going to be failure as a column - see Column#Equilibrium, instability, and loads. See also Buckling#Columns. If an attempt is made to drive a pin into timber with a single blow, or a small number of blows, the pin will inevitably fail as a column before it is fully inserted. Even at high speed from a gun or a tornado the pin would buckle as a column before it was inserted very far. That is why nails are usually hammered into place with a number of blows rather than one giant blow, and the nail is supported laterally until it is firmly established in the timber. Dolphin (t) 05:06, 12 January 2015 (UTC)

I seem to recall a piece of straw stuck into a tree by a tornado. At those speeds materials behave differently, as there isn't time for the buckling to occur. Similarly, if you watch a bullet shot through a rubber sheet using high speed photography, the rubber doesn't stretch, but fractures as if it was glass. StuRat (talk) 05:20, 12 January 2015 (UTC)

MythBusters busted the straw-in-a-tree example: [16]. DMacks (talk) 05:24, 12 January 2015 (UTC)

But others have proposed explanations for seeing the same result, and possibly also have actual experimental evidence contradicting MB's tests: [17]. DMacks (talk) 05:32, 12 January 2015 (UTC)

Yea, I've never been impressed by MythBusters. They often conclude, incorrectly, that since they couldn't do X, then X can't be done. StuRat (talk) 05:36, 12 January 2015 (UTC)

Body weight and g-force tolerance

Is it possible to get any meaningful calculation of how many G's would you theoretically tolerate based on your weight? Specifically, considering persons whose body mass index is lower than normal, for instance 58 kg for a 179-cm tall man (for 10 G, for example, this yields 580 kg, which is similar to Manuel Uribe). Brandmeister^talk 09:23, 11 January 2015 (UTC)

Our article, High-G training, links to several sources, including a NASA tech note that suggests astronaut-grade test-pilots can withstand 9g for 60 seconds while performing complicated tasks. In my experience flying the Citabria, most mortals start getting queasy or puking around a peak acceleration of +2g for just a fraction of a second - say, during the recovery from a spin - so although they will live through higher accelerations, they probably won't "tolerate" it. Here's a few videos from inside the cockpit and an external view of a Super Dec doing the same. Here's a tutorial video in a 7GCBC with a visible accelerometer on the panel. Quantitatively, the g-load a NASA test pilot would endure is some 5x greater than the peak accelerations experienced during these maneuvers. Nimur (talk) 09:49, 11 January 2015 (UTC)

A g-suit helps. I don't see why BMI should be relevant.--Shantavira|^{feed me} 10:06, 11 January 2015 (UTC)

And if without the suit? Lower value, of course, but still... Brandmeister^talk 10:19, 11 January 2015 (UTC)

Usually, queasiness/nausea (and stall/spin) is negative G-force with the feeling of falling. But I think the question is variations regarding body type and/or medical factors. I don't have the paper anymore but at one time, the air force studied whether their flight standards were based on anything more than a recruiting poster (i.e. 6' foot, 180 lbs, lean and physically fit). I think what they found was that shorter, slightly overweight, high blood pressure and near-sighted performed better at high-G. 5'6", 180 lbs, high blood pressure with glasses outperformed their "ideal" in stress tests. Some of the best videos are when pilots lose consciousness in the simulator. If you didn't know any better, it looks like the sim is producing a stress that the pilot is fighting. Then they go limp and it's clear all the stress is induced by the pilot to stay conscious through G-LOC.[18] This one has more funky chicken spasms. They go limp at the same G they were straining against. --DHeyward (talk) 10:32, 11 January 2015 (UTC)

JAR Professional Pilot Studies by Phil Croucher (p.1-28) says; "Your ability to withstand G forces is reduced by: • obesity • low blood sugar and • hypoxia". It doesn't say why though. Alansplodge (talk) 17:28, 12 January 2015 (UTC)

The PHAK has a whole chapter on this: Chapter 16 - Aeromedical Factors. The AIM also has Chapter 8, Medical Facts for Pilots. Nimur (talk) 19:32, 12 January 2015 (UTC)

Reserves and ressources

I know the difference between Reserves and Resources. Reserves are economically recoverable and resources not. But the resources are geologically probable. But what are recoverable ressources (like in File:Uranium known recoverable resources.svg)? I can't figure out, where these are in the McKelvey diagram. May you help me?--Kopiersperre (talk) 16:46, 11 January 2015 (UTC)

This sort of question earns big bucks for highly trained geologists and tax attorneys! I think the best we can do is point you to our article, which you've already found, and to the references section it contains. In particular, the United States frequently reclassifies the taxable status of speculative reserves of minerals and energy... so the answer will constantly be changing. Nimur (talk) 17:16, 11 January 2015 (UTC)

January 12

Poly oxalate

I have heard that Poly oxalate is applied after placing the foam spray in a structure, I want to know what properties does this chemical has? and how is this applied.120.28.45.234 (talk) 05:38, 12 January 2015 (UTC)Garry from Philippines.

Are you asking about Polyethoxylated_tallow_amine - it is commonly added as a surfactant to herbicides such as RoundUp - our article has some information about the properties of the chemical. SemanticMantis (talk) 20:03, 12 January 2015 (UTC)

different units used in blood pressure measurement

My doctor measured my blood pressure and told me the result was 18. As he is French and I am English, that meant nothing.Could someone please tell me what that is in pounds,shillings and pence and whether he had reason to be anxious. I am 66, Thank you. — Preceding unsigned comment added by 109.12.62.210 (talk) 12:17, 12 January 2015 (UTC)

My first reaction was to comment that you are unlikely to read this reply, but perhaps it depends on where the pressure was measured and in what units. The usual units are millimetres of mercury, but perhaps French doctors use different units (centibars? but 18 would be a bit high). Alternatively, perhaps the measurement was for systolic pressure measured in the pulmonary artery or right ventricle, then 18 might be normal, but this measurement is an invasive procedure done in a hospital. Dbfirs 12:31, 12 January 2015 (UTC)

You might call them centibars, yes, but the usual term is kilopascal (kPa). There's an online converter here. - Lindert (talk) 12:36, 12 January 2015 (UTC)

The following discussion has been closed. Please do not modify it.
Oh yes, I should have checked that. You should have been told two figures. I assume that the 18 is systolic, and equivalent to 135 mm Hg which would be classed as Prehypertension in the USA or just on the high side of normal in the UK (but not serious). We can't give medical advice, of course, so you should go back to your doctor if you are worried. Dbfirs 12:50, 12 January 2015 (UTC) I'm hiding ("hatting") this paragraph because it makes an unwarranted assumption with dangerous medical implications if the assumption is wrong. RomanSpa (talk) 13:12, 12 January 2015 (UTC)

In France blood pressure is measured in kiloPascals, while in the UK blood pressure is measured in "millimetres of mercury", which is almost exactly the same as another unit called the torr. There are technical differences in the way these different units are defined, and you can read about them here, here and here, but the main thing you need to know is simply the conversion factor, which is 7.5. That is, when your doctor said the result was "18" he meant "18 kPa", so to convert this into the measure you are used to you just multiply by 7.5. So 18kPa = (18 times 7.5)mmHg = 135mmHg. So his "18" is your "135".

As you know, Wikipedia is not able to give medical advice, but you will see from our article on blood pressure that doctors usually provide two measures of blood pressure, "systolic" and "diastolic". You can compare your reading with a standard table here, and should clarify with him whether your result was for systolic or diastolic blood pressure. In any case of illness or uncertainty, you should always contact your doctor. RomanSpa (talk) 12:56, 12 January 2015 (UTC)

One worrisome thing in this question is that you didn't ask the doctor. If you aren't even comfortable asking him what units your BP reading is in, and whether that's the diastolic or systolic reading, then I doubt if you are asking him any questions at all. Many studies have shown that such a lack of communication with your doctor is quite bad for your medical outcome. In the US, we even have a series of PSAs encouraging patients to ask their doctors questions. StuRat (talk) 16:01, 12 January 2015 (UTC)

Why do electric guitars have tunable bridges but acoustic guitar fixed ones

I'm not sure if this is the right forum for this, but I wonder why electric guitars have tunable bridges but acoustic guitars have fixed bridges and saddles. The tunable bridge allows the length of individual strings to be changed. I know that some acoustic guitars have compensated saddles, which come with different lengths set from the factory, but this is just a set and forget.

Also am I right in thinking that even for an electric guitar this won't ever change as long as the strings are uniform in thickness and weight along the length? -- ????

The general consensus here is that tunable bridges have too much mass for an acoustic and kill the tone. Also, tunable bridges have moving parts and, because an acoustic works by resonance through the body of the guitar, the moving parts will tend to vibrate against each other and rattle. This doesn't matter with an electric guitar as they have pickups that convert the vibrations of the strings directly above them into an electrical signal, but not vibrations from elsewhere in the guitar body. Richerman (talk) 14:25, 12 January 2015 (UTC)

That makes sense. The weight at the saddle is dead weight at the point where the string needs to vibrate the resonator. The moving parts bit also makes sense. In electric guitars the bridge can be fixed solid to avoid vibration, as the string is the only thing that needs to vibrate -- Q Chris (talk) 16:26, 12 January 2015 (UTC)

TTL IC L293D

I was playing with the TTL IC L293D when something interesting happends.

• http://www.datasheetcatalog.com/datasheets_pdf/L/2/9/3/L293D.shtml
• http://img252.imagevenue.com/img.php?image=107212339_L293Dhack_bb_122_552lo.jpg

Here's my layout:

1. Enable 1, 2: **Not connected** presumably LOW
2. Input 1: **Connected to +3V** HIGH
3. Output 1: Connected to a motor
4. GND: Grounded
5. GND
6. Output 2: Connected to a motor
7. Input 2: **Not connected** presumably LOW
8. VCC2: Connected to +3V
9. Enable 3, 4
10. Input 3
11. Output 3
12. GND
13. GND
14. Output 4
15. Input 4
16. VCC1: Connected to +3V

I left pin 1 unconnected.

The motor keeps running while the pin Enable 1, 2 is not connected.

It's alive! It's alive!

I thought the motor must be stopped. What was wrong with this? -- Toytoy (talk) 14:22, 12 January 2015 (UTC)

Why do presume "not connected" means "low"? Unless otherwise specified, I would usually assume that a pin not tied one way or another will float to wherever it wants. That why God invented pull-down resistors. --jpgordon^{::==( o )} 17:03, 12 January 2015 (UTC)

Indeed. Looking at the TI datasheet (page 7), the enable inputs have an internal pull-up resistor, so they need to be connected to ground to disable the output. With no connection, they'll be high and the output will be active. Tevildo (talk) 21:19, 12 January 2015 (UTC)

genetics

thx. I know it is basic, but I seem to have missed this lecture.72.183.121.78 (talk) 22:46, 12 January 2015 (UTC) my question is about the transcription of chromosomes in humans. for example, are all genes on both the maternal chromosome 1 and the paternal chromosome 1 transcribed? Or is either the maternal or paternal chromosome 1 shut down and only the other completely transcribed? or is there partial transcription of both? how does this happen? thx much.72.183.121.78 (talk) 16:32, 12 January 2015 (UTC)

The nature of recessive genes tells us that both parent's chromosomes can be used. Once the two haploids come together to make a diploid of genetic material, there is just "the two chromosomes" with zero differentiation between which one came from which parent (with the exception of a male offspring's Y obviously coming from the father). DMacks (talk) 17:25, 12 January 2015 (UTC)

thanks. so at that point are all of the genes of both chromosomes transcribed? if not, then why are some genes transcribed and some not?72.183.121.78 (talk) 17:44, 12 January 2015 (UTC)

You get half your genes from each parent (not counting mitochondrial genes, which come exclusively from the mother). So, there is a 50% chance you will inherit a gene from that parent, and a 50% chance you won't get that gene from that parent (although you might still get the same gene from the other parent). However, not all genes you inherit are activated. Many remain dormant. In some cases, you must inherit 2 copies of a gene (one from each parent) for it to be activated (or fully activate, at least). For example, the gene that causes sickle cell anemia is only a serious problem when 2 copies are present. Also, mutations can occur, in which case the gene you inherit isn't quite the same as the original in the parent. StuRat (talk) 17:51, 12 January 2015 (UTC)

Transvection (genetics) is one of several interesting aspects of the nature of the non-independent nature of the two different chromosomes' copies of some genes. The ABO blood group system is a case where both alleles are transcribed. I don't know much about the general idea of gene silencing in specific relationship to the presence of two copies. DMacks (talk) 18:01, 12 January 2015 (UTC)

• You seem to be talking about X-inactivation. μηδείς (talk) 18:03, 12 January 2015 (UTC)

thanks. that helps. I am interested in the autosomes.72.183.121.78 (talk) 18:14, 12 January 2015 (UTC)

I was confused, I read that as one single chromosome, rather than the first of 23 chromosomes, sorry. μηδείς (talk) 19:12, 12 January 2015 (UTC)

• Remember, the gene is just the location of the information, the allele is the version or type of information that is carried. For a certain gene X, every human has that gene, insofar as we all have some information in that location of our DNA. However, many of us will have different alleles at that location. It is very common to confuse the two concepts, but we should be clear about the distinction on the reference desk. SemanticMantis (talk) 19:57, 12 January 2015 (UTC)

• Our article says "locus" is the name of the location. As I understand it, the "gene" would then be something like "eye color", and the "allele" something like "blue eyes". StuRat (talk) 20:07, 12 January 2015 (UTC)

The difference is that a locus can be any region, e.g. a gene, a sequence, a portion of a chromosome, etc. Many people prefer to not use the word 'gene' at all, and instead use locus and allele for the separate concepts. This helps to avoid the nonsense of using 'gene' to mean both the region and the information stored at that region (which is what our askers and respondents usually do here on the ref desk). Still, the definition we use for 'gene' in our article makes it clear that it is ultimately a location or region:

“ "a locatable region of genomic sequence, corresponding to a unit of inheritance ”

(emphasis mine) The gene is not the "what" of inheritance, it is the "where." I just think we should make it a habit to use the right words for concepts on the ref desk, instead of perpetuating a common-but-incorrect usage. But your example is basically right (though there are many genes that control eye color) - everyone has genes for eye color, you get one allele from each parent. This also illustrates why it is technically incorrect to say "I got this gene from my father" - you would still have genes for eye color no matter who your father was, but a different father can lead to different alleles. I may seem picky here, but this is basic stuff, and is usually stressed in any intro bio course that covers DNA and inheritance. SemanticMantis (talk) 20:49, 12 January 2015 (UTC)

To quibble slightly, you can be missing genes. For example, a woman is simply missing SRY, has no place to put it, like anything on the Y chromosome. It's also possible that someone is missing both copies of some nonessential gene through deletion mutations, though far less likely. Where this gets tricky is that a fair number of characteristics, even common ones, are caused by null mutations in which the gene is functionally disrupted; it's as if it isn't even there, for many practical uses. But since often there is no actual deletion, just a frameshift mutation or a particularly bad point mutation, disrupted enhancer element, etc., the gene still recombines, so it's not really right to say that someone is "missing the gene"; just that what they have isn't active or effective. Wnt (talk) 02:56, 13 January 2015 (UTC)

Effective Lifetime of Hydrogen Peroxide Solution

If I have a sink filled with 10 gallons of a 4% hydrogen peroxide solution how long will it last? How would I calculate it? The temperature should be "cold" tap water. This would be indoors, but there would probably be some light. I basically want to figure how long it can be used to effectively kill yeast on produce before needing to mix a new batch. Thank you. Any other additional information that you think I should be aware of would be greatly appreciated. David Bradley I (talk) 20:09, 12 January 2015 (UTC)

I believe nucleation sites are critical to the formation of oxygen bubbles from hydrogen peroxide, meaning it there are many nucleation sites it won't last nearly as long. Note that washing food with it will "use it up", as well.

One rather simple way to test it would be to put a sample in a bottle and shake it. If it foams up (many tiny bubbles), it's still good. If it reacts like normal water (few, large bubbles), replace it. After doing this test several times you can get an idea for how long it tends to last, under your conditions. StuRat (talk) 20:15, 12 January 2015 (UTC)

Thanks for the tip. Is there a way of estimating how long it should last? I only need it to work for a couple hours. Also, I'll ask another question in another section which is related. David Bradley I (talk) 20:19, 12 January 2015 (UTC)

I don't think you could get a good estimate without testing it under your conditions. For example, if you wash produce with lots of surface area, it won't last as long. Under some conditions, I don't think it would last 2 hours.

BTW, in case you don't already know, you should wear gloves and safety glasses when using it. It will hurt a bit on any cuts or hangnails on your hands, and really hurt if it splashes in your eyes. StuRat (talk) 20:21, 12 January 2015 (UTC)

Even if it is active, it might not have the desired concentration. It is a conundrum for me. David Bradley I (talk) 20:25, 12 January 2015 (UTC)

Maybe I'll buy a cheap bottle of medical hydrogen peroxide and do some tests at home to see how long it lasts. Maybe that would be a good way of estimating how much we'll need. David Bradley I (talk) 20:46, 12 January 2015 (UTC)

Have you considered not putting it in a tub, but just pouring it over the produce ? If you keep it in a dark, sealed container, between uses, it will last longer. However, soaking in a tub will get more of it into contact with the produce (the hidden folds, etc.). What kind of produce is it, anyway ? StuRat (talk) 20:34, 12 January 2015 (UTC)

I think for our setup we couldn't just pour it over. I'm not sure how long the produce should soak in a 4% solution, but I was thinking 10 minutes. Is that too long? It might be possible to cover the sink to keep it fairly dark, but it wouldn't be sealed. David Bradley I (talk) 20:36, 12 January 2015 (UTC)

I think 10 mins is good. You might consider portable containers, where you can seal each batch of produce in and let it soak in hydrogen peroxide, then discard it when done. Ideally you should be able to cram the container full of produce, and invert it or shake it so it all gets wet. StuRat (talk) 20:38, 12 January 2015 (UTC)

We're basically talking about a couple hundred of pounds of produce over a period of two hours. The intent is to reuse the solution as much as possible. If we had to discard the solution after each soak then it wouldn't be an economical way of getting rid of the yeast. David Bradley I (talk) 20:55, 12 January 2015 (UTC)

I was thinking you could pack it in tightly, to limit the amount of solution used. You probably can't pack it in as tightly in an unsealed container, since some produce will float. You need the lid to push it down into the solution. StuRat (talk) 21:03, 12 January 2015 (UTC)

Another idea: Use some type of rotating wheel to move the produce in and out of the hydrogen peroxide. The same items would be dipped multiple times. This would have the advantage that the last batch would not encounter a much weaker solution. This rotating shoe rack might work (it would have to be rotated manually): Wikipedia:Reference_desk/Archives/Miscellaneous/2014_December_20#What_is_this_cylindrical_device.3F. StuRat (talk) 21:07, 12 January 2015 (UTC)

Also, if you can "recharge" the solution with a higher concentration of hydrogen peroxide, rather than discarding it, that might be less expensive. There's the cost of the water, but more importantly the remaining potency of the stale batch can be reused then, and you only need to add enough H₂O₂ to bring it back up to 4%. StuRat (talk) 21:21, 12 January 2015 (UTC)

Erm, given your phrasing and the scale you're talking about here and the question below, it comes across to me as that you're running some kind of commercial operation. If this is the case, I very much doubt you should be seeking advice about your production process from random strangers on the internet. If this is the case, I would strongly advise you to check the relevant legislation. Waste management for starters, if you're talking about hydrogen peroxide. If my assumption is wrong, please ignore! Fgf10 (talk) 22:43, 12 January 2015 (UTC)

That's the great thing about hydrogen peroxide, it breaks down into just water and oxygen, so no toxic waste barrels needed. StuRat (talk) 23:37, 12 January 2015 (UTC)

What are the most economical ways of removing or killing yeast on the surface of produce?

I've been looking into using a hydrogen peroxide soak, but perhaps someone else knows a better way of doing it. I'm basically trying to prevent fermentation, but I can't use any unnatural preservatives in the final product so I'm trying to get rid of the yeast on the produce prior to it being processsed. I'm unaware of any natural preservatives that would prevent fermentation. Thank you. David Bradley I (talk) 20:23, 12 January 2015 (UTC)

The other method that comes to mind is a UV light, but you would need to rotate the produce so all sides are exposed, and it wouldn't get into hidden folds. With that in mind, your hydrogen peroxide method sounds better, to me. I am of course assuming that cooking or using ionizing radiation (like gamma rays or X-rays) are both out. (The radiation method is inexpensive only on a large scale, and many people won't buy food treated with it.) StuRat (talk) 20:27, 12 January 2015 (UTC)

Cooking is out, but if hot tap water could kill the yeast then that might be an option. I know it also grows better in a more acidic environment. Does that mean a basic environment could kill it? It might just inhibit growth which wouldn't work at all, but if it could kill yeast then I'm sure there is an economical and safe way of turning large quantifies of water into a mild base. David Bradley I (talk) 20:33, 12 January 2015 (UTC)

Well, yea, I'm sure bleach would kill it, but that's much worse to work with than hydrogen peroxide. StuRat (talk) 20:35, 12 January 2015 (UTC)

How about if you plunge the produce into boiling water and then remove it immediately ? StuRat (talk) 20:37, 12 January 2015 (UTC)

I think that would work, but the people I work for say the labor cost on that would be too high. I've read that sulfur dioxide kills yeast, but I think it might not be legal to wash produce with a solution of it. Potassium sorbate works, but we aren't allowed to use that preservative. David Bradley I (talk) 20:43, 12 January 2015 (UTC)

That wouldn't be economical either, as you'd need breathing masks for your employees and/or a sealed system with an exhaust fan. StuRat (talk) 20:49, 12 January 2015 (UTC)

Oh, and don't forget the value of pre-washing it, as that will remove much of the yeast mechanically. The rest will be easier to kill with hydrogen peroxide or some other method. And if it's some type of produce where you can just discard the outer layers, like an onion, even better. StuRat (talk) 20:40, 12 January 2015 (UTC)

The pre-washing hasn't removed it or removed enough of it. Skinning this produce would be far too labor intensive and thus not economical. David Bradley I (talk) 20:43, 12 January 2015 (UTC)

David Bradley I, here's a reference: [19] is a detailed discussion of how to sanitize produce. It's published by the US government. A number of different solutions are discussed, including hydrogen peroxide (which is apparently one of the least used commercially, which might be why it's hard to find a source that answers your earlier question about how long it lasts.). Scroll down for a chart comparing the various methods and below that for references to the original studies.Taknaran (talk) 21:20, 12 January 2015 (UTC)

Yes, I think the issue is that he wants to do it "organically", and many chemicals don't qualify. StuRat (talk) 21:23, 12 January 2015 (UTC)

Vinegar (acetic acid) might also work, but I'm thinking that might be more expensive than hydrogen peroxide. StuRat (talk) 21:28, 12 January 2015 (UTC)

The way that sulfur dioxide is used to kill yeast is to use a solution of potassium metabisulfite. Home winemakers and brewers use it to sterilize their equipment before use. You would need an extraction system of some sort to draw away the sulfur dioxide that's produced but that would probably be the case with most sterilizing agents. I think the main question would be whether any sulfite would be left on the produce after the washing process. There is some information about the use of sulfites here. Richerman (talk) 22:36, 12 January 2015 (UTC)

Can dogs survive in the wild?

I'm trying to convince my idiot friend that evolution is true, and dogs proves it. I tell him to look at all the different kinds of dogs there are, and since these animals were made by humans via artificial selection, that proves that evolution is a fact. But he's dumb, and says that god made them all. So I want to counter that by saying that god couldn't have possible made them because dogs can't survive without humans taking care of them. I'm fairly certain that dogs, even large ones like Great Danes and what not can't survive in the woods without humans taking care of them, but I just want to make sure. Keep in mind, I'm not talking about animals like the dingo which used to be domesticated, but evolved to revert back to their feral state. 69.121.131.137 (talk) 03:09, 13 January 2015 (UTC)

Unfortunately, they can survive on their own. Many third world cities (without dog catchers) have large stray dog populations. StuRat (talk) 03:30, 13 January 2015 (UTC)

Artificial selection does not prove that "evolution is true". Whether "God made them" or not depends on how you define "God". ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:31, 13 January 2015 (UTC)

For a casual proof of evolution, you might point out that the human spine causes all sorts of problems because, in evolutionary terms, we very recently began walking upright, and the spine design has not yet caught up. Specifically, I'd say the spinal chord should not be inside the spine, which leads to pinched nerves. Instead there should be a tough rubbery cartilage there, and the spinal chord should be more like a notochord. If God designed us, he would have presumably done a better job of it. StuRat (talk) 03:34, 13 January 2015 (UTC)