Wikipedia:Reference desk/Archives/Science/2014 April 18

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April 18

Negative pH of acid mine drainage

Given that the molarity of hydrogen ions in pure sulfuric acid is not much less than the negative of the common log of 18 (the molarity of pure sulfuric acid), how can an aqueous solution (i.e. acid mine drainage) exceed that hydrogen ion concentration with a pH as low as -3.6? I know there's also iron oxidation contributing, but surely it can't be as important as the sulfuric acid present.--Jasper Deng (talk) 06:57, 18 April 2014 (UTC)

The paper traces back to [1]. The sulfate concentration is up to 760 g/L, but sulfuric acid has density 1.84, so it isn't all sulfuric acid (which only has pH -3 according to our article ... which is still lower than -log 18...). There are up to 200 g/L of other minerals present. Someone will have to get the paper to see what they are. Fundamentally, note that pH is not p[H], and that at low pH things get ... strange. According to our article the Nernst equation breaks down. But the bottom line is that you have to know exactly what you're measuring and not assume it means anything else when you're in that territory. Wnt (talk) 21:27, 18 April 2014 (UTC)

I got access to it via JSTOR, but it didn't elaborate too much on how those results were obtained. It did however consider the invalidity of the Nernst equation under those conditions and the need for a different definition of pH.

As I learned it, there was no distinction made between pH and p[H], but I never had to deal with solutions this acidic (i.e. it was a basic chemistry class).--Jasper Deng (talk) 04:48, 20 April 2014 (UTC)

Why is subculturing called passaging?

I've heard the word passaging pronounced with English and with French pronunciation rules. Is French the origin? And we just tack on English endings 'ed' and 'ing'?

If it's from the same root as the horsey sense (to move sideways) then it's from French passager, from Italian passeggiare and normally retains the French pronunciation, as for dressage, though, strangely, neither Wiktionary nor the OED record this fact. Dbfirs 20:59, 19 April 2014 (UTC)

Morphological diversity within a species

Although morphology may not be the best way to classify different species, it can be one practical way. However, even if two species may look very similar, they cannot mate with each other due to geographical isolation, temporal isolation, behavioral isolation, etc. Humans, on the other hand, seem to be the only exception. Humans can look widely different from one another and can potentially all mate with each other, and they are extremely mobile. They can travel from place to place, establish whole communities, and mate with the locals. Is there any other species that is so morphologically diverse as humans, or is this just one trait that makes humans more special and unique? 140.254.226.206 (talk) 14:19, 18 April 2014 (UTC)

Dogs are much more diverse. -- Finlay McWalterᚠTalk 14:21, 18 April 2014 (UTC)

For example, you might get an 8 pound Maltese and an 85 pound Alaskan Malamute; you won't find a tenfold mass differential between folks in one group of humans or another. -- Finlay McWalterᚠTalk 14:25, 18 April 2014 (UTC)

I think it would be best if the Alaskan Malamute is the female and the Maltese is male. The puppies need room to grow. 140.254.226.206 (talk) 14:39, 18 April 2014 (UTC)

Better give the Maltese a stepladder. :-) StuRat (talk) 21:17, 18 April 2014 (UTC)

See out-group homogeneity. We think that humans are different from each other because we are humans, and spent a lifetime trying to identify differences between people (both for good and evil purposes). You probably can't tell monkeys apart, but if you could ask a monkey whether he can tell his mommy apart from his daddy, he'll throw a rotten banana at you. Similarly a monkey might have a hard time distinguishing a black man from a white man, especially if both are fully clothed, and certainly won't understand why groups of seemingly indistinguishable people are trying to exterminate each other (Germans and Jews, Hutus and Tutsis, Turks and Armenians, etc). --Bowlhover (talk) 15:18, 18 April 2014 (UTC)

Yes, I used to be in charge of a breeding colony of Rhesus macaques and, to those of us who worked with them every day, they were all different to look at and quite easy to identify. Richerman (talk) 22:56, 18 April 2014 (UTC)

Humans only look different to us because we have evolved a lot of facial recognition to tell people apart. In part it has to do with our highly social nature, we are one of only a few eusocial mammals. To some hypothetical sentient alien, we'd all look pretty much the same. But sheep faces look very different to other sheep, and wasps look very different to other wasps, even though they all look pretty much the same to us [2] Paper_wasp#Facial_recognition. We are rather unique in our ability to mate with someone born on the other side of the planet. Finlay's dog example is pretty good for diversity, but of course dog breeds as we know them wouldn't exist without all the artificial selection we've put them through. See Sexual_dimorphism for other examples of extreme morphological diversity in non-human animals. (Post-EC:Bowlhover has a good point about outgroup homogeneity, this is in line with the biological examples I've given) (n.b. our article doesn't mention humans as eusocial animals, but E.O. Wilson considers humans to be eusocial, and as one of the most experienced experts in the field, I trust his judgment :)SemanticMantis (talk) 15:19, 18 April 2014 (UTC)

Calling human eusocial seems like a stretch to me -- true, there's a big mystery about homosexuality in mammals, and maybe you could think of it as a non-reproductive caste; or maybe you could argue that some others avoid reproducing for economic or religious reasons and play a similar role, but by and large, humans fail this criterion. In general the rearing of others' offspring seems more than a bit hit and miss. Of course it's just semantics and you can define a term however you like, and biology doesn't know theory. But recognizing facial features seems like a skill suitable for adversaries and competitors, and is often used for this purpose in modern society. Wnt (talk) 21:13, 18 April 2014 (UTC)

My main point is that we are highly social, and highly social animals tend to be better at distinguishing individuals of that species. As you say, it also involves adversaries, competitors (and friends, mates, kin, etc). As for the terminology, I sadly didn't get to ask Wilson how he was thinking about non-reproductive members of humanity, but I bet he'd have an interesting answer :) My own interpretation is that any child that helps rear its siblings, and and ~16-30 yr old that doesn't have children, are both types of humans that help us fit the definition. Also, it would just sound weird to say that humans are "semi-social"! SemanticMantis (talk) 13:39, 19 April 2014 (UTC)

Well, the social nature of modern humans seems largely forced by recent and rapid changes in the environment. I haven't done proper reading on the topic, but IIRC a few of the loci suspected of involvement with autism are also associated with the gregarious phase of locusts. In chimps one of the important genes is present in some individuals and absent in others [3]. So I'm suspicious that if you go back a few tens of thousands of years, that something related to we call autism might have had a fairly high prevalence in the population. I suspect we should even consider the possibility that aspects of the modern environment might provide a different background with epigenetic effects that could cause it to become common again. Admittedly that is a very speculative scenario, but I just mean to illustrate that historically speaking we don't know that humans were really all that social, or would be in more natural environments. Wnt (talk) 14:59, 19 April 2014 (UTC)

Our social behaviors are absolutely under environmental control. I personally think the theory that human civilizations were born from harsh conditions to be quite compelling, e.g. [4]. If life is easy and food grows on trees, why cooperate? But if water is scarce and agriculture is hard, cooperative societies have a strong advantage. But we're rather off-topic now, so I'll just leave it there  :) SemanticMantis (talk) 15:10, 19 April 2014 (UTC)

Correlation for appearance of fruit and vegetables and their quality (redefine quality more than once if you think that helps)

Is there any reason why a particular shade/saturation of colour of, for example, lemons or limes would be of better quality for their zest or juice? I suppose better quality would be highest concentration of components of value including acids, vitamins, oils. Is there any rational reason to go for the regular lemons which look a bit nicer than the anaemic SmartPrice ones? ----Seans Potato Business 15:27, 18 April 2014 (UTC)

If you're happy with the taste of the uglier cheap ones then go with them. Fruits and vegetables sell better when they look prettier, and can be sold at a higher price. I usually take advantadge of this during tomato season - you can pick up a bushel of Roma "seconds" for the price of a half-peck of the pretty ones, but the sauce comes out just as tasty either way. Katie R (talk) 15:48, 18 April 2014 (UTC)

If we define "better quality" as "better tasting," then I think there are several factors to consider: 1. Produce that is ripe tastes better than under/over ripe produce -- this is usually judged by appearance (color) and touch. 2. Some produce appears more attractive in color and size due to chemical treatments or genetic modification, but in this case the appearance is artificially achieved and doesn't correlate to the state of ripeness of the produce. 3. Perceptions of taste are affected by sight -- if a piece of produce appears unattractive then you may not think it tastes good, but perhaps you would find it tasty in a blind taste test. 4. Taste is subjective. Some people may prefer a bland or one-dimensionally sweet version of a piece of fruit versus a "fruitier" more complex-tasting version. Unfortunately I can't find citations for the above. It is sort of "conventional wisdom." You could do an experiment and buy one each of the lemons and do a taste test to see if you prefer one over the other.--Dreamahighway (talk) 16:23, 18 April 2014 (UTC)

Taking a more biological track, note that all our domesticated fruits are based off of wild ancestors that used color, flavor, and nutrition to attract seed dispersers, so, there is a long trend of visually striking food that also tends to taste better. However, under modern breeding, color and shelf-stability often take precedence over actual flavor. Compare the beautiful but bland tomatoes you see on the shelf to a weird looking but delicious heirloom. This is a pop-sci account of a recent finding specifically about good-looking but lame tomatoes [5]. Compare the good looks and early fruiting of e.g. Early Girl to the dark and delicious Cherokee purple. SemanticMantis (talk) 17:01, 18 April 2014 (UTC)

Yes, we are genetically programmed to prefer fruits and vegetables that are good for us, such as colorful ones with lots of phytonutrients. However, marketing guys then use our own biology against us, and add dye or otherwise get unhealthy food to look healthy (like the bag of yellow oranges in a red mesh bag that makes them look orange and ripe).

Then there's the fact that "perfect" fruit or veggies often require the use of artificial fertilizers and pesticides, either of which may be harmful to humans and/or the environment. StuRat (talk) 17:29, 18 April 2014 (UTC)

Statically determinate structure

1 - Are there any easy ways to determine whether a structure is statically determinate? I always miss whether it is and end up doing a stiffness analysis unnecessarily.
2 - In a stiffness matrix, how do you identify the free nodes. I thought all nodes that arent fixed are free nodes but I was told roller and pin supports are also treated as fixed nodes, if they're not nodes which are being analysed, which doesn't make sense to me. 3 - Am I correct in assuming that where there is a force on a member such a axial, shear or a moment, the row on the stiffness matrix, representing that force, becomes 0?

Clover345 (talk) 16:29, 18 April 2014 (UTC)

Regarding your first question: Have you looked at our Statically indeterminate article? Basically if you have more unknowns than equations, it is indeterminate.--146.163.159.12 (talk) 17:53, 18 April 2014 (UTC)--Dreamahighway (talk) 17:54, 18 April 2014 (UTC)

thanks but I meant by just looking at it, without writing down any equations. Clover345 (talk) 18:05, 18 April 2014 (UTC)

See also Underdetermined_system. Unless you've done so many of these problems that you've developed a strong intuition, you have to do at least a quick check on how many constraints and how many unknowns there are. SemanticMantis (talk) 15:02, 19 April 2014 (UTC)

Storing food at temperature fluctuating between -20 and -40 better or worse than constant -20?

Would storing food at a fluctuating temperature between -40 and -20 cause it to degenerate in a way that it wouldn't at a constant -20? ----Seans Potato Business 17:32, 18 April 2014 (UTC)

Celsius, Fahrenheit, or Kelvin? HiLo48 (talk) 17:56, 18 April 2014 (UTC)

It is fairly obvious that it's not Kelvin, unless you're in the habit of storing your food below absolute zero. (+)H₃N-Protein\Chemist-CO₂(-) 18:00, 18 April 2014 (UTC)

Given your username, Sean, I have to ask - does the food in question consist of potatoes? --Demiurge1000 (talk) 18:03, 18 April 2014 (UTC)

Potatoes are not involved at any level beyond that at which they exist in the mean average content of a Western European domestic freezer. ----Seans Potato Business 20:04, 18 April 2014 (UTC)

For what it's worth -40C is exactly the same temperature as -40F. So for the sake of simplicity, you could just read the question as "What happens if you raise/lower the temperature of food without going above the melting temperature of water?" in which case degrees C versus degrees F is pretty much irrelevant.(+)H₃N-Protein\Chemist-CO₂(-) 18:06, 18 April 2014 (UTC)

Well, you have two competing processes which will degrade food. There are chemical reactions, which occur less at lower temperatures, so from that POV a colder average is better. Then there's the thermal expansion and contraction cycles a varying temperature will cause. Since the temp stays below freezing, the expansion and contraction will be minimal. Still, with enough cycles, you might eventually get cracks propagating in hard foods (and most food is hard at those temps). So, I'm not sure which is better, it all depends on the relative scales of the two types of food degradation. StuRat (talk) 18:34, 18 April 2014 (UTC)

I've not noticed any real difference in the taste of caribou meat that has been harvested in the fall and stored outside over the winter. Nor have I heard of anyone getting sick from eating it in the spring. However, this is more a gradual change from −20 °C (−4 °F) to −40 °C (−40 °F) and back rather than rapid changes. See Cambridge Bay#Climate for where I am referring to. CBWeather, Talk, Seal meat for supper? 00:49, 19 April 2014 (UTC)

I take it the polar bears are all hibernating then ? Otherwise that temptation would presumably be too much for them. StuRat (talk) 00:52, 19 April 2014 (UTC)

No bears (polar) around here and as yet few grizzly. Loose dogs and foxes would be the culprits but who stores their food on the ground. Just get them up out of the way. CBWeather, Talk, Seal meat for supper? 02:37, 19 April 2014 (UTC)

Too bad that won't work against our squirrels. No bird feeder is safe around here. StuRat (talk) 02:56, 19 April 2014 (UTC)

Frozen food loses nutrients gradually anyway, frozen vegetables after 6 months or so, and frozen meat a few months after that. But as long as it stays frozen, it's still safe to cook and eat the food. I can't think of where anyone would get a chance to try storing food at -40F / C, other than the far north. OttawaAC (talk) 02:04, 19 April 2014 (UTC)

Source on frozen food losing nutrients? 86.128.79.70 (talk) 04:26, 19 April 2014 (UTC)

Frozen food#Effect on nutrients. Further reading has revealed that my food storage notions are based on FDA food storage guidelines that are themselves based on a perceived deterioration in quality, not nutrient levels. OttawaAC (talk) 13:49, 19 April 2014 (UTC)

StuRat, you could add another degradation mechanism: dehydration. Something stored at a constant temperature is more likely to have fewer (temporary) temperature differentials, which could lead to food losing moisture while another part of the freezer is colder than the food, which will not necessarily be reversed. This could be exacerbated by regular cycling of the temperature. Of course, this process does not need any cycling, only a temperature differential. For example, if the food is warmed by conduction from the shelf it rests on, and the heat is removed by a refrigerating element on inside the wall of the freezer compartment, there could be a continual migration of moisture sublimating from the food to the colder cooling element. —Quondum 04:43, 19 April 2014 (UTC)

Yes, that's the classic freezer burn, but good containers can reduce that. StuRat (talk) 23:20, 19 April 2014 (UTC)

Wigner effect and graphite density

In graphite-moderated nuclear reactors, can the Wigner effect be mitigated by producing graphite with more vacancy defects than other types (which would therefore be less dense), so that most of the displacements caused by each neutron amount to migrations of the existing vacancies rather than the creation of new Frenkel defects? NeonMerlin 18:02, 18 April 2014 (UTC)