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# September 22

## What red and green fruit grown in mexico looks like a smooth, oversized avocado?

I went grocery shopping, and was looking for something new to try. In the fresh fruit section they had these red and green fruit, about a liter in volume, somewhat like oversized smooth and less pear-shaped avocados. I haven't a clue what the inside looks like. They were labelled as "Mexico" where the actual name of the item, like "sweet onion" would appear, and I had to ask someone to read the tag on the fruit, which said, "Producto de Mexico"! Anyone have a guess? I can then do a google image search, but otherwise I have no idea where to begin. Thanks. μηδείς (talk) 03:33, 22 September 2016 (UTC)

Sounds like a Papaya to me. Tevildo (talk) 04:09, 22 September 2016 (UTC)
Papayas I've seen are yellow. StuRat (talk) 13:58, 22 September 2016 (UTC)
Mangos? [4] -Modocc (talk) 04:31, 22 September 2016 (UTC)
It's definitely not a papaya based on any images I have seen on google, which are too yellow. It does look like a mango based on google images, and is almost identical to our main image of a mango. I'll assume it's a mango, buy one, and see what I can do with it. I suppose I should have just bought one tonight, but I am busy with other matters, and too distracted to think as clearly as the 25% of US voters who are deplorable, let alone a Bernie supporter.
Thanks. (BTW, I settled on half-ripe bananas, since I knew what the were.) μηδείς (talk) 05:50, 22 September 2016 (UTC)
Resolved
Mangos are absolutely my favorite fruit, if you've never had it before, omg prepare yourself for some magic in your mouth. You have to get one that's ripe and ready to eat. It needs to be a bit soft, press not too had near the top where the stem is, it should "give" a little, like a ripe avocado or a peach I guess, not hard like an apple or pear. Vespine (talk) 06:11, 22 September 2016 (UTC)
I've never found the Mexican mangoes sold in New Zealand very good compared to those from Thailand, India or Australia. (Or those sold in Malaysia generally from Thailand, sometimes locally grown maybe sometimes from elsewhere in Asia.) I don't know if this is also true of those sold in the US. They are better than the Tommy Atkins (mango) often from Peru or Ecuador though. (Although I admit I haven't tried that many, but I've spoken to people with similar experiencse.) Nil Einne (talk) 09:49, 22 September 2016 (UTC)
Agreed, but a poor mango is still damn good fruit.
I think this could be a papaya, or close relative. There are plenty that are eaten green and some that are quite large.
A good use for these larger papayas is as a vegetable in a salad, rather than as fruit. Halve them, deseed them, peel them, and then use a mandoline (or a lot of fine chopping) to cut them into thin strips or julienne. Mix with similar shredded carrot. Then dress with some mix of light (rice) vinegar, a light oil like avocado oil and a bit of chilli, black pepper or maybe citrus juice. Andy Dingley (talk) 11:01, 22 September 2016 (UTC)
Are you quite sure it WASN'T an avocado? There is a wide variation in avocado varieties, in terms of texture and color. this article explains some of the differences. We're used to one basic variety in American supermarkets, the Hass avocado, but there are many varieties, some of which may be grown in Mexico, which look very different. I remember about 20 years ago at a pot luck where a guest from Puerto Rico brought what she called a "Puerto Rican" avocado which was smooth, bright green, and the size and shape of a small watermelon. --Jayron32 11:46, 22 September 2016 (UTC)
Indeed; our list of cultivars at avocado really doesn't do it justice. The volume of one liter is also on the high side, regardless of whether we're talking about mangoes, avocados, papayas or some unholy hybrid between them. Luckily, the seeds of these fruit are very dissimilar; cutting open the sample will make it unambiguous pretty quickly. Matt Deres (talk) 12:09, 22 September 2016 (UTC)
I'm surprised you've never seen a mango before, they are quite common in grocery stores here in Michigan. One warning, when ripe they are quite juicy, so peel it over a bowl in the sink (the bowl is so you can drink most of the juice). I would use a knife to peel it. Also, you will need the knife to separate the flesh from the pit, which looks like a giant white watermelon seed, but had fibers extending into the flesh (a fun trick on little kids is to say you just had a giant watermelon, and show them the mango pit as "proof"). These are good roughage, but do tend to get stuck between the teeth, so plan to floss after. The flavor I would describe as like fruity maple syrup. You can eat it plain or in a fruit salad, or basically anywhere you would use citrus fruit, like mixed with yogurt. StuRat (talk) 13:57, 22 September 2016 (UTC)

I have actually seen the meat of mangoes before, just not the whole unskinned fruit. This fruit is not an avocado, it would have weighed twice as much as it did, and I used to make the guacamole at TGIF. Next time I'm there I'll buy one. The also had ramatans, which thank god were not labelled as philippines from the Philippines. μηδείς (talk) 22:25, 22 September 2016 (UTC)

Would ramatans be rambutans? I've never heard them called that before. @ StuRat you might find this clip helpful, lose no juice and minimise the fibers with this method widely used in the UK. Richard Avery (talk) 06:49, 23 September 2016 (UTC)
Apparently they are the same thing, if you google image them you get the same fruit, although it looks like rambutan is the more common term. There are scary looking, like something out of The Expanse and I had never heard of or seen one until this week. μηδείς (talk) 16:28, 23 September 2016 (UTC)
Prickly pears are plenty scary, too. StuRat (talk) 16:49, 23 September 2016 (UTC)
Prickly pears are generally actually prickly. I guess you could prick yourself on the stalk of a rambutan, but that isn't that different from an apple or both ends of a banana. It's surely difficult to prick yourself on the hairs. Frankly the durian is probably scarier (although you're less likely to get a spike) but people often get too distracted by the smell to notice that. Still walking around a field of trees with ripe durians is best avoided. Recognising what you're seeing is I guess important. Some of the sharper looking Starfruit may look scary if you imagine the spikes are hard. Of course a fruit looking innocous doesn't mean it can't cause such inconviences. I wouldn't say the purple mangosteen looks particularly threatening but the the staining may be more annoying than anything you're likely to get from a rambutan or starfruit. (Although it is also annoying with the skin of the seed sticks to the rambutan flesh.) And since we spoke of smells, not a fruit but the petai smell and taste can be a bit offputting to some but like asparagus, it's probably the after effects that people notice more. Nil Einne (talk) 19:20, 23 September 2016 (UTC)
I've got a potted prickly pear, and my parents have them growing in their back yard. They might look dangerous and for good reason (their spines can pierce leather gloves even when they are grasped with aluminum foil), but the rambutan looks damn spooky, what with its red body and green tentacles. μηδείς (talk) 20:40, 23 September 2016 (UTC)

## Differences between electromagnetic field and electromagnetic induction

What are the differences between electromagnetic field and electromagnetic induction? Is electromagnetic induction always being a kind of electromagnetic field?--79.139.159.41 (talk) 09:39, 22 September 2016 (UTC)

Is electromagnetic induction being an electromagnetic work of nucleus of atoms and is electromagnetic field being an electromagnetic work of atoms?--79.139.159.41 (talk) 09:52, 22 September 2016 (UTC)
What are the differences between a gravitational field and a pendulum clock? Induction is a process that uses the field. —Tamfang (talk) 10:18, 22 September 2016 (UTC)
What vectors are always being the main a vectors of electromagnetic induction or vectors of electromagnetic field?--79.139.159.41 (talk) 10:35, 22 September 2016 (UTC)
Is nuclear always doing the work of atom or atom is always doing it self work?--79.139.159.41 (talk) 10:42, 22 September 2016 (UTC)
What are mechanical physics - mechanical models of atom says about that?--79.139.159.41 (talk) 11:02, 22 September 2016 (UTC)
It appears your native language is not English. If you can tell us your native language, we can direct you to another site, likely another version of Wikipedia, in your own language. What is your native language? --Jayron32 11:41, 22 September 2016 (UTC)
It is I’m. I’m interesting is universe being universal and unified, that is could mechanics being determines all?--Alex Sazonov (talk) 12:53, 22 September 2016 (UTC)
Your use of English is not good enough for anyone here to understand what you wish to know. If you tell us what language you speak normally, we can direct you to the correct venue to get your questions answered. What language do you speak? --Jayron32 13:08, 22 September 2016 (UTC)

I'm speak Russian. I want say that the USSR was universalized and unified all humanitarian and all technical knowledge to win in global economic, but the USSR was not won in global economic because the sources of the USSR exhausted.--79.139.159.41 (talk) 13:40, 22 September 2016 (UTC)

On explain of my country the USSR-Russia we could seeing that knowledge and technologies and also capitals are loses to mineral sources.--79.139.159.41 (talk) 14:00, 22 September 2016 (UTC)
Here is a link to the Russian Wikipedia's equivalent of the Reference Desk. If you ask your questions there in your native language, you will likely get better, more prompt responses than you would here. Because frankly, here at English Wikipedia, most of us can't understand you very well. --Jayron32 14:01, 22 September 2016 (UTC)
This was first notice by BenRG but that page is to a merged/deleted page. It links to ru:Википедия:Форум/Вопросы but that page says "Вопросы, не относящиеся к работе над Википедией, будут удалены. Поищите в Википедии, Гугле или Яндексе" which appears to mean something like "Questions not related to work on Wikipedia would be deleted. Search Wikipedia, Google or Yandex." So there appears to be no where on the Russian wikipedia that anyone can get help with these sort of questions. In the case of Alex Sazonov, it's a moot point anyway, they appear to be unwelcome on the Russian wikipedia for writing barely understandable nonsense ru:Обсуждение_участника:Alex_Sazonov and were blocked back in 2014 [5]. My impression is it was the same when they tried speaking in Russian here on en.wikipedia. So I don't think asking in Russian anywhere, even outside ru.wikipedia is going to help if Alex Sazonov speaks the same way. They need to have a far better level of language be it in Russian, English or some other language is they actually want people to help them. Nil Einne (talk) 14:53, 22 September 2016 (UTC)
Is always being matter only a size of available natural mineral sources and nothing more.--Alex Sazonov (talk) 15:56, 22 September 2016 (UTC)

@Alex Sazonov it is unlikely that we can help you further with the two Wikipedia articles[6][7] that you have cited unless you specify a sentence you don't understand. However you can read in most Russian libraries and encyclopedias about the radio pioneer Alexander Popov. Popov built receivers to detect the electromagnetic field that is radiated in all directions by the powerful currents in Lightning strikes. In his receivers, incoming electromagnetic field vibrations induce small current vibrations in an antenna and Coherer device that in turn passes a large current to an Electromagnet that produces physical force to ring a bell, to warn of an approaching storm. The USSR stamp shown says "Inventor of radio, A. S. Popov, 1859-1906. Demonstration of the first radio, 1895" AllBestFaith (talk) 16:01, 22 September 2016 (UTC)

Thank you. Is being interesting did the magnetic fields doing work same as electromagnetic fields?--79.139.159.41 (talk) 16:51, 22 September 2016 (UTC)
So, what a problem had the USSR-Russia if magnetic fields did always doing work same as electromagnetic fields?--79.139.159.41 (talk) 18:00, 22 September 2016 (UTC)
Вы должны прочитать школы книги, что вы понимаете о электромагнетизма. Это обсуждение концы. This discussion ends. AllBestFaith (talk) 19:23, 22 September 2016 (UTC)
Ok, this discussion was closed, but at the end of this discussion, I must to add that optical spectrum of magnetic field is same to optical spectrum of electromagnetic field, that’s why I was had a question what a problem had the USSR-Russia if magnetic fields are same to electromagnetic fields and their laws are same. Thanks to all for this discussion.--Alex Sazonov (talk) 16:09, 23 September 2016 (UTC)

# September 23

## Child sex abuse statistics

Recently, I volunteered for a program working with children. As part of the required training everyone had to review a set of materials discussing child sex abuse. In those materials were a disturbing set of unreferenced statistics. I'd like to figure out if the statistics presented were accurate / reliable or cherry-picked for dramatic effect. Claims:

1. Only 3% of the perpetrators of child sexual abuse are ever identified and prosecuted.
2. Over a lifetime, a perpetrator who isn't caught can victimize up to 500 children.

So far my google-fu hasn't been able verify or source either claim. I'm sure child sex abuse is underreported, but even so, 3% seems jaw-droppingly low. The 500 victims claim (7 / year for 70 years?) seems like an extreme worst case scenario, if it isn't simply an example of magical thinking. Can anyone help figure out where the claims might have come from and whether they are accurate? This is for a US context, if it helps. Dragons flight (talk) 09:46, 23 September 2016 (UTC)

This [8] says "The belief that child sexual abusers are incorrigible recidivists is also an oversimplication. In reality, the overall re-offense rate for child molesters is lower than that for other criminals." Refs 47-49 there also seem like they may have statistics on victimization counts. This [9] looks to be a very review good article, summarizing many key research studies and statistics. SemanticMantis (talk) 13:05, 23 September 2016 (UTC)
1) You will need to narrowly define "child sex abuse". Public urination, seen by a child, could be included, and men have ended up on the watch list because of it. Consensual sex between an 18 year-old male and a girl just below the age of consent can have the same result. Presumably, a large portion of such cases are never charged, especially if the genders are reversed, as the punishment seems wildly out-of-whack with the crime.
2) Note that any "statistic" containing the words "up to" means there was a single case, no claim beyond that was made. StuRat (talk) 13:20, 23 September 2016 (UTC)
The Metropolitan Police stated that the total number of alleged victims was 589, of whom 450 alleged abuse by Savile.[4][5]
Loraof (talk) 13:30, 23 September 2016 (UTC)
With this scale of horror, it seems odd to nitpick, but of that 450, "only" 80% were "children or young people" at the time, which is around 360. Smurrayinchester 13:51, 23 September 2016 (UTC)
• Well, the question has basically been answered, but in any case those two stats rise red flags for the concerned statistician. If "3% of the perpetrators (...) are ever identified and prosecuted", one absolutely needs to ask how that number was obtained, since by definition it is a figure that is hard to know (it is possible to estimate it with various methods, but never accept such claims without knowing what degree of credibility the methodology has).
The second one is an "up to" statistic; while it produces a significant emotional impact, it is of little relevance in that case (since that is a big statistical outlier). "Up to" stats can be useful, e.g. you want the bridge to hold "up to X kg", because even if traffic is usually low, you are not satisfied with one collapse per year; but more often than not, they are not the correct measure. That is of course why websites report "up to" X simultaneous visitors, etc. (And of course, a perpetrator "can" rape up to 100,000 victims if starting young enough as a despot, but "can" is the operative word.)
Of course, child abuse is still a big problem, but it does not justify abusing the statistics. I remember than for our driving test we were fed statistics about road deaths, and although some good ones would already have been impressive enough, they were often phrased in misleading way to make an even worse impression. E.g. "x% of road accidents happen on commuting", to tell you to pay attention even on the roads you know well, but of course the relevant number is the deaths by kilometer travelled (or per hour travelled, maybe), which could be either higher or smaller on commuting trips. TigraanClick here to contact me 16:15, 23 September 2016 (UTC)
The worse stats was "alcohol related car deaths", which could mean anyone in any vehicle involved had been drinking, even a passenger in a car that was hit, versus "alcohol caused", which is the relevant stat. StuRat (talk) 16:18, 23 September 2016 (UTC)
1. The claim rests on a source of "identifying" perpetrators. Such a source might be Child protection authorities who might see a ratio of 33 suspects who merit on-going investigation to every actual prosecution, or it might be a Mental health authority who observes a number of cases considered at risk. In either case the data source would be confidential and unapproachable.
2. The claim contains the weasel wording "up to" 500 that makes the claim almost meaningless, except for its shock value, and almost incontrovertable. Its illusory numerical accuracy leads only to a useless speculation whether exhaustion alone would limit a lifelong (say age 18 to 80) dedicated child molester to victimize (in ways unspecified) a new child on average every 45 days. A source might defend the claim by invoking a concept of collective victimization in a special environment such as a school, Seminary or enslaved area where Child sexual abuse was prevalent. AllBestFaith (talk) 16:49, 23 September 2016 (UTC)

## Can being fat ever be healthy?

People always say that being fat is unhealthy. But how fat does a person have to be to receive unflattering comments? Is it ever possible that a person just happens to be born with an undesirable body shape but manages a very balanced diet and maintains regular physical activity with no intention of changing the figure? Can such a fat but able person be possible and healthy? 64.134.39.172 (talk) 19:23, 23 September 2016 (UTC)

The answer may well depend on how fat the person is. If morbidly obese, then probably no, that can't be healthy. However, if just slightly overweight, then it's possible, especially since some extra weight is protective against some diseases that cause sudden weight loss. Not that it prevents the disease itself, mind you, but just that it prevents weight, blood sugar level, etc., from dropping to a dangerously low level. On the other side of the equation, susceptibility to heart disease, diabetes, and other medical problems also has a genetic component, so if someone is lucky enough to be resistant to those conditions, those few extra pounds are unlikely to be a problem.
As far as unflattering comments go, fashion models have set unrealistic expectations, and many of them are underweight, and/or their photos are altered so they look that way. So, a person may very well be normal weight, and yet be criticized for being fat. StuRat (talk) 19:29, 23 September 2016 (UTC)
Sumo wrestlers seem to have a very big figure. Are they considered more unhealthy than the rest of Japan's population? 64.134.39.172 (talk) 19:55, 23 September 2016 (UTC)
If this is a serious question you should be asking your doctor or nutritionist, not for our opinion on the subject. And where did the notion that the rest of Japan's population is unhealthy come from? μηδείς (talk) 20:31, 23 September 2016 (UTC)
From our article: "Sumo wrestlers have a life expectancy between 60 and 65, more than 10 years shorter than the average Japanese male. Many develop diabetes or high blood pressure, and they are prone to heart attacks due to the enormous amount of fat they accumulate." The question was not about the OP's own health, neither did it imply that the Japanese population are unhealthy. Tevildo (talk) 21:15, 23 September 2016 (UTC)
Well, like I said, if his question was serious. But try changing the word "fat" in his second sentence: "But how fat does a person have to be to receive unflattering comments?" to how effeminate, devout, short, or unable to tan, and get back to me on whether this is serious, or just trolling. μηδείς (talk) 01:56, 24 September 2016 (UTC)
Well, my doctor prefers that I should be slightly overweight rather than at my ideal BMI. So it is horses for courses. Greglocock (talk) 23:17, 23 September 2016 (UTC)
You can't be healthy and fat; if you stick to a healthy diet and get plenty of exercise and are nevertheless overweight, then you suffer from a medical condition like e.g. a thyroid problem. You have to consider this from the perspective of a hunter gatherer population, because our bodies evolved as hunter gatherers. Obviously becoming overweight on a normal calorie intake would be quite disastrous for a hunter gatherer, you would struggle to keep up with you fellow hunters when running down an antelope in the tropical heat. So, you would be of little use to society, you would be considered to be a handicapped person. Count Iblis (talk) 06:21, 24 September 2016 (UTC)
You are assuming everyone hunted. Don't forget those who gathered food and firewood, stayed home taking care of children, made weapons and tools, etc. There was a division of labor quite early on. StuRat (talk) 15:21, 24 September 2016 (UTC)
Yes, but I think you'll struggle to find obese people in the hadza community :) . Count Iblis (talk) 18:21, 24 September 2016 (UTC)
It's now very clear that, at least in wealthy western nations, people in the BMI range considered "overweight" tend to live longer than those in the so-called "healthy" weight range. There's a lay summary of this issue here. That source says that one study found that among Italian women, the longest life expectancy was for those with a BMI of 33, which is normally considered "obese". Adrian J. Hunter(talkcontribs) 08:30, 25 September 2016 (UTC)
The "unflattering comments" is a bullying thing, not a science thing. There was a fairly long period of time when smokers were known to be more unhealthy, without any possible genetic excuse, but received few if any negative commentary. And of course other non-harmful characteristics like skin color get bullying comments in some places. It is clear that extremes of weight have a negative impact on health, but so do many other things, and usually, people don't take them to be their business. As such, I have seen some news articles to suggest that Japan is more prone to such bullying (and, I suspect, other kinds as well). As for the science, it looks like Adrian beat me to the relevant reference, so I'll leave it there. Wnt (talk) 16:19, 26 September 2016 (UTC)

## 1036 Ganymed

What is the composition, temperature, and pressure at the center of 1036 Ganymed?144.35.45.81 (talk) 20:06, 23 September 2016 (UTC)

It is irregularly shaped. So, it is difficult to pinpoint its center, which makes the composition uncertain as the asteroid is likely inhomogeneous. As to the temperature it likely to be the same as the average surface temperature: ~ 160K. The pressure is probably low: ~${\displaystyle G\rho ^{2}R^{2}\sim 0.15}$ bar assuming ρ~1 g/cm3. Ruslik_Zero 20:36, 23 September 2016 (UTC)
The center is where the string points when you try to hang it in a large gravitational field. Now the center of a wok... Sagittarian Milky Way (talk) 22:41, 23 September 2016 (UTC)
I asked a somewhat related question at https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2015_March_6#Digging_into_Vesta Wnt (talk) 16:22, 26 September 2016 (UTC)

## WR 102

Currently the article on WR 102 has inconsistency, saying it's in Cygnus and elsewhere that it's in Sagittarius (and is also included in the Sagittarius template). I couldn't google a reliable source on that, but this book says it's in Cygnus. Could someone verify and fix this? Thanks. Brandmeistertalk 22:48, 23 September 2016 (UTC)

An online astronomical object catalog I checked says it's at 17 hours 45 minutes 47.56 seconds and negative 26 degrees 10 minutes 26.9 seconds. Cygnus is very far from there. Sagittarian Milky Way (talk) 23:05, 23 September 2016 (UTC)
Those co-ordinates are very close to the border of Sagittarius and Ophiuchus: we need to double check the co-ordinates given in the sources, and those of the border at present (precession and all that) carefully before making the necessary amendment.
[Update – as of Epoch 2000 (i.e. from Tirion & Sinnot's Sky Atlas 2000.0 2nd Ed 1998) they are just in Sagittarius, so I have corrected the text. I can't comment on Brandmeister's linked book claiming Cygnus, as I can't read Russian.]
However, I notice that these co-ordinates are in the Article cited to its reference 1, a paper which gives them for its Star 2 in Table 5, but I see nothing in that paper to confirm that this star is WR102. I don't suppose that it isn't, but we do perhaps need an explicit confirmation of the identity of the two. {The poster formerly known as 87.81.230.195} 90.202.211.191 (talk) 23:34, 23 September 2016 (UTC)

# September 24

## Feynman Lectures. 9–6Numerical solution of the equations [10]

I'm trying to solve equation ${\displaystyle d^{2}x/dt^{2}=-x}$ without the trick of taking mean speed during interval ε. But I see that if I take V(t+ε)=V(t)+εa(t) then the displasement increases xlsjpg. And when I take V(t+ε)=V(t)+εa(t+ε) then all is OK xlsjpg.

Feynman's trick also shows good results xls jpg.

So what should we actually do to solve ODE by numerical methods? What is correct way: to derive next step velocity from prev.step acceleration (V(t+ε)=V(t)+εa(t)), current step acceleration (V(t+ε)=V(t)+εa(t+ε)) or using trick V(t+0.5ε) = V(t-0.5ε)+εa(t)? The second case is simpler and shows as good results as 3rd.Username160611000000 (talk) 16:33, 24 September 2016 (UTC)

You're applying Euler's method, which is known to yield the wrong results when applied to many simple equations. Even "trivial" ODEs can be unsuitable for numerical methods. The correct procedure is to study numerical integration so that you can have many methods to choose from, as well as other analytical tools and context to analyze when a method will work well. Nimur (talk) 16:09, 25 September 2016 (UTC)
See also the Symplectic integrator article. Count Iblis (talk) 21:01, 25 September 2016 (UTC)

## Vitamin C content on orange juice

How stable is vitamin C? Is its content much higher in freshly pressed OJ? — Preceding unsigned comment added by 31.4.151.67 (talk) 12:43, 24 September 2016 (UTC)

Actually, it is usually much higher in packaged juice, but that is because vitamin C is added. EdChem (talk) 14:32, 24 September 2016 (UTC)
Comparing the RDA amounts for an actual orange to the amount in cartons of juice - I don't reach that conclusion. SteveBaker (talk) 14:44, 24 September 2016 (UTC)
For a carton of OJ (yeah, I know...not freshly pressed), you get 124mg of VitC from a 248g serving of juice. A typical orange yields 86g of juice - containing 43mg of VitC...so clearly it doesn't matter whether you're drinking juice from a carton or fresh pressed - you're still getting around 0.5mg of VitC per gram of juice.
A vitC pill (let's go with Amazon's best seller "Natures Bounty") contains 1000mg of VitC - which is equivalent to around 8 servings of OJ. The bottle I have has a 2 year expiration date...and the law says that it still has to have 100% of the stated amount of the active ingredient present by that date. I did find a study that said that unopened sample of the vitamin C developed by Hoffmann-La Roche had maintained it's purity and potency for 20 years. So clearly the degradation rate is extremely slow if the vitamin is kept dry and away from the air.
The RDA (recommended daily amount) for Vitamin C is about 60mg. So the juice of an orange and a half - or half a serving of OJ from a carton - or a tiny chip off of a pill should be just fine!
Vitamin C is really ascorbic acid (aka "ascorbate") - which does slowly oxidize to dehydroascorbic acid which (according to our article) "...is actively imported into the endoplasmic reticulum of cells via glucose transporters. It is trapped therein by reduction back to ascorbate by glutathione and other thiols." another article says "On exposure to oxygen, ascorbic acid will undergo further oxidative decomposition to various products including diketogulonic acid, xylonic acid, threonic acid and oxalic acid."
So it seems that Vit C does degrade by oxidation, albeit at a very slow rate. But even more than that, our bodies have adapted to this and can convert some of the decomposition products back into Vit C!
Hence the question of how long the stuff lasts is a tough one because it depends on the form of delivery - how much oxygen and humidity is present when it's stored - and which specific decomposition path it goes through. Using expired VitC capsules should be OK because all that's happening is that the quantity of VitC present is slowly decreasing - and it would take a very long time for 1000mg to degrade all the way down to 60mg - which is the amount you actually need! One source I found said that a year after the expiration date printed on the packaging, 500mg if VitC had degraded to just 480mg.
What I think we can conclusively say is that there is absolutely no benefit (from a Vitamin C perspective) to consuming fresh-pressed OJ compared to stuff that's been sitting in a carton on a supermarket shelf for a week or two. There are doubtless other reasons to consider consuming fresh-pressed OJ - but VitC degradation is absolutely not one of them!
The shelf life of OJ is vastly less than the shelf-life of the vitamin C it contains...so don't worry about it.
SteveBaker (talk) 14:44, 24 September 2016 (UTC)

## What is the real definition of organic compounds?

According to Hebrew wikipedia is "compounds which contain carbon and hydrogen", but according to English wikipedia is a compound which contain Carbon. "An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon.". So I would like to know what is the real or right definition. 93.126.88.30 (talk) 14:20, 24 September 2016 (UTC)

There is no single right answer: as the article organic compound states, any definition is "somewhat arbitrary". The Modern Classification section in that article gives as thorough an answer to your question as you're likely to get here. -- Ed (Edgar181) 14:25, 24 September 2016 (UTC)

## Find article for fuel gas transported through plumbing

Urban areas often have a system where fuel gas (short hydrocarbons) are transported to many homes and other buildings from a central location through plumbing (long pipes), and in the buildings it is used for heating or cooking. I'd like to find the article on this Wikipedia specifically on this system, in contrast to eg. Liquefied petroleum gas (fuel gas transported to homes in cylinders carried by vehicles). I tried to search and follow links, but can't find it. Maybe I'm dumb, but I can't find such an article. If there is no such article, then I'd like to know what terms are usually used in English to describe this system. – b_jonas 16:21, 24 September 2016 (UTC)

History of manufactured gas is the relevant article. The usual term in BrE is "gas main" or "gas pipe", both of which redirect to Pipeline transport. Tevildo (talk) 16:58, 24 September 2016 (UTC)
You will find most of what you want in the Natural Gas article. Wymspen (talk) 16:57, 24 September 2016 (UTC)
(Multiple EC) it probably should be covered in Pipeline transport however this mostly concentrates on long range transport including in the section on oil and natural gas. However "Distribution pipelines" are mentioned later on. There is also the somewhat weird Central gas system. Nil Einne (talk) 17:31, 24 September 2016 (UTC)
That last article linked by Nil Einne might be a candidate for Deletion if no-one can significantly improve it. Currently its one Reference links to a no-longer-extant web page, and there is nothing in the article to indicate that it's anything more than a theoretical concept with no real-world examples. {The poster formerly known as 87.81.230.195} 90.202.211.191 (talk) 17:41, 24 September 2016 (UTC)
Lack of reliable sources may be an issue, but there's no ban on articles on theoretical concepts. See Project Daedalus, for example. StuRat (talk) 17:55, 24 September 2016 (UTC)
A search on "central gas system" comes up with lots of pages like this, which describe the supply of gas to a site from a central tank - the opposite to the system described in the current article. It's probably possible to put together a new article about such installations, but it does seem as though the existing article needs to be changed. Tevildo (talk) 18:30, 24 September 2016 (UTC)
Note that the article in question appears to have been created by someone with a WP:COI [11] Nil Einne (talk) 19:46, 24 September 2016 (UTC)
That's true - I've therefore PRODded it. It is, of course, still open to anyone to salvage or recreate it. Tevildo (talk) 14:14, 25 September 2016 (UTC)
Thank you all. – b_jonas 13:26, 25 September 2016 (UTC)

## Diseases that attack fungi

We all hear about disease caused by fungi in humans and other organisms. However, are there any specific diseases that afflict fungi like mushrooms? Do any bacteria or viral phages attack fungal cells? 74.71.135.72 (talk) 16:33, 24 September 2016 (UTC)

Mycovirus is the name for viruses that infect fungi. There has also been some study of bacteria that infect fungi especially cultivated mushrooms, e.g. Pseudomonas fluorescens and several other Pseudomonas [12]. This source [13] seems to have a decent but brief overview. Note the list of parasites that affect fungi include fungi. Nil Einne (talk) 17:52, 24 September 2016 (UTC)
I notice that the apparently parallel term Mycobacterium is actually used to designate bacteria that infect mammals (etc?), not fungi, being so named merely because they may grow on culture mediums in a way resembling fungi. What – instead – are fungi-infesting bacteria called collectively? [I see that Nil Einne's link 28 uses "Mycopathogenic bacteria".] {The poster formerly known as 87.81.230.195} 90.202.211.191 (talk) 17:56, 24 September 2016 (UTC)
Note that bacteria which infect fungi may not infect fungi only, so may not be named after fungi in any way. StuRat (talk) 18:02, 24 September 2016 (UTC)
The Serbian source uses mycopathogenic bacteria however the book sources demonstrates it can get complicated what you want to include in this list given the variety of possible effects, e.g. antibiotics that affect fungi, lytic enzymes directed as fungal cell was degradation and so how you define the relationship between the bacteria and fungi. Nil Einne (talk) 18:13, 24 September 2016 (UTC)
(EC) Note the list of parasites that affect fungi include fungi, and these have also been studied both because of their effect on cultivated mushrooms but also apparently for biocontrol of fungi that affect cultivated plans e.g. [14] (if you do a research or even general search you should find lots of these). Mycoparasites appears to be the general term for parasites that affect fungi although it seems to be most commonly used in reference to fungi that affect fungi although that's probably because they appear to be of most interest to biocontrol. And biocontrol of fungal diseases of plants is of far greater interest that diseases affecting cultivated mushrooms given the relative sizes of the markets. Nil Einne (talk) 18:13, 24 September 2016 (UTC)
If I collect and eat mushrooms, would that qualify as me being a mushroom disease? Count Iblis (talk) 21:06, 24 September 2016 (UTC)
No, you would be a mushroom predator and all around fun guy. StuRat (talk) 22:48, 24 September 2016 (UTC)

## What is the basic structure of all amino acids?

Do all of the amino acids have the same structure of H2NCHRCOOH as it's illustrated in the picture that attached? I've read the article but I'm just want to ensure that I understood the answer for my question. (By the way is the letter R in the illustration symbolizes the right side? (if so, why only right side rather than left)

93.126.88.30 (talk) 17:24, 24 September 2016 (UTC)

Answers: 1. No, not all amino acids have that structure. An amino acid has both an acid group and an amino group, but they don't have to be connected through just one carbon atom. Other examples include p-aminobenzoic acid and GABA γ-aminobutyric acid. Even amongst the 20 naturally occurring amino acids used to make proteins, not all have a primary amine group (NH2). For example, look at tryptophan proline.Correcting the error noted below by Adrian J. Hunter.
2. The R does not refer to right but to the side chain. In glycine, the R group is an H atom, R = H. In alanine, the R group is a methyl group, R = CH3. Each naturally occurring amino acid has a different R group. EdChem (talk) 17:53, 24 September 2016 (UTC)
Very often, when people say "amino acids" they're really referring to the 20 proteinogenic amino acids – the 20 amino acids that are commonly used by cells to make proteins. The diagram you've provided illustrates the typical structure of these proteinogenic amino acids. The only one of the 20 that does not quite conform to this structure is proline.
EdChem, my chemistry is rusty, but doesn't tryptophan have a primary amine group? I thought proline was the only proteinogenic amino acid that does not. Adrian J. Hunter(talkcontribs) 08:16, 25 September 2016 (UTC)
Adrian J. Hunter thanks for the ping. You are absolutely correct, tryptophan has a primary amine group and it is proline with the secondary amine structure. I was thinking of proline, and have no idea why I typed tryptophan. I have corrected my error above and noted you pointed it out.  :) EdChem (talk) 12:54, 25 September 2016 (UTC)
There are a number of assumed caveats when we speak of "amino acids". The most important is that yes, we're usually thinking of amino acids with a single alpha carbon that connects the COOH and NH2, which is an important feature for polypeptide structure. Proline is an outlier in being a secondary rather than a primary amine, i.e. an "imino acid".[15] This variation in structure is very important for its role in the organism; it disrupts regular helix structure at designated points, allowing particular parts of proteins to be more accessible or to make turns at desired places, and there is a specific enzyme prolyl isomerase that is needed in order for it not to lock proteins into undesired conformations. I should note that our article recognizes selenocysteine as proteinogenic for a total of 21, even though its incorporation at a nominal stop codon can be somewhat inconsistent; we're not as consistent in recognizing the bacterial pyrrolysine, though in amino acid we actually have a claim of 23, not backed by sources... I should look into that but first I'd prefer to make sure nobody discovered the 23rd while I wasn't looking; I'm sure it's out there... There are also a number of non-proteinogenic amino acids that would often be considered "amino acids" in a narrower sense of things that can be isolated by hydrolyzing a protein, such as hydroxyproline and allysine; these are not added to proteins during synthesis but modified after the protein is made. And then there are lots of other primary amino acids with NH2 and COOH on an alpha carbon like L-DOPA that could go into a protein except biology doesn't want it to (in the case of that one, I think it's too reactive ... I wouldn't let that thing near a ribosome either with two OHs on a phenyl ring! That's expensive equipment there...) We make up these categories for a reason, but since our reasons differ sometimes we have to be very careful which category we're looking at. Wnt (talk) 16:36, 25 September 2016 (UTC)
@Wnt: that NCBI reference is wrong, proline is most definitely not an imino acid, though it can be enzymatically converted to the imino acid (S)-Δ1-pyrroline-5-carboxylic acid by pyrroline-5-carboxylate reductase. An imino acid requires an imine functionality, which proline lacks. The IUPAC Gold Book characterises the term as "obsolescent" for cases like proline, so I accept it was used historically (as our amino acid article recognises) but it is (formally) incorrect and I would avoid it. Further, the 20 standard protein amino acids are a subset of the broader term which definitely does include not only the others you mentioned but also GABA and PABA and many others. As for the claim of 23 in the standard set for protein synthesis, I have seen 22 quoted regularly (the regular 20 plus selenocysteine and pyrrolysine, as you mentioned), but don't recall seeing a claim of 23. EdChem (talk) 04:03, 26 September 2016 (UTC)
@EdChem: Thanks! I have seen the "imino acid" thing so many times I didn't think it could be wrong, even though the term never made a whole hell of a lot of sense. "Secondary amino acid" is more than fine as a replacement term. Wnt (talk) 15:28, 26 September 2016 (UTC)
@Wnt: Regarding #23 (the 20 obvious longterm standards, plus Sec and Pyl), N-formylmethionine (fMet) seems to sometimes/sort-of be considered. Our proteinogenic amino acid and amino acid articles keep wavering on the inclusion of it and their talkpages seem inconclusive. DMacks (talk) 04:36, 26 September 2016 (UTC)

## Tying up a horse in old TV shows and movies

They often just loop the reins once or twice around a post and call it good. The horse would easily be able to get loose. So, did/do people really tie knots around the post, or does the horse just follow the "honor system" and stay put, even if it could easily escape ? StuRat (talk) 18:35, 24 September 2016 (UTC)

The old movies showed short-term actions, the horse was not even unsaddled, it was sort of like parking your car on the street by the store while you shopped (or went to the bar and drank). If they tied reins to a post and the horse spooked and set back on the line, the horse would just break the reins anyway because they were thin leather and the bit would hurt their mouths in the process. The loop system (usually twice around in the real world) put some restraint on the horse (who would not be inclined to leave, as working horses learn to take their rest when they can get it; plus, there often were other horses there) but if all hell broke loose (i.e. fire, bar fight), the horse could get away without breaking equipment (still might step on one rein and break it later, but that's a different problem). If they were going to keep the horse tied for a long time, like overnight, they'd unsaddle and put on a halter and tie with a lead rope. Montanabw(talk) 20:08, 24 September 2016 (UTC)
Another reason they were tied that way is because real cowboys didn't go around carrying halters and lead ropes; they'd snag on brush and cause too many problems. From what I understand, it was hard enough to carry a lariat without it hanging up on stuff and potentially hurting the cowboy. Most Western horses used on ranches were taught to ground tie anyway. The horse would stand completely still if the ends of the reins were dropped on the ground, and remain there until the rider came back for it. That was particularly useful in places where there were no trees or anything to tie a horse to. White Arabian Filly Neigh 21:52, 24 September 2016 (UTC)
I'm amazed that horses can be so well-trained. Few dogs could be trained to that degree. StuRat (talk) 22:21, 24 September 2016 (UTC)
They will wander off eventually if they are completely ignored. Ground tying worked great for stuff like fixing fence or doctoring a calf. Not so good for eating lunch or drinking at the bar. Best images of how the real thing worked are probably paintings of C.M. Russell, he lived the life and was dedicated to authenticity. Montanabw(talk) 22:44, 24 September 2016 (UTC)
I am speculating here. My experience with dogs is that many of them will "sit and stay", so long as the owner remains in sight. Is this the same with horses and ground tying? DrChrissy (talk) 23:53, 24 September 2016 (UTC)
Pretty much. They do think for themselves. Also, horses are inherently a little bit lazy when given the opportunity, so they'd stay tied to the hitching post and not fight a minimal attachment because they could hang with their buddies and sleep! Montanabw(talk) 03:51, 25 September 2016 (UTC)
That has reminded me of an observation. In all those old movies I have never see anyone hitching up his horse and having a kid approaching offering to “mind his 'orse”. Horses back then (relative to a cheap Japanese cars today) cost a lot to fuel and maintain. Some US states hung horse thieves with-out trial. The saddle was the equivalent of a modern-day-lap-top-sitting-on-the-back-seat-just-there-for-the-taking. Yet, the cowboy and western films keep showing horse riders etc. hitching up their horses out side a saloon as if they expect their steeds, saddles and Winchester rifle, will still be there when they return. There were no food stamps back in those days, it was either risking the noose or starvation. So where are all those kids that horse minded? – too bothersome for the film companies to hire perhaps. Also, horses are very strong animals. If the reins don't break, the hitching post will, and as they are pulling, the bit has no effect.--Aspro (talk) 21:57, 24 September 2016 (UTC)
One advantage of snowmobiles is that it doesn't turn into rotting meat & poop if you forget its weekly 15 gallons of fuel one August. Sagittarian Milky Way (talk) 23:05, 24 September 2016 (UTC)
How is this possibly furthering the discussion - I was half tempted to delete the post. DrChrissy (talk) 23:48, 24 September 2016 (UTC)
Horses will die from thirst in storage and leave a half ton of rotten meat etc. in your garage while internal combustion devices will not. They need many gallons of fuel (hay and water) to prevent this. Maybe it was a stupid joke. Sagittarian Milky Way (talk) 00:07, 25 September 2016 (UTC)
Horses do have the advantage that those able to put in the substantial work involved can (on average) count on getting new ones for free. I'm not sure I'd count them out just yet. I'm seeing mention of horses, at least momentarily, cracking 55 miles an hour; no matter how slowly ordinary breeding [16] may improve them, I would not rule out more significant improvements from genetic engineering when it is done at a level of sophistication not currently imaginable. So I wouldn't rule out the day when horses that require much less maintenance and which can reach higher speeds with greater burdens can actually challenge the traditional automotive industry - especially if sinister trends like the tracking and I assume eventually restriction of what can be done with self-driving cars become extreme enough to drive a search for loopholes. Wnt (talk) 17:17, 25 September 2016 (UTC)
I'm rather skeptical. Genetic engineering can't overcome the inherent limitations of biological systems. Even if you could get a horse to go faster than that, it would die, along with any passengers, if it fell at such speeds, making it an extremely dangerous form of transportation. StuRat (talk) 17:43, 26 September 2016 (UTC)
Aspro, I'm a little unconvinced that the bit would have no effect. That might be true if the horse was backing up in a straight line, but if the horse was reacting to something that spooked it, their head would also be moving side to side and so the bit would likely cause damage. DrChrissy (talk) 22:05, 24 September 2016 (UTC)
This behaviour doesn't need the animal to consciously evaluative the situation. Bits don't control by producing pain but by exerting pressure which the animal quickly comes to understand. If the animal gets spooked and finds its natural response produces pain from the bit... doesn't it naturally stops witching its nose this way and that and just move forwards or backwards? You can see this same behaviour in little children that get confronted by two bullies. Second response (after witching) is to either try to forces their way through them rapidly or draw away rapidly. Even a <14 hands pony can break a hitching post like match-wood. Result: kid doesn’t receive any punches in his escape and 'orse doesn’t doesn't get injured either. However, you may well have come across equines with mouth injuries. What were the exact circumstances (if that doesn’t break patient confidentiality)? The OP is asking about the likes of Roy Rogers hitching up in films. Montanabw below talks about 'modern' nylon reins, 'modern' unbreakable hitching posts, and curb bits that the cow drivers used ( the modern day equivalent of the Ford Mustangs and Toyota pick-up trucks). Back in the day of the Wild West owners put their horse first and feed and watered them first after a long ride because their livelihood depended upon that animal. Also, if a driver (cowboy) did hitch up in front of a saloon with a curb bitted animal, isn't that all the more reason to hire a horse minder? No nylon reins, no unbreakable hitching posts in those days. For the film buffs out there. Have you ever seen horses being hitched with curb bits? Rowdy Yates (Clint Eastwood) in Rawhide (TV series) was a driver. Yet has anybody out there spotted a curb bit? One doesn't just get a horse shod and expect 20,000 miles out of it. It need to be re-shod about every three months. Also horses do not even achieve 40 miles to the gallon every day. One can just to forget to wash the car for a few weeks but if your livelihood depends on a horse, it gets groomed regularly and any hitching post provided by a general store, saloon or whatever that is not suitable causes the owner to lose custom. The OP is asking about horses as depicted in films.--Aspro (talk) 00:41, 25 September 2016 (UTC)
Aspro, you've never seen a horse tied hard and fast set back and hit a well-set post; it's damn scary. And while a cheap rail might break if tied with a solid rope, only an idiot ties a horse to a flimsy object. (Idiocy happens, but more often, the rail or post comes loose and the horse drags it off at a dead run). Usually, a horse sets back but gives up quickly if they aren't thrown into a worse panic by pain. If they fight the rope, more often the rope or the halter breaks. Montanabw(talk) 03:51, 25 September 2016 (UTC)
First off, reins are single-thickness pieces of strap leather, no more than about 3/4 of an inch across and at the most maybe 1/8' to 1/4" thick. Even a 500-lb pony can break them. But, the bit is in the mouth, which is sensitive, so even breaking reins hurts like heck and that actually increases the panic of the horse. I was chatting at my talk that I've seen people tie horses up with a bridle with nylon reins (modern material, doesn't break easily) and set back, resulting in their tongues being injured. Even if a horse sets straight back, a curb bit in particular will do some nasty things. The hitching post usually will NOT break... not if properly constructed. Montanabw(talk) 22:44, 24 September 2016 (UTC)
When I was learning to ride, I seem to remember that there were tying hoops embedded in concrete walls of the stables. However, there was a loop of string (not rope) attached to this which the reins or halter were tied to. Obviously this string was the weak link in the chain and the intention was this would snap before the horse was (seriously) injured. DrChrissy (talk) 19:40, 25 September 2016 (UTC)
There's A Love Knot In My Lariat Wilf Carter Strawberry Roan Bus stop (talk) 23:54, 24 September 2016 (UTC)
Whilst the films obviously have a lot of poetic licence, we were told when I was a young Scout that they're based on a highwayman's hitch.--Phil Holmes (talk) 10:53, 25 September 2016 (UTC)
On the bits, yes, a curb bit was what they used back then. A snaffle bit was seen as fit only for young untrained horses, plow horses, or carriage horses. Cowboys also rode one-handed most of the time, and the curb bit makes that easier, as a snaffles have the tendency to collapse in the middle when the rein is lifted (which is what you do to ride one-handed, lift the rein and touch it to the horse's neck in the way you want it to go, as opposed to pulling the horse's head around in two-handed riding.) White Arabian Filly Neigh 21:11, 25 September 2016 (UTC)
So as not to confuse. Have just watch a few clips of Rawhide (TV series) etc. (on youtube), where the main cast were all competent horsemen. They do appear to be using curbs -when out on the range. As you know Lassie was not one dog but several nearly identical trained collies. Each trained to excel for different scenarios. Same with horses and actors. Actors who may be not competent horsemen (which probably applies to most) in close-up just sit on their steeds whist delivering their lines. When they are galloping after the bad-guy, its always long-shots with a stunt-double in the saddle ( this is often insisted upon buy the insurance underwriter if it is a famous actor.) So the hitching up shots and close ups are often done with a trained horse with a snaffle. Hope I haven't destroyed anyone's delusions here about film reality vis. real life and the OP's question was about films (or as its about film should that be illusions). Also, has anyone noticed that every time cowboys, etc, are sitting around a camp-fire, there is always a wooden barrel there. Why...? Yes, you've guessed it. The hourly cost of filming is so high that they can't waist time kindling a fire and maintain continuity (fiction) over many takes and retakes. The fire has to appear the same all the time. Therefore, the barrel is were they hide the gas cylinder which fuels the fire and the wood on the fire isn't real wood either. --Aspro (talk) 20:00, 26 September 2016 (UTC)
This reminds me of some morning talk show (The Today Show ?) where their "expert" said that the proper way to start a fire in the fireplace was to put the large logs at the bottom, for stability, and the kindling on top. Needless to say, nothing happened, until they came back from commercial and had a blazing fire. I tried to spot the empty gasoline can nearby. :-) StuRat (talk) 00:12, 27 September 2016 (UTC)

# September 25

## Absolute zero

Why is it impossible to reach absolute zero? GeoffreyT2000 (talk, contribs) 00:23, 25 September 2016 (UTC)

Our page says:The laws of thermodynamics dictate that absolute zero cannot be reached using only thermodynamic means, as the temperature of the substance being cooled approaches the temperature of the cooling agent asymptotically. A system at absolute zero still possesses quantum mechanical zero-point energy, the energy of its ground state at absolute zero. The kinetic energy of the ground state cannot be removed. What more do you need?--86.187.169.34 (talk) 01:00, 25 September 2016 (UTC)
Another way to explain this is by pointing out that to cool something you either need to have something cooler or by letting the system perform work, the former s not going to be useful to reach 0 K and the latter method will in the best case conserve the entropy of the system while at 0 K the entropy is zero. Count Iblis (talk) 02:55, 25 September 2016 (UTC)
Absolute zero. AllBestFaith (talk) 11:31, 25 September 2016 (UTC)
I think this needs a better answer - unfortunately a better answer than I am prepared to give. Bear in mind that, say, the thermal oscillation of a diatomic molecule is quantized. [17] In theory, a single molecule of hydrogen could possess no extractable energy of this kind, hence be at 'absolute zero' in this sense. More surprisingly, there also seems to be a quantization of the rotation of such a molecule, imposing rotational transition, so that source of energy (relative to a bulk material) too could be depleted. If we can truly bring two molecules of hydrogen to absolute zero, is any mode of interaction between them also quantized such that it can be brought to genuinely zero? I'm thinking yes though I don't know. And if two, why not three, five, a hundred? I am not sure whether a substance can be brought to such a low temperature that its probability of being genuinely at absolute zero becomes significant, though of course, given the number of molecules, that requires a very low temperature. Wnt (talk) 16:48, 25 September 2016 (UTC)
To bring a system to 0K you need to evolve its quantum state to the ground state which requires a sort of Maxwell's Demon set up involving extracting the information that describes the exact quantum state and moving that to another system (e.g. the Demon's memory). There is no other way because the fundamental laws of physics are unitary, which means that two different states cannot evolve to the same final state. So, you cannot have a generic procedure that involves manipulating only a few of the many parameters of an isolated system (containing the gas that we want to cool plus and supportive systems allowing that to happen). If you can make it work for one of the possible microstates of the gas, then it cannot work for another microstate, because that other state must necessarily evolve to another final state. The pigeonhole principle thus applies, you need to move all of the information that defines the exact physical state of the gas to anpther system or else the procedure will not work for some initial states. Count Iblis (talk) 19:07, 25 September 2016 (UTC)
This is probably a very insightful answer, but I'm having some trouble swallowing it. The whole issue with Maxwell's demon, as I recall, is that the information requires a certain amount of energy input, but here, we kind of expect any refrigeration we set up to require power. As for the pigeonhole principle, well, I'm not understanding it. I would think that there is no physical law against bringing a chamber arbitrarily close to absolute zero. So if I have a chamber full of snowflakes that are 1, 10, 100, 1000, 10000 molecules in size, I would think that as I turn down the temperature, after a while some of the 1-molecule clusters will have zero point rotation and harmonic oscillation; then as I go lower, the same will be true of 2-molecule, then 10-molecule, eventually 10000-molecule clusters. I won't know which is at absolute zero with certainty unless I come up with some clever way to take their temperature without heating them at all, but some of them ought to be, right? Wnt (talk) 15:49, 26 September 2016 (UTC)
But apparently it's possible to go below 0K? See: "Quantum gas goes below absolute zero" in Nature. --Hillbillyholiday talk 19:25, 25 September 2016 (UTC)
See Negative temperature. It's a confusing numbering system (and I don't think Nature explained it very well) but a negative temperature is actually higher than a positive one - to reach a negative temperature, you don't have to go lower than 0 K but rather higher than infinity K. If temperature is negative, the majority of particles are in a higher energy state. Keep going, you'll reach "negative absolute zero", when all the particle are in the highest state. Smurrayinchester 20:22, 25 September 2016 (UTC)
When we talk about negative temperature, the definition of temperature is not "average kinetic energy of the particles." Understanding the definition is the key to understanding the situation where negative temperature is possible.
In most simple conditions, the definition of temperature works out such that the average kinetic energy of each particle is exactly equal to certain other statistical measurements. So, we can freely switch between definitions. In exotic scenarios where we have extremely high energy per particle, this exact equality breaks apart - and the statistical measurement ceases to correspond to the energy-per-particle. Now, we can call the temperature negative, if we use the statistiscal measurement; or we can call the temperature very large and positive, if we use the energy-per-particle measurement; and we can quibble endlessly over which definition is more "correct." The best way to proceed is to recognize that each methodology for defining temperature has a different purpose; grab a good book on statistical thermodynamics; and appreciate that these "negative temperatures" are a mathematical oddity in the statistics of very high energy matter.
Nimur (talk) 21:12, 25 September 2016 (UTC)
Why is it impossible to reach absolute zero?
I think previous answers have been great, but today I started meditating on this question a little more, and here's what I've got for today, sort of riffing on Mach's principle. My intent is to quickly summarize the answer in an intuitive way, without getting too technical. If you really want a better and more technical answer, a good book is Stowe's thermal physics book, which I consider to be one of the best books on pure physics at large.
Temperature is the ability for a particle to do work.
Work can be performed by colliding - especially inelastically - with another particle.
As long as there exists another particle, anywhere in the universe, who is not absolutely stationary with respect to your test particle, your test particle can, in principle, collide with it, and do work.
If you think of the temperature as the average kinetic energy, which is derived from the average velocity of the particle, then the only way to get the temperature to zero is to make the test-particle stationary - but because there is no universal reference frame, with respect what reference can we measure the velocity of the test particle? We sort of need to start expanding the volume we are considering, and compare our test-particle's velocity to the statistical average position of all other particles in an ever-expanding volume, up-to-and-including- the entire universe.
You can't slow a particle to zero velocity without slowing the velocity of every other particle, everywhere, also to zero, measured relative to your completely-arbitrarily-selected particle.
This is not a particularly precise formulation of the problem, but maybe it will give you some insights into how temperature gets defined. Ultimately, temperature is a statistical measure. As you approach zero temperature, your statistics get less and less relevant unless your particle population becomes bigger and bigger. This is why we can, in a laboratory, make a small clump of matter get really close to zero temperature; but we can't get it all the way to zero.
Nimur (talk) 21:28, 25 September 2016 (UTC)
The "average kinetic energy" formulation is not a bad conceptual place to start to get a mental image, but unfortunately a lot of people over-internalize it. Without special pleading and creative bookkeeping, it applies only to monatomic ideal gases. I have to object to your claim above that it works in "most simple situations", when actually it doesn't even work in solids. --Trovatore (talk) 15:25, 26 September 2016 (UTC)
Trovatore makes a very fair point; if anything, it highlights the difficulty in trying to explain thermodynamics without using complicated technical language and equations. It's difficult to be correct, precise, and easy to understand.
For the record, I just pulled three physics books off my shelf and got three differing qualitative descriptions for which definition of temperature is "most fundamental." My plasma book, Bittencourt, insists that mean kinetic energy is the correct definition, but further insists that because kinetic energy may exist in many different modes of motion, you must therefore use multiple different temperatures to describe each separate energy-mode for the same substance... so a solid may have a crystal lattice temperature and an electron temperature and it might even also have a distinct phonon-temperature for each eigen-phonon you can decompose its vibrational modes into...
I actually like this approach, because it keeps the definition simple at the expense of making the application of the principle quite difficult. (Well, ...it becomes tedious, more than it becomes difficult - and it's a great example of an application where a computer method can save the day by automating tedious-but-straightforward bookkeeping!)
My other book, Stowe, uses the entropy definition that we all know and love - making the explanation very complicated, but the calculation of temperature becomes trivial.
Suffice to say that there's a little bit of domain-specificity with respect to which definition one would prefer to use.
Nimur (talk) 15:42, 26 September 2016 (UTC)

# September 26

## Sub-Zero Kelvin

Hypothetically speaking, if by absurd even subatomic movement (as opposed to just inter-molecular movement) were to completely and utterly cease, would we reach sub-zero Kelvin ? If so, then what negative value, in Kelvin, would that be ? — 79.118.172.79 (talk) 09:35, 26 September 2016 (UTC)

We have an article about negative temperature. DMacks (talk) 09:43, 26 September 2016 (UTC)
Indeed we do... Unfortunately, what we don't have, is a Physics-to-English interpreter. :-) — 79.118.172.79 (talk) 10:17, 26 September 2016 (UTC)
The misleadingly named physics concept of negative temperature isn't actually about states colder than absolute zero. Rather this concept of negative temperature refers to configurations that are thermodynamically unnatural and unstable in such a way that they will always lost energy when brought into thermal contact with normal systems. As the article says, this means such states are in a sense hotter than all positive temperatures. A system possessing "negative temperature" can be constructed artificially by explicitly manipulating the microstates of the particles, but can never be reached by only adding or removed heat. Dragons flight (talk) 12:04, 26 September 2016 (UTC)
If it is possible to remove energy and further reduce the movement, then you haven't gotten to absolute zero yet. Once you reach absolute zero, it is no longer possible to remove energy via any process. The physical laws of quantum mechanics are such that even at absolute zero the motion doesn't actually cease (the so-called zero point energy), but this residual motion is not something that can be removed. To ask what if "movement... utterly cease" is essentially to ask, "if I did something impossible, what would happen". Its not a question that permits a natural answer. Dragons flight (talk) 12:04, 26 September 2016 (UTC)
I am aware of the fact that such cessation (or deceleration) of motion is not (yet) achievable, but is there really no purely theoretical framework which, when extrapolated to out-of-range values, would yield certain results (as untestable and hypothetical as they might be) ? — 79.118.172.79 (talk) 12:15, 26 September 2016 (UTC)
It would be an explicit contradiction of the uncertainty principle. It is not just "not yet achievable", rather it is explicitly forbidden by the laws of physics as we presently understand them. Dragons flight (talk) 12:28, 26 September 2016 (UTC)
It is debatable whether or not our present understanding of the laws of physics includes the fact that the uncertainty principle holds in the fundamental sense described by the Copenhagen interpretation. If you have a consistent picture of hidden variables, couldn't you argue that this theoretical limitation could be surpassed in the way the OP is looking for. (Although, you would have to negotiate all the other constraints on those theories.) I'm not sure you'd find many physicists willing to bet on this possibility though. 129.234.195.173 (talk) 15:14, 26 September 2016 (UTC)
No, it has nothing to do with one's interpretation of quantum mechanics. All the interpretations predict the same observations in any case. It's a fundamental consequence of the wave nature of matter (let's see if that comes up blue). --Trovatore (talk) 15:18, 26 September 2016 (UTC)
Indeed. As we unfortunately discovered in the preceding discussion, it seems that you can only pick two of three adjectives for the explanation: simple, precise, correct. Two of three, maximum. If you oversimplify, you lose either precision or correctness; if you overspecify, you lose either simplicity or correctness; .... Ultimately, if you want a completely correct understanding, there is no substitute for lengthy, careful, formal study of these topics.
I'm a bit crochety, but I have generally found that as soon as the word "interpretation" appears in a discussion of quantum physics, it is statistically certain that all subsequent discussion is about to rapidly diverge from real, actual science. I'd love to see an equation that captures and quantifies this type of evolution with respect to time.
Nimur (talk) 15:54, 26 September 2016 (UTC)
Really, you've never heard any physics professors talk about interpretations of quantum mechanics? I take your point that people casually and ignorantly abuse quantum weirdness all the time, but it's not like real scientists don't talk about interpretations. SemanticMantis (talk) 16:52, 26 September 2016 (UTC)
I won't speak for Nimur, but I don't think "real scientists care about it" is the same as "it's really science". Real scientists do, and IMO should, think about metaphysics, but that doesn't make metaphysics "science" sensu stricto.
Among the criticisms of metaphysics is that it's not science, but to me, this is not really a criticism unless you adhere to scientism, which I don't. There are other eliminative approaches to metaphysics, like positivism, but in my judgment none of them are an adequate way of thinking about the world. --Trovatore (talk) 17:04, 26 September 2016 (UTC)
It's a mixed picture within the physics community, the condensed matter people tend to take the view that it's waste of time to discuss interpretations, while the people doing more fundamental research tend to be more open about the relevance of such discussions. The often made statement that the different interpretations of QM are equivalent is not strictly speaking correct. E.g. Bohm Interpretation becomes ordinary QM only after assuming quantum equilibrium, and MWI and Copenhagen Interpretation are not equivalent either, Copenhagen predicts non unitary time evolution for sufficiently large isolated systems, while Copenhagen can be falsified if you could perform a thought experiment contemplated by David Deutsch involving simulating an observer using a quantum computer who performs a reversible measurement. Count Iblis (talk) 17:25, 26 September 2016 (UTC)
I wasn't trying to imply that interpretation is broadly considered a type of science, sensu stricto, merely that real physicists can and do talk about interpretations and strict science, all in the same paragraph. (Also, "what scientists do" is a perfectly reasonable definition of science that is floated in some contexts, and certainly interpreting mathematical expressions of research findings for real-world implications is a big part of many scientists' jobs these days. ) SemanticMantis (talk) 23:24, 26 September 2016 (UTC)

## Galapagos Rift and Chemosynthesis

In "Mapping the Deep" by Robert Kunzig, the author gives credit for the discovery of the Galapagos Rift and first observation of chemosynthesis to G Evelyn Hutchinson in 1979. The Wikipedia article on the Galapagos Trench doesn't mention its discovery. The article on Hutchinson doesn't mention the Galapagos Rift. The article on chemosynthesis gives credit to Colleen Cavanaugh for its discovery and doesn't mention Hutchinson. Was Kunzig writing fiction?Bobgustafson1 (talk) 16:19, 26 September 2016 (UTC)

The 1979 expedition included Childress, Ballard, and Karl, according to Karl's bio at PNAS. I can't be sure Hutchinson wasn't there. Cavanaugh proposed the mechanism, and later showed it to be accurate. That's not really what I mean by "discovery", but designating who gets credit for a discovery is always a bit murky.
Here [25] is a research paper from 1982 summing up the state of the art at that time. If nothing else it has a highly relevant ref list. Note the key citations to Childress, Cavanaugh, and Karl, while Hutchinson is cited only for a more general paper.
But 1979 can't be the discovery of the rift: Hydrothermal_vent#Discovery_and_exploration tells us Jack_Corliss led an expedition there in 1977. SemanticMantis (talk) 16:44, 26 September 2016 (UTC)
I am not sure that such a rift exists. Ruslik_Zero 19:34, 26 September 2016 (UTC)
Why does your surety matter? You are not a reliable source... --Jayron32 20:06, 26 September 2016 (UTC)
Here's some more evidence that nobody discovered the Galapagos rift in 1979. A 1976 research article says
Herron and Hertzler (1967) is a Science paper that says
Emphasis mine, but I think that's a good indicator that Hunzig got some important bits wrong, or worded the claims confusingly.
It seems much more reasonable that the 1977 submersible mission was the first time a human looked at a critter that was using chemoautotrophic endosymbionts. Here [28] is a web version of 25th aniversary CD put out by WHOI, so it will be a pretty reliable reference on the topic. It lists several members of that mission, Hutchinson not included. Tellingly, it says "No one imagined any need for a biologist on board." In 1977, Hutchinson was one of the leading ecologists in the world, and had he been present, I think he'd have been mentioned.
In sum, this indicates to me the Kunzig book either has some serious factual errors or very bad wording, without a direct quote, it's hard to say. SemanticMantis (talk) 21:36, 26 September 2016 (UTC)

## Can acids be oxidized?

Can acids be oxidized? — Preceding unsigned comment added by 31.4.156.140 (talk) 00:42, 27 September 2016 (UTC)

Some of 'em, sure. You want to narrow down the question a bit? Is this homework? --Trovatore (talk) 00:55, 27 September 2016 (UTC)