Wikipedia:Reference desk/Archives/Science/2008 June 25

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June 25

Icarus-style 'wings'

I'm looking for Icarus-style "wings" for flying but I'm not having too much luck. Am I missing something? —Preceding unsigned comment added by 82.120.108.31 (talk) 00:53, 25 June 2008 (UTC)

You are having a minor problem with the laws of physics: icarus-style wings will not work in earth gravity ant earth atmospheric pressure. Look a Gossamer Condor for the first human-powered flight. Look at paraglider if you are not an Olympic-class athelete. -Arch dude (talk) 01:31, 25 June 2008 (UTC)

I don't think you'd find this useful, but you might find it interesting: Gryphon (parachute system) --Shaggorama (talk) 02:20, 25 June 2008 (UTC)

Or, more generally, Wingsuit flying. Mangostar (talk) 08:17, 25 June 2008 (UTC)

Or for a more competitive version (where competitive means drinking lots of beer, tying cereal boxes to your arms and jumping off a jetty while people watch), Birdman Rally. Confusing Manifestation(Say hi!) 23:00, 25 June 2008 (UTC)

progesterone intake

is it dangerous to use a product like bouniful breast for breast growth ? supposedly this product is progesterone based. i read the progesterone article and it seems that progesterone is beneficial in a lot of cases. —Preceding unsigned comment added by 75.69.26.8 (talk) 02:16, 25 June 2008 (UTC)

Wikipedia does not provide medical advice. Consult a doctor, pharmacist, or other medical professional. — Lomn 04:30, 25 June 2008 (UTC)

All drugs are prescribed for different things, and "beneficial" may be good for something, but bad for another. Talk to your local pharmacist, if you're interested about a drug. Mac Davis (talk) 17:11, 25 June 2008 (UTC)

Electromagnetic relay

How coil current is related to pull-in and drop off voltage? —Preceding unsigned comment added by 122.166.11.179 (talk) 04:45, 25 June 2008 (UTC)

Relays and solenoids take a certain amount of electromagnetism to "pull in". This is usually stated in terms of ampere turns. That is, a given highly-sensitive relay may require (say) "10 ampere turns" to pull-in/pick-up. After that, it's all Ohm's law. For that hypothetical "10 ampere turn} relay mechanism, we could design a ten-turn coil and the relay will pick-up if you apply enough voltage to flow 1 Ampere through that ten turn coil. Or we could design a 1000 turn coil and the relay will pick-up if we apply enough voltage to flow 0.01 Amperes through that coil. Because this second coil is wound with many more turns of probably-finer gauge wire, it will have a lot more resistance than the first coil so it will probably require substantially more voltage than that first coil. But to pick-up the relay, both coils have to manage to produce the 10 ampere turns of electromagnetism that the basic mechanics of the relay require.

Pick-up takes more electromagnetic force than that required to hold the relay picked-up. (You need to overcome static friction and there's usually an air-gap in the magnetic circuit; this air-gap usually closes once the relay picks-up.) If the current is then reduced, you eventually reach a lower value (sometimes, much lower) value of electromagnetic force where the spring action in the relay finally causes the relay to drop-out.

Atlant (talk) 15:02, 25 June 2008 (UTC)

Nothingness

Is true nothingness (like before the universe began) the same thing as empty space. If not, whats the difference? —Preceding unsigned comment added by 79.76.249.57 (talk) 04:55, 25 June 2008 (UTC)

Empty space still has volume and time and is governed by the laws of physics. The singularity that was present before the Big Bang had none of these properties; see Timeline of the Big Bang. Because the laws of physics were not applicable during the Augustinian era (just as dividing by zero yields no result), extrapolating to that time period is meaningless. --Bowlhover (talk) 05:49, 25 June 2008 (UTC)

You are making an assumption that can't be tested. Maybe the Big Bang is the start of time and space, and maybe it isn't. The simple fact of the matter is that nothing we can measure is able to tell us definitively about "before" the Big Bang. Models like the Big Bounce would suggest that things existed before the Bang, but we have no meaningful way to test those theories. Dragons flight (talk) 06:04, 25 June 2008 (UTC)

How does the Big Bounce theory work with regards to time? Is there a continuous flow of time from one universe to the next? If not, then you need quotes around the second use of "before" as well! --Tango (talk) 14:57, 25 June 2008 (UTC)

Vacuum state -- Consumed Crustacean (talk) 05:51, 25 June 2008 (UTC)

"There was nothing before the universe" just means that there wasn't a before the universe, not that pre-universe space was empty. Similarly, saying "I see nothing out of the back of my head" means that I can't see out of the back of my head, and is very different than saying "I see pitch black out of the back of my head". Another example is the difference between a computer that has no hard drive, which truly has nothing in its memory, and a computer with a blank hard drive, which has several gigabytes of zeros in its memory. I suppose the best way to describe it is that empty space means a medium in its default state, where nothing means no medium. — DanielLC 18:16, 25 June 2008 (UTC)

I vaguely remember an author of one of my physics books lamenting over explaining this. His analogy was to ask "what's north of the North Pole?" It's not there is nothing, but there is no "north of the North pole" ie not even nothing. What was before the big bang is similar (according to these theories anyway). Kind of a Koan-type enlightenment thing going on there. --Bennybp (talk) 06:53, 26 June 2008 (UTC)

Nordic walking, also known as ski walking, pole walking or fitness walking

Does anyone know where and/or can point out to where I could get phthalate and bisphenol A free Nordic walking, ski walking, pole walking and/or fitness walking poles?68.148.164.166 (talk) 08:30, 25 June 2008 (UTC)

I wouldn't care about softeners in sports gear used outdoors, as they evaporate into the surrounding air and thus won't harm you. If you're perfectionist you would store them at home somewhere airy. Rather, I'd worry more about good nutrition. --Ayacop (talk) 09:05, 25 June 2008 (UTC)

Unfortunately softeners with bp >200C do not just evaporate.87.102.86.73 (talk) 17:47, 25 June 2008 (UTC)

A penetration through the skin of the hand of significant amounts of these compounds is highly unlikly.--Stone (talk) 10:00, 25 June 2008 (UTC)

Especially since you normally wear gloves for Nordic skiing. --Tango (talk) 14:51, 25 June 2008 (UTC)

Please don't ask the same question on multiple Reference Desks. -- Coneslayer (talk) 12:13, 25 June 2008 (UTC)

(Actually, it looks like your intent was to move the question to a more appropriate desk. That's fine, but you should make it clear to people here that you've asked it elsewhere and received some responses, either by providing a link to the old question, or copying the responses you've gotten. That way, people won't waste time duplicating previous answers.) -- Coneslayer (talk) 14:58, 25 June 2008 (UTC)

Rhesus macaque with a tumor?

click here to get a full resolution version of this photo

I'm not very familiar with the biology of the rhesus macaque, but it seems to me that this monkey has tumor on it's neck. Can anyone confirm or deny this? Mieciu K (talk) 09:48, 25 June 2008 (UTC)

Why should it not be possible that a macaque has tumor?--Stone (talk) 10:01, 25 June 2008 (UTC)

Monkey medical advice? :-) It could be a goitre, or maybe just a trick of the eye; they are pretty hairy and that may just be a clump of fur. Fribbler (talk) 10:14, 25 June 2008 (UTC)

I'm not questioning the fact that monkeys can have tumors. I have no medical experience so I want to get some independent opinions before I decide if I should insert "this monkey has a tumor" text into the description of this photo on Wikicommons. Mieciu K (talk) 10:18, 25 June 2008 (UTC)

You could say "this monkey appears to have a tumour, possibly a goitre." Since from the full resolution pic, it really does look like it, but we can never be totally sure. Fribbler (talk)

Is there a possibility it's a vocalization sac? Franamax (talk) 19:19, 25 June 2008 (UTC)

Should I be concerned about meeting with someone with hepatitis C?

I’m going to meet with someone in a very near future, and who is known to have hepatitis C. I can’t avoid this meeting any longer, is there anything I can do to protect myself? Or, is it dangerous to meet with this person? Chailai (talk) —Preceding comment was added at 11:49, 25 June 2008 (UTC)

(edit conflict) My advice? Buy a shotgun and binoculars TODAY. Scope them out, and when they start approaching just go into Zombie Attack mode. It's your LIFE on the line. Do what you gotta do. —Preceding unsigned comment added by 82.120.108.31 (talk) 12:14, 25 June 2008 (UTC)

Can I just clarify for the OP that this answer is complete nonsense.. — CycloneNimrod ^talk?_contribs? 12:20, 25 June 2008 (UTC)

Hepatitis C is spread through blood-to-blood contact and also unprotected sexual intercourse. Avoid those things and you're not at risk of catching the disease as it cannot be spread by saliva or any of the other germ-spreading mechanisms (e.g. coughing, sneezing etc) — CycloneNimrod ^talk?_contribs? 12:12, 25 June 2008 (UTC)

Hence the binoculars. In light of the fact that the disease is spread thru blood it is very important to be out of splatter range. —Preceding unsigned comment added by 82.120.108.31 (talk) 12:17, 25 June 2008 (UTC)

Oh you don't have to bother with binoculars either ;) — CycloneNimrod ^talk?_contribs? 12:20, 25 June 2008 (UTC)

Thank you kindly for your response. Like many, I like to help people but do not wish to get sick from doing that. Again, Thanks. Chailai (talk) 23:49, 25 June 2008 (UTC)

You could also ask that person about any precautions you should take, he or she might be more familiar. You can ask on phone, you probably can't be infected during that (or at least that's what the Golgafrinchans thought). – b_jonas 12:42, 27 June 2008 (UTC)

Let's apply some common sense here. If a person were diagnosed with a condition that was (a) dangerous and (b) so contagious that it could be passed on by normal social contact, don't you think they would be quarantined by the appropriate authorities ? Gandalf61 (talk) 13:05, 27 June 2008 (UTC)

I stalked through wiki with my shotgun and scoped this section[1]. Julia Rossi (talk) 13:20, 27 June 2008 (UTC)

Medical profession

Is there a contry where medical profession are not regulated and anyone can claim to be a Phisician? GoingOnTracks (talk) 12:29, 25 June 2008 (UTC)

The medical profession in Somalia is unregulated. But the same goes for absolutely everything in that country at the moment. Fribbler (talk) 14:47, 25 June 2008 (UTC)

Why? Are you trying to apply the knowledge of medicine that you obtained in here? 80.58.205.37 (talk) 16:05, 25 June 2008 (UTC)

That's a bit too much speculation don't you think? The OP could simply be curious. — CycloneNimrod ^talk?_contribs? 16:13, 25 June 2008 (UTC)

Indeed; we shouldn't assume he's GoingOnQuacks. Fribbler (talk) 16:16, 25 June 2008 (UTC)

No, I was not trying to pretend being a doctor somewhere in the 3rd world or play one on TV. It was just curiosity. GoingOnTracks (talk) 16:50, 25 June 2008 (UTC)

Australia? Though regulated, it seems anyone can claim to be one unless they don't get a way with it. see allegations and charges against Jayant Patel. Julia Rossi (talk) 03:18, 26 June 2008 (UTC)

I live in the US and every now and then I see expose reports on local news programs about unliciensed medical practitioners who operated a private practice for years before it was revealed that their degrees were fraudulent. The fact that the medical profession is regulated does not necessarily prohibit folks from making false claims, though it makes it more difficult and provides a few consequences. --Shaggorama (talk) 19:31, 26 June 2008 (UTC)

Anyone can claim to be a "doctor" in the UK without legal recourse. When health minister, Gerald Malone said that the title "doctor" was largely defined by common usage, but that "physician, doctor of medicine, licentiate in medicine and surgery, bachelor of medicine, surgeon, general practitioner and apothecary" did have special protection in law. Therefore nothing is stopping you from adding the title "Dr." to your name at any time. However, you may not claim to be a registered medical practitioner or any variation thereof for financial gain, or attempt to offer medical services under a title (unless you are registered). If you do you can be prosecuted. Rockpocket 05:35, 27 June 2008 (UTC)

I believe that is the same everywhere. Here in the U.S., we have PC Doctors, Rug Doctors, Tire Doctors... The name "doctor" has no clinical or legal meaning. Physician, surgeon, licensed are examples of terms that do have a clinical and legal meaning. -- kainaw™ 15:32, 27 June 2008 (UTC)

What distance is travelled on foot by an average person between birth and adulthood?

I just can't think of ANY way to estimate this. Any help? —Preceding unsigned comment added by 82.120.108.31 (talk) 12:31, 25 June 2008 (UTC)

Well, how far do you think the "average person" travels on foot in one day? You don't have to be exact—that's the point of estimating. Do you think it's 10 miles (16 km)? No, that's surely too much for an average. How about 100 yards/metres? No, that's not enough. So you might decide that a reasonable daily average is a quarter mile, or a mile, or something like that. Now we have to multiply that by the number of days, but surely our average child isn't walking from birth, and even once they learn to walk, they won't walk very far. So maybe we say there's 12 good walking years between birth and adulthood, and get (12 yr)*(365 days/yr)*(0.5 miles/day) = 2190 miles. Call it 2,000 miles. If you make different assumptions, you might get 1,000 miles or 5,000 miles, and that's OK. Now, how could we do better? Well, it might help to pin down whether we're talking about a sedentary kid in the suburbs, an African villager 5 miles from the drinking well, or someone in between (say, a New Yorker who actually walks to get places). We could also try to find relevant statistics—a couple of years ago, there was a trend of wearing a pedometer to record the number of steps you took each day, with the intent of meeting some goal. I bet those came with statistics on the average number of steps people took. I hope you see that the idea of estimating is that it's OK to start with a crappy estimate. Get some idea of what the answer should be. Rule out insane answers, like walking 100 miles a day. Then try to do a little bit better from there. If you start out by worrying that you're going to be "wrong", then you may be paralyzed by fear and not get anywhere. Estimation is all about letting yourself be a little wrong, to get an answer that's good enough. See also Fermi problem. -- Coneslayer (talk) 14:14, 25 June 2008 (UTC)

Edit conflict, comment: It depends on how you define the average person. If you consider yourself as average then you could base the estimates on your personal experiences. The best way is to calculate a value per year. Babies don't walk so you can rule out year 1. I would say year 2-5 a child would walk 1-2 miles a week, including just general activity like toddling around the house. Years 5 - 10 I would say this would be more like 10 miles per week. When the child goes to school they might walk up to 1-2 miles per day. This model doesn't take into account long trips and assumes the same activity everyday, but I think the innaccuracies will cancel. So we have (2[miles]*52[weeks])+(10[miles]*52[weeks])+(2[miles]*7[days]*52[weeks]) = 1352 miles. The best way though to get really good estimate would be to conduct a survey across a number of different age groups. Jdrewitt (talk) 14:28, 25 June 2008 (UTC)

Interesting. There's a campaign in the UK to "take 1000 10000 steps a day". Let's say you do, and one step is say 0.5metres. The average age of death in the UK is about 80. You're probably fully-mobile for 70 of those; since 1000 10000 steps and 0.5 m are probably both on the above-average side, assume you walk no distance at all during the 10 less-mobile years. Then you walk 100010000*0.5*365*70 = 127,750,000 metres = 79,000 miles. Which (unlike my first draft...) is staggeringly different to your estimate. But you've not averaged that back to one year and then expanded to cover human life...if you do, then you predict about 31,000 miles-per-life, but then you didn't include any guesstimates of later-life years. Splash - tk 15:24, 25 June 2008 (UTC)

Ah, the question was birth -> adulthood. Well, let's say that the average step-length increases linearly over the range 2-18 years, so is on average 0.25m over the time. Then in 16 years, 10000*0.25*365*16 = 14,600,000 metres = 9100 miles. Taking Jdrewitts estimates and using the number of years in the proposal, we get, if the 10miles/week holds for ages 5-18: (2[miles]*52[weeks]*3[years])+(10[miles]*52[weeks]*13[years])+(2[miles]*5[days]*35[weeks in a school year]*13[years]) = 11600 miles. Which is actually remarkably close to the 10000-steps estimate of 9100 miles. Since most people don't manage 10000 steps, both are probably over-estimates by a fairly large margin. As 10,000-steps is a target to aim for, probably the range is something like 4000-10000 steps in practise, so that a mid-point is 7000 steps a day, suggesting that both estimates are too much by 30-50%. So maybe something like 6000-7000 miles for a normal person up to adulthood. Splash - tk 16:23, 25 June 2008 (UTC)

I would have to agree, average person depends largely on how you define 'average person' For example, if you are talking about the world, which we can presume based on the fact you just said average person not average person in the US/UK/developed world/whatever, then we have to consider that the vast majority of kids by far live in the developing world. Most kids in the developing world probably travel a lot on foot more then those in the developed world. Also by average do you mean median or mean? If you mean 'mean' then given that the is a resonable number of kids who travel very, very far, e.g. refugees, this is going to push your average up quite high. The number of kids who travel very little is going to help push it down, but there's probably not enough of them. The median IMHO is likely to be signficantly lower then the mean. Nil Einne (talk) 03:26, 26 June 2008 (UTC)

Natural In-Store Herbs that have the Similar Euphoric Effects of Dihydrocodeinone

Are there any herbs found in legitimate natural food stores that have the similar euphoric effects of dihydrocodeinone? --Anthonygiroux (talk) 14:24, 25 June 2008 (UTC)

Lots of drugs have euphoric effects. Consult a physician? Your best bet is probably to pick a Recreational drug use and then try to find something that has it in there. If you're dead set on trying something, please have a trip sitter and take other safety precautions. EagleFalconn (talk) 18:18, 25 June 2008 (UTC)

Frog on a lily pad (or ??)

I'm doing a reality check on a story for preschoolers that includes a variation on the classic image of a frog seated on a lily pad. I've read that frogs in the wild (i.e. not just a landscaper's lily pond) do live in swamps, but I'm not sure that water lilies do. So now I need to know what sort of vegetation would grow on swampwater's surface and support the weight of your local frog. "Floating leaf" might do, though I'd prefer something more specific. The bottom line is that such a plant and behavior would be within the realm of actuality, not merely an exercise of poetic license. -- Thanks, Deborahjay (talk) 15:28, 25 June 2008 (UTC)

See this for evidence of water lillies in the U.S. south - which is what I assume you mean by swamp areas. Both water lillies and frogs are found all around the world, so seeing a frog on a lilly pad is not something purely imaginary. See this for photos of frogs on lilly pads. -- kainaw™ 17:15, 25 June 2008 (UTC)

If you've ever seen large lily pads, you know they can hold weight very well. I don't see why the biggest frog couldn't sit on one. Mac Davis (talk) 17:24, 25 June 2008 (UTC)

My problem isn't the frog/lily pad juxtaposition, but the swamp (vs. pond). Most if not all the water lily photos and texts seem to avoid the "s"-word, and that's what the author prefers: Wetlands with characteristic muddy bottom. My tendency was to play it safe with pond but I decided against such sanitizing so as to retain the muddy bottom element. -- Deborahjay (talk) 17:29, 25 June 2008 (UTC)

GIS for "water.lilies swamp" shows lots of lilies in swamps. This is allegedly a smoking gun. --Sean 18:00, 25 June 2008 (UTC)

In south-eastern australia I've never seen a live stationary frog in the open (and I've been looking). In dams and "wetlands" they hide in and around the water. I've heard that in the tropics things are different though.Polypipe Wrangler (talk) 22:09, 28 June 2008 (UTC)

Hypertension medication

I have heard from some doctors that the Pharmaceutical companies encourage doctors to prescribe drugs for lowering High Blood Pressure just to sell their products.The lower value of blood pressure which these doctors define as "high" is not 90 as they say but much more higher.Is it true ? —Preceding unsigned comment added by Amrahs (talk • contribs) 15:58, 25 June 2008 (UTC)

140/90mmHg is normal blood pressure so I don't really see how they've heightened it at all? Either way, I doubt it's true. Why would doctors do such a thing when there is no benefit to the doctor or the patient if they prescribe drugs for mild blood pressure. The only party is helps is the pharmaceutical company. The most efficient treatment (usually) in hypertensive patients consists of lifestyle changes. Medication is usually for more severe hypertension or hypertension which is not resolved by the lifestyle changes. — CycloneNimrod ^talk?_contribs? 16:12, 25 June 2008 (UTC)

140/90 does not sound "normal" to me, based on my US POV, and it looks right at the high edge of normal for the UK, based on our article. --LarryMac | Talk 17:56, 25 June 2008 (UTC)

Absent any other complications, a physician will tend to recommend exercise and dietary changes before prescribing medications for mild hypertension. The first-line prescription medication for treatment of mild hypertension, meanwhile, is usually a thiazide diuretic; such diuretics have been around for ages, and are sold as inexpensive off-patent generics: only modestly profitable to a drug company.

I recommend reading The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (link) to get some idea of the risks associated with, and recommended therapies for, hypertension. Interesting bits (supported by detailed studies):

"The relationship between BP and risk of cardiovascular disease (CVD) events is continuous, consistent, and independent of other risk factors. The higher the BP, the greater the chance of myocardial infarction, heart failure (HF), stroke, and kidney disease. For individuals aged 40 to 70 years, each increment of 20 mm Hg in systolic BP or 10 mm Hg in diastolic BP doubles the risk of CVD across the entire BP range from 115/75 to 185/115 mm Hg."

"In clinical trials, antihypertensive therapy has been associated with 35% to 40% mean reductions in stroke incidence; 20% to 25% in myocardial infarction; and more than 50% in HF. It is estimated that in patients with stage 1 hypertension (systolic BP, 140-159 mm Hg and/or diastolic BP, 90-99 mm Hg) and additional cardiovascular risk factors, achieving a sustained 12-mm Hg decrease in systolic BP for 10 years will prevent 1 death for every 11 patients treated."

Treating hypertension actually has pretty clear benefits from both financial and quality-of-life perspectives. While I agree that there are legitimate concerns about both over-medicalization and over-prescription, and that those problems are often driven by drug companies and their lobbyists, I don't think that hypertension is an area where this is a problem. TenOfAllTrades(talk) 16:53, 25 June 2008 (UTC)

I have spent the last five years providing data on well over two million patients to hypertension researchers. It is very clear that reducing BP below 140/90 (130/80 for diabetics) is critical for reduction of cardiovascular disease. How BP is reduced is a different topic. Most doctors push for diet and lifestyle changes along with medications. Of course, most people will refuse diet and lifestyle changes, so they are left with just medication. -- kainaw™ 17:09, 25 June 2008 (UTC)

a few years ago, people might have thought that 90 was normal. nowadays, more like 80. probably go down further in the future. what's "normal" for a middle-aged American turns out to be high for somebody who lives a "healthier lifestyle"; and turns out to have pretty clear risks. so we don't call it "normal" any more. Gzuckier (talk) 18:09, 25 June 2008 (UTC)

I don't agree. 90 is still 'normal' as it's more common. 80 is more ideal. — CycloneNimrod ^talk?_contribs? 21:09, 25 June 2008 (UTC)

I can say that the average of the 2.6 million patients in my database is 132/75. That includes patients who are taking hypertension medication. Because this is my field of work, I think it is important to note that 140/90 is not "normal". It isn't even average. It is a cutoff determined by comparing blood pressure to cardiovascular and stroke risk. If you are interested, type "10 year risk score" into Google and you'll find many calculators for risk. If you know your blood pressure, cholesterol, weight, age, and so on, you can check your own risk. -- kainaw™ 22:54, 25 June 2008 (UTC)

Probably mentioned already, but I saw a couple of references to 140/90. No, it's not average, and no it's not normal. In fact, it's borderline hypertension. Basic clinical physiology. Wisdom89 _{(T / ^C)} 01:44, 26 June 2008 (UTC)

Amine chirality

Tertiary amines with 3 different substituents (as well as secondary amines with 2 different substituent) are chiral at least in principle, but usually not at room temperature. At what temperature can the chirality be observed (let's assume the substituents are short-chained alkyls)? Icek (talk) 18:09, 25 June 2008 (UTC)

Before any (other) mean spirited person tells you to do your own homework (It really sounds like a homework problem by the way) allow me to point out that Amine#Chirality states

The energy barrier for the inversion of the stereocenter is relatively low, e.g., ~7 kcal/mol for a trialkylamine.

Now using that information can you work out at what temperature molecules have sufficient energy such that

a. a few molecules will have sufficient energy for inversion.

b. more than 1/2 the molecules will have sufficient energy for inversion.. etc

Hint you need to find out at what temperature only a very small percentage (or non of) of the molecules will have thermal energy more than 7kcal/mol

Did that make sense? Please ask if you need help with that.87.102.86.73 (talk) 18:41, 25 June 2008 (UTC)

Unfortunately it seems you didn't properly understand my question. Both states are of equal energy (except for a very small difference due to the chirality of the weak interaction which is not relevant here). So in equilibrium at any temperature, half of the molecules are in either state. With about 30 kJ/mol barrier one arrives at a Boltzmann factor of exp(-(3608 K)/T) for the transition state and Boltzmann factors of 1 for each of the ground states, so as a low temperature approximation a fraction of exp(-(3608 K)/T)/2 of the molecules being in the transition state; but that is assuming that we may calculate as if there was only a single transition state which I'm not sure of. Anyways, that's still not what I want to know; more relevant is the conversion rate. Let's assume that at every collision of 2 molecules, the probability that one enantiomer is excited to the transition state is exp(-(3608 K)/T); we could approximate by taking the mean free path and the average velocity of particles (see Maxwell distribution). More accurately we should integrate over the Maxwell distribution and take into account the kinetic energy in the probability for a transition ... you see, it's not all that easy as computing the Boltzmann factors, and the results of a simplified computation could be quite far from the real conversion rate, and therefore I really wanted to ask at which temperature it becomes practical to actually observe chirality (e.g. by rotation of the plane of polarization of light). Icek (talk) 20:32, 25 June 2008 (UTC)

I thought I did.. Anyway it looks like you already have the answer to your question almost complete - but read on - I have an idea - there certainly already exist easy methods to calculate how often two molecules collide (assuming it's still a gas)..

However if a molecule has exactly the barrier energy (ignoring other energy 'nodes' eg simplifying and ignoring vibrational energy etc) then that molecule will be in the 'sp2' planar state that leads to racemisation/inversion. So if a molecule has that energy or greater then you can assume racemisation has probability 1/2

Here's a bit I think you missed - if you can calculate/estimate the vibrational energy going from one isomer to the other eg the 'umbrella inversion' vibration - then from the energy you can get the frequency of vibration - and hence it's speed... Does that sound useful?87.102.86.73 (talk) 21:08, 25 June 2008 (UTC)

From there it looks like simple maths to convert 'percentage of molecules with enough energy to racematise' and 'rate of molecule inversion with energy ~7kc/mol' into a 'half life' or similar for an enantiomeric mixture.

(Of course you probably could observe one enatiomer by selectively trapping one form with another optically active acid) - but that would be cheating - I don't believe that's what you intended.87.102.86.73 (talk) 21:15, 25 June 2008 (UTC)

Thanks for the help so far. I could calculate the fraction of molecules with a kinetic energy higher than the inversion energy from the Maxwell distribution, but assuming that all collisions will cause an inversion with probability 1/2 seems only reasonable in the gaseous state. An important question for me is (and to what I actually hoped to get an answer here): What are the experimental results? I'm sure someone has experimented with this. Icek (talk) 22:01, 25 June 2008 (UTC)

I spotted a possible problem - the rate of inversion of molecules which have sufficient vibrational energy to do so I estimate at 10^14Hz - that figure is meaningless in the absense of the collision rate - but I 'll assume that it's far faster..

The problem is the energy exchange - on collision, since the molecules have the same mass the energies should just be swapped.. and the cross sectional area is constant - so the collisional volume should be proportional the the velocity ie sqrt(energy). I bit more work should give a real figure.

But any given molecule can collide with any other - with a range of energies - causing the distribution of racemisation vs energy to change over time. At this point I have to take back my previous statement "From there it looks like simple maths".. It looks to me like difficult maths. Difficult differential equations that you could hope to get help from on the maths desk.

Actually I have never seen any work on how a boltzmann (or other) distribution will exchange energy with another (identical one) over time. It might have been done.(or not)

Back to your real question - data definately exists - but I can't lay my hands on it. however here http://www.goiit.com/posts/list/0/organic-chemistry-amine-inversion-35215.htm

....between the enantiomers is very small (25 kJ mol-1)and hence they are rapidly interconverted by a process called nitrogen inversion or amine inversion. The rate of this inversion is very high (2.3x10*10sec-1) ...

might help - assuming this rate of reaction is for room temp - you could using the activiation energy work backwards using the any activation energy/rate of reaction equation you have to get the rate at low temp.. then pick a temperature at which you feel the 'half life' is long enough eg >1hr.. That really is all I can find - I big library might be able to help you out - I'd guess that n.m.r. experiments could be useful here - maybe chemical abstracts is online - and free? that might be a way to get the numbers.87.102.86.73 (talk) 23:03, 25 June 2008 (UTC)

Do you know where the data exists? I can usually get my hands on it...Someguy1221 (talk) 04:18, 26 June 2008 (UTC)

I've got a feeling a saw figures in the textbook "Mechanism and Theory in Organic Chemistry By Thomas H. Lowry, Kathleen Schueller Richardson" , not 100% certain.87.102.86.73 (talk) 12:02, 26 June 2008 (UTC)

Use Tröger's base in which the conformation is frozen, and the interconversion is nearly zero!

Nut better for your problem would be the Arrhenius equation gives you a reaction rate whic is reaction rate mol per time and a mol is 6*10^23 particle and you have it! --Stone (talk) 13:49, 26 June 2008 (UTC)

Thanks to all of you. If the Arrhenius equation is valid over the wide temperature range in this case and the mean lifetime at room temperature, 4.3x10^-11 s (multiplicative inverse of the number given by 87.102.86.73) is correct, the mean lifetime is about 1 s at 88 K with a 25 kJ/mol inversion barrier; 1 hour at 71 K; at the boiling point of nitrogen it's 114 seconds, and at the boiling point of neon it's far longer than the age of the universe (2.6x10³³ s).

I'm still hoping for experimental evidence. Icek (talk) 22:52, 26 June 2008 (UTC)

I suppose if I mixed the tertiary amine with a chiral acid - getting the stable chiral salt with one component enriched I could then add base - liberating the free amine, and at the same time observe the rate of reaction using a suitably fast technique; possibly nmr.. 87.102.86.73 (talk) 00:47, 27 June 2008 (UTC)

I took a good look through that book you mentioned; didn't see any numbers on this. It mentions it only in passing, then goes on to speculate on carbanion inversion. Any other books you can think of...I have a whole pile of orgo books available to me.

Someguy1221 (talk) 02:33, 27 June 2008 (UTC)

Shame - I remember more.. I was hoping it would be in the references.. - as I remember 'lowry and richardson' is pretty in depth for mechanism etc - so it looks like a search in chemical abstracts would be in order..87.102.86.73 (talk) 10:35, 28 June 2008 (UTC)

Youcould even use a non-resolved secondary amine with a nearby chiral center (i.e., the amine-inversion gives diastereomers). Look at ¹H-NMR signal of the N-H at different temperatures. When you get two well-resolved signals, you know the inversion rate is "slow" compared to the NMR timescale. DMacks (talk) 04:19, 27 June 2008 (UTC)

Medical grades

What is the difference between the various medical grades in the UK? Clinical Fellow, Teaching Fellow, Clinical Assistant, Assosciate Specialist, Staff Grade, etc. Thanks. 92.4.53.191 (talk) 21:03, 25 June 2008 (UTC)

Modernising Medical Careers would be the place to start. Any questions on the details, ask away, I'm sure somebody here can help. --Tango (talk) 22:00, 25 June 2008 (UTC)

That page talks about the training grade levels, from FY1 up to Consultant, but the ones I asked about are in regards to the non-consultant non-training pathway. I know that Clinical Assistants are often GPs who work a few hours in another department, e.g. dermatology or A&E, but not sure about the others. The Fellows, etc. 92.4.53.191 (talk) 11:13, 26 June 2008 (UTC)

Parrots and corvines

How likely is it that they could someday discover civilization (say, if humans were gone from the earth)? --Kurt Shaped Box (talk) 23:55, 25 June 2008 (UTC)

Crows already have a very well-developed society, they can learn and teach, they can make tools. And they've developed an air force. They might already be there for all we know. However, it seems that development of writing is essential to our definition of civilization. Franamax (talk) 01:31, 26 June 2008 (UTC)

Civilization is not a well defined term. See civilization for some of the various ways of defining it (eg, living in cities, farming, writing, "being civil", etc). That page also seems pretty clear in saying that the term is one that applies specifically to humans. Pfly (talk) 04:20, 26 June 2008 (UTC)

Franamax: you mind expounding on that little? Learning, teaching, and tool making are talents for sure, but i feel that a "well-developed society" implies a structured, organized cooperative that is sustained by its members through generations. Perhaps this could apply to a flock (or a murder I guess) but I don't know if there is enough structure or population in a flock of birds (at least crows) to qualify it as a society. I feel like maybe if there was evidence for some sort of "super-flock" maybe we could call that a society? I think penguins might be a good model. --Shaggorama (talk) 20:22, 26 June 2008 (UTC)

Crows work in large groups, with well-defined roles and leaders. Those groups roost together as well and I believe the membership stays stable. It's a lot of fun to watch a group of crows systematically go through a neighbourhood, spotting where the watch-crows are, listening to the calls as the working crows are warned and given permission to move around. They're definitely not just a mob. I'd call that a society, though others will differ. Franamax (talk) 22:26, 26 June 2008 (UTC)