Wikipedia:Reference desk/Archives/Science/2006 November 26

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November 26

Crystal structure affecting properties of Group 2 metals (retrieved from archive)

I'd be very grateful for any helpful pointers you have here, even if it is a just a link to a site with the answer. I've found out that Be and Mg are Hexagonal Close Packed crystal structures; Ba is Body Centred Cubic and Sr and Ca are Face Centred Cubic. However, I can't find anywhere telling me how this crystal arrangement can affect the physical properties of a pure metallic sample of the substance. Any guidance would be greatly appreciated! Thanks, --86.139.127.29 17:28, 24 November 2006 (UTC)

One immediate impact is the co-ordination number. HCP and FCC are close-packed structures with a co-ordination number of 12, but in BCC it is only 8.--G N Frykman 19:15, 24 November 2006 (UTC)

The physical properties (strength, melting point etc) of a HCP or FCC structure would be very similar all other things being equal.. So in your case atomic radius amongst other factors would be a big factor in the physical properties. As for Ba I can't see any logical reason why it would be BCC when 12 coordiantion is clearly easily attainable - are you sure it is body centered cubic?87.102.33.100 19:31, 24 November 2006 (UTC)

So crystal structure has little effect on physical properties? I was told that the fact that Calcium has a higher melting temperature than Be is because of the crystal structure of Ca. Why is this? As for the structure of Ba being body centred cubic, I got that information from the barium page... Is it incorrect? --86.139.127.29 21:26, 25 November 2006 (UTC)

(Be/Ba typo? above?)

Going down the group 2 metals (data from wikipedia)

m.p.: Be 1560 Mg 923 Ca 1115 Sr 1050 Ba 1000 (Ra 973?) (in kelvin)

Ignoring Mg for now, the melting point decreases going down the column.

(at least) Two factors contribute here; the mass of the atom - heavier things melt and boil higher (as in the flourine, chlorine, bromine, iodine series).

The other factor is the strength of interaction between the atoms - which will probably decrease going down the column. It seems that the interatomic interactions have the upper hand here.

I can't explain the 'blip' at magnesium..

Note that otherwise the harder elements melt higher (hardness is also a measure of interatomic interaction strength).

As for the crystal structure of Barium I haven't verified its structure but as I mentioned above - is there any reason why it would not be 12 coordinate close packed.. 83.100.138.7 22:51, 25 November 2006 (UTC)

THanks for the help! --86.139.127.29 15:56, 29 November 2006 (UTC)

Oxygen

I was just wondering, why exactly do we need oxygen to live? Is it just for the production of ATP or are there more reasons?

Combustion and respiration--Light current 02:50, 26 November 2006 (UTC)

Oxidation is a very important reaction in the metabolism of living organisms, and it requires oxygen. ☢ Ҡi∊ff⌇↯ 05:14, 26 November 2006 (UTC)

The primary reason is to allow for the production of the production of ATP. Take a look at oxidative phosphorylation. – ClockworkSoul 08:25, 26 November 2006 (UTC)

I think they're all as important as a primary reason, since we need all of the uses described to live for very long. X [Mac Davis] (DESK|How's my driving?) 08:38, 26 November 2006 (UTC)

To understand the need for Oxygen, you need to understand how the human body functions. Proteins are extremely important building blocks of your body. Proteins hold your genetic information (DNA), insure communication between neurons (neurotransmitters; e.g. your brain wouldn't be able to transmit a signal to your lungs without proteins), protect your body (antibodies), and do a thousand other useful tasks. Of course, proteins don't grow on trees; your body has to build them (ironically, from and using other proteins). The process is known as anabolism. Anabolism cannot take place unless energy is provided. The combustion of oxygen (oxidation or catabolism) inside your body's cells provides all the necessary energy. Additinally, your body needs the energy produced by oxidation to keep its temperature constant and of course to enable you to move your muscles around. There's a little more detail to it, but that's basically why we can't survive without Oxygen. LestatdeLioncourt ^talk 12:53, 26 November 2006 (UTC)

The previous post contains some ambiguous/erroneous statements. To clarify:

• Proteins do not hold your genetic information. DNA is not made of proteins, although proteins are important for packing DNA (histones), and synthesising DNA.
• Neurotransmitters are not in genereal proteins. As stated in the article, some amino acids serve as neurotransmitters, and some short peptides also do, but many neurotransmitters are other, small molecules. However, the receptors for neurotransmitters are proteins.
• Breathing results from the brain/medulla sending signals to your diaphragm and intercostal muscles, not to the lungs. However, bronchoconstriction is regulated in part by nervous signals.

--Norwegian Blue ^talk 13:38, 26 November 2006 (UTC)

I'm well aware of the overgeneralizations I made when it comes to the brain-lung connection and neurotransmitters. I just meant to illustrate a point in the simplest way possible. With regards to DNA, then I must admit it was a mistake. My apologies. LestatdeLioncourt ^talk 14:08, 26 November 2006 (UTC)

D. Gary Young, Young Living Essentials and Raindrop Therapy

Can someone write an article? quackwatch.org has a good one I think.

The best place to ask is WP:Requested Articles. --ColinFine 11:58, 26 November 2006 (UTC)

Lux-Flood acid-base definitions

What is the Lux-Flood acid base definition, and where is it used? --HappyCamper 04:30, 26 November 2006 (UTC)

Google on 'Lux-Flood' gives (inter alia) http://www.earthscape.org/r3/otg01/otg15.pdf --ColinFine 12:01, 26 November 2006 (UTC)

I can't access this... --HappyCamper 19:40, 26 November 2006 (UTC)

Hopefully you should be able to access this one http://pubs.acs.org/cgi-bin/abstract.cgi/inocaj/1966/5/i04/f-pdf/f_ic50038a038.pdf?sessid=1716

Just read the introduction and all your questions should be answered.

So in general it's used in molten salts reactions - an acid might typically be a metal ion eg Al3+87.102.20.219 17:11, 27 November 2006 (UTC)

Definitions also here:

http://neon.chem.uidaho.edu/~chem463/Lectures%20'06/Nov%201%20lecture.pdf

http://www.chem.lsu.edu/lucid/maverick/N-ch6.pdf

Barmuda triangle

What is meant by baruda triangle?

I believe you mean the Bermuda Triangle. Black Carrot 06:22, 26 November 2006 (UTC)

Perhaps there is a baracuda triangle ? :-) StuRat 09:37, 29 November 2006 (UTC)

Palmistry

I've read and heard that studying a person's hand can yield more useful results than "Your life line is very shor - LOOK OUT!!! Kidding." (Good times.) However, I'm having trouble finding information on it. All I can find is people saying Greek gods influence your live vs. people getting off on saying that's stupid.

I'm interested in things like:

What callouses most often form as a result of what kind of labor?

• Playing guitar or harp, I believe, tends to create characteristic callouses on the fingers and thumb, whereas wielding a shovel (as I know by experience) causes equally characteristic callouses on the side of the thumb, at the bases of the fingers, and across the heel of the hand.
• Don't forget bowling! My dad and I both have calluses at least on the side of my thumb, looking at my own. It's smaller and pretty soft and red now. Been a while, and it wasn't developed very well anyway. X [Mac Davis] (DESK|How's my driving?) 08:37, 26 November 2006 (UTC)

Do things like typing, painting, writing (by hand), playing an intstrument, etc. have visible effects on the skin, muscles, bones, ligaments, or soft fascia of the hand? Seems like they should.

• Extreme examples, of course, would be carpal tunnel syndrome or accidentially cutting off a finger chopping meat.
• Carpel tunnel doesn't happen from typing or writing or painting, as it says in the article. More like jackhammering kind of agitation. X [Mac Davis] (DESK|How's my driving?) 08:37, 26 November 2006 (UTC)

It seems that different manual activities would cause the muscles of the hand and forearm to grow to different sizes. Is the result visible and interpretable from the outside?

• Could I, for instance, determine whether a person uses their superficial digital extensor muscle more than usual without cutting their arm open?
• I have admired my abductor pollicis brevis[1] at times. I think it is disproportionatly pretty big since I exert it so much all the time. Might be my imagination or me just thinking I'm special. X [Mac Davis] (DESK|How's my driving?) 08:37, 26 November 2006 (UTC)

The hand, wrist, and forearm, like other areas of the body, build up layers of fat as the person they're attached to does, and they're generally in a certain proportion to the rest of the body. Pretend they're sticking their hand through a curtain. What could I tell about their build and general physical health?

• Obviously, if their hand is several times as thick as their wrist, they're unhealthy, and if their hands are tiny, they might be as well.

Different people care for their hand in different ways, and to different degrees. What characteristics of the hand that are under voluntary control are reliable indicators of characteristics of the person themselves?

• To get the ball rolling, an easy example is nail polish - red nail polish is a pretty reliable indicator that the owner of the fingers is female (or pretending to be), though black, neon, or pictoral polish is of course less certain.
• Men's hands biologically and environmentally tend to have rougher skin. Look at a hundred hands, and you can probably get good at picking out a man's hand or a women's hand unless they're all trying to fool you. X [Mac Davis] (DESK|How's my driving?) 08:37, 26 November 2006 (UTC)

I would like to hear both anecdotal and scientific claims, and I'd especially appreciate a link to someone who studies this for a living. Black Carrot 06:44, 26 November 2006 (UTC)

I'll give you something anecdotal, I'm left-handed and as a result if I write a lot with a pencil or a pen, I get a callous on the inside of my middle finger on my left-hand; a right-hander would get something similar or their right-hand. So you could at least tell what somebody's dominate hand is. --Cody.Pope 07:02, 26 November 2006 (UTC)

Callouses form due to different types of uses of the hands, but these are very temporary and only reflect recent work. I do not believe that bone structure, or the shape of hands can be used to determine anything about the labour a person has done in their lifetime (other than perhaps missing digits); there is just too much genetic variety that would cover any effects (if any) that continual use would have on their development. Furthermore even someone with "strong hands" would have more muscle mass in their forearms rather than visible in their hands themselves. - Rainwarrior 08:34, 26 November 2006 (UTC)

Clubbing or edema of the digits can be an indicator of various circulatory problems, and petechiae on the hands suggests hepatic insufficiency. Tuckerekcut 22:02, 26 November 2006 (UTC)

Necessity of Ejaculation

I know that there are a lot of ways to approach this question but I'm looking for an answer from a purely biological/medical perspective.

Are there any negative effects on males if they don't ejaculate regularly? What possible medical problems could happen to a man if he went a long time (say, months or years) without ejaculating? For the purposes of this question, the method of ejaculation (intercourse, masturbation, nocturnal emmission, etc.) is irrelevant. There are a few things that I have heard might happen but only from unreliable sources.

1. The body normally absorbs unused sperm from the testicles but it can only do so much of that. Too much absorbtion can cause sterility. I have anecdotal evidence for that. A friend of mine who recently has his vasectomy reversed was told by his doctor that he was probably still infertile because his immune system had begun attacking his sperm.
2. The seminal fluid in the prostate would either get reabsorbed by the body or harmlessly backed up into the bladder but again too much of that can cause damage. The article on prostate cancer says that frequent ejaculation can reduce the risk of getting prostate cancer.
3. The smooth muscles that cause ejaculation are just like any other muscle in the body and will entropy if they go too long without use.

I haven't read any scientific data about the possible problems that occur and it's not something that would have many cases, but I was wondering if anyone else was familiar with any research about this. --69.137.93.247 07:46, 26 November 2006 (UTC)

I've read it will have no effect (in one of those for-teenagers, get-to-know-your-body type books), and I'd buy that. It's not like people don't go for years without sex. And in the past, masturbation was rather less acceptable than it is now, so I'd bet there have been many people who went years, decades, or even their entire lives without it, especially religious leaders. Vows of chastity and all that. If there were a significant negative effect from it, it seems like I would have heard of it. However, I have read that frequently holding it in (for birth control, or something) can damage things mechanically. Black Carrot 07:53, 26 November 2006 (UTC)

I've heard that men who ejaculate regularly are less likely to have prostate problems in older age. By that I mean that men who continue to ejaculate after middle age are less likely. I don't know exactly how often ejaculation was necessary in order to make a difference, but I believe it was whatever would qualify a man as 'sexually active', like maybe once or twice a week or more. I don't have any references for that offhand tho. Anchoress 08:06, 26 November 2006 (UTC)

I don't think we have much of an idea about this at all anyway. X [Mac Davis] (DESK|How's my driving?) 08:27, 26 November 2006 (UTC)

When I was doing Physiology at Uni I asked the Professor who was (and is) one of the world experts in reproductive biology a similar question, basically the original question 1 above. He said the sperm were reabsorbed, and did not suggest that it would cause any long-term problems or that there were any limits to it (though bear in mind this was almost 20yrs ago so there could have been new findings since then).

I have heard from other sources about possible increases in risk of prostate cancer and other prostate problems, as noted in the Qu2, the article, and as Anchoress says.

Re Qu3 I think you mean atrophy, not entropy; for some reason I seem to remember that smooth muscle is far less prone to atrophy than is skeletal/striated muscle, but I don't have any references for that.

Also don't forget the possible role of nocturnal emissions as, I suppose you could say, a replacement or safety valve for intentional ejaculations, although I don't believe there's really any clearly demonstrated link or definitely known cause for nocturnal emissions. --jjron 13:07, 26 November 2006 (UTC)

Seriously could you actually go for say 1 week without having sex or masturbating? (males?) As if sperm would ever get chance to be reabsorbed - after a couple of days in my experience the hands go into autopilot no matter what, where or why.87.102.12.129 13:50, 26 November 2006 (UTC)

I'm not sure if that is a joke or not. You're fine. You can go for plenty of weeks. It has been done. X [Mac Davis] (DESK|How's my driving?) 16:13, 26 November 2006 (UTC)

Weeks - citation please - would be an interesting topic for a blog.. Day 4 Oh fuck it. 87.102.12.129 16:23, 26 November 2006 (UTC)

Ive gone atleast 10 days. Its not that hard, especially if your feeling low, and not particularly aroused. Im sure I could go much longer if I had a motive. Philc _T^E_C^I 00:03, 27 November 2006 (UTC)

Sort of like the question, "How many licks does it take to get to the center of a Tootsie Pop ? ...the world may never know". StuRat 09:46, 29 November 2006 (UTC)

I've found that not ejaculating leads to an extremely painful rupture of the seminiferous tubules, usually during a bowel movement. I suggest avoiding the experience. StuRat 09:46, 29 November 2006 (UTC)

Old people smell!

My grandma is staying over out our house for a few days, and I noticed a minute ago that the bathroom smells like old people. A while ago on the desk (many months, as I recall) somebody asked a question about "black people smell," and one of the answers was that some some black people have different sweat, or something like that. I have noticed this, some black people (particuarly ones that haven't washed for a while)... smell different from other people. Is it old people's sweat glands being old? Just kidding. I noticed that there was denture fluid in the room sitting out with her dentures in it— maybe that's it! What do you think? X [Mac Davis] (DESK|How's my driving?) 08:27, 26 November 2006 (UTC)

It could be something as simple as old people preferring certain types of perfume. Not just pure perfume, but also in soap and such, which is almost always perfumed (to my great disgust). DirkvdM 10:39, 26 November 2006 (UTC)

I assumed (without giving it much thought) that my grandmother's smell was related to her age until I found out it was the smell of her cosmetic powder.  --Lambiam^Talk 15:40, 26 November 2006 (UTC)

As someone who is neither young nor old could I point out that university students also smell - it's a strange smell - like raw soap - any clues?87.102.12.129 15:45, 26 November 2006 (UTC)

And then there is that nursing home smell where when you go to visit grandma your nostrils get hit with the smell of stale urine. The worst smell is the smell of patients with cancer and certain other illnesses. 71.100.6.152 17:03, 26 November 2006 (UTC)

Formaldehyde --Russoc4 20:57, 26 November 2006 (UTC)

Everybody smells. Its just that you have not got used to old people smell yet 8-)--Light current 01:09, 27 November 2006 (UTC)

Yup, but why do they smell different then? DirkvdM 07:29, 27 November 2006 (UTC)

Diet effects body odor, supposdly garlic and ginger are two culprits. -Ravedave ^{(help name my baby)} 05:24, 27 November 2006 (UTC)

Because the sense of smell tails off in older people, they tend not to notice smells as much. So they dont think anything particulartly smelly. So they dont feel the need to wash it/ freshen it up!--Light current 13:51, 27 November 2006 (UTC)

The scent you emit also depends a lot on diet. You can notice this easily if you shower up a while after eating a lot of garlic -- it ain't just your breath that contains the odor. But it's just as true on a more micro level based on your day-to-day diet.

Atlant 17:24, 27 November 2006 (UTC)

Hmmmm, "some black people (particuarly ones that haven't washed for a while)... smell different from other people." So, not all black people who haven't washed for a while smell different from other people? Do white or brown people who haven't washed for a while "smell the same as other people?" As each other? I'm going to have to go around sniffing people of different colors to see if this is true. Did you ask them how long it has been since they washed or if you smell different to them when you haven't washed for a while? And how long is a while? Days? Weeks? Years? Do I need a survey card for differently aged aromas or is ballpark good enough? I always wondered what people smelled like in the Middle Ages but never wanted to time travel to find out personally.

How many old people did you have to sniff to find out what they smell like? Unwashed people? KP Botany 22:05, 29 November 2006 (UTC)

Formulae relating to conductivity required

I need some formula for work, please can you guys help

1. One (or many) relating energy (eV) recquired to free electrons and number density of free electrons (e/m³) at a given temperature (K)
2. One (or many) relating number density of free electrons (e/m³), velocity of electrons (m/s) and current (A)
3. One (or many) relating number density of free electrons (e/m³), velocity of electrons (m/s) and voltage (V)

the variables given are not limiting, if further variables or constants can be brought in if neccesary, but if you do have to bring in further variables, It would be helpful if you helped me find them aswell, as I would like to able able to calculate conductance for a substance, given its ionisation energys. Thanks. Philc _T^E_C^I 12:57, 26 November 2006 (UTC)

(response to Q2) I can give you this one : Density of free electrons (e/m³) x Cross sectional area A (m²) x velocity of electrons (m/s) gives current in electrons per second. to get Amperes multilpy by the charge on an electron in coloumbs (–1.6 × 10–19 Coloumbs per electron)87.102.12.129 13:54, 26 November 2006 (UTC)

Response to Q3: The previous post practically gets you half way to this answer. The relation my friend up there reached is:

I = d × A × v × -e

where:

• I is the current in A.
• d is the density of free electrons in m.s^-3.
• A is the cross-sectional area in m².
• v is the velocity of the electrons in m.s^-1.
• e is 1.6×10^-19 C.

Using Ohm's Law which states that U = RI, where U is voltage (in V), R is resistance (in Ω), and I is current (in A), you can easily modify the above relation so that it becomes:

U = R × d × A × v × -e.

You can simplify R and e to get Φ (the magnetic flux in Wb). LestatdeLioncourt ^talk 14:33, 26 November 2006 (UTC)

Please explain???? Where does magnetic flux come into this? and how is it obtained from resistance and charge of an electron???87.102.12.129 14:41, 26 November 2006 (UTC)

You can deduce this relationship via dimensional anaylsis. R×e gives: [Ω] × [C] = [(Kg.m²)/(C².s)] × [C] = [(Kg.m²)/(C.s)] = [Wb] which the unit for magnetic flux. You can leave the relation as it was. I just thought that reducing the number of invovled variables might suit you better. LestatdeLioncourt ^talk 15:29, 26 November 2006 (UTC)

Interesting, but how does this help - is there a way of calculating magnetic flux so that it can be used to give an answer to one of the original three questions?87.102.12.129 15:36, 26 November 2006 (UTC)

I really gave no thought to the matter beyond somewhat-pure math, i.e. regardless of context. The question asks for a relation(s) between the given physical quanitites, and I'm providing two.

U = R × d × A × v × -e.

And,

U = Φ × d × A × v.

That's all :). LestatdeLioncourt ^talk 15:55, 26 November 2006 (UTC)

"if you do have to bring in further variables, It would be helpful if you helped me find them aswell" - ie we need a way to calculate or otherwise get the magnetic flux.87.102.12.129 15:58, 26 November 2006 (UTC)

Ah yes, you're right. Calculating the magnetic flux is a little complicated and depends on the conditions of the problem. One way is to integrate the negative value of the electromotive force in a circuit or to use the magnetic flux density, B (expressed in Tesla, T). In the latter method, the formula is dependent on the medium (e.g. for a loop it is equal to the scalar product of B by n, the normal vector to the loop obtained by the right-hand rule, multiplied by the surface area in square meters). It's probably much easier sticking to the first relation. LestatdeLioncourt ^talk 16:54, 26 November 2006 (UTC)

Dependency of climate on the Earth's axis of rotation

My daughter just asked me what the climate would be like on Earth if the Earth's axis of rotation were parallel to the ecliptic plane, instead of at the angle of approx 67 degrees that it has. My immediate answer was that the climatic variations would be extreme, since the 23 degrees off perpendicular is what causes the seasons. This would certainly be true for the poles, where the sun would be more or less in zenith all day in midsummer. But what about the equator, and the regions in between? Would any part of the planet have a comfortable climate? --Norwegian Blue ^talk 17:03, 26 November 2006 (UTC)

I'm not sure if science would have an adequate answer...the best is probably to say that we simply wouldn't know. However, it does sound like an Earth that wouldn't be a very fun place to live. The moderate temperatures probably couldn't be sustained in those regions in the long term due to the sensitive equilibria set up. --HappyCamper 18:06, 26 November 2006 (UTC)

Good question - the current equators would experience 24hr daylight and in 6months 24hr night (a bit like the poles today except this would be total daylight - total night). the poles would get the sun on the horizon as they do today when they are at the poles - but as the rotation moves the pole 90degrees round depending on the time of year they would get either 1 the sun stays fixed in the sky at the horizon, 2 (1/4year later) the sun goes from horizon to opposite horizon via directly over head (like summer 12hr day) and then back to 3 the sun stays fixed in the sky at the horizon (opposite side etc). So the poles would have a summer and a winter. But a point on the equator along the axis of rotation would have 1 day = 1/2year light then 1/2year day. This suggests to me that the ice caps would move completely around the earth in one year - move to the poles.... Happy Xmas83.100.250.53 20:28, 26 November 2006 (UTC)

I can't follow this. The current equator (there is only one) would still be an equator, having each day 12 hours of light and 12 hours of darkness (not counting twilight), assuming that the Earth rotates around its axis once every 24 hours (not counting the fact that now we need to consider the sidereal day). At midsummer and midwinter, the equator would have constant twilight. I agree with the hypothesis that the caps would move from pole to pole, but not in a continuous way. The cap would be much larger at its largest extent.  --Lambiam^Talk 00:01, 27 November 2006 (UTC)

In NorwegianBlue's hypothetical situation, Earth's axis of rotation is pointing toward the sun during summer. In other words, the tilt is 90 degrees instead of 23 degrees. The equator would be in 24-hour sunlight during both summer and winter, but it will have 12 hours of light and 12 hours of darkness during spring/autumn (when Earth's axis is pointing 90 degrees away from the Sun). Therefore, it will be hotter than it is right now.

As 83.100.250.53 said, one day at the poles would be 6 months long. However, the poles will be hotter than they are right now, because it's possible for the Sun to be directly overhead (whereas now the Sun can't rise higher than 67 degrees, i.e. 90-23). All other latitudes will spend some days/months in darkness, but for at least half a year they will never spend more than 24 continuous hours in darkness.

So, to conclude, Earth's average temperature would be higher. I don't think it would be higher than 40 degrees Celsius, though, so life would still have a chance to evolve. --Bowlhover 04:22, 27 November 2006 (UTC)

You assume the axis is constantly pointing towards the Sun, which would probably eventually happen if the situation were to last. But it could also stay in the same orientation relative to the solar system, which would cause extreme seasonal changes at the poles, too extreme for 'more developed' life, I assume. The equator would be a bit like the present poles at spring/fall twice a year and be as they are now (normal day/night pattern) during those other two seasons, as Lambian describes. This would be quite live-able because there would be no extreme long dark periods. Btw, Uranus has that. From the article: "Uranus is nevertheless hotter at its equator than at its poles, although the underlying mechanism which causes this is unknown." That's it. Not much help there. The Earth, however, has experienced a more tilted axis several times in its history. I can't find the article and I don't really have the time right now, but axial tilt might help. DirkvdM 07:49, 27 November 2006 (UTC)

In my answer I assumed that the axis initially points towards the sun but holds its position as the earth rotates around (so that after 1/4 year the axis of rotation is actually at right angles to the line connecting sun and earth). Hope that makes it clearer for anyone who was confused. And the polar regions change from one pole to two poles to one pole etc over 1/4 yearly intervals - I initially didn't get that..87.102.20.219 17:38, 27 November 2006 (UTC)

Thanks for your responses! Bowlhover, I think the maximum solar height at the poles is 23°, not 90°-23°, and Dirk, to me it is inconceivable that the axis would eventually point towards the sun all year. Rotating the planet's axis once a year would require an enormous amount of energy. I'll think a bit more about the celestial geometry on my hypothetical planet, and maybe post a follow-up on the maths desk. --NorwegianBlue ^talk 23:36, 27 November 2006 (UTC)

If the mass of the planet is unevenly distibuted between the poles, the heavier one will get drawn towards the Sun more and more. I'm not sure if a molten core will counteract or re-enforce this. Anyway, given that the Sun's attraction is the 'point of reference' here, it would actually cost energy to move in relation to that, and a pole moving away from the Sun would do just that. DirkvdM 05:57, 28 November 2006 (UTC)

I think this is what happened to the Moon, which is why the far side has much less mares than the near side. (See the pictures on the Moon article. The difference is amazing.) By the way, I think that having a (symmetrical) molten core will neither re-enforce nor counteract this process, as long as Earth's mass stays the same.

To NorwegianBlue: you're right, the Sun can only get to 23 degrees at the poles. I don't know why I said 90-23; it should have been 90-(90-23). --Bowlhover 01:34, 29 November 2006 (UTC)

--Bowlhover 01:32, 29 November 2006 (UTC)

Flu question

Why do I get far less hungry when I have the flu? JIP | Talk 18:21, 26 November 2006 (UTC)

Because your body is diverting resources (blood energy etc.) to fighting infection, and therefore has less available for digestion. So it will try to keep your food intake low making you not hungry, or throw up if you eat to much. It will still take a minimal amount of food, i.e. enough to survive happilly. Philc _T^E_C^I 18:30, 26 November 2006 (UTC)

I think the fever might have an effect on the functioning of digestive enzymes, although I've seen many graphs where digestive enzymes reach peak activity at around 40°C, so I'm not too sure about that. LestatdeLioncourt ^talk 19:12, 26 November 2006 (UTC)

Probably caused by molecules coming from your activated immune system, combined with other hormonal and neurological changes. This article on Cytokines and the Anorexia of Infection: Potential Mechanisms and Treatments is 6 years old, but still gives a good overview. -Seejyb 23:25, 26 November 2006 (UTC)

If your digestive system is infected, there's little point in eating, as you will likely vomit or have diarrhea to rid the digestive tract of the infection, so won't get much benefit from the food. StuRat 09:56, 29 November 2006 (UTC)

Who studies the origin of neurosis?

Are neurotic states studied only by psychiatrists or do neurologists try to discover their cause? My son had a severe anxiety disorder, the cause of which is unclear. We have seen numerous psychiatrists and therapists who mostly insist that family dynamics are responsible. This just doesn't seem a good enough explanation when we are a stable, rational, loving family. We have never been referred to a neurologist. Is this because such disorders are not part of their remit? Really Is it possible that anxiety disorders result from neurological impairment?

remeber thinking your normal, does not constitute normaility, and denile may be the tip of the iceberg of an underlying problem. Philc _T^E_C^I 21:05, 26 November 2006 (UTC)

Neurologists are not involved in the diagnosis or treatment of anxiety disorders, except possibly helping to exclude that "the disturbance is ... due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication) or a general medical condition (e.g., hyperthyroidism)." (This partial quote is from the descriptions of the conditions, and the main articles referred to in the page on anxiety disorders.) Usually a neurologist would get involved only when a general physician finds that he needs such an opinion. As far as dynamics are concerned, the difficulty is that what matters is not what you perceive, but rather what your son perceives - how his mind experiences things. These two may not correspond, and the reasons for that may be unknown to you at present. Seejyb 22:34, 26 November 2006 (UTC)

Several anxiety disorders have a genetic component to them. Thus they would not necessarily result from abnormal "family dynamics", but rather from some physiological cause. A good psychiatrist should know this, and prescribe treatment accordingly. In any case, this is usualy something not dealt with by a neurologist. Nrets 02:49, 27 November 2006 (UTC)

Thank you for taking the time to reply. The comment by Nrets was particularly useful for obvious reasons...I will not pursue a referral to a neurologist. I knew as I was writing my question that the automatic assumption would be to see me as in denial about the importance of family dynamics in anxiety disorders. But, where does this assumption come from? We no longer question why people suffer from disorders - we think we know by trawling life experiences for explanations. Sometimes traumatic experiences do cause mental disorders, but that does not mean that they always do. Causes may not always be environmental. No one would claim that the human mind is fully understood. There are so many areas of ignorance and ambiguity. It's just not good enough to automatically assume that family dynamics causes disorders in children or adults. It is not a given, just a possibility.Jazzy Holiday 19:09, 27 November 2006 (UTC)Jazzy

I would not automatically assume family dynamics problems as the cause of the anxiety either. Consider that if you son is in school age he could be a victim of bullying. Mr.K. 19:54, 27 November 2006 (UTC)

Do natural levees develop during floods because slower moving waters can only carry smaller particles?

I've always wondered this.

The Levee article seems to confirm your idea. Seejyb 22:38, 26 November 2006 (UTC)

Is this a House Sparrow?

I took this picture of a bird in New York City in mid-October. I believe it to be a House Sparrow; is this accurate? It looks like at least one of the pictures in the article. grendel|khan 22:07, 26 November 2006 (UTC)

Definitely a sparrow. Even more common than pigeons in North American cities. alteripse 22:31, 26 November 2006 (UTC)

Yes, it's a House Sparrow. Probably a molting or slightly immature male, the black "bib" is fainter than usual.

Vultur|my talk

atmospheric stagnation

are there any reasons for atmospheric stagnation other than high pressure, inversion or fair weather? thanks...

What is atmospheric stagnation ? Do you mean a lack of wind ? StuRat 09:59, 29 November 2006 (UTC)

I mean "a condition of light winds and poor vertical mixing (no rising air) that can lead to a high concentration of pollutants"

I think you've listed the major causes. One other I can think of is physical barriers, like the trees in a thick forest or jungle. StuRat 22:29, 29 November 2006 (UTC)

insulation?

When installing insulation in wall cavities in the pacific north west, should the vapor barrier go on the outside or the inside? Thanks!

Green side up! (oh, that's for sod!). Standard practice everywhere is for a breathable Tyvac (waterproof) outer cloth on the studs, and plastic on the inner studs, with insulation in the middle. --Zeizmic 00:41, 27 November 2006 (UTC)

So, from the outside in - shingles, breathable layer, insulation, plastic layer, drywall?

Not quite everywhere. The vapor barrier must face the warmer, more-humid side so as to prevent water vapor entering the insulation, traveling to the point in the insulation where the air cools to the dew point, and having the water vapor condense out as liquid water, wetting the insulation.

Whether it's the inside or the outside of the house that's warmer and wetter depends on both the local climate and often, the time of year. It's hard to reverse the insulation seasonally, though, so for much of the temperate zone, we compromise and put the vapor barrier facing the inside (which is the right answer for much of the year and not too wrong for the rest of the year). But I think you'll find that in the more tropical zones, when they insulate at all, they may put it up "backwards" because the air conditioning keeps the inside cooler than the outside's warm, humid air.

Atlant 17:34, 27 November 2006 (UTC)

This [2] shows the diagram. And it's tyvek house wrap. There are new framing techniques that prevent cold spots at corners, and it is quite the skill to properly wrap a house without holes. You should read books. --Zeizmic 13:25, 27 November 2006 (UTC)

Thank you - I do read books, but there is conflicting advice in some of the books on insulation that I have read where remodelling of older houses is concerned!