Wikipedia:Reference desk/Archives/Science/2007 May 19

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[edit] May 19

[edit] Where can I buy a spaceship

Where can I buy a spaceship

The first Google result for "buy a spaceship" says that the Spaceship Company will sell spaceships. A.Z. 01:40, 19 May 2007 (UTC)

Oh come on. Ebay. Duh! -- Phoeba WrightOBJECTION! 02:21, 19 May 2007 (UTC)

You might also be able to buy used spaceships (test ones or re-entry modules), say from Russia, who might appreciate the extra cash more than the memorabilia. StuRat 02:32, 19 May 2007 (UTC)
Russia may also sell a functional Soyuz stack. The full-up cost would probably range between $25-50 million USD, based on most some educated guesses by folks like James Oberg. - CHAIRBOY (☎) 02:37, 19 May 2007 (UTC)
Hmmmm. I wonder if you'd run into legal problems if you attempted to set it up and launch it unannounced from your own property (say, if you owned a large area of land in a remote-ish area of the US)? --Kurt Shaped Box 04:52, 19 May 2007 (UTC)
In the US, it would probably be classified as a flight vehicle, so you'd need to get FAA approval. They made a movie about this lately, didn't they? Astronaut Farmer or something -- Phoeba WrightOBJECTION! 06:08, 19 May 2007 (UTC)
You will probably have some problems with weapon regulations as you basically set up a launch platform for an ICBM.

... If only your father was Anakin Skywalker ... -- Toytoy 02:55, 19 May 2007 (UTC)

You could probably make your own, it would be cheaper...

MASA. anonymous6494 02:23, 22 May 2007 (UTC)

[edit] Evolution vs Cars

Will roadkill eventually be a thing of the past because animals who are not afraid of cars get hit? I am guessing yes, but I am surprised google doesn't turn anything up. -Ravedave 03:38, 19 May 2007 (UTC)

I did once read somewhere (I think it was in New Scientist magazine several years ago) that natural selection is starting to favour the hedgehogs that run instead of rolling into a ball when faced with a predator (i.e. car). --Kurt Shaped Box 04:58, 19 May 2007 (UTC)

Eventually, yes, but it may take thousands of years, and cars may not be used for that long. StuRat 05:20, 19 May 2007 (UTC)

I've noticed that gulls (or at least my local urban gulls) seem to have a strong concept of 'car'. If they're feeding in the road, they are constantly looking back and forth for oncoming traffic as they stand there. Come to think of it, the only roadkilled gulls I've ever seen have been young ones. The street pigeons, on the other hand don't seem to pay as much attention and do get hit quite frequently. --Kurt Shaped Box 05:30, 19 May 2007 (UTC)
Yes, I've noticed I need to swerve much more severely to hit a gull than a pigeon or person. :-) StuRat 06:03, 19 May 2007 (UTC)
The gull's reactions will probably be faster than yours (try it sometime and watch some real aerial skill). It's not unknown round here for chav jackasses to see birds on the road and deliberately speed up or swerve to hit them. --Kurt Shaped Box 06:28, 19 May 2007 (UTC)
"Chav" ? StuRat 22:50, 19 May 2007 (UTC)
http://en.wiktionary.org/wiki/chav. —Steve Summit (talk) 23:33, 19 May 2007 (UTC)
I take umbrage to that definition. Referring to chavs as 'working class' is pretty insulting to decent, working class people who don't feel the need to be antisocial petty criminals who overindulge in booze and smack. It's a state of mind - not a class/money thing. --Kurt Shaped Box 07:17, 20 May 2007 (UTC)
wiktionary:umbrage —Bromskloss 16:44, 21 May 2007 (UTC)

There is a precedent of an evolutional change of the type discussed here, long before Homo sapiens or Toyota Avensis. Indeed, some spiders, most notably Argiope, have evolved to add a stabilimentum to their web. The stabilimentum is thought to be a "don't run into me please" sign for rabbits and low-flying birds. A spider hit by a bird or a rabbit/hare is essentially roadkill, so an added conspicuousness is definitely beneficial rather than detrimental. (Note that Argiope sp. tend to be quite large, and webs over two feet across are not uncommon. So they are rather conspicuous anyway, at least wor a slow-walking human; but probably not conspicuous enough for a fast running hare). It is therefore not unthinkable that, instead of developing "car phobia", cats / skunks / hedgehogs will develop conspicuous "please don't squash me" markings; perhaps like these. Cheers, Dr_Dima

If natural selection works, then the result you posit should in time eventuate. I have read somewhere that rattlesnakes in the U.S. are far less noisy than they were when the country was thinly populated, because the noisiest snakes were most likely to get shot. Edison 16:41, 19 May 2007 (UTC)
I've heard that too. It used to be that a loud rattle kept them from being stepped on, while now it just gets them shot. StuRat 22:53, 19 May 2007 (UTC)

See also this thread from two days ago. —Steve Summit (talk) 23:37, 19 May 2007 (UTC)

I would think so, I would be surprised if urban pigeons have not learned to avoid cars. Some will always still be hit though. The amount of time it would take is more questionable. If every autophillic pigeon was hit and all autophobic pigeon survived, then the evolution could occur in months but I expect the time it would take to have a significant effect is more like 100 years. Ozone 02:54, 21 May 2007 (UTC)

[edit] A/C efficency

Currently the weather is hot during the day and cool at night. However I have a problem getting the cool air into my house. My house's ventilation system has a heat exchanger on it, so running the furnace fan doesn't do much good. It is a town house surrounded by townhouses, opening windows doesn't do much. So I run the A/C and worry about my elec bills. My question is, if it is 60F outside and 75F in my house will the A/C be almost as efficient as just running the fan? Coefficient of performance is the closest thing I could find. Another Q that is more of a gripe, and probably not answerable: Why the heck aren't new houses better designed to take advantage of outside weather conditions? -Ravedave 03:55, 19 May 2007 (UTC)

Sorry to ask another question rather than give an answer, but how does having a heat exchanger keep the furnace fan from doing what you would want? (I looked at the article you linked to, but I still can't figure it out.) --Allen 04:24, 19 May 2007 (UTC)
Hrm I used the wrong name for it, thats why. Energy recovery ventilation, better shown here http://www.fantech.net/hrv_erv.htm. Air from the outside goes past air from the inside going out. The heat is exchanged resulting in fresh air in the house, but little temperature change. -Ravedave 14:07, 19 May 2007 (UTC)

What you need are some window fans. Put fans on one side blowing in and on the other side blowing out. Make sure all doors between are open. Also, make sure all windows without fans are closed (counter-intuitively, this improves air flow). This will give you a nice flow. If you time the fans properly, you can save lots of money over A/C. Also, be sure to close the windows when it might rain. StuRat 05:17, 19 May 2007 (UTC)

That's exactly what I do. But when he said he's in "a town house surrounded by townhouses", I took that to mean he's in the middle of a hot little microclimate, surrounded by glass and metal and concrete, and the hot side of all his neighbors' heat exchangers, such that there's rarely any cool air just outside to let or blow in. --Steve Summit (talk) 13:55, 21 May 2007 (UTC)
So no idea on how efficient A/C is when there is a large temperature differential? -Ravedave 14:07, 19 May 2007 (UTC)
No easy way to quantify this. A test you could do yourself is spray the garden hose on the unit to keep it the temperature of the water as opposed to the hot air outside, (make sure you dont run more water on/in the unit than would normally occur in a heavy downpour). I doubt there would be an appreciable difference in temperature and efficiency is impossible to determine without a more isolated system(not a house). I think greater cooling would be sought by increasing duct flow by using more fans than just the central fan.

[edit] Thermogenerator efficiencie

theoricaly if a Thermogenerator wich as a 10% efficienci rating was in a box of aerogel with x quantity of heat , would the thermoganerator eventualy turn (almost) all the heat to electity or would something else happen?

In any thermodynamic system, one must first consider if the system is closed. In a standard system the container or 'box' can exchange enthalpy with the external environment, but not mass. Next, the enthalpy exchange is dependent on the material of the system. In this case the aerogel seems to indicate the insulative properties are ideal and the thermal conductivity is low. This would mean the enthalpy that is in the system stays there. The last question is to consider how the generator would be set up in the system. We need a temperature differential between a bimetalic or p-n doped silicon molecule. Thus, the generator would have to be set up inside and outside of the box. If this is some ideal aerogel system, the easy answer is that yes, most of the enthalpy would be converted to an electric potential difference(electricity). This would continue to happen until there was no temperature differential which is when the system reaches equilibrium. However, in a non-ideal system that any engineer would deal with, they would soon realize the box would be at equilibrium with the outside air and X heat would have to be added continuously to keep generating electricity with a Thermogenerator. Theoretically, if one uses an ideal generator that perhaps is a p-n type silicon junction which has no heat loss across it, I would expect efficiency to approach 100%. The article quotes typically 10% efficiency which is basically due to the conversion of a suitable fuel into enthalpy that will have a lot of loss before it is "put in the box". Compare this to a typical heat engine that has no more than 35% efficiency.

69.241.236.12 06:41, 19 May 2007 (UTC)Adam

[edit] what's are the processes that an electron emit and gain energy in form of photon ?

when electron collide with a photon, the electron gain energy leaving the photon weaker . when neutron, proton and other particles collide with electron what happen then ? electron emit photon when it is accelerated . so in an particle accelaratir when electrin is accelerated it radiates energy in form of photon as a result it's energy should be decreased . but the reverse happens how ?

Not sure if I quite understand all the questions. For the last question: I think when you are referring to the energy decrease from an accelerated particle emitting photons, you are correct in that it does decrease in energy. However, it is still accelerated at high velocities with large voltages and the overall change in energy is increased from the initial ground state of that quantum particle, proton or electron.69.241.236.12 07:09, 19 May 2007 (UTC)Adam

[edit] temperature question !

consider a fully thermal insulated box which contain a mixture of oxygen and fuel(gasoline). if the mixture is ignited then the resulting chemical reaction release energy(photon)that's why temperature inside the box increases and pressure inside the box increases . after a certain period of time temperature peaks at maximum and is stable . does pressure changes same way ?

If I understand your question properly, in a word the answer is 'yes'. Temperature is basically a measure of the motion of the particles in the system, in your case in the box. Following the release of energy from the chemical reaction the particles move faster, so the temperature rises. The faster moving particles bang into each other and the walls of the box harder and more often - this is the increase in pressure. So when temperature peaks and becomes stable, so will pressure (assuming everything else remains constant). Of course this ideal situation where the box is fully insulated and allows the temp to stabilise does not exist in reality. --jjron 17:28, 19 May 2007 (UTC)
Be sure to see this excellent illustration of the particles pinging the walls as Jjron described. The cumulative tiny pushes of those trillions of impacts is what creates pressure. --TotoBaggins 02:29, 22 May 2007 (UTC)

[edit] Submarine pens and air pressure.

A few TV shows and films I've seen feature completely-submerged buildings with a submarine pen -- a floor open to the ocean where submarines can rise and dive. (Image: http://img241.imageshack.us/img241/8343/vlcsnap2225370nx4.jpg) What sorceror's magic do these mermaid-architects use to avoid flooding the building? Would the room need to be pressurised, only enterable via an airlock? Froglars the frog 07:43, 19 May 2007 (UTC)

TV magic. In theory, you probably could pressurize it, but far easier would be to use a waterlock, or just have the actual building be above ground, so the water will, naturally, not try to come up... although that would give you problems with low-tide, unless you raised the building itself. -- Phoeba WrightOBJECTION! 07:52, 19 May 2007 (UTC)


I thought that those actually existed? Pressurized rooms inside a larger structure - e.g. deep sea exploration vessels? --Kurt Shaped Box 09:13, 19 May 2007 (UTC)

I don't think it makes sense. The building was slowly flooded, without waterlocking mechanisms built in. This was evidenced as we saw someone swim from the surface of the ocean to the inside without meeting any waterlock/porous membrane/whatever. The entire building is around 50-100 feet underwater.

Instead of pressurizing the room, a way to do it would be to pressurize the entire building. This also allows the building to be relatively lightly built, as the air pressure holds back the sea, instead of requiring a pressure hull like a submarine or bathysphere. Of course you then have the issue that people in the building will have to breathe the pressurized air (or a suitable breathing gas), just as scuba divers do, which limits the depth where this technique can be used. It would also mean that when a submarine was going to visit the place, its interior air pressure would have to be turned up to match the pressure in the building, and decreased again (slowly enough to avoid decompression sickness) after leaving the building. --Anonymous, May 19, 09:00 (UTC).
An equivalent analogy would be underwater caves with air pockets below sea-level. Such things occur naturally, but I'm not sure how stable they are in the long term, as air can slowly escape upwards and/or dissolve into the water (I think??). However, they do exist at least at shallow depths (and I think in some James Bond-type movies). --Cody.Pope 10:06, 19 May 2007 (UTC)
PS when I read the title I thought it was about the other kind of submarine pens. --Cody.Pope 10:18, 19 May 2007 (UTC)
See SEALAB. This link[1] has a diagram at the bottom. The SEALABs were pressurized to the ambient sea pressure, and divers entered and exited via a simple door in the bottom. -Arch dude 18:10, 19 May 2007 (UTC)
Oh man Arch dude, genius diagram, especially the shark cage around the port, that would have prevented Samuel Jackson from being eaten in Deep Blue Sea.

See Caisson (engineering).

Atlant 12:48, 21 May 2007 (UTC)

[edit] Eucalpytus balls

What are the spiked balls that fall off of eucalyptus trees called? Wiwaxia 08:30, 19 May 2007 (UTC)

From our eucalyptus article:

The woody fruits or capsules, known as gumnuts, are roughly cone-shaped and have valves at the end which open to release the seeds. Most species do not flower until adult foliage starts to appear; Eucalyptus cinerea and Eucalyptus perriniana are notable exceptions.

So I guess that means, gumnuts is the answer? --Cody.Pope 10:31, 19 May 2007 (UTC)
Thanks! I searched for "ball" and "spike" in the eucalyptus article and couldn't find the words. Wiwaxia 23:05, 19 May 2007 (UTC)

[edit] automobiles

Why do tractors have their rear wheels larger than their front ones?125.63.107.129 13:01, 19 May 2007 (UTC)

For more torque I believe. I apologize for the off the cuff answer. --Cody.Pope 13:18, 19 May 2007 (UTC)
Nope. all other things being equal, the bigger wheels would provide a less powerful pull, not more. But other things are not equal: The tractor's gear ratios are much lower than on a car to compensate for the large wheels. The wheels are large to provide a large surface area of contact with the ground so that they will not simply dig themselves into a muddy field. When a farm worker misjudges the situation, then whatever the tractor is hauling will begin to sink into the mud, increasing the required traction. The driver will try to compensate by adding power, and the tractor wheels will begin to dig in. If the driver persists, the tractor can sink all the way to the axle, and you generally then need to haul it out with a bulldozer. Instead, the driver should stop immediately. You can then detach the tractor from the equipment it's hauling and reposition the tractor to haul the equipment out backwards. The front wheels are small because they are not motorized and therefore do not dig themselves in. They also do not carry much weight relative to the rear wheels: it's relatively easy to do a "wheelie" with a tractor, and farmers regularly used to kill themselves by flipping the tractor over as the front came up past the vertical. Tractors now generally have roll bars.-Arch dude 17:56, 19 May 2007 (UTC)
Many tractors are also weighted so they are more stable (by placing mechanized parts low to the ground or adding ballast. This lowered center of gravity might make a wheelie impossible on some tractors. Nimur 00:34, 21 May 2007 (UTC)
A larger wheel will reduce torque at the ground, not increase it. A larger wheel will however give better traction and improve your ability to travel over uneven ground. Friday (talk) 17:38, 19 May 2007 (UTC)
which torque? since shaft is connected to engine through gear box it gets constant torque and rpm.MAY BE it is something related to mechanical advantage.125.63.107.131 12:12, 21 May 2007 (UTC)
And tractor "wheelies" are famously parodied in Cars.
Atlant 21:35, 21 May 2007 (UTC)

[edit] i.c.engines

I.C.ENGINES will be more efficient in winter or in summers & why?125.63.107.129 13:05, 19 May 2007 (UTC)

See Heat engine for guidance on this


In the winter, the air is colder and hence denser - so your engine gets more oxygen than it normally would - this allows it to burn more fuel and get more horsepower. But more horsepower doesn't mean better fuel economy. The engine runs inefficiently until it gets up to it's ideal operating temperature - which takes longer in the winter. So in all likelyhood, you'll get worse fuel consumption but more peak power. SteveBaker 18:08, 19 May 2007 (UTC)
We also have to consider that in the winter molecules are moving more slowly and the metal is smaller and more tightly compacted in the metallic crystal. Therefore not only would the viscosity of the oil increase adding to friction, but less clearance between machined metal parts may also add to friction. This should decrease power and fuel consumption which wouldn't make it more or less efficient, I think (right?).
That's all true for the first minute when you turn the engine on - but it's all pretty hot within a minute or so. Starting your engine in cold weather uses more gas and wears out engine and oil faster - but unless you are doing a lot of really short trips with long waits for the engine to cool down between them, this isn't a huge factor. SteveBaker 02:32, 20 May 2007 (UTC)
I once had a car that ran on 10-11 liters of gasoline per 100km in winter but needed only 6-7 in summer. What puzzeld me was that this even held for long traveling times when the motors temperature souldn't depend much on the outside temperature. 84.160.200.170 22:19, 19 May 2007 (UTC)
Cold weather makes the lubrication less effective in every part of the vehicle (even non-motorized wheels / axles). This may play a large factor in fuel efficiency. Nimur 00:36, 21 May 2007 (UTC)
so plz tell me gentlemen what is the final conclusion?125.63.107.131 12:05, 21 May 2007 (UTC)

[edit] effexor xr

i am trying to find out some info on the pescription drug effexor i have recently been given this drug and i have to submit to randon urine drug screening for methamphetamine will effexor make my ua,s test positive for amphetamine or methamphetamines

effexor™ also known by the common chemical name Venlafaxine is an antidepressent in a class known as SNRI. The difference between this drug and other antidepressents is that effexor acts on norepinephrine (nor-adrenalin) neurotransmitters as well as serotonin. This norephinephrine reuptake blocking may be similar to a low dose of cocaine. To answer your question, effexor, to my knowledge, will not turn into an amphetamine metabolite. I tried to research amphetamine metabolites and effexor metabolites but I couldn't find anything. However, just by analyzing the two structures of amphetamine and Venlafaxine, one can clearly see that amphetamine will be deaminated by the liver into a ethyl benzene while it looks like the liver may have problems deaminating the tertiary amine of Venlaxfaxine. Furthermore, even if it was deaminated there is still dimethyl ether group in a para position making it distinctly different. Therefore effexor will not produce amphetamine metabolites and will not make a common NIDA-5 show positive for amphetamine. —69.241.236.12 13:57, 19 May 2007 (UTC)Adam

[edit] planes in air

Can you tell me how many planes are in the air around the world at any one time or how many flights there are each day on earth please?

okay first we define plane. Fixed wing commercial jet aircraft? Then remember that in any commercial airport, many planes are flying in circles waiting for clearance to land and others waiting to take off. This means commercial airport throughput is the limiting factor here. This would be fairly simple to calculate if one did exhaustive research on every commercial airport's flight capacity. This is the only way to figure out the world's commercial air traffic, in my opinion, because some countries dont have centralized FAA like the United States. However, if your question includes non-commercial flights, I think your question is impossible to calculate unless you have access to huge RADAR arrays or imaging satellites.

69.241.236.12 14:18, 19 May 2007 (UTC)Adam

Or you can go here for U.S. flights. [2] At this instant, there are about 4,400 planes with flight plans in the air (doesn't include non-flight plan flights such as VFR flights). 45,000 arrivals in the last 24 hours. --Tbeatty 19:48, 19 May 2007 (UTC)

[edit] Purely Hypothetical

Lipids in the body are made up of fatty acids and glycerol. Acids and bases neutralize to form salt and water. This being said, what would happen to someone who consumed many bases? Would the bases somehow react with the acids and allow this person to trim fat? In essence, the question is: Is consuming large amounts of basic foods e.g. drinking tea beneficial to those who wish to lose weight? Conversely, does consuming large amounts of acid foods e.g. Coca Cola contribute to lipid stores in the body?

Thanks a lot 208.96.96.207 14:19, 19 May 2007 (UTC)


First of all remember the pH in the stomach is about 1 because of all the HCL, meanwhile the intestine is buffered by the pancreas. Second, the pH of the blood is kept constant by our various buffering systems to between 7.35 and 7.45. Dietary acids and bases are not going to effect the acid base chemistry of a human unless it is in a toxic dose. If the dose was toxic, yes, but not beneficial; acid base reactions would occur locally in the tissues of the alimentary canal and will cause tissue damage. However, lipid tissues that we call fat, is subcutaneous fat that resides between the muscle and skin. Therefore, there would be no way to react acid or bases with this tissue unless you had gross metabolic pathologies resulting from excess dietary intake. Basically, acid-base is biochemically regulated and in a healthy system will not be the deciding factor in any tissue formation or loss. Coca-Cola® with over 40 grams of high fructose corn syrup in a 12oz can will contribute to lipids stored in the body, but not with acid base chemistry that you describe. The insulin will spike and when the muscles and liver are full of glycogen (glucose and water) the extra simple sugars from fructose will be stored as lipids. Furthermore, remember that our body has many nucleic acids as well, so just by looking for the word acid in a bio-molecule isnt a really good indicator of what happens in situ. However, there are diets that do describe the corresponding weight gain and loss with respective acid and base foods, but for me the mechanism and evidence is not well understood.--InitialMan(adam) 02:14, 20 May 2007 (UTC)

[edit] How does Diabetes cause damage to blood vessels

Diabetes mellitus often results in longterm damage to blood vessels. How and why does this happen? AxelBoldt 16:18, 19 May 2007 (UTC)

Long term damage of small and large blood vessels known as micro and macroangiopathy, is a chronic complication of hyperglycemia. Histiochemically the lesions in the vessels are characterized by increased accumulation of glycoprotein. In addition, because the chemical components of the basement membrane in the blood vessel lumen can be derived from glucose, it causes an increased rate of formation and thickening of basement membrane. These cells do not require insulin for glucose use.--InitialMan(adam) 02:14, 20 May 2007 (UTC)

[edit] Area Moment of Inertia with Multiple Materials

I have a beam made of a layer of silicon and a layer of gold on top. I want to find the area moment of inertia (I) of the beam. I know that I have to use the ratio of the Young's Moduli to scale the widths to find the neutral axis, but must I also scale the widths when calculating the moment of inertia? --Joe 16:44, 19 May 2007 (UTC)

If you've calculated the moment of inertia of each material about it's own neutral axis, you can then combine that info using the parallel axis theorem to calculate the moment of inertia of each material about the resultant neutral axis (which you've already found), and then just total the two translated moments of inertia. Also, you can test that you have calculated the neutral axis correctly, by seeing if the beam will balance about that axis. If you have access to a lathe, place the beam on the lathe such that the neutral axis is the axis of rotation. If you are correct, it should spin nicely. If not, it should vibrate the lathe as it spins, from the imbalance. Start the lathe slowly, in case you were way off in your calcs, and always wear goggles and use the lathe guard. StuRat 17:17, 19 May 2007 (UTC)
But when I am calculating the individual section's inertia, should I still scale the base according to the Young's Moduli ratio? The total inertia is different if I scale the first material to the second or vice-versa. I can't really put it on a lathe as the total thickness of the beam is only 2 micrometers.--Joe 17:49, 19 May 2007 (UTC)

[edit] Isotretinoin / Roaccutane

About four years ago I went on two courses of "low dosage" roaccutane (isotretinoin) - and 4 years later my life has been extremely affected by it in a very detrimental way...

  • I have very dry eyes,
  • a very dry nose (where occasionally I have to remove the dry skin inside, sorry),
  • a reoccuring mild nasal infection,
  • my facial skin is dry and irritated (whereas at once stage after Roaccutane it was good),
  • as well as a generally dry mouth

all at the age of 20.
I am going to be scheduling appointments with an ENT (for my nose and mouth),
a dermatologist for my skin,
and I've seen several opthalmologists about my eyes.
I am seeking one of two outcomes: Either I must cure my symptoms or I must seek retribution.
I am even keen to try find a forensic dermatologist and possibly taking legal action against the manufacturer and/or my dermatologist.
Questions:

  1. Who is the best doctor(s) to see about reversing the long-term affects of Isotretinoin/Roaccutane?
  2. How should I go about proving isotretinoin as the cause of my problems?

Any advice on reversing the damage done by isotretinoin is greatly appreciated (I have scoured the Roaccutane survivor forums many times)
Thank you in advance...

We can't offer legal or medical advice, but I can offer some dietary advice. A low fat diet will lead to dry skin, and a high fat diet tends to lead to oily skin. Of course, you also need to keep in mind that some fats are unhealthy in other ways. Particularly avoid trans-fats, saturated fats, and animals fats. Vegetable fats, as in avocados and most salad dressings (but not mayo) are healthy for you, as are nuts and cold water fish, like salmon, which are high in omega-3 fatty acids. Learn to read labels to figure out which foods are high in good fats and low in bad fats. Also, avoid drying shampoos, soaps, and detergents, and instead use moisturizing products, like Dove (soap). You may need to regularly use a nasal spray to keep the inside of your nose moist. StuRat 22:31, 19 May 2007 (UTC)
Why no animal fats, other than for avoiding saturated fats (which seem to be less causative for cardiovascular disease than non-conjugated trans-fats)? A fish is not an animal? See also essential fatty acid interactions for information about omega-3 and omega-6 fatty acids. Unfortunately, I cannot offer any advice on the original question. Icek 22:20, 21 May 2007 (UTC)
Fish certainly are animals from a scientific POV, but dietitians tend to differentiate between "animals" and "fish". Cold water fish tend to have fats that are better for you than other animals. StuRat 07:49, 22 May 2007 (UTC)

[edit] purely hypothetical

What is the chemical structure of dithetamine, and is it toxic? Also, is it illegal to possess the substance in Maryland?

I searched PubMed and found nothing. Google only points to fictitious references to it, not the actual chemical. 69.140.164.142

is it even a real compound? Coolotter88 22:58, 19 May 2007 (UTC)
never heard of it InitialMan(adam) 01:57, 20 May 2007 (UTC)

[edit] green eyes

Hi there, I want to know that which haircolour heads mostly have green eyes: Red heads or Black heads? The reason I asked this question is that most of the time, blondes have blue eyes while brunettes have brown eyes and what blackheads? which eyecolour do they mostly have?

Wouldn't black-haireds most commonly have black eyes? I should imagine that Red-haireds most-commonly have green eyes. But this is all a guess. 138.130.23.133
A majority of humanity (at a guess) has black or brown hair and brown eyes. Most of the redheads I've known (including grandma and my ex-wife) had/have blue eyes. Most of the green-eyed people I've known had brown hair. I don't know where you'd look for solid statistics; there may be none because hair color varies continuously and thus there may be no consistent classification. —Tamfang 18:53, 19 May 2007 (UTC)
Comparing Template:Light hair coloration map and Template:Light eye coloration map, we can see that people with blue eyes have the lightest hair, and then people with green eyes have slightly darker (but still very light) hair. I would say brown would be most likely (red is a rare hair color). --Spoon! 22:11, 19 May 2007 (UTC)
How do you distinguish green eyes from blue eyes on that map? —Tamfang 19:39, 21 May 2007 (UTC)

[edit] ASTROPHYSICS

if an object is kept between 2 black holes having the same gravitational pull and everything thing is same ,where will the object go?

I don't study cosmology, but do we need to know if the object is past the event horizon. If I understand this correctly, two blackholes with over-lapping event horizons would be one black hole. Therefore, if an object is placed between two black holes (which would have to be outside the event horizon), then wouldn't it just have a gravitational pull such that it was between two stars of equal mass. Thus it would be stationary. Anyone else have anything to add?69.241.236.12 19:21, 19 May 2007 (UTC)Adam

woodn't it be torn in half?

If the two black holes were close enough and it was at the proper point, then it would, yes. Otherwise, the object would stay where it is, assuming no other force is acting upon it. This type of Lagrange point exists between every pair of objects, such as the Earth and Moon and Earth and Sun (there are also some other stranger types of Lagrange points). However, note that the two black holes would pull on each other, as well, and they would eventually merge, unless they were in orbit about each other as a dual black hole system. StuRat 19:44, 19 May 2007 (UTC)
Now I know what sucks more than getting sucked (no pun intended) into a black hole, getting sucked into two black holes at the same time...Someguy1221 22:15, 19 May 2007 (UTC)
Does a black hole get sent into orbit without merging because of Kinetic energy. Are two a black holes in orbit exhibiting rotational energy as well as translational energy(centripetal) which balance to create the orbit?
Any two objects can orbit one another, due to rotational kinetic energy. However, if there were material being sucked into the two black holes from outside the system, this would tend to drive them together. StuRat 06:08, 20 May 2007 (UTC)
Sometimes black holes collide. Here's a story about such an event. Here's a computer simulation of it occurring, with nifty video. I don't think it's true that two black holes with intersecting event horizons are automatically one black hole. Big black holes have event horizons on the order of the size of our solar system, so it would take at least some number of light-hours for the singularities to merge. --TotoBaggins 22:33, 19 May 2007 (UTC)
It's not really important that these are black holes - being at the mid-point of two equal mass stars or planets or anything else produces the same effect - the gravity fields are equal and opposite and cancel out. This happens somewhere between the Earth and the Moon - but this isn't a stable position - if your object moves even a little bit away from that precise mid-point, it'll be attracted fractionally more by the nearest black hole (or whatever) and fractionally less by the other - so it'll start to move towards that one - increasing the effect. Between two planets or even stars at a reasonable separation, the gravity field changes very gently and it might take a long time for the object to drift away from this 'zero g' midpoint - but with two black holes (especially if they are very close), moving even a tiny amount away from that midpoint would cause this instability to become evident. Keeping the object at the precise position where the fields cancel would be like balancing a coin on it's edge. It's an inherently unstable situation and even the slightest vibration would cause rapid motion away from the centerpoint. If the object is relatively large - compared to the rate of change of the gravitational field - then it might well be torn in half because each side of the object is closer to one or other of the black holes - so each side will be pulled in opposite directions - and if the black holes are big and close then getting ripped in two is possible I suppose. In reality, your two black holes would accellerate rapidly towards each other and 'kersplatt!' in the middle - right where your object is sitting. In order for this careful balance to exist, the black holes would have to be orbiting each other. When things with nice large gravity fields orbit each other (like the Earth and the Moon) - there are places called Lagrange Points that offer zero gravity and stability. An object in one of those places would stay firmly put - if it drifted a bit out of place, it would be pulled back into that perfect spot. Read Lagrange points for more information. SteveBaker 02:10, 20 May 2007 (UTC)
It's not my interpretation that all Lagrange points are stable. I believe the diagram at that article shows that points L1, L2, and L3 are stable in one direction, but not another, while L4 and L5 are stable in all directions. See Lagrange_Points#Stability. StuRat 08:00, 22 May 2007 (UTC)

[edit] Hygrometer animals?

In the 1950s and '60s weather barometer animal figurines were popular. They usually changed color when the weather was going to change from sunshine to rain or snow. After a period of time they stop working (changing color). I am curious as to what chemicals they were coated/painted with that made them work and if it would be possible to recoat one and have it work again. At the very least, anyone know where i can find out more information about them? I've had a quick search and come up blank. 80.229.228.229 20:11, 19 May 2007 (UTC)

Yeah - I know exactly what you mean. When I was a kid in the late 1950's and early 1960's we had animals made of a soft soap-like or perhaps waxy stuff that changed colour like that. I think the pigment was absorbing water from the air and changing colour as a result. When rain is due, humidity goes up - so the animal absorbed water - when the weather is turning sunnier, the humidity drops and the animal dries out - causing the colour to change back again. My recollection was that they went from red to blue. Desiccant#Coloured saturation indicators suggests this may have been Cobalt(II) chloride (See also Cobalt chloride paper). SteveBaker 02:22, 20 May 2007 (UTC)
Oh - and by the way - Cobalt Chloride is toxic. Back in the 1950's it was enough to print "WARNING - TOXIC" on the packaging and then to sell it to little kids...these days...I don't think so! If you are planning to rejuvinate these toy animals - please don't let your kids near them! SteveBaker 02:25, 20 May 2007 (UTC)
So these were hygrometers, not barometers. I've changed the header to match this.
Atlant 12:54, 21 May 2007 (UTC)
That's my belief - yes - but I don't have proof. It's hard to imagine a simple chemical change that would come about as a result of air pressure and which would have been commercially exploited in the 1950's - but since humidity is also some kind of a weather predictor - it might well be that. People claim to be able to predict the weather with pine-cones (for example) - and those open and close due to humidity - not air pressure. (Hmmm - neither pine cone nor weather lore mentions this yet it's a really common thing in the UK to see people keeping an old pine cone to predict the weather?!). Cobalt Chloride is also a guess - but it fits with my memory of the colour change from blue to pinkish red - and the stuff was well known for changing colour in the presence of moisture even back in the 1950's. Of course these days, so many people have air conditioning - which removes the humidity from the air - that this kind of trick isn't going to work anymore and a barometer makes more sense for indoor use. Also, the toxicity of Cobalt Chloride means that there is no way anyone is still going to be using the stuff in children's toys - but back in the '50s, you could get away with killing a few of your customers now and then. SteveBaker 23:08, 21 May 2007 (UTC)

[edit] Plants water purification

These are biologic questions.It would be nice if I take useful references and links: 1.How plants can purify the solutions and water in the ground and attract necessary substances? 2.how they can discern the particles of substances and elements , with what special characteristic of them? 3.Is the attraction according to the requirement or instinctive?Flakture 20:49, 19 May 2007 (UTC)

[edit] Venom

Hi, could anyone tell me which animal is the most venimous in the world? I've been wondering for a while. Gbgg89 21:09, 19 May 2007 (UTC)

According to this source [3] the worlds most venomous animal is the box jellyfish (the most venomous snake is the inland taipan and the most venomous fish, the stonefish.) Other animals are more poisonous - such as types of poison arrow frog - but do not "deliver their toxins by stinging, stabbing, or biting." Rockpocket 21:29, 19 May 2007 (UTC)
Terrific timing! anonymous6494 01:58, 20 May 2007 (UTC)

[edit] Pt as Hydrogen Catalyst

I am trying to find a source that describes how Pt acts as a catalyst for hydrogen combustion. I am trying to find the temperature range that it acts at. If anyone knows of an academic paper or website, please post. --Joe 21:21, 19 May 2007 (UTC)

It seems to varying considerable according to this 1995 journal article and can be controlled by varying the helium concentration in the gas stream. -- MarcoTolo 04:09, 20 May 2007 (UTC)

[edit] The hole truth

Are superlarge black holes less dense as Fred Pohl writes (i.e. we could be inside one right now)? If so, how are they created? I mean, if infinitely dense small black holes accrete enough mass to grow that big, what is the transition process? Clarityfiend 21:51, 19 May 2007 (UTC)

The singularity at the center is, in theory, infinitely dense for all black holes. If you mean the volume within the event horizon, the density there might very well vary, but I'm not sure in which direction. StuRat 22:06, 19 May 2007 (UTC)
He might also be referring to the fact that supermassive black holes have a larger event horizon, which is less gravitationally severe to enter than that of a small black hole. You would certainly survive entering the event horizon of such a black hole (though I wouldn't buy any green bananas), but the gravitational gradient at the event horizon of a small black hole would lead to spaghettification. Black holes are fascinating enough without having to insert any balderdash about us being inside one; I suggest you stick with reliable sources. --TotoBaggins 22:56, 19 May 2007 (UTC)
Reliable sources? Well, the article Schwarzschild radius says: "The Schwarzschild radius of a sphere with a uniform density equal to the critical density is equal to the radius of the visible universe." But I don't understand what value this critical density has. To me, it reads like the visible universe might have a density and radius such that the Schwarzschild radius is even bigger. In other words, we are inside of an universial black hole. 84.160.200.170 23:12, 19 May 2007 (UTC)
Hmm. I don't understand what critical density is, so I can't comment. I assumed the "we might be in a black hole" notion from a sci-fi author was a variation on the sort of "what if the whole universe is just an atom in a bigger universe" Gedankenexperiment that keeps frat boys in states of wonder. My apologies if we are indeed situated in a black hole. :) --TotoBaggins 00:55, 20 May 2007 (UTC)
Well, if the numbers for the universe agree to it, we are in a black hole. I see not much room for a "might". It is a precondition that the universe must be in a process of implosion to be a black hole. If the universe has less than critical density it expands forever and is not in a process of implosion and not a black hole. See Hoop Conjecture.
About the first question: Large black holes are less dense than small black holes in a certain sense, yes. The schwarzschild radius grows linear with the mass and the volume of a sphere grows with the third power of its radius, so the density = mass/volume falls with growing size. Please remember that the schwarzschild radius is a theoretical radius that the hole would have, if it's diameter to circumference ratio would be pi. Measured from the inside the volume will be something very strage, maybe even infinite.

[edit] Evolutionary purpose of eye colour

Surprisingly, neither our articles on eye colour nor iris answer this; is there any reason humans have evolved to produce such a wide range of eye colours? The eye is only part of the body which isn't always just some shade of pink or brown, yet it seems to play no role in life (a person with green eyes can't see any better than one with brown or blue eyes). Laïka 21:51, 19 May 2007 (UTC)

actually the article History of eye colors might help you Coolotter88 22:11, 19 May 2007 (UTC)
The obvious reason is that it's used for identification of specific individuals, and, at some point in the past, membership in an ethnic groups (by now eye color genes are so intermixed that it's no longer useful for that purpose). StuRat 22:15, 19 May 2007 (UTC)
That's an example of a question that sometimes bugs me: can variability itself be selected for? —Tamfang 19:47, 21 May 2007 (UTC)
That's a very good question. You might want to read chapter 8 of Mérő László, Moral Calculations for a good discussion of this. (I won't give a definite yes or no answer.) – b_jonas 12:55, 22 May 2007 (UTC)
Mutation of genes involved in melanogenesis, followed by genetic drift is the most likely reason. There is no statistical evidence of positive selection driving the spread of mutant alleles in pigmentary genes in humans, despite what the history of eye colors article suggests. (see PMID 10733465). Rockpocket 23:37, 19 May 2007 (UTC)
Surely the wide variation in human eye colour is actually a demonstration that eye colour isn't very important genetically. Things we (almost) all have in common - like having exactly ten fingers are likely to have evolved that way for really important reasons - things that are wildly different between us can't have a lot of importance from an evolutionary standpoint or one or other of the variations would come out clearly on top and we'd all be the same. So I would assume that the wide variety of eye colours indicates that there is so little evolutionary benefit to one colour versus another that no single eye colour has come to dominate our society whilst polydactylism (having more than 10 fingers or toes) is quite rare - even though it too is genetically linked. We may suppose that there have been strong evolutionary pressures to maintain a ten fingered population whilst there has been little or no pressure to allow blue-eyed people to take over the world. SteveBaker 22:54, 21 May 2007 (UTC)
I have to disagree partially on this. There's been talk about the extinction of non-black (or dark brown, whatever) colored eyes because of "interracial" breeding, because it's a dominant gene. Although it's been argued that the other colors won't go extinct, because they're still recessive and can occur, even if it's much rarer. But then this begs the question: Why is dark brown eyes a dominant gene if it has no evolutionary benefit? --Wirbelwindヴィルヴェルヴィント (talk) 08:03, 22 May 2007 (UTC)
A brown-eye gene says "produce brown pigment" where a blue-eye gene says "do nothing". If both are expressed, the brown pigment is produced. That's what dominance typically means: the action of one allele masks the non-action of the other. Are you asking why dark-eye genes are so much more common than pale-eye genes? —Tamfang 18:20, 22 May 2007 (UTC)
No, I'm asking why brown eyes is dominant compared to other colors. Is there a evolutionary benefit that causes it not to be an equally dominant gene as the other colors? --Wirbelwindヴィルヴェルヴィント (talk) 06:41, 23 May 2007 (UTC)
I just told you why brown eyes is dominant (perhaps someone else can paraphrase more clearly). I don't understand the other question. —Tamfang 21:01, 23 May 2007 (UTC)

[edit] Globular Clusters

Why is it that globular clusters are unlikely to support life? --Kitty who? 22:37, 19 May 2007 (UTC)

For one, the globular cluster article states that globular clusters are groups of tightly packed old stars which IIRC, the radiation kind of kills off life. The article also states that most of the stars are "population II" which means they have low metal content (I guess it would therefore mean a less likely chance of terrestrial planets like Earth forming).Coolotter88 22:45, 19 May 2007 (UTC)
Note that this is the astronomers' usage of "metal", which means "anything other than hydrogen or helium". So indeed a low "metal" content means that terrestrial planets are unlikely. Also, I think the closely spaced stars means that planetary orbits are more likely to be perturbed over time by other nearby stars and will not remain stable for the billions of years we see in our solar system. --Anonymous, May 20'07, 03:38 (UTC).

[edit] Volcanoes- Mount Krakatoa in Indonesia

When was Mount Krakatoa first created and what boundary was it created over ( divergent, convergent or hotspot) ?209.247.23.85 23:03, 19 May 2007 (UTC)

Is our Krakatoa article of any help ? StuRat 05:56, 20 May 2007 (UTC)
Plate tectonics is also useful. Krakatoa, like much of the Indonesian archipelago, is located at the convergent plate boundary where the Australian plate is subducting under the Eurasian plate. --mglg(talk) 00:07, 21 May 2007 (UTC)

[edit] Mount Everest

I'm not sure this is the right reference desk for my question. The article Mount Everest says "Radhanath Sikdar, an Indian mathematician and surveyor from Bengal, was the first to identify Everest as the world's highest peak in 1852, using trigonometric calculations based on measurements of "Peak XV" (as it was then known) made with theodolites from 240 km (150 miles) away in India." Can Mount Everest really be viewed from that far away? Or is it still visible even further away? (Provided ofcourse other physical features don't block the view) AecisBrievenbus 23:10, 19 May 2007 (UTC)

If we assume the earth to be a perfect sphere of radius 4000 miles, and Mount Everest to be six miles tall, then by the pythagorean theorem it is viewable from up to 219 miles away (did I get my math right?). You do this by constructing a triangle in that connects the peak of Everest, the person viewing it, and the center of the earth. As long as the leg from the viewer to the peak doesn't pass through the surface of the Earth, Everest can be viewed from that position. Someguy1221 23:22, 19 May 2007 (UTC)
Just as an aside, this math assumes your eyeballs are pretty much laying on the ground, standing on top of something tall will allow you to see quite further. Someguy1221 23:25, 19 May 2007 (UTC)
The computed value is correct according to Horizon, but it assumes that your viewpoint is at sea level. I don't know how rapidly the land drops off as you move away from Everest (and I don't have time to look now), but I don't think there's anything implausible about a sighting from 150 miles. --Anon, May 20'07, 03:44 (UTC).

Another issue is that you would need to have 240 km (150 miles) of visibility, which is rare just about anywhere, but especially in the mountains, which are prone to poor weather. StuRat 05:48, 20 May 2007 (UTC)

Visibility says "clean air in Arctic or mountainous areas, the visibility can be up to 70 to 100 km". But I personally have seen a mountain from ~150 miles (Nelson to Mt Taranaki in New Zealand). It wasn't a particularly clear day. Aaadddaaammm 08:54, 20 May 2007 (UTC)
In case anyone cares, you dont need pythagoras. The length is simply given by 4000*arccos(4000/4006)Zain Ebrahim 14:47, 21 May 2007 (UTC)
The practical problem when using that formulation is that when you plug in the numbers for the real radius of the earth, then the result of the inner division is a number very close to 1.0 - and because most pocket calculators and simulations of pocket calculators on computers use floating point arithmetic - you get a really inaccurate answer. Then taking the arc-cos of a number very close to 1.0 stresses the series expansion that the calculator uses and generates an even worse answer...which you proceed to multiply by the radius of the earth which magnifies the error still more. So whilst that equation is true, it's really poor for numerical reasons. Formulations that don't rely on that method work better in practice. SteveBaker 22:45, 21 May 2007 (UTC)
Ok Thanks. Just two questions. If you didn't use a series expansion to solve arccos (some sort of iteration perhaps) then would that significantly improve the method? What other formulations are there? Zain Ebrahim 08:28, 22 May 2007 (UTC)

[edit] Northern bluefin tuna

Is the Northern bluefin tuna really on the verge of extinction? Because I just saw an abc news story on the subject, and it suggested that they are practically an endangered species. However, our article on Northern bluefin tuna suggests that while the population has declined steadily, it's no where near as dire as the new story suggests. What's the best possible answer? No fish stories please--69.118.235.97 23:11, 19 May 2007 (UTC)

According to the IUCN page on the Northern Bluefin (which is in the references section of the wikipedia article), we don't know ("data deficient")... However, it also says the Eastern Atlantic stock is endangered and the Western Atlantic stock is critically endangered, so they're in a pretty bad way. The assessment by the IUCN is only from 1996 though. So I'd say they're pretty badly off, especially with high demand for quality sushi. ADW says "Many are concerned that bluefin tuna could easily become endangered due to high demand as a food source and resultant overfishing." —Pengo 02:29, 20 May 2007 (UTC)

Note, however, that being "endangered" isn't the same as being on "the brink of extinction". Many endangered species have recovered after action was taken to protect them. StuRat 05:35, 20 May 2007 (UTC)

"On the brink of extinction" is journalist talk, and could mean anything. Though I'd think it would be fair to say "critically endangered" (CR) species or stocks are on the brink of extinction. —Pengo 00:51, 21 May 2007 (UTC)

[edit] need help with birds

A few weeks ago, a bird set up a nest above my front doorway. (what a rare occurrence!) There were two eggs, and now they both hatched. (they look so cute, btw) Can anyone tell me what I should be feeding them? So far, my dad put in raw rice, but I don't know if they actually ate it yet. Am I supposed to give the two birds water?--Ed ¿Cómo estás? 23:55, 19 May 2007 (UTC)

Could someone please help me??? The birds might get hungry...--Ed ¿Cómo estás? 00:35, 20 May 2007 (UTC)

If the parents are still there, I'm sure they can take care of feeding their babies themselves. Coolotter88 00:41, 20 May 2007 (UTC)

It looks like the parents flew away...but they might come back--Ed ¿Cómo estás? 00:55, 20 May 2007 (UTC)
Put in rice? Did you put rice in the nest!?
There is Bird#Diet and Feeding, but I think the parents will come back, for evolutionary reasons: little birds whose parents didn't come back have died, and didn't pass on their genes that told them not to come back to feed their children. A.Z. 01:02, 20 May 2007 (UTC)
Parents who have been disturbed in their hatching will leave their children to die and breed new ones next summer instead of being eaten along their current ones this summer.

I kinda had to put the birds in a separate basket because they fell from the nest. Should I put them back in their original nest?--Ed ¿Cómo estás? 02:35, 20 May 2007 (UTC)

Yes, and try not to touch them, as they will then acquire your scent and the parents won't recognize them. I would watch for if the parents return. If they don't, then you can try to take care of the birds yourself. You will need to know what kind of birds they are, as some eat berries, some eat bugs, some eat seeds. I suppose you can offer them a selection of foods and they will likely take whatever they like. They will also need water, of course, if you are taking care of them. You'd better get a cage for when they start to fly. Chances are, they won't survive "in captivity", but you can still give it a try. If you take some pics and post them here or show them to a bird expert, we can try to identify the species and what they eat. StuRat 05:30, 20 May 2007 (UTC)
I heard that most species if not all of birds didn't reject young based on olfactory contamination. Has anyone else heard this was a fallacy? --InitialMan(adam) 13:31, 20 May 2007 (UTC)
Yes, that's true; most birds have a poor sense of smell. Snopes has a piece on it [4] here. I'm assuming the baby birds aren't turkey vultures! Matt Deres 01:49, 21 May 2007 (UTC)
What sort of birds are they? Did you muck around with the nest, put food in, etc, before the parents 'flew away'? When did you last see the parents visit the nest? If you do have to feed them (ie, the parents never come back), you'll have to do it very carefully. I imagine you'll have to pipette/syringe it into their beaks. Skittle 16:23, 20 May 2007 (UTC)
Some species of birds seem to abandon their young in the nest without actually doing so. We've often had nesting hummingbirds on our property. After the first few days, the babies are able to regulate their own temperature, so don't need Mom sitting on them all the time; after that, Mom is hardly ever around - she's spending the bulk of her time flitting around catching insects to feed the little poop-generators. (Amazing how much guano a pair of baby hummingbirds can generate.) So don't assume abandonment; it could easily be "oh crap, those annoying humans are there, let's wait until they leave so we can come back and feed the kids." (Currently, we've got Black Phoebe and House Finch nests at our summer place, and Black-chinned Hummingbirds at our regular home. The phoebes couldn't care less whether we're around, nor could the hummers; on the other hand, the finches fly off if we so much as look at them.) --jpgordon∇∆∇∆ 17:29, 20 May 2007 (UTC)
Ed, it looks like you are in the Chicago area. There should be a chapter of the Audobon Society in your area. They should be able to advise you on how to best care for the hatchlings, though they may ask you to give the birds to them. 161.222.160.8 23:14, 21 May 2007 (UTC)