Wikipedia:Reference desk archive/Science/2006 September 12

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[edit] September 12

[edit] Organ Transplant...

- Recently, someone I know was diagnosed with a serious disease. After some time, i di research on how organs can be transplanted and everything I could in my power to help. But in all seriousness, even if the information was useful, there were still some questions to ask, and my doctor would not answer:

1) How long do transplants last? 2) How effect are they? 3) What are the long term affects? 4) How much do they cost? Are there any help plans? 5) What are the chances for rejection? 6) What are the options for a person who's body is rejecting an organ? 7) If that person's body is rejecting an organ, how long do they live? 8) What steps must I take in order to prevent anything from happening ( to the person and to myself, it runs in the family)?

Please, no pictures

- Thank you ---Sam

What do you mean how long does it last? You mean the operation to take an organ out (could be any organ), or to put it in, or how long will the organ last? If the doctors know what they are doing the organs will be 100% effective, because it is a new one. Cost depends on the organ, rejection possibilities depend on the organ, options, depend on the organ, lifespan after rejection without a new organ depends on the organ and their condition... we need more information. — [Mac Davis] (talk) (Desk|Help me improve)

Here are accurate answers to your questions based on the information you provided us. Now do you understand why your doctor didnt give you specifics? Best wishes to both of you. alteripse 01:47, 12 September 2006 (UTC)

Depends on the organ. If it is working at a year, chances are good for a couple of decades, more or less. #Usually if it works, it works adequately.
Many long term effects. Damage from malfunction before transplant. Peri- and postoperative injuries & residual effects. Long-term immunosuppression increases cancer and infection risk. Drug side effects. Long term change of life perspective from life-threatening illness.
Depends on where you live. Depends on where you live.
Chance for rejection ranges from 10 to above 50% depending on the organ, the combination of immunosuppressive drugs, the quality of the match.
Artificial organ substitution (various methods depending on organ) or a new transplant.
How long they live depends on the organ and the effectiveness of the substitution methods and any other coexisting medical problems.
Steps to take to prevent something happening to the person? Depends on the organ, the disease, the available treatments, and the person's access to the treatments. Steps to take to prevent something happening to you? Depends on the inheritability of the disease and your genetic relationship, or on the contagiousness of the disease and your physical relationship and infection prevention measures, or on the other effects the person's disease might have on you (missed work, expense, cancelled plans, stress, etc etc).

Just to echo the above, it really depends on the transplant. A bone marrow transplant that works lasts a lifetime. A lung transplant may only last 5-10 years. Kidneys last decades. Etc. InvictaHOG 02:45, 12 September 2006 (UTC)

[edit] Sinusitis

Quite a few years back I had serious upper respiratory problems and a medical doctor decided to run x-rays of my sinuses. One of his comments was that I have a congenital defect: both of my frontal sinuses are absent. I never learned a technical term for this condition, which I understand is unusual. He mentioned that the absence of a sinus (or in my case a pair of sinuses) is associated with sinus problems, but the causal connection was unknown. What would be the medical term for this and how would I learn more? Durova 03:24, 12 September 2006 (UTC)

bilateral frontal sinus aplasia. If you look up "paranasal sinus aplasia" in Medline you may get some articles of interest. (The relationship between anatomic variations of paranasal sinuses and chronic sinusitis in children, "Benign" imaging abnormalities in children and adolescents with headache, Anatomic risk factors for sinus disease: fact or fiction?, etc.) Medline. - Nunh-huh 03:46, 12 September 2006 (UTC)

Thank you very much. Some of the abstracts were confusing - I'm not really sure how frontal sinusitis could be associated with frontal sinus aplasia (unilateral cases?) but it seems my abnormality is far more common than I had thought. Durova 04:01, 12 September 2006 (UTC)

[edit] What did I see on September 10?

On September 10, I went outside to see the Messier 27. I sketched the nebula as well as the stars around it. Using Cartes du Ciel, I identified all but one of the stars. Here is the star I couldn't identify:

http://72.136.70.187/mystery_star.jpg (north is up, this sketch was made at 02:15 GMT on September 10)

This star was about magnitude 9.7, but Cartes du Ciel showed no stars in the region brighter than magnitude 10.8. So what was the object that I saw? If it's a star or asteroid, why didn't Cartes du Ciel show it? If it's a variable star, which variable star is it? If it's a supernova (this is extremely unlikely), why isn't there a nearby galaxy in this region of the sky? --Bowlhover 04:14, 12 September 2006 (UTC)

Have you checked the other star charts? If so and its not there, youve found a new one! 8-)--Light current 04:17, 12 September 2006 (UTC)

No, but I will soon. --Bowlhover 16:26, 12 September 2006 (UTC)

Star charts won't show asteroids, and there are hundreds of thousands of them.--Shantavira 08:42, 12 September 2006 (UTC)

Cartes du Ciel does show 500 asteroids (most of which are much fainter than magnitude 9.7). It's not an asteroid. --Bowlhover 16:26, 12 September 2006 (UTC)

Dont those usually appear in the vicinity of that gaseous planetary giant? --Light current 10:30, 12 September 2006 (UTC)

The vast majority are in the asteroid belt, but there are other asteroids all over the show. Incidentally, list of asteroids just has to be the longest list on Wikipedia. List of noteworthy asteroids is somewhat more interesting (and also quite long).--Shantavira 12:00, 12 September 2006 (UTC)

You misunderstand me 8-)--Light current 12:29, 12 September 2006 (UTC)

"To be great is to be misunderstood". JackofOz 13:58, 12 September 2006 (UTC)

So you meant Patrick Moore, not Jupiter?--Shantavira 15:45, 12 September 2006 (UTC)

No its the large planet beginning with U. (again) Is it Uranium? 8-)--Light current 15:48, 12 September 2006 (UTC)

I've just made a comparison image between Cartes du Ciel, and your drawn diagram. The ringed star is there - as SAO 88052 - about 8th magnitude. I've ringed in white on your diagram the mystery star. It's interesting that there's an 8th mag star missing from your diagram that is there on Cartes du Ciel. I've checked the minor planet database, and the brightest object that's on that portion of the sky at the moment is about 15th magnitude - so it's unlikely to be that. I'd say it might be a drawing error - and that the missing star on Cartes has actually been drawn - and the extra star on the diagram is probably one of the ones on the Cartes map. It's easy to get stars in the wrong place on the diagram - as you are usually drawing the position relative to some other star - and these stars are all similar in brightness and easy to confuse with each other. Richard B 20:57, 12 September 2006 (UTC)

Hmmm...I was observing with a diagonal (sorry I didn't mention that!), so did you remember to flip the image horizontally? If not...

http://72.136.70.187/cartes.jpg

And if you rotate that picture 90 degrees clockwise...

http://72.136.70.187/cartes2.jpg --Bowlhover 22:19, 12 September 2006 (UTC)

[edit] I want to know that .....

How the control unit of a CPU/PROCESSOR/MICROPROCESSOR works ? I've cearched in wikipedia and in other sites but they all provide me with the information that microprocessors are made of IC/logic gate ; several electronic gates like and,or,not are described . What's the minimum number of logic gates that can form a microprocessor of embedded system(no matter how low the processing power/speed is) ? I want to know the process by which microprocessors control an electronic devie ; how I/O ports are connected with logic gates ? How logic gates are placed in a microprocessor ? Does the control unit of embedded system do the same work done by the microprocessor of a pc in the same way ?

I want to construct a control unit(something like used in embedded system)using IC/logic gate (no problem if the processing power/speed is low) for experimental purpose ; how the IC/logic gates have to be configured ?

If I recall correctly, the control unit typically impliments microcode to control the processor. As far as the minimum number of gates - I suppose there are some processors that do not have any centrally located control unit, so 0 is the answer. Raul654 05:35, 12 September 2006 (UTC)

Start here [1] Prepare for a long journey.

Also see the websites of many other hobbyists who have built similar machines:

* all-transistor CPU

* simplex 3

* 4-bit

* relay computer

* Don S.

* Magic 1

* TTL computer kit (in German)

--Wjbeaty 04:53, 13 September 2006 (UTC)

User:Wjbeaty has given a good answer, but you might also want to see this recent question: How processors work? – b_jonas 08:00, 14 September 2006 (UTC)

[edit] Conversion of units

I want to convert .21 Watts/meter Celsius to Watts/ meter Kelvin. Any suggestions please? -- Lost^(talk) 05:40, 12 September 2006 (UTC)

They're the same. Melchoir 05:45, 12 September 2006 (UTC)

Celsius and Kelvin have the same size degrees, so no conversion is needed. Kelvin is an absolute scale, while Celsius is not, but that doesn't require a conversion here. StuRat 05:46, 12 September 2006 (UTC)

Thank you -- Lost^(talk) 06:23, 12 September 2006 (UTC)

Furthermore, neither watts nor meters involve temperature., so there is no conversion anyway. ColinFine 23:14, 12 September 2006 (UTC)

[edit] Construction

Please tell me what is the name of the mixture containing cement and gravel in ratio 1:7 and used for construction.

Concrete. (Is this for real?) --Zeizmic 11:52, 12 September 2006 (UTC)

Wot? No sand?--Light current 13:06, 12 September 2006 (UTC)

Or water ? StuRat 14:25, 12 September 2006 (UTC)

[edit] Water

Why doesn't water have a taste or smell? Dismas|^(talk) 13:19, 12 September 2006 (UTC)

I find it has a taste, although not very much, but maybe this is to do with impurities. Perhaps it could be linked to ph value.

Your mouth is always full of the stuff. You could say that you've gotten used to the stuff, since it's the solvent that all of your cells are perpetually bathed in. TenOfAllTrades(talk) 13:37, 12 September 2006 (UTC)

(edit conflict)What would be the evolutionary advantage of tasting, or smelling, water? If it had a taste, that taste would run the risk of overpowering any impurities you wish to taste. When water tastes, or smells, when it shouldn't, you spit it out. Saving you from possible illness. --liquidGhoul 13:41, 12 September 2006 (UTC)

Right. And that's the same reason why air doesn't have a smell (only unusual things in the air have smells). StuRat 14:24, 12 September 2006 (UTC)

Many gases are odorless, even when they are in extreme concentration compared to their concetration in air. See hydrogen and helium. --Russoc4 23:55, 12 September 2006 (UTC)

Like Hydrogen sulphide (rotten egg gas). This occurs naturally, and is very toxic, so we can smell it in very low concentrations (and it smells horrible, so we move away). --liquidGhoul 14:34, 12 September 2006 (UTC)

Aren't elephants supposed to be able to smell water many miles distant? I can certainly smell the sea when I get near it, not to speak of the local canal. Seriously though, I can smell and taste water quite easily. Sheffield water tastes much better than Birmingham water, and Norwich water tastes dreadful.--Shantavira 14:50, 12 September 2006 (UTC)

Have you tasted distilled water? The stuff I have tasted all tasted like plastic, as that is what it was in. What you are tasting between different towns is just the different salts and impurities in the water. I love the water at my mum's house, which is tank water, and is close to rain water, probably with some rust from the tank and dilute bird crap from the roof. However, town water is terrible. It reminds me of pool water. Also, the smell of the sea is the fish, salt etc. --liquidGhoul 14:57, 12 September 2006 (UTC)

Salt doesn't smell. It's an ionic solid, and has an extremely low vapour pressure. --G N Frykman 17:09, 12 September 2006 (UTC)

What is the smell of the sea than? Microorgansims? — [Mac Davis] (talk) (Desk|Help me improve)

Salt most definitely does have a smell. We are able to detect many things in the air in extremely minute quantities, especially when doing so is, or was, necessary for our survival. Since lack of dietary salt was apparently quite a common problem for primitive people, the ability to detect salt was quite critical. Also, I believe that wave action causes tiny droplets of sea water to become airborn. The water then evaporates, leaving a tiny grain of salt floating in the air. Corrosion on metal roofs close to ocean water (but not in contact with the water), is known to be a problem, and building codes account for this. StuRat 02:45, 13 September 2006 (UTC)

Huh. I drink bottled water because the Los Angeles tap water tastes awful. User:Zoe|(talk) 02:36, 14 September 2006 (UTC)

Again, that isn't the taste of the H2O, but rather the impurities in the water. StuRat 09:56, 14 September 2006 (UTC)

[edit] toilet flushing on the equator

If north of the equator a toilet flushes clockwise and south of the equator it flushes counter clockwise, what happens if you flush a toilet on the equator?

It is a misconception that toilets flush differently on the northern and southern hemispheres. See the "Draining bathtubs/toilets" section in the article on the CorioliCoriolis effect. - Fredrik Johansson 15:27, 12 September 2006 (UTC)

I always liked this line of thinking as a way of dispelling the myth. Physics (the simple kind) isn't discontinuous, so there must be a band of uncertainty around the equator where the effect is too weak to determine toilet flow. And once you admit the existence of that band, why shouldn't it cover the whole globe? Melchoir 16:05, 12 September 2006 (UTC)

Careful though, it's quite common to have a discontinuity on a sphere. See Hairy ball theorem. DMacks 16:17, 12 September 2006 (UTC)

There's also spontaneous symmetry breaking. So the effect could be ambiguous in some places and not in others. -- Fuzzyeric 16:19, 12 September 2006 (UTC)

Yes yes, I know. But the Coriolis force is elementary stuff. It doesn't involve any complex systems, nor is its magnitude prevented from falling to zero. So it really should be overpowered by other effects at the equator, and lo and behold, it is. Melchoir 16:47, 12 September 2006 (UTC)

I think you'll find that "designed-in swirl" from the toilet's washdown jets probably overcomes the Coriolis Effect many times over. Tubs would be a different story, but you would need to take great care to assure that there's no residual swirl left over from the filling process, else the conservation of angular momentum from that initial motion would again swamp the Coriolis Effect.

Atlant 15:08, 13 September 2006 (UTC)

[edit] Bird's Sight

What are the characteristics of a bird's eye that give them such excellant vision?66.151.82.105 15:24, 12 September 2006 (UTC)RW McNamara

<--email removed to prevent spam-->

According to our article on bird anatomy, "Birds have acute eyesight, with raptors having vision eight times sharper than humans. This is because of many photoreceptors in the retina (up to 1,000,000 per square mm in Buteos, against 200,000 for humans), a very high number of nerves connecting the receptors to the brain, a second set of eye muscles not found in other animals, and, in birds of prey, an indented fovea which magnifies the central part of the visual field. Many species, including hummingbirds and albatrosses, have two foveas in each eye, and the ability to detect polarised light is also common."--Shantavira 15:38, 12 September 2006 (UTC)

Why would a bird need to differentiate polarized light? — [Mac Davis] (talk) (Desk|Help me improve)

Googling for bird "polarized light" reveals that it's useful for navigation. There's some more information about natural sources of polarized light in the Polarized light page. DMacks 16:01, 12 September 2006 (UTC)

[edit] Elasticity

which is more elastic rubber or steel? why?

Please take a moment to review with the instructions at the top of the page. We're pleased to help out with most questions, but I'm afraid that we have to ask you to Do your own homework. If you need help with a specific part or concept of your homework, feel free to ask, but please do not post entire homework questions and expect us to give you the answers. TenOfAllTrades(talk) 16:31, 12 September 2006 (UTC)

you dont know that thats a homework question. many questions asked here are far more complicated and homework looking. hes only asked 1 question and the reason why.--86.141.230.129 17:14, 12 September 2006 (UTC)

I beg to differ. Asking whether rubber or steel is more elastic is a transparently obvious homework question. That said, the answer is easily found in your textbook or a dictionary. — Lomn | Talk 17:25, 12 September 2006 (UTC)

If you're really stuck, click on the links I put in your question, or use the search box. Or just look up elasticity in a dictionary.--Shantavira 17:29, 12 September 2006 (UTC)

Please try before you ask for help. — [Mac Davis] (talk) (Desk|Help me improve)

What do you think an elastic band is more likely to be made out of, rubber, or steel?Tuckerekcut 22:55, 12 September 2006 (UTC)

Also see Young's modulus. If you can understand the article, the table indicates which material has the higher elasticity.--Light current 23:04, 12 September 2006 (UTC)

Well I don't know, squish a piece of steel, and a rubber ball and see which one snaps back into shape. Deltacom1515 02:05, 13 September 2006 (UTC)

Come on people. You dont get an 800 on your SAT unless you immediately recognize that the only possible answer to this question is the counterintuitive one, or it would not have been asked. Don't waste time, move on to the next question, recognize the pattern in the future. alteripse 02:35, 13 September 2006 (UTC)

Yeah if its a rubber band, you can deform that all you like and it wont come back; but steel would. BTW alterprise youre supposed to smile if youre joking! You were joking werent you?--Light current 02:39, 13 September 2006 (UTC)

I guess I am not sure if you are joking. I was speaking truth in jest but I will spell it out. The common immediate answer is that in the usual sense of the word elastic, the rubber elastic band is more elastic than steel and everyone knows it, but there would be no point in asking such a question if the academic answer were not the other. Understanding that this kind of question needs no more than one second of consideration is how you ace the SATs and get to leave first (it helps to know a lot of junk too). alteripse 02:48, 13 September 2006 (UTC)

I rarely joke as you should know! 9-) But the trick is knowing whether or not it is a trick question!--Light current 02:52, 13 September 2006 (UTC)

Elastic rubber. --Proficient 06:16, 14 September 2006 (UTC)

User:Alteripse: the problem here is that our anonyous poster has also asked "why?" so you can't just say it must be the counterintuitive answer. – b_jonas 07:49, 14 September 2006 (UTC)

[edit] Acrylamide in sultanas and other dried fruits

As a health precaution, until there is further clarification on if acrylamide is carcinogenic or not, I'm trying to avoid things containing it.

Can anyone tell me please how much acrylamide there is in sultanas - a form of dried grape. I have searched on the internet and emailed a sultana wholesaler about this without success.

There is a lot of acrylamide in prune juice - a prune is a dried plum. The browning process - possibly the Maillard reaction - creates acrylamide. Sultanas are dried grapes and undergo browning - they could also have similar levels of acrylamide (yes, I know grapes are otherwise good for you). Does anyone know for sure please? 81.104.12.39 18:39, 12 September 2006 (UTC)

Almost all natural food contains some sort of carcinogen. It's just that the other stuff usually makes up for it. Prunes are one of the healthiest things going (if consumed as part of a varied diet). To avoid all bad stuff, I suggest that you just eat highly purified sucrose. --Zeizmic 20:04, 12 September 2006 (UTC)

I disagree with all of your assertions. I'm looking for facts rather than homely armchair speculation please.

The fact of the matter is you would have to work rather hard to get all the acrylamide out of your foods. but from memory acrylamide is mainly an issue in foods cooked at high temperatures eg deep fried foods. the levels in most fruits etc seem to be quite low, [2], but sultanas aren't listed. Xcomradex 22:18, 12 September 2006 (UTC)

"The fact of the matter is you would have to work rather hard to get all the acrylamide out of your foods" - not true. If you avoid baked and fried foods, avoid coffee and chocolate, stick to either raw foods or foods cooked by boiling - then you can avoid acrylamide. You should also avoid olives and prunes and possibly other dried fruits. It is apparantly carbohydrates that are bad when fried or baked - some other foods seem to be OK according to the link you supplied. Bread can be replaced by mantou which should be OK as it is cooked by steaming at atmospheric pressure.

"but from memory" - you mean you havnt bothered to read the article acylamide?

"acrylamide is mainly an issue in foods cooked at high temperatures" No, really?.

"the levels in most fruits etc seem to be quite low" Yes for unprocessed fruits, but the question is about dried fruits.

Also, there is a great difference in toxicity and carcinogenicity between free acrylamide and polyacrilamide. If it is in the polymer form in the fruit you mention, the acrylamide will be harmless.Tuckerekcut 22:53, 12 September 2006 (UTC)

Thanks for an informative reply for a change.

[edit] Myocardium (heart muscles)

72.70.136.195 18:50, 12 September 2006 (UTC)How would aerobic excercise strengthen the heart? Is the heart muscle fast or slow twitch?There is an excercise movement called "Superslow" that teaches that aerobics are more harmfull than good, but that to build and strengthen skeletal muscles will make the heart efficient. This philosophy also teaches that the heart of an athlete pumps very little more blood per beat than a couch potatoe's heart. I know aerobics can do a lot of harm to joints. The aerobics also train the muscles in motor skills that make it "seem" like the heart is stronger. The point is, if the "Superslow" people are correct, then aerobics would definitley be unecessary. However, it seems walking is good for stress reduction, and a small amount of calorie burn. Bottom line is, "How" does aerbic activity really help the heart? Thanks to those who know the answer. Rich Stone

Aerobic exercise increases vascularization and (to a lesser extent) density of heart muscle. The increase in vascularization allows increases anastomization (redundant blood flow) and imparts resistance to ischemia (loss of blood perfusion). The amount of blood pumped by the heart depends on a lot of factors and is not a good indicator of overall health. The isolation of skeletal muscles in any exercise routine will not develop the heart muscle properly, and in extreme cases will be detrimental, as the increased stress introduced by growing muscles will not be matched by a stronger heart. In general, the heart will do its job just fine as long as it is "fed" properly. See myocardium, smooth muscle, atherosclerosis, aerobic exercise, and anaerobic exercise for more information.Tuckerekcut 22:48, 12 September 2006 (UTC)

[edit] Inertia

Is inertia a property of matter, or a force of some kind?

I think it's neither, really, but rather a corollary of the principle of relativity (the fundamental principle, as opposed to the consequences derived by Einstein). --Allen 19:26, 12 September 2006 (UTC)

Inertia is a property of matter. It is the property by which a body continues to move with constant velocity unless acted upon by an external force and comes from Newton's first law.

See the page talk:Inertia. This topic has been done to death there a number of times. --Light current 20:17, 12 September 2006 (UTC)

What is said there seems to supoort my thought that inertia is a property of mass. Or vice versa. In other words, they're two aspects of the same thing (which is yet to be named?). DirkvdM 07:36, 13 September 2006 (UTC)

I agree and I think youll find that that is what the page now says. Inertia is a concept, not a physical thing--Light current 16:54, 13 September 2006 (UTC)

"X is a property of Y" becomes a model-dependant statement at a certain point. In newtonian mechanics, the inertial mass (i.e. the mass that relates the force on an object to its acceleration) of an object turns out to be (for no particular reason) always the same as the gravitational mass, causing all objects to accelerate the same way under gravity. In General Relativity, as Allen notes above, this happens automatically because gravity isn't really a force after all and everything travels along null geodesics. -- SCZenz 15:32, 13 September 2006 (UTC)

Gravity is nothing more than curvature of spacetime. Simple--Light current 16:56, 13 September 2006 (UTC)

[edit] Newton's laws

I need help to explain my son's homework. A common saying goes," it's not the fall that hurts you; it's the sudden stop." Can you translate this into Newton's laws of motion? THANKS.

An object in motion tends to stay in motion. When you hit the ground, whatever body part touches first stops first. But the rest of you keeps going, tearing and crushing your organs. (The fall itself (through the air) is no problem -- you're changing speed as you fall, but your different body parts are changing speed together, so your body stays intact.) --Allen 19:32, 12 September 2006 (UTC)

It's even worse. While your body stops when you hit the ground, your organs (which are mainly lying loose in their place) keep moving and hit all sorts of things. The organs stay in motion while the body stops moving. - Mgm|^(talk) 08:05, 13 September 2006 (UTC)

Newton's second law says that the rate of change of velocity (acceleration) is proportional to the force. In a fall, the rate of change of velocity (g) is 9.8 m/s per second and the force acting on the body F=mg. This can be comfortably tolerated by people. Let us say that you have reached a velocity of 19.6 m/s, after a fall for 2 seconds. But when you reach the ground, the velocity reduces to zero. When you fall on solid ground, the time taken to reduce the velocity may be as small as 0.5 sec. Now calculate the decceleration. It is (19.6-0)/0.5 = 39.2 m/s per second. The force experienced by the body (F=m*a ) is now 4 times greater that that of free fall and this hurts. When you fall on sponge, the time taken for decceleration may be 1 second in which case, the decceleration will be 19.6 m/s/s and the force is twice as strong but it is more comfortable than landing on solid ground. Hope this helps and hope it is not too late for the homework :-) -- Wikicheng 13:01, 15 September 2006 (UTC)

[edit] velocity

When your car moves along the highway at constant velocity, the net force on it is zero. Then why do we continue running our engine?

We wouldn't have to, except for friction. --Allen 19:27, 12 September 2006 (UTC)

Think of it like this: The car is moving at a constant velocity because the engine is pushing it forwards, while friction is resisting this movement. The two forces are balanced, if they weren't, the car would either speed up or slow down. Gary 19:42, 12 September 2006 (UTC)

In fact, your highway gas mileage is almost totally dependent on the air friction. That is why sports cars with huge engines are very thrifty on gas on the highway. --Zeizmic 20:06, 12 September 2006 (UTC)

The Drag equation approximates the force experienced by an object moving through a fluid at relatively large velocity. The equation is attributed to Lord Rayleigh, who originally used $L^2 \$ in place of $A \$ (L being some length). The force on a moving object due to a fluid is:

$\mathbf{F}_d= - {1 \over 2} \rho v^2 A C_d \mathbf{\hat v}$ ^{see derivation}

where

F_d is the force of drag,

ρ is the density of the fluid (Note that for the Earth's atmosphere, the density can be found using the barometric formula),

v is the velocity of the object relative to the fluid,

A is the reference area, and

C_d is the drag coefficient (a dimensionless constant, e.g. 0.25 to 0.45 for a car).

The reference area A is related to, but not exactly equal to, the area of the projection of the object on a plane perpendicular to the direction of motion (ie cross-sectional area). Sometimes different reference areas are given for the same object in which case a drag coefficient corresponding to each of these different areas must be given. The reference for a wing would be the plane area rather than the frontal area.

The power required to overcome the aerodynamic drag is given by:

$P_d = \mathbf{F}_d \cdot \mathbf{v} = - {1 \over 2} \rho v^3 A C_d$

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Since power is the rate of doing work, exerting four times the force at twice the speed requires eight times the power. Of course, if you are going twice as fast, you would get to your destination in half the time. Thus the total energy consumption would be 4 times higher (instead of 8 times higher).

Ceterus paribus, that is. Most car engines are, however, designed to be most efficient at very high speeds. The SmILE is different in that respect, and it has a very low drag coefficient, resulting in a very fuel efficient car.

Extremely efficient cars, as used in fuel efficiency races (no article on that?) don't leave the engine running all the time. If I remember correctly, the engine is turned on for a short while to get to a certain speed and then turned off to let it roll untill it drops below a certain threshold speed. I can't find any info on this in Wikipedia. DirkvdM 08:15, 13 September 2006 (UTC)

Fuel-efficiency races = Eco-marathons --128.95.172.173 19:43, 13 September 2006 (UTC)

I like this quote: "it would be possible for the winning Shell Eco-Marathon UK car to travel three times around the equator on the same amount of fuel that Concorde needed to reach the end of the runway." DirkvdM 08:57, 14 September 2006 (UTC)

Some typical vehicular C_d values are tabulated at drag coefficient. -- 66.103.112.140 03:38, 14 September 2006 (UTC)

If you stop the engine, it takes much energy to restart it. That's why you don't stop it when you have to stop at a red traffic lights, and also why you don't stop it on the motorway. – b_jonas 07:45, 14 September 2006 (UTC)

Yes, I wondered about that too, but I have heard that that was done. Maybe a fly wheel is used? Or a different type of engine? Electric? DirkvdM 08:57, 14 September 2006 (UTC)

[edit] Inorganic Chemistry

What would be the transition energy in units of eV from the ground state to the second excited state of the Li(2+) ion? I'm more interested in an explination than an answer. Thanks! 130.207.180.37 20:02, 12 September 2006 (UTC) Dave

Look at the Bohr model of the atom, since this ion is "hydrogen-like" (has precisely one electron). All you have to do is note that the nucleus has thrice the charge of hydrogen; the change in mass is irrelevant since that model assumes an infinite nuclear mass anyway. Hope this helps. --Tardis 15:03, 13 September 2006 (UTC)

The bohr model assumes infinite nuclear mass? Not sure about that... --Bmk 15:34, 13 September 2006 (UTC)

I haven't studied it in detail recently, but that's how I understand it. All I meant was that you consider the nucleus entirely fixed when working out the dynamics, so its mass doesn't matter. --Tardis 17:01, 14 September 2006 (UTC)

This is a hydrogenic atom (one electron) as Tardis noted. The ground electron configuration is then 1s. The first excited state (Aufbau principle, ibid.) is 2s and the second excited state is 2p. (Unless there's a strong magnetic field which would induce the Zeeman effect.) By reference to the Lyman series, we may estimate the change in potential energy of the electron in the potential of a single proton (a.k.a. Hydrogen) between the 2p and 1s states. The potential in the given atom is greater because the charge is greater, so the energy is greater (by three times). -- 66.103.112.140 03:47, 14 September 2006 (UTC)

[edit] Question about energy states / emission spectrum of hydrogen

What is the position of the third line in the visible portion of the emission spectrum of atomic hydrogen, ie in Angstroms in wavenumbers? I just need a helping hand with this question more than anything else. Thx in advance! ~ Mark P.

Do you just need to know the answer, or do you need to know how to calculate the answer using energy quanta ? StuRat 04:00, 13 September 2006 (UTC)

You want to know about the Hydrogen spectral series. You're probably thinking of the n=5 -> n=3 Ballmer transition. -- 66.103.112.140 03:49, 14 September 2006 (UTC)

[edit] "Cause of Death"

I lost my brother about two and a half years ago in a car crash. He was driving alone and no one else was hurt. He simply lost control of his car on a patch of black ice and crashed into a utility pole. The attending doctor at the ER told me that the "cause of death" was a heart-attack. Yet my brother was in his 30's, and had no previous heart condition whatsoever. I wasn't in the mood to ask questions so I just left it at that. But over the past while I've been wondering about exactly what he meant when he said that the "cause of death" was a heart-attack. At first I assumed what appeared to be the most obvious: he was driving, had a heart-attack for whatever reason, and as a result of his heart attack he was inacapacitated and could no longer effectively control his car.

But then it occured to me that I may have it all wrong. Perhaps, when a healthy person suffers such a severe trauma to his body, perhaps the trauma causes the heart-attack. In other words, first he lost control of the car, then smashed into the pole, and only then, due to the trauma of the crash, did the heart-attack occur. Or perhaps even more simply, due to the crash, his heart simply stopped for whatever reason, and therefore, the "cause of death" was considered to be a heart-attack.

I'm wondering if there's anyone out there who may work in an ER, or somehow have knowledge of this sort. If a healthy person gets into a fatal car crash, what are the most likely terms used for the "cause of death"? Excluding instances where the heart-attack actually occurs prior to the trauma, is it rather common for a heart-attack to be considered the "cause of death" after the trauma occurs? Thanks. Loomis 21:07, 12 September 2006 (UTC)

I've heard it several times before. Silent ischemia can happen after trauma (cause as well?) — [Mac Davis] (talk) (Desk|Help me improve)

It is likely that the ER doc was talking about a pericardial tamponade. This is a catastrophic bleeding into the sac surrounding the heart which rapidly causes cardiac arrest. Tamponade occurs frequently in car crashes because the ligament (the ligamentum arteriosum) which connects two large blood vessels just above the heart often rips a hole in one of those vessels when the heart itself jerks out of place at the moment of impact. Blood fills the sac and prevents the heart from stretching and relaxing as it should. This is by a wide margin the most likely cause of cardiac arrest after trauma.Tuckerekcut 22:37, 12 September 2006 (UTC)

Yea, the guy that US Vice President Dick Cheney shot had a similar, trauma-induced heart attack. StuRat 22:50, 12 September 2006 (UTC)

The heart attack suffered by Harry Whittington was due to a pellet from Cheney's shotgun that lodged in the outer tissues of his heart. Probably the metal in the pellet altered the endogenous electrical ativity therein, causing atrial fibrillation. This is a completely different pathology, and can only loosely be considered "trauma".Tuckerekcut 23:02, 12 September 2006 (UTC)

Why is a pellet lodged in the myocardium only loosely considered to be trauma ? StuRat 02:32, 13 September 2006 (UTC)

Cheney's was the silent ischemia. I think. — [Mac Davis] (talk) (Desk|Help me improve)

i would have though gunshot wounds fell pretty squarely into the trauma category... Xcomradex 04:24, 13 September 2006 (UTC)

How was your brother's death officially filed? 1.2 million people die each year of car accidents. If some cases are filed as 'heart attack', the number might be even worse than that. DirkvdM 08:25, 13 September 2006 (UTC)

I mentioned that the gunshot wound in this case would only loosely be considered trauma because the underlying pathology was, in my relatively uninformed opinion, more likely due to chemical differences introduced by the pellet than by the physical trauma. That is, the atrial fibrilation was caused by the presence of exogenous conductive material near the elecrical fibers of the heart, and not by the introduction of physiologically damaging forces to the tissues of the area. In this way, his disorder would have been more like hypercalcemia (or hyper-steel-ball-in-the-heart-ia) than physical trauma. There was surely some damage caused by the pellet on its way to the heart, and by the other pellets as they penetrated the skin, but the life threatening detail, as far as I have read (which is not much), was a conduction syndrome.Tuckerekcut 21:56, 13 September 2006 (UTC)

Dirk, I'm really not sure exactly how it was filed. But I would only imagine that the heart-attack "cause of death" was more for the medical files and that the death would have been included as a "car accident" death for the purposes you're speaking of. When you think about it, the simple term "car accident" can't possibly be considered a "medical" cause of death, for "medical" purposes. I would only imagine that deaths like this are included as "car accidents" in the 1.2 million stat you mentioned. It's just that doctors have to be a bit more precise as to exactly how the car accident, medically speaking, caused the death. That's just my best guess.

And thanks Stu, I probably over-reacted, but that was very kind of you. Loomis 08:53, 14 September 2006 (UTC)

You're welcome. As for the question, I've often thought that, instead of a single "cause of death", a death cert should permit a "chain of events leading to death". Take my grandfather's death, for example:

He had diabetes.
That caused circulation problems.
He also had an ingrown toenail.
That combo caused an infection.
If younger, his immune system could have fought off the infection.
Failing to have the toenail removed caused the toe to turn gangrene.
Refusal to have the toe amputated caused the foot to turn gangrene, and could also be considered suicidal.
The gangrenous foot caused blood poisoning.
This caused a heart attack and death.

So, when asked to pick just one cause of death you have a choice of "diabetes", "poor circulation", "ingrown toenail", "infection", "old age", "suppressed immune system", "negligence", "suicide", "blood poisoning", or "heart attack". Obviously none of those alone is sufficient to describe what happened. And, since funds are allocated based on number of deaths from each cause, we really should document all causes of death, not just one. StuRat 09:53, 14 September 2006 (UTC)

Death certificates do allow for enumeration of contributory causes of death (there's usually space for three) as well as the (one) proximate cause. But "heart attack" does not mean "his heart stopped" and shouldn't be used on a death certificate unless a myocardial infarction is suspected (and then it should be called a myocardial infarction!). Similarly, "heart failure" also does not mean "his heart stopped". But the accuracy of a death certificate depends on the experience of the person filling it out. As to Loomis, what he is hinting at is the distinction between "mode of death" (suicide, homicide, accident, natural causes) and "cause of death". In StuRat's hypothetical, the death certificate really should read something like:

PART I. Enter the chain of events--diseases, injuries, or complications--that directly caused the death. DO NOT enter terminal events such as cardiac arrest, respiratory arrest, or ventricular fibrillation without showing the etiology. DO NOT ABBREVIATE. Enter only one cause on a line. Add additional lines if necessary. Sequentially list conditions, if any, leading to the cause listed on line a. Enter the UNDERLYING CAUSE (disease or injury that initiated the events resulting in death) LAST.

IMMEDIATE CAUSE (Final disease or condition resulting in death) --------->

a.__sepsis________________________________1 week duration_______

b.___necrotizing fasciitis of the left foot_______2 week duration________

c.___diabetes____________________________35 year duration________

d._______________________________________________________________

PART II. Enter other significant conditions contributing to death but not resulting in the underlying cause given in PART I.

- Nunh-huh 17:36, 14 September 2006 (UTC)

Thanks to all of you for your contributions. It's really helped me in better understanding something that I've been wondering about for a while, but only lately felt comfortable asking about. I'd just like to summarize what I've gotten out of all your contributions, and if you can, tell me if I've got it right or where I may still have it wrong:

Although it is of course technically possible for a person to have a heart-attack while driving, and due to the incapacity caused by the heart-attack lose control of his vehicle and end up dying in a fatal car accident, in my brother's case, it is FAR more likely that when the ER doc spoke of him dying of "a heart attack", what he meant is that the crash caused the heart-attack, not the other way around.

It is quite common for victims of fatal car crashes to be deemed to have died "due to a heart attack", when it was obviously the crash, not some underlying heart problem that caused the heart-attack.

In general, what Nunh-huh terms "mode of death" is never a medically satisfactory way of defining the "cause of death". As extreme examples, take the Challenger or Columbia tragedies. In both cases, a pure layman (such as myself) would describe the deaths of all of those on board as being caused, very simplistically, "because the shuttle blew up", and just leave it at that. After all, if you're in something like the Space Shuttle, and it blows up (before you have any chance to escape), there's pretty much zero chance of survival. The thing blows up, and so you die instantly (as a layaman such as myself would put it). No need to go into the gory details. However, am I right to assume, that even in tragic situtation like that, someone truly dedicated to the medical sciences would, at least in his own mind, look at it differently? Would s/he, for purely scientific purposes, describe the blowing up of the shuttle as merely the "mode of death", yet the actual "cause of death" would have to be some direct traumatic effect on the persons of the crew due to the explosion (and being a layman I won't even try to guess how that can be described!)?

Actually, that last paragraph was more out of general curiousity, and not nearly as important as the first two. I'm much more interested in knowing if I'm pretty much understanding things correctly about what happened to my bro. Thanks again to all of you. Loomis 19:45, 14 September 2006 (UTC)

In the absence of an autopsy, the "cause of death" is necessarily a "best guess", and is not necessarily correct; it's only as good a guess as the person making it can give. We don't know on what basis the ER physician in question made his assessment: was there an autopsy? was there a diagnostic EKG before death? Or was it a more seat-of-the-pants guess than that? We really don't know enough to say.

"Mode of death" is indeed not a strictly medical determination, but a medico-legal one, usually made by a coroner or inquest. "Cause of death" and "mode of death" are separate determinations.

Yes, the exploration of the deaths of the shuttle accident went beyond their modes of death and characterized their causes of death. Three, at least, survived the explosion proper and were alive at the time they impacted with the surface of the ocean. - Nunh-huh 01:56, 15 September 2006 (UTC)

[edit] Io MOTH

We have an Io Moth which has made a cocoon withing the oak leaves I gave it. It has been wrapped up in cocoon since Saturday, Sept 2. How long will it remain in the cocoon stage before it erupts and becomes the adult moth? We want to prepare it a branch that it can climb upon.

The only information I can find is in the pupa article, which states that the pupation stage can take anywhere from 2 weeks to many months. I assume in your case that you won't have to wait until the end of winter. freshofftheufo ΓΛĿЌ 02:41, 15 September 2006 (UTC)

[edit] PSS World Medical

Hey I was wondering if there was any information about PSS World Medical Inc, which is an organisation in America that supplies doctors and hospitals with medical supplies that they need?

Try this website: http://www.pssd.com - Cybergoth 14:05, 13 September 2006 (UTC)

[edit] Stroking a parrot?

Why do parrots like having their heads stroked but freak out if you touch their backs, wings or stomaches?

My bird loves to have her beak stroked, but not he rwings or stomach. Some birds like to be pet anywhere. It all depends on how the bird was handled after they hatched. If they get used to certain touches, they will be more accepting, but if you get a parrot after they have been raised for a few months or so, and it wasn't made acustom to certain touches, then it never will get used to them. My bird also fears gloves and socks, leaving us to believe that she may have been handled by someone wearing gloves and has had a bad experience. Just an assumtion, not necessarily true. --Russoc4 23:52, 12 September 2006 (UTC)

It is also species specific. Cockatoos love to be scratched on the skin, you have to go under the feathers. I have also heard that the skin around the beak is particularly sensitive, and a lot of birds like that. But mostly it is learnt behaviour, I used to have a Crimson Rosella (who we got as an adult) who would bite like crazy, and almost bit one of the cat's tails off! --liquidGhoul 02:50, 13 September 2006 (UTC)

Exactly how many tails does your cat have anyway? :) DMacks 04:20, 13 September 2006 (UTC)

nine of course. — [Mac Davis] (talk) (Desk|Help me improve)

Hehe, that's really cool! Didn't realise the whole nine live and cat o' nine tails thing before. --liquidGhoul 15:22, 13 September 2006 (UTC)

I've been guessing that they don't like being touched on the back because that's where birds of prey slam into them when they catch them. But that's just me --Bmk 15:36, 13 September 2006 (UTC)

Birds don't seem to actually like being 'stroked' (i.e. smoothing the feathers down) and some birds just don't like being touched at all. Have you tried rubbing the feathers up the 'wrong way'? They get itchy sometimes and they find this soothing, especially on top of the head where it's quite difficult for them to reach. --Kurt Shaped Box 17:40, 13 September 2006 (UTC)

[edit] Getting my head shaved - pros and cons?

Anyone know? Thnx.

havent we had a similar question quite recently?--Light current 23:23, 12 September 2006 (UTC)

(edit conflict) Do you mean actual head shaving, where all the hair is shaved off, or a buzz cut, where hair is cut very short (usually 2cm or less), or a "high and tight" which is sort of a mixture of the two? If you are balding, you may want to go with the first option. A buzz cut is vary easy to maintain (low maintenance). —EdGl 23:34, 12 September 2006 (UTC)

Pros:

You'll look like a tough guy.
You can wash your hair with a sponge.
No more messing around with combs and gel.

Cons:

Some drunken arsehole might try to start a fight with you because you look like a tough guy.
Sunburn on the scalp.
People patting you on the head as they walk past.
You *may* end up looking like Mr. Potato Head.
If your face is fat, it'll look even fatter.

--Kurt Shaped Box 23:58, 12 September 2006 (UTC)

Yeah, Kurt hit all of them. — [Mac Davis] (talk) (Desk|Help me improve)

What is your hair like? When my grandfather started getting bold he decided to shave his head every spring and then let it grow for the rest of the year. That is even lower maintenance than never cutting your hair, as I do, because I spend most of the time under the shower washing my hair. A nephew of mine, however, decided to shave his head and it turned out he had a really ugly skull. A bit of an oops experience that lasted several weeks. DirkvdM 08:31, 13 September 2006 (UTC)

Pros : You shall get kisses on the head like Fabien Barthez. -- DLL ^{.. T} 19:27, 13 September 2006 (UTC)

Ask your friends/family what they think before you do it. --Proficient 06:25, 14 September 2006 (UTC)

I've shaved my head a couple of times and I loved it. Some other posters seem to have assumed you're a man, and if so, I don't know if my advice applies, but I found that almost everyone treated me differently. I would be bald now except that I got tired of every single staff person in every single store I entered watching me like a hawk the whole time I was there, people calling me a dyke, security staff asking to see inside my bags, teenagers throwing things at me as they drove past, people trying to buy drugs off me on the street, etc. Anchoress 06:31, 14 September 2006 (UTC)

Here's a con for you: Some people (such as myself) think that shaved heads are unattractive. If you're trying to look good for someone or just in general, I'd get their opinion first. --Niroht 00:25, 18 September 2006 (UTC)

[edit] Small bass cab

Anyone know of a commercially available bass cabinet (or combo), less than 1 cu ft, that will reproduce frequencies down to about 40 Hz @ -3dB?--Light current 23:31, 12 September 2006 (UTC)

Perhaps Velodyne's MiniVee or similar 8inch subwoofers? -- Rick Block (talk) 02:32, 13 September 2006 (UTC)

This would be a good time to say that my headphones go from <10 Hz to >10,000 Hz. :D Good luck with your woofer man. Everybody except neighbors and sleeping people appreciate them! Don't find yourself with a combination. — [Mac Davis] (talk) (Desk|Help me improve)

Its not strictly a sub woofer I need. Its for bass guitar so it needs response to a few kHz as well.--Light current 14:15, 13 September 2006 (UTC)

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