Wikipedia:Reference desk/Archives/Science/2006 October 25

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October 25

Function of small intestine

I met a fellow last night who has had all his small intestine removed. He says he feels ok and can eat anything he wants. What is therefore the function of the small intestine?--Light current 00:18, 25 October 2006 (UTC)

Did you ask him what his bowel movements are like? As I understand it, he'll have diarrhoea every time he uses the toilet because his gut is now not long enough to absorb the majority of the moisture/grease from the food he eats. --Kurt Shaped Box 00:21, 25 October 2006 (UTC)

He didnt mention bowel movements but implied all as normal and he felt really fit!--Light current 00:24, 25 October 2006 (UTC)

Could just be one of those wierd strokes of luck, then (either that, or your buddy is trying to make light of things). There was once someone who got shot in the side of the head, lost almost 50% of his brain and still made a full recovery. Anyone know if that guy has a WP article? I saw a documentary on TV not so long back about him - I think he was Indian. --Kurt Shaped Box 00:32, 25 October 2006 (UTC)

Maybe he only had part of his small intestine removed. I didnt like to probe him too deeply in public 8-)--Light current 00:36, 25 October 2006 (UTC)

I believe the small intestine primarily removes nutrients from the food and passes them on to the body, while the large intestine primarily removes water. So, if his entire small intestine was removed he would have trouble getting his nutrients. If only a portion was removed, then his ability to absorb nutrients would only be reduced by that portion. Eating more food (and making sure it was nutritious) could compensate, in such a case. StuRat 03:30, 25 October 2006 (UTC)

Yes thinking about it, he cant have all of it removed or he'd be dead. What you say makes sense. 8-)--Light current 04:35, 25 October 2006 (UTC)

I believe there are people who've had almost their entire digestive system removed (due to cancer, for instance). They can still survive by getting their nutrition via an IV drip. Not pleasant, but preferable to death, for most people. StuRat 05:45, 25 October 2006 (UTC)

The small intestine has three parts, with different purposes. The duodenum receives digestive enzymes and chemicals from the gallbladder and pancrease, which mainly break down macronutrients, especially lipids, into manageable chunks, this section also neutralizes stomach acid. The jejunum pretty much is just a tube in which chemical digestion occurs and nutrients are absorbed. The ileum fulfills the same rolls, and also selectively absorbs vitamin B-12 and bile salts, and makes sure that the colon does not get overrun by bacteria by small intestreleasing lymphocytes. Water is absorbed mostly in the large intestine, so removal of the small intestine would not necessarily cause chronic diarrhea, though it probably often does. However, even with all of that, most of the jejunum and ileum can be removed without too much of a change in diet, because absortion of most nutrients can happen just about anywhere in the system. Tuckerekcut 21:43, 25 October 2006 (UTC)

Thats good to know!

--Light current 21:50, 25 October 2006 (UTC)

On a semi-related topic, there are people who have had their stomachs removed (I know of a group of cousins with a genetic tendency to stomach cancer) who seem to survive, needing only to eat less and more often. —Daniel (‽) 22:11, 25 October 2006 (UTC)

Latent heat

What is the explanation of latent heat of fusion or evaporation. Where does this energy actually go?--Light current 00:23, 25 October 2006 (UTC)

It takes energy to break the inter-molecular bonds.

Atlant 00:37, 25 October 2006 (UTC)

So its potential energy given to the substance?--Light current 00:39, 25 October 2006 (UTC)

I would say it's thermal energy converted into a higher energy state for the molecules. This heat energy would be returned during condensation. StuRat 03:15, 25 October 2006 (UTC)

Yeah but its not ordinary heat energy because the temperature doesnt rise whilst the latent energy is going in. So how is this extra energy stored? Is it bonding energy as Atlant says?--Light current 03:21, 25 October 2006 (UTC)

Seems like StuRat confused you a bit. The energy it takes to break molecular bonds is thermal energy, that is, heat. But there is indeed no change in temperature. This is why you distingish between "heat" and "latent heat" - the latter does not change the temperature, but it's still a form of heat. This is why temperature alone isn't enough to quantify the internal energy of the substance. --BluePlatypus 11:55, 25 October 2006 (UTC)

evaporation? in particular: "... as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling. ". Xcomradex 10:43, 25 October 2006 (UTC)

Same process, slightly different circumstances. The temperature of the liquid changes in that case because some of the energy required to break the bonds and evaporate is being drawn from liquid. But the temperature of the liquid and evaporated gas combined remains the same. --BluePlatypus 11:55, 25 October 2006 (UTC)

That's not quite true — the temperature of the combined system really can go down (especially if the escaping molecules "just manage it", so they're not moving very quickly). Of course, assigning a temperature to evaporating water is itself dodgy, since that system is not in thermodynamic equilibrium. The point is that water under no water vapor has an excess of energy (from the unnaturally complete degree to which the molecules are associated) relative to systems in equilibrium that seem to have the same temperature. So when some of the water evaporates, we discover that its "real" temperature is lower, corresponding to the state without the excess energy. --Tardis 15:15, 25 October 2006 (UTC)

Global population of gorillas?

Approximately what is the global population of gorillas? The article doesn't say. 68.37.115.8 00:28, 25 October 2006 (UTC)

The 2004 estimate was about 5000. [1] --liquidGhoul 01:11, 25 October 2006 (UTC)

Note that of the most famous variety, the Mountain Gorilla, there are only 380 left. DirkvdM 07:48, 25 October 2006 (UTC)

I didn't realize there were so few gorillas. --00:02, 30 October 2006 (UTC)

Volume of semen during ejaculations

I've measured the volume of my ejaculations and they usually vary between 4cc and 6cc. Isn't the average volume of an ejaculation supposed to be 10ccs? Does this mean that I'm less fertile than other men? I'm getting a bit worried about this but I'd feel stupid going to the doctors about it. --84.69.92.172 00:59, 25 October 2006 (UTC)

Do you have a measuring cylinder?--Light current 01:03, 25 October 2006 (UTC)

Yes. I know that sounds weird but I started checking it out after a woman said that my ejacualtions were weak. --84.69.92.172 01:05, 25 October 2006 (UTC)

Short answer: Most likely, no. Less semen is not an indication that you are less fertile. Maybe someone else would like to give the long answer.--Russoc4 01:05, 25 October 2006 (UTC)

Someone said here a few weeks a go that the more protein you eat the greater the volume is! 8-)--Light current 01:08, 25 October 2006 (UTC)

Almost right. I said that, since excess protein is used to create sperm, your sperm production will go up if you eat more protein. However, since the majority of seminal fluid is not sperm, but rather water, a reduction in the amount of sperm won't necessarily have a noticeable effect on the total volume. However, low sperm production does lead to a lowered sex drive, which could result in fewer ejaculations. In this case, each individual ejaculation could actually be larger in volume. StuRat 03:11, 25 October 2006 (UTC)

Someone said something about eating loads of asparagus too. No idea if it works or not - I can't stand the stuff, in spite of its alleged benefits. --Kurt Shaped Box 01:10, 25 October 2006 (UTC)

Ah-ha! Snopes' article on the band 10CC says the average is only about 3 cc anyway. Confusing Manifestation 02:36, 25 October 2006 (UTC)

1. Each ejaculate contains 3-10 million sperm cells or so. I don't know the exact figures, to be honest, but I think it's around that range. I highly doubt 3 million sperm cells are going to make you infertile.

2. The only thing I have heard about asparagus is that it makes semen taste and smell horrible to people who can detect the enzyme (if you eat asparagus and can smell an awful smell in your urine afterwards, you can).

3. I don't think it's extra protein, else if someone has no extra protein, they won't produce any ejaculate, which I don't think is true.

Yes, during periods of starvation, both male and female reproductive systems shut down, as part of the starvation response. StuRat 17:11, 25 October 2006 (UTC)

4. And as for the strength, there are excercises to strengthen it. I read a long time ago about a hot and cold home remedy for weak ejaculations. Something about alternating hot and cold somewhere by your genitals. But I have never tried, and I don't know if it's a myth or not.

5. Also, frequent ejaculations can make it weaker, I believe.

--Wirbelwindヴィルヴェルヴィント (talk) 05:50, 25 October 2006 (UTC)

I'd just like to point out that there really isn't much "extra" protein in the body. The pool of free amino acids in the body is only about 100mg in total. This amount is very strictly regulated by the urea cycle. Excess protein is very quickly degraded into aminos and turned into urea. There are plenty of proteins in semen, both intra- and extracellular, but semen is in no way an "overflow conduit" for excess protein, thats what urine is for. Also, sperm makes up a very small percentage of the volume of semen, most of the liquid comes from the seminal vesicles and prostate and BU glands, so volume is not a good indicator for number of sperm. Stimulating a cremaster reflex at the moment of ejaculation with a cold compress to the scrotum can help push all of the fluid out at the same time (by putting pressure on the perineum, there is little to no mobile fluid in the vas deferens themselves), but will not increase the overall volume. Finally, 6mL is typical for an adult, at least that's the "goal" volume for at least one sperm bank in my area. Tuckerekcut 21:31, 25 October 2006 (UTC)

It sounds like you misinterpretted my comments. I did not say that any excess protein is automatically changed into sperm, but rather I said that a certain amount of excess protein (beyond what is needed for life-critical functions) is needed for sperm production. Thus, an extremely low protein diet will lead to a substantial reduction in sperm count. StuRat 21:41, 25 October 2006 (UTC)

Fermenting blood to create an alcoholic beverage?

I'm sure that most people here have heard the urban legend that Jaegermeister is made from fermented deer's blood. I'm curious - would it actually be possible to ferment animal blood to make booze? --Kurt Shaped Box 01:37, 25 October 2006 (UTC)

Is there fermentation without sugar (or starch to turn into sugar)? Unless you are insulin-dependent diabetic, I don't think you'll have enough sugar in your blood to get any good results. Maybe the legend is based on diabetic deer. --Kainaw ^(talk) 01:41, 25 October 2006 (UTC)

Of course you could add sugar to the blood and ferment that. DirkvdM 07:56, 25 October 2006 (UTC)

Nope, never heard that legend. Seems a bit weird given how many people drink herbal-flavored distilled liquor. (E.g. Hungarian Unicum or Scandinavian Aquavit) Well anyway, it's possible to ferment into alcohol anything that has sugar in it. But blood doesn't have much sugar in it (even if you're diabetic). Grape juice, a popular object of fermentation, has over 100 times the sugar (by weight) that blood has. You'd be better of milking the deer and fermenting that. The Mongolians actually do that out of horse milk, see Kumis. --BluePlatypus 11:41, 25 October 2006 (UTC)

Though blood may have a small % of sugar. With a diferential mearsuring from 4% - 7%. It is possible to compound those sugar parts into a small volume. Having boiled blood to stabelize the environment for fermentaion I realized that all the blood tissue turns solid so addition water is needed. The water that remained when the clotted tissue is strained away contained sugar. It should be possible to rinse many gallons through one gallon of water. Or reduce the original batch by boiling off excess water (having myself condensed and carmalized the sugar to an imesurable state excess of 25%+). This extraction process has not been fermented long scale yet. The results will need studding. 11/13/08

Fermentation notes: Fermentation is slow or nothing. With a sugar level of 14% in 1/2quart volume. I added a small amount of Dried Malt Extract (DME). This addition was to support the yeast's nutritional needs. Later observation has shown a slow decrease in sugar. It may have been benificial to run a malt enzime to break down any sugar complexes in the blood sugar if they are in a complex form. Odor is pleasent. No visual defects. Sugar reading 12.5% 1/13/09

No, it was deer shit ;-) Sorry, this urban legend sounds just too brainless--Baruch ben Alexander - ☠☢☣ 04:52, 31 January 2010 (UTC)

Endangered large cats

What large cats are endangered? --68.37.115.8 01:47, 25 October 2006 (UTC)

There's a complete list (not just cats) at List of endangered animal species. I think the answer is roughly "all of them". -- Rick Block (talk) 02:20, 25 October 2006 (UTC)

thanks

Of the species mentioned in our article Big cat, the following are found on this list of endangered animal species:

• Tiger (Panthera tigris)
• Snow Leopard (Uncia uncia)
• Iberian Lynx (Lynx pardinus)

 --Lambiam^Talk 15:35, 25 October 2006 (UTC)

There are many more, e.g. the whole genus Parantica. Since they carry the common name "Tiger", I'm wondering if the information in Big cat is accurate. — Sebastian (talk) 20:37, 25 October 2006 (UTC)

Cotton

How does Damp Cotton Absorb Sulfuryl Chloride gas used in radical chlorination (what chemical reactions occur)?

So you've got cotton, "dampness", and sulfuryl chloride. What are the chemical formulas/structures of those things? What are some characteristic reactions of them (nucleophile, electrophile, acid, base, oxidant, reductant, radical initiator, radical quencher)? Can you think of a way any pair could react? DMacks 04:31, 25 October 2006 (UTC)

Also note that adding water to cotton will greatly increase the reaction surface area over plain water and a gas. StuRat 05:40, 25 October 2006 (UTC)

Electrolytes

How can you tell what is a strong or weak Electrolyte when you are given a chemical formula / compound(s)? Is there certain elements that define this? certain rules? (maybe like solubility rules ) And are most (strong) bases weak electrolytes and most (strong) acids are strong electrolytes? etc. In addition, the Strong electrolyte"For strong electrolytes, a single reaction arrow shows that the reaction occurs completely in one direction, in contrast to the dissociation of weak electrolytes, which both ionize and re-bond in significant quantities" how would you know when it would be both ionizes and re-bonds (or doesn't) if you just had the compounds' names? (sorry if i'm a little incoherrent)--Agester 04:20, 25 October 2006 (UTC)

The electrolytic strength of a compound is the degree to which it dissociates into ions in solution, which is always an equillibrium. So the strength/weakness is relative. Whether a strong acid/base is also a strong electrolyte depends on how it works. E.g. nitric acid dissociates very much into nitrate and hydrogen ions and is therefore a strong electrolyte. But ammonia, a strong base, will form ammonium ions from the hydrogen ions in solution, which has no effect on the solution's ionic strength. So it can correspond to both the solubility and the pKa, but not necessarily. --BluePlatypus 11:26, 25 October 2006 (UTC)

I understand what you said. However, how would you be able to know which is stronger or weaker electrolyte? For example H₂SO₄ is a strong electrolyte but H₂SO₃ maybe a weak electrolyte. What defines their difference with respect to electrolyte properties? --Agester 23:56, 25 October 2006 (UTC)

The best way is to look at the bond holding the H atom to the rest of the acid. If the remainder - what will eventually form the [conjugate base] or [acid anion] - contains some highly electronegative elements, the chances are that the bond to the H atom will be severely polarised and weakened, leading to a larger Ka value. Look at the Ka values of chloroethanoic acid, dichloroethanoic acid and trichloroethanoic acid to see what I mean.--G N Frykman 07:38, 26 October 2006 (UTC)

hmm... i see. I appreciate your help and everything and i understand it. However, I haven't learnt about pKa in my class yet so it's still a little unclear for me (I did read the pKa article and it would help me greatly if we were taught this when we were discussing what is a strong and weak electrolyte). Once again thanks for helping! However, i guess the only way for me to know is memorize what is a strong and weak electrolyte! 8( --Agester 00:51, 27 October 2006 (UTC)

Sense of Color In Animals

Is it true that some animals sense only black and white images not color images? Thanks!

Yes. its true. 202.168.50.40 05:17, 25 October 2006 (UTC)

Although grayscale might be a more accurate description than black and white. StuRat 05:35, 25 October 2006 (UTC)

Still more accurate might be 'light intensity'. DirkvdM 07:59, 25 October 2006 (UTC)

Also consider, for example, lepidoptera - butterflies - who ID flowers in the ultraviolet spectrum; the patterns and colors in the UV wavelength are drastically different than how we see them.Wolfgangus 05:54, 25 October 2006 (UTC)

This is known as chromacy. Humans are trichromats, because we see 3 "primary colors" (three sections of the "visible" spectrum) and mix them together to create our rainbow. As wolfgangus reports, some butterflies are tetra- or pentachromats, with four or five primary colors to work with. I have heard that there is some kind of shrimp that sees the world in eight primary colors, thus "octochromacy". Monochromacy is a more technical name for what you called "black and white" vision (with the additional explanations above). According to our article monochromat, sea mammals are monochromats, but not many other animals are. Dogs, as with most other land mammals, are dichromats, which have vision comparable to a color blind person. They can see colors, but not as many as the average human. See dichromat for further explanation. Tuckerekcut 13:05, 25 October 2006 (UTC)

The shrimp that you are thinking of is the mantis shrimp, which has the most advanced color vision in the animal kingdom. – ClockworkSoul 13:33, 25 October 2006 (UTC)

Let's not forget tetrachromats. --Kjoonlee 16:32, 26 October 2006 (UTC)

Thanks to Tuckererkcut - a far more comprehensive explanation, which taught me a number of things as well.Wolfgangus 13:46, 25 October 2006 (UTC)

400Hz Frequency Apllied to Copper Conductors.

Hi,

Can anyone tell me how the use of 400Hz frequency affects the cable characteristics used on a 230V 63Amp supply. I believe that the increase in frequency increases the inductive reactance, decreases the capacitive reactance by up to a factor of 8. This then in turn affects the resistance of the cable by increasing it by a factor of 8. If this is the case how would one go about estimating the approximate cable sizes required for such an installation.

Thank you very much.

As part of your project, see Skin effect. Then grab a good electromagnetics textbook and a computer modelling and graphics program which can solve for the current distribution as a function of frequency and current. Have fun. Edison 17:25, 25 October 2006 (UTC)

I believe 400Hz is a common supply frequency for aircraft--Light current 15:22, 26 October 2006 (UTC)

Cable sizes are usually worked out on current. You dont need to worry about frequency IMO.--Light current 15:23, 26 October 2006 (UTC)

As the frequency increases, more of the current flows along the outer portion. Once again, read Skin effect.Edison 22:52, 29 October 2006 (UTC)

"scientific" name for grass. . .

. . .no, not canabus but the grass in your lawn. That name is needed for my son's class and he has not been able to find it anywhere. I know there are many kinds of grass but he was to find the scientific name for "grass" in general. Please help. . . I tried to find it here but had no idea how to start correctly. I did try a little but came up with nothing. Thank you so much, Mary McVey (I am using a friend's computer)

• Take a look at the lawn article. You will find what you need there. :) – ClockworkSoul 17:22, 25 October 2006 (UTC)

• As a hint, try clicking on the links in the first proper sentence in that article. Skittle 22:48, 25 October 2006 (UTC)

Amazing stuff, grass (even if we exclude the cannabis variety). Not only very useful to humans, for our lawns, food, construction, musical instruments and paper. But also, it's extremely simple and successful (the most successfull plant family even?). Yet it has only evolved very recently; for 99.8% of the evolution time span there was no grass. I wonder if there was something similar that grass replaced. Surely if something so simple can be so successfull, evolution would have come up with something similar sooner, right? DirkvdM 13:57, 26 October 2006 (UTC)

Grasses (or grass like plants) have been around for quite a long time, dinousaurs ate them. Also, evolution doesn't 'know' that something is going to be successful. And generally, whether or not something is a 'success' depends a lot on other factors. We have been amazingly successful 'til now (at least compared to many of the larger mammals) but it took evolution a long time to come up with us... Nil Einne 14:24, 26 October 2006 (UTC)

Yeah, but we're complex. Grass is simple, and I suppose that is part of its strength. DirkvdM 09:34, 27 October 2006 (UTC)

Insulation R-values

I have noticed a difference in R-values between similar products in Australia and Canada. 90 mm fibreglass insulation in Canada has a fairly standard rating of R-12 but a 90 mm product in Australia only goes up to R-2. Is there a different standard applied or is the manufacturing process that different? Any feedback would be appreciated. Thanks 209.89.148.249 19:17, 25 October 2006 (UTC)

Insulation materials are often characterised by their R value. In countries like Australia, which use metric measures, the units of R are m²K/W. An R=2 insulation material passes 0.5 watts per square metre with a 1 degree temperature difference. In countries using imperial measure, R is based on imperial units and a 50mm rockwool batt would have an R of around 40. --Zeizmic 22:57, 25 October 2006 (UTC)

Temperature - Kinetic Energy Relationship

I can't find a cogent equation anywhere to relate the energy difference between two states with temps T1 and T2. Any help? Thanks

First, find out the specific heat capacity of the material. Then multiply it by the difference between T1 and T2. Multiply this result by the mass of the material. --Bowlhover 20:45, 25 October 2006 (UTC)

Thanks! I'd forgotten that

Self-dissolving Miracle-Gro

What is the opposite of evaporation? Well OK, that's too easy - it is just condensation, but that _may_ not be what I'm looking for. I've got a packet of Miracle-Gro which is a popular plant fertilizer. You can buy it in a number of forms, but in this case it a box containing a plastic bag of blue crystals (looking rather like copper sulphate crystals, but I guess its more than that). You dissolve a spoonful in water before watering your houseplants every couple of weeks. Now, after opening the bag and leaving it around for about a year or so (my plants have a poor, impoverished and generally undernourished life - hey they are lucky to get watered), the blue crystals appear to absorb moisture from the atmosphere, to the point where they self-dissolve to form an aqueous solution in the folds of the plastic bag.

This strikes me as slightly unusual. Plenty of solids absorb water from the atmosphere, but AFIK few do so to such an extent that they become a liquid. So what is this process called? -- Solipsist 21:33, 25 October 2006 (UTC)

Sounds like they are deliquescent. DMacks 22:05, 25 October 2006 (UTC)

Yeah. They Stu stew in their own juice! 8-)--Light current 22:56, 25 October 2006 (UTC)

Taste and aging

Are you born with the all the taste buds you'll ever have or do they continually regenerate, like hair? What causes the loss of taste as you grow older? Clarityfiend 22:15, 25 October 2006 (UTC)

Possibly because elder people tend to take more medications, which may in turn produce that side effect. I'm not completly sure though. Hello32020 22:41, 25 October 2006 (UTC)

It is not the tastebuds that die along the way to getting old, it is the olfactory receptor neurons that do. One's sense of smell, along with mouthfeel, texture, and gustatory system sensations are the main contributers to taste. X [Mac Davis] (SUPERDESK|Help me improve) 07:16, 26 October 2006 (UTC)

And yes, they regenerate. Dismas|^(talk) 19:09, 26 October 2006 (UTC)

green leaves all over the ground

In my area (eastern Iowa, USA), fresh green leaves, rather than yellow, red, and brown, are littering the ground. There are still plenty of green leaves on the trees as well as some colored ones. I've never seen this happen before. We've had fairly normal winds. The fall season has been abnormal, with very warm alternating with downright cold. What gives?

Also, what causes the leaves to separate from the tree in the first place? I read somewhere it's not because the leaves dry up, but rather that the leaves dry up because of some process in the tree that more or less casts them off. Is there anything to that? --Halcatalyst 22:23, 25 October 2006 (UTC)

Try the Color change in leaves article. It says, among other things, "In late summer, the veins that carry fluids into and out of the leaf are gradually closed off as a layer of special cork cells forms at the base of each leaf. As this cork layer develops, water and mineral intake into the leaf is reduced, slowly at first, and then more rapidly. It is during this time that the chlorophyll begins to decrease." I'm sure we should have something else on the process somewhere. Skittle 22:45, 25 October 2006 (UTC)

The process is called senescence, but our article isn't that great with it. You are right, the plant does not just dry up. A lot of energy goes into creating the cells of a leaf, so they take as much of that back as possible. The reason the leaves change colour is that the chlorophyll is one of the things the plant takes back for energy. This removes the green colour. Since the most abundant colour is gone, the next most abundant becomes visible. The plant obviously doesn't want to lose its leaves beofre it takes out all the nutrients, so the process of abscission is next, and only occurs once the plant is finished with the leaf. Abscission also occurs with fruit, but in the opposite direction. The plant pumps in the nutrients, and once that is done, it will remove the fruit. --liquidGhoul 01:23, 26 October 2006 (UTC)

That, however, does not yet answer the question. Why do the trees not take the chlorophyl out of the leaves? Are there two disitinct processes for that and the abscission? Might senescence be controlled by temperature and abscission by time? That would explain it. DirkvdM 14:12, 26 October 2006 (UTC)

I couldn't tell you why this has suddenly occured for those trees. My bet would be that there was some kind of stress which caused the trees to shed their leaves. I doubt it is global warming, but it could easily be some sort of pollution. The triggering of abscission comes from the end of senescence. A healthy, green, leaf is constantly creating a hormone called auxin. As the leaf goes through senescence, the auxin levels decrease, which begins a series of steps which eventually leads to abscission. I think the beginning of senescence comes from day length, but it is probably very complicated (as all things living are), so there will be other factors. --liquidGhoul 15:03, 26 October 2006 (UTC)

I probably should know be able to explain the basics but but I've kind of forgotten most of it. However this article appears to cover the basics [2] and the links are helpful. However it doesn't really answer your main question. But as you may have gotten from you reading, senescence and abscission (as with most plant processes) are rather complex processes involving multiple hormones and multiple signalling pathways and it's not actually something we have a complete understanding of yet. Nil Einne 14:42, 26 October 2006 (UTC)

File:Dscn6245 wikipedia.jpg

Trees in Amsterdam on 24 October 2006

Btw, here in Amsterdam, most trees are still largely green, which is very abnormal for this time of year. However, the leaves that have fallen aren't green, so we seem to have more intelligent trees. :) Don't know what kind of trees they are, though, which will of course be the most important thing here. DirkvdM 14:12, 26 October 2006 (UTC)

reverse casimer effect??

I read somewhere that someone claimed that the casimer effect couldbe changed to be repulsive rather than attractive how can that be if the plates push together because of the zero point energy pushing on the outside of the plates, you cannot add to the zero point energy so how can this work. This is based on the NASA webbsite that describes the casimer effect much like air pressure, less between the plates so more pushing on the outside so they push together, how can you reverse this? FRed

Funny, I thought it was called the Casimir effect!--Light current 22:53, 25 October 2006 (UTC)

The plates would have to be close to massless, and extremely far apart for the effect to be "reversed," and is fairly implausible. X [Mac Davis] (SUPERDESK|Help me improve) 07:13, 26 October 2006 (UTC)

The idea of a reverse Casimir effect was discussed in the context of speculations whether very advanced technology worm holes might allow for time travel. Apart from giving fodder to SF authors this is of interest in research on general relativity: Due to the grandfather paradox causality would break down if it turned out that the laws of physics allow for time travel and if only under most exotic circumstances. In reasoning for the chronology protection conjecture it was said that a worm hole cannot be stable enough to send something into the past, and the counter-argument was given by Kip Thorne et al. that negative Casimir pressure might be used to keep it open. As I forgot the details I googled for Thorne and Casimir. You might find these links interesting: This science column from Analog Science Fiction and Fact that explains Thorne et al.'s work for the laymen and these notes on the homepage of Thorne's collaborator Matt Visser. Simon A. 13:03, 29 October 2006 (UTC)