Wikipedia:Reference desk/Archives/Science/2006 December 17

From Wikipedia, the free encyclopedia

Science desk
< December 16 << Nov | December | Jan >> December 18 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.


Contents


[edit] December 17

[edit] Blood cells discarded per day

Page does not say how many blood cells die and are discarded per day in the human body. Anyone know?--Light current 00:13, 17 December 2006 (UTC)

Because of the different lifespan of red and white cells, it probably depends of their kind. According to Arizona Science Center, ca. 2 million die per second, so 172,800,000,000 die in 24 h. --Brand спойт 01:11, 17 December 2006 (UTC)
That seems like a rather large number, unless my math is off. Speaking only of red blood cells (and most of the blood cells are RBCs), their normal life-span is 120 days (this can be lower in intensively training athletes). Each day about 1% of RBCs are replaced. The blood volume in one human is approximately 4.7 liters or 4700 milliliters. There are about 5 million RBCs per milliliter. So that's 23,500,000,000 RBCs/human, and 1% of that is 235,000,000 replaced per day. Calculating another way, if there are 23,500,000,000 and they are replaced in 120 days, each day about 430,833,333 are replaced. So maybe a good estimate would be 300,000,000 RBCs/day. - Nunh-huh 02:19, 17 December 2006 (UTC)

[edit] Valence orbitals

Why do atoms "want" to have full valence shells? BenC7 02:05, 17 December 2006 (UTC)

It's the most stable configuration. --Wooty Woot? contribs 03:54, 17 December 2006 (UTC)
"Full" valence shell is a misnomer, of course. All atoms "want" is an s2p6 arrangement. A "full" valence shell would be 2n2 electrons, where n is the number of the shell. This s2p6 arrangement seems to have the highest ionisation energy, and lowest electron affinity, of any, and that is why it is a "stable" arrangement. --G N Frykman 08:51, 17 December 2006 (UTC)
"Wanting to have full valence shells" is the standard oversimplified explanation of molecular bonding. It more or less works as an explanation for highly polarised ionic bonds. However, in real life, the explanation of molecular bonding is much more complex and not completely understood - see valence bond theory, covalent bond, metallic bond and molecular orbital. Gandalf61 10:54, 17 December 2006 (UTC)
It's also possible that full valence shells have a spherically symmetrical distribution of 'charge' whereas unfilled shells don't - it's possible to make the link with the stability of full shells through 'hand waving' explanations.87.102.13.235 16:10, 17 December 2006 (UTC)
Note that Tin forms +2 and '+4' oxidation states - in the +2 case the valence shell is not full - but the complounds are stable - however the s shell is full. (correction Tin (2) usually attains a full valency shell by coordination with other lone pairs)83.100.250.252 09:18, 18 December 2006 (UTC)
In general this phenomona happens because there is a big gap in energy between the full valence shell and the state with "full valence shell plus one electron" - the difference is so large that it's very rare to find the valence shell 'overfilled' (I can't think of a single example), however having partially filled valence shells does sometimes happen (though the resultant products are reactive).
Explaing why there is stabilty for full shells is very difficult to do.83.100.132.121 18:03, 17 December 2006 (UTC)
As others have said, and perhaps I can just re-phrase, the metaphor of atoms as "wanting" agents is a bad approach to this. If you take for granted that full valence shells is the most stable condition, then by definition it is what atoms are going to fall into when they get the opportunity. Why stable states are, by definition, more stable, is a much more difficult and problematic question, because you are really trying to take apart what the definition of "stability" really is in physical terms. If I understand this correctly, which I don't pretend to necessarily do. --24.147.86.187 20:34, 17 December 2006 (UTC)
That seems like a good explanation - the first part. As I see it the problematic part is explaning why 'octets' and the like are stable - which is reasking the question again - even the latest theories of the atom don't actually explain why certain states are stable, or why the stabilty occurs at certain values 2,8,18 etc. There are formulas giving the number of electrons in each successive valence shell - but unfortunately no explanation of why those formulas (and not others) apply..83.100.132.121 22:16, 17 December 2006 (UTC)
The explanation for a configuration being stable is simply that the atoms want to be in that configuration :-P  --LambiamTalk 00:00, 18 December 2006 (UTC)
You just restated the question, didn't answer it..83.100.250.252 09:18, 18 December 2006 (UTC)
Ha, I remember in grade 9 and 10 science where to explain bonding, when you had ionic forms of atoms, they'd be the happiest with full valence shells, so in order that they don't become unhappy, they bond. 74.102.89.241 00:26, 18 December 2006 (UTC)

OK, so basically it is that they are more stable with a full valence shell. I knew that already. But why (usually) eight? Why not seven, or six? I am studying to be a science teacher and I want to be able to explain to students the reason why it is more stable to have a total of eight electrons per atom, given that it is more intuitive that an atom would simply want the number of electrons equal to its atomic number. I don't want to say to students "well, it's just more stable that way" when it would, on the surface, appear to be less stable. BenC7 00:59, 18 December 2006 (UTC)

In chemical science it's not 8 it's as the row increases 2,8,18,32 - if you want to be a chemistry teacher you'll should do a degree in chemistry - after 3 years the reasons for this (and the many flaws and discrepencies) will become apparent. As the second poster said this turns out to be a 'lie to children' in most part. The 'rules' are found experimentally and attempts made to fit the behaviour to a mathematical pattern. There is no real satisfactory answer to this question. I can only suggest you learn more (and formulate your own ideas) - (personally I've come to the conclusion that the current simplified teaching of chemistry leaves a lot to be desired - as it introduces concepts without giving an adequate explanation - as you have found out). There's a lot of infomation - but to get you started I suggest you look at platonic solids, atomic orbital, Symmetry group, Chemical bond and follow the links as necessary. Check everything you read for yourself - just because it's been printed doesn't mean it's right. Try to develop your own theories of bonding etc and Good Luck!(And remember the interpretation of experimental facts through a flawed theory may produce confusing results..)83.100.250.252 09:31, 18 December 2006 (UTC)
8 is a "magic number" for the following reasons. Electrons in an atom can be divided into shells. Within each shell, the electrons fall into orbitals. The lowest level orbital, called the s orbital, can contain up to 2 electrons; the next orbital, called the p orbital, can contain up to 6 electrons. These limits are due to various reasons to do with the Pauli exclusion principle, electron states and quantum numbers - see atomic orbital#Limitations on the quantum numbers for a quantitative explanation. So an atom with full s and p orbitals in its outer shell has 2+6=8 electrons in this shell. Combine this with the fact that full shells are stable configurations and you get the "wants to have 8 electrons in its outer shell" rule, which is a reasonably good rule of thumb for the simple chemistry of elements until you get to the transition metals where a d orbital enters the picture for the first time, and life gets more complicated. To see how complicated it can get, take a look at this table of oxidation states for transition metals. Gandalf61 15:47, 18 December 2006 (UTC)

[edit] Kill Mosquito Larvae in a Water Tank

How do I kill mosquito larvae in a drinking water tank without poisoning myself?203.202.140.72 02:12, 17 December 2006 (UTC)

A tank with decaying larvae? You probably should drain the tank. I've heard that a thin layer of oil on the water surface will suffocate the larvae by plugging their breathing tubes. But then you'd have both the dead larvae and some rancid oil. --Wjbeaty 04:29, 17 December 2006 (UTC)
I seem to remember that somewhere the WHO used styrofoam beads to cover the surface of ponds and prevent mosquitos from breeding without interfering with the fish living there. Dr Zak 05:01, 17 December 2006 (UTC)
Why not just skim them? And may I say that (for whatever reason, I'm not squeamish about bugs or much else), this is the grossest topic I've ever seen on the RD? ;-\ Anchoress 05:07, 17 December 2006 (UTC)
I don't think the OQ was asking about decaying larvae, but living ones. Apparently mosquito dunks are safe. User:Zoe|(talk) 06:48, 17 December 2006 (UTC)
Yeah but after he kills them, they will have to decay. --Username132 (talk) 10:02, 17 December 2006 (UTC)
Aaaaaand there's even an article about them here on Wikipedia. Mosquito dunk. Anchoress 10:05, 17 December 2006 (UTC)

So the question is how do you eliminate the dead and rotting mosquito carcasses? Adaptron 14:24, 17 December 2006 (UTC)

Why not filter it? --V. Szabolcs 16:50, 17 December 2006 (UTC)
Because only the undesolved products of the rotting larvae carcasses can be filtered effectively. Adaptron 19:09, 17 December 2006 (UTC)
Get a local river fish (like, say, a trout) into the tank it will efficiently get rid of all the larvae. Depending on a lot of factors it can either stay there for a rather long time or you will have to release it back into the river. Keria 17:14, 17 December 2006 (UTC)
yes that's a real solution - but suggest a smaller fish - remember the fish will polute the water. Hillstream loach and Chaetostoma (bulldog) plecs have actually been (reported) to have been used for this purpose. I wouldn't suggest trying this though - if the larvae are all eaten the fish will probably starve, die, rot and then pollute the water even worse!83.100.132.121 17:45, 17 December 2006 (UTC)

So the question now is how do you get rid of the bacteria and disolved fish feces and urine? Adaptron 19:09, 17 December 2006 (UTC)

For the original question: We use
  1. Barrier netting, mounted on a suitable frame, to stop mosquitoes getting to the water, if the reservoir tank does not have a lid.
  2. One of the Juvenile hormones (methoprene, pyriproxyfen) for killing an established infestation. The mosquito dunk idea seems pretty good, but I have never used the stuff (on reading the name I first thought it was a joke about a food or drink of some kind:)), and I wonder what it does to a lab bacteriological test.
From what I read in the Mosquito dunk article and references all of the test on mice - oral, inhalation and introvenus - were "acceptable." Like the viral bacteriocides this stuff is so specific that virtually everything else is safe. Adaptron 19:54, 18 December 2006 (UTC)
  1. Filter through basin of clean river sand if water is not clear, though a simple fine sieve regularly is mostly good enough. Clean filter regularly.
  2. Depending on your circumstances, you could chlorinate and filter the water with high tech apparatus, but unless you have serious contamination (lab test for bacteria - people tend to under utilise these facilities) it should not be necessary. --Seejyb 20:51, 17 December 2006 (UTC)

[edit] six pack

is there a name for not getting aligned six packs? —The preceding unsigned comment was added by 219.88.164.105 (talk) 06:35, 17 December 2006 (UTC).

No. Maybe you could invent one.--Shantavira 09:41, 17 December 2006 (UTC)
Just don't add it to an articel here untill it gets some external coverage. 68.39.174.238 23:13, 17 December 2006 (UTC)
Maybe you'll get more help at a bodybuilding or similar forum. From the quick search I did though, everyone was saying that's just the way it is for some people. They also says it better to have non-symmetrical [but defined] abs than a loads of fat.. --Username132 (talk) 10:07, 17 December 2006 (UTC)

Actually there is loads of fat, but if i compress my stomach i can see the non symmetrical six pack

Also one side of my six pack is bigger than the other

[edit] Which kinds of cells undergo cellular respiration?

I can't seem to find exactly what kind of organisms undergo cellular respiration. Which ones do besides plants and animals? Is it just eukaryotes? Thanks. --Proficient 06:40, 17 December 2006 (UTC)

Don't they all? I mean, the cellular respiration article defines it as "the metabolic reactions and processes that take place in a cell to obtain chemical energy from fuel molecules". That seems pretty universal to me; I dunno. --Spoon! 07:55, 17 December 2006 (UTC)
I can't think of any exceptions, and as far as I know there aren't any - it is the way organisms liberate energy, and if it can't get energy it can't live. It can be either aerobic respiration which uses oxygen, or Anaerobic respiration which doesn't. You may also like to check out Respiration. --jjron 12:43, 17 December 2006 (UTC)
It is this "breathing" connotation of respiration which seems to cause confusion, and one has to blame earlier generations of biologists for this. Retrospectively it was not a good choice. Remember that: viruses are not "cells", so they have no cellular respiration mechanisms. Here is a question to consider: Erythrocytes do not contain mitochondria; do the have cellular respiration? --Seejyb 21:07, 17 December 2006 (UTC)
Of course red blood cells have cellular respiration - from the article "Mammalian erythrocytes also lose their other organelles including their mitochondria and produce energy by fermentation, via glycolysis of glucose followed by lactic acid production". Prokaryotes like bacteria don't have mitochondria either, and of course they also respire. Re viruses, this is part of the reason for the debate on whether they are actually 'living' organisms. --jjron 07:12, 18 December 2006 (UTC)
All cells engage in cellular respiration. those without mitochondria (prokaryotes) simply respire through all of their cytoplasm as opposed to concentrating within organelles. However, don't confuse resperation with glycolysis or the kreb cycle those only occur in some cases Beckboyanch 06:15, 21 December 2006 (UTC)

[edit] SL & XR

Whats the difference between Sustained Release version of Wellbutrin compared to the Extended Release version? --Delma1 10:43, 17 December 2006 (UTC)

Sustained release tablets are standard pills which dissolve slowly and are generally taken twice a day to maintain therapeutic drug levels. The Extended Release versions consist of an insoluble shell filled with an aqueous solution of the drug. A small hole in the insoluble shell (covered over by a permeable membrane) allows the slow diffusion of the medication out of the pill over an extended period, allowing once a day dosing. (This is a drug delivery mechanism originally designed for Procardia XL). - Nunh-huh 11:01, 17 December 2006 (UTC)
Quick release tabs dissolve all at once, being compounded with something like starch. The SR is formulated so that the active ingredient is embedded in a matrix of insoluble substance (various: some acrylics, even chitin, these are often patented) so that the dissolving drug has to find its way out through the holes in the matrix. In some SR formulations the matrix physically swells up to form a gel, so that drug has first to dissolve in matrix, then exit through the outer surface. I believe that the holes in XL tabs are laser drilled. You may find that some SR and XL preparations use different salts of the active drug (I do not know whether this is true of bupropion). This is apparently something to do with the binding and solubility is in the matrix. Since novel delivery systems are patented, and quite profitable, specific manufacturing information is rather difficult to find. Maybe we should try the patent office:) --Seejyb 23:00, 17 December 2006 (UTC)
Thank you very much. It feels good to know. If there were some sources I would create the article based on above information regarding Quick release, Sustained Release & Extended Release--Delma1 04:28, 18 December 2006 (UTC)

[edit] water heater corrosion

Does the build up of sediment in the bottom of the water tank as well as the corrosion of the tank come from the reaction of the copper electrode and the iron lining of the tank and pipes or does it come from the temperature change of the water? Adaptron 14:05, 17 December 2006 (UTC)

I think most of it comes from the water itself. You will get sediment in a plastic tank too. Filtration can only remove so much gunk.--Shantavira 14:51, 17 December 2006 (UTC)
A bit of both. Sedimentation just happens when you hold water still in any tank, and there's not much you can do about it other than clean it out from time to time. Galvanic action, on the other hand, requires very specific conditions. A magnesium sacrificial rod is often used to stop this effect. Some corrosion will still occur with the rod, but at a greatly reduced rate. StuRat 14:52, 17 December 2006 (UTC)
Thanks. Galvanic action answers most of my question and that the corrosion comes from the reaction of oxygen in the water with the iron in the tank which the magnesium electrode prevents by reacting with the oxygen first. What I am wondering now is whether an electric current through an inert electrode would substitute for the magnesium or whether possibly some form of hydrogen interface or injection could be used? Adaptron 15:17, 17 December 2006 (UTC)
But what is the overall goal ? I would think a continuous electrical current would cost more than the magnesium rod, and could also pose a safety hazard. Another option is to line the water heater with something inexpensive and corrosion resistant, like glass. That does make them very heavy, unfortunately. StuRat 21:59, 17 December 2006 (UTC)
Living where I live is not inexpensive but if you work at it you can reduce living costs. Not only do magnesium rods cost $40 to $60 USD but most of the time you can not get them out of the water heater even using a torch. Since aluminum will also work it is possible to use it instead of magnesium but hey I have aluminum in my diet. The objective then is to find a better way to A.) reduce material costs and B.) to reduce labor costs. If an inert anode would evolve minute but sufficient amounts of hydrogen to keep those little oxygen molecules entertained then hey, let me use a carbon welding rod and a very low current and voltage circuit and goodbye corrosion forever or at least as long as I can afford to pay the electric bill. Adaptron 20:47, 18 December 2006 (UTC)
The US$40-$60 mag rod last for several years. Do you really think you can run an electrical device, even a low current and voltage circuit, for less than that ? StuRat 17:30, 20 December 2006 (UTC)

Why has no one mentioned water hardness as a cause?87.102.4.227 19:18, 20 December 2006 (UTC)

Well, you certainly can put a water softener in before the water heater, but I consider the salty water produced to be quite unacceptable, myself. I'd much prefer straight tap water to that. StuRat 22:20, 21 December 2006 (UTC)

[edit] Tin Reactions

As part of a lab, pieces of tin metal were emmersed in copper(II) nitrate and hydrochloric acid. Contrary to the activity series of metals, however, reactions did not take place. Are there any explanations for this? I have looked all over the internet. Thanks. -- Sturgeonman 15:31, 17 December 2006 (UTC)

What are your thoughts about the hydrochloric acid? --HappyCamper 15:41, 17 December 2006 (UTC)

Can you be a bit clearer - was the tin put in copper nitrate and then HCl or both at once.87.102.13.235 16:13, 17 December 2006 (UTC)

It's possible than the tin is coated with layer of tin oxide on the surface preventing reaction with the copper sulphate. I can't explain why it would not react with hydrochloric acid.83.100.132.121 17:55, 17 December 2006 (UTC)
tin should react with both. --75.73.155.34 00:07, 18 December 2006 (UTC)

[edit] Digital Extension

I have a very difficult question, one which many career anatomist, two physiatrists, and a hand surgeon have not been able to answer, but I thought maybe I'd get lucky here. Put your hand palm side down on a flat surface. Now flex your fourth digit so that it is bent under your palm, and the proximal phalange is flat on the surface. All other fingers should be straight. Now try to extend your third digit. Notice that there is a small range of movement. Now reposition your hand so that the third digit is flexed underneath and attempt to extend the fourth digit. In this case, there is no range of movement whatsoever. Why is it that extension is possible in one situation but not in the other? Consider that it is possible to move the "immobile" digit through extension with another mechanism (like the other hand) without pain, and that this phenomenon occurs with the second and third digit in the positions above too. Tuckerekcut 16:27, 17 December 2006 (UTC)

Actually, experiment proves that a small range of movement is possible, but only through quite a considerable amount of pain in the bent finger, as the controlling tendon is placed under extreme strain. (Thanks for putting me through that!) The answer is that while there are indeed four tendons in the back of the hand, one for extending each finger, there are only three muscles (located in the wrist) controlling those tendons, one for the little finger and two shared between the three middle fingers. Find someone with low body fat and watch them flexing the fingers to see the tendons move through the skin on the back of the hand; or get a hand from your anatomy friends, remove the skin, and play with the muscles of the wrist yourself. (On the base of the hand it's much simpler; each segment has its own muscle, although not everyone has the neurological ability to address those muscles separately.) Thus when one finger is at full flexion, the body is unable to restore the adjacent finger to full extension, because when the muscle pulls on the adjacent finger's tendon it is also pulling on the flexed finger's tendon - which cannot be extended. EdC 18:47, 17 December 2006 (UTC)
None of my colleagues were able to extend the fourth digit in the situation described, if you were able to, kudos to you. However I am most interested in knowing why there is such a difference in the difficulty between the third and fourth digits as described. I realize that the extensor digitorum provides extension for digits two through five, with ex. dig. minimi and indicus adding in for 2 and 5, but this does not explain the difference in difficulty, which really is the part that stumps me. Tuckerekcut 20:35, 17 December 2006 (UTC)
Incidentally, I meant no sarcasm with my last remark, if it seemed that way. I also wanted to point out that the pain seems (to me) to be in the muscular region of the extensor muscle, rather than the tendinous region, thus weakening your argument slightly. Tuckerekcut 20:38, 17 December 2006 (UTC)
Nah, to me it's definitely in the tendon, where it passes through the knuckle. I have a feeling the reason I'm able to do that might be that I broke my middle finger a while back, so it probably doesn't count.
Still, this a purely mechanical problem; the neurological wiring doesn't enter into it. Think of the hand as a series of hinges with springs to force them shut (the flexor muscles).
When the ring finger is fully flexed, the extensor tendon is close to full stretch. When the middle finger is fully flexed, even more so; when the index finger is fully flexed the extensor tendon is almost completely at full stretch. Thus when the ring finger is flexed the tendon can still be retracted a short distance, extending the other fingers. When the middle finger is extended the tendon can be retracted a little, giving less movement in the index finger than when the ring finger is extended, but even when the tendon is fully retracted this is insufficient to overcome the residual tension in the ring finger, so it does not extend.
Oh, and I'm not sure why it is possible to extend the ring finger when it's the index finger that's flexed. I suspect some amount of rotation or lateral movement is going on with the tendon, or it might be due to lateral banding. I'd have to get a hand to play with to be sure. --EdC 02:41, 18 December 2006 (UTC)

[edit] Fish mate

Someone told me of a deep sea fish specie of which the male is a 10th the size of the female. When finding a partner the male grabs the female and taps into her blood system (?) and insures she has a constant suply of sperm. The female then feeds for him and the male lives off their joint bloodstreams. What is the name of the fish? Are there other examples of such extreme couplings? Thank you. Keria 17:06, 17 December 2006 (UTC)

I'm sure it's not exactly what you're looking for, but here's one. And please don't let my humorous answer deter anyone from offering serious ones. Anchoress 17:53, 17 December 2006 (UTC)
It an anglerfish: [1]. Rmhermen 18:13, 17 December 2006 (UTC)

You might be looking for Anglerfish see Anglerfish#Reproduction, no doubt there are other deep sea fishes that do a similar thing.

"When scientists first started capturing ceratioid anglerfish, they noticed that all of the specimens were females"..."When a male of one of these species hatches .... extremely well developed olfactory organs .... They have no digestive system, and thus are unable to feed independently. They must find a female anglerfish, and quickly, or else they will die."..."When he finds a female, he bites into her flank, and releases an enzyme which digests the skin of his mouth and her body, fusing the pair down to the blood vessel level"..."then atrophies into nothing more than a pair of gonads"..."when the female is ready to spawn, she has a mate immediately available"...83.100.132.121 19:02, 17 December 2006 (UTC)

Thank you very much. Keria 00:06, 18 December 2006 (UTC)

Some gastropod molluscs from the genus Enteroxenos have just as 'extreme couplings'. --jjron 07:35, 19 December 2006 (UTC)

[edit] Parasitic Worm

I saw this video [2] on ebaumsworld and it says that a parasitic worm controls a crickets mind and forces it to commit suicide. While I know thats probably not true, can anyone tell me what exactly happened in this video? Imaninjapiratetalk to me 17:54, 17 December 2006 (UTC)

This sort of parasite mind control has been a popular recent topic - even as it relates to humans. Can't find any links right now though. Rmhermen 18:08, 17 December 2006 (UTC)
It's a Nematomorpha, otherwise known as a Gordian Worm. It apparently does make the grasshoppers seek out water and drown themselves, returning the worm to the water. Super creepy. I added a super-legit reference to the article (Nature, 2006) which is where that video is from. --24.147.86.187 20:01, 17 December 2006 (UTC)

Another similar example of brain control might be the rabies virus, which attacks the brain, increasing the aggressive tendencies of an animal, making it bite other animals and thus spread rabies to new hosts. StuRat 21:52, 17 December 2006 (UTC)

Wow that is scary. I didn't think of the connection between that and rabies either. I just didn't think a parasite would actually be able to control an animal like that. Imaninjapiratetalk to me 22:30, 17 December 2006 (UTC)

It's one of those extreme specialization things, like Emerald cockroach wasp. The downside to such controll is that they really don't know how to do anything else... 68.39.174.238 23:15, 17 December 2006 (UTC)
A similar phenomenon is the "brainwashing" of carpenter ants by the Cordyceps unilateralis fungi. The fungal spores get into the ant via its spiracles and starts to grow mycelia filaments inside the ant, being careful to avoid any vital organs. When its ready to sporulate, it projects mycelia to the ants brain. It then forces the ant to climb to the top of a plant and attach itself firmly to a leaf by biting with its mandibles. Now that its in a suitable position, the fungus will eat the ant's brain, sprout outwards through its head and explode, showering the area with spores that will try to invade other ants. As told in the BBC's Planet Earth, When other ants detect that one of their own has been infected, the carry the unfortunate ant as far away from their nest to die, in the hope that when the fungus sporulates, it will limit the chances of infecting the entire colony. There are lots of different types of fungus that do this, with different species being specific for diffferent types of arthropod. You can see more info, including footage here. Rockpocket 23:20, 17 December 2006 (UTC)
I don't think the parasitic barnacle sacculina driectly attacks the crab's brain, but it does attack its gonads to sterilise it, and then uses the crab's mating behaviour for its own procreation. --ColinFine 23:41, 17 December 2006 (UTC)
For more examples of parasitic "mind control", see Dicrocoelium dendriticum and Toxoplasma gondii.  --LambiamTalk 23:48, 17 December 2006 (UTC)
Of course, it's the "mind control" idea that intrigues the press, but it's a little bit silly and anthropomorphic. These are parasites that cause a change in behavior in their hosts, but there's no "mind control" in play. - Nunh-huh 01:25, 18 December 2006 (UTC)
Are you drawing a distinction between "mind control" and "brain control" ? StuRat 01:30, 18 December 2006 (UTC)
No, I wasn't. I suppose there is one, but that wasn't what I was trying to point out, which is that "control" implies the existence of a will on the part of the controlling agent, which is certainly lacking in these instances. - Nunh-huh 02:00, 18 December 2006 (UTC)
Can't one be controlled by inanimate things, such as money ? StuRat 03:38, 18 December 2006 (UTC)
Some people like to think so, but I would characterize people pursuing money as doing so under their own control. I don't think the alcohol made you do it, or really anything but yourself. - Nunh-huh 08:18, 18 December 2006 (UTC)
I'd call effecting a very calculated and deliberate change in behavior "mind control" under most people's common definitions. I'm not sure what other definition of "mind control" one would want to use. --24.147.86.187 01:48, 18 December 2006 (UTC)
If it were "calculated" or "deliberate", you'd have a point. But it's not, as there is no intelligent agency doing any calculating or deliberating. That's precisely the point. - Nunh-huh 01:58, 18 December 2006 (UTC)
There doesn't have to be an intelligent agency, that's the beauty of natural selection—you can render "nature" itself as a theoretical selecting agency. In any case, I don't think you've yet given a good reason for not considering it "mind control". Anything which can directly alter an organisms mental behavior in such a dramatic way sounds like "mind control" to me. --24.147.86.187 03:25, 18 December 2006 (UTC)
I understand the mechanism of evolution quite well. And to me, control implies a controlling agency (and in the instances cited, the parasite ain't it.) Your mileage may differ. - Nunh-huh 08:18, 18 December 2006 (UTC)

[edit] Sensitiveish Microphone Advice

I want a microphone that will pick up my voice from a few meters away so I can have Skype conversations when I leave my headphones somewhere or just don't feel like wearing them. My old headphone needs to be right near my face in order to pick up my voice clearly and is therefore not sensitive enough. Can someone advise me on how to choose a suitable (cheapest microphone effective at three meters for Skype) microphone on ebay? Micrphone type? Sensitivity level likely needed? --Username132 (talk) 19:29, 17 December 2006 (UTC)

Can you clarify Skype OK found it.?--Light current 19:30, 17 December 2006 (UTC)
Have you looked up microphone? You need to decide if you want unidirectional or omnidirectional response. I suspect you want omni to pickup your voice wherever you are in the room. It looks like you need an omni with a large diaphragm [3]. Have you considered using a LS in reverse? 8-)--Light current 19:39, 17 December 2006 (UTC)
I don't think that will work, even with a great microphone. To hear the other party you'll have to run Skype's output through the PC's speakers - and the microphone will hear that too. It's very hard to position things so you don't just get runaway feedback, and even then it'll sound garbage. If you must do this, you need to get a proper speakerphone attachment. Speakerphones implement advanced DSP algorithms to suppress feedback and echo. Googling for "skype speakerphone" shows a number of manufacturers make compatible units. I've not used their Skype unit, but Polycom's other conference phones are very good (not not at all cheap). -- Finlay McWalter | Talk 19:51, 17 December 2006 (UTC)
Yes Finlay is correct in that on a 2 wire line (full duplex) system you do need some sort of hybrid transformer system to prevent positive feedback. These are naturally buit in to (speaker) phones. I'm not sure if the Skype has such a hybrid system built in. One way to test would be to bring the headset mic close to the ear phones and listen for howling. If no howling then youre ok and the separate mic idea should work/.8-)--Light current 20:13, 17 December 2006 (UTC)
I really meant sonic echo, not electrical feedback (although if both parties had such homebrewed speaker & mic systems, you'd get insane sonic feedback too). That's sound (the remote party talking) coming out of the speakers, it bounces off walls and stuff, and flies back into that nice sensitive omnidirectional microphone. And because your room probably has four or more hard walls (plus the ceiling, plus large pieces of furniture) then the mic receives not one echo but one for each such surface, each at a different delay from the original sound. That's why fancy speakerphones play a little tune when you turn them on - they're measuring the echoes of those different surfaces, and their frequency-absorption characteristics. -- Finlay McWalter | Talk 20:26, 17 December 2006 (UTC)
Ohhh, you clever people. Skype doesn't stop this feedback but I've made a 'feature request' on their forum. --Username132 (talk) 20:35, 17 December 2006 (UTC)
You mean you actually tried the mic next to the earphoes and it howled? What frequency? 8-)--Light current 20:41, 17 December 2006 (UTC)
When my friend called me on her laptop (speaker and microphone), I could hear my own voice with a delay (I hated it). --Username132 (talk) 21:06, 17 December 2006 (UTC)
OK you got sonic echo!--Light current 21:44, 17 December 2006 (UTC)
Bluetooth works, but I find the extra weight uncomfortable. --Seejyb 22:37, 17 December 2006 (UTC)

[edit] Evil Beth

[According to Beth], I should bake my cake mixture for one hour at 180 C. After baking for just 20 minutes, the thing began to burn and make smoke. Is Beth really evil, or is there another, less sinister explanation? --Username132 (talk) 21:12, 17 December 2006 (UTC)

No, that is a pretty standard recipe and temperature for banana bread. Rmhermen 21:21, 17 December 2006 (UTC)
I wonder if the oven (I set to 350) is in Faranheit or Celcius... it's an oven in the Netherlands, but wouldn't an oven that goes to 350 Celcius be quite special and expensive? Maybe I should set the temperature lower and or have heat come from only the bottom of the oven (instead of also the top). --Username132 (talk) 21:37, 17 December 2006 (UTC)
Heat come from the top? Sounds like you've turned on the grill! My friend has an oven where it is possible to do this too. If you are baking you only want the heat from the bottom. Also, 180 degrees C is medium low, so depends what the scale of your oven is, what's the minimum and max you can set it to? My oven is in C and it goes from about 100 to 300 I think, so 350 might not be outrageous if it's near the top of the scale. Vespine 22:10, 17 December 2006 (UTC)

I suspect there's a problem with the temp sensor in your oven and it's not kicking off when it reaches the proper temp. Do you have a meat thermometer ? If so, stick it in the oven and see what it says the temp is. StuRat 22:16, 17 December 2006 (UTC)

There could also be a problem with the temp selection dial. Does it seem to turn properly or does it turn with difficulty or show some other problem ? StuRat 22:33, 17 December 2006 (UTC)
I agree with StuRat, get an oven thermometer so that you know in future exactly what that oven is doing - if you are baking cakes it sounds as if you are settling in for a longish stay. A baking neighbor may have one to lend. To what maximum is the oven marked? If it is in the region of 500 or more, then it is almost certainly in °F, but then I would expect an oven in the Netherlands to use the Celsius scale. Generally: If the pan is placed directly over the heating element one can burn the bottom of the cake, it may need to be shielded by a separate baking tray. The upper element/grill would not normally be used during baking (sometimes for preheating) --Seejyb 22:39, 17 December 2006 (UTC)
Max setting is 360. --Username132 (talk) 23:03, 17 December 2006 (UTC)
That iffy, it's either a Fahrenheit-scale oven that doesn't go very high or a Celsius scale oven that gets very hot, indeed, perhaps a self-cleaning oven ? StuRat 23:57, 17 December 2006 (UTC)
I'd bet on Celsius then. Even the mildest of cooking ovens should reach 430°F/220°C --Seejyb 05:20, 18 December 2006 (UTC)
I vote Celsius, my oven goes to 300, I don't think 380 is ridiculous. 180 celsius on my oven is if I turn the dial a little over half way. But also, read my post above! Heat should NOT be coming from the top! I BET you have a grill coil at the top of your oven that can be turned on, my friend has exactly the same thing and we burned our garlic bread by accidentally turning the grill coil on as well as the oven. Vespine 01:03, 18 December 2006 (UTC)
  • Since you said: "I wonder if the oven (I set to 350) is in Faranheit or Celcius..." I assuming you set it to 350. Since you're in the Netherlands it's almost certain you have a oven with Celcius scale, if you set it to 350 instead of 180, it's simply too hot. - Mgm|(talk) 11:14, 18 December 2006 (UTC)
If you don't want to buy a thermometer, try putting a glass of water into the stove and setting the temperature to 150. If the water boils, your stove is on Celsius. If it doesn't boil, your stove is on Farenheit. --Bowlhover 21:57, 19 December 2006 (UTC)
And if the glass breaks, you know your glassware isn't oven safe. ;-) Anchoress 22:04, 19 December 2006 (UTC)

[edit] Is the (north) polar ice cap floating ?

Or is it attached to the ocean floor ? Does this vary from summer to winter ? If it is attached, is there a risk of it breaking free soon due to global warming ? StuRat 22:30, 17 December 2006 (UTC)

The ice over the pole is floating, the ice cap over greenland is on the land. -- Finlay McWalter | Talk 22:33, 17 December 2006 (UTC)
In that case, what keeps the floating ice from drifting in the currents until it crashes into land ? StuRat 22:36, 17 December 2006 (UTC)
Yes, it floats (there is no land under most of it - the nearest bits of solid land to the North Pole are Ellesmere Island and Greenland). There is nothing "stopping" the ice from floating away (bit of ice, also known as icebergs, break off the polar ice cap all the time! The Titanic hit one, for instance...), but this doesn't affect the cap as a whole, because it only "exists" where the temperature is cold enough. As a thought experiment to understand this: Take the ice cap as it is at present, and move it a bit in one direction. Some of it will now be in a warmer region of the world (nearer the Equator), that bit will melt, while a bit of ocean in a colder part of the world will now become exposed, that bit will freeze. End result: The ice cap stays where it is.
Of course, the ice cap shrinks and expands considerably between summer and winter!
Something to remember about the northern polar cap: melting bits of it (because of global warming) will not change sea levels, because when you melt ice that's floating in water, the overall level of water doesn't change. Melting ice sheets which sit on top of land (eg Antarctica), that's where the problem is, for any melting there equates to a sea level rise.
Well, actually, Melting of Floating Ice Will Raise Sea Level (Discussion at PhysOrgForum). (When ice melts – to freshwater – it takes up a greater volume than the volume of salt water it displaced as ice, so the overall sea level rises.) Not by that much, but by enough to make a difference. --EdC 03:08, 18 December 2006 (UTC)
Finally, the northern ice cap has been shrinking in recent years due to rising temperatures - if it continues, the Northwest passage may actually open up part of the year! — QuantumEleven 22:41, 17 December 2006 (UTC)
have a look at the arctic in September and February. -- ExpImptalkcon 22:45, 17 December 2006 (UTC)
That pic seems to show that the ice touches land (Greenland and Ellesmere Island), even in summer, but just barely. Perhaps in just a few years that land bridge will be gone and it will be free to drift ? StuRat 00:06, 18 December 2006 (UTC)
This image
suggests that pretty soon, around Greenland and Ellesmere island will be about the only place the ice remains. Makes sense; in the open ocean the water gets heated up by sun and currents, but around the land the ice gets protected and replenished by calving glaciers. --EdC 03:08, 18 December 2006 (UTC)
On a tangent that is related to the North Pole, ice, and water:
I have a 1970's National Geographic Atlas here that suggests that Greenland is really more of an atoll than a solid island: on the western coast, there is a huge inlet, and a space in the middle filled with water. Because the whole lot is covered in ice, though, most of us mistakenly think of it as being one big block of solid land. Vranak 16:47, 18 December 2006 (UTC)
See Geography of Greenland#Climate change but note that the depressed land will slowly rise again after the ice melts as is still occuring in North America from the last ice age. Rmhermen 22:55, 18 December 2006 (UTC)
Thanks for the info, I wasn't aware of that atoll. :-) StuRat 17:09, 20 December 2006 (UTC)

[edit] Neurologist/Neurosurgeon

I read both articles, but what are the actual practioners doing? Are neurologist and neurosurgeon synonymous ? does a neurologist only give medication ? Thanks in advance.-- ExpImptalkcon 22:37, 17 December 2006 (UTC)

No, they are not synonymous. A neurosurgeon is a surgeon. A neurologist was considered a sub-specialist of internal medicine and does not perform surgeries. A neurosurgeon typically operates on the brain (eg. removing brain tumors) and some do spine operations and operates on nerves (eg. for carpal tunnel syndrome). Neurologists treat diseases like strokes, epilepsy, and Parkinson's disease, etc. - Cybergoth 22:53, 17 December 2006 (UTC)
Thanks very much. But how do Neurologist treat them, if they don't operate? drugs?-- ExpImptalkcon 22:55, 17 December 2006 (UTC)
Well, drugs is one option. Diet modification is another. In the case of stroke victims, they may need to relearn certain things and in the case of epilepsy victims, they may need to learn to avoid certain things which trigger seizures (blinking red lights, for example). StuRat 00:09, 18 December 2006 (UTC)
Yes, medication usually. Neurologists might also prescribe physiotherapy, speech therapy, and occupational therapy for stroke patients for example. - Cybergoth 03:54, 18 December 2006 (UTC)
They might prescribe it, but they dont actually do therapy themselves.
Ive seen 3 neurologists. The first 2 asked a lot of questions and hit my joints with rubber hammers, and scratched me with sticks. The third one spent a lot of time sticking big needles into my arms and legs and giving me electric shocks and looking for responses on a monitor. I do not recommend this procedure 8-)--Light current 13:45, 18 December 2006 (UTC)