Wikipedia:Reference desk/Archives/Science/2012 November 2

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November 2

Gravitational collapse

Hi, how big would a planet with the same composition as the Earth have to be before it collapsed into some kind of super-dense exotic matter? 86.151.118.165 (talk) 02:51, 2 November 2012 (UTC)

Well, something with the same composition as the Earth but with the mass to form a black hole wouldn't be a planet, it would be a star. That is, nuclear fusion would support it until everything that could fuse had fused, then it would collapse into a black hole. Around 10 times the mass of the Sun seems to be enough to form a black hole, but I'm not sure if the composition of that mass changes the equation. StuRat (talk) 03:07, 2 November 2012 (UTC)

I am not necessarily talking about a black hole. In fact, I specifically didn't mean a black hole. 86.151.118.165 (talk) 03:17, 2 November 2012 (UTC)

Like neutron stars? Plasmic Physics (talk) 03:45, 2 November 2012 (UTC)

Or white dwarfs perhaps... Whatever is the first stage of exotic matter that is far denser than any ordinary matter that we are familiar with on Earth could be. 86.151.118.165 (talk) 04:06, 2 November 2012 (UTC)

... also, I am specifically not asking about stars. I literally mean that you take a rocky planet, same composition as the Earth, scale it up by x amount, then how big before there's a big crunch and it squishes down to a lump of exotic matter. 86.176.211.219 (talk) 04:45, 2 November 2012 (UTC)

I just did a back of the envelope calculation which came as 78.2 times the radius of the earth for it to collapse into a neutron star (using 2.84 E 30 as the collapsing mass from the Netron star article and 5500 kg/m^3 as the density of the earth). But that doesn't sound right (also, apologies for the lack of math tags, its to early for me to remember how to do them) 80.254.147.164 (talk) 09:56, 2 November 2012 (UTC)

(edit conflict) Well, our white dwarf article says the smallest estimated mass for a white dwarf is 0.17 solar masses, which is about 56,000 Earth masses. So a rocky planet (I am assuming "rocky" means insufficient hydrogen or helium to support fusion reactions) with the same average density as the Earth but about 40 times the Earth's radius would collapse under its own gravity to form something like a white dwarf. I have no idea how such a massive "rocky planet" object would form in the first place - maybe we just have to assume it appears from nowhere. Gandalf61 (talk) 10:01, 2 November 2012 (UTC)

You don't necessarily need hydrogen or helium. Silicon and oxygen, the two most abundant elements in the Earth's crust, will undergo fusion if you get them hot enough and squeeze them tight enough.

Iron, on the other hand, will not, and I kind of doubt nickel will either; these are the main components of the core.

So the bottom line is that I kind of doubt StuRat's claim about fusion, but the question can't be disposed of completely trivially. --Trovatore (talk) 02:12, 3 November 2012 (UTC)

How's this for a paraphrase: How massive can a body be before degenerate matter appears at its core? —Tamfang (talk) 19:08, 2 November 2012 (UTC)

Metallic hydrogen is degenerate matter and is thought to be present in the cores of Jupiter and Saturn. Gandalf61 (talk) 19:24, 2 November 2012 (UTC)

Whenever the mass is large enough to cause a force that overcomes the atomic weak interaction ..?, But I also wonder what actually happens when a body of elements that are more dense than iron-26 gets forcefully compressed and heated ? Electron9 (talk) 18:29, 6 November 2012 (UTC)

Avalanche rescue

Is earth-moving equipment used to rescue avalanche victims? If so, how do they make sure that survivors are not accidentally killed by it? 24.23.196.85 (talk) 05:19, 2 November 2012 (UTC)

I've always wondered the same when it comes to rescuing survivors from debris after a tornado, building collapse, etc. Ks0stm ^{(T•C•G•E)} 05:27, 2 November 2012 (UTC)

Only a WAG, but I wouldn't think so. Time is of the essence and getting heavy equipment into position would take too much of it. Clarityfiend (talk) 07:35, 2 November 2012 (UTC)

Agreed, you have minutes, at most, to dig the person out. Also, if they are buried so deeply in snow that shovels won't work in time, then they are already dead, due to the pressure. And, the main problem isn't digging the hole to get them out, it's finding them in the first place. StuRat (talk) 17:28, 2 November 2012 (UTC)

The usual method is to for rescuers to form a line, poking through the snow with a long pole called an avalanche probe and hoping to be able to recognize the resistance when the probe hits a body. Trained dogs are used to refine the search. I found this photo of the Galtür Avalanche, which appears to be using this technique. This photo shows a dog guiding a team of rescuers armed with avalanche shovels. 20 people who had been buried were rescued but a further 31 died. Alansplodge (talk) 18:07, 2 November 2012 (UTC)

And I have just found our Avalanche rescue article. Alansplodge (talk) 18:08, 2 November 2012 (UTC)

Thanks for the input, everyone! Now, what if the avalanche also buries several buildings and cuts the only road into the area -- would a bulldozer be useful to uncover the buildings and/or clear the road, or would the same techniques be used as for the victims on the slopes? 24.23.196.85 (talk) 01:11, 3 November 2012 (UTC)

Yes, bulldozers or snowplows would be used to clear the road, provided there aren't any victims believed to be present, and in the area around buildings, but not the buildings themselves, if they were believed to contain victims. Buildings have more of a possibility of air gaps inside, so people might survive for quite some time. StuRat (talk) 01:18, 3 November 2012 (UTC)

Thanks a million, and clear skies to you! 24.23.196.85 (talk) 02:53, 3 November 2012 (UTC)

Mushrooms and mycelium

Hello there reference desk. I'm trying to work out what is known about fungal lifecycles in terms of the variety of types of mushroom a single 'lump' of mycelium can produce. I'm most interested in the Euholobasidiomycetes, as this seems to be the group containing most of the mushroom producing fungi.

I realise it's fairly hard to give good answers as the genetics of some fungi aren't that well understood at the moment. As far as I can tell, a single spore from a mushroom contains a haploid nucleus that will start a mycelium colony growing. Some species have asexual reproduction methods, but most will have to interact sexually with another 'compatible' mycelium colony before producing fruiting bodies. At this stage, I started getting bogged down in detail - but it seems that some species of mycelium have the ability to acquire and incorporate more and more genetic material. There was also talk about varieties of mushrooms previously though distinct that turn out to be genetically identical. My questions are:

1. When fungi are said to be sexually compatible, does this mean that they are the same species in a way analogous to plants and animals?

2. Many species seem to end up with multiple, genetically distinct, haploid nuclei in their cells after various complicated genetic processes. Will the spores dispersed by a mushroom represent the entire genetic material of a fungus, or are all spore from one mushroom the same (barring chance mutations.)

3. What kind of variety of mushrooms can one mycelium colony (assume indefinite sexual encounters if this is necessary) produce?

The main site I've been using is . I'm sure the information is in there, but it's very dense and I can only get comfortable with 10 or so terms of art per sitting...80.254.147.84 (talk) 08:46, 2 November 2012 (UTC)

1.Depends on how you choose to define species and what you mean by "sexual compatibility". Generally, a species is defined as "a group of organisms capable of interbreeding and producing fertile offspring". So...

• Yes, if by "sexual compatibility" you mean the capability of the individuals in the population to reproduce with another individual within the group (inclusive of mating type barriers between individuals among heterothallic fungi).
• No, if you mean sexual compatibility merely in the sense of individual mating type compatibility. In the same way that just because two human males can not reproduce with each other, does not mean they belong to different species (although the latter analogy is vastly oversimplified given that fungi can have thousands of "biological sexes").
• Overarching all that is the species problem. If you follow a morphologically defined concept of species, some fungi populations can remain morphologically identical (cryptic species), even when in truth they have diverged and achieved reproductive isolation from each other long ago. Indeed, until the very recently (2011 International Botanical Congress) fungi were given different scientific names for different morphs in their life cycles (see teleomorph, anamorph and holomorph), even if they are all the same species, largely because they can look radically different.

If you follow biological species concepts which relies on reproductive isolation, it can fail in complex reproductive relationships where some groups can reproduce with some other groups but not with others and vice versa; while others still are actually not reproductively isolated but will only mate under certain conditions that might be missed in laboratory environments; and it does not take into account where the capability of interbreeding may simply be the result of retained ancestral characters (plesiomorphy) when in truth the individuals themselves have become genetically isolated a long time ago.

Phylogenetic species concepts addresses the latter by restricting groupings based on shared ancestors, but it runs into the problem of where to place the boundaries. How do you divide into species what basically is a genetic continuum broken only by extinctions? The latter problem exists even in higher animals but is more evident among fungi, where even trying to define an "individual" itself is difficult due to the fact that they barely qualify as "multicellular organisms". So the similarities and differences on how higher organisms are classified depends on which system is followed or combinations thereof.

2.The most common, asexual spores, are of course geneticaly identical to the parent. Though apparently some long-lived fungi colonies have been discovered to essentially be genetic mosaics, possessing genetic variation within a sngle "individual", so spores from the same individual can be different in those circumstances even if produced asexually.

Sexual spores in contrast are the result of the meiosis of a typically brief diploid stage and thus will differ from each parent. Spores that result from mitosis after meiosis are of course genetically identical to each other, but not to the others.

Thus in Ascomycota, for example, the nuclei from the two parent individuals (not genetically identical) fuse to each other (karyogamy) and form the diploid zygote nucleus. The diploid zygote nucleus then undergoes meiosis, exchange genetic information here and there, and in the end divide into 4 genetically different haploid daughter nuclei. Each of the daughter nuclei then undergo mitosis, such that they create genetically identical copies of themselves. This usually results in 8 ascospores, with every two ascospore genetically identical with each other, but not to the other pairs. Basically, they're a set of 4 twins. This series of diagrams might help. Basidiospores are more or less the same, except that in Basidiomycota, the two haploid nuclei of the parent individuals coexist in the same cell (even vegetative ones) for a longer time without undergoing karyogamy.

3.I'm assuming you mean how many genetically different individuals can result from a single mycelium colony through sexual reproduction. Well as many as all the possible permutations I guess. :P That's a bit like asking how many genetically different children two human couples can produce assuming they have an indefinite number of sexual encounters. Barring twins, no two children will be genetically the same, though they can be genetically similar.

Disclaimer: not a mycologist, merely rehashing uni biology lessons. :P -- OBSIDIAN†SOUL 09:57, 4 November 2012 (UTC)

3d tracking tic-tacs

I have the following requirements. (Basically I would like to track the 3d location of a few things in near-field like bluetooth-distnace)

1. Glue ten tic-tac size devices to ten spots within a 40cm x 40cm x 40cm area.

2. Know in real time the location of each device #1 - #10 with a 2mm x 2mm x 2mm margin of error, within a 3m x 3m x 3m space (no tracking required if they leave this space). The response should be within 100 ms but preferably 15-20 ms.

Any technological solution could be considered.

--

My thoughts. The devices can be active (know their own location) or completely passive, like an RFID strip, and activated remotely by a reader or base station. It also doesn't matter if the location is only relative to some point of origin. And although the tic-tacs should be small, there can be a considerably larger base station or receiver.

Now, I realize there are many, many approaches here. Hollywood tends to use 3 or more cameras and interpolate exact position of the tic-tacs. The tic-tacs could have gps devices, then their precision and response is much, much worse than my requirements. The tic-tacs could be physically connected to rods that can move in 3d (in-and-out and pivot on a ball) that register their relative movements. Or they might somehow have radio signatures that the base station can interpret.

They could be magnetized and the magnetic signatures detected by a very large base station. They could be radioactive or emit xrays and be detected by their signatures on that basis. (Then the base station would have to have 3 planes, maybe).

What is the simplest, cheapest solution here? I would think that if there were some radiofrequency-based thing where there is a somewhat largish base station then it would work.

What do mimeo whiteboard digitizers use, for exmaple, like this - http://www.mimio.com/en-EM/Products/MimioCapture.aspx (scroll down)

or how do Wacom tablets digitize the location of a passive plastic stylus?

I don't really know the space of technologies that can meet the requirements. Your creativity is appreciated here, thank you. --91.120.48.242 (talk) 09:20, 2 November 2012 (UTC)

It sounds like a pretty traditional motion capture problem. I don't think there are many options out there other than optical systems like you mentioned. Does a marker and camera based solution work for your problem, or is there a reason you need something more technical? 209.131.76.183 (talk) 13:25, 2 November 2012 (UTC)

I just think that a passive radio emitter would be less technical, not more technical. RFID strips are incredibly low-cost. Isn't there a way to get a receiver to triangulate the position of a passive radio device? This seems like it's gotta be far less expensive from trying to get a line-of-sight and markets. I also just cannot believe that markers can be precise enough to my tolerances, e.g. 2-5 mm. --91.120.48.242 (talk) 14:58, 2 November 2012 (UTC)

That does sound like a sensible solution, though I think that's not "RFID" proper but some more basic type of radar signature - the key here is that waiting for digital operations to return a serial number seems like it should introduce too much timing uncertainty to measure the distance according to speed-of-light time delay. Triangulating the signal according to intensity or exact angle of displacement seems like it would be very tricky. But take what I say with a shaker of salt, because it's not my field. Wnt (talk) 18:06, 2 November 2012 (UTC)

You said they will be glued down, but glued down to what ? Rods ? StuRat (talk) 17:23, 2 November 2012 (UTC)

Hi! That is one possibility, but better is if they are just glued to the locations. The question is how to locate these in 3d space (not 6d, you don't need to know orientation at all). The rod idea is the worst one that I can think of, since it involves physically connecting these tic-tacs, instead of letting them move freely with the body they are on. 178.48.114.143 (talk) 17:47, 2 November 2012 (UTC)

What "body" are they on ? StuRat (talk) 18:02, 2 November 2012 (UTC)

Fine joints on a human body, glued on lightly thereto. In fact though they can be slightly tethered to some kind of slightly larger thing held on with a band, that is fine. this seems to be what the reference i found below was about. 178.48.114.143 (talk) 11:17, 3 November 2012 (UTC)

One potential problem, do we need to account for the possibility that one of the "tic-tacs" can be behind another, or behind a rod, from the POV of one of the detection devices ? StuRat (talk) 17:17, 2 November 2012 (UTC)

They can indeed be behind each other. I think something radio-based is the best idea. Does such technology exist? THey could be on different frequencies. So, the idea is if you have ten of these on ten unique frequency, say, and passive radio emitters that emit their frequency in response to a base frequency - then the receiver emits that frequency, and gets ten point sources corresponding to the ten different tic-tacs. THrough radio trangulation would it be possible to locate each to within 2mm by 2mm by 2mm? You don't need to know their orientation. 178.48.114.143 (talk) 17:47, 2 November 2012 (UTC)

The technology exists, but I don't think you can get that type of resolution out of it. Here's a company that offers such an RFID system, but to work on larger scales: [1]. StuRat (talk) 17:59, 2 November 2012 (UTC)

could you talk about the physics behind it ,and why it wouldn't work for radio, ultrasound, or magnetic-production and sensing respectively? 178.48.114.143 (talk) 11:17, 3 November 2012 (UTC)

The motion scan article claims that radio systems are less accurate, which makes sense when you start looking into the wavelength of the signals. Hollywood uses optical systems because they are relatively simple and have the best accuracy. Similar problems occur in industrial automation, and there is a large industry based around sensing locations in that market. If you have a good budget for this project, I recommend talking to motion capture or industrial sensing companies for ideas. If you're trying to make something from scratch on a low budget, optical is probably the simplest. 209.131.76.183 (talk) 18:08, 2 November 2012 (UTC)

This is an interesting contribution. Could you help me make sense of this research paper:

“ J Neurosci Methods. 1998 Sep 1;83(2):125-31.

Using miniature sensor coils for simultaneous measurement of orientation and position of small, fast-moving animals. Schilstra C, van Hateren JH. Department of Neurobiophysics, University of Groningen, The Netherlands.

Abstract

A system is described that measures, with a sampling frequency of 1 kHz, the orientation and position of a blowfly (Calliphora vicina) flying in a volume of 0.4 x 0.4 x 0.4 m3. Orientation is measured with a typical accuracy of 0.5 degrees, and position with a typical accuracy of 1 mm.

This is accomplished by producing a time-varying magnetic field with three orthogonal pairs of field coils, driven sinusoidally at frequencies of 50, 68, and 86 kHz, respectively. Each pair induces a voltage at the corresponding frequency in each of three miniature orthogonal sensor coils mounted on the animal.

The sensor coils are connected via thin (12-microm) wires to a set of nine lock-in amplifiers, each locking to one of the three field frequencies. Two of the pairs of field coils produce approximately homogeneous magnetic fields, which are necessary for reconstructing the orientation of the animal. The third pair produces a gradient field, which is necessary for reconstructing the position of the animal.

Both sensor coils and leads are light enough (0.8-1.6 mg for three sensor coils of 40-80 windings, and 6.7 mg/m for the leads, causing a maximal load of approximately 5.7 mg) not to hinder normal flight of the animal (typical weight 80 mg). In general, the system can be used for high-speed recordings of head, eye or limb movements, where a wire connection is possible, but the mechanical load on the moving parts needs to be very small."

”

if I understand it correctly, this is sensors lead by a small wire. THis would be fine for me - the sensors would be attached to the fine joints and lead to a wire on a band around a heavier body part. Would this be doable? very expensive? Could you help me interpret the science in this article? THanks. 178.48.114.143 (talk) 18:46, 2 November 2012 (UTC)

• Hmmm, I'm thinking two bar code scanners, if you have one with a red laser, one with a green laser. The tic tacs contain photosensors that can tell when red or green is detected with very good temporal resolution. If they know when the laser beam is supposed to reach a certain spot in a 2-d grid pattern, and they can do it based on two separated points with the red and green, then they know their 3d location. This assumes the laser makes a thorough grid sweep (enough to hit any given spot a tic tac can be) and that you have enough understanding of the software to know when it hits that spot with great temporal precision - not sure either is true for a standard scanner. Wnt (talk) 17:55, 2 November 2012 (UTC)

This is an interesitng thought, I will keep track of it along with the others. I wonder if making the actual end-point "sensors" dumber however and the receptor smarter isn't the better way to go maybe? 178.48.114.143 (talk) 18:46, 2 November 2012 (UTC)

Heat transfer and temperature

I'd like to know if it is possible to estimate how hot an object will get over time when placed near a heat source. My specific problem is this: I have a wood stove that will have a surface temperature of about 300-500 C (?). I also have paint for a concrete wall behind the stove and the paint can take about 120 C. What I'm wondering is how close to the stove I can paint this wall and not burn my paint later. The shortest distance between wall and stove is about 30 cm, the longest (from top of the stove to top of the wall) about 150 cm, and there is some airflow between stove and wall. The max time the stove would be used would be around 2-3 hours/day (the time it takes to make food & heat the room). I'd like to paint as close as possible. I've read articles about heat conductivity, radiation etc but I'm none the wiser.

I don't know if this question is enough about science, but I couldn't figure out another place to ask this. --88.148.221.134 (talk) 13:09, 2 November 2012 (UTC)

I suspect that the paint will be fine, especially if it is white to help reflect the radiated heat. The concrete wall should be able to wick heat out of the paint surface pretty quickly, and circulating air will also help cool the surface. Intuitively, I think the wall will get hot, but not so hot that you can't touch it, and not hot enough to boil water, so it should be below 120C. Higher-temperature paints are also available, but are more expensive. The best way to answer the question for sure is to run the stove before painting the wall and measure the temperature directly. One of those IR "laser" thermometers would work great, if you use something (a board, tin foil, pretty much anything) to shade the wall from the stove's radiative heat just before measuring in order to prevent interference in the reading. 209.131.76.183 (talk) 13:21, 2 November 2012 (UTC)

It is possible to calculate the wall surface temperature by using airconditioning formulae. There are formulae for estimating the heat flow via air flow and formulae for direct radiation. You need to estimate the emissivity of the paint surface, and look up the thermal conductivity of the wall - tables for all sorts of walls are published in airconditioning manuals. You will need high school algebra capability to use such formulae.

While you said you intend to only use the stove for 2 to 3 hours a day, for safety you should assume continuous operation with the stove well stoked. From my own experience, I suggest you view paint temperature specs with a GREAT deal of suspicion. In any case, if the wall is any sort of timber product, plasterboard etc, you want to keep it to 50 C or less. Concrete walls 90 C or less.

However, I purchased a wood stove some years ago, and it came with installation instructions which gave the minimum distance from walls. So check with the manufacturer of your stove.

Ratbone 121.215.21.99 (talk) 15:08, 2 November 2012 (UTC)

I suggest you place something between the wood stove and the wall, to protect it, since, even if the paint doesn't scorch, the constant heating and cooling will cause it to crack and peel before the rest of the paint. A chunk of drywall covered with aluminum foil on the side facing the stove should do the job nicely and cheaply. If you want to spend more and make something fancier, you can do that, too. StuRat (talk) 17:06, 2 November 2012 (UTC)

people mover using air pressure

Somewhere in India or near India is a people mover that uses air pressure to push a large box around a circular path. The air boxes are higher up and is attached by an arm to a lower box fills up with riders. The circular route has segments. The air from one is pumped from a forward void into an aft void. Does anyone has a photo of this mass transit system or any other printed information? I think I read about it in the Whole Earth Catalogue back in the 70’s. I've google it extensively with no results. Thanks. Dennis — Preceding unsigned comment added by Jdenwyatt (talk • contribs) 13:54, 2 November 2012 (UTC)

You might be interested to know that some of the earliest subways were pneumatic, like this: Beach Pneumatic Transit. The problem is, it only works for a small distance. StuRat (talk) 16:45, 2 November 2012 (UTC)

Taman Mini Indonesia Indah (TMII, an Indonesian theme park) has an elevated Aeromovel transportation system that is close to the system that you've described, though with the positions of the pumped air and the passenger compartment swapped. In the TMII Aeromovel system, there is a hollow concrete pipe (beneath the elevated tracks) through which air is constantly pumped. The vehicles have large paddles or 'sails' that extend down into this pipe; when the sails are perpendicular to the direction of travel the train is 'blown' along, whereas when the paddles are turned parallel to the airflow the train coasts. I've read about similar systems in the past (I have a vague memory of a Popular Science article from about 20 years ago), but I'm having difficulty locating additional references. TenOfAllTrades(talk) 19:46, 2 November 2012 (UTC)

Although it doesn't address the OP's specific query, the general topic of atmospheric railways might be of background interest. (The poster formerly known as 87.81.230.195} 90.197.66.19 (talk) 13:14, 3 November 2012 (UTC)

Ball point pens and pull-cord light switches

Is there a name for, and do we have an article on, the alternating up/down mechanism found in ball point pens, which I'm assuming is similar to that found in pull-cord light switches? Rojomoke (talk) 14:09, 2 November 2012 (UTC)

Some poking around at google indicates that retractable ballpoint pens use a type of cylindrical cam follower/ratchet mechanism, sometimes called a "Ratchet spring". --Jayron32 14:26, 2 November 2012 (UTC)

Fat soluble medicine

If a medicine is fat soluble, will we absorb more of it taking it with fat or without fat (just water)? 80.58.205.34 (talk) 16:19, 2 November 2012 (UTC)

Most such medicines are advised to be taken with food, read the label and consult with a doctor, pharmacist, or nutritionist. See also, fat-soluble vitamins. (I support re-openning this since it is a general question, not a request for specific individual advice.) μηδείς (talk) 16:38, 2 November 2012 (UTC)

I know that medicines will explain how do you have to take it. But my doubt was rather general. The requirement "take with food" could be motivated by other causes, like to protect the stomach from some medicine. I just wanted to know how it works physiologically, not in a real life scenario. If a medicine gets dissolved in fat, will we absorb more or it or excrete more of it? 80.58.205.34 (talk) 16:42, 2 November 2012 (UTC)

It should help to dissolve it in fat. A normal person's digestive system is quite capable of digesting fat, so there's no problem with it passing out of the body like that. Being more diluted in all that fat would also help to avoid irritating the intestinal lining by being exposed to high concentrations. StuRat (talk) 16:53, 2 November 2012 (UTC)

• This section really does border on giving medical advice. What if the IP changed how he took his medicine according to what was stated here and it had negative effects? IRWolfie- (talk) 16:56, 2 November 2012 (UTC)

The IP is not asking to change anything. if the IP takes a medicine, he will follow the label. 80.58.205.34 (talk) 17:04, 2 November 2012 (UTC)

• If they said they wanted advice on how to take their own meds, then you'd have a point. StuRat (talk) 17:00, 2 November 2012 (UTC)

Yes, the reason is for the presumed fat content of the food, some medicines are also taken with milk. The body preferentially absorbs fat (fat digestion), so unless you are just drinking two quarts of vegetable oil daily, or a eating the un-absorbable Olestra, it should lead to better absorption, not excretion. Of course this is biology so there are all sorts of caveats. You will find most actual pharmacists enjoy discussing this sort of thing (not register clerks) so I would suggest approaching a consultation window if you have questions about any specific medicine. μηδείς (talk) 17:01, 2 November 2012 (UTC)

• It appears that the answer depends on the specific vitamin or drug in question. See [2] where lutein appeared to require fat, but vitamin E didn't (but then again, a preceding study found it did...). It's important to remember in all this that chylomicrons are made, they're not just bubbles of free fat that carry intestinal contents into the blood, which would be bad! So I think the effect is not one where the vitamins hitch along for the ride the whole way - rather, the vitamin has to get in as an individual molecule, and then, if there are more blobs of fat on the far side, it's more likely to stick and make room for the next molecule. So I don't expect super dramatic effects here, unless the biology is being particularly creative (something which it tends to enjoy doing often). There are some fun details, like Xenical can reduce the rate of absorption of some things. Wnt (talk) 17:34, 2 November 2012 (UTC)

Why does a dead body float on water ?

Why does a dead body float on water ? (Not Homework) Thanks! 106.209.2.66 (talk) 18:05, 2 November 2012 (UTC)

Gas builds up in the intestines (mostly, I think), bloating the corpse. There's a specific "floating decay stage" which takes anywhere from a day to a week to begin depending on temperature. [3] Wnt (talk) 18:11, 2 November 2012 (UTC)

A fresh corpse will immediately sink in water[4]. After a certain amount of decomposition the bloating will float the body back up. After all the gas-containing cavity rot enough for the gas to leak out, the body will again sink into the water. A8875 (talk) 21:10, 2 November 2012 (UTC)

Human bodies differ in density, but are generally slightly more dense than water [5], for example, for males. A very fat corpse might be less dense than water and float initially. Air or CO2 in the stomach from consuming fizzy pop could also add to bouyancy. [6]. I have observed that I float with lungs full of air, but sink if I expel sufficient air. Air retained in clothing could also make a fresh corpse float (Which sounds a bit like the world's worst soda fountain confection!) Edison (talk) 23:02, 2 November 2012 (UTC)

But wouldn't a body normally have lungs at least partially full of air ? StuRat (talk) 23:04, 2 November 2012 (UTC)

Once you're dead the diaphragm relaxes, and the lungs deflate. Rojomoke (talk) 23:35, 2 November 2012 (UTC)

Archemedes principle190.56.105.253 (talk) 15:21, 3 November 2012 (UTC)

Is that when he went to take a bath, found a body in his tub, and yelled 'Eureka !' ?" StuRat (talk) 23:33, 3 November 2012 (UTC)

Cell Biology

Hi! Which are the most important discoveries in history of cell biology, important for medicine? Please name 10 to 15. Thank you in advance! --Atacamadesert12 (talk) 19:23, 2 November 2012 (UTC)

As you have been previously informed, we do not do people's homework for them. Please refer to that prior response for the reasons for our position. — TransporterMan (TALK) 21:15, 2 November 2012 (UTC)

I am surprised we don't have an article on Metachlorians. μηδείς (talk) 21:37, 2 November 2012 (UTC)

Midichlorians. Someguy1221 (talk) 21:46, 2 November 2012 (UTC)

Thought I must be misspelling it but one gets quite a few hits on the other. μηδείς (talk) 01:19, 3 November 2012 (UTC)

That would be the citizens of the planet Midichloria. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:32, 3 November 2012 (UTC)