Wikipedia:Reference desk/Archives/Science/2011 February 8

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February 8[edit]


A single pinhole lens provides a single, dim image with an infinite field of focus. So:

1) Can multiple pinhole images be combined to create a single, bright image of infinite focus, using either mirrors to combine the images or electronic image capture from each pinhole to combine them ?

2) Or, if combining all those slightly different images leads to a fuzzy image, could adaptive optics be used to restore the composite image to a perfect focus ? StuRat (talk) 04:05, 8 February 2011 (UTC)

Pinhole lenses are pretty much poor-man's optics. If you're already going to use mirrors/lenses/digital processing to resolve an image, it seems that the pinhole becomes pragmaticly worthless. I suppose you could technically do all of the above, but it strikes me as rather pointless to use a lens or mirror to focus multiple pinhole images into a brighter image where the lens or mirror itself would do the job better by itself... --Jayron32 04:11, 8 February 2011 (UTC)
I think this was a physics question, not an engineering question. Ariel. (talk) 05:34, 8 February 2011 (UTC)
Also, there are ideas to image distant planets using an enormous pinhole camera. Ariel. (talk) 05:38, 8 February 2011 (UTC)
Actually, despite the article's name, I don't think that's really a pinhole camera. It's basically an artificial eclipse, which screens out the parent star so that the planet can be seen with a telescope. It looks to me like it is not a device meant to create an image somewhere based on the physical separation of rays with different angles as they pass through the pinhole. Wnt (talk) 01:01, 9 February 2011 (UTC)
The multiple pinholes would have different points of view, so their combined image via mirrors would inevitably be blurred, if there is anything in the foreground and if the pinholes are any distance apart. And a pinhole image is inherently blurry, not at all of "infinite focus." It is more of "no focus." It's just that nearby and distant objects are equally blurry, with the blur circles related to the size of the pinhole. A large pinhole lets in more light but has more blur. A very small pinhole has more diffraction. There is an optimum, as discussed in books by Ansel Adams. I have made pinhole images on photographic paper, then scanned the (negative) image, reversed it via Photoshop, and sharpened it via Photoshop, resulting in a very pleasing image. Photographic paper or film does a nice job of integrating photons over an extended exposure. Edison (talk) 04:49, 8 February 2011 (UTC)
I think there may be some miscommunication here. In the limit of a hole of width zero, StuRat is quite correct that a pinhole image has perfect focus regardless of the location of the target (but also zero brightness). And it is indeed possible to reconstruct a scene from an image formed using multiple pinholes -- there is a substantial literature on "multiple-pinhole image reconstruction". The technique is particularly useful for images formed using types of radiation for which no good lenses or mirrors exist. Looie496 (talk) 05:17, 8 February 2011 (UTC)
If the goal here is to create an image with infinite depth of field, I think a simpler solution would be to use a traditional camera and focus stacking. --Daniel 05:21, 8 February 2011 (UTC)
Edison is correct. In the limit of zero width the image becomes blurry. Dauto (talk) 05:28, 8 February 2011 (UTC)
A pinhole of width zero has perfect focus in geometric optics. In the real world, however, a pinhole lens is diffraction-limited, giving it worse resolution (but better depth of field) than an equivalent refractive lens. --Carnildo (talk) 02:51, 12 February 2011 (UTC)

Anti-Histamines + Zantac[edit]

Is there a reason why no drug company has marketed a anti-histamine such as Allegra (H1 blocker) + Zantac (H2 blocker) in one pill? I have patients with serious hives taking it and I hear it works much better than an anti-histamine alone. Would Zantac alone help also? —Preceding unsigned comment added by (talk) 08:05, 8 February 2011 (UTC)

We do not give medical advice. And, yeah, that's it. --Ouro (blah blah) 12:30, 8 February 2011 (UTC)
Perhaps drug companies think that such pills will become cheaper than the price of the two separate pills. Count Iblis 14:11, 8 February 2011 (UTC)
I think we can answer parts of this question without violating the med advice restriction.
  • The first question "Is there a reason why no drug company has marketed..." is probably simply because the combination of H1 and H2 blockers hasn't been proven to be efficacious and the FDA (presuming this is referring to the US) has not approved the use of H2 antagonists for this purpose. If a well designed randomized controlled trial demonstrated that a combination drug was superior to the single drug standard of care, it would probably be marketed quickly to replace the old stand-bys. And I doubt that it would be cheaper -- they would come up with a fancy name like Zanyryx XR (lots of x's, y's, and z's means its a really good drug), package it up in a nice box, spend gazillions on marketing to convince the general public to "ask your doctor how Zanyryx can help you" and quadruple the price of the two individual components. Who wants to take two separate pills when you can take just one!
  • With regard to the last question "Would Zantac alone help also?" we can't really say for any given patient whether ranitidine would be helpful, but for general information about this topic we can point the OP towards references ([1] and [2]) the latter of which says: "An H2-antihistamine administered concurrently with an H1-antihistamine may modestly enhance relief of itching and wheal formation in some patients with urticaria refractory to treatment with an H1-antihistamine alone. The available evidence does not justify the routine addition of H2-antihistamine treatment to H1-antihistamine treatment."
Does that help? --- Medical geneticist (talk) 14:45, 8 February 2011 (UTC)
My guess is that the biggest reason you don't see an Allegra/Zantac combo pill (at least in the US) is that Allegra was approved for treatment of allergies, and Zantac was approved for treatment of stomach issues. Although doctors are free to prescribe drugs for off-label use once they are approved, the FDA has some pretty stringent rules on marketing drugs for off-label use. Who would you "officially" sell the combo pill to? People with both allergies and acid reflux? Combo pills like Ezetimibe/simvastatin (Vytorin) and amoxicillin/clavulanic acid (Augmentin) are sold because both drugs treat the same condition. A pill for treatment of two different conditions doesn't have as large a market (and you can't sell it to treat a single condition, because the drugs aren't approved to treat a single condition). Even if the combo does better than one drug alone, the FDA (or insert-country-specific-regulatory-agency) wouldn't approve it until you did a clinical trial to show that it did. That's a massive expenditure of cash for drugs which are off patent, even if prior approval means you can skip most of the safety stages. -- (talk) 16:22, 8 February 2011 (UTC)
Thanks for the answers. I don't really see how this is medical advice and it kind of irritates me how a lot of times when people ask questions that aren't really medical advice, its considered that. I work in a pharmacy and have seen the combination recommended more than once. I know it wouldn't be cheaper, but drug companies are always looking to make more money. For example, they combined Imitrex which is now available in generic with aleve to make a new migraine drug just to make a new brand name drug. Aleve isn't used to treat migraines, if anything, it can treat minor headaches at the most. —Preceding unsigned comment added by (talk) 05:57, 9 February 2011 (UTC)
What you are seeing is called "off-label use" as implied by user, when doctors prescribe a drug that is FDA approved for one use but is found by the medical community to be useful for something else. This practice is part of the discretion that a physician has in treating patients, but it is a little risky to prescribe a drug for something that has not been rigorously proven beneficial. p.s. the reason your question got flagged as possible med advice is that you mentioned a very specific patient scenario, about which we cannot give information --- Medical geneticist (talk) 12:09, 9 February 2011 (UTC)

What causes you to want to stretch in the morning?[edit]

What causes you to want to stretch in the morning? It seems as though it is almost an involuntary action, or at least that you would be very silly to resist the urge when it comes. I am looking for a reason on some molecular or cellular level if possible.

I asked some friends about this and we came to the educated guess that it had something to do with your muscles/other tissues wanting more oxygen, so they output some chemical that sends a signal to your brain to stretch, making more blood flow to your muscles....

Is this even remotely accurate? what are the processes involved and why does your body force you to stretch? 14:29, 8 February 2011 (UTC) —Preceding unsigned comment added by (talk)

I can't comment at the molecular level, but think the reason for it is to prevent muscle injuries. Just like you should stretch before running, you should also do that before using muscles for the first time each day. One thought is that it may be simply to increase the temperature, as muscles, tendons, etc., become more flexible and less likely to tear at higher temps. Locations far from the body core, like say the Achilles tendon, are perhaps most likely to be cold in the morning (especially if your feet stick out from under the blankets), and thus in most need of a few warm-up exercises. StuRat 16:58, 8 February 2011 (UTC)
As discussed in Stretching#Research and controversy, the research is unclear about whether a few minutes of static stretching (the typical kind) before activities like running actually does prevent any injuries, and pre-event stretching may even have a negative impact on performance. Stretching matters more in sports where you need a very large range of motion, but running isn't one of those. Others suggest that dynamic stretching may have more of a benefit, but there isn't much research on that either way. It is however good to stretch or participate in other cool-down activities after exercise (including running), because it helps the muscles relax gradually and that is clearly found to help prevent injury. What any of this means for the early morning stretch, I don't really know. Dragons flight (talk) 21:00, 8 February 2011 (UTC)
There is a stretching "controversy", lol. I don't know why but I find that really funny.. Forgive me I haven't had my coffee yet. Vespine (talk) 21:37, 8 February 2011 (UTC)
It's a combination of two things, first the fact that joints and muscles tend to stiffen when they are not in use due to the formation of adhesions between muscle fibers, second the properties of circadian rhythms. During the nighttime hours, body temperature drops and a variety of injury-repair mechanisms are activated -- both of these tend to promote formation of muscle and joint adhesions that are broken by stretching. Looie496 (talk) 22:54, 8 February 2011 (UTC)
Is it the same thing that causes cats and dogs to stretch and yawn after waking up from a nap? -- (talk) 19:06, 10 February 2011 (UTC)
Sure. The need to stretch is probably common to all mammals, and perhaps all animals. StuRat (talk) 07:21, 12 February 2011 (UTC)

A rifle with a barrel made of heat resistant ceramic[edit]

Is it possible to make something like this? ScienceApe (talk) 15:01, 8 February 2011 (UTC)

Yes. It is possible. However, it is not as good as a regular barrel. Instead, it is common to have a regular barrel with a ceramic lining or coating. -- kainaw 15:04, 8 February 2011 (UTC)
Ceramics are generally too brittle to absorb shock loads without damage. The elasticity of the types of steel used for rifle barrels is what allows them to contain the shock (abrupt change in pressure) of firing. I would like to see some evidence of User:Kainaw's claim that ceramic coatings or linings are common. I've seen and handled many different rifles in my life and I have yet to lay eyes on one with such a lining or coating. The overwhelming majority of rifle barrels are just steel with various finishes ranging from blueing, Parkerizing, nitriding, case hardening to plain and simple enamel paint. Roger (talk) 16:15, 8 February 2011 (UTC)
Something I know next to nothing about but I wonder about that too from my searches. These 2 refs from 2003-2004 suggest it's an area of active research for the US army but not currently very successful [3] [4]. Things may have changed a lot since then but if not I wonder how common it can be if even the army isn't doing it. It seems some companies to offer to coat existing guns, e.g. [5] [6] but this doesn't sound like something which would be common. Incidentally from some of those refs I think chrome line barrels may be somewhat common. Nil Einne (talk) 16:23, 8 February 2011 (UTC)
(ECx3)Ceramics can be resistant to high temperature, and can have great compression strength. Do ceramics have the tensile strength to prevent the barrel splitting open from the outward directed pressure, without having a ridiculous wall thickness making the weapon non-portable? Aren't they generally brittle? Edison (talk) 16:25, 8 February 2011 (UTC)
As a general rule, ceramics are not good at tensile strength. Some composite materials like carbon fiber might be able to give greater tensile strength then ceramics, but they might still be brittle enough to shatter in that application.

Hot body in vacuum[edit]

Suppose a solid sphere of metal of 1 sq.m (choose a convenient substance) of 100 deg.C perfectly isolated by any incoming energy in perfect vacuum. How much time it will take to get to the lowest temperature it can reach? --M121121121 (talk) 20:53, 8 February 2011 (UTC)

This sounds suspiciously like a homework question. No one here at Wikipedia is going to answer the question for you, but if you want some background on the concepts you need to solve it, see black body and thermal radiation. --Jayron32 21:03, 8 February 2011 (UTC)
Forever. Assuming it were perfectly isolated (which is impossible, but we can assume it anyway), it would radiate energy away in ever decreasing amounts as it's temperature decays towards but never actually reaches 0 K. For details, see Stefan-Boltzmann equation. Dragons flight (talk) 21:06, 8 February 2011 (UTC)

It's not homework, but you're right. Who/where should I ask for this calculus? Please advice. --M121121121 (talk) 21:24, 8 February 2011 (UTC)

The appropriate equation to apply is the Stefan–Boltzmann law, which defines the rate of heat loss from a body. It's worth noting that if the object is in the "empty vacuum of space", the relevant "cold sink" is the cosmic microwave background, at around 3 kelvins. Nimur (talk) 21:30, 8 February 2011 (UTC)
You said it is "perfectly isolated by any incoming energy":
A) Assuming "by" means "from", that would mean it would also be perfectly isolated as far as radiating out energy. If there was such a perfect thermos, it would stay the initial temperature forever.
B) If, however, we assume that it's the only source of energy in the universe, then it would radiate energy but not receive any back. In that case the temperature would decrease at a decreasing rate, but would still never quite reach absolute zero.
C) If we assume it's in the real universe, but far from any source of energy, as in a galactic void, then the temperature would again decline at a decreasing rate, gradually approaching the average temperature in that void. StuRat (talk) 22:50, 8 February 2011 (UTC)
Far out, when you were at school did you try to lecture your teacher about how there's no such thing as a perfectly frictionless surface? Don't take it personally but I completely don't see the problem with the way the question was asked. For the majority of hypothetical physics questions I've ever seen you are expected to leave the assumptions at the door. If it doesn't mention air resistance, ignore it, if it doesn't mention MBR: ignore it. If it says "perfect vacuum" don't think it actually means "real vacuum of space'… Given this premise, what is the result? Full stop. As far as I can tell, Dragon flight and StuRat answer B give the answer forever, which I think is correct, but if you had the "method" which I admit I don't, you could at least come up with some more meaningful replies, like maybe how long would it take to get to 50%, 1% and 0.1% of the absolute temperature. . Vespine (talk)
I have no problem with questions which have assumptions that don't exist in the real world, but we do need to be very specific about what those assumptions are, as they can change the answer dramatically. StuRat (talk) 06:18, 10 February 2011 (UTC)

Reformulating the initial question: how much time needs an isolated object to loose all (as much as possible) its energy only by radiation? A naked human in outer space will freeze? (leave the zero pressure problem at this time)M121121121 (talk) 07:39, 9 February 2011 (UTC)

The colder it gets the slower it radiates (temperature to the power 4), so there is no answer to your first question. To your second question, if the human is in sunlight they won't freeze (but will get a horrible sunburn). If in the shade they will freeze eventually, see Stefan–Boltzmann law for the numbers. Ariel. (talk) 08:41, 9 February 2011 (UTC)
Assuming that the sphere is hollow, painted black (special black to be a black body), and has a high conductivity, then the temperature will fall very quickly to a few (tens of) degrees Kelvin (because rate of fall in temperature is roughly proportional to the fourth power of absolute temperature if background microwave absorption is ignored). (The human body would lose heat much more slowly because of low conductivity.) I'm struggling with the constants to be able to find the solution to the differential equation. Perhaps someone more knowledgeable could make an estimate for a typical sphere. Dbfirs 08:44, 9 February 2011 (UTC)

Homemade cavendish experiment .[edit]

I do enjoy this facinating webpage. I like seeing the videos of the "mass attracting mass" but I am still a little skeptical.

It still seems a little strange to me to actually see gravity interacting with such homemade apparatus. Are the masses too small? Is there some kind of experimental error going on? Perhaps an electric force is causing this?

What do you think? —Preceding unsigned comment added by (talk) 21:09, 8 February 2011 (UTC)

Well, the Cavendish experiment is well known; and you can, using simple Newtonian physics equations, estimate what the force should be and decide if the magnitude of errors introduced by, say, turbulent air currents or electric forces are relevant. You can also eliminate (or at least, reduce) electrostatic effects by grounding all involved objects with electrically conductive wire. I have to say, the experiment seems pretty fantastic! But, as a firm believer in Gravity, I am at a loss to come up with a more plausible reason why the balance would torque in this way. (Though I admit, gravity is a bit implausible, but I observe it daily nonetheless). Nimur (talk) 21:39, 8 February 2011 (UTC)
Do objects tend to drift like this on say the ISS? Say they left a bowling ball hovering, would it accelerate towards the center of gravity on the space station? —Preceding unsigned comment added by (talk) 21:59, 8 February 2011 (UTC)
Assume a spherical hollow metal spaceship in orbit and a bowling ball released at a random spot inside, with no air currents. If I remember my physics course correctly, unless the spaceship accelerates, there is no reason for the bowling ball to move from its random release point, since the gravitation attraction of the spacecraft for its contents is effectively zero. The attraction from one part of the craft is cancelled by the attraction of the rest of the craft.
Center of Gravity? An object floating free in a orbiting vessel would be affected by the sum of the masses around it, relative speed and the air currents of the air conditioning system. Also, it may be deflected on route, by any skittles it meets on the way. The article on Micro-g environment may be of interest too.--Aspro (talk) 22:15, 8 February 2011 (UTC)
(ec) The ISS, and other manned spacecraft, are in "microgravity" - which is to say, not quite freefall. There's a small but measurable net force on the spacecraft at almost all times, caused by the acceleration due to non-ideal effects like gas drag and orbit correction maneuvering (stationkeeping). Stanford's Gravity Probe B might be interesting, though - an entire spacecraft was launched just to measure the gravitational nonlinearity under ideal conditions. Preliminary results were announced a couple of years ago (see this press release from April 2007's APS Plenary; unfortunately, the mission wasn't well-received when the data turned out to be noisier than expected. Nimur (talk) 22:18, 8 February 2011 (UTC)
Speaking of spacecraft that are solely to measure gravity, check out the Gravity Recovery and Climate Experiment. Here, two spacecraft make fine measurements of the Earth's (slightly non-uniform) gravitational field. It's pretty amazing being able to watch the mass of the amazon change depending on which season it is. Buddy431 (talk) 02:33, 9 February 2011 (UTC)
The experimenter apparently did nothing to rule out electrostatic attraction as an explanation for the effects. The plastic foam arm is an excellent insulator, as is the monofilament line, and it would be amazing if there were no electric charge on the arm or the weights. A metal support wire, a wooden arm, and a wooden frame holding the other weights and all connected together like the Cavendish apparatus would be an improvement, since wood is a poor insulator in static electric terms. I have seen demos of charging a piece of PVC pipe by friction from a piece of fur, then using it to make a can of pop roll rapidly toward it, a stronger force by orders of magnitude than the gravitational attraction of the small weights. Edison (talk) 00:04, 10 February 2011 (UTC)

The straw that stirs the drink[edit]

Whenever I pour a carbonated beverage into a glass and stick a straw in it, CO2 bubbles invariably attach to the straw, then lift it to the point where it seems like the straw should fall out of the glass. However, I have never had a straw actually fall out. What provides the force keeping the straw in place? Is there a length beyond which the straw will tumble? Hemoroid Agastordoff (talk) 22:03, 8 February 2011 (UTC)

I have often had a straw fall out. Perhaps I fill my glass fuller? (talk) 22:17, 8 February 2011 (UTC)
Surface tension will sometimes prevent the straw from falling out, even when the centre of mass is outside the rim of the glass, but it will often be insufficient to prevent a long straw from falling out of a full glass. Dbfirs 08:12, 9 February 2011 (UTC)
The straw acts as a condensation nucleus for the pressurized CO2. ~AH1(TCU) 22:47, 11 February 2011 (UTC)


why are clouds white? (talk) 22:11, 8 February 2011 (UTC)

Have you discovered our search box? It just so happens, we have a article section on the colour of clouds.--Aspro (talk) 22:23, 8 February 2011 (UTC)
White is simply the reflection of the entire visible spectrum. Cloud iridescence, irisation, corona, sundogs, infralateral arc, Mother of pearl clouds, auroras and atmospheric disturbances during a tornado outbreak (usually green), and translucent clouds or barely-visible clouds under high humidity (blue), haze and other factors can all alter the colour. ~AH1(TCU) 22:46, 11 February 2011 (UTC)

Sanitary drain(industrial sewer) sizing and design discharge flow rate estimate[edit]

how do I estimate discharge flow rate (L/s) based on the number of fixture units?-- (talk) 22:21, 8 February 2011 (UTC)

Kilos instead of larger units[edit]

Why planet and star masses are commonly indicated in kilograms instead of more handy larger units, such as gigatonnes or teratonnes (where no exponentiation would be necessary)? —Preceding unsigned comment added by (talk) 22:28, 8 February 2011 (UTC)

Actually, most astrophysicists use cgs units - that is, grams, to measure the mass of planets. Why? Because they're dealing with many orders of magnitude during different calculations, so they must use scientific notation anyway. In other words, exponentiation will be required, no matter what, so we might as well use it consistently. (Though, Griffiths and others attribute the cgs preference to electrodynamics, where the gauss and the convention of unitary permittivity- and permeability- of free space, require "less writing." Other physicists, cosmologists in particular, prefer dimensionless physical constants, so they prefer the ("horribly inconvenient") SI units normalized by the values fundamental constants, called "planck units." As physicists, when we study planets and space science, we try to isolate any "biases" we might have in our system of units that are historical artifacts of measuring the size of the Earth. SI and cgs is not entirely guilt-free in that respect, as the meter is historically defined as a ratio to the earth's circumference. But in any case, if you're going to measure a planet's mass, it's still going to be "huge", whether you measure it in grams, tons, or solar mass units; and if you measure two planets, chances are you'll need scientific notation in any unit system. Nimur (talk) 22:45, 8 February 2011 (UTC)
Careful there Nimur. If one uses solar masses than the mass of a planet will not be a huge number and in fact that is the most common choice among astrophysicists (That is the choice of most of my books). Also, the Planck units are not horribly inconvenient. If they were, nobody would use them. Finally, the Plank system of units is not based on the SI as you stated. Dauto (talk) 02:47, 9 February 2011 (UTC)
I think you misread Nimur's phrasing. To be fair to you, it was not as hard to misread as it could have been. The "horribly inconvenient" refers, I think, to SI rather than to Planck units, and I don't see anything that suggests Nimur claimed the latter were based on the former. --Trovatore (talk) 03:18, 9 February 2011 (UTC)
"Horribly inconvenient" was meant to be tongue-in-cheek; obviously, any reasonable unit system has a purpose. And regarding "huge": I consider 1x10-6 solar masses to be "huge", even if the number is represented as a minuscule fraction; my point was to illustrate that representational units don't actually change the size of the object. Nimur (talk) 07:56, 9 February 2011 (UTC)

Help understanding Parsec illustration[edit]

Can someone chime in at Talk:Parsec#Dots in image? I didn't understand the image used in the article and would appreciate some help in that regard. Thanks, Waldir talk 22:54, 8 February 2011 (UTC)

I think has been resolved. --Mr.98 (talk) 13:50, 9 February 2011 (UTC)

Trampolining gives you muscles?[edit]

An acquantance of mine has an amazing body. He has big legs, a six pack, good arms, and generally good upper body and back. When I asked him how many times a week he worked out he replied that hedidn't work out at all. He said he uses his mini trampoline every day. Can this be true? Google shows many health benefits of trampolining but it doesnt go into detail about muscle growth. I can understand how it might get you big legs but a six pack!?! Surely that would be reason enough for every guy anywhere to get one? Surely such a thing would widely known and not such a well kept secret? And asked him another day whether he really meant a mini trampoline and he replied affirmatively. I mean you cant ever do sommersaults on those! So how do you explain the good arms and upper body? Edit: oh and by 'big' I may be exaggerating slightly. He doesnt loook like a body builder but he does have a very impressive slim athletic physique. —Preceding unsigned comment added by (talk) 23:32, 8 February 2011 (UTC)

What he didn't tell you is about all the steroids he takes. Looie496 (talk) 01:32, 9 February 2011 (UTC)
I think as much as a lot of people argue to the contrary, not everyone is created equal. Genetics plays a not insignificant part in how your body will look as well as a countless number of other factors which might not even be considered "exercise". Things like diet and eating habits, sleep habits, lifestyle in general, things like how much you walk and even seemingly inconsequential things like do you "fidget", all these play a part in your physique. One very interesting comparison you can easily make is look at the competitors of fighting sports like UFC, they are all without a doubt extremely fit individuals who train very hard but they still have widely varying body types. No doubt some of the extremes are due to drugs like the above suggests, but I believe even if you excluded that, you would still see a big difference between body shapes, like shoulder width, muscle definition even amongst people who have similar exercise routines.. There was a time before my brother and I had ever gone to the gym but he's always been much bigger then me, we grew up eating the same foods and doing similar activities, even though he was only 18 months older then me, in our teens I weiged between 60 and 70 and he weighed between 80 and 90 and wasn't slim but not exactly what you'd call "fat". Vespine (talk) 02:49, 9 February 2011 (UTC)