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October 1

Sneezing when you look at the sun?

What is the mechanism that causes you to sneeze when you look at the sun? —Preceding unsigned comment added by 69.120.9.204 (talk) 02:17, 1 October 2008 (UTC)[reply]

See Photic sneeze reflex. --Tango (talk) 02:21, 1 October 2008 (UTC)[reply]

"Autosomal dominant Compelling Helio-Ophthalmic Outburst syndrome" is possibly the most absurd backronym I have ever encountered. Plasticup ^T/C 14:18, 1 October 2008 (UTC)[reply]

We seem to have been a bit more comprehensive (chatty?) on this subject a while back ;) hydnjo talk 00:34, 2 October 2008 (UTC)[reply]

Anti-Depressants and delayed orgasm

From a scientific/medical standpoint, what is it in the anti-depressants that causes delayed ejaculation? This effect is so strong that I have heard anti-depressants being used to treat premature ejaculation. Thank you. —Preceding unsigned comment added by 68.7.126.152 (talk) 02:33, 1 October 2008 (UTC)[reply]

Nobody knows for sure, but it's believed that SSRI's help PE due to increased levels of serotonin. Research into why is ongoing. Fribbler (talk) 11:45, 1 October 2008 (UTC)[reply]

I don't know either but I do know my wife is happy! —Preceding unsigned comment added by 69.77.185.91 (talk) 18:04, 3 October 2008 (UTC)[reply]

need a reaction

Hi, I need a chemical reaction which can produce opaque compounds from transparent ones by the application of electricity, and is also reversible in nature. That way it might be possible to control light passing through a chemical, I suppose. I am studying electrical engg. and some insight on the concepts of chemistry to be used here would very useful. Cheap chemicals would be nice.117.201.114.27 (talk) 06:43, 1 October 2008 (UTC)[reply]

Our article on smart glass touches on a number of approaches to this problem. TenOfAllTrades(talk) 07:00, 1 October 2008 (UTC)[reply]

Applying electricity isn't exactly a chemical change is it? Changing things from opaque to transparent and back is how LCDs work. --antilived^{T | C | G} 09:48, 1 October 2008 (UTC)[reply]

But in LCDs the change is disdrete, its completely opaque, or trans. I wonder why it can't be made partially transparent ?? 117.201.112.159 (talk) 05:52, 2 October 2008 (UTC)[reply]

Your problem there is that all the molecules are the same, so they will all undergo the same change. Maybe you could use a mixture of compounds (with different dipole moments?) that would give a stepwise change? Otherwise you would need a compound where the voltage (or frequency) would cause a uniform partial change - alignment and partial rotation of a dipolar molecule, or partial twisted nematic effect. What would happen if you used a partial voltage on a TN display? That would be easy enough to test - borrow your friend's laptop and sink the voltage going to the non-circuit screen power supply. Franamax (talk) 08:09, 2 October 2008 (UTC)[reply]

There are several kinds of LCD mechanism - some of them can do gradual change (the ones in my laptop display, for example, can show at least a couple of hundred gradations of transparency). But even with an on-off effect, you could still achieve what you want with a pulsed voltage. If the material only goes utterly opaque or utterly transparent then you could pulse the voltage on and off a couple of hundred times a second and have a window that APPEARED to be 50% transparent - alter the pulse/space ratio and you can choose any degree of transparency you like. You'd have to do it at least 100 times a second to avoid annoying flicker effects - so there might be a problem with materials that responded to the voltage only very slowly. So if that doesn't work, you could (like an LCD panel) structure the material as a bunch of very small separate cells ("pixels") and turn 50% of them on in a checkerboard pattern when you want 50% transparency - so long as the pixels are small enough - it'll look OK. If that's too difficult to arrange for some reason - then you could arrange for a bunch of thin layers of material to be laminated together - each of which would be thin enough to be less than 100% opaque when turned on - but by turning on several of them, all of them or none of them, have 50% transparency, 0.001% transparency or 100% transparency respectively. There are plenty of ways to do this with an on/off material. SteveBaker (talk) 11:03, 2 October 2008 (UTC)[reply]

We have a smart glass article. DMacks (talk) 17:03, 5 October 2008 (UTC)[reply]

control systems

Hi, I am learning control systems and have a trivial question in my mind. Is it not possible to create a control system, which can measure performance its own system, and calibrate its parameters (maybe more than one)on its own, so as to reach a desired goal. That way the system would quite easily adapt to changing conditions automatically with no external interference. Obviously, stability should be dealt with, through some algorithms..117.201.114.124 (talk) 07:40, 1 October 2008 (UTC)[reply]

What you are describing sounds like an adaptive system - read the article for further details and links. Gandalf61 (talk) 10:09, 1 October 2008 (UTC)[reply]

Such systems are not only possible - but used in practice in some very common situations. My car (a MINI Cooper) has an adaptive engine management computer. It "learns" by optimizing the engine parameters and is said to adjust to your driving style, the long-term prevailing weather conditions and the kind of gasoline available in the country you live in. It is noticable that when you get a new or used MINI, it takes a couple of tankfuls of gas for the fuel economy to really get good - and this is the time it takes for the adaptive controller to really settle in on the optimum parameters for the conditions. SteveBaker (talk) 12:18, 1 October 2008 (UTC)[reply]

That's interesting, but wouldn't its brains get scrambled by having two different drivers? OTOH, that's a great reason to not let the wife drive the Mini. :) Franamax (talk) 19:10, 1 October 2008 (UTC)[reply]

The MINI stores per-driver information in the "key" (which is actually a round plastic thing which talks to the car via a radio link while it's sitting in your pocket!)...of course if you swap keys - then all bets are off. The main reason not to let my wife drive my MINI is my rather clear memory of the cost of replacing the clutch after the last time she drove it. It also stores things like which key was in the car when some fault code occurs - which is apparently used by car rental companies and companies that use them as fleet cars. The key is also logged in the "black box" crash recorder thingy. SteveBaker (talk) 00:26, 2 October 2008 (UTC)[reply]

Now that's even more intriguing. If your wife did it right, she could activate her key just before yours when you tried to start the car. Then the stored settings would be going to her chip. If she had more time with the car (perhaps by taking it from your parking lot while you're working), she could train it to be unresponsive to your jabs at the accelerator pedal and aggressive steering inputs. And even if she never drives it, if she has a key, there's probably a way to null the heuristics - so she can probably always prevent you from being sporty. I'm not sayin' she's doin' it - I'm just sayin' :) Franamax (talk) 09:47, 2 October 2008 (UTC)[reply]

You misunderstand: The 'learned' settings don't stop you from doing anything - they just alter the fuel-efficiency with which the engine can do it. So (to pick an example that may or may not be true) if you habitually start the car and soon after demand full power then perhaps the idle RPM will be set a little higher so the engine will warm up sooner (using more gas in the process) and the acceleration phase will happen in a warmer engine - and thereby use less gas. If you habitually start the engine and drive slowly for 10 minutes before accelerating hard then the idle can be set lower because typically the engine will warm up enough during the slow driving. In the latter case, you can still turn the car on and immediately go fast - but the heavy acceleration with a cold engine is not so good for wear-and-tear and will consume more gas. SteveBaker (talk) 10:47, 2 October 2008 (UTC)[reply]

Permission to Use A Picture

Hello, I am a student in the Anatomy and Physiology Course in the Virtual High School (www.govhs.org) I have been assigned to choose a physiologist and learn more about him/her. I was wondering if I could use the picture of Claude Bernard and post it in my assignment. Acces to the assignment is limited to 24 people. I will cite the source of the picture. Thank you for your time. —Preceding unsigned comment added by 72.25.1.135 (talk) 12:00, 1 October 2008 (UTC)[reply]

The image of Claude Bernard at the head of the article is out of copyright and therefore free to use. If you click on the image and then read below the file you will see confirmation of this. 86.4.187.55 (talk) 12:04, 1 October 2008 (UTC)[reply]

Be aware that the subject of the photo is likely to retain personality rights. Wily D 12:15, 1 October 2008 (UTC)[reply]

Uh, no. Not for someone who died in 1878. And certainly not for a high school assignment. (Personality rights come into play if I were, say, trying to sell mugs with the person's picture on them. And even then it would not be an issue for someone who died over a hundred years ago. Much less a French hero.) --98.217.8.46 (talk) 13:02, 1 October 2008 (UTC)[reply]

List of Cathepsins

Where can I get information on all known cathepsins and their structures. I am particularly interested in Fasciola Herpatica cathepsins. Donek (talk) 12:26, 1 October 2008 (UTC)[reply]

I can't help much, but you'll find more in search engines if you use the correct spelling: Fasciola hepatica, not herpatica. - Nunh-huh 14:57, 1 October 2008 (UTC)[reply]

You're right, you can't help much! Can anyone else? Donek (talk) 16:11, 1 October 2008 (UTC)[reply]

Sounds like a job for PubMed. Maybe start at the MeSH for cathepsin. But Nunh-huh is actually right here...why would you respond sarcastically to someone who told you an important reason you may have had trouble searching for this info (you did try to search before asking for help, right)? DMacks (talk) 16:58, 1 October 2008 (UTC)[reply]

I did try, with the correct spelling as well. Thank you for your help. Donek (talk) 17:02, 1 October 2008 (UTC)[reply]

An article on the two main Fasciola hepatica excretion/secretion products, CL1 & CL2 (potential targets of a fascioliasis vaccine), is at [1] - Nunh-huh 17:10, 1 October 2008 (UTC)[reply]

Thank you for your help. Donek (talk) 17:11, 1 October 2008 (UTC)[reply]

geophysical and geochemical surveys

what are the basic techniques involved in geophysical and geochemical surveying? Its use in the petroleum sector.

Our article on exploration geophysics has some information that may be of interest. Franamax (talk) 19:07, 1 October 2008 (UTC)[reply]

Detergents, chlorine bleach

Hi, i bought some bleach which has detergent in it, but i wanted to add some normal washing powder as well because the water didnt look soapy enough, but i noticed on the washing powder box it says "Do not add chlorine bleach", is this because it'll denature the enzymes in the normal washing powder? —Preceding unsigned comment added by 58.174.201.126 (talk) 13:38, 1 October 2008 (UTC)[reply]

What brand is it? It may be a oxygen bleach, not chlorine; mixing the two may not ge a good thing. --—— Gadget850 (Ed) ^talk - 15:33, 1 October 2008 (UTC)[reply]

Yeah, depending on the ingredients there are a few reasons not to add chlorine bleach to things - damaging the enzymes is certainly one possibility, but it's more likely to be a safety thing - if you look at the Safety section of our article on Sodium hypochlorite there are various unpleasant chemicals produced if you mix it with acids and/or hydrogen peroxide, both of which may be found in other bleaching/cleaning products. ~ mazca ^{t | c} 18:00, 1 October 2008 (UTC)[reply]

Additionally, ammonia and sodium hypochlorite makes a particularly unpleasant combination. Its not unusual for bathroom cleaners, containing ammonia, to mix with those little bleach-containing toilet biscuits, and cause problems... Chlorine bleach is one of the more dangerous chemicals in your house... --Jayron32.talk.contribs 01:36, 2 October 2008 (UTC)[reply]

The amount of bubbles does not relate to a detergent's or soaps cleaning power... in fact, when your deal with a mix with chlorine they likely are using one of the low-suds detergents. Please, for your own safety follow the instructions on the packaging. ---J.S (T/C/WRE) 07:32, 2 October 2008 (UTC)[reply]

Hyperkalemia

What are causes and consequences of elevated (panic high)potassium levels in the bloodstream? —Preceding unsigned comment added by 98.228.1.6 (talk) 14:51, 1 October 2008 (UTC)[reply]

We have an article on hyperkalemia. Please let us know if it leaves your questions unanswered. - Nunh-huh 14:53, 1 October 2008 (UTC)[reply]

current density

is current density microscopic or macroscopic? —Preceding unsigned comment added by 117.197.161.250 (talk) 15:23, 1 October 2008 (UTC)[reply]

Sounds like this might be a homework question. See Current density, Electron, and Submicroscopic. --Allen (talk) 16:35, 1 October 2008 (UTC)[reply]

Current density can be characterized at a microscopic or even submicroscopic level. Edison (talk) 04:51, 2 October 2008 (UTC)[reply]

Atmospheric Pressure

I understand that atmospheric pressure near earth's equator exhibits significant diurnal variation due to atmospheric tides, and that this diurnal effect is almost non-existent in more polar regions, but why does atmospheric pressure show so little day to day variation at the equator than in polar regions? This observation was based on a comparison of atmospheric pressure data from Malaysia vs. Alberta, Canada.--216.99.65.64 (talk) 15:30, 1 October 2008 (UTC)[reply]

Equatorial climate is relatively more stable (i.e. boring), being in the Intertropical Convergence Zone. The weather in Alberta is much more dynamic, with high- and low-pressure cells moving about constantly, characteristic of continental climate. On any given week in Alberta, several cells could move through, so you would see more variation in atmospheric pressure. Franamax (talk) 19:03, 1 October 2008 (UTC)[reply]

So, what is this thing I had when I was a baby called?

First off, this is a question about medicine and about me, but I'm not seeking medical advice or anything :) I feel just fine.

You know how infants don't have a complete skull, but it's divided up into "bits"? (I'm sure there's a medical term for the "bits", but I don't know what it is). Well, I had this thing when I was a baby that the bits were fusing together WAY too fast. So the doctor had to go in and, well, basically saw my skull open to make room for my brain. This left me with a neat scar over my skull and an abnormally large and elongated head (I don't look like a freak, people don't notice it at all, but I've never had the pleasure of wearing a hat or a helmet that fit me well, if at all). I know this syndrome (or whatever) has a name, but I can't think of what it is. So that's my question: what is it called? 90.235.17.83 (talk) 16:29, 1 October 2008 (UTC)[reply]

Craniosynostosis (try saying that after a few pints!) if I am not mistaken. Fribbler (talk) 16:33, 1 October 2008 (UTC)[reply]

Yes, that's it! That kid in the picture is like me at four months old (except I was much handsomer)! Thank you very much! No wonder I couldn't remember the name, that's an imposing medical term. 90.235.17.83 (talk) 16:45, 1 October 2008 (UTC)[reply]

Hmm, I had a teacher at school with an arrestingly bulbous head, it was shaped remarkably like that baby's. Maybe this condition had something to do with it for him too. ~ mazca ^{t | c} 17:56, 1 October 2008 (UTC)[reply]

I was reading about craniosynostosis in a textbook the other day, fascinating condition. —Cyclonenim (talk · contribs · email) 20:19, 1 October 2008 (UTC)[reply]

Scarlet fever - After Effects?

What if you had Scarlet fever in your childhood but it was not treating properly, could there be any after effects from it in adulthood? --209.0.0.29 (talk) 18:06, 1 October 2008 (UTC)[reply]

Fevers in early childhood can cause developmental complications, most often mental retardation. -- MacAddct1984 ^{(talk  contribs)} 19:27, 1 October 2008 (UTC)[reply]

Rheumatic fever describes the problems that can occur. Our scarlet fever article includes a list of characters in literature who suffered complications. Fear of this disease (mainly, I think, the heart complications) led to long quarantines of patients and sometimes the destruction of the belongings (Velveteen Rabbit). Rmhermen (talk) 20:50, 1 October 2008 (UTC)[reply]

My recollection is that the long-term concerns have to do with joint disease and endocarditis (infection of the heart muscle and valves). In particular, untreated endocarditis can lead to damage/destruction of the heart valves, subsequently causing regurgitation of blood through the incompetent valve, and chronic heart failure. Try this ([2]) for a relatively recent review of the subject. Medical geneticist (talk) 22:03, 1 October 2008 (UTC)[reply]

Please be aware that we cannot provide any medical advice at Reference Desk. But heart valves can be damaged by untreated scarlet fever which progresses to rheumatic fever, per the articles linked Edison (talk) 04:49, 2 October 2008 (UTC)[reply]

Young's Modulus

Why is the Young's Modulus and other moduli of elasticity known as a modulus? --80.229.152.246 (talk) 18:57, 1 October 2008 (UTC)[reply]

The New Shorter Oxford English Dictionary (13th Ed) says a "modulus" (from the diminutive of the Latin word modus meaning measure) in this usage, is a number which combines other numbers (such as stress and strain, at the linear portion of a curve), to characterize the properties of a substance. It is a modulus because it compares a numerical cause to its numerical effect. They had to call it some specific coined term, so that others would know exactly what well defined measurement led to the number. Edison (talk) 20:24, 1 October 2008 (UTC)[reply]

Emedicine.com

What is the incentive for the authors of Emedicine.com? Is it that they're paid? If they're paid, how does Emedicine make profits? I haven't seen too many advertisements on their web site. Thanks in advance. —KetanPanchal^taLK 19:22, 1 October 2008 (UTC)[reply]

Did you see InfoCenters - Information from Industry? My guess is that "Industry" pays them. Lova Falk (talk) 19:53, 1 October 2008 (UTC)[reply]

What is the incentive for any author of any medical publication? Yes, money can be a factor but what's wrong with enjoying research and teaching? —Cyclonenim (talk · contribs · email) 20:18, 1 October 2008 (UTC)[reply]

Sorry for the delayed response. Likewise, thanks for your replies. Well, Cyclonenim, you seem to have gotten me wrong here. I was plain curious as the work involved is of quite high quality. And, of course, there's nothing wrong with doing some generous, voluntary work, but the thing with official publications is that they are widely recognized, and improve ones' reputation in ones' chosen field. Although, Emedicine articles are widely accessed, I don't think they add much to a professional's CV. I wouldn't find it wrong, even if the authors are paid for the work--there's nothing wrong in getting paid for writing a good, informative article (IMHO). Take care. —KetanPanchal^taLK 19:49, 6 October 2008 (UTC)[reply]

A humanoid changing facing in space

If a person or humanoid machine (mecha) were floating in space, can it change its facing quickly and easily without using thrusters? In other words, just by moving its arms, legs, twisting, shifting mass, etc can it change facing? 98.221.85.188 (talk) 21:01, 1 October 2008 (UTC)[reply]

Easily. Just move your arm real fast counter clockwise in circles. You will begin spinning about the line of axial rotation. You will spin this way forever. When you move your arm back to the initial start point, with the same quick motion, you will instantly stop. Sentriclecub (talk) 21:08, 1 October 2008 (UTC)[reply]

See reaction wheel. It's how the Hubble Space Telescope points at things without getting "exaust" on the mirror. Saintrain (talk) 21:30, 1 October 2008 (UTC)[reply]

It isn't possible to make yourself start spinning continuously from rest because angular momentum is conserved. You can change your orientation this way (since orientation isn't conserved) but I think the details are a bit different. -- BenRG (talk) 22:05, 1 October 2008 (UTC)[reply]

Sentriclecub's answer does not make sense to me. Surely stopping the movement of your arm would have and equal but opposite effect of moving it in the first place? Otherwise you'd be creating angular momentum out of the ether. It seems like to have any effect useful effect you would have to cartwheel your arm like you were a windmill until you were in the desired orientation. This would probably take a lot of practice to get right. APL (talk) 22:30, 1 October 2008 (UTC)[reply]

A lot of practice, but it can be done - I've seen a video clip of astronauts in space playing around by rotating themselves 90 degrees, saluting, and rotating another 90 degrees, etc., all with military precision (in time with eachother and everything). I don't remember exactly how they did it, but it involved rapidly moving their arms and legs. --Tango (talk) 22:39, 1 October 2008 (UTC)[reply]

I don't see how that's possible. (Translation: You are lying to me!) Conservation of angular momentum is a pretty fundamental thing - and those astronauts would certainly NOT be conserving it (at least not as you've described it). Something like the Hubble space telescope can do it because it has onboard gyros (big flywheels) that can be braked and speeded up - in that case, conservation of rotational momentum means that the spacecraft can turn ONLY if the heavy/fast flywheel turns in the opposite direction so that momentum is properly conserved within the entire closed system. External forces such as friction and air resistance allow us to do this down here on earth - but even so, momentum is conserved because if (for example) you are spinning around in your office chair then let friction slow you down to a stop - you are actually applying a torque to the entire planet and speeding it up a tiny bit to compensate. SteveBaker (talk) 23:05, 1 October 2008 (UTC)[reply]

::::: You only need to "hit" one atom, to generate yourself an angular velocity. Space is not a vacuum. From wikipedia there are still a few hydrogen atoms per cubic centimeter. Sentriclecub (talk) 00:08, 2 October 2008 (UTC) This is only what I wrote because I was scared (when 3 people disagree with my answer, and I only learned this stuff today, I'll question my accuracy). My original answer is accurate, but not great because it is ambiguous of how to stop your arms. Sentriclecub (talk) 03:01, 2 October 2008 (UTC)[reply]

Wait, I want to clarify Sentriclecub's tiny text here. It seems to me that Sentriclecub's original answer is not correct, and is not the consensus that's forming. Sentriclecub's original answer is wrong because of the line "You will spin this way forever." You will not spin forever, you'll "spin" only until you stop moving your arm. This is a very important difference. APL (talk) 13:16, 2 October 2008 (UTC)[reply]

Via "cat turns," movements similar to those used by gymnasts, by divers use to change orientation during a dive, or skaters to start or stop a turn (independent of what the skate blades are doing) or that a cat uses to land on its feet, it is possible for a human or a humanoid in orbit to rotate to face upside down, sideways, etc, without thrusters. The movements were described years ago in a science article, probably in Scientific American, called "Cat turns." They were pretty specific and economical and did not involve wildly waving, although that might work.To make one up based on simple physics, if, while floating "weightless" you started with hands at sides and suddenly rotated them upward while keeping them the same distance apart so they were overhead, and left them there, your body would start rotating forward slowly. When your orientation was about what you desired, bringing the arms back down through the same path would tend to cancel the rotation. Other movements should produce rotation in other planes.This was covered in Science 1899, page 933 [3] and in Science 1911 page 844 [4]. A different article discusses this at [5]. This may have been covered in New Scientist 1960 p 559 per the snippet view[6] .Edison (talk) 23:00, 1 October 2008 (UTC)[reply]

But only because they have friction and air resistance. I can do that on my office chair. If I twist my body clockwise with arms outstretched and then pull them in and straighten out (counter-clockwise) - then repeat that over and over - I'm not facing the same direction as I started - which appears to be a violation of conservation of angular momentum. However, the reason it works is that I speed up as I pull my arms in (to conserve momentum) - but because the frictional and air resistance forces are higher when you're moving fast compared to moving slowly - you can use that fact to get more frictional force in the clockwise direction than in the anticlockwise - and that gradually rotates you around. But that doesn't work out in space where there is no friction or air resistance. So divers and skaters can do it (and so can geeks in office chairs) - but it doesn't work in space. SteveBaker (talk) 23:12, 1 October 2008 (UTC)[reply]

The angular momentum of the whole body cannot change, but that of individual parts can. I think Edison's description is slightly in accurate - your body will move while you move your arms and will stop when you stop moving them (you can get them back to your sides by moving them down via the side of your body, rather than the front, the momentum from each arm will cancel out so you won't move, you can then bring your arms back up via the front if you have moved far enough). You can do the whole thing on a smaller scale with some practice, I imagine. --Tango (talk) 23:46, 1 October 2008 (UTC)[reply]

Neither friction nor air resistance are needed. And no change in angular momentum is necessary. Twists and somersaults can be done with zero angular momentum. A person floating in spase who moved a limb so as to create a moment would have to cause a compensating movement of the rest of the body. The old article went through considerable detail, and I wish I had a Scientific American index to track it down. I found an article which has some nice illustrations and explanations of assymettric arm and hip movements used to change orientation during freefall in diving here [7] and here [8]. Edison (talk) 23:24, 1 October 2008 (UTC)[reply]

:::Space IS NOT a vacuum. There are atoms which you can accelerate yourself against and have a angular velocity. Sentriclecub (talk) 23:59, 1 October 2008 (UTC) I'll re-update my answer, but this i'm 100% positive--just learned it today and wrote 12 pages of notes. http://www.youtube.com/watch?v=9A1Zb8109fg and the chapter in my book. However, if space were a perfect vacuum, then you cant change the way you face (unless you twist your body, which doesn't count as an angular reorientation which is what the OP is asking) Yeah this was wrong, I was right the first time. Sentriclecub (talk) 02:57, 2 October 2008 (UTC)[reply]

Space is close enough to a vacuum as makes no odds for this. The occasional atom of hydrogen isn't going to have any noticeable affect on a person waving their arms around. It's all just conservation of momentum - you move your arms one way, your body will move the other way. --Tango (talk) 00:13, 2 October 2008 (UTC)[reply]

That's why I wrote "you'll spin this way forever" and then you can stop. I calculated it out, its extremely small, but if the object is of very small mass, and can morph such a way to reduce its rotational inertia, then using some sample numbers for the density of a few atoms per ml and an object for 10 micrograms that can "pull its arms in" to reduce its effective rotational inertia to almost zero, then a revolution only takes seconds, not hours or days. I can't use higher digits because my calculator only displays 10. But yes for humans, it would take closer to the range of forever for a revolution. However, the effect of friction is even more negligibly small in a near vacuum. Sentriclecub (talk) 00:30, 2 October 2008 (UTC)[reply]

When you stop moving your arms, you'll stop spinning, otherwise you would be violating conservation of angular momentum. Friction isn't required. --Tango (talk) 00:35, 2 October 2008 (UTC)[reply]

For the human yes, but not my my micro-robot. A human, I can think of an apparatus, similar to a fan with stringlike rubber "paddles". You can spin them, with a hand-crank and then retract them into a tube-like reservoir and similar to a gyroscope you can "pull" yourself linearly wrt the spinning paddles. Pulling the paddles into the reservoir will cause a human to linearly move toward the apparatus. (the center of mass of the human + apparatus system won't change however). Its hard to describe succinctly, but if you think about creating a gyroscope in space, then pulling on it to create a relative linear monentum of the human, then letting go of the spinning apparatus (while it "sits" in space next to you) then you and the apparatus both doing some independent revolutions and you "grab" the apparatus once you are facing whichever way you like. Sorry to be unable to describe the thing in detail, but its real easy to picture. Just start some gyroscopic motion by "cranking it" and then release it from you with an angular velocity, and you will have an angular velocity (3rd law force pair) and voila! Sentriclecub (talk) 00:53, 2 October 2008 (UTC) The micro-robot wouldnt need this device, it could just flap its arms and morph into a nearly zero-inertial shape with just a few nano-radians per second of angular velocity.[reply]

If you 'calculated it' then you made a gigantic error someplace! There is about 1 hydrogen atom per cubic centimeter - so in all of the arm-waving and leg flapping - you maybe move a thousand atoms out of the way - at about the speed you move - let's say 1ms^-1 to be generous. There are 6.02214179(30)×10²³ hydrogen atoms per gram of hydrogen - so your thousand atoms weigh about 1/10²⁰ grams. 0.000000000000000000001 grams. Moving that much at 1 meter per second produces an external drag force that's so tiny that it wouldn't be able to accellerate one human chromosome by 1 nanometer per second...let alone your entire body at a noticable rate. So forget the pathetically tiny amounts of gas out in space - in all likelyhood your spacesuit is out-gassing a trillion times that amount - AND IT'S STILL NEGLIGABLE. For your nanorobot, you're statistically so unlikely to hit an atom at all - that it's STILL NEGLIGABLE. This has no bearing on the discussion here. If you can't understand that then you shouldn't be posting answers on the Science ref desk! SteveBaker (talk) 00:59, 2 October 2008 (UTC)[reply]

OK - so back to Tango & Edison. Would you guys please explain how come what you are claiming avoids the conservation of rotational inertia? That's a fundamental law - you can't just hand-wave it away. The manouver of (for example) raising your arms from your sides to above your head while keeping your hands together - in a 180 degree forward arc would produce the following effect (let's suppose your arms represent 10% of your total body rotational inertia):

As you start sweeping your arms upwards at (say) 10 degrees per second, your body will start to rotate in the opposite direction at 1 degree per second.
When you stop moving your arms upwards, your body stops rotating too.
When you move your arms back again - your body rotates again at the same rate but in the opposite direction.
When your arms return to their starting point, your body is back exactly where it was before.

In air - or in water, the resistance of the medium has an effect - your arms (because they are moving faster) create more drag than your body does (or maybe the body is bigger so it causes more drag than your arms) - either way - that differential of drag is enough to allow you to come up with complex sets of manouvers that produce more drag in one direction than in the other and that asymmetry in drag force allows that EXTERNAL force to appear to violate the conservation principle. But in space - no such luck (except to an entirely negligable degree that does not suffice to explain the phenomena described above). SteveBaker (talk) 00:59, 2 October 2008 (UTC)[reply]

The key thing is not to move your arms back by the same route. Start with your hands by your sides, lift them up above your head via holding them out in front of you and then move them back to your sides via holding them out to the side. --Tango (talk) 01:08, 2 October 2008 (UTC)[reply]

I didn't calculate it for a human, but for the microrobot. Sentriclecub (talk) 01:08, 2 October 2008 (UTC)[reply]

I dont know how you could have came to the conclusion that I was referring to both the human and the micro-robot. I thought I explained very well, that a human can only do it with the described apparatus. The microrobot could do it by "flapping its arms". I even wrote that it "would take forever" for the human to do a revolution. If I don't belong at the science desk, then read the answer below this one about hydrophobic properties of the GI tract and fat solubility in water. Then again maybe you can't read? I think there's clear straw man here if you thought I said a human can make a revolution in a few seconds. If you re-read what I wrote, or I can post it to your user:talk page. Done--its at your talkpage. Sentriclecub (talk) 01:15, 2 October 2008 (UTC)[reply]

It doesn't matter, we're not talking about nano-robots, we're talking about people. Using drag isn't feasible for a person, we're all agreed on that, so let's move on. --Tango (talk) 01:37, 2 October 2008 (UTC)[reply]

Yes tango, I agree, I am interested in reading the response that you and Edison raised. I read the links provided and it seems that doing a certain sequence of moves will cause rotation in one plane, even without air resistance because of the mathematical properties of Pseudovectors do not apply to normal vector addition and subtraction. I told Steve B. that I'll refrain from further posts, since I want to hear him address the points you and Edison raised here[9] [10] [11] [12] [13] [14] I'm also interested in this seeming contradiction of conservation. Sentriclecub (talk) 01:55, 2 October 2008 (UTC)[reply]

There is no contradiction - at all times the net angular momentum is zero, and that's all the matters (the individual parts of your body aren't a closed system, so there are no conservation laws for them individually). --Tango (talk) 02:16, 2 October 2008 (UTC)[reply]

There is an easy way to explain this. Suppose you want to face 'downward' from the direction you are currently facing. Assume you start with your hands at your sides and with zero rotation. You lift them up in front of you, then over your head, then wheel them back behind you ("doing windmills"). As you apply a torque to your arms, so do your arms apply a torque to you. Your arms are spinning upward (at the front) so you will spin downward at the front. Your arms are spinning one direction and you are spinning in the other, so the net angular momentum of the system is zero. When you are facing down, you stop moving your arms in circles. This requires you to apply a 'braking' torque to your arms, and so they will apply a 'braking' torque to you. When your hands stop moving, so do you. Now the system has reoriented itself (you are facing downward) but its total angular momentum is still zero. Drag and air resistance has nothing to do with it. Maelin (Talk | Contribs) 01:49, 2 October 2008 (UTC)[reply]

I agree with the correction that you would raise your arms from your sides to above the head, keeping them equidistant. This should result ins a forward rotation of the body, which I suppose would cease when you stopped the arm movement. If you then returned them to down by the sides by rotating them outwards, this would not negate the initial rotation. Repeat as needed to rotate the body so the head is where the feet were, facing the opposite way. Not even the slightest violation of any law of conservation. I wish to hell they would send a cat to the space station and record how he changed his orientation, as he sprung from surface to surface. It would be a good project to do just before the decommissioning, since there would be dander, hairballs, and other cat ick. My cat can reverse from feet-in-the-air to feet-on-the ground in a drop of one half foot, and he is quite old. I just tested it. The cat did not use thrusters, or a gyroscope. Marey, who invented the motion picture camera, filmed cat turns in the 1890's and wrote up the findings in Science. Edison (talk) 04:35, 2 October 2008 (UTC)[reply]

So you're saying that other animal forms may be able to change facing in a zero G environment even better than the humanoid form? 98.221.85.188 (talk) 05:48, 2 October 2008 (UTC)[reply]

I dunno about real animals, but cats are pretty twisty! If I and a cat were falling upside-down, my money would be on the cat landing right side up. I'd extend the bet to zero-g too - I have no idea how to twist around in free-fall, whereas a cat evidently does. But cats are gods, not mere mortals. Franamax (talk) 07:30, 2 October 2008 (UTC)[reply]

You tested it? Does that mean you held your cat upside down and dropped it? That sounds like animal cruelty to me... --Tango (talk) 18:06, 2 October 2008 (UTC)[reply]

I'm sure Edison meant that they merely altered space-time around the cat, whilst the cat itself remained unharmed. Franamax (talk) 07:52, 5 October 2008 (UTC)[reply]

Probably one of those kittens that Schrodinger was trying to give away after his experiment failed and the other cat got into the box. :) Franamax (talk) 07:55, 5 October 2008 (UTC)[reply]

I'm continually amazed--but I know I shouldn't be any more--that "Wikipedia has an article about that": Cat righting reflex. And even a secondary page: High-rise syndrome. DMacks (talk) 18:38, 2 October 2008 (UTC)[reply]

GI Tract

When the intestines absorb fat, some of the fat can permeate through the intestinal wall and the fat will conglomerate in to plaque. Why doesn't calcium or magnesium or proteins do this when the intestines absorb these chemicals?24.65.69.8 (talk) 23:35, 1 October 2008 (UTC)[reply]

Fats are hydrophobic and in water, they will get forced into a small group since the hydrogen bonding between interbonding water molecules will "squeeze out" the non-ploar molecules like fat. Fat isn't water soluble. Calcium and magnesium and about 75% of the proteins are hydrophilic and even the non-polar proteins usually have a polar region or a couple polar regions, so they are at least slightly water soluble. Sentriclecub (talk) 00:18, 2 October 2008 (UTC)[reply]

As a followup, its not really specific the the transportation process accross membranes, its just a property of lipids in an aqueous environment. Think of it like this way. Its not that the fat molecules are "actively" trying to amalgamate, but its just the fact that the water is the one actually trying to make as many bonds with other water molecules as possible. Then one hydrogen is near 18 other water molecules and near 3 lipid molecules, it will try to "improve" by surrounding itself with only other water molecules. Thus the observation of seeing fat molecules clump together, is actually through the water molecules "preference" to only surround itself with other water molecules. Sentriclecub (talk) 02:07, 2 October 2008 (UTC)[reply]

Likewise, before we anthropomorphise the world, there is no "trying" effort involved. Water is a polar molecule, with a net dipole moment. That means that water is a molecule with oppositely charged sides, or "poles". These charges assert an attractive force on opposite charges (like ALL electric charge). Since fat molecules are essentially non-polar, water molecules exert more force pulling on each other than they exert on the fat molecules, and so they sqeeze the fat molecules out of the way. Interestingly, due to the inductive effect, water molecules are actually MORE attracted to fat molecules than the fat molecules are to each other. This effect is overtaken by water molecule's attraction to other water molecules, which is why fats don't desolve. In fact, fats lack of attraction towards each other is why they tend to spread out so thin on the surface of the water; they are more attracted to the water than to each other, so they tend, if given the space, spread out into very thin layers, sometimes as thin as a single molecule. As to the mechanics of artierial plaque formation, I'm not sure I can be much help, and our Wikipedia article on the subject Atheroma, lacks any such info. --Jayron32.talk.contribs 04:58, 2 October 2008 (UTC)[reply]

I only provided the followup to make it easier to understand. I gave a think of it this way explanation just in case he or she is a high school student. I think your explanation about a dipole moment is over the person's head. The OP does not likely know about charges, or the F=kq1q2r^-2 formula. Sentriclecub (talk) 07:26, 2 October 2008 (UTC)[reply]

Tru dat. Your probably right... --Jayron32.talk.contribs 03:47, 3 October 2008 (UTC)[reply]

^{[citation needed]}. Does fat actually escape through the lining of the intestine to form plaques? I've not heard of this process before, and I'm not sure if it's an accurate representation of something which really happens to any significant extent.

There might be some confusion with visceral fat deposits, which is fat which accumulates around the abdominal organs (including the intestines). While these deposits aren't generally associated with good health or good diet (they're responsible for the 'beer belly' look), they're composed of ordinary fat cells (adipocytes), not 'free' fat in plaques.

Another possible confusion is with atherosclerotic plaques—extracellular fatty deposits which form inside blood vessels (not around the intestinal walls) and which are again related to poor diet. These plaques can form throughout the body, and include fats, calcium, and connective tissue. Their formation is rather complicated, and is not simply the result of poorly-water-soluble fats precipitating or coalescing. TenOfAllTrades(talk) 04:32, 3 October 2008 (UTC)[reply]

What will happen to planets when sun finally elapse to a white dwarf

What will happen to Jupiter, Saturn, uranus, and Neptune after when the sun collapse into white dwarf. What will happen to it's gaseous layers. Will it evaporate, strip away leaving a solid core? Will Earth survive or be deceaseb? Alot of new search say Earth will unable to escape su's engulfment. I say Earth is 70% chance to be decase when sun becoems a giant star.--SCFR eew ays 23:53, 1 October 2008 (UTC)[reply]

What will happen to the Earth is still very uncertain, while the Sun will probably expand to engulf the Earth's current orbit it may shed enough mass beforehand for the Earth's orbit to be enlarged enough for the Earth to escape. It's also possible that the Earth will survive being engulfed - the Sun won't be that big for long on an astronomical scale. Whatever happens, it certainly won't be inhabitable! The outer planets will continue in their (possibly slightly larger) orbits, although they'll now be in the cold and dark (Jupiter and Saturn are large enough that they may be able to keep themselves warm for a while). Eventually, due to passing stars, etc., the planets will be flung out of their orbits, but you could be talking quadrillions (10¹⁵) of years for that. --Tango (talk) 00:33, 2 October 2008 (UTC)[reply]

What about Venus' fate. I've elarnt Venus can also escape, but even if Venus escapes I thgoht the planet condition will just be worse. Venus' fate is not quite certain yet I thought. What you menat by eventually all planets will be flung out orbits. Will they drift away? So when sun becomes a white dwarf, it's gas will stay?--SCFR eew ays 00:41, 2 October 2008 (UTC)[reply]

What happen to Venus I thoguht have some questions. I thoguht Venus may also widen orbits. I seen few sources say Venus will actually survvie over white dwarf. Even if Venus still exist over white dwarf, I thought Venus will just be frozen, dark, and deep cold.--SCFR eew ays 00:52, 2 October 2008 (UTC)[reply]
Am I right saying this? Veuns fate is not that certain yet. If Venus still exist over sun's giant stage then it's surface will be total molten, all the atmospher' will totally been gone.--SCFR eew ays 00:57, 2 October 2008 (UTC)[reply]

I think there is a chance Venus' orbit could expand enough for it to escape, but it's less likely that for the Earth. When the Sun collapses to a white dwarf it's outer layers will be shed and will become a planetary nebula, which will quickly dissipate. The remaining planets (whichever ones survive) will become cold and dead (except maybe Jupiter and Saturn which may be able to generate their own heat for a while longer, I'm not sure how much longer they will generate heat for, they may have already stopped by then). --Tango (talk) 01:36, 2 October 2008 (UTC)[reply]

I saw on a documentary-style TV program that Jupiter and Saturn would be stripped of their gaseous layers. Remember that the sun shedding its outer layers is nothing compared to a supernova, but it'll still be very powerful (and fast-moving and hot). I don't know how to calculate something like that but maybe it's possible to, although there's probably a lot of uncertainty. ~A H 1^(TCU) 21:37, 3 October 2008 (UTC)[reply]

Also, see formation and evolution of the solar system. New orbital calculations show that the Earth will probably be pulled into the sun. ~A H 1^(TCU) 21:42, 3 October 2008 (UTC)[reply]

Was the theory that the exploding outer layers would strip the gas giants of their gas or that the increased energy from the sun during the red giant phase would strip them. The latter seems more likely to me. --Tango (talk) 23:21, 3 October 2008 (UTC)[reply]

By the time sun becomes a white dwarf, all gas giants could strip away gaseous envelopes leaving the core. For Earth, it seems to have greater chance to be engulf by 65%chance,then to survive at 35%chance about. Even if Venus and Earth survives over sun's white dwarf, it will just be total uninhabitatable. It will just change from surface fo molten rocks into a planet black, and bleak, and frozen cold. We do have questions to whether Venus will survive, it just don't have as many chance to survive than Earth does.--SCFR eew ays 23:32, 3 October 2008 (UTC)[reply]