Wikipedia:Reference desk/Archives/Science/2011 December 23

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December 23

Standing on a satellite

I know that astronauts and whatnot "float" around their spacecraft because they are in freefall, tumbling around the earth. If they were falling at the exact same rate, could an astronaut stand normally (albeit at a potentially reduced weight due to distance from the center of the earth) if the physical forces were lined up correctly? How about on a geosynchronous satellite? If not, what conditions would allow it? Mingmingla (talk) 01:52, 23 December 2011 (UTC)

An astronaut could "stand" on any object, so long as neither attempted to move. As soon as the astronaut stepped anywhere, or crouched, or did anything which exerted a force on the satellite, the two would fly off from each other in opposite directions (relative to their old position based on their difference in mass). In order for that not to happen, the "satelite" would have to be large enough to exert enough gravity to hold the astronaut fast. I'm not sure what size that would be, but it would be substantially larger than any object we could build and launch from earth. --Jayron32 02:02, 23 December 2011 (UTC)

The astronaut could be said to "stand" on the satellite if he can't jump fast enough to escape its gravitational pull. Assuming that the satellite is spherical and it has the same density as Earth, its escape velocity is proportional to the radius. The escape velocity of the Earth is 11 km/s, its diameter is 12700 km, jump speed is ~1 m/s, so the astronaut should be able to stand on any planetoid that is larger than ~1 km in diameter.--Itinerant1 (talk) 04:26, 23 December 2011 (UTC)

Whether a spaceship is orbiting or plummeting, you will not feel earth's gravity relative to your ship. (ie:You'll float around.)

If you were stationary compared to earth, but at a low orbital altitude, (Say, at the top of two hundred mile tall flag-pole) you would feel Earth's gravity, but somewhat reduced.

If you were stationary compared to earth, but with an geostationary altitude (Say, at the top of a 22,236 mile tall flag-pole) you wouldn't feel any gravity. It would be like free-fall. APL (talk) 02:16, 23 December 2011 (UTC)

The OP's question is answered in Hill sphere. HTH, Robinh (talk) 07:46, 23 December 2011 (UTC)

These help, thanks. So basically, if the geostationary satellite were the same size as a football field, an astronaut could not stride upon it like we would in an airplane, even if it were between him and the earth. I know it's way to small to have any significant gravitational effect (that's not what I was really going for to begin with anyway). Mingmingla (talk) 18:06, 23 December 2011 (UTC)

Right. I'll note that APL's description of a ludicrously tall flagpole is exactly the same situation as one would experience at different positions along the cable of a space elevator. TenOfAllTrades(talk) 16:50, 24 December 2011 (UTC)

Wanted: Uranium asteroids?

Is there any asteroids or space objects like in the asteroid belt or those that do a "fly-by", that contain Uranium(oxide) in any useful isotope and amount like >1% ..? Electron9 (talk) 04:22, 23 December 2011 (UTC)

Maybe? Probably? There are all but certainly asteroids with deposits of uranium. Asteroids of > 1% uranium and of substantial size (i.e. not just a fistful of uranium ore) are, I expect, highly unlikely, as that's orders of magnitude above the expected concentration of uranium. — Lomn 14:17, 23 December 2011 (UTC)

As Lomn notes, there will be trace amounts of uranium in just about any asteroid you care to lay your hands on—the difficulty is in finding a concentrated ore. Our article on uranium ore gives a pretty thorough overview of the natural processes by which uranium is typically concentrated to form commercially-viable deposits. All of the known processes involve flowing magma, flowing water, or copreciptiation or chelation with carbon compounds in water—or more often, a combination of these processes. Unfortunately, none of these things will happen to any great extent on an asteroid; they're too cold and too small for flowing water, let alone flowing rock. You may get very small, localized deposits, but that's it.

I suppose it's conceivable that a uranium-rich asteroid could be formed by a major impact event; if you hit a pre-existing planetary deposit of uranium ore with a big asteroid or comet, then at least some of the uranium ore could be kicked off into space to become a uranium-rich asteroid. (It's believed that the moon formed through one such particularly large impact.) Still, the odds against that happening are...astronomical. TenOfAllTrades(talk) 15:45, 23 December 2011 (UTC)

Well Uranium in any form would do, even Thorium in larger amounts. As both can be used to fuel a reactor to produce electricity beyond where solar power can be utilized. I wonder if any survey has been done at all regarding this. The article on the Asteroid belt mentions some elements. The Uranium on this planet was not produced here, so there ought to be more of it in space. The processes of magma, water flow, copreciptiation and chelation with carbon compounds in water can't be needed to produce these elements. Electron9 (talk) 03:28, 24 December 2011 (UTC)

Those processes aren't needed for production, but they are a key part of concentration. Asteroid mining is undoubtedly a good SF-style source of materials (of all types, not just radioactives), in large part because the whole thing is already out of Earth's gravity well. However, until practical industrial-scale interplanetary travel is achieved, bringing the cost of space industry below that of its terrestrial counterpart, the whole thing will remain strictly within the realm of SF. — Lomn 15:48, 24 December 2011 (UTC)

The point is to use the material for reactors used in space. Not to bring it to Earth. Small equipment that compensate size with time and the sun as an energy source would be the way. Bring radioactive material from and to space is a risky business. Electron9 (talk) 07:12, 26 December 2011 (UTC)

"prealloy"?

I was reading Ferrosilicon and came across the term "prealloy". What does it mean, and why isn't there a Wikipedia article for it? Looks like it's something to do with a state were metals and such are physically combined, but not yet alloys at the atomic level. Especially on guitar strings, apparently. --Shirt58 (talk) 06:04, 23 December 2011 (UTC)

Prealloy is an article that exists, but it is very short. It does have a rudimentary definition. There's also a reference in the article, which you could follow. --Jayron32 03:47, 24 December 2011 (UTC)

I'm fairly sure the editor who started that article may have added the article maintenance tag "This article may contain original research" because there is currently no "This is educated guess-work, but nevertheless still guess-work" article maintenance tag.--Shirt58 (talk) 13:45, 24 December 2011 (UTC)

motion in speed of light

why it is not possible to give a movement to an object with the speed of light? — Preceding unsigned comment added by Sahir jutt (talk • contribs) 06:30, 23 December 2011 (UTC)

Because, according to the math involved, it would require infinite acceleration. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:28, 23 December 2011 (UTC)

The closer to light speed you measure something to be moving, the less increase in speed you will get per unit of energy you use to speed the object up. The way this works out is so that no matter how much energy you put in, you will never get the object to quite light speed. If you are interested, look up Special Relativity, this is the subject that covers the details of why light speed is unobtainable and why it is important. Phoenixia1177 (talk) 08:42, 23 December 2011 (UTC)

That raises a question I've sometimes wondered about: How is it that photons can travel at light speed, with seemingly very little energy input? ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:03, 23 December 2011 (UTC)

I think it's because the photon is (as we presently understand it) massless. The infinite energy to accelerate to light speed bit holds true only for objects which have mass. --Ouro (blah blah) 16:43, 23 December 2011 (UTC) sorry this got lost in edit-conflict. DMacks (talk) 21:52, 23 December 2011 (UTC)

That's because photons have zero rest mass. They are massless. Dauto (talk) 17:10, 23 December 2011 (UTC)

Sorry about that, I shouldn't have left that that off. As, clearly answered above by Dauto, things travelling at light speed have zero rest mass. The converse also holds, things with zero rest mass travel at light speed. Phoenixia1177 (talk) 17:38, 23 December 2011 (UTC)

So, infinity times zero equals the speed of light? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:05, 24 December 2011 (UTC)

The mathematics of mechanics calculations at or near the speed of light aren't trivial. See Special_relativity#Physics_in_spacetime. No, I don't really understand it either. But it isn't as simple as the basic mechanics math you were taught in high school physics for calculating things like velocity and distance and time. --Jayron32 03:49, 24 December 2011 (UTC)

"[I]nfinity times zero" is Not a number (Indeterminate form). It is undefined. In some sense it equals every number, in some other sense it equals none. --Martynas Patasius (talk) 14:53, 24 December 2011 (UTC)

That's exactly what I'm getting at. If I understand Jayron correctly, the formula doesn't quite work when mass approaches zero. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:36, 25 December 2011 (UTC)

Actually, infinity times zero equals the energy of the photon (not its speed), and that can indeed be anything :). Dauto (talk) 16:12, 26 December 2011 (UTC)

Could Solar Roadways also reclaim the energy of vehicles pressing down on the pavement?

The Solar road movement is gaining momentum in various places. I now wonder whether even more use can come out of them by also capturing the energy of the weight of vehicles pressing down on said roadways.

Couldn't anyone else have thought of this idea already or am I the first one? (Please post links.)

How viable is it for solar roads to have the two ways to capture energy? Will it thusforth pay for itself faster? Thanks. --76.250.249.130 (talk) 07:39, 23 December 2011 (UTC)

Weight cannot produce energy unless some motion is involved. The energy would have to come from the engines of the vehicles travelling along the road, thus increasing fuel consumption and further polluting the planet. Sorry -- forget it! Dbfirs 07:48, 23 December 2011 (UTC)

Motion is VERY MUCH involved. The motion of the tires rolling onto each panel section is the motion needed, is it not? If not, then would a physics major please explain how? --76.250.249.130 (talk) 08:41, 23 December 2011 (UTC)

Work is done, and energy recovered, only if there is motion in the direction of the force. Weight acts vertically downwards. The motion of the car on a horizontal surface is perpendicular to the weight, so no energy can be obtained from the weight as the vehicle moves forward. Work is done against friction as the tyres roll forward, and energy could be obtained by placing miniature plates that are depressed by the tyres, but this will significantly increase "friction" and hence fuel consumption and pollution, and is a very inefficient way to produce energy. Forget the idea. It is a non-starter. Dbfirs 10:45, 23 December 2011 (UTC)

Why does concrete & asphalt need to be replaced every so often, and why are there weight limits for trucks? Isn't that because the pressure of all that traffic bearing down on the roads is wearing out the surface? Then as the weight is bore down on the roads, if that's not energy pressing down on it, then what else would it be? --75.39.138.86 (talk) 15:59, 23 December 2011 (UTC)

Moreover, if the weight pressing down on solar surfaces won't be a viable source of reclaimable energy, what about absorbing the heat from the tires? (And maybe the engines themselves, if their proximity is close enough?) --75.39.138.86 (talk) 16:05, 23 December 2011 (UTC)

(Edit Conflicts) There was mention of experiments (possibly in The Netherlands) with roadways designed to recover energy from vehicle movements in this way a couple or so years ago in New Scientist magazine, so someone has actually investigated the possibility. As I recall, the main drawback was that (just as the commenters above have said) the movements in the road's surface necessary for harvesting any appreciable energy significantly slowed the vehicles, causing them to burn more fuel for the same speed and/or mileage - effectively, the process converts some of the energy from the vehicles' stored fuel, via their engines, their wheels and the road's recovery system, to energy that then gets re-stored, very inefficiently. It would be far more efficient simply to allow the vehicles to move unimpeded as normal, and use the extra fuel not used to generate energy directly in a conventionally efficient engine. {The poster formerly known as 87.81.230.195} 90.197.66.126 (talk) 16:10, 23 December 2011 (UTC)

The weight limits for trucks are usually because of bridges, but the tyres of a heavy truck do gradually tear up the road surface, especially when braking and on corners. Recovery of heat from the tyres and engine is certainly possible, but is very inefficient. How would it be collected? Thank you to "The poster formerly known as 87.81.230.195" for explaining the problem more clearly than I did! Dbfirs 17:28, 23 December 2011 (UTC)

Placing solar panels in roads would be prohibitively expensive, and they would be quite inefficient because they would soon be covered with a layer of rubber from car tires. Making the roads black, so they absorb more sunlight and stay warmer in winter, requiring less salt to melt the ice, might be a way to get some benefit from sunlight. Perhaps a rather minimal use of solar panels in the road might work, say just a strip along each edge which powers LED lights at night to mark the edge of the road. This might work because the power requirements are so minimal and less rubber will accumulate there. StuRat (talk) 16:34, 26 December 2011 (UTC)

Rubber from the tires won't be a major problem: apart from skid marks (rare), tire rubber comes off as a very fine powder, which mixes with other sources of dirt on the roads and washes off to the sides when it rains (or when a street-sweeper comes along). --Carnildo (talk) 08:41, 27 December 2011 (UTC)

I disagree. I've seen cement roads where the areas where tires pass have all turned black. StuRat (talk) 20:31, 27 December 2011 (UTC)

Kinetic sidewalks: How viable are they?

If it's possible to build a Solar sidewalk, how easily developed & constructed can such sidewalks be made to recapture the kinetic energy of anyone walking on it? How much quicker would it pay for itself if it could also capture the energy of anything pressing its weight down on it? Thanks. --76.250.249.130 (talk) 07:39, 23 December 2011 (UTC)

This idea possibly has some validity, since walking is such an inefficient method of locomotion, but such a sidewalk would be noticeably harder to walk along and very expensive to maintain. A better idea would be capture the wasted energy of those who visit gymnasiums. Dbfirs 07:52, 23 December 2011 (UTC)

Sir, aren't solar panels made today already rated for a 20, 30 or 40-year lifespan? Longer than normal concrete/asphalt now, right? --76.250.249.130 (talk) 08:43, 23 December 2011 (UTC)

They are not designed for being walked on, and they cost many times the cost of concrete. Does anyone make solar panels with a 40-year guarantee? Dbfirs 10:57, 23 December 2011 (UTC)

Is walking an inefficient method of locomotion ? Isn't it one of the most efficient other than cycling (or possibly falling) ? Sean.hoyland - talk 08:07, 23 December 2011 (UTC)

Cycling is much more efficient because the centre of mass doesn't move up and down as it does with walking. Walking on a surface that moves down as you put your weight on it would be less efficient, and some energy could be recovered, but it would not be popular, and it would be very expensive to build, with many moving parts. Dbfirs 10:57, 23 December 2011 (UTC)

Cycling is a LOT more efficient mostly because of the mechanical advantage provided by gears. --Jayron32 00:19, 24 December 2011 (UTC)

On the contrary, energy is lost in any gearing mechanism, reducing the efficiency (but, of course, making it much easier to cycle uphill). Dbfirs 10:36, 24 December 2011 (UTC)

You'd get better power from a tidal generator rigged to a manhole cover... or a generator on a revolving door... seriously though, human powered systems don't deliver all that much power even when the full force of hard exercise goes straight into powering a device. It's not going to be cost effective to take a small fraction of this with a sidewalk which often is not in use at all. Bear in mind that sunlight is enough energy to substantially heat a sidewalk - think about how hard you'd have to rub a rough stone on a patch of sidewalk to heat it up as much as the sun does! Wnt (talk) 04:07, 29 December 2011 (UTC)

Whey

Does whey protein consumption cause hair loss or impotency? — Preceding unsigned comment added by 119.235.51.130 (talk) 11:28, 23 December 2011 (UTC)

No. Of course, if you're substituting a whey protein shake (human breast milk is high in whey content, so there's no issue of any protein "incompatibilities") for a proper diet, everything is possible, but it's not the whey. PЄTЄRS J V ►TALK 04:02, 25 December 2011 (UTC)

Time Dilation

Do we have an article that shows the derivation of the special relativistic formulae? — Fly by Night (talk) 13:40, 23 December 2011 (UTC)

Do you mean the Lorentz factor? There are a variety of ways to derive it; one is shown in the linked-to article. If you Google "lorentz factor derivation" you can find other approaches as well. As far as derivations go it is pretty straightforward — it is just relatively simple geometry with a constant speed of light. --Mr.98 (talk) 14:07, 23 December 2011 (UTC)

It's not too hard to just follow the derivations in section I of Albert Einstein's 1905 paper, in which he first explained his theory. Here's an English translation.[1] Red Act (talk) 15:37, 23 December 2011 (UTC)

Thanks to you both. I wasn't asking how to derive the formulae; I was asking if we have an article about how to derive the formulae. I couldn't find one, and was thinking about writing one. — Fly by Night (talk) 16:19, 23 December 2011 (UTC)

which colour light travels speed and for long distance?

dear frens, i have following query: among all known colours(including white),which colour light travels for larger distance? and which colour light travels with larger speed?

-Regards — Preceding unsigned comment added by Challenging arjuna (talk • contribs) 14:37, 23 December 2011 (UTC)

All colors of light travel at the same speed, the speed of light. And in space at least, all colors of light can essentially travel for arbitrarily long distances, although for such extremely long distances that red shifting due to the metric expansion of space is significant, light that starts out as violet is the visible light that can travel the furthest while still remaining in the visible spectrum (assuming all observers involved move along with the Hubble flow). Red Act (talk) 15:26, 23 December 2011 (UTC)

Well, all colors of light travel at the same speed in a perfect vacuum. Light travels a bit slower whenever it passes through any medium (air, water, glass, or whatever). The ratio between light's speed in a vacuum and its speed in a particular medium is that medium's index of refraction. Travelling through the air, light travels about 0.03% slower than it does in a vacuum; travelling through glass, light only goes about two-thirds as fast as it does through vacuum.

Further, the refractive index of a medium isn't the same for all wavelengths (colors) of light. The change in refractive index with wavelength is known as dispersion. (Dispersion is what makes it possible for a prism to separate a beam of white light into its component colors, as each color behaves a little bit differently as it enters, passes through, and exits the glass.) Inside a chunk of ordinary glass, blue light will travel about 2% faster than red light. In general, light at shorter wavelengths will travel faster through a medium than light at longer wavelengths. TenOfAllTrades(talk) 16:34, 23 December 2011 (UTC)

All light is the same. The color is just how energetic it is. That is, how "fast" it goes. As far as we can tell, they all go the "speed of light", but if you start moving, the color changes instead of the relative speed. If light is actually massive, and we just can't tell because it moves very, very close to the "speed of light", then higher energy light (bluer) is faster and lower energy light (redder) is slower. Also, the "speed of light" is a universal constant and isn't just how fast light goes. For one thing, it's the lowest upper bound for how fast massive objects can go. As such, it still means something even if light doesn't go that fast. — DanielLC 07:57, 25 December 2011 (UTC)

See Extinction (astronomy) and mass attenuation coefficient. ~AH1 ^(discuss!) 03:09, 27 December 2011 (UTC)

I think OP asks not only about speed, but also about long distance. See diffuse sky radiation which explains that in the atmosphere, red light can travel longer than blue light. – b_jonas 12:07, 27 December 2011 (UTC)

LED v/s CFL?

dear frens, i have following query: i have read articles on LED and CFL in net..but still can anyone of u pls tell me diff between LED and CFL in simpler terms. Which one would be best for large developing countries like india to invest on?CFL or LED considering energy efficiency and cost factor?

-Regards, — Preceding unsigned comment added by Challenging arjuna (talk • contribs) 14:40, 23 December 2011 (UTC)

India should invest on both IMHO. Dauto (talk) 16:34, 23 December 2011 (UTC)

Our Compact fluorescent lamp and LED lamp articles each have a section comparing the technologies. They differ in how much they cost to produce, how energy-efficient they are, and how long they last in various uses. The "best" choice is something we can't answer because there is no clear winner--neither is better in all aspects but both do have substantial advantages depending on what you think is important to consider. Dauto is right though...because it's a trade-off (up-front cost vs long-term savings, for example) they are both important to consider for current applications. DMacks (talk) 18:51, 23 December 2011 (UTC)

I would say buy CFLs now, and if the price goes down enough on LEDs in the future, then buy those. Since they both work with the same fixtures, it's not a major expense to switch over later. StuRat (talk) 21:24, 23 December 2011 (UTC)

CFL's should be recycled rather than dumped. They're also as fragile as eggshells. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:03, 24 December 2011 (UTC)

That remains unclear. I'm pretty sure many fixtures remain primarily designed for incandescents not CFLs. Either way, they often appeared to be not well suited for LED lamps. Definitely at the current time luminaires purposely designed for LEDs are likely to perform better due the heat management requirements. While there will undoutedly always be a market for replacement, it seems likely to me a purposely designed fixture will always be better overall with better heat management, as well as better handling of the output to give the effect you want (and reduce loss). And in fact on the point about most fixtures being designed for incadescents, in terms of handling the output it seems it would probably be easier to design an LED to replicate the output pattern of a incandescent then a CFL.

And on that point, if you want to use CFLs, it's questionable if you should use the incandescent replacement ones with integrated ballast. Quad pin ones where the electric ballast is in fixture seem a better bet to me. And non compact fluorescents are far more common including in households in parts of Asia then in much of Europe, the US and Australia/NZ anyway AFAIK. If you aren't talking about a desk lamp or something similar, I'm not convinced there's any real reason to go CFL or whether a normal non compact fluorescent lamps.

Perhaps I will one day eat my words, but of the two I think it's clear LEDs have a far brighter future (pun semi intentional) even if they still have a way to go before clearly overtaking a CFL. (Yes people hype LEDs too much some times but I think that's more about 'when' and 'how soon' rather then 'if'.) It appears I'm not the only one who thinks this because our article notes "Philips Lighting has ceased research on compact fluorescents, and is devoting the bulk of its research and development budget, 5 percent of the company's global lighting revenue, to solid-state lighting". Of course none of this is to suggest there aren't still plenty of problems LEDs have to face.

Nil Einne (talk) 13:04, 24 December 2011 (UTC)

It's pretty clear that CFLs' time has peaked. I expect LED bulbs will last long enough that people will take them with them when they move. They can also be disposed of normally versus CFLs. The main challenge right now (aside from costs, which are already dropping as volume ramps up) is that LED maximum light output is not matching CFLs (which are readily available in up to 200W incandescent luminescence equivalents). PЄTЄRS J V ►TALK 03:55, 25 December 2011 (UTC)

Why does a tubelight does not start as soon as it is switched on?

dear frens, this is my query:

1.Why does a tubelight does not start as soon as it is switched on?but an electric bulb/CFL will switch on as soon as it is switched on... — Preceding unsigned comment added by Challenging arjuna (talk • contribs) 14:47, 23 December 2011 (UTC)

Flourescent_tube#Starting pretty much explains that. FWIW CFLs in fact do have a delay, but this has been improved over the years; see Compact_fluorescent_lamp#Starting_time. It also depends on the design; some of my CFLs have a noticeable delay in starting (possibly around 1 sec) followed by a further period of up to a few minutes until they reach full brightness, others come on virtually immediately, are generally brighter when they come on, and while still having a delay before reaching full brightness this is quicker than the first design mentioned. Regards incandescent light bulbs, since these rely on the basic principle of simply heating a metal filament until it glows white hot, this can be achieved in a time imperceptible to our senses. --jjron (talk) 15:39, 23 December 2011 (UTC)

I have a CFL that does something a little different, it starts out dim, but instead of gradually getting brighter it snaps to full brightness a second later. I wonder how they got that effect. StuRat (talk) 21:22, 23 December 2011 (UTC)

While incandescents (generally) illuminate faster than fluorescents, it's not quite correct to say that the time that they take to turn on is completely imperceptible. If you compare an incandescent bulb and an LED lamp side by side, you will be able to see the difference quite clearly. The LED will 'snap' on and off, while the incandescent 'fades' in and out. This usually isn't an important difference, but it has a key application in automotive safety. Studies have found that replacing incandescent brake lamps with LED brake lamps improves driver response times by about 200 milliseconds: [2]. (At highway speeds, 200 ms is about 6 meters (20 feet) of travel.) TenOfAllTrades(talk) 16:17, 23 December 2011 (UTC)

I don't think any of this answers the OP's question. The tubelight has a chock to store the energy with which to strike the arc. The circuit’s electronics can only wait until the bimetallic switch has warmed up enough to complete the circuit to dump that energy between the tube's cathodes. That is where the delay occurs.--Aspro (talk) 21:57, 23 December 2011 (UTC)

And here is the circuit. The delay is due to component 'D'. Wikipedia had the answer all the time; should one look for it.--Aspro (talk) 22:11, 23 December 2011 (UTC)

Sugar = non-aqueous

I remember hearing in Chemistry class that sugar is a homogeneous mixture (I think), unlike salt which is aqueous. Does that mean that if you let a glass of water with sugar in it sit for long enough, without letting the water dissolve, that the sugar will not float to the bottom due to gravity? I'm assuming that the interactions between atoms of the molecules is enough to keep the sugar in such a state. Magog the Ogre (talk) 16:32, 23 December 2011 (UTC)

I think you are remembering that sugar (sucrose) is a covalent compound that stays as whole molecules when it dissolves in water whereas table salt (sodium chloride) is an ionic compound that separates into individual atoms when it dissolves in water. But either way, you have an actual homogeneous solution even down to the molecular level not simply macroscopic particles spread among each other (like sand in water). There are reasonably strong attractions between the solvent (water) molecules and solute (sugar molecules or salt ions) that actually keep them mixed and prevent settling-out or other spontaneous separations. Technically, it is more stable for them to be dispersed among each other than to coalesce into clusters apart from each other. DMacks (talk) 16:43, 23 December 2011 (UTC)

physics

well there was a question in which there was a very small angle, and in the question it was noted that the angle x is so small that sinx=tanx=x and while I was solving the problem, I chose the approximations in a way that the problem could be solved, for example, when there was

integral(sinx-tanx)d(tanx), what I did was: integral((1-1/cosx)sinx)d(tanx)=integral(1-1/cosx)sinx dx=-integral(1-1/cosx)dcosx=ln(cosx)-cosx

is it right in principle to do so?--Irrational number (talk) 19:50, 23 December 2011 (UTC)

You should probably try WP:RD/MA. Magog the Ogre (talk) 23:55, 23 December 2011 (UTC)

Hospital admission procedures

First-time poster.

At a gated Internet community, we're writing a collaborative science fiction story. It is a tale of inner-body travel, set in the year 2028. A 16-year-old boy named Steve has just been driven via ambulance to the hospital after passing out at his job site, having a prion-caused disease that kills everyone who has it.

What we'd like to know is: what are the procedures that doctors and nurses do with new patients admitted to a hospital? Among other things, we'd like to know what the standard list of questions for in-patients is. (Things like . . . "What's your full name?", "Are you allergic to any medications?", "What diseases and disorders do you have a history of in your family?")

If we could get some help from someone here who works in the medical professional, our online community would be eternally grateful. Enzingiyi (talk) 20:43, 23 December 2011 (UTC)

Starts with asking a Medical history. --BozMo talk 21:15, 23 December 2011 (UTC)

In the US, at least, they will want to know about your insurance, to determine if they should release you immediately or perform a million dollar surgery. :-) StuRat (talk) 21:17, 23 December 2011 (UTC)

With two ER admissions in the past year, I will try to recall. If you are conscious, the admissions nurse will ask why you are there, have you ever had a similar condition before, are you in pain? Do you have a family (or a regular) doctor? Who is it? Can we have permission to obtain your medical records? Where is the pain? How intense is it? When was the last time you ate? What did you have? Are you on any prescription medications? Have you taken any non-prescription drugs in the past week? How often do you consume alcohol? How often do you use any other drugs, legal or illegal? Are you allergic to any foods or medications? (This is just the beginning, and the sequence may be different.) A nurse will routinely take blood pressure, temperature, basic height and weight info. You will probably be asked to provide a urine sample. Insurance information will also be taken, but in the U.S., emergency facilities are required to treat emergency medical situations regardless. This is all before you see a doctor. The doctor may repeat some of these questions, and may ask for a routine blood sample to be drawn. Results of this preliminary exam will determine the direction it proceeds further. — Michael J 23:06, 23 December 2011 (UTC)

Thanks for all your help, guys! Enzingiyi (talk) 20:12, 24 December 2011 (UTC)

Given that it's 2028, I'd expect a few new procedures - for example, a screen for the full set of cytokines and especially alpha interferons to obtain the body's internal self diagnosis of any potential infection; more questions about medical diagnostic implants and (shudder) perhaps even brain interfaces, a question about whether the person has abused sleep 'replacement' medications, etcetera. And that's before we even get into the dystopian stuff... Wnt (talk) 04:14, 29 December 2011 (UTC)

Quenching and tempering

My understanding, which I've checked on the Wikipedia page is that, quenching steel increases its Vicker's Hardness, tempering should slightly decrease the Vicker's Hardness whilst increasing its ductility. However in a set of results I have for an experiment testing this, the Vickers Hardness of the quenched and tempered steel is slightly higher than that of the quenched. Is this likely an error in the experiment or is there a scientific explanation for this? Clover345 (talk) 23:06, 23 December 2011 (UTC)

Likely the manner of quenching/tempering: degree and manner of conversion of austenite to martensite and retained austenite, influence of the thickness of the material, and so on. You need to review your process in detail to work through its expected effect on the crystalline structure. How soon you measured hardness might also influence; on re-tempering, you need to allow 24-48 hours to pass before re-measuring hardness, but I don't know if that also applied to initial tempering. (Just curious, did you get the same results measuring hardness a couple of days later?) PЄTЄRS J V ►TALK 03:47, 25 December 2011 (UTC)

Aspirin and gastrointestinal bleeding

Why is the stomach damaged by Aspirin? Isn't it acid-resistant? Aspirin#Gastrointestinal describes the phenomenon, but does not explain the why. 88.8.69.150 (talk) 23:46, 23 December 2011 (UTC)

It's more about the the "salicylic___" aspect rather than the fact that it's an acid. That is, there's something else about the structure that matters. Aspirin is actually a fairly weak acid too, so it's not even noticeably "acidic" in already highly acidic stomach (that is, as you note, it doesn't seem reasonable for it to be causing acid burns or similar effects). As a result, it is likely to be mostly in its neutral form, and therefore can interact more easily with certain types of tissues and membranes. I don't know any of the specifics for it (which types of cells are affected, the actual mechanism, etc.) though. DMacks (talk) 08:00, 24 December 2011 (UTC)

If I recall correctly (which I may not), the reason aspirin can sometimes cause damage to the gastric lining is for the same reason that aspirin works — namely, that it inhibits the action of COX, and thereby interferes with the synthesis of prostaglandins. That's the way it controls inflammation and pain, but it also interferes with the way the gastric mucosa protects you from your own stomach acid.

By the way, I don't think salicylic acid in fact does act that way, particularly, though I'm not sure of that either. The aspirin article claims that aspirin works by irreversibly acetylating COX, which is something salicylic acid can't do (it has no acetyl group). --Trovatore (talk) 10:34, 24 December 2011 (UTC)

Well, it used to claim that. It seems to have been changed. I'm not sure what the exact situation is and would be interested in clarification from anyone who has better information. --Trovatore (talk) 07:13, 25 December 2011 (UTC)

To summarize what has already been stated above, there are multiple cox enzymes and aspirin inhibits all of them. For pain relief, only cox 2 inhibition is desired, and so came along the class of cox 2 specific inhibitors, like celebrex, bextra and vioxx -- but problems ensured with these medications and they were either discontinued or severely restricted. Cox 1 serves to build the stomach lining, and inhibiting it as well as cox 2 leads to decreased pain sensation but greater chance of stomach ulcers. DRosenbach ^{(Talk | Contribs)} 04:57, 28 December 2011 (UTC)

The problem results because aspirin is a substandard replacement for the willow bark based medications that you might have gotten, say, in the city of Ur in the time of Abraham. The natural salicylates are glycoconjugates which don't release so much of the active factor in the stomach. Aspirin itself was a first step toward reattaching the salicylate to something to keep it from getting loose, but a simple acetyl isn't really enough. Based on the misconception that the acidity of salicylic acid was to blame, people tried buffering aspirin; thus Bufferin, a popular brand. The problem has been better addressed by drugs such as salsalazine which tie up salicylates more extensively. However, as these are subject to prescription they are not so commonly used. NSAIDs reputedly kill 16,500 people yearly, often from gastrointestinal effects, but such is the price we pay to uphold the prescription bureaucracy and get antiinflammatories a little cheaper... (though to be fair, not even the natural glycoconjugates are entirely safe for the stomach) Wnt (talk) 04:26, 29 December 2011 (UTC)