Wikipedia:Reference desk archive/Science/2006 July 24

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[edit] Vindon, anthracite-based synthetic fibre

In reading a passage on North Korean history (written by an Englishman), I came across the following line: [North Korea] even managed to clothe its own population by inventing an anthracite-based synthetic fibre called vindon. [1]

Does this go by another name? I'm having trouble finding information on "vindon". --0g 06:11, 24 July 2006 (UTC)

Vinalon --Seejyb 19:32, 24 July 2006 (UTC)
Thank you --0g 23:37, 24 July 2006 (UTC)

[edit] Speed of time?Reality is instantaneous?

Imagine there is a string and a laser beam at one end, the other end of the string and a light detector seperated by one astronomical unit(mean sun earth distance).Suppose I were to pull the string and switch on the light at the same time, what would be observed at the other end? Is it that the light and string dislacement would be observed at the same time? or the string displacement would be noticed much much before?(guess light would take 7minutes to reach).

The light would arrive first, while the string-jerk would be delayed by many years. When you yank on a string, the yank is exactly the same as a sound wave. It's a sound wave inside a solid (a compression wave or "P-wave".) The "yank" will travel along the string at the speed of sound in taut string. What's that speed? The speed of sound in solids is typically far faster than in air, and the speed of sound in air is around 720 MPH. The "yank" in the string would travel at at least a few thousand MPH.
Whenever we pull or push upon any object, the entire object never moves as one. Instead, your hand pushes on one part, and that part moves slightly forward and pushes on the neighboring parts, which then move forward and push upon the next neighbors. The "push" and the forward motion is travelling as a wave. Since this wave usually travels at hundreds of MPH, to human eyes it looks as if the solid object moves as one. We don't notice the wave that zips rapidly from one end of the object to the other. The wave is too fast, and also too small. It's possible to see this type of wave if the wave is large and violent, and if it's filmed with a high-speed camera and then played back in extremely slow motion. --Wjbeaty 07:32, 24 July 2006 (UTC)
I like the question though - is reality instantaneous?
Also - I sometimes wonder, is there is no such thing as a solid in which every atom moves at the same time as every other atom because the universe wants to preserve the speed of light rule?
Also - say I'm standing on earth shining a torch at the moon. The light hits the moon. Then I swing the torch from the moon to an artificial satellite at the same distance from me as the moon. Say too, that I've been working on my reflexes and muscle fitness, and am able to swing the torch at very close to the speed of light. Does this mean the patch of light that swings from moon to artificial satellite moves faster than the speed of light, due to the greater distance covered by the same angle? If it does move faster than the speed of light, then is it allowed to because there's no way of someone on the moon using that patch of light to transmit information to the person on the artificial satellite? Or am I barking up the wrong tree entirely? Adambrowne666 07:46, 24 July 2006 (UTC)
The last option, I'd say. You're seeing the spot of light as an entity. Is it? What defines an entity, and thus if it should be allowed to travel faster than the speed of light? This sounds a bit 'quarky' - a 'tendency to exist'. Or how was that again?
Oh, and consider this. The same beam of light has a width, so it shines on more than one spot on the Moon, so does it exist at different points at the same time? DirkvdM 09:48, 24 July 2006 (UTC)
And another thing, related to the original question. I suppose that density determines how fast a 'push' (such as a sound wave) can travel through a material. So does the speed of light set a limit to how dense a material can be? DirkvdM 09:57, 24 July 2006 (UTC)
Re Adambrowne666's flashlight idea, I've heard of that in almost every Faster Than Light FAQ, and it's generally agreed that it doesn't break the rules for two reasons: The light is still moving, from you, at the same speed, and The people at the other end have no control over its motion. So, as you say, no information is transferred from anyone to anyone else faster than light. Black Carrot 10:21, 24 July 2006 (UTC)
The speed of light doesn't limit density because the wave speed equations that depend on density break down if the speed of the individual material particles becomes relativistic. (They probably break down well before then, actually; most such equations apply only in the limit of small (read: slow) oscillations.) In other words, a material wave travelling faster than light would require some propogating influence (e.g., electrostatic repulsion in most compression waves; particle collisions in gases) or material particle to be travelling faster than light, and that's already impossible without talking about density. --Tardis 03:10, 25 July 2006 (UTC)

They could tie a note to it.

If you're standing on the earth shining a light on the moon, then swing the flashlight over to another body, even if you swing the flashlight at any arbitrary speed, the signal still won't reach the other body until the light has traveled from your flashlight to the other body. There will be a light travel delay just like when you first switched on the flashlight. --198.125.178.207 15:11, 24 July 2006 (UTC)

Really? I don't get it. Isn't the light beam already long enough? Adambrowne666 22:42, 24 July 2006 (UTC)
Well, in a sense, but the light beam isn't a "thing". Once the photons leave the flashlight, they travel pretty much in a straight line. So when you swing the flashlight to point at something else, the photons that have already left the flashlight will continue in a straight line, and will hit whatever you were pointing the flashlight at. The new target of the flashlight won't be illuminated until the photons that have been "fired" toward it get there. —Bkell (talk) 23:43, 24 July 2006 (UTC)
Is reality instantaneous? What is "reality"? All we ever know of the universe is not what "is", but what we perceive there to be. We can never really know what "is". Our perceptions depend on a whole range of factors, such as the speed with which our brains compute and interpret signals from outside. Our perceptions are certainly not instantaneous. But as to whether reality is instantaneous - I would say the question has no meaning and therefore there is no answer, but if it did have a meaning, we could never know the answer. This is veering into religious territory, given that God is said to have called Himself, when speaking to Moses, I am that I am. In that sense, the only thing that "is", is God. You may not believe there is such an entity as God. If not, then nothing at all "is", and therefore the whole notion of "reality" goes out the window. JackofOz
Whew! Hey, sorry, JackofOz, not ignoring you, but I just wanted to mention something about Bkell's comment - I was beginning to think that if information was encoded into the beam of light, say the encoded thoughts of an artificial intelligence, and that beam of light was then swung from moon to artificial satellite, then information WOULD be being transmitted faster than light - but Bkell has cleverly put paid to that. Adambrowne666 05:51, 25 July 2006 (UTC)
It's really just like a hose. If you're spraying person A, then you swing the nozzle to spray person B, person A will still get sprayed for a few seconds, and person B won't get sprayed until a few seconds pass. It's exactly the same for a beam of light. --198.125.178.207 21:44, 25 July 2006 (UTC)
Oh, also, AdamBrowne asked a question up above about a material which responds instantaneously; i.e. an infinitely rigid material. And the answer is that such a thing does not exist. The reason is not because the universe wants to preserve the speed of light as a maximum speed, it's because the laws of physics never result in matter travelling faster than the speed of light. Essentially, photons mediate the relative movement of atoms in a rigid object like a bar. The atoms are held together in the bar by electrostatic interactions. When one atom moves, the electromagnetic field transmits the force from atom to atom, causing the other atoms to move, but not instantaneously; at the speed of electromagnetic wave propagation - at the speed of light! And the reason the bar does not move at the speed of light in response to a force is because the atoms are not massless; they have inertia, which effectively slows down the reaction. --198.125.178.207 21:48, 25 July 2006 (UTC)
Thanks, yeah - I guess I'm belabouring the point about the universe preserving causality by placing these limits not only on photons, but also particles of matter - I'm approaching it telologically, which might be a mistake - your point about the electrostatic forces is well taken; of course, electrostatic forces operate at the speed of light, so it's kind of the same thing as the light beam Adambrowne666 01:59, 26 July 2006 (UTC)

[edit] theoretical maximum EER

What is the theoretical maximum EER of an A/C? Assuming 70F inside, and 95F outside. (Or 21C and 35C.) I'm curious how much more improvement is (theoretically) possible in A/C's. 71.199.123.24 07:54, 24 July 2006 (UTC)

From your two temperatures you can work out the maximum possible COP using the equation at Coefficient of performance (COP = Tcold/(Thot-Tcold)). Then use the conversion factor from COP to EER at Seasonal energy efficiency ratio (EER = COP x 3.413). --Heron 17:07, 24 July 2006 (UTC)
Using your equations (and converting C to kelvin) I get a theoretical max of 71.71. Does that seem right? If so, I'm quite amazed at how poor A/C's (with a typical EER of 10-14) are! 71.199.123.24 22:06, 24 July 2006 (UTC)
I agree with your arithmetic. There is a big difference between an ideal Carnot cycle and a practical A/C, but I can't explain why. --Heron 21:39, 27 July 2006 (UTC)

[edit] The "i" in Apple

iPod. iMovie. iDVD. iEverything! I skimmed through a couple of articles on Apple stuff, but I didn't find a mention of how or why the omnipresent "i" got its start. I've gotten very curious, and I hope someone may have the answer. Thanks --71.117.43.53 08:02, 24 July 2006 (UTC)

I think it started with the first iMac. -- Koffieyahoo 08:21, 24 July 2006 (UTC)
Thanks for the help, Koffieyahoo; I read through the article and found the answer. In case anyone else wanted to know, the "i" in iMac stands for internet. Probably due to the commercial success of the iMac, Apple adopted the "i" as a prefix for all of its products. Thanks again, Koffieyahoo! --71.117.43.53 08:54, 24 July 2006 (UTC)
iSkimmed through a couple of articles on Apple stuff, but iDidn't find a mention of how or why the omnipresent "i" got its start. iVe gotten very curious, and iHope someone may have the answer There we go, much easier to read. Who knew the internet was so important?

iApplaud you.

[edit] Yellow Fever Vaccine & Meningitis A+C

I just need name of some Manufacturer of Yellow Fever Vaccine & Meningitis A+C Vaccine.

[edit] Difference between wood charcoal powder and steam coal dust

Can anybody tell me the basic difference between charcoal dust and coal dust produced during mining (i.e. steam coal dust) whether charcoal dust can be used in place of steam coal dust in foundry sand addition?

Nitin Poddar

Retrieved from "http://en.wikipedia.org/wiki/Talk:Coal_dust"

[edit] rn lpn rpn what is the difference

Could someone please tell me the difference between a practical nurse, a licenced practical nurse, a registered practical nurse and a registered nurse? Thanks.

See nurse for the difference between RN and LPN, which are the two main categories of nurses consistently recognized at least throughout the US. I have not heard the term RPN before and suspect it is one of the following:

  1. No such thing, someone's mistaken or made-up term;
  2. A locally devised name for a local program involving a bit of extra training or special certification for LPNs that fall short of full RN licensure, in which case the term has not found wide usage and may still be bound by the legal restrictions of LPN licensure;
  3. A status only found in another country with a specific definition; or
  4. Something different that I don't know anything about. I would tend to bet on definition 1 or 2, but I could be wrong. If you find a better definition, please let us know. alteripse 00:39, 25 July 2006 (UTC)
See our articles on the topics. Registered Nurses are usually allowed to perform more procedures with less supervision and may receive more education and training than Registered Practical Nurses. (LPN and RPN are terms for similar concepts.) The exact requirements and qualifications vary by jurisdiction. TenOfAllTrades(talk) 00:46, 25 July 2006 (UTC)

Thank-you everyone who responded.

[edit] Airoplane

As we know that there is less air at high altitude so also less oxygen. Also now a days an airoplane with more than 200 passengers is flying non stop for more than 12 hrs and the passenger section is sealed and pressurised. What arrangement is made in the air circulation system on the plane so that all passengers get fresh air with sufficient oxygen to breath with normal feeling & not getting suffocated.Is the air inside purified by removing the CO2 and adding oxygen from stocks carried on board ? Thanks. —The preceding unsigned comment was added by 59.95.58.45 (talk • contribs) .

The cabin is fed with fresh compressed air taken from the engines. See bleed air. Femto 14:06, 24 July 2006 (UTC)
Air is partially recycled, partially replaced from outside air. Fresh outside air needs to be compressed and heated, which requires energy, so recycling is used despite health concerns (remember SARS?). Recycled and fresh air are used in about 50/50 proportion, with the entire cabin air replaced with fresh air about every 3-5 minutes. Aviation authorities (e.g. the FAA) have regulations on how air must be refreshed on commercial aircraft. There is some information on this on the net, try googling for something like passenger air recycled, here's one: [2]. Weregerbil 14:15, 24 July 2006 (UTC)
In non smoking planes the air is completely recycled ever 1/2 hour. Philc TECI 15:47, 24 July 2006 (UTC)
If your plane is smoking, you may not be very concerned with how often the cabin air is being recycled. kmccoy (talk) 13:26, 27 July 2006 (UTC)
Ironically, in an effort to get the smoke out of the air in planes where smoking is allowed the air is of much better quality than that of non-smoking planes, where you cannot see how dirty the air is, and are therefore not concerned. Philc TECI 16:58, 28 July 2006 (UTC)

[edit] Life expectancy & such

Medical techlology is advancing very rapidly. Would it be possible, in my lifetime, for the information in my brain to be stored and placed in a new brain/body? I mean, I suspect that my brain is just stored information--would it be possible to map this information, and extract it to a new brain? If so, could we live forever? Sindweller 15:10, 24 July 2006 (UTC)

See, e.g., the article on mind uploading. Another search term for your favorite search engine is "whole brain emulation" (and you may also be interested in things like the technological singularity and some of Ray Kurzweil's writings). It has been discussed quite a bit online and, as far as I know, it's considered theoretically possible but technically very challenging. Some remain optimistic that it will happen in our lifetime though (usual predictions I've seen aim at around or before 2050). Personally I'm a little skeptical as I'm familiar with a lot of the technical challenges, but hopeful :) Digfarenough 16:02, 24 July 2006 (UTC)
Body transplant could also be interresting reading. DirkvdM 19:53, 24 July 2006 (UTC)
And don't forget technological singularity, which is sort of a rapture for geeks. -Quasipalm 02:17, 27 July 2006 (UTC)

[edit] Technology

When was the first computer invented?

Slightly before you posted the same question in the Computer/IT Reference Desk. --Kainaw (talk) 17:34, 24 July 2006 (UTC)
What a mature, adult response to a simple question. Try reading about Charles Babbage.
Simple? You apparently do not know the full definition of the word computer. This could be:
  • When was the first electronic device designed to automate the process of logical calculations was invented?
  • When was the first person who performed mathematical calculations (primarily for code-breaking) invented?
  • When was the first human-made device for performing calculations invented?
  • When was the first concept of using items laying around to calculate something invented?
This is not in any way a simple question. Which is why the questioner should look at the answer to the same question he cross-posted on the computer RD - and get a spanking for cross-posting. --Kainaw (talk) 12:36, 25 July 2006 (UTC)

try computer or perhaps abacus--Downunda 22:49, 24 July 2006 (UTC)

As the article on computer and history of computing hardware explain, what is "the first computer" is a matter of technical definitions, and according to one of the more popular definitions there was a device built in 1941 that was a computer, but nobody actually proved it to be so until 1998. --Robert Merkel 10:40, 26 July 2006 (UTC)

[edit] pronounce death

Where can I find each State's law concerning who can pronounce death?

Thanks.

  • There's a lot of states in the world. It would help if you were more specific. As far as I know pronouncing someone dead can only be done by a physician or trained medical professional, no matter where you are. In some places regular doctors (family doctor/physician) aren't allowed to do this. - Mgm|(talk) 20:31, 24 July 2006 (UTC)
  • If you are referring to the US states, any licensed doctor can pronounce death in every state I'm familiar with. Some states allow RNs, etc. Couldn't find anything comprehensive InvictaHOG 21:22, 24 July 2006 (UTC)
When I used to work as an EMT-B in Massachusetts, I was cleared to pronounce death in cases of lividity, decapitation, and advanced decomposition. It is likely that EMTs in other US states are able to do the same, possibly even in a broader range of situations (MA is known to have very strict rules for EMTs).Tuckerekcut 01:18, 25 July 2006 (UTC)
Those are pretty much the same situations as in NJ (plus "crispy critters": an EMT can pronounce someone who's burnt to a crisp). - Nunh-huh 11:31, 25 July 2006 (UTC)

Wouldn't it take a linguist? DirkvdM 06:21, 25 July 2006 (UTC)

RN = Registered Nurse? EMT = Electro Magnetic Transformer? NJ = New Jersey. MA = Massachusetts.

death can be pronounced by an EMT; emergency medical technician, nurse, doctor based on the following criteria: Decomposition, Decapitation or Transsection if it's in the field. In circumstances involving sudden death in a hospital: The coroner or medical examiner is required to pronounce in order to r/o malpractice, negligence.

So ... for the most part, excepting extreme situations (decapitations and transections for crying out loud) and in some nursing homes in a few states, a doctor must pronounce death. Correct?

[edit] Rotational Cooling?

I remember hearing something about something that could cool a can of soda by spinning it at high speed. Does anyone know how that might work? --Zemylat 20:12, 24 July 2006 (UTC)

  • Probably not. Rotating the can would cause friction (and thus heat) between the can's wall and the moving soda. Besides, even if it's cooled, the soda would burst out of the can as soon as you opened it because the building gas would need to escape, like when you shake it and make a "soda volcano". - Mgm|(talk) 20:29, 24 July 2006 (UTC)
I've seen devices that (claim to) cool a can/bottle of various beverages rapidly by spinning, but they do the spinning in a cooled environment (refrigerated or evaporative). I think the idea is that spinning causes the contents to mix. Instead of waiting for the temerature gradient from the cool outside to reach the center, the warm center material moves to the cool edge. Since a greater difference in temperature causes faster heat exchange, having "hot stuff" touch "cool outside" would cool faster than "hot stuff" touches "warm stuff" touched "cooler stuff" touches "cool outside". DMacks 00:58, 25 July 2006 (UTC)
So I suppose the spinning axis coincides with the cylinder's axis. But why would the warmer fluid move to the outside? Colder material is denser and thus heavier, so that would move to the outside. DirkvdM 06:27, 25 July 2006 (UTC)
I think it's just mixing (maybe there's some wobble or other off-axis motion too), not a mini-centrifuge. DMacks 08:31, 25 July 2006 (UTC)
    • Your probably remembering hearing about something like the Cooper Cooler trade mark. It either chilled or warmed beverages rapidly. To cool, it required active cooling, but provided a more rapid cooling of the contents by introducing convection within the can through spinning (i.e., the spinning didn't cool the contents, but transmited the heat out to a cold exterior more efficiently). Think of it like a convection oven, which cooks faster because the gases circulate. This system cools (or heats) facter because it causes the cans contents to circulate, allowing it to come more rapidly to equilibrium with a cold (or warm) environment around it. Suspect one can still buy these. John Henry 13:20, 25 July 2006 (UTC)

Presumably completely unrelated, there's the vortex tube which cools by means of a rotating gas flow. Femto 14:31, 25 July 2006 (UTC)

[edit] Birds and Trucks

If I weighed a lorry, full of birds sitting on perches, would it weigh the same if all the birds started to hover above their perch?

Ha! A lorry full of lories! Looking at our article on bird flight, it appears that when a bird flies, it exerts a downward force which would probably cancel out the decrease in weight caused by the lifting of the bird. Hyenaste (tell) 22:08, 24 July 2006 (UTC)

yes it would, as above. Xcomradex 22:24, 24 July 2006 (UTC)

Yes, a bird lifts itself by pushing air downward with it's wings. So the bird goes up, the air goes down, and the total weight of both is exactly the same. (The bird is no longer pressing on the perch, but the air it's pushing downward is pressing on the bottom of the lorry.) 71.199.123.24 22:45, 24 July 2006 (UTC)
However, if the truck (sorry, lorry) had no floor, I expect the weight would decrease. --Bmk 23:01, 24 July 2006 (UTC)

If the area that the birds were in was enclosed, then the weight of the truck would be the same (over a time average: every bird, when flapping, is exerting a force greater than it's weight to lift it, then it falls a little bit, so the weight of the truck may fluctuate slightly around the average). However, if the truck was open to the environment, the force from the birds may not be exerted on the truck. Think of the flapping action as pressurizing the air below the birds' wings and rareifying the air above it, which causes the birds to be lifted. The high pressure below the wing is likely to be dissipated before it hits the ground (or truck) in a pressure wave. This is why, when a bird flies over your head above a certain height, you won't feel it.Tuckerekcut 01:14, 25 July 2006 (UTC)

If I had a truck full of Tuckerekcuts ... sorry. :) DirkvdM 06:39, 25 July 2006 (UTC)