Wikipedia:Reference desk/Archives/Science/2008 April 26

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 26

Famciclovir or Acyclovir

Are there any instances in the literature of where short doses of fam/a/ciclcovir induced herpes zoster without prior infection? Also, adverse events such as peripheral neuropathy? Thank you.

75.73.61.30 (talk) 01:55, 26 April 2008 (UTC)Jonathan

Herpes Zoster is caused exclusively by the varicella zoster virus. Infection with VZV is necessary for herpes zoster, and thus neither aciclovir nor its derivatives (or anything, really) can induce this syndrome in an uninfected person. Peripheral neuropathy is not listed, per se as an AE in my dated (2004) PDR for acyclovir, though parasthesia is. Tuckerekcut (talk) 05:04, 26 April 2008 (UTC)

Thank you for answering. Kind of worded it wrong, inducing shingles in previously unshingled participants. I am aware dormant VZV is required. —Preceding unsigned comment added by 71.195.4.244 (talk) 20:12, 26 April 2008 (UTC)

Space and time as emergent phenomena

Kindly point out any references (books, webpages, etc.) on space and time as emergent phenomena. --Masatran (talk) 07:45, 26 April 2008 (UTC)

• Michael Lockwood's book The Labyrinth of Time (ISBN 978-0-19-921726-7) is a survey of the role of time in modern physics.
• Roger Penrose's The Road to Reality contains a good explanation of the links between the arrow of time, thermodynamics and cosmology.
• Julian Barbour's The End of Time: The Next Revolution in Our Understanding of the Universe - a radical and non-mainstream treatment - questions the objective nature of the concept of time. Gandalf61 (talk) 08:32, 26 April 2008 (UTC)

this sounds suspiciously like homework...hell, it's not even a question, jsut a demand for others to do research. GO TO A LIBRARY. If you can get to a college campus, try running a database keyword search, like on JSTOR or something. --Shaggorama (talk) 17:26, 26 April 2008 (UTC)

Please don't bite the questioners. This question is exactly what a reference desk is here for. --Sean 20:13, 26 April 2008 (UTC)

Science Without Numbers by Hartry H. Field or something similar?

I'm looking for Hartry H. Field's Science Without Numbers: A Defence of Nominalism in which, apparently, he describes physics without the use of any mathematics. It looks like it is out of print, and the used copies are rare and expensive. Since I'm in Brazil, a scientific and philosophical desert, this sort of thing is not really available in any place I've checked.

Is there any other way I could possibly get my hands on this book, or at least something similar? I'm very curious about this sort of approach. Thanks! — Kieff | Talk 08:58, 26 April 2008 (UTC)

Sorry, I don't know the book, but I always found Michael Faraday very inspiring. He achieved a high degree of scientific proficiency without much math. (Not that I hate math, just shows that it can be done.) Lisa4edit--71.236.23.111 (talk) 10:12, 26 April 2008 (UTC)

WH Smith in the UK claim to have it available [1] for £24.95 (that's about $50). Cheapest I've seen, the second hand copies seem to be selling for up to $200. I rather suspect though, that if you actually try and purchase the book from Smith's, it might turn out they don't actually have any. Other suggestions: you could try listing it on eBay as an item wanted - never know your luck; you could also ask here WP:Library. SpinningSpark 12:18, 26 April 2008 (UTC)

I don't think Faraday is the same thing by the way. Faraday was not actually against mathematics. Field apparently wants to expunge it from science. SpinningSpark 12:18, 26 April 2008 (UTC)

He's not trying to expunge mathematics as such, but rather mathematical objects (numbers, functions and such). In that book he shows how one can develop physics (he uses Newtonian gravitation as an example) with essentially its usual mathematical structure, but with all talk of dodgy non-existant objects replaced by talk of points in physical space and suchlike. A caveat to the OP: a JSTOR review has 'It should be added that this is not a popular work for the general reader; it is a technical work presupposing familiarity with current efforts to axiomatize physical theories by means of mathematical logic'. Algebraist 12:57, 26 April 2008 (UTC)

This may not help, but it may be worth a try:

Hartry Field, Silver Professor of Philosophy; Professor of Philosophy

Department of Philosophy / 5 Washington Place / New York, NY 10003

Phone: (212) 998-3795 / Fax: (212) 995-4179 / Email: hf18@nyu.edu

He is the author of Science Without Numbers (Blackwell 1980), which won the Lakatos Prize, of Realism, Mathematics and Modality (Blackwell 1989), and of Truth and the Absence of Fact (Oxford 2001). Current interests include objectivity and indeterminacy, a priori knowledge, causation, and the semantic and set-theoretic paradoxes.

Amazon has an offer for $145 plus a review which you may find interesting.

--Cookatoo.ergo.ZooM (talk) 12:49, 26 April 2008 (UTC)

Where in Brazil are you? There's an excellent book store in a lot of the larger cities called 'Livraria Cultura' that has a surprisingly good philosophy section, books in MANY languages, and will also order books for you. [www.mercadolivre.com Mercado Livre], Brazil's response to eBay might giv eyou some options too. Does amazon not deliver to Brazil? --Shaggorama (talk) 17:38, 26 April 2008 (UTC)

According to Worldcat, the university of Sao Paulo has a copy. -Arch dude (talk) 18:38, 26 April 2008 (UTC)

Yeah. Guess that's the best chance I have. I don't live in São Paulo, though, so it'll be tricky. Thanks, tho. — Kieff | Talk 19:02, 26 April 2008 (UTC)

Do they have interlibrary loans in Brazil? --Anon, 00:12 UTC, April 27, 2008.

Amazon do delivers to Brazil. 217.168.1.93 (talk) 12:14, 28 April 2008 (UTC)

I'm not gonna pay that much for a single book I'm merely curious about. — Kieff | Talk 23:04, 28 April 2008 (UTC)

Osmolarity and Cells

This image nicely summarizes the concept in question. Nimur (talk) 14:40, 26 April 2008 (UTC)

Hi, I'm a beginning student to this field, and I just have a quick question. Actually I'm wondering if my understanding of this is correct.

Imagine you have a cell which you place in a solution. If the solution is: Isotonic = no change in cell size
Hypertonic = cells shrink BECAUSE water flows to dilute higher solute concentration outside of cell
Hypotonic = cells expand BECAUSE water flows to dilute higher solute concentration inside of cell

Is this correct? It's just that my textbook says that the solutes diffuse and that the water follows them, but this makes no sense (in the hypertonic solution, wouldn't particles flow into the cell, causing it to expand?). Thanks Guycalledryan (talk) 10:33, 26 April 2008 (UTC)

See our article on tonicity which explains this. The solute will not pass through the cell membrane if the membrane is impermeable to that solute. If the solute cannot be exchanged, the concentration can only then be equalised with an exchange of water. SpinningSpark 12:42, 26 April 2008 (UTC)

The whole idea is that the cell membrane prevents some particles from diffusing. Due to Entropy, particles concentrated in a small area tend to disperse until the area they can inhabit is homogenized. The deal with cells is that they let some particles cross their membrane (like water) but they don't let others pass through. So, if you put a cell in a concentrated solution (HYPERtonic to the cell) water flows OUT of the cell in an attempt to equalize the concentration outside with the concentration inside, and the cell loses volume (i.e. shrinks). Conversely, if you put a cell in a HYPOtonic solution (like pure H20) water flows into the cell in an attempt to dilute the concentration inside the cell.

The general rule is that systems move towards equilibrium, which in this case is isotonicity. When your book says water follows solute, they're saying that in general the water well go where it can find the highest concentration of solute, because the tendency of the system is to dilute the high concentration. --Shaggorama (talk) 17:34, 26 April 2008 (UTC)

FUNDAMENTAL ATTRIBUTION ERROR

Am seeking someone who might have participated in a FAE study and /or an individual(s) whom have done some research in this area and has some stimulating theories as to our assumptions that a person's social and enviornmental influences a persons actions vs the kind of individual they are. How often do we find ourselves sliopping int those tendencies to judge?

And are we the Kind of person because of our social and eviornmental influences? ZLAW —Preceding unsigned comment added by Zeldawong (talk • contribs) 14:58, 26 April 2008 (UTC)

I don't know about research into FAE itself, but I encountered a recent example. First some stats were presented which showed that recent black immigrants from Africa to the US were as healthy as whites in the US, but that after a generation the African-Americans were less healthy than the white Americans. They then concluded that this was due to racism. I concluded that it was possibly due to diet and other factors, but that more research would be needed to be sure. They seemed to have a goal of proving something and interpretted the data accordingly. In any case where somebody "sets out to prove something", the results should be questioned. Instead, they should "set out to find the truth, whatever it is". StuRat (talk) 07:15, 29 April 2008 (UTC)

Check the authors of some of the recent sources cited on our Fundamental attribution error page? DMacks (talk) 07:32, 29 April 2008 (UTC)

StuRat, do you think it could have been regression to the mean? ie, if immigrants are self-selected to be healthier than average. --MagneticFlux (talk) 02:56, 1 May 2008 (UTC)

Are you sure that's an example? Doesn't really sounds like it to me at least from Fundamental attribution error. If anythimn, they're overattributing the situational explanation (since surely racism is a situational explanation, it's not that the authors were suggesting the second generation Africa-Americans were doing something that resulted in racism towards them is it?) while under-estimating the dispositional explaination but even that isn't necessarily true since diet for example can be a situational factor. In any case, the healthy immigrant effect doesn't seem to be limited to blacks [2] & Immigration to the United States (this is also rather interesting [3]) Nil Einne (talk) 11:35, 1 May 2008 (UTC)

Nuclear Testing on GIs

Can anyone direct me toward a good site that has interviews from GIs used as "guinea pigs" in the Nuclear Test sites during the Cold War. I keep coming up with some site about Guinea pig retinas and medical revolutions. :( —Preceding unsigned comment added by EWHS (talk • contribs) 15:56, 26 April 2008 (UTC)

The term for this, oddly enough, is Atomic veteran. (Wow, something WP doesn't have an article on! You can even get a license plate with it on it if you were one, in Alabama.) Here's a website all about interviews with veterans who participated in nuclear tests: Atomic Veterans History Project. --Captain Ref Desk (talk) 17:15, 26 April 2008 (UTC)

Outside of the US, "nuclear test veteran" or "nuclear veteran" seem common Nil Einne (talk) 18:33, 26 April 2008 (UTC)

Will they ever invent a microwave that wont freak out if I accidently leave my fork in there?

I heard this asked by Adam Corolla and it's always bothered me too. I figure there must be a reason why this happens. Bill Nye said it would be like trying to design a mirror that doesn't reflect. But there are mirrors that dont reflect. Two way mirrors. One side you can see thru. Microwave-safe cans still reflect (though,fainter), and there seems to be no problem there. What is the science here that explains why they cant invent an everything safe microwave?--Sunburned Baby (talk) 21:04, 26 April 2008 (UTC)

A lot of people misunderstand two-way mirrors -- what they do is reflect some of the light, and let (most of) the rest of it through. Works the same from either direction (hence the name two-way mirror). The apparent directionality comes from the fact that, when one side is lit much brighter than the other, the intensity of the reflection is so much greater than the intensity of the light coming through from the other side, that the eye can't make out the transmitted signal.

However I don't see why a microwave couldn't be developed that would detect that there's a fork in it, and turn itself off so that you don't get the arcing. But you would have to take the fork out before cooking the food. --Trovatore (talk) 21:33, 26 April 2008 (UTC)

See Two-way mirror. hydnjo talk 23:48, 26 April 2008 (UTC)

Microwaves are electromagnetic radiation, so they push around electric charges. A water molecule is like a little electric dipole (the oxygen side is negative and the hydrogen side is positive), so when microwaves hit water molecules they move around faster, and this motion of molecules is manifested as heat. Metals are conductors of electricity, which means electric charges can flow through them. When microwaves hit a metal, electric currents flow across the surface of the metal. (It's only the surface and not the whole volume of the metal because the surface currents cancel out the electric field of the microwaves; the waves only penetrate a microscopic distance into the metal.) The problem with putting a fork in the microwave is not simply that it's made of metal, the problem is that it has sharp points. As the electric currents flow across the sharp points, the charge builds up and creates a large electric field; much larger than the field of the microwaves themselves. If the field gets too high (3 kV/mm), the air undergoes electrical breakdown and turns into a plasma, which conducts electricity and makes the microwave oven "freak out".

I actually leave spoons in the microwave all the time, because I understand the physics and know that it's safe. As I said, it's not the metal itself, it's the sharp points act as focal points for the electric field.

So to answer your question, it's impossible to invent a microwave oven that doesn't do this, because it's just the way electromagnetism works. If you have strong electromagnetic waves hitting a sharp metal point, there's going to be a large field there no matter what. —Keenan Pepper 21:41, 26 April 2008 (UTC)

Understanding these focal points, are there ways to manipulate the arrangement of sharp points so as to prove different mechanics of electrics and electromagnetism? Say, for instance, to put in some forks arranged in a particular formation, along with the traditional ferromagnetic materials organized around a magnet of some kind? 81.93.102.185 (talk) 21:51, 26 April 2008 (UTC)

It would be far simpler to just use plastic forks. -- HiEv 02:59, 27 April 2008 (UTC)

I think the solution to this problem would be to create some sort of metal-polymer alloy that is metallic enough to stand up to dishwashers and years of use, but plastic enough not to create sparks in a microwave. Vranak (talk) 22:03, 26 April 2008 (UTC)

Or maybe the microwave could rearrange its field inside to makd a null at the pointy bits on the fork, so that no sparks are generated, but enough microwaves still heat up the food. You are unlikely to see such a machine though as it would cost more to make. Graeme Bartlett (talk) 22:13, 26 April 2008 (UTC)

You may not be able to leave a fork in the microwave, but how about making one along with cooking your dinner? (See http://www.nature.com/nature/journal/v399/n6737/full/399668a0.html or http://www.sciencedaily.com/releases/1999/06/990622055733.htm) It would make your TV dinner rather costly and wasteful, though.--Lisa4edit (talk) 02:14, 27 April 2008 (UTC)

there must be more to the phenomenon then "points:" this only explains fork arcing. what about aluminum foil and cd's? And split grapes? microwaves do some weird stuff, consult youtube. --Shaggorama (talk) 08:30, 28 April 2008 (UTC)

Aluminum foil and cds are to thin to handle the currents that microwaves put through them. The same process that cooks the food is what causes the microwave to freak out with metal objects. They can't be made to do one and not the other, that's a bit like saying you want your mirror to reflect the room you're in but not you, it just doesn't work that way. Mad031683 (talk) 15:02, 28 April 2008 (UTC)

Do microwaves put current thro conductors? Or do they just induce a voltage> —Preceding unsigned comment added by 79.76.217.249 (talk) 00:42, 29 April 2008 (UTC)

Moment of Inertia

I was given a moment of inertia problem that went somewhat at follows. We are considering a trebuchet, with a 60kg mass .14meters from the axel, and a .12kg rock 2.86meters from the axel. We are then asked to find the max speed of the rock. The question itself I answered, getting something close to 25m/s, and I did it using conservation of energy. But I have a few questions. First, is there another method of answering the question? Second, when doing conservation of energy, would the potential energy be mgh? Finally, if we wanted to determine whether the big or the small object fell, would we see which mass times distance was greater, or would we calculate which moment of inertia was greater, and why? —Preceding unsigned comment added by 76.69.240.138 (talk) 21:30, 26 April 2008 (UTC)

I remembered a TV program a few years back (History channel I think). They built a trebuchet and found that the wheels were not just for rolling the siege engine into position, but also figured into the equations of firing the missle. I tried to find a link for you, but I only found s.o. else who had seen the program mentioning it in a physics forum. Our page says the fact is disputed among scientist, but unfortunately doesn't have a reference link. --Lisa4edit (talk) 03:02, 27 April 2008 (UTC)

I saw that program, too. I thought the conclusion was that the wheels are needed for the recoil, to prevent forces from building up in the frame which would otherwise shake it apart. StuRat (talk) 06:00, 27 April 2008 (UTC)

I think I know what program you're talking about. I remember seeing it on Discovery Channel. Two competing groups built an English (fixed weight) and a French (hanging weight) trebuchet. It was pretty cool, but I couldn't find its name last time I checked. — Kieff | Talk 11:50, 27 April 2008 (UTC)

Conservation of energy is a good approach. Potential energy lost by counterweight - which is mgh - is equal to potential energy gained by rock and arm plus kinetic energy gained by rock, arm and counterweight. You could work out the net torque on the trebuchet arm at each point in its motion, then divide by the moment of inertia of the arm, rock and counterweight to find the angular acceleration of the system, then integrate this to work out the angular velocity and hence linear velocity of the rock at point of release - but you should get the same answer.

Calculating the net torque (which is how you know that the counterweight is heavy enough to move arm and rock) just involves multiplying weight x distance from pivot for rock, arm and counterweight - if the arm is a uniform beam then it can be treated as a point weight at its geometric centre. Don't confuse torque with momement of intertia - that is like confusing force and mass.

Note that both approaches neglect energy lost due to friction, air resistance, deformation of the terbuchet frame, and linear motion of the trebuchet if it is on wheels - so in real life your trebuchet performance will not be as good as your calculation suggests. You are also assuming that the trebuchet is a simple lever. More sophisticated trebuchets - see right - had the rock in a sling and the counterweight in a pivoted cage, so they were not just a simple lever. The mathematical anaylsis of a sling trebuchet is much more difficult, because of the complications introduced by the rotations of rock and counterweight about the additional pivots. Gandalf61 (talk) 08:32, 27 April 2008 (UTC)