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February 28

Chemistry: vapor and ideal gas

Hi! I'm wondering why once you have a vapor which near condensation point, why it doesn't behave like an ideal gas. I recently learned about what an ideal gas is. But I'm just wondering why when it liquifies it doesn't behave like an ideal gas (like PV = nRT). Thanks! —Preceding unsigned comment added by 69.4.130.179 (talk) 08:32, 28 February 2008 (UTC)[reply]

The ideal gas model assumes that the gas molecules don't interact with each other. In a real gas close to its condensation point the molecules interact strongly. --71.146.162.148 (talk) 08:52, 28 February 2008 (UTC)[reply]

The van der Waals equation is useful for describing a vapor near its condensation point. It takes two parameters, representing the volume of the molecules (which would be zero for an ideal gas) and the attraction between molecules. Icek (talk) 12:23, 28 February 2008 (UTC)[reply]

algae

What is a good surface for algae (like from my fresh water fish tank) to grow on and what things could i do to help algae to grow faster.

thanks —Preceding unsigned comment added by 76.236.187.176 (talk) 01:21, 28 February 2008 (UTC)[reply]

are your fish algae eaters, because usually the growth is undesirable. Wisdom89 _{(_T / ^C)} 02:15, 28 February 2008 (UTC)[reply]

Sunlight is of course needed for algae. I would suspect rough surfaces like rocks would help, also you need algae! There needs to be some algae present to start with. I think if you go to a pond/lake/rive etc and get some rocks/gravel and put that in the tank it would help growth a lot...--Shniken1 (talk) 03:15, 28 February 2008 (UTC)[reply]

Alga will grow on virtually any solid surface, witness many glass aquariums. More light and more nitrogenous matter in the water and you'll be up to your knees in no time. Richard Avery (talk) 08:42, 28 February 2008 (UTC)[reply]

It will grow almost anywhere, if you have tropical fish with warm water especially. Such a pain to remove it. (slightly off topic - Does anyone know of a product that could remove it without killing the fish?) TheGreatZorko (talk) 11:47, 28 February 2008 (UTC)[reply]

two methods - remove the nutrients, or use an algicide - both product exist. search for "algae control aquarium" or similar —Preceding unsigned comment added by 87.102.84.112 (talk) 11:55, 28 February 2008 (UTC)[reply]

There is a biological variation - add an algae eating fish/snail/shrimp + add plants to compete with the algae for nutrients NOTE the plants must not be edible by the fish/animals as this will just compound the problem..87.102.84.112 (talk) 12:32, 28 February 2008 (UTC)[reply]

Duckweed (or similar) works - it grows fast on the surface, removes nutrients, and cuts out light to below the water surface. There probably are many other ways..87.102.84.112 (talk) 12:32, 28 February 2008 (UTC)[reply]

Commercially available magnetic glass scrubbers are pretty effective for the tank walls. Nimur (talk) 18:22, 28 February 2008 (UTC)[reply]

Hi. To grow algae maybe cause global warming and then add water. Thanks. ~A H 1^(TCU) 22:45, 28 February 2008 (UTC)[reply]

In the past I have periodically used an ion exchange resin pouch to remove nitrate. Use a nitrate test kit to quantify the quality of nitrate in the water. William Avery (talk) 13:04, 4 March 2008 (UTC)[reply]

decibel levels of human screaming

What is the range of decibels when human beings scream? This is regarding the section stub at the article Screaming, is there any data on pitch?Cholga^talK! 04:14, 28 February 2008 (UTC)[reply]

Sharapova? at 101.2 decibels [1] Julia Rossi (talk) 07:53, 28 February 2008 (UTC)[reply]

Alan Myatt - 112.8 DECIBELS. Clarityfiend (talk) —Preceding comment was added at 09:13, 28 February 2008 (UTC)[reply]

My mother-in-law, when she first met our kitchen mouse, surely has to break all records (and a few window panes)! Sandman30s (talk) 12:55, 28 February 2008 (UTC)[reply]

Robert Graves wrote a short novel called The Shout, which puts all other claims in the shade. The premise was that there was a man who could kill people just by the volume of his shout. -- JackofOz (talk) 22:27, 28 February 2008 (UTC)[reply]

In Günter Grass's book (Nobel price in litterature) die Blechtrommel the hero manage to break all the windows of Danzig by screaming. —Preceding unsigned comment added by 216.195.17.16 (talk) 03:19, 29 February 2008 (UTC)[reply]

Hi. A few years ago I saw on TV (forgot what show it is) about a Japanese contest or something like that, where contestants scream as loud as possible. I think one pan recorded a very high figure, not sure what it was exactly, but probably between 120 - 160 decibels. Also when I scream or yell it frequently reaches (my estimate) maybe 90 decibels at 2 metre distance :P . Hope this helps. Thanks. ~A H 1^(TCU) 22:40, 28 February 2008 (UTC)[reply]

A quick googling finds some poor kids' mum screaming at 129 dB. Doesn't look terribly scientific though. Weregerbil (talk) 10:02, 29 February 2008 (UTC)[reply]

determination of urea

Give the report on how urea can be determined quatitatively using the diacetyl monoxime method —Preceding unsigned comment added by 82.206.143.13 (talk) 12:57, 28 February 2008 (UTC)[reply]

Hi. This question sounds very much as if it is a homework question - something which the reference desk will not answer. If you try it and tell us where you get stuck, then we can help. -mattbuck (Talk) 13:25, 28 February 2008 (UTC)[reply]

Search for "diacetyl monoxime method" using Wikipedia's search box and you'll get some useful results. --Bowlhover (talk) 13:29, 28 February 2008 (UTC)[reply]

Osteo-Odonto-Keratoprosthesis

Osteo-Odonto-Keratoprosthesis ???? any ideas —Preceding unsigned comment added by 12.171.224.124 (talk) 15:32, 28 February 2008 (UTC)[reply]

A keratoprosthesis is an artificial cornea. Osteo = bone; odonto = tooth. I can't imagine why one would make a bone-tooth-cornea-prosthesis, except as conceptual art. - Nunh-huh 17:12, 28 February 2008 (UTC)[reply]

After a bit of research, it appears that it is a type of prosthetic ~~lens~~ cornea which is surrounded by a thin layer of the patient's own bone (specifically, a tooth). This is done in cases where graft rejection has previously occurred, since having your own bone tissue surrounding the prosthetic ~~lens~~ cornea reduces its antigenicity. If you're looking at getting this procedure done, you should probably consult a physician/surgeon: despite it being a 40 year old concept, it's still considered "experimental". Here is a recent (2001) review by the UK NHS: [2]. (EhJJ)^TALK 17:28, 28 February 2008 (UTC)[reply]

And a news story about its use [3] Bazza (talk) 13:08, 29 February 2008 (UTC)[reply]

Mutation notation

From some article "mutant constructs encoding the I81_V85del, M266fsX4 and R325X SPRED1 proteins" - I understand the last notation - amino acid R replaced by X at position 325 but I'm less certain about the first two. A little help? —Preceding unsigned comment added by 145.29.21.165 (talk) 15:38, 28 February 2008 (UTC)[reply]

I may be mistaken, but my educated guess is "I81_V85del" is a deletion from I81 to V85. "M266fsX4" has something to do with a frameshift. (EhJJ)^TALK 16:58, 28 February 2008 (UTC)[reply]

I81_V85del = a deletion (del) from residue 81 (isoleucine) to 85 (valine)

M266fsX4 = a frame shifting change with methionine in position 266 as the first affected amino acid, with the new reading frame ending in a stop codon at position 4.

R325X = mutation resulting in a change from arginine to an undetermined amino acid at position 325.

The discussion of mutation notation here may be helpful to you. - Nunh-huh 17:07, 28 February 2008 (UTC)[reply]

(ec) I assume the article is this one, which contains some expanded information: We identified seven different mutations in SPRED1: three nonsense mutations (leading to R64X, K322X and R325X), two frameshift mutations (leading to M266fsX4 and S383fsX21), one missense mutation (leading to S149N) and one in-frame deletion (leading to I81_V85del). Recommended nomenclature for mutations can be looked up here. I81_V85del does indeed mean that amino acids 81 (which was an isoleucine, I) through 85 (which was a valine, V) have been deleted. M266fsX4 means a frame shift mutation that scrambles the meaning of amino acids 266 (which was a methionine, M) onwards, and creating a stop codon 4 amino acids later; the protein product thus has 265 correct amino acids followed by 4 nonsense amino acids. The notation R325X is called a nonsense mutation, but effectively means that amino acid 325 (which was an arginine, R) has been replaced by a stop codon, which causes the protein product to be truncated at this position. (Note that this is different from Nunh-huh's answer above.) --mglg_(talk) 17:19, 28 February 2008 (UTC)[reply]

Misunderstood

How can it possibly be true that there is no such insect as a spider??? —Preceding unsigned comment added by 79.122.82.130 (talk) 16:41, 28 February 2008 (UTC)[reply]

Spiders are arachnids (Class Arachnida), not insects (Class Insecta). They both belong, however, to the Phylum Arthropoda--the joint-legged animals. Insects have three body parts and six legs, while spiders have two body parts and eight legs.--Eriastrum (talk) 16:47, 28 February 2008 (UTC)[reply]

Looking for a name of

an insect (or not) that looks like a bunch of white fibers or white hair. Size is about 1 or 2 cm. —Preceding unsigned comment added by 89.0.140.163 (talk) 14:24, 28 February 2008 (UTC)[reply]

Mealybug?--Eriastrum (talk) 16:43, 28 February 2008 (UTC)[reply]

The larvae (caterpillars) of some moths are covered with white hairs. For example, the flannel moth caterpiller [4], which has stinging hairs--so watch out! Some of the wooly bear caterpillars have white hairs as well. These are in the families Megalopygidae and Arctiidae.--Eriastrum (talk) 19:21, 28 February 2008 (UTC)[reply]

No. Sorry. Look at the picture. —Preceding unsigned comment added by 89.0.52.106 (talk) 12:28, 29 February 2008 (UTC)[reply]

Looking for a name of a creature

I'm looking for a name of an insect / a spider or any other from of life that looks like a bunch of white fibers. It's size is about 1-2 cm. It looks a very primitive form of life So I don't think it is a spider or an insect. It's structure resembles a spider. When you put something next to it, it will jump on it. I saw two of it on my room today.—Preceding unsigned comment added by 89.0.140.163 (talk • contribs)

if this is NOT your questino why would you change the title and add your question instead of creating a new one —Preceding unsigned comment added by 79.122.82.130 (talk) 19:56, 28 February 2008 (UTC)[reply]

Done. What is it?—Preceding unsigned comment added by 89.0.140.163 (talk • contribs)

Do you have any pet birds? My parrot produces a lot of little down feathers (as seen on right) that look like that and often stick to things due to their static charge.(EhJJ)^TALK 22:10, 28 February 2008 (UTC)[reply]

Are you sure it's a spider? I've noticed some very light white spiderlike fluff sometimes on my kacket or outside. Could be perhaps some type of seed or jacket feather. It will float up in the air if I put it over the rectangular furnace home heating vent. It flies with a small wave of air. However if it is a spider and does move with absoludely no air currents, then please do not touch it or it may bite. However if it has more than eight legs it's most likely not a spider. Hope this helps. Thanks. ~A H 1^(TCU) 22:33, 28 February 2008 (UTC)[reply]

It doesn't look like a feather and I have no birds at home. I'm pretty sure it's not a spider. Maybe it's a seed. But it reacts to motions... —Preceding unsigned comment added by 89.0.52.106 (talk) 12:24, 29 February 2008 (UTC)[reply]

Hmmm you live in Israel so I guess you don't use a feather/down duvet either? I had something similar, I was trying to work out what the heck it was, it seemed to be living based on the way it was moving but eventually I realised it was probably just a piece of down or feather from my duvet that was moving in the wind Nil Einne (talk) 12:52, 29 February 2008 (UTC)[reply]

Just in case, have a look at the jumping spider link, [[5]] they can be very small. Richard Avery (talk) 18:57, 29 February 2008 (UTC)[reply]

Maths\Geometry\Thaumaturgic triangle

What is understood under a Thaumaturgic triangle? Is is more a theosophy and/or a Math issue? example

Thanks and greez, 88.64.94.148 (talk) 17:11, 28 February 2008 (UTC)[reply]

Yes, it's mysticism, not math. The thaumaturgic triangle is a triangle inscribed inside a circle. It is said by some modern-day witches to be used in demon-summoning ceremonies, and is given many innovative interpretations.. - Nunh-huh 17:17, 28 February 2008 (UTC)[reply]

We have articles on thaumaturgy and triangles. Historically, a lot of believers in the occult have placed high significance on geometric shapes for reasons that never really made much sense to me. Nimur (talk) 18:18, 28 February 2008 (UTC)[reply]

Eggs

Oh, and one final tip that most people don't know; if you want silky smooth scrambled eggs, that are suprememly tender, after mixing your eggs with whatever you are going to mix them with, pour them trough a fine-mesh wire strainer to remove the little protien strings found in the egg. What exactly are those filthy protein strings? --Seans Potato Business 21:18, 28 February 2008 (UTC)[reply]

They are probably referring to the chalaza -- 128.104.112.47 (talk) 22:41, 28 February 2008 (UTC)[reply]

Identify this bird?

Hi. Sometimes I notice this bird's song, especially in the warmer months. What brought me to attention was that today I noticed this bird singing for a few minutes this morning (at -20C temperatures!). Its song is a rather high-pitched and singsong "wree-oou" or sometimes "wroou-WHEE" and occasionally chirping. In sping and summer I've noticed these birds singing to each other. I know this bird only by song but I think I might have seen it but I'm not sure. I live in southern Ontario. Any ideas what bird this might be? Thanks. ~A H 1^(TCU) 22:16, 28 February 2008 (UTC)[reply]

While my crap work internet wont let me look at any of my birding sites I do know that the boreal forest areas of Ontario see about 300 different species of bird throughout the year. So without a bit more info it is going to be a tough call. Do you happen to remember where the bird likes to spend its time (trees, bushes, grassy areas)? That would help to narrow it down :) 161.222.160.8 (talk) 23:08, 28 February 2008 (UTC)[reply]

(ec) Hi right back atcha. You aren't giving us much to go on, I guess you know. Is the phrase repeated? How many times? Is it loud? Does it seem to be coming from up in a tree or down on the ground or where? Can you decribe the vocal quality—flute-like, raspy, hoarse, liquid, wheezy, etc.? Our article Bird vocalization is worth a look, especially "Identification and systematics", and there are some common bird calls free at Cornell. --Milkbreath (talk) 23:10, 28 February 2008 (UTC)[reply]

Hi. I'm guessing it maybe in tree because I said so (and where else could it go, other than maybe the metal-cold power lines or perhaps a bush/hedge on a snow-covered cold winter's morning)? I live in an urban area but there are lots of bushes and forests and fields nearby. I've seen hundreds of sparrows in the trees and feeding on seed in and near trees, bushes, and rooftops in winter, but if I remember correctly the sparrows I see usually chirp and have markings on their chest but I don't really think this is a sparrow. Its song sounds very singsong, and sort of flutelike I guess. With the wree-oou the first note is higher in the second, and I think the second note is usually longer than the first. I'm guessing the two notes together last maybe 1-2 seconds. It repeats on a predictable basis until it stops and/or flies away, maybe once every 5-15 seconds. I'm not sure but I think I remember when they sing to each other it sounds like: "Wroou-wree? Wree-woou! ... whroou-wree? Wree-woou!" I'm thinking from maybe 10-80 m away it is maybe 20-50 decibels. I heard this today shortly after sunrise, and it was a clear, bright, sunny day, but very cold (wind chill -27C!). I think on warmer days I've heard it maybe a few hours after sunrise on mainly sunny mornings. If you're wondering which one of the 5 great lakes I live nearest to when I heard this, probably Lake Ontario. I heard it this morning around 7am (local time). I tried looking through a bird identification book for eastern North America but I'm still not sure what it is. Any ideas? Thanks. ~A H 1^(TCU) 23:36, 28 February 2008 (UTC)[reply]

Thanks. I'm looking at the Black-capped Chickadee. The song is in the article under "Vocalization". It's two notes, first note higher, monotonously repeated, clear, and loud. If that ain't it, we can try again. --Milkbreath (talk) 00:00, 29 February 2008 (UTC)[reply]

Hi. I can't really download the song right now but the descriptions seem just about right. So I think this might be the one I'm looking for. Nayway I'm also finding http://identify.whatbird.com quite helpful and faster than any book (but it appears to be on the blacklist page for some reason) although it wouldn't be good for identifying it if I only know its song. Thanks. ~A H 1^(TCU) 01:24, 29 February 2008 (UTC)[reply]

Hi. This morning I heard the bird again at around 7 in the morning. Again, it was mainly clear except for some cirrostratus clouds near where the sun rose, blocking out the sun for a minute. I think the call was close to one second long. I also heard a crow-like call, as if they were calling to each other, one higher and one lower. One had 5 caws and the other one 4, I don't remember which was which. I also heard a similar call to the one in interest, except it sounds like the first note only, but cut short. I may have also heard some brief chirping after that. The 9 caws in total were about 3 seconds long. One similarity about this time to last time was that it was at 7 in the morning, the day before a winter storm. This time it was -10C outside. Thanks. ~A H 1^(TCU) 16:34, 2 March 2008 (UTC)[reply]

It sounds like you're hearing several different species of bird. The only thing that goes caw is a crow. A one-note song is a rarity, and makes me think blue jay messing around. Neither of those chirps. Birds of different species do not respond to each other's songs vocally. Of course, it could be a mockingbird making all those noises, but it seems a tad cold for him, and they like to be seen, flashing their wings on the ground and perching in the open to sing. Have you listened to any of the bird noises I pointed to? They would be good for comparison, like "sounds a little like this one, but weaker", or whatever. --Milkbreath (talk) 20:56, 2 March 2008 (UTC)[reply]

Jays are also mimics—not quite as good as mockingbirds, but they can make all sorts of odd noises. -- Coneslayer (talk) 16:33, 3 March 2008 (UTC)[reply]

Hi. I listened to the song here, and I think that sounds exactly like the one I heard, but I thought that the one I heard had perhaps a slightly longer interval between the calls, and that it hurt my head less than the song I played. Only the first 10 seconds or so (of the learnbirdsongs website, not the one on Wikipedia which I couldn't download) actually sounded like what I heard, although I might have heard the latter sounds in summer. Thanks. ~A H 1^(TCU) 22:32, 3 March 2008 (UTC)[reply]

February 29

Matrix algebra

Someone discovered that matrix algebra seemed to describe accurately some fundamental law of nature. Who and what was it? —Preceding unsigned comment added by 79.76.173.143 (talk) 02:07, 29 February 2008 (UTC)[reply]

If you look at List of matrices#Matrices used in science and engineering, there are quite a few listed. Possibly what you're thinking of is the Hamiltonian matrix, which is used in quantum mechanics. Confusing Manifestation(Say hi!) 03:35, 29 February 2008 (UTC)[reply]

Or, the matrix formulation of quantum mechanics? This is a common reference name to Heisenberg's approach. Nimur (talk) 15:37, 29 February 2008 (UTC)[reply]

Water

I got flamed by some noobs on reddit for saying the earth is mostly not water. I found the surface area of the water, but not the total volume. What is it? —Preceding unsigned comment added by 138.87.180.89 (talk) 08:08, 29 February 2008 (UTC)[reply]

This page gives some estimates of the amount of water in various forms. Rough calculation: if R is the radius of the earth and h the average depth of surface water then the volume of the earth is

4\pi R^{3}/3

and the volume of water

4\pi r^{2}h

, giving a ratio of

3h/R

. R is about 6370 km, and let's guess h = 3km, which gives 0.00141, or about 0.14%. The numbers from the USGS site give about the same answer: 0.12%. Either way, you win ;) AndrewWTaylor (talk) 08:37, 29 February 2008 (UTC)[reply]

The Earth can only be mostly water if it is flat. 206.252.74.48 (talk) 13:44, 29 February 2008 (UTC)[reply]

"The earth is mostly ___" probably is loose language to mean "most of the earth's mass is made of ___". If this more precise language is used, most of the earth's mass is iron. Alternatively, most of the earth's volume is silicon dioxide. See Earth for more details! Nimur (talk) 15:39, 29 February 2008 (UTC)[reply]

This has been covered in QI as well. Most people know that approx. 75% of the earth is covered in water, but when you're going to look at volume and weight, only a tiny part of the earth is water because there is a lot more beneath the earth's crust. You (the questioner) were totally in what you said. - 87.211.75.45 (talk) 15:49, 1 March 2008 (UTC)[reply]

Oh NO 87.211.75.45, that answer was just too obvious. I'm afraid it's minus ten points for you! -mattbuck (Talk) 23:27, 1 March 2008 (UTC)[reply]

Concentration

Could someone please answer this question without using words like molarity and molality? If you have 50ml ethanol in cup A and 50ml ethanol + 50ml water in cup B, does A necessarily have a higher concentration of ethanol? Zain Ebrahim (talk) 13:05, 29 February 2008 (UTC)[reply]

Assuming you mean pure ethanol in each case then yes Nil Einne (talk) 13:07, 29 February 2008 (UTC)[reply]

I did and thanks! Zain Ebrahim (talk) 13:09, 29 February 2008 (UTC)[reply]

For further detail, Cup B is approximately half as concentrated. It is not exactly half as concentrated, because when mixing 50 mL of ethanol with 50 mL of water, the resulting solution has a volume less than 100 mL. (It would be about 95.6 mL, see Ethanol#Physical properties for some details). For reasons such as this, chemists use molality (e.g., amount of ethanol per mass of water), and molarity (e.g., amount of ethanol per total amount of mixture) to be very precise when discussing concentration. Hopefully if you are studying chemistry, you will become familiar with this terminology, because it exists to reduce confusion (not to increase it) - and when weird stuff happens, like "50 mL + 50 mL = 96.5 mL" you want to be sure your descriptions are as accurate as possible. Nimur (talk) 15:47, 29 February 2008 (UTC)[reply]

BTW, to preface my original response, it doesn't actually matter if the ethanol was pure provided you used the same original concentration of ethanol in both cases. If you start to talk about solutions of different original concentrations then using molarity makes it much easier to come up with an accurate answer Nil Einne (talk) 04:56, 1 March 2008 (UTC)[reply]

Light photons and other EM radiation

I heard light and other Electro magnetic radiation travels in waves. But light is composed of photons. So do these photons move in waves, rather than in straight lines? 64.236.121.129 (talk) 14:34, 29 February 2008 (UTC)[reply]

see Wave–particle duality, I think. -- Aeluwas (talk) 14:47, 29 February 2008 (UTC)[reply]

So the photons do indeed move in waves then? 64.236.121.129 (talk) 15:37, 29 February 2008 (UTC)[reply]

A common phrase is that light travels like a wave, and collides like a particle. Depending on the application, the mathematics of the situation dictate whether you can call it a wave. Nimur (talk) 15:49, 29 February 2008 (UTC)[reply]

There's no easy answer to this. Photons sometimes act like what we would call a wave, sometimes like what we would call a particle. Bohr famously called this complementarity. A photon is not a wave or a particle; it is a photon, something different, something we don't have any first-hand experience with at a macroscopic scale. We can abstract it as a wave or particle (macroscopic metaphors) depending on how we measure or observe it, but each time we are only viewing part of its true existence. Deep stuff, dude. --98.217.18.109 (talk) 15:54, 29 February 2008 (UTC)[reply]

Yea I was about to say, I still have no idea whether photons travel in a wave or not. So we don't really know is what you are saying? 64.236.121.129 (talk) 16:52, 29 February 2008 (UTC)[reply]

Well, the thing that is very much the wrong idea is the notion that photons are tiny little billiard balls, moving in a wavy line. There probably is no easy answer that says what photons are. As photon says, they have properties of waves and particles. The article Wave–particle duality linked to above may not make it clear, but that's because photons aren't like any objects we're used to. Friday (talk) 17:01, 29 February 2008 (UTC)[reply]

I wouldn't say it's so much that "we don't know" (though to be sure, there's plenty left to decipher in this area) so much as we do know that statements like "a photon is a wave" or "a photon is not a wave" are too simplistic and thus incorrect. — Lomn 17:54, 29 February 2008 (UTC)[reply]

Electromagnetic waves don't move side to side as they propagate. Pictures like this are very misleading in that respect. A "photon" is basically a certain amount of energy in the form of light. Having 3 photons is like having three liters of water—you can't point and say "here's one, there's another", you just have a total of three. In quantum theory the number of photons usually has to be an integer, so if an atom absorbs some light, it has to absorb a whole photon at once, not just a little bit. It's in that sense that photons behave like particles. Another thing to keep in mind is that even in classical electromagnetism, where there are only waves and no particles, light still moves in straight lines for many purposes. So, photons move in straight lines for many purposes; photons move in waves (they are waves); and photons don't wave side to side as they move. —Preceding unsigned comment added by BenRG (talk • contribs) 18:38, 29 February 2008 (UTC)[reply]

Question about scientific theory vs. law

Is it true that a scientific theory never becomes a scientific law? In other words, they have completely different definitions.

Let me give an example. If we were to talk about evolution being a theory. If I could live forever, and travel back in time, and I go back to the origin of life on Earth and I document, and record evolution occurring right before my eyes over the course of billions of years all the way up to today. Then today in 2008, I go up to a scientist and I show him all of my video tape displaying evolution happening right before his eyes (time lapsed), and all the other evidence I have. The he says wow this is incredible, and he adds all this evidence to the existing theory of evolution. Even with all this new evidence, the videotapes showing evolution occuring in real time, etc, the theory of evolution still remains a theory. Right? Even though I saw it with my own eyes, and videotaped it? 64.236.121.129 (talk) 15:26, 29 February 2008 (UTC)[reply]

The distinction is mainly historical. See law of gravity and theory of gravity - they're the same thing. A few major historic theories have been frequently called "laws", but there's no real difference in meaning. You can gather more and more evidence that supports a particular theory, and it's still a theory. It's just becoming better supported. See scientific theory. Friday (talk) 15:31, 29 February 2008 (UTC)[reply]

Well I'm not sure about that. I heard that Scientific Law means a description of observed phenomena, while Scientific Theory means an explaination of observed phenomena. 64.236.121.129 (talk) 15:38, 29 February 2008 (UTC)[reply]

Btw, about the gravity thing. Those two things simply redirect to the same article (it's a wiki thing, the article covers both). They aren't the same thing if I'm not mistaken. The law of gravity describes the properties of observed gravity on our planet, while the theory of gravity is Newton's attempt at explaining why gravity exists, but has since been replaced by Einstien's theory of general relativity. 64.236.121.129 (talk) 15:41, 29 February 2008 (UTC)[reply]

(ec) We do have scientific law which seems to make a bit of a distinction along those lines. In my experience, the terms are used mostly interchangably. But it may depend on what field you're working in. More to the specific point of the original question- the scientific method does not include the idea that we make an observation and then say "Look, I proved the theory! Now it's not a theory anymore!" This notion sounds like it comes from the often-exploited public misunderstanding of what a scientific theory is. In order to be a scientific theory, it must already be supported by lots of evidence. You don't prove things in science. Friday (talk) 15:46, 29 February 2008 (UTC)[reply]

There is also an article on scientific law. Also, one on evolution as theory and fact, which makes the comparison between the fact and theory of gravity and the fact and theory of evolution. Evolution, as the article discusses, is both fact and theory. It is a scientific fact (no matter how much people deny it) that species evolve over time. This is the fact of evolution. How they evolve is what is up for debate and is considered theory. -- MacAddct  1984 ^{(talk  contribs)} 15:44, 29 February 2008 (UTC)[reply]

Yes, but this can be misleading if you're not careful. In science, a theory is much bigger and more important than a "fact". A "fact" is just an observation. A theory explains it. Contrast this to common usage, where we think of a "fact" as something that's true, and a "theory" is just speculation. Science does not deal with truth. Friday (talk) 15:50, 29 February 2008 (UTC)[reply]

Yeah, I didn't mean to give off that impression. Facts are boring, theories are the interesting bit, which, despite their stigmatized name, can be backed up with an immense amount of data (a.k.a. facts). -- MacAddct  1984 ^{(talk  contribs)} 15:58, 29 February 2008 (UTC)[reply]

Well wait a minute, of course Science deals with truth. I agree you can't prove things in science, but it certainly deals with truth. 64.236.121.129 (talk) 15:53, 29 February 2008 (UTC)[reply]

Science deals with falsehood better than it does truth. It is very easy to prove something wrong. It is very hard to prove something true. Ergo Popper's famous falsifiability constraint. --98.217.18.109 (talk) 15:59, 29 February 2008 (UTC)[reply]

In my opinion, the distinction is purely philosophical. Man describes some thing he observes. He calls it a Law, which is a bold statement about Man's flawless understanding (and control) of Causality and consistency of the Universe. Alternatively, humans observe some thing and timidly postulate a theory which seems internally valid and consistent, and proposes it to the scientific community, who tirelessly debate it and use large words to make it inaccessible to the general public, antagonizing religious zealots, until everyone is so bored with it that they stop caring. It's a sort of spectrum of pomposity, ranging from:

"So pompous as to presume that we can dictate the law of the universe" ("Law")...
...to "well, we've described the experiment in the simplest possible way" (good science),
...to "it's so complicated that only the super-intelligent elite can understand ("Theory"). In all cases, they've done the same thing, it's just how loudly they proclaim their greatness.

But, this is simply my opinion. Nimur (talk) 16:02, 29 February 2008 (UTC)[reply]

I think things in science are often often prefaced with statements like, "to the best of our current understanding". The same of can not be said of religion. -- MacAddct  1984 ^{(talk  contribs)} 16:12, 29 February 2008 (UTC)[reply]

In the world of science there is such a thing as dustbowl empiricism, in which the scientist simply collects facts. Having been an editorial consultant for a scientific journal, I claim that a paper which merely presents a set of facts or observations is less likely to get published than one which has facts/observations used to test a theoretical construct of interest. Dustbowl empiricism can go to the extent of a paper I once read called "The number of feathers in the laughing dove" which literally enumnerated facts such as "Laughing dove number one had 17,321 feathers. Laughing dove number 2 had 16,898 feathers, etc through a number of birds." (Makes one want to ask "So, bird, who's laughing now???") This can be the engineering side of scientific investigation, in which the raw data is collected by patient and careful plodders, which other insightful thinkers use to reach new heights of theory, leading to new testable predictions. Edison (talk) 16:17, 29 February 2008 (UTC)[reply]

The history of science contains many instances in which a law, based on the organisation of observations to reveal consistent patterns, is superseded by a theory, which gives a deeper causal explanation of the law. Four examples:

Kepler's laws of planetary motion were explained by Newton's law of universal gravitation, which was in turn explained by Einstein's theory of general relativity.
John Newlands' law of ocatves, Mendeleev's empirical periodic table, the law of definite proportions and the law of multiple proportions were all explained by atomic theory.
Mendelian inheritance was explained by the modern theory of genetics.
The Wallace line was explained by Darwin's theory of evolution.

Gandalf61 (talk) 19:46, 29 February 2008 (UTC)[reply]

Kanab ambersnail: two species? sub-species?

http://www.eol.org/taxa/16822383 http://www.eol.org/taxa/17245474

Is there two species with the name Kanab ambersnail? Or is this a subspecies? (Kanab was our 1.5 millionth article on en.wp.) -- Zanimum (talk) 15:48, 29 February 2008 (UTC)[reply]

Cold trap adequate to protect vacuum pump from HCl?

In my work, I have to evaporate small amounts of 6M HCl under high vacuum. I normally put a trap, which is cooled by a mixture of dry ice and alcohol, on the vacuum line to prevent the HCl vapors from reaching the pump. I've begun to wonder if this is adequate. I think the trap will equilbrate to ~ -78 C (the sublimation point of dry ice at 1 atm), and our article on HCl says it has a boiling point of -85 C. What do you think? ike9898 (talk) 16:29, 29 February 2008 (UTC)[reply]

I guess the HCL will come as an azeotrope with water.

Why not just put an acid trap eg NaOH pearls, before the pump trap.87.102.38.45 (talk) 17:33, 29 February 2008 (UTC)[reply]

I could do that but I'd still like to know if my current setup is adequate. ike9898 (talk) 18:44, 29 February 2008 (UTC)[reply]

Seeing as you have to ask you might be able to work out that the answer is no. Chances are it won't do any damage if you try anyway..

Anway given that your only using small amounts why not use an Aspirator, the hcl will be very much diluted, and 13mmHg is enough. Save you money too!87.102.38.45 (talk) 20:20, 29 February 2008 (UTC)[reply]

I don't understand the first part of your comment - why is the answer no because I had to ask? As to using an aspirator - no, a normal labortory aspirator won't generate a vacuum strong enough for my needs. This already takes hours at high vacuum. Can't someone comment on whether or not the vapors will condense in the situation I've described? ike9898 (talk) 22:15, 29 February 2008 (UTC)[reply]

Sorry, what I meant was that as you had doubts you could assume that your doubts were not founded on nothing..

A lab aspirator gives down to 13mmHg, and should easily give 20mmHg or less, a vac pump will get you down to fractions of mmHg pressure, but atmospheric pressure is 760mmHg, the extra vacuum ~~is totally neglible.~~ oops - the extra vacuum will just cause 'superheating' - ie bumping. You were just removing water and HCl right..

Take a look at this http://www.qvf.com/en/ProcessSystems_3/Mineral%20Acids/ConcentrationingofHydrochloricAcid.shtml it shows that the azeotrope increases in HCl concentration with decreasing pressure as you might expect. So initially your frozen hcl/water mixture will be more concentrated. But it will freeze. But this doesn't stop sublimation of this frozen mixture occuring - and your coolant is not cool enough to do it. So some hcl/water (very much enriched in hcl) will escape.. In other words - you need an acid trap for safe working.

If the time it takes to evaporate is a problem then I suggest a warm water bath combined with hand swirling, or much better a rotary evaporator - surely you can get one of these.

Good luck.87.102.79.228 (talk) 09:22, 1 March 2008 (UTC)[reply]

nitrogenous

I recenly asked a question on how to get algae to grow faster and some people said nitrogenous would help. i read the wiki> page on it but i still dont under sand completly where or what this stuff is. So i was wondering if any one knows if there are and house hold products or things like plants or bugs that might contain nitrogenous. thanks --Sivad4991 (talk) 21:11, 29 February 2008 (UTC)[reply]

How about Fertilizer?209.151.139.172 (talk) 03:42, 1 March 2008 (UTC)[reply]

you will need nitrogen containing fertilizer, which could be in the form or organics (blood and bone) or ammonia or nitrate. Other minerals are also needed by algae such as potassium, phosphate, iron, copper, magnesium, calcium. There could also be some other ultratrace elements required too like boron, molybdenum and nickel nd vanadium. Hydroponic fertilizers should do the job. Graeme Bartlett (talk) 03:34, 2 March 2008 (UTC)[reply]

Gradient rings in constant voltage particle accelerators

http://updatecenter.britannica.com/eb/image?binaryId=3367&rendTypeId=4

what are they for?

i suppose that they guide the electric field in some way, but I dont quite see how they help, surely the electric field will form a straight line from whatever the potential of the central eelctrode to the end electrode anyway, providing the field recquired.

or to create an equpotential across the area of the circle enclosed by the ring

or do they guide the charged particles through some method?

and are they connected via a series of resistors to ensure they are all an equal step down of the voltage along the length from the maximum to earth? —Preceding unsigned comment added by 172.142.196.236 (talk) 21:20, 29 February 2008 (UTC)[reply]

One possibility (guess) is that the gradient rings are charged the same as the particle- and so would keep the particle in a central line whilst moving left to ring.. that doesn#t explain the name though..87.102.38.45 (talk) 21:32, 29 February 2008 (UTC)[reply]

i dont think that would work as the area in the rings qould be an equipotential, and unable to guide the particle beam left or right. im pretty sure they are progressively stepped down voltages between the peak, central, voltage and the earth, end, voltages, but i dont see how they aid it at all, as surely the eelctric field would assume the same shape with or without the rings. —Preceding unsigned comment added by 172.142.196.236 (talk) 21:40, 29 February 2008 (UTC)[reply]

If the particle wass off centre with repsect to the rings it would experience a force pushing it back into the centre? Otherwise I agree with what you have said - ie don't see their purpose..87.102.79.228 (talk) 09:25, 1 March 2008 (UTC)[reply]

As some of the individuals above have speculated, the rings are indeed at uniformly stepped potential, from ground to peak potential at the center terminal, and back to ground again. In their absence, there would be distortions in the electric field due to the presence of other conductive, charged, and/or earthed objects inside the accelerator (the accelerator tank walls, the charging belt/chain, suspension cables, etc.). TenOfAllTrades(talk) 05:19, 1 March 2008 (UTC)[reply]

Bonus: Here are pictures and explanations from the FN tandem at the University of Notre Dame. You can see both the columns and the gradient rings. TenOfAllTrades(talk) 05:32, 1 March 2008 (UTC)[reply]

number of

I'm looking for the number of but the search box isn't helpful. —Preceding unsigned comment added by 79.122.6.248 (talk) 21:35, 29 February 2008 (UTC)[reply]

What :D\=< (talk) 21:53, 29 February 2008 (UTC)[reply]

First morning cigarette

Why is it that first cigarette in the morning always feels the best?? 77.105.46.131 (talk) 22:01, 29 February 2008 (UTC)[reply]

Because you're addicted to nicotine and overnight you're in the early stages of withdrawl.. the first cigarette restores you to the level of nicotine that your body is used to. Why do people smoke, it's filthy and disgusting.. and a waste of money. :D\=< (talk) 22:12, 29 February 2008 (UTC)[reply]

The sheets and blankets were pulled up tightly around his
head, but from somewhere half way down the length of the bed a hand slowly emerged from under the bedclothes and its fingers felt their way in little tapping movements along the floor. Working from experience, they neatly circumvented a bowl of sornething very nasty that had been sitting there since Michaelmas, and eventually happened upon a half-empty pack of untipped Gauloises and a box of matches. The fingers shook a crumpled white tube free of the pack, seized it and the box of matches, and then started to poke a way through the sheets tangled together at the top of the bed, like a magician prodding at a handkerchief from which he intends to release a flock of doves.
The cigarette was at last inserted into the hole. The cigarette was lit. For a while the bed itself appeared to be smoking the cigarette in great heaving drags. It coughed long, loud and shudderingly and then began at last to breathe in a more measured rhythm. In this way, Dirk Gently achieved
consciousness.
— Douglas Adams, The Long Dark Tea-Time of the Soul

—Preceding unsigned comment added by Keenan Pepper (talk • contribs) 23:50, 29 February 2008 (UTC)[reply]

HOW DID I NOT THINK OF THAT QUOTE O_O :D\=< (talk) 01:33, 1 March 2008 (UTC)[reply]

Anything First thing in the morning is great. You're alive again. Some Chocolate Pudding. A bite of some Strawberry Cheesecake. Maybe a fresh slice of Pizza. Some just cooked Trout from the river. Our bodies are machines. However we turn the dials, that's what makes all the difference...on differences. You individual you! Smoke em' if you got em'. --i am the kwisatz haderach (talk) 00:18, 1 March 2008 (UTC)[reply]

"Why do people smoke, it's filthy and disgusting.. and a waste of money."

"Anything First thing in the morning is great." Well,theres nothing quite like a cigarette in the morning :)...But yeah,its seems like its a withdrawl —Preceding unsigned comment added by 79.175.73.160 (talk) 00:41, 1 March 2008 (UTC)[reply]

Yeah, that's the one I *really* miss. It's the only one that gives me the 'kick' that started me smoking in the first place when I was a teenager (I have been told that it's not *just* the nicotine that causes that - rather a combination of nicotine, carbon monoxide and various toxins). Nicotine gum and this plastic cigarette that tastes a bit like smoke just don't cut it in the AM. --Kurt Shaped Box (talk) 01:12, 1 March 2008 (UTC)[reply]

I agree whole-heartly with Froth. Smoking is disgusting and a huge waste of money. I, for one, do not need some drug to be awake in the morning! *quaffs his 5th Frappuccino of the day* 206.252.74.48 (talk) 19:33, 3 March 2008 (UTC)[reply]

Hydrogen Peroxide

How dangerous is it to ingest hydrogen peroxide? Is it as dangerous as ipecac? Will it be fatal if small amounts are ingested over long periods of time? Any other information on hydrogen peroxide?

75.182.93.102 (talk) 23:40, 29 February 2008 (UTC)[reply]

According to this long abstract, it is dangerous to ingest hydrogen peroxide because it produces oxygen gas which can cause gas embolism. Concentrated solutions (much more concentrated than over-the-counter medical products) are even more dangerous because they corrode tissues. Ingesting small amounts of dilute solution over long periods of time is unlikely to be fatal because it decomposes so quickly in the body. It can't be healthy, though, because it causes oxidative stress. —Keenan Pepper 00:28, 1 March 2008 (UTC)[reply]

Is this some sort of bulimia thing? --Kurt Shaped Box (talk) 01:14, 1 March 2008 (UTC)[reply]

No there are people (read as crazy nuts) who think that it "cleanse" them somehow. Much like ozone thearapy I guess... Very sad that people can get promoting such things...But this isn't the place for rants now is it.--Shniken1 (talk) 14:08, 1 March 2008 (UTC)[reply]

Looking at the sky

Where do your eyes focus when you look up into the sky? I mean, if you traced a ray out from each eye, how far out would they intersect? Also are the lenses of each eye actually focused on this point? Is it any different when looking at the stars at night from looking at the blue sky during the day? How about clouds? :D\=< (talk) 23:45, 29 February 2008 (UTC)[reply]

When you look at a star, your eyes focus "at infinity", which means that the rays which converge at a single point on your retina were, for all practical purposes, exactly parallel before they got refracted by your corneas and lenses. The point where these rays intersect is therefore very ill-defined. It could be light-years away, or it could be only a few kilometers away, or there could even be a virtual intersection point far behind you. The amount of adjustment your eye (or any optical system) has to make is inversely proportional to the distance (see Optical power), so the farther away something is, the less important it is to know that distance accurately. Whether a star is one light-year away or a thousand makes absolutely no difference to your eye.

This is the reason why focusing rings on camera lenses have an infinity symbol which is surprisingly close to the finite numbers. —Keenan Pepper 00:08, 1 March 2008 (UTC)[reply]

March 1

Does anyone know the title of this painting about Galileo?

Dear Wikipedians:

Does anyone know what the title of the painting below is? It's supposed to be very famous, but I can't seem to find it anywhere on the net. It's about one of Galileo's experiments (I think).

Thanks.

L33th4x0r (talk) 00:48, 1 March 2008 (UTC)[reply]

See this page all about it. It's in Italian, but you should be able to get the gist. Apparently, the painting is part of a fresco in the Natural History Museum at Florence, by one Giuseppe Bezzuoli. --Milkbreath (talk) 01:04, 1 March 2008 (UTC)[reply]

Thanks so much! Now I know! 74.12.39.63 (talk) 01:51, 1 March 2008 (UTC)[reply]

I don't know enough Italian to easily understand the cites page, but I looked on it to see if I could tell what it said was the title. I thought Caduta dei gravi might be it, so I then did a Google search on that phrase restricted to pages that Google thinks are in English, looking for something easier to follow. Many of the pages were not really in English, but it only takes one good hit: this page gives the full title in Italian as L'esperienza della caduta dei gravi sul piano inclinato — which must mean "The Experiment on the Fall of Weights on an Inclined Plane". --Anonymous, 04:32 UTC, March 1, 2008.

Er, except that the one I found is not the same painting! It's small enough and dark enough that I didn't notice at first. It is very similar, though. I wonder if Bezzuoli painted the same scene more than once, or if one version might be a copy. Perhaps someone on the Humanities Desk would know something, or the Italian Wikipedia might have something if someone can read it well enough. --Anon, 04:40 UTC.

Thank you all for your help! I appreciate it! L33th4x0r (talk) 15:25, 1 March 2008 (UTC)[reply]

what is in Arizona sand?

We dug a bunch of sand out of a natural wash that runs behind our house in tucson Arizona to put in our childs sandbox. One of the children put a car in it that has magnets on it and it picks up tons of black magnetic material. What is this? —Preceding unsigned comment added by 71.215.107.211 (talk) 01:32, 1 March 2008 (UTC)[reply]

Lots of sand does that. We used to do it all the time when we were kids (in California, for me).

I did a google search for magnet sand black powder, and the second hit was this book, which says that the black powder is an iron oxide, Fe₃O₄, or magnetite. —Steve Summit (talk) 02:42, 1 March 2008 (UTC)[reply]

Another kind of black sand is ilmenite which contains iron and titanium. Graeme Bartlett (talk) 03:38, 2 March 2008 (UTC)[reply]

Persistence of hearing

Our house is pretty far away from the road, so we installed a wireless chime that rings inside the house when a car passes through the front gate. The chime is the familiar Big Ben ding-dong-ding-dong... pattern. Here's the odd thing: after it has rung, several different people hear ghost repetitions of the chime, sometimes over and over again, for quite a while -- it even stops for a while and then starts back up again. Kind of like an ear worm, but more ghostly. It's not a function of this house, either: we've got a guest house on the other side of the property, and there's a ringer there too, and the same persistence effect happens there. One more thing to add to the equation: the house is right on the river, at a noisy rapids, so there's always a significant amount of white noise in the background. My guess is that the white noise is cuing some sort of auditory memory or something like that. Has anyone ever seen anything of this sort in the literature? --jpgordon^∇∆∇∆ 03:13, 1 March 2008 (UTC)[reply]

Oliver Sacks explores the topic of "musical hallucination" in one of the chapters of Musicophilia: Tales of Music and the Brain. Your description sounds a lot like the way he describes it -- except that his description is not something applicable to every one. But in a mild form is fairly common, especially among older people, and definitely with some kind of noise source like a stream. I'm not sure it is the same as what you describe, but still you might find that chapter of his book interesting. Pfly (talk) 05:25, 1 March 2008 (UTC)[reply]

Maybe I'll get there; I adore Sack's work, but for some reason, Musicophilia isn't as compelling as his previous books. I bogged down, to my great surprise, since music and mind is one of my main interests. Thanks for the suggestion, though! --jpgordon^∇∆∇∆ 08:27, 1 March 2008 (UTC)[reply]

Just to say I get exactly the same thing from chimes, and did do even when I was young. Probably a very common phenonoma. I assumed it was something to do with those chimes being very clear notes - about which I intend to ask a question...87.102.79.228 (talk) 09:30, 1 March 2008 (UTC)[reply]

Furthermore, as I recall the ghost notes seem to be coming out of the noise ie I don't usually notice the noise - it's like a noise in my head/ears.. That is I think the chimes are causing me to hear noise after they have rung..87.102.79.228 (talk) 09:37, 1 March 2008 (UTC)[reply]

They might call in déjà entendu. I get it when I hear people talk about the "light at the end of the tunnel" in Iraq. Myles325a (talk) 23:30, 7 March 2008 (UTC)[reply]

SI Notation

I came across something unusual while reading a (very academic) paper: "Demonstration of the exponential decay law using beer froth" (Eur. J. Phys. 23:21-26). The author lists heights of beer foam in cm^-1, and the values start at 17 and end at 5. I am pretty sure this can't be 1/cm, since the values decrease with time, nor are they just cm, unless the beer glass is both very tall and filled with foam (possible, I suppose, but odd). Is cm^-1 a common notation for mm, or is this something more clever? Thanks, --TeaDrinker (talk) 05:12, 1 March 2008 (UTC)[reply]

Are you sure it was the foam height that the author gave? cm-1 = 1/cm, so it can be used when combined with another quantity, to express the magnitude of that quantity per cm. Ex. 23 J cm-1 = 23 J/cm --Bowlhover (talk) 06:32, 1 March 2008 (UTC)[reply]

I'm going to express the same concern/question here. There is no other way around it: Cm-1 = 1/cm and therefore over a given time period such a notation indicates an inverse. So if cm-1 decreases over time, the height is increasing. Can you link to the abstract? Wisdom89 _{(_T / ^C)} 06:44, 1 March 2008 (UTC)[reply]

Google finds several links to the paper at for-pay sites plus this one link that doesn't work at the moment. However, they also have a cached copy converted to HTML. This is somewhat garbled but good enough to see that there really is a table with this peculiar $cm^{-1}$ usage in its column headings. Specifically, the first column is headed t(s), which must be time in seconds, and the second column is headed $h^{exp}cm^{-1}$ . From context it seems clear that this means experimentally measured height in centimeters. (The third column shows the error in the height, and its heading also looks like $h^{exp}cm^{-1}$ to me; I assume a diacritical mark has gotten lost there.)

It occurs to me that if the height is 6 cm and you divide this value by cm, you get the pure number 6. So $h/cm$ or $h$ $cm^{-1}$ can be seen as a way of saying "height in centimeters". But I can't imagine why anyone would use this notation alongside the ordinary t(s) for "time in seconds". --Anon, 09:40 UTC, March 1, 2008.

I note that there is also a "-1" superscript on the best fit time constant line, τ_best(+/-RS)^-1. Clearly this is not measured in 1/s. My guess is the -1 is meant to refer to some kind of footnote rather than meant as an exponent. A more interesting question is why do the results only continue to 360 seconds? Did something happen to the beer after that short time? Another pertinent question: was the paper written on the same day as the experiment? SpinningSpark 12:10, 1 March 2008 (UTC)[reply]

There's a freely available PDF here. It is clear from this that Anon is correct. In Table 1, "

h^{exp}\ cm^{-1}

" is what we would normally write as "

h^{exp}/cm\

", meaning that the pure numbers in the table are measurements of the froth height in cm. In Figure 1 of the same paper, "

\tau /s\

" is used, so it's not as if the author is being consistent. The same goes for the best-fit time constant expression, which is actually "

\tau _{best}\ \pm \ \Delta \tau \ s^{-1}

", meaning that the numbers are measurements in seconds. "

cm^{-1}\

" and "

s^{-1}\

" in this context look to an English reader like a long-winded style of writing, but perhaps it is common practice in Germany, where the paper comes from. Any Germans reading this? --Heron (talk) 18:41, 1 March 2008 (UTC)[reply]

Thanks for all the replies! It sounds fairly reasonable that the measurements are in cm and the notation is expressing pure numbers, although (to my eye) unnecessarily complicated. Thanks again! --TeaDrinker (talk) 18:49, 1 March 2008 (UTC)[reply]

If you tabulate numbers without the unit, then the correct title of the column has to be divided by the unit (/cm) to make it mathematically correct. It then simply has the meaning "in cm". Сасусlе 13:51, 5 March 2008 (UTC)[reply]

door chimes

(also see question two above)

I've always though that door chimes gave very clear notes. Also any chime that is based on a hollow cylinder of metal (such as those wind chimes - when the winf blows a hammer to strike a cylinder)

I seems clearer than say a pure sine wave..

Can someone explain what quality of the note causes the clearness..

Also if you could relate the answer to the shape of the chime I would be interested. Thanks87.102.79.228 (talk) 09:34, 1 March 2008 (UTC)[reply]

The sound of a bell is fuller sounding than a sine wave because it is rich in harmonics. A traditional bell-shaped bell has a pronounced 13th harmonic (scientific notation = 12th overtone in music theory). This harmonic has a minor 3rd relationship with the fundamental and gives the bell its characteristic "minor key" sound. A tubular bell is also rich in harmonics, but does not have the pronounced 13th harmonic. To my ear they often have the bright sound of a "7th" chord, implying a strong 7th harmonic and clearly the lower ones are there as well. There have been attempts to cast traditional bells without a minor chord sound using computer calculations to predict the harmonic content of a particualr shape. Sorry, I do not have any references to hand but the shape of these bells differs from the traditional, firstly, in that there is a slight narrowing to a waist part way down and, secondly, there is no pronounced flare to the mouth of the bell. SpinningSpark 12:45, 1 March 2008 (UTC)[reply]

Ah, heres someone doing this [6] SpinningSpark 13:48, 1 March 2008 (UTC)[reply]

I wonder if the tubular bell lacks or has less 'inharmonic partials' as decribed in the links. When I here a bell shaped bell I often imagine I can here more than two notes competing. I'm guessing here (and I don't have the finest hearing) that the tubular bell might have less off these due to it being of constant width.

I'll have to try a 1st+7th harmonic next time I get near a frequency synthesiser and see if that sounds bright.87.102.83.246 (talk) 15:21, 1 March 2008 (UTC)[reply]

My guess would be that the simpler geometry of the tubular bell has far fewer modes of vibration, hence fewer opportunities for vibrations to develop out of harmonic relationships. Just mixing 1st + 7th sine waves will probably sound a bit odd, you will need some of the intervening harmonics also. SpinningSpark 16:39, 1 March 2008 (UTC)[reply]

Reflection

When a photon hits a mirror, exactly what happens, on a quantum level? In as plain language as possible, please. I'm just curious. Is it somehow absorbed and re-emitted, a la the Bohr atom (though it obviously can't be that if it is going to reflect), or something else?

Similarly, when people talk about an x-ray mirror, how does that work, on a physical level? Is it "true" reflection or is it something else? --98.217.18.109 (talk) 13:38, 1 March 2008 (UTC)[reply]

The photon is indeed absorbed and then re-emitted, although stricly speaking the reflected photon is not the same photon. The original is destroyed and a new one created. See this section of the Reflection article.

Regarding X-ray mirrors, these are no different in principle to regular mirrors. However, they are much more difficult to make because the wavelengths involved are much shorter than visible light. Hence the mirror surface needs to be orders of magnitude smoother. See [7] for NASAs' description of how they do it. SpinningSpark 17:59, 1 March 2008 (UTC)[reply]

The absorption and re-emission of the photon has to happen coherently - i. e. the intermediate quantum state is a mixture of different states where in each state another surface molecule has absorbed the photon. The direction of the reflected photon is then determined by constructive interference of these different states. Similar things must happen if a photon is refracted without being scattered. Icek (talk) 21:56, 1 March 2008 (UTC)[reply]

OK, those are both sort of what I wanted to know. I had imagined that it wasn't absorbed and re-emitted since I had been taught that the re-emission occurred in no particular direction at all. What is it about the properties of the atoms on the surface of the mirror that make them get re-emitted in the right direction? --98.217.18.109 (talk) 23:16, 1 March 2008 (UTC)[reply]

The special property is that the atoms have to be very close together so that emissions in the "wrong" directions are low probability because of destructive interferance of the wave states corresponding to emission by adjacent atoms. In other words, the surface must be smooth and shiny. A rough surface will have many atoms with no neighbours in a certain direction, emission in that direction is then possible because there is no other wave state to interfere. SpinningSpark 23:37, 1 March 2008 (UTC)[reply]

Thanks, that makes sense. --98.217.18.109 (talk) 03:04, 2 March 2008 (UTC)[reply]

Briefly following on to Spark's comment, the reflection in the right direction is the most likely, although there is a probability of some photons re-emitting in the "wrong" direction. This would correspond to what we typically call transmission (semi-transparent mirror). Every real mirror has some component of transmission and some component of reflection (and maybe some absorption as well); these numbers are typically provided if you purchase optical-grade scientific reflectors. Nimur (talk) 16:57, 2 March 2008 (UTC)[reply]

relativistic velocity masss ratio

If I have a particle of rest mass m₀ and I accelerate it to energy E, at which it is of a velocity comparable to c, so relativistic effects are clearly apparent, what proportion of the energy is velocity, and what preportion is converted to mass, via the mass energy equivalence? —Preceding unsigned comment added by 172.142.196.236 (talk) 13:56, 1 March 2008 (UTC)[reply]

All of the energy is mass because mass and energy are equivelant. They are the same thing, just different units and the conversion factor is C². However, this result from special relativity may help your understanding;

$E^{2}=E_{0}^{2}+(pC)^{2}$

where;
E is the total energy of the particle
E₀ is the energy at rest, ie the energy before you started acceleration the particle
p is the final momentum of the particle

In words E₀ is the component of energy due to the rest mass and pC is the component due to the motion. SpinningSpark 17:24, 1 March 2008 (UTC)[reply]

More than forty years ago, as a schoolboy, I recall reading a library book on Einstein and using the formula :

m={m_{0} \over {\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}\!

to calculate how much the mass of an object increases with speed. I discovered that NASA wouldn’t create a disaster if they forgot about this effect in their calculations, because the difference in mass at escape velocity is too small to show on my calculator. Even at a hundred times escape velocity, the effective mass increases by only 0.0007%. To double the effective mass, you need to travel at 94.28% of the speed of light. At that time, I made the same mistake as some physicists early last century in believing that this increase in mass was “real”. In fact, it is just the kinetic energy converted to mass using Einstein’s equation $E=mc^{2}$ . The situation is rather like driving round a sharp bend in a car. You feel what seems to be a “centrifugal force” pushing you outwards, but anyone standing outside the car knows that this is not a “real” force. You can treat it as “real” whilst you are in the car, and you get all the right answers, but once you take a more general view of the situation different equations are needed. In relativity, the idea of “relativistic mass” is rarely used because it only has meaning in the particular inertial frame of the observer. The true mass “rest mass” has not changed at all. The “extra mass” is simply the kinetic energy converted to mass. Mathematical physicists use a four-dimensional momentum vector to describe the situation. This includes the “rest mass” and the effects of the kinetic energy all in one vector which can be transformed to describe the situation for any observer. See Mass_in_special_relativity for full details. dbfirs 18:41, 1 March 2008 (UTC)[reply]

If your calculator is 40 years old as well, I would buy a new one. 94.28% C gives three times the effective mass. The correct answer for double mass is 86.6% C. In any case, the OP was not asking how significant the effect is at NASA velocities, he asked for the results at some unspecified velocity where the effect IS significant. Your example of centrifugal force in a car; all reference frames are equally valid (though not equally useful) according to General Relativity. This includes the frame referenced to the car, in which frame the force will be perfectly real. The idea that relativistic mass is an incorrect concept is highly controversial as is shown by the discussion on the special relativity talk page where I get the impression it is, in fact, a minority opinion. SpinningSpark 11:42, 2 March 2008 (UTC)[reply]

And even more controversial, it would seem, on the talk page of the article you referenced. SpinningSpark 11:57, 2 March 2008 (UTC)[reply]

Oops! No, not my calculator, my brain was at fault there. Sorry! (I set up a spreadsheet and used "Goal seek", then forgot what goal I was seeking.) My only excuse can be that I was distracted by losing internet access, hence the delay in my reply and not reading SpinningSpark's reply first. Also, I was not intending to imply that relativistic mass is a faulty concept, just that it is not the only way of looking at the situation. The idea that centrifugal force is an incorrect concept is also disputed, in fact it is a very useful tool to use in the frame of reference of the car, but many pedagogues insist that the force doesn't exist. It all depends on your point of view - it's all relative! dbfirs 08:01, 3 March 2008 (UTC)[reply]

Energy Question

If energy can neither be created nor can it be destroyed, why is it so important in our life or otherwise why is it so difficult to produce in plentiful amount? —Preceding unsigned comment added by 202.70.64.15 (talk) 14:38, 1 March 2008 (UTC)[reply]

I'm not quite sure what you're asking. If we simplify your question to why is energy so important in our life, the answer is obvious: it's important, we need it. It's not just important, it's vital: without food energy, we as organisms can't survive. And without various other forms of energy to manufacture and distribute our other creature comforts, our lives would be very, very different.

The fact that energy cannot be created just makes it all the more precious. —Steve Summit (talk) 16:37, 1 March 2008 (UTC)[reply]

There is for more energy around us than we could possibly use. The problem is: we can't use it. Although energy can't be destroyed, entropy can be created. One joule of heat is far less useful than one joule of electricity. — DanielLC 17:26, 1 March 2008 (UTC)[reply]

We want energy in a convenient form, such as chemical fuel (e.g. coal and petroleum), or stored electric potential (e.g. a electric battery). These forms are convenient for human machines and industries. Energy is also present in lots of inconvenient forms (e.g. waste heat; gravitational potential energy (such as the aggregate gravitational potential of all the matter which makes up our planet), but there is not an easy way to "plug in" to it. (See geothermal energy and hydroelectric power for some options). As you say, there is no "energy production", but rather energy "refining", which converts the form to something we can use. The previous answers have hinted at another core concept of thermodynamics, which is the entropy in our universe. To the best of our physical understanding, the universe started out with a certain level of entropy, and always operates to increase that level. When we cause energy to change forms, we are almost always increasing the entropy, which is an irreversible process. This sets hard theoretical upper-limits on the efficiency which we can perform energy-related tasks; but there are many other practical usability considerations to our energy needs which make energy "generation" difficult... for example, locating the petroleum, distributing the electricity, not generating harmful pollution in the process..., etc. Nimur (talk) 17:11, 2 March 2008 (UTC)[reply]

The principle behind diffusion

I think that I understand the process of diffusion. Gases or substances in solution move passively to areas of lower concentration down a concentration gradient, using molecular kinetic energy.

I do not, however, understand why this process works when applied to a system with lots of different substances. For example, during gas exchange in the lungs, why is there a gradient exclusively for oxygen and one exclusively for CO₂? Why does oxygen move into the blood simply because there is a low concentration there of oxygen? If there is a high concentration of gas in both the blood and the air space, why is there any net movement at all?

I hope I have made this clear. Thanks very much for your help!

86.146.107.210 (talk) 14:40, 1 March 2008 (UTC)[reply]

It's not so much that molecules know to move to a lower concentration area. Think of the space in which the gases are contained as a glass of water. If you dissolve salt (let's imagine that is the gas) in that water, it will spread through all the water so there is a constant concentration. The same goes on in the lungs. There just happens to be a barrier in between. —Preceding unsigned comment added by 87.211.75.45 (talk) 15:43, 1 March 2008 (UTC)[reply]

Each individual gas molecule is moving independently and bouncing off of other molecules. After a period of time, you can compute the probability that that particular molecule will be in a given location, for example on one side or the other side of a membrane. So the underlying principle is not that you compute independently for each substance. Rather, you compute independently for each individual molecule. For example, If I have pure pxygen on each side ofthe membrane, there is no net movement, but individual molecules move back and forth across the membrane.-Arch dude (talk) 15:49, 1 March 2008 (UTC)[reply]

Actually in the case of oxygen, the blood binds the oxygen - effectively converting it to another form (that does not diffuse accross the membrane - too big) - so there should be a low concentration of oxygen(gas) in the blood. the complexing agent is Hemoglobin 87.102.83.246 (talk) 15:58, 1 March 2008 (UTC)[reply]

The reason for diffusion is entropy. Entropy can be thought of as the degree of disorder in a system. A room in which the top 70% is nitrogen gas and the bottom 30% is oxygen is very ordered and thus entropically undesirable. A room where the two gasses are perfectly mixed is much more disorderd and thus entropically favoured. --Shniken1 (talk) 10:52, 2 March 2008 (UTC)[reply]

Every individual particle follows a uniquely random path - so the statistical aggregate of each particle is that everything diffuses, no matter what it is made of. As long as we can say that the inter-molecular forces are "negligible" (a good approximation for a lot of gas diffusion situations), each particle will diffuse just as if it were alone in an empty volume.

What would be surprising is when some unknown force causes two substances to stop diffusing - such as oil and vinegar. Something strange about those atoms appears (superficially) to defy the rules of thermodynamics! This usually involves strong formation of surface layers with unique alignment and chemical bonding, which prevents a normal diffusion process. In other words, we can no longer say that the molecules do not interact with each other.

The same thing can happen in an urban valley, when temperature inversion causes smog. If everything was diffusing normally, the pollution would mix thoroughly and dissipate, but instead it gets trapped, cannot diffuse, and becomes highly concentrated over the city. Nimur (talk) 17:18, 2 March 2008 (UTC)[reply]

Human evolution

what is the evolutionary explanation of sexual reproduction in animals? —Preceding unsigned comment added by 202.70.64.15 (talk) 15:04, 1 March 2008 (UTC)[reply]

That it is the mechanism by which individual species pass their genotypes to successive generations through their progency. Wisdom89 _{(_T / ^C)} 15:05, 1 March 2008 (UTC)[reply]

Take a look at evolution of sex. It's a major topic of discussion and research. --98.217.18.109 (talk) 16:49, 1 March 2008 (UTC)[reply]

Subsidiary question - bisexual reproduction

All the postulated advantages of sexual reproduction in the article (rapid response to change etc) would equally apply to creatures reproducing bisexually (eg, the paramecium) since genetic material is being shared, but without the huge disadvantage of reduced productivity since both partners are reproducing. It strikes me that there must be something more than the genetic advantages at work here, for instance, the division of labour between the sexes might confer advantages. Is there any research in this area? SpinningSpark 18:33, 1 March 2008 (UTC)[reply]

The explanation I've seen for this (in Matt Ridley's The Red Queen, if memory serves), is that in an all-bisexual population, a male-only mutation would be at a significant advantage, since it would still be able to breed with (almost) everyone, and wouldn't have to waste all that energy on pregnancy, laying eggs, or whatever. Once the males were well established, there would be selective pressure to become female-only (to maximize breeding opportunities). I don't know if this idea is at all accepted. Algebraist 22:50, 1 March 2008 (UTC)[reply]

Reverse transcriptase PCR

I think I have the main idea of the technique clear in my mind, but I'd like a complete noob's guide to the technique. Does anyone know of any practical tips and protocols that are not covered in the article and its links that could help me out? --87.211.75.45 (talk) 15:37, 1 March 2008 (UTC)[reply]

Working in lab, I've come to realize that the best provider of molecular biology kits and protocols is probably Ambion. Try this link [8]. Wisdom89 _{(_T / ^C)} 15:49, 1 March 2008 (UTC)[reply]

Hmm, looks helpful, but why do they start about real-time PCR? - 87.211.75.45 (talk) 16:07, 1 March 2008 (UTC)[reply]

Real Time RT-PCR is becoming the standard for quantifying expression/mRNA levels - it's basically a way of normalizing each sample and allowing them to all be within the exponential phase of the PCR reaction with minimal operator intervention. Wisdom89 _{(_T / ^C)} 20:39, 1 March 2008 (UTC)[reply]

composition of fecal matter

Is it true that most of the mass of human fecal matter consists of dead bacteria? --Halcatalyst (talk) 15:46, 1 March 2008 (UTC)[reply]

This paper [9] would seem to indicate that it is mostly water and fat. I would imagine that the majority of bacteria in the stool are still alive at the point of release. SpinningSpark 17:07, 1 March 2008 (UTC)[reply]

However, the abstract (at least) says nothing about bacteria, or about total mass; it seems to discuss only nutrients. --Halcatalyst (talk) 21:47, 1 March 2008 (UTC)[reply]

I could be wrong, but my reading of the paper is that it is quoting figures in terms of the total mass (. . . results were expressed as concentrations (g/100 g of feces) . . .). Their result of 68.7 to 96.1 g/100 g of water does not leave much room for anything else at all to be the majority constituent. You are, of course, right that bacteria are not mentioned at all. SpinningSpark 23:52, 1 March 2008 (UTC)[reply]

No, you're right; you read more carefully than I did. Thanks for the answer! --Halcatalyst (talk) 01:51, 2 March 2008 (UTC)[reply]

Some of that water is within the bacteria. The usual figures are for the percentage of the dry weight of the feces made up by bacteria. The specific figures vary widely according to techniques and assumptions as well as individual variation in diet, etc., and range from 10-42% of the dry weight made up of bacteria, mostly dead. So no, most is an overstatement; it would be more accurate to say that a considerable part of the mass of fecal matter consists of bacteria. - Nunh-huh 04:51, 2 March 2008 (UTC)[reply]

Dietary fiber makes up a significant portion of the dry mass. ike9898 (talk) 14:48, 3 March 2008 (UTC)[reply]

Parent/baby size

In honor of the 28" tall woman who recently gave birth to a normal-size baby, what species have the smallest and largest size ratio? Clarityfiend (talk) 17:27, 1 March 2008 (UTC)[reply]

As for smallest baby, my first guess would be a large marsupial, like the kangaroo. HYENASTE 17:46, 1 March 2008 (UTC)[reply]

Oh, gosh no, if it's not limited to mammals. --jpgordon^∇∆∇∆ 18:17, 1 March 2008 (UTC)[reply]

If we are going that way then bacteria have babies the same size as themselves, one at a time every 30secs..87.102.83.246 (talk) 18:37, 1 March 2008 (UTC)[reply]

More like 20 minutes, at the absolute minimum. Someguy1221 (talk) 04:20, 2 March 2008 (UTC)[reply]

Well, fungi spores can be microscopic and the fungus they grow into can be quite large. You said species, so I guess that counts too? — Kieff | Talk 05:05, 2 March 2008 (UTC)[reply]

Just as a reference frame, any organism that divides by mitosis produces daughter cells which are nearly identical in size - although, budding yeast produce daughter cells which are slightly smaller. Wisdom89 _{(_T / ^C)} 05:44, 2 March 2008 (UTC)[reply]

Moon at past

bsm. Is it correct that the moon at least one time taked part (tow parts) and then joined? if that is correct, when and how many?(11-12) —Preceding unsigned comment added by 80.191.15.10 (talk) 19:09, 1 March 2008 (UTC)[reply]

That is not the currently most popular theory of the Moons formation. See Giant impact hypothesis. SpinningSpark 19:25, 1 March 2008 (UTC)[reply]

See Moon#Formation for a list of the ideas considered most likely. We have no way of knowing which is correct. It's still a subject of current research. —Keenan Pepper 19:37, 1 March 2008 (UTC)[reply]

Hot and cold areas

some of areas of earth are cool (mountains, highlands ) some of these are very hot (salty deserts (Kavirs or Sahras). At school, we study it ( or did) and all of us know it, but why? waht is relation between hight and temperature? —Preceding unsigned comment added by 80.191.15.10 (talk) 19:20, 1 March 2008 (UTC)[reply]

because you are away from the earth, which retains heat, and are high in the air, which does not retain heat. —Preceding unsigned comment added by 81.132.248.74 (talk) 20:47, 1 March 2008 (UTC)[reply]

The preceding answer is somewhat correct, but misleading. From this site: "Since air is "clear," sunlight passes through it easily and heats the ground. The atmosphere then gets heated from the ground and the atmosphere is warmer near the ground. As warm air rises from the ground, it expands and cools, and the sum result is colder air at higher altitudes than at the surface." Apparently written by a meteorologist. Tanthalas39 (talk) 23:44, 1 March 2008 (UTC)[reply]

80.191, please have a look at our articles on climate, weather, Earth's atmosphere and the like to gain some understanding. If you have additional questions, feel free to ask.

81.132: Having looked at you edit history from 01.03.08 I would suggest you acquire some maturity. --Cookatoo.ergo.ZooM (talk) 23:57, 1 March 2008 (UTC)[reply]

Remember that the thermosphere is HOT because it is in the Van Allen Belt. Hope this helps. Thanks. ~A H 1^(TCU) 19:16, 2 March 2008 (UTC)[reply]

This phenomenon is due to two very simple things:

At higher altitude the air pressure is lower, because there is less air above pushing on it.
If air is compressed, it heats up (because we must do work on it to compress it), and if it expands it cools down.

With these things in mind, consider any well-stirred atmosphere. Any package of air that moves upwards expands and therefore cools down, and any package that moves downward is compressed and therefore heats up. The result is a thermal gradient, with temperature decreasing with height. (To be exact, this idealized situation creates an adiabatic temperature profile.) --mglg_(talk) 23:49, 4 March 2008 (UTC)[reply]

how long is a piece of string????

how long is a piece of string???? —Preceding unsigned comment added by 81.132.248.74 (talk) 20:46, 1 March 2008 (UTC)[reply]

3.2m. Your string may vary. Algebraist 22:44, 1 March 2008 (UTC)[reply]

See String theory for an answer to this knotty problem. --Cookatoo.ergo.ZooM (talk) 22:53, 1 March 2008 (UTC)[reply]

Double half its length.

1 - you may decide which answer you prefer. -mattbuck (Talk) 23:14, 1 March 2008 (UTC)[reply]

\int _{P_{1}}^{P_{2}}{\sqrt {1+\left({\frac {dy}{dx}}\right)^{2}+\left({\frac {dz}{dx}}\right)^{2}}}\,dx

where P₁ and P₂ are the ends of the string. SpinningSpark 23:28, 1 March 2008 (UTC)[reply]

As long a string as a string could string if a stringy string could string string. —Steve Summit (talk) 23:30, 1 March 2008 (UTC)[reply]

The answer is three, because "tri" is a piece of string. SpinningSpark 00:03, 2 March 2008 (UTC)[reply]

Umm, take a peek at 81.132.248.74's other contributions. :-( --hydnjo talk 00:30, 2 March 2008 (UTC)[reply]

Umm nevermind, it seems that I'm late to the party! :-) --hydnjo talk 00:35, 2 March 2008 (UTC)[reply]

Besides, the answer lies without or within. ;-() --hydnjo talk 00:42, 2 March 2008 (UTC)[reply]

Unfortunately, that esteemed publication Do Ants Have Arseholes? and 101 other bloody ridiculous questions does not cover this one. But it does answer equivalent (if differently worded) questions such as "If a deaf man goes to court, is it still called a hearing?", "Where is the middle of nowhere?", "Is there another word for synonym?", and "Why do birds suddenly appear, every time you are near?". A must-read for all Ref Desk questioners and volunteers. -- JackofOz (talk) 01:00, 2 March 2008 (UTC)[reply]

I was about to ask where I could buy that alleged "esteemed publication", because I assumed you had pulled it out of your own... er, that you had made it up out of whole cloth. But no: ISBN 978-0-7515-4041-3. Whouda thunkit! —Steve Summit (talk) 16:50, 2 March 2008 (UTC)[reply]

Thanks for trusting me on this one, Steve. I was never more serious in my life. I re-read it often (it takes about an hour), and it has re-crystallised my whole attitude to this important facet of my life. -- JackofOz (talk) 00:58, 3 March 2008 (UTC)[reply]

The correct and simplest answer is, of course, the measured distance between the two ends when the string is stretched just taut —Preceding unsigned comment added by 79.68.188.203 (talk) 02:26, 2 March 2008 (UTC)[reply]

Which German architect do you mean by "taut"? :P I suppose you meant taut! (EhJJ)^TALK 03:13, 2 March 2008 (UTC)[reply]

The one who's always tight, of course! —Preceding unsigned comment added by 79.68.188.203 (talk) 04:56, 2 March 2008 (UTC)[reply]

char array[]="piece of string";

printf("length is=%d\n;",sizeof(array))

length is 16

-Arch dude (talk) 00:23, 3 March 2008 (UTC)[reply]

Casein Polymerisation Experiment

After innocently attempting the polymerisation of casein from warm cow's milk using an acid, I have produced some confusing results - can anyone shed some light on these, please?

If the suspension of fat in milk makes it translucent, why is the milk rendered colourless after the polymerisation?

Using full-fat milk (which gives the most polymer, suggesting it also has more protein) and malt vinegar, I produced a reasonable quantity of the polymer. This I split in half: one half was left to dry and the other was placed in the microwave for 45 seconds. The first sample became elastic and bouncy after one day and, after three, had formed a beige resin. This continues to shrink in size. The identical sample placed in the microwave came out of the microwave as a rubbery solid, which I moulded into a sphere and also left to dry - this was extremely bouncy within a few hours and then hardened, as with the other. The difference, though, was that the microwave polymer had gone red - both have now dried, and one is beige but the other is a very deep red. Why?

Also, I produced another normal sample (this time using red wine vinegar) but added sodium bicarbonate powder before it had dried. I kneaded this into the polymer for around five minutes. Gradually, it became like dough and formed a single mass, rather than many compacted strands. When this would absorb no more sodium bicarbonate, it was a dark, gristly grey, and is hardening only very slowly. The only reason for this that I can think of involves some reaction with the vinegar.

Thanks!

86.146.107.210 (talk) 22:56, 1 March 2008 (UTC)[reply]

If you are using full fat milk, your final result will include a lot of milk fat, and you may have produced cheese. Graeme Bartlett (talk) 03:47, 2 March 2008 (UTC)[reply]

FYI, polymerization isn't the correct term for what is happening to the casein in the situation you describe. You could call it curdling or denaturation and coagulation. ike9898 (talk) 01:08, 3 March 2008 (UTC)[reply]

March 2

Stoichiometric flame

I am burning Isopropyl alcohol as a fuel. Isopropyl alcohol has the chemical formula C₃H₈O. I'm pretty sure I have the equation right but wanted to double check. I get C₃H₈O + 5-O₂ > 3-CO₂ + 4-H₂O + O. The free atom of oxygen seems to confirm my observation of complete combustion occurring under laminar (non-turbulent) flow using uncontaminated fuel, resulting in a flame that is perfectly stoichiometric. —Preceding unsigned comment added by 71.100.9.109 (talk) 04:05, 2 March 2008 (UTC)[reply]

Wait, why would you get an atom of free oxygen? The combustion equation for isopropanol is 2 C₃H₈O + 9 O₂ -> 6 CO₂ + 8 H₂O .Someguy1221 (talk) 04:18, 2 March 2008 (UTC)[reply]

...okay, my chemistry is a little rusty. Instead of an equation resulting in a free atom of oxygen I need to increase the number of molecules of Isopropyl until the equation is perfectly balanced. The flame would still be stoichiometric although very sensitive to non-laminar flow and/or fuel/air contaminants. —Preceding unsigned comment added by 71.100.9.109 (talk) 04:25, 2 March 2008 (UTC)[reply]

Analog Electric Gaussian Filter

Is there a device that reasonably approximates a Gaussian filter? There are digital Gaussian filters, of course, which make calculations to convolve a signal with a Gaussian function to blur images (for instance). But is there any physical device that gives a similar effect without digital computation? It needs to have an approximately Gaussian impulse response. Any dimension would be interesting. 75.168.199.1 (talk) 05:00, 2 March 2008 (UTC) Craig[reply]

Are you thinking of building something yourself, or did you just want to buy it off the shelf? If the latter, you are probably out of luck. It must be possible to calculate the filter elements for this as a Cauer or Sallen Key topology implementation but I have no references. This paper [10]expresses an approximation of the Gaussian filter as a number of cascade stages of

H(\omega )=Sinc(k_{n}\omega )

. This *looks* like it ought to transform into a circuit implementation but my maths is too crap to do it. If I had been asked to do this while I was still a design engineer, my approach, if I could not find a tame mathematician, would be to feed a vague approximation (Butterworth filter for example) into a network analysis program and then to hand adjust the component values with successive approximations until I got near enough to the desired result. Complete bodge, I know, but it should work. SpinningSpark 16:51, 2 March 2008 (UTC)[reply]

I'm going to be bold and say No. Here's my reasoning:

True Gaussian filters have infinite duration in time, (which can be worked around with feedback), but furthermore they are not causal (since half of them occurs in future-time!)
Digital filters work around this by windowing, truncating and introducing a constant time-delay.
Analog delay lines are not easy to build and are rarely linear with frequency.
If it could be built, surely a commercial part would exist, and I've not found any.

The question specifically asked for a "reasonable approximation" to a Gaussian filter, at which point I would demand a definition of "reasonable approximation," then suggest a Butterworth or Sallen-Key filter. Nimur (talk) 17:28, 2 March 2008 (UTC)[reply]

My reading of the OPs request was that he needs the output to be Gaussian in time domain to an input of a dirac pulse. In the same way that an ideal low pass filter will output a Sinc pulse in response to a dirac pulse, but with only the 0 to ∞ half and missing the -∞ to 0 half, I was assuming that the OP required the 0 to ∞ portion of the Gaussian pulse only. If that is right, my suggestion should work. If he needs the full pulse, you are right, he cannot do it precisely and will need a delay line going back to whatever point is his minimum required accuracy. I might mention at this point that I found this[11] patent claiming to make a quasi-gaussian filter out of directional couplers (microwave band) but did not include it in my previous post because, quite frankly, I cannot understand what it is claiming to be doing.

Accurate analogue delay lines are not easy to build. Accurate analogue anything are not easy to build, which is why analogue filters, especially ones using wound components, are badly out of fashion now (wish I'd known that at Uni - a lot of classes I could have skipped). My opinion is that this is the reason there is no component on the market and hence my original comment that the OP would be out of luck if he wants it OTS. One solution I have used in the past to meet the requirement for a delay line when working in the audio band is to use an acoustic echo chamber. These are large (eg bed sized) and expensive but the OP did say "any dimension". Perhaps the OP could let us know what band he is working in which would narrow down the possible solutions.

And why does it have to be analog? SpinningSpark 20:28, 2 March 2008 (UTC)[reply]

I'm only interested theoretically whether such a circuit can exist, I'm not interested in building one for a home project. There's a new mathematical approximation scheme that takes advantage of sums of Gaussians with a single variance, and I'm wondering if a Gaussian filter (because of its linearity) has any possible practical application in signal generation.

Yes. I would judge the circuit to be a reasonable approximation to a Gaussian filter based almost entirely on how close its impulse response is to a Gaussian function; i.e., its output needs to be Gaussian in time domain to an input of a dirac pulse, as SpinningSpark said. Any mean or variance is acceptable, but I do need it for all time and not just 0 to ∞. I'm assuming since the Gaussian drops off so quickly away from its mean, it is for all practical purposes 0 there. The delay criticism sounds valid, though. Reverb would mean the death of this approach.

"If it could be built, surely a commercial part would exist" is honestly the most helpful possible answer I imagined when I wrote the question. I have no practical experience with electronics, so I was hoping for this sort of expertise. Pressing on, though, I found the Bessel filter seems to have an approximately Gaussian impulse response, which I say based (entirely) on looking at the graph on p. 11 of [12]. How close does that mean it is to a theoretical Gaussian filter? (The so-called "Gaussian to 12db" filter on p. 14 has an impulse response that is a bad approximation to a Gaussian.) Is there any other circuit design that has a more accurate Gaussian impulse response? My ignorance and inexperience in this area is regrettably profound, but this limited intuition leads me to think that a Gaussian response should not be impossible (or even impractical) to generate.75.168.188.2 (talk) 21:05, 2 March 2008 (UTC) Craig[reply]

It must be analog for this imagined implementation, because I assume there would be a prohibitive time lag in processing the digital Gaussian filter of streams of real-time data. I may be wrong about that, though.75.168.188.2 (talk) 21:22, 2 March 2008 (UTC) Craig[reply]

WP has ref Wikipedia_talk:WikiProject_Electronics/Archive_1 —Preceding unsigned comment added by 79.76.194.191 (talk) 01:20, 3 March 2008 (UTC)[reply]

Blue flower identification

I took this photo at the Honolulu Zoo, and was wondering what type of flower it was. A quick search and I came up with Blue Petunias, but I wanted a second opinion. I know, like birds, flowers can look very similar and it can take a trained eye to identify them. So.... if anybody knows, please let me know! --ErgoSum88 (talk) 08:43, 2 March 2008 (UTC)[reply]

Plumbago or Plumbaginaceae should fill you in. Julia Rossi (talk) 09:44, 2 March 2008 (UTC)[reply]

Wow, that was fast. Thank you! --ErgoSum88 (talk) 10:35, 2 March 2008 (UTC)[reply]

Definitely Plumbago auriculata. Although native to South Africa, it is commonly planted as an ornamental shrub throughout the milder parts of the United States, including Hawaii.--Eriastrum (talk) 16:52, 2 March 2008 (UTC)[reply]

Taq polymerase storage

If Taq polymerase is good to go at 95 C, why does it need to be stored at -20? How quickly will it break down at room temperature? --Seans Potato Business 08:49, 2 March 2008 (UTC)[reply]

I usually see a labeled shelf life of a year-ish at -20, so I'd bet it's not so great at room temperature...and at 95 it only has to last for a few hours, usually. Someguy1221 (talk) 14:51, 2 March 2008 (UTC)[reply]

All enzymes for molecular biology, whether they be ligases, endonucleases, or polymerases should be stored in glycerol at -20C unfrozen. As someguy pointed out, it has a tremendously long shelf life. Taq poly is thermostable, which means it can operate at 95 degrees, but that's not the way to preserve it. At room temperature, the enzyme would still be functional, but it would be unsuitable for use in PCR after a few weeks. It's just terrible lab practice. Wisdom89 _{(_T / ^C)} 16:05, 2 March 2008 (UTC)[reply]

At the lab where I'm doing my internship, I've been told to do PCR reactions by making the PCR "master mix" with everything in it except Taq (which is kept on ice). Then I add template to the reaction tubes and then I add Taq to the master mix and distribute it among the reaction tubes. I think this is going unnecessarily far to protect the Taq. I think that it would be easier in some cases to add the Taq to the master mix, distribute it among the reaction tubes and THEN add the template (and take it to the PCR machine). I think the Taq would be fine.

Also, a couple of days ago, someone left an expensive Taq on ice overnight, so it was discovered floating about the next day. Despite my (admittedly weak) protest, it was thrown away (I suggested they could at least test it before throwing away the whole vial). Was this a waste? I'm not sure what kind of Taq it was, except that it wasn't one with red dye in it. ----Seans Potato Business 16:31, 2 March 2008 (UTC)[reply]

Whenever I do PCR, I create a master mix with all the reagents (excluding the template of course) including the polymerase. It works just fine. However, bear in mind that usually you make a little more of the MM before distributing, and thus you actually use less enzyme than you add, and it's expensive - but the cost might be negligible. Also, I agree, throwing away the entire tube of enzyme like that was really wasteful. It was probably fine. Wisdom89 _{(_T / ^C)} 19:15, 2 March 2008 (UTC)[reply]

Burning CuSO4-solution on paper

Hi Science, I need some help with a science project on the side of school.

I have made a paper structure stiffened by chickenwire, covered by cut paper, glued together (quite a bit of glue, around a pound's worth or more). Now, what I seek is to make a solution of water and CuSO4 (readily available), which when lit on fire, will burn green. All is good so far, but upon burning, I fear this will result in unhealthy amounts of SO3 (which follows from balancing the combustion equation). I am attempting to make perhaps around an entire litre of CuSO4, and the paper structure has an area of approximately 2 square meters.

The lighting on fire will take place outdoors, and I will have to be situated upwind (and nobody downwind). Is there no way I can add something to the solution, or apply after the coat, that will bind the SO3 at the stage of combustion, so that the health hazard is reduced? Don't be afraid of answering or guessing, since my professor has a degree in nonorganic chemistry, and whatever I do it will be carefully monitored if at all allowed. Thoughts related to other sides of the matter are also welcomed. Thank you!81.93.102.185 (talk) 11:02, 2 March 2008 (UTC)[reply]

A solution of CuSO4 and water will not burn! Did you mean you were going to soak the paper in the solution of CuSO4? If so, you won't see a lot of green because there won't be enough Cu to form a color (there will be the occasional green flash). I've tried this and speak from experience. No need to worry about SO3 production: it takes a lot of energy to dehydrate a sulfate. Delmlsfan (talk) 17:08, 2 March 2008 (UTC)[reply]

Or, you can put the CuSO4 in pure ethanol, which will burn. We used to put a lot of various salts in ethanol to make rainbow flames. I can not specifically remember if we used CuSO4 for our green flames (some salts dissolve very well in ethanol, and others do not). Also, I don't recall if there was any chemical reaction at all regarding the CuSO4 salt; it may have just been heated and providing color to the ethanol flame via atomic emission. In that case, there will be no harmful sulfur-containing gas. Nimur (talk) 17:30, 2 March 2008 (UTC)[reply]

@Delmlsfan: I believe it's obvious from what I wrote, that the solution will be used to coat the paper structure, and this is then lit on fire. Pardon my inaccuracies. I have also attempted to light this on fire, producing a green hint in the otherwise yellow and orange flame. I thought the matter was simply to increase the copper sulfate in the solution.

Now, if the flashpoint of the paper (newspaper type) is around 400ish, shouldn't it be fairly easy to light in fact ONLY the coat on fire, even if it has soaked the paper? To have a trail of the coat extend from the paper structure over to a metal plate, and light the coat on fire where it is on the plate, should the fire not then spread at an even 100 C over to the paper, and there avoid lighting it on fire? 81.93.102.185 (talk) 18:40, 2 March 2008 (UTC)[reply]

Don't think the amount of SO3 will be dangerous (as another states) - as an alternative convert the copper sulphate to copper hydroxide or copper oxide by adding base. Then use the oxide/hydroxide in your paint (note you could mix it with wallpaper paste)

Also note boric acid/borax also produce green flames - not health hazards here I can think of.87.102.93.158 (talk) 11:16, 3 March 2008 (UTC)[reply]

Women discharging too much of seminal fluid during intercourse affects their health

Hai, i have heard that women who discharge too much of seminal fluid during intercourse have their health affected and feel week , is it true? —Preceding unsigned comment added by 122.164.123.155 (talk) 14:45, 2 March 2008 (UTC)[reply]

If women are discharging seminal fluid, they're probably not a woman... -- MacAddct  1984 ^{(talk  contribs)} 16:28, 2 March 2008 (UTC)[reply]

The reference desk cannot and will not answer medical questions. Nimur (talk) 17:32, 2 March 2008 (UTC)[reply]

It only happens during "Feel Week", which starts on 29 February (and only occurs in leap years). (This is so named because many women don't actually want to propose to anyone - maybe they're already happily married, maybe they prefer to remain single, whatever - but most women like to cop a nice feel of another person's butt, crotch or chest, and they're allowed a whole week once every 4 years when they can do this to unsuspecting passers-by without fear of being charged with sexual harrassment.) For the remaining 207.6 weeks of the olympiad, nothing remotely like this is known to science. :) -- JackofOz (talk) 00:51, 3 March 2008 (UTC)[reply]

If you mean they feel weak if they don't retain seminal fluid discharged into them, then the long-standing safe use of condoms would suggest that what you heard is wrong. AlmostReadytoFly (talk) 09:20, 3 March 2008 (UTC)[reply]

Perhaps the OP is really asking about Skene's gland (warning contains gynecological imagery). Vranak (talk) 21:31, 3 March 2008 (UTC)[reply]

Fat Content In Soap?

If you gently place a bar of soap in water, it will float. Then how come me, covered in soap, wont float? Sounds pretty stupid I know, but think about it; Soap is supposed to displace water.--Sam Science (talk) 15:21, 2 March 2008 (UTC)[reply]

I just tried three different brands - they all sank. Regarding displacement, I think you are confused between Archimedes principle and the surfactant properties of soap. Soap is not fat, it is a salt of a fatty acid. Click on the blue words to see those articles. SpinningSpark 15:43, 2 March 2008 (UTC)[reply]

Most people do float in water, whether covered in soap or not, otherwise it would be very difficult for you to swim. Divers need weights to keeep themselves underwater. Soap will not normally float, unless you shape it like a boat.--Shantavira|^{feed me} 16:38, 2 March 2008 (UTC)[reply]

Ivory soap floats.--Eriastrum (talk) 16:48, 2 March 2008 (UTC)[reply]

What's specifically important there is that Ivory (and other floating soaps) are specifically aerated to allow them to float; "pure" soaps generally do not. This is analogous to pumice. — Lomn 17:01, 2 March 2008 (UTC)[reply]

Even if the soap material itself does float (i.e., not just because it's aerated, is carved out like a canoe, or has other physical attributes), covering yourself with it just adds a relatively small amount of bouyancy to your otherwise-apparently-sinky body. If you're 5 pounds heavier than the water you displace, then adding to that something that is less than 5 pounds lighter than the water it displaces will still make a net effect of "heavier than the water being displaced". DMacks (talk) 20:27, 2 March 2008 (UTC)[reply]

What is "first-strand DNA"?

What is "first-strand DNA"? ----Seans Potato Business 15:28, 2 March 2008 (UTC)[reply]

I think it just refers to the "first strand" of DNA extracted or synthesized (if the synthesis was from RNA). The only literal definition I could find was "For purposes of the present invention, first strand DNA is defined as initial DNA transcript produced from isolated viral DNA," from this patent. I've seen the term used in plenty of papers that weren't discussing viruses, but my first sentence here seems to fit all those uses I have seen of it. Someguy1221 (talk) 15:54, 2 March 2008 (UTC)[reply]

When performing RT-PCR, the first-strand DNA is the single strand of DNA synthesized by Reverse transcriptase from an RNA template. This first strand is then used to make a complementary DNA strand, and thus double-stranded DNA. -- Flyguy649 ^talk 05:51, 3 March 2008 (UTC)[reply]

Removal of sand from Sand Hills of Nebraska

Why couldn't sand from the Sand Hills of ND be relocated to beach areas suffering from chronic erosion? —Preceding unsigned comment added by Fredcowie (talk • contribs) 15:33, 2 March 2008 (UTC)[reply]

Apart from the expense, beaches suffering chronic erosion will continue to erode. So it would be a perpetual thing. Cheers Geologyguy (talk) 15:41, 2 March 2008 (UTC)[reply]

Sand will easily wash away. Large chunks of concrete last much longer, if the goal is to protect homes on the beach. Of course, large chunks of concrete make for a lousy beach for swimmers and sunbathers, so another approach is to construct a breakwater (structure) to protect the beach from wave erosion, then add more sand. It's normally cheapest to dredge the sand up from the bottom of a nearby lake, river, or other body of water, especially where a deeper channel is desired for ships. StuRat (talk) 19:43, 3 March 2008 (UTC)[reply]

chemistry

how to produce hydrogen at home —Preceding unsigned comment added by 117.193.96.108 (talk) 15:49, 2 March 2008 (UTC)[reply]

Simple Electrolysis. Wisdom89 _{(_T / ^C)} 16:06, 2 March 2008 (UTC)[reply]

(after edit conflict) By electrolysis of a solution where water is the solvent. See [13] for an efficient way to produce large quantities of hydrogen. Using this method, with a few modifications, I was able to make about ten bottles. --Bowlhover (talk) 16:11, 2 March 2008 (UTC)[reply]

Be aware, of course, that if hydrogen mixes with oxygen, it is highly reactive (explosive). --98.217.18.109 (talk) 16:48, 2 March 2008 (UTC)[reply]

Did you read the reference Bowlhover cited? It covers the safety aspects quite well. —Steve Summit (talk) 16:54, 2 March 2008 (UTC)[reply]

I did. I just wanted to re-emphasize it, like I would with anyone contemplating to do something that could be hazardous! --98.217.18.109 (talk) 20:21, 2 March 2008 (UTC)[reply]

Steel hand soap?

Hi. I have a bar of soap, triangular and made by company Michaelangelo in Germany, that is completely made from stainless steel. It removes odours, and does not lather. How does it work, and does it combine steel with water causing a molecular chemical reaction that peels away odours, and an unrelated question: can banana oil remove tough stains the way Stainz-R-Out does? Thanks. ~A H 1^(TCU) 16:39, 2 March 2008 (UTC)[reply]

~~Completely made from stainless steel? Maybe you mean they use microparticles as an abrasive. It seems very unlikely that pure steel can form anything remotely soap-like.~~

Stainless steel soap - solid evidence that Wikipedia organizes all of the world's information. Nimur (talk) 17:34, 2 March 2008 (UTC)[reply]

Wow! I've said it before -- W H A A O E! —Steve Summit (talk) 18:12, 2 March 2008 (UTC)[reply]

It seems likely that the odour molecules will bind preferentially to the metal (and not your hand), some people suggest that once on the metal, they odour molecules will be de-odorised - with the metal surface having a catalytic effect (probably oxidation)

Banana Oil - it might work on some stains - ... I can't say much more - might be good at grease spots - Sounds a bit unusual to try to use it..87.102.93.158 (talk) 11:12, 3 March 2008 (UTC)[reply]

Remember, the metal ONLY removes odors. Don't expect to be able to remove residues or bacteria. -- User:Mac_Davis 00:09, 4 March 2008 (UTC) —Preceding unsigned comment added by 216.120.217.92 (talk) [reply]

Firefox

Moved question to the Computing Reference Desk

Non-exorcise calories

Does the body use a lot of energy for functions outside of exercise and movement? Like brain activity, hair growth, blood cell production, etc, or is it a minuscule amount compared to exercise? 69.77.237.158 (talk) 22:25, 2 March 2008 (UTC)[reply]

Certainly! For example, in the USA, many people eat around 2,000 calories per day, do not exercise at all, and do not gain (much) weight. Most of your energy goes to keeping warm and keeping your systems in operation. Anyway, an exorcism would only take off 21 grams. :) -- Sean —Preceding unsigned comment added by 69.134.115.242 (talk) 22:42, 2 March 2008 (UTC)[reply]

But don't forget the weight of all the pea soup (and pee) that is expelled during the process. :-) StuRat (talk) 19:28, 3 March 2008 (UTC)[reply]

The base energy need of the body, without exercise, is called the basal metabolic rate. StuRat (talk) 19:28, 3 March 2008 (UTC)[reply]

Luminescent dry-erase boards

At my local pizza parlor, they have a dry-erase board that glows wherever the marker has marked. How does that work? Thanks. —Preceding unsigned comment added by 69.134.115.242 (talk) 22:44, 2 March 2008 (UTC)[reply]

It most likely has a black light on it. -- kainaw ™ 01:24, 3 March 2008 (UTC)[reply]

The ones I've seen are lit from inside, by what may indeed by a black light. There's a transparent sheet over a black background, and light shines through the upper edge of the glass, being mostly invisible except where it hits the neon marker and glows. I can't seem to find anything more technical than that, but that's how it looks to me. jeﬀjon (talk) 17:54, 3 March 2008 (UTC)[reply]

relativity

does the relationship $ke={\frac {1}{2}}\gamma m_{0}v^{2}$ hold up accurately for relativistic speeds, or is it just an approximation? —Preceding unsigned comment added by 172.142.196.236 (talk) 22:50, 2 March 2008 (UTC)[reply]

Well, the energy of a particle of mass m₀ and Lorentz factor γ is γm₀c². Subtracting the rest energy, we have a KE of (γ-1)m₀c², which, if my calculations are correct, is

{\frac {\gamma ^{2}}{\gamma +1}}m_{0}v^{2}

. Thus what you have is just an approximation, and an odd one at that. The leading order (in (γ-1)) approximation is just 1/2m₀v², and the next approximation is (I think) ((3γ-1)/4)m₀v². Algebraist 02:23, 3 March 2008 (UTC)[reply]

Speaking of relativity-

Sorry to be a pest fellas, but I got another question. The first one was kinda lame, this one is more interesting.

About time dilation. When Einstein said gravity slows time, is time thought of as atom movement? And is this why time is considered a "physical" property? Like if everything around you is moving at the same speed along with your atoms moving at the same rate (20x faster, 100x faster, etc.) you'd percieve time as the rate you're used to, even though you and everything around you is really moving "faster"? Also, its been said that if you fall into a black hole and reach singularity, all of time will have passed by, and you'd know it. How, if you need time itself to think?

We're probably not meant to understand the universe.Sam Science (talk) 23:25, 2 March 2008 (UTC)[reply]

Re: "We're probably not meant to understand the universe" well then, speak for yourself Sam. ;-) --hydnjo talk 01:09, 3 March 2008 (UTC)[reply]

You're quite right that you could never measure the rate of passage of your own time — what would you use, a clock? — but that's why it's called relativ[e]ity. The presence of a gravitational field within (or of acceleration of) an object causes other observers to see everything in that object happen at a reduced rate.

Similarly, but in reverse, when you fall into a black hole (assuming that you aren't killed first), the intense gravity causes most of the rest of the universe to appear (to you) to be running at ludicrous speed. In fact, as you cross the event horizon, the entire future history of the universe plays out for you, although so radically blue shifted that it's hard to understand (or to survive) the show.

Note that in special relativity, the slowing of clocks (and they only ever slow down, not speed up) is symmetric: A says B is slow precisely to the extent that B says A is slow. (This sounds paradoxical: see relativity of simultaneity.) In general relativity, which encompasses gravity, the slowdown is more "real" in that A says B is slow and B says A is fast. --Tardis (talk) 02:48, 3 March 2008 (UTC)[reply]

Small correction - the extreme blue shift phenomena only happens to an observer who attempts to hover just above the event horizon. A free-falling observer experiences much less blue shift. If the black hole is large enough to make tidal forces small then the free-falling observer can cross the event horizon with no adverse effects - although a second distant observer will never see this event. Gandalf61 (talk) 08:50, 3 March 2008 (UTC)[reply]

One of Einstein's key axioms is that time is what you measure it to be. It's not something external, some sort of magical fluid we are moving through. That's why he looks at a light clock and says that its behavior in various frames of reference tells us something about time itself. Re-thinking the nature of time and space is pretty much what (special) relativity is all about.

Time is change. Which makes sense if you think about it—every clock is just a little thing which measures regular amounts of change (tick, tock). The difference between something "frozen in time" and something not is change. We can tell when things are "sped up" or "slowed down" because change happens at a different rate. --98.217.18.109 (talk) 03:58, 3 March 2008 (UTC)[reply]

March 3

feeder fish

i need to know the habitat for the guppy and goldfish feeder fish. what would i do to habitate these fish? brie —Preceding unsigned comment added by 70.149.24.57 (talk) 00:03, 3 March 2008 (UTC)[reply]

I'm not sure what you mean by "habitate", but if you are asking about their habitat with the idea of releasing them, Don't! It's against the law in most areas to release aquarium or pond fish into the natural environment. By doing so, you risk introducing an invasive species or introducing diseases into natural bodies of water. If this is not what you meant, please clarify.--Eriastrum (talk) 00:42, 3 March 2008 (UTC)[reply]

I'm think (s)he's asking what sort of aquarium habitat would be suitable for raising the fish. -- MacAddct  1984 ^{(talk  contribs)} 01:38, 3 March 2008 (UTC)[reply]

guppy goldfish The answers are there87.102.93.158 (talk) 10:31, 3 March 2008 (UTC)[reply]

Or why not just search for "guppy keeping breeding" or whatever??87.102.93.158 (talk) 10:32, 3 March 2008 (UTC)[reply]

Or even "guppy habitat"87.102.93.158 (talk) 10:33, 3 March 2008 (UTC)[reply]

Did you mean 'natural habitat' or 'aquarium' habitat?87.102.93.158 (talk) 11:09, 3 March 2008 (UTC)[reply]

What if Jupiter were more dense?

Jupiter, when compared with the terrestrial planets, is relatively light for its size (1.326 g/cm³). If Jupiter were the density of, let's say, Earth (being the most dense at 5.5153 g/cm³) would it have any noticeable gravitational effects on the other planets? -- MacAddct  1984 ^{(talk  contribs)} 01:29, 3 March 2008 (UTC)[reply]

Noticeable? --hydnjo talk 01:39, 3 March 2008 (UTC)[reply]

Most likely yes, all gravitational forces created by an object within the solar system would produce an effect/change. I'm assuming the user asking the question is thinking hypothetically, as if it were possible to change the density of the planet now. Wisdom89 _{(_T / ^C)} 01:42, 3 March 2008 (UTC)[reply]

Yeah, just to clarify: All of a sudden, Jupiter's density became that of Earth's, while remaining the same volume that it is now. Would it be enough to significantly alter the orbits of surrounding planets or is it relatively negligible when compared to the Sun's current effects? -- MacAddct  1984 ^{(talk  contribs)} 01:46, 3 March 2008 (UTC)[reply]

I think a precise definition of "noticeable gravitational effects" is required. Even at its present mass, Jupiter does have significant effect on the solar system, creating stable orbits for the objects of the asteroid belt. Any mass change of Jupiter would change those stable orbits, which would be visible from Earth. At some critical value(s), Jupiter's mass would be large enough to destabilize other orbits. The mathematics of n-body orbital dynamics and stability is not trivial, so it's hard to say off hand what the required mass would be, say, to destabilize Earth's orbit. Nimur (talk) 06:01, 3 March 2008 (UTC)[reply]

Also, I can't help but probe your hypothetical "all-of-a-sudden" transition. What other things stay constant? Is the total angular momentum of Jupiter preserved, or is its orbital velocity preserved? What about the moons of Jupiter? Should we allow their orbits to collapse, or increase their velocities or masses to create new stable orbits for them? A lot of hypothetical questions self-defeat, if you pursue the nitpicky side-details. Nimur (talk) 06:07, 3 March 2008 (UTC)[reply]

Another way to ask the question would be, if Jupiter had the density of the Earth, then would the solar system exist in its current state? If not, what would be altered? That takes care of the all-of-a-sudden dilemma. Wisdom89 _{(_T / ^C)} 08:56, 3 March 2008 (UTC)[reply]

Scull preservation

Dug up an animal scull and want to preserve it. Can i boil it in salt water and then soak it in hydrogen peroxide to make it white again?

JERRYLEGO (talk) 02:06, 3 March 2008 (UTC)[reply]

Do you mean a scull or a skull? :-) —Steve Summit (talk) 03:08, 3 March 2008 (UTC)[reply]

Have an ant hill handy? Some sun, wind and weather? Julia Rossi (talk) 09:37, 3 March 2008 (UTC)[reply]

I love to see animals rowing. Edison (talk) 19:50, 3 March 2008 (UTC)[reply]

Your best bet, if there's a university, or museum of natural history nearby, is to call the department of anatomy or biology and ask if you can use their "bug room" to clean your skull. Dermestid beetles Dermestes maculatus are the best workers for the job. - Nunh-huh 02:58, 5 March 2008 (UTC)[reply]

physics

what is a fly wheel?84.254.189.64 (talk) 08:49, 3 March 2008 (UTC)[reply]

See the article Fly wheel. Cheers! Wisdom89 _{(_T / ^C)} 08:54, 3 March 2008 (UTC)[reply]

Animals used to attack forts

Which animal was used in the olden times for climbing onto high walls of forts? —Preceding unsigned comment added by 220.224.109.59 (talk) 12:26, 3 March 2008 (UTC)[reply]

Tortoise? Perhaps another animal name used as an analogy? AlmostReadytoFly (talk) 12:34, 3 March 2008 (UTC)[reply]

Just wondering is this a joke, or riddle, or as suggested above a siege machine with an animal name??? Otherwise perhaps a monkey with explosives attatched 87.102.93.158 (talk) 14:02, 3 March 2008 (UTC)[reply]

I'm not sure if war elephants were used for this, but it might work for a wall that was only about 10 feet tall. They could also smash down taller walls, unless they are made of thick stone. StuRat (talk) 19:11, 3 March 2008 (UTC)[reply]

Many "animals" were used in siege warfare. In addition to the Testudo formation, in ancient times, a tortoise referred to a covered, wooden shed on wheels, which was effectively a mobile shield defense, which could be adapted to many tasks during a siege: digging, ditch filling, boarding bridges, cover for the rams etc; by the Middle Ages these were given other names, including cat, owl, weasel,rat, sow. There's also a little-known wolf, which seems to have been used as a defence; it had iron gratings which could be snapped shut, trapping attackers in its jaws. A scorpion was a type of throwing machine; there's a raven, which was like a ram with a hook for pulling walls down. Wikipedia seems a little lacking on references to these, although at Siege engine you can see some tortoise/sow covers over some engines. And, of course, there's the Trojan Horse. If you want real animals, then Olga of Kiev supposedly destroyed a town by attaching burning tinder to birds' feet; John I captured Rochester Castle by burning the fat from 40 pigs; the Franks dropped hot oil, wax and fish on the attacking vikings during the Siege of Paris (885-886); see Early thermal weapons (if I might plug the article I'm currently working on) -Gwinva (talk) 00:21, 4 March 2008 (UTC)[reply]

Of course, there's the ram as well, which I managed to mention without referring to the sheep! Gwinva (talk) 02:38, 4 March 2008 (UTC)[reply]

Oxide solubility

Hi,

-which oxides of nitrogen, sulphur, phosphorus and carbon are soluble in water (I just need one example each)? Is there even one for nitrogen? I would also need their water solubilities, so it'd be great if you could point me to a reference where I can find these values.

Thanks, Duagloth (talk) 13:05, 3 March 2008 (UTC)[reply]

Nitrogen oxide and read the links to the different compounds.

Similarily carbon oxide, sulfur oxide

Also read Oxide it has a list - search this page for 'phosphorus'

Yes there are soluble nitrogen oxides

Note searching the web for "element + oxide" does work well and there are many pages aimed with education in mind eg http://www.google.co.uk/search?hl=en&q=phosphorus+oxides&meta=

Hint - many of these react with water to give new compounds.. Carbon dioxide is an exception - though it too does react a bit. Only a few are unreactive to water.

Don't forget to check the 'infobox' on the right eg Carbon dioxide right table sub heading "Solubility in water" gives 1.45 g/L 87.102.93.158 (talk) 13:58, 3 March 2008 (UTC)[reply]

If you have a text book try looking in the index or chapter headings for 'periodicity' and oxides - it's quite a common topic. —Preceding unsigned comment added by 87.102.93.158 (talk) 14:00, 3 March 2008 (UTC)[reply]

Acceleration

How can we detect whether a body is moving with acceleration or not?I mean to say that if we find something is moving with constant velocity with respect to a man living on the earth, it is moving with acceleration alongwith the motion of the earth because the earth itself is moving around the sun.If it is moving with constant velocity with respect to the solar system it is again moving with acceleration with respect to the galaxy etc etc.What is the absolute reference with respect to which we can measure acceleration of anything? Thank You —Preceding unsigned comment added by 202.70.64.15 (talk) 15:14, 3 March 2008 (UTC)[reply]

Inertial frame of reference may help. I believe the short answer is that no one frame of reference is inherently superior to any other. Friday (talk) 15:19, 3 March 2008 (UTC)[reply]

Coupled with that, it may be useful to make it explicitly clear that there is no "absolute" frame of reference. As Friday notes, any arbitrary frame is valid, and frames are generally selected for convenience. — Lomn 16:01, 3 March 2008 (UTC)[reply]

Acceleration can be measured with an accelerometer. The only problem is that an accelerometer cannot distinguish between gravitation and the more common sense of acceleration. You can get different measurements for acceleration by taking your measurements in different reference frames, but inertial reference frames will always agree on whether the accelerometer reads zero. Someguy1221 (talk) 19:19, 3 March 2008 (UTC)[reply]

The cheapest type of accelerometer is simply a cup of coffee. If you are accelerating, you will spill your coffee. If you are not accelerating, you will not. You can detect acceleration with relativity (you can't distinguish absolute movement of any sort between two inertial frames, but you can between accelerating frames), but, as Someguy1221 points out, you can't distinguish acceleration from gravity. But in many cases that doesn't really matter unless you are seriously worried about mysterious gravitational fields showing up unannounced. --98.217.18.109 (talk) 23:26, 3 March 2008 (UTC)[reply]

Energy Question

If the world is full of energy and matter then why is it so difficult to harness energy? —Preceding unsigned comment added by 202.70.64.15 (talk) 15:18, 3 March 2008 (UTC)[reply]

Because energy has to be in a useful form. You were given answers to a similar question above (March 1, once the archives kick in). — Lomn 15:58, 3 March 2008 (UTC)[reply]

Also we don't know how to harness all of it efficiently. There are technological hurdles to overcome. 64.236.121.129 (talk) 17:39, 3 March 2008 (UTC)[reply]

Lice in a sauna

Hi, can a sauna be an ultimate method of getting rid of lice? AFAIK they don't survive in temperatures above 60°C. Gil_mo (talk) 15:26, 3 March 2008 (UTC)[reply]

A google search for 'sauna lice' shows that it's often claimed as a good method, but I haven't found anything I'd cite as a reliable source so far. AlmostReadytoFly (talk) 16:20, 3 March 2008 (UTC)[reply]

what is electris current?

i want to know what is electric current really made of. most say it's flowing electrons but others speak of electromagnetic waves, sighting low drift velocities as evidence. i've read wiki's page on electric current but am still confused. please help. scoobydoo (talk) 16:22, 3 March 2008 (UTC)[reply]

Instantaneous electric current is, by definition

i(t)={\frac {dQ}{dt}}

. If you're not familiar with calculus, read the article derivative. --Taraborn (talk) 17:59, 3 March 2008 (UTC)[reply]

In semi-laymen's terms is the movement of charge measured in coulombs divided by time in seconds. Wisdom89 _{(_T / ^C)} 18:01, 3 March 2008 (UTC)[reply]

I'd go with the flowing electron model. The simplest way to think of electrons is as spherical particles, but a more correct way to think of them is as quanta of energy with a probability function describing their position. Pick whichever model you find most comfortable. StuRat (talk) 19:18, 3 March 2008 (UTC)[reply]

Electric current is exactly the flow of charged particles (typically, electrons, in most circuits; ions in some other cases). Nothing else is electric current. Electromagnetic waves can cause current; or they can be caused by current; and the complex interaction of current and waves are found via the application of Maxwell's equations of electrodynamics. In the case of "drift velocity", it is accurate to say that the drift velocity of an individual particle may be much slower than the net transfer of power through a system. In this case, the energy is propagating as a wave, closely coupled to a current. Because current can also travel as a wave, it is possible for a current to propagate farther than any individual charged-particle moves. This commonly happens when you turn on a switch to an electric light in your house. The electrons may never actually move from the switch through the light - but they each individually move such that energy propagates through the circuit. Nimur (talk) 19:46, 3 March 2008 (UTC)[reply]

Electric current can also be the flow of holes in a semiconductor or of positive ions. It is not always electron flow. Edison (talk) 19:50, 3 March 2008 (UTC)[reply]

(Depending on your school of thought, Edison, "hole transport" is just a different mode of electron transport)... and I did also mention ions, such as in some fluorescent lights and chemical batteries! Nimur (talk) 21:19, 3 March 2008 (UTC)[reply]

Your explanation was excellent. But I seem to remember, from an electrical engineering class long ago, an experiment which showed that hole current was the flow of positive charges rather than negative charges. Edison (talk) 02:58, 4 March 2008 (UTC)[reply]

For understanding drift velocity versus energy transfer, maybe this analogy will help. There's a glass bottle sitting on the ground, out of reach, and you want to tip it over. One way is to throw a rock at it. In that case the atoms making up the rock actually travel the whole distance from your hand to the bottle. Another way is to take a long stick (which happened to be conveniently lying on the ground between you and the bottle) and push the bottle with that. In that case the atoms making up the stick only move a small distance, much less than the length of the stick. Electricity works like the stick; the electrons (or holes or whatever) move only a small distance, but a small forced movement of electrons at one place in the circuit (the power source) is very quickly transmitted the whole way to the device being powered. -- BenRG (talk) 00:06, 4 March 2008 (UTC)[reply]

Travel in Space

If I was to travel in space in what could broadly be described as a straight line (from an Earth Orbit) at a constant acceleration of 1 gravity (32 feet per second per second) how long would it take:

a) For me, as I would experience duration, to pass within 93 million mile of the nearest star to the our Sun

b) From the viewpoint of an observer on Earth, who may use that reference point, to plan on receiving a radio signal in 4 1/2 years time from that point

c) Could I assume that if I was to accelerate for half the distance and decelerate for half the distance, duration (as both I and the observer on Earth would experience) be more or less exactly twice the answer to (a) above —Preceding unsigned comment added by Paul Hayward (talk • contribs) 17:16, 3 March 2008 (UTC)[reply]

(a) is basic calculus. a(t)=9.8 m/s²; v(t)=9.8t m/s; f(t)=4.9t². 93 million miles (150 billion meters, give or take) takes about 175000 seconds or 2 days. Your speed caps at about 0.6%c, so relativity can be safely ignored.

(b) I don't follow. Do you want to go 4.5 light years? Ignoring relativity, that would be 93 million seconds or about 3 years. However, that's a theoretical top speed of 3c. I'm not comfortable enough with the math for relativity to do any back-of-the-envelope calculation.

(c) Not at all. It's double the time to go halfway, which is not the same. In accelerating past your destination, the second half (distance) of the journey continues your positive acceleration. When stopping at your destination, the second half is under deceleration. It takes about 125000 seconds to go halfway from the Earth to the Sun at 1g (note that this is around 2/3 the transit time in (a)) so about 250000 seconds or 3 days to stop at the sun. Two days acceleration followed by 2 days deceleration would place you back at the Earth's orbit on the far side of the sun. — Lomn 18:42, 3 March 2008 (UTC)[reply]

I think the original question is trying to conceptualize travel and communication to Proxima Centauri, the star nearest to our solar system; the final destination being approximately earth-like orbit around Proxima Centauri.

First of all, the idea of traveling in a straight line defies orbital mechanics, but supposing that you wanted to waste a lot of effort and fuel to correct your trajectory to be "straight-line"-like, it could probably be done. It is not likely you could do this with a "constant acceleration", because you are working against a variable gravitational field.

In the interest of scientific accuracy, I think you should not try to apply straight-line kinematics to this problem; traveling across immense gravity wells is not the same at all as traveling on a straight road. See orbit for an introduction to the math you should apply to calculate your travel time, energy consumption, and trajectory. After you find the set of orbits which satisfy the fundamental gravitational constraints, you can begin worrying about things like speeding up to relativistic velocities. Nimur (talk) 19:54, 3 March 2008 (UTC)[reply]

Regarding the fuel bit, if you can sustain 1g indefinitely, then I figure to hell with any sort of efficient least-energy approach. Orbital mechanics matter to spacecraft because you can't accelerate willy-nilly. — Lomn 21:45, 3 March 2008 (UTC)[reply]

I'm a bit concerned about the calculation of 'top speed'. Neglecting the orbital speed of the Earth, a one gee acceleration (about 10 m/s^2) gets to 0.5 c (about 1.5e8 m/s) in about 1.5e7 seconds, or about six months. Relativity is definitely going to rear its ugly head.

In response to Nimur's comments, I will observe that while neglecting orbital mechanics is a bit sloppy, being able to supply a constant one-gee thrust over years of flight duration allows one to 'brute force' one's way out of quite a lot. Earth's orbital speed is about 30 km/s, which could be completely negated by a bit less than an hour's thrust. At Earth's distance from the Sun, acceleration due to solar gravity is less than 0.1% of one gee; nearly negligible. Yes, you're climbing out of a gravity well, but (per Lomn's comment) if you can pull one gee indefinitely then you can pretty much ignore the effect of the Sun and the planets. TenOfAllTrades(talk) 22:37, 3 March 2008 (UTC)[reply]

In special relativity the time it takes to travel a distance d at a constant acceleration a starting from rest is exactly

{\frac {c}{a}}\cosh ^{-1}\left(1+{\frac {ad}{c^{2}}}\right)

. By a happy accident, one gee times one light year is very close to c² (within about 3%), so at one gee acceleration the time in years is about cosh⁻¹ (1 + distance in light years). For small values of x, cosh x ≈ 1 + x²/2, so for short distances the time in years is around

{\sqrt {2\cdot {\mbox{distance in light years}}}}

, which is also the Newtonian answer. For large values of x, cosh x ≈ e^x/2, so for long distances the time in years is around

\ln(2\cdot {\mbox{distance in light years}})\,\!

. So the distance traveled is exponential in the time taken—you can travel a billion light years in about two decades (or four decades if you start decelerating halfway). But there are two serious problems. First, the amount of fuel you need is also exponential; second, at high enough speeds the CMBR and cosmic dust are blueshifted to lethally high energies. -- BenRG (talk) 23:26, 3 March 2008 (UTC)[reply]

Mineral residue in pan after boiling water

The air in my home has been extremely dry as of late, causing me to get nosebleeds. I've been trying to add moisture to the air by boiling water, but there is always a white residue of minerals and whatever else may be in drinking water stuck on the pan. What is this residue and is there anything I can add to the water for the residue to bind to instead of crusting up my pot? It's rather hard to scrub off... Also, why is it never apparent when food is in the water boiling along with it? Does the residue soak into the food (e.g. noodles) and is this unhealthy? Thanks! Jihiro (talk) 17:18, 3 March 2008 (UTC)[reply]

Why not just get a Humidifier? 64.236.121.129 (talk) 17:38, 3 March 2008 (UTC)[reply]

Thank you, but that's not the point. If I wanted to spend money on a humidifier, I wouldn't be taking the cheap easy way. ^_^; Jihiro (talk) 17:48, 3 March 2008 (UTC)[reply]

Spend the 15 bucks and get something that actually works. IMO, it's the simplest solution. 64.236.121.129 (talk) 15:35, 5 March 2008 (UTC)[reply]

You're right that it's minerals. For its composition and more, see Hard water. moink (talk) 17:51, 3 March 2008 (UTC)[reply]

There are coils of metal wire that usually go in kettles to which the 'scum' will preferetially attach. Unfortunately I can't remember for the life of me what they are called. But you need one of those.87.102.93.158 (talk) 17:54, 3 March 2008 (UTC)[reply]

I always assumed that the reason the buildup doesn't show up when boiling food is that you don't go through as much water; you boil the water for maybe 10 or 15 minutes, then you turn it off and dump the water. When humidifying, you're boiling for longer, and all the water that gets into your air came from the pan, leaving those minerals concentrated enough to condense (crystallize?) onto the pan. Since money saving is important to you, you might want to look at the utility cost difference, since boiling water on a stove is pretty inefficient. jeﬀjon (talk) 18:20, 3 March 2008 (UTC)[reply]

Some thoughts (are you moist with anticipation ?):

1) Minerals can build up from boiling food in water, but rarely do, since you don't typically boil much water away when food is prepared, dump the remaining water containing the minerals, and wash the pot after, which removes any small quantity of minerals along with the food residue.

2) Humidifiers also accumulate mineral residue, unless you use distilled water, which is rather expensive when used in such quantities. An exception is an ultrasonic humidifier, where the minerals don't accumulate, but rather go into the air. This might sound like an advantage, but having things like chlorine from the water vaporized into the air is quite annoying (it eventually becomes a white dust on the furniture), so it becomes even more important to use distilled water.

3) My suggestion: use the junkiest old pots you have (or can scam from friends and relatives) for boiling water, and don't worry about the mineral buildup. Avoid aluminum pans, however, or those with a nonstick surface, as you will sooner or later boil the pot dry and burn it. Fumes from overheated aluminum and nonstick pans can be toxic. An old cast-iron pot would be good to use.

4) You might also want to prepare more boiled foods in winter, like soup, since the extra heat and humidity is appreciated then, and use the microwave oven more often in summer, when heat and humidity are to be avoided.

5) Also be careful not to boil too much water, as the air in a house in winter can only hold so much moisture. If moisture starts condensing on windows and exterior walls, it's time to cut back on boiling water, as it's no longer staying in the air but only providing a breeding ground for mold.

6) If you have kids in the home, I wouldn't boil water either, as having a pot of boiling water on the stove all day dramatically increases the chances that they will suffer serious burns.

7) If you have a gas stove you use to boil water, beware that combustion products from the flames are filling your home. While the small amount produced by cooking isn't normally a problem, the much larger quantity of combustion products from continuous boiling of water can build up to toxic levels, as well as deplete the oxygen supply. You could, of course, open a window or two, but there goes the heat and humidity, too. If this is the case, you may need to bite the bullet and buy a humidifier. Another option is to just leave pans of water out so that evaporation will do the job for you. Water will, of course, evaporate much more slowly, but placing many trays of water where air from the furnace blows on them will help to speed things up a bit. This also has the advantage of being safer and cheaper.

8) The shower can also be used to humidify the house. If you would normally take a bath, instead turn it to the shower setting and fill the tub that way. To prevent the humidity from condensing out on the bathroom mirrors and walls, leave the door open and use a fan to blow air in and out of the bathroom. Also, don't drain the bath or shower when done, but leave it there at least until room temperature, and better yet until right before the next bath or shower.

9) To help with the nosebleeds, try a spray mister device that will spray saline solution into your nostrils. You should be able to find them in the pharmacy section of any store. If you also get chapped lips, use lip balm to help with that. If you have dry skin, use moisturizer. You should also check with your doctor, as nosebleeds can be a sign of disease.

10) Be sure to drink lots of water, as that helps keep your nose, lips, and skin moist.

11) As for food absorbing minerals, I doubt if much of this happens, but some of those minerals that are absorbed, like calcium and iron, are helpful, while others are not, like sodium and arsenic. However, the quantity absorbed of the unhealthy minerals is likely too low to matter. StuRat (talk) 18:26, 3 March 2008 (UTC)[reply]

Anyways, the residue usually is mostly CaCO3. It's hard to scrub, but it easily yields to any form of acid. Get vinegar or better a neutral vinegar concentrate, put 3 tablespoons or so in the pot, and let it stand for a while, then rinse and repeat as necessary. Heating the pot speeds up the process (but don't boil away all the vinegar). --Stephan Schulz (talk) 18:31, 3 March 2008 (UTC)[reply]

Why buy a device to spray liquid into your nose? Just inhale a few drops of tap water. It can't hurt, and I think it helped me when I had that problem. The other thing I did was, if I did get a bleed, to insert a tissue soaked in ice water into the nostril repeatedly until the cold stopped the bleeding. That way there was no residue of blood to become itchy when it dried. (Yes, this is Original Research.) --Anon, 22:51 UTC, March 3, 2008.

Can't hurt? If you've ever been swimming, you'll know that water up the nose hurts like the blazes. --Carnildo (talk) 23:51, 4 March 2008 (UTC)[reply]

I didn't mean that much water. --Anon, 00:53 UTC, March 5.

My humidifier fills up with mineral crust too if it is not emptied. You get concentrated mineral water. Graeme Bartlett (talk) 22:15, 3 March 2008 (UTC)[reply]

Sometimes it's enough to leave bowls of water in different areas and just trust in evaporation. And I agree with the tips especially keeping yourself hydrated, balm and nasal sprays and the bath water -- Julia Rossi (talk) 07:35, 4 March 2008 (UTC)[reply]

Dog run and swim speeds

Approximately how fast can a dog run, and how fast can it swim? The number doesn't need to be exact, in fact I will probably round it to something convenient. I am thinking of a black lab or a golden retriever, some kind of domestic dog that plays fetch. moink (talk) 17:43, 3 March 2008 (UTC)[reply]

From our article Greyhound (the fastest dog), it can reach speeds up to 72 km/h. The smallest and weakest breeds are slower than an average adult human, so probably less than 25 km/h or even 20 km/h. As for the swimming speed, I think they're pretty slow, slower than a front crawl swimmer, so my guess is... about 4km/h. --Taraborn (talk) 18:19, 3 March 2008 (UTC)[reply]

Given that the world-record-holding dog can swim 6.4 km in 73 minutes (5.3 km/h), Taraborn's guess is probably reasonable for average dogs. Moink, consider whether you want a burst speed or a sustained speed (like the above). For comparison, the human world record for a 10km run (26:17.53) is only about 67% the average speed of the record 60m sprint (6.39s). jeﬀjon (talk) 18:31, 3 March 2008 (UTC)[reply]

Thanks. I was hoping to be able to choose them to be two elements of a Pythagorean triple, but that's not happening it seems. So I'm going with a tenth of one, and choosing run speed=6.1 m/s, swim speed =1.1 m/s. Should be close enough to not require too much suspension of disbelief. moink (talk) 19:08, 3 March 2008 (UTC)[reply]

It sounds like you're squaring the velocities - are you trying to calculate the kinetic energy of a running dog? Nimur (talk) 19:56, 3 March 2008 (UTC)[reply]

No, I'm writing a homework question based on this experiment. Actually, following a link there to the published paper, the mathematician's Welsh Corgi ran at 6.4m/s and swam at 0.91 m/s. I only found the link after asking this question, figuring I should see if there was a published source for anecdotal story I had heard. moink (talk) 20:30, 3 March 2008 (UTC)[reply]

Circuit analysis

Was running over some circuit analysis and I met the emphasized point that you don't connect voltage sources in parallel or current sources in series because it would break down Kircoff's laws. So in reality what happends if you do these connections?Bastard Soap (talk) 19:10, 3 March 2008 (UTC)[reply]

Voltage sources and current sources are idealized concepts used in circuit analysis. No such devices exist in reality. What happens when you hook up various power-providing devices in various ways depends on the devices, and can sometimes be destructive. For example, hooking two sets of alkaline batteries with different nominal voltage outputs (which means different numbers of cells in series inside the battery), in parallel, will cause the higher-voltage one to charge the lower-voltage one, and can cause the latter to explode, getting acid all over your carpet. moink (talk) 19:18, 3 March 2008 (UTC)[reply]

For ideal current sources in series, there would have to be two different currents in the same wire, which is impossible. For two ideal voltage in parallel, there would have to be two different potential differences between the same two terminals. It would be a mathematical impossibility. For actual sources of current or voltage like batteries, regulated power supplies, or transformers, if the difference was very significant large currents could flow, damaging equipment, making wires heat up, making storage batteries explode, or (hopefully) blowing fuses. In the real world, two voltage sources connected by wires or even large copper bus bars would have the resistance of the wire or bus bar between them, and if its fraction of an ohm were put into the circuit analysis. you could calculate the huge current that would flow until something blew. Fault analysis in power systems works something like this. Edison (talk) 19:48, 3 March 2008 (UTC)[reply]

At a certain stage in standard academic treatment of the electrical engineering curriculum, the concept of "ideal" voltage and current sources ceases to exist. At this level of analysis, realistic models of a device are used; sometimes the configuration is such that it will be a "current source" or "voltage generator" circuit - and is a fairly standard "textbook" topology. In that case, connecting two model current-sources in series, for example, will have a real and calculable result - maybe you will over-current or under-current, change the voltages unexpectedly, etc. Furthermore, if you end up with an out-of-range parameter, your device may be destroyed as Moink and Edison described. Nimur (talk) 20:05, 3 March 2008 (UTC)[reply]

When jump-starting a car, you connect the batteries in parallel, and until you connect them they're at different voltages because one's charged and one's flat. Once you've connected the extra battery to the flat one, the voltage across both of them will be about the voltage across the extra battery. AlmostReadytoFly (talk) 00:28, 4 March 2008 (UTC)[reply]

A current source in the real world or for calculation purposes would be a very high voltage with a very high series resistance. Suppose you have 1,000 volts with 1,000,000 ohms in series, to produce 1 milliampere through a direct short. If instead of a direct short you presented 500 ohms between your thumb and index finger, the current would be 1,000/1,000,500 or .9995 milliamperes, 99.95% of the short circuit current, or the same current for all intents and purposes. (I have experienced such phenomena, and it is not pleasant!) A voltage source could be modelled as having a shunt resistance which was very low resistance, so that it would maintain about the same voltage even if you connected a very low resistance across it. See also Current source , Voltage source , Norton's theorem , Thévenin's theorem , and Kirchhoff's circuit laws. Edison (talk) 02:56, 4 March 2008 (UTC)[reply]

plate tectonics

is there evidence that suggest that the theory of plate tectonics is wrong? if so what. —Preceding unsigned comment added by 205.202.37.130 (talk) 19:44, 3 March 2008 (UTC)[reply]

I thought that by now it was fact. Is there anyone that doubts plate techtonics? The Flat Earth Society, maybe? 206.252.74.48 (talk) 19:49, 3 March 2008 (UTC)[reply]

See plate tectonics. This model is widely accepted. Friday (talk) 19:56, 3 March 2008 (UTC)[reply]

It is certainly not accepted amongst hard line biblical creationists as the time scale is not compatible with the Bibles' time line (if taken literally). This Google search turns up a random selection of their sites [14]' SpinningSpark 21:25, 3 March 2008 (UTC)[reply]

Sure, but the questioner asked about evidence, which is apparently neither necessary nor sufficient for the YEC crowd. --Sean 21:33, 3 March 2008 (UTC)[reply]

The Answers in Genesis site has a page on catastrophic plate tectonics along with supporting "evidence". Wikipedia also has a section discussing it on Flood_geology#Runaway_subduction. It seems like the standard creationist strategy: Take everything science has already discovered but come up with an explanation for a much shorter time span. -- MacAddct  1984 ^{(talk  contribs)} 22:46, 3 March 2008 (UTC)[reply]

This may be irrelavent but I personally think that there are more plates on Earth than previously thought, even if some of their faults don't extend perfectly from the surface to the mantle. Thanks. ~A H 1^(TCU) 22:02, 3 March 2008 (UTC)[reply]

I vaguely remember a claim that said that the relative motions of the plates do not add up, so that something is wrong, but again that is not evidence, and it probably was some inaccurate figures. Nowdays accurate GPS measurements can demonstrate movement. These also show that the plate model may not be as simple as is drawn with solid plate seperated by fault lines, and that there are regions of ground that are being compressed or stretched. (which of course is demonstrated by complex faulting or folding). Graeme Bartlett (talk) 22:11, 3 March 2008 (UTC)[reply]

If there were any evidence that it were not true it would not be an accepted scientific theory--Shniken1 (talk) 22:55, 3 March 2008 (UTC)[reply]

Um, actually in practice it doesn't quite work like that. There are often anomalies to any theory that don't quite fit but unless they are judged to be major it is assumed that they are either slight problems with the data or collection or otherwise will be explained later by a better theory. If scientists threw out any theory the second there was a problem with it then they'd have precious little left. Both General relativity and Quantum mechanics have at their core a major problem (they are incompatible with one another) but they are both considered accepted scientific theories though all physicists believe at some point they will be succeeded or improved one way or another. --98.217.18.109 (talk) 23:10, 3 March 2008 (UTC)[reply]

You could have a look at the arguments advanced by the proponents of the Growing Earth Theory and expanding earth theory (more or less the same thing), but they aren't very convincing. 200.127.59.151 (talk) 22:58, 3 March 2008 (UTC)[reply]

There are very very few who doubt plate tectonics. Karsten M. Storetvedt, Professor emeritus at the University of Bergen, Norway, has published a book about his own alternative theory: "Global Wrench Tectonics – Theory of Earth Evolution", ISBN 82-450-0072-8. According to this theory, the continents have just been twisting back and forth a bit. To my knowledge he is absolutely alone in supporting this view. EverGreg (talk) 13:07, 4 March 2008 (UTC)[reply]

Why no self poisoning?

Looking at the world's most poisonous creatures, for example, the King brown snake, Inland Taipan, marbled Cone snail, Australasian funnel-web spider and seeing that many kill their prey that way in order to eat them (not just in self defense), how come the poison doesn't affect eating it? Julia Rossi (talk) 23:05, 3 March 2008 (UTC)[reply]

Speculating a little here: The poisons are quite likely not as harmful when consumed orally as when injected. But even if they were just as potent orally, the predator would still be getting a smaller dose per unit time, because it presumably doesn't eat the whole thing at once after killing. And finally the predators may well have evolved some level of resistance to their own venom. --Trovatore (talk) 23:12, 3 March 2008 (UTC)[reply]

See Snake_venom#Immunity. It seems that most snakes are immune to their own venom, and some snakes are even immune to the venom of other snakes. This is probably because of the presence of antibodies that target the venom. --98.217.18.109 (talk) 23:18, 3 March 2008 (UTC)[reply]

Looking at it from a natural selection point of view, it's safe to assume that all poisonous-creature mutants who were born without immunity to their own poison but with a desire to eat their poisoned victims have long since gone extinct. --sean —Preceding unsigned comment added by 69.134.115.242 (talk) 00:02, 4 March 2008 (UTC)[reply]

Because the venom of most snakes is not toxic when ingested. Most snakes are not immune to their own venom. Note that the claim that they are in the snake venom article is unreferenced. (Species which feed on poisonous snakes, such as king snakes, are another matter.) This is a serious problem in zoos: In captivity, some species go a little wacko and bite themselves, with fatal results. However, except for a few species such as spitting cobras (which I assume must be immune), snake venom requires injection into the lymph (elapids) or blood (vipers) to be affective. You can drink most cobra or viper venom without ill effects, and similarly snakes can eat poisoned prey without ill effects even without immunity. kwami (talk) 00:23, 4 March 2008 (UTC)[reply]

Thanks all, that was fast! and explains a lot. To digress, I was also wondering about the poison-as-defense creatures (the Golden Poison Frog for example) getting close to each other, yet not dying, and it turns out they have inbuilt resistance factors. Interestingly, they get their poison from a beetle that carries it. Makes that old saying about meat and poison creepily more than a truism. Cheers, Julia Rossi (talk) 03:25, 4 March 2008 (UTC)[reply]

Chromosome number changes

I believe I have a good understanding of how evolution works, but I have not yet seen how evolution explains the difference in the number of chromosomes between organisms. Humans have 46; but some species have over a hundred, and it is (as best I have found) always an even number. Could someone direct me to an overview of how this process works? It might make a worthy addition to the evolution or the chromosome article, if it has not been explained there yet. Thanks. ~ S0CO^{(talk|contribs)} 23:00, 3 March 2008 (UTC)[reply]

The change in numbers can happen when a chromosome splits, or two join together. This could happen with a cross over mistake, a virus insertion break, or a repair mistake, or even a complete doubling due to failure to divide properly. It still has to be explained why the change can be preserved and that the organism is still fertile, and its offspring are still fertile. Bacteria have one chromosome. What caused Eucaryotes to have multiple chromosomes? Graeme Bartlett (talk) 08:00, 4 March 2008 (UTC)[reply]

Multiple chromosomes are benefitial for three reasons I can think of. Firstly, multiple chromosomes increases the ease of mitosis given the very large eukaryotic genomes. Secondly, changes in chromosome number allows a new method of possibly benefitial mutation. I have a hard time seeing how likely that one is, but there must be something to it given the variety in chromosome number between species. And finally, and most clearly benefitial, homologous recombination of chromosome pairs allows for nearly error-less reconstruction of a damaged chromosome (relative to the other methods available for fixing the loss of entire base pairs). For the OP, the mechanisms for changing chromosome number are described in chromosomal abberation and nondisjunction. Someguy1221 (talk) 08:27, 4 March 2008 (UTC)[reply]

see [15] for a theoretical basis for the evolution of chromosomes (and click on 'related articles" for more such.) - Nunh-huh 08:29, 4 March 2008 (UTC)[reply]

It seems that the inter-relation between chromosome structure (karyotype) and evolution is not at all clear. Chromsome number can vary between quite closely related species (see List of number of chromosomes of various organisms), and in some cases there is chromosomal polymorphism within a single species. Our karyotype article says "Although much is known about karyotypes at the descriptive level, and it is clear that changes in karyotype organization has had effects on the evolutionary course of many species, it is quite unclear what the general significance might be". Gandalf61 (talk) 10:38, 4 March 2008 (UTC)[reply]

How did Darwin account for this? I'm sure he would've been challenged. Zain Ebrahim (talk) 12:47, 4 March 2008 (UTC)[reply]

Darwin was not aware of the role of chromosomes in heredity. Although chromosomes were first observed in the 1840s, their role as carriers of genetic material was not established until Theodor Boveri carried out experiments with sea urchin eggs in 1901/1902. On the Origin of Species was published in 1859, and Darwin died in 1882. It is sometimes forgotten that Darwin developed the theory of evolution without any clear idea of the mechanism of heredity or any knowledge of modern genetics - which makes his achievement all the more remarkable. Gandalf61 (talk) 15:04, 4 March 2008 (UTC)[reply]

The reality is that the chromosome number is always changing in the evolutionary time frame. The degeneration and potential loss of the Y chromosome is well documented. Likewise doubling chromosomes is not uncommon, especially in plants leading to polyploidy. This is associated with genomic shock which leads to many rearrangements and deletions in the doubled set that soon become unique. Breeders have utlized this to vastly improve crops such as brassica and wheat. Finally chromomes can stick together to reduce the number. This appears to have haapened to the human chromosome 2 that has identity to two different chromosomes in the chimpanzee genome. This phenomena is known as Robertsonian translocation. It is also responsible for Familial Downs Syndrome that is a form of trisomy that is not due to a third chromosome 21 but due to a mutant chromosome that some people carry that has chromosome 21 co-joined to another autosome. David D. (Talk) 16:47, 4 March 2008 (UTC)[reply]

March 4

What was the goal of the Wright Brothers?

The wright brothers created a heavier-than-air air craft, but did they have a goal behind it? Did they imagine a world in where aircraft would be a form of transportation? Thanks. —Preceding unsigned comment added by Legolas52 (talk • contribs) 00:45, 4 March 2008 (UTC)[reply]

See Wright brothers. They were not the first to get a heavier-than-air craft to fly. They were focused on creating a steering system to make fixed-wing flight manageable. They succeeded. At the time, many people thought the future would be full of people flying around in small aircraft. Even in the 50's and 60's, it was imagined that personal airplanes were just a few years away. So, assuming that the Wright brothers didn't imagine a world full of airplanes would be very unconvincing. -- kainaw ™ 02:55, 4 March 2008 (UTC)[reply]

It's pretty amusing how many countries consider one of their own to be the inventor of true flight, simply by adjusting the lever on what constitutes true flight. Once in casual conversation a Brazilian mentioned to me that Alberto Santos-Dumont invented the airplane with as much surety as most Americans say the Wright brothers did so. :) --Sean 13:09, 4 March 2008 (UTC)[reply]

Yes, and New Zealand always trots out Richard Pearse. First flying machine makes interesting reading. Deciding who was "first" and determining it by control, or power, or distance is missing the point. The fact is no one person invented the aeroplane; there was a lot of parallel development late 19th/early 20th C, all of which, in small ways or large, contributed to the development of the modern aeroplane. As to why: well, everyone since Icarus has wanted to fly. Gwinva (talk) 20:22, 4 March 2008 (UTC)[reply]

Correct me if I'm wrong, but I believe nature was the inventor of true flight. We took a hell of a long time to catch up!206.252.74.48 (talk) 15:50, 4 March 2008 (UTC)[reply]

I flew just fine when I was a small fruit bat. In fact, I often bragged about my ability to zip from place to place in near complete darkness. Then there was that whole evolution thing and it's been downhill ever since. -- kainaw ™ 04:04, 5 March 2008 (UTC)[reply]

Glow-in-the-dark cats

Where on Wikipedia may I read an article about South Korean glow-in-the-dark cats?--The Fat Man Who Never Came Back (talk) 01:17, 4 March 2008 (UTC)[reply]

I would like to see pictures as well.--The Fat Man Who Never Came Back (talk) 01:18, 4 March 2008 (UTC)[reply]

It's not on Wikipedia, but I found an article and pictures. [16] Someguy1221 (talk) 01:21, 4 March 2008 (UTC)[reply]

Thanks to you!!!!!!!!--The Fat Man Who Never Came Back (talk) 01:44, 4 March 2008 (UTC)[reply]

You probably want to look into bacterial transformation (BT), green fluorescent protein (GFP). -- MacAddct  1984 ^{(talk  contribs)} 02:01, 4 March 2008 (UTC)[reply]

How about glow-in-the-dark pigs? [17] Sandman30s (talk) 14:35, 4 March 2008 (UTC)[reply]

The death of Betelgeuse

I am a fan and ardent reader of Wikipedia, especially the science pages. My question is: why is it so controvertial to discuss the imminent demise of Betelgeuse and what that means for humanity in the Wikipedia article?

Firstly, it is a celebrity star. It is one of the largest stars in the known universe; if it replaced Sol in our solar system, it would reach out almost to Jupiter. This red supergiant is very close, only a few hundred light years away, and it is the very shoulder of Orion: a star that surely each and every one of us can thank for untold choices made by our ancestors in its bright contenance.

Secondly, it is dying. Yes, it's only a few tens of millions year old but it's burning up very large atoms at the moment and there is no doubt that this utterly massive star is at its utter breaking point.

Thirdly, there is an extremely high probability that it will undergo a type II supernova. Perhaps it already has. It's possible, and not all that improbable, that tomorrow night the sky will be a canvas to the most spectacular (and anticipated!) supernova we've ever known. The sky will have a new full moon. The brightness will last for months and maybe even a few years, being visible even in broad daylight.

Orion will lose a shoulder, and a new moon will be born.

This isn't mysticism. It's not astrology. It's likelihood. Surely part of the point of Science is to inspire new generations by presenting facts that captivate. I understand turning down entries to articles that are outlandish though technically possible. But there are an undeniably strong contingent of articles out there that point to the supernova of Betelgeuse and what that implies for the landscape of the sky each and every one of us look upon. Sappysap (talk) 02:02, 4 March 2008 (UTC)[reply]

Quick answer - Wikipedia is not a crystal ball and Wikipedia is not a repository for original research. And for good measure, don't use weasel words.

Slightly longer answer - information in Wikipedia has to be verifiable with citations to reliable sources. Even in articles on mathematical subjects (at least the ones that have been labelled good or even featured, like 0.999...) use only information that can be referenced, even in the case of proofs which follow from known axioms. So if Betelgeuse is going to go supernova in the next million years, find a reference for it! If "some scientists say" something, say who. If something "may" happen, put a couple of citations next to it - one that says why it might happen, and one that says why it might not. And, as much as possible, make sure that those references are ones that have some degree of reliability - Physics Review is good, New Scientist is ok, a letter to the Washington Post is out of the question. Confusing Manifestation(Say hi!) 02:17, 4 March 2008 (UTC)[reply]

Fantastic use of buzzwords. Hands down, grats for that. But I don't think you have any grasp of the science of supernovae. I'm quite sure you did not research a single lick into why this particular star is unstable. When you want to present yourself as an authority, at least have the audacity of fact to support you. Sappysap (talk) 02:27, 4 March 2008 (UTC)[reply]

You asked a question about Wikipedia, Confusing Manifestation explained the issues within Wikipedia. You did not ask anything about the star, only about why things work like they do in Wikipedia. Confusing Manifestation did not attempt or pretend to present themself as an authority on supernovae, or say anything about the science of them. I suggest you reread what was written, perhaps apologise for jumping on someone trying to help you (rather than simply pointing you to the Help Desk where questions about Wikipedia are more properly addresses) and hopefully see that the answer to your question ("why is it so controvertial to discuss the imminent demise of Betelgeuse and what that means for humanity in the Wikipedia article?") has been thoroughly provided. Skittle (talk) 02:40, 4 March 2008 (UTC)[reply]

And, to add one more note to Confusing Manifestation's answer: Wikipedia is not a message board. Articles are not a good place to discuss anything. They are for referenced and encyclopedic content. If you want to discuss a possible supernova, go do a supernova message board. I'm sure there are hundreds of possible ones to choose from. -- kainaw ™ 02:50, 4 March 2008 (UTC)[reply]

Thanks guys. I just needed the publicity. I'm sure the article will be looked at and revised. Just glad this post is still hereSappysap (talk) 02:53, 4 March 2008 (UTC)[reply]

I must say that this is a very unusual way of having an article improved. It sure gave me a good laugh. --Bowlhover 03:36, 4 March 2008 (UTC) —Preceding unsigned comment added by Bowlhover (talk • contribs)

Hey, the whole purpose of the reference desk is to improve the quality of the articles, although we treat the purpose as to answer questions! Graeme Bartlett (talk) 05:53, 4 March 2008 (UTC)[reply]

I doubt such an event can outclass the Great Collapsing Hrung Disaster of Gal./Sid./Year 03758. 206.252.74.48 (talk) 16:23, 4 March 2008 (UTC)[reply]

What is a Hrung, and why should it choose to collapse there, particularly? --Trovatore (talk) 01:29, 5 March 2008 (UTC)[reply]

Photosynthesis question

I'm doing a sheet of 5 photosynthesis-related problems and I think I've gotten all of them except for 1, which has me totally stumped: "The photosynthetic rate of aquatic plants in a test tube can be determined by collecting and measuring the amount of oxygen that gases out of the water. If bicarbonate, the source of CO₂ for aquatic plants, is added to the water, the rate of oxygen evolution increases. If CO₂ is fixed by the Calvin cycle but oxygen is evolved by the light reactions, how can an increase in CO₂ supply increase the rate of oxygen evolution?" If anyone could point me in the right direction, I'd greatly appreciate it. Thanks, anon. —Preceding unsigned comment added by 70.18.18.201 (talk) 04:33, 4 March 2008 (UTC)[reply]

You need to consider the ratio of NADPH/NADP⁺. How does it affect the rate of photolysis? How does the concentration of carbon dioxide affect the ratio? David D. (Talk) 05:12, 4 March 2008 (UTC)[reply]

Be mindful in the future that the reference desk is not an appropriate place to seek answers to obvious homework questions. Wisdom89 _{(_T / ^C)} 05:16, 4 March 2008 (UTC)[reply]

I find homework questions perfectly acceptable on the reference desk. The top of this reference desk has a guideline stating:

"Do your own homework. The reference desk will not give you answers for your homework, although we will try to help you out if there is a specific part of your homework you do not understand. Make an effort to show that you have tried solving it first."

User:70.18.18.201 has not asked for answers and he showed that he tried solving the photosynthesis problem himself, so I see no problem with him asking for help here. --Bowlhover 05:41, 4 March 2008 (UTC)

Not only is there no problem with the question, there is no problem with the answer either. David D has not done the homework for the questioner, but provided him/her with hints and links to help him do it himself, as per guidelines. SpinningSpark 07:09, 4 March 2008 (UTC)[reply]

Don't totally misunderstand me. I wasn't admonishing anyone for providing the answer or asking the question. I was just alerting the user to the fact that such questions could be construed as such, and that editors at the reference desk will abstain from answering questions of that nature - in case he/she wasn't aware. It was more of just be careful in the future kind of thing. Wisdom89 _{(_T / ^C)} 00:30, 5 March 2008 (UTC)[reply]

It's not particularly helpful to indulge in hypothetical philosophical discussions about reference desk procedure with questioners. Best just to get out of the way and let the question be answered, if you don't care to answer it yourself. "Do your own homework" is a means of "biting the newbie" that has been too often tolerated here. - Nunh-huh 02:49, 5 March 2008 (UTC)[reply]

Equivalent of menstruation, but in men

Is there such a thing? Do men have cyclical hormonal changes?Mr.K. (talk) 12:10, 4 March 2008 (UTC)[reply]

No, there is no monthly cycle in men. Yes, men have cyclical hormonal changes, but they are diurnal, with testosterone levels slightly higher in the morning. But it's a daily cycle, and there's no cycle in men that's longer than a day. As men age, their testosterone levels become lower, but again, that's not a cyclical change, but one due to senescence. - Nunh-huh 12:24, 4 March 2008 (UTC)[reply]

Closest I can think of is accidental bloodletting, aka 'accidentally' cutting your finger while chopping vegetables, accidentally falling of your bike and scraping up your knees and elbows, accidentally getting clipped in the face with a hockey stick. Vranak (talk) 21:30, 4 March 2008 (UTC)[reply]

Depends on what you mean by equivalent. A nocturnal emission is somewhat equivalent- the body is casting off leftover stuff it wanted to use for reproduction. Friday (talk) 21:33, 4 March 2008 (UTC)[reply]

That's not very eqivalent. That only happens if you are aroused while sleeping. Dreaming about having sex, or thinking about having sex. That sort of thing. 64.236.121.129 (talk) 15:33, 5 March 2008 (UTC)[reply]

The OP is asking about hormonal cycles, not regular bleeding. Mr K, Chronobiology and Circadian rhythm might interest you.

The OP is asking about the equivalent of menstruation in men. Vranak (talk) 01:04, 5 March 2008 (UTC)[reply]

The Human Ship of Theseus thing...

You hear all the time people saying that the cells of your body get completely replaced every 7-10 years or so, questioning the identity over time of human beings by invoking the Ship of Theseus paradox. My question is this: that's just plain BS, isn't it? I mean, sure, some cells do get replaced all the time (skin cells, most obviously), but the cells that play a role in determining who you are, what your identity is, that's your brain-cells, and they don't get replaced, right? I've always been taught that when you hit puberty, you have as many brain cells as you're ever going to have. So doesn't that pretty much blow that little brain tickler clear out of the water (not the general paradox, but as applied to human beings)? 83.250.207.187 (talk) 13:26, 4 March 2008 (UTC)[reply]

brain cells might/can regenerate - see brain cell, also why assume they don't?87.102.44.156 (talk) 14:51, 4 March 2008 (UTC)[reply]

Some cells are rarely replaced, neurons being an excellent example of one such cell type. However, even in those cells, many of the molecules that compose it are regularly replaced or recycled. For example, the plasma membrane in many cells, again including neurons. The short answer is this: nope, no BS here. – Clockwork Soul 19:44, 4 March 2008 (UTC)[reply]

If every cell is replaced by its exact duplicate then the sum of its parts (you) will be exactly the same. Environmental and dietary factors will move you towards, away from, or equidistant to good health. Vranak (talk) 21:23, 4 March 2008 (UTC)[reply]

Identity is a complex topic, so to say that it depends entirely on a tangible, precise group of cells or molecules (or to imply that changing the cells changes the identity) makes many profound assumptions. Philosophy of mind may provide some insight. Nimur (talk) 07:03, 5 March 2008 (UTC)[reply]

Insects in vegetables?

Hi. I am asking this on behalf of a friend who is a vegetarian. I've heard in various places that the Food and Drug Administration (and in Canada too) allows a maximum number of insect body parts in certain vegetables. Can I get some stats on how many insect body parts are allowed in certain vegetables? I also heard that ant eggs are allowed in peanut butter. In fact, one time I discovered some tiny yellow-brown insects in (homemade) soup (cooked). Now, some people may think it's gross, but it is just extra protein, but for strict vegetarians this may be a problem. Can you give me some stats for Canada, and is there an article on this? They shouldn't spray the vegetables with pesticides to get rid of the bugs, because that might make us sick (which is why I always wash my fruit [except bananas]). Does organic vegetables have more or less maximum insects, or is the limit identical? Please provide some statistics for Canada and which vegetables and other food froducts are most likely to contain insect body parts. Thanks. ~A H 1^(TCU) 18:42, 4 March 2008 (UTC)[reply]

Its name completely escapes me, but there is a wax secreted from an insect that is used to replace the natural wax coating of apples. It often contains parts from the insect itself. 206.252.74.48 (talk) 19:38, 4 March 2008 (UTC)[reply]

Beeswax is often used for coating fruits & veggies. --Sean 20:00, 4 March 2008 (UTC)[reply]

While that is true, I'm thinking of another wax created by an insect. The fact that I can't recall its name is really bugging me (no pun intended, seriously). 206.252.74.48 (talk) 20:08, 4 March 2008 (UTC)[reply]

Google led me to here http://www.geocities.com/perfectapple/apple_wax.html so check out shellac.87.102.44.156 (talk) 21:22, 4 March 2008 (UTC)[reply]

Yep, that's the one! Thank you. 206.252.74.48 (talk) 13:33, 5 March 2008 (UTC)[reply]

http://www.cals.ncsu.edu/course/ent425/text18/food.html for canada recommend contacting the canadian equivalent of the 'ministry of food and agriculture'87.102.44.156 (talk) 19:43, 4 March 2008 (UTC)[reply]

To get you started, the maximum permissible quantities of insect (and other) bits in foods are specified by the FDA as food Defect Action Levels (DALs). The FDA DAL Handbook is online here: [18]. Canada's rules are probably somewhere on the Canadian Food Inspection Agency website: [19]. TenOfAllTrades(talk) 19:58, 4 March 2008 (UTC)[reply]

There are also standards for grain crops foreign matter (mostly stones and insects) that permit them at low levels as it is not practical to perfectly sort them.Polypipe Wrangler (talk) 22:15, 4 March 2008 (UTC)[reply]

I suppose it is probably not worthing saying that trying to eat a vegetarian diet without accidentally digesting insects at some level is going to be impossible. Insects are everywhere and they eat everything and it's a fact of life that some of them are going to get sucked up into the food processing apparatus every once in awhile even if you are doing it by hand! Personally I think there are more pressing moral and ethical issues in the world than whether or not you eat a few ants, assuming the objection is moral/ethical (as they pose no real nutritional benefit/deficit). --98.217.18.109 (talk) 14:10, 5 March 2008 (UTC)[reply]

quantity required of trypticase soy agar to test water for fecal coliform

Hi. How much trypticase soy agar is required to test water sample for fecal coliform?Sarah Orlowski (talk) 18:49, 4 March 2008 (UTC)[reply]

Thanks, Sarah Orlowski

I'm not sure how anyone could possibly answer the question as put; the quantity of medium you need would depend on the number of samples you're going to test, and on the lab protocol you're using for the testing (I also wonder why you're using trypticase soy agar vs MacConkey medium - unless you're making your own selective medium, in which case again quantity depends on the recipe you're using. - Nunh-huh 02:44, 5 March 2008 (UTC)[reply]

BBC Bird Question

In every early morning quiet scene in a British costume dramas, they'll show the protagonist looking pensively over the landscape for whatever reason. Then 4 times of 5, they'll throw in a soundbite of some English bird with a very shriekish call. It's supposed to set the ambiance or something. For instance, you hear it in the beginning of Part 4 of the 1995 version of Pride and Prejudice as Darcy looks over the moors. What is that bird?160.10.98.106 (talk) 19:57, 4 March 2008 (UTC)[reply]

Looking in my Collins Bird Guide and having listened to P&P a little, I think you might be hearing the goshawk. Most hawk screams are perfect for punctuating the wildness of an outdoor scene. According to Collins, there aren't many species of raptor in Derbyshire, only the goshawk, the sparrowhawk, the hen harrier, and Montagu's harrier. --Milkbreath (talk) 20:50, 4 March 2008 (UTC)[reply]

In the U.S., we use a Red-tailed Hawk scream as the avian version of the Wilhelm scream. -- Coneslayer (talk) 20:54, 4 March 2008 (UTC)[reply]

March 5

Avoiding the Nazi Swastika

While I was researching PETN looking for more efficient ways for the atoms and their connections to be drawn I became aware of the potential to draw this molecule in the pattern of a Nazi Swastika and that was before I read that the molecule was invented in Germany and patented by the German government and that the Homeland of the Nazis was Germany. Are there any other molecules that can be redrawn as a Nazi Swastika and if so what are they? Just curious in an odd sort of way.

Is this really science related? Wisdom89 _{(_T / ^C)} 00:26, 5 March 2008 (UTC)[reply]

More so that art related.

It kinda looks like a swastika in a 2d diagram as shown in the article. But in reality, the 3d structure of the middle carbon is different. Looking straight from above, you wouldn't see the "swastika". The middle part will look like a plus sign. If you look at it sideways, or from the plane of the molecule, the middle part looks like a seesaw. The point is that the swastika is invisible in the 3d structure.128.163.116.74 (talk) 01:19, 5 March 2008 (UTC)[reply]

Chemists have a way of describing this - you are looking for a molecule with C_4h symmetry.. (point group) - because of its 3 dimensional structure PETN doesn't actually have this symmetry.87.102.85.28 (talk) 15:09, 5 March 2008 (UTC)[reply]

Tetraethyl lead could be drawn as a swastika , but as above in 3D it doesn't have this structure.87.102.85.28 (talk) 16:03, 5 March 2008 (UTC)[reply]

rodents with large binocular field of view

Hi everyone. A simple question, but the search yielded nothing for some reason. The question is: are there any rodent species with a decent binocular field of view (FOV)? Most rodents have eyes set far off to the sides of the skull, hence the FOV of both eyes overlap only over a small angle (a few degrees AFAIK) in front of the animal. That, of course, makes sense: rodents have a large number of predators to watch out for, and therefore large coverage, even monocular, is more important than binocular vision. Still, do you know which rodent or lagomorph species have a relatively large binocular frontal FOV? Thanks in advance. --Dr Dima (talk) 06:44, 5 March 2008 (UTC)[reply]

relative calcium absorbtion into bones compared to teeth

I've read somewhere that 99% (or some other very high percentage) of calcium absorbed into your body is in your teeth, while only 1% goes to your bones. Can anyone verify this? Mitchell Cain (talk) 08:26, 5 March 2008 (UTC)[reply]

This paper states that 99% of the body's total calcium is in bone (but I suspect they are using "bone" to mean "bones and teeth", as prior animal studies use the figure 99% for bones & teeth). I don't find a reliable source differentiating teeth vs bones (but this retailer of calcium says teeth contain 1% of total body calcium, which seems reasonable: the calcium content of tooth and bone are similar (by weight), and all your teeth taken together weigh considerably less than all your bones taken together.) So I suspect that either you misunderstood what you read, or it was just plain wrong. - Nunh-huh 10:01, 5 March 2008 (UTC)[reply]

Another way of looking at it is that the human body is about 1.5% calcium by weight, so a 150-lb person would have about 2¼ pounds of teeth in her head, which seems rather high. --Sean 14:30, 5 March 2008 (UTC)[reply]

Physics

Can Kgf be used as a unit for Force in place of Newton. To be specific if I say that an aircraft wieghs 6000 kgf, does it mean 6000 N or 6000 x 9.81 N? Shary249900 (talk) 13:52, 5 March 2008 (UTC)[reply]

The latter is closer to correct. 6000 kgf = 9.80665 m/s² x 6000 kg = 543999 N. See kgf. jeﬀjon (talk) 14:04, 5 March 2008 (UTC)[reply]

Free protons? Free neutrons?

Free electrons are described as electricity. What would free protons and free neutrons be described as? 64.236.121.129 (talk) 15:37, 5 March 2008 (UTC)[reply]

How about dangerous?

Seriously though, a free proton is an ion of Hydrogen, that is a Hydrogen atom that's lost its electron. You can get neutron radiation, but other than that neutrons don't tend to hang around on their own. They decay into protons. —Preceding unsigned comment added by AlmostReadytoFly (talk • contribs) 15:55, 5 March 2008 (UTC) Damn! SineBot doesn't give you much chance! AlmostReadytoFly (talk) 15:56, 5 March 2008 (UTC)[reply]

Did you really think you could beat a robot? 206.252.74.48 (talk) 16:22, 5 March 2008 (UTC)[reply]

(ec) While electric currents definitely do involve electrons (well, usually), the situation is much more complex than a bunch of free electrons wandering down a wire. Signals in a metallic wire travel much faster (close to the speed of light) than the individual electrons that carry the current (drift velocity about a millimeter per second). (See also speed of electricity). The very same electrons that are 'free' in the sense of being able to move in a conduction band down the length of a wire don't just fall out the end of the cable when you unplug it—they're bound.

A 'free' electron – one not bound to other matter – might be called a cathode ray in some contexts, or a negative beta particle in others. Really though, a 'free electron' wandering about with relatively small kinetic energy is usually described as just that—a 'free electron'.

As an aside, when I saw the section header on this question my first thought was that there was some sort of giveaway of particles going on. Cheers! TenOfAllTrades(talk) 16:27, 5 March 2008 (UTC)[reply]

Whereas I thought someone was scrounging :P AlmostReadytoFly (talk) 16:32, 5 March 2008 (UTC)[reply]

I mean free protons and free neutrons. Not binded together. A Hydrogen atom that lost an electron still has a proton and a neutron. I'm talking about free protons and free neutrons, unbinded. 64.236.121.129 (talk) 16:26, 5 March 2008 (UTC)[reply]

No it doesn't usually. A Deuterium atom (which is a type of Hydrogen atom) has a proton, a neutron and an electron, but most Hydrogen has only a proton and an electron. If it loses the electron, all you have is a free proton. AlmostReadytoFly (talk) 16:32, 5 March 2008 (UTC)[reply]

Your standard hydrogen ion is just a proton, as above. Deuterium (a comparatively rare isotope) is the proton+neutron combo. 199.209.144.218 (talk) 16:30, 5 March 2008 (UTC)[reply]

There are free protons in the solar wind. But we don't encounter free protons and free neutrons in "everyday life", because their presence is an indication that there are some high energy nuclear processes happening - it takes much more energy to dislodge a nucleon from a nucleus than it does to free an orbital electron. If you find free protons or neutrons flying around, you should probably stand well back. Gandalf61 (talk) 16:40, 5 March 2008 (UTC)[reply]

So a free proton is just ionized hydrogen? Ok. What about free neutrons? 64.236.121.129 (talk) 16:56, 5 March 2008 (UTC)[reply]