Wikipedia:Reference desk/Archives/Science/2008 November 2

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November 2

Carboniferous

What caused the high oxygen content of the atmosphere in the carboniferous period? 24.77.21.240 (talk) 00:25, 2 November 2008 (UTC)

Try our article titled Carboniferous period which contains lots of good information. The first reference at the bottom of the article is a link to a journal article titled "Atmospheric Oxygen, Giant Paleozoic Insects and the Evolution of Aerial Locomotor Performance." You could follow that link, or any of the other references, should our article not contain the information you are seeking. As an alternate source, may I suggest that you look in the textbook that your teacher gave you at the start of the class, or perhaps you could review the notes you wrote down the day that your teacher discussed this in class. Cheers! --Jayron32.talk.contribs 00:35, 2 November 2008 (UTC)

Invention of lignin. Dragons flight (talk) 00:42, 2 November 2008 (UTC)

The question is then: What caused the low oxygen content of the current atmosphere? Who burnt so much coal and where is the resulting CO2 (presumably in carbonates)? Maybe subduction and vulcanism (how does coal react in the asthenosphere?). Icek (talk) 14:06, 2 November 2008 (UTC)

Coal has only been burnt in significant quantities since the industrial revolution, I doubt that's had any noticeable effect on oxygen levels. My guess would be simply an increase in animal life (with the resulting CO2 being dissolved in oceans, stored in carbonates, fossilised, etc.). --Tango (talk) 16:06, 2 November 2008 (UTC)

No, large-scale burning of coal probably happened in the Permian and many people now think the PETM was coal related as well. Coal can be ignited in situ by volcanism, or where it intersects the surface by wildfires/lightning. Even today, underground coal fires probably represent a few percent or carbon emission, and some coal fires, like Australia's Burning Mountain, have persisted for thousands of years. Though biological processes for dealing with lignin were surely necessary, much of the fall of atmospheric oxygen is thought to be connected to the erosion and oxidation (either by burning or by microbial consumption) of Carboniferous organic deposits during the Permian. Lower sea levels (drying out swampy areas and exposing recently buried organics) and higher volcanism in the Permian helped make that possible.

Oh, and yes scientists do measure the small decline in atmospheric oxygen (ususally expressed as the O2/N2 ratio) since the onset of the anthropogenic burning of fossil carbon. Since the atmosphere is 20% oxygen, the loss of a fraction of 1% isn't a big deal so far. Dragons flight (talk) 16:59, 2 November 2008 (UTC)

There was natural burning of coal, yes. Since the question was "who" I assumed it was just asking about human burning. --Tango (talk) 18:33, 2 November 2008 (UTC)

i think we're all off on a tangent here; where did all the oxygen come from, is "plants and cyanobacteria". Gzuckier (talk) 16:58, 3 November 2008 (UTC)

That wasn't the question, though. The question was what caused the high oxygen content during that time period. I think a fair interpretation of that question is "Why were the oxygen levels higher then than they are now?" --Tango (talk) 16:59, 3 November 2008 (UTC)

Just to clarify: I am pursuing this for my own interests, and my question is "Why was there more oxygen during the carboniferous than now?" —Preceding unsigned comment added by 24.77.21.240 (talk) 02:50, 4 November 2008 (UTC)

Geography buffs needed...

<removed> This is not a question. The reference desk does not appreciate being spammed with advertising - even if you're advertising a Wikipedia project. SteveBaker (talk) 15:01, 2 November 2008 (UTC)

Lovebirds and loneliness

Whilst it's a total myth that Lovebirds will wither and die if kept alone, I was wondering if long-term isolation in these birds is any more psychologically damaging than it is for other species, considering the extremely close social bonds they form and their super-affectionate natures. Anyone know? I'm just thinking about a particular male Peach-faced Lovebird that lives alone in a 30m x 30m aviary at a bird collection near where I live (actually, he *is* the bird collection at present!). --Kurt Shaped Box (talk) 01:44, 2 November 2008 (UTC)

Actually, most animals, if kept alone and unsocialized, general develop serious psychological problems, often referred to as Stereotypy. The sort of things where you see caged birds plucking all their feather's out, or bears in a zoo repeatedly pacing a small path despite having a large enclosure, are usually the result of the psychological damage done to social animals when they are kept in isolation for extended periods of time. --Jayron32.talk.contribs 02:35, 2 November 2008 (UTC)

Human children sitting in a foetal position rocking backwards and forwards. --Tango (talk) 13:38, 2 November 2008 (UTC)

Yeah, I'm (mostly) aware of all the above. I was wondering if Lovebirds specifically were any more susceptible to these problems, given that their entire raison d'être seems to be to stand as close as physically possible to other Lovebirds and snuggle. --Kurt Shaped Box (talk) 21:51, 2 November 2008 (UTC)

Well, if intervention is required, Christmas is coming up and you might like to give it a present/expand the collection. Maybe it would simply enjoy company in the form of other types of birds instead of rattling around in 30² metres by itself. Is there foliage/rocks, landscaping there as well? Give out a few hints perhaps, in the interest of plumage preservation at least... Julia Rossi (talk) 22:40, 2 November 2008 (UTC)

Yep, I was actually considering making a donation to enable them to buy some more lovebirds. They used to have loads of them in that enclosure but a combination of financial problems, disease, a lack of hens and the passage of time has significantly reduced the numbers. They've only got three Cockatiels now, in a (different) aviary built for 30 or more (their Zebra Finches are breeding like Zebra Finches, however).

FWIW, the Lovebird looks okay physically and seemed quite content to fly around and swing/gnaw on branches (the aviary has several trees and shrubs within). He comes to the bars and tweets whenever anyone approaches, so I guess that he's feeling somewhat lonely... --Kurt Shaped Box (talk) 22:58, 2 November 2008 (UTC)

Birds often interact with a mirror in thae cage. If they were humans, they might spend hours editing Wikipedia for a simulation of human interaction. Edison (talk) 03:50, 3 November 2008 (UTC)

parrots in general are pretty social.Gzuckier (talk) 16:59, 3 November 2008 (UTC)

pH

why ph value is not greater than 14 —Preceding unsigned comment added by Sush2luv (talk • contribs) 02:00, 2 November 2008 (UTC)

According to PH#Explanation, it is possible to have a substance with a pH greater than 14 (or less than 0), it's just unusual. There is nothing in the definition that creates an absolute maximum at 14. --Tango (talk) 02:12, 2 November 2008 (UTC)

Lots of solutions, not all that unusual, have pH's larger than 14 or less than 0. Also, it should be noted that substances can't have a pH, since pH is only measureable as a function of how the substance acts while in a water solution. pH is something which is a function of both of the substance and the concentration of that substance in water. I can, for example, create a solution of Acetic acid which has a lower pH (and this is more acidic) than a solution of Hydrochloric acid, even though acetic acid is a weaker acid than is hydrochloric (it has a higher pKa, or acid dissociation constant, than does hydrochloric).

The source of the 0-7-14 scale, incidentally, is not arbitrary; it has to do with a concept known as the autoionization of water, if you read that article it explains how pH is derived from this... --Jayron32.talk.contribs 02:30, 2 November 2008 (UTC)

Are you sure you don't have that $K_{a}$ inequality backwards? --Tardis (talk) 15:56, 2 November 2008 (UTC)

Nope, pKa is the negative logarithm of the Ka. Thus acids with lower Ka's produce MORE hydronium ions in solution, and thus are more acidic. Lower pKa = higher Ka = more acidic... pKa is often more convenient to work with than Ka because it is then on the same logarithmic scale as is pH... --Jayron32.talk.contribs 18:21, 2 November 2008 (UTC)

Sorry; I completely ignored the p and decided you were talking about the constants themselves. --Tardis (talk) 03:12, 4 November 2008 (UTC)

Atmosphere Seperation

Resolved

If there are many different gases in earths atmosphere why do they not seperate? Sediments seperate over time but gases don't seem to. Oxygen is heavier that nitrogen so why should it be mixed? —Preceding unsigned comment added by 202.154.155.124 (talk) 06:42, 2 November 2008 (UTC)

Perhaps it is due to air currents and air turbulence. Air currents are caused by air temperature differences that result from the sun striking the earth more obliquely toward the poles. Near the equator the warm air rises and returns toward the poles at a high altitude. This has a mixing effect for the gases. Also, mountains, hills, trees, and friction with the ground, all create air turbulence near the ground. Uneven heating of the air over land, sea, desert,and vegetation, also enters into it, causing air currents and mixing. As for sediment, the sedimentary particles have a greater specific gravity than water, resulting in their tendency to settle on the bottom. However, turbulence in rivers causes muddy waters all along the river's course. When the relatively still sea is reached, the particles may settle to create a delta. If there is no delta at the mouth of a muddy river, it is because coastal currents sweep the sediment away. —Preceding unsigned comment added by 98.17.34.3 (talk) 13:59, 2 November 2008 (UTC)

Gases diffuse into each other readily (technically each one effuses), which leads to mixing even if there weren't externally-driven air currents, because all molecules are always in a state of motion. Actually *all* things do this, but Graham's law explains that lighter particles do so more rapidly. Remember that gases move as individual molecules instead of solids (large aggregates of molecules). Once mixed, there is usually some intermolecular attraction that helps keep them mixed and mixing is favored by the increased entropy. Some mixtures of gases do separate, but it requires that they have a relatively large difference in molecular mass and do not have much if any intermolecular attraction. DMacks (talk) 18:32, 2 November 2008 (UTC)

For all practical purposes, diffusion is irrelevant to the atmosphere. Atmospheric mixing is totally dominated by wind and turbulence, which is also the reason that the atmosphere stays mixed. Dragons flight (talk) 18:44, 2 November 2008 (UTC)

So if you take a bit of air and put it in a special container, shielding fully from any turbulence (a kind of perfect container on earth at 1G with no movement in the ground, and fully sealed), will it seperate in layers of different gases after a long period? If yes, do we know how long? --Lgriot (talk) 01:26, 3 November 2008 (UTC)

For containers of practical sizes and gases at room temperature, there will be a small partial separation: i.e. a little more of the heavy gases at the bottom and little more of the light gases at the top. The diffusion time scale in absolutely still air will be $t\approx {l^{2} \over (0.2cm^{2}/s)}$, where l is the characteristic length of the system. After a few times the diffusion time scale one would expect the air to have separated to the degree it is able, but it would not be a big effect. Plugging in large length scales will show how diffusion is so much slower than wind and turbulence when it comes to rearranging air. Dragons flight (talk) 01:48, 3 November 2008 (UTC)

entropy? Gzuckier (talk) 17:00, 3 November 2008 (UTC)

What is the "characteristic length of the system"? Sorry I am only a curious layman ... Would that be the height in most containers (say a cylinder standing upright)? Also would l be expressed in centimetres like the volume? BTW, I had assumed s is a number of seconds, but now it seems it doesn't make sense, since the number of seconds is what we are trying to find out, so it can't be on the right of the formula. --Lgriot (talk) 00:30, 4 November 2008 (UTC)

The cm and s in that formula are "centimeter" and "second", not some count of them. l is the original length over which the gases are mixed and can be expressed in whatever units you like, but you have to divide by the units. I personally find it confusing to make the units be part of using the formula rather than part of writing it, but if it helps you can read that formula as "the number of seconds in the characteristic time of stratification is 5 times the square of the number of centimeters long the system is". --Tardis (talk) 03:20, 4 November 2008 (UTC)

Ok so please correct me if I am wrong: if my container is a standing cylinder with a diameter of 12cm, the number of seconds would be 720 seconds? I still don't understand the notion of "(characteristic) length of the system". I searched for "characteristic length", "length of a system", "length", but that does not give me anything. --Lgriot (talk) 00:42, 5 November 2008 (UTC)

It's probably easiest to take the diameter of the object as its characteristic length. But by diameter I meant the greatest distance between any two points in it, so how tall is your cylinder? For l=12 cm, your answer is correct. --Tardis (talk) 01:23, 5 November 2008 (UTC)

Ok, thanks, I understand. --Lgriot (talk) 03:54, 5 November 2008 (UTC)

what is the use of garlic?

what is the use of garlic? —Preceding unsigned comment added by 59.180.153.7 (talk) 08:16, 2 November 2008 (UTC)

Have you looked at the page on Garlic?--GreenSpigot (talk) 08:40, 2 November 2008 (UTC)

To make things delicious? --Jayron32.talk.contribs 18:49, 2 November 2008 (UTC)

To ward off vampires. Dragons flight (talk) 20:36, 2 November 2008 (UTC)

Antibacterial properties. --Lenticel ^(talk) 00:47, 3 November 2008 (UTC)

Stops people from hanging around talking to you for too long. Freshens up the armpits. (And makes things de-licious) Ooh, ooh, roast and put on toast! Franamax (talk) 08:22, 3 November 2008 (UTC)

A way for a gene to replicate? Nil Einne (talk) 15:09, 3 November 2008 (UTC)

significantly reduces effect of metabolic syndromeGzuckier (talk) 17:02, 3 November 2008 (UTC)

"Unperturbed chain"

In polymer science, what is meant by "an unperturbed chain"? Thanks —Preceding unsigned comment added by 87.67.14.94 (talk) 11:27, 2 November 2008 (UTC)

Need Resources - Can you help?

I am studying a scientific degree at the moment but I also have a keen interest in Association Football. Are there any sources of information I can use to find scientific studies of association football, like pubmed for medicine? I am particularly looking for statistical evidences and scientific tactical analyses, or anything like this. Donek (talk) 14:39, 2 November 2008 (UTC)

Efficacy of multi-sensory room.

I wanted to ask if there are any studies about the effect of these very expensive rooms on children with special needs especially those that approach the vegetable side. My gut feeling about it is that it is an expensive those of hope for the parents but I would like to educate my opinion if possible, thanks.Bastard Soap (talk) 17:02, 2 November 2008 (UTC)

Discovering intelligent extraterrestrial life

I recall reading somewhere that based off an estimation of the Drake equation and the amount of signals analyzed by SETI, there was a year by which we could hypothetically discover intelligent extraterrestrial life. Does anybody have this figure? Thanks in advance. QWERTY | Dvorak 17:22, 2 November 2008 (UTC)

Estimates of the parameters for the Drake equation vary enormously, so any such time estimate is going to be very approximate (and it's just a statistical expectation, not an actual prediction). --Tango (talk) 18:42, 2 November 2008 (UTC)

In principle - that ought to be a prediction we could make. The Drake equation(s) (there are several variations on the original idea) are a correct statement of how many alien civilisations ought to be 'out there'. All of the variations basically involve multiplying together between half a dozen and a dozen numbers. The trouble it that most of those numbers have HUGE error bars on them. When you multiply numbers with doubt associated with them - the amount of doubt goes up rapidly. Our article points out that any answer between 0.05 and 5,000 civilisations per galaxy is reasonable given 'educated guesses' for the values of the terms that we don't know.

There are terms in the Drake equation like "The number of years between a civilisation starting to broadcast messages to the stars and it's eventual downfall". We have no clue what that number is. Humans are not really capable of broadcasting that far - so the value for that term in the equation might be anywhere between zero and a hundred million years and we have no way to get a more accurate estimate. Since so many of the terms in the Drake equation are as hard to pin down as that one, any use of the resulting number to predict how long SETI might take is similarly vague.

Worst still, (as it's always worth-while pointing out), if you took the most powerful radio transmitter mankind has ever built and put it on the star that's nearest to our sun - SETI's equipment would not be sensitive enough to detect it. The nearest star is only 4 light years away - and radio waves get weaker as a function of the square of the distance. So if there were (say) just a couple of other civilisations in our 100,000 light-years-wide galaxy, then they could easily be 40,000 light years away - using transmitters like ours and producing a signal 100 million times weaker than SETI can detect! So it's perfectly possible that SETI simply isn't sensitive enough to pick up any of the messages that 5,000 alien species are screaming at us every day and from every direction in the sky!

It's also possible that we're somehow searching in the wrong manner. If the aliens habitually use 'spread-spectrum' radio techniques - or communicate with lasers rather than radio waves - then the radio-based SETI search will never find them.

SteveBaker (talk) 19:03, 2 November 2008 (UTC)

There's no way to get any sort of accurate estimate since we have no idea how common life is, let alone intelligent life. The only thing we can for certain is that in our own solor system, there is only one planet with intelligent life. I'm not sure if it's fair to count Earth because if we didn't exist, we wouldn't even be here to ask the question. Once you exclude Earth, the number of known intelligent civilizations is zero, which puts the result of the Drake equation at zero. We may very well be alone in the universe. 67.184.14.87 (talk) 23:01, 2 November 2008 (UTC)

I read somewhere "I think a true sign that intelligent life exists somewhere else is that we havn't been contacted." —Preceding unsigned comment added by 202.154.155.124 (talk) 04:46, 3 November 2008 (UTC)

Is this where you read it? —Angr 12:42, 3 November 2008 (UTC)

I think it's FAR too soon to assert that we are the only intelligent species in the solar system. There is plenty of scope for creatures living in the deep oceans under the ice of Europa - or on Titan. The only thing we know for sure is that if they ARE intelligent, they either cannot or choose not to transmit powerful, distinct radio signals at us and they do not build huge, visible cities. If a civilisation of water-dwelling creatures lived on Europa, they would be unable to see the sky or the stars because of tens of kilometers of ice over their heads. They would perhaps not have invented telescopes - never have realised that there is anything above the ice - and certainly never have tried to transmit message through it. That doesn't mean they couldn't be intelligent and have a rich and interesting society.

That's the problem with the Drake equation - we don't know the very first thing about what is or is not possible in terms of life...let alone intelligent life...let alone intelligent life with big-assed radio transmitters and a curiosity about life elsewhere. SteveBaker (talk) 19:15, 3 November 2008 (UTC)

Viscous hot water

Why does boiling water sound more "viscous" or "thicker" when you pour it than cold water? —Angr 18:44, 2 November 2008 (UTC)

I'm not sure about "sound" but every other fluid that comes to mind is more viscous at lower temperatures. You could try the Viscosity article, but it is simply an atrocious violation of WP:MTAA. SDY (talk) 20:32, 2 November 2008 (UTC)

Well, there's a reason I put "viscous" in scare quotes. I'm not saying it is necessarily actually more viscous by the scientific definition, just that when you pour just-boiled water from a tea kettle into a teacup, the sound the water makes is somehow "thicker" than if you pour cold water in. —Angr 21:10, 2 November 2008 (UTC)

Do you mean it has a deeper pitch? —Cyclonenim (talk · contribs · email) 21:43, 2 November 2008 (UTC)

I guess so, yeah. I'm sorry I'm not being very scientific about my description; I was hoping this was such a well-known phenomenon everyone else would know what I was talking about. Am I the only person here who has noticed for his entire life that very hot water sounds different when it pours than cold water? —Angr 21:58, 2 November 2008 (UTC)

Hot water has a lower density than cold water; so it makes sense that hot water would have a different resonant pitch than cold water would... --Jayron32.talk.contribs 23:14, 2 November 2008 (UTC)

Pouring very hot water into a container brings the liquid into contact with a (microscopically) rough surface, encouraging the formation of bubbles of water vapour. The formation and rapid collapse of these bubbles probably alters the sound. (I'm not sure that density differences in the liquid could account for the change in sound; water is only about 3% less dense at 95°C than at 4°C.) TenOfAllTrades(talk) 23:31, 2 November 2008 (UTC)

This thought actually occurred to me the other day and with a bit of Googling I found out that water is actually less viscous at higher temperatures, so the sound it makes is different. One source claimed the viscosity fell of particularly quickly close to boiling point, but our Viscosity article seems to suggest a linear relationship. Either way, my understanding is that it's this decrease in viscosity that results in the difference in sound between pouring hot water and pouring cold water. Maelin (Talk | Contribs) 01:49, 3 November 2008 (UTC)

Okay, then it's just my subjective impression that hot water sounds "thicker" even though actually it's less viscous. It makes sense that water that's about to become steam would be less viscous than water that's about to become ice. —Angr 06:25, 3 November 2008 (UTC)

i know what you mean; it makes more gloopy noises. i think it's because cavitation is more pronounced near the boiling point, and that's what you/me are hearing. Gzuckier (talk) 17:05, 3 November 2008 (UTC)

ZENN electrical motor

What type of AC motor is in the ZENN? Is it a wound rotor, squirrel cage, synchronous or switched reluctance motor? I believe the motor is made by Advanced Motor & Drives, p/n ACX-2043. --jcmaco (talk) 20:58, 2 November 2008 (UTC)

According to your link at environmentalmotors, it's a "3 Phase AC motor by Advanced Motors & Drives -- ACX 2043". That's an interesting method, since it's powered by a DC battery / ultracapacitor. I'm not sure why someone would build a 3-phase inverter into the powerline, rather than use a straight DC motor. We had a thread a little while ago here about why lawnmowers rectify single-phase AC to DC - and I wasn't all that clear on why they did that either. I made a small chase, because I had thought that AC motors developed more torque than DC, but my ship ran onto the rock of hard numbers. AM&D claims their designs to provide exceptional torque.

In any event, the AM&D website discusses their "standard AC motors" and various brush features. This sounds to me very much like a wound rotor. The site also prominently invites you to make direct contact, so that may be the best way to go.

The ZENN website may have info but I bailed out of it - someone decided that the best paradigm for web users used to clicking through pages was to introduce the concept of a "book" that you have to click-hold-drag the pages of, just so you could read their wonderful story, like Daddy used to tell you. OMG that's bad!

They're both pretty small companies, a direct approach might be best. Please report back here with any results! Franamax (talk) 08:17, 3 November 2008 (UTC)

Organic Functional Group Interconversion

Is there a simple way to convert a phenol group to a phenyl bromide? For a general example, can toluene be converted to bromobenzene? For a more specific example, can p-hydroxyaniline be converted to p-bromoaniline? Somehow I think that it's not possible, especially with an NH2 group activating the benzene ring, but I was just wondering. --Russoc4 (talk) 21:54, 2 November 2008 (UTC)

Larock lists a dozen refs for "ArOH→ArX", all involving things that could be considered strong electrophiles/Lewis acids. Looks like lots involve transiently deriving the OH into a leaving group, not sure if they formally would go by addition–elimination or elimination–addition. Your question is kinda weird though…there's no phenol in toluene (did you mean "phenyl"?) and where did the methyl of toluene go in the bromobenzene you expect to get? But for the very specific case you mention, wonder if reduction to aniline then very simple p-selective electrophilic aromatic substitution to get the halogen? DMacks (talk) 02:06, 4 November 2008 (UTC)

Library scanner things

When entering or leaving the library, when I walk through those things that scan to see if you're stealing books, and I'm wearing my iPod, there is a sudden intense squealing in my ears. If I take the earphones out of my ears before passing through, then put them back in on the other side, I hear no such thing. What causes this? Is it in any way damaging to my iPod? Cherry Red Toenails (talk) 22:56, 2 November 2008 (UTC)

From our article on Electronic article surveillance, I notice that these devices work by emitting radiowaves at certain frequencies. Maybe this is what you are hearing. Nanonic (talk) 23:03, 2 November 2008 (UTC)

I'd be more worried about your ears then your iPod. If you did want to worry about some object that isn't part of you, I'd worry more about the earphones Nil Einne (talk) 11:27, 3 November 2008 (UTC)

Electromagnetic interference. --Sean 14:23, 3 November 2008 (UTC)

I didn't ask about my ears for fear of bringing down the "NO MEDICAL ADVICE" vultures. =P I thought asking about the iPod might give me a clue though. And I figured it was some kind of electromagnetic thing, but wasn't sure what. The article you suggested helped though, thanks. Cherry Red Toenails (talk) 16:32, 3 November 2008 (UTC)

I don't think you need any medical advice beyond common sense - if the sound hurts your ears, take the earphones out before going through. If it doesn't hurt, then it probably isn't any worse than all the other loud noises you are exposed to on a regular basis, especially since it lasts a fraction of a second. --Tango (talk) 16:38, 3 November 2008 (UTC)

if it is that loud, i would worry about generating high voltage/currents in circuits such that the ipod isn't designed for, possibly frying something in the Ipod; but if it didn't actually fry it, then i'd stop worrying. Gzuckier (talk) 17:07, 3 November 2008 (UTC)