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

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April 23

Ibuprofen structure

What does the squiggly bond mean?

--75.40.204.106 (talk) 01:42, 23 April 2011 (UTC)

This is depicted in our article but that specific symbol depicts a bond that extends away from the observer. In this case, it is a bond linking a carbon adjacent to a carbonyl group (at right) and a methyl group represented by the end of that "squiggly" line (by convention, hydrogen atoms bound to carbon atoms are not shown). So, that methyl group is farther from the observer than the carbon to which it is attached. -- Scray (talk) 02:30, 23 April 2011 (UTC)

Actually, the squigly bond means that the structure is racemic. If the methyl group were going away from the viewer, it would be a "dashed" bond. A "wedge" bond is going towards the viewer. Racemic means that the actual medicine is a 50/50 mixture of both forms of the molecules. If the line is supposed to mean that it is going away, whoever created the picture used the wrong line. --Jayron32 02:36, 23 April 2011 (UTC)

Thanks for correcting me, Jayron32 - I was careless, thinking of the dashed bond! -- Scray (talk) 03:21, 23 April 2011 (UTC)

The main article about interpretting all the details of this sort of diagam is "Skeletal formula". DMacks (talk) 14:25, 23 April 2011 (UTC)

Perspiration

Why do some men of the same build and age, sweat more than others? —Preceding unsigned comment added by 74.100.193.38 (talk) 01:43, 23 April 2011 (UTC)

For the exact same reason that some men of the same build and age have different sounding voices or different colored eyes. The Wikipedia article titled Perspiration covers the process in more detail, as well as covering various conditions that can lead to increased or decreased perspiration. --Jayron32 02:40, 23 April 2011 (UTC)

how to pass entrance

SIR I AM A STUDENT OF 12 CLASS,HAVING SCIENCE ,OUGHT TO JOIN MEDICAL FIELD, MANY PEOPLE SAYS THAT IT IS DIFFICULT TO CLEAR THE ENTRENCE EXAM THEN WHAT SHOULD I HAVE TO DO. I M BELOGING TO NORMAL FAMILY HENCE CANT BE ABLE TO PAY LOTS OF COLLEGE FEE, i ought to join goverment college then what 2 do? PLEASE GUIDE ME I WILL PAY MY 100% TOWARDS UR ADVICE.... —Preceding unsigned comment added by 223.189.23.145 (talk) 02:47, 23 April 2011 (UTC)

• You need to tell us in what country you are interested in becoming a certified medical professional, and you would also need to say which medical job you want. After all, an American nurse is going to have a very different set of ceretifications and training than a Russian dentist is, and both will be very different from a South African doctor. Its literally impossible to answer your question without knowing where you are from and what your career aspirations are. --Jayron32 02:59, 23 April 2011 (UTC)

The IP geolocates to India.[1] Red Act (talk) 03:50, 23 April 2011 (UTC)

As a rule of thumb, an OP that addresses us as "Sir" is probably Indian. It's nice to be shown a little respect, rather than the insults and demands we get from some of our OPs! --Tango (talk) 13:09, 23 April 2011 (UTC)

To the original querant: It might help you to arrange a meeting with a local medical professional, to discuss options with them. If they take an interest they may be able to help you. You might also see whether they would allow you to work in their clinic. The experience with them may be very educational - in a practical way. -- Scray (talk) 03:25, 23 April 2011 (UTC)

Medical usually means Medicine.Curb Chain (talk) 11:33, 23 April 2011 (UTC)

Of course it does, but that doesn't necessary mean a doctor. The term can be used more generally to include nursing, dentistry, physiotherapy, nutrition, etc., etc., etc.. I expect the OP does want to become a doctor, though. --Tango (talk) 13:09, 23 April 2011 (UTC)

UHT milk in Greece

In Ultra-high-temperature processing, UHT milk's market share in Greece is only 0.9%.

The article says many northern European countries dislike UHT milk. I thought that Greece is in the south and it has very hot long summers. -- Toytoy (talk) 03:40, 23 April 2011 (UTC)

Do you have a question? That (poorly written and referenced) section also says "these figures conceal wide variations as in most European countries" whatever that means. If you can improve it please do so.--Shantavira|^{feed me} 11:07, 23 April 2011 (UTC)

According to the article "Pasteurization", there are two main types of modern pasteurization: flash pasteurization and ESL (extended shelf life) treatment. UHT is an alternative method of preparing the milk. Axl ¤ [Talk] 20:28, 23 April 2011 (UTC)

Shantavira's quote misses a key part of the sentence: "these figures conceal wide variations as in most European countries High Temperature/Short Time (HTST) pasteurized milk is more popular." Axl ¤ [Talk] 20:32, 23 April 2011 (UTC)

ELECTRONICS

How can we find out any faults in super hectrodyne radio receiver?please explain with the circuit diagramMathematics2011 (talk) 04:03, 23 April 2011 (UTC)

Radio frequency electronics can be very complicated; so it's impossible for us to diagnose every possible fault or error. Check for the usual sorts of things: are the DC bias voltages where you expect them at each stage? Have you accounted for RF parasitics? Depending on the frequency of your RF and IF, it may be impossible to diagnose you circuit unless you have a vector network analyzer (or at the very least an oscilloscope and spectrum analyzer). If you are in a poorly equipped lab, you can also use time domain reflectometry, which may be built in to your oscilloscope, or can be easily constructed from a waveform generator and a regular scope. We have a block-level diagram at Superheterodyne receiver, and each sub-element has its own article; but the circuit diagrams will vary widely based on the technologies available, the desired performance, specifications, and operating parameters. Nimur (talk) 18:05, 23 April 2011 (UTC)

You should not try to repair an AC powered device unless you are fully qualified by training and experience to follow all appropriate safety procedures. You will have to find your own circuit diagram, and a public library can provide you with books on radio circuit theory and troubleshooting. One popular troubleshooting method is signal injection, whereby a signal appropriate for a given stage is introduced from a signal generator. You could start with an audio signal in the final audio stage and work backward to the preamp stage, then inject a modulated radio frequency signal in the RF stages, working back to the antenna terminals. A complementary approach is signal tracing, where you use an oscilloscope or other probe to measure the amplitude and quality of signal at different stages. One good test is to make sure that each part of the circuit has the appropriate voltage. Your eyes can sometimes diagnose a burned out component, a poor solder joint or a short circuit. Your nose can sometimes aid in finding an overheated or burned out component. Sometimes tapping with an insulated probe can diagnose poor connections or microphonic tubes. In tube equipment, a tube tester or simple substitution of a good tube is useful. With the comparison method, you can compare the failed receiver at various points with a well functioning similar unit. In old radios, the filter capacitors often fail, resulting in hum and distortion. A blast of dry air from a can is useful in getting crud out of the tuning capacitor. Edison (talk) 20:00, 23 April 2011 (UTC)

These days you don't, because it's cheaper to buy a new one. – b_jonas 20:56, 27 April 2011 (UTC)

top-antibottom mesons existance?

Do top-antibottom mesons exist, or does the short half-life of top/bottom quarks, and π⁺/D_s^*+ mesons prevent them from forming? They are not listed on the list of mesons article. CS Miller (talk) 10:56, 23 April 2011 (UTC)

Our article, top quark, says: "The Standard Model predicts its lifetime to be roughly 5×10⁻²⁵s. This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons, giving physicists a unique opportunity to study a "bare" quark." So there aren't any hadrons, including mesons, that include top quarks. --Tango (talk) 13:42, 23 April 2011 (UTC)

Gold Vs. Silver

Gold, according to the article, is the most ductile and malleable metal.

Silver is not far behind though. I have a 99.9% gold necklace. Why is it so hard to find comparable purity in silver in jewelry? Most silver, when searched, is sterling silver (92.5% purity). It is said that silver is too soft so it must be alloyed with other metals, but this contradicts gold because gold is even softer; on top of this, but 24 karat gold is common.Curb Chain (talk) 11:31, 23 April 2011 (UTC)

24 Carat gold jewelry isn't that common either, especially in the West [2]. With both silver and gold, pure metal is typically only used when extreme malleability or softness is needed in crafting the part [3]. Where did you get your 24 carat gold necklace? Is it hand made, such that pure gold is necessary? Buddy431 (talk) 14:45, 23 April 2011 (UTC)

Supplemental question, if I may: is this extreme malleability somehow connected to the rareness of gold and silver on Earth, or to their aesthetic lustre? SamuelRiv (talk) 18:19, 23 April 2011 (UTC)

Most certainly, if you look at where they are located on the periodic table of the elements, gold and silver share a column with copper, the three together are sometimes called the coinage metals; and they all share a lot of chemical and physical properties, which are undoubtedly due to having similar electronic structure. --Jayron32 23:13, 23 April 2011 (UTC)

The malleability especially makes silver and gold desirable for jewelry: it would be hard make something like this out of iron or tin. Additionally, these metals (copper, silver, and gold) occur in large quantities in their native form, while others like iron do only occasionally, and some, like Aluminum, not at all. Historically, this means that these metals were some of the first known to man, being used both aesthetically, and also functionally (i.e. Bronze weaponry). Gold is especially valued, in that it won't rust or tarnish at all under normal conditions. Copper and silver will tarnish, but this oxidized layer then protects the rest of the metal from reaction (compare to iron, where rust will flake off, exposing more metal to the atmosphere). This muted reactivity is part of the reason why these metals are found in their native form, rather than in ores. Buddy431 (talk) 03:59, 24 April 2011 (UTC)

Oh, and for the "rareness" of gold and silver, look at the graph on the right. The abundance of metals is more related to their nuclear structure (how often they're formed in stars), and less to their chemical and physical structure. Silver, and even gold, aren't the rarest metals on Earth: Iridium, Ruthenium, and Rhodium are all much rarer, and, in some cases, more expensive (Rhodium briefly shot up to $10,000 per ounce, before the economic downturn brought it to more reasonable levels, currently about $2300 per ounce, still much higher than gold). Buddy431 (talk) 04:13, 24 April 2011 (UTC)

I thought Silver would tarnish under Sulfur. I got my necklace when my grandma died and her gold bangles where traded into divide into 5 parts for her grandchildren. The necklaces where traded in at Hong Kong. Maybe extreme purity silver is not found because of tarnish?Curb Chain (talk) 05:42, 24 April 2011 (UTC)

Even Sterling silver will tarnish, so I don't think that's the reason. You mention that the necklace was obtained in Hong Kong: in eastern Asia, it's much more common to have pure gold jewelry (I'm not sure why): see my first link [4] . Buddy431 (talk) 16:38, 24 April 2011 (UTC)

Yes, definitely: sterling silver does tarnish: According to silver, silver reacts with sulfur and hydrogen sulfide which results in the tarnish. I have read other online sources that the impurity in the silver cause tarnish: Is this true? Thanks Buddy431, I did look at that link when you first provided it. I can say that my 24k necklace does not seem any more fragile than a less pure necklace, so the question is still open as to why pure silver jewelery is so rare, and where one would be able to find pure silver jewelery, and maybe, why pure gold is popular in eastern Asia, but not elsewhere.Curb Chain (talk) 02:35, 25 April 2011 (UTC)

Our carat (purity) article has an dead ref list of common gold jewelry purities in various countries Nil Einne (talk) 16:47, 25 April 2011 (UTC)

Perhaps it has to do with the colors. That is, not too many things are gold, so adding other metals makes it look "less golden". Thus, even though pure gold is really too soft, some people may prefer it, due to the color. With silver, on the other hand, there are plenty of metals with a similar color, so you can get a "silvery" item without needing pure silver. In this case, there's little reason to pay more for a metal that's too soft. (I would probably take it to extremes and get a 100% stainless steel item, which would be less expensive and not tarnish.) Also, I think solid 24K gold is rare, it's more often a less expensive metal plated with 24K gold. This provides the best of everything; price, hardness, and color. See colored gold for a graphic showing how adding other metals changes the color of gold. StuRat (talk) 17:19, 25 April 2011 (UTC)

The necklace (I can not read chinese, I had my mom tranlate it) was traded at a gold shop: My mom, translating the certificate, said that the necklace was 99.9% gold. I even looked at the certificate and I had the arabic numerals 99.9%. Oh, after some research, I found that the gold shop is Chow_Tai_Fook_Enterprises. My necklace comes in a box with the icon and the certificate has the icon too. I don't know how corrupt this shop is though.Curb Chain (talk) 00:47, 26 April 2011 (UTC)

Also, according to silver, silver has a white shine, or is white in color, I guess more brilliant than other metals? So would stainless steel match silver's reflectivity and color? And also, wouldn't silver alloys be less reflective and brilliant than purity silver?Curb Chain (talk) 00:52, 26 April 2011 (UTC)

Young's double slit experiment

Approximately how much time does it take for a "one photon at a time" YDSE to generate a distinguishable (by a computer) pattern, assuming that all photons pass through the slits and do not hit the barrier. Also, are there screen detectors that can detect a single photon and its approximate (x,y) coordinates? Or do we still use photographic plates or click detectors on tracks for YDSE's?

I've added a section header for you. --Tango (talk) 13:31, 23 April 2011 (UTC)

And I changed it from "split" to "slit". StuRat (talk) 17:09, 25 April 2011 (UTC)

There is no number N such that you can distinguish the pattern using data from N subsequent photons but not from N-1 subsequent photons. The position where any given photon strikes is drawn statistically from a distribution. You may as well ask how often you have to toss a coin before you know P(heads)=1/2. The more data you have, the more certain you are that quantum mechanics predicts the correct position distribution for the photons (and the more coins you toss, the more certain you are that P(heads)=1/2), but in neither case is there a well-defined boundary between knowledge and ignorance of the pattern. 213.49.91.141 (talk) 17:35, 23 April 2011 (UTC)

Sure, but what if we say we want 95% confidence in rejecting the null hypothesis that there is no interference between photons? We should be able to find a good estimate for the N required for that. (Of course, we'll need to know things like the size of the slits and the distance between them, but I'm sure the OP won't mind if whoever is clever enough to work this out (which isn't me) just makes up some numbers for them.) --Tango (talk) 20:01, 23 April 2011 (UTC)

(I'm the OP here--forgot to sign--silly me--that's what comes of being in a hurry) I'd just like a rough estimate for an experiment (with given distances etc.) as a formula. It would also be fine if you could give the approx time for a YDSE conducted today (as in, using the technology today to require minimum time.) ManishEarth^{Talk • Stalk} 07:41, 24 April 2011 (UTC)

The effects of dreams on long term memory

Recently, I was recalling something that happened years ago- a conversation with a friend- but, after further thought, I realize that it was actually a dream. I wonder how much of my memories are actually falsified by these "dream memories"? Obviously we remember nightmares or other implausible events that occur in dreams as dreams. But there is a lot of random normal stuff that happens in dreams that, over time, get mixed in with the memories of actual events. Anyway, is there an article about this? I also wonder if there are extreme conditions where a person's dreams and reality are totally indistinguishable...like a psychological condition? I looked at Dream#Other associated phenomena and Memory#Disorderes (as well as scanning the rest of the articles), and am not finding much along these lines. Quinn ^{✩ STARRY NIGHT} 13:37, 23 April 2011 (UTC)

Well our memories are notoriously poor anyway and our brain outright makes things up to fill in gaps (there a number of books on the issues that the fallibility of human memory creates - e.g. reliabilty in court) so I suspect it wouldn't be difficult for dreams to integrate into memories and become things you think happened. The article Interference theory may be of interest though doesn't specifically related to dreams. ny156uk (talk) 16:18, 23 April 2011 (UTC)

Other people have speculated along the same lines, but the question seems nearly impossible to investigate scientifically. Regarding a state where dreams and reality are indistinguishable, it has been suggested that something like that happens in schizophrenia. Looie496 (talk) 01:39, 24 April 2011 (UTC)

Speaker wire

I've read the wiki article on speaker wire and found the information I was interested in but wonder if something should be included about interference on speaker wire such as the 60Hz line voltage? If the power cord and speaker wire are close together is it possible the 60Hz humm may be audible through the speaker?50.46.189.84 (talk) 15:38, 23 April 2011 (UTC)

You're welcome to edit the article and include the relevant information yourself if you believe it belongs somewhere in there, but try to include a reliable source for it. Note that you can do this even without creating an account, just as you edited this page. Try to make sure it's an encyclopaedic piece of information though, not a 'how to' guide, i.e., a 'how to construct a speaker wire' section would not be appropriate as it's not the aim of an encyclopaedia article. --jjron (talk) 16:57, 23 April 2011 (UTC)

It's not only possible, it's a very common source of interference. 60 Hz line noise is audible; it can couple via electromagnetic wave propagation (even though the wires are poor antennas at this frequency). More commonly, 60 Hz noise can couple through the speaker amplifier (hence, the noise gets amplified, even if it was very weakly coupled, and therefore at a low signal level). A good amplifier has a high power supply rejection ratio, meaning that the audio signal should be well isolated from the AC signal input; but in practice, poor- to moderate-quality electronics often propagate the "hum." High-end electronics eliminate this "hum" or line-noise in a variety of ways. Professional musicians may be familiar with "Humbuckers", as they are known in electric guitars; professional audio techs may know them as common-mode rejectors or differential signal transducers / amplifiers. Nimur (talk) 17:54, 23 April 2011 (UTC)

Or 50Hz. --ColinFine (talk) 07:42, 27 April 2011 (UTC)

If the geometries of the power cord and the speaker wires are specified, it is pretty straightforward to calculate the induced voltage. This is done all the time for power lines, and the equations would be the same, though the distances would be vastly smaller. Qualitatively speaking, the closer the speaker leads are to the power cord, the higher the voltage induced in the speaker wires. The more current the power cord is carrying, the higher the induced voltage. The farther apart the 2 conductors for power are from each other, the greater the induced voltage. Likewise, the farther apart the two speaker wire conductors are from each other, the greater the induced voltage. If the speaker wires and power cord are parallel, the voltage would be greater than if they are perpendicular, if memory serves. If either pair is twisted, the induced voltage would be lower. In general, the power cord for an audio system would be unlikely to induce enough voltage in the speaker wires for you to hear hum from the speaker, since the speaker impedance is quite low and the current in the power cord to an audio system is not all that great. The voltage induced in an audio cable going from a turntable or microphone to the amplifier would be much more likely to produce audible hum in the output circuit, unless well shielded audio cable is used and ground loops are avoided, since the signal in those input cables is vastly amplified before it goes to the speakers. I expect that a high enough electromagnetic field could be found around a power station or transformer, or near a cable carrying hundreds of amps, to produce audible hum from speaker wires audible through the speaker, even without amplification. Edison (talk) 19:44, 23 April 2011 (UTC)

You can minimize the 60 Hz hum in speaker cables by making sure that, if they MUST cross a power cable, to do so at 90 degree angles; cables which are orthogonal like this should, in theory, not interfere with one another. --Jayron32 23:15, 23 April 2011 (UTC)

Crosstalk between cables is minimised when the cables are Twisted pairs. Cuddlyable3 (talk) 21:39, 24 April 2011 (UTC)

Big echo here. Edison (talk) 00:43, 25 April 2011 (UTC)

What is a Tripletino?

In the wikipedia article on Proton Decay it talks about a 5 dimension mode of proton decay with two fermions and two Sfermions. It also mentioned that this involves a tripletino of mass M. I am a little familiar with supersymmetry and this name fits the naming conventions of supersymmetry particles. However, I have never heard of such a supersymmetric particle. It maybe a generic name like neutralino that refers to any neutral supersymmetric boson. It is the "triple" that throws me. A triple of what? What are the properties of this hypothesized particle? I have only one reference in the whole world wide web. It comes from your article in wikipedia, but is cut and pasted all over the web with no further information.75.201.50.204 (talk) 16:34, 23 April 2011 (UTC)

Maybe its another word for a Neutralino? Just a guess... --Jayron32 17:08, 23 April 2011 (UTC)

A full text search for "tripletino" on the arXiv yields zero hits, which is sufficient reason to remove the term from Wikipedia. A full text search for "tripletinos" yields exactly one hit. In that paper they appear to define it as a superpartner with color charge (i.e., a strongly interacting superpartner). But I'm wary of editing the article on that basis alone. I barely understand the physics.

The word was introduced in 2005 by User:Phys (edit), who unfortunately hasn't edited since 2005. -- BenRG (talk) 19:01, 23 April 2011 (UTC)

I started a thread at Talk:Proton decay#"Tripletino", but the talk page looks pretty inactive. -- BenRG (talk) 07:09, 24 April 2011 (UTC)

Ocean surface lumps above sea mounts

A Natnl. Geo. documentary entitled "Drain the ocean" states that all ocean sea mounts are mirrored by lumps at the ocean surface level, and that the ratio is 1-1000. That is that a 3000 Ft. ocean sea mount is marked by a 3 Ft. lump of water above it. I've searched a number of Sea level cites and find a lot if info. about sea level variations caused by water temperature, atmospheric pressures, currents etc. but I can't find any explanation about how a sea mount deep below the ocean can cause a lump on the surface. It seems understandable that a deep current welling up the side of a mount might produce a lump but not all sea mounts are subjected to the same degree of current. How is this possible?190.149.154.38 (talk) 16:56, 23 April 2011 (UTC)

It's actually just gravity. The rock that makes up a sea mount actually attracts the water, 'bunching it up' and very slightly increasing the local sea level. (There's a more detailed explanation here.) Because of this distortion, sea mounts have been detected by precise satellite altimetry: [5]. TenOfAllTrades(talk) 17:13, 23 April 2011 (UTC)

The technical term is gravity anomaly, which refers to the "anomaly" in measured gravity between a perfectly spheroid (or perfect, complex-geometric-model-oid) earth, and the true gravity, which is affected by topography and geological composition and density. A fluid, such as the ocean, follows the contour of the gravity potential field; but because of surface winds, turbulence, tides, and other dynamic effects, true sea-level measurements are confounded by lots of practical details. In the open ocean, wind waves regularly have crest-to-trough amplitudes of 20 or 30 feet - so if there's a 3 foot "bulge", it's tough (but not impossible) to measure it!

Usually, if you want millimeter-accurate measurements of anything related to geodesy, you start with a reference geoid, such as WGS-84; apply your needed corrections using Shuttle RADAR Topography Mission data. That brings you to around a 2 meter accuracy. If you need more accuracy, you can correct these measurements using a local reference. If you were out in the open ocean, and you wanted to measure the sea depth with accuracy to ~ 1 or 2 feet, you could use a RADAR or SONAR measurement from a fixed object, such as a buoy or a semi-permanent man-made or natural structure on the seafloor, or an acoustic beacon.

Here's a chapter out of a textbook on geophysical estimation; this runs down the entire process of estimating sea-level bulges, with actual data from a satellite overflight of Madagascar. Altitude of Sea Surface near Madagascar; and further related work, Madagascar numerical estimation. Nimur (talk) 17:31, 23 April 2011 (UTC)

Many thanks guys. Even I can understand it. Why didn't I think of that. (Rhetorical). 190.56.18.215 (talk) 17:47, 23 April 2011 (UTC)

Amazing. But that's why I'm glad I don't do real work. SamuelRiv (talk) 18:14, 23 April 2011 (UTC)

Recombining all the oxygen with H then how much more water?

General belief being that the proto earth was virtually devoid of free oxygen. It being a by-product of photosynthesis involving seperation of oxygen from water molecules, it seems that notwithstanding reactions with other elements that the number of water molecules (ie. the amount of water) must be substantially reduced from the original amount on the earth. Is it possible to calculate how much deeper the oceans would be if all the now free oxygen was recombined with Hydrogen.190.56.112.125 (talk) 19:11, 23 April 2011 (UTC)

I'm not sure how accurate your premise is (there has been a lot of reaction with other elements, so we can't really neglect it, for example), but we can do the calculation ignoring everything that could complicate it. Let's work in terms of mass, since that's nice and easy:

The mass of the atmosphere is 5x10¹⁸ kg (see Atmosphere of Earth). 21% of that is oxygen. Water is H₂O. Hydrogen has an atomic mass of 1, oxygen has an atomic mass of 16. That means a water molecule has a mass of 18/16 times the mass of the oxygen it contains. So, the mass of water that would be produced is 5x10¹⁸x0.21x18/16=1.2x10¹⁸ kg.

The density of water is 1kg per litre, so that's 1.2x10¹⁸ litres or 1.2x10¹⁵ m³.

The surface area of the Earth's water is 361,132,000 km² (see Earth). We divide the volume of water produced by the surface area and we get an increase in depth of 3.3 metres. (If someone could check my arithmetic, I would appreciate it!)

--Tango (talk) 20:14, 23 April 2011 (UTC)

This is a complex question, which brings interesting attention to the homeostasis of the deep earth and the unknown organisms that dwell within it. There are igneous rocks with differing levels of acidic or basic composition - though I typically think of basic as reducing, I'm not quite sure how well this matches up to their ability to react with oxygen. For example, pyrite decomposes in air, and both the sulfur and the iron take up oxygen. Ultramafic rock also contains a large amount of iron... anyway, there are rocks that have the potential to take up oxygen, and in our air they do; but if all the oxygen were bound into water, they would no longer do so - so there would be more oxygen left over. I have no idea how much oxygen you could draw out of the Earth in this way, given enough free hydrogen. The ability of deep microbes to catalyze specific chemical reactions would doubtless have much control over the rate. So while normally I think of photosynthesis as controlling the amount of oxygen, the process must really be more complicated than that. But we need some real geologists to chime in here.

If you look at our photosynthesis article, you will see that only half of the Earth's oxygen comes from water -- the other half comes from CO2, which is present in vast quantities dissolved in the Earth's mantle. Moreover, when the products of photosynthesis are metabolized, most of the water is returned. The numbers will be substantially reduced if those factors are taken into account. Looie496 (talk) 01:35, 24 April 2011 (UTC)

Gah, I'm an idiot. Actually all of the oxygen comes from CO2. Water plays a role in the reaction, but the amount of oxygen that the water contributes is equal to the amount that gets incorporated in sugar. Some of this oxygen may however eventually be released if the sugar is converted into hydrocarbons or fats. Looie496 (talk) 06:12, 24 April 2011 (UTC)

I don't think it makes sense to talk about whether the oxygen comes from the water or the carbon dioxide. The reaction breaks them up and recombines them. Which specific atoms go where doesn't make much difference. You could look at the reaction in stages and see what happens to each atom, which I tried to do based on our articles and rather struggled, but it actually looked to me like the free oxygen comes from the water. If you look at Photosynthesis#Light reactions it seems the first stage is breaking the water up into free oxygen and hydrogen ions, and then those hydrogen ions react the the carbon dioxide to produce glucose and some more water. --Tango (talk) 14:57, 24 April 2011 (UTC)

That's right. It doesn't really matter where the oxygen comes from. what matters is that for every oxygen molecule produced with a molecular mass of 32 one water molecule is consumed with molecular mass of 18. Looies's calculation is almost correct (within the simplified framework assumed in his answer). The only mistake is that a factor of 18/32 should be used instead of a factor of 18/16 which gives 1.6 meters of water. Dauto (talk) 15:44, 24 April 2011 (UTC)

Well, what does matter is that photosynthesis does not generate any free hydrogen. It generates carbohydrates and oxygen; and the carbohydrates contain H and O in the same proportion as water does. Looie496 (talk) 16:19, 24 April 2011 (UTC)

I think you are referring to my calculation, not Looie's. The 18/16 is correct. The mass of a water molecule is 18/16 times the mass of the oxygen atom it contains. That is where the 18/16 comes from. --Tango (talk) 17:40, 24 April 2011 (UTC)

You're right, I meant your calculation, and you are wrong, 18/16 should be replaced with 18/32 because you're comparing the molecular mass of the water with the molecular mass of the oxygen (not its atomic mass) since for every molecule of water consumed, one molecule of oxygen is produced. Dauto (talk) 11:30, 25 April 2011 (UTC)

THE SUPERNOVA 1987A

THE SUPERNOVA 1987A had charged neighbor cloud after exploding , the best idea for formation of planets in o'ort nebula (''such as now upgrades''I will discuss next time about in other field )shows that this nebula was charged by neighborhood supernova for containing oxygen carbon and heavy elements ,and it might create the pressure and temperature condition for production of water , methane and water contain carbon and oxygen and ammonia contain nitrogen which produce in carbon cycle , and all metals in earth crust have been oxidized , 23 %of earth crust and 21%of air contain oxygen--Akbarmohammadzade (talk) 06:26, 24 April 2011 (UTC)

I assume you mean the Oort cloud. I'm sorry, but it is difficult for us to understand your English. Wnt (talk) 06:54, 24 April 2011 (UTC)

Akbarmohammadzade

the first cloud which produced solar system could not produce water for its complex of hydrogen and helium ,this cloud might be charged with supernova remnant matter to contain elements which be produced at the core of stars and migrate here with supernova exploding event , so although the sun has carbon cycle but existing of heavy elements in terrestrial planets and ice and methane and ammonia in outer planets and comets shows that the inner system of o'ort cloud might be charged secondary , specially for the reason of this :if first prestellar nebula had such elements ,the percent of existing of them in sun and planetary system was equal , then the sun had absorbed 99percent of those elements and that could not be 4percent of total planetary system , but the fact is wise . notice that the condition which cause the production of water is special ,finally can earth's own global condition produce water?--78.38.28.3 (talk) 10:07, 24 April 2011 (UTC)

--78.38.28.3 (talk) 08:04, 24 April 2011 (UTC)

Active electronic metamaterials.

Does anybody have references to Metamaterials that change function by adding or removing electrons?

Just as an LCD display has an individually addressable transistor per pixel, each molecule in the active electronic metamaterial will act as a transistor that can selected and charged or discharged. The patterns formed would then interact with and direct electromagnetic waves and these patterns can be changed at the speed of electricity. Hcobb (talk) 19:47, 23 April 2011 (UTC)

Are you looking for the Sketched oxide single-electron transistor (SketchSET)?Smallman12q (talk) 21:22, 23 April 2011 (UTC)

No, that's an isolated electronic device that doesn't greatly change the properties of the bulk matter around it. Hcobb (talk) 22:48, 23 April 2011 (UTC)

Echos in the Treasury of Atreus

On a recent trip to Mycenae, my peers and I noticed that a person standing on one side of the interior of the Treasury of Atreus speaking softly into the wall could be heard very clearly from a person on the other side -- the speaker's voice is heard as coming out from the diametrically opposite point on the wall. What is the reason for this phenomenon? What is it about the shape of the tomb that causes the sound to be focused at that point, and are there any other points at which this happens? jftsang 23:26, 23 April 2011 (UTC)

Check out Whispering gallery. Clarityfiend (talk) 23:40, 23 April 2011 (UTC)

But the inside of the tomb is circular, so the two foci coincide at the centre. Why does this work if one stands at the edge? jftsang 23:51, 23 April 2011 (UTC)

Besides the center, there will be other nodes where the sound waves collect to have the same effect; its quite possible to create a room where one of those nodes is at the speaker's own head. --Jayron32 23:55, 23 April 2011 (UTC)

Also note that whereas the floor may be more or less circular, the "inside of the tomb" as a whole is rather complicated in shape (similar to a paraboloid or half of a prolate ellipsoid). Sound doesn't travel in only two dimensions. Deor (talk) 10:24, 24 April 2011 (UTC)

Whispering gallery modes primarily happen in circular rooms. Contrary to what the article implies, the phenomenon is distinct from the concentration of sound at the foci of an ellipse or circle. A true whispering gallery mode forms antinodes around the perimeter of the room, not in the center.--Srleffler (talk) 17:34, 26 April 2011 (UTC)