Wikipedia:Reference desk/Archives/Science/2012 June 8

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June 8

who edit Wikipedia in a sensitive subject... who is right ??

Hi: According to Wikipedia in English, in the page about "omega 3" they said that are really controversial the good effects that brings omega 3 in any mammal... if fact they cite research that say that is not a really big help for the human body.

In Wikipedia in Spanish, they say exactly the opposite, omega 3 is really a big help for the human body. Who is right ?? who edit this articles ?? what about if I am a mediocre doctor who just write something that I learned 100 years ago ?? to whom I have to believe is a kind of articles that involve a live risk ?? many thanks in advance. chau and sorry for my funny English — Preceding unsigned comment added by 186.2.50.237 (talk • contribs)

Because Wikipedia can be edited by anybody, you should always have doubt about what you see in a Wikipedia article. If you want to check, you should look at the sources that the article cites. If there are no sources, you should have a lot of doubt. Anyway, my understanding is that the English article is correct. (For convenience, our article is Omega-3 fatty acid. Looie496 (talk) 03:02, 8 June 2012 (UTC)

It's difficult to evaluate the claims in the Spanish article as instead of citing sources, they simply provided links, and those links are now broken. Someguy1221 (talk) 04:10, 8 June 2012 (UTC)

... and I hope that even mediocre doctors don't use Wikipedia as their medical text! Dbfirs 07:28, 8 June 2012 (UTC)

Spanish wikipedia has horrible administrators, some of them, revert all Ip's edits without reading them at all. Many requests are ignored. They take community decisions by votes instead of arguments.. though I have to admit that there is a lot more vandalism there than here. 65.49.68.173 (talk) 16:28, 8 June 2012 (UTC)

Thanks to all of you. chau — Preceding unsigned comment added by 186.2.50.237 (talk) 04:41, 9 June 2012 (UTC)

I think the English Wikipedia is not so reliable on these sorts of medicine related issues, because it gives far to much weight on the Institute of Medicine (IoM) reports; these reports are extremely conservative when it comes to accepting claims of benefit, while the burden of proof needed to include possible negative health effecs is extremely low. While this may be a good thing for compiling reports meant as advice to health care workers, what we need on Wikipedia is a balanced approached, one that gives equal weight to equally reliable evidence. Count Iblis (talk) 17:53, 8 June 2012 (UTC)

Helium dihydride cation

Why can't this exist? I'm talking about the species HeH₂²⁺, isoelectronic with the trihydrogen cation.--Jasper Deng (talk) 05:38, 8 June 2012 (UTC)

It's too unstable. HeH⁺ is already the strongest known acid, i.e. it is more likely to dump a hydrogen ion than any other compound ever discovered. There are a handful of funky looking sources claiming you can get HeH⁺ to accept a hydrogen atom, but not a hydride ion. My guess is that even if you could, the second hydride would be dumped almost immediately. Someguy1221 (talk) 05:47, 8 June 2012 (UTC)

Careful. The relevant unit would be a simple proton (H⁺), not "hydride" (H^–), which would instead give the neutral helium dihydride result. But the massive instability is certainly the key. Our helium hydride ion discusses the species mentioned by Someguy, and also evidence for and stability of HeH₂⁺ and others in this monocationic series. One could certainly so some ab initio calculations on HeH₂²⁺ to see what would be happening there. DMacks (talk) 14:22, 8 June 2012 (UTC)

Whoops, my bad. Thanks DMacks. Someguy1221 (talk) 18:16, 8 June 2012 (UTC)

And just to prove I'm not just making stuff up, HeH₂²⁺ (CAS #12519-50-5) has been studied in this manner, and is unstable in normal situations but is stable in the presence of high magnetic fields (like "surface of a neutron star")--see doi:10.1103/PhysRevA.81.042503. Note that all refs I found consider it as a chain--not sure if exactly linear in all cases, but anyway more structurally related to beryllium hydride than the trigonal trihydrogen cation you mention. DMacks (talk) 14:46, 8 June 2012 (UTC)

Water on the line

I work 50m away from a railway line in SE England. Yesterday, after a day of rain, when a train passed along the line, there was a spectacular noise followed by plumes of steam that stretched for a couple of hundred metres and reached well above the tree line. I've lived and worked next to this stretch of track for 17 years and have never seen anything like this before. I have not heard on the news that a train-load of people have been fried on the London to Dover line yesterday afternoon, so was the train acting like a Faraday cage and were the passengers in any danger? 83.104.128.107 (talk) 15:51, 8 June 2012 (UTC)

There's some missing info in your question. Is this an electric train, powered by an electrical rail ? If so, the electricity would want to go towards earth/ground, and standing water by the non-charged rail, in conjunction with electrical connections between the rails through the train's undercarriage, might have allowed that. There would be little "motivation" for the electricity to go into the passenger compartments, so a Faraday cage isn't necessary. StuRat (talk) 17:20, 8 June 2012 (UTC)

(@StuRat - Most of South East England is a 'third-rail' electrical pick-up system.)

At OP - Can you clarify more closely where you are in SE England and where this incident occured? Your description sounds like some kind of flashover effect, but I hadn't heard anything about such through my railfan contacts, and most modern trains have a specific trip so they don't produce the kind of effect you saw. Sfan00 IMG (talk) 15:49, 10 June 2012 (UTC)

Hello Sfan00, It was on the stretch of track between Faversham and Selling at around 16.40 on 14th June. The line crosses a farm where I saw it, I checked the train times and no journey in either direction seems to tie in, but there are often freight trains passing. I would love to know what the passengers/driver felt or saw! A friend did suggest that I might have seen a steam train, but there was no 'chugging' and there was no majestic view of it in the distance when I dashed up to the bridge. I am hoping that with more rain to come and the ground still saturated it might happen again this week. 80.176.84.184 (talk) 17:28, 10 June 2012 (UTC)

As I said, I hadn't heard anything, you could try asking on the uk.railway newsgroup :) Sfan00 IMG (talk) 18:25, 10 June 2012 (UTC)

@80.176, you said that this happened on June 14, which, unless you are talking about last year, will not occur for another four days. What did you intend? Falconus^{p t c} 21:03, 10 June 2012 (UTC)

D'oh - I meant the 7th! Looked at the wrong Thursday on the calendar! Having been a long-term stalker of the ref desks I am absolutely appalled at the lack of clarity of my original question and subsequent blunders (let alone somehow first posting the question on the Language Desk!). I think I'll stick to reading and not asking... but I would like to say what an amazing resource the Ref Desks are and it is incredible that we have such informed and interesting people to probe with our musings! 83.104.128.107 (talk) 08:34, 11 June 2012 (UTC)

Yes, the most difficult part in asking a question here is generalizing it so everyone around the world understands it. To you, a "train" is a third rail electrical train, while to me in Detroit, it's a diesel-electric train, with the third-rail system reserved for subways, which you call "the underground" (which to me means a covert organization) or "the tube" (which to me means television), etc. But learning to explicitly state all of your assumptions is a valuable lesson, in any event. StuRat (talk) 16:32, 11 June 2012 (UTC)

What cause brownian movement?

What makes gas molecules extert brownian motion ..? is it related to the electron shell?, proton/neutron core? quarks? the energy at least intermediately has to be stored somewhere. Electron9 (talk) 16:15, 8 June 2012 (UTC)

The energy isn't stored anywhere. It's a manifestation of the thermal kinetic energy of the individual molecules impacting the larger object.

In simpler language, you should know that temperature is really a measure of the average kinetic energy of the individual molecules in a substance. For solids this is just molecules vibrating, but in a fluid like water or air the molecules are free to move around each other. So when you put a small enough particle in a fluid and look at it under a microscope, only a few molecules are going to be hitting the (relatively) larger object at any one time, and the odds are good that they won't be hitting symmetrically. Therefore they impart a small amount of net kinetic energy to the larger object, and it moves slightly. It is a random process, so averaged over infinite time there will be no net motion, but it can still jiggle the object around a great deal over short time scales. -RunningOnBrains^(talk) 16:39, 8 June 2012 (UTC)

Short version of the above - Heat. Roger (talk) 16:51, 8 June 2012 (UTC)

No, it's not heat. Temperature and heat are very different concepts. 203.27.72.5 (talk) 07:22, 9 June 2012 (UTC)

If brownian motion is plainly a manifestation of thermal vibration. What parts of the atom is vibrating? electron shell? nuclei? quarks? Electron9 (talk) 17:44, 8 June 2012 (UTC)

The entire atom or molecule. StuRat (talk) 17:47, 8 June 2012 (UTC)

Further: Any macroscopic analogy is going to be at least partly incorrect, because we are dealing with individual molecules and atoms here, which are subject to quantum mechanics. However, I will do my best.

In a gas or liquid, molecules are never still. They are constantly moving, at a velocity that can be predicted by the temperature of the gas. As a 2-dimensional analogy, imagine a whole bunch of billiard balls flying around a giant pool table, with no friction to slow them down. They will stay at a constant velocity until they hit either the walls of the table or another billiard ball, and then they will go off at a different velocity in a different direction. It is very nicely illustrated by the image I posted at right: You have to remember that there is no friction at this scale, so unless the material is cooled or warmed, the average thermal velocity of the molecules is going to stay the same. Now if you introduced a larger object to the table, say a bowling ball, it's going to be jostled by the constant collisions, and so if you were standing far enough away that you could only see the bowling ball, it would appear to be vibrating randomly, just like in Brownian motion. -RunningOnBrains^(talk) 17:59, 8 June 2012 (UTC)

Thanks! (maybe should be added to the article), does thermal vibration cause the nuclei and electron shell to vary their distance to each other? ie will the atom deform in some way like air does for sound? Electron9 (talk) 19:43, 8 June 2012 (UTC)

Not really, but here we're really getting to the point where macroscopic analogies break down, because electrons really aren't in one place at any time, and electron shells aren't really a physical object: see electron cloud. I am also probably extremely unqualified to speculate on the exact quantum mechanical processes which take place when two atoms collide; it probably depends strongly on which atoms we're talking about. But it can be safely described as a purely elastic collision for the point of describing Brownian motion.-RunningOnBrains^(talk) 20:09, 8 June 2012 (UTC)

Actually, I disagree with Runningonbrains here. Absolutely, thermal vibration causes variations in the position of the different atomic particles relative to one another. As Runningonbrains rightly pointed out the (average) velocity of the particles that make up an object can be predicted from the object's temperature. The velocities of the individual particles vary according to the Maxwell-Boltzmann distribution. The deformation of the atoms or molecules leads to a higher energy state i.e. electrons repel one another altering the shape of their orbitals. These high energy states are relatively unstable and if a more stable configuration can be assumed, then it will be. Many molecules that decompose do so more quickly at higher temperatures. This can be modelled by saying that those molecules that have high energies are deformed by the motion of their constituent particles and assume a more stable state by breaking chemical bonds. The number of molecules with high energies is a function of temperature as predicted by the boltzmann distribution. Electrons can even be heated so much that they leave the atom all together, as in a thermal plasma. 203.27.72.5 (talk) 07:49, 9 June 2012 (UTC)

That would mean that the atomic nuclei (protons-neutrons) will deform in a plasma just like electrons does at a lower temperature? Electron9 (talk) 08:27, 9 June 2012 (UTC)

Somewhat more important in practice is that some thermal energy is stored by the rotation of molecules at temperatures above about 600 -700 K, (ie angular momentum, as well is the linear momentum mentioned above) and by the lengthening of inter-atomic bonds with increasing temperature, which further increases the fraction of heat energy stored in rotation. This is evidenced by the fact that noble gasses show specific heat independent of temperature, but large molecules have considerable variation in specific heat throughout the measureable temperature range. Only the fraction of heat energy stored in linear momentum drives brownian motion. Wickwack124.178.139.104 (talk) 11:42, 9 June 2012 (UTC)

A side question, would a tube between two vessels with a diameter just slightly larger than a single atom (or molecule) and a length significantly less than the average brownian motion distance. And funnel on one side make more atoms to move to one side than the other? especially when the mol/m³ is low. Electron9 (talk) 19:43, 8 June 2012 (UTC)

No. You're proposing a variation of Maxwell's demon, which violates the second law of thermodynamics (in this case, by creating a pressure and temperature gradient. The Brownian ratchet may also be of interest. — Lomn 20:01, 8 June 2012 (UTC)

Radiation

Do objects which absorb radiation reemit it? How does this work? — Preceding unsigned comment added by 176.250.228.38 (talk)

It depends a lot on what type of radiation you're talking about. All kinds of matter absorb and emit all kinds of radiation all the time. It is a continuous process. --Jayron32 18:54, 8 June 2012 (UTC)

Most things which absorb radiation with then give off radiation as well, although it may very well be a different form of radiation. For example, if you shine visible light (one form of radiation) onto a black object, it will radiate the energy back out, not as visible light, but as infrared light/heat. StuRat (talk) 19:02, 8 June 2012 (UTC)

There are chemical processes in which the electron shells surroundng atoms absorb radiation at one wavelength and them re-eimit it at another wavelength - this is called fluorescence. And there are processes in which radiation is absorbed and its energy is converted into a different form - see pair production, photoelectrochemical processes, photosynthesis, photoelectric effect, photovoltaic effect, concentrated solar power. Gandalf61 (talk) 10:18, 9 June 2012 (UTC)

Rules of science

Often in Biology, everything doesn't follow the known rule we've established. Can the same thing be said for physics & chemistry? 176.250.228.38 (talk) 20:00, 8 June 2012 (UTC)

Yes. I know in chemistry, there are lots of experiments that don't do what a hypothesis (based on literature precedent for similar experiments) says they "should"--exceptionally low yield, different geometric form, different part of a complex molecule reacts, nothing happens at all, or a totally different reaction occurs instead. There are probably a near-infinite number of combinations of experiments that would follow some not-yet-detected pattern, or an observed pattern that does not have any known underlying cause, where the data is all "out there" but nobody has even looked yet (i.e., to explain apparently random variations in yield, etc.). DMacks (talk) 20:06, 8 June 2012 (UTC)

This answer isn't exactly right. The answer to your question really depends on what question you're asking.

If you're asking if there are exceptions to the established laws of physics and chemistry, the answer is no. You're not going to get gravity to be different from one experiment to the next, and you're not going to get sodium and chlorine to react and form anything other than sodium chloride. They are called "Laws" for a reason.

However, if you're asking whether or not experiments can produce unexpected results, the answer is most definitely yes. You can never (probably) have an experiment that is completely controlled, where you know every bit of information about the initial conditions. You can get a different yield than you were expecting from a reaction, but this would be due to some contaminant you didn't know about, or some environmental factor that was different like temperature or moisture in the air. Maybe the yield is highly sensitive to the initial ratio of reactants, and the expiriment Maybe even some unforeseen quantum mechanical effect could change the expected results, if it's an especially complicated chemical reaction. Or, incredibly rarely, maybe your physics experiment has discovered a whole new particle or effect.

However, if you do exactly the same experiment every time, you will get exactly the same result. The reason that biology is such a messy science with many unexpected results is that there are just too many unknown factors to take them all into account; an organism is unimaginably complex, certainly not as easy to describe with simple laws as E=mc² and F=ma.-RunningOnBrains^(talk) 20:22, 8 June 2012 (UTC)

Another important point is that science is neither a set of laws, nor a primarily deductive enterprise. Science is a method for inductive reasoning. --Stephan Schulz (talk) 20:31, 8 June 2012 (UTC)

Running, your second third last paragraph sounds like determinism, which is not a necessary component of science, and indeed is contrary to some widely held interpretations of quantum mechanics. --Trovatore (talk) 20:36, 8 June 2012 (UTC)

Deterministic probabilities ? :-) Electron9 (talk) 21:52, 8 June 2012 (UTC)

I guess I interpreted the OP's question as a macroscopic sort of thing. You're right in that there is always some QM-related uncertainty (even if miniscule at macroscopic levels); but those would not be unexpected to an experimenter, and certainly follows the "known rule" as the OP put it. I would say that my final sentence above really sums up my point; maybe I shouldve just stuck to that :) -RunningOnBrains^(talk) 22:46, 8 June 2012 (UTC)

It depends a lot on what the OP means by "rules". Most scientific "rules" are actually models of some sort, and all models are approximations of reality, so there will always be real examples that lie outside of the predictions of the model. --Jayron32 03:04, 9 June 2012 (UTC)

As a former analogue electronics engineer, now involved in certain aspects of chemistry, I must say there is an immense difference between electronics and chemistry at an engineering/design level. In electronics, everything is ultimatey based on a limitted number of component parts - resistors, capacitors, inductors, conductors, and active devices (transistors etc). The behavior of these devices behave according to well established simple laws - so simple that a 12 year old can, if sufficiently interested, design a stereo (I did when I was 12). Real parts don't exactly follow these laws, but they are close enough. Understand those laws properly, and you can understand anything in analogue ectronics.

Chemistry is very different. The "almost fundamental" component parts of chemistry are the atoms. The behaviour of atoms in any situation can (in theory) be predicted by quantum mechanics. In practice, that's just too hard, so the "laws" of chemical engineering are fortutious theories like the kinetic theory of gasses, and the theories of chemical kinetics with regard to reaction rates. These theories have so many gaps, exceptions, an approximations, that to former electronic engineer, it is very frustrating. To calculate current in a circuit, I can alway do that to at least 3 figures accuracy - 6 figures, if I need it, is not hard. To calculate the rate of a chemical reaction, chemists are doing well if they get within the correct order of magnitude. As a further example, the kinetic theory of gasses pupports to give an understanding of specific heat (thermal capacity) and how it varies with temperature. It accuately gives the specific heat for noble gasses (but who cares), and is roughly right for low valency atoms, but seems to be very inaccurate otherwise.

In electrical enginering, if say, a power company wants a $100M EHV transmission line and distribution system, the engineers do some caculations, order the materials, get it built, and it will work just fine. In chemical engineering, if a company wants a new $100M processing plant, the engineers do some calculations, scour the world for somebody who has done something like it, tweak the calculations, then build a pilot plant and muck about with it untill it works. Then with that experience, do more calcs, scale it up, then order all the materials etc and build the BIG ONE. Then sometimes find out it doesn't work at all well, and $100M has been wasted.

In short, chemistry must conform to valid scientific laws, but those laws are too difficult, so in practice, rough semi-empirical approximations are used. And things don't always go according to plan.

If you understand "basics" like chemical kinetics (and that is not at all easy), you still may not be able to understand real world applications. By "understanding" I mean able to calculate and preduct accurately what will happen.

Ratbone124.182.45.112 (talk) 03:34, 9 June 2012 (UTC)

It's a subtle and important point - every science has different objectives to deal with different topic matter. Physics sets hard-and-fast absolute rules of what is impossible. Chemistry is more about figuring out what is practical. And biology is a science of the possible, where every "rule" has an exception. The continuum continues further in disciplines like psychology, where there is doubt if it is even a science, and perhaps, even to the tropes of fictional writing. Wnt (talk) 15:26, 9 June 2012 (UTC)

cephalosporin

are there any once a day oral cephalosporin antibiotics?--Wrk678 (talk) 22:56, 8 June 2012 (UTC)

It depends what it's for. Apparently some of the cephalosporins taken PO are administered qd, such as cefpodoxime (Vantin) for otitis media. DRosenbach ^{(Talk | Contribs)} 13:04, 12 June 2012 (UTC)

Mercuroketones

Are any of these possible?

Can any mercuroketones (compounds containing a C=Hg double bond), such as those in the image, exist? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:58, 8 June 2012 (UTC)

I don't really think so, because good luck getting mercury to hybridize its s and/or d orbitals to allow a covalent bond.--Jasper Deng (talk) 03:18, 9 June 2012 (UTC)

Then explain organomercury compounds. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 04:38, 10 June 2012 (UTC)

These either all have single bonds to Hg or Hg is part of a cation.--Jasper Deng (talk) 04:54, 10 June 2012 (UTC)

In your earlier post, you implied that the problem was with trying to get mercury to form covalent bonds. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:48, 12 June 2012 (UTC)

Look at Oxymercuration reaction in which a cyclic mercurinium ion is formed, Hg has lost an electron and has three bonds, two with adjacent carbons. Still no double bond though, and I could find no evidence of it on google either. Graeme Bartlett (talk) 07:28, 9 June 2012 (UTC)

Mercury can definitely form double bonds with oxygen, I don't know about carbon though. Plasmic Physics (talk) 12:02, 9 June 2012 (UTC)

"Mercuroketone" is probably not a good term for it, since mercury not very electronegative. More likely "methylene mercury" (or other coordination/description of the carbon part, as usual for ligands on metals) or a "mercury carbene" (161 google hits) complex or something like that. Hg⁺=CH₂ (apparent Hg(III) species), CAS#1234574-43-6, has been studied theoretically. But I'm also seeing lots of examples where what your type of connectivity is written as a Hg(II) ylide, for example, Hg⁺–C^–H₂, rather than a Hg=C double bond. As for some of the coordination examples, you have to be careful not to exceed an electron-count of 18 (the transition-metal analog to the octet rule used in main-group elements). DMacks (talk) 14:42, 9 June 2012 (UTC)

Mmm, can't comment on the specific molecules here, but I remember from my chemistry undergraduate that transition metals can form some pretty funky organometallics from time to time. In principle these molecules look plausible. LukeSurl ^{t c} 09:34, 10 June 2012 (UTC)

Have you yet attempted to model the proposed molecules? Nevermind the mercurylidenemethylidene group, the angle strain of tetragonal carbons alone, is enough to destablise most of these molecules. Plasmic Physics (talk) 10:13, 10 June 2012 (UTC)

Oooh yes, that triangular arrangement in 4 looks especially painful. I'm assuming the question is mostly about the idea of the C=Hg bond rather than the carbon skeletons I'm guessing the OP has just made up. 10:30, 10 June 2012 (UTC)

What about 1, 2, 6, and 7? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 15:28, 12 June 2012 (UTC)

How should the carbon be modified to form a kinetically stable stable bond? Perhaps, a persistent carbene? Plasmic Physics (talk) 13:58, 10 June 2012 (UTC)