Wikipedia:Reference desk/Archives/Science/2011 April 22

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April 22

What's the species?

Hi. Could someone help me in finding the species of this lizard? I took this photograph last week at the Horton Plains National Park, somewhere near the summit of the Kirigalpoththa mountain, in Sri Lanka. Rehman 01:39, 22 April 2011 (UTC)

Claiming no expertise in this at all, I looked at "Reptiles of Sri Lanka" and decided it looked like one of the Agamidae and not the other groups they list (I was assuming since this is a tourist snap that it's not a very rare species). Among the Agamidae are horned lizards Ceratophora. Searching for these, I found a "Ceratophora stoddartii" (last photo at [1]) which looks a lot like yours to my eye. Caveat: most of the images on a Google image search for this species don't look much like it and are all different colors. I've made no attempt to determine if that is chameleonlike change of color, genetic variation, iridescence, etc. Wnt (talk) 06:43, 22 April 2011 (UTC)

Thanks! After referring to srilankanreptiles.com you mentioned above, I am pretty sure it is the Rhino-horned lizard. Thanks again. Regards. Rehman 07:45, 22 April 2011 (UTC)

potentiometer question

Can a potentiometer that is designed for a tone control (i.e. bass or treble) work properly when used for a regular volume control? Bubba73 ^{You talkin' to me?} 05:25, 22 April 2011 (UTC)

Perhaps. The replacement potentiometer must of course have the same max resistance as the original pot. The wattage rating also has to be high enough, but that’s probably not going to be a problem.

Looking around at a few tone control circuits, I see that the first couple I looked at at least called for linear taper pots. In contrast, pots used for volume control, at least in more expensive devices, are sometimes logarithmic taper. But the difference isn't all that big of a deal; using a linear taper pot where a log taper pot is called for just means that there'll be a bigger perceived change in volume for the same angle change at one end of the dial than the other. But cheap devices generally go ahead and use the cheaper linear taper pots for volume control anyway, so the difference between a linear taper pot and a log taper pot really isn't anywhere near as important as just making sure the replacement pot has the same max resistance as the original pot.

There are a couple contributors here who can run circles around me at EE, so if anybody pipes in to disagree with what I've said above, listen to them instead of me. Red Act (talk) 07:29, 22 April 2011 (UTC)

ELECTRONICS

How an FM transmitter & receiver is designed27.97.64.66 (talk) 08:32, 22 April 2011 (UTC)

They are rather complicated. Have you read transmitter and receiver? Those articles will get you started.--Shantavira|^{feed me} 11:24, 22 April 2011 (UTC)

I feel the OP is more interested in some kind of circuit diagram, something like that. As wikipedia is not a HOWTO, such things are only found externally. 95.112.196.91 (talk) 13:17, 22 April 2011 (UTC)

marsh plant that needs pressure from flowing water to hold structure?

Has anyone heard about such a plant? A friend told me about it years ago - maybe from the northern parts of Australia? - she described it as having a porous or open lower end - the water flows up into it and gives it structure through hydrostatic pressure... Can someone name the plant for me? Thanks Adambrowne666 (talk) 10:00, 22 April 2011 (UTC)

Indian Thundershowers

Does anyone know why Southern India gets thunderstorms during April, but normal showers during Monsoon (July-October)? Yes Michael? •^Talk 11:41, 22 April 2011 (UTC)

What does the word "Pinkie" mean?

The word "Pinkie" is used in terms like "Pinkie finger" and "Pinkie blue"? What is the meaning of the word "Pinkie"? aniketnik 12:06, 22 April 2011 (UTC) — Preceding unsigned comment added by Aniketnik (talk • contribs)

The "pinky" or "pinkie" is the little finger. Gandalf61 (talk) 12:11, 22 April 2011 (UTC)

If you follow the little finger link, you'll find that the "pinky" in "pinky finger" is listed as being from the Dutch word pink, ultimately from a Proto-Indo-European word for "five", "finger". Note that this seems to be unrelated to "pink", the word for the color, as that is listed as being derived from "pinks", a name for Dianthus (carnations), a name referring to the frilled edge of the flower and probably deriving from the German "pinken", to peck. This latter meaning is also seen in the name "pinking shears". -- 174.31.219.218 (talk) 15:41, 22 April 2011 (UTC)

From Wiktionary it's apparent this root also leads to finger, cinco, quintet etc. Wnt (talk) 21:02, 22 April 2011 (UTC)

What connections should scientists explore?

How do scientists decide which variable could correlate? If some crackpot theorist claims that certain stones cure cancer, should scientists go on and test it empirically? Should scientists dismiss intuitively some claims? Quest09 (talk) 13:29, 22 April 2011 (UTC)

In an ideal world, scientists would test everything (with a few exceptions due to ethical concerns, perhaps). In the real world, there are limited resources so scientists test those things that they think are most likely to give an interesting result (of course, what's interesting to a scientist isn't necessary what would be interesting to everybody else!). For medicine in particular, the normal route is to test things in Petri dishes first, which is fairly easy so they can test all kinds of things, and then only test on real people those things that showed promise in the Petri dish. So, they may well test stones on cancer cells in a Petri dish, but unless they actually seemed to work, they wouldn't test them on people. --Tango (talk) 13:57, 22 April 2011 (UTC)

I could play devil's advocate for a moment and note that some therapies – particularly non-drug interventions – are not always amenable to in vitro testing. While I would be unsurprised to discover that therapeutic touch and magic rocks have no ability to slow the growth of malignant cells in culture, I have to admit that it's also difficult to maintain a regimen of healthy diet and aerobic exercise in a petri dish.

Testing a novel protocol in humans depends primarily on three things. First, you need to find a researcher who wants to do the trial; often that means that they believe the trial will work, but someone who's genuinely curious or who is interested in debunking a bad idea will do. Second, you need to be able to get ethics approval to carry out the trial. An ethical clinician can't and won't participate in a trial if they have a reasonable expectation that the experimental therapy will have a worse outcome than the current therapy (see also clinical equipoise). Third, you need to have the resources – trained medical personnel, equipment, magic rocks, and most importantly, willing and informed patient participants – to carry out the trial. In general, this means it is impossible to do a trial of magic rocks versus chemotherapy, because the experimental therapy isn't supported by any evidence and is likely to kill patients. On the other hand, one might be able to do a trial of magic rocks plus chemo versus chemo alone (or, better, chemo plus blinded 'placebo' rocks); the worst-case scenario is anticipated to be that the rocks are ineffective, so the patients do no worse than with chemo alone. The hard part is finding resources to do the trial, since there are many more plausible treatments ahead of the magic rocks in the queue for funding. TenOfAllTrades(talk) 15:29, 22 April 2011 (UTC)

A problem with doing not well motivated tests is that this tends to lead to a bias where only positive results are reported. Suppose you have good theoretical reasons to believe that X may cause Y (but it is not clear that this must be the case). Then you investigate this and you find that in fact X doies not cause Y. This result is then still interesting enough for peer reviewed journals to publish.

But without any good reason to believe that X may cause Y, a negative result wont merit publication in a peer reviewed journal. Now, suppose that in such a case, you find a positive result at 95% significance level and that in reality this is due to chance alone (so no relation exists and you just happen to be in the 1/20 of cases where you find a significant result). Then that is likely to yield a publication in a peer reviewed journal. Certainly, it is now interesting for other researchers to see if X really does cause Y. But this may take time, and all that the public hears is that: "researchers have found that X causes Y". Also, onses the results come in that debunk the relation, these don't make headline news.

This effect is partially to blame for the paranoia about mobile phones causing cancer, mobile phone relay transmitters near building being involved in all sorts of illnesses, GM foods possibly not being safe etc. etc. etc. Count Iblis (talk) 14:47, 22 April 2011 (UTC)

As usual, there is an all-too-close-to-reality xkcd on this topic. Don't forget to read the mouseover text. TenOfAllTrades(talk) 14:54, 22 April 2011 (UTC)

And for a more serious treatment, see also publication bias, including the bit about the 'file drawer effect'. TenOfAllTrades(talk) 14:56, 22 April 2011 (UTC)

There is no one prescription that describes how scientists do or should approach the question of what areas would be fruitful or interesting. In practice it is almost certainly about who is willing to fund what — all of these things cost money, and finding creative ways to justify a project to a sponsor is a full-time occupation of many PIs. Even the philosophers of science who believe in strict demarcation, like Karl Popper, do not believe that you can apply that kind of criteria to the sources of inspiration or interest, which are often haphazard (e.g., at the extreme end, dreams, hallucinations, falling fruit). The question is perhaps more systematically stated as to what studies should be funded — which is a trickier question that balances likelihood of success, benefits from success, reputation of researcher, things like that. --Mr.98 (talk) 15:40, 22 April 2011 (UTC)

What do you mean by "success"? A study that shows a null result conclusively is just as successful as one that shows a positive result conclusively, in my opinion. --Tango (talk) 16:31, 22 April 2011 (UTC)

Scientifically, yes, but economically, no. That is, most studies are funded in the hope of eventually making money off them. Finding that a (patentable) drug works well may lead to economic success, while finding that one doesn't work isn't as likely to do so. The economics behind science can lead to both a poor choice of studies and, even worse, biased results. Finding a neutral source of funding is difficult, though. Government funding (from taxpayer dollars) of university research may be less profit-motivated, and thus allow studies of things like herbal remedies and traditional Chinese medicine, where profit potential is limited. Political considerations may come into play there, though, such as prohibiting any research on the benefits of stem cells. Use of charitable donations is another option, but major contributors may also have agendas they wish to purse. StuRat (talk) 19:22, 22 April 2011 (UTC)

Proving, based on currently accepted principles, that something (say, a perpetuum mobile) is impossible saves a real lot of money and effort. The major back-draw is that the poor guy who publishes such a result gets nothing in return but the hatred of those who hoped for funds for investigation and building one. 95.112.196.91 (talk) 20:45, 22 April 2011 (UTC)

"Success" would be defined differently in different contexts. I'm not trying to claim one standard for it. Proving a null result conclusively is only "successful" in some contexts, not all. Proving that unicorns don't exist on the moon conclusively would do little to benefit scientific knowledge. Proving that there is no luminiferous aether in the early 20th century did. --Mr.98 (talk) 20:48, 22 April 2011 (UTC)

Thomas Kuhn's work deals extensively with this question. See Paradigm shift for information on his work. In essence his idea is that, contrary to the traditional idea that "ideally" scientists should treat all hypotheses equally, in fact scientists work within a model he called a paradigm, which guides their evaluation of which hypotheses are worth exploring. Hypotheses that make sense within the currently accepted paradigm are investigated, and various forms of peer pressure strongly discourage investigation of hypotheses that fall outside the current paradigm. The paradigm changes infrequently; perhaps every several generations. Paradigm shifts are usually a dramatic change rather than a gradual evolution.

This selection of hypothesis is, Kuhn argues, essential for science to work. The transition from prescientific research (e.g. alchemy) to true science (e.g. chemistry) is marked by the creation of the first paradigm for that field.--Srleffler (talk) 17:02, 25 April 2011 (UTC)

See also The Structure of Scientific Revolutions.--Srleffler (talk) 17:03, 25 April 2011 (UTC)

Reaction Gone Wrong

Hello. When I mix KI, HCl, and starch, my solution turns blue without adding any KIO₃. Why? Thanks in advance. --Mayfare (talk) 15:33, 22 April 2011 (UTC)

Are you sure your original KI was pure enough not to contain any I₂ impurities? 95.112.196.91 (talk) 15:49, 22 April 2011 (UTC)

The KI is pure enough not to contain any I₂. --Mayfare (talk) 20:40, 22 April 2011 (UTC)

Potassium iodide in the first paragraph states that "Aged and impure samples are yellow because of aerial oxidation of the iodide to iodine". Did you try your KI to the starch without HCl? I have no idea how sensitive the starch test is but I remember my wild days when I did some testing for iron and always got false positive until I found out that the test is so sensitive that it gives positive results on the little iron that is contained in the tap water used. 95.112.196.91 (talk) 20:53, 22 April 2011 (UTC)

can a relativistic proton change into a neutron? or break up into various particles?

Are these processes possible? They seem possible to me, if the proton has enough energy ... but can kinetic energy transfer into the weak or the strong interactions?

1. highly energised proton ---> neutron + positron + e-antineutrino
2. neutrino + highly energised proton ---> neutron + positron
3. proton ----> pion+ + positron + electron

John Riemann Soong (talk) 17:41, 22 April 2011 (UTC)

The principle of relativity implies that the internal structure of the proton does not change when the proton is moving. Just imagine the situation from the point of view of the proton: the proton thinks that it is at rest and that you are moving. Since there is no absolute motion there is no absolute "energisation" through kinetic energy and the proton doesn't care whether its moving in your frame of reference or not; if it doesn't decay in its own reference frame, it will not decay in yours either. --Wrongfilter (talk) 17:56, 22 April 2011 (UTC)

Why is this different for electron states then? The kinetic energy of a reactant is important in whether it overcomes a barrioer or not, e.g. there's a transition temperature in which singlet oxygen will be the dominant species over triplet oxygen. -- John Riemann Soong (talk) 21:25, 22 April 2011 (UTC)

I've taken the liberty of formatting your question so it renders properly. (Line-breaks are ignored in wiki-syntax). #1 is Positron emission; #2 is beta decay, with the anti-neutrino written "backwards," and I don't recognize #3. Nimur (talk) 18:26, 22 April 2011 (UTC)

Positron emission and beta (plus) decay are the same thing. 1 and 2 are the same formula, except that 2 assumes the existence of a neutrino that annihilates the antineutrino. 3 looks like nonsense to me. The positron and electron can just annihilate each other, so you have a proton changing into a pion+, which is equivalent to an up quark and a down quark changing into a single anti-down quark. I can't see any reason to believe that could ever happen. --Tango (talk) 18:49, 22 April 2011 (UTC)

Your first two reactions don't conserve lepton number. You can fix that by swapping the antineutrino with the neutrino.

The first reaction (decay) can't happen because the principle of relativity says it's physically the same as the decay of a proton at rest. In the second case the frame-independent properties of the input include a single relative velocity, and the reaction can happen if that is large enough.

Your third reaction (decay) isn't prevented by conservation of energy, because the total rest mass of a pion and two electrons is smaller than the proton rest mass. But it doesn't conserve baryon number, and more strongly, it doesn't conserve B − L. Decays that change the baryon number but not B−L, such as
p⁺
→
π⁺
+
ν
_e, are allowed by grand unified theories but have never been observed. In any case, the proton's speed makes no difference, because these theories still obey the principle of relativity. -- BenRG (talk) 21:28, 22 April 2011 (UTC)

What about the case of electronic transitions? Can't a highly kinetically energised hydrogen atom excite its shell electron? (Isn't that what happens in a plasma?) How is this different from an energetic proton exciting one of its quarks? Also, isn't it possible under a strong electric or gravitational field, to breakup a moving nucleus or a moving nucleon by tidal forces? John Riemann Soong (talk) 22:15, 22 April 2011 (UTC)

You're right, a proton excited state can decay to neutron + positron + neutrino. We all assumed you were talking about overall kinetic energy of the proton. This decay is probably also possible in a background electromagnetic field, although additional particles are involved then, so it's not exactly a decay. I see no reason why gravitational tidal forces couldn't break a proton apart, but that's not an experiment we can do, and nobody really understands quantum gravity. -- BenRG (talk) 23:12, 22 April 2011 (UTC)

But in electronic transitions, mere temperature alone provides the kinetic energy that supplies the activation energy to excite an excited electronic state. John Riemann Soong (talk) 06:35, 23 April 2011 (UTC)

Yes, but that happens because the oxygen molecules are colliding with each other allowing the kinetic energy to be released in the transition you describe. If a oxygen molecule is flying at high speed by itself and doesn't collide with anything else, the transition won't happen. Dauto (talk) 18:07, 23 April 2011 (UTC)

What kind of flowering tree?

I took this photo on 10 April at 39°48′44″N 86°12′9″W. Can anyone identify the species of the trees in this picture? All I can guess is that they're way too big for apples or cherries, and definitely the wrong shape and size and color for redbuds; I don't know what any other kind of tree flower looks like. Nyttend (talk) 19:57, 22 April 2011 (UTC)

I'm guessing dogwood. Looie496 (talk) 20:11, 22 April 2011 (UTC)

Dogwoods tend to be more rounded or slightly flattened. I think it might be a fastigiate pear like this. Obviously the trees are much older than the example, as one can see from the bark which has the cracked and flaky appearance of an old pear tree. Richard Avery (talk) 21:51, 22 April 2011 (UTC)

The species that you linked as "this" is Callery Pear, which sounds right: it's one of the most common ornamental trees in North America. Thanks for the help. Nyttend (talk) 23:03, 22 April 2011 (UTC)

Ornamental pears are excedingly common in the U.S. because they are super cheap and super fast growing, so builders often put them in all over the place. My neighborhood has one in front of just about every house. It would not be uncommon at all. Callery pears, cited above, are often called "Bradford Pears" or "Cleveland Pears" in the U.S., and have a distinctive odor when in bloom, reminiscient of ammonia or old fish; if you've got hundreds in one area it can be overwhelming. --Jayron32 02:44, 23 April 2011 (UTC)

Fission2

I asked a question about binding energy above and now am more confused than before, and feel like an idiot. Please explain the defect in my understanding:

In the nuclear fission of uranium, about 1/10th of 1% of the mass of the nucleus is converted to energy. (I added this information myself in this edit, quoting a 1950 article from the Bulletin of the Atomic Scientists.) That's super. However, our binding energy article, our nuclear fission article, our E=mc2 article, and the responses of knowledgeable editors to my previous question all agree that the masses of the fission products add up to a higher mass than the mass of the original uranium atom.

Some crucial part of this is clearly sailing about a foot above my head. If a uranium atom is in an imaginary box and the atom fissions, and the resulting gamma rays are allowed to escape the box but the fission products (say, krypton and barium) stay in the box, the contents of that box must be lighter, by the mass of the gamma rays. But, contradicting this understanding, all the information above informs me that the krypton and barium have a greater mass combined than the original uranium atom. The box is now heavier. Huh?

Your idiot,

Comet Tuttle (talk) 21:15, 22 April 2011 (UTC)

To give an example ²³⁵U + n -> ⁹²Kr + ¹⁴¹Ba + 3 n.

I get that the rest masses in amu are 235.044 + 1.009 -> 91.926 + 140.914 + 3*1.009

Which gives 236.053 -> 235.867, a mass loss of 0.186 amu (0.08% of the initial uranium mass).

Does that clarify things? Dragons flight (talk) 21:37, 22 April 2011 (UTC)

Yes; this is great; but see below. Comet Tuttle (talk) 22:08, 22 April 2011 (UTC)

If energy is released by a reaction then the total rest mass of the products is smaller than the total rest mass of the inputs; you're quite right about that. I don't think anybody said otherwise in the previous thread. It's confusing because of inconsistent use of the word "smaller" with negative numbers, as I said there. (But rest masses are never negative, so there's no ambiguity in what I said here.) -- BenRG (talk) 21:44, 22 April 2011 (UTC)

TenOfAllTrades wrote: "the atomic nucleus will always have a slightly lower mass than the sum of the masses of its constituent particles." (I'm not challenging him or her here because the same thing is echoed in the articles I cited above in this thread.) Wouldn't that mean atomic fission is endothermic, contradicting my imaginary box mass statements and reality? Comet Tuttle (talk) 22:08, 22 April 2011 (UTC)

Those "constituent particles" are the nucleons. Splitting a nucleus into individual nucleons does always consume energy (unless it's ¹H); therefore, creating a nucleus from nucleons releases energy. If you build two smaller nuclei using nucleons obtained from a big nucleus, you may release more energy than you spent breaking the larger nucleus apart. -- BenRG (talk) 22:24, 22 April 2011 (UTC)

Ahhhhhh! — so in Binding energy, in the line stating "Classically a bound system is at a lower energy level than its unbound constituents, its mass must be less than the total mass of its unbound constituents", by "constituents" it means to say "individual nucleons"? I had taken "constituents" to mean "any combination of smaller nuclei", so a barium nucleus and a krypton nucleus would count as "constituents" of the uranium nucleus and when added up, their masses had to add up to be greater than the uranium nucleus's mass. Comet Tuttle (talk) 22:46, 22 April 2011 (UTC)

Yep, that's the ticket. The binding energy is calculated relative to the completely disassembled nucleus: individual, separated protons and neutrons. TenOfAllTrades(talk) 23:25, 22 April 2011 (UTC)

"Individual nucleons" would be too narrow a definition of "constituents" to use in the binding energy article. In fact, I disagree with the sentence you quoted. It may be true when you take "constituents" to mean "nucleons", but there's no deep reason why it has to be true even in that case. In quantum mechanics, any system that can decay into components with a lower total rest mass will eventually do so, but the decay half life can be extremely large, like 10²⁰ years or more. Even a free neutron's 15-minute half lifeone second is incredibly long compared to the usual time scale of nuclear physics, which is attoseconds or less. It's reasonable to call these bound systems, and physicists do call them that. -- BenRG (talk) 05:22, 23 April 2011 (UTC)

I don't see that it's unreasonable to consider the individual nucleons as the specific "constituents" of a nucleus. If one were to ask what a uranium nucleus' constituents were, one would not expect 'krypton and barium nuclei, of course' as a response. The heavy nucleus doesn't exist with smaller nuclei as independent bound components within it. (Similarly, one wouldn't say that the "constituents" of trees are framing lumber, tongue depressors, and sawdust, even though those could be one valid set of 'fission products'.) TenOfAllTrades(talk) 17:24, 23 April 2011 (UTC)

I think I phrased it badly. What I meant to say is (1) the binding energy article can't reasonably define "constituents" as "nucleons" (that wouldn't make sense for gravitational binding energy, etc.), (2) I disagree with the idea that it's essential to the nature of a bound system that there's a net energy cost to separating the parts. There has to be an up-front energy cost (i.e., a potential barrier), but it's okay if you subsequently get back more energy than you put in. In a hypothetical world where the nuclear binding energy was positive, all nuclei except ¹H would be technically unstable, but their half-lives could still be long enough to make them stable for practical purposes. I used the free neutron half life only as an example of a long time and forgot that it's a bad example of "splitting into constituents", so I struck that out. -- BenRG (talk) 19:16, 23 April 2011 (UTC)

Nuclear binding energy is positive when you look at when nuclei are built up, say, when energy is released by p-p fusion in the sun. But it is negative in the sense that when you look at the resulting nucleus you get, this energy has gone away, and the net mass of the complete nucleus is lower than the net mass of the protons and neutrons that went into it. You can't split the nucleus back up again - at least, not all the way back to protons and neutrons - without getting energy from somewhere. This is true for any element (except ¹H...) because if the binding energy were positive, the nucleus could emit energy as it blew itself apart, and there would be no barrier to doing so. (Well, the extended periodic table talks about elements over maybe 173 that can't exist, but we haven't seen those. ;) )

Something that may shed some light on this: Nuclei heavier than iron release energy when they undergo nuclear fission. Nuclei lighter than iron do not. Instead, lighter nuclei release energy when undergoing nuclear fusion. Whether a fission reaction is exothermic or endothermic depends on the size of the nucleus and the size of the pieces. --Srleffler (talk) 17:19, 26 April 2011 (UTC)