Wikipedia:Reference desk/Archives/Science/2010 October 29

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October 29

Are "spectrum disorders" really just a way of saying "we don't know" ?

The ADD question a bit further up triggered this thought - Autism is a newly-recognized and poorly-understood spectrum disorder, meaning all sorts of different symptoms, to varying degrees of seriousness, can present as "autism". My gut feeling tells me the term spectrum disorder is a bit of a medical cop-out. Where do you draw the line between spectrum and a bunch of unrelated stuff? Are there other valid ailments with more establish medical histories that are classified as spectrum disorder? The Masked Booby (talk) 03:12, 29 October 2010 (UTC)

This being Wikipedia, we actually have an article that deals with the question: spectrum (psychiatry). Looie496 (talk) 03:30, 29 October 2010 (UTC)

"Spectrum" just means "it can present itself in varying degrees, from very mild to very extreme." The cut-off line is usually "does it actually negatively impact the patient's life," which is decidedly subjective, of course (and will vary by patient). I don't think it's a cop out so much as a recognition that a lot of what we consider to be "abnormal" human behavior is not often a "has it/doesn't have it" scenario, or at least, doesn't present that way. The bipolar, depressive, and schizophrenic spectrums are all pretty "well established" as far as mental disorders go (in the sense that they've been studied for a very long time). --Mr.98 (talk) 03:43, 29 October 2010 (UTC)

There's an interesting relationship in the genetics of autism and schizophrenia - in some cases the genetic aberrations are directly opposite one another. So the "spectrum" actually runs from the extremes of the one to the other, with most "normal" people occupying a band near the middle. Of course, any such argument is approximate, and this one is still quite controversial. Wnt (talk) 05:21, 29 October 2010 (UTC)

The concept of a psychiatric spectrum is an acknowledgement that the mind is a very complicated and tricky thing. For a long time, the sciences were very keen on breaking things down into discrete bits that were useful in formulating ideas. You were male or female, heterosexual or homosexual, left-handed or right-handed. Edge cases were simply disregarded. Concepts such as species are a very clear example of a thing we thought was immutable until it turned out that the clean breaks we thought existed between species don't apply in the real world. Someone above used the concept of blondeness to illustrate the point; it's not an on-off switch, it's a gradual shading that smiles at our attempts to pigeonhole it. As you walk around today, look at the people around you and "diagnose" them - are they blonde enough to be labelled "blonde" or are they "sort of blonde"? Do your categories change when you see new people? Do older blonde people with white hair still get called blonde? How about bald people? When we started, "blonde" seemed like a pretty simple thing to determine, but the longer you look at it, the trickier it gets; the same is true of psychiatric spectra. Some people are very clearly and obviously blonde, some people very clearly and obviously have ADHD, and some people very clearly and obviously have autism, but many cases are not so easy to determine. Matt Deres (talk) 14:52, 29 October 2010 (UTC)

It seems to me more like variation that can be naturally selected for. 65.88.88.75 (talk) 14:55, 29 October 2010 (UTC)

It's worth noting that even disorders like hypertension (which can be measured very precisely and quantitatively) are subject to similar concerns. You have to draw lines somewhere, and the place where the line ends up is often somewhat arbitrary. In the case of hypertension, our article gives an American Heart Association definition for normal systolic blood pressure as falling between 90 and 119 mmHg, and prehypertension as between 120 and 139 mmHg. Technically, this means that a patient with a blood pressure of 119/79 is 'normal' but another patient with a blood pressure of 120/80 is 'prehypertensive'; in reality, the distinction between the two of them is virtually meaningless. (Bonus question: why should nature have a particular fondness for round-number blood-pressure thresholds?) In psychology, it gets even murkier, and (as noted above) functional definitions are often important — are the person's symptoms sufficiently severe that they affect their ability to function successfully in society. TenOfAllTrades(talk) 15:59, 29 October 2010 (UTC)

Well, I have to point out that "ability to function successfully in society" isn't necessarily the best metric either for drawing the line with psychological disorders. I understand what you're saying, and the notion itself is of course valid – obviously, there has to be "a problem" if you are going to consider something to be "a problem". But it's important to point out that one can have a "severe" psychological disorder and still be quite able to "function successfully in society." Take the case of Dr. John Ratey, for example: "severe" (enough) case of ADHD – but a professor at Harvard Medical School, a best-selling author, a highly respected psychiatrist and psychopharmacologist, and (WP:OR) all-around good guy. :) There are many such examples, and it is important to keep that sort of thing in mind when talking about "mental illness" (the stigma of mental illness can in many ways be as "disadvantageous" as the illness itself!), though again I do understand what you mean to say and am in general agreement with it. WikiDao ☯ (talk) 18:46, 29 October 2010 (UTC)

120W power supply 30W load

Hi, I think that a 120W power supply is no less efficient than a 60W supply when powering a 30W load. Am I right? Presuming both are switch mode and passively cooled to the same temperature. -202.124.75.31 (talk) 03:59, 29 October 2010 (UTC)

I think it depends on the design, but yes, a switch mode power supply usually draw just slightly more power than is required by the load, not the maximum power at which it is rated, so there will not be much difference in efficiency. The same is true (but to a lesser extent because of higher losses) for an old-fashioned transformer. Dbfirs 07:39, 29 October 2010 (UTC)

See here for some sample power supplies. Click on some and see the efficiency graph. Obviously yours will be different, but you can get a feel for the approximate change in efficiency as you change how much power you use. Ariel. (talk) 08:37, 29 October 2010 (UTC)

(reply to original) Yes agree with you for switched mode.. infact the 120W may be slightly more efficient due to a lower internal resistance.. (probably a minor factor assumes internal resitance losses are greater when "on" than when the electronics are in "off" mode).77.86.42.103 (talk) 12:32, 29 October 2010 (UTC)

... so the 120w power supply will actually draw less current from the mains when running 60w (50%) than a 60w power supply does at full load? The difference seems to be small, but is is correct to say that half-load is optimum efficiency? The 120w unit would not be at its most efficient supplying only 30w. Dbfirs 19:07, 29 October 2010 (UTC)

Not sure about best efficiency at 50% load - the two numbers are power supply on resistance, and power supply off resistance - I'd be tempted to say that power supply off resistance is so high that the power losses (for off mode) will be negligable - so actually a (trivially) better efficiency is obtained with a heavily overspecced supply. But without the actual numbers I couldn't really be certain.Sf5xeplus (talk) 19:21, 29 October 2010 (UTC)

On the other hand a SMPS with good Power factor (ie smooth energy demand over the AC cycle) will switch more often than a basic chopper (electronics) circuit with poor Power factor - in which case the switching energy (and time spent inbetween on and off) could become a major factor in energy losses (resistive heating). Sf5xeplus (talk) 19:29, 29 October 2010 (UTC)

hand waving I'd guess that a simple chopper like SMPS (very slightly) increases in efficiency down to 10% rated power or lower.. Until the time spent actually switching is so small that the supply is drawing power through a 'spike' rather than a semi-square wave - at very low power demands the power supply is drawing much of its energy under switching conditions (ie neither on nor off) - much like a convential resistive or rheostatic voltage controller.Sf5xeplus (talk) 19:36, 29 October 2010 (UTC)

The reviews I've seen on anandtech.com show efficiency curves that typically peak between 50% and 80% of full load. Based on that, a 60-watt supply powering a 30-watt load (50% of full load) will be more efficient than a 120-watt supply powering the same load (25% of full load). --Carnildo (talk) 01:57, 30 October 2010 (UTC)

Thanks for the link to AnandTech I didn't know they did efficiency figures on PSUs - 50% does indeed seem to be best in most cases, and typically still good (and not much different) at both 20 and 80% load. By 10% load efficiency is starting to drop off - I was definately over-optimistic in my 'analysis' above.Sf5xeplus (talk) 11:49, 30 October 2010 (UTC)

OP here, thanks all. Many useful answers! Wanted to know 'cause I'm planning on building a low power computer and getting a power supply with a little margin for incorrect specs and marketing fibs seems to mean a factor of three or more. --203.22.236.14 (talk) 12:26, 30 October 2010 (UTC)

Phase behavior of pure substances below triple point pressure

Please help me understand what happens with a typical pure substance (say nitrogen) when held at a pressure below triple point pressure.

It seems to me this would be best presented by plotting constant pressure lines on a temperature-internal energy or temperature-enthalpy chart. I have made a thorough search of texts in the library of a local university, searched Wikipedia, and search elsewhere online. Just about all texts only discuss what happens above the triple point pressure - the most they say is that it cannot be liquid. I did find one advanced text that gave theory and no data - unfortunately it's way above my math skill level.

Soem textbooks show the region to the right of the triple point pressure line (ie after it intercepts the vapor sat line) and extendeing well right as "vapour". Surely it is not possible to exist in that region?

I found lots that cover other ways of plotting, eg P-V or P-H axes, but there always seemed to be something missing so I could not see a way of re-plotting with T-H axes.

NIST online thermophysical properties only gives data above triple point pressure.

Alan 05:15, 29 October 2010 (UTC)~ —Preceding unsigned comment added by 121.221.88.214 (talk)

You are asking about a temperature below triple point pressure. Presumably you mean a pressure below triple point pressure. Dolphin (t) 07:30, 29 October 2010 (UTC)

Here's such a thing for water http://www.btinternet.com/~martin.chaplin/phase.html

And a general one http://www.websters-dictionary-online.org/definitions/triple+point?cx=partner-pub-0939450753529744:v0qd01-tdlq&cof=FORID:9&ie=UTF-8&q=triple+point&sa=Search#922

It seems reasonable to state that at pressures below the triple point pressure the substance generally can exist either as a gas or solid (see sublimation) .. though odd exceptions such as Helium exist which has a superfluid state http://ltl.tkk.fi/research/theory/helium.html

(also you seem to have swapped "above" and "below" in pressures - assuming "above" means "more than")77.86.42.103 (talk) 12:29, 29 October 2010 (UTC)

This depends on the substance. See phase diagram.Smallman12q (talk) 20:05, 29 October 2010 (UTC)

electricity doesn't weight anything

So instead of heavy battery packs to generate electricity when needed (chemically) why don't electric cars store PURE electricity, which wouldn't weigh anything? 93.186.23.237 (talk) 07:37, 29 October 2010 (UTC)

How do you propose we store electricity in its "pure" form? Closest I can think of is in a capacitor, but capacitors have mass. --203.202.43.54 (talk) 07:42, 29 October 2010 (UTC)

Yeah, a capacitor basically stores pure electricity, i.e., it stores a charge simply as an imbalanced distribution of electrons, which indeed do weigh very little). Unfortunately, capacitors are limited by a breakdown voltage, such that they short out internally if you try to store too much electricity in them. The dielectric (a kind of insulator) inside that keeps a capacitor from shorting out is the thing that contributes the most to the weight of a capacitor. The resulting energy density of a capacitor winds up being considerably less than what's available with a battery. Red Act (talk) 08:30, 29 October 2010 (UTC)

I'm afraid the question asker doesn't really understand what electricity is. Therefore, I suggest you, question asker, have a look at our article electricity. --Belchman (talk) 08:34, 29 October 2010 (UTC)

We can still answer him. The simplest answer is the electricity repels itself. So you simply can not store a lot of it in one place without it leaking (what Red Act called the breakdown voltage). Instead what you do is store the energy chemically, and convert it to electricity as needed. Ariel. (talk) 08:39, 29 October 2010 (UTC)

Pure electricity is a lot of balls (see article). Cuddlyable3 (talk) 09:32, 29 October 2010 (UTC)

The OP might want to take a look at the hydraulic analogy. In this model the closed-circuit flow of water molecules replaces the electrons in an electronic circuit. It's not enough to store the electrons, indeed the number of electrons doesn't change as you consume their energy. There needs to be some way of forcing the water (electrons) around the circuit. Either a large piston with a very strong spring, or a battery. CS Miller (talk) 10:20, 29 October 2010 (UTC)

Pure electricity wold not be a heap of charged particles but an electromagnetic wave. It can be stored in a cavity but has very low density and is very quickly converted to heat due to losses. --Gr8xoz (talk) 11:26, 29 October 2010 (UTC)

If I can join in - I sometimes wonder about storing a huge amount of light in an internally mirrored box, and using that as a lightweight power supply. This idea was inspired by an old Noggin the Nog cartoon in which summer sunlight was stored in jars, to be released during the winter months, like jam. In the context of the cartoon this is a ridiculous, hilarious idea, but what's actually wrong with it? 81.131.53.127 (talk) 12:22, 29 October 2010 (UTC)

The fact that mirrors are not perfectly reflective (even the best ones). Googlemeister (talk) 12:38, 29 October 2010 (UTC)

A couple things. One, mirrors aren't 100% efficient, nor is the air in the box. Even in a perfect vacuum, a one-meter-cubed box with a 99.999% reflective mirror would have no light remaining after even one second, because there would have been 300 million reflections in that time. Two, light to useful power is not generally efficient, nor is the conversion equipment lightweight. — Lomn 12:39, 29 October 2010 (UTC)

What are the physical or practical limits on the efficiency of mirrors? 81.131.53.127 (talk) 13:07, 29 October 2010 (UTC)

The article Solar mirror notes that Alubond Solar Reflector panels are aluminium composites achieving over 93% reflectivity. The article Perfect mirror notes that a simple mirror may reflect 99.9% of the light, and a very complex dielectric mirror can reflect up to 99.999% of the light incident upon it, for a narrow range of wavelengths and angles. Cuddlyable3 (talk) 14:04, 29 October 2010 (UTC)

The article also notes that total internal reflection is possible; otherwise fiber optic cables wouldn't work for the same reasons. But no material is perfectly transparent... which makes me wish we had a better article on total external reflection (who knew?). But storage of light might be more practically implemented with slow light, though I've not yet heard of someone taking a large chunk of such a material and leaving it out in the sun. Either the energy density should become unreasonable, or something should give.

I should point out to the newcomers that storing light is the most plausible way of storing "pure electricity", as the photon carries electromagnetic energy. If you could bottle pure electrons they'd still have some mass, and the bottle would give way in a great arc (thus capacitors are limited). Light is a bit like an alternating current set free of rest mass. Wnt (talk) 18:21, 29 October 2010 (UTC)

If you could get pure electrons, perhaps one gram of them and store them in a litre container you would have a lot of energy. However existing technology does not allow this, and repulsive forces would be collossal. Graeme Bartlett (talk) 07:33, 30 October 2010 (UTC)

Actually you can store a 1 gram electrons in 25 000 Kg standard Electric double-layer capacitor, the energy content depends on the distance to the positive charge. In a Electric double-layer capacitor it is just a few nanometers.

The calculation is: 0.001 kg/9e-31 kg*1.6e-19 C/(6 Wh/kg*3600 s/h /3 V) --82.209.130.40 (talk) 11:13, 30 October 2010 (UTC)

Fuel Consumption vs CO₂ emmissions

Hi, I've been looking at the specs of two cars - the VW Golf GTD and the Volvo C30 with the 5-cylinder diesel engine. Both manafacturers reports the same overall fuel consumption: 55.4 miles per gallon, which is equal to 46.1 mpg(US) or 5.1 l/100km

However when it comes to CO₂ emmissions, the volvo is listed at 164g/km, and the VW only 134g/km - this has confused me, as the manafacturers' figures claim they both burn the same amount of fuel to cover a kilometer (51ml) so surely they should both put out the same amount of CO₂; I would've thought that burning a certain quantity of fuel will produce the same CO₂ regardless of whether its burnt in a volvo engine, a VW engine, a jet engine, or a paraffin lamp? This assumes that the fuel itself is the same, and complete combustion occurs.

We all know that some figures like these may not be achieved in real life, but I would expect them to be consistent with themselves - especially when the difference in the CO₂ figures of these car would mean the volvo owner paying £60 more each year in Road Tax based on these figures. Shouldn't CO₂ be proportional to the figures for fuel consumption (directly proportional if the fuel consumption is measured in l/100km, or inversely proportional to mpg figures)

The specs I've mentioned are here: Volvo, VW (emmissions), VW (fuel consumption).

Interestingly I found This page listing CO₂ outputs per litre for various types of fuel, and it lists Diesel at 2.68 kg/litre (so 2.68 g/ml). Multiplying this by the 51ml the carmakers claim their vehicles burn to drive 1km, this gives us 137 g/km, very close to VW's figure but miles away from the Volvo's. Is anyone able to explain why the figures that look like they should match don't? Cheers, davidprior ^t/_c 07:47, 29 October 2010 (UTC)

You are correct. If one of the cars used fuel, but didn't burn it; it would be polluting, but would not release CO2, so its CO2 numbers would be lower than what you would expect from fuel consumption. But I can't think of anything that would make more CO2 than the amount of carbon in the fuel. Is there any possibility they are trying to take into account other things? Oil? Manufacturing? Ariel. (talk) 08:43, 29 October 2010 (UTC)

Typo second column gives 134g/km as per VW, whereas the third Volvo column gives 164g/km (for the same miles per gallon).Occam's razor meets Murphy's Law 77.86.42.103 (talk) 12:18, 29 October 2010 (UTC)

Aha! Think you may be right that its an error in the volvo's specs, as I've noticed they're wrong elsewhere too (the engine in the middle column has a description row which says "Four cylinder turbocharged diesel", but the row for number of cyclinders has a 5 in it. So think they must have the CO₂ figures wrong too. Cheers, davidprior ^t/_c 09:55, 30 October 2010 (UTC)

Firing a ceramic

What happens chemically when a ceramic is fired? Specifically what causes the individual particles to fuse and become hard? Do they melt? Ariel. (talk) 08:49, 29 October 2010 (UTC)

It looks like the typical firing temperature lies below the melting point. The articles on ceramic engineering (subsection "The sintering process) and on sintering might be of use. ---Sluzzelin talk 11:00, 29 October 2010 (UTC)

Multiple tasks with both individual hands difficulty

What do you call it when someone can't perform two different tasks one by each hand or one task by a foot and another different task by a hand? There are cases we can manage and many cases we find it difficult if not impossible. Is there also a part of our body (e.g: brain) which has to do with?--Email4mobile (talk) 08:52, 29 October 2010 (UTC)

I thought it might be ambisinistrous (by analogy with ambidextrous), but that means to be equally clumsy with either hand, which I think is not quite what you're after. -- Jack of Oz ... speak! ... 09:10, 29 October 2010 (UTC)

There is a special keyboard (that to me looks like an ordinary one sold at an extraordinary price) available for persons unable to type with both hands. Cuddlyable3 (talk) 09:52, 29 October 2010 (UTC)

I mean to perform multiple tasks at once/synchronously. Example of this is when we try to write the number 6 (added by our hand), while revolving our foot clockwise.--Email4mobile (talk) 10:03, 29 October 2010 (UTC)

OR: It's easy if I draw the 6 clockwise or difficult anticlockwise. I'm still trying to write 8 without lifting the pen. Cuddlyable3 (talk) 10:44, 29 October 2010 (UTC)

I don't think there's a particular word for the phenomenon, but it's been discussed previously here. The higher brain can only handle one complex movement at once. However if that movement is repeated, it can be automated to a degree via motor learning, leaving the brain to concentrate on something else. the wub "?!" 10:48, 29 October 2010 (UTC)

I guess you could call it a task of "inter-limb" motor coordination. Drummers and organ players spend a lot of time "motor learning" for independence of their limbs. (So do cyclists, chauffeurs and cheerleaders and occupiers of many other occupations)---Sluzzelin talk 11:11, 29 October 2010 (UTC)

Energy Anomaly??

Sir, Einstein's Famous equation E=mc² suggests that energy and mass are just different forms of the same thing.They can be interchanged.Consider a case when infinite amount of energy is converted into mass.An infinite energy would produce matter that is infinitely massive.Or conversely an infinitely massive body should produce infinite energy.Is this phenomenon possible in our universe where energy is a constant?? —Preceding unsigned comment added by Vishnuthelegend (talk • contribs) 09:45, 29 October 2010 (UTC)

No. Cuddlyable3 (talk) 10:45, 29 October 2010 (UTC)

By the very definition of "infinite" you can never have it. And BTW it's not so easy to interchange mass and energy (although it is possible of course). Ariel. (talk) 10:52, 29 October 2010 (UTC)

Mass IS energy but it is rather hard to convert matter to other forms of energy effeciently. All forms of energy has mass. --Gr8xoz (talk) 11:09, 29 October 2010 (UTC)

Infinite energy and infinite mass mean nothing in our universe. But in an other, hypothetical, universe, yes, an infinite amount of energy could be used and converted into an infinitely large object which would have an infinite mass, but obviously, this would take an infinite amount of time, so you would never ever get there !! --Lgriot (talk) 12:13, 29 October 2010 (UTC)

As Gr8xoz pointed out, the mass–energy equivalence equation does not just say that mass and energy can be interchanged. It says that they are the same thing. Energy, in all of its forms, has mass; a photon has mass; a compressed spring has slightly more mass than when it is relaxed; a charged battery has slightly more mass than when it is uncharged; a moving object has more mass than when it is at rest. There is no need to "convert" the energy into matter to give it mass. Having said that, the concept of an infinite amount of energy/mass within a finite volume is definitely physcially unrealistic and more or less meaningless. Gandalf61 (talk) 12:46, 29 October 2010 (UTC)

Any references there Gandalf61? I'm intrigued by the notion that a spring has more mass when compressed than relaxed. I don't disbelieve you, and I see how it's consistent with physical theory, but what is the mechanism? I'm guessing to measure the mass increase due to compression you'd need a very lightweight spring with a very large spring constant and a very accurate scale. Is that right? SemanticMantis (talk) 14:21, 29 October 2010 (UTC)

The compressed (or stretched) spring is one of several examples in mass-energy equivalence#practical examples. You can use the potential energy stored in a compressed spring to accelerate an object, which increases its relativistic mass. If the mass of the compressed spring were not greater than the mass of the spring when relaxed, then accelerating the object would create mass from nothing, violating the principle of conservation of mass. Of course, the mass involved is tiny - about 10^-17 kilograms per joule - and I doubt there is any feasible way to observe it for "real world" springs. But my whole point is that you don't need a mechanism to turn energy into mass - energy just has mass (and vice versa). Gandalf61 (talk) 15:32, 29 October 2010 (UTC)

A better (rather, a more practical) example than the "compressed spring" is the mass error measured in atomic nuclei (i.e., two protons stuck together are not $2.{\overline {0}}$ times as heavy as a single proton). We call this a mass defect - a change in the mass because of a change in the energy-state of the nuclei. It is a real, measurable effect - we can measure it with a lab scale, or observe it indirectly by observing particle trajectories, and so on. In fact, we can even measure mass defects from non-nuclear binding energies: some inter-atomic binding energies (e.g., chemical reactions) are sufficiently large that we can measure their mass defects. A macroscopic compressed spring also has a mass defect because of a change in internal energy - but there is no lab equipment commonly available that is precise or accurate enough to measure it. To some degree, atomic or nuclear interactions are just a "different kind of spring" - there is a potential energy reservoir due to fundamental interactions; whereas a large metal coil spring has a potential energy reservoir because of billions and billions of fundamental-interactions averaging out. At the end of the day, energy is energy; it always behaves the same way; only, in some cases, it's easier to observe certain properties, like the mass-defect. Atomic physics was therefore a necessary experimental precursor to the modern theories about mass-energy equivalence - we will never build equipment that is accurate enough to observe relativistic effects in "ordinary" Newtonian kinematics scenarios. (Nimur (talk) 17:42, 29 October 2010 (UTC)

But if a compressed spring gains mass, is it not possible to exploit this in a reactionless drive and violate Newtons third law of motion?[Trevor Loughlin]80.1.80.4 (talk) 04:46, 1 November 2010 (UTC)

I don't see how this would work. Perhaps you could explain your idea in more detail. Gandalf61 (talk) 10:42, 1 November 2010 (UTC)

Is the thymus an endocrine gland?

Resolved

Our article Thymus says "It is largely degenerated in elderly adults and is barely identifiable, consisting mostly of fatty tissue, but it continues to function as an endocrine gland..." The caption of the top illustration in Endocrine system declares "Note: the Thymus (labelled 4.) is not an endocrine gland." A definitive answer to the question in the header would be appreciated. Thank you. --Hordaland (talk) 11:49, 29 October 2010 (UTC)

My impression is that the question can't be answered definitively. It has endocrine activity (it produces thymulin for example), but its most important role is to generate certain types of immune system cells. Looie496 (talk) 17:53, 29 October 2010 (UTC)

Oh, dear, oh, dear. I can change the sentence in thymus to read something about endocrine activity. But is the note on the illustration correct -- that the thymus "is not an endocrine gland"? That looks dumb and the thymus should be removed from the that illustration, I'd think. What do you think? Hordaland (talk) 18:34, 29 October 2010 (UTC)

I agree with Looie496, and would add that it appears undue weight is given to thymosins in the lede paragraph of the Thymus article. Secondary sources consistently describe the thymus as a primary lymphoid organ, whereas discussion of its endocrine function are mostly in primary sources. In addition, thymectomy is generally well-tolerated by human adults, with the only prominent phenotype having to do with reduced T cell function. -- Scray (talk) 18:51, 29 October 2010 (UTC)

There seems to be a fair amount of discussion of thymic endocrine function, including thymulin, thymosin alpha1, thymosin beta4, and thymopoietin, and other more general cytokines (see PMID 19273180). (thymosins can also be produced elsewhere - if cupping has any beneficial effect, I bet they are involved...) The problem is that endocrine organs are a pedagogic construct - probably every cell in the body secretes signalling molecules that have some general effect on the body; it's just that some glands do this disproportionately. It does seem more common to say that the thymus has endocrine function rather than that it is an endocrine gland, and perhaps it's best addressed in this way. Wnt (talk) 19:03, 29 October 2010 (UTC)

Thanks so much to you all! I am not competent to fix the lede nor to understand much of the rest. But I've changed wording in Thymus to "endocrine function". And in the caption to the top illustration in Endocrine system, I've changed the wording to "[Note: the Thymus (labelled 4.) has endocrine function, though it is not considered to be an endocrine gland.]. Hope it is OK to copy this entire section to the talk page(s). Hordaland (talk) 19:51, 29 October 2010 (UTC)

Clamped buttress

Resolved

What is a clamped buttress? The article St James' Church, Stretham is passing through a GA review at the moment and I have been asked to clarify the term clamped buttress. Is anyone able to help please? The term is sourced from Pugh (1953) Victoria County History of Cambridgeshire here.

The closest I can get is from here which states "clamp - In architectural construction, a device, usually metal, used to hold together blocks of stone of the same course. Also called a cramp". Also, OED meaning (1) gives "A brace, clasp, or band, usually of iron or other rigid material, used for giving strength and support to flexible or movable objects, or for fastening two or more things securely together. ... e.g. A bar of iron for binding together stones in a building"

--Senra (Talk) 12:10, 29 October 2010 (UTC)

Looking for "clamp buttress" (compound term, not generic adjective meaning) gives two consistent hits for a description that seems appropriate for this context: [1], [2]. DMacks (talk) 12:28, 29 October 2010 (UTC)

I suspect that the article text (Clamped buttresses dating from the 12th century are visible in the chancel) is wrong - this image inside the chancel oops [3] shows no buttresses I can see, but isn't clear. This image [4] from outside the chancel shows what I suspect to be "clamped buttresses" they are the thickening of the walls on the corners. Note how they appear to "clamp" the building at the corners, and are also buttresses .. buttresses are more common on the outside.

Also note the source http://www.british-history.ac.uk/report.aspx?compid=21908 - the 12th century parts of the church are show in this diagram http://www.british-history.ac.uk/image.aspx?compid=21908&filename=fig24.gif&pubid=93 also the text "There are clamped buttresses which date from the end of the 12th century" 77.86.42.103 (talk) 12:55, 29 October 2010 (UTC)

By the way the 'terms' section at the end of my architecture book describes a very similar outside structure as "clasping buttresses". see http://www.prestbury.net/magazine/church_architecture/page05.htm - that's what the chancel of this church has. 77.86.42.103 (talk) 13:19, 29 October 2010 (UTC)

For another example see [5] St. Peter's Church, Wilburton - the tower is described as "The tower is of three stages and dates from the middle of the 13th century. There are angle buttresses with two set-offs reaching to the top of the first stage, while the second stage has clamped buttresses rising from the string-course." [6] - you can see the (three steps of the) angled buttress in the images, and above that are the clamped (clasped) buttresses slight obscured by trees branches above the first horizontal string (which are just visible). There's a better image here [7]- the clamped buttresses are the buttresses in the middle section on the plain (unwindowed) section of the tower.77.86.42.103 (talk) 13:33, 29 October 2010 (UTC)

Thank you for the detailed and useful explanation. I have modified the article accordingly by adding a footnote which is sourced to the Pevsner Architectural Guides website --Senra (Talk) 15:38, 29 October 2010 (UTC)

on utilizing sound energy

can we ever use sound energy as a tool for producing other forms of energy? is there any application that already uses this idea of converting sound to other forms.how much energy do u get when a device produces a sound waves of 40 db —Preceding unsigned comment added by Vijayendra shastri (talk • contribs) 12:48, 29 October 2010 (UTC)

Imagine a device that turns the energy produced by the sound of your voice into electrical energy. Then, transmits that electrical energy to another device that a friend is holding. Your friend's device converts the electrical energy back into sound energy so your friend can hear your voice from a distance. We could call this something like distance sound, or if want to use Greek to make it cool, it could be telephone. -- kainaw™ 13:00, 29 October 2010 (UTC)

A Tin can telephone transports the actual mechanical energy of the speaker's voice but a modern electric telephone uses electric energy from an external supply (central battery) and the actual voice energy just modulates the current sent through the wires. Cuddlyable3 (talk) 13:42, 29 October 2010 (UTC)

Sound-powered telephones are used on Navy ships and in other places where communication must work even if the electricity goes out. Nimur (talk) 15:26, 29 October 2010 (UTC)

You could try refrigeration by sound. Rmhermen (talk) 13:20, 29 October 2010 (UTC)

The OP makes a common mistake of quantifying a sound level in dB (decibels) alone. "40 dB" means a power ratio equal to 10 000. It is a meaningful expression of Sound pressure (see article) only when the 0 dB reference pressure is given. If 0 dB is stated to be 20 µPa RMS, which is about the threshold of human hearing at 1 kHz, 40 dB w.r.t. 20 μPa is typical of normal conversation at 1 m. Cuddlyable3 (talk) 13:22, 29 October 2010 (UTC)

-40dB ...? (negative means less..)77.86.42.103 (talk) 14:06, 29 October 2010 (UTC)

Yes, -40dB means 1/10000, the opposite of "40 dB" because the "bel" scale is a logarithmic scale. Dbfirs 18:38, 29 October 2010 (UTC)

Sonoluminescence is cool! DMacks (talk) 13:31, 29 October 2010 (UTC)

As an experiment in semi-logical thinking - the blast waves from explosions are sort of like sound energy.. and can be used to liberate minerals such as coal - which is then used as an energy source...77.86.42.103 (talk) 13:36, 29 October 2010 (UTC)

But only sort of, because to stress rock enough to crack it the blast wave must break the Sound barrier in the rock i.e. stress it beyond its Elastic limit. Cuddlyable3 (talk) 13:48, 29 October 2010 (UTC)

There is research ongoing in this field: [8]. One possible application mentioned in the article is the use on highways. - Akamad (talk) 13:55, 29 October 2010 (UTC)

Since sound is vibration, our article on Energy harvesting is relevant. Small autonomous sensors could be powered by vibrations in the material they are embedded in, for instance a sensor tacked onto an engine. That article links to this story: [9] about a piezoelectric device that turns heat into sound which then is turned into electricity.

But "proof of principle" examples are easy to find. If you read the microphone article, you'll find that many microphones work by having a tiny piece of metal vibrate in a magnetic field, creating electricity. This is the principle of Electromagnetic induction which has been a way to produce electricity since the days of Faraday. EverGreg (talk) 14:24, 29 October 2010 (UTC)

The phonomotor was a device invented by Thomas Edison in 1878 which converted sound energy into rotary motion which could drive a machine such as a small saw or drill. A diaphragm vibrated when the sound waves, as of someone speaking, fell on it. Its back and forth motion operated a pawl on a ratchet wheel with very fine gear teeth, which produced rapid rotary motion of a flywheel and shaft. It was able to operate a small drill and drill a hole in a board, or saw wood.. See [10]. I would expect that the output power was minuscule. It was described as a "scientific toy." Edison (talk) 15:27, 29 October 2010 (UTC)

Phonomotor. 92.15.12.85 (talk) 14:18, 30 October 2010 (UTC)

Thanks for pointing to the article I just created. Edison (talk) 20:06, 30 October 2010 (UTC)

unfunny joke: Please read Wikipedia:Conflict_of_interest#Self-promotion.77.86.42.103 (talk) 00:35, 31 October 2010 (UTC)

Any loudspeaker is pretty effective at converting sound into electricity (AC). Cacycle (talk) 09:54, 30 October 2010 (UTC)

Big Cats

Are the big cats viz. Tigers, jaguars, and lions cannibals?

Alwaysshariff (talk) 13:58, 29 October 2010 (UTC)

Searching for http://www.google.co.uk/search?aq=0&oq=lion+cannib&sourceid=chrome&ie=UTF-8&q=lion+cannibalism etc seems to say yes (under some conditions).77.86.42.103 (talk) 14:03, 29 October 2010 (UTC)

Aviation Thermobaric Bomb of Increased Power

Our Aviation Thermobaric Bomb of Increased Power article (a.k.a. the "Father of All Bombs" article) says two or three times, basically, that it's more powerful than other bombs "because of nanotechnology". Is this just buzzword nonsense from a Russian PR flack? Comet Tuttle (talk) 16:53, 29 October 2010 (UTC)

Apparrently just some random crazy guy editing wikipedia.. diff ! (well that never happened before) Sf5xeplus (talk) 17:17, 29 October 2010 (UTC)

That's a good edit you highlighted, but it didn't touch (or edit) the claims about nanotechnology. Comet Tuttle (talk) 17:49, 29 October 2010 (UTC)

The ref http://news.bbc.co.uk/1/hi/world/europe/6990815.stm says nanotechnology was used in the development of the explosive - (I thought the nano claim was part of the crazy) - it's possible that nanotechnology could make a better explosive (if it's a mix explosive such as Ammonium Nitrate/Fuel oil - ANFO) (as used in a 'daisy cutter bomb' BLU-82 - though I'm not sure. Can't find the original source. Definately it's true that the finer the fuel mixture the better the bomb. Probably not incorrect.

In russia http://www.youtube.com/watch?v=iCmA7xFPIdU (I think it's some sort of finely divided metal (nano). A russian translation of this might help. Sf5xeplus (talk) 18:13, 29 October 2010 (UTC)

It's pretty unlikely that the BLU-82's high-explosive mix is "ANFO" or "ANFO-like." Do you have any reference for that claim? The military has access to better technology; while powerful, ANFO is a hallmark of the "improvised from household materials" explosive, not "major Air Force project with access to defense-contract funding and chemical factory." Better high explosive exists, and in most cases, the desirable ingredients are obvious - but access to the prerequisite materials is controlled. Major military powers have a little easier time accessing such materials. Nimur (talk) 18:50, 29 October 2010 (UTC)

I linked to ANFO as an example.. the old BLU-82 used ammonium nitrate and polystyrene (which is pretty close to ANFO chemically : since both fuel oil and polystyrene are both hydrocarbon sources), plus aluminium powder. (see article or http://science.howstuffworks.com/moab3.htm or http://www.globalsecurity.org/military/systems/munitions/blu-82.htm) - a slurry explosive (see Melvin_A._Cook#Explosives) plus aluminium. when I said as used in the BLU-82 I meant a mix explosive not specifically ANFO. I can see that statement was open to misunderstanding the way it was written.

Nevertheless a BLU-82 does use an ANFO-like explosive plus aluminium improver. Sf5xeplus (talk) 19:10, 29 October 2010 (UTC)

Polystyrene, a solid polymer, is not "similar" to fuel oil. They both contain carbon, hydrogen, and oxygen; but so do hamsters. It is flat out incorrect to call a professional-grade formed explosive "similar" to ANFO, except insofar as they both "explode." Nimur (talk) 18:04, 2 November 2010 (UTC)

Our entry links to this article which references a Russian news channel. So it's not the strongest list of sources in my opinion. If there was nanotechnology involved, it probably just means that they have found some way to use very small particle size. The fuel-air bomb article says that the FOAB uses nanoparticles of aluminum (which doesn't sound outrageously implausible to me, but what do I know), but the reference it gives doesn't actually say that. All of the links in that article relating to nanotech either lead to articles that don't say the same thing. --Mr.98 (talk) 18:02, 29 October 2010 (UTC)

There's something that comfirms that nanoparticles should work http://technologyreview.com/Nanotech/14105/ , but isn't about the russian bomb.Sf5xeplus (talk) 18:33, 29 October 2010 (UTC)

CFL bulbs afterglow "flashing"

I recently replaced my old "U-tube" compact fluorescent lamp bulb with a new, brighter one of those curly "bee-hive" spiral designs (first two pics in our article). Now CFL bulbs retain an afterglow when they're switched off, but this new one exhibits a stranger behaviour. Not only does it have an afterglow, but also, as if it had some sort of capacitance, it will "flash" brighter for a fraction of second once every 10s or so, before returning to residual afterglow levels. It continues to do this for minutes on end until eventually subsiding. Is this a known phenomenon? What could explain it? Unfortunately my cellphone camera is not sensitive enough to video it (the pic is totally black). Zunaid 17:22, 29 October 2010 (UTC)

This question has come up before eg http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_January_18#dim_flashes_from_a_Fluorescent_lamp

I think there are other examples but can't find them in the archives - my personal theory is that after the power is switched off the electronic charge pump that produces the tube volatage continues to operate on residual capacitance in the power supply stage of the device - and takes a long time to charge up to discharge voltage due to the low voltage remaining the the capacitors.. this happens a couple of times until the supply side capacitors are totally discharged...Sf5xeplus (talk) 17:32, 29 October 2010 (UTC)

I have a compact fluorescent lamp that regularly flashes hours after the supply has been switched off. From testing, I know that the cause is the tiny leakage current from old wiring through two-way and crossover switches (called three-way and four-way in the USA). The leakage is sufficient to light the neon on my tester screwdriver, but not sufficient to give an electric shock. I should have my wiring tested and possibly the old switches replaced, and I ought to advise you to do the same because it is possible that this flashing is a warning of a developing dangerous condition. Dbfirs 18:25, 29 October 2010 (UTC)

I have a new house and wondered about the 8 volts of current in a lamp outlet before I realized that the switch was turned off. --Chemicalinterest (talk) 22:30, 29 October 2010 (UTC)

"Volts" are units of electric potential, not of electric current whose units are Amps. An AC voltmeter with high impedance will show a small voltage with only a capacitive connection to a 120 or 240 VAC mains supply, which may be what you observed. Cuddlyable3 (talk) 22:57, 29 October 2010 (UTC)

my project

I wanted to know about George Washington Carver's family life and work.I read your article about him but it is too short because i need to wright 2 pages about him on every part of his biography. Thank you ever so much Yours Sincerely, Mim —Preceding unsigned comment added by 92.29.50.98 (talk) 18:05, 29 October 2010 (UTC)

You might be better off asking on the Wikipedia:Reference desk/Humanities desk about this.

You can try the links from the article eg George_Washington_Carver#References to get more information, or try Google books http://www.google.co.uk/search?q=George+Washington+Carver&hl=en&tbs=bks:1,bkv:p&source=lnt&sa=X&ei=oBHLTMfGBovoOcul1MkB&ved=0CBEQpwU or a library.Sf5xeplus (talk) 18:26, 29 October 2010 (UTC)

Toothpaste

Children are advised to use only about a pea-size (1 g??) of toothpaste to prevent accident swallowing. How much toothpaste would it be necessary to "accidentally" swallow to die from poisoning? (this is not medical advice, just curiosity) —Preceding unsigned comment added by 24.92.78.167 (talk) 18:17, 29 October 2010 (UTC)

To die, quite a lot (and it would depend on the brand of toothpaste). The idea of the advice is to prevent dental fluorosis, especially in areas where the water is already fluoridated. Physchim62 (talk) 18:36, 29 October 2010 (UTC)

Rough estimates are around over 10 tubes .. http://www.acsh.org/factsfears/newsID.188/news_detail.asp .. See also Fluoride_poisoning#Fluoride_in_toothpaste . In general eating a lot of toothpaste causes stomach pain long before the leathal dose is reached.Sf5xeplus (talk) 18:37, 29 October 2010 (UTC)

(edit conflict) Hmm, a quick search, not necessarily reliable source [11] reveals that "toothpaste for sensitive teeth" actually is using fluoride to poison the nerves at 0.22 percent (over the counter) to 1.1 percent (prescription). My that sounds like a dubious idea, but let's just use the number for now. A different source says that high-fluoride over the counter toothpastes contain 0.1 to 0.15 percent fluoride.[12] The low concentration there is 0.044/0.05/0.055 percent. (stated as 550 ppm, in case I fouled up) This sort of variation, the likelihood that someone will fail to consider some factor like this, is the reason why some people believe Wikipedia shouldn't give medical advice. I'll bet the medical professional you ask is going to flip an answer in a few seconds without asking what type of toothpaste, but it's their racket.

Now as for toxicity of fluoride, there I'll go by the article, which cites 0.2-0.3 mg/kg for gastrointestinal distress, while lethality begins 15-20x higher (32-64 mg/kg). So a 20 kg child could be uncomfortable eating 4 mg fluoride, which requires 363 mg of volume at 1.1% w/w. (Actually it is probably w/v but we can assume that the toothpaste is very nearly 1 g/ml like water). Now one of our articles 1_E-7_m³ says that the volume of a pea is 200 microliters, which is about half of this. Thus the pea-sized lump sounds relatively safe from gastrointestinal distress, even with toothpaste for sensitive teeth. But bear in mind that every person is a bit different, and most importantly, we haven't spoken of cumulative exposure.

To answer the question accurately, we must discard theory, which is never reliable in biology, and look at experimental data, e.g. PMID 16128790, which finds that 32% of the pea-sized lumps of toothpaste given to 4.5 year old Malaysian children ends up being swallowed. But some British kids apparently swallowed only a third as much (PMID 10365494) - must be a benefit of keeping a stiff upper lip. Another study didn't find that swallowing fluoride toothpaste caused fluorosis, but starting it before age 5 might (PMID 9758424). There's much more data there at PubMed - as usual, looking up the data demands we decide exactly what question we mean to ask. Wnt (talk) 18:47, 29 October 2010 (UTC)

If it's anything like the proton pump drugs for acid reflux, you don't need to kill the nerve cells to disable them. You just need to provide ions to neutralize the receptors. Whereas disabling acid-producing cells affect digestion in the long run, I don't know what the effects of disabling oral nerve cells are. Imagine Reason (talk) 02:21, 30 October 2010 (UTC)

Hmmm... I avoided saying anything solid there because I wasn't sure about the mechanism of action of fluoride in sensitive-teeth toothpastes, and the more I read the more confused I get. I've read that it soothes the nerves, that the tin in stannous fluoride blocks the tubules, even that it's actually the calcium and potassium in the toothpaste that has the effect by blocking the tubules (see PMID 20158016). For now I'll offer no opinion about it, beyond my gut feeling that it sounds worrisome.

As an aside, I'll admit I'm prone to suspect as-yet unknown regenerative actions from intact nerves. It's been my subjective impression that after a few days even a small chip at the end of a tooth causes a faint sensation of swollenness within it, and emission of a sweet, salty tasting fluid from the chipped area. I'm suspicious that somehow the nerves might sense damage and coordinate immune responses throughout the bulk of the tooth, but that's purely personal speculation — still, it's the reason behind my gut reaction above. Wnt (talk) 10:26, 30 October 2010 (UTC)

As an aside, it has nothing to do with children -- a pea-sized amount is recommended for people of all ages. Any more provides no greater efficacy and advertisements to the contrary (a la a full brush head shimmering in the light with a perfectly-arranged tilde of tri-color aquafresh) merely contributes to overuse and subsequent over-purchasing. DRosenbach ^{(Talk | Contribs)} 00:10, 31 October 2010 (UTC)

Hardness of human teeth

What would be the approximate hardness on the Mohs scale of an adult human incisor in good health? Thank you, DuncanHill (talk) 19:26, 29 October 2010 (UTC)

Tooth enamel is listed at 5 in our Mohs Scale article that you linked to. Several sources (here, here, and here) corroborate this. --Zerozal (talk) 19:40, 29 October 2010 (UTC)

Many thanks. DuncanHill (talk) 19:43, 29 October 2010 (UTC)

Shame on you Duncan ! - even I can remember your question Wikipedia:Reference_desk/Archives/Science/2009_March_2#Hardness_of_teeth and find it doing this [13] ... :) Sf5xeplus (talk) 19:44, 29 October 2010 (UTC)

How incredibly embarrassing! I wonder if I was watching the same episode of CSI:Miami then as I am now. DuncanHill (talk) 19:48, 29 October 2010 (UTC)

What looks like peas?

During the first week of October I was in Myrtle Beach, South Carolina and, since they are full grown, these trees must have been there in the past, but for the first time I realized that their fruit (or what I assume is fruit) looks like peas. There is another tree, possibly the same species but I don't think so, where I live in North Carolina. I never noticed this fruit before.Vchimpanzee · talk · contributions · 20:52, 29 October 2010 (UTC)

It's pretty difficult to say precisely without a better description, but peas are a member of the Fabaceae family of plants which contains 20,000 species, some of which are trees (e.g. Acacia and Gleditsia), and they all have seed pods called legumes which look the same as pea pods. SmartSE (talk) 22:34, 29 October 2010 (UTC)

I was wondering if you can/could point at a picture of such a tree at http://commons.wikimedia.org/wiki/Category:Myrtle_Beach,_South_Carolina (might remove some guesses from people who haven't been there but are biologists) Sf5xeplus (talk) 22:42, 29 October 2010 (UTC)

The Indian Bean Tree or Southern Catalpa is my bet. It has seeds in long (8 to 14 inches) pods that look like beans or peas[14]; they stay on the tree all through the winter. It's a native of south-eastern USA but there are some nice ones in Parliament Square in London. Alansplodge (talk) 22:55, 29 October 2010 (UTC)

We can rule out the Indian Bean Tree because there are no pods.Vchimpanzee · talk · contributions · 17:25, 30 October 2010 (UTC)

Hang on dude, you said to start with the fruit looks like peas, now you say there are no pods? Did you really mean the fruit is small, round and green, rather than the fruit is contained in things that look like peapods? --TammyMoet (talk) 19:46, 30 October 2010 (UTC)

Yes. I would have said they looked like pea pods if they did.

I walked past the trees near where I live and the leaves are falling off and the fruit is turning brown now.Vchimpanzee · talk · contributions · 18:47, 31 October 2010 (UTC)

Would you be able to take a few photos and upload them? DuncanHill (talk) 11:11, 1 November 2010 (UTC)

Lime trees perhaps? I see that even the article says "the tiny fruit, looking like peas". 92.24.189.164 (talk) 13:36, 1 November 2010 (UTC)

Good thinking - could be a lime. There's a picture here[15]. Each cluster has a bract - a sort of long wing. The American lime is native to the eastern North America, as far south as Texas. Alansplodge (talk) 17:53, 1 November 2010 (UTC)

That photo of just fruit does look very much like the fruit I'm seeing at home. I can't tell about the leaves, but they have sort of an elm shape. Definitely not the leaves in the lime tree article. I don't have a camera or anything, and I doubt seriously I would be able to upload the photos to Wikipedia anyway, but I might be able to provide a link to my Facebook page if I find a way. Wait ... then I'd be giving everyone my real name. I'm sure there are other web sites, though. The local trees I could probably ask someone about.Vchimpanzee · talk · contributions · 18:09, 1 November 2010 (UTC)

The leaves of lime trees and elms look similar. The long things next to the "peas" on Lime trees are not leaves, but bracts. 92.24.185.90 (talk) 20:34, 1 November 2010 (UTC)

There's a college near where I live. The trees may be on their land. I know there are classes tyhat go in the woods and learn to identify trees. I may be able to find someone who can answer this.

I still don't know about the trees in Myrtle Beach. The "peas" are in larger bunches and I'm thinking it's a different species. I may know who to ask there but they're not IN the park, just near it.Vchimpanzee · talk · contributions · 20:49, 1 November 2010 (UTC)