Wikipedia:Reference desk/Archives/Science/2011 June 9

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June 9

Small flows of water

My fairly small garden pond loses considerable volumes of water to evaporation in summer, but using a watering can to refill it disturbs the sediment and plant roots in an unsatisfactory way. Ideally the water would flow in very gently, perhaps even drip by drip, but I don't want to be standing holding a watering can for a couple of hours to achieve this. One solution I am thinking about, involves having a second container that can be topped up with water manually - perhaps a bucket or barrel sitting by the side of the pond, with a lid that can be closed after refilling to prevent clogging up with dead leaves or other garden detritus. The idea would be for the water to then flow through a pipe connected near the bottom of the container, and drip into the pond. So I'm talking about something gravity-driven, and in terms of scale of water-flow, imagine a dripping tap. This raises several practical questions:

1. How thin should the internal diameter of the pipe be to ensure there is a flow, but to minimise the volumetric flow rate? Japanese water features seem to produce a surprising flow even through a tube of bamboo. But if we get down to the couple-of-millimetres scale, there must be considerable risk of the tube clogging, and presumably at some point it just stops flowing at all.
2. What's the trick to getting the water to drip out (or just barely trickle out), rather than flow out? I'm guessing the idea is to have some sort of narrower cap fitting over the end of the tube?
3. Bearing in mind this is a gravity-fed contraption, are there restrictions on e.g. the length of the pipe, or the angle it need to run at? I suspect that a longer thinner pipe may need to be put at a steeper angle to ensure flow. The length of pipe I am thinking about is in the 10 to 30 cm region. It's Question Time (talk) 00:37, 9 June 2011 (UTC)

Since this is all quite empirical, I'm thinking you're best off with a stopcock or plug valve or an adjustable clamp on a piece of rubber tubing. To prevent annoying clogs, I think your tube should generally be wide open except for one key point. Wnt (talk) 00:52, 9 June 2011 (UTC)

An adjustable set-up makes sense - if it's set to produce nothing more than drips, does that have any impact on the length of tube that can be sustained, or the angle it needs to lie at? (It seems intuitive that a continuous flow can "push" further/harder.) It's Question Time (talk) 01:03, 9 June 2011 (UTC)

Wouldn't a simple soaker hose do the trick ? (That's a flat garden hose with many small holes in it and a cap at the end [1].) Curl the soaker hose around the perimeter of the pond, and adjust the water pressure at the tap down to a level where it drips out of the many holes slowly. Having so many tiny holes makes it unlikely they will all get clogged. StuRat (talk) 01:08, 9 June 2011 (UTC)

Also, a caution, having standing water on your property, like you described, can allow mosquitos to breed there, unless chemicals are added to prevent that. StuRat (talk) 01:14, 9 June 2011 (UTC)

The water container would have a lid on it, and should drain near-enough completely within a couple of hours at most, so it shouldn't act like a water-trough. Mosquitos already come to the pond to breed, although most of the larvae just get predated! The flat soaker is an alternative; would it work if connected to a standing water source? (The solutions on sale seem to be several metres long which is excessive for my needs, although the site you linked to has the interesting review snapshot "Cons: Inefficient (3), Leaks (3)" which suggests not everyone gets the point! I wonder if it's possible to rig one up from other materials) It's Question Time (talk) 01:25, 9 June 2011 (UTC)

I would just use a short length of old hose pipe and drill many tiny holes with the smallest drill bit I could find (and stop the free end). The hose could be fixed above the bottom of the pond to avoid disturbing the sediment, and fed by gravity from your container a foot or two above pond level. If the container empties after an hour or so, then there will be no problem with insects breeding there. The rate of flow will be roughly proportional to the difference in height between the surface of the water in the container and the surface of the water in the pond. Dbfirs 07:08, 9 June 2011 (UTC)

Once the container is nearly empty, there will very little pressure in the tube. Does that mean there's a minimum size of hole that water would be able to drip through? I'm imagining there will be surface forces that would make the water cling to the hole, so that some pressure is needed to force the water through (the same reason, I presume, that flat soakers nneed to be connected to a faucet with at least a little pressure) and that intuitively a smaller hole produces a greater contact force per volume of water. It's Question Time (talk) 12:38, 9 June 2011 (UTC)

Why not just use a watering can rose. Its what I used when I had a pond.--Aspro (talk) 11:52, 9 June 2011 (UTC)

I think StuRat/Dbfirs may be on to something with the soaker hose, which is more fault tolerant than a pipe with a single pinch point.

• For another point of view, consider why it is that you want to spend resources to keep the pond full all summer. What is your goal? Have you ever seen what happens when no water is added? Depending on where you live and how the pond was formed, it may just be a natural Ephemeral pool, which will attract a unique blend of flora and fauna. You also may be able to decrease evaporation by installing shading trees, or even water lilies. SemanticMantis (talk) 14:14, 9 June 2011 (UTC)

The pond is artificial (and indeed is already shaded). But the point is a good one! Unfortunately without topping up the surface level drops very rapidly into the pre-formed shell, and it gets more difficult e.g. for frogs to to get in and out. It's also less aesthetically attractive that way. It's Question Time (talk) 18:32, 9 June 2011 (UTC)

I was going to say a capped hose with pin pricks, but I see someone beat me to it. μηδείς (talk) 15:30, 10 June 2011 (UTC)

Although they said using a small drill bit ;) Will that make a difference? It strikes me that when the container has nearly drained) the difference between water surfaces will be < 10 cm then the pressure will be very low and I wonder if pin-holes will actually hold the water in. It's Question Time (talk) 21:57, 10 June 2011 (UTC)

Pinholes will quickly become blocked with bacteria and algae, so I recommend drilling holes of at least a millimetre (larger would be OK because the flow will be slow for many holes and low header). If all the holes are under the surface of the pond, and the header container is designed to drain completely, then there will be no water above pond level for most of the time, and the container and upper hose will dry out, mainly preventing growth of clogging agents. Using an opaque hose rather than a transparent one will also reduce growth of any "nasties". Dbfirs 09:42, 11 June 2011 (UTC)

You could have a large vertical cylinder pushed into the bottom of the pond. Fill it up with water, it will eventually reach the same level as the pond. It could have many holes in its sides - for example it could be made of a metal gauze (as a flour sifter is). Or have an open sack in the pond. Or you could make a cylinder out of twigs or chicken-wire. 92.24.181.38 (talk) 00:12, 12 June 2011 (UTC)

I didn't literally mean pinpricks, could you imagine driving them? Sheesh! Think one penny nail. μηδείς (talk) 21:12, 12 June 2011 (UTC)

I'm late on this one but no one suggested the 1st thing to come to my mind.. Get a big plastic bottle and fill it with water and put it in your pond so that it sits on top of the water sticking out upside down with the mouth just at the level at which you want the pond to be filled. Now work out some sort of bracket so the bottle will stay there but so that you can also take it out and fill it, when needed. When the water level drops below the mouth of the bottle, some water will fall out of the bottle until the pond is level again.. Simple. And if you don't want an ugly bottle sticking out of your pond, cover it with bamboo or reeds or something.. Vespine (talk) 01:39, 14 June 2011 (UTC)

Gauss's Law for Electric Fields

Brushing up on my E&M, I just realized the one of Maxwell's equations, Gauss's law for electric fields has the permittivity of free space. My questions is that is this law true in any kind of a medium or only in a vacuum? If I want to use this law in some other medium like water for example, do I need to change the constant? Thanks!-Looking for Wisdom and Insight! (talk) 02:40, 9 June 2011 (UTC)

Only vacuum. To apply to other dielectrics, one must multiply εo by the relative permittivity (εr) of the dielectric to get the effective permittivity of the medium.--78.148.131.253 (talk) 13:48, 9 June 2011 (UTC)

So the law is still valid in any medium as long as the value of the constant is appropriately changed? Another question I have, for magnetic fields there are diamagnets (which lower the strength of an externally applied magnetic field) and paramagnets (which increase the strength of an externally applied magnetic field). Comparing that with electric fields, I only know of dielectrics which weaken an externally applied electric field. Is there a paramagnetic analogue for electric fields? Have any experiments/research been done on this? What about gravitational fields? Any such matter which will strength or weaken an externally applied gravitational field?-Looking for Wisdom and Insight! (talk) 01:21, 10 June 2011 (UTC)

I would say so. The appropriate substitution for a magnet when considering an electric field would be an electret wouldnt it, rather than somwthing with different relative permittivity ?--78.150.235.218 (talk) 12:52, 10 June 2011 (UTC)

Second coming of Christ & research support

I am M.J.Varghese, the chief commender of LOVE (Liberation Organisation of Virtual Energy). LOVE is for doing charitable works in the name LOVE of Charity. Our supream commander is father God, who create, exist and controlling this nature. 2000 years ago, Jesus said that love each other because God is love. After 2000 years, I am saying that love everybody, then you get love because love is God.

Dear sir, I am contacting you to clear one of my doubts that is: there is BC that is before Christ, it means before the birth of Christ; and AD (after Christ), it means after the death of Christ. If so, the life time of Jesus is not accounted - 2000 AD is 2000 years after his death. If he come back by birth, he should born approximateky 33 years before 2000 AD, becasue then 2000 years after his birth is completed.

None of the incarnations or the prophets comes directly from heaven, and all of them born in between us. Hence, the second coming Jesus may be in between us, am I right?

Thanking you. With regards, M.J.V, C.C, LOVE.

I am exposing three ideas, want urgent research, I have no facility for research.

First one is: tender-coconut is the remedy to HIV, because HIV attacks our w.b.c., tender-coconut-water increases our w.b.c. rapidly, and the increased w.b.c. overlaps HIV. Hence, HIV cannot split up and attacks out w.b.c - thus, AIDS cannot forms. HIV happens like the seed thrown in to the cactus (the parable said by Jesus).

The second one is: water is a good fuel because it consist hydrogen and oxygen - by electrolysis, we can split water in to hydrogen and oxygen. This hydrogen burns in an engine chamber, we will get power to run a motor engine.

The third one is: the definition, location, and stages of mind. The modern medicine cannot define, locate, say about the stages of mind, but here I am saying about it. Mind consist of three main parts like a computer:

• Brain like monitor
• Heart like a CPU
• Kidney like keyboard

There is seven stages for the mind:

• Excited stage – positive in x-axis
• Depressed stage – negative in x-axis
• Doing rights only - positive in y-axis
• Doing evils only - negative in y-axis
• sexually excited - positive in z–axis
• sexually depressed - negative in z-axis
• absolute stability - it is only for God

Do need full research and inform me the progress.

Thanking you

M.J VARGHESE, C.C, LOVE — Preceding unsigned comment added by 117.206.58.137 (talk) 04:41, 9 June 2011 (UTC)

A.D. doesn't stand for "after death". It stands for Anno Domini, which is a Latin phrase meaning "in the year of our lord". There is no 33-year gap between the B.C. years and the A.D. years; indeed, there isn't even a year 0. 1 A.D. is the year immediately following 1 B.C. Red Act (talk) 05:04, 9 June 2011 (UTC)

Water isn't a fuel. Sure, you can electrolyze water into hydrogen and oxygen, and then burn the hydrogen. But the electrolysis requires energy in the form of electrical energy, that's actually somewhat more than the energy gained by burning the hydrogen, due to some heat loss in the process. So electrolyzing water and then burning the hydrogen results in a net loss of usable energy. Red Act (talk) 05:16, 9 June 2011 (UTC)

It isn't possible to do research into your idea that there are seven "stages for the mind", because that isn't a falsifiable hypothesis. I.e., without so much as a definition of what exactly a "stage of the mind" consists of, there is no experiment which can determine whether the number of "stages" the mind has is 7 or 42 or 666. Red Act (talk) 05:35, 9 June 2011 (UTC)

Although of course this is all fundamentally bizarre, the idea actually has something in common with the Big Five model of personality, except with three factors instead of five (and different ones, of course). Looie496 (talk) 06:54, 9 June 2011 (UTC)

(edit conflict)If you can prove that "tender-coconut is the remedy to HIV", then you deserve a Nobel Prize and you will probably become very rich. Unfortunately, others have not been able to find a remedy. Jesus never mentioned a cactus, by the way. In your "stages for the mind", why restrict yourself to three dimensions. The human mind is much more complex, with many more "axes". Dbfirs 06:57, 9 June 2011 (UTC)

Looie, I think you have something there! The axes of "extraversion" and "conscientiousness" would seem to fall pretty close to the energy/depression and good/evil stages he describes. I don't see from the article which of the Big Five axes is given credit for, shall we say, "Weiner games", but surely one of them must be.

It seemed like the tender coconut thing was too original for this person to have devised, and it is so - there's stuff about tender coconut water or coconut oil curing HIV all over Google. Looking back to see where the fire started I get PMID 11365012 "interviews and anecdotal reports": "The third interview reveals a patient's success at dropping HIV viral load and increasing CD4 counts using Naltrexone and NK911 and supplementing with coconut oil, garlic, and raw goat's milk." (1998, Posit Health News) Another article PMID 11366549 from that source talks about "transfer factor" as a prophylaxis for hepatitis, which somehow tied into coconut oil. Then PMID 12349090 (1999, Reprowatch) is an abstract about a trial that was going to be started in the Philippines about coconut milk and "monolaurin, a coconut oil byproduct". Then nothing, at least in NCBI. Another 2007 article PMID 20161889 talks about coconut being used in African traditional medicine for HIV. My guess is that there was some kind of flash in the pan about HIV and coconuts around the time of that Philippines trial, but it must not have come to anything.

I should say that I do hold traditional and herbal medicine in fairly high regard; I believe that likely half, or at least a third, of the treatments described by Dioscorides or extant in Chinese traditional medicine are somewhat effective, and of those only about half have been studied scientifically to this day. But traditional medicine for a new disease is a dicey business, and traditional medicine was never much good with diseases that take a long time to worsen or get better - things like lead and Aristolochia were used in traditional medicine on several continents, because only the short-term effect was apparent. With HIV, the alternative medicine is unfortunately all a matter of hoping for luck despite a lack of published success, whereas conventional treatments have with much difficulty evolved to the point of saving lives. Wnt (talk) 07:35, 9 June 2011 (UTC)

This is total gibberish. I'm finding it hard to tell if it's trolling, or just very weird. Zzubnik (talk) 10:43, 9 June 2011 (UTC)

Too weird to be trolling. HiLo48 (talk) 10:47, 9 June 2011 (UTC)

Cacti are native to the New World, so I don't think Jesus would have encountered them unless you adhere to Mormon beliefs. Googlemeister (talk) 14:18, 9 June 2011 (UTC)

Indeed. "Kidney like keyboard" should make our actual trolls hang their heads in shame. --Sean 15:41, 9 June 2011 (UTC)

The OP posted the same message here. The organisation of which the OP is chief commender(?) is unknown to Google. The OP should not be using the Ref. Desk as a soapbox for a bizarre collection of claims. Cuddlyable3 (talk) 21:05, 9 June 2011 (UTC)

Note that the OP's final comment "commends" responders here, "Do need full research and inform me the progress." I wonder what he thinks of the progress made so far? :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:41, 10 June 2011 (UTC)

This clip http://www.youtube.com/watch?v=TpicfnfcEiM is appropriate on many levels. μηδείς (talk) 15:32, 10 June 2011 (UTC)

See wp:NOT a RESEARCH LAB ;) - 220.101 talk^\Contribs 12:51, 11 June 2011 (UTC)

Can you explain what w.b.c. is supposed to mean? Also, many small electrical devices run on water, for example a water-activated battery, this thing, this thing, some other recent inventions worldwide], and another program I've encountered discussing a German company powering about a volt of energy from just a drop of water. For the Latin phrase you discussed, see Deus Caritas Est. ~AH1 ^(discuss!) 15:31, 11 June 2011 (UTC)

Could you please explain what "a volt of energy" is? (sounds German to me) 5BYv8cUJ (talk) 18:51, 11 June 2011 (UTC)

The volt is a fairly common electrical term. StuRat (talk) 19:00, 11 June 2011 (UTC)

But so what is "a volt of energy" ??? 5BYv8cUJ (talk) 19:14, 11 June 2011 (UTC)

Err, I meant a volt of potential difference in the context of a battery. Energy is measured in joules and in Coulombs for charge. ~AH1 ^(discuss!) 20:15, 11 June 2011 (UTC)

So why did they need a complete drop for *that*? And what was the effective energy output? I can make 2000 volts with a silk tie. 5BYv8cUJ (talk) 20:24, 11 June 2011 (UTC)

re w.b.c., I think the OP means White blood cell. - 220.101 talk^\Contribs 18:06, 11 June 2011 (UTC)

Oh, I was about to think it meant Westboro Baptist. ~AH1 ^(discuss!) 20:15, 11 June 2011 (UTC)

Water-activated batteries don't use water as their source of energy, even if some ill-informed reporter calls them "water powered". Water-activated batteries always have at least one other substance like sodium borohydride or something that's consumed in the process, that's actually the source of the chemical energy that gets turned into electrical energy. Once the chemical reaction involved has consumed all of that other substance, you can't get more energy out of the battery just by adding more water. Instead you need more of that other substance, which invariably is far less plentiful and far more expensive than water. I.e., it's really that other substance involved that gets consumed that reasonably should be called the fuel, not the water.

on the German company using the drop of water as an energy source, as well as on the phrase "some other recent inventions worldwide".

The Yi Cui thing looks like garbage to me, for multiple reasons. First, if he's really made some big breakthrough, why hasn't he published anything about it in a peer-reviewed journal? Google scholar turns up nothing about this from him. Second, sea water has a fairly low resistivity. If the electrodes have direct contact with the sea water (and it sounds like they do), why doesn't the sea water just short out any charge that's stored on the electrodes? Third, although it's hard to tell from a vague, rather nontechnical article in the popular press, it sounds like the basic principle that he's using is the fact that if you replace the dielectric in a capacitor with a different dielectric with a lower dielectric constant (sea water has a lower dielectric constant than pure water[2]) without changing the charge on the capacitor, the energy stored on the capacitor will increase. However, what he's neglecting to mention, and perhaps isn't even aware of, is that it requires as much mechanical energy to replace the dielectric in a situation like that as the increase in energy stored on the capacitor. It actually requires even more mechanical energy than that, due to the energy lost as heat. Where is that mechanical energy coming from? If he's neglecting that mechanical energy required, then that's a serious flaw in the idea, and he's got yet another flawed idea for a perpetual motion machine. Or if that mechanical energy is coming from the flow of the river, then all he's basically got is a different mechanism for producing hydroelectricity. Hydroelectricity doesn't use water as a fuel, i.e., it doesn't convert chemical energy in the water into a more useful form of energy. Instead, the output energy comes from stored gravitational potential energy. The fact that it happens to be water instead of some other substance that's the source of the gravitational potential energy isn't really important. Red Act (talk) 21:39, 11 June 2011 (UTC)

The coconut cure should be easy enough to test, so why not set up your own trials and see how many people with AIDS it cures ? As for using water as fuel, while it does require more energy to split it than you get back when you burn it, this still might make sense if you have a large source of electricity and want to produce oxygen and hydrogen gas as more portable sources of energy, such as for a car. There might be more efficient means of producing hydrogen alone, though (a car normally just uses atmospheric oxygen). Therefore, splitting water only makes sense if you have some use for the excess oxygen produced. StuRat (talk) 18:44, 11 June 2011 (UTC)

I looked back for that coconut oil study. What I found was http://www.coconut-info.com/aids.htm (a commercial site) which serves up the "full results" of the study (which say that it has "miraculous healing power" but that results "are not completed yet" and its effect is "mostly on the quality of life". Further digging reveals the study had 14 patients.[3] Now mind you, I do respect the Ayurvedic traditional medicine as representing centuries if not millennia of experience of trial and error experience regarding what is helpful against disease, and a very important source of future medical advances, but I don't respect people who sell "Ayurvedic medicine" against diseases that were not known more than a few decades ago. Wnt (talk) 22:21, 11 June 2011 (UTC)

Bootstrapping differential Manchester encoding

Is the first "transition" of a differential Manchester encoding signal the first time it deviates from its initial level or the first time it returns to that initial level? 76.254.22.47 (talk) 06:03, 9 June 2011 (UTC)

Or are signals from both possibilities generally tracked and chosen from after a sufficient number of samples to discern between have been observed? Can some kind of bit parity, start or stop bits make that easy? 76.254.22.47 (talk) 22:54, 9 June 2011 (UTC)

(crickets) I re-asked at the computing desk.[4] 76.254.22.47 (talk) 20:12, 13 June 2011 (UTC)

Infinity and superconductivity

Hello.

I've been told the concept of "infinity" is essential to explaining superconductivity. Why is that so?

Thanks! Leptictidium (mt) 06:24, 9 June 2011 (UTC)

We have an article that is essential preliminary reading - see Infinity#Physics. Dolphin (t) 07:39, 9 June 2011 (UTC)

After reading this, I've come to the conclusion that infinity cannot exist in the physical universe, that it's just a mathematical construct. Is that true? --Leptictidium (mt) 10:23, 9 June 2011 (UTC)

There are those who think that, but I think they're wrong, at least depending on what you mean by "cannot". For example it is consistent with all known observations that the physical universe itself is infinite (contains infinite volume, infinitely many particles).

A superconductor, according to theory as I understand it, has infinite conductivity, which simply means that a current passing through it does not dissipate any energy whatsoever to resistance (it can still lose energy by interaction with external electromagnetic fields). Whether that constitutes an infinite measurable quantity seems to be a question of definition. --Trovatore (talk) 10:35, 9 June 2011 (UTC)

Does that mean the universe has always been infinite? If so, how does that fit in with claims that the universe was infinitely dense just before the Big Bang? Thanks for your answers. --Leptictidium (mt) 10:45, 9 June 2011 (UTC)

My understanding is that, if the universe is infinite, then it always has been. But there are subtleties I've never completely come to terms with. You should ask User:BenRG, who seems to know about these things. --Trovatore (talk) 10:50, 9 June 2011 (UTC)

As a rule of thumb, when a physicist says "infinite" they mean "finite but much larger than the typical values in my problem". A mathematician, of course, knows that there are an infinite number of different infinities. Gandalf61 (talk) 11:02, 9 June 2011 (UTC)

However that is not what a physicist means by "the conductivity of a superconductor is infinite". According to theory, the conductivity of a superconductor is literally infinite. --Trovatore (talk) 11:07, 9 June 2011 (UTC)

(Which simply means that its resistivity is exactly zero.) --Trovatore (talk) 11:08, 9 June 2011 (UTC)

Well, yes, according to theory. But to what extent can this prediction be experimentally verified ? How can you experimentally tell the difference between exactly zero resistivity and a very, very small resistivity ? Sometime when a physicist says "zero", they mean "smaller than I can measure". Gandalf61 (talk) 12:32, 9 June 2011 (UTC)

If we assume the theory to be correct (because it is based on quantum mechanics and the approximations made are not relevant for this issue, otherwise the theory would not have been accepted as the explanation for superconductivity), then you can see that zero resistance arises in the limit of zero frequency. As long as the current has finite frequency components, the resistance is not exactly zero.

If you take a non-superconducting loop, and then move a magnet near it, there will then be a nonzero magnetic flux through the loop. If you then cool the loop so that it becomes superconducting, then you get a current if you move the magnet away from the loop. This is because the superconductor will keep the flux through the loop the same. This persistent current through the loop is then very stable, but according to the theory, it will slowly decay. The system is clearly not in the ground state and it can make transitions to lower energy eigenstates. But the time scales involved here are astronomical. Count Iblis (talk) 14:57, 9 June 2011 (UTC)

I am not completely up-to-date on this, but I don't really think your remarks about frequency are correct. I think what you mean is that the impedance is nonzero when there are finite frequency components. But impedance is not resistance. It does allow there to be a potential difference across the ends of the superconductor, but it does not allow any energy to be lost to thermal processes, which is the definition of resistance. --Trovatore (talk) 19:34, 9 June 2011 (UTC)

The real part of the impedance of any object at finite frequencies will be strictly larger than zero. If you have non-steady currents, you get all sorts of dissipative processes e.g. due to changing magnetic fields inducing currents elsewhere. So, if you have an LC-circuit and the current oscillates at some frequency, the current will die down on quite small time scales, nothing like the astronomically large time scales for superconducting rings carrying DC currents. I think that at a frequency of 1 kHz, the best superconducting coils have a quality factor of just 10^6 or so. The current will thus dissipate on a time scale of a few hours at that frequency. Count Iblis (talk) 02:15, 10 June 2011 (UTC)

Hmm, is it fair to attribute dissipation due to currents in nearby objects to resistance in the superconductor? It's a bookkeeping question, maybe, more than a physics one strictly speaking. --Trovatore (talk) 03:40, 10 June 2011 (UTC)

I think there are also other processes involving only the superconducting object. I think that the dominant source of the losses are due to processes in the surface layer of a superconductor. Electromagnetic fields penetrate a small distance into the superconductor, the perfect screening only happens some finite distance into the superconductor. An oscillating supercurrent will give rise to an oscillating electric field in the surface layer. There, the supercurrents are not effective in screening this out 100%, so this leaves room for charges there to oscillate with that electric field, causing dissipation. Count Iblis (talk) 15:13, 10 June 2011 (UTC)

Ah, but aren't you then saying that the surface layer is not in fact superconducting? So there is resistance, but it's not in the superconducting part of the object. Or no? I'm certainly no expert on superconductivity. --Trovatore (talk) 20:30, 10 June 2011 (UTC)

Yes, you could say that. I studied this quite a long time ago, so I don't know all the details. But it should be clear that in any material there are always degrees of freedom that are able to dissipate energy. What happens in a superconductor that carries a DC current is that all these processes are 100% frustrated. The supercurrent nullifies any potential difference, so there is nothing left for the dissipative processes to do. You can also say that putting a resistance of zero parallel to a resistance of R > 0 makes the net resistance zero. When you have a non-steady current, things are completely different. You can now excite all sorts of processes that were perfectly frozen in the DC case. Count Iblis (talk) 16:30, 11 June 2011 (UTC)

The statement that conductivity is infinite simply means that resistance is zero. No actual positive infinity is implied, or could be. μηδείς (talk) 20:40, 9 June 2011 (UTC)

Not sure what you mean by that. The conductivity is by definition the reciprocal of the resistivity; if the resistivity is zero, then the conductivity is infinite (in the Riemann sphere sense, say, although the more relevant structure is really the interval [0,+∞]). Your second sentence has the feel of an ideological rejection of infinity. --Trovatore (talk) 21:14, 9 June 2011 (UTC)

I think the statement that conductivity is infinite means that the resistance is theoretically zero, and is in practice too small to measure. No-one has yet provided experimental evidence that the resistance of an actual superconductor is exactly zero, and the theroetical models seem to make various simplifying assumptions (see spherical cow). Gandalf61 (talk) 06:10, 10 June 2011 (UTC)

"All observations are theory laden". See confirmational holism. --Trovatore (talk) 07:30, 10 June 2011 (UTC)

Conductivity is a potential, and is not the same as what is actually conducted. Any actual current will be finite, but it may meet zero resistance. Again, no actual infinity is involved. Of course conductivity is defined as the reciprocal of resistance. We might arbitrarily define the term "applelessness" as the reciprocal of the number of apples one has in one's lunch bag. But it would be absurd to pretend that saying someone with no apples in his bag has infinite applessness proves the existence of real infinities. Actual concrete existents are always finite because they are what they are, and no more (or no less), while infinities are not concrete entities, but are relative abstractions. μηδείς (talk) 15:46, 10 June 2011 (UTC)

Do you imagine that the numbers used to quantify, say, current, are less abstract than infinities? Take a current of 2 Amperes, and point out to me the 2 in that.

The somewhat valid point that you have here is that conductivity is defined as a ratio of things that we find intuitively more basic. It has that in common with intensive properties generally (although conductivity is an intensive property itself, that isn't really the issue here, because its intensiveness comes from the fact that it has area in the denominator, and we're not concerned with zero area). For example, density is an intensive property, and point particles may have infinite density (if they're truly point particles, that is).

However there may also exist concrete extensive infinities, as I alluded to above; the physical universe itself may well be infinite, and contain, for example, infinitely many baryons. --Trovatore (talk) 20:10, 10 June 2011 (UTC)

Both integers and the various concepts of infinity are abstractions, but the concept of infinity exists at a higher level of abstraction than do the counting numbers. Numbers are abstractionss and infinity is an abstraction form abstractions. Concrete realities, however, are not abstractions. Any real act of conduction or any real entity or charge or substance is a real existent. Any concepts we use such as the reciprocal of zero which deal in infinities are based on abstracted concepts of relationships. If, for example, we were to talk about the conductivity of water through a hose we could imagine that none of the pressure of the water entering the hose was converted into heat and that the water exiting the hose did so with zero loss of pressure. Only from those concrete relative terms could we manipulate the math and speak in terms of the infinite conductivity of the hose, but that would be like the infinite applelessness of the empty lunch bag, a derived formal infinity, not a real concrete infinity.

As for infinite baryons, the notion is not coherent. It would amount to saying that there is no actual number of baryons in the Universe, because whatever the actual number of baryons were, there would have to be even more. If the unioverse were infinite we couldn't even make a mathematical statement about it in any relation to any known object since the equation would be undefined, like dividing by zero. The standard theory of the universe is a finite closed but unbounded system having existed for some finite duartion, apparently a hyper(^x)sphere some 13,500+ million years in radius. There is no physical evidence of an infinite universe. Any such notion is incomplete or incoherent or at some point undefined. All very mysterious, but not infinite. μηδείς (talk) 02:00, 11 June 2011 (UTC)

If the curvature of the universe is negative, then the most natural simple model is not a finite 3-sphere, but rather a pseudosphere I think it's called, which would have infinite volume, and therefore (assuming constant density) infinitely many baryons. That's a very simple-minded analysis and as I say there are some subtleties I'm not extremely solid on; for more details ask User:BenRG.

There is nothing incoherent about the notion of infinitely many baryons (please, not "infinite baryons"; no one is suggesting that any individual baryon is infinite). Your remarks on that meaning that there would "not be any particular number of them" seem to come from a pre-Georg Cantor understanding of mathematics. --Trovatore (talk) 02:09, 11 June 2011 (UTC)

I hope I didn't say finite three sphere, did I? The negative curvature of spacetime is usually taken to mean that it is not gravitationally closed in the future, not that currently existing space is infinite, of which there is no evidence. And yes, I am familiar with the formal notion of commensurable and non-commensurable infinities, but there is no evidence of the actual existence of a concrete infinity of baryons, hence nothing to refute. μηδείς (talk) 17:55, 11 June 2011 (UTC)

No, I believe your second sentence is not true. If the curvature is negative (I think we're talking about the curvature of space, not spacetime, but I'm a little fuzzy on that point) then the most natural models do in fact have infinite extent in space. If that is the case, then the principle of uniformity would suggest that the number of baryons is infinite, and that would in fact constitute evidence (albeit somewhat indirect) that a concrete infinity of baryons exists. --Trovatore (talk) 19:43, 11 June 2011 (UTC)

No, the measurable negative curvature of spacetime is in the time dimension. It was originally assumed for aesthetic reasons that gravity would stop the expansion of space over time. Present observation shows that this is false, and that the expansion is speeding up over time. Look at this image, with time in the Y axis and space in the x axis: [5]. The closed cigar shape to the left shows a universe in which time is positively curved and space and time are finite and the universe ends in a big crunch. The image like an expanding horn on the right shows a universe with negative curvature in time, and no finite end, no boundary in the upward time dimension. But note that the cross section in the x axis representing space is finite at any point, although it does keep growing over time. (Note that even this universe does come to an end with local heat death, rather than a big crunch.)

If space were negatively curved, deep space would appear to be much more crowded with stars than local space because the volume of space would increase at a higher rate per distance along a radius. That has not been observed. μηδείς (talk) 18:16, 12 June 2011 (UTC)

I believe that is incorrect. The observations are consistent with (very small) negative spatial curvature, or with (very small) positive curvature, but seem most to resemble asymptotic flatness. Note that the simplest model for flat space is also infinite. --Trovatore (talk) 18:56, 12 June 2011 (UTC)

Also there is no indication, in the image you linked, that the cross-section shown represents the entire universe. It may be, say, just the observable universe, or just some collection of stars. That's a bit subtle of a point to get across in a simple graphic. Also I think astrophysicists, when popularizing, tend not to try to explain what it means for an infinite universe to be "expanding", not a particularly problematic notion but not as easy to convey to the public as the "inflating balloon" one. --Trovatore (talk) 19:12, 12 June 2011 (UTC)

Yes, I am familiar with the limitations of a two dimensional depiction of an object in five or more dimensions. But clearly you understand my point of the difference between the curvature of the space versus the time dimension, and you do not contest the fact that there is observational evidence for the negative curvature the universe in time, but not for the negative curvature of space, no? μηδείς (talk) 19:28, 12 June 2011 (UTC)

I never said there was evidence for the negative curvature of space. What I said, or at least what I meant, is that negatively-curved space is consistent with all known observations. The error bars all include the value zero. It couldn't be much negative curvature, but it doesn't take much; even asymptotically flat space is, in the simplest model, infinite.

To be clear, I am not saying that space is infinite. I am saying we don't know. There is no clear evidence one way or the other. (Such evidence could exist, in the form of a confidence interval for the curvature that does not include zero; that would constitute evidence for a finite universe if it were on the positive side, or an infinite universe if it were on the negative side. Even that would not be conclusive, as there are various loopholes, but it would certainly be evidence.)

You, on the other hand, seem to think that we do know. I haven't yet seen why you think that. The reasons you've offered sound naive; your later remarks seem to contradict that impression, so I have to assume your earlier ones were rushed or oversimplified. --Trovatore (talk) 20:08, 12 June 2011 (UTC)

Well, let me draw an analogy, and please take it as offered in a friendly manner, even if it sounds absurd. If we were to assume that time travel is possible, I could certainly form the (baseless) notion that you committed the Jack the Ripper murders. Of course, I have both no evidence for this and no coherent way of explaining in real terms how time travel would be possible. But I could hold that both arbitrary and incoherent idea. Yet I don't, because I prefer to stick to dealing with ideas which can be coherently expressed and for which there is actual evidence. Real human knowledge is both coherent and foundational. And so I don't expect you to have to disprove the possibility that you committed those murders before I will refrain from accusing you of them.

In effect, I am certainly not claiming to "know" in some positive sense that the universe is not infinite, just as I don't know in any positive sense that the Flying Spaghetti Monster didn't create the Rolling Stones. I simply have no evidence, and do not find that I can express the hypothesis in any way that ties in with the concrete reality I do know. The burden is upon him who makes the claim to express himself coherently and to provide the evidence.

μηδείς (talk) 21:27, 12 June 2011 (UTC)

It appears to me that you have asserted affirmatively that the universe is not infinite. It is not clear why you think lack of evidence should militate more towards a finite universe than an infinite one, or why the idea of an infinite universe is more "arbitrary and baseless" than a finite one.

As for coherent expressibility, what exactly are you looking for? We have detailed mathematical models of what the universe may look like, if it is infinite. If those are not "coherent", does it mean that you think they are self-contradictory?

Finally, let us suppose that when the error bounds on spatial curvature are sufficiently tightened by observation, they fall on the negative side of the line. How would you respond to such an observation? I don't get the impression that your distaste for the infinite-universe idea has much to do with such observations; certainly, it doesn't affect your earlier remarks about not being able to "make a mathematical statement about it in any relation to any known object since the equation would be undefined, like dividing by zero." --Trovatore (talk) 21:43, 12 June 2011 (UTC)

I believe in the burden of evidence. If you make the claim, please both provide the evidence and express it coherently. Vaguely asserted possibilities are cot testable evidential hypotheses. μηδείς (talk) 21:53, 12 June 2011 (UTC)

I think you're being rather selective. You made the claim that the notion of an infinite universe was "incoherent". You have not explained (ahem) coherently just what you mean by its alleged incoherency, nor supplied evidence for it.

In what way is an infinite universe a claim more in need of evidence than a finite one? --Trovatore (talk) 21:59, 12 June 2011 (UTC)

You seem to be under the mistaken impression that I am arguing with you and the words you are typing. I am interested in the verifiable concrete sensory evidence. You don't seem to understand that a word is meaningless if not related to concrete facts. Claims of an infinite universe, when such a term is not defined in relation to concrete facts, are as empty as claims to a callifragilistic universe, when callifragilistic is not defined in relation to concrete existence. Your entire point is that if there were evidence that the universe is XYZ there would be evidence that the universe is XYZ. That is tautology, not observation. But do let me know when you get some infinite observational evidence. μηδείς (talk) 22:28, 12 June 2011 (UTC)

I have outlined a concrete and not-implausible scenario under which there would be observational evidence, of a specific sort that I have specified, that the universe is infinite. Are you going to answer on the question of how you would respond to such a scenario? Also acceptable would be arguing that it's an implausible scenario, but I don't see how you're going to do that. If you default on both of these, then it appears to me that you have made a claim that you're unable or unwilling to justify. --Trovatore (talk) 22:34, 12 June 2011 (UTC)

That there would be evidence if there were evidence is not in itself evidence. μηδείς (talk) 00:55, 13 June 2011 (UTC) Next you will tell me O.J. was framed because someone says he might have been framed. μηδείς (talk) 00:55, 13 June 2011 (UTC)

OK, let's go back and see what the discussion was actually about. You asserted that "actual concrete existents are always finite". That is an affirmative assertion, for which the burden of proof is on you. I gave an example of something that may be a counterexample to your claim, depending on contingent facts as yet unknown, but possibly in principle knowable. You have not defended your original assertion against this claim. --Trovatore (talk) 02:28, 13 June 2011 (UTC)

I am not interested in arguing my point. I understand my position, and know I am right. I don't see any point in starting the disagreement over, assuming no one says that I have been unclear. Are you actually asking me to explain myself? If so, explain to me in your own words (a good faith effort) what you think I mean by a "concrete existent", and we can proceed from there. μηδείς (talk) 02:43, 13 June 2011 (UTC)

Coulomb's Law

I can show that Coulomb's Law + superposition implies $\nabla \cdot \mathbf {E} ={\frac {\rho }{\epsilon _{0}}}$ and $\nabla \times \mathbf {E} =\mathbf {0}$. I want to go the other way and derive Coulomb's law and superposition from the vector identities. I know from Gauss' Law that Gauss' Law implies Coulomb's law if we assume that the electric field is radial. Can the assumption be justified from $\nabla \times \mathbf {E} =\mathbf {0}$? And how does superposition emerge? Nevermind, that's easy to show. Thanks. 65.92.5.252 (talk) 07:36, 9 June 2011 (UTC)

Well $\mathbf {F} ={\frac {\mathbf {E} }{q_{1}}}$ and $\int dV{\rho }=q_{2}$ if you take the limit as V is small you will get the point charge used in Coulomb's Law. I think you are ontrack with Gauss's law which would apply when $\nabla \times \mathbf {E} =\mathbf {0}$.

Gauss' Law should apply whether or not the electric field is curl-free. My trouble is that I can't use curl E = 0 to show that E is radial and symmetric, which would be enough to prove Coulomb's Law. 65.92.5.252 (talk) 21:54, 9 June 2011 (UTC)

Well the next step is to use $\nabla \cdot$ in spherical coordinates.

$\nabla \cdot \mathbf {E} ={\frac {1}{r^{2}}}{\partial \over \partial r}\left(r^{2}E_{r}\right)+{\frac {1}{r\sin \theta }}{\partial \over \partial \theta }\left(\sin \theta E_{\theta }\right)+{\frac {1}{r\sin \theta }}{\partial E_{\varphi } \over \partial \varphi },$

This can then be simplified by assuming no variation with theta or phi, leaving $\nabla \cdot \mathbf {E} ={\frac {1}{r^{2}}}{\partial \over \partial r}\left(r^{2}E_{r}\right)$, which ends up with r^-1. The force will be proportional to derivative of E over r, yielding a r^-2 proportionality. Graeme Bartlett (talk) 13:16, 10 June 2011 (UTC)

Adrenaline sensing anti-perspirant/deodorant

Advertisers are such liars but they shouldn't go completely off the reservation in claims. I just acquired a stick of Degree "Adrenaline series" anti-perspirant/deodorant, which claims on its label that it "is designed to respond to increases in adrenaline..." Sounds like total bullshit to me. Is this possible?--Fuhghettaboutit (talk) 13:31, 9 June 2011 (UTC)

Phew, what's that smell Richard Avery (talk) 13:37, 9 June 2011 (UTC)

I would assume that it "responds" to increased moisture. The antiperspirant ingredients (generally aluminum compounds) can be encapsulated or otherwise designed to have low availability until wetted. Adrenalin (epinephrine) in the blood triggers increased secretion from sweat glands, so by a somewhat indirect route, they're not flat-out lying to say that their product responses to adrenaline. On the other hand, it's definitely not an adrenaline-specific response, and I'm not sure that the basic mechanism of action (sweating dissolves more antiperspirant ingredients, increasing their effect) is particularly novel or unique to this product. TenOfAllTrades(talk) 14:00, 9 June 2011 (UTC)

Just saying they designed it to do X doesn't mean they are competent designers. For example, would you deny that tinfoil hat creators have designed the hats to block mental transmissions? Of course they have. That doesn't mean such things exist or work, though. 20:37, 9 June 2011 (UTC)

Ah, so it's like all those “dermatologically tested” cosmetics. – b_jonas 14:55, 10 June 2011 (UTC)

science

how science and technology affect one life — Preceding unsigned comment added by 112.198.250.3 (talk) 14:58, 9 June 2011 (UTC)

Compare society as it exists today with how the bushmen live, which is similar to how our ancestors lived in Africa 150,000 years ago. Count Iblis (talk) 15:15, 9 June 2011 (UTC)

Hunter-gatherers use technology too. AndyTheGrump (talk) 15:22, 9 June 2011 (UTC)

Even Chimpanzees use technology of their own devising. --Jayron32 19:46, 9 June 2011 (UTC)

And don't forget my personal favourite, the new caledonian crows. See also Technology#Other_animal_species. SemanticMantis (talk) 20:13, 9 June 2011 (UTC)

That's pretty dismissive of Bushmen. They have the bow & arrow, after all. I would recommend looking at the hypocrite anti-tech bomber Ted Kaczynski instead. μηδείς (talk) 20:33, 9 June 2011 (UTC)

The question is about technology and science, i think it's pretty safe to say that so far we are the only species to employ science, and methodologically only fairly recently. I think this sounds like a homework question. Vespine (talk) 04:25, 10 June 2011 (UTC)

Earmarking Human Infants at Birth

I asked my mom about this Earmarking of mine, had it ever since I can remember. She told me I was born that way. I don't buy it. By the laws of science I tell you. I like to imagine I was a Genetically Modified Baby, created in joint-venture of the U.S. Government and IBM Labratories in Silicon Valley. Project: OLD NAZI FILE. The Project was scrapped and all test subjects terminated. I was the one that got away. I'm in Hollywood now, watching too many movies. I figure the reality of this marking probably not as cool as all that. Note, if thought leads towards marking a twin, I was born by C-section at 11 lbs, rules out the twin possiblity, unless my moms an elephant. She's not. I did much online research on this, found nothing. Anything known in the Wikiworld? For conversation, possibilities. Cheers, --i am the kwisatz haderach (talk) 16:08, 9 June 2011 (UTC)

Sorry but do you actually have a question for the reference desk? This isn't the place for medical advice, to have a conversation or for rambling ideas on your birth. (But hint: the Nazi's were before the role of DNA in carrying hereditary information was even clear; it's difficult to be sure but from the photo it looks like you were born before Flavr Savr; when what your suggesting is wackier then an episode of Fringe (TV series) you've perhaps gone too far; and if you're really the only one that got away posting on a highly public forum about it probably isn't a good idea) Nil Einne (talk) 17:12, 9 June 2011 (UTC)

So what am I supposed to be looking at on your lug'ole, that lumpy bit that is horizontally level (in the photo) with your tragus? Richard Avery (talk) 17:36, 9 June 2011 (UTC)

Instead of the non-serious tone I took to bastardize Hollywood productions, maybe amend question for OBJECTIVE Science. Click on image, where face meets top of ear, little hole. Fact: It is a Piercing. Question: Possible reasons on piercing an infant? --i am the kwisatz haderach (talk) 19:48, 9 June 2011 (UTC)

It certainly does not look like a congenital condition. Maybe mommy did something at some point, but doesn't want to confess? μηδείς (talk) 20:31, 9 June 2011 (UTC) I mistook you to be speaking about what looks like a mark from a stapler across your lobe--that would wscare me more than your vestigial extra gill hole.μηδείς (talk) 15:52, 10 June 2011 (UTC)

It looks like a freckle in that pic. But from your description, that could be the result of a routine medical test. I have something like that from the tine test administered on my shoulder (although it's 6 indentations, in my case). StuRat (talk) 20:37, 9 June 2011 (UTC)

It could easily just be the scar left from a pimple or boil. 92.24.129.68 (talk) 20:56, 9 June 2011 (UTC)

My son was born with a similar tiny hole on his ear and the doctor referred to it as a "preauricular dimple". Try googling that term or "preauricular pit" and see if the descriptions that you find match what you have. — Preceding unsigned comment added by 148.177.1.210 (talk) 21:04, 9 June 2011 (UTC)

(ec)Are you saying that hole goes all the way through? (Have you tried an earring in it?) Otherwise, to me it looks like a very small thing indeed, something like a dimple at most. (You should also examine the photo carefully in dimples of Venus for purely academic interest) Now your ear lobe looks unfamiliar to me - I expect them to be smoother - and somewhat reminds me of various paranoia about ear lobe creases and risk of heart disease.^[6] But, yours doesn't look like the ones I saw in the pictures, which were more diagonal and seemed less cartilage-y, so probably not. None of this should be taken in any way remotely as medical advice, as it is all purely speculation about natural physical diversity.

P.S. thanks 148.177 for getting the goods while I was too busy spouting off! Wnt (talk) 21:17, 9 June 2011 (UTC)

No, does not go all the way through. This 'Preauricular' thingy, very strange indeed, genetically that is. I also have a Pectus_excavatum to boot. Cheers, --i am the kwisatz haderach (talk) 21:33, 9 June 2011 (UTC)

Odd, there are actually nine different genes on OMIM in which both "preauricular" and "pectus excavatum" are mentioned.[7] You might find it interesting to go through the list and see if any have other effects that are familiar to you. (Remember, for every extreme case in which people have diagnosable genetic diseases, there are many others in which people simply tend a little in that direction as part of the healthy natural diversity of the human species). Wnt (talk) 21:39, 9 June 2011 (UTC)

We are definitely straying way too far into the field of medical diagnosis here, let's rein it in and call this question answered. If the "kwisatz" is concerned about a genetic disorder, he or she should see a doctor. --- Medical geneticist (talk) 22:22, 9 June 2011 (UTC)

As I said, we are dealing with normal, natural variation. This person is not sick; therefore this is not medicine. Wnt (talk) 22:37, 9 June 2011 (UTC)

You have no way of knowing that, and it is inappropriate for us to speculate. --- Medical geneticist (talk) 22:55, 9 June 2011 (UTC)

I'd say it was pretty natural, had it since birth, never had any infections, cysts, inflamations. Just a superficial skin marking. --i am the kwisatz haderach (talk) 19:58, 10 June 2011 (UTC)

There is an article on Preauricular sinus and cysts. --- Medical geneticist (talk) 21:19, 9 June 2011 (UTC)

And you'll find out more than you ever wanted to know at http://www.youtube.com/watch?v=M-aUukFk-tY (a presentation by a surgeon who deals with what happens in the worst case scenario). Wnt (talk) 21:34, 9 June 2011 (UTC)

To address the conspiracy question expressed by the OP (not even that unusual - from the forums it sounds like there are a lot of people with strange explanations about these pits; in any case I would wonder if some environmental factor influenced development), and because some people with them notice a smelly keratin-containing fluid coming out on a routine basis, I went hunting for "ear" in Dioscorides' Materia Medica (Osbaldeston's translation). There are very many sections describing ear treatments for purulence or sores, but his section on myrrh said that "rubbed on the ear externally it alleviates long-enduring discharges". Since this is the only section specifying externally I wonder if indeed this is a description of such pits from ancient times, but alas, it's just too vague to tell. There doesn't seem to be much sign that current herbalists do this, so I can't even argue by tradition. I feel like there ought to be some way to wring a clear mention of this out of ancient literature, but I haven't hit on it yet. Wnt (talk) 23:12, 9 June 2011 (UTC)

Not on humans, but the old Bible story of Jacob marking the healthy of Laban's flock, then making a deal to take only the Spotted and Striped. --i am the kwisatz haderach (talk) 23:41, 9 June 2011 (UTC)

Now that's a weird story. "Strength" is inherited, but coat color results from parents mating in front of willow branches with stripes?^[8] Wnt (talk) 00:04, 10 June 2011 (UTC)

I guess the only way I would believe is if like 148.177, I actually saw a baby coming out of a womb with this Preauricular Dimple. Seems more like an Earmarking, a Branding when the Nurses/Doctors take the baby to the side tray to clean and wrap before handing back to the mother. Because its close to the Sinus there are complications with infections later. This seems like better logic. I'm not a geneticist, so I could be wrong (more than likely). If the theme of my questioning is earmarking a baby then it isn't about diagnosable genetic diseases. For hard science, best answered by 148.177/Wnt/Medical geneticist. A co-worker brought up Satanists like in Roman Polanski's horror 'Rosemary's Baby'. I like that answer, but also far fetched. --i am the kwisatz haderach (talk) 23:41, 9 June 2011 (UTC)

It sounds like you're actually looking for imaginative explanations. On the Medhelp forum^[9] I read people who thought they'd been poked with the amniocentesis needle, or the holes were from being grasped with obstetrical forceps during delivery, or their parents had pierced their ears as a baby, or that they were "ghost holes"/"spirit holes" with some kind of psychic significance. Wnt (talk) 23:52, 9 June 2011 (UTC)

I still would like to see a birth and check for it being genetic (odds not in favor), maybe talk to an OB that's seen one right out the womb. In regards to marked humans, I've seen foreigners with the Smallpox Vaccination scar on upper arm. Leaves a pretty big mark in comparison to my marking. That could be from the actual vaccine. I am looking for both scientific and imaginative explanations. The more the merrier. Thanks much y'all. This is a lot to work with from just googling EARMARKING HUMAN INFANTS. --i am the kwisatz haderach (talk) 20:11, 10 June 2011 (UTC)

Safety on stairs

Running downstairs or only using every second stair is clearly more dangerous than walking and using every stair. But if someone is doing this dangerous thing, how much safer is the activity IF they grip the handrail? (Let's say a hypothetical "average person".)

My hunch is that using the handrail does not make it very much safer because a) a person can't maintain a good grip on the handrail when they have to "regrip" quickly due to running and b) most people are not strong enough to maintain a grip on it if their feet go out from under them (or they lose their balance in some other way.) Thanks, CBHA (talk) 18:45, 9 June 2011 (UTC)

Ask yourself what it would even mean to say "using the handrail is 12% safer". Now imagine what kind of data it would take to support that claim. I'll be surprised if anyone can give us a quantified answer, but who knows what kinds of data e.g. OSHA might have... SemanticMantis (talk) 19:45, 9 June 2011 (UTC)

Now if only we still did medical experiments on prisoners..... Wnt (talk) 21:01, 9 June 2011 (UTC)

Thank you. I understand that pinning this down to "X percent safer" would be very difficult or impossible. I was just thinking of three or four levels. For example, "trying to use a handrail while running downstairs"

- a) "makes it considerably safer",

- b) "makes it a bit safer",

- c) "does not make it safer" or

- d) "makes it more dangerous because it takes the runner's attention off the stairs".

Given the varied backgrounds of Reference Desk editors, I look forward to hearing from some with experience in running downstairs. ;o) Perhaps there are some movie stuntpeople answering questions here.

CBHA (talk) 21:32, 9 June 2011 (UTC)

Well, as somebody who at a younger age frequently used to run down stairs or take them two or three at a time, my opinion is that using a handrail is safer because it makes it easier to get your feet to land where you want them too. Also it steadies you on the landing. I don't think it has much value for saving yourself once you start to fall. Looie496 (talk) 00:19, 10 June 2011 (UTC)

Unrelated fun fact : In college I discovered that by jumping forwards, catching the handrails like they were parallel bars, and sort of flinging myself downwards, I could go down entire flights of stairs without touching a single step except the landings. In this manner I could go down 15 floors much faster than the elevators. I guess you need long arms to do this. Great for making up lost time when I was late for class. However, I can't make any claims as to how safe this was. Probably not very. APL (talk) 07:04, 10 June 2011 (UTC)

"most people are not strong enough to maintain a grip on it if their feet go out from under them". Is this really the case? I know there was a recent news story about most children not being able to hang from the monkey bars any more, but have our arms and hands really withered this much? I don't think of myself as especially strong (I couldn't go hand-over-hand on the monkey bars anymore), but I'm also someone who used to fall down the stairs a lot, and still have occasional 'incidents'. I find it is much safer to hold the handrail because a) it steadies you if you start to fall b) you can hold tightly and stop yourself pitching down the whole flight c) even if your grip is not strong enough to hold you there, it jerks you back so that you fall backwards and slide down the stairs, which still hurts but less severely than going head first or tumbling d) if you slip, you don't tend to slide as far if you have even an imperfect grip on the banister. 86.161.212.100 (talk) 14:16, 10 June 2011 (UTC)

I agree with the post above. Having a hand on the rail (not necessarily a grip) means that you can quickly grip the rail if you start to fall. It's pretty common to start to fall on stairs and to grab the rail and either prevent the fall or improve how you land.--Srleffler (talk) 17:05, 10 June 2011 (UTC)

"Cotton intended for food use"

The article Flavr Savr includes mention of "cotton intended for food use". Can someone tell me how cotton is put to use as food? Thanks, CBHA (talk) 18:56, 9 June 2011 (UTC)

Cottonseed oil -- Finlay McWalter ☻ Talk 18:58, 9 June 2011 (UTC)

There's been a few projects that attempt to genetically modify cotton so that the seeds can be used as human food. Ordinary cotton seeds have a substance on the seed coat that prevents them from being a useful food source. Here is a relevant link, which was the first google hit for /cotton seed food/ [10]. SemanticMantis (talk) 19:41, 9 June 2011 (UTC)

See Milo_Minderbinder#The_Syndicate for a humorous attempt at feeding cotton to people. --Jayron32 19:44, 9 June 2011 (UTC)

Jokes aside, cotton seeds contain gossypol, which is poisonous. Though presumably, if you somehow remove all traces of it, you might then use the detoxified cotton seeds for food. 67.169.177.176 (talk) 23:35, 10 June 2011 (UTC)

I don't know if that's the intended meaning here, but a frequent use of cotton yarn in cooking is dressing up and binding fowl, or roasts, or roulades. --Stephan Schulz (talk) 16:09, 11 June 2011 (UTC)

Electron spin

Why did they decide to give the two electron spins the values ±1/2 rather than ±1? --75.40.204.106 (talk) 20:33, 9 June 2011 (UTC)

Because there are two types of particles, fermions and bosons where the values of the spin are either 1/2 integer (fermions) or whole integer (bosons). Furthermore, they have unique properties regarding how each class of particles obeys certain physical laws, such as the Pauli exclusion principle. The mathematics of 1/2 integer and whole integer spins are covered by such topics as Fermi–Dirac statistics and Bose–Einstein statistics. But basically, the answer is that 1/2 spin particles like electrons have a spin which is half of the magnitude of whole integer spin particles, like photons or the Higgs particle. --Jayron32 20:45, 9 June 2011 (UTC)

I think the way to look at it is that Planck's constant relates the energy of light to its frequency. The "reduced Planck's constant" (h/2pi) is the "fundamental unit of angular momentum". Note this 2pi is the difference between radians and full cycles. Now if an electron wants to go from +1/2 to -1/2, it changes by emitting or absorbing a photon, and the reduced Planck's constant is the angular momentum of that photon. There is no particle that changes from 0 to +1/2 or +1/2 to 1 (unless I'm terribly wrong about something). That's because there are no half photons with half angular momentum. So there's no call to create a unit h/4pi and present that as a fundamental unit so leptons are odd and bosons are even - it would just make a sometimes confusing system much worse. Wnt (talk) 21:00, 9 June 2011 (UTC)

Not sure about changing, but it is possible for fermionic matter to form bosonic matter. mesons are bosons composed of two quarks, which are fermions. Likewise the Bose–Einstein condensate has bosonic properties (it violates the Pauli principle, for example) despite being otherwised composed of normal atoms (composed of fermionic protons, neutrons, and electrons). I do not, however, know of any process whereby fermionic matter can be created by multiple bosons. In other words, you can additively create whole integer spins out of even numbers of half-integer particles, but there is no way to get a half integer spin with nothing but whole integer spin particles. --Jayron32 00:49, 10 June 2011 (UTC)

Still, the OP raises the question if there is anything more intuitive about the current scheme of assigning integer and half integer spins to bosons and fermions respectively versus assigning them even and odd spins, or is it just a historical accident such as the choice of positive and negative charges? -- 110.49.241.141 (talk) 21:25, 10 June 2011 (UTC)

I'm pretty sure that is completely arbitrary; you could do all the math with odd/even spin numbers, and just do the math with spin/2 and get all the same results. It's probably one of those things where the standard is abitrary, but has to exist as a standard, i.e. someone had to pick SOME standard, so they chose halves and wholes instead of odds and evens, for no reason in particular other than preference. --Jayron32 00:36, 11 June 2011 (UTC)

The spin quantum number, s, is related to the physical angular momentum via $L=\hbar {\sqrt {s(s+1)}}$. That $\hbar$ is generally introduced first from the energy relationships in quantum mechanics, but is also ubiquitous in momentum problems as well. You can't really change either L or $\hbar$ (aside from redefining the units on both) without screwing up lots of relationships between classical and quantum mechanics. What one could do is define $s'=2s$, such that $L={\hbar \over 2}{\sqrt {s'(s'+2)}}$, and other similar relationships. I don't see anything wrong with that other than that it adds an arbitrary 1/2 or 2 everywhere. Personally, I suspect that equations of the form $L=\hbar {\sqrt {s(s+1)}}$, with s taking integer or half-integer values was simply preferred due to an economy of notation, i.e. it felt more "natural". Dragons flight (talk) 01:23, 11 June 2011 (UTC)

If you rotate a particle with spin 1/2 about its axis, you have to rotate it 720° to get back to the initial state. Rotating only 360° leaves the wavefunction with the wrong phase. Particles with integer multiples of spin always return to their initial state when rotated through 360°. This is mentioned in passing (phrased differently) at Spin (physics)#Spin and rotations.--Srleffler (talk) 17:47, 13 June 2011 (UTC)

color perception different in each eye

I've always had a slight difference in color perception between my eyes. I know this is not uncommon, but I only have anecdotal evidence - other people confirming they too have the same experience. I would like to find something written by a medical authority (journal article, book, something!) that confirms this, and might provide some explanation. Thanks, Kingturtle = (talk) 20:43, 9 June 2011 (UTC)

Unfortunately no refs were uncovered last time this was discussed Wikipedia:Reference desk/Archives/Science/2010 December 19#Unusual Vision? but perhaps it is still of interest Nil Einne (talk) 20:56, 9 June 2011 (UTC)

In the extreme case, there are reports of unilateral colorblindness: PNAS article (PDF). The subject of that paper had normal color vision in one eye, and deuteranopia in the other.

The previous Ref Desk discussion touched on a much more likely explanation for most cases of differential perception of color: transient changes in sensory adaptation, blood flow, and pigment bleaching. TenOfAllTrades(talk) 23:09, 9 June 2011 (UTC)

Amongst astronomers, particularly amateurs today and professionals in former times when visual as opposed to photographic & digital observations are/were more common (and describing the exact visually perceived colours of stars was thought interesting and/or useful - see Stellar classification), it was a commonplace that most observers' two eyes differed detectably, and sometimes obviously, in their colour perceptions, just as they usually do in various other parameters of focus and abberation.

One factor affecting this is that as the eyes' lenses age, they absorb relatively more at the blue end of the spectrum, and an individual's two eyes sometimes show the effects of age differentially (resulting partly from differential light exposure if he/she has favoured one over the other at the eyepiece). This becomes very obvious if he/she develops cataracts and has one lens removed or replaced (with compensation provided by an external spectacle or internal plastic lens) before the other (as is usual for obvious reasons) - the contrast between the gradually changed eye and the suddenly restored one is very noticeable, as was once described to me by the eminent amateur astronomer Commander Henry Hatfield following such an operation.

In addition to the lenses, presumably the colour absorbtions in the cornea, aqueous and vitreous humours of each eye might also differ slightly. {The poster formerly known as 87.81.230.195} 90.201.110.206 (talk) 14:22, 10 June 2011 (UTC)

Since the colour is transient, the tints between eyes may "switch". ~AH1 ^(discuss!) 15:10, 11 June 2011 (UTC)

My vision seems tinted blue in my left eye and orange in my right. I wonder if this has a benefit for distinguishing similar shades? When I took the standard vision plate test as part of a lab experiment in Biology 102 I (the only one out of some 30 students) received a perfect score, which the proctor complained was statistically impossible. I always wondered if it was my eyes or if I guessed well.μηδείς (talk) 18:02, 11 June 2011 (UTC)

I also have reddish vision in one eye and bluish in the other (consistently), but there's nothing extraordinary about my vision. Ratzd'mishukribo (talk) 12:55, 12 June 2011 (UTC)

Well, I din't mean to imply my vision was exceptional, only that I had hypothesized that my perfect result using the full test might be due at least in part to the difference between the eyes. Here is the relevant article: Ishihara color test. I note thta the most dificult plate with the number "2" does appear noticeably different to each eye. μηδείς (talk) 19:01, 12 June 2011 (UTC)

Good cholesterol

What foods have good cholesterol but no bad cholesterol? --75.40.204.106 (talk) 20:56, 9 June 2011 (UTC)

When people talk about "good cholesterol" and "bad cholesterol", they usually are referring to HDL and LDL, respectively. These actually aren't different cholesterols (all cholesterol is the same chemical compound), but rather different cholesterol-carrying complexes in your bloodstream. Because HDL and LDL are really only found in blood, it doesn't make sense to talk about food having "good cholesterol" or "bad cholesterol". (Animal derived foods/fats do have cholesterol in them, but not as HDL or LDL.) Different foods, however, will have different effects on your HDL vs. LDL levels. High-density lipoprotein#Diet and lifestyle mentions eating omega-3 fatty acids and soluble fiber, and avoiding trans fatty acids as some dietary ways of increasing your HDL levels. Other places have other recommendations - if you are specifically concerned about your HDL levels, your best bet is to talk to a dietitian or doctor. -- 174.31.219.218 (talk) 23:04, 9 June 2011 (UTC)

Specific articles you might find interesting which are related to this topic are Monounsaturated fat and Olive oil. Vespine (talk) 04:20, 10 June 2011 (UTC)

Just one possibly applicable example: Avacado#Nutritional value. ~AH1 ^(discuss!) 15:08, 11 June 2011 (UTC)

Another thing to keep in mind is that there is a plenty of ongoing controversy regarding the interpretation of the studies which gave rise to the terms you are asking about. As far as I can tell, you're much better off replacing fatty foods with fruits and vegetables, lowering your caloric intake, avoiding red meats in favor of vegetable protein sources, fish or poultry, and getting more exercise than spending any time thinking about cholesterol types, unless a doctor reviewing your test results tells to do something specific about them. 76.254.22.47 (talk) 20:18, 13 June 2011 (UTC)