Wikipedia:Reference desk/Archives/Science/2006 July 23

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Proton Exchange Membrane

A proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy.i want to use it for my science project."A Fuel Cell Engine".i am not to invest much.so. i want to go for some homemade article ,cloth,organic membrane that could serve my purpose.please help me the constituents of protonexchange membrane and any easily available substitute for that.--Sameerdubey.sbp 01:22, 23 July 2006 (UTC)

What's with the image? DirkvdM 06:29, 23 July 2006 (UTC)

I removed the image, they probably just hit the insert image button incorrectly. --Fastfission 14:30, 23 July 2006 (UTC)

On the topic, a proton permeable membrane can't be replaced by anything you find in the house, unless you happen to have some perfluorinated sulphonic acid lying around. It's a really specific type of material for the job, so you'll have to order it from a manufacturer. See Nafion. --Eh-Steve 00:42, 24 July 2006 (UTC)

A fuel cell doesn't 'require' a PEM. What it does require is an ion-exchange layer; in other words, an electrolyte. I recall an old fuel cell project article where they used nickel screen electrodes covered with platinum-black. These were placed on either side of a layer of filter paper wetted with potassium hydroxide solution, and this sandwitch was bolted between two disks of plexiglas with some rubber gaskets. Holes in the plastic allowed H2 and O2 to be blown across the electrode screens. The author used this fuel cell to run a small "solar cell motor," a motor which will spin when powered with about half a volt. --Wjbeaty 08:25, 24 July 2006 (UTC)

How many birds would you have to tie to your body in order for them to carry you into the air?

I'm sure everyone has seen cartoons where one of the characters holds onto a couple of small birds and is carried aloft by them. As it passes 2am on this Saturday evening, I find myself pondering the reality of this situation. As I'm in the UK and for the sake of argument, we'll be using our most numerous bird, the European Starling. Hypothetically-speaking how many starlings would I need to place into small harnesses and tie to myself (as an approx. 220lb man) in order for them (assuming that they're all pulling in the same direction) to lift me clear of the ground? I'm assuming that data exists for how much weight a single starling can carry whilst flying... --Kurt Shaped Box 01:23, 23 July 2006 (UTC)

Well, this site says a golden eagle can carry up to 8 pounds, so that would be 28 birds. I couldn't find similar info on starlings, but I've heard that swallows can carry coconuts long distances. The problem is I don't know how you could tie more than 30 birds to the same thing without them getting hopelessly tangled. Perhaps you could just tie yourself to one starling, steal its credit card, and fly together in an airplane?--Anchoress 01:54, 23 July 2006 (UTC)

If you used golden eagles, they'd probably start fighting. --Kurt Shaped Box 02:19, 23 July 2006 (UTC)

You're a Brit, it's Sunday morning 2 am *, so what do you do? :)

It shouldn't be too difficult to design a rigging that won't get entangled. But its weight should also be considered. The smaller the birds, the more you need, the more rigging, the more weight, the more birds you need ... . The starling is tiny compared to an eagle, so you'd need quite a flock. Luckily they do come in flocks, unlike eagles. So that may solve the fighting problem.

* Not a Simon and Garfunkel album. DirkvdM 06:45, 23 July 2006 (UTC)

Some folks are attaching radio transmitters to birds (PDF format). The lighter the bird the larger relative load it can carry. There is also a tradeoff: number of birds vs. airspeed vs. range (until the bird tires). Let's be humane and not tax the poor birds to the limit: give a 80-gram starling 6.5 grams of extra load, just like the scientists do. At 100 kg you need 15,000 starlings. You should be able to load the bird more but at some point you'll get the ASPCA on your case and the birds will start to object. Weregerbil 17:05, 23 July 2006 (UTC)

In which case we would of course tell those USians to mind their own business and worry about human rights in their own country first. DirkvdM 18:04, 23 July 2006 (UTC)

You might have trouble getting that many starlings, mind you (though there's always eBay). Grutness...wha? 06:53, 24 July 2006 (UTC)

I think you need a fiberglas lattice structure, sort of like those huge tetrahedron kites built by Alexander Graham Bell at the turn of the century. Just crazy-glue the starlings' feet to the fiberglass rods. Or use resin and carbon fiber for a lighter structure of the same strength. Then scream at them or fire a pistol in order to panic the whole flock into taking off at the same time. Of course you could follow tradition, and suspend yourself below this device in a lawn chair.

Skin

How do you it when a small portion of the skin is torn off due to mechanical means, especially when you play basketball with bare-feet?--Jimmyng 02:10, 23 July 2006 (UTC)

I think you've missed a word out there. :) Me? I'd cut/pull off any flap of loose skin that'd been raised up by the injury, wash the wound, dab it with neat TCP and put a sticking plaster on it. Is that what you wanted to know? --Kurt Shaped Box 02:18, 23 July 2006 (UTC)

Do you mean either blister or abrasion? Both of those articles have pictures and some information. --ByeByeBaby 04:00, 24 July 2006 (UTC)

Hand held scanners

Dear Sir/Madam My question is a easy one I hope. Hand held retail scanners used in supermarkets for ordering when they are used , information is sent via laser signal via the unit to a box located on the wall of the store to be saved in a computer file. The signal sent from the hand held unit in the middle of the floor to the wall unit how to you block ? desperate to know cheers (email removed)

I assure you that handheld scanners don't use lasers to communicate. --mboverload@ 03:27, 23 July 2006 (UTC)

Take a look at this page, specifically the part where the radio frequency link is described as being in the 2.4Ghz band. That's just for one specific manufacturer of barcode scanners, others may be different. Now, why do you need to block the radio signal?

Deep cycle batteries

Could you please explain their make up as opposed to the normal L/A batteries. Also if a simple recharging circuit is available. Further any safety hazards existing that might not be encountered using L/A. Thanking all in anticipation.

Kevin Kelly, Victoria, Australia....

I've added a little info to the Lead-acid battery article, but more is needed. --Heron 09:50, 23 July 2006 (UTC)

Hurricane energy

I'm not sure if this has come up here before, but global warming causes the oceans to warm up, thus creating more and heavier hurricanes. These hurricanes represent an enormous amount of energy. Wouldn't it be possible to harvest this energy from the warmer oceans, thus taking away the necessity to burn fossil fuels and taking away the energy source for the hurricanes? DirkvdM 11:41, 23 July 2006 (UTC)

No expert by any means, but I believe that to take advantage of a source of energy you need an energy gradient. Just plain warm water isn't enough. Correct me please if I'm wrong. --Ginkgo100 ^{talk · contribs · e@} 17:51, 23 July 2006 (UTC)

I think the warm water contacting the cool air creates updrafts which power hurricanes. I think the problem with harvesting that energy for human use is that any "collector" or turbine array or whatever would have to be staggeringly huge because the energy density is very low. If you think of hurricanes as a collector, it spans thousands of square miles - I think until we come up with crazy nanobots that can reproduce and fly or something, there's little possibility of designing a harvester to take advantage of the diffuse energy over such a huge area. But that's just my opinion. --Bmk 19:35, 23 July 2006 (UTC)

Good point. Then again, the local energy of the wind is tremendous, so that seems to counter your argument. Does a hurricane maybe concentrate the energy, drawing it in from its surroundings? If so, maybe we should use that and nip a hurricane in the bud. Maybe position a generator in the eye (nice and peaceful there) and make a huge windmill around it. This might be done with light material like sails on strings, maybe something like paragliders. We'd have to move it in very quickly then (a problem with such a huge generator), unless we can create the hurricane ourselves where conditions are ripe, thus preventing it from forming elsewhere. DirkvdM 09:10, 24 July 2006 (UTC)

Assuming that only the surface of the ocean warms up while the deep water stays cool, then you can use Ocean thermal energy conversion. If there are no thermal gradients at all, then you needn't worry because we'll probably all be dead anyway. --Heron 17:13, 24 July 2006 (UTC)

A chameleon related question

If you placed a chameleon in a room full of mirrors what color would it turn to? will it change at all? will it be transparent?

It would not change color. See chameleon#change of color it changes by its emotions, not surroundings. Reywas92 16:21, 23 July 2006 (UTC)

I wasn't the one who asked the question, but let's get philosophical now. Let's say you had a real thing that could change color to adapt to its surroundings, and you put it in a room of mirrors: what color would it become? zafiroblue05 | Talk 21:21, 23 July 2006 (UTC)

Well it would be affected by what you put it in there with, and if the mirrors had any tint. Philc _T^E_C^I 21:35, 23 July 2006 (UTC)

Assuming it has a colour change reponse time, then it i likely to stay whatever colour it was when placed in the room. IE, if it was blue, then it would see lots of blue and stay blue. -- SGBailey 22:36, 23 July 2006 (UTC)

If it's color-detector was calibrated correctly, the lisard would see blue and remain blue. But if it was off by a bit, it would see blue and then turn slightly blue-green (or perhaps blue-violet.) Then it would see the changed color and try to produce a color that's even more changed. A similar thing happens when you aim a color video camera at a TV monitor displaying the picture from the same camera. If the camera's color-balance is adjusted wrong, the monitor shows a cycling color display or perhaps even a crawling bullseye of rainbow bands. If lizards can't do this, try experimenting with flatfish or octopi. --Wjbeaty 08:05, 24 July 2006 (UTC)

It would turn mirror-colured Adambrowne666 07:51, 24 July 2006 (UTC)

A different version of that: it would get caught in a feedback-loop, picking up the dominant colour, assuming that, thus making that colour more dominant, etc. DirkvdM 09:20, 24 July 2006 (UTC)

As to the original question, the chameleon would see itself, probably thinking it's another chameleon, and react to that. If it's male, it might get aggressive. But then I don't know much about the emotional mindset of chameleons. Ask a psychoameleonalist. DirkvdM 09:20, 24 July 2006 (UTC)

Well, it wouldn't see one chameleon, it would see an army of them. It'd be surrounded by infinite other chameleons, all of which looked exactly like it. That would surely have an effect. Now, to make it more interesting, what if it (like dolphins) could recognize itself in a mirror? It would surely discount its own image as an indication of its surroundings, and would try to imitate whatever the tint of the mirrors and the color balance of the lights added up to. Black Carrot 12:52, 24 July 2006 (UTC)

Assuming that the mirrors do not reflect light perfectly (and so absorb some light), it would see a slightly darker version of itself in the mirror, so it would turn black in the end. —AySz88\^-^ 17:21, 24 July 2006 (UTC)

Nice one, even superceding the transparent-version. Were it not that Reywas92 already pointed out it changes colour according to it's emotional state rahter than the surrounding colour. DirkvdM 19:50, 24 July 2006 (UTC)

It would all come down to whether it recognised its reflection as another chameleon (as opposed to not noticing it at all or being self aware). If it did (thereby relying on visual cues to determine conspecifics), then it may well change colour as part of a social interaction. This would be interesting, as the reflection would obviously change colour too, and the chameleon may, in turn, react to that as another social cue. However, in reality, animal behaviour tends to require more than just visual cues. I would imagine the chameleon would work out pretty quickly that its reflection was not another conspecific and ignore it after a short time. Rockpocket 23:44, 24 July 2006 (UTC)

Tube based instrument

I am thinking about how to build a tube based instument similar to the ones used by Blue Man Group. In particular, I am wondering about how to build a set of PVC pipes that can be struck to produce various pitches. However, I do not know how to work out the length of the pipe that is needed to generate a certain pitch. I have tried using the formula listed at Acoustic resonance, but I think that must the wrong equation for such a problem as I seem to get odd results. For example, if I want to work out the length for producing a pitch of 440hz, I get a result of 0.64 meters. Is this right? If not, can you please point me in the right direction? Thank you. N.B. The PVC tube will be open at both ends. --80.229.152.246 13:00, 23 July 2006 (UTC)

Never mind, I have found a PDF that explains the physics for instruments such as the one I am trying to build. If anyone is interested, the file can be viewed here [1] (Note: it is a PDF!) --80.229.152.246 16:04, 23 July 2006 (UTC)

Pollination in Plants

What is the chief pollinating agent for Salvia plant?

Which species? Bees, butterflies, and hummingbirds all pollinate various species of Salvia.--Curtis Clark 20:05, 23 July 2006 (UTC)

Arrangement of Flowers

What is the one word for "arrangement of flowers on a twig or stem" ?

Here is some information on leaves: Leaf#Arrangement_on_the_stem. I couldn't find a word specific to flowers. --Ginkgo100 ^{talk · contribs · e@} 17:58, 23 July 2006 (UTC)

You may also have some luck browing through this site. --Ginkgo100 ^{talk · contribs · e@} 18:01, 23 July 2006 (UTC)

Inflorescence. MeltBanana 01:49, 24 July 2006 (UTC)

Related term - the botanical term for the arrangement of leaves on a stem is phyllotaxis. Gandalf61 09:43, 24 July 2006 (UTC)

space/time

Are there any descriptions of space/time in a black hole and how it affected by gravity between the event horizon and the singuarity? Is it possible to think of space /time as a moebius strip?

Have you looked at the black hole article? Specifically, the features and theories section? Basically: no, a moebius strip would be an incorrect model since it would suggest that one could move through spacetime within the event horizon and return to one's original position, which would let one take the same path over and over again, avoiding the singularity (if I'm understanding your question correctly). In reality, once you're past the event horizon it appears that you will be unable to avoid eventually reaching the singularity. Digfarenough 18:43, 23 July 2006 (UTC)

The OP would surely like the two popular books by Geroch and Wald (both highly respected physicists who are leading experts in general relativity) listed in General_relativity_resources#Popular. Enjoy! ---CH 02:53, 24 July 2006 (UTC)

Atom

Please tell me what is an electron subshell. Can You please give me a diagram representing it.

Have a look at Electron shell first. Sum0 15:51, 23 July 2006 (UTC)

Try Atomic orbital too. --Yanwen 16:08, 23 July 2006 (UTC)

Bug Identification

Anyone have and idea what this bug is? This in Minneapolis, Minnesota. We have several of these every day throughout the house. I'm curious how to get rid of them—I assume by eliminating their food source. With legs and antennae they are about the size of a pinky nail and they crunch when you squish them. —Bradley 16:21, 23 July 2006 (UTC)

I can tell that it is a beetle, maybe a common household ant poison would work. Reywas92 16:24, 23 July 2006 (UTC)

It's some type of weevil. --Fastfission 19:38, 23 July 2006 (UTC)

skid marks

hi, having always had good anal hygiene, the other day i found really quite severe skid marks in my (white) boxer shorts - does any one know if there are factors at play other than just hygiene? like sweat or diet? should i just be over zealous in my wiping? thanks 201.32.236.160 16:35, 23 July 2006 (UTC)

That's you isn't it? You're half way around the world but I would recognise your writing anywhere. As for skid marks: probably a one-off. Both your hygiene and your diet are beyond reproach I know. If that's not you, apologies. But that sooooooooo is you. Take care. --The Gold Miner 22:21, 23 July 2006 (UTC)

Has there ever been a more enigmatic exchange on the Science reference desk? Rockpocket 06:14, 24 July 2006 (UTC)

I've noticed that when eating certain foods, I have to use excess toilet paper to do a good job. If my habit was to always use the same amount, then those foods would no doubt create skid marks. On the other hand, maybe this is more a question of anal leakage than hygiene practices? ;) Never eat greasy huge bags of Olestra-laden junk food.

• The summer heat appears to have an effect on my hygiene. I need more toilet paper than usual and sometimes that's still not enough.

Dry toilet paper seems to be rather ill-suited to the job many times. I purchase flushable wet wipes. And yes, I'm brave enough to sign my name after this comment. --Ginkgo100 ^{talk · contribs · e@} 18:17, 24 July 2006 (UTC)

cheers guys that helps alot. and goldminer, it is me! hooray!! 201.50.56.55 15:18, 25 July 2006 (UTC)

What's the deal with these wet so-called "wipes"? I have a couple of friends who swear by them but I always think you're just "spreading the love" when you want to be absorbing it. What's the advantage? --87.194.21.177 20:29, 24 July 2006 (UTC)

If you'll allow me to butt in...wet wipes work better for the same reason as a damp cloth or wet sponge is better for cleaning a table; liquids adhere better to absorbent materials. Note that a few drops of moisturizer on the TP can be a less expensive alternative to wet wipes, and also has a subsequent moisturizing effect. I suggest finishing with dry TP, as that will remove the excess moisture. StuRat 03:32, 27 July 2006 (UTC)

As to the original question, excess flatulence can cause that effect, often without the victim feeling anything is wrong. StuRat 03:32, 27 July 2006 (UTC)

As for this question being gross, I'm just glad nobody asked for a photo. :-) StuRat 03:32, 27 July 2006 (UTC)

Moon change

Please Help!! How does the motion of the moon change when the season changes?

....How would seasons - which is completely human - reach out into space and push the moon? Am I missing something here? --mboverload@ 20:49, 23 July 2006 (UTC)

What makes you think the moon's motion changes with the season? Seasons are cultural things, not astronomical ones. - Nunh-huh 20:50, 23 July 2006 (UTC)

Seasons are definitely astronomical in origin, and to call them "completely human" or "cultural" is incorrect (as someone living in the Northeast USA knows well!). But, as our article on seasons explains, they are driven by the relative locations of the Earth and the Sun, not the moon. Our article on the moon seems to indicate that there are some changes in its appearance or motion based on the season (i.e. it is highest in the Winter), though I don't know the astronomical reasons for this. --Fastfission 21:55, 23 July 2006 (UTC)

Seasons are discontinuous, astronomical motion is continous. Some areas of the world have "Spring, Summer, Fall, and Winter", and other areas have "Rainy and Dry". - Nunh-huh 22:16, 23 July 2006 (UTC)

Now you're just playing with definitions. Seasons correspond with the changes which take place depending on the different ways the earth gets sunlight owing to the fact that it is tilted. Humans all over the world, during all times of the earth's history, have recognized that they can be generalized into either four or two categories, depending on the latitude of the location. Many animals and plants run on this cycle as well. These are not arbitrary cultural things, these are real changes in the weather. Depending where you live, they can be pretty discontinuous (because it is not a simple thing of temperature we are talking about—temperature changes end up correlating with precipitation changes, for example). --Fastfission 01:13, 24 July 2006 (UTC)

Definitions are cultural. And the motion of the moon doesn't change when the seasons change... no matter how you define "season". - Nunh-huh 03:50, 24 July 2006 (UTC)

Beware of talking as if the entire Earth experiences a single season all at the same time. When it's winter in North America, it's summer in Australia. If the moon is "higher in winter," whose winter do you mean? So perhaps the OP should ask questions about changes over different months of the year, not changes over different seasons.--Wjbeaty 07:48, 24 July 2006 (UTC)

Beware of talking as if the angle of the moon above the horizon is the same over all points on the surface of the earth. If the moon is more northerly, the moon appears higher in the northern hemisphere, and lower in the southern hemisphere (at least if the observer is ~28° or more away from the equator). In December (northern hemisphere winter, southern hemisphere summer), the moon appears higher in the northern hemisphere, and lower in the southern hemisphere. In June (southern hemisphere winter, northern hemisphere summer), the moon appears higher in the southern hemisphere, and lower in the northern hemisphere. So, yes, the moon is higher in winter, regardless of what hemisphere you're in. Chuck 18:15, 28 July 2006 (UTC)

I live in Calfornia - we only have 1 season =D --mboverload@ 08:13, 24 July 2006 (UTC)

The question didn't specify a causality (although the word order suggests one). The Moon helps cause the tides and those may have some effect on the seasons. As for (the notion of) seasons being manmade, pinning the change down to one specific date is. But the cyclic change is definitely real, so the seasons are too. DirkvdM 09:33, 24 July 2006 (UTC)

According to Wet_moon, it does change with the season. Black Carrot 10:38, 24 July 2006 (UTC)

Yes, the way I understand it, the way the moon travels in the sky from the perspective of Earth changes over the year because the Moon's orbit tilts towards or away from you at night depending on where "night" is. Looking down on the solar system, "night" is always directed away from the sun - so if you imagine the orbit of the Moon in the same plane as that of the Earth and pick a point on the Earth (in the temperate zones, not near the North Pole or the equator), you become tilted towards the Moon's orbit at night during certain parts of the year and tilted towards it in the daytime during the opposite part (such that you're tilted away from it in the nighttime).

When your hemisphere is tilted towards the Sun (summer), you're tilted away from the Moon's orbit at night, so your Moon is lower. The opposite is true in the winter: you're tilted away from the Sun and towards the Moon's orbit in the nighttime.

This all is simplified since we've assumed the Moon and the Earth orbit in the same plane, but things get more complicated when you introduce the tilt of the Moon's orbit, which can add to or subtract from the apparent movement. I'm not sure of the specifics of that, though. —AySz88\^-^ 18:05, 24 July 2006 (UTC)

See The Moon's orbit#Inclination of the lunar orbit. It's about 5°, so it does have some effect, but a much smaller one than the 23.4° of the earth's axial tilt. Thus, a full moon at midnight in winter (local winter!) can appear anywhere from 37° to 57° higher in the sky than a full moon at midnight in summer seen from the same place. Chuck 21:08, 27 July 2006 (UTC)

Lights & Insects

How come many nocturnal insects are attracted to lights? there appears to be no benefits to them for this. It allows larger creatures to know where they are to eat them as well as the fact that many will be killed by the heat, I suppose the same applies to some types of fish which can also be attracted to lights. Ken 21:40, 23 July 2006 (UTC)

There are two attractions that I've heard of. First, there is heat. Insects that bite large warm-blooded animals for nourishment are attracted to heat sources. Then, there is light. For some reason, some insects fly towards the moon to orient themselves. Light sources disorient them and they end up flying around the light in circles. --Kainaw ^(talk) 22:25, 23 July 2006 (UTC)

Per Kainaw's comment, many insects use the Sun or the moon as references to navigate. If an insect flies at a constant angle relative to the Sun or moon, that insect will travel in a straight line. Unfortunately, for light sources that are much closer (lights), an insect flying at a constant angle relative to the light source will end up flying in a circle—they appear to be 'attracted' by the light. TenOfAllTrades(talk) 01:35, 24 July 2006 (UTC)

I've heard apocryphally that the insects are actually looking for darkness, and because the night seems darker next to the bright light (all things being relative), that's where they head. As I say, it's apocryphal - might be completely untrue Adambrowne666 03:57, 24 July 2006 (UTC)

Note that some insects would spiral in towards the bulb, a few would fly in circles, while some would spiral outwards. It depends on the flight angle the insect tried to maintain with respect to the light source. Of course we would only notice the ones which spiraled inwards. Another conjecture from a few years ago: some male moths are attracted to the infrared spectrum of pheremone vapors coming from female moths. A light bulb puts out plenty of infrared, and the male moths mistake this as a large female pheremone cloud and fly toward it. (I don't know if this idea ever became widely accepted.) --Wjbeaty 07:41, 24 July 2006 (UTC)

I wonder what, with all of the bug-zappers out there and the fact that a lot of bugs die from the heat of artificial light -- how long until bugs stop being attracted to it? -Quasipalm 00:23, 27 July 2006 (UTC)

It is just as easy to evolve far more offspring per insect to make up for the numbers killed by artificial light. --Kainaw ^(talk) 00:58, 27 July 2006 (UTC)