Wikipedia:Reference desk/Archives/Science/2007 July 21

Science desk
< July 20	<< Jun | July | Aug >>	July 22 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 21

Cough cough

Can any animal cough in its sleep? —Pengo 00:35, 21 July 2007 (UTC)

Yes - my dogs do. SteveBaker 01:01, 21 July 2007 (UTC)

So why don't humans if dogs do? —Pengo 15:16, 21 July 2007 (UTC)

My wife does.

So now we have anecdotal evidence on two species of animals. --Halcatalyst 21:23, 21 July 2007 (UTC)

Economics Question

Just a bit stuck. What possible circumstances could lead to there being a concave curve of production possibility, i.e., circumstances in which the opportunity cost of a product falls as its production increases, I am only looking in simple 2-product systems, but I cant quite grasp this. Philc 01:27, 21 July 2007 (UTC)

I'm no economist, but I'd assume any situation involving economies of scale could easily make at least part of the curve concave. —Ilmari Karonen (talk) 11:26, 21 July 2007 (UTC)

Agreed. Let's say you need a fweeble to make a fwap and need a fwizzle to male a fwaz, and both fweebles and fwizzles are quite expensive (same high price) if you buy them retail, but you can only buy them wholesale (same low price) if you buy 1000 at a time. Then let's say you can afford 1000 of one at the wholesale price, but not 1000 of both. In that case, you would do best to build only fwaps or fwazzes, not both. StuRat 00:39, 23 July 2007 (UTC)

Is this proof of seagull intelligence?

http://news.bbc.co.uk/1/hi/scotland/north_east/6907994.stm

The bird has a favourite flavour of Doritos, it knows what's in the bag and it knows how to open the bag. Any thoughts? --84.64.224.162 01:42, 21 July 2007 (UTC)

One of my dogs is fairly adept at opening food packaging without tearing it, never seen a bird do that though...My own thoughts, the bird probably figured it out by trial and error. It has to figure out what normal seagully foods to eat anyway, so they must have an ability to learn things of that nature. Someguy1221 01:57, 21 July 2007 (UTC)

Gulls clearly do have a concept of 'things inside other things' - they routinely rip open rubbish bags and discarded takeaway containers to see if there's anything edible inside (I once saw a gull open a margarine tub, have a look inside, then start pecking away at the scrapings that were left inside). So, here we have a gull demonstrating that it understands the concept of of 'things inside things inside things' - tasty corn treats inside a shiny plastic bag, inside that strange cave that the apes use. --Kurt Shaped Box 08:32, 21 July 2007 (UTC)

While seagulls may have a fairly good understanding of human packaging equaling food (they often scavenge garbage dumps), I recall, as a young boy I'd add, feeding a seagull a whole stick of butter. He/She ate it up in one gulp, now how intelligent is that? --Cody.Pope 10:14, 21 July 2007 (UTC)

Pretty smart, IMO. Get it down his neck quickly so he doesn't have to share it with the other gulls against his will. He can digest it later... :) --Kurt Shaped Box 10:37, 21 July 2007 (UTC)

Swallowing impossibly large objects is something many gulls do. I suppose that it is an adaptation to being a scavenger and eater of carrion. I have often seen gulls with entire sea stars jambed halfway down their throats walking around for hours and finally swallowing it. These are sea stars 4 or 5 inches in diameter! This is on the central coast of California and the gulls are usually the large Western Gulls.--Eriastrum 15:39, 21 July 2007 (UTC)

Were they actually in the bird's crop, or do you mean that the gull was walking around with the thing half-swallowed and hanging out of its mouth? Gulls can fit enormous amounts of food into their crops - sometimes it looks like they've swallowed a baseball whole. It's pretty normal for them - if they discover that an item of food is slightly too big or hard, they vomit it back up immediately. --Kurt Shaped Box 21:01, 21 July 2007 (UTC)

The gulls with the sea stars have initially 2 or 3 arms hanging out of their beaks. After an hour or more there is just a big lump in their throat. I've never actually timed this, but I've never seen that they vomit it up again. If you do an image search on google using keywords gull and starfish, you will see what I'm talking about.--Eriastrum 18:20, 22 July 2007 (UTC)

Interesting, thanks - I see what you mean. I'm quite surprised that the other gulls don't follow the one with the half-swallowed crustacean and try to forcibly yank the thing back up out of its throat... --Kurt Shaped Box 20:28, 22 July 2007 (UTC)

(re-indent)Remember that seastars are not delectable, crunchy, yummy crustaceans! They are spiny, hard echinoderms. So my guess is that it is not looked at by other gulls as especially desirable: it's hard to digest and obviously takes a considerable investment in time to fully swallow.--Eriastrum 22:31, 22 July 2007 (UTC)

So Kurt, would you please stop organizing the gulls into a master criminal conspiracy? Thank you. Dragons flight 22:35, 22 July 2007 (UTC)

Don't say that I didn't warn you. --Kurt Shaped Box 21:09, 23 July 2007 (UTC)

I don't think it's anything special. Lions know what's in the Zebra "bag." They selectively chase it down, open the "bag" and eat the goods. Seagulls eat shellfish which they drop from the air to open on the rocks below. this behavior seems pretty common. --Tbeatty 05:48, 24 July 2007 (UTC)

Ice hardness

Is water ice harder at -40 degrees than it is at -5 degrees, or is ice the same hardness no matter what? 68.231.151.161 01:47, 21 July 2007 (UTC)

I'm guessing but from experience in both refrigeration work and in winter environments, yes. (Also vehicle travel over frozen lakes would also attest to the fact that sustain warm periods can greatly reduce both the thickness and the hardness of ice.) Clem 03:03, 21 July 2007 (UTC)

Yes, the "hardness" of ice is inversely proportional to the temperature (i.e. harder ice at lower temps). Here is a ref that claims ice at 0°C is a 1.5 on the Mohs hardness scale, while its Mohs 6 at -70°C - about 50х harder. -- MarcoTolo 03:12, 21 July 2007 (UTC)

"Harder ice at lower temps" I believe; "inversely proportional", don't be ridiculous. Where do you see a ratio of 50 between the two temperatures you cite? --Anonymous, July 21, 07:22 (UTC).

Don't worry, anon, you can always concoct a scale on which it works (provided you ignore all other temperatures). Someguy1221 08:29, 21 July 2007 (UTC)

"Is inversely proportional to" is not the right language here; "varies inversely with" should be used instead. (As I understand it, hardness scales are ordinal scales, not ratio scales.) --72.78.102.77 11:26, 21 July 2007 (UTC)

Moh's is indeed an ordinal scale, its values are based on the hardness of various readily-available minerals, which is of great utility for mineralogical diagnosis, but less so for engineering purposes. Other hardness scales include the Vickers hardness scale. DuncanHill 15:49, 21 July 2007 (UTC)

Skaters report that skating at very cold temperatures is harder, supposedly because the thin film of water melted under the pressure of the blade doesn't melt when it's too cold. Gzuckier 15:46, 23 July 2007 (UTC)

Sky colour question

Within an atmosphere humans can breathe without difficulty, is it possible for the sky to be a colour besides blue (during the day)? If it can, which colours? I checked the Rayleigh scattering article, but the relevant information was written too technically for me to get anything out of. 142.59.225.165 04:46, 21 July 2007 (UTC)

Yes - it's possible. If the earth was orbiting a red giant like Betelgeuse or something - we wouldn't have a blue sky because there would be no blue light there in the first place - so it's clearly possible to have a different coloured sky. I suppose it's possible that the particles that are doing the scattering could be a dramatically different size on some different world - that would result in a differently coloured sky too...but that's a harder sell because dramatically bigger particles would probably just settle out leaving a black sky. Obviously the sky can be grey or white - it is right here on earth on cloudy days. Imagine a planet with permenant cloud cover and you have a white/grey sky. SteveBaker 05:26, 21 July 2007 (UTC)

feline table manners

Do cats other than housecats (F. silvestris catus) play with their prey? —Tamfang 07:47, 21 July 2007 (UTC)

Yes they do. What better way to learn about the behaviour/movements of your prey? —The preceding unsigned comment was added by Canis sylvaticus (talk • contribs) 08:24, 21 July 2007 (UTC)

I believe the cubs of most if not all felidae play with their prey — it's how they learn to hunt. The mother brings live prey to the cubs and lets them play with it, thereby showing them what to hunt and how to catch it. As Canis sylvaticus points out, I'd expect this to be common behavior for most at least moderately intelligent predators. The persistence of this behavior to adulthood in housecats may simply be a symptom of the neoteny associated with domestication, although I believe I've also heard of wild adult felines playing with prey when they're reasonably sated and in no hurry to kill and eat it. —Ilmari Karonen (talk) 11:41, 21 July 2007 (UTC)

Barium

Does Barium conduct sound? 168.209.97.34 12:05, 21 July 2007 (UTC)

other metals conduct sound, I'd imagine barium is no different - the only possibility for it's not conducting sound would be if it was a rubbery material.

Does anyone know if barium has a rubbery texture?83.100.251.27 12:15, 21 July 2007 (UTC)

http://www.allmeasures.com/Formulae/static/formulae/speedofsound/97.htm

Barium is not like rubber - it is a metal! GB 01:54, 23 July 2007 (UTC)

centrifugal pump

after priming why do we close the outlet valve of a centrifugal pump?59.92.74.83 12:05, 21 July 2007 (UTC)

Do we? If we do, it is to stop anything getting in or out. The purpose of priming a pump is to fill it with liquid, since attempting to pump air could damage it. If you have been instructed to close the outlet valve, this will presumably be to stop air getting into the pump while it is not in use.--Shantavira|^{feed me} 13:32, 21 July 2007 (UTC)

sorry, i did not put it clearly.After priming till the pressure reaches it's rated value , the outlet valve is kept closed and then opened slowly,why?

Mouth-movements of puppets or animations

I assume that the voices of animations like the Simpsons are recorded first, and then the animations are fitted to the voices. I wonder how they decide when to open and close the mouths? But this Supermarionation article, talking about Thunderbird puppets, says:

"The heads contained solenoid motors that created the synchronised mouth movements for dialogue and other functions. The voice synchronisation was achieved by using a specially designed audio filter which was actuated by the signal from the pre-recorded tapes of the voice actors; this filter would convert the signal into a series of pulses which then travelled down the wire to the solenoids controlling the puppet's lips, creating lip movements that were precisely synchronised with the dialogue."

What would the audio filter consist of, and what features in the sound signal did it pick up on? Thanks 80.0.110.193 13:27, 21 July 2007 (UTC)

There is certainly computer software out there that attempts to do at least a basic fit of lipsynch to sound - but generally you need an animator to come in and fix up errors at the end. The special features in the Thunderbird DVD set talks about the automatic gadget - but doesn't go into details. Since they only had to open and shut the mouth, they didn't have to have anything anywhere near as sophisticated as modern animators expect. They were doing this stuff in the early 1960's well before Thunderbirds - Stingray, Fireball XL5 and Supercar all seem to use the same techniques - but I don't think Four Feather Falls did (although the mouths were still moved by solenoids). That pre-dates most fancy modern electronics so it couldn't have been much more complex than a set of filters. It would be really interesting to know what they did in detail. SteveBaker 14:09, 21 July 2007 (UTC)

Indeed, I believe the Teddy Ruxpin doll also used a technology somewhat similar to this. Though the mouth motions themselves were recorded on the tape in a "hidden" track and not made on the fly, he probably represented the nascent stages of a consumer version of such technology. --Cody.Pope 14:33, 21 July 2007 (UTC)

I had a toy which also "spoke" but it was just in response to sound. You could make it "talk" by just speaking very close to its little microphone. It wasn't discerning — if you clapped your hands it would also "speak". It's probably a very simple sound-detecting circuit. --24.147.86.187 20:25, 22 July 2007 (UTC)

In a related field, Daleks have lights on their dome that flash with each syllable; I was surprised to learn that even today the lights are manually controlled, rather than by a volume-threshold switch. —Tamfang 17:18, 24 July 2007 (UTC)

Honeysuckle species

I'm looking for a species name on this picture: http://www.flickr.com/photos/skenmy/864121885/in/photostream/ - I know it's a Honeysuckle but I'm wondering which species of honeysuckle it is, any help would be much appreciated! --Skenmy^(t•c•n) 15:26, 21 July 2007 (UTC)

There are quite a few species and cultivars of Lonicera. Where did you take the photo? Europe, Britian, Australia, the U.S.? Was it growing in a garden or was it a native plant? What are the leaves like?--Eriastrum 15:33, 21 July 2007 (UTC)

The photo was taken in a British garden today, as far as I know it's a native as it's not in a pot. The leaves are dark green, opaque, oval shaped, few on the stalk. A picture of the same plant earlier in the year is here: http://www.flickr.com/photos/skenmy/488629643/in/set-72157594370422977/ --Skenmy^(t•c•n) 17:25, 21 July 2007 (UTC)

I'm certainly not familiar with Lonicera species native to Britain (I live in California), but I doubt it is a native species. It looks to me like the hybrid Lonicera X heckrottii, known as Goldflame Honeysuckle. It is commonly grown in the U.S. and in Europe, I believe. It is indeed a beautiful type of Honeysuckle. Try doing an image search on Google to see if it matches your plant.--Eriastrum 19:23, 21 July 2007 (UTC)

That looks perfect to me! Thanks guys! --Skenmy^(t•c•n) 21:55, 21 July 2007 (UTC)

colour of compounds

i have learnt something in chemistry which goes lke this: the colour of a compound is the complementary of the wavelength of photon absorbed, when an electron jumps to a higher energy state. but in equilibrium, the no of electrons jumping up have to be equal to the no of electrons falling back, emitting the same wavelength photon(corresponding to the energy difference), so shouldnt the net result be white always? —Preceding unsigned comment added by 59.180.4.84 (talk • contribs)

Yes, but not all electrons will "fall back" through the same path. Some will jump up and then down, but some will jump up, change vibrational states, change multiplicity, and/or release the energy at other wavelengths or with no radiation at all. I am looking for a diagram on Wikipedia that is printed in almost every chemistry textbook, but I can't find it. I used a version I made in a report once and may post it, although I'm afraid it may not be 100% completely right. It would certainly help spruce up the articles on phosphorescence, fluorescence, intersystem crossing, etc, which look like they could use some help. --Bennybp 18:16, 21 July 2007 (UTC)

I posted the diagram on my webpage here. I think it needs a little touching up and updating before adding to Wikipedia, but the general ideas are there. Just a note, ISC stands for intersystem crossing, IC stands for internal conversion. The "up then down" you are thinking of is fluorescence I believe. Let me know if you have any more questions :) --Bennybp 18:33, 21 July 2007 (UTC)

Note that color of compounds involves human perception. Human eyes/brains see color, but they cannot see frequency. For example, a compound which passes a narrow band in the yellow frequencies would look just like a compound which passes two narrow bands; one in red, one in green. And humans have trouble seeing narrow absorption bands, while such bands are glaringly obvious on a specrum graph. If you don't want to involve human eyes and psychophysics, then you want to concentrate on the spectrum of a compound, and not on it's perceived color. --Wjbeaty 14:52, 22 July 2007 (UTC)

thanks. so the electron follows an alternate route back which loses energy at wavelengths which the human eye cannot percieve, to give the compound a specific colour. is that right? 59.180.19.231 17:59, 22 July 2007 (UTC)

Also, if a photon is absorbed and then emitted even at the same wavelength, it may be emitted in a different direction than the incoming photon. As a result, one can stand at a right-angle to a focused light-source on an object and see certain colors emitted (and those photons are hence not propagated in the incident direction). This is in addition to those photons being color-shifted due to various phenomema that occur between absorption and emission. See Raman scattering. DMacks 17:08, 23 July 2007 (UTC)

DNA and its being double-stranded

As I understand it, only one strand of the DNA can have functional genomic function? (Either the 5' strand or 3' strand.) I'm not saying that only 3' or 5' strand exclusively in the entire DNA can have all the genes. Rather, when a specific sequence on a strand contains a gene, the complement strand can't contain a gene. Am I getting all of the above correct?128.163.171.68 20:27, 21 July 2007 (UTC)

More or less. There is no "3' strand" and "5' strand", these are the names of the termini of each strand, named after the deoxyribose carbon molecule at the end. Genes may only be read from the 5' to 3' direction on either strand, but where a coding sequence is found on one strand, the other (complementary) strand is nonsense. So there are genes on both strands, but not at the same time. To form a functional protein from antisense RNA is as probable as reading a poem backwards and finding it makes perfect sense in another language. Protein function is far too complex for that to happen. Bendž|Ť 21:22, 21 July 2007 (UTC)

Should be noted that when the coding strand contains one gene the complementary strand can contain a different gene. This is quite evident in prokaryotes where there is a very high gene density.PvT 21:36, 21 July 2007 (UTC)

Believe it or not, the backwards poem happens more often than you'd think. Every genome so far studied has several: [1]. In addition, there are quite a few genes that partially or completely overlap other genes in the same direction, but frameshifted. (To continue the poem analogy, it's like moving every space in the poem one letter to the right and still getting a poem that makes sense.) They're particularly common in organisms like viruses where there's a strong evolutionary pressure to keep the total amount of genetic material carried compact. TenOfAllTrades(talk) 22:03, 21 July 2007 (UTC)

One example of overlapping genes on opposite strands is the mammalian melanin concentrating hormone gene (MCH) and the antisense-RNA-overlapping-MCH gene (AROM). [2]

Wow, I didn't know that. I guess the flexibilities of the genetic code make this possible; the poem is written in hieroglyphics. Bendž|Ť 07:53, 22 July 2007 (UTC)

I have a vague recollection from when I was in grad school of them finding some virus where both strands of the DNA were coded, so as to give the minimum possible size chromosome. Gzuckier 15:48, 23 July 2007 (UTC)

Viruses are excellent examples of effeiciently packed genomes--many viral genes include sections that are antisense to other genes. — Scientizzle 21:39, 23 July 2007 (UTC)

Thanks for the answers. Any official terms for this phenomenon so I can look it up? 128.163.245.26 10:03, 24 July 2007 (UTC)(question poster)

ethanol production

≥Can Distillers yeast be frozen to remove the ethanol and reactivated? If so what are the temperature limits. —The preceding unsigned comment was added by 207.199.249.186 (talk • contribs) 21:11, 21 July 2007 (UTC)

Freezing is deadly to most organisms, and I would expect yeast to be among them, unless we have evidence to the contrary. StuRat 14:46, 22 July 2007 (UTC)

That's not really true. Cold in itself doesn't really destroy cells the way heat does — any cellular damage from freezing is mostly caused by the uncontrolled formation of ice crystals, and there are many ways to prevent that from happening. In fact, quite a lot of organisms, even multicellular ones, can survive being cooled below the freezing point of water, in some form or other — if they didn't, things would be pretty barren here come spring. Even for organisms that can't do so normally, appropriate freezing techniques can allow succesful revival after freezing. As for yeast, I'm not sure about the fresh kind, but dry yeast can certainly revive and start growing happily after being frozen, thawed and rehydrated. (You could also try Googling for freezing yeast.) —Ilmari Karonen (talk) 16:45, 22 July 2007 (UTC)

You've interpreted frozen to mean "below the freezing point of water", while I took it to mean "has become a solid", which is the more usual definition, I believe. StuRat 00:13, 23 July 2007 (UTC)

For organic materials, "has become a solid" doesn't seem a very useful definition of frozen. For example, isn't the fresh live baker's yeast usually sold in blocks already pretty solid to begin with? As for mixing the yeast in water and freezing the water solid, this doesn't really imply anything about the state of the water inside the yeast cells, which is what matters for their survival.

Re-reading the original question, it does strike me that it may be somewhat misguided to begin with. What the original poster apparently wants is to separate the yeast from the ethanol it produces; while this could be done by freezing the water and the yeast and draining away the ethanol, it would seem more convenient to simply filter out the yeast and then separate the water and the ethanol any way you like (such as by distillation). —Ilmari Karonen (talk) 13:54, 23 July 2007 (UTC)

Since yeast multiplies rapidy, you can take a small sample to keep alive, and process the rest by freezing. GB 02:45, 23 July 2007 (UTC)

Not sure how you intend to separate the alcohol and water by freezing. ?? Gzuckier 15:49, 23 July 2007 (UTC)

Alcohol and water are seperated by freezing in the process known as Freeze distillation or Fractional freezing. DuncanHill 00:11, 24 July 2007 (UTC)