Wikipedia:Reference desk/Archives/Science/2008 September 29

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September 29

Oceanic Mammalian Question

I reckon that whales, seals, and dolphins have larger lungs than humans that allow them to dive for such long periods of time. However, they also have larger bodies than humans! Do they also have more efficient lungs which better oxygenate their bloodstream? Is that even a real thing?

Thanks! —Preceding unsigned comment added by 76.24.15.197 (talk) 02:33, 29 September 2008 (UTC)

Our article on whales simply states: "Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in oxygen." The dolphin article doesn't provide any more insight. -- kainaw™ 02:45, 29 September 2008 (UTC)

Dolphins aren't much bigger than humans - their lungs are probably no bigger. I suspect (without more knowledge) that their metabolism is designed such as to allow the animal to continue to function with much lower blood-oxygen levels than humans. But are dolphins really much better at this than humans? Tom Sietas can hold his breath underwater for over 15 minutes (although he cheats a bit by pre-breathing pure oxygen first - his "fair" record is a little over 10 minutes). One assumes that most humans could come close to that ability if they trained to do it since birth as dolphins are. Bottlenosed dolphins can only hold their breath for 30 minutes. So the disparity isn't as great as you might think. SteveBaker (talk) 02:57, 29 September 2008 (UTC)

I could be wrong, but don't most of the records just involve people holding their breath underwater for long periods of time? They don't involve people actually swimming or otherwise doing stuff underwater for that time and I'm not convinced the record will be as long if it did. With cetaceans though I think they maintain mostly the same level of cognitive/mental and physical functioning throughout the time of holding their breath Nil Einne (talk) 08:52, 29 September 2008 (UTC)

This is probably closest to what we want [1] 244 metres doesn't seem a great distance to me. Since time isn't a concern, it isn't mentioned but if we take double the world record World record progression 200 metres breaststroke that's only about 5 minutes. And even if the time is more then that, it would suggest the person is far from at optimal physical activity level Nil Einne (talk) 09:00, 29 September 2008 (UTC)

Actually the current record is 248m [2]. Also, I just remembered I forgot that was with fins, so they naturally should be faster then the world record set by someone with pseudofins so 5 minutes is definitely probably quite generous. Nil Einne (talk) 09:10, 29 September 2008 (UTC)

The discussion seems to be in the Cetacea article instead. It mentions higher myoglobin concentrations in muscle; myoglobin retaining oxygen better than haemoglobin. And argues that in addition, having more muscle mass (ie from larger body size) increases the oxygen storage capability because muscle stores oxygen, and because larger animals have slower metabolic rates.WikiJedits (talk) 12:54, 29 September 2008 (UTC)

Sperm_Whale#Diving_and_breathing has a bit, too, including some interesting stuff about bone-pitting due to decompression (diving). --Sean 13:57, 29 September 2008 (UTC)

One of the big differences between humans and whales is how much air is exchanged with each breath. A human will only exchange about 10% of the air in their lungs with a deep breath, while a whale will exchange almost 90%. --Carnildo (talk) 20:34, 30 September 2008 (UTC)

MATLAB question

I want to take an arbitrary length array (say, for example, like [1 2 3 4 5]) and convert that into an anonymous function with a function.

So I have a function called any_polynomial which will take an argument of such an array and return the anonymous function, which can be assigned a function handle. This is for an assignment, so I only really want a hint or two. The assignment tells us to use polyval, which is quite useless for this in my opinion, as then the anonymous function will be something like "@(x) polyval(input_array,x)". Thoughts? --M1ss1ontomars2k4 (talk) 03:56, 29 September 2008 (UTC)

I'm not sure if this is an appropriate question for the science reference desk (it being about Matlab and being homework), but I'll try to help a bit. First of all, I wonder if you haven't misinterpreted the assignment - the function polyval(p,x) evaluates a polynomial at x that has the values p(n) as its nth coefficient. I'm not sure what you mean when you say you want to "convert an array into an anonymous function". I guess what I'm saying is...the anonymous function you have described certainly does something, but it's not clear to me why you don't like it. Could you be more specific about what you want the anonymous function to do? --Bmk (talk) 04:58, 29 September 2008 (UTC)

Well, the science ref desk has "engineering" as one of the subjects that fits under it, and this class is taught by the MechE department. It doesn't have much to do with math or actual computer science, so I thought I'd find the best help here. At any rate, the questions asks us to basically take [1 2 3 4 5] and get @(x) x.^4 + 2.*x.^3 + 3.*x.^2 + 4.*x + 5. That's how I interpreted it; it actually asks for the polynomial to be returned, which I assumed meant the actual polynomial. At any rate, I've largely concluded that it would be really not worth the effort or the last whatever percentage of my grade to come up with such a ridiculous bit of code that has almost no real practical usage under any circumstances. Also, the next part of the assignment asks us to use our new function with fzero to find roots, so I explained in the comments for my code that, while the polynomial is not returned, something just as good is--it's a function that represents the polynomial and can be used with fzero. Thanks anyway! --M1ss1ontomars2k4 (talk) 06:01, 29 September 2008 (UTC)

Flatbed scanner covers

Why do flatbed scanners have covers? I have tried scanning with the cover open and with the cover closed, and it seems to make little or no difference in the quality of the scans, even when the document does not cover the entire scanning surface. —Lowellian (reply) 08:50, 29 September 2008 (UTC)

To reduce the light bouncing out and being annoying. If you're sat in a room scanning a document while working on something on your pc the last thing I could imagine wanting is a overly-bright light moving across the room from my scanner. I would have thought it also could make a difference with some documents scanning-quality but if for nothing else I would suspect it is just because the light is quite strong and it's better to try cancel it out with a simple sheet of plastic rather. Oh and it probably acts as a useful guard against damage occuring to the glass plate when the scanner isn't in use. 194.221.133.226 (talk) 08:53, 29 September 2008 (UTC)

On the contrary, I actually find it more annoying to close the cover since by not bothering with opening-and-reclosing the cover between each document, I can scan considerably faster and with more ease. However, the instruction manual seems to stress over and over again how important it is to close the cover. That's what I don't understand: is it somehow harmful in some way not to close the cover? If it isn't, why does the instruction manual stress closing the cover so much? —Lowellian (reply) 09:04, 29 September 2008 (UTC)

Aren't they at least partially there to help squash the document if it isn't flat, e.g. a book? Admitedly most dekstop scanner ones are so flimsy as to be almost worthless in that regard although they may allow you to apply more even pressure if you are holding it down. Also, I think there may be some difference if your scanning a thin single page and the scanner light is very bright Nil Einne (talk) 09:15, 29 September 2008 (UTC)

At least older scanners and copiers would copy any part of the surface not covered by the original or the cover in black, thus wasting a lot of toner. Some of the more modern ones may do some software-based cropping, but manuals change slowly (AFAIK, Apple still sends out battery care instructions that made sense three battery technologies ago). I'd also expect that there is some workplace safety issue with the bright light. It probably does not matter for people who only scan a few pages, but imagine someone doing nothing but scanning day in and day out. --Stephan Schulz (talk) 09:28, 29 September 2008 (UTC)

That doesn't happen for me. The scanner and software I'm using always properly detects the edge of the paper, with or without the cover.

But wait. "Workplace safety issue"? So is the light dangerous in any way, or is it just ordinary light? —Lowellian (reply) 19:19, 29 September 2008 (UTC)

—Lowellian (reply) 19:21, 29 September 2008 (UTC)

As mentioned, the cover holds the paper flat. Also, the cover helps with color/contrast by providing a nice white background. Without the cover closed, everything around the paper is black. Since the software is designed to look for white around the edges, finding black will cause differences in color/contrast. Newer scanners avoid this problem by having a white strip inside the machine that you don't see. I, also, have found it annoying to use the cover before. When I shut it, papers/photos move around. So, I use a small book to hold things down on the scanner. -- kainaw™ 11:13, 29 September 2008 (UTC)

A lot of people are paranoid about that light. Against all logic many people think it's some sort of dangerous radiation and insist on keeping the cover down. ("Better safe than sorry!") I imagine a scanner without a cover would not sell very well because it would make some people so nervous. Even if they knew intellectually that it was an irrational fear they'd find a reason to buy some other scanner.

Also, as everyone else has said, the light can be annoying in a dimly lit room, If you're standing there waiting for it to finish it can dazzle you and irritate your eyes, and the cover keeps things flat and stops them from blowing away if you're next to an AC vent. And finally it stops dust from accumulating on the glass while the scanner is not in use. APL (talk) 13:17, 29 September 2008 (UTC)

See Snow blindness and Over-illumination about having too much light. I had a look at the Interactive whiteboard article because they should have warnings attached about looking at the light, having them too bright and about problems with the eye no adjusting properly if the glare is peripheral giving rise to a temporary tunnel vision or even snow blindness if there is too much UV light. Dmcq (talk) 14:32, 29 September 2008 (UTC)

Copying thin paper with the lid open will make the copy/scan dark, because the light goes through the paper instead of bouncing back into the machine. I belive it will also worsen the problem of the text on the top side of the paper shining through. You might test this with a page from a newspaper. EverGreg (talk) 18:20, 29 September 2008 (UTC)

I have personal experience of someone using a scanner with the cover up, and having the person at the desk next to them get such a surprise from the sudden bright light that they poured hot coffee on their lap. There's a health-and-safety issue for you. :-) ~ mazca ^{t | c} 08:32, 30 September 2008 (UTC)

When blue planet?

Did we all think the planet earth was green until astronauts saw it from outer space? And if so, when did we realise the truth? Alan Rothwell (talk) 11:33, 29 September 2008 (UTC)

We knew that water was blueish and that the sky was blue for a long time before going into space, so it seems pretty reasonable one might have assumed "looks blue from there too". But the second part of your question is confusing: "if so" (i.e., "we all think the planet earth was green until astronauts saw it from outer space") then the answer is right there (when "astronauts saw it from outer space"). DMacks (talk) 13:13, 29 September 2008 (UTC)

Thank you, DMacks. That'll do. Regards Alan Rothwell (talk) 15:45, 29 September 2008 (UTC)

(Of course it wasn't astronauts who first saw the earth from outer space - it was people looking at photos from spy satellites. Before that, high altitude balloons and aircraft could tell that the planet would look pretty much blue from above.)

But anyway: for final proof, if you look back at colored atlasses and globes dating back hundreds of years, they always carefully painted the oceans blue - so I think it's pretty clear we expected them to look that way from a distance. Here, for example is an 1891 globe - and it's blue. SteveBaker (talk) 18:44, 29 September 2008 (UTC)

A child I know heard the rhyme "In 14 hundred and 92, Columbus sailed the ocean blue," and asked "What color was it before that?" Edison (talk) 19:36, 29 September 2008 (UTC)

The OP is quire correct: pre-1957, the general public thought the planet was green. This is clear from reading old science fiction, including thst written by the most scientifically literate writers. "The Green Hills of Earth," by Robert Hienlien, is an example. If nayone had asked one of those guys to analyze the actual color, most of them would have figured it out, but nobody asked. All of us who can remember the first color piictures from space can remember being startled by the fact that our planet is blue. -68.110.230.28 (talk) 02:02, 30 September 2008 (UTC)

That's not true! I vividly recall seeing the first color photos from orbit - and I don't recall anyone being in the slightest bit surprised. I don't think Heilein's title says much - he says the hills are green (which they pretty much are) - but he doesn't say that the entire planet is green - or indeed that his observation of green hills is from orbit. I repeat my earlier "proof" that globes dating back MANY hundreds of years have always had the oceans painted blue...why would they do that if they thought the world would look green from that perspective? SteveBaker (talk) 02:44, 30 September 2008 (UTC)

Please see this page. The first color image was apparently made in 1967. -Arch dude (talk) 04:43, 30 September 2008 (UTC)

I strongly disagree with the claim that people thought the earth was green before the space age. They certainly knew that most of the earth was ocean, and that oceans were blue. They also knew that deserts were not green. Note that Heinlein only referred to green HILLS. The blueness of pictures from space was startling only to the uninformed. Edison (talk) 05:31, 30 September 2008 (UTC)

Star Trek and plenty of other productions had shots of Earth (or Earthlike planets) seen from the Big Black; did they have green oceans? (I didn't have color television until 1981, so have no clear memory on this point.) The strikingly odd thing is that they had no clouds. —Tamfang (talk) 05:33, 30 September 2008 (UTC)

Star Trek started in 1966 - we had color photos from orbit in the late-1950's. I don't know which episode showed the earth from orbit - I'm trying to recall one that did and beginning to suspect that none of them ever did. But I'm not a committed Trekky. The decision to leave out the clouds may well have been an artistic choice. If you can't see the outlines of the continents clearly then you don't know it's earth that they're visiting...and that's a plot point that might well have overturned (ehem) Star Treks' typical "careful adherence to accurate science". :-) SteveBaker (talk) 11:24, 30 September 2008 (UTC)

I can't think of any episodes that did, but some of the films might of done. Films 1 and 4 certainly involved things in Earth orbit. --Tango (talk) 15:10, 3 October 2008 (UTC)

It would have to be "Assignment Earth"; but did I mention earthlike planets and other productions? —Tamfang (talk) 07:46, 4 October 2008 (UTC)

I seem to remember a a C.S. Lewis novel (That Hideous Strength?) in which space looks green when you go up in a rocketship. ike9898 (talk) 15:23, 1 October 2008 (UTC)

Seems to me a better thing to look at would be old coloured globes. For example Mapparium has blue oceans and while the colour of land is not intended to represent the real colour of land, I presume the oceans were made blue because that's the colour the artist felt best represents them. Image:Babsonglobe2008.jpg also has blue oceans and while the it was refurbished in Babson College#Babson Globe in 1993, I strongly suspect more note would have been made if the oceans had been repainted blue and had been green. True it was finished iin 1955 by which time perhaps there were colour photos from space but I strongly suspect it was designed before that and the artist didn't suddenly panic when he? saw photos from space with blue oceans. There's also The Daily News Globe [3]. I believed it was constructed in the 1930s [4] and while I presume it has been repainted several times, I see no evidence it ever had green oceans (although it did rotate the wrong way according to the earlier link). Even the Johannes Schöner globe appears to have blue oceans (albeit a bit light but that might be a matter of fading colours of the availability of pigments). All in all, I don't see any reason to presume that most people would make globes (and of course maps) with blue oceans but everyone thought when you went to space the earth would look green Nil Einne (talk) 12:37, 5 October 2008 (UTC)

Interesting note, related to Ike's comment: I'm reading We (written c. 1920), in which the author speaks of "the blue, silent, interplanetary space". Nyttend (talk) 14:18, 6 October 2008 (UTC)

Long time later I realise SB already said the same thing earlier and I didn't notice, oops Nil Einne (talk) 10:19, 25 December 2009 (UTC)

Digestive System

How does the Digestive system help the circulatory system function properly —Preceding unsigned comment added by 136.229.5.40 (talk) 12:11, 29 September 2008 (UTC)

Sounds like a homework question to me. Ask somewhere else. PS: the heart needs energy to function, so where does the energy come from? Food. :) 31306D696E6E69636B6D (talk) 13:25, 29 September 2008 (UTC)

Well, yes, but it sounds like a really bad homework question. Everyone knows that the rest of the body is just the liver's way of making other livers. - Nunh-huh 13:47, 29 September 2008 (UTC)

this is no place for bilious comments --Scray (talk) 02:59, 30 September 2008 (UTC)

DACs in CD players

I have just bought a new CD player with A delta-sigma converter that uses a switched capacitor DAC. These are sometimes called bit stream or 1 bit DACs.

I found it sounds quite different (warmer, richer etc) from my previous CD player which used the TDA 1514 DAC chip and associated digital filter chip. Can anyone point me to articles discussing why the two types of DAC sound so different?--GreenSpigot (talk) 13:46, 29 September 2008 (UTC)

May I suggest a double blind test to establish that the effect is real? If it is, I would expect differences in the quality and calibration of the pre-amp to affect the the sound much more than the DAC. Can you ensure that all other variables are eliminated? --Stephan Schulz (talk) 14:46, 29 September 2008 (UTC)

I dont think I need to do a DBT to know that the difference is remarkably obvious to my ears. I was totally surprised as I was not expecting to hear any difference whatsoever. So what could the possible reasons be for the unmistakable difference?--GreenSpigot (talk) 17:03, 29 September 2008 (UTC)

You'd be surprised at how easier it is for people to hear a difference that isn't there, even whey they aren't outwardly expecting it. Nil Einne (talk) 18:12, 29 September 2008 (UTC)

Unless one or the other was malfunctioning, there should not be any obvious difference, since it is such high fidelity, with wide frequency response, low noise level, wide dynamic range, and freedom from clicks, rumble, scratches, hiss, wow and flutter which plagued stereo listeners in the analog age. Edison (talk) 19:38, 29 September 2008 (UTC)

I agree. There is a deep problem with serious audiophiles. In the days of analog equipment, they had a lot of fun debating the pro's and cons of various turntables, amps, etc - tricking out turntables with different cartridges, endlessly arguing over the fidelity of vacuum tubes versus transistors. Then we got digital equipment, and now, even a $20 CD player can produce audio significantly better than the human ear can resolve. This has resulted in a lot of people with no hobby. The unfortunate consequence is people spending hundreds of dollars on gold plated nitrogen-injected digital audio cables(!) and other ridiculous junk. This reviewer says that his $300 (!) digital audio cable "The brightness is no longer a problem and now I get the chance to hear the seperation of the instruments and the kind of bass that is tight as a sludge hammer." -- well, I'm surprised he's looking for his audio to sound like a sludge hammer - but for 100% certain, a DIGITAL signal isn't going to sound any different whatever on a $1 cable or on a $300 cable...that's the entire point of digital signals. If someone can convince themselves that a cable (of all things) could possibly make any difference whatever (let alone a $300 difference!) then I'm equally sure that our OP isn't really hearing a difference. An honest double-blind test is undoubtedly called for. SteveBaker (talk) 23:10, 29 September 2008 (UTC)

Ok thanks for the opinion all. Now can someone point me to a site that discusses why there might be a difference?--GreenSpigot (talk) 13:43, 30 September 2008 (UTC)

[5] says a "16-bit/44.1-kHz CD standard" bottleneck is not detectable in double blind testing, compared to higher resolution players. See also High fidelity. Edison (talk) 18:55, 30 September 2008 (UTC)

I think we already have. As remarked above, presuming there is really a difference, it's probably not in the DAC but in something else other the DAC component. You haven't explained whether everything else is the same in your test setup. It seems rather unlikely to me it would be given that it's unlikely everything after the DAC is the same. Even presuming the speakers are the same, there's still the entire analog pathway likely including amplifiers and perhaps equalisers of the CD player you haven't ruled out. And these would be rather difficult to rule out, you'd probably need to modify the player such that you take the signal directly from the DAC output of each player and feed it into a seperate amplifier. To put it a different way, let's say I compare a piece of KFC chicken to a piece of chicken from a gourmet restaurant which is organically raised. It would be silly of me to ask from this "why does organically grown chicken taste better" Nil Einne (talk) 17:44, 2 October 2008 (UTC)

Everything else is exactly the same. I just unplugged my old CD player and inserted the new one. Believe me, Im as skeptical as the next man, but I can definitely hear a (positive) difference! BTW Im a musician also and used to using my ears in a very critical manner.--GreenSpigot (talk) 00:09, 3 October 2008 (UTC)

As I've already said, it's not possible everything else is the same unless you're really trying to convince me that your CD player really feeds the analog output of the DAC directly to your hifi system? which I highly doubt. Both systems almost definitely do some processing to the analog signal before it is output to your hifi system. (I presume your are outputting to your hifi system and not trying to claim everything is the same when you are outputting directly from the CD player to speakers). Heck for all we know, either player may process the signal in the digital stage as well. Have you ruled this out? Nil Einne (talk) 12:43, 5 October 2008 (UTC)

I know on my PS3, switching from Bitstream to LinearPCM output makes music sounds slightly *louder* when using the optical out. Overall loudness can change your perception how the music sounds. (I know in my home theater DTS always sounds "better" than Dolby Digital only because it's louder) How is the signal getting out of your CD player? If it's analog, I'd have a hard time believing there's any difference.

Is a 10% reduction of emissions reasonable?

In Australia, the Federal government's top climate adviser, Ross Garnaut, says that in 2020 a reduction of pollution levels by 10% of 2000 levels is a realistic target. WWF Australia chief executive, Greg Bourne, says that a 20% reduction is better.

http://news.smh.com.au/national/garnaut-wants-10-emissions-cut-by-2020-20080905-4a2d.html

I'm confused. I know little about global warming other than it is real. Does anybody have an argument or some short sharp facts to back up the claim that a larger than 10% reduction in pollution would be better for Australia?

What's a reasonable, realistic, economically responsible target to reduce pollution levels to?

Similarly to the above question, what about targets for the rest of the world? ExitRight (talk) 14:52, 29 September 2008 (UTC)

You may find Kyoto Protocol interesting. The UK has set a target of 60% reduction from 1990 levels by 2050 and seems to be on track, so large reductions are possible. Whether Australia can manage a 20% reduction would depend on what's happened in the last 8 years since we're nearly half way through the given time period. --Tango (talk) 14:59, 29 September 2008 (UTC)

In terms of what's beneficial - a 99.99% reduction would be beneficial from the point of view of avoiding global warming - but the larger the reduction you make, the more it costs the country to do it. Hence there is a balance between benefits to the atmosphere and detriments to the economy. Precisely where that balance is turns out to be almost impossible to calculate. Precisely how much (in monetary terms) is the extinction of the polar bear worth? We can't put a number on that. We can say how much it's going to cost to rebuild cities that get flooded by rising sea levels - and perhaps we can nail an estimate on the cost of crop losses...but because we don't know how much sea level rise there will be - we can't know. The cost to the economy also depends on how you make that reduction. If you buy technology that's already available, it costs some amount - if you throw a lot of cash into research and your country becomes not only a consumer of anti-global-warming technology but also a PRODUCER of it - then it's possible that tougher standards might actually IMPROVE the state of your economy. If you make CO2 reductions by cutting fuel consumption - you'll save money - if you do it by building damned great "carbon sequestration" plants and continue to burn carbon-based fuels - then it's going to cost you a small fortune. A lot depends too on what other countries do. If Australia makes a 20% reduction at huge expense to the taxpayer - but nobody else helps out - and Australian coastal cities get drowned and your fields turn to desert anyway - then that was a waste of money. But if everyone thinks that way - it's a self-fulfilling prophesy.

It's all very difficult - and that's precisely why we have to have the Kyoto accord (or something very much like it) - it's supposed to set standards that we're all going to work hard to meet so that we don't have this kind of debate anymore. However, since the US screwed it up by refusing to ratify it...we're back to arguing about it all over again. SteveBaker (talk) 18:35, 29 September 2008 (UTC)

heating element

what do we mean by buonet heating element. types of heating elements —Preceding unsigned comment added by 117.195.175.156 (talk) 15:08, 29 September 2008 (UTC)

Do you mean bayonet, such as http://www.secowarwick.com/aftermar/RN311-2.pdf? -- SGBailey (talk) 15:26, 29 September 2008 (UTC)

the details of callus formation

How *exactly* do calluses form? The more details the better. Is there some form of callus formation factor that gets released with repeated bruising or pressure that prevents dead skin from shedding and speeds cell death to form that protective layer? Seeing that it often occurs within mere hours of tedious work, it almost seems to me that there are some active factors that get secreted. Googling has been pretty frustrating, because they keep telling you it's the body's natural defence but they tell you nothing about the biology of callus formation. How far back up the phylogenetic tree does this reaction go? I'm also finding it hard to find any useful papers on callus formation, since they all seem to deal with various genetic transformation techniques, etc. John Riemann Soong (talk) 16:10, 29 September 2008 (UTC)

Our Callus article does not answer your question. If you do find the answer, please update the article. -68.110.230.28 (talk) 01:49, 30 September 2008 (UTC)

Also Keratin#Cornification - but it still doesn't elucidate the biomechanism. I would think it is due either to external factors released on death of epithelial (skin) cells, or internal factors generated by deformation of the cytoskeleton in living skin cells. However, searching the pathetically small literature I can access has turned up nothing good. Sorry. Franamax (talk) 08:35, 30 September 2008 (UTC)

reg.heavy duty trailers

dear sir, 'iwish to have the address of an automobile manufacturer in austrlia who r making long and heavy duty trailers containing more than 100 tyres and controlled by electronic sensors and devices. please give information about it.

thanking u, s.r —Preceding unsigned comment added by Rmohan14 (talk • contribs) 16:24, 29 September 2008 (UTC)

Jebus, 100 tyres? that sounds like an awful lot. Not that your question has anything to do with science... Why don't you try contacting the Australian commercial vehicles department or something? Edit: i guess you're looking for something like this [6] (not Australian) although not even all those beasts appear to have 100 tyres Nil Einne (talk) 18:26, 29 September 2008 (UTC)

I believe the concept in Australia is called Road train and according to our article, the world record for the longest road train is held by Marleys Transport with 45 trailers. It does not say how many wheels but its got to be at least 45x4 and probably a lot more. There are lots of links at the bottom of the article which may help you. SpinningSpark 19:04, 29 September 2008 (UTC)

I assumed we were talking about those hydraulic-drive platforms that they use for things like moving entire buildings and such. They do have maybe 100 tyres and are driven using fancy computer stuff to keep them dead level and to allow all 100 wheels to steer. SteveBaker (talk) 21:16, 29 September 2008 (UTC)

High and low biotechnology

What exactly are "high" and "low" biotechnology? I've seen my professor use these words in my biotechnology class, but since I don't have class for a few days, I figured I should ask here instead of looking like a moron in class. Nishkid64 _{(Make articles, not wikidrama)} 16:25, 29 September 2008 (UTC)

I don't know what they mean, and I think we can assume no one else in your class does, either, so far from looking like a moron, you'll look like a hero for being brave enough to ask! --Sean 19:10, 29 September 2008 (UTC)

I would speculate that "high" biotechnology is the cutting-edge stuff where you do precise gene insertions using viral vectors and such-like (ignoring the indiscriminate nature of integrase targeting); and "low" biotechnology is the old-fashioned stuff like using mutagens and plant breeding, then trawling through the results. Let me know if I score better than the moron. :) Franamax (talk) 07:42, 30 September 2008 (UTC)

Or, depending on context, it could be the difference between, say, what we today call genetic engineering and what is usually called selective breeding (e.g. pre-rDNA techniques). --98.217.8.46 (talk) 15:05, 30 September 2008 (UTC)

Lipids

Are lipids considered polymers? Or are they simply a backbone with the "head"? --MrE1 (talk) 21:27, 29 September 2008 (UTC)

Lipid monomers (like palmitate) can be part of polymers, like cutin, cutan, and suberin. These water-insoluble substances are not yet as well characterized as many other more-familiar polymers. --Scray (talk) 02:56, 30 September 2008 (UTC)

Lipids are not polymers because they are not made of a repeating unit cell. And I think you mean "fatty acids" and not necessarily lipids, because lipids refers to all biological material that is soluble in non-polar solvents, and while it does include the "backbone and head" structure you find in a fatty acid, the class of lipids ALSO includes the steroids, like for example cholesterol. Look at the article lipid for some example structures of common lipids. Proteins and nucleic acids could sometimes be considered biological polymers, however not in the strictest sense, since the unit cells are not identical, but merely drawn from a finite set of possible unit cells (about 20 for proteins, and 4 for DNA for example). Polysaccharides are the closest thing to true biological polymers, since they do contain long chains of identical monomers. There are some biological molecules that are made of lipid monomer cells, but that's still not what you are asking above... --Jayron32.talk.contribs 03:00, 30 September 2008 (UTC)

So what would a lipid membrane be called? It's not a polymer, because the units don't form covalent bonds or cross-link, but it does minimize free energy. Is there a generic term for such a self-assembling structure? Franamax (talk) 07:37, 30 September 2008 (UTC)

Interesting question. Does emulsion come close (doesn't seem to require a particular scale)? --Scray (talk) 02:48, 1 October 2008 (UTC)

Yes, that does come close, since an aqeuous (or other polar liquid) phase is required for the membrane to assemble. I'd previously considered and discarded colloid (which is why I asked here) - however looking again, I suppose it would be a colloid, and possibly an emulsion. Thanks! Franamax (talk) 03:53, 1 October 2008 (UTC)

Axully, emulsion doesn't really work either, since an emulsion is just a form of supersaturated solution; the substances want to separate, but the activation energy for the separation is too great. In a membrane, part of the membrane is actually water soluble, and part is not. The actual term for a membrane is an amphiphile or amphipathetic substance. That just means a substance that has different parts which are soluble in different media. Surfactants like soaps and detergents are also amphiphiles. --Jayron32.talk.contribs 04:25, 1 October 2008 (UTC)

I'm pretty sure that amphiphile would refer to the molecule (e.g. a phospholipid), not the structure (i.e. a membrane). So, I don't think that's an improvement on emulsion or colloid. --Scray (talk) 04:45, 1 October 2008 (UTC)

Well, in that case, the structure IS a membrane. There is no finer categorization than that. Emulsions and colloids and suspensions are entirely different organizations of substances. A membrane is, well, a membrane... Its easy to define, and unique from other categories. --Jayron32.talk.contribs 04:59, 1 October 2008 (UTC)

Note Franamax's question above - the question was how to categorize a membrane. I see nothing in the definition of emulsion that excludes a membrane. --Scray (talk) 05:08, 1 October 2008 (UTC)

Calling a membrane an emulsion is kind of like asking what sort of meat an apple is; membranes and emulsions are fundementally different on an organizational level. Membranes are highly organized structures; emulsions, like all suspensions, are essentially random. Once you remove the structure from the membrane, then you don't have a membrane anymore, as you yourself essentially pointed out; you may have a collection of membrane molecules, but that isn't the same thing. --Jayron32.talk.contribs 05:15, 1 October 2008 (UTC)

A cell membrane is a highly-organized structure, but a simple lipid membrane is not highly-organized at all, it spontaneously self-assembles and has a uniform composition. Franamax (talk) 05:22, 1 October 2008 (UTC)

(e/c) Not to categorize a generic "membrane" though - Saran wrap is a membrane (or can be). A lipid membrane has the property that it self-assembles in order to minimize free energy (or at least I think that's what it does). So similar to the way amino acids can polymerize and form a protein which adopts a structural conformation that minimizes free energy, what would be the term for a lipid assembly doing the same thing? A micelle does it too. Franamax (talk) 05:19, 1 October 2008 (UTC)

Yeah, but an emulsion does not self-assemble in that way. The whole point is, that self-assembled "little heads pointing down and little tails pointing up" structure of a lipid membrane is not an emulsion. Its a lipid membrane. I'm not sure you can categorize it as an emulsion, since the emulsion is the exact opposite. In a lipid membrane, you have separation of the lipid molecules from the solvent. In an emulsion, the molecules are dispersed within the solvent. Totally different. --Jayron32.talk.contribs 05:33, 1 October 2008 (UTC)

If the molecules were individually dispersed, they would be in solution. Instead, an emulsion is a dispersion containing aggregates of the dispersed liquid. A lipid membrane could be described as a self-assembling aggregation of lipid molecules. As Franamax pointed out, micelle is very close, too. --Scray (talk) 05:39, 1 October 2008 (UTC)

Yes, but in an emulsion, the aggregates stop aggregating. They are essentially stable aggregates as is, and repain dispersed. Taking the energy arguement; the emulsion remains not because it is a lower energy state than the seperate substances (it isn't; the seperated substances would have a lower free energy), however, the emulsion state is at a local energy minima; sort of like a crater on top of a mountain... But I'm losing track of this arguement. I think I need to get to bed. --Jayron32.talk.contribs 05:46, 1 October 2008 (UTC)

I think we may be stuck with "amphiphilic bilayer aggregate" or something clunky like that. :( Franamax (talk) 19:29, 1 October 2008 (UTC)

Mate selection in gulls

What criteria does a female herring gull (or the male, if he's the one that picks and chooses in this species - I don't actually know which way round it is) use when selecting a desirable mate from a lineup of likely candidates? From my observations of these birds, their mating behaviour in general is very subtle - the male and the female just seem to start 'hanging out' together after no discernible preamble, occasionally calling out or head-flicking in unison. So, does anyone know what physical features and behavioural attributes are considered desirable to the opposite sex in this species? As I say, I've been watching gulls for years and I have absolutely no idea... --Kurt Shaped Box (talk) 21:47, 29 September 2008 (UTC)

I guess it has to be features of their appearance and behaviour that define them as herring gulls within the gull family. If we assume that a while back there was one gull ancestor then successive generations, for reasons unknown to us, started selecting slightly different gulls that further selected these features until eventually a new species developed, much like the development of the various species of birds of paradise. I have no idea what makes a herring gull different from the rest of the gulls, perhaps you can help. Richard Avery (talk) 17:20, 30 September 2008 (UTC)

I presume they cue into many things. Symmetry is very important as a measure of fitness. And many seabird use voice to judge quality. Sabine's Sunbird talk 21:33, 30 September 2008 (UTC)

Do you have any idea if the female fights with the male as part of courtship in order to test his strength? I remember reading that somewhere (yeah, I know...). --Kurt Shaped Box (talk) 17:41, 1 October 2008 (UTC)

dogs kicking back after defecation

Why do dogs sometimes, after defecation, step aside and kick back scratching the ground, several times? --Halcatalyst (talk) 22:23, 29 September 2008 (UTC)

I suspect they are responding to some ancient wolfish instinct to bury their poop in order to mask their presence when hunting. However, being dogs, they've kinda forgotten why and only half-heartedly bother. SteveBaker (talk) 22:53, 29 September 2008 (UTC)

I know Steve well enough to know what he means (and it isn't what he typed). We can't claim wolves know why they bury their poop (or that they even know they are doing it). It is an evolutionary trait that increases the chance of survival. As such, animals that evolved from wolves carry the same traits - but possibly in a much weaker form. This is just one of those cases where it is easier to say "Wolves do X because of Y" or (worse) "Evolution made wolves do X." Applying human reasoning to animals leads to false statements. Applying human reasoning to evolution (as though it were an intelligent being) leads to false statements. But, it is much easier to treat everything as human (ie: My keyboard is trying to piss me off with this stupid sticky left shift key!) -- kainaw™ 23:17, 29 September 2008 (UTC)

Anthropomorphism Mac Davis (talk) 23:41, 29 September 2008 (UTC)

I've also heard the alternative version that dogs do this to spread their feaces to mark their territory in tyhe same way that they urinate on every tree in sight. 190.244.186.234 (talk) 23:46, 29 September 2008 (UTC)

Well, yes. To phrase it in a more concise manner: It seems likely that wolves have an instinct to bury their poop. Domesticated dogs do not need that evolutionary adaptation and are therefore losing the instinct...but it's not entirely gone yet. It's possible that the original instinct is to spread the stuff rather than bury it. It's hard to know for sure. From what I've observed in my dogs, they are definitely trying to bury it - but they do indeed give up after a couple of half-hearted scrapes. SteveBaker (talk) 02:38, 30 September 2008 (UTC)

Well actually y'all have no idea what goes on in dogs' or wolves' heads - maybe they all deductively reason out the pros and cons of poop-burial, and it's intelligence that was evolved. But that's just me being a trollish animal-rights person. --Bmk (talk) 06:28, 30 September 2008 (UTC)

Cats do carefully bury their poo, or at least try to. That's the whole point of kitty-litter, isn't it? Oop, silly me, carrying a cat into a dog conversation! :) From my observations, dogs pooping in soft soil, and female dogs, will more effectively use the kicking/scraping motion to bury their scat. All this leads me to believe that (well-reasoned or not on the dog's part) it's an action intended to accomplish the purpose of burial. Coyotes however leave their droppings right in the middle of the people-paths in the local (large) parks - again, I believe this action to be quite intentional. Franamax (talk) 07:29, 30 September 2008 (UTC)

It's hard to imagine it's a carefully reasoned behavior. If the dog were carefully considering both the need and it's ability to bury or not depending on soil conditions, terratorial boundary pushing, etc - then why would there be the half-hearted scrape? If this were consciously reasoned behavior then wouldn't it be all-or-nothing? That alone makes me believe it has to be instinctual. SteveBaker (talk) 11:09, 30 September 2008 (UTC)

If a dog/wolf was using rational deduction to decide that it was best to bury or not bury, then a dog in his own backyard wouldn't need to worry about predators or territory. A wolf in a zoo wouldn't need to worry about predators or territory. So, they would decide it was better just to poop in the corner. -- kainaw™ 15:21, 30 September 2008 (UTC)

You're assuming they understand their situation correctly. Rational deduction from an incorrect starting point can result in an incorrect conclusion. --Tango (talk) 00:15, 1 October 2008 (UTC)

• Has anybody noticed whether both males and females do it? Also, how often? My dog is male and does it maybe 10% of the time. --Halcatalyst (talk) 02:48, 2 October 2008 (UTC)