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

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December 21

gasoline vapor

Is gasoline vapor heavier than air. I am concerned about storage of small containers of gas in heated garage. —Preceding unsigned comment added by 72.240.19.105 (talk) 02:50, 21 December 2007 (UTC)

Gasoline vapour in air will be denser than air, but not by much as the vapour is not very concentrated, so you will want to have some ventillation to blow those fumes away. Only methane is significantly lighter hydrocarbon than air. All the ones likely to be in petrol/fuel will be denser. If you have butane, this is denser than air, and can form a high density of vapour, so this could be dangerous. Graeme Bartlett (talk) 02:54, 21 December 2007 (UTC)

Eclectus parrot: how much fruit should he be eating?

I've not had my eclectus that long. He likes his seed, he likes nuts, he likes table scraps but he doesn't seem that bothered about fruit. What percentage of his diet is supposed to be made up of fruit and veg? —Preceding unsigned comment added by 84.64.109.187 (talk) 08:27, 21 December 2007 (UTC)

Here is a site[1] that has some useful information. If you search 'eclectus diet' on Google you will have more sites than you can read.Richard Avery (talk) 09:02, 21 December 2007 (UTC)

I have always enjoyed Land of Vos. Here is a link to a thread on Eclectus' and fruit Forum at Land of Vos --168.236.43.89 (talk) 19:33, 21 December 2007 (UTC)

Machining

I have an assingnment on manufacturing that goes like this:

You are requested to draw up a basic work scheme for the production of a functional shaft, plain bearing and wheel assembly which is going to be used for a skateboard undercarriage.

Plain bearing Shaft Wheel The plain bearing is fixed to the wheel and it rotates freely on the shaft. In your report identify; The materials which can be used for the three individual parts The manufacturing techniques and procedures to manufacture the parts Any post manufacture surface treatments to reduce wear and increase lifetime It is suggested to back your choices with relevant information

Can anyone direct me to appropiate sites where a good general idea can be given? P.S. I would like to construct the elements out of organic materials if possible. —Preceding unsigned comment added by 193.188.46.254 (talk) 09:17, 21 December 2007 (UTC)

Why re-invent the wheel? Heh. No, seriously. The specifications and designs for skateboard wheels (and just about everything else that is manufactured) are covered already by standards. The trick is to find the standard that will cover what you're looking for. Here's how to do this. There are numerous organizations out there that publish standards, depending on what their focus is. So, for instance the organization ASTM is one, as is the ANSI, DIN, IEEE, BSI and other organizations. It would be quite difficult (unless you already knew) which of these organizations would be the one that would publish a standard that you're looking for. Fortunately, there's a private company called ILI Standards that keeps an updated database that indexes all of the Standards in the world - or pretty close to all of them. I don't know what "ILI" stands for - nobody knows (or at least nobody that I know knows).

Now here's where it gets tricky. This company makes its money by selling standards that they print. Because of this they do not make the standards freely available online or anywhere else - they're very fussy about that. You either have to purchase one of their standards (which can actually be expensive), or try to find the standard you're looking for in some library. It is often difficult to know whether a particular library has the standard you're looking for; quite often libraries do not list the standards they have in their collection in their online catalogs. Instead, you need to contact the library's Reference Desk directly and ask if they have "such and such standard" in their collection. If they have what you're looking for, you can go make some photocopies of the pages that cover what you're interested in doing. The standards will describe what type of materials need to be used, they'll often provide diagrams and blueprints for the design, and they'll give specifications for tensions stresses, etc.

Only some libraries collect standards, of course. The best libraries to look for standards are ones that support some kind of research involving manufacturing, engineering, design, etc. So libraries that are associated with universities that offer degrees in these subjects would be good places to look for standards. I do not know of any library that has all of the standards in the world - standards cost a lot of money, and unless the library staff that orders the standards feels that there would be a need for a particular standard, it is unlikely that they would spend their often limited resources on purchasing standards to put in their collection if they believed that they would never be used by anyone. What you're looking for is a standard for skateboards, and quite frankly this is not one of those things (I'm guessing here) that would be included in a lot of libraries. It might be tricky to find a library that has the standard you're looking for. To make things worse, libraries do not ship standards from one library to the next through their Inter-Library Loan system. This is due to copyright restrictions on them. So if you're lucky you might find a library close to you that has the standard you're looking for. Then you can go and make photocopies for free. Otherwise, in order to get the standard, you're going to have to pay for it.

ILI Standards has an online database where you may search for what you're looking for; it's called ILI Infobase. I did a cursory search using the word "skateboard" and came up with this standard:

Standard Number: BS 5715(1993)
English Title: SPECIFICATION FOR SKATEBOARDS FOR RECREATIONAL AND SPORTS USE
Version Date: 03/15/1993
Country: United Kingdom (GB)
Summary: Specifies requirements for non-motorized skateboards which are supplied as complete articles for use by a single rider at a time. Coverage includes definitions, performance, marking, and design and construction. Also includes annexes and diagrams.
Committee: TCM/56
Publisher: BSI (BRITISH STANDARDS INSTITUTION)
389 CHISWICK HIGH ROAD
LONDON
W4 4AL

Table of Contents:
Committees responsible
Foreword
Specification
1 Scope
2 Normative references
3 Definitions
4 Design and construction
5 Performance
6 Advice to users
7 Marking
Annexes
A Skateboard safety code
B Advice on maintenance and use
C Schedule of tests
D Wheel friction test
E Speed test
F Endurance test
G External design
H Drop test
J Impact test
K Pulsating force test for deflection of metal decks
Figures
1 Major components of a skateboard
2 Radiusing of edges of deck
D.1 Diagram of friction test apparatus
F.1 Diagram of endurance test apparatus
G.1 Example of use of test cylinder
H.1 Diagram of apparatus for drop test
K.1 Diagram of arrangement for pulsating force test
List of references

Although this standard has been superceded by another (BS EN 13613), the newer standard seems to focus not on the "nuts and bolts" of the construction of the wheel assemblies of skateboards, but is more focused on safety issues. So I would use the standard I've quoted to find diagrams and descriptions of wheel assemblies. I hopt this helps. -- Saukkomies 08:30, 21 December 2007 (UTC)

I find it hard to imagine constructing shafts and bearings from "organic materials" - wheels, maybe. But it's hard to imagine any organic material with the strength required here. You're supporting the entire weight of an adult on a couple of these things - and a lot of skateboards are used for tricks and jumps and things that will dramatically increase the forces on bearings and shafts. SteveBaker (talk) 15:13, 21 December 2007 (UTC)

Tanning is Skin Cells in Trauma

The latest propaganda campaign by the Australian Government is that all sun-tanning is extremely dangerous and that you absolutely should not tan.
The campaign also tries to explain that we get enough Vitamin D from foods, that even though you feel and look healthier with a tan the risks are not worth it.
You can view the TV ad here: http://www.darksideoftanning.com.au/campaign/tvc.aspx (the government has launched a whole website and media campaign against tanning
Is this paranoia or is well-founded truth? Previously I had asked on the reference desk about tanning, and discovered it's the UV rays that actually convert the Vitamin D and give you a tan. I also know it kills bacteria on the skin, and the sun helps you sweat, increases blood flow and has other benefits. Should I avoid the sun completely or is this campaign absolute nonsense to scare the masses into subjection? Rfwoolf (talk) 11:48, 21 December 2007 (UTC)

It's not really a good idea - it's not extremely dangerous like constantly getting deep sunburns would be, but it's certainly not a good thing to do, especially in booths (though I don't think this is a problem in Australia..) where there is a much larger risk. Most people do get enough Vitamin D from foods. Killing bacteria on the skin is a pretty silly excuse because there are lots and lots of bacteria, along with mites and other critters, on your skin and hair anyway, and regardless of how much laying in the sun you do they're not going to go away forever. So on a personal level, it's not a clear cut decision and rests with the priorities of the one making it: if you want to look tanned now, you're putting yourself up at a higher risk of skin cancer, and UV/sun can also make your skin look bad later in life too (and no, this is not medical advice, shush). On a more general level: the risk of metastasis is low in skin cancer excepting melanoma, which is relatively rare compared to basal cell carcinoma and squamous cell carcinoma. The scenario in the video does happen, but is extremely rare - still, the (somewhat overblown, probably due to it being a public health issue) campaign has a valid point. If I were them, I would be emphasizing premature aging and UV damage, not melanomas; for some, wrinkles trumps death! -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 12:38, 21 December 2007 (UTC)

• They should just advertise this picture and be done with it. --Sean 12:53, 21 December 2007 (UTC)

Why would the AU government spread anti-tanning "propaganda"? --Seans Potato Business 18:39, 21 December 2007 (UTC)

There is an important variable that one should consider when making a personal decision about the amount of sunlight one chooses to acquire, and that is the skin tone. One of the reason's Australia has such a problem with melanoma (and hence is so proactive in informing its people about it) is because a huge proportion of the population are northern European immigrants, and many are of Celtic origin, which is the greatest risk group for melanoma. Combine that with some of the highest UV levels [2] in the populated world and you have a recipe for public health problems. If you are pale and freckled, then you are probably better off avoiding UV as much as possible in Australia, as the Vitamin D benefits you mention can be achieved with much lower levels of UV exposure than if you had darker skin (Assuming a balanced diet, the amount of optimal exposure is tiny anyway, probably only a few minutes a day in sunny weather). In contrast, if you happen to be aboriginal to Australia, you can probably hang out in the sun for many hours without too much problem - melanoma in black skinned people is pretty rare.

The bottom line though, is that irrespective of skin tone, the direct benefits we can get from UV will be achieved, in Australia, by incidental exposure. There is absolutely no good biomedical reason anyone needs to "sun themselves" in Australia, which is why the government campaigns against it. Rockpocket 19:00, 21 December 2007 (UTC)

I meant to question the idea that the government would be partaking in some kind of conspiracy to...(I've no idea what the OP could be thinking)? --Seans Potato Business 23:47, 21 December 2007 (UTC)

I don't believe there's any consipracy. This is simply a public health initiative. There was a particularly effective campaign called "Slip Slop Slap" which was great at getting the sun protection message across a few years ago, but the public have short memories, or think these problems somehow disappear. Either way, the number of skin cancer deaths in Australia are increasing, and people are even dying of melanomas they've developed using solariums. As Rockpocket correctly points out, if you're a caucasian Australian, or even if you're just visiting, you don't need more than 5-10 minutes of incidental exposure per day to synthesise adequate Vitamin D, and more than that will cause sun damage, and that could end up killing you. Mattopaedia (talk) 02:41, 22 December 2007 (UTC)

Um, I would be a little careful being too sure about all this. A recent study has suggested that below-recommended levels of serum vitamin D are widespread (especially in Canada, where I was when it came out). And vitamin D deficiency is thought to predispose to cancer, including skin cancer. Also I believe that it takes fairly bright sunlight to make much vitamin D.

I don't know. When I lived in Canada I took oral supplements of vitamin D in the winter rather than seek out sun exposure. But experts have been slow to recommend oral supplementation, partly because overdose is possible, and partly because they're not sure it has the same effect as the natural sun-generated vitamin. My non-professional, non-warrantied advice would be -- don't do anything obviously stupid, and stay tuned to further developments. --Trovatore (talk) 03:01, 22 December 2007 (UTC)

Well, what the ad campaign fails to clarify, is what if you're not part of the pale-white caucasion section of the population? What if you have a natural olive-brown skin and can in fact tolerate a bit of suntan? Well then their ad campaign would still have you believe that tanning is still 100% out of the question. As to why this is "propaganda", it's obvious that it does its best to illicit fear and other emotional responses in order to get people to take action. In a hypothetical case tanning would become taboo, and any individual that dares to go to the beach and lie in the sun would have dozens of people pointing at them and saying "haven't you hear? You're about to get cancer". The ad fails to offer any balance - the balance is that certain skin tones are more susceptable to skin cancer than others, and that if you have a darker skin tone you can tan for longer periods or spend more time outdoors. That's the clarification I'm after. Because I have a darker skin tone I'm definitely going to be spending some time tanning, no thanks to this blatant shock-campaign. Rfwoolf (talk) 08:08, 22 December 2007 (UTC)

What you call "propaganda" is simply smart and effective public health policy. Epidemiologists have clearly concluded that the dangers of sun avoidance are hugely outweighed by the dangers of sun exposure for the vast majority of the Australian population (the message would likely be different for the Canadian population due to the difference in annual UV exposures). Public health initiatives have to be direct and simple: they don't work when they are loaded with caveats.

Consider the public health initiatives about HIV. What is not widely known is that about 10% of Europeans are essentially "immune" to HIV, they are safe from infection due to a genetic polymorphism. So is it "propaganda" that that the HIV awareness campaings don't make it clear that if you are of European descent, there is a 1/10 chance that you could have risky sex all you like, but that you will not get AIDS? Maybe it is, but is also clear that publicising that information as part of the message will likely make the safe sex message less effective, and thus is counter-productive to the public health.

Populations are, in general, not very smart. It takes pulling at the heart-strings and using shock tactics to get the message across, so that is what Governments do. Besides, if you are smart enough to seek further information and make an informed decision based on your personal situation, then you are probably not part of the demographic that ad-men were instructed to target with the campaign. Rockpocket 02:49, 23 December 2007 (UTC)

You might want to be careful with that 1/10-chance statistic—it's a bit misleading. The population of interest is people of Northern European descent; not all Europeans. In that population, between 10% and 15% of the population carry at least one mutant copy of the CCR5 receptor: HIV's usual route into the cell. These people are more resistant to HIV infection, but not immune. About 1% (one in one hundred) carry two mutant copies of the gene; it is these people who are nearly immune: [3]. However, even these people can be infected, as some strains of HIV can also enter cells through binding with the CXCR4 coreceptor (see HIV#Tropism). So really one could add to the public health campaigns the fine-print message "If you're of Northern European descent, you've got a 1 in 10 chance of being somewhat resistant to HIV infection, and a 1 in 100 shot at being very (but not completely) resistant. Good luck with that, and remember you're still 100% vulnerable to syphilis." TenOfAllTrades(talk) 03:16, 23 December 2007 (UTC)

Yes indeed, in demonstrating the basic principle I was over generalising. But as you note, that kind of re-reinforces that point I was trying to make: It would not be effective for a public health campaign to provide all the details and caveats. You provide some additional, simplified information as a caveat and you risk over simplifying (which can be counter-productively dangerous), so then you need to provide even more detail. Before you know it, only a genetics expert can fully appreciate the message, and they don't need to be told because they already know. Rockpocket 08:17, 23 December 2007 (UTC)

No, it really is just propaganda to sell spray-on tans. :-p Someguy1221 (talk) 02:53, 23 December 2007 (UTC)

Actually the ad seems accurate to me and more or less technically correct for all people. What you seem to have missed is that if you have 'natural olive-brown skin' and can tolerate more sun exposure, you don't tan anywhere near as much. The ad stated resonably accurately that the reason why you tan is because your skin is trying to protect itself. People with naturally darker skin can tolerate greater sun exposure and take a lot longer to 'tan'. They can't however (as far as I'm aware anyway) 'tolerate' more of a 'suntan' then people with lighter skin (as you seem to be suggesting)! In any case, the primary reason for the ad (which according to the ad was by the NSW state government not by the Commonwealth of Australia government) was to highlight the fact that a suntan is not in fact a sign of health as a lot of people seem to think. The ironic thing of course is that for many of the people with naturally darker skin, tanning is often still viewed negatively and they try to avoid it completely even to the extent of skin bleaching (as sun tanning says) which surely isn't a good idea either. I'm from New Zealand and while I haven't seen an ad like this but the slip slop ads are still quite common around summer. And given we have the highest? melanoma rate in the world (I'm guessing Australia is up there too), I'm pretty sure it isn't a big conspirary but a well meaning and well justified public health campaign. Besides that, as other have pointed out effective advertising requires that you simplify things. If you give too much information people just 'switch off'. Most sun exposure times in papers and stuff generally mention that they are for people with fair skin. More brocherues etc which can afford to give more information also usually mention that people with fair skin are the ones who have the most to worry about (although this is usually more of a 'if you have fair skin you need to be especially wary' then a 'if you have dark skin, don't worry' point) P.S. some of the highest UV levels in the world as someone pointed out is another key point. Me and others I know sunburn here much easier then in tropical Malaysia. Nil Einne (talk) 11:31, 25 December 2007 (UTC)

Why don't we eat carnivores?

I've been wondering for a while why (to my knowledge) carnivores are not eaten anywhere on the world. I know some cultures eat dogs, but these are not obligate carnivores...brown bears are eaten, but they are omniovorous, and I have never heard of polar bears being eaten. We do eat carnivorous fish, reptiles and birds, so it seems to be restricted to carnivorous mammals. Is it just because they would not taste good, or would it be unhealthy to eat carnivores? And if the latter, why? -- Ferkelparade π 12:20, 21 December 2007 (UTC)

Here are my (educated) guesses: for one, humans are not an exceptionarily strong species, especially when going up against big carnivores, so we have had much more of a difficult time hunting the hunters than hunting herbivores (we also seem to have better luck with speed rather than brawn, so that would have helped as well). The stupid ones who go trying to club lions get killed, so there's an evolutionary component to it, and even if you manage to take down a carnivore, you have expended a lot of effort. Only recently has man been able to pretty much take shots at whatever animal he cares to eat, and any cultures that traditionally eat carnivores would assuredly be in that position by force (no alternatives). So culturally, nobody wants to eat the carnivores either - the modernity of hunting with guns throws that out the window. Another suggestion would be that some carnivores carry more parasites and other nasties than herbivores, though if you're not chowing down on scavengers that's not as much of a problem. I don't think it's a issue of not tasting good - I think it's the old standby "we haven't done it before, so it's exotic - try it if you want, but our culture says eat herbivore X so you should probably just stick to that.". -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 12:46, 21 December 2007 (UTC)

And also think about how the method of food production would work on that—carnivores are at the top of the food chain, and there are usually a lot fewer of them than the "prey" species. So unless we happen to have a vast resource of carnivores around (like in the ocean), it makes more sense for us to eat prey species on the whole. On top of that, much of the modern Western meat diet is due specifically to modern modes of food production, and many of the foods we find so "natural" in Western culture are pretty specific to our time and place (chickens were not eaten as meat with great regularity until well into the 20th century, for example). --24.147.86.187 (talk) 12:56, 21 December 2007 (UTC)

(Edit conflict) There's also the ecological pyramid to consider: there's a *lot* of grass, rather fewer grass-eaters, and even fewer grass-eater-eaters. It's best not to base a diet on the pointy end. --Sean 13:01, 21 December 2007 (UTC)

I heard wild canids and felines meat had a very very strong taste and that is why we don't eat them. No source. Keria (talk) 13:26, 21 December 2007 (UTC)

Thanks for your input, everyone...I had also thought about the relative ease/danger of hunting carnivores vs herbivores, and of course there is always a relative abundance of herbivores and relatively few predators so it would be impractical for any culture to base a diet on carnivore meat; however, I am wondering why we do not eat carnivores at all. For example, lions and tigers have been hunted for milennia (probably since the invention of the bow) and their skins were displayed as hunting trophies, but nobody seemed to care much for their meat (or at least I have never heard of the pharao's court feasting on roast lion after a day of hunting, which would be an expected outcome if carnivores were considered edible - the more difficult to hunt and the more prestigious the success, the more of a status symbol it would be to serve lion or tiger to your guests). I guess Wooty's suggestion that it might be related to parasites comes closer to answering my question, but I'd be interested in a bit more data on that idea (which parasites, and why? And why do omnivores carry less parasites than obligate carnivores?) -- Ferkelparade π 13:39, 21 December 2007 (UTC)

Another point would be that it would be hard to farm carnivores. You would also have to farm their food, and their foods food. And stop them from eating all their food at once (lions in a paddock next to sheep?)Shniken1 (talk) 13:45, 21 December 2007 (UTC)

I don't know what their meat tastes like but carnivores tend to be extremely tough, bony and don't have much meat in any case. A big fat juicy cow/sheep/whatever is much better to eat. If you're into something exotic, why not a camel or pheasent or goose or something for your guess instead? Or perhaps caviar or whatever. Probably better then requiring your guests to pick through a very bony lion/tiger. Although quite a lot people do eat dog meat (ooops missed the part about obligate). Some people also eat crocodile (ooops missed the part about mammals too) or cat meat (although it's not clear whether these were common traditionally). Also carnivores are sometimes considered neither halal nor kosher. BTW some people do appear to eat tiger meat and lion meat although it's not clear how common this was traditionally. In terms of people hunting and that, well bear in mind that if these people wanted the pelt and head, it may have been far easier if they kept the tiger intact until someone could get around to deskinning it properly rather then quickly getting it ready for the dinner table. Plus eating it could perhaps be seen as degrading their kill (this was supposed to be a trophy, not food). P.S. people do eat polar bears [4] Nil Einne (talk) 14:54, 21 December 2007 (UTC)

We do eat lots of different carnivores. Most of the fish we eat are carnivorous, for instance. However, there's a problem with eating mammalian carnivore species - it has to do with the buildup of toxins (and even good things) in the internal organs and tissues of carnivores. Toxins are concentrated in the bodies of animals (and humans) the further one goes up the food chain. One of the most pernicious substances, though, is actually Vitamin A, which builds up in carnivores' livers and other organs - but especially livers. People will die or get very very sick if they eat too much Vitamin A. An example is the story of Xavier Mertz, an Antarctic explorer, who died after eating the liver of his sled dogs. So maybe as a result of this human societies developed food taboos regarding the eating of carnivores. -- Saukkomies 08:45, 21 December 2007 (UTC)

Yep, I think the term for that is biological magnification. The further up the food chain you go, the less "good for you" the meat is, to put it bluntly. Humans probably taste pretty awful, or at least aren't too good for you, though I have no personal experience on the matter to verify that. Wrad (talk) 16:49, 21 December 2007 (UTC)

Armin Meiwes claims that human meat essentially tastes like sweet pork. As for being good for you, human meat apparantly contains large numbers of prions, which over time may end up causing problems (such as everyone's favourite zebra, Kuru). GeeJo ^(t)⁄_(c) • 16:57, 21 December 2007 (UTC)

The obvious answer is, it wouldn't be practical. What we are trying to do is get energy. Where does this energy come from? The sun. But we can't absorb that energy directly, so we have to use intermediaries to get that energy. We can eat plants, or animals that eat plants. But why would we want to eat animals that eat animals that eat plants? Cut out the middle man, it's inefficient. It would be pointless to raise carnivores to eat them, because them we have to also raise herbivoirs to feed the carnivores. But we can just eat the herbivores directly ourselves. It's more cost and energy efficient that way. Also like someone else said, we do eat some carnivores, in the form of fish, but no one is raising those fish. We just pluck them from the trees so to speak. We don't have to provide their food source, like we would with farm animals. Also we can't consume their food source either, well at least no one would want to on a regular basis. 64.236.121.129 (talk) 17:36, 21 December 2007 (UTC)

Quite a lot of the fish you find in the store in my area (the US) is farm-raised. Maybe it's different in other parts of the world, I don't know. Friday (talk) 18:11, 21 December 2007 (UTC)

Cats are obligate carnivores, and according to cat meat, are eaten in certain parts of the world. So the basic premise that carnivorous mammal meat is never eaten is untrue. I think the other responses give good reasons why it is not widely eaten (e.g., inefficient use of resources in farmed animals; concentration of toxins and prevalence of parasites in wild animals). -- Coneslayer (talk) 17:58, 21 December 2007 (UTC)

Part of the reason there are fewer carnivores than herbivores and fewer herbivores than plants is that the higher up the food chain you go, the harder it is to get the energy you need to stay alive. Plants have it easy. They sit around and get energy from the sun. herbivores have to get that energy secondhand from the plants. Carnivores get it third (or fourth) hand from other animals. With each step, the work/benefit ratio gets worse and worse since food becomes harder to chase down, not to mention the fact that animals just don't deliver what plants can energy-wise. Wrad (talk) 18:34, 21 December 2007 (UTC)

Backcrossing

MyD88-/- mice were generated as described and backcrossed for 9 generations on an H-2d (BALB/c) background. - what's the backcrossing necessary for? --Seans Potato Business 20:15, 12 December 2007 (UTC)

When generating knockout mice, it's generally necessary to mix two different strains of mice. Backcrossing is used to reduce the genetic components of one of the founding strains. — Scientizzle 21:16, 12 December 2007 (UTC)

Here is an ugly graphical representation. After several generations of backcrossing, one can assume that the only non-BALB/c DNA in these mice is from the regions flanking the knocked-out gene — Scientizzle 21:21, 12 December 2007 (UTC)

That's great; thanks. So you only need to perform backcrossing when you have the knockout in a different genetic background than the one you want? Would it not be simpler to have performed the knockout in the genetic background in which you wanted it in the first place? Are some backgrounds in some way easier to use for producing knockouts? --Seans Potato Business 22:07, 13 December 2007 (UTC)

The formation of a genetic knockout mouse is moderately complex. A genetically modified embryonic stem cell of strain 1 is placed in the developing blastocyst of strain 2. In order to determine the efficacy of the implantation (and to plan subsequent breeding), it's useful to produce a chimera of strains with different coat colors. There's more information at Knockout mouse. — Scientizzle 22:22, 13 December 2007 (UTC)

But the diagram you link to uses three different strains. One cell type endures the knockout and is put into a blastocyst of another type. They then try to get the transgene in a C57BL/6 background by "backcrossing". If they (the scientists involved) had used C57BL/6 cells in the first place, they could put those cells in the same blastocyst as before, breed with a C57BL/6 mouse, and just like that, all the black offspring are heterozygous for the knockout and fully C57BL/6; no backcrossing necessary. --Seans Potato Business 13:30, 15 December 2007 (UTC)

As far as I can tell that is what this diagram shows. The founder is a chimera of C57BL/6 (abbreviated as B6) and 129/Sv cells and it is backcrossed to C57BL/6 mice. That is just two strains. However, you don't put B6 cells into a B6 blastocyst, because then its is much more difficult to identify which offspring are chimeric. Typically need your null allele to be incorporated into the DNA from a strain with a different coat colour, since this is the way you can identify your founders (129 mice are white, and B6 mice are black - chimeric mice will be a patchwork of white and black). So at N1, the first backcross, you will select mice that have one allele that is B6 and the other has to be the null allele, which is on a 129 background. Thus, at that point, you will have a 50/50 mixed genetic background. Rockpocket 19:35, 21 December 2007 (UTC)

Having a coat color chimera allows for a greater simplicity in creating a knockout strain--the chimeric progeny of a successful incorporation will be obvious, they're adorable little multicolored animals with the coat colors of both the recipient cell and the donor cell (the cell w/ the altered DNA). Those that have the color type of the donor in higher ratio, and especially if that coat color is found near the reproductive organs, are more likely to be heterozygous for the target mutation in their germ cells, which is the key. The progeny of those animals become your F1 generation if germline transmission is received. Because raising animals is expensive, and genotyping a new mutation can be difficult/expensive/time consuming, these shortcuts make it simpler to produce a strain.

One note--the mice I've been involved with ususally only use two strains, 129/SvEv cells injected into C57BL/6J, then further backcrossed onto C57BL/6J, for example. Why one would use three strains, I don't know...but using only one strain would cause large difficulties...it would be effectively impossible to determine the efficacy of any blastocyst implantation; one would be left with attempting to test every possible F1 pup for the genotype of interest. — Scientizzle 20:35, 21 December 2007 (UTC)

But aren't you assuming that the coat colour is linked to the chromosome holding the knockout? In reality, they will probably separate, being on different chromosomes, leaving a mouse with grey colour but homozygous positive (no knockout), indistinguishable from a mouse that has the same colour and is heterozygous.

Scheme:

Chimeric + White =

Grey hetero

Grey hetero + White =

Light grey hetero and light grey homo +ve

--Seans Potato Business 23:07, 21 December 2007 (UTC)

No.

1. DNA-altered ES cell from gray-coat-colored strain added to developing blastocyst of a black-coat-colored strain.
2. Resulting offspring are chimeric: stripes & patches of black and gray. The level of gray coloration is suggestive of the extent of the expansion of the altered cell into the various tissues, including the germ tissues.
3. Those mice are crossed with black mice. Those offspring will only be heterozygous for the mutation if their chimeric parent's germline cells were derived from the altered (gray) stem cell. Coat color may be, at this point, genetically independent of the mutation, as you suggested. (But! pups of variable color--half completely black and half of the litter completely gray--are suggestive of gray-type DNA in the germ cells, so that's usually a good sign.)
4. These putative F1 mice are then genotyped...and the rest is history.

The key to the whole process is that the genetically altered stem cell must end up as a progenitor to germline cells in order for the whole scheme to work. Mixing coat colors is a way to measure that efficacy. I'm not saying this is the best way to do it, but it is why it's done. If one only uses C57 cells in C57 embryos, one cannot easily know if any step (incorporation of ES cell, expansion of that cell into relevant tissue, inheritance of said cell's coat color phenotype) along the way, until genotyping the F1, has worked. — Scientizzle 23:59, 21 December 2007 (UTC)

Okay, I understand it. I'll try to make a nice SVG diagram for the article. Here's a method that I think would be better though; it requires approximately eight genotypings but no backcrossing. Is it flawed?

1. Transduce C57 cells and insert in 129 blastocyst
2. Cross chimera with C57 mice
3. Black offspring are heterozygous
4. Cross black offspring
5. Genotype approximately four males and four females to find one double negative of each type.
6. Breed as much as you like. They're all fully C57 background and so no backcrossing required. --Seans Potato Business 09:52, 22 December 2007 (UTC)

Sorry Sean, your scheme doesn't look too good. #3 is wrong because, unless the mutation of interest is on the same chromosome as the coat color gene(s), one cannot assume that the black offspring are the hets. In fact, if unlinked, black offspring have same odds of heterozygosity as non-black.

The backcrossing is necessary because any het F1s would, by definition, have ~50% 129 strain DNA. (The chimera parent has a mostly C57 body, but must have 129 sperm or eggs in order to contain the mutation.) Each F1 het would have a different profile of C57 and 129 DNA, too, so crossing them could make offspring that are between 0 and 100% genetically 129. Continued backcrossing against C57 +/+ animals reduces, each generation, the amount of (mutated-chromosome-unlinked) 129 DNA by 50%, until only the region of the altered chromosome is non-C57. This is important because different inbred mouse strains can have wide variability in many important features, including behavioral measures, drug metabolism, cancer development, etc. — Scientizzle 20:53, 22 December 2007 (UTC)

Okay, I messed up on the first scheme, but I'm not through yet!

=== Revolutionary Nobel-prize-winning method ===

1. Transduce C57 cells and insert in 129 blastocyst
2. Cross chimera with mouse of C57 background
3. 50% of black offspring are heterozygous - genotype approximately two males and two females to find one heterozygous of each gender
4. Cross heterozygous black offspring
5. 25% of offspring are homozygous negative - genotype approximately four males and four females to find one homozygous knockout of each gender
6. Breed as much as you like. They're all fully C57 background and so no backcrossing required

Stats to achieve two homo.neg. in required background: Total crossings = 2, total genotypings: 12

=== Standard Leading-brand method ===

1. Transduce 129 cells and insert in C57 blastocyst
2. Cross chimera with mouse of C57 background
3. 50% of not-black offspring are heterozygous - genotype approximately two mice to find a heterozygous negative mouse
4. Cross heterozygous negative with mouse of C57 background
5. Offspring are all about 75% C57 and 50% are heterozygous - genotype approximately two mice to find a heterozygous negative mouse
6. Repeat steps 4 and 5 10 more times to achieve mice with 99.98% C57 genome and genotype approximately two male and two female mice to find one heterozygous mouse of each gender
7. Cross these two mice to achieve 25% homozygous knockout mice with 99.99% C57 genome - genotype approximately four males and four females to find one homozygous knockout of each gender

Stats to achieve two homo.neg. in required background: Total crossings = 13, total genotypings: 32

Am I right in my understanding of the backcrossing procedure and/or my assertion that reversing the roles of the C57 and 129 mice is a sound suggestion? --Seans Potato Business 16:10, 25 December 2007 (UTC)

That's weird...we answered this question on Dec 12th. What's it doing back here again? The OP's signature is even from Dec 12th. SteveBaker (talk) 21:04, 21 December 2007 (UTC)

Sean brought it back for round 2... — Scientizzle 21:09, 21 December 2007 (UTC)

slack action and the physics professor

It seems that professors will often tell stories or use examples that just are not true. The story I have the biggest problem with is about slack action in trains. It goes something like this --It is impossible for a locomotive to start a 50 car train if all the slack is taken out. (ie the train in stretched) Therefore the engineer must back up his locomotive and bunch up the slack. Then he can move the train because he only has to pull one car at a time like 1,2,3,4,5 and so on." This is simply not true. How does the engineer start the train. He gets 6 locomotives with 6000 HP each for a total of 36000 Horsepower and he hooks it up to a 100 car train and with no slack in it just gives it hell and it will pull that coal train like there is no tomorrow. Locomotives have so much power that if an engineer were to follow the teachings of the professor he or she would lose their job because they would rip train apart from the jolt of the slack action.

Why then is this still taught? —Preceding unsigned comment added by 66.228.239.18 (talk) 18:50, 21 December 2007 (UTC)

Maybe 'cause it's a physics class and not train-driving/engineering school? --Seans Potato Business 19:13, 21 December 2007 (UTC)

There are plenty examples of things which are taught and taught and taught but not reconsidered or reexamined. Our scientific mythology discusses a few of these which are often told about the history of science, for example. Why is it taught? Usually because it serves a pedagogical purpose other than it being factually true (for example, scientists often have very confused ideas about the history of their own discipline, but their "myths" help reinforce the idea of how they think their community should function). --24.147.86.187 (talk) 19:31, 21 December 2007 (UTC)

See [5] which has some discussion of railroad couplers. I'm not finding a lot of free references regarding this, but I was once told by a railroad freight train conductor that freight trains have slack couplers and they start up as described, while passenger trains have couplers with less slack. He would curse any engineeer who accelerated excessively during the startup process, because of the extreme jolt experienced in the hindmost car, the caboose. What railroad are you describing which "gets 6 locomotives with 6000 HP each for a total of 36000 Horsepower and he hooks it up to a 100 car train and with no slack in it just gives it hell and it will pull that coal train like there is no tomorrow." Sounds like poor management to use more locomotives to start a freight train moving than are needed to maintain it in motion at the desired speed and get over the grades to be encountered. The engineer would not necessarily "rip the train apart" by gradually setting it in motion via the slack couplers if the speed remained constant, at a speed which did not create too great a jolt as each car is added. Note that the engine starts out addind one car to itself and ends up adding one car to 99 cars, so with a constant maximum traction force it should have less accelereation available at the end of the process than at the beginning. Fortunately each car brakes itself, so the stopping process need not be quite so incremental. Per the ref cited, the slack in each coupler is way less than an inch. Edison (talk) 20:13, 21 December 2007 (UTC)

6 locomotives is indeed a bit much, the BNSF coal trains that pass through my town routinly have 3-4 units and they are always the newest- SD70ACe, or somtimes GEVOs from General electric. Either way both types are in the 4000 HP range and they handle the 15000 ton trains with ease. Secondly on the artical about diesel locomtives it states "the electric drive system is designed to produce maximum traction motor torque at start-up, which explains why modern locomotives are capable of starting trains weighing in excess of 15,000 tons, even on ascending grades. Current technology allows a locomotive to develop as much as 30 percent of its loaded driver weight in tractive force, amounting to some 120,000 pounds for a large, six-axle freight (goods) unit. In fact, a consist of such units can produce more than enough drawbar pull at start-up to damage or derail cars (if on a curve), or break couplers (the latter being referred to in North American railroad slang as "jerking a lung"). Therefore, it is incumbent upon the engineer (driver) to carefully monitor the amount of power being applied at start-up to avoid damage. In particular, "jerking a lung" could be a calamitous matter if it were to occur on an ascending grade." This being said it appears taht the professor's assertion is incorrect as there is acctualy more than enough power avalible. —Preceding unsigned comment added by 66.228.239.18 (talk) 20:32, 21 December 2007 (UTC)

The only snag with this question is that the story it tells happens to be absolutely true.

This is one of those rare situations where I happen to be an expert on the subject! I used to work for Rediffusion Simulation - we mostly made flight simulators - but one time we made a railroad simulator for Burlington Northern railroads. Trust me - the story is completely true - it was one of the situations we were specifically called upon to simulate by BNR tp simulate the difference between static and dynamic friction. If the couplings are left tight by a rookie engineer - you may well have to back the locomotive up to slacken them off before you can go. Not all trains, not all locomotives, not all track slopes and curvatures and not all weather conditions - but it most definitely happens. The one time it doesn't happen for sure is when you have locomotives at both ends of the train. Then the tail end locomotives can get one car rolling at a time by squashing up the couplings and tight couplings aren't a problem.

The problem comes about when a novice pulls the train to a halt very gently and smoothly and thinks he's done a great job of it...sadly, that leaves the couplings tight, which at best is sub-optimal, and at worst will cause major grief. As you stop the train, you need to brake just a bit harder than seems reasonable in order to allow the train to compress up. This seems wasteful on speed and momentum - but you have regenerative braking on modern diesel-electric locomotives - so the energy isn't really wasted.

It wouldn't be a problem if (for example) there is a long steep grade somewhere on the route - under those circumstances, you'd have enough locomotives that you could certainly just get the whole thing moving no matter what as our OP suggests. But if the trip is across dead-flat middle-America - then they won't be sticking enough power on there just to allow an incompetent engineer to get away with a rookie error. The single biggest thing they pound into the heads of their engineers during training is fuel economy. Their profits are razor thin - and make-or-break comes down to fuel efficiency. If you go around sticking more power onto the train than it needs (and especially if you rev all of those locomotives up to full power like that), you'll be guzzling fuel and sinking profits. Their entire justification for paying us multiple millions of dollars for the simulator suite was because they believed they could get a good return on that investment from having better trained engineers.

There is a hell of a lot of stubtlety to driving a long coal train correctly - that's why they needed the simulator. On our simulated route, we had sections where there were hills that went up and down at similar spacings to the length of a typical train. Instinctively, the resulting situation is totally not what you expect. You head up a hill with loads of power on - and it's very tempting to ease off when the lead locomotive crests the top and starts to run down the other side...but if the train is longer than the hill, you really have to keep the power on because almost all of the load is still going uphill. Similarly - when you get to the bottom of a narrow valley, you are probably braking to keep the speed down - and it's tempting to ease off on the brakes and apply power as you head up the next hill - but somewhere about a mile behind you, cars are still just starting to descend the slope - and you need to keep the brakes on as you start to head up the next hill. With race-car drivers, they tell you to always have your mind lining up for the corner after the one you are just about to take...with train driving, you've got to have your head spread back over a mile from where you've just been. While you have a lot of power to get you out of trouble, you are continually trying to minimise fuel consumption - so you can't use brute force to do the job...not if you are any good at it anyway. SteveBaker (talk) 20:34, 21 December 2007 (UTC)

On a somewhat unrelated note, there is a great chapter in John McPhee's Uncommon Carriers which is all about driving coal trains. It's pretty interesting. --24.147.86.187 (talk) 20:48, 21 December 2007 (UTC)

Good points all of them. However as part of the thought experiment goes the fuel consumption is no object to the professor. The professor states that it is physicaly impossible to move a 15000 ton train that has been streched out. I would have no problem with taking the professor to the local railroad yard and watching them start the trains. I've never heard slack action on a priortiy coal train... —Preceding unsigned comment added by 66.228.239.18 (talk) 21:01, 21 December 2007 (UTC)

He might still be right under some circumstances - it depends on too many variables. If the train has been standing overnight in freezing rain and there is an inch of ice on the rails - then he's definitely right. If there are enough locomotives on the job and it's clear weather and there aren't too many cars or they aren't fully loaded then maybe he's wrong. It depends on an awful lot of factors that are unlikely to have been specified in his example. But to say that flat out you can definitely get any train moving regardless of whether the couplings are loose or tight is nonsense - sticktion is greater than friction - QED. SteveBaker (talk) 21:22, 21 December 2007 (UTC)

This would actually be an interesting thought experiment to figure out the point at which the mass of the train (unslack coupling) would be too great for the train to start. At some point the HP per wheel will cause them to spin on the track, even without ice. Friction is not limitless. This would explain the need for six engines to spread the HP over more wheels. But why the need for six trains if four is enough with slack couplings? The professors comment of physicaly impossible is out of context but almost certainly refers to a fixed number of drive wheels. Adding more trains to the front does not negate his statement, it is a different problem. David D. (Talk) 21:07, 22 December 2007 (UTC)

Neutral

If I'm in a fast-food line, is it okay to shift my automatic car into neutral for like a minute or so? I'm trying to save gas, but I don't want to mess up my engine. 71.218.36.45 (talk) 20:03, 21 December 2007 (UTC)

Your car has neutral for a reason- I've not heard anybody suggest it's harmful in any way. But why not use park? It's what people typically use when they don't want the car moving. Also.. what makes you think you're saving gas? If you want to save gas, turn the engine off. Friday (talk) 20:12, 21 December 2007 (UTC)

But, I've heard turning the engine on and off also wastes gas. 71.218.36.45 (talk) 20:15, 21 December 2007 (UTC)

That's much less true on modern cars than it used to be. Hybrids start and stop the engine routinely, and now some non-hybrid cars are beginning to do the same (e.g. the latest MINI (BMW)[6]). -- Coneslayer (talk) 20:19, 21 December 2007 (UTC)

Yeah, they call that a mild hybrid. It's possible starting the engine was wasteful in the carburetor days, but I don't think this is still true. Friday (talk) 20:22, 21 December 2007 (UTC)

It's clear that on non-carburettor cars that there is no wastage in stopping and restarting the engine like that...after all, the only reason they add this feature is to save gas. Incidentally, the MINI's auto-start feature only works in Europe - for some reason the feature is disabled on the US version (although I suspect it's just a software change). I have a vague recollection that having the engine start itself automatically is illegal in many US states. This was initially a problem for the Prius - but they managed to get dispensation because the gas engine doesn't actually drive the wheels on the Prius - so, technically, it's just a generator. Not so on the MINI - it's a conventional gasoline engined car. They are claiming that the 2009 MINI is going to have a mild version of regenerative braking too. It uses the starter motor as a generator (assisting conventional brakes)...then when you stop, the engine cuts out (as it does on the European version of the 2007/2008 version) - but when you put your foot on the gas, instead of starting the engine immediately, they use the starter motor to get the car rolling FIRST - and only start the engine once you're up to 10 to 15 mph. It's a clever trick because it doesn't require much new 'stuff' than the car already has - but for stop/start in-town driving, it's practically a hybrid - but without any of the disadvantages. It'll also have a 'sport-mode' button which turns all that stuff off if you actually want to burn rubber and blow away those wannabe VW bug and Scion xB owners (a particular obsession of mine). SteveBaker (talk) 20:49, 21 December 2007 (UTC)

Wait, wait.. Are you saying people driving a 100 hp shoebox try to act like they have a fast car?!? That's.. bizarre. Friday (talk) 20:54, 21 December 2007 (UTC)

Ok, I don't have a Mini or a Prius. I have a 2004 Hyundai Elantra. It is fuel injected, but I've heard it still wastes gas if you turn off the engine and quickly start it up again. Back to my original question, should I put my car in Neutral if I'm going to be waiting in line, or is Park better? 71.218.36.45 (talk) 21:04, 21 December 2007 (UTC)

Park would be safer- the car won't go rolling if you forget to keep your foot on the brake. I can't see any reason why one would waste any more or less fuel than the other. In either case, your engine should be just idling. Friday (talk) 21:30, 21 December 2007 (UTC)

take a look at your rpm's in park and neutral. Lower engine speed = less fuel.Furmanj (talk) 01:12, 22 December 2007 (UTC)

Walk? Shniken1 (talk) 15:32, 22 December 2007 (UTC)

Competition vs cooperation

Which one is better? (please, reply only if you really have something meaningful to say) --Taraborn (talk) 20:10, 21 December 2007 (UTC)

That's a terribly vague question. Someguy1221 (talk) 20:10, 21 December 2007 (UTC)

Maybe start at Prisoner's dilemma? —Preceding unsigned comment added by Coneslayer (talk • contribs) 20:13, 21 December 2007 (UTC)

Better for what? --24.147.86.187 (talk) 20:48, 21 December 2007 (UTC)

There has been a very convincing computer-based demonstration of how cooperation works...see Tit for tat. All of the "See also" links from that article are also well worth reading. SteveBaker (talk) 20:53, 21 December 2007 (UTC)

That article says "It is important to know that tit for tat still is the most effective strategy if you compare the average performance of each competing team.". Is it appropriate to refer to the reader (i.e. "if you compare") in a Wikipedia article? I would favour "if the average performance of each competing team is compared". --Seans Potato Business 21:34, 21 December 2007 (UTC)

No it's not appropriate. See WP:TONE. William Avery (talk) 21:38, 21 December 2007 (UTC)

Yeah - that's no good - but WP:BE BOLD - you can fix it more easily than you can complain about it. SteveBaker (talk) 01:56, 22 December 2007 (UTC)

Something meaningful to say : You need both for a proper Baseball game. I'd say some combination of the two is appropriate for most situations. APL (talk) 01:11, 22 December 2007 (UTC)

This concept of which is better - cooperation or competition - is the basis of the Nash Equilibrium theory that was named after John Forbes Nash, who won the 1994 Nobel Prize in Economics for it. Nash is also the real-life person that the movie A Beautiful Mind was based on. -- Saukkomies 02:30, 22 December 2007 (UTC)

It seems I must borrow a Game Theory book from the library. Thanks for you replies! --Taraborn (talk) 08:53, 22 December 2007 (UTC)

Greenhouse gas emissions and fuel efficiency

Out of curiosity, how much would annual greenhouse gas emissions be cut down if everyone got fuel efficient cars? Someguy1221 (talk) 21:12, 21 December 2007 (UTC)

Sorry to state the blindingly obvious, but since everyone doesn't have cars, greenhouse gas emissions would increase if everyone got one, fuel efficient or not. --NorwegianBlue ^talk 22:25, 21 December 2007 (UTC)

Ok, forgive my poor wording. "Out of curiosity, how much would annual greenhouse gas emissions be cut down if everyone [who has a car replaced it with a] fuel efficient car?" Someguy1221 (talk) 22:28, 21 December 2007 (UTC)

My point was not poking fun at your wording. The question you ask is a very important one. Everyone wants cars, and the greenhouse gas emissions caused by cars replacing bicycles in India and China will dwarf the savings caused by increasing fuel efficiency. So we are not talking about reducing greenhouse gas emissions, but about trying to cut the expected increase in greenhouse gas emissions. Increasing fuel efficiency of cars is undoubtedly important, even more so is encouraging people to use public transportation. --NorwegianBlue ^talk 22:49, 21 December 2007 (UTC)

Check out the APTA report: http://www.apta.com/media/releases/070926_fact_sheet.cfm

In the US, transportation accounts for 33% of gases, and 60% of those come from cars and light trucks, so thats 20% of all emissions in the US. If hybrids double the fuel economy, then there is a 10% reduction in total greenhouse gas emission. Furmanj (talk) 23:07, 21 December 2007 (UTC)

Total greenhouse gas emission, all types, weighted by global warming potential and broken down by sector for the year 2000.

Globally, transportation fuels are about 14% of total greenhouse gas emissions. My recollection is that cars represent about half of that, with the rest goes to planes, trains, buses, and heavy trucks, etc. So lets call it 7% of the global total. You need to estimate current average fuel economy and compare that to some guess for how things will improve. The corporate average fuel economy standards in the US, which are among the most lax in the world, require the current fleet of cars to average at least 27 miles per gallon (or 21 for SUVs and light trucks). In practice, existing cars are nearly always worse than that because efficiency tends to decline with age. For the sake of argument, lets pessimistically say that all the cars still in operation really only average 15 miles per gallon. If you replace them all with Priuses which have a real world performance of ~45+ miles per gallon, then you'd shave off as much as 2/3 of that 7% of the total gas emissions. In other words, replacing all the cars might (optimistically) net you as much as a 4.5% reduction in total greenhouse gas emissions. Assuming your don't increase the total number of cars in operation, or the amount that people are driving, etc. Dragons flight (talk) 23:29, 21 December 2007 (UTC)

Wow, that's disappointingly small. Thanks guys. Someguy1221 (talk) 23:43, 21 December 2007 (UTC)

The point is that EVERYTHING has to be halved (at least) - if you did nothing about cars and fixed everything else, then cars would be a HUGE percentage of the problem. Cars are actually uniquely difficult to fix because they are small and mobile, and require all of this complex infrastructure - which makes them an important target. But certainly we need to stop making electricity with fossil fuels, build much better insulated homes and workplaces, address aircraft, factories...you name it. No one of these things will fix the problem by themselves - we have to attack them all together. But, yeah - but even if we were all driving 60mpg cars tomorrow, we couldn't sit back and say "OK! That's global warming dealt with!" - it's a lot more hassle than that. SteveBaker (talk) 02:06, 22 December 2007 (UTC)

Grey meat

Why is the meat inside a cornish pasty and certain sausage rolls grey? --Seans Potato Business 21:28, 21 December 2007 (UTC)

meat turns brown on cooking from Maillard_browning, generally in combination with some carmelization. Its likely that if only the maillard reactions occur, such as in boiling or inside pastry, then the gray color is achieved.Furmanj (talk) 23:11, 21 December 2007 (UTC)

I would second Furmanj analysis of this. Indeed, the meat is grey because it has cooked inside a moist pasty without being exposed to air. Either that or it was boiled first before being added. Whenever I make beef stew I always char the meat first on a grill or in a frying pan to give it a nice brown outer color before adding it to the stew pot to boil. It makes it much more appealing for the person eating it if it's not just grey - which it would be if I hadn't done the first step. -- Saukkomies 23:20, 21 December 2007 (UTC)

Kelvin water dropper

What is the source of the energy in this device? I dont think its the gravity... 79.176.187.141 (talk) 23:48, 21 December 2007 (UTC)

The energy of the water descending from the upper reservoir to the lower buckets is what causes the device to develop a charge sufficient to make the sparks. The amount of electrical energy generated is probably quite small in Joules or kilowatt hours compared to the energy required to lift the water from the lower buckets to the upper reservoir. Edison (talk) 00:56, 22 December 2007 (UTC)

It is gravity: Only with the help of gravity will the charged droplets fall into the bucket with the same charge which repels them electrostatically. Icek (talk) 06:32, 22 December 2007 (UTC)