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September 13

Reason why muscles require excercise to stimulate growth

Is it true that muscles are the only organ in the body that require exercise in order to stimulate their growth? Like for example, if you are bed ridden, your muscles will begin to suffer from atrophy right? My question is, why is this? My guess is because of our evolution and how our species has been through many periods where famine ran rampant, so our bodies had to evolve a way to preserve as much energy as possible without wasting on muscle development unless it was absolutely necessary. Would this be a fair statement to make? Are there any other animals that do not suffer from this? Meaning their muscles will continue to grow whether exercise is stimulating them or not. ScienceApe (talk) 02:03, 13 September 2011 (UTC)

That's not entirely true. Neurons develop more dense connections with each other the more you work your brain. Your immune system develops antibodies the more infections you get, so it gets stronger with use. There are lots of systems within your body which atrophy with less use. --Jayron32 02:27, 13 September 2011 (UTC)

But neurons aren't organs, and neither is the immune system. I'm also not sure if "growth" is really appropriate to describe them either. I can accept that your brain or your immune system is better if they are "worked out" but are they growing? ScienceApe (talk) 03:04, 13 September 2011 (UTC)

The brain isn't an organ? That's news to me! --Jayron32 03:23, 13 September 2011 (UTC)

And we know from astronauts that if bones don't bear weight regularly, they lose density. Probably every organ must be used to remain at full efficiency. It just that with many, like the heart and lungs, you never get the chance to see what happens to them if not used for a while. StuRat (talk) 02:37, 13 September 2011 (UTC)

Right, heart and lungs are constantly being used. What about skin? I just recall hearing a doctor say that the muscles are the only organ that must be maintained in order to function properly. But would my hypothesis on why atrophy occurs be valid? ScienceApe (talk) 03:09, 13 September 2011 (UTC)

Well, skin seems to atrophy if contained in a cast. I think your logic is sound. The body tries to conserve energy any way it can, and therefore neglects to maintain anything not currently in use. StuRat (talk) 03:15, 13 September 2011 (UTC)

Gorillas eat and sleep all day long, yet they don't seem to suffer from this problem. Count Iblis (talk) 15:27, 13 September 2011 (UTC)

Not all day, they don't. A sloth might be a better example. I would guess they are rather weak. StuRat (talk) 18:12, 13 September 2011 (UTC)

I would just point out that your heart and lungs do lose strength over time if you don't exercise them. This is especially notable if you have some sort of injury to them — I know someone who had some severe lung issues several decades ago, and requires a lot of exercise to keep her lungs at "normal" strength. People who do not exercise much have all sorts of issues regarding blood pressure that are cardiac in origin. --Mr.98 (talk) 22:46, 13 September 2011 (UTC)

Forensic pathologists can detect from the robust bone structure and ligament attachments if the deceased was, say a blacksmith, and can tell if he was left or right handed, so besides microgravity causing bone density loss, hard work, high impact exercise, or weight lifting can cause bones to become more robust. See also [1]. Edison (talk) 18:03, 13 September 2011 (UTC)

"the muscles are the only organ that must be maintained in order to function properly." that's clearly wrong. If you deprive a person of sensory information or social contacts (therefore, not stimulating his brain), his brain would stop function properly. Apparently, his neuronal mass would suffer from this deprivation. Quest09 (talk) 21:48, 13 September 2011 (UTC)

Strange Rodent Found in Yorktown Heights, NY USA. Please help identify.

File:MVI 0226 — Preceding unsigned comment added by Barbaricslav (talk • contribs) 02:26, 13 September 2011 (UTC)

You didn't upload any file under that name. Please try again. --Jayron32 02:28, 13 September 2011 (UTC)

How do I load a miniclip? Barbaricslav (talk) 02:29, 13 September 2011 (UTC)

See Special:Upload. StuRat (talk) 02:31, 13 September 2011 (UTC)

(edit conflict) See Help:Files. The only video format accepted at Wikipedia is .ogg; if you are unable to use that format you may want to upload your video to a site like Youtube and then post a link here. --Jayron32 02:33, 13 September 2011 (UTC)

Or grab some stills in JPG format. StuRat (talk) 02:33, 13 September 2011 (UTC)

OK Here http://www.youtube.com/watch?v=J4ZS78cck1s Barbaricslav (talk) 02:48, 13 September 2011 (UTC)

Looks like a dark brown hamster to me. Not sure of the exact species. They aren't that exotic. --Jayron32 02:58, 13 September 2011 (UTC)

We found it wild in the woods. We thought the eyes looked strange...Barbaricslav (talk) 02:59, 13 September 2011 (UTC)

In that case, it may be a vole, which resemble mice except that they have shorter, hairier tails (mice have longer, bald tails). I still think it looks like a hamster; hamsters are widely kept as pets, and there may very well be feral populations in many places. Hamsters have impressively large cheek pouches in which they store food; though they often look like other small rodents when their pouches are empty. Maybe someone with more expertise can chime in, but my first choice would be a hamster, my second would be a vole. --Jayron32 03:05, 13 September 2011 (UTC)

And since you mentioned the eyes, I checked closer; the eyes on your video look very much like those of the Golden hamster, which despite the name is often bred in many color varients. --Jayron32 03:10, 13 September 2011 (UTC)

If it was as tame as that when you found it, it is not a wild animal -- probably somebody's pet hamster that either escaped or was "liberated" because the owner got bored with it -- which unfortunately happens pretty frequently. Looie496 (talk) 06:01, 13 September 2011 (UTC)

I think it's tragic that people just release hamsters into the wild like that ... when there are hungry pet snakes which would surely enjoy their company. StuRat (talk) 02:37, 14 September 2011 (UTC)

What do you have against hungry wild foxes or coyotes? Googlemeister (talk) 13:09, 14 September 2011 (UTC)

Screw torque and strength of grip

My question relates to dental implants, but the sort of data I am interested in is currently completely ignored in the literature and I am supposing that it would be equivalent to screws in wood, so I ask thus:

If I screw 2 identical 3-inch screws into two planks of equivalent wood -- one 3.5-inches thick and the other 0.5 inches thick -- and the wood type is sufficiently dense to cause the screws to torque-out (and they do so at the same toque value), is it true to say that the screw placed into the plank that completely envelops the 3-inch screw (and is thus exerting equal-and-opposite torque on the entire length of the screw) is stuck in the plank in a sturdier fashion?

I ask this because dental implants are placed into jawbones and there is consensus that implants that lock at particular torque values are sufficiently sturdy, but I wonder if we can easily be fooled because it is quite possible for only a very limited length of bone along the length of the implant to be causing all the locking and we can't really determine this with current technology. (For those knowledgeable about dental implants, I am speaking of primary stability and not about osseointegration -- thanks!) DRosenbach ^{(Talk | Contribs)} 03:08, 13 September 2011 (UTC)

I would think both would be equally stuck in place, provided the wood, or bone, didn't split. However, since splitting is more of a risk with thinner bone or wood, this must be considered. Then, in the case of the bone, it seems there would also be concern that the screw might damage or irritate whatever was beyond the bone (a carpenter would also be concerned about this). StuRat (talk) 03:34, 13 September 2011 (UTC)

Thanks! DRosenbach ^{(Talk | Contribs)} 05:43, 13 September 2011 (UTC)

There is little, if any, relationship between the torque applied to a screw thread, and how well it is 'stuck in' (whatever that means) unless (a) one is dealing with a particular set of materials, (b) one is dealing with a particular length of engaged thread, and (c) one is dealing with engaging threads made to similar - and close - tolerances. Given all the variables involved with dental implants, I'd think (WP:OR) that 'torquing out' would be a fairly unreliable indication of the soundness of a dental implant screw - but on the other hand, I'm not sure that there would be better methods either, without extensive statistical analysis of clinical trials etc. AndyTheGrump (talk) 03:50, 13 September 2011 (UTC)

I thought it would be fairly obvious that by 'stuck in,' I meant to refer to the manner in which a screwed screw cannot be unscrewed unless a degree of torque exceedingly that which was used to place the screw were used to reverse it -- in other words, it is wedged in the wood by the wood's force upon it and cannot be removed unless a greater force is applied in the opposite direction.

And saying that there is little to no relationship unless we are dealing with a particular set of materials or a particular length of engaged thread appears to me to be meaningless because, unless you specify your 'particulars,' any given material or length happens to be a particular material or length -- so, again, I don't really understand what you're trying to say. The fact is that dental implants, is ultimately successful, integrate into the bone in about 3-4 months, until which time the primary stability is relied upon to maintain its rigid positioning. But why is torquing out a "fairly unreliable indication" of the implant-bone-rigidity soundness? Perhaps you're just speaking from a very advanced physics/carpentry perspective, but I don't think I really understood any of the points you were trying to make. Sorry :( DRosenbach ^{(Talk | Contribs)} 05:43, 13 September 2011 (UTC)

Lack of bright colors in mammals

Mammals seem less colorful than insects, fish, amphibians, and reptiles. That is, there aren't too many blue, green, violet, or purple mammals (except for maybe eye color). When mammals are colorful, it seems to just be a portion of them, such as (in primates) a mandrill's snout and butt (an orangutan is all orange, but usually more brownish-orange than bright orange). So, why is it that mammals are mostly "earth tones" while other animals are not ? Or, put another way, why do we have the coloration of moths rather than butterflies ? StuRat (talk) 04:55, 13 September 2011 (UTC)

"no other member in the whole class of mammals is coloured in so extraordinary a manner as the adult male mandrills" - Charles Darwin

The exception that proves the rule, I suppose Jebus989^✰ 08:44, 13 September 2011 (UTC)

Because it doesn't improve the ability of individually brightly colored mammals to have brightly colored babies. --Jayron32 04:57, 13 September 2011 (UTC)

Being less conspicuous makes one less susceptible to predators. Giraffes are pretty brightly coloured, but can fight off most potential predators with a decent kick. HiLo48 (talk) 05:04, 13 September 2011 (UTC)

1. Because mammals have a purely melanin-based form of pigmentation. No one probably knows exactly why, but we lost all the other pigments other animals have and instead are left only with melanin, pigments that cause blacks, browns, reds, and yellows. But no blues and greens. Blue pigments have also actually been lost far earlier by all vertebrates. Not just mammals, but all vertebrates. The only vertebrate which has blue pigments are members of the fish family Callionymidae (dragonets), which independently reevolved a unique vivid blue color-containing organelle known as cyanophores.
2. Why then do birds and reptiles and frogs and fish and mandrills have blue and green colors? This is because coloration in animals are produced by two different methods - pigmentation and structural coloration. Structural coloration does not rely on pigments but on tiny microscopic structures (in the vicinity of nanometers) that scatter light in a certain way. The blue we see on a turkey's head or the iridescent greens and blues in a peacock's feathers are all structural coloration and are not caused by actual pigments. You won't be able to get a blue dye by squashing Dendrobates azureus, never mind that they're highly poisonous. ;) And yes, even the blue on mandrills are structural coloration.
3. Mammals have fur. Structural coloration can be produced by structures on bare skin, scales, exoskeleton, and the fine mesh on feathers, but not by fur. This is why mandrills are only blue in exposed skin. The closest we can get is by varying melanin deposition in different stages in hair growth resulting in striped hair which gives a certain... subtlety to what really is just brown and black and white fur. Bleurgh.
4. Mammals, on average, also have very poor color vision in contrast to other animal groups. Reptiles, amphibians, fish, cephalopods, crustaceans, and birds see at least as many colors as humans, usually far more (including the ability to see polarized light). Even insects have some form of color vision usually extending into the ultraviolet spectrum. In contrast, most mammals are dichromats, able to distinguish only three colors - blue, green, and yellow. They are also usually red-green color blind. This is probably because our common ancestors spent around 200 million years as scurrying nocturnal creatures perpetually underfoot dinosaurs and other giant reptilians. And nocturnal creatures have little use for color vision. This is also why most invertebrates which don't even have a sense of sight are brightly colored, forms of aposematism and crypsis against their normally visually acute non-mammalian predators. Mammals, on the other hand, usually eat other mammals or grass, it's a case of the color blind eating the color blind. The reason why a tiger is perfectly confident with his jarring orange and black stripes among green grass is because most of his prey can't tell the difference. Humans having color vision was a fortunate stroke of fate, as once upon a time in a steamy jungle somewhere, a group of herbivorous monkeys fancied fruit. And in order to tell ripe fruit from nasty unripe ones (as well as tender young red leaves from nasty rubbery old ones), they had to see red (angreh monkeh! cf. birds and red berries). That evolutionary pressure resulted in us today being trichromats and being able to enjoy M&M's even when the green ones taste exactly like the red ones.^{[citation needed]}
5. The previous reasons excludes old ladies with blue hair, which are a paraphyletic clade of mammals which have evolved independently to fit in.-- Obsidi♠n Soul 08:18, 13 September 2011 (UTC)

Acceleration

If a car produces 200BHP and 500lb-ft of torque, would it accelerate faster than a car with 400 BHP and 300 torque at a higher rpm? Both cars are of equal weight and shape. Just the engine is different.--213.107.74.132 (talk) 17:12, 12 September 2011 (UTC)

The RPM affects the BHP and torque, but doesn't figure in to it, here, since the BHP and torque are already known. Also, are we considering the possibility that the wheels will just spin, or do we assuming we maintain traction at all times ? StuRat (talk) 17:21, 12 September 2011 (UTC)

I know the rpm affects it, i'm not worried about it. If Car A has 200BHP and 500lb-ft torque at X rpm, and car B has 400BHP and 300 torqu at X rpm, which goes 0-60 fastest and which has highet top speed (MPH)? Both has traction. — Preceding unsigned comment added by 213.107.74.132 (talk) 17:24, 12 September 2011 (UTC)

Because these figures only provide the peak output, it is impossible to answer this question. Torque and HP are dependent on each other. Torque = (HP x RPM)/a coefficient. If you know the torque and the RPM then you know the HP. These figures are just intended to give a rough idea regarding vehicle performance. The reason torque figures are provided in vehicle specifications is to give a sense of the engine's low RPM output. If two vehicles are identical, aside from the engine, you would need a graph of engine out put over the RPM range (in torque or HP) in order determine which would be faster. --Daniel 18:42, 12 September 2011 (UTC)

Look at these:

3000rpm 360BHP 630 TQ
4000rpm 497BHP 693 TQ
5000rpm 542BHP 569 TQ REDLINE

Versus this higher-reving engine:

4000rpm 436BHP 572 TQ
5000rpm 509BHP 535 TQ
6000rpm 719BHP 629 TQ

These show 2 Engines, one with higher redline than the other. This shows the curve from 3000rpms before the redline. One has higher TQ, and one has higher HP. — Preceding unsigned comment added by 213.107.74.132 (talk) 18:56, 12 September 2011 (UTC)

That is true, but it doesn't change what I said. Torque and Horsepower are directly related and these figures confirm it. (630 TQ X 3000 RPM)/5252 (coefficient in this case) = 360. Your question can be boiled down to the very simple; which is better for acceleration, peak horsepower or peak torque? The problem is there isn't an answer. In order to determine which vehicle will accelerate faster, you need to look at the entire torque or hp curve, not just the peak. --Daniel 19:53, 12 September 2011 (UTC)

How about these: (TQ=Torque in lb-ft)

1000rpm  91BHP 477 TQ
2000rpm 229BHP 601 TQ
3000rpm 360BHP 630 TQ
4000rpm 497BHP 693 TQ
5000rpm 542BHP 569 TQ REDLINE
5000rpm is the redline

versus this one:

1000rpm  41BHP 214 TQ
2000rpm 196BHP 514 TQ
3000rpm 319BHP 559 TQ
4000rpm 436BHP 572 TQ
5000rpm 509BHP 535 TQ
6000rpm 719BHP 629 TQ REDLINE
6000rpm is the redline.

With max traction and equal weight and drag, which will do 0-60mph(0-97km/h) fastest and top speed in MPH (162km/h = 100 MPH).

Is it possible for a car to go more MPH than HP? The TQ always seems to peak before the HP for some reason...

Is it possible for a car to go more MPH than HP? Do you mean a car with higher top speed in MPH than the maximum engine power in HP? A lot of small cars do this, e.g. the current Fiat 500 has 69BHP and a top speed of 99MPH, and one variant of the Smart ForTwo does 92mph from 71BHP. --Colapeninsula (talk) 09:42, 13 September 2011 (UTC)

What about cars with 200-600 BHP

• • • • • Which of the 2 Power curves will be the fastest?--213.107.74.132 (talk) 12:32, 13 September 2011 (UTC)

It is still not possible to answer definitively without the gear ratios. Since the vehicles have different power curves they would need different gearboxes and final drive ratios to achieve an optimized acceleration. If you want to ignore the gearbox and get a rough idea, graph the HP or torque across the rev range for both vehicles, then calculate the area under each graph. The one with the large area is probably faster. --Daniel 19:11, 13 September 2011 (UTC)

Horsepower

How many HP,BHP,PS and/or lb-ft do you need to make a car that weighs 2,500 lbs, has a frontal area the same size as the McLaren F1 and has a drag coefficient of 0.32, to go 300 MPH? — Preceding unsigned comment added by 213.107.74.132 (talk) 09:28, 13 September 2011 (UTC)

If it is air resistance limited, then a 25% increase in top speed would require a 95% increase in horsepower. So, using the McLaren benchmark, it would need about 1200 hp. Of course that neglects the role of rolling resistance and and the fact that adding that many horses is probably impossible without also increasing the weight considerably. Dragons flight (talk) 14:39, 13 September 2011 (UTC)

So how come the Bugatti Veyron Super Sport can go only 268 MPH? Surely fifteen-hundred pounds of weight cannot make that much difference (32 mph) to the top speed, can it? BTW, how much more BHP is needed for 350MPH? Don't forget drag is even higher(Maybe a doubling in BHP will only increase speed by ~15% - i'm not sure, just a guess -) than before, so the 95% increase horsepower for 25% more speed rule may now be incorrect. — Preceding unsigned comment added by 213.107.74.132 (talk) 15:01, 13 September 2011 (UTC)

Once you get into high speeds above about 220mph, you can also no longer ignore the fact that air is compressible, so the simplified fluid dynamics models no longer apply. Googlemeister (talk) 16:12, 13 September 2011 (UTC)

It also isn't entirely about frontal area, at that speed the actual aerodynamics are equally if not more important. --Daniel 19:14, 13 September 2011 (UTC)

Is it true that Charles Darwin was not a scientist?

Topic says it all. ScienceApe (talk) 14:04, 13 September 2011 (UTC)

What defines a scientist? I'm sure that one can construe various definitions that do not consider Charles Darwin a scientist. Our "broad sense" definition, though, of "one engaging in a systematic activity to acquire knowledge" seems to fit the bill nicely. Darwin was a scientist. — Lomn 14:14, 13 September 2011 (UTC)

What a strange question ! In modern terminology, Darwin was certainly a scientist. But in the vocabulary of his period, he would more likley have described himself as a "naturalist". Gandalf61 (talk) 14:27, 13 September 2011 (UTC)

Right. Also maybe a natural philosopher or a natural historian. For a modern usage, we have the journal The American Naturalist, which covers evolution and ecology (among other topics). SemanticMantis (talk) 14:36, 13 September 2011 (UTC)

See the last two paragraphs (or one paragraph, depending on how one reads it) of the lead of Scientist; the word was not widely used in the UK until after Darwin's time, having been coined only in 1833. Deor (talk) 16:01, 13 September 2011 (UTC)

Darwin was notoriously systematic and detailed. That was one of the primary reasons it took him so long to publicize his revolutionary idea. If his super-careful study of many vastly different species of organisms did not make him a scientist, few people should be considered one. Imagine Reason (talk) 16:33, 13 September 2011 (UTC)

In my mind, the OP's statement that the "Topic says it all" says an awful lot about the OP. One would hardly ask such a question WITHOUT a "hidden" motive, so the topic probably doesn't say it all. Taking the title literally, maybe it should be moved to he Language ref desk. HiLo48 (talk) 17:29, 13 September 2011 (UTC)

One should assume good faith rather than speculating on the OP's "hidden motive" and this is clearly the correct ref desk. Edison (talk) 17:54, 13 September 2011 (UTC)

Questions are frequently not perfectly written. To fully answer someone's question it is often necessary to work out what they really wanted to find out. To not go beyond the literal meaning is often selling a questioner short. HiLo48 (talk) 17:59, 13 September 2011 (UTC)

"Chares Darwin was not a scientist" is Creationist trolling, although not very common as far as I know. I expect ScienceApe saw the claim on a Creationist site and wanted to know how scientists would respond to it. Looie496 (talk) 18:42, 13 September 2011 (UTC)

Neither of the Wright brothers held a pilots licence. Therefore they couldn't have invented the aeroplane. It must have been created by an Intelligent Designer instead... ;) AndyTheGrump (talk) 19:12, 13 September 2011 (UTC)

Are you saying that the Wright Brothers were not intelligent, or that they did not design their aircraft? Googlemeister (talk) 19:58, 13 September 2011 (UTC)

No. AndyTheGrump (talk) 23:54, 13 September 2011 (UTC)

[As the original poster, you would have done better by making the heading "Charles Darwin" instead of "Is it true that Charles Darwin was not a scientist?" and by making the original message "Is it true that Charles Darwin was not a scientist?" instead of "Topic says it all."

—Wavelength (talk) 20:34, 13 September 2011 (UTC)]

[I am revising my message by using the grammatical second person.

—Wavelength (talk) 21:33, 13 September 2011 (UTC)]

Charles Darwin was definitely a scientist in the early-to-mid 19th century British understanding of the profession. He was, though, a very late embodiment of the Romantic conception of science — his greatest scientific hero was Alexander von Humboldt. In his youth he went exploring (like Humboldt) and gained a lot of acclaim for that. As he grew older he spent more of his time collating other people's work, and some time conducting small-scale biological experiments at his home. And of course he eventually published his theories on evolution. There is really no way you cannot consider him a scientist. The idea of what it meant to do biological science changed quite a lot, though, over the course of the 19th century. A lot of work Darwin did looks decidedly antiquarian to people just a generation later. One might say, in a poetic vein, that if Newton was the last of the magicians (pace Keynes), then Darwin was the last of the Romantics. --Mr.98 (talk) 22:10, 13 September 2011 (UTC)

Charles Darwin was as much a Scientist as anyone has ever been. Even to this day he is a role model for many scientists and even many non-scientists, like me. Vespine (talk) 22:43, 13 September 2011 (UTC)

What I was indicating is that what it means to be a scientist is different at different points in history. If Charles Darwin magically showed up here tomorrow, many of his methods and approaches and ways of thinking would make him seem like a lovable old crank, not a modern biologist. But that's just because biology has changed a lot, and the professionalization of scientists has changed a lot since his time. Whereas if you picked someone from 1900, or 1920, they'd seem much more "modern" even if they were transported to the present. The late 19th century was a period of major transformation of the profession. --Mr.98 (talk) 01:47, 14 September 2011 (UTC)

Wow, I had no idea people would think I'm a creationist. That's a first. I'm an atheist and I accept evolution... I would think my screenname would have given that away though. I was just asking this question because I was under the impression that Charles Darwin was a layman who just happened to put forth a revolutionary scientific theory. ScienceApe (talk) 04:00, 14 September 2011 (UTC)

No. See Charles Darwin#Childhood and education and Charles Darwin#Works. PrimeHunter (talk) 04:09, 14 September 2011 (UTC)

He had a partial medical education and had read a lot of books. When he was on the Beagle he was more or less a "gentleman scientist". The fact that he did a good job on that voyage (systematically writing everything up, creating some compelling and ultimately correct theories about geology, etc.) lead to his being appointed a Fellow of the Royal Society. So again, by the standards of his day, he was certainly a "scientist" by the time he started publishing on evolution, decades later. He did not have a specialized degree for biology, but again, this was not standard in the early 19th century, before science completely professionalized. --Mr.98 (talk) 12:58, 14 September 2011 (UTC)

Could you cite some method from Darwin that would make him look like a 'lovable old crank'? His voyage, even if performed with simple means, seems pretty solid to me (scientifically speaking). Quest09 (talk) 22:47, 14 September 2011 (UTC)

approximate width of an actual circle

Empirically, given a circle with radius width, what is it's usual approximate width? (i.e. the width of the 'circumference'). Mathematically, this would be 0, but obviously in the real world that would make it invisible, and in that case what's to say that it's a circle there at all (and not a square or an unfilled outline of a unicorn with width 0)? So obviously real-world circles do have a width, and, empirically, what is this? 82.234.207.120 (talk) 15:01, 13 September 2011 (UTC)

The width is double of the radius, and the circumference is about 3.14285 times the width. — Preceding unsigned comment added by 213.107.74.132 (talk) 15:05, 13 September 2011 (UTC)

To be precise, the circumference is about 3.14159 times the width. You appear to have very precisely noted the approximation for pi (22/7); unfortunately this approximation deviates from the real pi after the 3rd decimal place. Weasley one (talk) 16:05, 13 September 2011 (UTC)

It sounds to me like you're talking about the width of a line used to draw a circle, but that's not a property of the circle itself, nor can anything be generalized: width of border can vary from 0 (consider a black circle on a white background, or consider a circular road sign) to an arbitrarily high value. Real objects do not require borders of meaningful width; their dimensions simply are. — Lomn 15:19, 13 September 2011 (UTC)

A fine pen nib is typically 0.2-0.3mm in width, if that's what you mean.--Shantavira|^{feed me} 15:32, 13 September 2011 (UTC)

I seem to recall an ANSI or ASME standard for line thicknesses. For a standards-compliant technical draft drawing, the width of the line for a circle depends on why you are drawing the circle. (For example: a circle drawn to indicate an extension of a fillet or round, for purpose of demarcating radius, is thinner than the actual part line; a circle used to indicate radial arrangement of objects is thinner than a circle indicating a machining instruction). Have a read at the line thickness in CAD Standards article. That article links to ISO 128, but I seem to recall an American standard (ANSI or ASME) that had different standard lines. I'll look this up in my drafting textbook when I get home. Nimur (talk) 15:45, 13 September 2011 (UTC)

From textbooks on visual science, the threshold value for a thin dark line is such that a thinner line can be seen than a dot of the same width. An extended dark line on a light background can be amazingly thin and still seen. For a bright line in darkness, it is the brightness rather than the visual angle that is the limiting value for a thin line. Edison (talk) 14:13, 14 September 2011 (UTC)

All this talk about a circle should be about the annulus whose border thickness is (R - r). Cuddlyable3 (talk) 13:04, 15 September 2011 (UTC)

Cosmetic Surgery

I was wondering, what are the most common significant cosmetic procedures? By significant, I mean something that is not an outpatient procedure (i.e. requires an overnight stay in the hospital.) Rabuve (talk) 16:34, 13 September 2011 (UTC)

Note that Wikipedia cannot provide any medical advice.Your doctor should be the adviser on such questions for a given patient. As general information, a review of the literature on plastic surgery shows that some pretty drastic procedures, involving surgical drains, for instance, send people home the same day, so "significant" is strangely defined here. Googling outpatient plastic surgery produces facelift, nose job, lip enhancement, boob job, tummy tuck. Medical Faculty Associates of George Washington University say "Virtually all cosmetic surgery can be done as an outpatient. Some patients choose to spend one or two nights in the hospital." They mention the option of home nursing care. You did not mention what country you are in. For the US, "Basics of the U.S. Health Care System"(2010) By Nancy J. Niles, page 120 describes the 4000 "Ambulatory surgery centers" which do 8 million operations or procedures a year, with plastic surgery being a commonly done procedure, on an outpatient basis. Even back in 1988, an article in "Working Mother" magazine said that most plastic surgeries were done on an outpatient basis. I could not find the requested list of plastic surgeries "which require an overnight stay in the hospital" but complications or special patient conditions (such as accident or burn victims) might be a factor in requiring hospitalization after what is typically outpatient surgery. "The Encyclopedia of Cosmetic and Plastic Surgery" (2009) page 25 says that breast reduction may be done in a hospital or an outpatient surgery center, for instance. Edison (talk) 17:33, 13 September 2011 (UTC)

Thanks for the answer. It was just as I expected; mostly it's the surgeris we think about right away. Rabuve (talk) 18:29, 13 September 2011 (UTC)

Surface tension

Another stupid question from my side, regarding Surface tension. I have read that the cause of surface tension is due to unbalanced forces on the top layer of particles in a liquid; an unbalanced downward force, perpendicular to the surface of the liquid. But, when we speak about surface tension, we represent it as a force (per unit length) along the surface of the liquid. Can anyone explain? Thanks! Lynch7 17:04, 13 September 2011 (UTC)

Sure, the "Unbalanced" perpendicular component of the force generates a potential energy which is proportional to the surface area. That's equivalent from the energetics point of view to having a surface tension. An other way to look at it is that the forces responsible for the surface tension are present everywhere but in the bulk they always cancel out. Dauto (talk) 21:24, 13 September 2011 (UTC)

Thank you Dauto. Well, I understand that dimensionally, Energy per unit area translates to Force per unit length, which is equal to the dimensions of Surface tension. Can I know how exactly the "per unit area" part comes in here? There is an unbalanced force, so there is free energy on the top layer, but how does it translate to energy per unit area? Thanks :) Lynch7 02:53, 14 September 2011 (UTC)

The larger the surface area is, the larger the number of molecules with missing neighbors will be. So the total potential energy is proportional to the surface area. Dauto (talk) 03:05, 14 September 2011 (UTC)

stability of solar systems?and star cluster and great walls....

Do we know about a multi-star system that is not hierarchical, which is stable? Is it theoretically possible? does a star cluster have a hierarchic? another thing, is it possible that a star after supernova, will be drag by a gravity of planet that rejected by an other solar system? I mean that ex-star will begin to rotate over him. is it possible that a planet will have more mass than some stars? and finally, last thing, what is the status about the "great walls"? I mean is it a new discovery? Exx8 (talk) —Preceding undated comment added 21:49, 13 September 2011 (UTC).

It looks like English isn't your first language, so let me try to break your questions down and answer them:

1) Can a star cluster be stable without being hierarchical ? I assume by that you mean it doesn't have a massive star which has mid-sized stars orbiting it and mini-stars orbiting them. Actually, that "hierarchical" system never exists, as far as I know. The far more common system has many stars of similar masses all orbiting one another. And, yes, I think it can be stable, but perhaps others can say how stable (thousands of years ? millions ? billions ?).

2) Is it possible for a small star to orbit a massive planet. I would say no. They could orbit one another, but the center of rotation (barycenter) would be outside the planet.

3) Are "great walls" a new discovery ? I don't know what you mean here. I'm guessing, since your first 2 questions were about astronomy, that this isn't about the Great Wall of China. StuRat (talk) 02:02, 14 September 2011 (UTC)

He's talking about Sloan Great Wall. Dauto (talk) 02:45, 14 September 2011 (UTC)

Or possibly CfA2 Great Wall. Dauto (talk) 02:47, 14 September 2011 (UTC)

The latter is the original great wall discovered some 20 years ago Dauto (talk) 02:50, 14 September 2011 (UTC)

In the long run all gravitationally bound systems are unstable. The question is in what time scale does the instability take over. For instance, Star clusters do evaporate. Dauto (talk) 02:56, 14 September 2011 (UTC)

"blue light" and time of day

In a textbook on plants, I'm stumbling on the "blue light-dependent system" of photosynthesis in certain plants, particularly shade plants. The textbook states that, in this model, blue light activates stomatal opening, and later on says that rapid opening of stomata is triggered at dawn ("when light is composed largely of blue wavelengths") and "during brief exposures to sunflecks". I'm sure I'm being confused by my simple human assumption that blue light would be blue light that I can see. Dawn and sunflecks do not strike me as being particularly 'blue' at all. I can't find a good link on the web or WP to times of day when there is more 'blue light' though, nor exactly what this means from a visual/time of day cycle. How should I be interpreting this blue light association? What about a sunfleck is more blue than shade? 82.71.20.194 (talk) 22:01, 13 September 2011 (UTC)

This is complicated. First of all, atmosphere scatters blue light more effectively than it scatters red light. When it is midday at your location, the sunlight has the least distance to travel through the atmosphere to reach you; therefore both the blue and the red light reach the surface effectively. When the sun is barely above the horizon, however, (in the morning or in the evening, or in winter near the Arctic circle), the path the light has to travel through the atmosphere is much longer and blue does not reach you as efficiently as red. At that time the relative balance of colors is shifted towards the red or orange. Now when the Sun is below the horizon, the opposite may be true: Earth curvature blocks the red (remember, it is scattered less, so more of it travels the direct path from the Sun), but the more-scattered blue can bypass the Earth curvature; therefore before sunrise or after sunset there are times when everything looks bluish. This, of course, depends a lot on the cloud cover, terrain, etc., so it's not always the case. Sharp shadow, too, may look bluish under some conditions, for the same reason: more red arrives directly form the sun and is blocked by the object that casts the shadow, but relatively more blue arrives from elsewhere in the sky and bypasses the object that casts the shadow. This is a fairly weak effect, however; usually too weak to even notice. Finally, there is a so-called Purkinje shift, which makes us see blue as more bright (compared to yellow) under dim light. This is a property of the human retina, however (rod receptors are more blue-sensitive than L and M cone receptors), and obviously has no effect on plants. Regarding the plants: chlorophyll can absorb both red and blue light; but chlorophyll-based photosynthesis is not the only light-dependent process in most plants. I know that orchids do not grow well under purely red or purely blue light; people who grow orchids indoors usually mix the "cool" and "warm" daylight fluorescent lights at 1:1 or 1:2 proportion. I do not know if the stomata opening is triggered by blue light only, but it should not make much of a difference because the amount of both blue and red light increases sharply at dawn and decreases sharply at dusk. The relative changes in red vs blue balance are more subtle. Hope this helps. --Dr Dima (talk) 23:22, 13 September 2011 (UTC)

N.B. You may also want to look up phototropin and cryptochrome, either here on Wiki or in the published articles. --Dr Dima (talk) 23:33, 13 September 2011 (UTC)

Note that on cloudy days, the direct red light may be blocked by clouds, with only the blue light getting through. StuRat (talk) 02:07, 14 September 2011 (UTC)

Interesting... Would plants adapted for polar night conditions (in the tundra, northern edge of taiga, etc.) also have more blue-light-dependent photosynthesis? 67.169.177.176 (talk) 00:39, 14 September 2011 (UTC)

Lightsaber

Don't the Jedi knights in Star Wars need to wear fireproof suits to protect them from the radiant heat emitted by their own lightsabers? I know those things use plasma, and that stuff is EXTREMELY hot! 67.169.177.176 (talk) 23:35, 13 September 2011 (UTC)

Lightsabers have variously contradictory physical properties. They are fictional. The nerds over at Wookipedia say that apparently the plasma is contained in some kind of force containment field, which also contains the heat. This has nothing to do with real physics. --Mr.98 (talk) 23:53, 13 September 2011 (UTC)

Solid light, possibly? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:17, 14 September 2011 (UTC)

I always pictured it as an extremely powerful laser that magically stops after a meter or so. If so, then it wouldn't generate much heat when just cutting through clear air, but would when it encountered and object. StuRat (talk) 02:10, 14 September 2011 (UTC)

The problem with the laser thing is that (like you said) a laser doesn't stop, it keeps on going. Also, it won't clash with physical objects or other laser lightsabers, it will pass right through them as if you were holding a flashlight. Plasma has the same kind of problem, even if you can contain it in a magnetic field (good luck with that) it won't clash with objects either. My idea that I pulled out of my ass is to use something like what the T-1000 is made out of. I guess millions of nanomachines that can morph into various objects. They should have good thermal conductivity but robust enough to tolerate being heated up. Just contain them in a lightsaber style handle thing, then when you turn it on, they morph into a blade which is then heated to intense temperatures by a power source. ScienceApe (talk) 03:53, 14 September 2011 (UTC)

Are you sure about the part where you said that plasma won't clash with objects? I've seen the History Channel show Star Wars Technology, and they said that plasma can behave as a solid when magnetically confined (and frankly, I can see how this can happen). 67.169.177.176 (talk) 00:59, 15 September 2011 (UTC)

Umm, and lasers "won't clash with physical objects"? So how do you account for their widespread industrial use for cutting? Indeed, how do you account for their use in pointing at PowerPoint images? If photons aren't bouncing off of the screen and being absorbed by the cones in your own retina, how do you manage to see them?—PaulTanenbaum (talk) 01:35, 15 September 2011 (UTC)

I think he/she meant that lasers won't clash with other lasers, as lightsabers do. Magnetically confined plasma, though, can clash with other plasma, see Diamagnetism for a more detailed explanation. 67.169.177.176 (talk) 01:47, 15 September 2011 (UTC)

Light doesn't bounce off of light. I was thinking of having a collapsible retroreflecting pole as the blade, with a mirror at the top, in order to cap the light to keep it from hitting the ceiling. The pole would give the weapon the ability to clash with another. →Σ _{^talkcontribs} 02:43, 15 September 2011 (UTC)

Lol that's not what I meant. Clash in the combat sense. When you swing a sword against an object, you encounter resistance. If you were to swing a "plasma sword" against something, you may burn it, but you won't encounter any resistance. It would be like swinging a flashlight or laser pointer at something. Diamagnetism is way too weak, you won't encounter resistance. That doesn't make for a very good sword. As for swinging two plasma swords together and having them clash magnetic fields? Michio Kaku seems to believe that they won't clash either. See the following, http://www.youtube.com/watch?v=wp_Hq1f8-0E&feature=related ScienceApe (talk) 19:28, 15 September 2011 (UTC)

Yeah, and he's also found a way to solve this problem: use a telescopic rod of high-temperature ceramic to enable parrying. I wonder if that will work. 67.169.177.176 (talk) 04:14, 16 September 2011 (UTC)

I don't think so. While the ceramic is heat resistant, it's also brittle. Not really something you want to smack things with. ScienceApe (talk) 05:27, 16 September 2011 (UTC)

Reinforce it with tungsten filaments, maybe? :-) 67.169.177.176 (talk) 06:01, 16 September 2011 (UTC)

September 14

Chainsaw as weapon

Seeing a suggestion in an earlier section on how to "improve" a sword by adding a cutting chain to it, would a chainsaw make a very effective weapon? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:16, 14 September 2011 (UTC)

Maybe? --Jayron32 00:18, 14 September 2011 (UTC)

Please be serious. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:21, 14 September 2011 (UTC)

Not really. It's fairly easy to derail chains, especially when using them to flail away at things; and once derailed, they're pretty useless. They look and sound scary, and they can of course intimidate and do real damage. But they're surprisingly fragile for the reason stated. --Tagishsimon (talk) 00:24, 14 September 2011 (UTC)

Maybe if you held the chain on with superstrong magnets or such? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:25, 14 September 2011 (UTC)

But that would tend to stop it from rotating, as much as it stopped it from derailing. So maybe not. --Tagishsimon (talk) 00:47, 14 September 2011 (UTC)

If you moved the magnet along with the chain... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:53, 14 September 2011 (UTC)

How are you going to do this without greatly increasing friction? You could as easily suggest an I shaped tooth such that the bottom of the I prevented the chain from being pulled free of the chain bar. This, too, would inevitably increase friction. A key problem for chainsaws is that chains stretch when they heat up. One of the reasons that by design the chain is lubricated with a continuous flow of oil is to minimise friction to prevent lengthening. Under either scheme - magnet or I - you're trading a perception of "more difficult to derail" for more friction, more heat, and thus chain lengthening. And if the chain is now held such that it cannot stretch as it heats, it will try to get free of its restraints, which will cause more heat and more stretching until the point that it snaps, or binds up. And all that would be why chains are not I shaped. Back to the drawing board for you, I'm afraid. You could, I suppose, argue that you could dynamically adjust the chain bar length to obviate the lengthening problem. But then when you turned the thing off, your mechanism would have to deal with chain contraction. It's one thing to control chain lengths as a bicycle does with derailleur gears. Quite another to do so at the speed a chainsaw chain is revolving. --Tagishsimon (talk) 01:06, 14 September 2011 (UTC)

How about if the only part that was magnetic was the part furthest from the axis of rotation? (Either that or use extremely strong metal...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:13, 14 September 2011 (UTC)

They already use extremely strong metal ;). You're trying to eat you cake and have it, by saying, in essence, use fewer magnets to decrease the added friction, but hope that they provide as much protection against derailing as was previously the case. You have to face it that the chainsaw business is big and very long established business, and were there a better solution, the probability is that one or other of the manufacturers would have arrived at it by now. But they haven't, and I think a) we can take it that that is for good practical reasons and b) in considering the suitability of chainsaws as weapons, we're going to have to stay within the bounds of the possible and not drift into wishful thinking. --Tagishsimon (talk) 01:20, 14 September 2011 (UTC)

This, for completeness, is the nearest thing to your ideal; the Stihl MS 460 Rescue Saw, designed to cut through metal sheet. The majority of the saw is shrouded to prevent derailling, and only the tip has protruding teeth to do the cutting. I confess I should not wish to meet you, unarmed, on a dark street at night, were you wielding one of these. You may now say "¡Ay, caramba!". --Tagishsimon (talk) 01:44, 14 September 2011 (UTC)

Okay. ¡Ay, caramba! Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:03, 14 September 2011 (UTC)

I think the main weaknesses of a chainsaw as a weapon are it's weight and short reach. If someone was chasing you with a running chainsaw, you could probably outrun them, especially if they were being careful not to injure themselves. If you had much of a weapon, you could probably get at them first. You could shoot them, stab them with a sword, or throw a knife at them before they got close enough to use the chainsaw. And then there's the lack of stealth. You can't exactly sneak up on somebody with a running chainsaw. The weight would also make the attacker likely to fall over (especially if you helped them by hitting them with a chair). If they fell on the running chainsaw, or it fell on them, that might take the fight out of them. StuRat (talk) 02:18, 14 September 2011 (UTC)

Chainsaws pose a serious danger to the user. At the "Stihl MS 460 Rescue Saw" site I read: "IMPORTANT INFORMATION/WARNING: The occurrence called “kickback” can cause serious or fatal injury." Kickback is also mentioned in this article. Bus stop (talk) 02:37, 14 September 2011 (UTC)

There's a risk of kickback, but you have to be using a chainsaw fairly inattentively to be injured by it. If you're gripping it correctly and it kicks back, the front-most of your two hands will trip a lever which brakes the chain. I guess if you're leaning over the bar as you're cutting, and you don't have a hardhat and face visor then ... maybe you;re asking for it. --Tagishsimon (talk) 20:10, 14 September 2011 (UTC)

Have there ever been any real life murders with chainsaws even? If there weren't, I wouldn't be surprised. They are slow, heavy, large and cumbersome. Not to mention loud as hell, that would attract a lot of unwanted attention. ScienceApe (talk) 03:26, 14 September 2011 (UTC)

Well, if the victim was previously knocked out or tied up, there's no reason they couldn't be finished off that way, although you'd need good luck to clean up that crime scene. StuRat (talk) 04:03, 14 September 2011 (UTC)

I'm surprised no one has mentioned this yet. here is a nice model that is being given away in a competition. Vespine (talk) 03:55, 14 September 2011 (UTC)

Chainsaws in popular culture mentions the problems with using them as weapons: Brian de Palma claims the chainsaw killing in Scarface was based on a real murder, but there's no evidence about the actual details of the crime. --Colapeninsula (talk) 11:47, 14 September 2011 (UTC)

Whereas Health & Safety authorities and Accident & Emergency departments continue to deal regularly with the consequences of incautious use of a chainsaw [2]Elen of the Roads (talk) 22:40, 14 September 2011 (UTC)

Solid light

Is it possible to solidify light? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:24, 14 September 2011 (UTC)

Not that I know of. 67.169.177.176 (talk) 00:35, 14 September 2011 (UTC)

What if you compressed lots of photons into a crystal of light? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:36, 14 September 2011 (UTC)

Doesn't work this way -- you can't "compress" photons because they're massless, uncharged and travel at the speed of light. You could focus a beam of light, but that's not the same thing -- even if you focus it to a width of one angstrom, it won't turn into a solid. 67.169.177.176 (talk) 00:42, 14 September 2011 (UTC)

You can't crystalise or compress photons. However, there does exist a type of object called a photonic crystal - type of substance that is composed of microparticles, that forms a quasicrystal in the presence of a certain frequency of light, held together by induced electrostatic attraction between the particles. It is a quasicrystal, because its components does not consist of discrete atoms or molecules. This technique has been demonstrated on polystyrene microbeads. Plasmic Physics (talk) 01:04, 14 September 2011 (UTC)

¡Ay, caramba! Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:07, 14 September 2011 (UTC)

Not solid, but still interesting... Count Iblis (talk) 01:17, 14 September 2011 (UTC)

That is interesting, though the military application may be worrisome. Somebody should set a SETI project looking for such things from deep space... Wnt (talk) 13:59, 15 September 2011 (UTC)

Put the light in a black hole? A Black hole isn't solid though... Has mass, but it's not solid. Very strange thing. ScienceApe (talk) 03:21, 14 September 2011 (UTC)

Mercury has mass but is not solid (it's a liquid, to be exact). 67.169.177.176 (talk) 00:51, 15 September 2011 (UTC)

What are you talking about? Plasmic Physics (talk) 23:05, 15 September 2011 (UTC)

Trying to make a point that objects don't have to be solid in order to have mass. 67.169.177.176 (talk) 01:45, 16 September 2011 (UTC)

Who said they did? Plasmic Physics (talk) 11:51, 16 September 2011 (UTC)

ScienceApe did, when he/she said that a black hole "has mass but it's not solid... very strange thing". 67.169.177.176 (talk) 19:57, 17 September 2011 (UTC)

He didn't make that point. He was proposing that if light enter a black hole, the light is somehow solidifies onto the singularity. He corrected himself, since the definition of a solid does not apply to a singularity. Then, he remembered you statement, "you can't "compress" photons because they're massless," and concluded that even though a black hole is not massless, neither is it a solid. It short, he refuted his own statement. Plasmic Physics (talk) 23:54, 18 September 2011 (UTC)

Using an ultracentrifuge for almost-suspended animation

Dear Wikipedians:

Modern ultracentrifuge are capable to reaching an acceleration of millions of g's. Since Einstein's General Relativity says time dilates in strong gravity fields, and the equivalence principle states that millions of g's of centrifuge acceleration is equal to millions of g's of gravity field, wouldn't time in a modern ultracentrifuge be massively dilated? And can I then use the ultracentrifuge for almost-suspended animation by placing some fresh food into it, spin it for 5 years, and retrieve the food to find it still warm and hot?

Interestingly, the article g-force states "Recent research carried out on extremophiles in Japan involved a variety of bacteria including E. coli and Paracoccus denitrificans being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an ultracentrifuge at high speeds corresponding to 403,627 g. Paracoccus denitrificans was one of the bacteria which displayed not only survival but also robust cellular growth under these conditions of hyperacceleration which are usually only to be found in cosmic environments, such as on very massive stars or in the shock waves of supernovas."

But how can Paracoccus denitrificans cellular growth be observed by humans in the lab's resting frame when the bacteria is massively accelerated to 403,627 g, and hence experience massive time dilation, so that typical cellular growth time for the bacteria might translate into thousands of years for human scientists in the resting lab frame?

Thanks,

174.95.169.5 (talk) 00:28, 14 September 2011 (UTC)

400000 g is still way too low to see noticeable time dilation effects. For that you'd really need something more like a hundred billion g's. Dragons flight (talk) 00:44, 14 September 2011 (UTC)

It works out to roughly (acceleration in gees) × (centrifuge radius in light years) = (time dilation factor)² − 1. For a time dilation factor of 2 and a centrifuge radius of 1 km, you need an acceleration of 3×10¹³ g. -- BenRG (talk) 23:01, 14 September 2011 (UTC)

You're not applying the equivalence principle correctly. In fact you should expect zero time dilation in this situation. Of course there will be time dilation due to the relative motion but that's another matter. Dauto (talk) 02:19, 14 September 2011 (UTC)

Let me give a more elaborate answer to that question.

• Starting with a thought experiment on a building on the Earth's surface. Suppose that a laser located at the bottom floor of the building sends a signal to the top floor of the building where it is detected and its frequency is carefully measured and it is observed that this frequency is slightly lower than the emitted frequency.

1. This frequency shift - a redshift - can be interpreted as gravitational time dilation.
2. Another way to look at this redshift is that the photons lost some of their energy because they climbed the gravitational potential well and, like anything else, had to pay the toll (gravitational potential energy) with some of its own energy. From Planck's relation $E=h\nu \,$ we see that this imply a redshift.
3. Note that what matters here is the gravitational potential $\phi =-{\frac {GM}{d}}$, not the gravitational acceleration $g={\frac {GM}{d^{2}}}$, so it is incorrect to say that the local gravitational acceleration causes the redshift. The local acceleration might even be zero (a point right in between two identical masses) and it would still be possible to observe time dilation. In short, gravitational time dilation has nothing to do with gravitational acceleration.

• Now apply the equivalence principle and replace the building on Earth with an accelerated building floating in out space away from any gravity source.

1. The equivalence principle states that if we make a similar experiment, an identical redshift shall be observed.
2. An observer that is not accelerating and see the building passing by as the experiment is performed interprets this redshift as a Doppler redshift because the detector at the top of the building is moving faster than the light source at the bottom of the building. It is moving faster because the detection happens after the emission giving it a bit of time to accelerate to a slightly higher speed.

The bottom line is: a non-accelerated observer (The scientist in the experiment you described) sees zero time dilation associated with an accelerated environment (The bacteria culture in the experiment you described). All he sees is Doppler effect. Dauto (talk) 18:48, 14 September 2011 (UTC)

You've messed up somewhere or else you're trying to make a distinction that I don't understand. It's a fact that an object in a spinning centrifuge will experience a shorter proper time than an object at rest in the lab. It's not strictly general relativity, since there's no spacetime curvature, but you could treat it as a gravitational redshift of the edge of the centrifuge relative to the center (where the acceleration is zero). -- BenRG (talk) 23:01, 14 September 2011 (UTC)

Yes, and it's quite easy to see this. The gamma factor to lowest order is 1 + 1/2 (v/c)^2. Working in the co-rotating frame, the centrifugal potential is V(r) = 1/2 omega^2 r^2, and sqrt[1 + 2 V(r)/c^2] which is the time dilation factor in the weak field limit, becomes 1 + 1/2 (v/c)^2. Count Iblis (talk) 23:43, 14 September 2011 (UTC)

I didn't mess up anything. I am indeed making a distinction, and I quote from my first post "Of course there will be time dilation due to the relative motion but that's another matter." If you read the OP's post carefully you will see that he is under the impression that there should be another time dilation factor beyond the normal time dilation factor due relative motion per special relativity. This extra time dilation factor would somehow be related to the local frame acceleration. That extra factor doesn't exist and that's what I was trying to demonstrate. Dauto (talk) 04:07, 15 September 2011 (UTC)

So what's the concensus? Do we have a time dilation? And would the 403,627g that bacteria experience in the centrifuge be equivalent to 403,627g of gravity experienced near a black hole? Thanks. L33th4x0r (talk) 03:00, 15 September 2011 (UTC)

No, there is no time dilation due to the 400 000 gees experienced by the bacteria. There is only the time dilation due to the relative motion which is negligible in this case. Dauto (talk) 04:14, 15 September 2011 (UTC)

Assuming a radius of $r=0.1m\,$, and an angular frequency of $\omega =60000RPMs\approx 6300rad/s\,$, we get the centripetal acceleration $a=\omega ^{2}r=3969000m/s^{2}=405000g$. We also get $v=\omega r=630m/s$, and the time dilation is $\gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}=1.0000000000022$. Clearly that is not much to look at. Dauto (talk) 04:43, 15 September 2011 (UTC)

We agree about everything except (possibly) wording. There is time dilation and it's easy to calculate the amount using special relativity alone. Instead of calculating it as an SR time dilation, you can treat it as a gravitational effect and get the same answer. There aren't separate SR and gravitational effects that add together; there's just the one effect that can be calculated in two different ways. That's what Dauto and I were trying to say, in different ways. The rate (relative to a distant clock) of a clock near a black hole experiencing 400,000 g will not be the same as the rate (relative to the lab) of a clock in a centrifuge experiencing 400,000 g. The amount of time dilation isn't a function of the acceleration. Acceleration, as such, doesn't cause time dilation. -- BenRG (talk) 08:54, 15 September 2011 (UTC)

So what you and Dauto mean to say is that the 400,000 g in a centrifuge is just an acceleration whereas the 400,000 g near a black hole is not just an acceleration, it is an acceleration caused by gravity of the black hole and the gravity is responsible for the massive time dilation. But in this case I would argue that Einstein's EP would say that a rocket accelerating at 400,000 g would also give its riders the same massive time dilation that the black hole would, in this case the time dilation has nothing to do with gravity at all but rather to do with the pushing force of the rocket exhaust. Arguing along this same line, would the normal force exerted by the wall of the centrifuge on its content be ultimately responsible for giving its content the 400,000 g of acceleration? Then wouldn't this normal force give the centrifuge's content a massive time dilation just the same way as the pushing force of the rocket and the gravity of the black hole? Thanks. 76.68.7.220 (talk) 22:43, 16 September 2011 (UTC)

I am sorry for adding a bit more to what I was just saying. I have always been taught that the starting point for GR is when Einstein took his axioms of SR and applied them to accelerated frames of reference. So I have always understood the absolute time dilation of GR to be a by-product of acceleration since the EP implied that there is nothing special about gravity as compared, say, to more mundane forces such as the exhaust of an accelerating rocket. However, what you and Dautos are arguing here seems to be that in addition to the acceleration, there is something special/magical that is present in gravity/rocket exhaust that is missing in the force of containment (normal force) provided by the wall of the centrifuge, such that even though all three forces can go up to 400,000 g, the time dilation one get with 400,000 g of gravity/rocket exhaust is missing in the normal force of the centrifuge wall. I am wondering what this special/magical element is that makes gravity/rocket exhaust able to dilate time, but not the normal force of the centrifuge wall. Even though all three should be equivalent under the EP. Thanks. 76.68.7.220 (talk) 22:56, 16 September 2011 (UTC)

No, you still don't seem to understand it. What we are saying is that time dilation has nothing to do with acceleration, neither in the centrifuge, nor in the blackhole. The time dilation in the blackhole can be related to the gravitational potential by the formula given by Count Iblis above. But that relationship is only valid in the weak field approximation. Dauto (talk) 01:34, 17 September 2011 (UTC)

Then what about time dilation experienced from accelerating rockets, as in the case of the twin paradox? There is surely no gravity in that scenario. Thanks. L33th4x0r (talk) 01:38, 17 September 2011 (UTC)

The fundamental rule is that the elapsed proper time is the length of the worldline. In other words, a clock marks off equal spacetime intervals on its own worldline. Spacetime geometry isn't the same as Euclidean geometry, but it's closely related mathematically. In Euclidean geometry there's a theorem that the shortest distance between two points is a straight line. In special relativity, there's a similar theorem: the longest spacetime interval (proper time) between two events is a straight (nonaccelerating) worldline. In the Euclidean case, if you have two curves connecting points A and B, one straight and the other not, the straight one will always be shorter. So straightness and length are related in a way. But the extra length of the other curve doesn't "happen during" the parts where it deviates from straightness. The length is a global property, it isn't concentrated in any particular part of the curve. The twin effect is the same. If one twin accelerates and the other doesn't, the one that accelerates will experience less proper time between the meeting events. But the difference doesn't "happen during" the acceleration, and isn't really caused by the acceleration as such.

An object in a centrifuge has a helical worldline in spacetime. An object at rest in the lab has a straight worldline that runs parallel to the helical worldline (or to the cylinder that contains it, at least). Although these worldlines can go on forever and never meet, it should be clear that they have different lengths, in some sense. In the Euclidean case, the helix is longer. If the slope of the helix is v/c, i.e., it moves a distance v "around" for each distance c that it moves "up", then the helix is longer by a factor of ${\sqrt {1+(v/c)^{2}}}$, by the Pythagorean theorem. In the case of spacetime geometry, the helix is shorter by a factor of ${\sqrt {1-(v/c)^{2}}}$, by the spacetime counterpart of the Pythagorean theorem.

It's much harder to visualize an object hovering near a black hole, because spacetime is curved in this case. But I hope it's not hard to believe what I said above, that the same acceleration (worldline curvature) does not translate into the same ratio of lengths in this very different situation. There's no formula relating a particular amount of curvature to a particular amount of time dilation. You have to consider the geometric relationship of the worldlines. -- BenRG (talk) 09:04, 17 September 2011 (UTC)

Wow! That is fascinating. I never thought of it before! So fundamentally it is the change in the geometry of spacetime caused by a given scenario that determines whether the given scenario will result in time dilation or not. I would like to learn more. Is there any book that I can read that can teach me how to do calculations to allow me to figure out whether there would be time dilation, and by how much, there is in any given scenario, be they black wholes, traveling twins, centrifuges or other scenarios involving forces/relative motion/other scenarios of GR/SR/Q. Thanks for teaching me. I feel enlightened. L33th4x0r (talk) 18:05, 17 September 2011 (UTC)

Lightsaber vs. chainsaw

Suppose a Jedi armed with a lightsaber encounters a zombie armed with a chainsaw. Assuming that both of them have equal skill in using The Force, who do you expect will win?  :-D 67.169.177.176 (talk) 00:54, 14 September 2011 (UTC) Die, zombie scum! :-D 67.169.177.176 (talk) 00:58, 14 September 2011 (UTC)

Lightsaber can cut chainsaw, chainsaw can't cut lightsaber, Jedi wins. (Unless you have ten thousand zombies attacking one Jedi...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:03, 14 September 2011 (UTC)

And if lots of folks go see that movie, George Lucas wins. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:14, 14 September 2011 (UTC)

Interesting idea for an Expanded Universe movie (or perhaps a Hardware Wars-style parody). Of course, you'd prob'ly have to get the old man's permission first... 67.169.177.176 (talk) 01:36, 15 September 2011 (UTC)

Yes, I would choose "light saber" in that scenario. Course', I can't imagine a scenario in which I wouldn't choose a light saber :) Quinn ^{░ RAIN} 03:44, 14 September 2011 (UTC)

Light saber vs. Tommy gun. Now THAT would be interesting. Quinn ^{░ RAIN} 03:46, 14 September 2011 (UTC)

I thought the Jedi had superhuman reflexes that allowed them to block bullets with their lightsabers? 67.169.177.176 (talk) 00:44, 15 September 2011 (UTC)

If it was zombie superman? I don't think a light sabre would cut superman. Then you'd want a cryptonite sword.. Mind you if superman ALSO had a chainsaw, then I think your best bet is to run and hope zombie superman can't gather up much speed. Vespine (talk) 03:48, 14 September 2011 (UTC)

Where did you get the idea that Superman is a zombie? 67.169.177.176 (talk) 00:45, 15 September 2011 (UTC)

As an aside, wrt the questioner's piped link, there were no zombies in the Texas Chainsaw Massacre (at least in the films I've seen) Jebus989^✰ 12:31, 14 September 2011 (UTC)

What about Leatherface? 67.169.177.176 (talk) 00:49, 15 September 2011 (UTC)

Where did you get the idea that Superman is a zombie? Same place the OP got the idea that you could fight zombies with light sabres: I made it up. It was a reply to I can't imagine a scenario in which I wouldn't choose a light saber. Vespine (talk) 01:17, 15 September 2011 (UTC)

In that case, would a lightsaber made of krypton plasma be effective against the abovementioned chainsaw-armed zombie Superman? ;-) 67.169.177.176 (talk) 01:23, 15 September 2011 (UTC)

If you'll excuse me for asking, what the heck is this discussion doing in the reference desk for science? Jedis? Lightsabers? Zombies? Since none of them even exists, the question, although a well-formed, grammatically valid English-language utterance, has no real-world meaning. Guess I just can't take a joke...—PaulTanenbaum (talk) 01:30, 15 September 2011 (UTC)

Just for the record, in case you haven't been paying extra careful attention to previous discussions, what started this whole thing was a previous discussion about swords, where someone mentioned adding vibration technology to the sword to improve cutting power, and I replied (in jest) that they might as well just add a cutting chain to get the same effect. And then the discussion took on a life of its own. 67.169.177.176 (talk) 01:44, 15 September 2011 (UTC)

And in fact, I'm taking issue with your claim that "lightsabers don't exist", because they actually do. :-) 67.169.177.176 (talk) 04:23, 16 September 2011 (UTC)

Automobile engines and altitude

If I've got an ordinary (non-whatever-charged) internal combustion automobile engine that's rated for a maximum power of 100 horsepower at sea level, is there a way to calculate its maximum power output at other altitudes (say, 10000 feet)? --Carnildo (talk) 01:00, 14 September 2011 (UTC)

The power output is an approximately linear function of manifold pressure (I know -- they don't talk about that outside flight training), so for a non-supercharged engine, the power output will fall off with the atmospheric pressure (by about 3.3% for every 1000 feet when below 9000 feet, slower at higher altitudes). Turbocharged engines will deliver an approximately constant power output regardless of altitude, and engines with gear-driven superchargers (generally only found on aircraft) will deliver a constant power output up to a certain altitude (generally up to about 10000 feet) and then experience a drop in power output in a similar way to unsupercharged engines. FWiW 67.169.177.176 (talk) 01:12, 14 September 2011 (UTC)

(non)Existence of God

Is there any evidence (other than religious texts) for or against the existence of God? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:01, 14 September 2011 (UTC)

AFAIK -- none either way (unless you count the Resurrection -- I know, a circular argument...) 67.169.177.176 (talk) 01:03, 14 September 2011 (UTC)

You can't find evidence, if you don't know what to look for. So, it would be impossible look for evidence if you exclude religious texts. What reasoning could you use otherwise? Plasmic Physics (talk) 01:17, 14 September 2011 (UTC)

There are lots and lots of arguments both for and against God. See Existence of God for a long run down. There are not limited to religious texts. None are generally recognized as uncontestable either way, though. Natural evidence (e.g. empirical evidence) plays a role in some of the arguments (e.g. Argument from evil, Argument from design). But there isn't any single piece of evidence that as of yet can distinguish between existence and lack of existence of God. --Mr.98 (talk) 01:35, 14 September 2011 (UTC)

There never will be such evidence, see Russell's teapot. Count Iblis (talk) 02:04, 14 September 2011 (UTC)

Russell's teapot says no such thing. It says there can be no ultimate evidence for a total negation, but it says nothing about evidence for, and it says nothing about evidence against specific, falsifiable conceptions of a God (e.g. I believe in a God who gives everyone free fish on Tuesdays). --Mr.98 (talk) 11:46, 14 September 2011 (UTC)

Yes, but then the "God hypothesis" all but falsified, that's the situation we're in. Count Iblis (talk) 15:28, 14 September 2011 (UTC)

If you could prove it, there would be no debate. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:07, 14 September 2011 (UTC)

The problem with trying to prove the existence of an omniscient omnipotent being is that you can't. Anything and everything becomes proof, the reason why I think the belief in a 'deity' ('architect[s]', if you will) can actually coexist with being a scientist.

But most religions are contradictorily literalist. It's fairly ridiculous how people claim a god that can not be comprehended and yet try to confine the idea in definable terms - like the way the words are arranged in a book, or worse, actually making him in a male human's image. Like a caveman worshiping an astronaut because the astronaut came from the flying ship and has magical things, a cargo cult perpetually concerned with retconning. That kind of man-made god - the wizard in the sky - seems rather weak to me.

If we do find evidence of design sometime in the future woven into the very fabric of the universe, it would be frankly exhilarating, imo. But in the meantime, it's really just a rather pointless question when our brains aren't even equipped to comprehend infinity yet.(Disclaimer: I'm an agnostic atheist)-- Obsidi♠n Soul 02:22, 14 September 2011 (UTC)

There is no evidence for the existence of god. Asking for evidence against the existence of god is as absurd as asking for evidence against the existence of the flying spaghetti monster. Long story short, god is just a fairy tale for adults. ScienceApe (talk) 03:16, 14 September 2011 (UTC)

Well, let's weigh the evidence: Against: Cancer; child molesters; natural disasters, etc. For: Unicorns and magic...Oh, wait...damn! Quinn ^{░ RAIN} 03:31, 14 September 2011 (UTC)

Saying you "can't" offer any kind of proof I think is only a very small piece of the question. Probably you can't offer proof of SOME kind of supernatural being, but most religions have a silly habit of actually making specific CLAIMS about their deity some of which CAN be empirically tested, i.e. God created the world in 6 days. This has been happening for centuries, as science discovers more and more, the "gaps" for God to exist become smaller and smaller and more and more of the core "beliefs" become figurative or allegorical instead of literal. If you are actually interested in the subject, I recommend a book called God: The Failed Hypothesis. It takes a far more scientific approach to the question then the popular "New Atheist's" books. Vespine (talk) 03:42, 14 September 2011 (UTC)

Some active practitioners say that justifiable evidence is recognisable in the form of conditioning. For instance, if one actively practices, they may find that otherwise improbable fortuitous events occur more often (I guess, it is analogues to Karma.) I do not know whether a statistical study has been done on this. Plasmic Physics (talk) 04:43, 14 September 2011 (UTC)

See Efficacy of prayer (not that this answers the question - because it isn't answerable) AndyTheGrump (talk) 04:57, 14 September 2011 (UTC)

It's not all about prayer, it's a lifestyle which requires 24/7 commitment, and active persuit. It's not like an ointment, that you apply only when you need it. Neither is it like an umbrella that you put away, just because the rain stopped. Plasmic Physics (talk) 05:24, 14 September 2011 (UTC)

Note that while it's impossible to prove that God doesn't exist, just like how it's impossible to prove the flying spaghetti monster doesn't exist, it IS possible to prove the opposite. If I ask God to show me a miracle and he rearranges the stars to say "GOD IS HERE", that would be solid evidence. If I ask God to violate the laws of physics and make light travel 50% slower, and he does so, that would be solid evidence. --140.180.16.144 (talk) 05:31, 14 September 2011 (UTC)

Nope. That would prove that either (a) God exists/Gods exist, (b) you are dreaming/deluded, (c) the world is being run by people determined to make you think that God/Gods exist, (d) that free will doesn't exist, and you had no choice but to ask God/the Gods to make it happen, and it had no choice but to happen, or (e)... Well, there are probably an infinite number of possible explanations - none of which can be disproved. The thing about Gods is that they (allegedly) can do inexplicable things. If something inexplicable happens, 'God did it' isn't an explanation. AndyTheGrump (talk) 05:45, 14 September 2011 (UTC)

I agree, also there's Clarke's third law. If you showed primitive people fire production from your hand, or could drop someone dead instantly at a distance with just a loud bang, they would no doubt think you are a god. Maybe there's some crazy advanced race of mischievous aliens that can read minds and teleport stars around at whim. Of course that's incredibly unlikely, but without further evidence, I'd say it's MORE likely then "God did it". Vespine (talk) 05:50, 14 September 2011 (UTC)

OR! The stars were just going to arrange them selves like that for some inexplicable but perfectly natural reason, and you just happened to be one of the people to be gazing up into the sky wondering if there was a God at that precise moment, lol.. Vespine (talk) 05:54, 14 September 2011 (UTC)

Andy, what a goofy thing to say. Perhaps true from a purely philosophical sense, but the same reasoning could be applied to all scientific or mathematical proofs. You don't normally see headlines saying "FERMAT'S LAST THEOREM PROVED, OR ALL MATHEMATICIANS CRAZY", or text books that say "All mammals require oxygen, or there is a global conspiracy to make all scientists believe that mammals require oxygen."

If the stars were suddenly rearranged to say "GOD IS HERE" in a language well-known before the stars were rearranged, I think we could count that as a "proof" of the existence of a god. That would be a proof more solid than any other scientific proof I can think of off the top of my head. APL (talk) 06:33, 15 September 2011 (UTC)

Why do you think that He will reveal Himself in such a way. He's not genie in a lamp. Plasmic Physics (talk) 06:39, 14 September 2011 (UTC)

How can you tell? There's just as much reliable evidence that God is a genii in a lamp as there is that he exists at all. It's just as hard to try to prove that he isn't a genii in a lamp as to try to prove that he doesn't exist at all. The same kind of rationalizations that work to explain why god is undetectable work equally well to explain why it isn't obvious to everyone that he's a genii in a lamp. I mean, sure you can't see his lamp, but obviously an all-powerful Genii is perfectly capable of making the Holy Lamp become invisible whenever he wants to. My guess is that he usually keeps his Lamp invisible as way of testing humans' faith, but that's just a guess, as mere humans can't be expected to be able to comprehend Genii's motives. Red Act (talk) 16:49, 14 September 2011 (UTC)

Something like that would defeat the whole purpose of a faith-based relationship. Plasmic Physics (talk) 06:42, 14 September 2011 (UTC)

It's interesting to debate why God would want such a relationship, back in the old testament he certainly didn't Jebus989^✰ 07:02, 14 September 2011 (UTC)

He changed His ways, since it didn't seem to work very well. Plasmic Physics (talk) 07:34, 14 September 2011 (UTC)

You have to admit it's awfully convenient that God has apparently set things so the world is fairly indistinguishable from there being no God at all. --Mr.98 (talk) 11:46, 14 September 2011 (UTC)

Convenient to who? Plasmic Physics (talk) 13:31, 14 September 2011 (UTC)

I think Mr.98 is saying that theists try to rationalize the real world so that it fits into their preconceived belief that god exists. It's kinda like saying "God always watches out for me". But when something bad happens, you rationalize it to yourself and say "it happened by god's will for a reason." It's basically just a way to delude yourself. ScienceApe (talk) 14:06, 14 September 2011 (UTC)

There is no evidence that can be provided to finite Man to prove the existence of an infinite God. An infinite God would know this and so any evidence offered must be faked, either by the hands of Man or by sufficiently advanced yet mortal aliens. Hcobb (talk) 13:39, 14 September 2011 (UTC)

How about a burning bush? Jebus989^✰ 13:44, 14 September 2011 (UTC)

"If I could just see a miracle... a burning bush, or the seas part, or my Uncle Sasha pick up a check." --Woody Allen in Love and Death ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:18, 15 September 2011 (UTC)

Consider God as described in the Bible in the way people interpreted it before the 17th century, so before major advances in science were starting to be made. Then, you have to consider if that interpretation is consistent with the scientific knowledge that has transpired since that time. It is wrong to adjust the interpretation of religious texts to make it compatible with scientific knowledge and then argue that this interpretation is consistent with the scientific knowledge. Count Iblis (talk) 15:45, 14 September 2011 (UTC)

You know what else is wrong? People who don't believe in a religious precept telling people who do that their method of believing it is incorrect. It's not a scientifically analyzable concept. It's like telling someone they are wrong for liking the music of Billy Joel or wrong for finding the poems of Robert Frost to be entertaining. --Jayron32 15:51, 14 September 2011 (UTC)

Yeah! It's not like religions ever proselytize. Oh wait, they do it all the time. Religions are unverifiable, and it bugs me when people say "Well, atheism is unverifiable too!" because atheists aren't the ones making extraordinary claims about magic being real without offering a single shred of evidence. --Goodbye Galaxy (talk) 17:13, 14 September 2011 (UTC)

Did I do any of that? --Jayron32 17:46, 14 September 2011 (UTC)

Did I claim you did? --Goodbye Galaxy (talk) 18:00, 14 September 2011 (UTC)

God is said to be unknowable. If God is unknowable, isn't it futile to ask whether or not something that is unknowable—exists? Bus stop (talk) 18:19, 14 September 2011 (UTC)

Said by whom? --Goodbye Galaxy (talk) 19:04, 14 September 2011 (UTC)

I find this sort of idea supported at for instance this web site in statements such as this:

"Some Christians, and most Jews and Muslims, say that God is beyond knowledge or understanding. The prophets talked with him, but the age of prophets has past. We can never personally experience God." Bus stop (talk) 20:16, 14 September 2011 (UTC)

I heard them say that too. If that's the case, why do they say all these things about him in their holy books? Religious people contradict themselves all the time. ScienceApe (talk) 20:33, 14 September 2011 (UTC)

Religious experiences can be caused by temporal lobe epilepsy. Count Iblis (talk) 21:41, 14 September 2011 (UTC)

Reminder, can we keep it civil? There is no need for patronising comments.

By "unknowable", it refer to His motives, rationale, and complete comprehension. You can assemble a pretty good character profile from religious texts.

Jebus: The burning bush is not external evidence, which is what the original question included. Plasmic Physics (talk) 22:23, 14 September 2011 (UTC)

Science can do a lot of things, but one area where it utterly fails is in the realm of spiritual guidance. That's where religion or faith comes in. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:11, 15 September 2011 (UTC)

The short answer is: there is no unargueable evidence for or against the existance of God. It can only for reasoned for or against. Plasmic Physics (talk) 02:33, 15 September 2011 (UTC)

The existence of God is not provable from science, because no matter how miraculous the composition of the world, natural philosophy must accept it as law. But there are events in human relations where all logic demands that nothing but endless cruelty and conflict are possible, and even if something else were attempted it would be crushed - yet someone acts instead in an inspired way and things turn out very differently. Just as a hunter would follow an animal by its tracks, one seeking to prove the existence of God must carefully note, explain, trace and follow the signs of goodness in the world. Wnt (talk) 14:48, 15 September 2011 (UTC)

Best kind of lightbulb?

I want to replace all of the old incandescent light bulbs in my house with something better. In terms of energy consumption, light emitted, and lifespan, what is the best? My guess is LEDs, but I'm not sure. ScienceApe (talk) 03:14, 14 September 2011 (UTC)

LEDs have the lowest energy consumption and longest life spans. Of course, there might be other things to consider such as up front price and light aspects such as tones brightness, etc... Dauto (talk) 03:18, 14 September 2011 (UTC)

LEDs are still quite expensive, and not much better than compact fluorescents, so you might do better economically to go with those, until the price comes down on LEDs. An exception seems to be for dim and maybe bright lights, where the compact fluorescents cost far more. I've noticed that you can get CF bulbs equivalent to 60-100W incandescent bulbs for $1 each, but be prepared to pay 10x as much outside that range. StuRat (talk) 03:25, 14 September 2011 (UTC)

Thought I'd chip in here - my summer job last year was as an LED lightbulb salesman. They are remarkably efficient - they'll outlast halogen bulbs (not sure about incandescents) by a factor of about eight or ten, and pay for themselves about thrice over in energy savings. You can also get "warm white" bulbs, which have a tone just a little colder than halogen/incandescent bulbs, but not by much – perhaps 3800K vs 3500K. However, we were selling 3W bulbs (equivalent to a 30W halogen) at £11, and 6W (equivalent to a 50W halogen) at £16, and a couple of pounds extra for dimmable bulbs, so I got a lot of cold shoulders from people who simply didn't have the spare cash to invest in efficient lighting. Shop around and you'll probably find some a lot cheaper. But as StuRat says, if you don't mind compact fluorescents, which take a little while to reach full brightness, these are probably the best choice. They are much cheaper up front, the light is more diffuse (LEDs are best used as spotlights) and they won't cost much more to run in total, in terms of bulb cost plus energy savings. Brammers (talk/c) 07:53, 14 September 2011 (UTC)

Depending on the electronic ballast, some fire up quite quickly, although I prefer the slower ones, at times, so my eyes have time to adjust. StuRat (talk) 22:48, 14 September 2011 (UTC)

LED bulbs have it all over compact fluorescents in some respects. The upfront cost is higher, but the higher efficiency and longer life make up for it. I object to the mercury content of CFLs, and at the end of life they often fail by making a popping noise, with the base becoming charred or turning dark brown, and by putting out bad smelling smoke which the manufacturers assure us is harmless. Earlier LEDs had poor color quality, and were mostly very low brightness bulbs only advertised as being for "accent purposes," with no more brightness than a 30 watt or 40 watt incandescent, but finally some are on the market which are as bright as a 60, 75, or 100 watt incandescent, if I recall correctly, at about 100 times the price of the incandescent equivalent. Obviously they only make sense for the long run, and not for temporary use or for use where someone can unscrew them and steal them. If the price is too high now, it will likely be much lower in a year. One big problem with LEDs is that they are intolerant of heat; if placed in a fully enclosed light fixture, the lifetime and light output can be degraded, since they still produce some heat in operation. They generally are not suited for operation on a conventional dimmer, but some can be dimmed by other means. In new construction, it will be common to have "permanent" LED fixtures with no provision for unscrewing and replacing the LED, and with the fixture providing assurance of proper ventilation. Edison (talk) 03:26, 15 September 2011 (UTC)

Wow. Are they really that certain they will last for the life of the building, or do they just not care ? StuRat (talk) 03:29, 15 September 2011 (UTC)

Installing new light fixtures, and providing sockets into which you plan to screw LED bulbs, is reminiscent of having a 1902 automobile with a socket for a buggy whip, just because vehicles always had a buggy whip socket. Will a new fixture with nonreplaceable LED last the lifetime of the building? Most of the cost would be in the LED and its electronics, not the metal/plastic/glass/ceramic portions of the light fixture. We are used to unscrewing the burned out incandescent bulb after a year, or the CFL after 4 years, but after 20 years or longer of an LED lamp being in service, when the LEDs burn out, , I would not feel too bad about replacing a 50 dollar fixture with the current style rather than screwing a new 45 dollar LED into the old fixture and saving 5 dollars (mileage may vary). As we transition to LED lights, there will certainly be a market for screw-in LED bulbs, but as mentioned above they may not be suitable for fully-enclosed fixtures. Edison (talk) 21:26, 16 September 2011 (UTC)

I personally don't care about this, but women tend to want things to match. Thus, when one LED burns out, it wouldn't just be necessary to replace that fixture, but every fixture in the house, so they all match. And if one (more frequently used) LED burns out in one-tenth the time of the rest, you've now increased the cost tenfold. Considering that LEDs are pricey to begin with, this is becoming a rather expensive and time-consuming proposition. StuRat (talk) 04:51, 17 September 2011 (UTC)

Are you heating or air conditioning the room that the bulb is in? Hcobb (talk) 17:55, 15 September 2011 (UTC)

For most people the answer is yes in summer, but, in winter, they provide needed heat where people are present, similar to space heaters or zone heating. So, the overall cost of this is negligible. I suppose you could use LEDs in summer and halogens in winter, though. StuRat (talk) 17:58, 15 September 2011 (UTC)

Lightbulbs aren't the best heating anyway, because they tend to be placed in the ceiling. Lightbulb waste energy all goes to heat, but that heat manifests as a warm spot on the ceiling, you would have been better off with LED lights, and baseboard heaters. (Even assuming that electricity is the cheapest form of energy available to you, which is not a safe assumption.)

Well, many bulbs are in lamps, too. And those on the ceiling might heat the floor above, which might be OK, if that floor is occupied, too. StuRat (talk) 05:19, 16 September 2011 (UTC)

Be careful of cheap, generic-brand LED bulbs. I bought a few of them and they lasted less than a year! The LED elements themselves were fine, but the accompanying electronics burned out making the "bulb" as a whole worthless. APL (talk) 22:40, 15 September 2011 (UTC)

Re; The transfer of coldsores or herpes labialis by touch- 13th September 2011-04.52am

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Jayron32 04:05, 14 September 2011 (UTC)

We can't give medical advice. See you doctor. But, on a personal note, I would avoid touching other person's genitalia with your nostrils until you get this figured out. Quinn ^{░ RAIN} 04:06, 14 September 2011 (UTC)

(edit conflict) Wikipedia has articles about herpes labialis but if the person who left the question is genuinely concerned about the issues they noted, they should ask their doctor pretty much the exact same questions they tried to ask here. --Jayron32 04:07, 14 September 2011 (UTC)

Fast cars

How many BHP, HP, PS, CV, LB-FT do you need to make a car that weighs 2,500 lbs, and has a drag of 0.28, and a frontal area 6 sq ft, to go 350, and 150 MPH?--213.107.74.132 (talk) 07:08, 14 September 2011 (UTC)

If Adrian Newey or any of his peers know the answer, they will probably keep it very much to themselves for as long as they can. {The poster formerly known as 87.81.230.195} 90.197.66.205 (talk) 15:10, 14 September 2011 (UTC)

One may apply this equation[3]

                              3
                  ( velocity )
    hp = weight x ( -------- )
                  (   234    )

to estimate the required horsepowers:

150 mph: 659 hp

350 mph: 8366 hp Cuddlyable3 (talk) 16:27, 14 September 2011 (UTC)

                             3
                 ( velocity )
   hp = weight x ( -------- )
                 (   234    )

What does this formula mean? Please explain it in the steps you do when you use the calculator, like hp*weight/drag or whatever. Do you get it?--213.107.74.132 (talk) 17:49, 14 September 2011 (UTC)

Cuddlyable3's equations don't work out in reality, particularly because they don't factor in the vehicles Cd. They also appear to be designed to determine trap speed in quarter mile drag racing, not top speed. Obviously a vehicle like the one you described would not need 650 hp to attain a maximum speed of 150 mph. These questions are hard to answer as there are many more variables at work here than you provide. To take a vehicle to 350 mph is very difficult, the only real world examples of vehicles that approach this speed are Top Fuel drag racers which reach about 325 mph (of course they can do it in a space of a quarter mile). Top Fuel cars have between 8000 and 10000 hp. A very rough estimate for your hypothetical vehicle to reach 350 mph would be 3000-5000 hp. --Daniel 18:04, 14 September 2011 (UTC)

Quote

One may apply this equation[4]

                              3
                  ( velocity )
    hp = weight x ( -------- )
                  (   234    )
 

::to estimate the required horsepowers:
::150 mph: 659 hp
::350 mph: 8366 hp Cuddlyable3 (talk) 16:27, 14 September 2011 (UTC)

You are wrong. The McLaren F1 has 2,500 lbs and less hp, yet can go 240 mph. — Preceding unsigned comment added by 213.107.74.132 (talk) 17:53, 14 September 2011 (UTC)

Yes as I said, Cuddlyable3's equation is not appropriate for your question which concerns top speed, not quarter mile trap speed. --Daniel 18:06, 14 September 2011 (UTC)

You may be interested in Land speed record. Modern attempts use jet engines whose output is generally not measured in HP. I just noticed that your hypothetical vehicle has tiny frontal area, less than that of a rocket car, but the Cd is a very mundane .28, similar to many common road cars. In any event there are some piston driven HP numbers that you can use to make rough guess. One attempt was made at 450 mph with a 2500 hp engine, although the Cd was certainly far less than .28. --Daniel 18:15, 14 September 2011 (UTC)

Red snow and snow plant

Are the two names equal? namely Red snow and snow plant. The concise oxford dictionary says so.But wiki search shows them to be an algae and a flowering plant. Also I could not locate this: protococcus nivalis, but only got the other nivalis for red snow. — Preceding unsigned comment added by 59.96.40.46 (talk) 10:34, 14 September 2011 (UTC)

In various dictionaries the two terms are sometimes confused (and also some use the term red snow plant), but the term snow plant is usually applied to a fleshy parasitic herb (Sarcodes sanguinea), whereas red snow is a term used for the alga protococcus nivalis which you mention. - David Biddulph (talk) 11:04, 14 September 2011 (UTC)

are Saturn's rings perfectly flat?

i am wanting to confirm whether Saturn's rings are perfectly flat. in other words, at the furthest known extension (distance from the surface), do they orbit at exectly the same longditude as the inner most circle? or is it slightly concave or convex? or is it a bit of both, with some rings tending up and others down?

i'm curious as the shape might suggest a bent space effect from the gravity of Saturn. 58.171.106.110 (talk) 12:47, 14 September 2011 (UTC)

See Rings of Saturn. -- kainaw™ 12:54, 14 September 2011 (UTC)

They're independently orbiting and of different thicknesses so with a strict definition of 'perfectly' flat, no. Differences in thickness and composition alone would lead me to favour 'some up some down', but as you can see from the images on the above-linked article, they are 'pretty' flat Jebus989^✰ 13:03, 14 September 2011 (UTC)

I believe the question is about the angle of the tilt of the rings. If so, it is answered in the introduction of the article that I linked. -- kainaw™ 13:04, 14 September 2011 (UTC)

Ah ok, I may have misunderstood. Though I can't find that information in the lead, only that pheobe is at 27 degrees to the others Jebus989^✰ 13:10, 14 September 2011 (UTC)

The Phoebe ring to which you refer, discovered only in 2009, is a much larger, diffuser and separate entity from the better (and longer-)known rings, as are other faint dust rings associated with some of the other satellites, and these might be better treated as somewhat different kinds of object. {The poster formerly known as 87.81.230.195 } 90.197.66.205 (talk) 15:24, 14 September 2011 (UTC)

Yeah I know, that's why I queried where the angle of tilt of the rings is in the lead Jebus989^✰ 15:27, 14 September 2011 (UTC)

I remember watching a Discovery Channel the other day, where it was mentioned that there are irregularities in the rings. The main ring can have a density variance as high as Everest from the mean. Plasmic Physics (talk) 13:38, 14 September 2011 (UTC)

With Saturn itself being something like 9 times as wide as the earth, a disk with a thickness of 29,000 feet is relatively quite thin. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:24, 14 September 2011 (UTC)

As this picture shows and the associated article explains, the rings are not perfectly flat, they have small vertical perturbations. Looie496 (talk) 15:30, 14 September 2011 (UTC)

Saturn's rings are rocks, so they can't be flat. →Σ _{^talkcontribs} 01:50, 15 September 2011 (UTC)

Not all rocks are round, as noted here: "It's hard to take a round stone / And try to bounce or flip it / And if you find a flat stone / You might as well just skip it." --Wiley, of B.C. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:01, 15 September 2011 (UTC)

There were also a couple of recent articles in Science (journal) about waves detected in Saturn's C ring, which, along with the previously known corrugations in the D ring, point to an impact from a debris cloud (likely from a comet) in 1983. [5]. In the same issue, scientists also examined photos of Jupiters rings, and concluded that waves seen there were from the Shoemaker-Levy 9 impact of 1994, when the entire ring system was tilted about 2 km [6]. It must be stressed that these pertubations are extremely minor, on the scale of their respective ring systems. Planetary rings are extremely thin and flat. Buddy431 (talk) 03:38, 15 September 2011 (UTC)

meaning of a steeper curve in a oxygen–haemoglobin dissociation curve

Assuming you're familiar with the typical shape of the (say, human) oxygen–haemoglobin dissociation curve, imagine a different curve, much further to the left, with a much less pronounced 'S' shape, where it rises very steeply, very quickly, over short partial pressure changes, and also approaches the plateau fairly quickly. Mammals are benefited by having a dissociation curve not shaped like the one I've just described. But why? The only answer I have come up with so far is that the mammal would experience very sudden changes in affinity for oxygen over very small changes in the partial pressure of oxygen. However, as well as seeming somewhat simple, I need to relate this benefit to the efficiency of oxygen release. I have trouble getting my head around these dissociation curves and wonder how a much steeper curve equates to lower oxygen release efficiency? Any help very much appreciated! 82.71.20.194 (talk) 13:51, 14 September 2011 (UTC)

A couple of things first, "human oxygen-dissociation curve" is vague, we have different curves for fetal and adult haemoglobin, as well as for myoglobin. This seems to be a homework question and you're on the right track, so to help you out myoglobin, found in muscle tissue, has a curve in the shape you describe, why do you think that would be an advantage in muscles? Jebus989^✰ 14:18, 14 September 2011 (UTC)

Okay, myoglobin binds oxygen very readily. I can see how that is an advantage in muscles! In my 'homework' question, it's plotted on the same graph as a 'normal' human adult oxygen-haemoglobin dissociation curve (very sigmoidal). It's steep as described, but it will still take up and give up its oxygen over a range (albeit a very narrow range) of partial oxygen pressures. How is that different in 'efficiency' from haemoglobin? For example, at 5 kPa it will be almost 100% saturated, and only 20% saturated at 1.5 kPa. How is that 'less efficient' than the range for the normal curve, where 100% is around 20 kPa and 20% is at 4 kPa. You could almost say that myoglobin is more efficient, because it can take up and release with smaller changes in partial pressure? I do understand that myoglobin doesn't form tetramers like that of the haem group, and so therefore it doesn't have a situation where the loss of one oxygen molecule makes it easier for the other ones to go, too. If that's the 'answer', I don't know how to relate it to the curve! My textbook even says, "The shape of the curve is crucial to how efficiently a pigment can act as an oxygen carrier.", but there isn't any explanation on other shapes or how they influence this. I feel very stupid. I've answered more complex questions on this graph, including an exercise/pH/carbon dioxide Bohr shift to the right and its consequences, but for some reason this part is really really confusing me!  :| Hopefully with more insight into my thoughts you will work out what obvious thing I am missing?! 82.71.20.194 (talk) 14:46, 14 September 2011 (UTC)

You're pretty much there. You know about co-operative binding, so you can see how that fits into haemoglobin's function as an oxygen carrier. When oxygenated blood enters the tissues, we want the oxygen to transfer to active muscles. So looking at the curve, in low pO₂ muscle capillaries, haemoglobin will dissociate from oxygen, releasing it to diffuse across into muscle tissue. Now, the myoglobin, with much higher affinity at lower pO₂, is able to efficiently bind this free oxygen (almost all of it) and transport to respiring cells. Also of interest, if that it will only release the oxygen when really needed (at lower pO₂ than haemoglobin), so this allows more efficient muscle use. The myoglobin article reminded me that Whales have shed-loads of myoglobin to utilise this kind of 'muscle oxygen storage'.

The basic idea/exam answer they are looking for is that the right-shifted, steep dissociation curve will more easily 'pick up' oxygen at lower partial pressures. I'm not sure what level you're studying it, so the biological context may or may not be relevant (but I think it helps to think of the overall process anyway, rather than just looking at datapoints on a curve). Hope that's helpful Jebus989^✰ 15:11, 14 September 2011 (UTC)

Another point I should have mentioned, myoglobin having such a curve means it can act as if operated by a switch: sucking up all the oxygen as it diffuses across from capillaries, and then releasing it all when required for respiration. So efficiency, in terms of oxygen transport, is heightened by taking up all the delivered oxygen, and by delivering it all quickly when required for respiration Jebus989^✰ 15:23, 14 September 2011 (UTC)

(e/c) Thank you very much. I hate to say this, but I'm still kind of confused. The biological context is the more important thing for me here (this is university level, second year (believe it or not), but I study on my own so have no tutor to ask!). I think I see fairly clearly how these two (haemoglobin and myoglobin) work together, and the necessity of myoglobin operating at a much reduced pO₂. But the question is about the curve's shape, not its position to the far left on the graph. I guess that's what is essentially perplexing me. I don't necessarily see how that shape affects efficiency of oxygen release. After all, it seems from the graph that, given the right pO₂, it will still keep or give up its oxygen just fine. The question is not so much about why or where that curve operates (which I understand) but about why it's 'so much more advantageous for the mammal' to have a haemoglobin dissociation curve be sigmoidal like it is, instead of more like the myoglobin dissociation curve. If I wasn't so bloody determined to get a first, I'd have made something up and moved on by now! 82.71.20.194 (talk) 15:28, 14 September 2011 (UTC)

Right ok, in that case I apologise for my tone earlier, I wasn't trying to be condescending but I remember A/AS-level questions along these lines (but I remember we did recover it on my Biology degree course too). As a final punt, the steep curve acts as a switch (explained above) while the shallow S sigmoid utilises co-operative binding, the biochemistry of the haemoglobin subunits is an interesting read to understand the mechanism. You wouldn't want an all-or-nothing response in normal haemoglobin. But it seems my explanations are not hitting the mark so I'll let someone give it a go! Jebus989^✰ 15:41, 14 September 2011 (UTC)

Generating MIST from still water

How much velocity / acceleration (linear) is needed to be imparted to water lying at rest (at atmospheric pressure) to convert it into MIST ? (pipeyoga 17:10, 14 September 2011 (UTC)) — Preceding unsigned comment added by Pipeyoga011 (talk • contribs)

Water is not converted to mist by velocity or acceleration. It's converted to mist by turbulent air flow on its surface. Dauto (talk) 17:19, 14 September 2011 (UTC)

let me re-phrase a bit as ;

 " I put water in open conduit (half pipe section for example) and put it 
   on top of Bullet Train (assuming conduit is welded to bullet train).
    Now will the water Lump ( mass) split into fine droplets (mist) ? "

(pipeyoga 17:43, 14 September 2011 (UTC)) — Preceding unsigned comment added by Pipeyoga011 (talk • contribs)

Yes, for the reason described by Dauto above: the flow of air over top the train is not laminar flow, but has a component of turbulent flow. This is also how mists are formed e.g. over the ocean. It is an interesting question to consider how fast the train must go to generate mist, but I will leave that for the fluid dynamicists :) (also, please sign your posts with four tildes (~)). SemanticMantis (talk) 18:04, 14 September 2011 (UTC)

I think they are using four tildes, but it looks like they have modified their signature so that it no longer has a link to their user or talk page. —Akrabbim^talk 18:12, 14 September 2011 (UTC)

I thought 'unsigned comment' (Autosigned by Sinebot) only occurred when no signature was added by user... SemanticMantis (talk) 18:21, 14 September 2011 (UTC)

See User:SineBot#What it looks for. - David Biddulph (talk) 07:35, 15 September 2011 (UTC)

Note that the most energy efficient means of creating mist may be to force water through small orifices (holes). Spray bottles do this. The velocity required there is very low. StuRat (talk) 21:49, 14 September 2011 (UTC)

Dear Friends, I know from my barbers shop that spray bottles can generate mist / mist like phenomenon!

But my question is pertaining to CALCULATION ....!

If I consider the drag equation :- F(drag) = 1/2 C*Rho*A*v^2

Problem No 1 is what profile should I consider viz Speherical / Conic / Parabolic / irregular ? Ther value ranges from 0.5 to 2 according to SERWAY depending on the profile. Rho = air density A = cross section area v = velocity .

Problem No 2 is What to equate the F(drag) to Van der Waal's Forces / Atomic Bond Forces ? The F(drag) must be > the Structural Stablizing force of the Water Bulk ! And Van der Waal's Eq in simple form ; (p+ a'/v^2 )(v-b') = kT; where a' = inter particle force, b= volume of particles, v= voulme of container !! Considering p = 1 bar ( open to atmosphere) , T = (25deg C+ 273 ) Kelvin & k = 0.008314. Please help through this sequence of thought process (pipeyoga 10:00, 1 October 2011 (UTC))

Gentlemen, is there any other forum inside wiki wherin I can post this query ? (pipeyoga 07:38, 9 October 2011 (UTC))

How to show TB test results?

HELP ME. I would like to know what is the propper way to show a negative 2-step TB test results on a lab report? — Preceding unsigned comment added by Jl1018 (talk • contribs) 17:45, 14 September 2011 (UTC)

I'm sorry, but the Wikipedia Reference desks cannot give medical advice. Looie496 (talk) 18:00, 14 September 2011 (UTC)

We assume the intended meaning of TB is Tuberculosis. Wikipedia has an article about Tuberculosis diagnosis which notes that many test methods are in use. A lab report should state the name of the tester, date, and concisely using accepted terminology what test was made, what result was obtained, and what conclusion was drawn. Cuddlyable3 (talk) 18:29, 14 September 2011 (UTC)

Pyruvate/Pyruvic Acid article in Wikipedia

I am no expert, but when looking at the figures of the molecule pyruvate in the "Biochemistry" subsection of the main article titled "Pyruvic Acid" I noticed that the figures represent pyruvic acid not pyruvate. To be precise, Pyruvate is the right molecule in that biochemical process but the figure itself represents the conjugate acid of pyruvate, which is pyruvic acid. I believe the carboxylate anion should be drawn there instead of the protonated molecule. I think the figure should be corrected but like I said, I am no expert and want to make sure this is correct. Any ideas? — Preceding unsigned comment added by Larios.leo (talk • contribs) 18:02, 14 September 2011 (UTC)

Yes, you are technically correct. Officially, the -ic acid ending is reserved for the protonated form and the -ate difference is for the deprotonated form. In practice, however, the difference is a purely pedantic one; most chemists understand that the two forms often coexist in equilibrium, which is highly dependent on small changes in pH, and so the -ate ending is often used for both forms interchangably. It is not purely, technically correct in the IUPAC sense, but in the actual language used by actual chemists, it is very common to here the -ate ending used even for the protonated form. --Jayron32 18:21, 14 September 2011 (UTC)

Pedant**2...it's common among biochemists to conflate the two because they tend to coexist (or at least equilibrate) and the difference doesn't matter in general pathway discussions because of that. Chemists often care because they're not always under equilibrating conditions or at a pH and solvent where both are reasonable possibilities. DMacks (talk) 18:39, 14 September 2011 (UTC)

True enough... It's one of those things that in contexts where it matters, the distinction will be made, and in contexts where it doesn't, then it doesn't. --Jayron32 01:32, 15 September 2011 (UTC)

Is there an upper limit for the amount of energy a single photon can carry?

The article "Absolute hot" seems to only apply to matter. --Goodbye Galaxy (talk) 19:59, 14 September 2011 (UTC)

No, there isn't because you can always postulate another observer moving relative to the first towards the direction the photon is coming from. That observer would see the same photon with a higher energy due to blue-shift Doppler effect. Dauto (talk) 21:22, 14 September 2011 (UTC)

"Absolute hot" would apply to a gas of photons as well as to ordinary matter. At very high temperatures there's no difference between photons and matter anyway. The energy of a single photon is meaningless, because for any single photon, and any given energy, there's an inertial reference frame in which that photon has that energy. (This is another way of saying what Dauto said.) But experiments that detect "high-energy photons" are really detecting the energy relative to the detection device, and that could have an upper limit—Dauto's argument doesn't apply any more because the only legitimate reference frame is the rest frame of the detector. In fact I'd expect general relativity to impose an upper limit of some sort for the usual reason: anything higher and the detector collapses into a black hole on impact instead of detecting the photon. -- BenRG (talk) 22:23, 14 September 2011 (UTC)

Yes, let's say for a single reference frame. --Goodbye Galaxy (talk) 04:37, 15 September 2011 (UTC)

Low-tech atmospheric reentry.

I'm writing a short story involving low orbital space travel in a somewhat "steam punk" setting. Putting aside the improbability of any kind of space travel with that low level of technology, what would be the simplest way of surviving atmospheric entry at orbital velocities? What shape would the entry vehicle need to be? What materials would it need to be made of? Would it be possible at all to survive such high temperatures without the aid of modern materials? 209.182.121.46 (talk) 20:41, 14 September 2011 (UTC)

The Apollo program's method would probably be the easiest. Heatshield, parachute, splashdown. I'm not sure what the heatshield would have to be made of, I don't think Victorians would have the advanced ceramics that NASA used, but if weight is no concern, I'm sure you could come up with a substitute. (It's OK if most of it burns away in the process.)

Really, the hardest part would be making sure you hit the atmosphere at precisely the right location and angle. I'm not sure how you'd do that without modern technology. APL (talk) 20:50, 14 September 2011 (UTC)

Tungsten could conceivably be used for the heat shield, couldn't it? 67.169.177.176 (talk) 01:18, 15 September 2011 (UTC)

If you have rocket launchers to get you to orbit - then you can launch enough material (possibly over multiple launches) to build an enormously large, thick heat-shield - which ought to be able to do what the few-inch-thick NASA shields did. From then it's a matter of parachutes - which we might reasonably assume they'd have because the parachute was invented in 1470 and successfully tested in 1617. APL's concerns over getting the right location and angle might require you to shoot a very large Babbage engine into orbit - but the data to feed it in terms of horizon angle, etc, ought to have been well within Victorian engineering capabilities. As for what it would look like, I would expect them to build a spherical heat shield - so that they wouldn't get into trouble if the aerodynamics were all wrong - and have it split in half to reveal the spacecraft within once sufficiently deep in the atmosphere for parachutes to be effective. You don't want the weight of what remains of your heat shield to have to be supported by the parachute...so you'd certainly have to jettison it. Also, if you have the rocketry (or whatever) to get you up there in the first place, you could also have retro-rockets to slow you down again and also to maintain attitude control. The problem for me is how the heck they'd get up there in the first place. They'd be able to make oxygen and hydrogen gasses from electrolysis (widely available in 1869) - but the control of such things would be tough without computers and electronics. But liquification of oxygen wasn't around until 1883 - and then only in microscopic quantities. So you simply couldn't get enough energy density into a small enough craft. 216.136.51.242 (talk) 21:06, 14 September 2011 (UTC)

Solid-fueled rockets could in principle be used both for the boosters and for the retro-rockets (possibly with some kind of gas vanes for control). As for the parachutes, the Garnerin design would be MUCH more practical than either the original Da Vinci design or any other early parachute designs. 67.169.177.176 (talk) 00:15, 15 September 2011 (UTC)

See Atmospheric entry. --Carnildo (talk) 22:31, 14 September 2011 (UTC)

How about room-temperature liquid fuels and oxidizers? Seem to recall that working for Goddard and the Nazis (in the liquid-fuel part at least...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:13, 15 September 2011 (UTC)

Godard used kerosene and LOX, von Braun used ethanol and LOX. In both cases LOX was used as an oxidizer. The Walther engine (used e.g. in the Me-163 Komet) used hydrazine and concentrated hydrogen peroxide, while the related Yangel engine (developed by the Russians after WW2 and used in the Proton rocket and in many Russian ICBMs) used hydrazine and nitric acid. Of these chemicals, concentrated nitric acid would have been available in the Victorian era, and possibly hydrogen peroxide as well (it's usually obtained as a byproduct from the manufacture of anthracene dyes), but I'm not so sure about hydrazine. FWiW 67.169.177.176 (talk) 00:30, 15 September 2011 (UTC)

According to the article, hydrazine was first synthesized in 1889 "by a circuitous route" (therefore could not be made in large quantities or at an acceptable cost), and was not produced industrially until 1907. 67.169.177.176 (talk) 00:33, 15 September 2011 (UTC)

Very low tech means could slow an orbiting object enough to de-orbit it. It only needs to lose about 1% of its orbital velocity in a typical reentry burn; the atmosphere does the rest. A compressed air or steam operated piston, a slingshot device, or a small rocket could slow an astronaut enough for de-orbit if he did not have to bring the spaceship down with him. The distance of application of the de-orbit deceleration would have to be long enough that the applied force was survivable. The heating during reentry is related to the area and shape of the heat shield and to the mass it must slow down. Canvas bags and a video camera survived reentry without being incinerated after the Columbia blowup, for instance, because their surface area was large relative to their density. MOOSE was a low tech proposal for a lightweight reentry system for an individual: a 1/4 inch thick ablative heat shield and a manually aimed small retro rocket, and a parachute. There was to be no capsule around the astronaut during reentry: his space suit and an oxygen bottle sufficed. Apparently it was a feasible way of getting a person down from orbit. The Atmospheric entry article describes an inflatable heat shield. Edison (talk) 03:14, 15 September 2011 (UTC)

An alternative would be to use an extremely large parachute to slow down while still in the upper atmosphere (the Russians had proposed something along these lines in the late 50's -- use a specially made parachute and deploy it at ~300,000 feet for initial braking, then cut it loose, freefall for a while, and deploy a second, more normal-sized parachute below 100,000 feet). The question is, would this profile be survivable for an unprotected cosmonaut? From what I remember, the article did say something about the aerodynamic pressure being enough to rip the first chute to shreds if it remained deployed below the cut-loose altitude (~150,000 feet if I remember rightly), so it would prob'ly be enough to cause considerable kinetic heating. 67.169.177.176 (talk) 03:54, 15 September 2011 (UTC)

As it's fiction (and you've already gotten into orbit in a rocket made of brass and teak that's fuelled by powdered anthracite, or something unlikely like that), I figure the amount of fun you have is proportional to how far you're willing to bend the laws of nature. So the following is a bit bendier than the more sensible ideas others had above:

• If you must have a heat-shield, it has to be made of asbestos (or similar materials like vermiculite); asbestos was the miracle nanomaterial of the steam age. If ordinary asbestos is too prosaic, use some fanciful "green asbestos from the lava tubes of the Kimberley deposit" to explain away the unpossible properties your heatshield needs.
• An atmospheric reentry to Earth typically uses a fast entry through the atmosphere, converting the massive kinetic energy of an orbiting body to heat (by friction). Because the reentry is so fast (90 minutes or less) that heat builds up faster than it can radiate away, so you get very hot, and so you need a heatshield to be able to survive. If you can reenter slowly then that heat doesn't build up. The trouble with that is that the upper atmosphere is so rarefied there's too little of it to "grab a hold of". If you can generate a massive drag very high in the atmosphere then you can deorbit gradually. The atmospheric entry article Edison linked to describes a "shuttlecock reentry", which does this a bit; it doesn't seem practical to do this for a full ex-orbital reentry, but you're writing fiction so you may wish to fudge that (with some bizarre fanfold wing arrangement that incrementally retracts as the vehicle falls). It's much the same idea with the ballute reeentry that 67.169.177.176 talks about - it's not totally inconceivable to build a bunch of these with some steampunky material ("the finest vermiculated Kweichow silk"), and it's a rather poetic image to have your little capsule trailing hundreds of massive diaphanous silken ballutes (each with dragons or whatever painted on them), shedding them like tears as it descends.
• If you're willing to seriously fudge the dynamics of the solar system, your intrepid spaceonauts can "capture" a comet, attach that to their capsule, deorbit the whole lot, and ride home on an explosively steaming icey heatshield.
• Heatshield/parachute/aerofoil reentries are the sensible choice for Earth, because Earth has a nice atmosphere suitable for aerobraking. But some bodies don't (Luna, Mercury), which means you have to shed all that KE with retro alone. That's very difficult to do with a conventional power source, but the Victorians did so love the (alleged) power of radium. You'd still need to eject reaction mass, so perhaps you'd retro brake with some crazy railgun that fires ball bearings.

Jules Verne fired people out of a cannon and H.G.Wells just used antigravity "stuff", demonstrating that ignoring the laws of physics (rather than trying simply to bend them) gives you better immunity from allegations of incredibility. -- Finlay McWalterჷTalk 11:01, 15 September 2011 (UTC)

As mentioned in our article Nose cone, some of the early Chinese vehicles apparently used wood as an ablative re-entry shield. {The poster formerly known as 87.81.230.195} 90.200.79.217 (talk) 15:38, 15 September 2011 (UTC)

Victorians were masters of ceremics manufacture. I'm sure Armitage Shanks could have knocked-up a decent heat shield. BTW, old H G Wells also used the giant gun spaceship in Things To Come. Alansplodge (talk) 22:22, 15 September 2011 (UTC)

If music is a universal component of human existence...

...why does it require years to learn? Using a vehicle is much easier for us humans, and we didn't drive vehicles along evolutions. Quest09 (talk) 22:37, 14 September 2011 (UTC)

How young were you when you first started to sing, vs. when you first drove a car? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:42, 14 September 2011 (UTC)

Most children learn the basics of music (like singing and keeping a beat with their hands and feet) without any formal training, soon after they learn to speak. If you mean learning how to read music or more advanced techniques, then I'd say those things aren't universal. StuRat (talk) 22:45, 14 September 2011 (UTC)

Singing and driving a car are pretty simple. Learning to read music and learning to be a mechanic are more difficult. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:49, 14 September 2011 (UTC)

I'm not sure that music is a "universal component of human existence". It wouldn't surprise me at all if there have been cultures and tribes with no concept of music.

But ignoring that, I think most people learn to sing or whistle well before they learn to drive. Most people, even without practicing, could hum a tune well enough to be recognizable.

Finally, tool use is very much a part of our evolution, so the ability to gain basic proficiency with bicycles and cars with only a little practice is definitely something that we evolved.

It may take "years" to master the Trumpet, but you can get one to belt out a simple tune with only a couple week's of practice. Similarly, it may take years to master a car to the point where you could win a pro-level road race, but you could safely get yourself to work with only a couple week's of practice.

So, uh, basically, I question every single premise your question is based on. APL (talk) 01:09, 15 September 2011 (UTC)

Also, if using a vehicle is so easy, how come there are so many auto accidents? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:35, 15 September 2011 (UTC)

Because using an auto while talking on the phone and eating a Big Mac is less easy. Googlemeister (talk) 13:27, 15 September 2011 (UTC)

If Muficke be the food of Loue, play on, Giue me exceffe of it: that furfetting, The appetite may ficken, and fo dye. Cuddlyable3 (talk) 15:04, 15 September 2011 (UTC)

"Singing... (is) pretty simple". OK Bugs, try the tenor part for the Faure Requiem. Let us know how you get on! Alansplodge (talk) 22:09, 15 September 2011 (UTC)

I would have to agree that music is a universal component of human existence, beginning with the exposure to our mother's rhythmic heartbeat in the womb when we are a fetus. It is thought that it is in the womb where music appreciation begins, and we all share that experience. Most importantly, music is not something you hear. It is something you feel. See Touch the Sound (2004) for more insight. Viriditas (talk) 13:49, 18 September 2011 (UTC)

Identification of a caterpillar

Beautiful caterpillar at Strandfontein, in the False Bay area of Cape Town.

I would appreciate it if someone who is knowledgeable about caterpillars in general, or at least about this one specifically, would reply with its name so that I can find out more about it from there. Kind regards, Adriaan Joubert. Adriaan Joubert (talk) 22:52, 14 September 2011 (UTC)

It's a Pine Emperor Moth caterpillar, Nudaurelia cytherea cytherea. Dominus Vobisdu (talk) 23:08, 14 September 2011 (UTC)

Wow—that is a totally awesome photograph! Bus stop (talk) 23:18, 14 September 2011 (UTC)

@Dominus Vobisdu, thanks so much, I really appreciate it!

@Bus stop, thanks, I used the Nikon Coolpix S9100. It still amazes me sometimes with its picture quality. Adriaan Joubert (talk) 23:22, 14 September 2011 (UTC)

September 15

Han Solo

Is it possible to survive being completely frozen in a block of dry ice? 67.169.177.176 (talk) 00:08, 15 September 2011 (UTC)

Han Solo wasn't frozen in a block of dry ice. --Elen of the Roads (talk) 00:12, 15 September 2011 (UTC)

No, at least not without some preparations which don't currently exist, since anti-freeze would be needed in every cell to prevent ice crystal formation, which tears the cells apart. BTW, I thought he was frozen in some kind of metal, not ice. StuRat (talk) 00:14, 15 September 2011 (UTC)

He was frozen in carbonite, which I expect would be similar to dry ice. Anyway it's clear from the dialogue between Darth Vader and the other Imperial characters present that extreme low temperatures are involved in the process. 67.169.177.176 (talk) 00:19, 15 September 2011 (UTC)

It says that carbonite is a "cryonic alloy", which confirms the use of extreme low temperatures. 67.169.177.176 (talk) 00:21, 15 September 2011 (UTC)

Yes, and a human body presumably can exist in suspended animation for quite some time at cryogenic temperatures, but the question is how to get it from normal temperature to frozen, and how to thaw it out, without causing extensive damage. StuRat (talk) 00:31, 15 September 2011 (UTC)

I take this answer to mean "not survivable". 67.169.177.176 (talk) 00:47, 15 September 2011 (UTC)

Not with current technology, no. StuRat (talk) 01:06, 15 September 2011 (UTC)

Keep in mind this was a long time ago in a galaxy far, far away, where they had developed faster-than-light speed, swords made of light, telekinesis, etc., so it's reasonable to suppose they might have developed survivable cryogenics as well. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:05, 15 September 2011 (UTC)

Cryonics is our article on this. (Minus the fictional "carbonite" substance from the Star Wars universe.) Comet Tuttle (talk) 00:57, 15 September 2011 (UTC)

And vitrification discusses the general problem of freezing without ice crystal damage, which is relevant to organ preservation for transplantation as well as some bulk food preservation. For example, soybeans in Japan (edamame) are worth much more if they do not have the mushy texture from cell wall damage resulting from ordinary freezing, but fresh soybeans will spoil. That's why the Japanese have the most advanced vitrification freezers at present.[7][8] However, mammilian studies of cryonics have been suspended for the reasons stated in Smith, A.U. (1957) "Problems in the Resuscitation of Mammals from Body Temperatures Below 0°C" Proceedings of the Royal Society of London. Series B, Biological Sciences, 147(929):533-544 (14 pages), which states: "Two of the galagos regurgitated and inhaled bicarbonate from the stomach during administration of artificial respiration. The other two galagos which had been treated with bicarbonate and then frozen for 45 minutes seemed to make an excellent recovery after thawing. One of them regained an appetite as well as normal posture and behaviour. Within 24 hours they both died. At post mortem the stomach was normal, but in one animal the duodenum and jejunum contained bloodstained fluid. In both instances there was oedema of the lungs and froth in the trachea. This may have been a terminal event. Survival may have been limited by some other physico-chemical or physiological derangement which, if diagnosed, might well have been susceptible to treatment. It was therefore decided to postpone further experiments on freezing the larger mammals until the effects on other organs of freezing in vivo and in vitro were better understood." (page 538.) Figure 60 on Plate 25 is captioned: "A frozen galago is being rewarmed with diathermy. It lies inside a Perspex tube surrounded by the output coil of the diathermy apparatus. Artificial respiration is being given by insufflating air into a tracheal cannula."

I expect mammalian studies to continue when vitrification freezers are capable of vitrifying several kilograms at a time; they are almost there. 70.91.171.54 (talk) 02:09, 15 September 2011 (UTC)

Also note that dry ice isn't all that cold. If you did manage to freeze a body, you'd want to keep it as cold as possible, to prevent decay. You would therefore at least use liquid nitrogen. StuRat (talk) 01:08, 15 September 2011 (UTC)

For completeness' sake, shall we stipulate that the question assumes we are discussing actual biology here on Earth, and that the reference to the Star Wars character is merely a colorful metaphor? If instead the question is about scientifically plausible exobiologies, then most bets are off. I imagine that such extraterrestrial life forms, if they are to achieve much complexity, would be built up of something analogous to our cells, but there's no reason to assume a priori that they'd necessarily contain a lot of water, or that their membranes would necessarily be susceptible to rupture due to the expansion of that water in freezing. Indeed, now that I think of it, there might be (cryophilic) extremophiles right here on Earth who withstand freeze-thaw cycles perfectly well; but we mammals aren't among them.—PaulTanenbaum (talk) 01:24, 15 September 2011 (UTC)

See also Water bear. 67.169.177.176 (talk) 01:29, 15 September 2011 (UTC)

Wasn't part of the story that carbonite was NOT used to freeze people, only cargo? So even in the movie, freezing Han was a big risk. That doesn't change the discussion, I just mean that it wasn't like a normal "run of the mill" thing they did to people. Vespine (talk) 03:31, 15 September 2011 (UTC)

That particular equipment was only used for cargo. They don't mention if the technology in general is used on humans. I figure it must be done from time to time in the Star Wars universe, since everyone seemed to know so much about the process. APL (talk) 06:02, 15 September 2011 (UTC)

Right, the whole point of freezing Han Solo was to test out the machinery to make sure that it wouldn't damage the intended subject -- Luke Skywalker. --- Medical geneticist (talk) 13:02, 15 September 2011 (UTC)

Old HDTVs and broadcast DTV in the US

Confused I am about the "new" digital TV broadcasting in the US, after having read Digital television transition in the United States, and having read this US government FAQ page. Question 1: The latter link seems to claim that all television sets that say "HDTV" contain digital tuners and can receive the new digital broadcasts. But what about old HDTVs from the early 2000s? Surely their tuners don't know about the digital spectrum range that is now in use. For example, Samsung's LN-R238W is an HDTV that seems to date from 2005; it is new enough to have an HDMI input, so it certainly can accept digital input; but it's sufficiently old that I don't think its internal tuner could be digital. Is that US government FAQ just misleading and wrong? Question 2: What TV format is broadcast now in the US? Is it a 1080p signal? 720p? Is every channel different? How does this comport with the amount of spectrum reserved for each station? (Our Digital television in the United States article is frustratingly vague about today's exact broadcast situation.) Comet Tuttle (talk) 01:11, 15 September 2011 (UTC)

The current US digital broadcast frequencies and formats were standardized in the early 1990s, mostly at MIT with the participation of a wide consortium of TV set vendors, but I don't know the names of the standards. 70.91.171.54 (talk) 02:17, 15 September 2011 (UTC)

Both 1080i and 720p are now broadcast in the US, and require similar bandwidth, but not 1080p, which requires considerably more. Some sub-channels are 1080i and some are 720p. It would be better if they could change the format of one sub-channel between the two, based on the type of program they wish to broadcast (fast action needs 720p, while slow programs benefit from 1080i), but they don't seem to do that. There may be a technical problem with doing that, such as if the digital tuner only determines the format when you first tune to that sub-channel.

Another option is to have one sub-channel in the one format, and another sub-channel in the other format, both with the same content. We had that in Detroit, with channels 2.1 and 2.2, but they then dropped 2.2. Apparently the cost of broadcasting in both formats outweighed the benefit. StuRat (talk) 03:39, 15 September 2011 (UTC)

Name of a phobia?

I have an intense fear of chemicals–to be specific, I fear man-made/synthetic chemicals. I also fear things like Clorox wipes , and a lot of products I use are made from plants or are home-made. Is there a name of a phobia for this? HurricaneFan25 01:12, 15 September 2011 (UTC)

Possibly Chemophobia --Tagishsimon (talk) 01:15, 15 September 2011 (UTC)

Concur -- chemophobia is the correct name. 67.169.177.176 (talk) 01:16, 15 September 2011 (UTC)

I agree the above answers the question, I think another article which is related and may be of interest is Naturalistic fallacy. Vespine (talk) 01:21, 15 September 2011 (UTC)

How can you possibly distinguish between synthetic and naturally occuring chemicals? For instance, you have a bottle of a vanillin extracted from vanilla pods, and next to it there is another bottle of synthesised vanillin. How could you possibly know which is which? Plasmic Physics (talk) 01:56, 15 September 2011 (UTC)

Exactly -- you can't, not even with the latest analytical methods. That's because they're the exact same substance. 67.169.177.176 (talk) 02:14, 15 September 2011 (UTC)

Guys, phobias are not rational. You can't make them go away by explaining to the phobic why their fears don't make any sense. If it could be explained away, it wouldn't be a phobia. --Jayron32 02:22, 15 September 2011 (UTC)

No, but we can try to understand them better. The point others made above is that it's impossible to tell whether some chemicals are man-made or not, so I too want to know how the OP thinks he can tell. HiLo48 (talk) 02:42, 15 September 2011 (UTC)

Scotsmen, for example, wear kilts because they have pantophobia. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:27, 15 September 2011 (UTC)

No that's because sheep can hear zips. Cuddlyable3 (talk) 11:51, 15 September 2011 (UTC)

That fearsome Chlorox? Bleach is made from sea salt. I'm actually surprised they don't market it as such. DMacks (talk) 02:24, 15 September 2011 (UTC)

Of course, naming phobias is more of a parlor game than anything else. Except for a few very common ones, doctors tend to just write "phobia of chemicals" rather than bother with a specific name that no one knows anyway. APL (talk) 02:24, 15 September 2011 (UTC)

The Martians that lived on its larger moon feared only fear itself. They had Phobos phobo phobia. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:30, 15 September 2011 (UTC)

So what would be the name of a phobia of very tall objects? I used to have a variation of this (a specific phobia of power-line towers), but have been cured. I'm just curious to know what's it called. 67.169.177.176 (talk) 02:28, 15 September 2011 (UTC)

I'm thinking "polephobia". I'm more curious to know how you got cured. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:31, 15 September 2011 (UTC)

According to List of phobias and other sites I found in google, it sounds like "batophobia". ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:35, 15 September 2011 (UTC)

Re. your question to me: I don't remember, since it was a while ago. But AFAIR this was close to the time that I started doing research for my first writing project (a detective novel in which the Paki intelligence service sets off an EMP device in LA, which I unfortunately had to abandon with only a couple chapters written), and this research required me to spend quite a lot of time around electrical substations and other high-voltage eyesores, so this might have something to do with it. Maybe this need to do research gave me the motivation to try to overcome my fear? 67.169.177.176 (talk) 03:40, 15 September 2011 (UTC)

Jayron: I was just trying to clear up some confusion, how does he know to identify what he fears; if he can't tell them apart, does he fear both or neither. Plasmic Physics (talk) 02:42, 15 September 2011 (UTC)

There's no big mystery. Even if you fear something obvious like spiders you don't feel fear if you don't know a spider is present. (Which is probably the majority of the time, given how well they hide.) It's not about scientifically determining if the thing you fear is present, it's about whether or not you think it's present. APL (talk) 02:57, 15 September 2011 (UTC)

Lots of folks are afraid of various things, but they're only phobias if they're (1) unreasonable and (2) disabling in some way. It's easy to be startled by a spider or a snake, but then you get your composure and deal with it - unless you have a true phobia, in which case you do the sensible thing: panic, take drugs, and call an Orkin team. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:06, 15 September 2011 (UTC)

APL: The scenario is that you know there is a man-made chemical present, you just don't know which one it is. Plasmic Physics (talk) 03:23, 15 September 2011 (UTC)

On a side note, there are phobias like a fear of wearing a pair missmatched socks, or a fear of non-round shaped buttons. Plasmic Physics (talk) 03:29, 15 September 2011 (UTC)

I don't think a fear of artificially created chemicals is all that unreasonable. The reason is that scientists create them and then they add them to our food, etc., with insufficient testing. To give just one example, naturally occurring trans fats were rare and not a health problem, then scientist learned how to create them, and put large quantities in our foods, oblivious to the health danger that entailed. StuRat (talk) 03:56, 15 September 2011 (UTC)

They put Clorox in foods??? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:59, 15 September 2011 (UTC)

Actually, I believe that bleach is used in various food processing steps, but hopefully most of it is removed from the final product. StuRat (talk) 04:21, 15 September 2011 (UTC)

For example, white bread Jebus989^✰ 10:15, 15 September 2011 (UTC)

They don't use CLOROX in white bread -- they use chlorine dioxide, which COMPLETELY EVAPORATES from the flour WELL BEFORE baking! Do you not know the difference, or are you purposely conflating the two? 67.169.177.176 (talk) 04:40, 16 September 2011 (UTC)

Of course not, we were talking about using bleach in food processing. I didn't mention chlorox at all Jebus989^✰ 08:20, 16 September 2011 (UTC)

The term "bleach" specifically refers to hypochlorite salts. Chlorine dioxide is not a hypochlorite, so calling it "bleach" is wrong. 67.169.177.176 (talk) 00:27, 17 September 2011 (UTC)

Bleach is any chemical which tends to remove color, as our article states. In fact, it specifically mentions chlorine dioxide at the top of the "Other Examples" section. StuRat (talk) 04:44, 17 September 2011 (UTC)

Only in China. As far as trans fats in food are concerned, those are NOT intentionally created, nor intentionally added to the food, but are formed as an UNINTENTIONAL byproduct during the hydrogenation of vegetable fats to produce margarine. Modern methods for margarine production are designed to reduce the formation of trans-fats as much as possible through accurate process control (which they hadn't bothered with until after the health effects of trans-fats became known). 67.169.177.176 (talk) 04:19, 15 September 2011 (UTC)

Our trans fat article say "Trans fats are used in shortenings for deep-frying in restaurants, as they can be used for longer than most conventional oils before becoming rancid". That sounds like the intentional use of trans fats. Is our article wrong ? StuRat (talk) 04:28, 15 September 2011 (UTC)

Used to be, perhaps. The same article also says that many US restaurants are phasing them out in favor of other substitutes. 67.169.177.176 (talk) 04:40, 15 September 2011 (UTC)

Some are, some aren't. White castle still has 14 grams in their 20 chicken rings and 13 grams in their 10 cheese sticks (both outside of New Jersey): [9]. And none of this takes away from my argument that new chemicals (or, in this case, a new way to create an old chemical) do present a danger. StuRat (talk) 15:08, 15 September 2011 (UTC)

No, StuRat, rational skepticism is a good thing; which is quite different than a phobia. The two concepts are completely unrelated. If a spider falls onto my back where I cannot see it, it is a reasonable survival instinct to freak out a little bit as I try to get it off me. However, people with a true phobia of spiders become paralyzed with fear in irrational ways; like seeing photographs of spiders which they know are photographs, or having people talk about spiders around them, etc. Being rationally wary of food additives is a good thing, and likely to be good for your health. Having panic attacks every time you come into contact with something which may or may not be a "man made chemical" (without even any understanding of what that means or how to identify them) is a different matter entirely. --Jayron32 04:15, 15 September 2011 (UTC)

Yeah, but I'm saying: man-made chemicals do not always have a lable that says "Hey, over here! Look at me! I'm synthetic!" It isn't always black and white. Plasmic Physics (talk) 07:20, 15 September 2011 (UTC)

I believe it's quite the contrary: most of the time this will be explicitly NOT stated. --Ouro (blah blah) 10:15, 15 September 2011 (UTC)

It doesn't matter whether something is natural or synthetic (e.g. baking soda made from trona ore vs. made synthetically by the Solvay process, or natural vanillin vs. synthetic); what DOES matter is whether something is harmful (trans fats, marijuana, etc.) or not (dihydrogen monoxide, ascorbic acid, carotene, etc.) 67.169.177.176 (talk) 02:17, 16 September 2011 (UTC)

However, newly synthesized chemicals (or old chemicals created by a new process) should be treated as if they are dangerous, until extensive safety testing is done on them, especially if the intent it to take them internally. The little testing which is done on such chemicals seems rather inadequate, to me, so I'd say they should be treated as dangerous for several decades, until the dangers would become obvious. For example, it was some 80 years after the introduction of aspirin that one of it's potentially fatal side effects, Reye's syndrome, was discovered. StuRat (talk) 05:02, 16 September 2011 (UTC)

That's what the FDA is for -- to test new foods and medicines for any dangerous health effects. As for "treating them as dangerous for several decades", this will (1) cause many times more deaths and suffering from the lack of medicines to treat dangerous diseases than would be the case in the worst-possible scenario for adverse effects under current testing laws, and (2) completely thwart ANY new medical research (because it would take several DECADES for it to even START paying off), thus further compounding the problem. We're ALREADY seeing this with the high costs and time delays of clinical testing discouraging pharmaceutical companies from developing new medicines (including some that could potentially cure lethal diseases such as cancer and even AIDS). To place further barriers in the way of medical research, as you have just proposed, would condemn MILLIONS of cancer sufferers and other sick people to die from lack of medicine for their condition, and would in fact be tantamount to legislative mass murder. 67.169.177.176 (talk) 05:57, 16 September 2011 (UTC)

Settle down. For foods, the long wait always makes sense, but for meds we need to do a "cost-risk" analysis. If the new med has no apparent benefits over existing meds, or isn't for any life-threatening condition, then the long wait makes sense there. If somebody actually comes up with the proverbial "cure for cancer", then a great deal of risk would be justified. StuRat (talk) 06:47, 16 September 2011 (UTC)

That's more like it. 67.169.177.176 (talk) 00:28, 17 September 2011 (UTC)

Interesting that you mention aspirin as an example of a "dangerous newly-synthesized chemical", since that's simply synthetic willow-bark extract. --Carnildo (talk) 23:48, 16 September 2011 (UTC)

I also said "or old chemicals created by a new process". These can present a danger in many ways:

A) It may not be quite the same as the natural chemical. A portion could be some type of isomer, for example, which doesn't occur in that ratio in the natural version.

B) There could be impurities left in from the manufacturing process, or a missing co-ingredient present in the natural form.

B) Manufacturing may allow the chemical to be used in large quantities, posing new hazards not present when the small amounts which naturally occur were used. This is likely the case with Reye's Syndrome, as it would probably take more willow-bark tea to get this effect than anyone was likely to consume. StuRat (talk) 18:15, 17 September 2011 (UTC)

I want to know, how he decides if something is natural or synthetic. On what basis does he decide whether he should be phobic or not of a particular chemical, if it's not labled as such? Plasmic Physics (talk) 09:47, 15 September 2011 (UTC)

I think you're over analysing this. Presumably, a liquid in a plastic bottle marked "Heavy duty toilet bleach" would be feared, while an injured plant leaking sap would not. It's fairly obvious the OP is not professing a sixth-sense whereby they can determine the synthetic process used to create any given chemical he sees Jebus989^✰ 10:12, 15 September 2011 (UTC)

One thing to note is that he mentioned products made from plants not plant material. I think you're missing the point, how does he decide for less obvious products? Plasmic Physics (talk) 10:36, 15 September 2011 (UTC)

I can only speculate HurricaneFan has developed some means of distinguishing "Organic aloe vera 100% natural cleansing solution" in a health shop from a bottle of "industrial extra-strength bleach" in Tescos Jebus989^✰ 10:45, 15 September 2011 (UTC)

There you go, obvious labling. On a side note, I've seen organic salt sold on the shelves. Yes, it was NaCl. Plasmic Physics (talk) 10:57, 15 September 2011 (UTC)

I'm curious to know how the OP managed to post this question without coming into contact with the evil man-made chemical synthetic plastic computer keyboard? Warning! This poster may contain dihydrogen monoxide. Roger (talk) 12:02, 15 September 2011 (UTC)

One has to distinguish between phobias and misunderstandings. Education can clear up misunderstandings. What is initially labeled a phobia might not be that at all. We should not be so quick to pigeonhole fears as irrational. There can in fact be a grey area in which an aversion to a certain stimuli is partially rational, partially irrational, and partially amenable to modification via education. Bus stop (talk) 12:10, 15 September 2011 (UTC)

Plasmic, you're still missing the point entirely. It absolutely and completely doesn't matter one iota if the phobic can definitively say that some substance or another is manmade, for the purpose of having the phobia. A person my have a phobia against apple juice. Maybe they scream and cry like a baby whenever they see a Volkswagen because they think that Volkswagens contain apple juice. It actually doesn't matter that a) Volkswagens don't have any apple juice in them or b) there's nothing to fear from apple juice or c) That you inform the phobic of either of these facts. It makes no difference to them to tell them to stop crying and cowering when they see a Volkswagen because it contains no apple juice. That technique would only work if the fear was a rational one. It isn't in this case. It doesn't make any difference if someone with a phobia of man-made chemicals even understands even one thing about such chemicals, or where they are, or anything else. The fear manifests itself randomly and without any rational cause. --Jayron32 16:38, 15 September 2011 (UTC)

Howie Mandel's situation is a good example. He's got a phobia about germs, crowds, etc. He's a very smart guy; he's been very open about it, and very aware of it; but that doesn't fix it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:44, 15 September 2011 (UTC)

Pigeon spikes on a TV aerial

Pigeons like to sit on my TV aerial and they poo all over my door step. If I attach plastic pigeon spikes to the aerial, will this have an affect on my TV reception? Alternatively is there another way to keep the pigeons away? Thanks! --TrogWoolley (talk) 09:10, 15 September 2011 (UTC)

Plastic ones won't (although, given the voodoo that is antenna operation, you might find the pigeons actually improved reception). -- Finlay McWalterჷTalk 09:29, 15 September 2011 (UTC)

I can't believe we don't have an article about bird deterrents, but this website has information about TV aerial defence that you might find useful.--Shantavira|^{feed me} 10:54, 15 September 2011 (UTC)

There's a Bird control spike article that the OP might find useful. Word to the wise about those spikes - they don't really stop birds from *trying* to fit their bodies around them and land there, and (speaking from a UK perspective, though this is likely true in a lot of other places too) if birds happen to get stuck on the spikes, you can find yourself in trouble with the law. --Kurt Shaped Box (talk) 11:17, 15 September 2011 (UTC)

Thanks. I looked everywhere for that article. I will add some links to it.--Shantavira|^{feed me} 11:38, 15 September 2011 (UTC)

Or one of these that work surprisingly well if you have a suitable site close to the aerial. Richard Avery (talk) 13:14, 15 September 2011 (UTC)

Those actually work on pigeons? Heh. Gulls and corvids will ignore them completely, from what I hear (presumably they see them as plastic owls). --Kurt Shaped Box (talk) 00:20, 16 September 2011 (UTC)

One obvious solution is to move your antenna so it isn't directly above your door step. It seems to me that such a location brings other risks, like icicles falling on you in winter and the entire antenna falling on you in high winds. StuRat (talk) 15:05, 15 September 2011 (UTC)

Resolved

Thanks for the advice - I've ordered spikes --TrogWoolley (talk) 17:51, 15 September 2011 (UTC)

DNA question (extended version)

I asked a question like this before but not like this, and the answers didn't really help :/ so I ask a new version, if you don't answer all of them, just give me a brief explanation that works...

What is the difference between the nuclei content of:

1.two different cells of one tissue in my body?(is there any?)

2.two cells of two different tissues in my body?(if they're identical, then why are the cells different?Is there a mechanism that doesn't let some genes work or something? explain)

3.a cell from my body and a cell from my brother's body?

4.a cell from my body and a cell from someone who is not closely related to me?

5.a cell from my body and a cell from a chimp's body?

and what is the difference between gene, DNA, genome and allele? I mean all they say is that in the nucleus is chromosomes which are made of DNA is it only made of DNA?is the DNA on the surface of the chromosome, or is it in its internal parts too?(I prefer visual answers...)... in order to fully understand the questions I asked above, do I need professional education?--Irrational number (talk) 10:44, 15 September 2011 (UTC)

The initial stages of human embryogenesis. (copied from here

The DNA in each cell nucleus in your body is exactly the same (save novel point mutations etc.) it is the epigenetics that differs between cell types. Cell differentiation is an important part of developmental biology, this field looks at how identical embryonic stem cells can from a human body with cell types that seem entirely unrelated. Alas, I hated developmental biology (too many ventraldermowhatsits) so I cannot give you a comprehensive answer. In simple terms, though, during development identical cells begin to differentiate based on different concentrations of diffusible chemicals, which gives them an idea of their 'location' in the developing embryo, and they have transcription factors which will then act to change gene expression in some cells, forcing them to enter a specific lineage.

The various levels of DNA organisation, showing how DNA makes up a chromosome.

To your last questions: DNA is packaged into chromosomes (see image). You don't need a professional education, just reading DNA, chromosome, genome and epigenetics would answer most of your questions Jebus989^✰ 10:57, 15 September 2011 (UTC)

Irrational number, you may be getting confused between "nuclei" and DNA. The nucleus is full of all sorts of things other than just the DNA, including the molecular machinery necessary to transcribe DNA into mRNA and to replicate DNA during the cell cycle. In any case, different cells of your body most certainly have different numbers of nuclei and hence different DNA content. Mature erythrocytes (red blood cells) have no nucleus and contain all the mRNA and protein they need for the 100-120 days they will circulate. Liver cells can undergo fusion and thus have polyploid DNA content of 4N or 8N. Muscle cells can do the same. Your mature gametes (egg and sperm) have a haploid DNA content of 1N. Although the DNA content certainly does have something to do with the function of the cell, the explanation Jebus gave above essentially describes how different cells in the body can express such different characteristics (compare a pyramidal neuron to an epithelial cell). There is more on this topic in cellular differentiation. In questions 3-5 you seem to be asking about the level of DNA identity between different people or organisms, not about the nuclei. Read gene and human genetic variation and then ask more specific questions if there are still things you don't quite understand. --- Medical geneticist (talk) 12:57, 15 September 2011 (UTC)

Actually liver cells don't fuse much that I know of, but they tend not to bother finishing with cell division after duplicating the nuclear DNA. As a rule such polyploidy is common throughout the animal kingdom in older, more specialized portions of tissues that are fulfilling some specialized function before eventually being eliminated by apoptosis, necrosis, shedding, or some other means. The cells that regenerate and replace organs tend to stay at the formal 2n chromosome number. Skeletal muscle is a very special case in that the cells fuse together into long tubes so that the individual actin and myosin fiber units can link up with maximum efficiency, but they retain separate nuclei.

Other variations occur in B lymphocytes and T lymphocytes, where snippets of DNA are randomly cut out to produce a variety of antibodies or T cell receptors that (perhaps) recognize different antigens. But it is amazing how seldom the cellular DNA is actually modified, considering how many cells are specialized and deactivate pieces of DNA by DNA methylation, histone modification and other means. Apparently DNA splicing, even in the hands of nature, is not altogether safe or sure for the patient. The ability of animals to be cloned from almost any somatic cell is not something required by evolution or any law of nature, but an odd happenstance. Wnt (talk) 14:14, 15 September 2011 (UTC)

I don't think you are going to get the level of answer you are looking for from a Wikipedia Reference desk. You really need to get hold of a good introductory book on basic genetics and read it. Looie496 (talk) 14:45, 15 September 2011 (UTC)

can u introduce one, Looie?--Irrational number (talk) 14:52, 15 September 2011 (UTC)

I'm not the best person to give a recommendation -- I've sort of absorbed this stuff out of the atmosphere over the course of 20 years. Both The Selfish Gene by Richard Dawkins and Genome by Matt Ridley are highly readable and contain the information you're looking for, but I can't assert that there isn't anything better out there. Looie496 (talk) 02:45, 16 September 2011 (UTC)

"Suitspace" question

how does your suitspace hel you travelon the planet — Preceding unsigned comment added by 122.108.36.167 (talk) 11:59, 15 September 2011 (UTC)

I created a new header for this question as it does not appear to be related to the one above. --- Medical geneticist (talk) 12:31, 15 September 2011 (UTC)

I believe your "spacesuit" provides you with your normal operating tolerances for breathing purposes as well as temperature tolerances, among other purposes. Ambient temperatures and available gasses for respiration may be hostile to normal human operating tolerances on other planets. Thus such needs as oxygen supply and temperature control are two important needs that may be provided by a spacesuit.

Besides the Space suit article, check out the articles linked to here. Bus stop (talk) 12:58, 15 September 2011 (UTC)

Maintaining proper pressure is also an important human need that is likely to be provided by the space suit. Bus stop (talk) 13:15, 15 September 2011 (UTC)

The basic answer to the original question is, "It helps you travel on the planet by keeping you alive." It serves the same purpose as a diving suit in the depths of the ocean, or a radiation suit in a contaminated area such as a nuclear plant. In some sense, it hinders travel because it's big and bulky. But that's the tradeoff for staying alive. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:18, 15 September 2011 (UTC)

American space suits seem to operate a 4.3 psi. Googlemeister (talk) 13:19, 15 September 2011 (UTC)

Which is still perfectly OK because that's 4.3 psi of pure oxygen. 67.169.177.176 (talk) 01:54, 16 September 2011 (UTC)

It helps you contact aliens, who then take you to other planets. Mitch Ames (talk) 14:52, 16 September 2011 (UTC)

How much DNA to I need?

How much DNA to I need? — Preceding unsigned comment added by 129.215.5.255 (talk) 12:24, 15 September 2011 (UTC)

It depends on what purpose you need it for. If it's a matter of forensically identifying who a drop of blood or bit of skin came from, a state of the art laboratory would only need the DNA from a few dozen cells. Roger (talk) 12:37, 15 September 2011 (UTC)

I believe each and every cell of your body needs its own set of your own personal DNA. Bus stop (talk) 12:48, 15 September 2011 (UTC)

Note: fully-mature red blood cells do not Jebus989^✰ 14:18, 15 September 2011 (UTC)

Then the simple answer to the question would be, "All of it." ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:12, 15 September 2011 (UTC)

Isn't a part of human DNA redundant? (i.e. useless)Quest09 (talk) 13:42, 15 September 2011 (UTC)

In a sense, half of your DNA is redundant (if you're a human female, or 22/46 of it if you're human male) because you have pairs of the same chromosome number (male X/Y excepted)--each of your two Chromosome 17, for example, contains a copy of every Chromosome 17 gene. That's redundant gene coding, but Monosomy is a serious problem. Also, lots of our DNA is "noncoding DNA", however, that article mentions numerous roles for these parts of the genome other than simple "coding for proteins". DMacks (talk) 14:11, 15 September 2011 (UTC)

A lot of junk DNA could be cut out - might even have positive effects to do so. Alas, as with all the junk that accumulates around the house, there is always some little thingummabob mixed in with it that you'll sorely miss if you throw it out. Wnt (talk) 14:50, 15 September 2011 (UTC)

Any examples of 'junk' DNA which are beneficial when lost? 'Junk DNA' is a very outdated term, only a fraction of what was initially considered 'junk' still bears that title Jebus989^✰ 15:41, 15 September 2011 (UTC)

Well, BRCA1 apparently has a role keeping junk DNA inactive [10] ... unfortunately it doesn't always work. I understand that biology uses everything, and by now some genes rely on repeat elements for regulation, which in a sense interact with every other repeat out there, making them all of some importance. And I understand that repeats, more typically interspersed between exons and genes, provide evolution with important guidance where to cut and paste. Even so, my guess is that if you could magically splice out the right 50% of the genome and make a few necessary corrections, the rest would work a lot better. Wnt (talk) 02:53, 16 September 2011 (UTC)

I'm sorry to say that guess is completely out-of-step with the current view of human genetics. The 0.1% of DNA deleted from 'gene deserts' in mice is a comparative figure, or the slightly larger percentage in yeast which was found to have no effect (of course, not a positive effect, else natural selection would have pruned the genome a long time ago). And you'll note that that nature summary does not contain the word 'junk', silencing genes and even repeat regions far from implies they are junk, just that they may have a function which is undesirable in a healthy/mature/specific cell Jebus989^✰ 08:33, 16 September 2011 (UTC)

There are species like Takifugu rubripes where the junk has been pruned. But there is an impediment to doing this: yes, there are bits of useful sequence scattered all throughout the junk. That doesn't mean though that the individual pieces of spam in the genome have some a useful role for the person who carries them. Wnt (talk) 15:07, 17 September 2011 (UTC)

Genome reduction should not be oversimplified as 'pruning junk', there is absolutely no evidence implicating 'junk DNA' (which I can't stress enough, is not a term a modern geneticist would use at all frequently). For another example (another obvious one), Mycobacterium leprae has lost masses of coding DNA in its genome reduction, there's no evidence of removing proportionally more 'junk' than protein coding genes. In fact it has lost so many coding genes that M. leprae is rendered an obligate host parasite Jebus989^✰ 18:35, 17 September 2011 (UTC)

As far as DNA is concerned, no one has the foggiest idea what would happen if snippets were removed. We barely know why so much mutation is non-random. Collect (talk) 18:20, 15 September 2011 (UTC)

I think that's selling a great deal of geneticists short; gene knockouts in model organisms are routine, we have a good idea of what happens when many genes are removed or silenced Jebus989^✰ 18:59, 15 September 2011 (UTC)

In the US, do they know who is a legacy student?

I suppose there is no official list (due to privacy issues), but can US students more or less guess who entered a specific institution through a legacy program? Quest09 (talk) 13:33, 15 September 2011 (UTC)

For reference, the OP is talking about legacy preferences, the practice of some U.S. universities of granting preference (through less-strict admissions criteria) to family members of alumni. For instance, there is rampant speculation that George W. Bush's 'legacy' status is what got him into Yale despite his lacklustre academic credentials (his father, George H.W. Bush, was a Yale grad). TenOfAllTrades(talk) 14:13, 15 September 2011 (UTC)

Useful to know although doesn't explain what the question has to do with science but I suppose only the OP can answer that Nil Einne (talk)

Universities are institutions dedicated to science. Quest09 (talk) 15:15, 15 September 2011 (UTC)

They can be, but more important then the universities is the question. Googlemeister (talk) 15:19, 15 September 2011 (UTC)

I don't believe the legacy preference is common among the selective criteria for science programs, which tend to be more oriented towards merit. I strongly associate it with law, political science and similar degrees. 88.9.108.128 (talk) 15:36, 15 September 2011 (UTC)

Undergraduates are usually admitted without specifying what program they're going into. You seem to be talking more about grad school, where I have never really heard of such a thing as legacy admissions. --Trovatore (talk) 22:04, 15 September 2011 (UTC)

They're also dedicated to humanities, languages, mathematics, computing, and miscellaneous, as well. (And some to entertainment, I suppose.) --Mr.98 (talk) 21:58, 15 September 2011 (UTC)

You know that guy who never goes to class, but he's been there for five years and they haven't kicked him out yet? If his dad has a major building on campus named after him, its a good chance the kid is getting some special treatment. It should be noted that it doesn't mean anything for you, the good student. What you get out of school is information; if you go to class every day and work hard you win, regardless of what the layabouts with the rich dads get for free. You aren't there to be a layabout rich asshole, you're there for an education. --Jayron32 16:30, 15 September 2011 (UTC)

Well, people don't go to college just for education, they also care about prestige. If potential employers don't know for sure if you are one of those layabouts with the rich dad or just the good learner, it's also your loss. Quest09 (talk) 19:51, 15 September 2011 (UTC)

I've spent a lot of time around Ivy League universities. The sure-fire way to tell if someone is a legacy is to see what they do on "Big Game" today. If they have to go to a family tailgate party where three generations of people come from around the country, you can be damned sure they're a legacy. I know of no other obvious way to tell. Their teachers do not get that information or anything like that. In my experience legacies are usually indistinguishable academically from the normal variation one sees in students. --Mr.98 (talk) 21:58, 15 September 2011 (UTC)

Do US Universities publish public lists of everyone graduating each year? It would be fairly simple, at least with unusual surnames, to refer to past lists and compare them to present-day students. As mentioned, if there's a building with your name, it might also be a clue. --Colapeninsula (talk) 09:52, 16 September 2011 (UTC)

heat exchanger

hi can anyone tell me why a heat exchanger is needed in steam power plants? in the steam plant cycle, water is boiled to get steam in high pressure and high temperature, and this high pressure is relieved in the turbine. so y do we need heat exchanger? we can directly pass the hot water to the boiler again to heat it rite, why cool down water and then heat it agin? — Preceding unsigned comment added by 117.192.216.156 (talk) 13:54, 15 September 2011 (UTC)

I think in simple terms it is to condense it. To turn steam back to a liquid at the same temperature would need as much energy to compress it as you took out of it. This is way outside my field so I would wait for other comments to be sure.-- Q Chris (talk) 14:41, 15 September 2011 (UTC)

I think you are discussing a closed system. The steam rises and then goes down a tube and back into the water. There are many problems with that design. The steam won't want to go back down unless it is cooled. Since it doesn't want to go down, the steam trying to rise has nowhere to go. All you get is a massive pressure buildup until something fails. By cooling the steam at the top, you can force it back down into the water supply, making room for more steam. -- kainaw™ 14:44, 15 September 2011 (UTC)

the cycle used in steam plants is like this (as mentioned in "Fundamentals of Thermodynamics", Sonntag, Borgnakke, Van Wylen, Wiley Publishers 2010): boiler heats water, steam is at high pressure (HP) and high temperature (HT). steam passes through turbine, steam is at HT and low pressure (LP). it then passes through condenser, it is now at low temperature (LT) and LP. the condensed water is again fed to the boiler. my question is that why we need condenser? anyway we boil same water again to make steam. — Preceding unsigned comment added by 117.192.205.91 (talk) 15:24, 15 September 2011 (UTC)

As explained above, if you don't cool down the steam before pumping it back into the the boiler, the act of pumping it in will require at least as much energy as you got from the turbine to begin with. Dauto (talk) 17:25, 15 September 2011 (UTC)

Actually, there's a more fundamental reason for the condenser. This is because the power station is a heat engine, and like all other heat engines, derives its power not just from heat, but from the transfer of thermal energy from a heat source (gas or coal burning in the boiler) to a heat sink. (If you want to, you could compare it to a power dam, with the heat source in the place of the reservoir, the heat sink in place of the outflow, and the heat engine simply replacing the water-wheels that harvest the energy from the falling water. This is an over-simplification, but it can help conceptually.) It therefore needs both of those to function properly -- without a heat source, it obviously won't have any thermal energy to turn into electricity, and without a heat sink, the thermal energy would just back up with no place to go, therefore no heat transfer and no power generated. What the condenser does is act as the heat sink, allowing the heat to flow into the cold water, thus maintaining the flow of thermal energy. Note that it's possible to use the thermal energy of the hot water from the condenser in various ways, e.g. for home heating, etc. 67.169.177.176 (talk) 00:00, 17 September 2011 (UTC)

Neutrino chemistry

I find it appealing to think about the far future universe as one where small particles acting on very long time scales form interesting chemistry, so naturally I find this talk about "neutrino nuggets" interesting. Alas, if I only understood it! It postulates a force between neutrinos of varying mass mediated by accelerons:

$F=-\left({\tfrac {\partial m_{\nu }}{\partial {\mathcal {A}}}}\right)^{2}e^{-m_{\mathcal {A}}r}r^{-2}$ (parsing error corrected; units added)

with a Feynman diagram of two neutrinos coming up from the bottom, linked horizontally by A, and moving away at top with acceleration ?? ${\frac {\partial m_{v}}{\partial A}}$.

Now that's an inverse square law that, well, isn't - I'm not sure how the exponential in A works, what a variation in mass over a variation in A means, etc.

• Is there a way to get from this to a normal looking physical law expressing the attraction of neutrinos toward one another in terms some typical power law force?

• Can you use this to predict the size of a "neutrino atom", i.e. the distance and speed with which two neutrinos should circle each other to have an angular momentum of 1/2 Planck's constant?

Wnt (talk) 14:39, 15 September 2011 (UTC)

I don't know anything about accelerons, but I'm pretty sure that equation is actually $F=-\left({\tfrac {\partial m_{\nu }}{\partial {\mathcal {A}}}}\right)^{2}e^{-m_{\mathcal {A}}r}r^{-2}$, where $m_{\nu }\!$ and $m_{\mathcal {A}}$ are the neutrino and acceleron masses. This is presumably supposed to be the force arising from the Yukawa potential $-\left({\tfrac {\partial m_{\nu }}{\partial {\mathcal {A}}}}\right)^{2}e^{-m_{\mathcal {A}}r}r^{-1}$, but they left out a factor of $(1+m_{\mathcal {A}}r)$ from the derivative for some reason. Maybe they left it out because the cosmological constant is so tiny that $m_{\mathcal {A}}r$ is negligible at scales below billions of light years, but in that case they should have left out $e^{-m_{\mathcal {A}}r}$ also. Regardless, you should be able to approximate this force as the inverse-square force $F=-g^{2}r^{-2}$ where $g={\tfrac {\partial m_{\nu }}{\partial {\mathcal {A}}}}$. This gives you a neutrino-ium Bohr radius of $\hbar /m_{\nu }cg$. But I don't know how to calculate g. -- BenRG (talk) 02:51, 16 September 2011 (UTC)

Thanks! I never thought about a simple parsing error. That said, I still don't actually understand the formula - what the heck kind of units is e to the (mass x distance) expressed in? I mean, the g constant can't even be in units of e^km or something, because e¹*e^km = e^1+km, not e^{1 km}. That question applies to the Yukawa potential in general. In any case, whatever it means, I take it to mean that the neutrino attractive force is inverse square at shorter distances, but peters out at a range of "1/m_A", whatever that is.

Miscellaneous: I wonder if the force is always attractive, or if there's any combination of neutrino-like particles that repel one another? According to [11] it sounds like the neutrinos might form "nuggets" but then (under current conditions) oscillate to a flavor that can get away, like some kind of neutrino nugget radioactivity, but I probably have that all wrong... then there's the thought of how neutrinos are quantized and how the Pauli exclusion principle works. If you dump three identical neutrinos into these nuggets, I would guess that they can't circle each other all the same way at the Bohr radius, because from the perspective of at least one neutrino there must be two others at the same spin in the same orbit. But at higher orbits would they form p orbitals and such based on different orientations of angular momentum just like atoms? Wnt (talk) 20:42, 16 September 2011 (UTC)

You have to use natural units here (believe it or not but using SI units is much more complicated than using natural units). In natural units, Mass has the dimensions of inverse length, so m r is dimensionless. Now, if you don't express mass in inverse meters, but in kilograms, or in electron volts, you must convert it to an inverse length. You can do that using the formula for the Compton wavelength lambda = hbar/(mc) which is, of course, the same as 1/m if you put hbar = c = 1.

You can think of SI units as using inconsistent units for quantitities, which then makes it necessary to put in conversion factors in formula. So, if you have a formula like L = L1 + L2 where the L's are lengths, but you insist on L1 always being given in kilometers and L2 in miles and you also insist on L1 having different dimensions than L2, because a lengths in Britain are fundamentaly incompatible with lengths in mainland Europe (you can't be in two places at the same time), then you would write: L = L1 + c L2, with c = 1.609344 kilometers/mile. Count Iblis (talk) 21:12, 16 September 2011 (UTC)

It might be a good idea to add something about units to Yukawa potential. Dragons flight (talk) 22:02, 16 September 2011 (UTC)

The problem I have with "natural units" is there are so many of them. If they're so natural there should only be one way to do it and no second thought about it. I like to have a check on an equation. Anyway, here it appears that the particle physics designation that h/2pi = c = 1 is being made, and therefore (reduced Planck constant) / (speed of light) = 1 = 1.054571726(47)×10⁻³⁴ J s / (299792458 m/s) = 3.51767264 ×10⁻⁴³ kg m. Thus 1 kg = 2.84278869 × 10⁴² m^-1 and vice versa. Anyway, according to the talk the acceleron mass is less (perhaps much less) than about 10^-4 eV = 1.78×10−40 kg, which divided by "one" = 500 m^-1. Thus the neutrino force would have a range of at least 0.2 mm, perhaps much further (the comparison made to quintessence I think implies potentially a factor of 10²⁹ further, i.e. a billion parsecs). Wnt (talk) 21:54, 16 September 2011 (UTC)

In the context of relativity and particle physics, you always add factors of c, ħ, and G (though obviously only if your problem is relativistic, quantum, and gravitational, respectively). You should think of ħ as the real fundamental constant of quantum mechanics; h = 2πħ is almost never used any more. It can be useful to carry the constants around as a check, but in my experience it's too distracting to be worth it. Also, it's often unclear where the constants ought to be. Mass and distance have traditional units, and exponents have to be unitless, so you're forced to write e^−mrc/ħ; but should you write ħcg², with g remaining unitless, or should you absorb the units into g²? The Newtonian tradition is to put the units in the force constant, but particle physics has a tradition of unitless coupling constants.

I assume that you would get some kind of shell structure in these neutrino nuggets, yes, and the atomic orbitals are probably a good first approximation.

It's a theorem of quantum field theory that forces mediated by even-spin bosons are always attractive. The spin-2 case is gravity. In fact, I've never really thought about this before, but there ought to be a Higgs-mediated attractive force in the Standard Model that would look a lot like gravity, since the Higgs couples to particles in proportion to their masses. Odd, that. -- BenRG (talk) 08:44, 17 September 2011 (UTC)

about "flow separation" and "boundary layer separation"

Are the flow separation and boundary layer separation the same things?--Wolfch (talk) 16:19, 15 September 2011 (UTC)

I'm not sure, but it seems from a few minutes of review that boundary layer separation is a more pronounced kind of flow separation that is necessarily associated with turbulent flow, while laminar flow can involve simple flow separation but not boundary layer separation. 69.171.160.167 (talk) 21:00, 15 September 2011 (UTC)

Both effects are caused by the same physics (Adverse pressure gradients), so the difference is mainly one of semantics and terminology. "Boundary Layer Separation" typically refers to the transition from a laminar boundary layer to a turbulent one (like this), which is a nearly unavoidable effect based on the local Reynolds Number. On the other hand, "Flow Separation" typically refers to turbulent conditions caused by low pressure areas in the wake of an object, like a wing at high angles of attack. Mildly Mad^T_C 14:51, 16 September 2011 (UTC)

Cabin Pressure vs. Outside

This BBC article about a man attempting to open the door of a plane at 36,000ft has got me intrigued, as the staff of the travel company said that it would have been impossible for the passenger to open the door, due to the pressure inside the cabin. This does not make sense to me. As I understand it, the pressure inside the cabin is greater than outside. Would this not have made it easier, rather than impossible, to open the door? KägeTorä - (影虎) (TALK) 17:07, 15 September 2011 (UTC)

No, because airplane doors open inward, with a lip holding them in. If not, airplane doors would blow off all the time. StuRat (talk) 17:08, 15 September 2011 (UTC)

Ah, yes, of course. Silly me. --KägeTorä - (影虎) (TALK) 17:11, 15 September 2011 (UTC)

Clarification: Those are emergency exit doors which open inward. Many main doors are "plug-type" in design, meaning the doors are bigger than the opening. These may still open outward, but must be pulled inward, rotated, then pushed out. StuRat (talk) 17:14, 15 September 2011 (UTC)

Things were not always like that. D._B._Cooper managed to open the airplane door at the old good days, in the 70s, at the end of the era of uninspected airline travel. Quest09 (talk) 19:46, 15 September 2011 (UTC)

Cooper jumped from an airstair, not a plug door. Regular (non-plug) hatches like those on airstair exits and cargo doors rely on a mechanical locking mechanism (a system of deadbolts) to keep the door secure and airtight. Cooper evidently knew a way to get the mechanism to unlock (even though the aircraft was at 10,000 feet (ref)); the flight crew felt the pressure drop as he did so, and once it was equalised he jumped. -- Finlay McWalterჷTalk 20:16, 15 September 2011 (UTC)

The pressurization was off, so a plug door could also have been opened anyway. Cooper most probably deliberately chose a 727 because it has an airstair in the tail, which is arguably the only "safe" usable mid-air exit on any common jet airliner that existed in the US at the time. Roger (talk) 20:31, 15 September 2011 (UTC)

The airstair doors were re-designed after this incident: see here Cooper_vane. Apparently, Cooper didn't need any special knowledge at his time to open this door. Quest09 (talk) 20:38, 15 September 2011 (UTC)

United Airlines Flight 811#Cause discusses the locking mechanism on a cargo door, and describes how an electrical fault caused this door to unlock at altitude and blow out. -- Finlay McWalterჷTalk 20:21, 15 September 2011 (UTC)

Philippine_Airlines_Flight_812 might be of interest here: it's the case of a hijacker who managed to open the door of an Airbus at the altitude of 1,800 meters. Quest09 (talk) 20:38, 15 September 2011 (UTC)

Airlines only usually pressurize to around 2500 meters equivalent altitude anyway, so the doors would open at low altitude. Googlemeister (talk) 20:44, 15 September 2011 (UTC)

Additionally, there is something else blocking the (plug) door: the air flowing around the plane won't let you open a door of a Boeing, for example, that it hinged like a car door. Quest09 (talk) 20:52, 15 September 2011 (UTC)

the matter of dark energy

as you know dark energy exsits surly.....a fact now understood by many but as to the expansion of the universe and dark energy as I understand what you think the universe will shrink ? I think not the dark energy will not allow this to happen that is the foremost and purpose of this matter wether it is in the physical of the now or in the physical of another dimension or the future minds no hinderence for the future is now,,,, as also is of the so called past... time is only an equation of the human mind as is this dimension taken that into perpective the human mind is not fully formed and for sure not working to its fullest..... we as race are only just born....I would love to speak to you ,,,you have proved many of my knowings often laughed at by those of so called intelligence to be not only wrong but miss conconcived please do not get me wrong but most scientist close there minds to the impossible but was not the atom an impossible thing 200 years ago as to was quark my knowings are by truma a strong way to learn my body has passed so called death more then once this i can prove medically also not a willing idea of my own but I side track as to the shrinkage of the universe you are wrong this will not happen the universe isa expanding into enthropie maybe may spelling is wrong but you did say space did not excist but your wrong a doiffernt type of space did excist AND THAT IS WHAT THE UNIVERSE IS EXPANDUING INTO before the universe was born only centinent intelligences of pure dark energy was alive of course not in pyhsical human way but alive for many a million years in our time problem was when they met all was ok problem was that when they took all that was they with them leaveing 0 for thew host ahhhhhhh time to create a mote in gods so called eye and the universe was born nbow i can keep what you know and you can keep what i know but a problem was also born lack of memory born to with the creation of physical life itself sorry if you would like to email me please do ny mind is afire — Preceding unsigned comment added by 180.180.190.24 (talk) 19:40, 15 September 2011 (UTC)

We have an article on the ultimate fate of the universe, which includes a section noting that current scientific consensus favors an expanding open universe driven in large part by dark energy. Beyond that, Wikipedia is not an appropriate venue for you to develop or publicize your personal philosophy. — Lomn 19:50, 15 September 2011 (UTC)

google "The Last Question" by Isaac Asimov and read it. — Preceding unsigned comment added by 24.45.168.74 (talk) 20:27, 15 September 2011 (UTC)

Yes, do read the articles, and allow your mind to cool a little from its fire. Dark energy, if it exists, is part of the physical universe, not some god-like intelligence. Dbfirs 20:34, 15 September 2011 (UTC)

I also suggest you learn about spell checkers. That is, only if you want us to read your questions, of course. --Lgriot (talk) 09:41, 16 September 2011 (UTC)

A little Learning is a dang'rous Thing;

Drink deep, or taste not the Pierian Spring:

There shallow Draughts intoxicate the Brain,

And drinking largely sobers us again.

Fir'd at first Sight with what the Muse imparts,

In fearless Youth we tempt the Heights of Arts,

While from the bounded Level of our Mind,

Short Views we take, nor see the lengths behind,

But more advanc'd, behold with strange Surprize

New, distant Scenes of endless Science rise!

So pleas'd at first, the towring Alps we try,

Mount o'er the Vales, and seem to tread the Sky;

Th' Eternal Snows appear already past,

And the first Clouds and Mountains seem the last:

But those attain'd, we tremble to survey

The growing Labours of the lengthen'd Way,

Th' increasing Prospect tires our wandering Eyes,

Hills peep o'er Hills, and Alps on Alps arise!

Pope. 86.164.76.231 (talk) 15:21, 16 September 2011 (UTC)

I have a jeweler's magnifying loupe with out any power marking.. How do I decipher the power?

I have a jeweler's magnifying loupe with out any power marking.. Is there any way to conveniently (or not, if necessary) decipher the power of this lens? — Preceding unsigned comment added by 24.45.168.74 (talk) 20:02, 15 September 2011 (UTC)

Measure how many times it enlarges a ruler's markings? 69.171.160.167 (talk) 21:05, 15 September 2011 (UTC)

I'm sorry if I seem a little inept but any suggestions on how to accurately mark the increase in size? — Preceding unsigned comment added by 24.45.168.74 (talk) 21:06, 15 September 2011 (UTC)

If you can print an image of known size on an acetate transparency, you could use a flashlight to project the image through the loupe onto a screen, and measure the output size. If you know the distance from the loupe to the screen (ideally at the focal distance), then you should be able to figure the out magnification... can anyone show us the specific equation to use for this calculation? Is it in lens_(optics)? SemanticMantis (talk) 21:30, 15 September 2011 (UTC)

Here's a quick, rough method (to which 69.171 alluded above):

Find a ruler with the same subdivisions (e.g. 1/10ths of an inch) over at least 6 inches (it can be a decimal ruler, the actual units don't matter).

Put the ruler on a flat surface which allows you to see its markings easily (such as a sheet of paper on a table top).

Put the loupe in one eye and move your head until the magnified markings are clear.

Keeping your other eye open, allow your vision to superimpose the magnified subdivisions seen through the loupe over the unmagnified subdivisions of the same value being seen by your naked eye (this may take a few minutes of practice).

Now simply count how many unmagnified subdivisions fit in to one magnified subdivision; the answer is the linear magnification in the "12 times" or "12 X dd" format commonly used for binoculars, telescopes and loupes, etc. [The "dd" refers to the diameter of the 'front' lenses of binoculars, etc, given in millimetres, so "12 x 50" is typical]. The result is actually quite likely to be 10x, because that's a common standard for jewellers' loupes.

As a former amateur astronomer, I have often used this method to find the approximate magnification of an eyepiece of unknown power (on a particular telescope of known focal length, and thence the focal length of the eyepiece), by looking at a distant brick wall. {The poster formerly known as 87.81.230.195} 90.197.66.32 (talk) 22:43, 15 September 2011 (UTC)

If language is a universal component of human existence...

...why does it require years to learn? Using a vehicle is much easier for us humans, and we didn't drive vehicles along evolution. Quest09 (talk) 20:44, 15 September 2011 (UTC)

It doesn't really require years. For children, I would say it takes some months to learn a new language. 88.9.108.128 (talk) 20:55, 15 September 2011 (UTC)

(edit conflict)Just so we know ahead of time, can you tell us how many times you are going to compare some aspect of human life to learning to drive a car?

For the record, every human can learn, without any training, the language of their parents in about 2-3 years before they are fairly fluent. Place a toddler at the drivers seat of a car and ask them to "figure it out by yourself" and see how long it takes before he can do so. Your question is silly because it is asking about different types of learning in humans from vastly different stages of their development. If you are genuinely interested in language acquisition (instead of just asking inane variations on "why is BLANK harder than driving a car"), back away from the computer and go to your local library and look for books on linguistics by Noam Chomsky and pay special attention to his writings about Universal grammar and Generative grammar. --Jayron32 21:01, 15 September 2011 (UTC)

A million times more people in this world know how to speak a language fluently than know to slow down, rather than speed up, when it's raining. Nevard (talk) 22:15, 15 September 2011 (UTC)

No kidding. Also, this question seems suspiciously familiar. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:27, 15 September 2011 (UTC)

Spoken language seems to arise spontaneously in human beings as part of their neurological development. Written language is a specific human invention, one that is relatively recent (in terms of evolution of the species), as far as we can tell, and has only been independently invented a handful of times. The analogy with your previous question is that spontaneous music seems rather innate in humans, but written music is not. --Mr.98 (talk) 01:42, 16 September 2011 (UTC)

Walking is a (nearly) universal component, but it takes around a year to learn (and much longer to learn how to throw a javelin at a deer, which is also fairly universal). Human beings (and all advanced organisms) have a natural development process: predators learn to hunt, birds learn to fly, etc. This involves physical and neurological development. --Colapeninsula (talk) 10:00, 16 September 2011 (UTC)

If politeness is a universal component of human existence...

...why does it require years to learn? Using a vehicle is much easier for us humans, and we didn't drive vehicles along evolution. Quest09 (talk) 21:09, 15 September 2011 (UTC)

Do you have something to say to me? Maybe we should step outside... --Jayron32 21:13, 15 September 2011 (UTC)

Evolution includes behavior, and how parents instruct their children on playing nice has had a long, long history. One of the advantages to having a brain is that you don't have to wait for biochemical mutation to change the adaptability of the species, you just change your behavior. Politeness, however, is a complex task and there isn't a single ideal way to do it, as various cultures have mutated with different approaches given different contexts. American culture is substantially less polite than, say, traditional Japanese culture, but the lack of politeness allows for other benefits, mostly in clearer communication. Even within a single culture there are usually several levels of politeness (within family, with friends, in business, in religious activities, etc...), and a lot of people being "impolite" is just applying the wrong level of politeness within their own culture. Driving is simpler, because there's generally, within a culture, one "right" way to do it. SDY (talk) 21:33, 15 September 2011 (UTC)

I don't know if American culture is less polite than traditional Japanese, I'd say simply that it's less marked, people care about different things, and you are not forced to show respect for some old dude, when in reality you don't care about him.88.9.108.128 (talk) 21:50, 15 September 2011 (UTC)

We have an instinct for empathy and a desire for 'tribe' to grow stronger, and a desire to be accepted by that tribe, but we are not born instinctively knowing whatever arbitrary rules of etiquette are in fashion this century. Even those instincts I mentioned are not truly "universal"; some people are selfish assholes, and like being selfish assholes.

As for the vehicle thing, tool use is absolutely something that gave us an evolutionary edge. Our ability to understand how machines work, without too much trouble, is definitely an ability we evolved. We have to learn how the specific tools work, but that kind of learning is easy for our species. (And, of course, we've had vehicles since the stone age, in the form of rafts and canoes.)

Now that we've answered your questions, where the heck are you getting these "universal component of human existence" nonsense, and why are you asking so many questions about it? APL (talk) 21:44, 15 September 2011 (UTC)

Through a Google search for "universal component of human existence" , I could find more of them. Pain, suffering are "universal components of human existence" according to Buddhism. And sport is too a "universal component of human existence" . 88.9.108.128 (talk) 21:54, 15 September 2011 (UTC)

Politeness is a weapon of war. And as with all arts of war, it is difficult to learn because it is not enough to be good at it, but to be better than most other people. People who feel no possibility of real conflict are perfectly rude to one another (the traditional nagging wife). Those who are a moment away from blood feud show perfect civility. But politeness is not merely a means to avert conflict; it is a method to keep information hidden, so that no one knows when they'll be stabbed in the back. It becomes a shared set of standards that people can singled out for violating (just see WP:Civility in action...). See also [12] on "good manners". Wnt (talk) 23:03, 15 September 2011 (UTC)

Humans have a tendency to seesaw between one extreme to another. People who are politically correct, tend to be too politically correct that it becomes blatantly farcical. Those who dislike being politically correct on the other hand, interpret not being PC as to be the rudest you can be as possible (schadenfreude). Both are attempts to 'rebel' against imposed social norms. And politeness is really just that - a social norm. Though it's not instinctive, empathy is (wincing at the sight of another person getting hurt for example). In the best possible usage, politeness is simply a deference to empathy, The Golden Rule, do not do unto other what you do not want others to do unto you. The willingness to mitigate the amount of hurt, shame, or simply even inconvenience inflicted on another person by your choice of words or actions, sometimes at a personal cost, something reflected in different religions and cultures.

But yeah, the extent of empathy is often limited in some people. The farther people are from the culture of the speaker, the less likely he will be to experience empathy for them. A throwback to tribalism I guess in which while you must be able to empathize with fellow tribe members, you must also be wary of strangers for the tribe's survival. Nationalism and racism are like this, on a larger scale, people from different cultures still view each other as potential rivals for resources necessary for their "tribe's" growth. The level of politeness shown to another is also reflective of the the imbalance in power and threat capability. The more powerful one party is over another (whether real or imaginary), the less likely they will be to observe politeness in communications (arrogance). See Politeness theory.

Westerners also tend to overestimate Asian cultural politeness because of Hollywood movies, outsider bias, and stereotyping. Some gestures deemed polite but 'covertly' hostile by westerners may actually be deliberately and blatantly insulting to another person from the same culture. The problem is a difference in interpretation of words and gestures. There's also a difference in the focus of politeness. American politeness focuses on positive politeness (inclusiveness, e.g. flattery, jokes, eye contact) while Japanese politeness focuses on negative politeness (non-intrusiveness, e.g. self-effacement, distancing, avoidance of eye contact). Both are simply different forms of politeness and both are structured along social hierarchies with the same purpose of easing communications between different parties. It backfires in cross-cultural communication I guess. Someone used to positive politeness will see negative politeness as cold and calculating. Someone used to negative politeness will see positive politeness as obnoxiously intrusive. See Intercultural competence and Face (sociological concept).-- Obsidi♠n Soul 00:31, 16 September 2011 (UTC)

September 16

Neutron foundries

How many neutrons are produced regularly at a small, university-sized LEU fission reactor? How many would produced by a reasonably large, but still-university sized tokamak, using today's technology? (I'm obviously not assuming the tokamak reaches breakeven — it need not produce more energy that goes into it, but should still produce some fusion neutrons.) --Mr.98 (talk) 03:33, 16 September 2011 (UTC)

I'm just looking for rough estimates... e.g. 10^x neutrons per hour of peak operation, but it can only run for y hours at a time, things like that. --Mr.98 (talk) 12:10, 16 September 2011 (UTC)

methane green house gas

The sanitary sewer is required to have vents at critical locations in the line to prevent traps from being sucked dry of water. These vents also allow methane to escape into the atmosphere and methane is a green house gas which is burned off at the plant. Is there any reason why sanitary sewer vents can not be tapped in a way that would allow methane to be captured, compressed and then used as fuel instead of being released into the atmosphere? --DeeperQA (talk) 04:59, 16 September 2011 (UTC)

Maybe there's not enough methane there to go through the trouble of capturing it. .... — Preceding unsigned comment added by 88.8.79.204 (talk) 05:30, 16 September 2011 (UTC)

Distance from the plant could also be a factor. On the other hand, it may be possible to flare the methane from the vents to prevent it from entering the atmosphere. 67.169.177.176 (talk) 05:45, 16 September 2011 (UTC)

Sewer gas contains much more than just methane: some of it is toxic and a lot of it smells really bad. You would have to collect it and separate the small part of methane from the rest of it, and then dispose of the remainder which probably isn't economically worthwhile (and environmental regulations are probably stricter on what you extract from sewer gas than what you let naturally float out). --Colapeninsula (talk) 10:04, 16 September 2011 (UTC)

Actually, the article sewer gas says it can be and sometimes is used as a fuel. But the reasons mentioned it's not entirely straightforward. --Colapeninsula (talk) 10:06, 16 September 2011 (UTC)

See this article. Alansplodge (talk) 21:29, 16 September 2011 (UTC)

Cell division and the onset of puberty?

I have a question about mitosis and how it relates (if at all) to the onset of puberty.

As I understand it, every so often, a human, autosomal cell will keep on dividing until it reaches the "Hayflick limit," after which, it simply collapses after a certain time. This is (more or less) what helps prevent cancer as well as what causes people to grow old and die.

I'm curious, though, whether this relates to sexual maturation in any way. Is there a "lesser Hayflick limit" (for lack of a more proper term) that triggers the end of childhood and the beginning of manhood? If so, does this occur in all autosomal cells, or does it only occur in cells of the endocrine system?

May a process similar to "immortalized cell lines"—theoretically, at least—be used to extend childhood to progressively later ages? Did any wikipedia article or any proteomics journal ever illustrate such a hypothesis? Pine (talk) 06:26, 16 September 2011 (UTC)

Puberty is caused by hormones, and we do have meds to block those, which can prolong childhood. I seem to recall a case where this was done with a disabled girl to make her "easier to manage". StuRat (talk) 06:41, 16 September 2011 (UTC)

You may be thinking of this controversial case, Ashley Treatment, which including drugs and surgery. Rmhermen (talk) 13:32, 16 September 2011 (UTC)

Yep, that's the case. StuRat (talk) 18:38, 16 September 2011 (UTC)

In general, I'd say cell division is more 'regulated' than being the 'regulator' of development (i.e. the outcome rather than the effector). Certainly blocking signals regulating development could prolong a pre-pubescent state, as was observed in Eunuchs Jebus989^✰ 10:02, 16 September 2011 (UTC)

Order D

Is there a rational about putting in cordinates the X first and then the Y and the Z? If so, what about 4-D? Exx8 (talk) —Preceding undated comment added 09:58, 16 September 2011 (UTC).

Cartesian coordinate system#Notations and conventions maybe? DMacks (talk) 10:32, 16 September 2011 (UTC)

In four dimensions it depends if you're dealing with 3 dimensions of space and one of time (i.e. spacetime) or with 4 space-like dimensions (see Four-dimensional space). 4D space-time coordinates are usually called either (t,x,y,z) or (x,y,z,t) (see Spacetime). In four-dimensional space (x,y,z,w) or (w,x,y,z) are commonly used (e.g. [13]).

As to why we have that ordering, alphabetical order is natural in 2 or 3 dimensions, as when you add z to x and y, but after that it's harder to know what's the logical order. Spatial coordinates are only conventional, i.e. there's no X, Y, or Z axis in nature, and you can swap the axes freely (subject to certain rules to preserve the handedness). --Colapeninsula (talk) 11:12, 16 September 2011 (UTC)

In n-dimensional euclidean spaces, you'll also see standard basis vector notation, which uses numerically ordered subscripts. For 4D, this would be (e_1, e_2, e_3, e_4). SemanticMantis (talk) 15:14, 16 September 2011 (UTC)

Or (e₁, e₂, e₃, e₄) if your brain doesn't process TeX:) DMacks (talk) 15:28, 16 September 2011 (UTC)

In other words, no. There is no reason, other than societal norm and mathematical historical convention that the "horizontal" coordinate should be denoted before the "vertical" component; nor that "x" corresponds to "horizontal," and so on. If you start studying more advanced physics and engineering, you will quickly see that in the general case, we do not always use "x" for "horizontal" and we do not always denote coordinates in this order; we rarely use rectilinear coordinates; and in many fields, we do not even use orthonormal coordinates. For example, the standard basis in elementary image-processing is the x/y cartesian grid: you denote pixel positions in (x,y) pairs. For historical reasons, a computer screen inverts the y-axis from historical mathematical convention; in many 3D toolkits, this means that a right-handed rule is not preserved. In many subfields of image processing, we do not use pixel-location; for example, in image compression, we use the spatial fourier transform to parameterize pixel data; and then we use a lossy compression scheme; so our coordinates are neither orthonormal nor spanning. In a modern video signal, we typically represent a time coordinate; the math we perform on the 2-D image signal is therefore a generalized "3-D" transform; but not in the conventional spatial interpretation. The "ordering" of these coordinates is actually very complicated; but at some point, the data is all serialized to a bit-stream, so if you felt like dragging mathematical idealizations through the muddy mire of engineering details, you could find a description of the "coordinate transform" of any particular pixel (x,y,t) to a (very complicated) linear combination of bitstream-offset coordinates.

Start by reading generalized coordinates. This topic is usually covered in greater detail in the first chapter of any textbook on linear algebra. Nimur (talk) 18:20, 16 September 2011 (UTC)

Huge trees

Do we know about any trees that their frond's thickness is about 20 meters? Exx8 (talk) —Preceding undated comment added 10:41, 16 September 2011 (UTC).

Palm trees and cycads have fronds, which are a type of leaf. But it seems very unlikely that a leaf would be 20 meters thick. Do you mean something else, like the length of the frond, or the thickness of a tree's trunk? Record breaking trees (see "stoutest tree") says the largest trunk is currently the Sunland Baobab, an African baobab (Adansonia digitata) at 10.64 metres diameter; the widest ever was an African baobab 15.9 m wide. --Colapeninsula (talk) 11:27, 16 September 2011 (UTC)

(edit conflict) As Colapeninsula said, fronds are fern, cycad, or palm leaves. If you meant the spread of the leaves on top of the trees, better terms to use are foliage, crown, or canopy. If you meant the trunk, use trunk or main stem. :) Either way, the answer probably lies in clonal colonies. Plants (or fungi) which at first glance looks like a group of several plants or even a small forest, when in reality they are vegetative clones (ramets) of a single organism that may or may not be interconnected underground. The most famous example is Pando (tree) (which may not even be the largest of its species), a clonal grove of a single male quaking aspen that covers a total of 106 acres. For individual trunks of trees, however, there are several sequoias with circumferences (note, this is measured at ground level, and is different from diameter at breast height) exceeding 20 m, see List of largest giant sequoias. A sweet chestnut named the Hundred Horse Chestnut is also recorded to once have a circumference of 57.9 m in 1780, though the trunk have now split to several trunks (though it's still a single individual).-- Obsidi♠n Soul 11:55, 16 September 2011 (UTC)

I always wondered why we want to count clonal aspen as a single organism, but we don't want to count identical twins as a single organism even though they too are clones of each other. Googlemeister (talk) 13:45, 16 September 2011 (UTC)

Identical twins aren't physically connected to each other underneath the soil. As for conjoined twins, you have two distinct central nervous systems, with some shared bodily resources, which makes comparison with plants difficult, let alone anywhere near politically correct. —Akrabbim^talk 13:55, 16 September 2011 (UTC)

(EC) It's not just that the aspen clones share the same DNA. The various ramets transport and exchange nutrients and fluids. "Above ground these plants appear to be distinct individuals, but underground they remain interconnected and are all clones of the same plant." But your comment is still apt. It is difficult to define a notion of 'individual' that applies well across all the myriad forms of life :) SemanticMantis (talk) 13:59, 16 September 2011 (UTC)

The inadequacy of the concept of an 'individual' is perhaps most striking among slime molds. :P -- Obsidi♠n Soul 14:40, 16 September 2011 (UTC)

Studies of people's competence vs their belief of how hard a task is

I'd like to see the results of studies if any like the following have been done. Take an arbitrary task and tell half of the test participants that the task they're about to do has a success rate of 10% (or some very low level) and tell the other half the opposite, and see if the average performance of the people primed to believe the test is easy do any better than the others. I don't have access to any papers open only to subscribing members only, either. 20.137.18.50 (talk) 15:07, 16 September 2011 (UTC)

The articles Overconfidence effect, Optimism bias don't answer your question but may give some clues, maybe for useful search terms.

List of cognitive biases is probably worth looking at for your purposes, Experimenter's bias seems like it could be useful for you. and goes into great detail listing more specific biases - one of these might describe the effect you are thinking about, and be helpful in a search.83.100.239.6 (talk) 23:01, 16 September 2011 (UTC)

Lifeform that has killed the most humans (other than humans)

What lifeform has killed the most humans in human history other than humans themselves. This includes indirect killing through transmitting viruses. Viruses themselves are (arguably) not lifeforms themselves so lets just ignore them. My guess is mosquitoes, am I right? ScienceApe (talk) 17:40, 16 September 2011 (UTC)

Mycobacterium tuberculosis and Vibrio cholera are good bets, maybe Streptococcus pneumoniae too. If you're asking about specific lifeforms, mozzys wouldn't feature but the human-specific members of Plasmodium might. An interesting question, but I don't think humans needed to be excluded, I would guess we kill each other less than other things kill us Jebus989^✰ 17:54, 16 September 2011 (UTC)

Maybe now. There's some statistic in the "Rational Optimist", which I think is that as many as 1/3 of the early human population were murdered (all forms or justifications). Grandiose (me, talk, contribs) 18:10, 16 September 2011 (UTC)

But with the exponential growth of human population. 1/3 of 'early humans' is a drop in the ocean today, and we're talking 'the most humans in human history' Jebus989^✰ 18:18, 16 September 2011 (UTC)

Wars and genocide have been blamed for about 200 million deaths during the last century. That's probably a large enough number to put human violence on the map, though probably not large enough to put it at the top of the list. Of course some of those deaths are also related to various diseases that hang around battle fields. Dragons flight (talk) 23:32, 16 September 2011 (UTC)

Again, you'll find that over the course of human history, that is a drop in the ocean. Smallpox is thought to have killed up to 500 million in 60 years^ref and for longer-term human pathogens the total is incalculably huge Jebus989^✰ 18:45, 17 September 2011 (UTC)

(e/c) Yeah, but early human populations were tiny, and if we're talking raw body counts, we really need to look at the killers of the modern age. Y. pestis would otherwise be worth a mention, but I doubt it makes it very high on the list despite some high impact outbreaks in China and Europe. P. falciparum is another suspect worth mentioning. SDY (talk) 18:26, 16 September 2011 (UTC)

table of compunds

Is there a table of compounds that is laid out with both the rows and columns of the tables listing the elements with the row and column intersections or cells showing the compound(s) that are or can be formed by each element? For instance, at the intersection of oxygen and oxygen the compound O₂ would appear. --DeeperQA (talk) 18:42, 16 September 2011 (UTC)

It wouldn't be plausible to construct such a table. Carbon chemistry alone is extremely complex, and the number of meaningful combinations even of just carbon and hydrogen probably numbers in the hundreds. SDY (talk) 18:46, 16 September 2011 (UTC)

There are almost 28 billion different C₃₂H₆₆ structural isomers (and many of those each have many different stereoisomers). DMacks (talk) 18:57, 16 September 2011 (UTC)

The possible theoretical combinations of carbon and hydrogen are almost infinite. The number of them that produce chemicals that anyone actually uses are far smaller, and I'm assuming for a reference table you'd limit it to ones with practical implications. SDY (talk) 19:02, 16 September 2011 (UTC)

SciFinder lists literature references for 142 different chemical entities (==unique CAS#) for that formula (considering elements alone, not different isotopic possibilities). DMacks (talk) 19:57, 16 September 2011 (UTC)

Assuming, for the sake of argument, that everything from 1-50 carbons or so has a similar number of studied (not necessarily useful) chemical entities, that'd still give a number in the 10^4 to the 10^5 range. Guessing that one in ten of those studied entities have some sort of "meaningful" (i.e. practical or common) use, that gives a lower number. Regardless, it was a random and fairly conservative estimate. Even if it were only hundreds the proposed table would be impractical. SDY (talk) 20:10, 16 September 2011 (UTC)

Well, that could be handled by making it a 3D table (or more practically, you could pick at an intersection to get an expanded list of the most common compounds, without worrying about isomers, etc.). Or, perhaps the OP meant to only allow 1:1 combos at each intersection, not variable numbers of each element. They didn't list ozone (O₃), for example. Of course, if you wanted to list common compounds of 3 or more elements, this table would rapidly get out of hand. StuRat (talk) 19:03, 16 September 2011 (UTC)

I realize there are a great number of possible combinations but I was assuming that these could be further divided and handled at the intersecting cell on the basis of numbers of atoms or other elements in the compound through links to a new table. Perhaps a better method would be to list the compounds as the dependent variables and the elements as the independent variables and the bonds (or other relations) in the intersecting cells, using links wherever expansion was necessary. --DeeperQA (talk) 12:56, 17 September 2011 (UTC)

Rhythmic audience clapping

Is it reasonable to think that a rhythmic audience clapping would keep its exact rate over a long period of time? Is there anywhere I could look for answers on that? Gil_mo (talk) 22:15, 16 September 2011 (UTC)

No, and attending any concert with any musician will substantiate this. Audiences can't hold tempo even with assistance. — Lomn 22:51, 16 September 2011 (UTC)

(ec) There is no such thing as an "exact" rate for a group of people clapping in imperfect synchrony, so the question doesn't really have an answer. You could make the question more reasonable by asking whether the frequency spectrum changes over time, and I'm sure the answer is yes, but I don't see any reason why anybody would have invested resources in doing a formal analysis: there are bound to be a zillion uncontrollable factors that influence audience clapping rates. Looie496 (talk) 22:53, 16 September 2011 (UTC)

For relevant audible frequencies, a clap is very much like an impulse function. A rhythmic train of perfect impulse functions is called a Dirac comb. These are well-known mathematical idealizations and the spectral properties are very thoroughly understood. In fact, our article lists the fourier series (the frequency-domain representation) of a dirac comb:

$\Delta _{T}(t)={\frac {1}{T}}\sum _{n=-\infty }^{\infty }e^{i2\pi nt/T}.$

It's improbable that the sound of a human clap is a true delta impulse; and it's improbable that the timing is perfect; but we can characterize both of those imperfections as types of noise: frequency spread and phase noise (and we could get more sophisticated, if we wanted). Both of these parameters are well-studied as well; they translate to frequency spectral characteristics (basically, a "blurring" of the ideal frequency spectrum). Entire texts - entire libraries - are devoted to the study and parametrization of noise. Nimur (talk) 23:53, 16 September 2011 (UTC)

Looie496, my question was regarding rhythmic clapping, not asynchronous clapping. My question came after listening to a concert after which the audience was clapping rhythmically for over 5 minutes, and the tempo did not change a bit. I understand that for taking a tempo in a laboratory you need a delta, but I'm considering 'tempo' to be derived from the interval between two 'mass centers' of the clapping. That is, the tempo I'd clap to join the crowd. Gil_mo (talk) 09:28, 17 September 2011 (UTC)

Anecdotally, it depends on how musical(ly trained) the audience is. An average audience taking part in a rhythmic clap will speed up, clapping faster and faster. A more musical audience is quite capable of keeping a fairly constant tempo for a while, just as a skilled orchestra, chamber group or choir is capable of keeping a constant tempo. 86.164.76.231 (talk) 14:35, 17 September 2011 (UTC)

Is evolution virtually testable, If so, has it been done?

Thinking about how logical evolution is, I thought is it possible to give computers of a model of the process, I mean the basic things are simple, a changing environment, some species that reproduce and randomly achieve traits while reproduction, and a little bit of time...?--Irrational number (talk) 22:46, 16 September 2011 (UTC)

Not only has it been done, but Genetic algorithms are actually sometimes used for problem-solving in general-purpose applications: see also Artificial life, Evolutionary algorithm etc. AndyTheGrump (talk) 22:55, 16 September 2011 (UTC)

thanks, and has there been new, unexpected species evolving in there?--Irrational number (talk) 23:10, 16 September 2011 (UTC)

Every time a genetic algorithm evolves an unexpected species, a numerical analyst tries to fix it. Unexpected behaviors are practically the norm in complex numerical modeling programs. Sorry, that was a bad pun. Nimur (talk) 23:45, 16 September 2011 (UTC)

These computer programs deal with "survival of the fittest" only in a very abstract sense. There are probably discernable "species" in them, but they aren't anything we'd recognize as living. Tierra (computer simulation) is just programs competing for CPU time, but in the abstract they still "reproduce", "mutate", "die", and "survive." SDY (talk) 23:47, 16 September 2011 (UTC)

My personal favorite AL programs are GenePool and Darwin Pond, both by Jeffrey Ventrella. They're free, visually appealing, and easily understandable by even young children. They're both swimbot programs and illustrate how sexual selection, environmental conditions and adaptations to it can steer the course of 'evolution' of the swimbots' "genes". It's limited because of the hardcoded nature of all the specific 'traits' however (they only have 15 'genes'). They're also all 'herbivores', i.e. no individual eats another, so there is no predator-prey 'arms race' evolutionary pressure. It's more accurate to view them as simulations of genetic drift that can happen within a species.

Another interesting easily accessible AL program is Creatures. It's actually a game with a twist. Had a lot of fun with this as a kid. Each individual creature has inheritable genes that control appearance, biochemistry, and behavior; each of those further affecting how the creature reacts to things around it in life. They can also mutate and can be inherited. Unlike swimbots their genes are far more complex. To an extent, they generate unpredictable mutations in a permutative sense, as all 'genes' are of course preliminarily defined (they're actually discrete strings of AI that utilize variables). An example is a mutation which affected the production a certain chemical, producing 'alchohol' continuously instead and making that particular creature, perpetually congenitally drunk. Their long lifespans however (in some cases, mutations can render them effectively immortal), doesn't make them ideal for showing selection pressures.-- Obsidi♠n Soul 03:30, 17 September 2011 (UTC)

There's a popular legend among computer scientists that I've heard many times but I can't track down to the source. (A link would be aprecieated.) The story goes like this :

It seems that some scientists did an evolutionary simulation to see if they could evolve simulated creatures with new and interested methods of locomotion. They set up their evolutionary simulation so that the beings that could walk the farthest before they got stuck would be considered "fit" and be used to populate the next "generation of beings". They set it up and sure enough their simulated beings were wiggling around on the simulated ground. They let it run for some long period of time and came back to it. When they looked into the simulation, they found that all their beings had evolved into extremely thin, and extremely tall cylinders. Why? Because if you're a mile tall you can move half a mile forward simply by falling over.

So this story, even if purely legendary, demonstrates a way that evolutionary algorithms can cause "unexpected" results, but not in the wonderful way the researchers were hoping. The simulation just found a way to "cheat" that the programmers hadn't anticipated.

I, personally, had a similar experience using evolutionary algorithms to create AIs opponents for a racing game I made in college. The AIs started off pretty stupid. They went fast, but more often than not they'd crash and burn. I turned off the graphics and let them run thousands of races overnight, the next day after class I came back and I played a game against the AIs I had grown. I was naively expecting that they had all become unbeatable, ultra-skilled, super-racers while I'd slept. Well, I guess I had made the penalty for a collision too severe, because all the AIs were piloting around the track in a single-file line at about 1/20th throttle. They would occasionally jockey for position in areas where the track was very wide, but even then they'd do it very, very slowly with exaggerated caution. Needless to say, I was disappointed. APL (talk) 04:06, 17 September 2011 (UTC)

The first example (falling over) seems like a defective design, since creatures that tall couldn't exist. However, you 2nd simulation seems like it worked, to me. Given the constraints on racers where safety is much more important than winning, that might be exactly how they would behave. In fact, I think they do behave much like that in real life. StuRat (talk) 04:29, 17 September 2011 (UTC)

Heh, what you described sounds like breve, but I dunno about the anecdote though. And yeah, the "unexpected" results are often bugs. In the previous example of Creatures, the immortality gene (colloquially known as the 'Highlander gene'), was one such thing. And it led to overpopulation and was fixed in subsequent versions, however, it again reappeared for wholly different reasons. Immortality, it seems was the logical conclusion of a world where resources never run out.-- Obsidi♠n Soul 04:41, 17 September 2011 (UTC)

If you are trying to accurately model the exact process of evolution which occurred on Earth with your program, it probably won't work. That's because we would need to know absolutely everything about their environment, like all the predators and prey, with precise numbers, as well as their own DNA, precisely, to predict accurately how it might mutate and evolve. StuRat (talk) 04:34, 17 September 2011 (UTC)

Magnetic rules -true brushless DC motors

I'm trying to recall some rule on magnetic forces (ie lorentz and laplace forces) when applied to the construction of an electric motor (ie a rotating machine)

Here's a typical setup -- mounted laterally on the edge around a rotating disc are N bar magnets all aligned the same way (parallel to the axis of rotation, call this "Z" plane) - this setup would be pretty much the same (in terms of shape of the magetic field) as a cylindrical magnetic (poles on circular faces) with the centre hollowed out, with the centre line co-axial with the axis of rotation. Clearly (?) the magnetic field lines will be like a bar magnet, except some with go from N to S through the centre of the hollow cylinder.. Does that make sense so far.?

The next step is to have a DC current in a loop at one end, with the loop in an radial plane. eg the plane defined by the "Z" and "Y" axis is such a plane. I was interested in the net force between magnet and current carrying wire due to "Laplace force" - I seem to remember that there was a (named) rule that states (or shows) that there can be no net force (assuming a constant Permeability (electromagnetism) exterior to the magnet and wire..) However it seems that since one half of the wire which produces an opposite force to the other half (due the the current being reversed due to the loop) is farther away the forces (and torques) will not balance.. - ie the net force will be in the direction given by the interaction between the part of the wire nearer to the magnet.

If there is a net force then this would be a simple brushless DC motor - which I though was not possible under these conditions?

Can someone either explain why there is no net force.. or if the opposite applies - please link to a page/book that describes "true" brushless DC motors in more detail. Thanks.83.100.239.6 (talk) 22:51, 16 September 2011 (UTC)

But how...

Why/how does the background begin waving? http://www.youtube.com/watch?v=EnrwrwMfNSs 65.92.5.209 (talk) 23:49, 16 September 2011 (UTC)

Simple answer is that the rotor is going faster when moving in the direction of the craft and slower when it is on the other side going back towards the rear. In the advancing mode, it experiences more lift – and rises: whilst in the retrograde it loses lift and bends down. The makes the horizon appear to rise and fall. --Aspro (talk) 00:04, 17 September 2011 (UTC)

But at one point the image inverts itself, how does that happen? 65.92.5.209 (talk) 03:38, 17 September 2011 (UTC)

The helicopter is probably changing directions and even flying inverted throughout the video. APL (talk) 03:42, 17 September 2011 (UTC)

Even in a single frame, the horizon seems very curved. The only explanation I can think of is that the camera uses some kind of raster scan, taking its picture from one end to the other, with vertical rows as seen on the YouTube video. Because helicopter blades constantly turn as they rotate, it would be at one angle at the beginning of the shooting of one individual frame, and at another angle, even 180 degrees opposed, at the end of it. No guarantees on this guess, however. Wnt (talk) 14:27, 17 September 2011 (UTC)

Yes, the exact explanation is going to be a bit more complicated. If one looks at the stationary shot, the angle of view is what one would expect from a normal lens. At speed however, you will notice that the angular distances between the sun and its reappearance is far, far less than 360 deg. This means that the camera is recording the forward and retrograde path of the rotor in one 'linearly' compressed frame due to the rotation being so much faster then the scan rate. Remember too, the pitch of the rotor is changing during each revolution. In forward flight, the advancing blade has to pitch down and the the other blade has to pitch up so to achieve the same lift on both sides of the chopper – for obvious reasons. It appears that the camera pitches with the blade that its mounted on. This will increase the apparent curve of the horizon. Must have been tricky getting the counter-balance right on the opposing rotor. --Aspro (talk) 16:46, 17 September 2011 (UTC)

September 17

law of microscopic reversibility and experimental enzyme kinetics

Do the kinetics data reported for this article agree with the law of microscopic reversibility? I am looking at Table 1, where two enzymes' specificities (and Vmax's and so forth) for reactions involving ethanol, acetaldehyde, NADH, NAD+, NADPH, NADP+ (and their various combinations). I'm trying to sort it out. In any case, the authors make the arguments that one enzyme (ADH2) "favoured" the reduction reaction over the oxidation reaction.

As I recall, there are several ways to make an enzyme "favour" a reaction, such as decreased substrate specificity for the product compared to specificity for the desired reactant -- but usually this requires the input of energy. This can occur, I suppose, with energy inputted by NADH/NADPH or the alcohol that would otherwise be released as heat? elle _{vécut heureuse} ^{à jamais} (be free) 06:06, 17 September 2011 (UTC)

The relevant text is "In the case of ADH1, similar Km values and kcat/Km ratios were obtained for ethanol and acetaldehyde, indicating similar activities in both the oxidation and reduction reactions. In the case of ADH2, however, a lower Km value and higher kcat/Km ratio were obtained for acetaldehyde, indicating that the enzyme activity is in favour of the reduction reaction." Now acetaldehyde is ethanol minus two H's at the end, and the NAD+/NADH + H+ or NADP+/NADPH + H+ pairs either accept or deliver those two H's.

My feeling is that the reason why this is not perfectly symmetrical is that they're looking at kinetics, not thermodynamics. The rate at which the enzyme functions when one molecule is in excess need not be the rate it functions when the other is in excess. For a different sort of example see Inward-rectifier potassium ion channel (or any other ion channel which does not actually let things in and out with equal affinity). The enzyme can't change where the thermodynamic equilibrium point is, but it can decide when and if it will help the reactants get there. Wnt (talk) 14:56, 17 September 2011 (UTC)

medical physiology

what are the tissues which are not dependent on insulin for utilization of glucose? this is my home work and i have partially enlisted the tissues/ e.g Brain. Nerves. Liver. Adrenal glands. Lens. Skeletal muscles during exercise. — Preceding unsigned comment added by 119.153.155.106 (talk) 06:29, 17 September 2011 (UTC)

Apple cider vinegar

I see this question come up all the time outside Wikipedia, so I have to ask: what is the current status of health claims about Apple cider vinegar (ACV)? Our article on the subject says that the "consumption of vinegar might reduce obesity". The article also says that consumption of ACV might "reduce bone density", although this is unsourced. What does the current medical literature say? I realize that this is somewhat controversial, so a calm answer would be appreciated. Thanks. Viriditas (talk) 10:40, 17 September 2011 (UTC)

It's a fad. Just one of thousands that have come and gone. Nothing new, nothing different. As for the Japanese study, it's just a single, non-relicated primary study. They are dime-a-dozen and generally don't have very much scientific value until they are reproduced, criticized and confirmed by other scientists. This doesn't mean I'm calling the integrity of the authors of the study into question- they almost certainly carried out the experiment and obtained the results they reported. It's just that a single primary study doesn't mean much besides that further study may be needed. Remember cold fusion? Dominus Vobisdu (talk) 11:07, 17 September 2011 (UTC)

I agree with all of that except for the fad part. This has been popular in the U.S. for at least a century, possibly longer. Based on what I've read and seen, it's probably popular with people who can't afford to see a physician or who live in rural areas. It also seems to be used by some religious communities. So it appears that ACV is used as folk medicine in the U.S. Viriditas (talk) 11:36, 17 September 2011 (UTC)

Folk medicine and fad are not mutually exclusive. Fad does not mean "recently invented or discovered", it means "recently become popular". Dominus Vobisdu (talk) 11:47, 17 September 2011 (UTC)

Re: Fad - "was or is briefly popular"

The practice dates to at least 1839 [14] "Desault and others assert that consumption is often brought on by a common practice with young people of taking vinegar to prevent obesity", [15] "'Every one knows' says Giacomini 'that when habitually taken it produces leanness from a sort of languor of the digestive process'"

I imagine that, if in order to consume your apple cider vinegar, you have lots of salads with it used as a dressing, then you probably will lose weight. StuRat (talk) 17:34, 17 September 2011 (UTC)

Race

Are there inherent differences in people's traits and capacities that are entirely due to their race? — Preceding unsigned comment added by 88.83.35.117 (talk) 13:20, 17 September 2011 (UTC)

No. Collect (talk) 13:26, 17 September 2011 (UTC)

I think Swedes are better than Kenyans in converting sunlight to Vitamin A... --Stephan Schulz (talk) 13:28, 17 September 2011 (UTC)

That may be true (as a statistical average), but that doesn't make 'race' a scientific concept about which one can make meaningful assertions about 'inherent differences in people's traits and capacities' - for a start, neither 'Swedes' nor 'Kenyans' are normally seen as 'races'. 'Race' is a social construct used to divide a continuously-varying population into arbitrary discreet groups, on whatever grounds are expedient for the purpose at hand. AndyTheGrump (talk) 13:44, 17 September 2011 (UTC)

So, explain away medical differences. After correcting for income, education, urban/rural location, age, gender, etc... people who identify themselves as "black" accelerate from prehypertension to hypertension significantly faster than people who identify themselves as "white". That is just one of thousands of medical examples (just look at "racial disparity" in any collection of medical journals). One of the big hurdles in modern medicine is combating the idea that there is no such thing as race. Scientifically and statistically, there are many differences on a genetic level between the races. Accepting that there are differences doesn't imply that one race is better than another. It doesn't imply that a person has to belong to one and only one race. It simply means that people are different at a genetic level and identifying the differences and similarities allows for better medical treatment. -- kainaw™ 16:31, 17 September 2011 (UTC)

Medical differences between individuals may very well be due to 'statistical differences' at the genetic level - that has nothing to do with the demonstrable fact that 'race' is a social construct. Or if it isn't can you provide scientific evidence to the contrary? Since there is no scientific definition for 'black' or 'white', there cannot be. If you want to match medical treatments on the basis of individual genetics, you should do just that, not make assumptions based on arbitrary cultural grounds that have little relation to individuals actual genetic heritage. AndyTheGrump (talk) 16:41, 17 September 2011 (UTC)

"Race" from a medical standpoint is "genetic testing by logical deduction." Of course actual genetic testing would be more accurate, but that would imply we know which genes are responsible or even how the mechanism works. Sure, it's a social construct, but it can be used to make helpful assumptions, which is particularly important in medical care since doctors are still mostly flailing in the dark when it comes to finding appropriate care for the specific patient in front of them. Sure, it's imperfect, but that doesn't mean it's worthless or should be dismissed out of hand. SDY (talk) 16:47, 17 September 2011 (UTC)

It is based on a politically-motivated argument that skin color and genetics have absolutely nothing to do with one another. I do not buy into that argument at all. I believe that a person's skin color is based on the person's genetics. I really don't care how "racist" that makes me. I refuse to force myself to be stupid. -- kainaw™ 16:50, 17 September 2011 (UTC)

I don't think you understand. Obviously skin colour is decided by genes. The problem with the concept of race is that it is arbitrary to separate the human species into 'races' based on this one particular genetic variability among humans. For example, there's also a genetic basis for the determination of blood group, and people of different blood groups have other medical differences (ie different susceptibility to certain diseases, like cholera), but no one would propose that we divide people into races based on blood type. 65.92.5.209 (talk) 17:04, 17 September 2011 (UTC)

Unfortunately, they do. Not really a "race" but in some parts of the world assumptions are made about your personality based on your blood type. There are also some weird diets that try to use this too. Mainstream science states that both of these attempts to link blood type to other traits are baseless, but that doesn't stop people from trying. SDY (talk) 17:13, 17 September 2011 (UTC)

It was just an attempt to claim that since "black" and "white" don't refer to blood type, they shouldn't refer to skin color. I disagree. -- kainaw™ 17:16, 17 September 2011 (UTC)

One could make the same argument about gender. That is, it's a continuum, rather than black and white, with intersex individuals in the middle. Does this mean that recommended breast exams for women and prostate exams for men should be eliminated because "gender is just a social construct" ? Of course not. Since most people identify as either male or female, having different medical guidelines for them makes sense, just as it does for people who identify as black or white. StuRat (talk) 17:19, 17 September 2011 (UTC)

I don't think the argument is about medical treatment. Obviously it is desirable to take genetics into consideration as much as possible when prescribing medical treatment, and if people with genes coding for darker skin are more likely to have genes influencing hypertension or whatever, doctors would be ill-advised to ignore it. But that says nothing about whether race makes sense as a scientific concept. Undoubtedly our awareness of the (relatively) few genetic differences between blacks and whites is because they've been studied so scrutinously, as they should be (for medical reasons). But hopefully in the future an individual's genome could be cheaply sequenced so as to allow much more individualized treatment. Where would the concept of race be then? 65.92.5.209 (talk) 18:05, 17 September 2011 (UTC)

It will be right there on the surface of the skin. Increased genetic data will not change the color of my skin and I seriously doubt it will change yours either. -- kainaw™ 18:16, 17 September 2011 (UTC)

Exactly. 65.92.5.209 (talk) 18:28, 17 September 2011 (UTC)

African and European populations were traditionally regarded as the two most different human races merely because of the striking differences in skin color. In contrast African pygmies and Melanesians are so phenotypically similar that they were classified as a single race. But the truth is rather different - Europeans and Africans are actually closer to each other genetically than to all other geographic populations. And African pygmies and Melanesians are the farthest from each other genetically. How useful is it then to call which black and which white?

Skin color in humans were the result of far stronger selection pressures depending on how close the population was to the equator, resulting very quickly in vast differences between melanin expression in different populations, even among close geographic neighbors. Just because a person is darker than you doesn't mean your genes are more genetically distinct from each other than to a person of a more similar shade. See this to get an idea of just how awkward it really is to arbitrarily split those into neat little chunks. And that's not even accurate nor complete, as genes among populations flow, ebb, well up, dry up, double back, spread out, and most importantly - merge (Central Asian hordes in Eastern Europe, early Southeast Asian sailors in Madagascar, European invasion of the Americas, the Slave Trade).

But I agree, phenotypic differences can be useful in quick determinations of which genetic population you might belong to and which diseases you are more susceptible to. But ascertaining geographic ancestry is a better indicator. Why then should we stick to a very inaccurate, very vague means of indicating possible genetic variation by the color of the skin when we can just do it far more efficiently and with little additional effort by merely saying 'West African', 'Native American', 'Central Asian', 'West European'? Even better if you can pinpoint the specific population - Yoruba, Iroquois, Pashtun, Basque. The same principle of genetic clustering applies, but with a more solid basis than just phenotype. After all, doctors don't exactly check your medical history and diagnose your disease by putting you next to a skin color wheel.-- Obsidi♠n Soul 19:42, 17 September 2011 (UTC)

There are two sides to this question. The first is, What do we mean by "race"? Once we've got that to a good situation, we can answer the main question.

Biologically, race has no particular scientific meaning. What this means is that there aren't just a handful of basic, discrete categories of human beings that are then "mixed" up. The human species isn't actually made of five primary "colors" (white, black, red, yellow, brown) like anthropologists in the 19th century used to believe. Genetic studies in particular have shown that all humans on all continents are heavily interrelated, and that genetically it is a totally smooth set of transitions between regions. The reason it looks like a few basic "colors" is because there are a few places in the world that, because of historical and geographical circumstances, managed to develop large, relatively homogenous looking populations. So we see the world as looking like white/Western Europe, yellow/China and Japan, black/Sub-Saharan Africa, red/North American plains, etc. This is an artifact of history, not biology.

Furthermore, we can't actually tell what "race" someone is genetically. There is no gene for "race". What there are are genes that are probabilistically indicative of having ancestors from one part of the world or another. So we can look at your genes and say, "hey, you have gene A15B (or whatever), and 80% of the other people who have that gene had ancestors in the last 10,000 years that came from Western Europe." That's as close as we get to having genetic tests for "race".

That doesn't mean that "race" doesn't have meaning as a social category (where its meaning is quite important and profound, and shapes people's lives). It doesn't even mean that it has zero meaning as a scientific category, if understood as a probabilistic statement about one's possible genetic ancestors. But it's not a firm category.

So. Probabilistically speaking, do people whose genetic ancestors hail from different parts of the world have inherent differences in traits and capabilities? The answer is, probabilistically, yes. Here's a canonical example for thinking about this: 1/3rd of all people whose ancestors are from Sub-Saharan Africa have a gene that makes them slightly more resistant to malaria. (This is the ultimate reason for Sickle-cell disease, which is when you get two recessives of that gene in the same person.) This is what I would call an inherent difference in traits and capabilities. It's also only probabilistic — you can't tell from looking at a token "black" person on the street whether they have this particular gene. It's not something that all people of that race have. And it's not something that's necessarily exclusive to that race (something similar exists in Mediterranean peoples as well — see Thalassemia.) It's a genetic difference that is real, has real effects on "capabilities and traits," but again, all things related to race as probabilistic, and only tell you about changes over populations, not individuals. These are ways to talk about differences between groups, not differences between people.

Note as well that "race" isn't often the most useful category for talking about origins. Fast twitch muscle fibers are probabilistically more common in people descended from East Africa than other groups. Is "black" the right category for talking about this mutation, or "East Africa", or something more specific?

We should not be surprised that there are differences between groups on the aggregate. We also should not exaggerate what they mean, nor confuse such differences and being the explanations for expressed results, which are filtered through many different layers of social context. Every group will have more or less similar variation on most qualities — there will be some people who are absolutely awful at some things, and absolutely brilliant at others, and as with all things genetics, a huge proportion, sometimes the majority proportion depending on the circumstances, has to do with the environment in which the individual develops as well. --Mr.98 (talk) 13:48, 17 September 2011 (UTC)

Theory aside, though, there are groups of traits that are found together on a reasonably common basis enough that "race" is a meaningful big picture concept. It's actually sort of relevant in blood banking, because certain red cell antigens are more or less only found in certain ethnic groups. This causes problems, since sickle cell anemia, primarily found in people of African descent, sometimes requires transfusions, and African-Americans as a group are not very well represented in the donor population. If you have a sickle cell patient with antibodies to the U antigen, testing a bunch of white people is extremely unlikely to find a compatible donor. While the color of the skin has nothing to do with it, and these genotypes/phenotypes may not be linked in the sense of being close on the same chromosome, you're still more likely to find a compatible donor among dark-skinned individuals, though even there that particular phenotype is pretty rare. SDY (talk) 16:23, 17 September 2011 (UTC)

There is no need for a "theory aside" with regards to my comment. If you read what I wrote you'll see what you're saying is completely compatible. I did not say that race was purely a social construct, nor that it had absolutely no biological use. It just doesn't mean what most people colloquially think it does, and its best seen as a fuzzy, probabilistic category regarding human populations, rather than individuals. --Mr.98 (talk) 21:26, 17 September 2011 (UTC)

I totally agree. I was just providing a very specific example of the practical utility of it. SDY (talk) 22:34, 17 September 2011 (UTC)

I'd just like to say, although I am not the OP, Mr. 98's is an awesome answer and he should feel good. 86.164.76.231 (talk) 22:21, 17 September 2011 (UTC)

vancomycin

I was a registered nurse for 19 years and I was reading the article regarding vancomycin which was posted on Wikipedia and it referred to it as a 'drug of last resort'. I've found this is not true. Often times when a patient was admitted to my floor, the doctors would prescribe it before the results of any blood cultures and sensitivities were ever submitted. Yes, after the blood cultures or sputum samples were collected, the doctors would either change the orders to some other antibiotic or keep the patient on vancomycin, so therefore, I disagree it is a 'drug of last resort.' Thank you, Lee Hollimon. — Preceding unsigned comment added by Owen7252 (talk • contribs) 13:36, 17 September 2011 (UTC)

I know I've seen the same complaint in print, and if I find it I'll add it... meanwhile though, I should point out that even in 2002 vancomycin was starting to see resistance with drugs like linezolid and quinupristin/dalfopristin vying for "last resort" status against Staphylococcus aureus.^[16] It also is facing some new competition from an engineered mutant.[17] Still, I see a lot of articles to this day calling it a drug of last resort, even though it is part of the initial regimen recommended by the CDC for patients with suspected bacterial meningitis.[18] Wnt (talk) 14:23, 17 September 2011 (UTC)

It could be worded better to place the claim in better context. With bacterial meningitis, the progress of the infection is so rapid that a doctor would not wast time on trying something else to see if it worked. For some other infections it is held in reserve in case all else fails. It is the treating physician call at the out set, as to which antibiotic is best for his patent and balance the risk of possibly inducing resistance at the same time.--Aspro (talk) 17:12, 17 September 2011 (UTC)

SPICE and opamps

Since Bob Widlar made the first integrated circuits at Fairchild before SPICE was available, how did he know they would work properly. Or did he use some other sort of simulation program?--78.148.142.217 (talk) 17:31, 17 September 2011 (UTC)

Binary sun

What would a binary star look like from the surface of a planet orbiting them? Would the motion of the two stars around each other be visible? Would the two stars even be visibly separate, or would they look like one blob? --75.33.217.234 (talk) 17:59, 17 September 2011 (UTC)

It depends entirely on the planet's orbit and the stars' orbit around one another. For example, the planet recently mentioned by NASA has an entirely different orbit time than the stars' orbit. So, every day, the sunrise of each star and sunset for each star will be different. They may be in sync. One may be long before the other. There will be times when they eclipse one another. There will be times that they are far apart. -- kainaw™ 18:03, 17 September 2011 (UTC)

I suppose you could even have the case where the planet is located at the barycenter between the two stars, so that they appear to rotate about it, always in opposition to one another, so you'd have a planet with no night, ever. I don't think that position would be stable over the long term, though. StuRat (talk) 19:10, 17 September 2011 (UTC)

normal-sized camera?

Having red about red-shift, it seems since there is no color shift in this picture, it means that the camera was not shrunk along with the person. Does this make sense? How could the person take the photo, it would seem like the weight of the camera would utterly crush him. 82.234.207.120 (talk) 18:40, 17 September 2011 (UTC)

srsly? --Daniel 19:00, 17 September 2011 (UTC)

on 82.234.207.120 (talk) 19:34, 17 September 2011 (UTC)

First, there is no redshift in this situation. Redshift is a change of frequency. If you throw tennis balls at a wall, they come back to you at the same rate that you threw them, regardless of the shape of the wall. Likewise light and the spoon. If you throw tennis balls at a wall while backing away from the wall, the later tennis balls will take longer to get back to you. That's an example of frequency shift from relative motion. But there is no relative motion in this case. Second, the only thing you can really see, and the only thing cameras detect, is light. If the light is distorted by bouncing off of a curved surface, that doesn't mean the person or camera that emitted the light is distorted. It just means that your brain is playing tricks on you, incorrectly interpreting the light. -- BenRG (talk) 19:15, 17 September 2011 (UTC)

you're saying that the camera could have been shrunk without distorting the picture? What about the fact that only 1/10th (or whatever) as many photons are hitting its receptors? I just find it hard to believe that that is not a full-sized camera, based on the picture quality. Can you address this please. 82.234.207.120 (talk) 19:37, 17 September 2011 (UTC)

Hmm, it looks to me as if the spoon was magnified rather than the photographer shrunken. But that would be too strange, so obviously it must just be something funny about perspective.

Redshift theory for shrunken objects is rather involved. We would need to know which shrinking method was used here: Desiccation shrinking (i.e. just removing the water), atomic shrinking (i.e. the atoms get smaller) or decimation shrinking (i.e. removing a certain percentage of atoms).

But we are not allowed to give medical advice anyway. If you need advice with a redshift problem you should really see your shrink. Hans Adler 19:43, 17 September 2011 (UTC)

practically speaking what is the technology in e.g. 'honey I shrunk the kids'? It's 2011 I assume this is what is in use, but it could also be a trick, that's why I'm enlisting the reference desk help for forensic photography references hopefully concerning actual science and not just conjecture. 82.234.207.120 (talk) 19:57, 17 September 2011 (UTC)

This is getting uncomfortably close to medical advice, and I'm afraid I have already said too much. If you are experiencing redshift phenomena or other shrinking symptoms you absolutely must see a doctor rather than asking random people on the internet for advice. Don't play with your life! Hans Adler 20:14, 17 September 2011 (UTC)

Your concern touches me so much that I am fapping. But I do not see any kind of redshift -- or any other artifact, that's the point. My conclusion is, since it is such a preeminently normal photo, without artifacts of any sort (except the oversized spoon) we can only conclude that the camera is normal-sized. Actually, someone might suggest that instead of the person being shrunk, the spoon was embiggened. Is there a way to tell from the photo, as this would cause a considerable shift in, um, focal length or something? (depth of field? focus? f-stop? I'm seriously out of my league here, I don't know anything about lenses or photography). Can someone who know the science behind photography analyze the photo for me and give me a definitive verdict, with justification, one way or another? This thing is, like some hypothetical remote control for prosthetic testicular implants, driving me nuts. 82.234.207.120 (talk) 21:40, 17 September 2011 (UTC)

After a detailed analysis, I propose it to be a novelty oversized spoon Jebus989^✰ 21:56, 17 September 2011 (UTC)

That is a very funny and clever interpretation, but the spoon seems too "perfect" for me to be a novelty item, it doesn't seem like something hand-made at that scale, but machine-stamped at the normal spoon scale. Look at high shiny it is as opposed to these pictures. But back to the scientific method, do you have any forensic evidence from the photography itself? Maybe based on the reflections, or something you can tell from the pixels? 82.234.207.120 (talk) 22:02, 17 September 2011 (UTC)

also look at the scratch in the spoon toward 6 o'clock. the spoon is relatively new/freshly pressed and has no other scratches. if it were a novelty oversized spoon, it would have a lot of little scratches all over, not big gashes like that. (Because of the scale of the things that would scratch it). A normal-sized spoon, on the other hand, could easily be scratched in a couple of characteristic scratches like that. It just seems to me to be a normal-sized spoon, magnified: in other words, if the picture was really taken, then it seems to me that it was the man that must have been shrunk. Occam's razer. 82.234.207.120 (talk) 22:11, 17 September 2011 (UTC)

Photoshop. I do not see the reflection of the arm in the bowl of the spoon. Collect (talk) 21:46, 17 September 2011 (UTC)

That reflection is interesting. If someone here could model mathematically the apparent curve of the spoon and use photoshop to dereflect around that plane couldn't we get a clear image of what the spoon is reflecting? We might actually be able to tell the relative dimensions of the person as compared with the rest of whatever is behind him or her that presumably hadn't been shrunk. 82.234.207.120 (talk) 22:05, 17 September 2011 (UTC)

I think that Collect may be misled by the fact that the reflection in the spoon is inverted - this is usual beyond a certain distance from a concave reflector. I think the only odd thing in the picture is an abnormally-large spoon. AndyTheGrump (talk) 22:10, 17 September 2011 (UTC)

Right. So how do you explain it? 82.234.207.120 (talk) 22:11, 17 September 2011 (UTC)

How do I explain an abnormally-large spoon? Someone decided to make it. It is hardly cutting edge technology. AndyTheGrump (talk) 22:14, 17 September 2011 (UTC)

Was that last bit a cutlery reference? If so I have no idea what importance whether it's a knife, fork, or spoon has to do with anything. Scientifically, there is certainly a given prior probability that an oversized spoon was manufactured; likewise, there is a prior probability that the human in the picture is a little person of such fantastically miniature proportions that this is how large they are in relation to a spoon; finally, there is a certainl chance that a spoon which was manufactured at normal size was embigenned, and a certain chance that a person grown to normal size was miniaturized. the question obviously is one of 1) the state of science, so that we can establish prior probability 2) forensic analysis as I've proposed above. This is the scientific method. Is manufacturing an oversized spoon within the realm of human technology? What about embigenning an existing spoon? shrinking a person? These are questions that need to be established for a good prior probability, but we are not Sophists here, we can look at actual facts and do real analysis, and not just philosophize. That is what I would like out of the picture. 82.234.207.120 (talk) 22:28, 17 September 2011 (UTC)

Note that while we are being silly, a strong argument against it being a regular sized spoon and a small sized person is that the shopping card, floor boards, and racks of food are all "normal" sized. So it would require the shrinking of the entire supermarket setting, except for a spoon. This seems to be a priori less likely than it being just an oversized spoon. (Aside from the very obvious facts that the technology currently exists to create larger-than-usual spoons, but so far as anyone knows, does not exist for shrinking or enlarging objects arbitrarily.) --Mr.98 (talk) 22:47, 17 September 2011 (UTC)

Arctic survival

Suppose a modern jetliner crashes on the Arctic ice pack, but a few of the passengers and crew survive the crash. What's the LONGEST time they could reasonably survive on the ice pack? (Assume that some of them, but not all, are trained in Arctic survival techniques.) 67.169.177.176 (talk) 20:01, 17 September 2011 (UTC)

That would depend on several factors. If they have something to burn, then pretty long, since they can heat themselves and obtain water. Otherwise, you have to hypothesize how long they will be without water, at what temperature they will be, how much food they would have... Wikiweek (talk) 21:12, 17 September 2011 (UTC)

Assume that the plane's fuel tanks are not ruptured and still contain some fuel, and that the food at their disposal includes that in the plane's galley (I know, that's not much) and the emergency rations stowed on the plane (if any). Had they been without water, it would have been impossible for them to survive for more than a week or so -- even I know that much. And the whole point is to prolong their survival as much as reasonably possible -- makes for a better plot this way.67.169.177.176 (talk) 21:50, 17 September 2011 (UTC)

Also, there's a supply of potable water on board the plane -- how could anyone forget that? 67.169.177.176 (talk) 22:03, 17 September 2011 (UTC)

Theoretically infinite. The Inuit have lived north of the Arctic circle for at the very least centuries, most likely a lot longer. It would be unlikely that plane crash survivors would have the skills or knowledge to pull it off. It sort of depends where in the Arctic they are, as well, since they'd have to be near animal life to live as the Inuit did. The lack of dogs would be a problem, but not a theoretically insurmountable one. SDY (talk) 22:06, 17 September 2011 (UTC)

On the ice pack somewhere in the Beaufort Sea (the plane in question is a nonstop Aeroflot flight from Moscow to Seattle). Anyway I'm not trying to have them live there for the rest of their lives (IMHO that would be a fairly anticlimactic ending), but I'd prefer to have them survive for at least a few weeks, maybe several months if possible, before being dramatically rescued while near death from hunger and exposure. 67.169.177.176 (talk) 22:18, 17 September 2011 (UTC)

Yeah, theoretically infinite. Assume that the plane was full of Inuits and in the cargo there were lots of Husky Siberians and protein rich food, not to forget the winter jackets, boots and other tools. Wikiweek (talk) 22:14, 17 September 2011 (UTC)

That's not my plan for them (see above). 67.169.177.176 (talk) 22:18, 17 September 2011 (UTC)

This reminds me of Alistair MacLean's novel Night Without End, in which a plane crashes on the Greenland icecap -- except in that book the survivors are helped out by the members of a nearby research station. Anyway, MacLean knew quite a bit about Arctic survival, so the book might be interesting to you -- if you could find it. He also wrote a much better-known book called Ice Station Zebra, about hijinks at a research station located on the floating ice. Looie496 (talk) 22:33, 17 September 2011 (UTC)

Sleep paralysis without Hallucination

Sorry, but we have a policy of not giving out medical advice, because we're random people on the Internet, we don't know your specific case, and we don't want to give you false hope or needlessly worry you.--el Aprel (^facta-_facienda) 22:48, 17 September 2011 (UTC)