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August 26

Leaf Color

I want to know why most plant leaves are green. I know that is it because of the pigments in the leave reflecting green light, but what I want to know is why that holds true for most all plants. Why is the green wave lenght of light something that needs to be reflected by the plant? Why not blue? Is there something about the middle of the visible spectrum that makes it disadvantagous to absorb? Does it have have to do with the amount of energy in that part of the spectrum?--98.240.70.102 (talk) 00:08, 26 August 2009 (UTC)

Chlorophyll is one of the main chemicals involved in absorbing light energy to begin the process of photosynthesis. If you use the search box at the top of this ref-desk page to look for "chlorophyll", you can find several previous discussions about its color. DMacks (talk) 00:24, 26 August 2009 (UTC)

(e/c) Its not so much that green light needs to be reflected, the reason most plants look green is a consequence of what wavelengths of lights need to be absorbed (and, as you said, the non-absorbed part of the light spectrum is what gives plants their colour).

Different wavelengths of light require different accessory pigments to be effective for photosynthesis. In green plants are green because for chlorophylls and carotenoids mainly absorb violet-blue and red light. Its difficult to know why green plants evolved their particular system to take advantages of the blue/red light, but it is clear these spectra are extremely effective in producing energy in the ecological niche green plants find themselves in. That is not always the case, though, in red algae, for example, the spectrum is different due to phycobilins, which absorb blue-green light. This allows algae to grow in deeper waters that filter out the longer wavelengths used by green plants. Again, their colour is a by product of the most effective absorption spectra for their niche. Rockpocket 00:33, 26 August 2009 (UTC)

For what it is worth, some researchers (PMID 17407409) have proposed that there is logic in why green plants do not absorb green light. The propose that the absorbance peaks are determined by three factors:

(1) the wavelength of peak incident photon flux; (2) the longest available wavelength for core antenna or reaction center pigments; and (3) the shortest wavelengths within an atmospheric window for accessory pigments.

Personally, I don't fully understand these three factors, but I thought I would throw them out there... Rockpocket 00:48, 26 August 2009 (UTC)

Really, red or blue plants would be even better. The Sun makes more green and yellow light than any other colors. Possibly no other photosynthetic chemicals were suitable? Is it albedo? Wavelength diffraction/scattering thing with some size scale of the cell? It's suprising. If this happened (red plants), and sentients evolved to have red blood, green wouldn't be especially calming and our instinctive color for danger and calming might be conflicted. Thank goodness the Borg didn't design plants or they'd be black from UV to IR and have gears. Sagittarian Milky Way (talk) 06:42, 26 August 2009 (UTC)

I'm pretty sure this has been discussed before and so should be somewhere in the archives Nil Einne (talk) 08:50, 27 August 2009 (UTC)

I thought this little black snake was harmless, can someone help ID it?

What type of Black Snake is this, I can't make a positive id

What type of Black Snake is this, I can't make a positive id

I was handingling this little black snake on a beach in southern BC and I thought it was a garter snake and I considered it harmless, but now that I am zooming in on the photo off camera it doesn't look so much like a garter snake anymore and I since I can't really identify it I was wondering if anyone recognized it or could make an id on it, as I would like to know if I almost got myself bit by a poisonous snake? GabrielVelasquez (talk) 03:32, 26 August 2009 (UTC)

• There are relatively few species of non-rattlesnake, non-coral snake (both of which are easily and instantly recognizable) in North America. So barring it being a Cottonmouth or a Copperhead (which it isn't), it isn't poisonous. (Hooray.) It looks like a racer to me, or even a garter. (Note that I guessed that BC meant either British Columbia or Baja California, so if either of those are wrong, you'd better make it more clear which BC you meant!) --68.50.54.144 (talk) 04:14, 26 August 2009 (UTC)

Sorry, British Columbia the Province in Canada, I have never been to Mexico.

It turns out that garter snakes do actually produce some poison, but not enough to be dangerous to people. See garter snake#Venom. --Anonymous, 04:22 UTC, August 26, 2009.

To a first approximation (as in: Don't Bet Your Life on it) all Snake venom which are harmful to humans have two prominent fangs, and snakes with just teeth and no fangs aren't lethal. But usually if you're close enough to see the fangs, you're too close for comfort. -- 128.104.112.102 (talk) 16:58, 26 August 2009 (UTC)

Despite what this article says, I believe quick way to check if a snake is venomous -- check the underside of the tail (posterior to the anal slit). Non-venomous snakes underbellies feature single scales that extend from left to right up until the anus but two adjacent scales posterior to the anal slit. Venomous snakes continue the single scale feature.[1] DRosenbach ^{(Talk | Contribs)} 22:06, 26 August 2009 (UTC)

Um, but then you're picking up a potentially venomous snake. (Also, the article's mentioning of stripes as a criteria really ought to say, "unless it is a coral snake") --68.50.54.144 (talk) 04:46, 27 August 2009 (UTC)

Are coral snakes the only venomous snakes which can't be identified about the scale thing? I have no idea. [2] does give the thing DRosenbach mentioned, although it notes it's useful for when the snake is dead (although do note even a dead snake must be handled with care), as do a number of other sources. But I noticed one thing; all of them are American including DRosenbach's one. Other sources such as our article which Rosenbach mentioned and [3] all say there is no single method when you are referring to diverse geographical locations. While the original question is referring to North America, DRosenbach's claim lacked any qualification (other then I believe) and you should be very careful when making a point blank statement of that sort. Does your method work throughout Asia? What about Australia? Africa? I don't know but it's entirely possible the answer is no. BTW, even if the method does always work in identifying venomous snakes, it may not be any use if all the snakes in the area have that feature including non-venomous ones as in that case you're going to be thinking all snakes are venomous (which is not a bad thing in any case, but clearly defeats the purpose). P.S. I found [4] which may be of interest Nil Einne (talk) 05:57, 27 August 2009 (UTC)

Yeaup, the good Doctor starts off saying all snakes have venom glands (page 11) and then starts a characteristic chart for non-poisonous snakes and poisonous snakes (page 14), and I'm left going "Oh shyt!" it has "broad ventral scales!" - but the tree continues and the the remaining level tells me it is not a Viper or Cobra. Interesting but incomplete. GabrielVelasquez (talk) 06:27, 28 August 2009 (UTC)

Would it be possible to run a power plant with dissimilar metals?

You see nuclear plants, but they take so long to build. You always hear that solar panel electricity costs too much money (but they're very useful for portable or low power and remote things) What could be something we could do right now and will be finished quicker, so it will tide us over and help a few percent and not cost as much money?

If you lay an enormous area of continous copper plates on a desert and paint them black maybe cover it with glass plates (finally the greenhouse effect will help us), place a similar zinc plate next to it, join them with power lines, and connect the other two ends to the power grid would any electricity flow? Or would that work only with expensive doped semiconductors? Would a conductive bath replacing the short wire help? Or use more traditional methods of temperature gradient exploitation with pipes and turbines and stuff except imstead of having to continously make the gradient with fuels we just do something as simple as change the thermal properties? Desert caves could be the cool end. The temperature just a little inside a cave is constantly similar to the average annual temperature, which is not hot. I've never heard of "caval energy" before. Edit: Or nearby high altitude mountains. Or find an already naturally dark desert and do.. something.

They can print solar panels now. On plastic film like an inkjet printer. So what about pouring them? Some sort of viscous liquid that would be dropped from planes or helicopters over a large square area of desert, left to dry set freeze cool down or whatever until it builds up a layer, and then do it all over again with the other pourable substances: the insulator, maybe a protectant and base layer, and of course the opposite semiconductor (p and n), then after that's done, we just build power lines connect it to the grid, and use it forever? If exploitation of artificially-created albedo (and thernal mass etc.) asymmetry is done on a truely massive scale, maybe we should be careful not to negatively impact local or even global climate, but even the entire global heating and precipitation from heat-island effect from partly changing the color of 0.01 of all land plus all the energy use is positively miniscule, and local precipitational changes are small, so it might be benign? Either that or find some ways to make solar panels less like microchips and more like roadwork. I'm all out of ideas now. Sagittarian Milky Way (talk) 06:05, 26 August 2009 (UTC)

Wikipedia is not a suitable forum for discussing original proposals for machines and such, so we can't go into detail here, but other forums on the internet are great for this kind of discussion. As for the question in your title, you have to consider that these metals are not found in their pure form in nature. It takes energy to extract them and purify them. So even if electricity did flow, you would probably spend more energy building this contraption than you would get out of it. And you'd be left with a lot of waste when the battery ran down. When it comes to using thermal gradients, you may enjoy reading up on our articles on geothermal energy and Heat pumps. EverGreg (talk) 08:48, 26 August 2009 (UTC)

FWiW, as far as I can remember, your proposal for covering the desert with copper and zinc plates is similar to one of Nikita Khruschev's pet projects, to surround all the steelmaking furnaces and whatnot with layers of semiconductor thermocouples to use the waste heat for electricity production. Well, it turned out that the amount of energy produced in this way would be negligible, more energy would be spent manufacturing and installing the thermocouples than they would produce, and in any case it was more economical to surround the furnaces with water jackets and tap the steam from the jacket to run a power turbine. So, sorry to shoot down your proposal, but it just won't work. 98.234.126.251 (talk) 09:55, 26 August 2009 (UTC)

Hmm, it would appear dissimilar metals are not needed for the thermoelectric effect. Hey, if it won't work, it won't work. There's always the black pipe and turbine method.. Sagittarian Milky Way (talk) 11:46, 26 August 2009 (UTC)

There is great potential to harvest solar energy in the desert, with photovoltaic panels, or with solar reflector arrays focussed on a boiler to make steam. For a building, solar heat can be collected with a home built or commercially made collector with glass over a black-painted sheet of metal. This can heat air, or it can heat liquid flowing through metal tubes connected to the metal plate inside the well insulated collector panel. I don't see any merit in the idea of having dissimilar panels in the desert. They would been to be connected by electrolyte to act as a simple primary battery. Just as in the early 19th century, the zinc plate basically is burned up in the process, and zinc costs far more than fossil fuel, even allowing for the high efficiency of battery versus engine. Electricity could have been economically important by the 1840's if anyone had realized that a motor could be used as a generator, and powered by falling water of a steam engine instead of batteries. There will likely be great advances in lowering the cost of making semiconductor photovoltaic panels. I particularly like the idea of "solar shingles" so the entire south-facing (in the northern hemisphere) roof half would be a solar collector, perhaps with the roof (where feasible) built at an angle equal to the latitude to maximize efficiency. The solar energy striking a collector is about a kilowatt per square meter at peak intensity. Such solar shingles should be lower cost and more durable than solar collectors now for sale. Another fruitful area for research is better storage batteries. In 1908, electric cars were commonly available which had a 100 mile all-electric range. A century later, car companies promise us that in just a few years we will be able to buy electric cars with--ready for this A 100 MILE RANGE! Of course today's cars go 70 miles per hour, and the 1908 cars went only about 15 miles per hour, but that just means that your days driving is over in about 2 hours. Edison (talk) 16:28, 26 August 2009 (UTC)

All those damn cul-de-sacs! Causing millions of solarly disadvantaged roofses to have random azimuths which would otherwise have the common N-S!

Doesn't the photoelectric effect only work with blue photons and higher? Why are solar panels usually deep blue then? Is this why they're so inefficient? I'm suprised they can even print (and eventually paint) solar panels cause usually when you think of semiconductors you think 99.9999... pure silicon doped with 1 atom in 10000 of gallium or something like that. This raw stuff looks like inky goop. Sagittarian Milky Way (talk) 17:06, 26 August 2009 (UTC)

Doesn't having an irradiance comparison between Earth and New Extrasolar Planets make sense?

New planets that are being found are being referred to as being in or out of their parent star's "Habitable zone,"
Which basically refers to the distance range that water would be liquid.
But the concept is being used to insinuate more than water being present, it is used to suggest these systems could have life.
That is easy to accept if you ignore all the other factors involved in the process, and believe Water=Life.
As there are many factors other than irradiances that would keep H₂O from being liquid,(Mass/cohesion, Abundance of elements/Metalicity, Excessive X-rays/M-type star, Amount of CO₂) it is a little deceptive and irresponsible to make the suggestion to people that a planet may have life because it is X distance from its star. The idea of a habitable planet is flawed as it is, but I would like to know if anyone can find fault with the Solar Constant comparison between Earth and other planets?
Simply as a comparison of heat, a more direct comparison, no insuations, as heat does not itself equal life.
(note: Irradiance, Insolation, and Solar Constant are synonymous.)

Basic Insolation Figures Chart

Planet Distance	Insolation (W/m2)	% of Earth's.
55 Cnc f Apastron Flux	380.136	27.74%
Mars' Aphelion Flux	494.00	36.06%
55 Cnc f Average Flux	547.395	39.99%
Mars' Average Flux	590.589	43.11%
Mars' Perihelion Flux	718.545	52.45%
55 Cnc f Periastron Flux	855.305	62.4%
HD 108874 b Apastron Flux	1234.655	90.12%
Earth's Aphelion Flux	1,321.544	96.74%
Earth's Average Flux	1,366.079	100.00%
HD 108874 b Average Flux	1413.557	103.18%
Earth's Perihelion Flux	1,412.903	103.43%
HD 108874 b Periastron Flux	1634.359	119.30%
Venus' Aphelion Flux	2,585.411	188.72%
Venus' Average Flux	2,620.693	191.30%
Venus' Perihelion Flux	2,656.70	193.93%
Gliese 581 c Apastron Flux	3,619.829	264.97%
Gliese 581 c Average Flux	4,870.841	356.56%
Gliese 581 c Periastron Flux	6,903.119	505.32%

GabrielVelasquez (talk) 07:52, 26 August 2009 (UTC)

I agree with the OP that Habitable zone is little more than a hopeful categorisation. It means a range where water existing in liquid form is not strongly ruled out but not that it does occur or even necessarily would be liquid. As our article says, the zone may be further restricted by galactic location. I don't understand the OP's line of questioning. I find no fault with the Insolation comparison chart for 3 local planets though one might need to look into the sources to find whether precision of 7 significant figures is justifiable. However to the lead question, having an irradiance comparison between Earth and Extrasolar Planets makes no sense as long as we lack data to create one, and no numerical criteria are in evidence for using it to set further limits to planetary habitability.Cuddlyable3 (talk) 08:32, 26 August 2009 (UTC)

Remember also that the local solar constant is not the only possible source of heat with which to keep water liquid (a basic but not necessarily valid assumption underlying some definitions of a "zone of life") Contributory factors, difficult or impossible to quantify from interstellar distances, include nuclear fission energy released from transuranics in the candidate body's core, and tidal heat generation caused by any orbital eccentricity around its parent primary, whether a star or a larger planet. In our own Solar system, several satellites of the gas/ice giants are well outside the Solar Constant-based "habitable zone", but nevertheless may have subsurface liquid water, even oceans, due to such factors.

Some of Gabriel's not entirely clear question (which seems a little contradictory since the basic "possibility of liquid water" calculations are just initial extrapolations from the calculated insolations he espouses) implies he is aware of such factors, but merely because they cannot be certainly measured does not make it valid to ignore them entirely and revert to a single-dimension comparison between Earth and extra-solar planets; this latter is in itself inadequate because other factors like the candidate's size (not to mention composition) are crucial - consider that the rather diminutive terrestrial planet Mars is by most criteria just outside the crude "zone of life", but if Mars were Earth-sized it would probably be just within it.

I disagree with Gabriel's proposition that "it is a little deceptive and irresponsible to make the suggestion to people that a planet may have life because it is X distance from its star . . . ." Saying that, according to the criterion in question, something may be possible is not a claim that it necessarily or even probably exists. Moreover, while the possibility is is intellectually interesting and may have philosophical or even religious implications for some people, it is of little importance in most people's day-to-day lives. 87.81.230.195 (talk) 12:49, 26 August 2009 (UTC)

If you want liquid water, you are also going to need an atmosphere probably at least equivalent to earth at 25,000 ft or lower, or all your water might boil away. Googlemeister (talk) 13:27, 26 August 2009 (UTC)

And as it boils it would be building a (water) atmosphere, so no problem there. Dauto (talk) 15:31, 26 August 2009 (UTC)

That is going to depend on the gravity of the planet as a small planet might not be able to prevent that vapor from escaping. Also if its sun had a high level of solar wind, that might continuously erode the atmosphere as fast as it is built. I would imagine that a planet we have discovered would be fairly large, so gravity might not be too big an issue, but solar wind we probably can not determine from here. Googlemeister (talk) 19:27, 26 August 2009 (UTC)

Even harder to determine would be the absence/presence and strength of any planetary magnetosphere, and the consequent protection from the solar wind it might afford. Mars seems to have suffered from the multiple effects of an over-wimpy gravitational field, a lack of magnetic field-generating molten-mantle convection currents, a lack of plate tectonic movement and subduction to recycle back into its atmosphere gases and water chemically bonded to its rocks, and (more speculatively) a lack of life to beef up its water cycle and facititate said tectonics (according to the extended Gaia theory).87.81.230.195 (talk) 14:33, 27 August 2009 (UTC)

to Cuddlyable3 (talk)'s point:
In a lot of cases the Radius and Effective temperature of a parent star is known, or can be calculated using the formulas at the Luminosity article. The formula that calculates luminosity from Radius and Temperature and the formaula that calculates luminosity from distance and insolation are obviously Equal for the Sun and Earth data. and basic algebra yields:

• $L=4\pi R^{2}\sigma T^{4}\,$ ...and
• $L=4\pi d^{2}\ f\,$ ...therefore,
• $4\pi R^{2}\sigma T^{4}\ =4\pi d^{2}\ f\,$ ... and
• $R^{2}\sigma T^{4}\ =d^{2}\ f\,$
• $\ f\ =(R^{2}\sigma T^{4}\,)/d^{2}$
  

...All I'm saying is it is not unknown.

code for Earth at Perihelion: $f_{p}={\frac {((6.955\times 10^{8})^{2})\times (5.67051\times 10^{-8})\times (5778^{4})}{((1-(1\times 0.016710219))\times 149597876600)^{2}}}=1,412.903\ W/m^{2}$

code for Gliese 581 c at Periastron: $f_{p}={\frac {((0.38\times 6.955\times 10^{8})^{2})\times (5.67051\times 10^{-8})\times (3480^{4})}{((0.073-(0.073\times 0.16))\times 149597876600)^{2}}}=6.9\times 10^{3}\ W/m^{2}$

Having said that I am not saying this should go directly into an article.
But I do remember reading a debate where it was pointed out that using known data with known formulas is not synthesis.
In a lot of cases scientists are going as far as to speculate on on effective temperature and surface temperatures, using this albedo or that emissivity,
but on the other hand if the algebra is correct then the insolation is closer to fact. Definitely less misleading than saying there may be life on Gliese 581 c:
(see Than, Ker (2007-04-24). "Major Discovery: New Planet Could Harbor Water and Life". www.space.com [5] )

${\frac {Gl\ 581\ c\ Periastron\ Insolation}{Earth's\ Solar\ Constant}}=$ ${\frac {6.9\times 10^{3}\ W/m^{2}}{1,366.079\ W/m^{2}}}=505\%$

GabrielVelasquez (talk) 07:40, 27 August 2009 (UTC)

I apologise for sounding so negative with my words "makes no sense". I do not mean that such a comparison using present estimates cannot be calculated. I do mean that it is not convicing that this gives such an improved criteria for habitability of planets that the water-as-liquid estimation must be discarded. If the OP's challenge is Find fault with this insolation calculation or confess that your ideas of habitable planets are flawed, deceptive and irresponsible, then I don't see that ever being resolved short of an interaction with lifeforms on Gliese 581 c. Cuddlyable3 (talk) 08:44, 27 August 2009 (UTC)

The OP sent the following spreadsheet to my home page. Cuddlyable3 (talk) 16:46, 31 August 2009 (UTC)

Since you seemed to be interested in the topic, I thought you might not have seen this:

Makeshift optical telescope

I've got a handful of different kinds of lenses and I'm trying to figure out a way to combine them into some sort of telescope. I don't need anything permanent, I'm not actually going to use it for anything, I'd just like to see how far I can see while keeping it in focus.

The different sorts of lenses I have:

- From my Nikon DSLR: 18-55mm 1:3.5-5.6G 55-200mm 1:4-5.6G (both are obviously complex lenses, I don't really know what that means towards putting them together with other lenses)

- Single simple lens (was junk), says 70-210mm 1:4-5.6 on it, but I think it might just be the top taken off of a larger photographic lens. either way, the single lens is convex on the outside and concave on the inside. According to the wiki page on lenses I think it's "negative miniscus" i.e. the concave lens is more extreme than the convex. Held close to my face it will slightly magnify my hand at a distance under 3 cm or so, and then it will only focus again if it's more than 20cm or so from my face.

- A pair of typical 7x35 binoculars (says 525 ft. at 1000yds.)

- A small fish-eye lens meant for a camcorder.

I know it's kind of a random assemblage of lenses, but I really don't know very much at all about optics, and even less about the math, so can anyone see any possible configuration that might give me a little more zoom than just the binoculars (at the moment, the most powerful of the lenses)? Thanks in advance! 210.254.117.186 (talk) 08:07, 26 August 2009 (UTC)

Good luck experimenting. I think you use the word "zoom" (variable focal length) when you really want just a fixed telephoto result. Wikipedia has articles on optics that can help. For cameras: Teleconverter and Tele extender. For Optical telescopes: Refracting telescope and Amateur telescope making. A problem you will encounter with telescopes is stable mounting. I think your Nikon 55-200mm lens with a teleconverter has possibilities. Cuddlyable3 (talk) 09:04, 26 August 2009 (UTC)

I concur with Cuddlyable3. Any telephoto camera lens is essentially a miniature telescope sans eyepiece, and can be used as the main or Objective lens (the big one at the front) of a telescope arrangement, but you will need to add an eyepiece or Ocular lens (the little one at the back you look through) whose qualities are more critical; obtaining actual telescope oculars should be both easy and relatively cheap given the number of small commercial telescopes around.

Your 3 main problems are to 1. mount the telephoto lens firmly, preferably on the biggest, heaviest moveable-head tripod you can find; 2. make a means of firmly attaching, and easily detaching, your ocular(s), exactly aligned with the optical axis of the main lens; and 3. incorporate a means of moving the ocular(s) back and forward to focus the arrangement - some sort of push-pull arrangement using nested tubes will be probably be much easier than more elaborate screw or rack & pinion mechanisms (though you could cannibalise a cheap microscope for the latter). Your resulting device will probably have a small field of view, making it quite difficult to find a target in the night sky, so you may need to add a pointing aid, which can be merely a slender open-ended tube fixed parallel to the lens body, through which you sight.

I myself once made a serviceable small telescope using an old theodolite tripod, a 600mm "mirror telephoto" camera lens (essentially identical to a small Catadioptric telescope) and an assortment of old eyepieces borrowed from my local Astronomy Club, plus various bits of camera mount conversions, plastic and/or cardboard tubes, etc. Good luck and have fun.87.81.230.195 (talk) 12:07, 26 August 2009 (UTC)

Thanks for the tips. Would the eyepiece from a crappy "toy" telescope work? I can get one of those easily, and hey the cheaper the better. And is there any system for testing out the "oculars" I have that I might be able to find something that actually magnifies quicker than just placing them all randomly? The main problem I can see just arranging them myself is that the field of view I get is almost always incredibly small, even as small as a dot in the near distance. 210.254.117.186 (talk) 12:54, 26 August 2009 (UTC)

A toy telescope eyepiece should certainly work (as might a toy microscope eyepiece), but the quality of image you will get in terms of general clarity (arising from the glass/plastic quality), resolution (fineness of detail), degree of aberration (distortions of the image) and width of field of view will doubtless be less than with higher quality telescope or microscope eyepieces (the latter are very similar in general design and quality to telescope eyepieces, and amateur astronomers sometimes use them).

As to magnification, bear in mind that this is not purely a function of the eyepiece alone, it arises from the combination of the eyepiece with the main lens: specifically M = F/f where M is the magnification, F is the focal length of the main lens, and f that of the eyepiece. For example, a telescope eyepiece of 10mm focal length (not untypical) combined with my telephoto lens of 600mm focal length would give a magnification of 60 times, but with your zoom lens racked out to 210mm the same eyepiece would give a magnification of only 21 times.

The apparent field of view you get depends more on the detailed design of the eyepiece - there are many different ones and new improvements are invented from time to time. In your actual situation, you can only see what different eyepieces you can actually get hold of and try them out to see what works best with whatever objective lens(es) you choose to use.

Depending on how far you want to get into this, you might benefit from getting hold of a relevant basic reference book, either new, second-hand or via a public library. A couple of venerable tomes from my own shelves are James Muirden's Beginner's Guide to Astronomical Telescope Making, Pelham Books 1975, ISBN 0 7207 0822 2, and J. B. Sidgewick's Amateur Astronomer's Handbook 4th Ed, Pelham Books 1979, ISBN 0 7207 1164 9, but there are many others with similar information. 87.81.230.195 (talk) 21:58, 26 August 2009 (UTC)

My understanding of a telescope is you need an object lens of long focal length to create an enlarged virtual image, then a lens of much smaller focal length to look through and magnify that image. Do not aim it at the sun, because it will start a fire or instantly blind you. If you have 2 lenses, check their focal lengths by forming an image from a distant light (do not set something on fire with a sun image). Then place the lens of longer focal length at the end of a stick or in a tube with duct tape (or precision machined holders). Aim it at the object you wish to observe and note where on the stick it forms a real image by holding a piece of paper parallel to the lens and moving it back and forth. Place your shorter focal length lens on the other side of that real image and remove the piece of paper on which the image from the object lens appeared. Adjust the spacing according to the lens formula or empirically. Look through your telescope and enjoy the world made closer. A fine adjustment method for the eyepiece lens is highly desirable. Cardboard or PVC tubes to exclude extraneous light, painted black inside to decrease reflections, are helpful. A larger object lens collects more light. Edison (talk) 03:05, 28 August 2009 (UTC)

Did Indians discovery Laws of Motion centuries before Kepler?

As a retired computer scientist, I've dabbled at reading some anthropological topics, including history of science, historical linguistics, and prehistoric discovery via Y-chromosome typing.

By coincidence(?) three of these topics had subtopics pointing to India. I'll ask a question about one, and make comments about the other two. The reason for combining three unrelated topics into one will become apparent.

1. History of laws of celestial motion.

The Laws of Motion of Kepler and Newton are a major triumph of Western civilization, and often treated as the single greatest discovery that ushered in Modern Science. Yet we see in Wikipedia and other websites that Indian astronomers, notably Aryabhatta and Bhaskara, had developed similar methods.

Is this true? I don't see a similar claim made in a 16-year old print encyclopedia. I'd hate to think that the claims of jingoists (associated with any country), abetted by tools like Wikipedia, could distort records of the history of science!

Assuming the claims about ancient Hindu astronomy are true, can anyone point to me on-line documents based on pre-Keplerian writings? In relevant Wikipedia pages I see no sources cited (except other source-free webpages). The matter affects me personally, as my own page recites these (unsourced?) claims.

  http://james.fabpedigree.com/mathmen.htm

2. Homeland of the Indo-European speakers

This age-old riddle was solved several years ago (at least by any "preponderance of evidence" standard), but some academic Indian writers continue to insist that the language originated in South Asia. Of these "Indocentric theorists", Harvard's eminent Professor of Sanskrit, Michael Witzel, writes:

"The revisionist and autochthonous project, then, should not be regarded as scholarly in the usual post-enlightenment sense of the word, but as an apologetic, ultimately religious undertaking ... [and such writings] should be regarded and used, not as scholarly contributions, but as objects for the study of the traditional mind."

3. Homeland of the R1a Y-chromosome Haplogroup

The most ancient Ydna Haplogroups of India (C5, H and L) are hardly found outside South Asia; this confirms that there has been no major post-paleolithic migration from India. The strong presence of R1a among Slavs and Hindu Brahmins confirms an "Aryan migration" from Central to South Asia (although the details are a mystery). Yet even this is denied by South Asian jingoists; nonsensical "theories" and faulty studies have polluted the relevant Wikipedia pages. Indian genetic studies suffer severe flaws which can be explained only as deliberate obfuscation of caste-haplogroup correlations. I have a page which discusses this:

  http://james.fabpedigree.com/hindu.htm

Summary. There is no need to debate the conclusions I offer in 2. and 3. As time permits, I will make corrections to the relevant Wikipedia pages. But I wonder if "Indian science" is like the caricature Americans used to have of "Soviet science."

Are the claims about the celestial motion knowledge of Aryabhatta and Bhaskara valid? Or do they suffer from jingoist misinterpretations similar to those of Indian genetic and linguistic "science"? —Preceding unsigned comment added by Jamesdowallen (talk • contribs) 08:40, 26 August 2009 (UTC)

• I would not call the website you have linked a reliable source as it does not appear to have the hallmarks of reliability (editorial control independent of the author; peer review), so making the claims you are making based SOLELY on the text of that website in an actual Wikipedia article would be a bad idea. If you have reliable sources which show independent confirmation of these claims, you may have something, but that website does not appear to be it. --Jayron32 12:51, 26 August 2009 (UTC)

Just a note... It is actually his own website, not just some website that he found. So, he is using his own writings to justify his point. -- kainaw™ 12:57, 26 August 2009 (UTC)

No, he made it clear that it's his own website: "The matter affects me personally, as my own page recites these (unsourced?) claims. http://james.fabpedigree.com/mathmen.htm" --99.237.234.104 (talk) 13:25, 26 August 2009 (UTC)

If you wish to comment on specific Wikipedia articles, it would be a big help if you mentioned the names of those articles. As far as I can see, our articles on Aryabhata and Bhāskara II do not claim that either of them discovered Kepler's laws of planetary motion. Both of these Indian astronomers may have postulated heliocentric systems, but that is a different matter. Gandalf61 (talk) 13:10, 26 August 2009 (UTC)

Hi, James again. First, my "complaint" wasn't "against" Wikipedia specifically -- I'm asking for knowledge, not Wiki editing. One claim is that Aryabhatta wrote orbits were ellipses. By itself this is only half of one of Kepler's Laws and of interest only if we can understand *how* Aryabhatta came to the conclusion. Brahmagupta is said to have discovered the law of universal gravitation; again it would be nice to read something close to contemporary. (Both these claims, by the way, are clearly made on the Wikipedia pages cited in preceding paragraph.) The claim that Bhaskara had equations of celestial motion as good as 18th-century Europe may not appear directly in Wikipedia, but is made elsewhere on 'Net. Again, my concern is NOT accuracy of Wikipedia itself, but rather: Are the claims true? Are there on-line translations of early (i.e. pre-Kepler) Indian writing to help one judge the claims? (My own pages are, of course, irrelevant to the question. I wouldn't have mentioned them if I'd anticiapted it wou lead to the confused tangential comments above.) Jamesdowallen (talk) 07:49, 27 August 2009 (UTC)

I agree that it's worthwhile to doublecheck these claims. Brahmagupta is quoted by al-Biruni as saying: All heavy things are attracted towards the center of the earth. [...] The earth on all its sides is the same; all people on earth stand upright, and all heavy things fall down to the earth by a law of nature. This is great, but it's not the law of universal gravitation which would have involved a mention of an inverse square. Neither do he seem to explain e.g. how the moon fail to fall down on earth. As for Aryabhatta it has been claimed that he proposed heliocentrism. Our article on him links to a rebuttal of this claim. The source of the misconception seems to be that his calculations involved an epicycle with a period of one year, which is how long it takes the earth to go around the sun once. The length of a year is ofcourse known to anyone keeping a calendar, even if they have no knowledge of celestial mechanics. Our article further states that no evidence has been found of him contemplating elliptical motions. In all this, it must be remembered that ancient civilizations were not completely isolated from each other. For instance, the Paulisa Siddhanta examplifies a transmission of greek astronomical theory to india. As for all the topics you've raised, I encourage you to edit any wikipedia articles that present false claims or which portray fringe opinions as mainstream facts. There's certainly room to mention differing opinions, but we should portray the opinion of the scientific community honestly. For that, we need people with knowledge of these topics. :-) EverGreg (talk) 12:56, 28 August 2009 (UTC)

Hoping for closure on this topic, I contacted a Professor of the history of math and science, who has written well-documented books on such topics; I learned that the claims about Hindu astronomy are exaggerated: Brahmagupta and Bhaskara seem to be very outstanding mathematicians but they used the Ptolemaic model and did NOT develop the celestial laws of Kepler and Newton. (Aryabhatta's contributions may be grossly exaggerated.)

A report from a single Professor may not be dispositive, but I will correct my own webpages. Some Wikipedia pages may parrot the exaggerations. I do not have the time, energy, or knowledge to correct them; is this message sufficient to bring the matter to the attention of appropriate Wiki editors, or is there a more appropriate forum?

Among Wikipedia pages which may need editing are: Bhaskara II:

"The study of astronomy in Bhaskara's works is based on a model of the solar system which is heliocentric and whose movements are determined by gravitation. Heliocentrism had been propounded in 499 by Aryabhata, who argued that the planets follow elliptical orbits around the Sun"

The page for Aryabhata already seems more correct: Aryabhata:

"It has even been claimed that he considered the planet's paths to be elliptical, but no primary evidence for this has been found"

Jamesdowallen (talk) 11:15, 29 August 2009 (UTC)

Thanks for researching this topic. I've edited the Bhaskara II article and I'll follow up any discussion that might arise from it. EverGreg (talk) 10:43, 31 August 2009 (UTC)

Cracking joints

Does any animal besides some H. sapiens do this habitually? -GTBacchus^(talk) 09:32, 26 August 2009 (UTC)

Most hedgehogs that I've had will stretch to the point of popping a few joints when they wake up. Since hedgehogs are at the very early part of mammal evolution and humans are at the very late part, I believe it is safe to assume that other animals in between do the same thing. -- kainaw™ 12:59, 26 August 2009 (UTC)

Hedgehogs are at the very early part of mammal evolution ? I would think that honor would go to the monotremes, like the platypus. StuRat (talk) 14:56, 26 August 2009 (UTC)

Hedgehogs have a smooth brain - which is a characteristic of early mammal evolution. I don't believe many mammals still have smooth brains. I don't what the wrinkles in the average brain are called, so it is difficult to look it up and see where in mammal evolution that trait falls. -- kainaw™ 16:08, 26 August 2009 (UTC)

Sulcus (anatomy)? Or Sulcus (neuroanatomy). Bus stop (talk) 16:17, 26 August 2009 (UTC)

Actually lots of mammals have smooth brains. Convolutions are more a function of body size than anything else -- so rats, mice, shrews, bats, and other very small mammals all have smooth brains. Looie496 (talk) 17:13, 26 August 2009 (UTC)

Thanks. I've only studied hedgehogs and mistakenly thought that their smooth brain was not so common a feature. -- kainaw™ 17:44, 26 August 2009 (UTC)

I think Kainaw is referring to a view (which AFAIK used to be the established one for most of 20th century, but not anymore) that order Insectivora - now defunct - contained the "basal" placental mammals, least changed for the last 100 My. As of now, AFAIK, the hedgehogs and gymnures are placed in Erinaceomorpha (Gregory, 1910), an order of their own. There are modern genetic studies attempting to figure out the proper cladistics and taxonomy of placental mammals. Still, I'd wait another 10-20 years for a new established view to emerge. But strictly speaking no, hedgehogs are not representative of the earliest part of evolution of mammals (or even placental mammals). --Dr Dima (talk) 16:36, 26 August 2009 (UTC)

The echidna, a monotreme, is sometimes called a hedgehog because it looks a lot like one -- however its evolutionary descent is quite different from that of true hedgehogs, which belong to Laurasiatheria. Looie496 (talk) 17:08, 26 August 2009 (UTC)

Hedgehogs are at exactly the same time of mammal evolution as humans. Specifically, the mammals around in the year 2009. — DanielLC 03:43, 27 August 2009 (UTC)

DanielLC, I think what kainaw means is that hedgehog species evolved a long time ago (maybe 15 million years) and have not evolved much since. Humans evolved between 250,000 and 400,000 years ago. Axl ¤ [Talk] 09:19, 27 August 2009 (UTC)

Well, we're getting into deep issues here. At a molecular-genetic level, hedgehogs have probably changed just about as much as humans over the same time scale. At the level of visible bodily form, hedgehogs look a lot more like their ancestors than humans do, but which is the correct level to look at, the molecular or the macroscopic? Most modern biologists seem to go with DanielLC in thinking the molecular level is more important; I personally am not quite convinced. Looie496 (talk) 16:09, 27 August 2009 (UTC)

Scientists do look at the molecular-genetic level. What changes have happened to hedgehogs in that time, I don't know, but such studies are done. --Tango (talk) 18:00, 27 August 2009 (UTC)

Darwin's tree of life implies otherwise. 98.14.223.69 (talk) 12:14, 29 August 2009 (UTC)

So, you guys are talking about the basal versus derived distinction, right? Are hedgehogs more basal than humans, or do we not know that? According to our article on Laurasiatheria, "Within the Laurasiatheria, the Erinaceomorpha appears (surprisingly) to be the most divergent branch." Does that address the issue at hand? -GTBacchus^(talk) 15:20, 30 August 2009 (UTC)

movement of knee

Hi if someone were to be standing up and then lift one of their knees off the ground towards their chest is this flexion of the hip? Is this also flexion of of the knee? Thanks RichYPE (talk) 12:42, 26 August 2009 (UTC)

Yes, both (as long as you're not trying to keep your leg straight). Fribbler (talk) 12:44, 26 August 2009 (UTC)

Thanks a lot! RichYPE (talk) 19:48, 26 August 2009 (UTC)

Consider this image of reference desker user:Fribbler on the way to a WP meeting to discuss this very question. Image:Ministry of Silly Walks.jpg --Cookatoo.ergo.ZooM (talk) 06:55, 27 August 2009 (UTC)

Just for the record... The image of John Cleese shows him with a flexed hip with an adducted and partially extended knee? Is that right? Thanks RichYPE (talk) 19:09, 29 August 2009 (UTC)

Doubling your gas mileage

I saw this cool video on YouTube on how to double your gas mileage. http://www.youtube.com/watch?v=UHAUsGlfbx8&feature=channel

I just wanted to do a reality check with some people here. Are these tips effective and safe? ScienceApe (talk) 15:06, 26 August 2009 (UTC)

Most of the stuff is common sense (proper inflation, correct spark, no excess junk, don't run the A/C), and he claims a modest improvement on them (which means he had a badly maintained car with lots of crap in the trunk before). But the biggest improvement he reports is due to adding acetone. Snopes says these claims are "false" and Mythbusters says they're "busted". Moreover, the Car Talk says it's "worse than useless", in that it also destroys o-rings in your fuel system. Heck, whenever someone tries to justify their claim with a conspiracy theory like "what the car companies don't want you to hear" that should set major alarm bells ringing. -- Finlay McWalter • Talk 15:16, 26 August 2009 (UTC)

Agree. Also see Acetone#Domestic_and_other_niche_uses and the linked sources. --Stephan Schulz (talk) 15:18, 26 August 2009 (UTC)

The thing about switching to synthetic oil is questionable. There's plenty of online postings that claim you get up to a 4% improvement (and plenty that claim less, or none at all), I've not found a single reliable source that supports any of these claims. Worse, the Wikipedia article synthetic oil#Advantages says it helps gas mileage, but doesn't cite any source at all. There are other reasons you might choose to run synthetic oil, but there doesn't seem to be real evidence that it'll help gas mileage (never mind that it'd be cost-effective). -- Finlay McWalter • Talk 15:36, 26 August 2009 (UTC)

You may wish to read Hypermiling, which runs the gamut from sensible maintenance to "strategies" of suicidal stupidity. -- Finlay McWalter • Talk 15:40, 26 August 2009 (UTC)

Far from trying to cover it up, car companies would be delighted if this were true. They make far more profit on their low mileage SUVs than they do on their fuel efficient models. An invention like this would increase demand for SUVs and so contribute to their profits. Wikiant (talk) 16:20, 26 August 2009 (UTC)

Yep - you can be sure that there aren't secrets that the car company doesn't want you to know. Good gas consumption is a HUGE selling point! Why on earth would they hide a simple, effective trick from you? In fact, with most cars, you'll find many of these tips right there in the owner's manual. My MINI Cooper'S manual says that correct tire inflation, minimal A/C usage, keeping the windows closed over 30mph, keeping your car regularly serviced (ie good oil, good spark, tight belts, etc) trying to keep the engine RPM within the 2000 to 3000 range and not using the "Sport" button will all improve your gas mileage...and that's true. All of those things work. Many of the other suggestions (acetone?! Eeek!) are either dangerous, counter-productive (because the car's computer will be confused) or damaging to the engine. The hyper-milers are a weird bunch...some of the things they claim, simply don't work. Other things (like putting the car into neutral and coasting whenever possible - or disconnecting the power steering pump) are downright dangerous. SteveBaker (talk) 17:11, 26 August 2009 (UTC)

Agreed, Steve. It's only really the maintenance-free, everlasting car that the car companies are suppressing the patents on. It's Big Oil that's keeping down the really cool fuel efficiency stuff - the water-powered car or the 10,000MPG engine, for example (much in the same way that the battery companies don't want us to know about the universal battery charger that can reliably recharge all types of disposable alkaline cells)... :) --Kurt Shaped Box (talk) 04:10, 27 August 2009 (UTC)

But bare in mind that the car companies, and specifically GM, do engage in conspiracies against the public interest. My first example is in the middle of the last century, when GM systematically bought up cheap and efficient public transportation systems in cities across the US and then destroyed them, to increase reliance on vehicles they produced. My second example is in the 1990's, where they worked to undermine California's mandate to create electric vehicles (see the movie Who Killed the Electric Car?). StuRat (talk) 12:48, 27 August 2009 (UTC)

What sources do you have for this? 98.234.126.251 (talk) 05:58, 28 August 2009 (UTC)

Take a look at Great American streetcar scandal. -Elmer Clark (talk) 08:15, 28 August 2009 (UTC)

You actually believe this conspiracist rubbish? For the record, it wasn't GM or the National City Lines or any other conspiracy that killed the trolleys, it was their own inherent shortcomings (namely, the lack of flexibility, and the high capital and maintenance costs required to run streetcar lines), along with changing demographic trends in the post-WW2 era (suburban sprawl, interstate freeways, cheap mass-produced automobiles, etc.) What I'm saying is that all those trolley lines would've gone broke anyway -- all that GM could be accused of doing (if anything) is to accelerate the process that was already happening across the nation. 98.234.126.251 (talk) 23:36, 29 August 2009 (UTC)

Yes, I certainly believe that both of those conspiracies were real. The most obvious point is that, in both cases, GM destroyed items which would have had resale value. In the case of streetcars, they could have been sold to other cities which used streetcars, but GM destroyed them instead, then ripped up the rails so the cities couldn't buy more streetcars and continue service. In the case of electric cars, they still had plenty of life and a line of buyers waiting to purchase them, but GM crushed them instead. Why ? Wasting money like that only makes sense during a conspiracy to destroy those systems. In many ways electric streetcars are more flexible than internal combustion engine vehicles. Since the electricity can be generated from any source and quite far away, streetcars can essentially be powered by coal, hydro-electric power, nuclear, solar, wind, etc. Try doing that with a diesel bus. They also don't pollute the air in the city (they may pollute the air where the electricity is generated, but only if fossil fuels are used there). And population densities remain high enough today in downtown areas to support streetcars, especially during working hours. As for high capital costs, those had already been paid when the streetcars were originally purchased and the rail lines laid. GM then destroyed that capital, making it necessary to pay for it all over again if any city wanted to restore their trolley system. Also, suburban sprawl was largely created by acts of Congress, including the creation of the Interstate Highway System and the GI Bill, which paid for people to build new houses in the suburbs but not for them to buy and fix up existing homes in cities. GM may have had a hand in getting those bills passed, with those provisions, too. (BTW, I used to work for GM.) StuRat (talk) 12:12, 30 August 2009 (UTC)

"In the case of electric cars, they still had plenty of life and a line of buyers waiting to purchase them, but GM crushed them instead." -- Your claim about "a line of buyers waiting to purchase them" is counterfactual, since sales records actually indicate that demand for electric cars was low.

"In the case of streetcars, they could have been sold to other cities which used streetcars, but GM destroyed them instead, then ripped up the rails so the cities couldn't buy more streetcars and continue service." -- Although I don't have any definitive evidence, I strongly suspect that the same lack of demand was at work in the case of the streetcars -- many cities were converting from streetcars to buses at the same time, so the demand just wasn't there. As for ripping up the tracks, this is routinely done when railroad lines (including trolley lines) are abandoned, partly for safety reasons, partly so that the rails and cross-ties could be reclaimed (for melting and re-manufacture in the case of rails, for firewood in the case of cross-ties). OR: there used to be a branch line of the Union Pacific Railroad near my home, and they ripped it up completely when they abandoned it (I've actually watched them lifting the rails and then picking up the cross-ties with a bulldozer, and loading them onto trucks). Would you say that this is evidence of a "conspiracy" by the UP to get rid of this particular branch line?

"In many ways electric streetcars are more flexible than internal combustion engine vehicles." -- Also wrong -- the fact that streetcars run on rails makes it impossible to create new streetcar routes without major capital investment (this was arguably THE most important factor that caused their demise).

"They also don't pollute the air in the city" -- Correct, but this has absolutely no effect on the economics of streetcar operations, which is what this debate is all about.

"And population densities remain high enough today in downtown areas to support streetcars, especially during working hours." -- Then why is it that none of the streetcar companies in the world (to the best of my knowledge) actually turns a profit?

"As for high capital costs, those had already been paid when the streetcars were originally purchased and the rail lines laid." -- This ignores the fact that even after the rails were laid and the wires strung, they required regular preventive maintenance, at considerable expense. That, too, was a factor against the continued operation of streetcars and for their replacement with buses.

"Also, suburban sprawl was largely created by acts of Congress, including the creation of the Interstate Highway System and the GI Bill, which paid for people to build new houses in the suburbs but not for them to buy and fix up existing homes in cities." -- StuRat, please tell me true: Given a choice, would you rather live in a nice single-story house in the suburbs with a lawn and a picket fence, or in a high-rise apartment somewhere in the inner city?

"GM may have had a hand in getting those bills passed, with those provisions, too." -- This is pure speculation on your part -- do you have any documents backing this up??? 98.234.126.251 (talk) 07:12, 31 August 2009 (UTC)

"...sales records actually indicate that demand for electric cars was low". That may be an argument not to build more, but it's no argument to crush the cars already produced. They could certainly have been sold for more money than the scrap value of the metal. View the movie I listed and you will see several people who were willing to buy them (most of whom had leased them previously), but were prevented from doing so by GM. If you had a working electric car, would you crush it or sell it ?

You note that many streetcar systems were destroyed at the same time, but this isn't a coincidence, that's due to the action of GM and others. Had it happened naturally, it would have taken a very long time, like the conversion from steam locomotives to diesels.

Saying that I'm wrong when I said that in many ways streetcars were more flexible completely ignores my argument that they are more flexible both for fuel sources and pollution. And the expense of adding new lines doesn't apply to existing lines. That might be an argument for not adding new streetcar lines for new areas, but it's no argument at all for destroying the existing lines. In fact, it's an argument against it. If a city spent all that money to set up such a system, it certainly isn't in their interest to destroy such a large capital investment. And if you argue that no city can have multiple systems of public transportation, I'd point out that many already have; combining subways, buses, etc.

I claimed that GM's actions were "a conspiracy against the public interest", which includes air quality as well as economics. Also, the two aren't entirely separate, as efforts to improve city air quality (like factory emissions standards), do have an economic impact.

I don't believe a streetcar system costs any more to maintain than buses, since the streetcars are much simpler than buses and don't have the maintenance-intensive internal combustion engines and all the other systems that go along with that. Although there may be an effect now that streetcars are so rare that you must pay premium prices for parts and labor. This wouldn't have been the case, had GM not acted, however.

It so happens I do live in the city of Detroit, (not a suburb thereof). As inner cities now are in the US (due to those two bills), very few would choose to live there. They decayed directly as a result of the people and thus revenue moving out of the cities. If we hadn't had those two bills, and our inner cities remained more like those in Europe, then many would prefer to live there.

Check out Who Killed the Electric Car? and watch the creepy "Hiroshima" commercial GM had for the electric car. Unlike most commercials, this one was designed to keep customers away, so they could argue that nobody wanted electric cars and they shouldn't be required to sell them.

As for not having evidence about GM's role in passing those bills, they wouldn't make such deals in public, would they ? And "absence of evidence isn't evidence of absence". StuRat (talk) 17:38, 31 August 2009 (UTC)

Well, as a rule I don't believe in debating a point once a thread has been archived, but these arguments are so stupid that I just have to respond.

"You note that many streetcar systems were destroyed at the same time, but this isn't a coincidence, that's due to the action of GM and others." -- No, that's due to suburban sprawl, which happened post-war in many US cities at the same time and which was the main factor why streetcars stopped being viable (the existing routes weren't bringing enough revenue anymore, and there was no money to build new ones, etc.)

"Had it happened naturally, it would have taken a very long time, like the conversion from steam locomotives to diesels." -- You should know that the conversion from steam trains to diesels took only a decade or so, and not "a very long time" as you claim. Also, keep in mind that the streetcar lines were in a period of decline since the Great Depression, long before the GM-sponsored conversion to buses.

"Saying that I'm wrong when I said that in many ways streetcars were more flexible completely ignores my argument that they are more flexible both for fuel sources and pollution." -- This ain't what "flexible" means as far as urban transit is concerned -- in this case, the word "flexible" applies ONLY to routing flexibility (and in this respect, buses beat streetcars hands-down).

"And the expense of adding new lines doesn't apply to existing lines. That might be an argument for not adding new streetcar lines for new areas, but it's no argument at all for destroying the existing lines. In fact, it's an argument against it." -- Once again, you choose to ignore the maintenance cost of the tracks and the overhead wires, which is considerable even for existing lines. Also, the changes in urban planning (namely, the above-mentioned suburban sprawl) often meant that existing streetcar lines were no longer viable, so they had to be abandoned because it cost more to maintain them than what they earned in revenue.

"And if you argue that no city can have multiple systems of public transportation, I'd point out that many already have; combining subways, buses, etc." -- True, but in the case of buses and streetcars, they would essentially be competing for the same transit niche, while buses and subways fill different niches. That is a different situation altogether -- in the latter case, the buses act as feeders for the subway and therefore both systems benefit from a symbiotic relationship, while in the former case, there is direct head-to-head competition which ultimately leads to one or the other system displacing the other.

"I don't believe a streetcar system costs any more to maintain than buses, since the streetcars are much simpler than buses" -- They may be simpler, but they need rails to run on and overhead wires to provide current, both of which are expensive to maintain.

"If we hadn't had those two bills, and our inner cities remained more like those in Europe, then many would prefer to live there." -- Oh, really? Historical precedent shows that on the whole, most Americans prefer wide-open spaces, as evidenced by all the westward migrations from 1776 to the present. This has to do with the historical development of the American character, with independence and the "pioneering spirit" and all that stuff. To say that most Americans would prefer to be crowded into high-density inner cities is presumptious to say the least.

"As for not having evidence about GM's role in passing those bills, they wouldn't make such deals in public, would they ? And "absence of evidence isn't evidence of absence"." -- That's the TYPICAL fallacy of a conspiracy nut like that which you just admitted to being -- first making unsubstantiated claims, and then claiming that the lack of evidence is proof of a cover-up. For the record, "absence of evidence is not evidence of absence" is the EXACT SAME argument used by conspiracy freaks who claim that the astronauts didn't land on the moon... or that Amelia was captured by the Japanese while on a secret mission... or even that the CIA blew up the World Trade Center! Geez, what ever happened to "innocent until proven guilty"?! 98.234.126.251 (talk) 07:51, 2 September 2009 (UTC)

When you say "you can be sure that there aren't secrets that the car company doesn't want you to know.", you're specifically talking about gas mileage, right? I can't imagine a vast multinational corporation that doesn't have at least some secrets. APL (talk) 14:02, 27 August 2009 (UTC)

Yeah - of course - we were talking in the context of fuel economy. They might well hide crappy fuel economy from you - but good fuel economy is something they want to talk about very much! SteveBaker (talk) 00:10, 28 August 2009 (UTC)

I'm not so sure that oil companies would necessarily want to hide fuel-saving technology. The big threat to oil companies isn't low gas prices. It is gas prices so high that it becomes worth while to develop alternate fuel sources. For the record, gas prices (as a % of median income) have been falling (on average) since the 1960s. For a gallon of gas to cost the same, in percentage of median income, as it did in 1960, the price would have to be around $4.75 per gallon. Wikiant (talk) 01:16, 28 August 2009 (UTC)

True, but us driving longer distances in bigger vehicles with more horsepower these days means that high gasoline prices are more of a problem, than they were back then. StuRat (talk) 15:25, 28 August 2009 (UTC)

But those big-a** square vehicles that were 19.5 feet long and weighed 5,500 lbs. (as much as SUVs) still had to cruise just as fast as cars of today. There couldn't possibly be enough percentage of SUVs + pickups on the road today to make the average fuel economy worse than it was then. Remember that today's more powerful engine could only guzzle fuel faster when accelerating.

If those things were true, why then did it seem like an era of gas cheapness never to be exceeded before or since? Remember, even if you drove half as much in 1960, gas would've felt like (2009$)2.37⁹ Sagittarian Milky Way (talk) 18:42, 28 August 2009 (UTC)

What 1960 cars weighed 5,500 lbs. ? Perhaps you're thinking of the early 1970's, by which time the cars had gotten much bigger (for example, compare the 1960 Ford Thunderbird, at under 4000 lbs., with the 1972 Ford Thunderbird, which could top out around 5000 lbs.). And gas-guzzling engines guzzle gas at constant speed, too. For one thing, they need to move the mass of those huge engines around. StuRat (talk) 12:01, 29 August 2009 (UTC)

I was thinking of a 50s(?) Lincoln I saw in a recent car magazine, which might have been as low as 5,000 lbs but I'm pretty sure it said 5,500 lbs. Fuel mileage was, near 10. And old engines were huge! How could they be lighter than today's? Sagittarian Milky Way (talk) 23:25, 29 August 2009 (UTC)

I think our view of the past is biased somewhat, because the biggest and most extreme vehicles from then are the most memorable and those that get the most press attention. There were also many economy cars in the 1950's (like the 1963 Dodge Dart), but they aren't all that collectible, so you don't hear as much about them today. The main concern at the time was keeping the purchase price down, but this also resulted in the unintended consequence of saving gas, as a smaller, lower horsepower car will also tend to sip gas. StuRat (talk) 11:47, 30 August 2009 (UTC)

Addition Reaction of Alkynes to Alkenes

Hello. Which geometric isomer is favoured when halogens react with alkynes to form alkenes? For example, does 1-butyne react with Br₂ to yield 1,2-dibromo-trans-1-butene? Does the hydrogenation of haloalkynes differ? For example, does 1-bromopropyne react with H₂ to form 1-bromo-trans-1-propene hypothetically? Thanks in advance. --Mayfare (talk) 15:46, 26 August 2009 (UTC)

I found two sources which contain generic answers:

[6] and [7]

There's a slightly higher level analysis here [8]

For hydrogenation it depends (I think on the process and catalyst) - however when the alkyne is absorbed on a solid catalyst it is usually to expect cis addition of H2, but there are plenty of ways this can not be the case.

83.100.250.79 (talk) 23:15, 26 August 2009 (UTC)

In my experience, hydrogen-transfer hydrogenation of haloalkynes does not have noticeably different cis/trans due to the halide. DMacks (talk) 00:30, 27 August 2009 (UTC)

Exotic Matter

My understanding is if we could replicate exotic matter which negated the attraction of mass (gravity) then we could practically move a bus into earth orbit using a model rocket engine since it would be essentially massless.

So then why don't we have scientists at NASA working around the clock determining how to make this stuff? Even if we don't know exactly where to start if we know the characteristics of the final product we should be able to invent a variety of testable methods. Is this being pursued at all? TheFutureAwaits (talk) 16:23, 26 August 2009 (UTC)

It's probably being pursued by someone somewhere on a creatively written grant. However, there is no reason to believe it actually exists. There are a great many forms of magic that would be amazing if they were only non-fictional; thankfully, NASA isn't working around the clock on any of them. 24.159.32.213 (talk) 16:37, 26 August 2009 (UTC)

I always thought that the lack of a consumer Star Trek Transporter shows that capitalism doesn't work. Similarly the lack of an immortality pill on the market... --Stephan Schulz (talk) 16:45, 26 August 2009 (UTC)

We have the technology to make a wired transporter anyways. But if you want to do it, set some time aside since the computers would take years to finish the scan before transmitting, and you better not change anything during the scan. Googlemeister (talk) 17:56, 26 August 2009 (UTC)

And for chrissakes don't forget the Heisenberg compensators. (I was privately betting myself $5 that this wouldn't be a redlink - and I won!) How do they work? "Very well indeed". SteveBaker (talk) 20:37, 26 August 2009 (UTC)

No, the lack of a transporter likely shows that capitalism does work. Given the number of breakthroughs required, at the moment, the present discounted value of the expected future profits are less than the present discounted value of the expected costs. Capitalism is working by not diverting scarce resources to something whose cost exceeds its payoff. Wikiant (talk) 20:40, 26 August 2009 (UTC)

Um, I'm pretty sure Stephan was joking... Nil Einne (talk) 08:34, 27 August 2009 (UTC)

The lack of any serious consideration of transporters is simply that the underlying physics prohibits it. Until/unless there is some very fundamental change in our understanding of the universe, you can't even consider making such things. Ditto with what our OP is asking. Until some very basic physics says that the most basic part of the mechanism could even theoretically work - there is absolutely no point in spending money on how to build one! The kinds of physics that might one day make either of these things conceivable is being done...but not with the intent of producing teleporters or intertia-less drives. SteveBaker (talk) 22:11, 26 August 2009 (UTC)

I don't see anything in the laws of physics that prevents transporting a human being. It's simply a matter of quickly scanning a person down to the individual atoms, sending that information to a remote site, then quickly reassembling those atoms in that specific order at the new location from a stockpile of the various elements there. This is certainly currently well beyond our capabilities in every step, but nothing we can't one day hope to achieve. StuRat (talk) 12:37, 27 August 2009 (UTC)

The Heisenberg uncertainty principle puts a limit on how accurately you can perform that scan. Whether that level of accuracy would be sufficient or not, I don't know. --Tango (talk) 16:10, 27 August 2009 (UTC)

That limits us to not being able to know the exact position of an electron (if, indeed it has an exact position), but shouldn't make it impossible to determine the identity of a specific atom. I believe we can already do that, for a few atoms at a time, especially if we don't care if we destroy the organism attached to those atoms, in the scanning process. We just need a way to do it for all the atoms in the body, very quickly. StuRat (talk) 19:27, 27 August 2009 (UTC)

Identifying an atom is relatively easy, but you can't know its exact position and momentum at the same time. I'm not sure how precisely that information would be required, but that is the main issue with transporters. --Tango (talk) 19:34, 27 August 2009 (UTC)

All you'd have to know is which molecule the atom is within, and that doesn't require all that much precision, does it ? StuRat (talk) 15:04, 28 August 2009 (UTC)

It is far more complicated than that. Organic chemistry involves very complex molecules, simply knowing how many of each atom are in a given molecule doesn't tell you anywhere near enough. --Tango (talk) 21:19, 28 August 2009 (UTC)

Yes, you'd have to know where in the molecule the atom is, too. StuRat (talk) 03:27, 29 August 2009 (UTC)

And you would have to know where the molecules is. The combination of those facts is the position of the atom, which is precisely what we cannot know precisely. --Tango (talk) 15:31, 30 August 2009 (UTC)

You certainly can know approximately where the atom is, which should be good enough to find it's location in the molecule. To put it another way, all you need to do is identify the molecules and their locations and orientations. StuRat (talk) 15:41, 31 August 2009 (UTC)

See AEGIS for a possible test to see if antimatter is such an exotic matter. In any case, it would be cheaper to move the entire population of the Earth to Mars with conventional methods than it would be to create enough exotic matter to move anything visible to the naked eye into space. Also, antimatter has an annoying tendency to annihilate itself when it touches matter, so it would be particularly impractical. By the way, this wouldn't make it massless for the purposes of faster-than-light travel. You don't seem to have made that mistake, but I feel I should point it out anyway. — DanielLC 03:39, 27 August 2009 (UTC)

Nobody actually expects AEGIS to show any significant difference between matter and antimatter, do they? It's just a test to double check something that everyone is pretty certain is true - such tests are very important in science, of course. There is no way to know what the cost of producing exotic matter will be until we know how to do it (if it is even possible). It might turn out to be really easy once we know how. --Tango (talk) 16:09, 27 August 2009 (UTC)

For it's worth CP violation produced some interesting results showing that antimatter is definately different to matter in some ways. Whether this applies to yuor statement I'm not sure. Elocute (talk) 20:09, 27 August 2009 (UTC)

Fusion

I checked out this section on nuclear fusion, http://en.wikipedia.org/wiki/Nuclear_fusion#Important_reactions but it didn't list fusion between two plain old hydrogen atoms to produce helium. Why is this? ScienceApe (talk) 16:49, 26 August 2009 (UTC)

Plain old hydrogen contains no neutrons, and helium without neutrons is unstable. You need at least one; ordinary helium has two. Looie496 (talk) 16:57, 26 August 2009 (UTC)

See diproton for more info. Looie496 (talk) 16:59, 26 August 2009 (UTC)

What about plain old hydrogen fused with deuterium to produce Helium3? ScienceApe (talk) 18:55, 26 August 2009 (UTC)

As the page you linked to says, if there is only one product it is difficult (if not impossible) to conserve both energy and momentum. The momentum of the sole product would need to equal the total momentum of the two reactants as would the energy, but energy and momentum are closely related so it probably won't be possible to get them both right. --Tango (talk) 19:17, 26 August 2009 (UTC)

I'm not sure I understand. Are you saying that the conservation of energy won't allow for that fusion event to take place? ScienceApe (talk) 04:32, 27 August 2009 (UTC)

It would make it very unlikely to take place. It could only take place if the initial momentum and energy was such that it could all be given to a single particle. I'm not sure if that is ever possible (I would need pen and paper to work that out, and I don't have any), it certainly isn't likely. --Tango (talk) 16:12, 27 August 2009 (UTC)

Tango is right that a reaction with just one product would be unlikely because of energy conservation. But nothing keeps it from sheding the extra energy as a photon (a second product) as you can see for instance in the article Proton–proton chain reaction. Dauto (talk) 02:06, 28 August 2009 (UTC)

Note that in order to "stick together", one of the protons must turn into a neutron through positron emission. I don't remember where I read it (and unfortunately got no way to find the source), but I've read somewhere that only a small fraction of protons do that upon colliding with another proton -- the vast majority just bounce off again. FWiW 98.234.126.251 (talk) 06:15, 28 August 2009 (UTC)

That's not the case for the specific reaction we are talking about which is H+D->He3+gamma. Dauto (talk) 15:34, 28 August 2009 (UTC)

I just read the article and explained the reason given therein, if it is wrong don't blame me! What you say makes sense, but there must be something else preventing that reaction taking place, otherwise it would be far more common than it is. --Tango (talk) 21:22, 28 August 2009 (UTC)

The article seems to be concerned with only pure nuclear reactions (Strong interaction) and the emition of a photon requires a mixed reaction that also includes the electromagnetic interaction since the photon does not interact through the strong interaction. I was just pointing out that the Hydrogen-Deuteron reaction is possible and non-negligible in many situations. Dauto (talk) 20:26, 29 August 2009 (UTC)

True, the article does explicitly say it is ignoring EM interactions. Do you know why the article doesn't like EM reactions? --Tango (talk) 15:33, 30 August 2009 (UTC)

drifting

Approximately how long does it take for something to drift from South America to Cape Hope? Just need a ballpark, 2 months about right? Googlemeister (talk) 17:37, 26 August 2009 (UTC)

1-3 mph is ballpark. Did you drop the engagement ring? Sagittarian Milky Way (talk) 19:31, 26 August 2009 (UTC)

Message in a bottle. Googlemeister (talk) 19:34, 26 August 2009 (UTC)

Yeah, I know. I threw one once. It washed back in seconds. Sagittarian Milky Way (talk) 19:54, 26 August 2009 (UTC)

Did it still have the same note? APL (talk) 20:00, 26 August 2009 (UTC)

Well, duh. Yes. If it was a different bottle now that'd be a coincidence.. Sagittarian Milky Way (talk) 20:12, 26 August 2009 (UTC)

Ah - but if it was the same bottle but a different message - it would be a conversation! SteveBaker (talk) 20:35, 26 August 2009 (UTC)

I was typing up a long detailed message in my other office, but had to run and shut off the computer without sending. Very briefly, you are going the wrong way. Chances are you will drift to the Indian Ocean, missing Africa all together. If you do hit Africa, it will be a long trip anywhere from about 1,000 to 2,000 miles (it is a circular current. The inside is shorter than the outside.) Your speed will be, on average, less than a knot. So, you are looking at a mile an hour (as Sagittarian Milky Way noted). Best luck will be about 40 days. Real experience will likely be much longer. Now, if you asked about going from Africa to South America (which is what I asked a long ago), you will get a completely different answer. -- kainaw™ 20:34, 26 August 2009 (UTC)

Human Genetic Trait Pairings

What are some Human unusual genetic trait pairings? I mean, for instance, if you have Human genetic trait 'A' most likely you have Human genetic trait 'B'. I think there is one pairing that I am familiar with and that is if you have unattached earlobes, you most likely are right handed. But that can be wrong. --Reticuli88 (talk) 20:25, 26 August 2009 (UTC)

Maybe take a look at epistasis. You may be right, but if you're wrong, does that make it left? DRosenbach ^{(Talk | Contribs)} 22:10, 26 August 2009 (UTC)

The OP may be referring to genetic linkage and/or linkage disequilibrium. Genes that are located physically close to each other on a chromosome will be paired (to some extent), since the probability of them splitting up during meiosis gets smaller the closer they are. Thus, historically, Charcot-Marie-Tooth disease was known to be paired with specific Duffy antigen alleles, it turned out the genes responsible are relatively near each other.

You might also be asking about different phenotypes resultant from the same genes. For example, red hair is a genetic trait paired (at a high frequency) with pale skin and freckling. This is because loss of function alleles of the MC1R gene is largely responsible for all three phenotypes. I'm not familiar with the data the suggests that handedness is linked to ear lobes, though. Rockpocket 06:18, 27 August 2009 (UTC)

you are right, Rockpocket --64.148.9.225 (talk) 11:22, 27 August 2009 (UTC)

One well-known linkage is the "ginger" genes, which provide for both red hair and uneven skin pigmentation (which means both freckles and a tendency towards getting sunburns). StuRat (talk) 12:27, 27 August 2009 (UTC)

As stated above, that should be gene (singular). The same gene is (largely) responsible for both phenotypes. Rockpocket 17:37, 27 August 2009 (UTC)

And of course don't forget the old malaria vs sickle cell anemia story. Aaadddaaammm (talk) 19:33, 27 August 2009 (UTC)

Dulce Base/Nightmare Hall/Underground Tunnels

I read some supposed UFO conspiracy reports online about how there are vast networks of underground tunnels all around the world that, for instance, one can travel from Wyoming to Italy in a matter of hours or something crazy like that. If that were remotely true, wouldn't something or someone pick up on some vibrations, noise, etc? Is it technologically possible to create something underground where it can be virtually undetected by the human population? --Reticuli88 (talk) 20:37, 26 August 2009 (UTC)

There are a couple of different concepts here: can you detect the construction (yes if you want to); and is anyone trying to (probably not). Seismologists might be keeping an ear out for such noise, but they have a lot of data to look at and might not be very interested. But the trouble with such conspiracy theories is that they're quick to dragoon whatever resources are required to make the conspiracy so: we presume that the national geological services of the major nations will ibein on the act. There are very many other practical objections to the existence of such infrastructure. I'm reasonably confident that our lizard-like overlords probably take British or American Airways like the rest of us. --Tagishsimon (talk) 21:03, 26 August 2009 (UTC)

There have been proposals for such things - but certainly they couldn't be constructed without someone noticing. Forget noise and vibration just consider the size of the hole: From Wyoming to Italy is about 8,000 km. If the tunnel was big enough to get some kind of a super-sonic high-speed train into it, it would need to be (let's say) 3meters in diameter. That's 200,000,000 cubic meters of dirt. About ten million truckloads. Where the heck do you think you're going to hide ten million truckloads of dirt and rock - and how are you going to prevent even one of the 10,000 truck drivers from blabbing something about it to the press? How would the spectacular cost of this get covered up? Why on earth would anyone want it anyway? If you are some kind of high-up world leader, get someone to strap you into an SR-71 Blackbird and at Mach 3.2 (about 4,000 kph) and you'll make the trip in almost exactly 2 hours. This is so unreasonable as to be hardly worth consideration! SteveBaker (talk) 22:05, 26 August 2009 (UTC)

"Where the heck do you think you're going to hide ten million truckloads of dirt and rock?" Come on, the aliens would just use their anti matter ray to shoot a hole all the way through. Just focus it to 3m and aim through the end points, simple ;) Vespine (talk) 22:23, 26 August 2009 (UTC)

I'm sorry - how foolish of me not to have considered that! So I guess these tunnels are there to relieve the wear and tear on their (evidently faster than light) flying saucers due to shipping people from Wyoming to their research center in Italy where they can 'probe' them. The solution is obvious when you approach this with a mind that's clear of all of these rigid preconceptions. SteveBaker (talk) 12:07, 27 August 2009 (UTC)

200,000,000 cubic meters of rock, at a density of about 2.5 g/cm², equates to 500,000,000,000 kg. Ignoring where you're going to get the 500,000,000,000 kg of antimatter from, the 1 trillion kg of mass would convert to 9×10²⁸Joules, or, at the sun's output of 3.846×10²⁶ W, equals about 3.9 minutes of total solar output. Or, for just the amount of sunlight striking the entire earth (1.740×10¹⁷ W), 16,400 years of total solar input to the earth. I'd imagine you'd detect the digging by the fact that your eyeballs had been boiled. Besides, if Hollywood movies taught us anything, you dispose of the dirt by shaking it out of your trouser cuffs on the baseball field. Just look for an infield in Wyoming that's 265 km higher than the surrounding area. -- 128.104.112.102 (talk) 17:05, 27 August 2009 (UTC)

That's the vactrain idea; right now it exists only in some very preliminary paper studies, and in the minds of conspiracy theorists. The prevailing conspiracy theory (if such thing can be said to exist) does indeed claim a vast underground network of such tunnels, centered at Area 51 and connecting military bases and government buildings around the US. Of course, like all conspiracy theories, absence of evidence is taken (by such folks) to be ironclad evidence of a cover-up, and whether the cost, noise, vibration, or excavation-effects of such a monumental undertaking would be evident isn't important - The Conspiracy has eyes and arms everywhere, and those who can see can soon be disposed of. Steve asks "Why on earth would anyone want it anyway?" - the answer is simple - the reptilian humanoids who really control the US government need it to travel around - presumably from the big flat rocks they have in Nevada (to keep warm) to the hatch they have under the Resolute desk, so as to order their puppet B.O. around, and then back to Nevada for a hearty dinner of gerbils a-la-mode. -- Finlay McWalter • Talk 23:53, 26 August 2009 (UTC)

Reality check: smuggler tunnels under the Palestine-Egypt border certainly exist and have been kept secret for a while. Unreality check: there is alleged to be an entrance between the paws of the Sphinx to an Underworld. Cuddlyable3 (talk) 09:11, 27 August 2009 (UTC)

An actual smuggler tunnel in Rafa, Egypt

Our Smuggling tunnel article has some surprising stories to tell of tunnels from Canada and Mexico into the USA - as well as details of the Gaza strip tunnels to which you refer. Gaza Strip smuggling tunnels has more info about the Egypt/Palestine tunnels. However: in the former article - talking about a tunnel between Canada and the USA: "Authorities were alerted when a neighbour noticed the large-scale construction work being undertaken ... On inspection, it was apparent that tons of construction material was entering, and piles of dirt were coming out." - and this was for a relatively short tunnel by UFO-nut standards. However, the Gaza-strip tunnels only have to be secret at one end - removing excavated material at the non-secret end is fairly trivial. The problem with alien/UFO tunnels is that (like the Canada/US tunnel) both ends have to remain secret. SteveBaker (talk) 12:07, 27 August 2009 (UTC)

Sodium Sulphate solubility

See Sodium sulfate specifically the solubility curve, can anyone explain the 'knee' in the graph? Specifically does anyone know (or want to guess) 'exactly' what the species are that predominate before and after the knee.. please..expert attention only..ie no Yahoo! answers.. 83.100.250.79 (talk) 21:55, 26 August 2009 (UTC)

The paragraph adjacent to the graph in that article has specific information about the weird shape. DMacks (talk) 22:25, 26 August 2009 (UTC)

This (?):

This nonconformity can be explained in terms of hydration, since 32.4 °C corresponds with the temperature at which the crystalline decahydrate (Glauber's salt) changes to give a sulfate liquid phase and an anhydrous solid phase.

Does that mean that the decahydrate is dissolving without dissociation ie as an ion pair surrounded by lots of H2O, or as clusters of (Na2SO4.nH2O)_m with a surface covered in -OH's ? (A bit like a sugar or polyol dissolving)

..And that these clusters break down above 35C

I didn't expect the decahydrate to survive per se on dissolution.

Is this a well known thing - I don't recognise the process I described above from any text book. Or is something else happening?83.100.250.79 (talk) 22:35, 26 August 2009 (UTC)

Or is all the above wrong? (the behaviour can be explained by the solid phase change of Glauber's salt)

Is it known what glauber's salt dissolves as ie as fully dissociated ions, or as the species I described above? I was thinking melting point depression - but that might not work -ie there might be the same number of species on dissolution despite being different species. Plus the glauber's salt would just come out of solution anyway. Vapor pressure I woundn't expect to work easily because the two components of the solution both have quite high vapour pressures..?

What to do?83.100.250.79 (talk) 23:53, 26 August 2009 (UTC)

Cerium Sulphate solubility

(edited once) Also the solubility behaviour of Cerium (3) sulphate with temperature - it decreases apparently? How can this be explained - anyone know? Specifically an theoretical model that explains this behaviour (it seems a no brainer that entropy will increase on dissolution - yet it appears that may be wrong?) Can it be that the high charge of Ce3+ induces medium range order into the solvent - decreasing entropy- anyone know about this sort of thing? 83.100.250.79 (talk) 21:34, 26 August 2009 (UTC)

Maxwwell's Demon

In the thought experiment, known as Maxwell's demon, there exists a hypothetical "demon" that guards a trapdoor between two containers filled with gases at equal temperatures. By allowing fast molecules through the trapdoor in only one direction and only slow molecules in the other direction, the demon raises the temperature of one gas and lowers the temperature of the other, apparently violating the Second Law of Thermodynamics.

I know this is only a thought experiment but even so shouldn't there exist a degree of reality if the results are to be taken seriously? I don't understand how this should work if the temperature of the gas is the same in both containers the speed of the molecules would also be the same? OK there is bound to be one molecules speed that would be faster or slower but then the experiment could not have started with both containers of equal temperatures?

I'm not an expert in these things so keep it light if that's possible

Thanks —Preceding unsigned comment added by Makemineateaplease (talk • contribs) 21:48, 26 August 2009 (UTC)

Saying that the temperatures are the same only means that the average speeds are the same. There is always a range of speeds. Imagine you have a pool table with a few dozen balls on it, and you shake the table: would you expect all the balls, as they bounce back and forth, to always move at exactly the same speed as each other? —Preceding unsigned comment added by Looie496 (talk • contribs)

Temperature is a statistical result for a large number of molecules, and there are lots of faster- and slower-than-average molecules. In fact, virtually none of them are actually the average value. Rather, there is a Maxwell–Boltzmann distribution (yup, same "Maxwell" guy:) of values (the math can be pretty dense, but the graph in that section is a good executive summary of the result that relates to your question). DMacks (talk) 21:59, 26 August 2009 (UTC)

Good one. Thank you. —Preceding unsigned comment added by Makemineateaplease (talk • contribs) 22:19, 26 August 2009 (UTC)

Incidentally, Maxwell's deamon only seems to break the 2nd law when you think about it at a superficial level. In reality, it can be shown that the energy it has to expend to measure the speed of the atoms and the effort to open and shut the trap-door cause it to consume more energy than it creates - hence it no more violates the 2nd law than does your refrigerator. SteveBaker (talk) 11:54, 27 August 2009 (UTC)

The 2nd law is how you show that. --Tango (talk) 16:15, 27 August 2009 (UTC)

That argument always seemed like begging the question to me: "A:Does the 2nd law *always* hold? ... how about a situation like Maxwell's demon? B:No. Maxwell's demon can't work because it violates the 2nd law." - Great, we can prove that the second law isn't broken by Maxwell's demon if we assume that the second law is valid when analyzing Maxwell's demon. -- 128.104.112.102 (talk) 16:47, 27 August 2009 (UTC)

You can't show by direct empirical observation that there is no possible way to implement Maxwell's Demon. The only way is to show that it violates a law that we have lots of empirical evidence for. --Tango (talk) 17:57, 27 August 2009 (UTC)

Tango and 128 were right and Steve was wrong, or at least misleading. The historical sequence is:

1. (1824) I have invented the 2nd law of thermodynamics: here it is. Can you falsify it?
2. (1867) I have invented Maxwell's demon. I can't build one, but there seems no reason it would be impossible, and it falsifies the 2nd law. Can you falsify my claim?
3. (1929) Yes! The demon must consume energy, so if it is possible to build one, the law can still be correct if Steve's statement about energy is also right. Therefore the 2nd law is not falsified.

Today we believe that the 2nd law is true, so from that point of view we can use it to prove things about Maxwell's demon, but only from that point of view. --Anonymous, 22:38 UTC, August 27, 2009.

If Wikipedia has multiple server sites, where is the real encyclopedia image (the one that gets edited) currently?

One can imagine all kinds of possible weird speed of light-related edits due to c, the speed of light in fiber optic cable, the different server continents, near-simultaneous edits to the same section of the same article, and the already irrational nature of relativity. What if the 3,000,000th article was created by two different people in two different continents, had the same name, but different text, the first bits arrived in Florida within 3 milliseconds of each other, and then the server synchronized. The later article had a closer sending PC, but longer fiber-optic path. The first PC to send bits had slower internet access so it wasn't finished till the other already did. The PCs were very near one other server site, and far from the other. One article version consisted of only a curse word repeated and was speedy deleted by a bot in milliseconds. Then the other was only barely above auto-bot deletion and deleted by a human doing recent changes patrol. Both PCs sent the edits in the form of a fast radio signal to their own fast private servers very close, but only to some of the Wikiservers. They automatically decoded them and made the same edits on local PCs held by fellow paradox creating comrades with senses of humor. And as we all know, if they do this fast enough, these will affect the servers before the ones on the Internet, because electromagnetic waves travel 200 million miles an hour faster through atmosphere than through glass fibers. They also did this with geostationary satellite internet connections. Another unrelated article arrived at Florida in the intervening time. Or maybe it was two other copies of 3,000,000A and B but they were encyclopedic ones. Okay, I'll stop now. Sagittarian Milky Way (talk) 22:21, 26 August 2009 (UTC)

I think I drifted off half way through. You measure the thing at one place (e.g. the nominated master database) based on one event (e.g. the completion of a database append operation). You do not concern yourself too much with the manifold other ways of considering the matter lest you go mad and start posting completely inarticulate queries about the issue. --Tagishsimon (talk) 22:34, 26 August 2009 (UTC)

If there are/is more than one 'main version' then I think they must converse changes to one another - otherwise there would be serious issues when editing, which I believe Sag..MilkyWay is talking about. Often I see a delay when submitting... An auxillary question would be - if there is/are more than one main server - how much bandwidth do they use on average.?83.100.250.79 (talk) 22:41, 26 August 2009 (UTC)

You might read federated database. That article explains the methodology of the computer system architecture that Wikipedia (and in fact, most other large data processing systems) use. The distribution of data over many different computers follows deterministic algorithms for resolving conflicts. Somewhere, somehow, there is a serialization process which maps the parallel processing task (executed on many computers, possibly geographically dispersed) into a serial-order-equivalent task - this is a basic tenet of modern parallel computing algorithms. You might also want to read Help:Edit conflict, which describes the result when two "simultaneous" edits cannot be automatically resolved by the algorithm. One or both edits fails to commit to the database, and it is up to the humans to either retry or abandon the edit(s). You might also be interested in data hazard, which formally defines (from the standpoint of computer science) the situation you have described. The computer can easily recognize that you have performed a "Write After Write" hazard - and it may choose from a wide variety of recovery methods to properly handle this. (Most commonly, the second write will be rolled back). Note that in the formal definitions of data management, a "delete" is the same as a "write", as they both involve a committed modification of data. Nimur (talk) 22:46, 26 August 2009 (UTC)

Okay, conflicting parts simply don't become part of the database, then. It always boils down to an edit conflict. It is just funny if it could be possible to have slightly disparate versions floating around, and there really is no absolute time frame of reference in relativity and then the servers have to synchronize. How often do they sync? I've seen changes to widely used templates that took 20 minutes to cascade down, maybe this is unrelated to synchronize frequency? Sligthly drunk. Usually this is a thing for the Internet Oracle, but I really wanted to know. Sagittarian Milky Way (talk) 23:27, 26 August 2009 (UTC)

There's only one server, but that's masked by degrees of caching. The database server has several read-only slaves, which try to replicate it in real time, but sometimes there's a lag (it's rarely more than 30 seconds). Then there's memcached caching, which caches pre-rendered(to HTML) fragments of articles. And then (mostly for signed-out visitors) there's squid webcaches in front of the web servers. So for editors there's a single definitive copy of the encyclopedia, but for visitors it's always a delayed (and often version-skewed) copy; visitors overwhelmingly don't know and don't care that they're lot looking at the absolute latest thing, but obviously for editors that's imperative. -- Finlay McWalter • Talk 23:37, 26 August 2009 (UTC)

And then there are templates, update to which must be applied to each instance of use of the template (that is not subst'd into the page); the amount of time to do the updates will depend in large part on the number of articles using the template, and the size of the job queue. Slightly drunk. Excellent. --Tagishsimon (talk) 23:49, 26 August 2009 (UTC)

The other issue is that the conversion of pages from the internal Wiki markup language to HTML+JavaScript is cached so that the task doesn't have to be repeated over and over when the same page is viewed by many people in quick succession. That process can sometimes lag the edit queue - so you make a change - and it's accepted without an edit conflict - but it takes a few seconds for that to be reflected on the viewable page. SteveBaker (talk) 11:50, 27 August 2009 (UTC)

August 27

Canine kidney failure

I just heard a story on the television about an old dog that died of kidney failure while locked in a car during 90+ºF heat. I can understand a dog dying after several hours in such a situation, but kidney failure? Unless the dog already had nephrological issues, how would the heat kill it in that way before killing it in some other way? Nyttend (talk) 03:26, 27 August 2009 (UTC)

A quick google search shows up a bunch of links, especially this one. Essentially, the extreme over-heating is going to cause massive tissue damage, and tissues that are most active (liver, brain) are going to go first. Kidneys are pretty active, and rely on very specific chemical reactions and fluid balances to function properly. In the heat the concentration of specific molecules in the blood would've been changed drastically, and could easily affect kidney function. If the kidneys hadn't failed something else probably would've soon. I can even imagine that since the brain and liver get so much blood compared to other portions of the body, they might survive (albeit completely irreparably damaged) long enough to make the cause of death the kidneys. ~ Amory (user • talk • contribs) 05:43, 27 August 2009 (UTC)

I cannot see how a dog can die from kidney failure after such a short time with out previous aetiology. Dying from kidney failure is not a sudden death but is caused by the accumulation of fluids and waste products over an extended period of days rather than hours. It is of course quite possible that this dog did have previous kidney problems and the extreme heating was the final straw. From my veterinary experience I would suggest that the dogs brain became overheated, it was not able to oxygenate properly and this caused heat prostration and death. 86.4.181.14 (talk) 07:25, 27 August 2009 (UTC)

Hmm Nyttend are you sure the storysaid the dog died of kidney failure while locked in the car? dogs.suite101.com/article.cfm/dogs_and_heat_stroke (spam blacklisted) and [9] and Amory's ref all note that kidney failure is something that dogs should be monitored for after suffering heatstroke so it's entirely plausible the dog died from kidney failure primarily as the result of being locked in the car even if it didn't die while in the car Nil Einne (talk) 08:31, 27 August 2009 (UTC)

Kidney failure is indeed the most likely mode of death. In the extreme heat, the dog attempts homeostasis of temperature by sweating and panting. This leads to dehydration and hypovolaemia. Axl ¤ [Talk] 10:47, 27 August 2009 (UTC)

It appears that the dog died hours later; here is the story from a newspaper website. I thought that the TV broadcast said in the car, but either it was wrong or (more likely) I remembered it wrongly. Nyttend (talk) 17:06, 27 August 2009 (UTC)

A380 and An-124

According to List of large aircraft An-124 is bigger than A380. According to articles, A380 is longer, has bigger wingspan, bigger max takeoff weight and so on, so how can an-124 be bigger? —Preceding unsigned comment added by 195.255.135.235 (talk) 08:39, 27 August 2009 (UTC)

A380? An-124 eats them for breakfast! --antilived^{T | C | G} 08:48, 27 August 2009 (UTC)

You should probably bring this up on the Talk: page of List of large aircraft. If you're sure of your facts, you can Be Bold and just go fix it yourself. SteveBaker (talk) 11:41, 27 August 2009 (UTC)

A380 is fairly new. Could be that no one has gotten around to updating that list. Also, not sure but are there any specific criteria defining "large"?

Looking at our article Antonov An-124, it seems that the An-124 was the largest production aircraft in the world at the time that it was introduced. It may also be the second-largest mass-produced aircraft (after the A380). Note that the Antonov An-225 is larger than both, but only one was ever completed. (Our article indicates that a second mothballed airframe is being refurbished, and is due to fly in 2010.) If someone wants to update our last, they should go ahead. TenOfAllTrades(talk) 14:03, 27 August 2009 (UTC)

I think you missread the article. It actually claims that the Antonov An-225 is the largest airplane, while A380 is the second largest. The An-124 is one line above the An-225 which may explain the mistake. 71.203.58.148 (talk) 01:13, 28 August 2009 (UTC)

Re-OP: Is it true that using known data with known formulas is not synthesis?

New planets that are being found are being referred to as being in or out of their parent star's "Habitable zone," Which basically refers to the distance range that water would be liquid. But the concept is being used to insinuate more than water being present, it is used to suggest these systems could have life.
That is easy to accept if you ignore all the other factors involved in the process, and believe Water=Life. As there are many factors other than irradiances that would keep H₂O from being liquid,(Mass/cohesion, Abundance of elements/Metalicity, Excessive X-rays/M-type star, Amount of CO₂) it is a little deceptive and irresponsible to make the suggestion to people that a planet may have life because it is X distance from its star. The idea of a habitable zone planet is flawed as it is, but I think a "Solar Constant" comparison between Earth and other planets is of value in-of-itself. Simply as a comparison of heat, a more direct comparison even than mass (less insuating than a mass), as heat does not itself equal life. In other words less speculative. (note: Irradiance, Insolation, and Solar Constant are synonymous.)

Basic Insolation Figures Chart

Planet Distance	Insolation (W/m2)	% of Earth's.
55 Cnc f Apastron Flux	380.136	27.74%
Mars' Aphelion Flux	494.00	36.06%
55 Cnc f Average Flux	547.395	39.99%
Mars' Average Flux	590.589	43.11%
Mars' Perihelion Flux	718.545	52.45%
55 Cnc f Periastron Flux	855.305	62.4%
HD 108874 b Apastron Flux	1234.655	90.12%
Earth's Aphelion Flux	1,321.544	96.74%
Earth's Average Flux	1,366.079	100.00%
HD 108874 b Average Flux	1413.557	103.18%
Earth's Perihelion Flux	1,412.903	103.43%
HD 108874 b Periastron Flux	1634.359	119.30%
Venus' Aphelion Flux	2,585.411	188.72%
Venus' Average Flux	2,620.693	191.30%
Venus' Perihelion Flux	2,656.70	193.93%
Gliese 581 c Apastron Flux	3,619.829	264.97%
Gliese 581 c Average Flux	4,870.841	356.56%
Gliese 581 c Periastron Flux	6,903.119	505.32%

In a lot of cases the Radius and Effective temperature of a parent star is known, or can be calculated using the formulas at the Luminosity article. The formula that calculates luminosity from Radius and Temperature and the formaula that calculates luminosity from distance and insolation are obviously Equal for the Sun and Earth data. and basic algebra yields:

• $L=4\pi R^{2}\sigma T^{4}\,$ ...and
• $L=4\pi d^{2}\ f\,$ ...therefore,
• $4\pi R^{2}\sigma T^{4}\ =4\pi d^{2}\ f\,$ ... and
• $R^{2}\sigma T^{4}\ =d^{2}\ f\,$
• $\ f\ =(R^{2}\sigma T^{4}\,)/d^{2}$
  

code for Earth at Perihelion: $f_{p}={\frac {((6.955\times 10^{8})^{2})\times (5.67051\times 10^{-8})\times (5778^{4})}{((1-(1\times 0.016710219))\times 149597876600)^{2}}}=1,412.903\ W/m^{2}$

code for Gliese 581 c at Periastron: $f_{p}={\frac {((0.38\times 6.955\times 10^{8})^{2})\times (5.67051\times 10^{-8})\times (3480^{4})}{((0.073-(0.073\times 0.16))\times 149597876600)^{2}}}=6.9\times 10^{3}\ W/m^{2}$

Having said that I am not saying this should go directly into an article.
But I do remember reading a debate where it was pointed out that using known data with known formulas is not synthesis.
In a lot of cases scientists are going as far as to speculate on on effective temperature and surface temperatures, using this albedo or that emissivity,
but on the other hand if the algebra is correct then the insolation is closer to fact. Definitely less misleading than saying there may be life on Gliese 581 c:
(see Than, Ker (2007-04-24). "Major Discovery: New Planet Could Harbor Water and Life". www.space.com [10] )

${\frac {Gl\ 581\ c\ Periastron\ Insolation}{Earth's\ Solar\ Constant}}=$ ${\frac {6.9\times 10^{3}\ W/m^{2}}{1,366.079\ W/m^{2}}}=505\%$

A few published formulas for comparison

$\sigma \cdot T_{\mathrm {p} }^{4}={\frac {\sigma \cdot T_{\ast }^{4}}{4\pi \cdot d^{2}}}\cdot {\frac {4\pi \cdot R_{\ast }^{2}}{4\pi \cdot R_{\mathrm {p} }^{2}}}\cdot \pi \cdot R_{\mathrm {p} }^{2}(1-A_{\mathrm {p} })$

$T_{\mathrm {p} }=T_{\ast }\left[\left({\frac {R_{\ast }}{d}}\right)^{2}{\frac {1-A_{\mathrm {p} }}{4}}\right]^{\frac {1}{4}}$

$T_{\mathrm {p} }=\left({\frac {L(1-A)}{16\pi \sigma D^{2}}}\right)^{\tfrac {1}{4}}$

These formulas have been published and used by scientist to suggest surface effective temperatures of terrestrial extrasolar planets. Would it be incorrect to use the same formulas for other extra solar planets where scientists have not bothered to publish these figures because (I suspect) they are not as reputation enhancing. Similarly, No one is likely to use these same formulas published by scientists to calculate the effective surface temperature of a extrasolar Gas Giant, but this overlooks potential habitable moons of the same Gas Giants. I know the difference between published speculation and unpublished fact, and I perfer the later and would like to know if I am alone in this or is it true that using known data with known formulas is not synthesis? GabrielVelasquez (talk) 07:40, 27 August 2009 (UTC)

It's starting to sound like you're asking us a question about the application of Wikipedia policy. Your best bet is to bring the matter up on the talk page of the article in question, or to file a request for comment to bring in outside editors. TenOfAllTrades(talk) 12:14, 27 August 2009 (UTC)

Yes Wikipedia:Synthesis redirects to Wikipedia:No original research, if your question is about policy probably that talk page, the help desk etc maybe a good place to ask. However I see no reason not to deal with it here as it seems easy to answer.

However. Without reading your entire question fully, it seems you are simply asking

"it is true that using known data with known formulas is not synthesis?"

I'm afraid the answer is "it is synthesis", technically. No question about it. Only in the most trivial cases can there be a get out clause eg covert degrees to fahrenheit.

83.100.250.79 (talk) 13:32, 27 August 2009 (UTC)

I think the rule of thumb is that if anybody expresses a "reasonable doubt" about what you're doing, then it is synthesis. Given the complexity of your presentation, I think it would be reasonable for people to express doubts about whether you got all the factors right. Looie496 (talk) 16:01, 27 August 2009 (UTC)

I've got to disagree with that - calculations producing unpublished results is always synthesis (excluding an absolutely known proceedure such as found in pure mathematics), whether or not there is any disagreement about the results. In the case of the above equations it would be bordering on original research.

Presenting a single example as a demonstration of the formula would probably be acceptable, generating an entire table would not.83.100.250.79 (talk) 17:16, 27 August 2009 (UTC)

This is a principle that sounds good but leads to absurdities -- for example, is it synthesis to say Jupiter is over twice as far from the Sun as Earth, giving a table of distances as reference? Looie496 (talk) 17:34, 27 August 2009 (UTC)

That doesn't require an equation - I (and the question poster) was talking about deriving new figures from published data and equations. In your example the tables of distance already exist. 83.100.250.79 (talk) 18:39, 27 August 2009 (UTC)

You may be conflating synthesis with analysis.83.100.250.79 (talk) 19:14, 27 August 2009 (UTC)

Working out whether a planet is in the "habitable zone" is relatively easy, working out all the other things you mention are much harder. That is why the habitable zone is used as a rule of thumb to give an idea of how to prioritise further investigations. Also, it is worth remembering that whenever we say "life" in this context we mean "life as we know it". There could be life built around very different principles than that on Earth that could exist in very different environments. (Work on other kinds of life has shown that our kind seems to work best out of all the kinds we have considered, but that doesn't rule out other kinds either being less efficient that ours or of a kind we haven't considered.) --Tango (talk) 16:22, 27 August 2009 (UTC)

To cut a long story short we have an article Synthesis, the first paragraph explains what it is. 83.100.250.79 (talk) 19:14, 27 August 2009 (UTC)

It's very simple. $1/planetAU^{2}*luminosity$ is the insolation the planet gets compared to Earth. If you want W/m² multiply that by Earth's value. Luminosity in solar units is found in the article of every planet's parent star so you don't have to originally recalculate it every time. (because the luminosity does not eminate from a single point, if the apparent angular size of the star at the planet is really large this might cause some problem, however if you have to worry about that – that planet ain't habitable.)

And albedo with the greenhouse effect are really important. Without one, Venus gets 2x insolation and is 2x as reflective, so it would be frigid! Sagittarian Milky Way (talk) 19:36, 27 August 2009 (UTC)

One of the crucial elements that you are forgetting is that known formula is subject to scientific dispute. Empirical formulas have limited applicability to problems. The job of an experimental scientist is to perform original research in deciding which formulation is relevant to a particular problem. When you make the claim that it is a "known formula", you are asserting a scientific truth, without attribution to a reliable source, that this is the correct equation that should be applied to this problem. Whether the result of that formula is trivial computation or not, you have still synthesized the scientific claim that this formulation should be used. That is the realm of research science; encyclopedias should serve to document what other scientists have agreed is the best formulation to apply. Nimur (talk) 22:00, 27 August 2009 (UTC)

You are mistaken, and ignored relevant parts of my question to make this nonsensical comment: I am not making that claim, the equilibrium temperature formulas have already been published and used the same way, Just check the references at the Gliese 581 c article, I am just extending their use to other planets. Obviously when I say known formulas I am refering to formulas used the same way not in a new way or unverified way so the use of the formulas is not synthesis by a new or different use of them.

Taken from an older version of Gliese 581 c

This is taken from an older version of Gliese 581 c and it was referenced: — The temperature estimate is arrived at by equating the power absorbed by the planet and the power radiated by it as a result of it being at a given temperature. This assumes the planet is in thermodynamic equilibrium. To calculate the amount of power absorbed by the planet, consider that the star radiates a certain amount of power. The power radiated from the star is termed its luminosity, given the symbol L. Assuming the star radiates isotropically, at a given distance D from the star, this power is spread out over the surface of a sphere of radius D. This gives the flux F of energy at the planet: $F={\frac {L}{4\pi D^{2}}}$ The power absorbed Pabs is the flux multiplied by the cross sectional area presented by the planet. For a spherical planet, the cross-sectional area is a disk with the same radius r as the planet. We also allow for the fact that the planet may reflect a certain fraction of the incident radiation by inserting a term called the albedo A. If the albedo is 1, then it reflects all incident radiation (absorbs none). If the albedo is 0, all incident radiation is absorbed. So: $P_{abs}={\frac {L\pi r^{2}(1-A)}{4\pi D^{2}}}={\frac {Lr^{2}(1-A)}{4D^{2}}}$ The next stage is to calculate the amount of power radiated by the planet. The planet is assumed to be a spherical black body of temperature T, and thus obeys the Stefan-Boltzmann law. The power radiated by the planet is thus: $P_{rad}=4\pi r^{2}\sigma T^{4}$ The absorbed and radiated powers can then be equated and rearranged to solve for T, the temperature of the planet: $T=\left({\frac {L(1-A)}{16\pi \sigma D^{2}}}\right)^{\tfrac {1}{4}}$

GabrielVelasquez (talk) 09:22, 29 August 2009 (UTC)

Reference Desk Organization

Is there a better way we could set up the reference desk pages? I've noticed several annoyances.

1. I can not track responses to a particular question. 2. When someone replies to someone else's response while there are multiple further responses it's very difficult to determine this has occurred with out rereading every post every time. This is a bit difficult to explain but it looks like this:

- Question 7 pm

- Reply 1 8 pm
  - Reply to Reply 1 9 pm
- Reply 2 8:30 pm
- Reply 3 10 pm
etc...

How can I tell there's been a reply to reply 1 without reading everything over again?

3. Topics remain on the reference page for quite some time but almost all the replies occur for questions asked in the past 2 days. Is there a way to reorder the format to encourage discussion of unanswered, older questions?

Finally, while there may be some back discussion page I believe it is the community's interest to have this posted for everyone's consideration as most people who use the reference desk read this page.

Your thoughts? TheFutureAwaits (talk) 10:35, 27 August 2009 (UTC)

{{Unanswered}}

I found this just today ironically, and removed mine minutes before you posted your question. It only indirectly addresses your issue, but I thought you would find interesting anyway. GabrielVelasquez (talk) 10:41, 27 August 2009 (UTC)

This type of question (and subsequent response) do not belong here. Discussions about the RD itself belong on the RD Talk: page which you can reach by clicking the "discussion" tab at the top of this page. SteveBaker (talk) 11:39, 27 August 2009 (UTC)

The formatting you describe sounds like it follows the guidelines at Wikipedia:Talk page, which you can discuss at Wikipedia talk:Talk page AlmostReadytoFly (talk) 12:17, 27 August 2009 (UTC)

Yes but the problem is no one looks at those pages (looking at the history there were 7-10 edits a day on the discussion page versus hundreds for the actual desk). I'm trying to get feedback from the general users of this page on whether they agree with my points and if there are ways we could improve it. If I posted this on the discussion page it would be largely ignored.

Also I consider this a serious issue that merits discussion on the main page since the page in its current form has some fundamental flaws. I wouldn't post criticisms within an actual article but given the reference desk is all about asking questions and I'm trying to get feedback I think it merits real consideration. TheFutureAwaits (talk) 13:41, 27 August 2009 (UTC)

Few edits doesn't mean no one watches the page. The vast majority of active contributors to the RD, and even a few who don't contribute to the RD much anymore are active on the talk page (I know because I've seen them!). Also you appear to have missed the whole religion desk controversy which was hardly lacking in edits. And BTW, by posting this on the science desk (although it has little to do with science) you're missing all those who don't check out the Science desk. Also this question will disappear from here in about 7 days and as you yourself have claimed will be way up at the top in a few days and likely missed by many. If you expect a major change like this to occur in 7 days, you're seriously mistaken. BTW, while you may be right that your discussion will be largely ignored on the talk page (because part of what your discussing is part of wider policy which many people agree with and the other part doesn't really have a solution) as has already been demonstrated your discussion is going to be even more ignored here. Finally this is not the main page, but the place for asking factual questions. We have a dedicate page for discussing ways to improve the reference desk which for the many reasons I've already mentioned is a far better place to discuss this. Nil Einne (talk) 19:15, 27 August 2009 (UTC)

P.S. I commented out the template as this issue has been resolved Nil Einne (talk) 19:18, 27 August 2009 (UTC)

Repeated static shocks.

Is there any known health issue surrounding repeated static shocks to some particular part of the body (the tip of a finger, for example)? Suppose someone gets 'zapped' by their car door handle several times a day - every single day for many years? SteveBaker (talk) 11:45, 27 August 2009 (UTC)

(Not a complete answer) I used to work in a job where I had to wrap large pallets with industrial cling film - the process was semi automatic - the pallet went on a sort of turntable - like a huge record player... Anyway the unrolling of the 'cling film' produced massive amounts of static electricity (near van der graff levels) - I was constantly being zapped on the forearms (like 5 times second for ~5 hrs a day)- for a few months. I'm still alive!

More reliably I don't remember being given any health and safety warnings or instructions - so I guess it's not considered a risk - that was more than 10 years ago. I would guess that if there is any doubt then the Health and Safety Executive (UK) or the equivalent organisation in another country will have info on it. So that would be a place to look. thanks for listening83.100.250.79 (talk) 13:21, 27 August 2009 (UTC)

Apparently the International Electro Technical Commission (what? no article?) states that a single transient or capacitive discharge, as is the case with static electricity, requires energy in excess of 5 Joules (5000mJ) to produce a direct serious risk to health. As for long term effects, according to the Oregon Occupational Safety and Health Administration, "There are no specific standards for static electricity" which likely means there is no data on adverse effects. Rockpocket 17:32, 27 August 2009 (UTC)

Try International Electrotechnical Commission. --Heron (talk) 20:25, 27 August 2009 (UTC)

Ah, Damn you, Heron! ;) Rockpocket 00:54, 28 August 2009 (UTC)

Sorted. --Tagishsimon (talk) 01:00, 28 August 2009 (UTC)

OT but maybe wear gloves when handling your MINI? Perhaps one of these? P.S. Happy belated MINIversary Nil Einne (talk) 18:44, 27 August 2009 (UTC)

It's not a MINI problem - my car is very well-behaved static-electricity-wise. The problem is at work where they replaced the front doors to our office suite with sexxy glass doors with big steel handles - and everyone is getting zapped by them. But it's not really a problem - that just triggered my curiosity. P.S It's not really a "belated" MINIversary - we're celebrating the whole year long! If you're in the Austin/Round Rock, Texas area next month, come along to the Texas "All British Car Day". SteveBaker (talk) 00:04, 28 August 2009 (UTC)

There are sprays (or even some clothes dryer antistatic sheets) which can provide a subtle conductive path to drain off the charge. Edison (talk) 02:54, 28 August 2009 (UTC)

I'd ask the company to have that door checked very thoroughly. It could very likely be that an electric door lock has some creeping current or a short to the door handle. 71.236.26.74 (talk) 04:08, 28 August 2009 (UTC)

When do Baby's start going to the toilet?

According to my mother, when i was born the nurse held me and the first thing i did was to urinate on her! this got me wondering.. when do baby's start peeing and pooing? Does this first occur in the womb or what? 80.47.174.113 (talk) 13:12, 27 August 2009 (UTC)

Amniotic fluid is predominantly fetal urine. For 'number two', see meconium. TenOfAllTrades(talk) 13:52, 27 August 2009 (UTC)

What? I've been soaking in my own urine for the first 9 months of my life?!? Why isn't this little factoid more well known? --antilived^{T | C | G} 19:05, 27 August 2009 (UTC)

Do babies keep their mouths shut for 9 months, or just cough up a lot of piss when they are born? I see various flaws with this set up.83.100.250.79 (talk) —Preceding undated comment added 19:19, 27 August 2009 (UTC).

They swallow the amniotic fluid during gestation. Amniotic fluid is actually over 98% water, with the remainder consisting of fetal cells, urea, creatinine, bile, hormones and various elecrolytes. It circulates through the the stomach and lungs of the fetus and turns over quite rapidly. Rockpocket 19:24, 27 August 2009 (UTC)

Well, technically, fresh urine is sterile and not really bad for you at all. It's only if it is left in air that bacteria gets into it and spoils it. Aren't there people who even claim that drinking it has health benfits? That's something I'm not willing to google from work ;) Vespine (talk) 23:54, 27 August 2009 (UTC)

No need, the 'paedia has it covered: Urophagia and Urine therapy Rockpocket 01:14, 28 August 2009 (UTC)

Brand new babies do not smell like pee. I call BS on this. Edison (talk) 02:52, 28 August 2009 (UTC)

And why are you so sure of this fact?!! Have you been peeing on babies?? hahah Vespine (talk) 00:40, 31 August 2009 (UTC)

You are working under the (mistaken) assumption that fetal pee smells like post-natal pee. It doesn't. The amount of urea in amniotic fluid is much less than you would typically find in urine. This isn't at all controversial, a cursory goodle search will reveal as much. Rockpocket 05:52, 28 August 2009 (UTC)

Even I know that babies receive a filtered food supply through the placenta - so a lot of the stuff that is extracted by the kidneys usually will be extracted by the mothers kidneys - it's not clear to me the extent of functioning of a foetal kidneys 83.100.250.79 (talk) 10:57, 28 August 2009 (UTC)

I believe human kidneys become functional around 12 weeks, urea is certainly found in AF around then. If there are fetal kidney defects, the fetus may not produce enough urine. The result of this is a reduced amniotic fluid volume which, in turn, results in respiratory defects in the newborn (since the AF is important for lung and trachea development). Rockpocket 17:01, 28 August 2009 (UTC)

"Aren't there people who even claim that drinking it has health benfits?" -- See Borat. 98.234.126.251 (talk) 06:30, 28 August 2009 (UTC)

No doubt there are, but "Borat" is a fictional character...83.100.250.79 (talk) 10:59, 28 August 2009 (UTC)

Choking

If you accidently choked by drinking large amounts of water, from a glass of water, but was able to recover say 10 minutes without blacking out, what happens to the liquid in your lungs? Does it get absorbed into the body somehow? And why when you really choke on something, and after 3 minutes of having a coughing fit and able to recover, does it seem impossible to keep your eyes open? --Reticuli88 (talk) 13:34, 27 August 2009 (UTC)

When you cough, you are moving liquid/mucous up into your throat. If you accidentally inhaled liquid into your lungs, unless there is a lot of it you would cough it into your throat and swallow it without noticing. If there was a lot you would cough it into your mouth most likely. As far as keeping your eyes open after a coughing fit, I have never had that problem myself so I am not sure. The Seeker 4 Talk 16:24, 27 August 2009 (UTC)

Sorry to be a pest on this spelling peeve, but I think a lot of folks just don't know this: mucous is an adjective, as in the phrase mucous membrane. The word you want is mucus, with no o. Same remarks apply to callus (a bit of thickened skin) and callous (an adjective, usually metaphorical). --Trovatore (talk) 22:18, 27 August 2009 (UTC)

I was recently watching a show we have about surf life savers and they rescued a girl who had nearly drowned. Even though she hadn't blacked out and appeared fine after coughing up some water they kept her under observation for a while because they claimed you can still suffer Secondary drowning. Vespine (talk) 00:06, 28 August 2009 (UTC)

How long till unmanned plants stop?

For a thing I am writing, I'd need to know the following. If the whole humanity were to disappear suddenly, how long would power plants work? Are there systems that would shut them down immediately? Would some of them keep working for hours/days? And what is the answer for other infrastructures (water and gas networks, say)? And am I right in thinking that communication and GPS satellites would keep working for a while, or is there some kind of necessary remote maintenance? Thanks, Goochelaar (talk) 14:04, 27 August 2009 (UTC)

See this article by the Straight Dope : "When the zombies take over, how long till the electricity fails?" It's an interesting read. (It is, however, North America specific.)APL (talk) 14:09, 27 August 2009 (UTC)

Hydroelectric, wind and solar plants would run a long time. Coal plants would run out of fuel fairly quickly (less then 48 hours) unless something happened to put them into automatic shutdown sooner. Not sure on nuclear, but if your power runs too long and people suddenly disappeared, then a large amount of fires might break out quickly from people who had food cooking on their stove and such. Googlemeister (talk) 15:05, 27 August 2009 (UTC)

The thrust of the article I linked seemed to be that unless specific steps were taken to allow things to fail gracefully, the whole system would come down almost immediately. Many power-plants would hit minor, routine difficulties and without operator intervention would be automatically shut down, this would screw up the whole grid, and that would in turn screw up even those power plants that would otherwise last a long time. APL (talk) 16:23, 27 August 2009 (UTC)

Having been involved in grid operation, I doubt that everything would immediately shut down. The grid would sectionalize, but it is full of automatic systems which are programmed to keep alive or reliven every section that is capable of withstanding system voltage. Hydro generation could go on a very long time. Solar and wind systems could automatically remain alive or resynchronize to a grid. Some such systems are designed to operate independently of the grid. Edison (talk) 02:51, 28 August 2009 (UTC)

Thanks a lot for the "Straight Dope" article (it exactly answers to most of my curiosities about power plants!) and the further remarks. Any idea about telecommunication satellites? Thanks, Goochelaar (talk) 17:01, 28 August 2009 (UTC)

Using antennas

I have a circuit which generates some sine wave. I have to transmit this signal by some antenna. May be I will use a loop antenna. Can anybody please tell me how to do that ? —Preceding unsigned comment added by 218.248.80.114 (talk) 15:24, 27 August 2009 (UTC)

Connecting the antenna to the circuit's output tap is the best way to couple the circuit oscillation into a propagating radio wave. In fact, the circuit is transmitting already - just weakly. The antenna will help match the impedance of the circuit to the surrounding air, and may provide directionality for the transmission. What frequency is the sine wave? What power is output (you might want or need a power amplifier). What do you plan to do to detect the signal? If you can answer these, you can narrow down your options significantly; otherwise your question is so broad that it's basically unanswerable. Nimur (talk) 15:49, 27 August 2009 (UTC)

Well the signal is probably 10 Mhz. The signal is to be recieved in a room 32 x 20 feet with recieving antennas at the corners. The reception antenna will be dipole type. Reception circuit is to be designed too. —Preceding unsigned comment added by 218.248.80.114 (talk) 16:19, 27 August 2009 (UTC)

HF is a tough spectrum. You either need large antennas (e.g. 10 meters), or fancy tricks you can't afford. However, you can get away with a crummy dipole whip antenna if you spend a little more effort on your power amplifier at the transmitter, and getting your receiver properly tuned (a nice low noise amplifier will help there, also). Are you simply transmitting a continous tone, or do you have any information modulated on this 10MHz signal? Are you trying to do position sensing? If so, you'll need some clock synchronization (there are a lot of ways to do this). Nimur (talk) 17:11, 27 August 2009 (UTC)

Well in that case i can in go to lower frequencies in the khz range. I will be sending a continuous tone and for position sensing of the sender by the receiver. Main consideration is to make the render antenna small and have low power consumption. Thanks.

Lower frequency will make it worse! You'll need an antenna thousands of meters long if you want to transmit effectively at VLF - and it's not very easy to build one. Nimur (talk) 18:39, 27 August 2009 (UTC)

Well then I will go for any higher frequencies that can be generated by an antenna the size of a cellphone (maybe loop type). And at the same time be received by a high gain low bandwidth antenna. —Preceding unsigned comment added by 218.248.80.114 (talk) 19:11, 27 August 2009 (UTC)

You could experiment with a VCR RF output, which is a TV transmitter, coupled to a dipole, and dipole receivers. In the US, the VHF band is presently vacant in many locations due to the changeover to digital, so interference might be minimal. US VCRs have RF output typically on Channel 3 (72-78 MHZ) and Channel 4 (78--104 MHZ). There are in the US readily available transmitters to send IPOD or cassette audio to car radios via FM at both the lower(circa 88 MHZ) and upper ends (circa 108 MHZ) of the US FM band. Similar gadgets are probably available in many countries, with suitable changes to the channel frequencies. Back in 1892-1908, US inventor Nathan Stubblefield broadcast voice and music at base band frequencies (no high frequency radio waves) using loop antennas and induction. Edison (talk) 02:45, 28 August 2009 (UTC)

Local anaesthetics

I'm curious as to what local anaesthetic I'm likely to receive when I have my tooth removed. I'm told I may need an incision, too, so it's being done at the hospital. Is there a most likely candidate for this? Vimescarrot (talk) 15:51, 27 August 2009 (UTC)

See Dental anesthesia. Probably lidocaine. Good luck with it; hope it goes well. --Tagishsimon (talk) 15:59, 27 August 2009 (UTC)

Frequently dentists use a topical anesthetic to numb the gums prior to using an injected anesthetic. The two may or may not use the same active ingredients. -- 128.104.112.102 (talk) 16:34, 27 August 2009 (UTC)

Topical anesthetic is generally 20% benzocaine. DRosenbach ^{(Talk | Contribs)} 15:28, 28 August 2009 (UTC)

Thanks. Vimescarrot (talk) 23:11, 27 August 2009 (UTC)

Via study and practice of Eastern Religions, might it be possible to transcend dental medications? Edison (talk) 02:47, 28 August 2009 (UTC)

Thank you, now kindly leave the stage! —Preceding unsigned comment added by 86.4.181.14 (talk) 07:10, 28 August 2009 (UTC)

I'd go for it if it was. Was that a quote? Vimescarrot (talk) 11:11, 28 August 2009 (UTC)

I believe it was a pun. -- Coneslayer (talk) 12:09, 28 August 2009 (UTC)

Dentist here. While there is no such thing as a "dental anesthetic" in that a drug is particular for dental medicine, if you are in the US, the dental anesthetic used be one of the following: 2% lidocaine 1:100K or 1:50K epi, 4% articaine 1:100K epi or 1:50K epi, 3% mepivacaine or 0.5% bupivacaine. That being said (because those are really the only local anesthetics used by dentists), mepivacaine is usually used only as a last resort because it doesn't last very long in the absence of epi. It's generally used for patients for whom low level intravascular injection of epiniephrine would be more detrimental than the average person (i.e. pregnant females and hypertensives). Bupivacaine is useful in that it may last up to 6 hours, but it's generally not a first-line drug. If you are being treated in the hospital (I suppose by an oral surgeon), you will likely be put under conscious sedation or general anesthesia, which involves an IV, along with the drugs used for those levels of sedation, such as propofol, midazolam, etc. The anesthetic, as I said above, will likely be lidocaine or articaine, or both. DRosenbach ^{(Talk | Contribs)} 12:40, 28 August 2009 (UTC)

The pun aside, the mental state has an effect on the reaction to dental procedures, in my experience. When the prepared adult understands that the scraping drilling, injection or whatever is necessary to health and to save teeth, it is different from the small child or wild animal which only perceives what seems like a destructive assault. Edison (talk) 15:15, 28 August 2009 (UTC)

Conscious sedation is what I'll be having. UK, not US. Why do they need to sedate me? Surgery while I'm awake doesn't concern me, so I'll be fairly calm... Vimescarrot (talk) 16:29, 28 August 2009 (UTC)

For several years, I was able to transcend dental medication when I decided that I didn't want to bother with bruising from the needle, walking around for hours with a non-working mouth, and the period as the anesthesia wore off when I would perceive an itch but couldn't scratch, which really drove me batty. So for minor cavities, I would just tell the dentist to start drilling and I'd tell him if he needed to stop (and then he would ask me five times if I was really, really sure). And indeed, proper mental preparation was the key, it actually went just fine, since I knew what was going on and that I could always stop him and ask for a shot. No Eastern religions were harmed in the making of those fillings. And no, I wouldn't do it for a root canal or extraction! Franamax (talk) 17:25, 28 August 2009 (UTC)

As a child, I was never even offered any kind of anaesthetic for cavities. I looked at my mother dumbfounded when my new dentist asked me, at age 13, if I wanted anaesthetic. Cavity fillings don't hurt...from memory of having teeth extracted before, injecting the anaesthetic is more painful. Vimescarrot (talk) 20:09, 28 August 2009 (UTC)

Sedation may be used for one of two reasons: patient-centered and operator-centered. The former could be when the patient says something like, "Oh no, Doc...I had a similar procedure done on the left side, and there is no way I'm staying awake for it again on the right side. You put me out!" It could also be because the patient is medically compromised and a sedated patient is in a more controlled environment, such that an acute medical emergency can be handled in a more appropriate fashion, as an IV is already in, etc. The latter could be because the procedure is going to be really long/annoying and the operator is not interested in having the patient completely awake for it, such as all four wisdom teeth being removed and the dentist knows the patient is a talker or reeeeeeally annoying. If the patient is fidgety, for example a child or a patient with mental retardation, OR dentistry may be the way to go. My wife works at the special care dental section at the New Jersey Dental School, and she sees patients almost every week in the OR for what would otherwise be routine dental work -- she just does all their work in 3 hours straight because they will not tolerate multiple appointments or people putting their hands in their mouth while awake. DRosenbach ^{(Talk | Contribs)} 19:36, 28 August 2009 (UTC)

White noise generator

Would one of these transmitting in the range of 800-2500 MHz have any effect on nearby mobile phones, or could they filter out everything but their own signal? If such a device was able to interfere with mobiles, what sort of power would it need? This is not expressing an intention to do something illegal, just curiosity at the practicality of a method of alleviating a common social problem.→86.132.239.98 (talk) 16:10, 27 August 2009 (UTC)

It depends on the strength of the signal - it's worth noting that white noise will be the simplest to filter out - a psuedo digital signal would probably intefere worse at lower signal strengths.83.100.250.79 (talk) 17:10, 27 August 2009 (UTC)

We have discussed cell phone jammers many times previously. There are commercially available cell-phone jammers; however, these rarely work by "jamming" (e.g. saturating the front-end amplifiers with a powerful interference signal). A white-noise generator might actually have a chance; but it's unlikely you can put enough power into 2 octaves of frequency-spectrum unless you have a very large power source. Instead, a commercial jammer is more properly described as a form of electronic countermeasure, and operates by transmitting a digital interferance (as 83.100 has pointed out above). In reality, mobile radiotelephones are extremely resilient to such jamming; they operate on a lot of bands with a lot of channel options and digital encoding schemes designed to tune out interference; and if you make a jammer that is even moderately powerful, you will certainly attract the attention of the phone company and the FCC (if you're in the US). It's much easier to block signal reception (with large concrete walls, for example) than to try to actively jam the signal. Nimur (talk) 17:17, 27 August 2009 (UTC)

Wouldn't small metal walls be better than large concrete ones? --Tango (talk) 17:51, 27 August 2009 (UTC)

I don't think this is how mobile phone jammers are supposed to work. As I understand it, it only needs to jam the signaling channel, which is used for setting up phone calls. The interference signal from a jammer, say one installed in a movie theater, only needs to emit enough power to stop the nearby mobile phones from listening to the signaling channel. --98.114.146.168 (talk) 12:04, 28 August 2009 (UTC)

The "Faraday cage" effect is just... it's just a bad, terrible, completely inapplicable approximation for almost any such physical context. We've discussed "faraday cages" with regard to microwaves, elevators, skyscrapers; ... the wavenlengths involved in mobile telephony are long enough that thin metal walls are pretty transparent. Tree leaves are a better "faraday cage" than a sheet of copper [11] [12] [13] (at least, at UHF and similar mobile-telephone bands). Try standing in an elevator and making a cellular telephone call - chances are, you'll have fantastic signal strength. Then try it in a basement - chances are, you'll have no signal strength (even just three or four feet underground). Nimur (talk) 18:36, 27 August 2009 (UTC)

Bear in mind, you are three or four feet underground vertically. The cell tower won't be directly above you, so will have to go through quite a lot of ground to reach you. --Tango (talk) 19:37, 27 August 2009 (UTC)

Thanks to diffraction, though, the radio wave can bend around corners [14]. The signal does not need to be line-of-sight. I suspect the lack of signal in the basement is more due to the presence of a building structure over you, rather than the ground surrounding you. Nimur (talk) 22:04, 27 August 2009 (UTC)

You must have a better phone than mine. Mine never works in elevators. APL (talk) 21:01, 27 August 2009 (UTC)

Visual acuity

Does a person with a visual acuity of 6/7.5 or 6/9 need glasses? 86.166.47.99 (talk) 16:49, 27 August 2009 (UTC)

Need glasses for what? To see? No. To see better? Yes.

You would have to consult with a optometrist and discuss your needs. However, both are probably sufficient to drive in the UK without requiring corrective lenses (In the United Kingdom, the legal standard of vision for driving is roughly equivalent to 6/10, though this not precise). Rockpocket 17:20, 27 August 2009 (UTC)

There is a lot more to consider than just visual acuity. My visual acuity is 6/5 (that is, better than "normal"), but I still have glasses that I wear for close up work (I should be wearing them now... oops!) to correct an astigmatism. --Tango (talk) 17:48, 27 August 2009 (UTC)

Whatever happened to "20/20?" Edison (talk) 02:35, 28 August 2009 (UTC)

6 meters is approximately 20 feet. Both are the standard distance for measuring vision. See Snellen chart. -- Tcncv (talk) 03:19, 28 August 2009 (UTC)

electrical technology

can you suggest two procedure for the determination of thevenin resistance. —Preceding unsigned comment added by 203.110.246.230 (talk) 17:14, 27 August 2009 (UTC)

Amazingly, two methods are provided in our article, titled Thévenin's theorem. You can also read Norton's theorem, which is closely related.

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Nimur (talk) 17:19, 27 August 2009 (UTC)

Sterilization of Psylocibe spores

Hello, my question is how can psylocibe spores be killed 100%(true heat, and if what temperature?) or are there any other safe methods?TY —Preceding unsigned comment added by 89.122.224.95 (talk) 20:12, 27 August 2009 (UTC)

? What do you mean "safe methods" and why would you want to? Are you trying to torch your neighbor's magic mushroom patch? In that case you'd have to destroy the Mycelium. 71.236.26.74 (talk) 03:55, 28 August 2009 (UTC)

I would expect that boiling water at 100°C for 10 minutes should kill all the fungus spores. Graeme Bartlett (talk) 09:26, 28 August 2009 (UTC)

Mix the spores into honey, and put the honey on a roaring coal fire.83.100.250.79 (talk) 10:54, 28 August 2009 (UTC)

Gravity waves

What is the fundamental difference between gravitational waves and the varying gravitational field that is produced by any moving mass (such as the earth orbiting the sun)? (I assume there is one because gravity waves are apparently extremely difficult to detect and yet variations in the gravitational field emanating from the moving Earth, say, as it appears to a fixed observer, would seem to be trivial to detect.)

A Gravitational wave is a fluctuation in the curvature of spacetime that propagates as a wave, traveling outward from the source. In contrast, if you're in a spaceship passing by the earth, the changes in spacetime curvature that you experience are just due to your motion relative to the earth. In other words, if you stay at a fixed location relative to the Earth, your spaceship will not experience any changes in spacetime curvature (changes in gravity).

Technically, for an isolated system to be a source of a gravitational wave, the third time derivative of the quadrupole moment of the system's stress-energy tensor must be nonzero. This will not be the case for a spherical object like the Earth or the sun that's just sitting there (or equivalently, moving at a constant speed), even if the object is spinning.

Two objects orbiting each other, such as the Earth-sun system, does radiate gravitational waves, resulting in the Earth slowly getting closer to the sun over time. However, the gravitational waves radiated by the Earth-sun system are only enough to stretch or squeeze a ring of particles by just 1 part in 10²⁶, which is much smaller than the 1 part in 10²¹ that can be detected by LIGO. Red Act (talk) 23:45, 27 August 2009 (UTC)

Thank you for your reply, Red Act. Let me be a bit more specific. Let's say I'm at some distance away from the solar system, and I have a very sensitive way of measuring the strength of the gravitational field. As the earth orbits the sun, I'll see a wave-like fluctuation in gravitational field strength (all other things being equal), with a period of one year, simply because of the relative change in the configuration of the two bodies, and this will emanate away from the solar system at the speed of light. Is that correct? But the thing that confuses me is whether this is the gravitational radiation that you refer to, or whether it's a completely different effect. 86.133.242.249 (talk) 00:59, 28 August 2009 (UTC).

I think that is the gravitational wave, if I understand your use of terminology. The fluctuations in the net observed gravitational field, due to the motion of a distant source (mass), propagate with a fixed speed and represent energy movement (at least, so goes the gravitational wave hypothesis). This phenomenon is a gravitational wave; it is not entirely clear what mechanism allows such a fluctuation in observed net gravitational force to exist. Some hypotheses include the graviton, a proposed particle which "carries" these energy fluctuations per wave particle duality; but they have as-yet never been definitely measured in an unambiguous way. Another problem is that such a mechanism implies that other wave phenomena, attributable to the higher order moments of the system's stress-energy tensor, are possible. This implies things like [[like polarization of the gravitational wave, (though these implications have not yet been observed). One of the key problems is that such energy propagation must satisfy conservation of energy - which means that simply by moving, a mass is radiating energy in the form of gravity waves; yet, with no fixed frame of reference, a particle can be said to be moving; and so we need a more elaborate method (such as general relativity) to describe the relationship between the induced gravitational wave and the particles' state description. Also, note that the term "Gravity wave" is not synonymous with gravitational wave - the first is a classical effect that is well-documented and observed in Earth's ocean surface, mesosphere, and elsewhere; the latter is the relativistic physics hypothetical phenomenon. Nimur (talk) 01:16, 28 August 2009 (UTC)

Thanks Nimur. If a gravitational wave is, as you say "fluctuations in the net observed gravitational field, due to the motion of a distant source (mass)", then I guess my question is: Why are the things so hard to detect? Couldn't an experiment be set up on earth using a rotating dumbbell apparatus with a very sensitive gravimeter nearby? And why are they necessarily waves? Wouldn't a mass in non-periodic motion generate a non-wavelike fluctuation? And finally, I thought that there was still some doubt about whether gravitational waves actually exist. It seems self-evident that the movement of a mass would affect the gravitational field at some remote location. How could it be any other way? I think some of my questions might betray some fundamental lack of understanding on my part. 86.133.242.249 (talk) 01:46, 28 August 2009 (UTC).

They are difficult to detect because they are very weak. The concepts involved in detecting them are very simple - you have two rods at right angles to each other and measure them continuously to see if they change length - but the amount they will change length by is extremely small. "Wave" in physics means anything that propagates, it doesn't have to be periodic. There isn't much doubt - gravitational waves are an obvious consequence of a finite speed of gravity. The only real doubt is whether we will be able to detect them. If they aren't there at all then the whole of general relativity goes up in smoke, which would be very surprising because it has made lots of very accurate predictions. Pre-general relativity the speed of gravity was assumed to be infinite, if there aren't any gravitational waves we would need to go back to that assumption. (And find other explanations for things like inspiraling pulsars.) --Tango (talk) 02:18, 28 August 2009 (UTC)

Thank you Tango. I'm sorry to labour this, but it's been confusing me for ages. I think my mistake was in assuming that any detection of a change in gravitational field due to a moving mass (which sounds easy) would be evidence of gravitational waves (i.e. some sort of "propagation" of gravity). From what you say this is wrong for two reasons: first, this would not (by itself) show that the speed of propagation is finite; second, it would not tell anything about the relativistic model of gravitation as a distortion of spacetime, which is the model in which the concept of gravitational waves is couched. Is this more or less correct? 86.133.242.249 (talk) 02:37, 28 August 2009 (UTC).

You may be assuming that you would measure the change in the field by measuring the field itself at different times and comparing them, that won't work - the obvious way of measuring a field is to measure the force is induces, but with gravity the force on your test mass will be the same as the force on your detector (since you are in free fall with respect to anything other than the Earth) so you won't detect anything at all. You have to measure the change directly by measuring the tidal forces, that is what the two rods at right angles I mentioned are doing. Those tidal forces are very weak since to get large changes in gravity you need fast moving, heavy objects that are close by, and there aren't any. We have to make do with fast moving, heavy objects that are far away. It should also be pointed out that movement isn't actually enough, you need acceleration. Somebody else will have to explain why, though, because I'm a little confused by that (I know it must be true because emitting gravitational waves costs energy so can't depend on motion, which is relative to the frame of reference, but can't work out how it works...). --Tango (talk) 03:03, 28 August 2009 (UTC)

August 28

invisibility

if a suit emmits a spectrum of light which can't be seen by the human eye i.e. infra red or ultra violet will it be invisible or will it produce a wave like affect or distorted image.--Meloxicam (talk) 01:48, 28 August 2009 (UTC)

It won't make any difference at all. It would still block the visible light from behind it and would probably reflect visible light from in front of it as well. What is happening in parts of the spectrum we can't see is pretty much completely irrelevant for determining what we will see. --Tango (talk) 01:59, 28 August 2009 (UTC)

A suit emitting IR might, like a red hot stove, produce distortion of light waves passing near it, by heating of the air. A suit emitting UV migh cause other objects in the scene to fluoresce, just like a black light bulb. Parts of the spectrum we cannot see can have visible effects. Edison (talk) 02:32, 28 August 2009 (UTC)

"IR" and "heat" are not the same thing. All objects at any temperature emit EM radiation, objects are every day temperatures happen to emit IR. It isn't IR that distorts light near hot objects, it is the hot air caused by the actual heat of the object. Any frequency of EM radiation will heat up anything that absorbs it, what matters is just the total energy being emitted, not the frequency (although the frequency will affect how much it is absorbed). A suit will only cause heat distortions if it is very hot. I don't think the OP intended the suit to emit the radiation by being at the appropriate temperature (which, for UV, would be thousands of degrees C), it would just use bulbs (which may involve a filament at that temperature, of course). --Tango (talk) 02:50, 28 August 2009 (UTC)

The front of most remote controls emit IR when a button is pressed, they get neither hot, nor invisible. Admittedly those are only small amounts but I've seen high power IR spotlights for night time security cameras and to the naked eye they appear just as cold and visible. Vespine (talk) 05:11, 28 August 2009 (UTC)

What clothes look like in infra-red! [through an image intensifier that has nothing to do with IR - wrong type of night vision! --Tango (talk) 14:15, 28 August 2009 (UTC)] (Tango is incorrect: Modern NVG's see almost entirely in the near infra-red. SteveBaker (talk) 18:05, 28 August 2009 (UTC)) Tango is never incorrect, you should know better than to say such things! Look at the image description, it is from an image intensifier, not IR goggles. If it was IR you would be able to see that it was lit by an IR bulb somewhere near the camera - it clearly isn't passive IR - and it doesn't look like that to me. --Tango (talk) 18:32, 28 August 2009 (UTC) Near-IR looks like that - and modern image-intensifiers such as found in military NVG's (which is what was used to take this picture) see predominantly in the IR. Mid to Far IR correlates better with 'heat' and those look quite different (eg faces glow more than clothing). This is 'near' IR. SteveBaker (talk) 19:55, 29 August 2009 (UTC) Near-IR night vision is active, yes? It should be lit by an IR bulb near the camera, that images looks like it is lit by something off to the left. --Tango (talk) 15:37, 30 August 2009 (UTC) No - when used by the military, it's generally passive. The last thing you want to do at night is to be shining lights around the place (even if they are IR lights). There is enough near IR produced by the moon and stars for these light amplifiers to cope with. The directional lighting in that image is probably moonlight. SteveBaker (talk) 17:55, 30 August 2009 (UTC)

More than that - you and your clothes DO emit infra-red light. You are very visible on an infra-red "night vision" camera because of that. You certainly aren't invisible - and because human eyes can't see into the infra-red, we can't see that light without help from some high-tech gear. SteveBaker (talk) 13:26, 28 August 2009 (UTC)

(I think you have swapped visible/invisible there.) But yeah, this is a good example. When you press the button on your remote, you don't see anything coming out of that little light bulb on the front. That's what IR looks like. If you view it through something sensitive to that band of frequencies—like a cell-phone camera—you can see it as if it were regular light (which is a neat trick to pull on those who otherwise don't know about that). Nothing fancy to it, but you can't see it with your naked eyes. --68.50.54.144 (talk) 13:17, 28 August 2009 (UTC)

No, SB's usage was correct. You're visible on an infra-red camera not invisible. Nil Einne (talk) 18:36, 28 August 2009 (UTC)

What clothes may look like in infrared no dispute, hopefully (colouring is artificial of course, you can't visualise what humans look like in infrared naturally since we can't see infrared) Nil Einne (talk) 18:44, 28 August 2009 (UTC) [Thermal IR, yes. Near-IR is rather different and that is what I expect the OP was talking about. --Tango (talk) 18:50, 28 August 2009 (UTC)]

• When you see a suit, what you actually see is a reflection from light around it, usually this light has all colors, so you can see a wide spectrum of different colors. For a red suit, almost all the visible non-red light is absorbed by the suit, while only the red light is reflected back to your eye, and the suit looks red. If the light shining on the red suit was completely blue only, with no red in its spectrum, that same suit would look black. A suit which only reflects back IR and UV, and nothing in the visible spectrum, would simply look pitch black, but since it is opaque, it would not function like an invisibility cloak. Sjakkalle (Check!) 09:07, 28 August 2009 (UTC)

No one has addressed my comment about a suit that emitted UV causing fluorescence of objects. For the sake of argument, I would assume the suit emits the equivalent of a 20 watt "blacklight" compact fluorescent bulb. And the OP did not specify that the suit emits the limited IR energy of a remote control or the normal clothing on a non-cloaked individual. Perhaps it radiates all the heat generated by the wearer, which is perhaps 60 watts, in the IR and UV regions, while absorbing incident light in the visible spectrum. It would be black to normal vision, it would be bright when viewed in IR sensitive optics such as security cameras, and it might well cause dayglo paint, tonic water, white paper, cleaning products, clothing washed in certain detergents or a white shirt to glow due to the UV. Thus emitting UV would be more likely to make the wearer easily detectable to the unaided eye at night than just emitting IR. Note: many years ago my rock band would sometimes kill the lights except for a couple of UV fluorescent tubes. Teeth, shirts,and other parts of clothing would fluoresce brightly, as would some of the image on advertising signs or labels or beverages. A cloaked person emitting similar UV would have been easily detected making his way through the room. Edison (talk) 14:58, 28 August 2009 (UTC)

The UV light would attract small flying insects (but not mosquitoes) like a Bug zapper without the zap. The wearer would see interesting UV watermarks on some stamps, banknotes, passports, credit cards and other documents, as well as any stains of body fluids such as semen, blood, bile and urine. Ultraviolet#Human health-related effects of UV radiation gives information that suggests (s)he should wear both insect repellant and sunblock creams and not bite on anything that looks like a candy[15].Cuddlyable3 (talk) 15:46, 28 August 2009 (UTC)

If you want an invisible cloak, you would likely want to consider Broadband Exterior Cloaking. [16][17] They haven't got it scaled up to humans at visible light frequencies quite yet though. ;) Franamax (talk) 17:54, 28 August 2009 (UTC)

People who have had cataract surgery can see a little way into the ultra-violet. My mother noted that some flowers which had been plain before had blue spots or stripes visible on their petals after her surgery. It's believed that plants do this to attract bees (which can see into the ultra-violet). SteveBaker (talk) 18:25, 28 August 2009 (UTC)

v

Gravitational wave triangulation

LIGO says:

These sites are separated by 3,002 kilometers (1,865 miles). Since gravitational waves are expected to travel at the speed of light, this distance corresponds to a difference in gravitational wave arrival times of up to ten milliseconds. Through the use of triangulation, the difference in arrival times can determine the source of the wave in the sky.

How can a single piece of information (the difference between two times) determine the source of the wave? You need three pieces of information to determine a position in 3D space (hence the name). I can imagine two pieces of information being useful since the universe is fairly sparsely populated so there is likely to be very few potential sources along the line (or curve) that you can narrow the source down to, but there being only one source on an entire plane (or surface) seems unlikely to me. --Tango (talk) 01:57, 28 August 2009 (UTC)

From the papers I'm reading (original 1991 LIGO paper in Science and 1999 publication in Physics Today) the purpose for two distant laboratories 3000 km apart is to filter out local noise sources. However, the latter source also states that "one determines the direction and polarization of a gravitational wave by measuring arrival-time differences between geographically dispersed detectors." So, this may also have been a design goal. Two arrival-times define two spheres; the intersection of two spheres is a circle (I think? Somebody check me on that). If so, the source must lie on that circle of intersection. Furthermore, there is polarization information because the two sites also have two arms each - so that can further narrow the possible source locations on that locus. I have not, however, found any papers which specifically discuss techniques or examples of such source location using the LIGO. My experience with electromagnetic waves source-determination suggests that you would still need three geographically-dispersed receivers; but there are a lot of games that you can play (also, space is pretty sparse, so there's only a few black holes that would even be candidates as sources for detectable waves - that can help narrow down the source locations). Nimur (talk) 05:20, 28 August 2009 (UTC)

The intersection of two spheres is a circle (or a point or empty), but that's irrelevant. You would only get a sphere if you knew the emission time as well as the arrival time (so you could calculate travel time, which gives you distance). With just the arrival time you have no information at all, with two arrival times you can calculate the difference and that is useful information, but only one piece of it. --Tango (talk) 14:19, 28 August 2009 (UTC)

In N dimensions, you need N pieces of independent information in order to identify a point uniquely. Hence, in 3D space, you need three pieces of information to determine a position unambiguously. With just the difference between two times - you have only one piece of information. For example - if the pulse were to arrive at exactly the same time at both places, you'd know that the source was equidistant from the two receivers...but that's all you'd know. That means that the source could be any point on a vertical plane that's at right angles to the line between the two receivers. Assuming that the point lies in the plane of the galactic disk narrows it down to a line - and because the solar system is on one of the outer arms of the galaxy, one might guess that the direction lies towards the center of the galaxy - which narrows the search down to a single direction...but those are assumptions that might not be true.

If they had a third receiver, they could unambiguously narrow the source down to any point on a line - and only with a fourth receiver could they determine the position exactly in 3D space. That's why your GPS reciever can't tell you where you are unless it can see four satellites. SteveBaker (talk) 13:20, 28 August 2009 (UTC)

GPS receivers do not need to see 4 satellites if they have a very good clock as the satellites themselves broadcast timestamps for the signals they send out. For an 'average' GPS receiver 4 satellites are required though to determine (x,y,z) and t to an accuracy better than the internal clock can provide. JMiall₰ 17:35, 28 August 2009 (UTC)

First I want to point out that pinpointing a source in the sky in that context means only the two coordinates of a point in the celestial sphere, namely right ascension and declination. Second, the time difference can be suplemented, as pointed out above, by the polarization information which helps pinpoint the source. Dauto (talk) 14:24, 28 August 2009 (UTC)

But they're not looking for a dirac-function, they're looking for a periodic wave (emanating from black hole rotations, for example). This gives phase and timing information (assuming a sub-wavelength separation); so two locations + timing information + phase information may be sufficient to uniquely identify the source (meaning that the N pieces of information criteria is satisfied - as long as the phase assumptions hold). Needless to say, I can't find any documentation of successful identification by this technique in the above papers. Nimur (talk) 15:52, 28 August 2009 (UTC)

Also if they find a source that lasts more than a few hours then they can use the fact that the baseline is moving to triangulate from different orientations of the baseline and get a better directional fix. Gandalf61 (talk) 16:01, 28 August 2009 (UTC)

Relatively local area network

Can I join the wireless home network of my friend who lives on a nearby street about 800 meters away? (Uh, half a mile, isn't it.) I asked this question in an electronics shop and the man said no, not unless I built a tall tower to provide line of sight over the intervening houses for the radio signal. Is there no better way? 81.131.51.80 (talk) 02:31, 28 August 2009 (UTC)

I don't think you need a tower, just an aerial on the roof of each house with some appropriate kind of booster. The Computing desk might be a better place to find out what you need to boost the signal. --Tango (talk) 02:42, 28 August 2009 (UTC)

OK, but just to squeeze every drop of science out of the question while I'm here - would this work even if I can't see his roof from my roof due to other people's roofs being in the way? I think the signal would have to go through about six of the things.81.131.51.80 (talk) 02:45, 28 August 2009 (UTC)

Yes. The signal will spread out from his house (or yours for the return journey) and then diffract around the roofs. Those roofs may weaken the signal, but shouldn't block it entirely. --Tango (talk) 03:06, 28 August 2009 (UTC)

In fact, for that reason, an aerial on the roof isn't strictly necessary at all, the aerial could be inside, but you'll get better signal strength with it on the roof. --Tango (talk) 03:07, 28 August 2009 (UTC)

Thanks! That was what I was hoping, having seen diffraction mentioned further up the page, but I wasn't sure if it would work over such large obstacles so many times in a row. (If I imagine water waves instead of radio waves, it seems less extraordinary.) 81.131.51.80 (talk) 03:16, 28 August 2009 (UTC)

Diffraction happens most when the wavelength and the size of the object being diffracted around are comparable. The wavelength for wireless networks is (I believe) on the scale of millimetres, the roofs are on the scale of metres, that is close enough to get significant diffraction. (You won't, however, get much diffraction of visible light (which is on the scale of 100s of nanometres), which is why you can't see the sun when it goes beneath the skyline.) I rather suspect I am oversimplifying the situation here (optics isn't really my area), but I think the general idea is right and that is all you need. --Tango (talk) 03:30, 28 August 2009 (UTC)

Ha, I like the relaxed notion of "comparable". In most situations I encounter, millimeters are not comparable with meters, but I'll take your word for it. I just went and looked up radio waves and saw that amateur radio wavelengths can be exactly house-sized, so I thought maybe that would be good to aim for, but perhaps converting LAN data to ham radio is not a practical idea, I couldn't say, I know nothing. Leaving it at the same frequency is undoubted cheaper, anyway. 81.131.51.80 (talk) 03:58, 28 August 2009 (UTC)

You may also need a license to use those wavelengths. It would certainly work, though - ham radios definitely work over 800m! The notion of "comparable" can be made precise, but for this kind of thing anything within a few orders of magnitude is close enough. --Tango (talk) 04:15, 28 August 2009 (UTC)

Typical consumer wi-fi gear has a range of only about 100m outdoors, you can get amps and directional antennas and stuff, but I think they claim to improve the signal by 50%-200%, not by 800%. I don't think you'll get 800m out of consumer gear without repeaters in between. There are things like Long-range Wi-Fi but I don't know how cheap and easy that would be to set up. Vespine (talk) 04:22, 28 August 2009 (UTC)

That's an excellent article. "just placing standard USB WLAN hardware at the focal point of modified parabolic cookware" is an inspiring phrase. (Does seem to want line of sight, though.) 81.131.51.80 (talk) 04:42, 28 August 2009 (UTC)

Converting "LAN data" into "HAM data" is commonly done. See AX.25, packet radio, and this great web resource from Tucson Area Packet Radio. With UHF (and a HAM license - you need a powerful transmitter, and you should be licensed to operate it!), UHF-based IP networks have been established with wireless ranges over 25 miles. Nimur (talk) 05:23, 28 August 2009 (UTC)

The 25-mile range isn't because of technical limitations, right? By transmitting LAN data at a shortwave wavelength and bouncing it off the ionosphere, I don't see why you can't transmit to the other side of the world. --99.237.234.104 (talk) 06:13, 28 August 2009 (UTC)

You will not be able to get anywhere near enough bandwidth to bounce off the ionosphere at high frequency. Also the ionosphere adds multipath distortion and is constantly changing. There are special HF modems that can do this job, but you will be lucky to get 9600 bps. You can certainly get multiple kilometers out of wifi. Both ends need a wire parabolic dish, you can get about 26 dBi from each antenna. You have to match polarization and line of site really is required. You could perhaps survive one roof in the way, but 10 or twenty will give you a total loss. Not only do you have to get your signal through, you also have to separate it from all the other WiFi signals around. Graeme Bartlett (talk) 09:21, 28 August 2009 (UTC)

Normal wifi gear operates at 2.4GHz or higher. This is strictly line-of-sight and will be attenuated by intervening walls: diffraction will not help. If you cannot see the neighbor's house, you are stuck. If you do have LOS, then you can get or make a pair of directional antennas that will work. The classical one is the "Pringle's can antenna." See [18] -Arch dude (talk) 13:12, 28 August 2009 (UTC)

Do directional antennas and diffraction mix, if you see what I mean? Can you have a situation where you're pointing a directional antenna at the edge of an object the waves are diffracting round, or is that just silly? 213.122.66.56 (talk) 14:08, 28 August 2009 (UTC)

You can get ranges as far as this from a pair of home WiFi units using the "Pringle can antenna" approach (just Google for that exact term). "Pringles" cans are foil-lined cardboard tubes - but for some (almost magical) reason, they work extremely well as highly-directional WiFi antennae. HOWEVER - you will definitely need a line-of-sight over the rooftops because you can only get that kind of a signal boost using very directional signals that would be disrupted by the intervening rooftops. SPECIFICALLY: You're going to need to be able to see his Pringle-can antenna from your Pringle-can antenna with nothing but air in-between - you'll need to tape a laser-pointer inside the can-antenna of one of them and have it shine onto the bottom of the can-antenna of the other. You'll need to mount them quite firmly (and obviously, waterproof them somehow) in order that the wind doesn't blow them out of alignmnent. If you manage that then you have a really good chance to make this work - even at 8 times the range the thing is designed to work at. However, if you don't make the antennae just right - and if they don't accurately line up - you definitely won't succeed. SteveBaker (talk) 13:04, 28 August 2009 (UTC)

As I understand it, Pringles cantennas aren't actually as good as people seem to think despite the hype and popularity. You're better off choosing a different can and doing things somewhat differently without really raising cost or difficult. This isn't something I've ever done myself or look into in depth, so I could easily be wrong but what I have seen before and re-reading thing things now, the theory and evidence seems fair enough [19] [20] [21] and in particular, I've never come across anyone claiming the opposite whether in theory or evidence/testing (although that doesn't always say much) Nil Einne (talk) 18:31, 29 August 2009 (UTC)

A more reliable alternative is an off-the-shelf microwave transmitter and receiver (this reply is being sent via one of these), but it still needs line-of-sight and is more expensive than the above solutions. I suppose wi-fi is microwave anyway, so the technology is the same, even if the name is different This range of frequencies uses a tiny dish as an aerial. Dbfirs 02:15, 3 September 2009 (UTC)

how to interpret

work done in a compression process in int(pdv).and shaft work in a compression process in int(vdp). how?how its possible? 220.225.98.251 (talk)

Consider some quantity of gas moving through the system and doing some mechanical work as it goes. The gas enters at volume V₁ and pressure P₁ and leaves at volume V₂, pressure P₂. The work it does is $\int _{V_{1}}^{V_{2}}{PdV}$ using the usual work forumla. Using integration by parts, $\int _{V_{1}}^{V_{2}}{PdV}=V_{2}P_{2}-V_{1}P_{1}-\int _{P_{1}}^{P_{2}}{VdP}$.

The $-\int _{P_{1}}^{P_{2}}{VdP}$ part is the shaft work and the $V_{2}P_{2}-V_{1}P_{1}$ part is the flow work. (Edit: I'm not sure this is right. I need to think about it.) Rckrone (talk) 06:48, 28 August 2009 (UTC)

This must relate to http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_August_2#why_so.3F.3F.2F

(removed confused stuff)83.100.250.79 (talk) 12:16, 28 August 2009 (UTC)

Ok, I think I understand this better now. Enthalpy#Open_systems talks about it a little. The total work that the apparatus does can be divided into two types: flow work, which is the work done to force the gas through, and shaft work which is mechanical work done on an external object like a turbine. The energy that the apparatus gets to do its work comes from energy donated by the gas passing through and heat added to the system ΔQ. For a steady-state process (internal energy in the control volume isn't changing) that's adiabatic (ΔQ = 0), the total work done by the apparatus is equal to the work done by the gas, so W_shaft = W_gas - W_flow = $\int _{V_{1}}^{V_{2}}{PdV}-(V_{2}P_{2}-V_{1}P_{1})=-\int _{P_{1}}^{P_{2}}{VdP}$. This is only true for a steady state adiabatic process. Rckrone (talk) 17:19, 28 August 2009 (UTC)

But the PV terms are not equal to the energy of the gas - the energy of the gas is kPV where k is a dimensionless constant relating to the number of degrees of freedom of the gas (I think)

ie δW = d(poutVout) − d(pinVin) + δWshaft

does not integrate to Work = change(PV) + shaft energy

The questioner has already asked a question based on a false supposition (linked above) - I would not be surprised that they are doing the same here.

I wouldn't waste any time on attempting to reverse engineer unfounded statements.

The PV terms aren't supposed to represent the internal energy of the gas, but the energy required to move the gas out of the control volume (and the energy gained when gas forces itself in). To push a volume of V out against a pressure of P requires work PV. This is called flow work or pV work. Here's a source I found on it [22]. The change in internal energy of the gas is measured by the work that the gas does (since in an adiabatic process the two are equal). Some of the internal energy that the gas is donating goes toward pushing itself out of the control volume (flow work) and the remainder is shaft work. δW = d(poutVout) − d(pinVin) + δWshaft does integrate to Work = change(PV) + shaft energy. You might be right about the OP trying to waste everyone's time though (but maybe not). Rckrone (talk) 18:01, 28 August 2009 (UTC)

To the OP:

Can you give a single example (such as a book reference or web page) where this formulation int(VdP) is used?

You've already asked one question that assumed something was true when it wasn't ie your question linked to above.

Please don't expect others to do your work for you.

I have suspicions that you are deliberately wasting other peoples time - Can you please prove me wrong and give a source from where you are getting these statements?

If you do not I will treat any further posts as vandalism - if you feel this is unfair then feel free to complain about it.

83.100.250.79 (talk) 17:35, 28 August 2009 (UTC)

Firefighting with seaplanes

Recently, in the fires that desolated Greece, I got the impression that the fire fighting seaplanes were picking up water directly from the sea. Do they really use seawater against fire? Quest09 (talk) 10:21, 28 August 2009 (UTC)

Sure. But they prefer fresh water, if that's handy. Our article on aerial firefighting doesn't really address this, but salt water is more likely to lead to corrosion and other conditions that require extra maintenance hours, so sea water isn't the preferred source of water. Still, if sea water's what they've got, that's what they'll use; an emergency is an emergency, after all. -- Captain Disdain (talk) 11:01, 28 August 2009 (UTC)

However, would they use this water on forest fires too? And, wouldn't that ruin the ground for many years? It seems less damaging to let it burn... Quest09 (talk) 11:34, 28 August 2009 (UTC)

The salting the earth question is interesting: but how long would it take to leach out the salt added in the firefighting operation? And for practical purposes, is the amount of salt deposited of real moment, in comparison with, for instance, wind-blown spray over the millennia, or the salts deposited by the conflagration? --Tagishsimon (talk) 11:49, 28 August 2009 (UTC)

This page says salt contamination is taken into consideration for sensitive vegetation and water supply areas. I guess several things need to be considered: how much damage the fire would cause, how far away a fresh water supply is, how much water (and thus salt) would be needed, and what the effects of that amount of salt will be on the land type in question. 88.114.222.252 (talk) 11:56, 28 August 2009 (UTC)

one way salb

i looked evry where , without any use . now designing a one way slab we put the main reinforcement in the short direction but when you take astripe in each direction you will find that the one in the long direction is carrieng more load and resisting more moment . so shouldnt we be putting the main reinforcement in the long direction.please dont use math i need avery clear exponation even other people beside engineers can figure it out ....? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 12:09, 28 August 2009 (UTC)

Usually reinforcement is put in any part that is too weak as it is to carry, support, or withstand an expected load.

Also what is the "one way slab" for, what is it for?83.100.250.79 (talk) 12:21, 28 August 2009 (UTC)

Without further details it's impossible to say where the reinforcement should go in your example.83.100.250.79 (talk) 12:19, 28 August 2009 (UTC)

will the way i visualized it like this ... assuming a two beams crossing each other at midspan now to carry a specified load applied at that point of intersection then which one of the two beams need the biggest reinforce steel ratio to support that load ... —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 12:47, 28 August 2009 (UTC)

It's still not clear, please supply a diagram, or actual dimensions.83.100.250.79 (talk) 12:50, 28 August 2009 (UTC)

This sounds like a civil engineering matter where some mathematics is unavoidable and viability of the resulting structure could have legal consequences. I don't think we can provide the kind of consultation that requires. Cuddlyable3 (talk) 12:53, 28 August 2009 (UTC)

If the slab is long but not very wide, then obviously the main tendancy to bend will be along the long direction - so the main reinforcement beams need to go along the length to resist that bending. However, I presume you need some reinforcement across the width too - resulting in a "waffle-slab" approach. The trouble is that the spacing and depth of the beams and the degree of post-tensioning that goes on does indeed require some math - and it depends on the results of a proper soil survey too. I would have thought that you'd either have a book or table of some kind that specified what you need for different shapes and sizes and under different soil conditions - or that you'd employ a structural engineer to design the slab properly using math and stuff. The consequences of a slab cracking years after the building is completed are pretty severe for the owners (I know - it's happened to me!) and I'd be horrified if someone was just guessing how much reinforcement the thing needed on the basis of asking a question to a bunch of unknown people on the Internet! SteveBaker (talk) 12:53, 28 August 2009 (UTC)

But a one-way slab is by definition supported across the short way. What you're thinking of is a case where you can only support at the distant ends. Or in the case of a two-way slab (W > 0.5L), you would need to consider the long direction as well as the short one. Franamax (talk) 18:55, 28 August 2009 (UTC)

And isn't there another option: diagonal reinforcement ? Those would have the advantages of providing more rigidity and stopping cracks parallel to any of the walls, but some would need to be somewhat longer than a straight reinforcement, in order to reach from one corner to another, and others would be shorter. If the reinforcement is free-floating, this might work fairly well. However, if attached to the frame at the ends, this would be a bit trickier (if the components don't meet at a right angle).

If we're still discussing length-wise or cross-wise reinforcements, the site will make a big difference. Is this on a hill ? If so, I'd put the reinforcement in the direction going up and down the hill. But, better yet, put in reinforcement in both directions, so you're covered no matter what the stresses are. StuRat (talk) 14:52, 28 August 2009 (UTC)

will .... first of all in engineering they call it one way slab and the wright way is to provide steel reinforcement along the short dimension , so its known where to put the steel . what iam asking for is why ,,, i think we should provide the steel along the long direction . and we cannt provide steel reinforcement along both directions because it wont be economical at all .

How do you know one way is the right way - give a reference for your statements or stop wasting peoples time. ok? Why do you think the short reinforcement is supposed to be the right way to do it -does it say so somewhere? Where?

Stop wasting peoples time with you unfounded statements ok?.83.100.250.79 (talk) 17:24, 28 August 2009 (UTC)

You need to provide some reference for your statements that

the wright way is to provide steel reinforcement along the short dimension

This seems wrong - please provide evidence showing from where you got this statement. Otherwise I will assume that you, like others are making up false statements in an attempt to waste other peoples time. I view that sort of behaviour as vandalism and will treat it accordingly.

You should realise that disruptive behaviour is vandalism.

If you feel have been falsely accused of disruptive behaviour by me please provide evidence that your statements have a legitimate basis, if you feel I am treating you unfairly then please feel free to complain.

83.100.250.79 (talk) 17:41, 28 August 2009 (UTC)

Iam acivil engineer ... thats how i know ... because we design it ... but i need a full understanding about it theres alot of terms that we use all the time but we didnt have afull understanding for it ...?? and i think you should cool alittle bit ... iam not intersted in wasting your time ... ????????????????????????????????/ —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 17:52, 28 August 2009 (UTC)

You know what - I don't believe you. Why is a civil engineer asking simple questions on the internet - you should already know the answer. You should also know as an engineer that you need to communicate the problem clearly to other people - something you have failed to do - You have not supplied any information about dimensions, material, points of attatchment, etc despite being asked. You have failed to provide any source for your statement that "reinforcement should be across the short length".

Why should people waste their time (which is what you are doing) trying to justify statements that you have not provided a source for, and may not even be true.83.100.250.79 (talk) 18:04, 28 August 2009 (UTC)

83.100, you seem to enjoy hectoring posters here more than actually answering their questions. If you wanted to know what a one way slab is, you could have tried that handy new thing called Google. If you want a source that short way is the right way, you could have looked that up pretty easily too, since the answer is "all of them". But if it will make you feel any better, here's a nice Powerpoint with lots of pictures.[23] Now please try to provide answers in a polite and helpful way, and if you're worried about people's time being wasted, well, the only time you control is your own. I didn't have any trouble understanding the question or giving a simple non-numeric answer. Franamax (talk) 18:45, 28 August 2009 (UTC)

Also 83.100.250.79, please consider that an OP's first language might not be English. Not all the other language wikis have reference desks. If you don't understand what the person is asking, then tell them so politely and ask them to clarify. Also there is no requirement for questioners to produce sources for their statements, you may ask for them politely, but they don't have to give you any. Asking or answering questions on the ref desk isn't like editing an article. Also please assume good faith. 152.16.15.144 (talk) 06:15, 30 August 2009 (UTC)

Your problem is that the slab is supported all around, so your assumption that there is more stress in the long direction is incorrect. The load is borne primarily in the short direction. Think of it as the load wants to find something to hold it up as quickly as possible, so it "looks" for whatever support is closest. Franamax (talk) 18:08, 28 August 2009 (UTC)

Or for another way to think about it, why does the slab care how long it is? If it 1 meter wide and 10 meters long, why is that any different than if it was 10 kilometers long? It would only be important if you were supporting the slab only at the widely separated ends, in which case you would definitely need to reinforce it the long way (and if it's 10km long, you will need an awful lot of rebar;). Franamax (talk) 18:12, 28 August 2009 (UTC)

you could look at it like this ... at midspan where the moment is maximum and assuming that the slab is consist of two strips crossing each other at midspan now ,,, deflection will be the same amount at midspan because as we know both strips are attached at that point . and using this info that elastic strain in ex. concrete is 0.003 then the short side need more steel to prevent strain from exceed this value where cracks could start to form . so if you provide enough steel in the short direction to prevent cracks cracks surly wont form along the long direction. mabey this is the answer. and mr 83.100.250.79 please dont call people lair ... unless ofcoarse if its make you feel good .--Mjaafreh2008 (talk) 18:43, 28 August 2009 (UTC)

Or here's yet another way of looking at it, related to the first thought experiment of two crossing beams: pretend you have two beams of equal cross-section, one (beam A) 3 times longer than the other (beam B), with no load, just their own weight. We know for sure that A will have a higher deflection than B. But we also know that if the beams are joined at the centre, they must have the same deflection, so in effect, beam B is supporting A, and A is actually two beams of length A/2 (actually it's a compound beam with two spans, but whatever). Now stick in a few more "B" beams across the width. Now you have A as a compound beam with four spans of length A/4. Since deflection varies as L^3 and stress varies as L^2, pretty soon you don't have to worry at all about A. Everything is carried by the "B" beams, except right at the very ends of the slab. Don't know if that makes it clearer or not... Franamax (talk) 19:12, 28 August 2009 (UTC)

thank you very mush ... will as you said i could google it , but its better to disscus it with someone , soory for wasting your time .--Mjaafreh2008 (talk) 20:11, 28 August 2009 (UTC)

Not a problem, and I don't think you wasted anyone's time. We all choose how to use our time here. It's easy enough to search for things on Google or look them up in books, and you can always find the equations. But when you get stuck on why the equations are the way they are and need help in understanding the conceptual basis, well, that's exactly what we're here for. Hopefully at least some of us helped you, and feel free to ask more questions. (And I see that our concrete slab could use a bit of work, I'll put that on my list) Franamax (talk) 22:56, 28 August 2009 (UTC)

Comparing male/female weight loss on The Biggest Loser

Sorry about this banal question, but I'm going to be competing with some female friends in a weight loss race, and I want to make it fair so they cant complain when I win. I see in The Biggest Loser that it's proportional - they use percentage of body weight lost - is that how they deal with the fact that males tend to lose weight faster than females?

thanks Adambrowne666 (talk) 12:20, 28 August 2009 (UTC)

I suggest you agree with your friends about how your weight changes will be compared before starting the race. Then there need be no complaints afterwards. Cuddlyable3 (talk) 12:48, 28 August 2009 (UTC)

If that's all they do then that's all they do, so there's your answer. One of the reasons why men and women tend to lose weight differently is that, when working out, women often gain a fair portion of muscle mass. That dulls the weight loss they might otherwise notice. So if you wanted to be completely correct about it, percentage wouldn't inherently be correct, but it should be more than sufficient for your purposes. ~ Amory (user • talk • contribs) 13:11, 28 August 2009 (UTC)

Exercise increase the basal metabolic rate, what fat you burn at rest on a fasting stomach. According to our dieting article, this increase accounts for a lot of the weight loss from exercising. With equal heights the BMR is roughly BMR = 10*weight + s where s is a constant. Depending on whether you'r male or female s is +5 or -161. This means that the weight-term dominates the equation. Given two people who exercise equally, the fattest will loose the most weight. So as a measure of who's exercising most during a diet, percentage loss is a good measure and gender can be ignored. EverGreg (talk) 13:13, 28 August 2009 (UTC)

You have neglected to say what units you are measuring weight in... --Tango (talk) 14:28, 28 August 2009 (UTC)

I think on the biggest loser, it's not done that way just to compare male and females, but also people that are different amounts over weight. It's much more feasable to lose 100 lbs if you're 350lbs than if you're 250lbs to start with, for example. The % loss is probably a fairly fair way to go about it (although as pointed out it ignores muscle gains). Perhaps you could also compare BMIs (which will suffer from the same problem). TastyCakes (talk) 14:50, 28 August 2009 (UTC)

Doesn't this question request medical advice? You should consult your doctor before participating in a "weight loss race." Wikipedia can't specifically advise you on what a safe or desirable weight should be; nor what weight-loss regimen is healthy. Nimur (talk) 15:54, 28 August 2009 (UTC)

But we can speculate on what makes a fair competition, no? An egg eating contest might well have health implications, but we could still pontificate on the best way to judge such a competition (clearly most eggs as a percentage of body weight would be fairest). TastyCakes (talk) 16:00, 28 August 2009 (UTC)

This isn't medical advice, it is advice about judging a competition. There is no diagnosis, prognosis or treatment suggestion involved. --Tango (talk) 16:02, 28 August 2009 (UTC)

A lot of the time, it's the skinny ones who cram down the most eggs in absolute terms, so judging based on % body wt. might just skew things even farther in their favour. And I agree this is not a mediq per se, but a warning that rapid weight loss can be quite dangerous is certainly appropriate. Franamax (talk) 19:19, 28 August 2009 (UTC)

Yeah, look how many skinny people are champion gurgitators. Body mass has little to do with it, if anything it should be handicapped by height but even that's hard to correlate. --66.195.232.121 (talk) 20:28, 28 August 2009 (UTC)

I think those people are skinny precisely because they have an overactive metabolism (which also leads to their increased appetite). I should know, because I'm thin as a stick but I absolutely devour buffets and am constantly hungry. (Perhaps I have an enzyme deficiency or something...) John Riemann Soong (talk) 21:56, 28 August 2009 (UTC)

Possibly true, but when you're ingesting eggs at a rate of one a second, your metabolic rate isn't really going to help you fit more in, since the contest is over basically before the digestive process has even begun. I would rather speculate that a relative lack of fatty tissue around the stomach allows it to expand more in a short period of time. (And if you are able to enjoy eating lots of food while avoiding weight gain, I'd be thinking enjoy it while it lasts! Good food is one of the true pleasures of life. :) Franamax (talk) 22:42, 28 August 2009 (UTC)

Thanks, all, for your informative answers. Adambrowne666 (talk) 08:01, 31 August 2009 (UTC)

Recharging Electronics in Different Countries

If I take my iPhone to different countries around the world and plug it in to recharge from empty will the charge time vary based on the local electric power standards? TheFutureAwaits (talk) 16:35, 28 August 2009 (UTC)

Probably not, but make sure you have an adapter that can cope with all the different voltages you may encounter (ie 110V and 230V). SpinningSpark 17:26, 28 August 2009 (UTC)

And in addition to the voltage difference, be aware that plug configuration varies a lot around the world, beyond just the standard North American and European shapes. Franamax (talk) 20:53, 28 August 2009 (UTC)

Assuming everything works correctly, the wall voltage goes through a transformer which changes it to the proper voltage for the iPhone to use (and converts it to DC). At that point there's no difference in what the phone is receiving. Rckrone (talk) 17:39, 28 August 2009 (UTC)

Ah, thanks this makes sense. Though I was hoping higher voltage meant faster charge time... TheFutureAwaits (talk) 21:34, 28 August 2009 (UTC)

I hate to pass on rumours[24] but they say there is a problem of iphones exploding. Cuddlyable3 (talk) 13:37, 29 August 2009 (UTC)

what is the counterion for DNA?

Okay, I should prolly know this, but they don't ever mention where the positive counterion for the phosphate in DNA goes! I mean, if you have millions or billions of basepairs of this stuff in a single chromosome, it seems to me you have some major charge separation ... is it like sodium and potassium ions around the DNA? And when you're during agarose gel electrophoresis and you do DNA extraction, I assume these counterions are still hanging around in solution (or you'd have a major test tube of negativity, lol...), and it is these ions that flow in opposite direction of the DNA? But I'm really amazed, because chromatin gets wound into these megadense structures and I would think there would be some major electrostatic repulsion. John Riemann Soong (talk) 17:32, 28 August 2009 (UTC)

At first I was thinking that, the phophates may be protonated at physiologic pH, which would mean that counterions would be unneccessary. Upon actual research, that turns out not to be the case. However, This 2004 study implies that the DNA is actually in a diffuse sea of sodium and potassium cations, which provides the charge balance; however the counterions don't actually bond to the phosphates directly. This google search turns up LOTS of material on this topic. --Jayron32 18:44, 28 August 2009 (UTC)

Hmm, I'm just perplexed at why everyone seems to neglect to mention where the counterions go (or how they affect things) at the elementary level. The paper you cite gives short-length DNA chains -- but let's take say, a chromosome. Why don't the negative phosphates generate some major repulsion? I'm sure that the K+ and Na+ will have hard time reaching the phosphate groups deep within the chromosome. For that matter, I'm kind of perplexed at why DNA is called an "acid", when the NH2 groups and phosphate groups would seem to make it at least weakly basic. If DNA is already negatively charged, I'm sure that the pKa of DNA (or of one base pair unit) must make it a weaker acid (and a stronger base) than water. John Riemann Soong (talk) 21:46, 28 August 2009 (UTC)

Have a look at the histone article. There is a discussion of exactly what you are asking under the sub-heading "Structure". From the article: "Helix-dipoles from alpha-helices in H2B, H3, and H4 cause a net positive charge to accumulate at the point of interaction with negatively charged phosphate groups on DNA". --- Medical geneticist (talk) 00:54, 29 August 2009 (UTC)

I don't really know the answer to that question. I have always assumed that there would be enough hydrogen atoms around to balance the charges. Isn't that why DNA is considered an acid? Dauto (talk) 03:30, 29 August 2009 (UTC)

Well shouldn't it be called deoxyribonucleic conjugate base then? Are Na+ / K+ really the primary counterions, or is it H+? John Riemann Soong (talk) 20:04, 29 August 2009 (UTC)

If you get full dissociation in aqueous solution, there isn't really any "possession" of counter ions - that is, you can't say "these ions are associated with DNA, these with these acidic metabolites, these with acidic protein sidechains, etc." The neutralization of charge is a bulk effect - all positively charged species contribute to countering all negatively charged species, and vice versa. The closest you come to is when histones and other proteins bind to the DNA. The remaining charges are neutralized by whatever else is around. In large part this depends on the pH and what else is dissolved. At pH 7-8, there isn't a lot of H⁺ around, and other ions are needed (indeed - if the other ions haven't been added, you wouldn't *be* at pH 7-8). Inside the cell there are some positively charged amines floating around, but I imagine that most of the cations would be potassium rather than sodium (cytosol concentrations of ~200 mM vs. 5 mM - for E. coli, from Bionumbers). In an agarose gel, it will be countered by whatever counterion you've placed in the buffer. For TAE buffer/TBE buffer, that would be Tris. -- 128.104.112.102 (talk) 20:01, 31 August 2009 (UTC)

t--

Is K+ (as well as Ca++, Mg++ and whatever cations happen to be there) at a higher concentration in the nucleus? Basically the issue is that DNA would seem to be a pretty concentrated mass of negative charges, and a neutral histone could probably form polar bonds with DNA, helping to delocalise some of the charge, but this means negative charge areas would be created on "another" side (inside the histone?). DNA must create a pretty strong electric field inside the cell that would probably pull cations towards it! So these cations could be "associated" with DNA, roughly speaking. John Riemann Soong (talk) 00:49, 1 September 2009 (UTC)

Also, bacteria don't have histones, but I imagine that with a circular chromosome you're still going to get quite the localisation of negative charge .... wouldn't it be in quite a high energy conformation? John Riemann Soong (talk) 00:56, 1 September 2009 (UTC)

Histones aren't neutral. They usually contain a large number of lysine and arginine residues, which are positively charged at physiological pH. In fact, this is generally true of all nucleic acid binding proteins - overall, they have a net positive charge. The coulombic attraction between the positively charged proteins and the negatively charged nucleic acid adds to the binding affinity, and also serves to neutralize the negative charge on the phosphate backbone. I don't know about the difference in ion concentrations in the nucleus and cytoplasm, but it could be slightly different, although there is a bunch of other negatively charged items in the cytoplasm (ribosomes, mRNA, ATP, various small molecule and protein phosphates, various organic acid metabolites) which may boost the amount of cations in the cytoplasm. Remember also that water has a pretty strong dipole moment, and as such can shield/solvate charged particles quite well, so strict neutrality isn't needed. (Indeed, there is usually an electrostatic membrane potential that is maintained by the cell.) Also, while bacteria don't have histones per se, they do have histone like DNA binding proteins, as well as a host of other DNA binding proteins. -- 128.104.112.102 (talk) 15:30, 1 September 2009 (UTC)

Brain Development

Am I right in thinking that the brain stops developing at age 18 and the between the ages of 18 and 24, the brain only changes in the way it works in order to adapt to the adult social environment. In other words the brain of an 18 year old brain is fully developed structurally and has the same capabilities as a 25 year old brain but has just not yet adjusted to the adult environment. Thanks in advance for any answers. 86.139.54.213 (talk) 20:44, 28 August 2009 (UTC)

Neuroplasticity drops off sharply before puberty (and this seems related to the linguistic critical window). Neural stem cells continue to be active for most of the adult life (though neural stem cells are more active in children). Are you in an argument about maturity of 18-year-olds or something? "Structure" and "social environment" are all pretty vague terms. If you amputated an adult arm, the part of the brain that used to control that arm will be restructured to do something else. (though not perfectly -- sometimes you get phantom limbs.) John Riemann Soong (talk) 21:26, 28 August 2009 (UTC)

I've been reading around this area and alot of research suggests that the brainc ontinues to develop after age 18 up to about 25. However I don't quite understand how. The assumption I made above was that by age 18 the structuring process of the brain which occurs during adolescence has finished and the brain has its full capabilities and that after that the change is more of a change like you described with phantom limbs to adapt to the adult environment. 86.139.54.213 (talk) 21:35, 28 August 2009 (UTC)

As far as I understand, the brain was thought to stop developing at around 18, but more recent thinking is that it can continue to change or develop at any age. One example is registered London taxi drivers who have to memorise a lot of streets - known as "The Knowledge" - and the part of their brain that remembers things grows larger. 89.240.194.145 (talk) 22:54, 28 August 2009 (UTC)

Brain development has many aspects, and some of them continue throughout life, although most of the structure is in place by ages 5-6. Most of the brain's nerve cells are created before birth, and there is actually a drop in numbers after birth as redundant cells are eliminated, but there are a couple of special areas where new neurons are apparently created throughout life. One is the dentate gyrus of the hippocampus, and there is evidence that the newly created neurons play a role in storing new memories. This is just one aspect; a complete answer to the question would be very long. Looie496 (talk) 23:23, 28 August 2009 (UTC)

There was a mid-decade newsmagazine article that said the body pretty much reaches adultivity at 18, but brain development isn't really complete until about 22, and somewhat even until way into the 20s, so the traditional 21 age of complete majority would really be 22 psychologically. (though some things about wisdom teeth and bones aren't until 22) Does anyone know the paper(s) this was based on? Sagittarian Milky Way (talk) 00:07, 29 August 2009 (UTC)

I'm not quite sure what everybody means when they say the brain "stops developing". The brain continues to have the ability to learn throughout your life, which requires the formation of new connections between neurons. StuRat (talk) 14:30, 29 August 2009 (UTC)

I'd say your assessment is quite accurate. The brain stops 'expanding horizons' at about 18, and after that it's filling in the gaps left by that expansion, so to speak. Vranak (talk) 16:42, 29 August 2009 (UTC)

(Wrote this while ago but got distracted and never posted) As most of the discussions above indicate, this is a rather complicated and in some ways I would say unanswerable question since it depends by what you mean by structural brain development, stops etc. Generally speaking your brain is going to be changing until you die. Precisely how will depend of course on a variety of factors particularly how you train it. Size wise (well weight), the brain is already about 25% of the adult brain at birth [25] and broadly speaking is structurally very similar. Of course human brain development is much more then just getting larger and taking on the right structure. As said earlier, the brain is always changing and I'm pretty sure there are some quite significant changes past 18. For example, one thing that often comes up particularly when it comes to driving is that the parts of the brain involved in risk taking continue to change significantly until about 25 [26] [27] [28] [29]. It's sometimes said that the brain reaches maturity or adulthood at 25, but as I've indicated this is really overtly simplistic Nil Einne (talk) 20:23, 30 August 2009 (UTC)

Kirchhoff current law validity

It was quiet interesting when I had a discussion with some friends about Kirchhoff current law. Someone told me that there is some current lost in the case of a lamp/bulb due to electrons-ions effect. I'd like to verify this, and how can I restate Kirchhoff current law?--Email4mobile (talk) 21:44, 28 August 2009 (UTC)

It sounds like somebody is playing games with the definition of a closed system. Kirchoff's current law always holds, because conservation of current is equivalent to conservation of particles (# electrons in = # electrons out). There are no relevant electronic processes which create or destroy electrons; photon radiation by incandescent heating certainly does not create or destroy electrons. It might be *remotely* possible that some electrons thermally escape from the hot filament, and result in a static charge buildup on the exterior of the lightbulb; this is a very minor effect, if it is even measurably present in a lightbulb. Anyway, current is still conserved, if you count the flow of electrons via thermionic emission as part of the wire-in, wire-out system. A more general way of stating Kirchoff's law is in the form of the displacement continuity equation, $\nabla J=-{\frac {\partial \rho }{\partial t}}$; most people consider the charge buildup to constitute current (by definition). Nimur (talk) 22:16, 28 August 2009 (UTC)

In fact, Kirchoff's current law holds even if electrons are created or annihilated since electrical charge is always conserved. Rckrone (talk) 01:13, 29 August 2009 (UTC)

General fomula for electric fusing

Given a material's characteristics (type, length, cross sectional area) is there a formula to relate time-current fusion assuming normal conditions?--Email4mobile (talk) 21:49, 28 August 2009 (UTC)

Yes there is, the resistance of the material is a major factor, you need to make assumptions about how fast it will radiate heat, (and whether or not it's local surroundings form insulate the heat produced.

You also need a formula for Thermal_radiation - when the heat (due to resistance, dependent on current) generated is greater than the heat that can be dissapated at the fuse melting point the fuse fails. Note that the resistance depends on temperature too.83.100.250.79 (talk) 22:01, 28 August 2009 (UTC)

By "fusing" do you mean "melting?" Model the energy dissipated in a unit length of the material versus the heat radiated or conducted, along with the ambient temperature and tension on it. A bare conductor would carry more current without melting than an insulated conductor, and a conduit filled with conductors would lead to melting at lower current than the same conduit with one pair of conductors. Conductors at a very high ambient temperature would melt at lower current than conductors at low ambient temperature. Even the surface color or emmisivity of a conductor would affect the current it could carry before melting. In some household plug fuses, the spring tension on a fuse element causes it to open at a lower current than if it were not under tension. Edison (talk) 00:34, 30 August 2009 (UTC)

Yes I do mean "melting". The reason I raise this question is to estimate an approximate but general formula for the fuses melting curve given in data sheets, thanks..--Email4mobile (talk) 21:55, 31 August 2009 (UTC)

why is ammonia more acidic than water?

Is it because it has more protons to donate? It's kind of curious to me, because shouldn't oxygen tolerate the negative charge better than the ammonia? Or does having more hydrogens to delocalise the negative charge improve ammonia's acidity? If NH2- is a stronger base than OH-, why is NH3 more acidic? John Riemann Soong (talk) 21:52, 28 August 2009 (UTC)

Ammonia is a weak base. It is not more acidic than water. You should read that article, which describes its ionization process, and Ammonium for some electrochemical properties of the ion that forms. This MSDS from Texas A&M Chemistry says Ammonia has a pH of 11.6 at 1M and describes it as a dangerously corrosive alkaline. Ammonia also has interesting properties when mixed in low concentrations with chemical solvents at other net pH 's - it can become dramatically more dangerous and can create hazardous fumes. Nimur (talk) 22:06, 28 August 2009 (UTC)

I just did. I was actually curious about its pKa, and I note its value (9.75) is even lower than that of phenol (9.95). But NH2- has no resonance stabilisation! Why is it so acidic? I know it's a weak base, but ammonia seems to have some significant (though not symmetric) amphoterism. Water is usually known as an amphoteric substance, but ammonia seems to give water a run for its money. John Riemann Soong (talk) 22:11, 28 August 2009 (UTC)

What do you mean ammonia is not more acidic than water? Water's pKa is 15.74 ... a drastically weaker acid than ammonia. In fact, I'm wondering why hydrogen bonding doesn't form between ammonia molecules as it does for HOH molecules, since ammonia has a lone pair to donate, and it also has protic hydrogens to donate as well. Is it the lack of symmetry (3 protic hydrogens and 1 lone pair versus 2 protic hydrogens and 2 lone pairs)? Here's my working hypothesis: ammonia's 3 protic hydrogens give it an advantage over water, which only has two, resulting in a higher pKa. But nitrogen isn't as good at handling negative charge, so I wonder why those two effects don't cancel out. (I note that water is only an order of magnitude or two more acidic than alcohols, when it has twice the number of acidic hydrogens, so surely ammonia having 50% more acidic hydrogens can't lower the pKa that much??) John Riemann Soong (talk) 22:18, 28 August 2009 (UTC)

There are multiple definitions of acid and base. I think you're using an uncommon definition, and incorrectly applying it to compare Ammonia's dissociation constant to that of water. See also this detailed description of Ammonia and its pKa. You might also want to read Amphoterism about chemicals which have both acidic- and alkaline- properties, simultaneously. Nimur (talk) 22:19, 28 August 2009 (UTC)

It's uncommon to define acidity as a function of pKa? I suppose I don't know what the solvent context for the reported pKa value in question. If the 9.75 value is the self-ionization value, then the pKb of ammonia (in ammonia) should also be 9.75, shouldn't it? (Since there would always be equal amounts of NH2- and NH4+ with pure ammonia). Plus, I'm not sure how you would measure the self-dissociation constant of a gas...so I'm guessing the 9.75 value is that of ammonia in water? I don't see how I'm using pKa incorrectly here. If ammonia's pKa in water is 9.75, and water's pKa in water is 15.76, surely ammonia must be more acidic than water? John Riemann Soong (talk) 22:37, 28 August 2009 (UTC)

Also, what is the mathematical relationship between the number of acidic hydrogens (assuming that they are chemically equivalent) and pKa? I note that ethylene glycol has a pKa of 14.22 whereas ethanol has a pKa of 15.9. I actually suspect that the (straight-chain) alkyl group stabilises the negative charge on a deprotonated alcohol via hyperconjugation, so perhaps a 50% decrease in the amount of acidic hydrogens by itself should actually result in a much greater pKa difference than the pKa of alcohols would suggest? (Having a tert alcohol increases the partial negative charge on the carbon next to the alkoxy oxygen, but would probably only negate a minority of the stabilising effect, so perhaps it's possible that having more or less protic hydrogens can affect pKa that drastically, an effect which the alkyl group mostly masks?) And is it true that NH2- enjoys some hyperconjugative stabilisation? John Riemann Soong (talk) 22:37, 28 August 2009 (UTC)

Sorry for the 3 posts in a row, but can I double check to ensure that the 9.75 value is correct? A google search is telling me that some people think ammonia has a pKa of 9.25, which makes it even more acidic than I thought it was. John Riemann Soong (talk) 22:39, 28 August 2009 (UTC)

(see below) Basically google is giving you the wrong figure. It pKa ammonia =34

The OP (J R S) is talking about this acidity

NH3 >>> NH2- + H+

not the acidity/basicity in water -

I think there must be some wrong figures somewhere - Sodium amide definately deprotonates water.

I think you may have got the pKa for ammonium, not ammonia - that's an error on the part of the people who write the books/web pages - they say the pKa of ammonia when they are describing the pKa of NH4+

This is better [30] pKa ammonia/amide is 34 , (ammonium is 9.24) I assume this is near enough to 9.75 to not cause any problems

The 3 H's on N should add slightly to the acidity (compared to a hypothetical NH2, or an OH2 were the N and O have the same electronegativities), but this won't be a major factor. Less than 1 pKa unit.

83.100.250.79 (talk) 22:48, 28 August 2009 (UTC)

Wow, thank you .... I've gone back and fixed the article. It makes me so mad when people are sloppy and end up describing the pka's or pkb's of the ions instead. I was guessing solvent acidity because it's kind of hard to self-dissociate as a gas. How do you measure the self-dissociation constant of a pure gas anyway? One more question though ... I assume a 50% increase in the number of protic hydrogens results in a pKa decrease of around (or less than 1), but a 50% decrease (ceteris paribus) seems to affect the pKa way more than this (in alcohols the alkyl group's hyperconjugation probably masks this somewhat). Am I right in thinking that the relationship of the number of protic hydrogens to (pKa1) acidity isn't linear? John Riemann Soong (talk) 22:53, 28 August 2009 (UTC)

Wait a minute - alcohol hyperconjugation - you mean like in ethylene glycol? There's a much simpler thing going on here which is the stabilisation of -O^- by an 'adjacent' OH group

     H
    /
   O   O-
   |   |
 2HC---CH2

You can see how the H can be 'shared' by the two O groups - think resonant hybrids - is this what you meant - I don't think that is usually termed hyperconjugation. (I might have forgotten)

The effect of having more H's is complex - you can view it theorectically as having N times more hydrogen (ie equivalent to the concentration being N times more concentrated). As a first approximation this would change the pKa by log(N). (does this make sense to you?)

It's possible to draw up more complex models - but they usually fall apart outside a narrow range of compounds - because of all the other things that can alter acidity.83.100.250.79 (talk) 23:05, 28 August 2009 (UTC)

Wow, thanks for addressing ethylene glycol. I guess I don't have to make a new question after all! Is the inductive effect also at play in ethylene glycol? (Or is the single oxygen too far away?) I'm thinking something analogous to what happens in trichloroacetic acid. Would making the OH groups further apart basically weaken this "H+ delocalisation" significantly? If I had OH groups substituted on opposite ends of n-octane, for instance, would approximately see a pKa decrease of log 2 compared to n-octanol? John Riemann Soong (talk) 23:15, 28 August 2009 (UTC)

Also, by "hyperconjugative stabilisation" I was referring to the possibility that the alkyl group on ethanol for instance, helps delocalise some of the negative charge of the EtO- anion. Theoretically the difference in pKa between water and ethanol should be 0.30, right? But we observe a pKa difference of 0.14. The alkyl group seems to mitigate half of the lost acidity. John Riemann Soong (talk) 23:18, 28 August 2009 (UTC)

And does a tert alkyl group actually destabilise the conjugate base because the tert-carbon is likely to have more partial negative charge than say, a methylene carbon? What would explain say, isopropyl alcohol's increased acidity compared to n-propanol? Interestingly, methanol has a pKa of 15.5 -- it's more acidic than water! So the hyperconjugative stabilisation seems to have some observable effects (pKa stabilisation of 0.56? theoretically methanol's pKa should be 16.06 compared to water if the alkyl group didn't do anything...) John Riemann Soong (talk) 23:28, 28 August 2009 (UTC)

The inductive effect always works a bit, even 4 atoms away - but it gets weaker an weaker.. So 3chloro propanol will be ever so slightly more acidic than plain propanol. etc. Same goes for OH groups..

The log 2 effect I think would appply to any di-alcohol, that's just the effect of having more OH groups (don't quote me on that because I haven't got a reference - but I'm sure the reality isn't far off)

The H+ delocalisation should work best when the compound can make 5 and 6 membered rings (eg 1,2 and 1,3 diols) - (5 and 6 membered rings are the best - anything over get's a bit 'wobbly')

The difference in pKa between water and alcohol - the 0.3 figure is a very rough estimate (ie the value should be the same order of magnitude) - but maybe yes.

t-butanol is less acidic than s-propanol - this could be the electronic effect of the alkyl group - BUT - the larger the size of the alkyl group the more sterically hindered the O- is - which affects solvation - in other words in t-butanol the O- anion of the base is more difficult to solvate - I would expect this to have quite a significant effect in this case (the relative electron withdrawing abilities of the different plain alkyl groups being about the same.) In the absence of the solvation effect t-butanol might be expected to be as acidic as ethanol - because the larger molecule can very weakly stabilise the anion very slightly, and the other factors (excluding solvation) are nearly the same.

I think the difficult of solvation effect must be greater than the stabilisation due to hyperconjugation in t-butanol - as you mentioned above - measuring gas phase acidities would cut out the solvation effect - I don't know much about gas phase methods - if you want to know I suggest a separate question for it.

Yes methanol is a good example of hyperconjugation .

There's actually one book that covers all this (and super acids) very well - it's called "Physical and mechanistic organic chemistry" by R.A.Y Jones . Don't know if it's still in print - but you can get it from amazoncom from $1.40 (used)! (academic books are always expensive - typically about £30 for this new = ~50US $.) It should be library gettable - it's quite a common text for higher level chemistry. It's the size of a paperback novel, It may or may not be too complex - I haven't got a copy so this is from memory. But it definately covers all these topics.83.100.250.79 (talk) 00:14, 29 August 2009 (UTC)

I've given a link [31] - it seems to be out of print which may explain why some people are asking $150 for one on amazon. 83.100.250.79 (talk) 00:18, 29 August 2009 (UTC)

There's a link here [ http://books.google.co.uk/books?id=z3jXKOYuqQAC&pg=PA245&lpg=PA245&dq=methanol+acidity&source=bl&ots=dKaix0e3Or&sig=6jNkscLbVbfbwPrr1jPbfMXI6VU&hl=en&ei=Q3qYSs_ICpPajQet1IW3BQ&sa=X&oi=book_result&ct=result&resnum=8#v=onepage&q=methanol%20acidity&f=false] for the gas phase acidities of alcohols - page 245. It doesn't use the term hyperconjugation - but the data can be explained in terms of hyperconjugation quite well. It also covers solvation effects on page 246. It should go some way to answering most of your alchohol questions.83.100.250.79 (talk) 00:50, 29 August 2009 (UTC)

August 29

Alpha particle scattering experiment

If we perform alpha particle scattering experiment what will happen if electrons come across alpha particles? —Preceding unsigned comment added by Tipusultan11 (talk • contribs) 00:36, 29 August 2009 (UTC)

Electrons are not alive, so they cannot "come across" anything. They can be scattered elastically, though. Since the rest mass of an alpha-particle is much larger than that of an electron, the momentum of an alpha-particle in laboratory frame does not change significantly in that process. I assume you are talking about Rutherford experiment (a.k.a. Geiger–Marsden experiment), and you have read the article. --Dr Dima (talk) 01:26, 29 August 2009 (UTC)

An alpha particle is just a positively charged helium ion, He²⁺. So an alpha particle attracts electrons, and can bind with one electron to form an He¹⁺ ion, or bind with two of them to form a neutral He atom. Red Act (talk) 01:32, 29 August 2009 (UTC)

I think the alpha particles are moving too fast in this kind of experiment to stand much chance of capturing electrons. It is not impossible, though. --Tango (talk) 17:31, 29 August 2009 (UTC)

Unless the He++ e- pair can transfer energy to something the resultant He+ will be of such high energy that it would break apart again - the common method of losing energy would be to emit raditation, thus:

He2+ + e- >>> He+ + hv

83.100.250.79 (talk) 18:51, 29 August 2009 (UTC)

It is not easy to calculate rates of various He²⁺ + X <==> He⁺ + Y⁺ processes (photoionization and photorecombination, electron impact ionization and three-body recombination, charge transfer, etc.) even in a dilute gas or plasma; in a solid foil it is almost hopeless. However, Rutherford and his students used a foil so thin that electromagnetic interaction of an alpha-particle with electrons in the foil did not appreciably change the alpha-particle momentum, no matter what the end states were of that interaction. --Dr Dima (talk) 22:39, 29 August 2009 (UTC)

Parallax method

What is Parallax method? Please explain its use. —Preceding unsigned comment added by Tipusultan11 (talk • contribs) 00:46, 29 August 2009 (UTC)

The Parallax method is the use of two different vantage points to calculate the distance to an object. For example, if you stick a finger in front of you and open your eyes alternately, your finger moves with respect to the more distant objects in the background. It can be used to measure the distance to faraway objects, but the Parallax article does a very good job of explaining it (with diagrams), so I won't repeat that here. Awickert (talk) 00:55, 29 August 2009 (UTC)

I once saw a cow move its head from side to side while looking at me across a fence, as if it was using the parallax method to see how far I was away. I have done this myself in exactly the same way. Poor genius cow - turned into beefburgers. 89.243.198.115 (talk) 19:00, 29 August 2009 (UTC)

Uncertainty principle-another question

Uncertainty principle#Wave mechanics explains uncertainty principle of position and momentum of a particle.

It says: "If the wave (note by the poster: the wavefunction of the particle) extends over a region of size L and the wavelength is approximately λ, the number of cycles in the region is approximately L / λ. The inverse of the wavelength can be changed by about 1 / L without changing the number of cycles in the region by a full unit, and this is approximately the uncertainty in the inverse of the wavelength"

I think this is about one particle, but the above process includes changing the inverse of the wavelength without changing the number of cycles in the region by a full unit. If we are to measure only one particle, there seem to be no way of knowing the number of cycles in the region, on the other hand, if we are to measure a bunch of particles, capturing the shape of the wave seems possible, and therefore the wavelength and position. How should I understand this? Like sushi (talk) 08:35, 29 August 2009 (UTC)

You do need to repeat your measurement on many "identically prepared systems" in order to see evidence of the uncertainty principle, and you can by such repeated experiments build up a picture of the whole wavefunction. But knowing the whole wavefunction doesn't tell you the position and momentum because that information simply isn't there. Actual experiments aside, position and momentum can't be mathematically encoded in the wave function to better precision than what's given by the uncertainty principle. That's what the argument you quoted is meant to illustrate, I think.

Think in terms of systems, not particles. There's almost nothing that distinguishes the "fundamental" particles from any other system in quantum mechanics. The uncertainty principle applies to quantum systems regardless of the fundamental particles in them. I don't mean that it applies to the system indirectly by way of its constituent particles, I mean that it applies directly to the system as a whole. It's systems that are described by wavefunctions, not particles. Unless your system happens to consist of exactly one particle, the wavefunction of the system is not made up of wavefunctions of constituent particles. -- BenRG (talk) 13:17, 29 August 2009 (UTC)

You seem to be under the impression that the uncertainty comes from some difficulty in measuring the shape of the wavefunction. That's not the case. The uncertainty is an intrinsic property of the wavefunction even if we have a full knowlege of its shape. Dauto (talk) 13:23, 29 August 2009 (UTC)

Thank you for both. If we can build up the picture of the whole wavefunction, can we not tell the wavelength by measuring the distance between the peaks?

Like sushi (talk) 03:51, 30 August 2009 (UTC)

Only if the wavefunction is exactly periodic like a sine function in which case it would have infinite extension and you would pay your exact knowlege of the wavelength (and momentum) with complete uncertainty about the position. The particle could be anywhere along that sine wave. Simply cutting the sine function after some finite extension and setting the wavefunction to zero outside of that "box" doesn't solve the problem bacause you introduce other wavelegths into the fourier analysis of that modified wavefunction other than the original wavelength.In other words, you pay for your partial determination of the position of the particle with uncertainty about the wavelength (and momentum). That unavoidable feature of the fourier analysis is very much the spirit behind the uncertainty principle. Dauto (talk) 06:50, 30 August 2009 (UTC)

Sorry to bring up once more the constituent particles, but doesn't determining the shape of the wavefunction include determining the positions of each particles? I mean as parts of the picture like dots. ! I might have got it. The wavelength of the system can be known with the positions of particles, but not with the distribution of the positions of all particles in the system? That is what Mr. BenRG (I guess he is a man) means by "it applies directly to the system as a whole"?

(But where has "changing the inverse of the wavelength without changing the number of cycles in the region by a full unit" gone? I thought change in this limitation in the wavelength and the size of the wavefront at the distance have something to do with it.)

Mmmm... I don't know, but wavefunctions of particles are changes of some fields, right? Then as the field has no end, the wavefunction must have an infinite possibility of positions of particles, or have infinite areas of value zero? How does infinite areas of value zero influence the accuracy of determining wavelength?

Like sushi (talk) 08:01, 30 August 2009 (UTC)

I'm afraid I can't make head or tail of most of what you just wrote. I think you need to get all these wrong ideas out of your head and start from scratch. The wave function is not a wave in space. Particles don't have wave functions. Particles don't appear as dots or bumps in wave functions. A wave function and a quantum field are different things. You still seem to think that there's something special about particles and that you'll get a better understanding of quantum physics by starting with the particles. That's not true either. Forget about particles. In fact, forget about quantum mechanics for the time being. The uncertainty principle is a property of any kind of wave, not just a quantum wave function. To the extent that the frequency of a wave is well defined, the "position" (effectively the region where it's nonzero) is spread out, and vice versa. -- BenRG (talk) 10:31, 30 August 2009 (UTC)

I thought I might have got something, but that (you say) is wrong.

(Skip this if you are not interested in what I thought)I thought wavefunction spread in space (which has no end) and when observed, had one position like a dot (and can be seen as a particle). I thought observing a wavefunction might leave different dots and they could form a shape of the wavefunction.

So, what is Uncertainty principle?

It is a property of any kind of wave. And it is that "to the extent that the frequency of a wave is well defined, the "position" (effectively the region where it's nonzero) is spread out, and vice versa".

I don't know where to ask you to start, but one thing I feel not clear is what "position" is.

Like sushi (talk) 12:03, 30 August 2009 (UTC)

Okay, that paragraph (the one you believed) is pretty accurate, except that the wave function isn't defined in 3D space, it's defined in a "configuration space" where the points are different configurations of the system. When you do a measurement to find the state of the system you find some configuration where the wavefunction was nonzero. After the measurement you can treat the wavefunction as having "collapsed" such that it's zero everywhere except for a narrow peak around the configuration you actually got. This doesn't mean the system has collapsed to a point in 3D space, it means that the parts are fairly definitely in a particular arrangement, which might be spread out over a large area in 3D space. The dimensions of the configuration space are degrees of freedom (mechanics), arbitrary parameters that describe the arrangement of the system. You could call this the "position of the system", but it's not a point in 3D space; the system might occupy a large region of space. A point particle of the sort they talk about in undergraduate quantum mechanics (which is not quite the same as a particle-physics particle) can be described by three numbers giving a spatial position, so in a single-particle system you can identify the configuration space with 3D space. With two particles, though, the configuration space has six dimensions. With one rigid body it has six dimensions (three for position and three for angular orientation). With two rigid bodies it has twelve dimensions, and so on.

The classical time derivatives of the position and the angular orientation (momentum and angular momentum respectively) are not independent coordinates in the configuration space. Instead, they are the derivatives of the wave function with respect to the position or angular orientation. That means you can't have an object in a definite position or definite orientation, because then the derivatives don't exist and the momenta aren't well defined. There has to be some spread in the position. But the narrower the spread, the more the derivative varies, and so the less precisely the momentum or angular momentum is defined.

You can't work out the whole shape of the wavefunction by consecutive measurements on the same system because of the collapse, but you can work it out with independent measurements on a bunch of "identically prepared systems" (meaning, effectively, systems that all have the same wave function). However, even knowing the whole wave function you can't work out both the precise configuration and the precise time derivative of the configuration because they aren't both present in the wave function. Also, if you measure the "position of the system" then the wave function collapses to a narrow peak, meaning the momentum becomes very uncertain. If you measure the momentum then the position becomes very uncertain. -- BenRG (talk) 13:54, 30 August 2009 (UTC)

Well, it's true that in general a wave function can't be thought of as a function on 3D space, but for the simplest case of a single particle ignoring spin the only degrees of freedom are its position, so you can view the wave function as a function on space (or as a function on the momentum space).

To the OP: Uncertainty is as you said a property of any wave function. It follows mathematically from the way we define the momentum operator relative to the position operator. The Uncertainty principle#Derivations part goes into how you might prove that. Rckrone (talk) 19:17, 30 August 2009 (UTC)

I haven't thought that wavefunctions can have so many dimensions. So it has dimensions for positions plus dimensions for angular orientaions. What are these angular orientations? Do they have something to do with uncertainty?

I don't know what you mean by "parts" and "arrangement" in "...the parts are fairly definitely in a particular arrangement, which might be spread out over a large area in 3D space. The dimensions of the configuration space are degrees of freedom (mechanics), arbitrary parameters that describe the arrangement of the system."

And why collapse into "a narrow peak around the configuration" may not result in fairly accurate position and the wavefunction "might be spread out over a large area in 3D space"?

"you can't have an object in a definite position or definite orientation, because then the derivatives don't exist and the momenta aren't well defined". Derevatives are like, for example, tangent lines for a parabola, right? Then derivatives in the case of a definite position or definite orientation are not 0?

Like sushi (talk) 03:15, 31 August 2009 (UTC)

'Hottest' chilli pepper

We've been given a plant that is claimed to be the worlds hottest chilli pepper (not 100% sure though) and were wondering how to know when it's ripe?... They're green at the moment and look big enough but we're not sure whether that's the right colour and we don't know what variety it is... If anyone knows anything about the matter any help would be appreciated... Thanks —Preceding unsigned comment added by 83.33.75.101 (talk) 12:55, 29 August 2009 (UTC)

The "worlds hottest pepper" plants sold in department stores will turn orange or bright yellow when fully ripe. You can use them when still green as they're already very hot. --Digrpat (talk) 17:09, 29 August 2009 (UTC)

Bhut jolokia? Axl ¤ [Talk] 00:02, 1 September 2009 (UTC)

Hottest pepper

The above question inspired a desire in me to know what the spiciest pepper and spiciest foods are. Ks0stm ^(T•C) 17:18, 29 August 2009 (UTC)

See Scoville#List_of_Scoville_ratings. --Tango (talk) 17:32, 29 August 2009 (UTC)

Other flavours comparied with spiciness are substances like piperine from ground pepper and whatever it is that gives wasabi its flavour. I don't know what the most peppery/wasabi-y foods are, mind. Vimescarrot (talk) 17:51, 29 August 2009 (UTC)

Scoville scale generally measures only Capsaicin heat, and not piperidine (pepper corn) or Isothiocyanate (horseradish, mustard, and wasabi) are not generally measured on that scale. The methodology used to develop the Scoville scale could could be used seperately for piperidines and isothiocyanates, but it generally isn't necessary to develop a "mustard" scale or a "peppercorn" scale, since the botanical variation in these types of foods aren't as great as in the Chili peppers. Horseradish and peppercorn are just not known for having dozens of varieties, each with unique culinary uses, which would necessitate a "scale" for measuring them on. When you use peppercorn or Wasabi in a dish, you pretty much know exactly what you are getting. Chili peppers are a MUCH different sort of thing, and it is important to recognize the difference between a Poblano pepper, a Jalapeno pepper, and a Habenero pepper, lest you screw up a dish horibly... --Jayron32 19:27, 29 August 2009 (UTC)

Going off on a slight tangent here — does it strike anyone else as strange that most languages have no exact translation for hot as in spicy? In Italian, for example, the closest word is piccante, but that can also apply to spices that are definitely not hot (such as garlic).

I really don't think this is a culturally constructed category -- hot spices (the ones mentioned above, plus ginger) genuinely produce a sensation of heat, as in temperature, and non-hot ones don't. So why isn't there a word? --Trovatore (talk) 19:35, 29 August 2009 (UTC)

It's also intriguing that English doesn't have two separate words for knowledge: a word for knowledge that resulting from recognition and knowledge resulting from understanding...it's a trait that the German language has, yet English is lacking. Ks0stm ^(T•C) 19:43, 29 August 2009 (UTC)

Well, that's a little different — English is unusual in conflating kennen and wissen, conoscere and sapere. That can be seen as a quirk of English. In the hot case, though, English has a word for a natural, biologically based category, where no other language I'm aware of has such a word. So that's a "quirk" of all other languages, which is something that needs explanation. --Trovatore (talk) 19:47, 29 August 2009 (UTC)

I suppose that's like Irish where you're supposed to say if you know something from experience, from reading it in a book, or because somebody told you. But as to spices, I don't experience hot spices as hot in the sense of boiling water or burning as in the sense of a burn. So I see no reason at all why any other language should use the corresponding word for hot. Actually I think the Italian grouping is better though still not very good. In short I think it is a cultural construct. Dmcq (talk) 21:09, 29 August 2009 (UTC)

Well, I think you're just wrong on the facts here. The sensation of hot spices is not hot as in a burn, no, but it is definitely hot as in temperature. This is probably measurable — hook up some sort of sensor to the thermoreceptors in the tongue and the bucal epithelium, and you'll see a response. --Trovatore (talk) 00:50, 30 August 2009 (UTC)

Capsaicin may be of relevance hear, particularly Capsaicin#Mechanism of action. Capsaican does indeed activate one of the known temperature sensors. However I don't know whether you can say the stimulation is exact, as there are other sensors which are not activated including probably some we don't know about which are likely essential for our perception of normal temperature Nil Einne (talk) 08:51, 30 August 2009 (UTC)

One significant factor would be that spices (mild or hot) found their way to Europe rather late and people just "tweaked" exsting words to fit the novel sensation. I have no knowledge of languages on the Indian subcontinent or in SE-Asia, but I would not be surprised if "proper" terms existed for "hot" and "spicey" ingredients. --Cookatoo.ergo.ZooM (talk) 21:53, 29 August 2009 (UTC)

I think so. "Bedus" means "hot" in Javanese. I don't know how one would say spicy, but I'm fairly certain "bedus" isn't it. AlmostReadytoFly (talk) 22:31, 29 August 2009 (UTC)

In Malay wiktionary:pedas means spicy hot and wiktionary:panas means temperature hot (see also [32]). I don't think the word would be used for something like garlic, but perhaps that's partly because the effect is weak. I'm not sure you'd say it in relation to ginger either for that matter. ([33] says pedas means has a Chilli feeling/taste but I can't imagine any other word you'd use for something like Wasabi and the Malay Wikipedia article Ms:Wasabi does indeed use pedas.) I've always been intrigued by the lack of such a distinction in English and wondered how common it was and have even thought of asking it on the RD (WP:RD/L obviously) but never got around to it. As with Cookatoo, I've always expected it was because of the late introduction of hot spicy food into most English speaking cultures. This issue is always going to be complicated by the fact that most cultures lack a history of all the various foods that can be called 'hot' and for some cultures if the sensation is mild and/or overridden by other sensations and tastes that it may not be enough that it's likely to be called 'hot'. Actually personally I think a distinction between wasabi hot and chilli+pepper (or capsacain+piperine) hot is not unreasonable as their sensation is IMHO clearly different and from what I can tell from a brief glance at [34] and [35] (both need subscription) the receptors involved are different too. Interesting enough, it looks like garlic does in fact activate both the wasabi and capsacian receptors (second link) so perhaps it should be called 'hot' and the Italian usage is better then it seems. The entry at wiktionary:hot provides some clue on other languages but it's very incomplete and also could be wrong in some instances. Interesting enough Finnish appears to have a distinction but Hindi and Marathi appear to lack it. The lack of a distinction can of course be problematic e.g. when someone says their food is hot in some circumstances it's unclear what they mean. Nil Einne (talk) 08:26, 30 August 2009 (UTC)

In English, there is "to know", "to understand", and "to grok", in order of increasing understanding. We also have an article on Knowledge by acquaintance which goes over some of the kennen/wissen duality. As for the description of taste, Hebrew has distinct words for hot: "kham" for temperature and "khariff" for taste. It is the same in Russian, too: "goryachiy" is for temperature and "ostryi" or "perchennyi" are for taste. --Dr Dima (talk) 23:00, 29 August 2009 (UTC)

I'm not sure I think kennen/wissen is really about degree of understanding. You kennst a person; you weisst (or is it wisst? I've forgotten) a fact. I suspect that to wissen a person would have a Biblical meaning, the way Adam knew Eve. But I'm out of my depth here -- just speculating, really. I do think I've heard that Adam seppe Eve in Italian. --Trovatore (talk) 01:28, 30 August 2009 (UTC)

What's it mean "to grok"? I've never heard that word before. BTW, in Russian, "ostryy" literally means "sharp" (as of a knife, for instance), and "perchennyy" means "peppery" -- which would relate to spiciness on the Scoville scale. FWIW 98.234.126.251 (talk) 05:10, 30 August 2009 (UTC)

"Grok" is a word made up by Robert Heinlein and first used in the novel Stranger in a Strange Land in 1961. If you didn't grow up in the sixties doing magic 'shrooms and LSD, it's not at all surprising that it's unfamiliar. Its meaning is "to understand profoundly". - Nunh-huh 06:25, 30 August 2009 (UTC)

Incidentally — is it possible to damage one's tongue (whether you want to call it "burning" or otherwise) by eating overly spicy foods? Not a request for medical advice. Nyttend (talk) 13:41, 30 August 2009 (UTC)

I have two things to say here. Firstly, on the language issue noted above, Japanese uses 'karai' for 'hot' (as in spicy), but this can also mean 'salty' (even though there is also another more specific word for that). Secondly, I think garlic can be considered hot. Have you ever bitten into a piece of raw garlic (very common in Korean food)? I would say that is definitely hot as in the spicy sense of the word, so the Italian word definitely fits for me. --KageTora - (영호 (影虎)) (talk) 14:32, 30 August 2009 (UTC)

Ohm's law and Johnson–Nyquist_noise

I was just wondering how Ohm's law is valid given that resistance is related to the temperature of something. I mean it would be valid at any given instance but how would it work over time? Suppose you took something like a circuit with the light bulb. When the filament in the light bulb is cool its resistance is "x" ohms. However doesn't the resistance increase when you increase the temperature of the substance? When you completed the circuit and the light bulb lit up it's resistance would increase, which would make the current across the light bulb filament decrease. (EDIT:) Forgot to include that the current would then go down, causing the temperature to go down, and causing the resistance to go down, thus increasing the current and repeating the cycle. It seems like it would never reach a equilibrium. Is this fluctuation the Johnson–Nyquist_noise mentioned in the Ohm's law article? 66.133.196.152 (talk) 17:37, 29 August 2009 (UTC)

No, the filament will quickly reach an equilibrium point where the heat generated by ohmic resistance exactly matches the heat lost by radiation. Johnson-Nyquist noise, more commonly known as thermal noise does not represent any kind of oscillation by the applied current and is present even when the applied current is zero. It is, however, dependent on the resistance (as well as temperature) which is increasing with increased current. SpinningSpark 18:09, 29 August 2009 (UTC)

Lots of conductors have the resistance change when the temperature changes, or even when the current flow changes. Many conductors and semiconductors , diodes, transistors, vacuum tubes, mercury arc rectifiers, or arcs in general cannot be analyzed as simple Ohmic resistances. Edison (talk) 19:51, 29 August 2009 (UTC)

Exactly. In the case that the voltage-current relationship is not linear, the "resistance" is not constant, so generally it is said that the circuit is "non-ohmic" or that Ohm's law doesn't apply (at least, not with a constant R. Terms and definitions can be minced here). However, this is not really the cause for thermal noise; the theoretical basis for Johnson noise is usually attributable to the statistical, but non-deterministic, electron flow pathways at the atomic level. The mathematics of Brownian motion and Johnson noise discusses the necessary modeling from a pedagogical point of view. J. B. Johnson's original 1928 paper, Thermal Agitation of Electricity in Conductors, attributes the noise to thermodynamic equilibrium of the electrons and the atoms of the conductor material. Simple approximations can relate the thermal noise to the observed ohmic resistivity, but an in-depth analysis reveals that they have different causes and are separate effects. Nimur (talk) 00:50, 30 August 2009 (UTC)

Temperature dependent resistors, thermistors, sensistors etc do not obey Ohm's law. —Preceding unsigned comment added by 79.75.25.53 (talk) 00:57, 31 August 2009 (UTC)

Le Chatelier's principle

Hello. Why does the equilibrium shift in the reverse direction if the pressure increased by decreasing the volume for the following reaction: 6CO_2(g) + 6H₂O_(l) ↔ C6H12O6(s) + 6O2(g)? Thanks in advance. --Mayfare (talk) 18:20, 29 August 2009 (UTC)

Does it not follow the nitrogen hydrogen example in Le Chatelier's principle#Pressure? But I don't know in this case which is the greater volume of the two sides of the reaction. --Tagishsimon (talk) 18:27, 29 August 2009 (UTC)

I imagine H20 constributes to the vapour press, but only slightly. At very high pressures the CO2 will liquify first.

Mayfare, can you explain where you got the idea that the supposition you provided is actually true? Or at least give some other indication of the conditions?83.100.250.79 (talk) 18:47, 29 August 2009 (UTC)

According to the basic premises of LeChatelier's principle, this equilibrium should not be pressure dependent to a first approximation. The hypothetical solution to changes in pressure should be no change since there are the same number of moles of gas on both sides of the reaction (6 vs. 6) so NEITHER direction actually reduces the stress, so the reaction should favor neither direction in the case of increasing pressure. In actual practice, there are LOTS of factors that LeChatelier's Principle does not take into account, so there is a very good chance that changing pressure WILL cause an equilibrium shift, slightly, but that is largely due to a gap between the rather simplistic model that LeChatelier's Principle is based on, and the actual reality of the effects off pressure changes on all sorts of processes. --Jayron32 19:19, 29 August 2009 (UTC)

83.100.250.79, my tutor taught me this. I myself am as confused as you are. --Mayfare (talk) 02:28, 30 August 2009 (UTC)

The important thing is you understand the principle, which it seems you do. As for your tutor - do they make mistakes often - possibly the forgetful type? I hope they're not just incompetent :)

83.100.250.79 (talk) 12:25, 30 August 2009 (UTC)

This reaction is extremely unlikely to go in the forward direction unless there are some serious help involved, such as imput of energy and enzymes. In nature this would involve many other reactions that would have different rates and equilibria and competing side products. Graeme Bartlett (talk) 22:44, 30 August 2009 (UTC)

The other issue is that at a given air pressure the oxygen level partial pressure is constant, whereas the carbon dioxide partial pressure can vary a lot in the environment. So in a green house for example an enhanced carbon dioxide level can help plants grow faster. Graeme Bartlett (talk) 22:49, 30 August 2009 (UTC)

Bathroom scales inaccurate

The big disadvantage with the bathroom scales I've used are that the recorded weight varies by a large amount according to whether you lean slightly forward or slightly back. This is no good for precision weighing while dieting. Perhaps this problem has been due to always buying the cheapest bathroom scales available. Are there any types or brands of bathroom scales that do not have this problem please? Or do even the most expensive scales have this problem? 89.243.198.115 (talk) 18:54, 29 August 2009 (UTC)

If the reading is varying when you lean, that's probably because you're tilting the platform so that part of it is resting on the frame of the scale and taking some weight off the mechanism. If you want an accurate measurement you should look for the highest reading, which is probably going to be when your weight is centered. I don't have any good advice for finding a more accurate brand of scale though. Rckrone (talk) 19:08, 29 August 2009 (UTC)

This problem is easily solved with the 4-point scales. Often, they look like a glass plate on 4 rather chunky feet. Each foot is actually a miniature scale. Shifting weight off one foot will increase weight on another foot and the measured overall weight will not change. -- kainaw™ 19:12, 29 August 2009 (UTC)

Do you have any brand names for 4-point scales please? My Google search found nothing. 89.243.198.115 (talk) 19:24, 29 August 2009 (UTC)

Try this. Those are all glass, but you can see the manufacturers and locate more models. -- kainaw™ 19:33, 29 August 2009 (UTC)

The important feature is 4 load-cell technology (see this). The reason for inaccuracies (when leaning etc.) is that the weight distribution "web" for either a spring or a single load-cell scale is notoriously inaccurate particularly after exposure to a steamy bathroom for a few months (primarily due to friction at the pivot points). A four load-cell system truly applies the correct weight at each corner and sums those weights. hydnjo (talk) 20:26, 29 August 2009 (UTC)

Wikipedia as Education

Could Wikipedia and Wikiversity educate a child, without access to any other learning tools, to a university level? TheFutureAwaits (talk) 19:37, 29 August 2009 (UTC)

In the United States, you only need to score well on either the SAT or ACT to be considered "University Level". Those have a little mathematics, which is covered in both Wikipedia and Wikiversity. Mostly, they are reading comprehension problems, which is a skill that anyone can learn by reading Wikipedia and attempting to recall what was read. -- kainaw™ 19:41, 29 August 2009 (UTC)

If I had sought to educate myself with these tools, I would have studied what delighted me and avoided what I disliked. I speak mostly of Wikipedia and not Wikiversity. There would have been gaps, as is common among autodidacts. Who would enforce general distribution requirements in the curriculum? The student would have to be a glutton for punishment to learn science and math if only interested in art and music, or contrariwise. And reading an article about calculus, differential equations, matrix algebra, electrical engineering, physics or chemistry would not leave the pupil capable of solving problems in those fields. Reading the best articles that could be written about art or music would not produce a student whose performance level was high. Some subjects, like chorus, band or orchestra require a group. Group study can be very helpful in diverse fields such as math, the sciences, philosophy or law. Most self-taught scholars are weak on doing difficult homework in technical subjects. How would an autodidact do writing and learn from thoughtful criticism? Edison (talk) 19:49, 29 August 2009 (UTC)

The SAT is a test for admission to university. "University level" usually refers to things that are taught at university. --Tango (talk) 20:02, 29 August 2009 (UTC)

Starting from what level? You can't learn to read from Wikipedia. Once you've reached a reasonable level with the key skills you could learn quite a lot from Wikipedia, but generally it would just be learning facts. Wikipedia doesn't teach you how to do things. Wikiversity does, but it isn't anywhere near developed enough to be used in isolation yet. --Tango (talk) 20:02, 29 August 2009 (UTC)

Wikipedia and Wikiversity could probably be used as the only study materials as part of homeschooling. The parent or tutor would need some separate material to guide the student as to what to study in order to pass . Using Wikipedia (even the simple enghish version) as the only material to teach kindergarden and first grade would be impractical but not impossible. If you mean "to the level of a university graduate" I think you will need to allow for theuse of th erest of the internet, not just Wikipedia. A well-rounded student must also have some social interaction, of course, and sports and music are hard to do by yourself. -Arch dude (talk) 20:36, 29 August 2009 (UTC)

This case-study points out some of the flaws and limitations of web-based education. The case in question was using a web-based distance-education software (not Wikipedia), but the lack of interaction and feedback were found to be a source of frustration and impaired learning. Information-seeking strategies of novices using a full-text electronic encyclopedia, published in 1989, analyzes the case of encyclopedia-based learning. It is found that novice users have a very different strategy for learning than experienced learners. "The results demonstrated that, in general, young novice users could successfully use a full-text, electronic encyclopedia with minimal introductory training. Subjects in third or fourth grade were less successful and took more time than subjects in the sixth grade. ... Many, especially the younger searchers, used sentences or phrases as queries, reflecting an ill-defined mental model of the search-system, a kind of hybrid between a print-encyclopedia and an interactive computer program." Again, though, this assumes basic literacy as a prerequisite. Further, there is a big difference between being able to use an encyclopedia/ information database, and being a well-rounded student equipped for further academic study or career productivity. Nimur (talk) 01:04, 30 August 2009 (UTC)

You say that "there is a big difference between being able to use an encyclopedia/ information database, and being a well-rounded student." I would very much so argue that life with Wikipedia has allowed me to give myself a much more well-rounded body of knowledge than I would have gotten through traditional schooling. Mac Davis (talk) 04:30, 30 August 2009 (UTC)

That is a false dicotomy. You don't have to choose between Wikipedia and traditional schooling. I have made use of both and therefore have the problem solving skills, social skills, useful but boring skills and knowledge that come from school and the very broad body of knowledge that comes from spending far more time than is healthy on the Wikipedia reference desks. --Tango (talk) 16:00, 30 August 2009 (UTC)

I like Wikipedia just fine (and don't know Wikiversity well), but I don't really seem how they would replicate a "real" education. You need interactivity, you need assignments, you need more than lists of facts however well written. Sometimes, though it is miserable, you need drilling and route memorization. Sometimes you need someone to push you on your writing and on your performance. I don't really see how these sources can do it, any more than a giant Encyclopedia Brittannica would. Obviously such a thing could supplement an education periodically but the education is the method, not the specific tool. --98.217.14.211 (talk) 01:25, 30 August 2009 (UTC)

Education involves a lot more than a collection of facts organized for easy consumption. Wikipedia can never be more than such a collection of facts, and it and other print media can be a VERY IMPORTANT part of education, but it cannot and should not be the only tool. Lots of education, such as interpersonal feedback; which includes the ability to get questions answered AND the ability to have someone watch you learn and interpret the problems you are having and help correct those problems without you even realizing you had a problem that you needed to ask a question about. Also, the ability to practice a skill, to watch others with expertise perform a skill, to have someone watch you perform a skill wrong and provide correction; the ability to provide appropriate approximations which build your knowledge from the superficial to the deep learning, the ability to provide context to facts and to connect them to each other in ways that have meaning. All of that needs another person to do for you. Wikipedia certainly contains all of the raw facts covered in any typical university program; but it does not have any ability to provide you with any of the skills and activities that are the real core of any education. --Jayron32 01:47, 30 August 2009 (UTC)

St Augustine, in his "Confessions" from the 4th century or so, emphasized the importance to his early education of having the teacher beat the student when he preferred playing outside to learning things such as Greek and Latin grammar, which are not "fun." It is hard to get the encyclopedia to wield the cane in the form of grading or report cards or evaluations of any form, or directing the attention to things which "should" be learned rather than things which are intrinsically rewarding. Edison (talk) 03:28, 30 August 2009 (UTC)

When those argue that it is important to be beaten when you prefer to learn about some subjects and not other ones, they are arguing against freedom over your own education. They argue that each student needs a fine structure—all to often every student gets almost exactly the same structure and we definitely do not "take them seriously." Some children may need to be schooled, and some need to be unschooled. There is no specific body of knowledge that is, or should be, required of a child just as there is no one right way to live. Mac Davis (talk) 04:26, 30 August 2009 (UTC)

The flaw in your argument (actually, a great gaping chasm in your argument) is that an undeveloped brain without the necessary knowledge is ill-placed to decide which things are important and which are not - an untutored mind - given complete freedom to pick and choose what is learned - doesn't even know of all of the wonderful things they might want to learn about. Children require the guidance of someone who has already learned the material to guide them as to what needs to be learned (even if it's a pain to do that). A child is unlikely to voluntarily subject her/himself to the rigors of memorizing the multiplication tables - but without that, you're unable to perform any kind of arithmetic - and without that, most of science and mathematics would be shut out from their attention. Even a child who might otherwise grow into an adult with a passion for math would be exceedingly unlikely to simply stumble on that without guidance - and indeed some pressure to learn things that he/she seems to dislike. No matter how much the child resists - the multiplication tables have to be learned as a 'gateway' to giving that child the option to learn physics/chemistry/biology/etc in the future. There are also things that people have to learn to do despite hating to do it. People NEED to be able to read. Learning to read is not an option - it's a requirement. Your conclusions sound great - but are ludicrously over-simplistic in practice. SteveBaker (talk) 14:29, 30 August 2009 (UTC)

I agree with your main point, but I disagree with your example - I recently graduated with a 1st class MMath having never learned multiplication tables. I still don't know them. I do, however, know how to multiply. That is far more useful. I have no idea what 6x8 is, but I know that I can work it out very quickly because I know various landmarks (for example, I know my squares) and I know the rules of arithmetic, so I can do 6x8=6x(2+6)=6x2+6x6=12+36=48. I can do that in a fraction of a second, it doesn't really take any longer than it probably takes for you to recall that fact and use it (using it is generally so much slower than calculating/remembering it that is the only relevant part for the total time taken). My example (which applies to me, it won't apply to everyone - that is a key point in itself) is writing. I used to hate writing. I wasn't very good at it and I didn't enjoy it (the two are undoubtedly related, but I don't know what direction the causal link is in). I was, however, forced to do it. I can now confidently express myself in writing (although my handwriting is still terrible - just about legible, though!), which is a skill I now realise is extremely important for pretty much any application of those skills I did enjoy (maths, say). Had I been allowed to choose what I wanted to learn I would now know lots of maths but not being able to do anything with it. --Tango (talk) 16:00, 30 August 2009 (UTC)

A certain third grader I once taught the multiplication tables to could have furnished the answer faster than your claimed "fraction of a second," by learning 1x1 through 12x12, then speeding the recitation until it was as fast as the numbers could be spoken, then learning them backwards and sideways (breaking up the use of one rote order). It was something the student wanted to do, and not something externally required. The student went on in later years to far surpass my math accomplishments. Edison (talk) 18:50, 31 August 2009 (UTC)

Being able to recite them all in order is a completely useless skill. What is useful is being able to get the right answer to a specific question. I don't claim that knowing your multiplication tables by rote is useless, but I think the time would be better spent learning how to multiply. Tell me, how good was this third grader at his 13 times table? --Tango (talk) 22:50, 31 August 2009 (UTC)

Yes, as long as the only thing they needed to learn about was Family Guy. DJ Clayworth (talk) 20:14, 31 August 2009 (UTC)

Fruit beginning with U

Are there any fruits (of the culinary or botanical definition) whose names start with U in English, other than the Ugli fruit? --✶♏‭ݣ 20:49, 29 August 2009 (UTC)

Did you mean Ugni molinae? --Tagishsimon (talk) 20:51, 29 August 2009 (UTC)

No, I really did mean the ugli fruit but that's another good one. :) --✶♏‭ݣ 20:53, 29 August 2009 (UTC)

Ulster cherry, Uva di Troia, Usakhelauri, Ume --Tagishsimon (talk) 20:55, 29 August 2009 (UTC)

Well, the fruit of almost any flowering plant who's name begins with a 'U' would strictly meet your need. There are about a quarter million species of flowering plants - many of which are known by several common names - so there could easily be a million possible 'fruit names' - which probably means there are tens of thousands of candidates - vastly too many for us to list or even research! (For example: The Elm tree has the scientific name Ulmus - so it's fruit is an "Ulmus fruit".) But in terms of edible fruit - we'd have to refer you to List of culinary fruits - which lists only one - the Ugniberry - the Ugni molinae, which Tagishsimon already mentioned. I bet there are lots of others - but they'll be hard to track down. SteveBaker (talk) 14:15, 30 August 2009 (UTC)

Smell after rain

What does the smell after rain consist of? Mac Davis (talk) 21:31, 29 August 2009 (UTC)

See http://science.howstuffworks.com/question479.htm Who then was a gentleman? (talk) 22:05, 29 August 2009 (UTC)

They didn't list one of the bad smells, drowned worms decaying on the sidewalks. StuRat (talk) 13:00, 30 August 2009 (UTC)

I wonder (without proof) whether this is a Neural adaptation kind of phenomena - like the illusion where you stare at a brightly colored object for 30 seconds - then look at a blank, white sheet of paper and see the same image in complementary colors. Is it possible that we've become 'adapted' to the smells of our normal environment and have stopped registering them - then the rain washes those smells away, leaving behind 'pure' air - and (like the white paper) causing us to smell the complement of the smells that we've been ignoring. Just like an optical afterimage. Hence the air might seem sweet even though there is no substance in the air producing that smell. I have no idea whether that's really the reason - but I can see no reason why it shouldn't be true - and it fits with the smell seeming to dissipate very soon after it first appears. SteveBaker (talk) 13:59, 30 August 2009 (UTC)

An example: During a cross-country drive, I once stayed in a hotel in Sterling, Colorado (I had reserved the room from out-of-town because their rates were half of the surrounding towns). When I arrived, I found a huge cattle feed lot next door, and the whole town stank of manure. I asked the desk clerk if it always smells like this, and she said "Smells like what ?". StuRat (talk) 15:31, 31 August 2009 (UTC)

An interesting idea, and we certainly do stop noticing smells after a while and notice sudden changes in smells, however I don't see how a smell can have a complement. Eyes convert stimuli to a 3D space, the nose converts stimuli to a far larger space (about 400D according to Olfactory receptor). The concept of complements doesn't really work in that context. (Interesting fact of the day that I've just learned from that article: About 3% of the mammalian genome is devoted to genes for different olfactory receptors. That's an enormous amount!) --Tango (talk) 16:09, 30 August 2009 (UTC)

Well, if you agree that we stop noticing smells after a while - and yet we still notice when that smell goes away - isn't that the exact effect I'm speculating about here? There is an analogy with sound too - you can sit in an office all day with the fan running on your PC and not notice it. You'd swear there were no noises - but notice a more profound silence when you turn it off. If it works for sound and vision - it would be surprising if it didn't work for smell also. SteveBaker (talk) 17:47, 30 August 2009 (UTC)

With vision we see the absence of red as cyan, a colour in its own right. With smell and hearing we just perceive the absence of a given smell or sound as an absence (as you say, you hear a profound silence, you don't suddenly start hearing a different sound). --Tango (talk) 23:38, 30 August 2009 (UTC)

Severed vine

I have severed a vine that leads to a nice pumpkin I am growing in my garden. Oops. Is there any way to patch together the vine and save the pumpkin? Panasonic phones (talk) 22:01, 29 August 2009 (UTC)

Grafting might have some information on effective ways to do this. Rckrone (talk) 22:56, 29 August 2009 (UTC)

Proximate the severed ends, ensure they are tightly connected, and hope for the best. Time is of the essence. Also Google "milk fed pumpkin." Maybe additional nutrients would help. Edison (talk) 00:21, 30 August 2009 (UTC)

Done, and hoping. Thanks. Panasonic phones (talk) 00:05, 31 August 2009 (UTC)

Hurricanes in Southern California

weather.com is warning that Hurricane Jimena may hit Baja California in 3 or 4 days. Has a hurricane ever hit Southern California (note - I'm talking about Southern California, not Baja) while still at hurricane strength? Who then was a gentleman? (talk) 22:04, 29 August 2009 (UTC)

List of California hurricanes. -Atmoz (talk) 22:27, 29 August 2009 (UTC)

Great, thanks. Who then was a gentleman? (talk) 22:30, 29 August 2009 (UTC)

No known TC has officially struck California at hurricane strength, though the 1858 San Diego hurricane may have done so. –Juliancolton | ^Talk 19:29, 31 August 2009 (UTC)

Engineering - 'agricultural drain"

I am looking for details on how to make an 'agricultural drain'. What I understand so far: These 2 words do not seem to appear together as a phrase on wiki - only as 2 separate words in an article. It may have a more technical name and maybe that's why I can't find it.

It involves plastic sheeting with some sort of tube or foam which is buried underground where water normally collects and doesn't drain ie. next to a wall. This 'system' channels the water away to a desired area. I believe landscapers use it. I really want all the details possible... the depth, the slope, covering.

looking forward to seeing something about this on the website soon. —Preceding unsigned comment added by 41.208.48.176 (talk) 22:58, 29 August 2009 (UTC)

Try Tile drainage and Drainage system (agriculture) and the articles they link to. This has been an important, but expensive part of U.S. farming since the early 20th century. It makes muck into productive farmland. I am not sure that plastic sheeting is part of it. Landscaping also involves ditches, swales and berms. Try Googling those terms. Edison (talk) 00:15, 30 August 2009 (UTC)

It could be a varient of a French drain, which IS a common landscaping tool for keeping water off of the surface of an area, and it matches the OP's description almost exactly. French drains are very commonly installed next to structural walls to prevent water from resting next to a wall and damaging it. Our article describes their construction and use quite well, and also contains links to external sites. There's lots of good DIY websites describing how to construct and maintain a french drain... --Jayron32 01:38, 30 August 2009 (UTC)

Another option, for those with fields which are perpetually flooded, is to just plant crops which thrive in such an environment, such as rice. StuRat (talk) 12:55, 30 August 2009 (UTC)

Assuming there is infrastructure and demand to support such crops. They would also need to have a suitable climate to grow.

That can be impractical against a foundational wall; and may lead to other problems as planting directly next to a house can produce "root pry" problems. While in the open, carefully chosen plants may be a better solution than a French drain, against the foundation of ones house, a french drain is often a very efficient means of draining away water. --Jayron32 03:41, 31 August 2009 (UTC)

August 30

QUANTUM NUMBERS

What is quantum and quantum number? How electrons move around the nucleus? Explain.

Please do your own homework, as we will not do it for you. However, I will suggest the following articles: Bohr model, Bohr Theory and Balmer–Rydberg Equation, Quantum number, Principal quantum number, and Spectroscopic notation. ~ Amory (user • talk • contribs) 02:34, 30 August 2009 (UTC)

'Explain'? Readjust your attitude. And your grammar. Seriously, this is a volunteer reference desk. It's also part of an encyclopedia that you can search. Awickert (talk) 06:56, 31 August 2009 (UTC)

Blood pH

I was thinking about this and wondering: What substance in the blood keeps it slightly alkaline (7.35-7.45)? Why does the body maintain a slightly alkaline pH? bibliomaniac15 04:30, 30 August 2009 (UTC)

The major system used by most living things to is the bicarbonate buffering system. This, combined with the ability of the kidneys to filter extra H⁺ ions from the blood, and you have a pretty solidly maintained pH. – ClockworkSoul 04:43, 30 August 2009 (UTC)

As for the second question: the binding of O2 to hemoglobin is influenced by pH level, so the blood pH is maintained at a level that optimizes both the O2 binding in the lungs, and its unbinding in tissue capillaries. (Note that O2 binding decreases with lower pH, so an increase in blood CO2 concentration, which lowers pH ever so slightly, causes oxygen to unbind from hemoglobin exactly when and where it's needed most. Neat, huh?) 98.234.126.251 (talk) 04:51, 30 August 2009 (UTC)

That's a cool mechanism! DMacks (talk) 17:52, 30 August 2009 (UTC)

No single substance, though it all gets conceptualized as concentration of [H⁺]. Blood pH is maintained by a number of mechanisms, the most important of which are respiratory regulation (blowing off CO₂ by breathing more rapidly, or retaining it by breathing more slowly) and the bicarbonate-carbonic acid and dihydrogen phosphate-hydrogen phosphate-hydrogen blood buffer systems. Hemoglobin also has some effect as a pH buffer. See the Henderson-Hasselbalch equation, respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalosis articles for more detail. Your "why" question, taken locally, is that if the blood becomes too acidic, you die, and if the blood become too alkalotic, you die (because enyzmatic reactions necessary for life are pH-dependent). Taken more broadly, because that's how the system evolved: the blood's pH mimics that of the primeval sea in which it was evolved, in order to maintain the functioning of the enzymes that require that pH. Specifically, the transition to air-breathing led to relatively high CO₂ plasma tension and led to the development of the bicarbonate buffer system. See Some Aspects of the Evolution of Vertebrate Acid-Base Regulation. - Nunh-huh 05:06, 30 August 2009 (UTC)

Cell phone jamming

Here's a question related to the discussion about "White noise generator": Where I live, you always see drivers yakkin' (or textin', or even worse, readin' stuff on the internet) on their cell phones and not paying attention to the road ahead (that's how that big rig rear-ended my Mustang, the driver was talkin' on his cell phone and didn't see me stop at a crosswalk to let a lady with a little kid get across the road). So when I saw the discussion about "White noise generator", it got me thinking: is it possible to rig up some device that would prevent cell phones inside the car from transmitting / receiving any signals, while at the same time having minimal effect on cell phones outside the car? 98.234.126.251 (talk) 06:19, 30 August 2009 (UTC)

Theoretically. Cars can potentially act as Faraday cages. The pragmatic issue is that the cellphone frequency band prolly wouldn't be ideal. John Riemann Soong (talk) 06:49, 30 August 2009 (UTC)

And also you'd probably have to figure out a way to disable it when the car isn't running! 124.154.253.31 (talk) 08:00, 30 August 2009 (UTC)

I really doubt that this would be practically possible - and it would certainly be illegal. SteveBaker (talk) 13:47, 30 August 2009 (UTC)

Passive interference is legal, in the US anyway (which it sort of has to be—you can't blame an architect for happening to make a structure that doesn't conduct cell phone signals efficiently). Active interference (e.g. saturating a spectrum with noise) is prohibited by the FCC. --98.217.14.211 (talk) 14:00, 30 August 2009 (UTC)

Again, as I've pointed out numerous times, calling anything that is made of metal a "faraday cage" is a stretch at best. All you have to do is sit in your car and make a cell phone call to demonstrate, beyond reasonable doubt, that the car's metal frame is not a faraday cage - it's just a bunch of metal. It isn't attenuating the mobile telephone radio signal. It's probably not attenuating any radio signal (except maybe when you get towards the visible light frequencies - solid bodies are good at attenuating those!) A faraday cage needs to be specifically designed if it's going to be even slightly effective. It's going to have a specific frequency response. Even if it actually did suppress a particular frequency, the cell phone probably will be able to decode its signal anyway, because it uses a complicated digital spreading code. If you go around calling every piece of metal a "Faraday cage", you're devaluing the design and complexity of actual Faraday cages. Attenuation isn't a "qualitative thing" - it can be quantitatively analyzed, and I suspect that the attenuation of UHF radio through a car body is so close to zero that it's really creative application of terminology to call it a "shielding" effect. Nimur (talk) 14:45, 30 August 2009 (UTC)

I would point out as I did last time that GSM (and in fact the vast majority of 2G systems) doesn't use CDMA but TDMA. I appreciate that this discussion appears to relate to the US but your answer didn't clearly specify you were only referring to the US. Whether this makes a difference to the answer or not, I don't know but given a large percentage of the world uses GSM; with cdmaOne and 3G networks like CDMA2000, UMTS and others combined I strongly suspect remaining a minority I don't think it's wise to discuss this as if most mobile phones use CDMA. (My suspicions are supported by this [36] although it's hardly a neutral source.) Of course when we move to 4G we'd likely be using FDMA based on current proposals but it's a long way away before they take over given that 3G networks are still a distinct minority. Nil Einne (talk) 16:20, 30 August 2009 (UTC)

I think you are mistaken. GSM does use TDMA for packet scheduling and collision avoidance, but individual packets are coded with MSK, which is effectively a digital frequency spreading code. In fact, it's a more sophisticated frequency spreader than CDMA. I am not aware of any mobile telephony systems in operation, worldwide, that do not use a frequency spreading scheme for the digital encoding. We should make clear the difference between CDMA, the marketing-ese word for US-standard-radiotelephony, and CDMA, the technically-correct-description-for-code-spreading. The first paragraph of the CDMA article makes this distinction clear. Nimur (talk) 16:47, 30 August 2009 (UTC)

It may use spread spectrum. But that's irrelevant to me since the issue I raised was whether it used code division multiple access (which was the article you linked to, and also what you mentioned in a previous question). Although [37] appears to suggest to me (see below) that it's inaccurate to say GSM uses CDMA and our article doesn't seem to say it does either, if you say it does, then I accept that, since it's not something I understand very well. But if not, I feel my point still stands. And just to be clear, my point is that GSM doesn't use CDMA. I think the US marketing issue is somewhat irrelevant here since W-CDMA is commonly marketed as UMTS despite the fact it uses CDMA without dispute (actually it appears it's possible to use something other then W-CDMA, but all of them are CDMA and in any case, all use W-CDMA AFAIK) so I don't think there's any real confusion about what CDMA is, simply whether all spread spectrum techniques used by mobile phone networks are correctly called CDMA. P.S. I appreciate you did not specifically mention CDMA earlier on in this thread even if you did link to it, but I think it's inherently confusing to solely link to an article on CDMA (and not even as a sublink to the specifics) if (since I don't know) GSM doesn't use CDMA. It would be better to link to an article on spread spectrum (or multiple articles if you feel it's necessary, e.g. because our other articles don't explain it so well) since my understanding at the moment is that while CDMA is inherently a form of spread spectrum and is used by multiple mobile phone network systems, many 2G ones don't use it but use TDMA with spread spectrum techniques and possibly most 4G ones won't use it either, so solely linking to a CDMA article to explain spread spectrum techniques used by mobile networks is problematic. Again, if I'm wrong on this, apologies but I feel it's worth clearing up.

• Note that spread spectrum is not a modulation scheme, and should not be confused with other types of modulation. One can, for example, use spread-spectrum techniques to transmit a signal modulated by FSK or BPSK. Thanks to the coding basis, spread spectrum can also be used as another method for implementing multiple access + GSM, for instance, combines TDMA and FDMA. GSM defines the topological areas (cells) with different carrier frequencies, and sets time slots within each cell etc

Nil Einne (talk) 21:05, 30 August 2009 (UTC)

This is an issue that's worth further investigation; let's take this discussion offline since it's really peripheral to the OP's question anyway. I'll do some reading and follow up later in the week; I've been repeating this claim because I'm pretty sure it's correct; but if there's any doubt about it, then I should re-check my terminology and my facts before proceeding. Nimur (talk) 01:06, 31 August 2009 (UTC)

Nimur it is wrong to say: "MSK...is effectively a digital frequency spreading code. In fact, it's a more sophisticated frequency spreader than CDMA". Far from being a spreading code, MSK is a narrow band digital modulation method. Cuddlyable3 (talk) 16:00, 31 August 2009 (UTC)

This source, from our article: from Aerospace Corporation, has power spectral density plots for several variants of MSK and GMSK. I suppose it's up to the reader to decide whether 1 MHz consitutes "wide" or "narrow" bandwidth. I would put 1MHz channel width solidly in the realm of wide-band spectrum-spreading signal (considering the audio data is 3 kHz). Nimur (talk) 01:49, 1 September 2009 (UTC)

It would be technically straightforward to re-program the cell towers to refuse to connect to a moving cell phone. This requires no on-vehicle electronics other than the cell phone, and it allows you to pull over and stop and use your cell phone. It would even be possible to add specialized systems inside busses and trains to re-enable cell phones for their occupants. Harder, but not impossible, to permit the passengers but not the drivers in busses and trains. Very difficult or impossible to disable for car drivers but not for their passengers. The problem is that the voters will resist such a system. Similarly, it is technically straightforward to catch all speeders, but it's politically impossible. -Arch dude (talk) 14:59, 30 August 2009 (UTC)

I believe most of the signals you receive on the phone in the car now come through the windows of the car, other than that they should act as pretty good faraday cages as pointed out above. So I would think applying a film like they use on some trains to block out signals through the windows (see this article) would probably work about as well as it works in these trains (I don't know how well they work). TastyCakes (talk) 16:39, 30 August 2009 (UTC)

Excellent idea, TastyCakes -- a conductive film on the windows would work much better than an active jammer (which is expensive and can cause harmful interference) or reprogramming the cell towers (which can cause erroneous applications of the protocol). As they say, the simplest solution works best. (BTW, a wire mesh embedded in the windows could work just as well.) 98.234.126.251 (talk) 07:29, 31 August 2009 (UTC)

Programming cell towers to drop moving signals would not be a very good solution. The problem is drivers yakking on the phone. Passengers in all kinds of vehicles should not be limited as they are not operating the vehicle. Googlemeister (talk) 13:13, 31 August 2009 (UTC)

Is it not illegal to use a mobile while driving in the US? It certainly is in the UK (3 points on licence and £60 penalty) - unless it's 100% hands free. As regard signals getting in the car - I think it's the large amount of windows. On my metal boat - it kills the signal, unless you stand next to the window (or outside!)  Ronhjones  ^(Talk) 18:49, 31 August 2009 (UTC)

To address the question of the legality of using a cell while driving in the US, that depends on where you are. I think that it is legal most places, but I do know of at least one city where it is not. Googlemeister (talk) 20:12, 31 August 2009 (UTC)

Single celled organisms and evolution

Until I gave it a good think, I had previously assumed that simpler microorganisms (particularly single-celled varieties such as the amoeba) had survived essentially unchanged since the emergence of more complex/multi-celled organisms. But this shouldn't be the case right? It doesn't make sense to me that an Amoeba proteus from 2009 would look the same as an amoeba 10 million years ago, or that the flagella of Giardia lamblia hasn't changed in the past million years or so. But certain things I've been reading seem to hint at the contrary. Chlorophyceae seems to be organised according to the type of flagella each species/family has, which implies that the same flagella is ancestral to all species within that class. This seems incredible, considering the fact that larger species such as humans have structurally very little evidence of having ever been water-breathers, and water mammals have little evidence of ever having had legs! Could it be that there are many simple organisms that have been mis-classified because of such re-evolutions, or is there really a fundamental difference in the way simple organisms evolve?

Lastly, are there any single-celled organisms that (for example) show signs of having evolved into single-celled organisms after having been multi-celled? I can imagine the analysis of the genome of such an organism showing it as a member of a group exclusive to multi-cellular organisms, despite the obvious structural differences. Sorry for asking so many questions! 124.154.253.31 (talk) 08:00, 30 August 2009 (UTC)

I think you really want the distinction eukaryote versus prokaryote. The eukaryotes include single celled animals and plants and the multicellular animals and plants evolved independently. Amoeba is a eukaryote. You're probably thinking of bacteria and archaea which are much less complex and have had a very long time to evolve into something fairly optimal. They have changed of course and continue to do so but it's a bit like frogs - they look alike to us but genetically there's probably more difference between two random types of frogs than there is between us and the birds. Dmcq (talk) 12:27, 30 August 2009 (UTC)

Yes, sorry, I meant to refer exclusively to single-celled eukaryotes, as well as prokaryotes actually. I guess I didn't realize that there could be so many significant changes genetically without much physical evidence of it. 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

"...water mammals have little evidence of ever having had legs" ? Sure they do. Whales have non-functional, residual rear legs, which don't protrude beyond the skin, even to this day: [38]. Their front legs, fingers included, are now their fins. StuRat (talk) 12:47, 30 August 2009 (UTC)

Argh. I recently watched a video about this and they made a lot of fuss about the discovery of residual legs in a primitive whale found in Egypt; the way they worded it made it sound like the bones no longer existed in modern whales. I guess all I can say then is that they no longer have toes? 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

Micro-organisms certainly evolve. They do it continuously and rapidly. That's why we have so much trouble with drug resistance - we treat simple organisms with drugs that are supposed to kill them - the few that survive go on to become the whole population. Over many generations of micro-organisms, you have a drug that no longer works anymore. This is an extremely common phenomenon. But our ability to track that evolution into the distant past is limited. Looking at the appearance of bacteria doesn't tell you much about what's going on biochemically inside - and we don't have that detailed information about bacteria from the distant past. It's not like a large organism like (say) a horse. We can find the fossilised bones of ancient proto-horses and deduce a lot about how they evolved - but our ability to do that kind of thing for micro-organisms is extremely limited. SteveBaker (talk) 13:41, 30 August 2009 (UTC)

True, but we can compare the genes of single-celled organisms with those of multicellular organisms. To the extent that they are the same, it's reasonable to conclude that both groups have preserved an ancestral structure. Looie496 (talk) 00:28, 31 August 2009 (UTC)

The bacterial flagellum is a favourite of creationists. Because it is fairly complex they think it couldn't have evolved. Cilia are a similar thing. Richard Dawkin's book The Ancestor's Tale has a bit about them, especially the Mixotricha paradoxa, it's a pity wiki doesn't have a nice picture of that. Dmcq (talk) 16:41, 30 August 2009 (UTC)

You can also check out Kenneth Miller's The Flagellum Unspun, published in 2004 by Cambridge University Press. DRosenbach ^{(Talk | Contribs)} 20:35, 30 August 2009 (UTC)

The concept of punctuated equilibrium is probably relevant to the original question. Single celled organisms evolve so rapidly that they quickly reach highly optimized forms, which can persist with only minimal changes for a very long time. Looie496 (talk) 00:28, 31 August 2009 (UTC)

Wow! If punctuated equilibrium is true, than that explains a lot to me. I understand that there are competing controvercial theories, and that of course as SteveBaker says the micro-organisms are evolving, but due to the extremely specific niches that most of these organisms have evolved to occupy it makes sense that they would give appearances of having met some sort of equilibrium, a cancelling out of multiple evoluctionary changes. Dmcq made the point about frogs, but have they really changed functionally that much? It seems like an example of genetic rearrangement over enormous spans of time only to result in an organism that does virtually the same thing maybe more efficiently but without any extra tricks (of course, most individual species of frog have developed lots of tricks, but I'm attempting to refer to frogs as a group of species).

I have previously thought of the idea of "highly optimized" or "perfectly evolved" forms as silly, almost narcissistic, but now I can see how it might not be such a strange concept. 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

An organism can be perfectly evolved for a given environment, but a change in the environment would tend to necessitate a change in the organism. Generalists like humans are more likely to be able to adapt behaviorally, like by wearing more or less clothes, as the climate changes, while specialists like finches must evolve physically, such as the shape of their beaks as their food source changes. StuRat (talk) 19:00, 31 August 2009 (UTC)

Micro-organisms can generally evolve much more rapidly though - their extremely short life-cycles (some can produce a new generation every 10 minutes!) allows them to evolve vastly more quickly than (say) humans who require 16 to 30 years to do the same thing. Large animals have to be at least somewhat generalists because there simply isn't time for them to evolve. But bacteria could conceivably be so super-specialised that they might suite an environment that changes so often that the bacteria are continuously evolving to fit its changes. But whether you'd say that a generalist was "well suited" to any particular environment is a tough call. SteveBaker (talk) 05:33, 1 September 2009 (UTC)

Genus Canis

What are the best sources for up-to-date information on the coywolf and other contorversies surrounding the family tree and phylogenetics of the genus Canis? NeonMerlin 08:01, 30 August 2009 (UTC)

It looks like the Journal of Mammology, the Journal of Systematic Zoology, and Conservation Biology have all published articles. The articles I found were The Taxonomic Status of Wild Canis (Canidae) in the South Central United States, The Taxonomic Status of Wild Canis in Arkansas, etc. You can find these sorts of journals in a university library, or online (if you have subscription access through your school, library, etc). Nimur (talk) 14:56, 30 August 2009 (UTC)

Parameters of Planet Habitability for people? (not Extremophiles)

There is an article that refers to habitabilty of Extremophiles "ETs" but I was wondering if there is any matter or thought on the parameters of survivability of a planet for Human Beings? I know the Habitable zone article talks about one dimension there, temperature ranges from 0°C to 100°C but most people wouldn't survive through 70% of that range. Also gravity, atmosphere composition and emissivity, atmosphere pressure, hydrosphere size, magnetosphere strength, irradiance, eccentricity, axial tilt, albedo, etc. must have referable boundry limits were people are concerned, does anyone know what these ranges are?? Cpt. J. Tiberio Kirk (talk) 08:31, 30 August 2009 (UTC)

There's a difference for people, where we can live in a place that doesn't meet all our survival needs, by trading with others who have those items we lack. Thus people can live in a wider variety of places than we could if we were all hermits. Remote whaling villages are one example from a couple centuries back, and people living at the South Pole or on the International Space Station are some extreme examples from today, where they are provided with everything they need, in this case in exchange for research. So, do you mean to ask where people can survive if provided with all their needs from outside, or where they can live in total isolation ? StuRat (talk) 12:37, 30 August 2009 (UTC)

We don't even need to trade, technology (even something as simple as a warm coat) can dramatically increase the range of environments we can survive in. --Tango (talk) 15:42, 30 August 2009 (UTC)

Sure, but where did you get that warm coat? Unless you single-handedly grew the plant fiber; smelted the steel and forged the industrial sewing machine; operated the vertically integrated fiber-to-cotton-to-coat industry... you had to trade something to get that coat. Chances are, much of the material and labor for that industrial chain came from a more habitable region, depending on how far back into the supply-chain you look. Nimur (talk) 18:11, 30 August 2009 (UTC)

In modern times, yes, but specialisation on a large scale is a fairly recent part of human history (just since the industrial revolution, really, it existed to a lesser extent for a few millennia before that). A caveman could have killed a large animal and turned its skin and fur into a coat without any trade involved. --Tango (talk) 19:23, 30 August 2009 (UTC)

Agreed. So a human with some basic technology, like the ability to make animal skin clothes, has a wider range than one without. We can see that by where Inuits and other similar people live (which doesn't extend all the way to the poles, however). Without any technology at all, people would be forced to live only in tropical areas near a food and fresh water supply. But once a high level of technology and trading is added, people could live just about anywhere on Earth, and even in space, provided that those who remain on Earth are willing to send them what they need to survive in exchange for the research/exploration/experimentation they do. StuRat (talk) 15:04, 31 August 2009 (UTC)

Just as we are if you will, not a space station or "technology:"

(Human Environmental Tolerances.)

Attribute	Minimum	to	Maximum	Earth eg./avg.
Temperature:	0°C	to	30°C	14°C
Gravity:	0g	to	??g	1.0g
Atmosphere composition:
Oxygen	??% min		??% max	21%
Nitrogen	??% min		??% max	78%
??	??% min		??% max
??	??% min		??% max
Emissivity:	from ??	to	??
Atmosphere pressure:	?? mb min	to	?? mb max.	1013.25
Hydrosphere size:	??% min	to	100% max.	71%
Magnetosphere strength:	?? min		?? max	0.3-0.6 gauss
Irradiance:	???? W/m2	to	???? W/m2	1366.078 W/m2
Eccentricity:	0 min	to	0.3022 max.	0.016710219
Axial tilt:	0 °	to	??° max	23.44°
Albedo:	0.?? min	to	0.?? min	1.0 = Absolue zero

I'm looking mostly for help with references... ...does anyone know what these ranges are, for ANY planet Habitation?? Cpt. J. Tiberio Kirk (talk) 08:31, 30 August 2009 (UTC)

Some of these terms are poorly defined, e.g. magnetosphere strength, and even incident radiation (What does this mean - total radiation? Blackbody-style radiation with a peak near visible light? I'm pretty sure that 1 kW of gamma radiation is much more hazardous than 1 kW of visible-light!) Atmospheric composition will have varying effects ranging from temporary to permanent health problems; do you have a criteria for quantifying these? Are you seeking the LD50 or something similar for these parameters? How long do the humans have to survive (a few hours, weeks, months, years?) It seems unlikely we can find habitability data for humans regarding the orbital parameters, as we have only experienced life on Earth; but I can't imagine what an eccentricity has to do with anything (except its effect on other planet parameters, like temperature and radiation). Nimur (talk) 06:07, 1 September 2009 (UTC)

• IS THIS THE SCIENCE REFERENCE DESK or the "I can't imagine" so I'll bash the question desk??

You need an English lesson? -> Habitability and Habitation,

How do you confuse "Median lethal dose" with "Habitiability" and still think you should comment here?

If you don't understand the question should you be commenting with ignorant questions?Cpt. J Tiberio Kirk (talk) 08:34, 1 September 2009 (UTC)

Didn't we come to the conclusion in a thread some time ago that humans could probably/possibly survive at 2x earth gravity? --Kurt Shaped Box (talk) 11:34, 1 September 2009 (UTC)

"NOx" written in expanded form as...?

Is "oxides of nitrogen" or "nitrogen oxides" appropriate for a research paper to be published in an international journal? I'm cleaning up a manuscript for a Chinese professor and the original has "oxides of nitrogen" which seemed a bit off to me.

Google shows both are present in the vernacular, so I'm wondering if anyone with direct experience in a related field could give me a definitive answer (or even a definitive "they're both ok")...

Thank you, 61.189.63.152 (talk) 13:37, 30 August 2009 (UTC)

Both are fine. Nitrogen oxides may be better, especially if it is to be indexed by a computer.83.100.250.79 (talk) 14:27, 30 August 2009 (UTC)

I'm not a chemist. To me, between the two, I'd prefer "oxides of nitrogen", as it communicates very clearly that we're talking about a group of compounds. For retrieval purposes, I'd suggest including both as index terms. --98.114.146.57 (talk) 14:51, 30 August 2009 (UTC)

NOx is a perfectly acceptable "technojargon" term in certain communities, and does not need expanding. While in a strictly chemical context, an expanded form may be more appropriate, I think it would confuse readers from other disciplines (like atmospheric research, combustion research) who are more used to seeing "NOx" and knowing unambiguously what is meant. Nimur (talk) 15:00, 30 August 2009 (UTC)

Highly dependent on the conventions for the specific journal (some have style-guides with lists of accepted/standard abbreviations) and/or the target audience. DMacks (talk) 17:51, 30 August 2009 (UTC)

I agree. Check the manual of style for the particular journal. Google Scholar found 477,000 usages. Nimur (talk) 17:59, 30 August 2009 (UTC)

Coal & Fossils

Coal, like oil, as I am lead to believe, is formed from the compression of carbon based material (i.e. animals and plants) over time. Why is it that some animals become fossils, yet others become coal? Also, related question, why do we have coal and oil fields? It seems like all these animals all died in the same place. Any info would be appreciated. --KageTora - (영호 (影虎)) (talk) 14:17, 30 August 2009 (UTC)

Fossils in coal are actually very common - search for "fossils coal" - here's a fish [39], and image search may be even better.83.100.250.79 (talk) 14:24, 30 August 2009 (UTC)

Thanks. So, if there are fossils even in coal, where does all the rest of the coal come from? --KageTora - (영호 (影虎)) (talk) 14:36, 30 August 2009 (UTC)

Ah, I think that last question has just been answered by an Gimage search. It said that in the case of that particular image, the coal in question was fossilized peat, which would lead me to believe that the surrounding coal on the image of the fish in your answer would also be some such similar thing, such as vegetation. --KageTora - (영호 (影虎)) (talk) 14:41, 30 August 2009 (UTC)

Fossil forming requires circumstances conducive to it. Fossils are by no means a certainty when you have organic matter entombed in mineral matter. See rarity of fossils. Bus stop (talk) 15:15, 30 August 2009 (UTC)

(ec) Fossils can be present in coal, but most coal is not made of decayed animal. It is made from Type III kerogen, "terrestrial plant matter that is lacking in lipids or waxy matter" like peats and grasses (and trees, maybe). Different kinds of plant matter (like marine algae, lake plants, and terrestrial plants) are different kerogen material, and typically result in different kinds of fossil-fuel. However, few fossil-fuels are actually made of animal fossil. Nimur (talk) 15:17, 30 August 2009 (UTC)

Thanks, Nimur, but in my original question, I did actually mention plants, too. --KageTora - (영호 (影虎)) (talk) 16:28, 30 August 2009 (UTC)

Ok, but it seems like the kerogen article will link you to the information you want. Why do certain regions form oil or coal, while others do not? See petroleum geology for an in-depth answer. To summarize: you need several conditions to occur - presence of a kerogen source (meaning the correct type of plant or organic matter), and the presence of a reservoir rock that can hold that matter; presence of a seal rock; and mild seismic activity (geothermal energy) to cook the kerogen without fracturing the seal. This is a rare combination, so only certain regions result in liquid hydrocarbon or economically extractable natural gas. Coal, on the other hand, doesn't need a seal rock; and is less sensitive to seismic activity; so it is much more common. I might have misinterpreted one of your original questions, "Why is it that some animals become fossils, yet others become coal?" In truth, no animals become coal; only certain plants can become coal; but even those must be subjected to the proper geological conditions (as I described above), so coal will only form in certain regions. Nimur (talk) 17:21, 30 August 2009 (UTC)

I see, thanks. You have cleared it up. Basically, the reason why we have coal fields is because those conditions only exist in certain places. Animals don't become coal, so that is why we have fossilized animals in coal. I get it, now. Thanks. --KageTora - (영호 (影虎)) (talk) 17:58, 30 August 2009 (UTC)

As an extra tidbit, the two main depositional enviornments that I think of for coal are (a) oxbow lakes in subtropical to tropical meander belts that slowly fill up with sediment, and (b) costal/tidal plains. Awickert (talk) 06:51, 31 August 2009 (UTC)

Puzzling Puzzle

This is already on the Miscellaneous desk. We discourage cross-posting of questions. // BL \\ (talk) 16:22, 30 August 2009 (UTC)

Wouldn't it fit better on the Math desk? -GTBacchus^(talk) 16:26, 30 August 2009 (UTC)

Transparent objects

Why transparent objects are transparent.? —Preceding unsigned comment added by 121.245.107.152 (talk) 18:13, 30 August 2009 (UTC)

At the risk of sounding glib, because you can see light through them. The article Transparent materials is reasonably clear even for a non-scientist. // BL \\ (talk) 18:30, 30 August 2009 (UTC)

The article is reasonably clear? How fitting to the subject matter! No wonder the article on black holes seems a bit less enlightening to me. --Cookatoo.ergo.ZooM (talk) 19:24, 30 August 2009 (UTC)

It is important to remember that transparency is dependant on the wavelength of light in question. We usually mean the visible part of the EM spectrum, but something being transparent in that part (or not) does not mean it is necessary transparent (or not transparent) in other parts. For example, the glass in a greenhouse is transparent to visible light but not to far infra-red light (that's part of why it traps heat). A bin bag is opaque to visible light, but transparent to far IR (there is a picture of that further up this page in the "invisibility" section). I believe it is all to do with electron energy levels - to absorb a photon there has to be en electron in the substance that can rise to another energy level an amount of energy higher equal to the energy of the photon (which is inversely proportional to wavelength). --Tango (talk) 19:19, 30 August 2009 (UTC)

Greenhouses mostly trap heat by trapping hot air. The greenhouse effect isn't very significant in greenhouses. — DanielLC 22:45, 31 August 2009 (UTC)

Have you considered why non-transparent things are like they are - once you understand this you may be able to come to terms with transparency.83.100.250.79 (talk) 21:20, 30 August 2009 (UTC)

That is essentially exactly the same question, so how is that helpful? --Tango (talk) 22:38, 30 August 2009 (UTC)

No it isn't - I was suggesting that they look at why things absorb light. Once that is understood transparent things should be obvious.83.100.250.79 (talk) 00:01, 31 August 2009 (UTC)

Of course it will be - you'll already have the answer because it is the same question. Something is transparent if it doesn't absorb (or reflect - don't forget that possibility, although arguably it is temporary absorption) light, so if you know why something absorbs light you also know why other things don't. They are the same question, just from a different direction. --Tango (talk) 00:11, 31 August 2009 (UTC)

The question is "why do these things let light through" - I thought it might help to consider "why do some things not let light through" - obviously they are two sides of the same coin. - Non tranparency is (in my opinion) less 'mysterious' (in a psychological sense consider how excited people get about gadgets with transparent bits)than transparency at a very basic level, which is where we are.83.100.250.79 (talk) 00:44, 31 August 2009 (UTC)

What gadgets? Cuddlyable3 (talk) 15:38, 31 August 2009 (UTC)

Controllers for games consoles, and some handhelds, come in semitransparent versions. Vimescarrot (talk) 15:52, 31 August 2009 (UTC)

Hair follicle imitator

Is there a plant or animal that looks like a hair follicle, including the root (white or clear "bulb")when pulled out that is much stiffer and thicker than surrounding follicles and which does not soften or react to isotropy alcohol but dies or dissolves when iodine is applied as an antiseptic? 71.100.5.63 (talk) 19:39, 30 August 2009 (UTC)

Are you asking if an animal or plant exists that would be lodged into a human scalp, so that when plucked it would resemble a hair and its follicle? DRosenbach ^{(Talk | Contribs)} 20:28, 30 August 2009 (UTC)

Why did you say scalp??? ...but yes. 71.100.5.63 (talk) 21:16, 30 August 2009 (UTC)

I'm curious if you mean what is sometimes called in slang "fledges" - a form of 'pubic' like hair that grows on the shoulders etc, as people get older - this is thicker and stiffer that normal hair.?

What exactly happens when you add iodine ?83.100.250.79 (talk) 21:18, 30 August 2009 (UTC)

The original one I found was about 1.5" from the corner of my mouth. I thought at first it was a petrified blackhead. The end looked more like a glob of grease than a root. The one on my scalp that I put iodine on simply vanished. The third one I have now became much softer after the iodine but has not dissolved completely yet or gone away. Never heard of "fledges." What is it? 71.100.5.63 (talk) 21:31, 30 August 2009 (UTC)

It sounds to me like an ingrown hair, which may grow much thicker than a normal hair and have the appearance of a pimple before it emerges. Unpleasant, but not a sign of disease or infestation. I've had them along the jawline, and when they emerge they have an appearance like what you're describing. --FOo (talk) 22:23, 30 August 2009 (UTC)

No curling or folding backwards. I've had ingrown hairs but none that were thick, tough, and straight. This is definitely a species that has come here from outer space to infiltrate Earth to spy on us by pretending to be a hair. 71.100.5.63 (talk) 23:22, 30 August 2009 (UTC)

Morgellons syndrome. --TammyMoet (talk) 08:56, 31 August 2009 (UTC)

Fish safety

For years I've enjoyed tunafish - both as BBQed steaks and also raw in sushi. A while ago I saw sushi grade tuna for sale at a fish place, and for the first time enjoyed raw fish as a meal in its own right rather than with rice. Delicious. I've bought tunafish steaks a couple of times since.

My question is, isn't raw meat (including fish) supposed to be extremely prone to food poisoning? Is this safe? What is the difference between "safe" raw fish (used worldwide in sushi) and "unsafe" raw fish if any? (assuming it's from a reputable source, fresh, washed, cold, etc)

What's the risk if I carry on indulging myself by buying raw fish at reputable stores and taking it home to make my own sushi and raw fish meals at leisure? What precautions and other safety rules do I need to be aware of?

Thanks for any answers.

FT2 ^{(Talk | email)} 19:51, 30 August 2009 (UTC)

This might help -- you can google "raw fish safety" yourself for more info. DRosenbach ^{(Talk | Contribs)} 20:27, 30 August 2009 (UTC)

Thanks :) FT2 ^{(Talk | email)} 21:39, 30 August 2009 (UTC)

It's not a good idea to overdo the tuna, even if it's cooked. From the mercury poisoning article: "the consumption of fish is by far the most significant source of ingestion-related mercury exposure in humans" and "larger species of fish, such as tuna or swordfish, are usually of greater concern than smaller species". This is especially true for certain at-risk groups (see the article), for whom the FDA recommends limiting the consumption of albacore tuna to no more than 6 oz per week, and all other fish and shellfish to no more than 12 oz. per week. My niece developed mercury poisoning a few years ago, while in her late teens, after eating nothing but tuna fish and blueberries for 6 months (she had an eating disorder). The symptoms of mercury poisoning have pretty much ruined her life. Red Act (talk) 11:59, 31 August 2009 (UTC)

So far parasites have been mentioned, as has mercury (which is just as much of a problem in cooked fish). The other major threat of raw fish is bacteria, which is worse when they have started to decay. This would result in the classic food poisoning symptoms of nausea, vomiting, and diarrhea. Cooking fish properly should kill of all (or almost all) of the bacteria, but then they can regrow if it's left around too long. There may also be some virus which can be passed from fish to a person, that I'm not sure about. In short, cooking meat and fish is one of the best ideas humans ever invented, and skipping it seems too risky for me. StuRat (talk) 14:47, 31 August 2009 (UTC)

When you say 12 oz. per week, how many ounces in a normal meal, say at a seafood place down in Florida, with dinner sized fish & a side dish or two?4.68.248.130 (talk) 18:57, 31 August 2009 (UTC)

A typical fillet of flounder is four to six ounces, for example. --Sean 19:10, 31 August 2009 (UTC)

I've filets 3-4 times in a week-long vacation, but then hardly ever eat it throughout the year. that's probably safe. Your mileage may vary, though some may depend on how deep the water is it comes from, and your size; I'm pretty much average build and close to ideal weight. I love mahi mahi and grouper myself.Somebody or his brother (talk) 23:18, 31 August 2009 (UTC)

Trying to figure out the name of a car part

Hi. I was looking at a Volkswagen Passat yesterday and there seemed to be rust on part of the wheel/axle but I am not sure what the part is so I can look it up (the salesman told me that it was caused by brake dust and wasn't a problem). I can't find a clear picture of the part but it was basically a drum shape that seems to be at the very end of the axle, and has the wheel bolted to it (so it sits ust behind the hub cap). It is circular, maybe six inches deep and nine inches in diameter (very rough estimates). I wondered if anybody could help me find the name please, so that I can investigate the rust issue more thoroughly. Thanks HungryAvocado (talk) 19:55, 30 August 2009 (UTC)

red calipers, brake disk and the rotating plate of the wheel hub

In that area, you tend to have the wheel hub (comprising wheel bearings and a plate for mounting the wheel itself - good engineering drawings); attached to the static part of the hub are brake calipers; attached to the rotatable wheel mounting plate is the brake disk ... the calipers fit around the disk and brake pads sit within caliper. The whole thing then tends to have a metal shroud around the back of it (at least in my memory it does), and, err, that's about all there is. Any other parts in the vicinity will be suspension or steering. Does this help any? --Tagishsimon (talk) 20:06, 30 August 2009 (UTC)

Thanks very much, that is very helpful. The specific part where the rust was seemed to be was the cylinder that protudes from the large disk in the photo and has the holes in the end of it. Is there a specific name for that, or is it just part of the brake disk? Thanks again for your help. Thanks HungryAvocado (talk) 20:44, 30 August 2009 (UTC)

Normal rusting on a wheel hub

I think it would be described it as the moving part of the wheel hub. Compare with this car part advert. However elsewhere it appears to be an integral parl of the brake disc (brake rotos in USian) - see here. Your's probably looks much more like the second photo I've posted. IMO surface rusting here does go with the territory and in general is nothing to worry about. If the metal has started flaking away, that's another thing entirely. --Tagishsimon (talk) 21:06, 30 August 2009 (UTC)

And in closing the part you pointed to, on a Passat, does appear to be integral to the brake disk - and costs $36. --Tagishsimon (talk) 21:13, 30 August 2009 (UTC)

Thanks for all this help. For some reason the part that I saw doesn't actually look very similar to the brake disk on partstrain.com. It looks more like the original image you linked to, in the sense that the cylinder was much deeper (maybe even deeper than your original photo). I have slightly doctored the original photo here to show was the rust looked like (it was in patches and looked quite superficial). Thanks again HungryAvocado (talk) 21:27, 30 August 2009 (UTC)

No probs. The part you coloured plays no direct functional role; sounds like it's fine. --Tagishsimon (talk) 22:33, 30 August 2009 (UTC)

I know very little about car specifics - but with localised rust like that - would it be worth looking for a source - perhaps the car has been left standing for a long time and some water found a way to drip through the bodywork - hole in the wheel arch.?83.100.250.79 (talk) 00:39, 31 August 2009 (UTC)

Cars which have been idle (not driven at all) for even just a few days (depending on climate) will develop a rust film on their brake discs. This is extremely common, and disappears within a few miles of driving as the brakes are used again. Here are some forums where this is discussed: [40] [41] [42] [43] with some posters reporting rust appearing within days or hours after the discs get wet. Nimur (talk) 01:17, 31 August 2009 (UTC)

I wish there was a International Standard Part Number (ISPN) that was stamped on every manufactured item, not just for car parts, like an ISBN number for books. This would make getting a replacement part from eBay or whereever so much easier - I speak from experience. If a non-standard alphabet was used that had 50 or 60 characters rather than the traditional 10 or 24+9, then the ISPN need not be very long. 78.147.28.17 (talk) 10:31, 1 September 2009 (UTC)

August 31

Why do dogs sometimes chase their own tails?

I am not a dog owner, nor have I ever owned a dog - but I have noticed dogs doing the tail chasing thing when I've been out and about. Sometimes I've even seen them manage to successfully bite their own tails - quite hard, if the dog's pained yelp and jump immediately afterwards is anything to go by.

Now, I'd always put it down to dogs not being particularly smart and failing to realize that their tails are part of their own body - but thinking about it now, that doesn't really make any sense at all. Presumably the dog receives sensory feedback from its tail telling the brain where the tail is in relation to the rest of the body, so even if the dog saw its tail in its peripheral vision it would have a good idea that it belonged to its body and wasn't a prey animal/chew toy to pursue and attack...

So, what's really going on here? Some sort of canine body integrity identity disorder or other neurological/psychological issue? Too many recessive genes due to inbreeding? --Kurt Shaped Box (talk) 00:44, 31 August 2009 (UTC)

Dogs may not be anywhere close to the intelligence level of humans, but they're much smarter than people often give them credit for. I suspect it's more likely a form of play. – ClockworkSoul 01:00, 31 August 2009 (UTC)

I'd say it's exactly that. Cats often do it as well (and they're much smarter than dogs :D). Next time you see an animal do this, take a look at it - usually, you can tell there's an element of playfulness there as it chases its tail around. Young cats and dogs will often play fight - it's more common in wild cats like lions - training to hunt and survive on their own. You might also ask why children play with dolls are pretend to be superheros. It's creative entertainment. ~ Amory (user • talk • contribs) 01:28, 31 August 2009 (UTC)

Don't think that I hadn't considered that myself - but is it really normal to bite one's own body parts hard enough to cause what appears to be significant pain during play activities (excluding certain human sexual practices... ^_^)? --Kurt Shaped Box (talk) 01:33, 31 August 2009 (UTC)

One of our cats does it frequently (once a week that we see). Perhaps it is some form of pleasure, sexual or otherwise. -hydnjo (talk) 02:12, 31 August 2009 (UTC)

The fundamental error here is to assume that everything an animal does is for a reason. Every action has a cause, but not every action needs to have a reason -- that is, not every action needs to result from a plan formulated with the aim of accomplishing an understood goal. It seems likely to me that the dog is responding automatically to a certain type of movement, just as you or I automatically look toward a bright light that flashes in front of us. Looie496 (talk) 02:58, 31 August 2009 (UTC)

Even if there was no real reason to chase a tail in the first place, a dog may learn that chasing his tail grabs a lot of attention from humans (who usually consider it funny), which may reinforce the behavior. Unilynx (talk) 22:12, 31 August 2009 (UTC)

How about drinking? What's the percentage of people that "hurt" themselves while drinking in a "playful" manner? And how many do it again the next weekend? Roughly 98.63% of college students, at my last count. It's a different situation, we could also look at punching a wall or pounding a table in anger or frustration. I've seen no research on it, but it's probably a feature of highly intelligent creatures to be able to do things that seem to cause themselves immediate pain and harm (mind over matter). ~ Amory (user • talk • contribs) 03:19, 31 August 2009 (UTC)

I disagree with the above, i think dogs might not be aware that the tail is their own when they are chasing it. I can't see any reason to doubt it apart from our human interpretation of how "dumb" that would be and how "smart" we think dogs are. Not suggesting it is directly related but most animals, including dogs do not pass the Mirror test. Vespine (talk) 04:02, 31 August 2009 (UTC)

OR here, but I always thought that, similar to Looie496's comment, the chasing of tails is related to dogs' built-in chase reaction. Dogs will react to a fleeing squirrel (or dog, or cat, or human) by chasing it, and my belief is that tail chasing is related. Tempshill (talk) 06:29, 31 August 2009 (UTC)

I'd say that they are aware that it's their tail at a certain level, but that's not enough to overcome the instinct to chase and bite at wiggling objects. For a similar example in humans, if I see a bunch of bugs on TV, my skin gets itchy and I just have to scratch, even though I'm fully aware that those bugs aren't actually on me. StuRat (talk) 12:01, 31 August 2009 (UTC)

Young dogs almost always do it occasionally - but if your dog does it a lot - or fails to grow out of the habit - then you have a seriously bored dog who needs more stimulation - either from human contact - or perhaps with some chew toys or something. SteveBaker (talk) 18:16, 31 August 2009 (UTC)

If your dog need more stimulation, get him a humpy toy. StuRat (talk) 18:54, 31 August 2009 (UTC)

World Drug List

About a year ago, I found a file online that had every prescription drug name (both brand name and generic name) for the entire world. I remember it being hosted by the WHO. However, I simply cannot find it anymore. Can someone provide a link to such a file? I already have the NDC file from the FDA. That file is so full of typos and omissions that it is useless. I'm looking for a file that has all brand names and generic names without typos and without omissions. -- kainaw™ 01:59, 31 August 2009 (UTC)

http://www.who.int/medicines/publications/essentialmedicines/en/ - this one? - use Google with a site limiter e.g. list of drug site:www.who.int  Ronhjones  ^(Talk) 18:39, 31 August 2009 (UTC)

Thanks. That is not what I am looking for, but it is a list of medications (a list of what is considered "essential" for a proper health care system). I meant to use this list for another project and forgot about it. According to the WHO, these medications are "essential". I wanted to match them up against what different insurance agencies and drug programs consider to be "essential". -- kainaw™ 02:05, 1 September 2009 (UTC)

Carl Linnaeus translated to English?

Can anyone point me to some of Linnaeus's scientific writings translated to English please? Thanks Adambrowne666 (talk) 08:05, 31 August 2009 (UTC)

The Wikipedia article is Carl Linnaeus. This[44] gives some of his writing in Latin with English translation.Cuddlyable3 (talk) 14:16, 31 August 2009 (UTC)

I'd imagine that most of the translations of his major works are in printed form (such as this). Online, things are probably more difficult: There's an old translation of the Ordines et genera insectorum, so disfigured by scanning errors as to be practically unreadable, here; and a few other things are available behind subscription walls. Wikisource has a (very) partial text of an Introduction to Botany that seems to be an exposition in English of Linnaeus' systematic work. Just search for Linnaeus English translation and poke around. Deor (talk) 15:38, 31 August 2009 (UTC)

Ground

If there is no solid ground on the giant planets, what stops you from going underneath their surfaces? —Preceding unsigned comment added by Jc iindyysgvxc (talk • contribs) 08:21, 31 August 2009 (UTC)

At a certain distance, it might be hard to push through the heavily-compressed gas, but otherwise nothing prevents you from going underneath their surface. --99.237.234.104 (talk) 08:30, 31 August 2009 (UTC)

Extreme pressures, winds, and, in some cases, temperatures. StuRat (talk) 11:49, 31 August 2009 (UTC)

Galileo (spacecraft) sent a probe beneath the atmospheric surface of Jupiter. It certainly vaporized before hitting the metallic hydrogen interior. -- kainaw™ 11:57, 31 August 2009 (UTC)

In my case a lack of transport. Cuddlyable3 (talk) 13:56, 31 August 2009 (UTC)

Or, as a linguistic exercise, if there is no solid ground, what does "underneath the surface" even mean? — Lomn 13:59, 31 August 2009 (UTC)

Not a thing. You'd sink right in. Probably not all the way to the core, but you'd sink for many many miles. Until you got so deep that the air pressure was high enough to crush you like a tomato. APL (talk) 14:47, 31 August 2009 (UTC)

OMG! I had no idea tomatoes were so likely to crush me! I need to be MUCH more careful near my refrigerator. SteveBaker (talk) 18:12, 31 August 2009 (UTC)

Yes, that's why they are called "rotten tomatoes" ... those evil fruits masquerading as innocent veggies ! StuRat (talk) 18:40, 31 August 2009 (UTC)

No, no, "rot10 tomatoes" would be dywkdyoc, which stands for "Do You Want Ketchup? Do You? Or Catsup?" --Anonymous, 20:08 UTC, August 31, 2009.

If you have a way to slow down (e.g. re-entry shield and then a parachute. You will eventually begin descending slowly and approximately vertically. Your descent will stop at the point where the density of your spacecraft equals the density of the gas, assumiig that your spacecraft is strong enough to resist crushing. You can go deeperby usig power or by increasing your denisty (e.g., by compressing some of your internal atmosphere) similar to the way a submarine operates. -Arch dude (talk) 15:24, 31 August 2009 (UTC)

You must be using an ablative shield, as atmospheric pressure has apparently blown away the closing parenthesis for that first sentence, the "n" in "assuming" (where the existing "i" was also split into two), the space between "deeper" and "by", and the "n" in "using". The letters in "density" were apparently also shaken out of position. I'm just glad that any of your paragraph managed to survive at all. :-) StuRat (talk) 18:51, 31 August 2009 (UTC)

This is what happens when every component of your paragraph lander has been made by the lowest bidder. ;) Franamax (talk) 20:07, 31 August 2009 (UTC)

It would be a straightforward engineering exercise to calculate how large a gas bag would support a small pressure cabin, so that a vessel could descend in the atmosphere of a gas giant to a level where the pressure would not crush the pressure cabin and the gas bag would give the entire craft neutral bouyancy. For extra credit, could it jettiston ballast, expand the gas bag and ascend to a higher altitude, then launch a rocket to escape the planet? Edison (talk) 18:40, 31 August 2009 (UTC)

Isn't Jupiter also highly radioactive? Googlemeister (talk) 20:09, 31 August 2009 (UTC)

not especially so radioactive in the body of the planet, it is the magnetosphere of Jupiter that is full of radiation. Graeme Bartlett (talk) 21:41, 31 August 2009 (UTC)

Moon

Why doesn't the Moon have an official name? Jc iindyysgvxc (talk) 08:50, 31 August 2009 (UTC)

What about Luna? -- Aeluwas (talk) 10:48, 31 August 2009 (UTC)

The other earth moon is called Cruithne —Preceding unsigned comment added by 79.75.25.53 (talk) 10:57, 31 August 2009 (UTC)

The Moon does have an official name. According to the IAU, it is called "Moon", alternatively "Earth I". Perhaps you are thinking of other natural satellites, which are commonly called moons, with a lower-case "m"? There is only one Moon, the one in our sky. Sorry I can't pop up the link just now, this is my last post before bed. Franamax (talk) 11:47, 31 August 2009 (UTC)

Nahh, I lied, I have one more post in me. From the IAU page, you go to the link they supply and voila - it's called "Moon"! Franamax (talk) 11:56, 31 August 2009 (UTC)

An etymological dictionary[45] implies that until 1665 the only moon to consider was the Moon. The first non-earth moon identified as such was Titan in 1655. (Galileo saw 4 of Jupiter's moons in 1610 but called them the Medician Stars.)Cuddlyable3 (talk) 13:53, 31 August 2009 (UTC)

This is going to get confusing if we ever start communicating with other civilisations. I'll bet everyone calls their moon "Moon". APL (talk) 14:44, 31 August 2009 (UTC)

And I bet everyone also calls their own planet some variation of the theme of "Earth." Thankfully, they probably won't speak English, so we can just call their moon "J'klorb" or whatever their word is. ~ Amory (user • talk • contribs) 15:42, 31 August 2009 (UTC)

• It works for countries here. There are several countries or ethnic groups whose names mean "the people" or "people who can talk" (i.e. in a comprehensible language), but we just use their words for that, or a form of them. Two examples that come to mind are the Slavs and the Inuit. --Anonymous, 20:17 UTC, August 31, 2009.

"They" will probably communicate in high frequency, highly directional pure sound tones that cause your eyeballs to burst when spoken to...83.100.250.79 (talk) 18:35, 31 August 2009 (UTC)

Similar question came up before http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2007_September_5#Names_of_Sun_and_Moon

83.100.250.79 (talk) 14:52, 31 August 2009 (UTC)

Genetic modification of pubic hair for transplant?

Could pubic or body hair be modified by genetic or chemical methods to permanently resemble head hair, and then be transplanted on to balding mans scalps?80.2.197.71 (talk) 10:54, 31 August 2009 (UTC)

Pubic hair (and armpit hair) is about as far from head hair as you can get, but arm hair and leg hair is a bit closer. However, if we could do that level of genetic manipulation, we could convince the hair follicles on the head to produce more hair. StuRat (talk) 11:47, 31 August 2009 (UTC)

The Wikipedia article Hair transplantation reports that transplanted hairs grow and last just as they would have at their original home. It mentions that donor hairs may be extracted from the chest, legs or beard. It does not mention Pubic hair that is often closer in colour to the eyebrows than to scalp hair, but I find no suggestion that genetic modification would be needed to transplant them.Cuddlyable3 (talk) 13:29, 31 August 2009 (UTC)

Spider identification

Unknown green spider.

I don't think I've ever seen a green spider, much less one that was pale and translucent. Anybody know what species this thing is? --ErgoSum•talk•trib 14:11, 31 August 2009 (UTC)

Hmmm, so far it looks like a close match to the green lynx spider, perhaps a juvenile? I'm not an expert on spiders. --ErgoSum•talk•trib 15:02, 31 August 2009 (UTC)

Where (geographically speaking) was this taken? What region/country/state/etc.? Might help narrow down the species. The Seeker 4 Talk 17:44, 31 August 2009 (UTC)

Arkansas. I think the photo of the green lynx spider in the article closely resembles my photo. I'll probably just delete the picture since there is already a better quality photo of the spider in place. I was under the assumption that all spiders were black or brown, so I was quite surprised to see a green spider. Thanks anyway! --ErgoSum•talk•trib 22:33, 31 August 2009 (UTC)

I think your photograph is great. It very clearly shows in detail the structure of the legs. Beautiful. Bus stop (talk) 22:43, 31 August 2009 (UTC)

Yup. I voted keep on Ergo talk page, and have boldly added the image to the article's gallery. --Tagishsimon (talk) 22:49, 31 August 2009 (UTC)

Thanks guys, this is why I love this place! I'll leave the photo uploaded. Happy editing. --ErgoSum•talk•trib 00:19, 1 September 2009 (UTC)

Swine flu - dead birds

Anyone know of a link between "swine flu", and large apparently healthy looking birds dropping out of trees stone dead - I ask because swine flu has recently been identified in my area, and I have recently noticed an unusually large number of dead birds on the grass verges near to where I live, seemingly not the victims of "road kill" ?

thanks.83.100.250.79 (talk) 15:36, 31 August 2009 (UTC)

I don't think Swine flu infects birds. Here in central California the West Nile virus (carried by mosquitoes) has kille a lot of birds that way, but I don't know whether that could happen in the Sheffield area. Looie496 (talk) 15:41, 31 August 2009 (UTC)

Looie is right. Birds cannot catch swine flus (although pigs can be infected with avian flus, potentially making them very dangerous) so you don't have to worry about that. ~ Amory (user • talk • contribs) 16:33, 31 August 2009 (UTC)

A little followup research shows that there have been reports of West Nile in British birds this year. In California corvids such as crows and magpies have been most strongly affected -- do you know what types of dead birds you are seeing? Looie496 (talk) 16:52, 31 August 2009 (UTC)

All pigeon type birds, probably Wood Pigeons rather than "town pigeons". No dead crows as yet.83.100.250.79 (talk) 18:11, 31 August 2009 (UTC)

If H1N1 ("Swine flu") had indeed crossed over to birds, that would be a rather worrying thing because that would increase the chances of a gene exchange with H5N1 ("Bird flu") resulting in H5N1 variants being able to be passed from human to human rather than only from birds to humans as currently is the case. SteveBaker (talk) 18:10, 31 August 2009 (UTC)

Of course there a numerous other explanations which don't involve a global human catastrophe, I'm still panicking though, just to be on the safe side...83.100.250.79 (talk) 19:20, 31 August 2009 (UTC)

You could always call your local health authority and ask. When West Nile first came to my region, the public was asked to report any dead crows, jays, other large birds. They might be interested in getting a recent corpse for testing. (And we were told not to handle them ourselves) Franamax (talk) 20:25, 31 August 2009 (UTC)

Yes, already e-mailed local "enviromental health department" as they are called here.83.100.250.79 (talk) 20:34, 31 August 2009 (UTC)

Well, H5N1 had been found in pigs years ago, and while it may not be perceived as as big of a threat as it once was, H5N1 is definitely still around so the possibility certainly exists. ~ Amory (user • talk • contribs) 19:54, 31 August 2009 (UTC)

H1N1 is not synonymous with "Swine flu". There are loads of strains of H1N1, some of which are probably definitely (Avian flu#Subtypes) already in birds. The current outbreak is just one strain of H1N1. --Tango (talk) 20:21, 31 August 2009 (UTC)

This year's pandemic novel swine flu H1N1 virus has indeed been detected in turkeys at a farm in Chile[46] and in pigs in several countries. 75.41.110.200 (talk) 03:26, 1 September 2009 (UTC)

Bug control with garlic water?

Is this advice (found on the Internet) useful or merely wishful thinking? Thanks. Wanderer57 (talk)

"Get rid of bugs on plants by spraying them with garlic water.

Peel and chop three garlic cloves, put them in a mason jar and fill 3/4 full with water. Put on the lid and shake then let soak for a week or two. Place water in a spray bottle and spray directly onto your plants. Do not soak, just mist. Do this for a few days in a row and this should get rid of your problem. Repeat as needed. "

It sounds like a harmless experiment. Why not do it yourself and report the results? It should be a fairly easy thing to check out. It is at least possible that chemicals in the garlic may act as a natural deterrant to some insects. But if you actually do them experiment, you may find out yourself... --Jayron32 18:12, 31 August 2009 (UTC)

And, if it does work, it's possible that garlic developed those strong smelling chemicals exactly because they kept bugs from eating it. I believe many spices developed their flavors that way. While those spices might taste nice when properly diluted, mixed with sugar, etc., the straight plants would also seem noxious to us, in many cases. StuRat (talk) 18:31, 31 August 2009 (UTC)

I will try a experiment at the next opportunity. My sense if that this method actually worked it would be well known that it works and I would not have to ask. Thanks Wanderer57 (talk)

Do snakes has vision

Yes it is true that snakes has eyes but can they see. Or they sence through there toung. —Preceding unsigned comment added by 125.18.239.135 (talk) 18:06, 31 August 2009 (UTC)

See Snake#Perception. -- Coneslayer (talk) 18:07, 31 August 2009 (UTC)

(edit conflict)Sure they can see. Some snakes may not be able to see well, or may use other senses more to help them navigate, but I am fairly certain that nearly all snakes have some sense of vision of some sort. --Jayron32 18:10, 31 August 2009 (UTC)

The smallest hole water can penetrate

How can I calculate the minimal diameter of hole in flat surface water can penetrate in standart conditions? Renaldas Kanarskas (talk) 20:48, 31 August 2009 (UTC)

You would need to more clearly define what standard conditions are. Water that is under pressure can go through a smaller hole because surface tension is less of an impact, and your pressure is going to probably be determined by how deep the water is at the level of your hole. Shape would also play a part, however, the use of the word diameter would indicate a circular hole? Googlemeister (talk) 21:15, 31 August 2009 (UTC)

20C temperature, 1 atm. pressure. Lets take the heigth of water in, e.g., cylinder, as variable, which we will use in formula. As I understand, it will depend not only on water surface tension but also on contact angle with the the material where the hole is made. Renaldas Kanarskas (talk) 22:17, 31 August 2009 (UTC)

Do you know the relationship between contact angle and 'surface energy'? There is one, but I don't have it to hand - it can be derived however. You can use the surface energy of water/hole material to work out how much energy the H2O will need to leave the bulk water, and enter the hole.

Using an energy distribution equation you can work out what percentage of water molecules have enough energy to enter the hole.

The height of water converts to increased pressure - which gives a change in relative energies on either side of the hole. I'm not sure how to directly relate this to rate of reaction - though it will obviously favour an equilibrium in one direction through the hole.

Is that the sort of calculations you were thinking of making.?83.100.250.79 (talk) 22:43, 31 August 2009 (UTC)

For diffusion of water molecules you need is the molecular size, though the diffusion will be affected by the interaction of the substance the material that contains the hole is made of with water. ie the hydrophobicity of the hole material.

You are looking for the minimum swept area for motion of a H2O molecule.

See Water (data page) - I would estimate somwhere between 10^-10 to 2x10^-10 meter for the minimum size (this is a hole that would only allow 1 molecule through at a time). This is assuming that the material is hydrophilic.

83.100.250.79 (talk) 21:55, 31 August 2009 (UTC)

You seem to be interpreting the Q in a completely different way than I did. I thought the Q was about what size hole would allow drops of water to drip thru, in which case the answer is likely in the millimeter to centimeter range, depending on the material. StuRat (talk) 00:06, 1 September 2009 (UTC)

There are going to be a couple of "knee point" diameters, at which the mass flux per unit-area will dramatically change. Between these "knee points", a continually decreasing diameter will result in slower fluid flow, probably along a rough 1/r^2 law; at the knee-points, this law will probably change. (I don't claim the following analysis to be complete or authoritative, but I think the proper methodology is to consider all the relevant physical effects that impede water flow, and start listing the characteristic length scales that they occur on). Starting with a large hole, the first impediment to flow will be the cavitation limit, which probably occurs around a few centimeters diameter, depending on the fluid head. Above this diameter, the water will exhibit laminar flow down the drain; below that limit, it will start to be predominantly turbulent (and spinning on its way). The next critical point, probably on the order of a few millimeters, is when the capillary action force is going to become critical - the adhesion of water to the wall orifice will approximately equal the force of gravity, and so the flow will be impaired (but not stopped). This rate will be highly dependent on the material the water is flowing through (as mentioned above, with hydrophilic and hydrophobic materials at the extrema). The next limits are going to be permeability limits, dictated by the porosity of the material. Now, the fluid will still flow, but it will do so in a slow, meandering style. This is the regime of reservoir engineering in the parlance of petroleum engineering (or aquifer/water engineering); it is an active area of research, as the presence of fluid inside a porous medium changes the medium's properties - the result is a very nonlinear fluid flow. Assuming a subsonic fluid, I think these are the primary physical scenarios which can occur; if, for some reason, the water is sufficiently pressurized or accelerated, it may also have a sonic-shock crossover, (again resulting in a nonlinear flow analysis). It should be noted that fluid mechanics is one of the most complicated areas of classical physics, and empirical observations often contradict theoretical predictions for even complex models; probably, the best way to get an answer suitable for your needs is to define the regime of interest and experimentally test a few conditions. Nimur (talk) 00:28, 1 September 2009 (UTC)

I can't help wondering if this condition is meant, in which any further increase in height causes the droplet to burst - ie the contact angle is "90 degrees" ? HappyUR (talk) 12:51, 1 September 2009 (UTC)

click to expand

Cockroaches

Do they live in herds? If they do, how big are those herds? --Soppaluu (talk) 21:57, 31 August 2009 (UTC)

See Cockroach#Behavior for some information. In short, they aggregate into complex social groups and display emergent behavior. By the way, the collective noun for cockroaches is unlikely to be "herd"., According to List of collective nouns for fish, invertebrates, and plants (unsourced), it is an "intrusion of cockroaches", though various academic studies seem to prefer the term "group". As for the size of these groups, it seems to depend on resources available. According to Cockroaches: ecology, behavior, and natural history by William J. Bell, Louis Marcus Roth, Christine A. Nalepa, up to 100,000 have been observed in a single apartment (nice!), however in general most species live in much smaller groups: on average 2-8 adults and 5-8 nymphs. Rockpocket 22:28, 31 August 2009 (UTC)

Would New York City's subway be designed any differently now?

Sagittarian Milky Way (talk) 23:01, 31 August 2009 (UTC)

If someone were building a subway now, in a dense city like New York (and you wouldn't build a subway elsewhere) then the cut-and-cover method used to build the new york subway would probably antagonise too many people. The advent of tunnel boring machines makes a deeper bore a more affordable option than it was when the NY subway was built. Other than that, electric light rail is much the same world over, and new underground systems are built with mostly off-the-shelf components, and one is much like the others. -- Finlay McWalter • Talk 23:07, 31 August 2009 (UTC)

Also bear in mind that it grew organically (see History of the New York City Subway) , and that if starting from scratch now the designers would be able to optimise for current population and travel patterns.

Did you have a specific aspect of design you had in mind - there are many - architecture, route, technology used, track geometry, construction methods and materials, etc

Have you considered any of these or were wondering about a specific area?83.100.250.79 (talk) 23:37, 31 August 2009 (UTC)

Also please try to think a little for yourself, or at least show that you have attempted to consider some part of your own question.83.100.250.79 (talk) 23:38, 31 August 2009 (UTC)

I was thinking of locally specific, mostly routing, there's not much to be said in the ways of tech that's either not obvious (use fluorescent tunnel lighting), or didn't change) I won't be familiar with many lines. Others can make suggestions. D and 4 duplication in Bronx, lack of desire to go turn from Manhattan early to go into Queens. 42 St Shuttle saves only one stop over the 7, 6th Avenue PATH, MTA duplication in Manhattan. Many PATH stations are very close to sea level and their tunnels are below it (hurricane storm surge + high tide + 21st century sea level rise). Queensboro Plaza and Queens Plaza not having transfers. Duplication in Flatbush Avenue in Brooklyn All because the system was built by 3 companies competing for riders. (I'm very sleepy, forgive the haste, will fix in the morning) Sagittarian Milky Way (talk) 06:57, 1 September 2009 (UTC)

Routing is the most difficult of all the questions you could have asked :)

It would probably be easier to rebuild the entire city from scratch :)

One suggestion I'd make lightly is to have entirely parallel N/S tracks (under manhattan) turning east at S end (no crossing points) - with a series (about 6) of shorter high capacity crossing routes (again starting at the west end under manhattan) connecting 'at right angles' (topologically speaking) all the N/S tracks - this would have the effect of meaning that no subway journey would require more than 2 changes.

Where meaninful the e/w tracks could be extended east, and fanned out to form full length lines

Basically a grid system with dangling ends going into the subburbs.

It's not based on any knowldege of new york...83.100.250.79 (talk) 12:22, 1 September 2009 (UTC)

They would likely build it deeper down, as there's more stuff in the way at shallow depths now due to all the construction since then. StuRat (talk) 00:00, 1 September 2009 (UTC)

If you're interested specifically in how a new line would be constructed today see Second Avenue Subway. That doesn't say much about how the overall system would be designed if it were built today, but it provides some insight into things like construction methods. Rckrone (talk) 00:04, 1 September 2009 (UTC)

I don't know about the state of the NY subway now, but when I was there in 1996, I was negatively surprised by the construction quality, poor station layout, and state of the rolling stock. The noise was unbelievable compared to the more modern designs I was used to from e.g. Munich (essentially all remodeled for the 1976 Olympic games and kept reasonably up to date since). I think a new system would probably be somewhat deeper, more level along the tracks, and the stations designed more generously, and much higher (for improved lighting, better ventilation, and less claustrophobia). I also suspect new routes would be found to correspond to current and anticipated commuting patterns. Again, in Munich distances from the city center influence housing prices, but "distance" is not measured in meter or miles, but in minutes, usually walking to the next light rail station and riding into the city. As a result, housing prices essentially follow the star shaped layout of the light rail network. --Stephan Schulz (talk) 07:45, 1 September 2009 (UTC)

Mice Trap

Hi evry one .... i have abig problem with mice and i tried evry thing , but it just wont work , this creature is so clever .

so is an act of dispair i tried to make an electric trap ...

strik one : i take a phase from the source and connect it to a plate then connect the other side of the plate with the earth,then i put some cheese , nothing happened except he got hte cheese.

strike two: i connect a fan to the power then connect the plate to the nutral coming back from the fan , also no use .

strike three : i talked to afreind about the secound try and he said i had should connect the plate to the phase comming from the source to feed the fan because the power coming back wont be enuogh to kill the mice , so i did that and still nothing.

please what should i do , these mice are killing me , and i'am running out of cheese.

why these trys failed....--Mjaafreh2008 (talk) 06:11, 1 September 2009 (UTC)

Mice are fast, but not really that clever. Try some of the many types of traps listed at Mousetrap? If they don't work, its unlikely your Heath Robinsonesque trap will. Rockpocket 06:28, 1 September 2009 (UTC)

Get a cat or two. They'll keep the mice under control. Baseball Bugs ^{What's up, Doc?} carrots 08:54, 1 September 2009 (UTC)

I understood that you connected the phase to the plate and then the other side (same connection!) to the earth. Then how would you expect to cause a small electric shock for instance? It is already a short circuit to the earth, and no voltage drop will go across the rat or mouse. The same problem is done in the second step, where the neutral has almost 0 volts with the earth at all.--Email4mobile (talk) 09:02, 1 September 2009 (UTC)

Strange calculations of C

Can you have a look at this website [47]; although it is discussing the speed of light in a sort of religion or philosophy. I tried hard to understand the calculations but because I lack for sophisticated knowledge in astronomy, I think someone here might understand them better. What I need to understand; are those calculations completely true and accurate? or is there some trick in the calculations?--Email4mobile (talk) 07:56, 1 September 2009 (UTC)

here is a quick link to the calculations [48].--Email4mobile (talk) 07:59, 1 September 2009 (UTC)

It looks like a big fudge to me. Cutting through the verbiage and hyperbole, here's what seem to be going on at that site:

1. A rather strained interpretation of a verse from the Quran that says "this affair travels to Him a distance in one day, at a measure of one thousand years of what you count" is used to create the claim that the distance travelled by light in one day is equal to the distance travelled by the Moon in 12,000 orbits around the Earth. First fudge: there are not exactly 12 lunar orbits in one year - even if you use the synodic period of the Moon, 29.5 days, the Moon goes through approximately 12.4 cycles of phases in one year. But if you calculate the distance that the Moon travels in 1,000 years you get about 1.24 light days, which is 24% greater than claimed - so the time period has been rounded down to 12,000 lunar cycles to reduce this error.
2. A calculation of how far the Moon travels in 12,000 synodic periods gives about 1.2 light days, so this is still a 20% error. Second fudge: to further reduce the size of this error, the site switches from synodic periods to the shorter sidereal period, 27.3 days. In 12,000 sidereal periods, the Moon travels about 1.11 light days - so still an 11% error.
3. There is then a very complicated argument that claims that if the gravitational influence of the Sun is removed (why ??) then the Moon's orbital speed and the Earth's speed of rotation (and hence the definition of "one day") would change by just enough to compensate for this 11% error. This looks like one big third fudge to me.

Gandalf61 (talk) 09:28, 1 September 2009 (UTC)

I guess the website refers to 1 lunar year, because for Arab, the year deal with is around 354 days not 365, and that's why the arguement confirmed, "...of what you count" in the Quran. The 3rd point you mentioned was the one I couldn't get along with and thus asked for some more information.--Email4mobile (talk) 09:58, 1 September 2009 (UTC)

Even if the site uses a lunar year, i.e. 12 synodic periods, as the definition of one year, then point 2, the switch from synodic periods to sidereal periods, is still a big fudge. 12 sidereal periods, or 327.6 days, is a completely arbitrary time period, unrelated to any definition of a lunar year. A lunar year is much closer to 13 sidereal periods than to 12. Gandalf61 (talk) 10:42, 1 September 2009 (UTC)